Broadband on-chip near-infrared spectroscopy based on a plasmonic grating filter array

Abstract

We demonstrate an ultra-compact, broadband on-chip near-infrared (NIR) spectroscopy system based on a narrow-band plasmonic filter array. The entire filter array, consisting of 28 individual subwavelength metallic gratings, was monolithically integrated in a thin gold film on a quartz substrate, covering a 270 nm spectra from 1510 nm to 1780 nm. In order to achieve a high spectral resolution, extremely narrow slits are created for the gratings with a polymer waveguide layer on top, generating narrow-band guided-mode resonances through coupling with the surface-plasmon resonances of the metallic gratings. Experimental results show that the transmission bands of the filter array have full width at half-maximum of only 7 nm-13 nm, which is sufficient for NIR spectroscopy. The NIR absorption spectroscopy of xylene using the on-chip plasmonic filter array matches very well with the results from conventional Fourier transform infrared spectroscopy, which proves the great potential for NIR sensing applications.

Nano-structured transmissive spectral filter matrix based on guided-mode resonances

“…Compared with previous works [38], we use a higher fill factor to realize the low sideband spectra by reasonable scarifying the transmission efficiency, but still with narrow bandwidth. This helps our future biomedical application to collect the light information at certain wavelengths in both visible and near infrared range [4]. However, a higher fill factor means the smallest filter metal grating gap has to be fabricated down to around 30 nm in our case, which is quite challenging.…”

“…Ideally, the transmission function of the filter is as sharp as possible and should change from pixel to pixel, whereas the pixel distance of modern CMOS chips is in the range of a few micrometers [2,3]. Since each pixel refers to a separate wavelength, the image of the CMOS sensor can then be transferred directly into an optical spectrum [4,5]. In addition to the high spatial resolution [6], in order to allow e.g.…”

Surface plasmon excitation using a Fourier-transform infrared spectrometer: Live cell and bacteria sensing

“…The combination of infrared spectroscopy with the surface plasmon excitation requires a broadband coupler. Several such couplers have been developed recently, and they include multipath diffraction grating, 18 plasmonic filter array, 7 wide-band plasmonic nanoantenna, 8,9 or specially etched Si substrate. 19 Still, these couplers have limited bandwidth, and the traditional Kretschmann's geometry based on a metal-coated prism 20 remains a preferred setup for broadband surface plasmon excitation.…”

“…1 Based on this success, much effort was spent to push the surface plasmon technology into the infrared range. [2][3][4] The infrared surface plasmon wave is at the core of emerging methods for label-free and real-time probing of molecules, 2,[5][6][7] organic layers, [8][9][10] and live cells. 11 It would be especially advantageous to combine the surface plasmon technique and infrared spectroscopy together to achieve highly sensitive spectroscopic measurements.…”

Metal-insulator-metal plasmonic grating filter with suppressed Rayleigh anomaly

“…The first category of plasmonic filters use hole arrays (2D gratings) to achieve color filtering [4][5][6][7][8][9]. The second category of plasmonic filters are based on subwavelength gratings [10][11][12][13][14][15][16][17][18][19]. Since hole arrays usually have wider bandwidth (BW) compared to grating based filters, for applications requiring higher spectral resolution, grating based filters are preferred.…”