Understanding: Working Principles of Fiber-Optic Sensors and Features of Photoelectric Sensors

Sensors are important technologies for sensing, detection, monitoring and signal conversion. Fiber-optic sensors integrate optics and electronics to form a new type of sensor.

A fiber-optic sensor converts a measured parameter into an optical parameter (intensity, phase, polarization, frequency, wavelength). Light from a source enters the modulator via fiber; interaction between the measurement parameter and light in the modulation region changes optical properties (such as intensity, wavelength, frequency or phase), producing a modulated signal. The light then reaches a photodetector for measurement.

Unlike traditional sensors, fiber-optic sensors use optical signals to carry the measured information. Optical signals can be directly sensed and converted by optoelectronic components, easing electronic integration. Fiber is both a sensitive element and an excellent low-loss transmission medium, making fiber-optic sensors suitable for remote measurements not possible with conventional sensors.

Fiber-optic sensing includes two functions: sensing the external parameter and transmission. Sensing refers to how external parameters modulate optical wave parameters in the fiber (intensity, wavelength, frequency, phase, polarization). Transmission refers to delivering the modulated optical wave to a photodetector to extract the measurement and process the data.

Basic Principle of Fiber-Optic Sensors

An optical fiber typically consists of a core and cladding made of silica with differing refractive indices; the core diameter is about 0.1mm. Fiber-optic sensing originated from observing how external disturbances affect light transmission in the fiber. Changes in external conditions cause variations in transmitted optical parameters, which correlate with the external physical quantities and enable sensing.

Fiber-optic sensors are composed of a light source, sensing fiber, sensing element or modulation region, and photodetector. Parameters such as intensity, wavelength, amplitude, phase and polarization may be affected by temperature, pressure, acceleration, voltage, displacement, vibration, rotation, bending, strain, chemical and biochemical quantities. Fiber-optic sensors detect corresponding physical quantities by measuring these parameter changes.

Features of Fiber-Optic Sensors

Photoelectric sensors use object shielding or reflection of a light beam and synchronous selection circuitry to detect object presence. Any object that reflects light can be detected. Photoelectric systems convert input currents into light signals at the emitter, and detection is based on received light intensity. Photoelectric technology is widely applied across OEM and project industries.

Fiber-optic sensors have advantages such as high sensitivity, immunity to electromagnetic interference, corrosion resistance, good insulation, simple structure, small size, low power consumption and flexible optical paths. With rapid development, domestic fiber-optic sensor technology in China has matured and gained market share. Fiber-optic sensors are widely used in packaging machinery, electronics manufacturing and printing machinery.