JPS60112004A - Optical waveguide device - Google Patents

Abstract

PURPOSE:To make optical damage hard to occur to an optical waveguide by heating a crystal substrate on which the optical waveguide is formed. CONSTITUTION:The crystal substrate 2 on which the optical waveguide 2 is formed is stored in the space formed of a box type heater 14 and an upper lid 16, and the substrate 2 is heated by the heater. The box type heater is provided with a temperature detecting means such as a thermocouple, and a power source detects, for example, voltage variation from the detecting means and varies the applied voltage to the heater on the basis of the extent of the variation to control the temperature of the substrate within the range of, for example, 80-500 deg.C. The threshold value at which optical damage occurs by the heat is increased to make optical damage hard to occur to the optical waveguide device.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to an optical waveguide device, and particularly to an optical waveguide device in which an optical waveguide is formed on a crystal substrate.

[Prior art]

When trying to realize an optical deflector or optical modulator using an integrated optical structure, the currently widely used optical waveguide substrates have excellent piezoelectricity, photoacoustic effects, electro-optic effects, and low optical propagation loss. Less lithium niobate (hereinafter referred to as LiNbO)
3) crystals and lithium tantalate (hereinafter referred to as LiT)
(denoted as aO3) is made of crystals, etc. In addition, BNN
(Ba2NaNb5015), 5BN(SrxB
a1-xNb206), KTN (K(Ta,
Nb)03), KDP(KH2PO4), B
It is also conceivable to use a strong flange crystal such as 14Ti4012.

A method for forming a thin film optical waveguide on such a crystal substrate is to thermally diffuse titanium (hereinafter referred to as Ti) onto the surface of the crystal substrate to form an optical waveguide layer having a refractive index slightly larger than the refractive index of the substrate. The alternative method is to form a

However, the thin film optical waveguide formed by this method has the disadvantage that it is susceptible to optical damage and can only introduce light with low power into the waveguide. Here, optical damage is defined as [when the intensity of light input to an optical waveguide is increased, the intensity of the light propagated through the optical waveguide and taken out to the outside is proportional to the intensity of the human-powered light due to scattering. ``a phenomenon in which a person's growth stops increasing.''

Such optical damage is thought to occur through the following mechanism. For example, when laser light enters a crystal, its energy excites electrons from impurity levels to the conduction band. Electrons excited to the conduction band drift in the C-axis direction within the crystal. It then falls into a trap near the boundary of the laser beam. By repeating this process, a positively charged part where electrons are lost and a negatively charged part where all electrons are captured are generated, and as a result, the Pockels effect is caused and inside the crystal. The refractive index of changes. Due to this refractive index change, the incident light is scattered, resulting in optical loss and
quotient is caused.

Therefore, such an optical component is not suitable for brazing.
You can see that it can be erased by doing this. That is, the space electroforming is eliminated by raising the temperature of the entire crystal substrate or by detonating carriers by uniform light irradiation.

In fact, heat was applied to the optical waveguide that caused optical damage9.
Alternatively, the optical damage can be eliminated by uniformly irradiating with ultraviolet f/1 light.

However, in any case, it is not possible to provide an optical waveguide that does not cause optical damage, and the methods are limited to workarounds for how to restore an optical waveguide that has suffered optical damage to its original state.

Conventionally, an optical waveguide device that is used while irradiating the optical waveguide with ultraviolet rays has been proposed as an optical waveguide device that is less likely to cause optical damage, but this is not desirable because the device is complicated and there may be stray light other than the guided light. Ta. In addition, it was necessary to take out the waveguide at regular intervals, making maintenance of the device troublesome and rare.

1: Object of the Invention The present invention has been made in view of the above-mentioned conventional problems, and its object is to provide an optical waveguide device in which optical damage to the optical waveguide is less likely to occur.

[Summary of the invention]

In order to achieve the above object, an optical waveguide device according to the present invention is characterized in that a heating means is provided for heating a crystal substrate on which an optical waveguide is formed, and the threshold value at which optical damage occurs is increased by the heat. do.

[Embodiments of the invention]

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

FIG. 1 is a schematic perspective view showing the structure of a substrate on which a thin film optical waveguide is formed. As already mentioned,
A thin film optical waveguide layer 3 (hereinafter referred to as waveguide 3) is formed on the surface of the crystal substrate 20.
) is formed.

