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High-power and high-linearity photodiodes (PDs) are of critical importance to achieve high-efficiency analogue fibre links. A small-signal analysis is utilised on the nonlinear responsivity of the modified uni-travelling-carrier PDs to understand the theoretical limitation on the third-order output intercept point (OIP3) of the link. It is theoretically shown that a nonlinear responsivity depending on both the voltage and the current can give rise to an enhanced OIP3 at certain bias and current values.

A novel transverse InP/InGaAs/InP pn junction waveguide photodiode is demonstrated using in situ zinc diffusion before a regrowth step inside an organometallic vapour phase epitaxy reactor. The detector exhibits high speed, low leakage current, low capacitance and high breakdown voltage characteristics.

Asymmetric intra-step-barrier quantum wells (IQWs) are examined to show that an electric field directed from the deeper well to the step barrier can produce suppression in electroabsorption. The IQW electroabsorption modulator is shown experimentally to delay electroabsorption up to /spl sim/2.5 V. Preliminary optical saturation measurement of the modulator indicates that the RF link gain does not saturate up to /spl sim/12 dBm optical power.

An equivalent RF circuit model for electroabsorption modulators (EAMs) is proposed and verified. Circuit parameters extracted from measured S/sub 11/ values for an MQW EAM are used to model the modulator E/O responses. Which are found to be consistent with the measurement. The model clarifies the effect of optical power to the EAM impedance and modulation bandwidth.

The wavelength response of fused fibre wavelength division multiplexers with channel spacings between 8 and 24 nm was altered by exposure to high intensity ultraviolet light. Wavelength shifts are shown to be the result of changes in the index of refraction of the glass in the fused region of the couplers, with effective index of refraction changes in the illuminated area estimated to be between 10/sup -3/ and 10/sup -2/.

The high frequency saturation characteristics of an InGaAs/InP waveguide pin photodetector are measured. At a wavelength of 1.3 μm, the detector has a responsivity of 0.5 A/W and a flat frequency response from 800 MHz to 20 GHz. With a bias of −4 V, the normalised frequency response of the detector remains unchanged when optical powers up to l0 mW are incident on the detector.

An InGaAs/InP rib-loaded waveguide pin, photodetector integrated with a microwave coplanar waveguide transmission line on a semi-insulating InP substrate is demonstrated. The detector has a 3 dB frequency response in excess of 20 GHz. The DC responsivity of the waveguide photo-detector remains constant at 0.21 A/W over a range of incident optical powers from 400 μW to 20 mW.

High-speed, low-dark-current, front-side-illuminated InGaAs PIN photodiodes with a self-passivated-mesa structure have been fabricated on semi-insulating InP substrates. These detectors have a nearly flat frequency response beyond 22GHz. Their quantum efficiency is 65% without AR coating and the dark current is about 5nA at –10V.

An externally modulated mode-locked laser diode is proposed to transmit high centre frequency, fractional bandwidth microwave signals over optical fibres. We demonstrate the feasibility of this scheme using an external Bragg cell to modulate (at 68.7 MHz) an actively mode-locked laser diode (mode-locked at 2.05GHz).

A vertical cavity GaInAsP/InP surface-emitting laser at 1.3 μm wavelength is demonstrated with a hemispherical cavity structure. The laser consists of a circular mesa buried (passivated) in polyimide and is made on a semi-insulating InP substrate. CW operation was obtained at 77 K with a threshold current density of 90 kA/cm2.

A self-aligned diffusion process has been demonstrated in the fabrication of n-InP JFETs on semi-insulating InP. This process utilises the anisotropic and selective etching properties of InP/GaInAs materials. Using this technique, sub-micrometre gate lengths can be achieved even with conventional photolithography. Devices with trans-conductance of >35mS/mm, leakage current of < 10nA/mm and gate capacitance of

Double-heterostructure (DH) GaInAsP/InP buried channel waveguide electroabsorption (EA) modulators are demonstrated. They are designed for external intensity modulation of 1·3 μm laser light and direct coupling to single-mode fibre. For a 650 μm-long device, a 30 dB on/off ratio has been achieved at a bias voltage of - 9 V. The substrate light is found to be a limiting factor of the measured extinction ratio for short modulators, but not for long (1·8 mm) modulators.