JP2001255424A - Optical waveguide circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical waveguide circuit having practically satisfactory characteristics wherein the deterioration of various circuit characteristics such as the increase of a circuit size and an excessive loss is restrained. SOLUTION: In the optical waveguide circuit having an optical waveguide 20 consisting of a clad and a core, plural grooves 21 parting the core respectively are formed so as to mutually array at an interval, plural grooves 21 are formed so that distances parting the core become ununiform, and moreover one or more grooves 21 small in the distance parting the core of plural grooves 21 are arranged in the end or in the vicinity of the end of the array.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical waveguide circuit, and more particularly, to an optical waveguide circuit in which a groove is formed by removing a part of a waveguide or a material having appropriate characteristics is inserted into the groove. Things.

[0002]

2. Description of the Related Art Hitherto, research and development of a planar lightwave circuit (PLC) composed of a silica-based glass waveguide formed on a silicon substrate has been actively conducted. Such P
In LC, there are a circuit that realizes optical wavelength multiplexing / demultiplexing, such as an arrayed waveguide diffraction grating (AWG), and a circuit that realizes optical path switching, such as a thermo-optic (TO) switch. As a hybrid PLC on which an optical element is mounted, there is an external resonator type frequency stabilized laser or the like.

For details on AWG, see (H. Takahashi
et al., "Arrayed-Waveguide Grating for Wavelength
Division Multi / Demultiplexer With Nanometer Resolu
tion ", Electron. Lett., vol.26, no.2, pp.87-88, 19
90.). FIG. 9A shows the circuit configuration of the AWG, and FIG. 9B shows an enlarged view of the line AA ′ in FIG. 9A. 9A and 9B, an input waveguide 2, a first slab waveguide 3, an array waveguide 4, a second slab waveguide 5, an output waveguide 6, and a waveguide core are provided on a Si substrate 1. 7, a cladding 8 is provided.

For details on the TO switch, see (M. Okun
o et al., "8x8 Optical Matrix Switch Using Silica-
Based Plannea Lightwave Circuits ", IEICE Trans. El
ectron., vol. 76-C, no. 7, pp. 1215-1223, 1993.). FIG. 10A shows a circuit configuration of the TO switch, and FIG. 10B shows an enlarged cross-sectional view taken along line BB ′ in FIG. In FIGS. 10A and 10B, Si
A substrate 101 includes an input waveguide 102, two directional couplers 103 and 105, and two arm waveguides 104a and 104.
04b, an output waveguide 106, a waveguide core 107, a clad 108, a thin film heater 109, and a wiring 110 are provided.

[0005] For details of an external cavity type frequency stabilized laser, see (T. Tanaka et al., "Integrated Extra C"
avity Laser Composed of Spot-Size Converted LD and
UVWritten Grating in Silica Waveguide on Si ", Ele
ctron. Lett., vol.32, no.13, pp.1202-1203, 1996.)
It is described in. FIG. 11 shows a circuit configuration of the frequency stabilized laser. A semiconductor laser diode (LD) 202, a waveguide core 203, a clad 20
4, a light-induced grating 205 in the waveguide core is provided. In the figure, reference numeral 206 denotes a portion from which quartz glass is removed for mounting a semiconductor LD, and is called a silicon terrace.

In an optical waveguide circuit such as the above-mentioned planar lightwave circuit, a part of the waveguide is removed to form a groove, or a material having an appropriate characteristic is inserted into the groove to further improve the circuit characteristics. Improvements and new features of the circuit can be exploited.

As an example, a groove formed by partially removing a clad and a core is formed in an AWG array waveguide, and the groove has a refractive index temperature coefficient having a sign different from that of the effective refractive index of each waveguide. Material (hereinafter referred to as "temperature compensation material")
There is a method of eliminating the temperature dependence of the transmission wavelength of the AWG by inserting the AWG. The details of this method are described in International Publication No. WO 98/36299.

