Applications of interferometer are countless both in the research and commercial world. Laser sources offer precise measurements of relative path difference between two interfering beams. An exciting example is LIGO (laser Interferometer for Gravitational Observatory), which is aiming to resolve length change as small as 10^-19 m over a 4 km length for detection of gravitational waves. However, laser is a disadvantage for microscopic imaging and surface topography applications usually required in semiconductor industry. A different approach for microscopy is to use white light in place of laser. White light due to its limited temporal coherence offers a multitude of benefits for imaging applications. An immediate benefit from white light is the sharp localisation of interference fringe that makes the 3D topography construction or OCT (Optical Coherence Topography) realisable using a Scanning White Light Interferometer (SWLI) imager. In Mirau Mode, SWLI performs high resolution imaging; whereas in Michelson mode Fourier Transform Spectroscopy (FTS) is realised. SWLI can easily be modified into PUPS (Pupil Plane SWLI) for Ellipsometry. Superimposing Michelson Interferometer known as VISAR (Velocity Interferometer System for Any reflector) can form interference fringes even in presence of wide angle light scattered from a moving illuminated object. This paper describes work undertaken at Nanometrics (UK) on simulation of SWLI fringes including high Numerical Aperture (NA) applications, thin film characterisation, OCT generation and Zemax modelling of compact dispersion-free vibration-immune Fourier-Transformed spectrometer. VISAR as a modified Mach-Zehnder Interferometer is also discussed based on the work at Rutherford-Appleton laboratory (UK).

We have developed a new technique of optical micro-patterning using micro bubbles based on light induced self- assembly of materials using thermo-optic tweezers. Presently, we use a liquid matter- Soft Oxo-Metalate (SOMs) that have high absorption near the wavelength of the tweezers laser at 1064 nm. An aqueous dispersion of the sample solution is taken in a glass sample chamber and introduced into the translation stage of our tweezers set-up (inverted microscope) where a highly focused laser beam is aimed at SOM particles adsorbed on the top surface of the sample chamber. The high absorptivity of SOMs ensures the creation of a local `hot-spot' which leads to the nucleation of a micro-bubble in this region. Thus, a large local surface-tension gradient is introduced in the vicinity of the micro-bubble due to the temperature gradient produced at the two ends of the bubble, which leads to a Marangoni type convective ow around the bubble. This ow causes material to be self-assembled at the base of the bubble. As the translation stage is moved, the `hot-spot' moves simultaneously, and due to the resulting ow dynamics, the microbubble is also translated thus causing continuous accumulation of the SOMs around it. Simultaneously, due to the sudden thermal shock generated when the `hot-spot' is moved away from the self-assembled SOMs, they undergo a phase transition from soft (liquid) to hard (crystalline) state, resulting in the formation of a stable permanent pattern of choice on the glass substrate. This technique can have diverse applications with materials other than SOMs including carbon nano tubes, organic dyes, catalysts and conducting polymers, etc, being co-deposited from aqueous dispersions of the particular material with the SOMs. The patterns thus formed have been used for various applications including the development of catalytic micro-chips, and solution processed printable micro-circuits.

The aim of integrating plasmonic functionality with photonic devices is twofold: on the one hand, plasmonic nanoantennas can enhance the functionality of photonic devices and enable their miniaturization. On the other hand, photonic devices can be a part of plasmonic transmission lines and act e.g. as plasmon detectors. Here, we present results on both aspects in a CMOS-compatible device setup using Ge PIN-photodetectors and Al nanostructures. Plasmonic nanoantennas are metallic nanostructures that enable the control and manipulation of optical energy in the visible and near-infrared spectrum and have been proposed as a means to enhance absorption and quantum yields for photovoltaics, to increase spatial resolution for optical microscopes and to enhance the energy efficiency of light-emitting devices. We present experimental results on the enhancement of Ge PIN-photodetector efficiency by Al nanoantennas. In order to investigate plasmon waveguiding and detection, metal grating structures and metal-insulator-metal slot waveguides were fabricated by electron beam lithography in the Al metallization layer of Ge PIN-photodetectors. Photocurrent maps of the devices under local illumination show that plasmons can be optically excited at the grating and are then guided by the slot waveguide towards the Ge PIN-photodetector where they are detected as photocurrent. Using Ge PIN-photodetectors and Al nanostructures as a CMOS-compatible device setup, we show how plasmonic nanostructures can be used for efficiency enhancement of photonic devices and discuss plasmon detection with Ge PIN-photodetectors with possible applications.

The set of orthogonal Walsh filters consists of groups, members of which are self-similar. The corresponding axial and transverse intensity distributions in the farfield diffraction patterns of these filters possess self-similarity. Results of our investigations on the same are presented.

Importance of various measurement schemes in studying thermal lens (TL) signal for laser based TL experiments is explored. We show that two different measurement schemes can result in two contrasting outcomes. In one experiment, two measurement schemes show diverging results for TL signal measurements, which gives a convoluted result and in the other experiment, the two measurement schemes give a converging result.

This paper reports the imaging behavior of an optical system consisting of a uniaxial birefringent lens sandwiched between two linear polarizers suffering from primary spherical aberration. The optic axis of the birefringent crystal is perpendicular to the lens axis. The said system is illuminated with a polychromatic beam of light having flat-top spectral profile and the quality of image formed by the system is evaluated by means of the intensity point spread function (IPSF) and optical transfer function (OTF). The proposed system has high tolerance to primary spherical aberration under broadband illumination.

The polarization introduced due to Thirty Meter Telescope (TMT) optics is calculated using an analytical model. Mueller matrices are also generated for each optical element using Zemax, based on which the instrumental polarization due to the entire system at the focal plane is estimated and compared with the analytical model. This study is significant in the estimation of the telescope sensitivity and also has great implications for future instruments.

In this communication a comparative study of one to one coherent imaging through double and single hololens configurations have been presented. Resolutions using the two imaging configurations are found to be 28 and 32 lines/mm respectively.

We present our studies on apodization of pupils with various amplitude filters with respect to images of point objects. The central intensity distribution, first maxima and first minima are compared with and without apodisation. The effects of aberrations and aperture obscuration are also studied. It is shown that in certain cases, the aberrated images can be improved with the help of suitable amplitude filters.

