JP3474978B2 - Waveguide type optical multiplexer / demultiplexer and optical line monitoring system using waveguide type optical multiplexer / demultiplexer - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a waveguide type optical multiplexer / demultiplexer used for optical fiber communication and the like, and an optical line monitoring system using the waveguide type optical multiplexer / demultiplexer.

[0002]

2. Description of the Related Art 1 of an optical communication system using an optical fiber
As one of them, there is telephone communication, and it has already been put into practical use to connect trunk lines between large cities by optical fibers for communication. In the future, it is considered to connect the central office side and the subscriber side with an optical fiber cable, and to perform the telephone communication by the optical fiber between the central office side and the subscriber side. It is expected that a large amount of sophisticated communication will be performed by laying out an optical communication network using optical fibers. However, if any trouble such as disconnection occurs in the optical subscriber line of the optical fiber cable that connects the telephone office side and the telephone subscriber side, communication troubles such as telephone communication cannot occur, which is a serious problem. In order to constantly monitor the optical fiber cable on the telephone station side and detect the presence or absence of a disconnection, for example, an optical line monitoring system as shown in FIG. 2 has been proposed.

In the figure, a station 18 is connected to an optical subscriber 19 via an optical subscriber line 15 formed by an optical fiber cable, and the station 18 side has a station side communication device 11 and an optical filter 12. An optical multiplexer / demultiplexer 21 and a test monitoring device 14 are provided, and an optical filter 16 and a subscriber side communication device 17 are provided on the optical subscriber 19 side. The station-side communication device 11 functions as a light source that emits communication light of a specific communication wavelength,
Communication light from the station-side communication device 11 enters the terminal P ₀₁ of the optical multiplexer / demultiplexer 21 through the optical filter 12, exits from the terminal P ₀₄ side and enters the optical subscriber line 15, and the optical subscriber line After propagating through 15, it enters the subscriber side communication device 17 via the optical filter 16.

The test monitoring equipment 14 is an OTDR (Optical Ti
me domain reflectmeter) or the like, and emits a test monitoring light having a wavelength different from the wavelength of the communication light from the station-side communication device 11. This test monitoring light is used by the optical multiplexer / demultiplexer 21. The light enters the optical multiplexer / demultiplexer 21 from the terminal P ₀₂ , exits from the terminal P ₀₄ side, and enters the optical subscriber line 15. Then, while propagating through the optical subscriber line 15 to the optical subscriber line 19 side, after being scattered by the optical subscriber line 15, it goes back to the optical multiplexer / demultiplexer 21 side and returns, and this return light of the optical multiplexer / demultiplexer 21. Terminal P ₀₂
It returns from the side to the side of the test monitoring equipment 14 and is monitored by the test monitoring equipment 14.

The return light due to the scattering is, for example, the well-known Rayleigh scattering or the like, in which a minute portion of the light propagating through the optical fiber or the like is scattered, and the scattered light is
Light is scattered in the direction opposite to the propagation direction, and the subscriber line 15
Is returned to the test monitoring equipment 14 while undergoing a predetermined attenuation. Therefore, the intensity of the light returning to the test monitoring equipment 14 changes depending on where on the subscriber line 15 the light is scattered. Therefore, it is possible to clarify the difference in loss depending on the position of the optical subscriber line 15 by measuring the intensity of the return light in the light receiving section of the test monitoring equipment 14 in the time domain. The presence or absence of an abnormality such as a disconnection is detected, and the optical line of the optical subscriber line 15 is monitored.

The optical filters 12 and 16 are filters capable of sufficiently attenuating the test monitoring light so that the station monitoring communication light 11 and the subscriber communication device 17 are not adversely affected by the test monitoring light. Has been formed. The optical filter 16 attenuates the intensity of the test monitoring light propagating to the optical subscriber 19 side through the optical subscriber line 15 so that the test monitoring light does not enter the subscriber side communication device 17. Further, the optical filter 12 emits from the terminal P ₀₁ side of the optical multiplexer / demultiplexer 21 among the return light of the test monitoring light scattered on the optical subscriber line 15 and returning to the station 18 side, and communicates with the station side. Light that propagates to the device 11 side is attenuated so that it does not enter the station communication device 11.

