JPH0675134A - Production of rare earth ion-added optical waveguide film and optical waveguide - Google Patents

Abstract

PURPOSE:To provide the method for forming films having good transmittance without the possibility of incorporating impurities therein which can form core films for optical waveguides added with the rare earth ions of a high refractive index on substrates with lessened warpage and with easy control of the film thicknesses and refractive indices thereof and the process for production of the rare earth ion-added optical waveguide film and optical waveguide which can easily control the amt. of the impurity ions to be added. CONSTITUTION:The substrates 7 are disposed in the upper part in a chamber 2 under evacuation to a vacuum and are heated. An evaporating source 3 is disposed below the substrates 7. Tablets 4 formed by mixing powders of Si3N4 and the oxide of the rare earth element at desired weight ratios, then solidifying the mixture by a hot press are housed into the evaporating source 3 and thereafter, the tablets 4 are irradiated with electron beams while gaseous O2 is introduced into the chamber 2, by which the tablets are evaporated and the optical waveguide films of Six0yNz contg. the rare earth ions are formed on the substrates 7.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rare earth ion-doped optical waveguide film and a method for producing an optical waveguide, in which a high refractive index core film for an optical waveguide to which rare earth ions are added is produced by an electron beam evaporation method.

[0002]

2. Description of the Related Art In recent years, research and development aimed at realizing a laser or an optical amplifier by adding a rare earth element into the core of a glass waveguide has been attracting attention.

FIG. 5 shows a conventional example of a method of adding a rare earth element into the core of a glass waveguide. That is, the core glass glass film on the substrate obtained in the step of forming on the substrate a glass optical waveguide film having a core portion through which light propagates and a clad layer around the core portion, transitions with a rare earth element. Immerse in a solution containing one or more kinds of elements selected from metallic elements, add the element to the core portion at a predetermined concentration, dry and sinter, and then apply photolithography and dry etching processes on the core portion surface. This is a method for obtaining a rare earth element-doped glass waveguide for laser or optical amplifier by depositing a clad layer (JP-A-2-2508).
3 gazette).

[0004]

The above-mentioned conventional method for manufacturing a rare earth ion-doped glass waveguide has the following problems.

In order to manufacture a glass waveguide having a large refractive index difference between the core and the clad, a core glass film having a high refractive index containing a refractive index control additive is formed on the buffer layer, and the entire substrate is A warp is caused by a difference in the coefficient of thermal expansion, and the warp amount becomes a large value far exceeding 10 μm, so that it is difficult to pattern an optical circuit with high dimensional accuracy. In this respect, there is a limit to increase the difference in refractive index.

It has also been found that there is a limit to the difference in refractive index between the core and the clad. That is, even if a porous film for core having a high refractive index is deposited, the additive for controlling the refractive index is volatilized in the sintering process, and it is difficult to realize a core layer having a high refractive index, and the maximum refractive index is 1.47. Never exceeded. Therefore, the relative refractive index difference is limited to about 1% at most.

It has been difficult to uniformly add a rare earth element into the core portion. That is, since the above-mentioned method is a method of impregnating a glass porous film with a liquid, it has a concentration distribution in the thickness direction of the glass porous film, and the concentration gradient of the rare earth element in the core part is the excitation efficiency. Was in decline.

It has been difficult to add a large amount of rare earth element in the core portion.

It is difficult to control the film thickness and the refractive index because it is a method of depositing a porous glass film and then sintering it to obtain transparent glass.

Impurities are easily mixed in through the liquid, making it difficult to reduce the loss.

Therefore, the present invention has been devised to effectively solve the above-mentioned problems, and its main purpose is to provide a core film for an optical waveguide, to which a rare earth ion having a high refractive index is added, on a substrate. A method for forming a film with good transmittance, which can be formed with a small amount of warpage, and whose film thickness and refractive index can be easily controlled, and a rare earth ion which can easily control the addition amount of rare earth ions The present invention provides a method for manufacturing an added optical waveguide film and an optical waveguide.

