With the rapid growth of Internet IP data services, the demand for transmission line bandwidth has continued to increase. Although the DWDM (dense wave division) technology is the most effective method for solving the width expansion of the line, CWDM (thick wave division) technology has advantages in terms of system cost and maintenance.

Both CWDM and DWDM belong to the wave division reuse technology, which can be transmitted together to the single -core optical fiber and transmit it together.

The latest standard of CWDM's ITU is G.695, which stipulates 18 wavelength channels between 2071nm to 1611nm. Considering the impact of ordinary G.652 optical fiber, 16 channels are generally used. Because the channel interval is large, the components and laser are cheaper than the DWDM device.

The DWDM channel interval is different from the needs of 0.4nm, 0.8nm, 1.6nm, etc., and the interval is small and requires additional wavelength control devices. Therefore, equipment based on DWDM technology is higher than CWDM technology.

The PIN Optical Diode is between P -type and N -type semiconductors with high concentrations of mixed concentrations. A layer of light -doping N -type material is called I (Intrinsic, this sign) layer. Due to light doping, the electronic concentration is very low, and a wide depletion layer is formed after diffusion, which can improve its response speed and conversion efficiency.

The APD avalanche Optoelectronics diode, which not only has the effect of light/electricity conversion, but also has an internal amplification effect. Its amplification effect is completed by the avalanche multiplied effect inside the tube. APD is a gain of an increased photovoltaic diode. In the occasion where the sensitivity of the optical receiver is high, the use of APD is conducive to extending the transmission distance of the system.