Dr. Rakesh Kumar currently serves as Assistant Professor (Sl. Gr) at the Department of Electronics and Communication Engineering, Amrita School of Engineering, Amritapuri.

Rakesh Kumar obtained a doctorate in Optical Sciences & Engineering from the University of New Mexico in the USA in 2015, where his dissertation study was focused on three-dimensional imaging using pupil phase engineering. He got interested in Optics while pursuing Masters in Physics at IIT Delhi, and since then has worked in different fields in Optics such as Fiber Optic Telecommunication, Free space Laser Communication, Photovoltaics and Imaging Sciences. He brings with him a long academic as well as industrial experience.     


Publication Type: Conference Paper
Year of Publication Publication Type Title
2013 Conference Paper Kumar Rakesh and Sudhakar, P., “PSF ROTATION WITH CHANGING DEFOCUS AND APPLICATIONS TO 3D IMAGING FOR SPACE SITUATIONAL AWARENESS”, presented at the 09/2013, 2013.[Abstract]

By exploiting the notion of orbital angular momentum of light beams, we have recently demonstrated a novel pupil-phase-engineered point-spread function (PSF) design in which as a function of defocus the PSF merely rotates without changing its shape materially over a considerable range of defocus values. Here we explore general properties of the rotating PSF design with respect to 3D imaging, including trade-offs between transverse and longitudinal resolutions. We also present the results of simulation of reconstruction of 3D scenes consisting of point sources from noisy image data based on this design.

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2011 Conference Paper C. Alexander D., E., C. Jose, Paul, H., A., R. Glenn, Kumar Rakesh, K., K. Raymond, Deming, Z., M., R. Juan, Shelby, V., P.A., L. Vincent, James, G., and Adria, B., “Holographic CPV field tests at the Tucson Electric Power solar test yard”, in CONFERENCE RECORD OF THE IEEE PHOTOVOLTAIC SPECIALISTS CONFERENCE, 2011.[Abstract]

Holographic concentrators incorporated into PV modules were used to build a 1600 W grid-tied PV system at the Tucson Electric Power solar test yard. Holograms in concentrating photovoltaic (CPV) modules diffract light to increase irradiance on PV cells within each module. No tracking is needed for low concentration ratios, and the holographic elements are significantly less expensive than the PV cells. Additional advantages include bi-facial acceptance of light, reduced operating temperature, and increased cell efficiency. These benefits are expected to result in higher energy yields [kwh] per unit cost. Field tests of the holographic concentrator system are reported here. A performance ratio greater than 1 was observed. The field tests include comparison with other flat plate non-tracking PV systems at the same test yard. Predicted yields are also compared with the data. More »»
2010 Conference Paper C. Jose E., M., R. Juan, Starr, H. - C., Kumar Rakesh, and Glenn, R., “Reduced Temperature of Holographic Planar Concentrators”, in Imaging and Applied Optics Congress, 2010.[Abstract]

We present the temperature data for several examples of holographic planar concentrators. The extended holographic regions act as radiative transfer surfaces which reduce the temperature of the cells used with the concentrating film. More »»
2006 Conference Paper Kumar Rakesh, S., T. J., M., R. Bradley, and K., B. James, “Reducing IFOV Errors in Microgrid Imaging Polarimeters”, in Frontiers in Optics, Rochester, New York United States, 2006.[Abstract]

Microgrid polarimeters suffer from IFOV error, as two different pixels are used to obtain the Stokes parameter at a given point in the scene. We study interpolation techniques and hardware solutions to minimize this error. More »»
Publication Type: Journal Article
Year of Publication Publication Type Title
2007 Journal Article Kumar Rakesh, J., S. Tyob, and M., R. Bradley, “Motion-based nonuniformity correction in DoFP polarimeters”, PROCEEDINGS OF SPIE - THE INTERNATIONAL SOCIETY FOR OPTICAL ENGINEERING, vol. 6682, 2007.[Abstract]

Division of Focal Plane polarimeters (DoFP) operate by integrating an array of micropolarizer elements with a focal plane array. These devices have been investigated for over a decade, and example systems have been built in all regions of the optical spectrum. DoFP devices have the distinct advantage that they are mechanically rugged, inherently temporally synchronized, and optically aligned. They have the concomitant disadvantage that each pixel in the FPA has a different instantaneous field of view (IFOV), meaning that the polarization component measurements that go into estimating the Stokes vector across the image come from four different points in the field. In addition to IFOV errors, microgrid camera systems operating in the LWIR have the additional problem that FPA nonuniformity (NU) noise can be quite severe. The spatial differencing nature of a DoFP system exacerbates the residual NU noise that is remaining after calibration, and is often the largest source of false polarization signatures away from regions where IFOV error dominates. We have recently presented a scene based algorithm that uses frame-to-frame motion to compensate for NU noise in unpolarized IR imagers. In this paper, we have extended that algorithm so that it can be used to compensate for NU noise on a DoFP polarimeter. Furthermore, the additional information provided by the scene motion can be used to significantly reduce the IFOV error. We have found a reduction of IFOV error by a factor of 10 if the scene motion is known exactly. Performance is reduced when the motion must be estimated from the scene, but still shows a marked improvement over static DoFP images. More »»
2007 Journal Article R. Bradley M., Kumar Rakesh, J., S. Tyo, K., B. James, T., B. Wiley, and M., B. David, “Mitigation of image artifacts in LWIR microgrid polarimeter images”, ARTICLE in PROCEEDINGS OF SPIE - THE INTERNATIONAL SOCIETY FOR OPTICAL ENGINEERING, vol. 6682, 2007.[Abstract]

