Adjustment of double resonance in short cavity Brillouin fiber lasers

Abstract

We present detailed analysis of the algorithm for adjustment of double resonance in short-length Brillouin ring fiber laser. Adapted laser cavity is simultaneously resonant for the pump and Stokes radiations. Demonstrated approach is equally useful for design of single mode fiber lasers with ultra-narrow optical spectra, Q-switched Brillouin fiber lasers as well as for the applications which required high power fiber resonators free from stimulated Brillouin scattering.Keywords: Brillouin fiber lasers, doubly resonant cavity INTRODUCTIONStimulated Brillouin scattering (SBS) through the resonant interaction of light photons with acoustic phonons is a nonlinear process with the lowest threshold in optical fibers 1 . For a monochromatic pump at 1550 nm, the Brillouin gain factor is almost three orders of magnitude higher than the Raman gain, providing an amplification band of ~35 MHz. Therefore, Brillouin gain is commonly used for narrow-line lasing in fiber configurations enabling a variety of the performance characteristics 2-7 . Lately developed Brillouin fiber lasers with a so-called doubly-resonant cavity (DRC) demonstrate low threshold, high spectral purity and low intensity noise 8-16 , and are very promising for a variety of special uses, such as coherent optical communication, interferometric sensing, coherent radar detection, and microwave photonics. In DRC lasers, a singlefrequency Stokes radiation is generated within a short ring cavity which is simultaneously resonant for pump and Stokes waves. Typically, in order to obtain an established single frequency operation, various forms of active 8-10 or passive 11,12 control systems are used. However, such systems are generally designed for the mode hopping control and cannot provide the adjustment of the resonance conditions itself. In order to achieve double-resonance operation in the ring fiber cavity, we have to provide precise and reliable coincidence of the pump laser frequency with one of the cavity resonant modes. Second, we have to be sure that the Stokes wave generated in the cavity by the resonating pump is also resonant to the cavity, i.e. the peak of the Brillouin gain spectrum induced by the pump in the cavity fiber coincides with one of the cavity resonant modes. Generally, it is not precisely the case, especially, for short cavities of several meters. At the resonance, the Brillouin threshold power is minimal. Therefore, commonly used techniques are based on piece-by-piece cutting of the ring fiber with intention to minimize the Brillouin threshold. Such procedure is boring, time-consuming, and gives rather rough approach to the resonance. Here we report a procedure for precise setting of the ring fiber cavity to the Brillouin resonance for any *vaspir@cicese.mx

Self-injection locking of the DFB laser through ring fiber optic resonator

“…With eqs. (14,15) we calculate transmitted and reflected powers versus coupling coefficient k 1 for the following values of our experimental parameters: k 2 = 0.01, γ 1 = γ 2 =0.1dB, ς = 0.2 dB and α 0 =0.17 dB/km. The reflected power reaches zero at k 1 = 0.08, that, therefore corresponds to critical coupling.…”

“…Low-loss optical fiber ring resonator with an ordinary communication fiber and directional couplers or other waveguide structures [8][9][10] can be used as high finesse filter for this purpose. Such resonators extensively investigated for number of application in fiber communications, including modulation and optical filters, fiber dispersion compensation, fiber optical laser, wavelength switching and others [11][12][13][14][15][16][17][18][19][20]. The optical transfer characteristics of the ring resonator strongly depend on coupler factor.…”