Conception et fabrication d'un laser a fibre accordable par une cavite Fabry-Perot microfabriquee en silicium.

摘要

We present a tunable micro-optical filter made of monocrystalline silicon. Silicon is a material with interesting mechanical and optical properties. This tunable filter can be used in optical telecommunications networks, as an active element in ROADM, as a refractometer, an optical accelerometer or as a micro spectrometer. As part of this work, the filter is used to tune a fiber laser.;The filter is inserted into the cavity of a ring fiber laser. Erbium doped fiber is the amplifying medium. Erbium is used because of the wide range of its high gain. The laser is pumped using a laser diode emitting at 1480 nm through a WDM coupler. We use an optical isolator to ensure a one way lasing direction. By using the tunable filter within the laser cavity we can tune the laser. The tuning range of the laser is 35 nm from 1539 to 1574 nm with a maximum power output of 1.8 mW. The spectral width of the laser is below 0.03 nm.;The filter is made of two dielectric mirrors, called Bragg mirrors, placed in front of each other to form a Fabry-Perot (F-P) cavity. One of the two mirrors is operated by a comb drive to vary the F-P cavity length, thus to tune the transmitted wavelength. The optical filter behavior is simulated by transfer matrix method. The mirrors and the cavity properties are studied first by simulations and then compared to experimental results. The filter is manufactured in accordance with standard microfabrication processes. A photolithography step is followed by silicon dry etching using DRIE. The MEMS is released by liquid HF etching. Then supercritical drying prevents the structure from sticking. The free structure is maintained in suspension by four springs. The resonant frequency of the device is 14.4 kHz which enable fast tuning of the device. The maximum operating voltage is below 50 V. The tuning range of the filter is more than 90 nm from 1531 to more than 1621 nm using 40.7 V. The spectral width varies between 4.4 and 7.6 nm. The transmission losses vary from -9 to -24 dB. In addition, we show that it is possible to attenuate the signal of 3dB by moving a single wall of a Bragg mirror.