As light cannot be stopped or directly stored in any media, optical delay lines are usually used to temporally trap the optical signals. We report a wide-range continuously tunable optical delay line chip consisting of a ring resonator array and a Mach–Zehnder interferometer (MZI) switch array on the 60-nm-thick silicon waveguide platform. The ring delay line provides continuous delay tuning of more than 10 ps with a push–pull differential tuning method. The MZI switchable delay line provides digitally programmable delay tuning with a resolution of 10 ps upon reconfiguration of the MZI switches to establish different optical routing paths. Dual-stage MZI switches are used to ensure low crosstalk with an improved signal-to-noise ratio. The delay line chip can generate a maximum delay of $>1\mathrm{ns}$ with an on-chip insertion loss of 12.4 dB. Optical pulse time-division multiplexing and quasi-arbitrary waveform generation are realized based on the delay line chip. These results represent a significant step towards the realization of highly reconfigurable optical signal processors enabled by optical delay manipulation with broad applications for optical communications and microwave photonics.

We design, fabricate, and characterize a 7-bit reconfigurable optical true time delay line consisting of Mach-Zehnder interferometer (MZI) switches on the silicon photonics platform. Variable optical attenuators (VOAs) are embedded to suppress the inter-symbol crosstalk caused by the finite extinction ratio of switches. The device can provide a maximum of 1.27 ns delay with a 10 ps resolution over a wide wavelength range. Eye diagram measurement of a 25 Gbps 2⁵¹-1 pseudo-random bit sequence (PRBS) signal reveals the power penalties only increase 0.17 dB and 0.77 dB after transmission through the shortest (reference) and the longest (1.27 ns delay) paths, respectively.

Low-power reconfigurable optical circuits are highly demanded to satisfy a variety of different applications. Conventional electro-optic and thermo-optic refractive index tuning methods in silicon photonics are not suitable for reconfiguration of optical circuits due to their high static power consumption and volatility. We propose and demonstrate a nonvolatile tuning method by utilizing the reversible phase change property of GST integrated on top of the silicon waveguide. The phase change is enabled by applying electrical pulses to the μm-sized GST active region in a sandwich structure. The experimental results show that the optical transmission of the silicon waveguide can be tuned by controlling the phase state of GST.

We report a LiDAR transmitter incorporating both a hybrid-integrated tunable external cavity laser and a high-resolution 2-D optical phased array beam-steerer. Widely tunable single-mode lasing over a span of approximately 100 nm is achieved with >42 dB side-mode-suppression-ratio, 18 mW output power, and 2.8 kHz linewidth. Two-dimensional beam steering in a field-of-view of 140° × 16° exhibits a beam divergence of 0.051° × 0.016° measured in full width at half maximum. Leveraging the low propagation loss, negligible nonlinear loss, and low thermal sensitivity of silicon nitride, and combining the high mode confinement and efficient thermal tuning of silicon, the device affirms the feasibility of high-power on-chip lasing, power bottleneck elimination, and low on-chip insertion loss. It represents the first demonstration of a fully integrated LiDAR transmitter on the multi-layer silicon-nitride-on-silicon photonic platform, revealing the potential of complementary integration in the effort toward a LiDAR transmitter of sufficient optical power budget.

Chip-scale lasers with a wide tunable range and a narrow linewidth have rich applications in optical communications, sensing, and light detection and ranging systems. External cavity lasers (ECLs) have the advantage of a wide tuning range and a narrow linewidth compared with their counterparts such as distributed feedback lasers and distributed Bragg reflector lasers because the passive filter separated from the gain section can be widely tuned and the low-loss external cavity extends the photon lifetime. However, so far, the tuning range achieved by the chip-scale ECLs is in the range of 80–120 nm, smaller than that of the bulk free-space ECL (typically >160 nm). The bottleneck in reaching an ultrabroad tuning range for chip-scale ECLs lies in the unsuppressed side modes of the external cavity. Here, we demonstrate a hybrid-integrated ECL consisting of a broadband III–V reflective semiconductor optical amplifier and a low-loss Si₃N₄ wavelength-selective reflector. A record 172-nm lasing wavelength tuning range together with a more than 40 dB side-mode suppression ratio is achieved beyond the free spectral range of the Vernier ring filter due to the enhanced lasing mode selection from a tunable Sagnac loop reflector. The Si₃N₄ platform enables a low-loss external cavity, facilitating laser linewidth reduction below 4 kHz over the full tuning range. The on-chip output power reaches 26.7 mW at a wavelength of 1550 nm.

We experimentally demonstrate a $16\times 16$ reconfigurably nonblocking optical switch fabric using a Benes architecture. The switch fabric consists of 56 $2\times 2$ Mach–Zehnder interferometer based elementary switches, with each integrated with a pair of waveguide microheaters. The average on-chip insertion loss is $\sim 5.2\mathrm{dB}$ for both of the “all-cross” and the “all-bar” states, with a loss variation of 1 dB over all routing paths. The cross talk for all switching states is better than $-30\mathrm{dB}$. The switching time of the switch element is about 22 μs. The switching functionality is verified by transmission of a $40\mathrm{Gb}/\mathrm{s}$ quadrature phase-shift keying optical signal.