In this thesis, ridge waveguide laser, quantum well intermixing, 1x1 and 2x2 optical switching and ring resonator with multimode-waveguide turning mirror couplers have been investigated. We develop a new design that the perturbation is the minimum when the crossing occurs at the self-image location in a low-loss multimode waveguide. We use a center-fold low-loss multimode waveguide with a single self image at the center. Such waveguides can cross at 90 degrees or 60 degrees at the center with minimal cross talk. One can reflect the incident mode into an intersecting waveguide by introducing an idea reflecting plane. In practice, the reflector is replaced by a plane for total internal reflection with correction for Goos-Hanchen shift. Passive component for£f = 1.41 £gm samples, 1x1 60-degree multimode-waveguide turning mirror, 1x1 90-degree multimode-waveguide turning mirror, 2x2 90-degree multimode-waveguide turning mirror and a single ring resonator with 2x2 multimode-waveguide turning mirror couplers have been fabricated. (1) The multimode-waveguide turning mirror coupler with cross coupling factor (K) of 0.15 is achieved by an etched facet with a correction for Goos-Hanchen shift. (2) The length of the multimode-waveguide turning mirror coupler is only 33% of the length of conventional straight 2x2 MMI coupler with K=0.15. (3) The circumference of the curve waveguide in this ring resonator is decreased by 50%. (4) The characterization of the InP-based single ring resonator incorporating 2x2 multimode-waveguide turning mirror couplers with K= 0.15 has a free spectral range of 82 GHz, a contrast of 4 dB, and a full-width at half-maximum (FWHM) of 0.24 nm for the drop port. (5) This single resonators in In0.53Ga0.47As/In0.53Ga0.26Al0.21As grown by molecular beam epitaxy (MBE), and In0.67Ga0.33As0.6P0.4/In0.71Ga0.29As0.74P0.26 grown by metal organic chemical vapor deposition (MOCVD) have been demonstrated, respectively. We have also developed quantum well intermixing technique for the photonic integration. (1) Argon plasma bombardment followed by rapid thermal annealing for InGaAs/InGaAlAs multiple-quantum-well structures grown by MBE has been found to strongly enhance the intensity of room-temperature photoluminescence signal by more than an order of magnitude. The strength of the photoluminescence signal is found to be dependent on the plasma RF power and bombardment time. The resulting blue shift of the photoluminescence wavelength due to quantum well intermixing is found to be under 15 nm. (2) Process combining inductively-coupled-plasma reactive ion etching (ICP-RIE) and SiO2 sputtering film has been investigated for the InGaAsP and InGaAlAs multi-quantum wells (MQWs). Optimal distance is of 300 nm for InGaAsP, and of 200-nm-thick for InGaAlAs between MQWs and the upper cladding by ICP-RIE and bombardment. The process resulted in a bandgap blue-shift of 90 nm for InGaAsP, and of 60 nm for InGaAlAs. The result is very useful to regrown, the sacrificing layer and to integrate the fabrication.

In this work , impurity free vacancy diffusion (IFVD) quantum well intermixing(QWI) technology by high thermal-expansion-induced stress is used to perform bandgap engineering. In this paper, 1530nm InGaAsP multiple QWs sandwiched by p-InP (2£gm thickeneess, top) and n-InP (bottom) material is used as testing material structure also laser fabrication material, where contact materials (InGaAs and InP) on p-InP are used for comparison. By the difference between thermal expansion coefficients of SiO2 on the different material (InGaAs, InP), large different behaviors of QWI are observed, while low different dependence on defects created by ion-implantation is found. Above 70nm photo luminance (PL) wavelength shift of InGaAsP MQW below 2£gm thick InP is realized in this method. Further more, CW in-plane laser structures are also successfully fabricated and demonstrated by such QWI, giving the same shift as PL. It shows that good qualify of material can be obtained in such QWI method. Using local deposition of SiO2 causes different bandgap materials, re-growth free processing for monolithic integration can be expected, offering a powerful scheme of QWI for bandgap engineering.

The main objectives of this thesis are to develop viable process and/or device technologies for bandgap tuning of 1300-nm InGaAs/GaAs quantum-dot (QD) laser structures, and broad linewidth 1300-nm InGaAsP/InP quantum well (QW) superluminescent diode structures. The high performance bandgap-engineered QD laser structures were achieved by employing quantum-dot intermixing (QDI) based on impurity free vacancy diffusion (IFVD) technique for eventual seamless active-passive integration, and bandgap-tuned lasers. QDI using various dielectric-capping materials, such as HfO2, SrTiO3, TiO2, Al2O3 and ZnO, etc, were experimented in which the resultant emission wavelength can be blueshifted to ∼ 1100 nm ─ 1200 nm range depending on process conditions. The significant results extracted from the PL characterization were used to perform an extensive laser characterization. The InAs/GaAs quantum-dot lasers with QDs transition energies were blueshifted by ~185 nm, and lasing around ~1070 – 1190 nm was achieved. Furthermore, from the spectral analysis, a simultaneous five-state lasing in the InAs/InGaAs intermixed QD laser was experimentally demonstrated for the first time in the very important wavelength range from 1030 to 1125 nm. The QDI methodology enabled the facile formation of a plethora of devices with various emission wavelengths suitable for a wide range of applications in the infrared. In addition, the wavelength range achieved is also applicable for coherent light generation in the green – yellow – orange visible wavelength band via frequency doubling, which is a cost-effective way of producing compact devices for pico-projectors, semiconductor laser based solid state lighting, etc. [1, 2] In QW-based superluminescent diode, the problem statement lies on achieving a flat-top and ultra-wide emission bandwidth. The approach was to design an inhomogeneous active region with a comparable simultaneous emission from different transition states in the QW stacks, in conjunction with anti-reflection coating and tilted ridge-waveguide device configuration. In this regard, we achieved 125 nm linewidth from InGaAsP/InP multiple quantum well (MQW) superluminescent diode with a total output power in excess of 70 mW with an average power spectral density of 0.56 mW/nm, and a spectral ripple of ≤1.2 ± 0.5 dB. The high power and broadband SLD with flat-top emission spectrum is a desirable as optical source for noninvasive biomedical imaging techniques employing low coherence interferometry, for instance, optical coherence tomography (OCT).