U.S. patent application number 14/617735 was filed with the patent office on 2016-08-11 for optical components.
The applicant listed for this patent is Pasi Kostamo, Ari J. Tervonen. Invention is credited to Pasi Kostamo, Ari J. Tervonen.
Application Number | 20160231257 14/617735 |
Document ID | / |
Family ID | 55361973 |
Filed Date | 2016-08-11 |
United States Patent
Application |
20160231257 |
Kind Code |
A1 |
Kostamo; Pasi ; et
al. |
August 11, 2016 |
Optical Components
Abstract
The following relates to assessing the quality of an optical
component. The optical component comprises an arrangement of a
first and a second optically transmissive component grating having
a component relative orientation angle, and the quality is assessed
in terms of a deviation of the component relative orientation angle
from a desired relative orientation angle. A master component
comprises a substantially matching arrangement of a first and a
second optically transmissive master grating having the desired
relative orientation angle. The components are supported with the
first and second component gratings in the vicinity of the first
and second master gratings, and first and second fringe patterns
formed by the first gratings and second gratings respectively are
used to output a quality assessment, which is based on the fringe
spacing of the second fringe pattern when the fringe spacing of the
first fringe pattern is substantially maximal.
Inventors: |
Kostamo; Pasi; (Espoo,
FI) ; Tervonen; Ari J.; (Vantaa, FI) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Kostamo; Pasi
Tervonen; Ari J. |
Espoo
Vantaa |
|
FI
FI |
|
|
Family ID: |
55361973 |
Appl. No.: |
14/617735 |
Filed: |
February 9, 2015 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G01N 2021/9511 20130101;
G01N 21/8851 20130101; G02B 27/4255 20130101; G01M 11/0264
20130101; G02B 27/4277 20130101; G01N 21/958 20130101; G02B 5/1866
20130101; G02B 5/1819 20130101 |
International
Class: |
G01N 21/958 20060101
G01N021/958; G01N 21/88 20060101 G01N021/88 |
Claims
1. A quality assessment apparatus for assessing the quality of an
optical component, the optical component comprising an arrangement
of a first and a second component grating having a component
relative orientation angle, wherein the quality is assessed in
terms of a deviation of the component relative orientation angle
from a desired relative orientation angle, the apparatus
comprising: a configurable support system configured to support a
master component comprising a substantially matching arrangement of
a first and a second master grating having the desired relative
orientation angle and to support the optical component with the
first and second component gratings in the vicinity of the first
and second master gratings, the apparatus further comprising: a
light sensor configured to receive light which has interacted with
both of the first gratings and light which has interacted with both
of the second gratings, and to generate sensor data from the
received light; a drive mechanism coupled to the support system;
and a controller configured (i) to control the drive mechanism
based on the sensor data to reconfigure the support system from a
current configuration to a new configuration in which the fringe
spacing of a first fringe pattern formed by the first gratings is
substantially maximal and (ii) to measure from the sensor data the
fringe spacing of a second fringe pattern formed by the second
gratings in the new configuration, and to output a quality
assessment based on the measured fringe spacing which is indicative
of the deviation of the component relative orientation angle from
the desired relative orientation angle.
2. A quality assessment apparatus according to claim 1, wherein the
optical component and the master component comprise alignment marks
located so that, when the marks are aligned, the first fringe
pattern is observable, wherein the sensor senses the marks, and
wherein the controller is configured based on sensor data
pertaining to the marks to reconfigure the support system from the
current configuration to an intermediate configuration, in which
the alignments marks are substantially aligned and from which the
support system is then reconfigured to the new configuration.
3. A quality assessment apparatus according to claim 1, wherein the
light sensor comprises a camera which captures images of the first
fringe pattern as the support system is reconfigured, and wherein
the controller comprises an image recognition module which performs
an automatic image recognition procedure to detect the first fringe
pattern in the images, wherein the controller reconfigures the
support system based on the results of the image recognition
procedure.
4. A quality assessment apparatus according to claim 3, wherein the
images are also of the second fringe pattern, the automatic image
recognition procedure detects the second fringe pattern, and the
controller measures the fringe spacing of the second fringe pattern
based on the results of the image recognition procedure.
5. A quality assessment apparatus according to claim 1, wherein the
light sensor comprises a sensor component which receives light of
only a small portion of the first fringe pattern as the support
system is reconfigured, and the controller reconfigures the support
system based on the rate at which the intensity of that light
changes.
6. A quality assessment apparatus according to claim 5, wherein the
light sensor comprises another sensor component which receives
light of only a small portion of the second fringe pattern, and the
controller measures the fringe spacing of the second fringe pattern
based on the rate at which the intensity of that light changes.
7. A quality assessment apparatus according to claim 1 comprising a
laser which provides a beam and a beam expander which expands the
beam to illuminate the gratings with an expanded beam that
substantially encompasses the gratings so as to enhance the
visibility of the fringe patterns.
8. A quality assessment process for assessing the quality of an
optical component, the optical component comprising an arrangement
of a first and a second component grating having a component
relative orientation angle, wherein the quality is assessed in
terms of a deviation of the component relative orientation angle
from a desired relative orientation angle, wherein the optical
component and a master component comprising a substantially
matching arrangement of a first and a second master grating having
the desired relative orientation angle are supported by a
configurable support system with the first and second component
gratings in the vicinity of the first and second master gratings,
the process comprising: receiving sensor data, the sensor data
generated from light received which has interacted with both of the
first gratings and light which has interacted with both of the
second gratings; reconfiguring the support system based on the
sensor data from a current configuration to a new configuration, in
which the fringe spacing of a first fringe pattern formed by the
first gratings is substantially maximal; measuring from the sensor
data the fringe spacing of a second fringe pattern formed by the
second gratings in the new configuration; and outputting a quality
assessment based on the measured fringe spacing which is indicative
of the deviation of the component relative orientation angle from
the desired relative orientation angle.
9. A quality assessment process according to claim 8, wherein the
optical component and the master component comprise alignment marks
located so that, when the marks are aligned, the first fringe
pattern is observable, and wherein the process comprises
reconfiguring the support system from the current configuration to
an intermediate configuration, in which the alignments marks are
substantially aligned and from which the support system is then
reconfigured to the new configuration.
10. A quality assessment process according to claim 8, wherein the
component gratings are formed by surface modulations on the surface
of the optical component.
11. A quality assessment process according to claim 8, wherein the
surface modulations are on substantially parallel portions of the
surface of the optical component.
12. A quality assessment process according to claim 8, wherein both
the component gratings are formed by surface modulations on frontal
portions of the surface of the optical component.
13. A quality assessment process according to claim 8 wherein one
of the component gratings is formed by surface modulations on a
frontal portion of the surface of the optical component and the
other is formed by surface modulations on a rearward portion of the
surface of the optical component.
14. A quality assessment process according to claim 8, wherein the
optical component comprises polymer or is a mould for moulding such
optical components.
15. A quality assessment process according to claim 8, comprising
performing a microfabrication process on the master component to
fabricate the master gratings prior to performing the steps of
claim 8.
16. A quality assessment process according to claim 8 comprising
testing the master component gratings to assess the quality of the
master component prior to performing the steps of claim 8.
17. A quality assessment process according to claim 8, wherein the
first component grating has a period d.sub.1 and the second
component grating has a period d.sub.2, and the desired orientation
angle of the master gratings is substantially
arccos(d.sub.1/(2d.sub.2)).
