JPH05181028A - Optical ring resonator - Google Patents

Abstract

PURPOSE:To provide a variable finesse optical ring resonator by varying the ratio of optical coupling between an input/output optical path and a ring-shaped optical unit. CONSTITUTION:A ring optical waveguide 2 which constitutes a closed loop is arranged in a clad layer 1a on a silicon substrate 1 and optically coupled with an input optical waveguide 3a and an output optical waveguide 3b. The optical coupling part of the ring-shaped optical waveguide 2, input optical waveguide 3a, and output optical waveguide 3b consists of a Mach-Zehnder interferometer circuits 11 and 21 and the optical coupling ratio is variable. Consequently, proper filter characteristics are obtained and light can be guided out.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical ring resonator which is one of sensors of an optical frequency filter or optical sensor system used for optical frequency multiplex communication and optical frequency measurement in the field of optical communication.

[0002]

2. Description of the Related Art As one of future large-capacity transmission systems, a low loss wavelength of 1.55 μm in a silica optical fiber is used.
In the optical band, optical frequency division multiplexing (FD) for multiplexing and transmitting optical signals of hundreds to thousands of channels at frequency intervals of several GHz
M) Transmission is considered. In this transmission method, an optical frequency filter that extracts one signal from the multiplexed optical signals is required. Further, it is necessary to generate light having a frequency interval of several GHz, which is a carrier wave of a signal, at the same time and at a stable frequency. Therefore, an absolutely stabilized light source system and an optical frequency having a transmission or blocking frequency periodically are required. A simultaneous laser frequency stabilization system combining filters has been considered. Moreover, in the optical sensor system using the silica-based optical fiber or the optical waveguide,
It is considered to use an optical frequency filter as a sensor unit of an optical gyro that utilizes the Sagnic effect and as a sensor unit of an optical temperature sensor that utilizes the temperature dependence of the refractive index. As one of the optical frequency filters,
Optical ring resonators are known. This optical ring resonator is composed of a ring-shaped optical path and an optical input / output optical path arranged so as to be optically coupled to the ring-shaped optical path. Depending on the construction method of the optical path, 1) bulk type and 2) fiber type 3) Classified as a planar waveguide type.

In the bulk type, an optical path and an optical coupling portion are constituted by lenses, prisms, mirrors, half mirrors and the like. The fiber type has a single mode fiber as an optical path and a single mode fiber coupler as a coupling portion. The planar waveguide type is composed of an optical path and a coupler by a single mode optical waveguide produced by a combination of a technique of forming a material for forming an optical path on a planar substrate and a photolithography process of processing the film to form an optical path. It From the viewpoint of fabrication and characteristics of the optical frequency filter, the planar waveguide type is expected to be more promising because of its compactness, mass productivity, stability and controllability as compared with the bulk type and fiber type.

FIGS. 8A to 8D are configuration diagrams showing a conventional example of a planar waveguide type optical ring resonator. FIG. 8 (A) shows
8B is a plan view thereof, and FIGS. 8B, 8C, and 8D are enlarged cross-sectional views taken along the line segment AA ′, the line segment BB ′, and the line segment CC ′, respectively. This planar waveguide type optical ring resonator is composed of a ring-shaped optical waveguide 2, an input optical waveguide 3a, and an output optical waveguide 3b which are arranged on a substrate 1 and form a closed loop having a perimeter L. And the input / output optical waveguides 3a and 3b are close to each other to form directional couplers 4a and 4b, respectively. A phase shifter 5 for finely adjusting the optical path length of the ring-shaped optical waveguide 2 is installed on the ring-shaped optical waveguide 2 over a predetermined length. Further, when the ring-shaped optical waveguide 2 has a birefringence which is a difference in refractive index due to polarization, a polarization compensator 6 is provided for compensating the influence on the characteristics due to the birefringence.

