Enhanced spectral response of π-phase shifted fiber Bragg gratings in closed-loop configuration

Abstract

The transmission spectrum of a ring resonator enclosing a π-phase shifted fiber Bragg grating (π-FBG) shows a spectral feature at the Bragg wavelength that is much sharper than resonance of the π-FBG alone, and that can be detected with a simple integrated cavity output technique. Hence, the resolution of any sensor based on the fitting of the π-FBG spectral profile can be largely improved by the proposed configuration at no additional fabrication costs and without altering the sensor robustness. A theoretical model shows that the resolution enhancement attainable in the proposed closed-loop geometry depends on the quality factor of the ring resonator. With a commercial grating in a medium-finesse ring, a spectral feature 12 times sharper than the π-FBG resonance is experimentally demonstrated. A larger enhancement is expected in a low-loss, polarization maintaining setup.

Super-Resonant Intracavity Coherent Absorption

“…An evenly intense, evenly spaced mode spectrum is in fact approached through a loss-induced transparency behavior, where the transmission of the dark modes increases and eventually matches that of the bright modes. At the same time, the mode splitting approaches its maximum allowed value of c / 2L 22 . The transmission of a RCPA super-mode in the regions at the left and right of the critical point is illustrated in Fig.…”

“…In such a FP-ring coupled cavity, split-resonances arise again from the symmetric and antisymmetric modes, but near the FP resonant wavelengths, where the backreflection drops abruptly, the splitting reduces and the two peaks tend to superimpose, generating a narrow interference in the transmission spectrum 22 23 , as shown in Fig. 1a .…”

Fibre Bragg Grating Based Strain Sensors: Review of Technology and Applications

“…These resonant sensor systems are mainly built using FBGs with complex scattering sources (SCs) which couple two counter-propagating modes (traveling wave (TW)) in a ring resonator. This mode coupling generates a spectral response characterized by two asymmetric resonance lines (called ”mode splitting” in the scientific literature and used for many applications, besides the strain sensing [ 31 , 32 , 33 , 34 , 35 , 36 , 37 , 38 ].…”

“…The following illustrations in Figure 11 shows different architectures based on the mode-splitting operating principle [ 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 , 37 , 38 , 39 ].…”

Impedance self-matching ultra-narrow linewidth fiber resonator by use of a tunable π-phase-shifted FBG

“…have attained ~0.5 pm (60 MHz) wavelength resolution 13 . Recently, cavity enhanced methodology has been realized by fabricating a FBG based ring resonator 14, 15 , or more often, by fabricating a fiber based Fabry-Perot interferometer 16–19 , where it is easy to obtain a high wavelength resolution cavity (~1 pm, 125 MHz for a 12 mm long cavity typically). In cavity enhanced methodology, an improvement of wavelength resolution can be achieved by increasing the cavity finesse or the cavity length.…”