Conversion between Optical ASK and Optical FSK
Using Nonlinear Dynamics of Semiconductor
Lasers
Sheng-Kwang Hwang1,2,*, Sze-Chun Chan3, Shiuan-Li Lin1, Cheng-Hao Chu1,
and Yu-Han Hung1
*skhwang@mail.ncku.edu.tw
1 Department of Photonics, National Cheng Kung University, Tainan, Taiwan
2 Advanced Optoelectronic Technology Center, National Cheng Kung University, Tainan, Taiwan
3 Department of Electronic Engineering, City University of Hong Kong, Hong Kong, China
1
Outline
• Optical Modulation Formats – format categories and types – format conversion schemes • Proposed Method
– nonlinear laser dynamics – static characteristics – dynamical characteristics • Summary
2
Various Optical Modulation Formats
• Amplitude-Shift Keying (ASK)
- on-off keying (OOK): includes RZ & NRZ, most commonly used now simple transmitter/receiver, low spectral efficiency, short-range communication - CSRZ, CRZ, DB, AMI, VSB, SSB …
• Phase-Shift Keying (PSK)
- binary PSK (BPSK), quadrature PSK (QPSK), multi-level PSK - differential BPSK (DPSK), differential QPSK (DQPSK) • Frequency-Shift Keying (FSK)
- wideband FSK - narrowband FSK
formats other than OOK are proposed for various purposes and considerations even though they are more complex in system configuration and operation, such as, high spectral efficiency, long-range communication, more robust to noise, dispersion, and nonlinearity etc.
Short Haul Network Long Haul Network ASK FSK / PSK Conversion Center
Some Proposed Format Conversion Schemes
• OOK-to-PSK conversion
– optical semiconductor amplifier based on cross phase modulation effect M. Mishina et al., J. Lightwave Technology, vol. 24, pp. 3751, 2006
C. Yan et al., IEEE Photonics Technology, vol. 20, pp. 1530, 2006 W. Hong et al., Optics Express, vol. 15, pp. 18357, 2007 – optical fiber based on cross phase modulation effect
M. Mishina et al., Optics Express, vol. 15, pp. 8444, 2007
S. Arahira et al., IEEE Photonics Technology, vol. 20, pp. 1530, 2008 W. Astar et al., Optics Express, vol. 16, pp. 12039, 2008
• PSK-to-OOK conversion
– semiconductor laser based on injection locking-unlocking effect Y. Awaji et al, Optics Letters, vol. 26, pp. 1538, 2001
• FSK-to-PSK conversion
– Mach-Zehnder modulator based on double-sideband suppressed-carrier scheme T. Kawanishi et al., Optics Express, vol. 13, pp. 8038, 2005
Semiconductor Laser Dynamics: Before Injection
Laser Diode
f2
laser output : continuous wave (before injection) fr fr fcr= f2 cavity resonance (before injection)
fr: relaxation resonance frequency 5
?
Semiconductor Laser Dynamics: After Injection
Laser Diode laser output : ??? (after injection) fcr cavity resonance (after injection) f2 f1 optical injection f2 f1 fs c s b g f 4
linewidth enhancement factor
gain before injection gain after injection
results of dynamical competition
attempts to pull laser oscillation toward f1
(Injection-pulling-effect)
attempts to pull laser oscillation toward fcr
(Red-shift-effect)
6
Proposed Scheme: Period-One (P1) Dynamics
Laser Diode
f1
f2
f3 fcr f4
laser output : periodic oscillation (after injection) fr fr optical injection 7 f2 f1
Proposed Scheme: Period-One (P1) Dynamics
Laser Diode f1 f2 f3 fcr f4 fr fr 8 Change relative injection frequency Intensity and Frequency are both changed
f1
f2
f3 fcr f4
laser output : periodic oscillation (after injection) fr fr optical injection f2 f1 f2 f1
Proposed Scheme: Period-One (P1) Dynamics
Laser Diode f1 f2 f3 fcr f4 fr fr 9Change Injection Level Intensity and Frequency are both changed
f1
f2
f3 fcr f4
laser output : periodic oscillation (after injection) fr fr optical injection f2 f1 f2 f1
Numerical Result of Static Characteristics (1)
changes in injection levellead to changes in output frequencyand intensity
10 lower sideband ( squares ) upper sideband (circles ) central component ( up-triangles) Injection Level
