We present design and fabrication of ring cavity semiconductor lasers and single ring filter with simple fabrication processes. A 1.55-£gm symmetric quantum well InGaAlAs epi-layer wafer is used to fabricate the lasers. In device design, we apply loop mirror to obtain reflection instead of cleaved facet and take 1x2, and 2x2 Multi-Mode Interference (MMI) with different splitting ratio(50%:50%¡F15%:85%) as a coupler. Then we combine MMI couplers with ring cavities to control the output of specific wavelength. Therefore we can obtain filter and lasers with the property of wavelength selection. We also design two kinds of special waveguides to achieve low reflectivity. One is a tapered spiral waveguide tail. The other waveguide is expanded in a curve and then cut off at the Brewster¡¦s angle. In loop mirror, two curvature radius(260,160£gm) were introduced to study bending loss and material loss. In single ring filter, we design two kinds of resonator lengths(1479,1385£gm) and the corresponding Free Spectrum Range (FSR) are 63.4, 67.75GHz, respectively. In fabrication, owing to the unstable dry etch condition for InGaAlAs, we adopted multi-step etch technology. In the part of curved waveguide, we also use this method to make deep-etching to increase the difference of refractive index between waveguide and the outside part. Finally, we use the etch solution (HBr:HCl:H2O2:H2O=5:4:1:70) to smooth the sidewall of the waveguide, and to reduce scattering loss of the device.

This paper presents design and fabrication of ring cavity semiconductor lasers with simple fabrication processes and good potential for integration. A 1.55-£gm symmetric quantum well InGaAsP epi-layer wafer is used to fabricate the lasers. The fabrication processes involve a bi-level deep etching to reduce the bending losses. Two geometric types of ring cavity semiconductor lasers have been investigated. For the type 1 ring cavity in the form of race tracks, two different designs are presented. One has a single ring resonator (SRR) design and the other has a coupled double ring resonators (DRR) design. The resonator of the type 2 ring cavity is formed between a cleaved facet and a loop mirror. Both a single ring resonator (SRR) design and a double ring resonator (DRR) design are presented for this type of cavity also. The maximum saturation output light powers of 0.479 and 0.409 mW are observed in room temperature L-I measurements for type 1 and type 2 ring cavity semiconductor lasers respectively. The spontaneous emission spectra of the type 1 ring cavity semiconductor lasers show a red-shift phenomenon under increasing drive currents. The type 1 ring cavity semiconductor lasers with ring resonators of 100 and 200 £gm radii have also been found to exhibit an interesting wavelength clamping phenomenon of the output light.

This paper presents design and fabrication of ring cavity semiconductor lasers and optical filters with simple fabrication process. A 1.55

In this thesis, we use InP based multiple quantum well epi-wafer with modulation doping in the active layer to design the semiconductor optical amplifier and ring laser for the optical communication at 1.55£gm wavelength. We also finish the mask design and fabrication of theses two devices. Besides, we have established an optical measurement system, including the L-I measurement, the optical spectrum measurement and the far field measurement, to test the device parameters. In the device process, we use the new method, called the Multi-Step Undercutting, to precisely control the undercut in the wet etching process. With this technique, we can get a smooth and vertical sidewall for our devices. For the semiconductor optical amplifier, we design two different types, one is the Fabry-Perot Amplifier and the other is the Traveling Wave Amplifier. We use the Multi-Step Undercutting process in the fabrication of these two devices. The main parameters for semiconductor optical amplifier are the change of the output power versus the input current, the spontaneous emission spectrum and the photocurrent spectrum. For the ring laser, we combine the concept of Loop Mirror and Asymmetric Mach-Zehnder Interferometer to obtain the laser with good side mode suppression for a single wavelength light source.

In this thesis, we focus on the investigation of semiconductor optical amplifier and ring laser. We use InP based multiple quantum well epi-wafer with modulation doping in the active layer to design the semiconductor optical amplifier and ring laser for the optical communication at 1.55£gm wavelength. We combine the concept of Loop Mirror and Asymmetric Mach-Zehnder Interferometer to obtain the laser with good side mode suppression for a single wavelength light source. For the semiconductor optical amplifier, we design two different types, one is the Fabry-Perot Amplifier and the other is the Traveling Wave Amplifier. Furthermore, We use the Multi-Step Undercutting process in the fabrication of these two devices. We have established an optical measurement system, including the L-I measurement, the optical spectrum measurement and the far field measurement, to test the device parameters. After annealing, these devices with two different serial number exhibited the contact resistances of 9£[ and 16£[, respectively. Under CW operation, these FPA exhibited the threshold current of 62mA and 70mA at 20¢J, respectively. The stimulated emission wavelength was at 1531nm and 1522nm, respectively.

The goal of the thesis is to fabricate the integrated asymmetric Mach-Zehnder Interferometer and Optical waveguide Ring Resonator with simple fabrication process. A 1.49£gm symmetric quantum well InGaAlAs epitaxial wafer is used to fabricate the devices. In the asymmetric Mach-Zehnder Interferometer design, we design asymmetric straight waveguides with difference of optical path, and asymmetric bend waveguides with difference of curvature radius. By this design, we can observe the interference variation of output light by difference of optical path. Using these properties, it will get the index change caused by electric field and the loss of bend waveguide. In optical waveguide ring resonator design, we improve the problem of the length of original K=0.15 Multi-Mode Interference (MMI) by stepped-width waveguide. And we obtain different transmission spectrum by adjusting the splitting ratio of MMI couplers (K=0.85, 0.5, and 0.15) and cascading doudle rings. We apply K0=0.5, K1=0.15 and K2=0.5 MMIs to design and fabricate optical filters with square transmission spectrum. In fabrication process, we get smooth sidewall and highly perpendicularity waveguide by multi-step wet etch method. In order to reduce waveguide loss, we make deep etching for the outside of curve waveguide and MMI. Finally, we use polyimide to smooth out the sides of the ridge waveguides and evaporate metal pad over the polyimide.

