JPH02153329A - Acoustooptic effect type waveguide type frequency shifter - Google Patents

Abstract

PURPOSE:To obtain a sufficient optical frequency shift quantity and eliminate the need for a mode converting element, and to reduce the size of the constitution by propagating surface acoustic waves to both ends of an optical waveguide from both sides of an inter-digital electrode and converting the mode of incident light at least twice. CONSTITUTION:When a voltage is applied to a couple of inter-digital electrodes 14 provided halfway in an optical waveguide 12, the surface acoustic waves 16 and 20 are propagated to both sides of the electrodes 14 toward the end parts of the waveguide 12. The mode of the incident light from one end of the waveguide 12 is converted at least twice with those surface waves 16 and 20 to shift the frequency by acoustooptic effect and projection light which is reconverted to its original mode is projected from the other end of the waveguide 12. The sufficient optical frequency shift quantity is obtained by this acoustic effect type and the need for the mode converting element is eliminated to reduce the size of the constitution of the acoustooptic type waveguide type frequency shifter.

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to a waveguide frequency shifter.

(Prior Art and Problems to be Solved by the Invention) This type of waveguide frequency shifter is used in measurement systems and the like, and shifts the frequency of light.

There are two types of waveguide type frequency filters: electro-optic effect type and acousto-optic effect type.

FIG. 4 is a diagram showing a schematic configuration of an electro-optic effect type waveguide type frequency chic. The waveguide frequency shifter 2 shown in FIG. 4 is configured to have a pair of electrodes 6.6 on both sides of an optical waveguide 4, and to apply an electric field between the electrodes 6.6 using a voltage source 8. There is.

Such an electro-optic effect type waveguide frequency shifter 2
Now, the waveform of the output voltage V output from the voltage source 8 is changed in a sawtooth shape as shown in FIG. It is designed to apply an electric field.

In the waveguide frequency shifter 2 having the above configuration,
A light wave is propagated from one side of the optical waveguide 4 on the left side in the figure to the other side on the right side in the figure, and both electrodes 6.
By applying an electric field between the optical waveguides 6 and 6, the frequency of light that enters from one side of the optical waveguide 4 and is transmitted to the other side is shifted.

By the way, in such a waveguide type frequency shifter 2, in order to increase the shift amount of the optical frequency, it is necessary to repeatedly change the sawtooth output voltage V steeply, but it is necessary to change the sawtooth output voltage V sharply and repeatedly. Due to the influence of this, there was a limit to the steep change, and the maximum frequency shift amount was only about several tens of M82.

FIG. 6 is a diagram showing a schematic configuration of an acousto-optic effect type waveguide frequency shifter. This waveguide type frequency nofter 10 has a configuration in which a pair of comb-shaped electrodes 14.14 are arranged in the middle of an optical waveguide 12, and the pair of comb-shaped electrodes 14.1
By applying a high frequency voltage between the comb-shaped electrodes 14.
A surface acoustic wave 16 is made to propagate onto the optical waveguide 12 on one side (to the right in the figure) from the arrangement location of the surface acoustic wave 14. The surface acoustic wave 16 propagating through the optical waveguide 12 has a periodic structure and is regarded as a diffraction grating having a grating vector of a size corresponding to the period.

Therefore, in such a waveguide type frequency shifter 10, the frequency of the light is softened by the interaction between the surface acoustic wave I6 and the light propagating through the optical waveguide 12.

By the way, in this acousto-optic effect type waveguide frequency shifter 10, as shown in FIG. The light is converted into mode 2 light with a propagation vector β2 obtained by adding the lattice vector k to β1.

Therefore, since the light is mode-converted in the acousto-optic effect type waveguide frequency shifter 10, a mode conversion element is required to convert the light to its original mode. There were problems in that the physical size of the device was increased and the cost was also high.

The present invention has been made in view of the above problems, and is capable of obtaining a sufficient amount of frequency shift of light, and does not require a mode conversion element, which means that the physical size is small and the cost is low. The purpose is to provide a waveguide type frequency shifter.

(Means for Solving the Problems) In order to achieve such an object, in the waveguide type frequency filter of the present invention, the optical waveguide is It has a structure in which a surface acoustic wave is propagated in the direction of each end of the waveguide, and the surface acoustic wave modulates the light incident from one end of the optical waveguide on one side from the pair of comb-shaped electrodes at least twice. It is characterized in that the light is emitted from the other end of the optical waveguide on the other side.

(Function) Since it has a structure in which surface acoustic waves are propagated toward each end of the optical waveguide from each side of the pair of comb-shaped electrodes provided in the middle of the optical waveguide, The light incident from one end of the optical waveguide on one side is mode-converted at least twice by the surface acoustic wave and exits from the other end of the optical waveguide on the other side,
As a result, the amount of frequency shift can be increased as an acousto-optic effect type, and the mode conversion element required in the conventional type is eliminated.

