A sensitive fiber-optic Fabry-Perot interferometer

A Fabry-Perot interferometric sensor utilizing a single-mode optical fiber has been demonstrated, exhibiting a finesse of 18 and a sensitivity to phase modulation of7.9 times 10^{-7}rad/sqrt{Hz}at 1 kHz.     

Fibre-optic spectrophone

The first operation of a fibre-optic spectrophone is reported. A 2.54 cm diameter coil of single-mode fibre was fused into one arm of an all-fibre Mach-Zehnder interferometer. The device operated as a highly sensitive optoacoustic detector.     

Suboptimum multiuser receivers for convolutionally codedasynchronous DS-CDMA systems

Motivated by the high complexity of the optimal sequence estimator for convolutionally coded asynchronous code-division multiple-access (CDMA) systems, developed by Giallorenzi and Wilson (see ibid., vol.44, no.8, p.997, 1996), and the potentially poor performance of the conventional receiver due to multiuser interference and the near-far problem, we examine relatively simple multiuser receivers which perform nearly as well as the optimal receiver. The multiuser receivers discussed are of two types. The first set of approaches are partitioned approaches that treat the multiuser interference equalization problem and the decoding problem separately. The second set of approaches are integrated approaches that perform both the equalization and decoding operations together. We study linear, decision feedback, and trellis/tree-based approaches in each category. The asymptotic efficiency of this receiver relative to an uncoded coherent binary phase shift keying (BPSK) receiver (termed asymptotic multiuser coding gain, or AMCG) is used as a performance criterion throughout. Also, computer simulations are used whenever the computation of the AMCG is not feasible. It is shown that a number of the approaches which are introduced achieve a high performance level with a moderate complexity     

Noise characteristics in line-narrowed semiconductor lasers with optical feedback

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.     

Saturation and discharge studies in the He-Cd laser

The results of experimental studies of the various saturation effects and of discharge processes that occur in He-Cd lasers are presented and interpreted. It was found that the laser output can be adequately described by means of the rate equations. Based on these rate equations and the experimental results, the output and configuration of the He-Cd laser may be optimized. An estimate of the transfer cross section between the helium metastable and the cadmium atom is also presented.     

Optical fibre magnetic field sensors

A class of high sensitivity fibre-optic magnetic sensors has been developed and successfully tested in the laboratory for the first time. The magnetic sensors employ magnetostrictive jacketing materials in conjunction with conventional single-mode optical fibres. An all-fibre Mach-Zender interferometer was used to detect the magnetically induced changes in optical path length which arise because of strains transferred to the fibre from the magnetostrictive jacket.     

Diode laser sensor

A new sensor capable of detecting sinusoidal displacements as small as ~9 ×10?5 nm has been constructed. The sensor, employing phase modulation of light fed back into the laser cavity by an external reflector, has been successfully tested as an acoustic sensor.