As 3/4th of the earth’s surface is covered with water, there is a need for a high speed mode of communication underwater that is often used by experts for oceanography, seafloor monitoring, and offshore oil exploration. The underwater wireless sensor network communication technology has greater bandwidth but at the same time, it undergoes strong attenuation. The region under the blue-green light spectrum is relatively smaller and its laser diode is appropriate for source for underwater wireless sensor network communication .
In the proposed architecture for enhanced underwater optical network communication at the passive front end, the received beam of the signal is coupled with the optical fiber prior to its processing initiation. The light source is beam-sized and diverging in nature whereas the optical fiber is having a numerical aperture and core diameter.
The coupling efficiency can be manipulated with the help of a coupling lens and suitable focal length at its front end. The highest efficiency reported in 2-m calm water is 39%. The advantage of using an underwater optical network communication at the passive front endis its quality of low loss at the visible light spectrum. High efficiency of coupling is needed to deduce the maximum received Signal to Noise Ratio or SNR.
The coupling efficiency can be enhanced if the NA of the lens and optic fiber can be equal.
Issues in the current technology
The primary issue of underwater optical network communication at the passive front end is that the water is a medium that highly absorbs optical signals; the second problem is optical scattering due to the particles present in the sea.
The coupling of the signal beam and the optical fiber is done underwater. The transmitter deployed here was an LDM9LP fiber pigtailed green laser diode of 520 nm.
We measured the beam quality of the seed light and the amplified laser light by the CCD camera beam profiler. It shows that the Mopa system kept the beam quality of the seed light.
The seed laser used in the research proposal of underwater optical network communication at the passive front end is modulated using Manchester Encoding as per the response of the signal of the amplified light.
In the future, a solution for increasing the power of the frequency light can be proposed.
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