JP2003315575A - Optical multiplexer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical multiplexer in which deviation of a wavelength characteristic and the influence of a fluctuation on a multiplexing characteristic are reduced and optical circuits are made small. <P>SOLUTION: A first optical circuit part 11, a second optical circuit part 12, a Y branching part 20 and an output optical waveguide 17 are formed on a substrate 10 from an input end face 10a side toward an output end face 10b side in this order to constitute an optical multiplexer 1A. The first optical circuit part 11 is composed of a Mach-Zehnder interferometer consisting of a first optical waveguide 21, a second optical waveguide 22 and optical couplers 27 and 28. The second optical circuit part 12 is composed of a Mach-Zehnder interferometer consisting of a third optical waveguide 31, a fourth optical waveguide 32 and optical couplers 37 and 28. Output ends of the optical waveguides 22 and 31 are respectively connected to an input side of the Y branching part 20. The output optical waveguide 17 is connected to an output side of the Y branching part 20. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical multiplexer used to combine signal lights in an optical transmission system such as a wavelength division multiplexing transmission system in which a plurality of signal lights having different wavelengths are propagated. Is.

[0002]

2. Description of the Related Art Due to social needs due to the advent of the advanced information society, research and development on large-capacity high-speed communication such as image communication using an optical fiber transmission line and long-distance communication such as international communication are actively conducted. ing. Here, wavelength multiplexing (W
BACKGROUND OF THE INVENTION DM (Wavelength Division Multiplexing) transmission systems perform optical communication by transmitting multi-wavelength signal light composed of a plurality of signal lights having different wavelengths through an optical fiber line, and in recent years, there has been a demand for communication such as the Internet. It is being developed and introduced as a means of responding to the rapid increase.

In a WDM transmission system, a plurality of signal lights having different wavelengths contained in the multi-wavelength signal light are combined with a multi-wavelength signal light transmitted on an optical transmission line such as an optical fiber transmission line. It may be necessary to wave. Examples of the planar waveguide type optical circuit having the function of combining the multi-wavelength signal lights include an arrayed waveguide grating (AWG) type optical circuit and a Mach Zehnder interferometer (MZI: Mach Zehnder). Int
erferometer) type optical circuit is used.

[0004]

An example of the above-mentioned optical multiplexer that multiplexes signal lights having different wavelengths is described in the document "BHVe".
rbeek et al., "Integrated Four-Channel Mach-Zehnde
r Multi / Demultiplexer Fabricated with Phosphorous D
oped SiO ₂ Waveguides on Si ", JOURNAL OF LIGHTWAVE
TECHNOLOGY Vol.6 No.6, p.1011 (1988) "describes an optical multiplexer using an MZI type optical circuit. In this optical multiplexer, a plurality of signal lights are multiplexed by an optical circuit in which asymmetrical Mach-Zehnder interferometers in which a predetermined optical path length difference is set between upper and lower waveguides are connected in multiple stages.

However, the optical multiplexer having such a structure has a problem that the optical circuit becomes large when the number of wavelengths of the signal light to be multiplexed increases. For example, 4
In order to combine the signal lights of the wavelengths, the Mach-Zehnder interferometers are connected in two stages in series as described in the above document, and in order to combine the signal lights of the eight wavelengths, a Mach-Zehnder interferometer is used. It is necessary to have a structure in which three columns are connected in series. Further, in the optical multiplexer using the Mach-Zehnder interferometer, the wavelength band width of the transmission spectrum of the light when the signal light is multiplexed is relatively narrow, and the deviation of the center wavelength due to the manufacturing variation of the optical circuit or the temperature change It is easily affected by fluctuations in wavelength characteristics.

The present invention has been made in order to solve the above-mentioned problems, and it is possible to reduce the influence of the shift or fluctuation of the wavelength characteristic on the multiplexing characteristic and to downsize the optical circuit. An object is to provide a possible optical multiplexer.

[0007]

In order to achieve such an object, an optical multiplexer according to the present invention comprises a substrate and an optical waveguide formed on the substrate in a predetermined waveguide pattern. Is an optical multiplexer for multiplexing signal lights having wavelengths different from each other, comprising: (1) a first optical waveguide having a first input end as one end, and a second input end as one end A first optical circuit section having a second optical waveguide optically coupled to the first optical waveguide via at least two directional couplers to form a first Mach-Zehnder interferometer together with the first optical waveguide and the directional coupler. And (2) a second optical circuit section having at least a third optical waveguide whose one end is the third input end,
(3) An output optical waveguide whose output end is one end, and (4) a first
An end of the optical circuit unit opposite to the input end of the first optical waveguide or the second optical waveguide, and an end of the second optical circuit unit opposite to the input end of the third optical waveguide or another optical waveguide. A Y-branch part having one end connected to one side and an end opposite to the output end of the output optical waveguide connected to the other side, and (5) a first input end, a second input end, and a second input end. It is characterized in that the signal lights inputted from the respective three input ends are multiplexed and outputted from the output end.