Numerical Result of Static Characteristics (2)
changes in injection frequencylead to changes in output frequency and intensity lower sideband ( squares ) upper sideband (circles ) central component ( up-triangles)
Relative injection frequency
Numerical Result of Dynamical Characteristics (3)
output modulation depth depends on injection condition monotonically and continuously
lower sideband ( squares ) upper sideband (circles ) central component ( up-triangles)
ASK to FSK ASK to FSK ASK to FSK
Injection Level
ASK to FSK
Relative injection frequency
Numerical Result of Dynamical Characteristics (4)
output modulation depth depends on injection condition monotonically and continuously
13 lower sideband ( squares ) upper sideband (circles ) central component ( up-triangles)
FSK to ASK FSK to ASK FSK to ASK
Injection Level
FSK to ASK
Relative injection frequency
Numerical Result of Bit-Error Ratio & Eye Diagram (1)
similar observations are found for other injection conditions
AM-to-FM AM-to-FM 14 lower sideband ( squares ) upper sideband (circles ) central component ( up-triangles) ASK to FSK ASK to FSK
Numerical Result of Bit-Error Ratio & Eye Diagram(2)
similar observations are found for other injection conditions
FM-to-AM FM-to-AM 15 lower sideband ( squares ) upper sideband (circles ) central component ( up-triangles) FSK to ASK FSK to ASK
Experimental Set-up of ASK to FSK Format Conversion
16 TL EM LD Filter OSA PD PSA Oscilloscope BERT BERT
(2.5Gb/sec) TL: Tunable LaserEM: External modulator LD: Laser Diode PD: Photo detector
ASK generation Unit ASK to FSK converter
Signal analysis
f f f f
Filter
Experimental Set-up of ASK to FSK Format Conversion 17 TL EM LD Filter OSA PD PSA Oscilloscope BERT BERT
(2.5Gb/sec) TL: Tunable LaserEM: External modulator LD: Laser Diode PD: Photo detector
ASK generation Unit ASK to FSK converter
Signal analysis
f f f f t
Filter
Experimental Set-up of ASK to FSK Format Conversion
18 TL EM LD Filter OSA PD PSA Oscilloscope BERT BERT
(2.5Gb/sec) TL: Tunable LaserEM: External modulator LD: Laser Diode PD: Photo detector
ASK generation Unit ASK to FSK converter
Signal analysis
f f f f t
Filter
Experimental Result of ASK to FSK Format Conversion (1)
Free-running Laser Diode Incoming signal Period-one dynamics
Experimental Result of ASK to FSK Format Conversion (2)
19.53GHz
Free-running Laser Diode Incoming signal Period-one dynamics
Experimental Result of ASK to FSK Format Conversion (3)
21 39.67 GHz
Free-running Laser Diode Incoming signal Period-one dynamics
Experimental Result of ASK to FSK Format Conversion (4)
22
( With DATA )
Free-running Laser Diode Incoming signal Period-one dynamics
Experimental Result of ASK to FSK Format Conversion (5)
23 Filter
( With DATA )
Free-running Laser Diode Incoming signal Period-one dynamics ( With DATA )
Experimental Result of ASK to FSK Format Conversion (6)
24 111
0000000
The original data is “0000000111” and the data rate is 2.5Gbits/s.
Experimental Result of ASK to FSK Format Conversion (7)
25 1111111
000
The original data is “0000000111” and the data rate is 2.5Gbits/s.
Frequency Offset (GHz)
Experimental Result of ASK to FSK Format Conversion (8)
26 Non-Inverted data Inverted data Back-to-Back Received power (dBm)
Summary
• All-optical modulation format conversion between ASK and FSK using period-one nonlinear dynamics in semiconductor lasers is proposed and demonstrated
• Characteristics:
- only a typical semiconductor laser is required as the conversion unit - bi-directional (ASK-to-FSK, FSK-to-ASK) format conversion is feasible - large dynamic range for input modulation depth
- output modulation depth can be adjusted by adopting different spectral components or different injection conditions
- simultaneous frequency shift of optical carrier occurs and can be adjusted via injection condition
