oSIST prEN ISO 14880-2:2023

SLOVENSKI STANDARD
oSIST prEN ISO 14880-2:2023
01-junij-2023
Optika in fotonska tehnologija - Vrste mikroleč - 2. del: Preskusne metode za
ugotavljanje odstopanja valovne fronte (ISO/DIS 14880-2:2023)
Optics and photonics - Microlens arrays - Part 2: Test methods for wavefront aberrations
(ISO/DIS 14880-2:2023)
Optik und Photonik - Mikrolinsenarrays - Teil 2: Prüfverfahren für
Wellenfrontaberrationen (ISO/DIS 14880-2:2023)
Optique et photonique - Réseaux de microlentilles - Partie 2: Méthodes d'essai pour les
aberrations du front d'onde (ISO/DIS 14880-2:2023)
Ta slovenski standard je istoveten z: prEN ISO 14880-2
ICS:
31.260 Optoelektronika, laserska Optoelectronics. Laser
oprema equipment
oSIST prEN ISO 14880-2:2023 en,fr,de
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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oSIST prEN ISO 14880-2:2023

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oSIST prEN ISO 14880-2:2023
DRAFT INTERNATIONAL STANDARD
ISO/DIS 14880-2
ISO/TC 172/SC 9 Secretariat: DIN
Voting begins on: Voting terminates on:
2023-04-12 2023-07-05
Optics and photonics — Microlens arrays —
Part 2:
Test methods for wavefront aberrations
Optique et photonique — Réseaux de microlentilles —
Partie 2: Méthodes d'essai pour les aberrations du front d'onde
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
ISO/CEN PARALLEL PROCESSING
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NATIONAL REGULATIONS.
ISO/DIS 14880-2:2023(E)
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NOTIFICATION OF ANY RELEVANT PATENT
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PROVIDE SUPPORTING DOCUMENTATION. © ISO 2023

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oSIST prEN ISO 14880-2:2023
ISO/DIS 14880-2:2023(E)
DRAFT INTERNATIONAL STANDARD
ISO/DIS 14880-2
ISO/TC 172/SC 9 Secretariat: DIN
Voting begins on: Voting terminates on:

Optics and photonics — Microlens arrays —
Part 2:
Test methods for wavefront aberrations
Optique et photonique — Réseaux de microlentilles —
Partie 2: Méthodes d'essai pour les aberrations du front d'onde
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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NATIONAL REGULATIONS.
Website: www.iso.org ISO/DIS 14880-2:2023(E)
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ii
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PROVIDE SUPPORTING DOCUMENTATION. © ISO 2023

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oSIST prEN ISO 14880-2:2023
ISO/DIS 14880-2:2023(E)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Symbols and abbreviated terms.1
5 Apparatus . 2
5.1 General . 2
5.2 Standard optical radiation source. 2
5.3 Standard lens . 2
5.4 Collimator . 2
5.5 Beam reduction optical system . 2
5.6 Aperture stop . 3
6 Test principle .3
7 Measurement arrangements . 3
7.1 Measurement arrangement for single microlenses . 3
7.2 Measurement arrangements for microlens arrays . 3
7.3 Geometrical alignment of the sample . 4
7.4 Preparation . 4
8 Procedure .4
9 Evaluation . 4
10 Accuracy . 5
11 Test report . 5
Annex A (normative) Measurement requirements for test methods for microlenses .7
Annex B (normative) Microlens test Methods 1 and 2 usingMach-Zehnder interferometer
systems . 9
Annex C (normative) Microlens test Methods 3 and 4 usinga lateral shearing interferometer
system.15
Annex D (normative) Microlens test Method 5 using a Shack-Hartmann sensor system .20
Annex E (normative) Microlens array test Method 1 using a Twyman-Green interferometer
system.22
Annex F (normative) Measurement of uniformity of microlens arraydetermined by test
Method 2 .24
Bibliography .27
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oSIST prEN ISO 14880-2:2023
ISO/DIS 14880-2:2023(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 14880-2:2006), which has been
technically revised.
The main changes are as follows:
— Text for Annex E revised
— Figure E.1 replaced
— References and numbering confirmed
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.
iv
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oSIST prEN ISO 14880-2:2023
ISO/DIS 14880-2:2023(E)
Introduction
This document specifies methods of testing wavefront aberrations for microlens arrays. Examples of
applications of microlens arrays include three-dimensional displays, coupling optics associated with
arrayed optical radiation 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 for defining microlens arrays. 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.
Microlenses are used as single lenses and also in arrays of two or more lenses. The characteristics
of the lenses are fundamentally evaluated with a single lens. Therefore, it is important that the basic
characteristic of a single lens can be evaluated. However, if a large number of lenses is formed on a
single substrate, the measurement of the whole array will incur a lot of time and cost. Furthermore,
methods for measuring lens shapes are essential as a production tool.
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.
This document specifies methods for measuring wavefront quality. Wavefront quality is the basic
performance characteristic of a microlens. Characteristics other than wavefront aberrations are
specified in ISO 14880-3, ISO 14880-4 and ISO/TR 14880-5.
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oSIST prEN ISO 14880-2:2023

