JPH1123890A - Laser wavelength stabilizing element and method of manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable the adjustment of a filter characteristic at an arbitrary wavelength so that the intensity of optical signal transmitted through the filter becomes a zero point wavelength by coating a partial section of at least one optical waveguide from among two optical waveguides with an organic material or a glass material having high refractive index. SOLUTION: A branching interference type wavelength filter is formed by a branching device 20, a multiplexer 21 and two asymmetric optical waveguides 3, 4 whose lengths are different from that of the composition (material) of an optical waveguide. A coating part 25 coated with an organic or glass material is formed in a part of two asymmetric optical waveguides 3, 4, whose lengths are different from that of the composition of an optical waveguide. When an organic material or a glass material having higher refractive index than air exists on the surface being in contact with a core layer in which a light beam propagates in the optical waveguides 3, 4, a photosensitive equivalent refractive index is increased. Then, the phase of light propagating through the optical waveguides 3, 4 is changed and the intensity of optical signal transmitted through the branching interference type wavelength filter is shifted in reference to the wavelength.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser wavelength stabilizing element and a method of manufacturing the same, and more particularly, to stabilizing a laser at an arbitrary wavelength by partially changing the refractive index of an optical waveguide. And a method of manufacturing the same.

[0002]

2. Description of the Related Art A branch interference type wavelength filter is an optical filter that utilizes an interference effect that occurs when light is branched into two asymmetric optical waveguides and multiplexed again. As shown in FIG. 8, by differentially detecting the output light output from the branch interference type wavelength filter, the intensity of the filter transmitted light signal 1 transmitted through the branch interference type wavelength filter becomes sinusoidal with respect to the wavelength. Change.

In a laser using a laser wavelength stabilizing element constituted by this branch interference type wavelength filter, if the stabilized wavelength of the laser beam is the wavelength (λ _A ) shown in FIG. The deviation of the oscillation wavelength from _A ) is detected as a change in the intensity of the signal transmitted through the filter from the zero-point wavelength position, and the laser light wavelength is stabilized by applying feedback to the laser.

At this time, the stabilized wavelength 2 which is the wavelength (λ _A )
However, if the position deviates from the zero-point wavelength position of the sine wave function (filter transmitted light signal intensity function), the operation of the feedback system becomes very complicated, but it is stabilized near the zero-point wavelength position of the sine wave function. Is performed, a large change in light intensity is obtained with respect to a small deviation in oscillation wavelength, and highly accurate wavelength stabilization can be realized.

In the conventional laser wavelength stabilizing element constituted by the branch interference type wavelength filter, when the intensity of the optical signal transmitted through the filter is stabilized at the zero-point wavelength position, the filter characteristics are controlled by adjusting the temperature of the entire element. The stabilization wavelength 2 is controlled so as to be at the zero-point wavelength position of the filter transmitted light signal intensity. This uses the temperature dependence of the refractive index of a branching interference type wavelength filter to change the refractive index of the optical waveguide by changing the temperature of the entire device, thereby moving the zero-point wavelength position to an arbitrary wavelength. It is.

When the refractive index is changed, the peak wavelength of the light transmitted through the filter of the branching interference type wavelength filter shifts, so that the zero-point wavelength position of the intensity of the signal transmitted through the filter can be shifted to the stabilized wavelength 2. . In a quartz optical waveguide, the temperature dependence of the wavelength of light is about 0.01 nm / ° C., and in a semiconductor optical waveguide, it is 0.1 nm / ° C.
The temperature dependence of the refractive index is used to adjust the filter characteristics to a stabilized wavelength.

[0007]

However, in the above-described method, when the filter characteristics of each of the branch interference type wavelength filters, which are laser wavelength stabilizing elements, are different due to an element manufacturing process error or the like, the individual laser wavelengths are different. It was necessary to adjust the temperature of the stabilizing element at different set temperatures. Therefore, a separate temperature control circuit is required for each laser wavelength stabilizing element.

