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.

We propose and analyze a new type of intersectional optical switch using positive refractive index variation in quantum well structure. The switch structure has a built-in refractive index difference in the waveguide, due to which the incident light is reflected to cross port at the OFF state. When the electric field applied to the electrode (ON state), the built-in refractive index difference vanishes by the positive refractive index variation in the quantum well, and the light transmits to straight port. Low insertion loss of lesser than 1 dB and high extinction ratio of more than 20 dB can be obtained at both cross and straight port.

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.

To realize three-dimensional (3D) optical interconnection on large-scale integration (LSI) circuits, layer-to-layer couplers based on Si-photonics platform were reviewed. In terms of optical cross talk, more than 1 µm layer distance is required for 3D interconnection. To meet this requirement for the layer-to-layer optical coupler, we proposed two types of couplers: a pair of grating couplers with metal mirrors for multi-layer distance coupling and taper-type directional couplers for neighboring layer distance coupling. Both structures produced a high coupling efficiency with relatively compact (∼100 µm) device sizes with a complementary metal oxide semiconductor (CMOS) compatible fabrication process.

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.

Lasing action in GaInAs/GaInAsP quantum-wire structure, fabricated by two-step OMVPE growth, electron beam lithography, and wet chemical etching techniques, was obtained for the first time at 77 K with pulsed current injection. GaInAs quantum-wires with size of 10 nm thick and about 30 nm wide were completely separated and embedded in GaInAsP optical confinement layers so as to form a separate-confinement-heterostructure quantum-wire (SCH-QW) laser. The evidence of quantum-wire levels was confirmed by comparing its emission spectrum with that of quantum-film (QF) structure both experimentally and theoretically. The results indicate that there is no serious defects or damages in the laser operation of quantum-wires fabricated by the combination of electron beam lithography, wet chemical etching, and regrowth techniques.

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.

The permissible optical input power of a semiconductor optical switch/modulator for maintaining high performances was derived by taking account of reduction of internal electric field due to absorption-induced photo-current. It was found that the extinction ratio degrades with the increase of absorbed optical power. The permissible optical input power, at which the extinction ratio decreases 3 dB, was found to be higher than 20 mW for reflection type optical switch/modulator.

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.

Fabrication of 1.5 µm GaInAsP/InP laser by OMVPE on p-type substrate is reported. Low threshold current density (1.2 kA/cm2) was obtained by reduction of growth time in order to prevent Zn diffusion from substrate. CW operations at room temperature were obtained in buried heterostructure (BH) devices fabricated by OMVPE-LPE hybrid growth method. No degradation was observed after 2000 hours' aging test.

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.

An intersectional optical switch structure based on the field induced refractive index variation was fabricated by the use of LPE grown GaInAsP/InP MQW wafer. The first switching operation in a MQW intersectional switch structure was achieved. The field induced refractive index variation in quantum well was estimated to be around 0.45% at the applied field of 13 V/µm from the experimentally obtained switching ratio. Finally a small X-type modulator with low chirp, low power saturation is proposed which make use of the reflection phenomenon caused by field induced rafractive index variation instead of absorption phenomenon as in conventional absorption type modulators.

Photonic integrated circuits (PICs) produced by large-scale integration (LSI) on Si platforms have been intensively researched. Since thermal diffusion from the LSI logic layer is a serious obstacle to realizing a Si-based optical integrated circuit, we have proposed and realized athermal wavelength filters using Si slot waveguides embedded with benzocyclobutene (BCB). First, the athermal conditions were theoretically investigated by controlling the waveguide and gap width of the slot waveguides. In order to introduce the calculated waveguide structures to wavelength filters, the propagation losses and bending losses of the Si slot waveguides were evaluated. The propagation losses were measured to be 5.6 and 5.3 dB/cm for slot waveguide widths of 500 and 700 nm, respectively. Finally, athermal wavelength filters, a ring resonator, and a Mach-Zhender interferometer (MZI) with a slot waveguide width of 700 nm were designed and fabricated. Further, a temperature coefficient of -0.9 pm/K for the operating wavelength was achieved with the athermal MZI.

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.