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technical
area
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The
The present invention relates to a device for combination
of light of different wavelengths. The invention relates
in particular to a lighting unit, which light of
red, green
and blue narrowband light sources to combine white light
can. However, the invention also relates to a lighting unit,
which white light in red, green
and split blue partial beams is able.
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today
Projectors working on the projection of light for imaging
can essentially be divided into 2 categories:
Such for the
each of the three color channels
red (R), green
(G) and blue (B) each provide an imaging element (3P projectors
= 3 panel projectors). The red color channel is light with
wavelength
within the wavelength interval
from 600 nm to 780 nm. The green color channel is light with
wavelength
within the wavelength interval
from 500 nm to 600 nm. The blue color channel is light
with wavelengths
within the wavelength interval
from 420 nm to 500 nm.
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It
But there are also such projectors that only with an imaging
Element and color sequential work (CS projectors = Color Sequential
Projectors).
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A
further classification can be made in the way that the imaging
Element modulates light to pass on image information. A widespread
Class of imaging elements subjects the incoming light
one locally
resolved
Polarization modulation. This polarization modulation is then using
polarization-selective optical elements in an intensity modulation
transferred. This type of imaging elements must be with
polarized light are applied. In the focus of this description stand
however, lighting devices for another class of imaging
Elements with unpolarized light or only partially
polarized light can be applied. The required lighting devices
should be able to prepare unpolarized light for exposure.
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Become
broadband, white light sources used in 3P projectors,
so must first
the white light can be split into the three colors red, green and blue.
A possibility
to do this is the use of dielectric edge filters. One
Edge filter has the task of light in a first wavelength range
almost 100% reflect during
in a second adjacent wavelength range, it is nearly 100% of the
Light should transmit. The area in which the wavelength ranges
adjacent, is called the filter edge. Becomes a first edge filter
with a filter edge at 500 nm in the beam path of a white light source
placed, so will first
the blue color of the yellow light associated with the blue color channel
cleaved. Yellow light is additive in this case
green
and red light together. Will now be in the beam path of the yellow
Light an edge filter with an edge placed at 600 nm so
will go ahead
split off from red light.
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Which one
the wavelength ranges
is reflected or transmitted, depends on the design of the
respective edge filter from. In general, an edge filter which
the wavelength range
with the smaller wavelengths
transmitted while
larger
wavelength
be reflected, referred to as low pass. An edge filter which
the wavelength range
with the smaller wavelengths
reflected while transmitting larger wavelengths
will be called a high pass.
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Become
narrowband light sources, such as the light of LEDs
used in CS projectors, so there is the lighting arrangement
the task the light paths of a red, green and blue narrowband
Light source to unite and the light beams on the one imaging
To steer element. Again, you can
Edge filters are used: a first, which for example
the light path of red and green light combined and
a second, which the light path of the blue light with the two
combined with other light paths.
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One
problematic aspect here is the fact that light both
white light sources, as well as light narrowband LEDs in the
Usually not unpolarized, but at least not completely polarized light
deliver.
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typically,
But edge filters are using dielectric interference layer systems
realized on otherwise transparent glass substrates. Interference coating systems
however, have characteristics related to polarization dependence
prove to be detrimental to the edge filters described herein.
In order not to throw a component of the light back into itself,
namely, the edge filters become
arranged at an angle inclined to the optical axis.
The problem with this is that thereby the reflection and transmission behavior
of the interference filter becomes polarization dependent. In particular, both depends
the position of the edge as well as the reflection and transmission in the
Wavelength ranges,
the edges adjoin the polarization. For light sources,
working with unpolarized or only partially polarized light
does this
to misdirections of light components. This has one hand
Loss of light result and on the other hand, on the respective
Color coordinates unfavorable
impact.
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In
In the present specification, the optical path is the blue one
Part of the light
has been called a blue channel. The proportion of the light source
radiated blue light that arrives at the imaging element,
is called blue channel transmission. Accordingly, one of
Rotkanalransmission and spoken by a Grünkanaltransmission.
