Photonics Integrated Interferometric System Simplifies High-Quality Imaging

An imaging system based on interferometry called SPIN (sparse-aperture and photonics-integrated) could provide higher-quality imaging than other similar techniques, including segmented planar imaging detector for electro-optical reconnaissance (SPIDER). A research group from Changchun Institute of Optics, Fine Mechanics and Physics (CIOMP), led by professor Xuejun Zhang, developed SPIN to advance interferometric imaging quality. The researchers’ latest system additionally simplifies the process of image reconstruction.

The group used a Fizeau configuration for its interferometer imaging system instead of the Michelson configuration that is used with SPIDER. The Fizeau configuration gives SPIN a more concise structure, with fewer apertures and wavebands than SPIDER. The lens array patterns used by SPIDER to reduce size, weight, and power (SWaP) provide low-frequency intensive, but high-frequency sparse, measurements of the visibility function. Zhang’s group found that sparse measurements of high-frequency visibility introduced Gibbs-ringing artifacts in the image reconstruction, diminishing the imaging quality of SPIDER.

The SPIN imaging system provides enhanced optical transfer functionality. This makes Gibbs-ringing artifacts less obvious, improving the imaging quality with equivalent aperture diameter, compared to SPIDER, the researchers said.

While working on SPIN, the researchers observed that apodization, or the elimination of coupling restriction at the tip of a waveguide, interfered with the imaging system’s ability to extract fine details. To eliminate the effect, the researchers added a microscope to their setup. They also used a waveguide array to receive the finer details of the image and enlarge SPIN’s field of view.

Illustration of degraded images obtained with different systems. (a) Original clear image. (b) Degraded image of SPIN imaging system. (c) Degraded image of SPIDER imaging system with direct instrument transfer function. A research team has shown that the SPIN technique can be used to obtain a more uniform response in the spatial frequency domain than that which the SPIDER technique delivers. Further, it can receive most spatial frequency signals within the diffraction limit. Courtesy of T. Chen.

After the researchers magnified the light with the microscope, they established the proper parameter settings for the device. They analyzed the relation between the field of view and the waveguide array, and investigated the coupling efficiency of the waveguides and the crosstalk errors between the waveguides in the array. The team also analyzed the modulation transfer function and point spread function of SPIN.

The analyses revealed that the received image was degraded by point spread function and noise. Based on the analyses of the apodization effect, field of view, and crosstalk, the researchers formulated an imaging principle. They developed a hyper-Laplacian-based imaging reconstruction algorithm to reconstruct the ground truth from the images obtained in SPIN.

A simulation of the SPIN imaging system, using seven apertures and one imaging waveband to demonstrate its high imaging quality, revealed that SPIN delivered higher-quality imaging performance than that which SPIDER delivers with the same aperture diameter.

By using PICs and replacing bulky lens systems with compact lenslet arrays, the SPIDER system reduces SWaP by by one to two orders of magnitude, compared with conventional diffraction-limited optical systems. The SPIN system also uses photonics-integrated technology to further advance imaging quality. SPIN is compact in structure and stable in measurement. It can significantly reduce the number of apertures and the number of imaging wavebands required for high-quality interferometric imaging.

The researchers’ analyses showed that SPIN can obtain a more uniform response in the spatial frequency domain than SPIDER. Further, it can receive most spatial frequency signals within the diffraction limit.

The research was published in Optics Express (www.doi.org/10.1364/OE.444421).