JPH10206911A - Optical monitor circuit and method of manufacturing the same - Google Patents

Abstract

(57) Abstract: An optical waveguide type directional coupler of an optical monitor circuit is capable of easily changing a branching ratio and reducing insertion loss of an optical monitor. . An optical monitor circuit having an optical waveguide type directional coupler has a trench portion having a depth reaching or less than a core, and a trench portion located immediately above a coupling portion of the optical waveguide type directional coupler. And a heater positioned above the joint.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical communication device, an optical integrated circuit, and an optical monitor circuit used for adjusting, inspecting, and monitoring the state of an optical fiber network, and a method of manufacturing the same.

[0002]

2. Description of the Related Art Conventionally, a directional coupler or a Y-branch circuit having a predetermined branching ratio has been used for an optical monitor circuit for adjusting, inspecting and monitoring the state of an optical communication device, an optical integrated circuit and an optical fiber network. Have been. These directional couplers and Y-branch ratio circuits can take out light output at a fixed branch ratio, and can monitor light at the branch.

[0003] A directional coupler is an important element for dividing or coupling an optical circuit, and couples two parallel optical waveguides arranged close to each other and propagates one of the optical waveguides. This is to propagate light energy to the other optical waveguide. The directional coupler needs to have a certain branching ratio depending on the application, and this branching ratio varies depending on the distance between two parallel optical waveguides and the length of the coupled optical waveguide. In general, the smaller the interval, the larger the branch,
When it is wide, it becomes small. Further, the longer the length of the coupled optical waveguide, the larger the branch. However, if the length exceeds the maximum branch length (the length at this time is referred to as a coupling length L), the branch becomes smaller. . The branching ratio is minimized at twice the coupling length L, and maximizes again at three times the length. Thus, the branching ratio varies periodically with the length of the bond.

[0004] The bond length L is expressed as in equation (1).

[0005]

Equation (1) L = π / (2χ) where χ
Is a coupling coefficient, which represents a degree of light power transfer between two parallel optical waveguides.

If the spacing between the two optical waveguides and / or the length of the coupled optical waveguides can be changed in any way, the branching ratio can be changed. However, since the shape of the distance between the two optical waveguides and the length of the coupled optical waveguides are fixed in the directional coupler, it is difficult to adjust the distance and the length of the optical waveguides to an arbitrary value. It is.

Further, in the conventional optical monitor circuit, even when the state of the optical communication device, the optical integrated circuit, and the optical fiber network are not adjusted, and the inspection and monitoring are not performed, a constant branch optical output is output. turn into. Therefore, in the optical communication device, the optical integrated circuit, and the optical fiber network as a whole, the monitor light is a kind of leakage light, which has been a factor of increasing the loss.

[0008]

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to easily change and adjust the branching ratio of a directional coupler in an optical monitor circuit. And an optical monitor circuit that takes out monitor light only during monitoring and stops taking out monitor light when it is not necessary, so as not to cause loss to the optical communication device, optical integrated circuit, optical fiber network, etc. It is to provide a manufacturing method thereof.

[0009]

According to a first aspect of the present invention, there is provided an optical monitor circuit having an optical waveguide type directional coupler.
Immediately above the coupling portion of the optical waveguide type directional coupler, a trench portion reaching or smaller than the core, a filler filled in the trench portion, and a heater located above the coupling portion are provided. It is characterized by having.

According to a second aspect of the present invention, an optical waveguide type directional coupler in which two optical waveguides are brought close to each other is formed on a substrate, and reaches a core immediately above a coupling portion of the optical waveguide type directional coupler. After forming a trench portion with a depth of less than or equal to that by etching, the trench portion is filled with a filler, and a heater is formed above the joint portion.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, a minute groove (trench) is formed directly above a coupling portion of a directional coupler, a filler is buried therein, and the refractive index of the filler is changed. Secondly, the same effect as actually changing the distance between the two optical waveguides and the length of the coupled waveguide is obtained. That is, when the refractive index of the filler is changed, the exudation of the evanescent light to the cladding of the optical waveguide changes, and as a result, the coupling coefficient の of the two optical waveguides changes. When the coupling coefficient 変 化 changes, the coupling length of the optical waveguide effectively changes in inverse proportion to the value of χ, as is clear from equation (1). As described above, since the branching ratio changes depending on the length of the coupling length, the branching ratio can be changed by changing the refractive index of the filler. The groove may have a depth reaching the core or a depth smaller than that.

