DE2313202C2 - Optical waveguide - Google Patents

Description

^AU 5 ^g wave guide according to claim 4, characterized in that the core layer (12) consists of a material which is doped with at least one of the oxides of titanium, tantalum, tin, niobium, zirconium, aluminum, lanthanum, germanium or boron. . _.

6 waveguide according to at least one of the preceding claims, characterized in that the Core layer (12) consists of fused silica which is doped with a maximum of 20% by weight of titanium oxide.

7. Waveguide according to at least one of the preceding claims, characterized in that the The ratio of the width and thickness of the core layer (12) is equal to or less than 10

8 waveguide according to at least one of the preceding claims, characterized in that a unsintered part of the core layer (12) is removed before application of the cover layer (20)

9. Waveguide according to claim 8, characterized in that the sintered part of the core layer (12) and a part of the substrate (10) are provided with the cover layer (20).

10. Waveguide according to one of the preceding claims, characterized in that the refractive index / 7 _{2 of} the core layer is greater than the refractive index n _{t of} the substrate (10)

The invention relates to an optical waveguide according to the preamble of claims 1 and 2

An optical waveguide according to the preamble of claims 1 and 2 is disclosed in US Pat. No. 3,388,787 Furthermore, the US-PS 33 86 787 is also essentially the formula of claim 2 for the thickness the core layer as known. . .

The optical waveguide according to US-PS 33 86 787 consists of two layers, between which one Cavity is designed for receiving a gaseous or liquid medium, the cavity with the gaseous or nutty medium forms the core area of the waveguide when the refractive index in the core area should be greater than the refractive index of the cover layers, as z. B. in column 3, line 51 Is conveyed in the case of the use of a gaseous medium in the core area, the fulfillment of predetermined ones Temperature conditions necessary to ensure a refractive index gradient in the core area or a mixed liquid is used in the core area whose refractive index is generally greater than that Refractive index of solids is both when using a gaseous medium, in which case the Compliance with predetermined temperature requirements is essential, as well as when using a liquid so Medium inevitably results in much greater problems and difficulties than with an optical one Waveguide that is composed only of solids. . . . .

From DE-CS 19 24 994 a waveguide is known in which a single vibration form is used to propagate a dielectric waveguide is used, after which according to 3eite 3, paragraph 2, the use a core embedded in a substrate is considered to be disadvantageous.

From DE-OS 21 22 896 an optical waveguide is known which, with a coaxial structure, has a central one

The underlying task is to create a planar optical waveguide with the smallest possible Attenuation * and absorption losses as well as low scatter, especially at the interfaces of the core

and create coat. ",,

According to the invention, this object is achieved by the characterizing part of claims 1 or 2 drawn Further refinements result from the subclaims.

Waveguides according to the invention are explained in more detail below with reference to the drawing. It shows F i g. 1 a first layer applied to a substrate,

F i g 2 a second layer applied to the j'th layer,

F i g. 3 a planar optical waveguide made up of a core and cladding layer, F i g. 4 a first layer, F i e, provided in the form of a narrow strip. 5 the on the e? '. E layer according to F i g. 4 applied second layer,

F i g. 6 an optical waveguide, the first layer of which contains a stripe generated by laser beams,

F i g. 7 shows the second layer applied to the first layer in the embodiment according to FIG. 6, and

F i g. 8 shows a finished planar optical waveguide corresponding to the structure according to FIG. 6 and FIG. 7th
1 shows a substrate 10 of an optical waveguide, on which at least partially a coating 12 made of a glass with a higher refractive index than that of the substrate is applied, for example by flame hydrolysis. For application, a gas vapor mixture is fed to a burner 14 and hydrolyzed by its flame 16 to soot, which is applied in the form of a stream to one of the surfaces of the substrate 10; while the substrate is moved back and forth and back and forth. The movement in only one direction is sufficient if several burners are provided distributed over the substrate surface.

F i g. Figure 2 shows that a second coating layer 20, e.g. B. also by flame hydrolysis, is upset. If the layer 12 is to form the core and the layer 20 is to form the cladding of the optical waveguide, the refractive index of the cladding is selected to be smaller than that of the core. The one knocked down by flame hydrolysis Carbon black is sintered when it is applied or afterwards. Both layers can be used simultaneously or separately be sintered.

