DE2511046C2 - Imaging system for a waveguide - Google Patents

Description

LX = AhN ₁₁ W * ,,

suffice, in which A is an integer for simple mapping, according to patent 24 45 150.1, characterized in that the refractive index η of the waveguide material in the dimension y perpendicular to the layer plane follows a general function η - η (y) and that the effective refractive index of the imaging condition over a limited layer width W ₂ corresponding to the size W _n is set equal to the effective refractive index JV "= clV _{ß of} this mode given by the phase velocity ν _{μ of} a mode with which the imaging is to take place, where c is the speed of light in free space.

2. Imaging system according to claim 1, characterized in that the waveguide is formed by implantation of foreign substances into the surface of a substrate over a width W ₁ corresponding to the size W _eQ or by diffusion of ions from the surface and that the refractive index profile is in the substrate surface outside the area limited to the width W ₁ differs significantly from that of the waveguide.

3. Imaging system according to claim 1 or 2, characterized in that surface areas of the substrate on both sides of the strip-shaped Waveguide are etched away.

4. Imaging system according to claim 2, characterized in that the refractive index profile in the substrate to the side of the region of the waveguide limited to the width W ₂ changes continuously over a width of the order of magnitude of a wavelength to reduce image defects.

5. Imaging system according to claim 2, characterized in that a light-absorbing material (A) is diffused into the surface of the substrate for apodization at the lateral edges of the waveguide.

6. Imaging system according to one of the preceding claims, characterized in that that to form a line crossing on the two opposite end faces of the self-imaging Waveguide (3) with a distance next to each other two narrower strip conductors (1, 2 or 1 ', 20 are connected, which add or remove the information that crosses one another to lead.

7. Imaging system according to claim 6, characterized in that when the width W _{z of} the self- imaging waveguide is very small, the length L of the relationship

I.-A, (a / 2) IJV, -AT ₁ | -i

is sufficient, where JV ₀ and JV _{1 are} the effective refractive indices of two modes that are still viable over the width W _{2 of the waveguide.} 8. Imaging system according to one of the preceding claims, characterized in that a plurality of juxtaposed strip conductors each satisfying the imaging condition are provided, the width of which increases continuously from one end to its other end, and that the outer strip conductors (S ₀ ) the inner strip conductors are somewhat wider ($)

The invention relates to an imaging system for imaging an object with a layered waveguide with reflective interfaces, the length L being the distance of the object from the BUd measured along the axis of the waveguide and at least one variable W _eq corresponding to a typical transverse dimension of the waveguide taking into account a effective refractive index JV "and the wavelength> at least approximately the imaging condition

suffice, in which Λ is an integer for a simple mapping, according to patent 24 45 150.1.

The imaging system proposed in the main patent, in which a layer or strip-shaped Waveguide with a constant refractive index over the waveguide cross-section is used, has the property that it has an object located on its one end face on the opposite Depending on the design, the front face is upright or reversed in focus in the same or changed size, if its dimensions are chosen according to the development condition.

Such an imaging system is particularly important in the field of integrated optics. A major advantage is z. B. in the fact that the elements of classical optics, such as lenses odei Mirror, replacing integrable self-imaging system of the type proposed is considerably simple can be prepared as known systems ("Appl. Optics", Vol. 10, p. 2077 or US-PS 36 14 198), because they have straight edges and with regard to the layer thickness and the refractive index with the waveguides supplying and removing the light coincide Hnn. Furthermore, the proposed Self-imaging system simply the various requirements of the integrated optics be adapted, for example to enlarge the field of view, to reduce aberrations or in combination with lasers, filters, etc.

Another important advantage is the possibility of having effective index N _{u of} those fashion must be

in the case of an integrated arrangement more complicated optical which the self-imaging is to take place. Here can

Systems on a common substrate - there is in the general case only one of the

multiple, interference-free crossing between or several modes, but in special cases also under certain circumstances

To form strip conductors, whereupon 5 are several modes below. Only when using the

