oSIST prEN ISO 14880-4:2023

SLOVENSKI STANDARD
oSIST prEN ISO 14880-4:2023
01-junij-2023
Nadomešča:
SIST EN ISO 14880-4:2006
Optika in fotonska tehnologija - Vrste mikroleč - 4. del: Preskusne metode za
geometrične lastnosti (ISO/DIS 14880-4:2023)
Optics and photonics - Microlens arrays - Part 4: Test methods for geometrical properties
(ISO/DIS 14880-4:2023)
Optik und Photonik - Mikrolinsenarrays - Teil 4: Prüfverfahren für geometrische
Eigenschaften (ISO/DIS 14880-4:2023)
Optique et photonique - Réseaux de microlentilles - Partie 4: Méthodes d'essai pour les
propriétés géométriques (ISO/DIS 14880-4:2023)
Ta slovenski standard je istoveten z: prEN ISO 14880-4
ICS:
31.260 Optoelektronika, laserska Optoelectronics. Laser
oprema equipment
oSIST prEN ISO 14880-4:2023 en,fr,de
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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oSIST prEN ISO 14880-4:2023

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oSIST prEN ISO 14880-4:2023
DRAFT INTERNATIONAL STANDARD
ISO/DIS 14880-4
ISO/TC 172/SC 9 Secretariat: DIN
Voting begins on: Voting terminates on:
2023-04-11 2023-07-04
Optics and photonics — Microlens arrays —
Part 4:
Test methods for geometrical properties
Optique et photonique — Réseaux de microlentilles —
Partie 4: Méthodes d'essai pour les propriétés géométriques
ICS: 31.260
This document is circulated as received from the committee secretariat.
THIS DOCUMENT IS A DRAFT CIRCULATED
FOR COMMENT AND APPROVAL. IT IS
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NATIONAL REGULATIONS.
ISO/DIS 14880-4:2023(E)
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oSIST prEN ISO 14880-4:2023
ISO/DIS 14880-4:2023(E)
DRAFT INTERNATIONAL STANDARD
ISO/DIS 14880-4
ISO/TC 172/SC 9 Secretariat: DIN
Voting begins on: Voting terminates on:

Optics and photonics — Microlens arrays —
Part 4:
Test methods for geometrical properties
Optique et photonique — Réseaux de microlentilles —
Partie 4: Méthodes d'essai pour les propriétés géométriques
ICS: 31.260
This document is circulated as received from the committee secretariat.
COPYRIGHT PROTECTED DOCUMENT
THIS DOCUMENT IS A DRAFT CIRCULATED
FOR COMMENT AND APPROVAL. IT IS
© ISO 2023
ISO/CEN PARALLEL PROCESSING
THEREFORE SUBJECT TO CHANGE AND MAY
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
NOT BE REFERRED TO AS AN INTERNATIONAL
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the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
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NATIONAL REGULATIONS.
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ii
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PROVIDE SUPPORTING DOCUMENTATION. © ISO 2023

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oSIST prEN ISO 14880-4:2023
ISO/DIS 14880-4:2023(E)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Coordinate system .3
5 Test methods . 3
5.1 Pitch and surface modulation depth measurement . 3
5.1.1 Use of stylus instrument . 3
5.1.2 Use of confocal microscope . 5
5.2 Physical thickness. 8
5.2.1 Principle . 8
5.2.2 Set-up and preparation . 8
5.3 Radius of curvature. 8
5.3.1 Principle . 8
5.3.2 Measurement arrangement and test equipment . 10
5.4 Surface preparation of microlens array for measurement . 11
6 Procedure .12
6.1 Measurement of pitch and surface modulation depth (lens sag) .12
6.1.1 Preliminary measurements.12
6.2 Making measurements and interpreting the results .12
6.3 Measurement of physical thickness .12
6.4 Measurement of radius of curvature .12
7 Results and uncertainties .13
8 Test report .13
Annex A (informative) Measurement with a Fizeau interferometer system .15
Annex B (informative) Uniformity of array spacing .18
Bibliography .21
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oSIST prEN ISO 14880-4:2023
ISO/DIS 14880-4:2023(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www.iso.org/patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to
the World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see
www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 172, Optics and Photonics, Subcommittee
SC 09, Laser and electro-optical systems.
This second edition cancels and replaces the first edition (ISO 14880-4:2006), which has been
technically revised.
The main changes are as follows:
— Introduction revised
— Updated the references to terms defined in 14880-1.
— Figure 8 replaced.
— References updated.
A list of all parts in the ISO 14880 series can be found on the ISO website.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.