Microgrid polarimeters, also known as division of focal plane (DoFP) polarimeters, are composed of an integrated array of micropolarizing elements that immediately precedes the FPA. The result of the DoFP device is that neighboring pixels sense different polarization states. The measurements made at each pixel can be combined to estimate the Stokes vector at every reconstruction point in a scene. DoFP devices have the advantage that they are mechanically rugged and inherently optically aligned. However, they suffer from the severe disadvantage that the neighboring pixels that make up the Stokes vector estimates have different instantaneous fields of view (IFOV). This IFOV error leads to spatial differencing that causes false polarization signatures, especially in regions of the image where the scene changes rapidly in space. Furthermore, when the polarimeter is operating in the LWIR, the FPA has inherent response problems such as nonuniformity and dead pixels that make the false polarization problem that much worse. In this paper, we present methods that use spatial information from the scene to mitigate two of the biggest problems that confront DoFP devices. The first is a polarimetric dead pixel replacement (DPR) scheme, and the second is a reconstruction method that chooses the most appropriate polarimetric interpolation scheme for each particular pixel in the image based on the scene properties. We have found that these two methods can greatly improve both the visual appearance of polarization products as well as the accuracy of the polarization estimates, and can be implemented with minimal computational cost. More »»
2005 Journal Article B. M. Ratliff, Kumar Rakesh, Black, W., Boger, J. K., and J. Tyo, S., “Combatting infrared focal plane array nonuniformity noise in imaging polarimeters”, PROCEEDINGS OF SPIE - THE INTERNATIONAL SOCIETY FOR OPTICAL ENGINEERING, vol. 5888, 2005.[Abstract]

One of the most significant challenges in performing infrared (IR) polarimetery is the focal plane array (FPA) nonuniformity (NU) noise that is inherent in virtually all IR photodetector technologies that operate in the midwave IR (MWIR) or long-wave IR (LWIR). NU noise results from pixel-to-pixel variations in the repsonsivity of the photodetectors. This problem is especially severy in the microengineered IR FPA materials like HgCdTe and InSb, as well as in uncooled IR microbolometer sensors. Such problems are largely absent from Si based visible spectrum FPAs. The pixel response is usually a variable nonlinear response function, and even when the response is linearized over some range of temperatures, the gain and offset of the resulting response is usually highly variable. NU noise is normally corrected by applying a linear calibration to the data, but the resulting imagery still retains residual nonuniformity due to the nonlinearity of the photodetector responses. This residual nonuniformity is particularly troublesome for polarimeters because of the addition and subtraction operations that must be performed on the images in order to construct the Stokes parameters or other polarization products. In this paper we explore the impact of NU noise on full stokes and linear-polarization-only IR polarimeters. We compare the performance of division of time, division of amplitude, and division of array polarimeters in the presence of both NU and temporal noise, and assess the ability of calibration-based NU correction schemes to clean up the data. More »»
2005 Journal Article J. K. Boger, J. Tyo, S., Ratliff, B. M., Fetrow, M. P., Black, W. T., and Kumar Rakesh, “Modeling precision and accuracy of a LWIR microgrid array imaging polarimeter”, PROCEEDINGS OF SPIE - THE INTERNATIONAL SOCIETY FOR OPTICAL ENGINEERING, vol. 5888, 2005.[Abstract]

Long-wave infrared (LWIR) imaging is a prominent and useful technique for remote sensing applications. Moreover, polarization imaging has been shown to provide additional information about the imaged scene. However, polarization estimation requires that multiple measurements be made of each observed scene point under optically different conditions. This challenging measurement strategy makes the polarization estimates prone to error. The sources of this error differ depending upon the type of measurement scheme used. In this paper, we examine one particular measurement scheme, namely, a simultaneous multiple-measurement imaging polarimeter (SIP) using a microgrid polarizer array. The imager is composed of a microgrid polarizer masking a LWIR HgCdTe focal plane array (operating at 8.3-9.3 μm), and is able to make simultaneous modulated scene measurements. In this paper we present an analytical model that is used to predict the performance of the system in order to help interpret real results. This model is radiometrically accurate and accounts for the temperature of the camera system optics, spatial nonuniformity and drift, optical resolution and other sources of noise. This model is then used in simulation to validate it against laboratory measurements. The precision and accuracy of the SIP instrument is then studied. More »»
2004 Journal Article A. Kumar, Varshney, R. K., and Kumar Rakesh, “SMS fiber optic microbend sensor structures: effect of the modal interference”, Optics Communications, vol. 232, pp. 239 - 244, 2004.[Abstract]

We examine the effect of modal interference on the performance of a single mode–multimode–single mode (SMS) fiber optic microbend sensor structure. The study shows that if the coupling from higher order modes of the sensing multimode fiber to the lead-out single mode (SM) fiber is not zero, the output power and hence the microbend sensitivity of the structure depends strongly on the position of the microbends in the fiber. A simple experiment is carried out to study the above effect whose results agree very well with the theoretical predictions. More »»
2004 Journal Article S. T. M. and Kumar Rakesh, “2.5-Gbps amplified retro-modulator for free- space optical communications”, PROCEEDINGS OF SPIE - THE INTERNATIONAL SOCIETY FOR OPTICAL ENGINEERING, vol. 5550, 2004.[Abstract]

The results of experiments demonstrating the first amplified retro-modulated free-space optical communications link are presented. The amplifier increases the effective area of the retro-modulator by a factor of 318. The first experimental demonstration of a retro-modulator operating at a data rate of 2.5-Gbps is also presented. We will present the details of the experimental system, a simple theoretical model explaining the system performance, and the results of the first amplified retro-modulated link experiments. More »»
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