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

• Published in: Optics letters Vol. 40; no. 9; p. 2124
• Main Authors: Malara, P, Campanella, C E, De Leonardis, F, Giorgini, A, Avino, S, Passaro, V M N, Gagliardi, G
• Format: Journal Article
• Language: English
• Published: United States 01.05.2015
• ISSN: 1539-4794
• DOI: 10.1364/OL.40.002124

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.