In optical wavelength division multiplexing communication and the like, in order to stabilize the wavelengths of a large number of laser lights, it is desired to stabilize a plurality of laser light wavelengths collectively by one temperature control circuit. For this reason, there has been a demand for controlling the refractive index by a method other than temperature adjustment and finely adjusting the filter characteristics between different laser wavelength stabilizing elements.

Further, by using a semiconductor optical waveguide as the two optical waveguides and making the compositions (materials) and the lengths of the two optical waveguides different from each other, a branch interference type wavelength filter (hereinafter, referred to as a wavelength filter) independent of temperature. A temperature-independent semiconductor wavelength filter).

FIG. 9 is a top view showing a schematic configuration of the temperature-independent semiconductor wavelength filter. As shown in the figure, the temperature-independent semiconductor optical filter is composed of a splitter 20, a multiplexer 21, and two asymmetric optical waveguides (3, 4) having different compositions and lengths of optical waveguide materials. .

In this temperature-independent semiconductor wavelength filter, when the temperature changes, the refractive index of the optical waveguide (3, 4) changes, and the phase of the propagating light changes. However, the difference between the change in the refractive index of the two optical waveguides (3, 4) and the difference in the length is such that the phase relationship is changed when the two lights are multiplexed by the multiplexer 21. , The phase relationship of the transmitted light passing through the temperature-independent semiconductor wavelength filter becomes constant without depending on the temperature.

For this reason, even if the temperature is changed to move the zero-point wavelength position of the intensity of the signal transmitted through the filter of the temperature-independent semiconductor wavelength filter to a specific wavelength, the filter characteristics do not depend on the temperature. Impossible.

As described above, in the temperature-independent semiconductor wavelength filter, since the filter is designed so that the temperature dependency becomes zero, the conventional method of adjusting the filter characteristics by temperature adjustment cannot be applied at all. There was a point.

As described above, in a branch interference type wavelength filter having a temperature dependence or a semiconductor wavelength filter having no temperature dependence, the refractive index of an optical waveguide is changed by a method other than utilizing the temperature dependence. It has been desired to vary the filter characteristics.

SUMMARY OF THE INVENTION The present invention has been made to solve the problems of the prior art, and an object of the present invention is to provide a laser wavelength stabilizing element comprising a branch interference type wavelength filter and a method of manufacturing the same. It is an object of the present invention to provide a technique capable of adjusting a filter characteristic so that an intensity of a signal transmitted through a filter becomes a zero-point wavelength at an arbitrary wavelength.

The above and other objects and novel features of the present invention will become apparent from the description of the present specification and the accompanying drawings.

[0017]

SUMMARY OF THE INVENTION Among the inventions disclosed in the present application, the outline of a representative one will be briefly described.
It is as follows.

In a laser wavelength stabilizing element comprising a branching interference type wavelength filter having two optical waveguides having different lengths or different refractive indexes, at least one of the two optical waveguides has It is characterized in that some sections are coated with an organic material or a glass material having a high refractive index.

In a laser wavelength stabilizing element composed of a branch interference type wavelength filter having two optical waveguides having different lengths or different refractive indexes, at least one of the two optical waveguides has An electric field application electrode for applying an electric field is provided in some sections.

In a laser wavelength stabilizing element comprising a branching interference type wavelength filter having two optical waveguides having different lengths or different refractive indexes, at least one of the two optical waveguides has A temperature control unit is provided in some sections.

A laser wavelength stabilizing element comprising a branching interference type wavelength filter having two optical waveguides having different lengths or different refractive indexes, wherein at least one of the two optical waveguides has an optical waveguide. In a method of manufacturing a laser wavelength stabilizing element in which a portion of a waveguide is coated with an organic material or a glass material having a high refractive index, a predetermined portion is coated with an organic material or a glass material, then cleaved, and then coated. And removing the organic material or the glass material.

