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A static full-Stokes Fourier transform imaging spectropolarimeter incorporating a liquid-crystal polarization modulator (LPM) and birefringent shearing interferometer (BSI) is reported. It can decode the polarization information at each wavelength along the spatial dimension of a two-dimensional data array. The LPM has a high-speed time-division architecture and employs two ferroelectric liquid crystals and two wave plates to produce four polarization states, providing full-Stokes polarimetric information with a high signal-to-noise ratio. The BSI comprises two birefringent crystal plates and generates an optical path difference with good linear distribution for broadband interference, allowing a fast and high-precision spectral recovery. The optimized design of LPM and BSI are introduced in detail. Subsequently, the signal reconstruction is verified through simulations and experiments. The proposed scheme is highly efficient, exhibits a higher spectral resolution, and constitutes a compact technical approach to realize high-dimensional optical measurement.

An iterative local Fourier transform (ILFT)-based high-accuracy wavelength calibration for Fourier transform imaging spectrometer (FTIS) is proposed. The wavelength calibration for FTIS is to determine the relation between the wavelength and the wavenumber position. However, the wavenumber position solved by conventional method is only accurate up to integers restricted by the picket-fence effect of discrete Fourier transform. While the proposed ILFT can increase the accuracy of calculating the wavenumber position by combining the local Fourier transform and a few iterations. In this paper, the method is investigated in theory and then by simulations and experiments. The simulations show that the accuracy of the wavenumber position calculated by the ILFT is increased by 100 times than conventional method with noise, phase error, and non-uniform sampling of optical path difference. And the experimental results indicate that the ILFT decreases the absolute error of wavelength calibration from about 2.03 nm to 0.16 nm. Therefore, the method provides theoretical and technical support for FTIS and promotes the development of superior resolutions therein.

Fourier Transform Imaging Spectrometer(FTIS) is an instrument cable of acquiring two-dimensional spatial information and one-dimensional spectral information. The FTIS has attracted much attention and is widely applied in the fields like military reconnaissance, remote sensing, biomedicine, environmental monitoring, etc. The FTIS acquires the spectral intensity in different wavelengths by performing Fourier transform on the white light interference signal of the target generated by the FTIS. The spectral curve obtained directly by Fourier transform reflects the relationship between the wavenumber order and the spectral intensity. So wavelength calibration is required to convert the above relationship into the relationship between the wavelength and the spectral intensity, which makes it more intuitive. Therefore, wavelength calibration is a necessary step for FTIS to recovery spectrum. The traditional wavelength calibration method can only get the wavenumber order in the range of integer because of the picket fence effect in Fourier transform. It will definitely ignore the fractional part which results in the inaccurate wavenumber order, which will directly affect the precision of the wavelength calibration result. In order to solve this problem, a high-precision wavelength calibration method based on Fourier transform imaging spectrometer is proposed according to the principle of FTIS and Fourier transform. This method can calculate the wavenumber order with the precision of percentile, which will reduce the error of wavelength calibration effectively. As a result, the precision of spectral calibration can be increased eventually. This method realizes high-precision wavelength calibration by the way of adding zero to the interference fringe in the spatial domain. The core of the method is getting a more precise wavenumber order. The brief process of obtaining wavenumber order is as follows: First, the FTIS acquires the interference fringe of a monochromatic laser. Second, the original interference fringe is extrapolated with zero. Third, the subtle spectrum can be obtained by performing Fourier transform on the extrapolated interference fringe. Finally, the precise wavenumber order is calculated by dividing the abscissa of the peak value by the extrapolation multiple. The principle of this method is investigated and related simulations are then carried out. The simulation results indicate that the wavenumber order calculated by the method have the same precision with the preset parameters, which illustrates that the method can calculate the wavenumber order more accurately. Therefore, the method can improve the precision of the spectral calibration. Besides, related experiments are also performed. The laser interference fringes of different wavelengths generated by the actual FTIS all apply the method to get the wavenumber orders in the frequency domain. Then a curve which is the wavelength calibration function is fitted using the discrete relation between the wavelengths and the wavenumber orders. A laser whose wavelength is known is measured by the FTIS with the wavelength calibration function got by the proposed method. The error of the wavelength measurement result is one-fifth of the traditional method. The simulations and the experiment results indicate that the proposed method can improve the precision of the wavelength calibration, which provides the theory and technology support for spectral measurement using FTIS. It also provides a possibility for the development of FTIS towards the super resolution direction.

This study proposes a polychromatic interferometric illumination and polarimetric sensor-based imaging method for spectrum, polarization, and 3D shape, which are significant physical parameters of feature analysis for target detection. 5D-fusion sensing refers to the joint detection and fusion of the above 5D information, which is currently a great challenge. The method generates a polychromatic interference pattern using a Sagnac lateral shearing interferometer and projects it to the target. Then, interferograms modulated by the target are acquired during scanning. Fast Fourier transform (FFT) is performed on the interferograms to obtain their frequency spectra. The spectral and polarization information is extracted from the moduli of the frequency spectra. The 3D shape is recovered from the phase of the frequency spectra using the calibration data. The theory of 5D-fusion sensing is investigated, and verification experiments are then performed. The experiments indicate that the proposed method can fulfill 5D-fusion sensing in one scanning and with FFT using only one device compared with other separate methods. Consequently, the proposed method can improve the sensing and recognition ability of optical imaging technology, which provides great application potential in biomedicine, food safety, material analysis, criminal investigation, archeology, and other fields.

A new Fourier transform imaging spectrometer based on a focal plane birefringent interferometer (FPBI) is presented. The FPBI, located in front of the detector, is capable of performing spectral imaging measurements. It mainly consists of a birefringent plate and a birefringent wedge. The ordinary and extraordinary rays—with an optical path difference—are split by the FPBI and interfere on the focal plane. The spectral image of the target can be acquired via scene scanning and spectral recovery. The principle of interferometric imaging of the FPBI is investigated, and verification experiments are then performed. The experiments indicate that the FPBI not only provides effective spectral imaging measurements, but also presents the advantages of being ultra-compact and lightweight. As a result, it can be effectively applied in situations such as outdoor surveillance and airborne remote sensing.

A compact birefringent interferometer (CBI) for Fourier transform hyperspectral imaging is presented. The CBI employs only two birefringent crystal plates: a shearing plate (SP) and a compensation plate (CP). The SP generates the optical path difference (OPD) associated with the field of view for broadband interference. The CP compensates the constant term and square term OPDs of the SP to adjust the position of the zero-order fringe pattern and suppress inconsistent total OPDs and other nonlinear OPDs. This paper details the theoretically deduced OPDs and then presents simulation analyses and verification experiments conducted to investigate the OPD distribution characteristics. To verify the CBI performance, experimental spectral measurements and hyperspectral imaging were performed. The experimental results demonstrate that the CBI can suppress inconsistent total OPDs and other nonlinear OPDs with only two birefringent crystal plates, and therefore offers much promise for miniature and high-precision Fourier transform hyperspectral imaging.