KR101264950B1 - Device for combining light having different wavelengths - Google Patents

Abstract

The present invention relates to a method for combining or splitting optical paths of substantially unpolarized light having three or more different wavelength intervals. According to the invention, if the optical paths of light with two different wavelength intervals have already been combined or are still combined, the optical paths of light with wavelength intervals lying between different wavelength intervals are split or combined. The invention also relates to an illumination unit comprising a white light source, which uses the method for splitting white light into red, blue and green light beams by an interference filter. The invention also relates to an illumination unit comprising red, green and blue light sources, which method is used to combine the light paths of the light sources by interference filters.

Light path, wavelength spacing, white light source, illumination unit, interference filter.

Description

Combined device of light with different wavelengths {DEVICE FOR COMBINING LIGHT HAVING DIFFERENT WAVELENGTHS}

The present invention relates to a coupling device for light having different wavelengths. The invention relates in particular to an illumination unit capable of combining white, green and blue narrowband light sources to form white light. The invention also relates to an illumination unit capable of splitting white light into red, green and blue partial beams.

Modern projectors based on the projection of light for image generation can be divided into two categories: one for each of the three color channels, ie red (R), green (G) and blue (B), respectively. An imaging element is provided (3P projector = 3 panel projector). The red color channel is assigned light with a wavelength within a wavelength interval of 600 nm to 780 nm. The green color channel is assigned light with a wavelength within a wavelength interval of 500 nm to 600 nm. The blue color channel is assigned light having a wavelength within a wavelength interval of 420 nm to 500 nm.

However, some projectors operate in color sequential operation with only one imaging element (CS projector = color sequential projector).

Another classification may be made according to how the imaging device modulates light to convey image information. An enlarged class of imaging elements polarize modulates incident light locally resolved. The polarization modulation is converted into intensity modulation by a polarization selective optical element. Imaging elements of this manner must be provided with polarized light. However, the focus here lies with other classes of illumination units for imaging elements, which can be provided with unpolarized light or only partially polarized light. The lighting unit required for this must be able to propagate to provide unpolarized light.

If a broadband white light source is used in a 3P projector, the white light must first be split into three colors, red, green and blue. The possibility to do this is the use of dielectric edge filters. Edge filters have the challenge of reflecting light up to nearly 100% in the first wavelength range while transmitting nearly 100% of light in the second adjacent wavelength range. The range where adjacent wavelength ranges are called a filter edge. If a first edge filter with a filter edge of 500 nm is placed in the light path of the white light source, the clarified light assigned to the blue color channel is first split from the yellow light. In this case, yellow light is additionally constructed from green and red light. If an edge filter with an edge of 600 nm is placed in the light path of the yellow light, the green light is split from the red light.

Which wavelength range is reflected or transmitted depends on the configuration of each edge filter. In general, an edge filter that transmits a wavelength range having a small wavelength while reflecting a wavelength range having a large wavelength is called a low pass filter. An edge filter that reflects a wavelength range with a small wavelength while transmitting a wavelength range with a large wavelength is called a high pass filter.

If a narrowband light source, such as an LED, is used in a CS projector, the task of the lighting unit is to integrate the light paths of the red, green and blue narrowband light sources to deflect the light beam into the imaging element. Again edge filters can be used: for example a first edge filter combining light paths of red and green light, and a second edge filter combining light paths of blue light with two other light paths.

The problem is that the light of a white light source and the light of a narrowband LED generally do not provide light that is not polarized, at least not fully polarized.

Typically the edge filter is implemented on a transparent glass substrate by a dielectric interference layer system. However, the interference layer system has the characteristics that appear as a disadvantage in the edge filters described herein with respect to polarization dependence. In order to reflect certain components of light to itself, the edge filter is arranged at an angle inclined to the optical axis. The problem here is that the reflection and transmission properties of the interference filter depend on the polarization. In particular, reflection and transmission in the position of the edge and in the wavelength range adjacent to the edge depend on the polarization. In the case of a light source operating with light that is not polarized or only partially polarized, this causes misrouting of the light components. This leads to light loss on the one hand and on the other hand can be undesirable for each color coordinate.

In this specification, the optical path on which the blue component of light lies is called a blue channel. The component of blue light that is emitted from the light source and reaches the imaging element is called blue channel transmission. Correspondingly, red channel transmission and green channel transmission are mentioned. Misrouting of light components causes a reduction in channel transmission.

