1. Fiber Optic Network Design
Class 8
C. S. Yan, X. Wu, M. Y. Li
Dept. of Opt. Engr., ZJU
2013

2. Content Introduction Development of optical fiber communication
Bottlenecks
Basic theory of COC
Advantages, Principles, Structures and types
DPSK
DP-QPSK
Simulation of DPSK system by Optisystem
Pulse generation
Sequence decoder
Balanced receiver
Exercise today
Reference

3. Introduction Higher Spectral Efficiency Higher Data Rates
Higher Receiving Sensitivity

4. Introduction
Development process on optical transmission rate and transmission distance product for thirty years
Moore's Law
bottlenecks
Revolution?

5. Development of optical fiber communication in the earlier years
Introduction
Development of optical fiber communication in the earlier years
Year
Development
1966
C. K. Kao: fiber as communication medium
1976
Fiber loss <0.47dB/km (1.2um)
44.7Mb/s, 10km (Atlanta, multi-mode fiber)
34Mb/s (100Mb/s), 64km (Japan)
1983
400Mb/s (1.6Gb/s), 3400km, (Japan’s north-south route)
1988
6400km, TAT-8 Atlantic submarine cable
1989
13200km, TPC-3/HAW-4 Atlantic submarine cable

6. What is the bottlenecks for DWDM
Introduction
What is the bottlenecks for DWDM
1. Chromatic dispersion
2. polarization mode dispersion
色度色散：最远传输距离与速率成反比
偏振模色散：最远传输距离与传输速率的平方成反比

7. What is the bottlenecks for DWDM
Introduction
What is the bottlenecks for DWDM
3. Nonlinear effect
Nonlinear effect
Bottlenecks
Stimulated Raman Scattering
SNR degradation as the number of channel increases
Four-wave mixing
Limit the channel spacing
Cross phase modulation
Limit the number of channels
4. Electronic rate
色度色散：最远传输距离与速率成反比
偏振模色散：最远传输距离与传输速率的平方成反比
When >30GHz，limited by electronic circuit and ADC chip

8. How to break through the bottlenecks
Introduction
How to break through the bottlenecks
——Optical Time Domain Multiplexing (OTDM)?
Electronic signals
Optical signals 4x
40Gb/s
delayed S
色度色散：最远传输距离与速率成反比
偏振模色散：最远传输距离与传输速率的平方成反比
1x 160Gb/s

9. The advantages of OTDM Characteristics Advantages
Introduction
The advantages of OTDM
Characteristics
Advantages
Single wavelength operation
No gain flattening
Simple dispersion managing
All-optical digital signal processing
Overcome the electronic bottleneck
Improve network capacity
Network signal stream all-optical regeneration
Reduces signal noise and crosstalk accumulation
Truly transparent transmission of optical signals
Bandwidth on demand
Flexibility to provide emergency service access
Achieved through the slot allocation routing
Data format and protocol transparent transmission

10. The Disadvantages of OTDM
Introduction
The Disadvantages of OTDM
High price
Ultra-narrow optical pulse laser
Optical clock extraction and de-multiplexing
Severe nonlinear effects
近年来，随着用户对高速数据、图像和宽带流媒体等业务需求的不
断增长，光纤通信的发展方向已成为在无信号再生基础上实现更高速率
和更长距离传输。由于光纤和光放大器的带宽有限，需要提高谱效率
(bit／s／Hz)；由于光纤非线性对传输功率的限制，需要提高功率效率，即
降低光信噪比(OSNR)需求，提高接收灵敏度。于是高谱效率和高灵
敏度的传输方式开始引起人们的关注。在常规的非相干传输系统中，由
于接收机和放大器噪声的影响，灵敏度往往比量子极限低很多，同时由
于调制方式的限制，使得谱效率的提高也很难实现。与非相干系统相比，
相干光传输系统在提高谱效率和灵敏度方面具有很大优势。
相干光通信是指：在发射端，除使用幅度调制外，还使用频率、相
位调制等，充分利用光载波的相干性；在接收端则采取相干检测，来自
光波系统的信号光与另一个称为本振的窄线宽激光器发出的光波混合，
然后一起输入光电二极管相干混频，混频后的差频信号经后接信号处理
系统处理后进行判决。

11. Combination of OTDM and WDM
Introduction
Combination of OTDM and WDM
4 x 40Gb/s
160Gb/s
OTDM multiplexers
WDM multiplexer of Add-Drop
WDM demultiplexer of Add-Drop
40Gb/s
OTDM add-drop
OTDM demultiplexer
160Gb/s regenerated

12. Coherent Optical Communication
Basic theory of coherent optical communication
How to breakthrough?
COC?
Phase Frequency Polarization Modulation
Amplitude Modulation
WDM
OTDM
Coherent Optical Communication

13. Opportunities come again COC
Basic theory of coherent optical communication
Opportunities come again COC
2004, M. G. Taylor, PTL, Proposed to restore the signal using DSP, Digital coherent receiver technology
2004, 20Gbit/s, QPSK system
solve the problem of channel attenuation
But hard to large scale Commercial
Replaced by EDFA in the 1990s
2002, R. A. Griffin (UK), DQPSK

