=Paper= {{Paper |id=Vol-3668/paper3 |storemode=property |title=Dynamic Random Access Memory Based on Fiber Optic Lines for Optical Computers. Computer Modeling |pdfUrl=https://ceur-ws.org/Vol-3668/paper3.pdf |volume=Vol-3668 |authors=Andriy Semenov,Serhii Tsyrulnyk,Olena Semenova,Serhii Baraban,Anton Khloba |dblpUrl=https://dblp.org/rec/conf/colins/SemenovTSBK24 }} ==Dynamic Random Access Memory Based on Fiber Optic Lines for Optical Computers. Computer Modeling== https://ceur-ws.org/Vol-3668/paper3.pdf

Dynamic Random Access Memory Based on Fiber Optic
Lines for Optical Computers. Computer Modeling
Andriy Semenov 1, Serhii Tsyrulnyk 2,3, Olena Semenova 1, Serhii Baraban 4 and Anton
Khloba 1
1 Vinnytsia National Technical University, Khmelnytske highway, 95, Vinnytsia, 21021, Ukraine
2 Vinnytsia Technical College, Khmelnytske highway, 91/2, Vinnytsia, 21021, Ukraine
3 Vinnytsia National Agrarian University, str. Sonyachna, 3, Vinnytsia, 21008, Ukraine
4 Poznan University of Technology, plac Marii Skłodowskiej-Curie 5, Poznan, 60965, Poland

Abstract
The study proposes the structure of construction and technical implementation of an optical operational
storage device based on fiber-optic lines for optical computers. The basic element is a ring-type storage
device on fiber-optic lines, in which information circulates as a wave packet of optical pulses along a
closed fiber circuit. The operating range of 1550 nm is used to reduce optical losses. Using NZDSF fiber
of the SMF-LS type is justified to compensate for the polarisation mode dispersion. An SOA amplifier is
used to restore the optical signal level. An electro-optical directional splitter is used to input/output
optical signals. To work with optoelectronic memory on fiber-optic lines, it is recommended to use a
femtosecond fiber laser and the wave-coding method. The study found that using fiber-optic lines can
increase the speed of information flow up to ten times by reducing the time spent on the RAM operation.

Keywords
Optical RAM, NZDSF type SMF-LS, SOA amplifier, mode dispersion compensation, wave coding. 1

1. Introduction
The appearance of optical fibers with low losses and a large product of length by bandwidth is
opening up prospects in optical signal processing. It becomes possible to create fiber-optic
devices when performing operations such as convolution, calculation of correlation functions,
matrix operations, filtering, pulse generation, code combinations, pulse compression, and
matched filtering [1, 2].
However, the dynamic storage of light pulses for optical computers and optical information
transmission systems is very relevant. Potentially, a light beam can have a spectral width
comparable to its carrier frequency, i.e., can be of the order of 10-13 ~ 10-14 seconds. Paper [3]
considers the basic element of an optical dynamic operational storage device that can store both
analog and digital optical information. The basic element is a ring-type storage device on a fiber-
optic line, in which information circulates in the form of a burst of optical pulses along a closed
fiber circuit [4].
Paper [5] presents the results of a study of n-bit optical dynamic RAM. The cells of this optical
dynamic RAM have arbitrary access for writing, reading, and updating operations during optical
computing. In the proposed RAM [5], the authors implemented a 1-bit memory element based on
a semiconductor optical amplifier with random asynchronous access. Also, [5] presents the study
results of this 1-bit memory element. In [6], the authors proposed the structure of an
optoelectronic dynamic RAM. Optical information is stored in the memory element using a fiber-
optic delay line. This made it possible to develop a high-speed buffer memory without losing
optical information [6]. In [7], a structure of n-bit optical dynamic RAM was proposed, which

COLINS-2024: 8th International Conference on Computational Linguistics and Intelligent Systems, April 12–13, 2024,
Lviv, Ukraine
semenov.a.o@vntu.edu.ua (A. Semenov); sovmsvom@gmail.com (S. Tsyrulnyk); semenova.o.o@vntu.edu.ua (O.
Semenova); serhii.baraban@put.poznan.pl (S. Baraban); hlobaanton@gmail.com (A. Khloba)
0000-0001-9580-6602 (A. Semenov); 0000-0002-5703-9761 (S. Tsyrulnyk); 0000-0001-5312-9148 (O.
Semenova); 0000-0001-9535-1644 (S. Baraban); 0009-0007-6743-2456 (A. Khloba)
© 2024 Copyright for this paper by its authors.
Use permitted under Creative Commons License Attribution 4.0 International (CC BY 4.0).