As another example, a groove in which a clad and a core are partially removed is formed in an arm waveguide of a TO switch, and a refractive index temperature having a sign different from the temperature coefficient of the effective refractive index of the arm waveguide is formed in the groove. There is a method of reducing the power consumption of a TO switch by inserting a temperature compensation material having a coefficient (polymer-assisted TO switch). For details of this method, see Japanese Patent Application Laid-Open No. 2000-029079.
(Japanese Patent Application No. 10-192223).

As another example, a groove in which a clad and a core are partially removed is formed in a waveguide between a light-induced grating and a semiconductor LD of a frequency-stabilized laser, and the temperature of the refractive index of the semiconductor LD is formed in the groove. There is a method of suppressing a mode hop of a frequency-stabilized laser due to a temperature change by inserting a temperature compensation material having a refractive index temperature coefficient having a sign different from that of the coefficient. This method is described in detail in
No. 1-097784 (Japanese Patent Application No. 9-255122).

FIG. 12A shows the structure of an AWG in which the transmission wavelength is made temperature-independent. In the array waveguide 13 of FIG. 12A, a straight waveguide portion 16 is provided at the center of the array waveguide of the AWG of FIG.
Has been added. Here, 11 is an input waveguide, 12 is a first slab waveguide, 14 is a second slab waveguide, 15
Is an output waveguide, 17 is a groove, and the groove 17 is filled with a temperature compensation material. FIG. 12B is an enlarged view of the groove 17. The length of the array waveguide 13 removed by the groove 17 is also proportional to ΔL ′ in accordance with the array waveguide 13 that is gradually increased by a constant amount ΔL.
It has a shape that becomes longer each time.

The temperature compensation material to be filled in the groove 17 has a refractive index temperature coefficient dn '/ dT which is different from the effective refractive index temperature coefficient dn / dT of the arrayed waveguide.
In addition, a temperature compensating material in which | dn '/ dT | is sufficiently larger than | dn / dT | is preferable. As the temperature compensating material under such conditions, for example, there is a silicone resin, and (dn' / dT) −−40 × (dn / dT).

FIG. 13 shows the aforementioned polymer assisted TO.
5 shows an arm waveguide portion of the switch. Where 1
11a and 111b are arm waveguides, 112 is a thin film heater, 113 is a wiring, 114 is a groove, and the groove 114 is filled with a temperature compensation material. The groove 114 is formed on the arm waveguide 111a on one side, and the thin film heater 112
Is located between the arm waveguides 111a and 111b. Further, as a temperature compensation material to be filled in the groove 114,
Like the AWG in which the transmission wavelength is made temperature-independent, a silicone resin or the like is preferable.

FIG. 14 shows the configuration of a frequency-stabilized laser in which mode hops due to the above-mentioned temperature change are controlled. Here, 211 is a semiconductor LD, 212 is a waveguide, 2
13 is a photo-induced grating, 214 is a silicon terrace, 215 is a groove, and the groove 215 is filled with a temperature compensation material. Further, as the temperature compensation material to be filled in the groove 215, a silicone resin or the like is preferable as in the case of the AWG in which the transmission wavelength is made temperature-independent.

In an optical waveguide circuit having a groove formed by removing a part of a waveguide or an optical waveguide circuit in which a material having appropriate characteristics is inserted into the groove, excessive loss due to radiation loss in the groove is caused. Occurs. Excess loss in the groove is AW
The G or TO switch means deterioration of the loss characteristic of the circuit as it is, and the frequency stabilized laser increases the threshold current for oscillation. FIG. 15 shows a case where a part of the quartz glass waveguide is removed to form a groove, and a silicone resin is inserted.
It shows the radiation loss for the groove width, ie the length of the waveguide removed. As shown in FIG. 15, the radiation loss increases rapidly with respect to the groove width. Thus, excess loss can be reduced by dividing the groove into a plurality. That is, from FIG. 15, it can be seen that the radiation loss is reduced by dividing the constant groove width into a plurality. In order to increase the loss by forming the groove, reflection loss at the boundary between the waveguide and the groove can be considered in addition to the radiation loss in the groove, but the radiation loss is dominant. Therefore, by dividing the groove into a plurality of parts, an increase in loss due to the formation of the groove can be reduced.

