An integrated photonic millimeter-wave receiver with sub-ambient noise

TL;DR

This work addresses the noise limitations of electronic mmWave receivers by introducing a room-temperature integrated cavity electro-optic receiver based on LiTaO3 photonics that transduces mmWave signals into optical sidebands. The approach leverages a triply resonant, room-temperature EO interaction with a mmWave cavity to achieve bidirectional transduction, reaching an on-chip efficiency of 2.5% and a single-photon coupling rate of 3.11 kHz at 59.33 GHz, while operating in the reversed-dissipation regime. Directly observing Johnson noise in the transduction process, the study confirms that the transduced thermal noise is governed by the cavity’s thermal occupation $n_{cav} = k_B T / (ħ Ω)$, validating the quantum-limited nature of the device at room temperature. Demonstrations show -100 dBm mmWave detection with high dynamic range (154 dB) and a sub-ambient input-referred noise floor (Te ≈ 250 K at 59.33 GHz), highlighting an EMI-resilient, scalable photonic front end that can outperform state-of-the-art LNAs and enable optical-domain processing for mmWave systems. The work points to future pathways for unity cooperativity, broader bandwidth, and integration with quantum and photonic architectures.

Abstract

Decades of progress in radiofrequency (RF) transistors and receiver frontends have profoundly impacted wireless communications, remote sensing, navigation, and instrumentation. Growing demands for data throughput in 6G networks, timing precision in positioning systems, and resolution in atmospheric sensing and automotive radar have pushed receiver frontends into the millimeter-wave (mmW) and sub-mmW/THz regimes. At these frequencies, however, the noise performance of field-effect transistors (FETs) degrades rapidly due to parasitic effects, limited carrier mobility, hot electrons, and shot noise. Parametric transducers that couple electromagnetic signals to optical fields offer quantum-limited sensitivity at room temperature. Electro-optic materials enable receivers that convert RF signals into optical phase shifts. While early demonstrations used resonant devices and recent efforts have focused on cryogenic microwave-to-optical quantum transduction, room-temperature electro-optic receivers have yet to achieve noise figures comparable to their electronic counterparts. Here we demonstrate a room-temperature integrated cavity electro-optic mmW receiver on a lithium tantalate (LiTaO3) photonic integrated circuit with 2.5% on-chip photon-number transduction efficiency, achieving 250 K noise temperature at 59.33 GHz--matching state-of-the-art LNAs. We report the first direct resolution of thermal noise in cavity electro-optic transduction, showing the system is fundamentally limited by thermal photon occupation (~100) in the mmW cavity. Our work establishes integrated photonics as a path to surpass electronic LNAs while offering exceptional resilience to strong electromagnetic inputs and immunity to EMI, establishing cavity electro-optics as a low-noise, chip-scale, EMI-resilient receiver frontend for mmW applications and scalable analog processing in the optical domain.

Figures (4)

• Figure 1: Cavity electro-optics based mmWave-photonics interface. (a) Typical schematic of an electronic receiver. LNA: Low-noise amplifier; MIX: mixer; L.O.: local oscillator; RX: receive. (b) Operating principle of a photonic receiver. EO: electro-optics; BPD: Balanced photodiode. (c) Electro-optics transducer by room temperature cavity electro-optics. The $\chi^{(2)}$ interaction enables bidirectional transduction between optical and mmWave modes, resonantly enhanced by cavity coupling. (d,e) Spectrum diagram for the electronics and photonics receivers. (f) Schematic of the hybrid integrated cavity electro-optic (EO) transducer, comprising a monolithically integrated $\lambda$ mmW microwave resonator operating in the second fundamental mode, and a thin-film LiTaO3 photonic racetrack microresonator. An auxiliary ring is employed to suppress the Stokes sideband in the transduction process. (g) Measured reflection coefficient $S_{11}$ of the mmWave resonator. (h) Measured optical transmission with and without sideband suppression. (i) The frequency scaling of single photon coupling rate $g_0\propto \Omega$ at $m=1$ (29.66 GHz) mode and $m=2$ (59.33GHz) mode.
• Figure 2: Characterization of millimeter-wave-to-optical bidirectional transduction. (a) Microscope image of the fabricated cavity electro-optic device. (b) Microwave-to-optics (up-conversion) setup: An RF signal and continuous wave optical pump are coupled into the device; the optical output is measured with an optical spectrum analyzer (OSA). (c) Optics-to-microwave (down-conversion) setup, the generated mmW spectrum measured by electronic spectrum analyzer (ESA). (d) Measured up-conversion spectrum of 59.33 GHz mmWave input and optical output. (e) Measured down-conversion spectrum of optical input and mmWave output. (f) The conversion efficiency spectrum for both down-conversion (optics to mmWave) and up-conversion (mmWave to optics) process with on-chip optical pump power of 5 mW (below Raman threshold) (g) On-chip conversion efficiency for mmWave to optics in continuous pumped regime. The saturation is due to the Raman lasing threshold.
• Figure 3: Probing millimeter-wave Johnson noise with cavity electro-optic transducer. (a) The thermally induced motion of electrons in the microwave cavity can be transduced into the optical domain by the electro-optic effect in the cavity EO system. (b) Experiment setup for weak optical noise characterization: quantum-limited heterodyne measurement. FBG: fiber-Bragg-grating; FPC: fiber-polarization controller; ESA: electronic spectrum analyzer. (c) Illustration of thermal noise spectrum at room temperature. In the reversed dissipation regime ($\Gamma > \kappa$), the measured noise spectrum is shaped by the optical response. (d, e) Input-referred noise for the $\lambda/2$ (29.66 GHz) and $\lambda$ (59.33 GHz) modes matches the predicted thermal occupation $k_B T / h \Omega$ at 290 K.
• Figure 4: Ultra-sensitive millimeter-wave signal detection. (a, b) Detection of a $-100\,\mathrm{dBm}$ mmWave signal at $29.66\,\mathrm{GHz}$ (a) and $59.33\,\mathrm{GHz}$ (b) using the cavity electro-optic approach at 2MHz resolution bandwidth (RBW), compared with a commercial electronic receiver (R&S FSW67 with FSW-B24 LNA option). The input-referred noise floor is reduced by $4.8\,\mathrm{dB}$ at $29.66\,\mathrm{GHz}$ and by $11.2\,\mathrm{dB}$ at $59.33\,\mathrm{GHz}$ using the photonic approach. (c) Linearity and input-referred 1dB compression point (IP1dB) for the photonic receiver scheme. (d) Input referred noise figure versus cooperativity, estimated from measured added noise (see Supplementary Information). (e) Theoretical noise figure of the cavity electro-optic front-end as a function of frequency for fixed on-chip pump powers of 1mW, 5 mW and 50 mW, compared with state-of-the-art electronics LNAs reported in literature.