CEUR
ceur-ws.org
Workshop ISSN 1613-0073
Proceedings
consists of a matrix of 1-bit optical dynamic RAM elements. The single-bit cells of the optical
dynamic RAM are built based on a semiconductor optical amplifier using a fiber optic loop [7].
All the variants of optical dynamic RAM proposed in publications [3-7] have a limited speed of
about 10 Gbit/s. The aim of this work is a model study of the physical parameters and
characteristics of a variant of the implementation of a dynamic optical random access memory
device based on fiber-optic lines for optical computers with a speed of more than 10 Gbit/s.

2. Models and Methods
The block diagram of the basic element of the dynamic optical operational storage device
(DOOSD) on fiber-optic lines (FOLs), shown in Figure 1, allows you to input an optical signal
either through Ubx1 or U bx 2 . Similarly, the information can be read out either through U bux1 or
U bux 2 .

Figure 1: Block diagram of the basic element DOOSD

According to [8], the polarization mode dispersion coefficient for NZDSF fiber of SMF-LS type
is equal to T  0.5 ps / km , and the chromatic dispersion coefficient D  3.5 / nm  km .
Considering the presence of two electro-optical switches, the polarization mode dispersion
coefficient should be increased to 1. The polarization mode dispersion is determined from the
formula [9]:
 pmd  T  L . (1)

The distance L at which the chromatic and polarization dispersion become equal:
2
 T   1 
2

L0        32.65 cm . (2)
 D       3.5  0.05 
Liouville's theorem [10, 11] shows that single-mode fiber optic fibers are compatible with
single-mode planar, channel, and strip optical fibers in an integrated design. Paper [12] discusses
the peculiarities of the transition of homogeneous media to a wafer (silicon substrate with a
diameter of 300~400 mm), which allows the implementation of optical computing systems for
various purposes on their basis. The dimensions of the wafer actually determine the size of the
optical fiber ring [13]. If we assume the length of the optical fiber optic ring of the basic element
of the DOOSD to be 32.65 cm, the ring diameter is equal to:
L 32.65
D   10.4 cm . (3)
 3.14
The selected size of the optical fiber ring allows it and additional elements (electro-optical
switches) to be placed on the wafer. Thus, the optical pulse must make 100000 revolutions to
cover a distance of 32.65 cm.
Let's calculate the attenuation of the optical signal in the basic element of the DOOSP. The
signal attenuation depends on the signal attenuation in the optical fiber, the signal loss introduced
by the electro-optical switch, and the bending loss of the fiber. According to [14], bending losses
can be neglected if the bending radius is of the order of 10 mm, which is the case (the bending
radius of the optical fiber ring is 52 mm). The signal attenuation in an optical fiber is equal to:
 fib  K  L0  0.25  32.65  8.16 dB , (4)
where K is the maximum attenuation of the SMF-LS fiber [8]; L0 is the distance at which the
chromatic and polarization dispersion is equal to each other.
According to [4], the loss of an electro-optical switch is 4 dB, and since two of them are
required (Figure 1), the total loss from electro-optical switches is 8 dB. Thus, the total loss is equal
to:
  8.16  8.0  16.16 dB . (5)
The wave coding method is used to encode the information sequence and store it in the DOOSP.
The frequency plan of WDM systems provides for 37 nominal central wavelengths for 100 GHz
increments in the range 1538.77 nm...1560.61 nm, so there are no complications with the choice
of wavelengths 1 and 2 [15].
Femtosecond fiber lasers can generate pulses with tens of tens of femtoseconds to 5~6 fs,
which implies stable and steady operation without needing constant system adjustment. The low
cost and stability of femtosecond fiber lasers make it possible to use them to generate an
information sequence of optical pulses for the DOOSD [16].
The information capacity is equal to the number of pulses with a duration of 100 fs that can be
placed in the time T that a light pulse will travel through an optical ring of 32.65 cm in length:
L 0.3265
T   1.088  109 s , (6)
c 3 108

