Proceedings Volume 9516

Integrated Optics: Physics and Simulations II

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Proceedings Volume 9516

Integrated Optics: Physics and Simulations II

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Volume Details

Date Published: 19 May 2015
Contents: 9 Sessions, 34 Papers, 0 Presentations
Conference: SPIE Optics + Optoelectronics 2015
Volume Number: 9516

Table of Contents

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Table of Contents

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  • Front Matter: Volume 9516
  • Photonic Integration
  • Devices and Circuits I
  • Devices and Circuits II
  • Photonic Crystals and Plasmonic Devices
  • Subwavelength Structures
  • Theory, Simulation, and Design
  • Materials and Fabrication
  • Poster Session
Front Matter: Volume 9516
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Front Matter: Volume 9516
This PDF file contains the front matter associated with SPIE Proceedings Volume 9516 including the Title Page, Copyright information, Table of Contents, Introduction, and Conference Committee listing.
Photonic Integration
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Towards an automated design framework for large-scale photonic integrated circuits
Sergei Mingaleev, André Richter, Eugene Sokolov, et al.
We present our approach towards an automated design framework for integrated photonics and optoelectronics, based on the experience of developing VPIcomponentMaker Photonic Circuits. We show that design tasks imposed by large-scale integrated photonics require introducing new “functional” types of model parameters and extending the hierarchical design approach with advanced parameter scripting capabilities. We discuss the requirements imposed by the need for seamless integration between circuit-level and device-level simulators, and illustrate our approach for the combination of VPIcomponentMaker Photonic Circuits and VPImodeDesigner. We show that accurate and scalable circuit-level modeling of large-scale photonic integrated circuits requires combination of several frequency- and time-domain simulation techniques (scattering-matrix assembly, transmission-line models, FIR and IIR digital filters, etc) within the same circuit simulation. We extend the scattering-matrix assembly approach for modeling linear electronic circuits, and motivate it being a viable alternative to the traditional modified nodal analysis approach employed in SPICE-like electronic circuit simulators. Further, we present our approach to support process design kits (PDK) for generic foundries of integrated photonics. It is based on the PDAFlow API which is designed to link different photonic simulation and design automation tools. In particular, it allows design and optimization of photonic circuits for a selected foundry with VPIcomponentMaker Photonic Circuits, and their subsequent export to PhoeniX OptoDesigner for layout verification and GDSII mask generation.
Passive and electro-optic polymer photonics and InP electronics integration
Hybrid photonic integration allows individual components to be developed at their best-suited material platforms without sacrificing the overall performance. In the past few years a polymer-enabled hybrid integration platform has been established, comprising 1) EO polymers for constructing low-complexity and low-cost Mach-Zehnder modulators (MZMs) with extremely high modulation bandwidth; 2) InP components for light sources, detectors, and high-speed electronics including MUX drivers and DEMUX circuits; 3) Ceramic (AIN) RF board that links the electronic signals within the package. On this platform, advanced optoelectronic modules have been demonstrated, including serial 100 Gb/s [1] and 2x100 Gb/s [2] optical transmitters, but also 400 Gb/s optoelectronic interfaces for intra-data center networks [3]. To expand the device functionalities to an unprecedented level and at the same time improve the integration compatibility with diversified active / passive photonic components, we have added a passive polymer-based photonic board (polyboard) as the 4th material system. This passive polyboard allows for low-cost fabrication of single-mode waveguide networks, enables fast and convenient integration of various thin-film elements (TFEs) to control the light polarization, and provides efficient thermo-optic elements (TOEs) for wavelength tuning, light amplitude regulation and light-path switching.
Rethinking the surface of optical waveguides
D. Melati, F. Morichetti, S. Grillanda, et al.
The interface between the core and the cladding of optical waveguides exhibits a number of physical phenomena that do not occur in the bulk of the material. For this reason, the behavior of nanoscale devices is expected to be conditioned, or even dominated, by the nature of their surfaces. Roughness-induced losses, backscattering and crosstalk between adjacent waveguides, together with surface states absorption impact on the optical and electrical properties of the waveguides must be considered in the design of any integrated optoelectronic device. The detrimental effects and the possibility of their exploitation are carefully reviewed, presenting in particular the ContacLess Integrated Photonic Probe to be used as transparent power monitor.
