SIST EN ISO 14880-2:2007
(Main)Optics and photonics - Microlens arrays - Part 2: Test methods for wavefront aberrations (ISO 14880-2:2006)
Optics and photonics - Microlens arrays - Part 2: Test methods for wavefront aberrations (ISO 14880-2:2006)
This standard specifies methods for testing wavefront aberrations for microlenses within microlens arrays. It applies to microlens arrays with very small lenses formed inside or on one or more surfaces of a common substrate.
Optik und Photonik - Mikrolinsenarrays - Teil 2: Prüfverfahren für Wellenfrontaberrationen (ISO 14880-2:2006)
Dieser Teil der ISO 14880 legt die Verfahren zum Prüfen der Wellenfrontaberrationen für Mikrolinsen innerhalb von Mikrolinsenarrays fest. Er gilt für Mikrolinsenarrays mit sehr kleinen Linsen in oder auf einer bzw. mehreren Oberflächen eines gemeinsamen Substrats.
Optique et photonique - Réseaux de microlentilles - Partie 2: Méthodes d'essai pour les aberrations du front d'onde (ISO 14880-2:2006)
L'ISO 14880-2:2006 spécifie des méthodes d'essai des aberrations du front d'onde pour les microlentilles en réseaux. Elle s'applique aux réseaux de très petites lentilles qui composent l'intérieur ou bien une ou plusieurs surfaces d'un substrat commun.
Optika in fotonska tehnologija - Vrste mikroleč - 2. del: Preskusne metode za ugotavljanje odstopanja valovne fronte (ISO 14880-2:2006)
General Information
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Standards Content (Sample)
SLOVENSKI STANDARD
SIST EN ISO 14880-2:2007
01-marec-2007
2SWLNDLQIRWRQVNDWHKQRORJLMD9UVWHPLNUROHþGHO 3UHVNXVQHPHWRGH]D
XJRWDYOMDQMHRGVWRSDQMDYDORYQHIURQWH ,62
Optics and photonics - Microlens arrays - Part 2: Test methods for wavefront aberrations
(ISO 14880-2:2006)
Optik und Photonik - Mikrolinsenarrays - Teil 2: Prüfverfahren für
Wellenfrontaberrationen (ISO 14880-2:2006)
Optique et photonique - Réseaux de microlentilles - Partie 2: Méthodes d'essai pour les
aberrations du front d'onde (ISO 14880-2:2006)
Ta slovenski standard je istoveten z: EN ISO 14880-2:2006
ICS:
31.260 Optoelektronika, laserska Optoelectronics. Laser
oprema equipment
SIST EN ISO 14880-2:2007 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
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EUROPEAN STANDARD
EN ISO 14880-2
NORME EUROPÉENNE
EUROPÄISCHE NORM
December 2006
ICS 31.260
English Version
Optics and photonics - Microlens arrays - Part 2: Test methods
for wavefront aberrations (ISO 14880-2:2006)
Optique et photonique - Réseaux de microlentilles - Partie Optik und Photonik - Mikrolinsenarrays - Teil 2:
2: Méthodes d'essai pour les aberrations du front d'onde Prüfverfahren für Wellenfrontaberrationen (ISO 14880-
(ISO 14880-2:2006) 2:2006)
This European Standard was approved by CEN on 12 November 2006.
CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European
Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references concerning such national
standards may be obtained on application to the Central Secretariat or to any CEN member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by translation
under the responsibility of a CEN member into its own language and notified to the Central Secretariat has the same status as the official
versions.
CEN members are the national standards bodies of Austria, Belgium, Cyprus, Czech Republic, Denmark, Estonia, Finland, France,
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Slovakia, Slovenia, Spain, Sweden, Switzerland and United Kingdom.
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© 2006 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 14880-2:2006: E
worldwide for CEN national Members.
