Characteristics Analysis of Hybrid Optical Amplifier with Doped Fiber Variations for Fiber Optic Communications Network

Optical communication networks are vital in the digital era, but data transmission becomes weak the longer the distance traveled by light. Erbium-Doped Fiber Amplifier (EDFA) technology is commonly used as an optical amplifier, but it still produces a small gain, Q-factor, and a significant noise figure. This study characterized the Hybrid Optical Amplifier (HOA) combinations that contain EDFA with various doped fibers. The characterization was performed through Optisystem software simulation by observing and analyzing the gain, noise of figure, and Q-factor generated by each doped fiber variant. The results showed that the combination of Ytterbium-doped Fiber produced the most significant gain of 15.83 dB, less noise figure of 5,661 dB, and a relatively high Q-factor of 35,615 at 1,550 nm. It indicates that the HOA combination is suitable and ideal for long-distance transmission in fiber optic communication network applications.


Introduction
The optical fiber network is a vital component of communication technology that can transfer data with high speed, large capacity, and long-distance transmission [1,2].The network also has better energy efficiency that becomes the base for innovation in future technology [3].The reliability of optical fiber networks is essential for many applications, such as video streaming, cloud computing, and the Internet of Things (IoT) [4,5].Network communication has become the backbone of profound digital infrastructure growth and progress in various sectors [6].Because of the higher need for data transmission over extensive areas, a system network of optical fiber requires comprehensive bandwidth gain and good performance to handle the burden of a sufficient network at long distances.The technology that can be used to optimize the bandwidth gain on the network fiber optical is Erbium Doped Fiber Amplifier (EDFA) implementation [7].The optical amplifier applies by doping the core of singlemode optical fiber with Erbium atoms to strengthen the optical signal [8].However, EDFA must develop as a Hybrid Optical Amplifier (HOA) to increase performance in optical transmission systems [9].
HOA applications can improve the performance of fiber optic networks because they can handle large loads in the network [10].The hybrid amplifier is applied to optimally increase gain bandwidth, reduce losses caused by nonlinearity induction, and prevent high costs to improve gain stability [11][12][13].Compared to electronic regenerators, HOA can change the system data rate according to needs [14] and simultaneously transmit data through multiple channels without modifying the in-line transmission link or other components [15].HOA using EDFA combination had been studied in previous research.The HOA built by combining EDFA reinforcement with Fiber Bragg Grating (FBG) increased the gain by 13 to 16 dB.However, the data transmission design only uses EDFA with 5 meters [16].The gain of an optical network built with a Raman -EDFA hybrid amplifier can produce a gain of 28.94 dB, but the Q-factor value shifts further from the ideal limit in the more extended transmission link [17].Applying the combination of EDFA amplifier with holmium-doped fiber with a wavelength of 2030 -2100 nm produces a noise of a figure of 4-6 dB [18].The HOA built from hafnia-bismuth erbium fiber doped material connected in series with EDFA using a wavelength of 1520 to 1610 nm produces a gain of 12.1 dB and a noise figure of less than 11.8 dB [19].Based on this elaboration, a new optical communication network must be designed to transmit data stably over long distances without needing FBG devices and additional resources, such as pumps, to increase the optical signal level and reduce the cost of implementing optical communication networks.In addition, optical communication network design requires doped fiber connected with EDFA to expand data transmission capabilities and improve signal quality on various channels in optical communication networks.
This study aims to find the ideal hybrid optical amplifier model with a significant gain, Q factor, and a slight noise value.The design characteristics of optical fiber networks with HOA reinforcement have been analyzed and compared using several variations of doped fiber.The doped fiber variations are configured in series using EDFA to determine the best combination of Hybrid Optical Amplifier variants for optical communication network applications.

