Transcript
HYBRID MICROWAVE FIBER OPTIC LINKS John A. A MacDonald and Allen Katz
Linear Photonics, LLC 3 Nami Lane, Suite 7C, Hamilton, NJ 08619 609-584-5747
[email protected]
LINEAR PHOTONICS, LLC Bringing Performance to Light!
June, 2008
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Hybrid Photonics • LPL has developed Hybrid Microwave Photonic Link Components – – – –
Directly-modulated Microwave-over-fiber extended to Ku Band Very small Size and Weight Lower Cost & Complexity than external modulation High Dynamic Range: equivalent to external modulation Microwave Photoreceiver
Microwave Laser Transmitter June, 2008
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Directly Modulated Links • Directly-Modulated (DM) Fiber Optic Links – Transmitter: RF pre-amplification, biasing, and matching to low-impedance low impedance laser diode
G1 F1
• Output is Intensity Modulated • Modulation Efficiency = ratio of peak output modulation envelope to peak microwave input current
– Receiver: PIN photodiode photodiode, matching from highhigh impedance diode, RF post-amplification
Link Noise Figure, Figure F and Output Noise Power Density, Nout
Link Input Intercept, IIP3 June, 2008
Laser Diode
OPTICAL OUT Pout
• Responsivity = ratio of generated current to incident light intensity • PIN diode performs direct envelope detection Link Gain, GL
RF IN
Link Length
GL (dB) = Gref − 2 ⋅ OL
OPTICAL IN
F (dB) = N out (dBm / Hz ) + 174 − G L (dB) N out
c shot −OL crin − 2 OL ⎡ cth ⎤ = 10 log⎢10 10 + 10 10 + 10 10 ⎥ ⎣⎢ ⎦⎥
OIPeq + IIPeq ⎡ ⎢ 10 10 IIP3 (dBm) = 10 log ⎢ OIPeq IIPeq + GL 10 ⎢⎣10 + 10 10
⎤ ⎥ ⎥ ⎥⎦
Pin
Photodiode
G2 F2
RF OUT
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Packaged Laser Limitations • Low Cost Commercial Laser Transmitters utilize packaged laser diodes – Widespread use in CATV, RF-over-Fiber
• Thermal and Frequency Limitations – Frequency Response Limited by package parasitics – Thermal Operation limited by changing gain slope – TEC-cooled “butterfly” packages solve thermal problem – At expense of even lower bandwidth (more package effects) – Uncooled “TO-Can” packages can operate to ~ 4 GHz – Slope change limits thermal range for stable link gain to ~ 0 to 50 C
Cooled “butterfly” laser Frequency Response < 3 GHz High Current (TEC) y ((TEC)) Low Reliability
June, 2008
Uncooled “TO” laser Frequency Response < 4 GHz Limited Thermal Range
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Laser Diode Thermal Operation Cyoptics 293BT - S/N 448
Laser L-I curve over Temperature
8 GHz Link Gain over Temperature Cyoptics 293BT S/N 449 - S21 Gain - LO2
4.000
1
3.500
0
1 -1
3.000
-2 2.500
70C
2.000
-3 Gain (dB)
Optica al Output Power (mW)
-20C
1.500
-4
-5 1 000 1.000
-6 0.500
-7
0.000
-8 0
10
20
30
40
50
60
70
80
-9 8.000
-0.500
Laser Current (m A) 0 de g C
+25 de g C
8.050
8.100
8.150
8.200
8.250
8.300
8.350
+50 de g C
+75 de g C
8.450
8.500
-20 deg C, 50 mA
0 deg C, 50 mA
+25 deg C, 50 mA
+50 deg C, 75 mA
+75 deg C, 100 mA
Results in large variation in link gain over temperature
• Link g gain = f(Slope ( p Efficiency) y) Link Gain = f(Optical ( p Power)) • Bias adjust can maintain optical power, but not slope efficiency • Use of TEC maintains laser temperature • Requires ~ 2 W DC power • Not suitable for high high-reliability reliability • TEC MTBF may be less than Laser Diode MTBF • Hi-Rel, Low Power solution is RF Variable Attenuation June, 2008
8.400
Frequency (GHz)
Slope efficiency and Threshold change with temperature -20 de g C
90
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Hybrid Laser Transmitter OPTICAL SECTION –
Uncooled Laser Diode • •
–
Optical Alignment to Single Mode fiber •
RF in
High Reliability, Low Noise 1310 nm Low DC Power (no TEC) Focusing Optics and Optical Isolator
+5 +12
MICROWAVE INPUT SECTION – –
Temperature Compensation Network Optimal Microwave Matching • •
– –
Broadband or narrowband tuning (application specific) Provisions for Preamp / Predistortion
MICROWAVE INPUT
OPTICAL SECTION
Optical out
Analog hybrid on ceramic • • • •
June, 2008
CONTROL CIRCUIT
Package parasitics removed Operation to inherent laser diode frequency range (12 GHz+)
ANALOG CONTROL SECTION –
PWR MON
Power supply conditioning Constant Current bias loop Thermal Control Backfacet telemetry