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EN ISO 14880-2:2006 (E)
Foreword
The text of ISO 14880-2:2006 has been prepared by Technical Committee ISO/TC 172 "Optics
and optical instruments” of the International Organization for Standardization (ISO) and has
been taken over as EN ISO 14880-2:2006 by Technical Committee CEN/TC 123 "Lasers and
photonics", the secretariat of which is held by DIN.
This European Standard shall be given the status of a national standard, either by publication of
an identical text or by endorsement, at the latest by June 2007, and conflicting national
standards shall be withdrawn at the latest by June 2007.
According to the CEN/CENELEC Internal Regulations, the national standards organizations of
the following countries are bound to implement this European Standard: Austria, Belgium,
Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary,
Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland,
Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland and United Kingdom.
Endorsement notice
The text of ISO 14880-2:2006 has been approved by CEN as EN ISO 14880-2:2006 without any
modifications.
2
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INTERNATIONAL ISO
STANDARD 14880-2
First edition
2006-02-01
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
Reference number
ISO 14880-2:2006(E)
©
ISO 2006
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ISO 14880-2:2006(E)
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ii © ISO 2006 – All rights reserved
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ISO 14880-2:2006(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 arrangement. 3
7.1 Measurement arrangement for single microlenses . 3
7.2 Measurement arrangement for microlens arrays . 3
7.3 Geometrical alignment of the sample. 4
7.4 Preparation . 4
8 Procedure . 4
9 Evaluation. 4
10 Accuracy. 4
11 Test report . 5
Annex A (normative) Measurement requirements for test methods for microlenses. 6
Annex B (normative) Microlens test Methods 1 and 2 using Mach-Zehnder interferometer systems. 8
Annex C (normative) Microlens test Methods 3 and 4 using a lateral shearing interferometer
system. 13
Annex D (normative) Microlens test Method 5 using a Shack-Hartmann sensor system . 18
Annex E (normative) Microlens array test Method 1 using a Twyman-Green interferometer system . 20
Annex F (normative) Measurement of uniformity of microlens array determined by test Method 2. 22
Bibliography . 25
© ISO 2006 – All rights reserved iii
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ISO 14880-2:2006(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.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. Draft International Standards
adopted by the technical committees are circulated to the member bodies for voting. Publication as an
International Standard requires approval by at least 75 % of the member bodies casting a vote.
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.
ISO 14880-2 was prepared by Technical Committee ISO/TC 172, Optics and photonics, Subcommittee SC 9,
Electro-optical systems.
ISO 14880 consists of the following parts, under the general title Optics and photonics — Microlens arrays:
⎯ Part 1: Vocabulary
⎯ Part 2: Test methods for wavefront aberrations
⎯ Part 3:Test methods for optical properties other than wavefront aberrations
⎯ Part 4: Test methods for geometrical properties
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ISO 14880-2:2006(E)
Introduction
This part of ISO 14880 specifies methods of testing wavefront aberrations for microlens arrays. Examples of
microlens array applications 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 is generating an urgent need for agreement on basic terminology and test
methods for a definition of the microlens array itself. Standard terminology and a clear definition 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 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 first. 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.
Appraisal methods of the characteristic parameters are defined by 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 part of ISO 14880 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 and ISO 14880-4.
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INTERNATIONAL STANDARD ISO 14880-2:2006(E)
Optics and photonics — Microlens arrays —
Part 2:
Test methods for wavefront aberrations
1 Scope
This part of ISO 14880 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 referenced documents are indispensable for the application 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 14880-1:2001, 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.
4 Symbols and abbreviated terms
Table 1 — Symbols, abbreviated terms and units of measure
Symbol Unit Term
Φ λ wavefront aberration
Φ λ peak-to-valley value of wavefront aberration
P-V
Φ λ root-mean-square value of wavefront aberration
rms
λ µm wavelength
Θ degree acceptance angle
NA none numerical aperture
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ISO 14880-2:2006(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 an interference
pattern analyser system.
