AJP	ISSN : 0971 – 3093 Vol  23, No. 4, October, 2014

 

Vol. 23, No. 4 (2014) 509-515

Digital shear speckle pattern interferometry with holo-elements

 

The paper discusses the theory of digital shear speckle pattern interferometry (DSSPI). DSSPI is used mainly for non-destructive testing but can also be used for quantitative evaluation of strains, slopes and curvatures. Use of holo- and/or diffractive elements due to their multi-function capabilities makes their use in DSSPI attractive. © Anita Publications. All rights reserved.

 Vol. 23, No. 4 (2014) 517-526

Real-time amplification of light signals in photorefractive ferroelectric liquid crystals

 

The photorefractive effect in ferroelectric liquid crystalline mixtures containingphotoconductive chiral compounds was investigated. Ter-thiophene compounds with chiral structures were chosen as the photoconductive chiral compounds, and they were mixed with an achiral smectic C liquid crystal. The mixtures exhibit the ferroelectric chiral smectic C phase. The photorefractivity of the mixtures was investigated by two-beam coupling experiments. It was found that the ferroelectric liquid crystals containing the photoconductive chiral compound exhibit a large gain coefficient of over 1200 cm-1 and a fast response time of 1 ms. Real-time dynamic amplification of anoptical image signal of over 30 fps using the photorefractive ferroelectric liquid crystal was demonstrated.© Anita Publications. All rights reserved.

 Vol. 23, No. 4 (2014) 527-534

 Three-dimensional object recognition with joint fractional Fourier transform

correlator using digital Fresnel holography

 

Three-dimensional (3D) object recognition with joint fractional Fourier transform correlator is proposed in which the technique of digital Fresnel holography is used. Digital Fresnel hologram of a 3D object is synthesized and reconstructed digitally. Performance measure parameters, such as, discrimination ratio, peak-to-correlation energy, and peak-to-sidelobe ratio have been computed to check the strength of the correlation scheme. © Anita Publications. All rights reserved.
Keywords: Digital holography; Fresnel diffraction; fractional Fourier transform; joint transform correlator.

 Vol. 23, No. 4 (2014) 535-542

Compact telephoto objectives with zero Petzval sum using varifocal lenses

 

We present two non-conventionaltelephoto objectives that havezero Petzval sum. These devicesemploytwo or three varifocal lenses, which may be implemented by using a pair of free-form optical elements. Every pair is here denoted as a vortex pair. To our end, we revisit the Gaussian optics of a zoom system having a single varifocal lens. Next, we unveil a telephoto system that uses two varifocal lenses with zero Petzval sum. This system does not require of any axial movement. The optical powers of the varifocal lenses are related by the condition K₁ = − K₂ = q K₀. These lenses are separated by a distance d = 1/QK₀; where q and Q are positive real numbers such that 1 ≤ q < Q. We show that this optical system has extremely low telephoto ratios M = 1 – q/Q. Finally, we describe a 3-lens solutionwith zero Petzval sum, which uses three varifocal lenses and it requires anaxial displacement.This latter solution may be useful for reducing other type of aberration rather than field curvature. We discuss what we believe to be the first formulas representing theseimaging devices. © Anita Publications. All rights reserved.

Total Refs : 22

Vol. 23, No. 4 (2014) 543-560

Self-Similarity in the Farfield Diffraction Patterns of Annular Walsh Filters

 

P Mukherjee and L N Hazra
Department of Applied Optics and Photonics, University of Calcutta, Acharya Prafulla Chandra Shiksha Prangan, JD-2,

 Vol. 23, No. 4 (2014) 561-566

Development of a multiaperture imaging system using a microlens array

 

Unnikrishnan Gopinathan, Amit Agarwal, Amit Aran, Rashmi Negi, Arun Kumar and Ajay Kumar

Multiaperture imaging systems can achieve performance comparable to single aperture systems with reduced system volume and weight. This paper discusses the design and development of a multiaperture imaging system using Microlens arrays. The shift in the microlenses of the array is used to enhance the resolution of an image produced by a single microlens. © Anita Publications. All rights reserved.

