JPH0361163B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Integrated optical circuits are the basis of the emerging field of optical transport. Light is guided through the integrated optical circuit by a flat optical waveguide made of amorphous or crystalline dielectric material that is transparent to the transmitted energy. What is referred to herein as a "planar optical waveguide" is a film or layer of the dielectric material having a thickness approximately equal to the wavelength of the transmitted light or energy and having a certain desired width. A normal waveguide is said to be flat if its width is much larger than its thickness, but a waveguide whose width is not much larger than its thickness is called a rectangular waveguide. but,
For the purposes of this invention, we will use the term planar waveguide to refer to all non-circular waveguides, regardless of the width to thickness ratio of the waveguide.

It is well known to those skilled in the art that light can be made to travel along transparent members that have a higher refractive index than the surrounding refractive index. Planar optical waveguides are useful in integrated optical circuits for computers or for coupling, demodulation, or other purposes in optical communication devices. The advantages of integrated optical circuits over electrical circuits include signal transmission speed, strength, and long life. Waveguides made for these purposes must avoid excessively attenuating the transmitted light. Furthermore, to be an effective transmission medium in integrated optical circuits, planar waveguides must not only transmit light without excessive attenuation, but also must be able to transmit light without causing excessive dispersion in the transmitted light. Instead, only a preselected mode of light must be transmitted along the waveguide. To the extent that planar waveguides have traditionally been fabricated, these waveguides have not been known to provide high transmission capabilities.

Some theories of operation and other pertinent information regarding planar optical waveguides can be found in the articles below. JEMidwinter, “Evanescent Field Coupling to Thin Film Waveguides”
Coupling into a Thin-film Waveguide”
IEEE Journal of Quantum Electronics, Vol.
QE-6, No. 10, October, 1970, pp583-590),
PKTien, "Light waves and integrated optics in thin films" (PKTien, Applied Optics, Vol. 10, No.
11, November, 1971, pp2395−2413), E.
A.G. Markatsuchiri, “Dielectric rectangular waveguides and directional couplers for integrated optics” (EAJ
Marcatili, “Dielectric Rectangular
Waveguided and Directional Coupler for
Integrated Optics”, The Bell System
Technical Journal, Vol.48, No.7, September
1969, pp2071−2102).

The propagation of light waves is governed by the same laws of physics that govern the propagation of microwaves, and therefore:
It can be determined by the mode. Since each mode of light traveling along a planar waveguide propagates at its characteristic velocity, the information initially supplied to all modes is dependent on the length of the waveguide for a given length of the waveguide due to the different propagation velocities. After moving, it will be dispersed. Creating satisfactory planar optical waveguides is one of the most difficult problems in the development of effectively integrated optical circuits.

An object of the present invention is to provide a planar optical waveguide.

Another object of the present invention is to provide a planar optical waveguide that does not cause excessive light absorption loss and that does not excessively disperse the transmitted light, and that It is an object of the present invention to provide a planar optical waveguide that prevents the formation of light scattering centers.

Roughly speaking, the planar optical waveguide of the present invention is:
By depositing on at least a portion of one side of a sufficiently flat glass substrate having a constant desired refractive index a first coating of glass having a refractive index that increases the refractive index of the glass substrate, a flat surface can be obtained. An optical waveguide is created. A second glass coating having a lower refractive index than the first coating is then applied to the exposed surface of the first glass coating. The thickness of the substrate and second coating is
It is at least about twice the thickness of the first coating. The thickness of the first coating if it had a desired finite width is equal to or less than the thickness a if the first coating had an infinite width. Thickness a is determined according to one of the following equations.

