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Active mode mismatch sensing and control can facilitate optimal coupling in optical cavity experiments such as interferometric gravitational wave detectors. In this paper, we demonstrate a radio-frequency (RF) beam wavefront curvature modulation-based mode mismatch sensing scheme inspired by the previously proposed RF beam jitter alignment sensing scheme. The proposed mode mismatch sensing scheme uses an electro-optic lens (EOL) device that is designed to provide the required beam wavefront curvature actuation, as well as a mode converting telescope that rephases the RF second-order modes and generates a non-vanishing mode mismatch sensing signal. We carefully investigate the total second-order mode generation from the wavefront actuation both analytically and numerically, taking the effects of Gaussian beam size evolution and the second-order mode phase mismatch cancellation into consideration. We demonstrate the second-order mode generation as a function of the incident beam waist size and the electro-optic crystal size which, along with a “trade-off” consideration of the beam size at the edges of the crystal and the clipping loss, provides us with guidance for designing the beam profile that interacts with the crystal to improve the EOL modulation efficiency.
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In-plane beam focusing via integrated photonic gradient-index subwavelength grating metalens
We present an in-plane beam converter scheme that can focus a large Gaussian slab mode into a tightly focused spot approximately hundreds of micrometers away from the chip facet. Our approach involves designing the modal expander that converts a photonic waveguide mode to a large Gaussian slab mode and engineering the two-dimensional (2D) gradient-index subwavelength grating arrays that modify modal wavefront to be focused as the beam propagates. The device is designed on a monolithic silicon nitride scheme, which is transparent at the visible wavelength regime and readily available for the complementary metal-oxide-semiconductor process. Our device can be utilized in various chip-scale photonic applications, especially involving biochemical species and target samples ranging from one to tens of micrometer scales.
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- Award ID(s):
- 2144568
- PAR ID:
- 10558923
- Publisher / Repository:
- Optical Society of America
- Date Published:
- Journal Name:
- Optics Express
- Volume:
- 32
- Issue:
- 26
- ISSN:
- 1094-4087; OPEXFF
- Format(s):
- Medium: X Size: Article No. 46225
- Size(s):
- Article No. 46225
- Sponsoring Org:
- National Science Foundation
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