Rugate filters are a special kind of graded-index films that may provide advantages in both, optical performance and mechanical properties of the optical coatings. In this work, design and optimization of a high reflection rugate filter having reflection peak at 540nm has been presented which has been further optimized for side-lobe suppression. A suitable number of apodization and matching layers, generated through Quintic function, were added to the basic sinusoidal refractive index profile to achieve high reflectance of around 80% in the rejection window for normal incidence. Smaller index contrast between successive layers in the present design leads to less residual stress in the thinfilm stack which enhances the adhesion and mechanical strength of the filter. The optimized results show excellent side lobe suppression achieved around the stopband.

The primary mirror for a 10 meter class telescope will be made of many individual segments rather than a monolithic mirror, because of the ease with which the segments can be made, transported and replaced. An f1 primary mirror with an RoC of 20 meter is modeled using Zemax. The theoretical evaluation of the basic properties of the individual segments such as dimensions, orientation and location, has been carried out. The dimensions of each segment is different because the primary mirror is curved and aspheric. These parameters are further optimised with respect to the image spot size and also to minimise the narrow, uniform gap between the segments. The results of this optimisation is discussed in this paper.

Small and compact scientific payloads may be easily designed constructed and own on high altitude balloons. Despite the fact that large orbital observatories provide accurate observations and statistical studies of remote and/or faint space sources, small telescopes on board balloons or rockets are still attractive because of their low cost and rapid response time. We describe here a near ultraviolet (NUV) spectrograph designed to be own on a high{altitude balloon platform. Our basic optical design is a modified Czerny-Turner system using off the shelf optics. We compare different methods of aberration corrections in such a system. We intend the system to be portable and scalable to different telescopes. The use of reflecting optics reduces the transmission loss in UV. We plan on using an image intensified CMOS sensor operating in photon counting mode as the detector of choice.

Broadband Multilayer Antireflection (AR) coatings markedly improve the transmission efficiency of any optical component such as lens, prism, beam-splitter, beam combiner or a window. By reducing surface reflections over a wide wavelength range, broadband antireflection coatings improve transmission and enhance contrast which is desired in avionic displays. The broadband antireflection coating consisting of MgF₂, ZrO₂ and Al2O₃ were designed to cover the whole visible spectrum and fabricated on optical grade glass substrate. The optical characterization of these coatings indicates reduction of the reflection to 2.28% as compared to 8.5 % at 545 nm (i.e. design wavelength of most avionic displays) for bare substrate making them useful in optical displays for avionic applications.

Multi-layer reflective thin film filters optimized for oblique incidence angles were deposited on glass substrates using Electron Beam evaporation technique with in situ thickness monitoring. The present study involves deposition and optical characterization of 5 layered multi-layer structures of TiO₂-Al2O₃ and TiO₂-SiO₂ having different thicknesses for varied wavelength ranges in the visible region. Three TiO₂-SiO₂ multi-layer thin film filters were deposited having peak reflectance at 480 nm, 540 nm and 675 nm respectively corresponding to light sources in the blue, green and red wavelength regions. Similarly, a TiO₂-Al2O₃ multi-layer was fabricated having peak reflectance of around 64% at 610nm. These filters were deposited at an elevated temperature of 250° C in an oxygenated reactive environment for better adhesion, mechanical strength and proper stoichiometry. Reflectance measurements of these multi-layer filters at oblique incidence angles reveal high reflectance of around 70 ~ 75% with a reasonably broad reflection band which can have wide applications in beam steering, shaping and folding applications in various complex optical systems facing constrained space and weight requirements.

In the new era of astronomy, we go for bigger telescopes having segmented primary and secondary mirrors. But once segmentation is done, aligning and phasing mirror segments so that altogether they act like a monolithic mirror of a large diameter, becomes critical. Co-phasing is a complex task that needed to be done after aligning the segments. Diffraction limited resolution is only possible by a large segmented telescope, if mirror segments are co-phased. Co-phasing techniques rely on physical optics and in one of the technique implemented in Keck telescope is based on analysis of diffraction pattern generated by Shack Hartmann sensor. This same technique is being further explored by us in laboratory experimentation. In this paper we present our effort to develop a simple but robust phasing technique for a large segmented mirror telescope proposed to be installed in India. After rigorous mathematical exercise , analytical formulation for the phasing technique is derived, which is further used to simulate in MATLAB. The MATLAB results are cross checked with the ZEMAX. There after, a preliminary laboratory experiment has been conducted to check the feasibility of using this technique for phasing segmented mirrors.

Development of Laser based instruments like laser range finder and laser ranger designator has received prominence in modern day military application. Aiming the laser on the target is done with the help of a bore sighted graticule as human eye cannot see the laser beam directly. To view Laser spot there are two types of detectors available, InGaAs detector and Ex-CCD detector, the latter being a cost effective solution. In this paper optics design for Ex-CCD based camera is discussed. The designed system is light weight and compact and has the ability to see the 1064nm pulsed laser spot upto a range of 5 km.

One of the three planned back-end systems for the proposed National Large Solar Telescope (NLST) is the Solar Dynamics Imaging System (SDIS) which is intended to obtain near simultaneous images in multiple wavelengths. As a first step, a prototype system with two channel imaging has been developed and installed at the back-end of the White light Active Region Monitor (WARM) telescope at Kodaikanal Observatory. A two-mirror Coelostat serves as a light feeding system to a refracting objective while an optical breadboard serves as a platform for the back-end instruments. A re-imaging system is used before the prime focus to get two light channels for the observations in two wavelengths. The re-imaging system is designed using ZEMAX and the alignment of the system is done using a laser. Full disk images are obtained using a red filter (674.2nm/10nm) and a G-band filter (430.5nm/0.84nm). Design aspects of the re-imaging system, preliminary observations and image reduction methods are described in this paper.

A promising technique for precise spectral characterization of solid Etalon operating in SWIR wavelength is demonstrated using tunable laser with a minimum wavelength scan step interval of 1 picometer. Measurement is carried out for 1640nm - 1660nm, an important region containing greenhouse gas absorption spectra. The etalon considered for characterization is made of fused silica. The thickness is nearly 346 micron with physical diameter of 25.4 mm and clear aperture of 23 mm. The etalon has a finesse of 7.25 and extremely narrow bandwidth like 0.4 nm or 400 picometer. The measurement was as well carried out with an Optical Spectrum Analyzer (OSA). The conventional OSA instrument had a resolution of 80 picometer limiting the measurement capability to detect a spectral shift as fine as 50 picometer. Also the measured bandwidth had an error of ± 40 picometer over a spectral bandwidth of 400 picometer which is nearly ±10 %. This leads to the use of a tunable laser exhibiting a provision to vary the wavelength at a step of 1 picometer. This method provides measurement accuracy at least 4 times better than the earlier method. Accuracy may be further improved by making the wavelength scan step interval even finer. The absorption due to presence of greenhouse gas like methane is higher for the etalons with narrower bandwidth. This method can provide very good accuracy for characterization of etalons with spectral bandwidth as narrow as 50 picometer.

