Hiroyuki Nobuhara

Very high speed GaInAs metal-semiconductor-metal photodiode incorporating an AlInAs/GaInAs graded superlattice

A lateral structure metal‐semiconductor‐metal photodiode has been fabricated on GaInAs, in which an AlInAs/GaInAs graded superlattice has been incorporated. This photodiode has exhibited a dark current lower than 100 nA, an internal quantum efficiency of greater than 80% at a wavelength of 1.3 μm, and a capacitance of 40 fF, all at the bias voltage of 10 V. The response speed of this photodiode has been characterized by electro‐optic sampling to exhibit a full width at half maximum of 14.7 ps.

Optoelectronic integrated four-channel transmitter array incorporating AlGaAs/GaAs quantum-well lasers

A four-channel optoelectronic integrated transmitter array which is fabricated on a single GaAs substrate and operates at 834 nm is described. Each of the circuits incorporates a laser, a photodiode for laser power monitoring, and a laser driver circuit consisting of three GaAs field-effect transistors and a resistor. Laser threshold current of 15-21 mA, transmitter conversion efficiency of approximately 6 mW/V and high-speed operation at a bit rate of more than 1.5-Gb/s NRZ with allowable crosstalk have been demonstrated. A preliminary aging test of the lasers indicated that their stability is comparable to that of discrete devices. The results have demonstrated the feasibility of applying the transmitter array to optical components that process multichannel optical signals at high speed. >

Low threshold current density 1.3-/spl mu/m strained-layer quantum-well lasers using n-type modulation doping

We have developed 1.3 /spl mu/m n-type modulation-doped strained-layer quantum-well lasers. Modulation-doped lasers with long cavities (low threshold gain) exhibit much lower threshold current densities than conventional lasers with undoped barrier layers. The lowest threshold current density we obtained was 250 A/cm/sup 2/ for 1500 /spl mu/m long lasers with five quantum wells. The estimated threshold current density for an infinite cavity length was 38 A/m/sup 2//well. This is the lowest value for InGaAsP-InGaAsP and InGaAs-InGaAsP quantum well lasers to our knowledge.<<ETX>>

Four‐channel AlGaAs/GaAs optoelectronic integrated transmitter array

A monolithic four‐channel optical transmitter at 0.8 μm wavelength has been fabricated. This has been achieved by using AlGaAs/GaAs optoelectronic integrated circuit (OEIC) approach. The OEIC chip contains four transmitter channels and each channel is composed of a graded‐index waveguide separate‐confinement heterostructure single quantum well laser, a monitor photodiode, and a laser driver circuit. The characteristics have been shown to be very uniform over four channels and pulse modulation responses over 1 Gb/s have been achieved.

Dependence of differential quantum efficiency on the confinement structure in InGaAs/InGaAsP strained-layer multiple quantum-well lasers

An internal efficiency of 91% was obtained with In/sub 0.7/Ga/sub 0.3/As/InGaAsP strained-layer multiple quantum well (MQW) lasers emitting at a wavelength of 1.5 mu m. The dependence of the reciprocal differential quantum efficiency on the length of the laser cavity shows that the absorption loss in the InGaAsP ( lambda =1.3 mu m) confinement layer caused by carrier overflowing into the confinement layer reduces the internal efficiency.<<ETX>>

High-speed operation of strained InGaAs/InGaAsP MQW lasers under zero-bias condition

5 High-speed zero-bias operation of 1.5- mu m In/sub 0.62/Ga/sub 0.38/As/In compressively-strained-MQW (multi-quantum-well) lasers at high temperatures is reported. This is achieved by optimizing the SCH (separate confinement heterostructure) composition to minimize the lasing delay time. Using a laser with an optimized SCH composition, zero bias 1-Gb/s modulation at 70 degrees C with a large eye opening time of 700 ps is demonstrated. In the optimization, strong carrier lifetime dependence on the SCH composition is observed. To see this dependence more precisely, the SCH structure dependence of effective carrier recombination coefficient B, which is an essential parameter for the carrier lifetime, has been experimentally investigated. >

High-temperature operation of InGaAs/InGaAsP compressive-strained QW lasers with low threshold currents

We investigated the influence of the band gap wavelength of barrier layers and separate confinement heterostructure (SCH) layers lambda /sub SCH/ on the high-temperature operation of InGaAs/InGaAsP compressive-strained quantum-well (QW) lasers. The optimum lambda /sub SCH/ was 1.2 mu m, at which carriers were sufficiently confined into quantum wells. The QW laser with lambda /sub SCH/ = 1.2 mu m exhibited low threshold currents of 2.3 mA at 20 degrees C and 9.7 mA at 100 degrees C and CW lasing up to 150 degrees C.<<ETX>>

Low-threshold tensile-strained InGaAs-InGaAsP quantum-well lasers with single-step separate-confinement heterostructures

The authors studied tensile-strained InGaAs-InGaAsP quantum-well lasers with single-step separate-confinement heterostructures (SCH). They obtained threshold currents below 2 mA at 20 degrees C and below 10 mA at 100 degrees C with indium mole fractions of 0.3 and 0.35 in the active layers. They found that the poorer carrier confinement of the longer wavelength SCH layer lowered the characteristic temperature at high temperatures. A laser with two In/sub 0.35/Ga/sub 0.65/As wells and a 1.1- mu m composition InGaAsP SCH layer produced a 1.6-mA CW threshold current at 20 degrees C and lasing at 120 degrees C. Using this laser, very short lasing delays under zero-bias current over a wide temperature range and 2 Gb/s modulation under zero-bias current at 70 degrees C were achieved. >

Separate‐confinement heterostructure dependence of the effective carrier recombination coefficient of strained InGaAs/InGaAsP multiple quantum well lasers

We experimentally investigated the separate‐confinement heterostructure (SCH) layer thickness and SCH band‐gap wavelength dependence of the effective carrier recombination coefficient of strained InGaAs/InGaAsP multiple quantum well lasers. The dependence is explained by the carrier transport between the SCH layers and the wells.

V PON receiver IC with a high-speed ATC circuit

We fabricated a +3.3 V single-supply burst-mode receiver IC for a passive optical network (PON) system with Si-bipolar technology. This IC consists of a high-speed ATC (Automatic Threshold Control) circuit and limiter amplifier. To achieve both high sensitivity and fast response of the ATC, we designed a new peak detector circuit that includes a sensitive small-signal detector and a high-speed large-signal detector. Measured results show that the ATC circuit responds within 1 mV error at 156 Mb/s. The burst-mode receiver demonstrates high-speed response at the beginning of cells, and a high loud/soft ratio of more than 27 dB. We obtained a minimum sensitivity about -25 dBm at 622 Mb/s. The sensitivity at 622 Mb/s can be improved to -29 dBm by optimizing the bandwidth of the limiter amplifier.