Presence Of Optical Nonlinearity Research Articles

A Perspective on Synthetic Dimensions in Photonics

AbstractThe concept of synthetic dimension has recently emerged as a versatile way to overcome limitations in the number of effectively available dimensions by leveraging non‐spatial degrees of freedom to mimic additional geometric ones. In particular, the field of photonics offers a plethora of technological possibilities for controlling photons and their degrees of freedom, such as polarization, frequency, or orbital angular momentum. Consequently, a broad range of higher‐dimensional physical phenomena is already experimentally accessible in lower‐dimensional photonic devices and has been used and celebrated, for instance, for the exploration of topological physics. The field of synthetic dimensions is currently even further boosted due to additional mathematical mapping procedures, which pave the way toward even higher synthetic dimensions or, in the presence of optical nonlinearities, can translate to multi‐particle quantum systems, allowing appealing alternatives for quantum simulation. In this perspective, current experimental approaches for harnessing synthetic dimensions to probe higher‐dimensional physics on various light‐based platforms are summarized and discussed including an outlook on promising future prospects in this field.

Physical Layer Cryptographic Key Generation by Exploiting PMD of an Optical Fiber Link.

We present a symmetric physical layer based secret key generation scheme for Point-to-Point Optical Link (PPOL) communication by exploiting Polarization Mode Dispersion (PMD) as a random and inimitable channel characteristic. The randomness and security strength of generated cryptographic keys based on PMD is significantly high. In this paper, we present that random modulation of a probe signal caused by PMD in a high-speed data communication network (40Gb/s and 60Gb/s) is reciprocal with average Pearson correlation coefficient of 0.862, despite the presence of optical nonlinearities, dispersion, and noise in the system. 128-bit symmetric cryptographic key has been successfully generated using the proposed scheme. Moreover, PMD based encryption keys passed the National Institute of Standards and Technology (NIST) tests. We have shown through simulations with a 50km link that, with optimal key generation settings, symmetric keys can be generated with high randomness (high P-values for NIST randomness tests) and with sufficient generation rates (>50%). Furthermore, we considered an attack model of a non-invasive adversary intercepting at 10km into the link and found that the generated keys have high average key bit mismatch rates (>40%).

Nonlinear effects in aspect ratio based far-field characterization of single-mode trapezoidal index fibers

We investigate the effect of Kerr nonlinearity on the angle of beam divergence of single-mode trapezoidal index fibers from its linear and nonlinear values. From comparison of angle of beam divergence in presence and absence of Kerr nonlinearity, the nonlinear effect for each aspect ratio is observed to be more profound in lower values of normalized frequency. Moreover, the triangular index profile supersedes the other index profiles in respect of relative change of angle of beam divergence. It should give the system users and developers a much better control over far-field related calculations and can be widely used for experiments in presence of optical nonlinearity.

Effect of nonlinearity on the dynamics of Bragg-induced optical Rabi oscillations in a one-dimensional periodic photonic structure

Propagation of wide optical beams in transverse periodic lattices have been reported to induce power oscillations between Fourier modes related by the Bragg resonance condition, resulting from the coupling between the beam and the periodic structure. These oscillations have been referred to as Rabi optical oscillations due to the analogy with matter Rabi oscillations. In this work, we investigate the behavior of Bragg-induced Rabi-type oscillations of a multimode Gaussian beam in the presence of optical nonlinearity. We find a combination of oscillation and spectrum broadening under both self-focusing and self-defocusing nonlinearities, in the sense that the oscillations are maintained while the spectrum is broadened and therefore partially transferred to the twin frequency. For intense self-focusing nonlinearities a complete leak of the initial mode profile to other modes is rapidly attained so that no oscillation is observed. In contrast, for intense self-defocusing nonlinearities the redistribution rate is so dramatic that oscillations cease and power only fades away.

Simple but accurate method to compute LP11mode cutoff frequency of nonlinear optical fibers by Chebyshev technique

We propose a simple method to compute the first higher order mode cutoff frequency of a single-mode fiber in the presence of optical nonlinearity. We consider optical Kerr-type nonlinearity for these fibers having dispersion-shifted and dispersion-flattened profiles. Our analysis involves the Chebyshev method but introduces a linearization of cubic terms of fields due to Kerr-type nonlinearity. Our results are shown to match excellently with the available exact numerical values. Thus, this formulation and stepwise algorithm should be considered as a simple but accurate alternative to deeply involved numerical technique and used as a guideline in calculating and minimizing the modal noise in single-mode nonlinear fibers.

Prediction of modal dispersion in nonlinear single mode optical fiber using simple Chebyshev technique

We have predicted the normalized group delay and modal dispersion in Kerr nonlinear single mode fibers using a recently proposed simple and efficient Chebyshev method in presence of optical nonlinearity. It is seen that the proposed technique estimates the dispersion parameters accurately since results obtained by our method agree excellently with those from rigorous techniques over a large range of normalized frequency. Although we’ve considered step index fiber as a typical example, our analysis is also applicable to graded index fibers as well.

Optimum pre-emphasis in ultra-long-haul networks

We investigate experimentally and theoretically the shape of the optimum spectral pre-emphasis for ultra-long-haul networks and systems in the presence of optical nonlinearities. In a 40×10 Gbits/s×2240 km system, we experimentally show the advantages of a pre-emphasis scheme that ensures minimum variations of path-averaged power among the wavelength-division-multiplexing channels between the cleanups performed by dynamic gain-flattening filters. This is achieved by enforcing a straight-line spectrum near the middle of the link between two consecutive gain-flattening nodes. We explain these results by a simple model, in which we derive the conditions for optimum pre-emphasis in the presence of either distortionlike (e.g., self-phase modulation) or noiselike (e.g., four-wave mixing) nonlinearities. We show that, for relatively small gain ripple, both of these optimum pre-emphasis techniques are equivalent to equalizing the optical signal-to-noise ratio for all channels and producing a flat power spectrum near the middle of the link. Hence, enforcing the straight-line spectrum in the middle of the link is the closest practical approximation to the optimum pre-emphasis.