Zeping Zhao

InP/InGaAs‐based heterojunction phototransistors (HPTs) are promising for ultrasensitive short‐wave infrared (SWIR) detection due to their high internal gain, low excess noise, and low power consumption. This work demonstrates an HPT achieving a high optical gain of ∼1200 at −2 V bias, with dark current lower than state‐of‐the‐art avalanche photodiodes (APD). To further push its sensitivity to the limit for weak light/ultra‐long‐distance imaging, the noise mechanism in low frequency (LF) regime and its origins have been investigated, by which generation current in depletion region caused by the defect‐related traps is explored and studied. In particular, the LF noise power is found to be independent of the internal gain. A Hooge's constant of 2.1 × 10 ⁻⁵ is reported for the first time in gain‐based detectors, comparable to HgCdTe devices. Remarkably, temperature‐dependent multi‐level random telegraph signal (RTS) analysis reveals two dominant origins of the generation current, corresponding to relaxation processes of two typical types of mid‐gap traps. One is Zn‐related extrinsic defects caused by Zn diffusion into the InP emitter, while the other is Ga‐related intrinsic defects in InGaAs collector. As the guideline for optimizing the HPT detector design, this work paves the way to further improve the sensitivity for low‐flux SWIR photodetection.

A photonic frequency discrimination and phase identification system based on an on-chip dual Mach–Zehnder modulator (MZM) is proposed. By utilizing the power cancellation (PCD) condition, the system achieves high-precision frequency discrimination and phase identification of multi-frequency radio frequency (RF) signals. The system adopts an on-chip dual-MZM architecture, effectively reducing phase interference in signal transmission caused by environmental factors. This is achieved through precise bias control and the adjustment of the local oscillator (LO) signal’s optical path delay using a tunable optical delay line (TODL), ensuring that the dual MZM operates in the phase inversion condition. When the LO frequency matches that of an RF signal, a significant power attenuation is observed at the system output. The phase of the RF signal is extracted from the corresponding PCD. Experimental results demonstrate that the system achieves a bandwidth of 30 GHz, a frequency resolution of 700 kHz, and a frequency resolution error of less than 498 kHz, with a phase identification range from 0° to 65°. With high integration, the system demonstrates excellent accuracy in multi-frequency signal measurement and phase identification, offering a reliable solution for complex RF scenarios.

A 90° optical hybrid employing an MMI coupler was fabricated on a thin-film lithium niobate (TFLN) platform that can be used for integrated coherent transceivers. The fabricated 90° optical hybrid exhibited a CMRR greater than 20 dB, a phase error below ±7.5°, and an excess loss less than 1.8 dB (including contributions from the 90° hybrid, a 1 × 2 MMI coupler, and an optical delay line, after subtracting the losses from the coupler and delay line, the 90° optical hybrid introduced less than 0.9 dB of loss) over the C-band with a compact footprint of 13.8 × 250 μm², facilitating the future development of high-bandwidth optical coherent transceivers heterogeneously integrated on TFLN.

In this paper, a photonics-assisted multi-path interference (MI) cancellation system based on the combination of the digital domain and analog domain is proposed and demonstrated. The cancellation in the photonics-assisted analog domain avoids oversaturation of the analog-to-digital converter (ADC) signal at the input while the adaptive feedback control in the digital domain can also compensate for the optical path’s undesirable factors, thus making MI cancellation in the best state all the time. Initially, the differences in MI cancellation between small-signal and large-signal modulations are analyzed. Subsequently, the MI residual power of the multi-tap photonics-assisted cancellation system is derived theoretically by modifying the Wiener solution. Finally, the adaptive feedback control algorithm based on the received signal strength indicator (RSSI) is evaluated by simulation, and the simulated multi-path interference cancellation depth (MICD) reaches 48.4 dB when the convergence condition is satisfied. In addition, the compensation effect of the digital domain on the modulator bias point drift is analyzed.

In this paper, a four-channel optical emission module is developed using hybrid integration technology that integrates directly modulated laser (DML) chips, low-noise amplifier (LNA) chips, and control circuits, with dimensions of 24.4 mm × 21 mm × 5.9 mm. This module enables high-gain signal output and minimizes crosstalk between neighboring channels while improving integration. An equivalent circuit model of radio frequency (RF) signal transmission is established, and the accuracy of the model and the effectiveness of the approach to improve signal gain are verified using simulations and experiments. With optimized thermal management, the module has the ability to operate at stable temperatures across an ambient range of −55 °C to 75 °C. The module has a channel wavelength spacing of approximately 1 nm, and the −3 dB bandwidth of each channel exceeds 20 GHz. The crosstalk between neighboring channels is less than −65 dB. In the range of 0.8~25 GHz, the four-channel gain is approximately 15 dB through the integration of the LNA chip. The module achieves a noise figure (NF) of less than 30 dB.

In this paper, we propose a tunable optical filter with a high Q factor based on photonic crystal technology, achieving a Q factor of 442.85 using thin film lithium niobate technology. By proportionally adjusting the dimensions of the unit structure, this filter enables coarse tuning across the 1520–1570 nm range (C band). Furthermore, by utilizing the thermo-optic effect of lithium niobate, we can achieve fine-tuning of the optical filter within a temperature range of 300 K to 600 K, allowing for a center wavelength tuning capability of up to 3.7 nm. This design not only enhances the filter’s performance but also broadens its potential applications in optical communication and optical signal processing.

This article reports a photonic-assisted instantaneous frequency measurement system based on a multi-group asymmetrical Mach-Zehnder interferometer structure, applicable in contemporary electronic countermeasure. Additionally, we introduce a novel method to obtain measurement results based on probability theory. Employing this method allows for a broader measurement range compared to traditional approaches utilizing amplify compare function without a deterioration in accuracy. Sufficient and systematic experimental results show that the measurement range can be at least 30 GHz and the mean error is 0.102 GHz using our proposed system and method. Moreover, we propose an optimization algorithm based on our method. By using this algorithm, we can adjust measurement range for proposed system with minimal asymmetrical MZI structures, ensuring no compromise in accuracy. In addition, the system is easy to realize hybrid integration or even monolithic integration due to the use of microwave photonics technology.

A novel microwave photonic true-time-delay (TTD) system using carrier compensation technology is proposed and experimentally demonstrated. Wavelength division multiplexing combines ten lasers into a single beam. We separate one channel from the laser as a compensating carrier, and the compensation carrier is combined with the time-delayed optical signals to be detected. Meanwhile, sideband signals are amplified effectively thanks to carrier-suppressed double-sideband (CS-DSB) modulation. Therefore, the power of both the central optical carriers and sidebands is guaranteed, which produces a better beat frequency result than the TTD system without carrier compensation. The simulation results confirm that the signal amplitude has an order of magnitude improvement due to the compensation. With employing the delay fibers based on multiple-fiber Bragg gratings (MFBGs), the experimental delay and response time reach 90.160 μs and 160.80 ns. The proposed technique can find applications in time-delay beamforming of phased array antennas (PAAs).