Specifically, as the optical waveguides 2, 3a and 3b shown in FIGS. 8A to 8D, quartz single mode optical waveguides formed on a silicon substrate can be used. As the phase shifter 5, a thin film heater that induces a change in the refractive index due to the thermo-optic effect can be used. A compressive stress is applied to the silica-based optical waveguide formed on the silicon substrate, which causes the effective refractive index of the optical waveguide to be 10 ^{− for} vertical polarization (TM polarization) and horizontal polarization (TE polarization). There are different birefringence in the order of ⁴ . Therefore, the polarization compensator 6 is required, and an amorphous silicon thin film capable of changing the birefringence by applying stress in a direction to relax the stress applied to the ring-shaped optical waveguide 2 can be used.

9 (A) and 9 (B) are diagrams showing optical frequency characteristics of the above optical ring resonator. That is, FIG. 8 (A)
In the optical ring resonator shown in FIG.
When the optical frequency of the signal light (light intensity Pin) input to a-1 is changed, the output end 3a-2 and the output optical waveguide 3b
9A and 9B show changes in the light intensities Pout1 and Pout2 of the respective output signal lights from FIG. The optical frequency characteristic of the optical ring resonator of FIG. 9 is characterized by a resonance peak unique to the optical ring resonator. That is, an optical signal that matches the optical frequency fr at the resonance peak is output to the output optical waveguide 3b, and the output end 3a-
2, the optical ring resonator shown in FIGS. 8A to 8D acts as an optical frequency filter. This resonance peak is not a single resonance peak but a so-called FSR (Free Spectral Range).
A number of resonance peaks appear at constant resonance frequency intervals called e). The FSR value is the perimeter L of the ring-shaped optical waveguide 2.
And have the following relationship.

FSR = c / nL (1) (c is the speed of light, n is the refractive index of the optical waveguide) For example, in order to realize FSR = 5 GHz by a silica glass optical waveguide (n≈1.45). Is L = 41.
It needs to be set to 3 mm.

The phase shifter 5 provided on the ring-shaped optical waveguide 2 changes the effective optical path length n · L by a maximum of about one wavelength to change the position of the resonance frequency fr to FS.
Tuning can be performed by changing within the range of R width.

The sharpness of this resonance peak can be represented by the finesse F. When the input and output light intensities of the directional couplers 4a and 4b are represented by the respective optical coupling ratios k _a and k _b , the finesse F has the following relationship with the optical coupling ratios k _a and k _b .

[0010] F = FSR / △ f ... ( 2) (△ f is half the frequency width of the resonance ^{peak) = π / 2sin -1 ((} (1-R) 2/2 / (1 + R 2)) 1/2) ... (3) R = (1 -k a) · (1-k b) · exp (-Γ / 8.69) ... (4) (Γ light intensity loss per ring round) for example, the light intensity loss gamma = 0.56 dB / in order to realize the finesse 30 by the optical waveguide of one round, k _a = k
Set _b = 4%.

[0011]

However, since the finesse cannot be made variable, an optical ring resonator having a large finesse as compared with the stability of the light source frequency can increase the desired signal from the multiplexed signal. It was difficult to take out with efficiency. That is, since the light source frequency of the signal fluctuates, the output light intensity at the output optical waveguide 3b in FIG. 8A suddenly weakens, and the transmission characteristic deteriorates. At the same time, the light intensity at the output end 3a-2 rapidly increases, and the blocking characteristic deteriorates. Further, when the optical ring resonator is incorporated into the system, adjustment is required to match the resonance peak fr of the optical ring resonator with the frequency of the signal. By adjusting the optical path length of the ring-shaped optical path by finely adjusting the phaser 5, the resonance frequency fr of the optical ring resonator can be matched with the signal frequency. However, in the system to be configured, when a ring having a narrow band filter characteristic is used, that is, when an optical ring resonator having a large finesse is used, the resonance frequency fr of this optical ring resonator is the optical frequency of the signal. There is a problem in that the light intensity at the output end hardly changes even if it is slightly separated from, and it becomes difficult to adjust the resonance frequency fr to the signal frequency by the phase shifter 5.

The object of the present invention is to solve the above-mentioned drawbacks,
An object is to provide an optical ring resonator having a variable finesse.

[0013]

In order to achieve the above object, an optical ring resonator according to the present invention comprises a ring-shaped optical path, an optical coupling portion, and the ring-shaped optical path coupled through the optical coupling portion. And at least one of the optical coupling sections is an optical coupling section with variable input / output light intensity.

