Wavelength-Tunable Infrared Source Based on Micro-Electromechanical System

Objective In recent years, hardware-in-the-loop (HITP) simulation technology has become one of the key techniques in the development of precision-guided weapon systems. To enhance the ability of precision-guided weapons to identify targets in complex environments, simulating the spectral characteristics of the targets has become a key focus of HITP simulation technology. Multispectral infrared scene generation technology enables the simultaneous simulation of spectral radiation characteristics of the target across multiple infrared bands. One of the primary challenges in the development of multispectral infrared scene generation technology is to achieve rapid and precise control over the operating wavelength and radiative intensity of infrared signals. Micro-electromechanical system (MEMS) devices, composed of subwavelength structural units, are artificially engineered composite devices with unique and tunable optical properties. Their actively tunable spectral radiation characteristics offer an available approach for multispectral infrared scene generation. In this study, we proposed a wavelength-tunable infrared source based on MEMS technology. Under intensity-modulated laser excitation, the device was capable of generating infrared radiation peaks, whose central wavelength was tunable via the modulation frequency. A plasmonic resonance model was established to explain the mechanism of this spectral tuning phenomenon.Methods The optical properties of MEMS devices were determined by unit structures and materials. The MEMS device investigated in this study consists of three structural components: a metallic nanochain aggregated radiation layer, a supporting layer, and a microcavity substrate (Fig. 1). Metal atoms exhibit high plasma frequencies and tunable plasmonic resonance characteristics across the ultraviolet to infrared spectral range. The nanochain aggregated structure can generate pronounced plasmonic resonance effects. The supporting layer is composed of a material with excellent mechanical and dielectric properties, providing structural support for the radiation layer. The microcavity substrate enhances the mechanical integrity of the device and facilitates heat conduction along the z-axis. In the experiment, an intensity-modulated laser illuminated the surface of the MEMS device, and the emitted infrared spectrum was collected with an infrared spectrometer. The resulting spectrum resembled blackbody thermal radiation superimposed with a narrowband radiation peak, whose central wavelength shifted in response to the modulation frequency of the incident laser. To explain this tuning phenomenon, a physical model based on plasmonic resonance was established by combining the resonant enhancement of the microcavity structure with the plasmonic resonance strength of the radiation layer. A series of experiments was then conducted to investigate the spectral tuning characteristics of the MEMS device.Results and Discussions The results show that the fabricated MEMS device exhibits a decrease in both the central wavelength and the full width at half maximum (FWHM) of the radiation peak as the modulation frequency of the excitation laser increases (Figs. 10 and 11). In the mid-wave infrared (MWIR) range, the device enables continuous tuning of the radiation peak with a 20 nm interval in central wavelength, while in the long-wave infrared (LWIR) range, a 100 nm interval can be achieved (Fig. 12). When the incident laser power density is increased, both the apparent temperature and the normal peak radiative intensity of the MEMS device rise significantly (Fig. 13). The radiation directional characteristic is similar to Lambertian emitter, with the peak radiative intensity in the normal direction enhanced by increasing the laser power density (Figs. 14 and 15). Under dual-frequency laser excitation, where two lasers with different modulation frequencies illuminate the same position on the device surface, two distinct radiation peaks are generated, each corresponding to one of the modulation frequencies. These peaks are mutually independent, with the central wavelength of each peak remaining unchanged as the other frequency varies (Fig. 16). Finally, as the bandwidth of the laser modulation frequency increases, the normal peak radiative intensity of the radiation peak decreases exponentially, while the spectral FWHM increases linearly (Fig. 17). This behavior is attributed to the distribution of laser energy over a broader frequency range. It causes the energy of the radiation peak to spread across a wider spectral band, thereby reducing its peak intensity and broadening its spectral width. All experimental results are in strong agreement with the simulation result, confirming the correctness of the plasmonic resonance model.Conclusions In this study, we design a wavelength-tunable infrared source based on MEMS technology. A novel MEMS device is fabricated. It is capable of generating infrared radiation peaks whose central wavelengths vary with the modulation frequency of the incident laser. A plasmonic resonance model is established to describe this spectral tuning behavior. Based on the proposed model, both simulations and experiments are performed to characterize the spectral tunability of the MEMS device, ultimately confirming the correctness of the plasmonic resonance model. The results demonstrate that this MEMS device exhibits excellent continuous tunability; its normal peak radiative intensity can be enhanced by increasing the laser power density, and it is capable of generating multiple infrared radiation peaks, each of which is independent and remains fixed as the other modulation frequency varies. This technology offers a feasible solution for applications in infrared spectroscopy, infrared communication, and multispectral infrared scene generation.