In this work we theoretically study spectral multipole resonances of parallelepiped- and pyramid- silicon nanoparticles excited by linearly polarized light waves. We apply the numerical finite element method to calculate the scattering cross-sections as a function of the nanoparticles geometrical parameters. We use the multipole decom- position approach to explore optical resonances in silicon nanoparticles and the influence of second and third order multipoles to scattering diagrams. In contradistinction to our previous investigations, now we explore effects in near-IR spectral range. Apart from basic study we also obtained non-symmetrical combination of multipole contributions due to illumination from top and bottom sides of pyramids. Our work provides important information about the role of high-order multipoles in the light scattering by non-spherical and non-symmetrical nanoparticles. Our results can be applied, for example, for development of metasurfaces and metamaterials in near-IR spectral range.

Successful power scaling of the Er-doped fiber laser heavily depends on Er dopant concentration. In order to scale the power up to a kW class, core absorption should be well over the limits defined by current commercial doping techniques. Recently developed nanoparticle (NP) doping technique of fabrication of erbium-doped fibers allows the desired dopant concentration increases while mitigating both Er upconversion and clustering effects. Here we present the latest resonantly-pumped Er fiber laser power scaling results enabled by further development of the NP doping technique of Er-doped fiber fabrication. Using resonantly cladding-pumped (at 1530 nm) large mode area 20/125 µm fiber with the Er-NP-doped core we achieved pump-limited CW power of over 30 W at ~1605 nm with the slope efficiency versus absorbed pump power of ~63%. These are, to the best of our knowledge, the highest power and efficiency demonstrated so far for from the Er-NP-doped fiber. Further considerations on fiber design optimization are presented as well.

The present work displays a thorough study of the optical spectroscopy of multilevel RE-doped tin oxide nanocrystals. Our study provides the structural grounds about the behavior of the RE emission under site-selective excitation as well as the capability of the host to hold the RE ions at the nanocrystal lattice sites and, as a consequence, the possibility to reach the RE excited states by direct host excitation.

Transparent oxyfluoride glass-ceramics obtained by the adequate heat treatment of Nd³⁺-doped glass with composition SiO₂-A_l2O₃-Na₂O-LaF₃ are investigated. X-ray diffraction (XRD) and high resolution transmission electron microscopy (HR-TEM) show that the precipitated nanocrystals are LaF₃ with a crystal size between 9-12 nm. Furthermore, energy dispersive X-ray (EDX) analysis shows the incorporation of Nd³⁺ ions into the LaF₃ nanocrystals. Site-selective and time-resolved emission and excitation spectra of the ⁴F_3/2 and ⁴F_5/2 states, allows to unambiguously isolate the emission of Nd³⁺ ions in LaF₃ nanocrystals which shows well defined spectra, similar to those obtained for pure LaF₃ crystal.

Erbium doped fiber lasers are attractive candidates for high energy lasers (HELs) used in directed energy applications because they operate at wavelengths that are both safer to the eye and in a high atmospheric transmission window. A significant issue for erbium doped fibers is detrimental clustering effects such as upconversion and quenching. We have investigated the use of ytterbium-erbium co-doping in both solution and nanoparticle form, where Yb ions are used to help disperse and separate the Er ions in order to avoid these effects. Both solution doping and nanoparticle doping were investigated and optimal concentrations for both were determined. By optimizing variables such as Yb/Er ratio and Al precursor concentrations during synthesis we have been able to increase erbium concentration levels in Silica fiber cores while minimizing detrimental clustering effects. In-band pumping of Er ions at 1475 nm in a single-mode master oscillator power amplifier set-up was used to investigate lasing efficiency, and therefore the Yb ions do not absorb and are optically passive. This ensures that the fibers are operating in the eye-safer regime. We have achieved optical to optical slope efficiencies of 50% for Yb-Er NP and solution doping in a single mode fiber with Er concentrations that are much greater than are achievable with conventional solution doping. Results indicate improved potential for power scaling.

We compare the laser performance of a low Tm3+-doped silica fiber laser as pumped at 800 nm to one as pumped at 1620 nm. Using 800 nm non-resonant (³H₆→³H₄) pumping, 5.5 W of 1940 nm at 32% optical slope efficiency was demonstrated while 1620 nm resonant pumping (³H₆→³F₄) yielded 13 W with 55% slope efficiency from the same Tm-doped fiber. We also include experimental results our first demonstration of 1620 nm resonant pumping of a Tm-doped fiber with 15.5 W and 67% slope efficiency using an optimized fiber coupled source.

We present the fabrication and properties of active fiber laser materials fabricated by a newly developed solution doping technique. The contribution focusses on Aluminum, Phosphorus, Ytterbium as well as Boron doped SiO₂ for the use as fiber laser material. More specifically low doping concentration in the vicinity of the molar ratio of Al₂O₃:P₂O₅ = 1:1 will be elucidated. The effect of fabrication parameters on optical properties like refractive index, absorption and emission properties will be covered. Currently it is possible to achieve cw output powers greater than 4 kW using Al, P, Yb doped fibers fabricated with this method. Fibers additionally codoped with Boron are as well suitable for kW class applications as well.

We will report the new experimental results on MID femtosecond laser based on a multi-stage optical parametric amplifier, a new nonlinear crystal, SiC, was used for the three waves interaction. Comparative research with KTA crystal were also carried out. With optimized conditions, laser energy up to 520 μJ was obtained with central wavelength of 2.8 μm at 1kHz repetition rate. In this experiment, a home-made femtosecond Ti:sapphire laser system was used as pump laser. The seeding signal was introduced from the 3-mm YAG plate based white continuum and then pre-amplified in three non-collinear amplification stages. With 10-mJ pump energy in the last stage amplifier, laser energy up to 1.8 mJ for signal wave and 520 μJ for idler wave were obtained. Corresponding to a total conversion efficiency of 23.2% (signal plus idler). To maximize the bandwidth of the idler, a numerical model was developed to give an optimum non-collinear angle. As the result, the bandwidth as wide as 525 nm was realized, supporting 27 fs transform-limited pulse generation.

Several holographic and interferometric applications would benefit significantly from a diode laser based coherent light source near 633 nm. For this purpose a miniaturized master-oscillator power-amplifier (MOPA) was developed. The MOPA is integrated in a sealed package together with a custom-built CdMnTe-based micro-optical isolator to shield the MO from optical feedback. The MOPA reaches an optical output power of up to 30 mW near 633 nm. Its single-mode emission is tunable over 0.5 nm by temperature and 1.0 nm by a grating heater. The package offers the integration of a gas cell and a polarization maintaining fiber port.