That is, the present invention is most suitable for stabilizing control of the wavelength of a laser beam by partially changing the refractive index of at least one of the two optical waveguides constituting the branching interference type wavelength filter. The filter characteristic is adjusted (moved) to the state. This makes it possible to stabilize the wavelength of laser light at a constant wavelength irrespective of errors in the device manufacturing process. It is possible to stabilize with high accuracy.

[0023]

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

In all the drawings for describing the embodiments, those having the same functions are denoted by the same reference numerals, and their repeated description will be omitted.

[First Embodiment] FIG. 1 is a top view schematically showing the configuration of a laser wavelength stabilizing element according to an embodiment of the present invention.

The branch interference type wavelength filter according to the present embodiment also includes a splitter 20, a multiplexer 21, and two asymmetric optical waveguides (3, 3) having different lengths from the composition (material) of the optical waveguide material.
4). However, in the present embodiment, the coating portion 25 in which the organic material or the glass material 5 is coated is formed on a part of the two asymmetric optical waveguides (3, 4) having different compositions and lengths of the optical waveguide material. .

FIG. 2 is a sectional view showing a schematic configuration of the coating section 25 shown in FIG.

As shown in the figure, the core layer 7 of the optical waveguide in which light is confined is surrounded by cladding layers (6, 8) having a smaller refractive index than the core layer. The light seeps into the cladding layers (6, 8) having a small refractive index, and the refractive index (equivalent refractive index) that is actually affected by the light is the cladding layer (6, 8).
It varies depending on the refractive index of 8) and the shape of the optical waveguide (3, 4).

In this embodiment, an organic material or a glass material 5 is coated on a part of the two asymmetric optical waveguides (3, 4) in the branch interference type wavelength filter. Core layer 7 through which light propagates in optical waveguides (3, 4)
On the surface in contact with
Organic material or glass material having a higher refractive index than air 5
Is present, the equivalent refractive index felt by light increases.

When the equivalent refractive index of the optical waveguides (3, 4) changes, the phase of the light propagating in the optical waveguides (3, 4) changes, and the intensity of the optical signal transmitted through the branch interference type wavelength filter changes. , Shift with respect to wavelength. By utilizing this change, the zero-point wavelength position of the filter transmitted light signal intensity can be moved to a wavelength stabilization point.

Here, to adjust the wavelength stabilization point, it is necessary to shift the filter characteristic by several tens to several hundreds of GHz. The change in the refractive index of the optical waveguide (3, 4) required for this change is as follows. 10 to ⁴ of the order. On the other hand, the effect of canceling the peak spacing of filter characteristics, which is an important element characteristic of the laser wavelength stabilizing element, and the effect of temperature dependence is reduced by the optical waveguide (3, 4).
Is determined on the order of 10 to ² of the refractive index. For this reason, if the equivalent refractive index of the optical waveguides (3, 4) is slightly changed, the wavelength dependence of the light transmitted through the filter can be adjusted without substantially affecting the important characteristics of the laser wavelength stabilizing element. It is possible to do.

When coating a part of the branching interference type wavelength filter with the organic material or the glass material 5, if the coating is performed after measuring the filter characteristics, the organic material or the glass material adheres also to the end face of the optical waveguide,
It becomes difficult for light to enter the branching interference type wavelength filter. In order to prevent this, an organic material or a glass material 5 is coated in advance before the element is cut out by cleaving, and then cleaving for exposing the end face of the optical waveguide is performed. Adjustment of the filter transmission characteristics with respect to wavelength can be performed by removing the coated material by an arbitrary area.

In this case, since the organic material or the glass material 5 can easily remove an arbitrary area with oxygen plasma, fluoride gas plasma or the like after the deposition, the filter characteristics can be easily controlled. Therefore, it is possible to easily adjust the wavelength stabilization point to an arbitrary wavelength.

