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We designed, fabricated and characterized a flat multi-level diffractive lens (MDL) comprised of only silicon with diameter = 15.2mm, focal length of 19mm, and operating over the longwave infrared (LWIR) spectrum of 8um to 14um. We experimentally demonstrated field of view of 46deg, depth of focus >7mm and wavelength-averaged Strehl ratio of 0.46. All these metrics were comparable to those of a conventional refractive lens. The active device thickness is only 8um and its weight (including the silicon substrate) is less than 0.2g.

In this work, we demonstrate three ultra-compact integrated-photonics devices, which are designed via a machine-learning algorithm coupled with finite-difference time-domain (FDTD) modeling. Through digitizing the design domain into "binary pixels" these digital metamaterials are readily manufacturable as well. By showing a variety of devices (beamsplitters and waveguide bends), we showcase the generality of our approach. With an area footprint smaller than ${\lambda_0}^2$, our designs are amongst the smallest reported to-date. Our method combines machine learning with digital metamaterials to enable ultra-compact, manufacturable devices, which could power a new "Photonics Moore's Law."

This letter reports proof-of-principle demonstration of 3D printable, low-cost, and compact THz spectral splitters based on diffractive optical elements (DOEs) designed to disperse the incident collimated broadband THz radiation (0.5 THz - 0.7 THz) at a pre-specified distance. Via inverse design, we show that it is possible to design such a diffractive optic, which can split the broadband incident spectrum in any desired fashion, as is evidenced from both FDTD simulations and measured intensity profiles using a 500-750 GHz VNA. Due to its straightforward construction without the usage of any movable parts, our approach, in principle, can have various applications such as in portable, low-cost spectroscopy as well as in wireless THz communication systems as a THz demultiplexer., Comment: This work has been submitted to the IEEE for possible publication. Copyright may be transferred without notice, after which this version may no longer be accessible

Multilevel diffractive lenses (MDLs) have emerged as an alternative to both conventional diffractive optical elements (DOEs) and metalenses for applications ranging from imaging to holographic and immersive displays. Recent work has shown that by harnessing structural parametric optimization of DOEs, one can design MDLs to enable multiple functionalities like achromaticity, depth of focus, wide-angle imaging, etc. with great ease in fabrication. Therefore, it becomes critical to understand how fabrication errors still do affect the performance of MDLs and numerically evaluate the trade-off between efficiency and initial parameter selection, right at the onset of designing an MDL, i.e., even before putting it into fabrication. Here, we perform a statistical simulation-based study on MDLs (primarily operating in the THz regime) to analyze the impact of various fabrication imperfections (single and multiple) on the final structure as a function of the number of ring height levels. Furthermore, we also evaluate the performance of these same MDLs with the change in the refractive index of the constitutive material. We use focusing efficiency as the evaluation criterion in our numerical analysis; since it is the most fundamental property that can be used to compare and assess the performance of lenses (and MDLs) in general designed for any application with any specific functionality., Comment: Initial manuscript version of the published article. Some comments were removed in the final published version at the discretion of the reviewers and not of the authors. However the authors would still like to include the discussion for the benefit of the optics community

Compound eyes found in insects provide intriguing sources of biological inspiration for miniaturized imaging systems. Inspired by such insect eye structures, we demonstrate an ultrathin arrayed camera enabled by a flat multilevel diffractive microlens array for super-resolution visible imaging. We experimentally demonstrated that the microlens array can achieve large fill factor (hexagonal close packing with pitch=120um), thickness of 2.6um, and diffraction-limited (strehl ratio = 0.88) achromatic performance in the visible band (450nm to 650nm). We also demonstrate super-resolution imaging with resolution improvement of 1.4 times by computationally merging 1600 images in the array.