For TM _pn mode, where m is an even integer, 2a/λ(n ₂ ² −n ₁ ² ) ^1/2 = m+1+1/πtan ⁻¹ (n ₁ ² −n ₃ ² /n ₂ ² −n ₁ ² ) ^1/2 (n ₂ / n ₃ ) ² If m is an odd integer, for TM _pn mode, 2a/λ (n ₂ ² − n ₁ ² ) ^1/2 = m + 1-1/πcot ^-1 (n ₁ ³ −n ₃ ² /n ₂ ² −n ₁ ² ) ^1/2 (n ₂ /n ₃ ) ² Assuming that m is an even integer, for TE _pn mode, 2a/λ(n ₂ ² − n ₁ ² ) ^1/2 = m+1+1/πtan ^-1 (n ₁ ² −n ₃ ² /n ₂ ² −n ₁ ² ) ^1/2 If m is an odd integer, for TE _pn mode, 2a/λ (n ₂ ² - n ₁ ² ) ^1/2 = m+1-1/πcot ^-1 (n ₁ ² - n ₃ ² / n ₂ ² - n ₁ ² ) ^1/2 where m is equal to 10 or If the value is smaller than that, it is the highest mode order propagated in a waveguide with an infinite width and the thickness of the first coating is a, λ is the wavelength of the light propagating in the waveguide, and n ₂ is the 1 the refractive index of the coating, one of n ₁ and n ₃ is the refractive index of the substrate,
The other of n ₁ and n ₃ is the refractive index of the second glass coating. The thickness of the first glass coating is such that the propagation constant of the waveguide is equal to or less than K ₁ , where K ₁ is K ₃
, and K ₁ and K ₃ can be determined as described above when defined by the following equations.

K ₁ =2πn ₁ /λ K ₃ =2πn ₃ /λ When manufacturing the planar optical waveguide of the present invention, a laser beam may be used. That is, a laser beam is directed toward the first coating layer on the substrate, and relative movement is caused between the laser beam and the substrate so as to form a path of sintered glass.

The unsintered portions of the first layer can be removed from the substrate and a second glass layer with a lower index of refraction can be deposited over the molten glass path and at least a portion of the adjacent exposed surface of the substrate.

Hereinafter, the present invention will be explained in detail with reference to embodiments shown in the drawings.

Referring first to FIG. 1, a first coating layer 12 of glass is deposited on a substrate 10. As shown in FIG. A first coating layer 12 is deposited on at least a portion of one exposed surface of the glass substrate 10 and has a refractive index greater than the refractive index of the substrate 10 .

First coating layer 12 is shown applied to substrate 10 by flame hydrolysis burner 14 . The burner 14 produces a flame 16 in which the gas and steam mixture is hydrolyzed to produce decomposition products (hereinafter referred to as soot). The soot leaves the flame 16 in a stream 18 and forms a coating on one of the planar surfaces of the substrate 10. This flame hydrolysis method will be explained in detail later.

The substrate 10 is suitably placed in the path of the soot stream 18 and moved back and forth so that the first coating layer 12 is applied to the entire surface or desired portion of the substrate 10. The device for moving the substrate 10 in the manner described above can be a known device such as the bed of a milling machine or a two-motor stand having a chuck for fixing the substrate. The limits of this movement are controlled by a microswitch coupled to the motor reversing drive.

Instead of the nearly concentric burners shown, ribbon burners can be used that produce long streams of soot;
Then the board only needs to be moved in one direction. Additionally, multiple burners 14 may be used in a row so that the substrate only needs to be moved in one direction. By arranging a plurality of burners at appropriate intervals over the entire surface of the substrate to which the coating layer is to be applied, there is no need to move the substrate. Similarly,
If the surface to which the coating layer is to be applied is small, the single burner shown can apply the coating to the entire surface of the substrate without moving the substrate.

Referring now to FIG. 2, a second glass coating layer 20 having a predetermined desired refractive index is applied to the exposed surface of the first coating layer 12 by the same flame hydrolysis method described above. do. As shown in FIG. 2, the soot flows away from the flame 16 as a flow 22, and the
Flows toward the exposed surface of 2. In order to uniformly deposit this second coating layer of soot, the substrate and first coating layer 12 are moved as before. First coating layer 12
forms the core of the planar optical waveguide, and the substrate 10 and second coating 20 form its outer jacket. As described below, the refractive index of the waveguide envelope must be smaller than the refractive index of the core.

When depositing the coating layers 12 and 20 by flame hydrolysis, the deposited soot is removed at the same time as the deposition.
Or it must be sintered after deposition to form a uniform, dense material. According to the invention, the covering layer 12 can be sintered and its outer surface must be suitably finished before the second covering layer 20 is applied. In such instances, the second coating layer 20 must then be sintered either simultaneously with or after deposition.