High energy lasers (HELs) operating around 1.5 μm are considered eye-safe and are highly sought-after for use in defense, industrial processing, communications, medicine, spectroscopy, imaging and various other applications where the laser is expected to travel long distances in free space. Compared to YAG, GaN has a higher thermal conductivity, lower thermal expansion coefficient, and lower temperature coefficient of the refractive index (dn/dT) around 1.5 μm. Hence, HELs based on erbium doped GaN (Er:GaN) are expected to outperform those based on Er:YAG in terms of average power, power density, temperature stability and beam quality. Here, we provide a brief overview on the progress made in authors’ laboratory for the realization of freestanding Er:GaN wafers of 2-inches in diameter with a thickness on the millimeter scale. These freestanding wafers were obtained via growth by hydride vapor phase epitaxy (HVPE) in conjunction with a laser-lift-off process. Optical absorption and resonantly excited photoluminescence emission spectra have enabled the construction of energy level diagrams pertaining to the excitation and emission mechanisms of Er:GaN eye-safe HELs operating around 1.5 μm. The results have shown that the common excitation and emission scheme of Er:YAG is not entirely applicable to achieve Er:GaN eye-safe lasers. In addition to higher thermal conductivity of Er:GaN over Er:YAG gain medium, Er:GaN eye-safe lasers appear to possess lower quantum defects than Er:YAG lasers.

We investigated the effect of Rapid Thermal Annealing (RTA) process on Quantum Dot Semiconductor Optical Amplifiers (QD SOAs). The devices are composed of 30-layer stacks of InAs quantum dot by using strain compensation method. The lateral size and height of QD are 30 nm and 4 nm, respectively. Our QD SOAs have emission wavelengths within 1.5 μm-band. We applied RTA process to improve the characteristics of internal quantum efficiency (ηi ) and optical loss (αi ) of ridge laser diode for QD SOAs. In this case, the operating temperatures of RTA process were set at 600°C, 620°C, 640°C and 660°C for 30 seconds each. In addition, the devices are cleaved to form a cavity length at 0.06 cm, 0.08 cm, 0.10 cm, 0.12 cm and 0.14 cm. According to the L-I characteristic result of ridge laser diode structure for QD SOAs at 640°C, the best minimum threshold current ( I_th ) is 47.93 mA. Moreover, according to the plot between 1 η_d⁻¹ (external quantum efficiency) and cavity length, we can optimize the internal quantum efficiency and optical loss for a ridge laser diode structure to be 66.39% and 9.87 cm^-1 respectively at 640°C RTA’s temperature. Finally, The RTA process helps to achieve 1.4 times higher in internal quantum efficiency as well as a minimal increase in internal optical loss comparing to without RTA.

Guided acoustic waves Brillouin scattering (GAWBS) processes in standard optical fibers allow for sensing of liquids outside the cladding boundary, where light does not reach. Optical waves stimulate the oscillations of elastic modes of the fiber. The linewidths of these modes, in turn, depend on the mechanical impedance of surrounding media. These linewidths are monitored through photo-elastic scattering of optical probe waves. However, acoustic guided waves scatter light in the forward direction. The timing of forward-scattering event cannot be identified directly, hence distributed analysis based on GAWBS could not be performed, and measurements were restricted to point-sensing only. In this work we show a way around the problem. The exchange of optical power among two optical tones that stimulate the acoustic wave is monitored through careful analysis of Rayleigh back-scatter. Distributed GAWBS analysis is performed over 3 km of fiber with resolution between 100-200 meters. The measurements successfully distinguish between water and ethanol based on mechanical impedance.

A review of our work on all-optical gas sensors is presented with an emphasis on the development of both new infrared (IR) sources and IR to visible converters. Many radicals spectroscopic signatures associated to gases of interest are in the 2.5 -15 μm spectral range (4000-350 cm^-1). This spectral domain matches rare-earth ions emissions when embedded into chalcogenide glasses which are well- known for having low phonon energies. We present here results concerning the development of IR sources and IR to visible converters based on rare earth doped chalcogenide fibers. The development of all-optical gas sensors in the 3 to 5 µm spectral range is described showing IR signal conversion into visible light using specific excited state absorption mechanisms in rare earth doped materials. This wavelength conversion enables the use of silica fibers to transport the “gas” signal over large distances considerably increasing the scope of possible applications. An example of all-optical sensor using this photon conversion is presented in the case of CO₂ detection. The implementation of this type of sensor for different gases such as methane is finally discussed. This all-optical sensor can be typically used over a kilometer range, with sensitivity around hundreds of ppm with cost effective detection heads, making this tool suitable for field operations. Finally, the photon conversion at the heart of this all-optical sensor is discussed as a general mean to detect infrared radiations avoiding the use of infrared detectors for a large span of applications.

Optical fiber sensing techniques have been attractive in various applications to mechanical, chemical, biological, and environmental industries for measurement of temperature, strain, ambient index, liquid level, and so on. Fiber-optic interferometric sensing probes based on all-fiber Mach-Zehnder interferometers (MZIs), Fabry-Perot interferometers (FPIs), and Saganc interferometers have been investigated extensively. Various In-line MZIs using the combination of a single-mode fiber (SMF) with a multimode fiber (MMF) were proposed to realize refractometers or pressure sensors. To obtain high temperature sensing probe, multiple MZIs have been developed by using a piece of MMF sandwiched between two SMFs cascaded with a tapered SMF. Fiber-optic relative humidity (RH) sensors have been widely investigated in a variety of applications in meteorology, medicine, agriculture, and architectural engineering fields. To improve the RH sensitivity of the fiber-optic sensing probe, many structures of fiber-optic sensing probes have been proposed, such as a polyvinyl alcohol (PVA) coated photonic crystal optical fiber, a fiber FPI with a PVA thin film, a Michelson interferometer with chitosan coating. In this paper, a few-mode microfiber knot resonator (FM-MKR) is presented for measurement of RH. The proposed FM-MKR includes two optical phenomena, such as optical modal interference in the few mode microfiber and optical coupling in the FM-MKR. When the waist diameter of the microfiber is 4 m, two modes, such as HE11 and HE12, should be excited and interfered together in the nonadiabatically tapered region of the SMF. After making a tie with the few-mode microfiber with a diameter of 4 m, the FM-MKR can be fabricated. In the FM-MKR, two modes must be circulated within the optical knot and cross-coupled independently with a phase delay. To detect RH, the FM-MKR is coated by using the PVA which effectively absorbs humidity in the external environment. For the microfiber with a diameter of 4 m, the difference of group effective refractive indices between HE11 and HE12 modes becomes nearly zero and the sensitivity of the FM-MKR to RH can be successfully improved. Transmission characteristics of the proposed FM-MKR with variations in RH are measured.

Fiber Bragg gratings (FBGs) have been attractive in fiber-optic sensors because of their many advantages, such as wavelength-selective nature, easy installation and adaptability, and low insertion loss. External perturbations like temperature, strain, and bending basically make the center wavelength of FBGs shifted. It is necessary to improve the sensitivity of the FBG sensing probe to external perturbation change to realize high quality of fiber-optic sensors. Recently, the weak value amplification (WVA) technique based on a quantum effect or interference has been proposed to enhance a degree of sensitivity in the process of measurement. The polarization-dependent WVA was experimentally suggested to realize the increment in a degree of sensitivity of the FBG strain and temperature sensors. The previous method, however, has many drawbacks, such as sophisticated structure, instability and difficulty in polarization adjustment, and experimental inconvenience due to polarization. In this paper, we propose a new method of the WVA based on the optical attenuation to improve the performance of the FBG sensor, which has a simple structure compared to the polarization-based WVA. The proposed WVA based on optical attenuation is configured by a broadband light source, two 3-dB optical couplers, two optical circulators, two FBGs with the same center wavelengths, and an optical attenuator. In the proposed WVA, the sensitivity of the sensing FBG to external perturbation can be enhanced by increasing the amplification factor depending on the optical attenuation. The strain sensitivity of the FBG sensor using the proposed attenuation-based WVA was successfully enhanced by a factor of 2.73 compared with that without the WVA.

