Browsing by Author "Gopinath, Shivasubramanian"

Now showing 1 - 20 of 30

3D incoherent imaging using an ensemble of sparse self-rotating beams
(Optics Express, 2023) Bleahu, Andrei-ioan; Gopinath, Shivasubramanian; Kahro, Tauno; Angamuthu, Praveen Periyasamy; Rajeswary, Aravind Simon John Francis; Prabhakar, Shashi; Kumar, Ravi; Salla, Gangi Reddy; Singh, Ravindra P.; Kukli, Kaupo; Tamm, Aile; Rosen, Joseph; Anand, Vijayakumar
Interferenceless coded aperture correlation holography (I-COACH) is one of the simplest incoherent holography techniques. In I-COACH, the light from an object is modulated by a coded mask, and the resulting intensity distribution is recorded. The 3D image of the object is reconstructed by processing the object intensity distribution with the pre-recorded 3D point spread intensity distributions. The first version of I-COACH was implemented using a scattering phase mask, which makes its implementation challenging in light-sensitive experiments. The I-COACH technique gradually evolved with the advancement in the engineering of coded phase masks that retain randomness but improve the concentration of light in smaller areas in the image sensor. In this direction, I-COACH was demonstrated using weakly scattered intensity patterns, dot patterns and recently using accelerating Airy patterns, and the case with accelerating Airy patterns exhibited the highest SNR. In this study, we propose and demonstrate I-COACH with an ensemble of self-rotating beams. Unlike accelerating Airy beams, self-rotating beams exhibit a better energy concentration. In the case of self-rotating beams, the uniqueness of the intensity distributions with depth is attributed to the rotation of the intensity pattern as opposed to the shifts of the Airy patterns, making the intensity distribution stable along depths. A significant improvement in SNR was observed in optical experiments.
4D imaging using accelerating airy beams and nonlinear reconstruction
(2023) Bleahu, Andrei; Gopinath, Shivasubramanian; Anand, Vijayakumar; Rosen, Joseph; Juodkazis, Saulius; Tamm, Aile; Kukli, Kaupo; Rajeswary, Aravind Simon John Francis; Katkus, Tomas; Pristy, Agnes; Ng, Soon Hock; Praveen, P. A.; Kahro, Tauno; Smith, Daniel; Arokiaraj, Francis Gracy; Kumar, Ravi
Deep Deconvolution of Object Information Modulated by a Refractive Lens Using Lucy-Richardson-Rosen Algorithm
(2022) Praveen, P.A.; Arockiaraj, Francis Gracy; Gopinath, Shivasubramanian; Smith, Daniel; Kahro, Tauno; Valdma, Sandhra-Mirella; Bleahu, Andrei; Ng, Soon Hock; Reddy, Andra Naresh Kumar; Katkus, Tomas; Rajeswary, Aravind Simon John Francis; Ganeev, Rashid A.; Pikker, Siim; Kukli, Kaupo; Tamm, Aile; Juodkazis, Saulius; Anand, Vijayakumar
A refractive lens is one of the simplest, most cost-effective and easily available imaging elements. Given a spatially incoherent illumination, a refractive lens can faithfully map every object point to an image point in the sensor plane, when the object and image distances satisfy the imaging conditions. However, static imaging is limited to the depth of focus, beyond which the point-to-point mapping can only be obtained by changing either the location of the lens, object or the imaging sensor. In this study, the depth of focus of a refractive lens in static mode has been expanded using a recently developed computational reconstruction method, Lucy-Richardson-Rosen algorithm (LRRA). The imaging process consists of three steps. In the first step, point spread functions (PSFs) were recorded along different depths and stored in the computer as PSF library. In the next step, the object intensity distribution was recorded. The LRRA was then applied to deconvolve the object information from the recorded intensity distributions during the final step. The results of LRRA were compared with two well-known reconstruction methods, namely the Lucy-Richardson algorithm and non-linear reconstruction.
