The demand for high capacity and large instantaneous bandwidth has driven radio frequency (RF) systems to operate at higher frequencies and in a greater number of bands, thereby placing more stringent requirements on microwave frequency conversion technology. However, the traditional electronic frequency conversion methods cannot meet the current demand due to its limited frequency and bandwidth, poor tunability, complex system, and susceptibility to electromagnetic interference, making it difficult to realize high-precision frequency conversion with ultra-broadband and large spans. Microwave photonic technology, which effectively utilizes the advantages of broadband, high-speed, low power consumption, and resistance to electromagnetic interference in the optical domain, can successfully address the challenges inherent in traditional electronic solutions. However, this technology exhibits certain deficiencies in precision tuning, while traditional electronic methods achieve high precision at the expense of being unable to realize ultra-broadband and large-span frequency conversion. The scheme proposed in this study aims to realize the high-precision frequency conversion of broadband microwave signals over a large span with a small volume and simple structure, breaking through the “electronic bottleneck” and solving electromagnetic interference and other problems in the traditional scheme.

In this study, a parallel multichannel joint optimization scheme with photonic-electronic collaboration is proposed. This approach maximizes the inherent advantages of the optical domain, such as broad bandwidth, extensive dynamic range, and resistance to electromagnetic interference, as well as the precise and flexible characteristics of the electronic domain, thereby achieving a large-span, high-precision frequency conversion of broadband signals. The system is mainly composed of three parts: 1) optical frequency comb generation, 2) channelization filtering and channel selection, and 3) frequency shifting and signal loading. First, two Mach?Zehnder modulators (MZMs) were utilized to generate optical frequency combs (OFCs) with free spectral ranges (FSRs) of 25 and 30 GHz, respectively, which served as local oscillators (LOs) for frequency conversion. Subsequently, channelization filtering and channel selection were performed using a 1×13 demultiplexer and 13×1 high-speed optical switch to manage the switching of the frequency channels and thereby obtain the signal carrier and LO. Finally, dual parallel MZMs (DP-MZMs) were employed to modulate the signal onto the carrier and control the frequency shift of the local oscillator. The modulation format was carrier-suppressed single-sideband modulation. Frequency conversion was then realized using a photodetector (PD) after the signal and LO were combined. Through theoretical analysis and simulation experiments, we verified that the proposed scheme is capable of large-span high-precision broadband frequency conversion.

To verify the feasibility of the proposed scheme, we established an experimental simulation platform for the frequency conversion system (Figs. 1 and 3), with detailed parameter settings listed in Table 1. First, we analyzed the frequency conversion range. By setting input signal frequencies to 3 GHz and 5 GHz, the simulation results (Fig. 6) demonstrated converted signals spanning 8 to 68 GHz and 10 to 70 GHz, both with 5 GHz intervals. The carrier-to-noise ratios (CNRs) of the two signals exceeded 50.6 dB and 49.7 dB, respectively, while power fluctuations were 2.14 dB and 2.00 dB. Next, we tested 512 MSym/s QPSK input signals at 3 GHz and 5 GHz. As shown in Fig. 6, the system output exhibited signal-to-noise ratios (SNRs) exceeding 31.2 dB and 30.6 dB, respectively, with power fluctuations of 3.19 dB and 4.59 dB. To further evaluate signal quality across modulation formats, input signals were configured as follows: 5 GHz 512 MSym/s QPSK, 300 MSym/s 8PSK, and 200 MSym/s 16QAM. After conversion to 70 GHz, the error vector magnitudes (EVMs) for these formats (Fig. 7) were 6.97%, 7.51%, and 9.62%, respectively, all meeting communication quality standards. Finally, we assessed precise frequency shifting capability using a 5 GHz 512 MSym/s QPSK signal with frequency shifts ranging from 100 MHz to 500 MHz. The results (Fig. 8) showed slight signal quality degradation post-shift. These findings confirm that the proposed scheme achieves large-span, high-precision frequency conversion while maintaining signal integrity.

To address the limitations of traditional electronic frequency conversion technologies, including restricted frequency bandwidth, large size, high energy consumption, poor tunability, and susceptibility to electromagnetic interference, this study proposed a photonic-electronic collaborative multichannel parallel microwave photonic frequency conversion scheme. This scheme enables the large-span, high-precision frequency conversion of broadband signals while ensuring conversion quality.

The feasibility of the proposed scheme was first demonstrated through a theoretical derivation, followed by a simulation validation of the functionality of the system. The frequency conversion of broadband signals was then verified under a conversion range of 10 to 70 GHz, covering the C, Ku, and K bands up to the EHF band. The quality of the frequency-converted signals at different rates and modulation formats was then analyzed, confirming that the converted signals meet communication quality standards. Finally, the frequency-shifting performance was validated, enabling the precise tuning of the converted signals while maintaining signal quality. The system also allows for flexible frequency selection strategies tailored to various scenarios. This endows the system with significant adaptability and potential applications in future fields such as wireless communications, radar systems, phased array antennas, and electronic warfare.