Simulation of self-organized waveguides for self-aligned coupling between micro- and nano-scale devices
Tetsuzo Yoshimura
We propose an optical coupling technique based on the reflective self-organized lightwave network (R-SOLNET), where optical devices with different core sizes are connected, for nano-scale-waveguide-based optical interconnects. Growth of R-SOLNET between a 3-μm-wide waveguide and a 600-nm-wide waveguide, on the core edge of which a luminescent target has been deposited, is simulated by the finite-difference time-domain method. The two waveguides are placed with gap distances ranging from 16 to 64 μm in a photopolymer with a refractive index that increases upon exposure to a write beam and luminescence. When a 400 nm wavelength write beam is introduced from the micro-scale waveguide, 470 nm luminescence is generated from the target. In the area where the write beam and the luminescence overlap, the refractive index increases rapidly. The write beam and the luminescence thus attract each other to merge into one through the self-focusing, forming a self-aligned coupling waveguide of R-SOLNET with a coupling loss of 1.5–1.8 dB, even when a lateral misalignment of 600 nm exists between them. This indicates that the R-SOLNET can be used as an optical solder to connect a micro-scale waveguide to a nano-scale waveguide. The optimum writing time required to attain the minimum coupling loss increases with increasing lateral misalignment. The dependence of the optimum writing time on the misalignment is reduced with increasing gap distance, and it almost vanishes when the distance is 64 μm, enabling unmonitored optical solder formation. R-SOLNET utilizing the two-photon photochemistry is briefly described as the next-generation SOLNET.
Devices and Circuits I
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Nonlinear optical signal processing in high figure of merit CMOS compatible platforms
Photonic integrated circuits that exploit nonlinear optics in order to generate and process signals all-optically have achieved performance far superior to that possible electronically - particularly with respect to speed. Although silicon-on-insulator has been the leading platform for nonlinear optics for some time, its high two-photon absorption at telecommunications wavelengths poses a fundamental limitation. We review the recent achievements based in new CMOS-compatible platforms that are better suited than SOI for nonlinear optics, focusing on amorphous silicon and Hydex glass. We highlight their potential as well as the challenges to achieving practical solutions for many key applications. These material systems have opened up many new capabilities such as on-chip optical frequency comb generation and ultrafast optical pulse generation and measurement.
High-speed and low-power silicon-organic hybrid modulators for advanced modulation formats
M. Lauermann, S. Wolf, R. Palmer, et al.
We demonstrate silicon-organic hybrid (SOH) modulators for generating advanced modulation formats at high data rates and with low energy consumption. SOH integration combines slot waveguides on conventional silicon-on-insulator substrates with highly efficient electro-optic materials. With this approach we generate 16QAM signals at symbol rates of 28 GBd and 40 GBd leading to gross data rates (net data rates) of up to 160 Gbit/s (133 Gbit/s) for a single polarization. This is the highest value achieved by a silicon-based modulator up to now. With a maximum symbol rate of 28 GBd, low drive voltages of only 0.6 Vpp are sufficient and result in a record-low energy consumption of only 19 fJ/bit. This is the lowest energy consumption that has so far been reported for a 16QAM modulator at 28 GBd.
A numerical investigation of silicon-based optical sampling
M. Jazayerifar, D. Bross, K. Jamshidi
Optical sampling based on four wave mixing in silicon nano-waveguides is numerically investigated. A model for nonlinear propagation in silicon is developed which is used together with a mode-solver software to obtain optimum waveguide designs for optical sampling. Performance of the system using optimum waveguides is then evaluated.
Devices and Circuits II
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Silicon nanophotonic integrated devices enabling multiplexed on-chip optical interconnects
Daoxin Dai, Jian Wang, Sitao Chen
Advanced multiplexing technologies including wavelength-division-multiplexing (WDM), polarization-division multiplexing (PDM), and mode-division multiplexing (MDM) have been utilized as a cost-effective solution to enhance the capacity of an optical-interconnect link. The on-chip (de)multiplexers, including WDM filters, PDM devices, and MDM devices, are the most important key components in a multi-channel multiplexed optical interconnect system. Hybrid (de)multiplexer to enable various multiplexing technologies simultaneously are becoming more and more important to achieve many channels. In this paper we give a review for our recent work on silicon photonic integrated devices for realizing multi-channel multiplexed on-chip optical interconnects.
