Applied Optics

Space-borne sensors can provide valuable spatial image data, which play an irreplaceable role in ground target observation. In this paper, we have derived a parameter called the scattering efficiency per unit area (SEA), which is used to describe the ability of different media to change the energy of an incident field in the far zone. Over the range of Hyperion wavelengths, the SEA are unequal, w…

Pose estimation for spacecraft is widely recognized as an important technology for space applications. Many space missions require accurate relative pose between the chaser and the target spacecraft. Stereo-vision is a usual mean to estimate the pose of non-cooperative targets during proximity operations. However, the uncertainty of stereo-vision measurement is still an outstanding issue that nee…

Star trackers, optical attitude sensors with high precision, are susceptible to space light from the Sun and the Earth albedo. Until now, research in this field has lacked systematic analysis. In this paper, we propose an installation orientation method for a star tracker onboard sun-synchronous-orbit spacecraft and analyze the space light distribution by transforming the complicated relative mot…

An enhanced methodology of the standard on-orbit calibration of the day-night band (DNB) of the visible infrared imaging radiometer suite on board the Suomi National Polar-orbiting Partnership satellite is presented, specifically for the low-gain stage. The range of the "sweet spot" for the fully illuminated scans in the calibration events is expanded from 4° to 7.8° in order to increase the numb…

Fata Morgana mirages are frequently seen at Lake Geneva. We show the first photographs of them, including a real-time video, and explain their main features, which are due to the very turbulent entrainment zones of capping inversions, especially in valley circulations.

We evaluated the use of a commercial flatbed scanner for digitizing photographic plates used for spectroscopy. The scanner has a bed size of 420 mm by 310 mm and a pixel size of about 0.0106 mm. Our tests show that the closest line pairs that can be resolved with the scanner are 0.024 mm apart, only slightly larger than the Nyquist resolution of 0.021 mm expected from the 0.0106 mm pixel size. We…

Orbital angular momentum (OAM) beams allow for increased channel capacity in free-space optical communication. Conventionally, these OAM beams are multiplexed together at a transmitter and then propagated through the atmosphere to a receiver where, due to their orthogonality properties, they are demultiplexed. We propose a technique to demultiplex these OAM-carrying beams by capturing an image of…

A novel and high-efficiency linear frequency-modulated continuous-wave (FMCW) ladar system for synthetic aperture imaging is proposed and experimentally demonstrated. This novel system generates wide-bandwidth linear FMCW ladar signals by employing an electro-optic LiNbO₃- in-phase and quadrature modulator with an effective bias controller. The effectiveness of the proposed system is e…

Array spectroradiometers are attractive alternatives to scanning spectroradiometers in solar ultraviolet measurements. However, the measurement of solar spectral irradiance imposes stringent requirements for the linearity of the instruments. In this article, two array spectroradiometers were characterized for nonlinearity. Significant nonlinearities, in excess of 10%, as a function of analog-to-d…

Low timing jitter is a unique merit of superconducting nanowire single-photon detectors (SNSPDs) for time-correlated applications. Quantitative analysis was performed for the SNSPD system. Aided by an oscilloscope with an optimal signal amplitude, we were able to measure a full width at half-maximum system timing jitter as low as 14.2 ps for a high-switching-current SNSPD using a room-temperature…

Material made of artificial molecules fabricated from cage-shaped granules of conductor (CGC) is introduced and its electrical and magnetic characteristics are presented. Its refractive index, calculated using complex relative permittivity and complex relative permeability, is 1.504 at 35 GHz. A two-element lens, consisting of a pair of spherical plano-convex lenses, was designed and fabricated b…

In this paper, we propose what we believe is a novel all-optical analog-to-digital converter (ADC) based on photonic crystals. The proposed structure is composed of a nonlinear triplexer and an optical coder. The nonlinear triplexer is for creating discrete levels in the continuous optical input signal, and the optical coder is for generating a 2-bit standard binary code out of the discrete level…

In on-board photographing processes of satellite cameras, the platform vibration can generate image motion, distortion, and smear, which seriously affect the image quality and image positioning. In this paper, we create a mathematical model of a vibrating modulate transfer function (VMTF) for a remote-sensing camera. The total MTF of a camera is reduced by the VMTF, which means the image quality …

In uncooled long-wave IR camera systems, the temperature of a focal plane array (FPA) is variable along with the environmental temperature as well as the operating time. The spatial nonuniformity of the FPA, which is partly affected by the FPA temperature, obviously changes as well, resulting in reduced image quality. This study presents a real-time nonuniformity correction algorithm based on FPA…

In the streak tube laser imaging system, there are two conflicts: the first is between high spatial resolution and wide field of view (FOV). The second is between high temporal resolution and deep depth of field (DOF). In this paper, a new non-scanning streak tube laser imaging system is presented. A microlens array with three different apertures is used to non-uniformly collect data from the ima…

A highly sensitive temperature sensor based on an all-fiber Sagnac loop interferometer combined with metal-filled side-hole photonic crystal fiber (PCF) is proposed and demonstrated. PCFs containing two side holes filled with metal offer a structure that can be modified to create a change in the birefringence of the fiber by the expansion of the filler metal. Bismuth and indium were used to exami…

Benefiting from rapid development of imaging sensor technology, modern optical technology, and a high-speed computing chip, the star tracker's accuracy, dynamic performance, and update rate have been greatly improved with low power consumption and miniature size. The star tracker is currently one of the most competitive attitude measurement sensors. However, due to restrictions of the optical ima…

The quasi-optical modulation of linear polarization at millimeter and sub-millimeter wavelengths can be achieved by using rotating half-wave plates (HWPs) in front of polarization-sensitive detectors. Large operational bandwidths are required when the same device is meant to work simultaneously across different frequency bands. Previous realizations of half-wave plates, ranging from birefringent …

Due to the introduction of the intensified image detector, the dynamic performance of the intensified star tracker is effectively improved. However, its attitude update rate is still seriously restricted by the transmission and processing of pixel data. In order to break through the above limitation, a multiexposure imaging approach for intensified star trackers is proposed in this paper. One sta…

Angular velocity information is a requisite for a spacecraft guidance, navigation, and control system. In this paper, an approach for angular velocity estimation based merely on star vector measurement with an improved current statistical model Kalman filter is proposed. High-precision angular velocity estimation can be achieved under dynamic conditions. The amount of calculation is also reduced …