As described above, by providing the optical filters 12 and 16, the optical line test monitoring system as shown in FIG. 2 does not affect the communication between the station 18 side and the optical subscriber 19 side. The optical subscriber line 15 can always be monitored independently of communication.

In the system as described above, as the optical multiplexer / demultiplexer 21, a fiber type optical multiplexer / demultiplexer obtained by melting and extending an optical fiber has been conventionally used, but recently, for example, as shown in FIG. A waveguide type optical multiplexer / demultiplexer using a planar lightwave circuit has been proposed. In addition, in (a) of FIG.
A plan view of a waveguide type optical multiplexer / demultiplexer is shown, in which (b) is an enlarged view in a broken line frame 9 of (a), and (c) is
The sectional view taken along the line A-A in FIG. In these figures, a first optical waveguide 3 and a second optical waveguide 4 are formed in parallel on a substrate 5 with a space therebetween, and these first and second optical waveguides 3 and 4 are formed. In the middle of
Two directional couplers 1 and 2 formed by arranging the first optical waveguide 3 and the second optical waveguide 4 close to each other are arranged in series.

Between these two directional couplers 1 and 2, there is provided a phase shift section 7 in which the lengths of the first optical waveguide 3 and the second optical waveguide 4 are relatively different. As described above, the waveguide type optical multiplexer / demultiplexer used in the optical line monitoring system has the Mach-Zehnder interferometer structure having the two directional couplers 1 and 2 and the phase shift section 7 interposed therebetween. The circuit has the optical coupling section 13 of. In the waveguide type optical multiplexer / demultiplexer shown in FIG. 1, the coupling lengths L ₁ (not shown) and L ₂ of the two directional couplers 1 and ₂ are both formed to be equal to L. First optical waveguide 3 in the sex couplers 1 and 2
The waveguide pitches of the second optical waveguide 4 and p are also equal to each other.

The optical multiplexer / demultiplexer 21 is used in the optical line monitoring system shown in FIG. 2, and at this time, the incident side end portion P _A of the first optical waveguide 3 is communicated from the station side communication device 11. The incident type end portion P _B of the second optical waveguide 4 constitutes an incident portion of the test monitoring light having a wavelength different from that of the communication light.
The emission side end portion P _D of the second optical waveguide 4 serves as a connection portion of the optical subscriber line 15 as the communication optical transmission optical line.

The waveguide type optical multiplexer / demultiplexer as described above is formed, for example, as follows. First, as shown in FIG. 1 (c), the thickness of silicon or quartz is 0.5
A lower clad layer 6a containing quartz as a main component is formed on a flat substrate 5 having a mirror surface of about 1 mm by a known method such as a flame deposition method, a plasma CVD (plasma chemical vapor deposition) method, a vacuum vapor deposition method, a sol-gel method. And the relative refractive index difference between the lower clad layer 6a and the lower clad layer 6a is about 0.3%, and the refractive index is slightly larger than the lower clad layer 6a (layers of the optical waveguides 3 and 4).
1 are sequentially formed, and then an unnecessary portion of the core layer is removed by photolithography using a reactive ion etching method or the like to form a predetermined waveguide pattern.
(A) of the waveguide core (first,
The second optical waveguides 3, 4) are formed.

Then, an upper clad layer 6b having the same refractive index as that of the lower clad layer 6a is formed by the same method as that of the lower clad layer 6a to cover the core layer, thereby completing the planar lightwave circuit. The dimensions of the waveguide core are
For example, the width is 8 μm and the thickness is about 8 μm. The curvature of the first and second optical waveguides 3 and 4 is 35000.
To about 50,000 μm, the coupling length L of each directional coupler 1, 2 is about 0 to several thousand μm, and the optical waveguide pitch p is 10 to 15 μm.
It is considered as a degree.

