JP3090293B2 - Optical circuit and manufacturing method thereof - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical circuit having an optical waveguide disposed on a substrate and a method of manufacturing the same. More specifically, the present invention relates to an optical circuit having a desired polarization dependence by adjusting the birefringence of the optical waveguide. Or an optical circuit configured to have polarization independence and a method of manufacturing the same.

[0002]

2. Description of the Related Art A silica-based glass waveguide that can be formed on a silica-based glass substrate or a silicon substrate has features such as low loss, high stability, good workability, and good matching with a silica-based fiber. Since it is very useful in forming practical waveguide type optical components such as an optical multiplexing / demultiplexing circuit, research and development are being advanced.

[0003] In recent years, the production of highly functional and highly integrated planar optical circuits utilizing their characteristics has been promoted. Among them, an optical circuit using a phase of light is important because it enables a circuit that cannot be realized by an electronic circuit.

In a quartz optical waveguide, undercladding layer deposition → core layer deposition → core etching →
The core-cladding structure is formed by the manufacturing process of over-cladding deposition. However, in a highly functional and highly integrated optical circuit using the phase of light, the phase of light depends on the refractive index and propagation length of the waveguide. Above minute refractive index and fluctuation of the waveguide shape, and stress applied to the waveguide greatly affect the element characteristics. Therefore, in order to improve the productivity of a highly integrated optical circuit, it is necessary to correct minute fluctuations in manufacturing and the like, and an optical circuit in which the refractive index and the birefringence are locally controlled has been desired.

An MZ (Mach-Zehnder) interferometer, which is an important element constituting such a planar optical circuit, will be described as an example. The MZ interferometer is composed of two directional couplers and two waveguides connecting the directional couplers, and is an indispensable component in configuring an optical switch or an optical demultiplexer.

However, in the MZ interferometer, not only the silica-based optical waveguide but also a slight change in the refractive index, the shape of the waveguide, and the stress applied to the waveguide greatly affect the element characteristics.

When the MZ interferometer has an optical path length difference L1, the output intensity of the MZ interferometer is related to the frequency f (or wavelength λ) of the incident light.

[0008]

(Equation 1)

It is known that the optical device has a characteristic of having a period as an optical device, and an optical device operating as an optical switch, an optical frequency multiplexer / demultiplexer, or the like is realized by utilizing the periodic characteristic of the output light intensity.

However, the birefringence of the waveguide causes a shift in the phase of the periodic characteristic of the optical interferometer due to the polarization direction.
Unless the polarization direction of the incident light is adjusted in advance to either the horizontal (TE polarized) or the vertical (TM polarized) with respect to the substrate, the operating characteristics as an optical switch or an optical frequency multiplexer / demultiplexer will be significantly deteriorated. Will be.

Therefore, in an optical circuit using an MZ interferometer, it is necessary to correct a minute fluctuation in manufacturing in order to improve productivity, and an effective adjustment method has been desired.

At present, as a method of locally finely adjusting the birefringence, a stress-imparting film such as amorphous silicon is processed into an appropriate shape and is placed near the waveguide to adjust the birefringence or to adjust the birefringence. In the vicinity of the wave path, a groove is carved to adjust the birefringence.

[0013]

However, these methods have a problem that the number of steps for fabricating the waveguide increases and the method is complicated.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to provide an optical circuit in which the refractive index and birefringence are effectively and locally adjusted to improve the productivity. Is to provide.

Another object of the present invention is to provide an optical circuit having a polarization control function.

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 The present invention is disclosed in the present application.
A brief description of typical inventions will be given below.
It is as follows. That is, the present invention is provided on a flat substrate.
An optical waveguide, wherein the optical waveguide has a core portion and a front portion.
It is provided around the core portion and has a refractive index higher than that of the core portion.
An optical circuit comprising a low cladding part,
Optical _waveguide, GeO 2, TiO ₂ or, is Ce ₂ O ₃
Made with added quartz glass
It is characterized by the following. In addition, the present invention provides a semiconductor device provided on a flat substrate.
Mach-Zehnder interferometer having two optical waveguides
The optical waveguide is provided around a core portion and the core portion.
And a clad part having a lower refractive index than the core part.
An optical circuit comprising:
Optical _waveguide, GeO 2, TiO ₂ or, is Ce ₂ O ₃
Made with added quartz glass
It is characterized by the following.