As a specific form of dividing the groove into a plurality,
In the AWG of FIG. 12A, as shown in FIG.
7, the groove width changes only at the end 17a, and the other portion 17b
Are equal in width. In the portion where the groove width of the end portion 17a changes, the length of the array waveguide 13 to be removed is Δ
Groove 1 is set to increase by L '.
7 has a groove width of w to 2w (w = k × ΔL ′,
k: a natural number), and the next waveguide 13
, The width is returned to w, and another groove 17 is added. By adopting such a shape, the total length of the removed portions of each array waveguide 13 is increased by ΔL ′, and the removed length of the array waveguide 13 is It can be at most 2w.

In the polymer assisted TO switch shown in FIG. 13, the arm waveguide 111a is divided by a plurality of grooves 114 as shown in FIG. The removed length of the arm waveguide 111a is w per location. Further, in the frequency stabilized laser in which the mode hop is suppressed in FIG.
17, the waveguide 212 is divided by the plurality of grooves 215.

Here, when dividing these grooves, if the distance d between the grooves is too short, the groove shape will be approximately as shown in FIG.
There is no division as in (b), and the effect of reducing radiation loss is reduced. It is necessary to secure d at least about 20 times the optical wavelength.

On the other hand, in the planar lightwave circuit, it is possible to reduce the radius of curvature of the curved portion of the waveguide by increasing the relative refractive index difference of the waveguide, thereby realizing the miniaturization of the circuit. For more information on high relative index difference waveguides and their applications, see (S. Suzuki et al., "High-Den
sity Integrated Planar Lightwave Circuits UsingSiO
₂ -GeO ₂ Waveguides with a High Refractive Index Dif
ference ", J. Lightwave Techonol., vol.12, no.5, p
790-796, 1994.). As for the AWG and the TO switch, the size of the circuit can be reduced by applying the high relative index difference waveguide. In a hybrid PLC circuit equipped with a semiconductor LD, the coupling loss between the semiconductor LD and the silica glass waveguide can be reduced by applying a high relative refractive index difference waveguide.

At present, there is a strong demand for the overall miniaturization and cost reduction of the AWG. To this end, not only the miniaturization by applying the high relative refractive index difference waveguide but also the above-mentioned transmission wavelength is controlled by the temperature. It is very important to eliminate the temperature control by applying the technology to make it independent. At the same time, miniaturization and low power consumption of the TO switch are required, and it is also important to apply a high relative refractive index difference waveguide to the polymer assisted TO switch.

AWG, TO using high relative index difference waveguide
When the groove is formed for a switch and a frequency-stabilized laser, the radiation loss in the groove becomes larger than that of a normal relative index difference waveguide. For example, as shown in FIG. 15, the radiation loss of the waveguide having the relative refractive index difference of 1.5% is twice or more in dB compared to the case of the waveguide having the relative refractive index difference of 0.75%. . Therefore, when a high relative index difference waveguide is used, it is necessary to apply the above-mentioned divided groove shape in order to obtain practical loss characteristics.

[0021]

As described above, an optical waveguide circuit using a high relative index difference waveguide has advantages such as small size and low loss coupling with a semiconductor optical device. For application of a high relative index difference waveguide, it is essential to divide a groove filled with a temperature compensation material. However, when the excess loss is reduced by dividing the groove, it is necessary to secure a certain interval between the grooves. Therefore, as the division of the groove increases, the length of the linear waveguide portion for arranging the groove needs to be increased. .