Another important influence factor on channel transmission is the respective emission characteristic of the light source (s). Thus, optical elements and filters used for illumination should generally have a specific angular acceptance expressed in F-numbers. The F-number is inversely proportional to the numerical aperture NA defined by the product of the refractive index of the medium and the half-opening angle of the illumination cone. In other words, the smaller the F-number, the larger each acceptance required. In calculating channel transmission, the effect of different angles of incidence on the transmission characteristics of the edge filter must be taken into account. The position of the edge and the reflection and transmission in the area adjacent to the edge depend on the angle of incidence. To account for this, different angles of incidence are weighted and integrated. In channel transmission, light is misrouted in the edge region because the initially steep edge for the angle of incidence loses its steepness by integration over a different angle.

It is an object of the present invention to provide an apparatus which overcomes or at least reduces the disadvantages of the prior art. In particular, the device according to the invention should be a solution to an illumination unit with unpolarized light for a projector, which is cheap compared to the prior art.

To solve the above problem, unlike the prior art, the green channel lying between two adjacent wavelength intervals is processed separately, while the red and blue light channels are already combined (for narrowband light sources) or still (white light sources). Is combined). That is, a very simple edge filter can be used to separate the red light path from the blue light path or to combine the red light path and the blue light path, the edge of the filter being almost randomly dependent on polarization within the green wavelength interval and / or each Can be relied upon, and the red or blue separation or binding does not degrade significantly. Thus, it is questionable in this case whether the edge filter is mentioned in the sense of the above definition. In view of this, it is generally referred to as an RB splitter in the scope of the present specification. In particular, when blue light is transmitted and red light is reflected, it is called an RB splitter low pass filter. Therefore, when blue light is reflected and red light is reflected, it is called an RB splitter high pass filter.

With regard to color management systems for reflective, locally polarized modulation imaging elements, separate processing of the green channel is already known. However, the color management system here must propagate the polarized modulated and reflected light in part at one polarization part and in part at another polarization part before the polarization sensing optical element converts the polarization modulation to intensity modulation.

In contrast, a polarization selective element is not used in an illumination unit for an imaging element in which polarization is not important. According to the invention, a so-called green band filter is required and used. Such a filter is provided, for example, with a low pass filter with an edge of about 600 nm on one side of the substrate, while a high pass filter with an edge of about 500 nm is provided on the other side. Due to this, blue light is reflected by the high pass filter on the side, and red light is reflected by the low pass filter on the side. Only green light is transmitted through both sides of the substrate. This allows for the efficient combining of green light with light components comprising red and blue light and / or efficient separation of green light from the light components. As mentioned above, the additional filter is preferably an RB splitter. In the green wavelength range, which forms a transition between the red and blue wavelength ranges, it does not have to meet the specification and effects such as polarization variations or angular variations are not important or at least play a secondary role.

In a particularly preferred embodiment of the invention, the band pass filter is provided on one side rather than on two sides of the substrate. That is, a band pass filter is implemented by a layer system on one side of the substrate. On the other side, only one antireflective layer is provided comprising fewer layers if necessary. Such one side band filters are usually considered difficult to manufacture. However, the new, statistical design method significantly simplifies this challenge. Surprisingly, it has been shown that such one side designs can be made very inexpensively with less complex coating methods with only 60% of the total thickness of similar two side designs.

According to the invention, a method for splitting unpolarized white light into three unpolarized components,

Splitting substantially unpolarized white light into a first component and a second component, wherein the first component comprises substantially non-polarized light of a first wavelength interval, the second component A substantially unpolarized light of second and third wavelength spacing, wherein the first wavelength spacing lies between the second and third wavelength spacing; And

Splitting the second component into a third component having substantially unpolarized light of the second wavelength interval and a fourth component having substantially unpolarized light of the third wavelength interval; An optical splitting method is provided.

According to the invention, a first substantially non-polarized light beam of a first wavelength interval of a first light source, a second substantially non-polarized light beam of a second wavelength interval of a second light source, and a third of a third light source A method for combining optical paths of a third substantially unpolarized light beam of a wavelength interval, wherein the first wavelength interval lies between the second and third wavelength intervals,

Combining the optical paths of the second and third light beams to form a first combined optical path such that the polarization of each light beam is substantially unaffected, and

Combining the optical path of the first light beam with the first combined light path such that the polarization of each light beam is substantially unaffected.