[0013]

By the way, generally, the coupling efficiency C of a planar lightwave circuit having a Mach-Zehnder interferometer structure is such that the coupling lengths of the directional couplers 1 and 2 are L ₁ and L.
_2, complete coupling length L _c1, L _c2, the equivalent coupling length and L _off1, L _off2 by lead waveguide, yet phase shifter 7,
When the propagation constant of the propagating light is β and the path difference between the two waveguides 3 and 4 is ΔL, it can be expressed by the following equation (1).

C = cos ² (βΔL / 2) · sin ² (φ ₁ + φ ₂ ) + sin ² (βΔL / 2) · sin ² (φ ₁ −φ ₂ ) (1)

However, in the equation (1),

Φ ₁ = (π / 2) · (L ₁ + L _off1 ) / L _c1 (2)

Φ ₂ = (π / 2) · (L ₂ + L _off2 ) / L _c2 (3)

It is represented by Further, the coupling efficiency C _DC of each of the directional couplers 1 and 2 used here is expressed by the following equation (4).

C _DC = sin ² (φ) (4)

However, in the equation (4), φ is φ ₁ or φ ₂ . Incidentally, in the directional coupler 2, the complete coupling length L _c1 and L _c2 lead waveguide equivalent coupling length L _off1 and L _off2 by the coupling length and the waveguide pitch (distance between the centers of the two waveguides therein p) is a function of p, so that when the curvature of the core (the first and second optical waveguides 3 and 4) and the relative refractive index difference between the core and the cladding 6 are constant, the coupling length L and the waveguides there are guided. When the waveguide pitch p is determined, each length L
_{C1, L c2, L off1,} L off2 is uniquely determined. Therefore, each coupling efficiency C _DC in each directional coupler 1, 2 is
It is determined by the coupling length L and the waveguide pitch p there.

Conventionally, an optical multiplexer / demultiplexer having a Mach-Zehnder interferometer structure used in an optical line monitoring system as shown in FIG.
In 21, the various parameters of the two directional couplers 1 and 2 were set so that the value of their coupling efficiency C _DC was generally C _DC = 0.5. That is, φ = π / 4
Various parameters are set to be + Nπ (N is an integer of 0 or more). At this time, the coupling efficiency C of the entire optical multiplexer / demultiplexer 21 is defined by the following equation (5).

C = cos ² (βΔL / 2) (5)

The optical multiplexer / demultiplexer as described above functions as an optical multiplexer / demultiplexer between the wavelength band in which the coupling efficiency C is approximately 0 and the wavelength band in which the coupling efficiency C is approximately 1. Therefore, when designing an optical multiplexer / demultiplexer, for example, the wavelength band in which the coupling efficiency C is 1 (100%) is the wavelength band of communication light, and the wavelength band in which the coupling efficiency C is 0 is the test monitoring light. The path difference ΔL of the phase shift unit 7 is set so as to be in the wavelength band, and the optical multiplexer / demultiplexer is manufactured.

In other words, in FIG. 1, when the communication light of wavelength λ ₁ is made incident from the incident end P _{A of} the first optical waveguide 3, the light is almost 100% and is emitted from the second optical waveguide 4. The light is emitted from the end P _D , while the incident end P of the second optical waveguide 4 is supplied.
_When the test monitoring light of wavelength λ ₂ is incident from _B , the light is also emitted from the emission end P _{D of} the second optical waveguide 4 by almost 100%.

