Y. Matsui

Terahertz-rate optical pulse generation from a passively mode-locked semiconductor laser diode

We report what is to our knowledge the first demonstration of terahertz-rate optical pulse generation by harmonic passive mode locking in a distributed-Bragg-reflector laser diode. Along with the fundamental repetition rate of 38.8 GHz, we observed 400-GHz, 800-GHz, and 1.54-THz harmonics, depending on the bias condition of gain section. The pulse envelope for 1.54-THz pulses was in good agreement with a calculation from the Fourier transformation of the optical spectrum, indicating that the output pulses are transform limited.

500 GHZ OPTICAL SHORT PULSE GENERATION FROM A MONOLITHIC PASSIVELY MODE-LOCKED DISTRIBUTED BRAGG REFLECTOR LASER DIODE

A 500 GHz optical short pulse train was generated from a passively mode‐locked distributed Bragg reflector laser diode (DBR‐LD). The repetition frequency was thirteen times the fundamental round trip frequency in the LD, and harmonic mode‐locking occurred. The pulse duration was 700 fs and the time‐bandwidth product was 0.51, very close to the transform‐limited value of a Gaussian waveform, 0.44. To our knowledge, this is the first report on the harmonic mode locking of a monolithic passively mode‐locked laser diode.

High‐power and high‐speed 1.3 μm V‐grooved inner‐stripe lasers with new semi‐insulating current confinement structures on p‐InP substrates

A significant improvement in the maximum output power of a 1.3 μm GaInAsP/InP laser with a semi‐insulating current confinement structure is reported. The improvement has been achieved by interposing an n‐type InP layer between a p‐InP substrate and an Fe‐doped InP layer. A maximum cw output power of 180 mW and a modulation bandwidth of 8.5 GHz have been obtained.

High‐power 1.48 μm multiple quantum well lasers with strained quaternary wells entirely grown by metalorganic vapor phase epitaxy

This letter describes 1.48 μm multiple quantum well (MQW) lasers with strained GaInAsP quaternary wells entirely grown by metalorgainic vapor phase epitaxy. The GaInAsP quaternary layers with 1.5% biaxially compressed strain showed an excellent crystal quality and an abrupt interface within half‐monolayer fluctuations which was verified with photoluminescence spectroscopy. The maximum continuous wave output power of 140 mW was obtained at 20 °C with 1500‐μm‐long lasers whose facets were coated by anti‐ and high‐reflection films. The small internal loss of 12 cm−1 and a high internal efficiency of 70% were obtained.

High‐power and high‐speed semi‐insulating blocked V‐grooved inner‐stripe lasers at 1.3 μm wavelength fabricated on p‐InP substrates

A maximum cw power of 90 mW at 25 °C was obtained for a GaInAsP/InP laser with a semi‐insulating InP current blocking layer grown by metalorganic vapor phase epitaxy on a p‐type InP substrate, a 700‐μm‐long cavity, and an antireflection coating on the front facet. The 3 dB bandwidth was in excess of 6 GHz with a low parasitic capacitance of 15 pF despite the long cavity. The semi‐insulating layer with the resistivity of 5×107 Ω cm was formed by doping only Fe. The current blocking characteristics of the blocking layer with the same configuration as the lasers were examined under various temperatures.

Spectral characteristics of an InP/InGaAs distributed absorbing Bragg reflector

An InP/In0.53Ga0.47As distributed absorbing Bragg reflector is investigated by reflectance and group-delay-time spectroscopy. The measured reflectance is suppressed and shows a minimum at the low-wavelength side of the high-reflectance band. This suppression of reflectance is due to an enhancement of optical absorption. The enhancement of optical absorption originates from an increase in the overlap of the optical field with the absorbing InGaAs layers since an intense optical field is confined near the surface in the spectral range of the enhancement.

Ion channeling effect on lattice relaxation in strained In1−xGaxAs/InP multiple‐quantum‐well structure

The ion channeling phenomena for the strained and strain partially relaxed In1−xGaxAs/InP multiple‐quantum‐well (MQW) structures, which are grown by metalorganic vapor phase epitaxy, are presented. In addition to a well‐known channeling phenomenon of strained‐layer MQW structures, which cause an enhanced dechanneling along 〈110〉, it was found that dechanneling in the substrate covered with strained MQW structure is enhanced in comparison with the strain partially relaxed MQW structure. This phenomenon is observed clearly for the 〈100〉 oriented substrate rather than that along the inclined 〈110〉 axis. It is suggested that a distortion perpendicular to the 〈100〉 growth direction is induced near the interface between the buffer layer and the MQW structure by the strain stored in MQW structure. This effect is less observed in the strain partially relaxed MQW structure than in the strained MQW structure.

Time-frequency spectroscopy of an InGaAs/InP quantum-well exciton Bragg reflector

Ultrafast absorption saturation in an exciton Bragg reflector, consisting of InGaAs quantum wells embedded in InP/InGaAsP Bragg layers, is characterized by pump-induced transient reflectance spectroscopy at room temperature. Spectral modulation of the reflected probe pulses is caused by ultrafast absorption saturation of excitons in the quantum wells. The spectral modulation leads to an optical phase shift of 1.6 π. The exciton-induced phase shift is more than four times as large as that induced by free carriers in a Bragg reflector.

CARRIER RELAXATION IN AN INP/INGAAS NONLINEAR BRAGG REFLECTOR

Carrier dynamics in absorption saturation in an InP/InGaAs nonlinear Bragg reflector is studied by transient reflectance measurements. An ultrafast process of the relaxation time shorter than 100 fs is observed and identified as carrier-carrier scattering. Such an ultrafast process is not observed in the transient reflectance of bulk InGaAs measured with the same photoexcitation level. The difference between these transient reflectance characteristics indicates an enhancement of carrier-carrier scattering in the nonlinear Bragg reflector.

Carrier-induced optical pulse shaping in a semiconductor nonlinear Bragg reflector

Soliton-like pulse shaping in a semiconductor nonlinear Bragg reflector is discovered. Carrier-induced nonlinearity produces positive pulse chirping, and the pulse chirping is compensated by negative group-delay dispersion of the Bragg reflector.