IEC 62906-5-2:2016

Laser display devices - Part 5-2: Optical measuring methods of speckle contrast

IEC 62906-5-2:2016(E) specifies the standard measurement conditions and measurement methods for determining the monochromatic speckle contrast of laser display devices (LDDs). The LDDs may include hybrid types using both a laser or lasers, and spontaneous emission-based light sources, such as LEDs.
NOTE: The monochromatic speckle contrast measurements do not include image quality issues.

General Information

• Status: Published
• Publication Date: 06-Jun-2016
• ICS: 31.260 - Optoelectronics. Laser equipment
• Technical Committee: TC 110 - Electronic displays
• Drafting Committee: WG 10 - TC 110/WG 10
• Current Stage: PPUB - Publication issued
• Start Date: 07-Jun-2016
• Completion Date: 31-Jul-2016

Overview

IEC 62906-5-2:2016 - "Laser display devices - Part 5-2: Optical measuring methods of speckle contrast" specifies standardized measurement conditions and methods for determining the monochromatic speckle contrast of laser display devices (LDDs). The standard covers LDDs including hybrid systems that combine laser(s) and spontaneous-emission light sources (e.g., LEDs). Note: these speckle contrast measurements are focused on optical speckle metrics and do not address general image quality.

Key technical topics and requirements

• Scope and purpose
  • Defines how to measure monochromatic speckle contrast for LDDs (front and rear projection geometries).
  • Applies to hybrid systems containing laser diodes (LD) and LEDs.
• Standard measurement environment
  • Temperature: 25 °C ± 3 °C
  • Relative humidity: 25 % to 85 %
  • Atmospheric pressure: 86 kPa to 106 kPa
• Darkroom and background limits
  • Background illumination reflected from the device under test (DUT) must be ≤ 1/20 of the display’s lowest black level; otherwise background subtraction is required and must be reported.
• Measurement geometry and coordinate system
  • Defines projection and viewing directions using inclination (θ) and azimuth (φ) angles; includes guidance for front and rear projection setups.
• Measuring equipment and procedures
  • Use of a light measuring device (LMD) to simulate the observer; recommendations on sensor pixel size and measurement conditions are provided (see informative Annex B).
  • Calibration and diagnostic procedures for determining highest and lowest speckle contrast values (C).
• Safety and normative references
  • Measurements must comply with laser safety requirements (IEC 60825-1).
  • Terminology aligned with IEC 62906-1-2.
• Informative annexes
  • Spectral behavior of laser diodes, sensor pixel-size recommendations, theoretical speckle formulation and common error sources.

Practical applications and users

Who benefits from IEC 62906-5-2:

• Display manufacturers developing laser and laser-hybrid projection systems who need repeatable speckle metrics.
• Test laboratories and QA teams performing standardized speckle characterization and certification testing.
• R&D engineers evaluating speckle mitigation techniques (e.g., spatial/temporal decorrelation).
• System integrators and product managers assessing perceived speckle risk in projection products and compliance with industry measurement practice. Practical uses:
• Benchmarking speckle performance across prototypes and production units.
• Verifying effectiveness of speckle-reduction solutions and optical designs.
• Producing reproducible measurement reports for suppliers and customers.

Related standards

• IEC 60825-1 - Safety of laser products (equipment classification and requirements)
• IEC 62906-1-2 - Laser display devices - Vocabulary and letter symbols

Keywords: IEC 62906-5-2, laser display devices, speckle contrast, monochromatic speckle, LDD, laser diode (LD), LMD, front projection, rear projection, speckle measurement, darkroom conditions.