[0012]

In order to achieve the above object, a first invention is to arrange a substrate in an upper part of a chamber which is being evacuated to a vacuum and heat the substrate, and to evaporate a source in a lower part of the substrate. Is placed, and the powder of Si ₃ N ₄ and the oxide of the rare earth element is mixed in the evaporation source at a desired weight ratio, and the tablet hardened by hot pressing is housed, and then O ₂ gas is introduced into the chamber. At the same time, the tablet is irradiated with an electron beam to evaporate it to form an optical waveguide film of Si _x O _y N _z containing rare earth ions on the substrate, and the second invention is The substrate is placed in the upper part of the chamber which is being evacuated to a vacuum and heated, and at the lower part of the substrate, an evaporation source containing Si ₃ N ₄ tablets and an oxide tablet containing at least one rare earth element are provided. The contained evaporation source After location, O into the chamber
_While introducing ₂ gases, each of these tablets is irradiated with an electron beam to be vaporized to form an optical waveguide film of Si _x O _y N _z containing at least one rare earth ion on the substrate. In the third invention, as a tablet to be put into the above-mentioned one evaporation source, SiO ₂ is used instead of Si ₃ N ₄ , or SiO ₂ containing at least one refractive index controlling oxide and Si ₃ N ₄ powder. A mixture obtained by mixing in a desired weight ratio and hardening by hot pressing is used. Further, a fourth invention is that, as the substrate, a substrate having a refractive index lower than that of a film formed on the surface thereof, or a layer having a lower refractive index than the film formed on the surface thereof is previously formed. In the fifth invention, the optical waveguide film obtained by the method of the invention is processed into a substantially rectangular pattern by photolithography and dry etching, and the optical waveguide film is formed on the surface of the substantially rectangular pattern. It is formed by coating a clad film having a refractive index lower than that of the wave film.

[0013]

As described above, the present invention, according to the first and second inventions, contains rare earth ions and has a refractive index of 1.46.
A high refractive index film having a value close to 5 to 2.0 can be formed. Moreover, even if this film is formed on the SiO ₂ substrate to have a thickness of about 10 μm, the warpage of the substrate becomes extremely small. Further, since the film is formed by the electron beam evaporation method, the rare earth element and Si _x O _y can be adjusted by adjusting the current value of the electron gun.
The deposition rate with N _z can be easily controlled. This means that the amount of rare earth ions added to Si _x O _y N _z can be controlled by the above current value. Further, since the electron beam evaporation method can form the film while monitoring the film thickness, the film thickness can be controlled. In addition, by adjusting the degree of vacuum during film formation, that is, the O ₂ partial pressure amount, Si
The values of x, y, and z of _x O _y N _z can be controlled, and as a result, the refractive index can be easily controlled. Furthermore, since the film formation is performed in a vacuum, it is possible to form a film with good transparency with less impurities mixed therein. Incidentally, as the rare earth element,
Er, Nd, Yb, Eu, Sm, Tm, Ho, Pr or the like can be used. Er ₂ may be used as these oxides.
O ₃ , Nd ₂ O ₃ , Yb ₂ O ₃ or the like can be used.

According to the third invention, Si _x O _y N _z
It is possible to easily obtain an optical waveguide film in which x, y, and z are set to desired values. That is, x, y, and z can be set according to the desired weight ratio of the powders of SiO ₂ and Si ₃ N ₄ , which means that the refractive index value can be selected as a desired value. Here, when the melting points of SiO ₂ and Si ₃ N ₄ are compared, the values are 1500 ° C. and 1900 ° C., which are high melting point materials having relatively close values. It is convenient. Instead of SiO ₂ described above, SiO ₂ contains P ₂ O ₅ , TiO ₂ , Nb ₂ O ₃ and T.
If oxides such as a ₂ O ₅ and Al ₂ O ₃ are added, in addition to adjusting the refractive index, it is used for amplification of optical signals, prevention of lowering of energy conversion efficiency of excitation light, activation of high concentration rare earth ions. It becomes possible to have a function as a use.

According to the fourth aspect of the invention, the substrate is made of glass (quartz system, multi-component system), semiconductor (Si, GaAs, In).
P, etc.), ferroelectric gas (LiNbO ₃ , LiTaO _3, etc.), magnetic substance, sapphire, etc. can be used, so optical devices having various functions (amplification, oscillation, modulation, multiplexing, (Demultiplexing, distribution, etc.) can be manufactured, and a low-priced optical device can be realized by selecting a low-priced substrate.