18. An apparatus comprising: one or more processors; and a
computer-readable storage medium having stored thereon code for
assessing the quality of an optical component, the optical
component comprising an arrangement of a first and a second
component grating having a component relative orientation angle,
wherein the quality is assessed in terms of a deviation of the
component relative orientation angle from a desired relative
orientation angle, wherein the optical component and a master
component comprising a substantially matching arrangement of a
first and a second master grating having the desired relative
orientation angle are supported by a configurable support system
with the first and second component gratings in the vicinity of the
first and second master gratings, the code configured when executed
by the one or more processors to cause operations comprising:
receiving sensor data, the sensor data generated from light which
has interacted with both of the first gratings and light which has
interacted with both of the second gratings; reconfiguring the
support system based on the sensor data from a current
configuration to a new configuration, in which the fringe spacing
of a first fringe pattern formed by the first gratings is
substantially maximal; measuring from the sensor data the fringe
spacing of a second fringe pattern formed by the second gratings in
the new configuration; and outputting a quality assessment based on
the measured fringe spacing which is indicative of the deviation of
the component relative orientation angle from the desired relative
orientation angle.
19. An apparatus according to claim 18, wherein the optical
component and the master component comprise alignment marks located
so that, when the marks are aligned, the first fringe pattern is
observable, wherein the sensor data includes sensor data pertaining
to the marks, and wherein the operations comprise reconfiguring,
based on the sensor data pertaining to the marks, the support
system from the current configuration to an intermediate
configuration, in which the alignments marks are substantially
aligned and from which the support system is reconfigured to the
new configuration.
20. An apparatus according to claim 18 wherein the sensor data
comprises images of the first fringe pattern and the operations
comprise performing automatic image recognition on the images to
detect the first fringe pattern, wherein a drive mechanism coupled
to the support system is controlled based on the results of the
image recognition procedure.
21. A computer-readable storage medium storing code for assessing
the quality of an optical component, the optical component
comprising an arrangement of a first and a second component grating
having a component relative orientation angle, wherein the quality
is assessed in terms of a deviation of the component relative
orientation angle from a desired relative orientation angle,
wherein the optical component and a master component comprising a
substantially matching arrangement of a first and a second master
grating having the desired relative orientation angle are supported
by a configurable support system with the first and second
component gratings in the vicinity of the first and second master
gratings, the code configured when executed on a processor of a
device to cause operations comprising: receiving sensor data, the
sensor data generated from light received which has interacted with
both of the first gratings and light which has interacted with both
of the second gratings; reconfiguring the support system based on
the sensor data from a current configuration to a new
configuration, in which the fringe spacing of a first fringe
pattern formed by the first gratings is substantially maximal;
measuring from the sensor data the fringe spacing of a second
fringe pattern formed by the second gratings in the new
configuration; and outputting a quality assessment based on the
measured fringe spacing which is indicative of the deviation of the
component relative orientation angle from the desired relative
orientation angle.
22. The computer-readable storage medium according to claim 21,
wherein the optical component and the master component comprise
alignment marks located so that, when the marks are aligned, the
first fringe pattern is observable, and wherein the operations
comprise reconfiguring the support system from the current
configuration to an intermediate configuration, in which the
alignments marks are substantially aligned and from which the
support system is then reconfigured to the new configuration.
23. The computer-readable storage medium according to claim 21,
wherein the component gratings are formed by surface modulations on
the surface of the optical component.
24. The computer-readable storage medium according to claim 21,
wherein the surface modulations are on substantially parallel
portions of the surface of the optical component.
25. The computer-readable storage medium according to claim 21,
wherein both the component gratings are formed by surface
modulations on frontal portions of the surface of the optical
component.
26. The computer-readable storage medium according to claim 21,
wherein one of the component gratings is formed by surface
modulations on a frontal portion of the surface of the optical
component and the other is formed by surface modulations on a
rearward portion of the surface of the optical component.
27. The computer-readable storage medium according to claim 21,
wherein the optical component comprises polymer or is a mould for
moulding such optical components.
28. The computer-readable storage medium according to claim 21,
further comprising performing a microfabrication process on the
master component to fabricate the master gratings prior to
performing the operations of claim 21.
29. The computer-readable storage medium according to claim 21,
further comprising testing the master component gratings to assess
the quality of the master component prior to performing the
operations of claim 21.
30. The computer-readable storage medium according to claim 21,
wherein the first component grating has a period d.sub.1 and the
second component grating has a period d.sub.2, and the desired
orientation angle of the master gratings is substantially arc
coss(d.sub.1/(2d.sub.2)).
31. The computer-readable storage medium according to claim 21,
wherein the sensor data comprises images of the first fringe
pattern and the operations comprise performing automatic image
recognition on the images to detect the first fringe pattern,
wherein a drive mechanism coupled to the support system is
controlled based on the results of the image recognition procedure.
Description
BACKGROUND
[0001] Optical components can be used in optical systems to alter
the state of visible light in a predictable and desired manner, for
example in display systems to make a desired image visible to a
user. Optical components may also be used as e.g. moulds for making
other optical components. Optical components can interact with
light by way of reflection, refraction, diffraction etc.
Diffraction occurs when a propagating wave interacts with a
structure, such as an obstacle or slit. Diffraction can be
described as the interference of waves and is most pronounced when
that structure is comparable in size to the wavelength of the wave.
Optical diffraction of visible light is due to the wave nature of
light and can be described as the interference of light waves.
Visible light has wavelengths between approximately 390 and 700
nanometres (nm) and diffraction of visible light is most pronounced
when propagating light encounters structures similar scale e.g. of
order 100 or 1000 nm in scale. One example of a diffractive
structure is a periodic diffractive structure. Periodic structures
can cause diffraction of light which is typically most pronounced
when the periodic structure has a spatial period of similar size to
the wavelength of the light. Types of periodic structures include,
for instance, surface modulations on a surface of an optical
component, refractive index modulations, holograms etc. Herein, a
"diffraction grating" (or simply "grating") means any (part of) an
optical component which has a diffractive periodic structure. A
diffraction grating has a grating period, which is the distance
over which its structure repeats. When propagating light encounters
the periodic structure, diffraction causes the light to be split
into multiple beams in different directions. These directions
depend on the wavelength of the light thus diffractions gratings
cause dispersion of polychromatic (e.g. white) light, whereby the
polychromatic light is split into different coloured beams
travelling in different directions.
[0002] When the period structure is on a surface of an optical
component, it is referred to a surface grating. When the periodic
structure is due to modulation of the surface itself, it is
referred to as a surface relief grating (SRG). An example of a SRG
is uniform straight grooves in a surface of an optical component
that are separated by uniform straight groove spacing regions.
Groove spacing regions are referred to herein as "lines", "grating
lines" and "filling regions". The nature of the diffraction by a
SRG depends both on the wavelength of light incident on the grating
and various optical characteristics of the SRG, such as line
spacing, groove depth and groove slant angle. SRGs have many useful
applications. One example is an SRG light guide application. A
light guide (also referred to herein as a "waveguide") is an
optical component used to transport light by way of internal
reflection e.g. total internal reflection (TIR) within the light
guide. A light guide may be used, for instance, in a light
guide-based display system for transporting light of a desired
image from a light engine to a human eye to make the image visible
to the eye.
[0003] In the case of a waveguide-based display system, different
gratings forming part of the same waveguide may serve various
functions. Waveguide-based display systems typically comprise a
light engine, which collimates light of an image into collimated
input beams which form a virtual version of that image at infinity.
The input beams may be directed towards an incoupling grating of
the waveguide, which is arranged to couple them into the waveguide
at angles which are sufficiently steep to cause TIR of the
incoupled beams within the waveguide. An outcoupling (exit) grating
on the waveguide may receive the incoupled beams internally and
diffract them outwardly in directions that match the input beams
(so that they form the same virtual version of the image). A user's
eye can then reconstruct the image when looking at the exit
grating. Usually, the exit grating is also arranged to provide beam
expansion of the outputted beams so as to provide an eyebox of
increased size compared with viewing the light engine directly.