Reference is now made to FIG. 3 in which a planar optical waveguide 24 is shown including a substrate 10, a first cladding layer 12, and a second cladding layer 20. The thickness of the first coating layer, that is, the core 12 is indicated by a.

Referring now to FIGS. 4 and 5, these figures show that the first coating layer 26 has been removed by the flame hydrolysis burner 14.
The formation of a planar optical waveguide is shown as being deposited as a narrow strip on substrate 28. As explained with reference to FIG. 1, the burner 14 has a flame 16
issue. In this flame, the mixture of gas and steam is hydrolyzed to form hydrolysis products, or soot. This soot forms a stream 18 and emits flame 16. The first coating layer 26 has, for example, a width to thickness ratio of
Adhered to a narrow width such as less than 10. 1st
After depositing the covering layer 26 on the substrate 28, a second covering layer 30 is deposited on at least the externally exposed surface 32 of the first covering layer 26. The second coating layer 30 has a refractive index less than the refractive index of the first coating layer 26 and is formed by ejecting soot from the flame 16 as a stream 34, as described above with reference to FIG. . When the width of the first covering layer 26 becomes sufficiently narrow, the externally exposed surface 32 of the first covering layer 26 as shown in FIG.
It is necessary to apply the second covering layer 30 to both side parts. Such a second coating layer deposited on the sides of the first coating layer with a low width-to-thickness ratio is required to provide low signal loss and effective waveguide operation.

The materials of the substrate and first and second coatings of the planar optical waveguide must be made from minimally light-absorbing glass, and although any optical glass can be used, a particularly suitable base glass is fused silica. For structural and other practical considerations, it is desirable that the core glass and the envelope glass have similar physical properties. Since the refractive index of the glass for the core must be greater than the refractive index of the glass for the outer sheath, the glass for the core is made by adding a small amount of other substances to the same base glass as the glass for the outer sheath. The refractive index must be increased. Therefore, if pure molten glass is used as the outer glass, fused silica doped with a substance to increase the refractive index can be used as the core glass.

There are many suitable materials that can be used satisfactorily as additives alone or in combination. These materials include titanium oxide, tantalum oxide, lanthanum oxide, niobium oxide, zirconium oxide, aluminum oxide, germanium oxide, and boron oxide. The amount of additive used must be carefully controlled for various reasons. For example, since extra additives increase the refractive index, the difference between the refractive index of the outer sheath glass and the refractive index of the core glass also increases, which causes the permissible core area of the planar waveguide to increase, as will be explained later. (Core) thickness will have to be reduced. Furthermore, if an excessive amount of additive material is added to the base material, the loss of transmitted light will increase. Preferably, precise amounts of additives must be added to the base material for the primary purpose of changing the refractive index. For the purposes of the present invention, the amount of additive is preferably about 40% of the total composition by weight.
Try to keep it below %. For example, aluminum oxide can be added up to about 40% by weight, and titanium oxide must be kept below about 20% by weight.

The first and second coating layers can be deposited by a variety of methods including sintering of soot deposited by flame hydrolysis, chemical vapor deposition, deposition of glass frit followed by sintering of the frit, and the like. It is clear that the first and second coating layers can be applied either in the same way or in different ways.

6-8 show another embodiment of the invention. 6th
As shown in the figure, the laser beam 22 is irradiated onto a predetermined portion along the first coating 12 . The light from the laser 40 is directed through the first coating 12 by a lens system 26 to form a very narrow section or path.
It can be focused on. The wavelength of this laser light is the first
This wavelength is such that it is absorbed by at least one component of the glass particles of the coating layer 12. The intensity of the laser beam can be adjusted by inserting a suitable filter 30 into the path of the laser beam. Laser light can be focused very small. The minimum diameter of the focal point is diffraction limited and therefore depends on the wavelength of the laser light. f-
A bright lens with a number close to 1 can focus a parallel laser beam to a small point with a diameter of 2.44λ when the surrounding medium is air. The wavelength of the laser light is selected such that the base glass component of the green particles, or impurities therein, absorb the laser light. For example, a thin powdered fused silica layer has a wavelength of 10.6μ
It absorbs about 90% of the incident light of wavelength m, and light of this wavelength can be obtained with a carbon dioxide laser. The minimum focusing radius of such a laser beam is 2.44 x 10.6 μm or approximately 26 μm.
It is m. At short wavelengths, ie in the ultraviolet range, the molar absorption coefficients of various additives cause strong absorption. The amount of energy absorbed is given by:

I (absorption) = I (incidence) (1-e ^- 〓 ^cd ) where ε is the molar absorption coefficient of the additive, c is the concentration of absorbed ions, and d is the thickness of the absorption layer. It can be seen from the above-mentioned relationship between the wavelength and the diameter of the focused light spot that the light spot of ultraviolet light can be made smaller than that of the carbon dioxide laser. Ultraviolet light with a wavelength of 0.3μm is approximately 0.8μm
can be focused to a point with a diameter of A smaller light spot can be obtained by placing the coated substrate in a medium with a higher refractive index than air. Such a medium is of course necessary to provide an appropriate refractive index,
It can also be used to control the intensity of light incident on unsintered glass particles. The heat generated by absorption of the laser light sinteres the unsintered glass particles of the coating layer 12 to form channels 28 of uniform density material. Due to the sintering of the previously unsintered particles, the thickness of the channels 28 becomes thinner than the thickness of the first coating layer 12. Either the laser light or the substrate 10, or both, can be moved to sinter the desired path 28.

The unsintered portions of the first coating layer 12 are then removed. This removal is performed using any suitable technique for removing particles from the surface of the glass substrate. high pressure spraying,
Techniques such as brushing, soaking in cleaning agents, solvents, rinses, etc. can be used. Particles that resist removal by these techniques can be dissolved by acid solutions. This acid solution dissolves particles remaining on the surface of the substrate much more easily than the substrate itself. Residual acid can be removed with a rinse solution.

The structure thus formed functions as a planar optical waveguide since the path 28 is capable of transmitting optical energy. However, dust and other surface contaminants that tend to occur on exposed surfaces can significantly reduce the optical transmission properties of this optical waveguide. Furthermore, by placing a medium with a higher refractive index than air on the surface of the path 28, an excellent optical waveguide can be obtained. This can be done, for example, by immersing the adjacent portion of the channel 28 and the substrate 10 in a liquid having a suitable index of refraction. However, the preferred medium for surrounding channel 28 is a glass cladding. Prior to depositing a glass layer having a predetermined refractive index that is less than the refractive index of the channels 28 on the exposed surfaces of the channels 28 and at least a portion of the surface of the substrate 10 adjacent to the channels 28, the surface of the channels 28 is suitably coated. can be finished. This second layer of glass can be deposited by methods such as radio frequency sputtering, sintering of a soot coating deposited by flame hydrolysis, chemical vapor deposition, and sintering of a frit powder coating.

A particularly effective method of applying the coating layer is by a flame hydrolysis method similar to that disclosed in US Pat. Nos. 2,272,342 and 2,326,059.
An example of the application of a modification of the method disclosed in the latter patent to the production of titanium-doped fused silica is described below. _SiCl4 by weight ratio
Dry oxygen is blown into a mixture containing about 53% TiCl 4 and about 47% TiCl ₄ at about 35°C to create bubbles. _SiCl4 and _TiCl4
The vapor is absorbed by the oxygen and then passed through a gas and oxygen flame where it is hydrolyzed to form small glass particles, or soot. The composition of the glass particles is approximately 95% SiO ₂ and approximately 5% TiO ₂ by weight.
This glass product leaves the flame in a steady flow and adheres to at least a portion of one surface of the substrate. The thickness of the resulting coating layer is determined by the amount of soot deposited. This amount is controlled by the flow rate, the deposition time, and the speed at which the substrate is moved. The soot deposited in this manner is sintered simultaneously with or after deposition to form a uniform, dense coating.

