On-chip mode division (de)multiplexer for multi-band operation

We propose an on-chip mode division (de)multiplexer based on asymmetric directional couplers (ADCs) for multi-band operation. In mode-coupling process, the minimum coupling length is wavelength-dependent. The longer the wavelength is, the shorter the minimum coupling length is. A light of longer wavelength can be coupled back and forth multiple times with a total coupling length which equals to the minimum coupling length of a shorter wavelength light, thus realizing multi-band transmission at different wavelengths. As a proof-of-concept experiment, a four-mode (de)multiplexer for joint operation in the C- and O-Bands is designed and experimentally demonstrated. For the four modes (TE0, TE1, TE2 and TE3), the measured insertion losses (ILs) and crosstalk (CT) of the (de)multiplexer are < 4.7 dB and < -10.1 dB respectively from 1290 nm to 1360 nm, and they are < 3.5 dB and < -11.8 dB respectively from 1510 nm to 1580 nm.