IEC 62595-2-4:2020

Display lighting unit - Part 2-4: Electro-optical measuring methods of laser module

IEC 62595-2-4:2020(E) specifies the electro-optical measuring methods of laser modules with multiple laser devices and an optical output for various displays and display lighting applications which require photometric and colorimetric measurements, covering the wavelength range of 380 nm to 780 nm. The module has multiple laser devices such as edge-emitting laser diodes (LDs), vertical cavity surface-emitting laser diodes (VCSELs), or photon up-conversion laser devices including second-harmonic generation (SHG). The module has an optical output such as an optical fibre, waveguide, light guide, lens unit, or other optics, emitting a laser beam combining the output of the multiple laser devices.

General Information

• Status: Published
• Publication Date: 28-Sep-2020
• ICS: 31.120 - Electronic display devices
• ICS: 31.260 - Optoelectronics. Laser equipment
• Technical Committee: TC 110 - Electronic displays
• Drafting Committee: WG 19 - TC 110/WG 19
• Current Stage: PPUB - Publication issued
• Start Date: 29-Sep-2020
• Completion Date: 30-Oct-2020

Overview

IEC 62595-2-4:2020 - “Display lighting unit – Part 2‑4: Electro‑optical measuring methods of laser module” specifies standardized electro‑optical measurement methods for laser modules used in display and display‑lighting applications. The standard covers photometric and colorimetric measurements across the visible wavelength range (380 nm to 780 nm) for modules containing multiple laser devices (edge‑emitting LDs, VCSELs, photon up‑conversion devices including SHG). It applies to modules with optical outputs such as optical fibres, waveguides, light‑guides, lens units or combined optics that deliver a combined laser beam.

Key topics and requirements

• Standard measuring conditions - environmental, dark‑room, device under test (DUT) and laser module definitions to ensure repeatable measurements.
• Safety requirements - guidance to address laser safety during measurement.
• Photometric and colorimetric tests - spectral measurements, chromaticity and centroid wavelength evaluation for narrow‑linewidth laser emissions.
• Electrical/optical characteristics - current vs. optical output (I–P) curves including CW and PWM operation, threshold current measurement and procedures.
• Far‑field pattern (FFP) - monochromatic and colorimetric FFP measurement methods for beam and illumination pattern characterization.
• Speckle measurement - monochromatic and colour speckle analysis and conversion methods to standardized, speckle‑free representations.
• Temperature dependence - procedures to characterize power and wavelength shifts with temperature for high‑ and low‑power modules.
• High‑speed modulation - pulse waveform and eye‑diagram measurement methods for fast‑modulated display lasers.
• Informative annexes - device structures (LD, VCSEL, SHG), module configurations (monochrome & RGB), wavelength/linewidth effects on chromaticity, fibre NA, coordinate conversions and measurement examples.

Applications and users

This standard is practical for:

• Display and projector manufacturers specifying and validating laser light engines.
• Optical component and laser module manufacturers for product characterization and compliance.
• Test laboratories performing repeatable photometric/colorimetric and speckle measurements.
• Lighting designers and integrators ensuring color accuracy and uniformity in display lighting systems.
• Standards and safety engineers aligning measurement methods with regulatory and quality requirements.

IEC 62595-2-4 helps ensure consistent specification, measurement and communication of laser module performance in display applications - enabling interoperability, reliable colorimetry, and safer test procedures.

Related standards

• Other parts of the IEC 62595 series (display lighting unit family) for broader system requirements.
• Relevant laser safety and photometric standards such as IEC 60825 (laser safety) and international photometry/colorimetry references.

Standards Content (Sample)

IEC 62595-2-4 ®
Edition 1.0 2020-09
INTERNATIONAL
STANDARD
colour
inside
Display lighting unit –
Part 2-4: Electro-optical measuring methods of laser module
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IEC 62595-2-4 ®
Edition 1.0 2020-09
INTERNATIONAL
STANDARD
colour
inside
Display lighting unit –
Part 2-4: Electro-optical measuring methods of laser module

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 31.120, 31.260 ISBN 978-2-8322-8912-9