Further , the present invention is provided on a flat substrate.
An optical waveguide, wherein the optical waveguide includes a core portion and the core
Provided around the portion and having a lower refractive index than the core portion.
A method for manufacturing an optical circuit comprising a lad portion,
GeO ₂ , TiO ₂ , or Ce
_The optical waveguide is made of quartz glass to which ₂ O ₃ is added.
Forming a path, and applying visible or ultraviolet light to the optical waveguide.
By irradiating light laser light, the birefringence value of the core portion is set to a predetermined value.
Adjusting to a value. Also,
The present invention has two optical waveguides provided on a flat substrate.
A Mach-Zehnder interferometer, wherein the optical waveguide is
A portion, provided around the core portion, from the core portion
Optical circuit composed of a low refractive index cladding
Manufacturing method, using a quartz-based glass as a material, and,
At least one of the optical waveguides, GeO _2, TiO _2, is
There is, to include Ce ₂ O _3, wherein the planar substrate 2
Forming an optical waveguide of the book, the at least one of the
The optical waveguide is irradiated with visible or ultraviolet laser light,
Adjusting the birefringence value of the core portion.
Sign.

Further , the present invention is provided on a flat substrate.
Equipped with a Mach-Zehnder interferometer having two optical waveguides,
The optical waveguide is provided around a core portion and the core portion.
And a clad part having a lower refractive index than the core part.
A method for manufacturing an optical circuit to be formed, comprising:
And at least one of the optical waveguides is made of ultraviolet light.
On the planar substrate to include line sensitive dopants
Forming the two optical waveguides;
Irradiate one optical waveguide with visible or ultraviolet laser light.
Adjusting the birefringence value of the core,
Adjusting the phase due to the polarization of the interferometer.
And features. Further, the present invention provides a semiconductor device provided on a flat substrate.
Mach-Zehnder interferometer with two optical waveguides
The optical waveguide is provided around a core portion and the core portion.
Or a clad part having a lower refractive index than the core part.
A method for manufacturing an optical circuit comprising a quartz glass
And the at least one optical waveguide,
The planar substrate includes an ultraviolet-sensitive dopant.
Forming the two optical waveguides on top,
Irradiate visible or ultraviolet laser light to one of the optical waveguides.
To adjust the birefringence value of the core,
A step of eliminating polarization dependence of theender interferometer .

Further , the present invention is provided on a flat substrate.
Equipped with a Mach-Zehnder interferometer having two optical waveguides,
The optical waveguide is provided around a core portion and the core portion.
And a clad part having a lower refractive index than the core part.
A method for manufacturing an optical circuit to be formed, comprising:
And at least one of the optical waveguides is made of ultraviolet light.
On the planar substrate to include line sensitive dopants
Forming the two optical waveguides;
One of the optical waveguides is irradiated with visible or ultraviolet laser light to adjust the birefringence value of the core portion, and the Mach-Zen
And increasing the polarization dependence of the interferometer .

[0021]

The main part of the above-mentioned means is to irradiate at least one of the waveguides of the MZ interferometer with light in the visible or ultraviolet region in the method of manufacturing a waveguide type MZ interferometer composed of a silica glass waveguide. Control the birefringence of the core by
It adjusts the phase depending on the polarization of the Z interferometer, that is, the output.

As for the control of the refractive index of the waveguide, there is a similar report by Malo et al. On the change of the refractive index of an optical fiber (B. Malo, et al., Opt. Lett. 15, 953,
1990). According to the report, it has been reported that the refractive index of the core was changed by 3 × 10 to ⁵ by irradiation with ultraviolet light in the GeO ₂ -doped quartz optical fiber.

A similar optically induced refractive index change Δn is also observed in a quartz optical waveguide formed on a silicon substrate. At this time, the refractive index measured by irradiating light in the TE and TM directions of the waveguide is measured. If the changes are Δn _TE and Δn _TM respectively,
The magnitudes of Δn _TE and Δn _TM are different.

According to the present invention, by using this principle,
It adjusts the birefringence of an MZ interferometer of a GeO ₂ -doped quartz glass waveguide.

First, the principle by which the phase of the MZ interferometer of the GeO ₂ -doped quartz glass waveguide can be adjusted will be described below.

