Polarization-independent all-optical switching in a nonlinearGaInAsP-InP highmesa waveguide with a vertically etched Bragg reflector

We have theoretically designed and experimentally demonstrated polarization-independent all-optical switching in a nonlinear GaInAsP-InP highmesa distributed feedback (DFB) waveguide. The device, which is composed of a highmesa waveguide stripe and a vertically etched Bragg reflector, can be simply fabricated using one-step electron beam lithography and a reactive ion etching process. The device is suitable for integration with other photonic devices such as semiconductor optical amplifiers and wavelength converters. The structural birefringence of the device has a dependence on the waveguide parameters such as the refractive index and thickness of core and cladding. The structural birefringence was successfully eliminated by adjusting the width of the highmesa waveguide. The nonlinear vertical-groove DFB highmesa waveguide is attractive for a polarization-independent all-optical switch from the viewpoint of a large grating coupling coefficient, as compared with a grating-loaded DFB highmesa waveguide. The polarization dependence of the grating coupling coefficient has also been investigated experimentally. It is possible to obtain the polarization-independent grating coupling coefficient by adjusting the grating depth in the vertical-groove DFB highmesa waveguide, together with structural zero-birefringence of the device. Polarization-independent all-optical thresholding and bistable switching operations have been successfully demonstrated in the nonlinear vertical-groove DFB highmesa waveguide     

掺半导体玻璃波导光栅耦合器及其功率限制作用

本文报导了在掺半导体玻璃波导上用离子刻蚀的方法制备出了表面刻蚀光栅耦合器。观察到了光栅耦合器的耦合效率随着输入激光功率增加而下降的功率限制作用。     

Semiconductor laser with external resonant grating mirror

A resonant grating composed of an ion exchanged slab waveguide on a glass substrate with a corrugation grating at its surface is shown to perform as a wavelength selective external mirror of a semiconductor laser. Preliminary wavelength tuning is demonstrated.     

Wavelength selection in an integrated multiwavelength ring laser

The wavelength selection mechanism of a compact integrated multiwavelength ring laser is demonstrated. The device contains four semiconductor optical amplifiers, a compact arrayed waveguide grating and passive waveguides integrated on a single InP wafer. The device can produce seven different wavelengths through biasing one or two out of the four amplifiers. Comparison of calculated and measured subthreshold laser spectra demonstrates the role of crosstalk in the arrayed waveguide grating in the laser and allows the crosstalk to be quantified. A rate-equation model of the laser and measurements are presented that describe the switching between wavelengths of the laser as a function of bias currents. A comparison between the measured data and the model is made.     

Non-polarization and high-coupling-efficiency coupler using multilevel grating structure

A multilevel grating coupler based on silicon-on-insulator (SOI) material structure is proposed to realize the coupling between waveguide and waveguide or waveguide and fiber. This coupler is compatible with the current fabrication facilities for complementary metal oxide semiconductor (CMOS) technology with vertical coupling. This structure can realize coupling when the beams with transverse electric (TE) polarization and transverse magnetic (TM) polarization are incident at the same time. The influences of the grating coupler parameters including wavelength, the thickness of waveguide layer, the thickness of SiO₂ layer and the number of steps on the TE mode and TM mode coupling efficiencies are discussed. Theory researches and simulation results indicate that the wavelength range is from 1533 nm to 1580 nm when the TE mode and TM mode coupling efficiencies are both more than 40% as the grating period is 0.99 μm. The coupling efficiencies of the incident TE and TM modes are 49.9% and 49.5% at the wavelength of 1565 nm, respectively, and the difference between them is only 0.4%.     

Demonstration of a semiconductor external cavity laser using a UVwritten grating in a planar silica waveguide

The authors report the first demonstration of a semiconductor external cavity waveguide laser, modulated at 2.5 Gbit/s over 100 km of standard optical fibre using a UV written grating in a planar silica waveguide as the feedback element     

Characteristics of a hollow-core distributed feedback CO2laser

Using perturbation theory and a plane wave analysis, the scattering amplitudes and coupling coefficients for a planar, hollow-core, double grating distributed feedback (DFB) waveguide laser are derived. Waveguide reflectivity has been compared for a single and double grating waveguide configuration. For a waveguide dimension of 100 μm over a 10 cm length, reflectivity is enhanced from 75 percent for a single grating to 98 percent using a double grating configuration. Included in this analysis is the effect of phase relationship between the two gratings. Using this analysis a means has been devised whereby reflectivity of the DFB waveguide may be optimized during operation of the laser. With the double grating configuration, coupling is enhanced such that a greater plate separation is possible in nearly all cases. Use of a double grating allows the plate separation of the waveguide to be increased from 80 to 100 μm, reducing total waveguide loss from 15.9 to 8.1 dB/m. These results have led to a method of solving heretofore prohibitive characteristics of single grating hollow-core DFB waveguides. Formal relationships for the waveguide parameters where a double grating configuration is used have been presented for designing hollow-core DFB waveguide lasers operating at 10.6 μm.     