Intermediate grating(s) of the same waveguide may provide
additional beam expansion to further increase the size of the
eyebox.
[0004] For some such waveguide grating arrangements, the
incoupling, outcoupling and (where applicable) intermediate
grating(s) will only manipulate the image light as intended if
their various gratings are oriented relative to one another in a
specific manner. Deviation from this intended orientation can cause
degradation of the final image as perceived by the user. When such
waveguides are manufactured in bulk for incorporation in different
waveguide display systems, each should preserve these specific
relationships to avoid degrading the quality of the final display
systems. Other types of optical component with various applications
may also comprise different gratings where it is desirable for the
relative orientation of those gratings to match a desired value as
closely as possible.
SUMMARY
[0005] This Summary is provided to introduce a selection of
concepts in a simplified form that are further described below in
the Detailed Description. This Summary is not intended to identify
key features or essential features of the claimed subject matter,
nor is it intended to be used to limit the scope of the claimed
subject matter. Nor is the claimed subject matter limited to
implementations that solve any or all of the disadvantages noted in
the Background section.
[0006] The disclosure considers an optical component comprising an
arrangement of a first and a second component grating having a
component relative orientation angle. The quality of the optical
component is assessed in terms of a deviation of the component
relative orientation angle from a desired relative orientation
angle. A quality assessment is made by comparing the optical
component to a master component comprising a substantially matching
arrangement of a first and a second optically transmissive master
grating having the desired relative orientation angle.
[0007] When the optical and master components are supported with
the first and second component gratings in the vicinity of the
first and second master gratings, a first fringe pattern is formed
by the first gratings as their relative orientation angle (first
relative orientation angle) is changed towards zero, the fringe
spacing of which increases as that first relative orientation angle
decreases. Similarly, a second fringe pattern is formed by the
second gratings as their relative orientation angle (second
relative orientation angle) is changed towards zero, the fringe
spacing of which also increases as that second relative orientation
angle decreases. The disclosure recognizes that, when the fringe
spacing of the first fringe pattern is substantially maximal (the
first relative orientation angle thus being substantially zero),
the fringe spacing of the second fringe pattern--which is
indicative of the second relative orientation angle in general--is
also indicative of the deviation of the component relative
orientation angle from the desired relative orientation angle (as
this deviation is substantially equal to the second relative
orientation angle when the first relative orientation angle is
substantially zero), and is thus indicative of the quality of the
optical component.
[0008] A first aspect is directed to a quality assessment apparatus
for assessing the quality of such an optical component. The
apparatus comprises a configurable support system, a light sensor,
a drive mechanism and a controller. The support system is
configured to support such an optical and such a master component
with the first and second component gratings of the optical
component in the vicinity of the first and second master gratings
of the master component. The light sensor is configured to receive
light which has interacted with both of the first and light which
has interacted with both of the second gratings, and to generate
sensor data from the received light. The drive mechanism is coupled
to the support system. The controller is configured to control the
drive mechanism based on the sensor data to reconfigure the support
system from a current configuration to a new configuration in which
the fringe spacing of a first fringe pattern formed by the first
gratings is substantially maximal. In addition, the controller is
configured to measure from the sensor data the fringe spacing of a
second fringe pattern formed by the second gratings in the new
configuration, and to output a quality assessment based on the
measured fringe spacing which is indicative of the deviation of the
component relative orientation angle from the desired relative
orientation angle.
[0009] Second and third aspects are directed to a quality
assessment process, and a computer program product comprising code
configured, when executed, to implement that process. Such an
optical component and such a master component are supported by a
configurable support system with the first and second component
gratings of the optical component in the vicinity of the first and
second master gratings of the master component. The process
comprises the following. Sensor data is received, the sensor data
generated from light which has interacted with both of the first
gratings and light which has interacted with both of the second
gratings. The support system is reconfigured based on the sensor
data from a current configuration to a new configuration, in which
the fringe spacing of a first fringe pattern formed by the first
gratings is substantially maximal. The fringe spacing of a second
fringe pattern formed by the second gratings in the new
configuration is measured from the sensor data. A quality
assessment is outputted based on the measured fringe spacing which
is indicative of the deviation of the component relative
orientation angle from the desired relative orientation angle.
BRIEF DESCRIPTION OF FIGURES
[0010] FIG. 1A is a frontal view of an optical component;
[0011] FIG. 1B is a schematic illustration of an optical component,
shown interacting with incident light and viewed from the side;
[0012] FIG. 2A is a schematic illustration of a straight binary
grating, shown interacting with incident light and viewed from the
side;
[0013] FIG. 2B is a schematic illustration of a slanted binary
grating, shown interacting with incident light and viewed from the
side;
[0014] FIG. 2C is a schematic illustration of an overhanging
triangular grating, shown interacting with incident light and
viewed from the side;
[0015] FIG. 3A is a frontal view of an optical component comprising
an arrangement of gratings;
[0016] FIG. 3B is a frontal view of a master component comprising a
substantially matching arrangement of gratings;
[0017] FIG. 4A is a perspective view of the optical component and
the master component during a quality assessment process;
[0018] FIG. 4B shows fringe patterns observed at different points
in time during the quality assessment process;
[0019] FIG. 5 is a block diagram of a quality assessment
apparatus.
DETAILED DESCRIPTION
[0020] FIGS. 1A and 1B show from the top and the side respectively
an optical component 2, such as a waveguide or a mould for making
other optical components, having an outer surface S. The optical
component is optically transmissive in this embodiment, but may not
be optically transmissive in other embodiments. The optical
component 4 comprises a grating 4, formed by (that is, whose
periodic structure arises as a result of) surface modulations over
the surface S, which constitute a surface grating (specifically, an
SRG). The modulations comprise grating lines which are
substantially parallel and elongate (substantially longer than they
are wide), and also substantially straight in this example (though
they need not be straight in general).
[0021] FIG. 1B shows the optical component 2, and in particular the
grating 4, interacting with an incoming illuminating light beam I
that is inwardly incident on the grating 4. The light I is white
light in this example, and thus has multiple colour components. The
light I interacts with the grating 4 which splits the light into
several beams directed inwardly into the optical component 2. Some
of the light I may also be reflected back from the surface S as a
reflected beam R0. A zero-order mode inward beam T0 and any
reflection R0 are created in accordance with the normal principles
of diffraction as well as other non-zero-order (.+-.n-order) modes
(which can be explained as wave interference). FIG. 1B shows
first-order inward beams T1, T-1; it will be appreciated that
higher-order beams may or may not also be created depending on the
configuration of the optical component 2. Because the nature of the
diffraction is dependent on wavelength, for higher-order modes,
different colour components (i.e. wavelength components) of the
incident light I are, when present, split into beams of different
colours at different angles of propagation relative to one another
as illustrated in FIG. 1B.
[0022] FIGS. 2A-2C are close-up schematic cross sectional views of
different exemplary gratings 4a-4c (collectively referenced as 4
herein), formed by modulations of the surface S of the optical
component 2 (which is viewed from the side in these figures). Light
beams are denoted as arrows whose thicknesses denote approximate
relative intensity (with higher intensity beams shown as thicker
arrows).
[0023] FIG. 2A shows an example of a straight binary grating 4a.
