Demonstration of Optical Orthogonal
Frequency Division Multiplexing
Dr. Ali Setoodehnia1
Dr. Feng Huang1
Dr. Hong Li 2
Dr....
Outline

1.

Overview of Carriers

2.

Introduction to OFDM

3.

Introduction to various realizations.

4.

The possible r...
Overview of carriers
•In a single carrier system, a single fade or interferer can
cause the entire link to fail
•In multi-...
OFDM
Using the overlapping multi-carrier
modulation technique, we save more of the
bandwidth.
To realize the overlapping m...
Concept of OFDM

•The OFDM signal, multiplexed in the individual spectra with a
frequency spacing b equal to the transmiss...
Concept of OFDM
Each subcarrier has exactly an integer
number of cycles in the interval T, and the
number of cycles betwee...
Introduction to OFDM and optical implementation
Orthogonal Frequency Division Multiplexing and optical
realization.
Why op...
Information transmission
•Tb/s transmission
speed: free space/
fiber pigtailed
•Benchmark image
transmission
•No bit error...
Viewing the pulse shaper as a DSP instrument
At (1), the input ultrafast pulse contains the whole
spectrum at the same bea...
Full use of the capacity of optical fiber capacity

TRAFFIC TYPE

BIT RATE (Mb/s)

Voice
Data
High Fidelity Audio
Teleconf...
Available Spatial Light Modulators for pulse shaping

Fixed Mask, Holographic, Real-time Holographic
 Phase and Amplitude...
Programmable Pulse Shaping Using Liquid Crystal
Modulator (LCM) Array
• Same 4f configuration as the AOM pulse shaper
•Usi...
Ch
Ch ann
el
Ch ann
1
el
Ch ann
2
el
an
3
ne
l4
Ch
...
an
ne
lN

Wavelength

Chirped Pulse WDM of Bell Labs

Time

Princip...
Programmable Pulse Shapers: Movable and Deformable Mirrors

Using the same optical setup, instead of AOM or LCM, a
Mirror ...
Array-Waveguide-grating Pulse Shaper

• A double arrayed waveguide grating with a spatial phase
Filter forms a nearly inte...
Combine WDM and TDM

Eout (ω) = Ein (ω) M (ω)
Eout (t ) = Ein (t ) ⊗ M (t )

Synthesis of shaped fs
optical pulses through...
Advantage of Ultrafast Communication

Immunity to EMI
No Cross-Talk Between Wires
Difficult to Tap - High Security
Light W...
Optical OFDM communication
Traditional optical point to point communication
 One or a few channels only, low-powered infr...
Time

TDMA

A: accessing
WDMA

Channel N

Channel 1
Channel 2
Channel 3
Channel 4
...

Channel N

Channel 1
Channel 2
Chan...
CDMA as the coding scheme-WD-CDMA

Why Wavelength Domain
–Optical Bandwidth(5 THz) v.s. Electronic Speed
(~1GHz)
O/E Inter...
Intensity

Wavelength

New Protocol WD-OFDM

Time

Wavelength

Pulse Shaping WDM: hundreds time increase of
Date Transmiss...
Experimental results
1
BER for the proposed transmission
BER for the nomal transmission
Two channel turned off

0.9

S (ω ...
Experimental results
4

3.5

Bit Error Rate

3

BERX100 for the proposed transmission
BER for normal transmission
channel ...
Conclusions and the following works
Novel techniques like optical OFDM and Pulse Shaping
can achieve 2Tb/s with commercial...
Applications of AOM spectral encoder
Spectrum phase and amplitude control implemented via diffraction
from a modulated tra...
Typical Experimental Setup

PCI

Ultrafast FL
IMRA

(GPIB)

PC
GPIB
AWG

RF circuit

CCD
Scope
(Or
OSA)

