High-Integrated-Photosensitivity Negative-Electron-Affinity GaAs Photocathodes with Multilayer Be-Doping Structures

The effect of changing Be doping concentration in GaAs layer on the integrated photosensitivity for nega- tive-electron-affinity GaAs photocathodes is investigated. Two GaAs samples with the monolayer structure and the muhilayer structure are grown by molecular beam epitaxy. The former has a constant Be concentration of 1 × 10^19 cm^-3, while the latter includes four layers with Be doping concentrations of 1 × 10^19, 7 × 10^18, 4 × 10^18, and 1 × 10^18 cm^-3 from the bottom to the surface. Negative-electron-affinity GaAs photocathodes are fabricated by exciting the sample surfaces with alternating input of Cs and O in the high vacuum system. The spectral response results measured by the on-line spectral response measurement system show that the integrated photosensitivity of the photocathode with the muhilayer structure enhanced by at least 50% as compared to that of the monolayer structure. This attributes to the improvement in the crystal quality and the increase in the surface escape probability. Different stress situations are observed on GaAs samples with monolayer structure and muhilayer structure, respectively.

Simulation of a Monolithic Integrated CMOS Preamplifier for Neural Recordings

A monolithic integrated CMOS preamplifier is presented for neural recording applications. Two AC-coupied capacitors are used to eliminate the large and random DC offsets existing in the electrode-electrolyte interface. Diode-connected nMOS transistors with a negative voltage between the gate and source are candidates for the large resistors necessary for the preamplifier. A novel analysis is given to determine the noise power spectral density. Simulation results show that the two-stage CMOS preamplifier in a closed-loop capacitive feedback configuration provides an AC in-band gain of 38.8dB,a DC gain of 0,and an input-referred noise of 277nVmax, integrated from 0. 1Hz to 1kHz. The preamplifier can eliminate the DC offset voltage and has low input-referred noise by novel circuit configuration and theoretical analysis.

A Wavelength Tunable DBR Laser Integrated with an Electro Absorption Modulator by a Combined Method of SAG and QWI

We report a wavelength tunable electro-absorption modulated DBR laser based on a combined method of SAG and QWI. The threshold current is 37mA and the output power at 100mA gain current is 3.5mW. When coupled to a single-mode fiber with a coupling efficiency of 15% ,more than a 20dB extinction ratio is observed over the change of EAM bias from 0 to -2V. The 4.4nm continuous wavelength tuning range covers 6 channels on a 100GHz grid for WDM telecommunications.

An Electroabsorption Modulator Monolithically Integrated with a Semiconductor Optical Amplifier and a Dual-Waveguide Spot-Size Converter

A semiconductor optical amplifier and electroabsorption modulator monolithically integrated with a spotsize converter input and output is fabricated by means of selective area growth,quantum well intermixing,and asymmetric twin waveguide technology. A 1550-1600nm lossless operation with a high DC extinction ratio of 25dB and more than 10GHz 3dB bandwidth are successfully achieved. The output beam divergence angles of the device in the horizontal and vertical directions are as small as 7.3°× 18.0°, respectively, resulting in a 3.0dB coupling loss with a cleaved single-mode optical fiber.

Butt-Joint Monolithicaily Integrated DFB-LD/EA-MD Light Source for 10Gbit/s Transmission

This paper reports on the design, fabrication, and performance of an integrated electro-absorptive modulated laser based on butt-joint configuration for 10Gbit/s application. This paper mainly aims at two aspects. One is to improve the optical coupling between the laser and modulator; another is to increase the bandwidth of such devices by reducing the capacitance parameter of the modulator. The integrated devices exhibit high static and dynamic characteristics. Typical threshold current is 15mA,with some value as low as 8mA. Output power at 100mA is more than 10mW. The extinction characteristics,modulation bandwidth, and electrical return loss are measured. 3dB bandwidth more than 10GHz is monitored.

Monolithically Integrated Laser Diode and Electroabsorption Modulator with Dual-Waveguide Spot-Size Converter Output

A 1.60μm laser diode and electroabsorption modulator monolithically integrated with a novel dualwaveguide spot-size converter output for low-loss coupling to a cleaved single-mode optical fiber are demonstrated.The devices emit in a single transverse and quasi single longitudinal mode with an SMSR of 25.6dB. These devices exhibit a 3dB modulation bandwidth of 15. 0GHz, and modulator DC extinction ratios of 16.2dB. The output beam divergence angles of the spot-size converter in the horizontal and vertical directions are as small as 7. 3°× 18. 0°,respectively, resulting in a 3. 0dB coupling loss with a cleaved single-mode optical fiber.

