Noncritical phasematching behavior in thin-film lithium niobate frequency converters

Integrated quantum optical phase sensor in thin film lithium niobate

The quantum noise of light, attributed to the random arrival time of photons from a coherent light source, fundamentally limits optical phase sensors. An engineered source of squeezed states suppresses this noise and allows phase detection sensitivity beyond the quantum noise limit (QNL). We need ways to use quantum light within deployable quantum sensors. Here we present a photonic integrated circuit in thin-film lithium niobate that meets these requirements. We use the second-order nonlinearity to produce a squeezed state at the same frequency as the pump light and realize circuit control and sensing with electro-optics. Using 26.2 milliwatts of optical power, we measure (2.7 ± 0.2)% squeezing and apply it to increase the signal-to-noise ratio of phase measurement. We anticipate that photonic systems like this, which operate with low power and integrate all of the needed functionality on a single die, will open new opportunities for quantum optical sensing.

Broadband second-harmonic generation in an angle-cut lithium niobate-on-insulator waveguide by a temperature gradient

Frequency conversion via nonlinear wave mixing is an important technology to broaden the spectral range of lasers, propelling their applications in optical communication, spectroscopy, signal processing, and quantum information. Many applications require not only a high conversion efficiency but also a broad phase matching bandwidth. Here, we demonstrate broadband birefringence phase matching (BPM) second-harmonic generation (SHG) in angle-cut lithium niobate-on-insulator (LNOI) ridge waveguides based on a temperature gradient scheme. The bandwidth and shift of the phase matching spectrum can be effectively tuned by controlling the temperature gradient of the waveguide. Broadband SHG of a telecom C-band femtosecond laser is also demonstrated. The approach may open a new avenue for tunable broadband nonlinear frequency conversion in various integrated photonics platforms.

Lithium niobate photonics: Unlocking the electromagnetic spectrum

Lithium niobate (LN), first synthesized 70 years ago, has been widely used in diverse applications ranging from communications to quantum optics. These high-volume commercial applications have provided the economic means to establish a mature manufacturing and processing industry for high-quality LN crystals and wafers. Breakthrough science demonstrations to commercial products have been achieved owing to the ability of LN to generate and manipulate electromagnetic waves across a broad spectrum, from microwave to ultraviolet frequencies. Here, we provide a high-level Review of the history of LN as an optical material, its different photonic platforms, engineering concepts, spectral coverage, and essential applications before providing an outlook for the future of LN.