40 Gb/s optical subassembly module for a multi-channel bidirectional optical link

A 40 Gb/s bidirectional optical link using four-channel optical subassembly (OSA) modules and two different wavelengths for the up- and down-link is demonstrated. Widely separated wavelengths of 850 nm and 1060 nm are used to reduce the optical crosstalk between the up- and down-link signals. Due to the integration capabilities of silicon, the OSA is implemented, all based on silicon: V-grooved silicon substrates to embed fibers and silicon optical benches (SiOBs) to mount optical components. The SiOBs are separately prepared for array chips of photodiodes (PDs), vertical-cavity surface-emitting lasers (VCSELs), and monitoring PDs, which are serially configured on an optical fiber array for direct coupling to the transmission fibers. The separation of the up- and down-link wavelengths is implemented using a wavelength-filtering 45° mirror which is formed in the fiber under the VCSEL. To guide the light signal to the PD another 45° mirror is formed at the end of the fiber. The fabricated bidirectional OSA module shows good performances with a clear eye-diagram and a BER of less than 10(-12) at a data rate of 10 Gb/s for each of the channels with input powers of -8 dBm and -6.5 dBm for the up-link and the down-link, respectively. The measured inter-channel crosstalk of the bidirectional 40 Gb/s optical link is about -22.6 dB, while the full-duplex operation mode demonstrates negligible crosstalk between the up- and down-link.