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oSIST prEN ISO 14880-4:2023
ISO/DIS 14880-4:2023(E)
Introduction
This document specifies methods for testing geometrical properties of microlens arrays. Examples of
applications for microlens arrays include three-dimensional displays, coupling optics associated with
arrayed light sources and photo-detectors, enhanced optics for liquid crystal displays, and optical
parallel processor elements.
The market in microlens arrays has generated a need for agreement on basic terminology and test
methods. Standard terminology and clear definitions are needed not only to promote applications
but also to encourage scientists and engineers to exchange ideas and new concepts based on common
understanding.
This document contributes to the purpose of the series of ISO 14880 standards, which is to improve the
compatibility and interchangeability of lens arrays from different suppliers and to enhance development
of the technology using microlens arrays.
Characteristic parameters are defined and examples of applications given in ISO 14880-1, Vocabulary.
It has been completed by a set of three other International Standards, i.e. Part 2, Test methods for
wavefront aberrations, Part 3, Test methods for optical properties other than wavefront aberrations and
Part 4, Test methods for geometrical properties.
The measurement of physical characteristics of pitch and surface modulation depth can be made using
a stylus instrument and non-contact optical probe system. Physical thickness can be measured with a
micrometer. The measurement processes are described in the body of this document.
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oSIST prEN ISO 14880-4:2023
DRAFT INTERNATIONAL STANDARD ISO/DIS 14880-4:2023(E)
Optics and photonics — Microlens arrays —
Part 4:
Test methods for geometrical properties
1 Scope
This document specifies methods for testing geometrical properties of microlenses in microlens arrays.
It is applicable to microlens arrays with very small lenses formed on one or more surfaces of a common
substrate and to graded-index microlenses.
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.
ISO 14880-1, Optics and photonics — Microlens arrays — Part 1: Vocabulary
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 14880-1 and the following
apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
NOTE 1 The symbols adopted for this document are chosen for clarity in this application to microlens arrays
but some may not be those commonly used for surface texture measurement.
NOTE 2 The parameters P , P and h are used in this document to describe geometrical parameters
x y
encountered in the measurement of surface texture. P , P are spacing parameters and are defined as the average
x y
value of the length of the mean line section containing a profile peak and adjacent valley. An amplitude parameter,
h, is defined as the average difference between peak of the lens profile and the rim. Figure 1 illustrates the
geometrical properties of microlens arrays which are to be measured.
3.1
pitch
P , P
x y
distance between the centres of adjacent lenses which may vary across the array and will vary with
direction
Note 1 to entry: See Figure 1.
Note 2 to entry: The pitch is expressed in millimetres.
[SOURCE: ISO 14880-1:2019, term 3.4.1.5]
Note 3 to entry: For a stylus instrument this will generally equate to the mean width of the profile elements
calculated from the roughness profile, RSm (see 3.2.2 and 4.3.1 in ISO 4287:1997).
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oSIST prEN ISO 14880-4:2023
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3.2
surface modulation depth
h
peak-to-valley variation of the surface height
Note 1 to entry: See Figure 1.
Note 2 to entry: For a purely refractive microlens, this will be the same as the lens sag.
Note 3 to entry: The surface modulation depth is expressed in millimetres.
[SOURCE: ISO 14880-1:2019, term 3.4.1.8]
Note 4 to entry: For stylus instruments this will generally equate to Rz (see 4.1.3 in ISO 4287:1997).
3.3
physical thickness
T
c
maximum local thickness of the array
Note 1 to entry: See Figure 1.
Note 2 to entry: The physical thickness is expressed in millimetres.
[SOURCE: ISO 14880-1:2019; term 3.4.1.9]
3.4
radius of curvature
R
c
distance from the vertex of the microlens to the centre of curvature of the lens surface
Note 1 to entry: See Figure 1.
Note 2 to entry: The radius of curvature is expressed in millimetres.
[SOURCE: ISO 14880-1:2019, term 3.3.3]
Note 3 to entry: For rotationally invariant microlenses or cylindrical microlenses.
Key
1 substrate
T physical thickness
c
R radius of curvature
c
P , P pitch
x y
h surface modulation depth (lens sag)
Figure 1 — Geometrical parameters of microlens arrays
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oSIST prEN ISO 14880-4:2023
ISO/DIS 14880-4:2023(E)
4 Coordinate system
To measure the geometrical properties of a microlens array, a Cartesian coordinate system is used, as
shown in Figure 2 (Figure 1 in ISO 14880-1). In a right-handed Cartesian set, the x- and y-axis lie in the
substrate plane and the x-axis provides the direction of trace. The z-axis is the outward direction from
the material to the surrounding medium.
Key
1 substrate
2 microlens
3 light paths
Figure 2 — Microlens array with a Cartesian coordinate system
5 Test methods
5.1 Pitch and surface modulation depth measurement
5.1.1 Use of stylus instrument
5.1.1.1 Principle
[1] [2][3][4]
The basic principle using a stylus instrument is to obtain a profile of the surface of the array ].
