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Optics Express

Optics Express

  • Editor: C. Martijn de Sterke
  • Vol. 20, Iss. 4 — Feb. 13, 2012
  • pp: 4232–4247
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Inner- and outer-scale effects on the scintillation index of an optical wave propagating through moderate-to-strong non-Kolmogorov turbulence

Xiang Yi, Zengji Liu, and Peng Yue  »View Author Affiliations


Optics Express, Vol. 20, Issue 4, pp. 4232-4247 (2012)
http://dx.doi.org/10.1364/OE.20.004232


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Abstract

By use of the generalized von Kármán spectrum model that features both inner scale and outer scale parameters for non-Kolmogorov turbulence and the extended Rytov method that incorporates a modified amplitude spatial-frequency filter function under strong-fluctuation conditions, theoretical expressions are developed for the scintillation index of a horizontally propagating plane wave and spherical wave that are valid under moderate-to-strong irradiance fluctuations. Numerical results show that the obtained expressions also compare well with previous results in weak-fluctuation regimes. Based on these general models, the impacts of finite inner and outer scales on the scintillation index of an optical wave are examined under various non-Kolmogorov fluctuation conditions.

© 2012 OSA

1. Introduction

An optical wave propagating through a turbulent atmosphere will experience random fluctuations in irradiance commonly known as scintillation. Turbulence-induced scintillation is a serious issue for optical wireless communications for both terrestrial as well as ground-to-space or space-to-ground data links, as it can produce deep random fades in the received signal [1

1. L. C. Andrews and R. L. Phillips, “Impact of scintillation on laser communication systems: recent advances in modeling,” Proc. SPIE 4489, 23–34 (2002). [CrossRef]

3

3. H. G. Sandalidis, “Performance of a laser Earth-to-satellite link over turbulence and beam wander using the modulated gamma-gamma irradiance distribution,” Appl. Opt. 50(6), 952–961 (2011). [CrossRef] [PubMed]

]. Past studies concerning the scintillation of optical waves have led to many analytical results for Kolmogorov turbulence [4

4. L. C. Andrews and R. L. Phillips, Laser Beam Propagation through Random Media, 2nd ed. (SPIE Optical Engineering Press, 2005). [CrossRef]

8

8. K. J. Mayer, Effect of Inner Scale Atmospheric Spectrum Models on Scintillation in All Optical Turbulence Regimes, Ph.D. dissertation, University of Central Florida, 2007.

]. However, recent experimental data indicate turbulence in certain portions of the atmosphere does not exhibit Kolmogorov statistics [9

9. D. T. Kyrazis, J. B. Wissler, D. B. Keating, A. J. Preble, and K. P. Bishop, “Measurement of optical turbulence in the upper troposphere and lower stratosphere,” Proc. SPIE 2120, 43–55 (1994). [CrossRef]

11

11. A. Zilberman, E. Golbraikh, N. S. Kopeika, A. Virtser, I. Kupershmidt, and Y. Shtemler, “Lidar study of aerosol turbulence characteristics in the troposphere: Kolmogorov and non-Kolmogorov turbulence,” Atmos. Res. 88(1), 66–77 (2008). [CrossRef]

]. This prompts the need for reinvestigations of optical scintillation in the context of atmospheric turbulence representing non-Kolmogorov properties.

In this paper, by use of the generalized von Kármán spectrum model and the extended Rytov method, we first develop the theoretical expressions for the scintillation index (SI) of a plane wave and a spherical wave both propagating through moderate-to-strong non-Kolmogorov turbulence along a horizontal path. Then, we present some numerical results to illustrate the influences of the inner- and outer-scale on scintillation under various fluctuation conditions.

2. Generalized von Kármán spectrum

The generalized von Kármán spectrum model is given by [18

18. I. Toselli, L. C. Andrews, R. L. Phillips, and V. Ferrero, “Angle of arrival fluctuations for free space laser beam propagation through Non-Kolmogorov turbulence,” Proc. SPIE 6551, 65510E–1–12 (2007).

]
Φn(κ,α)=A(α)C˜n2exp(κ2/κm2)(κ2+κ02)α/2,0κ<,3<α<4,
(1)
where κ denotes the magnitude of the spatial-frequency with units of rad/m, α is the generalized power law that takes all values ranging from 3 to 4; A(α) is the generalized amplitude factor that has the form A(α) = Γ (α – 1) · cos(απ/2)/(4π2) with Γ(·) being the Gamma function [24

24. L. C. Andrews, Special Functions of Mathematics for Engineers, 2nd ed. (SPIE Optical Engineering Press, Bellingham, Wash., 1998).

]. The factor C˜n2 is the generalized refractive index structure parameter with the units m3−α. The remaining parameters κm and κ0 are basically reciprocals, respectively, of the inner scale l0 and outer scale L0 of refractive index fluctuations, that is, κm = c (α)/l0 with c(α) = {Γ[(5 – α)/2] · A(α) · 2π/3}1/(α−5) and κ0 = 2π/L0. The inner and outer scale parameters l0 and L0 are characteristic length scales associated with the smallest and largest scale sizes, respectively, in the turbulent atmosphere that causes random fluctuations in refractive index. The inner scale is generally on the order of millimeters while the outer scale is on the order of meters. It is noted that the spectrum model Eq. (1) reduces to the generalized Kolmogorov spectrum [12

12. I. Toselli, L. C. Andrews, R. L. Phillips, and V. Ferrero, “Free-space optical system performance for laser beam propagation through non-Kolmogorov turbulence,” Proc. SPIE 6457, 64570T–1–11 (2007).

, Eq. (2)] when l0 tends to zero and L0 tends to infinite, and reduces to the conventional von Kármán spectrum [6

6. W. B. Miller, J. C. Ricklin, and L. C. Andrews, “Effects of the refractive index spectral model on the irradiance variance of a Gaussian beam,” J. Opt. Soc. Am. A 11(10), 2719–2726 (1994). [CrossRef]

. Eq. (1)] when α = 11/3, A(α) = 0.033, and C˜n2=Cn2. Here, Cn2 represents the conventional structure parameter that has units of m−2/3.

It is known that the conventional von Kármán spectrum cannot feature the high wave number rise (or bump) prior to the dissipation range that is revealed in experimental data [25

25. R. Mahon, C. I. Moore, H. R. Burris, W. S. Rabinovich, M. Stell, M. R. Suite, and L. M. Thomas, “Analysis of long-term measurements of laser propagation over the Chesapeake Bay,” Appl. Opt. 48(12), 2388–2400 (2009). [CrossRef] [PubMed]

], but, because of its relatively tractable mathematical form, the conventional von Kármán spectrum is widely used in theoretical calculations [4

4. L. C. Andrews and R. L. Phillips, Laser Beam Propagation through Random Media, 2nd ed. (SPIE Optical Engineering Press, 2005). [CrossRef]

, 6

6. W. B. Miller, J. C. Ricklin, and L. C. Andrews, “Effects of the refractive index spectral model on the irradiance variance of a Gaussian beam,” J. Opt. Soc. Am. A 11(10), 2719–2726 (1994). [CrossRef]

, 8

8. K. J. Mayer, Effect of Inner Scale Atmospheric Spectrum Models on Scintillation in All Optical Turbulence Regimes, Ph.D. dissertation, University of Central Florida, 2007.

]. Furthermore, although the von Kármán model does not agree with all scintillation values predicted by the modified atmospheric spectrum (a well-known analytically tractable model that can characterize the high wave number bump) [4

6. W. B. Miller, J. C. Ricklin, and L. C. Andrews, “Effects of the refractive index spectral model on the irradiance variance of a Gaussian beam,” J. Opt. Soc. Am. A 11(10), 2719–2726 (1994). [CrossRef]

, Eq. (3.31)], the von Kármán spectrum captures most of the behavior of the optical wave [4

4. L. C. Andrews and R. L. Phillips, Laser Beam Propagation through Random Media, 2nd ed. (SPIE Optical Engineering Press, 2005). [CrossRef]

, Chap. (9.6.4), 8

8. K. J. Mayer, Effect of Inner Scale Atmospheric Spectrum Models on Scintillation in All Optical Turbulence Regimes, Ph.D. dissertation, University of Central Florida, 2007.