The lighting unit according to the invention

A first light source for emitting a first substantially unpolarized light beam at a first wavelength interval,

A second light source for emitting a second substantially unpolarized light beam at a second wavelength interval, and

A third light source for emitting a third substantially unpolarized light beam at a third wavelength interval,

The first wavelength interval comprises a wavelength lying between the second and third wavelength intervals;

The second light source and the third light source are arranged such that the optical paths of the emitted light intersect;

A first interference filter is provided for combining the optical paths in an area of intersection to form a first combined optical path;

The first light source is arranged such that the light path of the first light source intersects with the combined light path;

A second interference filter is provided at the intersection of the optical path of the first light source and the combined optical path to couple the first optical path and the combined optical path.

Table 1 shows the layer thickness (nm) distribution of the band filter on two sides, the RB splitter, and the antireflective layer on the back of the RB splitter.

Table 2 shows the layer thickness (nm) distribution of the bandpass filter on one side and the antireflective layer on the back side of the bandpass filter.

1a shows a lighting unit with a white light source according to the prior art with two edge filters.

1b shows a lighting unit with 3 LEDs according to the prior art with two edge filters.

2a is a lighting unit according to the invention with a white light source and two side band filters and an RB splitter;

2b is a lighting unit according to the invention based on LED, with a band-pass filter and an RB splitter on two sides;

3A shows a transmission spectrum of a light green band filter incident at 45 ° for parallel provision and for provision of an F-number of 1.0.

3B shows the transmission spectrum of an RB splitter high pass filter for light incident at 45 ° for parallel presentation and for F-number 1.0;

3C is an illustration of incident angle weighting.

4A shows blue channel transmission as a function of wavelength (solid line), and spectral distribution of a blue LED.

4b shows the green channel transmission as a function of wavelength (solid line), and the spectral distribution of the green LED.

4C shows the red channel transmission as a function of wavelength (solid line), and the spectral distribution of the red LED.

5A shows blue channel transmission in LED illumination.

5B shows green channel transmission in LED lighting.

5C shows red channel transmission in LED illumination.

6 shows transmission comparison through a band pass filter on one side (dashed line) and on two sides (solid line).

7 is a schematic configuration of a projector with an LED lighting unit according to the invention.

Hereinafter, with reference to the accompanying drawings of the present invention will be described in detail.

1a schematically shows a situation according to the prior art in the case of a white light source. In the illumination unit of FIG. 1A a white light source emitting white light W is shown. Downstream in the optical path, a high pass filter 5 having a filter edge of about 500 nm is arranged at 45 ° for the reflection of blue light B and for the transmission of green light G and red light R. Further downstream in the optical path is a low pass filter 7 with an edge of about 600 nm which transmits green light G and reflects red light R is arranged at 45 °.

1b schematically shows a lighting unit 10 according to the prior art in connection with a narrowband light source to be combined. A blue LED 11, a red LED 13 and a green LED 15 are shown, the light of which is combined by a low pass filter 7 and a high pass filter 5.

2a shows a lighting unit 20 according to the invention for a 3P projector with a white light source 3. This may for example be a recent UHP lamp. Downstream of the light source, a green band filter 21 is disposed at 45 ° and a high pass filter 23 is provided with an edge of 500 nm on one side of the band pass filter, and 600 nm on the other side of the band pass filter. A low pass filter 25 with an edge is provided. Preferably, the band pass filter is arranged such that the high pass filter 23 faces the light source. Because of this, blue light, which is generally most strongly and unintentionally absorbed by the thin film material, should be minimally transmitted by the thin film layer. Thus, the absorption effect is minimized. The combination of the high pass filter 23 and the low pass filter 25 forms a green band pass filter 21 that reflects blue light and red light and transmits green light. Downstream, following an optical path of red and blue light, an RB splitter high pass filter is disposed which substantially reflects blue light and transmits red light. Of course, an RB splitter low pass filter is also possible, but for the reasons described above with respect to absorption of blue light, it is preferable to reflect the blue light. An anti-reflection layer may be provided on the back side of the substrate of the RB splitter.

All filters include a thin film replacement layer system of high and low refractive layer materials. For example, Nb ₂ O ₅ was used for the high refractive index layer (H) and SiO ₂ was used for the low refractive index layer (L). Table 1 shows the layer thickness (nm) distribution of each filter, measured from the substrate. The total layer thickness of the band pass filter 21 is 4360 nm.

3A shows the transmission characteristics for unpolarized light of a green band pass filter from two side coatings. The solid line shows the characteristic of the 45 ° incidence angle. Characteristic “ends” at 495 nm and 560 nm are the result of polarization dependence. The dotted line shows the characteristics given when a band pass filter with an F-number of 1.0 is provided. Here, it is evident that the edge is enlarged by the enlargement of each spectrum so that the transmission is reduced to a maximum as compared with the case of 45 °. As a result of edge enlargement, the polarization "ends" disappear.

