Fig. 1. (a) PON wavelength plan. US, upstream; DS, downstream; BW, bandwidth. (b) PON configuration with the coexistence of GPON and 10G GPON. (c) Structure schematic diagram of a quadplexer.

Fig. 2. Schematic configurations: (a) proposed quadplexer; (b) MWG-based filter, consisting of a mode (de)multiplexer and an MWG-based filter; (c) mode (de)multiplexer based on an adiabatic dual-core taper; and (d) longitudinal apodization for the MWG.

Fig. 3. (a) Calculated dispersion curves of an SOI strip waveguide for the TE0 and TE1 modes at four wavelength bands (i.e., 1270, 1310, 1490, and 1577 nm). Simulated transmissions of the designed mode (de)multiplexer for the wavelength band of (b) 1270/1310 nm and the wavelength band of (c) 1490/1577 nm. Insets: simulated light propagation in the designed adiabatic taper.

Fig. 4. Calculated transmittance spectra at the drop and through ports for the designed MWGs at the channels of (a) 1270, (b) 1310, (c) 1490, and (d) 1577 nm.

Fig. 5. Simulated transmissions at the drop port of the designed MWG filter at the 1577 nm channel when assuming that there is some core-width variation (i.e., Δw=±10  nm and ±20  nm).

Fig. 6. (a) Microscope image of the fabricated quadplexers on silicon. SEM images of the grating couplers working around (b) 1300 nm and (c) 1530 nm, parts of gratings for (d) 1270 nm, (e) 1310 nm, (f) 1490 nm, and (g) 1577 nm.

Fig. 7. Measured spectral responses for the four channels of (a) 1270 nm, (b) 1310 nm, (c) 1490 nm, and (d) 1577 nm.

Fig. 8. (a) Measurement setup for the eye diagram, including tunable lasers, polarization controllers (PCs), Mach–Zehnder modulators (MZMs), pulse pattern generators (PPGs), an off-chip multiplexer (MUX), the device under test (DUT), an optical receiver (Recv.), and a digital communication analyzer (DCA). Measured eye diagrams for the channels of (b) 1271 nm, (c) 1311 nm, and (d) 1577 nm.

Fig. 9. (a) Microscopy picture of the fabricated identical MWG-based filters; (b) measurement responses at the drop-port; (c) the central wavelength deviation and (d) the 3 dB bandwidth deviation among six samples.