]. The modified atmospheric spectrum has also been generalized to apply in non-Kolmogorov turbulence [20

20. B. D. Xue, L. Y. Cui, W. F. Xue, X. Z. Bai, and F. G. Zhou, “Generalized modified atmospheric spectral model for optical wave propagating through non-Kolmogorov turbulence,” J. Opt. Soc. Am. A 28(5), 912–916 (2011). [CrossRef]

]. But due to lack of experimental data for non-Kolmogorov turbulence in the upper troposphere and stratosphere, some coefficients in this spectrum model have not yet been determined. Therefore, our analysis here is based on the generalized von Kármán spectrum like [21

21. L. Y. Cui, B. D. Xue, L. Cao, S. L. Zheng, W. F. Xue, X. Z. Bai, X. G. Cao, and F. G. Zhou, “Irradiance scintillation for Gaussian-beam wave propagating through weak non-Kolmogorov turbulence,” Opt. Express 19(18), 16872–16884 (2011). [CrossRef] [PubMed]

].

3. The plane-wave spatial coherence radius and phase structure function

3.1. Spatial coherence radius

It is known that weak-fluctuation and strong-fluctuation conditions for an unbounded plane wave or spherical wave based on the generalized Kolmogorov spectrum are characterized by σ˜R2<1 and σ˜R21, respectively [15

15. I. Toselli, L. C. Andrews, R. L. Phillips, and V. Ferrero, “Scintillation index of optical plane wave propagating through non Kolmogorov moderate-strong turbulence,” Proc. SPIE 6747, 67470B (2007). [CrossRef]

, 16

16. P. Deng, X. H. Yuan, and D. X. Huang, “Scintillation of a laser beam propagation through non-Kolmogorov strong turbulence,” Opt. Commun., accepted for publication.

]. Here
σ˜R2=8π2A(α)Γ(1α/2)α1sin(απ/4)C˜n2k3α/2Lα/2
(2)
is the non-Kolmogorov Rytov variance for a plane wave [15

15. I. Toselli, L. C. Andrews, R. L. Phillips, and V. Ferrero, “Scintillation index of optical plane wave propagating through non Kolmogorov moderate-strong turbulence,” Proc. SPIE 6747, 67470B (2007). [CrossRef]

], k = 2π/λ is the wave number at the wavelength λ, and L is the path length. However, for an arbitrary spectrum model, we should rely on the more general parameter L/kρpl2(α) as a measure of the strength of irradiance fluctuations [4

4. L. C. Andrews and R. L. Phillips, Laser Beam Propagation through Random Media, 2nd ed. (SPIE Optical Engineering Press, 2005). [CrossRef]

, 6

6. W. B. Miller, J. C. Ricklin, and L. C. Andrews, “Effects of the refractive index spectral model on the irradiance variance of a Gaussian beam,” J. Opt. Soc. Am. A 11(10), 2719–2726 (1994). [CrossRef]

]. Here ρpl (α) is the spatial coherence radius of a plane wave [15

15. I. Toselli, L. C. Andrews, R. L. Phillips, and V. Ferrero, “Scintillation index of optical plane wave propagating through non Kolmogorov moderate-strong turbulence,” Proc. SPIE 6747, 67470B (2007). [CrossRef]

]. The corresponding criterion for distinguishing between weak-fluctuation and strong-fluctuation conditions in terms of the parameter L/kρpl2(α) is defined by the following sets of inequalities [4

4. L. C. Andrews and R. L. Phillips, Laser Beam Propagation through Random Media, 2nd ed. (SPIE Optical Engineering Press, 2005). [CrossRef]

, Chap.7]:
L/kρpl2(α)1,weak-fluctuationconditions,L/kρpl2(α)1,strong-fluctuationconditions.
(3)
Obviously if we want to develop a general scintillation model that can cover a wide range of fluctuation conditions (weak to strong) on the basis of the generalized von Kármán spectrum, we need an in-depth understanding of the plane-wave spatial coherence radius. Specifically, to include the effects from inner scale, we need to know the form of the plane-wave spatial coherence radius which is much less than the inner scale of turbulence.

The spatial coherence radius is determined by the wave structure function (WSF) [4

4. L. C. Andrews and R. L. Phillips, Laser Beam Propagation through Random Media, 2nd ed. (SPIE Optical Engineering Press, 2005). [CrossRef]

, 23

23. B. E. Stribling, B. M. Welsh, and M. C. Roggemann, “Optical propagation in non-Kolmogorov atmospheric turbulence,” Proc. SPIE 2471, 1–17 (1995).

]. For non-Kolmogorov turbulence, the WSF associated with a plane wave is given by [19

19. L. Y. Cui, B. D. Xue, X. G. Cao, J. K. Dong, and J. N. Wang, “Generalized atmospheric turbulence MTF for wave propagating through non-Kolmogorov turbulence,” Opt. Express 18(20), 21269–21283 (2010). [CrossRef] [PubMed]

, 23

23. B. E. Stribling, B. M. Welsh, and M. C. Roggemann, “Optical propagation in non-Kolmogorov atmospheric turbulence,” Proc. SPIE 2471, 1–17 (1995).

]
Dpl(ρ,α)=8π2k2L0κΦn(κ,α)[1J0(κρ)]dκ,
(4)
where ρ is the separation distance between two observation points at the receiver plane; J0 (·) is a Bessel function of the first kind [24

24. L. C. Andrews, Special Functions of Mathematics for Engineers, 2nd ed. (SPIE Optical Engineering Press, Bellingham, Wash., 1998).

]. By substituting Eq. (1) into Eq. (4) and expanding the Bessel function in the integrand in a Maclaurin series, we find
Dpl(ρ,α)=8π2A(α)C˜n2k2Ln=1(1)n1(ρ)2n22n(n!)20κ2n+1exp(κ2/κm2)(κ2+κ02)α/2dκ.
(5)
Then, by making an appropriate change of variable, we deduce that
Dpl(ρ,α)=4π2A(α)C˜n2k2Lκ02αn=1(1)n1n!(κ0ρ/2)2nU(n+1;n+2α2;κ02κm2),
(6)
where we have used [24

24. L. C. Andrews, Special Functions of Mathematics for Engineers, 2nd ed. (SPIE Optical Engineering Press, Bellingham, Wash., 1998).

, Eq. (10.28)] to evaluate the integral in terms of the confluent hyper-geometric function of the second kind U (a;c;x) [24

24. L. C. Andrews, Special Functions of Mathematics for Engineers, 2nd ed. (SPIE Optical Engineering Press, Bellingham, Wash., 1998).

]. In the present study, it suffices to know the form of the WSF only in the asymptotic regime ρl0. For small ρ, we can approximate Eq. (6) by the first term of the series to obtain
Dpl(ρ,α)π2A(α)C˜n2k2Lκ04αU(2;3α2;κ02κm2)ρ2,ρl0.
(7)
Under most conditions of atmospheric turbulence we find that κ02/κm21, so by making the further approximation U (a;c;x) ≅ Γ(c – 1)x1−c/Γ(a),0 < x ≪ 1 [24

24. L. C. Andrews, Special Functions of Mathematics for Engineers, 2nd ed. (SPIE Optical Engineering Press, Bellingham, Wash., 1998).

