Development of Star-Shaped Four-Channel CWDM Optical-Subassembly Module

We developed an optical sub-assembly (OSA) module for a four-channel coarse wavelength division multiplexing (CWDM) transceiver that satisfied the size requirement for XENPAK, X2 and XPAK multisource agreement (MSA). This module is composed of a frame structure with compact star-shaped optics paths, die-on-header laser or photodetector, thin film filters, ball lens and SC receptacle. The star-shaped optics design minimizes the reflective surfaces and makes the optics path shortest by using the concept of die-on-headers that are similar to To-can packages. The maximal optics path is 17.25mm from the laser diode to the fiber and the minimum is 12.00mm in the transmitter of optical subassembly (TOSA). In the receiver of optical subassembly (ROSA), the maximal optics path is 17.98mm from the fiber to photodetector and the minimum is 12.73mm. The designs of the die-on-header laser or photodetector and the frame structure provide both the passive and the active alignment versatilities. By the passive alignment method, we achieved the optimal optical condition for each channel in which the wavelengths varied from 1275nm to 1350nm. Furthermore, by using the active alignment method in the last stage of the assembly process, we compensated inaccuracies in the assembly process. As a result, the component assembly tolerance range of the OSA module increased up to 18-folds. Besides, the concept of hermetic sealing can also be executed in this design. From the analysis, it was found that the developed OSA module, no matter it is made of tool steel or optics plastic, shows good thermal stability for coupling efficiency when temperature changes from room temperature to -40degC and 85degC