Elimination of polarization sensitivity in silica-based wavelengthdivision multiplexer using a polyimide half waveplate

This paper proposes a low-loss technique for eliminating polarization sensitivity in a silica-based planar lightwave circuit (PLC) which uses a polarization mode converter formed at the center of the circuit. This converter consists of a waveguide gap housing a polyimide half waveplate. The excess loss of the converter was drastically reduced to 0.26 dB with a Δ=0.75% waveguide by employing an 18 μm-wide waveguide gap and a 14.5 μm-thick polyimide half waveplate. A polarization mode conversion crosstalk of -37 dB was achieved at 1.55 μm. Using this converter, we successfully eliminated the polarization sensitivity in some silica-based PLC-type wavelength division multiplexers. The converter is also insensitive to temperature and offers long term stability     

Optical waveguides in SIMOX structures

Propagation characteristics determined experimentally and theoretically for planar optical waveguides formed in separation by implantation of oxygen (SIMOX) structures are discussed. All samples were found to support both TE and TM modes at both 1.15 μm and 1.523 μm with a lowest propagation loss of 8 dB/cm. This loss was measured at a wavelength of 1.15 μm for the TE₀ mode of a planar waveguide with a 2.0-μm-thick Si guiding layer     

Simplified Z-propagating DC bias stable TE-TM modeconvertor fabricated in Y-cut lithium niobate

A TE-TM mode converter, useful at either 0.632 or 0.840 μm, has been fabricated on y-cut LiNbO₃ by Ti indiffusion with the channel waveguide placed parallel to the z-axis. For TE polarized input, the maximum TM modulation depth is 97 percent at 0.632 μm with a 5-V (pp) drive and 99 percent at 0.840 μm with a 12-V (pp) drive. A similar device operating at 1.3 μm displays 98-percent TE-TM switching at 68 V. Operation involves only coplanar electrodes placed alongside the channel acting on the r₆₁ electrooptic coefficient. A separately deposited buffer layer is unnecessary. Testing indicates a substantially greater tolerance to electrode misalignment than afforded by similar structures formed in x-cut substrates. Data illustrating immunity to photorefractive drift in the presence of a DC bias voltage is presented for 0.840-μm wavelength operation     

Simdified 12-GHz Low-Noise Converter with Mounted Planar Circuit in Waveguide (Short Papers)

A 12-GHz low-noise converter consisting of a planar circuit mounted in waveguide is described. This circuit consists of a metal sheet with proper patterns that is inserted in the middle of a waveguide parallel to the E plane. All circuit elements required for the converter are pressed or etched. This circuit is very useful for low-cost mass production and good performance. A measured noise figure of 4.5 dB was obtained with a 12-GHz signal frequency and a 420-MHz intermediate frequency.     

Wafer-fused optoelectronics for switching

Wafer fusion technique for realization of compact waveguide switches and three-dimensional (3-D) photonic integrated circuits is investigated theoretically and experimentally. Calculations based on beam propagation method show that very short vertical directional couplers with coupling lengths from 40 to 220 μm and high extinction ratios from 20 to 32 dB can be realized. These extinction ratios can be further improved using a slight asymmetry in waveguide structure. The optical loss at the fused interface is investigated. Comparison of the transmission loss in InGaAsP-based ridge-loaded waveguide structures with and without a fused layer near the core region, reveals an excess loss of 1.1 dB/cm at 1.55 μm wavelength. Fused straight vertical directional couplers have been fabricated and characterized. Waveguides separated by 0.6 μm gap layer exhibit a coupling length of 62 μm and a switching voltage of about 2.2 V. Implications for GaAs-based fused couplers for 850 nm applications will also be discussed     

Spot-size converted 1.3 μm laser with butt-jointed selectivelygrown vertically tapered waveguide

A 1.3 μm laser has been developed with a butt-jointed selectively grown spot-sire converter (SSC). The SSC vertically tapered waveguide and strained multiquantum well (MQW) active region are independently optimised. The laser was buried with semi-insulating InP to reduce optical loss in the SSC. A threshold current of 7 mA and an output power of >20 mW were obtained. Minimum coupling loss to a flat-end fibre of 1.06 dB was achieved. Long-term stability was also confirmed     

