Direct modulation of InGaAsP/InP double heterostructure lasers

Direct modulation of an InGaAsP/InP double heterostructure laser was investigated experimentally. Sinusoidal modulation up to 2.5 GHz was achieved with almost constant modulation efficiency. Pulse responses showed that the damped relaxation oscillation in light output was well suppressed.     

Etched-coupled-cavity InGaAsP/InP lasers

A new structure for coupled-cavity lasers operating at 1.25 ?m wavelength is presented. Using chemical etching, we made a three-cavity laser from an index-guided channelled-substrate Fabry-Perot laser. It oscillates in a single longitudinal mode with a side-mode suppression ratio of 200:1 in the pumping current range of 120 mA to 220 mA. The same mode was maintained at a fixed current of 160 mA as the heat-sink temperature was varied from 9°C to 45°C. The advantages of this laser over other coupled-cavity lasers are the simplicity of fabrication, the accuracy of cavity length control, and the possibility of incorporating short-etalon sections in the coupled cavities.     

InGaAsP/InP dual wavelength lasers

The first successful dual wavelength lasers emitting at 1.2 ?m and 1.3 ?m wavelengths are described. The lasers operated up to 0°C.     

Facet oxidation of InGaAsP/InP and InGaAs/InP lasers

The facet oxidation of InGaAsP/InP and InGaAs/InP lasers is investigated after aging under high constant optical output power or high current stress. Facet oxidation in InGaAsP/InP lasers is negligibly small under several thousand hours of practical operation. The thickness of oxide film increases in proportion to optical output power and logarithm of aging time. The growth rate of facet oxide film weakly depends on the junction temperature and the activation energy is estimated to be 0.07 eV within a experimental range between 25 and 150°C. The facet of InGaAs/InP lasers are oxidized more easily than that of InGaAsP/InP lasers but are about two orders of magnitude more stable against oxidation than that of AlGaAs/GaAs lasers.     

Properties of wide-mesastripe InGaAsP/InP lasers

Wide-mesastripe InGaAsP/InP heterostructure lasers emitting at 1.3–1.5 µm were grown by metal-organic chemical vapor deposition (MOCVD). Radiation-power-current and spectral characteristics of the lasers have been studied in pulsed and continuous wave (cw) operation in the temperature range of 10–60°C. The temperature of the active region of the diode laser is higher by 30–60°C than that of the copper heatsink upon saturation of the cw output power. The temperature dependence of the differential quantum efficiency strongly affects the cw output power. Output powers of 3 and 2.6 W are achieved in mesastripe lasers in cw operation, and 9 and 6.5 W in pulsed operation, at wavelengths of 1.3 and 1.5 µm, respectively.     

InGaAsP/InP BH lasers on p-type InP substrates

A 1.55 ?m InGaAsP/InP BH laser is achieved on a p-type InP substrate resulting in a simple fabrication process. A threshold current as low as 40 mA under CW operation and a pulsed power rating of several hundred mW at 8 A peak current are achieved in buried-heterostructure lasers.     

Low-threshold-current distributed-feedback InGaAsP/InP CW lasers

Distributed-feedback buried-heterostructure InGaAsP/InP lasers with room temperature CW threshold current as low as 50 mA, corresponding to a current density of 2.3 kA/cm2, are presented. CW operation in the temperature range from ?20°C to 58°C was confirmed.     

Aging characteristics of InGaAsP/InP DFB lasers

Aging tests of InGaAsP/InP DFB lasers with a constant light output of 5 mW/facet and ambient temperatures 25°C and 40°C have been carried out. Up to the present, with an aging time of more than 2000 h for six lasers, appreciable degradations have been observed in their driving currents and spectra. This indicates that the corrugation grating near the active region has little influence on short-term reliability of DFB lasers.     

Temperature dependence of bistable InGaAsP/InP lasers

An increase of hysteresis current width in bistable lasers with two or three sections was observed at higher temperatures. A rate equation analysis was performed where both carrier density dependence on lifetime and the bleaching of saturable absorption by the spontaneous emission were taken into account. We show that the increased loss of injected carriers due to Auger recombination process causes the increase in the hysteresis width. A small-signal stability analysis for the switch-off point revealed that increased coupling between carriers in the gain and absorption regions, through the absorption of superradiant emission, has the effect of raising the switch-off point to higher current levels. It was shown experimentally that, without changing the temperature, the current hysteresis width can be controlled by adjusting the current distribution in three sections.     

Spectral hole burnings at high energy tails in spontaneous emission and hot carrier relaxation in InGaAsP lasers

Spectral hole burnings in spontaneous emission spectra from 1.3 μm InGaAsP lasers were found. The results are understood on the basis of population burnings of holes associated with the saturation of intervalence-band absorption. Theoretical results on hot carrier relaxation are shown to explain the population burnings, pointing out an importance of nonequilibrium optical phonon populations in the active layers of long wavelength InGaAsP lasers and light emitting diodes (LED's).     

Dynamics of spatial hole burning effects in DFB lasers

A lumped small-signal model for intensity and frequency modulation response of semiconductor lasers, including the effects of longitudinal spatial hole burning (SHB), is presented. It is shown that the laser dynamics including SHB-effects can be accurately described by three small-signal rate equations. The simplicity of the model gives new insight into SHB-effects on modulation response and cavity state stability. It is shown that SHB-effects have a cut-off frequency that depends on the carrier lifetime (including stimulated recombination) and the feedback of perturbations in the longitudinal intensity distribution during modulation     

Hybrid LPE/MBE-grown InGaAsP/InP DFB lasers

InGaAsP/InP distributed-feedback (DFB) lasers operating at 1.5 ?m have been successfully fabricated by a hybrid growth technique of liquid phase epitaxy (LPE) and molecular beam epitaxy (MBE). A threshold current of 180 mA at 23°C and single-longitudinal-mode operation have been obtained.     

Monolithically integrated InGaAsP/InP composite-cavity distributedfeedback lasers

Linewidth reduction to 1 MHz for monolithically integrated extended-cavity DFB lasers that are designed to achieve high optical coupling to a low-loss extended cavity is described. Since a high-efficiency extended cavity at the same time degrades the frequency-modulation (FM) response, an active gain section is integrated at the end of the extended cavity, and its use as a modulator section that maintains a flat FM response at 0.7 GHz/mA is shown. The linewidth and FM characteristics of this DFB extended-passive/active-cavity laser are compared to those of the conventional DFB extended-passive-cavity laser and a two-section DFB laser     

Phase-locked arrays of buried-ridge InP/InGaAsP diode lasers

Phased-locked arrays of buried-ridge InP/InGaAsP diode lasers, emitting at 1.3 μm, were investigated both theoretically and experimentally. These arrays consist of index-guided buried-ridge lasers which are coupled via their evanescent optical fields. The field patterns and the modal gains of the array supermodes were calculated by using a simple waveguide model. The theoretical results show that buried-ridge arrays can be designed such that only the fundamental supermode is excited. In that case, the array lasers are coupled in-phase, which yields single-lobed, diffraction limited far-field patterns. The buried-ridge InP/InGaAsP arrays were grown by liquid phase epitaxy. These arrays exhibited single-lobed beams less than 4° in width up to more than twice the threshold current. Comparison of the measured field patterns and the calculated ones indicated that these arrays oscillated mainly in the fundamental supermode.     

Widely tunable continuous-wave InGaAsP/InP sampled grating lasers

The 1.55 μm widely tunable sampled grating lasers described here show significant improvements over those previously reported. The authors have obtained, for the first time, continuous wave (CW) operation with 62 nm CW tuning range, 30-50 dB MSR, 10 mW output power, and monotonic tuning     

High power output InGaAsP/InP buried heterostructure lasers

A novel InGaAsP/InP buried heterostructure (BH) laser was fabricated on a p-InP substrate. This laser can provide a peak pulse output of 0.8 W per facet with a stable lateral transverse mode oscillation and enables the fault location measurement of a single mode fibre cable over 20 km.     

Oxide defined TJS lasers in InGaAsP/InP DH structures

Transverse junction stripe lasers in the InGaAsP-InP systems have been fabricated by Zn diffusion through oxide windows into DH structures of InGaAsP/InP with all epitaxial layers n-type. The quaternary layer composition is such that room temperature laser emission is at 1.18 μm. TJS laser mode behavior with accompanying single longitudinal mode operation and kink-free light-output characteristics are seen at 77 K. As the temperature is increased, this behavior persists up to about 130 K, when parallel electron injection through the p-n junction in the InP layers becomes so large that, in parallel with the TJS laser filament, a normally operating DH laser filament starts operating. At higher temperatures only the latter is seen to operate.     

Growth and characterization of Cd-Doped InGaAsP/InP double heterostructure lasers

The liquid phase epitaxial growth of Cd-doped InGaAsP/InP double heterostructure lasers (1.3 μm) has been studied. Cd has been found to have a smoothing effect on the morphology of the quaternary layers and a typical terracing effect on that of InP found also by doping with Zn. The defects, revealed by etching, were found to propagate in one to one correspondence from the substrate throughout the whole structure with no generation of defects even in a highly doped material. Electrical saturation at p ~2.10^l8Cm^-3 was found in InP by Hall measurements while no saturation was found in the quaternary up to a hole concentration of ~2.10^l9cm^-3. A lattice mismatch which is linearly dependent on the amount of Cd in the liquid was found by X-ray analysis. Cd was found to greatly facilitate the location of the p-n junction within the active region because of its low diffusion. Low threshold, very high external differential quantum efficiency, and high uniformity characterize the lasers made of this material. The results obtained in this work suggest that Cd should be considered as a promising candidate for a p-type dopant in fabrication of quaternary devices.     

λ/4-shifted InGaAsP/InP DFB lasers

lambda/4-shifted InGaAsP/InP DFB lasers were studied theoretically and experimentally. The effect of reflectivities at the end of a DFB region and that of alambda/4shift position were analyzed in terms of stability of single-longitudinal-mode operation and asymmetric power distribution. The shift of thelambda/4-shift position from the center to a certain place in the DFB region, with the end reflectivities less than several tenths of a percent, seemed most effective for efficient power extraction and reproducible DSM operation. The devices emitting at 1.5 μm range were fabricated by using negative and positive photoresists and employing one-step holographic exposure. They exhibited single-longitudinal-mode operations just at or closely around the center of the stopband, i.e., the Bragg wavelength. The slight wavelength deviations from the center were found to be attributed to the accidental phase-shift variations from the optimal value. Concerning such deviations in the fabricated devices, a simple and useful criterion, for example,P_{0}/P_{1} geq 2-3atI/I_{th} = 0.9, for stable DSM operation was presented. Statistically, single-longitudinal-mode operations were observed in 95 devices out of 100, and the theoretical prediction was verified. The side-mode-suppression ratios under high-speed direct modulation were 35 dB or more.     

InGaAsP/InP double heterostructure lasers grown by atmospheric-pressure MOCVD

Room-temperature operation of InGaAsP-InP double-heterostructure lasers grown by atmospheric pressure metalorganic chemical vapour deposition is reported. Optically pumped laser operation at 1.36 ?m and 1.45 ?m has been achieved and broad-area injection lasers operating at 1.37 ?m with threshold current densities as low as 3.6 kA/cm2 have been demonstrated.