Investigation of spectral narrowing mechanism in a volume Bragg grating optical parametric oscillator modulated by PPLN electro-optic polarization-mode converters

• Main Authors: Ning Hsu, 徐寧
• Other Authors: Yen -Hung Chen
• Format: Others
• Language: zh-TW
• Published: 2012
• Online Access: http://ndltd.ncl.edu.tw/handle/82536570390094184204

碩士 === 國立中央大學 === 光電科學研究所 === 100 === Single Longitudinal Mode (SLM) lasers have narrow linewidth, high degree of brightness and directionality properties, and they can be applied to many areas such as spectroscopy, remote sensing and fiber communic- ating. SLM can be achieve according to many traditional methods such as insert intra-cavity etalons in the short cavity, and constructing Fox-Smith interferometer oscillating single frequency with etalon. After that, we can use the ring cavity and Faraday rotator to let the electromagnetic waves become traveling waves instead of standing waves in the laser resonator to eliminate spatial-hole burning effect in homogeneous broadening mechanism to get rid of unwanted transverse modes and achieve SLM with narrow linewidth. Although those methods mentioned above can achieve SLM, many problems such as high insertion loss and complicated alignment in the ring cavity still remain. This thesis demonstrates another way to attain the SLM: Volume Bragg Grating (VBG) is a linewidth narrowing element, and it can be used as the output coupler of Optical Parametric Oscillator’s (OPO’s) resonator to reduce the output linewidth of OPO signal. If the nonlinear gain medium is pumped by the relatively lower peak power laser in this case, the gain profile of OPO is similar to homogeneous broadening. Next, we employee two Electro-Optic Polarization Mode Convertors (EO PMCs) to modulate the polarization states of narrow linewidth forward and backward signal waves become orthogonal. Finally, the signal waves reach SLM in a compact manner with linear cavity and few elements compares with traditional setups. We investigate and compare the OPO signals in their spectra, mode profiles and pulse durations with OPO signals operated at traveling wave mode and standing wave mode, which are controlled by EO PMCs. Under the traveling wave operation, the spectra linewidth (FWHM) of OPO signals were narrower both in the relatively lower gain regime (0.02nm to 0.01nm) and the relatively higher gain regime (0.1nm to 0.05nm) than under the standing wave operation. Meanwhile, the M2 of OPO was improved by two EO PMCs from 2.47 to 1.25.