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11/1/2007 PHOTONIC SYSTEMS INTEGRATION LABORATORY – UCSD JACOBS SCHOOL OF ENGINEERING
UCSD Photonics
1Photo: Kevin Walsh, OLR
Photonics Systems Integration Lab
University of California San DiegoJacobs School of Engineering
Photonics Systems Integration Lab
University of California San DiegoJacobs School of Engineering
Fast, Two-Dimensional Optical Beamscanning by Wavelength Switching
Fast, Two-Dimensional Optical Beamscanning by Wavelength Switching
T. K. Chan, E. Myslivets, J. E. FordT. K. Chan, E. Myslivets, J. E. Ford
11/1/2007 PHOTONIC SYSTEMS INTEGRATION LABORATORY – UCSD JACOBS SCHOOL OF ENGINEERING
UCSD Photonics
2
Flat mirrors
Deformable MEMS mirror
• Free Space Optical Communications:
• Dynamic connections: platform and environment– Require fast, active alignment and tracking
• Retro-reflecting modulators Single sided alignmentMEMS (Chan et al, J. Light. Tech, 24(1), 2006)MQW (Rabinovich et al. CLEO 2003, 2003)
• Scanning/Tracking Challenges:– Fast (<<1 ms switching)– Accurate and repeatable– Wide angle range ± 5°, (± 60° ideally)– Physically small & robust
Introduction
11/1/2007 PHOTONIC SYSTEMS INTEGRATION LABORATORY – UCSD JACOBS SCHOOL OF ENGINEERING
UCSD Photonics
3
Existing Scanning Technologies
Bulk, power, reliability~10mm~ 30°KHzGalvanometric
Drive current, angle range~10mm~ 1°MHzElectro-optic
Speed, environmental constraints>100mm~ 60°100 HzLiquid Crystals
Angle range~10mm~ 1°KHz Acousto-optic
Aperture, power handling~1mm~ 5°KHzMEMS mirror
Key limitationAperture RangeSpeed
Aperture Accuracy
Field of View
Speedtradeoff
Question: How to decouple fast response from other performance parameters?
11/1/2007 PHOTONIC SYSTEMS INTEGRATION LABORATORY – UCSD JACOBS SCHOOL OF ENGINEERING
UCSD Photonics
4
Diffract wavelength to angle: Decouples aperture from speed
Wavelength ScanningFast λ-tuning Laser source
Fixed collimator and diffraction grating
Vertical angleRandom-access scan
δθx
Far-field distribution
Θy
δθy
H=kλ
How fast?• Grating-assisted codirectionalcoupler with rear sampled reflector (GCSR) lasers
Simsarian, J. E. et al, IEEE Phot. Tech. Let. 15 (8) p1038, 2003.– < 50 ns switching times in– 40 nm scanning range– > 1.5 dBm per channel
• What about 2D scanning?
11/1/2007 PHOTONIC SYSTEMS INTEGRATION LABORATORY – UCSD JACOBS SCHOOL OF ENGINEERING
UCSD Photonics
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Concept: 2D Wavelength Scanning
- 2 5
- 2 0
- 1 5
- 1 0
- 5
0
1 5 2 0 1 5 3 0 1 5 4 0 1 5 5 0 1 5 6 0 1 5 7 0 1 5 8 0 1 5 9 0 1 6 0 0
W a v e le n g t h ( n m )
Inse
rtio
n Lo
ss (d
B)
FSR = 7.7 nm(0.998 THz)
Diffraction order m:198 197 196 195 194 193 192 191 190 189
Channel 1
Channels 2 - 8
FSR = 8.5 nm(0.998 THz)
Wavelength (nm)
High-order gratingArrayed waveguide grating (AWG)VIPA free space echelon grating
Low-order gratingBlazed reflection gratingHolographic transmission grating
λ1,1
λ1,2
λ2,3
λ2,4
11/1/2007 PHOTONIC SYSTEMS INTEGRATION LABORATORY – UCSD JACOBS SCHOOL OF ENGINEERING
UCSD Photonics
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2D Integrated Optics Demux
• Hybrid wavelength demultiplexerT. K. Chan et al, J. Light. Tech. 25(3) 2007– Combines a 1x40 channel AWG and a free space grating demultiplexer
Fourier-Transform Lens focal length = f
Blazed Gratingline spacing = d
AWG Demultiplexer
Demultiplexed plane(optoelectronic / MEMS device)
11/1/2007 PHOTONIC SYSTEMS INTEGRATION LABORATORY – UCSD JACOBS SCHOOL OF ENGINEERING
UCSD Photonics
7
2-D Single mode fiber demux
• 1x40 AWG + 50 lines/mm grating• 600 nm wavelength range• 7-15 dB insertion loss into SMF• 0.1 dB power penalty @ 10 Gb/s
Grating
Lens
40 AWG
Outputs
1x40 input array
Outputfiber
1092 channels (39 x 28 grid)
11/1/2007 PHOTONIC SYSTEMS INTEGRATION LABORATORY – UCSD JACOBS SCHOOL OF ENGINEERING
UCSD Photonics
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2D Beamscanner
JDSU 1x8AWGTunable Source
Grating3rd order