The paper deals with the analytical description of the sensitivity and dynamic characteristics of the birefringent fiber temperature response usable for realization of thermal field disturbance sensors. The response is given by changing the phase shift development between two polarization modes in birefringent fiber, caused by body heat transfer of different temperatures. The aim is to analyze sensitivity and dynamic behaviors, which are significant when optical fiber is used as a sensor of temperature field disturbance. The result shows a very good match with measured time responses, especially due to a specific arrangement for suppressing the influence of conduction and convection.

ZnGa₂O₄:Cr³⁺ is an optical material well known for its deep red persistent luminescence properties which are centered in the first biological window. In this work, Yb³⁺, Cr³⁺ co-doped zinc gallate oxide has been prepared in the form of glass-ceramics. The studied samples have been elaborated via conventional melt quenching process leading to nanometer scale phase separated glass which was subsequently crystallized to obtain nanocrystals embedded in a transparent glass matrix. In these as-prepared ZnGa₂O₄:Cr³⁺,Yb³⁺ glass-ceramics, regular Cr³⁺ emission (at around 695 nm) as well as Yb³⁺ emission (between 950 and 1100 nm) is observed. Several photoluminescence emission and excitation experiments have been recorded in order clarify (i) the simultaneous emission of these cations in different optical windows and (ii) the energy transfer process between these two emitting centers. Further studies proved that Yb³⁺ is not only active in photoluminescence but also in persistent luminescence, leading to a material demonstrating persistent luminescence properties in both first and second biological windows (650-950 and 1000-1350 nm respectively). Thermoluminescence experiments have been carried out on these materials in order to gain deeper information about the persistent luminescence process.

More and more applications utilize the short wave infrared (SWIR) spectral range. The SWIR range is defined from about 0.9 to 3 μm. SWIR applications can be found for example in inspection processes of circuit boards, solar cells, bottles and food. The SWIR range is used in identification, sorting, surveillance, inspection and more. With SWIR applications characteristics can be visualized that normally would not be detectable with visible light, like rotten fruits in fruit sorting, fakes in paintings, content levels in visually non-transmitting bottles. For all these machine vision applications specific optics are used that in the ideal case have transmittance in the visual spectral range and in the SWIR range. Optical designs require materials that are transmittance in the visible and the SWIR range, sometimes even up to 4 μm. Most optical glasses have a good transmittance up to 2 μm, but at 2.5 μm the transmittance strongly decreases. There is also not much available information on the details of the transmittance curve in the SWIR range available of optical glass. This presentation will demonstrate SCHOTT optical glasses with good transmittance even up to 4 μm. If applications require transmittance at even larger wavelengths, it is possible to utilize IRG infrared material with transmittance up to 8 µm, that still can be used in the visible down to 0.6 μm. Other critical information for the optical designs are the dispersion and index change with temperature (dn/dT) characteristics in the SWIR range of these materials. This paper will discuss the availability of such data.

Especially in the market of sensors, LED lighting and medical technologies, there is a growing demand for precise yet low-cost glass optics. This demand poses a major challenge for glass manufacturers who are confronted with the challenge arising from the trend towards ever-higher levels of precision combined with immense pressure on market prices. Since current manufacturing technologies especially grinding and polishing as well as Precision Glass Molding (PGM) are not able to achieve the desired production costs, glass manufacturers are looking for alternative technologies. Non-isothermal Glass Molding (NGM) has been shown to have a big potential for low-cost mass manufacturing of complex glass optics. However, the biggest drawback of this technology at the moment is the limited accuracy of the manufactured glass optics. This research is addressing the specific challenges of non-isothermal glass molding with respect to form deviation of molded glass optics. Based on empirical models, the influencing factors on form deviation in particular form accuracy, waviness and surface roughness will be discussed. A comparison with traditional isothermal glass molding processes (PGM) will point out the specific challenges of non-isothermal process conditions. Furthermore, the underlying physical principle leading to the formation of form deviations will be analyzed in detail with the help of numerical simulation. In this way, this research contributes to a better understanding of form deviations in non-isothermal glass molding and is an important step towards new applications demanding precise yet low-cost glass optics.

Ultrafast laser inscription (ULI) has previously been employed to fabricate volume diffraction gratings in chalcogenide glasses, which operate in transmission mode in the mid-infrared spectral region. Prior gratings were manufactured for applications in astrophotonics, at wavelengths around 2.5 μm. Rugged volume gratings also have potential use in remote atmospheric sensing and molecular spectroscopy; for these applications, longer wavelength operation is required to coincide with atmospheric transparency windows (3-5 μm) and intense ro-vibrational molecular absorption bands. We report on ULI gratings inscribed in IG2 chalcogenide glass, enabling access to the full 3-5 μm window. High-resolution broadband spectral characterization of fabricated gratings was performed using a Fourier transform spectrometer. The zeroth order transmission was characterized to derive the diffraction efficiency into higher orders, up to the fourth orders in the case of gratings optimized for first order diffraction at 3 μm. The outcomes imply that ULI in IG2 is well suited for the fabrication of volume gratings in the mid infrared, providing the impact of the ULI fabrication parameters on the grating properties are well understood. To develop this understanding, grating modeling was conducted. Parameters studied include grating thickness, refractive index modification, and aspect ratio of the modulation achieved by ULI. Knowledge of the contribution and sensitivity of these parameters was used to inform the design of a 4.3 μm grating expected to achieve > 95% first order efficiency. We will also present the characterization of these latest mid-infrared diffraction gratings in IG2.

Random anti-reflecting subwavelength surface structures on optical components have been proven to enhance transmission by reducing Fresnel reflection losses. These structures have a broadband anti-reflective effect, high angle-of-incidence tolerance, and polarization insensitivity, which makes their performance comparable to more complex multilayered anti-reflective coatings. Conformal anti-reflective multilayered thin-film coatings on grating structures have coverage issues, especially in deep grooves of gratings, thereby impacting the diffractive characteristics of the gratings. We fabricated the random anti-reflective structures on preexisting fused silica binary gratings, using a reactive ion etching process, and compared the prior and postimplementation optical properties of the gratings. We observed that fabrication of random anti-reflective subwavelength surface structures on existing binary gratings retained the diffractive performance of the original gratings, such as the angle of diffraction and intensity balance of the orders, while reducing Fresnel reflection. Transmission and reflection data of the non-evanescent diffracted orders were collected at normal and Bragg incidence, for both incident polarizations, S (TE) and P (TM). The measurements were taken using a selectable multi-wavelength He-Ne laser working at 543nm, 594nm, 604nm, 612nm and 633nm. The reflected intensity of the η₀ and η₊₁ orders at 1st Bragg angle of incidence were suppressed to 0.5% -1.0% for the rARSS fused silica grating, from the original 3% - 8% for the planar fused silica gratings, at all test wavelengths. Our results indicate that modification of existing binary gratings with added rARSS is possible without adverse effects on the grating performance.

