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We present a photonically driven on-chip millimeter wave (mmWave) source enabled by the heterogeneous integration of a high-speed InGaAs/InP photodiode and silicon nitride (Si₃N₄) microcavity solitons. The chip delivers mmWaves with −18dBm of electrical power at a frequency of 98 GHz with kHz-class linewidth and low phase noise and marks a significant advancement in on-chip photonic mmWave source performance. This breakthrough not only demonstrates capabilities of heterogeneous photonic integration but also offers a compact and scalable solution for future low-noise mmWave applications in communications and sensing technologies. 

We demonstrate InGaAs/InAlGaAs/InP waveguide photodiodes on Si₃N₄with up to 81 GHz 3-dB bandwidth, 0.76 A/W responsivity, and -1.8 dBm and -9 dBm output RF power at 50 GHz and 100 GHz, respectively. 

Abstract The generation of ultra-low-noise microwave and mmWave in miniaturized, chip-based platforms can transform communication, radar and sensing systems^1–3. Optical frequency division that leverages optical references and optical frequency combs has emerged as a powerful technique to generate microwaves with superior spectral purity than any other approaches^4–7. Here we demonstrate a miniaturized optical frequency division system that can potentially transfer the approach to a complementary metal-oxide-semiconductor-compatible integrated photonic platform. Phase stability is provided by a large mode volume, planar-waveguide-based optical reference coil cavity^8,9and is divided down from optical to mmWave frequency by using soliton microcombs generated in a waveguide-coupled microresonator^10–12. Besides achieving record-low phase noise for integrated photonic mmWave oscillators, these devices can be heterogeneously integrated with semiconductor lasers, amplifiers and photodiodes, holding the potential of large-volume, low-cost manufacturing for fundamental and mass-market applications¹³. 

We demonstrate InGaAs/InP balanced photodiodes onSi₃N₄waveguides with record-high 3-dB bandwidth of 30 GHz, 0.72 A/W responsivity, and high common mode rejection ratio (CMRR) of 26 dB at 30 GHz. 

We investigate the feasibility and performance of photon-number-resolved photodetection employing single-photon avalanche photodiodes (SPADs) with low dark counts. While the main idea, to splitnphotons intomdetection modes with a vanishing probability of more than one photon per mode, is not new, we investigate here a important variant of this situation where SPADs are side-coupled to the same waveguide rather than terminally coupled to a propagation tree. This prevents the nonideal SPAD quantum efficiency from contributing to photon loss. We propose a concrete SPAD segmented waveguide detector based on a vertical directional coupler design, and characterize its performance by evaluating the purities of Positive-Operator-Valued Measures (POVMs) in terms of number of SPADs, photon loss, dark counts, and electrical cross-talk.