temperature stabilized measurements of laser spectra
DESCRIPTION
Temperature Stabilized Measurements of Laser Spectra. T. Flick, Wuppertal University Mini Opto Workshop 4.-5. March 2010 CERN. Overview. Introduction Measurement purpose Measurement principle Setup Performed measurements Temperature behavior Spectra Status and future plans. - PowerPoint PPT PresentationTRANSCRIPT
Temperature Stabilized Measurements of Laser SpectraT. Flick, Wuppertal UniversityMini Opto Workshop4.-5. March 2010CERN
T. Flick, Temperature Stabilized Measurements of Laser Spectra 2
Overview•Introduction
▫Measurement purpose▫Measurement principle
•Setup•Performed measurements
▫Temperature behavior▫Spectra
•Status and future plans
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T. Flick, Temperature Stabilized Measurements of Laser Spectra 3
Introduction• In the innermost of the existing HEP detectors VCSEL need to
stand severe radiation environments• This will get worse with future experiments• Main damaging effects for lasers:
▫ Radiation Damages▫ Temperature effects inside the semiconductor material (at the
junction)• Mostly both effects come along together, but heat can be cooled
away.• This study is investigating the possibility to quantify a measure
and prepare an improvement possibility for the cooling.• Similar work has been investigated by Markus Axer (Jan,
Francois) for the CMS experiment and we inherit a lot from this work.▫ I will use several slides from him to explain the principle
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T. Flick, Temperature Stabilized Measurements of Laser Spectra 4
Wavelength Spectrum• The wavelength spectrum emitted by a laser diode is a perfect indicator of the device’s
internal temperature – the junction temperature Tj
• The wavelength spectrum is red-shifted when the device is heated by increasing the ambient temperature or the input power
• If a given cavity mode remains at the same wavelength, the junction temperature Tj must be constant
• The change in junction temperature due to varying the input power Pin to the laser can be cancelled by a change in the heat sink temperature, so as to keep the selected mode fixed in wavelength (nulling method Paoli method)
• The thermal resistance is found from the ratio of the change in heat sink temperature to the change in input power.
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Wavelength [nm]
Data Gaussian Fit Peak Wavelength
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130012961292
Wavelength [nm]
Typical wavelength spectrum of a Fabry-Perot type laser measured with an Optical Spectrum Analyzer
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T. Flick, Temperature Stabilized Measurements of Laser Spectra 5
L-I Characteristic Light-Current (L-I) characteristic of a non-irradiated laser at Tamb=20°C
IthDL
DI Eff=DL/DI
Thermal rollover
Threshold current Ith laser starts to emit coherent light
Efficiency Eff slope of L-I curve in linear part
Thermal rollover non-linear part of L-I curve where non-radiative recombination mechanisms (Auger) become dominant due to internal temperature
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T. Flick, Temperature Stabilized Measurements of Laser Spectra 6
Spectral Behavior during Irradiation
optjths
ambj
optin
ambj
diss
ambjth PVIRI
TTPPTT
PTT
R
=
=
=2
1298.4
1298.2
1298.0
1297.8
1297.6
1297.4
1297.2
1297.0
Pea
k M
ode
Wav
elen
gth
[nm
]
543210
20 MeV Neutron Fluence [1014n/cm2]
XP439D03, CD/DFluence = 0.24656D/DFluence = 0.090094D/DFluence = 0.061354D/DFluence = 0.049894D/DFluence = 0.042622
The behavior of certain mode peaks is unique for all LDs:
• “Slight” red-shift with increasing fluence at the same input current level
• “Large” red-shift when increasing the input current
10mA
25mA
45mA
55mA
•Rs is constant during irradiation term is mainly affected by I
•Ith increases during irradiation term is mainly affected by irradiation
Popt is affected by I and by irradiation
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T. Flick, Temperature Stabilized Measurements of Laser Spectra 7
Paoli Method
T0
T1
100%1%
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Specific Mode Peak Wavelength [nm]
T0,DC0
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Specific Mode Peak Wavelength [nm]
T0,DC0
T0,DC1
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Specific Mode Peak Wavelength [nm]
T0,DC0
TX,DC1
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Specific Mode Peak Wavelength [nm]
T0,DC0
T1,DC1
Am
bien
t Tem
pera
ture
Input Pulse Duration
internal heating
exte
rnal
coo
ling
T1,DC1 = T0,DC0
T0,DC0
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1,0,, == xDCVIPwith xxxxin
10
00,11,
0,1,
)()()(
TT
TTTTPPR
jj
ininth
=
=
T. Flick, Temperature Stabilized Measurements of Laser Spectra 8
The Paoli MethodT0
T1
100%1%
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Specific Mode Peak Wavelength [nm]
T0,DC0
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Specific Mode Peak Wavelength [nm]
T0,DC0
T0,DC1
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Specific Mode Peak Wavelength [nm]
T0,DC0
TX,DC1
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Specific Mode Peak Wavelength [nm]
T0,DC0
T1,DC1
Am
bien
t Tem
pera
ture
Input Pulse Duration
internal heating
exte
rnal
coo
ling
T1,DC1 = T0,DC0
T0,DC0
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€
Rth =Tj,0 −T0Pin,0 − Popt ,0
≈Tj,0 −T0Pin,0
0,1,
1,
11, , jj
in
jth TT
PTT
R =
1000,11,0,1, )()()( TTTTTTPPR jjininth ==1,0,, == xDCVIPwith xxxxin
T. Flick, Temperature Stabilized Measurements of Laser Spectra 9
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Wavelength [nm]
Temp=30.04(°C)Current=-10(mA)Total Power=-10.42(dBm)
• Extraction of spectrum properties
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Wavelength [nm]
'Peak Maximum' 'Fit'
Temp=30.04(°C)
Cavity Mode-40
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Wavelength [nm]
'Peak Maximum' 'Fit'
Temp=30.04°CMean=1304.3nmWidth=2.7274nm
Gain
The Paoli Method Step by Step05.03.2010
T. Flick, Temperature Stabilized Measurements of Laser Spectra
Thermal Effects during Irradiation
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Pin=52.8mWPin=55.0mWPin=56.9mW
24.8
24.6
24.4
24.2Am
bien
t Tem
p T a
mb
[°C
]
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Wavelength [nm]
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T=24.2°C T=24.5°C T=24.9°C
//
j amb inth
diss in opt amb
T T PTRP P P T
D DD= =
D D
• A parameter that describes the device’s efficiency to release heat generated inside the laser is called Thermal Resistance Rth
/ 0.09 /ambT nm CD D =
• D/DPin monitored during irradiation:
/0.0153 /
inPnm mW
D D=
0.0153 1700.09
C CmW W
= =
• D/DTamb measured in an oven:
T. Flick, Temperature Stabilized Measurements of Laser Spectra 11
Measurement Setup•In Wuppertal a similar setup as used by
Markus has been realized:▫DUT is kept in a thermally isolated box▫Cooling and heating capabilities are realized
using a Peltier element and a temperature control / regulation circuit
▫Optical fibres connected to an OSA (Yokogawa A6319)
▫Laser driving using external pulser / waveform generator and current source.
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T. Flick, Temperature Stabilized Measurements of Laser Spectra 12
Setup Schematic
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Current Source
Waveform Generator Temperature
Regulation
PCLabView Control Program
OSA
Thermal Enclosure
Peltier
DUT
Data Stream
Cooling
Spectra Mesaurement
T. Flick, Temperature Stabilized Measurements of Laser Spectra 13
Setup Pictures
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ThermalEnclosure
Waveform Generator
Spectrum Analyser
Current Source for
Laser
T. Flick, Temperature Stabilized Measurements of Laser Spectra 14
Temperature Studies• Different regulation
algorithms have been studied
• PID algorithm has been chosen to control the Peltier element
• Temperature regulation is very fast▫ O(few mins)
• Temperature remains very stable ▫ < ±0.05 °C
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T. Flick, Temperature Stabilized Measurements of Laser Spectra 15
Optical Measurements• OSA measurement time is
depending on the resulotion and span:▫ 1.5 - 25 s per measurement
(10 pm resolution)• Different analysis possible,
directly in the OSA or offline on the raw data
• Scan of temperature dependent spectra shows the wished behavior
• Red shift of the spectrum while warming the laser
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T. Flick, Temperature Stabilized Measurements of Laser Spectra 16
Red Shift vs Temperature• Monitoring 3 peaks from the
spectrum under temperature change
• Temperature range 10-30°C in 1°C steps
• Spectrum peaks change by ▫ 0.0780 nm/K▫ 0.0779 nm/K▫ 0.0786 nm/K
• Zooming into the range of 16-18°C measured in 0.1°C steps shows a jump
• It is not yet fully understood and needs further investigation
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Temperature [°C]
Temperature [°C]
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T. Flick, Temperature Stabilized Measurements of Laser Spectra 17
Interesting Topic to Look at• Peak does not shift, but
more transforms into another
• Polarization effect?
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Wavelength [nm]
Inte
nsity
[dB
m]
T. Flick, Temperature Stabilized Measurements of Laser Spectra 18
Duty Cycle Dependency• First DC measurements
performed• Increase of wavelength
with introduced power• Error is RMS of the peak• Careful handling of the
peak error needed• Inclusion of this
measurement into the Paoli Method to be done
• This measurement shows the working principle only
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T. Flick, Temperature Stabilized Measurements of Laser Spectra 19
Status of the Setup and Further Plans• The measurement itself (Paoli Method) is automized• Temperature depending spectra and duty cycle (power) depending
spectra are taken automatically • Analysis tools are under investigation:
▫ Evaluate peaks▫ Fit the Gaussian▫ Extract the l shift and the gain curve▫ Conclude for thermal resistance▫ …
• Different types of optical components (simple diode, transmitter board, …) need to be implemented, but this is prepared already.
• Planned:▫ Laser package optimization studies▫ Test several different laser diodes (different materials, speed,
wavelength … compare properties)▫ Package optimization studies (heat coupling)▫ Irradiation
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T. Flick, Temperature Stabilized Measurements of Laser Spectra 20
Summary and Outlook• The setup used at CERN for CMS studies has been
reproduced in Wuppertal• First measurements have been taken• Spectra measured in dependence on temperature
and power have been performed• Measurement can be run automatically
• Analysis software is under way• More devices will be tested and the setup will be
qualified further• Will be used to qualify lasers afterwards
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