JP2004085852A - Light intensity controller - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light intensity controller with a compact construction, with which intensity of light propagating through a channel waveguide is monitored and fedback. <P>SOLUTION: The optical intensity controller is provided with a substrate, a waveguide structure containing a slab waveguide and the channel waveguide mounted on the substrate, a light extraction part extracting a part of the light propagating through the channel waveguide to the outside of the waveguide structure mounted on the channel waveguide, an optical detector to detect intensity of a part of the propagating light extracted at the light extraction part and a controller to control the optical intensity of the light propagating through the channel waveguide based on the optical intensity detected by the optical detector. <P>COPYRIGHT: (C)2004,JPO

Description

これらの材料から２種を選択し、屈折率の高いほうを導波路層とし、低い方をクラッド層とすることができる。なお、クラッド層は電気光学材料でなくてもよい。空気をクラッド層とすることもできる。
【００３９】
コントローラは、光の進行方向を制御できるものであればよい。直角プリズムの他種々のプリズムを用いることができる。入射光を斜めに受ける１つの光学界面でもよい。プリズムを用いる場合もその数は任意に増減してよい。プリズム制御用の電極は上下でその材料を変えてもよい。
【００４０】
チャネル導波路の配置も種々に変更できる。２組の複数のチャネル導波路を対向させる場合に限らず、１つのチャネル導波路と複数のチャネル導波路を対向させてもよい。スラブ導波路の周囲に複数のチャネル導波路を配置してもよい。
【００４１】
以上実施例に沿って本発明を説明したが、本発明はこれらに制限されるものではない。例えば種々の変更、改良、組合わせが可能なことは当業者に自明であろう。
【００４２】
【発明の効果】
以上説明したように、本発明によれば、チャネル導波路の一部に光分岐構造を形成し、その上方に光検出器を配置できるので、光強度制御装置を小型化することが容易になる。
【００４３】
多チャネル光デバイスを高集積度で形成することが容易になる。
【図面の簡単な説明】
【図１】本発明の実施例による光デバイスの構成を示す平面図及び断面図である。
【図２】図１（Ｂ）に示す光導波路構造の製造方法を示す断面図及び平面図である。
【図３】本発明の他の実施例による光取り出し機構を概略的に示す断面図である。
【図４】従来の技術による光強度制御装置の構成を概略的に示すブロック図及び断面図である。
【符号の説明】
ＷＧＳ　導波システム
ＣＨＩ　入力チャネル
ＣＨＯ　出力チャネル
ＳＷ　切り換えスイッチ
ＣＬＩ　入力側コントローラ
ＣＬＯ　出力側コントローラ
ＳＬ　スラブ導波路
ＣＨ　チャネル導波路
ＣＥ　制御電極
Ｌ　レンズ部
ＰＤ　光検出器（ホトダイオード）
ＦＣ　ファイバのコア
Ｇ　グレーティング
ＰＢ　回路基盤
ＣＴＬ　制御回路
ＤＲ　駆動回路
１０　ＬｉＮｂＯ_３基板
１１　Ｔｉ層
１２　ＬｉＮｂＯ_３：Ｔｉ層
１３　ＳｉＯ_２層
Ｒ　表面荒れ
Ｔ　テーパ構造[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a waveguide type optical device requiring high-speed, large-capacity signal transmission, and more particularly to a light intensity control device for controlling light intensity of a channel waveguide.
[0002]
2. Description of the Related Art In some cases, a plurality of input channel waveguides and a plurality of output channel waveguides are used to change the propagation path of an optical signal between input and output. When a prism is formed from an electric or optical effect material and the applied voltage is changed, the prism function changes, and the direction in which light travels can be changed. By combining such a variable prism with each channel waveguide, an optical signal input from a certain channel waveguide can be supplied to a desired one selected from a plurality of channel waveguides facing each other to perform optical switching.
[0003]
It is desirable to monitor whether a sufficient amount of optical signal is supplied to the selected channel waveguide. When the amount of light is insufficient, the light intensity can be adjusted by adjusting the traveling direction of the light using a variable prism.
[0004]
FIG. 4A schematically shows the configuration of a conventional optical device. Optical device 50 includes a waveguide structure on a substrate. The waveguide structure includes an input-side slab waveguide and an output-side channel waveguide. The input light IN travels through the slab waveguide, and its traveling direction is changed by the control unit 52. The coupling unit 53 is disposed between the slab waveguide and the channel waveguide, and includes a lens unit.
