Optical Communications Technology and Modulation Formats 16

Transcription

Avid LEMUS
[email protected]!
Optical Digital Communications !
Technology & Modulation Formats
16 October 2008!
Agenda
•  Digital Communications Basics
•  Optical Impairments
•  From 10 to 40Gbps
•  Modulation Schemes
•  Comparison
•  Performance at 40Gbps
CONFIDENTIAL © 2007 STRATALIGHT COMMUNICATIONS ALL RIGHTS RESERVED.
2
Digital Optical Communications very very
Basics
StrataLight proprietary and confidential information
Digital Optical Communications
•  Carrier
•  Modulator
•  Detector •  Channel = Air
•  Distance = 1km
•  Speed of Light
•  V=d/t => t= 3.3 μs
300,000,000m/s
4
Fiber Optics Communications
•  Transmitter
At 2.5Gbps direct on/off
At 10Gbps use MZM
•  Channel = Fiber
Speed of Light in Silica
200,000,000m/s
•  Distance = 1km
V=d/t => t= 5.0 μs
•  Distance 1000km
t= 5 ms
5
Optical Impairments
Optical Impairments
•  Attenuation
• 
• 
• 
Loss of signal strength
Limits transmission distance
Optical amp compensates
•  Optical Signal to Noise
Ratio (OSNR)
• 
• 
• 
• 
Noise introduced by optical
amplifiers
Function of data rate—rule of
thumb,
2X data rate = 3 dB higher OSNR
Limits number of amps hence
distance
Forward error correction and
regen counter impact
•  Chromatic Dispersion (CD)
• 
• 
• 
• 
Amps allow greater distance leads
to Distortion of pulses
Limits transmission distance
Inverse to the square of the data
rates
Tunable dispersion compensator
StrataLight
proprietary and confidential information
(TDC) compensates for
effects
Optical Impairments
•  Polarization Mode
Dispersion (PMD)
• 
• 
• 
Caused by non-linearity
of fiber geometry
Very disruptive at higher
bit rates (> =10G)
PDMC or regen compensate
•  Four Wave Mixing (FWM)
• 
• 
• 
Effects in multichannel systems
Effects for higher bit rates
CD, unequal channel spacing,
larger spacings
•  Self/Cross Phase Modulation
(SPM, XPM)
• 
• 
• 
Effected by high channel power
Effected by neighbor channels
CD, reduce launch power,
larger spacings
From 10 to 40 Gbps
From 10 Gbps to 40Gbps
•  Optics
• 
• 
• 
• 
• 
OSNR lowered by 6 dB (1/4)
CD tolerance goes down by 16
PMD tolerance goes down by 4
ROADM tolerance
Nonlinear effects
•  Electronics
•  bandwidth increases by 4
•  power dissipation
•  footprint •  Economics
•  40G system price expected to be x2.5-x3 the price of a 10G system CONFIDENTIAL © 2007 STRATALIGHT COMMUNICATIONS ALL RIGHTS RESERVED.