, Eq. (10.30a)], we obtain
Dpl(ρ,α)π2A(α)Γ(2α/2)C˜n2k2Lκm4αρ2,ρl0.
(8)
When α = 11/3, Eq. (8) reduces to Dpl(ρ,11/3)=3.28Cn2k2Ll01/3ρ2 which is the correct result for conventional von Kármán spectrum [4

4. L. C. Andrews and R. L. Phillips, Laser Beam Propagation through Random Media, 2nd ed. (SPIE Optical Engineering Press, 2005). [CrossRef]

, Eq. (8.88)].

By setting Eq. (8) equal to 2 and solving for ρ, we deduce the plane-wave spatial coherence radius as
ρpl(α)=[0.5π2A(α)Γ(2α/2)C˜n2k2Lκm4α]1/2,ρpl(α)l0.
(9)
It is noted that the spatial coherence radius given by Eq. (9) is consistent with conventional Kolmogorov result [4

4. L. C. Andrews and R. L. Phillips, Laser Beam Propagation through Random Media, 2nd ed. (SPIE Optical Engineering Press, 2005). [CrossRef]

, Eq. (6.64)] when α is set to 11/3.

3.2. Phase structure function

Knowledge of the plane-wave phase structure function (PSF) is crucial for developing scintillation results in the strong fluctuation regimes [4

4. L. C. Andrews and R. L. Phillips, Laser Beam Propagation through Random Media, 2nd ed. (SPIE Optical Engineering Press, 2005). [CrossRef]

, 7

7. L. C. Andrews, R. L. Phillips, C. Y. Hopen, and M. A. Al-Habash, “Theory of optical scintillation,” J. Opt. Soc. Am. A 16(6), 1417–1429 (1999). [CrossRef]

, 15

15. I. Toselli, L. C. Andrews, R. L. Phillips, and V. Ferrero, “Scintillation index of optical plane wave propagating through non Kolmogorov moderate-strong turbulence,” Proc. SPIE 6747, 67470B (2007). [CrossRef]

]. To include inner-scale effects, we need to know the form of the plane-wave PSF in the asymptotic regime ρl0.

The plane-wave PSF can be determined by [23

23. B. E. Stribling, B. M. Welsh, and M. C. Roggemann, “Optical propagation in non-Kolmogorov atmospheric turbulence,” Proc. SPIE 2471, 1–17 (1995).

]
DS,pl(ρ,α)=4π2k2L010κΦn(κ,α)[1J0(κρ)][1+cos(Lκ2ξk)]dκdξ,
(10)
where ξ is the normalized path length parameter. For small separation distances in which ρl0, we can use the small-argument approximation for the Bessel function (i.e., J0 (κρ) ≅ 1 – (κρ)2/4) to obtain
DS,pl(ρ,α)=π2k2Lρ2010κ3Φn(κ,α)[1+cos(Lκ2ξk)]dκdξ.
(11)
If we write the cosine function in Eq. (11) as cosx = Re(eix) through use of Euler’s formula, the substitution of Eq. (1) into Eq. (11) leads to
DS,pl(ρ,α)=A(α)π2C˜n2k2Lρ2Re010κ3(κ2+κ02)α/2×{exp(κ2κm2)+exp[κ2(1+iQm(α)ξ)κm2]}dκdξ,
(12)
where Qm(α)=[c(α)]2L/(kl02) is a nondimensional inner-scale parameter. Next, the inside integration yields ([24

24. L. C. Andrews, Special Functions of Mathematics for Engineers, 2nd ed. (SPIE Optical Engineering Press, Bellingham, Wash., 1998).

, Eq. (10.28)])
DS,pl(ρ,α)=0.5Γ(2)A(α)π2C˜n2k2Lρ2Re01{κ04αU(2;3α2;κ02κm2)+κ04αU(2;3α2;κ02(1+iQm(α)ξ)κm2)}dξ.
(13)
Because κ02/κm2l02/L021, we can use the small-argument approximation of the confluent hypergeometric function given by [24

24. L. C. Andrews, Special Functions of Mathematics for Engineers, 2nd ed. (SPIE Optical Engineering Press, Bellingham, Wash., 1998).

, Eq. (10.30a)] to reduce Eq. (13) to
DS,pl(ρ,α)=0.5A(α)π2Γ(2α2)C˜n2k2Lκm4αρ2Re01{1+(1+iQm(α)ξ)α22}dξ=A(α)π2Γ(2α2)C˜n2k2Lκm4αρ2Re{12+[1+iQm(α)]α/211iQm(α)(α2)}.
(14)
By simplifying the last expression above, we are led to our general result
DS,pl(ρ,α)=0.5ΞA(α)π2Γ(2α/2)C˜n2k2Lκm4αρ2,ρl0,
(15)
where
Ξ=1+2sin[α22tan1Qm(α)](α2)[Qm(α)]2α/2{1+1[Qm(α)]2}α24.
(16)
When α = 11/3, Eq.(15) reduces to DS,pl(ρ,11/3)=1.64Cn2k2Ll01/3[1+0.64(kl02/L)1/6]ρ2 which matches well with conventional Kolmogorov result [4

4. L. C. Andrews and R. L. Phillips, Laser Beam Propagation through Random Media, 2nd ed. (SPIE Optical Engineering Press, 2005). [CrossRef]

, Eq. (6.66)].

4. Scintillation index in the strong fluctuation regime

The extended Rytov method presented in [4

4. L. C. Andrews and R. L. Phillips, Laser Beam Propagation through Random Media, 2nd ed. (SPIE Optical Engineering Press, 2005). [CrossRef]

, 7

7. L. C. Andrews, R. L. Phillips, C. Y. Hopen, and M. A. Al-Habash, “Theory of optical scintillation,” J. Opt. Soc. Am. A 16(6), 1417–1429 (1999). [CrossRef]

] makes use of known expressions for both the weak and strong fluctuation regimes. Fortunately, Cui et al. [21

21. L. Y. Cui, B. D. Xue, L. Cao, S. L. Zheng, W. F. Xue, X. Z. Bai, X. G. Cao, and F. G. Zhou, “Irradiance scintillation for Gaussian-beam wave propagating through weak non-Kolmogorov turbulence,” Opt. Express 19(18), 16872–16884 (2011). [CrossRef] [PubMed]

] have developed analytical expressions for the weak fluctuation regime based on the generalized von Kármán spectrum. Here we develop expressions for the strong fluctuation regime.

In the strong fluctuation regime, the asymptotic theory predicts that the SI for an unbounded plane wave or spherical wave can be expressed in the form [4

4. L. C. Andrews and R. L. Phillips, Laser Beam Propagation through Random Media, 2nd ed. (SPIE Optical Engineering Press, 2005). [CrossRef]

, 15

15. I. Toselli, L. C. Andrews, R. L. Phillips, and V. Ferrero, “Scintillation index of optical plane wave propagating through non Kolmogorov moderate-strong turbulence,” Proc. SPIE 6747, 67470B (2007). [CrossRef]

]
σI2(α)=1+32π2k2L010κΦn(κ,α)sin2[Lκ2ξ2k]×exp{01DS,pl[Lκkw(τ,ξ),α]dτ}dκdξ,L/kρpl2(α)1,
(17)
where τ is a normalized distance variable and the exponential function acts like a low-pass spatial filter defined by the plane-wave PSF DS,pl (ρ,α). The function w(τ,ξ) is defined by [4

4. L. C. Andrews and R. L. Phillips, Laser Beam Propagation through Random Media, 2nd ed. (SPIE Optical Engineering Press, 2005). [CrossRef]

]
w(τ,ξ)={τ(1Θ¯ξ),τ<ξ,ξ(1Θ¯τ),τ>ξ,
(18)
where the parameter Θ̅ = 0 for a plane wave and Θ̅ = 1 for a spherical wave.