As the embodiments according to FIG. 4 and FIG. 5 show, the first layer 26 is applied to the substrate 28 as a fine line, e.g. B. applied with a ratio of width to thickness less than 10. A waveguide with Such a narrow core is particularly suitable for integrated optical circuits that require little space Then z. B. also by flame hydrolysis on the surface 32 of the first layer 26 a second Layer 30 has been applied with a smaller refractive index (Fig. 5). Be at a very fine line according to FIG. 5 also covers the side walls of the layer 26 forming the core, whereby with small Ratio of width to thickness the signal losses of the waveguide are reduced.

Another embodiment of a planar optical waveguide is shown in FIGS. 6 to 8. A laser beam 22

was directed to certain parts of the first layer 12 in this embodiment. A focusing lens system 26 inserted into the beam path of the laser 24 can be used to produce very narrow or narrow parts or paths. The wavelength is selected such that the laser light is absorbed by at least one component of the glass particles of the layer 12. The V> llen length also determines the refraction and thus also the minimum diameter of the lenses with a correspondingly qualified diameter of z. B. 2.44 λ point-like focusable laser surface. A thin layer of powdered fused silica absorbs around 90% of the incident radiation from a CO ₂ laser source with a wavelength of 10.6 μ: the minimum size of the focused point is then

2.44x10.6 = 26 µ.

At short wavelengths, i.e. in the ultraviolet range, the molar extinction coefficients cause different ones Dopants strong absorption; the amounts of energy absorbed result from the equation

I (itnorbien) = ! (Incident) (1 - e- ' ^od ) 40

where ε is the molar extinction coefficient of the dopant, c is the concentration of absorbing ions and d is the thickness of the absorbing layer. B. CO2 radiation, e.g. B. to a point size of only 0.8 μπι at a wavelength of 0.3 μπι. Even smaller points are obtained by immersing in a medium with a refractive index greater than that of air, which at the same time regulates the intensity of the radiation falling on the unsintered glass particles 28 Consolidated of uniform density The laser beam can be steered along the desired path. The thickness of the sintered web 28 is less than that of the layer 12.

The remaining unsintered part of the layer 12 was cut to a suitable thickness in this waveguide removes, for example, with a high pressure jet, by brushing or scrubbing, dipping in detergents, Solvents and detergents or the like. Stubborn residues can be removed with a suitable acid will.

The path 28 is used to propagate light energy. The body produced so far is therefore fundamental suitable as an optical waveguide. But because dust and other impurities are on the open surface Light propagation can be impaired and better properties arise when the medium is above the If the web has a greater refractive index than air, the body with the web 28 is either in a liquid immersed with a corresponding refractive index or, preferably, coated with a glass layer, their Refractive index is lower than that of the web. The surface of the web can first be cleaned. Thereon this glass layer, corresponding to the previously described second glass layer on the surface of the web 28 and at least the adjoining parts of the substrate 10 are applied as explained in more detail above

It is particularly advantageous to apply one or both layers of the optical waveguide by flame hydrolysis after a modification of the process described in US Pat. No. 2,272,342 and 2,326,059. For the preparation for example, a Oberzugs of titanium oxide doped fused silica dry oxygen at 35 ° C is bubbled through a 53 wt .-% SiCl ₄ and 47% TiCl ₄ containing tank; the vapors absorbed by the oxygen are passed through a gas-oxygen flame, hydrolyzed and the resulting soot, consisting of fine particles of 95% SiO ₂ and 5% TiO _{2, is} deposited on the surface to be coated in a continuous flow. The layer thickness depends mainly on the throughput, the duration of precipitation and

the speed of movement of the substrate. The layer is applied immediately or later, if necessary sintered together with the second layer, which can be applied in a corresponding manner. at In the example described, the starting material for the production of the second RnlLehicht contains less or less No TiCU at all, so the refractive index of the cladding or the first layer is lower than that of the core or the second layer will.

