JP4182758B2 - Optical add / drop device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a wavelength division multiplexing add / drop device for separating / inserting a predetermined wavelength in an optical network node using wavelength demultiplexing / multiplexing technology.
[0002]
[Prior art]
With the rapid expansion of optical communication transmission capacity, the spread of wavelength multiplexing technology is progressing. The wavelength-multiplexed signal is extracted (or inserted) at a node provided on the network, and only a certain wavelength signal is extracted (or inserted), and the remaining wavelength signal is transmitted as light to the network without being converted into an electric signal (OADM) (Optical Add Drop Multiplexer) has attracted attention. In recent OADMs, there is an expectation for ROADM (Reconfigurable OADM) that can freely change the wavelength signal selected in each node at any time.
[0003]
In general, the ROADM is composed of two optical elements, a wavelength multiplexer / demultiplexer and a spatial optical switch array. The function is to spatially separate a signal of a certain wavelength band propagating in the optical fiber for each wavelength by a wavelength demultiplexer, and then selectively extract only a desired wavelength signal by a spatial switch array or insert it in reverse. The wavelength signal is multiplexed by a wavelength multiplexer and returned to the optical fiber.
[0004]
In a conventional optical ADM apparatus, a configuration in which a plurality of AWGs (arrayed waveguide diffraction gratings) are used as wavelength multiplexers / demultiplexers and a plurality of 2 × 2 Mach-Zehnder TO switches (thermo-optic switches) are arranged as a spatial switch array is common. Is.
For example, a 16-channel AWG add / drop multiplexer has been proposed in which two types of components of four sets of AWGs and Mach-Zehnder type 2 × 2TO switches are monolithically integrated on the same optical waveguide substrate (for example, see Non-Patent Document 1). ).
FIG. 8 is a schematic diagram showing an outline of this conventional optical add / drop multiplexer. As a diffraction grating for multiplexing and branching, four AWGs 71, 72, 73 and 74 and a double gate TO switch 51 in which two TO switches are connected in order to improve crosstalk are arranged in an array. ing. In this configuration, the main signal light that has been transmitted through the optical transmission line is demultiplexed after being incident on the AWG 74 and is input to each double gate TO switch to be used as a main passing signal or a drop signal. Switching takes place. Each port of the switch is connected to AWG 71 and AWG 72 for multiplexing, and is multiplexed there and output as main passing signal light or drop signal light. On the other hand, the plurality of wavelength signal lights to be inserted are demultiplexed by the AWG 73, pass through the corresponding double gate switches 51, are combined by the AWG 72, and are emitted as part of the main passing signal light. .
[0005]
However, the above-described conventional optical ADM device has several problems with respect to the size of the device, power consumption for driving, manufacturing yield, and the like.
First, the crosstalk of a single Mach-Zehnder 2 × 2TO switch is at most about −25 dB, and a sufficiently low crosstalk value cannot be obtained. Therefore, in the above-described conventional example, two stages of Mach-Zehnder type 2 × 2TO switches are connected to improve crosstalk. In this case, however, power consumption for driving the switches is doubled. In addition, since a Mach-Zehnder type TO switch performs switch switching using the phase change of propagating light due to the thermo-optic effect, when the distance between the switches becomes short, one heat for switching affects the other switch, so that Will worsen the crosstalk. In order to avoid this problem, it is necessary to increase the distance between the switches to some extent. As a result, the occupied area of the switch array unit is increased, so that the size of the optical ADM device itself is increased. This problem becomes more conspicuous when a two-stage connection of a Mach-Zehnder type TO switch is employed as in the conventional example described above.
[0006]
Further, in the above-described conventional example, four AWGs are integrated as a multiplexer / demultiplexer. However, in order to function as an add / drop multiplexer, the center wavelengths of the four AWGs must match. When a deviation occurs in the center wavelengths of the four AWGs, the optical insertion loss and the add / drop function characteristics of the apparatus are significantly deteriorated. Usually, since the center wavelength of the AWG is expected to be shifted to some extent within the wafer surface, the temperature of each AWG is individually adjusted to match the center wavelength. However, since four AWGs are close to each other, a problem of thermal crosstalk accompanying temperature adjustment is newly generated. Therefore, the integrated elements having the same center wavelength of the four AWGs are selected on the wafer. In this case, the element yield per single wafer is remarkably deteriorated. Furthermore, in the above-described conventional example, since the optical waveguides connecting the AWGs and the AWGs intersect each other, signal crosstalk occurs at the intersections, which causes deterioration in crosstalk between channels.
