We propose and demonstrate a highly efficient photonic-assisted microwave signal harmonic frequency down-conversion using four-wave mixing (FWM) in a silicon waveguide with a reverse-biased P-i-N junction. In the proposed method, two Mach-Zehnder modulators (MZMs) are driven by a radio frequency (RF) signal and a low-frequency local oscillation (LO) signal, separately. Then, the modulated LO signal is injected into the silicon waveguide. Besides, the FWM phenomenon occurred in the integrated waveguide due to the doped regions of the junction can increase the efficiency of free carrier removal from the waveguide region. As the applied bias voltage on the silicon waveguide is increased, the generated harmonic sidebands are further enlarged. Correspondingly, the conversion efficiency is up to 12.8 dB with the bias voltage of 30 V. The silicon waveguide is fully packaged with a grating coupling fiber array and a wire-bonded printed circuit board (PCB) to make the module stable and compact. By simply adjusting the low-frequency electrical LO, the down converter based on FWM can realize accurate tunable and ultra-wide frequency operation. Due to the strengths of silicon integrated waveguide doped with reverse-biased P-i-N junction, the high-order LO modulated optical sidebands can be generated and used to down-conversion high-frequency RF microwave signal. This scheme can significantly reduce the high-frequency demand for LO source. In the experiment, the RF signals ranging from 8 GHz to 31 GHz are all down converted within 2 GHz by utilizing the 5.8 – 8.2 GHz LO signals, and signal-to-noise ratios (SNRs) larger than 50 dB are achieved. Moreover, the phase noise of the intermediate frequency (IF) signal is as low as -80.12 dBc/Hz at an offset frequency of 10 kHz and spurious free dynamic range (SFDR) is 105.5 dB · Hz ^2/3 with 3 ^rd -order FWM effect for the LO signal and 103.8 dB · Hz ^2/3 with 4 ^th -order FWM effect for the LO signal. This shows that the down conversion signal is reliable to further use in modern electrical systems such as microwave photonic radar.

We propose and demonstrate a Frequency Modulated Continuous Wave (FMCW) laser source realized through sideband modulation and four-wave mixing (FWM). A silicon waveguide, featuring a reverse-biased P-i-N junction, is designed to excite FWM process. With the increase of the applied bias voltage, the efficiency of the FWM effect in the silicon waveguide is improved due to more effective removal of free-carriers. The silicon integrated waveguide enables a high conversion efficiency of -12 dB. In the experiment, the radio frequency (RF) signal swept over a range of 9 GHz to 11 GHz. A laser was modulated by a Mach-Zehnder modulator to generate a first-order sideband. Meanwhile, the FWM process in silicon waveguide expand threefold frequency sweeping span to 6 GHz, thereby enhancing spatial resolution to 2.5 cm. The original tuning range of 2 GHz and tuning rate of 0.2 GHz/s is multiplied by 3 times to 6 GHz and 0.6 GHz/μs respectively. The results show that FMCW laser source has a wider frequency bandwidth of 6 GHz, a high linearity of 11.5×10 ^-5 , and a fast chirp rate of 0.6 GHz/μs. The frequency-modulated light source exhibits excellent linearity, low noise, narrow linewidth, and fast tuning rates, which are critical attributes for modern electrical systems such as FMCW light detection and ranging (LiDAR) system. Additionally, the system obviates the need for intricate linearization algorithms, offering the advantages of simplicity in structure, high precision and easy to integrate.

Optical frequency combs have been widely used in spectrum analysis, coherent optical communication, and accurate distance measurement. We propose a straightforward method to improve the flatness of optical frequency combs. First, we derived the output of the optical signal for the configuration of a cascaded MZM and two PMs. Second, we identified the parameter value when the flatness was optimal after traversing different parameter spaces. The optimal flatness conditions could be automatically determined from an existing sample dataset by using neural networks and Bayesian optimization, which significantly reduced the calculation cost. Furthermore, a broad spectrum and low power consumption were also achieved. Finally, the generated optical frequency comb signal was divided into eight carriers with 50 GHz intervals, and the optical transmission system was verified by applying a 16-QAM modulation of 40 GBaud/s to each channel. The constellation diagram proved the feasibility of this optical comb generation scheme.

In this letter, we packaged a DFB laser diode chip and a thin film LiNbO3 modulator chip in a single shell through hybrid integration, and formed an integrated laser emission module. This module exhibits an output power of 15.6mW, an optical insertion loss of 5.60dB, a linewidth of 15.2kHz, a 3dB bandwidth of 36.7GHz. And at 10GHz, it exhibits an 1dB compression point of 13.0dBm, a gain of −39.8dB, an input third-order intercept point of 26.9dBm, and a spurious-free dynamic range of 89.9dB $\cdot $ Hz ${}^{\mathrm {3/2}}$ .

In this paper, we present a directly modulated laser (DML) using a partially corrugated grating (PCG) and integrated with a semiconductor optical amplifier (SOA). The influence of the quasi-high-pass filter properties of the SOA on the bandwidth was explored, resulting in high optical power output at lower current levels, with a bandwidth surpassing 25 GHz and an output power above 25 mW. The PCG design boosts the lasing mode’s resistance to random phase fluctuations at the rear facet, hence boosting the mode stability of the laser with a side-mode suppression ratio (SMSR) of over 44 dB. Furthermore, we performed back-to-back (BTB) 26.5625 Gbps NRZ data transmission experiments at room temperature (25 °C) with a modulation current of 60 mA. The results reveal that the transmitter and dispersion eye closure (TDEC) of the fabricated DML is lower than that of a conventional laser when the SOA area current reaches a specific threshold, demonstrating the enhanced signal transmission capabilities of our design. This laser structure offers a fresh strategy for the development of high-power, high-speed DMLs.

We propose and demonstrate a photonic-assisted approach for generating arbitrary microwave waveforms based on a dual-polarization dual-parallel Mach–Zehnder modulator, offering significant advantages in terms of tunability of repetition rates and anti-dispersion capability. In order to generate diverse microwave waveforms, two sinusoidal radio frequency signals with distinct frequency relationships are applied to the dual-polarization dual-parallel Mach–Zehnder modulator. By adjusting the power of the applied sinusoidal radio frequency signal, the power ratio between these orthogonal polarized optical sidebands can be changed, and thereby desired radio frequency waveforms can be obtained after photoelectric conversion. In our proof-of-concept experiment, we systematically varied the repetition rate of triangular, rectangular and sawtooth waveforms. Meanwhile, we calculated the Root Mean Square Error (RMSE) to assess the approximation error in each waveform. The RMSEs are 0.1089, 0.2182 and 0.1185 for the triangular, rectangular and sawtooth microwave waveforms with repetition rate of 8 GHz, respectively. Furthermore, after passing through 25 km single mode fiber, the optical power decreased by approximately 5.6 dB, which verifies the anti-dispersion transmission capability of our signal generator.