JPS60120318A - Optical waveguide - Google Patents

Abstract

PURPOSE:To prevent an optical breakage in an optical waveguide having electro- optic or acousto-optic effect and propagating the waveguide light different from the 1st waveguide light which utilizes said effect through the same optical path. CONSTITUTION:An optical waveguide layer 2 is formed by diffusing Ti, on a substrate 1 made of LiNbO3 crystal, and prism light couplers 3, 4, and 5 and a comb-shaped electrode 6 are formed thereupon. When semiconductor laser light 7 with 780nm wavelength is inputted by the incidence prism photocoupler 3 in the X-axis direction of the optical waveguide 2 on the crystal substrate 1, the waveguide light 8 is diffracted with a surface acoustic wave 9 which is generted by a comb-shaped electrode 6 and propagates in the (z) axi direction of the crystal substrate 1 and projected from the prism photocoupler 5. Then, HeNe laser light 10 for external irradiation which has shorter wavelength of 632.8nm than the laser light 7 is made incident to the optical waveguide 2 by the prism coupler 4 in the (-z) direction of the crystal substrate 1. Consequently, the current density in the optical waveguide 2 in an irradiation direction 7 is increased to prevent an optical breakage.

Description

TECHNICAL FIELD The present invention relates to optical waveguides, and more particularly to optical waveguides for use in integrated optical structures.

[Prior art]

Currently, lithium niobate (hereinafter referred to as LiNb0.) crystal and lithium tantalate (hereinafter referred to as LiTaO3) crystal, which have excellent acousto-optic effect or electro-optic effect and low optical propagation loss, are widely used as optical waveguide substrates. There is.

A typical method for producing a thin film optical waveguide using the crystal substrate is to heat titanium (hereinafter referred to as TI) on the surface of the crystal substrate by thermally diffusing it at high temperature. There is a method (9) of forming an optical waveguide layer having a refractive index slightly larger than that of the substrate. However, thin film optical waveguides fabricated by this method are susceptible to optical damage and have the disadvantage that only light of very low power can be introduced into the waveguide. Optical damage here refers to ``When the intensity of light input to an optical waveguide is increased, the intensity of the light propagating within the optical waveguide and taken out to the outside decreases to the intensity of the input light due to scattering. ``a phenomenon in which it ceases to increase proportionately.''

The above optical damage phenomenon is caused by the LiNbO3 crystal and the L I
Not limited to T aOa crystals, but also barium sodium niobate [hereinafter referred to as B & 2NaNb 5015],
Strontium barium niobate [hereinafter 5rXBa1-
XNb20. (denoted as H), potassium tantalate (hereinafter referred to as K)
TaOs], barium titanate (hereinafter referred to as na4T)
It has also been observed in crystals such as (denoted as i, 0.2), and has become a major problem in producing various waveguide-type optical devices that utilize the acousto-optic effect or the electro-optic effect.

Conventionally, in order to reduce this optical damage, a method has been proposed in which light of a shorter wavelength than the laser beam used for the optical waveguide element is irradiated from outside the optical waveguide element (Inventor: Lucero S John A.

EP 0028538 AI). Although the above method reduces optical damage, it has the problems of requiring a large device for irradiating light from the outside, and requiring a large amount of power to irradiate from the outside. Was.

[Object of the present invention]

SUMMARY OF THE INVENTION In view of the above-mentioned prior art, it is an object of the present invention to provide an optical waveguide which is compact and simple in structure and can reduce optical damage with low power consumption.

The above objects are achieved by propagating a second guided light, which is different from the first guided light, using the electro-optic effect or the acousto-optic effect, on the optical path of the first guided light.

[Example of the present invention]

Hereinafter, the present invention will be described in detail using the accompanying drawings.