[0007]
In another conventional example, a TO switch is not used, but since the optical waveguides connecting the AWGs cross each other, high crosstalk characteristics cannot be expected (see, for example, Patent Document 1).
[0008]
[Non-Patent Document 1]
K. Okamoto et al., “16-Channel Optical Add-Drop Multiplexer Composed of Arrayed Waveguide Grating and Double Gate Switch”, Electronics Letter, August 1, 1996, Vol. 32, No. 16, p1471-1472
[Patent Document 1]
JP 2002-031768 (page 5-7, FIG. 1)
[0009]
[Problems to be solved by the invention]
SUMMARY OF THE INVENTION An object of the present invention is to provide an optical ADM element configuration that solves the above-described problems and that can provide a sufficient amount of crosstalk for optical communication and that can manufacture a small-sized and low power consumption optical ADM device with high yield. Become.
[0010]
[Means for Solving the Problems]
To achieve the above object, an optical add / drop device according to the present invention outputs light input from a first port to a second port and outputs light input from the second port to a third port. Are connected between the first optical circulator and the second optical circulator that output to the second optical circulator, and the second port of the first optical circulator and the second port of the second optical circulator. An optical circuit that reflects light of a predetermined wavelength and transmits light of another wavelength, and the first port and the third port of the first optical circulator are connected to the input port of the wavelength multiplexed optical signal and the predetermined wavelength, respectively. An optical add port that separates the optical signals of the second optical circulator, the first port and the third port of the second optical circulator as input ports for inserting optical signals of a predetermined wavelength and output ports for wavelength multiplexed optical signals. Do A-up apparatus,
An optical circuit includes a first arrayed waveguide grating element (AWG), an optical switch array, and a second AWG, and the optical switch array is connected to the first and second AWGs according to external control. It is characterized in that light of a predetermined wavelength is reflected back to the first and second AWGs.
In addition, the optical switch array reflects light of a predetermined wavelength from the first AWG to the first AWG through the same path and returns the predetermined wavelength from the second AWG according to control from the outside. The light is reflected by the second AWG through the same path , and the reflection intensity is attenuated and returned. The attenuation is variable.
Each optical switch included in the optical switch array includes an optical waveguide, a groove that separates the optical waveguide perpendicular to the optical axis, and the groove can be moved horizontally, with one surface being a flat surface and the other surface being a curved surface. Provide a mirror.
Each optical switch included in the optical switch array includes an optical waveguide, a groove that separates the optical waveguide perpendicular to the optical axis, and the groove can be moved horizontally. One surface is a plane mirror and the other surface is a surface. A mirror having a region where the reflectance decreases is provided.
Further, the reflectance decreasing region is formed by any one of light absorbing means, light scattering means, and light diffracting means, or a combination of a plurality of means.
Two AWGs and an optical switch array are integrated on the same substrate.
Moreover, the slab waveguide with which two AWGs are provided cross | intersects each other.
Further, a temperature adjusting unit for controlling the temperature of the substrate and a switch control unit for driving and controlling the switch array are incorporated in the same package.
[0011]
(Function)
In the optical ADM apparatus of the present invention, an input wavelength multiplexed signal is spatially separated by a wavelength demultiplexer, and each separated single wavelength signal is controlled by each reflection type optical switch. When the reflection type optical switch is OFF, the wavelength signal passes through the optical switch, enters the corresponding port of the wavelength multiplexer, is spatially combined, and is output to a single output port. When the reflection type switch is ON, the wavelength signal spatially separated by the wavelength demultiplexer is reflected by the optical switch and returned to the wavelength demultiplexer again. Output to the input port of the duplexer. The wavelength signal light output to the input port is guided to the drop port by the optical circulator. On the other hand, a light wave having a signal having the same wavelength as the drop wavelength is input from one end (add port) of the optical circulator connected to the output port of the wavelength multiplexer, and is reflected in the ON state by the reverse action of the multiplexing, that is, demultiplexing. It is incident on the type optical switch and returned to the wavelength multiplexer again by reflection. The light reflected and incident on the wavelength multiplexer passes through the output port of the multiplexer, is guided to the optical circulator, and is output to a port different from the add port. This function is due to the fact that the optical path blocking and reflection functions of the reflective optical switch installed between the wavelength demultiplexer and the wavelength multiplexer are symmetric with respect to the bi-directional incidence of light. In addition, the reflection type optical switch can be realized with a small size and low power consumption by using a micro electrical mechanical switch (MEMS) having a double-sided movable mirror.
