JPH06183751A - Production of optical waveguide film - Google Patents

Abstract

PURPOSE:To obtain an optical waveguide film useful for an optical amplifier and laser by carrying out film formation by plasma CVD with a quartz glass to which an org. compd. of a rare earth element has been added. CONSTITUTION:When a rare earth element-added quartz glass film is formed, an org. compd. of the rare earth element is used as starting material for adding the rare earth element and film formation is carried out by plasma CVD to obtain the objective optical waveguide film. A beta-diketone compd. represented by the formula (where X is a rare earth element and each of R and R' is an alkyl) may be used as the org. compd. Silance (SiH4) or an org. compd. of silicon such as tetraethoxysilane as a silicon source and pure oxygen or nitrous oxide (N2O) as oxygen source are suitable for use as starting materials for the quartz glass film. This optical waveguide film preferably contains P, Al, etc., as constituents because it is used for an optical amplifier and laser.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical waveguide film used for optical communication, optical signal processing, waveguide type optical components for optical measurement, and more specifically, a rare earth-doped silica optical fiber used for lasers and optical amplifiers. The present invention relates to a method for manufacturing a wave film.

[0002]

2. Description of the Related Art For example, a rare earth-doped oxide glass optical waveguide film represented by erbium (Er) has a laser transition wavelength in an optical communication wavelength band (1.3 μm band, 1.5 μm band, etc.). Has been considered promising for use in waveguide-type optical components such as lasers and optical amplifiers, and research for practical use is currently underway.

In practical use of a rare earth-doped optical waveguide film as an optical component, improvement of the gain per pumping light intensity is a problem. To this end, the power of pumping light is reduced by reducing the size of the waveguide. It has been theoretically and experimentally pointed out that it is very effective to substantially increase the density.

Conventionally, as a method of forming a rare earth-doped optical waveguide film using a thin film technique essential for reducing the waveguide size, Er is known.
Only one example is reported by the sputtering method with addition of. In the method of forming the rare earth-doped optical waveguide film by the sputtering method with Er added, the fluorescence lifetime is relatively long, so that the waveguide material is SiO ₂ · Na ₂ O _0.20 · CaO _0.
A multi-component glass with a composition of _.117 · Er _0.028 is selected.
This glass target is sputtered on the thermal oxide substrate by a magnetron sputtering device to form an optical waveguide film. Then, after film formation, heat treatment is performed at 600 ° C. to improve film quality. Further, a waveguide pattern is formed by an ion beam etching method, silicon gel is applied as an upper clad layer, and E
Create an r-doped optical waveguide. The core size of the waveguide is 1.3 μm in height × 6 μm in width, and a small-sized waveguide is realized.

[0005]

However, in the waveguide formed by the method for forming the rare earth-doped optical waveguide film by the above-mentioned sputtering method, the following is caused by the relationship between the glass composition itself and the film-forming technique called the sputtering method. There is a problem in the manufacturing method. First of all, since the glass composition is complicated and the expansion coefficient is large, it is usually difficult to make a large-sized glass target. Secondly, the film formation rate must be suppressed to 50 A / min at the maximum so that the target does not crack thermally during film formation. And thirdly, during processing, Na ₂ O, CaO and Er
In order to remove the above component, there is no choice but to rely on a physical method such as an ion beam etching method, which causes a restriction on the processing method.

Also in the optical characteristics of the waveguide, the scattering loss is as large as about 1 dB / cm due to internal scattering due to the complexity of the composition, and in order to compensate for this loss as an amplifier, it is 7-8 wt%, which is higher than usual. There is a problem in that Er must be added in an amount that is an order of magnitude higher. Actually, the actual situation is that a substantial signal light gain has not yet been obtained even with the above addition amount.

The present invention is intended to solve such problems, and it is a problem of manufacturing restrictions in an Er-doped multi-component glass optical waveguide formed by a sputtering method, and optical scattering loss of the waveguide. Er which has the characteristics of optical gain and signal light gain, is relatively easy to manufacture, and has optical optical quality.
It is an object of the present invention to provide a method for producing an optical waveguide film that can be used in a rare earth-doped optical waveguide represented by.

[0008]

The method for producing an optical waveguide film of the present invention for achieving the above object is a silica glass film to which a rare earth element is added, wherein an organic compound of a rare earth element is used as a raw material for adding the rare earth element. It is characterized by being used and forming a film by a plasma CVD method.