In the above-mentioned optical multiplexer, the optical multiplexer of the MZI type optical circuit is provided for the optical multiplexer of the latter stage connected to the first optical circuit which is the optical coupler of the former stage using the Mach-Zehnder interferometer. But by the Y branch,
The optical waveguide from the first optical circuit section and the optical waveguide from the second optical circuit section are joined to the output optical waveguide. As described above, by using the Y-branching portion in which the light coupling rate does not have wavelength dependence, the influence of the shift or fluctuation of the wavelength characteristics on the multiplexing characteristics is reduced. Further, the Y branch section is smaller than the MZI type optical circuit, and it is possible to reduce the size of the entire optical circuit of the optical multiplexer.

In addition, in the optical multiplexer, the second optical circuit section has the fourth optical circuit section.
It has a fourth optical waveguide which has the input end as one end and is optically coupled with the third optical waveguide through at least two directional couplers to form a second Mach-Zehnder interferometer with the third optical waveguide and the directional coupler. It is characterized by As described above, according to the configuration in which the Y-branching units are cascaded in the subsequent stages of the first optical circuit unit and the second optical circuit unit, which are the two MZI optical circuits arranged in a row, the signal lights of four wavelengths are multiplexed. It is possible to obtain an optical multiplexer.

Further, at least one of the first optical waveguide and the second optical waveguide is preceded by a fifth optical waveguide having the fifth input end as one end, and a sixth input end as one end, and at least two directional characteristics are provided. A third optical waveguide optically coupled to the fifth optical waveguide through the coupler to form a third Mach-Zehnder interferometer with the fifth optical waveguide and the directional coupler.
It may be configured to further include an optical circuit unit. As described above, according to the configuration in which the MZI type optical circuits are connected in the multistage cascade in the preceding stage of the Y branching unit, it becomes possible to multiplex the signal lights of multiple wavelengths.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Preferred embodiments of an optical multiplexer according to the present invention will be described in detail below with reference to the drawings. In the description of the drawings, the same elements will be denoted by the same reference symbols, without redundant description. Further, the dimensional ratios in the drawings do not always match those described.

FIG. 1 is a block diagram showing an embodiment of an optical multiplexer according to the present invention. The optical multiplexer of the present embodiment is composed of a planar waveguide type optical circuit using an optical waveguide formed on a substrate. This optical multiplexer can be suitably applied as an optical circuit that multiplexes signal lights having mutually different wavelengths in an optical transmission system such as a WDM transmission system.

An optical multiplexer 1A shown in FIG. 1 includes a substrate 10 and
The optical circuit includes an optical waveguide formed on the substrate 10 in a predetermined waveguide pattern. In the present optical multiplexer 1A, the left end face of the substrate 10 is the input end face 10a used for inputting the signal light to be multiplexed and the right end face is, as indicated by the arrow in the figure, the signal light propagation direction. The output end face 10b is used for outputting the multiplexed signal light.

On the substrate 10, as an optical waveguide forming the optical multiplexer 1A, the first optical circuit portion 11 and the second optical circuit 11 forming an input side optical circuit are provided between the input end face 10a and the output end face 10b. A circuit portion 12 and an output optical waveguide 17 which constitutes an output side optical circuit are formed. In addition to the optical circuit parts 11 and 12 and the optical waveguide 17, a Y branch part 20 is formed on the substrate 10. These optical circuit parts constituting the optical multiplexer 1A are arranged such that the first optical circuit portion 11 and the second optical circuit part 11 are arranged from the input end face 10a side toward the output end face 10b side.
The optical circuit section 12, the Y branch section 20, and the output optical waveguide 17 are arranged in this order.

The first optical circuit section 11 has two optical waveguides, a first optical waveguide 21 and a second optical waveguide 22.

The first optical waveguide 21 is an optical waveguide formed with the input end 23 provided on the input end face 10a as one end. Further, the input end 23 is a first input end for inputting the signal light into the optical multiplexer 1A. This first
With respect to the optical waveguide 21, from the first input end 23,
Two optical couplers (directional couplers), that is, an optical coupler 27 and a second optical coupler 28 are provided.