[0005]
The optical signal introduced into the channel waveguide from the coupling unit 53 exits the channel waveguide and enters the beam splitter 5, and a part of the light is branched and becomes the reference light REF. The reference light is about 5% of the incident light. Light that has traveled straight through the beam splitter 5 forms an output signal OUT.
[0006]
The reference light REF split by the beam splitter 5 is detected by the photodetector PD. The output signal of the photodetector PD is converted into a control signal and controls the control unit 52. By controlling the traveling direction of the light by the control unit 52, the control is performed so that the maximum optical signal is incident on the channel waveguide on the output side.
[0007]
FIG. 4B shows a configuration example of the beam splitter 5. The beam splitter 5 has a configuration in which, for example, collimating lenses 60 and 62 are arranged on an input side and an output side of a 2 mm square beam splitter element 61, respectively. Single mode optical fibers 65 and 66 are arranged on both sides of the collimating lenses 60 and 62, respectively. The beam splitter element 61 branches about 5% of the light incident from the left side downward, and enters the photodiode PD.
[0008]
With the configuration shown in FIG. 4A, the intensity of light traveling in the channel waveguide can be monitored. However, an optical member such as the beam splitter 5 is arranged outside the optical device 50, particularly, downstream of the traveling direction of light. There is a need to. In order to configure a multi-channel optical device, it is necessary to provide a beam splitter for each channel, so that the system becomes large in size and has a structure unsuitable for high integration.
[0009]
[Problems to be solved by the invention]
As described above, the configuration in which the beam splitter is provided outside the channel waveguide, a part of the propagating optical signal is branched, and the light intensity is monitored and fed back is not suitable for high integration.
[0010]
SUMMARY OF THE INVENTION It is an object of the present invention to provide a light intensity control device having a compact configuration capable of monitoring and feeding back the light intensity traveling in a channel waveguide.
[0011]
It is another object of the present invention to provide a light intensity control device that does not require a beam splitter outside a channel waveguide.
[0012]
[Means for Solving the Problems]
According to one aspect of the present invention, a substrate, a waveguide structure provided on the substrate and including a slab waveguide and a channel waveguide, and a waveguide structure provided in the channel waveguide and transmitting light in the channel waveguide. A light extraction part for extracting a part out of the waveguide structure, a light detector for detecting the intensity of a part of the propagation light extracted by the light extraction part, and a light intensity detected by the light detector, A controller for controlling the intensity of light propagating through the channel waveguide.
[0013]
According to another aspect of the present invention, there is provided a substrate, and a waveguide structure provided on the substrate, wherein the plurality of input channel waveguides, the plurality of output channel waveguides, and the plurality of input channel waveguides are provided. A waveguide structure disposed between the plurality of output channel waveguides and a slab waveguide common to the plurality of input channel waveguides and the plurality of output channel waveguides; and each of the output channel waveguides. A light extraction unit that extracts a part of the propagation light in the output channel waveguide out of the waveguide structure, and a photodetector that detects the intensity of a part of the propagation light extracted by each of the light extraction units. A controller for controlling the intensity of light propagating through the output channel waveguide based on the light intensity detected by the photodetector.
[0014]
BEST MODE FOR CARRYING OUT THE INVENTION
FIG. 1A is a plan view schematically showing a configuration of a waveguide system WGS which is an optical device having a switch function. The waveguide system WGS has a plurality of input channels CHI on the input side and a plurality of output channels CHO on the output side, and has a changeover switch SW having a channel switching function therebetween. The changeover switch SW has an input-side controller CLI at a position close to each input channel, and has an output-side controller CLO at a position close to each output channel CHO.
[0015]
Each input-side controller CLI is composed of, for example, a pair of right-angle prisms. The oblique sides are arranged in parallel, and the entrance surface and the exit surface are perpendicular to the incident light. The form of the prism pair is not limited to this. For example, a function of refracting incident light downward by an upwardly convex prism is provided, and a function of refracting incident light upward by a downwardly convex prism. That is, the light incident from the horizontal direction can be scanned up and down by the pair of prisms. The output-side controller CLO is also composed of a pair of prisms, and can return the light incident from an oblique direction to the horizontal direction. The input and output can be switched and used. In this specification, when one is called an input side, the other is called an output side. Note that one prism can be used instead of a pair of prisms.
