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The continuous tuning range of a three-section DFB amplifier-filter with a passive centre section can be strongly enhanced by combining the carrier-induced Bragg wavelength shift with the conventional wavelength shift due to the phase shift between the two lateral gain sections. This principle is demonstrated by the fabrication of filters exhibiting a nearly constant gain of 15 dB as well as a 4 GHz filtering bandwidth over a 2.2 nm continuous tuning range.

The authors report, for the first time to their knowledge, a full-duplex sensitivity of -27 dBm at 155 Mbit/s (RX)-54 Mbit/s (TX) which meets system requirements with an in-line transceiver assembly using a commercially available transimpedance amplifier.

The authors demonstrate extremely low threshold and high CW output power in 1.55 µm gain coupled DFB lasers. The structure is an MQW strain compensated active layer with first-order grating etched on the upper wells. The lowest thresholds of 2.5 mA at 20°C and 10 mA at 80°C are obtained using one HR facet coating. With an AR front facet, the CW output is increased up to 40 mW, while the threshold current remains < 10 mA.

The authors report the transfer of six Bragg gratings at the same location into semiconductor material. Measurements on an active device demonstrate that all the gratings have the same efficiency for guided light. This technology is an attractive alternative to the sampling effect for providing multiwavelength filter functionality at predefined wavelengths.

Simultaneous emission and reception have been demonstrated with an in-line-type transceiver emitting at 1.3 µm and receiving at 1.55 µm. A receiver sensitivity of –14.6 dBm is reported at 68 Mbit/s by modulating the 1.3 µm laser simultaneously at 50 Mbit/s. The power penalty caused by the modulation was 7.4 dB.

A high efficiency optical frequency discriminator/photodetector exhibiting a conversion efficiency exceeding 1 mV/GHz is described. The operating principle consists in monitoring the intracavity optical power change induced by optical FM signals through the voltage change in the phase shifter region of an injection-locked 1.53 mu m GaInAs/GaInAsP/InP three-section two-contact lambda /4-shifted MQW DFB laser. This principle is demonstrated by demodulating FSK signals at 700 Mbit/s using neither an interferometer nor an additional photodetector. A receiver sensitivity of -21.9 dBm is reported with an NRZ (2/sup 7/-1) PRBS.

We report results of comparative noise measurements on AlGaAs semiconductor laser amplifiers of the Fabry-Perot and travelling-wave types. We show that, for the same net gain, the electrical baseband signal/noise ratio of a photodetector placed at the amplifier output (after an optical filter) is higher for a travelling-wave-type amplifier, especially at high-gain values where the Fabry-Perot amplifier is operated at oscillation threshold. For a net gain of 20.5 dB, the signal/noise ratio of the travelling-wave-type amplifier is 4?5 dB better.

1.5 μm Fabry-Perot lasers exhibiting extremely low threshold currents have been obtained with a buried ridge stripe (BRS) structure. Threshold currents are 5.7 and 15.5 mA for 300 μm and 1mm cavity lengths, respectively, in CW operation. The optical losses of the buried waveguide have been determined from the external quantum efficiency dependence with cavity length.