Moiré pattern, produced by the overlapping of two radially sheared beams emerging from two longitudinally shifted focal points of a birefringent lens has been experimentally demonstrated. Coherent and incoherent Moiré patterns are generated with and without analyzer. Birefringent samples like mica sheets with opposite crystal axis to that of the birefringent lens modulate the Moiré pattern. Mica sheet of different thicknesses have been used to demonstrate the effect of thickness on phase retardation, hence on fringe pattern. Experimentally birefringence has been calculated by fringe analysis and compared with theoretically simulated birefringence.

A method is presented to measure refractive index of a plane parallel plate of optical glass. We have applied focal displacement method to measure refractive index of a plane parallel plate of an optical glass having thickness of the order of millimeters. The best focus position is found by applying edge detection algorithm. We have measured LAF2 optical glass using focal displacement method and obtained the value 1.746, which is within 0.1% of the standard value 1.747 at 555 nm. In comparison to Abbe refractometer, this method is simple in terms of sample preparation, experimental set up and for measuring high refractive index of Zinc Sulfide. Using this method, refractive indices of other optical glasses are also measured.

Silicon is widely used in IR optics, X-Ray optics and electronics applications. These applications require Silicon of optical quality surface as well as good form accuracy. To get the desired finish and dimensional accuracy, diamond turning is preferable. Taylor-Hobson Nanoform-250 diamond turning equipment is used to machine flat Silicon mirror. Negative rake diamond tool is used with a tool nose radius of 1.5 mm. A series of SPDT machining operations are performed in the sequential combinations of tool feed rate, Spindle Speed and depth of cut. In order to find out the effect of machining parameters on the Surface Roughness during turning, Response Surface Methodology (RSM) is used and a prediction model is developed related to average Surface Roughness (Ra) using experimental data. The surface quality is analyzed in terms of arithmetic roughness (Ra) and Power Spectral Density for uniform evaluation. In addition, a good agreement between the predicted and measured Surface Roughness is observed.

The aim of this study is to model edge enhancement effect in purely phase samples. A self compensating interferometer similar to Sagnac’s, employed with a polarizing beam splitter where two counter propagating orthogonally polarized mutually coherent beams are modulated by the phase shifts introduced by a phase sample. An afocal imaging system is used to image the phase sample on the CCD so that one of the images is slightly defocused. Real-time subtraction of two images results in intensity modulation of phase interfaces.

Significant advances have been made in the field of fabrication of optical components over the years. While plano and spherical surfaces are polished mostly by full aperture polishers made of pitch or polyurethane pads, no such approach is possible for aspheric surfaces as polisher needs to conform to the changing local curvature of aspheric surface. For such aspheric and freeform surfaces sub aperture polishing is a very attractive option as it forms a small polishing spot over the surface of the optics and the path of this spot in multi axis configuration is precisely controlled by the computer. This polishing process follows a deterministic approach and material removal information is very much necessary to control surface form or surface accuracy of the optical component. Here we have carried out the polishing of several glass substrates to find out the response of various glass types to this polishing process.

Holographic optical elements (HOEs) play important role in realization of compact and cost effective systems. Use of HOE not only give above mentioned advantages but an HOE can also be used to design and develop unusual system configurations which may not be possible, at all, using the concepts of conventional optics. Present paper describes fabrication of an HOE which contains both, reference and object, beams required for recording an off-axis hologram of phase objects. Illumination of HOE with a collimated beam generates two spatially separated collimated beams which intersect each other in the hologram recording plane. This combined HOE reduces a large number of opto-mechanical components and alignment related issues, generally encountered in off-axis holography. Fabrication of HOE and recording of holograms of phase objects using the HOE is described and experimental results of reconstructed holograms are presented.

This study aims at developing a non-invasive technique to evaluate periodontal loss of attachment in the oral cavity. A method of imaging periodontal loss of attachment based on time-domain optical coherence tomography is proposed and studied. Based on measurements, boundaries of gingival tissue and tooth were seen separated by ≈0.3 mm. Further study is in progress to image the anatomical landmarks and evaluate the periodontal loss of attachment. The conventional time domain OCT systems acquisition speed is limited by the speed of the mechanical scanning system. In order to overcome this issue, a novel electro-optic based scanning system is proposed and demonstrated. Studies were performed initially with lithium niobate and potassium titanyl phosphate crystals and the tuning range observed were low. In order to increase the tuning range, a crystal with high electro-optic coefficient – potassium tantalite niobate was identified and experiments were carried out to characterise the crystal and electro-optic based phase tuning is demonstrated.

Power transformers are the vital equipment in the network of power generation, transmission and distribution. Mineral oil in oil-filled transformers plays very important role as far as electrical insulation for the winding and cooling of the transformer is concerned. As transformers are always under the influence of electrical and thermal stresses, incipient faults like partial discharge, sparking and arcing take place. As a result, mineral oil deteriorates there by premature failure of the transformer occurs causing huge losses in terms of revenue and assets. Therefore, the transformer health condition has to be monitored continuously. The Dissolved Gas Analysis (DGA) is being extensively used for this purpose, but it has some drawbacks like it needs carrier gas, regular instrument calibration, etc. To overcome these drawbacks, Ultraviolet (UV) -Visible and Fourier Transform Infrared (FTIR) Spectro-photometric techniques are used as diagnostic tools for investigating the degraded transformer oil affected by electrical, mechanical and thermal stresses. The technique has several advantages over the conventional DGA technique.

A simple edge enhancement technique in the digital holo-microscopy is presented here. In Digital Holo-microscopy (DHM) the intensity distribution of the CCD is produced by the interference of a plane reference wave and that scattered by the object. The reconstruction is accomplished by multiplication of the digitally stored hologram with a digital model of the reference wave and subsequent numerical determination of the diffracted field of the object in a defined image plane. Hence, a focused and a defocused version of the object may be reconstructed from only one recorded hologram by varying the reconstruction distance during numerical reconstruction. The edge enhancement of the object is possible by simply subtracting this numerically reconstructed defocused real image from the focused real image. It is interesting to note that using this technique edge enhancement technique is possible for amplitude and phase objects. The simulation and experimental results presented validate our theoretical expectations.