Engineering axial resolution realtime and postrecording of incoherent holograms using hybridization techniques
(2024) Gopinath, Shivasubramanian; Rajeswary, Aravind Simon John Francis; Anand, Vijayakumar
Enhanced design of multiplexed coded masks for Fresnel incoherent correlation holography
(Scientific Reports, 2023) Gopinath, Shivasubramanian; Bleahu, Andrei; Kahro, Tauno; Rajeswary, Aravind Simon John Francis; Kumar, Ravi; Kukli, Kaupo; Tamm, Aile; Rosen, Joseph; Anand, Vijayakumar
Fresnel incoherent correlation holography (FINCH) is a well-established incoherent digital holography technique. In FINCH, light from an object point splits into two, differently modulated using two diffractive lenses with different focal distances and interfered to form a self-interference hologram. The hologram numerically back propagates to reconstruct the image of the object at different depths. FINCH, in the inline configuration, requires at least three camera shots with different phase shifts between the two interfering beams followed by superposition to obtain a complex hologram that can be used to reconstruct an object’s image without the twin image and bias terms. In general, FINCH is implemented using an active device, such as a spatial light modulator, to display the diffractive lenses. The first version of FINCH used a phase mask generated by random multiplexing of two diffractive lenses, which resulted in high reconstruction noise. Therefore, a polarization multiplexing method was later developed to suppress the reconstruction noise at the expense of some power loss. In this study, a novel computational algorithm based on the Gerchberg-Saxton algorithm (GSA) called transport of amplitude into phase (TAP-GSA) was developed for FINCH to design multiplexed phase masks with high light throughput and low reconstruction noise. The simulation and optical experiments demonstrate a power efficiency improvement of ~ 150 and ~ 200% in the new method in comparison to random multiplexing and polarization multiplexing, respectively. The SNR of the proposed method is better than that of random multiplexing in all tested cases but lower than that of the polarization multiplexing method.
Enhanced design of pure phase greyscale diffractive optical elements by phase-retrieval-assisted multiplexing of complex functions
(2023) Gopinath, Shivasubramanian; Bleahu, Andrei; Kahro, Tauno; Rajeswary, Aravind Simon John Francis; Kumar, Ravi; Kukli, Kaupo; Tamm, Aile; Rosen, Joseph; Anand, Vijayakumar
Enhanced design of pure phase greyscale diffractive optical elements by phase-retrieval-assisted multiplexing of complex functions
(Society of Photo-Optical Instrumentation Engineers (SPIE), 2023) Gopinath, Shivasubramanian; Bleahu, Andrei; Kahro, Tauno; Rajeswary, Aravind Simon John Francis; Kumar, Ravi
Extending the Depth of Focus of Infrared Microscope Using a Binary Axicon Fabricated on Barium Fluoride
(2024) Han, Molong; Smith, Daniel; Kahro, Tauno; Stonytė, Dominyka; Kasikov, Aarne; Gailevičius, Darius; Tiwari, Vipin; Xavier, Agnes Pristy Ignatius; Gopinath, Shivasubramanian; Ng, Soon Hock; Rajeswary, Aravind Simon John Francis; Tamm, Aile; Kukli, Kaupo
Axial resolution is one of the most important characteristics of a microscope. In all microscopes, a high axial resolution is desired in order to discriminate information efficiently along the longitudinal direction. However, when studying thick samples that do not contain laterally overlapping information, a low axial resolution is desirable, as information from multiple planes can be recorded simultaneously from a single camera shot instead of plane-by-plane mechanical refocusing. In this study, we increased the focal depth of an infrared microscope non-invasively by introducing a binary axicon fabricated on a barium fluoride substrate close to the sample. Preliminary results of imaging the thick and sparse silk fibers showed an improved focal depth with a slight decrease in lateral resolution and an increase in background noise.
Faithful Transfer of 3D Propagation Characteristics of Deterministic and Random Optical Fields to Coded Aperture Imaging Systems Using Lucy-Richardson-Rosen Algorithm
(2023 International Conference on Next Generation Electronics (NEleX), 2023) Xavier, Agnes Pristy Ignatius; Arockiaraj, Francis Gracy; Gopinath, Shivasubramanian; Rajeswary, Aravind Simon John Francis; Reddy, Andra Naresh Kumar; Ganeev, Rashid A.; Singh, M. Scott Arockia; Tania, S.D. Milling; Anand, Vijayakumar
Engineering the complex amplitude and polarization of light is essential for various applications. In this direction, many deterministic and random optical beams such as Airy Bessel, and self-rotating beams were developed. While the above beams satisfied the requirements for the targeted applications, they are not suitable for imaging applications in spite of the valuable axial characteristics they possess, as they are not effective object-image mapping elements. Consequently, when exotic beams were implemented for direct imaging, only a distorted image was obtained. However, the scenario is different in coded aperture imaging (CAI) methods, where the imaging mode is indirect, consisting of optical recording and computational image recovery. Therefore, the point spread function (PSF) in CAI is not the recorded intensity distribution but the reconstructed intensity distribution. By employing a suitable computational reconstruction method, it is possible to convert the recorded intensity distribution into a Delta-like function. In this study, Lucy-Richardson-Rosen algorithm has been implemented as a generalized image recovery method for a wide range of optical beams, and the performance is validated in both simulation and optical experiments.
