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Optics Express

Optics Express

  • Editor: Andrew M. Weiner
  • Vol. 21, Iss. 7 — Apr. 8, 2013
  • pp: 8298–8310
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A possible approach on optical analogues of gravitational attractors

Damián P. San-Román-Alerigi, Ahmed B. Slimane, Tien K. Ng, Mohammad Alsunaidi, and Boon S. Ooi  »View Author Affiliations


Optics Express, Vol. 21, Issue 7, pp. 8298-8310 (2013)
http://dx.doi.org/10.1364/OE.21.008298


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Abstract

In this paper we report on the feasibility of light confinement in orbital geodesics on stationary, planar, and centro-symmetric refractive index mappings. Constrained to fabrication and [meta]material limitations, the refractive index, n, has been bounded to the range: 0.8 ≤ n(r⃗) ≤ 3.5. Mappings are obtained through the inverse problem to the light geodesics equations, considering trappings by generalized orbit conditions defined a priori. Our simulation results show that the above mentioned refractive index distributions trap light in an open orbit manifold, both perennial and temporal, in regards to initial conditions. Moreover, due to their characteristics, these mappings could be advantageous to optical computing and telecommunications, for example, providing an on-demand time delay or optical memories. Furthermore, beyond their practical applications to photonics, these mappings set forth an attractive realm to construct a panoply of celestial mechanics analogies and experiments in the laboratory.

© 2013 OSA

1. Introduction

Einstein’s general relativity theory allows us to understand the dynamics of mass and massless particles as they travel through space-time. From it, we learn that matter and geometry are inextricably related; the latter transfigures the metric of space-time, and this alteration in turn modifies the geodesics, the paths of particles, resulting in a manifold of relativistic effects, v. gr. the apparent shift in the position of the stars due to the gravitational lensing effect, depicted in Fig. 1(a), where photons traveling near a massive star are deflected from their otherwise straight path due to the curvature of space-time; or trapping in multifarious orbits around black holes with respect to the initial conditions and shape of the gravitational attractor [1

1. J. Levin and G. Perez-Giz, “A periodic table for black hole orbits,” Phys. Rev. D 77, 103005 (2008) [CrossRef] .

3

3. T. Müller and J. Frauendiener, “Studying null and time-like geodesics in the classroom,” Eur. J. Phys. 32, 747–759 (2011) [CrossRef] .

], see Figs. 1(b) and 1(c).

Fig. 1: Comparison of sidereal and laboratory frame geodesics for light beams in (a) the vicinity of a star, (b) and (c) spinning black hole at different initial conditions, and (d) the laboratory across an heterogeneous monotonic increasing refractive index medium.

The latter analogy reveals a connection between both examples, a weft where both realms [sidereal and laboratory] can be understood as manifestations of the same mathematical ground, albeit significantly different physics, differential geometry. Einstein’s general theory of relativity tells us that geometry and gravity are linked by means of the metric tensor of space-time; in optics the intricacy of the relation between geometry and the physical properties of materials (permittivity and permeability) has been evinced by miscellaneous methods, most based on differential geometry [4

4. U. Leonhardt and T. G. Philbin, “Transformation optics and the geometry of light,” in Progress in Optics53, 69–153, E. Wolf, ed. (Elsevier, 2008) [CrossRef] .

7

7. D. Schurig, J. B. Pendry, and D. R. Smith, “Calculation of material properties and ray tracing in transformation media,” Opt. Express 14, 9794–9894 (2006) [CrossRef] [PubMed] .

].

Concerning trapping and light confinement in particular, different methods have been proposed [2

2. F. T. Hioe and D. Kuebel, “Characterizing planetary orbits and trajectories of light in the Schwarzchild metric,” Phys. Rev. D 81, 084017 (2010) [CrossRef] .

, 15

15. D. Genov, S. Zhang, and X. Zhang, “Mimicking celestial mechanics in metamaterials,” Nat. Phys. 5, 687–692 (2009) [CrossRef] .