FIGS. 2(a) and 2(b) are an exploded configuration diagram and a perspective view of essential parts of a first embodiment of an optical waveguide device according to the present invention.

In the figure, a substrate 1 is housed in a box-shaped heater 4 and fixed with screws 5. The box-shaped heater 4 is heated by a power source (not shown) and heats the substrate 1.

Although this embodiment has a simple structure, since the waveguide 3 is in direct contact with the outside air, the temperature control of the substrate becomes somewhat unstable.

FIGS. 3(a) and 3(b) are an exploded configuration diagram and a perspective view of a main part of a second embodiment of an optical waveguide device according to the present invention,
FIG. 3(c) is a sectional view taken along the line AA in FIG. 3(,). 3(a) and (b), the substrate 1 is fixed to the box heater 4 in the same manner as in FIG. is fixed.

In this embodiment, a case is shown in which the input and output of the laser beam is performed on the upper surface of the waveguide 3, so the upper cover 6 is provided with openings 8p and 9 for introducing and extracting the laser beam. . In this case, a prism coupler, grating coupler, fiber coupler, or the like is used as the optical coupler.

As shown in FIG. 1'g3 (c), the center part of the upper cover 6 is raised one step higher and is separated from the surface of the waveguide 3. The reason for this is that if the top cover contacts the waveguide 3, the waveguide characteristics will change, and also to avoid contact with the electrodes provided on the waveguide 3 when performing optical modulation, optical deflection, etc. be.

FIGS. 4(a) and 4(b) are an exploded configuration diagram and a perspective view of the main parts of the third embodiment, showing a case where laser light is input and output at the end face of the waveguide 3. FIGS. In the figure, a box-shaped heater 10 is provided with openings 11 and 12 for introducing and leading out laser light, and a substrate 1 and an upper lid 13 are each fixed in the same manner as in FIG. 3. Note that as the optical coupler in this case, a butt coupler, end fire coupler, etc. are used.

Next, temperature control when heating the substrate 1 will be explained using the optical waveguide device shown in FIG. 3 as an example.

FIGS. 5(a) and 5(b) show a fourth embodiment of the optical waveguide device according to the present invention, and are an exploded configuration diagram and a perspective view when a thermocouple is used as the temperature detection means. a
) The box-shaped heater 14 is provided with a connector 15, which is connected to a heater (not shown). Board 1
is fixed to the box-shaped heater 14 as shown in FIG. The upper lid 16 is provided with openings 8) and 9 as in FIG. 3, and four heat fixing sockets 17 are attached.

Thermocouple 18 is fixed by socket 17 so as to contact point 19 on waveguide 3 and connected to lead wire 20 . Thermocouples have a small heat capacity and are suitable as temperature sensing means.

In FIG. 5(b), a lead wire 20 connected to the thermocouple 18 is connected to a temperature detection terminal of a temperature control power source 21. In FIG. A connector 22 of a power terminal of a temperature control power source 21 is coupled to the connector 15 of the box-shaped heater 14 to supply current to the heater.

The temperature control power supply 21 detects all voltage changes from the thermocouple 18, changes the voltage applied to the box heater 14 based on the amount of change, and adjusts the temperature of the substrate 1 from 80°C to 500°C.
control within the range of

Note that the upper lid 16 is desirably formed of metal in consideration of thermal conductivity. Further, it is suitable that the surface of the box-shaped heater 14 in contact with the substrate 1 and the surface in contact with the upper lid 16 are also made of metal.

In this embodiment, the structure shown in the figure is set to '-, but it goes without saying that temperature control can be performed in the same way even in the structures shown in FIGS. 2 and 4. be able to.

In addition, the box-shaped heater 4.10 in FIGS. 2 to 5
．． and 14, the temperature of the substrate 1 is set to 80°C as described above.
It only needs to have a capacity that can be controlled in the range of ~500°C, and does not depend on the format. FIG. 6 shows an example of the box-shaped heater 14. Of course, the box-shaped heaters 4 and 14 can also adopt the same configuration. 1 FIG. 6(, ) is a plan sectional view of the box-shaped heater 14, and FIG. 6(b) is a top sectional view of the J-plane. . In FIG. 6, the heater wire 23 connected to the connector 15 is connected to the insulator 2
A metal member 25 is fixed on the insulator 24 to form a box. Therefore, the heat generated by the heater wire 23 is transmitted to the metal member 25 via the insulator 24,
In order to uniformly heat the metal member 25, the substrate 1 housed within the box-shaped heater 14 is heated efficiently and uniformly.

