Fast Optical Communication Components Optical Fibers and... · Optical Fiber An optical fiber is a...
-
Upload
truongmien -
Category
Documents
-
view
215 -
download
1
Transcript of Fast Optical Communication Components Optical Fibers and... · Optical Fiber An optical fiber is a...
![Page 1: Fast Optical Communication Components Optical Fibers and... · Optical Fiber An optical fiber is a cylindrical dielectric waveguide that transmits light along its axis, by the process](https://reader038.fdocuments.in/reader038/viewer/2022110223/5aef75537f8b9ad0618cd54c/html5/thumbnails/1.jpg)
Fast Optical Communication Components
![Page 2: Fast Optical Communication Components Optical Fibers and... · Optical Fiber An optical fiber is a cylindrical dielectric waveguide that transmits light along its axis, by the process](https://reader038.fdocuments.in/reader038/viewer/2022110223/5aef75537f8b9ad0618cd54c/html5/thumbnails/2.jpg)
Fiber optics
In optical communications, fiber replaces copper coaxial cables used in wired networks
![Page 3: Fast Optical Communication Components Optical Fibers and... · Optical Fiber An optical fiber is a cylindrical dielectric waveguide that transmits light along its axis, by the process](https://reader038.fdocuments.in/reader038/viewer/2022110223/5aef75537f8b9ad0618cd54c/html5/thumbnails/3.jpg)
Fiber optics
![Page 4: Fast Optical Communication Components Optical Fibers and... · Optical Fiber An optical fiber is a cylindrical dielectric waveguide that transmits light along its axis, by the process](https://reader038.fdocuments.in/reader038/viewer/2022110223/5aef75537f8b9ad0618cd54c/html5/thumbnails/4.jpg)
Fiber optic telephone communication system
![Page 5: Fast Optical Communication Components Optical Fibers and... · Optical Fiber An optical fiber is a cylindrical dielectric waveguide that transmits light along its axis, by the process](https://reader038.fdocuments.in/reader038/viewer/2022110223/5aef75537f8b9ad0618cd54c/html5/thumbnails/5.jpg)
Optical Fiber
An optical fiber is a cylindrical dielectric waveguide that transmits light along its axis, by the process of total internal reflection.
The fiber consists of a core surrounded by a cladding layer. To confine the optical signal in the core, the refractive index of the core must be greater than that of the cladding.
![Page 6: Fast Optical Communication Components Optical Fibers and... · Optical Fiber An optical fiber is a cylindrical dielectric waveguide that transmits light along its axis, by the process](https://reader038.fdocuments.in/reader038/viewer/2022110223/5aef75537f8b9ad0618cd54c/html5/thumbnails/6.jpg)
Optical Fiber Numerical ApertureThe Numerical Aperture of the fiber is the sine of the maximum angle of an incident beam that can be guided in the core
2 2core cladNA n n ;= −
For example, taking ncore=1.62 and nclad=1.52, we find the NA to be .56.
The corresponding angle, Θ = arcsin(.56) = 34 deg
The “acceptance angle” = 2Θ = 68 deg
![Page 7: Fast Optical Communication Components Optical Fibers and... · Optical Fiber An optical fiber is a cylindrical dielectric waveguide that transmits light along its axis, by the process](https://reader038.fdocuments.in/reader038/viewer/2022110223/5aef75537f8b9ad0618cd54c/html5/thumbnails/7.jpg)
Dispersion in optical fibers
![Page 8: Fast Optical Communication Components Optical Fibers and... · Optical Fiber An optical fiber is a cylindrical dielectric waveguide that transmits light along its axis, by the process](https://reader038.fdocuments.in/reader038/viewer/2022110223/5aef75537f8b9ad0618cd54c/html5/thumbnails/8.jpg)
Optical Fiber Attenuation
For long distance communications optical sources and detectors operating at 1300 nm and 1600 nm are needed.
