Research On Integration Of Novel Subwavelength Grating And Semiconductor Photodetector For Optical Communication System

With the rapid development of high-speed optical communication systems and networks, more requirements are proposed on the optoelectronic devices. The multi-function integrated receiving device is one of the inevitable needs for the development of optical communication.Subwavelength grating as a new type of micro-nano structure has been widely used in high-performance optoelectronic devices, especially sub-wavelength grating structure using nano-size, novel structure, or even non-periodic structure, will produce beam focusing, beam steering and other new optical properties. The novel subwavelength grating integrated with semiconductor photodetector can greatly improve the performance of the device.In the thesis, the subwavelength gratings are researched as the basic device, aiming to realize the high performance of integrated semiconductor photodetector. The theoretical model and design of the novel subwavelength grating, the preparation of the integrated semiconductor photodetector and the experimental system test are mainly studied. The main contents and innovations are listed as follows:1. A 1D non - periodic subwavelength high contrast grating (HCG)reflector with a deflection angle of 20° was designed and successfully fabricated. With the normal incidence of TM polarized light, the reflected power peaked at 17.2° at the wavelength of 1550 nm, which is in good accordance with the simulation results of 17.35°. Moreover, the reflected power spectrum was also measured. Under different incident wavelengths around 1550 nn, reflected powers all peaked at 17.2°. Compared with the near 6° small angle of beam deflection proposed in other literatures, the designed HCG show that the proposed non-periodic HCGs reflector has a good reflection and beam steering ability in a wavelength range as wide as 40 nm around 1550 nm.2. A stripe high-contrast grating (HCG) focusing reflector with the focal length of 15mm is proposed and successfully fabricated. A 1550 nm TM polarized incident light of 11.86 mm in focal length and 0.8320 in reflectivity is obtained in experiment. At a distance of 11.86 mm, the light is focused to a round spot with the highest concentration, which is much smaller than the size of the incident beam. The FWHM of the reflected light beam decreases to 120 nm, and the intensity increases to 1.18.The wavelength dependence of the fabricated HCGs from 1530 nm to 1580 nm is also tested. The test results show that the focal length is in the range of 11.81-12 mm, the reflectivity is almost above 0.56 within a bandwidth of 50 nm. The literature presented an HCG reflector with a focal length of 17.2mm, a reflectivity of 80% -90% and a spot diameter of 150 ?m. In contrast, the designed reflector shows that the fabricated grating has a good focusing ability with a high reflectivity at a relatively wide bandwidth.3. On the basis of the stripe HCG focusing grating, a non-periodic concentric circular high index contrast grating (CC-HCG) focusing reflector with a focal length of 15 mm is proposed and successfully fabricated for the first time. The circular structure based HCG focusing reflector has a spot of high concentration at the 10.87 mm with normal incidence for radially polarization. The focusing efficiency of approximately 80% is observed at 1550 nm The FWHM spot size of the focusing beam decreases from 400 ?m to 260?m, and the intensity increases to 1.26 compared with the incident beam. Thus these can prove a good ability of reflect and beam focusing.4. A polarization beam splitter with focusing ability based on the two-layer 1D sub-wavelength grating is designed for the first time. When the TE and TM mixed light with a wavelength of 1550 nm incidents, the device separates the two polarized beams, and each of them is focused. The simulation results show that the total transmittances under TE and TM polarized light incidence are 78.3% and 93%, respectively. The polarization extinction ratios are 13.8 dB for TE light and 10.3 dB for TM light.5. A 2D sub-wavelength grating based power splitter with the size of 250 × 250?m2 and the focal length of 200 ?m is designed and successfully fabricated for the first time. The device can realize the property of polarization-insensitive transmission and power equalization under TE and TM mixed waves at the wavelengths of 1550 nm. The test at 600 ?m below the grating transmission surface shows that the intensity ratio of the two beams of output light is 1: 0.9, and the distance between the two spots is about 500 ?m. The test at about 190 ?m below the grating transmission surface shows that the intensity ratio of the two beams of output light is 1:0.85 and the distance the two spots is about 210 ?m. They are very close to the designed power beam splitter with the focal length of 200 ?m, and the distance between the two focal points of 250?m.6. The integrated device of InGaAs / InP PIN photodetector with 99%reflector, stripe and concentric circular focusing gratings are designed and successfully fabricated. The integration of two devices is realized by BCB bonding. The integrated photodetectors with different diameters of 180 ?m to 40 ?m are measured. The output current under different optical power and the corresponding responsively are obtained by the experimental measurement. The results show that the integrated device with the 40 ?m diameter and combined with concentric circular focusing gratings enhance the highest responsively.7. Subwavelength beam splitter grating hybrid integrated PIN photodetector array is fabricated and tested with other people for the first time. The measurement results show that the saturation current of the hybrid integrated PIN photodetector array is 64 mA, and RF powers is 3.0 dBm.