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oSIST prEN ISO 14880-2:2023
DRAFT INTERNATIONAL STANDARD ISO/DIS 14880-2:2023(E)
Optics and photonics — Microlens arrays —
Part 2:
Test methods for wavefront aberrations
1 Scope
This document specifies methods for testing wavefront aberrations for microlenses within microlens
arrays. It is applicable to microlens arrays with very small lenses formed inside or on one or more
surfaces of a common substrate.
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 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/
4 Symbols and abbreviated terms
Table 1 — Symbols, abbreviated terms and units of measure
Symbol Unit Term
Φ µm wavefront aberration
Φ µm peak-to-valley value of wavefront aberration
P-V
Φ µm root-mean-square value of wavefront aberration
rms
λ µm Wavelength
Θ degree acceptance angle
NA none numerical aperture
NOTE The wavefront aberration, peak-to-valley values of wavefront aberration and root-mean-square values
of wavefront aberration are often expressed in units of ”λ” based on the results of interferometer measurements.
Wavefront aberration is expressed in multiples of ”λ” (wavelength (μm) ) of the laser light source used in the
interferometer.
1
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oSIST prEN ISO 14880-2:2023
ISO/DIS 14880-2:2023(E)
5 Apparatus
5.1 General
The test system consists of a source of optical radiation, a collimator lens, a method of limiting the
measurement aperture, a sample holding apparatus, imaging optics, an image sensor and a system for
[1][2][4][5][8][11][21]
analysing interference patterns .
5.2 Standard optical radiation source
A source of optical radiation shall be used, which is suitable for the testing of wavefront aberrations of
microlenses. The aberrations of the wavefront incident on the test equipment shall have a rms deviation
of λ/20, at the wavelength of operation, over an area corresponding to the effective aperture of the
microlens to be tested.
Properties of the source to be specified include centre wavelength, half-width of the spectrum, the
type of optical radiation source, states of polarization (randomly polarized optical radiation, linearly
polarized optical radiation, circularly polarized optical radiation, etc.), radiance angle (in mrad), spot
size or beam waist parameters. Otherwise, the specification of the radiation source shall be described
in the documentation of the experimental results.
NOTE 1 He-Ne gas lasers are sometimes used. Other gas lasers, solid-state lasers, semiconductor lasers (LD),
and light emitting diodes (LED) are also used.
NOTE 2 LDs and LEDs are used with beam-shaping optics where necessary.
5.3 Standard lens
Where a standard lens is used as a reference or for generating an ideal spherical wave, the wavefront
aberrations of the standard lens shall be smaller by at least one order of magnitude compared to that of
the lens to be tested or shall be less than λ/20 rms deviation.
The objective lens of an optical microscope used as the standard lens shall be specified with the
effective numerical aperture. The following shall be given:
— effective aperture;
— effective focal length at the wavelength of operation.
The test geometry for the measurement of wavefront aberrations is restricted to the case with lens
conjugates ∞/f.
5.4 Collimator
The collimator optics shall have a numerical aperture greater than the maximum numerical aperture
of the test sample sufficient to avoid effects due to diffraction. The wavefront aberrations should be
less than the Maréchal criterion value and/or the Strehl definition value (both λ/14: 0,07λ rms). It is
however recommended that they are less than λ/20 at the operational wavelength.
Otherwise the specification used should be described in the test report.
5.5 Beam reduction optical system
A telescopic system consisting of two positive lenses in an afocal arrangement is used to adapt the
beam cross-section to the array detector. The ratio of the focal lengths gives the reduction factor. It is
recommended that the wavefront aberrations are less than λ/20 at the operational wavelength.
NOTE The diameter of the lens area to be evaluated can be selected with an effective aperture defined by
software to avoid additional diffraction at a physical aperture.
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oSIST prEN ISO 14880-2:2023
ISO/DIS 14880-2:2023(E)
5.6 Aperture stop
A physical stop is placed in the optical radiation beam of the test equipment to limit the diameter of
the optical radiation beam incident on the lens to be tested. Alternatively, the stop may be defined by
truncation software during evaluation.
6 Test principle
The wavefront aberrations of the test microlens shall be determined with an interferometer or another
wavefront test device as described in the Annexes. When small-diameter Gaussian beams are used,
care should be taken because geometrical optical theory does not apply to the propagation of such
beams. The detector surface shall be conjugate with the entrance or exit pupil of the test microlens. An
[9][10][12][13][14]
aperture is used to analyse the data for the wave aberrations .
The test method shall be chosen to suit the application. Single-pass applications require testing using
[9]
single-pass interferometers .
NOTE Interferometers often use laser sources for the interferometric test. Dielectric boundaries between
lenses contribute to spurious reflections and unwanted fringe patterns. This can cause severe problems if a
double-pass arrangement using reflected optical radiation is chosen, such as when Fizeau or Twyman-Green
interferometers are used.