![Page 9: Fast Optical Communication Components Optical Fibers and... · Optical Fiber An optical fiber is a cylindrical dielectric waveguide that transmits light along its axis, by the process](https://reader038.fdocuments.in/reader038/viewer/2022110223/5aef75537f8b9ad0618cd54c/html5/thumbnails/9.jpg)
Dispersion in optical fibers
![Page 10: Fast Optical Communication Components Optical Fibers and... · Optical Fiber An optical fiber is a cylindrical dielectric waveguide that transmits light along its axis, by the process](https://reader038.fdocuments.in/reader038/viewer/2022110223/5aef75537f8b9ad0618cd54c/html5/thumbnails/10.jpg)
Dense Wavelength Division Multiplexing
Nortel has demonstrated 6 Tb/s 1000 km DWDM using 160 different wavelengths 40 Gb/s each
![Page 11: Fast Optical Communication Components Optical Fibers and... · Optical Fiber An optical fiber is a cylindrical dielectric waveguide that transmits light along its axis, by the process](https://reader038.fdocuments.in/reader038/viewer/2022110223/5aef75537f8b9ad0618cd54c/html5/thumbnails/11.jpg)
Optoelectronic modulation
The role of modulator is to impress the information onto the optical signalfrom laser or from LED.
Modern optical communication systems require ultra-fast (10-100 Gb/s) modulation
![Page 12: Fast Optical Communication Components Optical Fibers and... · Optical Fiber An optical fiber is a cylindrical dielectric waveguide that transmits light along its axis, by the process](https://reader038.fdocuments.in/reader038/viewer/2022110223/5aef75537f8b9ad0618cd54c/html5/thumbnails/12.jpg)
Direct laser current modulation
E
RB
Simplest way to impress the information onto the optical beam –direct laser current modulation
Current
Time
Optical power
TimeIdeal laser response to the
current modulation
![Page 13: Fast Optical Communication Components Optical Fibers and... · Optical Fiber An optical fiber is a cylindrical dielectric waveguide that transmits light along its axis, by the process](https://reader038.fdocuments.in/reader038/viewer/2022110223/5aef75537f8b9ad0618cd54c/html5/thumbnails/13.jpg)
Direct laser current modulation issues:relaxation oscillations frequency
Laser high-frequency equivalent circuit
Electron – Photon interaction in the cavity
Laser response to a step-like bias
Electron concentration
Optical power
Threshold concentration
![Page 14: Fast Optical Communication Components Optical Fibers and... · Optical Fiber An optical fiber is a cylindrical dielectric waveguide that transmits light along its axis, by the process](https://reader038.fdocuments.in/reader038/viewer/2022110223/5aef75537f8b9ad0618cd54c/html5/thumbnails/14.jpg)
Direct laser current modulation issues:Dispersion and chirp
Chirp is the shift of the laser’s center wavelength during single pulse durations
![Page 15: Fast Optical Communication Components Optical Fibers and... · Optical Fiber An optical fiber is a cylindrical dielectric waveguide that transmits light along its axis, by the process](https://reader038.fdocuments.in/reader038/viewer/2022110223/5aef75537f8b9ad0618cd54c/html5/thumbnails/15.jpg)
Chirp in directly modulated laser
![Page 16: Fast Optical Communication Components Optical Fibers and... · Optical Fiber An optical fiber is a cylindrical dielectric waveguide that transmits light along its axis, by the process](https://reader038.fdocuments.in/reader038/viewer/2022110223/5aef75537f8b9ad0618cd54c/html5/thumbnails/16.jpg)
Effective pulse broadening due to chirp and fiber dispersion
different levels of fiber dispersion
![Page 17: Fast Optical Communication Components Optical Fibers and... · Optical Fiber An optical fiber is a cylindrical dielectric waveguide that transmits light along its axis, by the process](https://reader038.fdocuments.in/reader038/viewer/2022110223/5aef75537f8b9ad0618cd54c/html5/thumbnails/17.jpg)
External optical modulation
Signal(information)
Laser(optical carrier)
Direct modulation scheme
Modulator Channel (Fiber)
External modulation scheme
![Page 18: Fast Optical Communication Components Optical Fibers and... · Optical Fiber An optical fiber is a cylindrical dielectric waveguide that transmits light along its axis, by the process](https://reader038.fdocuments.in/reader038/viewer/2022110223/5aef75537f8b9ad0618cd54c/html5/thumbnails/18.jpg)
Franz-Keldysh Effect
