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.

With the advances in the field of ultrafast photonics occurring so fast, the demand for optical modulation devices with high performance and soliton lasers which can realize the evolution of multiple soliton pulses is gradually increasing. Nevertheless, saturable absorbers (SAs) with appropriate parameters and pulsed fiber lasers which can output abundant mode-locking states still need to be further explored. Due to the special band gap energy values of few-layer indium selenide (InSe) nanosheets, we have prepared a SA based on InSe on a microfiber by optical deposition. In addition, we demonstrate that our prepared SA possesses a modulation depth and saturable absorption intensity about 6.87% and 15.83 MW/cm2, respectively. Then, multiple soliton states are obtained by dispersion management techniques, including regular solitons, and second-order harmonic mode-locking solitons. Meanwhile, we have obtained multi-pulse bound state solitons. We also provide theoretical basis for the existence of these solitons. The results of the experiment show that the InSe has the potential to be an excellent optical modulator because of its excellent saturable absorption properties. This work also is important for improving the understanding and knowledge of InSe and the output performance of fiber lasers.

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.