Analysis of Phase-to-Intensity Noise by multiple ...
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Analysis of Phase-to-Intensity Noise by multiple reflections in 100G-PAM SMF links
T i hi K O tTaichi Kogure, OpnextKiyo Hiramoto, OpnextJon Anderson, Opnext
Next Gen 100GbE Optical SG, Hawaii, March 2012
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Introduction
• At the Newport Beach, 2011 SG meeting, PAM-N scheme with a singleAt the Newport Beach, 2011 SG meeting, PAM N scheme with a single wavelength was proposed (bhoja_01_0112_NG100GOPTX). During the discussion, it was pointed out that multiple reflections may deteriorate PAM signal quality.g q y
• This contribution provides extensive analysis of phase-to-intensity noise (Link RIN) induced by multiple reflection in 100G-PAM SMF links.
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PAM-8 System Model
BW
ORL
Two additional parameters, laser source spectral width (BW) and optical return loss in the link (ORL), are introduced to calculate Link-RIN for a performance verification of PAM-8 system model previously proposed (bhoja_01_0112).
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Simulation Model with “Multiple reflections”<Single-link case Cabling>
L
Direct path signal
(TX) (RX)
R1 (ORL) R2 (ORL)
RIN spectrum induced by multiple reflections in the link for longer delayed paths (longer than coherent length) can be described as a following equations1);
Double-reflected signal
t a co e e t e gt ) ca be desc bed as a o o g equat o s ;
)12()(
4)( 2221 >>⋅Δ⋅⎥
⎦
⎤⎢⎣
⎡Δ+
Δ⋅⋅= τνπ
νν
π fRRfRIN
where Rn is an effective reflection coefficient of the link connections (assumed polarization axis of the two fields are the same as the worst case condition), Δν is a spectral width of the laser and τ is a round-trip path (reflection) delay time.
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1) J.L.GIMLETT and N.K.CHEUNG, “Effects of Phase-to-Intensity Noise Conversion by Multiple Reflections on Gigabit-per-Second DFB Laser Transmission Systems,” J.Lightwave Technol. Vol.7, No.6, pp. 888-895 (1989).
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-80 -80
Calculated RIN spectra at Rx side (Laser RIN = -149 dB/Hz, BW = 10 MHz)
140
-120
-100
N (
dB/H
z)
140
-120
-100
N (
dB/H
z)Source RINdominant Link RIN negligible
-180
-160
-140
0 1 1 10 100 1000 10000 100000
RIN
-180
-160
-140
0 1 1 10 100 1000 10000 100000
RIN
-80
0.1 1 10 100 1000 10000 100000
Frequency (MHz)
0.1 1 10 100 1000 10000 100000
Frequency (MHz)
-80
ORL = 60 dB (APC connection) ORL = 40 dB (SPC connection)
-140
-120
-100
N (
dB/H
z)-140
-120
-100
N (
dB/H
z)
Link RIN dominantLink RIN effective
-180
-160
140
0.1 1 10 100 1000 10000 100000
RIN
-180
-160
140
0.1 1 10 100 1000 10000 100000
RIN
5
Frequency (MHz)Frequency (MHz)
ORL = 27 dB (ITU-T standard) ORL = 21 dB (IEEE 100G-LR4)
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Related Specification
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Related Specificationp
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# Parameters Category Value Units Remarks
Case1: Calculation parameter List for PAM8 (Based on current standard)# Parameters Category Value Units Remarks
1 Wavelength Tx 1310 nm “bhoja_01_0112”
2 Spectral width Tx 10 MHz assumption, normal DFB-LD
3 Extinction ratio Tx 8.0 dB “bhoja 01 0112” (*2)3 Extinction ratio Tx 8.0 dB bhoja_01_0112 ( 2)Sub-eye #7(mark) / #1(space)
4 RIN Tx -149 dB/Hz “bhoja_01_0112”
5 Transmitter reflectance Tx -12 dB 802.3ae Table 88-7
6 Responsivity Rx 1.0 A/W assumption
7 Receiver bandwidth Rx 12.5 GHz root raised cosine filter (*1)
8 Dark current Rx 100 pA assumption, negligible
9 Input referred noise Rx 15 pA/sqrt(Hz) “bhoja_01_0112”
10 Receiver reflectance Rx -26 dB 802.3ae Table 88-8
11 Rx OMA Link -7.75 dBm “bhoja_01_0112”
12 Transmission distance Link 1000 m12 Transmission distance Link 1000 m
13 Optical return loss Link Parameter dB*1) Both filter profile and formula are shown in Appendix.A*2) All sub-eyes have the same OMA.