Of course, misdirections of light components lead to a reduction
the channel transmission.
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One
Another important factor influencing the channel transmission
the Winkelabstrahlcharakteristik the light source or the light sources.
The for
The lighting used optical elements and filters must therefore
have a certain angular acceptance, which is usually due to the
F-number expressed
becomes. The F number is inversely proportional to the numerical aperture
(NA), by the product of refractive index of the medium and half the opening angle
the illumination cone is defined. That the smaller the F number,
the bigger the
required angular acceptance. When calculating the channel transmission
the effect that the different angles of incidence on the
Transmission characteristics of the edge filters have to be considered.
It depends
both the position of the edge and the reflection and transmission
in the areas adjacent to the edge, from the angle of incidence
from. To take this into account
will over
the different angles of incidence weighted integrated. For the channel transmission
this means that the for
an angle of incidence first
steep edges through integration over different angles
lose steepness and thus misdirected light in the edge area
becomes.
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Task of
invention
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Of the
The invention is therefore based on the object of specifying a device
which overcomes or at least reduces the disadvantages of the prior art.
In particular, the device according to the invention is intended to be compared to the
State of the art cost-effective
solution to be prepared
for a
Display lighting system with unpolarized light for projectors.
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Overview of the
present invention
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The
solution
the task is deviating from the prior art the
between the two adjacent wavelength intervals lying green channel
to treat separately while
red and blue light channel still (in the case of the white light source)
or already combined (in the case of narrow-band light sources)
are. This means that to separate the red light path from
blue light path, or to the combination of the red and the blue light path
a very simplified edge filter can be used whose edge
within the green
Wavelength interval
almost arbitrary polarization-dependent
and / or angle-dependent
can be essential without the separation or combination of red-blue
to impair.
It is therefore even questionable whether this case of an edge filter in
Meaning of the definition given above should be spoken. the
In the context of this description, it is generally assumed by
talked about a RB splitter. Especially from an RB splitter low pass,
when blue light is transmitted and red light is reflected.
Correspondingly of a RB splitter high pass, when blue light reflects
and red light is transmitted.
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in the
Connection with color management systems for reflective, locally polarization-modulating imaging
Elements is such a separate treatment of the green channel
already known. However, here the color management system must be light,
partly in one and partly in the other polarization of the
imaging element polarization modulated and reflected light
propagate before a polarization-sensitive optical element
converts the polarization modulation into an intensity modulation.
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at
Lighting arrangements for
Imaging elements where polarization is irrelevant
In contrast, no polarization-selective element is used.
According to the present
Rather, a so-called green bandpass filter is needed and invention
used. Such a filter can be
for example, realize that on one side of a substrate
a low-pass filter with edge layer is applied at about 600 nm,
while
on the other side a high pass filter with edge position at approx.
500 nm is applied. In this way, blue light will be on
Page reflected with the high pass filter and red light at the
Page reflected with the low pass filter. Only green light
is transmitted through both sides of the substrate. This allows
the efficient combination and / or splitting off of the green light
with or from light components that are both red and blue
Include light. It is advantageous, as already described above,
that extra
Filter can be a RB splitter. In the green wavelength range, the transition
between red wavelength range
and blue wavelength range
This does not have to meet specifications and therefore may have effects
like polarization shift or angle shift none or at least one
play a minor role.
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In
a particularly preferred embodiment
however, the bandpass filter does not become the present invention
realized on two sides, but new on one side of the substrate
applied. That on one side of the substrate becomes the bandpass filter
realized by means of a layer system. On the other hand,
if for
necessary, only a few layers of antireflective coating
intended. Such unilateral bandpass filters are commonly considered
difficult to manufacture. New, essentially statistical design methods
but simplify this task considerably. Amazingly
showed that such a one-sided design with only 60% of
Total thickness of a comparable two-sided design with essential
less coating costs and therefore much more cost-effective
can be produced.