will be entered sooner. effective indices Ν _μ , which for a given index

In the main patent (cf. in particular profile n (y) have certain, discrete values there, Fig. 13) proposed self-imaging system, the principle described in the main patent can be a strip conductor in the form of a discrete imaging waveguide applicable to the general layer on a substrate , e.g. B. by vapor deposition 10 my shift leader, because the usual Bre- or cathode sputtering can be produced. The index of the layer conductor material is, in the present invention, the idea of a common layer conductor cannot be clearly stated,
reasons that the advantages of the proposed self- Another essential point in the application imaging system can also be implemented in a more general manner of the principle described in the main patent on optical waveguides. An example of a general shift conductor is the technical design, shift conductors are already known per se, for example, the "walls" which define the width W _{1 of} the strip in a suitable substrate by means of introducers or conductors. A direct mechanical (or out-diffusion of ions are produced, or otherwise) processing of the layer conductor to reauch by bombarding the surface with rapid reduction of its width to the value W ₂ is possible, ions (Appl. Physics Letters 21 [1972], p. 72 , 87 and ao is not required, rather it is from 95, Appl. Physics Letters 22 [1973], p. 326). If the layer conductor is modified in this way, the difference in the effective refractive index Ν _{μ of} the refractive index profile used has an absolute maximum in the layer conductor mode outside of the strip of the surface or in the immediate vicinity (some white Width W _x another (usually shorter) length) of the same. The zone has a higher value than within the strip. In the interest of the refractive index, however, it can also lie deeper inside a high spatial resolution of the (Appl. Physics Letters 21 [1972], p. 584). In the strip conductor, the N "values should be inside and ner the maximum in the index profile n (y) need not be as different as possible outside the strip, but rather a relative one, so that in the strip conductor a large number of maximums (J Opt. Soc. Am. 65 [1975], p. 46). There are 30 guided fashions. The modification of the even one zone reduced refractive index of refraction Ν _μ can z. B. be done in that index, if this zone is not too narrow and the outside of the width W ₂ a superficial layer transition to the high index of the substrate sharp of the layer conductor z. B. is removed by etching, is (Appl. Physics 1 [1972], p. 55). It is sufficient to keep the zone of increased

The object of the invention is therefore to find a more general 35 chung index n (y) or also an adjacent one

Possibility of realizing a self-imaging zone with at least a lower refractive index

systems of the proposed type indicate which ones to partially remove. Instead of removing material

only a waveguide that is easy to manufacture outside the width W can also be used to form the

necessary and in particular as an element of the inte- layer conductor through diffusion or implantation with-

grated optics. 40 using a suitable mask from the start on one

This object is limited by the strip of width W _{z in claim 1.}

marked imaging system solved. Preferred embodiments of the invention

Important for the purpose of interest here is now explained in more detail with reference to the drawing

in each case that the shift leader is a homogeneous one. It shows

two-dimensional propagation medium for electro- 45 Fig. 1 different index profiles of an optical

represents magnetic waves. The spread should be shift leader for the self-imaging system,

be as loss-free as possible. Low losses due to Fig. 2 a line crossing for the integrated

Absorption or radiation (in the so-called optics with an imaging system according to the

»Leaky guides«) interfere with self-mapping, however,

not. The propagation always takes place 5n a certain 50 F i g. 3 different striplines with the possibility of spatial waveforms or "modes", the possibility of reducing image errors,
can be designated by numbers μ - 0,1, 2 ... Fig. 4 Imaging systems with large facial features. Each mode has a specific phase velocity and

speed v, "whose numerical value from the given FIG.

Index profile depends. The "effective index" / V _{M of} a 55 like.

Mode is then defined as FIG. La shows the index profile of a stripline

according to the main patent, d. H. of a waveguide with

_ constant refractive index n _v over its thickness W _y

N _μ - c / v _M , _the largest ,. j _st as that of the under the wave

60 conductor located substrate and of course also as

where c is the speed of light in free space being that of the medium above it (air),

indicates. In contrast, for example, by

According to the invention, from a layer conductor ion implantation into the surface of a substrate of the general type (n = n (y)), a self-imaging or, through outdiffusion, also a layer conductor er strip conductor can be obtained simply by generating 65 whose refractive index η = n (y) from the layer a struggle of the width W, = W _tt an absolute maximum at the substrate top according to the imaging condition cut out area (y = 0) with increasing depth (-y) after the, whereby the refractive index to be used of the curve shown in Fig. Ib decreases . It can

s 6

also an absolute maximum of the refractive index. In the case of only two existing modes with which are sufficient, the indices N ₀ and N _{x of} the stripline itself, which are effective a few wavelengths, or lower below the surface, as shown in FIG. 1 c can then show the length L by the relationship or Id. According to FIG. 1e, it can also suffice to reduce or increase the 5 L = A (λ / 2) IiV - N h ^: refractive index below a certain depth to form a relative maximum, as shown in FIG. Determine 4 e or 4f.

