This PDF file contains the front matter associated with SPIE Proceedings Volume 7934, including the Title Page, Copyright information, Table of Contents, and the Conference Committee listing.

Silicate based transparent glass-ceramics containing YLiF₄(YLF) nanocrsystals have synthesized by conventional melt quenching of glass followed by controlled heat treatment of the precursor glass. X-ray diffraction powder pattern of the glass-ceramic revealed that precipitated crystalline phase was solely YLF. The averaged diameter of primary crystallites was roughly about 8 nm. It was confirmed by comparison of the fluorescent properties of rare-earth ions-doped precursor glass and glass-ceramic that rare-earth ions could be successfully incorporated into YLF nano-crystals in the glass-ceramics. This transparent glass-ceramic containing YLF nano-crystals is promising as a gain medium in rare earth-doped fiber lasers and amplifiers.

Transparent Ce:GdYAG ceramics were synthesized from the oxide powder produced by a co-preparation method in the composition of (Gd_γY_0.999-γCe_0.001)₃Al₅O₁₂. The sample showed transparency as high as 80 % at 800 nm. A broad emission band of Ce³⁺: 5d→4f transition shifted from 530 nm to 560 nm with increasing Gd content. The color coordinates (x, y) under blue LED excitation and quantum yield (QY) were evaluated with an integrating sphere. The color coordinates of the sample under blue LED excitation were increased with increasing thickness. By substituting Gd³⁺ for Y³⁺, the color coordinates also shifted to lower right and became closer to the Planckian locus in the chromaticity diagram. The red shift was explained by the energy change of 5d level of Ce³⁺ by the substitution of Gd³⁺for Y³⁺. With increasing excitation wavelength, the color coordinates of the γ=0 sample shifted from blue to yellow. This result is related to the shape of excitation band of the sample. The QY of the γ=0 sample was almost excitation wavelength independent in the range of 400 ~470 nm.

In this paper, we present our recent investigation of highly doped Tm³⁺ tellurite glass. The optical properties of series of tellurite glass samples (75 mol % TeO₂ - 20 mol ZnO - 5 mol % Na₂O) highly doped with Tm³⁺ ions were reported and discussed. An exhaustive set of samples from low concentration to very high have been used in this study. Cross relaxation process has been studied and cross-relaxation parameter has been calculated.

In this work, we report the upconversion emission from Pr³⁺ and Nd³⁺ ions in potassium lead chloride crystal KPb₂Cl₅after excitation in the ⁴F_5/2,3/2 levels of Nd³⁺ ions. We have observed violet, blue, green, orange, and red emissions at room temperature. Blue emission from Pr³⁺ ions is induced by near infrared laser excitation of Nd³⁺ through energy transfer from Nd³⁺ to Pr³⁺ ions. The mechanisms leading to the visible emissions have been investigated by studying the dependence of the upconversion luminescence on the excitation wavelength and intensity of the IR pump light.

Optical gain clamping is an all-optical method to control the gain of optical amplifiers. Recent results show that this technique is very robust and reduces impairments in amplification of typical traffic from optical burst (and packets) switching networks, where the traffic profile is very dynamic. Nevertheless, recent results have also shown that interplay between the characteristics of the optical gain clamping optical amplifier (OGC-OA) and particular traffic profiles may induce chaotic behavior caused by resonance in the OGC-OA lasing cavity. The aim of this investigation is to assess the impact of burst duration and inter-arrival time on these chaotic behavior cases. The investigation shows that the resonating frequency in which chaotic variation of the OGC-OA gain occurs is shifted - and even reduced - when the burst duration and inter-arrival time are changed. For this investigation, continuous trains of bursts were used, with fixed burst generation frequency throughout each case considered.

Although the new polymer based nano-composite materials that have been proposed for magneto-optic applications provide a high Verdet constant, they also exhibit high losses. These materials present a different challenge for realizing efficient integrated magneto-optic devices compared to traditionally used materials such as garnets. In this paper we study the figure of merit of 1D and 2D slot waveguide geometries and compare their advantages. In 2D slot waveguides the non-reciprocal TE/TM mode conversion, and in asymmetric 1D slot waveguides the non-reciprocal phase shift, respectively, are analyzed.

Spectral characteristics of fiber Bragg gratings are affected by both strain and temperature. While this makes gratings useful for sensing, care must be taken to ensure adequate discrimination between spectral shifts associated with strain and those due to changes in temperature. Recently, monitoring of cladding modes has been utilized for this purpose. In this paper, such measurement capabilities are evaluated at high temperature by exploiting the characteristics of Type II femtosecond infrared written gratings, achieving similar responsivity with significantly improved thermal durability.

The phase response of a commercial saturable absorber based on semiconductor quantum wells embedded in a resonant cavity is investigated. The nonlinear absorption change is accompanied by a variation of the spectral phase characteristic. Also, a nonlinear change in the refractive index of the material, induced by the modified carrier density, produces a weak shift in the resonant wavelength of the cavity. These effects can be exploited to realize an optically-controllable phase shifter. Simulations based on a nonlinear model are also carried out in order to investigate the effect of the various cavity parameters and phase response of the device under different operating conditions. The results from this characterization and numerical analysis show that such device can have the potential for practical applications in telecom systems, including dynamic dispersion compensation, tunable nonlinear effects compensation, and nonlinear signal processing and all-optical regeneration of phase-modulated optical signals.

