JP2000314814A - Optical attenuator, horizontal waveguide type optical circuit equipped therewith, and attenuation system having the optical circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical attenuator or the like that facilitates manufacturing and that is miniaturizable. SOLUTION: The optical attenuator is such that a plurality of Mach-Zehnder waveguide elements are parallelly arranged on a common substrate 11. Each of such waveguide elements is equipped with an inputting optical waveguide 121, first directional connector 131, two optical waveguides 141, 151, second directional connector 161, outputting optical waveguide 171, monitoring optical waveguide 181, and a heater 191 for adjusting the temperature of either one of the two optical waveguides 141, 151 (i=1 to 8). In particular, between the mutually adjacent Mach-Zehnder waveguide elements, one monitoring optical waveguide 181 and the other outputting optical waveguide 171 are arranged so as to cross each other.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a multi-channel optical attenuator having a plurality of Mach-Zehnder waveguide elements, a planar waveguide optical circuit having the optical attenuator, and an optical attenuation system having the optical attenuator. Things.

[0002]

2. Description of the Related Art Hitherto, an optical attenuator using a Mach-Zehnder type waveguide device has been known (for example, M.Ka
wachi, et al., OFC / IOOC'93 Technical Digest, TuH4
And JP-A-5-173101). This optical attenuator includes, as shown in FIG. 5, an input optical waveguide 2, a first directional coupler 3, a first optical waveguide 4, a second optical waveguide 5, a second directional coupler. 6, an output optical waveguide 7 and a monitoring optical waveguide 8 are provided on the base 1 and a heater 9 for adjusting the temperature of the first optical waveguide 4 is provided. The signal light input to the input optical waveguide 2 is
The light is branched by the first directional coupler 3, passes through the first optical waveguide 4 and the second optical waveguide 5 in order, and reaches the second directional coupler 6. The signal light reaching the second directional coupler 6 is output from the second directional coupler 6 to the output optical waveguide 7.
The light is output to each of the monitoring optical waveguides 8 at a predetermined branching ratio. This branching ratio is controlled by a plate 9 for adjusting the temperature of the first optical waveguide 4. The heater 9 controls the temperature of the first optical waveguide 4 (that is, the optical path length) while detecting the power of the signal light output to the monitoring optical waveguide 8 by the light receiving element, thereby obtaining the input optical waveguide 2. The ratio (Pout / Pin) of the power Pin of the signal light input to the optical waveguide and the power Pout of the signal light output to the output optical waveguide 7, that is, the optical attenuation is controlled.

Further, as shown in FIG. 6, a multi-channel optical attenuator can be realized by providing a plurality of Mach-Zehnder waveguide elements in parallel on a common substrate. The multi-channel optical attenuator shown in this figure has a substrate 1 in which eight Mach-Zehnder waveguide elements are shared.
It is provided in parallel above. Each Mach-Zehnder type waveguide element has an input optical waveguide 2 _i , a first directional coupler 3 _i , a first optical waveguide 4 _i , and a second optical waveguide 5, similarly to the structure shown in FIG. _i , a second directional coupler 6 _i , an output optical waveguide 7 _i , and a monitoring optical waveguide 8 _i , and a heater 9 _i for adjusting the temperature of the first optical waveguide 4 _i. (I = 1 to 8).

Furthermore, a multi-channel output circuit (for example, AWG: Arrayed Wavegu
ide Grating) and a multi-channel optical attenuator having a Mach-Zehnder waveguide element corresponding to each output channel of the multi-channel output circuit are provided on a common substrate, so that the output power between channels can be reduced. A small planar waveguide optical circuit with small deviation is realized.

[0005]

However, in a multi-channel optical attenuator as shown in FIG. 6 and a planar waveguide type optical circuit having this optical attenuator, an output optical waveguide 7 and a monitoring optical waveguide 8 are provided. And are alternately arranged adjacent to each other. That is, a light receiving element for detecting the power of the light output to each monitoring optical waveguide 8 needs to be provided between each output optical waveguide 7 for guiding the signal light further to the subsequent stage. Such a configuration is difficult to manufacture and has limitations in miniaturization.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and is an optical attenuator which can be easily manufactured and reduced in size, a planar waveguide type optical circuit having the optical attenuator, and It is an object of the present invention to provide an optical attenuation system having the optical attenuator.

