This work was aimed to develop low cost devices for clear underwater exploration combined together with visible light communication (VLC) systems. This would be a new expectation of VLC application systems in the future. The complete system consisted of transmitter and receiver parts. The transmitter is responsible for transmitting sensor information data, using light emitting diode (LED). At the receiver, a photodiode is used to receive the light signal and convert into electrical signal. The pH and temperature values are displayed on the application in smartphone with Android operating system, using Bluetooth communication systems. The VLC systems work well at the maximum distance between transmitter and receiver was 80 centimeters long, and the maximum distance of Bluetooth was 10 meters.
The effects of fiber nonlinearity in Coherent Optical Orthogonal Frequency-Division Multiplexing (CO-OFDM)
transmission, such as self-phase modulation (SPM) and cross-phase modulation (XPM), are a major concern. In this
paper, we investigate the use of RF-Pilot (RFP) based nonlinearity compensation scheme in frequency domain to
compensate for fiber nonlinearity in a coherent OFDM optical system. It shows that the RFP-based compensation
scheme has superiority over a conventional pilot-based compensation scheme at FEC threshold.
Combination of quadrature amplitude modulation with coherent detection is attractive for optical transmission systems,
since it permits an increase of data rate without increasing the symbol rate or the required bandwidth. 16-point
Quadrature Amplitude Modulation (16-QAM) is most interesting in this context. In-phase (I) and quadrature (Q) signals
transmit 2 bit each. Together with polarization division multiplex this amounts to 8 bit/symbol.
2.5 Gbit/s synchronous coherent 16-QAM data is transmitted and received in a realtime intradyne setup with BER below
FEC (7% overhead) threshold. A phase noise tolerant feedforward carrier recovery concept with hardware-efficient
implementation was tested. Transmission was error-free in a back-to-back electrical test for various PRBS lengths. The
carrier recovery does not contain any feedback loop and is therefore highly tolerant against laser phase noise.