A second glass coating layer is then applied to the exposed surface of the first coating layer. The physical properties of the second coating layer, such as expansion coefficient and refractive index, must be appropriate.
A particularly effective means for forming the second coating layer is to sinter the soot layer of the desired material deposited by the flame hydrolysis method described above. Since the refractive index of the second glass coating layer must be smaller than the refractive index of the first coating layer, the glass material of the second coating layer is the same material as the glass of the first coating layer except for the doping agent. , or a less doped glass than in the case of the first covering layer. If the second coating layer is applied by flame hydrolysis, either the starting mixture is TiCl ₄ free, such that the second coating is pure SiO ₂ , or the resulting coating is better than the first coating. The parameters used in the method are approximately the same as those used for the first coating, except that a small amount of TiCl ₄ is added to include a small amount of TiCl ₄ .

The property of a planar optical waveguide necessary to transmit the required amount of light is that it is independent of optical energy lost due to radiation by light scattering centers and optical energy that is excessively absorbed by the transmitting material.
These scattering centers are caused by small air bubbles or impurities at the junction of the waveguide core and jacket. The method described above combines a very clean and strong bond to eliminate most light scattering centers. Furthermore, the above-described method provides very pure films and the composition is easy to vary. The method described above also makes it possible to apply uniform coatings over large surfaces and to control the OH groups naturally present in the glass.

In a planar optical waveguide containing three types of media, the waveguide can be modified to limit the propagation of light along the waveguide to a preselected mode, depending on whether single mode or multimode operation is desired. Various parameters must be adjusted according to the equation:
The three types of waveguide media are the substrate, the core, and the jacket. As mentioned above, in order to operate this waveguide effectively, the refractive index of the core (n ₂
must be larger than the refractive index (n ₁ , n ₃ ) of the substrate or envelope.

For TM _pn mode, where m is an even integer, β _a −π(m+1)=tan ⁻¹ α/β(n ₂ /n ₁ ) ² +tan ⁻¹ γ/β(n ₂ /n ₃ ) ² (1) When m is an odd integer, for TM _po mode, β _a −π(m+1)=−cot ⁻¹ α/β(n ₂ /n ₁ ) ² −cot ⁻¹ γ/ β(n ₂ /n ₃ ) ² (2) If m is an even integer, for TE _pn mode, β _a −π(m+1)=tan ^-1 α/β+tan ^-1 γ/β (3) When m is an odd integer, for TE _pn mode, β _a −π(m+1)=−cot ⁻¹ α/β−cot ⁻¹ γ/β (4) where, β ² =K ₂ ² −h ² (5) α ² =h ² −K ₁ ² (6) γ ² =h ² −K ₃ ² (7) K ₁ =2πn ₁ /λ (8) K ₂ =2πn ₂ /λ (9) K ₃ =2πn ₃ /λ (10). These equations are the propagation constant h of the planar optical waveguide
Applicable when is equal to or smaller than the larger of K ₁ and K ₃ and the width of the core is infinite. For simplicity, the subscripts 1 and 3 will be attached to either the substrate or the overcoat. K ₁ is K ₃
If K 1 is larger than , then K ₁ defines the cutoff propagation constant h for the mth mode. This is (1),
Substituting into equations (2), (3), and (4), the cutoff equation is obtained as follows.

When m is an even integer, for TM _pn mode, 2a/λ(n ₂ ² − n ₁ ² ) ^1/2 = m+1+1/πtan ⁻¹ (n ₁ ² − n ₃ ² /n ₂ ² − n ₁ ² ) ^1/2 (n ₂ /n ₃ ) ² (11) When m is an odd integer, for TM _pn mode, 2a/λ(n ₂ ² −n ₁ ² ) ^1/2 = m+1-1/πcot ^-1 (n ₁ ² - n ₃ ² / n ₂ ² - n ₁ ² ) ^1/2 (n ₂ / n ₃ ) ² (12) If m is an even integer, TE _pn mode For, 2a/λ(n ₂ ² −n ₁ ² ) ^1/2 = m+1+1/πtan ⁻¹ (n ₁ ² −n ₃ ² /n ₂ ² −n ₁ ² ) ^1/2 (13) m is 2a/λ(n ₂ ² − n ₁ ^{2 ) 1/2} = m+1−1/πcot ⁻¹ (n ₁ ² −n _{3 2} /n ₂ ² −n ₁ ² ) ^1/2 (14) Here, m10, the thickness of the first coating or core is a, the highest mode order propagating in a waveguide with an infinite width, and λ is as shown above. Wavelength of light propagating in the waveguide, n ₂ is the refractive index of the core, n ₁
or n ₃ is the refractive index of the substrate,
The other is the refractive index of the second coating layer.

