Dr. Sabyasachi Chattopadhyay Profile

Dr. Sabyasachi Chattopadhyay

at South African Astronomical Obs

SPIE Involvement:

Author

Publications (18)

Proceedings Article | 29 August 2022 Poster + Paper

Performance testing and end-to-end mapping of the fiber cable on the SALT NIR integral field spectrograph

Joshua Oppor, Matthew A. Bershady, Marsha J. Wolf, Michael P. Smith, Sabyasachi Chattopadhyay, Kurt Jaehnig, Jeffrey Percival, Mark Mulligan, Kathleen Jurgella, Briana Wirag

Proceedings Volume 12188, 121885P (2022) https://doi.org/10.1117/12.2630176

KEYWORDS: Polishing, Spectrographs, Surface finishing, Epoxies, Telescopes, Prototyping, Near infrared, Calibration, Collimators, Fiber optics

Read Abstract +

Proceedings Article | 29 August 2022 Poster + Paper

The design and construction of the fiber instrument feed for the SALT NIR integral field spectrograph

Michael P. Smith, Joshua E. Oppor, Matthew A. Bershady, Marsha J. Wolf, Sabyasachi Chattopadhyay, Kurt Jaehnig, Jeffrey Percival, Mark Mulligan, Kathleen Jurgella, Briana Wirag, Andromeda Swissdorf

Proceedings Volume 12188, 121885N (2022) https://doi.org/10.1117/12.2630399

KEYWORDS: Spectrographs, Telescopes, Near infrared, Polishing, Mirrors, Collimators, Astatine, Observatories, Interfaces, Astronomy

Read Abstract +

Proceedings Article | 29 August 2022 Paper

Design and fabrication of a silicon based micro fiber holder for DOTIFS Integral field unit and associated IFU tests

Annu Jacob, A. N. Ramaprakash, Chaitanya Rajarshi, Pravin Khodade, Hillol Das, Sabyasachi Chattopadhyay, Amitesh Omar

Proceedings Volume 12184, 121847D (2022) https://doi.org/10.1117/12.2629966

KEYWORDS: Semiconducting wafers, Spectrographs, Polishing, Microlens, Photomasks, Optical alignment, Manufacturing, Cameras, Calibration, Optical fibers

Read Abstract +

Devasthal Optical Telescope Integral Field Spectrograph (DOTIFS) is a new multi-object integral field spectrograph being built by the Inter-University Centre for Astronomy and Astrophysics (IUCAA), Pune, India for the 3.6m Devasthal Optical Telescope, (DOT). Spectrographs, which disperse the light to study various aspects of the source, traditionally follow long slit to enter the light into to the instrument. However, varying slit width, atmospheric dispersion, crowded object field etc, causes this approach to lose its efficiency. A 2D field access using optical fibres solves most of these issues and introduces additional modularity. However, the circular shape of the fibre tip causes light loss as the fill factor < 80 %. There are mainly two ways to solve these issues, one is with 2D field splicers which are usually mirrors which break the field and reflect the beams in different directions, the other a more convenient alternative is using micro lens arrays (MLA) coupled with optical fibres, increasing the fill factor < 90 %. Even with this advantage, the miss alignment of the optical fibre with the MLA can cause increase in optical entropy and hence loss of effective transmission. Therefore, making a precise fiber to micro-lenslet array holder is a necessity. In DOTIFS which uses a combination of MLA and fibers to transmit the light, the IFU unit of the spectrograph consist of fiber array held on a mask and glued to a micro lenslet array. The plano-convex MLA (PCMLA) forms a hexagonal honeycomb structure of 12×12 spaxels. The on-sky footprint of an IFU is designed to be 8.7”×7.4” for a spatial sampling of 0.8”/300µm. The PCMLA has a thickness of 2.32 mm to create the pupil at its flat surface where fibers would be butted to sample the pupil. Each microlens curved side will receive a f/21.486 beam from the magnifier optics assembly sitting between IFU assembly and the Cassegrain side port selection mirror of the telescope. The microlens converts the incoming beam from the magnifier to f/4.5 beam and creates an ideal pupil of 76µm diameter at its at back surface. In this paper we present deep reactive ion etching technique based fibre holder manufacturing for holding the fibres of IFU of DOTIFS spectrograph. We present the design details, fiber routing scheme, manufacturing and gluing and polishing concepts for fibre holder and the tests and results on the IFU deployment system.

