DE2336626A1 - OPTICAL PHASE FILTER - Google Patents

Description

.-ini '· R. B-: ε τ Z eerW

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8 »AlB» h * n22, Sleinsdorfeir. 11

81-21.110P (21.111H) July 18-1973

HITACHI, LTD., Tokyo (Japan)

Optical phase filter

The invention relates to an optical phase filter having a simple structure in the form of a plate made of translucent material.

The invention relates to an optical phase filter that exhibits wavelength dependency, and it is particularly aimed on an optical phase filter that has a different band characteristic for a spatial frequency of incoherent light with a certain wavelength band like that of natural light depending on the May have wavelength of this light.

The preferred field of application for the invention is in color television cameras with a single pickup tube,

81- (Item 30 26I) DfF

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and therefore the difficulties that arise when using more usual will first be described in more detail below optical filter result in this field of application.

In a color television system widely used today, chrominance signals are transmitted in such a manner that that signal band for the red and blue color components, that is, the special frequency band for these colors is compressed while the green color component occupies a relatively wide frequency band. The three color components mixed together in a given ratio. This mode of operation is based on the fact that the luminance and chrominance signals within a limited one available for transmission Transmitted in the frequency band. On the other hand, the demand for a miniaturized leads Implementation of the color television cameras that for the separation and the extraction of the signals for the above mentioned three color components, hereinafter referred to as R component, G component and B component for short should, only a single pickup tube can be provided. Now, however, it is necessary to use the special Make frequency bands for the R, G and B components different from each other. For this purpose, the usual color television cameras a dichroic mirror or similar means are provided to separate the R, G and B components from one another prior to their entry into the pickup tube to separate so that there is an optical bandwidth limit for the spatial frequency of the so separated Let achieve color components in an independent manner. With a single color television tube however, such a bandwidth limit is not intended. To overcome this disadvantage is already a system

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has been proposed in which the optical bandwidth limitation is carried out by a spatial filter that shows a lower wavelength dependency and with - an additional electrical bandwidth limitation for those corresponding to the R, G and B components electrical signals is combined by means of an electrical filter each.

However, this conventional system has the disadvantage that a very wide spatial area for the pickup tube Frequency band is required.

In the above example, reference is made to a color television camera, but in many cases it results also for other optical devices the requirement for an optical filter that has a different Bandwidth as a function of the spatial frequency component, i.e. as a function of that in a color component of the wavelength of the light contained signal and thus the color component.

The invention is therefore based on the object of designing a phase filter of the type mentioned at the outset so that When building from a simple structure, it is one of the respective color component in visible light, i.e. of the Has different spatial frequency characteristics dependent on the wavelength of the light, in particular the green color component is treated differently from the red and blue color component and is preferred with no limitation should experience in the spatial frequency band.

According to the invention, this object is achieved in that the optical thickness of the structure is in relation to the plate surface perpendicular direction a different distribution over the plate surface along one or two

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Has dimensions and between the maximum value and the minimum value for the phase change when passing through Light lying in the visible wavelength range to the maximum value or the minimum value having optical Generated because of a difference of more than 2 I /.

The design according to the invention leads to an optical phase filter in which the optical thickness, ie the optical path length, perpendicular to the surface of its planar structure, one or two-dimensionally different Has distribution, so that for light which passes through at a point with maximum optical thickness, compared to light passing through a minimum optical thickness, a difference of more than 2 IT in the Phase rotation results for each wavelength contained in visible light (natural light). Under optical The thickness is usually the product of the refractive index. translucent structure and their to understand geometric thickness.

The optical filter according to the invention is characterized in that it shows a wavelength dependency, in which the spatial frequency behavior depends on the wavelength of the light for incoherent light in a certain Wavelength range such as that of visible light (natural light) is different fails. The term plate-shaped design used above and below is to be understood as that it not only comprises a geometric plane, but also a plane structure with one over its surface includes above toothing, as shown in an embodiment described below

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is. Furthermore, the term "simple structure" used above and below only refers to that it has a single filter with a spatial one that differs according to the wavelength of the light Frequency characteristic referred to, of course, the arrangement of frames for the definition and retention of the filter is not intended to be excluded by this term.