Keywords: Microlens array, Multiaperture imaging

 Vol. 23, No. 4 (2014) 567-572

Effect of pump intensity on Two photon induced UV Photoluminescence in PLD thin film of ZnO

 

Archana Kushwaha, Satchi Kumari and Alika Khare

Laser and Photonics Lab, Department of Physics, Indian Institute of Technology Guwahati

In the present work, high quality transparent ZnO thin film has been deposited on sapphire substrate via pulsed laser deposition (PLD) technique at room temperature. Epitaxial growth of ZnO thin film on sapphire substrate was confirmed by Raman spectrum. The optical band gap was found to be 3.2 eV, which is in accordance with that of single crystal ZnO. A blue shifted two photon induced broad ultraviolet photoluminescenec (UV-PL) having peak at 3.57 eV, was observed via pumping with a 30 mW He-Ne laser at 633 nm. Effect of pump intensity on UV- PL from the ZnO film was studied. The slope of linear fit of the log-log plot of PL intensity vs pump intensity, was found to be ~1.95 confirming the two-photon absorption phenomenon in the film. © Anita Publications. All rights reserved.

Keywords: ZnO thin film, Photoluminscence, Two-photon absorption, excitonic emissions.

 Vol. 23, No 4 (2014) 573-579

THz generation in DAST through DFG-Cherenkov phase matching

 

Nimish Dixit¹, Maria Farooqui², Ajay Mishra¹, Vijay Kumar² and Arun Kumar Gupta^1
1Photonics Research Center, Instruments Research & Development Establishment (IRDE)

Defence Research & Development Organisation (DRDO), Dehradun-248008, INDIA

Numerical simulation has been done to study the Cherenkov difference frequency generation (DFG) in the DAST crystal. Discrete regions of THz frequency in DAST have been identified to study the tuning characteristics. A maximum of 9.4 MW Cherenkov DFG power was obtained at 0.82 THz corresponding to which the Cherenkov angle was 32.76°. We have also simulated the spatial field distribution for 0.82 THz in DAST crystal, which clearly exhibits the wedged- shape phase fronts of THz radiation. The tuning characteristic of Cherenkov DFG has been compared with that of collinear DFG. A maximum of 2.6 W of collinear DFG power was obtained at 0.48 THz while at the same frequency the Cherenkov DFG power was found to be 5.17 MW. The variation of Cherenkov DFG power with the input beam spot size has also been investigated. It was found that Cherenkov phase matching was almost twice more sensitive towards spots size variation as compared to collinear phase matching. © Anita Publications. All rights reserved.

Keywords: Cherenkov phase matching, collinear phase matching, difference frequency generation, DAST.

 Vol. 23, No 4 (2014) 581-590

Characterization of multichannel deformable mirror for adaptive optics applications

 

Awakash Dixit^{1, 2},Vikash Porwal¹ and Sanjay Kumar Mishra¹

Deformable mirror is used for correcting the aberrations of an optical wavefront in adaptive optics. In this paper, 97 channel deformable mirror having PZT actuation mechanism is characterized and results are presented. Performance of deformable mirror depends on the various parameters such as initial mirror surface figure, single actuator stroke, inter-actuator stroke, inter-actuator coupling and mirror response functions. These parameters are measured experimentally using an Interferometer and a Shack-Hartmann wavefront sensor. Results are discussed by analyzing the interferograms of the deformable mirror surface and phase data from the Shack-Hartmann wavefront sensor for various cases. © Anita Publications. All rights reserved.

Keywords: Adaptive optics, Deformable mirror, Shack-Hartmann wavefront sensor.

 Vol. 23, No 4 (2014) 591-596

Design of long period waveguide grating filters using genetic algorithm optimization

 

Girish Semwaland Vipul Rastogi

¹Instrument Research and Development Establishment Dehradun-248008, India

Global optimization properties of genetic algorithms (GA) have been utilized to design long period waveguide grating devices for the application specific spectra. Pre-defined target spectra corresponding to specific application have been considered. The grating parameters of corrugated grating have been obtained using GA optimization to achieve these target spectra. The simulation results show that the method is easy to implement and useful to design the grating for any pre-defined application specific spectra. © Anita Publications. All rights reserved.

