Chongfan Technology

News

All Categories >

Home page

2025

Nature Communications | Programmable and multifunctional integrated microwave photonic chip based on thin-film lithium niobate

Author:

Introduction

The demand for bandwidth, functionality, and reconfigurability in radio frequency (RF) signal processing for next-generation wireless communication and radar systems continues to grow. Traditional RF systems based on electronic devices and chips face significant challenges and struggle to meet future requirements. Microwave photonics technology, with its ultra-wide bandwidth and flexible tunability, shows great potential in high-frequency signal processing.

However, realizing truly applicable integrated microwave photonic systems requires simultaneous high-performance electro-optic modulation and programmable signal processing networks on photonic chips, while also possessing excellent RF performance, including high link gain, high dynamic range, and low noise figure. Although progress has been made on silicon-based and silicon nitride platforms, it remains difficult to strike a balance between integration and RF performance.

Thin-film lithium niobate (TFLN), with its superior electro-optic properties, is changing the landscape of integrated photonics, enabling seamless integration of key components such as electro-optic modulators and signal processors onto a single chip, significantly improving system compactness, efficiency, and performance. Based on this advantage,Researchers from the University of Twente and City University of Hong Kong have collaborated to design a highly integrated TFLN microwave photonic chip, providing a new approach to overcome the current bottlenecks in integrated microwave photonic systems.

The results were published inProgrammable multifunctional integrated microwave photonic circuit on thin-film lithium niobateinNature CommunicationsUniversity of Twente PhDWei Chuangand City University of Hong KongDr. Feng Hankeare the co-first authors of the paper, University of TwenteProfessor David MarpaungandProfessor Wang Cheng of City University of Hong Kongare the corresponding authors of the article.

Experimental principles and results

The structure of the TFLN chip designed by the team is shown in Figure 1The chip consists of a TFLN intensity modulator and four cascaded programmable micro-rings. The intensity modulator converts the RF signal into an optical signal, while the generated sidebands are processed by the Mach-Zehnder interferometer-assisted micro-ring, whose coupling coefficient and resonance wavelength can be adjusted by the thermal phase shifter. This design forms the basis of the chip's multifunctional capabilities.

Figure 1: Schematic diagram of the integrated TFLN microwave photonic chip

Source:Nature Communications

Figure 2shows microscope images of the chip and the experimental setup. The chip uses an edge-coupling structure, and light is input and output through a lens fiber. The RF signal is loaded onto the modulator electrode through a GSG structure RF probe, while a 26-channel DC probe array is used to control the operating state of the cascaded micro-rings.

Figure 2: Microscope image of the chip and the corresponding experimental setup

Source: Research team

The schematic diagram of the microwave photonic link is shown in Figure 3aBy controlling two micro-ring resonators with different coupling states, the researchers shape the phase and amplitude of the modulation sidebands to realize a microwave photonic band-stop filter with an ultra-high suppression ratio. The key to this filter is to make the resonance positions of the two micro-rings symmetrical with respect to the optical carrier, one in an over-coupled state and the other in an under-coupled state, and with the same suppression depth. After optical detection, the signal frequencies of these resonance centers undergo destructive interference, resulting in an ultra-high filtering suppression ratio.

Figure 3bshows the spectrum at different nodes in the link. After the optical carrier passes through the intensity modulator, two in-phase modulation sidebands (node II) are generated. The spectrum after processing by the two micro-rings is shown as node III, where the resonance positions of the two micro-rings are symmetrical with respect to the optical carrier, and the suppression ratios are the same. The difference is that one micro-ring is in an under-coupled state with 0 phase shift, and the other micro-ring is in an over-coupled state with π phase shift. This configuration satisfies the condition of destructive interference, thus achieving an ultra-high suppression ratio. At the same time, the modulation sideband part that has not been processed by the micro-ring can still be coherently superimposed, ensuring high link gain of the system.

Figure 3cshows the response of the tunable band-stop filter when the modulator is operating at the quadrature bias point. The maximum link gain of the filter is -7 dB, the suppression ratio is up to 80 dB, and the tuning range is 1.5 GHz to 21.5 GHz. In addition, when the modulator is operating at zero point and another two micro-rings are turned on, the output spectrum is shown as node V. Based on the same working principle, a tunable dual-band band-stop filter can be realized, with a maximum link gain of up to 0 dB and a suppression ratio of up to 60 dB (Figure 3d).

Figure 3: Tunable microwave photonic band-stop filter

Source:Nature Communications

When two RF signals with different frequencies are input to the microwave photonic system, intermodulation distortion will occur, which limits the dynamic range of the system. The research team used the response of the micro-ring to control the optical carrier, thereby successfully suppressing the third-order intermodulation distortion (IMD3) ( Figure 4c) and improving the spurious-free dynamic range (SFDR) ( Figure 4d， Figure 4e). Figure 4ashows the relative position between the optical carrier and the micro-ring resonance peak when realizing the ultra-high dynamic range band-stop filter ( Figure 4b).

Figure 4: Ultra-high dynamic range band-stop filter

Source:Nature Communications

In practical applications, radio frequency (RF) front-ends can be susceptible to interference from high-power signals. When the target signal and interference signal are extremely close in frequency, ultra-high-resolution filters are needed to eliminate the interference. However, realizing ultra-high-resolution microwave photonic filters is a significant challenge. This team proposed a method for suppressing high-power interference signals based on a TFLN chip; the experimental link diagram is shown below. 5aas shown.

Figure 5bshows the RF and optical spectra at different nodes in the link. When a high-power RF signal is input, high-order modulation sidebands are generated (Node II). The researchers used the response of the microring to process the high-order sidebands (Node III), which can suppress the high-power interference signal under specific conditions. Low-power target signals are not affected because they do not generate high-order modulation sidebands.Figure 5cshows the RF output without suppression, whileFigure 5dshows the RF output after suppression. It can be seen that only the high-power signal is suppressed, with a suppression ratio of 56 dB.

Figure 5: Suppression of high-power interference signals

Source:Nature Communications

Based on existing achievements, the research team will further improve system integration in the next stage, while continuously optimizing the waveguide coupling structure to further reduce coupling loss, and research waveguide optical amplifiers based on erbium or other gain media to achieve key performance indicators such as higher link gain and better noise figure. In addition, the team will actively expand application scenarios, such as coherent communication, nonlinear optics, and quantum information processing, to promote the application of high-performance photonic and microwave signal processing technology in a wider range of fields.

Paper Information

Wei, C., Feng, H., Ye, K. et al. Programmable multifunctional integrated microwave photonic circuits on thin-film lithium niobate. National Gazette16, 2281 (2025).

https://doi.org/10.1038/s41467-025-57441-1