10
Increasing Capacity per Channel
• 
At 10Gbps 50GHz is o.k. with minor crosstalk
penalty
• 
At 40Gbps even 100GHz grid support is a
challenge
• 
50GHz grid not possible with 40Gbps NRZ
• 
Added spectrum degradation due to ROADMs
• 
Need more spectrally efficient modulation format
10Gbps NRZ + 40Gbps NRZ at 100 GHz Spacing
I
193.100 THz
1552.52nm
193.200 THz
193.300 THz
193.400 THz
193.500 THz
1549.32nm
10Gbps NRZ + 40Gbps NRZ at 50 GHz Spacing
I
193.100 THz
1552.52nm
193.200 THz
193.300 THz
193.400 THz
193.500 THz
1549.32nm
11
Modulation Schemes
LASER Light properties to Modulate
•  Intensity
•  On/Off keying
•  Widely used for up to 10Gbps
•  Easy to modulate and easy to detect
I
•  Phase
• 
•  Phase shift keying •  Frequency shift keying
•  Well know technique outside optics
Polarization
•  Well know but not understood
•  Relatively new
•  Detection can be a little more difficult
Φ
P
13
Modulation Schemes
Modulation Attributes
Amplitude
NRZ
CS/RZ
Phase
DPSK
PSBT
DQPSK
Polarization
PM-’X’
QPSK
QPSK—Quadature Phase Shift Keying
(N)RZ—(Non) Return to Zero
PM-’X’—Polarization Multiplexing
PSBT—Phase Shaped Binary Transmission
CS-RZ—Carrier Suppressed Return to Zero
DPSK—Differential Phase Shift Keying
DQPSK—Differential Quadature Phase Shift Keying
Non Return to Zero (NRZ)
Intensity modulation format only
Widely used at 10Gbps
Simplest Transmitter/Receiver Configuration
Optical Spectrum has a carrier
Optical Spectrum is medium spectral
efficiency
•  Spectral efficiency in actual systems at
10Gbps and 50GHz grid => 0.2 bits/Hz
LASER
• 
• 
• 
• 
• 
43G
I
Φ
1 1 0 1 0
3/2π
π
1/2π
0
NRZ
1/2π
Im
1 √2
Re
π
OOK
0
3/2π
15
Carrier Suppressed Return to Zero (CS-RZ)
•  Intensity modulation format
•  Slightly more Complex Transmitter Design
21.5G Clk
• 
43Gbps Data
•  Pulse train has RZ pulse shape with alternate
π shifts between bits slots
•  Optical Spectrum has suppressed carrier
•  Higher tolerance to non-linear effects
•  Higher receiver sensitivity
21.5G Clk
I
Φ
1 -1 0 -1 0
3/2π
π
1/2π
0
CS-RZ
1/2π
Required additional clock modulation
Im
-√2 -1
1 √2
0
Re
π
3/2π
16
Phase Shaped Binary Transmission (PSBT)
43G
Pre-Code
•  Intensity modulation format
LPF
LASER
• 
43G
Pre-Code
•  Pulse train has NRZ like pulse shape with
some residual light within “0” symbols
•  Narrow Optical Spectrum
LPF
I
Φ
Required data pre-coder + low pass filter
1 1 0 -1 0
• 
• 
3/2π
π
Increased spectral efficiency
Increased chromatic dispersion tolerance
1/2π
0
Duo Binary 1/2π
Im
-√2 -1
1 √2
Re
π
PSBT
0
3/2π
17
Differential Phase Shift Keying (DPSK)
•  Phase Modulation only
LASER
• 
• 
43G
Pre-Code
LPF
I
Φ
Can be implemented via amplitude modulation only
Simpler than Duo-Binary
• 
• 
1 1 0 1 0
Required data pre-coder
Simpler than Duo-Binary
3/2π
π
•  Optical Spectrum is medium
1/2π
0
1/2π
DPSK
• 
Im
-1
1
0
Re
π
•  Higher receiver sensitivity by 3dB
• 
DBPSK
Can propagate on a 50GHz grid
More complex receiver
3/2π
18
Return to Zero Differential Phase Shift Keying (RZ-DPSK)
•  Mainly phase modulation format
21.5G Clk
• 
43G
Pre-Code
•  Pulse train has RZ pulse shape in every slot
with data encode in differentially phase only
•  Optical Spectrum is wide
•  Higher receiver sensitivity by 3dB
21.5G Clk
I
Φ
1 1 0 1 0
3/2π
π
1/2π
0
RZ-DPSK
1/2π
Im
-1
1
0
Re
π
RZ- DBPSK
Required additional clock modulation
3/2π
19
Transmitted Spectra
ROADM
50GHz Profile
NRZ
10Gbps
PSBT
A narrow spectrum (i.e longer pulses) improves tolerance to CD, PMD, and ROADM tolerance.