17

17. S. L. Cacciatori, F. Belgiorno, V. Gorini, G. Ortenzi, L. Rizzi, V. G. Sala, and D. Faccio, “Spacetime geometries and light trapping in travelling refractive index perturbations,” New J. Phys. 12, 095021 (2010) [CrossRef] .

]. Of particular interest is Genov et al study, which presented an isotropic inhomogeneous refractive index mapping which was able to confine light mimicking a closed orbit around a black hole [15

15. D. Genov, S. Zhang, and X. Zhang, “Mimicking celestial mechanics in metamaterials,” Nat. Phys. 5, 687–692 (2009) [CrossRef] .

]. As the authors noted, such mapping could be implemented on a dielectric photonic crystal, composed of air-gaps in Gallium-Arsenide.

In our work, we posit theoretical traps that provide an optical analogue to celestial mechanics to realize light confinement, trapping in a region of space, by means of two-dimensional stationary refractive index mappings, which could be implemented under current technological and photo-refractive [meta]materials, constraint to optical frequencies, which could be easily integrable on all-optical-chips [18

18. D. P. San-Román-Alerigi, T. K. Ng, M. Alsunaidi, Y. Zhang, and B. S. Ooi, “Generation of J0-Bessel-Gauss beam by an heterogeneous refractive index map,” J. Opt. Soc. A 29, 1252–1258 (2012) [CrossRef] .

21

21. D. P. San-Román-Alerigi, D. H. Anjum, Y. Zhang, X. Yang, A. B. Slimane, T. K. Ng, M. N. Hedhili, M. Alsunaidi, and B. S. Ooi, “Electron irradiation induced reduction of the permittivity of chalcogenide glass (As2S3) thin fim,” J. App. Phys. 113, 044116 (2013) [CrossRef] .

]. The mathematical and physical background to make these effects possible could bring forth an exciting ground to test sidereal mechanics in the laboratory; and provide the key to enable a miscellany planar optical systems that are of great interest for diverse photonic applications, ranging from time delays, to temporal optical memories, or random resonators, to name a few; thence its significance.

2. Deriving the model

We regard a model equation based in the paraxial approximation of non-linear electrodynamics, by looking into a medium where the index of refraction can be modulated in space and time by some smooth varying function f, e.g. in photo-refractive media index of refraction is a real valued function f of the incident light intensity I; therefore n(x⃗) = f(I(x⃗)), where x⃗ is the space-time quadrivector which corresponds to the coordinates {x0 : x1, x2, x3}. In this representation x0 corresponds to the time coordinate, and the rest to the usual three-dimensional space. In this context the photon’s path is governed by the geometry of the space the light is propagating on, which in general has the metric tensor gij, and the infinitesimal length element ds2 = gijdxidxj. Therefore, if we parameterized the path followed by light with reference to the proper time τ, i.e. x⃗(τ), we can analytically derive the path equations by means of Lagrange-Euler equations, whit a Lagrangian of the form:
L=12[gijxiτxjτ],
(1)
where the derivatives are taken in respect to the affine parameter τ, i.e. the proper time.

Yet, we are still to determine the relation between the metric tensor gij and the refractive index n. This can be achieved by means of conformal mappings, where it is possible to build the relation between the metric and the electromagnetic properties of a [meta]material [4

4. U. Leonhardt and T. G. Philbin, “Transformation optics and the geometry of light,” in Progress in Optics53, 69–153, E. Wolf, ed. (Elsevier, 2008) [CrossRef] .

6

6. J. B. Pendry, D. Schurig, and D. R. Smith, “Controlling electromagnetic fields,” Science 312, 1780–1782, 2006 [CrossRef] [PubMed] .

]. Specifically, if the line element of space-time takes the form ds2 = g00dx0dx0giidxidxi, it is possible to map the curved space-time to an isotropic, non-dispersive and non-absorbing medium as [4

4. U. Leonhardt and T. G. Philbin, “Transformation optics and the geometry of light,” in Progress in Optics53, 69–153, E. Wolf, ed. (Elsevier, 2008) [CrossRef] .