The straight binary grating 4a is formed by a series of grooves 7a
in the surface S separated by protruding groove spacing regions 9a
which are also referred to herein as "filling regions", "grating
lines" or simply "lines". The grating 4a has a spatial period of d
(referred to as the "grating period"), which is the distance over
which the modulations' shape repeats. The grooves 7a have a depth h
and have substantially straight walls and substantially flat bases.
As such, the filling regions have a height h and a width that is
substantially uniform over the height h of the filling regions,
labelled "w" in FIG. 2A (with w being some fraction f of the
period: w=f*d).
[0024] For a straight binary grating, the walls are substantially
perpendicular to the surface S. For this reason, the grating 4a
causes symmetric diffraction of incident light I that is entering
perpendicularly to the surface, in that each +n-order mode beam
(e.g. T1) created by the grating 4a has substantially the same
intensity as the corresponding -n-order mode beam (e.g. T-1),
typically less than about one fifth (0.2) of the intensity of the
incident beam I.
[0025] FIG. 2B shows an example of a slanted binary grating 4b. The
slanted grating 4b is also formed by grooves, labelled 7b, in the
surface S having substantially straight walls and substantially
flat bases separated by lines 9b of width w. However, in contrast
to the straight grating 4a, the walls are slanted by an amount
relative to the normal, denoted by the angle .alpha. in FIG. 2B.
The grooves 7b have a depth h as measured along the normal. Due to
the asymmetry introduced by the non-zero slant, .+-.n-order mode
inward beams travelling away from the slant direction have greater
intensity that their .+-.n-order mode counterparts (e.g. in the
example of FIG. 2B, the T1 beam is directed away from the direction
of slant and has usually greater intensity than the T-1 beam,
though this depends on e.g. the grating period d); by increasing
the slant by a sufficient amount, those .-+.Tn counterparts can be
substantially eliminated (i.e. to have substantially zero
intensity). The intensity of the T0 beam is typically also reduced
very much by a slanted binary grating such that, in the example of
FIG. 2B, the first-order beam T1 typically has an intensity of at
most about four fifths (0.8) the intensity of the incident beam
I.
[0026] The binary gratings 4a and 4b can be viewed as being formed
by spatial waveforms embedded in the surface S that have a
substantially square wave shape (with period d). In the case of the
grating 4b, the shape is a skewed square wave shape skewed by
.alpha..
[0027] FIG. 2C shows an example of an overhanging triangular
grating 4c which is a special case of an overhanging trapezoidal
grating. The triangular 4c is formed by grooves 7c in the surface S
that are triangular in shape (and which thus have discernible tips)
and which have a depth h as measured along the normal. Filling
regions 9c take the form of triangular, tooth-like protrusions
(teeth), having medians that make an angle .alpha. with the normal
(a being the slant angle of the grating 4c). The teeth have tips
that are separated by d (which is the grating period of the grating
4c), a width that is w at the base of the teeth and which narrows
to substantially zero at the tips of the teeth. For the grating of
FIG. 4c, w.apprxeq.d, but generally can be w<d. The grating is
overhanging in that the tips of the teeth extend over the tips of
the grooves. It is possible to construct overhanging triangular
grating gratings that substantially eliminate both the
transmission-mode T0 and the .-+.n-mode beams, leaving only
.+-.n-order mode beams (e.g. only T1). The grooves have walls which
are at an angle .gamma. to the median (wall angle).The grating 4c
can be viewed as formed by a spatial waveform embedded in S that
has a substantially triangular wave shape, which is skewed by
.alpha..
[0028] The grooves and spacing regions that form the gratings 4a-4c
constitute surface modulations.
[0029] Other type of grating are also possible, for example other
types of trapezoidal grating patterns (which may not narrow in
width all the way to zero), sinusoidal grating patterns etc. and
have a modulation width that can be readily defined in a suitable
manner. Such other patterns also exhibit depth h, linewidth w,
slant angle .alpha. and wall angles .gamma. which can be defined in
a similar manner to FIG. 2A-C.
[0030] A grating 4 has a grating vector (generally denoted as d),
whose size (magnitude) is 2.pi./d, and which is in a direction
perpendicular to the grating lines which form that grating--see
FIG. 1A.
[0031] In light guide-based display applications (e.g. where SRGs
are used for coupling of light into and out of a light guide of the
display system, and/or for providing beam expansion of beams
coupled into the waveguide), d is typically between about 250 and
500 nm, and h between about 30 and 400 nm. The slant angle .alpha.
is typically between about -45 and 45 degrees and is measured in
the direction of the grating vector.
[0032] FIG. 3A shows a frontal view of an optical component 2C. The
optical component 2C is of the general type described above, and
comprises a fixed arrangement of a first and a second component
grating 4iC, 4iiC, which can be of any of the general types
discussed above. Herein, a fixed arrangement of gratings means that
at least the orientation of those gratings relative to one another
is fixed. The gratings 4iC, 4iiC are optically transmissive parts
of the optical component 2C; that is, at least those parts are
formed of optically transmissive material that allows at least some
light to pass through the component gratings 4iC, 4iiC (all the way
through the optical component 2C) in a direction generally normal
to the gratings (parallel to the z-axis shown in FIG. 3A). In this
example, the gratings 4iC, 4iiC lie substantially parallel to the
same plane (xy-plane). The gratings 4iC, 4iiC are formed by surface
modulations (specifically, lines and grooves) over respective
portions of the optical component's surface, each lying
substantially parallel to the xy-plane. The surface modulations are
on frontal surface portions of the optical component 2C from the
viewpoint of FIG. 3 (in alternative optical component 2C, one of
the gratings may be formed by reward surface modulations on a rear
surface portion instead).
[0033] The optical component 2C may be a mass-produced optical
components (that is, one of a large number of optical components
produced in bulk e.g. in a factory set-up), in which for example
the optical component 2C is moulded from polymer.
[0034] As indicated above, in various applications, it is desirable
for different gratings of the same optical component to have
orientations relative to one another that match a desired
orientation as closely as possible (e.g. some idealized
relationship, at which the performance of the optical component is
optimized with respect to its intended functions, which may be
revealed though a suitable mathematical analysis).
[0035] For example, in one type of known display system--in which
an incoupling, intermediate and exit grating of an optical
component (which acts as a waveguide) function in tandem to cause
two-dimensionally expanded versions of beams incoupled at the
incoupling grating to be outputted at the exit grating--the
incoupling and exit gratings should have a relative orientation
angle 2.rho. (i.e. relative to one another) which is double that of
the incoupling and intermediate gratings (itself .rho.). Moreover,
that relative orientation angle .rho. of the incoupling and
intermediate gratings (i.e. relative to one another) should have a
specific relationship with the grating periods d.sub.1, d.sub.2 of
the incoupling and intermediate gratings, namely .rho.=arc
cos(d.sub.1/(2d.sub.2)). Deviation from these relationships can
cause degradation in the quality of the final image as perceived by
the user. Hence, the relationships should be preserved as closely
as possible to ensure that the waveguide does not significantly
degrade the image.
[0036] However, in practice and particularly in the context of
mass-manufacturing, it can be difficult to ensure that all such
optical components are manufactured to the same standard of
quality. Various inaccuracies and imprecisions can develop in the
manufacturing set-up which can cause degradation of the final
products. Such inaccuracies and imprecisions can be difficult to
detect, and become increasingly so as the scale of the
manufacturing operation is increased. Of particular concern in the
present context is degradation in the form of misalignment of
different gratings on the same optical component.
[0037] Hereinbelow, techniques are presented which facilitate an
automatic quality assessment that is both quick and reliable, in
which the quality of an optical component (e.g. 2C) comprising at
least two gratings (e.g. 4iC, 4iiC) is assessed in terms of a
deviation of their actual relative orientation (relative to one
another) from a desired relative orientation e.g. that at which the
performance of the optical component 4C is optimized with respect
to its intended function.