FIG. 18 shows the dependence of the excess loss of the AWG having the groove shape of FIG. 16 on the groove width w, and the dependence of the length of the linear waveguide portion 16 required for disposing the groove 17 on the groove width w. Things. The parameters of the AWG are such that the difference ΔL between the lengths of the adjacent array waveguides 13 is 60 μm,
Were set to 150, and the relative refractive index difference of the waveguide was set to 1.5%. With this design, an arrayed waveguide grating having a wavelength channel interval of 0.8 nm and 16 channels is realized. The length difference ΔL ′ between adjacent arrayed waveguides 13 removed by the groove 17 is 1.25 μm, and the distance d between the adjacent grooves 17 is 50 μm. The grooves were formed by photolithography and reactive etching. Silicone resin was used as a temperature compensation material.

In order to sufficiently reduce the excess loss, w = 5
It is necessary to finely divide the groove 17 to 10 μm, and the length of the linear waveguide portion 16 required at that time is about 200 μm.
0 μm, which leads to an increase in circuit size. This means that the effect of miniaturization by applying the high relative index difference waveguide cannot be sufficiently obtained. That is, in the AWG, in order to reduce the size by applying a high relative refractive index difference waveguide, to make the transmission wavelength independent of temperature, and to realize practical loss characteristics, the number of divisions of the groove filled with the temperature compensation material should be as small as possible. Less
In addition, it is necessary to reduce excess loss in the groove.

FIG. 19 shows a TO having the groove shape of FIG.
FIG. 4 shows the dependence of the excess loss of the switch or the frequency-stabilized laser on the groove width w, and the dependence of the length of the linear waveguide portion required for disposing the groove on the groove width w. The relative refractive index difference of the waveguide is 1.5%, the length of the waveguide removed by the groove is 300 μm in total, and the distance d between adjacent grooves is 50 μm.
m. The grooves were formed by photolithography and reactive etching. In addition, a silicone resin was used as a temperature compensation material.

In this case as well, in order to sufficiently reduce the excess loss, it is necessary to finely divide the groove up to w = 5 to 10 μm.
As a result, the circuit size increases. Furthermore, in the TO switch, the area to be heated by the thin film heater is expanded, that is, the power consumption is increased. In the frequency stabilized laser, the maximum modulation speed is reduced due to the increase in the laser cavity length. Therefore, also in the TO switch or the frequency stabilizing laser, it is necessary to reduce the number of divisions of the groove filled with the temperature compensation material as much as possible and to reduce the excess loss in the groove.

The present invention has been made in view of such a problem, and an object of the present invention is to provide an optical waveguide circuit in which a groove is formed by removing a part of a waveguide, or that the groove has appropriate characteristics. In an optical waveguide circuit in which a material is inserted, by adopting a groove shape in which the number of divisions of the groove is small and the excess loss in the groove is small, deterioration of various circuit characteristics such as an increase in circuit size due to the formation of the groove is suppressed. Another object of the present invention is to provide an optical waveguide circuit having practically sufficient characteristics in which deterioration of various circuit characteristics due to excessive loss in a groove is suppressed.

[0027]

In order to achieve the above object, according to the present invention, in an optical waveguide circuit having an optical waveguide comprising a clad and a core, a plurality of grooves for dividing the core are spaced apart from each other. Formed to be arranged,
The plurality of grooves are formed so that the core division distance is non-uniform, and one or more grooves having a small core division distance among the plurality of grooves are arranged at or near the end of the array. We propose the one that features.

In the case of the divided groove shape as shown in FIGS. 16 and 17, as a result of detailed analysis of the radiation loss in each waveguide, the loss does not occur evenly in each groove, but is relatively located at the end. It was found that the loss in the groove (the groove through which light passes first or the groove through which light passes at the end) was particularly large. The reason is that the radiation loss of the middle groove is reduced by the coupling of the radiation mode from the adjacent groove,
It is considered that the coupling is weak at the end. Therefore, in the present invention, a small number of grooves arranged relatively at the end of each waveguide are formed as thin as possible. With this groove shape, it is possible to suppress excessive loss in the groove without increasing the number of divisions of the groove.