[0014]

According to the present invention, the optical ring coupler comprises a ring-shaped optical path, an optical coupling section, and at least one optical input / output optical path coupled to the ring-shaped optical path through the optical coupling section. By using at least one of the sections as an optical coupling section with variable input / output light intensity, for example, the optical coupling ratio K of the equations (3) and (4)
_{It is possible to make a} and K _b variable. Therefore, according to the present invention, unlike the conventional technique, there is an advantage that the finesse can be made variable.

[0015]

Embodiments of the present invention will now be described with reference to the drawings.

1 (A) and 1 (B) are plan views and A, respectively, showing an optical ring resonator according to a first embodiment of the present invention.
It is sectional drawing which expands and shows the cross section along the A'line.

This optical ring resonator and FIGS. 8 (A) to 8 (D)
The conventional example shown in FIG.
It is the same in that the ring-shaped optical waveguide 2 forming a closed loop is arranged in a, and the ring-shaped optical waveguide 2 is optically coupled to the input optical waveguide 3a and the output optical waveguide 3b, respectively. In the present embodiment, the optical coupling ratio is variable by configuring the optical coupling part with the ring-shaped optical waveguide 2 by the Mach-Zehnder optical interferometer circuit surrounded by broken lines 11 and 21. Is very different from.

The Mach-Zehnder interferometer circuit 11 is constructed by connecting the directional couplers 12a and 12b with two optical waveguides 13a and 13b having lengths different from each other by ΔL. In addition, here, the optical waveguide 13a
Share a part of the ring-shaped optical waveguide 2, and the optical waveguide 13b
Share a part of the input optical waveguide 3a. Phaser 14
Thin film heaters a and 14b are arranged on the cladding layer 1a above the core portions of the optical waveguides 13a and 13b.

Like the Mach-Zehnder interferometer circuit 11, the Mach-Zehnder interferometer circuit 21 has a directional coupler 2.
2a and 22b are connected by two optical waveguides 23a and 23b whose lengths differ from each other by ΔL. Here, the optical waveguide 23a shares a part of the ring-shaped optical waveguide 2, and the optical waveguide 23b shares a part of the input / output optical waveguide 3b. Thin film heaters are used as the phase shifters 24a and 24b, and the optical waveguides 23a and 23
It is arranged on the clad layer 1a above the core portion of b.

Mach-Zehnder optical interferometer circuits 11 and 2
One of the optical waveguides that compose 1 (here, the optical waveguide 1
3a and 23a) and above the portion of the ring-shaped optical waveguide 2 which is not shared with the optical waveguides 13a and 23a, a thin film heater 5 as a phase shifter and an amorphous silicon thin film 6 as a polarization compensator are provided. Each is arranged.

The single mode optical waveguide of this embodiment is made of SiC.
Fabricated on a silicon substrate 1 by a known combination of a silica-based glass film deposition technique utilizing a fire hydrolysis reaction of a glass forming raw material gas such as l ₄ or GeCl ₄ and a silica-based glass film processing technique by reactive ion etching. can do. Optical waveguides 3a, 3b, 13a, 13b, 23
As shown in FIG. 1 (B), a, 23b, 2 and the like are embedded in the clad layer 1a having a thickness of about 50 μ, and the optical waveguides 3a, 3b, 13a, 13b, 23a, 23b,
The size of the core portion such as 2 is about 6 μm × 6 μm, and the relative refractive index difference between the core and the clad is about 0.75%.

The silica type single mode optical waveguide having such a structural parameter can withstand bending with a curvature of about 4 mm. The ring-shaped optical waveguide 2 was manufactured to be a perfect circle having a radius R = 6.57 mm according to the formula (1) in order to set the FSR to 5 GHz. Further, the thin film heaters 14a, 14b,
As 24a, 24b and 5, here, a Cr metal thin film (width 50 μm, thickness 0.3 μm) was formed by a vacuum deposition technique over a length of about 2 mm. Furthermore, an amorphous silicon thin film 6 (width 200 μm, thickness 9 μm) is formed by a sputtering technique over a length of about 1 mm,
The resonance characteristics of the vertically polarized wave (TM polarized wave) and the horizontally polarized wave (TE polarized wave) were matched.

