OFC SYSTEMS Performance & Simulations BC Choudhary NITTTR, Sector 26, Chandigarh
High Capacity DWDM OFC Link Capacity of carrying enormous rates of information in THz 1.1 Tb/s over 150 km ; 55 wavelengths WDM 2.6 Tb/s over 120 km ; 132 wavelengths WDM
Typical OFC link & Performance Parameters Performance-measurement parameters of users interest
Testing System Performance z=0 z=l Attenuation z=0 z=l Dispersion Attenuation & Dispersion degradation as a function of distance
Performance Evaluation Performance of any communication system can be evaluated by one of the following methods: Eye Diagrams / Patterns. Q- factor /Bit Error Rate Measurements.
Eye Diagram Analysis Often used for assessing the quality of received signal and indeed the quality and integrity of system transmitting it. Eye diagram showing sample measurements of 20-80% rise time, jitter, full width noise and the mean 0 & 1 levels. Although qualitative; provides useful data in terms of trends and system operation as per specifications. Semi-quantitative information about the transmission quality Determination of Q -value and hence BER.
Sampling for Q-factor & BER Estimation
Noise Vs Distortion
Major physical phenomena affecting light propagation in optical fibers Signal degradation.
Path Degradation/Engineering Fiber Fiber Original Signals Degraded & Dispersed Signals Amplified & Corrected Signals w/ Noise & Nonlinear gain Unusable Signal from Noise Generally amplifiers (Repeaters) are used to achieve the required SNR or depending on signal health, regenerators are used for amplification as well as shaping the signal to desired level. To compensate the dispersion (pulse broadening)- DCFs or FBGs are used either in pre- or post-compensation scheme.
Four possible applications of Optical Amplifiers In-line amplifiers to increase transmission distance Preamplifiers to improve receiver sensitivity Booster of transmitted power Booster of signal level in a LAN
Optical Amplifiers SOAs offer a key technology for amplification, switching, wavelength conversion & regeneration in optical networks However, the drawbacks to SOAs include high-coupling loss, polarization dependence, and a higher noise figure.
Fiber Amplifiers 1480 nm pump spectrum and a typical output signal at 1540 nm with associated ASE noise.
INITIAL DWDM SIGNAL All channels roughly equal power FINAL DWDM SIGNAL After a series of amplifiers Signal to noise reduced Some channels stronger than others
Gain Flattening Gain of EDFA is wavelength dependent in its normal operating window of 1530-1560 nm & 1560-1600 nm. Need to be equalized over the spectral range of operation in multichannel systems. Numerous techniques; Use of gain compensating fiber gratings or Raman fiber amplifiers.
Hybrid Integration Platform Hybrid Integration Platform Facilitates Photonic Circuits Elements of the HyBoard platform for a typical design. The hybrid integrated device consists of a planar silica single-mode waveguide motherboard (bottom left), an optoelectronic semiconductor device array such as semiconductor optical amplifier arrays (bottom right) and a silicon submount or daughterboard (bottom center). Arrays of optical fibres can be connected to the motherboard via a silicon arrowhead (top right).
Optical Power Requirements Each amplifier add some amount of noise ( 3dB) SNR degradation as a function of link length over which noise increases with number of amplifiers For a given channel transmitted over a link containing several optical amplifiers, SNR starts out at high level. It then decreases at each amplifier as the amplifier ASE noise accumulates through the length of the link.
Dispersion Compensating Fibers (DCF) Designed for specific purpose, now used in high data networks
Dispersion Compensating Fibers (DCF) Design is different from conventional configurations. SMFs with Negative Dispersion Characteristic Total dispersion of the link to be ~Zero : D 1 L 1 +D 2 L 2 =0 Pulse Spread compensation with a DCF
Manufacturers to modify Design of DCFs Refractive index profile ( ) Relative Index value ( ) Decreasing Core radius (a), MFD 4.5 m
Dispersion Compensator- FBG Based Dispersion Compensation of 100 km standard fiber at 1.55 um using 6 cm chirped grating and optical circulator
Dispersion Compensator
Dispersion & Power Maps Approach to reduce the effects of dispersion is to use passive dispersion compensation using DCF- negates the accumulated dispersion of the transmission fiber. Dispersion maps and Power maps for (a) pre-compensation and (b) postcompensation schemes.
High Capacity OFC System Experimental setup for 55 wavelengths WDM transmission using 1550nm optimized fibers and DCFs in the link Transmitted data rate of 1.1 Tb/s over 150 km
OFC Systems Simulations
Why Use Optical System Software? "As optical systems become more and more complex, scientists and engineers must increasingly adopt advanced software simulation techniques for vital assistance with design issues. PDTS's power & flexibility facilitates efficient & effective photonic designs and Analysis" Dr. Govind P. Agrawal Professor - Institute of Optics University of Rochester
Simulation and Modeling Tools Uses numerical methods to predict and evaluate the behaviors of individual fiber optic components, links and networks. Computer based simulation and modeling tools that integrate components, links and network functions make the design process more efficient, cheaper and faster. Rapid proliferation and increase in capabilities of PCs led to development of many sophisticated simulation programs - Photonic design automation (PDA) tools based on well established numerical methods Simulate factors such as connector losses due to geometric or position mismatches of fibers, efficiencies of coupling optical light from source into fiber, signal behaviors of passive and active components and performance of complex optical networks. Model devices such as waveguide couplers, optical filters, waveguide grating arrays, optical amplifiers and optical sources. Enable a user to visualize and simulate a system quickly with reasonable accuracy.
