Yoshio Itaya

The temperature dependence of the threshold current of GaInAsP/InP DH lasers

The temperature dependence of the threshold current of GaInAsP/InP lasers was considered in terms of linear gain, loss, and carder lifetime. The linear gain was calculated taking into account electronic intraband relaxation effects. The carrier lifetime, intraband relaxation time, loss in the active region, and dipole moment, all of which determine the threshold condition, were estimated from the experiments. The main loss mechanism which determines the temperature dependence of the differential quantum efficiency appears to be the absorption due to transitions between the split-off and heavy-hole valence bands. The temperature dependence of the theoretical threshold current Ithcalculated in terms of these parameters was compared with the measured results and reasonable agreement was obtained.

NRZ operation at 40 Gb/s of a compact module containing an MQW electroabsorption modulator integrated with a DFB laser

NRZ operation at 40 Gb/s has been successfully performed using a very compact module of a multiple-quantum-well (MQW) electroabsorption modulator integrated with a distributed-feedback (DFB) laser. While the DFB laser is injected with a constant current, the integrated MQW electroabsorption modulator is driven with a 10-Gb/s electrical NRZ signal. A clearly opened eye diagram has been observed in the modulated light from the modulator. And a receiver sensitivity of -27.2 dBm at 10/sup -9/ has been experimentally confirmed in the bit-error-rate (BER) performance.

Low Threshold Current Density (100) GaInAsP/InP Double-Heterostructure Lasers for Wavelength 1.3 µm

Low threshold current density (100) GaInAsP/InP DH lasers emitting at 1.3 µm with thin active layer were studied experimentally and theoretically. The two phase solution growth technique was applied with low cooling rate of 0.08°C/min, which gave 0.05 µm thick uniform active layer. The threshold current density was minimized down to 770 A/cm2 with 0.13 µm thick active layer by reducing the concentration of Zn dopant, whereas the normal V–I characteristic was kept. The residual internal and the external absorption losses of the active layer were estimated to be about 70 cm-1 and 30 cm-1, respectively, in order to know the theoretical threshold limit. The narrowest beam divergence obtained was 23° for the active layer 0.05 µm thick. Both the threshold current density dependence on the thickness of the active layer and the beam divergence were in good agreement with the theory which was calculated by using the relative refractive index difference of 8.7%. A narrow stripe laser with undoped thin active layer had a tendency to emit in a single longitudinal mode.

Spot-size converter integrated laser diodes (SS-LDs)

A laser diode integrated with a spot-size converter has been developed for low cost optical modules. This device involves a mechanism that matches its optical field with fiber or planar lightwave circuits (PLC). This improves the alignment tolerance of the optical coupling and allows for an easy passive alignment approach. This device was fabricated on a 2-in substrate using MOVPE for crystal growth, stepper for photolithography and dry etching for mesa formation, which were all fit for mass production. Thus, the cost of the device is reduced. This device offers high coupling efficiency with single-mode fibers and high reliability, so that it can be widely implemented in coming advanced optical networks.

Fabrication and lasing properties of mesa substrate buried heterostructure GaInAsP/InP lasers at 1.3 µm wavelength

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

TM mode gain enhancement in GaInAs-InP lasers with tensile strained-layer superlattice

A novel tensile strained barrier (TSB) structure is proposed as the active layer to enhance the transverse-magnetic (TM) mode gain in long wavelength laser diodes. The band diagram of the TSB structure is described theoretically and experimentally. The gain difference between transverse-electric (TE) and TM modes is discussed for layers with various strain values and well layer thicknesses. The characteristics of TM-mode enhanced devices are reported as applications of the mode gain control using the TSB structure. In Ga/sub 0.27/In/sub 0.53/As-Ga/sub x/ In/sub 1-x/As tensile strained layer superlattice structures, controllability of a mode gain difference is achieved by changing the strain value and/or thickness of wells. >

Ga x In 1-x As y P 1-y /InP injection laser partially loaded with first-order distributed Bragg reflector

GaInAsP/InP distributed Bragg reflector (DBR) lasers with a first-order grating were demonstrated experimentally for the first time at a wavelength of 1.3 μm. Single longitudinal mode oscillation was obtained at low temperature, and the temperature dependence of the lasing wavelength was 0.7-0.8 A/deg. The equivalent refractive index of GaInAsP at the lasing wavelength of 1.3 μm was 3.50 at 186 K.

Reliability of 1300-nm spot-size converter integrated laser diodes for low-cost optical modules in access networks

This paper discusses the degradation behaviors and reliability of spot-size converter integrated laser diodes fabricated using the full wafer process with dry etching and metal organic vapor phase epitaxy (MOVPE). Failure criteria applicable to actual access networks were determined based on the degradation behavior exhibited in several aging tests, and device lifetimes were then estimated. The far-field patterns and wide-temperature operation required for low-cost system application scarcely changed during degradation, even after a 150% increase in threshold current. Within this degradation range, the device life for system application is estimated to be more than 10/sup 5/ h at 60/spl deg/C and 10 mW.

High-quality 1.3-μm GaInAsP-BH-lasers fabricated by MOVPE and dry-etching technique

High-quality and high-reliability GaInAsP-InP Fabry-Perot-type buried heterostructure strained-multi-quantum-well lasers operating at 1.3 pm have been produced by metalorganic vapor phase epitaxy growth and the dry-etching technique. We compare two types of chemical treatments to slightly etch damaged mesa-walls before regrowth after dry-etching. Slight chemical etching prevents Zn in the p-type buried layer from diffusing to the active layer during regrowth of buried hetero layers. Two step treatment using the combination of selective and unselective wet chemical etching produces a superior mesa-wall which has limited Zn-diffusion to the active layer. BH laser fabricated by MOVPE and the dry-etching technique is also confirmed as having high-reliability in practical usage.

1.6 µm Wavelength Buried Heterostructure GaInAsP/InP Lasers

GaInAsP/InP buried heterostructure lasers with anti-melt back layer emitting at 1.6 µm wavelength were fabricated and operated in a single mode in cw condition at room temperature. The gain suppression in spontaneously emitting resonant modes due to the lasing mode was found out, and it was significantly larger than that in lightly doped GaAs/AlGaAs DH lasers.