In this paper we will discuss the influence of atmosphere pressure microwave plasma on the background loss and the radial distribution of several dopants in specialty, especially rare-earth (RE) doped, preforms and fibers for high power application. In conclusion we were able to demonstrate a significant improvement in the homogeneity of the distribution of the codopants within the silica matrix. Furthermore, we used the plasma process for the functionalization of pure and doped particles as basic raw material in the powder-based reactive powder sintering of silica (REPUSIL) process. In further experiments we will use plasma technology for the all-in-one doping of both active and passive dopants for a brightness adjustment of the refractive index of specialty fibers.

Performing attenuation measurements in unclad single crystal sapphire fiber has traditionally been accomplished through use the cutback method. Because single-crystal sapphire fibers do not cleave easily like silica fibers, this method requires repeated cutting and polishing of the sapphire fiber sample; which is very time consuming and introduces uncertainty in each loss measurement. In this paper, we present a new method to measure attenuation in sapphire or other single-crystal fibers based on distributed sapphire Raman optical time domain reflectometry (OTDR). This method is both nondestructive, significantly faster than the cutback method, and capable of measuring the local loss along the entire length of the fiber.

One of the main advantages of photonic crystal fibers (PCFs) is their ability to host novel functional materials in the airholes of the cladding. Here, we demonstrate a unique post-processing method which allows the integration of materials with significantly different thermo-mechanical properties inside the voids of silica PCF. We first present the material properties of silica, As₂Se₃ and polydimethylsiloxane (PDMS) in terms of their refractive indices and viscosity profile. The latter suggests that the proposed materials are not suitable for direct fiber drawing and thus we present the development of a multi-material As₂Se₃/PDMS/Silica PCF based on a solution-processed and pressure-assisting method. The integration of both As₂Se₃ chalcogenide glass films and PDMS was made in ambient conditions using a costeffective approach. The deposition of the high-index chalcogenide glass films revealed distinct resonances in the visible and near-infrared region while the high thermo-optic coefficient of PDMS provides the ability to thermally control the intensity of the antiresonant bands. The proposed method opens new directions towards multimaterial silica-based PCFs for novel tunable devices and sensors.

The recently suggested probabilistic design-for-reliability (PDfR) concept, and particularly its physically meaningful and flexible analytical Boltzmann-Arrhenius-Zhurkov (BAZ) model, can be effectively employed as an attractive replacement of the widely used today purely empirical and physically unsubstantiated power law relationship for assessing/predicting the static fatigue (delayed fracture) lifetime of optical silica fibers. The BAZ model can be used to estimate the static fatigue lifetime of a coated optical silica “specialty” fiber intended for high temperature applications and subjected to the combined action of tensile loading and an elevated temperature. BAZ relationship is one of the possible predictive models of the recently suggested probabilistic design for reliability (PDfR) concept. This concept has its experimental basis in the highly-focused and highly-cost-effective failure-oriented accelerated testing (FOAT). Such testing is absolutely crucial, if one intends to understand the underlying reliability physics. It is shown how the PDfR concept, BAZ model and FOAT data can be employed, when there is a need to assess the expected static fatigue lifetime of a coated optical fiber subjected to the combined action of the tensile loading and elevated temperature. The general concept is illustrated by a practical example. The approach could be easily extended for any type of optical fibers, including laser fibers, or even to other types of accelerated testing of optical materials, fibers and devices.

We propose and demonstrate a Silicon MSM photodetector integrated on Silicon Nitride-on-SOI platform. The demonstration shows the feasibility of an integrated photonic circuit platform in the visible to NIR wavelength with an integrated Silicon photodetector. We present a planarization free oxidation based Silicon Nitride waveguide fabrication on SOI. DC measurements on photo-detectors with the top illumination of 850 nm light observe the best responsivity of 0.1 A/W at 20 V with a dark current of 570 nA.

We report an uncooled, lattice-mismatched InGaAs photodiode for coherent spectroscopy that demonstrates linear performance up to a photocurrent of 70 mA and has a broad spectral coverage from 1.2 to 2.2 micron wavelength. The fiber-packaged photodiode module can deliver up to +13 dBm of continuous-wave RF output power, i.e. 2.8 V peak-to-peak amplitude, and does not require any further RF amplification to maximize the effective number of bits (ENOBs) for the backend digitizers. These photodiodes have a −3 dB bandwidth of 6 GHz and can coherently detect up to 6 spectral lines within a 1 ns temporal window.

An InGaAs Multi-Pixel Photon Counter (MPPC) has been developed for detecting the near-infrared and shortwave infrared wavelength. Numerous studies were made to develop silicon-based photomultipliers with sensitivity in the nearinfrared region, so they can be applied in various applications such as distance ranging. However, achieving sensitivity at 1.0 μm and longer wavelengths was hard to implement. Therefore a hybrid photon counting device was designed by improving the InGaAs avalanche photodiode. In our approach, the sensor layer and the circuit layer are prepared separately, and this configuration brings more flexibility to both layers. The 3x3 pixel matrix and the dedicated circuit were fabricated, and characterizations were performed in terms of the sensitivity uniformity and the other essential parameters of a photon counting device such as dark count rate, photon detection probability and so on. An excellent uniformity was observed across the active regions in both a single device and the 3x3 matrix device, which indicated that no any abrupt breakdowns were formed. The DCR was 844 kHz and PDP was 8% under the typical conditions of V_e = 1.1 V and T = 253 K. The 3x3 matrix device also exhibited the capability of resolving photon numbers, and the result means this work can be applied to numerous photon-counting applications in infrared.

Miniaturized optics are main-components in many different areas ranging from smart devices over medical products to the area of automotive and mobility. Thus several millions if not billions of small lenses are merged into objectives. One characteristic type of objective holder is the lens barrel. The successful assembly of lenses with diameters of just a couple of millimeters into a lens barrel is an error-prone task antagonized with mass production and an optical inspection at the end of the assembly. Obviously, this process is neither time- nor cost-effective. Furthermore, the increasing imaging qualities demand for highly accurate aligned lens systems. The demand for high-quality optics in large quantities together with the small dimensions of the lenses make assembling a complex process. The Fraunhofer IPT investigates a much more elegant way inspecting the optical system during the fully automated assembly. In the assembly cell, our six-axis micromanipulator aligns the lens camera-led in the lens barrel. Next, the wavefront sensor analyses the imaging function of the lens and compares the actual status with the data from the optic model. This feedback loop between wavefront sensor and micromanipulator continues until the best position is found. We save this information as a digital twin and continue with the next lenses until the optics is completed. The observation of the optical function during the assembly process leads to high quality objectives produced in short cycle times. Moreover, our assembly cell is modular and this allows us to adopt the setup for new lens barrels easily.