Proceedings Article | 29 August 2022 Poster + Paper

Slit mask integral field units for the Southern African Large Telescope

Sabyasachi Chattopadhyay, Matthew Bershady, Marsha Wolf, Michael Smith

Proceedings Volume 12184, 121845V (2022) https://doi.org/10.1117/12.2629826

KEYWORDS: Polishing, Spectrographs, Spectral resolution, Prisms, Received signal strength, Telescopes, Large telescopes, Beam splitters, Galactic astronomy, Collimators

Read Abstract +

SPIE Journal Paper | 5 May 2022

Optimum telescope focal ratios for microlens-to-fiber coupled integral field spectrographs

Sabyasachi Chattopadhyay, Matthew Bershady, Marsha Wolf, Michael Smith

JATIS, Vol. 8, Issue 02, 025001, (May 2022) https://doi.org/10.1117/12.10.1117/1.JATIS.8.2.025001

KEYWORDS: Telescopes, Microlens, Diffraction, Spectrographs, Zemax, Performance modeling, Manufacturing, Systems modeling, Monochromatic aberrations, Collimators

Read Abstract +

Proceedings Article | 16 December 2020 Poster + Presentation + Paper

Optimization of telescope focal ratios for MLA-fiber coupled integral field units

Sabyasachi Chattopadhyay, Matthew Bershady, Marsha Wolf, Michael Smith

Proceedings Volume 11451, 1145168 (2020) https://doi.org/10.1117/12.2562900

KEYWORDS: Telescopes, Optical fibers, Spectrographs, Spectroscopy, Astronomical imaging, Field spectroscopy, Imaging spectroscopy, Step index fibers, Manufacturing, Optical components

Read Abstract +

Proceedings Article | 13 December 2020 Poster + Presentation + Paper

The prototype telescope and spectrograph system for the AMASE project

Renbin Yan, Matthew Bershady, Michael Smith, Nicholas MacDonald, Dmitry Bizyaev, Kevin Bundy, Sabaysachi Chattopadhyay, James Gunn, Kyle Westfall, Marsha Wolf

Proceedings Volume 11447, 114478Y (2020) https://doi.org/10.1117/12.2563195

KEYWORDS: Spectrographs, Prototyping, Telescopes, Optical instrument design, Spectroscopy, Lenses, Field spectroscopy, Spatial resolution, Spectral resolution, CMOS sensors

Read Abstract +

Proceedings Article | 13 December 2020 Presentation + Paper

SDSS-V local volume mapper instrument: overview and status

Nicholas Konidaris, Niv Drory, Cynthia Froning, Anthony Hebert, Pavan Bilgi, Guillermo Blanc, Alicia Lanz, Charles Hull, Juna Kollmeier, Solange Ramirez, Stefanie Wachter, Kathryn Kreckel, Soojong Pak, Eric Pellegrini, Andrés Almeida, Scott Case, Ross Zhelem, Tobas Feger, Jon Lawrence, Michael Lesser, Tom Herbst, José Sanchez-Gallego, Matthew Bershady, Sabyasachi Chattopadhyay, Andrew Hauser, Michael Smith, Marsha Wolf, Renbin Yan

Proceedings Volume 11447, 1144718 (2020) https://doi.org/10.1117/12.2557565

KEYWORDS: Telescopes, Spectrographs, Spectroscopes, Stars, Solar system, Lanthanum, Observatories, Clouds, Spectral resolution, Atmospheric sciences

Read Abstract +

Proceedings Article | 13 December 2020 Poster + Paper

Development and characterization of a precisely adjustable fiber polishing arm

Michael Smith, Sabyasachi Chattopadhyay, Andrew Hauser, Joshua Oppor, Matthew Bershady, Marsha Wolf

Proceedings Volume 11451, 114516W (2020) https://doi.org/10.1117/12.2563201

KEYWORDS: Polishing, Surface finishing, Astronomy, Spectrographs, Inspection, Matrices, Near infrared, Spectral calibration, Calibration, Interfaces

Read Abstract +

SPIE Journal Paper | 27 June 2020 Open Access

Fiber positioning in microlens-fiber coupled integral field unit

Sabyasachi Chattopadhyay, Matthew Bershady, Marsha Wolf, Michael Smith, Andrew Hauser

JATIS, Vol. 6, Issue 02, 025002, (June 2020) https://doi.org/10.1117/12.10.1117/1.JATIS.6.2.025002