Method
Analysis of the characteristics of the HOA combination was obtained from fiber optic network simulation using Optisystem 20 software.The components used in the research scheme are divided into three parts: transmitter, transmission media, and transceiver.The transmitter section consists of a Continuous Wave (CW) Laser, Nonreturn to Zero (NRZ), Mach-Zehnder Modulator (MZM), and Pseudo Random Bit Sequence (PRBS) Generator.CW laser is a device that transmits signals into an optical fiber with high stability characteristics for long-distance data transmission [20].Nonreturn to Zero is a modulation format generally used in optical communication networks because it is simple and easy to implement [21].Mach-Zehnder Modulator is a high-speed optical wave modulator that suits network design [22].PRBS Generator serves as a component of an information waveform generator in digital format that generates random bits for testing purposes of optical communication network design results [23].
The transmission medium used a single-mode optical fiber with a length of 10 km because it has lower attenuation characteristics compared to multimode cable for the implementation of long-distance optical communication [24].The last part is the receiver, which consists of a Positive-Intrinsic-Negative (PIN) detector to detect and convert incoming optical signals into electrical signals.The PIN detector can detect various wavelengths [25] from 3R (reshaped, re-timed, and re-amplified) generators that amplify optical signals over long distances [26].Then, the data received by the 3R is forwarded to the Bit Error Rate (BER) analyzer, which measures the bit error rate in digital communication systems [27].Figure 2 shows the fiber optic network used in this study.
In this study, the types of doped optical fiber amplifiers were manipulated.There are Holmium (Ho) doped fiber, Ytterbium (Yb) doped fiber, Praseodymium (Pr) doped fiber, Erbium (Er) doped fiber, Thulium (Tm) doped fiber and Erbium-Ytterbium (Er-Yb) doped fiber.The type of doped optical fiber was arranged in series with EDFA.The other components in this study became controlled variables.The response variables as characteristics observed in this simulation are Gain, Noise of Figure (NF), and Qfactor.These three variables are observed to analyze, identify, and understand the performance of optical communication network design in terms of gain, Noise of Figure as a measure of the ability of optical systems to reduce interference on optical signals, and Q-factor as a parameter used to measure link quality in optical communication systems.These variables are measured at each 10 nm wavelength increase from 1530 nm to 1620 nm.Each doped fiber optic amplifier type has different optical gain characteristics at different wavelength ranges.When transmitted through optical fiber, the wavelength range experiences relatively low attenuation [28].