Expanding sampling in a SWIFTS-Lippmann spectrometer using an electro-optic Mach-Zehnder modulator
Fabrice Thomas, Samuel Heidmann, Joran Loridat, et al.
In this work, we propose an alternative to the sub-sampling limitation in the single-waveguide configuration of SWIFTS technology using the electro-optical properties of Lithium Niobate (LiNbO3) technology. A Mach-Zehnder intensity modulator, with an initial imbalance between the arms, is coupled with a linear SWIFTS-Lippmann spectrometer. With quite reasonable control voltages (<100V), "dynamic" wide band fringes (generated by the unbalanced interferometer) can be moved under the nanodots to compensate the sub-sampling related to their spacing and rebuild the interferogram with a good sampling in a very short time, thanks to the electro-optical performances of Lithium Niobate technology. We present the measurements of broadband sources' interferograms sampled by this setup, and the considerations for spectral reconstructions for a SLED source at λ = 850 nm. The study leads to a better understanding of the behavior of the spectrometer with model and local measurement of the cross-talk phenomenon between nanodots and pixels, photometries and efficiencies of diffusion. This work opens the way to electro-optic devices where external optical path delay scan could be replaced by internal phase-modulation using electro-optic effect.
High resolution TE&TM near infrared compact spectrometer based on waveguide grating structures
G. Martin, F. Thomas, S. Heidmann, et al.
Integrated optics spectrometers can be essentially classified into two main families: based on Fourier transform or dispersed modes. In the first case, an interferogram generated inside an optical waveguide is sampled using nanodetectors, these scatter light into the detector that is in contact with the waveguide. A dedicated FFT processing is needed in order to recover the spectrum with high resolution but limited spectral range. Another way is to extract the optical signal confined in a waveguide using a surface grating and directly obtain the spectrum by means of a relay optics that generates the spectrum on the Fourier plane of the lens, where the detector is placed. Following this second approach, we present a high-resolution compact dispersive spectrometer (δλ =1.5nm at λ=1050nm) based on guided optics technology. The propagating signal is dispersed out of a waveguide thanks to a surface grating that lays along it. Focused Ion Beam technique is used to etch nano-grooves that act as individual scattering centers and constitute the surface grating along the waveguide. The waveguide is realized using X-cut, Ypropagating Lithium Niobate substrate, where the effective index for TE and TM guided modes is different. This results in a strong angular separation of TE and TM diffracted modes, allowing simultaneous detection of spectra for both polarizations. A simple relay optics, with limited optical aberrations, reimages the diffracted signal on the focal plane array, leading to a robust, easy to align instrument.
Photovoltaic maximum power point search method using a light sensor
The main disadvantage of PV panels is their low efficiency and non-linear current-voltage characteristic. Both of the above depend on the insolation and the temperature. That is why, it is necessary to use the maximum power point search systems. Commonly used solutions vary not only in complexity and accuracy but also in the speed of searching the maximum power point. Usually, the measurement of current and voltage is used to determine the maximum power point. The most common in literature are the perturb and observe and incremental conductance methods. The disadvantage of these solutions is the need to search across the whole current-voltage curve, which results in a significant power loss. In order to prevent it, the techniques mentioned above are combined with other methods. This procedure determines the starting point of one of the above methods and results in shortening the search time. Modern solutions use the temperature measurement to determine the open circuit voltage. The simulations show that the voltage in the maximum power point depends mainly on the temperature of the photovoltaic panel, and the current depends mainly on the lighting conditions. The proposed method uses the measurement of illuminance and calculates the current at the maximum power point, which is used as a reference signal in power conversion system. Due to the non-linearity of the light sensor and of the photovoltaic panel, the relation between them cannot be determined directly. Therefore, the proposed method use the modified correlation function to calculate current corresponding to the light.
Photonic Crystals and Plasmonic Devices
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Plasmonic nanoantenna coherent absorption switches for integrated photonics
Otto L. Muskens, Roman Bruck
We investigate chains of plasmonic gold nano-antennas as coherent perfect absorbers on silicon waveguides by means of 3D finite-difference time-domain simulations. In such structures, absorption can be tuned to any percentage by manipulating the phase relation of two counterpropagating waves in the waveguide. Thus, they find applications as ultracompact all-optical switches and modulators in coherent networks. We show that the choice of the waveguide cross section has significant influence on the performance of individual nano-antennas. As a result, the length of the chain of antennas for perfect coherent absorption varies strongly with the waveguide cross section. We analyze the implications of this dependency on the fabrication process.
