Pointing, acquisition, and tracking architecture tools for deep-space optical communications

Quality Metrics and Reliability Analysis of Laser Communication System

“…however, a diverged beam usually causes significant loss of average received power and large aperture telescope generally collects more background optical noise as well. Therefore, the benefits of increasing the optical power and/or using slightly diverging beam with larger receiver aperture (larger than or close to the long term laser spot size) may not balance the laser communication performance loss/degradation [14][15][16] . Therefore, laser communication is still considered as an emerging technology and is widely being researched, particularly with regard to the mitigation/ compensation of signal degradation caused by the turbulent atmosphere 6,14,15 .…”

“…The conventional data coding and/or modulation techniques can effectively be used to equalise/compromise the first two effects with respect to the weather condition at a given instant of time. The third and fourth effects can't be resolved without incorporating the adaptive optics i.e., beam stabilisation and wavefront aberration correction elements 4,[12][13][14][15][16] . Resolving these problems is mandatory for the successful installation of the laser communication system 8,9,14,15 .…”

“…The third and fourth effects can't be resolved without incorporating the adaptive optics i.e., beam stabilisation and wavefront aberration correction elements 4,[12][13][14][15][16] . Resolving these problems is mandatory for the successful installation of the laser communication system 8,9,14,15 . One of the main reasons for the failure of laser communication is the absence of beam pointing, acquisition and tracking (PAT) system and therefore, a perfect and continuous adaptive alignment is important to reduce the pointing loss 3,4,14,15 .…”

“…In the case of a laser beam, attenuation rather leads to a displacement of the excitation than to photons being extinguished. In addition, atmospheric turbulence also leads to phase-front distortions resulting, for example, in deflection of the beam i.e., beam wander [12][13][14][15] . All these effects result in both average received power loss and instantaneously received power fluctuation, called fading, at the receiver aperture.…”

“…This is primarily because of factors such as the unpredictability of the FSOC channel effects at the optical frequencies as well as difficulties associated with stabilising the transmitting and receiving platforms against wind and other disturbing agents which affect the quality of beam alignment, power fluctuations (intensity noise) and wavefront aberration (phase noise) 8,[12][13][14] . Optical beam propagation through the turbulent atmospheric channel severely suffers from the atmospheric attenuation (A att ), angular deflection and phase distortion in horizontal (terrestrial) propagation rather than the vertical 6,8,14,15 . Attenuation here is described as photons being extinguished.…”