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.