When the spatial coherence radius of the optical wave ρpl (α) is much less than the inner scale of turbulence l0, the PSF for a plane wave based on the generalized von Kármán spectrum can be calculated by Eq. (15). Hence, for the plane wave case, we find that
01DS,pl[Lκkw(τ,ξ),α]dτ=αΓ(2α/2)Ξ16Γ(1α/2)sin(απ/4)×σ˜R2[Qm(α)]2α/2(Lκ2k)ξ2(123ξ).
(19)
Also, the sine function in Eq. (17) may be approximated by its leading term, which yields
sin2[Lκ2ξ2k]L2κ4ξ24k2.
(20)
By substituting Eq. (1), Eq. (19), and Eq. (20) into Eq. (17), we deduce that
σI,pl2(α)=1αΓ(1α/2)sin(απ/4)σ˜R2(Lk)3α/201ξ20κ5(κ2+κ02)α/2×exp{κ2κm2{1αΓ(2α/2)Ξ16Γ(1α/2)sin(απ/4)×σ˜R2[Qm(α)]3α2ξ2(123ξ)}}dκdξ.
(21)
Next, we evaluate the inside integration in Eq. (21) by [24

24. L. C. Andrews, Special Functions of Mathematics for Engineers, 2nd ed. (SPIE Optical Engineering Press, Bellingham, Wash., 1998).

, Eq. (10.28)], which leads to
σI,pl2(α)=1α2Γ(1α/2)sin(απ/4)σ˜R2(Lk)3α/201ξ2κ06αΓ(3)×U(3;4α2;κ02κm2{1αΓ(2α/2)Ξ16Γ(1α/2)sin(απ/4)×σ˜R2[Qm(α)]3α2ξ2(123ξ)})dξ.
(22)
As discussed in [8

8. K. J. Mayer, Effect of Inner Scale Atmospheric Spectrum Models on Scintillation in All Optical Turbulence Regimes, Ph.D. dissertation, University of Central Florida, 2007.

, Appendix H], we can use the small-argument approximation for U (a;c;x) [24

24. L. C. Andrews, Special Functions of Mathematics for Engineers, 2nd ed. (SPIE Optical Engineering Press, Bellingham, Wash., 1998).

, Eq. (10.30a)] and then obtain
σI,pl2(α)=1αΓ(3α/2)2Γ(1α/2)sin(απ/4)σ˜R2[Qm(α)]3α/2×01ξ2{1αΓ(2α/2)Ξ16Γ(1α/2)sin(απ/4)σ˜R2[Qm(α)]3α2ξ2(123ξ)}3α/2dξ.
(23)
The evaluation of the last integral in closed form is not known. But it can be integrated easily by the numerical integration method. For brevity, we rewrite Eq. (23) as
σI,pl2(α)=1+Cpl(α){σ˜R2[Qm(α)]3α/2}2α/2,αΓ(2α/2)σ˜R2[Qm(α)]2α/216Γ(1α/2)sin(απ/4)1,
(24)
where we have used −αΓ(2 − α/2) σ˜R2[Qm(α)]2α/2/[16Γ(1α/2)sin(απ/4)]1 to represent the strong-fluctuation conditions when ρpl (α) ≪ l0 [based on Eq. (9)], and defined
Cpl(α)=αΓ(3α/2)2Γ(1α/2)sin(απ/4)×01ξ2{σ˜R2[Qm(α)]α/23αΓ(2α/2)Ξ16Γ(1α/2)sin(απ/4)ξ2(123ξ)}3α/2dξ.
(25)

In the spherical-wave case, we first note that
01DS,pl[Lκkw(τ,ξ)]dτ=αΓ(2α/2)Ξ48Γ(1α/2)sin(απ/4)×σ˜R2[Qm(α)]2α/2(Lκ2k)ξ2(1ξ2),
(26)
which leads to
σI,sp2(α)=1αΓ(3α/2)2Γ(1α/2)sin(απ/4)σ˜R2[Qm(α)]3α/2×01ξ2(1ξ)2{1αΓ(2α/2)Ξ48Γ(1α/2)sin(απ/4)σ˜R2[Qm(α)]3α2ξ2(1ξ2)}3α/2dξ.
(27)
For brevity, we rewrite Eq. (27) as
σI,sp2(α)=1+Csp(α){σ˜R2[Qm(α)]3α/2}2α/2,αΓ(2α/2)σ˜R2[Qm(α)]2α/216Γ(1α/2)sin(απ/4)1,
(28)
where
Csp(α)=αΓ(3α/2)2Γ(1α/2)sin(απ/4)×01ξ2(1ξ)2{σ˜R2[Qm(α)]α/23αΓ(2α/2)Ξ48Γ(1α/2)sin(απ/4)ξ2(1ξ)2}3α/2dξ.
(29)

5. Scintillation index for plane wave

In this and the following section, the extended Rytov method suggested in [4

4. L. C. Andrews and R. L. Phillips, Laser Beam Propagation through Random Media, 2nd ed. (SPIE Optical Engineering Press, 2005). [CrossRef]

, 7

7. L. C. Andrews, R. L. Phillips, C. Y. Hopen, and M. A. Al-Habash, “Theory of optical scintillation,” J. Opt. Soc. Am. A 16(6), 1417–1429 (1999). [CrossRef]

, 15

15. I. Toselli, L. C. Andrews, R. L. Phillips, and V. Ferrero, “Scintillation index of optical plane wave propagating through non Kolmogorov moderate-strong turbulence,” Proc. SPIE 6747, 67470B (2007). [CrossRef]

] is used to derive expressions for the SI of an optical wave that are valid under moderate-to-strong irradiance fluctuations. In applying the extended Rytov method, we here rely on a minor modification of the “effective non-Kolmogorov spectrum”
Φ˜n,e(κ,α)=Φ˜n(κ,α)G(κ,l0,L0,α)=Φ˜n(κ,α)[GX(κ,l0,L0,α)+GY(κ,α)],
(30)
where Φ˜n(κ,α)=A(α)C˜n2κα is the generalized Kolmogorov spectrum, G(κ,l0, L0,α) is an amplitude (irradiance) spatial filter that consists of a large-scale spatial filter GX (κ,l0, L0,α) and a small-scale spatial filter GY (κ,α). To include the effects from the inner scale and outer scale, we represent the large-scale and small-scale spatial filters by
GX(κ,l0,L0,α)=f(κ,l0,α)g(κL0)exp(κ2κX2),
(31)
GY(κ,α)=κα(κ2+κY2)α/2,
(32)
where f (κ,l0,α) is a factor that describes inner scale modifications of the basic non-Kolmogorov power law, and g(κL0) describes outer scale effects. The parameter κX in the large-scale filter function is a cutoff spatial frequency for the large-scale turbulent cell effects, and κY in the small-scale filter function is a cutoff spatial frequency for the small-scale turbulent cell effects. In this fashion, G(κ,l0, L0,α) acts like a linear spatial filter that only permits low-pass spatial frequencies κ < κX and high-pass spatial frequencies κ > κY at a given propagation distance L. The effects of mid-range scale sizes which contribute little to scintillation under strong fluctuations can therefore be filtered out by using G(κ,l0, L0,α). Note that outer-scale effects and the inner-scale factor f (κ,l0,α) is assumed to act only on the large-scale fluctuations, i.e., the small-scale filter has exactly the same form as assumed for zero inner scale [15

15. I. Toselli, L. C. Andrews, R. L. Phillips, and V. Ferrero, “Scintillation index of optical plane wave propagating through non Kolmogorov moderate-strong turbulence,” Proc. SPIE 6747, 67470B (2007). [CrossRef]

]. However, we do assume κY depends on inner scale. In our modeling of inner scale and outer scale effects, we choose f(κ,l0,α)=exp(κ2/κm2) and g(κL0)=1exp(κ2/κ02) with κ0 = 8π/L0 for the purpose of capturing the underlying physics, but also for mathematical tractability. In this context, the large scale filter function takes the form
GX(κ,l0,L0,α)=exp(κ2κm2)[exp(κ2κX2)exp(κ2κX02)],
(33)
where κX02=κX2κ02/(κX2+κ02). Hence, it follows that the large-scale log-irradiance scintillation in this case can be expressed as a difference, that is,
σlnX2(l0,L0,α)=σlnX2(l0,α)σlnX2(L0,α).
(34)
If we invoke the extended Rytov method, then the total SI can be expressed in the form
σI2(α)=exp[σlnX2(l0,α)σlnX2(L0,α)+σlnY2(l0,α)]1,
(35)
where σlnY2(l0,α) represent the small-scale log-irradiance scintillation in the presence of a finite inner scale.