A new family of organic-inorganic hybrid materials will be introduced as an undoubted candidate for advanced photonics applications. Alternating oxo-copolymers modified with organic functional groups were prepared through solventless and catalyst-free process. A variety of optical functional centers such as rare-earth ion, organic dye and metal/semiconductor nano-particles can be introduced into the systems with an excellent dispersivity to attain efficient optical activities. In the present paper, doping of rhodamine 6G dye or/and Au particles, etc., was demonstrated. Reversible photorefractive effect was observed in dye-doped hybrid thin film. Photothermal processing was used to attain such a reversible effect in combination with the slow dynamics of glassy nature of the photorefractive material. Rewritable holographic memory with a novel operating mechanism was studied.

A polarization tunable circular Dammann grating (CDG) was generated from an azo-dye (Methyl Red from Aldrich) doped liquid crystal (LC, E7 from Merck) cell. A simple multi-exposure photo-aligned process, based on cell assembled with non-rubbing glass substrates, was used to fabricate the binary phase liquid crystal CDG zone plane consisted of even zone with homogenous LC structure and odd zone with TN LC structure. Different twist angle of fabricated TN structure for odd zone can be obtained by adjusting photo exposure intensity or time. CDG with equal-intensity rings was produced through a Fourier-transform and then captured by a charge-coupled-device in our experiment. The maximum 0^th and 1^st diffraction orders of obtained CDG can be separated achieved by rotating the analyzer's polarization direction. If the chosen analyzer's direction leads to a zero phase difference of output light from even and odd zones, the maximum 0^th diffraction order will be achieved, in contrast, if the chosen analyzer's direction leads to a π phase difference of output light from even and odd zones, the maximum 1^st diffraction order will be produced. The TN structure of azo-dye doped liquid crystal cell fabricated by photo alignment technique provides a new method to generate CDG with polarization-dependent property. A broad wavelength band of lasers used to generate CDG, if far away from MR azo-dye absorption peak, expands the device's application range and shows a great advantage comparing to previously reported CDG fabricated by fixed materials, where only one fixed working wavelength is allowed.

A hybrid structure of Si-LiNbO₃ micro-ring resonator was fabricated. Free standing single crystal LiNbO₃ microplatelets (mm long and 1 um thick) were obtained from a bulk LiNbO₃ wafer by ion implantation and thermal shock. They were then transferred, positioned and bonded to Si micro-ring structure. In this hybrid structure, a large portion of the TM field is located above and below the Si waveguide. Then, the effective index of the Si waveguide can be changed by varying the refractive index of the LiNbO₃ cladding layer. Theoretical calculation with finite difference method proved that the ratio between effective index change of the Si waveguide and index change of LiNbO₃ cladding layer was 0.31 (Δn_Si/Δn_LNO=0.31) for TM mode. Then, calculated Δn_Si was about 1×10^-4 with 3 V. The effective r coefficient of Si and tuning sensitivity were about 7.2 pm/V and 2.55 GHz/V, respectively. These values are comparable to current active Si photonics with plasma dispersion methods. In addition, high speed modulation (over 40 GHz) is possible in this hybrid structure. This demonstration of a single crystalline LiNbO₃ acting as the upper cladding shows the possibility of integrating a very good EO and NLO material into the silicon-on-insulator photonics technology.

We developed a 300,000-pixel ultrahigh-speed CCD with a maximum frame rate of 2,000,000 frames per second. The shooting speed of the CCD was possible by directly connecting CCD memories, which record video images, to the photodiodes of individual pixels. The simultaneous parallel recording operation of all pixels results in the ultimate frame rate. We analyzed a voltage wave pattern in the equivalent circuit model of the ultrahigh-speed CCD by using a SPICE simulator to estimate the maximum frame rate. The pixel area was consisted of 410 and 720 pixels in the vertical and horizontal and divided into 8 blocks for parallel driving. An equivalent circuit of one block was constructed from an RC circuit with 410 × 90 pixels. The voltage wave pattern at the final stage of an equivalent circuit was calculated when a square wave pulse was input. Results showed that the square wave pulse became blunt when the driving speed was increased. After estimation, we designed the layout of the new ultrahigh-speed CCD V6 and fabricated the device. Results of an image capturing experiment indicated a saturation signal level of 100% that was maintained up to 300,000 frames per second. A saturation signal level of 50% was observed in 1,000,000 frames per second and of 13% in 2,000,000 frames per second. We showed that the maximum frame rate is dependent on a drop of the saturation signal level resulting from the driving voltage wave pattern becoming blunt.