[0029]

DESCRIPTION OF THE PREFERRED EMBODIMENTS (First Embodiment) An optical waveguide circuit according to a first embodiment of the present invention will be described with reference to FIGS. Here, as an optical waveguide circuit,
An array waveguide diffraction grating (AWG) in which the above-mentioned transmission wavelength is made temperature-independent will be described. FIG. 1 is a view for explaining the shape of a groove formed in an array waveguide portion of an AWG, and FIG. 2 is a graph showing the groove width dependence of the excess loss and the groove width dependence of the length of the linear waveguide portion in the AWG. .

This AWG has the same configuration as the conventional AWG described above with reference to FIG. 16, and the array waveguide 20 is divided by a plurality of grooves 21. This AWG
Then, the groove width of the leftmost groove 21 through which light passes first is set to w _min
The width of the other groove 21 is w. Also,
Portions where the groove width of the end portion 21a is changed, the left end of the groove 21 w _min ~w _min + varies linearly with w, the other groove 21 w
It has a shape that changes linearly at ~ 2w.

FIG. 2 shows the dependence of the excess loss of the AWG having the groove shape of FIG. 1 on the groove width w, and the dependence of the length of the linear waveguide portion required for arranging the groove on the groove width w. is there.
FIG. 2 also shows, for comparison, the dependence of the excess loss of the conventional AWG having the groove shape of FIG. 16 on the groove width w. Here, the parameters of the AWG correspond to the adjacent array waveguides 20.
Is 60 μm, the number of arrayed waveguides 20 is 150, and the relative refractive index difference of the waveguides is 1.5%. With this design, the wavelength channel interval is 0.8 nm and the number of channels is 1
6 are realized. Length difference Δ between adjacent arrayed waveguides 20 removed by groove 21
L ′ is 1.25 μm, and the distance d between adjacent grooves 21 is 50 μm. The groove 21 was formed by photolithography and reactive etching, and was set to a minimum groove width w _min = 5 μm in consideration of etching reproducibility. In addition, a silicone resin was used as a temperature compensation material.

As can be seen from FIG. 2, by applying the groove shape shown in FIG. 1 in which the width of the groove through which light passes first is reduced to AWG, excess loss is reduced as compared with the conventional example shown in FIG. can do. For example, the excess loss at w = 15 μm is reduced by 0.2 dB to 1.0 dB from the conventional 1.2 dB.

Second Embodiment An optical waveguide circuit according to a second embodiment of the present invention will be described with reference to FIGS. Here, as an optical waveguide circuit, an arrayed waveguide diffraction grating (A
WG) will be described. FIG. 3 is a diagram for explaining the shape of the groove formed in the array waveguide portion of the AWG, and FIG. 4 is a graph showing the groove width dependence of the excess loss and the length of the linear waveguide portion in the AWG. .

This AWG has the same structure as the conventional AWG described above with reference to FIG. 16, and the array waveguide 30 is divided by a plurality of grooves 31. All grooves 3
1 of the groove width has become a w, also part groove width of the end portion 31a is changed are shaped to vary the width w _min ~w _{m in} + w. This shape is obtained by reducing the width of the groove 31 through which the light finally passes.

FIG. 4 shows the dependence of the excess loss of the AWG having the groove shape of FIG. 3 on the groove width w, and the dependence of the length of the linear waveguide portion required for arranging the groove on the groove width w. is there.
FIG. 4 also shows, for comparison, the dependence of the excess loss on the groove width w of the conventional arrayed waveguide grating having the groove shape of FIG. The AWG parameters are the same as in the first embodiment. The length difference ΔL ′ between adjacent array waveguides 30 removed by the groove 31 is 1.25 μm,
The distance d between the adjacent grooves 31 is 50 μm. The groove 31 is formed by photolithography and reactive etching, and considering the reproducibility of the etching, the end 31 of the groove 31 is formed.
Let w be the groove width (minimum groove width) at the tip of the portion where the groove width of a changes.
_min = 5 μm was set. In addition, a silicone resin was used as a temperature compensation material.