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 at the operational wavelength impinging on the test equipment
shall have a rms deviation of u λ/10 over 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 Usually, He-Ne gas lasers are 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 together with a suitable optical wavefront aberration compensation system.
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 u λ/10 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 operational wavelength.
The test geometry for the measurement of the wavefront aberrations is restricted to the case ∞/f for the
conjugates of the lens.
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 shall be less than λ/20 rms
deviation 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 for the adaptation of
the beam cross-section to the array detector. The ratio of the focal lengths gives the reduction factor.
NOTE The diameter of the evaluated lens area can be set to the effective aperture by software to avoid additional
diffraction at a physical aperture.
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ISO 14880-2:2006(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 realized by a 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 optics 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 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 single-
pass interferometers.
NOTE Modern interferometers use laser sources for considering the setting up of the interferometric test but it
causes severe problems if a double-pass arrangement is chosen in reflected optical radiation, when Fizeau or Twyman-
Green interferometers are used. All dielectric boundaries between lenses contribute to spurious fringe patterns.
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 therefore be the first choice for this aim.
7 Measurement arrangement
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 arrangement 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 test of single lenses selected out of an array will be done with spherical wave irradiation of the
sample lens this is in general not possible with array tests. In this case, a plane wave irradiation is more suitable or special
provisions using diffractive array wavefront shaping elements have to be used (see e.g. Reference [9]).
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ISO 14880-2:2006(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 microlens array wavefront aberrations are described in the Annexes E and F.
9 Evaluation
The wavefront aberration can be calculated from the interferogram (see References [8] and [12]) 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 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 6 times the rms figure instead.
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 aberrations.
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ISO 14880-2:2006(E)
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
2) root-mean-square value of wavefront aberration Φ ;
rms
3) Zernike polynomials or other polynomial coefficients.
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ISO 14880-2:2006(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 and 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 worse 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 measuring errors.
Since the microlens diameters cover a range between 10 µm and a few millimetres, it is necessary to provide
a means for changing the magnification by at least two orders of magnitude in order to fill the aperture of the
array photo-detector, typically a CCD-matrix, to obtain sufficient lateral resolution so that also strongly
deformed wavefronts can be tested without the violation of the sampling theorem. Due to the great span of
magnifications in combination with the requirement of a plane wave interferometer, the imaging microscope
shall be incorporated into the test arm for high magnification ratios commonly obtained with short working
distances of the imaging microscope objective. If the imaging objective is to be used outside the
interferometer structure, special objective designs are necessary to enable high magnification ratios in
combination with long working distances. Two alternative solutions will be discussed in some detail to
demonstrate Mach-Zehnder interferometers for the test of wave aberrations. The imaging microscope will
preferably be of the telescopic type in order to maintain in the test arm plane waves at the beam combiner.
The change of magnification requires special measures to adapt the splitting ratio between the two arms of
the interferometer to obtain sufficient contrast of the interference fringes. The best choice for such an aim is a
polarizing splitting unit consisting of a polarizing beam splitter in combination with two quarter-wave plates
(QWP), one in each arm of the interferometer and a half-wave plate (HWP) in front of the splitting unit for
rotating the polarization vector.
It is also necessary to provide means for varying the mean intensity independently from the splitting ratio
because the photo-detector might be driven into the state of saturation producing incorrect measuring results
due to non-linear signal distortions.
The measurement of wave aberrations requires the irradiation of the test lens from the rear by a spherical
wavefront produced by a high-quality microscope objective having a numerical aperture exceeding that of the
lens under test. This objective shall have a Strehl definition above 95 % to ensure a simple test philosophy
making calibrations obsolete in most test situations.
For the characterization of small numerical aperture lenses, it is advisable also to provide plane wave
irradiation of the sample. Plane wave irradiation enables the measurement of the focal length of the lens.
Plane wave irradiation can be used for the determination of the focal length for high aperture lenses in the
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