Fresnel incoherent correlation holography with Lucy-Richardson-Rosen algorithm and modified Gerchberg-Saxton algorithm
(2023) Anand, Vijayakumar; Juodkazis, Saulius; Rajeswary, Aravind Simon John Francis; Arockiaraj, Francis Gracy; Gopinath, Shivasubramanian; Bleahu, Andrei
Fresnel incoherent correlation holography with Lucy-Richardson-Rosen algorithm and modified Gerchberg-Saxton algorithm
(Society of Photo-Optical Instrumentation Engineers (SPIE), 2023) Bleahu, Andrei; Gopinath, Shivasubramanian; Arockiaraj, Francis Gracy; Rajeswary, Aravind Simon John Francis; Juodkazis, Saulius
Holographic solution to a fundamental problem in diffractive optics: resolution beyond diffraction and lithography limits
(2023) Bleahu, Andrei; Gopinath, Shivasubramanian; Xavier, Agnes Pristy Ignatius; Kahro, Tauno; Reddy, Andra Naresh Kumar; Arockiaraj, Francis Gracy; Smith, Daniel; Ng, Soon Hock; Katkus, Tomas; Rajeswary, Aravind Simon John Francis; Angamuthu, Praveen Periyasami; Pikker, Siim; Kukli, Kaupo; Tamm, Aile; Juodkazis, Saulius; Rosen, Joseph; Anand, Vijayakumar
Implementation of a Large-Area Diffractive Lens Using Multiple Sub-Aperture Diffractive Lenses and Computational Reconstruction
(Licensee MDPI, 2022) Gopinath, Shivasubramanian; Praveen, Periyasamy Angamuthu; Kahro, Tauno; Bleahu, Andrei-Ioan; Arockiaraj, Francis Gracy; Smith, Daniel; Ng, Soon Hock; Juodkazis, Saulius; Kukli, Kaupo; Tamm, Aile; Anand, Vijayakumar
Direct imaging systems that create an image of an object directly on the sensor in a single step are prone to many constraints, as a perfect image is required to be recorded within this step. In designing high resolution direct imaging systems with a diffractive lens, the outermost zone width either reaches the lithography limit or the diffraction limit itself, imposing challenges in fabrication. However, if the imaging mode is switched to an indirect one consisting of multiple steps to complete imaging, then different possibilities open. One such method is the widely used indirect imaging method with Golay configuration telescopes. In this study, a Golay-like configuration has been adapted to realize a large-area diffractive lens with three sub-aperture diffractive lenses. The sub-aperture diffractive lenses are not required to collect light and focus them to a single point as in a direct imaging system, but to focus independently on different points within the sensor area. This approach of a Large-Area Diffractive lens with Integrated Sub-Apertures (LADISA) relaxes the fabrication constraints and allows the sub-aperture diffractive elements to have a larger outermost zone width and a smaller area. The diffractive sub-apertures were manufactured using photolithography. The fabricated diffractive element was implemented in indirect imaging mode using non-linear reconstruction and the Lucy–Richardson–Rosen algorithm with synthesized point spread functions. The computational optical experiments revealed improved optical and computational imaging resolutions compared to previous studies.
Implementation of a Large-Area Diffractive Lens Using Multiple Sub-Aperture Diffractive Lenses and Computational Reconstruction
(2023) Gopinath, Shivasubramanian; Angamuthu, Praveen Periysamy; Kahro, Tauno; Bleahu, Andrei; Arockiaraj, Francis Gracy; Smith, Daniel; Hock Ng, Soon; Juodkazis, Saulius; Kukli, Kaupo; Tamm, Aile; Anand, Vijayakumar
Direct imaging systems that create an image of an object directly on the sensor in a single step are prone to many constraints, as a perfect image is required to be recorded within this step. In designing high resolution direct imaging systems with a diffractive lens, the outermost zone width either reaches the lithography limit or the diffraction limit itself, imposing challenges in fabrication. However, if the imaging mode is switched to an indirect one consisting of multiple steps to complete imaging, then different possibilities open. One such method is the widely used indirect imaging method with Golay configuration telescopes. In this study, a Golay-like configuration has been adapted to realize a large-area diffractive lens with three sub-aperture diffractive lenses. The sub-aperture diffractive lenses are not required to collect light and focus them to a single point as in a direct imaging system, but to focus independently on different points within the sensor area. This approach of a Large-Area Diffractive lens with Integrated Sub-Apertures (LADISA) relaxes the fabrication constraints and allows the sub-aperture diffractive elements to have a larger outermost zone width and a smaller area. The diffractive sub-apertures were manufactured using photolithography. The fabricated diffractive element was implemented in indirect imaging mode using non-linear reconstruction and the Lucy–Richardson–Rosen algorithm with synthesized point spread functions. The computational optical experiments revealed improved optical and computational imaging resolutions compared to previous studies.
