Injection Locked Oscillators Optoelectronic Applications

1
Injection Locked Oscillators Optoelectronic
Applications
Q1, ?1
Q2, ?2

• E. Shumakher, J. Lasri, B. Sheinman, G.
  Eisenstein, D. Ritter
• Electrical Engineering Dept. TECHNION
• Haifa ISRAEL

2
General Concept
Single oscillator
Interlocked oscillators
3
Fundamental Locking

• First formulated by R. Adler (1946)
• Principal locking criteria
• Given a master oscillator, coupled uni-
  directionally to a slave oscillator
• with
• Locking takes place within the locking range

4
Harmonic Locking

• Two possible configurations
• Sub-harmonic injection locking
• Super-harmonic injection locking
• Consequences
• Injected signal does not satisfy
• Lifetime is very short inside the oscillating
  loop
• Dynamics of the loop can not be altered

5
Harmonic Locking

• Locking requires mediation by a non-linearity
• Harmonics generation
• Mixing with harmonics and
• creates a component at which locks the
  slave oscillator

6
Unidirectional Locking

• Improved signal quality
• Superharmonic IL further improvement
• or
• Synchronization Timing extraction
• Harmonic IL Multirate timing extraction

7
3rd Harmonic Unidirectional Locking
-20
1st Q2 free
3rd Q2 free
-40
1st Q2 locked
3rd Q2 locked
1st Q1
-60
-80
-100
-120
2
3
4
5
6
7
10
10
10
10
10
10
Offset Frequency Hz

• Coupled oscillators
• 1st harmonic of Q2 exhibits a lower noise than
  the 1st harmonic of the
• higher quality injected signal by
• Explainable through correlated noise
  considerations

8
3rd Harmonic Unidirectional Locking
1st harmonics of Q1 at
Initially uncorrelated signals
Signals turn into correlated
Correlated signals
1st 4th harmonics of Q2 at ?2
9
Unidirectional Coupling Experiment
1st Q2 free
1st Q1 injected
1st Q2 locked
3rd Q2 locked
Offset Frequency Hz

• Injected frequency is followed by the
  corresponding harmonics

10
Unidirectional Coupling Multi Rate Timing
Extraction
11
Multi Rate Timing Extraction
Extracted electrical clock
Frequency GHz
RZ signal or optically processed NRZ signal
Lasri et. al 2002
12
10 Gb/s and 40 Gb/s modulated RZ signals
Transmitter Schematic
10 Gb/s 40 Gb/s Multiplexer
DBR
40 Gbit/s
10 Gbit/s
10 GHz
BER Transmitter
Data Out
Phase shifter
Modulated RZ signal toward the photo HBT based
oscillator
(231-1 _at_ 10 Gb/s)
Lasri et. al 2002
13
Clock recovery of RZ data by direct optical IL of
Photo-HBT based oscillator
Recovered Clock
Lasri et. al 2002
14
Clock Recovery Results
10 GHz Locking
40 GHz Locking
injected signal
injected signal
Free running signal
4th harmonic signal
10 kHz/div
40
9.9998
10.0004
10.0012
Detected Power dBm
Detected Power dBm
Injection locked signal
Injection locked signal
10 kHz/div
10.0002
10.0006
10.001
40
Frequency GHz
Frequency GHz
Lasri et. al 2002
15
BER performance for 10 GHz Locking
Direct Clock
-1
Recovered Clock
-3
-5
Log ( BER )
-7
-9
Optical Power dBm
Lasri et. al 2002
16
3rd Harmonic Bidirectional Locking
Generalized Van der Pol

• Coupled oscillators
• Injections strength is inversely relative to the
  quality factor

17
3rd Harmonic Bidirectional Locking
Phase noise at offset
Power Spectral Density
1st Q2 free
101
251
71
51
21
1st Q1 free
15
12
11.5
11
1.51
21
51
71
101
251
1.51
11.5
15
11
12
Injection Ratio P2 / P1
Offset Frequency Hz
18
Bidirectional CouplingExperimental Setup
19
Bidirectional CouplingExperimental Results
1st Q2 free
1st Q2 free
1st Q1 free
1st Q1 free
1st Q2 locked
1st Q2 locked
3rd Q2 locked
3rd Q2 locked
1st Q1 locked
1st Q1 locked
Offset Frequency Hz
Offset Frequency Hz
20
Ultra Low Jitter Pulse Sources

• Active mode-locking of fiber/diode lasers
• Clark et al. ( NRL Labs )
• Ng et al. ( HRL Labs )
• Jiang et al. ( MIT )
• In all cases, ultra low phase-noise microwave
  source employed
• Self starting approach Coupled OEOs ( Yao and
  Maleki )