Subwavelength Structures
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High-efficiency fully etched fiber-chip grating couplers with subwavelength structures for datacom and telecom applications
Daniel Benedikovic, Pavel Cheben, Jens H. Schmid, et al.
Surface grating couplers are key components to couple light between planar waveguide circuits in silicon-on-insulator (SOI) platform and optical fibers. Here, we demonstrate by using simulations and experiments that a high coupling efficiency can be achieved for an arbitrary buried oxide thickness by judicious adjustment of the grating radiation angle. The coupler strength is engineered by subwavelength structures, which have pitch and feature sizes smaller than the wavelength of light propagating through it, thereby frustrating diffraction effects and behaving as a homogeneous media with an adjustable equivalent refractive index. This makes it possible to apodize the grating coupler with a preferred single etch fabrication process. The coupling efficiency of the grating coupler is optimized for operating with the transverse electric (TE) polarization state at the wavelengths near 1.3 µm and 1.55 µm, which are the bands relevant for datacom and telecom interconnects applications, respectively. The design and analysis of the grating coupler is carried out using two-dimensional (2-D) Fourier-eigenmode expansion method (F-EEM) and finite difference time domain (FDTD) method. The simulations show a peak fiber-chip coupling efficiency of ‒1:61 dB and ‒ 1:97 dB at 1.3 µm and 1.55 µm wavelengths, respectively, with a minimum feature size of 100 nm, compatible with 193 nm deep-ultraviolet (DUV) lithography. The measurements of our fabricated continuously apodized grating coupler demonstrate fiber-chip coupling efficiency of ‒ 2:16 dB at a wavelength near 1.55 µm with a 3 dB bandwidth of 64 nm. These results open promising prospects for low-cost and high-volume fabrication of surface grating couplers in SOI using 193 nm DUV lithography, which is now used in several silicon photonics foundries. It is also predicted that a coupling efficiency as high as ‒ 0:42 dB can be achieved for the coupler structure with a bottom dielectric mirror.
High efficiency blazed fiber-chip grating coupler with interleaved trenches
C. Alonso-Ramos, D. Benedikovic, P, Cheben, et al.
We demonstrate a fiber-chip surface grating coupler that interleaves standard full and shallow-etched trenches to maximize directionality in the upward direction. The coupler is implemented in a regular SOI substrate with 220 nm silicon thickness and etch depths of 220 nm (full etch) and 70 nm (shallow etch), as offered by silicon photonic foundries. The blazing effect is controlled by adjusting the separation between the two sets of trenches. This way, grating directionality exceeding 95% is achieved independently of the bottom oxide (BOX) thickness. Couplers have been fabricated at LETI using 193 nm DUV lithography on 200 mm SOI wafers with 2 μm BOX. The measured coupling efficiency is -2.1 dB with a 3 dB bandwidth of 52 nm.
Fiber-chip edge coupler with large mode size for silicon photonic wire waveguides
Fiber-chip edge couplers are extensively used in integrated optics as one of the key structures for coupling of light between planar waveguide circuits and optical fibers. In this work, a new fiber-chip edge coupler concept with large mode size for coupling to submicrometer silicon photonic wire waveguides is presented. The coupler allows direct coupling to conventional SMF-28 optical fiber and circumvents the need for lensed fibers. We demonstrate by simulations a 95% mode overlap between the mode at the chip facet and a high numerical aperture single mode optical fiber with 6 μm mode field diameter (MFD). We also demonstrate a modified design with 89% overlap between the mode at the chip facet and a standard SMF-28 fiber with 10.4 μm MFD. The coupler is designed for 220 nm silicon-oninsulator (SOI) platform. An important advantage of our coupler is that large mode size is obtained without the need to increase buried oxide (BOX) thickness, which in our design is set to 3 μm. This remarkable feature is achieved by implementing in the SiO2 upper cladding two thin high-index Si3N4 layers. The high-index layers increase the effective refractive index of the upper cladding layer near the facet and are gradually tapered out along the coupler to provide adiabatic mode transformation to the silicon wire waveguide. Simultaneously, the Si-wire waveguide is inversely tapered along the coupler. The mode overlap at the chip facet is studied using a vectorial 2D mode solver and the mode transformation along the coupler is studied by 3D Finite-Difference Time-Domain simulations. The couplers are optimized for operating with transverse electric (TE) polarization and the operating wavelength is centered at 1.55 μm.