KEYWORDS: Etching, Semiconducting wafers, Microlens, Photoresist materials, Optical lithography, Silicon, Photomasks, Telescopes, Near field, Spectrographs

Read Abstract +

A generic fiber positioning strategy and a fabrication path are presented for microlens-fiber-coupled integral field units (IFUs). It is assumed that microlens-produced microimages are carried to the spectrograph input through a step-index, multimode fiber, but our results apply to micropupil reimaging applications as well. Considered are the performance trades between the filling percentage of the fiber core with the microimage versus throughput and observing efficiency. A merit function is defined as the product of the transmission efficiency and the étendue loss. For a hexagonal packing of spatial elements, the merit function has been found to be maximized to 94% of an ideal fiber IFU merit value (which has zero transmission loss and does not increase the étendue) with a microlens-fiber alignment (centering) tolerance of 1-μm RMS. The maximum acceptable relative tilt between the fiber and the microlens face has been analyzed through optical modeling and found to be 0.3 deg RMS for input f-ratio slower than f / 3.5, but it is much more relaxed for faster beams. From the acceptable tilt, we have deduced a minimum thickness of the fiber holder to be 3 mm for 5 μm clearance in hole diameter relative to the fiber outer diameter. Several options of fabricating fiber holders have been compared to identify cost-effective solutions that deliver the desired fiber positioning accuracy. Femto-second laser-drilling methods from commercial vendors deliver holes arrayed on plates with a relative position accuracy of ±1.5-μm RMS, similar diameter accuracy, and with an aspect ratio of 1:10 (diameter:thickness). One commercial vendor combines femtosecond laser-drilling with photolithographic etching to produce plates with thickness of 5 mm, but with similar (±1-μm RMS) positioning accuracy and conical entry ports. Both of these techniques are found to be moderately expensive. A purely photolithographic technique performed at Wisconsin Center for Advanced Microelectronics (a facility at the University of Wisconsin, Madison), in tandem with deep reactive ion etching, has been used to produce a repeatable recipe with 100% yield. Photolithography is more precise (0.5-μm RMS) in terms of hole positioning and similar diameter accuracy (1-μm RMS) but the plate can only have a thickness of 250 μm.

DOWNLOAD PAPER

SPIE Journal Paper | 11 July 2018

Noise characterization of IUCAA digital sampling array controller

Sabyasachi Chattopadhyay, A. N. Ramaprakash, Bhushan Joshi, Pravinkumar Chordia, Mahesh Burse, Kalpesh Chillal, Sakya Sinha, Sujit Punnadi, Ketan Rikame, Sungwook Hong, Dhruv Paranjpye, Haeun Chung, Changbom Park, Amitesh Omar

JATIS, Vol. 4, Issue 03, 036002, (July 2018) https://doi.org/10.1117/12.10.1117/1.JATIS.4.3.036002

KEYWORDS: Interference (communication), Charge-coupled devices, Electrons, Analog electronics, Clocks, Amplifiers, Power supplies, Sensors, Field programmable gate arrays, Statistical modeling

Read Abstract +

The IUCAA digital sampling array controller (IDSAC) is a flexible and generic yet powerful CCD controller that can handle a wide range of scientific detectors. Based on an easily scalable modular backplane architecture consisting of single board controllers (SBC), IDSAC can control large detector arrays and mosaics. Each of the SBCs offers the full functionality required to control a CCD independently. The SBCs can be cold swapped without the need to reconfigure them. IDSAC is also available in a backplane-less architecture. Each SBC can handle data from up to four video channels with or without dummy outputs at speeds up to 500-kilo pixels per second (kPPS) per channel with a resolution of 16 bits. Communication with a Linux-based host computer is through a USB3.0 interface, with the option of using copper or optical fibers. A field programmable gate array (FPGA) is used as the master controller in each SBC, which allows great flexibility in optimizing performance by adjusting gain, timing signals, bias levels, etc., using user-editable configuration files without altering the circuit topology. Elimination of thermal kTC noise is achieved via digital correlated double sampling (DCDS). The number of digital samples per pixel (for both reset and signal levels) is user configurable. We present the results of noise performance characterization of IDSAC through simulation, theoretical modeling, and actual measurements. The contribution of different types of noise sources is modeled using a tool to predict noise of a generic DCDS signal chain analytically. The analytical model predicts the net input referenced noise of the signal chain to be 5 electrons for 200-k pixels/s per channel readout rate with three samples per pixel. Using a cryogenic test setup in the lab, the noise is measured to be 5.4 e (24.3 μV), for the same readout configuration. With a better-optimized configuration of 500-kPPS readout rate, the measured noise is down to 3.8 electrons RMS (17 μV), with three samples per interval.

