Jian Huang

This paper presents a miniaturized, broadband near-infrared (NIR) spectrometer with a flame-retardant 4 (FR4)-based scanning micrograte. A 90° off-axis parabolic mirror and a crossed Czerny–Turner structure were used for creating an astigmatism-free optical system design. The optical system of the spectrometer consists of a 90° off-axis parabolic mirror, an FR4-based scanning micrograte, and a two-color indium gallium arsenide (InGaAs) diode with a crossed Czerny–Turner structure optical design. We used a wide exit slit and an off-axis parabolic mirror with a short focal length to improve the signal-to-noise ratio (SNR) of the full spectrum. We enabled a miniaturized design for the spectrometer by utilizing a novel FR4 micrograte for spectral dispersion and spatial scanning. The spectrometer can detect the full near-infrared spectrum while only using a two-color InGaAs diode, and thus, the grating scanning angle of this spectrometer is small when compared to a dual-detector-based spectrometer. In addition, the angle signal can be obtained through an angle sensor, which is integrated into the scanning micrograte. The real-time angle signal is used to form a closed-loop control over the scanning micrograte and calibrate the spectral signal. Finally, a series of tests was performed. The experimental results showed that the spectrometer has a working wavelength range of 800–2500 nm. The resolution is 10 nm at a wavelength range of 800–1650 nm and 15 nm at a wavelength range of 1650–2500 nm. Similarly, the stability of these two wavelength ranges is better than ±1 nm and ±2 nm, respectively. The spectrometer’s volume is 80 × 75 × 65 mm³ and its weight is 0.5 kg. The maximum spectral fluctuation does not exceed 1.5% and the signal-to-noise ratio is 284 after only one instance of averaging.

This paper performs a detailed investigation on the electromagnetic angle sensor integrated in the flame retardant 4 (FR4)-based scanning micromirror. An accurate theoretical model is presented, especially considering the coupling effect between the driving and sensing coils. Experimental results agree well with the theoretical results, and show a sensitivity of 55.0 mV_p/° and a high signal-to-noise ratio (SNR) of 71.9 dB. Moreover, the linearity of the angle sensor can still reach 0.9995, though it is affected slightly by the coupling effect. Finally, the sensor’s good feasibility for feedback control has been further verified through a simple closed-loop control circuit. The micromirror operated with closed-loop control possesses better long-term stability and temperature stability than that operated without closed-loop control.

This paper presents a dispersive near-infrared spectrometer with features of miniaturization, portability and low cost. The application of a resonantly-driven scanning grating mirror (SGM) as a dispersive element in a crossed Czerny–Turner configuration enables the design of a miniaturized spectrometer that can detect the full spectra using only one single InGaAs diode. In addition, a high accuracy recalculation is realized, which can convert time-dependent measurements to spectrum information by utilizing the deflection position detector integrated on SGM and its associated closed-loop control circuit. Finally, the spectrometer prototype is subjected to a series of tests to characterize the instrument’s performance fully. The results of the experiment show that the spectrometer works in a spectral range of 800 nm–1800 nm with a resolution of less than 10 nm, a size of 9 × 7 × 7 cm³, a wavelength stability better than ±1 nm and a measuring time of less than 1 ms. Furthermore, the power consumption of the instrument is 3 W at 5 V DC, and the signal-to-noise ratio is 3267 at full scale. Therefore, this spectrometer could be a potential alternative to classical spectrometers in process control applications or could be used as a portable or airborne spectroscopic sensor.