Aluminum telescopes are usually considered only for IR wavelengths, due to the inability of aluminum to be surfaced to the surface quality and roughness needed to minimize scatter at visible wavelengths. Yet Al6061T6, a material routinely specified into IR optical sensors due to its heritage, high yield strength, and fracture toughness, has been economically surfaced to equivalent mid and high spatial frequency error as glass surfaces typically specified into visible wavelength sensors. However, microroughness data can correlate poorly with scatter performance where microdefects dominate scatter. To show the performance of aluminum surfaces for visible wavelength applications, BRDF data is measured for low roughness Al6061T6 surfaces. The impact of the BRDF derived scatter for Al6061T6 is evaluated for a nominal TMA telescope.

The retina employs a unique hemispherical architecture that provides a low-aberration image with wide field of view. However, owing to established optoelectronic fabrication technologies, conventional imagers are limited to a planar architecture. Despite that limitation, intensive endeavors have been made on mimicking the hemispherical detector geometry. The most critical limitation of the existing approaches is the increased spacing between adjacent detectors on deformation to form non-developable three-dimensional array surfaces. Here, we demonstrate retina-like imagers that do not suffer from pixel spacing enlargement upon transforming into the desired three-dimensional hemispherical shape. The approach employs fabrication processes that are generally employed for optoelectronics on planar flexible plastic foils followed by the unique elongation-free conformal deformation on an elastomeric transfer handle. Using these methods, we demonstrate hemispherical imagers with high optical performance, high yield, and, importantly, unchanged pixel density upon deformation and transformation from a developable two-dimensional to a non-developable three-dimensional surface. This approach is compatible with batch fabrication of imagers with many high performance crystalline materials including but not limited to Si, GaAs, InGaAs, and etc. The demonstrated methods provide a practical path of making high pixel density imaging system on non-developable surfaces.

A new few-mode fiber design taking advantage of a micro-structured core consisting of 19 secondary cores embedded in a pedestal geometry is presented. This design offers the possibility of precisely tailoring the rare earth ion distribution in the core in order to manage the differential modal gain. An optimized configuration of an erbium-doped few-mode fiber supporting 10 modes in the C-band with a theoretical low gain excursion is designed and realized. Preliminary optical characterizations of this fiber are presented.

Large-Mode-Area (LMA) fibers are key elements in modern high power fiber lasers operating at 1 μm. LMA fibers are highly ytterbium-doped and require a fine control of the core refractive index (RI) close to the silica level. These low RI have been achieved with multi-component materials elaborated using a full-vapor phase Surface Plasma Chemical Vapor Deposition (SPCVD) process, enabling the fabrication of large core diameter preforms (up to 4 millimeters). Following the technology demonstration, presented in Photonics West 2017, with results on 10/130 (core-to-clad diameters (in μm) ratio) fibers, this paper aims to present updated results obtained for double-clad 11/130, 20/130 and 20/400 LMA fibers, with numerical apertures at, respectively, 0.08 and 0.065. The study is based on aluminosilicate core material co-doped either with fluorine or phosphorus to achieve optimal radial RI tailoring. The fiber produced exhibit low background losses (<20dB/km at 1100nm) and high power conversion efficiencies, up to 74% for output powers of 100W limited by our test setup. The Gaussian beam quality has been evaluated using the M² measurement. Photodarkening behavior will be discussed for both fluorine and phosphorus-doped aluminosilicate materials and particularly the use of cerium as co-dopant. The SPCVD technology can indeed be used for the production of Yb-doped LMA fibers. Current development is now focused on other rare-earth doped fibers.

Erbium-ytterbium co-doped phospho-silicate double-clad fibers are used in many applications were powerful 1.5 μm sources are needed, such as telecommunication systems, LIDAR, medical lasers and much more. These fibers are typically pumped with diodes emitting at 915, 940 or 976nm to excite Ytterbium ions, which in turn transfer their energy to erbium ions through a phonon-assisted mechanism, thus leading to 1.5 μm emission. This energy transfer requires a large phosphorous content in the core of the fiber and therefore these fibers exhibit typically high numerical apertures. Properly optimized, the ytterbium to erbium ratio will minimize parasitic emission at 1 μm which provokes system failures through non-controlled spurious laser effects. We have recently observed, on such optimized fibers exhibiting 12 μm core diameter and 0.20 numerical aperture, that long term operation in CW mode in both amplifier and laser configuration, leads to a slow and irreversible decrease of the output power. This phenomenon starts at moderate signal power of just 7W and increases rapidly with the output power. This phenomenon is also observed in polarization maintaining version of the very same fibers. We have studied this phenomenon which resembles the well-known photodarkening effect in Ytterbium doped fibers. Our experiments show that all the commercially available fibers tested exhibit the same behavior. We will present a tentative explanation of the phenomenon and some solutions we implemented to drastically stabilize the output powers up to 20W enabling the use of such fibers in many industrials applications.

Cascaded Raman lasers enable high powers at various wavelength bands inaccessible with conventional fiber lasers. However, the input and output wavelengths are fixed by the multitude of fiber gratings in the system providing feedback. In this work, we demonstrate a high power, tunable, grating-free cascaded Raman fiber laser with an output power of >30W and a continuous tuning range from 1440nm to 1520nm. This corresponds to the entire in-band pumping region of Erbium doped gain media. Our system is enabled by three novel aspects – A grating free feedback mechanism for Raman lasers, a filter fiber to terminate the Raman cascade at the required wavelength band and a tunable high-power Ytterbium doped fiber laser as input. In this work, the primary system is a novel, cascaded Raman conversion module which is completely color blind to the input pump source and does wavelength band conversion at high efficiency. In addition, the conversion module also provides high spectral purity of greater than 85% at the required wavelength by terminating the cascade using high distributed losses provided by specialty Raman filter fibers. Using a high-power Ytterbium doped fiber laser continuously tuned from 1060nm to 1100nm and Raman filter fiber with distributed loss beyond 1520nm, we achieve a continuously tunable 1440nm to 1520nm laser corresponding to 5th or 6th Raman Stokes shift of the input. To the best of our knowledge, the reported powers at these wavelengths have been the highest for tunable Raman fiber lasers and is currently only limited by the input power.

Continuous-wave(CW) supercontinuum sources find applications in various domains such as imaging, spectroscopy, test and measurement. They are generated by pumping an optical fiber with a CW laser in the anomalous-dispersion region close to its zero-dispersion wavelength. Modulation instability(MI) sidebands are created, and further broadened and equalized by additional nonlinear processes generating the supercontinuum. This necessitates high optical powers and at lower powers, only MI sidebands can be seen without the formation of the supercontinuum. Obtaining a supercontinuum at low, easily manageable optical powers is attractive for many applications, but current techniques cannot achieve this. In this work, we propose a new mechanism for low power supercontinuum generation utilizing the modified MI gain spectrum for a line-broadened, decorrelated pump. A novel two-stage generation mechanism is demonstrated, where the first stage constituting standard telecom fiber slightly broadens the input pump linewidth. However, this process in the presence of dispersion, acts to de-correlate the different spectral components of the pump signal. When this is sent through highly nonlinear fiber near its zero-dispersion wavelength, the shape of the MI gain spectrum is modified, and this process naturally results in the generation of a broadband, equalized supercontinuum source at much lower powers than possible using conventional single stage spectral broadening. Here, we demonstrate a ~0.5W supercontinuum source pumped using a ~4W Erbium-Ytterbium co-doped fiber laser with a bandwidth spanning from 1300nm to 2000nm. We also demonstrate an interesting behaviour of this technique of relative insensitivity to the pump wavelength vis-a-vis zero-dispersion wavelength of the fiber.

