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
Technical Committee
Current Stage
PPUB - Publication issued
Completion Date
29-Sep-2020
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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
IEC 62595-2-4:2020-09(en)
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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

Warning! Make sure that you obtained this publication from an authorized distributor.

® Registered trademark of the International Electrotechnical Commission
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– 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

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

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IEC 62595-2-4:2020 © IEC 2020 – 3 –

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

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

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– 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

package ................................................................................................................................ 66

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IEC 62595-2-4:2020 © IEC 2020 – 5 –
Figure I.2 – Example of temperature dependence of I-P characteristics of an LD

package with higher thermal resistance R .......................................................................... 67

Figure I.3 – Example of temperature dependence of I-P characteristics of an LD

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

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

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– 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

1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising

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8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is

indispensable for the correct application of this publication.

9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of

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.
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IEC 62595-2-4:2020 © IEC 2020 – 7 –

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.
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– 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.
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IEC 62595-2-4:2020 © IEC 2020 – 9 –
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
...

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