Proceedings Article | 10 July 2018 Paper

Multiple rooks of chess: a generic integral field unit deployment technique

Sabyasachi Chattopadhyay, A. Ramaprakash, Pravin Khodade, Kabir Chakravarti, Shabbir Shaikh, Haeun Chung, Sungwook Hong

Proceedings Volume 10706, 107065S (2018) https://doi.org/10.1117/12.2313798

KEYWORDS: Detection and tracking algorithms, Target acquisition, Telescopes, Robots, Space telescopes, Astronomy, Spectrographs, Computer simulations, Astronomical imaging

Read Abstract +

Proceedings Article | 10 July 2018 Presentation + Paper

A new photolithography based technique to mass produce microlens+fibre based integral field units (IFUs) for 2D spectroscopy

Sabyasachi Chattopadhyay, Vishal Joshi, A. Ramaprakash, Deepa Modi, Abhay Kohok, Haeun Chung

Proceedings Volume 10706, 107062D (2018) https://doi.org/10.1117/12.2313729

KEYWORDS: Photomasks, Optical lithography, Microlens array, Polishing, Microlens, Metals, Spectrographs, Ultraviolet radiation, Photoresist materials, Back illuminated sensors

Read Abstract +

Long-slit astronomical spectroscopy has various limitations when dealing with optimum slit width, atmospheric dispersion, extended source spectroscopy, etc. to name a few. Most of these issues can be solved by the use of optical fibers as the light carrier from the telescope focal plane to the spectrograph. The approach is technically and scientifically flexible in terms of instrument modularity and target acquisition. Implementation of Integral Field Unit (IFU) provides a continuous sampling of extended objects and has a distinct advantage over the single fiber. Using a microlens array in front of the fibers improves the sky coverage by increasing the fill factor. Devasthal Optical Telescope Integral Field Spectrograph (DOTIFS) is a novel instrument being built by the Inter-University Centre for Astronomy and Astrophysics, Pune for the 3.6m Devasthal Optical Telescope (DOT) constructed by Aryabhatta Research Institute of Observational Sciences, Nainital. Each of the 16 DOTIFS IFUs consist of 12x12 spatial elements (spaxels) distributed in a hexagonal honeycomb structure covering 8.7"x7.8" in the sky. Each IFU is made by a photolithography technique to transfer the corresponding microlens array pattern to create a mask which holds the fibers at the focal plane end of an integral field unit. These masks are aligned with the microlens array and fibers are inserted before gluing and polishing. The fiber array can be positioned with a peak positioning error less than 5 μm from the desired position within a fiber array, compared to a requirement of 10 μm. The slit end is made by wire EDM cutting technology and fibers are placed with an accuracy of ~0.3 pixels compared to a 6.75 pixel center-to-center gap between two spectra on the detector. In this paper we provide details of deriving requirements and error budgets. The process of photolithography and the use of generated masks to create an IFU are also discussed. The technique allows very cost effective mass production of IFUs which are very accurately matched with the corresponding microlens array.

Proceedings Article | 9 July 2018 Paper

DOTIFS: fore-optics and calibration unit design

Haeun Chung, A. Ramaprakash, Pravin Khodade, Chaitanya Rajarshi, Sabyasachi Chattopadhyay, Pravin Chordia, Amitesh Omar, Changbom Park

Proceedings Volume 10702, 107027U (2018) https://doi.org/10.1117/12.2312394

KEYWORDS: Calibration, Telescopes, Lamps, Mirrors, Integrating spheres, Spectrographs, Lenses, Light, Optical instrument design, Optomechanical design

Read Abstract +

Proceedings Article | 8 July 2018 Paper

DOTIFS: spectrograph optical and opto-mechanical design

Haeun Chung, A. N. Ramaprakash, Pravin Khodade, Deepa Modi, Chaitanya Rajarshi, Sabyasachi Chattopadhyay, Pravin Chordia, Vishal Joshi, Sungwook Hong, Amitesh Omar, Swara Ravindranath, Yong-Sun Park, Changbom Park