Note
8
Case1: One end of reflection is Tx, and the other depends.
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20 20
Case1: Calculated Q values of PAM8
14
16
18
alue
(dB
)
14
16
18
alue
(dB
)
10
12
14
1 2 3 4 5 6 7
Q v
a
10
12
14
1 2 3 4 5 6 7
Q v
a
12.6 dB (BER=1E-5) 12.6 dB (BER=1E-5)
1 2 3 4 5 6 7
Eye Number
1 2 3 4 5 6 7
Eye Number
20 20
ORL = 60 dB (APC connection) ORL = 40 dB (SPC connection)
14
16
18
valu
e (d
B)
14
16
18
valu
e (d
B)12 6 dB (BER 1E 5) 12 6 dB (BER 1E 5)
10
12
14
1 2 3 4 5 6 7
Q v
10
12
14
1 2 3 4 5 6 7
Q v12.6 dB (BER=1E-5) 12.6 dB (BER=1E-5)
9
Eye Number Eye NumberORL = 27 dB (ITU-T standard) ORL = 21 dB (IEEE 100G-LR4)
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25Case2: Simulation Result taking into account Link RIN
2060
27
ORL (dB)
15
Q (
dB)
21
12 6 dB (BER=1E-5)
10
Q 12.6 dB (BER=1E-5)
520 15 10 5 0 5-20 -15 -10 -5 0 5
Rx OMA (dBm)
The result shows current Transmitter reflectance spec is not suitable
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The result shows current Transmitter reflectance spec is not suitable for 100G-PAM8 to achieve required Q values.
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# Parameters Category Value Units Remarks
Case2: Calculation parameter List for PAM8 (PMD reflectance Improved)# Parameters Category Value Units Remarks
1 Wavelength Tx 1310 nm “bhoja_01_0112”
2 Spectral width Tx 10 MHz assumption, normal DFB-LD
3 Extinction ratio Tx 8.0 dB “bhoja 01 0112” (*2)3 Extinction ratio Tx 8.0 dB bhoja_01_0112 ( 2)Sub-eye #7(mark) / #1(space)
4 RIN Tx -149 dB/Hz “bhoja_01_0112”
5 Transmitter reflectance Tx -30 dB Practical value of 100G-LR4
6 Responsivity Rx 1.0 A/W assumption
7 Receiver bandwidth Rx 12.5 GHz root raised cosine filter (*1)
8 Dark current Rx 100 pA assumption, negligible
9 Input referred noise Rx 15 pA/sqrt(Hz) “bhoja_01_0112”
10 Receiver reflectance Rx -30 dB Practical value of 100G-LR4
11 Rx OMA Link -7.75 dBm “bhoja_01_0112”
12 Transmission distance Link 1000 m12 Transmission distance Link 1000 m
13 Optical return loss Link Parameter dB*1) Both filter profile and formula are shown in Appendix.A*2) All sub-eyes have the same OMA.
Note
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Case2: Both ends of reflection are cabling fiber connectors.
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20 20
Case2: Calculated Q values of PAM8
14
16
18
valu
e (d
B)
14
16
18
valu
e (d
B)
10
12
14
1 2 3 4 5 6 7
Q v
10
12
14
1 2 3 4 5 6 7
Q v
12.6 dB (BER=1E-5) 12.6 dB (BER=1E-5)
20
1 2 3 4 5 6 7
Eye Number
1 2 3 4 5 6 7
Eye Number
20
ORL = 60 dB (APC connection) ORL = 40 dB (SPC connection)
14
16
18
valu
e (d
B)14
16
18
valu
e (d
B)
10
12
14
1 2 3 4 5 6 7
Q v
10
12
14
1 2 3 4 5 6 7
Q v
12.6 dB (BER=1E-5) 12.6 dB (BER=1E-5)
12
Eye NumberEye Number
ORL = 27 dB (ITU-T standard) ORL = 21 dB (IEEE 100G-LR4)
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25Case2: Simulation Result taking into account Link RIN
2060
27
ORL (dB)
15
Q (
dB)
21
12 6 dB (BER=1E-5)
10
Q 12.6 dB (BER=1E-5)
520 15 10 5 0 5-20 -15 -10 -5 0 5
Rx OMA (dBm)
Even PMD reflectance is improved, the result shows current ORL spec of
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Even PMD reflectance is improved, the result shows current ORL spec of cabling fiber is marginal for 100G-PAM8 to achieve required Q values.