The second optical waveguide 22 is an optical waveguide formed between an input end 25 provided on the input end face 10a and an output end 26 connected to the input side (one side) of the Y branch 20. Is. Further, the input end 25 is a second input end for inputting the signal light to the present optical multiplexer 1A. The second optical waveguide 22 is optically coupled to the first optical waveguide 21 via each of the optical couplers 27 and 28 described above.

Further, the waveguide portions of the first optical waveguide 21 and the second optical waveguide 22 between the optical couplers 27 and 28 are
The arm waveguide 29 has a predetermined optical path length difference ΔL1 between the optical waveguides 21 and 22. As a result, the first optical waveguide 21, the second optical waveguide 22, the first optical coupler 27, and the second optical coupler 28 are included in the first optical circuit unit 11
And an asymmetric first Mach-Zehnder interferometer in.

The second optical circuit section 12 has two optical waveguides, a third optical waveguide 31 and a fourth optical waveguide 32.

The third optical waveguide 31 is an optical waveguide formed between an input end 33 provided on the input end face 10a and an output end 34 connected to the input side (one side) of the Y branch 20. Is. The input end 33 is a third input end for inputting signal light into the optical multiplexer 1A. For this third optical waveguide 31, two optical couplers (directional couplers), a first optical coupler 37 and a second optical coupler 38, are provided in order from the third input end 33.

The fourth optical waveguide 32 is an optical waveguide formed with the input end 35 provided on the input end face 10a as one end. The input end 35 is a fourth input end for inputting the signal light into the optical multiplexer 1A. This 4th
The optical waveguide 32 is optically coupled to the third optical waveguide 31 via each of the optical couplers 37 and 38 described above.

The waveguide portions of the third optical waveguide 31 and the fourth optical waveguide 32 between the optical couplers 37 and 38 are
The arm waveguide portion 39 has a predetermined optical path length difference ΔL2 set between the optical waveguides 31 and 32. Thereby, the third optical waveguide 31, the second optical waveguide 32, the first optical coupler 37, and the second optical coupler 38 are included in the second optical circuit unit 12.
And an asymmetric second Mach-Zehnder interferometer in.

The output optical waveguide 17 has an input end 18 connected to the output side (the other side) of the Y branch 20 and an output end face 10.
It is an optical waveguide formed between the output end 19 provided on b. The output end 19 is an output end for outputting the signal light multiplexed from the optical multiplexer 1A.

The Y branch 20 is an optical branch having a Y-shaped optical waveguide structure. As described above, the output end 26 of the second optical waveguide 22 from the first optical circuit unit 11 and the output end of the third optical waveguide 31 from the second optical circuit unit 12 are provided on the input side of the Y branch unit 20. 34 is connected. An input end 18 of the output optical waveguide 17 is connected to the output side of the Y branch section 20.

In the above structure, the signal lights P1 and P2 having different wavelengths respectively inputted from the first input end 23 and the second input end 25 are supplied to the first optical waveguide 21,
The Mach-Zehnder interferometer of the first optical circuit unit 11 including the second optical waveguide 22 and the optical couplers 27 and 28 multiplexes the light, and the Y-branching unit 2 passes through the output end 26 of the second optical waveguide 22.
It is input to the input side of 0.

The third input terminal 33 and the fourth input terminal 35 are also provided.
The signal lights P3 and P4 having different wavelengths respectively input from the respective
2, and the second optical circuit unit 12 including the optical couplers 37 and 38.
Of the Mach-Zehnder interferometer, and is input to the input side of the Y branch section 20 via the output end 34 of the third optical waveguide 31.

Then, the signal light P from the first optical circuit section 11
1 + P2, and the signal light P3 + P from the second optical circuit unit 12
4 is further multiplexed by the Y branch unit 20, and the multiplexed signal light Pout is output from the output end 19 of the output optical waveguide 17.

The effect of the optical multiplexer according to the present embodiment will be described.

In the optical multiplexer 1A shown in FIG. 1, the optical multiplexers at the front stage and the rear stage are connected in two columns to form an optical circuit for multiplexing the signal light. An optical multiplexing unit using an MZI type optical circuit is used for a rear optical combining unit connected to the first optical circuit unit 11 and the second optical circuit unit 12 which are the former optical combining unit using the Mach-Zehnder interferometer (MZI). The optical waveguide 22 from the first optical circuit unit 11 is provided by providing the Y branching unit 20 that functions as an optical multiplexing unit instead of providing the optical unit.
And the optical waveguide 31 from the second optical circuit section 12 are merged into the output optical waveguide 17.