[0038] To this end, a comparison is made between the optical
component 2C and a high-quality master component 2M, which is
itself a high-quality optical component but the nature of which may
make it unsuitable for use in mass-manufactured end-products (e.g.
because to do so would be too costly and/or time-consuming). The
master component 2M is shown in FIG. 3B.
[0039] As shown in FIG. 3B, the master component 2M comprises a
fixed arrangement of gratings, which are first and second master
gratings 4iM, 4iiM, also of the general type discussed above and
which are optically transmissive in the same manner as the
component gratings 4iC, 4iiC (though in other embodiments they may
not be optically transmissive). The grating arrangement of the
master component 2M substantially matches the grating arrangement
of the optical component 2C; that is, the master grating
arrangement is such that the master gratings 4iM, 4iiM have
approximately (though not necessarily exactly) the same orientation
relative to one another as the component gratings 4iC, 4iiC, the
first master grating 4iM (resp. second master grating 4iiM)
substantially matches the first component grating 4iC (resp. second
component grating 4iiC) and, moreover, when the master component 2M
is placed at a location forward of the optical component 2C at
which at least part of the first component grating 4iC is
observable through the first master grating 4iM, at least part of
the second component grating 4iiC is observable through the second
master grating 4iiM at the same time. Note that "observable" in
this context simply means that there exists a line of sight in the
general .+-.z-direction that intersects both first gratings 4iC,
4iM (resp. both second gratings 4iiC, 4iiM), along which light can
propagate through both components 2C, 2M so as to interact with
both first gratings 4iC, 4iM (resp. both second gratings 4iiC,
4iiM), which light is detectable upon exiting the components 2C, 2M
having interacted thus. In this case, the master component 2M of
FIG. 3A, the master gratings 4iM, 4iiM also lie substantially
parallel to the xy-plane when the optical and master components 2C,
2M are suitably aligned relative to one another.
[0040] The master component 2M may have substantially the same
overall shape as the optical component 2C and/or substantially the
same overall optical characteristics, though this is not
required.
[0041] The master component 2M may, for instance, be formed of
fused silica or some other suitable material that has been subject
to a microfabrication process, in which the master gratings 4iM,
4iiM are formed by etching of and/or deposition on the surface of
the material. Using such microfabrication processes, it is possible
to create master gratings 4iM, 4iiM having the desired relative
orientation to a very high level of accuracy (i.e. of very high
quality, as the term is used herein), which can be verified by
performing suitable tests on the master gratings to measure the
relative orientation of the master gratings to ensure that it is
indeed precisely the desired orientation and/or by testing the
optical characteristics of the master gratings to ensure that the
master component functions in same the manner in which the
to-be-tested optical components are intended to function. Such
tests, whilst generally accurate, tend to be costly and
time-consuming, and thus not suitable per-se for application to
mass-produced optical components. However, once it has been
verified that the master component 2M is of the requisite high
quality, as indicated, the quality of such mass-manufactured
optical components (e.g. 2C) can be assessed quickly and reliably
by way of comparison with the master component 2M in the manner set
out below.
[0042] Returning to FIG. 3A, the first component grating has a
grating vector cl.sub.iC (first component grating vector) and the
second component has a second grating vector d.sub.iiC (second
component grating vector), each parallel to the respective grating
lines of the relevant grating and lying in the plane of that
grating. An angle .DELTA..phi..sub.C is shown, which is the angle
between the component grating vectors d.sub.iC, d.sub.iiC as
measured in the xy-plane and which is referred to herein as the
relative orientation angle of the first and second component
gratings 4iC, 4iiC or simply as the "component relative orientation
angle"--it is this angle which is intended to precisely match a
desired relative orientation angle, and the processes described
herein provide an automatic assessment of the extent to which that
match has been realized in practice.
[0043] Returning to FIG. 3B, the first master grating has a grating
vector d.sub.iM (first master grating vector) and the second
component has a second grating vector d.sub.iiM (second master
grating vector), each perpendicular to the respective grating lines
of the relevant grating and lying in the plane of that grating. An
angle .DELTA..phi..sub.M is shown, which is the angle between the
master grating vectors d.sub.iM, d.sub.iiM as measured in the
xy-plane and which is referred to herein as the relative
orientation angle of the first and second master gratings 4iM,
4iiM--it is this angle which is known to be the desired relative
orientation angle to a high level of precision, and the quality of
the (e.g. mass-produced) optical component 4C is assessed in terms
of the size of a deviation of 4c from .DELTA..phi..sub.C from
.DELTA..phi..sub.M i.e. in terms of
|.DELTA..phi..sub.c-.DELTA..phi..sub.m|. When this deviation is
substantially zero, the quality of the optical component 2C is
considered to be optimal.
[0044] The optical and master components each comprise respective
alignment marks 12C, 12M shown in FIGS. 3A and 3B respectively. The
alignments marks are arranged such that, when the master component
2M is moved forward of the optical component 2C to bring the master
marks of 12C into alignment with the component marks 12M when
viewed in the z-direction, the first master grating 4iM is at least
approximately aligned (by angle) with the first component grating
4iC. This is discussed below.
[0045] A quality assessment process will now be described with
reference to FIGS. 4A and 4B.
[0046] FIG. 4A is a perspective view of the master and optical
components 2M, 2C during the process, in which the xy-plane 3 is
shown. The master component 12M is supported forward of the optical
component 12C and substantially parallel to the xy-plane, with the
first component grating 4iC opposing the first master grating 4iM,
and the second component grating 4iiC opposing the second master
grating 4iiM. In this configuration, the first gratings 4iC, 4iM
lie substantially parallel to the same plane as one another (which
is the xy-plane 3), and the second gratings 4iiC, 4iiM also lie
substantially parallel to the same plane as one another (which is
also the xy-plane 3).
[0047] The respective geometric projections of the component
grating vectors d.sub.iC, d.sub.iiC and master grating vectors
d.sub.iM, d.sub.iiM in the xy-plane 3 are shown. Note that herein
(including in the figures), the notation d.sub.iC, d.sub.iiC,
d.sub.iM, d.sub.iiM is used interchangeably to denote both the
grating vectors themselves and the geometric projections of the
grating vectors in the xy-plane, and it will be clear from the
context which is meant. For the sake of clarity, the master
projections d.sub.iM, d.sub.iiM are represented by thicker arrows
than the component projections d.sub.iC, d.sub.iiC in FIG. 4A.
[0048] In addition to the relative orientation angle
.DELTA..phi..sub.c of the first and second component gratings 4iC,
4iiC (which is an inherent property of the optical component 2C)
/and the relative orientation angle .DELTA..phi..sub.M of the first
and second master gratings 4iM, 4iM (which is an inherent property
of the master component 2M), an angle .DELTA..phi..sub.i is shown,
which is the angle between the first master grating vector d.sub.iM
and the first component grating vector d.sub.iC as measured in the
xy-plane 3, and which is referred to herein as the relative
orientation angle of the first gratings 4iM, 4iC or simply as the
"first relative orientation angle". Another angle
.DELTA..phi..sub.ii is shown, which is the angle between the second
master grating vector d.sub.iiM and the second component grating
vector d.sub.iiC as measured in the xy-plane, and which is referred
to herein as the relative orientation angle between the second
gratings 4iiM, 4iiC or simply as the "second relative orientation
angle". The angles .DELTA..phi..sub.i, .DELTA..phi..sub.ii are
properties of the current orientation of the optical component 2C
relative to the master component 2M, and change as that orientation
is changed.
