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Optics Express

Optics Express

  • Editor: C. Martijn de Sterke
  • Vol. 20, Iss. 14 — Jul. 2, 2012
  • pp: 15301–15308
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Experimental verification of fiber-coupling efficiency for satellite-to-ground atmospheric laser downlinks

Hideki Takenaka, Morio Toyoshima, and Yoshihisa Takayama  »View Author Affiliations


Optics Express, Vol. 20, Issue 14, pp. 15301-15308 (2012)
http://dx.doi.org/10.1364/OE.20.015301


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Abstract

Optical communication is a high-capacity method that can handle considerable satellite data. When common-fiber optical devices such as optical fiber amplifiers based on single mode fibers are used in free-space laser communication systems, the laser beam has to be coupled to a single-mode fiber. Under atmospheric turbulence it would be difficult to make the required fiber coupling efficiency in satellite-to-ground laser propagation paths. A fast-steering mirror that can operate at high frequencies under atmospheric turbulence is fabricated, and its tracking performance is verified in real satellite-to-ground laser communication experiments. The measured fiber coupling loss of 10–19 dB in satellite-to-ground laser communication links under atmospheric turbulence shows good agreement with the predicted fiber coupling efficiency of 17 dB.

© 2012 OSA

1. Introduction

2. Theory of fiber coupling efficiency for ground-to-satellite laser links

2.1 Fiber coupling efficiency in the presence of atmospheric turbulence

a=DR2πWmλf,
(2)
Ac=πρc2,
(3)
AR=πDR2/4,
(4)
ρc=(1.46Cn2k2L)3/5.
(5)

H=h0+Lcos(ζ),Cn2(h)=0.00594(v/27)2(105h)10exp(h1000)
(7)
+2.7×1016exp(h1500)+Aexp(h100).
(8)

Structure function for atmospheric turbulence Cn2 is shown in Eq. (8) as the atmospheric turbulence model [10

10. L. C. Andrews, R. L. Phillips, and P. T. Yu, “Optical scintillations and fade statistics for a satellite-communication system,” Appl. Opt. 34(33), 7742–7751 (1995). [CrossRef] [PubMed]

]. Here h0 is the height above the ground, ζ is the zenith angle, and v is the rms windspeed. We extend Eq. (1) to obtain the fiber coupling efficiency for a slanted atmospheric transmission path by adapting Eq. (6) in Eq. (1). We can calculate the fiber coupling efficiency of the ground-to-satellite laser communication for any satellites for swapping Ar and As in Eq. (1),

As=πρs2.
(9)

2.2 Predicted fiber coupling efficiency

Figure 1
Fig. 1 Cn2 profile associated with the H–V model as a function of the altitude, where A = 1.2 × 10−13 m−2/3 and h0 = 122 m.
shows the Cn2(h) profile associated with the Hufnagel–Valley (H–V) model as a function of the altitude calculated using Eq. (9). In the prediction, we assume an optical ground station having A = 1.2 × 10−13 m−2/3 and h0 = 122 m [11

11. M. Toyoshima, Y. Takayama, H. Kunimori, and T. Jono, “Probability density function of the atmospheric turbulence-induced signal fluctuation in a ground-to-low earth orbit optical communication link,” Proc. 25th LSS, 30–36, (2007).

].

Figure 2
Fig. 2 Fiber coupling efficiency as a function of A for Cn2 and λ = 0.850, 1.060, 1.330, and 1.550 μm, where L = 1000 km, DR = 0.318 m, Wm = 5.2 μm, λ = 0.850 μm, v = 21 m/s, h0 = 122 m and f = 0.1.
shows the fiber coupling efficiency as a function of A in Eq. (8) under atmospheric turbulence Cn2 with DR = 0.318 m, Wm = 5.2 μm, λ = 0.850 μm, f = 0.1 m, L = 1000 km, and ζ = 58°. The fiber coupling efficiency decreases when the refractive index structure constant increases; the efficiency is degraded to less than half when A change from 10−15 m-2/3 to 10−13 m-2/3.

3. Satellite-to-ground laser link experiments

3.1 Experimental configuration

3.2 Fine tracking system

The fine tracking system consists of a beam splitter, the FSM, a single-mode fiber coupler, and a QD sensor. Figures 5
Fig. 5 Photograph of the FSM at experiment.
and 6
Fig. 6 Configuration of the fine tracking system from telescope to optical bench.
show a photograph of the FSM and its configuration, respectively [12

12. T. Abe, T. Kizaki, H. Kunimori, Y. Takayama, and M. Toyoshima, “The development of two-axes fast steering mirror and high efficiency driver,” Proc. 52nd Space Science and Technology Conference, 487–490, (2008).

]; Table 1

Table 1. FSM specifications [12]

table-icon
View This Table
| View All Tables
lists its specifications. As the resonance frequency is 6.4 kHz and the frequency at the phase of 90° is 6 kHz according to the frequency characteristics based on FSM, it sufficiently meets the required specification of 2 kHz. The inherent hysteresis property in the piezo-element has appeared remarkably with the large stroke; however, it may not cause any particular problem because the hysteresis with the small stroke is lower than that with the large stroke when a closed-loop control system is incorporated. With a resolution of less than 1 μrad achieved, it sufficiently meets the required specification of 10 μrad. The optical signal is received by a 1.5 m telescope and transmitted along the coude path. The sub-aperture of 31.8 cm was used for the proposed fine tracking system. Therefore, this optical system received a part of 1.5m telescope. The beam diameter was 2 cm on the optical bench. The FSM is placed on the coude optical bench. Part of the beam is divided by the beam splitter, and the QD detects the incident angle of the laser beam. The beam is reflected by the FSM. The QD sensor and the FSM are controlled as a closed loop. The FSM is controlled so that the optical signal remains at the center of the QD sensor. The received laser beam is adjusted so that the spot of the laser beam can be coupled into the single-mode fiber.

The received power was measured by two photodiodes (PDa and PDb). PDa measured the laser light received by the single-mode fiber, and PDb was used to compare the received power without fiber coupling. The loss of the optical system was measured before the experiments. The coupling loss was determined as the difference between the received power with fiber coupling, PPDa, and the received power without fiber coupling, PPDb. The fiber coupling efficiency can be evaluated experimentally using this setup.

3.3 Experimental results

3.3.1 Comparison of fiber coupling efficiencies in laboratory test and real measurements

We compared the fiber coupling efficiencies in a laboratory test and real measurements using OICETS. The fiber coupling loss ll was determined by comparing the received power coupled into the single-mode fiber and the received power without the fiber coupling, obtained by monitoring PPDb. Similarly, ls is the fiber coupling loss in the real measurements, which was determined by PPDa and PPDb using OICETS. The degraded fiber coupling loss can be compared by using the loss measured in the laboratory tests and the real measurements using the laser source from OICETS.

3.3.2 Measurements of the fiber coupling efficiencies with OICETS

In the experiments, the optical signal was not received by the fiber coupled detector when the FSM was turned-off, which prevented us from determining the fiber coupling efficiency. This was caused by a telescope jitter error due to mechanical telescope tracking errors. If there was no tip/tilt tracking control, no optical signal was coupled into the fiber in the experiment.

4. Conclusion

References and links

1.

M. Toyoshima, “Trends in satellite communications and the role of optical free-space communications [Invited],” J. Opt. Netw. 4(6), 300–311 (2005). [CrossRef]

2.

V. W. S. Chan, “Optical satellite networks,” J. Lightwave Technol. 21(11), 2811–2827 (2003). [CrossRef]

3.

Y. Koyama, Y. Takayama, and H. Kunimori, “Optical fiber amplifiers for space environments,” Int. Conf. Struct. Surf. 2009(37), 221–225 (2009).

4.

J. C. Ricklin and F. M. Davidson, “Atmospheric turbulence effects on a partially coherent Gaussian beam: implications for free-space laser communication,” J. Opt. Soc. Am. A 19(9), 1794–1802 (2002). [CrossRef] [PubMed]

5.

F. Fidler and O. Wallner, “Application of single-mode fiber-coupled receivers in optical satellite to high-altitude platform communications,” EURASIP J. Wirel. Commun. Netw. 2008, 864031 (2008).

6.

M. Toyoshima, “Maximum fiber coupling efficiency and optimum beam size in the presence of random angular jitter for free-space laser systems and their applications,” J. Opt. Soc. Am. A 23(9), 2246–2250 (2006). [CrossRef] [PubMed]

7.

Y. Dikmelik and F. M. Davidson, “Fiber-coupling efficiency for free-space optical communication through atmospheric turbulence,” Appl. Opt. 44(23), 4946–4952 (2005). [CrossRef] [PubMed]

8.

T. Jono, Y. Takayama, K. Arai, K. Shiratama, I. Mase, B. Demelenne, M. Toyoshima, and D. Giggenbach, “Overview of the inter-orbit and the orbit-to-ground lasercom demonstration by OICETS,” Proc. SPIE 6457(645702), 1–10 (2007).

9.

J. H. Churnside, “Aperture averaging of optical scintillations in the turbulent atmosphere,” Appl. Opt. 30(15), 1982–1994 (1991). [CrossRef] [PubMed]

10.

L. C. Andrews, R. L. Phillips, and P. T. Yu, “Optical scintillations and fade statistics for a satellite-communication system,” Appl. Opt. 34(33), 7742–7751 (1995). [CrossRef] [PubMed]

11.

M. Toyoshima, Y. Takayama, H. Kunimori, and T. Jono, “Probability density function of the atmospheric turbulence-induced signal fluctuation in a ground-to-low earth orbit optical communication link,” Proc. 25th LSS, 30–36, (2007).

12.

T. Abe, T. Kizaki, H. Kunimori, Y. Takayama, and M. Toyoshima, “The development of two-axes fast steering mirror and high efficiency driver,” Proc. 52nd Space Science and Technology Conference, 487–490, (2008).

13.

M. Toyoshima, H. Takenaka, and Y. Takayama, “Atmospheric turbulence-induced fading channel model for space-to-ground laser communications links,” Opt. Express 19(17), 15965–15975 (2011). [CrossRef] [PubMed]

OCIS Codes
(010.1330) Atmospheric and oceanic optics : Atmospheric turbulence
(060.2605) Fiber optics and optical communications : Free-space optical communication
(140.3325) Lasers and laser optics : Laser coupling

ToC Category:
Atmospheric and Oceanic Optics

History
Original Manuscript: April 30, 2012
Revised Manuscript: June 15, 2012
Manuscript Accepted: June 15, 2012
Published: June 22, 2012

Citation
Hideki Takenaka, Morio Toyoshima, and Yoshihisa Takayama, "Experimental verification of fiber-coupling efficiency for satellite-to-ground atmospheric laser downlinks," Opt. Express 20, 15301-15308 (2012)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-20-14-15301


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References

  1. M. Toyoshima, “Trends in satellite communications and the role of optical free-space communications [Invited],” J. Opt. Netw.4(6), 300–311 (2005). [CrossRef]
  2. V. W. S. Chan, “Optical satellite networks,” J. Lightwave Technol.21(11), 2811–2827 (2003). [CrossRef]
  3. Y. Koyama, Y. Takayama, and H. Kunimori, “Optical fiber amplifiers for space environments,” Int. Conf. Struct. Surf.2009(37), 221–225 (2009).
  4. J. C. Ricklin and F. M. Davidson, “Atmospheric turbulence effects on a partially coherent Gaussian beam: implications for free-space laser communication,” J. Opt. Soc. Am. A19(9), 1794–1802 (2002). [CrossRef] [PubMed]
  5. F. Fidler and O. Wallner, “Application of single-mode fiber-coupled receivers in optical satellite to high-altitude platform communications,” EURASIP J. Wirel. Commun. Netw.2008, 864031 (2008).
  6. M. Toyoshima, “Maximum fiber coupling efficiency and optimum beam size in the presence of random angular jitter for free-space laser systems and their applications,” J. Opt. Soc. Am. A23(9), 2246–2250 (2006). [CrossRef] [PubMed]
  7. Y. Dikmelik and F. M. Davidson, “Fiber-coupling efficiency for free-space optical communication through atmospheric turbulence,” Appl. Opt.44(23), 4946–4952 (2005). [CrossRef] [PubMed]
  8. T. Jono, Y. Takayama, K. Arai, K. Shiratama, I. Mase, B. Demelenne, M. Toyoshima, and D. Giggenbach, “Overview of the inter-orbit and the orbit-to-ground lasercom demonstration by OICETS,” Proc. SPIE6457(645702), 1–10 (2007).
  9. J. H. Churnside, “Aperture averaging of optical scintillations in the turbulent atmosphere,” Appl. Opt.30(15), 1982–1994 (1991). [CrossRef] [PubMed]
  10. L. C. Andrews, R. L. Phillips, and P. T. Yu, “Optical scintillations and fade statistics for a satellite-communication system,” Appl. Opt.34(33), 7742–7751 (1995). [CrossRef] [PubMed]
  11. M. Toyoshima, Y. Takayama, H. Kunimori, and T. Jono, “Probability density function of the atmospheric turbulence-induced signal fluctuation in a ground-to-low earth orbit optical communication link,” Proc. 25th LSS, 30–36, (2007).
  12. T. Abe, T. Kizaki, H. Kunimori, Y. Takayama, and M. Toyoshima, “The development of two-axes fast steering mirror and high efficiency driver,” Proc. 52nd Space Science and Technology Conference, 487–490, (2008).
  13. M. Toyoshima, H. Takenaka, and Y. Takayama, “Atmospheric turbulence-induced fading channel model for space-to-ground laser communications links,” Opt. Express19(17), 15965–15975 (2011). [CrossRef] [PubMed]

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