Wavelength Meter on thin Film Lithium Niobate Based on Superconducting Single Photon Detectors

Photonic integrated circuits (PICs) present significant benefits with respect to tabletop optical systems regarding footprint, stability, and power consumption. Among the materials used to fabricate PICs, thin film lithium niobate (TFLN) is one of the most attractive ones, as its $\chi^{(2)}$ nonlinearity and electro-optic properties allow to implement on-chip light generation and routing [1]. On-chip detection of light has also been demonstrated on TFLN, based on the waveguide integration of superconducting nanowire single photon detectors (SNSPDs) [1]. Combining efficient detectors with TFLN nanophotonic waveguides holds promises for the realization of quantum photonics experiments fully on-chip. On the other hand, the sensitivity of SNSPDs changes with the wavelength of the detected photons [2], setting a boundary to the longest detectable wavelength and limiting the use of the wide transparency window of TFLN. However, this wavelength dependency in the response of SNSPDs can be leveraged to achieve new on-chip functionalities. In this work, by performing a straightforward analysis of the light signal measured at different bias currents [2], we operate hairpin SNSPDs on TFLN as waveguide-integrated wavelength-meters in the telecom bandwidth.