Environmental Monitoring: A Comprehensive Review on Optical Waveguide and Fiber-Based Sensors

Abstract

Globally, there is active development of photonic sensors incorporating multidisciplinary research. The ultimate objective is to develop small, low-cost, sensitive, selective, quick, durable, remote-controllable sensors that are resistant to electromagnetic interference. Different photonic sensor designs and advances in photonic frameworks have shown the possibility to realize these capabilities. In this review paper, the latest developments in the field of optical waveguide and fiber-based sensors which can serve for environmental monitoring are discussed. Several important topics such as toxic gas, water quality, indoor environment, and natural disaster monitoring are reviewed.

Keywords: environmental monitoring; gas sensing; optical fiber; optical waveguide; photonic sensors; volatile organic compounds; water quality monitoring.

Figure 1

Illustration of evanescence field sensing.

Figure 2

The environmental monitoring applications.

Figure 3

HC-PCF-based gas sensor, (a) schematic of MZI developed using a small stub of HC-PCF [58], (b) experimental schematic for sensor characterization and interrogation [58], (c) the response of the sensor to CO₂ gas concentration [58], (d) the response of the sensor to temperature change [58].

Figure 4

Recently proposed waveguide-based gas sensors, (a) schematic view of the gas sensor measuring setup [78], (b) experimental realization of the gas cell [78], (c) schematic of the polarization independent hybrid plasmonic waveguide for gas sensing [84], (d) SEM image of the suspended rib waveguide [86].

Figure 5

Schematic of slot microring gas sensor.

Figure 6

Integrated chip (a) an illustration of the sensor arrangement [122], (b) an illustration of one of the sensing patches in cross-section, highlighting the isolation layer, waveguide, and placement of the surface chemistry [122], (c) a visual representation of light movement along the waveguide chip [122].

Figure 7

Indoor environment monitoring.

Figure 8

(a) Sensor device with PDMS chamber and SiN waveguides. Waveguides for the input and output had a 5 mm offset [132], (b) SEM image of the waveguide and inset shows the side wall [132], (c) near-field pattern of the fundamental mode [132].

Figure 9

(a) PDMS-coated FBG sensor schematic diagram [135], (b) sensor spectral response for each VOC [135].

Figure 10

Flood monitoring (a) image of the modified U-shaped sensor profile [178], (b) photo of the wireless POF prototype and the MICA2DOT unit [178], (c) representation of the universal wireless POF sensor system [178].

Figure 11

Time distribution of the anomalous infrasound signals before the earthquakes during 2002–2009 [185].

Figure 12

(a) Schematic of the RR ultrasound sensor: a RR on a square membrane (blue). (b) Cross-section of the membrane region, showing the various layers and their thickness. Membrane thickness is 2:65 μm. A glass platelet seals the air cavity under the membrane. (c) Microscope image of the membrane with the RR, taken from below. The membrane size is 84 μm × 84 μm [190].

Figure 13

MediGator (left) and experimental setup (right). The MediGator comprises the tunable light source of high brightness (upper part) and the photonic integrated circuit of MZI and PDs (lower part). Each PD is connected to a TIA. (TEC, thermoelectric cooling; WDM, wavelength division multiplexer; FBG, fiber Bragg grating; PIC, photonic integrated circuit; PD, photodetector; TIA, trans-impedance amplifier; AWG, arbitrary waveform generator; MMI, multi-mode interferometer) [190].

Figure 14

Landslide monitoring, (a) the large-scale physical replica underwent the and slide during testing [187], (b) views from the top and sides of the instrumented fume show the clamping bars as vertical dashed lines in the top image [187].