No abstract

Spectral resonances in the mid-infrared region with polarization independence and angle tolerance are useful for filtering applications in infrared spectroscopy and imaging systems, when used with unpolarized light and across a wide field-of-view. Guided mode resonances are particularly attractive for this purpose due to the simple fabrication procedure to realize grating structures and the robust filter characteristics achievable through design. In this paper, the electromagnetic design, fabrication, and experimental characterization of polarization-independent, angle-tolerant mid-infrared spectral resonance using amorphous-germanium two-dimensional fully-etched high index contrast gratings on a calcium fluoride substrate is presented. The resonance, centered at 7.42 µm wavelength, exhibits polarization-independent, notch-type characteristics with minimal change across a 0 to 30° incidence angle. The angle tolerance of such dielectric high contrast grating filters is found to be intermediate between the highly angle sensitive dielectric partially etched grating structures and least angle sensitive metallic nano-aperture structures.

High bandwidth, low voltage electro-optic modulators with high optical power handling capability are important for improving the performance of analog optical communications and RF photonic links. Here we designed and fabricated a thin-film lithium niobate (LN) Mach-Zehnder modulator (MZM) which can handle high optical power of 110 mW, while having 3-dB bandwidth greater than 110 GHz at 1550 nm. The design does not require etching of thin-film LN, and uses hybrid optical modes formed by bonding LN to planarized silicon photonic waveguide circuits. A high optical power handling capability in the MZM was achieved by carefully tapering the underlying Si waveguide to reduce the impact of optically-generated carriers, while retaining a high modulation efficiency. The MZM has a $$V_\pi L$$ V π L product of 3.1 V.cm and an on-chip optical insertion loss of 1.8 dB.

Broadband integrated thin-film lithium niobate (TFLN) electro-optic modulators (EOM) are desirable for optical communications and signal processing in both the O-band (1310 nm) and C-band (1550 nm). To address these needs, we design and demonstrate Mach-Zehnder (MZ) EOM devices in a hybrid platform based on TFLN bonded to foundry-fabricated silicon photonic waveguides. Using a single silicon lithography step and a single bonding step, we realize MZ EOM devices which cover both wavelength ranges on the same chip. The EOM devices achieve 100 GHz EO bandwidth (referenced to 1 GHz) and about 2-3 V.cm figure-of-merit ( V π L ) with low on-chip optical loss in both the O-band and C-band.

We report advancements in the fabrication of electro-optic Mach-Zehnder modulators made by bonding an unetched thin film of lithium niobate to a second chip with rib waveguides in another material, such as silicon. Devices were fabricated after storing bonded silicon-lithium niobate chips in a common laboratory environment for more than three years. The chips survived the full processing flow and yielded modulators with greater than 50 GHz 3-dB electro-optic bandwidth, and VπL less than 3 V-cm at 1550 nm and equivalent performance to freshly-bonded and processed chips. Furthermore, we demonstrate the co-integration of hybrid bonded thin-film lithium niobate modulators and silicon photonics based high quality-factor ring resonators and higher-order coupled microring optical filters. The silicon microring resonators are used for photon-pair generation at 1550 nm using spontaneous four-wave mixing. These results show the feasibility of a modular modulator fabrication procedure, where the planarization and bonding steps are performed for a batch of chips at one time and smaller sub-batches are customized by end users at a much later time according to their needs and convenience.