Semiconductor photonic integrated circuits (PICs) refer to that subset of optoelectronic integrated circuits (OEICs) which focus primarily on the monolithic integration of optically interconnected guided-wave optoelectronic devices. The principal motivation for PIC research is the expected cost reduction and packaging robustness associated with replacing individually aligned, single-mode optical connections between discrete optoelectronic devices with lithographically produced integrated waveguides. This field has recently seen significant advances resulting from improved III-V epitaxial crystal growth and related processing techniques. A discussion is presented of the design and fabrication issues, illustrated by a number of recently demonstrated InP-based PICs. >

Semiconductor photonic integrated circuits

WASPNET is an EPSRC-funded collaboration between three British Universities: the University of Strathclyde, Essex University, and Bristol University, supported by a number of industrial institutions. The project which is investigating a novel packet-based optical WDM transport network-involves determining the management, systems, and devices ramifications of a new network control scheme, SCWP, which is flexible and simplifies optical hardware requirements. The principal objective of the project is to understand the advantages and potential of optical packet switching compared to the conventional electronic approach. Several schemes for packet header implementation are described, using subcarrier multiplexing, separate wave lengths, and serial transmission. A novel node design is introduced, based on wavelength router devices, which reduce loss, hence reducing booster amplifier gain and concomitant ASE noise. The fabrication of these devices, and also wavelength converters, are described. A photonic packet switching testbed is detailed which will allow the ideas developed within WASPNET to be tested in practice, permitting the practical problems of their implementation to be determined.

WASPNET: a wavelength switched packet network

The progress in long-wavelength compressively and tensile-strained InGaAs(P) quantum-well semiconductor lasers and amplifiers is reviewed. By the application of grown-in strain, the device performance is considerably improved such that conventional bulk and unstrained quantum-well active-layer devices are outperformed, while a high reliability is maintained. >

Progress in long-wavelength strained-layer InGaAs(P) quantum-well semiconductor lasers and amplifiers

We present detailed modeling and experimental results for an improved design of an InGaAsP-InP wavelength demultiplexer based on a monolithically integrated Rowland circle grating. The design incorporated ten wavelength channels at 1.55 /spl mu/m with a uniform spacing of 2 nm. The total on-chip loss was about 10 dB and the crosstalk between adjacent channels was as low as -25 dB. It was shown that low-loss etched turning mirrors can reduce the total on-chip loss by about 4 dB compared to traditional 90/spl deg/ curved multimode waveguides. By replacing standard flat grating facets with retro-reflecting V-shaped facets in the echelle grating, the loss was further reduced by 4 dB. Polarization independent operation within a passband of 0.5 nm was achieved by using multimode output waveguides. The potential sources producing the crosstalk have been analyzed and fabrication modifications for further improvement are suggested.

Monolithic integrated wavelength demultiplexer based on a waveguide Rowland circle grating in InGaAsP/lnP

A detailed study of the design issues relevant to long-wavelength monolithic mode-locked lasers is presented. Following a detailed review of the field, we have devised a validated travelling wave model to explore the limits of mode-locking in monolithic laser diodes, not only in terms of pulse duration and repetition rate, but also in terms of stability. It is shown that fast absorber recovery is crucial for short pulse width, that the ratio of gain to absorption saturation is key in accessing ultrashort pulses and that low alpha factors give only modest benefit. Finally, optimized contact layouts are shown to greatly enhance pulse stability and the overall operational success. The design rules show high levels of consistency with published experimental data.

https://iopscience.iop.org/article/10.1088/1367-2630/6/1/179/pdf

Long-wavelength monolithic mode-locked diode lasers

Transmission of 10 Gbit/s over 100 km of standard fibre at 1540 nm is reported for a strained multiquantum well electroabsorption modulator without prechirping of the laser source. The device has been optimised for chirp performance using computer simulations and is fully compatible for monolithic integration with a distributed feedback laser.

Transmission beyond the dispersion limit using a negative chirp electroabsorption modulator

An integrated InGaAsP/InP wavelength demultiplexer operating around 1.5 μm wavelength, using total internal reflection from dry-etched collimating mirrors and transmission grating, has been realised in polarisation insensitive symmetrical slab waveguide. The device exhibits polarisation dispersion that equates to less than 1 nm spectral dispersion, losses down to 7.2 dB and crosstalk less than –20 dB.

Demonstration of low loss integrated InGaAsP/InP demultiplexer device with low polarisation sensitivity

The performance of a monolithic spectrometer operating by total internal reflection of a slab-guided mode from vertical dry-etched mirrors is reported. Device outputs are almost diffraction-limited and exhibit a signal-to-noise ratio of 15–20 dB. Losses for the collimating mirrors and the grating are 2 and 2.5 dB, respectively.

Optical performance of integrated 1.5 mu m grating wavelength-demultiplexer on InP-based waveguide

The threshold current density of InGaAs/InGaAIAs/InP SCH MQW lasers with various cavity lengths and numbers of wells has been measured. The gain of each well depends logarithmically on current density from 200 to at least 2000 A cm−2. Curves are presented for optimising the number of wells. Comparisons are made with GaAs/AIGaAs MQW lasers.

Logarithmic gain/current-density characteristic of InGaAs/InGaAlAs/InP multi-quantum-well separate-confinement-heterostructure lasers

The effect of carrier transport across the heterostructure on wavelength chirp in 1.5 μm InGaAs/InGaAsP MQW lasers is described both theoretically and experimentally. A reduction in the FSK chirp to below the resolution limit of the measurements is observed together with an increased modulation bandwidth as the carrier transport time is reduced.

G.H.B. Thompson

Papers

Transmission beyond the dispersion limit using a negative chirp electroabsorption modulator

Demonstration of low loss integrated InGaAsP/InP demultiplexer device with low polarisation sensitivity

Optical performance of integrated 1.5 mu m grating wavelength-demultiplexer on InP-based waveguide

Logarithmic gain/current-density characteristic of InGaAs/InGaAlAs/InP multi-quantum-well separate-confinement-heterostructure lasers

Influence of carrier transport on wavelength chirp of InGaAs/InGaAsP MQW lasers