Pulse
Picker
Driv...
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  1. 1. Demonstration of Optical Orthogonal Frequency Division Multiplexing Dr. Ali Setoodehnia1 Dr. Feng Huang1 Dr. Hong Li 2 Dr. Kamal Shahrabi1 email: asetoode@kean.edu 1. Technology Department, Kean University, US 2. College of Technology, CUNY, Brooklyn, NY
  2. 2. Outline 1. Overview of Carriers 2. Introduction to OFDM 3. Introduction to various realizations. 4. The possible realization and the proposed optical OFDM. 5. Why do we want to implement the proposed system 6. Possible implementations of the pulse shaper, advantageous and disadvantageous 7. The proposed system, channel equalization capability and security of information transmission. 8. Results 9. Conclusions, the education perspectives, and things we will like to do in the future.
  3. 3. Overview of carriers •In a single carrier system, a single fade or interferer can cause the entire link to fail •In multi-carrier system, only a small percentage of the sub-carriers will be affected. •The total signal frequency band is divided into N nonoverlapping frequency sub-channels. Each sub-channel is modulated with a separate symbol and then the N subchannels are frequency-multiplexed. •Good to avoid spectral overlap of channels to eliminate inter-channel interference. However, this requires guard band which leads to inefficient use of the available spectrum.
  4. 4. OFDM Using the overlapping multi-carrier modulation technique, we save more of the bandwidth. To realize the overlapping multi-carrier technique, we need to reduce crosstalk between sub-carriers, which means that we want orthogonality between the modulated carriers. In OFDM, the carriers are linearly independent (i.e., orthogonal) Applying the discrete Fourier transform (DFT)
  5. 5. Concept of OFDM •The OFDM signal, multiplexed in the individual spectra with a frequency spacing b equal to the transmission speed of each subcarrier •At the center frequency of each sub-carrier, there is no crosstalks from other channels. Therefore, if we use DFT at the receiver and calculate correlation values with the center of frequency of each sub-carrier, we recover the transmitted data with no crosstalk.
  6. 6. Concept of OFDM Each subcarrier has exactly an integer number of cycles in the interval T, and the number of cycles between adjacent subcarriers differs by exactly one. This property accounts for the orthogonality between the subcarriers
  7. 7. Introduction to OFDM and optical implementation Orthogonal Frequency Division Multiplexing and optical realization. Why optical OFDM  Channel equalization;  Extremely large bandwidth (5 THz for 200fs optical pulse) utilized by 100 MHz RF modulation bandwidth with date fusion technique (TDM). Ultrafast pulse shaping techniques  Ultrafast pulse: Within the pulse envelop only a few circles of the carrier wave  Advantage of pulse shaping: Arbitrary pulse synthesis; high speed communication, coherent control etc.
  8. 8. Information transmission •Tb/s transmission speed: free space/ fiber pigtailed •Benchmark image transmission •No bit error found
  9. 9. Viewing the pulse shaper as a DSP instrument At (1), the input ultrafast pulse contains the whole spectrum at the same beam, (2) At (2), different colors are spread in spatial domain, the beam at different location will have less spectrum component; the corresponding pulse duration is longer. (1) (Time to spatial dispersed frequency component) At (3), combined into the same beam again, if there is no pattern put into the pulse, it will correspond to the input pulse; if there are any phase mask to the AOM, the pulse will spreading depends on the FT of the pattern imposed on the AOM (3) AOM Modulator (spatial dispersed frequency component to time again) RF Mixer FFT FFT
  10. 10. Full use of the capacity of optical fiber capacity TRAFFIC TYPE BIT RATE (Mb/s) Voice Data High Fidelity Audio Teleconferencing Entertainment Video 0.064 0.01-10 1.0 1.5 50-150 1. Wire Pair 2. Coax Cable 3. Waveguide 4. Single Mode Fiber LOSS (dB/km) 1 10.0 1.0 0.1 1 MHz 2 3 4 1 GHz 1 THz BANDWIDTH • Hybrid OOFDM/WDM/TDM gives flexible, cost- effective solution to the opto-electronic bottleneck problem
  11. 11. Available Spatial Light Modulators for pulse shaping Fixed Mask, Holographic, Real-time Holographic  Phase and Amplitude; no pixels; no wire LCM-Arrays  Phase and Amplitude; pixels; multi-line wires Deformable Mirror  Phase; no pixels; multi-line wires Acousto-optic modulator, best for our application: higher update rate, high resolution. Speed of modulation, bandwidth resolution, update rate, Oriented for different applications.
  12. 12. Programmable Pulse Shaping Using Liquid Crystal Modulator (LCM) Array • Same 4f configuration as the AOM pulse shaper •Using the LCM array, multiple lines attached to the pixels •Most of time phase only or phase-and-amplitude (using two sets of 4f system or two sets of LCM arrays. •Using the liquid crystal to change the polarization of lights therefore the phase of the input pulse. •Typically 128 pixels on 100 µm centers; up to 512 pixels reported. •Reprogramming time > 10 ms •Low attenuation •Demonstrated to below 10 fs •Phase and amplitude response must be calibrated