[0016]
The light input from any one of the input channels CHI is controlled by the corresponding input-side controller CLI, and its traveling direction is changed toward a desired output-side controller. The traveling light has its traveling direction adjusted again by the output-side controller CLO, and travels to the output channel CHO.
[0017]
FIG. 1B is a plan view schematically showing a configuration near one output channel. The waveguide structure includes a slab waveguide SL continuous from an input side and a channel waveguide CH on an output side, and a lens portion L is coupled therebetween. Above and below the slab waveguide SL, triangular control electrodes CE are arranged. The triangular electrode is, for example, in the shape of a right-angled triangle having a long side of about 500 μm and a short side of about 100 μm across a right angle. Although one triangular electrode prism is shown, two triangular electrode prisms may be used as shown in FIG.
[0018]
By applying a voltage between the triangular electrodes, the refractive index of the slab waveguide sandwiched between the upper and lower electrodes changes. When the refractive index of the prism changes, the prism action changes, and the traveling direction of light is controlled.
[0019]
The lens L has a lens shape as shown in the figure, and has a lens function in the plane due to the difference between the refractive indexes of the media on both sides. The channel waveguide CH is a striped waveguide continuously formed on the output side of the lens L, and a grating G is formed on a partial surface thereof. Above the grating G, a photodetector PD such as a photodiode is arranged. An optical fiber core FC is arranged near the output end of the channel waveguide CH. That is, the light emitted from the channel waveguide CH enters the fiber core FC.
[0020]
The grating G has a function of diffracting incident light upward (forward in the plane of the paper) and causing the diffracted light to enter the photo die auto PD. For example, about 5% of the input light is diffracted and 95% goes straight.
[0021]
FIG. 1C is a schematic sectional view showing a configuration including the output channel shown in FIG. 1B and its feedback system. The substrate 10 is, for example, a LiNbO ₃ substrate, and a high-refractive-index layer 11 made of, for example, LiNbO ₃ : Ti and having a thickness of about 10 μm is formed on the surface thereof. The high refractive index layer 11 is a layer of an electro-optic material that forms a waveguide and changes the refractive index when an electric field is applied. The planar shape of the high refractive index layer 11 is patterned as shown in FIG.
[0022]
FIG. 1 (C) shows the vicinity of the output channel corresponding to FIG. 1 (B). A slab waveguide is formed in the left part, a planar lens L is formed in the middle part, and a striped output channel guide is formed in the right part. A wave path CHO is formed. A triangular control electrode CE is formed above the slab waveguide SL and the lower surface of the corresponding substrate.
[0023]
The control electrode CE is formed of, for example, indium tin oxide (ITO). When a metal electrode is formed directly on the waveguide, a phenomenon occurs in which the TM mode is attenuated. From this point, it is preferable to use a transparent material such as ITO. However, when a low refractive index cladding layer is further provided on the high refractive index layer, the electrode formed thereon may be a metal such as Al.
[0024]
A grating G is formed on a part of the upper surface of the channel waveguide CHO by etching or the like, and diffracts light traveling in the channel waveguide CHO upward. A printed circuit board PB is arranged above the substrate 10. A photodiode PD is provided on the printed circuit board PB. A photo diode PD is arranged at a position where the diffracted light from the diffraction grating G is incident.
[0025]
Further, a solder bump SB is arranged on the upper surface of the control electrode CE so as to supply a voltage to the triangular control electrode CE, and is connected to the wiring on the circuit board PB. A control circuit CTL and a drive circuit DR are mounted on the circuit board PB, and an output signal of the photo diode auto PD is controlled by the control circuit CTL and supplied to the drive circuit DR to generate a voltage for driving the control electrode CE. . Feedback control may be performed not only on the output-side control electrodes but also on the input-side control electrodes.
[0026]
An optical fiber core FC is disposed close to the right side of the waveguide structure. Since it is not necessary to arrange a beam splitter again, it is suitable for downsizing the configuration. Further, the branched light diffracted by the grating G travels upward and enters the photoauto PD. For this reason, the photo die auto PD is arranged at a position closer to the control electrode CE. By providing the control circuit CDL and the drive circuit DR on the circuit board PB, the feedback control system can be integrated in a small area and arranged above the substrate 10.
[0027]
2A to 2E are a cross-sectional view and a plan view illustrating a method for manufacturing an optical device having a waveguide structure as shown in FIG. 1B.
As shown in FIG. 2A, a Ti layer 11 is formed on the surface of the z-cut LiNbO ₃ substrate 10 by, for example, sputtering. The Ti layer 11 has a thickness of, for example, 50 nm.
[0028]
As shown in FIG. 2B, the substrate 10 is heated to 1100 ° C. in air for 10 hours. Ti diffuses from the Ti layer 11 into the LiNbO ₃ substrate 10, and a LiNbO ₃ : Ti (Ti diffused LiNbO ₃ ) layer 12 having a depth of about 10 μm is formed on the surface thereof. The LiNbO ₃ : Ti layer 12 is a material having a higher refractive index than the LiNbO ₃ substrate 10 and exhibiting an electro-optic effect.
[0029]
As shown in FIG. 2C, an SiO ₂ layer 13 having a thickness of, for example, 200 nm is formed on the LiNbO ₃ : Ti layer 12 by plasma CVD as needed. Note that the SiO ₂ layer 13 becomes a clad layer, but may be omitted. In the following description, an example in which the SiO ₂ layer 13 is not provided will be described.
[0030]
As shown in FIG. 2D, patterning of the waveguide layer 12 is performed using a resist mask. In the drawing, for example, a rectangular slab waveguide SL is left on the left side, a lens portion L having an arc-shaped boundary in a portion facing the slab waveguide SL in the center portion, and a linear boundary on the right side. After patterning, the channel waveguide CH is patterned on the output side of the lens unit L. This dry etching also slightly etches the substrate 10, but does not cause any functional problem.
[0031]
As shown in FIG. 2E, for example, an ITO layer is formed on the surface of the slab waveguide portion of the waveguide layer by sputtering, and the ITO layer is patterned by dry etching using a resist pattern. Thus, a triangular control electrode CE is formed on the slab waveguide SL. Note that a triangular control electrode is formed at a position corresponding to the lower surface of the substrate.
[0032]
Using a resist mask, the diffraction grating pattern is etched on a part of the surface of the channel waveguide CH. The grating constant of the diffraction grating G is selected so as to generate diffracted light in a desired direction. As a method for forming the grating G, a known grating forming method such as a two-beam interference method can be used. The light intensity to be diffracted is about 5% of the incident light intensity. The intensity of the diffracted light is adjusted by adjusting the depth of the diffraction grating.
[0033]
Thus, the substrate-side structure of the optical device shown in FIG. As the photo diode PD arranged to face the substrate, for example, a photo diode having InGaAs as an active layer can be used. The control circuit CTL and the drive circuit DR are each configured by, for example, a semiconductor integrated circuit on a separate chip. It should be noted that a control integrated circuit that includes both circuits as a single unit may be used.
[0034]
Although the case where the light traveling through the channel waveguide is branched using the grating has been described, the mechanism for branching the light is not limited to the grating.
FIG. 3A shows a case where a rough surface R is formed on the surface of the core layer C as a mechanism for extracting light traveling through the core layer C sandwiched between the upper and lower cladding layers CL1 and CL2. The surface roughness R serves as a light scattering source and scatters incident light upward. Although only a part of the scattered light can travel in the desired direction, it can be made easier than a grating.
[0035]
FIG. 3B shows another example of the light extraction mechanism. The lower surface of the core layer C sandwiched between the upper and lower clad layers CL1 and CL2 forms a tapered structure that is lifted upward. That is, the optical interface between the core layer C and the lower cladding CL1 bends upward at the tapered portion, reflects the incident light upward, and guides the light to the outside of the core layer C. Although the case where the lower interface of the core layer C protrudes upward has been described, another configuration may be adopted.
[0036]
FIG. 3C shows a tapered structure in which the upper interface of the core layer C protrudes downward. This configuration can be easily realized by etching the core layer C. The incident light travels upward by refraction.
[0037]
In the waveguide layer, at least the prism portion needs to be formed of a material having an electro-optic effect. The following materials are known as materials having an electro-optic effect.
[0038]
[Table 1]

Two types can be selected from these materials, and the higher refractive index can be used as the waveguide layer and the lower refractive index can be used as the cladding layer. Note that the cladding layer may not be made of an electro-optic material. Air may be used as the cladding layer.
[0039]
The controller only needs to be able to control the traveling direction of light. Various prisms other than the right-angle prism can be used. One optical interface obliquely receiving incident light may be used. When using prisms, the number may be arbitrarily increased or decreased. The material of the electrode for controlling the prism may be changed up and down.
[0040]
The arrangement of the channel waveguide can be variously changed. The present invention is not limited to the case where two sets of a plurality of channel waveguides are opposed to each other, and one channel waveguide and a plurality of channel waveguides may be opposed. A plurality of channel waveguides may be arranged around the slab waveguide.
[0041]
Although the present invention has been described with reference to the embodiments, the present invention is not limited thereto. For example, it will be apparent to those skilled in the art that various modifications, improvements, and combinations are possible.
[0042]
【The invention's effect】
As described above, according to the present invention, a light branching structure is formed in a part of a channel waveguide, and a photodetector can be arranged above the light branching structure. Therefore, it is easy to reduce the size of the light intensity control device. .
[0043]
It becomes easy to form a multi-channel optical device with a high degree of integration.
[Brief description of the drawings]
FIG. 1 is a plan view and a cross-sectional view illustrating a configuration of an optical device according to an embodiment of the present invention.
2A and 2B are a cross-sectional view and a plan view showing a method for manufacturing the optical waveguide structure shown in FIG.
FIG. 3 is a cross-sectional view schematically illustrating a light extraction mechanism according to another embodiment of the present invention.
FIG. 4 is a block diagram and a sectional view schematically showing a configuration of a light intensity control device according to a conventional technique.
[Explanation of symbols]
WGS waveguide system CHI input channel CHO output channel SW changeover switch CLI input side controller CLO output side controller SL slab waveguide CH channel waveguide CE control electrode L lens part PD photodetector (photodiode)
FC fiber core G grating PB circuit board CTL control circuit DR drive circuit 10 LiNbO ₃ substrate 11 Ti layer 12 LiNbO ₃ : Ti layer 13 SiO ₂ layer R Rough surface T Tapered structure

Claims (10)

Board and
A waveguide structure provided on the substrate, including a slab waveguide and a channel waveguide,
A light extraction unit provided in the channel waveguide, for extracting a part of the propagation light in the channel waveguide out of the waveguide structure;
A photodetector that detects the intensity of a part of the propagation light extracted by the light extraction unit,
A controller that controls the intensity of light propagating through the channel waveguide based on the light intensity detected by the photodetector,
A light intensity control device having: The light intensity control device according to claim 1, wherein the light extraction unit has one of a grating, a rough surface, and a tapered structure. The light intensity control device according to claim 1, wherein the photodetector is disposed at a position facing the waveguide structure. 4. The light intensity control device according to claim 3, further comprising a circuit board arranged so as to face the waveguide structure, wherein the photodetector is arranged on the circuit board. The slab waveguide includes a layer of an electro-optical material, the controller includes a pair of prism-shaped electrodes provided on both sides of the slab waveguide, and a control circuit provided on the circuit board, The light intensity control device according to claim 4, wherein the control circuit controls a voltage applied to the prism-shaped electrode based on an output of the photodetector. The light intensity control device according to claim 1, wherein the substrate is a LiNbO ₃ substrate, and the waveguide structure includes a LiNbO ₃ : Ti layer. Board and
A waveguide structure provided on the substrate, wherein the plurality of input channel waveguides, the plurality of output channel waveguides, and the plurality of output channel waveguides are disposed between the plurality of input channel waveguides and the plurality of output channel waveguides. A waveguide structure including a slab waveguide common to the plurality of input channel waveguides and the plurality of output channel waveguides,
A light extraction unit provided in each of the output channel waveguides, for extracting a part of the propagation light in the output channel waveguide out of the waveguide structure;
A photodetector that detects the intensity of a part of the propagation light extracted by each of the light extraction units,
A controller that controls the intensity of light propagating through the output channel waveguide based on the light intensity detected by the photodetector,
A light intensity control device having: The light intensity control device according to claim 7, wherein the photodetector is arranged at a position facing the waveguide structure. 9. The light intensity control device according to claim 8, further comprising a circuit board arranged to face the waveguide structure, wherein the photodetector is arranged on the circuit board. The slab waveguide includes a layer of electro-optic material, and the controller corresponds to each of the input channel waveguides and each of the output channel waveguides, and has a pair of prism shapes provided to sandwich the slab waveguide. And a control circuit provided on the circuit board, wherein the control circuit controls a voltage applied to the corresponding prism-shaped electrode based on an output of each of the photodetectors. Light intensity control device.

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