As described above, the wavelength band width of the transmission spectrum of the light when the signal light is multiplexed is obtained by using the Y branching unit 20 in which the light coupling rate does not have wavelength dependency in the optical combining unit in the subsequent stage. Can be wide. Therefore, compared with the case where a Mach-Zehnder interferometer with a relatively narrow wavelength band of the transmission spectrum is used in the optical multiplexing section in the subsequent stage, the shift of the center wavelength due to manufacturing variations of the optical circuit, or the fluctuation of the wavelength characteristics due to temperature changes, etc. The effect on the multiplexing characteristics of is reduced, and the optical multiplexer 1A having stable multiplexing characteristics is realized.

The optical multiplexing section using the Y branch section 20 is M
The size is smaller than the case where the ZI type optical circuit is used, and the size of the entire optical circuit of the optical multiplexer 1A can be reduced. Further, the Y-branching portion is easier to process than an MZI type optical circuit including a directional coupler, and the manufacturing variation is small. Therefore, it is possible to obtain the optical multiplexer 1 </ b> A which has good multiplexing characteristics and whose manufacturing cost is reduced.

Further, in the optical multiplexer 1A shown in FIG. 1, both the first optical circuit section 11 and the second optical circuit section 12 which are the optical circuit sections of the preceding stage are configured as MZI type optical circuits. As described above, according to the configuration in which the Y branch units 20 are connected in cascade at the subsequent stage of the two MZI type optical circuits arranged in a row, the optical multiplexer 1A capable of multiplexing the signal lights of four wavelengths is obtained.

The optical multiplexer 1A shown in FIG. 1 can be applied to an optical transmission system such as a WDM transmission system. Here, as a WDM transmission system, in order to realize high-speed and large-capacity optical communication in a long-distance trunk line system,
Dense wavelength division multiplexing (DWDM: De)
nse-WDM) transmission systems have been developed. On the other hand, as an application to optical communication in an access system in urban areas, the development of a transmission system using a wide wavelength division multiplexing (CWDM: Coarse-WDM) system in which a wavelength band to be used is relatively wide. There is. The optical multiplexer 1A having the above configuration can be suitably applied to any of these DWDM transmission system and CWDM transmission system.

For example, in the CWDM transmission system, the wavelength band of signal light used and the wavelength interval between adjacent channels of signal light are wide. Therefore, even if the wavelength characteristics of the optical components such as the oscillation wavelength of the laser light source and the center wavelength of the wavelength band that can be combined by the optical multiplexer are shifted to some extent by the influence of temperature change, etc. There is an advantage.

Therefore, in the CWDM transmission system,
There is no need for a temperature controller to keep the temperature constant,
Alternatively, it is possible to use low-priced optical components, such as a loose specification range for wavelengths. However, even in such a case, if there is a large influence on the optical characteristic when the wavelength characteristic of the optical component is deviated or changed, the CW
It cannot be suitably used as an optical component in a DM transmission system.

On the other hand, the optical multiplexer 1A shown in FIG.
Then, the first optical circuit unit 11 including a Mach-Zehnder interferometer
By using the optical circuit configured by connecting the Y branching unit 20 in the subsequent stage of the second optical circuit unit 12, the influence of the shift or fluctuation of the wavelength characteristic on the multiplexing characteristic of the signal light is reduced. As a result, the CWD has a wide wavelength band of the signal light to be used and a wide wavelength interval between the adjacent channels of the signal light.
An optical multiplexer 1A having optical characteristics applicable to various optical transmission systems including the M transmission system can be obtained.

The effects and the like of the optical multiplexer according to the above embodiment will be described more specifically. Here, the optical multiplexer 1A having the configuration shown in FIG. 1 will be examined in comparison with a conventional optical multiplexer.

FIG. 2 is a block diagram showing a conventional optical multiplexer which is a comparative example with respect to the optical multiplexer 1A shown in FIG. The optical multiplexer 6 includes a first optical circuit section 61, a second optical circuit section 62, and a third optical circuit section 63 formed on the substrate 60 between the input end face 60a and the output end face 60b.

The first optical circuit section 61 has an optical waveguide 71 having one end at the first input end 73 to which the signal light P1 is input and an optical waveguide 71 having one end at the second input end 75 to which the signal light P2 is input. And 72. These optical waveguides 71 and 72 are optically coupled via optical couplers 77 and 78, respectively, to form a Mach-Zehnder interferometer that multiplexes the signal lights P1 and P2.