[0007]

An optical attenuator according to the present invention comprises: an input optical waveguide through which signal light propagates; a first directional coupler connected to the input optical waveguide; Two optical waveguides connected to the directional coupler, a second directional coupler connected to the two optical waveguides, and an output optical waveguide connected to the second directional coupler An optical attenuator provided with a plurality of Mach-Zehnder waveguide elements each having a monitoring optical waveguide and a temperature controller for adjusting the temperature of one of the two optical waveguides is provided on a substrate. An output optical waveguide of each of the plurality of Mach-Zehnder waveguide elements is provided along a first direction on the substrate, and an output port of the monitoring optical waveguide of each of the plurality of Mach-Zehnder waveguide elements is provided on the substrate. It is provided along any of the second and third directions that intersect the first direction. Thus, the monitoring optical waveguides of each of the plurality of Mach-Zehnder waveguide elements can be provided in an area different from the area where the output optical waveguides of each of the plurality of Mach-Zehnder waveguide elements are arranged.

This optical attenuator has multiple channels having a plurality of Mach-Zehnder waveguide elements. It works as follows for each channel. The signal light input to the input optical waveguide is branched by the first directional coupler, and reaches the second directional coupler after passing through each of the two optical waveguides. The signal light is output from the second directional coupler to the output optical waveguide and the monitoring optical waveguide at a predetermined branching ratio. The branching ratio is determined by the temperature controller.
It is controlled by adjusting the temperature of any of the optical waveguides of the book. The temperature controller controls the temperature of the optical waveguide (that is, the optical path length) while the light receiving element detects the power of the light output to the monitoring optical waveguide, so that the signal light input to the input optical waveguide is controlled. (Pout / Pout / Pin) of the power of the signal light output to the output optical waveguide
Pin), that is, the amount of light attenuation is controlled. In the Mach-Zehnder type optical waveguide elements adjacent to each other, it is preferable that the crossing angle between one monitoring optical waveguide and the other output optical waveguide is 1.1 ° or more and 2.1 ° or less.

In this optical attenuator, the monitoring optical waveguide of each channel has an output port in a region different from the region where the output optical waveguide of each channel is provided. Thus, the light receiving elements that receive the light output from the output port of the monitoring optical waveguide of each channel can be arranged collectively. Further, optical fibers for inputting the signal light output from the output ports of the respective output optical waveguides of the respective channels can be collectively arranged on the end face of the substrate. Therefore, this optical attenuator is easy to manufacture and can be miniaturized.

In the optical attenuator according to the present invention, the monitoring optical waveguides of each of the plurality of Mach-Zehnder type waveguide elements are provided parallel to and separated from each other, and a groove crossing these is formed on the substrate. A light receiving element for receiving light output from an output port of each monitoring optical waveguide is provided in the groove.
In this case, since the optical attenuator including the light receiving element is integrated, the size can be reduced also in this respect.

The planar waveguide type optical circuit according to the present invention has a multi-channel output circuit for outputting multi-channel signal light, and a Mach-Zehnder type waveguide element corresponding to each output channel of the multi-channel output circuit. And the optical attenuator are provided on a common substrate. In this planar waveguide type optical circuit, the signal light output from each output channel of the multi-channel output circuit is adjusted in attenuation by the multi-channel optical attenuator, and is output to each output optical waveguide of the optical attenuator. The signal light powers can be made substantially equal to each other. In this planar waveguide type optical circuit, not only a multi-channel optical attenuator but also a multi-channel output circuit for outputting multi-channel signal light is provided on a common substrate. Is easy to manufacture and can be miniaturized.

In addition, an optical attenuation system according to the present invention includes an optical attenuator having the plurality of Mach-Zehnder type optical waveguide elements, and monitors the power of light output to the monitoring optical waveguide using a light receiving element. And a control system for controlling the temperature controller based on the monitoring result.

[0013]

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings. In the description of the drawings, the same elements will be denoted by the same reference symbols, without redundant description.

First, an embodiment of the optical attenuator according to the present invention will be described. FIG. 1 is a diagram showing the structure of an embodiment of an optical attenuator according to the present invention and an optical attenuator system having the optical attenuator. This optical attenuator is an eight-channel optical attenuator in which eight Mach-Zehnder waveguide elements are provided in parallel on a common substrate 11. The Mach-Zehnder type waveguide element of each channel includes an input optical waveguide 12 _i , a first directional coupler 13 _i , a first optical waveguide 14 _i , a second optical waveguide 15 _i , and a second directional coupler. 16 _i , output optical waveguide 17
_i and monitoring optical waveguide 18 _i are formed, and a heater 19 _i for adjusting the temperature of the first optical waveguide 14 _{i (i} = 1~8).