The design of an optical phase filter according to the invention enables, in particular, a bandwidth limitation solely for the R and B components, while the G component remains unaffected, as this in conjunction with the above-mentioned construction principle aimed at miniaturization in construction for a Color television camera is required.

In a preferred development of the invention, the optical thickness of the structure can be perpendicular to the plate surface be adjustable so that there is an absolute value for the transfer function of the filter, which is for im red and light lying in the blue wavelength range close to full and for light lying in the green wavelength range Light is close to one.

According to another development of the invention it can be provided that the simple structure is a flat one Comprises substrate and light-permeable strips arranged on its surface in one- or two-dimensional fashion, the thickness of which is adjustable so that the difference in phase changes for passing through the strips Light on the one hand and light passing through sections of the substrate that are not covered with strips on the other hand for in the red and / blue wavelength range

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lying light is roughly an odd multiple of

Jl and for light lying in the green wavelength range is approximately an integral multiple of 2 / Γ.

Another embodiment of the invention is characterized in that the optical thickness and its distribution are adjustable so that the minimum value for the absolute value in the optical transfer function of the filter is almost at zero and that the optical transfer function for in the green wavelength range lying light at the lowest spatial frequency at which the optical transfer function for im red and light lying in the blue wavelength range remains at the minimum value, is more than 0.5.

A preferred development of the invention consists in that the simple structure comprises a flat substrate and light-permeable strips arranged on its surface in a one- or two-dimensional mode, a first type of which has a phase difference of H for light in the green wavelength range and a second type for light lying in the green wavelength range a phase difference equal to an integral multiple of 2 (I generates, whereby a section of the stripes of the first type is superimposed on a section of the stripes of the second type in such a way that the first type of stripe and you the second Type of stripes superimposed section effect a band limitation for the spatial frequency with respect to light lying in the green wavelength range, while the stripes of the first type and a section of the stripes of the second type not superimposed therefrom cause a band limitation for the spatial frequency with respect to the red and blue wavelength ranges cause abundant lying light.

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For the further explanation of the invention and its advantages, reference is now made to the drawing, in which preferred exemplary embodiments for optical phase filters designed according to the invention are illustrated are; show -in the drawing:

1 shows a section from a perspective illustration for a first Embodiment of one according to the invention. formed optical phase filter;

Figures 2A, 2B, 2C and 2D are graphical representations to illustrate the operation of the optical phase filter shown in FIG. 1;

Figs. J5A and 3B are graphs for Illustration of the relationship between the wavelength and a minimum value for the optical transfer function at the optical phase filter of Fig. 1;

4a and 4b are graphic representations for illustration the operation of another embodiment. for a optical phase filter designed according to the invention;

Fig. 5 is a graphical representation for illustrative purposes the relationship between the wavelength and the minimum value for the optical transfer function in the Filter design according to FIGS. 4A and 4B;

6a shows a partial section through a second embodiment for an optical phase filter designed according to the invention;

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Pig. βΒ and 6C graphs for illustration the operation of the embodiment shown in Fig. 6a of the invention and

Fig. ΒΒ a graph to illustrate the optical transfer function for the embodiment of the invention shown in Fig. 6k.

First of all, with reference to FIG. 1, a section from an optical phase filter designed according to the invention reproduces in a perspective representation, shown that such a thing according to the invention

bti'detes optical phase filter a special spatial one

Frequency behavior, namely a frequency band limitation shows. As the illustration in FIG. 1 shows, the phase filter selected as an example has a planar substrate 1, which consists of light-permeable material, and a plurality of strips applied parallel to one another on one side of the substrate, which are made of a material similar to the substrate 1 and also consist of translucent material. The strips 2 have a width a and a thickness A , and they have a period 4a

in the longitudinal direction and parallel to each other on the one e _

Surface of the substrate 1 applied.