3B shows the transmission characteristics for unpolarized light of the RB splitter high pass filter for an angle of incidence 45 ° (solid line) and an F-number of 1.0 (dashed line). Despite very small F-numbers, very small losses are shown. In addition, it should be noted that the RB splitter is chosen to have a flat "edge" already at 45 ° incidence. In this case, the slope is dT / dλ <2% / nm, T is transmittance (%), and λ is the wavelength of light (nm).

Of course, the indication of the F-number and hence its transmissive properties is only important when it is clear how the angular distribution inside the lighting cone is weighted. For this reason, FIG. 3C shows each weighting in different radial directions of the light source, which is based on the transmission characteristics.

Considering the channel transmission for blue, green and red as in FIGS. 4A-4C, it can be seen that when the F-number is 1.0, a very large amount of light reaches through each channel, i.e. the light loss remains within a narrow limit. have. However, additional measures must be taken to trim the color channel. In particular, in the blue channel of FIG. 4A, it is shown that the green light component should be blocked to the maximum at 560 mn by the trimming filter. However, since color splitting has already appeared, this trimming filter can be placed downstream of the RB splitter vertically in the optical path. Similarly, simple trimming filters can be used for the red and blue channels.

Suitable bandpass filter 21 and RB splitter high pass filter 27 according to FIG. 2b are used in the illumination unit for combining the light of blue LED 11, green LED 13 and red LED 15. In this case, if the emission spectrum of the photodiode is ignored, the same channel transmission as shown by solid lines in Figs. 4A to 4C is obtained. 4A-4C further illustrate the spectral distribution of the LEDs belonging to the color channel as dashed lines. To know how much light actually combines to form white light, this spectral distribution must be multiplied by the channel transmission curve. The results are shown in FIGS. 5A-5C. The dashed line again represents each emission spectrum of the LED and the solid line represents the color channel transmission associated therewith. The figures show that the total light energy radiated by the LEDs and supplied into the channels is almost transmitted through each color channel.

In a particularly preferred embodiment of the invention, the green band pass filter is implemented by one side design. Table 2 shows the layer structure of the band pass filter of 1 side. On the other side of the substrate an antireflective layer is provided. In this embodiment, only 60% of the layer thickness of the two side band filter system, especially since the total layer thickness, including the antireflective layer, is only 2568 nm. 6 shows the transmission curves for the one and two side designs for F-number 1.0. Solid lines relate to the one side design and dashed lines relate to the two side design. In the region where the LED considered here has its emission maximum, the filters are equivalent within 2-5%. In the green channel, the 1 side design blocks slightly better.

7 shows a projector 100 based on 3 LEDs. The projector 100 comprises a lighting unit 103 according to the invention. The component parts of the lighting unit 103 are one or more red LEDs 105, one or more blue LEDs 107 and one or more green LEDs 109. In the 45 ° arrangement as shown here, the green LEDs 109 and the blue LEDs 107 are arranged in parallel while the red LEDs 105 are placed perpendicular to this. Another component is the RB splitter high pass filter 111. As shown in FIG. 7, it is also possible to arrange the blue LED 107 and thus the RB splitter high pass filter 111 by arbitrarily rotating about the axis XX '. This may be desirable in many cases, for example for reasons of location. It is also possible to place 30 ° instead of 45 ° for red and blue. This reduces the polarization effect and further simplifies the production of the RB splitter. An important component of the lighting unit 103 is the band pass filter 113. The band pass filter 113 shown here comprises a substrate side facing the green LED and having an anti-reflection layer 115, and a substrate side remote from the green LED and having a band filter layer system 117. Due to this arrangement, blue light is reflected directly off the surface and does not need to propagate through the substrate. Absorption is minimized by this arrangement because light, which is typically primarily shortwave, is absorbed in the substrate. Another source of absorption loss is the layers themselves necessary for the construction of the layer system 117. Upon detection of the bandpass filter layer system 117, a statistical thin film optimization program can be preferably used. Note that during detection the blue light is already reflected as nearly as possible in the outermost layer, again preventing the absorption.

