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Analysis of Effect of Input Power and RF Optical
Signal Rate on Optical Communication System
with OOK-NRZ Modulation
To cite this article: A Nikmah et al 2023 J. Phys.: Conf. Ser. 2623 012027
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Seminar Nasional Fisika (SNF) Unesa 2023
Journal of Physics: Conference Series
2623 (2023) 012027
IOP Publishing
doi:10.1088/1742-6596/2623/1/012027
Analysis of Effect of Input Power and RF Optical Signal Rate
on Optical Communication System with OOK-NRZ
Modulation
A Nikmah, L D Mauludi, and R A Firdaus *
Department of Physics, Faculty of Mathematics and Natural Sciences, Universitas
Negeri Surabaya, Indonesia
*E-mail: rohimfirdaus@unesa.ac.id
Abstract. This study analyzed optical and RF signals in optical communication systems using
the On-Off Keying Non-Return to Zero (OOK-NRZ) modulation method and the directdetection receiver model with PIN photodiodes. In this study, a simulation was carried out using
Python software. Changes in optical modulation input power and Symbol rate (Rs) were explored
to understand their effect on signal characteristics. Models of ideal photodiodes (noiseless) and
noisy photodiodes (considering thermal noise, shot noise, and bandwidth constraints) were used
to compare receiver signals. The eye diagram analysis was employed to visualize receiver signal
variation in a given time span. The results of this analysis provide a better understanding of the
influence of changes in input power and symbol rate on optical communication systems through
the OOK-NRZ method and insight into the characteristics of the receiving signal under realistic
conditions. This study is able to provide guidance for the design and evaluation of optical
communication systems using OOK-NRZ modulation and direct detection receivers.
1. Introduction
The modulation process is necessary for fulfilling signal transmission needs [1,2]. The modulation
process is a process of converting information signals or laying on data signals into specific forms.
Optical modulation is a technique that utilizes light beams as pulses of light waves as a carrier signal [1]
[3]. The choice of modulation type used can be determined by the expected application, such as the
characteristics of the channel used, available bandwidth, and channel susceptibility to changes (fading)
[4]. Optical modulation techniques have several advantages over conventional modulation techniques
that use electrical signals as information carrier signals [4,5]. Among them is that the resistance to noise
is high; this is because the signal cannot be influenced by electromagnetic fields. Another advantage is
the signal transmission or bit rate speed, which reaches hundreds of gigabits per second [6].
The method in this study employed a scheme of OOK modulation, where it seems to be a switch that
has two conditions at the time of on and off [1,3]. Bit 1 is interpreted as "on" or representing the optical
pull that occupies either all or part of the bit duration. In contrast, a bit value of 0 is interpreted as "off"
or representing the absence or disappearance of the optical pulse [2,7]. OOK modulation consists of two
sub-systems, namely OOK-NRZ and OOK-RZ. On the type of Non-Return to Zero (NRZ) OOK
modulation, it indicates when bit 1 occupies the entire bit interval and bit 0 has no pulse [8,9].
Content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution
of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.
Published under licence by IOP Publishing Ltd
1
Seminar Nasional Fisika (SNF) Unesa 2023
Journal of Physics: Conference Series
2623 (2023) 012027
IOP Publishing
doi:10.1088/1742-6596/2623/1/012027
Meanwhile, the OOK Return to Zero (RZ) modulation type can be interpreted at a time when bit 1
occupies only part or half of the bit interval, and bit 0 is not expressed by a pulse signal [10].
Measurement and analysis of optical signals are essential for signal quality assessment, optical
performance monitoring (OPM), fault diagnosis, and fault detection [10]. In intensity-based modulationdirect detection (IM-DD) systems, the eye diagram serves as the primary analysis tool for
comprehensively modeling the quality of the optical signal and intuitively displaying the characteristics
of various impairments in optical communication systems [11]. Eye diagram analysis focuses on signals
by methods of On-Off Keying (OOK) and pulse amplitude modulation (PAM), which are widely used
in optical access and optical network data centers [12,13]. A lot of information can be drawn from eye
diagrams, including important characteristic parameters (such as high and low levels, cross percentage,
and eye height and width), overall signal performance indicators (including modulation format, Qfactor, and OSNR), link properties and information (such as fiber transmission distance), and
interference features caused by device imperfections [1,12]
Previous research by A. M. Zaiton compared modulation performance evaluation with OOK NRZ
and Carrier-Less Amplitude Phase (CAP), which produces an eye diagram with input variations. This
study was performed by varying the input modulator's value and the symbol's rate. This aimed to obtain
the visualization results of signal characteristics in the form of radio frequency and optical signal
spectrum and the form of an eye diagram to determine the transmission of optical signals.