For the definition of the horizontal and the vertical direction in the plane of the substrate 1 are shown in FIG an X-axis and a Y-axis are drawn, which together define an X-Y plane.

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From perpendicular to the XY plane in Fig. I ^- incident light of a wavelength Λ · traverses a portion of both the substrate 1 and the applied thereto strip 2 and thus sets in the illustrated Phasßnfilter back an optical path P, while another part SIeses light passes only through the substrate 1 at an optical value P '. The phase difference Q between these two light components after passing through the phase filter, i.e. after passing through the optical a-path P or P ^^^ e ^ h ^ bellBrid ^ phase difference Q can then be expressed as:

(D

iofefet ^ fiTTur denotes the refractive index de ^ s ^ Msfee ^ iäärs ^ of the "substrate and the StreiferrlTTüir ^ the" passing light. This expression gives a difference between the phase rotation (phase change) for the light in its Passage through the strips 2 on the one hand or through the layer of air of length A remaining between them on the other hand again.

Therefore, for the following ST consideration

at the

"through the passage of light" subsirate 1 can be neglected can that d ± e-Oi5erf mentioned phase difference is an odd number of IT and that the ^ -Trans parence "~ g" (x) to light of the wavelength as shown in the illustration in Figure 2A. , ".- == -,

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- ίο -

To simplify the description, the transparency g (x) with respect to light is a special one above Wavelength λ, but it is general in optics known that the spatial frequency behavior of an optical filter in the form of an autocorrelation coefficient for the transparency g (x) can be given, as is done, for example, in a book by J.W. Goodman with the title "Introduction to Fourier Optics" is described on pages 101-156.

If one denotes the autocorrelation coefficient for the transparency g (x) with e (x), then the following applies:

(2)

g (J) dJ

where g (ξ) is a complex number conjugated to g (\).

On the other hand, there is the relationship X = Ad / U for the spatial frequency / U, which corresponds to the value χ at the filter, so that the spatial frequency characteristic H ( Ai) can be written as H ( Ai) = e ( A. d / U ), where d denotes the distance of an image from a lens (filter). It should also be noted that H ( Ai) is to be regarded as an optical transfer function and is referred to as OTF for short in the following.

The OTF corresponding to the transparency g (x) as shown in FIG. 2A is shown in FIG. 2B, the Ordinate is the value of the autocorrelation coefficient for g (x), i.e. the gain for the spatial frequency characteristic

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- ii -

Hi / u), while the representation along the abscissa corresponds to the expression λ d Ai H ( , ii) . The abscissa in the example shown is g (x) as Λ, taking into account the transparency. d Ai , however, it is clear that the illustration in FIG. 2B shows a relationship between the spatial frequency Ai and the gain H ( Ai) for the signal corresponding to the frequency> u, that is to say the spatial frequency response H (, u), since the frequency A 'and the distance d of the filter

to the image plane are constant as long as one

special color component is considered.

If the width a of the strips 2, the wavelength A of the light, the maximum value / ^ _{max of} the spatial frequency and the distance d of the & FHrfeers "^ level are set so that the

/ ^u max - λ, -d

then the filter is a low-pass filter that allows light to pass through at a spatial frequency between, - ~

Q _

and prevents the passage of light with a frequency in the range ~~ r ~ ä ~ = 2 / ^u έ ¹ relative to light of the color complex of the wavelength λ , as can be seen from FIG. 2B. It should also be noted that the +) as shown in Fig. 2B and the ^ oIgender ^ -Flgüi ⁵ «^^ have a uniformly divided scale along the abscissa for a more convenient description, but that in the case of representation with logarithmic graduation, as shown as a scale graduation for Such graphical representations are particularly suitable, the parameter H at a value of about 0.5 can be viewed as not attenuated, since it is then on

'') spatial frequency characteristic

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on the logarithmic scale has a value of 3dB.

