JPH01158413A - Optical waveguide device - Google Patents

Abstract

PURPOSE:To decrease the power consumption and to reduce mutual interference (crosstalk) by separating part of an optical waveguide substantially from a substrate and providing a heater for adjusting the length of an optical path finely on the separated optical waveguide. CONSTITUTION:Grooves 11a and 11b are formed in part of a clad layer 3 in the lengthwise direction of a core part and reach the silicon substrate. Part of the silicon substrate 1 is etched away so as to link the bottom parts of those grooves 11a and 11b, and thus a silicon substrate removal area 12 is formed to suppress heat conduction from the heated optical waveguide part 13 to the substrate 1. Namely, the thin film heater 4 as a heating body for adjusting the phase is loaded on the optical waveguide part 13 separated from the silicon substrate 1. The heating efficiency of the optical waveguide is improved. Consequently, the power consumption is made small and the mutual interference (crosstalk) is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a single mode optical waveguide, and more particularly to an optical waveguide device that can adjust the optical path difference of an optical waveguide.

[Prior Art] Conventionally, single-mode optical waveguides fabricated on flat substrates, particularly silica-based glass single-mode optical waveguides fabricated on silicon substrates, have the cross-sectional dimensions of their core portions that are normally used. Since it can be set to about 5 to 10 μm to match a single mode optical fiber, it is expected to be a means of realizing a practical waveguide type optical component with excellent compatibility with the optical fiber.

In particular, waveguide optical interferometers constructed from silica-based glass single-mode optical waveguides are expected to be important optical components for single-mode optical fiber communications and optical sensors.

In the field of waveguide optical interferometers, it is necessary for optical waveguides to have a function of adjusting the phase of propagating light.

FIG. 5 shows an example of a schematic configuration of a conventional silica-based glass optical waveguide having a phase adjustment section. FIG. 5(a) is a plan view of the above-mentioned optical waveguide, and FIG. 5(b) is a plan view of the above-mentioned optical waveguide.
It is a sectional view along the A' line. Here, 1 is a silicon substrate, 2 is a core made of silica glass, 3 is a cladding layer made of silica glass that embeds the core 2 and surrounds the core 2, and 4 is a cladding layer 3 on the core 2. This is a thin film heater as a phase adjuster formed on the surface of.

In the above configuration, when the thin film heater 4 is energized and the core portion 2 is heated through the cladding layer 3, a so-called thermo-optic effect occurs.
As a result, the refractive index of the core portion 2 increases, the effective optical path length under the thin film heater 4 changes, and the phase of the propagating light can be changed. Temperature coefficient dn of refractive index of silica glass
/dT is about 1O-5 (1/t), so 1 c
If the temperature of the optical waveguide is increased by 10° C. over a length of m, the optical path length can be changed by about 1 μm.

The above-mentioned phase adjustment section that utilizes the thermo-optic effect is effective as a phase adjustment means for a glass optical waveguide that does not have a significant electro-optic effect.

[Problems to be solved by the invention] However, since "heat" is used, the following practical problems arise.

The heat generated by the thin film heater 4 is used to raise the temperature near the core part 2, and most of the heat is also used to increase the temperature in the vicinity of the core part 2.
This has led to problems such as poor heating efficiency and increased power consumption.

Furthermore, if a plurality of thin film heaters 4 used for phase adjustment are integrated on the same silicon substrate 1, the silicon substrate 1
There was a problem in that the heat of one thin film heater 4 was transmitted to the vicinity of the other thin film heater 4 via the thin film heater 4, causing mutual interference (crosstalk).

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to solve the above-mentioned problems and provide an optical waveguide device in which the heating efficiency of the heater is good, the increase in power consumption is suppressed, and mutual interference is less likely to occur. It's about doing.

