Reducing/cancelling the effects of vitreous floaters using a phase retrieval method based on coded diffraction patterns (2017 - 2020)

Project leader Varis Karitans

Agreement No

Research application No

The project goal is to develop a non-invasive optical system and method for reduction/cancellation of the undesired effects of the vitreous floaters. The vitreous floaters manifest themselves as chains, bubbles and other structures floating in the field of view. These structures are actually transparent phase diffraction gratings. This problem causing the visual discomfort is experienced by about 80 % of all people. The problem will be solved using the method of coded diffraction patterns to measure the structure of these objects and modulate the light so that the effects of the floaters are reduced. The method of coded diffraction patterns is one of the most popular numerical methods for measuring the phase and structure of objects. This method is suited for measuring the optical aberrations, determining the structure of complexes of proteins, structure of crystals and other purposes. During the project the applicability of this method for designing a new type of wavefront sensors in astronomy and determining the structure of objects floating in microfluidic systems will be evaluated. Such studies are essential for Latvian industry by facilitating development of high-tech products and companies.

The project will be realized at the Institute of Solid State Physics (ISSP) in collaboration with the optics laboratiry at the Dublin University College. The project will be multidisciplinary and will be realized in the field of innovative materials and technologies – natural sciences (1.1 Mathematics, 1.3 Physical sciences, 1.4 Chemical sciences) and engineering sciences and technologies (2.5 Materials engineering). The project activities are related to RIS3 as its goal corresponds to the specified directions of transformation of national economy and the 1st, 2nd, 3rd and 6th priority of the economic growth. The project matches the following specialization areas: 1) advanced materials, technologies and engineering systems; 2) Information and communication technologies and key technologies identified by EC (nanotechnologies, micro- and nano-electronics, photonics, advanced materials and manufacturing systems, biotechnologies).

The total duration of the project is 36 months, the total cost is 133,805.88 EUR.

Project progress

May 07, 2019

The applicability of the Gerchberg-Saxton algorithm and PhaseLift algorithm for phase retrieval depending on the optical and geometrical properties of wavefront modulators has been analyzed. An optical system for measuring the structure of a wavefront modulator using modulated information in several wavelengths has been planned. In March 2019, A revised manuscript discussing the results of the aforementioned activities has been submitted to the journal “Journal of Astronomical Telescopes, Instruments, and Systems”.

The Institute of Chemical Physics was attended where experience in modifying the surface of polydimethylsiloxane (PDMS) has been gained to improve the hydrophilicity of the surface and create strong bonding between PDMS and plastics. An eye model for simulating static vitreous floaters has been designed. The static floaters have been simulated using microstructures etched in glass. The microstructures have been formed using photolithography methods and etching the glass in a buffered fluoric acid. These microstructures have been measured and analyzed using the white light profiler Zygo NewView 7100. A manuscript discussing the results of the aforementioned activities is to be submitted to the journal “Optics Letters”.

An abstract has been prepared and submitted to the congress “Imaging and Applied Optics” organized by the Optical Society of America (OSA). The abstract was accepted in April, and the results will be presented as a poster in the congress. Posters have also been presented in the annual conference of the Institute of Solid State Physics and in the conference VISPEP in Vilnius. A popular scientific lecture about the activities of the postdoctoral project is being prepared for pupils of the Riga 94th secondary school. This lecture will be given as a part of a campaign “Back to school/Back to University 2019”. A list of optical/optomechanical/chemical materials necessary for the project has also been summarized.

Project progress

November 05, 2018

Thesis “Optical lithography for studying vitreous floaters” has been submitted to the International Symposium on Visual Physiology, Environment, and Perception “VISPEP 2018”. An oral presentation “Optical lithography for filtering images” about designing microstructures and filtering images has been presented to pupils in a seminar “Beta”. The method of phase retrieval to be used in the project has been discussed in an exhibition “Environment and Energy 2018”, Kipsala.

The Gerchberg-Saxton method for phase retrieval has been studied using differently defocused diffraction patterns. Parameters of copper (II) oxide CuO thin films have been optimized for reducing the coefficient of reflection and increasing the coefficient of absorption in the optical system. The technical document about designing wavefront modulators has been prepared and a poster “Wavefront Recovery From Intensity Measurements Using a Single Amplitude Modulating Mask” has been presented in an international conference “Functional Materials and Nanotechnologies 2018”.

Project progress

June 15, 2018

Studies on the method of coded diffraction patterns and aberrometry have been continued. Structures of various size and shape to be used for phase retrieval of the vitreous floaters in a model eye have been designed. Applicability of Zernike polynomials for filtering out the optical noise in the calculated wavefront has been studied. Results on analysis of aberrations have been presented in the 34th scientific conference of ISSP on 21.02.2018. and the scientific seminar of ISSP on 29.03.2018.

A research paper has been submitted to the proceedings of a SPIE conference “Optical Systems Design” (Frankfurt, Germany from 14.05.2018. to 17.05.2018.). The paper was published on 28.05.2018.

Varis Karitans; Edgars Nitiss; Andrejs Tokmakovs; Kaspars Pudzs. “Optical phase retrieval using four rotated versions of a single binary mask – simulation results”. Proc. SPIE 10694. DOI: 10.1117/12.2311861

Results on a study investigating detection of the vitreous floaters have been presented in the conference “Developments in Optics and Communications” (an invited talk: Simulation of Vitreous Floaters using an Eye Model with Microfluidics System).

Project progress

March 15, 2018

During the initial stages of the project the method of coded diffraction patterns has been customized to measure the structure of microoptical elements designed in a photoresistive layer. A good relation between the method of coded diffraction patterns and the non-contact profilometry has been proven. The method of coded diffraction patterns is realized using the photolithography method while the non-contact profilometry employs MATLAB tool LightPipes providing possibility to simulate propagation of a wavefront in a free space. In very near future a manuscript will be submitted to a journal of the Optical Society of America (OSA). In the manuscript, both methods will be compared.

Up to now, applicability of different plastics (PET, PVC etc.) for forming microfluidics contacts has also been analyzed. The strength of contacts between different plastics and polydimethylsiloxane (PDMS) has been determined. It has been observed that a good contact can be achieved using a non-modified polycarbonate (PC). Polyurethane bonds are formed on the PC surface and after being inserted in an ozone cleaner -OH groups are formed. In order to reduce aberrations in the microfluidics system, the eye model incorporating the microfluidics system has also been improved.

An optical system using 4 CMOS cameras are being developed so that 4 coded diffractions patterns can be measured at the same time thus reducing the measurement time. The MATLAB code calculating the structure of the object based on the intensity measurements has also been optimized. After optimization the computational time has been reduced very significantly.

The results obtained have been presented at the 34th annual conference of the Institute of Solid State Physics (ISSP). Thesis has also been submitted to a conference “Optical Systems Design” being held in May 2018 in Frankfurt, Germany. The thesis has been approved and the results will be reported in an oral presentation.