Coupling efficiency in grating tuned carbon dioxide waveguide lasers

The coupling efficiency in typical CO₂ waveguide lasers when the feedback element is a diffraction grating is investigated theoretically. A scalar diffraction integral approach is adopted, and the laser is assumed to operate on its lowest loss waveguide mode.     

Integrated band demultiplexer using waveguide grating routers

We present a novel band demultiplexer design for planar lightwave circuits. It consists of two perfectly sampled waveguide grating routers connected by sets of equal-path-length waveguides separated on one side. Its advantages are compactness, sharp passband corners, and a lack of chromatic dispersion.     

Laser-beam modulation using grating diffraction effects

An alternative system for producing an electro-optic grating modulator is discussed. A polarisation grating is used to overcome electric-field reduction occurring with closely spaced electro-optic grating electrodes.     

Laser-beam modulation using grating diffraction effects

An optical-diffraction modulator, using an electro-optic crystal excited by a periodic array of metallic conductors, is described. The operation of the device is in some ways similar to that of an acoustoelectric modulator; it differs from it in that it has a bandwidth, potentially very wide, which extends from d.c. It may therefore find application as a baseband modulator.     

Apodised sampled grating using InGaAsP/InP deep-ridge waveguide with vertical-groove surface grating

An apodised sampled grating was fabricated using an InGaAsP/InP deep-ridge waveguide with vertical-groove surface grating for use in a tunable optical filter. The fabricated grating exhibited a comb-like filter response with a relatively wide transmission bandwidth of 52 GHz and a high extinction ratio of 15 dB.     

Resonant grating waveguide structures

Under certain conditions, a resonance phenomenon can occur in waveguide grating structures. Such structures have multilayer configuration, the most basic of which is comprised of a substrate, a thin dielectric layer or semiconductor waveguide layer, and an additional transparent layer in which a grating is etched. When such a structure is illuminated with an incident light beam, part of the beam is directly transmitted and part is diffracted and subsequently trapped in the waveguide layer. Some of the trapped light is then rediffracted outwards, so that it interferes destructively with the transmitted part of the light beam. At a specific wavelength and angular orientation of the incident beam, the structure “resonates”; namely, complete interference occurs and no light is transmitted. This paper reviews previous investigations on the resonance phenomena and presents analytic and numerical models for evaluating the resonance as a function of the geometric and optical parameters of the structures and incident radiation     

Phased-array radiator reflection coefficient extraction fromcomputer waveguide simulator data when grating lobes are present

Commercially available finite-element software that solves Maxwell's equations for arbitrary three-dimensional bounded structures has enabled phase-array radiator designers to perform waveguide simulator modeling of phased-array radiating elements on the computer very efficiently. Published work on waveguide simulator design has concentrated on array performance in the absence of grating lobes, a requirement for many radar applications. For such simulators, the reflection coefficient of each propagating mode at the waveguide simulator port gives the radiator reflection coefficient at a discrete scan angle. However, the design of limited scan arrays can lead to selection of an array element spacing that allows grating lobes in real space. When a waveguide simulator is modeled on the computer, and a grating lobe is present, the two waveguide modes representing the main lobe and the grating lobe will propagate in the waveguide simulator and they will be coupled together. The simulator port-reflection coefficient of either mode is not the true reflection coefficient seen by the radiating element. We describe a method for extracting the reflection coefficient of the radiating element from the waveguide simulator data when one or more grating lobes are present     

Extended range interrogation of wavelength division multiplexed fibre Bragg grating sensors using arrayed waveguide grating

A technique for interrogating multiplexed fibre Bragg grating (FBG) sensors using an arrayed waveguide grating (AWG) is described. The approach considerably extends the sensing range from that achieved previously, while providing a strain resolution of 17n/spl epsiv///spl radic/Hz at 30 Hz.     