, 15

15. D. Genov, S. Zhang, and X. Zhang, “Mimicking celestial mechanics in metamaterials,” Nat. Phys. 5, 687–692 (2009) [CrossRef] .

]:
n=ε=μ=ggijg00,
(4)
where g = det(gij). Furthermore if we consider Minkowski’s metric of special relativity, the tensor g has the entries:
g=diag(g00,g11,g22,g33)=diag(1,1,1,1),
(5)
then the refractive index n = n(x0, r⃗) can be found using Eq. (4). And consequently, the length element ds of Eq. (2) can be written as:
ds2=1n2dx0dx0dxidxi,i=1,2,3
(6)

2.1. Path equations and the inverse problem

Accordingly, from the Lagrange-Euler (1) we can derive the light-path, which in cylindrical coordinates takes the form:
r¨=rϕ˙2+t˙2rnn3,
(7)
ϕ¨=2rr˙ϕ˙+t˙2ϕnn3r2,
(8)
ϕ¨=t˙2znn3,
(9)
t¨=t˙(t˙tn+2(z˙zn+ϕ˙ϕn+r˙rn))n,
(10)
where all derivatives marked by □̇ and □̈ are with respect to the affine parameter τ, e.g. = ∂r/∂τ. Equation (7) through Eq. (9) describe the parametrized path of a light beam traveling in a space-time with such geometry or equivalent refractive index.

We will describe light being trapped, when the geodesics are perpetually bounded to some region of space, for as long as the material properties remain unchanged. In this sense a light trapping geodesic is one where any of the following conditions arise:
  1. , ϕ̇ → 0,
  2. → 0 and ϕminϕϕmax,
  3. ϕ̇ → 0 and rminrrmax,
  4. rminrrmax and ϕ̇minϕ̇ϕ̇max,
for all ττ*; where τ* marks the moment at which the initial conditions for trapping are met. The first condition is only possible if the refractive index n goes to infinity, or if the refractive index co-moves with the wave [16

16. Piwnicki and U. Leonhardt, “Optics of moving media,” App. Phys. B 72, 51–59 (2001) [CrossRef] .

, 17

17. S. L. Cacciatori, F. Belgiorno, V. Gorini, G. Ortenzi, L. Rizzi, V. G. Sala, and D. Faccio, “Spacetime geometries and light trapping in travelling refractive index perturbations,” New J. Phys. 12, 095021 (2010) [CrossRef] .

]. The other three cases can be realized in stationary refractive index [15

15. D. Genov, S. Zhang, and X. Zhang, “Mimicking celestial mechanics in metamaterials,” Nat. Phys. 5, 687–692 (2009) [CrossRef] .

, 22

22. X. Ni and Y.-C. Lai, “Transient chaos in optical metamaterials,” Chaos 21, 033116 (2011) [CrossRef] [PubMed] .

]. Thus, they can be imposed as general conditions to solve the inverse problem to Eq. (7) through Eq. (10).

The inverse problem begins by defining a set of a priori conditions that describes a generalized trapping scenario. If we impose premises 1 to 4, described earlier, the path equations reduce to new set of equations where the affine parameter is time itself; whence we can rework Eq. (7) through Eq. (10) into polar coordinates:
r¨=nrϕ˙22r˙ϕ˙ϕnr˙2rn+r2ϕ˙2rnn,
(11)
ϕ¨=2nrr˙ϕ˙r˙2ϕn+r2ϕ˙2ϕn+2r2r˙ϕ˙rnnr2.
(12)

Since we are interested in the general stationary case, we impose the fourth condition above, ensuing 0 ≤ max and ϕ̇minϕ̇ϕ̇max, on Eq. (11) and Eq. (12), and find a non-singular refractive index distribution, n(r, ϕ), that satisfies them. Notice that we require the refractive index to be smoothly varying and C2 continuous, i.e. ∇n ·e⃗iM, where M is a real valued number, and e⃗i a vector in a give direction in space-time. The general solution to this problem, however, is complex and a unique solution is not guaranteed [18

18. D. P. San-Román-Alerigi, T. K. Ng, M. Alsunaidi, Y. Zhang, and B. S. Ooi, “Generation of J0-Bessel-Gauss beam by an heterogeneous refractive index map,” J. Opt. Soc. A 29, 1252–1258 (2012) [CrossRef] .

