Cavity electro-optics in thin-film lithium niobate for efficient microwave-to-optical transduction

Abstract

Linking superconducting quantum devices to optical fibers via microwave-optical quantum transducers may enable large-scale quantum networks. For this application, transducers based on the Pockels electro-optic (EO) effect are promising for their direct conversion mechanism, high bandwidth, and potential for low-noise operation. However, previously demonstrated EO transducers require large optical pump power to overcome weak EO coupling and reach high efficiency. Here, we create an EO transducer in thin-film lithium niobate, a platform that provides low optical loss and strong EO coupling. We demonstrate on-chip transduction efficiencies of up to and of optical pump power. The transduction efficiency can be improved by further reducing the microwave resonator’s piezoelectric coupling to acoustic modes, increasing the optical resonator quality factor to previously demonstrated levels, and changing the electrode geometry for enhanced EO coupling. We expect that with further development, EO transducers in thin-film lithium niobate can achieve near-unity efficiency with low optical pump power.

Bidirectional interconversion of microwave and light with thin-film lithium niobate

“…A maximum on-chip conversion efficiency of 1.02% (internal efficiency of 15.2%) is recorded with a peak pump power adjusted to 13.0 dBm in the waveguide. The corresponding cooperativity reach a value of 0.041, which is significant improved over previously obtained values [42,43]. We note that the cooperativity no longer increases linearly with peak pump power in high power regime.…”

“…To tackle this issue, thinfilm Lithium Niobate (TFLN) is a promising candidate because of its strong Pockels nonlinearity [41]. This can lead to significantly larger vacuum coupling rate (g eo ), which has been demonstrated recently [42,43]. Nevertheless, the achieved conversion efficiency is limited to ∼ 10 −5 , which falls far behind the expectation considering the much larger EO coefficient of LN.…”

Integrated silicon carbide modulator for CMOS photonics

“…As a result of our work, we measure the Pockels coefficient (1.5 pm/V) of 3C-SiC at an infrared wavelength for the first time. Moreover, the modulator is able to operate continuously with high optical intensities of up to 913 kW/mm 2 without signal degradation, facilitating low-noise microwave photonics 36 or parametric conversion of single photons 37 .…”

“…2 Vpp, showing that the modulator correctly modulates the light intensity according to the applied digital sequence. Figure 3c shows the modulator operates at low drive voltages and an optical input power of 6.8 mW across a range of modulation speeds, with the eye-diagram quality (QE) factors greater than 2.7, which lead to bit-error ratios (BERs) below the hard-decision forward error correction (HD-FEC) limit The ability for modulator to handle high optical powers is important for enhancing signal to noise ratio in the growing field of microwave photonic applications 4,36 , as well as for quantum transduction 37 and nonlinear photonics 27 . To quantify the operation at high and continuous optical intensities, we measure the EO responses of the modulator with varied optical input power.…”

“…The ability for modulator to handle high optical powers is important for enhancing signal to noise ratio in the growing field of microwave photonic applications 4,36 , as well as for quantum transduction 37 and nonlinear photonics 27 . To quantify the operation at high and continuous optical intensities, we measure the EO responses of the modulator with varied optical input power.…”