Interference Microscope with exception of the widely used Mirau objective, involves a setup having Michelson or Mach-Zender Configuration. The present work proposes an in-line interference laser microscope configuration.

The fabrication of complex aspheric and freeform surfaces are possible with accurate iterative metrology feedback during correcting polishing process. The tool path of the machine is generated based on the measured surface data for corrective material removal. The computer controlled polishing machines are compatible with various metrology tools. This paper presents annular null based interferometric in- process metrology for deterministic corrective polishing for aspheric surface of infrared optical material.

Present communication reports investigations undertaken towards testing applicability of Talbot interferometry for measurement of impurity in water. Because of presence of impurities in water, the refractive index of the sample (water) changes. The variation of refractive index is mapped as change in the fringe order of the Talbot interferometric fringes. Experimental investigation with ethanol and salt water as impurities has been reported. High accuracy and precision has been achieved.

We describes the design, development and testing of a cost effective and miniaturized version of a flow analyzer. It is designed to detect fluorescence labeled immunocytes in human blood sample. Availing of advancements in micro fluidics and nanolithographic technique, we fabricated a PDMS based device with integrated micro channels for accommodating the optical fibers. The lensed fibers serves as the waveguides for illumination and collection of laser and scattered signals respectively. As a cell crosses the interrogation point the forward scatter, side scatter and fluorescence are detected. Photomultiplier tubes used in conventional flow cytometers have been replaced here with APDs (avalanche photo detectors) and supplemented with digital signal processing. The prototype was tested with different sized polymer beads as well as the live cells.

In this work, admittance loci method is used to model and analyze performance of a chalcogenide prism based plasmonic biosensor comprising of gold metal nanoparticle film for detection of wavelength dependent refractive index change of human blood sample under angular interrogation mode. The wavelength dependent performance of the plasmonic biosensor based on the choice of chalcogenide (2S2G) as a coupling prism material has been discussed with the help of performance parameter plots.

A zero cross sensitivity (CS) deliverable self-referencing (S-R) surface plasmon resonance sensor (SPR) experimental scheme is presented based on the retroreflecting prism configuration with single spectroscopic read out. The relationship between external and internal incident angle in retroreflection configuration results in the excitation of two spectroscopically distinct surface plasmons (SPs) modes corresponding to each side of the prism. The characteristics of two SPs modes are independent and thus used in differential refractive index (RI) sensing via S-R modes technique. By applying SR sensing theory, it is shown that the CS can be minimized to zero through the demonstrated configuration. This configuration is flexible for using in wavelength interrogation measurement method as well. The excited SPs modes are also tunable to acquire either identical or non-identical sensitivity by selecting corresponding metal film thickness on the either sides of the prism. From the preliminary experimentation on SR configuration and theoretical investigation on deliverability of zero CS, it can be expected that the presented scheme is a better SR configuration for high accurate differential RI sensing applications.

Partial Discharges (PDs) are reported as one of the main reason of insulation degradation and its measurement is most effective, non destructive test often applied to know the insulation condition. Among many available methods acoustic method of PD test is quite popular due to several advantages.In the presented work, a Fiber Bragg Grating (FBG) based sensor has been developed for on-line condition assessment, capturing the acoustic wave produced by the PD event in a prototype power transformer. A variation in acoustic pressure, changes the wavelength of the FBG reflected light, which gives the indication of PD activity. Developed FBG based sensor is found to be superior over conventional PD sensors.

In present analysis a semiconductor-based surface plasmon resonance structure using Gr-IV materials (Silicon and Germanium) has been analyzed in spectral interrogation mode which can be used for efficient environmental monitoring and Infrared (IR) gas-sensing purposes. The Silicon-Germanium (Si-Ge) combination structure is able to confine an extremely high evanescent field in the sensing region due to their extraordinary high refractive indices (RI). Higher concentration of optical field in the sensing area provides enhanced spectral sensitivity for infrared gas-sensing. Better detection accuracy and adequate dynamic range are other additional advantages offered by such semiconductor-based surface plasmon resonance (SPR) configurations. Analysis of the SPR structure has also been carried out in terms of detection accuracy, figure of merit and Q-factor of the gas-sensor.

Theoretical and experimental investigation of surface plasmon resonance (SPR) assisted radially sheared interference imaging using a birefringent lens having two longitudinally shifted focal points has been reported. As Wolllaston prism can introduce lateral shear between the two mutual orthogonal polarizations of radially sheared pattern, Moiré-like pattern is produced at overlapping region of those patterns. Brief theory and experimental demonstration of coherent and incoherent Moiré fringe generation has been done. Surface plasmon resonance (SPR) mediated Moiré pattern has been demonstrated which can be further utilized for other nanophotonic applications.

This paper aims to report simulation based study of performance properties of Titanium Nitrides and their efficient use as substitutes to metals for excitation and propagation of surface plasmon polariton wave.

Paper presents Opto-Mechanical intrusion sensor fence with FBGs attached to mechanical accelerometers and strain sensors, optimized on SolidWorks 2013 for desired frequency to 35 Hz, picking up accelerations/ strains and its deployment for perimeter security. The accelerometer structure consists of inertial mass supported by an L-shaped modified cantilever beam having non-uniform cross section area connected to base by a thin neck element which acts as strain concentrated centre hence an optimum zone for FBG sensors placement. Bragg wavelength shifts were obtained on Optigrating software for the obtained strain values on mechanical assembly of fence. CFD wind analysis is performed on the assembly to obtain the spot for accelerometer’s placement to avoid false alarms up to wind velocities of 20 m/s.

The Shack Hartmann wavefront sensor (SHWS), named after Johannes Franz Hartmann and Roland Shack, is one of the most well-known and popularly used optical wavefront sensor that finds numerous applications in various optical technologies. SHWS samples the incident wavefront by means of a lenslet array to produce an array of regular 2D array of focal spots on the detector plane of a digital camera, in the case of an unaberrated plane wavefront. If the incident wavefront is aberrated or deviates from a plane wavefront, the respective focal spots get shifted from its reference positions corresponding to the regular grid. If the incident wavefront aberration increases or has a very large curvature, the focal spot of one lenslet may enter the detector sub-aperture of the nearby lenslet. Thus, the SHWS has a limited dynamic range that is restricted to aberrations which do not allow the sub-images to be displaced out from their own detector sub-array. It makes the SHWS sensitive to cross-talk when higher order aberrations are present thereby unavoidably a ecting the wavefront estimation process. The array of tiny lenses of the SHWS can be replaced by an array of gratings followed by a focusing lens, generating an array of focal spots which is similar to that as in the case of a SHWS. In this paper, the spatial frequency of such a grating array based zonal wavefront sensor is configured to produce lesser number of rows of focal spots. The reduction in the number of focal spot rows reduces the amount of cross talk in the vertical direction. In this paper we present preliminary experimental results to demonstrate the above stated reduction in crosstalk.