We demonstrate an inverse designed achromatic, flat, polarization-insensitive diffractive optic element, i.e., multilevel diffractive lens (MDL), operating across a broadband range of UV light (250 nm - 400 nm) via numerical simulations. The simulated average on-axis focusing efficiency of the MDL is optimized to be as high as ~86%. We also investigate the off-axis focusing characteristics at different incident angles of the incoming UV radiation such that the MDL has a full field of view of 30 degrees. The simulated average off-axis focusing efficiency is ~67%, which is the highest reported till date for any chromatic or achromatic UV metalens or diffractive lens to the best of our knowledge. The designed MDL is composed of silicon nitride. The work reported herein will be useful for the miniaturization and integration of lightweight and compact UV optical systems., Comment: accepted for publication in OSA Continuum

It is generally thought that correcting chromatic aberrations in imaging requires multiple surfaces. Here, we show that by allowing the phase in the image plane of a flat lens to be a free parameter, it is possible to correct chromatic aberrations over a large continuous bandwidth with a single diffractive surface. We experimentally demonstrate imaging using a single flat lens of diameter > 3mm, focal length = 5mm (NA = 0.3, f/1.59) that is achromatic from 0.45um to 1um. This combination of size, NA and operating bandwidth has not been demonstrated in a flat lens before. We experimentally characterized the point-spread functions, off-axis aberrations and the broadband imaging performance. In contrast to conventional lens design, we utilize inverse design, where phase in the focal plane is treated as a free parameter. This approach attains a phase-only (lossless) pupil function, which can be implemented as a multi-level diffractive flat lens that achieves achromatic focusing and imaging., Comment: arXiv admin note: text overlap with arXiv:1907.06251

To date, various optimization algorithms have been employed to design and improve the performance of nanophotonic structures. Here, we propose to utilize a machine-learning algorithm viz. binary-Additive Reinforcement Learning Algorithm (b-ARLA) coupled with finite-difference time-domain (FDTD) simulations to design ultra-compact and efficient on-chip integrated nanophotonic 50:50 beam splitters (T-junctions). Here we present the design of two T-junction splitters each with a footprint of only 1.2 $\mu$m x 1.2 $\mu$m. To the best of our knowledge, these designs are amongst the smallest ever reported till date across either simulations or experiments. The simulated net power transmission efficiency for the first T-junction design is ~ 82% and the second design is ~ 80% $at 4\lambda = 1.55 \mu$m. We envision that the design methodology, as reported herein, would be useful in general for designing any efficient integrated-photonic device for optical communications systems.

Flat lenses enable thinner, lighter, and simpler imaging systems. However, large-area and high-NA flat lenses have been elusive due to computational and fabrication challenges. Here, we applied inverse design to create a multi-level diffractive lens (MDL) with thickness <1.35{\mu}m, diameter of 4.13mm, NA=0.9 at wavelength of 850nm. Since the MDL is created in polymer, it can be cost-effectively replicated via imprint lithography.

It is generally assumed that correcting chromatic aberrations in imaging requires optical elements. Here, we show that by allowing the phase in the image plane to be a free parameter, it is possible to correct chromatic variation of focal length over an extremely large bandwidth, from the visible (Vis) to the longwave infrared (LWIR) wavelengths using a single diffractive surface, i.e., a flat lens. Specifically, we designed, fabricated and characterized a flat, multi-level diffractive lens (MDL) with thickness {\pounds} 10{\mu}m, diameter ~1mm, and focal length = 18mm, which was constant over the operating bandwidth of l=0.45{\mu}m (blue) to 15{\mu}m (LWIR). We experimentally characterized the point-spread functions, aberrations and imaging performance of cameras comprised of this MDL and appropriate image sensors. We further show using simulations that such extreme achromatic MDLs can be achieved even at high numerical apertures (NA=0.81). By drastically increasing the operating bandwidth and eliminating several refractive lenses, our approach enables thinner, lighter and simpler imaging systems., Comment: arXiv admin note: substantial text overlap with arXiv:1907.06251