The second optical circuit section 62 has an optical waveguide 81 having one end at the third input end 83 to which the signal light P3 is input and an optical waveguide 81 having one end at the fourth input end 85 to which the signal light P4 is input. 82 and. These optical waveguides 81 and 82 are optically coupled via optical couplers 87 and 88, respectively, to form a Mach-Zehnder interferometer that multiplexes the signal lights P3 and P4.

The third optical circuit section 63 has an optical waveguide 91 in which the optical waveguide 72 of the first optical circuit section 61 is connected to the input end.
And an optical waveguide 92 in which the optical waveguide 81 of the second optical circuit section 62 is connected to the input end. These optical waveguides 91,
The optical signal 92 is optically coupled via the optical couplers 97 and 98, so that the signal light P from the first optical circuit unit 61 is transmitted.
1 + P2 and signal light P3 + P4 from the second optical circuit unit 62
It constitutes a Mach-Zehnder interferometer for multiplexing. The multiplexed signal light Pout is output from the output end 96 of the optical waveguide 92.

First, for simplification, multiplexing of signal light using an optical circuit composed of a one-stage Mach-Zehnder interferometer will be described (for example, refer to the optical circuit section 61 in FIG. 2).

In order to combine the signal lights P1 and P2 having different wavelengths λ ₁ and λ ₂ by the one-stage MZI type optical circuit, between the upper and lower waveguides in the arm waveguide portion of the asymmetric Mach-Zehnder interferometer. The optical path length difference ΔL of the condition λ ₂ −λ _{1
= Λ 1 · λ 2 / (} 2n g ΔL) may be set so as to satisfy. Here, _ng is the effective refractive index of the core of the optical waveguide, and when a silica glass waveguide is used, _ng = 1.
45.

To give a concrete example, the MZI having a one-stage structure
Type optical circuit, λ ₁ = 1550 nm, λ ₂ = 1555
When nm and _ng = 1.45, the optical path length difference is ΔL = 1.
It becomes 66.224 μm. Also, λ ₁ = 1550 nm,
When λ ₂ = 1560 nm and _ng = 1.45, the optical path length difference is ΔL = 83.379 μm.

As is clear from the above equations and calculation examples, the wavelength interval λ ₂ − of the two wavelengths of the signal light to be multiplexed.
The smaller λ ₁ becomes, the larger the required optical path length difference ΔL in the Mach-Zehnder interferometer becomes, and the longer the chip length of the optical circuit becomes. For example, when the chip length is calculated for each of the above two calculation examples, λ ₁ = 1550 nm and λ ₂ = 1555.
In the former example in which signal lights of two wavelengths of nm are combined, the chip length is 13.4 mm. Also, λ ₁ = 1550 nm,
In the latter example in which signal lights of two wavelengths of λ ₂ = 1560 nm are multiplexed, the chip length is 11.6 mm. Here, the chip length of the optical circuit is calculated assuming that the radius of curvature at the curved portion of the optical waveguide forming the optical circuit is R = 4 mm.

The conventional optical multiplexer 6 shown in FIG.
Type optical circuits are connected in two stages in cascade, and four wavelengths λ ₁
It is possible to combine the signal light P1~P4 of to [lambda] _4. In such a configuration, the wavelengths of the signal lights to be multiplexed are λ ₁ = 1540 nm, λ ₂ = 1545 nm, and λ ₃
= 1550 nm and λ ₄ = 1555 nm, the chip length of the entire optical multiplexer 6 in the signal light propagation direction is 2
It becomes 3.9 mm. When the chip length becomes long like this,
There is a problem that the cost of the optical circuit becomes high, and the optical circuit becomes large in size, which makes it practically difficult to use in an optical transmission system.

On the other hand, in the optical multiplexer 1A according to the present invention shown in FIG. 1, the first optical circuit section 11 and the second optical circuit section 12, which are MZI type optical circuits, and the Y branch section 20 are connected in series. It has a configuration and has four wavelengths λ, like the optical multiplexer 6 shown in FIG.
It is possible to combine the signal lights P1 to P4 of _{1 to} λ ₄ . In such a configuration, the wavelengths of the signal lights to be multiplexed are similarly λ ₁ = 1540 nm and λ ₂ = 1545n.
If m, λ ₃ = 1550 nm and λ ₄ = 1555 nm,
The chip length of the entire optical multiplexer 1A in the signal light propagation direction is 16.6 mm, which is significantly shorter than that of the optical multiplexer 6 in FIG. As described above, according to the optical multiplexer having the configuration in which the MZI type optical circuits and the Y branch units are connected in cascade, the optical circuit can be downsized and the cost thereof can be reduced.