Guided wave modulators in Ti ion implanted LiNbO3waveguides

Electrooptic modulators in Ti-ion-implanted LiNbO₃ waveguides are discussed. Low loss (<1-dB/cm) planar and channel waveguides were fabricated and compared to indiffused waveguides. Higher Δn values are obtained, allowing smaller waveguide geometries and tighter mode confinement. Wavelengths of 0.85 and 1.3 μm are used. The small mode profiles resulting from the Ti doses up to 4×10¹⁷ Ti/cm² resulted in V-L products of 8.8 V-mm at 0.85 μm and 20 V-mm at 1.3 μm. These values are lower than any previously reported for a Mach-Zehnder modulator using a buffer layer. Comparison of diffused and implanted waveguide modulators indicated that modular efficiency can be optimized by electrode gap spacing and enhanced with smaller mode profiles achievable in implanted guides     

A 2D CMOS microfluxgate sensor system for digital detection of weakmagnetic fields

This paper presents a CMOS two-dimensional (2-D) vector magnetic sensor system integrating two planar microfluxgate sensors and the complete electronics for sensor excitation and signal readout. The system is based on an industrial 0.8-μm double-poly, double-metal CMOS technology with ferromagnetic NiFeMo cores added in a simple postprocessing sequence. The fluxgate sensors are embedded in a ΣΔ analog-to-digital converter for a stable and precise digital detection of weak magnetic fields. A cascaded ΣΔ modulator topology is utilized to obtain second-order noise shaping and to suppress pattern noise. Within the range of ±50 μT, the system nonlinearity is less than 1.5 μT. The angular resolution as a 2D vector sensor is less than 4° for a measured magnetic induction of 50 μT. This makes the 2-D microfluxgate magnetometer suitable for use as fully integrated electronic compass     

A three-dimensional microelectrode array for chronic neuralrecording

Describes a 3-D microelectrode array for the chronic recording of single-unit activity in the central nervous system. The array is formed by a microassembly of planar silicon multishank microprobes, which are precisely positioned in a micromachined platform that resides on the surface of the cortex. Interconnects between the probes and the platform are formed using electroplated nickel lead transfers, implemented using automated computer control. All dimensions are controlled to ±1 μm and shank/probe separations as small as 100 μm are possible. Four-probe 16-shank prototype arrays have been tested chronically in guinea pig cortex. After three months in vivo, no significant tissue reaction has been observed surrounding these structures when they remain free to move with the brain, with normal appearing tissue between shanks spaced at 150 μm to 200 μm intervals. The array structure is compatible with the use of signal processing circuitry both on the probes and on the platform. A platform-based signal processing system has been designed to interface with several active probes, providing direct analog access to the recording sites, performing on-chip analog-to-digital conversion of neural activity, and providing simple binary-output recognition of single-unit spike events using a user-input threshold voltage     

Theoretical modeling of relaxation oscillations in Er-dopedwaveguide lasers

An analysis of relaxation oscillations (λ_s~1.5 μm) in locally Er-doped optically pumped (λ_p~1.48 μm) waveguide lasers is reported. The theoretical model is based on time dependent rate equations for a quasi-two-level-system and on the equation of continuity for a gain medium. For the first time a numerically reliable simulation of the elementary properties of the laser oscillations was possible: the build-up time and decay of the relaxation oscillations, the time-dependent repetition period, the steady state signal output power and the evolution of the pump power versus time. Mathematically the problem can be characterized as a large boundary value problem, which can approximately be replaced by a stiff initial value problem of ordinary differential equations. In this report, pump- and signal evolution versus time are presented for planar Er-diffused Ti:LiNbO₃ waveguide lasers. The numerically obtained results show a good quantitatively agreement with experimental investigations     

A matrix approach to study the propagation characteristics of ageneral nonlinear planar waveguide

A simple matrix approach, which involves multiplication of 2×2 transfer matrices, is developed to study the propagation characteristics of a nonlinear planar waveguide. Numerical results for some nonlinear structures are presented and compared with the exact and previously published numerical results. It is shown that results obtained by the present approach are very accurate. In addition, the present method can be applied to arbitrary refractive index profiles with arbitrary nonlinear dependence     

Design of wavelength-flattened coupler using a novel diagram

A novel diagram which describes the condition of 3 dB coupler is proposed. Using the proposed diagram, the design of a wavelength-flattened 3 dB directional coupler composed of a uniform coupled waveguide is investigated. Normalized waveguide parameters are introduced to characterize a five-layer planar waveguide. This enables us to generalize the discussion and to reduce the number of parameters required for characterizing a coupled waveguide. A broadband 3 dB coupler having 50±5% coupling ratio over a wavelength range of 1.1-1.7 μm is designed     

Birefringence control of silica waveguides on Si and itsapplication to a polarization-beam splitter/switch