Arrangements using transmitted optical radiation are less affected by spurious fringes than reflection
type interferometers. It is preferable to use interferometers of the Mach-Zehnder or lateral shearing
type or Shack-Hartmann arrangements in transmitted optical radiation. For the measurement of wave
aberrations a single-pass geometry in transmitted optical radiation will often be the first choice for
reducing spurious reflections.
7 Measurement arrangements
7.1 Measurement arrangement for single microlenses
Interferometers or wavefront detectors shall be used to measure the transmitted wavefront of the
microlens under test. Single-path interferometers such as Mach-Zehnder, lateral shearing or double-
pass interferometers such as Fizeau, Twyman-Green, and Shack-Hartmann wavefront detectors can be
used for testing as shown in Annexes B to D.
The requirements for the measurement shall be defined. Typical criteria for choosing a specific method
are:
— required accuracy,
— required properties to be measured,
— flexibility of the measurement,
— costs,
— spot test on one lens or complete measurement.
For more details see ISO/TR 14999-2.
7.2 Measurement arrangements for microlens arrays
Interferometers or wavefront detectors shall be used to measure simultaneously whole arrays or parts
of them in the transmitted radiation. Typical test arrangements are described in Annexes E and F.
NOTE While the testing of single lenses selected from an array can be carried out by illuminating with a
spherical wave this is in general not possible with array tests. In that case, illuminating with plane wave is more
[9]
suitable or special provisions using diffractive array wavefront shaping elements have to be used .
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oSIST prEN ISO 14880-2:2023
ISO/DIS 14880-2:2023(E)
7.3 Geometrical alignment of the sample
Usually the microlens being tested and its coupling optics shall be set or adjusted into co-axial
alignment with the wavefront measuring instruments. Optical alignment instruments and/or devices
are commercially available for this purpose.
NOTE The sample is mounted on a stage such as an air-chuck, which has two or three directions of freedom
for adjustment.
7.4 Preparation
The test equipment shall be maintained in a temperature-controlled environment and not exposed to
vibration so as to obtain consistent results.
The optical surfaces to be tested shall be clean. Uncoated glass surfaces may be safely cleaned with
alcohol and cotton wool. The cotton wool should be soaked in a very small amount of solvent before
touching the surface and wiped only once across it before being discarded. This minimizes the chances
of scratching the surface. Dust may be removed using a clean camel-hair brush or filtered compressed
air.
Coated optical surfaces such as antireflection surfaces should be treated with great care and not
cleaned unless absolutely necessary. They may be dusted using filtered compressed air.
Guidance should be sought on the correct use of solvents, cotton wool or other wiping materials.
8 Procedure
Measurement requirements and typical methods for measuring the wavefront aberration of individual
lenses are described in the Annexes A to D.
Examples for measurements of wavefront aberrations of microlens arrays are described in the
Annexes E and F.
9 Evaluation
[8][12]
The wavefront aberration can be calculated from the interferogram or from other wavefront
measuring systems described in Annexes A to F. From the wavefront aberrations of spherical lenses
with circular apertures primary Zernike coefficients can be derived with a prescribed software
aperture.
NOTE 1 Typical wavefront aberrations described by Zernike coefficients are:
— spherical aberration,
— astigmatism,
— coma.
NOTE 2 For other lens aperture shapes (such as rectangular), see ISO/TR 14999-2.
The measured wavefront aberrations of samples shall be evaluated and quoted, for example, as peak-
to-valley or root-mean-square values.
Care should be taken to interpret peak-to-valley values because they are influenced by spurious values.
It is recommended to use multiple times (at least three times) the rms figure instead.
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oSIST prEN ISO 14880-2:2023
ISO/DIS 14880-2:2023(E)
10 Accuracy
The wavefront aberrations of a sample are measured by a wavefront test system, which may introduce
some aberration of its own. The accuracy of measurement can be improved by subtracting the system
[6][7]
aberrations .
11 Test report
The test results shall be recorded and shall include the following information if applicable:
a) general information:
1) test has been performed in accordance with ISO 14880-2:2005;
2) date of test;
3) name and address of test organization;
4) name of individual performing the test;
b) information concerning the tested lens:
1) lens type;
2) manufacturer;
3) manufacturer’s model;
4) serial number;
c) test conditions (environmental conditions):
1) temperature;
2) relative humidity;
d) information concerning testing and evaluation:
1) test method used;
2) optical system used;
3) irradiation:
i) source type,
ii) wavelength,
iii) half-width of optical radiation spectrum,
iv) polarization status,
v) irradiance angle,
vi) spot size;
4) detector;
5) aperture;
e) test results:
1) peak-to-valley value of wavefront aberration Φ ;
P-V
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oSIST prEN ISO 14880-2:2023
ISO/DIS 14880-2:2023(E)
2) root-mean-square value of wavefront aberration Φ ;
rms
3) Zernike polynomials or other polynomial coefficients.
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oSIST prEN ISO 14880-2:2023
ISO/DIS 14880-2:2023(E)
Annex A
(normative)