21
Self-Starting Ultra Low Jitter Optical Pulse
Source
10 GHz RF signal
10 GHz optical pulse-train

• Actively mode-locked diode laser
• Photo-HBT based oscillator
• Extended cavity optoelectronic oscillator

Lasri et. al 2002
22
Bidirectional Coupling Pulse Source Experimental
Setup
23
Bidirectional Coupling Pulsed SourceExperimental
Results

• Pulsed Source
• Mode locked diode laser
• Modulated at its 6th harmonics (
  )
• Driven by 3rd harmonics of the EO ( )
• Repetition rate
• Resulting locked signal has better phase noise
  then the free running OEO

Electrical Signal
1st Q2 free
1st Q1 free
1st Q2 locked
3rd Q2 locked
-140
Offset Frequency Hz
24
Self-Starting Ultra Low Jitter Optical Pulse
Source
Electrical 10 GHz signal
Optical Spectrum
Open Loop
Power mW
Open loop
Power dBm
Closed loop
1543.5
1542.5
1543
1544
1544.5
Wavelength nm
Closed Loop
DtDn 0.47
10 GHz
5 kHz/div
Power mW
Phase noise at 10 kHz offset Open loop -98
dBc/Hz Close loop -108 dBc/Hz
1542.5
1543
1543.5
1544
1544.5
Wavelength nm
25
Lasri et. al 2002
Jitter Measurements
Harmonic spectral analysis (van der Linde
technique)
Amplitude noise contribution
Jitter contribution
0
0
Open loop
Closed loop
-20
-20
Harmonic number
Harmonic number
Power dBm
Power dBm
-40
-40
5
5
-60
-60
1
-80
-80
1
10-50 GHz
10-50 GHz
5 kHz/div
5 kHz/div
26
Lasri et. al 2002
Jitter Measurements
Closed Loop
100 Hz 1 MHz
500 Hz 1 MHz
500 Hz 15 kHz
Curve fit to
RMS Noise mW
Harmonic number
4
1
Harmonic Number
Offset Frequency Hz
Note that the 40 fs jitter (with a power of 6
dBm and 10 km fiber) could not be improved with
higher powers or longer fibers.
27
Conclusion

• Photo HBT based oscillator versatile multi
  functional system
• Accurate numerical model
• Fundamental and Harmonic injection locking
• Uni and bi-directional locking
• Improved noise performance due to correlated
  noise interaction in Harmonically locked
  oscillators
• Multi rate timing extraction
• Bi-directional locking characteristics
  determined
• by mutual locking efficiency and relevant Q
  factors
• Self starting low jitter mode locked diode laser

28
Fundamental Locking

• The locking mechanism
• Injected signal x1 (t) saturates the gain
• Loop lifetime is long
• Free running dynamics are overwritten by
• x1 (t) for

29
1st Q1 lock
3rd Q1 lock
1st Q2 lock
3rd Q2 lock
11
1st Q1 lock
3rd Q1 lock
1st Q2 lock
3rd Q2 lock
21
30
1st Q1 lock
3rd Q1 lock
1st Q2 lock
3rd Q2 lock
51
1st Q1 lock
1st Q1 lock
3rd Q1 lock
3rd Q1 lock
1st Q2 lock
1st Q2 lock
3rd Q2 lock
3rd Q2 lock
71
101
31
1st Q1 lock
1st Q1 lock
3rd Q1 lock
3rd Q1 lock
1st Q2 lock
1st Q2 lock
3rd Q2 lock
3rd Q2 lock
1.51
11.5
1st Q1 lock
3rd Q1 lock
1st Q2 lock
3rd Q2 lock
251
32
Feedback Model

• Phenomenological model
• Self starting from noise
• Easy injection modeling
• Polynomial Non-Linear Gain function
• BPF implemented as IIR filter

• Time domain simulation
• Transmission line like propagation
• Decimation in time incorporating long FIR filter
• Ensemble averaged PSD

33
Numerical Results Single Oscillator
-20
1st harmonics
-30
Linear fit
2nd harmonics
3rd harmonics
-40
4th harmonics
-50
Period Time Variance s2
-60
-70
-80
-90
-100
2
3
4
5
6
10
10
10
10
10
Time µS
Offset Frequency Hz

• Noise parameter c derived for
• Resulting PSDs agree perfectly
• PSD has a single pole functional form
• Indicates Gaussian statistics
• CAN NOT be predicted by small signal analysis