Review of Optical Fiber Sensors for Temperature, Salinity, and Pressure Sensing and Measurement in Seawater

Abstract

Temperature, salinity, and pressure (TSP) are essential parameters for the ocean. Optical fiber sensors (OFSs) have rapidly come into focus as an ocean detection technology in recent years due to their advantages of electromagnetic interference, light weight, low cost, and no waterproof requirement. In this paper, the most recently developed TSP sensors for single parameter and multi-parameter TSP sensing and measurement based on different OFSs are reviewed. In addition, from the practical point of view, encapsulation methods that protect fibers and maintain the normal operation of OFSs in seawater, and the response time of the OFS, are addressed. Finally, we discuss the prospects and challenges of OFSs used in marine environments and provide some clues for future work.

Keywords: ocean detection; optical fiber sensor; salinity and pressure; temperature.

Figure 1

(a) Schematic diagram of the dislocation fiber MZI-based sensor [48]. (b) Schematic of HBEF sensor based on a Sagnac loop [51]. (c) Schematic diagram of an SI based on a PMF with a circle [53]. (d) Diagrammatic sketch of the PDMS-coated microfiber sensors [60]. (e) The sensing probe with cascaded MZI and FBG [62]. (f) Schematic of temperature measurement system [63].

Figure 1

(a) Schematic diagram of the dislocation fiber MZI-based sensor [48]. (b) Schematic of HBEF sensor based on a Sagnac loop [51]. (c) Schematic diagram of an SI based on a PMF with a circle [53]. (d) Diagrammatic sketch of the PDMS-coated microfiber sensors [60]. (e) The sensing probe with cascaded MZI and FBG [62]. (f) Schematic of temperature measurement system [63].

Figure 2

(a) Schematic diagram of an FPI based on offset splicing [68]; (b) SI generalized setup [70].

Figure 3

(a) Illustration of the multiplexed FBG sensing element [78]. (b) Production process of composite structure [79]. (c) Schematic diagram of SPR-based OFS [83]. (d) Schematic diagram of the FPI in single configuration and the Vernier sensor [91]. (e,f) Schematic diagrams of different FPIs based on offset splicing [93,94].

Figure 4

Schematic diagram of (a) the sensor [98] and (b) experiment setup [99] for the measurement of TS in seawater by OMC. (c) Schematic diagram of the hybrid MZI [102]. (d) Schematic diagrams of tapered fiber structure [103]. (e) Combining the in-line MMZI with tapered SF or Sagnac loop [104]. (f) The fabrication process of a microfiber MZ interferometer with a knot resonator structure [106]. Reprinted with permission from Ref. [106]. Copyright 2016 IEEE.

Figure 4

Schematic diagram of (a) the sensor [98] and (b) experiment setup [99] for the measurement of TS in seawater by OMC. (c) Schematic diagram of the hybrid MZI [102]. (d) Schematic diagrams of tapered fiber structure [103]. (e) Combining the in-line MMZI with tapered SF or Sagnac loop [104]. (f) The fabrication process of a microfiber MZ interferometer with a knot resonator structure [106]. Reprinted with permission from Ref. [106]. Copyright 2016 IEEE.

Figure 5

(a) Structure design of C-type micro-structured FG [111]. (b) Schematic diagram of the fiber-tip FPI sensor [114]. (c) Schematic diagram of the all-encapsulated and semi-encapsulated MMZI [116]. (d) Diagram of the cascaded MZI with SF [118].

Figure 5

(a) Structure design of C-type micro-structured FG [111]. (b) Schematic diagram of the fiber-tip FPI sensor [114]. (c) Schematic diagram of the all-encapsulated and semi-encapsulated MMZI [116]. (d) Diagram of the cascaded MZI with SF [118].

Figure 6

(a) Schematic diagram of an SPR-based OFS [121]. (b) Schematic diagram of the all-encapsulated and semi-encapsulated MMZI [123]. (c) Diagram of the cascaded MZI with SF [125].

Figure 7

Schematic diagram of (a) PDMS-coated FBG [126]. (b) Semi-coated FBG [127]. (c) Encapsulation method of FPI sensors [131]. (d,e) Encapsulation method of MMZI sensors [62,133].

Figure 8

Schematic diagram of (a) full-encapsulated [116] and (b) part-encapsulated MMZI in a stainless steel C-type slot [104]. (c,d) Improved encapsulation method of MMZI [136].