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Broad area travelling wave GaAlAs SQW optical amplifiers have been fabricated and characterised. Using a 600 μm wide and a 1000 μm long double pass amplifier, 12 W of peak pulsed output power was achieved with a 0.08° wide diffraction limited far-field lobe. Small signal gain of 31 dB was measured in a 400 μm wide active area device.

A new technique for sinusoidal intensity modulation of light, based on injection-locking of two longitudinal modes of a single laser to FM sidebands of another laser, is described. A 35 GHz microwave signal with a linewidth of less than 10 Hz was generated.

A new technique for overcoming polarisation-induced fading in coherent optical fibre communications is described. The technique generates two IFs, which fade in antiphase, by mixing the signal light with orthogonally polarised local oscillator modes which have been separated in the frequency domain.

Single far-field lobe and single-mode operation of a 20-element GaAlAs gain-guided coupled-stripe array with 315 mW of output was obtained by injection locking with 3.9 mW of incident power. The 0.31° lobe width was near the diffraction limit. An external small-signal gain of 19 dB was obtained.

Large losses (dropouts) of the output RF signal of a fibreoptic link are reported. Measurements in the 2–18 GHz range with 0.7–1.6 km fibre lengths indicate that optical feedback induced laser longitudinal mode instabilities coupled with fibre dispersion result in more than 45 dB loss of RF signal during mode hops or multimode operation.

Reports the interferometric measurement of the phase noise characteristics of a diode laser-pumped solid-state Nd:YAG 1.3 mu m laser based on a nonplanar ring cavity. Results show that the device has a low-frequency phase noise approximately three orders of magnitude lower than that observed with semiconductor diode lasers. The use of this source in fibre sensing applications is discussed. >

We report offset phase-locking of two Nd:YAG nonplanar ring lasers by electronic feedback. The difference frequency is continuously tunable in three bands from 6 to 34 GHz and exhibits a hold-in range and linewidth of 82 MHz and

Effects of optical-feedback-induced line-narrowing on low-frequency amplitude and phase noise of semiconductor lasers are reported. Free-running laser noise is compared with that of lasers operating with external mirror feedback. While less than 1 dB difference in the amplitude noise with and without feedback is observed, line-narrowed lasers exhibit 15?20 dB reduction in low-frequency wavelength instability, or phase noise.

The injection locking of a laser diode to FM sidebands of a second, modulated laser has been investigated. Locking to sidebands as far as 9.5 GHz removed from the fundamental lasing frequency was observed.

Near-diffraction limited single lobe emission of an AlGaAs broad stripe laser diode is achieved up to 2.8 times threshold bias (650 mW free running output power) by placing the laser in a external resonator cavity with an angle selective reflection.

A fibre-optic frequency shifter has been constructed using a birefringent single-mode fibre positioned asymmetrically within two acoustic resonators driven 90° out of phase. The incident wave in one polarisation state is coupled to a frequency-shifted wave in the orthogonal state. Sideband suppression of better than 20 dB is achieved.

A 9.6 GHz GaAs FET oscillator was optically injection locked at the fundamental frequency. The locking bandwidth was 1.6 MHz. The optical injecting signal was generated using coherent mixing of two semiconductor lasers injection locked by different FM sidebands of another laser.

The temporal dependence of the frequency shift in a current-modulated single-mode semiconductor laser is measured and compared with calculations based on solutions to the thermal diffusion equation. The effects of carrier density change, thermal diffusion in the semiconductor, and heat sink thermal resistance are identified.

The centre of the locking frequency range of a GaAlAs laser is found to shift to longer wavelengths with increasing injected power by an amount proportional to the square root of the injected power level. These observations are in good agreement with predictions based on an analysis relating equilibrium photon and carrier densities in the laser cavity.

Pairs of 1.0 ps optical pulses, each focused onto a different region of a planar GaAs transferred electron device, were separated by a variable delay time τ to initiate and then inhibit dipole domain formation. The minimum pulse durations which could trigger domains were thus observed; the minimum value of τ which generated domains in the device studied was 7 ± 3 ps.

A neodymium-doped fibre laser has been actively mode-locked to produce pulses shorter than 120 ps using an intracavity acousto-optic loss modulator. The laser operated at 1.088 mu m at an average power of 5 mW when pumped by an injection-locked diode array, which coupled approximately 40 mW of 0.82 mu m into the fibre. A peak pulse power of 1 kW was obtained in Q-switched operation.

Heterodyne detection of the light from two slave lasers injection locked to FM sidebands of a modulated master laser is used to generate a narrowband microwave signal at 10.5 GHz.

Feedback effects in a laser diode due to Rayleigh back-scattering in a 50 m fibre with or without end reflections are reported. Linewidth reduction by more than 200 and wavelength instability on a millisecond scale are observed. An analytical model based on the statistical nature of the back-scattering shows good agreement with the experimental results.

The spectrum of a slave laser in which two different wave-lengths are injected is investigated. A simple rate equation analysis is in reasonable agreement with the experiment and accounts for the asymmetrical response of the induced FM.

Injection locking of a GaAlAs laser by coupling into non-lasing Fabry-Perot modes is described. Locking of a slave laser mode as far as 22 mode spacings (60 A) away from the gain curve centre is obtained. The dependence of the locking bandwidth on the injected power and the wavelength separation between the free-running and injected mode (Δλ) is described. The dependence of the power required for locking on the magnitude of Δλ is consistent with a 192 A-wide quadratic gain profile.

Upsets of nanosecond duration were induced in a 3 GHz GaAs divide-by-2 integrated circuit, by illuminating circuit components with focused 100 ps, 830 nm optical pulses. The nature and severity of the upsets depended upon the region of the circuit which was illuminated. An upset recovery time varying logarithmically with the incident optical energy indicated that the circuit recovers as the excess carriers recombine.

A compact fibre-optic phase modulator with a single-mode fibre positioned along the axis of a cylindrical PZT acoustic transducer is investigated. The fibre is bonded inside a glass capillary tube, which is in turn epoxied inside the transducing cylinder to give a solid, mechanically stable structure. The maximum sensitivity of the phase shifter is 0.058 rad/V cm at 6.02 MHz. No polarisation modulation is observed.

A new technique for mixing optical waves to generate microwave-frequency signals using an injection laser diode and a fibre-optic interferometer is reported. A beat signal is produced by interfering light from the laser with light from the same laser emitted earlier at a different frequency. The interferometer consists of an evanescent-field fibre coupler joined to a length of single-mode optical fibre. The laser is tuned by pulsed or bipolar current waveforms superimposed on a DC bias current. Feedback from an external cavity stabilises the laser frequency and reduces its linewidth. Efficient mixing at difference frequencies from 250 MHz to 2 GHz is obtained, with spectral widths of less than 1% of the centre frequency.