Enables Role of Simulation in Photonics Study of complex inter-and intra-component interactions numerically correct prediction of interactions Implementation of rapid design cycles using latest technologies Simulator and its libraries become standard design platforms for individuals/ research teams in Universities/ Research Labs/ Companies for communication of design electronically in standard format. Complex interactions could involve intermodulation, feedback, reflections, resonances and non linearities.
Characteristics of Simulation and Modeling Computer-aided PDA tools offer to assist in analyzing the design of an optical component, circuit and network before costly prototypes are built. Consider the approximation and modeling assumptions in the design Theoretical models Most Telecom systems are designed with several db of safety margin approximations are reasonably accurate and acceptable in general. Computational efficiency allows a tradeoff between accuracy and speed allows quick estimates of system performance in the early stages of a design. Enable a user to visualize and simulate a system quickly created using libraries and GUI.
Ingredients of a Photonics Simulator GUI : Allows models of devices, components and subsystems to be selected and wired - should have several visualizers for visualizing data Scheduler : Sets the execution order and ensures each module has appropriate I/P before execution Libraries: Contains Libraries of Photonics components such as Lasers, Fibers, EDFAs, SOAs, Receivers, Monitors etc Cosimulation Features: Allows interoperability with 3 rd Party software (e.g. Matlab, C/C++ etc) Verification: Should give results close to experimental values
PTDS Simulations & Modeling Tools Photonic Transmission Design Suites (PTDS) - commercial softwares : VPI- Transmission maker RSOFT- OptSim & ModeSys Optiwave- OptiSystem These can be used for designing either a photonic component to be used in communication systems, a complete optical communication link or system, or an optical network. PTDS has component library of detailed physical models of photonic devices and a graphical user interface to combine them easily as well as visualization tools for interactive displays. These system design tools enables the users to simulate a wide range of network
Simulation and Analysis Results in Optical Link Signal waveforms Signal eye diagrams Signal spectra Frequency chirp Bit error rate & Q curves Dispersion and power maps X-Y plots Power penalties Loss budgets And more
System Simulation: 4-Channel WDM Fiber input showing 4 distinct wavelength channels Fiber output showing the effects of four-wave mixing
Sample Topologies Several of the Common topologies displayed here include repetition loops (above), parallel optical bus (top right) and optical ring network (bottom left)
Many ways to view and analyze simulation results Contour eyes Q contours BER contours Combined signal and frequency chirp plots
Dispersion Compensation
PMD Simulation Transmitter High PMD fiber Waveform plot X polarization Waveform plot X polarization
CATV Networks
Optical System Software
Modulation Formats and Spectra NRZ RZ CS-RZ MD -RZ ~ 80 GHz ~ 160 GHz ~ 120 GHz Suppression of unmodulated carrier Adding of tones at +\- NB/2, N is integer Suppression of unmodulated carrier Suppression of the other tones at +/- NB/2
DPSK Optical Signals 33% duty-ratio 50% duty-ratio 66% duty-ratio
EDFA YDFA EYDFA RFA Optical Amplifier Design
Optimizations : Gain Flattening Filter
Using Matlab/Simulink models Matlab/Simulink model
Multimode Link
Free Space Optics
Performance Budget Validation Example Experimental Set up
Performance Budget Validation Example Simulation Set up Transmitter Block Transmission Loop Receiver Block
Q 2 (db) Performance Budget Validation Results 18 16 Q_exp Q_sim 14 12 10 0 5 10 15 20 25 30 35 40 45 50 55 60 65 Ch # Comparison of simulation results for selected channels with measured data.
SENSITIVITY For 10 10 Gbit/s Validation Measured Eye Diagrams -9.5 a) At 0 km b) At 40 km Simulated Eye Diagrams -9 BER(dBm) -10.0-10.5-11.0 Measured Simulated -11.5-12.0 0 40 80 120 160 200 Time [ps] 0 40 80 120 160 200 Time [ps] c) At 0 km d) At 40 km -12.5 0 20 40 60 80 100 120 DISTANCE [km]
30 Gbit/s Cooled Laser : Direct Modulation Validation Measured Simulated Received signal Laser drive signal 500 1000 1500 2000 Time [ps]
PDTS s Key Capabilities Usability: Powerful yet easy to use. Integrated design, simulation and analysis environment offers the fastest learning curve in the industry Accuracy: Users can enter parameters that can be measured from real devices. It integrates with test & measurement equipment from different vendors. Expandability: Users can incorporate new components based on subsystems and user-defined libraries, or utilize co-simulation with a third party tool such as MATLAB or SPICE Flexibility: Automation of design and simulations using integrated VBScript.
Thank You For any help, contact me at: Dr. BC Choudhary, Cell: 09417521382, Email: <bakhshish@yahoo.com>