We present the characterization results on a recent generation of InGaAs/InP Single-Photon Avalanche Diodes (SPADs) operating up to 1700 nm. The improved performance makes them very promising for many NIR single-photon counting applications since they show low dark count rate, good photon detection efficiency and quite low timing jitter. First we characterized an important drawback of InGaAs/InP SPAD, namely afterpulsing: traps in the InP high-field region capture carriers during the avalanche current flow and release them with delay, thus triggering another avalanche and generating additional noise. Using the double pulse method, we measured the afterpulsing probability as a function of time delay from the avalanche triggering. We carried out measurements at different temperatures and at different excess bias in order to find the best operating conditions. Moreover, we biased the detector at different voltage levels during the OFF period, so as to change the electric field during the de-trapping period in order to study how it affects the carrier release. Then we characterized SPAD timing jitter, that leads to the time spread between photon absorption and avalanche detection. We measured timing jitter with focused and un-focused light in order to determine the effects of light absorption position on jitter.

An antireflective two-dimensional subwavelength structure and a one-dimensional periodic structure with large phase retardation were fabricated on the glass surfaces by glass-imprint process. Novel low-Tg optical glasses based on bismuth phosphate and bismuth borate systems have been developed for the fabrication of these structures. These glasses had refractive indexes higher than 1.8 and deformation temperatures lower than 500 °C. Antireflective structure optimized by rigorous coupled-wave analysis was fabricated on an SiC mold having a curved surface for lens formation by using electron-beam lithography and dry etching techniques. Reflectivity at the imprinted surface relief decreased to about one-tens as compared with that at the polished surface in the visible region, and had less dependence on incident angle and wavelength. Mold shape has been optimized to fabricate one-dimensional structure with a high aspect ratio. A phase retardation of 0.23λ was observed between TE- and TM-polarized beams at 400 nm in the glass plate on both the surfaces of which one-dimensional structures were fabricated.

We demonstrate four-wave mixing based broadband (>68 nm) wavelength conversion and flattened supercontinuum generation spanning from 900 to 2800 nm in a 36-cm long tellurite microstructured fiber which has a high nonlinearity. By reducing the size of air holes of the tellurite microstructured fibers, single mode propagation and small dispersion slope are obtained without the propagation loss enhancement. Our results show that chromatic-dispersion controlled tellurite microstructured fibers are promising candidates for nonlinear applications.

We report about preparation technique and characterization of structured fibers composed of HMO core glasses and silica cladding. Two processes as material preparation techniques have been developed based on glasses prepared by melting of SAL (e.g. 70SiO₂-20Al₂O₃-10La₂O₃) glasses and the reactive powder sintering (REPUSIL) method. The melted glasses have been characterized by dilatometrical methods to find T_g values of 827-875°C and expansion coefficients between 4.3 and 7.0×10^-6 K^-1. The latter is one order of magnitude higher than the expansion coefficient of pure silica glass. Structured fibers (SAL core, silica cladding) were fabricated following the Rod-in-Tube (RIT) and Granulate-in-Tube (GIT) process. The HMO glasses were chosen due du their high lanthanum content and the expected high nonlinearity, suitable for nonlinear applications (e.g. supercontinuum sources). The partial substitution of lanthanum by other rare earth elements (e.g. Ytterbium) allows the preparation of fibers with extremely high rare earth concentration up to 5 mol% Yb₂O₃. The concentration of alumina in the HMO glasses as "solubilizer" for lanthanide was adjusted to about 20 mol%. So we overcame the concentration limits of rare earth doping of MCVD (maximum ca. 2 mol% RE₂O₃). Nevertheless, the investigated HMO glasses show their limits by integration in structured silica based fibers: Optical losses are typically in the dB/m range, best value of this work is about 600 dB/km. The mechanical stability of fibers is influenced by mechanical strain caused by the high thermal expansion of the core material and the lower network bonding stability of the HMO glasses, but partially compensated by the silica cladding.

The simulation, fabrication and measurement of nonlinear photonic crystals (PhCs) with hexagonal symmetry in epitaxial BaTiO₃ were investigated. The optical transmission properties of a PhC were simulated by a 2-D finite-difference time domain (FDTD) method. A complete bandgap exists for both the TE and TM optical modes. The fabricated PhC has a well-defined stop band over the spectral region of 1525 to 1575 nm. A microcavity structure was also fabricated by incorporation of a line defect in the PhC. Transmission of the microcavity structure over the spectral region from 1456 to 1584nm shows a well-defined 5 nm wide window at 1495nm. Simulations indicate that the phase velocity matched PhC microcavity device of 0.5 mm long can potentially serve as modulator with a 3 dB bandwidth of 4 THz.

This paper presents planar long period grating (LPG) devices based on a periodic thickness variation in the waveguide core, fabricated by etching into the lower cladding layer prior to definition of the waveguide layer. This periodic geometric change results in a stable grating structure and a permanent refractive index modulation of 10^-4 or higher, which is comparable to the index modulation in Ge-doped silica material induced by photo irradiation techniques widely used in fiber grating fabrication. This grating produces a strong resonance at a particular wavelength in the transmission spectrum, enabling a range of applications from wavelength filtering to signal distribution in communication networks. In this work, a polymer and silica hybrid architecture has been implemented in order to achieve wavelength tunability. Using a thermally oxidized silicon layer as a lower cladding, a Ge-doped silica ridge is patterned using conventional photolithography and reactive ion etching to form the waveguide core, which is then covered with a low index fluorinated polymer cladding. While the silica waveguides offer a lower propagation loss and an easy processability, the top polymer allows the device to be thermally tuned over a wide wavelength range by exploiting the opposite thermo-optic coefficient between fluorinated polymer and silica, and the high sensitivity of the underlying LPG to the refractive index of the cladding layer. Strong rejection bands have been demonstrated in the C+L band, in good agreement with theoretical calculations. Corrugated structures have been defined across an extended area under multiple waveguides resulting in coupling of light from the fundamental mode into cladding modes and back into the neighboring waveguides located far from the evanescent coupling distance. This kind of coupler can facilitate devices that require extraction and control of a particular waveguide mode for applications such as multiple channel signal distribution and temporal pulse shaping. Implementation of LPGs for these applications will be discussed.