Next, how the optical waveguide device according to the invention is superior to the conventional one will be explained using a specific experimental example.

First, substrate 1 was created as follows.

After polishing one surface of the LiNbO3 crystal substrate (for example, the Y soil surface) with a thickness of 2 in the Y direction and 1 inch in each of the X and 2 directions to a flatness within a few Newton rings, methanol, trichlene, acetone, and pure water were used. The sample was subjected to normal ultrasonic cleaning, dried by blowing room floor gas, and further subjected to beta testing at 120° C. for 20 minutes in nitrogen.

This LiNbO5 substrate is coated with a conventional method (for example, ILL).
A Ti film of 200× was formed by beam evaporation). Subsequently, the LiNbO3 substrate on which the T1 film was formed was placed in a holder made entirely of fused silica, and set in a first thermal diffusion furnace at 965°C. Moist 02 gas as atmospheric gas at 0.5 A
was introduced into the first diffusion furnace at a flow rate of /min.

The temperature inside the furnace was raised by tX gold at a rate of 16°C/min from 4 to 965°C, and after 1 hour the temperature inside the furnace became constant.
It was held at 965°C for 2.5 hours. And the total temperature of the board is 600℃
The sample was then transferred to a second thermal diffusion furnace where it was maintained at .

When the substrate was set in the second diffusion furnace, the supply of electricity to the second diffusion furnace was stopped and the substrate was allowed to cool from 600° C. to room temperature. Board 9
The reason for rapid cooling from 65°C to 600°C is to prevent the formation of LINb50s in the substrate by slow cooling and to form an optical waveguide with low optical propagation loss, which is 1°5 to 1 dB.
If a light propagation loss of about /crn can be tolerated, it may be formed by cooling from 965 °C using a single thermal diffusion furnace.Measure the characteristics of the Ti internally diffused optical waveguide obtained after cooling. Therefore, He of wavelength 6328X is transmitted from the rutile prism.
-When Ne light was introduced and the optical propagation loss was measured, it was 0.3d.
It was found that a high quality optical waveguide of B/cm was fabricated.

A rutile prism was brought into close contact with the thus obtained Ti internally diffused LiNbO3 optical waveguide substrate (ie, substrate 1), and the substrate was placed and fixed in a box-shaped heater.

7(a) and (b) ic are an exploded view and a perspective view of the optical waveguide device shown in FIG. 5, in which the rutile prism 26 is fixed through the apertures 8 and 9 of the optical waveguide device. ing. However, for temperature control, heating means such as the source 21 and thermocouple 18 are not shown.

Subsequently, the box-shaped heater 14 of the optical waveguide device configured as shown in FIG. 7(b) was energized to heat the substrate 1 to 80° C. and maintain it at that temperature. There, the wavelength 6:32 s
f(e-Ne laser light of i was input into the rutile prism 26 of the aperture 8 so that the TFJo mode propagated through the waveguide 3 (input light 27). The optical beam diameter of the input light 27 was 1
It is between.

In order to find out the degree of optical damage, the intensity ratio of the input light 27 and the output light 28 was measured while changing the light intensity of the input light 27. According to this measurement, the conventional waveguide 3 is 0.5m
W artificial light 27 causes optical damage within 10 seconds, whereas the waveguide 31410 mW artificial light 27 in the device according to the invention shown in FIG. 7(b) remains multistable for several hours. It was found that the output light 28 can be obtained. Therefore, regarding optical damage, the optical waveguide in the RTC device of the present invention has an optical damage threshold M which is more than 20 times that of the conventional one.
I will do it.

The next experimental example uses a semiconductor laser with a wavelength of 7800X and a grating coupler as an optical coupler.

As shown in FIG. 8(a) and (b), a grating cover 29 is formed on the substrate 1 formed in the same manner as in FIG. It was configured so that light could enter and exit. However, the heating means is not shown in FIG. 8 as well as in FIG. 7.

As in the experimental example described above, the temperature of the substrate 1 was maintained at 160° C., and the intensity ratio between the human power light 30 and the output light 31 was measured. The results showed that the conventional unheated optical waveguide suffered optical damage within 10 seconds with 1 mW of input light 30 , whereas the optical waveguide in the device according to the invention suffered from 40 mW of input light 30
is multistable and necessarily fc for several hours.

