The Study On Optical System Of Imaging Fiher-Optic Spectrometer With Wide Field-of-view

Increasing field of view (FOV) can improve the work efficiency of imagingspectrometers, and large FOV wide coverage is the development trend of the nextgeneration of imaging spectrometers. In generally, remote sensor weight and volumeincreases with the enlargement of FOV, therefore, how an imaging spectrometer canreach wide FOV and simultaneously keep a compact configuration and a lightweight is a tradeoff for the designers. To break the restriction of weight and volumeon FOV, imaging fiber-optic spectrometer (IFOS) is presented in which imagingfiber bundles replace the slit of dispersive imaging spectrometer and connecttelescope and spectrometer. Utilizing the properties of flexibility and separability offiber bundles, segment the wide linear FOV of telescope into several smaller FOV,and then fold and set separately them on the objective plane of spectrometer,ultimately be dispersed and imaged depends on wavelength. Since those smallerFOV share one spectrometer and imaged individually, dimension and spectraldistortion can be controlled while a large FOV obtained. As for spectrometerstructure, concentric configurations are well-known best option. Several concentricspectrometer are analysed and ultimately the Offner structure with Féry prisms usedin double pass is selected to use as spectrometer. According study goal, a spaceborneIFOS with linear FOV of72mm is designed. Design process is describled and design results are presented. The results show IFOS inherits the advantages of compactstructure and neglectable distortion of Offner system and meanwhile lacks of thedisadvantages of low diffraction efficiency and overlap between different orders.IFOS is a double sampling imaging system, so the shift-invariant assumption isno longer valid. On the other hand, the coupling effect of fiber bundles andaberrations and specification difference make the sampling process disordered andhence the imaging performance degressive. Thus it is need to build a modulationtransfer function (MTF) model to evaluate imaging performance. Starting from thecalculation of linear spread function (LSF), we derive the model of LSF and buildcascade MTF model, using which we evaluate the imaging MTF of designed IFOS.In order to show the advantages of IFOS, we compare which with slit-based Offnerimaging grating spectrometer under same specification demand and presentcomparison results. The results indicate the IFOS volume is about one fifth of theother and spectral distortion is controlled but the MTF less than the other. Thisindicates the wide FOV and compact structure can be obtained simultaneously at thesacrifice of partial MTF value. For fiber there are focal ratio degradation and lowefficiency coupling in the power transmission. To overcome them, we propose tocompose fiber-microlens model on the two ends of fiber bundles by addingmircolens before the fiber ends. The perform principle and sampling process offiber-microlen arrays are analysed. The results show fiber-microlens spectrometerlacks the defect of IFOS and has a good performance, but has some difficulties tofabricate and align fiber-microlens array because of complex structure and lots ofmodules. The imaging fiber-microlens spectrometer needs deep studies beforeengineerization.