For the plane-wave case, the first term on the right-side in Eq. (34) is given by
σlnX,pl2(l0,α)=8π2k2L010κΦ˜n(κ,α)exp(κ2κm2)exp(κ2κX2)×{1cos[Lκ2kξ]}dκdξα4Γ(1α/2)sin(απ/4)σ˜R201ξ2dξ×0η2α/2exp(ηQm(α)ηηX)dη,
(36)
where we have used a geometrical optics approximation
1cos[Lκ2kξ]12[Lκ2kξ]2,κκX,
(37)
and the parameter changes η = 2/k in the second step, and defined ηX=LκX2/k. The geometrical optics approximation is valid here because the large scale filter excludes high spatial frequency contributions in the moderate-to-strong fluctuation regimes. Upon evaluation of the last expression in Eq. (36), we obtain
σlnX,pl2(l0,α)=αΓ(3α/2)12Γ(1α/2)sin(απ/4)σ˜R2(ηXQm(α)ηX+Qm(α))3α/2.
(38)
Note that when l0 → 0 (i.e., Qm (α) → ∞), Eq. (38) reduces to
σlnX,pl2(α)=αΓ(3α/2)12Γ(1α/2)sin(απ/4)σ˜R2(ηX)3α/2,
(39)
which is the large-scale log-irradiance variance result for the zero scale case [15

15. I. Toselli, L. C. Andrews, R. L. Phillips, and V. Ferrero, “Scintillation index of optical plane wave propagating through non Kolmogorov moderate-strong turbulence,” Proc. SPIE 6747, 67470B (2007). [CrossRef]

, Eq. (28)].

To determine the low-pass nondimensional cutoff frequency ηX, we use the asymptotic result [7

7. L. C. Andrews, R. L. Phillips, C. Y. Hopen, and M. A. Al-Habash, “Theory of optical scintillation,” J. Opt. Soc. Am. A 16(6), 1417–1429 (1999). [CrossRef]

, Eq. (26)]
ηX=1c1(α)+c2(α)L/kρpl2(α){1/c1(α),L/kρpl2(α)1,kρpl2(α)/c2(α)LL/kρpl2(α)1,
(40)
as well as established behavior of the SI in these asymptotic regimes provided by [21

21. L. Y. Cui, B. D. Xue, L. Cao, S. L. Zheng, W. F. Xue, X. Z. Bai, X. G. Cao, and F. G. Zhou, “Irradiance scintillation for Gaussian-beam wave propagating through weak non-Kolmogorov turbulence,” Opt. Express 19(18), 16872–16884 (2011). [CrossRef] [PubMed]

, Eq. (35)]
σ˜PL2=σ˜R2sin(απ/4){[1+1Qm2(α)]α/4sin[α2tan1Qm(α)]α2[Qm(α)]1α2},σ˜R2<1,
(41)
and Eq. (24). In the weak fluctuation regimes where inner-scale effects can be ignored, we approximate σlnX,pl2(l0,α) by σlnX,pl2(α), and assume that σ˜PL2 reduces to σ˜R2. In this fashion, the scale constant c1 (α) can be deduced by imposing σlnX,pl2(α)0.49σ˜R2 similar to the zero scale case. The result is
c1(α)=[5.88Γ(1α/2)sin(απ/4)αΓ(3α/2)]2α6.
(42)
Since inner-scale effects tend to diminish under strong irradiance fluctuations, we approximate σlnX,pl2(l0,α) by σlnX,pl2(α) once again. Based on Eq. (24) and the identity σI2(α)1+2σlnX2(α), L/kρpl2(α)1 [4

4. L. C. Andrews and R. L. Phillips, Laser Beam Propagation through Random Media, 2nd ed. (SPIE Optical Engineering Press, 2005). [CrossRef]

, Eq. (9.35)], we impose
σlnX,pl2(α)Cpl(α)2{σ˜R2[Qm(α)]3α/2}2α/2,αΓ(2α/2)σ˜R2[Qm(α)]2α/216Γ(1α/2)sin(απ/4)1.
(43)
Thus, we find
c2(α)Lkρpl2(α)={Cpl(α)2{σ˜R2[Qm(α)]3α/2}2α/212Γ(1α/2)sin(απ/4)αΓ(3α/2)σ˜R2}2α6
(44)
By substituting Eq. (42) and Eq. (44) into Eq. (40), we obtain
ηX=1/c1(α)1+[1.02Cpl(α)]2α6σ˜R2[Qm(α)]2α2.
(45)
Thus, by inserting Eq. (45) into Eq. (38), we find that the large-scale log-irradiance scintillation including inner scale parameter can be written in the form
σlnX,pl2(l0,α)=αΓ(3α/2)12Γ(1α/2)sin(απ/4)σ˜R2×{Qm(α)1+c1(α)Qm(α)+c1(α)[1.02Cpl(α)]2α6σ˜R2[Qm(α)]3α2}3α/2
(46)
By an entirely analogous evaluation, it follows that the large-scale log-irradiance scintillation with outer scale parameter becomes
σlnX,pl2(L0,α)=αΓ(3α/2)12Γ(1α/2)sin(απ/4)σ˜R2(ηX0Qm(α)ηX0+Qm(α))3α/2,
(47)
where
ηX0=ηXQ0ηX+Q0=Q01+c1(α)Q0+c1(α)[1.02Cpl(α)]2α6σ˜R2Q0[Qm(α)]2α2,
(48)
and where Q0=Lκ02/k=64π2L/kL02.

Because the form of the filter function is the same for the small-scale log-irradiance scintillations in this case as that for the zero inner scale case, these scintillations are again described by [15

15. I. Toselli, L. C. Andrews, R. L. Phillips, and V. Ferrero, “Scintillation index of optical plane wave propagating through non Kolmogorov moderate-strong turbulence,” Proc. SPIE 6747, 67470B (2007). [CrossRef]

, Eq. (37)]
σlnY,pl2(l0,α)=α(α2)Γ(1α/2)sin(απ/4)σ˜R2ηY1α/2,
(49)
where ηY=LκY2/k. To determine the high-pass nondimensional cutoff frequency ηY, we impose σlnY2(l0,α)0.51σ˜PL2 in weak fluctuations and σlnY2(l0,α)ln2 in strong fluctuations. By using the asymptotic results [7

7. L. C. Andrews, R. L. Phillips, C. Y. Hopen, and M. A. Al-Habash, “Theory of optical scintillation,” J. Opt. Soc. Am. A 16(6), 1417–1429 (1999). [CrossRef]

, Eq. (27)]
ηY=c3(α)+c4(α)L/kρpl2(α){c3(α),L/kρpl2(α)1,c4(α)L/kρpl2(α),L/kρpl2(α)1,
(50)
we find
ηY=[α0.51(α2)Γ(1α/2)sin(απ/4)σ˜R2σ˜PL2]2α2(1+0.732α2σ˜PL4α2).
(51)
And therefore Eq. (49) becomes
σlnY,pl2(l0,α)=0.51σ˜PL2(1+0.732α2σ˜PL4α2)1α/2.
(52)
We note here that although the small-scale filter Eq. (32) does not explicitly contain a inner scale factor like the large-scale filter Eq. (33), the cutoff spatial frequency κY for the small-scale filter does depend on the inner scale [see (51)] and, hence, small-scale scintillation described by Eq. (52) also depends on the inner scale, particularly, in the weak fluctuation regime. Outer-scale effects are negligible here. Finally, by combining Eq. (46), Eq. (47), and Eq. (52), the SI for an infinite plane wave in the presence of a nonzero inner scale and a finite outer scale is given by
σI,pl2(α)=exp[σlnX,pl2(l0,α)σlnX,pl2(L0,α)+σlnY,pl2(l0,α)]1,0σ˜R2<.
(53)