T 1.088 109
I   10.88  103  10 Kbit . (7)
ti 0.1 1012

The storage time can be defined as the time for a light pulse to travel a distance L0 :
L0
tst   1.088  104 s  100 ms . (8)
c
The duration of the read and write cycle is determined by the length of the optical fiber ring
and is equal to T :
tR  tW  T  1.088  109 s . (9)
The speed of the electro-optical switch determines the access time at the first access (Latency)
and is equal to tL  10 ps . The maximum data throughput (baud rate) is defined as the ratio of the
number of pulses located in the optical fiber ring with a length of 32.65 cm to the time of their
passage through the ring:
l 10 103
BW    10 Tbit / s . (10)
T 1 109
The parameters of the basic element of the DOOSD are given in Table 1.
Table 1
Limit operating parameters of the basic element of the DOOSD
Parameter Unit of measurement Value
Information capacity Kbit 10
Organization 10Kbit×1
Information storage time µs 100
Read cycle time ns 1
Write cycle time ns 1
Access time at the first access ps 10
Transmission rate Tbit/s 10
Signal attenuation dB 16
The wavelength of the optical
nm 1560 + 10
signal
Optical power of the input
mW <10
signal

When optical pulses pass through the FOC, nonlinear phenomena occur: stimulated Brillouin
scattering (SBS), stimulated Raman scattering (SRS), self-phase modulation (SPM), quarter-wave
shift, etc. [8]. Nonlinear interaction between the optical signal and the optical fiber transmission
medium occurs when the optical signal power is increased. To preserve the optical pulses, it is
necessary to use the linear mode of optical pulse propagation in the fiber. At the optical signal
power Pin  10 mW , the nonlinear interaction between the optical signal and the optical fiber
does not occur.
As the pulses circulate along the circuit, the shape, amplitude, and position of the pulses
change [17]. To reduce optical losses, the operating range of 1550 nm is used in the DOOSD, and
to compensate for polarization mode dispersion, NZDSF fiber of SMF-LS type is used; however,
according to calculations (Table 1), the pulse amplitude is reduced by 16 dB. Therefore, in order
to restore or further use the optical information sequence, it must be restored (regenerated). For
this purpose, an optical amplifier with a gain of 16 dB should be used, which introduces as little
noise as possible and allows it to be made in an integrated design for combining in one housing
with the DOOSD cell.
Semiconductor optical amplifiers are small in size and weight [18]; they use direct conversion
of electrical energy into optical energy, which results in significantly lower power consumption
[19]; they are cheaper and have come close to fiber optic amplifiers in terms of their technical
characteristics [20]. The amplifying medium in SOA is a semiconductor structure made of
(GaAl)As crystal with geometric dimensions of no more than a few millimeters, which makes it
possible to integrate such amplifiers together with other elements of integrated circuits, for
example, with the basic element of a DOOSD [21].
In [22], the description and main characteristics of the SOA amplifier for the range of
1530...1560 nm are given. It can be used as an optical signal amplifier to restore its level after
storage in the DOOSD.

3. Results and Discussion
Computer modeling aims to confirm the possibility of implementing the DOOSD on FOCL [5]. The
software package Synopsys OptSim for Optical Communication, which is a CAD program for
modeling fiber-optic systems, was used for the research. In the course of the research, the
following tasks were set:
• Determination of the optical signal loss with a wavelength of 1.55 µm when passing
through the NZDSF fiber of SMF-LS type at a distance of 33~35 km;
• Determination of the influence of polarization mode dispersion on the waveform and the
possibility of its compensation;
• Determination of the optical input power value at which the linear mode of signal
transmission in the FOCL is ensured.
As a result of the experimental studies, the following results were obtained. Figure 2 shows a
PRBS generator that forms a digital information sequence, an NRZ transmitter, an optical filter,
an attenuator, a receiver, a BER tester, a spectrum analyzer, and an oscilloscope. The NRZ
transmitter consists of a CW laser, an electric generator (NRZ driver), an external Mach-Zehnder
modulator, and an attenuator. The waveform and spectrum of the signal input to the fiber are
shown in Figure 3.