In this thesis, we have established an optical measurement system to measure the device characteristics. We focus on the investigation of semiconductor optical amplifier, Fabry-Perot laser, and ring cavity filter. We used InP-based multiple quantum wells epitaxial wafer with modulation doping in the active layer. A 1.41 £gm symmetric InGaAlAs/InP quantum well structure is used to fabricate the optical waveguide ring resonator devices for the optical communication region at 1.55£gm wavelength. For the semiconductor optical amplifier and lasers, we designed two different types: Fabry-Perot Amplifier (FPA), and Traveling Wave Amplifier (TWA). The InGaAlAs-FPA structure has three lasing peaks at 1514 nm, 1528 nm, and 1544 nm. The InGaAlAs-TWA-a structure has only one peak at 1510 nm. The InGaAsP-TWA-b structure has a gross gain = 8.5 dB (wavelength = 1575 nm) at pumping current = 22 mA. We used Hakki-Paoli method and transparency current to calculate gain spectrum. For ring cavity filter, the optical spectrum has a FSR = 41.25 GHz.

The goal of the thesis is to fabricate the integrated asymmetric Mach-Zehnder Interferometer and optical waveguide ring resonator with simple fabrication process. 1.41£gm and 1.49£gm symmetric quantum well InGaAlAs epitaxial wafer is used to fabricate the devices. In the asymmetric Mach-Zehnder Interferometer , we design asymmetric straight waveguides with difference optical path differences £GL=480£gm, 970£gm, and 1900£gm. And asymmetric bend waveguides with curvature radius differences £GR=260£gm, 200£gm, 160£gm, and 100£gm. By this design, we can observe the interference variation of output light. In optical waveguide ring resonator design, we reduce the length of original K=0.15 Multi-Mode Interference (MMI) by stepped-width waveguide. By three-stepped width waveguide MMI design, it can be reduced 33.2% length. We obtain different transmission spectrum by adjusting the splitting ratio of MMI couplers (K=0.85, 0.5, and 0.15) and cascading doudle rings. We use a series of two ring resonators by MMI (K0=0.5,K1=0.15,K2=0.5) to get the FSR=50GHz. In fabrication process, we combined dry etching method with RIE-ICP and wet etching to get smooth sidewall and highly vertical waveguide. In measure , we get the FSR= 41.25 GHZ in throughput port in double ring filters . No signal in drop port was obserred due to material absorption, bending loss, and waveguide loss.

A novel non-planar and multi-reentrant two-spherical-mirror ring cavity is demonstrated. It is compact and free of astigmatism compare to the commercial ring cavity systems. The multi-reentrant condition of the ring cavity is derived and the stability of the laser cavity is analyzed. The study of polarization evolution in this kind of ring cavity is also presented. Unidirectional operation is achieved by use of reciprocal and nonreciprocal polarization rotators to differentiate the round-trip loss. The multi-reentrant ring cavity has been utilized in single frequency laser and passively Q-switched laser. Single frequency laser possesses the advantages of high coherence and low noise, which can be used to the applications such as precision measurement. In the methods of single frequency generation, ring cavity configuration was shown to be the most robust one. Using this ring cavity, an IR and its intra-cavity frequency doubled green laser were demonstrated which the amplitude noise is lower than 0.3%. Passively Q-switched laser is an efficient and compact way to generate high-peak-power laser pulses because high voltages and fast driving electronics are not required. Its high power is useful for diverse applications including nonlinear optical processes, micromachining, material processing and range finders. But the major drawback of a passively Q-switched laser is its inherent large timing jitter, which is mainly originated from the photo dynamics in the cavity, environmental instabilities and spontaneous noise from the gain medium. In our study, we demonstrated the operation of a low-jitter, passively Q-switched laser by using the reentrant two-mirror unidirectional ring cavity, which generates a pulse width of 63ns, peak power of 250 W laser output. Due to the elimination of spontaneous noise and spatial hole burning effects, the timing jitter can be maintained below 3% over a wide range of pump powers with integrations of over 52,000 pulses.

Micro ring-cavity, like the Fabry-Perot cavity, is an optical device that resonates at certain frequencies. It is used as a phase compensator, and filter. Easily fabricated, the micro ring-cavity can be mass-produced, the ring-cavity is becoming evermore important as integrated opto-electronic technology advances. In this thesis, we begin with a novel one-dimensional theory that considers bi-directional traffic in the micro-ring cavity. By separating the device into easily manageable regions, and employing only fundamental modes in each of the sections, we obtain a closed-form formula for the transmission and reflection coefficient of this device. Under certain circumstances, when the directional coupler length is short but its coupling strength is strong, we observed a significant amount of reflection of optical energy at some frequencies. This phenomena is currently unknown to the opto-electronic industry. To further study this, we developed a more rigorous multi-mode propagation method for two-dimensional bi-directional ring cavities. The problem at hand is first being sliced into regions of multi-layered sections. Within each section, we can express the fields in terms of the underlying waveguide modes of the structure. At the interfaces of these sections, we construct coupled integral equations, which are derived from the continuity requirement of the tangential fields. We have complete formulations for both TE and TM cases, down to the coupled matrix equation for the unknown modal coefficients at each junction.