, 23

23. B. Gangand and L. Peijun, “Inverse medium scattering problems for electromagnetic waves,” J. App. Math. 65, 2049–2066 (2005).

, 24

24. M. Piana, “On uniqueness for an isotropic inhomogeneous inverse scattering problems,” Inv. Problems 14, 1565–1579 (1998) [CrossRef] .

].

The latter being said, the problem can be simplified further if we recall that a trapping orbit occurs when the radius r is bounded to a region of space, i.e. rminrrmax, for all ϕ; whence (rmax) = (rmin) = 0, and r can be written in terms of the angle ϕ or the time t. Hence a natural solution to the inverse problem is an autonomous refractive index that varies with the radial variable, i.e. n = n(r). This refractive index map resembles the centro-symmetric characteristics of gravitational fields, where, as pointed out independently by Genov and Ni [15

15. D. Genov, S. Zhang, and X. Zhang, “Mimicking celestial mechanics in metamaterials,” Nat. Phys. 5, 687–692 (2009) [CrossRef] .

, 22

22. X. Ni and Y.-C. Lai, “Transient chaos in optical metamaterials,” Chaos 21, 033116 (2011) [CrossRef] [PubMed] .

], light would behave similarly to that traveling in curved space-time. Such distribution can be constrained to the conditions listed previously.

This result is significant in terms of fabrication where novel photo-refractive [metal]materials could be used. The refractive index in these composites can be modulated by the intensity of the change-inducing beam; which can be controlled by shaping its transversal profile [18

18. D. P. San-Román-Alerigi, T. K. Ng, M. Alsunaidi, Y. Zhang, and B. S. Ooi, “Generation of J0-Bessel-Gauss beam by an heterogeneous refractive index map,” J. Opt. Soc. A 29, 1252–1258 (2012) [CrossRef] .

21

21. D. P. San-Román-Alerigi, D. H. Anjum, Y. Zhang, X. Yang, A. B. Slimane, T. K. Ng, M. N. Hedhili, M. Alsunaidi, and B. S. Ooi, “Electron irradiation induced reduction of the permittivity of chalcogenide glass (As2S3) thin fim,” J. App. Phys. 113, 044116 (2013) [CrossRef] .

]. Accordingly several families of refractive index distributions can be achieved, e.g. Gaussian, Laguerre, or Bessel, which are all centro-symmetrical.

2.2. System stability and dynamic equillibrium

Since the refractive index is a function of the radius, Eq. (11) and Eq. (12) can be rewritten in the form (13):
x¨=h(x,x˙)g(x),
(13)
r¨=(r2ϕ˙2r˙2)rlnn+rϕ˙2,
(14)
ϕ¨=2r˙ϕ˙n+rrnnr,
(15)
the system’s symmetry now allows us to integrate Eq. (15), hence:
ϕ˙=μr2,μ=n2,
(16)
where is a constant of integration. This equation is reminiscent of orbital mechanics, with the sole exception that μ, the mass in celestial mechanics, varies with the radius. Substituting the latter result into Eq. (14), and rearranging yields:
r¨=(2n4r4r2r˙2)rlnn+2n4r4r.
(17)
Equation (17) arrangement allows us to calculate the ratio of external energy supply, which is a measure of the equilibrium stability of the system [25

25. D. W. Jordan and P. Smith, Nonlinear ordinary differential equations (Oxford University Press, 2007).

, 26

26. F. Verhulst, Nonlinear differential equations and dynamical systems (Springer Verlag, 1990) [CrossRef] .

]; simplifying we get:
r=ddt=r˙h(r,r˙)=r˙(2n4r2r˙2)rlnn.
(18)

By virtue of Bertrand’s theorem [15

15. D. Genov, S. Zhang, and X. Zhang, “Mimicking celestial mechanics in metamaterials,” Nat. Phys. 5, 687–692 (2009) [CrossRef] .