In the present invention, a change in the refractive index of the filler due to the thermo-optic effect is used to increase the variable width of the refractive index. For this reason, it is preferable to use, as the filler, an organic material having a temperature coefficient of the refractive index larger than that of the cladding (for example, quartz glass (temperature coefficient of the refractive index + 0.00001)). However, the magnitude of the temperature coefficient of the refractive index is compared by an absolute value.

The main components of those having a large change in refractive index with temperature which are preferably used as a filler in the present invention are listed below, and the refractive index and the temperature coefficient of the refractive index are shown.

[0014]

[Table 1]

In the present invention, a change in refractive index with temperature is small, but a transparent material having a refractive index at a wavelength of 1.55 μm smaller than that of quartz glass cladding and a material shown in Table 1 above are appropriately combined with each other at room temperature. A material whose refractive index is adjusted to be 1.444, which is the same as the refractive index of quartz glass, may be used as the filler.

The effect of the change in the refractive index of the filler filling the groove on the branching ratio is that the length of the two parallel waveguides is long.
At the same time, the longer the groove, the greater the effect on the coupling coefficient, and thus the greater the effect. In the optical monitor circuit of the present invention, for example, the coupling length of the optical waveguide is twice as long as the coupling length L, and the optical waveguide is manufactured based on a quartz-based directional coupler having a branching ratio of 0%. Further, a minute groove is provided directly above the joint, a filler having the same refractive index as that of the quartz glass clad is buried therein, and a heater is provided above the filler. Here, the heater may be a thin film heater (circuit). Note that the heater is one means for controlling the refractive index of the filler, and other means such as direct irradiation of infrared rays may be used as long as the temperature of the filler can be increased. Also, the shape of the heater is not limited to the shape of the embodiment of the present invention.

If, for example, an organic material having a large temperature coefficient of the refractive index is used as the embedded filler, the refractive index of the filler changes greatly due to a temperature rise by the heater, the branching ratio becomes larger than 0%, and monitor light is extracted. Will be able to do it. When the heater is turned off, the monitor light is not output because the branching ratio becomes 0% at room temperature. Therefore, if the heater is turned off when monitoring is not being performed, no loss is caused to the optical circuit and the optical line, and since the heater is turned off, a longer life and power saving of the optical monitor circuit can be expected.

[0018]

EXAMPLES Hereinafter, the present invention will be described specifically with reference to examples, but the present invention is not limited to these examples.

(Embodiment 1) FIGS. 1A and 1B show the structure of an optical monitor circuit according to the present invention.
FIG. 1A is a plan view of an optical monitor circuit, and FIG.
A cross-sectional view taken along the line A 'is shown. The monitor circuit of the present invention comprises a lower cladding 2 on a silicon substrate 1.
An upper clad 4 is provided, and a core 3, a groove 5, and a heater 7 are provided on the lower clad. The groove 5 is filled with a filler 6.

FIG. 2 is a perspective view of the optical monitor circuit.
8 is an input port a, 9 is an input port b, 10 is an output port a ', and 11 is an output port b'.

The fabricated optical monitor circuit has a wavelength of 1.55 μm.
m, the core diameter is 6.5 μm × 6.5 μm, the refractive index of the cladding is 1.444, the refractive index of the core is 1.455, the gap of the coupling part is 3 μm, and the length of the coupling part is 3000 μm.
The groove has a width of 10 μm, a length of 3000 μm, and a depth of 30 μm (corresponding to the thickness of the upper cladding) along the center lines of the two waveguides at the coupling portion. A chromium / gold heater having a width of 25 μm and a length of 3000 μm is disposed on the upper clad.