We theoretically suggest ultra-sparse 1D and 2D arrays of high-index dielectric wires as broadband, omnidirectional reflectors and polarizers. Using diffraction potential arguments and numerical simulations, we show the proposed device for 1D array supports a high-extinction polarizing function. For an optimized 1D SrTiO3-wire array, a TE reflection resonance has a remarkably wide bandwidth while the TM wave almost freely passes through the array in the entire zero-order spectral domain. Based on the theoretically observed performance of the 1D array, we design fully conical omnidirectionality in the reflection for the 2D extension at the center wavelength of the fundamental-mode resonance condition. We briefly discuss possibility of the proposed 1D and 2D wire grid architectures for space-variant beam transforming optics and vector beam generations. Applications to THz photonic components and other long-wave devices such as radio-wave telescopes and satellite antenna are envisioned.

A new electro-optic modulator for compensating the nonlinear distortion is proposed. The third-order intermodulation distortion (IMD3) in receiver output is optically suppressed by the frequency-chirp modulation in the dual-parallel Mach-Zehnder modulator (DPMZM) structure. All of optical branches of the DPMZM are symmetric. The performance was analyzed by numerical calculations.

First, we made an experiment to confirm the performance using a DPMZM with a microwave hybrid coupler for applying 10GHz two-tone signals to each electrode of the DPMZM. The chirp parameters of two Mach-Zehnder modulators (MZMs) of the DPMZM were set to opposite signs to each other, +1 and −1. It is seen from the experiment that the intensity ratio of IMD3 to signal in the receiver output was less than −58dB at modulation indices below 0.55 (0.175π) rad and that the minimum of the ratio was less than −80dB at around 0.5 (0.16π) rad. In contrast, for a conventional single-MZM the ratio was less than −27dB below 0.55rad modulation indices. These experimental results agreed well with the calculation ones.

Next, we designed and fabricated the modulator of the single-chip structure and the single-input operation for smallsizing and simple operation. The microwave rat-race circuit (RR), which operates as a 180° hybrid coupler, was designed on a Lithium Niobate (LN) substrate at 10GHz and was integrated with modulation electrodes of the DPMZM. The RR and modulation electrodes were formed with a gold thin film pattern at a time. The IMD3 suppression operation was confirmed for the fabricated modulator as well.

Retarders or waveplates are tools for polarization modification in bulk optical systems. These devices usually have a strong wavelength dependence in their performance, making them suitable for use over a wavelength band on the order of a few percent of the center wavelength for which they are made. Display and tunable laser applications are examples that can require consistent polarization modification over a much broader wavelength range. We discuss new methods and designs for dramatically increasing range of performance and review older methods as well. We show examples of achievable performance using modern polymer and liquid crystal materials.

Both ordered and random anti-reflective surface structures (ARSS) have been shown to increase the transmission of an optical surface to >99.9%. These structures are of great interest as an alternative to traditional thin film anti-reflection (AR) coatings for a variety of reasons. Unlike traditional AR coatings, they are patterned directly into the surface of an optic rather than deposited on its surface and are thus not prone to the delamination under thermal cycling that can occur with thin film coatings. Their laser-induced damage thresholds can also be considerably higher. In addition, they provide AR performance over a larger spectral and angular range. It has been previously demonstrated that random ARSSs in silica are remarkably insensitive to incident polarization, with nearly zero variation in transmittance with respect to polarization of the incident beam at fixed wavelength for angles of incidence up to at least 30°. In this work, we evaluate polarization sensitivity of ARSS as a function of wavelength for both random and ordered ARSS. We demonstrate that ordered ARSS is significantly more sensitive to polarization than random ARSS and explain the reason for this difference. In the case of ordered ARSS, we observe significant differences as a function of wavelength, with the transmittance of s- and p-polarized light diverging near the diffraction edge. We present results for both silica and spinel samples and discuss differences observed for these two sets of samples.

Light manipulation in sub wavelength geometries is an attribute that nano photonics offers. Propagation and guiding, beaming, and confinement of the light are the most studied concepts in this area. Design of an ideal “black body” absorber with absorption of unity is one of the ultimate goals in the field of sub wavelength light confinement. Up to now, several methods and architectures are exploited to obtain high performance black absorber. One of the most commonly used approaches is to utilize metal-insulator (MI) multilayer stack. It was theoretically demonstrated that the use of periodic MI pairs can provide impedance matching in a broad frequency range [1]. Later, It was theoretically and experimentally proved that Cr-SiO2 multilayer can provide highest light absorption over 90% in a broad wavelength range between 400 nm-1400 nm [2]. In this paper, we demonstrate a facile, lithography free, and large scale compatible fabrication route to fabricate ultra-broadband wide angle perfect absorber based on metal-insulator-metal-insulator (MIMI) stack design. 600 nm bandwidth (400 nm – 1000 nm) is attained utilizing this planar design. This design is later improved by intro-duction of non-uniform texturing [3] and employing disordered nano hole plasmonic patterns where the overall process is large scale compatible and lithography free. Our findings show that the optimized design can retain light absorption above 0.9 over a wide range wavelength of 400 nm – 1490 nm, as shown in Fig. 1. To the best of our knowledge, this bandwidth is the highest among other reported studies that employ this multilayer architec-ture. Fig. 1: The measured absorption spectra for a) planar, b) non-uniform texturing, and c) nanohole plasmonic cases. REFERENCES 1. Mattiucci, N.; Bloemer, M. J.; Aközbek, N.; D’Aguanno, G. Impedance Matched Thin Metamaterials Make Metals Absorbing. Sci. Rep. 2013, 3, 3203. 2. Deng, H.; Li, Z.; Stan, L.; Rosenmann, D.; Czaplewski, D. Broadband Perfect Absorber Based on One Ultrathin Layer of Refractory Metal. Opt. Lett. 2015, 40 (11), 2592–2595. 3. Ghobadi A.; Dereshgi, S, A.; Hajian, H.; Bozok, B.; Butun, B.; and Ozbay, E. Ultra-broadband, wide angle absorber utilizing metal insulator multilayers stack with a multi-thickness metal surface texture. Sci. Rep. 2017, 7, 4755.

