Contents 1. Introduction
The spectroscopy now encompasses our scientific and industrial scenes as one of indispensable optical measurement and signal processing technologies [1]–[3] and much finer spectral treatment is getting more important [4]–[7]. The spectroscopic technique can be roughly classified into interferometric and dispersive methods [8]. They have specific advantages and disadvantages in terms of measurement speed, spectral resolution, compactness, and maintainability. Among them, a polychromator-type dispersive spectrometer has been one of well-distributed methods because it can provide attractive advantages such as high-speed measurement, compactness, robustness without any mechanical scanning architecture. While these advantages encourage the method to be prevailed, its spectral resolution is inferior to that of other methods. The spectral resolution of a current polychromator-type dispersive spectrometer is mainly restricted by the pixel size of a multi-channel photodetector array which is set on the observational plane. In general, we cannot distinguish two spectral lines of which apart each other by a distance smaller than the pixel size. As well known, Moiré fringes can magnify very small mutual displacements of two similar patterns and it has been widely used in metrology [9]. In particular, in the linear displacement case, a pair of linear line gratings are used and it is called Vernier fringes. Vernier scale in various gages is also based on the same principle and a pair of similar scales such as line gratings can be used for the measurement of very small linear displacements. To this day, Moiré effect still continues to have a strong effect on various fields in metrology. In fact, the super resolution method using Moiré effect has recently succeeded in exceeding the diffraction limit which restricts spatial resolution in microscopy [10], [11].
