Bridging mid and near infrared by combining optomechanics and self mixing

TL;DR

The paper tackles bridging near-IR and mid-IR signals using an optomechanical interface based on self-mixing in a quantum cascade laser system. It demonstrates that a near-IR excitation beam can drive a trampoline membrane via light-induced forces while a mid-IR QCL provides SM readout, enabling encoding of the excitation signal into the probe across wavelengths. Quantitative results show that mid-IR power red-shifts the membrane resonance at 14.28 ± 0.17 Hz/mW and near-IR power shifts it at 98.8 ± 1.1 Hz/mW, with Conf.2 AM modulation yielding a blue-shift of 102 ± 4 Hz/mW, and thermal effects revealing a bandwidth below 40 Hz, all well below the mechanical resonance near 90 kHz. The work establishes a broadband, wavelength-agnostic transduction pathway with potential as a communication gate and sensing/imaging platform that could link mid-IR channels to telecom or other spectral regions.

Abstract

This work describes a self-mixing-assisted optomechanical platform for transferring information between near- and mid-infrared radiation. In particular, the self-mixing signal of a mid-infrared quantum cascade laser is used to detect the oscillation of a membrane driven by light-induced forces exerted by a near-infrared excitation beam, which is amplitude-modulated at the membrane resonance frequency. This technique benefits from spectral broadness and, therefore, can link different spectral regions from both the excitation and probe sides. This versatility can pave the way for future applications of this self-mixing-assisted optomechanical platform in communication and advanced sensing systems.

Figures (5)

• Figure 1: Schematic of the SM setup. M: mirror, W: window, PD: photodetector, L: lens, PZT: piezoelectric actuator, AOM: acousto-optic modulator. The configuration used to characterize the membrane resonance frequency by acting on the piezo, namely Conf. 1 is depicted in green. The configuration where the membrane is excited via the AM-modulated near-IR radiation is depicted in blue, namely, Conf. 2.
• Figure 2: a): Amplitude peak normalized to its maximum value as a function of PZT modulation frequency, plotted at different values of probing mid-IR optical power, when the membrane oscillation is excited by the PZT and no excitation light is sent onto the membrane. Each peak is fit with a Lorentzian function, allowing the estimation of the resonance frequency at each impinging power value reported in the legend. b) Membrane resonance frequency, estimated via the Lorentzian fit, as a function of mid-IR probing power. The data (blue points) are fit with a straight line (red curve). The error bar (blue lines) is calculated as the standard deviation of the repeated measurements of the resonance frequency for a certain power value.
• Figure 3: a): Normalized amplitude peak to its maximum value as a function of PZT modulation frequency, plotted at different values of near-IR impinging power, when the membrane oscillation is driven via the PZT and the mid-IR probe beam is kept at a fixed working condition, emitting a power of 6.2mW. Each peak is fitted via a Lorentzian function, which allows us to estimate the resonance frequency at the peak value for the different values of impinging power. The obtained values are depicted as blue points in graph (b). b): Membrane resonance frequency as a function of near-IR impinging power. The data (blue points) are fitted via a linear fit (red line). Here, the error bars, obtained as in Fig. \ref{['fig:freq_shift_pzt_QCL']}, are not visible.
• Figure 4: a): Amplitude peak normalized to its maximum value as a function of AM modulation frequency, plotted at different values of AM-modulated near-IR impinging power, when the mid-IR probe beam is kept at a fixed working condition at a power of 6.2mW. Each peak is fitted via a Lorentzian function, which allows us to estimate the resonance frequency at the peak value for the different values of impinging power. The obtained values are depicted as blue points in graph (b). b): Membrane resonance frequency as a function of near-IR impinging power. The data (blue points) are fit to a straight line (red curve). The error bars are obtained as in Fig. \ref{['fig:freq_shift_pzt_QCL']}.
• Figure 5: Characterization of the thermal relaxation time scale onto the membrane peak of resonance when the system is driven in Conf.1 and a slow AM modulation (see the legend) is added on the excitation beam.