As can be seen from FIG. 4, by applying the groove shape of FIG. 3 in which the width of the groove through which light finally passes is narrowed, the same as the groove shape of FIG. 1 can be applied to the conventional example shown in FIG. In comparison, excess loss can be reduced. For example, w =
The excess loss at 15 μm is reduced by 0.4 dB to 0.8 dB from the conventional 1.2 dB.

(Third Embodiment) An optical waveguide circuit according to a third embodiment of the present invention will be described with reference to FIGS. Here, as an optical waveguide circuit, an arrayed waveguide diffraction grating (A
WG) will be described. FIG. 5 is a diagram for explaining the shape of the groove formed in the array waveguide portion of the AWG, and FIG. 6 is a graph showing the groove width dependence of the excess loss and the groove width dependence of the length of the linear waveguide portion in the AWG. .

This AWG has the same configuration as the conventional AWG described above with reference to FIG. 16, and the array waveguide 40 is divided by a plurality of grooves 41. The groove 41 is
1 and has a composite shape the shape shown in FIG. 3, the width of the left edge of the groove 41 is narrower and w _{mi n,} the groove width of the other grooves 41 is to w. The portion where the groove width of the groove end portion 41a is changed, changes in the left end of the groove 41 w _min ~2w _min, in other has a shape that varies the width w _min ~w _{m in} + w.

FIG. 6 shows the dependence of the excess loss on the groove width w of the arrayed waveguide diffraction grating having the groove shape of FIG. 5 and the dependence of the length of the linear waveguide portion required for arranging the groove on the groove width w. It is shown. FIG. 6 also shows, for comparison, the dependence of excess loss on the groove width w of the conventional arrayed waveguide grating having the groove shape of FIG. The parameters of the arrayed waveguide diffraction grating are the same as in the first embodiment. The length difference ΔL ′ between adjacent arrayed waveguides 40 removed by the groove 441 is 1.25 μm, and the interval between adjacent grooves 41 is 50 μm. The groove 41 is formed by photolithography and reactive etching. In consideration of the reproducibility of the etching, the width of the leading end of the portion where the groove width of the groove end 41a changes and the width of the left end groove 41 (minimum groove width). To w _min = 5μ
m. Silicone resin was used as a temperature compensation material.

As can be seen from FIG. 6, by applying the groove shape of FIG. 5 in which the width of the groove through which light passes first and last is reduced, excess loss can be reduced as compared with the conventional example shown in FIG. Can be reduced. Also, it can be seen that the effect of reducing the excess loss is greater than the groove shape in the first and second embodiments. For example, the excess loss at w = 15 μm is reduced to 0.6 dB from 1.2 dB of the conventional example, and is comparable to the conventional excess loss of 0.5 dB at w = 5 μm. However, while the length of the linear waveguide required when w = 5 μm is 1900 μm, the length of the linear waveguide required when w = 15 μm is:
It is 650 μm which is 35% of that.

(Fourth Embodiment) An optical waveguide circuit according to a fourth embodiment of the present invention will be described with reference to FIGS. Here, the above-described polymer assisted thermo-optic (TO) switch will be described as an optical waveguide circuit. FIG. 7 is a view for explaining the shape of the groove formed in the arm waveguide portion of the TO switch, and FIG. 8 is a graph showing the groove width dependence of the excess loss and the groove width dependence of the length of the linear waveguide in the TO switch. It is.

In this polymer assisted TO switch, the polymer assisted T switch described above with reference to FIG.
It has the same configuration as the O-switch, and has the arm waveguide 5
0 is divided by a plurality of grooves 51. In this polymer assisted TO switch, the width of the groove 51 through which light passes first and last is narrower than the other grooves 51.

FIG. 8 shows the dependence of the excess loss of the polymer assisted TO switch having the groove shape of FIG. 7 on the groove width w, and the dependence of the length of the linear waveguide portion required for disposing the groove 51 on the groove width w. It is shown. FIG. 8 also shows, for comparison, the dependence of the excess loss on the groove width w of the conventional polymer assisted TO switch having the groove shape of FIG. The relative refractive index difference of the waveguide is 1.5%, the length of the waveguide removed by the groove 51 is 300 μm in total, and the interval between adjacent grooves 51 is 50 μm. The groove 51 was formed by photolithography and reactive etching, and was set to a minimum groove width w _min = 5 μm in consideration of reproducibility of etching. Silicone resin was used as a temperature compensation material.