Further, the method for producing an optical waveguide film of the present invention is characterized in that an organic compound of a rare earth is used as a raw material for adding the rare earth and the film is formed by a low pressure CVD method.

In this case, the rare earth organic compound usable in the present invention is represented by the general formula X (RCOCHCOR ').
Examples include β-diketone compounds represented by ₃ (where X is a rare earth and R and R ′ are alkyl groups), and any rare earth organic compound.

As the β-diketone compound, those having volatility and capable of being transported by sublimation are preferable, and specifically, 2,2,6,6-tetramethyl-3,5-heptanedionerbium (Er (DPM) ₃ ), 1, 1, 1,
Examples include 5,5,5-hexafluoro-2,4-pentanedione erbium (Er (HFA) ₃ ).

On the other hand, as a raw material of the quartz glass film used in the present invention, silane (SiH ₄ ) or an organic compound of silicon (for example, tetraethoxysilane (TEOS)) is used as a silicon source, and pure oxygen (is used as an oxygen source). O ₂ ) or nitrous oxide (N ₂ O) are preferred. Further, from the application fields of laser and optical amplifier, it is preferable that the present glass film contains phosphorus, aluminum or the like as a component. As a phosphorus source, phosphine (PH ₃ ) or an organic compound of phosphorus (for example, phosphorus alkoxide (PO (OC
H _{3) 3} or _{PO (OC 2 H 5) 3} )), an organic compound of aluminum in aluminum source (e.g. aluminum alkoxide (Al (OCH _{3) 3} or Al (OC ₂ H _5)
3 ) or β-diketone compounds (Al (DPM) ₃ or Al (HFA) ₃ ) are preferred.

The mixing ratio of the above-mentioned rare earth organic compound represented by Er with respect to the glass raw material is the addition concentration of the rare earth corresponding to the characteristics required for the finally obtained optical waveguide film, and the kind of the above-mentioned mixed raw material. It is decided in consideration of such conditions.

[0014]

Embodiments of the present invention will now be described in detail with reference to the drawings.

FIG. 1 is a schematic configuration of an apparatus used for forming an optical waveguide film for carrying out the method for manufacturing an optical waveguide film according to the first embodiment of the present invention. FIG. 2 shows the prepared Er-doped optical waveguide. A graph of the propagation loss characteristic of the waveguide, and FIG. 3 is a graph of the signal light gain characteristic of the Er-doped optical waveguide with respect to the pumping light intensity.

In this embodiment, an example of forming a film by a plasma CVD method using erbium (Er) as a rare earth element is shown. As shown in FIG. 1, 1 is a glass raw material supply unit, 2 is a supply pipe system, 3 is an Er organic compound supply unit, 4A is a counter electrode (high frequency side), 4B is a counter electrode (ground side), and 5 is a vacuum chamber. , 6 is an exhaust system, 7 is a pressure regulating valve, 8 is a substrate, 9 is a heating power source, 10 is an internal heater, and 11 is a high frequency power source.

The optical waveguide film is formed as follows using this optical waveguide film forming apparatus. First, raw materials such as silicon, oxygen, phosphorus, and aluminum are supplied in the glass raw material supply unit 1. If this raw material is a liquid raw material, it is evaporated by a bubbler, and if it is a solid raw material, it is sublimated, and both are sent to the supply piping system 2 by a carrier gas. Also, Er
An Er organic compound raw material such as (DPM) ₃ is sublimated in the Er organic compound supply unit 3 at a temperature of room temperature or higher and 350 ° C. or lower and sent to the supply pipe system 2 by a carrier gas. These raw materials are merged in the supply piping system 2 and introduced into the vacuum chamber 5 through the gas blowing holes of the counter electrode (high frequency side) 4A. The pressure inside the vacuum chamber 5 is adjusted to a constant value between 0.1 and 10 Torr by a pressure adjusting valve 7 attached to the exhaust system 6.

The substrate 8 is the other counter electrode (ground side).
Internal heater 1 attached to 4B and connected to heating power source 9
It is heated to a constant temperature in the range of 300 ° C to 500 ° C.

By applying a high frequency of 13.56 MHz to the counter electrode (high frequency side) 4A by the high frequency power supply 11 in such a state, plasma is formed between the counter electrodes, and the introduced raw material is decomposed in the plasma. A glass film is deposited on the substrate 8 by bonding. This deposition rate is typically
It is in the range of 200 to 400 A / min, which is considerably faster than that of the conventional multi-component glass sputtering technique.