Next, the optical characteristics of the optical multiplexer shown in FIGS. 1 and 2 will be compared.

FIG. 3 is a graph showing the calculation result of the multiplexing characteristic in the conventional optical multiplexer shown in FIG. In this graph, the horizontal axis represents the signal light wavelength (nm) of the signal light to be multiplexed by the optical multiplexer 6, and the vertical axis represents the signal light loss (dB) between the input end and the output end. ing. Regarding the graphs F1 to F4, the graph F1 shows the loss characteristics of the output signal light Pout of the input signal light P1 from the first input end 73,
A graph F2 is a loss characteristic of the output signal light Pout of the input signal light P2 from the second input end 75, a graph F3 is a loss characteristic of the output signal light Pout of the input signal light P3 from the third input end 83, and a graph F4. Is the input signal light P from the fourth input end 85
4 shows the loss characteristics of the output signal light Pout of No. 4 respectively.

FIG. 4 is a graph showing the calculation result of the multiplexing characteristic in the optical multiplexer according to the present invention shown in FIG.
In this graph, the horizontal axis represents the signal light wavelength (nm) of the signal light to be multiplexed by the optical multiplexer 1A, and the vertical axis represents the signal light loss (dB) between the input end and the output end. ing. Regarding the graphs G1 to G4, the graph G1 is the output signal light Pou of the input signal light P1 from the first input end 23.
The loss characteristic at t, the graph G2 is the loss characteristic at the output signal light Pout of the input signal light P2 from the second input end 25, and the graph G3 is the output signal light Pout of the input signal light P3 at the third input end 33. And the graph G4 shows the loss characteristics of the input signal light P4 from the fourth input terminal 35 in the output signal light Pout.

Comparing the graph of FIG. 3 for the optical multiplexer 6 with the graph of FIG. 4 for the optical multiplexer 1A, the insertion loss for the signal light in the optical circuit of the optical multiplexers 6 and 1A is The optical multiplexer 6 has a loss of 0.2 dB or less, while the optical multiplexer 1A has a slightly large loss of 3.2 dB. On the other hand, when comparing the 3 dB bandwidth of the transmission spectrum of light in each of the channels P1 to P4, that is, the wavelength bandwidth when the loss becomes 3 dB larger than the minimum value, it is 4.4 nm in the conventional optical multiplexer 6. On the other hand, the optical multiplexer 1A has a width of 9.9 nm, which is twice as large as that of the optical multiplexer 6.

As described above, in the optical multiplexer 1A using the Y branch section 20, the wavelength band width of the transmission spectrum of the light when the signal light is multiplexed is wider than that of the conventional optical multiplexer 6.
As a result, in the optical multiplexer 1A, stable multiplexing characteristics are obtained even when the center wavelength of the wavelength characteristics is shifted due to manufacturing variations of the optical circuit, or when the wavelength characteristics are changed due to environmental temperature change or the like. be able to.

FIG. 5 is a block diagram showing another embodiment of the optical multiplexer. The optical multiplexer 1B of the present embodiment has a configuration in which one more MZI type optical circuit is connected in cascade to the optical multiplexer 1A shown in FIG.

The optical multiplexer 1B shown in FIG.
It is a planar waveguide type optical circuit composed of an optical waveguide formed on a substrate 10 in a predetermined waveguide pattern. In the present optical multiplexer 1B, the left end face of the substrate 10 is the input end face 1 as indicated by the arrow in the drawing for the signal light propagation direction.
0a, the right end face is the output end face 10b.

On the substrate 10, six optical circuit sections 11 to 16 each composed of an MZI type optical circuit, a Y branch section 20, and an output optical waveguide 17 are formed. Of these, the optical circuit portion on the output end face 10b side, that is, the first optical circuit portion 11 and the second optical circuit portion 12, the Y branch portion 20, and the output optical waveguide 17 are provided.
The configuration of is the same as that shown in FIG. Further, in the present embodiment, the MZ at the front stage of the Y branch unit 20 is
First optical circuit unit 11 and second optical circuit unit 1 which are I-type optical circuits
2, the optical circuit units 13 to 16 at the previous stage are further provided.