A pixellated grating array using photoelectrochemical etching on aGaAs waveguide

We have demonstrated and evaluated a grating array outcoupler fabricated by photoelectrochemical (PEC) etching, a manufacturable and practical approach for fabrication of grating-based III-V semiconductor waveguide devices. An array of submicron period gratings was etched into photolithographically delineated areas in a single PEC step. The fabricated devices are: 10-μm wide rib waveguides with 0.35-μm first-order outcoupling gratings; and 10-μm wide rib waveguides with 10 μm×10 μm pixellated areas of gratings. Device characterization demonstrates the effectiveness of outcoupling grating fabrication using PEC and that the pixellated grating outcoupler is an effective and simple means of generating an optical beam array     

Fabrication of low loss, waveguide grating filters using electronbeam lithography

A single step, electron beam writing process for the fabrication of low loss grating filters on AlGaAs rib waveguides is described. The technique allows both waveguide and grating to be defined in a single processing step. Linear loss measurements are presented which show that the presence of the grating has no significant effect on the throughput of the waveguides     

Active semiconductor-based grating waveguide structures

Under certain conditions, a high-finesse resonance phenomenon can occur in a grating waveguide structure (GWS). By varying these conditions, a shift in the resonance wavelength can be achieved. Specifically, utilizing the high finesse property of the GWS, small changes in the refractive index can result in a tuning range larger than the resonance bandwidth. Here, we consider different electric-field and charge carrier mechanisms that can affect the refractive index in semiconductor materials, and exploit them in order to control the refractive index change and, therefore, the resonance wavelength in the GWS. The predicted results are verified experimentally with an active GWS formed with semiconductor materials and operated in a reverse voltage configuration     

Reflective arrayed waveguide grating multiplexer

A high-performance reflective arrayed waveguide grating multiplexer/demultiplexer designed for compatibility with silicon integrated circuit processing is described. The grating, folded by a flat reflecting surface, can be printed in a single-exposure field of a photolithographic stepper. Advanced plasma assisted deposition is used to prepare waveguides with very low loss and minimum birefringence. Multiplexers with 40 channels separated by 100 GHz show intrinsic insertion losses of -2.4 dB, channel uniformity less than 0.6 dB, and very low polarization dependent wavelength shift of 0.012 nm.     

Compact design waveguide grating routers

A novel generic design for waveguide grating routers is demonstrated in the InP-InGaAsP material system that reduces the chip size by 50%, while still maintaining relaxed processing tolerances. Experimental results confirm no degradation in device performance for the compact design when compared to conventional devices     

Aberration theory of arrayed waveguide grating

The general aberration theory of arrayed waveguide grating (AWG) is proposed in this paper. The derived conclusions can be applied to any symmetrical AWGs. With the aberration theory, the spectral response can be optimized. Some performances of an AWG, for example, crosstalk and channel number, are expected to be improved by reducing the aberrations. A common AWG with the Rowland geometry has low aberrations for the absence of the second-order aberration. To further reduce the aberrations, nonstandard AWGs are considered. The AWG based on three stigmatic points is proved to have a perfect performance     

Double-chirping of the waveguide grating router

Although chirping only the arm lengths of the waveguide grating router allows each input-output port combination to have a dominant passband in one grating order with the peak transmissivities in other orders suppressed, all but one of the dominant passbands necessarily have reduced peak transmissivities and increased widths, and the extraneous grating order passband suppression is limited. We show here that simultaneously chirping both the arm lengths and the angular distribution of the arms in one of the star couplers eliminates these deficiencies.     

Tunable narrow-band thin-film waveguide grating filters

A tunable, narrow-band thin-film filter consisting of two uniform grating filter sections separated by a phase-shift section is proposed, and the theoretically predicted performance of these new components is verified experimentally. A straightforward method of calculating the reflection spectrum of these structures is also presented; the technique is particularly well suited to accounting for the effects of parasitics in practical structures. Finally, a qualitative model useful for intuitive analysis of these filters and their spectra is described.     

Silicon sandwiched slot waveguide grating couplers

Grating couplers for efficient coupling between silicon sandwiched slot waveguides and standard singlemode fibres are demonstrated. Coupling efficiency up to 20% is experimentally measured for TM polarisation and a wavelength of 1550 nm. A 20 nm 1 dB bandwidth is also obtained. Higher coupling efficiency is expected for particular designs according to simulation results.     

硅基波导光栅耦合器与波导传输损耗的研究

对硅(Si)基波导光栅耦合器的设计与耦合性能进 行了研究。采用本征模展开法对光栅耦合器进行设计与 优化,通过实验测量了光栅的耦合性能,并对均匀光栅、自聚焦光栅和反射光栅等3种光栅 耦合器的耦合 性能进行了比较,耦合效率分别达到了达到47.86、56. 36和48.98%,自聚焦光栅可以有效改善光纤到 光纤的传输效果,耦合效率提高了8.5%。通过实验测量了基于耦合光 栅技术的Si基条形波导和槽型波导的 传输损耗,结果显示,条形波导和槽型波导的传输损耗分别为2.34d B/cm和6.31dB/mm。