Next, the deposited glass film is heated to a temperature (400 ° C. to 110 ° C.) higher than the above film forming temperature (substrate heating temperature).
The film is densified and stabilized by heating at a constant temperature in the range of 0 ° C.), that is, by annealing to obtain a desired optical waveguide film.

Hereinafter, a method of manufacturing an Er-doped optical waveguide using the above-mentioned optical waveguide film will be described, and evaluation results of optical characteristics of the waveguide as an amplifier will be shown.

Here, an example is shown in which a silica-based optical waveguide film containing phosphorus as a component is used for producing an optical waveguide, but the same film forming / processing method is used even when other aluminum or the like is used alone or as a component. Can be used to fabricate an optical waveguide.

In terms of steps, first, a lower clad layer (thickness: 3) having a refractive index equivalent to that of quartz is formed on a silicon substrate by a flame deposition method.
0 μm) was formed. Subsequently, a core layer which is an optical waveguide film was formed by the method of this example. That is, silane and nitrous oxide gas and tetramethoxyphosphate (PO (OCH ₃ ) ₃ ) vaporized at 80 ° C. and transported as a carrier gas.
Er (D
PM) ₃ is introduced into the vacuum chamber of the plasma CVD apparatus, and
The raw material was plasma decomposed at a substrate heating temperature of 00 ° C. to deposit a glass film on the buffer layer. After the deposition, it is heated in an electric furnace in an inert gas at a temperature of 500 ° C. to be densified to form an optical waveguide film having a core layer having an Er addition concentration of 5000 ppm, a thickness of 4 μm and a relative refractive index difference of 1.6%. Filmed Further, the core layer is patterned by the photolithography process and the dry etching process similar to the LSI manufacturing,
Again, the upper clad layer (thickness 30 μm) having the same refractive index as quartz is formed by the flame deposition method, and the waveguide length is 7.5c.
An embedded waveguide having a small core size of m, a height of 4 μm, and a width of 4 μm was produced.

A graph of the propagation loss characteristic of the Er-doped optical waveguide thus manufactured is shown in FIG. From the figure, absorption due to Er ions is seen at a wavelength of 1.53 μm.
The propagation loss of 0.17 dB / cm at 1.40 μm represents the scattering loss due to the waveguide scattering that is not caused by this absorption, and it can be seen that the waveguide of small scattering loss is realized by the method of this embodiment.

In FIG. 3, this Er-doped optical waveguide has a wavelength of 0.
9 is a graph of signal light gain characteristics with respect to pumping light intensity when pumping with a 98 μm titanium sapphire laser and passing signal light with a wavelength of 1.53 μm from a wavelength tunable laser through a waveguide. From the figure, 0 is obtained by compensating for the scattering loss of the waveguide.
It can be seen that the threshold value for the dB gain is as low as 23 mW, and a substantially high gain of 5 dB (0.67 dB / cm per unit length) is obtained with the pump light intensity of 420 mW. Therefore, the method of this embodiment is effective for improving the characteristics of the Er-doped waveguide type laser and the optical amplifier.

FIG. 4 shows a schematic configuration of an apparatus used for forming an optical waveguide film for carrying out the method for manufacturing an optical waveguide film according to the second embodiment of the present invention.

In this embodiment, an example of forming a film by a low pressure CVD method using erbium (Er) as a rare earth element is shown. As shown in FIG. 4, 1 is a glass raw material supply unit, 2 is a supply pipe system, 3 is an Er organic compound supply unit, 6 is an exhaust system, and 7 is an exhaust system.
Is a pressure control valve, 8 is a substrate, 9 is a heating power source, 12 is a quartz tube, 13 is a quartz boat, and 14 is a heater.

The optical waveguide film is formed as follows using this optical waveguide film forming apparatus. First, raw materials such as silicon, oxygen, phosphorus, and aluminum are supplied in the glass raw material supply unit 1. If this raw material is a liquid raw material, it is evaporated by a bubbler, and if it is a solid raw material, it is sublimated, and both are sent to the supply piping system 2 by a carrier gas. Also, Er
An Er organic compound raw material such as (DPM) ₃ is sublimated in the Er organic compound supply unit 3 at a temperature of room temperature or higher and 350 ° C. or lower and sent to the supply pipe system 2 by a carrier gas. These raw materials are merged in the supply pipe system 2 and introduced into the quartz tube 12 through the gas inlet. The pressure inside the quartz tube 12 is adjusted to a constant value between 0.1 and 10 Torr by a pressure adjusting valve 7 attached to the exhaust system 6.