2. Methods
This study was started with a literature study on fiber optic modulation related to the OOK-NRZ method.
Exploration in this research was carried out thoroughly using Python software. This study is OOK-NRZ
modulation, which is a modulation with the condition that bit 1 will occupy the entire bit interval and
bit 0 does not have a pulse. Followed by data acquisition in Python software, the following steps are
followed: 1) Manipulating the modulator input by giving an increase starting from -30 dBm to 10 dBm.
2) Manipulating symbol rate (Rs) manipulation at each modulator input. 3) Performing optical
modulation on RF signal and optical signal spectrum. 4) Applying the eye diagram on the spectrum of
the optical signal and the RF signal obtained to visualize the signal characteristics. 5) Conducting visual
analysis of the eye diagram, RF signal, and optical signal spectrum. Figure 1 is an electronic photodetector design with a trans-impedance connection of the photodiodes with an OPA847 low-noise
operational amplifier of large bandwidth [1].
Figure 1. The diagram of the photo-detector connection
with the equivalent circuit of a photodiode.
2
Seminar Nasional Fisika (SNF) Unesa 2023
Journal of Physics: Conference Series
2623 (2023) 012027
IOP Publishing
doi:10.1088/1742-6596/2623/1/012027
3. Result and Discussion
This section presents data from observations in Python simulations for various modulation schemes,
with modulator inputs of -30 dBm to 10 dBm and symbol rates of 105 and 109. The results for the average
power data of the modulated optical signal are as Table 1.
Optical signal
power at modulator
input (dBm)
10
-30
Table 1. Average power data of modulated optical signal.
Average power of
Average power of modulated
Rs (Symbol Rate) modulated optical
optical signal [dBm]
signal [mW]
109
4.993
6.984
105
4.983
6.975
9
10
0.001
-32.999
5
10
0.001
-33.011
Table 1 represents the average power of the optical signal generated from the OOK-NRZ modulation
process by manipulating the input power parameters of the modulator and the symbol rate. When
changing the input value of the modulator's optical power, the average power of the optical signal
generated after the modulation will change. An increase in input power will increase the average power
of the optical signal. At the same time, a decrease in input power also leads to a decrease in the average
power of the optical signal. This can have an impact on optical signal strength and optical system
performance. The changes in symbol rate or Rs in OOK-NRZ modulation will affect the variation in the
speed of electrical pulses within the modulation signal, where the increase in the symbol rate will result
in the electrical pulse changing at a higher speed. Changes in the rate of this symbol also affect the width
of the optical signal spectrum after modulation. Previous studies have also proved that NRZ has a high
transmission frequency, resulting in a higher maximum data capacity transferred in 1 second due to
changes in the symbol rate [5,14]. Next, it will be discussed about the graph of radio frequency signals
and optical signals after being modulated.
(a)
(b)
(c)
(d)
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Figure 2. Radio frequency signal spectrum, a) Input 10 dBm, Rs = 10 , b) Input 10 dBm, Rs = 105,
c) Input -30 dBm, Rs = 109 dan, d) Input -30 dBm, Rs = 105.
3
Seminar Nasional Fisika (SNF) Unesa 2023
Journal of Physics: Conference Series
2623 (2023) 012027
IOP Publishing
doi:10.1088/1742-6596/2623/1/012027
Figure 2 shows the Radio Frequency signal spectrum, which describes the frequency power
distribution of the RF signal with different input values and symbol rates. The y–axis shows the
amplitude range, where the range gives an idea of the RF signal power generated. The modulation input
power given to the optical signal can affect the amplitude of the RF signal generated after the opticalelectrical modulation process. Thus, if the modulation input power in the optical signal increases, then
the amplitude of the RF signal produced also tends to increase. The symbol rate (Rs) also affects the
bandwidth and number of frequencies of the RF signal. If the symbol rate value increases, the bandwidth
required for the optical signal transmission also increases, leading to an increase in frequencies to cover
the signal spectrum.
(a)
(b)
(c)
(d)
Figure 3. RF Binary Signal, a) Input 10 dBm, Rs = 109, b) Input 10 dBm, Rs = 105, c) Input -30 dBm,
Rs = 109 dan, d) Input -30 dBm, Rs = 105.
