A novel polarization beam splitter based on an anti-symmetric sidewall Bragg grating in a multimode silicon-on-insulator strip waveguide is demonstrated. Anti-symmetric spatially periodic refractive-index perturbations are designed for strong coupling between the fundamental (${\mathrm{TE}}_0$) and the first-order transverse electric modes (${\mathrm{TE}}_1$), while not for transfer magnetic modes. An adiabatic coupler is cascaded at the input-port, so as to drop the ${\mathrm{TE}}_1$ reflection. The Bragg grating has a compact length of $\sim 20\mathrm{\mu m}$ (55 periods). The polarization isolations of the through- and drop-ports at the wavelength of 1557 nm are 34 and 31 dB, respectively. A broad bandwidth of 64 nm and a large fabrication tolerance of 80 nm for polarization isolation over 20 dB are also achieved.

We demonstrate a silicon $1\times 64$ optical phased array by using carrier-depletion-based phase shifters. The 5-mm-long phase shifter exhibits an electro-optic bandwidth of 700 MHz, a modulation efficiency of 2.3 V.cm, and an ultra-low power consumption of < 0.45 nW/ $\boldsymbol {\pi }$ . A steering range of ±18° is realized in the phased-array axis by tuning the phase of each antenna. Besides, the beam steering in the other (wavelength-controlled) axis by tuning the wavelength achieves a dispersion efficiency of 0.17° /nm. Although the carrier-depletion effect induces a nonuniform optical amplitude distribution among the antenna array, the OPA chip is still able to form high-quality far-field beam patterns with side lobe suppression ratios of $\boldsymbol {\sim }10$ dB. Our measurement and simulation results indicate that the carrier-depletion-based OPA is a promising candidate for future high-speed and power-efficient solid-state Lidars.

A narrow-band add-drop filter based on an anti-symmetric cladding-modulated multimode Bragg grating (CMMBG) is demonstrated on the silicon-on-insulator (SOI) platform. The CMMBG is implemented by using periodic placements of silicon cubes along a multimode waveguide. The coupling strength is varied by changing the distance between the cubes and the multimode waveguide. An unlimited free-spectral range (FSR) and weak coupling strengths for TE0-TE1 modes conversion are achieved. Sidewall-misalignment-modulation (SMM) apodization is applied to achieve a high sidelobe suppression ratio (SLSR). The experimental results show that the designed filtering device has a 3-dB bandwidth of 0.8 nm, an insertion loss of -0.65 dB and a SLSR of 20.3 dB. The devices with different grating duty cycles and multimode waveguide widths were also fabricated and analyzed. Our devices are promising for on-chip applications that require narrow bandwidths such as WDM channel filters.

An integrated-optics, flat-top add-drop filter with low excess loss and high sidelobe suppression ratio (SLSR), is demonstrated. The filter is based on apodized multimode waveguide Bragg grating (AMWBG) developed on a silicon-on-insulator (SOI) platform. Antisymmetric periodic refractive-index perturbations are imposed on both sides of the waveguide to couple light contra-directionally between the fundamental (TE0) and the first-order transverse electric modes (TE1). To achieve a Gaussian apodization profile, the lateral-misalignment between the two sides of the waveguide is modulated by adjusting the positions of both sides of the grating features in a complementary manner. In this way, the undesired phase errors, which exist in conventional misalignment-modulated Bragg gratings and distort the grating responses, can be eliminated. Experimental results show that our AMWBG has a high-quality flat-top response, a high SLSR of >21 dB, a 3-dB bandwidth of 8 nm, a low excess loss of 0.24 dB, and a high roll-off rate at the filter edge. We also demonstrate a dual-stage filter that has a flat-top, drop-port response with a 3-dB bandwidth >7.5 nm, a SLSR >40 dB, and an excess loss<0.5 dB.

We demonstrate flat-top, sharp-edge, silicon add-drop filters using apodized grating-assisted contradirectional couplers (contra-DCs). Periodic sidewall corrugations are imposed on both sides of two asymmetric strip waveguides for contradirectional coupling between the first two TE supermodes of a two-waveguide system. Gaussian apodization is applied to suppress the sidelobes. By laterally shifting the positions of both waveguide Bragg gratings in a complementary manner, which is called complementary lateral-misalignment modulation, our devices avoid phase errors which impair the spectral responses for conventional lateral-misalignment modulated contra-DCs. We demonstrate a complementary lateral-misalignment modulated (CLMM) contra-DC that has a flat-top, rapid roll-off, drop-port spectral response with a sidelobe suppression ratio (SLSR) of 20 dB. We also demonstrate a series-cascaded CLMM contra-DCs that has a higher SLSR of 39 dB and a sharper filtering edge. ©

We demonstrate the design, fabrication and characterization of a two-mode silicon add-drop filter, which is based on multimode grating-assisted contra-directional couplers (MGACCs). The mode conversions between two asymmetry strip waveguides are realized by using spatially periodic corrugations in one side-wall of a multimode waveguide at the phase-match condition. Experimental results show that the fundamental mode of a single-mode waveguide is successfully coupled to the first two modes of the multimode waveguide in the opposite direction. The corresponding mode conversion bandwidths and extinction ratios are also measured. The demonstrated add-drop filter may find their applications in a hybrid multiplexing system by combing wavelength division multiplexing (WDM) technology and mode-division multiplexing (MDM) technology for on-chip optical interconnect.