A polarization-insensitive optical filter based on silicon and silicon nitride film is demonstrated. The lateral-shift apodization is introduced to suppress the sidelobes. The fabricated optical filter shows polarization-insensitive performances with large 3dB-bandwidths of 3.5–5.1 nm, low losses of 1.72-1 dB, decent SLSRs of 18.5-19.1 dB for both polarizations.
ultra-compact silicon mode (de)multiplexers are demonstrated based on asymmetric directional couplers with subwavelength structure (ADCWSS), the subwavelength structure is a series of corrugation on the sidewalls of waveguides, and the two arrays of corrugation extend into the gap region between the waveguides and interlace with each other. The coupling length of ADCWSS are 5.6μm, 6.5μm, and 7.9μm for TE0-TE1, TE0-TE2, TE0-TE3 mode (de)multiplexers, respectively. The four-mode mode-division-multiplexing (MDM) link was fabricated and measured. The insertion losses of TE0-TE0-TE0, TE0-TE1-TE0, TE0-TE2-TE0, and TE0-TE3-TE0 are 0.2dB, 0.7dB, 0.7dB and 0.9dB (around 1.55μm). The maximum insertion losses and crosstalk are 2.4dB, 2.9dB, 3.0dB, 4.0dB and -18dB, -19dB, -16dB, -18dB for the TE0, TE1, TE2 and TE3-mode channels over a 50-nm bandwidth.
Based on cascaded Mach-Zehnder lattice filter, an eight-channel silicon photonic (de-)multiplexer with flat passband is demonstrated in the O-band. The insertion loss of the device is -0.55~-2.48dB and the channel crosstalk is below -7dB. The FSR and channel spacing are about 36nm and 4.4nm respectively.
Space-chip coupling using silicon photonic grating coupler is of great significance for OPA-based LIDAR (Optical Phased Array, OPA), free-space data communication, and so on. However, Silicon-based grating couplers are commonly used for fiber-chip coupling and space-chip coupling is rarely mentioned. In order to obtain the optimal coupling effect, commercial three-dimensional Finite Difference Time-Domain (3D FDTD) software is employed to simulate the coupling process and analyze the characteristics of spatial light coupling. Because the spot size is in the order of micrometer, we first build a vector beam with three variables of numerical aperture, lens diameter and beam diameter for simulation. Afterwards, the incident location of the spatial light beam, the incident angle and the grating width are scanned to explore the influence of these parameters on coupling efficiency. We have found that the total coupling efficiency changes with grating width exponentially. That is, the total coupling efficiency firstly increases with the grating width, and does not change after reaching the maximum value. However, the coupling efficiency of the fundamental mode decreases gradually after reaching the maximum value. This indicates that higher-order modes are more likely to be excited when the width is greater than the optimized grating width. Besides, the coupling efficiency varies parabolically with the incident angle and location of the spatial light beam. There exists optimal incident angle and location on the parabola symmetry axis to get the maximum coupling efficiency. Furthermore, the best incident position is half of the beam diameter from the beginning of grating coupler.
We present that the linearity of silicon ring modulators in microwave photonics links can be improved by manipulating the quality factor in the cavity. By reducing Q factors of silicon ring modulators from 11000 to 5880 and tuning the operation wavelength for modulation, the measured Spurious-Free Dynamic Ranges of the third-order intermodulation distortion are improved from 98.5 dB·Hz2/3 to 104.3 dB·Hz2/3 and from 90.6 dB·Hz2/3 to 94.7 dB·Hz2/3 at 1 GHz and 10 GHz, respectively.
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