Fig. 1. Illustration of optical crosstalk from space-division multiplexing (SDM) and photonic integration.

Fig. 2. Schematic of (a) crosstalk induced by coherent detection and (b) crosstalk mitigation using low-coherence matched detection. (Base, modulated ASE bandwidth; Bs, signal bandwidth; Δt, temporal path length difference between the signal and LO.)

Fig. 3. (a) Measured optical spectra of an ASE-based low-coherence source (LCS) with different Base. (b) Setup for measuring inteferogram of a low-coherence source and (c) interferogram for an LCS with Base of 0.5 nm, 1 nm, and 2 nm.

Fig. 4. (a) Setup of ASE-based low-coherence matched detection and (b) achieved BER for ASE with different Base as a function of Δt.

Fig. 5. (a) Setup for characterizing system performance with various crosstalk levels using low-coherence matched detection and (b) measured BER versus crosstalk for various Base.

Fig. 6. (a) Setup for mitigating the polarization crosstalk after SMF transmission with different transmission distances; (b) schematic of the integrated DP-IQ MZM with 2-ps temporal delay between two polarization states; BER using MIMO-less DSP versus the time delay through tuning the delay line for (c) 10-m and (e) 5-km transmission; recovered QPSK constellations of the y-pol from both receivers at time around 4 ps for (d) 10-m and (f) 5-km transmission, including the results using maximum ratio combining (MRC).

Fig. 7. (a) Setup for individual spatial and polarization mode detection by mitigating the modal crosstalk, (b) BER for the spatial mode: LP11b mode using only 2×2 MIMO DSP, and (c) BER for the spatial and polarization mode: LP11bx mode using MIMO-less DSP versus the time difference Δt between the signal and matched LO.

Fig. 8. Measured BER with spatial mode crosstalk mitigation as a function of Base while transmitting both LP11a and LP11b modes over (a) 10-m, (b) 0.5-km, (c) 1-km, and (d) 1.5-km three-mode MMF.

Fig. 9. (a) Setup for wavelength- and mode-multiplexed transmission over 1.5-km MMF with modal crosstalk mitigation using ASE-based matched detection; optical spectra of the wavelength-multiplexed signal after (b) 10-m and (c) 1.5-km 3-mode MMF transmission; recovered QPSK constellations and measured BER for (d) the LP11a mode using a CW laser with a 100-kHz linewidth, and (e) both LP11a and LP11b modes with Base=2  nm at four wavelengths.