, 27

27. Y. Zarmi, “The Bertrand theorem revisited,” Am. J. Phys 70, 446–449 (2002) [CrossRef] .

], we know that ≠ 0, for all time t; then from premises 3 and 4 it follows that minmax, where min < 0; and from the definition of n(r) as a monotonous decreasing function it follows that r ln n ≤ 0. Therefore, as the radius decreases, the radial velocity goes to its minimum and t ≤ 0, therefore the system approaches the equilibrium point and the amplitude of the path decreases. On the other hand, as the radius increases, the velocity tends to a maximum, and t ≥ 0, thus the system is driven away from the equilibrium point and the amplitude of the path increases. In Fig. 2 we show t for a Gaussian like refractive index described in section 3.1. Observe that in the light confinement scenario we will see an oscillatory behavior in t.

Fig. 2: Ratio of external energy supply, t, for a radial symmetric system, where x = r and y = . Notice that there exists a xc, critical radius, at wich for all phase space pairs {x, y|x ≥ xc} t = 0, which implies that the light geodesics do not describe an orbital motion.

To conclude we study the stability of the orbits. by means of Lyapunov’s stability theory for the governing Eq. (17), and derive the constraints applicable to the refractive index mapping to attain stable orbital paths [15

15. D. Genov, S. Zhang, and X. Zhang, “Mimicking celestial mechanics in metamaterials,” Nat. Phys. 5, 687–692 (2009) [CrossRef] .

]. First, let us rewrite Eq. (17) as:
r˙=ϰ,ϰ˙=(r2β2ϰ2)χ(r)+rβ2,
(19)
with β = ϕ̇ and χ(r) = r ln n. Then, if we introduce small perturbations r = ro + δ and ϰ = ϰo + ε, expand χ(r) in a Taylor series around ro, and drop all higher order terms for δ and ε; we can rewrite Eq. (19) as a linear system of equations for the perturbation terms:
(δ˙ε˙)=(01W2V)(δε)V=ϰoχo,W=2χoβ2ro+χo'(ro2β2ϰo2),
(20)
where χo and χo are the linear terms of the Taylor expansion of χ(r) around ro. Ensuing the eigenvalues of the matrix above are given by:
λ1,2=V±V2+W.
(21)

The geodesics will be stable if the real part of the eigenvalues of Eq. (20), ℜ{λ1,2}, are negative or equal to zero. Recall that 0 ≤ β ≤ limr→∞n(r)−1, and χ(r) ≤ 0; and therefore the condition for Lyapunov stability is reached if:
rχ(r)|r=roϰ0,V2+W0,
(22)

This constrained is met for all points r near the stability point ro = 0, provided the radial velocity meets o ≤ 0. In general, since the refractive index is monotonous decrescent, the system will be Lyapunov stable at points where ≤ 0, see, for example, the phase-space plots in Figs. 6(b) and 8(b). In addition, it is interesting to analyze whether the system will be Lyapunov stable under the conditions necessary to sustain a circular orbit. In this case ϰo = 0, and ro = a, constant, for all time t; consequently V = 0, W ≤ 0, and the second term in the equality (22) is imaginary, provided that χ(r) ≤ 0; thus resulting in ℜ{λ1,2} = V = 0. These conditions, however, result in a different family of refractive indexes. In our study we focus on Gaussian-like refractive index distributions, feasible through photo-refraction, where ϰ ≠ 0, ergo the system will not describe closed circular orbits.

3. Results and discussion

In this section we explore three refractive index distributions based on Gaussian profiles. The first two mimic light trapped in the vicinity of a black hole, and the third case that of a particle moving in-between two planets.