Graphene has received great attention over the past decade because of its extraordinary optical, electrical, and mechanical properties. The outstanding thermal properties can be another advantage of graphene, which enabled various applications such as transparent flexible heaters, photo-thermal therapy, and thermo-optic modulator based on graphene. Graphene-based thermo-optic modulators have been recently investigated based on several platforms including tapered fibers and a ring resonator fabricated with silicon waveguides, or micro-fibers to increase graphene-light interaction. But the device exhibiting high extinction ratio and low insertion loss at broad spectral range has not been reported yet. In this work, we propose a highly efficient all-optical, fiber-optic modulator assisted by photo-thermal effect in monolayer graphene. We use a side-polished fiber (SPF) covered with monolayer graphene, where the guided light experienced strong absorption at graphene layer in the presence of matched index over-cladding. Photo-excited electrons generated by strong optical absorption are then converted to thermal energies via ohmic heating around the graphene sheet, which subsequently changes the refractive index of the over-cladding material possessing large thermo-optic coefficient. This leads to variation of mode-field distribution of guided light at the SPF, resulting in significant absorption change at graphene layer. As a result, the transmitted optical power in our device could be efficiently controlled. Experimental results showed an optical output power variation of ~ 30 dB at 1550 nm in our device with relatively low insertion loss when we adjusted the control beam power by 100 mW at the wavelength of 980 nm.

Recently, a simple and self-consistent formalism that accurately gives the complex refractive index η = n - iκ of arbitrary absorptance thin films from a single transmittance curve has been introduced. Without any approximation, this analysis method makes use of a “corrected transmittance curve” for which the transmittance maxima values reach 1. With actual values of n(λ) and κ(λ), this last condition must be fulfilled. When these dispersion curves are not known, the method remains valid, but one must rely on “initial approximate dispersion curves” obtained by any mean, including theoretical formulations. In addition, this method shows that when the envelope profiles of transmittance curves are known, the need to determine initial approximate dispersion curves is not required. The challenge lies in finding the actual envelope profiles. Here, we show new developments on procedures to extract the envelope profiles. In case of weak absorption, using cubic spline interpolations, this can be done with little to no error, except for experimental and computational ones. In case of strong absorption bands, the slope in the transmittance curve shifts the extrema, which no longer correspond to the tangent points with their respective envelopes. This is remedied by applying a “rectifying process” that gives a “partially corrected transmittance curve”, which then leads to a fully corrected curve. However, in case of strong and narrow absorption bands, the small number of transmittance fringes might reduce the accuracy. Then, the reflectance curve appears beneficial to circumvent this weakness.

Silica is the ideal material for a wide range of optical applications on account of its many desirable linear properties. For many important non-linear optical applications, such as second harmonic generation (SHG), silica cannot be used as it doesn’t possess an even ordered optical non-linearity. For some time now thermal poling has been used to create an artificial second order non-linearity in silica. While early results suggested that the resulting non-linearity was not large (less than 1 pm/V) or extensive enough (only 5 microns penetration into the substrate) to be practical, there has been a concerted effort to find new ways to improve upon and harness this ‘artificial’ non-linearity. In this presentation, we will show our recent results in SHG in both poled and unpoled multi-layer silica structures. We believe that these structures, of alternating doped and undoped silica, can be used to increase the size of the non-linear region in glass and improve the efficiency of poled devices. The second harmonic generated in our samples is compared to that produced in both a silica substrate and quartz. We show that a non-zero second order non-linearity is intrinsic to multi-layer structures and study the impact of varying the number of layers and doped/un-doped duty cycle. We then investigate impact of poling on the SHG in these samples. For un-poled samples we study the effect of using different dopants or varying the concentration. We conclude by discussing applications of these structures.

Mid-infrared cascaded Stimulated Raman scattering (SRS) is experimentally investigated in an AsS optical fiber which fabricated based on As₃₈S₆₂ and As₃₆S₆₄ glasses and whose fiber loss was ∼0.09 dB/m at ∼2000 nm. Using a nanosecond laser operated at ∼1545 nm as the pump source, mid-infrared cascaded SRS up to eight orders is obtained in a 16 m AsS fiber. To the best of our knowledge, this is the first demonstration of eighth-order cascaded SRS in non-silica optical fibers, and it may contribute to developing tunable Raman fiber lasers in the mid-infrared region based on the C-band pump sources. When the pump wavelength switches to ∼2000 nm, only mid-infrared cascaded SRS up to five orders is obtained.

We investigated terbium doped halide crystals. These materials were investigated by exposing them to blue and violet diode laser sources. Optical spectroscopy and lifetime measurements are performed for unambiguous assignment of spectral transitions and detect quenching phenomenon, if any. Terbium doped halide crystals revealed bright white light under low power diode laser excitation. Chromaticity diagrams are developed from spectral measurements. Color coordinates and color temperature are estimated. Our measurements indicate that terbium-doped fluorides are suitable for white-light generation under diode laser excitation.

Optical waveguide trajectories formed in an AA/PVA a photopolymer material photosensitive at 532 nm are examined. The transmission of light by this materials is discussed. The bending and arching of the waveguides which occur are investigated. The prediction of our model are shown to agree with the observed of trajectories. The largest index changes taking place at any time during the exposure, i.e. during SWW formation are found at the positions where the largest light intensity is present. Typically, such as maxima exist close to the input face at the location of the Primary Eye or at the location of the Secondary Eyes deeper with in the material. All photosensitive materials have a maximum saturation value of refractive index change that it is possible to induce, which is also discussed.

The mid-infrared (MIR) range is of great interest because fundamental molecular vibrational absorption bands exist in the MIR range. In the MIR range, typically, lasing can be generated using quantum cascade lasers, cascaded Raman lasers, and optical parametric oscillators (OPOs). Recently, fiber OPOs (FOPOs) in the MIR range have received attention because of their flexibility of the parametric gain curve designing the chromatic dispersion. Chalcogenide glass is the promising candidate for MIR FOPO because of their wide transmission window and high nonlinear coefficient. In the present paper, we design the chromatic dispersion of four-hole As₂S₅ chalcogenide suspended core fiber (SCF), and demonstrate a far-detuned four-wave mixing (FWM) for MIR FOPO. We design the four-hole As₂S₅ chalcogenide SCF for far-detuned FWM using a ∼2 μm pump source. A four-hole As₂S₅ chalcogenide SCF which has a core diameter of 3.25 μm is fabricated using a homemade draw tower. We experimentally observed far-detuned FWM in the four-hole As₂S₅ chalcogenide SCF. A detuning frequency of over 80 THz is measured in 21 cm long fiber using a 2.7 ps pulse laser at 1.96 μm. The experimental observation was confirmed by numerical demonstration.

The practical feature of Fresnel-lens has been traditionally designed to satisfy the phase-difference function for a certain object point which is the result of ultra-high index method. For many cases, the practical blazed surface is used only on one side of the lens. Thus, as shown by our former study, the aberration can be reproduced only for a certain object point and cannot be reproduced even in the vicinity of this certain object point. This means that the one side blazed Fresnel lens has intrinsically aberration whether it is basically designed by high-index method or not. Since DOE or Fresnel lens are applied to many optical lens, we should consider the aberration caused by one side blazed Fresnel lens especially for a precise optics. In this paper, we derive the limit of Fresnel lens as F -number of DOE or Fresnel lens surface.

