The Scanning Goniometric Radiometer:A Revolutionary Technique for Characterizing

Divergent Light Sources: Laser Diodes, VCSELs,Optical Fibers, Waveguides, LEDs,…

Presented by:Jeffrey L. Guttman, Ph.D.

Photon Inc.

www.photon-inc.cominfo@photon-inc.com

IEEE Santa Clara ValleyLasers & Electro-Optics Society

Who is Photon Inc.?Photon Inc. is a San Jose, CA manufacturer ofinstruments that measure the spatial properties oflight from virtually any light source—lasers, laserdiodes, light-emitting diodes, optical fiber,waveguides, and VCSELs. Since its founding in 1984,Photon has been committed to offering uniquesolutions to difficult challenges and providing superiorafter-sales service and support. Abiding by thismission has resulted in robust products that meet theneeds of satisfied customers worldwide.

Photon instrument profile…Laser diodes and VCSELsOptical componentsCollimators based on laser diodes, VCSELs,and fibersOptical assembliesLensed, tapered and/or single-mode fibersMedical lasers and systemsSolid state lasers and systemsIndustrial lasers and systemsGas lasersLaser scanners and systemsOptical memory

Photon instruments measurethese parameters

Spot size and profileBeam positionMultiple beam analysisCollimation or divergenceGaussian fitM2

Near-field profilesFar-field profilesMode field diameterEffective areaNumerical aperture

Scanning Goniometric RadiometerABSTRACT

Measurements of the irradiance pattern of light sources has traditionallybeen performed using instrumentation systems commonly referred to as“goniometers” or “goniophotometers”. These systems comprise a detectorand a fixture for holding the source, and the measurement is made eitherby moving the detector about the source at a fixed radius or by rotating thesource on a rotation stage with the detector stationary. With thesesystems, the time required to measure the far field pattern along a singleazimuth ranges typically from a few minutes up to an hour. These timeconstraints made it difficult if not practically impossible to perform morecomplete characterization of the irradiance pattern of optical sources. Animprovement to these methods, the “scanning goniometric radiometer”,offers up to 3 or more orders of magnitude increase in measurementspeed, up to 2 orders of magnitude improvement in angular samplingresolution, and a measurement field-of-view up to 360°. Details of the newtechnique, and application examples for measurements of laser diodes,VCSELs, LEDs and optical fiber will be presented.

Irradiance Measurement of Divergent Light Sources

New Scanning Goniometric Radiometer Technique

Measurement Examples: LDs, VCSELs, Fiber, LEDs

Near-Field Characterization from Far-Field Measurement

Summary

Scanning Goniometric RadiometerPRESENTATION OUTLINE

Why Perform Measurements?

• Research & Development

Verify Designs

Data for Modeling

• Manufacturing

Qualify Devices (prior to value-added packaging)

Device Life Testing

Product Quality Assurance

Scanning Goniometric RadiometerMeasure Divergent Light Sources

Semiconductor Lasers• Edge-emitting Laser Diodes (LDs)• Vertical Cavity Surface Emitting Lasers (VCSELs)

Light Emitting Diodes (LEDs)Optical Fibers

• Single-mode Fiber• Multi-mode Fiber• Specialty Fibers

Optical WaveguidesSemiconductor Optical AmplifiersPhotonic Bandgap StructuresDiffuse Scatterers

• e.g., Laptop Computer Diffuser ScreensNovel Sources….

Scanning Goniometric RadiometerApplications – Divergent Light Sources

Measure:• Angular width of Fast and Slow axes• Beam Pointing• Kink Onset• Spatial Mode StructureVerify Component SpecificationsQualify devices before adding Value

Scanning Goniometric RadiometerApplication: Laser Diodes

Scanning Goniometric RadiometerApplication: Fiber Optics

Single-Mode FiberMulti-Mode FiberSpecialty Fiber• TEC• Erbium Doped• DCF• Others…

Lensed FiberFiber Bundles

Scanning Goniometric RadiometerApplication: Scatterometry

Bi-directional Scatter Distribution Function (BSDF)• Reflectance (BRDF)• Transmittance (BTDF)• Volume (BVDF)

Total Integrated Scatter (TIS)

Scanning Goniometric RadiometerApplication: Illumination

Measure Illuminance of Luminaires• Lamps• Lighting Fixtures• Headlights• Traffic Signals• etc…

Goniometric Radiometer Conventional Goniometric Measurement

SOURCE

DETECTOR

R

SOURCE DETECTOR

Stationary Source/Moving Detector

Moving Source/Stationary Detector

Scan Time Typically Slow: seconds to hour range

New Goniometric Scanning Method: Stationary Source/Stationary Detector

•Real-Time Single Azimuth Scans

•Provides 3D Measure on Hemisphere

SCAN MECHANISM

SOURCE

DETECTOR

Goniometric Radiometer New Goniometric Scanning Method

Stationary Source/Stationary Detector

ROTATING OPTICAL FIBER, FIBERBUNDLE, OR LIGHT PIPE

SOURCE

DETECTOR

MOVEABLE MIRROR ORIENTED @45° TO THE INCIDENT BEAM

ROTATING OPTICAL FIBER, FIBERBUNDLE, OR LIGHT PIPE

SOURCE

DETECTOR

ωSource at center of scan

Fold Mirror at center of scanwith source below

Goniometric RadiometerPrinciple of Operation

SIGNAL

InGaAs or SiDETECTOR

ROTATION AXIS(OPTICAL AXIS)

OPTICAL FIBERBUNDLE

SOURCE

AMPLIFIER

ANGULAR POSITION ENCODER

ENTRANCEAPERTUREMIRROR

SERVO MOTOR

ADAPTER PLATE

STEP MOTOR

Angular Transformation

θθ

θ=

+

+ +

⎡

⎣⎢

⎤

⎦⎥−cos

cos '

cos '1

2 2 2

d R

R d Rd

Converts angles in Scan space to angles in Source space.

θ′

θ d

R

α

α

δ

r

R

SOURCE POSITION

SCAN CENTER

Obliquity Factor Correction

The Collection fiber bundle points at Scan Center.

Obliquity Factor = 1/cos(θ-θ’) = 1/cos (δ)

θ′

θ d

R

α

α

δ

r

R

SOURCE POSITION

SCAN CENTER

Scan Eccentricity Correction

r R d Rd( ' ) cos 'θ θ= + +2 2 2

VIRTUAL SOURCE

R

d

θ

CENTER OF ROTATION

r(θ’

θ’

Angular Field-of-View

Instrument Field-of View is determined by:Length “L” of the Fold Mirror

Distance “d” between source and fold mirror

NA of Collection Fiber Bundle can also be a factor when d ~ Rscan

Example: For L = 10 cm and d= 1.5 cm: FOV = ± 73.3°

Width of the Fold Mirror determines allowable Source Dimension

Goniometric Radiometer Scan Geometry

FRONT OF INSTRUMENT

φ = 0°

θ = 90°

OPTICAL AXIS

SCAN DIRECTION0.05° sampling

φ = 90°

θ = 0°

θ = -90°

DETECTOR(0.69° nominal FOV)

0.9° azimuth angleincrements

θ

φSOURCE

Scanning Goniometric RadiometerPossible to Scan at Arbitrary Radii

DATA SIGNAL

ENCODER SIGNALOPTICALCOMMUTATOR

DETECTOR withAPERTURE STOP

ENTRANCEAPERTURE MIRRORSTEP MOTOR withENCODER

HUB MOTOR

ENTRANCEAPERTURE MIRROR

OPTICALSOURCE

R1

R3R2

Rn Mexit

Ment

ANGULAR POSITIONENCODER

LIGHTBAFFLE

Goniometric RadiometerLD 8900, LD 8900R

Goniometric RadiometerLD 8900, LD 8900R

LD 8900/LD 8900RData Acquisition

0.055° or Finer Sample Resolution3241 Data Points/ScanScan Radius: 84 mmMaximum Field of View: ± 72°Single or Perpendicular Scan Modes

Arbitrary Azimuth Angle3D Scan Mode

10, 20, 50, 100, or 200 Azimuthal ScansCW or Pulsed Sources

Use Like a Power MeterCenter the Source in the ApertureSet the GainAcquire Profile Data/ParametersSimple GUISimple Custom Interfacing

Goniometric RadiometerEase of Use

Simple Mechanical Device Mounts• Positions the Source in the Aperture

Alignment Pins• Mechanical Reference to Optical Axis

Goniometric RadiometerDevice Interface

WARNING!The following containsgraphical depictions ofactual optical deviceirradiance profiles.

Viewer Discretion Advised!

LD 8900 Goniometric RadiometerLD Measurements

LD 8900 Goniometric RadiometerEdge-emitting Laser Diode

Orthogonal Scans: Rectangular View

LD 8900 Goniometric RadiometerEdge-emitting Laser Diode

Orthogonal Scans: Polar View

LD 8900 Goniometric RadiometerPackaged LD: Topographic View

LD 8900 Goniometric RadiometerPackaged LD: 3D Rectangular View

LD 8900 Goniometric RadiometerPackaged LD: 3D Polar View

LD 8900 Goniometric RadiometerPackaged LD: 3D View

LD 8900 Goniometric RadiometerPackaged LD with Dust on Window

LD 8900 Goniometric RadiometerPackaged LD with Fingerprint on Window

LD 8900 Goniometric RadiometerLED Measurements

LD 8900 Goniometric Radiometer3D Polar Logarithmic Profile of an LED

LD 8900 Goniometric RadiometerLED Measurements

LD 8900 Goniometric Radiometer3D Rectangular Profile of an LED

LD 8900 Goniometric RadiometerTopographic Profile of an LED

LD 8900 Goniometric Radiometer3D Profile of an LED

LD 8900 Goniometric RadiometerPower View: LED Data

Goniometric Radiometer Beam Statistics View with

Pass/Fail Limit Analysis

LD 8900 Goniometric RadiometerSample Data: LED Device

LD 8900 Goniometric RadiometerVCSEL Measurement

LD 8900R Goniometric RadiometerSample Data: VCSEL

LD 8900R Goniometric RadiometerVCSEL Modes @ 7, 15, 19, 24, 29 mA

LD 8900R Goniometric RadiometerSample Data: Single-Mode Fiber

0.001

0.01

0.1

1

10

100

1000

10000

100000

1000000

10000000

-100 -80 -60 -40 -20 0 20 40 60 80 100

Degrees

Am

plitu

deLD 8900HDR Goniometric Radiometer

Far-Field Profile Data:Single-Mode Fiber

LD 8900HDR Goniometric Radiometer3D Far-Field Profile Data:

Single-Mode Fiber

200 Azimuthal Scans in ~1 Hour Conventional techniques require 200 hours (5 weeks)

LD 8900HDR Goniometric RadiometerFar-Field Profile Data:

Dispersion-Shifted Fiber

0.01

0.1

1

10

100

1000

10000

100000

1000000

10000000

-90 -75 -60 -45 -30 -15 0 15 30 45 60 75 90

Degrees

Am

plitu

de

LD 8900HDR Goniometric Radiometer3D Far-Field Profile Data:Dispersion-Shifted Fiber

Scanning Goniometric RadiometerMFD vs Wavelength

10.3000

10.4000

10.5000

10.6000

10.7000

10.8000

10.9000

11.0000

11.1000

1500 1510 1520 1530 1540 1550 1560 1570 1580 1590 1600

MFD MIN

MFD MAX

MFD AVE

250 Measures At Each Wavelength:1 Man-Year Labor Using Conventional Goniometer

1 Man-Day with New Scanning Goniometer Technique

Mod

e-Fi

eld

Dia

met

er (

µm)

Wavelength (nm)

Near Field Characterization

ApplicationsFibers - MFD, Aeff

LDs - Modes, GeometryVCSELs - Modes GeometryWaveguides - Modes, GeometryTapered Fibers - Spot SizeQuantum Dots - Modes, GeometryOther “μm-subμm” structures

Direct Near-Field SourceMeasurement Techniques

Camera/Magnifying ObjectiveDiffraction Limited for “μm-subμm” StructuresNA, MTF, and λ Dependence of OpticsAccess to Aperture Field

Scanning Knife-EdgeAccess to Aperture Field

Near Field Scanning Optical Microscopy (NSOM)Speed of MeasurementAccess to Aperture FieldExpensive

Indirect Near-Field Characterizationfrom Far-Field Measurement

Calculate Near Field quantitiesfrom measured Far FieldMinimal Optics LimitationsNo Access ConstraintsEase of MeasurementProvides “sub-µm” Measures

Indirect Near-Field Characterizationfrom Far-Field Measurement

Fiber MFDPetermann II Integral

Fiber Aeff

Hankel Transform of Far-Field PowerDiffraction Limited 1/e2 “Spot” Size

Calculated from Far-Field Divergence (d=4λ/πθ)Account for M2: d=4Mλ/πθ

Aperture Field2D Fourier Transform Methods

Far-Field Measurement of Mode-FieldDiameter of Optical Fiber

θθθθ

θθθθπλ θ

θ

θ

θ

dI

dIMFD

)cos()(sin)(

)cos()sin()(2)/(

3∫

∫

−

−=

TIA/EIA FOTP-191 Direct Far-Field Method“Reference Method”Petermann II Integral:

Far-Field/Near-Field Measurements ofFocused 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 TechniqueGoiometric Radiometer

Far-Field/Near-Field Measurements ofEdge-Emitting Laser Diode

Device Axis Near Field

100x Objective Lens/Camera " Diffraction Limit" Width

(µm)2D Fourier Transform

(µm)1/e2 Width

(µm)Laser Diode "Fast" 1.20 1.11 1.10Laser Diode "Slow" 2.96 3.30 3.20

Measurement TechniqueFar Field

Goniometric Radiometer

Far Field/Near FieldVCSEL Mode @ 7mA

Far Field/Near FieldVCSEL Mode @ 15mA

Far Field/Near FieldVCSEL Mode @ 19mA

Far Field/Near FieldVCSEL Mode @ 24mA

Far Field/Near FieldVCSEL Mode @ 29mA

Scanning Goniometric RadiometerSummary

New Technique Provides:Measurement Speed and Accuracy• Single Scans in Real Time• 3D Profiles with Resolution Better than CCDs• Angular Sampling Resolution to 0.001°

Wide Angular FOV• W/ fold mirror … approaching 180°

• w/o fold mirror … up to 360°Single Detector• No calibration issues

Scanning Goniometric RadiometerSummary Continued

High Dynamic Range• Up to >100 dB Optical Power Range

Ease of Use• Compact System• Use like a Power Meter0151—simply point and measure• Operates in any orientation• Source can be stationary; e.g. wafer level testing

Wide Applicability

In Conclusion, a REVOLUTIONARY Technique!!