The optical coupling ratio of the directional couplers 12a, 12b, 23a and 23b was designed to be 50%.
The waveguide length difference ΔL was made to be 1.08 μm.
This is n · ΔL = m · λ (m is an integer, λ is the wavelength used)
As a result, the optical coupling ratio from the input optical waveguide 3a to the ring-shaped optical waveguide 2 can be made almost 100%. Here, n =
The waveguide length difference ΔL was set from 1.45, m = 1 and λ = 1.56 μm. Directional couplers 12a, 12b, 23
The optical coupling ratios of a and 23b and the values of the waveguide length difference ΔL are the optical coupling ratio from the input optical waveguide 3a to the ring-shaped optical waveguide 2 in a state where the phase shifters 14a, 14b, 24a and 24b are not operated, and It is designed from the variable range of the optical coupling ratio. For example, the optical coupling ratio from the input optical waveguide 3a to the ring-shaped optical waveguide 2 is set to 0% in a state where the phase shifters 14a, 14b, 24a, and 24b are not operated, and the optical coupling ratio range to be changed from 0 When the ratio is 50%, the directional coupler 1
The optical coupling ratio of 2a, 12b, 23a and 23b is set to 25
%, And the value of the waveguide length difference ΔL is designed to be 0.504 μm. This design can be easily inferred from the design of a known waveguide type Mach-Zehnder optical interferometer. However, when the waveguide length difference ΔL becomes large, the finesse becomes worse as compared with the conventional example, and the resonance peak starts to split. Therefore, it is desirable that the waveguide length difference ΔL is 0 or as small as possible. 2A to 2E are shown in FIG.
FIG. 6 is a frequency characteristic diagram illustrating the operation of the optical ring resonator of FIG. 2A to 2D show power consumption of the thin film heaters 14a and 24a, which are phase shifters, of 0.3 W,
It is set to 0.5W, 0.7W, and 0.9W.
Further, FIG. 2 (E) shows that the power consumption of the thin film heaters 14a and 24b is 0.7W. FIG. 3 is a graph showing changes in finesse when the same electric power is consumed by the thin film heaters 14a and 24a.

FIG. 4 shows the relationship between the finesse and the transmittance at the resonance peak. The hatched range is the value obtained by changing the thin film heaters 14a, 14b, 24a and 24b.

FIG. 5 is a plan view showing an optical ring resonator of the second embodiment of the present invention. This optical ring resonator has a first
The Mach-Zehnder optical interferometer circuit 21 of the above embodiment is replaced with the directional coupler 4. That is, the output optical waveguide 3 b is optically coupled to the ring-shaped optical waveguide 2 via the directional coupler 4.

One of the optical waveguides (optical waveguide 13a in this case) constituting the Mach-Zehnder interferometer system circuit 11 and the portion of the ring-shaped optical waveguide 2 above the optical waveguide 2 which is not shared with the input optical waveguide 13a. A thin film heater 5 as a phase shifter and an amorphous silicon thin film 6 as a polarization compensator are arranged in each of the above.

The single mode optical waveguide of this example was manufactured in the same manner as in the first example. Optical waveguides 2, 3a, 3b, 1
3a and 13b are clad layers 1a having a thickness of about 50 μm.
The optical waveguides 13a, 13b and the like are embedded in the core, and the dimensions of the core are about 6 μm × 6 μm, and the relative refractive index difference between the core and the clad is about 0.75%. Further, the ring-shaped optical waveguide 2 was manufactured to be a perfect circle having a radius R = 6.57 mm in order to set the FSR to 5 GHz as in the first embodiment. Further, as the thin film heaters 14a, 14b and 5, here, a Cr metal thin film (width 50 μm, thickness 0.3) is used.
μm) was formed by a vacuum deposition technique over a length of about 2 mm. Furthermore, the amorphous silicon thin film 6 (width 2
A thickness of 00 μm and a thickness of 9 μm) was formed by a sputtering technique over a length of about 1 mm, and the resonance characteristics of the vertically polarized wave (TM polarized wave) and the horizontally polarized wave (TE polarized wave) were matched.