Further, the test monitoring light emitted from the emission end P _{D of} the second optical waveguide 4 is incident on the optical subscriber line 15 and then scattered on the optical subscriber line 15 to be again reflected by the second optical waveguide. It returns to the output end P _D side of the waveguide 4, but almost all of this return light
100% of the light exits from the incident end P _{B of} the second optical waveguide 4, returns to the test monitoring device 14, and does not propagate to the station side communication device 11 side. Therefore, if a waveguide-type optical multiplexer / demultiplexer with a Mach-Zehnder interferometer structure is manufactured so that the coupling efficiency C = 0 for light in all wavelength bands of the test monitoring light, as shown in FIG. It is considered possible to omit the optical filter 12 in various optical line monitoring systems.

However, when the waveguide type optical multiplexer / demultiplexer is manufactured, the coupling efficiency C for the light of the test monitoring wavelength is 0.
Even if so, since the coupling efficiency C = 0 is not obtained for the light in all wavelength bands of the test monitoring wavelength band, the test monitoring light in the wavelength band deviated from the wavelength where the coupling efficiency C = 0 is obtained. Scattered on the optical subscriber line 15, goes backwards and returns to the optical multiplexer / demultiplexer 21 side,
This return light is emitted from the terminal P ₀₁ side of the optical multiplexer / demultiplexer 21 side and propagates to the station side communication device 11 side.

Therefore, in the conventional optical line monitoring system using the waveguide type optical multiplexer / demultiplexer having the Mach-Zehnder interferometer structure, in order to prevent the test monitoring light from entering the station side communication equipment 11, an optical filter is used. There is a problem that 12 cannot be omitted, and therefore the cost of configuring the system becomes high.

Further, the filter 12 is at least 40d in the entire optical line monitoring system for the entire wavelength band of the test monitoring light.
It is difficult to increase the yield of the optical filter 12 itself because a filter having a blocking characteristic that can give a loss of about B must be provided, and thus the yield of the optical line monitoring system construction is also reduced. There was also the problem of being lost.

Further, in the system shown in FIG. 2, the terminal P ₀₃ of the optical multiplexer / demultiplexer 21 has a non-reflecting end, but in the future, an optical terminal device will be connected to this terminal P ₀₃ , and from the terminal P _01. It is considered that a part of the communication light incident on the optical multiplexer / demultiplexer 21 is branched to the terminal P ₀₃ side and is incident on the optical monitoring device, thereby monitoring the communication light. However, in the conventional waveguide type optical multiplexer / demultiplexer having the Mach-Zehnder interferometer structure, all the communication light is emitted from the terminal P ₀₄ and propagates through the optical subscriber line 15. The part could not be propagated from the terminal P ₀₃ side to the optical monitoring device side.

The present invention has been made to solve the above problems, and an object thereof is to construct an optical line monitoring system having a high yield and a low cost. An object of the present invention is to provide a waveguide type optical multiplexer / demultiplexer and an optical line monitoring system using the waveguide type optical multiplexer / demultiplexer, which are capable of constructing an optical line monitoring system capable of monitoring light.

[0031]

In order to achieve the above object, the present invention provides means for solving the problem by the following constitution. That is, in the waveguide type optical multiplexer / demultiplexer of the present invention, the first optical waveguide and the second optical waveguide are arrayed in parallel on the substrate with a space therebetween. In the middle of the optical waveguide of the first optical waveguide and the second optical waveguide
2 with the same optical coupling characteristics
Two directional couplers are arranged in series, and a phase shifter having a first optical waveguide and a second optical waveguide having different lengths is interposed between the two directional couplers. The optical coupling portion of the Mach-Zehnder interferometer structure is provided, the incident side end portion of the first optical waveguide is a communication light incident portion from the light source, and the incident side end portion of the second optical waveguide is A waveguide type optical multiplexer / demultiplexer that forms an incident portion of test monitoring light having a wavelength different from that of the communication light, and an emission side end of the second optical waveguide forms a connection portion of an optical line for transmitting the communication light. The coupling efficiency of the waveguide type optical multiplexer / demultiplexer has different values for the communication light and the test monitoring light, and the coupling efficiency of the two directional couplers for the light of the test monitoring wavelength is 50, respectively. % Of the two directional couplers, and
The coupling efficiency for light of the communication wavelength is other than 50%
It is characterized in that they are formed in the same size as each other .

