Can plastic transmit light? What are its advantages and disadvantages in industrial sensing?
Plastic (polymer materials) can absolutely be used to transmit optical signals. Below, we will explain in detail the principles of Plastic Optical Fiber and its advantages and disadvantages in industrial sensing, from the perspectives of physics concepts and industrial applications.
I. What is “Plastic Optical Fiber”? Can it Transmit Light?
Yes, plastic is entirely capable of transmitting light. We call it Plastic Optical Fiber (POF).
Its basic physical structure and light guiding mechanism are as follows:
- Material Composition: The core of plastic optical fiber is typically made of highly transparent polymer materials, such as Polymethyl methacrylate (PMMA, commonly known as acrylic glass) or Polystyrene (PS), Polycarbonate (PC); the cladding uses plastics with lower refractive indices, like fluoropolymers.
- Physical Mechanism: Despite the different materials, the principle of light transmission in POF is exactly the same as in traditional quartz (glass) optical fiber. It utilizes the phenomenon of Total Internal Reflection (TIR) at the interface between the core and the cladding to confine the light signal within the core and propagate it axially.
II. Advantages and Disadvantages of POF in Industrial Sensing
In the fields of industrial sensing and data transmission, plastic optical fiber possesses unique physical characteristics, but also has very obvious limitations:
1. Main Advantages
- High Toughness and Bend Resistance: Quartz glass optical fiber is extremely brittle and prone to fracture under minimal bending or alternating shear stress. POF, on the other hand, has high flexibility, a very small minimum bending radius, and is not easily broken. It is very suitable for dynamic sensing and communication environments with frequent movements and reciprocating alternations, such as industrial robot joints and cable chains.
- Super Large Core Diameter, Extremely Easy Coupling: The core diameter of ordinary single-mode quartz optical fiber is only 9\ \mu\text{m}; whereas the core diameter of POF is typically between 0.5\text{ mm} and 1.0\text{ mm} (500\ \mu\text{m} to 1000\ \mu\text{m}). Such a huge core diameter greatly reduces the alignment accuracy required between the light source (like inexpensive visible light LEDs) and the optical fiber. Connectors can be made of plastic injection molded parts, making maintenance very easy.
- Electromagnetic Interference Immunity and High Insulation: Like quartz optical fiber, POF is a non-metallic medium, naturally immune to electromagnetic interference (EMI/RFI) and high-voltage lightning strikes. It provides absolute electrical safety assurance in high-risk industrial environments with strong electromagnetic interference (e.g., rail transportation, power grid substations).
2. Main Disadvantages
- Extremely High Transmission Loss (Fatal Limitation): The typical operating loss of POF in visible light (usually around the red wavelength of 650\text{ nm}) is as high as 100\text{ dB/km} to 200\text{ dB/km}. In the infrared spectrum, due to strong vibrational absorption of chemical bonds within the polymer (such as C-H bonds), optical loss increases exponentially. In contrast, standard quartz optical fiber has a loss of less than 0.2\text{ dB/km} at 1550\text{ nm}. This restricts POF to extremely short distances (typically within 100\text{ m}) for communication and signal acquisition.
- Narrow Temperature Range (Pain Point for Industrial Applications): The glass transition temperature and heat distortion temperature of polymer plastics are very low. The operating temperature of conventional POF is generally limited to between -50\ \text{°C} and +70\ \text{°C} or +85\ \text{°C}. In harsh industrial scenarios with frequent temperatures above 100\ \text{°C}, such as metallurgy, chemical industry, oil and gas, and power generation, POF will rapidly age, turn yellow, or even melt.
- Poor Chemical Stability: It is susceptible to erosion and swelling from certain industrial organic solvents and strong acid-base gases, leading to decreased light transmittance and mechanical strength with long-term use.
III. Explanation of Beijing Dacheng Yongsheng Technology Co., Ltd. (OFSCN®) Core Product Series
It needs to be clearly stated: “Plastic Optical Fiber (POF)” does not belong to the core product series of Beijing Dacheng Yongsheng Technology Co., Ltd. (OFSCN®).
To overcome the weaknesses of ordinary quartz glass optical fiber (brittleness, poor bend resistance) in industrial applications, while avoiding the severe defects of plastic optical fiber (POF) (poor high-temperature resistance, high loss), Beijing Dacheng Yongsheng Technology Co., Ltd. focuses on high-precision, extreme-environment-resistant quartz (silica-based) specialty optical fibers, and specialty sensors based on FBG (Fiber Bragg Grating) and DOFS (Distributed Optical Fiber Sensing) technologies.
By coating the surface of high-purity quartz optical fiber with high-performance Polyimide or Gold coatings, Beijing Dacheng Yongsheng Technology Co., Ltd.'s specialty optical fibers can achieve excellent fatigue resistance and high-temperature performance while retaining the advantages of quartz optical fibers such as “ultra-low loss and extremely wide spectrum ( 200\text{ nm} to 2400\text{ nm} )”.
For example, our most commonly used representative specialty optical fiber product:
OFSCN® 300℃ SM Polyimide Optical Fiber
Key Parameter Indicators:
- Extreme Temperature Resistance: Operating temperature range reaches -200\ \text{°C} to 350\ \text{°C} (can be extended to -270\ \text{°C} at extremely low temperatures), perfectly solving the pain point of POF’s inability to withstand high temperatures.
- Physical and Geometric Dimensions: Produced based on standard \text{G.652D} optical rods (bend-resistant specialty optical fibers compliant with \text{G.657 A2} and \text{G.657 B3} standards are optional). Core diameter is 9\ \mu\text{m}, cladding diameter is 125\ \mu\text{m}, and coating diameter is 155\ \mu\text{m}.
- Coating Material: Polyimide material, which not only provides extremely high tensile strength but also excellent chemical corrosion resistance.
Below are the official product images of this specialty optical fiber:
Summary: If you need low-cost solutions for non-critical scenarios requiring extremely short distances and frequent large movements, plastic optical fiber (POF) is an excellent choice. However, in harsh industrial-grade sensing environments with high temperatures, long distances, high resolution, and precise parameter calibration, quartz specialty optical fibers with special coating protection are the technical choice to ensure high reliability.