A subwavelength structured multimode interference coupler for the 3-4 micrometers mid-infrared band
Alejandro Sánchez-Postigo, Juan Gonzalo Wangüemert-Pérez, Robert Halir, et al.
The mid-infrared is attracting increasing attention since many molecules, including potentially hazardous gases such as methane and carbon dioxide, exhibit very specific absorption spectra in this wavelength region. Integrated silicon photonics circuits are envisioned to enable compact and low-cost measurement solutions for these molecules. Multimode interference couplers (MMIs) are basic building blocks for photonic circuits and a broad operational bandwidth is key if flexible operation is to be achieved, e.g. to detect different gases. Here we overcome the bandwidth limitations found in classical MMIs by segmenting the multimode region at a sub-wavelength pitch to engineer its refractive index and dispersion. We achieve less than 0:5 dB imbalance and excess loss in the complete 3 ̶ 4 µm wavelength range. The sub-wavelength MMI not only exhibits nearly threefold improvement in bandwidth, but is also about three times shorter than the conventional device.
Simulations of waveguide Bragg grating filters based on subwavelength grating waveguide
Subwavelength grating waveguides represent a flexible and perspective alternative to standard silicon-on-insulator nanophotonic waveguides. In such structures, waves propagate in the form of Bloch modes, in contrast to standard longitudinally uniform waveguides. Tunability of parameters of subwavelength grating structures possesses a great advantage of a broad variability of the (effective) refractive index and its dispersion, without significantly increasing fabrication complexity. A subwavelength grating structure is based on a (quasi)-periodic arrangement of two different materials, i.e. rectangular nanoblocks of silicon, embedded into a lower-index superstrate, with a period (much) smaller than the operational wavelength of the optical radiation. Clearly, by changing the filling factor, i.e., the duty-cycle of the subwavelength grating structure, its effective refractive index can be varied essentially between that of the superstrate and that of silicon. Our contribution is devoted to a detailed numerical analysis of Bloch modes in subwavelength grating waveguides and Bragg gratings based on subwavelength grating waveguides. Two independent versions of 3D Fourier modal methods developed within last years in our laboratories are used as our standard numerical tools. By comparison with results obtained with a 2D FDTD commercially available method we show that for reliable design of subwavelength grating waveguide devices of this kind, full-vector 3D methods have to be used. It is especially the case of Bragg gratings based on subwavelength grating waveguides, as analyzed in this paper. We discuss two options of a subwavelength grating modulation – designed by changing the subwavelength grating duty cycle, and by misplacement of Si blocks, and compare their properties from the point of view of fabrication feasibility.
Theory, Simulation, and Design
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Circuit modeling based optimization of high speed carrier depletion silicon modulators
Simple RC model, which only considered PN junction capacitance and series resistor, and complete circuit model considering parasitic capacitances of a carrier depletion based optical modulators are studied. Modulation efficiency and bandwidth of the modulators are investigated using analytical models and numerical simulations respectively. Through particle swarm optimization (PSO) a repetitive algorithm is applied to find the feasible maximum of circuit bandwidth.
Modeling of anisotropic grating structures with active dipole layers
In our previous paper [T. Fördös, et al., J. Opt. 16 (2014) 065008] we have proposed a new approach for modeling of polarized light emission from anisotropic multilayers with active dipole layers. The method is suitable to model spin-polarized light emitting diodes (spin-LED) and spin-lasers. This paper deals with generalization of the approach to scattering matrix (S-matrix) formalism and to laterally periodic structures in the frame of rigorous coupled wave algorithm (RCWA). We use expansion of the permittivity tensor in a grating layer into Fourier series and the periodic electromagnetic field in the structure is expressed using a matrix method including appropriate boundary conditions. The new approach based on S-matrix formalism is also suitable for modeling of monomode emission from MQW laser structures with multiple source layers.