FIG. 1 shows an optical waveguide according to a first embodiment of the present invention.
2 is a y-plate LINbO crystal substrate, 2 is an optical waveguide layer in which TI is diffused, 3, 4.5 are prism optical couplers, and 6 is a comb-shaped electrode. The crystal substrate or the guiding waveguide is not limited to the above embodiments, but any material that causes optical damage can be used. Semiconductor radar light 7 with a wavelength of 780 nm is inputted into the optical waveguide 2 in the X-axis direction of the polycrystalline substrate 1 by the input prism optical coupler 3, and the guided light 8 is input to the comb-shaped electrode 6.
It is diffracted by the surface acoustic waves 9 generated from the crystal substrate 1 and propagated in the biaxial directions of the crystal substrate 1, and is emitted from the prism optical coupler 5. In the present invention, the inside of the optical waveguide 2 is irradiated by guiding light having a shorter wavelength than the radar light 7, in addition to the laser light 7 for optical deflection or light modulation. In this example, an OHeN laser beam 10 having a wavelength of 632.8 nm was made to enter the optical waveguide through the prism optical coupler 4 in the direction of one or two axes of the crystal substrate l. Laser light for external irradiation 10
1 laser beam for optical deflection or optical modulation without inputting
When only the laser beam was guided into the optical waveguide 2, an optical damage phenomenon occurred when the power of the output radar beam 11 exceeded 0.1 mW/H. However, as shown in the first embodiment of the present invention (
5) As shown, when the external irradiation laser beam IO is incident at a power of 5 mW/11, the output laser beam 11 is No optical damage phenomenon occurred even when the power was 5 rnW/mx. As explained above, in this embodiment, by converting the external irradiation light into guided light, the energy density of the irradiation light within the optical waveguide can be made extremely high, and the consumption of the irradiation light is accordingly increased. This has the effect of reducing power consumption.

Next, we will discuss the second embodiment of the optical waveguide according to the second embodiment of the present invention.
This will be explained using figures. In Fig. 2, 1 is a y-plate LiN
b0. a crystal substrate; 2 is an optical waveguide layer in which TI is diffused; 3;
5 is a prism optical coupler, 6 is a comb-shaped electrode, 15 is a diffraction grating type optical coupler, and 16 is a reflection plate. In the second embodiment, as in the first embodiment, the semiconductor laser beam 7 with a wavelength of 780 nm is applied to the crystal substrate 1! The guided light 8 is input into the optical waveguide 2 by the prism optical coupler 3 in the axial direction, and is diffracted by the surface acoustic wave 9 generated from the comb-shaped electrode 6, and then output from the prism optical coupler 5. do. On the other hand, the wavelength is 632.8
A total of 10 nm HeNe laser beams are made to enter the optical waveguide through the diffraction grating type optical coupler 15 in the direction of one of the two axes (6) of the 10-crystalline substrate 1. On the other hand, since reflection plates 16 are provided on the two end faces of the crystal substrate on the side where the diffraction grating type optical coupler 15 is located and the opposite side, the guided light 12 incident from the diffraction grating type optical coupler 15 is reflected by the reflected light. It is reflected by the plate 16 and propagated in the +Z-axis direction. The reflector plate 16 is prepared by polishing the end face on which the reflector plate is provided.
It was fabricated by depositing a thin film of t. The optical waveguide according to the second embodiment has the effect that the energy density of externally irradiated light can be further increased by providing a reflecting plate on one end face.

Next, regarding the optical waveguide according to the third embodiment of the present invention, the third
This will be explained using figures. In Figure 3, 1 is the X plate LIN
bO, crystal substrate; 2 is optical waveguide layer in which Ti is diffused; 21
．． 22 is a diffraction grating type optical coupler, 6 is a comb-shaped electrode, and 23 is a semiconductor laser with a wavelength of 780 nm. In the optical waveguide of the third embodiment, a semiconductor laser 23 is directly coupled to the polished end face of the optical waveguide facing in the biaxial direction, and the guided light incident from the semiconductor laser light is used as external irradiation light. .

