A Novel Wavelength Shift Keying Technique for the Transmission of Bidirectional Data over FSO Link

Abstract

We proposed a simple and elegant model to achieve the Optical wavelength shift keying (OWSK), the transmitter side with modulation and the receiver side with demodulation are designed in a different way. A simple Mech-zehnder interferometer (MZI) that is phase modulated with the electrical data signal from NRZ pulse generator. The two wavelengths λ1= 1550nm and the λ2= 1554nm are phase modulated according to the 10Gbps input NRZ electrical signal. Concept of cross coupler (X-Coupler) is used and the two wavelengths are filtered separately through the optical filters at the receiver side. The combined optical modulated signal with symbol rate of 10G symbols/sec or 10Gbps data rate is transmitted over the free space optical channel (FSO Link). At the receiver side the separate modulated optical signals are detected, demodulated, and the received digital data containing 1’s and 0’s are added using the subs-tractor. At the receiver end when both the signals of λ1=1550nm and λ2=1554nm are received then impact of the combined signals improves the performance, reliability and the feasibility of the system in the real scenario. This is basically implemented for the downstream signal received. For uplink data processing in this technique the downstream signal received is again reused or re modulated for the upstream data processing. As previously the 1’s data stream is received at λ1=1550nm and the 0’s data stream at λ2= 1554nm, while we have extracted the data at the receiver side. Now for the uplink data processing we reuse the downstream data by combining the copy of 0’s data stream (λ1=1550nm) and 1’s data stream (λ2= 1554nm) at the receiver side. The wavelengths will be different for these combined data stream (pulses). There will be existence of one pulse in each bit slot/time. This mean now we have a signal that comprises both 1’s and 0’s pulses in time domain. Now this signal is used for the uplink data processing. For getting our desired result we used the simple OOK modulation for uplink data processing. It is clearly seen in the proposed technique. The optical carriers that were used only for downstream (downlink) data processing in one direction can now be reused or re-modulated for the uplink data processing. It shows there is no need of optical carrier (LASER source) for uplink data transmission. This clearly makes the setup bi-directional for the sending of data over FSO-channl