Materials and Fabrication
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Epitaxially grown vertical junction phase shifters for improved modulation efficiency in silicon depletion-type modulators
High-speed silicon modulators based on the plasma effect in reverse-biased p(i)n junction phase shifters have been extensively investigated. The main challenge for such modulators is to maximize their modulation efficiency without compromising high-speed performance and insertion losses. Here, we propose a highly efficient silicon modulator based on a Mach-Zehnder Interferometer in which the doping profile of a vertical pin junction is precisely controlled by means of in-situ doping during silicon epitaxial growth. The precise level of control afforded by this fabrication procedure allows separately optimizing doping concentrations in the immediate vicinity of the junction and in surrounding electrical transport layers at the nanometric scale, enabling high performance levels. Free carrier absorption losses are minimized by implementing high carrier densities only in the waveguide regions where they benefit the most, i.e., in the immediate vicinity of the junction. Since these devices rely entirely on single crystal silicon, performance degradation caused by poor transport and high optical losses in poly- or amorphous silicon (as utilized in similar vertical phase shifter geometries such as semiconductor-insulator-semiconductor capacitive phase shifters) is avoided. Furthermore, unlike conventional plasma effect silicon phase shifters, the bandwidth of the proposed phase shifters is largely independent of the applied reverse voltage and the phase shift versus applied voltage is linearized, making them more suitable for complex modulation formats. The efficiency of the single ended phase shifters is expected to reach a VπL of 0.56 V•cm and absorption losses of α=4.5 dB/mm, a good performance metric for depletion-type modulators. Lumped element Mach-Zehnder Modulators as well as travelling-wave modulators with phase matching based on meandered waveguides have been designed and their RF characteristics simulated and optimized with Ansoft HFSS. First experiments have validated the growth of the epitaxial stack and complete devices are currently being fabricated.
Photoluminescence of graphene oxide integrated with silicon substrates
M. Casalino, I. Rea, L. Sansone, et al.
In this work we have investigated the photoluminescence signal emitted by graphene oxide (GO) nanosheets infiltrated in silanized porous silicon (PSi) matrix. We have demonstrated that a strong enhancement of the PL emitted from GO by a factor of almost 2.5 with respect to GO on crystalline silicon can be experimentally measured. This enhancement has been attributed to the high PSi specific area. In addition, we have observed a weak wavelength modulation of GO photoluminescence emission, this characteristic is very attractive and opens new perspectives for GO exploitation in innovative optoelectronic devices and high sensible fluorescent sensors.
Pixel isolation in Type-II InAs/GaSb superlattice photodiodes by femto-second laser annealing
Sona Das, Utpal Das, Nutan Gautam, et al.
A 775 nm femto-second laser annealed approach for the inter-pixel isolation, without mesa etching, to reduce dark currents of type-II InAs/GaSb superlattice photodiodes is presented. A greater than two fold improvement of the pixel isolation and a corresponding reduction in the dark current are observed for laser annealed superlattice photodiodes with a 5.5 μm cutoff wavelength, operating at 10K. A higher band gap barrier material from the superlattice structure in the inter-pixel region is expected to form after femto-second laser annealing, which has been explained on the basis of a superlattice inter-diffusion model. The increase in inter-pixel barrier height at 10K is estimated to be ~ 4 meV in the laser annealed superlattice photodiodes.
Poster Session
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Algorithm applying a modified BRDF function in Λ-ridge concentrator solar radiation
This paper presents an algorithm that uses the modified BRDF function. It allows the calculation of the parameters of Λ-ridge concentrator system. The concentrator directs reflected solar radiation on photovoltaic surface, increasing its efficiency. The efficiency of the concentrator depends on the surface characteristics of the material which it is made of, the angle of the photovoltaic panel and the resolution of the tracking system. It shows a method of modeling the surface by using the BRDF function and describes its basic parameters, e.g. roughness and the components of the reflected stream. A cost calculation of chosen models with presented in this article BRDF function modification has been made. The author’s own simulation program allows to choose the appropriate material for construction of a Λ-ridge concentrator, generate micro surface of the material, and simulate the shape and components of the reflected stream.