As already mentioned, the fact that an optical phase filter designed according to the invention has a high band filter characteristic relative to the spatial frequency Ai is treated for the sake of more convenient description on the basis of a light component with the special wavelength Λ To impress spatial frequency behavior only on the light component of the particular wavelength Λ, but to create a filter that has a spatial frequency behavior that is different over the entire wavelength range of visible light and therefore shows a wavelength dependency.

In the following description, the general case of visible light is intended to be in a wavelength band of about 400 to about 800 nm can be treated.

The corresponding phase filter is constructed in the same way as the example shown in FIG. For the following considerations it is assumed that there is a phase difference between the phase rotations which the light undergoes on the optical path P through the substrate 1 and a strip 2 on the one hand and on the optical path P 'through a section of the substrate 1 not covered with strips β and that the transparency g (x) for the light on the two light paths P and P ^{1 has} the values 1

OK
or e.

These courses of transparency g (x) and their transfer functions are illustrated in FIGS. 2C and 2D, where

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the representation there corresponds to the representations in FIGS. 2A and 2B. From this illustration it can be seen that the spatial frequency characteristic of FIG. 2B differs from the spatial one shown in FIG. 2D Frequency characteristic differs in that in the first case it has a minimum value of zero in the OTF while the minimum value of the OTF in the second case is not zero. The minimum value for the OTF can be calculated using equation (2) given above for a phase filter constructed in accordance with FIG to:

^H mln = I (1 + oos 0) = I £ 1 + cos

This expression shows that the minimum value for the light signals passing through the phase filter over a certain bandwidth of the spatial frequency, namely the frequency band between a ^, A., ud ^ = £ a, i.e. between -? Hr ^ / a J = -v §— for the filter mentioned above, is kept constant. This minimum value is a function of the phase difference 0 between the phase rotations for the light, i.e. a function of the wavelength A, of the light, the refractive index η and the thickness Δ of the strips 2.

The minimum value EL ^ _{n of} the OTF depends on the wavelength under the assumption of a constant refractive index η and a constant thickness Δ. for the strips 2 together in the manner shown in Figs. 3A and 3B show two exemplary embodiments, in which the thickness Λ of the strips 2 is different in each case. In the two representations

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- i4 -

the gain is plotted along the ordinate and the wave number, i.e. the reciprocal of the wavelength Λ of light, is plotted along the abscissa. As the illustrations show, the minimum value H _min varies cyclically with the wavelength Λ, according to a cos O relationship, the zeros of the curves being where the phase difference Q is an odd multiple 2 | f (nl) / \. l / Λ of It, and the curve amplitude assumes the value 1 at the points where the phase difference θ is an even multiple of Jj.

Accordingly, assuming that the wavelength range for the visible light falls within the area indicated by the letters R, G and B in Figs. 5A and JB, an optical low-pass filter for the R and B components of the light as shown in FIG is determined by the spatial frequency response according to FIG. 2B, since the minimum value H _011n for these components is approximately equal to zero, while the same filter allows all spatial frequency components for the G component of the light to pass unhindered. Such a filter is therefore readily suitable for use as a band limiting filter for the color television cameras mentioned above.

Next, an embodiment for an optical phase filter which has a band limitation will be described numerically for the R and B components of light, but no band limitation for the G component of the light.

The thickness Δ of the strips 2 one. such a filter is determined by the fact that the phase difference is 0 and the wave

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■ length A of the light can be brought to specified values must, in between the relationship:

(* - DA

exists, as already mentioned above, and the Refractive index η for the transparent material of the strips 2 depends on this material.

For example, the refractive index η and the thickness A for the strips 2 can be determined in such a way that they cause a phase difference of 4 IT compared to green light of wavelength 546.1 nanometers (standard light according to CIE). In this case, the wavelengths for phase differences of J Ij and 5 IT are in the range of red and blue light at values of 728 and 439 nanometers, respectively θ of 6 II for the green light, the wavelengths for phase differences θ of 5 W and 711 are at 655 and 468 nanometers, respectively, and are again in the range of red and blue light.