1.55μm Laser Diode Monolithically Integrated with Spot-Size Converter Using Conventional Process

A novel 1.55μm laser diode with spot-size converter is designed and fabricated using conventional photolithography and chemical wet etching process.For the laser diode,a ridge double-core structure is employed.For the spot-size converter,a buried ridge double-core structure is incorporated.The laterally tapered active core is designed and optically combined with the thin and wide passive core to control the size of mode.The laser diode threshold current is measured to be 40mA together with high slop efficiency of 0.35W/A.The beam divergence angles in the horizontal and vertical directions are as small as 14.89°×18.18°,respectively,resulting in low-coupling losses with a cleaved optical fiber (3dB loss).

Novel electroabsorption modulator monolithically integrated with spot-size converter

A novel 1.55-μm spot-size converter integrated electroabsorption modulator was designed with conventional photolithography and chemical wet etching process. A ridge double-core structure was employed for the modulator, and a buried ridge double-core structure was incorporated for the spot-size converter. The passive waveguide was optically combined with a laterally tapered active waveguide to control the mode size. The figure of merit is 4.1667 dB/V(/100 μm) and the beam divergence angles in the horizontal and vertical directions were as small as 11.2 deg. and 13.0 deg., respectively.

Integrated electroabsorption-modulated DFB laser by using an improved butt-joint method

An improved butt coupling method is used to fabricate an electroabsorption modulator (EAM) monolithically integrated with a distributed feedback (DFB) laser. The obtained electroabsorption-modulated laser (EML) chip with the traditional shallow ridge exhibits very low threshold current of 12 mA, output power of more than 8 mW, and static extinction ratio of -7 dB at the applied bias voltage from 0.5 to -2.0 V.

Narrow-beam divergence 1.55μm laser diodes with integrated self-aligned spotsize conVerter

This paper describes the high performance of narrow-beam divergence spot size converter (SSC) integrated separately confined heterostructure (SCH) LD. The upper optical confinement layer (OCL) and the butt-coupled tapered thickness waveguide were regrown simultaneously, which not only offered the separated optimization of the active region and the integrated spotsize converter, but also reduced the difficulty of the butt-joint selective regrowth. The threshold current was as low as 5.4 mA, the output power at 55 mA was 10.1 mW, the vertical and horizontal far field divergence angles were as low as 9°and 15°, and the 1-dB misalignment tolerances were 3.6 and 3.4μm, respectively.

High-speed electrooptical VOA integrated in silicon-on-insulator

In this paper, we present simulation results of an electrooptical variable optical attenuator (VOA) inte-grated in silicon-on-insulator waveguide. The device is functionally based on free carriers absorption toachieve attenuation. Beam propagation method (BPM) and two-dimensional semiconductor device simu-lation tool PISCES-Ⅱ were used to analyze the dc and transient characteristics of the device. The devicehas a response time (including rise time and fall time) less than 200 ns, much faster than the thermoopticand micro-electromechanical systems (MEMSs) based VOAs.

Integrated MMI Optical Couplers and Optical Switches in Silicon-on-Insulator Technology

Integrated multimode interference (MMI) coupler based on silicon-on-insulator(SOI) has been becoming a kind of more and more attractive device in optical systems. SiO2thin cladding layers (＜1.0 μm) can be usedin SOI waveguide due to the large index step be-tween Si and SiO2, making them compatible with VLSI technology. The design and fabrica-tion of MMI optical couplers and optical switches in SOI technology are presented in thepa-per. We demonstrated the switching time of 2 × 2 MMI-MZI thermo-optical switch is less than 20 μs:

Co—Design of Monolithically Integrated Photo—Detectorand Optical—Receiver

A behavioral model of the photodiode is presented．The model describes the relationship between photocurrent and incident optical power，and it also illustrates the impact of the reverse bias to the variation of the junction capacitance．According to this model，the photodiode and a CMOS receiver circuit are simulated and designed simultaneously under a universal circuit simulation environment．

Tunable Distributed Bragg Reflector Laser Fabricated by Bundle Integrated Guide

The tunable BIG-RW distributed Bragge reflector lasers with two different coupling coefficient gratings are proposed and fabricated.The threshold current of the laser is 38mA and the output power is more than 8mW.The tunable range of tthe laser is 3.2nm and the side moded suppression ratio is more than 30dB.The variation of the output power within the tunable wavelength range is less than 0.3dB

1.5μm Self-Aligned Spotsize Converter Integrated DFB Fabricated by Selective Area Grown MOVPE

High performance 1.57μm spotsize converter monolithically integrated DFB is fabricated by the technique of self-aligned selective area growth. The upper optical confinement layer and the butt-coupled tapered thickness waveguide are regrown simultaneously, which not only offeres the separated optimization of the active region and the integrated spotsize converter, but also reduces the difficulty of the butt-joint selective regrowth. The threshold current is as low as 4.4mA. The output power at 49mA is 10.1mW. The side mode suppression ratio (SMSR) is 33.2dB. The vertical and horizontal far field divergence angles are as small as 9° and 15° respectively, the 1dB misalignment tolerance are 3.6μm and 3.4μm.