Dielectrically loaded thin-film lithium niobate (LiNbO₃) on insulator (LNOI) platforms have enabled a range of photonic integrated circuit components, such as high-speed optical modulators, switches, and nonlinear devices, while avoiding the direct etching of the LiNbO₃ thin film. Silicon nitride (Si₃N₄) is one of the most attractive dielectric loading materials as it has a similar refractive index and transparency window to LiNbO₃ and can be deposited and patterned by mature fabrication processes. The patterning of Si₃N₄ opens the opportunity to fabricate grating couplers in the same fabrication step, providing efficient optical interfaces for wafer-scale testing. In this paper, we investigate and demonstrate single-step etched grating couplers on a Si₃N₄-LNOI (X-cut) platform. The grating couplers (straight and curved) are designed and fabricated for TE-polarized modes along the Y and Z crystallographic directions, considering the LiNbO₃ crystal’s birefringence. The experimentally demonstrated coupling losses are as low as 4.02 and 4.24 dB along the crystallographic Y and Z directions, respectively. The corresponding peak wavelengths are 1609 and 1615 nm, respectively. The measured 3-dB bandwidths are wider than 70 nm for both crystallographic directions. We also numerically investigated the influence of fabrication variations and the fiber angle on the transmission. To the best of our knowledge, this work is the first demonstration of grating couplers with different light propagation directions on the Si₃N₄ loaded LNOI platform.

The mode-order converter is a building block in a multimode optical transmission and switching system. It can be used for switching signals carried on different mode channels. However, such devices constructed by conventional structures can commonly accomplish one mode-order conversion process. It is because the phase-matching condition, which is utilized by a majority of designs, can usually be fulfilled between only one mode pair for specific device geometry. In this Letter, we propose a dual-polarization mode-order converter referring to the concept of a silicon planar metasurface. It can realize mode-order conversions on transverse electrical and transverse magnetic polarizations in parallel. In order to verify our concept, we design and experimentally demonstrate a prototype that can realize conversions from ${\mathrm{TE}}_0$ to ${\mathrm{TE}}_1$ and from ${\mathrm{TM}}_0$ to ${\mathrm{TM}}_1$ simultaneously. The footprint is $4\mathrm{\mu m}\times 1.6\mathrm{\mu m}$. The measured insertion losses for both polarizations are smaller than 2.3 dB, and the crosstalk is lower than $-11.5\mathrm{dB}$ within the wavelength range of 1525–1565 nm. We envision that the device can be a building block in polarization and mode multiplexed optical switching systems and endow the systems with simpler structure and a more compact footprint.

Currently, the reversible logic circuit is a popular research topic in the field of information processing as it is a most effective approach to minimize power consumption, which can achieve the one‐to‐one mapping function to identify the input signals from its corresponding output signals. In this letter, we propose and experimentally demonstrate an optical Feynman gate for reversible logic operation using silicon micro‐ring resonators (MRRs). Two electrical input signals (logic operands) are applied across the micro‐heaters above MRRs to determine the switching states of MRRs, and the reversible logic operation results are directed to the output ports in the form of light, respectively. For proof of concept, the thermo‐optic modulation scheme is used to achieve MRR’s optical switching function. At last, a Feynman gate for reversible logic operation with the speed of 10 kbps is demonstrated successfully.

We experimentally demonstrate a compact temperature sensor using a microfiber-based Mach-Zehnder interferometer with a knot micro-ring resonator. The arm with a knot micro-ring resonator is embedded in polydimethylsiloxane (PDMS), which acts as the temperature transducer. The scattering matrix method is employed to establish the numerical model of the device. Owing to the high thermo-optic coefficient of PDMS, the response spectrum of the device will blue-shift when the ambient temperature increases. The device is characterized by changing temperature in two different environments (air and liquid), respectively. For temperature sensing operated in air, the device is tested utilizing a heating platform, which shows a sensitivity of -35.12 pm/°C when the temperature of the heating platform varies at a range of 15.5 °C. After that, a sensitivity boosting up to -41.58 pm/°C is measured when the device is immersed in a salt solution (25 ⁰ / ₀₀ in concentration) with the temperature changing from 22.2 °C to 32.9 °C.

Reconfigurable optical mode multiplexers/demultiplexers have attracted increasing attention in the academic community, because they enable convenient construction of flexible and complex on-chip optical networks. Here, we propose and demonstrate a scheme of reconfigurable and scalable optical mode multiplexer/demultiplexer with large operation bandwidth, based on three-waveguide-coupling structures. As proof of concept, a reconfigurable device that can multiplex input signals to the fundamental and first-order quasi-transverse electric mode is fully fabricated and demonstrated successfully. Static response spectra show that the optical crosstalk at the output ports of the device are less than −14.3 dB and −13.7 dB over the entire C band (> 40 nm), respectively. The dynamic performance with data transmission speeds of 40 Gbps for each multiplexing channel are also demonstrated successfully. The presented device is believed to be a potential candidate for future on-chip optical network with large-scale integration, flexible functionality, and low cost.