Fig. 1. 3D illustration of the proposed ROADM utilizing the scheme of redistributing the modal fields. Here the launched TE0, TE1, and TE2 modes are converted to the TE0B′, TE1B′, and TE2B′ supermodes, whose modal fields are redistributed to be localized at regions #0, #1, and #2, respectively.

Fig. 2. Details of the MRR. (a) Coupling region of the thermally tunable MRR switch. (b) Cross section of the SOI photonic waveguide with a microheater on the top.

Fig. 3. Design of the SWG mode evolution region. Simulated light propagation in the SWG MBW and the redistributed modal fields of the (a) TE0B′, (b) TE1B′, and (c) TE2B′ supermodes, respectively.

Fig. 4. Design of the microring waveguide. (a) Calculated effective indices of the supermodes and the fundamental modes of each MRR waveguide as wr varies. (b) Calculated power coupling coefficient for three MRRs as the coupling length Lc varies. Here the coupling length is defined as Lc=NΛ, where N is the period number of the grating.

Fig. 5. Simulation results for the designed switches. Simulated light propagation for switch (a) #0, (b) #1, and (c) #2 at the resonant wavelength of 1550 nm when the TE0, TE1, and TE2 modes are launched in the MBW, respectively. Here the mode conversion region and the mode coupling region are included. Calculated transmissions at the drop port of the whole ROADM structure for the (d) TE0, (e) TE1, and (f) TE2 mode-channels.

Fig. 6. Fabrication tolerance analysis. Analysis of the fabrication tolerance for switches #0, #1, and #2 when assuming that the core width wr of the ring waveguide has a variation of ±10nm. (a) EL and (b) intermode cross talk.

Fig. 7. Microscope image of the fabricated devices. (a) The whole fabricated PIC for switches #0, #1, and #2. The enlarged view of MRR switches (b) #0, (c) #1, and (d) #2.

Fig. 8. Measured transmission results for the switches and the dual-core adiabatic taper mode (de)multiplexer. Normalized transmission spectra at drop port Di covering a bandwidth of 1530-1605 nm when light is launched from port Ii [(a) i=0, (b) i=1, and (c) i=2]. Normalized transmission spectra at output port Oi of the back-to-back dual-core adiabatic taper mode (de)multiplexer when light is launched from port Ii [(d) i=0, (e) i=1, and (f) i=2].

Fig. 9. Wavelength cross talk measurement of the switches. Transmission spectra of switches (a) #0, (b) #1, and (c) #2 when the resonant wavelengths are thermally tuned with a channel spacing of Δλ=0.8, 1.6, and 3.2 nm.

Fig. 10. Characterization of the thermal tuning performance. (a) Measured transmission of drop port D1 when different electric powers are applied for the MRR tuning. (b) Calculated tuning efficiency of the MRRs.

Fig. 11. Data transmission experiment. (a) Data transmission setup including tunable lasers, PCs, modulators (MOD), PPGs, device under test (DUT), erbium-doped fiber amplifier (EDFA), optical receiver (Recv), and digital communication analyzer (DCA). (b) Measured eye diagrams for data carried by each mode-channels, where a reference eye diagram of a straight single-mode waveguide is also shown. (c) Measured eye diagram when the input data are carried by two wavelength-channels with Δλ=0.8, 1.6, and 3.2 nm simultaneously.