Optical Device Sensing Application Fields
Our modern lives are surrounded by a large variety of sensors. For example, while walking in your neighborhood, the accelerometer and GPS antenna in your smartphone in your pocket, the street security cameras, the drive recorders and anti-collision sensors in passing cars, the infrared automatic door sensors on stores and buildings, etc., are all sensing your presence and actions without your conscious awareness. In other words, it is not an exaggeration to say that we receive the benefits of living in a sensing society.
This lecture entitled Optical Device Sensing Application Fields explains what type of optical sensing devices are available from Anritsu and in which application fields they can be used. The following explains non-communications applications for our optical devices using wavelengths in the near-infrared region from 800 to 2000 nm.
Figure 1 shows the healthcare applications fields for optical devices.
Fig. 1. Healthcare Applications Fields
The abbreviation OCT in Fig. 1 means Optical Coherence Tomography, which is a non-contact and non-invasive technology for measuring the roughness of surfaces and generating accurate tomographic images of living bodies using optical interference phenomena. This technology was first introduced in the ophthalmologic field because it is a non-contact inspection method that is ideal for examining semi-transparent living materials, such as the eye, causing relatively little optical scattering.
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The 1060 nm wavelength in the near-infrared region has low absorption by water, which is ideal for Optical Biometer measuring the long axis of the eye and is especially useful for selecting the correct magnification power of the intraocular lens supplied to cataract patients.
Laser perforation using pulsed near-infrared lasers at 1500 nm is a new application now in commercial use for in-vitro fertilization of fertilized eggs.
While the 1650 nm wavelength in the near-infrared region has excellent glucose absorption sensitivity and is the development focus for a non-invasive blood-glucose sensor, there is also interest in development in the mid-infrared region.
Figure 2 shows the industrial measurement applications fields for optical devices.
Fig. 2. Industrial Measurement Applications Fields
At the shorter 800 to 900 nm wavelengths, there are applications for auto-focus units, laser scales, and micro- encoders with high positioning precision. The spot size is smaller at shorter wavelengths, offering the advantage of improved resolution in free space.
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As described previously, the 1060 nm wavelength has low water absorption, facilitating Watt-level amplification using fiber-laser technology for applications in laser welding.
At 1300 nm, there are applications in thickness gauge of semiconductor wafers. Originally, the ideal wavelength for thin-film measurement is 1200 nm, but the 1300 nm wavelength range is now generally used due to considerations about ease of obtaining optical parts and reducing costs.
The unfamiliar abbreviation IR-OBIRCH means Infra-Red Optical Beam Induced Resistance Change, which is a technology for analyzing current leak pass and wiring shorts by illuminating and scanning metallic wiring parts with near infrared light. By using light with a longer wavelength than the 1100 nm bandgap of silicon, it is also possible to analyze Si substrate and chips from the back face.
Furthermore, wavelengths higher than 1400 nm are called “Eye-safe wavelengths” (1400 to 2600 nm) supporting relatively safe inspection for the eye. Bands near these wavelengths are used for applications with light in free space, such as displacement measurement, industrial OCT, 3D shape measurement, etc. In particular, displacement and 3D shape measurement use a method called Optical Frequency Domain Reflectometry (OFDR) applying the coherence of laser light for non-contact, high-precision measurement of distance ranges to target objects.
Figure 3 shows the applications fields for optical devices in other fields.
Fig. 3. Applications in Other Fields
The spread of microplastic pollution in marine ecosystem has become a problem in recent years. Microplastics are small plastic particles less than 5 mm in size and their detection in and removal from seawater is the subject of ongoing research. Near-infrared lasers at wavelengths of the microplastic absorption spectrum offer good hopes for detecting microplastics.
LiDAR is the abbreviation for Light Detection And Ranging, which is a technology used for automobile anti-collision detection and for weather observations. The measurement target is illuminated in free space by pulsed laser light and the returning reflected and scattered light from the target is used to calculate the target range and composition. Since it relies upon capturing extremely weak reflected light, it must use wavelengths far from visible-light noise sources. Additionally, since the power of the radiated optical pulse must be quite high, there are benefits to using wavelengths higher than the 1400 nm Eye-safe region to minimize any risks to people.
Looking at longer-wavelength regions, these wavelengths can be used for detecting various gases. For example, methane (CH4) can be detected at the 1650 nm and 1725 nm absorption lines, while nitric oxide (NO) can be detected at the 1795 nm line. Since each gas has a unique absorption spectrum, it should be possible to detect different gas species by selecting the laser wavelength matching the gas.
This lecture has introduced some application fields for the infrared regions, but the future will undoubtedly see new measurement technologies and applications. We are continuing to explore new measurement needs and development of optical devices matching these needs.
Finally, please be sure to contact us if you have any questions or things to discuss about what is the best optical device for your application or if you have a need for a laser with a specific output and wavelength. Our business section will be pleased to help.