14. Advantages of COC Advantages High sensitivity and long distance relay
Basic theory of coherent optical communication
Advantages of COC
Advantages
High sensitivity and long distance relay
Sufficiently close to the quantum limit by raising the power of the LO light.
Good wavelength selectivity and large communication capacity
Large dispersion and nonlinear toleration
linear system, The linear distortion owing to dispersion and PMD can be completely compensated.
Use DSP to restore the data
Use electronic devices for Dispersion compensation and Polarization equalization
Low cost, high reliability, Commercialization,
Support various modulation schemes
M-PSK, M-QAM , OFDM, with higher spectral efficiency

15. The principle of COC
Basic theory of coherent optical communication

16. The principle of COC Detector Responsivity Optical power
Basic theory of coherent optical communication
Detector Responsivity
Optical power

17. The principle of COC Homodyne detection Heterodyne detection
Basic theory of coherent optical communication
Homodyne
detection
Heterodyne detection
Advantages:
Disadvantages:
High frequency stability
Narrow bandwidth
Frequency tunable
Optical phase locked loop (PLL)
SNR is two times lower than homodyne

18. Structures and types of coherent receivers
Basic theory of coherent optical communication
Structures and types of coherent receivers
(Differential phase shift keying)
(Quadrature Amplitude Modulation)

19. Signal Modulation of Differential phase shift keying (DPSK)
Basic theory of coherent optical communication
Signal Modulation of Differential phase shift keying (DPSK)
 phase change between 0 and 1 code

20. Coherent demodulation process of DPSK
Basic theory of coherent optical communication

21. Modulation formats comparison of coherent receivers
Basic theory of coherent optical communication
Modulation formats comparison of coherent receivers
100Gbit/s
OSNR=0.2dB
50GHz channel spacing

22. Modulation formats comparison of coherent receivers
Basic theory of coherent optical communication
Modulation formats comparison of coherent receivers
Dispersion can be compensated by DSP. For the same dispersion, it has different requirement for the computing power of the DSP (serials)
After 1600km transmission in standard single-mode fiber

23. Polarization separation
Basic theory of coherent optical communication
Coherent receiver of Dual-polarization quadrature phase shift keying (DP-QPSK)
Polarization separation
Demodulation
Balanced receiver
TIA: Trans-impedance amplifier
Phase  intensity
Optical  Electrical

24. 90 phase shift mixer of DP-QPSK
Basic theory of coherent optical communication
90 phase shift mixer of DP-QPSK
Optical fiber type
Free space type

25. 90 phase shift mixer of DP-QPSK
Basic theory of coherent optical communication
90 phase shift mixer of DP-QPSK
LiNbO3 waveguide type
Si-based monolithic integration
Bell Lab 2010

26. 90 phase shift mixer of DP-QPSK
Basic theory of coherent optical communication
90 phase shift mixer of DP-QPSK
Si-based monolithic integration type
Furukawa
InP-based monolithic integration type
Bell Lab 2011

27. 90 phase shift mixer of DP-QPSK
Basic theory of coherent optical communication
90 phase shift mixer of DP-QPSK
Major international manufacturers of 100Gbit / s coherent receiver

28. 90 phase shift mixer of DP-QPSK
Basic theory of coherent optical communication
90 phase shift mixer of DP-QPSK
Physical map of InP based monolithically integrated coherent receiver by HHI and U2T

29. DPSK—pulse generation
Simulation of DPSK system by Optisystem software
DPSK—pulse generation
Constellation
diagram

30. M-ARY pulse generator and Threshold detector
Simulation of DPSK system by Optisystem software
M-ARY pulse generator and Threshold detector
input M-ary signal
pulse position
linear gain
bit period
parameter Bias
duty cycle
if the signal input has a value of -3.3, the output level will be -3, since -3.3 is between -3.5 and -1.5.

31. DPSK—pulse generation and decoding
Simulation of DPSK system by Optisystem software
DPSK—pulse generation and decoding

32. Simulation of DPSK system by Optisystem software
DPSK sequence decoder
The DPSK decoder will calculate the value of i from the phase difference between consecutive signals k and k-1:

33. Simulation of DPSK system by Optisystem software
DPSK sequence decoder
Assuming ϕ=0, if bits per symbol (n) equals 2, and M=4, then the values for I and Q will be:
Assuming ϕ=0, if bits per symbol (n) equals 3, and M=8, then the values for I and Q will be:

34. Simulation of DPSK system by Optisystem software
Balanced receiver

35. Balanced receiver Eliminate intensity noise, improve sensitivity
Simulation of DPSK system by Optisystem software
Balanced receiver
Eliminate intensity noise, improve sensitivity

36. Exercise today
Set up and study the system

37. Reference 刘卫华. 用于100Gbit/s 相干通信的90°相移光混合器研究. 华中科技大学博士学位论文. 2012
王甲琛. 基于FPGA的DPSK调制解调技术的设计与实现. 西安电子科技大学硕士学位论文. 2010