Figure 1. Design of FSO with Controlled Pump Laser
Laser source is an inevitable source for generating light waves which act as a carrier in wired or wireless medium. LED is a modulation source which reduces the wavelength in visible light medium. In this paper, different laser sources with free space channel and optical fiber in the wavelength of 1550μm are used to evaluate the performance of Quality Factor and Bit Error Rate (BER). The controlled pump laser, directly modulated measured laser and empirical measured laser are reviewed with free space and optical fiber channels. The corresponding modulated signal source is received and the maximum probability of quality factor and minimum bit error rate is determined. The reason for choosing the laser over LED is that the laser has more bandwidth and power efficiency and is compatible with both single and multimode fibers. Laser has higher SNR than other source of optical communication.
The basic principles of lasers are external pumping and internal light amplification. With external pumping, the carriers are excited to higher energy states and release the energy as they return to ground state by generating photons (Klotzkin, 2020; Tsai et al., 2020). In most of the cases, external pumping is done by current injection into conduction band. Then, the electron is supplied by conduction band and hole is supplied by valence band through generating photons. Amplification is needed for coherent light generation through a process called stimulated emission and spontaneous emission, which provides incoherent light generation. The light detection is possible by converting optical energy into electrical energy by PIN diode. The data rate of the optical transmission for free space and optical fiber varied with frequency and power. In today's technology, laser source is the major light carrier for long haul transmission (Anita, 2019; Jiang et al., 2020).
The user generator sequence sent the signals to the nonreturn zero pulse generator and are guided via fiber cable with controlled pump laser light carriers to the receiver. The same experiment is done with the free space channel of microwave frequency limits. The direct modulated laser consumes less energy and it can be used in both analog and digital transmission systems (Zhu et al., 2017). An empirical measured laser contains the random measurement of laser parameters by considering laser properties (Lambertus et al., 2018). The spin orientation of injected carriers is done by optically pumped vertical cavity surface emitting lasers ( Fan et al., 2012; Gross et al., 2020).
From the previous analysis, the desirable characteristics of optical sources include narrow spectral width, high speed, linearity in modulation, good reliability and light emission within low loss window of spectrum ( Zhu et al., 2017). Light Emitting Diode (LED) or visible light source has a smaller life time compared to infrared coherent laser sources ( Lambertus et al., 2018). Lasers are powerful and provide faster speed than LEDs. Laser sources have a more reactive optical cavity, for which it will last long time. The transmission of fiber optical communication involves the transmission of light in form of ray, photon and waveform. Although there are many representations of the light signal, the properties of light are similar in all cases.
The need for large bandwidth and high data rate is increasing day by day. Optical communication media is providing higher bandwidth than coaxial cable and twisted pair cables ( Klotzkin, 2020). The coaxial cable shares the frequency of 30 MHz to 300 MHz in Electromagnetic spectrum and waveguides shares frequency of 3 GHz to 300 GHz.
The proposed system is simulated using Optiwave's software, OptiSytem version 16.1. From the simulation of the experiment results, the maximum quality factor and minimum bit error rate are drawn. Laser source in single longitudinal mode is needed for high bit rate optical communication than conventional lasers in order to avoid chirping effect ( Hovel et al., 2005). The control of chirp depends on the driving current and the intensity of modulation. Optical lasers are compatible than light sources for modulation in single mode fiber (Anita, 2020).
The date rate of controlled pump laser user is 3 Gbps and the global data rate for simulation is 5 Gbps, with 10 Gbps sampling rate shown in Figure 1 and Figure 3. The maximum distance achieved is 3kms, after which the repeater is needed for both FSO and fiber. The attenuation rate of FSO is 1dB/km. As the frequency increases, the Quality factor increases with minimum distance. The corresponding results are shown in Figure 2 and Figure 4.
Figure 1. Design of FSO with Controlled Pump Laser
Figure 2. Eye Plot of FSO with Controlled Pump Laser
Figure 3. Design of Optical Fiber with Controlled Pump Laser
Figure 4. Eye Plot of Fiber with Controlled Pump Laser
The direct modulated pump laser user date rate is 5 Gbps and the global data rate is 5 Gbps with 10 Gbps sampling rate shown in Figure 5 and Figure 7. The maximum distance achieved for FSO is 20 km and after that repeater is needed. The attenuation rate of FSO is 1dB/km.
The direct modulated pump laser user date rate is 5 Gbps and the global data rate is 5 Gbps with 10 Gbps sampling rate. The maximum distance achieved for optical fiber is 20 km, after that repeater is needed. The frequency of transmission is 1550 μm. The corresponding results are shown in Figure 6 and Figure 8.
Figure 5. Design of FSO with Direct Modulated Measured Laser
Figure 6. Eye Plot of FSO Direct Modulated Measured Laser
Figure 7. Design of Fiber with Direct Modulated Measured Laser
Figure 8. Eye Plot of Fiber with Direct Modulated Measured Laser
The empirical measured laser user date rate is 2.5 Gbps and the global data rate is 5 Gbps with 10 Gbps sampling rate. The maximum distance achieved is 10 km for optical fiber, after that repeater is needed. The design layout is shown in Figure 9 and Figure 11.The attenuation rate of FSO is 0.2 dB/km and maximum distance achieved is 1 km. The corresponding results are shown in Figure 10 and Figure 12. Table 1 and Table 2 illustrate the maximum and minimum probability of quality factor and bit error rate with free space channel and optical fiber channel.
Figure 9. Design of FSO with Empirical Measured Laser
Figure 10. Eye Plot of FSO with Empirical Measured Laser
Figure 11. Design of Fiber with Empirical Measured Laser
Figure 12. Eye Plot of Fiber with Empirical Measured Laser
Table 1. Experiment Result of FSO
Table 2. Experiment Result of Optical Fiber
From the above experiment, it can be concluded that, at 3 Gbps with optical wire transmission channels, the maximum quality factor obtained is 979.699 with zero bit error rate and a maximum spacing of 3 km distance. The direct modulated laser has the value of 102.724 quality factor. With free space channel, maximum quality factor attained is 72.3447 in controlled pump laser having zero bit error rate. The maximum repeater spacing of free space is 3km. Empirical measured laser has the least quality factor among all of about 16.9361 in free space channel mode of transmission.
The author likes to thank her college for providing support and good infrastructure to go beyond theoretical study into practical methodology.