Measurement requirements for test methods for microlenses
The test for wave aberrations of microlenses shall be performed in transmitted optical radiation and
in a single-pass arrangement, an interferometer like a Mach-Zehnder interferometer, a lateral shearing
interferometer, or a Shack-Hartmann wavefront sensor. A single-pass test device is required for sharp
imaging of the lens aperture onto the detector or sensor array to avoid the strong disturbances due to
spurious reflections in a double-pass arrangement as in a Fizeau or a Twyman-Green interferometer. In
a double-pass geometry the lens under test will deliver two images of the lens aperture one being out of
focus causing diffraction effects like edge ringing in the rim region of the lens under test. Such effects
can be avoided by using a single-pass arrangement because all reflections from lens surfaces in the
auxiliary optical system in the forward direction are negligible, being reflected twice at antireflection
coated surfaces. In addition, due to sharp imaging of the lens aperture, there are no ambiguities
concerning the definition of the wave aberrations.
The test device shall not introduce aberrations of its own. In a Mach-Zehnder geometry, where the test
sample is put into one arm of the interferometer and the reference arm delivers a plane wavefront,
the beam splitting/combining optical elements are traversed by plane waves only. Spherical waves
would produce spherical aberration or other aberrations for non-symmetric beam splitters. Similar
requirements are also valid for a Shack-Hartmann sensor although no beam splitters are used in this
case.
In the case of lateral shearing interferometers, it is necessary to keep the design of the shearing device
symmetric and as simple as possible (see for example the shearing interferometer based on two-phase
gratings in a series arrangement [array tests]) in order to avoid additional measurement errors.
Since microlens diameters cover a range between a few micrometres and a few millimetres, it is
necessary to provide a means for changing the magnification by at least two orders of magnitude. This
is in order to fill the aperture of the array ph
...