Although FIG. 1 shows the case of a high-mesa type optical waveguide, a ridge type or buried type optical waveguide may be used as long as the coating material is located in the filter portion sufficiently close to the core layer. In addition, the coating unit 25
May be provided in one of the optical waveguides (3 or 4).

[Embodiment 2] FIG. 3 is a top view schematically showing the configuration of a laser wavelength stabilizing element according to another embodiment of the present invention.

As shown in the figure, in this embodiment, an electric field application electrode 9 is provided on a part of two asymmetric optical waveguides (3, 4) having different compositions and lengths of the optical waveguide material. is there. The refractive index of a semiconductor changes when an electric field is applied. For this reason, when the optical waveguides (3, 4) are semiconductor optical waveguides, a voltage is applied to the electric field application electrode 9 provided in a part of the optical waveguides (3, 4), whereby the optical waveguides (3, 4) are formed. 4) It is possible to slightly change the equivalent refractive index.

When the equivalent refractive index of the optical waveguides (3, 4) changes, the phase of the light propagating in the optical waveguides (3, 4) changes, and the intensity of the optical signal transmitted through the branch interference type wavelength filter changes. , Shift with respect to wavelength. By utilizing this change, the zero-point wavelength position of the filter transmitted light signal intensity can be moved to a wavelength stabilization point.

In this embodiment, the electric field applied to the two optical waveguides (3, 4) from the electric field applying electrode 9 is controlled to break the filter characteristic peak interval and the temperature-independent condition. It is possible to adjust the wavelength stabilization point to an arbitrary wavelength without any need. Further, the electric field applying electrode 9 may be provided on one of the optical waveguides (3 or 4).

[Embodiment 3] FIG. 4 is a top view showing a schematic configuration of a laser wavelength stabilizing element according to another embodiment of the present invention.

As shown in the figure, in the present embodiment, an optical waveguide heating heater 10 is provided in a part of two asymmetric optical waveguides (3, 4) having different compositions and lengths of the optical waveguide material. Things. The refractive index of a semiconductor has temperature dependence. Therefore, when the optical waveguides (3, 4) are semiconductor optical waveguides, heat is applied to the optical waveguides (3, 4) by the optical waveguide heating heater 10 provided in a part of the optical waveguides (3, 4). With this addition, the equivalent refractive index of the optical waveguide (3, 4) can be slightly changed.

When the equivalent refractive index of the optical waveguides (3, 4) changes, the phase of the light propagating through the optical waveguides (3, 4) changes, and the intensity of the optical signal transmitted through the branch interference type wavelength filter changes. , Shift with respect to wavelength. By utilizing this change, the zero-point wavelength position of the filter transmitted light signal intensity can be moved to a wavelength stabilization point.

In this embodiment, by controlling the heat applied to the two optical waveguides (3, 4) by the optical waveguide heating heater 10, the peak interval of the filter characteristics and the temperature-independent condition are broken. It is possible to adjust the wavelength stabilization point to an arbitrary wavelength without any need.

In the present embodiment, a Peltier cooling element may be used instead of the optical waveguide heater 10. Further, the optical waveguide heating heater 10 may be provided in one of the optical waveguides (3 or 4).

Furthermore, in each of the above embodiments, the embodiment in which the present invention is applied to a temperature-independent semiconductor wavelength filter has been described. However, the present invention is not limited to this, and the present invention has a temperature dependency. It goes without saying that the present invention is applicable to a branch interference type wavelength filter.

[Fourth Embodiment] FIG. 5 is a top view showing a schematic configuration of a laser wavelength stabilizing element according to another embodiment of the present invention.

As shown in the figure, in this embodiment, a plurality of branch interference type wavelength filters are manufactured in an array on one semiconductor substrate. Here, the optical waveguide of each branching interference type wavelength filter is composed of two asymmetric optical waveguides (2
3, 24). A wavelength stabilization control unit 11 is provided in a part of the two asymmetric optical waveguides (23, 24) of each branch interference type wavelength filter. The wavelength stabilization control unit 11 corresponds to the coating unit 25, the electric field application electrode 9, or the optical waveguide heating heater 10 described in the first to third embodiments. In addition, the wavelength stabilization control means 11 controls one of the optical waveguides (2
3 or 24).

