Long-Period Waveguide Gratings on Silicon-on-Insulator(SOI) Substrates Fabricated by Anisotropic Wet Etching

• Main Authors: Guo-ShianWang, 王國賢
• Other Authors: Ricky-Wenkuei Chuang
• Format: Others
• Language: zh-TW
• Published: 2012
• Online Access: http://ndltd.ncl.edu.tw/handle/40092447045030721014

碩士 === 國立成功大學 === 微電子工程研究所碩博士班 === 101 === Long-period gratings (LPGs) are functioned based on the light coupling between the core guiding modes and the cladding modes at specific wavelengths (resonance wavelengths). However, the conventional FBG implemented on the optical fiber inevitably faces the geometry and material constraints associated with the fiber, which impose significant limitations on the device functionalities. To bypass the foregoing constraints, a long-period waveguide grating (LPG) employing a waveguide structure has been developed instead to provide an additional flexibility needed in designing various LPG-based devices. In general, the traditional long-period waveguide gratings were manufactured using low refractive index materials. In this thesis, high-refractive index silicon was used for the first time to explore its practicality for the long-period waveguide gratings fabrication. Specifically, the device was etched and patterned on SOI wafer via an anisotropic wet etching technique and eventually the long-period waveguide gratings were successfully fabricated with silicon ridge waveguide incorporated as an optical waveguide core layer. In addition, the cladding layer based on amorphous silicon with refractive index slightly lower than the crystalline silicon was deposited using plasma-enhanced chemical vapor deposition (PECVD) by judiciously controlling the flow rate of SiH4. With the amorphous silicon used as the cladding layer, the gratings with pitch as long as tens of micrometer could now be defined and patterned using the conventional photolithography. As mentioned previously, the wet etching was adopted to overcome the line width restriction entailed by the use of a much cheaper plastic mask; making the device feature size less than 20μm easily realizable, specifically, waveguides with a line width of 20, 18, 15, 12, 10 and 8μm had all been successfully fabricated to cut down the number of guided modes present in the core region. Additionally, a commercial software was used to design gratings with six different pitches needed, namely, Λ20=100μm, Λ18=107μm, Λ15=93μm, Λ12=95μm, Λ10=109μm and Λ8=91μm. The subsequent experimental results demonstrate that the LPWG devices appear to resonate within a wavelength range between 1563 and 1578nm, and the waveguide width of 8μm has delivered a dip contrast as high as 20 dB, while the device with the waveguide width of 10μm has its FWHM measured as narrow as 3.3nm. Then the experimental results with polarization controller inserted into the measurement setup show that the devices resonate within a wavelength range between 1563 and 1580nm, and the waveguide width of 8μm has delivered a dip contrast as high as 30 dB, while the device with the waveguide width of 12μm has its FWHM measured as narrow as 1.76nm with input light polarized as transverse electric (TE) wave. With transverse magnetic (TM) polarized wave provided as an input, the waveguide width of 10μm yields a dip contrast as high as 14.5 dB, while the device with the waveguide width of 10μm has its FWHM measured as narrow as 1.32nm.