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A report is presented on the growth and characterization of the first InGaAs-InP-based graded-index separate-confinement-heterostructure (GRIN-SCH) strained quantum-well lasers operating near 1.47 mu m. The structure features linearly graded InGaAsP waveguide layers for both optical and carrier confinement in a very narrow, strained quantum-well layers. The excellent structural quality of the active and waveguide regions has been confirmed by transmission electron microscopy (TEM) and secondary ion mass spectroscopy (SIMS) analysis results. Strained quantum-well lasers with well widths as narrow as 5-6 nm were fabricated with threshold current densities as low as 750 A/cm/sup 2/. Buried-heterostructure lasers based on strained quantum-well active lasers exhibit threshold currents as low as 10-15 mA with quantum efficiency of 70-80%. With antireflection coating on one side of the sample, the laser shows threshold current of 35 mA with highest output power of 160 mW. >

A novel counter-receiving heterodyne detection (CRHD) scheme for a four-section integrated coherent transceiver for access networks is proposed. Error free detection at 100 Mbit/s is achieved with the CRHD scheme. This scheme leads to the relaxation of the design requirements of integrated coherent transceivers and facilitates duplex transmissions with coherent transceivers. A novel full-duplex transmission approach is also proposed and experimentally demonstrated.

An integrated four section distributed Bragg reflector filter was employed as a channel filter and power controller/equaliser in an eight channel wavelength division multiplexed (WDM) system. Automatic channel locking and dynamic gain control within a range of 12 dB were achieved with a channel rejection ratio of 20 dB. This device has the potential to be a good candidate to simplify the management of a WDM network.

Lasing characteristics of GaInAsP/InP buried heterostructure butt-jointed built-in distributed Bragg reflector integrated lasers (BH-BJB-DBR lasers) intended for dynamic single mode operation in the wavelength range of 1.5-1.6 \mu m are given. In the first section, the coupling property between the active region and the butt-jointed external waveguide region is calculated to show the possibility of large fabrication tolerance. A coupling coefficient of more than 95 percent is estimated. Secondly, the GaInAsP/InP integrated lasers were fabricated and tested in the view of the static characteristics and the axial mode selection property. Lateral mode control was achieved by the use of a buried heterostructure, so that the axial and lateral modes were maintained to a fixed single mode. The lasers thus fabricated were operated in CW conditions at room temperature with a threshold current of about 100 mA. Single longitudinal mode operation was observed with a temperature dependence of about 0.13 nm/deg with the temperature range of more than 50-65\deg C at around 0°C. Differential quantum efficiency as high as 13 percent/ facet was obtained for the laser with power output of more than 5 mW/facet. The output spectrum below threshold indicated the strong wavelength selectivity of the DBR region, and the net gain difference between the main DBR mode and the adjacent submode was measured to be about 6 cm-1. No appreciable degradation and change of characteristics have been observed even after CW operation of more than 9770 h at 20°C.

1.6μm wavelength GaInAsP/InP buried heterostructure (BH) lasers were fabricated by the LPE technique using an antimeltback layer. A new fabrication process was used in order to prevent thermal damage of the etched wafer for second growth and to promote smooth growth. The low threshold current of 23 mA was obtained for a cavity length of approximately 300μm and a stripe width of 3-5\mu m. Transverse single-mode operation up to more than three times the threshold was obtained. Room temperature CW operation was also obtained with a threshold current of 28 mA and a differential quantum efficiency of approximately 30 percent. Temperature dependences of threshold current and differential quantum efficiency were measured and explained taking account of intervalence band absorption loss due to the split-off band.

Fabrication and lasing properties of novel GaInAsP/InP injection lasers at 1.3 μm, with buried heterostructure grown on mesa substrate and fabricated by single-step crystal growth are reported. In this mesa substrate buried heterostructure (MSB) laser, the GaInAsP active layer was grown separately on the top of a mesa structure formed along the surface of a

Fabrication and single-mode laser oscillation were demonstrated for modified DFB lasers where the phase of the corrugations was shifted at the centre by a quarter guided-wavelength and which, in principle, provided a resonance at the Bragg wavelength and stable single-mode oscillation. Phase-shifted corrugations were fabricated using electron-beam lithography.

Low threshold current CW operation of a 1.5-1.6 μm-wavelength GaInAsP/InP buried heterostructure distributed Bragg reflector integrated twin guide (BH-DBR-ITG) laser was obtained up to 12°C. Single wavelength operation was obtained at a temperature range of 25 deg. The temperature dependence of lasing wavelength was 0.10 nm/deg. At 248 K, the threshold current, the differential quantum efficiency and the maximum output power were 37 mA, 16.3%/facet and 6 mW, respectively.

1.6 μm wavelength GaInAsP/InP buried heterostructure (b.h.) lasers were fabricated by a new process. The low threshold of 25 mA was obtained for a cavity length of about 300 μm and stripe width of 3–5 μm. Room temperature c.w. operation was also obtained with the threshold of 37 mA. Transverse single-mode operation up to more than three times the threshold was obtained.

DFB lasers with CW threshold currents as low as 8 mA at room temperature have been fabricated using the VPE transport process. The low threshold currents are attributed to narrow active stripes and to the high coupling strength of the grating. Single-mode lasing at 1.53μm up to I = 8Ith and during high-speed direct modulation has been confirmed.

CW operation of a 1.60 μm GaInAsP/InP buried-heterostructure integrated laser with butt-jointed built-in distributed-Bragg-reflection waveguide (BH BJB DBR integrated laser) was achieved at room temperature. Single longitudinal-mode operation at fixed mode was obtained in a temperature range of about 60 deg C, under the CW condition, and it was also maintained under rapid direct modulation of 1.6 GHz.

The intensity fluctuation of a longitudinal mode in a modulated dynamic single-mode laser consisting of a 1.6 ?m GaInAsP/InP buried-heterostructure laser with butt-jointed built-in distributed-Bragg-reflector (BH-BJB-DBR) was suppressed to 30 dB less than that of a conventional laser. The possibility of wideband single-mode-fibre communications in the 1.5?1.6 ?m wavelength region without degradation of the bandwidth caused by mode partition noise is suggested.

The frequency modulation characteristics of a VPE-transported 1.53 mu m wavelength GaInAsP-InP DFB semiconductor diode laser was measured. Below approximately 0.7 mW optical output power per facet, it exhibited a smooth, blue-shifted, frequency modulation response from DC to 2 GHz. In the modulation frequency range of 10 MHz to 100 MHz it exhibited a mod Delta f/ Delta I mod of 0.5-1.8 GHz/mA, depending on the biasing level. >