Laser light for polarization or modulation with a wavelength of 830 nm 7
is inputted into the optical waveguide by the diffraction grating type optical coupler 21, and the incident guided wave light 8 is diffracted by the surface acoustic wave 9 generated from the comb-shaped electrode 6, and is output from the diffraction grating type optical coupler 22. Emits light. On the other hand, the directly coupled semiconductor laser 23
The guided light for external irradiation is propagated within the optical waveguide 2 at a horizontal angle that is similar to the divergence angle of the laser, as shown by reference numeral 24 in FIG. Similar to the first embodiment, an optical damage measurement experiment was conducted, and it was found that when the external irradiation laser beam was not added, an optical damage phenomenon occurred when the output power of the deflected or modulated laser beam 11 exceeded 1 mW/gin. On the other hand, when the external irradiation waveguide light 24 is irradiated,
Even when the output power of the laser beam 11 was 10 mW/IBm, no optical damage phenomenon occurred. In order to investigate the relationship between the wavelengths of the external irradiation light and the modulating laser light, we set the wavelength of the modulating laser light to 780 nm, which is the same as that of the external irradiation light.
nm, and optical damage experiments were conducted, but similar to the above results, no optical damage phenomenon was found even when the output power was 10 mW/xi. In addition, the wavelength of the modulating laser light is 632.8 nm, which is shorter than that of the external illumination light (λ-780 nm).
When conducting an experiment with m, optical damage occurs when the output power of the laser beam 11 exceeds 0.2 mW/mm.
It has been found that this method is effective when the wavelength of the guided light for external irradiation is the same as or less than the wavelength of the modulating radar light. It was also found that there is no particular difference between the case where the guided light for external irradiation is propagated in two axial directions and the case where it is propagated in the -Z axis direction. As explained above, the optical waveguide of the third embodiment, like the first and second embodiments, does not require less power consumption for the irradiation light, and the end face of the optical waveguide is Simply couple the semiconductor laser directly to the
It has a simple structure and is compact, which is effective.

Next, regarding the optical waveguide according to the fourth embodiment of the present invention,
This will be explained using figures. In Fig. 4, 1 is an X-plate LiN
b0. 2 is a crystal substrate, 2 is an optical waveguide layer in which TI is diffused, 25 is an electro-optic practical comb-shaped electrode, 23 is (9) a semiconductor laser, 21.22 is a diffraction grating type optical coupler, 1
6 is a reflecting plate. Laser light 7 with a wavelength of 830 nm is input into the optical waveguide through a diffraction grating type optical coupler 21 in the y direction of the crystal substrate, and the incident guided wave light 8 is input into the electro-optic practical comb-shaped electrode 25. The light is diffracted and output from the diffraction grating type optical coupler 22. On the other hand, guided light 24 for external irradiation enters into the waveguide 2 from a semiconductor laser 23 directly coupled to two surfaces of the crystal. Similar to the third embodiment, the guided light 24 is a diverging light. In the fourth embodiment, the end face 26 on the opposite side to the end face where the semiconductor laser is provided is connected to the waveguide light 26.
By setting the curvature so that 4 is specularly reflected and applying a reflective coating to the end face 26, it has become possible to increase the energy density of the guided light for external irradiation. Book 4
It has been confirmed that by using the configuration of the embodiment, the power required for the external irradiation laser 23 is smaller than that of the third embodiment.

Next, an optical waveguide according to a fifth embodiment of the present invention will be explained using FIG. In FIG. 5, l is yt1^8-plate LiNb0. a crystal substrate, 2 a T1 diffused optical waveguide layer, 6
Comb-shaped electrode, 21.22 is a diffraction grating type optical coupler, 23
30 is a semiconductor laser, and 30 is an optical waveguide lens.
As the optical waveguide lens, any one of a Lunebul lens, a geode i, a cleansing lens, and a grating lens may be used, but in this experiment, a Luneble lens made of niobium pentoxide (Nb205) was used. In the case of the third and fourth embodiments, since the guided light for external irradiation is diverging light, there is a drawback that the energy density of the guided light for external irradiation within the optical waveguide is spatially different. Book 5
In the embodiment, in order to solve the above problem, the divergent waveguide light 24 from the directly coupled semiconductor laser 23 is converted into parallel waveguide light 31 using an optical waveguide lens 30,
Since the optical waveguide 2 is irradiated, the energy density of the irradiated light becomes uniform.