Simulation of structural design with high coupling efficiency in external cavity semiconductor laser

For external cavity semiconductor lasers(ECSLs),high coupling efficiency is critical to reducing the linewidth.In this paper,the coupling efficiency between the laser diode and the waveguide grating has been improved,with proposals for its improvement presented,including adding spot-size conversion(SSC)and using a silicon-on-insulator(SOI)waveguide.The results indicate an increase of coupling efficiency from 41.5%to 93.1%,which exhibits an improvement of approximately 51.6%over conventional schemes.The relationship between coupling efficiency and SOI waveguide structures is mainly concerned in this article.These findings provide a new way for the future research of the narrow linewidth of ECSL.     

Multistripe array grating integrated cavity (MAGIC) laser: a new semiconductor laser for WDM applications

A novel semiconductor laser formed by monolithically integrating an array of active stripes with a passive planar waveguide bearing an etched-in diffraction grating is reported. Laser emission occurs from different stripes at different, precisely predetermined, wavelengths. It is expected that this laser will find widespread application in wavelength division multiplexed networks.<>     

Analysis of grating surface emitting lasers

An approach to the analysis of grating-coupled semiconductor lasers is presented. It is shown that there are only two resonant solutions when the grating has infinite extent. The solutions are either symmetric or antisymmetric about the center of the longitudinal coordinate system where the antisymmetric solution is nonradiating. The field in the grating layer is expressed in terms of grating eigenfunctions and rigorously matched to the boundary conditions at the waveguide interface. Solutions to the finite-length grating problem are expressed as linear combinations of the infinite-length solutions. It is shown that the two diffraction parameters in the coupled-wave equations are composed of sums and differences of the eigenvalues from the infinite-length problem     

Proposal for a Grating Waveguide Serving as Both a Polarization Splitter and an Efficient Coupler for Silicon-on-Insulator Nanophotonic Circuits

A grating waveguide is introduced and designed to serve as both a polarization splitter and an efficient vertical coupler between a fiber and a silicon-on-insulator (SOI) nanophotonic waveguide. Through this grating waveguide, the light from the fiber can be efficiently coupled into an SOI chip where the two orthogonally polarized waves are separated to travel towards the opposite directions along the waveguide. According to our simulations, the optimized structure can give a high coupling efficiency of about 50% for both polarizations, as well as a large bandwidth of over 70 nm and a very low polarization crosstalk below ${-}$22 dB at the output ports.      

Grating-assisted coupling of light between semiconductor and glasswaveguides

Floquet-Bloch theory is used to calculate the electromagnetic fields in a leaky-mode grating-assisted directional coupler (LM-GADC) fabricated with semiconductor and glass materials. One waveguide is made from semiconductor materials (refractive index ≈3.2) while the second is made from glass (refractive index ≈1.45). The coupling of light between the two waveguides is assisted by a grating fabricated at the interface of the glass and semiconductor materials. Unlike typical GADC structures where power is exchanged between two waveguides using bound modes, this semiconductor/glass combination couples power between two waveguides using a bound mode (confined to the semiconductor) and a leaky mode (associated with the glass). The characteristics of the LM-GADC are discussed. Such LM-GADC couplers are expected to have numerous applications in areas such as laser-fiber coupling, photonic integrated circuits, and on-chip optical clock distribution. Analyses indicate that simple LM-GADC's can couple over 40% of the optical power from one waveguide to another in distances less than 1.25 mm     

Optical surface wave mode converters and modulators utilizing static strain-optic effects

Periodic perturbations of dielectric waveguides can be obtained by an evaporated SiO2thin film grating through the static strain-optic effect. These waveguides are applied to TE-TM mode converters and modulators in Ti-diffused LiNbO3waveguides. Using a coupling length of 3 mm in an optical surface waveguide, we have demonstrated a TE-TM mode conversion efficiency of 80 percent and a TE-TM mode modulator with 100 percent modulation with an applied field of 2 V/μm. A theoretical analysis of a reflector for a semiconductor laser waveguide is also described.     