[0032]

Further, in the optical line monitoring system using the waveguide type optical multiplexer / demultiplexer according to the present invention, the first optical waveguide and the second optical waveguide are arranged in parallel on the substrate with a space therebetween. In the middle of these first and second optical waveguides, two directional couplers having the same optical coupling characteristics and formed by placing the first optical waveguide and the second optical waveguide in close proximity are arranged in series. An optical coupling section of a Mach-Zehnder interferometer structure in which a phase shift section in which the lengths of the first optical waveguide and the second optical waveguide are relatively different is provided between these two directional couplers. Is provided, and the coupling efficiencies of the two directional couplers with respect to the light of the communication wavelength and the light of the test monitoring wavelength are equal to each other except at least 50%. one or more the present waveguide-type optical demultiplexer being Connected in series to the communication light incident side of the light waveguide multiplexer-demultiplexer, and configured to incident communication light from a light source through a waveguide multiplexer-demultiplexer that this connection to the communication light incident portion It is configured to do what you did.

In the present invention having the above-mentioned structure, since the coupling efficiencies C _DC of the two directional couplers with respect to the light having the test monitoring wavelength are equal to each other except 50%, the above equation (2) ) And (3), the values of φ ₁ and φ ₂ are φ ₁ = φ ₂ , and these values are φ ₁ = φ ₂ = φ
Then, the coupling efficiency C of the waveguide type optical multiplexer / demultiplexer can be expressed by the following equation (6).

C = cos ² (βΔL / 2) sin ² (2φ) (6)

In the waveguide type optical multiplexer / demultiplexer of the present invention,
The path difference Δ in the phase shift section is such that light in the test monitoring wavelength band, which interferes with communication, is not coupled, while light in the communication wavelength band is coupled.
Although L is selected by the means shown in the conventional example, there is only one wavelength at which the coupling efficiency of the optical multiplexer / demultiplexer becomes 0% within the band of the test monitoring wavelength, and the wavelength in the vicinity thereof is minute. Have a bond of.

However, since the coupling efficiency C _DC is a value other than 50%, the sin ² term in the equation (6) is less than 1. As a result, even if the wavelength of the test supervisory light deviates from the wavelength at which the coupling efficiency C of the waveguide type optical multiplexer / demultiplexer is completely 0, the coupling efficiency C _DC is 50% and the sin ² term is 1 The coupling efficiency C for the light of the test monitoring wavelength is smaller than that of the conventional waveguide type optical multiplexer / demultiplexer, and when the waveguide type optical multiplexer / demultiplexer of the present invention is used in an optical line monitoring system, optical addition is performed. The proportion of the return light of the test supervisory light returning from the main line side to the optical multiplexer / demultiplexer propagates to the light source side of the communication light via the optical multiplexer / demultiplexer becomes small. Therefore, even if the blocking characteristic of the optical filter used to suppress the return light of the test monitoring wavelength from entering the communication light source is smaller than before, the test monitoring light can be sufficiently incident on the communication light source. It becomes possible to prevent it.

Also, if the coupling efficiencies C _{DC of the} two directional couplers with respect to the communication light are formed to be equal to each other than 50%, the sin of the above formula (6) can be applied to the light with the communication wavelength. ^{When the} term ² is less than 1, all the light in the communication wavelength band that is incident from the incident side end of the first optical waveguide is not emitted from the emission side end of the second optical waveguide, and the communication light Will be emitted from the emission side end of the first optical waveguide. Therefore, the communication light can be monitored by connecting an optical monitoring device for monitoring the communication light to the end of the first optical waveguide on the emission side.