The wavelength for the achievement of Phase differences corresponding to even multiples of (T can be selected relatively largely freely from the range of green light. If, for example, the wavelength A of 520 nanometers is selected from the range of green light to achieve a phase difference 9 of 6 \\, for the wavelengths with phase differences θ of 5 Ff and 7 W, the values 625 and 446 nanometers, respectively, result

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- ιβ -

lie in the area of red or blue light.

As explained above, the wavelengths belonging to a light color extend over a certain amount Bandwidth, resulting in a corresponding design freedom for the construction of the phase filter results.

As described above, the representations in FIGS. J> k and 3B show a state in which the phase difference θ relative to the G component of the light is set to a value of approximately 4 ι or a value of 6 ».

As already mentioned, it is sufficient to select a phase difference Q above 2 TT in order to create a single filter that is wavelength-dependent, that is to say maximum and minimum values with regard to the minimum value H. the optical transfer function OTP for light lying in the visible range.

In the illustrated embodiment, the strips 2 are on the substrate 1 in a regular manner arranged, but this is not a necessary condition for the correct puncture method of the invention, rather these strips 2 can also be formed on the substrate 1 in an arbitrary manner.

Such an embodiment in which the strips 2 are provided in an arbitrary manner is shown in Figs. 4A and 4B illustrated. In this exemplary embodiment, the phase filter contains a transparent substrate 1 and thereon applied strips 2 of rectangular cross-section,

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as is also the case in the embodiment according to FIG. 1, but the arrangement of the strips 2 is carried out in accordance with a quasi-arbitrary sequence. 4A shows the transparency g (x), which is established when the strips 2 are arranged on the sections designated by 1 of a sequence which results from the repetition of a quasi-arbitrary sequence which has a period ⁷ Ta

m = (0, 0, 1, 0, 1,1,1)

where a is the width of the stripes 2, and the phase difference due to the stripes 2 is a odd multiple of J | .

The OTF corresponding to the transparency g (x) of FIG. 4A is shown in FIG. 4B, and the minimum value H ₁ for this OTF can be written to

¹ Wn = T ° ⁺ * ^{00S θ)}

where 0 denotes the phase difference which, as in the exemplary embodiment according to FIG. 1, results as a result of the stripes. A graphical representation of the dependence of the minimum value _{n of} the OTF according to FIG. 4B corresponding to the curves in FIGS. In general, the use of a quasi-arbitrary sequence of length 2 ^m "leads to the relationship

nnin 2 ^m -l

where m is equal to or greater than 2, in relation to the wavelength / L for which the transparency g (x) is the two Assumes values "+ 1" and "-1", so that IL- increases with increasing m goes to zero.

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The advantage of the above-mentioned embodiment compared to that illustrated in Figs. J5A and JB Embodiment is that the areas of space ual frequency in which the relationship

holds, can easily be expanded by using a long, quasi-arbitrary sequence. In other words, from the point of view of creating a spatial low-pass filter, the OTF according to FIG. 2B is less preferred than it shows undesirable high-pass behavior, as can be seen when the representation is converted along the abscissa and on a logarithmic scale for the spatial frequency is applied. On the other hand, the use of a quasi-arbitrary sequence with a length of 2 ^m -1 leads to the relationship H ( Ai) - H _min in the range

a ζ / ()

scj that an increase in the value of m leads to an improvement leads in high-pass behavior. This means that an irregular arrangement of the strips 2 on the substrate 1 leads to an extension upper limit for obtaining the minimum value H. which in turn leads to the spatial frequency characteristic As a result, there are hardly any unnecessary signal components in the upper band.

In the exemplary embodiment described above, the minimum value H _n ^ _{n is set} approximately to the value zero, but it is obvious that the absolute value for that is the optical transfer function is only set to one

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Minimum needs to be brought.

In connection with the above-mentioned embodiments, an example has been described in which the band limitation is primarily made with respect to the R and B components of light, but not for the G-component of light becomes effective.