Optimization design of pulse compression multilayer dielectric gratings
Shuwei Fan, Liang Bai, Shenli Jia
The pulse compression multilayer dielectric grating (MDG) is one of the key elements of high-power laser systems. Mixed metal multilayer dielectric gratings(MMDG) with wider spectrum and higher diffraction efficiency are gradually becoming hot topic in chirped pulse compressor. In this paper, we studied the reflection and diffraction characteristics of pulse compression grating, i.e MMDG. First the thin-film structure, which would be applied to MMDG, was designed by combining characteristic matrix method and global optimization algorithm and the influence of the metal thickness and the number of layer film to reflectivity was also analyzed. Grating design software based on reflectivity vector theory (RCW)was developed to analyze the diffraction characteristic of MMDG. Combining generic algorithm and RCW, the optimization design of MMDG is studied. Comparing the diffraction efficiency of before and after optimization design, the highest diffraction efficiency is higher than 99% and bandwidth of MMDG is over 200nm, 50nm wider than that of MDG.
Ultra-long photonic nanojet formed by dielectric cubes
Cheng-Yang Liu, Li-Jen Chang
The capability of generating photonic nanojets using dielectric cubes working in the visible light region is introduced and investigated numerically. The simulation of electric intensity distributions for a dielectric cube is performed using the finite-difference time-domain method. The focusing characteristic of the photonic nanojets is evaluated in terms of both focal length and transversal full width at half maximum along both transversal directions. Moreover, the ultra-long photonic nanojet is studied by theoretical calculations for a dielectric cube. By changing the dimension of the dielectric cube, it has been demonstrated that the focus point is moved from inside to outside the cube with a high intensity nanojet. The super resolution imaging of the dielectric cube can be expected from the focal length and the maximum intensity. The photonic nanojet enhancement and super resolution technique could be functional for the imaging of nanoscale targets on substrates and films.
Electrooptic 1*2 switch based on proton-exchanged channel waveguides in LiNbO3
Integrated-optic 1×2 switch utilizing electro-optically controllable Y-fed directional coupler has been fabricated in LiNbO3 substrates with proton exchange technology. Such an integrated-optic switch has the newly designed Y-branching power divider allowing for high switching contrast at the both optical output ports and low driving voltage. To obtain an acceptable value of the interaction-length-to-coupling-length ratio, the novel trimming procedure is proposed. A rather high switching contrast ≥ 23 dB (power extinction ratio) at any output port and 2.5 dB insertion losses were obtained for a device with the 9 mm electrodes length.
Estimation of the sinusoidal oscillation parameters in the adaptive optics system based on the example of the photovoltaic system
In adaptive optics systems, there is a problem of a sinusoidal oscillations rejection. This paper presents the estimation method that can be used to reject these oscillations on the example of the photovoltaic system. In such a system, photovoltaic panels generate the DC signal converted by the inverter to the AC signal with specified parameters. This paper focuses on the fast and accurate estimation of these parameters taking into account the presence of harmonics in the sinusoidal signal. The estimation method is based on using maximum decay sidelobes windows and the Fast Fourier Transform procedure. In reality, the AC signal is not a pure sinusoid and it is often distorted in a deterministic manner by harmonics, and in a random manner by white, “colored” or quantization noise. The estimation error depends on the systematic error, i.e. the error caused by the quantization noise and the error caused by harmonic components. Several parameters determine which error component is dominant in the estimation results. The value of the error caused by harmonic components depends mainly on the distance between the harmonic component and the fundamental component in a frequency domain and the THD (Total Harmonic Distortion) ratio of the signal. The level of this maximum relative error is approximately 10-3 for the tested signal with THD=50%. It is important to use a filter that reduces unwanted harmonics before the data processing. The information provided in this paper can be used to determine the approximate level of estimation error before starting the estimation process.
Terahertz material characterization for nonreciprocal integrated optics
Interest in nonreciprocal terahertz (THz) integrated optics makes necessity to look for new materials active in this region and precisely characterize their optical properties. In this paper we present important aspects of the methods for determination of optical functions in far infrared (FIR) and THz spectral range. The techniques are applied to polyethylene cyclic olefin copolymer (Topas) and hexaferrites (BaFe12O19, SrFe12O19). Topas is promising material in integrated optics for THz radiation, thanks to its low absorption in this region. On the other hand, hexaferrites with its magneto-optic properties can be used for nonreciprocal integrated optic parts and radiation control. Samples were studied by THz time domain spectroscopy (THz-TDS) in spectral range 2 - 100 cm-1 by transmission and reflection. Advantage of presented THz time domain spectroscopy is measurement of the electric field wavefunction, which allows to obtain both the amplitude and phase spectra. In results we provide measured data, processing, and final computed optical properties of Topas and hexaferrites which reveal interesting optical behaviour in THz spectral range.
