| Summary: | 碩士 === 國立臺灣大學 === 應用力學研究所 === 92 === With the progressively technological development in small forms, and its associated miniaturization specification in fiber-optic communication as well as the increasing demand in transmission capacity with low cost scheme, the miniaturized tunable laser is being driven to become an increasing role of active sources, which is able to provide multiple functions with a small-form configuration. In this study, leveraging MEMS technology in device miniaturization, and thus in small-form configuration of a whole system, the tunable laser based on a MEMS-based external cavity of wavelength-selective self-seeding mechanism leads to miniaturization in a small-form requirement. The miniaturized external-cavity tunable laser is significant in simplified components in system level, single- and dual-wavelength output, and independent wavelength ON/OFF tuning.
In this study, the MEMS-based external-cavity tunable laser system is comprised of a simple and inexpensive Fabry-Perot laser diode as a light source, a bulk grating for wavelength dispersion in free space, and an addressable micro corner mirror array for wavelength selection and switching. Among those components in this optical system to be the most critical is the corner mirror that requires nearly perfect verticality for reflection to be fed back into the laser diode. The corner mirror requires two orthogonal planes that include in-plane mirror and vertical mirror. The in-plane mirror that serves as the top electrode is freely tortional across a certain gap to its bottom electrode underneath. Therefore, with the voltage application across these electrodes, the in-plane mirror is able to be electrostatically attracted down onto the bottom electrode substrate so as to no longer maintain its orthogonal form for reflection lasing. In addition, the micro corner mirror array placed in a lightpath of first-order diffraction of the optical system is addressable for wavelength selection in free space. The resultant selected wavelength was then reflectively fed back to its original source as a seeding wavelength for resonance in overall output. Of particular interest is its verticality of micro corner mirrors that determines reflection back into its laser diode in a long travel of external cavity. The deviation out of its right angle was measured to be approximate 0.015o.
In this MEMS-based wavelength-tunable external-cavity diode laser, the single mode side mode suppression ratio was measured to be up to 15 dB. Furthermore, by maintaining two distant micro corner mirrors in “ON” state in which four in-plane mirrors in between those two were torsionally driven down, the dual wavelength output in 1532.2 nm and 1540.1 nm simultaneously were accomplished. At last, the micro corner mirrors has proven to be successfully used in wavelength selection as well as wavelength switching in the external-cavity wavelength tunable diode laser.
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