A lens performs an approximately one-to-one mapping from the object to the image planes. This mapping in the image plane is maintained within a depth of field (or referred to as depth of focus, if the object is at infinity). This necessitates refocusing of the lens when the images are separated by distances larger than the depth of field. Such refocusing mechanisms can increase the cost, complexity and weight of imaging systems. Here, we show that by judicious design of a multi-level diffractive lens (MDL) it is possible to drastically enhance the depth of focus, by over 4 orders of magnitude. Using such a lens, we are able to maintain focus for objects that are separated by as large as ~6m in our experiments. Specifically, when illuminated by collimated light at lambda=0.85mm, the MDL produced a beam that remained in focus from 5mm to ~1500mm from the MDL. The measured full-width at half-maximum of the focused beam varied from 6.6um (5mm away from MDL) to 524um (1500mm away from MDL). Since the sidelobes were well suppressed and the main-lobe was close to the diffraction-limit, imaging with a horizontal X vertical field of view of 20deg x 15deg over the entire focal range was demonstrated. This demonstration opens up a new direction for lens design, where by treating the phase in the focal plane as a free parameter, extreme depth-of-focus imaging becomes possible., Comment: arXiv admin note: text overlap with arXiv:1907.06251

We designed and fabricated a flat multi-level diffractive lens (MDL) that is achromatic in the SWIR band (875nm to 1675nm). The MDL had a focal length of 25mm, aperture diameter of 8.93mm and thickness of only 2.6um. By pairing the MDL with a SWIR image sensor, we also characterized its imaging performance in terms of the point-spread functions, modulation-transfer functions, and still and video imaging.

It is generally thought that correcting chromatic aberrations in imaging requires multiple surfaces. Here, we show that by allowing the phase in the image plane of a flat lens to be a free parameter, it is possible to correct chromatic aberrations over an almost unlimited bandwidth with a single diffractive surface. Specifically, we designed, fabricated and characterized a flat multi-level diffractive lens (MDL) that images at the wavelengths from 450nm to 850nm. We experimentally characterized the focusing efficiency, modulation-transfer function, wavefront aberrations, vignetting, distortion and signal-to-noise ratio performance of a camera comprised of this MDL and a conventional image sensor. Further, we designed two MDLs with operating wavelengths from 500nm to 15{\mu}m, and from 2{\mu}m to 150{\mu}m, respectively. With no apparent limitation in the operating bandwidth, such flat lenses could replace multiple refractive surfaces that are traditionally required for chromatic corrections, leading to thinner, lighter and simpler imaging systems with bandwidth limited primarily by the quantum efficiency of the sensor.

We experimentally demonstrate imaging in the longwave-infrared (LWIR) spectral band (8um to 12um) using a single polymer flat lens based upon multi-level diffractive optics. The device thickness is only 10{\mu}m, and chromatic aberrations are corrected over the entire LWIR band with one surface. Due to the drastic reduction in device thickness, we are able to utilize polymers with absorption in the LWIR, allowing for inexpensive manufacturing via imprint lithography. The weight of our lens is less than 100 times those of comparable refractive lenses. We fabricated and characterized two different flat lenses. Even with about 25% absorption losses, experiments show that our flat polymer lenses obtain good imaging with field of view of ~35degrees and angular resolution less than 0.013 degrees. The flat lenses were characterized with two different commercial LWIR image sensors. Finally, we show that by using lossless, higher-refractive-index materials like silicon, focusing efficiencies in excess of 70% can be achieved over the entire LWIR band. Our results firmly establish the potential for lightweight, ultra-thin, broadband lenses for high-quality imaging in the LWIR band.

