An embedded optical fiber pressure sensor was made by sandwiching a piece of polarization maintaining photonic crystal fiber (PM-PCF) between two polymer foils. The excess birefringence induced by the transverse pressure applied in different directions with respect to the birefringent axes of the PM-PCF was numerically calculated and the slow axis was identified to be the most sensitive direction. An experimental test was carried out by incorporating the embedded PM-PCF sensor in a Sagnac interferometer; the output interference fringes were found to shift linearly with the applied transverse pressure with a peak wavelength to pressure sensitivity of 1.764 nm MPa–1, which corresponds to a birefringence to pressure sensitivity of 2.476 × 10−6 MPa−1.

The wavelength tuning characteristics of a widely tunable modulated grating Y-branch laser operating in a large temperature range was investigated experimentally. The linear fine-tuning was realized by sweeping the phase region current, and the fine lookup table was created with a high resolution of less than 0.1 pm. We found experimentally that the tuned wavelength has an excellent linear correspondence and there are small intercepts among the parallel tuning lines of different temperatures. Based on this special characteristic, an online simple wavelength re-calibration method of ‘one-wavelength bias pick-up and full wavelength range re-calibration’ was proposed and verified experimentally. The verification experiments proved its feasibility, and a high-tuned wavelength precision and accuracy of ∼0.1 pm within a temperature range of −25 °C to +75 °C was achieved. The tuning accuracy improvement is about two orders for magnitude.

An all-optical fiber photoacoustic gas sensor with double resonant signal enhancement is presented. The sensor uses a fiber-tip graphene nano-mechanical resonator operating at one of its resonances as the acoustic detector and a micro-acoustic resonant tube, whose resonant frequency is matched to that of the graphene resonator, as the PA gas cell. Compared with the single resonant detection with a graphene resonator, a five-fold signal enhancement is achieved. With 138-mW pump power and 1-s lock-in time constant, a noise equivalent concentration of ~25-ppb C ₂ H ₂ is achieved, corresponding to a normalized noise equivalent absorption of 1.29 × 10 ^-8 cm ^-1 WHz ^-1/2 .

We propose and demonstrate experimentally a low-noise closed-loop fiber optic gyroscope (FOG) driven by two broadband sources simultaneously. The basic characteristic of built-up super broadband light source (SBLS) consisting of two superluminescent diodes (SLDs) with different wavelengths was designed and analyzed. The dispersion characteristic of half-wave voltage of multifunction integrated optical circuit (MIOC) was investigated theoretically and experimentally. The tested results agree well with the theoretical model and confirm that the customized MIOC can operate well over a large spectral bandwidth. An experimental FOG driven by the SBLS was built with a solid-core polarization maintaining photonic crystal fiber coil and the closed-loop operation was realized well. Its bias drift and scale factor were tested preliminarily, and high performance is achieved compared with the FOGs with a single SLD source.

Spin-exchange relaxation-free atomic spin gyroscope (SERF gyro) has ultrahigh theoretical sensitivity and is regarded as one of the most potential atomic gyroscopes. To investigate its rotation response, a high linear atomic spin precession detection module was developed firstly by modifying the fiber reflective Sagnac interferometer for atomic spin precession detection and operating it in closed-loop mode. The SERF gyro based on K-Rb- ²¹ Ne comagnetometer was built and tested and appeared obvious nonlinear response feature. The nonlinear rotation response model was deduced by assuming the rotation-induced nuclei spin procession detecting as an in-situ magnetometer inside the SERF gyro and the fitting curves are in good agreement with the experimental results. The optimized pump power for maximum sensitivity and measurable dynamic range were analyzed theoretically and demonstrated experimentally. The investigation results show that the nonlinear rotation response is an intrinsic property of SERF gyro and its measurable dynamic range is limited due to the saturation characteristic of the sum of pumping and relaxation rate. This indicates that SERF gyro is propitious to a position gyroscope with high sensitivity.