How does an IR sensor work? Key components and principles.

Infrared (IR) sensors are vital in a range of applications, from automation and proximity sensing to high-speed wireless communications. All IR sensors detect light beyond the visible spectrum. However, the mechanism of "sensing" varies with context and intent.

Foundational principles and components

Every IR system features these core elements:

• Emitter: An IR LED or laser diode that generates infrared light, encoded for specific tasks.
• Receiver/Detector: A photodiode, phototransistor, or an advanced avalanche photodiode (APD), which absorbs incoming IR and converts it to electrical signals for processing. This is the "sense" function, whether for detection or communication.
• Optical Elements & Signal Processing: Lenses, filters, and circuits amplify, refine, and interpret the incoming IR signal for practical use, from automation triggers to decoding communications packets.

Sensing applications for IR sensors

In proximity sensors and motion detectors, IR emitters send energy into a space. Receivers monitor changes in the reflected IR signal (from people, objects, or surfaces) or, using passive sensors, detect naturally emitted IR from warm bodies. This change in IR energy signals the presence, motion, or distance of objects. This data is fundamental for security systes, automation, and other interactive devices.

Communications applications for IR sensors

Communications systems, including free-space optical communications and fibreoptic links, also rely on sensing, but here the receiver is tuned so that it only detects a deliberate, modulated IR transmission sent by the paired emitter. IR wireless communications, seen in everything from high-performance data centre links to TV remote controls, work by encoding information onto IR light pulses, which are sent directly to a receiver that senses and decodes these transmissions.

The components of an infrared link using free space optical communications (FSOC)

Key points:

• Both transmitter and receiver act intentionally, and the receiver senses only the intended signal, not ambient IR or reflections.
• The IR signal is modulated to distinguish communication packets from noise. Point-to-point links demand accurate alignment and line-of-sight for reliable data transfer.
• The sensing mechanism remains foundational: the receiver detects incoming IR and translates it to usable data through demodulation and decoding.

Advanced IR sensor evolution

Innovators like Phlux Technology push these boundaries with antimony-enhanced avalanche photodiodes, enabling ultra-sensitive, low-noise IR sensing for both object detection and robust communications, even in demanding applications like LiDAR and high-speed optical networks.

IR sensing summary

Whether for environmental detection or direct communications, infrared sensors are based on sensing IR light, either from the environment, reflective objects, or targeted transmitters. What changes is the context: in sensing, environmental signals are interpreted; in communications, the sensor is designed to detect only the transmitter's modulated IR pulses. Both rely on a "sense and respond" mechanism, but the engineering adapts to the application's purpose.