[0012]
In the configuration of the present invention, since the number of multiplexers / demultiplexers such as AWG can be reduced as compared with the conventional one, improvement in manufacturing yield and miniaturization can be realized at the same time.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail with reference to the drawings.
FIG. 1 is a block diagram showing an outline of an optical ADM apparatus according to the present invention. A reflection type optical switch array 3 is arranged between the wavelength demultiplexer 2 and the wavelength multiplexer 4, and each reflection type optical switch 11 is connected to the output port 12 of the wavelength demultiplexer 2 and the wavelength multiplexer 4. Are optically connected to the input port 13. An input port 14 of the wavelength demultiplexer 2 is optically connected to the optical circulator 1, and an output port 15 of the wavelength multiplexer 4 is optically connected to the optical circulator 5. Each reflection-type optical switch 11 has a function of reflecting a light wave incident from the port 12 or the port 13 in the switch ON state in a direction opposite to the incident direction and transmitting the light wave in the incident direction in the switch OFF state.
[0014]
Next, the operation of this configuration will be described. A main WDM (Wavelength Division Multiplexing) signal incident on the optical circulator 1 is demultiplexed by the wavelength demultiplexer 2 via the input port 14 and is incident on the optical switch array 3. An optical signal having a wavelength that is dropped among the wavelength-demultiplexed optical signals is reflected by the ON operation of the corresponding optical switch 11 and is sent back to the output port 12. The reversely transmitted wavelength signal is multiplexed from the wavelength demultiplexer 2, enters the optical circulator 1 again through the port 12, and is finally output as a drop signal. On the other hand, the add signal light having the same wavelength as the drop signal light incident on the optical circulator 5 is demultiplexed by the wavelength multiplexer 4 and incident on the optical switch 11 in the ON state, and is reflected back to the wavelength multiplexer 4 again. Sent. The reversely transmitted optical signal is multiplexed by the wavelength multiplexer 4, passes through the optical circulator 5, and is transmitted as a part of the main passing signal. Further, the signal light having the wavelength incident on the optical switch 11 in the OFF state from the port 12 on the wavelength demultiplexer 2 side is sent to the wavelength multiplexer 4 via the port 13, and is combined and incident on the optical circulator 5. And then sent out as a main passing signal.
[0015]
FIG. 2 is a schematic view showing an embodiment in which the add / drop device 40 of the present invention is realized on a quartz substrate. An array type diffraction grating duplexer 31 composed of an input slab waveguide, an array waveguide, an output slab waveguide, and an output waveguide on a quartz substrate 30 and an array type diffraction grating multiplexer 32 having the same configuration are provided. A reflection type optical switch array 33 is formed, in which reflection type optical switches are integrated in an array between the output waveguide of the array type diffraction grating duplexer 31 and the input waveguide of the array type diffraction grating multiplexer 32. The optical wave circulators 37 and 38 are connected to the optical wave input port 36 and the optical wave output port 35, respectively. Further, the respective optical waveguides formed on the quartz substrate do not cross each other, and the problem of crosstalk between channels as in the conventional example can be avoided.
In the configuration of the present invention, the part of the optical circuit including the multiplexer / demultiplexer can be easily formed by using a quartz-based PLC (Planar Lightwave Circuit) technique, and the reflective optical switch array can be easily formed by using a MEMS technique.
