The Research On Wavelength-Selective Photodetector And Laser Based On Microring Resonator

Recently, optical microresonators attracted much attention and have been extensively studied. Devices such as microring, microdisk and microsphere are compact and easy to be integrated. They are widely used as laser resonator, optical filter etc. The microring laser and microdisk laser have been studied extensively Now photodetectors based on microresonator (MRPD) have attracted much attention, but the photodetectors based on microring resonator solely made of semiconductor material is not achieved at present. MRPD combining the advantages of waveguide photodetetor and Resonant-Cavity Enhanced (RCE) photodetector has the characteristics of compactness, easy planar integration, capable of selecting wavelength, high speed and high quantum efficiency which have bright application future in the Optics Electronics Integrate Circuit (OEIC) and Dense Wavelength Division Multiplexing (DWMM) optical communication system.The research in this paper is supported by grants from The National Basic Research Program of China (No. 2003CB314902, 2003CB314902), Program for New Century Excellent Talents in University of China (No. NCET-05-0111), National Natural Science Foundation of China (No. 60576018, 90601002), Program of Key International Science and Technology Cooperation Projects(No. 2006DFB11110).The theoretical and experimental research on wavelength selective photodetector based on microring resonator is carried out. The microring and micro-racetrack photodetectors which contain the InGaAs absorption layer are fabricated by the material of InP/InGaAsP, and the spectrum is measured. The main achievements in this paper are listed as follows. 1. The coupling coefficient of straight and microring is analyzed by the3-dimension coupled mode theory in combination with transfer matrix method. Influence of all parameters of coupling coefficient is analyzed. The results show that the coupling efficient decreases with the increase of waveguide width and thickness, gap and increases with the increase of the radius of the microring laser.2. A novel design of microring photodetecor is proposed. The photodectorhas a separated filtering part consisting of a microring part and an absorption part. Compared to the Microring photodetector whose resonance cavity have filtering and absorption function, this novel photodetector avoids the problem of very low confinement factor on the condition of critical coupling for its microresonator has no attenuation and is more practical. The- expression of quantum efficiency of microring photodetetor is derived. The influence of radius of resonator on quantum efficiency is analyzed and the influence of transmission coefficient on FWHM is analyzed. The result shows that the FWHM decreases with the increase of radius of the microresonator and the transmission coefficient. Under critical coupling condition, the quantum efficiency of this novel microring photodetector can approach 1 in theory.3. A microring photodetector which resonator contains the absorptionlayer that lies out the plane of resonator is proposed. Microring photodetector (MRPD) is analyzed by three dimension coupled-mode theory in combination of the theory of bending coupling. The coupling coefficient and the ratio between arc length of absorption layer and mirroring perimeter which influence the quantum efficiency and FWHM of MRPD are analyzed. The parameter of microring photodetetor is dedueced according to the relation between coupling coefficient and effective absorption coefficient of microring under the condition of critical coupling. The effective absorption coefficient is crucial to microring photodetector. The quantum efficiency of microring photodetector decreases with the increase of effective absorption. The full-width at half maximum (FWHM) and the critical coupling coefficient increase with the increase of effective absorption. The quantum efficiency and FWHM of the designed MRPD can reach 85%and 0.4 nm respectively.4. Experiments on mirroring photodetector are carried out. The microringand the micro-racetrack photodetector which contains the InGaAs absorption layer are fabricated by the material of InP/InGaAsP. The spectrum of throughout port is measured. For microring photodetector whose radius is 80μm, the FSR is 0. 75 nm and FWHM is 0. 5nm. For the micro-racetrack photodetector whose radius is 80μm and the length of straight waveguide which connects to the arc is 30μm, the FSR is 0. 7nm and FWHM is 0. 4nm.5. The microring laser threshold is analyzed by using the self-reproducecondition in combination with analytical expression of coupling coefficient. Influence of all parameters of semiconductor microring laser on microring laser threshold is analyzed. The threshold of microring laser increases with the increase of waveguide width and thickness, waveguide gap and decreases with the increase of and microring radius. This method is simple and requires less calculation and has clear physical meaning.