We demonstrate the use of etched fiber Bragg gratings for sensing refractive index in the range of 1.350-1.453. Experiments are carried out using FBGs with different etch depths and their relative performances are compared.

Real time (label-free) detection and sizing of single protein molecule at its natural state is “holy grail” in biosensing field. This non-destructive technique is useful for predicting the dangerous diseases at very early-stage. Herein, we report the synthesis and characterization of efficient nanoplasmonic antennas, which could be useful to fabricate an ultrasensitive nanoplasmonic-whispering gallery mode hybrid microresonator for the real time detection and sizing of single protein molecule. This hybrid microresonator could be easily converted as an ultrasensitive single molecule biosensor by anchoring suitable anti-bodies on the surface of the plasmonic nanoantenna.

We report a transmission line based analysis of a subwavelength nanostub coupled to a metal-dielectric-metal (MDM) waveguide along with a differential intensity based sensing application related to detection of concentration of glucose in aqueous solution.

A compact surface plasmonic two mode interference waveguide component having silicon core and silver and GaAsInP side cladding is proposed for optical processor elements. Coupling operation is obtained by using index modulation of GaAsInP cladding with applied optical pulse.

We explore the exact optical similaritons of a generalized nonlinear Schrodinger equation(GNLSE) with space-time modulated dispersion, nonlinearity, external potential and inhomogeneous source. As an application, we study the dynamics of these similaritons for a spatial Bessel modulated nonlinearity.

We demonstrate that the localized nonlinear gain induces stable chirped dissipative double-kink, fractional-transform, bell, and kink type solitons in optical mediawith quadratic nonlinearity. To compensate spatially uniform loss in both fundamental-frequency (FF) and second-harmonic (SH) component of the system, a strongly localized ”hot-spot”, carrying the nonlinear gain, is added, acting either on FF component or on the SH one.

All-optical systems for binary to Gray code conversion and Gray code to binary conversion are proposed where the input and output binary digits are expressed as the presence (=1) or the absence (=0) of a light signal. The intensity based optical XOR logic operation is used here to develop the scheme.

The dynamics of a quantum cascade laser (QCL) have been analyzed theoretically using a three level rate equation model. It is observed that the electric field and the temperature affect the QCL turn-on transients significantly.

Enhancement of higher order nonlinear susceptibilities are investigated in three level quantum well with a ladder configuration in the regime of electromagnetically induced transparency. We have identified the existence of giant third and fifth order nonlinear susceptibilities of the order ~10^-22 m⁴/V⁴ at pump wavelength of 9.6 μm. The group velocity is reported to be slowed down by 10⁴ times compared to the speed of light in vacuum.

Photonic bandgap of two dimensional semiconductor photonic crystal structures of square and triangular lattices are studied using plane wave expansion method. The bandgap and dispersions also studied by introducing point and line defect in that structure. Hence a comparative study has been presented among the various structures.

Quantum Zeno and anti-Zeno effects in an asymmetric nonlinear optical coupler are studied. The asymmetric nonlinear optical coupler is composed of a linear waveguide (χ ⁽¹⁾) and a nonlinear waveguide (χ⁽²⁾) interacting with each other through the evanescent waves. The nonlinear waveguide has quadratic nonlinearity and it operates under second harmonic generation. A completely quantum mechanical description is used to describe the system. The closed form analytic solutions of Heisenberg's equations of motion for the different field modes are obtained using Sen-Mandal perturbative approach. In the coupler, the linear waveguide acts as a probe on the system (nonlinear waveguide). The effect of the presence of the probe (linear waveguide) on the photon statistics of the second harmonic mode of the system is considered as quantum Zeno and anti-Zeno effects. Further, it is also shown that in the stimulated case, it is easy to switch between quantum Zeno and anti-Zeno effects just by controlling the phase of the second harmonic mode of the asymmetric coupler.

We report on development of tunable, cw, single frequency ultraviolet (UV) source based on intra-cavity frequency doubling of an optical parametric oscillator (OPO). The singly resonant OPO (SRO) is realized using 25 mm long MgOdoped periodically poled stoichiometric lithium tantalite (MgO:sPPLT). The SRO, pumped in the green, is intra-cavity frequency doubled using two different crystals β-BaB2O4 (BIBO) and periodically poled KTiOPO4 (PPKTP) to generate tunable UV radiation. The BIBO based source produces UV radiation with output power as much as 770 mW at 398.24 nm in elliptic (0.66) spatial beam while pumping at 8W of green power. The UV source can be tuned across 355.2-418 nm with a continuous wavelength tunability of 62.8 nm in single frequency radiation with instantaneous line-width of 14.5 MHz. On the other hand, the PPKTP based UV source generates maximum UV power of 336 mW at 398.28 nm and wavelength tunability of 18.1 nm in a TEMOO spatial mode with ellipticity of 0.93 for 5W of green pump power. The line-width of the UV radiation is measured to be 18.5 MHZ. In comparison, PPKTP based UV source provides better performance than BIBO in terms of beam quality and power stability.

Photonic nanojet (PNJ), the sub wavelength confinement of light by dielectric microspheres is finding applications in nanoscale imaging, spectroscopy and nano lithography. These applications require control over the length and lateral dimension of the nanojets. In the paper we present the results of numerical simulation to show that a core shell microspheres can be used to generate photonic nanojet with controllable length and confinement by varying the relative refractive index of the microspheres and the separation between the core and shell centers. We show that a length of up to 27λ can be achieved when the core microsphere has lower refractive index than the shell and lateral dimensions down to λ/3 with core microsphere having higher refractive index.

Vertical 2D PhC having a T-type three port channel on top of InGaAs/GaAs broadband IR LED is considered. Top PhC is created by 2D periodic repetation of InAs rods in air. T-Channel is created by replacing some solid rods by air. Light from LED is focussed within the channel. Part of LED light having wavelength out side the PhC bandgap will pass normally and wavelength within PhC will be guided by the channel. By introducing two different defects in the two arms of ‘T’ channel tuning of two demultiplexed narrowband sources is obtained.

