The 100G CWDM4 module has been shipped in the millions with initial success. Its 200G and 400G silicon modules are also expected to be mass-produced in the second half of 2020.

CWDM4 module adopts the wavelength of 1271,1291,1311,1331 nm and the longest transmission distance up to 10km. It is encapsulated by QSFP28 and has two temperature specifications of 0-70℃ and 15-55℃.

CWDM4‘s TX and RX chips are separate. TX is composed of 4 III-V/Si hybrid integrated lasers, 4 MZ optical modulators and modulator driver chips, MUX and fiber coupling part based on EDG technology. RX consists of 4 Ge/Si detectors, TIA, PLC based DEMUX, and fiber coupling components. TX and RX clock and data recovery using MACOM 4-channel 25G CDR chip. The redundant tail fiber of TX and RX fiber array is arranged and fixed by disk fiber.

1. The TX light chip

The TX terminal of CWDM4 module, the laser, modulator and MUX are integrated on the same chip. The laser adopts the direct bonding technology of III-V material and Si waveguide to produce lasers of four wavelengths of 1271,1291,1311,1331 nm, respectively. Iii-v material is responsible for gain and Si waveguide is responsible for mode selection. Evanescent wave principle is used for coupling between the two. Silicon modulator is a 4-mZ modulator, and its high-speed modulation adopts multi-stage electrodes coupled with flip-chip bonding modulator to drive, which can reduce the attenuation of high-speed signals. The two arms of the MZ modulator are respectively equipped with a phase modulator for bias adjustment. In addition, the output port of the modulator has two monitoring optical waveguides, one for mode-level TX optical monitoring and the other for MZ modulator debugging and monitoring. The light modulated by the 4-way MZ modulator is multiplexed through EDG and coupled to the optical fiber through SSC and Lens.

2. The RX light chip

The RX end of CWDM4 module is composed of PLC DEMUX, 4 Ge detectors and TIA. The end of the DEMUX is a 45° reflective end that deflects the light by 90° and is coupled to the Ge detector.