Title: Nonlinear Optical Processing Of DPSK Communication Signals

p.1 

Nonlinear Optical Processing of DPSK 

Communication Signals 

Chester Shu and Mable P. Fok 

Department of Electronic Engineering 

The Chinese University of Hong Kong 



International Symposium on Next-Generation 

Lightwave Communications 2007

DPSK Format Introduction 

p.2 

Field 

0 1 1 0 1 0 1 1 

Time 

DPSK format has constant amplitude for bit “0” and bit “1” 

 

 

 

 

Larger tolerance to degradation caused by channel-tochannel 

interaction through XPM 

Less pattern dependent gain modulation in SOAs 

smaller pulse-to-pulse intensity fluctuation 

3 dB improvement in receiver sensitivity with balanced 

detection 

When used with ASK, orthogonal modulation format can 

be supported 





Outline 

p.3 

1. DPSK optical signal processing 

2. All-optical wavelength conversion 

3. FWM wavelength conversion in highly nonlinear bismuth oxide fiber 

- single pump 

- dual pump 

- polarization-diversity 

- polarization-multiplexed ASK-DPSK signal 

4. XPM wavelength conversion in SG-DBR laser integrated SOA-MZI 

5. Wavelength multicasting 

6. Summary 





All-Optical Processing of DPSK signals 

p.4 

 

 

Signal regeneration 

- amplitude noise reduction (Fok et al., CLEO 2007, ECOC 2006) 

- phase noise reduction (Fok et al., OECC2007) 

- extinction ratio improvement (Fok et al., CLEO 2006) 

Wavelength conversion 

- dual-pump broadband (Fok et al., OFC 2007) 

- polarization diversity (Fok et al., CLEO 2007) 

- multicast wavelength conversion (Fok et al., PTL 2007) 

Logic operation (Fok et al., CLEO/Europe 2007) 

Tunable optical delay (Fok et al., OFC 2007, ECOC 2006) 





Wavelength Conversion 

p.5 

Important in a wavelength routed optical network 

 

 

Utilization of fiber bandwidth 

Prevention of network blocking 

Examples of wavelength conversion using 

 

 

 

 

 

 

Sum and difference frequency generation 

Cross-gain modulation 

Cross-phase modulation 

Cross-absorption modulation 

Cross-polarization rotation 

Four-wave mixing 





Characteristic of Four-Wave Mixing 

p.6 

Advantages: 

 

 

Transparent to data modulation format and bit rate 

Allows simultaneous conversion of multiple wavelengths 

Disadvantages: 

 

 

Narrow conversion bandwidth 

Polarization sensitive 





Four-Wave Mixing Basic 

p.7 

signal pump 1 

ω 4 

ω ω 

s ω p1 ω 3 

E 3 

= (E p1 · E s 

*)E p1 

γ(ω p1 

– ω s 

) exp[i(ω 3 

t + ∆Φ 3 )] 

E 4 

= (E s · E p1 

*)E s 

γ(ω s 

– ω p1 

) exp[i(ω 4 

t + ∆Φ 4 )] 

field amplitudes of 

signal, pump 1 complex coupling coefficient 

∆Φ 3 

= 2Φ p1 – Φ s 

Interaction between the pump 1 

(ω p1 

) and signal (ω s 

) 

creates index grating 

scatters pump 2 

transfer phase and amplitude information 

signalpump 1 

E 6 

= (E p1 · E s 

*)E p2 

γ(ω p1 

– ω s 

) 

exp[i(ω 6 

t + (Φ p1 

– Φ s 

+ Φ p2 

))] 

pump 2 

ω 

ω s 

ω p1 ω 3 ω 7 

ω p2 ω 6 





Highly Nonlinear Bismuth Oxide Fiber (Bi-NLF) Basic 

p.8 

Nonlinear coefficient 

γ = 1100 (W·km) -1 at 1550 nm 

2πn 

2 

γ = 

λA eff 

result from: (1) highly nonlinear nature of Bi 2 O 3 

(2) small effective core area 

Ref.: Juliet T. Gopinath,et al., JLT 

vol. 23, no. 11, pp. 3591-3596 

(2005) 

n 2 (m 2 /W) 

MFD (µm) 

BiO fiber 30 to 110x10 -20 1.97 

SiO 2 fiber 3x10 -20 10.4 

Short length of fiber is sufficient for four-wave mixing 

High SBS threshold 

Acknowledgement: N. Sugimoto and S. Ohara, Asahi Glass 





Single Pump Four-Wave Mixing 

p.9 

DPSK 

Signal 

32-cm 

Bi-NLF 

Laser 

BPF 

3-dB bandwidth = 12 nm 

Input Signal 

Converted Signal 

Power penalty ≤ 3 dB 

Signal (a.u.) 