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Transmitter Layout Control Electronics
RF Launch (GPO)
DC Interface
Fiber Pigtail (9/125 SM)
June, 2008
Optical Platform
RF Matching & Attenuator
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Link Performance Typical Performance for Microwave Links Examples: C-Band and Broadband Links available tuned any bandwidth to 12 GHz
Bandwidth Optical Power RF Link Gain Gain Variation with Frequency Gain Variation with Temperature RF Input/Output Return Loss Input IP3 Noise Figure SFDR
C-Band 3.2 to 4.0 GHz 6 dBmo -12 dB 0.5 dBp-p 2 dBp-p 10 dB 32 dBm 29 dB 118 dB (1 Hz)
Broadband 4 to 12 GHz 6 dBmo -15 dB 2 dBp-p 2dBp-p 10 dB 28 dBm 32 dB 113 dB (1 Hz)
DC P Power @ -10 C @ 25 C @ 70 C Operational Temperature Range Transmitter Weight (less pigtail) Receiver Weight (less pigtail) June, 2008
375 mW 450 mW 600 mW 20 to +70 70 C -20 19 grams 5 grams 8
Link Performance C-Band IF Link
June, 2008
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Design Flexibility • Link optimization – Microwave matching design for any bandwidth requirement – Integrated preamplification for lower noise • Receive side antenna remoting
• Integrated Predistortion Linearization – Improves Intermodulation Distortion
• Bandwidth Extension to 20 GHz – Units available 4Q08 Q June, 2008
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Linearity Improvement • Linearization: Methods of improving the linearity of a nonlinear network – Predistortion Linearization is one technique • Employs a nonlinear element in the microwave signal path • Operates at instantaneous microwave rate – N Nott lilimited it d by b delay d l as iin ffeedback db k or ffeedforward df d approach h – Not limited by overly complicated component-count – Limited primarily by microwave matching, preamplifiers, etc.
• Linearizer Technology Technology, Inc Inc. (Linear Photonics’ Photonics sister company) has been manufacturing linearizers and linearized networks for > 15 yrs – Technology T h l iis readily dil applied li d tto fib fiber optic ti networks t k
Linearizer Technology, Inc. June, 2008
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Predistortion Linearization 3
Output Power
2 1 0 -1 -2 2 -3 -4 -5 -5
-4
Input Power -3
-2
-1
0
1
-3
-2
-1
0
1
4
Phase
3 2 1 0 -1 -2 -5
-4
Input Power
• Nonlinear Device exhibits Gain and Phase Compression
June, 2008
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Predistortion Linearization 3
5 4
Output Power
3
Output Power
2 1
2 0
1
-1
0 -1
-2 2
-2 -3
-3 -4
-4 -5
-5
-5
-4
Input Power -3
-2
-1
0
1
4
-5
-4
Input Power -3
-2
-1
0
1
-3
-2
-1
0
1
4
Phase
3
Phase
3
2
2
1
1
0
0
-1
-1
-2
-2 -5
-4
-3
-2
-1
Input Power
0
1
-5
-4
Input Power
• Nonlinear Device exhibits Gain and Phase Compression • Precede it with another nonlinear device that exhibits gain and phase expansion, p , in conjugate j g with the device to be linearized ((the linearizer))
June, 2008
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Predistortion Linearization 3
5 4
Output Power
3
2
Output Power
2 1
Output Power
1 0
2 0
1
-1 -1
0
-2
-1
-2 2
-2
-3
-3
-3 -4
-4
-4 -5
-5
-5
-5
-4
Input Power -3
-2
-1
0
1
4
-5
-4
Input Power -3
-2
-1
0
-4
Input Power -3
-2
-1
0
1
0
1
3
4
Phase
3
-5
1
Phase
3
Phase
2 1
2
2
1
1
0
0
-1
-1
-2
-2
0 -1 -2 -3 -4
-5
-4
-3
-2
-1
Input Power
0
1
-5
-5
-4
-3
-2
-1
Input Power
0
1
-5
-4
Input Power -3
-2
-1
• Nonlinear Device exhibits Gain and Phase Compression • Precede it with another nonlinear device that exhibits gain and phase expansion, in conjugate with the device to be linearized (the linearizer) • The Th desired d i d outcome t iis an ideal id l limiter li it – The linearity of an ideal limiter cannot be improved June, 2008
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Predistortion Linearization • Result is reduction in IMD:
• SFDR iis iimpacted t d1 1:3 3 (dB) with ith IMD
June, 2008
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Results: Gain and Phase Transfer 1.5 dB 5.7 dB
Non linearized @ 8 GHz P1 dB is 5.7 dB from saturation Phase compression rapidly above sat
June, 2008
Linearized @ 8 GHz P1 dB is 1.5 dB from saturation Phase nonlinearity held to < 1° past sat
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