Analysis of a novel sensor interrogation technique based on fiber cavity ring-down (CRD) loop and OTDR

Abstract

We present the analysis of a remote sensor based on fiber Cavity Ring-Down (CRD) loop interrogated by an Optical Time Domain Reflectometer (OTDR) taking into account both practical limitations and the related signal processing. A commercial OTDR is used for both pulse generation and sensor output detection. This allows obtaining a compact and simple design for intensity-based sensor applications. This novel sensor interrogation approach is experimentally demonstrated by placing a variable attenuator inside the fiber loop that mimics a sensor head.

Cavity Ring-Down Spectroscopy: Recent Technological Advancements, Techniques, and Applications

“…The fiber as well as the couplers contributes toward various losses such as the fiber’s transmission loss, insertion, and coupling losses, etc., which can significantly reduce the inherent ring-down time of the resonator. To recompense these losses, amplifiers such as erbium-doped fiber amplifiers (EDFA) are utilized, which provide a gain for maintaining the signal strength. , The sensing region is usually composed of a normal or tapered fiber but might consist of other components such as a gas cell, FBG, or a variable attenuator . Flexibility of incorporating different sensor elements is also one of the major advantages of fiber-based CRDS techniques.…”

“…40,43 The sensing region is usually composed of a normal or tapered fiber 39 but might consist of other components such as a gas cell, 44 FBG, 41 or a variable attenuator. 45 Flexibility of incorporating different sensor elements is also one of the major advantages of fiberbased CRDS techniques. Lately, many modifications in the design of the fiber-based CRDS systems have been demonstrated for various chemical, pressure, temperature, and magnetic field sensing applications.…”

“…They also utilized a similar multichannel setup for pressure sensing where the sensing location was also determined by working out the distance using the signal in the spatial domain. 48 For simplification of the input-output systems in fiber-based CRDS, the utilization of an optical time domain reflectometer (OTDR) has been observed, 41,45,49 wherein an OTDR sends a pulsed optical input to a fiber and analyzes the reflected or scattered light from the fiber. The OTDR response is given in decibels, which enables a linear output that can be better correlated to the sample attenuation and would reduce errors that arise in fitting of exponential ring-down time decay plots.…”

An Effective Spectral Processing Method for Low‐Cost Fiber Loop Ring‐Down Systems

“…In these systems, various sensing structures or materials, for example, air gap, coating, capillary, photonic crystal, and fiber grating were utilized to detect the physical, [3][4][5][6][7][8] chemical, [9][10][11] and biomedical parameters. [12][13][14] Lately, many improvements have been proposed [15][16][17][18][19][20][21] by combining suitable technologies (i.e., frequency shift, phase shift, chaotic correlation, optical frequency-domain reflection, optical time-domain reflection, and plasma) into the traditional structures. According to the laser sources used, fiber loop ring-down DOI: 10.1002/adts.202200865 systems can be categorized as pulse and continuous types.…”