– 2 – IEC 62595-2-4:2020 © IEC 2020
CONTENTS
FOREWORD . 6
INTRODUCTION . 8
1 Scope . 9
2 Normative references . 9
3 Terms, definitions, abbreviated terms, and letter symbols . 9
3.1 Terms and definitions . 9
3.2 Abbreviated terms and letter symbols . 11
3.2.1 Abbreviated terms . 11
3.2.2 Letter symbols . 12
4 Standard measuring conditions . 14
4.1 Standard measuring environmental conditions . 14
4.2 Standard measuring dark-room conditions . 14
4.3 Safety requirements . 14
4.4 Standard DUT conditions . 15
4.5 Standard LMD requirements . 15
4.6 Standard measurement setup and coordinate system . 17
5 Measuring methods . 20
5.1 General . 20
5.2 Current-light output characteristics . 21
5.2.1 General . 21
5.2.2 I-P and I- P / P characteristics . 21
o o i
5.2.3 CW and PWM operations . 22
5.2.4 Threshold currents (I ) . 23
th
5.2.5 Measurement procedures . 24
5.3 Spectra (wavelength) and chromaticity measurements . 25
5.3.1 General . 25
5.3.2 Measurement procedures . 25
5.4 FFP . 26
5.4.1 General . 26
5.4.2 Monochromatic FFP . 26
5.4.3 Colorimetric FFP . 27
5.5 Monochromatic speckle and colour speckle . 30
5.5.1 General . 30
5.5.2 Monochromatic speckle measurement affected by FFP . 30
5.5.3 Colour speckle measurement affected by FFP . 32
5.6 Temperature dependence . 35
5.6.1 General . 35
5.6.2 High-power LD module . 35
5.6.3 Low-power RGB LD module . 36
5.7 High-speed pulse modulation properties . 37
5.7.1 General . 37
5.7.2 Optical output pulse waveform measurement . 37
Annex A (informative) Laser devices . 40
A.1 Edge-emitting laser diode . 40
A.2 Single- and multi-transverse modes . 41
A.3 Single- and multi-longitudinal modes . 42

A.4 Vertical cavity surface-emitting laser diode (VCSEL) . 43
A.5 Photon up-conversion laser device. 45
Annex B (informative) Structure of laser module . 46
B.1 Monochromatic laser module . 46
B.2 RGB laser module . 47
B.3 Other output optics . 48
Annex C (informative) Narrow-linewidth emission spectra of laser modules . 49
C.1 Spectra of monochromatic high-power LD modules . 49
C.2 Spectra of multi-colour, single-longitudinal mode LD modules . 51
C.3 Spectra of multi-colour, multi-longitudinal mode LD modules . 51
C.4 Chromaticity measurements using a colorimeter . 52
Annex D (informative) Chromaticity accuracy when measuring narrow spectral
linewidth . 53
D.1 General . 53
D.2 Wavelength accuracy to keep chromaticity accuracy < 0,001 or < 0,005 . 53
D.3 Spectral bandwidth to keep chromaticity accuracy < 0,001 . 55
Annex E (informative) Numerical aperture (NA) of fibre . 58
E.1 Fibre NA and maximum divergence angle . 58
E.2 Colour-dependence of fibre NA . 58
Annex F (informative) Conversion of the spherical and Cartesian coordinate systems . 59
Annex G (informative) Centroid wavelength . 60
Annex H (informative) Examples of colour speckle pattern on colorimetric FFPs of
fibre output . 62
H.1 General . 62
H.2 Measured FFP . 62
Annex I (informative) Temperature dependence of LDs . 65
I.1 Formulation of the thermal performance of LD chips . 65
I.2 Calculated examples of I-P characteristics . 66
o
I.3 Temperature dependence of emitting wavelengths . 69
I.4 Temperature dependence of colour speckle and FFP . 69
Annex J (informative) Eye diagram . 71
J.1 Eye diagram . 71
J.2 Examples of measured eye diagrams . 72
Bibliography . 73

Figure 1 – Measurement setup and coordinate system (spherical) . 18
Figure 2 – Measurement setup and coordinate system (Cartesian) . 19
Figure 3 – Measurement setup and coordinates for speckle-related optical performance . 20
Figure 4 – Example of I-P and I- P / P characteristics . 22
o o i
Figure 5 – Pulse repetition waveforms of PWM drive with respect to duty cycle . 23
Figure 6 – I and I-P characteristics . 24
th o
Figure 7 – Example of measured colorimetric FFP . 29
Figure 8 – Example of conversion of the measured speckle data on the FFP into data
on a uniform pattern . 31
Figure 9 – Example of conversion of measured normalised illuminance data of colour