Improved Classification of Blurred Images with Deep-Learning Networks Using Lucy-Richardson-Rosen Algorithm
(Licensee MDPI, 2023) Jayavel, Amudhavel; Gopinath, Shivasubramanian; Angamuthu, Praveen Periyasamy; Arockiaraj, Francis Gracy; Bleahu, Andrei; Xavier, Agnes Pristy Ignatius; Smith, Daniel; Han, Molong; Slobozhan, Ivan; Ng, Soon Hock; Katkus, Tomas; Rajeswary, Aravind Simon John Francis; Sharma, Rajesh; Juodkazis, Saulius; Anand, Vijayakumar
Pattern recognition techniques form the heart of most, if not all, incoherent linear shift-invariant systems. When an object is recorded using a camera, the object information is sampled by the point spread function (PSF) of the system, replacing every object point with the PSF in the sensor. The PSF is a sharp Kronecker Delta-like function when the numerical aperture (NA) is large with no aberrations. When the NA is small, and the system has aberrations, the PSF appears blurred. In the case of aberrations, if the PSF is known, then the blurred object image can be deblurred by scanning the PSF over the recorded object intensity pattern and looking for pattern matching conditions through a mathematical process called correlation. Deep learning-based image classification for computer vision applications gained attention in recent years. The classification probability is highly dependent on the quality of images as even a minor blur can significantly alter the image classification results. In this study, a recently developed deblurring method, the Lucy-Richardson-Rosen algorithm (LR2A), was implemented to computationally refocus images recorded in the presence of spatio-spectral aberrations. The performance of LR2A was compared against the parent techniques: Lucy-Richardson algorithm and non-linear reconstruction. LR2A exhibited a superior deblurring capability even in extreme cases of spatio-spectral aberrations. Experimental results of deblurring a picture recorded using high-resolution smartphone cameras are presented. LR2A was implemented to significantly improve the performances of the widely used deep convolutional neural networks for image classification.
Modulating Axial Resolutions of Scenes Recorded Incoherently Using Cubic Phase Masks by Chaos-Engineering
(2023 International Conference on Next Generation Electronics (NEleX), 2023) Gopinath, Shivasubramanian; Anand, Vijayakumar
Axial and lateral resolutions form the cornerstones of any imaging system including coded aperture imaging systems. The above characteristics are intertwined and it is not possible to change one characteristic without affecting the other using conventional means i.e., by changing the numerical aperture. Recently, using computational imaging concepts, the interdependency between lateral and axial resolutions was broken and axial resolution was tuned without affecting the lateral resolution. However, the above capability is possible only by engineering of coded phase masks before recording and impossible after completing the recording process. In this study, we propose and demonstrate a novel computational imaging method that allows to tune axial resolution with a constant lateral resolution after completing the recording process. A total of four unique cubic phase masks (CPMs) were designed for generating Airy patterns with different 3D paths relatively chaotic with respect to one another. The 4 CPMs were used to record the point spread and object intensity patterns. The axial resolution was tuned by creating synthetic point spread and object intensity patterns by summing the patterns recorded using different CPMs. The axial resolution improved with an increase in chaos that is proportional to the number of patterns that were summed to create the synthetic patterns. The object is reconstructed using Lucy-Richardson-Rosen algorithm. Experimental studies were carried out to confirm the capability to tune axial resolution of pictures post recording.