Transition metal (TM) doping in silica core optical fiber is one of the research area which has been studied for long time and Chromium (Cr) doping specially attracts a lot of research interest due to their broad emission band covering U, C and L band with many potential application such as saturable absorber or broadband amplifier etc. This paper present fabrication of Cr doped nano-phase separated silica fiber within yttria-alumina-silica core glass through conventional Modified Chemical Vapor Deposition (MCVD) process coupled with solution doping technique along with different material and optical characterization. For the first time scanning electron microscope (SEM) / energy dispersive X-ray (EDX) analysis of porous soot sample and final preform has been utilized to investigate incorporation mechanism of Crions with special emphasis on Cr-species evaporation at different stages of fabrication. We also report that optimized annealing condition of our fabricated preform exhibited enhanced fluorescence emission and a broad band within 550- 800 nm wavelength region under pumping at 532 nm wavelength due to nano-phase restructuration.

A trench assisted, 0.15-NA, effective single mode leaky Erbium Doped Fiber Amplifier is proposed for high power applications. The segmented-core of the fiber enables to achieve 783 μm² mode area which reduces nonlinearity and increases power handling capacity of the fiber. The leakage loss of the modes is controlled by annular core segments and low index trench in the cladding. The leakage loss of the LP₁₁ mode is 10.49 dB/m and that of the fundamental mode is 0.017 dB/m at 1530 nm wavelength. We have injected 20 mW power into each mode and have calculated the gain for 26 m length of the fiber using 250 W pump at 980 nm wavelength. The signal power in the LP01 mode is amplified to 122 W and that in the LP₁₁ mode drops down to 5.78×10^-27 W. The low output signal power in LP₁₁ mode ensures selective single mode amplification of fundamental mode. Selective single mode amplification confirms good beam quality at the output end.

A traveling wave time domain model of bulk InGaAs/InP uni-traveling carrier photodiode is presented in terms of integral carrier density rate equation. The wavelength dependent responsivity at different absorption width has been derived from quantum mechanical principle. Output photocurrent response with time is found in close agreement with the experimental value.

A mathematical model to study the phase difference introduced between the two orthogonal components of light wave due to electro-optic effect in a trapezoidal shaped lithium niobate single crystal has been made. Here, the electrodes are placed on the two opposite non-parallel faces such that the field is nearly perpendicular to the light beam direction. It is found that for the said geometry of the device structure, the maximum phase difference is a function of oblique angle between the two non-parallel faces, which has a critical value. Using random optimization technique based on genetic algorithm, the device parameters can be optimized for any required phase change between the two components of light wave. The phase difference between the two orthogonal components of light can be made tunable by using a multi-strip electrode structure. The advantage of this technique is that tunability can be obtained with a constant voltage source.

Differential Quadrature Phase Shift Keying (DQPSK) is considered as an acceptable modulation technique for long-haul high speed communication owing to its ability to diminish the Polarization Mode Dispersion (PMD), non-linear effects and has constant envelope over the communication. The assessment includes Carrier Suppressed Return to Zero (CSRZ) modulation format. The combination of CSRZ and DQPSK techniques would result in a high bit rate with better Bit Error Rate (BER) in Wavelength Division Multiplexing – Passive Optical Network (WDM-PON) setup. The Radio Frequency (RF) signal is obtained finally for wireless service which can be assessed. . The optical communication system is expanded by comprising Polarization Multiplexing (PM) which improves the user scope and the spectral efficiency. The goal is to experimentally analyze the performances of CSRZ-DQPSK modulated non-coherent receiver for wire and RoF (Radio over Fiber) system for wireless service. Also, equal amount of power is provided for both the services. The PMD is reduced both the services. The Proposed system can provide flexible, cost-effective and high bandwidth utilization with reduced BER.

We experimentally observed the emission of phase-matched resonant radiation in the form of solitonic dispersive wave in a fabricated photonic crystal fiber by pumping picosecond and femtosecond pulses close to zero-dispersion wavelength in normal dispersion regime. The generation of such phase matched radiation does not require a soliton to be formed and red-shifted in nature. Shock front from the leading edge of the input pump initiates the resonant radiation. The radiation develops in the anomalous dispersion domain and found to be confined both in spectral and temporal domain. The resonance mechanism can be well explained from the numerical simulation governed by generalized nonlinear Schrödinger equation.

Presence of photonic band-gap (PBG) in an all-solid microstructured optical fiber (MOF), made of two fabrication compatible chalcogenide (Ch) glasses is theoretically investigated for potential application in the functional mid-infrared (IR) wavelength range. Cross-section of the MOF is formed by assuming periodically arranged wavelength scale circular air holes in a hexagonal pattern embedded in a uniform matrix. One type of Ch-glass is considered as the background material whereas another type of Ch-glass is assumed to fill the air holes. The relative index contrast between these two Ch-glasses is ~ 24%, for which PBG appears only for a suitable range of non-zero longitudinal wave vector. We have studied the scalability of this PBG by varying the lattice parameter of MOF and optimized the cross-section to attain the PBG at ~ 2 μm wavelength. Then by utilizing the thermo-optic properties of the glasses, the effect of external temperature (T) on the PBG is studied, and finally we have proposed a T-tunable wavelength filter/sensor at mid-IR wavelength with tuning sensitivity as high as ~ 140 pm/°C.

Multimode Interference (MMI) based on self imaging phenomenon is investigated using matrix approach. Experimentally MMI is verified using singlemode-multimode-singlemode and multimodesinglemode structures of optical fiber. The results obtained are also verified by BPM technique.

We propose the stronger optical guiding of an electromagnetic beam in a plasma by considering the amplitude modulation of the fundamental beam. With the advent of high power source of electromagnetic radiation, the electron velocity in a plasma may become quite large (comparable to the light velocity in free space). Thus, the effect of relativistic mass variation must be taken into account. The relativistic effect of the laser propagation in a plasma leads to self-focusing because of the dielectric constant of a plasma being an increasing function of the intensity. The ponderomotive force of the laser beam pushes the electrons out of the region of high intensity, which reduces the local electron density and increases the plasma dielectric function further, leading to even more selffocusing of the laser. In this work, we consider a short pulse laser of finite spot size as an amplitude modulation in time. Our findings show an efficient optical guiding mechanism based on amplitude modulation signal propagation in plasmas. Medium nonlinearity becomes stronger if an amplitude modulated beam is introduced, which contributes significantly in laser guiding in plasmas. Furthermore, the rate of laser self-focusing is increased with modulation index due the fact of stronger Kerr effect. The study related to amplitude modulated optical signal may be useful for communication technology.