Subwavelength metallic gratings were proposed as integrated polarized-RGB (red, green, and blue) color filters here and their performance was further numerically optimized with the rigorous coupled-wave analysis (RCWA) method and the genetic algorithm (GA). Grating types include the single-layer type and the double-layer one while parameters to be optimized are the period, filling factor, and thickness of each layer. The ideal performance is defined both by the large extinction ratio over the visible range and by the high transmittance aiming at wavelengths of 700 nm (R), 546.1 nm (G), and 435.8 nm (B). Results showed that a double-layer grating achieves about 50% transmission efficiency and a large extinction ratio (60dB), which are better than those in previous studies. If the proposed design can integrate with popular liquid crystal display panels, a promising way can be paved to reduce the volume and cost of display electronics.

We introduce a polarization-insensitive tunable bandpass filter design having the following unique properties: (i) high peak transmittance (~ 80 - 90%) that is independent of input polarization, (ii) non-mechanical tuning over a potentially large wavelength range (> 100 nm) with a narrow passband (< 10 nm possible), (iii) low-cost, simple, and compact (thin-film) construction with a large clear aperture suitable for many simple camera systems. This is a stacked birefringent filter approach similar to Lyot and Solc fiters but with significantly less loss due to the removal of polarizers from the system. The filter is based on a stacked configuration of polymer polarization gratings (PGs) and either fixed or tunable wave plates. PGs are a class of thin film anisotropic diffraction gratings, which exhibit unique properties including zero-order transmittance that is independent of incident polarization, and practically all diffracted light appears within the zero- and first-diffraction orders with efficiency ranging from nearly 100% to 0%. In this work we explore a variety of filter stack configurations and analyze them theoretically using Jones Calculus and Poincare Sphere reasoning. Both fixed and tunable filter configurations are presented and analyzed in terms of finesse, full width at half maximum, free spectral range, and tuning range. We then present preliminary experimental data for a three stage fixed bandpass filter.

In this paper we report emission from Bi doped gallium lanthanum sulphide (Bi:GLS) glass with a full width at half maximum (FWHM) of 600 nm which is flattened and covers the entire telecommunications window. The excitation wavelength of this emission was 1020 nm, the quantum efficiency (QE) was 17%, the lifetime was 160 μs and product of the emission cross section and lifetime (σ_emτ) was 2×10^-25 cm²s. The maximum room temperature QE was 32% at 900 nm excitation. At cryogenic temperatures the FWHM reached 850 nm with 974 nm excitation and we observed two new bismuth emission bands at 2000 and 2600 nm. The QE reached 40% for both 974 and 808 nm excitation at cryogenic temperatures. Emission spectra, normalized to the excitation power, taken with excitation wavelengths of 480-1300 nm, revealed 4 absorption bands at 680, 850, 1020 and 1180 nm. The 1180 nm absorption band was previously unobserved. Deconvolution of the emission spectra into Gaussians indicated 5 distinct emission bands over the entire excitation range. The maximum room and cryogenic temperature lifetimes were 175 and 280 μs, respectively. Their respective emission and excitation wavelengths were ~1500 and 974 nm; and ~1600 and 808 nm. By examining previously published models of Bi emission in glasses to see if they could account for the 2000 and 2600 nm emission bands, and reviewing other previously published evidence, we propose that the origin of the emission in Bi:GLS is Bi₂ (2-) dimers.

Nanoparticle-doped optical fibers are causing significant scientific interest in different application fields. Nanoparticle-doping of silica glass layers during optical fiber preform fabrication was so far reported by sol-gel and solution doping processes, by flame hydrolysis spraying and by pulling hollow cylinders from nanoparticle suspensions. A new method for fabrication of high quality nanoparticle-doped fibers is suggested. Proposed method is based on "flash vaporization" deposition process, previously reported as method to fabricate rare earth- and metal ion-doped specialty optical fibers. Experiments were made where SiO2 layers were deposited using "flash vaporization"-equipped MCVD system, adding vapors carrying metal or oxide nanoparticles into deposition zone. Analysis of produced preforms confirms presence of nanoparticles in deposited layers, albeit with low deposition rate due to weak thermophoretic forces acting on very small particles or agglomerations. Based on results, a number of improvements were suggested and implemented in fabrication process, device design and choice of precursor materials. "Flash vaporization" method was demonstrated as suitable method for deposition of nanoparticles in silica layers, permitting in-situ fabrication of complete preforms, providing easy upgrade path for existing MCVD and OVD deposition systems and allowing simultaneous co-doping by a wide range of other co-dopants.

