Search

Recent progress in the field of quantum dot/dash based semiconductor optical amplifiers (SOAs) for slow and fast light is discussed. Room temperature fast light has been obtained in InAs/InP QDash based SOAs by means of coherent population oscillation and four wave mixing (FWM) effects. Typical optical delays amount to 55 ps at 2 GHz. Growth optimization of the QDashes allowed us to achieve high modal gain, leading to very similar performances, e.g. gain and FWM efficiency, to those of a bulk SOA. A novel approach based on linear spectrograms is also introduced to measure the phase shift induced by wave mixing in an SOA.

The ability of the InGaAs/InGaAlAs multi-quantum-well (MQW) system to achieve ultra-low-chirp operation under 10-Gb/s operation is experimentally demonstrated. The MQW active layer has been grown by a solid-source molecular beam epitaxy (MBE) method. Two metalorganic chemical vapor deposition (MOCVD) regrowths were used to fabricate the distributed-feedback (DFB) buried ridge structure (BRS) lasers. DFB BRS lasers with good static and spectral performance have been obtained. Under 10-Gb/s modulation those lasers exhibited a chirp value as low as 0.11 nm at -20 dB, which is attributed to an extremely small phase-amplitude coupling coefficient of 1.8. An analysis of the AM and FM modulated laser field under digital pseudorandom signal confirms the observed spectra and shows the possibility of an optimum spectrum width for lasers with small chirping. >

The linewidth enhancement factor of an InGaAs/InGaAsP strained multiquantum well optical amplifier was measured interferometrically. It varied from 3 to 18 over the wavelength range from 1500 to 1600 nm with injection currents varying from one to four times the lasing threshold of the uncoated device. A rate equation model gave differential gain and refractive index change per carrier, respectively, in the range 0.3 to 2.5*10/sup -15/ cm/sup 2/ and -5 to -8*10/sup -20/ cm/sup 3/. >

A new tunable laser structure using a single electroabsorption (EA) tuning super structure grating section for fast wavelength switching operation, has been realized. The tuning mechanism of this absorption change distributed Bragg reflector (DBR) laser is based on a localized absorption variation induced in a multielectrode EA-SSG section. These devices exhibit a 2.5-nm tuning range with three modes and a switching time, between two successive wavelength channels, shorter than 250 ps. The output power variation under tuning is lower than 1.2 dB.

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.

A new compact photonic-integrated modulator utilising a four-element reflective electro-absorption modulator-semiconductor optical amplifier (EAM-SOA) array and silica interferometric guide arrangement is presented. The EAM-SOA active layer consists of AlGaInAs quantum wells designed in selective area growth technology, which enables an insertion gain, and the mature silica platform provides reduced optical losses. As a result, error-free 50 Gbit/s RZ-QPSK signal generation is shown.

A novel and very simple approach is demonstrated for distributed feedback laser-electroabsorption modulator monolithic integration. This uses the same strained multiquantum well active layer for both optical functions. Very high performance (13.6 dB extinction ratio at 1.5 V operating voltage for a 70 mu m long modulator) is reported at 1.5 mu m.

An optimised sampled-grating DBR laser, with two tuning currents, exhibits a record number of 80 accessible wavelength channels over 33 nm, with a SMSR>30 dB. A small signal AM bandwidth >3 GHz has been measured on all channels, compatible with 2.5 Gbit/s modulation. Handling of this device requires low tuning currents, leading to low power consumption.

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.

Four-wavelength DBR laser arrays have been fabricated using a very simple approach that yields very high performance devices (10-15 mA threshold currents, 15 mW output powers at 100 mA active current, 12 nm tuning ranges and 7 GHz IM bandwidths). The array tuning range is 28 nm with 50 accessible channels.

A pigtailed transceiver module which exhibits a record responsivity of 0.5 A/W is described. A single laser chip of Fabry-Perot type V-on-U-groove (VUG) laser is packed in a butterfly type package. By improving the fibre-chip coupling, a responsivity as high as 0.5 A/W is demonstrated together with a bandwidth of 1.5 GHz. The power penalty, compared with that of a p-i-n photodiode within the same experimental configuration, is only 1.2 dB at 800 Mbit/s. >

Low‐current cw stripe double‐heterostructure (DH) lasers have been realized using a shallow proton‐bombardment technique; unlike usual proton DH lasers they involve a resistive p (GaAl)As confinement layer and a rather highly doped GaAs active region both to reduce spreading current and stripe injected carrier outdiffusion. Threshold currents are on the order of 50 mA for a 12‐μm‐wide by 200‐μm‐long cavity.

A new (GaAl)As stripe laser in which a refractive index step is created by a zinc diffusion on both sides of a conventional proton stripe structure, called a diffused bombarded stripe (DBS) laser, is presented. This diffusion provides passive transverse guiding with a relatively simple technology. The index step can be adjusted by controlling the diffused zinc concentration in relation to the active region doping level. A self-alignment technique for the diffused and bombarded stripes reduces the current leakage through the diffused regions. Lasing threshold currents as low as those of conventional proton stripe lasers are obtained. A significant improvement of light-current linearity, transverse mode stability and longitudinal mode structure are observed with the DBS lasers.