 Vol. 23, No 4 (2014) 597-612

A cryptosystem for watermarking based on fractional Fourier transform using a random phase mask in the input plane and a structured phase mask in the frequency plane

 

Hukum Singh*, A K Yadav, Sunanda Vashisth, and Kehar Singh

Department of Applied Science

A watermarking scheme has been proposed in the fractional Fourier transform (FrFT) domain, using a random phase mask in the input plane and a phase mask based on the devil’s vortex Fresnel lens (DVFL) in the frequency plane. The use of a structured phase mask based on the DVFL provides an advantage of extra encryption parameters, besides overcoming the problem of axis alignment associated with an optical set-up. The encrypted image resulting from the application of FrFT is attenuated by a factor and combined with a host image to provide a watermarked image. The decryption process is the reverse of the encryption. Digital implementation of the proposed scheme has been performed using MATLAB 7.1. The validity of the proposed scheme has been established by comparing the results of decryption with the input images. The performance of the scheme has been evaluated in terms of mean-squared-error (MSE). In addition, the sensitivity to encryption keys such as DVFL parameters and the FrFT orders has been studied. The proposed technique provides enhanced security. © Anita Publications. All rights reserved.

Keywords: Fractional Fourier transform, watermarking, devil’s vortex Fresnel lens, mean-squared-error, peak-to-signal-noise ratio.

 Vol. 23, No 4 (2014) 613-622

Periodically poled lithium niobate for Mid-IR tunable wavelength generation using nonlinear frequency downconversion

 

In the present work, we demonstrate a high repetition rate mid-infrared tunable wavelength generation in a singly resonant Optical Parametric Oscillator (OPO). A multi-grating periodically poled LiNbO₃ (PPLN) fabricated in our laboratory has been used as a nonlinear converter. Multi-grating PPLN chip, which has been fabricated using electric field (E-field) poling technique, contained gratings with varying periodicity from 25.0 to 32.0 µm in the steps of 0.5 µm. The gratings have been observed to have around 45% duty cycle that is required for efficient parametric conversion. This period variation corresponds to the generation of signal beam from 1.3 to 1.9 µm and Idler beam from 2.4 to 4.8 µm, respectively for 1064 nm pump beam. A 1064 nm Q-switched Nd:YVO₄ laser at 10 KHz repetition rate and pulse width of 18.7 ns was used to pump the OPO. A maximum of 200 mW signal power and 150 mW of Idler power have been obtained with an input pump beam of power 2.6 W, for a period of 29.5 µm. A maximum optic-optic conversion efficiency of 14 % and 6 % in the idler has been observed. It has been observed that as we increase the period of the grating output power increases.© Anita Publications. All rights reserved.

PACS: 42.65.Ky, 42.65.Lm, 42.65.Yj, 42.65.Mp

Keywords: Optical Parametric Oscillator, PPLN, Parametric Generation, Frequency down conversion

 Vol. 23, No 4 (2014) 623-626

Core technology for Terahertz applications

 

Surya P Tewari
Formerly at Advanced Centre of Research in High Energy Materials and School of Physics

The terahertz (10¹² Hz) frequency range generation in condensed matter by asymptotic approaches from microwave side and from optics side needs to give way to the core Technology, which requires small device with low input power for the development and use of THz science for evolving technologies, which will take process monitoring and biological researches to high level of sophistication. © Anita Publications. All rights reserved.

Keywords: Terahertz, Harmonic oscillator/s, nonlinear interactions

 Vol. 23, No 4 (2014) 627-630

Wave propagation in ternary photonic crystal with metamaterials

Laxmi Shiveshwari

The photonic band structure of one dimensional ternary photonic crystal made of a conventional dielectric material, a negative permittivity and a negative permeability metamaterial is studied theoretically using the transfer matrix method. The proposed structure eliminates the Brewster’s angle transmission resonance giving a complete photonic band gap, completely independent of polarization dependent weakly on angle of incidence.© Anita Publications. All rights reserved.