In strong electric field the band edges get tilted
There is a probability for the electron, which absorbed the photon with the energy less than the bandgap to transfer into the conduction band
![Page 19: Fast Optical Communication Components Optical Fibers and... · Optical Fiber An optical fiber is a cylindrical dielectric waveguide that transmits light along its axis, by the process](https://reader038.fdocuments.in/reader038/viewer/2022110223/5aef75537f8b9ad0618cd54c/html5/thumbnails/19.jpg)
Quantum –confined Stark Effect:the analogous of Franz-Keldysh effect in QWs
Electron wave function compression in the
quantum well structure
![Page 20: Fast Optical Communication Components Optical Fibers and... · Optical Fiber An optical fiber is a cylindrical dielectric waveguide that transmits light along its axis, by the process](https://reader038.fdocuments.in/reader038/viewer/2022110223/5aef75537f8b9ad0618cd54c/html5/thumbnails/20.jpg)
Electro-absorption in QW structure in electric field
Eabs
![Page 21: Fast Optical Communication Components Optical Fibers and... · Optical Fiber An optical fiber is a cylindrical dielectric waveguide that transmits light along its axis, by the process](https://reader038.fdocuments.in/reader038/viewer/2022110223/5aef75537f8b9ad0618cd54c/html5/thumbnails/21.jpg)
MQW Electro-absorption modulator
![Page 22: Fast Optical Communication Components Optical Fibers and... · Optical Fiber An optical fiber is a cylindrical dielectric waveguide that transmits light along its axis, by the process](https://reader038.fdocuments.in/reader038/viewer/2022110223/5aef75537f8b9ad0618cd54c/html5/thumbnails/22.jpg)
Electro-Optical Modulators The principle of operation is based on the linear electro-optic effect, or the Pockels effect: a change of optical refractive index in the waveguide due to application of an electric field.
Pockels effect: rij is the electro-optic coefficient
![Page 23: Fast Optical Communication Components Optical Fibers and... · Optical Fiber An optical fiber is a cylindrical dielectric waveguide that transmits light along its axis, by the process](https://reader038.fdocuments.in/reader038/viewer/2022110223/5aef75537f8b9ad0618cd54c/html5/thumbnails/23.jpg)
Mach – Zehnder modulator
V
The light velocity in the waveguide: v = c/neff ;The time to travel the distance l (the length of the interferometer):
t = l/v = l neff /c;When the electric field is applied, the refractive index changes by ∆n;The travel time change:
∆t = l ∆n /cThe electric field causes the beam to delay by π if ∆t =T/2 (where T is the wave period);For the light beam, T = λ/c;T/2 = λ/(2c) = l ∆n /c;The required index change ∆nπ = λ/(2l)
l
![Page 24: Fast Optical Communication Components Optical Fibers and... · Optical Fiber An optical fiber is a cylindrical dielectric waveguide that transmits light along its axis, by the process](https://reader038.fdocuments.in/reader038/viewer/2022110223/5aef75537f8b9ad0618cd54c/html5/thumbnails/24.jpg)
Mach – Zehnder modulator (continued)
V
The required index change ∆nπ = λ/(2l)For the Pockels effect, the difference between top and bottom indices:
30r ijn n r E∆ =
If the thickness is d, then E = (V/d)/2 - the applied voltage is divided between the two arms.
From this, we find the voltage Vπ needed to delay the beam by π (i.e. by λ/2)
l
( )30 2 2r ijn n r V d l/ /( )π π λ∆ = = ( )3
0ij rV d l r nπ λ=
![Page 25: Fast Optical Communication Components Optical Fibers and... · Optical Fiber An optical fiber is a cylindrical dielectric waveguide that transmits light along its axis, by the process](https://reader038.fdocuments.in/reader038/viewer/2022110223/5aef75537f8b9ad0618cd54c/html5/thumbnails/25.jpg)
Mach – Zehnder interferometer:electro-optical RF modulator
![Page 26: Fast Optical Communication Components Optical Fibers and... · Optical Fiber An optical fiber is a cylindrical dielectric waveguide that transmits light along its axis, by the process](https://reader038.fdocuments.in/reader038/viewer/2022110223/5aef75537f8b9ad0618cd54c/html5/thumbnails/26.jpg)
Example: Mach – Zehnder modulator Vp calculation
Vl
Interferometer waveguide is made of LiNbO3n = 2.3; rij = 10.8 *10-12 m/V;
The waveguide thickness d = 1 µmThe modulator length, l = 1mm;
The optical beam wavelength, λ = 1.3 µm
( )30ij rV d l r nπ λ=
V = 9.9 V