A detailed numerical solution of the design criteria of in-phase lateral and single-longitudinal-mode operation GaInAsP/InP DFB laser arrays is presented. The analysis, including broad-area pumped and stripe-geometry pumped index-guided arrays, was carried out on the basis of the eigenvalue equation method. It is shown that there exists a cut-off array pitch co, at which all of the higher-order array modes are cut off. For the pitch larger than the cut-off pitch co, the modal discrimination is evaluated by the threshold gain difference between the in-phase lateral and higher-order array modes. As a result, the modal discrimination was found to decrease with the increase of the number of elements and the array pitch which is limited to be smaller than twice the cut-off pitch co to attain a stable in-phase lateral- and single-longitudinal-mode operation.

The basic properties of 1.55µm GaInAsP/InP distributed reflector (DR) laser were analyzed from the view points of active region structure and π/2 phase shift position. By introducing SCH structure with thin active layer, differential quantum efficiency could be improved up to 60-70% without sacrificing threshold current density. Optimum π/2 phase shift position for high power operation was found to be located inside the active region at a distance of 0.3 times of active region length from the joint portion between active and passive regions.

Current leakage along longitudinal direction, from active region to connected external waveguide or neighboring opto-electronic (O-E) functional region, commonly occurs in integrated type semiconductor lasers. This current leakage degrades not only lasing characteristics but also interrupts operation of neighboring functional devices. In this paper, the longitudinal current leakage is analytically given for an integrated laser by introducing an effective length of leakage current along the longitudinal direction. The minimum lengths of active region and isolation region to minimize the influence of longitudinal current leakage were clarified. As the results, shortening of current injection region with respect to the active region length as well as increasing sheet resistance were found to be effective for reduction of leakage current.

Bundle-integrated-guide (BIG) structure distributed-Bragg-reflector (DBR) lasers based on 1.5-1.6 µm GaInAsP/InP system are presented. The significance of this structure is the suitability for the planar fabrication process of integrated optical devices, such as DBR lasers, which comprise active and passive waveguide regions. The BIG structure enables easier fabrication of buried hetero-structure (BH) of such an integrated waveguide device. High coupling efficiency between those waveguides of 95-99 percent is theoretically available with sufficiently large tolerance in thickness and composition of waveguide layers. Devices with different lengths of the active region, such as 200 µm, 100 µm and 50 µm, were fabricated and tested both for DC operation and rapid direct modulation. Threshold current as low as 28 mA and output power of 6.5 mW/facet were obtained for BH-BIG-DBR lasers with 100 µm long and 3 µm wide active region. Side-mode suppression ratio (SMSR) of more than 32 dB was obtained at the bias current of 1.2 times the threshold and it was not much degraded by rapid direct modulation.

A dynamic-single-mode bundle-integrated-guide distributed-bragg-reflector (BIG-DBR-DSM) laser with short active region was experimentally demonstrated for low threshold current and high sub-mode suppression. CW threshold current of 22 mA was obtained for the case of active region length of 50 µm. Sub-modes were suppressed more than 35 dB.

A new type of a dynamic-single-mode laser, which has distributed reflector (DR) both in active and passive regions, is proposed and analyzed to attain high output efficiency with the superior single mode property without increase of threshold current density.

Operation characteristics of tapered-waveguide traveling wave semiconductor laser amplifier (TTW-SLA) are calculated in terms of quasi adiabatic single mode propagation, signal gain and saturation output power, device efficiency(the efficiency of conversion between the electrical and amplified optical power), and amplified spontaneous emission (ASE) power, and their dependences on the shape of the taper are compared for linear, quadratic, Gaussian and exponential functions, It was found that in the allowed quasi adiabatic single mode propagation condition, linear and Gaussian TTW-SLA have higher saturation output power property, while the exponential TTW-SLA has higher device efficiency property and lower ASE noise of about 0.1 times that of a broad type TW-SLA.

In this study, our recent research activities on nanophotonic devices with semiconductor quantum nanostructures are reviewed. We have developed a technique for nanofabricating of high-quality and high-density semiconductor quantum dots (QDs). On the basis of this core technology, we have studied next-generation nanophotonic devices fabricated using high-quality QDs, including (1) a high-performance QD laser for long-wavelength optical communications, (2) high-efficiency compound-type solar cell structures, and (3) single-QD devices for future applications related to quantum information. These devices are expected to be used in high-speed optical communication systems, high-performance renewable energy systems, and future high-security quantum computation and communication systems.

A new way to reduce the linewidth enhancement factor of Distributed Reflector dynamic-single-mode (DR-DSM) lasers is proposed, which is detuning of lasing wavelength from the Bragg wavelength. The linewidth enhancement factor αof DR-DSM laser was found to be reduced to half of medium defined value αmedium when the phase shift value between the active and the passive distributed reflectors is 0.25π.

A low-voltage operation and highly-reliable nonvoltatile semiconductor memory with a large capacity has been manufactured using 0.8-µm CMOS technology. This 3-volt, 1-Mbit, full-featured MONOS EEPROM has a chip size of 51.3 mm2 and a memory cell size of 23.1µm2. An asymmetric programming voltage method fully exploits the abilities of the MONOS device and provides 10-year data retention after 106 erase/write cycles. Because of its wide-margin circuit design, this EEPROM can also be operated at 5 volts. High-speed read out is provided by using the polycide word line and the differential sense amplifier with a MONOS dummy memory. New functions such as data protection with software and programming-end indication with a toggle bit are added, and chips are TSOP packaged for use in many kinds of portable equipment.

As THz wave has the advantages of enough resolution and penetration to materials, it has been examined to be used for the imaging system. The propagation distance of THz wave is limited to be short. That is also the advantage for application to the indoor wireless communication etc. For the achievement of the ultra-high frequency oscillator (and concurrently transmitter) device, the properties of small, electronic excitation, the antenna constructed and being on the wafer are important. For the purpose, the Negative differential resistance Dual channel transistor (NDR-DCT) proposed by AIST is utilized. In this paper, as an initial theoretical analysis, we simulated the oscillation frequency of this device at about 100 GHz-1THz within the Terahertz band on which the above applications was expected. The equivalent circuit model of NDR-DCT was shown based on the analogy with the resonant tunnelling diode (RTDs), and the antenna as the resonance circuit part was designed by the numerical analysis. The possibility of the THz oscillation of this device was confirmed. The slit reflector that we proposed can realize the slot antenna on the device effectively and is suitable for three terminal structure semiconductor. its manufacturing is relatively easy.

Direct modulation characteristics, such as the side mode suppression ratio and the dynamic wavelength shift, of BIG-DBR (Bundle Integrated Guide Distributed Bragg Reflector) lasers were investigated by applying both sinusoidal and pulse-like modulations to two different kinds of samples with 100 µm and 200 µm active region lengths. The higher side mode suppression ratio of more than 30 dB was obtained for the sample with short active region length of 100 µm within all the frequency range up to 2 GHz even under pulse-like modulation, whereas the dynamic wavelength shift became larger than that of longer active region sample.

Mass-transport and conventional buying techniques were combined to fabricate narrow active stripe lasers. Lowest threshold current of 9.6 mA was obtained under CW operation for the active layer width of 1µm in 1.5 µm wavelength region. The maximum light output power and differential quantum efficiency were 10.6 mW and 17 percent/facet, respectively. With this structure, complete single transverse mode operation was achieved both for Fabry-Perot (FP) type and bundle-integrated-guide distributed Bragg reflecter (BIB-DBR) type lasers.

Wavelength-tunable 1.5 µm GaInAsP/InP bundle-integrated-guide distributed Bragg reflector (BIG-DBR) dynamic-single-mode lasers are presented. Tuning is due to free carrier plasma effect generated by the injected tuning current at the monolithically integrated tuning regions. Low threshold current CW operation of 28 mA was obtained in junction-up mounting. Wide-range continuous wavelength tuning more than 9 was demonstrated for the first time.