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We propose and theoretically investigate integrated photonic filters based on coupled Sagnac loop reflectors formed by a self-coupled wire waveguide. By tailoring coherent mode interference in the device, three different filter functions are achieved, including Fano-like resonances, wavelength interleaving, and varied resonance mode splitting. For each function, the impact of device structural parameters is analyzed to facilitate optimized performance. Our results theoretically verify the proposed device as a compact multi-functional integrated photonic filter for flexible spectral shaping.

Microcombs are powerful tools as sources of multiple wavelength channels for photonic radio frequency (RF) signal processing. They offer a compact device footprint, large numbers of wavelengths, and wide Nyquist bands. Here, we review recent progress on microcomb-based photonic RF signal processors, including true time delays, reconfigurable filters, Hilbert transformers, differentiators, and channelizers. The strong potential of optical micro-combs for RF photonics applications in terms of functions and integrability is also discussed.

We propose and experimentally demonstrate a photonic generation scheme for multiband ultra-wideband (MB-UWB) signal by employing a dual-drive Mach–Zehnder modulator (DDMZM). In this scheme, four electrical binary pulse streams with different bit rates are combined to drive one radio frequency (RF) port of the DDMZM, while the other RF port is modulated by the sum of their 1-b delayed duplicates. By properly adjusting the bit rate and the amplitude of each pulse stream, as well as the bias voltage of the DDMZM, an MB-UWB signal with four sub-bands can be obtained and the transmission capacity can be quadrupled. The feasibility of the proposed scheme is verified by a system demonstration, where the signal modulated by amplitude-phase-shift-key format reaches a high bit rate of 2 Gb/s.

We propose and experimentally demonstrate a new method to generate a 3-D ultrawideband (UWB) signal by utilizing a dual-drive Mach-Zehnder modulator (DDMZM). Three degrees of freedom of the generated 3-D UWB signal are pulse position, pulse phase, and pulse amplitude. In this scheme, each radio frequency (RF) port of the DDMZM is modulated by a combination of two encoded signals with different amplitudes. By properly adjusting the amplitudes of the encoded signals and the bias voltages of the two RF ports, a 5-Gb/s 3-D UWB signal with a central frequency of 3.5 GHz and a 10-dB fractional bandwidth of 163% is successfully generated by using only a single DDMZM.

We propose and experimentally demonstrate a fiber-to-slot-waveguide grating coupler based on a double-strip waveguide, together with a double-strip-to-slot waveguide mode converter. By employing the double-strip waveguide, we improve the coupling efficiency from a fiber to the slot waveguide by ~ 1.2 dB, compared with previous grating-based two-stage schemes. In addition, the double-strip-to-slot waveguide mode converter, consisting of two S bends and a taper pair, occupies a short conversion length of only 4 μm. Parameters, including taper length and S-bend length are numerically optimized. Bandwidth and fabrication error tolerance are also analyzed. Experimental results verify the feasibility of the proposed scheme.

We propose and demonstrate a nested configuration of a silicon microring resonator possessing multiple coupling regimes in one passive device. For different resonance notches of the transmission intensity spectrum, diverse notch depths and bandwidths owing to multiple coupling regimes are designed and experimentally achieved. The phase response of the proposed configuration is also investigated. Experimental observation of fast and slow lights at different resonance wavelengths further verifies the realization of multiple coupling regimes.

A mode-selective grating reflector based on a hybrid plasmonic waveguide, together with a two-to-one coupling structure, is proposed and analyzed. The grating structure is designed to reflect only the fundamental even mode existing in the hybrid plasmonic waveguide, and to pass through the fundamental odd mode at a 1550-nm wavelength with an extinction ratio of ~16.7 dB. The simulated transmission spectra verify our analysis and the expected features of the mode-selective hybrid plasmonic Bragg grating.