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According to the invention, a method is provided for splitting substantially unpolarized white light into three substantially unpolarized fractions having at least the following steps:
- Splitting the substantially unpolarized white light into a first portion and a second portion, wherein the first portion comprises substantially unpolarized light of a first wavelength interval and the second portion comprises substantially unpolarized light of a second and a third wavelength interval and the first wavelength interval between second and the third wavelength interval
- - Splitting the second portion into a third portion having substantially unpolarized light of the second wavelength interval and a fourth portion of substantially unpolarized light of the third wavelength interval.
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The invention also provides a method for combining the beam paths of a first, substantially unpolarized light beam of a first wavelength interval of a first light source, a second, substantially unpolarized light beam of a second wavelength interval of a second light source and a third, substantially unpolarized light beam of a third wavelength interval of a third A light source, wherein the first wavelength interval is between the second and the third wavelength interval and the method comprises at least the following steps:
- - Combining the beam paths of the second light beam and the third light beam to a first combined beam path, such that substantially the degree of polarization of the respective light beams is not affected;
- - Combining the beam path of the first light beam with the first combined beam path such that substantially the degree of polarization of the respective light beams is not affected.
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In the description, a lighting unit according to the invention is disclosed, comprising
a first light source for emitting a first, substantially unpolarized light beam of a first wavelength interval,
a second light source for emitting a second, substantially unpolarized light beam of a second wavelength interval,
a third light source for emitting a third, substantially unpolarized light beam of a third wavelength interval,
wherein the first wavelength interval includes wavelengths that are between the second and third wavelength intervals;
and the second light source and the third light source are arranged so as to intersect the beam paths of the emitted light;
and in the area of the intersection a first interference filter is provided for combining the beam paths to a first combined beam path;
and the first light source is arranged such that the beam path of the first light source with the com crossed beam path crosses;
and in the region of the intersection of the beam path of the first light source and the combined beam path, a second interference filter is provided for combining the first beam path with the combined beam path.
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Short description
the figures
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tab
1 layer thickness distribution of the two-sided bandpass filter as well
the RB splitter and the anti-reflection coating on the back
of the RB splitter in nanometers
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tab
2 layer thickness distribution of the single-sided bandpass filter as well
the anti-reflective coating of the back
of the bandpass filter in nanometers.
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1a Lighting unit with white light source according to the prior art with two edge filters
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1b Illumination unit with 3 LEDs according to the prior art with two edge filters
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2a Inventive lighting unit with white light source and two-sided band-pass filter and RB splitter
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2 B Inventive lighting unit based on LEDs with two-sided band-pass filter and RB splitter
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3a Transmission spectrum of a green bandpass filter for light, incident below 45 ° both for parallel application and for loading with F number 1.0
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3b Transmission spectrum of an RB splitter High pass for light, incident below 45 ° both for parallel application and for loading with F number 1.0
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3c Assumed weighting of angles of incidence
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4a Blue channel transmission as a function of wavelength (solid), and spectral distribution of a blue LED
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4b Green channel transmission as a function of wavelength (solid), and spectral distribution of a green LED
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4c Red channel transmission as a function of the wavelength (solid), and spectral distribution of a red LED
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5a Blue channel transmission with LED lighting
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5b Green channel transmission with LED lighting
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5c Red channel transmission with LED lighting
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6 Comparison of the transmissions by bandpass filters, one-sided (dotted line) and two-sided (solid line)
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7 Schematic structure of a projector with inventive LED lighting unit.
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detailed
Description of the invention
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in the
The invention will now be described by way of example and with reference to the figures
explained in detail
become.
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1a schematically illustrates the situation according to the prior art in the case of a white light source. In the lighting arrangement 1 of the 1a shown is a white light source, the white light W radiates. Located downstream in the light path below 45 ° is a high pass filter 5 with filter edge at about 500 nm for reflection of blue light B and transmission of green light G and red light R. Further downstream placed in the light path at 45 ° orientation is a low-pass filter 7 with edge layer at about 600 nm, the green light G transmits and red light R reflected.