Propagation characteristics of an electromagnetic wave through parallel plane waveguide filled with nanoparticles is studied. The dispersion relation reveals two modes, a surface plasmon like mode for ω≥ω_pe √3 pe ω≤ω , (ω is electromagnetic wave frequency and ω_pe is electron plasma frequency of nanoparticles) and another normal electromagnetic mode for ω≥ω_pe √3 . The plasmon like mode is sensitive to plate separation and the excitation frequency is higher for smaller plate separation. The cutoff frequency of electromagnetic mode can be varied by changing the concentration or size of the nanoparticles and also the plate separation.

In this paper a novel architecture has been proposed and developed for full-duplex transmission of 80 channel CATV signal over 80 km single mode fiber (SMF) using various techniques such as mutually injection locking, optical carrier suppression (OCS) and remodulation etc. The up/downlink transmission performances are observed by the low bit error rate (BER) values and impressive eye diagrams. The satisfactory values of CNR, CBT and CSO verify the successful transmission of CATV signals through our proposed configuration.

In this paper a simple architecture has been developed for full-duplex transmission of different services like Ethernet, FTTX etc through single optical carrier wavelength employing polarization multiplexing technique in the transmitter end and the user end simultaneously. 10 Gbps and 2.5 Gbps datarates are bidirectionally transported over 50 km single mode fiber (SMF) to provide Ethernet and FTTX services concurrently to the user. Reflective semiconductor optical amplifier (RSOA) is used to reuse and remodulate the downlink signal to uplink transmission. The upstream and the downstream transmission performances are observed by the bit error rate (BER) values and the eye diagrams obtained by the BER analyzer at both ends.

We report the results of simulations as well as experiments to study the performance of a fiber interrogator based on cavity ring-down principle.

The translational symmetry of the periodicity in a photonic crystal can be disturbed by introducing a controlled defect in its periodicity. The photon localization causes a pass band in the photonic bandgap. Based on this concept, we are proposing the design of a tunable narrow band filter for multiple wavelengths used for coarse wave length division multiplexing (CWDM) system. To achieve that, a multiple stack Fabry Perot structure with suitable stack materials and controllable defect is considered. The proposed Fabry Perot structure consists of periodic layers of electro optic material Lithium Niobate (nH) and Magnesium Fluoride (nL). The optical length of each such layer is their corresponding quarter wave length width at the design wavelength λ₀ (1.55 μm). The reflection band of the quarter wavelength multilayer structure is formed due to the periodic repetition of the (LH)^NL, where L and H are the quarter wavelength width of the nL and nH material respectively and N is the number of bilayers. A quarter wave layer L is then inserted between the groups of (LH)^N and (HL)^N to form the Fabry Perot resonator structure which can be used for narrow band transmission filter. The simulation has been carried out in both FDTD and TMM method and compared. As the refractive index of the Lithium Niobate can be tuned electro-optically, the filter can also be made tunable.

This paper introduces the importance of nonlinearity in a Photonic Bandgap (PBG) Fiber using Finite Difference Time Domain (FDTD) simulation. It is shown that, the amplification of the weaker optical signal in a PBG fiber due to the constructive interference between two incoming signals can be controlled using nonlinearity.

In the present work, a PT-symmetric closed-form quadrimer waveguides system has been considered. We observe the saturation of the optical powers in the gain-guides in nonlinear regime under the coupling scheme considered. Moreover, we also find that accumulation of optical powers in the g-r parametric space (‘g’ is the gain/loss parameter, ‘r’ nonlinearity co-efficient) in the different waveguides significantly depends on the nature (i.e. focusing or defocusing) and the strength of nonlinearity and gain/loss profile. The potential applications of this quadrimer system might be in generating high constant-power optical sources.

In the present communication, a procedure for the synthesis of an optical finite impulse response (FIR) birefringent filter generating arbitrary spectral output is presented. The basic filter consists of a cascaded system of n identical retarders between two polarizers at the two ends. A mathematical model of the optical FIR filter is introduced using the FIR theory of digital filter design. The parameters determined by the synthesis procedure are the angles of the optic axes of the individual crystals and the angle of the output polarizer. Classical FIR filter design method along with the optical backward transfer technique has been used. Two different arbitrarily specified spectral output profiles have been studied. However, the method is equally applicable for any periodic transfer function whose corresponding impulse response is real and causal.

We propose an experimental technique for two dimensional Jones matrix imaging of transparent and anisotropic sample using polarization interferometer. Employing this technique, the Jones matrix components are measured for polarizer and quarter wave plate and results are compared with theoretical results of the samples.

We construct a orbital angular momentum (OAM) Poincar´e sphere in which we can represent 2-D superposition states of arbitrary OAM. In addition, we represent the mixed states of OAM as non separable states inside the sphere. We also give an experimental set up to generate all points on this sphere.

A mathematical model which has been developed for interferometric analysis of birefringent sample is experimentally verified using a modified Mach – Zehnder arrangement. It is shown that full field analysis of samples with varying birefringence in magnitude and orientation is possible.

The polarization parameters of light transmitted through biological cells contain morphological and functional information for biomedical purposes. As more imaging became available to research applications, Mueller imaging’s importance has increased regularly in biomedical approach over the years. This paper summarizes the context of Mueller imaging and polarization optical analysis on blood cells for medical applications. Basically this method is related to Mueller Matrix Imaging Polarimetry. Knowing all 16-element Mueller matrix using 36 independent polarization states completely describes the blood cells in terms of birefringence properties.

A software simulation testbed for measuring the RF characteristics of an Optical Beamforming Network (OBFN), being designed and simulated in Optical circuit simulator software.

The main objective of the present project is to explore the viability of an adaptive optics control system based exclusively on Field Programmable Gate Arrays (FPGAs), making strong use of their parallel processing capability. In an Adaptive Optics (AO) system, the generation of the Deformable Mirror (DM) control voltages from the Wavefront Sensor (WFS) measurements is usually through the multiplication of the wavefront slopes with a predetermined reconstructor matrix. The ability to access several hundred hard multipliers and memories concurrently in an FPGA allows performance far beyond that of a modern CPU or GPU for tasks with a well-defined structure such as Adaptive Optics control. The target of the current project is to generate a signal for a real time wavefront correction, from the signals coming from a Wavefront Sensor, wherein the system would be flexible to accommodate all the current Wavefront Sensing techniques and also the different methods which are used for wavefront compensation. The system should also accommodate for different data transmission protocols (like Ethernet, USB, IEEE 1394 etc.) for transmitting data to and from the FPGA device, thus providing a more flexible platform for Adaptive Optics control. Preliminary simulation results for the formulation of the platform, and a design of a fully scalable slope computer is presented.