Nanoparticles of noble metals exhibit variety of colors in the visible wavelength region due to the surface plasmon resonance. The size-induced properties of nanoparticles offer the flexibility in material design to conventional material systems for a variety of fields. In many composite materials, the aim is to design a material with desired electrical and optical properties. The dielectric properties of nanocomposites can be calculated by an effective medium approximation (EMA). Maxwell-Garnett (M-G) and Bruggeman models are well known mixing rules in EMA. In the M-G model, the available region is restricted to relatively small volume fraction of the inclusions because of the assumptions imposed on the model. For large volume fraction of the inclusions and for randomly intermixed constituents, Bruggeman derived EMA by considering the host material as an effective medium. The aim of this study is to examine the applicability of the effective medium theory to the synthesized ZrO₂-Ag compsite materials. The silver nanoparticle/ZrO₂ thin film composites were prepared by the sol-gel method with various silver fill fractions. The films were analyzed by a UV-Vis- NIR spectrophotometer, a transmission electron microscope and an X-ray diffractometer. The absorption due to the silver surface plasmon resonance was simulated using the dielectric function reflecting the M-G and the Bruggeman mixture rules. It was found the applicability of M-G model is limited to smaller densities than 50 mol% and that of the Bruggeman model is over 70 mol% of silver density in this composite system.

The photodoping phenomenon was found by Kostyshin in Russia in 1965. Many researches have carried out studying on the photodoping phenomenon of Ag /a-As₂S₃ system, and various interesting behaviors have been reported. However, there are few works on the research of the photodoping phenomenon of Ag /a-GeS₂ double layer system. It was reported that the lateral diffusion was small at the photodoping phenomenon of Ag /a-GeS₂ system compared with the Ag /a- As₂S₃ system. Therefore, the feasibility of application for fine patterning is expected for the Ag /a-GeS₂ system. In general, a light beam with the photon energy near the optical gap energy (ca. 3.3eV) of a-GeS₂ is irradiated to cause photodoping. In this study, the photodoping characteristics of multilayer films, GeS₂/Ag/GeS₂ and Ag/GeS₂/Ag, were fabricated and characterized. The photodoping characteristics are compared with the conventional two layer films. In the GeS₂/Ag/GeS₂ three layered system, strong selectivity of photodoping property relating with the incident light wavelength was found. The feasibility to apply three layered films to optical memories and waveguides were suggested.

We report broad near-infrared soliton source generation in a TeO₂-Bi₂O₃-ZnO-Na₂O tellurite microstructured optical fiber pumped by a 1557 nm femtosecond fiber laser. A continuous soliton wavelength shift from 1582 nm to 1851 nm was realized through a tellurite microstructured optical fiber as short as 6.5 cm. Experimental results are in good agreement with the numerical simulations using a generalized nonlinear Schrödinger equation. In addition, an analytical description of the Raman response function of tellurite glass is provided, and a Raman contribution factor of 0.51 is obtained from the actual Raman gain spectrum.

Supercontinuum (SC) generation has the important applications such as broadband light source, optical coherence tomography, ultra-short pulse compression, and optical frequency metrology, etc. Tellurite glass is transparent in the mid-infrared range, and has a higher n₂ than silica glass by at least one order of magnitude. We have fabricated the hexagonally shaped tellurite air-clad fiber with a core diameter of around 1 μm through controlling the temperature field exactly in the process of fiber-drawing. Since the SC generation strongly depends on the chromatic dispersion, which is determined by the microstructure of fiber, it is interesting to investigate and demonstrate such dependence for such a small core fiber in detail. In this work by pumping a positive pressure of nitrogen gas into the holes of preform, we obtained 1 μm core fibers with diameter ratio of holey region to core (DRHC) varied from 3.5 to 20. The dispersion was tailored effectively by the variation of DRHC. Dependences of SC on the microstructure and dispersion were demonstrated. The pump lasers were picosecond and femtosecond fiber lasers. One octave flattened SC generation was obtained for the fibers pumped by 1064 nm picosecond fiber laser with the pulse energy of several hundred pJ. Intense second and third harmonic generations were obtained under the pump of a 1557 nm femtosecond fiber laser. The correlation of dispersion and SC spectra was analyzed. Such tellurite microstructured optical fibers (MOFs) with high nonlinearity and controlled dispersion are significant in nonlinear applications.

The interaction of light with a sub-wavelength periodic grating can be approximated by a uniform medium with an effective index. The effective index is a function of the grating structure, the indices of its composite materials and the polarization of light. A polarization hologram is designed which makes the light in certain linear polarized mode diffract and the perpendicular linearly polarized mode transmit based upon this principle. In the hologram, an area with a sub-wavelength grating and another area with a flat surface are placed periodically and a high index film is deposited on both areas. The structure of the sub-wavelength grating and thickness of the film are adjusted that the phase shifts of the light generated in both areas balance each other out, and a design with a low aspect ratio below 1.0 is achieved. Also fabrication and testing the hologram is operated.