3.1. Guassian distribution, single attractor

A Gaussian refractive index distribution has the form:
n=naer2/σ2+nc.
(23)

Then making it possible to constrain the maximum and minimum of the refractive index distribution to feasible values, e.g. 0.8n ≤ 3.8. Hence, given a range of values for the back-ground and maximum refractive index, nc and na, respectively, we can evaluate different light confinement scenarios, see Fig. 3.

Fig. 3: Light path dynamics for Gaussian refractive index shape for different na and nc. The maximum value of n in all cases is 3.8 at the center of the device. σ is constant for all results. Notice the increment in the internal radius rmin as nc increases, and the orbit width reduces.

Fig. 4: Inner and outer radius as a function of the background refractive index nc. As it increases we observe that the outer radius diminishes, while the inner increases.

In Fig. 5 we show the 2D open orbit for a refractive index map where nc = 0.8 and na = 3.0. As detailed in Fig. 6(a), the radial velocity describes an oscillatory form, which indicates that the radius follows a similar motion, swinging between two extrema, as expected in a confine and open orbital motion. The latter can be observed in greater detail by analyzing the phase-space, plotted in Fig. 6(b); notice that when the velocity reaches zero the orbit radius r reaches an extrema; for a closed single loop the amplitude of the velocity oscillation would be zero, and the phase space would become a horizontal line at = 0. The behaviour of the angle versus the radial velocity, and consequently to the radius movement, is described by Fig. 6(c), where the absolute value of the radial velocity is plotted against the angular position, which results in a periodic motion. Observe that in the limit at every angle there would be a time at which the radial velocity would be zero, which is typical of open orbits.

Fig. 5: Confinement orbit for light traveling in a Gaussian attractor where na = 3.0 and nc = 0.8. (a) Shows a schematic representation of the planar trapping device where the refractive index increases towards the center, where red indicates maximum refractive index n = 3.8, and light blue n = 0.8; (b) polar-2D path as calculated by the simulation routine.
Fig. 6: Phase space for Gaussian-like refractive index map with na = 3.0, nc = 0.8. The plots show: (a) radial and angular ϕ̈ velocities, (b) radial phase space, and (c) radial velocity as a function of the angle (c).

3.2. Mexican hat distribution

We study a variation on the Gaussian trap to understand the potential modifications on the trapping orbits when large modifications ∼ 20% of the refractive index take place. The mathematical description of the mexican hat is:
n=(nandr2σ2)er2/σ2+nc
(24)

Fig. 7: (a) Schematic of Mexican hat like refractive index map where na = 3.0 and nc = 0.8 and depression is nd = 0.2; (b) depicts the resulting trapped orbit in polar coordinates as calculated by the simulation routine.
Fig. 8: Phase-space for a mexican hat refractive index map with na = 3.0, nc = 0.8. The plots show: (a) radial and angular ϕ̇ velocities, (b) radial phase space, and (c) radial velocity as a function of the angle (c).

These variations in the trapping conditions could potentially be used to differentiate trapping in transient optical memories to allocated binary data.

3.3. Double attractors

Interested in observing phenomenologically trapping in a binary system we evinced a planar refractive index map resulting from the superposition of two Gaussian functions,
n=na(e(rroff1)2/σ2+e(rroff)2/σ2)+nc.
(25)

The resulting orbits are shown in Fig. 9. A binary system, however, presents a relatively higher sensitivity to modifications in the refractive index, where a distortion of Δn > 0.03 modifies the trapping orbits, in some cases releasing the light beam.Yet, it is possible to confine the light beam to an orbit which mimics the behaviour of Newton’s three body problem, where, as expected, small perturbations result in sundry possible solutions to the path equation, i.e. chaos.

Fig. 9: Geodesics for light in a binary system. Observe that trapping also occurs for certain initial conditions at specific background and maximum refractive index.