The optical circuit section 13 has an optical waveguide 41 and an optical waveguide 42 which is optically coupled to the optical waveguide 41 via two optical couplers to form a Mach-Zehnder interferometer. The input ends of the optical waveguides 41 and 42 are provided on the input end face 10a, and are the first input end and the second input end for inputting the signal lights P1 and P2 to the optical multiplexer 1B, respectively. . The output end of the optical waveguide 42 is connected to the first optical circuit unit 1
It is connected to the input end of the first optical waveguide 21.

The optical circuit section 14 has an optical waveguide 43 and an optical waveguide 44 which is optically coupled to the optical waveguide 43 via two optical couplers to form a Mach-Zehnder interferometer. The input ends of the optical waveguides 43 and 44 are provided on the input end face 10a, and are the third input end and the fourth input end for inputting the signal lights P3 and P4 to the present optical multiplexer 1B, respectively. . The output end of the optical waveguide 43 is connected to the first optical circuit unit 1
It is connected to the input end of the first optical waveguide 22.

The optical circuit section 15 has an optical waveguide 45 and an optical waveguide 46 which is optically coupled to the optical waveguide 45 via two optical couplers to form a Mach-Zehnder interferometer. The input ends of the optical waveguides 45 and 46 are provided on the input end face 10a, and are the fifth input end and the sixth input end for inputting the signal lights P5 and P6 to the optical multiplexer 1B, respectively. . The output end of the optical waveguide 46 is connected to the second optical circuit unit 1
It is connected to the input end of the second third optical waveguide 31.

The optical circuit section 16 has an optical waveguide 47 and an optical waveguide 48 which is optically coupled to the optical waveguide 47 via two optical couplers to form a Mach-Zehnder interferometer. The input ends of the optical waveguides 47 and 48 are provided on the input end face 10a, and are the seventh input end and the eighth input end for inputting the signal lights P7 and P8 to the optical multiplexer 1B, respectively. . The output end of the optical waveguide 47 is connected to the second optical circuit unit 1
It is connected to the input end of the second fourth optical waveguide 32.

In the above configuration, the optical circuit unit 13
Signal light P1 and P2 input from each of the two input ends
Are multiplexed by a Mach-Zehnder interferometer composed of the optical waveguides 41 and 42, and input from the output end of the optical waveguide 42 to the first optical waveguide 21 of the first optical circuit unit 11. Also,
The signal lights P3 and P4 input from the two input ends of the optical circuit unit 14 are combined by the Mach-Zehnder interferometer including the optical waveguides 43 and 44, and the optical waveguide 43
Is input to the second optical waveguide 22 of the first optical circuit unit 11.

Similarly, the signal lights P5 and P6 input from the two input ends of the optical circuit section 15 are combined by the Mach-Zehnder interferometer composed of the optical waveguides 45 and 46, and output from the optical waveguide 46. The light is input from the end to the third optical waveguide 31 of the second optical circuit unit 12. In addition, the optical circuit unit 16
Signal light P input from each of the two input ends in
7, P8 are multiplexed by a Mach-Zehnder interferometer composed of optical waveguides 47 and 48, and input from the output end of the optical waveguide 47 to the fourth optical waveguide 32 of the second optical circuit unit 12.

Further, in the first optical circuit section 11, the signal light P1 + P2 from the optical circuit section 13 and the signal light P3 + P4 from the optical circuit section 14 are combined by the Mach-Zehnder interferometer composed of the optical waveguides 21 and 22. , Optical waveguide 2
It is input to the input side of the Y branching unit 20 via the output terminal of 2. In the second optical circuit unit 12, the signal light P5 + P6 from the optical circuit unit 15 and the signal light P7 + P8 from the optical circuit unit 16 are combined by the Mach-Zehnder interferometer including the optical waveguides 31 and 32, and the optical waveguides are combined. It is input to the input side of the Y branch unit 20 via the output end of 31.

Then, the signal light P from the first optical circuit unit 11
1 + P2 + P3 + P4 and the signal light P5 + P6 + P7 + P8 from the second optical circuit unit 12 are further multiplexed by the Y branch unit 20, and the combined signal light Pout is output from the output end of the output optical waveguide 17.

As described above, according to the configuration in which the MZI type optical circuits are connected in the multistage cascade in the preceding stage of the Y branch unit 20, the one stage MZI type optical circuits and the Y branch units are connected in the cascade, as shown in FIG. As compared with the configuration shown, it becomes possible to combine signal lights of more wavelengths (8 wavelengths in this embodiment). Even in such a multi-stage configuration, the effect of downsizing the optical circuit by using the Y branch portion is the same as that of the optical circuit shown in FIG.