[Means for Solving the Problems] In order to achieve the above object, the present invention includes a substrate and an optical waveguide disposed on the substrate with a core portion covered with a cladding layer, and a part of the optical waveguide is A heating element for finely adjusting the optical path length is disposed on the cladding layer, and heat conduction from the optical waveguide heated by the heating element to the substrate is suppressed.

[Function] According to the present invention, a portion of the optical waveguide is substantially separated from the substrate, and a heater for finely adjusting the optical path length is provided above the separated optical waveguide. It is possible to provide an optical waveguide device that has good heating efficiency for the waveguide, and therefore has low power consumption and low mutual interference (crosstalk).

[Example] Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

Embodiment 1 FIG. 1 shows the configuration of an embodiment of the present invention. Figure 1 (a
) is a plan view thereof, and FIG. 1(b) is a sectional view taken along line BB' in FIG. 1(a). In this example, the fourth
Unlike the conventional optical waveguide shown in the figure, the cladding layer 3
Grooves 11a and llb are provided along the longitudinal direction of the core portion 2 in a portion thereof, and reach the silicon substrate 1. A part of the silicon substrate 1 is removed by etching so that the bottoms of these grooves 11a and llb are communicated with each other to form a silicon substrate removed region 12, thereby preventing heat conduction from the heated optical waveguide section 13 to the substrate 1. Configure to suppress. As described above, the thin film heater 4 as a heating body for adjusting the phase is loaded on the top of the optical waveguide section 13 separated from the silicon substrate 1.

The structural specifications of the optical waveguide having such a configuration can be determined in various ways, but here they are determined as follows. That is, the thickness of the silicon substrate 1 is 0.7 mm, and the thickness of the cladding layer 3 is 0.7 mm.
Thickness is 50μm 1 Core section 2 cross-sectional dimensions are 8μm x 8μ
The relative refractive index difference between the m1 core part and the cladding layer was set to 0.2%.

Such a silica-based optical waveguide structure has a 5fCJ24°T
It is produced by a combination of glass film deposition technology using flame hydrolysis reaction of raw material gas such as iCIL4 and reactive ion etching technology (Masao Kawachi: "Microfabrication of quartz-based optical waveguides", Japan Society of Applied Physics Optics Journal of the Konwakai Micro-Optics Research Group, 1986, Vol. 4, No.
, 2, pp. 33-38).

The groove width of grooves 11a and llb is 60 μm, and the length of each is 2 m.
The separation optical waveguide section 13 was arranged so that the width of the separated optical waveguide section 13 was 60 μm. Grooves 11a and llb are formed in the cladding layer 3.
It is formed by removing a portion of the silicon substrate 1 by reactive ion etching until the silicon substrate 1 is exposed. Through these grooves 11a and llb, a portion of the silicon substrate 1 is removed by chemical etching to a depth of approximately 50 μm, thereby forming a separated optical waveguide section 13.

As the chemical etching solution for the silicon substrate 1, hydrofluoric acid,
A mixture of nitric acid and acetic acid was used.

The thin film heater 4 has a thickness of 0.3 μm and a width of 50 μm, for example.
A chromium metal film was formed by vacuum evaporation over an effective length of about 2 mm. Approximately 1 (When 1 mW of power is applied to the thin film heater 4, the optical path length of the optical waveguide becomes 0.2 μ.
m was observed to increase. This increase in optical path length is caused by the core portion 2 of the separated optical waveguide portion 13 located below the thin film heater
This corresponds to an approximately 10°C increase in temperature near .

For comparison, when an optical waveguide with a conventional phase adjustment section shown in FIG. 5 was constructed (the structure of the thin film heater 4 was the same as that in FIG. 1), the optical path length increased by 0.2 μm. The power required to be applied to the thin film heater 4 was approximately 100 mW.

As is clear from this comparative example, according to the configuration of the present invention, phase adjustment can be realized with approximately one partner power consumption compared to the conventional configuration.