Silicon lenses are widely used for infrared applications. Especially for portable devices the size and weight of the optical system are very important factors. The use of aspherical silicon lenses instead of spherical silicon lenses results in a significant reduction of weight and size. The manufacture of silicon lenses is more challenging than the manufacture of standard glass lenses. Typically conventional methods like diamond turning, grinding and polishing are used. However, due to the high hardness of silicon, diamond turning is very difficult and requires a lot of experience. To achieve surfaces of a high quality a polishing step is mandatory within the manufacturing process. Nevertheless, the required surface form accuracy cannot be achieved through the use of conventional polishing methods because of the unpredictable behavior of the polishing tools, which leads to an unstable removal rate. To overcome these disadvantages a method called Ion Beam Figuring can be used to manufacture silicon lenses with high surface form accuracies. The general advantage of the Ion Beam Figuring technology is a contactless polishing process without any aging effects of the tool. Due to this an excellent stability of the removal rate without any mechanical surface damage is achieved. The related physical process - called sputtering - can be applied to any material and is therefore also applicable to materials of high hardness like Silicon (SiC, WC). The process is realized through the commercially available ion beam figuring system IonScan 3D. During the process, the substrate is moved in front of a focused broad ion beam. The local milling rate is controlled via a modulated velocity profile, which is calculated specifically for each surface topology in order to mill the material at the associated positions to the target geometry. The authors will present aspherical silicon lenses with very high surface form accuracies compared to conventionally manufactured lenses.

Both ground-based and satellite applications have demonstrated that acousto-optical spectrometers of radio-signals represent really reliable signal-processing technique for sub-millimeter and millimeter radio-astronomy due to these devices exhibit rather well efficiency as well as present sufficiently high frequency resolution in reasonably large frequency bandwidth. The key component of spectrometer is the acousto-optical cell, which dictates the basic parameters of signal processing. Its operation is based on the ability of cell to produce a large amount of independent from one another dynamic acoustic diffractive gratings, so that each of them reproduces the amplitude and frequency of only one spectral component from the incoming radio-signal. A multi-pixel CCD linear array detects and digitizes the obtained responses in the Fourier plane of a large-aperture integrating lens. The main peculiarity of this prototype lies in exploiting a large-aperture tellurium dioxide crystalline acousto-optical cell, which is oriented under a small angle to the [001]- and [110]-axes, in the regime of anomalous light scattering by extremely slow acoustic waves providing the improved frequency resolution. This circumstance determines the majority of technical requirements to the framing sub-systems and performances of prototype as a whole. Due to an extremely high anisotropy of this crystal, the efficiency of light scattering depends essentially on the incident light polarization, so that high-efficient operation needs the eigen-state polarization, which is determined by the incidence angle, light wavelength, and accuracy of the cell's crystallographic orientation. The first trial experiments have shown frequency resolution of about 45 KHz within about 1500 parallel frequency channels in real time scale.

The features of the Furnace Chemical Vapor Deposition (FCVD) method of manufacturing preforms for special optical fibers are considered. It is shown that misalignment of substrate silica tube and furnace hole axes has a negative effect on the quality of fabricated preforms, leading to angular and radial asymmetry of the refractive index profile. Ways of getting rid of this and other disadvantages of the FCVD method are described. Some advantages of the FCVD method over the MCVD method are shown. It was demonstrated that the FCVD method, despite some drawbacks, allows to manufacture high-quality fiber preforms with good symmetry of the refractive index profile, and thus it is promising for fabrication of dispersion, dispersion varying and active fibers.

Photocurrent spectra of doped black silicon (BSi) samples were investigated using metal-semiconductor-metal (MSM) structure. The BSi samples were fabricated through femtosecond-laser doping method. Two pieces of samples were annealed in nitrogen ambient for 30 minutes at different temperatures 350°C and 700°C. One control sample remains without annealing. It was found that the doped black silicon samples have an electron mobility as low as 40~50 cm²/V s but a conductivity as high as 4 ~ 5 Scm^-1. The high conductivity allows making electrodes by directly contacting metal stripes onto the black silicon surfaces. For the sample without annealing, its photocurrent spectrum covers a wavelength range from 400 nm to 1200 nm. For the sample annealed at 350°C, no significant improvement was found except disappearance of a defect induced photocurrent peak at 660 nm. Further annealing at 700°C, as observed for the third sample, was found to greatly help enhance photoresponse in the wavelength range from 400 nm to 800 nm. The photocurrent spectra under different biases were also measured. With the increasing of bias from 0 to 0.6 V, the peak photoresponse was enhanced by about 5 times while large dark current brought in substantial noise level as well.

Ceramic materials are interesting alternative to single crystals for various optoelectronic applications including high-power lasers and phosphors. Main advantages of ceramics compared to their single crystal counterparts are lower costs of production, ability to incorporate higher dopant concentrations and possibility to manufacture larger elements. In the present work, the spectroscopic properties of ceramics obtained by two different methods are compared. First method relies on solid-state reaction of nanometric oxide powders, i.e. Al₂O₃, Y₂O₃ and Nd₂O₃. The oxides with addition of tetraethyl orthosilicate were sintered under vacuum and anealled. Second method is the synthesis of neodymium-doped aluminium garnet (Nd:YAG) nanocrystalline powders prepared by coprecipitation technique. The powders were calcined and vacuum-sintered in optimized process conditions. For all ceramic samples fluoresce and decay data is presented. Presented results indicate that the ceramic samples obtained by reactive sintering method have superior spectroscopic properties compared to the samples synthesized from Nd:YAG nanocrystalline powders. The optimization of manufacturing process allowed to demonstrate ceramics having the properties comparable to single crystal counterparts. Optical quality and luminescent properties make the ceramics manufactured at the Institute of Electronic Materials Technology an interesting candidate for laser applications.