A novel polarization-beam splitter/switch with a Mach-Zehnder interferometer configuration was fabricated using a silica-based planar lightwave circuit (PLC) on a silicon substrate. The polarization-beam splitter/switch was realized by accurately controlling the waveguide birefringence and the phase state by laser trimming two kinds of stress-applying amorphous silicon film with widths of 50 μm and 95 μm. Fiber-waveguide-fiber insertion loss of 0.5 dB and crosstalk attenuations of over 25.6 dB were attained     

A full Nyquist 15 MS/s 8-b differential switched-current A/Dconverter

This paper describes the architecture and circuit design of an experimental 8-b differential 15 MS/s CMOS A/D converter, implemented using the switched-current (SI) technique. Particular emphasis has been given to maintaining analog bandwidth and hence the effective number of bits right across the input Nyquist band. Individual cells have also been optimized for inherent accuracy to achieve good performance in a simple uncorrected conversion algorithm. The converter is fabricated in a standard 0.8 μm 5 V digital CMOS process and occupies 2.4 mm²      

A broadband 800 GHz Schottky balanced doubler

A broadband planar Schottky balanced doubler at 800 GHz has been designed and built. The design utilizes two Schottky diodes in a balanced configuration on a 12 μm thick gallium arsenide (GaAs) substrate as a supporting frame. This broadband doubler (designed for 735 GHz to 850 GHz) uses a split waveguide block and has a relatively simple, fast, and robust assembly procedure. The doubler achieved ≈10% efficiency at 765 GHz, giving 1.1 mW of peak output power when pumped with about 9 mW of input power at room temperature     

Compact mode expanders using resonant coupling between a taperedactive region and an underlying coupling waveguide

A novel technique for enhanced laser-fiber coupling, based on resonant power coupling between a tapered active waveguide and an underlying coupling waveguide, is presented. Spot-sizes are transformed from 2.0×1.1 μm in the active region to 6.0×3.1 μm in the coupling waveguide, over a length of 200 μm, with a mode transformation loss of only 0.36 dB. Butt-coupling efficiencies of 55% (2.6 dB loss) are estimated to standard cleaved single-mode fibers at 1.55 μm. The proposed device requires a single epitaxial growth and conventional processing techniques, making it amenable for low-cost manufacturing     

利用时域有限差分法进行光波导器件的仿真

将理想匹配层（PML）吸收边界条件用于平面光波导结构的时域有限差分法（FDTD）分析，并对微腔体谐振环进行了数值计算模拟。证明了采用PML吸收边界条件的FDTD法应用于平面光波导结构分析的有效性。本方法对平面光波导的计算机辅助设计（CAD）具有实际意义，可用于分析任意复杂结构的平面光波导。     

Low threshold 1.3 μm-GaInAsP/InP tensile strained single quantumwell lasers grown by low-pressure MOCVD

1.3 μm Ga_0.49In_0.51As_0.7P_0.3-1.15% tensile strained single quantum well (SQW) lasers are successfully fabricated. The lowest threshold current for a 200 μm-long, 20 μm-wide ridge waveguide laser with high reflectivity coating is as low as 6 mA, corresponding to a very low threshold current density of 150 A/cm²     

ARROW-type polarizer utilizing form birefringence in multilayerfirst cladding

A waveguide polarizer using an ARROW (antiresonant reflecting optical waveguide) structure, of which the first cladding consists of three thin layers, is proposed. Theoretical calculation shows that this polarizer can achieve isolation over 30 dB/cm with an insertion loss of 0.01 dB/cm at 1.3 μm. Isolation of 83 dB/cm with insertion loss of 4.3 dB/cm was experimentally obtained at 0.633 μm. This structure is suitable for the integration of a polarization splitter and photodetector     

Vertical cavity devices as wavelength selective waveguides

We show that novel wavelength-sensitive devices can be fabricated by coupling a semiconductor vertical cavity resonator to a low index waveguide. The optical mode in the resonator propagates at an angle, and the resonator resembles a high index waveguide. A taper in the thickness of the resonator allows different parts of the waveguide to operate at different wavelengths. These structures are analyzed using both thin film equations and waveguide normalism. Concentrating on a waveguide demultiplexer, simple design equations are derived, and a demonstration device is fabricated for TE mode at 0.75 μm operation. Using AlGaAs/AlAs multilayers and a polymer top waveguide, the spectrometer exhibited a dispersion of 29 nm/cm, a wavelength resolution of better than 1 nm, and an intrinsic device efficiency of about 90%. A similar structure containing a light-emitting quantum well operated as a multiwavelength light source by modifying the spontaneous emission into the polymer waveguide