FIG. 2 shows a configuration example of a second embodiment of the present invention. FIG. 2(a) is a plan view of the same, and FIGS. 2(b) and (c) are the lines C-C' and D-, respectively, in FIG. 2(a).
FIG. 3 is a sectional view taken along line D'.

The section taken along the line CC' shown in FIG. 2('b) has the same structure as that shown in FIG. 1. In this embodiment, unlike the first embodiment, there are a plurality of grooves 21a, 21b, 22a, and 22b.

23a, 23b are provided, grooves 21a, 21b and 22a, 2
2b and the bridge structure 318° between the grooves 22a, 22b and 23a, 23b 31b and 32a, 32b
(See FIG. 2(a)). These grooves 21a, 2
1b, 22a, 22b, 23a, and 23b are as shown in FIG. 2(b), whereas the bridge structures 31a, 31b, 32a, and 32b are as shown in FIG. 2(C). In addition, the cladding layer 3 has a bridge shape. For this purpose, the separated optical waveguide section 13 corresponding to the portion where the thin film heater 4 is arranged is connected to each bridge structure section 3.
Silicon substrate 1 by 1a, 31b, 32a, 32b
is supported by

By adopting such a configuration, it is possible to suppress heat conduction from the heated optical waveguide portion I3 to the substrate 1. Here, the separated optical waveguide section 13 is the core section 2.
It is divided into a plurality of pieces along the longitudinal direction and supported by the silicon substrate 1 by bridge structures 31a, 31b, 32a and 32b.

The cross-sectional dimensions of the core portion 2 in this embodiment can be determined in the same manner as in the first embodiment. In addition, in this example, the valley grooves 21a, 21b
, 22a, 22b, 23a and 23b are determined to have a longitudinal length of 440 μm, and the bridge structure portions 31a, 31b
.

The width of 32a and 32b was 60 μm. In this way, the total length of the groove and the width of the bridge structure is 500
The bridge structure is repeated with a period of μm, and the length is 10 mm.
A separated optical waveguide section 13 and a silicon substrate removal region 12 having a length of . In FIG. 2(a), only a three-period bridge structure is shown to simplify the illustration.

On the upper surface of the separated optical waveguide section 13, a thin film heater 4 having a length of about 10 ma+ was formed based on chromium metal thin film deposition.

By employing the bridge structure as described above, it was possible to maintain the formation of the separation leading cover 13 loaded with the relatively long thin film heater 4, which is several millimeters long or more, without being damaged.

When a power of 50 mW was applied to the thin film heater 4 described above, the optical path length changed by about 1 μm. Incidentally, in the case of the conventional configuration in which the separation optical waveguide section 13 is not formed, the thickness is 1 μm.
It should be noted that an applied power of about 500 mW was required to achieve a change in optical path length of . This shows that by providing the separated optical waveguide section 13, the heat generated by the thin film heater 4 is effectively utilized without being wastedly diffused into the silicon substrate 1, and also that the bridge structure sections 31a, 31b , 32a, 32b to the silicon substrate 1 has a sufficiently high heat insulation property.

FIG. 3 shows the configuration of a third embodiment of the present invention, which is an example of application to an optical switch array.

In FIG. 3, four rows of optical switches are closely integrated on the same silicon substrate 1. In FIG.

In FIG. 3, 41a, 41b, 42a, 42b, 4
3a, 43b.

44a and 44b are directional optical couplers (3dB couplers) constructed of silica-based optical waveguides; 41c and 41d;
2c and 42d, 43c and 43d, 44c and 44d are directional couplers 41a and 41b, 42a and 42b, respectively.
, 43a and 43b, and 44a and 44b are arranged to connect as a pair and are used for phase adjustment. For example, the directional couplers 41a and 41b are connected via optical waveguides 41c and 41d with thin film heaters to form an optical circuit of a symmetrical Matsuzha-Zehnder optical interferometer. 41e and 41f, 42e and 42f, 43e and 43f
, 44e and 44f are optical couplers 41a, 44f, respectively.
42a, 43a, and 44a. 41g and 41h, 42g and 112h, 43g and 43h, 443 and 44h are optical couplers 41b, 42b, and 43b, respectively.
, 44b.