speckle on the FFP into data on a uniform pattern . 33

– 4 – IEC 62595-2-4:2020 © IEC 2020
Figure 10 – Example of conversion of measured colour speckle chromaticity data on
the FFP into data on a uniform pattern . 33
Figure 11 – Temperature dependence measurement setup for high-power laser

modules . 36
Figure 12 – Temperature dependence measurement setup for low-power laser modules . 37
Figure 13 – Measurement setup for output pulse waveform . 38
Figure 14 – Example of input/output pulse waveforms . 38
Figure A.1 – Schematic structure of narrow-stripe edge-emitting laser diode. 40
Figure A.2 – Schematic structure of wide-stripe edge-emitting laser diode . 41
Figure A.3 – Single- and multi-transverse mode patterns . 42
Figure A.4 – Single- and multi-longitudinal mode patterns . 42
Figure A.5 – Schematic structure of VCSEL . 44
Figure A.6 – VCSEL array . 44
Figure A.7 – Conceptual image of photon up-conversion . 45
Figure A.8 – Example of SHG laser device emitting at 532 nm . 45
Figure B.1 – High-power monochromatic laser module . 46
Figure B.2 – High-power RGB laser module . 47
Figure B.3 – Low-power RGB laser module . 48
Figure B.4 – Other types of optical output . 48
Figure C.1 – Superposition of multi-mode structures of three LDs . 49
Figure C.2 – Spectral power density S(λ) with a resolution of 0,1 nm . 50
Figure C.3 – Spectral power density S(λ) with a resolution of 1 nm . 50
Figure C.4 – Example of RGB single-longitudinal mode spectra . 51
Figure D.1 – Calculated wavelength accuracy to keep |∆x|, |∆y| < 0,001 . 54
Figure D.2 – Calculated wavelength accuracy to keep |∆x|, |∆y| < 0,005 . 54
Figure D.3 – Calculated wavelength accuracy to keep |∆u’|, |∆v’| < 0,001 . 55
Figure D.4 – Calculated wavelength accuracy to keep |∆u’|, |∆v’| < 0,005 . 55
Figure D.5 – Assumption for calculating the spectral bandwidth accuracy . 56
Figure D.6 – Calculated spectral bandwidth accuracy to keep |∆x|, |∆y| < 0,001 . 56
Figure D.7 – Calculated spectral bandwidth accuracy to keep |∆u’|, |∆v’| < 0,001 . 57
Figure E.1 – Fibre cross-section of MMF (step-index) . 58
Figure G.1 – Example of laser spectrum (peak and centroid wavelengths) . 60
Figure G.2 – Comparison of chromaticity error distributions between the data obtained
by the peak wavelength and the centroid wavelength . 61
Figure H.1 – Measured colour speckle patterns on colorimetric FFP for the low-power
RGB laser module with an SMF output . 62
Figure H.2 – Measured speckle-free colorimetric FFPs for the low-power RGB laser

module with an SMF output . 63
Figure H.3 – Example of speckled FFPs projected on the standard diffusive screen
(x‑y plane) out of the MMF of a high-power RGB laser module . 63
Figure H.4 – Example of un-speckled FFPs projected on the standard diffusive screen
(x‑y plane) out of the MMF of a high-power RGB laser module . 64
Figure I.1 – Example of temperature dependence of I-P characteristics of an LD
o
package . 66

Figure I.2 – Example of temperature dependence of I-P characteristics of an LD
o
package with higher thermal resistance R . 67
th
Figure I.3 – Example of temperature dependence of I-P characteristics of an LD
o
package for I = 0,25 (A) and T = 100 (K) . 68
th 0
Figure I.4 – Example of temperature dependence of output power, P , for an RGB
o
laser module . 68
Figure I.5 – Example of temperature dependence of R, G, B wavelengths
for an RGB laser . 69
Figure I.6 – Example of temperature dependence of speckled FFP for an RGB laser . 70
Figure J.1 – Example of PRBS . 71
Figure J.2 – Example of eye diagram . 71
Figure J.3 – Eye diagrams for digital frequencies at 100 MHz, 200 MHz, 300 MHz, and
500 MHz (R channel at I = 38mA) . 72

Table 1 – Letter symbols (quantity symbols/unit symbols) . 12
Table 2 – Summarised results of the colour speckle measurements (example) . 34
Table A.1 – Features of single- and multi-mode LDs . 43
Table C.1 – CIE 1931 chromaticity calculated from the higher to the lower resolution
spectra . 51

