Abstract
In this paper, we present a novel ultra-narrow linewidth fiber resonator formed by a tunable polarization maintaining (PM) π-phase-shifted fiber Bragg grating and a PM uniform fiber Bragg grating with a certain length of PM single mode fiber patch cable between them. Theoretical prediction shows that this resonator has ultra-narrow linewidth resonant peaks and is easy to realize impedance matching. We experimentally obtain 3 MHz narrow linewidth impedance matched resonant peak in a 7.3 m ultra-long passive fiber cavity. The impedance self-matching characteristic of this resonator also makes itself particularly suitable for use in ultra-sensitive sensors, ultra-narrow band rejection optical filters and fiber lasers applications.
Highlights
Narrow linewidth fiber Bragg gratings (FBGs) become of paramount importance in many applications such as Bragg reflectors[1, 2], optical filters[3, 4], and optical sensors[5,6,7,8,9,10], because of its significant advantages of easy to integrate and electromagnetic interference immunity[11]
The configuration of fiber resonator is composed of a tunable polarization maintaining (PM) π-phase-shifted fiber Bragg grating (PM-PSFBG) and a PM uniform fiber Bragg grating (PM-FBG) with a certain length of PM single mode fiber patch cable (PM-FIBER) between them
Operation that the whole structure is fabricated by a polarization maintaining process, and the input light has a linear state of polarization aligned to the slow axis of PM fiber
Summary
We experimentally studied the reflection spectrum of PSFBG-F-FBG resonator. The experiment setup is showed in Fig. 6, the PSFBG-F-FBG resonator was formed by a polarization maintaining phase-shifted grating (TeraXion) and a polarization maintaining uniform grating (TeraXion) which are linked by a polarization maintaining fiber patch cable. The PSFBG-F-FBG resonator was placed in a thermo-acoustic isolation enclosure to reduce the fluctuation of laser polarization and cavity length caused by ambient temperature or sound pressure. The experimental results agree well with the theoretical predictions with a large index number where means a large frequency detuning between the laser frequency and the Bragg frequency of PSFBG, but have low confidence when the index number is small This is because the grating parameters of experiment cannot be exactly the same as theoretical calculation, which will lead to an inappropriate estimate of dispersion effect of PSFBG. The drive signal of the phase modulator was generated by a voltage-control oscillator, to scan the frequency of second carriers to obtain the relative frequency between 3 MHz narrow linewidth resonant peak of PSFBG-F-FBG resonator and the laser carrier. To the 3 MHz narrow linewidth resonant peak, its temperature resolution can reach to 0.002 °C
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