By having such an optical circuit configuration, the input terminal 41e
The signal light incident from the output terminal 4 is
It is emitted from 1h. However, when the optical waveguide 41c or 41d with a thin film heater is energized to change the optical path length by an amount equivalent to 1/2 of the signal light wavelength, the output end from which the light is emitted changes from 41h to 41g due to the well-known optical interference principle. do. In other words, such a Matsuha-Zehnder optical interferometer circuit acts as an optical switch.

An example of the approximate dimensions of the arrangement of the optical waveguides in FIG. 3 is the input ends 41e, 41f, 42e, 42f, 43e,
43f.

44e and 44f have a pitch of 250 μm, and the output end 41
g.

41h, 42g, 42h, 43g, 43h, 44g, 4
The pitch for 4h was also the same. The optical waveguide with a thin film heater of this example had a segmented single optical waveguide structure similar to that of Example 2 shown in the second diagram, and its effective heating length was 10 mm. The dimensions of the silicon substrate 1 were 1 cm in length and 4 cm in width.

Generally, in a structure in which multiple optical switches are integrated on the same silicon substrate, when electricity is applied to a thin film heater for the switching operation of a specific optical switch, the generated heat is transferred to the adjacent thin film heater via the silicon substrate. Conventional optical switches using the thermo-optic effect have had the problem that the interference is transmitted to the optical switch, causing malfunction of adjacent optical switches, that is, mutual interference (crosstalk) occurs.

However, in the optical switch using the separated optical waveguide according to the present invention and the phase shifter using the thin film heater, the above-mentioned conventional problems are suppressed to a minimum. In fact, with the configuration shown in Figure 3, a switching operation is performed by energizing an arbitrary thin film heater.
When the intensity change of signal lights passing through adjacent optical switches at the same time was observed, the intensity change was less than 0.1%. On the other hand, although the scale is the same as that of the embodiment shown in FIG.
However, when an optical switch array without a separated optical waveguide section was formed with the same configuration as the conventional example, a change in intensity of several percent was observed, which was inconvenient in practice.

The configuration of this example achieves approximately one order of magnitude lower power consumption than the conventional configuration, and it cannot be overlooked that the reduction in power consumption contributes to the reduction of crosstalk. be.

In the above embodiment, the core part 2 was completely separated from the silicon substrate 1 in the silicon substrate removal region 12, but as shown in the next embodiment, the object of the present invention can be achieved even if the core part 2 is not completely separated. can do.

Embodiment 4 FIG. 4 is a sectional view showing the configuration of a fourth embodiment of the present invention. The difference from Example 1 shown in FIG. 1 is that the silicon substrate in the silicon substrate removed region 12 below the separated optical waveguide section 13 is not completely separated, leaving a connecting section 51. In this example as well, the silicon substrate removed region 12 is configured to suppress heat conduction from the heated optical waveguide section 13 to the substrate 1.

As an example, the width of the separated optical waveguide portion 13 was approximately 60 μm, and the width of the connecting portion 51 was approximately 20 μm at its narrowest point. In such a structure, a part of the cladding layer 3 is removed by reactive ion etching using C2F8 gas as the main etching gas to form grooves 11a and llb, and then the etching gas is changed to SF6 to form a so-called under-etching layer on the silicon substrate 1. It was made by dry etching with a slight cut.

In this embodiment, compared to the first embodiment, although the connecting portion 51 remains, the width of the connecting portion 51 is relatively narrow.
Compared to the conventional structure shown in the figure, heat conduction to the silicon substrate 1 is slight, and a nearly one-digit reduction in power consumption has been achieved. It is true that power consumption and crosstalk are reduced slightly compared to Example 1 shown in FIG.
It has the advantage that it is easy to maintain its mechanical strength and can withstand use in environments where mechanical vibration is applied.