As can be seen from FIG. 8, by applying the groove shape of FIG. 7 in which the width of the groove 51 through which light passes first and last is reduced, the excess loss compared with the conventional example shown in FIG. Can be reduced. For example, the excess loss at w = 15 μm is 0.4 dB compared to 0.8 dB of the conventional example.
B, which is equivalent to the excess loss of 0.4 dB at w = 5 μm of the conventional example. However, the required length of the linear waveguide portion when w = 5 μm is 3000 μm, whereas the required length of the linear waveguide portion when w = 15 μm is 750 μm, which is 25% of the length.

In this embodiment, the polymer assisted TO switch has been described as an example of the arrayed waveguide. However, the present invention can be applied to a frequency-stabilized laser by forming the same groove shape as in this embodiment. can do.

From the above four embodiments, it has been confirmed that, in the optical waveguide circuit of the present invention, although the number of divisions is relatively small, excess loss is reduced as compared with the related art. As a result, according to the present invention, the number of divisions of the groove is reduced, that is, the length of the linear waveguide portion required for arranging the groove is shortened, and while the deterioration of various circuit characteristics such as an increase in circuit size is suppressed, the groove is simultaneously And it is possible to obtain an optical waveguide circuit having practically sufficient characteristics.

In the four embodiments described above, A
Although examples related to the WG, the TO switch, and the frequency stabilizing laser are given, the present invention is not limited to these circuits, and a part of the waveguide is removed to form a groove, or further, the groove is formed. The present invention covers all optical waveguide circuits in which a material having appropriate characteristics is inserted.

In the above-described four embodiments, the relative refractive index difference of the waveguide is limited to a specific value. However, the applicable range of the present invention is not limited to this specific refractive index difference.

Further, in the first to third embodiments, A
Although the parameters of the WG are limited to specific values, the scope of the present invention is not limited to these parameters.

[0050]

As described above in detail, according to the present invention, in an optical waveguide circuit, a groove is formed by removing a part of a waveguide, or a material having appropriate characteristics is inserted into the groove. In this case, while the required length of the linear waveguide portion is kept to a necessary minimum, the excess loss in the groove can be kept relatively small, and an optical waveguide circuit having practically sufficient characteristics can be realized.

[Brief description of the drawings]

FIG. 1 is a view for explaining the shape of a groove formed in an array waveguide portion of an AWG.

FIG. 2 is a graph showing the groove width dependence of the excess loss and the groove width dependence of the length of the linear waveguide portion in the AWG.

FIG. 3 is a view for explaining the shape of a groove formed in an array waveguide portion of an AWG.

FIG. 4 is a graph showing the groove width dependence of the excess loss and the groove width dependence of the length of the linear waveguide portion in the AWG.

FIG. 5 is a view for explaining the shape of a groove formed in an array waveguide portion of an AWG.

FIG. 6 is a graph showing the groove width dependence of the excess loss and the groove width dependence of the length of the linear waveguide portion in the AWG.

FIG. 7 is a view for explaining the shape of a groove formed in an arm waveguide portion of the TO switch.

FIG. 8 is a graph showing the groove width dependence of the excess loss and the groove width dependence of the length of the linear waveguide portion in the TO switch.

FIG. 9 is a configuration diagram of a conventional AWG.

FIG. 10 is a configuration diagram of a conventional TO switch.

FIG. 11 is a configuration diagram of a conventional frequency stabilized laser.

FIG. 12 is a configuration diagram of a conventional AWG in which the transmission wavelength is made temperature-independent.

FIG. 13 is a configuration diagram of a conventional TO switch in which the transmission wavelength is made temperature-independent.

