All Publications

  • Single-mode squeezed-light generation and tomography with an integrated optical parametric oscillator. Science advances Park, T., Stokowski, H., Ansari, V., Gyger, S., Multani, K. K., Celik, O. T., Hwang, A. Y., Dean, D. J., Mayor, F., McKenna, T. P., Fejer, M. M., Safavi-Naeini, A. 2024; 10 (11): eadl1814


    Quantum optical technologies promise advances in sensing, computing, and communication. A key resource is squeezed light, where quantum noise is redistributed between optical quadratures. We introduce a monolithic, chip-scale platform that exploits the χ(2) nonlinearity of a thin-film lithium niobate (TFLN) resonator device to efficiently generate squeezed states of light. Our system integrates all essential components-except for the laser and two detectors-on a single chip with an area of one square centimeter, reducing the size, operational complexity, and power consumption associated with conventional setups. Using the balanced homodyne measurement subsystem that we implemented on the same chip, we measure a squeezing of 0.55 decibels and an anti-squeezing of 1.55 decibels. We use 20 milliwatts of input power to generate the parametric oscillator pump field by using second harmonic generation on the same chip. Our work represents a step toward compact and efficient quantum optical systems posed to leverage the rapid advances in integrated nonlinear and quantum photonics.

    View details for DOI 10.1126/sciadv.adl1814

    View details for PubMedID 38478618

  • Integrated frequency-modulated optical parametric oscillator. Nature Stokowski, H. S., Dean, D. J., Hwang, A. Y., Park, T., Celik, O. T., McKenna, T. P., Jankowski, M., Langrock, C., Ansari, V., Fejer, M. M., Safavi-Naeini, A. H. 2024; 627 (8002): 95-100


    Optical frequency combs have revolutionized precision measurement, time-keeping and molecular spectroscopy1-7. A substantial effort has developed around 'microcombs': integrating comb-generating technologies into compact photonic platforms5,7-9. Current approaches for generating these microcombs involve either the electro-optic10 or Kerr mechanisms11. Despite rapid progress, maintaining high efficiency and wide bandwidth remains challenging. Here we introduce a previously unknown class of microcomb-an integrated device that combines electro-optics and parametric amplification to yield a frequency-modulated optical parametric oscillator (FM-OPO). In contrast to the other solutions, it does not form pulses but maintains operational simplicity and highly efficient pump power use with an output resembling a frequency-modulated laser12. We outline the working principles of our device and demonstrate it by fabricating the complete optical system in thin-film lithium niobate. We measure pump-to-comb internal conversion efficiency exceeding 93% (34% out-coupled) over a nearly flat-top spectral distribution spanning about 200 modes (over 1THz). Compared with an electro-optic comb, the cavity dispersion rather than loss determines the FM-OPO bandwidth, enabling broadband combs with a smaller radio-frequency modulation power. The FM-OPO microcomb offers robust operational dynamics, high efficiency and broad bandwidth, promising compact precision tools for metrology, spectroscopy, telecommunications, sensing and computing.

    View details for DOI 10.1038/s41586-024-07071-2

    View details for PubMedID 38448697

  • Mid-infrared spectroscopy with a broadly tunable thin-film lithium niobate optical parametric oscillator OPTICA Hwang, A., Stokowski, H. S., Park, T., Jankowski, M., Mckenna, T. P., Langrock, C., Mishra, J., Ansari, V., Fejer, M. M., Safavi-Naeini, A. H. 2023; 10 (11): 1535-1542
  • Integrated quantum optical phase sensor in thin film lithium niobate. Nature communications Stokowski, H. S., McKenna, T. P., Park, T., Hwang, A. Y., Dean, D. J., Celik, O. T., Ansari, V., Fejer, M. M., Safavi-Naeini, A. H. 2023; 14 (1): 3355


    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.