A Bidirectional WDM/TDM-PON Using DPSK Downstream Signals and a Narrowband AWG

We present an innovative architecture to realize a single feeder bidirectional amplified wavelength-division-multiplexing/time-division-multiplexing passive optical network based on modified nonreturn-to-zero differential phase-shift keying (DPSK) downstream signals at 20 Gb/s and a narrowband arrayed waveguide grating (AWG). The AWG plays at the same time the role of channel distributor, simultaneous demodulator for all DPSK channels, and eliminates the need for chromatic dispersion compensation. A saturated semiconductor optical amplifier (SOA) provides bidirectional amplification to compensate the splitter losses. The remodulated upstream signals are obtained at 1 Gb/s by means of a reflective SOA. Experimental results show error-free operation on both downstream and upstream signal.     

非互易波导光栅的滤波特性与应用

根据磁光材料的非互易特性和波导光栅的滤波特性,介绍了一种磁光波导光栅的非互易滤波特性及其应用.该磁光波导光栅采用法拉第旋转系数为4800°/cm的掺铈钇铁石榴石(Ce:YIG)材料、单模的脊型补偿墙截面结构和cosine型变迹光栅结构的设计.利用有限差分法和等效折射率法模拟该磁光波导光栅非互易效应的大小,同时结合耦合模理论和转移矩阵法对该磁光波导光栅的非互易滤波特性进行分析.结果表明,对于TE模和1550 nm波段,该磁光波导光栅正反向传输的中心波长偏移0.8 nm,带宽0.4 nm(-20 dB).这种非互易滤波特性可以用来实现波长选择光隔离器和光分插复用器(OADM)等集成光学器件.     

A rigorous analysis of tunable semiconductor lasers with built-ingrating-assisted vertical coupler filter

A general theoretical model is established and analyzed for a tunable semiconductor laser with a built-in co-directional grating-assisted vertical coupler filter. Possible internal reflection at the gain-coupler junction is included. A rigorous coupled-mode formulation based on the composite modes in the absence of the grating perturbation and a mode-matching method at the waveguide junctions is combined with multimode rate equation analysis. The dispersion of the semiconductor material is also included in the model. The accuracy and the scope of validity of the model are verified for both weakly and strongly coupled filter structures. Simple expressions for equivalent mirror reflectance, lasing wavelength, threshold gain and side-mode suppression ratio (SMSR) are derived and typical examples examined. The effects of the filter and the internal reflection on the longitudinal mode selectivity are discussed     

Bandstop Filter Design Using a Dielectric Waveguide Grating

Precision design techniques are obtained for dieletric waveguide (DW) bandstop filters with bandwidths up into the 5-10-percent range. Dielectric waveguide bandstop filters are realized in the form of a grating in the DW image guide which utilizes notches of varying depth and length. The grating is designed from a transmission-line prototype which has a prescribed stopband and also prescribed Chebyshev passbands. An approximate synthesis procedure for such prototypes is presented. Design data for grating notches were obtained from tests on uniform gratings, while DW dispersion is compensated for by calculations based on the "effective dielectric constant" method. Excellent agreement between computed and measured attenuation response is obtained. Two such grating structures used with loads on one end and a 3-dB coupler can be used to form a bandpass filter.     

An asymmetric discrete-time approach for the design and analysis ofperiodic waveguide gratings

A discrete-time approach is introduced for the analysis of periodic waveguide gratings with gain (or loss) extending concepts developed for transfer matrix and Gel'fand-Levitan-Marchenko (GLM) inverse scattering techniques. The periodic waveguide grating with gain (or loss) is modeled as a lossy layered dielectric that allows for a digital signal processing (DSP) formulation of the forward and inverse scattering problem. It is shown that the DSP forward scattering formulation as an asymmetric two-component wave system is equivalent to the impedance matching matrix method. A numerical example is presented to emphasize this result. The DSP formulation is an exact discrete design, not just an approximation to a continuous design, and includes all multiple reflections, transmission scattering losses, and absorption effects. A comparison of the continuous GLM, discrete GLM, and discrete Krein inverse problem formulations for a medium with gain (or loss) is presented. The discrete lossy formulations generalize previous lossless results and are found from two different types of reflection data. Since slab gratings are discrete (not continuous) structures, the integral equations used to describe the continuous inverse problem are shown to become matrix equations. Thus, our result enables fast algorithms to be used to solve the inverse problem. A fast algorithm is presented allowing for the complete reconstruction of the grating parameters from its two-sided response in a recursive (slab by slab) fashion     

Digitally tunable laser based on the integration of a waveguidegrating multiplexer and an optical amplifier

A novel monolithic semiconductor laser is demonstrated. The optical cavity comprises a 1×N waveguide grating multiplexer connected to N optical amplifiers. By driving a specific output port, laser oscillation is obtained at the wavelength determined by the wavelength path through the multiplexer. Such a laser is very useful for WDM systems because it is capable of producing a comb of precisely spaced frequencies