In the present embodiment, the optical coupling ratio between the ring-shaped optical waveguide 2 and the output optical waveguide 3b of the directional coupler 4 is set to 20 in order to set the finesse to 20 when the thin film heaters 14a and 14b do not consume electric power. 10%, and the directional couplers 12a and 12 of the Mach-Zehnder optical interferometer 11 are manufactured.
The optical coupling ratio of b was 50%, and the difference ΔL in length between the two optical waveguides 13a and 13b was 0.43 μm.

The finesse was 28 when the power consumption of the thin film heater 14a as the phaser was 0.9 W, and the finesse was 20 when the power consumption was 0 W. With such a configuration, as in the first embodiment, the finesse can be reduced when the thin film heater 14a that is the phase shifter is operating, and the desired finesse can be obtained when the phase shifter is not operated.

FIG. 6 is a plan view showing an optical ring resonator according to the third embodiment of the present invention. This embodiment is different from the first and second embodiments in that the optical coupling section is only the optical coupling section 11.

The Mach-Zehnder optical interferometer circuit 11 is constituted by connecting the directional couplers 12a and 12b with two optical waveguides 13a and 13b having lengths different from each other by ΔL. In addition, here, the optical waveguide 13
a shares a part of the ring-shaped optical waveguide 2 and
b shares a part of the input optical waveguide 3a. Phaser 1
Thin film heaters 4a and 14b are arranged on the cladding layer 1a above the core portions of the optical waveguides 13a and 13b.

One of the optical waveguides (the optical waveguide 13a in this case) forming the Mach-Zehnder interferometer circuit 11 and the portion of the ring-shaped optical waveguide 2 above the optical waveguide 2 that does not share the optical waveguide 13a. Is provided with a thin film heater 5 as a phase shifter and an amorphous silicon thin film 6 as a polarization compensator.

The single mode optical waveguide of this example was manufactured in the same manner as in the first example. Optical waveguides 2, 3a, 13
a, 13b, etc. are buried in the cladding layer 1a having a thickness of about 60 μm, and the optical waveguides 2, 3a, 13a, 13b
The size of the core portion is about 8 μm × 8 μm, and the relative refractive index difference between the core and the clad is about 0.3%.

The silica type single mode optical waveguide having such a structural parameter can endure bending with a curvature of about 35 mm. In the ring-shaped optical waveguide 2, a semicircle with a radius of curvature R of 50 mm has a length of 49 mm in order to set the FSR to 0.5 GHz.
It was manufactured as a race track type connected by a straight line of mm. Further, as the thin film heaters 14a, 14b and 5, here, a Cr metal thin film (width 50 μm, thickness 0.3 μm) was formed over a length of about 5 mm by a vacuum deposition technique. Furthermore, the amorphous silicon thin film 6 (width 200 μm
m, thickness 9 μm) with sputter technology and length of about 1.6
The resonance characteristics of the vertically polarized wave (TM polarized wave) and the horizontally polarized wave (TE polarized wave) are matched with each other. Each coupling ratio of the directional couplers 12a and 12b was designed to be 20%. The waveguide length difference ΔL was made to be 0. The optical coupling ratio from the input optical waveguide 3a to the ring-shaped optical waveguide 2 can be made approximately 40%. The optical coupling ratio of this coupling part is 0 to 40.
%, And the finesse of this circuit was variable from 5 to 9.

FIG. 7 is a plan view showing an optical ring resonator of the fourth embodiment of the present invention. The present embodiment is different from the third embodiment in the configuration of the optical coupling section 11 and the input / output optical waveguides 7a and 7b, which is composed of one curved waveguide.

The Mach-Zehnder optical interferometer circuit 11 is constructed by connecting the directional couplers 12a and 12b with two optical waveguides 13a and 13b whose lengths are different from each other by ΔL. The input optical waveguide 7a is connected to the optical waveguide 13a, the output optical waveguide 7b is connected to the optical waveguide 13b, and intersects with the ring-shaped optical waveguide 2. As the phase shifters 14a and 14b, the thin film heater is the cladding layer 1 above the core portion of the optical waveguides 13a and 13b.
It is placed on a.