In this embodiment, when the filter characteristics of the branch interference type wavelength filter, which is a laser wavelength stabilizing element, are different due to an element manufacturing process error or the like, the above-described embodiment is applied to each element. The wavelength stabilization point is adjusted by using the method according to the first to third embodiments. In the prior art, the wavelength at the stabilization point is controlled by adjusting the element temperature of the branch interference type wavelength filter, but is controlled by a method other than the temperature adjustment.

Thus, in the present embodiment, compared with the conventional example in which the stabilization point is kept constant by a separate temperature control circuit for each laser wavelength stabilizing element, in this embodiment, one temperature control circuit 12 is used. Thus, the stabilization points of a large number of laser wavelength stabilizing elements on one semiconductor substrate can be kept constant,
A plurality of laser light wavelengths can be collectively stabilized by one temperature control circuit.

In each of the above embodiments, the refractive index of the same length section of both of the two asymmetric optical waveguides (3, 4 or 23, 24) is changed, but only one of them is changed. It may be used or the length of the two sections may be changed. A calculation example in that case is shown below.

[Calculation Example when Refractive Index is Changed] (1) When Only Refractive Index of One Optical Waveguide Is Changed Two asymmetric optical waveguides (3, 4 or 23, 24)
Let L ₁ and L _{2 be} the lengths, and let n ₁ and n ₂ be the equivalent refractive indices of the respective optical waveguides (3, 4, or 23, 24), and propagate the optical waveguides (3, 4, or 23, 24). If the loss is ignored, the signal intensity of the light transmitted through the filter is expressed by the following equation (1).

[0051]

(Equation 1)

FIG. 6 shows the filter transmission light signal intensity characteristics at this time.

Next, L ₁ of the length of the optical waveguide (3, 23,
Alternatively, the refractive index n is set to n ₁ + Δn ₁ by using the method described in the first to third embodiments over the length L ′.
To change. At this time, the filter transmission light signal intensity characteristic is expressed by the following equation (2).

[0054]

(Equation 2)

At this time, the intensity characteristics of the signal transmitted through the filter are as shown in FIG. 7, and the peak position (A) 13 in FIG.
Shifts to the peak position (B) 15 and the stabilization wavelength (zero-point wavelength position) shifts from 14 to 16. In this manner, the wavelength stabilization point can be adjusted by shifting the characteristics of the filter with respect to the wavelength.

(2) When the refractive indexes of the two optical waveguides are different from each other, and the refractive indexes of the two optical waveguides are changed. Two asymmetric optical waveguides (3, 4, or 23, 24)
Let L ₁ and L _{2 be} the lengths, and let n ₁ and n ₂ be the equivalent refractive indices of the respective optical waveguides (3, 4, or 23, 24), and propagate the optical waveguides (3, 4, or 23, 24). If the loss is ignored, the intensity of the signal transmitted through the filter is expressed by the following equation (3).

[0057]

(Equation 3)

Next, the optical waveguides (3, 4 or 23, 24) having the lengths L ₁ and L ₂ are connected to the lengths L ₁ ′ and L 2, respectively.
_The refractive index is changed to n ₁ + Δn ₁ and n ₂ + Δn ₂ by using the method described in the first to third embodiments over ₂ ′. At this time, the filter transmitted light signal intensity is expressed by the following equation (4).

[0059]

(Equation 4)

In this case, the peak position A shifts to the peak position B in the filter transmission light signal intensity characteristic as in FIGS. In this manner, the wavelength stabilization point can be adjusted by shifting the characteristics of the filter with respect to the wavelength.

As described above, the invention made by the present inventor is:
Although a specific description has been given based on the above-described embodiment, the present invention is not limited to the above-described embodiment, and it is needless to say that various modifications can be made without departing from the gist of the invention.

