K.G. Ray

1.5-/spl mu/m InGaAsP-InP slab-coupled optical waveguide lasers

We report the demonstration of high-power semiconductor slab-coupled optical waveguide lasers (SCOWLs) operating at a wavelength of 1.5 /spl mu/m. The lasers operate with large (4/spl times/8 /spl mu/m diameter) fundamental mode and produce output power in excess of 800 mW. These structures have very low loss (/spl sim/0.5 cm/sup -1/) enabling centimeter-long devices for efficient heat removal. The large fundamental mode allows 55% butt-coupling efficiency to standard optical fiber (SMF-28). Comparisons are made between SCOWL structures having nominal 4- and 5-/spl mu/m-thick waveguides.

20 GHz optical analog link using an external modulator

Reported is an experimental fiber-optic analog link with an electrical insertion loss of 34 dB at 20 GHz, a noise figure of 41 dB, and an intermodulation-free dynamic range of 108 dB/Hz/sup 2/3/. The link uses a diode-pumped Nd:YAG laser, a bandpass integrated-optical intensity modulator, and a p-i-n detector; it contains no amplifiers.<<ETX>>

Effect of annealing on photorefractive damage in titanium-indiffused LiNbO/sub 3/ modulators

We have evaluated photorefractive effects at 1320-nm and 1064-nm optical wavelengths in interferometric modulators built using Ti-indiffused waveguides in lithium niobate. The sensitivity to photorefractive damage is substantially increased by anneals in non-oxygen atmospheres at temperatures /spl ges/200/spl deg/C. The sensitivity can be reduced by an anneal in oxygen. Properly annealed modulators operated for 150 h with 400 mW at 1320 nm with no photorefractive effects other than a 3/spl deg/ change in bias point.<<ETX>>

Input impedance conditions for minimizing the noise figure of an analog optical link

It has been previously shown that 3 dB is the lowest noise figure attainable for an amplifierless optical link with perfect lossless impedance matching to the RF source. In a prior experimental link with near-perfect impedance matching, dissipative loss in our input matching circuit prevented us from achieving a measured noise figure of less than 4 dB. Investigation of the effects of input impedance mismatch indicates that mismatch can actually lower the noise figure to below 3 dB even in the presence of some dissipative loss in the input circuit. We have verified this theory by using the mismatch effect to reduce the measured noise figure of our link to 2.5 dB at 130 MHz. We believe this is the first demonstration of amplifierless link noise figure of less than 3 dB. We confirmed the validity of our measurement technique by also measuring the noise figure of a 2.5 dB RF attenuator to be 2.5 dB.

Design and reliability of mesa-etched InP-based Geiger-mode avalanche photodiodes

Design modifications to InP-based Geiger-mode avalanche photodiodes are described that improve reliability. Geiger-mode aging at multiple conditions can cause significant degradation in some design variants while linear mode (below breakdown) aging does not.

InGaAsP/InP quantum-well electrorefractive modulators with sub-volt Vpi

Advanced analog-optical sensor, signal processing and communication systems could benefit significantly from wideband (DC to > 50 GHz) optical modulators having both low half-wave voltage (Vpi) and low optical insertion loss. An important figure-of-merit for modulators used in analog applications is Tmax/Vpi, where Tmax is the optical transmission of the modulator when biased for maximum transmission. Candidate electro-optic materials for realizing these modulators include lithium niobate (LiNbO3), polymers, and semiconductors, each of which has its own set of advantages and disadvantages. In this paper, we report the development of 1.5-um-wavelength Mach-Zehnder modulators utilizing the electrorefractive effect in InGaAsP/InP symmetric, uncoupled semiconductor quantum-wells. Modulators with 1-cm-long, lumped-element electrodes are found to have a push-pull Vpi of 0.9V (Vpi*L = 9 V-mm) and 18-dB fiber-to-fiber insertion loss (Tmax/Vpi = 0.018). Fabry-Perot cutback measurements reveal a waveguide propagation loss of 7 dB/cm and a waveguide-to-fiber coupling loss of 5 dB/facet. The relatively high propagation loss results from a combination of below-bandedge absorption and scattering due to waveguide-sidewall roughness. Analyses show that most of the coupling loss can be eliminated though the use of monolithically integrated inverted-taper optical-mode converters, thereby allowing these modulators to exceed the performance of commercial LiNbO3 modulators (Tmax/Vpi ~ 0.1). We also report the analog modulation characteristics of these modulators.

Chamber conditioning process development for improved inductively coupled plasma reactive ion etching of GaAs/AlGaAs materials

Dry-etch tool preparation, which is critical to ensuring reproducible etch conditions, is particularly important in multiple-user, multiple-process-tool settings. A reproducible dry-etch process has been developed, utilizing inductively coupled plasma reactive ion etching (ICP-RIE) of GaAs and AlGaAs materials, for the fabrication of ridge structures in slab-coupled optical waveguide semiconductor diode lasers and amplifiers. A commercial ICP-RIE system was used, configured with aluminum-oxide-coated chamber components and a SiCl4/Cl/Ar etch gas mixture. Passivation of etch chamber component surfaces by preconditioning or “seasoning” contributed to a chemically stable etch environment as monitored by tracking the GaAs etch rate. The etched areas and sidewall profiles obtained using this process were smooth, and run-to-run etch depth control was ±2% of the desired target depth of ∼1.25 μm. Energy dispersive analysis x-ray of the etch chamber surfaces before and after chamber conditioning is reported.

Direct modulation and wavelength stabilization of high power slab-coupled optical waveguide lasers

A slab-coupled optical waveguide laser is wavelength stabilized with a fiber Bragg grating and characterized under a narrow pulse high repetition rate direct modulation scheme suitable for efficient pulse position modulation format optical communication systems.

Performance of Reliable Mesa-Etched InP-based Geiger-Mode Avalanche Photodiodes and Arrays

The fabrication of reliable InP-based Geiger- mode avalanche photodiodes are described. Devices passivated with polyimide coated with silicon nitride have not degraded even while aging under more strenuous conditions than those used in fielded systems.

Sub-volt-V/sub /spl pi// InGaAsP electrorefractive modulators using symmetric, uncoupled quantum wells

In this paper, we report the demonstration of InGaAsP ER Mach-Zehnder (MZ) modulators incorporating uncoupled, symmetric quantum wells.