FIG. 1 is a diagram for explaining the principle that the phase of an MZ interferometer of a GeO ₂ -doped silica glass waveguide can be adjusted, wherein 1 a and 1 b are directional couplers, and 2 a and 2 b are 2
Waveguides connecting two directional couplers, 1 to 4 are ports. Here, the same thing two directional couplers of the MZ interferometer for simplicity, the coupling length of the directional coupler and L _0. At that time, in the MZ interferometer of FIG. 1, it is assumed that the refractive index changes by Δn in a portion of the length ΔL ₁ of one waveguide (2a). At this time, assuming that the light having the wavelength λ enters the port 1 of the MZ interferometer, the output ratio I ₄ / (I ₃ + I ₄ ) from the ports 3 and 4 is represented by the following equation.

[0027]

(Equation 2)

Here, L _c (λ) is the complete coupling length of the directional coupler. As is clear from equation (2),

[0029]

(Equation 3)

When the condition is satisfied, the output is inverted. Assuming that Δn changes by 3 × 10 to ⁵ at a wavelength of 1.3 μm, 3.3 cm is obtained as the value of ΔL ₁ . Therefore, MZ
If the length of the waveguide constituting the interferometer is sufficient, the characteristics of the MZ interferometer can be adjusted.

Here, the refractive index of the core changes at a wavelength of 245.
nm due to the absorption associated with GeO ₂ . Therefore, the laser used for changing the refractive index only needs to have an oscillation wavelength near 245 nm. Further, a laser having an oscillation wavelength in the visible region can also be used. This is because a laser in the visible region induces a similar change by two-photon absorption. That is, in the present invention, the laser used is the He-Cd laser, N ₂ laser, various excimer lasers, Ar ion laser, Nd ³⁺ : YAG laser, and Alexandrite (Cr ³⁺ : BeAl ₂ O ₃ ) laser. 2
Next, third and fourth harmonics, such as those having a wavelength in the ultraviolet / visible region, may be used.

The above as the refractive index change [Delta] n due to the light irradiation, the polarization state and the irradiation conditions of the irradiation light, the refractive index change relates to the refractive index change [Delta] n _TE and TM direction component regarding TE direction component of the waveguide [Delta] n _TM is different.

Therefore, the birefringence of the waveguide can be adjusted by appropriately setting the irradiation intensity and irradiation time of the ultraviolet or visible laser light.

The effect of the present invention is permanent even if the irradiation of the ultraviolet or visible laser beam is stopped.

[0035]

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

(Embodiment 1) In Embodiment 1 of the present invention, the characteristics of the MZ interferometer were adjusted with an excimer laser in a silica-based optical waveguide.

FIG. 2 shows the MZ fabricated in the first embodiment.
FIG. 2 is a configuration diagram of an interferometer optical circuit, where 1c and 1d are directional couplers, 2c and 2d are waveguides, 3a, 3b, 3c and 3d are optical fibers, 4a is a silicon substrate, and 5 is a metal mask for shielding. , 6 is an excimer laser, 7 is a mirror, and 8a and 8b are lenses.

The MZ interferometer of FIG. 2 is asymmetric, and the waveguide 2c is longer than 2d. This type of MZ interferometer operates as a frequency or wavelength demultiplexer. The MZ interferometer of FIG. 2 is designed so that the optical path length difference ΔL ₂ between the _two waveguides 2 c and 2 d is about 1 cm, and the incident light can be split at a frequency of 10 GHz.

First, Ge is formed on a silicon substrate by an ordinary method.
An O ₂ -doped silica glass waveguide type MZ interferometer was manufactured.
The waveguide core is rectangular and has a size of 7 × 7 μm. The refractive index difference between the core and the clad was 0.75%. In the directional couplers 1c and 1d, the coupling ratio was set to be approximately 50% at a wavelength of 1.3 μm.

A Kr having a wavelength of 248 nm was applied to the MZ interferometer.
Irradiation with an F excimer laser was performed, and changes in characteristics before and after the irradiation were examined. The KrF excimer laser light is emitted from the upper part of the waveguide as shown in FIG.
As shown in the figure, a portion not covered with the metal mask was irradiated. Therefore, the excimer laser light induces a change in the refractive index only in a part of the waveguide 2e. The irradiation power of the KrF excimer laser was 100 mJ / cm ² , the pulse repetition was 50 Hz, and the irradiation time was 20 minutes.

In order to examine the characteristics of the MZ interferometer, a current sweep type semiconductor laser having a center wavelength of 1.3 μm was introduced into the optical circuit from the fiber 3e. In the first embodiment, a change in the characteristics of the MZ interferometer could be monitored during the irradiation with the excimer laser.