[0049] A first line of sight (LOS1) is shown, which lies
substantially parallel to the z-axis and which intersects both the
first gratings 4iC, 4iM of the optical and master components 2C, 2M
respectively. A second line of sight (LOS2) is shown, which also
lies substantially parallel to the z-axis but which intersects both
the second gratings 4iiC, 4iiM of the optical and master components
2C, 2M respectively.
[0050] The disclosure recognizes that, when the optical component
2C and the master component 2M are held in a relative
xy-orientation such that the first relative orientation angle
.DELTA..phi..sub.i of the first gratings 4iC, 4iM is substantially
zero (substantially perfect alignment)--which can be achieved by
effecting xy-rotation of one or both of the master and optical
component 2M, 2C--the size of the second relative orientation angle
|.DELTA..phi..sub.ii| of the second gratings 4iiC, 4iiM will be
substantially equal to |.DELTA..phi..sub.c-.DELTA..phi..sub.M| i.e.
the size of the deviation of the component relative orientation
angle .DELTA..phi..sub.c of the component gratings 4iC, 4iiC from
the desired relative orientation angle .DELTA..phi..sub.M that
separates the master gratings 4iM, 4iiM, which as discussed above
is precisely the quantity that is indicative of the quality of the
optical component 2C. The size of the second relative orientation
angle at a point in time when .DELTA..phi..sub.i=0 is denoted
|.DELTA..phi..sub.ii|.sub..DELTA..phi..sub.i.sub.=0=|.DELTA..phi..sub.C-.-
DELTA..phi..sub.M|. When
|.DELTA..phi..sub.ii|.sub..DELTA..phi..sub.i.sub.=0=|.DELTA..phi..sub.C-.-
DELTA..phi..sub.M|=0, the optical component 2C is considered to
have optimal quality, with larger
|.DELTA..phi..sub.ii|.sub..DELTA..phi..sub.i.sub.=0=|.DELTA..phi..sub.c-.-
DELTA..phi..sub.m| being considered lower quality.
[0051] In changing the relative xy-orientation of the two
components 2C, 2M, the orientation .DELTA..phi..sub.c of the
component gratings 4iC, 4iiC relative to one another is unchanged,
as is the orientation .DELTA..phi..sub.M of the master gratings
4iM, 4iiM relative to one another (these being inherent properties
of the respective components). In contrast, what is changed is the
orientation of the component gratings relative to the master
gratings--in particular the orientation .DELTA..phi..sub.ii of the
first component grating 4iC relative to the first master grating
4iM, and the orientation of the .DELTA..phi..sub.ii of the second
component grating 4iC relative to the second master grating 4iM,
which are each changed by substantially the same amount when the
xy-orientation of the components 2C, 2M is changed from a current
xy-orientation to a new xy-orientation.
[0052] The disclosure further recognizes that, when the first
gratings are in near, but not perfect alignment--e.g. about
(5/100).degree..ltoreq..DELTA..phi..sub.i.ltoreq.about
(1/1000).degree. (near alignment range)--a first fringe pattern
will be visible along the first line of sight LOS1, that pattern
formed by light which has propagated through or been reflected
from, and which has thus interacted with, both first gratings 4iC,
4iM, which are effectively overlaid on one another when viewed
along the first line of sight LOS1. The first fringe pattern
exhibits a fringe spacing that increases as .DELTA..phi..sub.i
decreases, becoming maximal (theoretically infinite) when
.DELTA..phi..sub.i=0. When .DELTA..phi..sub.i is within
approximately the aforementioned approximate near alignment range,
the fringe spacing will be measurable i.e. such that the fringes
are neither too small nor too large to be undetectable. For
example, when .DELTA..phi..sub.i.apprxeq.((5/1000).degree., the
fringe pattern will typically have a fringe spacing around 2 mm,
which is readily observable. The period of the fringe pattern is
.apprxeq.d/.DELTA..phi. (the approximation is very accurate with
small angles), with d the grating period and .DELTA..phi. in
radians. The fringes appear perpendicular to the grating lines.
[0053] Eventually, as .DELTA..phi..sub.i tends towards zero, it
will become sufficiently small that the fringes become larger than
the surface area of the first gratings (or at least larger than a
portion that area if only that portion is being observed).
Typically, this will occur around
.DELTA..phi..sub.i.apprxeq.(1/1000).degree., at which point the
fringe spacing is considered substantially maximal and
.DELTA..phi..sub.i substantially zero--by adjusting the relative
xy-orientation alignment of the optical and master component 2C, 2M
from an initial configuration to the point at which that
substantially maximal fringe spacing is reached (new
configuration), it is thus possible to align the first gratings
4iC, 4iM to that level of accuracy.Moreover, when the first
gratings 4iC, 4iM are thus aligned in the new configuration with
.DELTA..phi..sub.i substantially zero, provided
|.DELTA..phi..sub.ii|.sub..DELTA..phi..sub.i.sub.=0 is itself with
the aforementioned approximate near alignment range, a second
fringe pattern will also be visible along the second line of sight
LOS2, formed in an equivalent manner by light which has passed
through or reflected from the surfaces with gratings and thus
interacted with both of the second gratings 4iiC, 4iiM, which are
similarly effectively overlaid on one another when viewed along the
second line of sight LOS2. The larger the fringe spacing of the
second fringe pattern in the new configuration, the smaller
|.DELTA..phi..sub.ii|.sub..DELTA..phi..sub.i.sub.=0=|.DELTA..phi.-
.sub.C-.DELTA..phi..sub.M|. That is, the larger the fringe spacing
of the second fringe pattern in the new configuration, the higher
the quality of the optical component 2C i.e. the smaller the
deviation of the component relative orientation angle .phi..sub.c
between the two component gratings 4iC, 4iiC from the desired
relative orientation angle .phi..sub.m between the corresponding
master gratings 4iM, 4iiM.
[0054] This is illustrated in FIG. 4B, which shows exemplary first
and second fringe patterns as visible over an area 7 (also shown in
FIG. 4A), as viewed generally along the lines of sight LOS1, LOS2.
The fringe patterns are shown in FIG. 7B at various points in time
during the quality assessment process.
[0055] The far-left hand side of FIG. 4B shows a view of the area 7
when the components 2C, 2M are in an initial configuration, in
which the first gratings 4iC, 4iM of the optical and master
component 2C, 2M are in near alignment. In this example, the
initial configuration is achieved by aligning the alignment marks
12C of the optical component 2C with the corresponding alignment
marks 12M of the master component 2M as viewed in a direction
generally parallel to the z-axis (intermediate configuration),
which alignment marks 12C, 12M are such that, when so aligned in
the intermediate configuration, .DELTA..phi..sub.i is within the
aforementioned approximate near alignment range. The optical
component 2C can be provided with the alignments 12M marks at the
time of its manufacturing process (e.g. for a moulded optical
component, alignment mark structure can be included on the same
mould from which the grating structure is imparted). Typically, the
nature of the manufacturing process in question means that,
notwithstanding potential imprecisions/inaccuracies of the kind
being tested for by the present process, it is possible to provide
suitable alignment marks that can be used to achieve such near
alignment within the near alignment range.
[0056] Alternatively, the process may be performed without
alignment marks, and the xy-orientation of the two components 2C,
2M can simply be scanned from any arbitrary starting point until
the first fringe pattern becomes visible (such scanning could also
be used if, for some reason, .DELTA..phi..sub.i is not in fact
within the approximate near alignment range even when such
alignment marks are so aligned e.g. due to unexpectedly large
manufacturing errors). Typically, the use of alignment marks
reduces the time it takes to make the quality assessment, which can
be particularly significant in terms of the overall efficiency of
the process when there are a large number of optical components to
be assessed.