According to the present invention, the width of the core is finite and m
When solving equations (11) to (14) in the case of 10,
Is it equal to the value determined by equations (11) to (14)?
It is known that suitable planar optical waveguides can be made with cores having smaller thicknesses and any desired finite width. (11)
Equation (14) applies to planar waveguides with a finite width, but is also approximately correct for planar optical waveguides with a core width to thickness ratio of up to about 10. If the ratio is less than 10, a large error will enter the calculation, so you should consider solving for the various parameters included in the equation according to the paper by EAJ Marcatili mentioned above. It is.

For the case where n ₁ = n ₃ and the width of the core is infinite, equations (11) to (14) can be easily written as the following equations, and this equation can be used for both TM _pn and TE _pn . Applies to mode.

2a/λ(n ₂ ² −n ₁ ² ) ^1/2 = m+1 (15) A special example of the planar optical waveguide of the present invention is as follows. Pure fused, quartz with a thickness of at least 20 μm is carefully polished and cleaned to obtain an optically flat surface. Approximately 26.1% TiCl ₄ and approximately 26.1% SiCl ₄ by weight
Heat the mixture containing 73.9% to 35°C. Dry oxygen is blown into this liquid, and this oxygen causes
Take out the vapors of SiCl ₄ and TiCl ₄ . The oxygen-containing vapors are then passed through a gas-oxygen flame where they are hydrolyzed to about ₂ % TiO2 by weight.
A steady stream of spherical particles with a diameter of about 0.1 μm is produced, with a composition of about 98% SiO ₂ . This stream is applied to the optically flat surface of the substrate, and the particles are approximately 5.4 μm thick.
Make a layer thinner than that, but about the same thickness. Next, the liquid SiCl ₄ is heated to about 35°C, and dry oxygen is blown into the liquid to extract the SiCl ₄ vapor. This steam-laden oxygen is then passed through a gas-oxygen flame,
There, _SiCl4 vapor is hydrolyzed to produce a steady stream of 100% _SiO2 particles. This flow is applied to the exposed surface of the first coating layer to form a SiO ₂ layer with a thickness of approximately 40 μm. Next, this structure is placed in an induction furnace heated to 1500° C. in an oxygen atmosphere to sinter the first and second layers. This sintering process reduces the thickness of these layers by approximately half. The planar optical waveguide thus obtained has a core with a thickness of 2.7 μm or less, and an outer jacket with a thickness of about 20 μm on both sides of the core. The refractive index of the first coating layer or core is approximately 1.4633. The refractive index of the substrate and the second coating layer is approximately 1.4584. The refractive index of fused silica, 1.4584, is a value commonly obtained when measured with sodium light at a wavelength of approximately 5893 Å. The planar optical waveguide described in this example can only propagate a single rectangular TM _pl , TE _pl mode combination.

Regarding the substrate on which the core of the planar optical waveguide of the present invention is formed, it has only been explained that it is substantially flat, and nothing has been said about the length of the waveguide. As can be readily seen, the length of the waveguide is determined by each application and is not relevant for the purposes of the present invention. Furthermore, the term "bobo-flat" means that the substrate is flat for practical purposes with respect to the finite length and width of the waveguide, and is somewhat flat in terms of its total length and width. may be bent. Similarly, the core and outer sheath are illustrated as being almost linear, but
These may curve to both sides. However, as in any optical waveguide where such bends are excessive, they cause light loss.

Although the present invention has been described above with reference to specific embodiments, such description is not intended to limit the scope of the present invention, except as set forth in the claims.