In general, with color television cameras, there is a need for band limitation in some optics because of the G-component of the light required a very wide bandwidth, no special attention should be paid to it, however, there are some cases where the band limitation against the G component is useful in a different way is made as for the R and B components of light · With this purpose an additional band limitation can be used be provided by an optical filter that does not show any wavelength dependency, that is, in each case causes the same band limitation for each of the spatial frequency components R, G and B, and this additional The filter can then be applied to the band limitation with the aid of an optical phase filter designed according to the invention become effective with wavelength dependence. However, the structure of the filter designed according to the invention leads to an optical phase filter, which enables the achievement of a wide bandpass limitation for the G component and a allows narrow bandpass limitation for the R and B components of the light.

In general, a superposition of a filter with an OTF of Hl and a filter with an OTF of H2 not to a filter, which has an OTF of H1H2, so that for the production of a phase filter the last kind some skill is required.

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An optical formed in the manner according to the invention A phase filter which is suitable for achieving such a band limitation is illustrated in FIGS. 6A to 6D.

Fig. 6k shows a cross section through this phase filter, which is constructed so that it has a period of 12a. The illustrated filter contains a substrate 1 and strips 2 of rectangular cross-section applied to it in the manner illustrated in the drawing, and it extends perpendicular to the plane of the drawing in the illustration in FIG. 6a. It should also be noted that the thickness A of the individual strips 2 in FIG. 6A is shown greatly exaggerated in comparison to the dimensions in the horizontal X direction.

The representations in FIGS. GB and 6C show the result of the superimposition of the transparency g (x) and the phase change or phase variation (angle of deviation) <g (x) resulting when the light passes through the strips 2. The graphical representation in Fig. ΒΒ corresponds to the relationships for light with a wavelength in the range of the G component of light, while the representation in Fig. 6C shows the relationships for light whose wavelength is in the range of the R component of light and is about twice as large as that for G component.

As the drawing shows, the phase rotation <g (x) _G assumes four values for the G component of light, zero, TT, 6 II and 7 Π, with the transparency g (x) _G for even numbers

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Points corresponding to multiples of "" T such as "0" and "6 Ii" take the value "-1" and points corresponding to odd multiples of If such as "IT" and "7 ^" take the value "+ 1", so that overall results in a course of the transparency g (x) _G with respect to the G component of the light, as shown in FIGS. βΒ by a dashed line.

In contrast, the phase shift .c. g (x) -o for the R component the values 0, 5 / 6Ti and 35/6 '! fan if the corresponding values for the G component are 0, If, 6' (T and 7iT, respectively. The above values for the R component can be approximately equal to 0 if% 5 and 6! [set so that the phase variation or phase variation 6C reproduced course receives by the solid line in Fig.. the transparency of g (x) _R with respect to the R -Component of light assumes the value "-1" at even-numbered multiples of jf such as "0" and "6 TT" corresponding points, while it assumes the value "+" for odd multiples of ff such as "Tf" and "5lf" 1 ″, so that overall the course shown in FIG. 6c by a dashed line results. This also applies to the B component of the light as far as the transparency is concerned.

The representation of the transparency g (x) _Q for the G component of light is enlarged three times with regard to its abscissa compared to the transparency shown in FIG. 2A, while the representation for the transparency g (x) _R compared to the R component of the Light is plotted along the abscissa with the same scale as in Fig. 2A. This results in a curve for the spatial frequency

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characteristic, as shown in Fig. 6D including the ratios for all three components R, G and B of light is shown schematically.

This representation shows that the filter for the G component is in the wide band between 0 and 5a / A. d is permeable, for the R and B components, however, only in the narrower band between 0 and j5a / A d.

The above method, in which the band is limited relative to the green light, can also be applied to the case that a quasi-arbitrary sequence is used. In more general terms, the phase change έ- g (x) can be divided as follows:

where the boundary condition applies that L · g. (x) for green light assume the two values 0 and ff and / L g ₂ (x) for this light the values 0 and 6'lj. Next, the value for the transparency g (x) is selectively set to "+1" and "-1" for these wavelengths. If then the value for ^ go (x) compared to green light when fulfilling the conditions g (x) = -1 and g ₁ (x) = ίί equals 0, while under other conditions it results in 6 Π, then the desired phase change ^. g (x) is obtained.