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Case2: Simulation Result taking into account Link RIN25
20
15
Q (
dB)
12 6 dB (BER=1E-5)
10
Q 12.6 dB (BER=1E-5)
Rx OMA (dBm)
510 20 30 40 50 60
-10 -5 0
Rx OMA (dBm)
10 20 30 40 50 60
Optical Return Loss of Link (dB)Less than 27 dB of ORL spec seems too steep for FEC to be used
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Less than 27 dB of ORL spec seems too steep for FEC to be used due to FEC nature (Steep I/O performance of error correction).
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Conclusion
1. Multiple reflections in the SMF-Link may induce phase-noise converted RIN (Link RIN) which is different from intrinsic laser RIN.
2 C t ifi ti f b th ti l t l f SMF Li k2. Current specification of both optical return loss for SMF-Link connectors (21 dB) and reflectance for PMD (Tx -12 dB, Rx -26 dB) is not suitable for 100G PAM 8 or beyond.
3. Need further experimental verification of Link RIN effect under the practical conditions, i.e. state of polarization, laser linewidth and reach variation (coherent length).
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AppendixAppendix(Backup)
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A. Root raised cosine filter to be used for Q value Calculation10
-20
-10
0
e (d
B)
3 dB bandwidth = 12.5 GHz
50
-40
-30
20
Res
pons
e
-60
-50
0 5 10 15 20 25 30 35 40
Frequency (GHz)
Filter frequency-domain description is given by:
⎪⎪⎪⎧
+⎪⎫⎪⎧ ⎤⎡ ⎞⎛ ⎤⎡
−≤
TTT
fT
1112
1,2
βββπ
β
⎪⎪⎪
⎩
⎪⎨
+>
+≤<
−⎪⎭
⎪⎬⎫
⎪⎩
⎪⎨⎧
⎥⎦
⎤⎢⎣
⎡⎟⎟⎠
⎞⎜⎜⎝
⎛⎥⎦⎤
⎢⎣⎡ −
−⋅+⋅=
Tf
Tf
TTfTTfH
21,0
21
21,
21cos1
2)(
β
ββββπ
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where T is the symbol period and β is roll-off factor. In calculation, T = 29 ps (=34.375 Gbaud) and β = 1 are used.
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-80
Calculated RIN spectra at Rx side-80
(Laser RIN = -149 dB/Hz, BW = 1 MHz)
140
-120
-100
N (
dB/H
z)
140
-120
-100
N (
dB/H
z)
-180
-160
-140
0 1 1 10 100 1000 10000 100000
RIN
-180
-160
-140
0 1 1 10 100 1000 10000 100000
RIN
-80-80
0.1 1 10 100 1000 10000 100000
Frequency (MHz)
ORL = 60 dB (APC connection) ORL = 40 dB (SPC connection)
0.1 1 10 100 1000 10000 100000
Frequency (MHz)
-140
-120
-100
N (
dB/H
z)-140
-120
-100
N (
dB/H
z)
-180
-160
140
0.1 1 10 100 1000 10000 100000
RIN
-180
-160
140
0.1 1 10 100 1000 10000 100000
RIN
18
Frequency (MHz)Frequency (MHz)
ORL = 27 dB (ITU-T standard) ORL = 21 dB (IEEE802.3)
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-80 -80
Calculated RIN spectra at Rx side (Laser RIN = -149 dB/Hz, BW = 100 kHz)
140
-120
-100
N (
dB/H
z)
140
-120
-100
N (
dB/H
z)
-180
-160
-140
0 1 1 10 100 1000 10000 100000
RIN
-180
-160
-140
0 1 1 10 100 1000 10000 100000
RIN
-80
0.1 1 10 100 1000 10000 100000
Frequency (MHz)
0.1 1 10 100 1000 10000 100000
Frequency (MHz)
-80
ORL = 60 dB (APC connection) ORL = 40 dB (SPC connection)
-140
-120
-100
N (
dB/H
z)-140
-120
-100
N (
dB/H
z)
-180
-160
140
0.1 1 10 100 1000 10000 100000
RIN
-180
-160
140
0.1 1 10 100 1000 10000 100000
RIN
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Frequency (MHz)Frequency (MHz)
ORL = 27 dB (ITU-T standard) ORL = 21 dB (IEEE 802.3)
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