Transcript Modal and Material Dispersion

Modal and Material Dispersion
Daniil Y. Gladkov
Outline
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Hardware
Types of Dispersion
Data
Transfer Function
Future Project Proposals
Why does dispersion matter ?
• Understanding the effects of dispersion in
optical fibers is quintessential in optical
communications in order to minimize pulse
spreading.
• Pulse compression due to negative dispersion
can be used to shorten pulse duration in
chirped pulse lasers
Hardware and setup
Laser Diode Power Output Profile
Pulsed Fiber Laser System
From Wesley Hughes and Jared Green’s Presentation
Pulse Generator and Amplifier
Modal Dispersion
• Pulse Spreading:
𝜎𝑓𝑖𝑏𝑒𝑟 ≈
∆
𝐿
2𝑐1
where
𝑐1 = 𝑐0 /𝑛1
• Number of modes:
𝑀≈
4 2
𝑉
2
𝜋
• Fiber Used:
where
𝑉 = 194.58,
𝑉=
𝑎
2𝜋 𝑁𝐴
𝜆0
𝑀 ≈ 78
Material Dispersion
• Pulse Spreading:
𝜎𝑓𝑖𝑏𝑒𝑟 = 𝐷 𝜎𝜆 𝐿
• Dispersion Coefficient:
𝐷𝜆 =
𝑆0
[𝜆
4
−
𝜆40
]
𝜆3
Anomalous Dispersion
• Pulse’s higher frequency have faster phase
velocity than the lower frequency
components
• Responsible for negative dispersion, pulse
compression, and soliton formation
• http://www.falstad.com/dispersion/normal.ht
ml
150 Picosecond Pulse Generator
1 Nanosecond Pulse with Amplifier
Femtosecond Pulse Laser
1km, 2km, 3km Fiber with
Femtosecond Pulse Laser Results
• 1 km - pulse width: 215 ps
σ: 572ps
• 2 km - pulse width: 385 ps
σ: 2.4ps
• 3 km - pulse width: 382 ps
σ: 1.62ps
• Results do not agree with theory
20.56 km Fiber with 1 Nanosecond
Pulse Laser Results
Multimode Fiber
Transfer Function
Input Pulse Fitting
Output Pulse Fitting
Computation of Transfer Function
Suggestions for Future Projects
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Use Optical amplifier to boost output signal
Spectral profiling of pulses
Anomalous Dispersion modeling
Better fitting and transfer function modeling
High powered laser to overcome attenuation
More variations of fiber lengths
Soliton formation