The substrate 8 is placed on the quartz boat 13,
The heater 14 connected to the heating power source 9 heats at a constant temperature in the range of 300 ° C to 900 ° C. By this heating, the introduced raw materials are once pyrolyzed and bonded again on the substrate to deposit a glass film having a desired composition. Deposition rates are typically in the range of 300 to 600 A / min, much faster than with conventional multi-component glass sputtering techniques.

Next, the deposited glass film is heated to a temperature (400 ° C. to 110 ° C.) higher than the above film forming temperature (substrate heating temperature).
The film is densified and stabilized by heating at a constant temperature in the range of 0 ° C.), that is, by annealing to obtain a desired optical waveguide film.

The manufacturing process of the Er-doped optical waveguide using the above-mentioned optical waveguide film is the same as that of the above-mentioned embodiment except for the core layer forming process. Therefore, here, the core layer formed by the low pressure CVD method is used. Only the forming process will be described in detail.

Gases of cyan, pure oxygen and phosphine (PH ₃ ) and Er (DPM) ₃ sublimated at 140 ° C. and transported as a carrier gas were used as raw materials, and the gas was introduced into a quartz tube of a low pressure CVD apparatus. By introducing and heating the substrate to a temperature of 600 ° C. by a heater, the raw material was thermally decomposed to deposit a glass film on the buffer layer. Then, after the deposition, it is annealed in an electric furnace at a temperature of 700 ° C. in an electric furnace to be densified, and the Er addition concentration is 5000 ppm.
An optical waveguide film having a core layer having a thickness of 4 μm and a relative refractive index difference of 1.6% was formed.

The final optical waveguide has a waveguide length of 7.5 cm,
It is a buried waveguide having a small core size of 4 μm in height and 4 μm in width.

The present waveguide exhibits the same propagation loss characteristics and signal light gain characteristics as those in FIGS. 2 and 3 described in the above-mentioned embodiment, and an optical waveguide having a low signal loss and a high signal gain can be obtained. I understand. Therefore, the method of manufacturing the optical waveguide film of this embodiment by the low pressure CVD method is also effective for improving the characteristics of the Er-doped waveguide laser and the optical amplifier.

[0035]

As described above in detail with reference to the embodiments, according to the method for producing an optical waveguide film of the present invention, in the rare earth-added silica-based glass film, a rare earth element is used as a raw material for adding the rare earth element. Plasma CVD using organic compounds
Method or low pressure CVD method, the film formation and processing are easy in the manufacturing method, and a rare earth-doped optical waveguide film with small scattering loss can be produced optically. It is possible to improve the characteristics. Further, since the CVD method, which is a non-equilibrium thin film technology, is used, it is easy to increase the concentration of phosphorus or aluminum and reduce the waveguide size, and further improvement in characteristics can be expected. Furthermore, the reduction of the waveguide size enables a single mode, and the characteristics of optical circuits such as a laser and an optical amplifier can be stabilized.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an apparatus used for forming an optical waveguide film for implementing an optical waveguide film manufacturing method using a plasma CVD method according to a first embodiment of the present invention.

FIG. 2 is a graph showing a propagation loss characteristic of an Er-doped optical waveguide manufactured by the optical waveguide film of the present invention.

FIG. 3 is a graph showing signal light gain characteristics with respect to pumping light intensity of an Er-doped optical waveguide manufactured by the optical waveguide film of the present invention.

FIG. 4 is a plasma low pressure CVD according to a second embodiment of the present invention.
It is a schematic block diagram of the apparatus used for film-forming of the optical waveguide film for enforcing the manufacturing method of the optical waveguide film using the method.

[Explanation of symbols]

 1 Glass Raw Material Supply Section 2 Supply Piping System 3 Er Organic Compound Supply Section 4A Counter Electrode (High Frequency Side) 4B Counter Electrode (Ground Side) 5 Vacuum Chamber 6 Exhaust System 7 Pressure Adjustment Valve 8 Substrate 9 Heating Power Supply 10 Internal Heater 11 High Frequency Power Supply 12 Quartz tube 13 Quartz boat 14 Heater

Claims (2)

[Claims] 1. A method for producing an optical waveguide film, comprising forming a rare earth-added quartz glass film by a plasma CVD method using an organic compound of a rare earth as a raw material for adding the rare earth. 2. A method for producing an optical waveguide film, comprising forming a rare earth-added quartz glass film by a low pressure CVD method using a rare earth organic compound as a raw material to which the rare earth is added.