  13. 13. Ch Ch ann el Ch ann 1 el Ch ann 2 el an 3 ne l4 Ch ... an ne lN Wavelength Chirped Pulse WDM of Bell Labs Time Principles: A mode-lock laser ~150 fs, using fiber to stretch the pulse to ~30 ns and spectrum is spread in this time range, using fast EO modulator (8 GHz) to modulate the stretched pulse and create about 300 WDM channels Advantages: High density WDM, individual programmable bandwidth for each WDM channel Disadvantages: Strong time wavelength coupling
  14. 14. Programmable Pulse Shapers: Movable and Deformable Mirrors Using the same optical setup, instead of AOM or LCM, a Mirror was placed in the center Fourier Plane. • Pivoting Mirror provides a linear spectral phase shift, hence a delay! •Spectral phase only control •Reprogramming time ~ 1 msec •Low attenuation •Continuous spatial modulation,
  15. 15. Array-Waveguide-grating Pulse Shaper • A double arrayed waveguide grating with a spatial phase Filter forms a nearly integrated pulse shaper •Has been demonstrated for fixed dispersion slope compensation For 2*40 WDM channels in C and L bands simultaneously.
  16. 16. Combine WDM and TDM Eout (ω) = Ein (ω) M (ω) Eout (t ) = Ein (t ) ⊗ M (t ) Synthesis of shaped fs optical pulses through shaped µs RF pulses Arbitrary spectrum modulation (both phase and amplidue offers possibilities for any encoding scheme (ASK, PSK, FSK ...) High fidelity amplification achievable using standard techniques It is also shown one can propagate the Acoustic wave in parallel with the light wave.
  17. 17. Advantage of Ultrafast Communication Immunity to EMI No Cross-Talk Between Wires Difficult to Tap - High Security Light Weight and Small Cable Size and compact system No Ground-Potential Difference Currents
  18. 18. Optical OFDM communication Traditional optical point to point communication  One or a few channels only, low-powered infrared lasers AirFiber (Nortel Networks), claims to have a product that, when deployed throughout a metropolitan area, creates a meshed architecture that can transmit data in up to four directions at 622 Mbit/s simultaneously in a distance range between 200 and 450 meters. TeraBeam Corp (Lucent Technologies Inc.), can be used as a point-tomultipoint product that uses a hub-and-spoke architecture. it can achieve data rates of 100 Mbit/s. 1-2 Km. Proposed optical point to point satellite communication  OFDM functionality: Power equalization, Channel Add-Drop, etc.  A compact system
  19. 19. Time TDMA A: accessing WDMA Channel N Channel 1 Channel 2 Channel 3 Channel 4 ... Channel N Channel 1 Channel 2 Channel 3 Channel 4 ... Traditional Multiplexing Methods Wavelength Time WD-OFDM
  20. 20. CDMA as the coding scheme-WD-CDMA Why Wavelength Domain –Optical Bandwidth(5 THz) v.s. Electronic Speed (~1GHz) O/E Interface needs High Ratio (104) Data Compression Implementation of WD-OFDM –Spectral Encoder (Spread Time) Amplitude Only (Optical Codes, PPM) Phase Only (Binary Codes)
  21. 21. Intensity Wavelength New Protocol WD-OFDM Time Wavelength Pulse Shaping WDM: hundreds time increase of Date Transmission rate (DTR) combined with TDM Pulse Shaping CDM: hundreds time increase of Channel number combined with TDM High Spectrum Efficiency
  22. 22. Experimental results 1 BER for the proposed transmission BER for the nomal transmission Two channel turned off 0.9 S (ω ) = ∫ S (i )e −iωt dt 0.7 Bit Error Rate 0.8 N (ω ) = ∫ N (i )e −iωt dt 0.6 C (ω ) • ( S (ω ) + N (ω )) C (i ) ⊗ ( S (ω ) + N (i )) c(ω ) ⊗ ( S (ω ) + N (ω )) 0.5 0.4 0.3 0.2 0.1 0 0 10 20 30 Channel 40 50 60
  23. 23. Experimental results 4 3.5 Bit Error Rate 3 BERX100 for the proposed transmission BER for normal transmission channel transmission pattern 2.5 2 1.5 1 0.5 0 0 10 20 30 Channel 40 50 60
  24. 24. Conclusions and the following works Novel techniques like optical OFDM and Pulse Shaping can achieve 2Tb/s with commercially available components: Components level  Introduction to various femtosecond pulse shaping techniques  Channel Equalization from OFDM System level  Optical OFDM communication and information transmission Following work  Developing demo system for education and external funding purpose.
  25. 25. Applications of AOM spectral encoder Spectrum phase and amplitude control implemented via diffraction from a modulated traveling acoustic wave. Components level  Channel Equalization  Tunable Dispersion Compensation  Adaptive phase feedback System level  DWDM/TDM Network
  26. 26. Typical Experimental Setup PCI Ultrafast FL IMRA (GPIB) PC GPIB AWG RF circuit CCD Scope (Or OSA) Pulse Picker Driver Scope AWG: Arbitrary waveform generator, OSA: optical spectrum analyzer (HP 71451B)

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