Chirp Managed Laser (CML) and Applications - IEE Managed Laser (CML) and Applications Daniel Mahgerefteh ... Methods for modulation of light: ... Direct Laser Modulation (e.g., DFB):

May 4, 2007 F I N I S A R C O R P O R A T I O N

Chirp Managed Laser (CML) and

Applications

Daniel Mahgerefteh

March 23, 2011

Outline of Talk   What is Chirp Managed Laser (CML)?   How CML works?   Applications of CML

  > 360 km reach 10 Gb/s NRZ with pluggable optics   RZ-Alternate Mark Inversion   RZ-DPSK, DPSK, DQPSK generation

  CML Device Technology   C band Tunable MGY DBR for 10 Gb/s CML   4 x 25 Gb/s FM DBR Array   PLC based CML

3

What is Chirp Managed Laser (CML™)?

  Methods for modulation of light:   External Modulation (e.g., EML):

+  Dispersion Limit (80km @ 10G) -  Requires modulator (e.g. EA, LiNbO3) -  Lower Output Power -  Power hungry Driver, higher cost

Direct Laser Modulation (e.g., DFB): +  Compact, Low consumption, low cost -  Dispersion Limit (5 km @ 10 G)

Chirp Managed Laser: +  Compact, Low consumption, low cost +  Dispersion Limit (> 200 km @ 10 G) +  Tolerance to negative dispersion +  Phase-Amplitude coding possible

Laser Modulator

Electrical DATA Optical DATA

Laser


Laser


Filter

1. Externally Modulated Laser

2. Directly Modulated Laser (DML)

Chirp Managed Laser (CML)

4

Value Proposition: Use Directly Modulated Laser as a low-power consumption, compact, high performance alternative to externally modulated sources for metro and long-haul.

EML InP-MZ

CMLTM

CML: Better performance at Lower cost without external Modulators

LiNbO3-MZ

CMLTM

MZ + Dispersion Comp. DFB/EML EML/MZ 2- 40 km 40 - 8km 80km-320km >2400km

5

What is Chirp?   Chirp is change in instantaneous frequency

(or wavelength) of an optical pulse with time   EMLs use negative transient chirp to

increase reach to 80 km @ 10 Gb/s   Red shifted chirp at rising edge   Blue shifted chirp at trailing edge   Blue is faster than red @ 1550 in SMF   Trailing edge catches up to rising edge   Pulse compresses after fiber   Bit Error Rate is improved up to a certain

distance before it gets progressively worse   DMLs have positive transient chirp, which

limits reach to 5 km at 10 Gb/s   Blue shifted chirp at rising edge   Red shifted chirp at falling edge

  DMLs also have adiabatic chirp   CML chirp and its use is a different story

El

ectr

ic F

ield

Time (fs)

Intensity Envelope Optical Carrier

Red Shift Blue Shift

Gaussian Pulse with Chirp

Vblue Vred

6

How CML works?   Ingredients for CML:

1.  High speed FM (Freq. Mod. source; DFB) 2.  Passive Optical Spectrum Reshaper (OSR) Filter 3.  Supporting Optics

  Main Recipe for CML: 1.  Reduce transient chirp 2.  Reshape amplitude profile 3.  Set adiabatic chirp appropriately 4.  Reshape frequency profile using OSR 5.  Lock DFB wavelength to OSR 6.  Compensate for Thermal Chirp

  Key characteristics of CML: 1.  CML is not an external cavity laser 2.  CML uses an isolated single mode DFB 3.  Mode stability, wavelength tuning determined by

DFB characteristics 4.  DFB wavelength is locked to OSR filter

DFB

Optical Filter

CML in TOSA package

Isolator

Multi-cavity Filter

PD1

PD2

10 Gb/s

DML

10 Gb/s

DML Multi-cavity Filter

PD1

PD2

Isolator

Multi-cavity Filter

PD1

PD2

10 Gb/s

DML

10 Gb/s

DML

10 Gb/s

DML

10 Gb/s

DML Multi-cavity Filter

PD1

PD2

Isolator

7

-6

-4

-2

0

2

4

0 200 400 600 800 1000Time (ps)

Transient chirp

Adiabatic chirp

Transient chirp

Not All Chirp in A Direct Mod Laser is Bad Chirp!

