MEPhI, Bauman Moscow State Technical University and Lebedev FIAN: Method for assessing distortions in optical systems

2022: Development of a method for measuring distortion in optical systems

At the Laboratory of Photonics and Optical Information Processing, NRNU MEPhI together with colleagues from the Bauman Moscow State Technical University and Lebedev FIAN developed a method for measuring distortions that light undergoes in optical systems using holograms. This was reported on November 1, 2022 at the NRNU MEPhI.

An optical system in this case refers to any (but usually quite complex) optical device - for example, a telescope or a camera lens. And any optical device not only transmits a light flux through itself, but also introduces unwanted aberrations into it. Any lens, any mirror used in a telescope, periscope or camera contributes to the total amount of distortion.

In some cases, these distortions can be neglected. However, where the thinnest measurements depend on the optical device (and this is so, for example, in astronomy or optical calculations), those arising in the optical aberration system must be measured and, if possible, compensated. This problem is solved by a special physical and technical discipline - the so-called adaptive optics. An important element in adaptive optics systems are special devices - wavefront sensors, which, in fact, measure distortions in optical devices. It is this campaign to develop such sensors that is proposed at NRNU MEPhI.

The peculiarity of the proposed method consists in the fact that computer-synthesized holograms are used to evaluate optical aberrations. Scientists took advantage of the fact that the hologram is very informative: its diffraction structure contains information about three-dimensional objects. The essence of the technology is as follows: a model of diffraction structure calculated on a computer is supplied to the so-called space-time light modulator (this device looks like a small translucent screen); this screen is then fed with a beam of light (best of all a laser) passed through the optical system being evaluated - say, a telescope. A beam of light is scattered - or defragged, scientists say, as it passes through a hologram on a screen. By assessing the nature of this scattering, and comparing it with the scattering of the reference (that is, not passing through the telescope) laser beam, one can judge the nature of the aberrations, and, accordingly, take measures to correct them, told a laboratory researcher, doctor of physical and mathematical sciences, Evgeny Zlokazov.

An important feature of the technology is that this method is implemented using any commercially available space-time light modulator (amplitude, phase or binary).

Compared to existing technologies, this method has the following features: firstly, due to the high spatial resolution of samples of space-time light modulators (up to 10 million pixels), it is possible to measure aberrations with high accuracy, and secondly, the method is implemented in any scheme using a space-time light modulator, such as coherent Fourier processor schemes, without additional complications.

As of November 1, 2022, scientists have already created a prototype of the device, which is called the "Holographic Wave Front Sensor with a Controlled Phase Modulator."

The results of the research have already been published in a number of scientific journals and a publication in the journal Photonics is being prepared.