FIG. 3 shows the wavelength dependence of the output from the fiber 3c after irradiation for 20 minutes in comparison with that before irradiation.
In FIG. 3, the vertical axis represents the insertion loss (Insertion loss),
The horizontal axis is the wavelength (Wavelength).

Before the KrF excimer laser irradiation, the output light spectrum characteristics from the fibers 3c and 3d are different between the TE polarized light and the TM polarized light as shown in FIG. 3, and this MZ interferometer has a polarization dependency. Had.

After the irradiation, as shown in FIG.
The optical spectrum characteristics of the M-polarized light coincided, and the polarization dependence of the signal light near 1.3 μm could be eliminated by excimer laser light irradiation.

From the above results, according to the first embodiment,
It was confirmed that the birefringence of the MZ interferometer was adjustable.

The concentration of GeO ₂ is not particularly limited because it can be adjusted by the length of the MZ interferometer. In the first embodiment, GeO ₂ is used as a dopant. However, other dopants such as TiO ₂ and Ce ₂ O ₃ which absorb in the ultraviolet region and are sensitive to ultraviolet light may be used.

Example 2 In Example 2, an optical circuit for an MZ interferometer was constituted by a quartz glass waveguide, and a KrF excimer laser beam was irradiated to produce a polarization splitting optical circuit.

FIG. 4 is a conceptual view of the configuration of a polarization splitting optical circuit manufacturing apparatus according to the second embodiment, wherein 1e and 1f are directional couplers, 2e and 2f are waveguides, 3e, 3f, 3g, 3h is an optical fiber, 4b is a silicon substrate, 6 is an excimer laser,
7 is a mirror, and 8a and 8b are lenses.

First, Ge is formed on a silicon substrate by an ordinary method.
An O ₂ -doped silica glass waveguide type MZ interferometer was manufactured.
The waveguide core is rectangular and has a size of 7 × 7 μm. The refractive index difference between the core and the clad was 0.75%. In the directional couplers 1e and 1f, the coupling ratio was set to be approximately 50% at a wavelength of 1.3 μm.

In the second embodiment, 7 mirrors and 8a, 8b
By exposing the waveguide 2e locally to excimer laser light and adjusting the birefringence of the waveguide 2e, when the TE polarized light is incident from the optical fiber 3e, the optical fiber 3h, When light of TM polarization is incident, output light is obtained from the optical fiber 3g.

FIG. 5 shows the insertion loss (Inserti) of the output light from the optical fiber 3h when the light enters from the optical fiber 3e.
on loss) characteristics. In FIG. 5, TE ', TM'
Is the light output after irradiation. The output light from the optical fiber 3h is a desired optical frequency (relative optical frequency: Relative frequency).
(y: 24 GHz), it is shown that TE-polarized light is obtained at an intensity of 20 dB or more as compared with TM-polarized light.

As can be seen from the above description, the present embodiment 2
According to this, the MZ interferometer optical circuit can add a polarization separation function of TE and TM.

The present invention relates to optical fibers 3e, 3f, 3g,
This does not prevent the use of an optical fiber having polarization maintaining property for 3h.

As described above, the present invention has been specifically described based on the embodiments. However, it is needless to say that the present invention is not limited to the above-described embodiments, and can be changed without departing from the gist of the present invention.

[0055]

As described above, according to the present invention, it is possible to provide an optical circuit whose characteristics are effectively and simply adjusted without requiring a change in a conventional optical circuit manufacturing method. . Further, since the present invention is implemented for an optical circuit that has already been manufactured, a circuit having an output characteristic that is out of the standard can be set to a desired characteristic, and there is an advantage that the productivity of the optical circuit is improved.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an MZ interferometer optical circuit for explaining the principle of the present invention;

FIG. 2 is an arrangement diagram of an optical system and a waveguide used in Embodiment 1 of the present invention,

FIG. 3 is a diagram showing an output light wavelength spectrum characteristic of the waveguide used in the first embodiment;

FIG. 4 is an arrangement diagram of an optical system and a waveguide used in Embodiment 2 of the present invention,

FIG. 5 is a diagram showing a relative optical frequency-insertion loss characteristic of the second embodiment.

[Explanation of symbols]

1a, 1b, 1c, 1d, 1e, 1f ... directional couplers,
2a, 2b, 2c, 2d ... optical waveguides, 3a, 3b, 3
c, 3d, 3e, 3f, 3g, 3h ... optical fiber, 4
a, 4b: a silicon substrate with a waveguide, 5: a laser beam shielding mask, 6: an excimer laser, 7: a mirror, 8a: a lens, 8b: a cylindrical lens.