can be seen. In any case, it is expedient that in Fig. 3 three embodiments of the index profile n (v) in the waveguide are clear. self-imaging stripline, in which there is a possibility, different from the one outside the strip, to detect its image errors, as already mentioned. reduce and thus increase its spatial * »Resolutionver- A simple embodiment for an optical like. For this purpose, the effective BRE component with a self-mapping strip index of the layer from which the strip conductor, which is formed from a layer conductor with general, is slightly changed at the edges. Index profile can be produced is the line crossing shown in FIG. It consists essentially of the change by attaching narrow strips borrowed from a (in the simplest case) rectangular material with a different refractive index on the piece of a layer conductor 3 of such dimensions L side edges of the strip, as in the main patent and W ₁ , that thus the initially defined image was proposed. Another possible condition with integer, odd h and μ is, according to FIG. 3b or 3c, which is filled with an effective index Ν _{μ of} the layer conductor er thickness W _y or the index profile n (y) of the layer loop. On the opposite short ters the side edges do not change abruptly, the end faces of the rectangle are each two narrower but only gradually, over a stretch of strip conductor 1, 2 or 1 ', 2' for supply and discharge of the order of a wavelength . This provided the optical information. Expediently, this can be done particularly easily if the strip is self-imaging these narrower strip conductors in an arsenic conductor with diffusion through a mask production passage with the rectangular shape. The unavoidable lateral diffusion of strip conductors is produced. Adjacent narrow sion automatically creates a gradual stripline should not couple with each other. Transition of the effective refractive index N of Unlike the so-called »bifurcation κ of a 30 its relatively high value within the waveguide strip, these narrower strips of width W ₁ to a lower external value should be clearly separated from each other up to the field of view agrees a single square strip conductor. fenleiter per se with a width W ₁ coincide, the The effect of this arrangement will now be examples size but in many cases according to the illustration of play so that the strip back condition in the Streifenleitem 1 and 2 of 35 only at very great length L to the left (in Fig.2) Light arrives The ends of the ladder «would suffice. As shown in FIG. 4a, these striplines together form the object which, in principle, is already proposed in the main patent by the rectangular stripline on which "a right front end face (FIG. 2) is imaged to enlarge the field of view same stripline next to each other on Da h _z was assumed to be odd, the post 40 or are arranged in the same substrate that the imaging parastroids are guided by the strip conductors 1 'and 2' dm h in the imaging condition is even. From scattering and absorption losses then the individual images are added at the output of the see, this arrangement transmits all incoming strips ( x - L) in the same way as light from 1 to 1 'and from 2 to 2'. It is the object kt at the entrance of the strip (x = 0) is therefore equivalent to a so-called »zero-db- corresponds. The strips are expediently made from couplers from microwave technology and are made in the form of an extended layer conductor, e.g. B. result a crossing of the striplines 1 and 2 by etching narrow grooves to the full dar. It is clear that this principle of a constant isolation of adjacent strips can also be applied to more than two lines - Lines must be observed This line crossing of larger striplines can be used, as it can also be enlarged or reduced . Here, the window ladder is trapezoidal instead of rectangular, in particular the possibility of a “is worth mentioning. In many cases it will be desirable to use the outer strip conductors S _a in FIG. 4b, the length: length of the line crossing to be as short as possible than the inner strip conductor S ₁ , in the z-Rich. According to the mapping condition, this requires that the width W _{1 of} the rectangular strip conductor S _{1 be} slightly wider than the inner stripes, so that it is selected to be as small as possible in accordance with the mapping conditions. In this case, however, there is a lower limit when the image length is correspondingly greater: Sit to cross.

of two lines, the width W _x must be at least so large that in the embodiment of a stripline two modes of the 65 according to FIG. 5 causes a on the sides of the strip

Stripline are viable. In this borderline case, absorbent material A is provided

For very narrow striplines, the specified apodization applies. The absorbent material can ζ. Ε

However, a thin metal layer on the sides can only be approximated

edges is vapor-deposited (Fig. 5b). Alternatively, according to FIG. 5 a, a very narrow strip made of the absorbent material A can be used, the width of which in the z-direction is on the order of / 1/4 and which is applied to the surface of the strip conductor in the immediate vicinity of the side edges. Another possibility, which is often preferred in the case of an integrated stripline, of bringing about apodization of the stripline image is the lateral diffusion of light-absorbing ions (heavy metals) into the lateral edges of the stripline.

It goes without saying that there are also many other exemplary embodiments a self-imaging waveguide of the type proposed in the main patent (e.g. with irregularly shaped end faces) with continuously increasing width to enlarge the image, with narrow reflectors on one or both end faces to form a laser, or with two on each strip conductors connected to both end faces to form a wave filter or wave coupler) according to the present invention can be carried out using self-imaging Waveguides in general, any Au are suitable as components of integrated optics.

Furthermore, it should be noted, that "the ß Abbildungsparametcr not h in all filling nanzimhlig must be. If one selects the lung L of the imaging condition with a broken parameter h (e.g. 1/2, 3/2, etc.), then instead of a simple self-imaging, a multiple imaging, which is desirable in many practical cases, results. A waveguide of the same size can in particular serve as a beam splitter or beam coupler. As has been suggested elsewhere (patent application P 25 06 272.0), the mapping parameter h - ■ = plq should be selected in such cases, where /> and q are integers that are partially foreign to one another and q indicates the number of images.

Finally, it should be noted that the width W _{t of} the strip-shaped waveguide does not have to correspond exactly to the size W _{eQ of} the imaging conditions. In particular, under certain circumstances the so-called goos chicken penetration depth must be added to the width W _{1, but this is very small and often negligible.}

For this purpose 3 sheets of drawings

Claims (1)

Patent claims: 1. Imaging system for imaging an object with a layered waveguide with reflective interfaces, the length L being the distance of the object from the image measured along the axis of the waveguide and at least one variable W _tq corresponding to a typical transverse dimension of the waveguide taking into account an effective refractive index Nj ₁ and the wavelength λ at least approximately the imaging condition