The branching ratio when light enters the input port a is defined as follows.

Branch ratio (%) = (output of output port b ')
/ (Output of output port b '+ output of output port a') ×
100 Communication light input to input port a (wavelength 1.55 μm)
Are all output to the output port a 'at room temperature (25 degrees) and have a branching ratio of 0%. Here, in order to extract the monitor light from the output port b ', when a current was applied to the heater to set the temperature of the coupling portion to 50 ° C, light was output from the output port b' at a branching ratio of 11%. Then, when the heater was turned off and the joint was returned to room temperature, the branching ratio returned to 0%. The response speed at this time was several milliseconds to several tens of milliseconds. This operation could be repeated any number of times, all with reproducibility. Here, the monitor light was extracted 10,000 times, but the value of the branching ratio did not change.

When the monitor light is extracted using a conventional directional coupler of a fixed split ratio, the light is split even when monitoring is not required, and as a result, the light input to the input port is split. Power was lost, giving a large insertion loss. On the other hand, in the optical monitor circuit shown in Example 1, the heater current was supplied only when monitoring was desired, and the monitoring was performed. When the monitoring became unnecessary, the branching ratio could be easily returned to 0%. Accordingly, the present invention has been improved so that the insertion loss of the entire circuit or the fiber network by the monitor can be reduced.

(Embodiment 2) FIGS. 3A to 3D are schematic views sequentially showing a method of manufacturing an optical monitor circuit. Hereinafter, a method for manufacturing the optical monitor circuit according to the present invention will be specifically described with reference to FIGS.

First, quartz glass soot is deposited on the silicon substrate 1 by using a flame deposition method, and then heated and melted.
Lower cladding 2 (refractive index: 1.444, wavelength: 1.55μ)
m) was formed to have a thickness of 30 μm. Next, a core layer (refractive index: 1.455, wavelength: 1.55 μm) is formed to a
It was formed to have a thickness of μm. However, the refractive index of the core layer was made slightly larger than the refractive index of the lower cladding 2. Thereafter, reactive ion etching was performed by photolithography using a photoresist as a mask, the mask was removed, and the core portion 3 of the directional coupler was processed so that the core width was 7 μm. When the heater is not heated, the gap is 3 μm and the length of the coupling is 3000 μm so that the branch ratio of the directional coupler is 0%.
m. Next, a wafer was formed by depositing the upper clad to a thickness of 36 μm using a flame deposition method. FIG. 3A shows a cross section of the wafer at this point.
Shown in In order to measure the branching ratio, chips were cut out from one of the wafers at this time, and the branching ratio was measured. The branching ratio was approximately 0%.

FIG. 3 shows a cross section of the obtained wafer with a groove formed above the joint of the directional coupler.
(B). The groove 5 has a width of 10 μm, a length of 3000 μm,
The size is 30 μm in depth. The groove 5 was formed by performing reactive ion etching directly on the core 3 using a photoresist as a mask by photolithography and then removing the mask to form the groove 5.

FIG. 3C shows a cross section of the chip in a state where the filler 6 is embedded in the groove. The wafer on which the grooves 5 were formed was cut into chips. However, the cutting was performed after a protective seal was put on the chip so that the shavings did not enter the groove when cutting out the chip. An epoxy resin is filled in the groove 5 as the filler 6 and ultraviolet light (mercury xenon lamp, 20
(0 W) for 5 minutes, and then heat-treated at 80 ° C. for 3 hours. However, the composition of the epoxy resin was adjusted, and the curing conditions were determined to be constant so that the refractive index of the epoxy resin after curing was 1.444, which is the same as that of quartz glass.