The configuration in which the optical coupler section 11 of this configuration is replaced with a directional coupler is used as a ring laser using an Er-doped silica optical waveguide as the optical waveguide (Japanese Patent Application No. 3-281579). .. This directional coupler 12a, 12
Laser oscillation can be performed by setting the optical coupling ratio of b to several percent or less at the frequency of the excitation light and the oscillation frequency in the ring. In this case, the oscillation condition is critical with respect to the optical coupling ratio, and it is difficult to set the optical coupling ratio with high accuracy due to manufacturing error. However, by configuring this portion with the optical coupling portion of this embodiment, this optical coupling ratio can be set to an appropriate value.

One of the optical waveguides (the optical waveguide 13a in this case) constituting the Mach-Zehnder interferometer circuit 11 and the portion of the ring-shaped optical waveguide 2 above the optical waveguide 2 which is not shared with the optical waveguide 13a. Is provided with a thin film heater 5 as a phase shifter and an amorphous silicon thin film 6 as a polarization compensator.

The single mode optical waveguide of the present embodiment is Er manufactured by the flame deposition method and the reactive ion etching method.
A silica optical waveguide containing (1% by weight) was used. The optical waveguides 2, 7a, 7b, 13a, 13b, etc. are embedded in the clad layer 1a having a thickness of about 60 μm.
The core size of 7a, 7b, 13a, 13b etc. is 5 μm x
About 5 μm, the relative refractive index difference between the core and the cladding is 0.75%
It is a degree.

The silica type single mode optical waveguide having such a structural parameter can withstand bending with a curvature of about 4 mm. The ring-shaped optical waveguide 2 was manufactured as a perfect circle having a radius of curvature R of about 15.9 mm in order to set the FSR to 2 GHz. Further, as the thin film heaters 14a, 14b and 5, here, a Cr metal thin film (width 50 μm, thickness 0.3) is used.
μm) was formed by a vacuum evaporation technique over a length of about 5 mm. Furthermore, the amorphous silicon thin film 6 (width 2
(00 μm, thickness 9 μm) was formed by a sputtering technique over a length of about 1.6 mm, and the resonance characteristics of the vertical polarization (TM polarization) and the horizontal polarization (TE polarization) were matched. The coupling ratio of the directional couplers 12a and 12b is 0.98 at the excitation wavelength.
It was manufactured so that it was 0% at μm and 50% at an oscillation wavelength of 1.60 μm. The waveguide length difference ΔL was made to be 0. As a result, the optical coupling ratio from the input optical waveguide 3a to the ring-shaped optical waveguide 2 was 0% at the excitation wavelength of 0.98 μm and 100% at the oscillation wavelength of 1.60 μm. By setting the power consumption of the thin film heater 14a, which is a phaser, to 0.1 W, oscillation was achieved with an oscillation threshold of 30 mW and a differential efficiency of 20%.
As described above, in the first, second, third and fourth embodiments, the silica single mode optical waveguide on the silicon substrate is used as a basic element.
This is because it has excellent refractive index matching with a silica single mode optical fiber for optical communication. The optical waveguide that can be used in the present invention is not necessarily limited to the silica optical waveguide, and it is needless to say that it can be applied to the waveguide system of other materials. As the target optical waveguide system, in addition to quartz system, multi-component glass system ion diffusion waveguide, LiNb
Examples include O ₃ -based waveguides. Further, the present invention can be realized by an optical fiber or a bulk type and is not limited to an optical waveguide.

Further, although the thin film heater is used as the phase shifter, a phase controller such as a liquid crystal cell capable of controlling the phase by applying a voltage can also be used, and the phase shifter which can be used in the present invention is not necessarily a thin film heater. It is not limited to. In the case of the aforementioned LiNbO ₃ system waveguide, it is also possible to use a phase shifter utilizing the electro-optic effect as the phase shifter.

Further, in the present embodiment, the Mach-Zehnder interferometer circuit is used for the optical coupling section, but a groove is carved between two optical waveguides of the directional coupler, and a refractive index matching liquid is put in the groove. However, the optical coupling ratio can be made variable by appropriately adjusting the refractive index, and the optical coupling section that can be used in the present invention is not necessarily limited to the Mach-Zehnder interferometer circuit.

