JPS62212631A - Optical multiplexer and demultiplexer - Google Patents

Abstract

PURPOSE:To guide only incident light with specific wavelength out of one waveguide by constituting periodic disturbance of a refractive index which composed of grooves diferring in refractive index periodically between two asymmetrical optical waveguides and arranging electrodes which induce electrooptic effect in the optical waveguides. CONSTITUTION:A buffer layer 4 is formed of silicone oxide, etc., on the surface of a ferroelectric substrate 1 and electrodes 5 and 6 are formed on the top surface on the optical waveguides 2 and 3. Plural rectangular grooves 8 which have specific pitch A in the lengthwise direction are formed between the light guides 2 and 3 on the surface of the ferroelectric substrate 1 and buffer layers 4 are charged in the grooves 8 to form the periodic disturbance 7 of the refractive index. Consequently, the condition of phase matching between waveguide modes is satisfied and only incident light with specific wavelength is guided out of one waveguide. Further, a proper voltage is applied between the electrodes 5 and 6 to vary the wavelength which satisfies the matching condition, thereby varying the wavelength of light to be guided out.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to an optical multiplexer/demultiplexer required for wavelength multiplexed optical transmission, and is particularly suitable for optical integrated circuits used in single mode optical transmission systems. This invention relates to a variable wavelength optical multiplexer/demultiplexer.

[Conventional technology]

Conventionally, as an optical multiplexer/demultiplexer, two asymmetrical optical waveguides are formed on a dielectric substrate, and parameters are set so that the propagation constants of these two optical waveguides are the same at a specific wavelength. One that utilizes directional coupling is known.

[Problem that the invention seeks to solve]

In the conventional optical multiplexer/demultiplexer described above, the center value of the wavelength to be demultiplexed is set only by the refractive index distribution and dimensions of the two optical waveguides, so there is little freedom in designing the multiplexer/demultiplexer circuit. There is a problem.

[Means for solving problems]

The optical multiplexer/demultiplexer of the present invention allows only incident light of an arbitrary wavelength to be -
This makes it possible to extract the light from the optical waveguide.

The optical multiplexer/demultiplexer of the present invention forms grooves with periodically different refractive indexes in parallel between two asymmetric optical waveguides formed on a ferroelectric substrate, and uses this as a periodic perturbation of the refractive index. In addition, each optical waveguide is provided with an electrode that produces an electro-optic effect.

〔Example〕

Next, the present invention will be explained with reference to the drawings.

Fig. 1 is a perspective view of one embodiment of the present invention, and Fig. 2 is its
It is a sectional view along a line.

As shown in the figure, on the surface of a ferroelectric substrate 1 made of L i N b Os with a predetermined thickness, Ti is thermally diffused to form two optical waveguides 2.3 which are asymmetrical, that is, have different cross-sectional dimensions. are doing. Here, each optical waveguide 2.3 is configured to have a tapered shape or a shape close to this. A buffer layer 4 made of silicon oxide or the like is formed on the surface of the ferroelectric substrate 1, and the optical waveguide 2.3 is formed on the upper surface of the buffer layer 4.
Electrodes 5.6 are formed at the upper position. Here, two electrodes 5 and 6 are respectively arranged at appropriate intervals in the length direction of the optical waveguides 2 and 3.

A voltage is applied between these electrodes 5.6 and the substrate 1,
Due to the electro-optic effect according to this voltage, the optical waveguide 2
．． The structure is such that the refractive index of each of the three lenses can be changed.

On the other hand, a plurality of rectangular grooves 8 having a predetermined pitch in the longitudinal direction are formed between the optical waveguides 2 and 3 on the surface of the ferroelectric substrate 1, and the buffer layer is formed in the grooves 8. A periodic perturbation 7 of the refractive index having a configuration filled with 4 is formed. That is, the refractive index of this part is reduced by this groove 8,
A periodic refractive index unevenness is formed between the substrate 1 and the other substrate 1,
This functions as a periodic perturbation of the refractive index.

In this configuration, it is assumed that the input light (1) is incident on one end of the optical waveguide 3, and the output lights Ox, Ox are outputted on the other ends of the optical waveguides 2 and 3, respectively. Here, the input light is λ8
．． It consists of light of N wavelengths λ2...λ9, and the output light 0□ shows the case where only the light of λ7 is demultiplexed. It goes without saying that the output light O1 is light of other wavelengths.

Next, the operating principle of the optical multiplexer/demultiplexer having the above configuration will be explained.

Figure 3 shows the dispersion characteristics d, , d, of the respective waveguide modes of the two optical waveguides 2.3, where C is the speed of light in vacuum, ncl
n! +n3 are respectively substrates 1. This is the refractive index of waveguide 2 and waveguide 3. Now, the wavelength λ7°, that is, the angular frequency ω,
Focusing on the incident light of (-2πC/λ7), the propagation constant β2 of the two waveguides. β.

During this time, a phase difference of Δβ=β, −β2 (1) occurs, and the interaction between the two waveguide modes is very small. Therefore, by supplying a phase difference of Δβ==Δ/2π... (2) by periodic perturbation of the refractive index, the two waveguide modes interact effectively, and the two waveguide modes Periodic power transitions occur.

Therefore, if the periodic perturbation 7 of the refractive index is designed so that the product of the coupling coefficient and the interaction length between the two waveguides 2.3 is (2m+1)Xπ/2, the phase matching condition is satisfied. Only the human power light with wavelength λ7 can be taken out from the other waveguide 2 coupled to the input optical waveguide 3. In this case, if the product of the coupling coefficient and the interaction length does not satisfy the above equation, a voltage may be applied to the electrode 5.6 to satisfy the condition.

According to this configuration, periodic grooves 8 are formed between the two optical waveguides 2.3 of the substrate 1, and the grooves 8 form periodic irregularities in the refractive index, that is, periodic perturbations 7 in the refractive index. By doing so, it is possible to satisfy the phase matching condition between the waveguide modes and extract only the incident light of a specific wavelength from the negative waveguide.

Further, by applying an appropriate voltage to the electrodes 5.6, the wavelength that satisfies the matching condition can be changed, and the wavelength of the light to be extracted can be changed. From a different perspective, this optical multiplexer/demultiplexer can be thought of as a wavelength switching element.

Here, the periodic perturbation of the refractive index may be formed by periodic grooves 8A formed in the buffer layer 4, as shown by reference numeral 7A in FIG. By lowering the refractive index, periodic irregularities in the refractive index are formed.
With this, the same effect as the previous example can be obtained.

Note that by forming the optical waveguide into a tapered structure, it is possible to control the demultiplexed wavelength band, and it is also possible to eliminate polarization dependence.

〔Effect of the invention〕

As explained above, the present invention constitutes a periodic perturbation of the refractive index consisting of grooves with periodically different refractive indexes between two asymmetrical optical waveguides, and each optical waveguide is provided with an electrode that produces an electro-optic effect. This allows it to satisfy the phase matching conditions between the waveguide modes in the two four-wavelength optical waveguides, extract only the incident light of a specific wavelength from the negative waveguide, and apply an appropriate voltage to the electrodes. By doing so, the wavelength that satisfies the matching condition can be changed, and the wavelength of the light to be extracted can be changed.

[Brief explanation of drawings]

FIG. 1 is a perspective view of one embodiment of the present invention, FIG. 2 is a sectional view taken along the on line in FIG. 1, FIG. 3 is a diagram showing the dispersion characteristics of the waveguide mode, and FIG. FIG. 2 is a sectional view similar to FIG. 2; 1... Ferroelectric substrate, 2.3... Optical waveguide, 4...
- Buffer layer, 5.6... Electrode, 7,7A... Periodic perturbation of refractive index, 8,8A... Groove.

Claims (4)

[Claims] (1) In an optical multiplexer/demultiplexer equipped with two asymmetrical optical waveguides formed by thermal diffusion of titanium or the like on a ferroelectric substrate, there is a periodic difference in refractive index between the two optical waveguides in parallel with them. An optical multiplexer/demultiplexer characterized in that grooves are formed to constitute periodic perturbations in the refractive index, and each optical waveguide is provided with an electrode that produces an electro-optic effect. (2) The optical multiplexer/demultiplexer according to claim 1, wherein a plurality of grooves at a predetermined pitch are formed on the surface of a ferroelectric substrate to constitute a periodic perturbation of the refractive index. (3) Optical multiplexing according to claim 1, wherein a plurality of grooves at a predetermined pitch are formed on the surface of a buffer layer provided on the surface of a ferroelectric substrate to constitute periodic perturbation of the refractive index. Duplexer. (4) The optical multiplexer/demultiplexer according to claim 1, which comprises two optical waveguides formed in a tapered shape.