Project: Measurement Techniques for Optical Fiber Dispersion

This project delves into the critical topic of dispersion in optical fiber communication systems. It begins with an executive summary highlighting the importance of optical fiber as a high-speed data transmission medium and the challenges posed by dispersion. The project investigates different types of dispersion, including modal and chromatic dispersion, with a focus on measurement techniques. The literature review provides a comprehensive overview of dispersion, measurement methods, and previous studies, covering techniques like pulse delay, phase-shift, and differential phase-shift methods. The research questions, aim, and sub-goals are clearly defined, focusing on proposing a novel estimation technique for chromatic dispersion using Frequency Modulated Continuous Wave (FMCW) interferometry. The theoretical content explains the principles of FMCW interferometry and its application in measuring dispersion. The experimental setup is described, including the use of an Agilent TLS 81640A tunable light source and the setup for measuring chromatic dispersion. The project presents the results, outcomes, and their relevance to the field. The project also includes a project planning section with a Gantt chart and concludes with a summary of findings and references.

Running head: ENGINEERING PROJECT PREPARATION
Engineering project preparation: Measurement technique for dispersion in
optical fiber communication
Student Name:
University Name:

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Executive Summary
In a communication system, the optical fiber is considered as the most critical media for
communication. It is used for transmitting high-speed data as it is versatile and there is negligible
loss during transmission. The optical fiber is widely used for the development of
telecommunication as it supports communication over long distance. However, there is an
existence of dispersion. Hence, it is essential to understand the types of dispersion and test the
existence of dispersion in the optical fiber. In multimode fiber, a noteworthy part is played by
mode dispersion though, in single mode fiber, the fundamental system is chromatic dispersion or
intramodal dispersion. In this paper, another estimation technique for chromatic dispersion has
been proposed for the higher-arrange methods of an optical fiber with the assistance of
Frequency Modulated Continuous Wave (FMCW) interferometry. In single mode fiber,
dispersion occurs as bottleneck in optical communication systems where transmission of data
occurs for long term. This results into limitation on bit rate as well as repeater-less distance.

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Table of Contents
1. Introduction..................................................................................................................................3
2. Literature Review........................................................................................................................3
2.1 Overview of dispersion..........................................................................................................3
2.2 Types of dispersion................................................................................................................4
2.3 Measurement methods for chromatic dispersion...................................................................4
2.4 Previous studies on measurement of dispersion....................................................................5
3. Research Questions, Aim and Sub-goals.....................................................................................6
4. Theoretical Content.....................................................................................................................7
5. Experimental Set-up....................................................................................................................9
6. Results, Outcome and Relevance..............................................................................................10
7. Project planning and Gantt chart...............................................................................................11
8. Conclusion.................................................................................................................................13
9. References..................................................................................................................................15

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1. Introduction
An optical fiber is only a variable fiber of clear glass powerful at conveying information
as light. Optical materials are hair-thin structures made by framing pre-shapes, which are glass
poles. Few-mode optical fibers (FMFs) which are also referred to as higher order mode fibers,
have already been versatilely used in several purposes for dispersal settlement in long-haul
transmission systems (Leo et al. 2013). It is important to conduct mode analysis along with
measurement of chromatic dispersion in context to FMF such that the performance of the optical
devices and sensors can be upgraded. Hence, this study will be conducted to propose an
estimation procedure to measure the chromatic dispersions existing in optical fibers. It will be
accomplished with the help of a Frequency Modulated Continuous Wave (FMCW)
interferometry by using a tunable laser and a straightforward interferometer.
2. Literature Review
2.1 Overview of dispersion
Dispersion is depicted as heartbeat disseminating in an optical fiber. As a beat of gentle
spreads through a fiber, segments, for example, numerical gap, the essential distance across,
refractive list page, wavelength, and laser point width make the beat expand. Dispersion
increments over the fiber length. The general effectuation of dissemination on the execution of a
fiber optic process is known as Intersymbol Disturbance (ISI) (Temprana et al. 2015).
Intersymbol impedance happens when the beat disseminating caused by conveyance triggers the
profitability beats of a framework to cover, rendering them imperceptible. Dispersion is typically
divided into three types: modal distribution, chromatic distribution and polarization function
dispersion.

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2.2 Types of dispersion
Modal distribution is identified as pulse dispersion brought on by the time wait between
lower-order methods and higher obtain modes. Modal distribution is difficult in multimode fiber,
producing bandwidth limitation.
Chromatic Distribution (CD) is pulse dispersion as a result of the fact that various
wavelengths of gentle propagate at slightly multiple velocities through the fiber as the index of
refraction of glass fiber is a wavelength dependent volume; multiple wavelengths propagate at
various speeds (Dar et al. 2013)
Polarization Style Distribution (PMD) occurs as a result of birefringence along the length
of the fiber that creates multiple polarization methods to visit at various speeds that will lead to
rotation of polarization orientation across the fiber.
2.3 Measurement methods for chromatic dispersion
In the area, three significant techniques can be found for deciding the chromatic
dispersion in context to optical fibers. They are depicted by three TIA/EIA business criteria: the
beat postpone technique (FOTP-168 standard), the adjusted stage move system (FOTP-169
standard), and the differential stage change procedure (FOTP-175 standard).
Phase-shift and differential phase-shift techniques are very similar. In the two methods, a
regulated asset is infused at the contribution of the fiber under test. The phase of the sinusoidal
balancing signal is looked into at the creation of the fiber and contrasted with the phase of an
examination flag, regulated with precisely the same (Brasch et al. 2016). In the stage move
procedure, the reference flag includes a set wavelength, while the other adjusted flag is tuned in
wavelengths. In the differential stage move methodology, the two signs are tuned in wavelengths