Time (50 ps/div.) 

Signal (a.u.) 






Dual-Pump Four Wave Mixing for Wavelength Conversion 

p.10 

DPSK signal: 

Pump 1 Signal Pump 2 10-Gb/s 10 31 -1 PRBS 

 

 

Signal power: 17 dBm 

Pump power: 20 dBm 

Signal: 1550 nm 

Pump 1 : 1548 nm 

Pump 2 : 1543 to 1573 nm 

 

 

3-dB bandwidth 

Single-pump: 12 nm 

Dual-pump: >30 nm 

Conversion efficiency 

Single-pump: -20 dB 

Dual-pump: -18 dB 

Ref.: M. P. Fok et al., JThA52, OFC/NFOEC 2007 





Dual-Pump Four Wave Mixing for Wavelength Conversion 

p.11 

Signal (a.u.) 

B2B 1545 nm 1557 nm 1568 nm 

Signal (a.u.) 

Signal (a.u.) 

Time (50 ps/div.) Time (50 ps/div.) Time (50 ps/div.) Time (50 ps/div.) 

Signal (a.u.) 

At BER of 10 -9 

Power penalty

Polarization Diversity Loop for Wavelength Conversion 

p.12 


signal 

TL 

32-cm 

Bi-NLF 

output 

Signal (a.u.) 

DPSK input 


Signal (a.u.) 

DPSK output 


Ref.: M. P. Fok et al., CLEO 2007 





Polarization Multiplexed ASK-DPSK Wavelength Conversion 

Polarization A Polarization B 

p.13 

LD 

ASK-DPSK 

Generation 

Polarization 

multiplexing 

DL 

Signal (a.u.) 

Signal (a.u.) 

Time (50 ps/div.) Time (50 ps/div.) 

Signal (a.u.) 

Polarization A 


Signal (a.u.) 

Polarization B 


Ref.: M. P. Fok et al., CLEO/Europe 2007 



Pol B 

32 cm 

Bi-NLF 

Pol A 

BPF 

CW 



Integrated Approach – XPM in SOA Based Device 

Tunable 

Laser 

CLK 

10 Gb/s 

PM 


decoder 

DATA 

p.14 

DATA# 

Input SOA 1 

SG-DBR Laser 

Input SOA 2 

SOA 

SOA 

MZI SOA 

MZI SOA 

Phase 

Phase 

Signal (a.u.) 


DATA 

DATA# 

SG-DBR Laser 

integrated 

SOA-MZI 

BPF 

Converted 

DPSK signal 

Signal (a.u.) 

Ref.: M. P. Fok et al., CLEO/Europe 2007 






DBR Laser Integrated SOA-MZI 

p.15 

Input SOA 

Mirror 

Laser SOA 

SG-DBR 

Input SOA 

Signal (a.u.) 

1548.6 nm 

1553.9 nm 

1559.1 nm 

1569.9 nm 

MZI-SOA 

phase 

Laser SOA 

MZI-SOA 


 

By controlling the mirror 

of the SG-DBR 

wavelength tuning over 32 nm 





Wavelength Multicasting 

p.16 

Wavelength multicast of DPSK signal 

WDM 

source 

λ pump1 

λ pump2 

λ pump3 

SOA 

BPF 

Ch 1 

6 x 10 GHz output 

Ch 3 

Ch 2 

Ch 5 

Ch 4 

Ch 6 

λ signa 

l 

TL 

PM 

BERT 

Output 

Ref.: M. P. Fok et al., PTL 2007 

50 ps DI 



Intensity (a.u.) 

Intensity (a.u.) 

Input signal 


Multicast output 




Summary 

p.17 

 

 

Demonstrated all-optical processing of DPSK signals: 

signal regeneration, wavelength conversion, logic operation, 

and tunable optical delay. 

Achieved compact fiber and semiconductor-based approaches 

for tunable DPSK wavelength conversion 

- FWM in 32-cm Bi-NLF 

- XPM in SG-DBR laser integrated SOA-MZI 

 

Developed efficient DPSK wavelength multicast approaches 

using FWM in SOA and nonlinear PCF

Title: Nonlinear Optical Processing Of DPSK Communication Signals

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