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Spatial bandwidth considerations for optical communication through a free space propagation link.
1The Optical Sciences Company, 1341 S. Sunkist Street, Anaheim, California 92806-5614, USA. glenn.a.tyler@tosc.com
Optics Letters
|December 6, 2011
Summary
This study analyzes spatial bandwidth limitations in free-space optical communication. The spatial bandwidth, measured in bits per photon, is found to be logarithmically dependent on the Fresnel number of the optical link.
Area of Science:
- Optical communication
- Quantum information science
- Free-space optics
Background:
- Free-space optical communication links face transverse limitations due to finite apertures.
- Transmitted states, representing spatial information, are crucial for data transmission.
- Orbital angular momentum (OAM) states are candidates for efficient information encoding.
Purpose of the Study:
- To investigate the spatial bandwidth limitations in free-space optical communication links.
- To quantify the spatial bandwidth in terms of bits per transmitted photon.
- To analyze the impact of aperture size, wavelength, and propagation distance on bandwidth.
Main Methods:
- The study models the optical propagation link with finite apertures.
- It assumes transmission of orbital angular momentum (OAM) states with controlled radial functions for minimum energy loss.
- Spatial bandwidth is calculated as the product of average link efficiency and channel entropy.
Main Results:
- The spatial bandwidth is found to be approximately equal to log base 2 of the Fresnel number.
- The Fresnel number is defined by transmitting and receiving aperture diameters, wavelength, and propagation distance.
- This indicates a direct relationship between the physical parameters of the link and its information capacity.
Conclusions:
- Finite apertures in free-space optical communication significantly limit spatial bandwidth.
- The derived formula provides a method to estimate the maximum achievable data rate per photon.
- Optimizing OAM states and link parameters can enhance the capacity of free-space optical communication systems.
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