[Brief explanation of drawings]

FIG. 1 is a schematic perspective view showing how the first coating layer is attached in the manufacture of a planar optical waveguide, FIG. 2 is a schematic perspective view showing how the second coating layer is attached, and FIG. 3 is a schematic perspective view showing how the second coating layer is attached. FIG. 4 is a schematic perspective view of another embodiment of the invention showing the deposition of a relatively narrow first coating layer; FIG. 5 is a perspective view of the waveguide of FIG. 4; FIG. 6 is a schematic perspective view showing how a sintered glass path is formed on a substrate, and FIG. 7 is a schematic perspective view showing how the second coating layer is attached during the formation of the optical waveguide of the present invention. FIG. 8 is a schematic perspective view showing how the second coating layer is deposited therein, and FIG. 8 is a perspective view of the planar optical waveguide of the present invention. 10, 28... Substrate, 12, 26... First coating layer, 14... Burner, 20, 30... Second coating layer, 24... Planar optical waveguide.

Claims (1)

[Scope of Claims] 1. A substantially flat glass substrate having a predetermined desired refractive index; and one flat surface of the glass substrate having a refractive index greater than the refractive index of the glass substrate. a first applied glass coating deposited on and affixed to at least a portion of the glass substrate;
an exposed outer surface substantially parallel to two flat surfaces, the thickness of the first deposited glass coating being defined by the surfaces; the first deposited glass coating, the width of the coating having a dimension orthogonal to both the thickness and the optical propagation axis of the first deposited glass coating; and having a refractive index smaller than that of the glass substrate and different from the refractive index of the glass substrate, and deposited on at least the exposed outer surface of the first applied glass coating and attached to the exposed outer surface. a second deposited glass coating, a clean and strong bond is formed at the boundary between the first deposited glass coating and the second deposited glass coating, and the first deposited glass coating is bonded to a desired limit. The thickness of the coating when the width is equal to or smaller than the thickness a when the coating has an infinite width, where m is an even integer. For a certain TMom mode, 2a/λ(n ₂ ² −n ₁ ² ) ^1/2 = m+1+1/πtan ⁻¹ (n ₁ ² −n ₃ ² /n ₂ ² −n ₁ ² ) ^1/2 ( n ₂ /n ₃ ) ² In the case of TMom mode where m is an odd integer, 2a/λ(n ₂ ² −n ₁ ² ) ^1/2 = m+1−1/πcot ⁻¹ (n ₁ ² −n ₃ ² /n ₂ ² −n ₁ ² ) ^1/2 (n ₂ /n ₃ ) ² In the case of TEom mode where m is an even integer, 2a/λ(n ₂ ² −n ₁ ² ) ^{1/ 2} = m + 1 + 1 / πtan ^-1 (n ₁ ² - _{n 3} ² / n ₂ ² - _{n 1} ² ) ^1/2 In the case of TEom mode where m is an odd integer, 2a / λ (n ₂ ² - n ₁ ² ) ^1/2 = m+1-1/πcot ^-1 (n ₁ ² - n ₃ ² /n ₂ ² - n ₁ ² ) ^1/2 determined according to one of the formulas, where m
≦10 and is the highest mode dimension to be allowed to propagate in a waveguide of thickness a and infinite width, and λ is the maximum mode dimension that the first applied glass coating has a thickness a
is the wavelength of light to be propagated in the waveguide having infinite width, n ₂ is the refractive index of the first attached glass coating, and one of n ₁ and n ₃ is the refractive index of the glass substrate. , the other of n ₁ and n ₃ is the second attached glass coating, and the other of n 1 and n 3 is the second attached glass coating, and the other of n 1 and n
The thickness of the impregnated glass coating is such that the propagation constant of the waveguide is equal to or less than K ₁ , K ₁ is greater than K ₃ , K ₁ =2πn ₁ /λ K ₃ =2πn ₃ / λ , the respective thicknesses of the glass substrate and the second applied glass coating are at least about twice the thickness of the first applied glass coating; A planar optical waveguide characterized in that the first applied glass coating forms the core of the planar waveguide and the second applied glass coating forms the cladding of the planar waveguide.