Theoretical Modeling of Multi-Channel Intracavity Spectroscopy Technology Based on Mode Competition in Er-Doped Fiber Ring Laser Cavity.

An analytical model for analyzing multi-channel intracavity spectroscopy technology (ICST) is established based on rate equations of Er-doped fiber laser. With the consideration of the amplified spontaneous emission, how the mode competition influences the iterative process for a stable output is analyzed. From the perspective of iterative times, the sensitivity-enhanced mechanism of the ICST is explained. Moreover, the theoretical modeling is employed to analyze the role that the mode-competition effect plays in switching the sensing channel automatically. It is demonstrated that, owing to the mode-competition effect in the laser cavity, the modulation of the cavity loss can be used to tune the sensing channel automatically. Furthermore, our proposed theoretical modeling is verified using a multi-channel ICST sensing system. It is indicated that the calculated estimates agree well with those data from the experimental absorption spectra. The principle will play a significant role in realizing the multiplexing of ICST.

High-sensitivity magnetic field sensor based on a dual-core photonic crystal fiber.

A high-sensitivity magnetic field sensor based on a dual-core photonic crystal fiber has been designed with an extremely short device length of 2000 µm in this paper. The two cores of the fiber are separated by one air hole filled with magnetic fluid. The sensitive properties are investigated by the full-vector finite element method. Simulation results illustrate that the highest sensitivity can reach -442.7 pm/Oe in the magnetic field strength range of 30-520 Oe. The photonic crystal fiber filled with magnetic fluid, serving as an excellent platform for magnetic field sensing, has great potential applications in complex environments, remote sensing, and real-time monitoring fields.

Square-lattice alcohol-filled photonic crystal fiber temperature sensor based on a Sagnac interferometer.

A square-lattice alcohol-filled photonic crystal fiber temperature sensor based on a Sagnac interferometer (SI) is designed and analyzed by the finite element method. Alcohol is filled in all air holes in the cladding. The temperature-sensing properties of the proposed fiber sensor are investigated. Simulation results exhibit the transmission spectrums of the fiber SI will shift with the change of temperature, because the birefringence of the alcohol-filled fiber will change under different temperatures. The temperature sensitivity is obtained from the fitting line of the temperature and resonant wavelength. The average sensitivity can reach to 16.55 nm/°C in the range from 45°C to 75°C. This designed fiber temperature sensor has advantages in simple structure and high sensitivity. It can be used to detect temperature in complex environments.

High-Resolution Temperature Sensor Based on Single-Frequency Ring Fiber Laser via Optical Heterodyne Spectroscopy Technology.

We demonstrate a high-resolution temperature sensor based on optical heterodyne spectroscopy technology by virtue of the narrow linewidth characteristic of a single-frequency fiber laser. When the single-frequency ring fiber laser has a Lorentzian-linewidth <1 kHz and the temperature sensor operates in the range of 3-85 °C, an average sensitivity of 14.74 pm/°C is obtained by an optical spectrum analyzer. Furthermore, a resolution as high as ~5 × 10-3 °C is demonstrated through optical heterodyne spectroscopy technology by an electrical spectrum analyzer in the range of 18.26⁻18.71 °C with the figure of merit up to 3.1 × 105 in the experiment.

Intracavity absorption multiplexed sensor network based on dense wavelength division multiplexing filter.

We report the system design and experimental verification of an intracavity absorption multiplexed sensor network with hollow core photonic crystal fiber (HCPCF) sensors and dense wavelength division multiplexing (DWDM) filters. Compared with fiber Bragg grating (FBG), it is easier for the DWDM to accomplish a stable output. We realize the concentration detection of three gas cells filled with acetylene. The sensitivity is up to 100 ppmV at 1536.71 nm. Voltage gradient is firstly used to optimize the intracavity sensor network enhancing the detection efficiency up to 6.5 times. To the best of our knowledge, DWDM is firstly used as a wavelength division multiplexing device to realize intracavity absorption multiplexed sensor network. It make it possible to realize high capacity intracavity sensor network via multiplexed technique.

A reflective photonic crystal fiber temperature sensor probe based on infiltration with liquid mixtures.

In this paper, a reflective photonic crystal fiber (PCF) sensor probe for temperature measurement has been demonstrated both theoretically and experimentally. The performance of the device depends on the intensity modulation of the optical signal by liquid mixtures infiltrated into the air holes of commercial LMA-8 PCFs. The effective mode field area and the confinement loss of the probe are both proved highly temperature-dependent based on the finite element method (FEM). The experimental results show that the reflected power exhibits a linear response with a temperature sensitivity of about 1 dB/°C. The sensor probe presents a tunable temperature sensitive range due to the concentration of the mixture components. Further research illustrates that with appropriate mixtures of liquids, the probe could be developed as a cryogenic temperature sensor. The temperature sensitivity is about 0.75 dB/°C. Such a configuration is promising for a portable, low-power and all-in-fiber device for temperature or refractive index monitoring in chemical or biosensing applications.

Surface plasmon resonance sensor based on polymer photonic crystal fibers with metal nanolayers.

A large-mode-area polymer photonic crystal fiber made of polymethyl methacrylate with the cladding having only one layer of air holes near the edge of the fiber is designed and proposed to be used in surface plasmon resonance sensors. In such sensor, a nanoscale metal film and analyte can be deposited on the outer side of the fiber instead of coating or filling in the holes of the conventional PCF, which make the real time detection with high sensitivity easily to realize. Moreover, it is relatively stable to changes of the amount and the diameter of air holes, which is very beneficial for sensor fabrication and sensing applications. Numerical simulation results show that under the conditions of the similar spectral and intensity sensitivity of 8.3 × 10(-5)-9.4 × 10(-5) RIU, the confinement loss can be increased dramatically.