    View details for DOI 10.1038/s41467-023-38246-6

    View details for PubMedID 37291141

    View details for PubMedCentralID 9352777

  • Experimental evaluation of digitally verifiable photonic computing for blockchain and cryptocurrency OPTICA Pai, S., Park, T., Ball, M., Penkovsky, B., Dubrovsky, M., Abebe, N., Milanizadeh, M., Morichetti, F., Melloni, A., Fan, S., Solgaard, O. 2023; 10 (5): 552-560
  • Experimentally realized in situ backpropagation for deep learning in photonic neural networks. Science (New York, N.Y.) Pai, S., Sun, Z., Hughes, T. W., Park, T., Bartlett, B., Williamson, I. A., Minkov, M., Milanizadeh, M., Abebe, N., Morichetti, F., Melloni, A., Fan, S., Solgaard, O., Miller, D. A. 2023; 380 (6643): 398-404


    Integrated photonic neural networks provide a promising platform for energy-efficient, high-throughput machine learning with extensive scientific and commercial applications. Photonic neural networks efficiently transform optically encoded inputs using Mach-Zehnder interferometer mesh networks interleaved with nonlinearities. We experimentally trained a three-layer, four-port silicon photonic neural network with programmable phase shifters and optical power monitoring to solve classification tasks using "in situ backpropagation," a photonic analog of the most popular method to train conventional neural networks. We measured backpropagated gradients for phase-shifter voltages by interfering forward- and backward-propagating light and simulated in situ backpropagation for 64-port photonic neural networks trained on MNIST image recognition given errors. All experiments performed comparably to digital simulations ([Formula: see text]94% test accuracy), and energy scaling analysis indicated a route to scalable machine learning.

    View details for DOI 10.1126/science.ade8450

    View details for PubMedID 37104594

  • Power monitoring in a feedforward photonic network using two output detectors NANOPHOTONICS Pai, S., Valdez, C., Park, T., Milanizadeh, M., Morichetti, F., Melloni, A., Fan, S., Solgaard, O., Miller, D. B. 2023
  • Bias-stable Sub-Volt Visible Electro-optic Modulator in Thin-Film Lithium Niobate Celik, O., Ammar, N., Stokowski, H. S., Park, T., Safavi-Naeini, A., IEEE IEEE. 2023
  • Tunable dual wavelength laser on thin film lithium niobate Lufungula, I., Mayor, F. M., Herrmann, J. F., Park, T., Stokowski, H. S., Hwang, A. Y., De Beeck, C., Atalar, O., Jiang, W., Kuyken, B., Safavi-Naeini, A. H., IEEE IEEE. 2023
  • High-efficiency second harmonic generation of blue light on thin-film lithium niobate. Optics letters Park, T., Stokowski, H. S., Ansari, V., McKenna, T. P., Hwang, A. Y., Fejer, M. M., Safavi-Naeini, A. H. 2022; 47 (11): 2706-2709


    The strength of interactions between photons in a chi(2) nonlinear optical waveguide increases at shorter wavelengths. These larger interactions enable coherent spectral translation and light generation at a lower power, over a broader bandwidth, and in a smaller device: all of which open the door to new technologies spanning fields from classical to quantum optics. Stronger interactions may also grant access to new regimes of quantum optics to be explored at the few-photon level. One promising platform that could enable these advances is thin-film lithium niobate (TFLN), due to its broad optical transparency window and possibility for quasi-phase matching and dispersion engineering. In this Letter, we demonstrate second harmonic generation of blue light on an integrated thin-film lithium niobate waveguide and observe a conversion efficiency of eta0=33, 000%/W-cm2, significantly exceeding previous demonstrations.

    View details for DOI 10.1364/OL.455046

    View details for PubMedID 35648910

  • Cascaded optical resonator-based programmable photonic integrated circuits OPTICS EXPRESS Park, T., Jeong, Y., Yu, K. 2021; 29 (3): 4645–60

    View details for DOI 10.1364/OE.415545

    View details for Web of Science ID 000614617700133