Figure - available from: Applied Optics
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Concept of the pixelated gradient thickness filter illustrating the wavelength-selective transmission of different pixelated filters in the filter array. Each pixelated gradient thickness filter is designated by the label ${P}q(r)$ . The inset (on the right side) shows the side view of the extreme filter arrangement with the optimal values of the cavity layer thicknesses as ${t_L}$ and ${t_H}$ .
Source publication
A miniature low-cost pixelated gradient thickness optical filter is proposed to achieve spectroscopy in the visible wavelength range. The optical filter consists of a two-dimensional array of metal-dielectric-metal thin films arranged in Fabry–Pérot filter configurations with discretely varying cavity thicknesses. The wavelength-selective character...
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Citations
... Miniature spectroscopic devices play indispensable roles in a variety of applications, including space observations, nondestructive everyday analysis, health monitoring, and pollution detection. [1][2][3][4] They also provide a vital platform for in situ measurements such as spectroscopic sensing and hyperspectral imaging [5][6][7][8][9][10][11] through lab-on-a-chip devices. The microelectromechanical systems (MEMS)-based Fabry-Pérot filter (FPF) [12][13][14][15] has paved the way for the realization of miniature, cost-effective, and lightweight spectrometers compared to conventional grating-based 16,17 and Fouriertransform infrared 18,19 spectrometers. ...
We fabricate a microelectromechanical systems (MEMS)-based device configuring the tunable air gap Fabry–Pérot filter (FPF) with a static gradient thickness filter on the same platform. The proposed double filter configuration offers a wavelength calibration approach that accurately estimates the air gap dimension in the tunable air gap FPF. The wavelength calibration is performed by utilizing the spectrally-selective and spatially-resolved transmission characteristics of the tunable air gap FPF and the static gradient thickness filter, respectively. The MEMS-compatible chip-level integration of the static gradient thickness filter facilitates device miniaturization to enable its use in handheld devices.
... T UNABLE Fabry-Pérot filters (FPFs) have emerged as versatile and indispensable components across a multitude of scientific and industrial fields, including astronomy, metrology, optical communications, nondestructive everyday analysis, medical diagnostics, and environmental monitoring [1], [2], [3], [4], [5], [6], [7], [8]. The advent of tunable FPFs driven by microelectromechanical techniques has significantly advanced the development of complementary metal oxide semiconductor (CMOS)-integrated lab-on-a-chip devices such as miniature spectrometers [9], [10], [11], [12], [13], [14], [15], [16] and hyperspectral imaging systems [17], [18], [19], [20]. ...
A tunable air-gap Fabry–Pérot filter consisting of distributed Bragg reflectors as cavity mirrors was developed to operate in the visible wavelength range. The wavelength tunability of the filter was achieved based on the piezo actuation mechanism. Four in-plane identical piezo actuators were employed to simultaneously achieve both wavelength tunability and cavity air-gap parallelism in the filter. Two pairs of piezo actuators positioned at crossed locations enabled independent control of cavity air-gap dimensions along orthogonal directions in the cavity plane. Optical transmission measurements were performed at different spatial positions on the cavity region to estimate the cavity air-gap dimensions. The initial maximum spectral separation among different spatial positions owing to the initial non-parallelism of the cavity air gap was estimated to be ∼28 nm. After achieving cavity air-gap parallelism via piezo actuation, the final maximum spectral separation was reduced to ∼3 nm. The proposed device configuration significantly improved the cavity air-gap parallelism by minimizing the maximum variation of the cavity air-gap dimension from an initial value of 535 nm to a final value of 18 nm, resulting in an improvement by a factor of ∼30. This device prototype can enable high-resolution and high-throughput spectral transmission with improved spatial uniformity across a large cavity area, showing great promise for advancing hyperspectral imaging systems.