Keywords: Metamaterial, Complete band gap, Photonic crystals.

 Vol. 23, No 4 (2014) 631-640

Thermally actuated MEMS micromirror: Design Aspects

 

V Mere^{a, b}, Vikram Maharshi^a, Aditi^{a, b} and Ajay Agarwal^{a, b}

 ^aCSIR- Central Electronics Engineering Research Institute (CSImR-CEERI), Pilani-33303,  India

The paper presents thermally actuated micro-mirrors with three degrees of freedom. The bimorph actuators are made of aluminum and silicon. The mirror and actuators are connected and thermally isolated through meander springs. Heaters with aluminum as the heater element were optimized using COMSOL simulation. The maximum actuator deflection is achieved at heater temperature of 106.59°C at applied voltage 0.2 V, with a response time of 0.9 ms. The resulting tilt angle of the mirror is ±4.73 degrees. In piston mode the mirror displacement of 30 mm is achieved for the same applied voltage.© Anita Publications. All rights reserved.

Keywords: Bimorph, Spring, Micro-mirror, Heater element.

 Vol. 23, No 4 (2014) 641-644

 must be accurately centered with respect to the optical axis. The level of accuracy depends on the intended application. Even a relatively small centering error influences the image quality of an objective in a serious way. Such errors can rapidly multiply in a lens system and lead to alignment issues and nonsymmetrical aberrations. Constant demands on improved image quality have resulted in a continuous improvement of centering process and its measurement. Centration tolerance is very sensitive to control in meniscus shape lenses as both the radii of curvature lie on the same side of lens surface. Meniscus shape lenses are generally used to control spherical aberration and commonly used in thermal imaging system. In this work we have shown a method for controlling and high precision measurement of centering error in reflection mode as infrared materials such as silicon, germanium etc are non transparent to visible light so transmission methods are not applicable for centering error measurement using the visible light source. © Anita Publication. All rights reserved.

Keywords: Deep curvature meniscus lens, centering error, Infrared Lens.

 Vol. 23, No 4 (2014) 645-650

We report the effect of tunable wavelengths obtained from femto seconds laser on low temperature gallinium arseide (LT-GaAs) based dipole types Photo conductive (PC) antennas with gap of 5 micron for the generation of terahertz (THz) signals. Two sets of PC antennas (having similar design and substrate material) marked as LT₁ and LT₂ are subjected to 140 femto seconds laser pulses at 80 MHz frequency of different power, biasing voltages and tunable wavelengths to evaluate their THz generation efficiency. The generated THz power is measured by low noised pyroelecric detector. The femto seconds laser is tuned between 700-1000 nm range to access the effect of photo-generative charge carriers. On comparison, we observed that LT1 generate 294 nW at 865 nm whereas LT2 produces 186.7 nW at 880 nm. The THz frequency spectrum range of LT-GaAs is extended upto 4.0 THz range. Generated THz radiation is also used to record the absorption of the paper of different thickness at 0.5 THz range. © Anita Publications. All rights reserved.

 Vol. 23, No 4 (2014) 651-657

We present the design and fabrication of binary phase-only Computer Generated Hologram (CGH) to generate a pattern in the far-field. The design method based on iterative Fourier transform algorithm is described. The CGH of about 10 mm × 10 mm size with 10µm × 10 µm cell size is realized in Photoresist using a maskless lithography system. The replication of fabricated CGH using soft-lithography technique is also discussed. © Anita Publications. All rights reserved.

 Vol. 23, No 4 (2014) 659-663

Micro lens array characterization using focal length interferometric and MTF evaluation

 

L M Pant, K K Pant, M P Singh and A Ghosh

Due to very small in dimensions micro lens array are fabricated using very specialized techniques and the physical and optical parameters of micro lenses like shape, radius of curvature, focal length, surface quality, as well as optical performance plays very important role in performance of those lenses. Present work focuses on the evaluation and characterization of micro lenses in terms of their physical and optical parameters. A setup is rigged up for the measurement of very short focal length (less than 10 mm) and implemented to micro lens. The microlens array was further evaluated for surface profile with aberration analysis and MTF. © Anita Publications. All rights reserved.

