Vertical Fibre Interfacing Interleaved Angled MMI for Thermal-Tuning-Free Wavelength Division (de)Multiplexing and Low-Cost Fibre Packaging

We propose and experimentally demonstrate a vertical fibre interfacing interleaved angled MMI (AMMI) for wavelength division (de)multiplexing (WDM) near 1550 nm. This 6-channel WDM device is composed of two 1 × 3 AMMIs and a Mach-Zehnder interferometer (MZI) with an apodized bidirectional grating acting as both vertical optical coupler and 3-dB power splitter. By thoroughly design the bidirectional gratings, a high coupling efficiency of 72.5% and low return loss of −34 dB is obtained by simulation. The AMMI couplers are designed and optimized using the Eigenmode expansion method. For wavelength matching between the MZI and AMMIs, the circuit simulation model of the interleaved AMMI is built by importing the S-parameter matrices of all the optical components extracted from the physical-level simulations. The device was fabricated using the standard CMOS technology and the feature size is compatible with the 193 nm deep-UV lithography. Experimental results obtained without thermal tuning are in good agreement with the simulation results, the device exhibits a small insertion loss (IL) varies between 3.3 and 4.58 dB (including the grating coupling loss), channel spacing of 6 nm, crosstalk (XT) below −20 dB. To investigate the fabrication tolerance, devices on two different chips are measured individually. The results show good consistency in device performance. Also, the fibre misalignment tolerance of the device is experimentally investigated.