3.4. The space-time equations, trapping

Briefly, we show that the same Gaussian solution explored in section 3.1 fulfills the trapping conditions in the full eikonal space-time, Eq. (7) through Eq. (9). The results are shown in Fig. 10.

Fig. 10: Phase space of the trapping orbit for na = 3.0, nc = 0.8. The plots show: (a) radial and angular ϕ̇ velocities, (b) radial phase space, and (c) radial velocity as a function of the angle.

In this case we observe a similar behaviour to that of the Gaussian trap in the stationary approximation, the difference in the amplitude values is due to normalization. An oscillatory behaviour in the radius and angular velocities is described in Figs. 10(b) and 10(c); as it would be expected from a centro-symmetrical refractive index mapping.

3.5. Material realization

Recent advancement in photo-refractive materials [18

18. D. P. San-Román-Alerigi, T. K. Ng, M. Alsunaidi, Y. Zhang, and B. S. Ooi, “Generation of J0-Bessel-Gauss beam by an heterogeneous refractive index map,” J. Opt. Soc. A 29, 1252–1258 (2012) [CrossRef] .

21

21. D. P. San-Román-Alerigi, D. H. Anjum, Y. Zhang, X. Yang, A. B. Slimane, T. K. Ng, M. N. Hedhili, M. Alsunaidi, and B. S. Ooi, “Electron irradiation induced reduction of the permittivity of chalcogenide glass (As2S3) thin fim,” J. App. Phys. 113, 044116 (2013) [CrossRef] .

] could enable the construction of the light confinement devices discussed. For example, a prototype Gaussian trap could be fabricated by stacking different photo-refractive [meta]materials like AsxS1−x in multiple layers. Recalling that in photo-refraction the optical properties of the material, permeability and permittivity, change as a function of the light intensity, allowing the fabrication of a continuously varying refractive index as the one required by a centro-symmetrical attractors. Moreover, since photo-refractivity is elastic, i.e. reversible, it allows one to modify the refractive index of the layers combined in time, thence enabling or disabling the trap at will.

4. Conclusions

Acknowledgments

The authors wish to acknowledge David Ketcheson, Carlos Argaez, Pedro Guerra, and Jose Alcantara-Felix for their suggestions, corrections and valuable discussions while preparing this manuscript.

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Piwnicki and U. Leonhardt, “Optics of moving media,” App. Phys. B 72, 51–59 (2001) [CrossRef] .

17.

S. L. Cacciatori, F. Belgiorno, V. Gorini, G. Ortenzi, L. Rizzi, V. G. Sala, and D. Faccio, “Spacetime geometries and light trapping in travelling refractive index perturbations,” New J. Phys. 12, 095021 (2010) [CrossRef] .

18.

D. P. San-Román-Alerigi, T. K. Ng, M. Alsunaidi, Y. Zhang, and B. S. Ooi, “Generation of J0-Bessel-Gauss beam by an heterogeneous refractive index map,” J. Opt. Soc. A 29, 1252–1258 (2012) [CrossRef] .

19.

A. Zakery, “Optical properties and applications of chalcogenide glasses: a review,” J. Non-Crystaline Solids 330, 1–12 (2003) [CrossRef] .

20.

S. B. Kang, M. H. Kwak, B. J. Park, S. K., H. C. Ryu, D. C. Chung, S. Y. Jeong, D. W. Kang, S. K. Choi, M. C. Paek, E. J. Cha, and K. Y. Kang, “Optical and dielectric properties of chalcogenide glasses at terahertz frequencies,” ETRI J. 31, 667–674 (2009) [CrossRef] .

21.

D. P. San-Román-Alerigi, D. H. Anjum, Y. Zhang, X. Yang, A. B. Slimane, T. K. Ng, M. N. Hedhili, M. Alsunaidi, and B. S. Ooi, “Electron irradiation induced reduction of the permittivity of chalcogenide glass (As2S3) thin fim,” J. App. Phys. 113, 044116 (2013) [CrossRef] .

22.