Figure 2: Structure-function diagram of the optical information sequence source shape study

b)
Figure 3: Waveform a); spectrum b) of the transmitter signal
At the output of the optical signal receiver (RX_NRZ), we observe the picture (Figure 4). To
measure the losses during the passage of an optical information sequence (see Figure 3) through
a 35 km long NZDSF fiber, the scheme shown in Figure 5 is used.

Figure 4: Eye diagram at the output of the optical signal receiver

Figure 5: Scheme for the study of losses in the fiber

Figure 6 and Figure 7 show the waveforms of the transmitter and receiver respectively (the
effect of polarization is not considered). Figure 6 and Figure 7 shows that the optical signal loss
equals D  4.75   3.8  8.55 dB , corresponding to the parameters (Table 1).

Figure 6: The transmitted optical signal
Figure 7: The received optical signal (the length of the fiber is 35 km)

Accordingly, the eye diagram will look like the one shown in Figure 8. The effect of polarization
mode dispersion is studied according to the scheme shown in Figure 9. The fiber length is chosen
to be 33 km; the PMD polarization coefficient is 1.0 ps / km1/ 2 .

Figure 8: Eye diagram of the received signal

Figure 9: OPTSIM software window with a diagram for studying the effect of polarization mode
dispersion on the optical signal shape when passing through DSF, NZDSF fiber
The signal characteristics are shown in Figure 10. Figure 11 shows that the NZDSF fiber of
SMF-LS type with a negative chromatic dispersion compensates for the effect of polarization
mode dispersion at a distance of 33-35 km, which can be used to build a DOOSD on the FOCL. To
study the power level to be input to the DOOSD, we use the scheme shown in Figure 12.

b)
Figure 10: The result of the effect of polarization mode dispersion on signal propagation in DSF
fiber, oscillogram of the signal at the fiber output a); eye diagram of the photodetector b)

For the linear mode of operation of the FOCs, it was recommended to use an input optical
power of less than 10 mW [5]. The tests were carried out twice: at 10 mW, the modulator output
was 10 dB, and at 50 mW, 17.5 dB. The initial parameters of the signal source are shown in Figure
13.
a)

b)
Figure 11: The result of the effect of polarization mode dispersion on signal propagation in
NZDSF (SMF-LS) fiber, waveform of the signal at the fiber output a); eye diagram of the
photodetector b)

Figures 14 and 15 show that at an input power of more than 10 mW, a nonlinear mode of
operation occurs in the fiber, which leads to distortion of the information stored in the DUT.
Therefore, the input power of the optical information sequence input to the storage device should
be less than 10 mW.
Figure 12: Scheme for studying the level of optical power to be introduced into the fiber

Figure 13: CWLaser parameters before starting the test

a) b)
Figure 14: Eye diagram at a signal source power of 10 mW (10 dB) at the fiber input a); at the
fiber output b)
a) b)
Figure 15: Eye diagram at a signal source power of 50 mW (17.5 dB) at the fiber input a); at the
fiber output b)

4. Conclusions
The results of computer modeling confirmed the possibility of implementing a dynamic random
access optical storage device based on fiber-optic lines for optical computers. To reduce optical
losses in a dynamic optical random access memory, it is advisable to use the operating range of
1550 nm. To compensate for PMD, NZDSF type SMF-LS should be used. An SOA amplifier can be
used to restore the optical signal level. Optical signals are input/output through an electro-optical
directional coupler. To work with optoelectronic memory on fiber optic lines, it is recommended
to use a femtosecond fiber laser and the wave coding method. In further research, the authors
will develop an experimental model of a dynamic optical random access storage device based on
fiber optic lines for optical computers. The authors will perform experimental studies. The
authors will compare the results of experimental studies with the results of computer modeling
and draw conclusions about the prospects of the proposed dynamic optical random access
storage device based on fiber optic lines for optical computers.

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