In this analytical approach, electro-optically tunable second-order cascaded nonlinearity was targeted to investigate the potential of ultrashort pulse compression in a tapering nonlinear medium. The proposed framework is ideally suited to generating high-intensity pulses with small pulse widths by exploiting second-harmonic generation and the electro-optic effect in a bulk beta-barium borate with exceptional optical advantages. Considering both linear and nonlinear absorption losses, the necessary and sufficient conditions for the compression of ultrashort pulses were developed using the generalized nonlinear Schrödinger equation. In agreement with simulations, an attempt is made to compress an optical pulse from 120 to 39 fs using an external voltage of ∓5.69 KV, which leads to a phase mismatch ( Δk ) = ± 124.8 m − 1, a phase shift ( ΔϕNL ) = ± 1.26π, and an effective cascaded refractive index (n2cascade)=±3.371×10−20 m2/W. The results suggest that the technology developed in this study will open the door to a plethora of applications, including fields as diverse as laser surgery, range finding through LIDAR, and many more.
The present work introduces the concept of a total-internal-reflection (TIR)-based optical rotation, quasi-phase-matching (QPM) technique for generating highly efficient second-harmonic optical output in a rectangular slab of magnesium oxide-doped lithium niobate crystal coated with a thin layer of yttrium oxide. Combinational effects of TIR optical rotation QPM and fractional QPM techniques are experienced at certain bounce points inside the slab, thereby enhancing the conversion efficiency. In this analysis, the thin-film is used for controlling the phase-shifts accompanying the propagation of p- and s-polarized light at the slab-film interface during TIR. A conversion efficiency of 32%, corresponding to a second-harmonic wavelength of 532 nm has been observed using computer-aided simulation. Optical losses such as surface roughness, absorption, and interference effect due to the nonlinear law of reflection have also been incorporated.
Bend-induced loss in microbending fiber-optic sensor has proved to be an effective one for the direct and indirect measurement of various physical parameters. In this research, a novel and highly sensitive microbend sensor has been explored by launching a zero order Bessel-Gauss beam inside a waveguide arrangement having a No-core fiber bonded amidst two special higher-order mode supporting fibers. By harnessing the special characteristics of the Bessel-Gauss beam, pairing of manifold high-order modes has been affirmed inside the sensor structure. The captivating feature of such sensor is that it defies the conventional wisdom and significantly improves the sensitivity without any intricate fabrication techniques like in tapering, bending etc. To our knowledge, such realization of Bessel-Gauss beam-shined microbend sensor has not been reported earlier in any of the contemporary literature. In support of our theoretical analysis; a Beam propagation method is employed in OptiBPM software (Optiwave Systems Inc.) to envisage the full transmission spectrum of the waveguide. For different bend radii, the sensor response has been numerically investigated and it is anticipated that the sensitivity is expected to be enhanced by a gentle reduction in the bend radius. With the presence of six microbends, the proposed sensor manifests an average bend sensitivity of 2.8 dB/mm which is 3.2 times superior to the classical microbend sensing configuration. Due to such superior sensing performance, the present paradigm paves the way for many potential applications, like damage detection of various engineering structures, and measurement of different physical parameters like temperature and pressure.
We present a theoretical perspective on the notion of a highly sensitive multimode fiber optic evanescent wave absorption-based sensor by exploiting a zero-order Bessel–Gauss beam to determine the concentration of sodium chloride (NaCl) from its aqueous solution. The phenomenon of excited waveguide modes inside the sensor structure has been assessed by using a classical wave-optic model. By harnessing the advantages of the Bessel–Gauss beam, the difference in transmitted output power is evaluated for various concentrations of NaCl, ranging from 0 to 360 g/L. To corroborate our theoretical predictions, the computer-aided simulation in Mode Solutions software has been performed on the proposed sensing configuration. In contrast to the conventional concentration sensor using Gaussian beam, the projected scheme yields a maximum 14.40-fold superior sensitivity of 0.072 dB / gL − 1 with a commendable sensing resolution of ∼0.013 g / L. Also, attention has been paid to the Bessel–Gauss beam shined U-bent fiber-optic absorption-based concentration sensor, where the sensor response has been numerically investigated for different bending radii, and it is concluded that the sensitivity can be enhanced appreciably by gently reducing the bending radius. Due to ultrahigh sensitivity, the present paradigm is very much alluring and evocative, establishing pivotal implication in chemical and biological sensing fields.
A proposal toward the enhancement in the sensitivity of a multimode interference-based fiber optic liquid-level sensor is explored analytically using a zero-order Bessel–Gauss (BG) beam as the input source. The sensor head consists of a suitable length of no-core fiber (NCF) sandwiched between two specialty high-order mode fibers. The coupling efficiency of various order modes inside the sensor structure is assessed using guided-mode propagation analysis and the performance of the proposed sensor has been benchmarked against the conventional sensor using a Gaussian beam. Furthermore, the study has been corroborated using a finite-difference beam propagation method in Lumerical’s Mode Solutions software to investigate the propagation of the zero-order BG beam inside the sensor structure. Based on the simulation outcomes, the proposed scheme yields a maximum absolute sensitivity of up to 3.551 dB / mm and a sensing resolution of 2.816 × 10 − 3 mm through the choice of an appropriate length of NCF at an operating wavelength of 1.55 μm. Owing to this superior sensing performance, the reported sensing technology expedites an avenue to devise a high-performance fiber optic-level sensor that finds profound implication in different physical, biological, and chemical sensing purposes.
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.
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.
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.
Fiber-optic displacement and vibration sensor are described in a single set up with higher dynamic range. Hard polymer clad silica fiber is used for both transmission and reception of light. The sensor system consists of coherent optical source, transmitting fiber, bi-convex lens, receiving fiber array, detectors and electronic circuitry. Light of (lambda) equals 980 nm is launched to transmitting fiber and light reflected from the target is received by fiber array and detected by p-i-n diode. Detected power of two adjacent fibers is subtracted by difference amplifier and followed by a level shifter. A mathematical model relating focal length of lens, radius of fiber, spacing between transmitting and receiving fiber, distance of the fiber from optical axis has been developed. The range of linear displacement, and angular displacement using four receiving fiber array is 0 to 1365 micrometers and 0 degrees to 0.5, respectively. The same concept of measurement is also applied to develop a vibration sensor. The range of measurement of peak to peak amplitude of vibration using three fiber array is obtained as 910 micrometers .
A step index planar microlens fabrication process is described for obtaining low spherical aberration. This microlens can be used to achieve effective light coupling between different optical elements and microcircuits in integrated optics. Polymethyl methacrylate (PMMA) doped with N, N'-dihexyl-amino-nitrostelbene (DHANS) is used as lens materials. A concave surface of 580 micrometers diameter is made on Germenia-Silica glass substrate of refractive index 1.4537 at (lambda) equals 1.3 micrometers . Films of different refractive indices are deposited one upon another on the concave surface to obtain multi-layered step index microlens. Refractive index variation of different layers is controlled by percentage of DHANS doping in PMMA. Spherical aberration of the lens is minimized by using step index multi-layered structure of the lens. Theoretical model for longitudinal and lateral spherical aberration is developed using ray theory. The lateral and longitudinal spherical aberration is minimized to a lower value of 1.55 micron and 48.87 micron respectively with the numerical aperture of the lens NA equals 0.0209 and focal length f equals 13.78 mm.
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