Editorial Feature

What are Optical Sensors Used For?

Optical sensors detect and measure light intensity, converting light rays into electrical signals. The sensor is connected to an electrical trigger sensitive to light changes. Optical sensors are applied in many devices, including computers and motion detectors. This article will discuss the types of optical sensors that have been developed and their applications.

optical sensor

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Types of Optical Sensors

The main principle of optical sensors is the transmission and reception of light. The light reflected or interrupted by the target object is evaluated by several types of optical devices based on the type of material, such as wood, metal, plastic, transparent, or colored product.

Different types of light sources are used in optical sensors, which must be monochromatic, long-lasting, and compact. The two common types of light sources are Light Emitting Diodes (LEDs) and Light Amplification by Stimulated Emission Radiation (LASER).

Optical sensors are either placed externally or internally in a device. External optical sensors, also known as extrinsic sensors, gather and transmit a required quantity of light. In contrast, internal or intrinsic sensors are commonly used to measure the bend and other changes regarding the direction of light. Intrinsic sensors are typically embedded within an optical fiber or other devices.

Based on the application, different types of optical sensors are used. For instance, in photoconductive devices, optical sensors measure the resistance by converting a change in incident light to a change of resistance.

The sensors convert the incident light into an output voltage in solar cells. A photodiode converts the incident light to the output current. The function of a phototransistor, a type of bipolar transistor, is similar to a photodiode but with an internal gain. Some of the common types of optical sensors are discussed below.

Through-beam sensors

In through-beam sensors, the two components, namely, the transmitter and the receiver, are positioned opposite each other. The interruption of light is interpreted as a switch signal by the receiver.

This sensor covers a considerable operating distance and can detect independent object surfaces, structure, and color.

Retro-reflective sensors

The transmitter and receiver are placed in the same system in retro-reflective sensors. Similar to the through-beam sensor, the retro-reflective sensor also initiates via switching operation and covers large operating distances. All objects interrupting the light beam are detected independently and accurately by this sensor.

Diffuse reflection sensors

The receiver and transmitter are housed in one system in diffuse reflection sensors. This sensor detects the light reflected by the objects.

Latest Advancements in Optical Sensor Applications

Optical sensors are applied in various devices, including computers and copy machines. They are also used in light fixtures that automatically turn lights on in the dark.

Optical sensors are used in alarm systems and photographic flashes. Some of the other latest applications of optical sensors are discussed below:

Biomedical and healthcare applications

Photoplethysmography: heart rate monitoring

Optical sensors have been widely used in the biomedical field, including developing an optical heart-rate monitor that uses light. In this device, an LED focuses on the skin and an optical sensor analyzes the reflected light. As blood absorbs more light, fluctuations in light intensity can be translated into the heart rate. This process is known as photoplethysmography.

Contactless sanitizer dispensers

The coronavirus disease 2019 (COVID-19) pandemic has created an unprecedented need for contactless sensing. In this regard, a common application of optical sensors includes contactless sanitizer dispensers used in healthcare facilities.

Breath analyzers

Breath analysis is achieved by using a tunable diode laser.

Detection and quantification of biomarkers in human serum 

Serum is essential for proteomic analysis as it carries key markers of overall health status. However, detecting some diagnostic biomarkers, especially those of the low-molecular-weight (LMW) peptidome and circulatory proteome, is challenging due to their dynamic concentration in serum.

A novel strategy has recently been formulated to improve the detection of LMW amino acids. This method combines mid-IR (MIR) and near-IR (NIR) spectroscopic data to detect LMW compounds in a complex serum matrix.

Agricultural application

agriculture, optical sensors

Image Credit: Hryshchyshen Serhii/Shutterstock.com

Optical sensors have enabled on-site detection of pesticides in agricultural food products. Recent advancements in optical sensing technology include target-responsive hydrogels, fluorescence sensors, tube enzyme-linked immunosorbent assay, enzymatic fiber-optic biosensor, lateral flow immunoassay, wearable glove-based sensors, double-signal fluorescence strategy, and paper-based sensors, which have enabled on-site detection of pesticide residues in food products.

Environmental application

Food security and human health are significantly affected by heavy metal pollution, such as cadmium, in soil.

Although microelectronic sensors based on fluorescence spectrometry (XRF) are frequently used to detect heavy metals in soil, their accuracy and sensitivity are questioned.

A high-detection-efficiency photodiode (HDEPD) has been developed that has substantially increased the accuracy of the analyzer.

Industrial and commercial applications

Optical sensors are used to detect liquid levels in engineering facilities. For instance, optical sensors detect petroleum levels in hydrocarbon refineries and tanks. An ambient light sensing system is used in smartphone devices, which increases battery life. In addition, optimal screen brightness in accordance with the amount of light in the environment is achieved through the application of optical sensors.

Future of the Optical Industry

By analyzing the increased demand for optical sensors, an overall rise in the compound annual growth rate (CAGR) is estimated to be around 9.5% from 2022 to 2032.

With the discovery of automatic lamps, position sensors, smartphones, and photoelectric sensors, optical sensors have attracted much attention, particularly in the electronics industry.

As various optical sensors for critical biomedical analysis can be developed at a low cost, the future looks promising in this industry. The significant growth of the biometric market, associated with the deployment of fiber optics sensors in aerospace, defense, and the development of smart homes, has triggered the sales of optical sensors.

References and Further Reading

Gu, H. and Wang, L. (2022) A High-Detection-Efficiency Optoelectronic Device for Trace Cadmium Detection. Sensors, 22(15), pp.5630. https://doi.org/10.3390/s22155630

Veettil, T.C.P. and Wood, B.R. (2022) A Combined Near-Infrared and Mid-Infrared Spectroscopic Approach for the Detection and Quantification of Glycine in Human Serum. Sensors, 22(12), pp.4528. https://doi.org/10.3390/s22124528

Umapati, R. et al. (2022) Advances in optical-sensing strategies for the on-site detection of pesticides in agricultural foods. Trends in Food Science and Technology, 119, pp. 69-89. https://doi.org/10.1016/j.tifs.2021.11.018

Saha, S. Optical Sensor Market. (2022) [Online] Available at: https://www.futuremarketinsights.com/reports/optical-sensor-market

Pirzada, M. and Altintas, Z. (2020) Recent Progress in Optical Sensors for Biomedical Diagnostics. Micromachines11(4), pp. 356. https://doi.org/10.3390/mi11040356

Regtien, P and Dertien, E. (2018) Optical sensors. Sensors for Mechatronics, pp. 183-243. https://doi.org/10.1016/B978-0-12-813810-6.00007-0

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Dr. Priyom Bose

Written by

Dr. Priyom Bose

Priyom holds a Ph.D. in Plant Biology and Biotechnology from the University of Madras, India. She is an active researcher and an experienced science writer. Priyom has also co-authored several original research articles that have been published in reputed peer-reviewed journals. She is also an avid reader and an amateur photographer.

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