[0016]
FIG. 3 is a perspective view showing an embodiment of the reflective optical switch 34 in FIG. An optical waveguide 6 is formed on the quartz substrate 8, and a movable groove 9 is formed so as to cross the optical waveguide 6. A double-sided mirror 7 that can move in parallel along the movable groove 9 and that regularly reflects both light emitted from the optical waveguides separated by the groove by 180 ° is disposed. In the configuration of the present invention, the double-sided mirror 7 is disposed so as to block the optical waveguide 6 when the optical switch is ON, and the double-sided mirror is translated along the movable groove 9 when the optical switch is OFF. The optical axis along the optical waveguide 7 is arranged at a position that does not block the optical axis. By using this optical switch, an add / drop operation can be performed as described in the operation of FIG.
[0017]
The operation of the double-sided mirror 7 can be realized by using an electrostatic force often used in MEMS (Micro Electrical Mechanical Switch) or the like. An example of the mechanism is shown in FIG. Using a high-resistance Si substrate, using a MEMS manufacturing method, one is easily bent horizontally and the other is formed with a cross-finger-shaped reflector. An electric field is applied between the interdigitated structures, and only the double-sided mirror 7 held by the supporting beam that is easily bent by electrostatic force is displaced in the horizontal direction and reflects the waveguide output light 10 that is output from the optical waveguide 6. Cut off. By adopting such a configuration, it is possible to remarkably reduce power consumption, and the problem of thermal crosstalk between optical switches can be improved as in the case where a thermo-optic switch is used.
[0018]
FIG. 5 is a perspective view showing a second embodiment of the reflective optical switch 34. One of the mirror surfaces of the movable mirror 20 disposed in the movable groove 9 provided on the quartz substrate has a curved surface shape. In the structure of the present invention, when the movable mirror 20 is moved along the movable groove 9, a change occurs in the reflection angle and the reflected beam diameter of the light wave emitted from the optical waveguide 9 on the curved reflecting mirror 21. The optical coupling rate of the reflected light will change. As a result, it is possible to adjust the optical power of the add signal light that is multiplexed and transmitted with the main passing signal light. Conventionally, the optical power adjustment of the add signal light, which has been performed using a VOA (Variable Optical Attenuator) element, can be realized in the optical switch of the present invention.
[0019]
FIG. 6 shows a double-sided reflection mirror having a function of reflecting one waveguide light facing the double-sided mirror back to the original optical waveguide with reduced intensity and returning the other waveguide light by regular reflection by 180 °. Can also be realized. A non-specular surface portion 23 having a low reflectivity, such as scattering, absorption, and diffraction, is formed on one side of the double-sided mirror 7 of the reflective optical switch shown in FIG. By movement due to the electrostatic force between the crossing fingers, the light emitted from the optical waveguide is regularly reflected by 180 ° (FIG. 6A), or transmitted without being blocked (FIG. 6C), or partially non-specular surface portion 23. (FIG. 6B) can be controlled. By this operation, the amount of light returning to the optical waveguide reflected and emitted by the partially non-specular double-sided mirror 22 can be controlled. Instead of the non-specular surface portion 23, a mirror body on which a film that causes an optical phenomenon of absorption, scattering, or diffraction may be used, and these optical phenomena may be partially changed on the mirror body. As the absorption film, Ge, Te, or the like can be used for a material that does not have a transmission region at the wavelength used, for example, 1.55 μm wavelength light. Further, since these materials have a high refractive index, it is desirable to further provide an antireflection film on the surface.
[0020]
FIG. 7 is a schematic diagram showing one embodiment of an optical functional module incorporating the add / drop device 40 of the present invention. An add / drop device 40 realized on the quartz substrate of FIG. 2, an optical switch drive unit 63 for driving an optical switch array provided in the add / drop device 40, and a temperature control unit for controlling the temperature of the add / drop device. 61 and an external signal processing unit 62 that controls the optical switch driving unit 63 and the temperature control unit 61 by a control signal are arranged on the mounting substrate 60. In the optical functional module of the present invention, it is possible to insert and separate light waves with respect to arbitrary wavelength signal light in a certain wavelength band by an appropriate external electric signal.
[0021]
【The invention's effect】
As described above, in the configuration of the optical ADM apparatus according to the present invention, the total number of optical demultiplexers and optical multiplexers can be reduced by using a reflective optical switch, and a large amount of power consumption is required like a thermo-optical switch. In addition, there is no problem of thermal crosstalk. The effect of the configuration of the present invention is particularly enhanced by the integration of optical functional circuits using PLC technology. That is, the reduction in the total number of optical multiplexers / demultiplexers realizes improvement in element yield and element miniaturization, and the reflection type optical switch without heat generation enables a close optical switch array configuration, thereby contributing to miniaturization. Therefore, according to the present invention, it is possible to provide an optical add / drop device capable of simultaneously improving the element yield, reducing the size, and reducing the power consumption.
[Brief description of the drawings]
FIG. 1 is a block diagram showing an outline of a configuration of the present invention.
FIG. 2 is a schematic view showing an outline in which the optical add / drop device of the present invention is configured on a quartz substrate.
FIG. 3 is a schematic diagram showing a configuration of a reflective optical switch used in the optical add / drop device of the present invention.
FIG. 4 is a schematic diagram showing a configuration of a movable double-sided mirror included in a reflective optical switch used in the optical add / drop device of the present invention.
FIG. 5 is a schematic diagram showing the configuration of a second embodiment of the reflective optical switch used in the optical add / drop device of the present invention;
FIG. 6 is a schematic diagram showing the configuration of a third embodiment of the reflective optical switch used in the add / drop device of the present invention.
FIG. 7 is a schematic diagram showing an outline of an optical functional module incorporating the add / drop device of the present invention.
FIG. 8 is a schematic diagram showing an outline of a conventional optical add / drop multiplexer.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Optical circulator 2 Wavelength demultiplexer 3 Reflection type optical switch array 4 Wavelength multiplexer 5 Optical circulator 6 Optical waveguide 7 Double-sided mirror 8 Quartz substrate 9 Movable groove 10 Waveguide outgoing light 11 Reflective optical switch 20 Movable mirror 21 Curved surface reflection Mirror 22 Partial non-specular double-sided mirror 23 Non-specular portion 30 Quartz substrate 31 Array diffraction grating duplexer 32 Array diffraction grating multiplexer 33 Reflective optical switch array 34 Reflective optical switch 40 Add / drop device 60 Mounting substrate 61 Temperature control unit 62 External signal processing unit 63 Optical switch drive unit

Claims (7)

A first optical circulator and a second optical circulator that output light input from the first port to the second port and output light input from the second port to the third port;
Connected between the second port of the first optical circulator and the second port of the second optical circulator, reflects light of a predetermined wavelength according to external control, and emits light of other wavelengths And an optical circuit that transmits
The first port and the third port of the first optical circulator are used as an input port for wavelength-multiplexed optical signals and an output port for separating the optical signal of the predetermined wavelength, and the first port of the second optical circulator And an optical add / drop device having a third port as an input port for inserting an optical signal of the predetermined wavelength and an output port of the wavelength multiplexed optical signal,
The optical circuit includes a first arrayed waveguide grating element (AWG), an optical switch array, and a second AWG.
The optical switch array, according to the control from the outside, to back light of a predetermined wavelength from the first AWG is reflected to the first AWG by the same route, from the second AWG Means for reflecting light of a predetermined wavelength to the second AWG through the same path and attenuating the reflection intensity to return, the attenuation being variable;
The optical add / drop device according to claim 1 . Each optical switch provided in the optical switch array,
An optical waveguide;
A groove for separating the optical waveguide perpendicular to the optical axis;
The mirror is horizontally movable, and one side is a flat surface and the other surface is a curved surface.
The optical add / drop device according to claim 1 . Each optical switch provided in the optical switch array,
An optical waveguide;
A groove for separating the optical waveguide perpendicular to the optical axis;
The groove is horizontally movable, one side is a plane mirror, and the other side includes a mirror having a region where the reflectance is reduced in the plane.
The optical add / drop device according to claim 1 . The region where the reflectance is reduced is formed by any means of light absorption means, light scattering means, light diffraction means, or a combination of the plurality of means.
The optical add / drop device according to claim 3 . The two AWGs and the optical switch array are integrated on the same substrate.
The optical add / drop device according to claim 1. In the two AWGs, slab waveguides provided in the AWG cross each other.
The optical add / drop device according to claim 5 . A temperature control unit for controlling the temperature of the substrate and a switch control unit for driving and controlling the switch array are incorporated in the same package.
The optical add / drop device according to claim 5 .

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