Figure 3 shows an RF signal that has been optically modulated in the time domain. The Label on the
chart is "RF binary signals," and the y-axis shows the amplitude of the RF signal in arbitrary units (a.u.).
The RF signal reflects the modulation of the optical signal with binary data.
Figure 4 shows a graph of a modulated optical signal by showing the distribution of optical power
over a specific frequency range. Modulation input power in optics has a direct influence on the
amplitude of the optical signal and its power produced. The greater the input power, the greater the
amplitude produced. It also has an impact on the signal strength and noise levels in the modulation
system, all of which can affect the quality and performance of the overall modulation system.
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Seminar Nasional Fisika (SNF) Unesa 2023
Journal of Physics: Conference Series
2623 (2023) 012027
(a)
IOP Publishing
doi:10.1088/1742-6596/2623/1/012027
(b)
(c)
(d)
Figure 4. Optical Signal Spectrum, a) Input 10 dBm, Rs = 109, b) Input 10 dBm, Rs = 105, c) Input 30 dBm, Rs = 109 dan, d) Input -30 dBm, Rs = 105.
(a)
(b)
(c)
(d)
9
Figure 5. Optical Modulated Signal, a) Input 10 dBm, Rs = 10 , b) Input 10 dBm, Rs = 105, c) Input
-30 dBm, Rs = 109 dan, d) Input -30 dBm, Rs = 105.
Figure 5 shows a graph of the modulated optical signal with the amplitude of the optical signal in the
time domain. The input modulation power can affect the strength of the resulting optical signal, and the
amplitude also gets bigger. In addition, the symbol rate also affects the speed at which optical signals
change in the time domain. When there is an increase in the symbol rate, the optical signal changes per
period faster.
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Seminar Nasional Fisika (SNF) Unesa 2023
Journal of Physics: Conference Series
2623 (2023) 012027
(a)
IOP Publishing
doi:10.1088/1742-6596/2623/1/012027
(b)
(c)
(d)
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Figure 6. Ideal Modulated Optical Signal, a) Input 10 dBm, Rs = 10 , b) Input 10 dBm, Rs = 105, c)
Input -30 dBm, Rs = 109 dan, d) Input -30 dBm, Rs = 105.
Figure 6 uses the ideal photodiodes model without noise or noiseness, and there is no bandwidth
limitation. It is used to produce an ideal receiving signal by applying photodiodes to the amplitude
portion of the modulated optical signal. Figure 7 uses a photodiode model with noise or noisy photodiode
concerning noise types, such as thermal noise, shot noise, and bandwidth limitations. It is used to
generate realistic receiver signals. Through Figures 6 and 7 above, the analysis of the eye diagram was
carried out. This function allows you to visualize the variation of the signal in a certain time range.
Through analyzing the eye diagram, it can be described the influence of noise on system performance.
In addition, it can compare an ideal receiving signal and a noisy receiving signal in terms of waveform,
jitter, and distortion that may occur. This result is supported by previous research, namely the
modulation of the OOK eye diagram. Figure 7 is significantly distorted due to the magnitude of the
input. [6,5].
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Seminar Nasional Fisika (SNF) Unesa 2023
Journal of Physics: Conference Series
2623 (2023) 012027
(a)
IOP Publishing
doi:10.1088/1742-6596/2623/1/012027
(b)
(c)
(d)
Figure 7. Modulated Optical Signal with Noise, a) Input 10 dBm, Rs = 109, b) Input 10 dBm, Rs =
105, c) Input -30 dBm, Rs = 109 dan, d) Input -30 dBm, Rs = 105.
4. Conclusions
The On-Off Keying Non-Return to Zero modulation method can be used in optical communication
systems represented by the presence or absence of an optical signal binary information. Changes in input
modulation power affect the average power of the modulated optical signal, where an increase in input
power can result in an increase in the average power of the optical signal. Meanwhile, the symbol rate
can affect the characteristics and shape of RF signals and optical signals. There are two models of
photodiodes used: the ideal (noiseless) photodiode and the noisy photodiode. These models are then
analyzed using an eye diagram to visualize the ideal receiver signal and the receiver signal with noise.
This result helps in the understanding of waveforms, jitter, and distortions that may occur in the
receiving signal.
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Journal of Physics: Conference Series
2623 (2023) 012027
IOP Publishing
doi:10.1088/1742-6596/2623/1/012027
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