The substrate and coating material should absorb light as little as possible. Basically all glasses are opt ^; Fused silica glass is particularly favorable. The core and cladding elements have the same or similar physical characteristics and consist, for example, of the same glass that is lightly doped with a suitable material for the core in order to increase the refractive index is. Examples of a suitable dopant are, for. example dm oxides of titanium, tantalum, tin, niobium, zirconium, aluminum, Lenthan, germanium, boron.

The amount must be set precisely because too much doping material weakens the light transmission and because if the refractive index difference is too great, the permissible core thickness is smaller. The proportion becomes appropriate kept below 40% by weight of the total, e.g. B. 40% for aluminum oxide, below 20% for titanium oxide. the Application takes place by flame hydrolysis or z. B. by chemical precipitation from the vapor phase, by sputtering at radio frequency, by applying and sintering a glass frit, etc., the two being Layers can each also be applied in different ways.

In the case of the optical waveguide, particularly clean and firm adhesion of the layers is desired. This means that contamination or air inclusions, especially at the interfaces between the core and Light scattering centers that can be traced back to the jacket are largely eliminated. The layers stand out great purity. It is also favorable that the composition of the layers can be changed easily. Advantageously It is also possible to check OH in the glass. The optical one also works on larger surfaces Waveguide a very uniform coating can be achieved.

In a three-media planar optical waveguide, a number of parameters must be coordinated according to the following equations in order to constrain propagation along the waveguide to one or more waveforms (modes). Of the three media substrate, core and cladding or cover layer, the refractive index of the core nj must be greater than the refractive index of the cladding or that of the substrate (n \, / J3).

The following applies:

NS. TMom forms if / no is an even integer:

β - ^V ' ⁽¹⁾ for TMom forms if / no is odd integer:

ß _a - π (/ η +1) = -cot " ¹ - ( —2-J - cot" ¹ - i-jjM> ^ '

for TEom forms if / n is an even integer:

ßa-x (m + 1) = tan -'- ^ + tan -'- ^ -, (3)

and for TEo _n , forms when m is an odd integer:

ßc- x (m + 1) - -cot -'- j-cot -'- ζ ·.

(4)

50

(5)

(6)

55

(7)

(9)

ss (10)

IO

20th 25th 30th 35 40 45 50 55 60

These equations are valid if the propagation constant h of the plaijible waveguide is equal to or small, than the larger of the values Ki and K ₃ and the core width is infinite. For the sake of simplicity, 1 and 3 apply to the parameters of both the substrate and the clad.

If K \ is greater than Ki, then K \ defines the cutting propagation constant h for the / nth form. Substituting into equations (1), (2), (3) and (4), the following equations are obtained

for TMom forms when m is an even integer:

₊ l ₊ itan - '(44) ff \ "2 -" ι /

' ²

for TMom forms when w is an odd integer:

Il _(n 2_ _n 2y / 2 _{= m + 1} _ J_ _cot -i ("\ -" lY ² (jhY λ Tt \ Hi ~~ ϊ \\ J \ i3 /

for TMom forms if m is an even integer:

if {n \ -n \) ^m = m + 1 + - tan " ¹ (" \ ~ ⁿ \ Y \ λ π \ Π2 ~ ^η ι /

and for TMom forms, if m is an odd integer:

- ² f

where mi is 10 and the largest order of the waveform to be propagated by a waveguide with a core of thickness "a" and infinite width, λ is the wavelength in such a waveguide, tii is the refractive index of the core, /? i and Tt _{3 is} the refractive index of the Designate the substrate or the second layer. The planar optical waveguide has a core of any limited width and a core thickness according to equations 11 to 14 for a core of infinite width and m equal to an integer up to 10. Although established for an infinite width, these equations also give an exact calculation for a Ratio of core width to thickness down to 10; errors arise below this, and the calculation must be carried out according to Marcatili.