Standards Content (Sample)

IEC 62906-5-2 ®
Edition 1.0 2016-06
INTERNATIONAL
STANDARD
colour
inside
Laser display devices –
Part 5-2: Optical measuring methods of speckle contrast
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IEC 62906-5-2 ®
Edition 1.0 2016-06
INTERNATIONAL
STANDARD
colour
inside
Laser display devices –
Part 5-2: Optical measuring methods of speckle contrast

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 31.260 ISBN 978-2-8322-3455-6

– 2 – IEC 62906-5-2:2016 © IEC 2016
CONTENTS
FOREWORD . 4
1 Scope . 6
2 Normative references. 6
3 Terms, definitions and abbreviations . 6
3.1 Terms and definitions . 6
3.2 Abbreviations . 6
4 Standard measuring conditions . 7
4.1 General . 7
4.2 Standard measuring environmental conditions . 7
4.3 Measurement coordinate system . 7
4.4 Darkroom conditions . 8
4.5 Standard conditions of measuring equipment . 8
4.5.1 General . 8
4.5.2 Adjustment of LDD . 9
4.5.3 Conditions of measuring equipment . 9
4.6 Screen conditions . 10
4.6.1 General . 10
4.6.2 Report . 10
5 Measuring methods of speckle contrast . 10
5.1 Speckle contrast measurement of still image . 10
5.1.1 Purpose . 10
5.1.2 Measuring conditions . 10
5.1.3 Measuring the monochromatic speckle contrast of front projection . 10
5.1.4 Measuring the monochromatic speckle contrast of rear projection . 12
5.2 Calibration and diagnosis of the LMD . 12
5.2.1 General . 12
5.2.2 Calibration procedure and diagnosis for the highest C . 13
s
5.2.3 Calibration procedure and diagnosis for the lowest C . 13
s
Annex A (informative) Spectral behaviour of the LD . 15
A.1 Spectral behaviour of a single-longitudinal mode LD . 15
A.2 Spectral behaviour of a multi-longitudinal mode LD . 15
Annex B (informative) Recommendation on imaging sensor pixel size . 16
Annex C (informative) Fundamental formulation of speckle contrast and the effects of
measurement variables . 18
C.1 Fundamental formulation . 18
C.2 Effect of observation distance and iris radius . 18
Annex D (informative) Possible errors and their sources . 20
Bibliography . 21

Figure 1 – Coordinate system for projection direction and viewing direction. 8
Figure 2 – Example of measurement geometries for monochromatic speckle contrast
of front projection . 11
Figure 3 – Example of measurement geometries for monochromatic speckle contrast
of rear projection . 12
Figure 4 – Example of measurement geometries for C calibration . 13
s
Figure A.1 – Example of spectral behaviour of a single-longitudinal mode LD . 15
Figure A.2 – Example of spectral behaviour of a multi-longitudinal mode LD . 15
Figure B.1 – Minimum subjective speckle grain size as a function of the F-number . 17
Figure C.1 – Measurement result of C by changing NA . 19
s screen-Iris
Table B.1 – Example of s . 16
subj
– 4 – IEC 62906-5-2:2016 © IEC 2016
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
LASER DISPLAY DEVICES –
Part 5-2: Optical measuring methods of speckle contrast

FOREWORD
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International Standard IEC 62906-5-2 has been prepared by IEC technical committee 110:
Electronic display devices.
The text of this standard is based on the following documents:
FDIS Report on voting
110/760/FDIS 110/768/RVD
Full information on the voting for the approval of this standard can be found in the report on
voting indicated in the above table.
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.
A list of all parts in the IEC 62906 series, published under the general title Laser display
devices, can be found on the IEC website.

The committee has decided that the contents of this publication will remain unchanged until
the stability date indicated on the IEC website under "http://webstore.iec.ch" in the data
related to the specific publication. At this date, the publication will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
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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 publication using a colour printer.

– 6 – IEC 62906-5-2:2016 © IEC 2016
LASER DISPLAY DEVICES –
Part 5-2: Optical measuring methods of speckle contrast

1 Scope
This part of IEC 62906 specifies the standard measurement conditions and measurement
methods for determining the monochromatic speckle contrast of laser display devices (LDDs).
The LDDs may include hybrid types using both a laser or lasers, and spontaneous emission-
based light sources, such as LEDs.
NOTE The monochromatic speckle contrast measurements do not include image quality issues.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and
are indispensable for its application. 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 62906-1-2:2015, Laser display devices – Part 1-2: Vocabulary and letter symbols
3 Terms, definitions and abbreviations
For the purposes of this document, the terms and definitions given in IEC 62906-1-2, as well
as the following apply.
3.1 Terms and definitions
3.1.1
fully developed speckle
FDS
speckle when the speckle contrast ratio is equal to one (C = 1)
s
[SOURCE: Goodman:2006] [1]
3.2 Abbreviations
DN digital number
DUT device under test
LD laser diode
LMD light measuring device
MTF modulation transfer function
NA numerical aperture
PPUT projection plane under test
PSF point spread function
___________
Numbers square brackets refer to the bibliography.

