Abstract
All-optical signal processing based on four wave mixing (FWM) in a highly nonlinear fiber (HNLF) to enhance the sensitivity of a fiber sensor is demonstrated and comprehensively reviewed in this paper. The principle is based on the frequency chirp magnification (FCM) by FWM. Degenerated FWM, cascaded two-stage FWM and pump-pulsed FWM with optical parametric amplification (OPA) are experimentally utilized for magnifying the frequency chirp. By using the pump pulse modulation to increase the peak power, OPA can be induced with the use of a dispersion-optimized HNLF. Therefore, ultra-highly efficient FWM can be realized due to the high peak power and OPA. By using the fiber Bragg grating (FBG) laser as the FWM pump, the wavelength drift of the FBG can thus be magnified due to the FCM. We obtain a sensing performance of 13.3 pm/με strain sensitivity and 141.2 pm/°C temperature sensitivity for a conventional FBG, which has an intrinsic strain sensitivity of only ~1 pm/με and an intrinsic temperature sensitivity of only ~10 pm/°C, respectively.
Highlights
Sensitive optical fiber sensors have been used in many areas due to the advantages, including compactness, all-fiber structure, immunity to electro-magnetic irradiation, waterproofness, and Photonics 2015, 2 so on [1,2]
Wavelength-interrogated sensors are intrinsically based on the measurement of the wavelength drift to extract the sensing signal, such as fiber Bragg grating (FBG)
We demonstrated four wave mixing (FWM)-based optical signal processing for the sensitivity enhancement of FBG sensors
Summary
Sensitive optical fiber sensors have been used in many areas due to the advantages, including compactness, all-fiber structure, immunity to electro-magnetic irradiation, waterproofness, and Photonics 2015, 2 so on [1,2] Among those fiber sensors, wavelength-interrogated sensors are intrinsically based on the measurement of the wavelength drift to extract the sensing signal, such as fiber Bragg grating (FBG). To measure such a small amount of strain, one needs to use a very sophisticated system to interrogate the FBG sensors [9] Such a nanoscale amount of strain is totally invisible for the 20-pm resolution OSA based on the conventional FBG sensor. Assisted by OPA and high-order FWM, record performances of 13.3-pm/με strain sensitivity and 141.2-pm/°C temperature sensitivity for silica FBG sensors are obtained, respectively.
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