Proceedings Volume 10702, 107027A (2018) https://doi.org/10.1117/12.2311594

KEYWORDS: Spectrographs, Cameras, Charge-coupled devices, Optical design, Collimators, Optical filters, Spectral resolution, Tolerancing, Optomechanical design, Optical fibers, Thermal analysis

Read Abstract +

Proceedings Article | 27 July 2016 Paper

Evaluating noise performance of the IUCAA sidecar drive electronics controller (ISDEC) based system for TMT on-instrument wavefront sensing (OIWFS) application

Mahesh Burse, Sabyasachi Chattopadhyay, A. Ramaprakash, Sakya Sinha, Swapnil Prabhudesai, Sujit Punnadi, Pravin Chordia, Abhay Kohok

Proceedings Volume 9915, 991520 (2016) https://doi.org/10.1117/12.2232265

KEYWORDS: Sensors, Wavefront sensors, Control systems, Analog electronics, Multiplexers, Stars, Field programmable gate arrays, Power supplies, Electrons, Interfaces

Read Abstract +

Proceedings Article | 27 July 2016 Paper

IDSAC-IUCAA digital sampler array controller

Sabyasachi Chattopadhyay, Pravin Chordia, A. Ramaprakash, Mahesh Burse, Bhushan Joshi, Kalpesh Chillal

Proceedings Volume 9915, 991524 (2016) https://doi.org/10.1117/12.2232477

KEYWORDS: Charge-coupled devices, Video processing, Cadmium sulfide, Video, Analog electronics, Interference (communication), Clocks, Sensors, Power supplies, Signal to noise ratio

Read Abstract +

In order to run the large format detector arrays and mosaics that are required by most astronomical instruments, readout electronic controllers are required which can process multiple CCD outputs simultaneously at high speeds and low noise levels. These CCD controllers need to be modular and configurable, should be able to run multiple detector types to cater to a wide variety of requirements. IUCAA Digital Sampler Array Controller (IDSAC), is a generic CCD Controller based on a fully scalable architecture which is adequately flexible and powerful enough to control a wide variety of detectors used in ground based astronomy. The controller has a modular backplane architecture that consists of Single Board Controller Cards (SBCs) and can control up to 5 CCDs (mosaic or independent). Each Single Board Controller (SBC) has all the resources to a run Single large format CCD having up to four outputs. All SBCs are identical and are easily interchangeable without needing any reconfiguration. A four channel video processor on each SBC can process up to four output CCDs with or without dummy outputs at 0.5 Megapixels/Sec/Channel with 16 bit resolution. Each SBC has a USB 2.0 interface which can be connected to a host computer via optional USB to Fibre converters. The SBC uses a reconfigurable hardware (FPGA) as a Master Controller. IDSAC offers Digital Correlated Double Sampling (DCDS) to eliminate thermal kTC noise. CDS performed in Digital domain (DCDS) has several advantages over its analog counterpart, such as - less electronics, faster readout and easier post processing. It is also flexible with sampling rate and pixel throughput while maintaining the core circuit topology intact. Noise characterization of the IDSAC CDS signal chain has been performed by analytical modelling and practical measurements. Various types of noise such as white, pink, power supply, bias etc. has been considered while creating an analytical noise model tool to predict noise of a controller system like IDSAC. Several tests are performed to measure the actual noise of IDSAC. The theoretical calculation matches very well with practical measurements within 10% accuracy.

Proceedings Article | 18 July 2014 Paper

DOTIFS: a new multi-IFU optical spectrograph for the 3.6-m Devasthal optical telescope

Haeun Chung, A. Ramaprakash, Amitesh Omar, Swara Ravindranath, Sabyasachi Chattopadhyay, Chaitanya Rajarshi, Pravin Khodade

Proceedings Volume 9147, 91470V (2014) https://doi.org/10.1117/12.2053051

KEYWORDS: Spectrographs, Optical fibers, Galactic astronomy, Iterated function systems, Telescopes, Microlens, Charge-coupled devices, Optical telescopes, Software development, Astronomy

Read Abstract +

Showing 5 of 18 publications

View contact details

UPDATE YOUR PROFILE

Is this your profile? Update it now.

Sign into your SPIE.org account

Don’t have a profile and want one?

Create an account on SPIE.org

Keywords/Phrases

Search In:

Publication Years