In the above description, exemplary embodiments are treated in which the transparency of the filter in one dimension and varied in stages. These execution forms can be easily realized from the optical point of view and they have from the practical point of view a high value. However, there is also a certain amount of improvement in the spatial frequency characteristic

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Need that more general transparencies are preferably provided. As part of the basic principle Many of the properties of the present invention can be used depending on the properties required for each filter Consider variations for transparency.

In the exemplary embodiments shown, the strips 2 run on the substrates 1 only in one direction, so that there is a one-dimensional band limitation, but they can of course also be arranged crosswise so that a two-dimensional band limitation can be obtained. In addition, instead of a stepped If the strips 2 emerge from the surface of the substrate 1, there is also a continuous transition be provided between the substrate surface and the strip.

Purely the production of the strips 2 on the substrates 1 numerous methods have already been proposed; for example enables the use of a multi-layer dielectric coating material the setting of a predetermined phase difference 0, whereby a filter with high mechanical stability results.

With this method of manufacture, however, the finished filter generally shows poorer properties because of the reflections occurring at the layer boundaries. It should also be noted that in such a case the above mentioned Equation (1) and similar relationships become somewhat more complicated, but we shall not go any further here are included, since multilayer dielectric coatings are widely used in optics and their properties therefore are well known.

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The phase filter designed according to the invention has the advantage that the spatial frequency characteristic shows a strong dependence on wavelength. This advantage can not only be used for selective band limitation relative to the wavelength of light for images in color television cameras or color image recorders with a Take advantage of the receiving tube, but there are also numerous applications in other areas of the incoherent Light optics open.

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Claims (5)

Claims / ij Optical phase filter with a simple structure in the form of a plate made of translucent material, characterized in that the optical thickness of the structure in a direction perpendicular to the disk surface is different Has distribution over the plate surface along one or two dimensions and between the maximum value and the minimum value for the phase change when passing through in the visible wavelength range lying light on the maximum value or the minimum value exhibiting optical paths a difference of more generated as 2 if. 2. Phase filter according to claim!, Characterized in that that the optical thickness of the structure perpendicular to the plate surface can be adjusted so that an absolute value for the transfer function of the filter results in that for lying in the red and blue wavelength range Light is close to 0 and for light lying in the green wavelength range is close to 1. 3. Phase filter according to claim 1, characterized in that the simple structure a flat substrate (1) and arranged on its surface in one- or two-dimensional modes comprises translucent strips (2), the thickness of which is adjustable so that the difference in the phase changes for light passing through the strips on the one hand and through sections of the which are not covered with strips Light transmitted through the substrate, on the other hand, for the red AO9807 / 0362 and light lying in the blue wavelength range, for example an odd multiple of jT and, for light in the green wavelength range, roughly an integer Multiple of 2 i | amounts to. 4. phase filter according to claim 1, characterized in that that the optical thickness and its distribution are adjustable so that the minimum value for the absolute value in the optical transfer function of the filter is almost 0 and that the optical transfer function for Light lying in the green wavelength range at the lowest spatial frequency, at each the optical The transfer function for light lying in the red and blue wavelength range remains at the minimum value, is more than 0.5. 5. Phase filter according to claim 4, characterized in that the simple structure is a flat substrate (1) and comprises translucent strips (2) arranged on its surface in one- or two-dimensional fashion, of which a first type for light lying in the green wavelength range has a phase difference of '/ and a second type for light lying in the green wavelength range a phase difference equal to an integral multiple of 2 ίΓ, being a section of the strip of the first type is superimposed on a portion of the strips of the second type in such a way that the first type of Stripes and their portion superimposed on the second type of stripes a band limit for the spatial frequency cause light lying opposite in the green wavelength range, while the stripes of the first type and a a portion of the strips of the second type not superimposed therefrom opposes a band limitation for the spatial frequency cause light lying in the red and blue wavelength range. 409807/0362 Blank page