In this way, the implementation of the present invention can be carried out in several different ways depending on the field of application. ! ! 1 (Example 1) and incomplete separation (Example 4) can be used.

In the above embodiments, the present invention was explained using a silica-based glass optical waveguide on a silicon substrate as an example.
This is because a silica-based glass optical waveguide is practically advantageous in terms of compatibility with optical fibers. However, the present invention is not limited only to silica-based glass optical waveguides, but can of course be applied to optical waveguides made of other glass materials, for example, silicon nitride as a core portion.

Furthermore, in forming the silicon substrate isolation region, in the above embodiment,
Although a configuration in which a part of the silicon substrate is removed by etching has been shown, it is of course possible to adopt a method of etching and removing a desired area of the silicon substrate from the back surface of the silicon substrate depending on the case.

[Effects of the Invention] As explained above, according to the present invention, a part of the optical waveguide is substantially separated from the substrate, and a heater for finely adjusting the optical path length is provided above the separated optical waveguide. Since the heating efficiency of the optical waveguide is good,
Therefore, it is possible to provide an optical waveguide device with low power consumption and low mutual interference (crosstalk).

Furthermore, in the present invention, the structure configured to suppress heat conduction from the heated optical waveguide section to the substrate is not limited to the upper side, but may include, for example, arranging a spacer made of a material with low thermal conductivity in the area where the silicon substrate is removed. From the viewpoint of materials, it is also possible to configure the optical waveguide to suppress heat conduction from the heated optical waveguide section to the substrate.

The optical waveguide device of the present invention is extremely effective in providing a wide variety of waveguide optical components by imparting tuning and switching functions to glass optical waveguides.

[Brief explanation of the drawing]

FIGS. 1(a) and (b) are a plan view and a cross-sectional view taken along the line B-B', respectively, showing the configuration of a first embodiment of the present invention; FIGS. 2(a), (b), and (c) is the second aspect of the present invention.
A plan view, a sectional view taken along line CC', and a sectional view taken along line D-D', showing the configuration of the embodiment, respectively; FIG. 3 is a plan view showing the configuration of an optical switch as a third embodiment of the present invention; FIG. 4 is a sectional view showing the configuration of a fourth embodiment of the present invention, and FIGS. 5(a) and 5(b) are a plan view and a cross section taken along line A-A', respectively, showing the schematic configuration of a conventional optical waveguide. It is a diagram. DESCRIPTION OF SYMBOLS 1...Silicon substrate, 2...Core part, 3...Clad layer, 4...Thin film heater, 11a, llb...-groove, l2...Silicon substrate removal area, 13...Separation Optical waveguide section, 21a, 21b, 22a, 22b, 23a, 23b -
--Groove, 31aJ1b, 32a, 32b--Bridge structure, 41a, 41b, 42a, 42b, 43a, 4
3b, 44a, 44b = directional coupler, 41c, 41d, 42c, 42d, 43c, 43d, 4
4c, 44d... Optical waveguide with thin film heater, 41e, 41f, 42e, 42f, 43e, 43f, 4
4e, 44f...Input end, 41g, 41h, 42g, 42h, 43g, 43h, 4
4g, 44h...Output end, 51...Connection part. Patent applicant Nippon Telegraph and Telephone Corporation

Claims (1)

[Scope of Claims] 1) A substrate and an optical waveguide disposed on the substrate with a core portion covered by a cladding layer, and a heating body for finely adjusting the optical path length of a portion of the optical waveguide is provided on the cladding layer. An optical waveguide device, characterized in that the optical waveguide device is arranged on a layer and configured to suppress heat conduction from the optical waveguide heated by the heating body to the substrate. 2) The core part and the cladding layer are each made of S.
The optical waveguide device according to claim 1, wherein the optical waveguide device is made of silica-based glass containing iO_2 as a main component.