Results and discussion
The characteristics of the fiber optic network that will be analyzed include Gain, Bit Error Rate, Qfactor, and Noise.These characteristic variables were observed in the CW laser wavelength range of 1530 nm to 1620 nm for transmission on optical communication networks.Measurements are generated using each hybrid optical amplifier variant, especially the doped Fiber type installed in series with the EDFA. Figure 2 shows the gain characteristics of the fiber optic network for each HOA combination.The combination of EDFA amplifier with Ho-Doped Fiber, Yb-Doped Fiber, and Pr-Doped Fiber produces a relatively higher gain than other types of doped fiber, around 15 dB in the wavelength range of 1530 to 1570 nm.At 1550 nm, the HOA combination produces the highest gain of 15.83 dB.However, the gain value on using the three doped fibers experienced a decrease gradually from 11 to 13 dB after 1570 nm.Due to EDFA working at a wavelength of 1550 nm, the gain above the wavelength has decreased [29].
Compared with other HOA combinations, the gain in the combination of EDFA and Tm doped fiber decreased successively from 1530 to 1620 nm.The most significant results were obtained at 1530 nm with a gain value of 11.631 dB.Furthermore, the gain value decreased gradually from 10 to -23.967 dB.It happens because Tm-doped fiber works optimally at a wavelength of around 1650 to 2100 nm [30].In addition, Er-Yb Doped Fiber was used for the amplifier combination after EDFA.In the initial wavelength of 1530 nm, the smallest gain was obtained at -4.282 dB.However, after a higher wavelength to 1620 nm, the gain increases from 7 to 11 dB.The maximum gain results are obtained at 1570 nm of 11.835 dB.Furthermore, the NF is analyzed to determine the amount of noise that occurs by each optical fiber amplifier.Figure 3 shows that optical fiber doped with Holmium (Ho), Ytterbium (Yb), and Praseodymium (Pr) produces the same and relatively constant NF value of about 5 dB at the interval of 1530 to 1600 nm.It is due to the Ho, Yb, and Pr are classified as rare earth dopants [31].The constant values show a good performance in reducing noise.However, NF decreased after 1610 nm.The combination of HOA with Ho-doped fiber and Yb-doped fiber still produced the same NF, while the NF with Pr-doped fiber is lower at -10,596 dB.
At 1540 nm, Er-Yb-doped optical fiber produces more considerable NF than the three previous doping, around 14 dB.However, with the longer wavelength, the NF of the doped Fiber decreased to near zero until the same as the three previous doping in the 1570 to 1600 nm range.The desired NF value on different doping is nearly zero.It corresponds to the fact that the lower the NF value, the less noise of the amplified signal [32].When using Er-doped fiber, the most significant NF occurs at a wavelength of 1530 nm of 15,319 dB and then decreases as the source wavelength increases until it reaches the same as the several variations of doped fiber described earlier.
Unlike the other five doping, which produced positive NF values, Tm-doped fiber produced negative NF values of -100 dB at 1530 to 1580 nm.However, the NF value increased in the higher wavelength and obtained the highest NF around 24 dB in 1620 nm of the other variations.This phenomenon is related to the unique characteristics of the doping Tm and the interaction between the optical signal and the noise in the amplifier.In the wavelength interval of 1530 nm to 1580 nm, Tm doping reduces the noise in the amplified optical signal.It is indicated that the amplifier with Tm doping reduces noise more than the amplified signal [33].
The response of the NF to wavelength change depends on the characteristics of optical fibers, the doping type, and the doping process used.As the extended wavelength, the effect of doping on the fiber changed and affected the interaction between the optical signal and the NF in the amplifier [34].The characteristic Q-factor is also analyzed to measure signal quality and describes the extent to which the signal can be separated from noise in the system.Based on Figure 4, the best HOA Q-factor was produced by combining EDFA with a Pr-doped fiber of 41.2417 at a wavelength of 1530 nm.From this hybrid optical fiber simulation, the Q-factor value of the Pr-doped fiber variation decreases when the wavelength is enlarged.It is due to the combination of EDFA and Pr-doped fiber with high gain, high saturation power, low noise, and low crosstalk [35].At the same time, the HOA with the Tm-doped fiber amplifier variant produces a small Q-factor in the wavelength range of 1590 to 1620 nm.These results were obtained because Tm-doped fiber and EDFA work at different wavelengths.Usually, the Tm-doped fiber amplifier applies at mid-infrared wavelengths.In contrast, EDFA works in near visible wavelengths.Therefore, the combination performance between Tm-doped fiber and EDFA at 1620 nm could be more optimal, resulting in a low Q-factor [36].
According to Table 1, the characteristic of the HOA variant of the type of Yb-doped fiber is the most proportional implemented in optical communication at 1550 nm.It produced the most significant gain than other variants.Yb-doped fiber also generated a considerably low noise figure and high Q-factor at the wavelength.The noise of the figure value indicates that the optical signal interference on the transmission media is relatively small.Inversely, the Tm-doped fiber variant results in measurements of gain, noise of figure, and Q-factor characteristics that are less good at implementing optical communication networks.At 1550 nm, it generated the most negligible gain and negative noise value, even though the Q-factor is sufficient.

Table 1 .
Characterization results of each HOA variant at a wavelength of 1550 nm.The variation characteristics of the EDFA optical amplifier combination with six doped fiber variations in an optical network have been analyzed by observing the gain, noise of figure, and Q-factor parameters generated by the optical communication network simulation design.According to the analysis, Ybdoped fiber can produce the most significant gain of 15.827, a low noise figure of 5.661 dB, and a considerable Q-factor of 35.615 at 1550 nm.Therefore, it became the ideal HOA for optical communication networks to increase bandwidth capacity and transmission distance.