The phase of a negative axicon is combined with that of a Fresnel zone lens (FZL) to obtain an element labelled as conical FZL, which can generate a focused ring pattern at the focal plane of the FZL. The phase integration is achieved by modifying the location and width of zones of FZL in accordance with the phase variation of the negative axicon. The element was designed for a high power laser with a wavelength of 1064 nm, focal length and diameter of conical FZL of 30 mm and 8 mm respectively and for a ring diameter of 50 μm. The element was fabricated using photolithography. The pattern was transferred from the resist layer to the borosilicate glass plates by dry etching to achieve an etch depth of 1064 nm. The etch depth measured using confocal microscope was 1034 nm at the central part and 930 nm for the outermost part of the device with a maximum error of 12.5% at the outermost part and 3% at the central part. The element was used in an optical trapping experiment. The ring pattern generated by the conical FZL was reimaged into the trapping plane using a tightly focusing microscopic objective. Polystyrene beads with diameters of 3 μm were suspended in deionized distilled water at the trapping plane. The element was found to trap multiple particles in to the same trap.

The proposed work describes optical transformations such as Fourier transformation and Fresnel transformation based encryption and decryption of images using random phase masks (RPMs). The encrypted images have been embedded in some secret cover files of other formats like text files, word files, audio files etc to increase the robustness in the security applications. So, if any one wants to send confidential documents, it will be difficult for the interloper to unhide the secret information. The whole work has been done in MATLAB®

A beam of light stimulates the retina weakly when its entry to the pupil is gradually shifted from the centre toward the edge. For single pupil entrance point the light, irrespective of its coherence would still show the Stiles-Crawford effect with diminished visibility toward the edge of the pupil. Only when coherent light is incident from opposing points in the pupil can the effect be cancelled. This paper has attempted a theoretical computation of how the contrast in an interference pattern formed on the retina controls the retina’s response in three ways; first, by completely disregarding the Stiles Crawford diminution of effective brightness for unit contrast; next, taking the traditional SCE route for zero contrast, and finally enhancing the diminution in the effective brightness by giving an opposing boost to the visibility in commensurate with a contrast intermediate between the two extremes of unity and zero.

According to Vector diffraction theory, focusing properties of azimuthally polarized annular multi Gaussian beam through dielectric interface is numerically studied. It is observed that the presence of dielectric interface generates focal shift and the inclusion of annular obstruction at the aperture enhances the focal depth and minimized the focal hole size. By properly tuning the annular obstruction, a focal hole of FWHM 0.606 λ having super long focal depth of 3080λ is achieved. The focal depth of the dark channel achieved is found to be much larger than all the previously proposed methods.

This paper discusses the detailed experimental investigations on the performance of interferometer based fiber optic hydrophones with different Phase Generated Carrier (PGC) demodulation algorithms for their interrogation. The study covers the effect on different parametric variations in the PGC implementations by comparison through Signal to Noise And Distortion (SINAD) and Total Harmonic Distortion (THD) analysis. This paper discusses experiments on most popular algorithms based on PGC like Arctangent, Differential Cross Multiplication (DCM) and Ameliorated PGC. A Distributed Feed-Back Fiber Lasers (DFB-FL) based fiber optic hydrophone, with Mach-Zehnder Interferometer having active phase modulator in reference arm and mechanism to cater polarization related intensity fading were used for the experiments. Experiments were carried out to study the effects of various parameters like the type and configuration of low pass filter, frequency of the modulation signal, frequency of acoustic signal etc. It is observed that all the three factors viz. the type of low pass filter, frequency of modulating and acoustic signal plays important role in retrieving the acoustic signal, based on the type of algorithms used and are discussed here.

To meet the growing demands of data traffic in long haul communication, it is necessary to efficiently use the low-loss region(C-band) of the optical spectrum, by increasing the no. of optical channels and increasing the bit rate on each channel .But narrow pulses occupy higher spectral bandwidth. To circumvent this problem, higher order modulation schemes such as QPSK and QAM can be used to modulate the bits, which increases the spectral efficiency without demanding any extra spectral bandwidth. On the receiver side, to meet a satisfy, a given BER, the received optical signal requires to have minimum OSNR. In our study in this paper, we analyses for different modulation schemes, the OSNR required with and without preamplifier. The theoretical limit of OSNR requirement for a modulation scheme is compared for a given link length by varying the local oscillator (LO) power. Our analysis shows that as we increase the local oscillator (LO) power, the OSNR requirement decreases for a given BER. Also a combination of preamplifier and local oscillator (LO) gives the OSNR closest to theoretical limit.

Fast and efficient segmentation of iris from the eye images is a primary requirement for robust database independent iris recognition. In this paper we have presented a new algorithm for computing the inner and outer boundaries of the iris and locating the pupil centre. Pupil-iris boundary computation is based on correlation filtering approach, whereas iris-sclera boundary is determined through one dimensional intensity mapping. The proposed approach is computationally less extensive when compared with the existing algorithms like Hough transform.

In this paper, we implement a novel optical information processing tool termed as gyrator wavelet transform for the application of double image encryption using amplitude- and phase-truncation approach. This approach enhances the key space in an asymmetric cryptosystem by adding supplementary security layers, i.e., family of mother wavelet and the gyrator transform order. Double input images bonded with random phase masks are independently gyrator transformed. Amplitude truncation of obtained spectrum generates individual and universal keys while phase truncation generates two real-valued functions. Each of the retrieved amplitude function is discrete wavelet transformed, which results into four different frequency bands. We have fused the obtained wavelet spectrum of an individual image by again gyrator transforming them following amplitude- and phase truncation. The obtained real-valued functions corresponding to each image are bonded to form the encrypted image. After using the correct universal key, individual asymmetric key, type of wavelet, and correct gyrator transform order, the original images are retrieved successfully. Numerical simulation results prove that the proposed scheme is more flexible and effective than existing wavelet fusion schemes.

A watermarking scheme is proposed based on optical asymmetric cryptography using double random phase encoding in the gyrator transform domain. It is based on the phase and amplitude truncation during the encryption process. The scheme is validated through computer simulations showing the scheme's sensitivity to decryption keys and orders of the gyrator transform. The occlusion and noise attacks have also been analysed. The proposed scheme is significantly resistant to both these attacks.