Magnetoplasmonic waveguiding structure with nonreciprocal dispersion of guided TM modes
In this paper we present our study of waveguiding structure with nonreciprocal dispersion of guided modes. The considered structure is based on the Silicon waveguide core and the plasmonic (gold) 1D periodic grating. The waveguide and the grating are separated by low refractive index layer (SiO2). The structure operates as follows. The evanescent field of the guided mode is used for the excitation of the surface plasmon polaritons (SPPs) at the top side of the grating. To achieve non-reciprocity the magneto-optical dielectric garnet is assumed to be on the top of the grating. The presence of the transversal magnetization in the garnet leads to the nonreciprocal shift of the SPP. Together with the evanescent coupling of guided modes this leads to the nonreciprocal dispersion of guided mode. The grating period is varied to achieve coupling of grating’s resonances with the waveguide evanescent field and therefore possible enhancement of the nonreciprocal response.
Light trap with reactive sun tracking for high-efficiency spectrum splitting photovoltaic conversion
We present a design for a modification of a previously proposed light-trapping solar collector that enables reactive solar tracking by the incorporation of an optically activated transparency-switching material. The material forms an entry aperture whose position reactively varies to admit sunlight, which is focused to a point on the receiving surface by a lens or set of lenses, over a wide range of solar angles. An analytic model for assessing device performance based on statistical ray optics is described and confirmed by raytrace simulations on a model system.
Transparency-switching optical element for sun tracking applications
Harry Apostoleris, Samuele Lilliu, Matteo Chiesa, et al.
We present a novel optical element that behaves as a dynamic aperture capable of tracking a moving light source. The element is based on a composite material which when heated undergoes reversible transition from an opaque to transparent state, resulting from a phase transition in one of its components that modifies the microstructure of the material. The material has been designed to undergo a localized transparency transition at the point of illumination by a focused beam, activated by the absorption and conversion to heat of a portion of the incident light. As a result of this mechanism the aperture reactively tracks a moving light spot, such as that created by focusing sunlight onto a surface during the sun’s apparent motion through the sky. Such an element has been proposed as a solution to the sun tracking problem of solar concentration, as it allows admission of sunlight into a concentrating light trap over a wide range of solar angles.
Side band suppression for wide band optical RoF systems
Hraghi Abir, Samir Ben Abid, Mourad Menif
In this paper, we propose a flexible monocycle generator that is based on multi-tonal excitation of a dual-arm MZM. The proposed generator permits the generation of different waveforms, such as Gaussian, first order Gaussian derivative, sinusoidal, cosine and sinc pulses. We exploit the proposed generator in order to generate the International Telecommunication Union-Radiocommunication( ITU-R) recommended channelization which contains four carrier frequencies, spaced by 2.16 GHz (58.32 GHz, 60.48 GHz, 62.64 GHz and 64.80 GHz). This millimeter waves (mmwaves) have attracted a great deal of attention in the Radio over Fiber (RoF) systems. The main challenge of the RoF system is to provide higher bands and increase significantly data rate with using millimeter-wave (mm-wave) band.
Femtosecond writing of depressed cladding waveguides in strongly cumulative regime
Mikhail A. Bukharin, Dmitriy V. Khudyakov, Sergey K. Vartapetov
We proposed a novel approach for direct femtosecond inscription of waveguides. It consisted in formation of cladding with reduced refractive index in fused silica. Depressed cladding was based on peripheral regions of individually written neighbored tracks, which should be inscribed in strongly cumulative regime. It was shown, that due to shot time interval between femtosecond laser pulses and relatively slow thermal diffusion, the exposed focal region surrounds by significantly wide cladding with reduced refracted index. Based on proposed approach we demonstrated depressed cladding waveguide inscription in fused silica using emission directly from commercially available femtosecond oscillator without correcting optical systems and second harmonic generation. It was shown, that the new approach provides formation of easily adjustable single mode waveguides with desired mode field diameter. Such depressed cladding waveguides exploit both advantages of fused silica material and depressed cladding geometry. We also verified our suggestion by experiment and inscribed depressed cladding waveguides with two different mode field diameters at similar femtosecond pulse characteristics. The obtained structures provided low propagation losses and good coupling with Gaussian mode. The waveguides supported propagation of both polarizations with nearly identical characteristics. Obtained experimental results were in good agreement with numerical simulation.