Recently, there has been an explosion of interest in metalenses for imaging. The interest is primarily based on their sub-wavelength thicknesses. Diffractive lenses have been used as thin lenses since the late 19th century. Here, we show that multi-level diffractive lenses (MDLs), when designed properly can exceed the performance of metalenses. Furthermore, MDLs can be designed and fabricated with larger constituent features, making them accessible to low-cost, large area volume manufacturing, which is generally challenging for metalenses. The support substrate will dominate overall thickness for all flat optics. Therefore the advantage of a slight decrease in thickness (from ~2{\lambda} to ~{\lambda}/2) afforded by metalenses may not be useful. We further elaborate on the differences between these approaches and clarify that metalenses have unique advantages when manipulating the polarization states of light., Comment: 4 figures, 2 tables

Standard memory modules to store (and access) data are designed for use with a single system accessing it. More complicated memory modules would be accessed through a memory controller, which are also designed for one system. For multiple systems to access a single memory module there must be some facilitation that allows them to access the memory without overriding or corrupting the access from the others. This was done with the use of a memory arbiter, which controls the flow of traffic into the memory controller. The arbiter has a set of rules to abide to in order to choose which system gets through to the memory controller. In this project, a regular RAM module is designed for use with one system. Furthermore, a memory arbiter is also designed in Verilog that allows for more than one system to use a single RAM module in a controlled and synchronized manner. The arbiter uses a fixed priority scheme to avoid starvation of the system. In addition one of the major problems associated with such systems i.e. The Address Clash Problem has been nicely tackled and solved. The design is verified in simulation and validated on a Xilinx ML605 evaluation board with a Virtex 6 FPGA., Comment: 121 pages, 87 figures, 1 table. Mini Project Report

The Quine-McCluskey method is useful in minimizing logic expressions for larger number of variables when compared with minimization by Karnaugh Map or Boolean algebra. In this paper, we have tried to put together all of the computer codes which are available on the internet, edited and modified them as well as rewritten some parts of those collected codes our self, which are used in the implementation of the Quine- McCluskey method. A brief introduction and the logic of this method are discussed following which the codes have been provided. The Quine-McCluskey Method has been implemented using computer languages like C and C++ using some amount of variations. Our effort is to list them all, so that the readers well versed in any of the particular computer language will find it easy to follow the code written in that particular language., Comment: 45 pages, 8 tables

In this paper, the forward and backward propagating modes in an optical waveguide structure namely the fiber Bragg filter also considered as a one dimensional photonic crystal, are analytically computed as a function of grating length for coupled optical modes. AlxGa1-xN/GaN material composition is considered as a unit block of the periodic organization, and refractive index of AlxGa1-xN/GaN is taken to be dependent on material composition, bandgap and operating wavelength following Adachi's model. Expressions of propagating wave are derived using coupled mode theory. Simulated results help us to study the propagation of forward and backward wave propagating modes inside fiber and waveguide devices., Comment: 17 pages,15 figures. This paper is similar except the reflectivity discussion with arXiv:1312.4442

In this paper, forward and backward propagating waves and reflectivity in an optical waveguide structure namely the fiber Bragg reflector also considered as a one dimensional photonic crystal, are analytically computed using coupled mode theory for different grating lengths and coupling conditions. AlxGa1-xN/GaN material composition is considered as unit block of the periodic organization, and refractive index of AlxGa1-xN is taken to be dependent on material composition, bandgap and operating wavelength following Adachis' model. The structure being considered is the Bragg grating where increase in grating length enhances the reflection of electromagnetic wave, and strong coupling provides larger bandgap spectral width. Input wavelength is made different from Bragg wavelength to study the characteristics of propagating waves. A suitable combination of grating length and coupling coefficient is helpful in designing the photonic bandgap at 1550 nm wavelength. These characteristic curves can be utilized to study how waves propagate through the optical waveguides which have a special place in optical communications, Comment: 11 pages, 8 figures. arXiv admin note: substantial text overlap with arXiv:1312.4762

Network technologies are traditionally centered on wireline solutions. Wireless broadband technologies nowadays provide unlimited broadband usage to users that have been previously offered simply to wireline users. In this paper, we discuss some of the upcoming standards of one of the emerging wireless broadband technology i.e. IEEE 802.11. The newest and the emerging standards fix technology issues or add functionality that will be expected to overcome many of the current standing problems with IEEE 802.11., Comment: 9 pages, 4 figures, 4 tables. A longer version of this paper could be found at arXiv:1307.2661. There is also substantial text overlap with the mentioned arXiv paper

