We consider a light wave propagation in tapered photonic crystal fibres (PCFs) wherein the wave propagation is described by the variable coefficient nonlinear Schrödinger equation. We solve it directly by means of the theta function identities and Hirota bilinear method in order to obtain the exact periodic waves of sn, cn and dn types. These chirped period waves demand exponential variations in both dispersion and nonlinearity. Besides, we analytically demonstrate the generation of a train of ultrashort pulses using the periodic waves by exploiting the exponentially varying optical properties of the tapered PCFs. As a special case, we discuss the chirped solitary pulses under long wave limit of these periodic waves. In addition, we derive these types of periodic waves using the self-similar analysis and compare the results. © 2016 Informa UK Limited, trading as Taylor & Francis Group.

Senthilnathan K

Department of Physics

School of Advanced Sciences

Vellore Campus

Atuba S.O

Nakkeeran K

Chow K.W

Babu P.R

Manimegalai A

Fulltext

Vellore Institute of Technology (VIT) is a private university located in&nbsp;Tamil Nadu, India. Founded in 1984, as Vellore Engineering College, the institution offers 20 undergraduate, 34 postgraduate, four integrated and four research programs. It has campuses in Vellore, Amravati, Bhopal and Chennai.

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Generation of a train of ultrashort pulses using periodic waves in tapered photonic crystal fibres

Journal of Modern Optics

This work stems from the motivation of a recent investigation on single- and pulse-train compression schemes using solid core as well as chloroform-filled photonic crystal fiber (PCF), with both hyperbolic secant and raised-cosine pulse profiles. To study the robustness of the proposed optical pulse compressor, we perturb the loss coefficient and study the deviations in the pedestal energy and compression factor for both pulse profiles. To this end, we perturb the loss coefficient of the solid core PCF over a range of&nbsp;<figure class="image"><img src="https://www.tandfonline.com/na101/home/literatum/publisher/tandf/journals/content/tmop20/2013/tmop20.v060.i05/09500340.2013.777810/20130409/images/tmop_a_777810_o_ilm0001.gif" alt=""></figure>% and, in a similar way, we carry out this study for the chloroform-filled PCF, but with the perturbation restricted to a lower level, i.e. over a range of 300 % due to the higher value of the nonlinear growth rate. We compare the intensity profiles of the perturbed compressed pulses with that of an unperturbed pulse. Although the self-similar analysis essentially demands that the loss coefficient matches the nonlinear growth rate for the realization of ideal pulse compressors, based on the numerical results we confirm that the proposed compressor is capable of producing good quality short pulses with negligible amount of pedestals and high compression factor even if there is a deviation of admissible level from the above mentioned condition. Consequently, we corroborate that the proposed compressor is very robust against perturbations.

Realizing a robust optical pulse compressor operating at 850 nm using a photonic crystal fiber

We consider an optical pulse propagating in a tapered photonic crystal fiber (PCF) wherein dispersion as well as nonlinearity varies along the propagation direction. The generalized nonlinear Schrödinger equation aptly models the pulse propagation in such a PCF. The design of the tapered PCF is based on the analytical results, which demand that the dispersion decrease exponentially and the nonlinearity increase exponentially. In this paper, we adopt the generalized projection operator method for deriving the pulse-parameter equations of the Lagrangian variation method and the collective variable method. Besides, we consider another pulse profile called raised cosine (RC), which is aimed at replacing the conventional hyperbolic secant pulse. From the detailed results, we infer that the initial RC pulse evolves into a hyperbolic secant pulse. Further, in order to minimize the input power requirement, we employ the idea of replacing the solid core in the PCF with chloroform. In addition to the single pulse compression, we also investigate the possibility of multisoliton pulse compression. Here, we consider eight chirped hyperbolic secant pulses as input and generate a train of ultrashort pulses at 850 nm based on the chirped multisoliton pulse compression. In a similar way, we extend this pulse compression with eight RC pulses.

IEEE Photonics Journal

Generation of a Train of Ultrashort Pulses Near-Infrared Regime in a Tapered Photonic Crystal Fiber Using Raised-Cosine Pulses

Nearly pedestal-free optical pulse compression using self-similar chirped optical solitons near the photonic bandgap (PBG) structure of nonlinear fiber Bragg gratings (NFBGs) with exponentially decreasing dispersion is investigated using the generalized nonlinear coupled-mode equations (NLCMEs). The full dispersion characteristics and the effect of PBG are included. We find that the ratio of the frequency detune of the pulse's center frequency from the Bragg frequency of the NFBG to coupling coefficient of the NFBG is an important design parameter of the NFBG optical pulse compressor. We carried out a comprehensive study on the effect of the ratio of frequency detune to coupling coefficient, grating length, initial chirp, initial dispersion, and initial pulsewidth on the self-similar optical pulse compression. We also studied the compression of both the hyperbolic secant and Gaussian-shaped pulses and the effect of variation in the initial pulsewidth on the optical pulse compression. © 2006 IEEE.

Journal of Lightwave Technology

Modeling Self-Similar Optical Pulse Compression in Nonlinear Fiber Bragg Grating Using Coupled-Mode Equations

Journal of the Optical Society of America B

High-power pulse trains excited by modulated continuous waves

Nonlinear Fiber Optics

Highly Nonlinear Fibers

Journal	Journal of Modern Optics
Publisher	Informa UK Limited
ISSN	0950-0340
Open Access	No