Study on the single-mode condition for x-cut LNOI rib waveguides based on leakage losses.

Lithium niobate-on-insulator (LNOI) has recently emerged as a promising material platform for high-density and advanced photonics integrated circuits (PICs). And single-mode waveguides (SMW) are the most basic building blocks for structuring various PICs. In this paper, single-mode conditions (SMCs) for shallowly etched LNOI rib waveguides in x-cut LNOI wafer are investigated with the finite element method (FEM) in consideration of the lateral leakage and the magic width for the first time, to our best knowledge. Our results indicate that due to the lateral leakage and the magic width these shallowly etched x-cut LNOI rib waveguides have unique and complex SMCs. Our method and results provide a guidance in designing low-loss LNOI SMW and high-performance PICs.

Low-power total internal reflection thermo-optic switch based on hybrid SiON-polymer X-junction waveguides.

We propose and demonstrate a low-power 2×2 total internal reflection thermo-optic switch based on an X-junction configuration formed with a silicon oxynitride (SiON) core and polymer cladding. Unlike X-junctions reported thus far, our proposed configuration features a slot formed on the center of the X-junction and filled with polymer cladding. With such a configuration, the opposite thermo-optic characteristics of SiON and polymer and, hence, heat utilization efficiency can be fully utilized. Our fabricated proof-of-principle switch shows extinction ratios of larger than 15.34 dB and switching powers of less than ∼59.6 mW. The rise time and fall time of switching are 1.42 and 0.85 ms, respectively. The insertion losses are less than 10.6 dB for all channels, and the polarization-dependent loss is ∼0.3 dB.

Compact and electro-optic tunable interleaver in lithium niobate thin film.

We propose and experimentally demonstrate a compact and electro-optic (EO) tunable interleaver in X-cut lithium niobate thin film using an asymmetrical Mach-Zehnder interferometer configuration. Our typical fabricated device has an EO interactive length of ∼1.35 mm and a total length of ∼4.0 mm. Over a wide wavelength range from 1528 to 1605 nm, the device exhibits polarization-insensitive center wavelengths and channel spacing of ∼49.7 GHz, but a slightly different extinction ratio of 10-20 and 12-23 dB, and electrical wavelength tuning sensitivity of ∼18 and ∼16 pm/V for the transverse electric- and transverse magnetic-polarized input light, respectively. The proposed interleaver also has the potential to be used as a tunable filter or a wavelength-selective switch.

Scalable and reconfigurable true time delay line based on an ultra-low-loss silica waveguide.

A scalable and reconfigurable on-chip optical true time delay line consisting of Mach-Zehnder interferometer (MZI) switches and delay waveguides is proposed and demonstrated with the ultra-low-loss silica waveguide platform. The MZI switches provide the reconfiguration of the light traveling paths and hence different delays. Our proposed structure can be easily scaled to an M bit delay line with a slight increase in dimensions. The footprint of our fabricated 1 bit delay line is 33 mm×13 mm (length×width) and can provide a delay of 6.0 ps with an insertion loss of 1.2 dB at the operating wavelength of 1550 nm, while the footprint of the 4 bit delay line is 43 mm×14 mm and can provide a discrete delay tuning from 6.0 to 90.2 ps with a delay deviation lower than 0.2 ps and a tuning response time of 0.84 ms. The insertion losses are lower than ∼2.34 dB, and the extinction ratios are greater than 20.42 dB. The average switching power is ∼132.6 mW. Our proposed optical true time delay lines could find applications for optical beamforming in phased array antennas.

Reconfigurable broadband mode (de)multiplexer based on an integrated thermally induced long-period grating and asymmetric Y-junction.

We propose a reconfigurable broadband mode (de)multiplexer based on a thermally induced long-period grating integrated with an asymmetric Y-junction. Either of the two spatial modes of a two-mode waveguide launched into the grating end of the device can be switched into either of the two output ports of the Y-junction by controlling the electric power applied to the electrode heater that induces the grating. Our typical device fabricated with polymer material that has a length of ∼14 mm shows a mode selectivity higher than 12 dB over the C+L band at a switching power of 198 mW. The device could find applications in reconfigurable mode-division-multiplexing systems.