Network technologies are traditionally based on wireline solutions. But the introduction of the IEEE 802.11 standards have made a huge impact on the market such that laptops, PCs, printers, cellphones, and VoIP phones, MP3 players in our homes, in offices and even in public areas have incorporated the wireless LAN technology. Wireless broadband technologies nowadays provide unlimited broadband access to users which were previously offered only to wireline users. In this paper, we review and summarize one of the emerging wireless broadband technology i.e. IEEE 802.11,which is a set of physical layer standard for implementing wireless local area network computer communication in the 2.4,3.6,5 and 60GHz frequency band. They fix technology issues or add functionality which is expected to be required by future applications. Though some of the earlier versions of these technologies are obsolete (such as HiperLAN) now but still we have included them in this review for the sake of completeness., Comment: 19 pages, 4 figures, 3 tables

The aim of the project was to develop a HMI (Human-Machine Interface) with the help of which a person could remotely control and monitor the Vacuum measurement system. The Vacuum measurement system was constructed using a DAQ (Data Acquisition & Control) implementation instead of a PLC based implementation because of the cost involvement and complexity involved in deployment when only one basic parameter i.e. vacuum is required to be measured. The system is to be installed in the Superconducting Cyclotron section of VECC. The need for remote monitoring arises as during the operation of the K500 Superconducting Cyclotron, people are not allowed to enter within a certain specified range due to effective ion radiation. Using the designed software i.e. HMI the following objective of remote monitoring could be achieved effortlessly from any area which is in the safe zone. Moreover the software was designed in a way that data could be recorded real time and in an unmanned way. The hardware is also easy to setup and overcomes the complexity involved in interfacing a PLC with other hardware. The deployment time is also quite fast. Lastly, the practical results obtained showed an appreciable degree of accuracy of the system and friendliness with the user., Comment: 111 pages, 38 figures, 25 tables. Project Report of the winter research work done at Variable Energy Cyclotron Centre,India

Now-a-days, a lot of research is being carried out in the development of USVs (Unmanned surface vehicles), UAVs (Unmanned Aerial Vehicles) etc. Now in case of USVs generally, we have seen that wireless controlled vehicles use RF circuits which suffer from many drawbacks such as limited working range, limited frequency range and limited control. Moreover shooting infrared outdoors on a bright sunny day is often problematic, since sunlight can interfere with the infrared signal. Use of a GSM network (in the form of a mobile phone, a cordless phone) for robotic control can overcome these limitations. It provides the advantages of robust control, working range as large as the coverage area of the service provider in comparison with that of an IR system, no interference with other controllers. This paper presents a Global System for Mobile Telecommunication (GSM) network based system which can be used to remotely send streams of 4 bit data for control of USVs. Furthermore, this paper describes the usage of the Dual Tone Multi-Frequency (DTMF) function of the phone, and builds a microcontroller based circuit to control the vehicle to demonstrate wireless data communication. Practical result obtained showed an appreciable degree of accuracy of the system and friendliness through the use of a microcontroller., Comment: 8 pages, 6 figures, 4 tables. A different version of the paper at arXiv:1306.5296

Usually broadband wireless access networks are considered to be enterprise level networks providing us with more capacity as well as coverage. We have seen that in remote inaccessible areas wired networks are not at all cost effective. Wireless networking has offered us an alternative solution for such problem of information access. They have definitely changed the way people communicate and share information among themselves by overcoming problems nowadays associated with distance and location. This paper provides a comparison and technical analysis of alternatives for implementing last-mile wireless broadband services. It provides detailed technical differences between 802.11 (Wi-FI) wireless networks with 802.16 (WiMAX), a new technology that solves many of the difficulties in last-mile implementations., Comment: 5 pages, 4 figures, 1 table