SNR signal to noise ratio
4 Standard measuring conditions
4.1 General
An LDD is featured by using coherent or partially-coherent light sources. Speckle is created
particularly by coherence of the light sources. Therefore, measuring methods and equipment
particularly designed for speckle are necessary.
When carrying out optical measurements of LDD, the measuring environment, equipment and
methods shall be compliant with IEC 60825-1 for human safety.
4.2 Standard measuring environmental conditions
Optical measurements related to speckle shall be carried out under the standard
environmental conditions, at a temperature of 25 °C ± 3 °C, a relative humidity of 25 % to
85 %, and pressure of 86 kPa to 106 kPa. When different environmental conditions are used,
they shall be noted in the report.
4.3 Measurement coordinate system
The projection direction is the direction of a beam coming from the LDD to the projection
plane under test (PPUT). The projection direction is defined by two angles: the angle of
φ (also
inclination θ (relative to the surface normal of the PPUT) and the angle of rotation
called azimuth angle) as illustrated in Figure 1 a). Although the azimuth angle is measured in
the counter-clockwise direction, it is related to the directions on a clock face as follows: φ = 0°
is the 3 o'clock direction ("right"), φ = 90° the 12 o'clock direction ("top"), φ = 180° the
9 o'clock direction ("left") and φ = 270° the 6 o'clock direction ("bottom").
The viewing direction is the direction under which the observer looks at the point of interest
on the device under test (DUT), including the projection plane under test (PPUT). During the
measurement, the light-measuring device (LMD) simulates the observer, by aiming the LMD at
the point of interest on the DUT from the viewing direction. The viewing direction is defined by
two angles: the angle of inclination θ (relative to the surface normal of the DUT) and the angle
of rotation φ (also called azimuth angle) as illustrated in Figure 1. Although the azimuth angle
is measured in the counter-clockwise direction, it is related to the directions on a clock face
as follows: φ = 0° is the 3 o'clock direction ("right"), φ = 90° the 12 o'clock direction ("top"),
φ = 180° the 9 o'clock direction ("left") and φ = 270° the 6 o'clock direction ("bottom").

– 8 – IEC 62906-5-2:2016 © IEC 2016
Z Z
DUT (LDD) LMD or
θ human eye
θ
Y Y
12:00 12:00
φ
X X
φ
9:00 3:00 9:00 3:00
6:00 6:00
IEC
a) PPUT (screen) for front projection b) PPUT (screen) for front projection,
or DUT (LDD) for rear projection
Figure 1 – Coordinate system for projection direction and viewing direction
4.4 Darkroom conditions
The LDD should be measured under controlled lighting conditions. Unwanted background
illumination except the light generated by the LDD itself shall be minimized, typically by
illuminating the display in a darkroom. The darkroom luminance contribution from the
background illumination, which is the measurement illumination reflected off the DUT, shall be
≤ 1/20 of the lowest black level of the display. If this condition is not satisfied, then
background subtraction is required and it shall be noted in the report. It is recommended that
the background for each pixel of the imaging device be subtracted. In addition, if the
sensitivity of the LMD is inadequate to measure at these low levels, then the lower limit of the
LMD shall be noted in the report.
Unless stated otherwise, the standard background lighting conditions shall be the darkroom
conditions.
4.5 Standard conditions of measuring equipment
4.5.1 General
It is assumed that all measurements are performed by personnel skilled in the general art of
radiometric and electrical measurements as the purpose of this standard is not to give a
detailed account of good practice in electrical and optical exp
...