Characterization of the Near-Field Profile of Semiconductor … · 2017-02-27 · ABSTRACT...
Transcript of Characterization of the Near-Field Profile of Semiconductor … · 2017-02-27 · ABSTRACT...
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Characterization of the Near-FieldProfile of Semiconductor Lasers and the
Spot Size of Tightly Focused LaserBeams from Far-Field Measurements
Jeffrey L. Guttman and John M. FleischerPhoton Inc.
6860 Santa Teresa Blvd.,San Jose, CA 95119
7th International Workshop on Laser Beam and OpticsCharacterization
September 18-19, 2002
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ABSTRACT
Characterization of the near field of typical semiconductor lasers and thespot size of tightly focused laser beams poses significant challenges todirect near-field profile measurement techniques. Far-field measurementsare considerably easier to perform and offer an attractive alternative for thischaracterization. To assess this alternative, profiles of edge-emitting laserdiodes and VCSELs, and the spot size of focused laser beams weredetermined from far-field and near-field measurements. In the far field,measurements were made using a 3D-scanning goniometric radiometer thatprovides irradiance profiles with angular extent to approximately ±70°.Indirect measures derived from these data using different methods arereported, including the spot size using the M2 times-diffraction-limitedapproximation, the Hankel transform Petermann II mode-field diameterused for optical fiber characterization, and a measure obtained from 2DFourier transform inversion of the far field using phase retrieval. In thenear field, direct profile measurements were made using scanning slit andknife-edge profilers, and a CCD camera with magnifying lenses.
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PRESENTATION OUTLINE
Applications of Near Field CharacterizationMeasurement Techniques
• Direct Near Field• Indirect Far Field
Near and Far Field Data• Focused HeNe• Edge Emitting Laser Diode• VCSEL
Analysis MethodsSummary of ResultsConclusion
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Near Field Characterization
ApplicationsTightly Focused Laser BeamsLDs - Modes, GeometryVCSELs - Modes, GeometryFibers - MFD, Aeff
Waveguides - Modes, GeometryTapered Fibers - Spot SizeQuantum Dots - Modes, GeometryOther “μm-subμm” Sources
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Direct Near Field SourceMeasurement Techniques
Camera/Magnifying LensDiffraction Limited for “μm-subμm” ResolutionNA, MTF, and λ Dependence of OpticsAccess to Aperture Field
Scanning Slit or Knife-EdgeAccess to Aperture Field
Near Field Scanning Optical Microscopy (NSOM)Speed of MeasurementAccess to Aperture FieldExpensive
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Indirect Near Field Characterizationfrom Far Field Measurement
Calculate Near Field quantitiesfrom measured Far FieldMinimal Optics LimitationsNo Access ConstraintsEase of MeasurementProvides “sub-µm” Measures
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Indirect Near Field Characterizationfrom Far Field Measurement
Diffraction Limited 1/e2 Diameter• Calculated from Far-Field Divergence (d=4λ/πθ)
Mode-Field Diameter (MFD)• Petermann II Integral
Near Field 1/e2 Diameter• 2D Fourier Transform with Phase Retrieval
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Edge-Emitting Laser Diode Near FieldCCD with 100x Objective
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Edge-Emitting Laser Diode Far Field3D Rectangular View
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Edge-Emitting Laser Diode Far Field3D Logarithmic Rectangular View
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Edge-Emitting Laser Diode Far Field3D Polar View
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Edge-Emitting Laser Diode Far FieldAnalysis: Fast and Slow Axes
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Edge-Emitting Laser Diode Far FieldAnalysis: Fast and Slow Axes
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Focused HeNe Laser Beam Near Field - Scanning Slit
Typical Profiles
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Focused HeNe Laser Beam Near Field - Camera/40X Lens
Typical Profiles
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Focused HeNe Laser Beam Far Field - Goniometric Radiometer
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Far Field/Near Field Measurements ofVCSEL Modes
Near Field
Far Field
7mA 15mA 19mA 24mA 29mA
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Near Field Profiles of VCSEL: Increasing Drive Current
VCSEL Near Field Profiles
0
50
100
150
200
250
-6 -5 -4 -3 -2 -1 0 1 2 3 4 5 6 7
POSITION (microns)
AM
PLIT
UD
E (A
rbitr
ary
Uni
ts)
7mA
15mA
19mA
24mA
29mA
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Far Field Profiles of VCSEL: Increasing Drive Current
VCSEL Far Field Profiles
1
10
100
1000
10000
100000
-50 -40 -30 -20 -10 0 10 20 30 40 50
ANGLE (degrees)
AM
PLIT
UD
E (A
rbitr
ary
Uni
ts)
4mA5mA6mA7mA15mA19mA24mA29mA
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Near Field 1/e2 Diameter fromGaussian Approximation
• Equation for Diffraction Limited Width:
2
2
/1
/1
4
e
eD
πθλ
=
• Near-Field Diameter Calculated Using MeasuredFar-Field Divergence Angle
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“Mode-Field Diameter” of Source
θθθθ
θθθθπλ θ
θ
θ
θ
dI
dIMFD
)cos()(sin)(
)cos()sin()(2)/(
3∫
∫
−
−=
Calculated using Petermann II Integral1,2:
1TIA/EIA Standard for Single-Mode Fiber2Integral Limit Adjusted for Background Scatter
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VCSEL Far Field MFD Analysis:Principal Axes
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Near Field 1/e2 Diameter from 2D FourierTransform of Far Field
Phase Retrieval Technique:“Error-Reduction” Algorithm*
)](exp[)()](exp[)()(
)]([)](exp[)()(
)](exp[)()(
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11
1
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kkk
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g
GFgg
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gFGG
θθ
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φ
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′
==
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++
−
*J. R. Fienup, “Phase retrieval algorithms: a comparison,”Applied Optics Vol. 21, No. 15, pp. 2758-2769, Aug. 1982.