FIG. 14 is a configuration diagram of a conventional frequency-stabilized laser whose transmission wavelength is made temperature-independent.

FIG. 15 is a graph illustrating the relationship between the length of a waveguide removed by a groove and radiation loss.

FIG. 16 is a view for explaining a groove shape in a conventional AWG in which a transmission wavelength is made temperature-independent.

FIG. 17 is a view for explaining a groove shape in a conventional TO switch in which the transmission wavelength is made temperature-independent.

FIG. 18 is a graph showing the groove width dependence of the excess loss and the groove width dependence of the length of the linear waveguide portion in the conventional AWG.

FIG. 19 is a graph showing the groove width dependence of the excess loss and the groove width dependence of the length of the linear waveguide portion in the conventional TO switch.

[Explanation of symbols]

1: Si substrate, 2, 11: input waveguide, 3, 12: first
Slab waveguides, 4,13 ... array waveguides, 5, 14 ...
2nd slab waveguide, 6, 15 ... output waveguide, 7 ... waveguide core, 8 ... clad, 17 ... groove, 20, 30, 40 ...
Array waveguide, 50 ... arm waveguide, 21, 31, 4
1, 51: groove, 101: Si substrate, 102: input waveguide, 103, 105: directional coupler, 104a, 104
b, 111a, 111b: arm waveguide, 106: output waveguide, 107: waveguide core, 108: clad, 10
9, 112: thin film heater, 110: wiring, 114: groove,
201: Si substrate, 202, 211: semiconductor laser diode, 203: waveguide core, 204: clad, 20
5,213 ... light-induced grating, 206,214 ...
Silicon terrace, 212: waveguide, 215: groove

Continuation of the front page (72) Inventor Yasuyuki Inoue 2-3-1 Otemachi, Chiyoda-ku, Tokyo Within Nippon Telegraph and Telephone Corporation (72) Inventor Akio Sugita 2-3-1 Otemachi, Chiyoda-ku, Tokyo Date F-term (for reference) within the Telegraph and Telephone Corporation 2H047 KA04 KA11 KA12 KA15 KB04 LA02 QA01 TA00 TA01 2H050 AB03Z AC82 AC84

Claims (9)

[Claims] 1. An optical waveguide circuit comprising an optical waveguide comprising a clad and a core, wherein a plurality of grooves for dividing the core are formed so as to be arranged at an interval from each other, and the plurality of grooves are separated from each other by a dividing distance of the core. Is formed non-uniformly, and one or more grooves having a small core separation distance among the plurality of grooves are arranged at or near the end of the array. 2. The optical waveguide circuit according to claim 1, wherein a groove having a minimum separation distance of the core is arranged at one end of the array. 3. The optical waveguide circuit according to claim 1, wherein grooves having a minimum separation distance of the core are arranged at both ends of the array. 4. The optical waveguide circuit according to claim 1, wherein the clad and the core are made of quartz glass. 5. The optical waveguide circuit according to claim 1, wherein a material different from that of the core is inserted into the groove. 6. The optical waveguide circuit according to claim 5, wherein the material inserted into the groove has a refractive index temperature coefficient having a sign different from that of the effective refractive index of the optical waveguide. 7. An optical waveguide comprising a plurality of arrayed waveguides, comprising a slab waveguide connected to both ends of the arrayed waveguide, wherein the groove is formed across the arrayed waveguide. The optical waveguide circuit according to claim 1, wherein: 8. The optical waveguide includes two arm waveguides having different lengths, a directional coupler connected to both ends of the arm waveguide, and the groove connects one of the arm waveguides. The optical waveguide circuit according to claim 1, wherein the optical waveguide circuit is formed to cross. 9. A light-induced grating is formed in the optical waveguide, a semiconductor laser diode is mounted on an end of the optical waveguide, and the groove forms an optical waveguide between the light-induced grating and the semiconductor laser diode. The optical waveguide circuit according to claim 1, wherein the optical waveguide circuit is formed to cross.