The optical multiplexer according to the present invention is not limited to the above-mentioned embodiments and examples, but various modifications are possible. For example, as a specific configuration of the Mach-Zehnder interferometer provided before the Y branch unit, various configurations may be used according to the wavelength band, wavelength interval, etc. of the signal light to be multiplexed.

Further, in the optical multiplexer 1A shown in FIG. 1, Y
Although the first optical circuit section 11 and the second optical circuit section 12 connected to the preceding stage of the branch section 20 are both MZI type optical circuits, only one of the optical circuit sections 11 and 12 is MZI.
It may be configured as a photonic circuit. Alternatively, MZ may be further added to the optical multiplexers 1A and 1B shown in FIGS.
It is also possible to connect the I-type optical circuits in multistage cascades and combine the signal lights of multiple wavelengths.

[0067]

As described in detail above, the optical multiplexer according to the present invention has the following effects. That is, MZ
A first optical circuit section which is an I-type optical circuit and a second optical circuit section which is an MZI-type optical circuit or an optical circuit other than the MZI-type optical circuit are connected with a Y-branch section as an optical combining section in the subsequent stage, According to the optical multiplexer that joins the optical waveguide from the optical circuit section and the optical waveguide from the second optical circuit section to the output optical waveguide, the influence of deviation or fluctuation of the wavelength characteristics on the multiplexing characteristics is reduced. It Further, the Y branch portion is smaller than the MZI type optical circuit, and the optical circuit in the entire optical multiplexer can be miniaturized.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an embodiment of an optical multiplexer.

FIG. 2 is a configuration diagram showing a conventional optical multiplexer as a comparative example.

3 is a graph showing a multiplexing characteristic in the optical multiplexer shown in FIG.

FIG. 4 is a graph showing a multiplexing characteristic in the optical multiplexer shown in FIG.

FIG. 5 is a configuration diagram showing another embodiment of the optical multiplexer.

[Explanation of symbols]

1A, 1B ... Optical multiplexer, 10 ... Substrate, 10a ... Input end face, 10b ... Output end face, 11 ... First optical circuit section, 12 ... Second optical circuit section, 13-16 ... Optical circuit section, 17 ... Output light guide Waveguide, 18 ... Input end, 19 ... Output end, 20 ... Y branch, 2
DESCRIPTION OF SYMBOLS 1 ... 1st optical waveguide, 22 ... 2nd optical waveguide, 23 ... 1st input end, 25 ... 2nd input end, 26 ... Output end, 27 ... 1st optical coupler, 28 ... 2nd optical coupler, 29 ... Arm Waveguide section,
31 ... Third optical waveguide, 32 ... Fourth optical waveguide, 33 ... Third
Input end, 34 ... Output end, 35 ... Fourth input end, 37 ... First
Optical coupler, 38 ... Second optical coupler, 39 ... Arm waveguide section, 41-48 ... Optical waveguide.

Claims (3)

[Claims] 1. An optical multiplexer comprising an optical circuit having a substrate and an optical waveguide formed in a predetermined waveguide pattern on the substrate, and which multiplexes signal lights having mutually different wavelengths. And a first optical waveguide having a first input end as one end, and a second input end as one end, being optically coupled to the first optical waveguide via at least two directional couplers, A first optical circuit unit having a first optical waveguide and a second optical waveguide forming a first Mach-Zehnder interferometer together with the directional coupler, and a second optical circuit having at least a third optical waveguide having a third input end as one end. Section, an output optical waveguide having an output end as one end, an end of the first optical circuit section opposite to the input end of the first optical waveguide or the second optical waveguide, and the second optical circuit Part of the third optical waveguide or another optical waveguide Y opposite end is connected to one side, the opposite end is connected to the other side to the output end of the output optical waveguide
And a branching portion, wherein the signal light input from each of the first input end, the second input end, and the third input end is multiplexed and output from the output end. Wave instrument. 2. The second optical circuit unit has a fourth input end as one end, and the third optical circuit unit is connected to the third optical circuit unit via at least two directional couplers.
The optical multiplexer according to claim 1, further comprising a fourth optical waveguide which is optically coupled to the optical waveguide and constitutes a second Mach-Zehnder interferometer together with the third optical waveguide and the directional coupler. 3. A fifth optical waveguide having a fifth input end as one end and a sixth input end as one end before at least one of the first optical waveguide and the second optical waveguide. A third optical circuit section having a sixth optical waveguide which is optically coupled to the fifth optical waveguide via a directional coupler and constitutes a third Mach-Zehnder interferometer together with the fifth optical waveguide and the directional coupler. The optical multiplexer according to claim 1, further comprising: