Masato Ishino

Multiquantum-well lasers with tapered active stripe for direct coupling to single-mode fiber

We demonstrate narrow beam divergence in 1.3-/spl mu/m wavelength multiquantum-well (MQW) lasers with an active stripe horizontally tapered over the whole cavity, for direct coupling to single mode-fibers. The lasers have reduced output beam divergence in a simple structure which does not contain an additional spot-size transformer. The fabricated laser shows narrow beam divergence of /spl sim/12/spl deg/, while a low-threshold current of 6.9 mA and a high efficiency of 0.62 mW/mA are realized. Furthermore, a direct-coupling efficiency to a single-mode fiber is -4.0-dB and -3-dB alignment tolerance is /spl plusmn/2.5 /spl mu/m.

High slope efficiency and low noise characteristics in tapered-active-stripe DFB lasers with narrow beam divergence

We report high slope efficiency and low noise characteristics in a distributed feedback (DFB) laser lasing at 1.3 /spl mu/m with narrow beam divergence by employment of a laterally tapered active stripe over the whole cavity. This tapered structure is designed to realize narrow beam divergence, low threshold current, and high longitudinal mode selectivity. The fabricated tapered-active-stripe DFB lasers demonstrated of 9.20/spl times/13.40 and a record slope efficiency, for a narrow beam DFB laser, of 0.59 mW/mA. The temperature characteristics from -10/spl deg/C to 85/spl deg/C shows high output power at high temperature, stable single longitudinal mode oscillation and stable far-field patterns. Furthermore, for the first time ever, a low relative intensity noise characteristic of under -155 dB/Hz has been realized when butt-coupling into a single-mode fiber.

Single longitudinal mode operation of long, integrated passive cavity InGaAsP lasers

We propose a new 1.3‐μm wavelength InGaAsP laser—the integrated passive cavity (IPC) laser—and demonstrate its device performances compared with conventional lasers fabricated under similar procedures. The long IPC laser (3.55‐mm‐long passive cavity), as well as the short IPC laser, exhibited single frequency oscillation even just above the threshold, and the maximum ratio of longitudinal main to submode exceeded 30 dB. They also showed favorable effects in the oscillation frequency stabilization.

High-power 1.55-/spl mu/m mass-transport-grating DFB lasers for externally modulated systems

High-output-power operation of 1.55-/spl mu/m-wavelength distributed-feedback (DFB) lasers with a novel mass-transport grating (MTG) structure which is composed of InAsP buried with InP are reported. To improve high output power characteristics, we have investigated the influence of the width of the active layer on the light output power and the spectral linewidth at high injection current. It is confirmed that the increase of the active layer width is effective to realize high output power and to reduce the linewidth power product. The fabricated lasers show high single-longitudinal-mode output power of 180 mW, which is the highest value reported for 1.55-/spl mu/m DFB lasers. They also exhibit narrow spectral linewidths less than 0.3 MHz and low noise characteristics of -159 dB/Hz. Moreover, we have obtained the mean time to failure of longer than 10/sup 5/ h with a lifetime test over 200 h at 50/spl deg/C.

1.5-/spl mu/m strained-layer MQW-DFB lasers with high relaxation-oscillation frequency and low-chirp characteristics

1.5-/spl mu/m wavelength strained-layer multiple-quantum-well (SL-MQW) distributed-feedback (DFB) lasers for optical video distribution systems, including optical-fiber amplifiers, are studied with respect to the relaxation-oscillation frequency and wavelength chirp characteristics. Several types of lasers are examined as parameters of amount of strain, optical confinement, and detuning. It is confirmed that the introduction of negative detuning has an obvious effect on the increase in relaxation-oscillation frequency f/sub r/ and the reduction in chirp /spl Delta/F. The SL-MQW DFB lasers with low optical confinement and negative detuning show extremely low FM response /spl Delta/F//spl Delta/I of less than 60 MHz/mA as well as high f/sub r/ over 10 GHz for the first time. Additionally, low-chirp value /spl Delta/F of 180 MHz with modulation depth of 10% is realized at relatively low bias current (I/sub h/=I/sub th/+30 mA).

High-power, wide-temperature range operation of 1.3-μm gain-coupled DFB lasers with automatically buried InAsP absorptive grating

DFB lasers operating at 1.3 /spl mu/m with gain-coupling structure show single-mode operation over a wide temperature range of -20/spl sim/85/spl deg/C and up to a high power of 130 mW. These lasers have InAsP absorptive grating, which can be formed by a substantially simplified fabrication process, involving annealing a corrugated InP substrate in an atmosphere of mixed arsine and phosphine.

Barrier composition dependence of differential gain and external differential quantum efficiency in 1.3-/spl mu/m strained-layer multiquantum-well lasers

Dependence of the differential gain and the external differential quantum efficiency on the composition of InGaAsP barrier layers were investigated for 1.3 /spl mu/m InGaAsP-InGaAsP compressively strained layer (SL) multiquantum well (MQW) lasers. In this investigation, we compared between SL-MQW lasers and unstrained MQW lasers having the same well thicknesses and the same emitting wavelength in order to clarify the effect of strain for each barrier composition. As a result It has been found that the barrier composition has large influence on the differential gain and the external differential quantum efficiency in the SL-MQW lasers. Narrower band-gap barrier means little effect of strain on the differential gain due to the electron overflow from a well layer, while wider band-gap barrier means degradation in the differential gain and the external differential quantum efficiency due to the nonuniform injection of hole into a well layer. In this experiment, the barrier composition of 1.05 /spl mu/m is suitable for 1.3 /spl mu/m InGaAsP-InGaAsP SL-MQW lasers to realize large differential gain and high external differential quantum efficiency simultaneously.

Enhanced relaxation oscillation frequency of 1.3 /spl mu/m strained-layer multiquantum well lasers

Dependence of relaxation oscillation frequency (f/sub r/) on the bandgap wavelength of InGaAsP barrier layers (/spl lambda//sub g//sup b/) and number of quantum wells (N/sub w/) were investigated for the first time, for 1.3 /spl mu/m InGaAsP/InGaAsP compressively strained multiquantum well (MQW) lasers. 1.3 times higher f/sub r/ was confirmed for strained-layer MQW lasers with large N/sub w/ (N/sub w//spl ges/7) and wide bandgap barrier layers (/spl lambda//sub g//sup b/=1.05 /spl mu/m) at the same injection level, compared with unstrained MQW lasers having the same well thicknesses and the same emitting wavelength. This enhancement mainly results from increased differential gain due to strain effects separated from the quantum-size effect.<<ETX>>

Control of double diffusion front unintentionally penetrated from a Zn doped InP layer during metalorganic vapor phase epitaxy

Unintentional Zn diffusion during metalorganic vapor phase epitaxy causes serious damages in semiconductor devices. In this work, profiles of unintentionally diffused Zn atoms from a p-InP layer to the adjoining InP substrate during growth of the p-InP layer are measured by secondary ion mass spectrometry. Zn diffusion profiles with a double diffusion front, which is composed of a shallow front with high Zn concentration and a deep front with low Zn concentration, are investigated as an approach to controlling unintentional diffusion. Diffusion depth of each front is controlled in proportion to Zn dosage, which is proposed as a value calculated as Zn concentration without regard to saturation limit. The diffusion depth for the growth time of 60 min increases in proportion to the Zn dosage as the slope of 0.16 μm/1018 cm−3 for the shallow front and that of 0.32 μm/1018 cm−3 for the deep front at a growth temperature of 600 °C. The deep front expands two times faster than the shallow front, which is normall...

High-temperature operation of 1.3-/spl mu/m tapered-active-stripe laser for direct coupling to single-mode fiber

High-temperature operation of 1.3-/spl mu/m wavelength multiquantum-well (MQW) lasers with an active stripe horizontally tapered over whole cavity, for direct coupling to single-mode fibers (SMFs), are reported. The lasers have reduced the output-beam divergence in a simple structure which does not contain an additional spot-size transformer. To improve high-temperature characteristics, we have investigated the influence of the thickness of separate-confinement-heterostructure layers and the number of quantum wells (QWs) on the threshold current and the output-beam divergence at high temperature. As a result, the fabricated lasers show low-threshold current (/spl sim/18 mA) and high-slope efficiency (/spl sim/0.4 mW/mA) with narrow output-beam divergence (/spl sim/12/spl deg/) at 85/spl deg/C. Moreover, we have obtained maximum coupling efficiency of -4.7 dB in a direct coupling to a SMF, and the reliability of longer than 10/sup 5/ h (MTTF) by a lifetime test of over 2000 h at 85/spl deg/C.