ONU CompQosition

Optical modem is composed of sending, receiving, control, interface and power supply. The data terminal equipment provides the sent data in the form of binary serial signals, which are converted into internal logic levels through the interface and sent to the sending part, and are modulated into the signal required by the line through the modulation circuit and sent to the line. The receiving part receives the signal from the line, and after filtering, anti-modulation and level conversion, it is restored to a digital signal and sent to the digital terminal equipment. Similar to the modulation and demodulation of high-frequency carriers in electrical communication, optical modems can modulate and demodulate optical signals. Regardless of whether it is an analog system or a digital system, the electrical signal with information input to the optical transmitter is converted into an optical signal through modulation. The optical carrier is transmitted to the receiving end through the optical fiber line, and then the receiver converts the optical signal into an electrical signal through demodulation.

The optical modulator is an E/O conversion component composed of a microwave-encapsulated high-frequency DFB laser diode and APC and ATC control circuits. The UHF laser diode is directly modulated by the RF microwave signal to generate an intensity-modulated optical signal, which is then coupled to a single-mode fiber. , After about 5km of optical fiber transmission, the O/E conversion is completed by the optical demodulator. The optical demodulator is composed of PD components of high-speed transimpedance amplifiers and broadband low-noise amplifiers.

The conversion must ensure high linearity and low distortion transmission. Therefore, it should be done by reducing the RF input power and increasing the amplifier gain. The focus of the design lies in the microwave packaging of the device, impedance matching, simulating the equivalent circuit of the device, designing a reasonable coplanar microstrip circuit, and final