[0015] eight output optical waveguide 17 _{1-17 8} respectively, are arranged parallel to each other along the arrow S _1, the substrate 1
1 has an output port on the end face. Eight each monitoring optical waveguide 18 _{1-18 8,} the optical waveguide 1 for the eight output
And an output port in an area different from the 7 _{1-17 8} is provided area. That is, the monitoring optical waveguides 18 ₁ to 18 ₁
8 ₄ has an output port to the groove 11A provided on the substrate 11. The monitoring optical waveguide 18 _{5-18 8,}
The groove 11B provided in the substrate 11 has an output port.

In the vicinity of the groove 11A, the monitoring optical waveguide 18 ₁
To 18 ₄ provided in along the arrow S ₂ parallel to and a predetermined distance apart from each other, the grooves 11A are formed so as to cross them. Further, the grooves 11A, the light receiving elements 20 ₁ to 20 ₄ is provided for receiving the light output from the optical waveguide 18 _{1-18 4} respective output port for monitoring. The light receiving elements 20 ₁ to 20 ₄ may be of individually, preferably one that is formed in an array on a common substrate.

[0017] Similarly, in the vicinity of the groove 11B, the monitoring optical waveguide 18 _{5-18 8} is provided in parallel to and a predetermined distance apart from each other along the arrow S _3, the grooves 11B, like crossing these Is formed. Also, in the groove 11B,
The light receiving element 20 _{5-20 8} is provided for receiving the light output from the optical waveguide 18 _{5-18 8} each output port for monitoring. The light receiving element 20 _{5-20 8} may be of individually, preferably one that is formed in an array on a common substrate.

Furthermore, in the optical attenuation system according to the present invention, the light receiving elements 20 ₁ to 20 ₄ and 20 ₅ -
The output of 20 ₈ is monitored by the control system 100,
k control system 100 is performing the temperature control of the heater 19 ^1-19 ₈ while monitoring the output variation of the light receiving elements 20 ₁ to 20 _8.

The optical attenuator according to this embodiment is as follows.
Works like Input optical waveguide 12_iEntered in
The signal light is supplied to the directional coupler 13._iBranched by
Road 14 _IAnd optical waveguide 15_iThrough each, directional coupling
Table 16_iTo reach. The signal light is transmitted to the directional coupler 16._i
To output optical waveguide 17_iAnd monitoring optical waveguide 18_iPlace
Output at a fixed branching ratio. The branch ratio is determined by the heater 19_iBy
Adjusted optical waveguide 14_iIs controlled by the temperature of
Then, the monitoring optical waveguide 18_iPower of light output to
Is the light receiving element 20_iAnd the heater 1
9_iThe optical waveguide 14_iTemperature, that is, optical path length is controlled
As a result, the input optical waveguide 12_iThe letter entered in
Power Pin of signal light and output optical waveguide 17_iOutput to
The ratio (Pout / Pin) to the power Pout of the signal light, that is, the light
The amount of attenuation is controlled.

In this embodiment, since the output optical waveguide 17 and the monitoring optical waveguide 18 intersect on the substrate 11, crosstalk of signal light between them becomes a problem.
That is, if the crossing angle is not appropriate, crosstalk occurs due to mode coupling between the output optical waveguide 17 and the monitoring optical waveguide 18, and the signal light transmittance is reduced. FIG. 2 is a graph in which the transmittance is plotted with respect to the intersection angle between the output optical waveguide 17 and the monitoring optical waveguide 18.

From this graph, it can be seen that when the intersection angle θ is 30 degrees or more, the transmittance is converged at 99%.
However, in order to set the intersection angle θ to 30 degrees or more, it is necessary to increase the distance D between the monitoring waveguides 17 _i (the center distance between the optical waveguides). For example, if the radius of curvature is 5 mm
In this case, the interval D needs to be 670 μm or more. Therefore, this case is not always appropriate for miniaturization.

On the other hand, from this graph, the intersection angle θ is about 2
It can be seen that the transmittance decreases as the intersection angle θ decreases in a range of not less than about 10 degrees and about 10 degrees, but the transmittance reaches a maximum (transmittance peak) at a certain intersection angle θ in a range of about 2 degrees or less. . Specifically, when the intersection angle θ is 1.44 degrees, the transmittance is 96%, and the crosstalk is −3.
8 dB. When the intersection angle θ is 1.44 degrees, the distance D between the monitoring waveguides 17 _i can be reduced. Therefore, this case is preferable for miniaturization.