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1b schematically shows a lighting arrangement 10 according to the prior art with respect to narrow-band light sources to be combined. Shown is the blue LED 11 , the red LED 13 and the green LED 15 , their light by means of low-pass filter 7 and high pass filter 5 combined.
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In contrast, shows 2a a lighting arrangement according to the invention 20 for 3P projectors with white light source 3 , This could be, for example, a UHP lamp that is common today. Downstream of the light source is a green bandpass filter 21 placed at 45 °, on one side of the substrate, a high-pass filter 23 with edge layer at 500 nm is applied and on the other side a low-pass filter 25 is applied with edge layer at 600 nm. Preferably, the band-pass filter is arranged such that the high-pass filter 23 facing the light source. In this way, the blue light, which is usually most unintentionally absorbed by thin film materials, must transmit minimally through thin film layers. Absorption effects are thereby minimized. Through this combination of high pass filter 23 and low pass filters 25 A green bandpass filter is created 21 that reflects blue and red light and transmits green light. Downstream, following the path of the red and blue lights, an RB splitter high pass is arranged, which reflects substantially blue light and transmits red light. Here, of course, an RB splitter lowpass would be possible, but for the reasons mentioned above in terms of absorption of the blue light, it is again advantageous to reflect the blue light. An antireflection coating may be provided on the back side of the substrate of the RB splitter.
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All filters include thin film alternating layer systems of a high refractive and a low refractive layer material. In the example, Nb 2 O 5 for the high refractive index layer H and SiO 2 for the low refractive index layer L were used as coating materials. Table 1 gives the layer thickness distribution of the respective filters in nanometers, starting from the substrate. The total layer thickness of the bandpass filter 21 adds up to 4360 nm.
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3a shows the transmission characteristic for unpolarized light of the green bandpass filter resulting from the two-sided coating. The solid line represents the characteristic at 45 ° angle of incidence The characteristic "steps" at 495 nm and 560 nm are a consequence of the polarization dependence The dotted line represents the characteristic that results when the band pass filter with an F number of Here, it becomes clear that the widening of the angle spectrum softens the edges and thus, for example, reduces the transmission at the maximum in comparison to the 45 ° case, likewise as a consequence of the softening of the edges, the polarization "stages" have disappeared.
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3b shows the transmission characteristic for unpolarized light of the RB splitter high-pass for incident angle 45 ° (solid line) and F-number 1.0 (dotted line) It is clear that despite the very small F-number losses are very low. In addition, it should be noted that the RB splitter is chosen to have a flat "edge" even at a mere 45 ° angle of incidence, in the present case the slope is dT / dλ <2% / nm where T is the transmission in percent and λ is the wavelength of the light in nanometers.
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Of course, the specification of an F-number and the associated transmission characteristic makes sense only if it is clear at the same time how the angular distribution within the illumination cone was weighted. This is why in 3c shown the transmission characteristic underlying angle weighting of the different emission directions of the light source.
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Looking now at the channel transmission for blue, green and red as in 4a -C shown, it can be seen that at an F-number of 1.0 a very considerable amount of light passes through the respective channel, ie the loss of light is kept within narrow limits. However, additional measures must be taken here to trim the color channels. Especially in the blue channel 4a becomes clear that, for example, by means of a trim filter green light components with maximum at 560 nm must be blocked. However, since the color splitting has already taken place, such a trim filter can be arranged substantially perpendicular to the RB splitter in the beam path. For the red channel and the blue channel analog simple trim filters can be used.