  How a standard Direct Mod is used:   Biased close to threshold, Ith   High transient chirp limited fiber

transmission   How CML Direct Mod is used:

  Bias high above laser threshold ~ 5 x Ith   Drive DFB to get 1-2 dB Extinction Ratio   Higher damping in DFB   Transient chirp reduced   High Extinction Ratio will be achieved by

Passing this signal through OSR filter

Determines Adiabatic Chirp

In the rest of this presentation when we say Chirp we mean Adiabatic chirp

8

•  Extinction Ratio: AMER = 1-2 dB

Dielectric Coatings Cavity

•  Extinction Ratio: ER = AMER + S x FM •  ER ~ 10-12 dB

AM ER ER

Filter increases Extinction Ratio by FM to AM conversion

Optical frequency Time

Before OSR After OSR

Inte

nsity

0 bits 1 bits

FM

OSR filter

Time

Inte

nsity

  Adiabatic chirp makes 1 bits blue shifted relative to 0 bits   Difference between optical frequency of 1 bits and 0 bits is FM ~ 3-8 GHz   Output of Direct Mod Laser is aligned with transmission edge of OSR filter   OSR filter discriminates 1s and 0s higher ER; filter edge slope ~ 1-2 dB/GHz

1 bits

0 bits Tr

ansm

issi

on

9

Key to Dispersion Tolerance of CML: Destructive Inter-symbol Interference

Standard NRZ

Constructive interference Pulses in phase

CML

Φ=0 Φ=0

Φ=0 Φ=π Destructive interference

Φ=0 Φ=π Pulses π out of phase

Dispersion

Dispersion

  Adiabatic Chirp to ~ ½ the bit rate 5 GHz for 10 Gb/s   CML Phase Rule: 1 bits separated by odd # of 0 bits are π out of phase   Destructive interference of 1 bits in the middle 0 bit slot keeps eye

open after fiber dispersion 0 km

100 km

150 km 200 km

100 km

250 km

0 km100 km

150 km 200 km

100 km 0 km100 km

150 km 200 km

100 km

250 km

CML @ 200 km

EML @ 80 km

10

Chirp ~ ½ Bit Rate makes carrier phase to slip by π every 0 bit

  Set adiabatic Chirp ΔfA ~ 5 GHz at 10 Gb/s

  Continuous π phase slip for each 0 bit   1 bits separated by odd # of 0s are π out of phase   Same as Optical Duobinary phase rule

ππφ =××=Δ psGHz 10052

Aligned with peaks

Time

Intensity Envelope

Optical Carrier

Red Shifted 0 bit

Φ = 0 Φ = π Time Ticks

1 bit

Aligned with troughs

Phase slipping…

1 bit

CML has no carrier and ½ the BW Standard NRZ

Φ=0 Φ=π

=

Φ=π

Φ=0

+

10 Gb/s

5 Gb/s

20 dB BW: 15 GHz

CML Laser

No Carrier

Standard NRZ

Carrier

20 dB effective BW: 33 GHz

Effective BW

  ½ of bits have 0 phase, ½ have π phase   Power in optical carrier is:

  Spectrum is ½ size of NRZ- 2 ways to see it:   1) Correlation between bits (e.g. 1 0 1 and 1

0 0 -1 cannot occur only 1 0 -1, and 1 0 0 1)   2) Random bit sequence @ 10 Gb/s is sum of

two sequences @ 5 Gb/s: e.g.

0~)()0(2

∫+∞

∞−== dttEP ω

But… Chirp = ½ bit rate is not enough!

  Simulations and experiments show that having chirp = ½ the bit rate (5 GHz for 10 Gb/s)…

for example, by using a DFB for FM generation and EA for get high Extinction Ratio…

can only get us to 120 km…

leaving 5 dB penalty at 200 km!

 What is missing?

What’s Missing?

Need to Convert Adiabatic Chirp to Flat Top Chirp with abrupt phase shifts

Freq

uenc

y (G

Hz)

0

5

10

15

20

-10

-5

0

5

10

1 0 1 1 0 0 1 0 0

Inte

nsity

Adiabatic Chirp

0

5

10

15

20

-5

-4

-3

-2

-1

0 Ph

ase

(x π

radi

ans)

Inte

nsity

Adiabatic Phase Change 0

5

10

15

20

-50 -40 -30 -20 -10 0 10

Freq

uenc

y (G

Hz)

Flat Top Chirp

Inte

nsity

In

tens

ity

0

5

10

15

20

-5

-4

-3

-2

-1

0 π π

2π

Phas

e (x

π ra

dian

s) Abrupt Phase Change

Adiabatic Chirp vs Flat Top Chirp

  Nonlinear phase across pulse   Perfect cancellation at one point   Incomplete cancellation in 0 bits   5 dB penalty at 200 km

  Constant phase across pulse   Cancellation across pulse   Better destructive interference in 0 bits   1 dB penalty at 200 km

Filter Convert Adiabatic to Flat Top Chirp by AM to FM conversion

  Pass signal through a filter edge   Ignore phase of filter for now…

  OSR adds weighted 2nd derivative of AM to frequency profile

Δ+

′−Δ

=Δ

−

))()(()(tan)(

)(

1

tbatAtAb

dtdt

tAfter

ωω

ω

ω

)()()( inputinput tEdtdibtaEtEAfter +=

ωω baT +=)(OSR

Input signal

The i in this term converts AM to FM

-100 -80 -60 -40 -20 0 20 40 60 80 100 -0.02

0

0.02 Fr

eque

ncy

(GHz

) -100 -80 -60 -40 -20 0 20 40 60 80 100 0

0.5

1

Inte

nsity

Time

)(tA is envelope of input signal

)()( tAt ∝ω is input adiabatic chirp

b is OSR slope

Flat Top Chirp

Spike Chirp

After OSR

Flat Top Chirp and Abrupt Phase Change Require High OSR Slope

0

1

2

3

4

5

6

7

-400

-300

-200

-100

0

100

1.1 1.2 1.3 1.4 1.5 1.6Time (ns)

Low Slope OSR 1 dB/GHz

High Slope OSR 1.8 dB/GHz

High resolution measurements courtesy of APEX


  200 km reach at 10 Gb/s pluggable XFP transceiver product   > 360 km reach 10 Gb/s NRZ with driver pre-emphasis   RZ-Alternate Mark Inversion   RZ-DPSK, DPSK, DQPSK generation


18

EDC ON

111213141516171819202122

-3000 -2000 -1000 0 1000 2000 3000 4000 5000 6000

DISPERSION (ps/nm)

Req

uire

d O

SN

R fo

r B

ER

= 1

x10-3

(dB

)

1-dB window: -2150ps/nm to +4000ps/nm

111213141516171819202122

-3000 -2000 -1000 0 1000 2000 3000 4000 5000 6000

DISPERSION (ps/nm)

Req

uire

d O

SN

R fo

r B

ER

= 1

x10-3

(dB

)

EDC OFF

1-dB window: -1900ps/nm to +3600ps/nm

-1700ps/nm +3400ps/nm 0ps/nm

S. Chandrasekhar et al. OFC 05 Post Deadline paper PD30

DFB

OSR

DM200 CML™ reaches over 5 x dispersion limit

Standard externally modulated transmitter is limited to ~ 1600 ps/nm

Detectors

18.3 mm x 78 mm x 8.5 mm

XFP

Demonstration of 360 km Reach using pre-emphasis CML

9© 2008 Finisar Corporation, Confidential

Fig.5

Fig.5 Performance comparison of CML with Uni-polar chirp and EDC.Fig.5 Performance comparison of CML with Uni-polar chirp and EDC.

10111213141516171819

0 100 200 300 400

Transmission Distance (km)

Req

uire

d O

SNR

(dB

/0.1

nm)

  At 250 km the reach of CML is limited by distortion of the 1 0 sequence

  Pre-emphasis on 1 0 transitions (uni-polar transient chirp) mitigates distortion of isolated 1 bits after fiber

  Uni-polar chirp red shifts trailing edge of isolated 1s and cause destructive interference with adjacent 0 bit

  Used Finisar driver with 1 bit Digital Signal Processing (DSP) pre-emphasis

  Power consumption of DSP = 30 mW   SFP+ Transceiver Power consumption,

including Tx, and Rx < 1.2 W   Longest Reach/Power Consumption solution

for > 300 km reach

Xueyan Zheng et al. OFC 2009

300 km BB

© 2008 Finisar Corporation, Confidential

Comparison of the key bits with and w/o uni-polar chirp

Proprietary and Confidential Information of Azna LLC

t t

t t

VB > VR

VR

VB

VR

VB > VR

VR

VT

VR>VT

Before Fiber After Fiber

With Uni-Polar Chirp

Without Uni-Polar Chirp

Destructive Interference

No Interference

RF with uni-polar function

RF without uni-polar function

  Drive CML with standard RZ signal   Adiabatic chirp ~ 10 GHz   Adiabatic chirp generates π shift

between adjacent 1 bits (RZ-AMI):

  Narrower spectrum than RZ-OOK, and suppressed carrier

  Higher Tolerance to dispersion, nonlinearity:

  1 dB penalty dispersion window: -450 ps/nm to 950 ps/nm (compared with +/-550 ps/nm for RZ-OOK)

  Replaces DFB + MZ + 1 bit delay line interferometer

  9000 km transmission with CML RZ-AMI

CML can generate RZ-Alternate Mark Inversion (AMI)

ER ~ 15 dB

+1 -1 0 +1 -1 0 0 +1

Example of an AMI bit sequence

50 ps

~10 GHz

AM

FMππ =×× ps5GHz 102 0

S. Chandrasekhar et al. ECOC Post Deadline session 2, (2005)

21

CML can generate RZ-DPSK signal

Patents Pending

  Drive CML with a 3 level RZ driver at bit rate B:   Apply ΔI during 1st ½ bit period to get π shift chirp = bit rate   Apply 2ΔI during 1st ½ bit period to get 2π shift chirp = 2 x bit rate   OSR filter equalizes amplitudes and produces abrupt phase transitions   No differential coding needed! (since phase shift is integral of chirp)

FINISAR CONFIDENTIAL 27

Frequency

CML Output Power

f2

Time

DFB Current

I0

f1

f0

I1 I2

23

CML can generate RZ-DPSK

• Drive current change 2ΔI causes adiabatic chirp 2Δf for a 2π phase change representing a Zero bit

• Drive current change ΔI causes adiabatic chirp Δffor a π phase change representing a One bit

ZERO

ONE

0 0 1 0 1Input

Cur

rent

Pha

se

0 π

Chi

rp (G

Hz)

Tππ2π3π4π5

0

0

f2f1f0

Driver Output

Output after OSR

Laser OutputBefore OSR

Time

0

π

0

0

π

0 π

I2Δ IΔ

f2Δ fΔ

Demonstrations of RZ-DPSK using CML •  RZ-DPSK at 2.67 Gb/s (J. Franklin et al.)

•  Tri-level swings 13 mA pp and ~26 mA pp •  Chirp levels = 3 GHz and 6 GHz •  1550 nm DFB FM efficiency 0.24 GHz/mA •  Output power of CML 3.5 dBm •  0.7 dB penalty compared to RZ-DPSK

generated using 2 x LiNbO3 modulators

•  RZ-DPSK CML at 10 Gb/s requires 20 GHz chirp Not sufficient FM efficiency in current 10 G DFB (1550 nm BH)

•  DPSK- CML at 10 Gb/s requires 10 GHz chirp: use 0 phase instead of 2π

•  Current DFB has sufficient FM efficiency

•  W. Jia et al. demonstrated DPSK CML as well as DQPSK CML (OFC 2011) using standard 10 G CML in XFP

•  Performance of at 10 G limited by bandwidth, of DFB laser used

-56 -55 -54 -53 -52 -51 -50 -49 -48 -47 -46-10-9

-8

-7

-6

-5

-4

-3

-2

Received Power (dBm)

Log(

BER

)

Lithium NiobateCML-RZ-DPSK

J. Franklin et al. OFC 2008

Wei Jia et al. PTL 23, p. 173 (2011)

RZ-DPSK @ 2.67 Gb/s

DPSK CML at 10 Gb/s


  > 360 km reach 10 Gb/s NRZ pluggable optics   RZ-Alternate Mark Inversion   RZ-DPSK, DPSK, DQPSK generation


Gain

FilterBS

PD

PD

BS

PD

OSR Filter10-Gb/s MG-Y laser

Gain

MMI (phase)DBR

PDS bendMMI

DBR

C band Tunable 10 Gb/s Modulated Grating Y branch (MGY) DBR CML

Active

MG DBR Right

MG DBR Right

12µm gap12µm gap

50µm

50µm

200um penetration

200um penetration

350µm350µmPassivePassive

GainGainGainMMI (Phase)MMI (Phase)MMI (Phase)

S bend (thermal chirp compensation)S bend (thermal chirp compensation)S bend (thermal chirp compensation)MG DBR Left

MG DBR Left50µm

50µm

1.38Q, 350nm thick1.38Q, 350nm thick1.38Q, 350nm thick

MG DBR Right

MG DBR Right

12µm gap12µm gap

50µm

50µm

200um penetration

200um penetration

350µm350µmPassivePassive

GainGainGainMMI (Phase)MMI (Phase)MMI (Phase)

S bend (thermal chirp compensation)S bend (thermal chirp compensation)S bend (thermal chirp compensation)MG DBR Left

MG DBR Left50µm

50µm

1.38Q, 350nm thick1.38Q, 350nm thick1.38Q, 350nm thick

  Injection tune DBR L,R with Vernier effect Full C band tuning

  FM efficiency (FM) and relaxation oscillation frequency, fr are diluted by the passive section

  Key Elements of Design:   Reduce passive length   Very high speed, high FM Active section

PD = photodiode BS = beam splitter

%54≈+

∝PassiveActive

Active

LLLFM

%74≈+

∝PassiveActive

Activer LL

Lf

Yasuhiro Matsui et al. ECOC Post Deadline paper p1-2 (2009)

Tunable high speed, high FM MGY DBR

•  Laser Design parameters: •  Y branch gap reduced from 30 um for CW laser design to 12 um

reduce S bend increase Lactive/Ltot

•  Gain: 8 strained MQWs High speed: fr = 11-15 GHz •  Gain: 100 nm SCH layers High FM efficiency: 0.13-0.18 GHz/mA •  fr varied with wavelength due to detuning and with DBR bias due to loss

• 

-6

-3

0

3

6

0 5 10 15Frequency (GHz)

FM

res

po

nse

(d

B)

35°C - 1536nm35°C - 1567nm50°C - 1538nm50°C - 1570nm

3-dB BW: 18 GHz at 35°C

FM frequency response


Resonant Frequency of MGY laser, fr > 10 GHz

10

11

12

13

14

15

16

1520 1530 1540 1550 1560 1570 1580Wavelength (nm)

Res

onan

t fre

quen

cy (G

Hz) Injection to DBR

Fr: 11 GHz – 15 GHz

Injection to DBR increases loss in DBR:• Reduces differential gain and therefore Fr

Fr : 11 GHz – 15 GHz• Fr at longer wavelength is smaller due to detuning from gain peak• Dilution of Fr compared to FP laser is ~ 75% near gain peak (expected)• Detune loading effect slightly favors Fr at the expense of FM

High

LowFP for 300µm cavityFr = 17 GHzK factor = 0.17 ns

24 1

g tot z

Kdg

π ευ α

= +

Γ ⋅

K factor: 0.3ns – 0.5ns

H

Low

Relaxation oscillation frequency


24% mask margin

Tunable MGY CML using Delayed-Line Interferometer filter for < 100 km

FSR=21 GHz DLI filter shape

-60

-50

-40

-30

-20

-10

0

1538.8 1538.9 1539 1539.1 1539.2 1539.3 1539.4Wavelength (nm)

Tran

smis

sion

(dB

)

Output SpectrumInput Spectrumfilter with 21 GHz FSR

Before DLIBefore DLIBefore DLI

After DLIAfter DLIAfter DLI

-60

-50

-40

-30

-20

-10

0

1538.8 1538.9 1539 1539.1 1539.2 1539.3 1539.4Wavelength (nm)

Tran

smis

sion

(dB

)

Output SpectrumInput Spectrumfilter with 21 GHz FSR

Before DLIBefore DLIBefore DLI

After DLIAfter DLIAfter DLI

  Use Delay Line Interferometer (DLI) OSR filter instead of 3 cavity band-pass used before

  DLI filter is not bandwidth limiting   Rise-fall times after DLI filter are shorter than at

output of laser due to FM/AM conversion   Improved mask margin for CML   Dispersion tolerance limited to 100 km

Higher harmonics passed throughHigher harmonics Higher harmonics passed throughpassed through

1.E-121.E-111.E-101.E-091.E-081.E-071.E-061.E-051.E-041.E-03

-32 -30 -28 -26 -24 -22 -20

Received Power (dBm)

Bit

Erro

r Rat

e

1565-L

1559-H

1553-L

1533-L

1529-H

1553 L

1535 H

1553 H

1559 H

1565 H

OSNR = 26 dB/0.1 nm1600 ps/nm@ 10.5 Gb/sPRBS 231-1

OSNR = 26 dB/0.1 nm1600 ps/nm@ 10.5 Gb/sPRBS 231-1

4 x 25 Gb/s DBR Laser Array CML (S. Matsuo et al. NTT)   Key design feature: FM generated by in-

cavity phase modulation   Speed of FM limited only by RC time constant

and cavity FSR   speed not limited by gain dynamics   Loss modulation of phase section has to be

minimized (high α modulator)   Using SOA to compensate loss of MMI   OSR filter BW = 20 GHz, slope = 0.8 dB/GHz   2 Vpp applied to phase 10 GHz chirp   Demonstrated Performance:   Extinction Ratio = 5 dB   40 km reach at 25 Gb/s   Potential Application to DWDM 100 G

S. Matsuo et al., PTL , vol. 20 p. 1494 (2008)

Phase section

Data modulation

gain MMI combiner

Photonics Integrated Circuit (PLC) CML (Y. Yokoyama NEC)

  Feature of device:   10 G DFB flip-chipped onto Si platform   SiON waveguide on Si ring resonator OSR

filter no optical isolator needed   Single ring equivalent to single cavity filter

BW and slope are constrained   Metal heater on ring adjusts wavelength   Monitor diodes used to lock laser

wavelength to ring filter by tuning temperature of PLC

  Size: 2 mm x 2.9 mm   Performance:   ER = 7 dB   300 km reach @ 10 Gb/s ~ 15 dB OSNR   Power consumption for XFP < 3 W

PLC based CML

Conclusion

Laser Chirp is a Good Thing!

May 4, 2007 F I N I S A R C O R P O R A T I O N

Backup Slides


Digital pre-emphasis of CML: Towards 500 km Reach at 10 Gb/s   Digital pre-emphasis concept:   At each distance a particular sequence of ‘problem bits’ limit the BER   Problem bits up to 200 km: 101   Problem bits for 300-400 km: 010, 011, 110

  Pre-emphasis of ‘problem’ bit sequence by driver DSP to clean up distortion after fiber

  Longer distance requires more bits   Simulation:   Reach > 450 km with 6 bit DSP   Eye remains open 0-450 km   Back-to-back eye suffers some penalty   Driver DSP power consumption 200mW

assuming Bi-CMOS technology   Work needed to further optimize reach   EDC at receiver can extend reach further

Bit time slots

5

7

9

11

13

15

17

19

21

23

25

0 100 200 300 400 500

Transmission Distance (km)

Requ

ired

OSNR

for 1

0-3

BER 6 Bit DSP

1 Bit DSP

Simulation courtesy of Bob Drost, Finisar

Other features needed to make CML work

1.  OSR filter limits band width of resulting spectrum Increases rise-time/fall times Less dispersion

–  OSR bandwidth chosen to be ~ 8 GHz for 10 Gbps 2.  Lock DFB wavelength to OSR

–  OSR edge doubles up as in-line wavelength locker 3.  Compensate for Thermal Chirp

–  Heating of laser by injection generates unwanted red chirp at low frequencies base line wonder of chirp

–  Thermal chirp compensated using low frequency bias circuit –  Integrate incoming data with 20 MHz low pass filter –  Use this signal to pull laser DC bias to generate proportionate blue chirp

–  Requires DFB to have sufficiently high FM efficiency –  For DBR laser, phase section or DBR section provide independent knob

for better compensation

Compensate for Thermal Chirp using Low Frequency Circuit

  Thermal chirp shifts to the red for long series of 1 bits

  Adiabatic chirp blue shifts   Compensation circuit pulls bias

up for long series of 1s   Additional blue shift cancels

thermal red shift   Circuit BW < 100 MHz

Time

Laser Current

Laser Temperature

Laser Frequency drift due to Thermal Chirp

High Density of 1s High Density of 0s

Intensity Output of OSR without Thermal Compensation

Time

Laser Frequency with Thermal Chirp Compensation

Laser Package

CF

RF

RF

50Ω

R1

R1 R2

RL

Driver

DATA

DATADC

Block

C1

CF

+-

-5V

-+

-5V

-5V

5V

R3

Laser Package

CF

RF

RF

50Ω

R1

R1 R2

RL

Driver

DATA

DATA

Driver

DATA

DATADC

Block

C1

CF

+-

-5V

-+

-5V

-5V

5V

R3

Compensation circuit

CML Chirp Tolerance for 200 km

  There is only ~ 1 dB sensitivity penalty for +/-15% change in chirp   Aging of DFBs show < 3% change in FM over 110 yrs (limited by measurement

error 3σ +/5%)   Interference power scales as cos2(Δφ), which is slow near 0 good

tolerance

-28 -27 -26 -25 -24 -23 -22 -21 -20 -19 -18

-40 -30 -20 -10 0 10 20 30 Change in Chirp (%)

Sens

itivi

ty a

t BER

=1e-

12 (d

Bm

) BB 200km

Clean zero Bump does not close the eye

Intensity

Flat Top Chirp

Isolated 1 Bits Compress by Destructive Interference

blue

red red

Back-back 200 km

  Isolated 1 bit interferes with 0 bit in leading edge   Oscillations open the eye around isolated 1 bit   After a certain distance bump in leading edge generates 01 errors

Documents

Chirp Managed Laser (CML) and Applications - IEE Managed Laser (CML) and Applications Daniel Mahgerefteh ... Methods for modulation of light: ... Direct Laser Modulation (e.g., DFB):