Care shall be taken to ensure that the profile passes through the centre of each lens and that the stylus
remains in contact with the surface throughout the measurement process. This enables the pitch and
surface modulation depth to be determined.
5.1.1.2 Set-up and preparation
The measurement of the geometrical characteristics of a microlens array is similar in principle to the
measurement of any surface using a stylus instrument. A typical stylus instrument consists of a stylus
that physically contacts the surface and a transducer to convert its vertical movement into an electrical
signal. Other components can be seen in Figure 3 and include the following: a pick-up, driven by a motor
and gearbox, which draws the stylus over the surface at a constant speed; an electronic amplifier to
boost the signal from the stylus transducer to a useful level; a device for recording the amplified signal
or a computer that automates the data collection.
The part of the stylus in contact with the surface of the array is usually a diamond tip with a carefully
manufactured profile. Owing to their finite shape, some styli on some arrays may not penetrate into
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oSIST prEN ISO 14880-4:2023
ISO/DIS 14880-4:2023(E)
valleys and will give a distorted or filtered measurement of the surface. The effect of the stylus forces
can have a significant influence on the measurement results. Too high a force can cause damage to the
surface of the array. Too low a force and the stylus will not stay reliably in contact with the surface.
The stylus instrument shall be used in an environment that is as free as possible from dust, vibration
and direct sunlight in a location where the ambient temperature is maintained in the range 20 °C ± 5 °C
(with a condensation-free humidity below 70 % relative humidity). Remove any gross contamination
from the surface of the instrument preferably by blowing the surface with filtered air. Any oil or grease
may be removed using a suitable solvent.
Due consideration shall be given for testing under more adverse conditions.
Key
1 base
2 fixture
3 microlens under test
4 stylus
5 probe (pick-up)
6 measurement loop
7 column
8 drive unit
Figure 3 — Elements of a typical stylus instrument
The electrical unit on the stylus instrument shall be switched on at least one hour before any
measurements take place. This will allow time for the instrument to stabilize (the manufacturer’s
instructions will normally specify a minimum stabilization time for a given instrument). Calibration of
the instrument is essential prior to measurement. Before calibration of the instrument takes place the
stylus should be checked for signs of wear or damage. A damaged stylus tip can lead to serious errors.
After measurement of the calibration artefact the indicated value shall be compared with the value
attached to the test object. If the measured value differs from the value that is shown on the calibration
certificate then re-calibration is required.
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oSIST prEN ISO 14880-4:2023
ISO/DIS 14880-4:2023(E)
5.1.1.3 Stylus size and shape
It is important that the dimension and shape of the stylus are chosen appropriately as this can affect the
accuracy of the traced profile in a number of ways. On arrays with deep, narrow valleys the stylus may
not be able to penetrate fully to the bottom because either the tip radius or the flank angle of the stylus
is too large. In such cases, the value of the surface modulation depth will be smaller than the true value.
The ideal stylus shape is a cone with a spherical tip. This usually has a cone angle of either 60° or 90°
with a typical tip radius of 1 µm, 2 µm, 5 µm or 10 µm.
5.1.2 Use of confocal microscope
5.1.2.1 Principle
[14]
The confocal principle can be used for the measurement of surface topography . Depth is
discriminated by moving the surface of the object through focus and measuring the reflected intensity
using a detector and confocal pinhole. When the object point lies at the focus, the maximum intensity is
detected whereas the signal is reduced when the object point is displaced from the focus. The principle
has been established in the scanning confocal microscope. By scanning an imaged light spot over the
object an area is measured point by point.
5.1.2.2 Set-up and preparation
The principle of the confocal microscope has been developed by generating an array of light spots on
the object using a multiple pinhole mask (Nipkow disc) which allows for parallel data acquisition of
multiple object points. The Nipkow disc can be replaced by a microlens array in order to improve the
light efficiency, as shown in Figure 4.
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oSIST prEN ISO 14880-4:2023
ISO/DIS 14880-4:2023(E)
Key
1 light source 5 sample
2 beam splitter 6 imaging lens
3 rotating microlens disc (analogue to a Nipkow disc) 7 pinhole
4 objective 8 detector
Figure 4 — Confocal microscope measurement System A
Figure 5 shows another configuration of the confocal microscope using a microlens array and a pinhole
array. It will enhance the optical radiation collection efficiency and improve the scanning speed, which
depends on the pinhole array with parallel scanning. An example of a measurement is shown in Figure 6.