[0043]

As described above, the present invention has the following effects. (1) According to the invention of claim 1, the optical coupling ratio between the input / output optical path of the optical ring resonator and the ring-shaped optical path is made variable,
The finesse of the optical ring resonator can be made variable, which allows
Even if the desired optical frequency is fluctuating, it can be extracted with appropriate filter characteristics. Therefore, the optical ring resonator of the present invention is expected to find wide applications in optical frequency multiplex transmission systems, optical frequency measurement fields, optical sensor systems, and the like. (2) According to the second aspect of the present invention, the optical coupling portion is configured by a combination of the Mach-Zehnder interferometer and the phase shifter, so that the optical coupling ratio, and thus the finesse, can be set with high accuracy and in a wide range. Therefore, the optical ring resonator of the present invention can realize the characteristics of the optical ring resonator suitable for the system used, and the high performance of the system is expected. (3) The invention of claim 3 can be expected to improve the performance of an optical fiber, particularly a system using a silica optical fiber.

[Brief description of drawings]

1A and 1B are a plan view and a cross-sectional view taken along the line AA ′, respectively, showing an optical ring resonator according to a first embodiment of the present invention.

FIG. 2 is a diagram showing an optical frequency characteristic when the power consumption of the phaser of the optical ring resonator of the first embodiment is changed.

FIG. 3 is a diagram showing changes in finesse with respect to power consumption of a phaser of the optical ring resonator according to the first embodiment.

FIG. 4 is a diagram showing the relationship between the finesse that can be set in the optical ring resonator of the first embodiment and the transmittance at the resonance peak.

FIG. 5 is a plan view of an optical ring resonator according to a second embodiment of the present invention.

FIG. 6 is a plan view of an optical ring resonator according to a third embodiment of the present invention.

FIG. 7 is a plan view of an optical ring resonator according to a fourth embodiment of the present invention.

8A, 8B, 8C and 8D are plan views and AA ′, respectively, showing a conventional example of an optical ring resonator.
It is a line sectional view, a BB 'line sectional view, and a CC' line sectional view.

9A and 9B are diagrams showing optical frequency characteristics of a conventional example of an optical ring resonator.

[Explanation of symbols]

 1 Silicon Substrate 1a Cladding Layer 2 Ring Optical Waveguide 3a Input Optical Waveguide 3b Output Optical Waveguide 4a, 4b Directional Coupler 5 Thin Film Heater 6 Polarization Compensator 11, 21 Mach-Zehnder Optical Interferometer Circuit 12a, 12b, 22a, 22b Direction Sexual coupler 13a, 13b, 23a, 23b Optical waveguide 14a, 14b, 24a, 24b Phaser

Claims (3)

[Claims] 1. A ring-shaped optical path, an optical coupling section, and at least one optical input / output optical path coupled to the ring-shaped optical path via the optical coupling section, and at least one of the optical coupling sections. An optical ring resonator, which is an optical coupling unit with variable input / output light intensity. 2. The optical coupling section with variable input / output intensity is composed of a Mach-Zehnder optical interferometer, and the optical path length is finely adjusted along the two optical paths forming the Mach-Zehnder optical interferometer, and the light transmittance is adjusted. 2. The optical ring resonator according to claim 1, further comprising a phase shifter that adjusts. 3. The ring-shaped optical path and the light input / output optical path are single-mode optical waveguides formed on a flat substrate, and the single-mode optical waveguide is a silica glass arranged on the flat substrate. The Mach-Zehnder optical interferometer is a silica-based optical single-mode optical waveguide in which a ring-shaped silica-based optical single-mode optical waveguide and an input / output silica-based optical single-mode optical waveguide are formed. The phase shifter is composed of two directional couplers arranged close to each other at two points and two silica-based optical single-mode optical waveguides connecting the two directional couplers. 3. A thin film heater disposed on a cladding layer above the core part in at least one of two silica based single mode optical waveguides connecting two directional couplers of an optical interferometer. Optical ring resonator.