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with a set interval. The reviewed modulated signal, tuned in wavelengths, is in comparison to a
detailed reference signal, also tuned in wavelength; however, the wavelength space is constant.
The pulse-delay techniques calculate the time that various wavelength companies journey
through the fiber under test, either by photon counting or by testing the hyperlink size with a
multi-wavelength OTDR. The CD-OTDR releases multiple laser impulses in to one end of the
fiber under test, ultimately applying more than four various wavelengths significantly for better
accuracy (Lopez et al. 2013). After that, it examines the time and energy to get back following a
back-reflection from the connection at the other end. The full-time delay as a purpose of the
wavelength is deduced by evaluating the changing times of journey of the laser pulses.
2.4 Previous studies on measurement of dispersion
Romaniuk et al. (2015), has arranged an intricate framework, where WLANs are
connected in to a fiber optic framework to grow DAS in circulation lines in the financially
suitable way. They have composed a DAS remote connection for arranged association
framework utilizing IEEE 802.11 a WLAN building and plausibility inspected tentatively
concerning effective sign speed and delicacy of the received signal. Bufetov et al. (2014), have
examined optical straight back proliferation (OBP) approach that used two to a significant degree
nonlinear strands to pay for sign fiber non-direct impacts. Walczak, Randoux and Suret (2015),
has inspected the rising frameworks for building up the transfer speed for data transmission using
fiber optic for the broadband systems.
Zuo et al. (2015), have arranged a savvy association stage program (SCPS) based place to
approve the bent of program execution connected to deal with and help the association
framework in issue regions. Amiri, Nikoukar and Ali (2013), tentatively appeared for at first,
millimeter-wave (mm-wave) time in the Eband (71– 76 GHz and 81– 86 GHz) fixated on

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photonics time system. Udayakumar, Khanaa and Saravanan (2013), permit us a method to
survey the information limit of a nonlinear course and figured the decrease in course limit with
regards to fiber optic association frameworks. A shiny new frame to style long run fiber optic
association strategies has been made by DeCusatis, C. ed. (2013). Okumura and Terada (2014),
analyzed the application type of fiber optic association for satellite correspondences as a result of
its negligible fat, expansive data transfer capacity limit and basic engineering for data
transporting, electromagnetic aggravation (EMI), insusceptibility and value viability.
Futami and Hirota (2014), analyzed 10 GB/s non-dispersal managed and dispersal
managed wavelength team multiplexed program that uses pre-payment, article payment or dual
payment of every route to minimize dispersal and nonlinear effects. They realize that dual
payment provides a minimal penalty for every single dispersal managed WDM systems. Winzer
(2015), planned a concise tunable fibre Bragg grating (FBG) that uses distributed thin movie
heaters at first glance of the fibre to dynamically improve the article dispersal payment at 40
GB/s non come back to zero sign system. They have shown the first dispersal compensating FBG
at long pseudorandom touch collection sample lengths. They discover that a system itself
requires only a Bragg grating and a tapered thin steel movie covering to shift and chirp the FBG
wavelength by changing the used current through the movie which improves time-varying
dispersal routes and may reduce energy penalty associated with nonlinear sign impairments and
other variations.
3. Research Questions, Aim and Sub-goals
The questions that have been prepared for this particular study are illustrated as below:
 What is the basic cause of transmission loss in communication systems?

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 What is the importance of testing dispersion in optical fiber?
 What are the existing dispersion measurement methods for optical fibers?
This study aims at understanding the types of dispersion and testing the existence of
dispersion in an optical fiber. It is essential to perform measurement of chromatic dispersion in
context to FMF for upgrading optical devices as well as sensors performance that are based on
FMF (DeCusatis, C. ed. 2013). Henceforth, this study will be led to propose a novel estimation
technique for chromatic dispersions of most energized routes in optical filaments.
The sub-goals in context to this study for measuring dispersion in optical fibers are listed
as below:
 To analyze the concept of dispersion and understand the various types.
 To evaluate previous studies on the measurement methods and gain insight into
the
 To demonstrate a new technique to measure dispersion.
4. Theoretical Content
The first FMCW interferometer process is comprised of Michelson interferometer along
with Tunable Laser Source (TLS) where there is utilization of swept center frequency. It is being
used as an alternative for movable delay line which is incorporated in an Optical Low Coherence
Reflectometer (OLCR). Typically, FMCW interferometry is used for determining positions of
the existing irregularities in a Single Mode Optical Fiber (SMF) that has high sensitivity as well
as spatial resolution. Each mode present in the Fiber under Test (FUT) is being propelled with
frequency-swept coherent light (Kschischang 2015). Then, another light emitted from
interferometer’s reference arm is interfered with the lights that are transmitted from the modes in