For the special case of n \ = / 73 and a kernel of infinite width, equations 11 to 14 can be simplified for both TEn ™ and TMo ™ forms:

2a

11/2

m + 1

An embodiment with a substrate made of pure fused silica with a thickness of at least 20 μm was carefully polished and cleaned so that an optical surface was created. A 26.1 wt% TiCU and Mixture containing 73.9% SiCU was heated to 35 °. SiCU and TiCU were taken through bubbling oxygen Vapors and was directed into a gas-oxygen flame in which the vapors become uninterrupted Soot stream was hydrolyzeda This consisted of about 0.1 micron particles and contained nearly 2% T1O2 and 98% S1O2. The soot stream was directed onto the optical surface until a layer not quite 5.4 μm thick was built. Then liquid SiCU heated to 35 ° was bubbled through with oxygen, the SiCU vapors recorded. The oxygen containing the vapors was passed into the flame, in which the vapors were 100% off S1O2 existing soot were hydrolyzed. The electricity was applied to the free surface of the first layer directed until a 40 μm thick layer of soot was built up. The coated piece was then placed in an induction furnace placed with a 1500 ° hot oxygen atmosphere, the two layers of soot were sintered. In doing so, their thickness was reduced to about half. The resulting planar optical waveguide had a core with a thickness of less than 2.7 μ and a 20 μ thick jacket on both sides. The index of refraction of the first layer, d. H. of the core, was 1.4633, that of the second layer or clad was 1.4584 (1.4584 is the generally accepted refractive index of fused silica for sodium light with a wavelength of 5893 A). This waveguide is only for the propagation of the rectangular TE «and TMot waveforms suitable

The length of the waveguide depends on the intended use. The plane level applies Form for the respective functional, limited length and width, while also one over the entire length Certain curvature is possible The core and cladding can also have a certain curvature in both directions exhibit. However, as is known from waveguides, too great a curvature leads to light losses.

For this purpose 4 sheets of drawings

65

Claims (2)

Patent claims: 1. Optical waveguide with a core area between two layers in which the refractive indices of the two layers are smaller than the refractive index in the core area, with λ = wavelength m = highest mode order of the waveform to be propagated UuIi ₃ = refractive indices of the layers Λ2 = refractive index in the core area and the mutually facing surfaces of the layers are essentially parallel to each other, characterized, that the one layer with the refractive index m is formed by a substrate (10) and is at least partially provided with a core layer (12) made of glass which forms the core area, that with a finite width of the core layer (12) for n _t φη ₃ the thickness of the Core layer (12) is equal to or smaller than the thickness a of the core layer (12) of infinite width and the thickness a is determined as follows: for TMoni modes, if m is an even integer: ■ -7 for TMom modes, if m is an odd integer: 2f. * i - J- cot- (Φ4) " ² (ülV π \ n \ -n \ J \ n ₃ J for TEom modes, if m is an even integer: 2s. (n \ n] Y (4 ^ λ π \ n \ -n \ for TEom modes, if m is an even integer: that m < 10, that the propagation constant Λ of the waveguide has the inequality, met, with K ₁ = -
that K _t > K ₃ , with _v 2 π n ₃ and that the thickness of the substrate (10) and the cover layer (20) at least about twice the value of Thickness c / correspond to the core layer. 2. Optical waveguide with a core area between two layers in which the refractive indices of the two layers are smaller than the refractive index in the core area, with A = wavelength m = highest mode order of the waveform to be propagated n _t , n ₃ = refractive indices of the slides /? 2 = refractive index in the core area and the mutually facing surfaces of the layers are essentially parallel to each other, characterized, that the one layer with the refractive index n \ is formed by a substrate (10) and is at least partially provided with a core layer (12) made of glass forming the core region, that with a finite width of the core layer (12) for n \ = n ₃ die Thickness of the core layer (12) equal to or less than the thickness a of the core layer (12) of infinite width, where the thickness a results in a known manner as follows: that τη <10 and the third layer OZJ has a thickness a and an unlimited width,, ",." ". that λ represents the cut-off wavelength of the transmitted light, that the thickness of the core layer (12) is determined in such a way that the propagation constant of the waveguide is equal to or less than Xi that the thickness of the substrate (10) and of the cover layer (20) is at least approximately twice the value of the thickness ^ wTlleilleiternacKnspiuch 1 or 2, characterized in that the core layer (12) and the Cover layer (20) consist of sintered layers applied by flame hydrolysis. 4 waveguide according to claim 1, 2 or 3, characterized in that the core layer (12) is made of doped Fused silica consists, while the cover layer (20) consists of an iron material from the group with pure Fused silica and fused silica, which is dosed to a lesser extent than the core class, 12),