[0062]

The effects obtained by typical ones of the inventions disclosed in the present application will be briefly described as follows.

(1) According to the present invention, the refractive index of at least one of the two asymmetrical optical waveguides is partially changed to shift the zero-point wavelength position of the filter transmitted light signal intensity, That is, the filter characteristics can be adjusted.

(2) According to the present invention, it is possible to stabilize the wavelength of a laser beam at a constant wavelength irrespective of an error in an element manufacturing process. As a result, it is possible to widen the tolerance in the device manufacturing process, and it is possible to stabilize the laser light having a predetermined wavelength with high accuracy.

[Brief description of the drawings]

FIG. 1 is a top view showing a schematic configuration of a laser wavelength stabilizing element according to an embodiment of the present invention.

FIG. 2 is a sectional view showing a schematic configuration of a coating unit shown in FIG.

FIG. 3 is a top view showing a schematic configuration of a laser wavelength stabilizing element according to another embodiment of the present invention.

FIG. 4 is a schematic top view showing a schematic configuration of a laser wavelength stabilizing element according to another embodiment of the present invention.

FIG. 5 is a top view schematically showing a schematic configuration of a laser wavelength stabilizing element according to another embodiment of the present invention.

FIG. 6 shows Embodiments 1 to 3;
5 is a graph showing an example of a filter transmitted light characteristic before changing a refractive index of an optical waveguide.

FIG. 7 is a diagram illustrating Embodiments 1 to 3;
9 is a graph showing an example of a filter transmitted light characteristic after changing a refractive index of an optical waveguide.

FIG. 8 is a graph showing a filter transmitted light signal intensity of the branch interference type wavelength filter.

FIG. 9 is a schematic top view showing a schematic configuration of a temperature-independent semiconductor wavelength filter.

[Explanation of symbols]

3, 4, 23, 24: optical waveguide, 5: organic or glass material, 6, 8: clad layer, 7: core layer, 9: electrode for applying electric field, 10: heater for heating optical waveguide, 11: wavelength stability Conversion control means, 12: temperature control circuit, 20: branching device, 21: multiplexer, 25: coating part.

Claims (5)

[Claims] 1. A laser wavelength stabilizing element comprising a branching interference type wavelength filter having two optical waveguides having different lengths or different refractive indexes.
A laser wavelength stabilizing element characterized in that at least one section of one of the optical waveguides is coated with an organic material or a glass material having a high refractive index. 2. A laser wavelength stabilizing element comprising a branch interference type wavelength filter including two optical waveguides having at least one of different lengths or different refractive indexes.
A laser wavelength stabilizing element, wherein an electric field application electrode for applying an electric field is provided in at least a part of one of the optical waveguides. 3. A laser wavelength stabilizing element comprising a branch interference type wavelength filter including two optical waveguides having at least one of different lengths or different refractive indexes.
A laser wavelength stabilizing element characterized in that a temperature control section is provided in at least one section of at least one of the optical waveguides. 4. A laser wavelength stabilizing element according to claim 1, wherein said laser wavelength stabilizing element is an arrayed laser wavelength stabilizing element formed on one semiconductor substrate. A laser wavelength stabilizing device comprising: controlling the laser wavelength stabilizing elements formed in an array on the one semiconductor substrate by the one temperature control circuit to stabilize the wavelengths of a plurality of laser beams. element. 5. A laser wavelength stabilizing element comprising a branch interference type wavelength filter provided with two optical waveguides having at least one of different lengths or different refractive indexes.
In a method of manufacturing a laser wavelength stabilizing element in which at least one section of at least one optical waveguide of the present optical waveguide is coated with an organic material or a glass material having a high refractive index, a predetermined portion is coated with an organic material or a glass material. A method for manufacturing a laser wavelength stabilizing element, comprising a step of performing cleavage afterward, and then removing the coated organic material or glass material.