(Example) Hereinafter, an example of the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic diagram of a waveguide type frequency nofter according to an embodiment of the present invention. The waveguide type frequency filter of this embodiment is applied to an acousto-optic effect type. In FIG. 1, parts corresponding to those in the conventional example shown in FIG. 6 are given the same reference numerals. That is, in the waveguide type frequency filter 18 of this embodiment shown in FIG. 1, 12 is an optical waveguide, I4,
14 is a pair of comb-shaped electrodes, and I6 is a surface acoustic wave that propagates through the optical waveguide 12 in the right direction in the figure from the location where the comb-shaped electrodes 14 and 14 are arranged.

The characteristic configuration of the waveguide type frequency shifter 18 of this embodiment is as follows. That is, the waveguide type frequency shifter 18 of this embodiment not only propagates the surface acoustic waves 16 in the right direction from the location where the comb-shaped electrodes 14.degree. It is characterized by propagating 20.

When the surface acoustic wave 16.20 is propagated in both the left and right directions from the location of the comb-shaped electrodes 14.14, the mode of light propagating in the optical waveguide 12 in the right direction is from mode l as explained in the conventional example. Converted to mode 2. and,
The modes of light propagating in the optical waveguide 12 in the left direction are from mode 2 to mode! It will be converted to . therefore,
In the figure, light propagating from the left side to the right side is one surface acoustic wave 2.
0, and then the other surface acoustic wave I6
will be converted to the original mode.

For this reason, the waveguide frequency shifter 18 of this embodiment does not require a mode conversion element.

FIG. 2 is a perspective view showing a specific configuration of a waveguide frequency shifter compatible with TM mode light waves.

In the waveguide type frequency shifter shown in FIG. 2, an optical waveguide I2 is formed across both ends of a substrate 22 made of Y-cut lithium niobate (L i Nb Oa), and an optical waveguide I2 is formed in the center of the optical waveguide 12. A pair of comb-shaped electrodes 14.14 are provided, and a surface acoustic wave absorption layer 24.2 is provided midway on both sides of the optical waveguide 12 with the comb-shaped electrodes 14.14 in between.
4 is provided.

In the waveguide type frequency shifter shown in FIG. 2, when TM mode incident light 26 is input from the left end of the optical waveguide 12, the incident light 26 is converted into TE mode light by the surface acoustic wave 20, and then Surface acoustic waves! 6, the light is converted back to the original TM mode light and is emitted from the right end of the optical waveguide 12 as an emitted light 28. At this time, the emitted light 28
undergoes a frequency shift of twice that of the incident light 26.

FIG. 3 is a perspective view showing a specific configuration of a waveguide frequency shifter compatible with TE mode light waves.

The waveguide frequency shifter shown in FIG. 3 basically has the same configuration as that in FIG. 2, so corresponding parts are given the same reference numerals. In the waveguide frequency shifter shown in FIG. 3, the optical waveguide is located between the surface acoustic wave absorption layers 24 and 24! It is a multi-mode type in which the diameter of the second portion 12a is thick.

That is, in the waveguide type frequency shifter shown in FIG.
2, when TE mode incident light 30 is incident from the left end, the incident light 30 is converted into a plurality of mode lights at surface acoustic waves 16 and 20.

In other words, by changing the frequency of the surface acoustic wave, the incident light 30
is the mode light according to its frequency, for example, the incident light 30 is T
If it is EO mode light, it is converted into various mode lights such as TMO mode, TE first mode, TM first mode, 182nd mode, TM second mode, etc., and then the emitted light 32 becomes TEO mode light. It will be emitted as

The frequency of the output light 32 then undergoes various frequency shifts relative to that of the input light 30.

(Effects of the Invention) As is clear from the above explanation, according to the present invention,
As an acousto-optic effect type, it is not only possible to obtain a sufficient amount of frequency shift of light, but also eliminates the need for a mode conversion element, which is considered a disadvantage of an acousto-optic effect type, resulting in smaller physical size and lower costs. Accordingly, it is possible to provide a waveguide frequency filter that is inexpensive.

[Brief explanation of the drawing]

1 to 3 relate to an embodiment of the present invention, and FIG. 1 is a schematic configuration diagram of a waveguide frequency shifter according to the embodiment, and FIG.
The figure is a specific configuration diagram of the waveguide type frequency filter according to the same embodiment when the incident light is in the TM mode, and FIG.
FIG. 3 is a specific configuration diagram of the waveguide frequency shifter according to the same embodiment in E mode. 4 to 7 relate to conventional examples, FIG. 4 is a schematic configuration diagram of an electro-optic effect type waveguide frequency shifter, and FIG. 5 is an explanation of the operation of the waveguide frequency shifter according to the conventional example. FIG. 6 is a schematic configuration diagram of an acousto-optic effect type waveguide frequency shifter, and FIG. 7 is a diagram for explaining the operation of the waveguide frequency shifter according to the conventional example. 12... Optical waveguide, 14... Comb-shaped electrode, 16.20
...Surface acoustic waves.

Claims (1)

[Claims] (1) It has a structure in which surface acoustic waves are propagated toward each end of the optical waveguide from each side of a pair of comb-shaped electrodes provided in the middle of the optical waveguide, and from the pair of comb-shaped electrodes to one side. An acousto-optic effect type waveguide frequency shifter, characterized in that light incident from one end of an optical waveguide is mode-converted at least twice by the surface acoustic wave, and is emitted from the other end of the optical waveguide on the other side. .