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oSIST prEN ISO 14880-4:2023
ISO/DIS 14880-4:2023(E)
Key
1 light source 5 objective
2 rotating microlens disc 6 sample
3 beam splitter 7 imaging lens
4 pinhole array (Nipkow disc) 8 charge-coupled device (CCD) camera
Figure 5 — Confocal microscope measurement System B
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oSIST prEN ISO 14880-4:2023
ISO/DIS 14880-4:2023(E)
Dimensions in micrometres
Figure 6 — Example of the microlens array surface structure using a confocal microscope
measurement system
5.2 Physical thickness
5.2.1 Principle
The two anvils of the micrometer contact the top and bottom surfaces of the array to measure
the physical thickness of the array at a given point. The anvils of the micrometer may be parallel or
spherical.
5.2.2 Set-up and preparation
The micrometer shall be calibrated using a gauge block or a similar procedure prior to the measurement.
Thoroughly wipe the spindle and the measuring faces of the micrometer using clean lint free paper or
cloth. Leave the instrument and the microlens array long enough to adjust to room temperature (at least
1 h). Care shall be taken to ensure that the micrometer is not subject to sudden temperature changes,
direct sunlight, radiant heat or air currents that may cause significant temperature variations.
5.3 Radius of curvature
5.3.1 Principle
The basic principle is to locate, by optical means as shown in Figure 7, the vertex of the microlens under
test. The displacement necessary to locate the focal position or the centre of curvature of the surface
is then measured. This enables the radius of curvature Rc to be determined respectively. Care shall be
taken to avoid incorrect settings b) and c) as shown in Figure 7.
NOTE It is only possible to locate the centre of curvature of the test surface using this method if the lens
surface is spherical. Otherwise light is not retroreflected to form a confocal image. If it is suspected that the test
[12]
surface is not spherical, the shape can be estimated from a zonal analysis using interferometry .
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oSIST prEN ISO 14880-4:2023
ISO/DIS 14880-4:2023(E)
a) Example of correct setting
b) Example of incorrect setting
c) Example of incorrect setting
Key
1 substrate surface
2 optical probe
Rc radius of curvature
Figure 7 — Location of the centre of curvature and the spherical lens surface with an optical
probe
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oSIST prEN ISO 14880-4:2023
ISO/DIS 14880-4:2023(E)
5.3.2 Measurement arrangement and test equipment
5.3.2.1 General
The testing of microlenses is similar in principle to testing larger lenses. In many cases however, the
measurement of very small lenses presents practical problems, which make it difficult to use standard
equipment. In general, two optical techniques can be used. One is based on microscopy, the other is
based on interferometry.
The first technique uses a microscope fitted with a displacement transducer, suitable light source, test
object, microscope video camera, monitor and image analyser (line intensity scan). This microscope
is used to locate, by focusing, the vertex of the microlens. The radius of curvature is deduced from
a measurement of the displacement necessary to reposition the microscope and locate the centre of
curvature of the surface as in Figure 8.
A focusing aid in the microscope such as a split-field focusing graticule enables the featureless vertex
of a microlens to be more readily located when viewing with reflected light. The position of the centre
of curvature may be located when the microscope is focused close to the centre because a confocal
image is formed by retroreflection of the rays at near-normal incidence on the lens surface. Tests may
be performed in white light or monochromatic illumination.
The second technique uses interferometry to generate interference patterns that indicate the location
of the test surface or the centre of curvature. The test interferometer may be one of several types, for
[5][6]
example a Fizeau, a lateral shearing or Twyman-Green. One advantage of interferometry is that
for strongly aberrated lenses, the variation in radius of curvature with aperture radius can be readily
deduced from the interference patterns. Interferometry is sensitive to small variations in optical
path lengths and it is usually necessary to mount the interferometer on an anti-vibration table and to
minimize air-borne disturbances.
Clauses 5 to 8 concentrate on the microscope technique while an interferometric technique is described
in Annex A.
Key
1 source to illuminate lens surface
2 microscope objective
3 microlens under test
4 beam splitter
5 camera (image sensor array)
6 lateral (x, y) adjustment to centre microlens
7 axial (z) adjustment of microscope to locate lens vertex and centre of curvature
Figure 8 — Microscope used to measure the radius of curvature of the microlens surface
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oSIST prEN ISO 14880-4:2023
ISO/DIS 14880-4:2023(E)
5.3.2.2 Test system
5.3.2.2.1 Microscope
A microscope fitted with a focusing aid such as a split-image rangefinder is used to enable focus settings
to be made on featureless surfaces and to enable the centre of curvature to be located by confocal
imaging. The displacement of the test surface relative to the microscope objective is measured with a
calibrated displacement transducer.
Note that the area of the lens surface sampled for the radius measurement is limited by the NA
(numerical aperture) of the microscope objective.
5.3.2.2.2 Light source
A light source em
...