Further, according to the fifth invention, it is possible to realize a rare earth ion-doped optical waveguide having a low loss and a high relative refractive index difference. For example, excitation light (eg, wavelength 1.48 μm) and signal light (wavelength 1.
It is possible to realize a waveguide type optical amplifier having a function of amplifying signal light by propagating (light of 5 μm band).

[0017]

An embodiment of the present invention will be described in detail below with reference to the accompanying drawings.

FIG. 1 shows a first embodiment of the method for producing an optical waveguide film according to the present invention. As shown in the figure, an umbrella-shaped substrate holder 6 is arranged in an upper part of the vacuum chamber 2 which is evacuated to a high vacuum by a vacuum exhaust system 10, and a plurality of substrates made of SiO ₂ are provided on the lower surface of the substrate holder 6. 7 are held, and these substrates 7 are heated to a desired temperature by a heater 8 located above the substrate holder 6. Further, a vessel-shaped evaporation source 3 is arranged below the substrate 7, and Si ₃ N ₄ is placed in the evaporation source 3.
A tablet 4 in which the powder of the rare earth element oxide and a powder of the rare earth element oxide are mixed at a desired weight ratio and solidified by hot pressing is housed. An electron gun 5 is provided near the evaporation source 3, and the tablet 4 housed in the evaporation source 3 is provided.
It is designed to irradiate an electron beam to evaporate it. An oxygen gas introduction system 9 is connected to the bottom of the vacuum chamber 2 so that oxygen gas is introduced into the vacuum chamber 2.

Next, the manufacturing method of the present invention will be described.

As shown in the figure, first, the vacuum chamber 2
To a high vacuum (10 ⁻⁶ to 10 ⁻⁷ To by vacuum evacuation system 10).
rr), and at the same time, the plurality of substrates 7 attached to the substrate holder 6 are heated to 100 to 60 by the heater 8.
Heat to 0 ° C range. Next, while irradiating the tablet 4 housed in the evaporation source 3 with an electron beam from the electron gun 5 and introducing oxygen gas from the oxygen gas introduction system 9 into the chamber 2, the tablet 4 is evaporated into fine particles. . The evaporated Si ₃ N ₄ particles combine with oxygen to form Si
_x N _y O _z . Further, the evaporated rare earth element oxide is contained in Si _x N _y O _z , and a Si _x N _y O _z film containing rare earth ions is formed on the substrate 7. Here, the values of x, y, and z of the Si _x N _y O _z film can be adjusted by the substrate temperature, the oxygen gas flow rate, the degree of vacuum, and the gun current of the electron gun. The content of rare earth ions in the Si _x N _y O _z film can be adjusted by the weight ratio of Si ₃ N ₄ of the tablet 4 to the oxide of the rare earth element. For example, since the melting point of Er ₂ O ₃ as an oxide of a rare earth element has a close value, it is vaporized at a similar evaporation rate by electron beam irradiation. Therefore, Si ₃ N ₄ and Er ₂
The film is formed with a composition ratio substantially proportional to the weight ratio of O ₃ . From this, the content of Er ion is from 100ppm to several%
It is easy to control in the range of. As oxides of rare earth elements, Nd ₂ O ₃ and Y other than Er ₂ O ₃ described above can be used.
b ₂ O ₃ , CeO ₂ , Eu ₂ O ₃ , Pr ₆ O ₁₁ , Sm ₂
O ₃ , Ho ₂ O ₃ , Tm ₂ O ₃ or the like can be used. The refractive index of the Si _x N _y O _z film (wavelength 0.63
The value in μm) can be changed from 1.465 to near 2.0 by the values of x, y and z.

Next, FIG. 2 shows a second embodiment of the method for producing a rare earth ion-doped optical waveguide film of the present invention.
This has two evaporation sources 3 and 3a at the bottom of the vacuum chamber 2.
A tablet 4 is provided in each of these evaporation sources 3 and 3a.
And 4a are accommodated, and the tablets 4 and 4a are evaporated by irradiating them with an electron beam from the electron guns 5 and 5a. Si ₃ N ₄ is used for the one tablet 4 as described above, an oxide containing at least one rare earth element is used for the other tablet 4a, and an oxide containing at least one rare earth element is used. What was mentioned above can also be used. In this method, Si _x
The content of rare earth ions in the N _y O _z film is tablet 4
It can be controlled by adjusting the gun current of the electron gun to a. That is, in this method, the evaporation rate of each fine particle can be controlled by adjusting the gun currents of the electron guns 5 and 5a to the tablets 4 and 4a, respectively, and the content of rare earth ions can be easily controlled. You can The partition plate 16 in FIG.
Is for preventing evaporants from one evaporation source from mixing into the other evaporation source. In FIG. 2, the tablet 4 is made of SiO ₂ instead of Si ₃ N _4.
Alternatively, at least one oxide for controlling the refractive index is added to SiO _2.
When the powder containing the seeds and Si ₃ N ₄ are mixed in a desired weight ratio and hardened by hot pressing,
_x N _y O _z in x, y, and more precise control the value of z can be deposited on the substrate 7. This is SiO ₂ and Si ₃
Since the melting points of N ₄ are 1500 ° C. and 1900 ° C. and are relatively close to each other, when the integrated tablet of these is irradiated with an electron beam from an electron gun, it vaporizes in almost the same state. is there. Further, according to the method shown in FIG. 2, it is possible to form a film having a refractive index higher than that of the film obtained by the method shown in FIG.
Further, the addition of the refractive index controlling oxide acts not only for adjusting the refractive index but also for matching the coefficient of thermal expansion between the film and the substrate.

Next, FIG. 3 shows an embodiment of a method of manufacturing an optical waveguide from the optical waveguide film obtained by the above method, which is roughly classified into six processes shown in (a) to (f). Consists of. First, as shown in FIG.
A buffer layer 14 having a refractive index n _b is formed thereon, and a core film (refractive index n _w ) 1 is formed thereon by the method shown in FIGS.
After forming 6, the metal film 17 for the metal mask is formed on the core film 16. Here, the thicker the buffer layer 14 is, the smaller the propagation loss can be made.
The range of 0 and several μm is preferable. The film thickness of the core film 16 is preferably in the range of several μm to several tens of μm for single mode propagation, and in the range of several tens of μm to several tens μm for multimode propagation. Next, in FIG. 3, (b) and (c)
As shown in, a photoresist film is applied on the metal film 17 and exposed to ultraviolet light through a mask to form a photoresist pattern 18 (photolithography process). Then, the photoresist film 18 is used as a mask to etch the metal film. The etching of this metal film is performed by dry etching using NF ₃ gas. Then, as shown in FIG. 3D, the photoresist pattern 18 on the upper surface is removed, and then dry etching is performed using the metal mask pattern 17 to pattern the core film 16 into a substantially rectangular shape. To do. In this case, the etching is performed to such a depth that the buffer layer 14 is also slightly etched. CHF ₃ gas is used for this etching. Then, as shown in FIG. 3E, the metal mask pattern 17 is removed by etching, and finally, as shown in FIG. 3F, the cladding having a value lower than the refractive index n _w of the core film 16 is used. An optical waveguide can be obtained by coating the film 19 (refractive index n _c <n _w ). Here, the formation method of the clad film 19 is plasma CVD, heat C
A manufacturing method such as a VD method, a flame CVD method, a flame deposition method, or a coating method can be used.