In addition, the inventors have confirmed that the above-described optimum intersection angle fluctuates due to the difference in the relative refractive index difference Δ of each optical waveguide with respect to the substrate 11. FIG.
For a different relative refractive index difference Δ of each optical waveguide with respect to 1,
5 is a graph in which transmittance is plotted with respect to an intersection angle between an output optical waveguide 17 and a monitoring optical waveguide 18. In addition,
In FIG. 3, graph G100 shows the relationship between the crossing angle and the transmittance at Δ = 0.45%, and graph G200 shows Δ =
Relationship between crossing angle and transmittance at 0.75%, graph G
300 shows the relationship between the crossing angle and the transmittance at Δ = 1.00%, and the graph G400 shows the relationship between the crossing angle and the transmittance at Δ = 1.50%. The relative refractive index difference Δ of each optical waveguide with respect to the substrate 11 is given as follows.

Δ = (n ₁ ² −n ₂ ² ) / 2 n ₁ ² ≒ (n ₁ −n ₂ ) / n ₁ where n ₁ is the refractive index of each optical waveguide, and n ₂ is the refractive index of the substrate. Yes, in this specification, Δ is expressed as a percentage.

As can be seen from the graphs of FIG.
As the relative refractive index difference Δ of each optical waveguide with respect to 1 increases, the optimum crossing angle at which the transmittance peaks increases with this increase. For example, the crossing angle at which the transmittance peak is obtained in the graph G100 is 1.1 °, the crossing angle at which the transmittance peak is obtained in the graph G200 is 1.4 °, and the graph G3 is obtained.
The crossing angle at which the transmittance peak takes place at 00 is 1.7.
{Circle around (2)}, the intersection angle at which the transmittance peak is obtained in the graph G400 was 2.1 °. In consideration of the above measurement results, it is preferable that the optimum intersection angle for minimizing the crosstalk between the output optical waveguide 17 and the monitoring optical waveguide 18 be 1.1 ° or more and 2.1 ° or less.

The optical attenuator according to this embodiment
, The eight monitoring optical waveguides 18₁~ 18₈Respectively
Are eight output optical waveguides 17₁~ 17₈Territory where was established
It has an output port in an area different from the area. this thing
The monitoring optical waveguide 18 ₁~ 18₈Each output port
Light-receiving element 20 for receiving light from a light source₁~ 20₈Put together
Can be arranged. Also, the output optical waveguide 17₁
~ 17₈Signal light output from each output port
Input optical fiber 30₁~ 30₈On the end face of the substrate 11
They can also be placed together. Therefore, this implementation
The optical attenuator according to the embodiment is easy to manufacture and small in size.
Is possible.

Furthermore, in the optical attenuator according to this embodiment, the grooves 11A provided on the substrate 11, the light receiving elements 20 ₁ to 20 ₄ and 20 ₅ to 20 ₈ to 11B are arranged, the two groups 20 _{1 to} 20 ₄ and 20 ₅
20 ₈ are integrated, respectively. Therefore, also in this respect, the optical attenuator can be downsized.

Next, an embodiment of a planar waveguide type optical circuit according to the present invention will be described. FIG. 4 is a diagram showing a configuration of a planar waveguide optical circuit according to this embodiment and an optical attenuator system having the planar waveguide optical circuit. In this planar waveguide optical circuit, an AWG, which is a multi-channel output circuit that outputs multi-channel signal light, and the above-described optical attenuator are provided on a common substrate 11. AWG includes an input optical waveguide 31 and a slab waveguide 3
2, an array waveguide section 33 and a slab waveguide 34 are provided. Moreover, the slab waveguide 34 of the AWG is connected to the input optical waveguide 12 ₁ to 12 ₈ of the optical attenuator.

A slab waveguide 32 for diffracting and guiding the signal light input from the input optical waveguide 31 makes the signal light incident on each of a plurality of optical waveguides constituting the arrayed waveguide section 33. Further, a slab waveguide 34 for diffracting and guiding the signal light input from the array waveguide section 33.
It is to be incident on the input optical waveguide 12 ₁ to 12 ₈ of the optical attenuator. The array waveguide section 33 provided between the slab waveguide 32 and the slab waveguide 34 is composed of a plurality of optical waveguides, and the optical path lengths of the plurality of optical waveguides are different from each other by a predetermined length. To give a phase difference to the light.