6. Scintillation index for spherical wave

Under weak irradiance fluctuations, the SI based on the generalized von Kármán spectrum leads to [21

21. L. Y. Cui, B. D. Xue, L. Cao, S. L. Zheng, W. F. Xue, X. Z. Bai, X. G. Cao, and F. G. Zhou, “Irradiance scintillation for Gaussian-beam wave propagating through weak non-Kolmogorov turbulence,” Opt. Express 19(18), 16872–16884 (2011). [CrossRef] [PubMed]

, Eq. (35)]
σ˜SP2=σ˜R2sin(απ/4){31α2[1+9Qm2(α)]α/4sin[α2tan1(Qm(α)3)]α2[Qm(α)]1α2},σ˜R2<1.
(54)
In the strong fluctuation regime, the corresponding approximation to the SI is given by Eq. (28). As in the plane-wave case, we assume the large-scale filter function is Eq. (33), which contains both inner scale and outer scale parameters. Under the geometrical optics approximation, the large-scale scintillation due to inner scale alone is described by the log-irradiance variance
σlnX,sp2(l0,α)=8π2k2L010κΦ˜n(κ,α)exp(κ2κm2)exp(κ2κX2)×{1cos[Lκ2kξ(1ξ)]}dκdξα4Γ(1α/2)sin(απ/4)σ˜R201ξ2(1ξ2)dξ×0η2α/2exp(ηQm(α)ηηX)dη=αΓ(3α/2)120Γ(1α/2)sin(απ/4)σ˜R2(ηXQm(α)ηX+Qm(α))3α/2.
(55)
When l0 → 0 (i.e., Qm (α) → ∞), Eq. (55) reduces to
σlnX,sp2(α)=αΓ(3α/2)120Γ(1α/2)sin(απ/4)σ˜R2(ηX)3α/2.
(56)
Similar to the plane-wave case, we rely on Eq. (56) rather than Eq. (55) to determine ηX. Thus, we impose the conditions
σlnX,sp2(α){0.49β˜02,σ˜R2<1,Csp(α)2{σ˜R2[Qm(α)]3α/2}2α/2,αΓ(2α/2)σ˜R2[Qm(α)]2α/216Γ(1α/2)sin(απ/4)1,
(57)
where β˜02=Γ(α/2)Γ(1+α/2)σ˜R2/Γ(α) is the non-Kolmogorov spherical wave Rytov variance [14

14. L. Tan, W. Du, J. Ma, S. Yu, and Q. Han, “Log-amplitude variance for a Gaussian-beam wave propagating through non-Kolmogorov turbulence,” Opt. Express 18(2), 451–462 (2010). [CrossRef] [PubMed]

, Eq. (9)]. Then, by using the asymptotic results for ηX [Eq. (40)], we derive
ηX=1/d1(α)1+Δ(α),
(58)
where
d1(α)=[58.8Γ(1α/2)sin(απ/4)Γ(α/2)Γ(1+α/2)αΓ(3α/2)Γ(α)]2α6,
(59)
and
Δ(α)=[1.02Γ(α)Csp(α)Γ(α/2)Γ(1+α/2)]2α6σ˜R2[Qm(α)]2α2.
(60)
By substituting Eq. (58) into Eq. (55), we obtain
σlnX,sp2(l0,α)=αΓ(3α/2)120Γ(1α/2)sin(απ/4)σ˜R2×(Qm(α)1+d1(α)Qm(α)+d1(α)Δ(α)Qm(α))3α/2.
(61)
Similarly, the large-scale scintillation due to outer scale effects is derived by
σlnX,sp2(L0,α)=αΓ(3α/2)120Γ(1α/2)sin(απ/4)σ˜R2×{Q0Qm(α)Q0+Qm(α)+d1(α)Q0Qm(α)[1+Δ(α)]}3α/2.
(62)
The small-scale log-irradiance variance is once again given by Eq. (49), but in this case ηY is described by
ηY=[α0.51(α2)Γ(1α/2)sin(απ/4)σ˜R2σ˜SP2]2α2(1+0.732α2σ˜SP4α2).
(63)
Hence, the small-scale log-irradiance variance becomes
σlnY,sp2(l0,α)0.51σ˜SP2(1+0.732α2σ˜SP4α2)1α/2.
(64)
If we combine Eq. (61), Eq. (62), and Eq. (64), we obtain the SI for a spherical wave in the presence of a finite inner scale and outer scale described by
σI,sp2(α)=exp[σlnX,sp2(l0,α)σlnX,sp2(L0,α)+σlnY,sp2(l0,α)]1,0σ˜R2<.
(65)

7. Numerical results

In this section, we show numerical results of the analytical SI for the plane wave and the spherical wave model. For numerical calculations we set the wavelength λ = 1.55μm, the generalized structure parameter C˜n2=1013m3α, and allow the path length L to vary. In this fashion, the increment of the path length corresponds to increases in turbulence strength.

In Fig. 1(a) and 1(b) we illustrate the SI of a plane wave Eq. (53) and a spherical wave Eq. (65) as a function of the path length and several values of power law α (solid line). We take the atmospheric conditions described by the generalized von Kármán spectrum with inner scale size of l0 = 3mm and outer scale L0 = ∞. For comparison purposes, we also plot the SI based on the asymptotic behavior Eq. (41) and Eq. (54) under weak irradiance fluctuations (dotted line) and the asymptotic theory approximation Eq. (24) and Eq. (28) for strong irradiance fluctuations (dashed line). As expected, our general scintillation models Eq. (53) and Eq. (65) track the corresponding weak and strong turbulence curves fairly closely, providing visual indications that calculations and assumptions used to develop them are correct. In addition, we note that when power law is lower than 11/3 (≈ 3.67), the SI increases initially within the regime of weak irradiance fluctuations with increasing values of the path length. It then increases beyond unity and reaches its maximum value. And after that, the SI gradually decreases, saturating at a level on the order of unity as the path length increases without bound. This general behavior is basically the same as that for conventional von Kármán spectrum (also see [8

8. K. J. Mayer, Effect of Inner Scale Atmospheric Spectrum Models on Scintillation in All Optical Turbulence Regimes, Ph.D. dissertation, University of Central Florida, 2007.

. Fig. 4 and 5]). However, as the value of the power law decreases, peak scintillation occurs at shorter and shorter path lengths. We also note that for power law values higher than 11/3, the peak scintillation phenomenon vanishes and the SI increases monotonically toward a limiting value above unity with the increment of the path length. This behavior is similar to what is observed for the zero inner scale case [15

15. I. Toselli, L. C. Andrews, R. L. Phillips, and V. Ferrero, “Scintillation index of optical plane wave propagating through non Kolmogorov moderate-strong turbulence,” Proc. SPIE 6747, 67470B (2007). [CrossRef]

, Fig. 3].

Fig. 1 Scintillation index vs. path length, (a) plane wave model, (b) spherical wave model.
Fig. 3 Spherical wave scintillation vs.L.

As presented in Section 4, in arriving at Eq. (24) we have used the small-argument approximation for the confluent hypergeometric function U (a;c;x) that appears in Eq. (22). Such approximation has been successfully applied to develop expression for the SI in the saturation regime based on the conventional von Kármán spectrum with α = 11/3 [8

8. K. J. Mayer, Effect of Inner Scale Atmospheric Spectrum Models on Scintillation in All Optical Turbulence Regimes, Ph.D. dissertation, University of Central Florida, 2007.

, Appendix H]. To justify the validity of such approximation for other values of α, we evaluate the integral in Eq. (22) numerically. All of the parameters selected in numerical integration of Eq. (22) are the same as that used in the evaluation of Eq. (24) except that L0 = 1000m (a finite outer scale parameter is required in calculating Eq. (22), so, we use a large outer scale value to approximate an infinite outer scale.) The results of the numerical integration of Eq. (22) are also plotted in Fig. 1(a) with several values of α (open circles). It can be seen that the approximation results based on Eq. (24) agree well with the numerical results of Eq. (22) for all α values, indicating that the approximation that we have made is valid. From Fig. 1(b) it is clear that the approximation results based on Eq. (28) are also valid in the spherical-wave case. In addition, note in Fig. 1(a) and 1(b) that the total SI Eq. (53) and Eq. (65) match with the SI in the saturation regime Eq. (24) and Eq. (28) at different path lengths for different α values. This is because the validity of Eq. (24) and Eq. (28) are determined by the conditional statement in Eq. (24) that is a function of α. For example, the conditional statement in Eq. (24) is satisfied at L = 2000m for α = 3.07 (in this case, the conditional statement is 113≫1), but for α = 3.87, L need to increase to 6000m to make the conditional statement established (in this case, the conditional statement is 125≫1). The studies based on the generalized Kolmogorov spectrum [15

15. I. Toselli, L. C. Andrews, R. L. Phillips, and V. Ferrero, “Scintillation index of optical plane wave propagating through non Kolmogorov moderate-strong turbulence,” Proc. SPIE 6747, 67470B (2007). [CrossRef]

, 16

16. P. Deng, X. H. Yuan, and D. X. Huang, “Scintillation of a laser beam propagation through non-Kolmogorov strong turbulence,” Opt. Commun., accepted for publication.

] have used σ˜R21 to define the strong-fluctuation conditions. However, this conditional statement is not applicable in the present case. For example, σ˜R2 for α = 3.07 at L = 2000m is equal to 9.8 which is not satisfied σ˜R21, but as revealed in Fig. 1(a), the SI for α = 3.07 does indeed enter into the saturation regime at L = 2000m.

Fig. 2 Plane wave scintillation vs.α.

In Fig. 3 we plot the SI of spherical wave deduced from Eq. (65) as a function of L, with inner scale values of l0 = 3 and 8mm and outer scale L0 = ∞ (solid lines). The dashed lines are comparable scintillation values that arise with all parameters the same except L0 = 1m. We set α = 3.07, 3.37, 3.67, and 3.87 in the Fig. 3(a), 3(b), 3(c), and 3(d), respectively. It is observed that for an arbitrary value of α, the outer scale has a negligible effect on the SI of a spherical wave under weak fluctuations associated with short path lengths. However, with an increase in path lengths, the presence of a finite outer scale in the scintillation model is quite clear. Namely, the outer-scale effect initially reduces scintillation at a steeper rate toward its limiting value of unity than would occur with an infinite outer scale. Also, for an arbitrary value of α, the influence of inner scale on scintillation is not significant under weak fluctuation conditions. Under moderate-to-strong fluctuations, the SI predicted for the smaller inner scale value (l0 = 3mm) is always less than that predicted for the larger inner scale value (l0 = 8mm). Specifically, for power law values lower than 11/3 (viz., α = 3.07, 3.37), the increment of inner scale significantly increases the SI near its peak value. As the path length increases, the gap between the larger and smaller inner scale SI curves becomes narrower and narrower, suggesting that inner-scale effect on scintillation tends to diminish with the increment of turbulence strength. For power law values higher than 11/3 (viz., α = 3.87), the predicted SI over the whole moderate-to-strong fluctuation regimes is only slightly higher for a large inner-scale value than for a small inner-scale value.

8. Conclusion

In summary, the outer scale has a negligible effect on scintillation under weak turbulence conditions for all values of power law. However, the presence of a finite outer scale causes a more rapid drop in scintillation at larger values of the path length. The decreasing rate of the SI from its peak value to its saturation value is dependent on power law. On the other hand, the inner scale plays a noticeable role in the SI under weak fluctuations. In this regime, whether the predicted SI for the larger inner scale values is greater than that predicted for the smaller inner scale values depends on the value of power law. However, under moderate-to-strong fluctuations, the predicted SI for the smaller inner scale values is always less than that predicted for the larger inner scale values. Furthermore, when power law is lower than 11/3, the increment of inner scale significantly increases the SI near its peak value. As turbulence strength increases, the inner-scale effect on scintillation tends to diminish. When power law is higher than 11/3, the increment of inner scale leads to a slight increase in scintillation over all strong fluctuation regime.

Acknowledgments

This work is supported by the project of State Key Laboratory on Integrated Services Networks, and partly by the National Nature Science Foundation of China grant (no. 60902038).

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K. J. Mayer, Effect of Inner Scale Atmospheric Spectrum Models on Scintillation in All Optical Turbulence Regimes, Ph.D. dissertation, University of Central Florida, 2007.

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I. Toselli, L. C. Andrews, R. L. Phillips, and V. Ferrero, “Free space optical system performance for a Gaussian beam propagating through non-Kolmogorov weak turbulence,” IEEE Trans. Antenn. Propag. 57(6), 1783–1788 (2009). [CrossRef]

14.

L. Tan, W. Du, J. Ma, S. Yu, and Q. Han, “Log-amplitude variance for a Gaussian-beam wave propagating through non-Kolmogorov turbulence,” Opt. Express 18(2), 451–462 (2010). [CrossRef] [PubMed]

15.

I. Toselli, L. C. Andrews, R. L. Phillips, and V. Ferrero, “Scintillation index of optical plane wave propagating through non Kolmogorov moderate-strong turbulence,” Proc. SPIE 6747, 67470B (2007). [CrossRef]

16.

P. Deng, X. H. Yuan, and D. X. Huang, “Scintillation of a laser beam propagation through non-Kolmogorov strong turbulence,” Opt. Commun., accepted for publication.

17.

J. Cang and X. Liu, “Average capacity of free-space optical systems for a partially coherent beam propagating through non-Kolmogorov turbulence,” Opt. Lett. 36(7), 3335–3337 (2011). [CrossRef] [PubMed]

18.

I. Toselli, L. C. Andrews, R. L. Phillips, and V. Ferrero, “Angle of arrival fluctuations for free space laser beam propagation through Non-Kolmogorov turbulence,” Proc. SPIE 6551, 65510E–1–12 (2007).

19.

L. Y. Cui, B. D. Xue, X. G. Cao, J. K. Dong, and J. N. Wang, “Generalized atmospheric turbulence MTF for wave propagating through non-Kolmogorov turbulence,” Opt. Express 18(20), 21269–21283 (2010). [CrossRef] [PubMed]

20.

B. D. Xue, L. Y. Cui, W. F. Xue, X. Z. Bai, and F. G. Zhou, “Generalized modified atmospheric spectral model for optical wave propagating through non-Kolmogorov turbulence,” J. Opt. Soc. Am. A 28(5), 912–916 (2011). [CrossRef]

21.

L. Y. Cui, B. D. Xue, L. Cao, S. L. Zheng, W. F. Xue, X. Z. Bai, X. G. Cao, and F. G. Zhou, “Irradiance scintillation for Gaussian-beam wave propagating through weak non-Kolmogorov turbulence,” Opt. Express 19(18), 16872–16884 (2011). [CrossRef] [PubMed]

22.

J. Cang and X. Liu, “Scintillation index and performance analysis of wireless optical links over non-Kolmogorov weak turbulence based on generalized atmospheric spectral model,” Opt. Express 19(20), 19067–19077 (2011). [CrossRef] [PubMed]

23.

B. E. Stribling, B. M. Welsh, and M. C. Roggemann, “Optical propagation in non-Kolmogorov atmospheric turbulence,” Proc. SPIE 2471, 1–17 (1995).

24.

L. C. Andrews, Special Functions of Mathematics for Engineers, 2nd ed. (SPIE Optical Engineering Press, Bellingham, Wash., 1998).

25.

R. Mahon, C. I. Moore, H. R. Burris, W. S. Rabinovich, M. Stell, M. R. Suite, and L. M. Thomas, “Analysis of long-term measurements of laser propagation over the Chesapeake Bay,” Appl. Opt. 48(12), 2388–2400 (2009). [CrossRef] [PubMed]

OCIS Codes
(010.1290) Atmospheric and oceanic optics : Atmospheric optics
(010.1300) Atmospheric and oceanic optics : Atmospheric propagation
(010.1330) Atmospheric and oceanic optics : Atmospheric turbulence

ToC Category:
Atmospheric and Oceanic Optics

History
Original Manuscript: December 20, 2011
Revised Manuscript: January 29, 2012
Manuscript Accepted: January 29, 2012
Published: February 6, 2012

Citation
Xiang Yi, Zengji Liu, and Peng Yue, "Inner- and outer-scale effects on the scintillation index of an optical wave propagating through moderate-to-strong non-Kolmogorov turbulence," Opt. Express 20, 4232-4247 (2012)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-20-4-4232


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References

  1. L. C. Andrews and R. L. Phillips, “Impact of scintillation on laser communication systems: recent advances in modeling,” Proc. SPIE4489, 23–34 (2002). [CrossRef]
  2. A. Zilberman, E. Golbraikh, and N. S. Kopeika, “Some limitations on optical communication reliability through Kolmogorov and non-Kolmogorov turbulence,” Opt. Commun.283(7), 1229–1235 (2010). [CrossRef]
  3. H. G. Sandalidis, “Performance of a laser Earth-to-satellite link over turbulence and beam wander using the modulated gamma-gamma irradiance distribution,” Appl. Opt.50(6), 952–961 (2011). [CrossRef] [PubMed]
  4. L. C. Andrews and R. L. Phillips, Laser Beam Propagation through Random Media, 2nd ed. (SPIE Optical Engineering Press, 2005). [CrossRef]
  5. W. B. Miller, J. C. Ricklin, and L. C. Andrews, “Log-amplitude variance and wave structure function: a new perspective for Gaussian beams,” J. Opt. Soc. Am. A10(4), 661–672 (1993). [CrossRef]
  6. W. B. Miller, J. C. Ricklin, and L. C. Andrews, “Effects of the refractive index spectral model on the irradiance variance of a Gaussian beam,” J. Opt. Soc. Am. A11(10), 2719–2726 (1994). [CrossRef]
  7. L. C. Andrews, R. L. Phillips, C. Y. Hopen, and M. A. Al-Habash, “Theory of optical scintillation,” J. Opt. Soc. Am. A16(6), 1417–1429 (1999). [CrossRef]
  8. K. J. Mayer, Effect of Inner Scale Atmospheric Spectrum Models on Scintillation in All Optical Turbulence Regimes, Ph.D. dissertation, University of Central Florida, 2007.
  9. D. T. Kyrazis, J. B. Wissler, D. B. Keating, A. J. Preble, and K. P. Bishop, “Measurement of optical turbulence in the upper troposphere and lower stratosphere,” Proc. SPIE2120, 43–55 (1994). [CrossRef]
  10. M. S. Belen’kii, S. J. Karis, J. M. Brown, and R. Q. Fugate, “Experimental study of the effect of non-Kolmogorov stratospheric turbulence on star image motion,” Proc. SPIE3126, 113–123 (1997). [CrossRef]
  11. A. Zilberman, E. Golbraikh, N. S. Kopeika, A. Virtser, I. Kupershmidt, and Y. Shtemler, “Lidar study of aerosol turbulence characteristics in the troposphere: Kolmogorov and non-Kolmogorov turbulence,” Atmos. Res.88(1), 66–77 (2008). [CrossRef]
  12. I. Toselli, L. C. Andrews, R. L. Phillips, and V. Ferrero, “Free-space optical system performance for laser beam propagation through non-Kolmogorov turbulence,” Proc. SPIE6457, 64570T–1–11 (2007).
  13. I. Toselli, L. C. Andrews, R. L. Phillips, and V. Ferrero, “Free space optical system performance for a Gaussian beam propagating through non-Kolmogorov weak turbulence,” IEEE Trans. Antenn. Propag.57(6), 1783–1788 (2009). [CrossRef]
  14. L. Tan, W. Du, J. Ma, S. Yu, and Q. Han, “Log-amplitude variance for a Gaussian-beam wave propagating through non-Kolmogorov turbulence,” Opt. Express18(2), 451–462 (2010). [CrossRef] [PubMed]
  15. I. Toselli, L. C. Andrews, R. L. Phillips, and V. Ferrero, “Scintillation index of optical plane wave propagating through non Kolmogorov moderate-strong turbulence,” Proc. SPIE6747, 67470B (2007). [CrossRef]
  16. P. Deng, X. H. Yuan, and D. X. Huang, “Scintillation of a laser beam propagation through non-Kolmogorov strong turbulence,” Opt. Commun., accepted for publication.
  17. J. Cang and X. Liu, “Average capacity of free-space optical systems for a partially coherent beam propagating through non-Kolmogorov turbulence,” Opt. Lett.36(7), 3335–3337 (2011). [CrossRef] [PubMed]
  18. I. Toselli, L. C. Andrews, R. L. Phillips, and V. Ferrero, “Angle of arrival fluctuations for free space laser beam propagation through Non-Kolmogorov turbulence,” Proc. SPIE6551, 65510E–1–12 (2007).
  19. L. Y. Cui, B. D. Xue, X. G. Cao, J. K. Dong, and J. N. Wang, “Generalized atmospheric turbulence MTF for wave propagating through non-Kolmogorov turbulence,” Opt. Express18(20), 21269–21283 (2010). [CrossRef] [PubMed]
  20. B. D. Xue, L. Y. Cui, W. F. Xue, X. Z. Bai, and F. G. Zhou, “Generalized modified atmospheric spectral model for optical wave propagating through non-Kolmogorov turbulence,” J. Opt. Soc. Am. A28(5), 912–916 (2011). [CrossRef]
  21. L. Y. Cui, B. D. Xue, L. Cao, S. L. Zheng, W. F. Xue, X. Z. Bai, X. G. Cao, and F. G. Zhou, “Irradiance scintillation for Gaussian-beam wave propagating through weak non-Kolmogorov turbulence,” Opt. Express19(18), 16872–16884 (2011). [CrossRef] [PubMed]
  22. J. Cang and X. Liu, “Scintillation index and performance analysis of wireless optical links over non-Kolmogorov weak turbulence based on generalized atmospheric spectral model,” Opt. Express19(20), 19067–19077 (2011). [CrossRef] [PubMed]
  23. B. E. Stribling, B. M. Welsh, and M. C. Roggemann, “Optical propagation in non-Kolmogorov atmospheric turbulence,” Proc. SPIE2471, 1–17 (1995).
  24. L. C. Andrews, Special Functions of Mathematics for Engineers, 2nd ed. (SPIE Optical Engineering Press, Bellingham, Wash., 1998).
  25. R. Mahon, C. I. Moore, H. R. Burris, W. S. Rabinovich, M. Stell, M. R. Suite, and L. M. Thomas, “Analysis of long-term measurements of laser propagation over the Chesapeake Bay,” Appl. Opt.48(12), 2388–2400 (2009). [CrossRef] [PubMed]

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