FIG. 3D shows a cross section of the chip in a state in which a heater is formed on the upper clad so as to cover the filler filled in the groove 5. Using a vacuum deposition apparatus, chromium was deposited to a thickness of 10 nm on the upper clad using a vacuum deposition apparatus so as to cover the embedded filler.
The heater 7 was formed by vapor deposition to a thickness of 0 nm. However,
The heater was fabricated so as to cover the groove and have a width of 20 μm and a length of 3000 μm above the core 3.

After fabricating the directional coupler using the flame deposition method as in the prior art, it is only necessary to add three steps of fabricating a groove, forming an epoxy resin groove, and forming a heater. Since the optical monitor circuit of the present invention can be manufactured,
Even when compared with the conventional optical monitor circuit of the fixed branching ratio type, the optical monitor circuit of the variable branching ratio type was able to be manufactured without much increase in price.

[0031]

According to the present invention, a groove is formed immediately above a coupling portion of an optical waveguide type directional coupler, a filler having a temperature coefficient of change in refractive index larger than that of a clad is put therein, and a heater is provided above the filler. The monitor light did not appear at room temperature, and the light was monitored at the branch by heating the heater, so that the monitor light could be extracted only when necessary.

Further, if the optical monitor circuit of the present invention is used, it is not necessary to give an extra insertion loss to the optical fiber network by turning off the heater after the inspection and adjustment of the optical fiber network, so that the loss of the optical fiber network itself is reduced. As a result, the transmission distance could be further extended. In addition, it has become possible to add a new optical device and to allow for a margin for loss in the design and equipment of an optical fiber network.

Since signals of various wavelengths are used in the wavelength division multiplexing (WDM) system, a programmable wavelength filter,
A complicated optical integrated circuit that can handle many wavelengths, such as a loop-back type arrayed waveguide grating circuit and an optical dispersion equalizer, is required. These optical integrated circuits often require an optical monitor circuit in the circuit for circuit adjustment and inspection. The use of the variable branch type optical monitor circuit of the present invention did not cause excessive loss as in the related art, so that the original performance suitable for practical use could be exhibited.

[Brief description of the drawings]

1A is a plan view showing the structure of an optical monitor circuit of the present invention, and FIG. 1B is a cross-sectional view showing the structure of the optical monitor circuit of the present invention.

FIG. 2 is a perspective view of an optical monitor circuit according to the present invention.

FIG. 3 is a diagram illustrating a method of manufacturing the optical monitor circuit of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Silicon substrate 2 Lower side clad 3 Core 4 Upper side clad 5 Groove 6 Filler 7 Heater 8 Input port a 9 Input port b 10 Output port a '11 Output port b'

────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification symbol FI H04B 10/08 H04B 9/00 W 17/02 K (72) Inventor Mitsutoshi Hoshino 3-19-2 Nishishinjuku, Shinjuku-ku, Tokyo No. Within Nippon Telegraph and Telephone Corporation (72) Kenji Yokoyama, Inventor Kenji Yokoyama 3-19-2, Nishi-Shinjuku, Shinjuku-ku, Tokyo Japan Within Telegraph and Telephone Corporation (72) Ken, Sukegawa 3-2-1, Nishi-Shinjuku, Shinjuku-ku, Tokyo No. Japan Telegraph and Telephone Corporation

Claims (2)

[Claims] 1. An optical monitor circuit having an optical waveguide type directional coupler, wherein a trench having a depth reaching or less than a core is provided immediately above a coupling portion of the optical waveguide type directional coupler. A filling material filled in the trench portion,
An optical monitor circuit comprising: a heater located above the coupling portion. 2. An optical waveguide type directional coupler in which two optical waveguides are brought close to each other on a substrate, and reaches a core just above a coupling portion of the optical waveguide type directional coupler or is located therefrom. A method of manufacturing a monitor circuit, comprising: forming a trench portion having a shallow depth by etching, filling the trench portion with a filler, and forming a heater above the joint portion.