We are trying to develop high performance mid-infrared (MIR) and far-infrared (FIR) optical filters with mechanical strength and robustness for thermal cycling toward cryogenic infrared astronomical space missions. Multilayer interference filters enable us to design a wide variety of spectral response by controlling refractive index and thickness of each layer, however, in longer MIR and FIR (30-300μm) wavelength regions, there are a few optical materials known to have both good transparency and physical robustness, which makes difficult to realize high performance filters because of limited refractive index values. It is also difficult to deposit thick layers required for MIR/FIR multilayer filters by conventional method. Furthermore, multilayer interference filters are realized by thin film coatings having different coefficients of thermal expansion (CTE), which makes filters fragile for thermal cycling. To clear these problems, we introduce sub-wavelength structures (SWS) for controlling the refractive index. Then, only one material is necessary for fabricating filters, which enables us to fabricate filters with mechanical strength and robustness for thermal cycling. In 30-300μm wavelength regions silicon is very suitable for filter material because not only silicon has little absorption and physical robustness but also SWS are easily fabricated by micro-electro mechanical systems (MEMS) technology. As a first step, we have fabricated anti-reflection SWS layer on silicon wafers to demonstrate the refractive index control by simple SWS (periodic cylindrical holes on a silicon wafer). Comparing measured transmittance with both effective medium approximation (EMA) theory and rigorous coupled wave analysis (RCWA) simulation, we confirm that the refractive control of SWS layer is verified.

The absorption and fluorescence characteristics of Er doped and Nd, Er codoped fluoride glasses were investigated under illumination of the simulated sunlight, laser or a monochromatic light filtered from a Xe lamp. Er was used as a sensitizing agent enhancing the energy conversion and the emission efficiency of Nd ions in fluoride glass intended for the sunlight excitation. Er doped fluoride glasses showed four emission peaks under simulated sunlight illumination at the wavelengths of 550, 848, 980, and 1530 nm attributed to the electronic transitions of Er³⁺ ions. The quantum efficiency of the emission from all of the bands had a peak at x = 0.5 mol. % Er and with the maximum of 73 %. The intensity of each emission band showed different ratios for various ErF₃ contents. It is expected that concentration quenching of ⁴S_3/2 state is easy to occur with high concentration of ErF₃ compared to the other states. The energy transfer from Er to Nd was studied using a monochromatic light illumination which is absorbed by Er³⁺ ions only. Strong contribution of Er absorption to the 1.05 μm emission of Nd, Er co-doped fluoride glass was observed. Er was confirmed as a suitable sensitizer for the enhanced energy conversion and emission efficiency of Nd ions in ZBLAN glasses which are proposed for highly efficient solar pumped fiber lasers.

We report the fabrication and performance characterization of 1550 nm separate absorption, grading, charge, and InP/InAlAs hetro-multiplication avalanche photodiodes (SAGCHM APDs) for single photon detection applications. The linear mode performance of the fabricated APDs are firstly characterized that the dark current at 95% of the breakdown voltage was 30 pA and 15 nA at 200K and 300K, respectively. The gain-bandwidth product of 62 GHz was obtained at room temperature. For single photons detection characterization, however, our APD was operated in the gated passive quenching mode, at lower temperature and incorporated with an optimizing spike-cancellation self-differencing circuit. Under the temperature of -50°C and the gate repetition frequency of 100 KHz with pulse width of 2 ns, the lowest dark count probability (P_dc) of 1.2 x 10^-5, the highest single-photon detection efficiency (η_det) of 22.5%, and the lowest noise equivalent power (NEP) of 1.5x10^-15 W/(Hz)^1/2 were obtained, respectively. Moreover, we demonstrated the transmission distance as a function of quantum bit error rate (QBER) based on the obtained performance parameters. The maximum transmission distance, at QBER=15%, of 43 km was achieved.

An equivalence theory based on a unitary optical system of a generalized elliptical phase retarder was derived. Whereas the elliptical phase retarder can be treated as the combination of a linear phase retarder and a polarization rotator equivalently. Three fundamental parameters, including the elliptical phase retardation, the azimuth angle and the ellipticity angle of the fast elliptical eigen-polarization state were derived. All parameters of a generalized elliptical phase retarder can be determined from the analytical solution of the characteristic parameters of the optical components: linear phase retardation and fast axis angle of the equivalently linear phase retarder respectively, and polarization rotation angle of an equivalent polarization rotator. In this study, the experimental verification was demonstrated by testing a twisted nematic liquid crystal device (TNLCD) treated as a generalized elliptical phase retarder. A dual-frequency heterodyne ellipsometer was setup and the experimental result demonstrates the capability of the equivalent theory on elliptical birefringence measurement at high sensitivity by using heterodyne technique.