All-solid tellurite-glass optical rod and fiber with transversely-disordered refractive index profile were successfully fabricated to study the transport of infrared images by using transverse localization of light. The fabrication was carried out by using stack-and-draw and rod-in-tube techniques. The fabricated tellurite optical rod and fiber were composed of high-index and low-index units which were arranged randomly in the transverse plane but were invariant in the longitudinal direction. The diameter of each unit was approximately 1.0 μm. The high-index and low-index materials were TeO₂-Li₂O-WO₃-MoO₃-Nb₂O₅ (TLWMN) glass and TeO₂-ZnO-Na₂O-La₂O₃ (TZNL) glass, respectively. At 1550 nm, their refractive index difference ∆n is 0.096. To investigate the optical image transport capability, A CW laser light at 1550 nm was used as an input probe beam and the 1951 U.S. Air Force test target was installed in front of 10-cm-long segments of the fabricated rod and fiber in the experimental setup. The output signal was recorded by a beam profiler. As a result, clear transported images of numbers and lines on the test target were obtained.

A tellurite all-solid photonic bandgap fiber (ASPBF) whose cladding consists of 60 high-index rods arranged periodically around a central core was successfully fabricated. The diameter of high-index rod was about 5.0 μm and the distance between the center of two adjacent high-index rods was approximately 8.0 μm. The high-index rod was made of the TeO₂-Li₂O-WO₃-MoO₃-Nb₂O₅ (TLWMN) glass, the cladding was made of the TeO₂-ZnO-Na₂O-La₂O₃ (TZNL) glass as the background glass material and the central core was made of TZNL glass doped with 0.5 wt% of Nd₂O₃. A supercontinuum light from 0.6 to 2.4 μm was coupled into the core of fiber which is 2.2 cm long to measure its transmission spectrum. High transmission bands were obtained in the vicinity of 0.75 and 1.3 μm but the transmission was suppressed in the wavelength range from 1.0 to 1.06 μm. When a titanium∶Sapphire laser source at 0.75 μm was used, the emission spectrum was obtained with two peaks at 1.06 and 1.33 μm which are attributed to the ⁴F_3/2→⁴I_11/2 and ⁴F_3/2→⁴I_13/2 transitions of Nd³⁺ ion, respectively. The intensities of those emission peaks were compared with those obtained from a bulk glass having the same doping concentration of Nd³⁺. The results showed that by using tellurite ASPBF, the intensity of the 1.06-μm emission was suppressed by one-twelfth but the intensity of the 1.33-μm emission was maintained. This feature is very advantageous to filter out the 1.06-μm emission of Nd³⁺ ion in order to realize practical amplifier devices at 1.3 μm.

This work reports, for the first time, the results of the development and study of an Yb-fibre master oscillator, in which a variety of mode-locked regimes may be created in a controlled way electronically, including regimes producing picosecond single-scale pulses and double-scale trains. The possibility of electronic switching among generation regimes of the developed laser relies on a non-linear amplifying loop mirror of a new generation featuring two stretches of active fibre with two independently controlled pump modules. This work presents a detailed description of the experimental set-up and discusses the application prospects of the newly developed universal laser.

Mid-infrared frequency conversion via normal dispersion modulation instability in chalcogenide fibers has been numerically investigated by calculating the phase matching conditions and solving the generalized nonlinear Schrödinger equation. The core material of the chalcogenide fibers is As₂Se₃ and the cladding material is As₂S₅. Usually, the larger converted wavelength spacing between the pump and the far-detuned converted signal, the smaller gain. Therefore, the dispersion of the chalcogenide fibers are optimized to balance the gain and the converted signal wavelength spacing. The results show that the converted far-detuned mid-infrared signal can be tuned to 10 μm. The results also show that for a pumping source with the fixed wavelength, the far-detuned frequency conversion can be optimized by controlling the core size of step-index chalcogenide fibers. By using the simple step-index structure and controlling the core size of the chalcogenide fibers, the far-detuned mid-infrared frequency conversion can be achieved.

The Photo-controlled deformable mirror (PCDM) presents an interesting alternative to the conventional deformable mirror technologies as it addresses their two major bottlenecks. It offers enormous spatial resolution while keeping its complexity low due to its elegant control of the deformable surface by light projection. The PCDM prototype was a membrane type deformable mirror driven by a modified commercial mini-projector. Unique properties of PCDM allowed experimental study of actuator array disposition influence on the wavefront shaping performance of the deformable mirror. While keeping all other aspects and parameters of the experiment constant, the four actuator-array configurations were compared and resulting wavefront shaping performance assessed.

Moreover, the Photo-controlled deformable mirror was numerically modelled and the experimental results were reproduced with high degree of fidelity. By using the numerical model of PCDM, a novel method to control high spatial resolution wavefront corrector was studied with promising results.

Understanding light absorption in random lasers and its distribution within the scattering gain media is a key issue to increase the lasers’ efficiency. Here we compare monodispersed and polydispersed powders of Nd³⁺:YVO₄ and investigate the influence of the powder size distribution on scattering mean free path, absorption volume and, eventually, the lasers efficiency. The highest efficiency is achieved for polydispersed powders and we conjecture that these polydispersed powders, composed of pockets containing small grains trapped between large particles, present locally higher pump power densities than the monodispersed powders. We establish a figure of merit, based on measurable powder parameters, that agrees well with the obtained output power results of the monodispersed and polydispersed samples.

This paper presents a simple, compact, stable and inexpensive in-line solution based on catastrophic fuse effect micro-cavity interferometers for edge-filter strain interrogation of a fiber Bragg grating sensor. By using a commercial spliced machine and recycling damage fiber for the catastrophic fuse effect it is possible to construct a micro-cavity with high contrast of more than 20dB, and acceptable half free spectra range (FSR) around 13nm of interrogation range. The strain from 0 to 1440μStrain of the FBG sensor is measured with evidences of high repeatability and stability. Future work will investigate the use of the proposed method for applications requiring higher interrogation rates.

Zinc Selenide (ZnSe) has long been recognized as a nonlinear optical material and is used in many optoelectronic devices such as light emitting diodes. ZnSe is known for its remarkably wide transmission range for infrared radiation leading to its use in infrared laser applications. In this report, we discuss higher order harmonic generation when exposing ZnSe to tunable femtosecond mid-IR laser pulses with wavelengths ranging from 2.7 μm to 8.0 μm and pulse energies between 3 and 17 μJ. Higher order harmonic generation was in some instances strong enough to be directly seen by the unaided eye. We also compare these results with measurements taken for other optical materials.

Tb³⁺/Yb³⁺ co-doped CdF₂ single crystals were successfully fabricated by the Bridgman technique from a vacuum furnace in fluoride atmosphere. The structural and luminescent properties were investigated by X-ray diffraction, optical absorption and luminescence techniques at room temperature. The emission spectra exhibit a weak blue and green emission under 350 nm excitation and a strong emission under 975 nm in the spectral range 450 – 510 nm and 510 – 570 nm which are assigned to ⁵D₄ → ⁷F₆ and ⁵D₄ → ⁷F₅ transitions of Tb³⁺ ions, respectively. Furthermore, the time resolved decay time spectra are also obtained using pulse laser. The obtained upconversion spectra under 940 nm diode laser excitation at different powers showed the two-photon absorption process responsible of blue, green and red emissions.