Bit error rate performance on passive alignment in free space optical links using large core fibers

Abstract

A 20-meter free-space optical link (FSOL) is proposed for data transmission between external ISS payload sites and the main cabin at a target rate of 10 Gbps (gigabits per second). Motion between a payload site and the main cabin is predicted to cause up to 5 cm in lateral misalignment and 0.2 degrees of angular misalignment. Due to the harsh environment of space it is advantageous to locate the optical transceivers inside the spacecraft or in a controlled environment. With the optical components and transceivers in separate locations, a fiber optic cable will be required to carry light between the two. In our past work we found that the use of large-core fibers provide an increased misalignment tolerance for such systems and could eliminate the need for active control of the optics. In that work, it was shown that a 105 m core diameter fiber optic cable offered a viable low SWaP (size, weight, and power) solution for the ISS application; however, the effects of modal dispersion were not investigated. This paper will present bit error rate performance of the FSOL using these large-core fibers.

Low-complexity turbulence resilience enabled by a multi-mode bi-directional transceiver

“…8 is valid under the assumption that aperture clipping is a more significant source of loss than focal plane coupling for a given pointing error. This assumption is not valid over short propagation lengths, as the loss due to pointing errors is associated with significant displacement in the focal plane and variations in the fiber-mode coupling [30][31][32]. However, when considering pointing errors over significant propagation lengths of hundreds or thousands of meters, the loss is dominated by the effect of aperture clipping rather than focal plane offset.…”

“…FSO systems built upon widely-available commercial components, such as SFPs and industry standard optical fibers, could allow for the rapid and effective deployment of high-speed communication links. Multi-mode (MM) fibers offer an interesting alternative, as these have a larger acceptance angle and spatial bandwidth, allowing for the efficient coupling of a received beam with an aberrated PSF due to turbulence [11,13,[26][27][28][29], as well as increased resilience to pointing errors [30][31][32]. However, intermodal coupling within MM fibers is commonly considered to limit their usage as effective transmitters for FSO applications because the higher-order output field will be considerably more divergent than an equivalent field created by an SM fiber based transmitter.…”

Low-complexity turbulence resilience enabled by a multi-mode bi-directional transceiver

“…8 is valid under the assumption that aperture clipping is a more significant source of loss than focal plane coupling for a given pointing error. This assumption is not valid over short propagation lengths, as the loss due to pointing errors is associated with significant displacement in the focal plane and variations in the fiber-mode coupling [30][31][32]. However, when considering pointing errors over significant propagation lengths of hundreds or thousands of meters, the loss is dominated by the effect of aperture clipping rather than focal plane offset.…”

“…FSO systems built upon widely-available commercial components, such as SFPs and industry standard optical fibers, could allow for the rapid and effective deployment of high-speed communication links. Multi-mode (MM) fibers offer an interesting alternative, as these have a larger acceptance angle and spatial bandwidth, allowing for the efficient coupling of a received beam with an aberrated PSF due to turbulence [11,13,[26][27][28][29], as well as increased resilience to pointing errors [30][31][32]. However, intermodal coupling within MM fibers is commonly considered to limit their usage as effective transmitters for FSO applications because the higher-order output field will be considerably more divergent than an equivalent field created by an SM fiber based transmitter.…”