Nonlinear Reconstruction of Images from Patterns Generated by Deterministic or Random Optical Masks—Concepts and Review of Research
(Journal of Imaging, 2022) Smith, Daniel; Gopinath, Shivasubramanian; Arockiaraj, Francis Gracy; Reddy, Andra Naresh Kumar; Balasubramani, Vinoth; Kumar, Ravi; Dubey, Nitin; Ng, Soon Hock; Katkus, Tomas; Selva, Shakina Jothi; Renganathan, Dhanalakshmi; Kamalam, Manueldoss Beaula Ruby; Rajeswary, Aravind Simon John Francis; Navaneethakrishnan, Srinivasan; Inbanathan, Stephen Rajkumar; Valdma, Sandhra-Mirella; Praveen, Periyasamy Angamuthu; Amudhavel, Jayavel; Kumar, Manoj; Ganeev, Rashid A.; Magistretti, Pierre J.; Depeursinge, Christian; Juodkazis, Saulius; Rosen, Joseph; Anand, Vijayakumar
Indirect-imaging methods involve at least two steps, namely optical recording and computational reconstruction. The optical-recording process uses an optical modulator that transforms the light from the object into a typical intensity distribution. This distribution is numerically processed to reconstruct the object’s image corresponding to different spatial and spectral dimensions. There have been numerous optical-modulation functions and reconstruction methods developed in the past few years for different applications. In most cases, a compatible pair of the optical-modulation function and reconstruction method gives optimal performance. A new reconstruction method, termed nonlinear reconstruction (NLR), was developed in 2017 to reconstruct the object image in the case of optical-scattering modulators. Over the years, it has been revealed that the NLR can reconstruct an object’s image modulated by an axicons, bifocal lenses and even exotic spiral diffractive elements, which generate deterministic optical fields. Apparently, NLR seems to be a universal reconstruction method for indirect imaging. In this review, the performance of NLR is investigated for many deterministic and stochastic optical fields. Simulation and experimental results for different cases are presented and discussed
Optimizing the temporal and spatial resolutions and light throughput of Fresnel incoherent correlation holography in the framework of coded aperture imaging
(2024) Arockiaraj, Francis Gracy; Xavier, Agnes Pristy Ignatius; Gopinath, Shivasubramanian; Rajeswary, Aravind Simon John Francis; Juodkazis, Saulius; Anand, Vijayakumar
Fresnel incoherent correlation holography (FINCH) is a well-established digital holography technique for 3D imaging of objects illuminated by spatially incoherent light. FINCH has a higher lateral resolution of 1.5 times that of direct imaging systems with the same numerical aperture. However, the other imaging characteristics of FINCH, such as axial resolution, temporal resolution, light throughput, and signal-to-noise ratio (SNR), are lower than those of direct imaging systems. Different techniques were developed by researchers around the world to improve the imaging characteristics of FINCH while retaining the inherent higher lateral resolution of FINCH. However, most of the solutions developed to improve FINCH presented additional challenges. In this study, we optimized FINCH in the framework of coded aperture imaging. Two recently developed computational methods, such as transport of amplitude into phase based on the Gerchberg Saxton algorithm and Lucy–Richardson–Rosen algorithm, were applied to improve light throughput and image reconstruction, respectively. The above implementation improved the axial resolution, temporal resolution, and SNR of FINCH and moved them closer to those of direct imaging while retaining the high lateral resolution. A point spread function (PSF) engineering technique has been implemented to prevent the low lateral resolution problem associated with the PSF recorded using pinholes with a large diameter. We believe that the above developments are beyond the state-of-the-art of existing FINCH-scopes.
Post-ensemble generation with Airy beams for spatial and spectral switching in incoherent imaging
(Optica Publishing Group, 2024) Gopinath, Shivasubramanian; Anand, Vijayakumar
Spatial, temporal, and spectral resolutions and field-of-view are important characteristics of any imaging system. In most, if not all, it is impossible to change the above characteristics after recording a digital picture, video, or hologram. In recent years, there have been investigations on the possibilities to change the above characteristics post-recording. In this Letter, for the first time, to the best of our knowledge, we report novel recording and reconstruction methods built upon the principles of coded aperture imaging that allow changing the axial and spectral resolutions post-recording. We named this method—post-ensemble generation with Airy beams for spatial and spectral switching (PEGASASS). In PEGASASS, light from an object point is converted into Airy beams and recorded such that every recording has a unique Airy pattern. An ensemble of Airy patterns is constructed post-recording and the axial and spectral resolutions are tuned by controlling the chaos in the ensemble. The above tunability is achieved without adversely affecting the lateral resolution. Proof-of-concept experimental results of PEGASASS in 3D in both (x,y,z) and (x,y,λ) and 4D in (x,y,z,λ) are presented. We believe that PEGASASS has the potential to revolutionize the field of imaging and holography.
Preface: International Conference on Holography Meets Advanced Manufacturing (HMAM2)
(2023) Anand, Vijayakumar; Jayavel, Amudhavel; Palm, Viktor; Gopinath, Shivasubramanian; Bleahu, Andrei; Rajeswary, Aravind Simon John Francis; Kukli, Kaupo; Balasubramani, Vinoth; Smith, Daniel; Ng, Soon Hock; Juodkazis, Saulius
The CIPHR group, Institute of Physics, University of Tartu, Estonia, and Optical Sciences Center, Swinburne University of Technology, Australia, jointly organized the interdisciplinary online conference “Holography Meets Advanced Manufacturing” during 20–22 February 2023.