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According to 2 B become corresponding bandpass filters 21 and RB splitter high pass 27 in a Be Illumination arrangement for combining the light of a blue LED 11 , a green LED 13 and a red LED 15 used. As a result, if the emission spectrum of the LEDs is neglected, substantially the same channel transmission as in FIGS 4a C is shown with the solid line in each case. The 4a In addition, the dotted lines show the spectral distribution of the LED associated with the color channel. To find out how much of the light is actually combined into white light, these spectral distributions must be multiplied by the channel transmission curves. This results in the 5a c. Again, the dotted line indicates the respective emission spectrum of the LED and the solid line indicates the associated color channel transmission. It can be seen from the figures that almost all of the light energy emitted by the LEDs, which is fed into the channels, is transmitted through the respective color channel.
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In a particularly preferred embodiment of the present invention, the green bandpass filter is realized by means of a one-sided design. Table 2 shows the layer structure of the single-sided bandpass filter. On the other side of the substrate an antireflection coating is provided. Noteworthy in this embodiment is, inter alia, that the total layer thickness, including the layers for the antireflection coating summed to only 2568 nm, making up only 60% of the layer thickness of the two-sided bandpass system. In 6 the transmission curves for the one-sided and the two-sided design for the F-number 1.0 are compared. The solid line refers to the one-sided design, the dotted line refers to the two-sided design. In the areas in which the LEDs considered here have their emission maximum, these filters are equivalent within 2-5%. In the green channel, the one-sided design cuts even better.
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7 outlines a projector based on 3 LEDs 100 the lighting unit according to the invention 103 includes. Part of the lighting unit 103 are at least one red LED 105 , at least one blue LED 107 and at least one green LED 109 , In a 45 ° arrangement, as shown here, are green LED 109 and blue LED 107 oriented substantially parallel, while the red LED 105 oriented perpendicular thereto. Another ingredient is a RB splitter high pass 111 , Deviating from what is in the 7 is shown, it is of course possible the blue LED 107 and according to the RB splitter high pass 111 rotated arbitrarily about the axis XX 'to order. This may be advantageous for reasons of space in some cases, for example. It is also possible to deviate from the 45 ° geometry for red and blue and, for example, to go to 30 °. This reduces the polarization effect and additionally simplifies the production of the RB splitter. An essential part of the lighting unit 103 is the bandpass filter 113 , The bandpass filter shown here 113 includes a substrate side facing the green LED which is an antireflective coating 115 and a substrate side facing away from the green LED and a bandpass filter layer system 117 having. Due to this arrangement, the blue light is reflected directly at the surface without having to propagate through the substrate. Since typically shortwave light is absorbed in the substrate, the absorption by such an arrangement can be minimized. Another source of absorption losses are those for the construction of the layer system 117 required layers themselves. In the determination of the bandpass filter layer system 117 For example, a thin-film statistical optimization program may be advantageously used. If, during the determination, care is taken to ensure that blue light is reflected as far as possible on the outermost layers, this procedure again counteracts the absorption.
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After the illumination unit the optical paths of the radiation of the 3 LED are identical. Downstream is a lens in the now common optical paths 121 arranged the light in the integrator 123 focused. Usually, color sequencing means such as a color wheel would be provided in front of the input of the integrator. However, if the LEDs can be turned on and off quickly enough, no color wheel is needed. At the exit end of the integrator 123 there is a homogeneous light field, which by means of the lens 125 on a DMD chip 127 is projected. In the way between the lens 125 and the imaging element, in this case DMD chip 127 , is a prism 129 arranged. The DMD chip 127 comprises a matrix of individually controllable, movable mirrors. Depending on the position of these mirrors, the light reflected by the mirror passes through the prism 127 to the projection lens 133 or it is reflected away from the projection lens. This way a picture can be created.
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In the 7 were drawn, starting from the light sources, several radiation angles for clarity. Downstream, from the integrator, these angles have been omitted and only the central beam along the optical axis drawn.
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In the present description, lighting units for projectors operating with substantially unpolarized light have been presented. However, it is clear that the application of the invention not limited to projectors only. Wherever unpolarized light, possibly even with a wide angular distribution with respect to wavelength intervals must be split and / or merged, the present invention can be advantageously used.
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