The Imaging Fourier Transform Spectrometer (IFTS) is the temporal modulated Michelson interferometer in which a single-element detector is replaced by an area focal plane arrays. Each pixel of detector arrays records observed area radiation and then yield the corresponding spectrum by Fourier transforms. While, area focal plane arrays improve spatial resolution and expand area coverage. However, this innovation technology has many technical challenges to be overcome. In this paper, the challenges caused by area focal plane arrays are discussed. The simulations of
interference modulation (IM) of Fourier transform spectral imaging are presented. The IM changes as the extensions of pixel are simulated and analyzed. And a phenomenon that interference modulation deteriorates with spectral resolution improvement is discussed. The results show that, the off-axis pixels are sampled at slightly shorter OPDs, compared with the pixel in the center. The decrease of interference modulation caused by area focal plane arrays is related to both the position of each pixel and maximum optical path difference. Interference modulation decline in the format of a quadratic function as the pixel position extends. And this decrease in short waveband is more significant than that in long waveband. It is noticed that there is a key spectral resolution for IFTS interference modulation. When the spectral resolution is set below the key point, the IM decrease smoothly and slowly at the high level. However, if the spectral resolution keeps improving over the key point, the modulation will decline abruptly.
With the development of the optical technology, wavelength division multiplexing (WDM) is becoming an important technology for the enhancement of bandwidths of fiber-optical networks. Bragg gratings utilize the fact that light is diffracted from a grating only if the Bragg condition is fulfilled. In the paper a new kind of measure called directly layered multiple VBGs (volume Bragg gratings) is presented, which is fabricated by photorefractive volume holographic technology, and the multiple VBGs fabricated by this method with layered structure is more compact, the corresponding system could, more sufficiently, utilize the volume of photorefractive lithium niobate crystal. In our experiment the VBGs can be formed by illumination of interference field of two thin sheet beams expanded and collimated through two cylindrical lenses, and then multiple VBGs can be accomplished at the same location by angle-multiplexing technique. And then the layered structure can be formed by space-multiplexing holographic technique, i.e. after the fabrication of the previous layer, the following layer is able to be created by above multiple illuminations through moving crystal along the sheet beam normal with a certain space. The steady layered multiple VBGs in LiNbO3:Fe crystal can be achieved through thermal fixing technique. Several layered structures are fabricated, that are respectively composed of four superimposed VBGs in LiNbO3 crystal. The spectrum distribution of each layer gratings transmittance was measured by utilizing Ando AQ6317C optical spectrum analyzer
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