 Vol. 23, No 4 (2014) 665-669

Enhanced performance of diffraction free Airy and Bessel beams: a comparative study

 

Raj Bahadur Yadav,  Pramod Kumar Sharma and Arun Kumar Gupta

Any ordinary optical beam of light spreads as it travels due to diffraction of light. Quite recently, non spreading freely accelerating Airy beams have been realized in optics community. In this paper, we have reported Airy beam as diffraction free beam, which consists of two important properties viz freely acceleration and nonspreading. We have carried out simulation study for both 1-D and 2-D Airy beam propagation respectively. We have also made comparison among Airy beam, Bessel beam and Gaussian beam and our results infer that Airy beam propagates diffraction freely for a long distance in parabolic trajectory. While Bessel beam is less diffraction free and travels along linear axis. © Anita Publications. All rights reserved.

Keywords: diffraction, propagation, Airy beam, Bessel beams, Gaussian beams.

 Vol. 23, No 4 (2014) 671-678

Transition from non-resonant feedback random lasing to resonant feedback random lasing

 

Arun S and V P N Nampoori

International School of Photonics

Zinc oxide nanoparticles of size 300 nm were prepared using polyol method. These particles were dispersed in Rhodamine 6G solution and random lasing was then observed from this solution. When the scatterer concentration was varied an optimum particle density value range was observed below which no lasing occurred. The transition from Non-Resonant Feedback lasing to Resonant Feedback lasing was clearly observed. © Anita Publications. All rights reserved.

Keywords: Random Lasing, Coherent Backscattering, Nanoparticle.

 Vol. 23, No 4 (2014) 679-682

Macroscopic polarization and thermal conductivity of InN

 

B K Sahoo

InN is a promising material for optoelectronic devices. The macroscopic polarization is a unique and peculiar property which affects optical and thermal properties of InN. Our theoretical calculation shows that polarization mechanism enhances the thermal property of InN. We estimated elastic constant, Debye temperatue and the thermal conductivity of InN. Analysis shows that these parameters are significantly enhanced by the polarization effect. The revised thermal conductivity at room temperature is found to be increased by 18% in InN. The result can be used for simulation of heat energy in the active region of InN optoelectronic devices to minimize the self heating. © Anita Publications. All rights reserved.

Keywords: Wurtzite InN, Macroscopic polarization, Thermal properties.

 Vol. 23, No 4 (2014) 683-686

Tuning of particle size and band gap of CdSe nanoparticles prepared by reflux method

 

Anju K Augustine, V P N Nampoori and M Kailasnath

We have synthesized CdSe nanoparticles with particle sizes in the range 4.6–5.2 nm through aqueous method using reflux process. The absorption spectra clearly show a tunable change in absorption edge from 430-510 nm. Sharp excitonic peaks in the spectra indicate monodispersion of the CdSe nanoparticles. Red-shift in emission peak arises due to the increase in size of the nanoparticles, as the reflux time is increased. Energy band gap of the nanoparticles shows a variation  from 2.52 -2.35 eV as the particle size increased. ©Anita Publication. All rights reserved.

Keywords: Nanoparticle, emission, bandgap.

 Vol. 23, No 4 (2014) 687-691

Interferometric Fiber Optic Accelerometer

 

Ajay Prakash*, Pradeep Kumar and Jagannath Nayak

An interferometric fiber optic accelerometer based on Fiber Bragg grating (FBG) is designed and simulated. An L-shaped cantilever and Mach-Zehnder interferometer (MZI) is used to convert acceleration induced wavelength shift into phase variation. Simulation is carried out to find sensitivity, range of the preferred configuration. Acceleration sensitivity of the order of 2.0 µg is reported. © Anita Publications. All rights reserved.