Next, FIG. 4 is a sectional view of an optical waveguide which can be realized by the method for manufacturing an optical waveguide of the present invention. The optical waveguide 15a shown in FIG. 4A has a structure in which, for example, quartz glass (quartz, Vycor glass, etc.) is used for the substrate 15, and the buffer layer 20 is also used as the substrate 15. The optical waveguide 15b shown in FIG. 4B has an optical waveguide structure realized by the manufacturing method shown in FIG. 3, and the substrate 15 is made of glass (quartz-based glass, multi-component glass),
Semiconductors (Si, InP, GaAs, etc.), ferroelectrics (L
iNbO ₃ , LiTaO _3, etc.), magnetic substance (YIP, G
GG etc.) can be used, and the degree of freedom in designing the optical waveguide can be expanded. Further, the optical waveguide 15c shown in FIG. 4C has a so-called ridge type optical waveguide structure in which the thickness of the cladding 21 is thin. In this way, the substrate 15 is made of glass (quartz type, multi-component type), semiconductor (Si,
GaAs, InP, etc., ferroelectric gas (LiNbO ₃ ,
Various devices such as LiTaO ₃ ), magnetic materials, sapphire, etc. can be used, so optical devices having various functions (amplification, oscillation, modulation, multiplexing, demultiplexing, distribution, etc.)
Can be manufactured, and a low-priced optical device can be realized by selecting a low-priced substrate.
Further, it is possible to realize a rare earth ion-doped optical waveguide having a low loss and a high relative refractive index difference. For example, excitation light (for example, wavelength 1.48 μm) is introduced into an optical waveguide to which Er ions are added.
By propagating the signal light (light having a wavelength of 1.5 μm band) with the waveguide optical amplifier having a function of amplifying the signal light.

[0024]

In summary, according to the present invention, it is possible to form a core film for an optical waveguide, to which a rare earth ion having a high refractive index is added, on a substrate with a small warp, and to easily control the film thickness and the refractive index. Since it is possible to form a film with good transmittance without the risk of containing impurities, low loss, ultra small size, low cost,
It is possible to manufacture an optical waveguide type circuit with high dimensional accuracy.
It has an excellent effect.

[Brief description of drawings]

FIG. 1 is a schematic view showing an example of a method for producing a rare earth ion-doped optical waveguide film of the present invention.

FIG. 2 is a schematic view showing a second embodiment of the method for producing a rare earth ion-doped optical waveguide film of the present invention.

FIG. 3 is a process drawing showing an embodiment of the method for producing a rare earth ion-doped optical waveguide of the present invention.

FIG. 4 is a cross-sectional view showing a structure of an optical waveguide that can be realized by the method for producing an optical waveguide containing rare earth ions according to the present invention.

FIG. 5 is a process chart showing a conventional method of manufacturing an optical waveguide.

[Explanation of symbols]

 2 Vacuum chamber 3 Evaporation source 4 Tablet 5 Electron gun 7 Substrate

Claims (5)

[Claims] 1. A substrate is placed in an upper portion of a chamber which is being evacuated to a vacuum and is heated, and an evaporation source is placed in a lower portion of the substrate. Si ₃ N ₄ and a rare earth element are placed in the evaporation source. After the oxide powder was mixed in a desired weight ratio and the tablet hardened by the hot press was housed, while introducing O ₂ gas into the chamber, the tablet was irradiated with an electron beam to evaporate it. A method for producing a rare earth ion-doped optical waveguide film, which comprises forming an optical waveguide film of Si _x O _y N _z containing rare earth ions on a substrate. 2. A substrate is placed in an upper portion of a chamber which is being evacuated to a vacuum and heated, and Si ₃ is placed in a lower portion of the substrate.
After arranging an evaporation source containing N ₄ tablets and an evaporation source containing oxide tablets containing at least one kind of rare earth element, while introducing O ₂ gas into the chamber, an electron beam is applied to each of these tablets. Of the rare earth ions on the above substrate by irradiating
A method of manufacturing a rare earth ion-doped optical waveguide film, which comprises forming an optical waveguide film of Si _x O _y N _z containing a seed. 3. A tablet placed in the one evaporation source is SiO ₂ or SiO ₂ instead of Si ₃ N _4.
S containing at least one oxide for controlling the refractive index
_{3. The} method for producing a rare earth ion-doped optical waveguide film according to claim 2, wherein i ₃ N ₄ powder is mixed in a desired weight ratio and hardened by hot pressing. 4. A substrate having a refractive index lower than that of a film formed on the surface thereof, or a substrate on which a layer having a lower refractive index than the film formed on the surface thereof is previously formed as the substrate. The method for producing a rare earth ion-doped optical waveguide film according to claim 1, wherein the optical waveguide film is used. 5. The optical waveguide film obtained by the method according to claim 1, after being processed into a substantially rectangular pattern by photolithography and dry etching,
A method of manufacturing an optical waveguide, characterized in that the surface of the substantially rectangular pattern is coated with a clad film having a refractive index lower than that of the optical waveguide film.