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

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

Introduction Higher Spectral Efficiency Higher Data Rates Higher Receiving Sensitivity

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

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) 1976-1978 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

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

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

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

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

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。

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

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

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

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

The principle of COC Basic theory of coherent optical communication

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

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

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)

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

Coherent demodulation process of DPSK Basic theory of coherent optical communication

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

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

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

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

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

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

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

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

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

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.

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

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:

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:

Simulation of DPSK system by Optisystem software Balanced receiver

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

Exercise today Set up and study the system

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