[0039]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. In the description of this embodiment, the same reference numerals are given to the same names as those in the conventional example, and the duplicated description will be omitted. The waveguide type optical multiplexer / demultiplexer according to the first embodiment of the present invention is the waveguide type optical multiplexer / demultiplexer having the Mach-Zehnder interferometer structure shown in FIG. 1, and this embodiment example is different from the conventional example. The main thing is that the two directional couplers 1,
The coupling efficiencies C _DC with respect to the light having the test monitoring wavelength of No. 2 are equal to each other except 50%. Specifically, the coupling efficiencies C _DC with respect to the test monitoring light having a wavelength of 1.55 μm are 88 respectively. % Is formed.

Further, the waveguide type optical multiplexer / demultiplexer of the present embodiment example
As with the conventional example, 21 is used by being incorporated in an optical line monitoring system as shown in FIG. 2, and in the present embodiment example, the station side communication device 11 emits communication light having a wavelength of 1.31 μm band. The test monitoring device 14 emits test monitoring light having a wavelength of 1.55 μm. It should be noted that the directional couplers 1 and 2 in the optical multiplexer / demultiplexer 21 of the present embodiment have a wavelength of 1.31
The coupling efficiencies C _DC for the light of μm are 50%, respectively.

The core width w of each of the first and second optical waveguides 3 and 4 of the optical multiplexer / demultiplexer 21 is approximately 8 μm, and the core height h of each of the first and second optical waveguides 3 and 4 is approximately each. 8 μm and the first and second optical waveguides 3 and 4 have a curvature of 5000
0 μm, the relative refractive index difference between the first and second optical waveguides 3 and 4 and the cladding 6 is 0.35%. Each coupling length L of the directional couplers 1 and 2 is 491 μm, and the waveguide pitch p is 11.0.
μm, the path difference ΔL between the first optical waveguide 3 and the second optical waveguide 4 in the phase shift section 7 is about 2.68 μm, and the first and second optical waveguides 3 and 4 and the cladding 6 are , Each of which is made of a material whose main component is quartz glass. The structure of this embodiment other than the above is the same as that of the conventional example.

The example of the present embodiment is configured as described above, and in order to confirm the optical coupling characteristics of the waveguide type optical multiplexer / demultiplexer of the example of the present embodiment, the waveguide type optical multiplexer / demultiplexer of the example of the present embodiment is used. In each of the optical multiplexer and the conventional waveguide type optical multiplexer / demultiplexer,
Both the communication light and the test monitoring light are incident from the incident type end P _A of the optical waveguide 3 of FIG.
_When the intensities of the communication light and the test monitoring light emitted from _D were measured, the light intensities of the communication light in the conventional example and the present embodiment were almost the same. On the other hand, the intensity of the test monitoring light is
It has been confirmed that the value of the present embodiment is smaller than that of the conventional example in the entire wavelength range from 1.50 μm to 1.60 μm.

In FIG. 3, the waveguide type optical multiplexer / demultiplexer according to the present embodiment changes from the incident side end portion P _A to the emitting side end portion P _D with respect to the test monitoring light having a wavelength of 1.50 μm to 1.60 μm. Insertion loss is shown. This insertion loss is caused by allowing the test monitoring light in the wavelength band to be incident from the incident side end portion P _A of the first optical waveguide 3 and then being emitted from the emission side end portion P _{D of} the second optical waveguide 4. It is obtained by measuring the light intensity. For comparison, the insertion loss similarly obtained for the conventional waveguide type optical multiplexer / demultiplexer is also shown in FIG. As is clear from the figure, the waveguide type optical multiplexer / demultiplexer 21 of the present embodiment example has a wavelength of 1.50 μm to 1.50 μm compared to the conventional waveguide type optical multiplexer / demultiplexer.
The insertion loss of the test monitoring light up to 60 μm is generally high, and for example, the wavelength range in which the insertion loss is 20 dB or more is about 1.55 ± 0.02 μm in the conventional optical multiplexer / demultiplexer, whereas this embodiment example It can be seen that the optical multiplexer / demultiplexer of is as large as about 1.55 ± 0.03 μm or more.