[0057] Once near alignment of the first gratings 4iC, 4iM has been
so achieved, the xy-orientation of the component 2C, 2M is fine
tuned to a new configuration in which the fringe spacing of the
first fringe pattern (indicated by a distance labelled D in FIG.
4B) is substantially maximal and thus in which
.DELTA..phi..sub.i.apprxeq.0--this is shown on the far right of
FIG. 4B. The intervening views of FIG. 4B represent the changing
view as the components 2M, 2C are moved to change their
xy-orientation from the initial configuration on the far-left to
the new configuration on the far-right. The fringe spacing of the
second fringe pattern (indicated by a distance labelled D' in FIG.
4B) in the new configuration can then be measured, and the measured
fringe spacing used to output a quality assessment, with the
quality assessment indicating lower (resp. higher) quality the
smaller (resp. larger) the measured fringe spacing.
[0058] Should the fringe spacing of the second fringe pattern in
the new configuration be substantially zero (i.e. should both the
fringe spacing of the first fringe pattern and the fringe spacing
of the second fringe pattern be substantially zero simultaneously),
that indicates there to be substantially no deviation of
.phi..sub.C from .phi..sub.M and that the optical component 2C is
thus of substantially optimal quality.
[0059] Although FIG. 4A shows the fringe patterns as having been
created by light which has passed though both gratings by way of
example, it is not required that light passes through both plates
(thus the optical components do not have to be optically
transmissive) for the fringe patterns to appear so the
gratings--the patterns can be formed of reflected light (e.g. light
of reflective diffraction modes). In practice the fringe patterns
are usually most visible when the light is reflected from the
surfaces of the gratings as compared with a situation in which the
light passes through both.
[0060] FIG. 5 is a block diagram of the quality assessment
apparatus 1, which comprises a controller 20, a drive mechanism 22,
a configurable support system 24 and a sensor 6 (which is also
shown in FIG. 4A, disposed along the lines of sight LOS1,
LOS2).
[0061] The configurable support system 24 supports the optical and
master components 2C, 2M in a configurable configuration. The
system 24 can be configured to effect relative motion between the
two components 2C, 2M to align the alignment marks 12C, 12M, and
moreover to effect the subsequent fine-tuning--that is, to change
at least the xy-orientation of the master and component to vary
.DELTA..phi..sub.i and .DELTA..phi..sub.ii in the manner described
above. The drive mechanism 22 is coupled to the support system 24,
and is controllable to change the configuration of the system 24 in
a controlled manner.
[0062] The light sensor 22 receives light from (senses) the first
gratings 2iM, 2iC and from the second gratings 2iiM, 2iiC, and in
particular from the second fringe patterns described above, from
which it generates sensor data that is received by the controller
20.
[0063] Based on the received sensor data, the controller 20
controls the drive mechanism 22 to reconfigure the configuration of
the components 2C, 2M until the sensor data indicates that the
substantially maximal fringe spacing D of the first fringe pattern
has been achieved. The controller 20 also measures from the sensor
data the fringe spacing D' at that point in time. Based on this
measured fringe spacing, the controller 20 outputs a suitable
quality assessment e.g. to an operator of the apparatus 1 via a
user interface of the controller 20, or to some other component of
the apparatus 1 (not shown) e.g. computer storage, in which the
assessment is stored for later use.
[0064] The sensor 6 may also capture light of (that is, sense) the
alignment marks 12C, 12M, and the controller 20 may--prior to
performing the fine tuning reconfiguration--perform an initial
reconfiguration to achieve alignment of the alignment marks 12C,
12M based on sensor data pertaining to the alignment marks as
received from the sensor 6. For example, the sensor 6 may capture
images of the marks 12C, 12M, on which image recognition is
performed to detect those marks and to identify when the detected
marks are aligned.
[0065] The controller 20 can be implemented as code executed on a
suitable processor.
[0066] In practice, visibility of the fringe pattern can be
increased by suitable illumination of the apparatus. For instance,
to enhance the visibility of the fringe pattern, a laser (not
shown) may be used to provide a beam that is directed towards the
gratings 4iC, 4iM, 4iiC, 4iiM so that part passes though both the
first gratings 4iC, 4iM and another part through both the second
gratings 4iiC, 4iiM. A beam expander (not shown) may be used to
expand the beam before reaching the gratings 4iC, 4iM, 4iiC, 4iiM,
so as to increase the size of the area (e.g. 7) over which the
visibility is enhanced. For example, the beam may be expanded to
encompass the gratings 4iC, 4iM, 4iiC, 4iiM to provide the enhanced
visibility of the fringe patterns over the full extent of the
gratings 4iC, 4iM, 4iiC, 4iiM.
[0067] In a first embodiment, the sensor 6 comprises an image
sensing component in the form of a camera, which supplies images of
at least the area 7 to the controller 20 (such images capturing
views of the type shown in FIG. 4B). The controller comprises an
image recognition module which performs an automatic image
recognition procedure on the received images to detect the fringes
of the fringe patterns when captured in the images. The controller
adjusts .DELTA..phi..sub.i until the results of the image
recognition procedure indicate that the fringe spacing D of the
first fringe pattern is substantially maximal, and then measures
the fringe spacing D' of the second fringe pattern at that point in
time, again based on the results of the image recognition
procedure.
[0068] The fringe spacing can be so measured in various different
ways, for instance in terms of a spatial period-type metric (which
is D' in FIG. 4B) or a spatial frequency-type metric e.g. by
counting the number of fringes visible within a predetermined
distance (lower frequency indicating larger fringes thus higher
quality).
[0069] In a second embodiment, the sensor 6 comprises a first and a
second photodiode (or other suitable first and second sensor
components), which are shielded from surrounding light but for a
respective small pinhole--e.g. having a diameter .about.1 mm (order
of magnitude)--through which only a small portion of the first and
second fringe pattern is observable respectively. That is, such
that the only light received by the first (resp. second) photodiode
is from a small portion of the first (resp. second) fringe pattern
the size of the respective pinhole, so that once the relevant
gratings are in near alignment, the fringes are larger than the
pinhole. The controller 20 then changes the xy-orientation of the
component 2C, 2M, e.g. at a uniform rate. As the gratings (4iC,
4iM/4iiC, 4iiM) are brought into alignment, the fringe spacing of
the relevant fringe pattern increases, which effectively results in
movement of those fringes (this is evident in FIG. 4D). Thus the
intensity of the light received by the photodiodes oscillates
between high (when only part of a light fringe is observable
through the pinhole) and low (when only part of a dark fringe is
perceivable through the pinhole) as the xy-orientation of the
components 2C, 2M is changed. As the fringe spacing increases, the
rate of this oscillation will decrease due to the light and dark
fringes becoming progressively larger so that the rate of
oscillation observed by the first photodiode through the first
pinhole is minimal as .DELTA..phi..sub.i becomes substantially
zero--in the second embodiment, the controller adjusts the
xy-orientation until that minimum rate of oscillation is achieved,
and measures the fringe spacing D' of the second fringe pattern in
terms of the rate of oscillation observed by the second photodiode
through the second pinhole at a point in time at which that minimum
rate of oscillation as observed by the first photodiode through the
first pinhole is achieved.
[0070] The rate of oscillation can be so measured in various
different ways, for instance in terms of a temporal period-type
metric e.g. obtained by timing individual oscillations or temporal
frequency-type metric e.g. obtained by counting the number of
oscillations that occur over an interval of predetermined
length.
[0071] As mentioned, the optical component can be a mould for
making other optical components. Moulds are needed in large
quantities because the end product is needed in very high
quantities. Thus it's also useful to have a quick method for
analysing moulds.