Next, the operation of the planar waveguide type optical circuit according to this embodiment will be described. It is assumed that the signal light input to the input optical waveguide 31 of the AWG has _eight wavelengths λ _{1 to} λ ₈ . The signal light input to the input optical waveguide 31 of the AWG propagates through the input optical waveguide 31 and then enters the slab waveguide 32. In the slab waveguide 32, the input signal light propagates while diffracting toward the array waveguide 33. Each wavelength component of the signal light input to the arrayed waveguide 33 propagates through all of the plurality of optical waveguides of the arrayed waveguide 33 and then reaches the slab waveguide 34. Each wavelength component of the signal light propagates while diffracting the slab waveguide 34 toward the input optical waveguide 12 ₁ to 12 ₈ of the optical attenuator.

At this time, since the optical path lengths of the plurality of optical waveguides of the arrayed waveguide section 33 are different from each other by a predetermined length, the signal light propagating through each of them is given a phase difference corresponding to the wavelength. When the light propagates through the array waveguide section 33 and the slab waveguide 34 and reaches the input optical waveguide 12 _i , the signal light of the wavelength λ _i reinforces, while the other wavelengths λ _i
The signal light of _j (j ≠ i) cancels out (i, j = 1 to 2).
8). Therefore, the signal light having the wavelength λ _i is output to the input optical waveguide 12 _i (i = 1 to 8). That is, AWG
Acts as an optical splitter.

The signal light of the wavelength lambda _i which is input to the input optical waveguide 12 _i of the optical attenuator is split by the directional coupler 13 _i, through a respective optical waveguides 14 _i and the optical waveguide 15 _i, the directional coupler it reaches the vessel 16 _i. The signal light is output from the directional coupler 16 _i to the output optical waveguide 17 _i and the monitoring optical waveguide 18 _i at a predetermined branching ratio. Note that the branching ratio is controlled by the heater 19 _i adjusting the temperature of the optical waveguide 14 _i . Then, the power of the output to the monitoring optical waveguide 18 _i light is detected by the light receiving element 20 _i, the optical waveguide 1 by a heater 19 _i
4 _i of temperature, that is, by the optical path length is controlled, the ratio of the signal light power Pout is output power Pin of the optical signal input to the input optical waveguide 12 _i to the output optical waveguide 17 _i (Pout / Pin), that is, the amount of light attenuation is controlled.
At this time, the wavelength lambda _i to be output to the output optical waveguide 17 _i
As the power of the signal light are substantially equal to each other, the temperature of the optical waveguide 14 _i by the heater 19 _i, i.e. the optical path length is controlled, the optical attenuation amount with respect to the signal light of the wavelength lambda _i is controlled.

In the planar waveguide type optical circuit according to this embodiment, not only a multi-channel optical attenuator but also an AWG which is a multi-channel output circuit for outputting multi-channel signal light.
Also, since the planar waveguide type optical circuit is provided on the common substrate 11, the planar waveguide type optical circuit can be easily manufactured and can be reduced in size.

The present invention is not limited to the above-described embodiment, but can be variously modified. For example,
A multi-channel output circuit that outputs multi-channel signal light,
The invention is not limited to the AWG, and may be an optical branch circuit, an optical switch circuit, or the like.

[0035]

As described above in detail, the optical attenuator according to the present invention has a plurality of Mach-Zehnder type waveguide elements provided on a substrate, and has an output for one of adjacent Mach-Zehnder type waveguide elements. By intersecting the optical waveguide and the other monitoring optical waveguide, the output optical waveguides of each of the plurality of Mach-Zehnder waveguide elements are provided in the first region on the substrate, and the plurality of Mach-Zehnder waveguide elements are provided. The output port of each monitoring optical waveguide is provided in a second area different from the first area on the substrate. Thus, a light receiving element that receives light from the output port of the monitoring optical waveguide of each channel can be provided integrally. Further, the optical fibers for inputting the signal light from the output ports of the respective output optical waveguides of the respective channels can be collectively arranged on the end face of the substrate. Therefore, the optical attenuator and the optical attenuation system having the optical attenuator can be easily manufactured and can be downsized.

In the second region, the monitoring optical waveguides of each of the plurality of Mach-Zehnder waveguide elements are provided in parallel with and separated from each other, and a groove provided on the substrate so as to cross the waveguides. In the case where a light receiving element for receiving light output from each output port of each monitoring optical waveguide is disposed, the optical attenuator and the optical attenuation system having the same are integrated together with the light receiving element. Therefore, miniaturization is also possible in this regard.