•Fourier transform estimate
•Substitute measured modulus
•Inverse Fourier transform
•Apply support constraints
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Near Field from Far FieldEdge-Emitting Laser Diode
3D View
2D Fourier Transform Camera Near Field
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Near Field from Far FieldVCSEL @ 7 mA
3D View
Near Field Profile from 2D FourierTransform of FF with Phase Retrieval
Near Field Profile from Camera with100X Objective Lens
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Near Field from Far FieldVCSEL @ 15 mA
3D View
Near Field Profile from 2D FourierTransform of FF with Phase Retrieval
Near Field Profile from Camera with100X Objective Lens
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Near Field from Far FieldVCSEL @ 15 mA
3D View
Near Field Profile from 2D FourierTransform of FF with Phase Retrieval
Near Field Profile from Camera with100X Objective Lens
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Near Field from Far FieldVCSEL @ 15 mA
Topographic View
Near Field Profile from Camera with100X Objective Lens
Near Field Profile from 2D FourierTransform of FF with Phase Retrieval
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Far Field/Near Field Measurements ofFocused HeNe Laser Beam Spot Size
Lens AxisObjective Lens/CCD Camera XY Slit Profiler
"Times Diffraction Limit" Width (µm) MFD (µm) 1/e2 Width (µm) 1/e2 Width (µm)
1 Horizontal 5.46 5.22 5.52 5.671 Vertical 5.68 5.35 5.93 6.252 Horizontal 6.00 5.64 5.96 6.332 Vertical 5.93 5.65 6.34 6.36
Measurement TechniqueGoniometric Radiometer
Summary of Results
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Far Field/Near Field Measurements ofEdge-Emitting Laser Diode
Device Axis Near Field
Camera/100X Lens
" Diffraction Limit" 1/e2 Width (µm)
Mode-Field Diameter* (µm)
2D Fourier Transform
1/e2 Width (µm)1/e2 Width (µm)
Laser Diode "Fast" 1.20 1.12 *(40 deg) 1.10 1.10Laser Diode "Slow" 2.96 3.07 *(16 deg) 3.30 3.20
Measurement TechniqueFar Field
Goniometric Radiometer
Summary of Results
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Far Field/Near Field Measurements ofVCSEL for Different Modes
Device Axis Near Field
Camera/100X Lens " Diffraction Limit" Width
(µm)Mode-Field Diameter
(µm)2D Fourier Transform
(µm)D4σ Width
(µm)VCSEL @ 7mA 1 7.86 7.83 7.92 7.87
2 7.71 7.52 7.83 7.60VCSEL @ 15mA 1 3.99 4.34 4.47 8.95
2 4.02 4.35 4.67 9.63
Measurement TechniqueFar Field
Goniometric Radiometer
Summary of Results
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Conclusion
Measurements of NF and FF• Focused HeNe, LDs, and VCSELs• NF: Camera/Objective Lens, Slit Profiler• FF: Scanning Goniometric Radiometer
Comparison of Results• NF: 1/e2 , d4σ,• FF: Gaussian, MFD, 2D FFT 1/e2
Favorable Comparison ~5-10%• Tends to Validate Far Field Methods
Further Development Recommended
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“Mode-Field Diameter”
θθθθ
θθθθπλ θ
θ
θ
θ
dI
dIMFD
)cos()(sin)(
)cos()sin()(2)/(
3∫
∫
−
−=
Far Field Petermann II Integral:
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Far Field/Near FieldVCSEL Mode @ 7mA
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Far Field/Near FieldVCSEL Mode @ 15mA
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Far Field/Near FieldVCSEL Mode @ 19mA
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Far Field/Near FieldVCSEL Mode @ 24mA
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Far Field/Near FieldVCSEL Mode @ 29mA
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