T. Kunii

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.

Transform-limited optical short-pulse generation at high repetition rate over 40 GHz from a monolithic passive mode-locked DBR laser diode

The fabrication of monolithic InP-based passively mode-locked distributed-Bragg-reflector (DBR) laser is reported. An optical short-pulse train with a duration of 3.5 ps was generated at a repetition rate of over 40 GHz. The time-bandwidth product was 0.43, and it was very close to the transform-limited value of a Gaussian waveform. Peak power of 60 mW has been achieved. This laser is promising as an optical source for a high-bit-rate soliton transmission system.<<ETX>>

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.

Negative-chirp electroabsorption modulator using low-wavelength detuning

The negative chirp of an electroabsorption modulator having an /spl alpha/-parameter value of 0 to -0.5, at an input light wavelength of 1.55-1.56 /spl mu/m, has been developed by optimizing the bandgap energy of an InGaAsP bulk absorption layer. We have demonstrated successful transmission with 10 Gb/s NRZ modulation over a 100-km span of standard fiber without resort to dispersion compensation.<<ETX>>

Generation of wavelength-tunable transform-limited pulses from a monolithic passively mode-locked distributed Bragg reflector semiconductor laser

Generation of wavelength tunable transform-limited picosecond pulses from a monolithic passively mode-locked distributed Bragg reflector (DBR) laser is demonstrated for the first time. A wide tuning range of 12 nm is realized by changing the refractive index of the passive DBR region through a thin-film heater embedded on the DBR section without causing significant changes in pulse characteristics.<<ETX>>

Narrow-linewidth (<200 kHz) operation of 1.5- mu m butt-jointed multiple-quantum-well distributed Bragg reflector laser

Linewidths as narrow as 200 kHz were achieved with a 1.5 mu m butt-jointed multiquantum-well (MQW) distributed Bragg reflector (DBR) laser. A low threshold current of 8 mA and a high output power of 28 mW were also realized, as well as narrow-linewidth operation. The device was fabricated by a five-step metalorganic vapor-phase epitaxy (MOVPE) process. These results were realized by introducing a high-quality MQW active layer, a long DBR region with a very small coupling coefficient, and a butt-jointed region with high coupling efficiency.<<ETX>>

Lasing characteristics for four-section MQW-DBR laser

A MQW-DBR laser with two active sections and low tuning efficiency has been developed. The device showed excellent lasing characteristics: a low threshold current of 10 mA, a high slope efficiency of 0.26 mW/mA, and a narrow linewidth of 280 kHz at P/sub out/=15 mW. A red-shift carrier-induced FM response was obtained by nonuniform current injection to two active sections. A flat FM response with wide bandwidth (>2 GHz) was confirmed. The linewidth broadening due to wavelength tuning was suppressed through the reduction of tuning efficiency. A continuous tuning range of 0.8 nm was observed while maintaining the linewidth below 4 MHz.<<ETX>>

Narrow spectral linewidth, high output power operation and FM response characteristics in 1.5 /spl mu/m butt-jointed DBR lasers

Narrow spectral linewidth(600kHz). high Output power(>20mW) operation and a flat and large FM response(which is not distorted by tuning wavelength) are presented with the newly fabricated two types of 1.5~rm butt-jointed tunable DBR lasers. In the coherent optical communication systems, the narrow spectral linewidth, high output power and tunable laser diode is required as a light source. FM response characteristics are also important for a transmitter LD in FSK systems. In this paper, we present two types of Df3R LDs which show suitable characteristics for a local oscillator(TypeA) and for a transmitter(Type6). Device structure Fig.1 shows the schematic diagram of 1.5pm DBR lasers which were fabricated by a 5-steps LPE growth method. An active layer and a passive guide layer are butt-jointed to obtain high couding efficiency. To form a high coupling structure, we used two growth techniques, which were island like selective etching and two phase solution growth. Fig.2 shows an SEM photograph around butt-joint region. The coupling efficiency between the two layers was estimated about 80-90%. Two types of DBR lasers were fabricated, one is for a local osciIlator(TypeA) and another is for a transmitter(Type6). In TypeB chips, an active layer was separated into two sections to obtain a flat FM response[l]. Furthermore, TypeB chips were mesa-etched to reduce the parasi tic capacitance. Narrow spectral linewidth and high output power operation (TypeA) Fig. 3 shows an example of outputpower-current characteristics and sDectraI linewidth. The threshold current was 18mA and lasing wavelength was 1:52pm. Output power exceed 20mW without mode hopping. Spectral linewidth decrease with increasing output power. The minimum linewidth of 6OOkHz was observed at the maximum output power. Fig.4 is the characteristics of spectral linewidth versus lasing wavelength for each mode. Total tuning range of 4.5nm was obtained. Continuous tuning range of 1.4nm(below 12MHz) and 0.4nm(below 5MHz) are also obtained.