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We report novel optoelectronic functions in a resonant-tunnelling triangular-barrier optoelectronic switch (R-TOPS). We successfully observed optically controlled S- and N-shaped negative differential resistances (NDRs) simultaneously in a single device. Different types of optoelectronic bistabilities originating from S- and N-shaped NDRs were obtained by changing the input light power. We also obtained the differential gain characteristics and latch characteristics from S-shaped NDR by changing the bias voltages. These characteristics with their different behaviours make it possible to realize novel optoelectronic switching.

We report a novel optical bistable device, resonant-tunneling triangular-barrier optoelectronic switch (R-TOPS), which consists of a double-barrier resonant-tunneling diode (DB-RTD) and a triangular-barrier phototransistor (TBP), grown by gas source molecular beam epitaxy (GSMBE). First, we studied the potential of the GSMBE to grow a DB-RTD and a TBP. The DB-RTD with In 0.53 Ga 0.47 As(well)/AlAs(barrier) exhibited clear negative differential resistance (NDR). Interfaces between In 0.53 Ga 0.47 As and AlAs in the DB-RTD were of good quality without dislocations in spite of the strained AlAs layers. On the other hand, the TBP with n-i-δp-i-n structure composed of In 0.53 Ga 0.47 As/In 0.52 Al 0.48 As layers was fabricated on InP, which was the first demonstration of a TBP at 1 μm wavelength range operation to our knowledge. On these basis, we fabricated the R-TOPS devices. Sharp NDR with clear bistability was successfully observed, and its characteristics were dependent on optical input power. Bistability was observed in the relation between input-light power and output-current. By connecting the device to a laser diode, clear optical bistability and sharp optical NDR property with high contrast and at low input-light power were also demonstrated. We found that both the TBP and the DB-RTD worked well in the R-TOPS grown by GSMBE.

We report a novel optical functional device, triangular-barrier optoelectronic switch (TOPS), which consists of a triangular-barrier phototransistor (TBP) with avalanche multiplication, grown by gas source molecular beam epitaxy (GSMBE). At first we fabricated and examined the TBP, which was composed of In 0.53 Ga 0.47 As/In 0.52 Al 0.48 As layers to confirm its fundamental characteristics such as high sensitivity. On this basis, we optimized the structure, mainly about a δp gate layer, to introduce avalanche multiplication at low bias voltages into the TBP. We examined the characteristics of the TOPS with an input light of 1.55 μm wavelength. We observed significant S-shaped negative differential resistance (NDR) characteristics. Clear differential gain, bistability and latch characteristics were obtained by only changing the bias voltages, while the input-light power was less than 600 nW and the optical gain was more than 7000. We also found that it is very important to optimize the thickness of the gate layer to fabricate the TOPS. We can apply the TOPS to optical functional devices such as an optical logic device and an optical memory.

We report the first successful room-temperature CW operation of GaInAs/AlInAs multiquantum-well (MQW) injection lasers fabricated by molecular beam epitaxy (MBE). The emitting wavelength and threshold current were 1.57 μm and 530 mA, respectively, for an SiN-defined stripe laser with a 12 μm-wide, 600 μm-long cavity.

Longitudinal-mode behaviour of λ/4-shifted InGaAsP/InP DFB lasers fabricated by the nega-posi method have been studied. The deviation of the main mode from the centre of the stopband, which was attributed to an accidental additional phase shift introduced around the λ/4-shifted position, was related to the intensity ratio of the main to side mode below the threshold, and it was much larger compared to conventional DFB lasers for the devices with small deviation. The intensity ratio above the threshold was about 35 dB or more in 100% direct modulation for most of the lasers.

λ/4-shifted InGaAsP/InP DFB lasers were fabricated by a novel method, that is, simultaneous holographic exposure of positive and negative photoresists. The λ/4-phase-shift in the first-order corrugations formed on an InP substrate was confirmed through SEM views and diffracted beam patterns. A strong resonance peak below the threshold and single-wavelength operation above it at the Bragg wavelength were observed.

Room temperature CW operation of distributed-feedback buried-heterostructure InGaAsP/InP lasers emitting at 1.57 μm was achieved. A DC threshold of about 250 mA at 25°C and a temperature coefficient of the lasing wavelength of 1.0 A˚/°C were obtained. Some of these lasers manifested single longitudinal mode operation both in DC condition and in deeply modulated condition at 500 Mbit/s.