300 lp/mm
Mirror
8x Microscope Objectivef = 25 mm
Lensf = 100 mm
V-groove array635 um pitch
Source Options:• Tunable Laser• Broadband noise source
+ Tunable Filter
Focal length determines angular range
Modifications:(1) Substitute JSDU 1x8 AWG to increase # of diff. orders(2) Increased grating frequency to cover a greater angle range(3) Add a mirror and short focal length objective for beamscanning
NA determines aperture
11/1/2007 PHOTONIC SYSTEMS INTEGRATION LABORATORY – UCSD JACOBS SCHOOL OF ENGINEERING
UCSD Photonics
9
2D Beamscanning Demonstration
Tunable laser1535 – 1590 nm
sweep
AWG V-Groove fiber array
Microscopeobjective Free-space
reflection grating
11/1/2007 PHOTONIC SYSTEMS INTEGRATION LABORATORY – UCSD JACOBS SCHOOL OF ENGINEERING
UCSD Photonics
10
2D Beamscanner Demonstration
Angular Output (degrees)
Ang
ular
Out
put (
degr
ees)
-8
-4
0
4
8
-8 -4 0 4 8
11.0 °
10.3 °
1545.0 nm 1586.4 nm
1547.0 nm 1588.3 nm
Calculated Directions
C-Band ASE illumination
Gaussian Output Beam ProfileCoherent illumination
1/e2 diameter6 mm
Numerical aperture = 0.12 Lens focal length = 25 mm
1/e2 diameter = 6 mm
For a telephoto lens Lens focal length = 100 mm1/e2 diameter = 24 mm
11/1/2007 PHOTONIC SYSTEMS INTEGRATION LABORATORY – UCSD JACOBS SCHOOL OF ENGINEERING
UCSD Photonics
11
Fast tuning
“Microelectromechanical tuneable filters with 0.47 nm linewidth and 70 nm tuning range,” Tayebati, et al, Electronics Letters 34(1) 1998.
• 80 nm span tunable etalon filter• ~100 µs sweep times• Channel bandwidth = 0.47nm res
Coretek/Nortel MEMS Tunable Filter
JDSU 1x8AWG
Grating3rd order
300 lp/mm
Mirror
8x Microscope Objectivef = 25 mm
Lensf = 100 mm
V-groove array635 um pitch
OpticalAmplifier
CoreTek TunableFilter
ASE Source
11/1/2007 PHOTONIC SYSTEMS INTEGRATION LABORATORY – UCSD JACOBS SCHOOL OF ENGINEERING
UCSD Photonics
12
Fast Sweeping w/ Tunable Filter
• AWG channel pitch = 50 GHz
• Narrow bandwidth source is desired.
• higher dispersive device more diffraction orders over the same bandwidth!
1546.7 nm
1578.2 nm183 µs
switching time
-20
-15
-10
-5
0
1531 1532 1533 1534
Wavelength (nm)
Inse
rtio
n Lo
ss (d
B) Filter Passband
AWG channels
11/1/2007 PHOTONIC SYSTEMS INTEGRATION LABORATORY – UCSD JACOBS SCHOOL OF ENGINEERING
UCSD Photonics
13
Virtually Imaged Phased Array: VIPA
r = 95%
VIPA echelle grating conceptM. Shirasaki, Fujitsu Sci. Tech. J., 35(1), 1999.
• Virtual line sources are created by multiple reflections• Large spatial offset between source origins create high-order echelle grating• Free-space optics equivalent to planar arrayed waveguide grating
r = 100%
2D Dispersion using a VIPAS. Xiao and A. M. Weiner, Optics Express 12 (13), p.2895-2902, 2004Multi-order VIPA + free space grating 41 Channels (~4x10)
11/1/2007 PHOTONIC SYSTEMS INTEGRATION LABORATORY – UCSD JACOBS SCHOOL OF ENGINEERING
UCSD Photonics
14
Future directions: Planar integration
Tunable Source
VIPA design parameters- 100 µm slab with n = 1.5, 2.5° tilt
Transmission grating: 500 lp/mm
Scan Output: • Scan area = 5.4° x 8.1°• Wavelength Range = 1400 – 1600 nm• Number of Rows = 26
Caution: tight alignment tolerances required
VIPA
High-resolution 2-D scanning possible
Grating
11/1/2007 PHOTONIC SYSTEMS INTEGRATION LABORATORY – UCSD JACOBS SCHOOL OF ENGINEERING
UCSD Photonics
15
Conclusion
• 2D beamscanning can be achieved by combining 2 dispersive elements orthogonally
– Direction is wavelength dependant via raster scanning– Speed is determined by wavelength tuning source, not the optical deflectors
• Combined an AWG with a free-space grating– Demonstrated 183 µs switching using off the shelf parts– Discrete 6x8 directional array– 11.0° by 10.3° direction range
• More desirable to combine a VIPA with a free-space grating– Continuous scanning in one direction– Very dispersive (more diffraction orders over the wavelength range)
• Wavelength tuning determines sweep speeds– ~10s ns wavelength sweeps are commercially available