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FUT (Uddin, Rahman & Ali 2015). The detection of power of the lights that are interfered is
done with the help of slow photo-detector and beating oscillations that have proportional
frequencies with respect to time delays. If there should be an occurrence of a multimode visual
fiber, each setting moves with an alternate spread normal and incorporates a different class
speed. Therefore relative time delay, which fits to each function inside an MMF, may be
calculated with an FMCW interferometry. The chromatic dispersion of every function inside an
MMF may be also received by testing wavelength-dependent time delay in a FMCW
interferometer by spanning the middle wavelengths of the tunable laser. The wavelength-
dependent a.c. sensor voltage of an interfered indicate in a FMCW interferometry is generally
identified by:
Wherever Um and ϕm would be the constant amplitude and phase of an interfered
indicate involving the fundamental function of the reference fibre and the m-th get function of
the FUT, respectively. D is exactly how many the thrilled ways in a multimode optical fiber. λ
may be the center wavelength of a tunable laser source. A frequency-tuning rate γ(λ) is a settable
constant value of our tunable laser source (Leo et al. 2013). It presents the mild volume change
per device time. Relative party delay Δτm may be the huge difference between the time delay of
the m-th thrilled function of an MMF and the fundamental function of a SMF since the reference
fiber.

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5. Experimental Set-up
The underneath figure 1 is a schematic chart of the test set-up to measure the chromatic
dispersion of revived settings in a FMF using a transmission-sort FMCW interferometer. An
Agilent TLS 81640A tunable light source (TLS) is utilized with focusing range from 1520 –
1580 nm and focusing selection (Δλ) of 2 nm as seemed in the specked package of the figure.
The wavelength-tuning charge was collection to 5 nm/s or γ = 625 GHz/s at 1550 nm wavelength
indicated while the slant of the satisfied immediate frequency as an element of time, that will be
revealed such as for instance a found enamel waveform in beneath figure. The optical energy of
the TLS is kept at 2 mW amid the frequency focusing process (Lopez et al. 2013). Beating signs
were gained using an information procurement stock up with an activating indication developed
each time toward the beginning of frequency sweep.
Figure 1: Experimental setup for measurement of chromatic dispersion

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After frequency cleared light from the TLS is part utilizing a 3 dB visual coupler, fifty for
each penny of the visual vitality goes into a dependable Michelson shape fiber interferometer, as
found in a dashed bundle in figure 1. The helper interferometer is utilized to check the
nonlinearity of the frequency convey rate γ as a reason for time. By considering time-changing
time of a beating sign in the helper interferometer with help from Hilbert change remuneration
strategy, about all of slip-ups identified with the nonlinear frequency convey rate of our TLS
were easily expelled (Okumura & Terada 2014). A greater part Mach-Zehnder interferometer is
utilized as the primary interferometer, where the lingering visual vitality is part afresh utilizing a
3 dB fiber coupler. A pattern proliferated by method for a FUT is alongside yet another pattern
from the examination supply with an extensive segment splitter, and they make aggravation signs
at a photograph locator. A carefully assembled few mode fiber (FMF), of which the essential
length and the record huge contrast is roughly 8 pm and 0.026, individually, is utilized for
instance fiber under test.
6. Results, Outcome and Relevance
In the described estimation scheme, dispersions are gotten particularly and instinctually
by measuring the time deferments of the modes with respect to wavelength. Another good
position is a clear trial set-up involving a tunable laser source and an essential interferometer.
Diverse techniques need to gauge the chromatic dispersion of the LP01 strategy for an example
FMF with a conventional stage control methodology to get the dispersion of a higher demand
mode for every case FMF. Regardless, this system does not need to measure the dispersion of the
LP01 for every example FMF. Since the dispersion information of a SMF is prominent, if a
standard SMF is used as a sort of viewpoint fiber in the estimation setup, no further reference
dispersion estimations would be required. In addition, various tunable lasers for commercial

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purpose have been developed in the recent years with different wavelengths. Moreover, that
procedure could be connected to the strategic assessment for various forte visual strands, for
example, for example, photonic precious stone filaments, empty visual strands with a few modes.
7. Project planning and Gantt chart
Project plan refers to the process of developing the scope and objectives along with
determining the steps for achieving the goals of the project. It is one the essential process that
helps to manage a project efficiently. The project plan also defines the approach as well as
process that the team will use for management of the project according to the defined scope. The
plan for this research project has been illustrated as below:
Figure 2: Timeline for the research
The project plan comprises of the various activities that are required for completion of the
research successfully. The plan has been designed along with the required time to complete each
activity. The total duration that has been estimated to accomplish the research project and
achievement of project objectives is 42 days that is the project will begin from 25 October 2017
and end on 12 December 2017. The description of the activities required to accomplish the
research project is being presented in the below sections: