Optical Short Pulse Generation and Measurement Based on Fiber Polarization Effects

Transcription

1 Opical Shor Pulse Generaion and Measuremen Based on Fiber Polarizaion Effecs Changyuan Yu Deparmen of Elecrical & Compuer Engineering, Naional Universiy of Singapore, Singapore, A*STAR Insiue for Infocomm Research (I2R), Singapore

2 Thanks o Jing Yang Dr. Zhaohui Li Dr. Yixin Wang Dr. Ting Luo Dr. Alan E. Willner

3 Applicaions of Opical Pulse Train Reurn-o-zero (RZ) and carrier-suppressed RZ (CSRZ) modulaion formas can be creaed from pulse rains. RZ and CSRZ have been shown o be robus o fiber-based degrading effecs for many high-speed, long-disance ransmission sysems. Oher applicaions: high speed opical ime division muliplexing (OTDM), all-opical regeneraion and opical sampling. Cos-effecive, high speed, chirp-free RZ and CSRZ pulse rain generaion is desired.

4 Ouline 1. Inroducion 2. Muli-Channel 4-GHz Opical Pulse Train Generaion 3. Muli-Channel 16-GHz Opical Pulse Train Generaion 4. Measuremen of Pulse Widh of Shor Pulses 5. Summary

5 High-Repeiion-Rae Pulse Train Generaor Convenional Mehod: Shor Pulse Mode-locked Laser Expensive High-Speed Pulse Train Spliing/Delay/Mux Mode-locked laser is expensive equipmen. Single channel. The uning range of he wavelengh is limied.

6 High speed Opical Pulse Train Generaion Prior Work Elecro-absorpion (EA) modulaor: high exincion raio and muli-channel operaion are hard o achieve and expensive drive elecronics is required. Fiber based opical parameric amplificaion (OPA) o conver a pulsed pump source a a fixed wavelengh ino a pulsed signal a a unable idler wavelengh: requires a very high power EDFA.

7 Pulse Train Generaion Based on MZM Prior Work Elecro-opical (E-O) Mach-Zehnder inensiy modulaor (MZM) driven by an elecrical clock wih peak-o-peak volage value of V π a he desired daa rae: requires he use of a high-speed inensiy modulaor and driver for RZ generaion. MZM driven a half he bi rae bu wih a peak-o-peak volage value of 2V π wih differen biases: he high peak-opeak volage is difficul o achieve a high frequency. Dual-driven MZM which requires wo ses of elecrical drivers.

8 Ouline 1. Inroducion 2. Muli-Channel 4-GHz Opical Pulse Train Generaion 3. Muli-Channel 16-GHz Opical Pulse Train Generaion 4. Measuremen of Pulse Widh of Shor Pulses 5. Summary

9 Pulse Train Generaion Based on Phase Modulaor We demonsrae 4-GHz opical pulse rain generaion by employing an E-O phase modulaor ha is driven by a clock a only half he bi rae and a peak-o-peak volage value of V π, wih a polarizaion-mainaining (PM) fiber as inerferomeer. (C. Yu e al., PTL 26.) We exend his echnique for WDM applicaions and demonsrae ITU-grid muli-channel high-speed opical pulse rain generaion by using a single se of phase modulaor and PM fiber. (C. Yu e al., CLEO 27.) Advanages: cos-effecive and seamlessly inegraed wih opical fiber sysems, and has no high-power requiremen.

10 Concep of Pulse Generaion Using a Phase Modulaor and PM Fiber PSP 1 Phase Mod. Ligh 45 o PSP 2 PM Fiber phase T 2T phase Polarizer Afer half-frequency (2-GHz) sinusoidal phase modulaion, he ligh is spli equally ino he wo principal-saes-of-polarizaion (PSPs) of he PM fiber. Differenial group delay (DGD) provides a one-bi ime shif (T=25 ps) beween he wo polarizaion componens of he ligh. A he oupu of he PM fiber, due o beaing of he wo replicas of he ligh, one polarizaion, aligned 45 o wih respec o he PSPs, generaes an 4-GHz RZ pulse rain, whereas he orhogonal polarizaion generaes a 4-GHz CSRZ pulse rain. beaing 45 o Inensiy T Pulse Train

11 Calculaion of 4-GHz Pulse Generaion The opical fields of hese wo replicas afer he PM fiber: PSP1: PSP2: E E 1 2 = = A π π cos( sin 2 2 T + ω) A π π ( T ) cos sin 2 2 T + ω = A 2 π π cos( sin 2 T + ω) when ωt = kπ and k is an ineger. Afer a polarizer: +45 o o PSPs (33%RZ): -45 o o PSPs (67% CSRZ): E E E 2 E π π Acos( sin ) cos( ω ) 2 T = E For 4 GHz pulse generaion, f=4 GHz and T=1/f=25 ps. The generaed pulse rains are chirp free. + 2 E π π Asin( sin )sin( ω ) 2 T =

12 Experimenal Seup ITU-grid WDM laser sources PC 2 G Clock phase Phase Mod. PC 25 ps PM fiber phase T PC 2T PBS Inensiy T 4G RZ Pulse Train Inensiy T 4G CS-RZ Pulse Train A polarizaion conroller (PC) is used o align he ligh o be along he direcion of 45 o o he PSPs of he PM fiber. Anoher PC is used o align he polarizaion beam splier (PBS) o also be 45 o o he PSPs of he PM fiber.

13 Transmission Specrum of he Inerferomeer Transmission (db) Pol. 1 Pol Ligh Frequency Spacing (GHz) Noe ha PM fiber wih PBS works as one-bi delay (T=25 ps) inerferomeer wih a FSR of 1/T (4 GHz). Therefore, he channel spacing should be inegral imes of 2 GHz, which maches he 1-GHz-channel-spacing ITU-grid DWDM sysems.

14 Opical Specra (Channel THz) 4-GHz RZ Pulse Train 4-GHz CSRZ Pulse Train (dbm) nm (4 GHz).5 nm (dbm) nm (4 GHz).5 nm nm nm In our experimen, 4-channel ITU grid lighs wih a channel spacing of 2 GHz are launched ino he sysem a he wavelenghs of nm (193.8 THz), nm (193.6 THz), nm (193.4 THz), and nm (193.2 THz).

15 Opical Specra (The Oher 3 Channels) Channel THz Channel THz Channel THz (dbm) -2 RZ.32 nm (4 GHz).5 nm (dbm) -2 RZ.32 nm (4 GHz).5 nm (dbm) -2 RZ.32 nm (4 GHz).5 nm nm nm nm (dbm) -2 CSRZ.32 nm (4 GHz).5 nm (dbm) -2 CSRZ.32 nm (4 GHz).5 nm (dbm) -2 CSRZ.32 nm (4 GHz).5 nm nm nm nm The unwaned 2 GHz ones of RZ are suppressed by > 3 db. The opical carriers of CSRZ are suppressed by > 35 db.

16 Waveforms of he Generaed RZ and CS- RZ Pulse Trains (Channel THZ) 4-GHz RZ Pulse Train 1 ps 4-GHz CSRZ Pulse Train 1 ps The observed waveforms of 33% RZ and 66% CSRZ look similar due o he bandwidh limiaion of he phoodiode.

17 Ouline 1. Inroducion 2. Muli-Channel 4-GHz Opical Pulse Train Generaion 3. Muli-Channel 16-GHz Opical Pulse Train Generaion 4. Measuremen of Pulse Widh of Shor Pulses 5. Summary

18 ITU-grid muli-channel 16-GHz Pulse Train Generaion Based on Phase Modulaor Our Mehod: Low cos Easy operaion f/4 Clock Laser Phase Mod. PM Fiber Seamlessly inegraed wih fiber sysems No high-power requiremen Pulse Train Repeiion Rae: f PM Fiber We demonsrae single-channel 16-GHz opical pulse rain generaion by employing a phase modulaor wih wo sages of PM fiber. We hen exend his echnique for WDM applicaions and demonsrae ITU-grid muli-channel 16-GHz opical pulse rain generaion. C. Yu e al., ICICS 27

19 16-GHz Pulse Generaor Using a 4-GHz Phase Modulaor and PM Fiber f/4 Phase Mod. f=16 GHz Phase T=1/f=6.25 ps 4T Laser f/4 Clock Phase Mod. 2T PM Fiber 1 s Sage f/2 RZ f CSRZ Ampliude Inensiy -45 o 45 o 2T PM Fiber 2 nd Sage T An 8-GHz opical RZ pulse rain is generaed by consrucive beaing of a 4-GHz phase modulaed ligh a he firs sage. A 16-GHz opical CSRZ pulse rain is generaed by desrucive beaing of he wo replicas of he ligh a he second sage.

20 1 s Sage: f/4 Phase Mod. f/2 RZ Pulse Train f/4 Phase Mod. f/2 RZ Phase 4T 2T Phase Mod. Ligh 2T PSP 1 phase 4T 45 o PM Fiber E 1 PSP 2 E 2 beaing 45 o phase Polarizer E 3 Ampliude 2T DGD of PM fiber makes a wo-bi ime (2T) shif beween he wo replicas (E 1 and E 2 ) of he ligh. Afer he polarizer, he componens of E 1 and E 2 consrucive bea wih each oher and produce: E 3 (E 1 + E 2 ). E 3 is chirp-free 33% RZ pulse rain a a repeiion rae doubling he frequency of phase modulaion.

21 1 s Sage: f/4 Phase Mod. f/2 RZ Pulse Train Afer PM Fiber (When ωt = kπ ): (For 16G pulse generaion, f=16 GHz and T=1/f=6.25 ps) E E 1 2 = = A 2 A 2 π cos( sin 2 π 2T + ω); π π ( 2T ) cos sin + ω 2 2T E1 + E2 π π E3 = Acos( sin )cos( ω) 2 2 2T = A 2 π cos( sin 2 π 2T + ω) Afer Polarizer: (by consrucive beaing of a 4-GHz phase modulaed ligh) (f/2 = 8GHz chirp-free 33% RZ pulse rain) (f/4=4g Phase Modulaion)

22 2 nd Sage: f/2 RZ f CSRZ Pulse Train f/2 RZ f CSRZ Ampliude PSP Ampliude 1 E beaing 3a E 45 o 3 45 o + E 4 PM Fiber PSP 2-2T E 3b 2T Polarizer Inensiy T DGD of PM fiber makes a one-bi ime (T) shif beween he wo replicas (E 3a and E 3b ) of he ligh. Afer he polarizer, he componens of E 3a and E 3b desrucive bea wih each oher and produce: E 4 (E 3a E 3b ). E 4 is chirp-free 5% CSRZ pulse rain a a repeiion rae doubling he repeiion rae of E 3.

23 2 nd Sage: f/2 RZ f CSRZ Pulse Train Afer 2 nd PM Fiber (When ωt = 2kπ ): (For 16G pulse generaion, f=16 GHz and T=1/f=6.25 ps) π π E (f/2 = 8 GHz RZ pulse rain) 3 a Acos( sin )cos( ω) 2 2T π π ( T ) π π E3 b Acos sin cos( ) Acos( cos )cos( ) 2 2T ω = ω 2 2T Afer 2 nd Polarizer: (by desrucive beaing of he wo replicas of he ligh) E3a E3b π π π π E4 = = f ( ) A cos( sin ) cos( cos ) cos( ω) 2 2 2T 2 2T f ( + T ) = f ( ); f ( NT + T / 2) = (f = 16 GHz chirp-free 5% CSRZ pulse rain)

24 Simulaion Resuls for Waveforms of Pulse Trains 8-GHz 33% RZ afer he 1 s Sage 16-GHz 5% CS-RZ afer he 2 nd Sage VPI Simulaion shows ha 8-GHz RZ and 16-GHz CSRZ are generaed, which is consisen wih calculaion resuls.

25 Transmission (db) Transmission Specra of he Inerferomeers (relaive o THz) he Firs Sage he Second Sage Relaive Frequency of he Ligh (GHz) The 1 s sage of he PM fiber wih polarizer works as wo-bi delay (2T=12.5 ps) inerferomeer wih a FSR of 1/(2T) (8 GHz). The 2 nd sage works as one-bi delay (T=6.25 ps) inerferomeer wih a FSR of 1/T (16 GHz). Therefore, he channel spacing should be inegral imes of 16 GHz, which maches he 8-GHz-channel-spacing ITU-grid DWDM sysems. Transmission (db) Relaive Frequency of he Ligh (GHz)

26 Experimenal Seup of 16-GHz Pulse Generaion Using Phase Modulaor and PM fiber 4 G Clock 8G RZ Pulse Train 16G CS-RZ Pulse Train ITU-Grid WDM Laser Source Phase Mod ps PM fiber 6.25 ps PM fiber PC Polarizer PC PC PC 45 o 45 o 45 o 45 o Sage 1 Sage 2 Polarizer PCs are used o align he ligh o be along he direcion of 45 o wih respec o he PSPs or polarizer. All he PCs could be eliminaed by 45 o splicing he PM fiber. 4-channel ITU grid lighs wih a channel spacing of 8 GHz are launched ino he sysem.

27 Simulaion Resuls of Opical Specra (Channel THz) 8-GHz 33% RZ afer he 1 s Sage (dbm) 8 GHz (.64 nm) 1 nm 16-GHz 5% CSRZ afer he 2 nd Sage (dbm) 16 GHz (1.28 nm) 1 nm nm nm Afer he 1 s sage, he unwaned 4-GHz ones are filered ou. Afer he 2 nd sage, he unwaned carrier and 8-GHz ones are filered ou.

28 Opical Specra (The Oher 3 Channels) Channel THz Channel THz Channel THz (dbm) (dbm) (dbm) 1 nm 1 nm 1 nm -1 (dbm) nm 1 nm -1 (dbm) nm 1 nm -1 (dbm) nm 1 nm nm nm nm The oher 3 channels have he same resuls. The channel spacing is 8 GHz (5 imes of 16 GHz).

29 1 s Sage: 4-GHz Clock 8-GHz RZ Pulse Train (dbm) Opical Specrum 8 GHz.64 nm nm 1 nm Auocorrelaor Measuremen.5 ms Scale Facor: 7.41 ps/ms The unwaned 4-GHz one in he specrum of he RZ pulse rain is suppressed by abou 3 db. The measured pulse widh:.8*7.41*.74=4.4 ps, close o heoreical value of 4.16 ps.

30 2 nd Sage: 8-GHz RZ Pulse Train 16-GHz CSRZ Pulse Train (dbm) Opical Specrum 16 GHz 1.28 nm nm 1 nm Auocorrelaor Measuremen.5 ms Scale Facor: 7.41 ps/ms The unwaned lower ones (4 & 8 GHz) are suppressed by more han 25 db. The measured pulse widh:.45*7.41*1.=3.3 ps, close o heoreical value of 3.12 ps.

31 Ouline 1. Inroducion 2. Muli-Channel 4-GHz Opical Pulse Train Generaion 3. Muli-Channel 16-GHz Opical Pulse Train Generaion 4. Measuremen of Pulse Widh of Shor Pulses 5. Summary

32 Auocorrelaor for Measuremen of Pulse Widh Convenional Auocorrelaor Concep f(τ) Delay Sage (τ) τ Nonlinear Effec f(τ) τ Michelson inerferomeer Second harmonic generaion (SHG), Two-phoon absorpion (TPA) Free space based, difficul alignmen All fiber based, wavelengh independen, easy alignmen are desirable for an auocorrelaor.

