What Is an Optical Converter?
An optical converter, also known as an optical media converter, is a device designed to convert electrical signals into optical signals and vice versa.
In communication systems that use metal cables like LAN cables, electrical signals are used to transmit data. However, as the transmission distance increases, these electrical signals can suffer from attenuation and can be susceptible to electromagnetic interference, leading to communication errors.
Optical fiber communication, on the other hand, relies on light pulses to transmit signals. Optical signals in fiber optics have low attenuation and are immune to electromagnetic interference, making them ideal for stable long-distance communication. Optical converters are used to bridge the gap between metal cables and optical fibers in such systems.
Applications of Optical Converters
Optical converters find applications in various scenarios, including connecting optical lines to homes and office LAN systems and linking WiFi communication facilities to national optical networks.
As networks connect computers, peripherals, manufacturing equipment, and household appliances, data communication facilities are essential. Optical fiber, with its advantages of low attenuation, noise immunity, lightweight, and corrosion resistance, is being deployed extensively in communication networks worldwide.
Devices connected to these networks operate using electrical signals, but optical signals transmitted via optical fiber cannot be directly utilized. Optical converters play a crucial role in converting these optical signals into electrical signals for use by connected devices.
Principle of Optical Converter
1. Electrical to Optical (EO) Conversion
EO conversion involves converting electrical signals into optical signals. This is achieved using a semiconductor laser as the light source for the optical signal. Two common laser light modulation methods are direct modulation, where the electrical signal directly drives the semiconductor laser, and external modulation, where the semiconductor laser is continuously driven, and its light is modulated by an external modulator.
While direct modulation is compact and simple in terms of modulation circuitry, it can suffer from waveform degradation due to the semiconductor laser’s direct drive, making it less suitable for long-distance communication. External modulation is preferred for such applications.
2. Optical to Electrical (OE) Conversion
OE conversion involves converting optical signals into electrical signals. This is achieved using a photodiode, which is a semiconductor device also known as an optical sensor. When light strikes the photodiode, it generates electrons and holes in the PN junction, resulting in current flow. The photodiode converts the optical input into an electrical signal.
An Optical converter is a combination of EO and OE converters, allowing bidirectional conversion between electrical and optical signals.
Additional Information on Optical Converters
Circuit Pattern of Optical Converter
Effective utilization of optical converters requires careful design of circuit patterns and mounting layouts.
1. Impedance Matching
In Gbps-class modulation, impedance matching becomes critical, especially when dealing with millimeter-scale circuit lengths. It’s essential to ensure impedance matching between the semiconductor laser and the laser driver. Poor impedance matching can lead to signal reflections and ringing, degrading the modulation waveform. Verification of characteristics through simulation during the design phase is often necessary.
2. Photodetector and First-Stage Amplifier Configuration
A very weak signal flows between the photodetector and the first-stage amplifier. Minimizing noise in this signal path is crucial to meet specified minimum photosensitivity requirements. Since photosensitivity can vary depending on assembly and layout, characteristic verification during mounting is often necessary, in addition to impedance matching considerations.