Keywords: accelerometer, fiber Bragg grating, Mach-Zehnder interferometer

 Vol. 23, No 4 (2014) 693-695

Generation and characterization of 2.1 mm laser from 1.06 mm pumped KTP OPO

 

K C Bahuguna*, N S Vasan, S P Gaba and S S Negi

Instruments Research and Development Establishment, Dehradun (Uttarakhand)

Potassium Titanyl Phosphate (KTP) crystals are widely used in optical parametric oscillators (OPO) because of their high effective non-linear coefficient, good thermal conductivity, exceptionally large temperature bandwidth and high optical damage threshold. Despite these advantages, KTP has certain limitations like beam walk-off and gray-tracking which limit its performance in an OPO. To overcome these limitations, crystals developed with new techniques viz. adhesive-free bonded KTP that has negligible beam walk-off characteristics and high gray track resistant (HGTR) KTP have been studied and used to design an OPO cavity. We present here the experimental results of a degenerate OPO using HGTR KTP that generates 2.1 µm output. An average output power of 8 W at 10 KHz has been achieved that includes both signal as well as idler powers near degeneracy using 20 W average power from a 1.064 µm pump source. The optical to optical conversion efficiency of the OPO is nearly 38%. © Anita Publications. All rights reserved.

 Vol. 23, No 4 (2014) 697-703

Optimization of S-bend waveguide parameters for delay line based phase shifter in integrated optics

 

Rajini V Honnungar, Soumya N, and T Srinivas

The design and optimization of a optical phase shifter at 1.55µm using Beam Propagation Method is proposed. The idea is to generate a differential phase shift using straight waveguides and S-bend waveguides. The paper discusses the design of integrated optic (IO) elements of the Phase shifter block. The optimized parameters could be used in the practical realization of the device. Phase shifts obtained are validated using  interferometric technique. The modulated RF signal obtains the phase shift in the optical domain which is transferred to the RF signal by heterodyning techniques. ©Anita Publications. All rights reserved.

Keywords: Integrated optics, Bent waveguides, Heterodyning.

 Vol. 23, No 4 (2014) 705-712

Design and optimization of micro ring resonator for multimode condition

 

Soumya M, Rajini V Honnungar and T Srinivas

The paper aims at design of integrated optical Micro Ring Resonator (MRR). The ring resonator would normally be designed with the single mode condition, and its dimensions, but this paper mainly concentrates upon designing ring resonator for multimode condition that is obtained by breaking the single mode condition which is already available. The multimodal condition will result in many resonating frequencies (or wavelength) because the basic higher order modes will be guided through the core. The band of frequencies obtained can be utilized for WDM applications also. © Anita Publications. All rights reserved.

Keywords: Integrated optics, Microring resonator, Multimode condition

 Vol. 23, No 4 (2014) 713-720

Performance analysis of Mach-Zehnder modulator for analog WDM links

 

Meena D^1,2, Srinivas Talabattula¹, DC Pande², Dipin E³, Fredy Francis³, Sarath K T³

¹Applied Photonics Lab, Indian Institute of Science, Bangalore

²Electrical Communication Engineering, Indian institute of Science, Bangalore

The Mach Zehnder Interferometer (MZI) modulator has wide acceptance in optical communication systems because of its advantages like lower chirp, high output power and the capacity to handle high power. The advancement in Microwave photonics made possible the transmission of high frequency signals over fiber links. These applications require sources with external modulation capability like in MZI modulators. This work brings out some of the analysis carried out on MZI modulators with various high frequency waveforms like Continuous wave (CW), Pulsed CW, Linear Frequency Modulated (LFM) and Non-Linear Frequency Modulated (NLFM) waveforms. Thus the paper describes about both mathematical and co-simulation model to have a better comparison. Further, accuracy of the model is verified with experimental results using a WDM link. The results observed were in compliance with developed model results. The model is also evaluated with variations in different parameters like input power, input dc bias voltage and modulator full swing voltage. Thus the paper includes analysis results of above observations. © Anita Publications. All rights reserved.

Total Refs : 14