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Hiroaki Yamada 1-6, Uchisaiwaicho, Chiyoda-ku, Tokyo Nippon Telegraph and Telephone Corporation (56) References JP-A-6-27337 (JP, A) JP-A-Hei 3-67204 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) G02B 6/12-6/14

Claims (7)

(57) [Claims] An optical waveguide provided on a flat substrate is provided.
The optical waveguide is provided around a core portion and the core portion.
And a clad part having a lower refractive index than the core part.
An optical circuit to be formed, wherein the optical waveguide is made of GeO ₂ , TiO ₂ , or Ce ₂
Made from quartz glass with O ₃ added
Optical circuit, characterized by that. 2. Two optical waveguides provided on a flat substrate
A Mach-Zehnder interferometer, wherein the optical waveguide is provided around a core portion and the core portion.
And a clad part having a lower refractive index than the core part.
An optical circuit to be formed, wherein the at least one optical waveguide includes GeO ₂ , TiO ₂ ,
Alternatively, a quartz glass to which Ce ₂ O ₃ is added is used as a material.
Optical circuit you characterized in that it is created as. 3. An optical waveguide having an optical waveguide provided on a flat substrate.
The optical waveguide is provided around a core portion and the core portion.
And a clad part having a lower refractive index than the core part.
A method for manufacturing an optical circuit to be formed, wherein GeO ₂ , TiO ₂ , or Ce
_The optical waveguide is made of quartz glass to which ₂ O ₃ is added.
Forming a path, and irradiating the optical waveguide with visible or ultraviolet laser light.
Adjusting the birefringence value of the core portion to a predetermined value.
A method of manufacturing an optical circuit, comprising: 4. Two optical waveguides provided on a flat substrate
A Mach-Zehnder interferometer, wherein the optical waveguide is provided around a core portion and the core portion.
And a clad part having a lower refractive index than the core part.
A method for manufacturing an optical circuit to be formed, wherein a quartz glass is used as a material, and the at least one of the
Optical waveguide, GeO _2, TiO _2, or a Ce ₂ O ₃
The two optical waveguides are formed on the planar substrate so as to include
A step of forming, on said at least one optical waveguide, visible or Murasakisotokore
Laser light to adjust the birefringence value of the core.
Producing how the optical circuit characterized by having a degree. 5. Two optical waveguides provided on a plane substrate
A Mach-Zehnder interferometer, wherein the optical waveguide is provided around a core portion and the core portion.
And a clad part having a lower refractive index than the core part.
A method for manufacturing an optical circuit to be formed, wherein a quartz glass is used as a material, and the at least one of the
As the optical waveguide contains a UV-sensitive dopant,
Forming the two optical waveguides on the planar substrate
And a quartz glass as a raw material on the flat substrate,
A step of forming an optical waveguide of the present invention , and irradiating at least one of the optical waveguides with visible or ultraviolet laser light to adjust a birefringence value of the core portion ;
Adjusting the phase of the Mach-Zehnder interferometer due to polarization . 6. Two optical waveguides provided on a plane substrate
A Mach-Zehnder interferometer, wherein the optical waveguide is provided around a core portion and the core portion.
And a clad part having a lower refractive index than the core part.
A method for manufacturing an optical circuit to be formed, wherein a quartz glass is used as a material, and the at least one of the
As the optical waveguide contains a UV-sensitive dopant,
Forming the two optical waveguides on the planar substrate
And at least one of the optical waveguides has visible or ultraviolet light.
Irradiation of laser light to adjust the birefringence value of the core portion.
The process of eliminating the polarization dependence of the Mach-Zehnder interferometer
A method of manufacturing an optical circuit, comprising: 7. Two optical waveguides provided on a plane substrate
A Mach-Zehnder interferometer, wherein the optical waveguide is provided around a core portion and the core portion.
And a clad part having a lower refractive index than the core part.
A method for manufacturing an optical circuit to be formed, wherein a quartz glass is used as a material, and the at least one of the
As the optical waveguide contains a UV-sensitive dopant,
Step to create the two optical waveguides on the planar substrate
And at least one of the optical waveguides has visible or ultraviolet light.
Irradiation of laser light to adjust the birefringence value of the core portion.
Process for increasing the polarization dependence of a Mach-Zehnder interferometer
And a method for manufacturing an optical circuit.