Extension of the Measurable Wavelength Range for a Near-Infrared Spectrometer Using a Plasmonic Au Grating on a Si Substrate.

Yu Suido,Yoshiharu Ajiki,Yosuke Yamamoto,Tetsuo Kan,Gaulier Thomas

doi:10.3390/mi10060403

Abstract

In this paper, we proposed near-infrared spectroscopy based on a Si photodetector equipped with a gold grating and extended the measurable wavelength range to cover 1200–1600 nm by improving a spectrum derivation procedure. In the spectrum derivation, photocurrent data during alteration of the incidence angle of the measured light were converted using a responsivity matrix R, which determines the spectroscopic characteristics of the photodetector device. A generalized inverse matrix of R was used to obtain the spectrum and to fit a situation where multiple surface plasmon resonance (SPR) peaks appeared in the scanning range. When light composed of two wavelengths, 1250 nm and 1450 nm, was irradiated, the two wavelengths were distinctively discriminated using the improved method.

Highlights

Near-infrared (NIR) spectroscopy is a method of analyzing an object by its optical spectrum, and this method is used in many fields, such as agriculture, chemistry, and medicine [1,2,3,4]
Since a Schottky barrier is formed at an interface of the grating metal/silicon (Si), coupled surface plasmon resonance (SPR) on the grating is directly detected as a current on the device
The photodetector is integrated with a plasmonic grating, this method is well suited for constructing compact NIR spectrometers

Summary

Introduction

Near-infrared (NIR) spectroscopy is a method of analyzing an object by its optical spectrum, and this method is used in many fields, such as agriculture, chemistry, and medicine [1,2,3,4]. Plasmonic-based spectrometers are attracting attention because dispersal of the incident light is performed with a thin layer to allow a compact optical system [5,6,7,8,9]. Since a Schottky barrier is formed at an interface of the grating metal/silicon (Si), coupled surface plasmon resonance (SPR) on the grating is directly detected as a current on the device. Since the resonant angular positions are determined by the wavelength, the spectral information can be derived using the data plots This measurement was performed only on a device surface, so the proposed method did not require an optical path to disperse the light

Spectral Calculation Procedures

Materials and Methods