Further, the planar waveguide type optical circuit according to the present invention comprises a multi-channel output circuit for outputting multi-channel signal light, and a Mach-Zehnder type waveguide element corresponding to each output channel of the multi-channel output circuit. The above-described optical attenuator is provided on a common substrate. The planar waveguide type optical circuit and the optical attenuation system having the same are easy to manufacture and can be miniaturized.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of an optical attenuator according to the present invention and an optical attenuation system having the optical attenuator.

FIG. 2 is a graph in which transmittance is plotted with respect to an intersection angle between an output optical waveguide and a monitoring optical waveguide.

FIG. 3 is a graph in which transmittance is plotted with respect to an intersection angle between an output optical waveguide and a monitoring optical waveguide for a plurality of samples having different relative refractive index differences of a shell optical waveguide with respect to a substrate.

FIG. 4 is a diagram showing a configuration of a planar waveguide optical circuit according to the present invention and an optical attenuation system having the planar waveguide optical circuit.

FIG. 5 is a diagram showing a configuration of a conventional optical attenuator.

FIG. 6 is a diagram showing a configuration of a conventional multi-channel optical attenuator.

[Explanation of symbols]

11 ... substrate, 12 _{1 to} 12 ₈ : input optical waveguide, 13 ₁ to
13 ₈ : first directional coupler, 14 _{1 to} 14 ₈ : first optical waveguide, 15 ₁ to 15 ₈ : second optical waveguide, 16 _{1 to} 16 ₈
... second directional coupler, 17 _{1 to} 17 ₈ ... output optical waveguide, 18 ₁ to 18 ₈ ... monitoring optical waveguide, 19 _{1 to} 19 ₈ ... heater, 20 _{1 to} 20 ₈ ... light receiving element, 31 ... Input optical waveguide, 32: slab waveguide, 33: array waveguide section, 34
... Slab waveguide.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2H047 KA03 KB04 KB09 NA01 TA01 TA43 2H079 AA02 AA12 BA03 CA05 EA05 EB27 FA04 GA04 HA11

Claims (6)

[Claims] 1. An optical attenuator comprising a plurality of Mach-Zehnder waveguide elements arranged on a substrate, wherein the plurality of Mach-Zehnder waveguide elements are an input optical waveguide through which signal light propagates, and the input optical waveguide. A first directional coupler having an input end and two output ends connected to the optical waveguide; two optical waveguides connected to two output ends of the first directional coupler; A temperature controller for adjusting the temperature of at least one of the optical waveguides, a second directional coupler having two incident ends and two output ends respectively connected to the two optical waveguides,
An output optical waveguide connected to one of the output ends of the second directional coupler, and a monitoring optical waveguide connected to the other of the output ends of the second directional coupler, The monitoring optical waveguide included in one of the Mach-Zehnder waveguide elements adjacent to each other among the plurality of Mach-Zehnder waveguide elements crosses the output optical waveguide included in the other of the mutually adjacent Mach-Zehnder waveguide elements. An optical attenuator, which is arranged. 2. A monitoring optical waveguide included in one of the Mach-Zehnder waveguide elements adjacent to each other among the plurality of Mach-Zehnder waveguide elements, and an output optical waveguide included in the other of the Mach-Zehnder waveguide elements adjacent to each other. 2. The optical attenuator according to claim 1, wherein the intersection angle θ with the wave path is not less than 1.1 ° and not more than 2.1 °. 3. The monitoring optical waveguides included in the Mach-Zehnder waveguide elements adjacent to each other among the plurality of Mach-Zehnder waveguide elements are arranged in parallel at a predetermined distance from each other and are adjacent to each other. 2. The optical attenuator according to claim 1, wherein the output optical waveguides included in the Mach-Zehnder waveguide device are arranged in parallel at a predetermined distance from each other. 4. The output optical waveguides of the plurality of Mach-Zehnder waveguide elements are arranged along a first direction, and are groups separated from the monitoring optical waveguides of the plurality of Mach-Zehnder waveguide elements. One extends along a second direction that intersects the first direction, and the other of the divided groups extends along a third direction that intersects both the first and second directions. The optical attenuator according to claim 1, wherein the optical attenuator extends. 5. A substrate; an optical attenuator according to claim 1 provided on said substrate; and an optical attenuator provided on said substrate, outputting signal light propagating through each output optical waveguide group of said optical attenuator. And a multi-channel output circuit. 6. An optical attenuator according to claim 1, wherein the light propagating through the optical waveguide for monitoring the optical attenuator is monitored, and one of the temperature controllers in the optical attenuator is controlled based on the monitoring result. An optical attenuation system including a control system.