33 (T. Luo e al., PTL 26) OFC 25 Previous All-Fiber Based Technique Delay Sage (τ) Tunable Differenial-Group- Delay (DGD) Elemen New Technique Delay Sage (τ) Tunable DGD Elemen Nonlinear Effec f(τ) Polarimeric FWM in HNLF High opical power is required Nonlinear Effec f(τ) Pulse s Degree of Polarizaion (DOP) Much simpler, no high opical power is required

34 DOP Dependence of DGD and Pulse Widh x (fas axis) W 45 y (slow axis) DGD elemen (DGD) DGD DOP = 1 < DOP (DGD, W) < 1 x y DOP ( DGD ) = R in (DGD) 2R + R () in in (-DGD) = R in(dgd) R in() R in is he auocorrelaion funcion of he pulse

35 Auocorrelaor Concep 45 τ fas axis DOP(DGD) Tunable DGD Elemen (DGD) slow axis DOP Measuremen DGD Delay sage: he pulse is spli ino wo polarizaion saes and he wo replica have a relaive delay of DGD DOP Measuremen: DOP depends on he shape of he incoming signal and DGD. The race of DOP vs. DGD emulaes he auocorrelaion funcion of he pulse Pulse FWHM = DOP Trace FWHM *Scaling Facor

36 Simulaion Resuls of DOP Measuremen for Pulses 8 GHz and 16 GHz pulse rains GHz pulse GHz pulse.8.8 DOP ps ps Relaive delay/dgd (ps) Relaive delay/dgd (ps) DOP changes periodically wih DGD. Full Widh a Half Maximum (FWHM) of he DOP race is proporional o he pulse widh.

37 Experimenal Seup Pulse Under Tes 45 Tunable DOP DGD Meer Pulses under es: 1, 2 and 4 GHz RZ Pulse Trains Mode-Lock Laser Pulse Train Opical power for DOP measuremen: -6 dbm dbm Resoluion of unable DGD: 1.4 ps

38 DOP (%) Experimenal Resuls RZ Pulse Scaling Facor Calibraion 12.6 ps 22.6 ps 47 ps Trace FWHM : 47, 22.6, 12.6 ps Oscilloscope: 43, 23, 12.5 ps GHz RZ 2 GHz RZ 4 GHz RZ DGD (ps) DGD (ps) Scaling facor = 1 Pulse FWHM = Trace FWHM *1 The scaling facor of RZ pulses is 1. The measuremen resuls are close o he resuls of oscilloscope.

39 Experimenal Resul Mode-Lock Laser Pulse Our approach SHG approach Pulse Widh: 3.3*.71=2.3 ps mode-lock laser pulse 1 ms DOP (%) Trace FWHM 3.3 ps.4 ms DGD DGD (ps) (ps) Pulse Widh: 3.3 *.71 = 2.3 ps Pulse Widh:.4*7.41*.71=2.1 ps Pulse Widh: 2.1 ps

40 Summary We demonsrae a simple echnique for ITU-grid mulichannel high-speed chirp-free opical pulse rain generaion: Afer 2-GHz sinusoidal phase modulaion, and filered by PM fiber as one-bi delay inerferomeer, muli-channel 4-GHz RZ and CSRZ opical pulse rains are generaed. Afer 4-GHz sinusoidal phase modulaion, and filered by wosages of PM fiber as inerferomeers, muli-channel 16-GHz chirp-free CSRZ opical pulse rains are generaed. An auocorrelaion echnique is also demonsraed using a unable DGD elemen and a DOP meer. This echnique is all-fiber based, wavelengh independen and requires less alignmen, less opical power.