20
Quadrature Phase Shift Keying (QPSK)
21.5G
•  Four Level Phase Modulation
•  Complex Transmitter Design
Pre-Code
• 
1/2π
21.5G
•  Decrease line rate by ½
•  Increased PMD tolerance
•  Increased chromatic dispersion tolerance
•  Increased spectral efficiency
•  Decreased receiver sensitive with respect to
DSPK but increase w.r.t. NRZ
Pre-Code
I
Φ
1 1 0 1 0 0 1 0
3/2π
π
1/2π
0
Duo Binary 1/2π
Two phase modulators nested within phase shift
Im
√2
-1
1
Re
π
PSBT
0
3/2π
21
Differential Quaternary Phase Shift Keying (DQPSK)
21.5G
•  Four Level Phase Modulation
•  Complex Transmitter Design
Pre-Code
• 
1/2π
21.5G
•  Decrease line rate by ½
•  Increased PMD tolerance
•  Increased chromatic dispersion tolerance
•  Increased spectral efficiency
•  Decreased receiver sensitive with respect to
DSPK but increase w.r.t. NRZ
Pre-Code
I
Φ
1 1 0 1 0 0 1 0
3/2π
π
1/2π
0
Duo Binary 1/2π
Two phase modulators nested within phase shift
Im
√2
-1
1
Re
π
PSBT
0
3/2π
22
Dual Polarization Quadrature Phase Shift Keying (DP-QPSK)
•  Dual Polarization plus Four Level Phase Modulation
•  Reduced line rate to ¼ the transmission rate
Great spectral efficiency, increased chromatic dispersion tolerance, increase
PMD tolerance by a factor of 4! (i.e. same as 10Gbps)
Very complex transmitter
•  2x (phase modulators nested in phase shifter) + polarization maintaining
• 
• 
10.75G
Pre-Code
PBS
PBS
1/2π
I
10.75G
Pre-Code
Φx
10.75G
Pre-Code
1 1 0 0
0 1 1 0 1 0 1 1 0 1
3/2π
π
1/2π
0
Φy
3/2π
1/2π
π
10.75G
Pre-Code
1/2π
0
23
Transmitted Spectra
ROADM
50GHz Profile
NRZ
10Gbps
DQPSK
DP-QPSK
24
Comparison
Transmitter Block Diagrams
PSBT
Iin
NRZ data
DQPSK
NRZ data
Iin
NRZ data
26
Receiver Block Diagrams
27
DWDM Filter Compatibility
40Gbps Modulation Scheme Comparison
Stratalight
PSBT
NRZ-DPSK
RZ-DPSK
DQPSK
PM-QPSK
Relative cost estimate
0%
+10%
+30%
+50%
+70%
Spectral efficiency
0.8bits/Hz
0.8bits/Hz
0.8bits/Hz
0.8bits/Hz
2bits/Hz
Intrinsic CD tolerance
320ps/nm
100ps/nm
60ps/nm
200ps/nm
(1)
1st order PMD tolerance
2.1ps
2.5ps
2.8ps
5ps
30ps
2nd order PMD tolerance
HIGH
MEDIUM
LOW
HIGH
HIGH
OSNR sensitivity
17.5dB
13.9dB
13.9dB
15dB
11dB
Reach
800km
1,600km
1,600km
1,000km
2,000km
Penalty per ROADM
negligible
0.2dB
0.2dB
negligible
negligible
low
low
high
high
Non-linear X-talk from 10G low
(1)
CD tolerance depends on # taps in FIR filter
33
Performance at 40Gbps
DPSK Propagation in TWC
5.3 dB of margin
2.6 dB of margin
4dB
OSNR
Margin
1.7 dB of margin
FEC cliff: 9.4
Good margin and low nonlinear penalties after 1440 km of NDSF
NL x-talk from neighboring 40G channels much smaller than from 10G neighbors
35
DPSK WDM Penalty
• 50G grid: at the optimum power (0dBm
/ch), non-linear penalties are < 1 dB
• 100G grid: penalties are <1dB at 2dBm/ch
optimum launched power • very low non linear penalties for a system
populated with 40G lambdas only
• 3ch, 5ch , and 7ch simulations return
