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- Vigneron, Pierre-Baptiste, et al.
(författare)
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8.5-fm resonances in an amplified slow-light fiber Bragg grating for high-precision metrology
- 2020
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Ingår i: Optical, Opto-Atomic, and Entanglement-Enhanced Precision Metrology II. - San Fransisco : SPIE - International Society for Optical Engineering.
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Konferensbidrag (refereegranskat)abstract
- Fiber Bragg gratings (FBGs) with strong apodized index modulations behave like an in-line Fabry-Perot interferometer and exhibit a series of narrow resonances in the short-wavelength portion of their transmission spectrum. These resonances have proven invaluable for detecting extremely small strains (30-femtostrain/√Hz level) or temperature changes (millidegreeC/√Hz level). The sensitivity of these fiber sensors is limited by the linewidth and peak transmission of the resonance used to interrogate the sensor, which are themselves limited by the intrinsic loss of the grating. In this work, significantly narrower and stronger resonances are demonstrated by introducing a small amount of optical gain in the FBG to offset the intrinsic loss and create a resonator with a much smaller net internal loss. The fiber Bragg grating is written in an Er-doped single-mode fiber and optically pumped to provide the required gain. The device reported here is a 6.5-mm grating with an AC index modulation of 1.59×10-3. With only 30 μW of pump power absorbed by the grating (32.6 mW launched), the fundamental resonance of the FBG was observed to narrow from 737 fm in the absence of pump to a record linewidth of 8.5 fm. The measured peak transmission of the resonance improved from ~-37 dB to -0.2 dB. A new model that predicts the slow-light resonance spectrum of a slow-light grating in the presence of optical gain is presented. This model is in good quantitative agreement with the measured evolution of the resonance linewidth as the pump power and the power of the laser that probes the resonance lineshape are varied.
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| 2. |
- Vigneron, Pierre-Baptiste, et al.
(författare)
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Loss-compensated slow-light fiber Bragg grating with 22-km/s group velocity
- 2020
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Ingår i: Optics Letters. - 0146-9592 .- 1539-4794. ; 45:11, s. 3179-3182
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Tidskriftsartikel (refereegranskat)abstract
- This Letter reports the behavior of the slow-light resonances of a strong apodized fiber Bragg grating (FBG) in which the intrinsic loss is compensated for by a small internal gain. The 6.5-mm FBG, written with a femtosecond laser in an Er-doped single-mode fiber, was pumped at similar to 4475 nm just below the lasing threshold to offset most of its intrinsic loss, thereby narrowing its resonances. The fundamental slow-light resonance was measured to have a linewidth of 8.5 fm, or a record group velocity of similar to 22 km/s, and a peak transmission near unity (-0.2 dB). The measured dependencies of the linewidth and peak transmission on pump power agree well with a new model that predicts the transmission spectrum of loss-compensated FBGs in the presence of pump and signal saturation.
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