The next experimental example is a comparison when the original deflector was created.

First, the optical waveguide substrate 1 with grating and coupler used in the previous experimental example was washed and dried again.

and positive photoresist) with a T-spinner to a thickness of 1 to 1.
It was spinner-coated to a thickness of 5 μm and exposed in close contact with a negative mask with square-shaped electrodes, so that only the comb-shaped electrode parts remained. After washing with water, drying and loading into a vacuum evaporator, IX
The atmosphere was evacuated to 10-6 Torr, and At (1500× m thick) was deposited by gB evaporation. After evaporation, the At film on the photoresist was removed by lift-off by soaking in acetone for several minutes, leaving only the comb-shaped electrode part as a light guide. Formed on the wave top. The comb-shaped electrode in this case was designed so that the center wavelength of the elastic cloth wave was 600 Ml (z), so the 1d pole width of the comb-shaped electrode and the electrode spacing were both 1.45 μm.
◇In this way, all the comb-forming poles are installed on the V optical waveguide.
The original waveguide was made with an original deflection.

The optical waveguide circular deflector thus obtained was compared under two conditions: one used conventionally at room temperature and one installed in the apparatus according to the present invention.

The input source is f (e-Ne laser gold used, comb type J, 0.6WvRF4 force is applied to the pole/J) with a wavelength of 6328X.
I did 11. When the RF frequency is 600 MHz, the diffraction efficiency is about three times higher for the deflector installed in the device according to the invention than for the conventional one used at room temperature.

In addition, the intensity of the He-Ne laser beam was measured at 1 mW or less, but the intensity was 5 mW, 10 mW,
When the laser light intensity was increased to 15 mW, optical damage occurred even at an input intensity of 5 mW when used at room temperature, and the output light decreased catastrophically. In contrast, with the deflector installed in the device according to the present invention, even when the input intensity exceeded 15 mW, the output light intensity increased in proportion to the input light intensity, and it was found that no optical damage occurred. [Effect of the Invention] As explained in detail above, the optical waveguide device according to the present invention stabilizes an optical modulator, an optical deflector, etc. having an optical waveguide in order to prevent optical damage from occurring in the optical waveguide. This has the great effect of significantly improving performance and reliability across all layers.

[Brief explanation of the drawing]

FIG. 1 is a schematic perspective view of a substrate on which a thin film optical waveguide is formed, FIG. b) is a perspective view of the main part of the first embodiment, FIG. 3(,) is an exploded perspective view showing the main part configuration of the second embodiment of the present invention, and FIG. FIG. 3(c) is a sectional view taken along line A-A in FIG. 3(a); FIG. FIG. 5(b) is a perspective view of the main part of the third embodiment, FIG. 5(a) is an exploded perspective view showing the structure of the main part of the fourth embodiment of the present invention, and FIG. 5(b) is the fourth embodiment. FIG. 6(a) is a plan view of the box-shaped heater, and FIG. 6(b) is a perspective view showing the configuration of the box-shaped heater.
1111 plane cross-sectional view, FIG. 7(a) is an exploded perspective view showing the main part of the fourth real cube example using the prism converter,
FIG. 7(b) is a perspective view of the fourth disaster example using a prism coupler, FIG. 8(a) is an exploded perspective view showing the configuration of the fourth disaster example using a grating coupler, FIG. (b) is a diagram of the fourth example using a grating coupler (shown in perspective view. 1...Substrate, 2...Crystal substrate, 3...Waveguide, 4)
, 10° 14... Box heater, 6.13.16...
Top lid, 18...Thermocouple, 21...4 sources for temperature control, 2
3... Heater wire, 26... Rutile prism, 29
...Grating Kabra. @31Kari (b) in 4 figure (G) 曾6 figure (0) 24 gX6 figure (b)

Claims (4)

[Claims] (1) An optical waveguide device having a crystal substrate on which an optical waveguide is formed, characterized in that a heating means for heating the crystal substrate is provided. (2) The optical waveguide device according to claim 1, wherein the crystal substrate is a ferroelectric material. (3) The optical waveguide according to claim 1, wherein the heating means has a detection means for detecting the temperature of the crystal substrate, and the temperature is controlled based on the detection output of the detection means. Device. (4) The optical waveguide device according to claim 3, wherein the detection means is an fA couple.