similar results  it’s ok to sun simulations
with 3 ch
36
ROADM Tolerance in NDSF
margin
•  9 spans of NDSF, 80km,17dB
•  ROADM: SG 3rd order, 37.6 and 44GHz
FWHM
•  in-line DCM, 90%comp
•  0dBm/ch in NDSF; -8dBm/ch in DCM
•  50GHz grid, 1 x 40G + 4 x 10G
•  21.5dB OSNR at RX
• Both DPSK and PSBT have good ROADM tolerance: at least 9 ROADMs can be supported on a 9x80km link
with a 50G grid
• DPSK penalty on a 37.6GHz ROADM: ~1dB/ROADM (few ROADMs); ~0.5dB/ROADM (many ROADMs)
• PSBT penalty on a 37.6GHz ROADM: <0.3dB/ROADM
• 44GHz ROADM penalty: <0.4dB/ROADM for DPSK ,0.15dB/ROADM for PSBT
• DPSK always has a better performance than PSBT thanks to higher B2B performance
37
Conclusions and Summary
•  Metro Applications
• 
PSBT provides best cost/performance
• 
DPSK viable where higher performance is required
•  LH/ULH Applications
• 
DPSK provides best cost/performance
•  Optional PMDC supports high PMD requirements
•  DQPSK – expensive; no significant performance advantage
• 
Improved dispersion tolerance with poorer OSNR
• 
Modest PMD improvement still requires PMDC to be practical
Conclusions and Summary
•  PM-QPSK
•  High cost, very complex, optically and electronically
•  Advantages in niche applications at 40Gbps
•  Very poor fiber and excessive cascading of narrow filters
•  Unnecessary cost for vast majority of applications
•  Performance
•  Limited to low launch powers, incurs penalty on long or high loss spans
•  Difficulty with adjacent channel 10G
•  Great spectral efficiency
•  Applications
•  Leading contender at 100Gbps where investment in optics and electronics can be
justified.
Technical Leadership
40
100Gbps Requirements
High level market requirements
• 
• 
• 
• 
Must retrofit into existing DWDM infrastructure
•  Support 50GHz channel spacing
•  Support up to 24 cascaded ROADMs @100GHz spacing
•  Support up to >10 cascaded ROADMs @50GHz spacing
•  Reach up to 1,500km
•  No change to existing line equipment (e.g. no extra amplification
required, use current in-line DCMs)
•  Same CD/PMD tolerance as current 10G (with integration of TDC
/PMDC if need be)
•  Operate without in-line DCM Power/footprint same as current 40G
Price 2x current 40G
First HW samples March ‘10
10/16/08Client Logo
42
Transmitted Spectra – Potentials
ROADM
50GHz Profile
NRZ
10Gbps
DQPSK
40Gbps
DP-QPSK
40Gbps
43
Development solution – PM-QPSK
Tx Block Diagram
4x25Gb/s
[25Gbaud]
inputs CW laser
PBS Gray
MZII
π/2
TE
Gray
MZIQ
Gray
MZII
TM
Gray
Iout
π/2
MZIQ
Rx Block Diagram
90º hybrid
(phase/polarization
diversity)
Iin
Local
Oscillator
10/16/08Client Logo
Balanced
Photodiode
Balanced
Photodiode
Balanced
Photodiode
Balanced
Photodiode
ADC/DSP
4x25Gb/s
[25Gbaud]
outputs 44
Thank-you
Questions & Comments
Please Contact me at: [email protected]

Optical Communications Technology and Modulation Formats 16

Transcription

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