The authors report a novel optical bistable device, the resonant-tunnelling triangular-barrier optoelectronic switch (R-TOPS), which consists of a double-barrier resonant-tunnelling diode and a triangular-barrier phototransistor. Clear negative differential resistance and bistability with high contrast and high sensitivity are demonstrated.

Side-mode suppression ratio and main-mode wavelength were measured in the 3000 h life test of 1.55 μm γ/4-shifted InGaAsP/InP DFB lasers. Degradation of the single-wavelength property and the wavelength shift of the main mode were observed in lasers which showed relatively large degradation rates of about 10−4/h at 50°C.

Spectral behaviour of 1.3 μm GaInAsP/InP integrated twin-guide lasers with first-order distributed Bragg reflectors under high-speed direct modulation was measured. It was confirmed that stable single-longitudinal-mode operation is maintained for applied modulating current pulse width of only 1 ns. The rise time and width of the light output pulse were less than 0.3 and 3 ns, respectively.

A 1.5 ~ 1.6 μm GaInAsP/InP buried-heterostructure integrated twin-guide laser with distributed Bragg reflector (BH-DBR-ITG laser) was realised, for the first time, and CW operation was achieved up to 255 K. Single-wavelength operation was obtained at temperatures between 228 K and 245 K with the temperature dependence of lasing wavelength of 10 A˚/deg. At 233 K, the threshold current, the output power and the differential quantum efficiency were 110 mA, 2.2 mW and 4.8%/facet, respectively.

A new structure is proposed for multimode interference photonic switches which have partial index-modulation regions to obtain control of the power switching between multiple output ports.The switching characteristics for a 3 × 3 configuration are analysed by the wide-angle finite-difference beam propagation method. This analysis confirms that complete switching can be obtained with low crosstalk levels of ~23 dB.

A 15GHz optical pulse train with time-bandwidth product of 0.32 for soliton transmission was generated by a sinusoidally driven InGaAsP electroabsorption modulator, for the first time. By using the pulse compression effect caused by the nonlinear attenuation response to the applied voltage, a transform-limited optical pulse train with a width of 14 ps and a spectral width of 23GHz was successfully generated just using sinusoidal modulation, without using any electrical and optical resonators.

Wavelength selectivity of a quarter-wave-shifted DFB laser is analysed taking into account the effect of a mirror facet at the end of the corrugation. The structure with no reflection is found to be the most promising. The effect of a cleaved facet at an end is not serious as long as KL is as large as 3–5.

By using a distributed feedback buried heterostructure InGaAsP/InP laser diode emitting at 1.53 μm, 21.7 km single-mode fibre transmission at 280 Mbit/s was successfully carried out without any noticeable degradation In a waveform and an error rate. This result indicates that a long-haul optical telecommunication system with a repeater span of over 70 km is possible in the fibre low-loss region of 1.5 μm to 1.6 μm wavelength.

Novel optoelectronic bistabilities in a resonant-tunnelling triangular-barrier optoelectronic switch (R-TOPS) are reported. Optically controlled S-shaped and N-shaped NDRs were observed simultaneously in a single device. Different types of optoelectronic bistabilities originated from S-shaped and N-shaped NDRs were obtained by changing the input light power.

A novel optical functional device, the triangular-barrier optoelectronic switch (TOPS) is reported, which consists of a triangular-barrier phototransistor with avalanche multiplication. Clear differential gain, bistability and latch characteristics with high sensitivity and high gain were obtained by only changing the bias voltages.

The room-temperature operation of 1.5–1.6 μm GaInAsP/InP integrated twin-guide lasers with first-order distributed Bragg reflectors is reported. Single-longitudinal-mode oscillation was observed up to 1.4 times the threshold current. The temperature dependence of lasing wavelength was only 0.8 A˚/degree.

The optical response time of an InGaAs/InP heterostructure avalanche photodiode (HAPD) with InGaAsP buffer layers is reported. It is shown that the buffer layers play an important role in reduction of the pile-up effect and are considered to be effective in achieving high-speed InGaAs/InP HAPDs.

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.

1.53 μm GaInAsP/InP buried-heterostructure integrated twin-guide laser with distributed Bragg reflector (BH-DBR-ITG laser) was directly modulated with microwave modulation current superimposed on a DC bias which was fixed at 1.1 times the threshold current, and single-wavelength operation was experimentally confirmed with a modulation frequency up to 1 GHz and a modulation depth of 100%.