X. Ni and Y.-C. Lai, “Transient chaos in optical metamaterials,” Chaos 21, 033116 (2011) [CrossRef] [PubMed] .

23.

B. Gangand and L. Peijun, “Inverse medium scattering problems for electromagnetic waves,” J. App. Math. 65, 2049–2066 (2005).

24.

M. Piana, “On uniqueness for an isotropic inhomogeneous inverse scattering problems,” Inv. Problems 14, 1565–1579 (1998) [CrossRef] .

25.

D. W. Jordan and P. Smith, Nonlinear ordinary differential equations (Oxford University Press, 2007).

26.

F. Verhulst, Nonlinear differential equations and dynamical systems (Springer Verlag, 1990) [CrossRef] .

27.

Y. Zarmi, “The Bertrand theorem revisited,” Am. J. Phys 70, 446–449 (2002) [CrossRef] .

OCIS Codes
(230.1150) Optical devices : All-optical devices
(290.3200) Scattering : Inverse scattering
(350.4600) Other areas of optics : Optical engineering
(350.5720) Other areas of optics : Relativity
(080.5692) Geometric optics : Ray trajectories in inhomogeneous media

History
Original Manuscript: January 14, 2013
Revised Manuscript: March 3, 2013
Manuscript Accepted: March 4, 2013
Published: March 28, 2013

Citation
Damián P. San-Román-Alerigi, Ahmed B. Slimane, Tien K. Ng, Mohammad Alsunaidi, and Boon S. Ooi, "A possible approach on optical analogues of gravitational attractors," Opt. Express 21, 8298-8310 (2013)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-21-7-8298


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  17. S. L. Cacciatori, F. Belgiorno, V. Gorini, G. Ortenzi, L. Rizzi, V. G. Sala, and D. Faccio, “Spacetime geometries and light trapping in travelling refractive index perturbations,” New J. Phys. 12, 095021 (2010). [CrossRef]
  18. D. P. San-Román-Alerigi, T. K. Ng, M. Alsunaidi, Y. Zhang, and B. S. Ooi, “Generation of J0-Bessel-Gauss beam by an heterogeneous refractive index map,” J. Opt. Soc. A 29, 1252–1258 (2012). [CrossRef]
  19. A. Zakery, “Optical properties and applications of chalcogenide glasses: a review,” J. Non-Crystaline Solids 330, 1–12 (2003). [CrossRef]
  20. S. B. Kang, M. H. Kwak, B. J. Park, S. K., H. C. Ryu, D. C. Chung, S. Y. Jeong, D. W. Kang, S. K. Choi, M. C. Paek, E. J. Cha, and K. Y. Kang, “Optical and dielectric properties of chalcogenide glasses at terahertz frequencies,” ETRI J. 31, 667–674 (2009). [CrossRef]
  21. D. P. San-Román-Alerigi, D. H. Anjum, Y. Zhang, X. Yang, A. B. Slimane, T. K. Ng, M. N. Hedhili, M. Alsunaidi, and B. S. Ooi, “Electron irradiation induced reduction of the permittivity of chalcogenide glass (As2S3) thin fim,” J. App. Phys. 113, 044116 (2013). [CrossRef]
  22. X. Ni and Y.-C. Lai, “Transient chaos in optical metamaterials,” Chaos 21, 033116 (2011). [CrossRef] [PubMed]
  23. B. Gangand and L. Peijun, “Inverse medium scattering problems for electromagnetic waves,” J. App. Math. 65, 2049–2066 (2005).
  24. M. Piana, “On uniqueness for an isotropic inhomogeneous inverse scattering problems,” Inv. Problems 14, 1565–1579 (1998). [CrossRef]
  25. D. W. Jordan and P. Smith, Nonlinear ordinary differential equations (Oxford University Press, 2007).
  26. F. Verhulst, Nonlinear differential equations and dynamical systems (Springer Verlag, 1990). [CrossRef]
  27. Y. Zarmi, “The Bertrand theorem revisited,” Am. J. Phys 70, 446–449 (2002). [CrossRef]

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