Abstract

Mid-infrared wavelengths are called the molecular fingerprint region because it contains the fundamental vibrational modes inherent to the substances of interest. Since the mid-infrared spectrum can provide non-destructive identification and quantitative analysis of unknown substances, miniaturized mid-infrared spectrometers for on-site diagnosis have attained great concern. Filter-array based on-chip spectrometer has been regarded as a promising alternative. In this study, we explore a way of applying a pillar-type plasmonic nanodiscs array, which is advantageous not only for excellent tunability of resonance wavelength but also for 2-dimensional integration through a single layer process, to the multispectral filter array for the on-chip spectrometer. We theoretically and experimentally investigated the optical properties of multi-periodic triangular lattices of metal nanodiscs array that act as stopband filters in the mid-infrared region. Soft-mold reverse nanoimprint lithography with a subsequent lift-off process was employed to fabricate the multispectral filter array and its filter function was successfully extracted using a Fourier transform infrared microscope. With the measured filter function, we tested the feasibility of target spectrum reconstruction using a Tikhonov regularization method for an ill-posed linear problem and evaluated its applicability to the infrared spectroscopic sensor that monitors an oil condition. These results not only verify that the multispectral filter array composed of stopband filters based on the metal nanodiscs array when combined with the spectrum reconstruction technique, has great potential for use to a miniaturized mid-infrared on-chip spectrometer, but also provide effective guidance for the filter design.

Highlights

  • Mid-infrared wavelengths are called the molecular fingerprint region because it contains the fundamental vibrational modes inherent to the substances of interest

  • With the measured filter function, we tested the feasibility of target spectrum reconstruction through digital signal processing (DSP) based on a regularization method for an ill-posed linear problem and examined the effect of the number of filters on the spectral reconstruction resolution

  • Unlike the metal NHA structure, the metal nanodisc arrays (MNDAs) appear to have simple single stopband spectra having a relatively small linewidth and deep depth. This is because MNDAs exhibit a strongly enhanced reflectance peak due to the coupling between localized surface plasmons (LSPs) and the grating of metal nanodiscs, which forms a corresponding transmission ­dip[20,21,22]

Read more

Summary

Introduction

Mid-infrared wavelengths are called the molecular fingerprint region because it contains the fundamental vibrational modes inherent to the substances of interest. With the measured filter function, we tested the feasibility of target spectrum reconstruction using a Tikhonov regularization method for an ill-posed linear problem and evaluated its applicability to the infrared spectroscopic sensor that monitors an oil condition These results verify that the multispectral filter array composed of stopband filters based on the metal nanodiscs array when combined with the spectrum reconstruction technique, has great potential for use to a miniaturized mid-infrared on-chip spectrometer, and provide effective guidance for the filter design. Plasmonic antennas and resonators tailored to a specific target wavelength have been often used to amplify spectroscopic molecular absorption signals through strongly enhanced light-matter i­nteraction[2,3] Benchtop equipment such as Fourier Transform Infrared (FTIR) spectrometer has been used for spectroscopic analysis of organic and inorganic m­ aterials[4]. The FP filters are not suitable for high-density integration and mass production

Methods
Results
Conclusion
Full Text
Published version (Free)

Talk to us

Join us for a 30 min session where you can share your feedback and ask us any queries you have

Schedule a call