– 6 – IEC 62595-2-4:2020 © IEC 2020
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
DISPLAY LIGHTING UNIT –
Part 2-4: Electro-optical measuring methods of laser module

FOREWORD
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indispensable for the correct application of this publication.
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patent rights. IEC shall not be held responsible for identifying any or all such patent rights.
International Standard IEC 62595-2-4 has been prepared by IEC technical committee 110:
Electronic displays.
The text of this International Standard is based on the following documents:
FDIS Report on voting
110/1224/FDIS 110/1246/RVD
Full information on the voting for the approval of this International Standard can be found in
the report on voting indicated in the above table.
This document has been drafted in accordance with the ISO/IEC Directives, Part 2.
A list of all parts in the IEC 62595 series, published under the general title Display lighting
unit, can be found on the IEC website.

The committee has decided that the contents of this document will remain unchanged until the
stability date indicated on the IEC website under "http://webstore.iec.ch" in the data related to
the specific document. At this date, the document will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
IMPORTANT – The 'colour inside' logo on the cover page of this publication indicates
that it contains colours which are considered to be useful for the correct
understanding of its contents. Users should therefore print this document using a
colour printer.
– 8 – IEC 62595-2-4:2020 © IEC 2020
INTRODUCTION
Laser modules, in general, have been used widely for various applications such as, optical
communications, laser beam machining, bar-code reading, optical disc drives and so on. The
laser module in this document is limited to display applications. It is a key light source for
laser displays, laser backlight/front light units for liquid crystal displays (LCDs), holographic
displays and so on. A typical laser module for display applications comprises multiple laser
devices, electrical inputs and an optical output combining the outputs of the laser diodes
(LDs). The laser device used in the laser module here is an edge-emitting laser diode (LD), a
vertical cavity surface-emitting laser diode (VCSEL), or a photon up-conversion laser
including second-harmonic generation (SHG).
The optical output is usually provided out of an optical component such as a pigtail fibre, a
fibre with a connector, a waveguide, a light guide, or a lens unit for the convenience of users.
In advanced display applications, not only visible laser diodes but also near infrared (near IR)
laser diodes are included in the module for sensor applications such as the LiDAR system
(light detection and ranging, or laser image detection and ranging).
Therefore, the wavelength range for display applications covers all the visible wavelengths
from 380 nm to 780 nm, including the laser diodes for pumping phosphors. That is, a violet
laser diode emitting at 405 nm is included. Photometric and colorimetric measurements are
the primary focus of this document. The near IR LD for a LiDAR system included in the
module can be measured as a monochromatic light output using the light measuring device
(LMD) covering the IR wavelength region. However, the measurements of IR lasers are out of
the scope of this document.
It is important for the designing of the above display systems and devices to standardise the
electro-optical measuring methods of the laser modules. Photometric and colorimetric
measurements are particularly important for display applications because each LD has
different electrical and optical performances, such as threshold currents, efficiency, spectrum,
far field pattern (FFP) of the output laser beam, speckle-related behaviours and their
temperature dependence.
Particularly for the colour speckle of the output laser beam, the measured speckle data are
very useful to predict the visual quality of laser displays and to design speckle reducing
devices.
DISPLAY LIGHTING UNIT –
Part 2-4: Electro-optical measuring methods of laser module

