Ardhendu Saha

Broadband fractional total internal reflection quasi phase matching based second harmonic generation in reverse tapered isotropic semiconductor considering the effect of nonlinear reflection

This paper analyzes a highly efficient broadband second-harmonic generator in the mid infrared region using an isotropic reverse tapered semiconductor slab configuration, using fractional total internal reflection quasi-phase matching technique. A computer aided simulation has been performed using ZnTe as the nonlinear material which provides an extremely high conversion efficiency of 22.94% with a 3dB bandwidth of 200nm. Effect of varying the slab dimensions on the performance parameters has also been analyzed. Finally, the catastrophic effect caused by destructive interference due to nonlinear law of reflection has also been incorporated in the analysis thereby giving more accurate results.

Surface plasmon enhanced reflected second harmonic generation in periodically poled whispering gallery resonator

This paper analytically describes the surface plasmon enhanced very low threshold second harmonic generation formed by a 29 nm thin gold layer is sandwiched between a BK7 prism plane and 20 nm thin GaAs layer. Here the electric field with incident optical radiation of picowatt level is amplified upto milliwatt level through surface plasmon phenomenon at off resonance condition. This amplified output further coupled to a whispering gallery resonator, which facilitates the generation of second harmonic for an incident optical radiation of picowatt level. In this proposed configuration with an incident optical power of 94.6 pW generated second harmonic through whispering gallery resonator found to be 14.6 mW.

Total internal reflection quasiphase matching-based broadband second harmonic generation in a plane-parallel uniaxial crystal of lithium niobate

Abstract. The present work analytically investigates the generation of broadband second harmonic (SH) using total internal reflection (TIR) quasiphase matching technique in a plane-parallel uniaxial crystal having optic axis nonparallel with respect to the horizontal base. A computer-aided simulation has been performed using lithium niobate as the nonlinear material to determine the possibility of generating broadband SH intensity when broadband fundamental laser radiation is allowed to undergo TIR inside the crystal. The simulated results indicate a peak conversion efficiency of 5.22% with a spectral bandwidth (BW) of 116 nm, centered at 2.258  μm in a 10-mm-long slab. The effect of variation in operating temperature, crystal length, crystal thickness, angle of deviation of optic axis, and angle of incidence of fundamental beam at the air–prism interface on efficiency and BW of resulting SH output has been studied.

Electro-optically induced nonlinear phase shift in RTP crystal by cascaded second-order nonlinearity

An electro-optically tunable nonlinear phase shift is introduced in RTP by applying an electric field on x-y plane of the crystal. The nonlinear phase shift results from cascaded second-order nonlinearity in phase mismatched condition.

Multimode interference based high sensitivity refractive index sensor by shining zeroth order Bessel-Gauss beam

A novel fiber optic multimode interference based refractive index sensor by shining zeroth order Bessel-Gauss beam is reported and investigated. The proposed sensing scheme offers a 9.22 times higher sensitivity and an improved refractive index sensing resolution in the magnitude of around tenth order than the sensor using Gaussian beam.

Improved single stage grid connected solar PV system using multilevel inverter

A multilevel inverter based single stage grid connected solar PV system is proposed in this paper so as to reduce THD of the inverter voltage and reduce the size of filter circuit. A maximum power point tracking algorithm is implemented to obtain optimal performance of solar cell at different irradiance and temperature. Independent control of active and reactive power flow from inverter to the grid is obtained by implementing the control scheme in synchronously rotating reference frame. For interfacing the PV cell to the grid a 5kVA 3phase 3 level NPC Inverter is designed and fabricated. Space vector modulation scheme is used to generate the switching pulses for the inverter. Redundant switching states of a three level inverter are judiciously chosen to obtain capacitor voltage balancing. One of the most attractive features of a multilevel inverter is that it can generate output voltages with lower value of harmonic distortion and hence filter requirement is less. For hardware implementation the control scheme is implemented with a DSP. Complete scheme is simulated in MATLAB/ Simulink and verified in a 5kVA laboratory prototype.

Dispersion compensated optical amplifier in Ti-diffused PPLN ridge waveguide.

Nonlinear optical phase conjugation is known to be an effective technique for dispersion compensation in optical fibers. It requires an optical filter to separate out only the phase conjugated signal at the output to achieve signal pulse re-narrowing by its subsequent propagation through an identical medium. In this paper, a compact design, which integrates the optical phase conjugator and the filter on a single substrate of periodically poled lithium niobate and facilitates the use of a single pump source for both phase conjugation and amplification, is proposed and analyzed using computer simulations.

Broadband second harmonic generation in GaAs slab of hyperbolic upper surface using TIR-QPM

We have analytically described broadband SHG in GaAs crystal having hyperbolic upper surface profile. The SHG analysis in ppp polarization domain shows simulation results of enhanced 3dB bandwidth of 880nm with improved conversion efficiency of 1.3% around 8μm-10.5μm, considering reflection and absorption losses.

Enhanced lateral shifts with Gaussian beam and Laguerre-Gaussian beam in presence of surface plasmon resonance

First time a theoretical approach towards the enhancement of spatial and angular Goos-Hanchen (GH) shift and Imbert-Fedorov (IF) shift for a Gaussian beam and Laguerre-Gaussian beam are observed, designed and simulated in four layer Kretschmann-Raether geometry at a free space wavelength of 1550 nm. Here the proposed configuration comprises a ZnSe prism and a liquid crystal layer of E44 between two silver layers through which spatial and angular GH shift and IF shift can be observed for Gaussian beam as well as Laguerre-Gaussian beam whereas the exact output beam position can only be accurately identified with the composite effect of spatial and angular GH shift and IF shift. Here with the variation of incident angle from 400 to 500, the spatial and angular GH shift and IF shift have been calculated for two types of beams. This idea expedites the concept of optical tuning at μm ranges and reveals the exact output beam position for every experiments with different beams.

Polarization tunable spatial and angular Goos-Hänchen shift and Imbert-Fedorov shift using long range surface plasmon

A new proposal towards the polarization tunable Goos-Hänchen (GH) and Imbert-Fedorov (IF) spatial and angular shifts is explored analytically in a four layer Kretschmann-Raether geometry comprising a ZnSe prism, a dielectric layer of PMMA-DR1 (Polymethylmthacryalate-Disperse red) and two metal layers of silver having thicknesses of 50 nm and 200 nm respectively. Observations from the different graphical representations reveal that in correspondence of the long range surface plasmon (LRSP) resonant angle both spatial and angular GH shifts get appreciably enhanced in case of p polarized light whereas negligible or very less amplification of spatial and angular GH shifts are obtained for s polarized light. With the switching of polarization of the incident light beam on the proposed configuration through the half wave plate, the spatial and angular GH shift is tuned from -17.35 μm to 0.105 μm and -0.631 μrad to 4.28 nrad respectively and the spatial and angular IF shift is tuned from 94.16 μm to -53.58 μm and about 7.774 μrad to -11.17 μrad respectively. To the best of our knowledge, several articles have been devoted for depicting the GH shift without considering the IF shift, whereas the exact beam position of the output beam can only be identified with the composite effect of GH and IF spatial and angular shifts. The above new proposal can be implemented in the field of fine tuning of optical switching at the μm ranges with varying polarization, optical sensors applications and serves interesting opportunities to make atomic mirrors.