Experimental demonstration of single-mode fiber
coupling over relatively strong turbulence with
adaptive optics
MO CHEN,
1,2,3
CHAO LIU,
1,2
AND HAO XIAN
1,2,
*
1
Key Laboratory on Adaptive Optics, Chinese Academy of Sciences, Chengdu 610209, China
2
Institute of Optics and Electronics, Chinese Academy of Sciences, Chengdu 610209, China
3
University of Chinese Academy of Sciences, Beijing 100049, China
*Corresponding author: xianhao@ioe.ac.cn
Received 14 July 2015; revised 2 September 2015; accepted 8 September 2015; posted 9 September 2015 (Doc. ID 245976);
published 7 October 2015
High-speed free-space optical communication systems using fiber-optic components can greatly improve the sta-
bility of the system and simplify the structure. However, propagation through atmospheric turbulence degrades
the spatial coherence of the signal beam and limits the single-mode fiber (SMF) coupling efficiency. In this paper,
we analyze the influence of the atmospheric turbulence on the SMF coupling efficiency over various turbulences.
The results show that the SMF coupling efficiency drops from 81% without phase distortion to 10% when phase
root mean square value equals 0.3λ. The simulations of SMF coupling with adaptive optics (AO) indicate that it is
inevitable to compensate the high-order aberrations for SMF coupling over relatively strong turbulence. The SMF
coupling efficiency experiments, using an AO system with a 137-element deformable mirror and a Hartmann–
Shack wavefront sensor, obtain average coupling efficiency increasing from 1.3% in open loop to 46.1% in closed
loop under a relatively strong turbulence, D∕r
0
15.1. © 2015 Optical Society of America
OCIS codes: (060.2605) Free-space optical communication; (010.1080) Active or adaptive optics; (060.2430) Fibers, single-mode;
(010.1330) Atmospheric turbulence.
http://dx.doi.org/10.1364/AO.54.008722
1. INTRODUCTION
Free-space optical communication, with high speed and high
confidentiality, is the key technology for achieving a high-speed
broadband network of satellite–satellite, satellite–ground, and
deep-space links in the future. To achieve higher link capabil-
ities and longer link distance, fiber optical components, such as
transmitter and receiver modules, erbium-doped fiber ampli-
fiers, and multiplexer units, are required. In such a system
the received signal beam must be coupled into a single-mode
fiber (SMF) before being amplified and detected. However,
propagation through the atmospheric turbulence seriously de-
grades the spatial coherence of the signal beam and limits the
SMF coupling efficiency [1,2]. Theref ore, the way to improve
SMF coupling efficiency has become one of the key technol-
ogies for high-sp eed free-space optical communications. A con-
siderable improvement is expected using adaptive optics (AO)
in the system that can compensate the wavefront distortion
caused by atmospheric turbulence [3,4].
The SMF coupling efficiency for partially coherent light
through horizontal atmospheric channel was discussed by
Winzer and Leeb in 1998 [2]. The influence of the random
angular jitter caused by turbulence for SMF coupling efficiency
has also been studied extensively [5]. Arimoto et al. describe a
method to increase the SMF coupling efficiency using a fast
steering mirror [6]. However, it can only be used over weak
turbulence. In 2005, the method using a coherent fiber array
as a receiver was investigated [7]. However, beam combination
in the high-speed optical communication systems introduces
mismatches of the code elements. Weyrauch et al. describe a
fiber coupling system for free-space optical communications
using an AO system without wavefront sensors [8]. It has
the ability to correct the high-order aberrations caused by
the atmospheric turbulence and increases the coupling effi-
ciency significantly. However, the low convergence rate of
the system limits the range of the strength of the atmospheric
turbulence to which it can be applied.
In this study, we analyze the relationships between atmos-
pheric turbulence and the SMF coupling efficiency with the
theory of pattern matching. After that, we present the method
to increase SMF coupling efficiency over relatively strong
turbulence with, first, the implementation of preliminary cou-
pling by using a fast steering mirror to correct the tip and tilt
8722
Vol. 54, No. 29 / October 10 2015 / Applied Optics
Research Article
1559-128X/15/298722-05$15/0$15.00 © 2015 Optical Society of America