Downstream of the lighting unit the light path of the beam of 3 LEDs is the same. A lens 121 is now disposed downstream in the common optical path, which focuses the light on the integrator 123. Typically, color sequencing means, such as a color wheel, are provided before the inlet of the integrator. However, if the LED can be connected and disconnected quickly enough, no color wheel is needed. On the outlet side of the integrator 123 is given a uniform light field, which is projected onto the DMD chip 127 by the lens 125. A prism 129 is disposed between the lens 125 and the imaging device, in this case DMD chip 127, in the optical path. DMD chip 127 includes a matrix of movable mirrors, which are individually controllable. Depending on the position of the mirror, light reflected from the mirror is reflected through the prism 127 to the projection lens 133 or away from the projection lens. This may result in one image.

In figure 7 a number of radiation angles from the light source is shown for clarity. Downstream, the angle is omitted after the integrator and only the center beam along the optical axis is shown.

In the scope of this specification, lighting units have been described for projectors operating with substantially unpolarized light. However, the application of the present invention is not limited only to the projector. Wherever unpolarized light is to be split and / or combined in a wide angular distribution over a wavelength interval, the present invention is preferably applied.

Claims (13)

A method for splitting unpolarized white light into three unpolarized components, Splitting unpolarized white light into a first component and a second component, the first component comprising unpolarized light in a first wavelength interval, the second component being second and third A non-polarized light of wavelength spacing, wherein the first wavelength spacing lies between the second and third wavelength spacing; And Splitting the second component into a third component having unpolarized light of the second wavelength spacing and a fourth component having unpolarized light of the third wavelength spacing, And the third wavelength interval of the fourth component comprises a wavelength smaller than the second wavelength interval of the third component. 2. The apparatus of claim 1, wherein a first interference filter is disposed in the optical path for splitting the white light into the first and second components, the first interference filter transmitting light at the first wavelength intervals. And the first interference filter reflects light at the second and third wavelength intervals. 3. The second interference filter of claim 2, wherein a second interference filter is disposed downstream of the first interference filter within the optical path of the second component to split the second component into the third and fourth components. 2 The interference filter transmits the third component and reflects the fourth component. delete 4. The method of claim 2 or 3, wherein the first interference filter is provided on one side of a substrate on which the layers of the first interference filter reflecting light of the second and third wavelength intervals support the layers. And the optical splitting method is configured to be. The said 3rd wavelength spacing of a said 4th component has a wavelength length smaller than the 2nd wavelength spacing of a said 3rd component, The 1st interference filter and a 2nd interference filter are the said 4th Wherein the component light is arranged to be reflected at the surface of the first interference filter and the second interference filter, respectively, without previously transmitting the substrate including the first interference filter and the second interference filter. How to put. An unpolarized first light beam of a first wavelength interval of a first light source, an unpolarized second light beam of a second wavelength interval of a second light source, and an unpolarized third light of a third wavelength interval of a third light source 10. A method for combining optical paths of a beam, wherein the first wavelength interval lies between the second and third wavelength intervals, Combining the optical paths of the second and third light beams to form a first combined optical path such that the polarization of each light beam is not affected; And Combining the optical path of the first light beam with the first combined light path such that the polarization of each light beam is not affected, In order to combine the optical path of the first light beam with the first combined optical path, a first light source is arranged such that the optical path of the first light beam intersects with the first combined light path and, in an intersection area, the second light beam. And a fourth interference filter for reflecting the third light beam and transmitting the first light beam, And said fourth interference filter is provided with layers reflecting said second and third light beams on one side of a substrate supporting said layers. 8. The light source of claim 7, wherein, in order to combine the optical paths of the second and third light beams, a light source intersects the optical paths of the second and third light beams and transmits the second light beam to an intersection area. And a third interference filter for reflecting said third light beam. delete delete As the lighting unit, A first light source for emitting a first unpolarized light beam at a first wavelength interval, A second light source for emitting a second unpolarized light beam at a second wavelength interval, and A third light source for emitting a third unpolarized light beam at a third wavelength interval, The first wavelength interval comprises a wavelength lying between the second and third wavelength intervals; The second light source and the third light source are arranged such that the optical paths of the emitted light beams intersect; A first interference filter is provided for combining the optical paths in an area of intersection to form a first combined optical path; The first light source is arranged such that the light path of the first light source intersects with the combined light path; A second interference filter is provided at the intersection of the optical path of the first light source and the combined optical path, for coupling the optical path of the first light source and the combined optical path, And said second interference filter is provided with layers reflecting light beams of said second and third light sources on one side of a substrate supporting said layers. 12. The lighting unit of claim 11, wherein said second interference filter transmits light from said first light source and reflects light from said second and third light sources. delete

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