In this research, a novel linear polarization modulation heterodyne ellipsometer (LPMHE) integrated with a digital signal processor is able to measure ellipsometric parameters of a specimen was developed. In this setup, a pair of orthogonally circularly polarized lights with slightly different frequency of the laser beam is used which behaves like a linear polarization rotator at high speed. By integrating with a digital storage oscilloscope, LPMHE is able to real-time measure ellipsometric parameters precisely. When the incident angles of laser beam are set at 60° and 70° in LPMHE, an accuracy of less than 0.7% on ellipsometric parameters measurement of the SiO₂ thin film deposited on silicon substrate was demonstrated.

Practical applications confirm that acousto-optical spectrometers of optical and radio signals provide efficient and accurate processing of data in real time scale. The key component of similar spectrometers is an acousto-optical cell, which dictates performances of the optical scheme arrangement. Within non-collinear arrangement of spectrometer, the most compact and simplest scheme of really wide-aperture light beam expander appears with exploiting an even number of prisms. This arrangement of beam expander does not deflect light beam, provides rather high transmission, and needs less precision for alignment than as a lens telescope requires. We describe a four-prism beam expander providing a 35-time magnification and about 65%-transmission at a distance of 10 cm. Within elliptical polarization, this expander exhibits properties of an amplitude filter being sensitive to the angle of beam incidence. In a view of obtaining the needed eigen-states of elliptical polarization at the output of expander, the detailed analysis of polarization features is performed, numerically estimated, and selectively compared with experimental data.

Fiber optic rings are used for synchronization of modes and optical pulses shaping in fiber lasers. The resulting pulses are characterized by stable amplitude and reduced chirp. The length of fiber ring is chosen so as to avoid loss of laser light coherence. New application of optical fiber loops is their inclusion in the closed loop during their excitation by laser light modulated by low-frequency signal and middle frequency signal. If loop also includes amplifying fiber which covers losses incurred by couplers will thus be possible evaluated a signal delay in long loop and thus measure the length of fiber. Reverse task is possibility to measure n_1eff if we know the length of SM fiber loop. This type of designed fiber optic oscillator consists of single-mode optical fiber SM28e in lengths of order of kilometers. This fiber is connected in a series with erbium doped fiber that covers loop losses. Loop, which acts as an oscillator is excited by DFB lasers both at a wavelength of 1550 nm and at wavelength of 1310 nm. The paper will demonstrated the comparison between active and passive fiber loops and their influence to accuracy of effective refractive index measurement.

Continued innovation with optical components and optical materials not only increases the utility and value of optical sensors and devices, it also mandates the development of new test methods and test hardware. Thus, in order to evaluate the enhanced performance of these new optical components and systems - SWIR imagers, silicon-based photodetectors, and single-photon detectors; as well as detectors that may utilize novel materials for highly specific spectral regions - equally enhanced test and measurement equipment must be used. A task such as this is greatly simplified for these detectors when a minimal amount of hardware can be used to test, measure, and calibrate the benchmarks of their performance; benchmarks such as SNR, uniformity, sensitivity, linearity, and dynamic range. The role of the test hardware is driven by its ability to provide high resolution, uniform, and stable broadband output. A broadband source encompassing the UV through the SWIR region of the electromagnetic spectrum capable of producing high daylight irradiance levels down to low star light irradiance levels. All of this functionality is integrated into one calibrated test set. A test set that is robust but does not sacrifice precision and accuracy. This paper will explore characterization testing and the advantages and drawbacks of various types of broadband sources spanning UV through SWIR over a high dynamic range of output. This paper will further suggest standardization of test methods and presentation of results (for example, SNR) such that results from various detectors can be compared directly.

This article presents the effect of low-dose gamma-ray irradiation on a newly developed randomly distributed holes optical fiber (RDHF). The single-mode fiber has a cladding diameter of 125 μm and 0.21 dB/km attenuation in the 1550 nm wavelength. The effect of gamma irradiation on the presented fibers was studied by comparing their transmission performance at 1550 nm wavelength with standard single-mode telecommunication fiber (SMF). RDHF along with SMF were irradiated with 0.662 MeV gamma-rays at absorbed dose rate of 4 mGy(Si)/hr and total dose of 1.5 Gy(Si). Results revealed that the performance of optical fiber under irradiation is not only dependent on the bulk material but also on the physical structure of the fiber.

Thin films of two different dielectric materials (Yttrium Oxide and Tantalum Pentoxide) were deposited by reactive sputtering and reactive evaporation to determine their suitability as a host for a rare earth doped planar waveguide upconversion laser. The optical properties, structure and crystalline phase of the films were found to be dependent on the deposition method and process parameters. X-ray diffraction (XRD) analysis on several of the 'as-deposited' thin films revealed that the films vary from amorphous to highly crystalline depending on material and process parameters. SEM imaging of the Yttrium Oxide layers revealed a regular column structure confirming their crystalline nature and SEM imaging of the Tantalum Pentoxide layers revealed a smooth amorphous layer confirming their XRD diffractrograms. The dielectric thin film layers which allowed guiding in both the visible and infra-red regions of the spectrum had a more amorphous structure.