1 Scope
This part of IEC 62595 specifies the electro-optical measuring methods of laser modules with
multiple laser devices and an optical output for various displays and display lighting
applications which require photometric and colorimetric measurements, covering the
wavelength range of 380 nm to 780 nm. The module has multiple laser devices such as edge-
emitting laser diodes (LDs), vertical cavity surface-emitting laser diodes (VCSELs), or photon
up-conversion laser devices including second-harmonic generation (SHG). The module has an
optical output such as an optical fibre, waveguide, light guide, lens unit, or other optics,
emitting a laser beam combining the output of the multiple laser devices.
NOTE See 3.1.1 for a definition of a laser device inside the laser module.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their
content constitutes requirements of this document. For dated references, only the edition
cited applies. For undated references, the latest edition of the referenced document (including
any amendments) applies.
IEC 60825-1, Safety of laser products – Part 1: Equipment classification and requirements
IEC 62906-5-2, Laser display devices – Part 5-2: Optical measuring methods of speckle
contrast
IEC 62906-5-4, Laser display devices – Part 5-4: Optical measuring methods of colour
speckle
3 Terms, definitions, abbreviated terms, and letter symbols
3.1 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following
addresses:
• IEC Electropedia: available at http://www.electropedia.org/
• ISO Online browsing platform: available at http://www.iso.org/obp
3.1.1
laser device
semiconductor-based or compactly assembled solid-state up-
conversion laser
EXAMPLE Edge-emitting laser diode, vertical cavity surface-emitting laser diode, or photon up-conversion laser
including second-harmonic generation (SHG), or third-harmonic generation (THG).
Note 1 to entry: See Annex A.
– 10 – IEC 62595-2-4:2020 © IEC 2020
3.1.2
laser module
display light source with an optical output combining the emitted
lights of multiple laser devices
3.1.3
monochromatic laser module
display light source with an optical output combining the emitted
lights of multiple laser devices within the wavelength range of 10 nm
Note 1 to entry: See Figure B.1 in Annex B.
3.1.4
multi-colour laser module
display light source with an optical output combining the emitted
lights of multiple laser devices emitting at different monochromatic wavelengths
3.1.5
RGB laser module
display light source with an optical output combining the emitted
lights of red, green, blue monochromatic laser devices
Note 1 to entry: See Figure B.2 and Figure B.3 in Annex B.
3.1.6
laser display
display using a laser or lasers, based on stimulated emission
Note 1 to entry: This term is specified as "laser display device (LDD)" in IEC 62906-1-2. However, the term "laser
display" covers more widely and appropriately than "laser display device".
3.1.7
fibre output power
optical output power of the optical fibre facet equipped with the laser
module
3.1.8
wall-plug efficiency
WPE
power efficiency of the optical output power by the electrical input power of
the laser module
3.1.9
threshold current
current input level of a laser module at which an optical output of the laser
module, combining the emitted lights of multiple laser devices, starts laser oscillation
3.1.10
near field pattern
NFP
output power distribution on the output aperture of the laser module
3.1.11
far field pattern
FFP
monochromatic FFP
output power distribution measured on the plane at a distance which is
significantly greater than W / λ, where λ is the wavelength and W is the largest dimension in
the output aperture
3.1.12
colorimetric far field pattern
colorimetric FFP
colour FFP
output chromaticity distribution measured on the plane at a distance which
is significantly greater than W / λ, where λ is the wavelength and W is the largest dimension
in the output aperture
3.1.13
XYZ filters, pl.
set of optical filters which will produce an optical measuring device that approximately has the
spectral responsivity of colour matching functions in the CIE 1931 standard
x,,yz
colorimetric system when used together with the intended lens, sensors, and other
components
3.1.14
laser multi-meter
light measuring device for measuring centroid wavelengths and radiometric quantities of laser
light sources with very narrow spectral linewidths using non-spectrometric methods, also
deriving colorimetric and photometric quantities using the colour-matching functions
Note 1 to entry: See [1] .
3.2 Abbreviated terms and letter symbols
3.2.1 Abbreviated terms
ACC automatic current control
APC automatic power control
BW bandwidth
CW continuous wave
DBR distributed Bragg reflector
DUT device under test
FFP far field pattern
FWHM full width at half maximum
IR infrared
LCD liquid crystal display
LD laser diode
LiDAR light detection and ranging (or laser image detection and ranging)
LMD light-measuring device
MMF multi-mode fibre
MTF modulation transfer function
NA numerical aperture
ND neutral density
NFP near field pattern
NRZ non-return-to-zero
PCB printed circuit board
PD photodiode
___________
Numbers in square brackets refer to the Bibliography.

– 12 – IEC 62595-2-4:2020 © IEC 2020
PPG pulse pattern generator
PRBS pseudo-random binary (or bit) sequence
PWM pulse width modulation
QPM quasi-phase-matching
RGB red, green, blue
RMS root mean square
RT room temperature
SHG second harmonic generation
SLM spatial light modulator
SMF single-mode fibre
SHG second-harmonic generation
TE transverse electric
TEC Thermo-electric cooler
THG third harmonic generation
TM transverse magnetic
VCSEL vertical cavity surface-emitting laser diode
WPE wall-plug efficiency
3.2.2 Letter symbols
The letter symbols for a laser module are shown in Table 1.
Table 1 – Letter symbols (quantity symbols/unit symbols)
Definition Symbol Unit
Electrical
Current I A
I
Threshold current A
th
Voltage V V
IV, P
Input electrical power W
i
Definition Symbol Unit
Optical output
P
Optical output power W
o
P
Output of red power W
R
P
Output of green power W
G
P
Output of blue power W
B
Wall-plug efficiency
P / P
-
o i
optical output (W) / electrical input (W)
η
Slope efficiency W/A
s
Size of output aperture W nm
Wavelength λ nm
λ
Centroid wavelength nm
c
λ
Peak wavelength nm
p
Spectral power density S (λ) W/nm
CIE 1931 chromaticity x, y -
CIE 1976 chromaticity u', v’ -
t , t
Rise/fall time of output waveform s
r f
t
Delay time of output waveform s
d
Period of output waveform T s
Direct measurement setup
Distance from DUT output to measurement plane along z L m
Azimuth angle φ degree
Zenith angle θ degree
Screen measurement setup (speckle measurement)
L
Distance from DUT output to screen centre m
s
D
Distance from LMD to screen centre m
s
θ
Angle between LMD and DUT degree
s
Speckle
C
Speckle contrast -
s
C
Speckle contrast for red colour -
s-R
C
Speckle contrast for green colour -
s-G
C
Speckle contrast for blue colour -
s-B
C
Photometric speckle contrast -
ps
σ
u’-variance of CIE 1976 chromaticity distribution of colour speckle -
u’
σ
v’-variance of CIE 1976 chromaticity distribution of colour speckle -
v’
µ
Covariance of CIE 1976 chromaticity distribution of colour speckle -
u’v
– 14 – IEC 62595-2-4:2020 © IEC 2020
Definition Symbol Unit
Temperature/Thermal
T
Atmospheric temperature °C
a
T
Case temperature °C
c
T
Junction temperature (LD) °C
j
Characteristic temperature of I (LD) T
°C
th 0
*
T
Characteristic temperature of η (LD)
°C
s
R
Thermal resistance (LD) K/W
th
R
Series resistance (LD) Ω
s
Others
θ
Critical angle (fibre) degree
c
θ
Maximum incident angle to fibre degree
max
Wavelength accuracy of LMD ±δ nm
λ
Reference wavelength nm
r
Spectral bandwidth of LMD ∆λ nm
CIE 1931 chromaticity differences ∆x, ∆y -
CIE 1976 chromaticity differences ∆u’, ∆v’ -

4 Standard measuring conditions
4.1 Standard measuring environmental conditions
Measurements shall be carried out under the following standard environmental conditions:
– temperature: 25 °C ± 3 °C
– relative humidity: 25 % to 85 %
– pressure: 86 kPa to 106 kPa
When different environmental conditions are used, they shall be reported.
4.2 Standard measuring dark-room conditions
The background illuminance of the standard dark-room shall be less than 0,01 lx except when
the DUT and the LMD are covered under the same dark-room conditions or when both are
fibre-connected.
4.3 Safety requirements
The DUT and the measurement conditions shall be strictly in accordance with the safety
requirements of IEC 60825-1.
Laser modules are mostly intermediate (B2B) products. Some of the high-power laser
modules are categorized as class 4. The measurements shall be carried out carefully in the
laser- controlled area, by putting on laser protection glasses, so that the maximum
permissible exposure levels in IEC 60825-1 are not exceeded by persons in the area. That is,
the laser safety class label on the DUT shall be confirmed, and the measurement of
environmental conditions shall be kept as specified in IEC 60825-1, depending on the DUT
laser class.
4.4 Standard DUT conditions
The position for measuring the case temperature T shall be determined depending on the
c
laser module type and its structure. It should be determined usually at the surface closest to
the heatsink of the internal LD assembly.
The accuracy of standard case temperature T shall be ±0,5 °C.
c
The measurements shall be started after the DUT and the LMD have achieved stability.
Regarding the DUT, the stability shall be achieved when the output power of the DUT varies
within ±3 % over the entire measurement timeframe.
Most laser modules for display applications are usually operated in ACC (automatic current
control). The current level (CW) or the time-averaged current level (PWM) for the
measurements shall be noted in the report.
The DUT shall be operated under the current conditions less than the absolute maximum
rating, both for CW and PWM (pulse peak) operations. The PWM operation for LDs is
explained in detail in 5.2.3. If the laser module manufacturer provides the driver circuitry or
module, it should be used.
If the laser module includes a thermo-control function, e.g., TEC (thermo-electric cooler), the
thermo-control capability in the specifications shall be noted in the report.
4.5 Standard LMD requirements
The LMD performance for CW operation shall be as follows.
When an LMD with a different performance is used, its specifications shall be noted in the
report.
a) ampere meter
1) current range: zero to the absolute maximum rating
2) accuracy: ±2 %
b) voltmeter
1) voltage range: zero to the absolute maximum rating
2) accuracy: ±2 %
c) optical power meter/laser power meter
1) power range: from zero to the absolute maximum rating. A calibrated ND filter may be
used if the power meter cannot cover the maximum rating
2) accuracy: ±4,5 %
3) spectral range: covering at least the wavelengths of the laser module
4) launch condition: underfilled launch for total optical power measurement, overfilled
launch for optical power density measurement
d) spectral irradiance meter
1) irradiance range: from zero to the absolute maximum rating. A calibrated ND filter may
be used if the power meter cannot cover the maximum rating
2) wavelength accuracy: ±0,3 nm
3) spectral range: covering at least the wavelengths of the laser module
4) spectral bandwidth: ≦ 5 nm
e) luminance meter/illuminance meter (using a v(λ) filter)
1) shall be calibrated by the spectral radiance / Irradiance meter

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f) colorimeter (using XYZ filters)
1) shall be calibrated by spectrometric LMD
g) wavelength meter
1) spectral range: covering at least the wavelengths of the laser module
2) power range: zero to the absolute maximum rating. A calibrated ND filter may be used
if the power meter does not cover the maximum rating
3) wavelength accuracy: ±0,3 nm
h) spectrum analyser
1) wavelength range: covering at least the wavelengths of the laser module
2) power range: zero to the absolute maximum rating. A calibrated ND filter may be used
if the power meter does not cover the maximum rating
3) wavelength accuracy: ±0,3 nm
4) spectral bandwidth: ≦ 1 nm
i) laser multi-meter
1) wavelength range: covering the wavelengths of the laser module
2) power range: zero to the absolute maximum rating
3) wavelength accuracy: ±0,3 nm
j) speckle measurement equipment
1) wavelength range: covering at least the wavelengths of the laser module
2) the MTF of the optics shall be equivalent to that of the human eye
NOTE See [1], IEC 62906-5-2 and IEC 62906-5-4 regarding the MTF of optics (consisting of iris, lens, imaging
devices and so on) inside the speckle measurement equipment.
For measuring laser modules operated in PWM, the RMS voltmeter and the time-averaged
power meter shall be used. To keep the accuracy of the measurements, the measurement
time (integrating time) shall be sufficiently longer than the period of the PWM as explained in
5.2.3.
The laser modules use laser devices as light sources. Their emission spectra are very narrow,
and their chromaticity coordinates are plotted almost on the wavelength locus of the
chromaticity diagram. Therefore, the chromaticity accuracy is very sensitive to wavelength
because the curvature of the wavelength locus at the LD wavelength affects the chromaticity
accuracy.
The wavelength accuracy of ±0,3 nm specified in d), g), h), and i) above, is a practical value
mostly common to the conventional display measurements. Precise spectrometric methods
should be the reference of the wavelength measurements.
If it is necessary to guarantee a specific value of chromaticity accuracy at a specific
wavelength, the wavelength accuracy shall be evaluated. Examples of the wavelength
accuracy curves with respect to visible wavelengths are shown in Annex D.
When multi-colour laser modules are measured, the LMDs shall not be wavelength-dependent,
or shall be calibrated for their spectral responsivity for all the laser wavelengths for spectral
radiant flux measurements.
The edge-emitting LDs operate in the TE-polarized (linearly polarized) mode explained in
Annex A. The linearly polarized laser light incident to the isotropic optical fibres is converted
into a circularly polarized light. That is, the output beam of the laser modules which is
combined with multiple laser beams can include various polarization states depending on the
output optics. The LMDs for direct measurements shall detect the optical power of a
polarization state as is.
Therefore, the optics inside the LMD shall be polarization-independent. It is much easier for
laser beams with a very narrow divergence to design polarization-independent optics because
the beam incident normal to a multi-layered coated surface or total reflection surface is
polarization-independent. For the case of relatively large beam divergence, the detector
angular dependence regarding polarization should be described. A simple LMD structure with
a photodiode only is much better than the com
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