Next, a leading waveguide according to a sixth embodiment of the present invention will be explained using FIG. 6. In FIG. 6, 1 is a y-plate LiNb0.
A crystal substrate, 2 a Ti diffused optical waveguide, 3 and 5 a prism optical coupler, and 6 a comb-shaped electrode. In the first to fifth embodiments, the propagation direction of the guided light for external irradiation was perpendicular to the propagation direction of the laser beam 7 to be deflected or modulated, but as shown in the sixth embodiment, the above-mentioned The propagation direction of the laser beam 7 and the propagation direction of the guided light for external irradiation may be the same. As shown in FIG. 6, a laser beam 7 with a wavelength of 780 nm for deflection and a wavelength 6 for external irradiation are used.
The 32.8 nm laser beam 35 is guided into the optical waveguide 2 by the same input prism optical coupler 3. In this case, since the laser beam 7 and the external irradiation laser beam 350 have different wavelengths, the angles at which they enter the prism optical coupler 3 are different. The guided light 8 of the laser light 7 is incident on the surface acoustic wave 9 generated from the comb-shaped electrode 6 at the Black angle, so that it is diffracted and output from the prism optical coupler 5 . On the other hand, the guided light 36 of the laser light 35 for external irradiation is guided across the entire propagation path of the guided light 8, and similarly exits from the prism optical coupler 5. A portion of the guided light 36 is also diffracted by the surface acoustic wave 9, but since the guided light 8 and the guided light 36 are emitted from the prism optical coupler 5 at different angles, the emitted laser light 11 is deflected or modulated. does not imply.

The sixth embodiment has the advantage that it requires the simplest configuration because it does not require any other optical coupler or optical waveguide lens in addition to the input/output optical coupler.

[Effects of the present invention]

In the optical waveguide of the present invention as described above, optical damage can be reduced with a simple and compact element structure and with extremely low power for external light irradiation.

[Brief explanation of drawings]

1 to 6 are all schematic diagrams showing embodiments of the optical waveguide according to the present invention. In each figure, l is the substrate, 2 is the optical waveguide, 3°4.5 is the prism optical coupler, 6 is the comb-shaped electrode, 7 is the incident laser beam, 8 is the guided light, 9 is the surface acoustic wave, and 10 is external illumination. 11 is the output laser beam, 12 is the guided light, 15
, 21 and 22 are diffraction gratings (13) and optical couplers, 16 is a reflection plate, 23 is a semiconductor laser,
30 is an optical waveguide lens. (IA'+ 1st Figure 1i 2 Figure 3 Figure 1 Figure II4

Claims (1)

Scope of Claims: (1) In an optical waveguide having an electro-optic effect or an acousto-optic effect, a second guided light different from the first guided light that utilizes the effect is transmitted to the first guided light. (2) irradiating the entire optical path of the first guided wave with the second guided wave;
Optical waveguide in the first term. (3) The guiding waveguide according to item 1, wherein the wavelength of the first guided light is longer than or equal to the wavelength of the second guided light. (4) It has an end face structure in which the propagation direction of the first guided light and the propagation direction of the second guided light are different, and the second guided light is specularly reflected, and the end face is coated with a reflective coating. Optical waveguide in the first term. (5) Using a semiconductor laser as a light source of the second waveguide light,
2. The optical waveguide according to item 1, wherein the semiconductor laser is provided on an end face of the optical waveguide. (1) (6) The optical waveguide according to item 5, wherein an optical waveguide lens is provided at a position where the diverging light of the semiconductor laser can be converted into parallel light. (7) The optical waveguide according to item 1, in which both the first guided light and the second guided light are input and output through the same optical coupler.