[0072] The quality assessment outputted by the controller can take
a number of forms. For example, the controller may simply output a
value of the second pattern fringe spacing D' as measured at a
point in time when the fringe spacing D of the first pattern is
substantially zero (e.g. expressed as a measured spatial period,
spatial frequency, temporal period, temporal frequency etc.) as
this is directly indicative of the quality of the component.
Alternatively, the controller could compute some suitable quality
metric based on the measured fringe spacing, for example in the
simplest case a binary metric that can take one of two values, one
of which indicates acceptable quality (when the measured fringe
spacing is above a predetermined threshold) and the other
unacceptable quality (when the measured fringe spacing is below
that threshold), though more complex quality metrics can
alternatively be used to provide richer information.
[0073] Whilst in the above, the exemplary first gratings 4iC, 4iM
(resp. second gratings 4iiC, 4iiM) match due to the fact that they
are both formed of substantially straight grating lines, in general
gratings which are considered to "substantially match" do not
necessarily have to be formed of straight grating lines, nor do
they have to be formed of identically shaped curved grating lines.
In general, two gratings "substantially match" provided some parts
of their respective structures are similar enough for it to be
possible to create an observable fringe pattern that exhibits a
discernible fringe spacing by overlaying those parts (even though
other parts of their structure may be markedly different). Matching
gratings may or may not have the same grating period.
[0074] Whilst in the above, the component gratings 4iC, 4iiC (and,
correspondingly, the master gratings 4iM, 4iiM, which are in a
substantially matching arrangement) are formed by modulations over
substantially parallel surface portions, this does not have to be
the case in general (for non-parallel gratings, the various angles
shown e.g. in FIG. 4A can be equivalently defined by way of
geometric projection onto a suitable plane e.g. whose normal is in
the direction of the vector sum of the normals of the non-parallel
gratings, which is the direction of the mean of those directions).
Further, whilst in the above the surface modulations are over
substantially flat surface portions, the disclosed techniques can
also be applied to curved gratings e.g. formed by modulations on
curved surface portions.
[0075] Further, in general the terminology "opposing gratings" (or
similar) encompasses gratings which are not parallel. Two gratings
are considered to be opposing when there exists a line of sight
intersecting both gratings (e.g. in a direction that substantially
matches the normals to those gratings), along which a resulting
fringe pattern can be observed when those gratings are in near
alignment. Whilst the above has been described with reference to
opposing gratings, the techniques can be applied to non-opposing
gratings, whereby the fringe pattern is formed for instance by a
beam which has been guided onto both gratings by reflection.
[0076] The various gratings 4iC, 4iiC, 4iM, 4iiM can be binary
(slanted/non-slanted), sinusoidal, trapezoidal (e.g. triangular) in
shape (among others) and need not have the same shape, slant a,
width w, depth h etc. as one another (though this is not
excluded).
[0077] Whilst the above considers a substantially
software-implemented controller 20, the functionality of the
controller can be implemented using software, firmware, hardware
(e.g., fixed logic circuitry), or a combination of these
implementations. The terms "module," "functionality," "component"
and "logic" as used herein generally represent, where applicable,
software, firmware, hardware, or a combination thereof. In the case
of a software implementation, the module, functionality, or logic
represents program code that performs specified tasks when executed
on a processor (e.g. CPU or CPUs). The program code can be stored
in one or more computer readable memory devices. The features of
the techniques described below are platform-independent, meaning
that the techniques may be implemented on a variety of commercial
computing platforms having a variety of processors.
[0078] For example, the apparatus may also include an entity (e.g.
software) that causes hardware of a computer of the apparatus to
perform operations, e.g., processors functional blocks, and so on.
For example, the computer may include a computer-readable medium
that may be configured to maintain instructions that cause the
computer, and more particularly the operating system and associated
hardware of the computer to perform operations. Thus, the
instructions function to configure the operating system and
associated hardware to perform the operations and in this way
result in transformation of the operating system and associated
hardware to perform functions. The instructions may be provided by
the computer-readable medium to the computer through a variety of
different configurations.
[0079] One such configuration of a computer-readable medium is
signal bearing medium and thus is configured to transmit the
instructions (e.g. as a carrier wave) to the computing device, such
as via a network. The computer-readable medium may also be
configured as a computer-readable storage medium and thus is not a
signal bearing medium. Examples of a computer-readable storage
medium include a random-access memory (RAM), read-only memory
(ROM), an optical disc, flash memory, hard disk memory, and other
memory devices that may us magnetic, optical, and other techniques
to store instructions and other data.
[0080] In embodiments of the various aspect set out in the Summary
section, the optical component and the master component may
comprise alignment marks located so that, when the marks are
aligned, the first fringe pattern is observable, wherein the sensor
senses the marks, and wherein the controller is configured based on
sensor data pertaining to the marks to reconfigure the support
system from the current configuration to an intermediate
configuration, in which the alignments marks are substantially
aligned and from which the support system is then reconfigured to
the new configuration.
[0081] The light sensor may comprise a camera which captures images
of the first fringe pattern as the support system is reconfigured,
and wherein the controller comprises an image recognition module
which performs an automatic image recognition procedure to detect
the first fringe pattern in the images, wherein the controller
reconfigures the support system based on the results of the image
recognition procedure.
[0082] The images may also be of the second fringe pattern, the
automatic image recognition procedure detects the second fringe
pattern, and the controller measures the fringe spacing of the
second fringe pattern based on the results of the image recognition
procedure.
[0083] The light sensor may comprise a sensor component which
receives light of only a small portion of the first fringe pattern
as the support system is reconfigured, and the controller may
reconfigure the support system based on the rate at which the
intensity of that light changes.
[0084] The light sensor may comprise another sensor component which
receives light of only a small portion of the second fringe
pattern, and the controller may measure the fringe spacing of the
second fringe pattern based on the rate at which the intensity of
that light changes.
[0085] The apparatus may comprise a laser which provides a beam and
a beam expander which expands the beam to illuminate the gratings
with an expanded beam that substantially encompasses the gratings
so as to enhance the visibility of the fringe patterns.
[0086] The optical component and the master component may comprise
alignment marks located so that, when the marks are aligned, the
first fringe pattern is observable, and the process may comprise
reconfiguring the support system from the current configuration to
an intermediate configuration, in which the alignments marks are
substantially aligned and from which the support system is then
reconfigured to the new configuration.
[0087] The component gratings may be formed by surface modulations
on the surface of the optical component. The surface modulations
may be on substantially parallel portions of the surface of the
optical component.
[0088] Both the component gratings may be formed by surface
modulations on frontal portions of the surface of the optical
component.
[0089] One of the component gratings may be formed by surface
modulations on a frontal portion of the surface of the optical
component and the other is formed by surface modulations on a
rearward portion of the surface of the optical component.
[0090] The optical component may comprise polymer or may be a mould
for moulding such optical components.
[0091] A microfabrication process may be performed on the master
component to fabricate the master gratings prior to performing the
steps of the second aspect.
[0092] The master component gratings may be tested to assess the
quality of the master component prior to performing the steps of
the second aspect.
[0093] The first component grating may have a period d.sub.1 and
the second component grating may have a period d.sub.2, and the
desired orientation angle of the master gratings may be
substantially arccos(d.sub.1/(2d.sub.2)).
[0094] Although the subject matter has been described in language
specific to structural features and/or methodological acts, it is
to be understood that the subject matter defined in the appended
claims is not necessarily limited to the specific features or acts
described above. Rather, the specific features and acts described
above are disclosed as example forms of implementing the
claims.
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