This can be said also when the test monitoring light is made incident from the emission side end P _D of the second optical waveguide 4 and emitted from the incidence side end P _{A of} the first optical waveguide 3. Yes, a wavelength of 1.50 μm from the output side end P _{D of} the second optical waveguide 4.
When the test monitoring light of m to 1.60 μm is made incident, the amount of the light emitted from the incident side end portion P _{A of} the first optical waveguide 3 in the light is determined by the optical multiplexer / demultiplexer of the present embodiment. 21 is smaller than the conventional optical multiplexer / demultiplexer 21.

Therefore, when the optical multiplexer / demultiplexer 21 of the present embodiment is used in the optical line test monitoring system of FIG. 2, the wavelength 1.55 μm band (for example 1.50 μm) transmitted from the test monitoring equipment 14 is used.
The test monitoring light of (m-1.60 μm) enters the optical subscriber line 15 through the optical multiplexer / demultiplexer 21, is scattered while propagating through the optical subscriber line 15, and the scattered return light of the optical multiplexer / demultiplexer 21. Although it is incident on the second optical waveguide 4 from the output side end P _D via the terminal P ₀₄ , of this light, for example, light having a wavelength of 1.55 ± 0.03 μm is almost attenuated when passing through the optical multiplexer / demultiplexer 21. Then, the light is emitted from the incident side end portion P _{A of} the first optical waveguide 3 with a very small intensity.

Therefore, the optical filter 12 provided in the station 18
Even if the blocking characteristic of is not higher than that of the conventional one, it is possible to prevent the test monitoring light from entering the station-side communication device 11, and it is possible to improve the yield when manufacturing the optical filter 12. In addition, it is possible to improve the yield when constructing the entire system and reduce the cost.

Next, a second embodiment of the waveguide type optical multiplexer / demultiplexer according to the present invention will be described. This embodiment example is also a waveguide type optical multiplexer / demultiplexer having a Mach-Zehnder interferometer structure of the configuration shown in FIG. 1, like the first embodiment example, and this embodiment example is the first embodiment example. What is characteristic is that the coupling efficiency of the directional couplers 1 and 2 with respect to the light of the communication wavelength is equal to each other except 50%. It should be noted that in the present embodiment example, FIG.
Has a coupling length L of 278 μm, other dimensions, relative refractive index differences between the first and second optical waveguides 3 and 4 and the cladding 6, the first and second optical waveguides 3 and 4, and Clad 6
By forming the material for forming the substrate 5 in the same manner as in the first embodiment, the coupling efficiency C _DC of the directional couplers 1 and 2 with respect to the light of the communication wavelength (1.31 μm) is 35%, and the test monitoring is performed. The coupling efficiency C _DC for light of wavelength (1.55 μm) is 71
%.

The example of the present embodiment is configured as described above, and the example of the present embodiment has the same effect as that of the example of the first embodiment. Furthermore, in the example of the present embodiment, the directional coupler 1, By forming each coupling efficiency C _DC with respect to the communication light of No. 2 to a value other than 50%, a part of the communication light incident from the incident side end portion P _{A of} the first optical waveguide 3 is made into the first light guide. can be branched into the emergence end portion P _C side of the waveguide 3 is emitted from the exit side end P _C.

FIG. 4 and FIG. 5 respectively show the first
The insertion loss from the incident side end portion P _A of the first optical waveguide 3 to the emitting side end portion P _C in the waveguide type optical multiplexer / demultiplexer according to the second embodiment and the second embodiment is shown. In producing these graphs, communication light in the 1.31 μm band and test monitoring light in the 1.55 μm band are made incident from the incident side end portion P _{A of} the first optical waveguide 3, and at this time, The intensity of light of each wavelength emitted from the emission side end portion P _C is measured, and as is clear from these figures, the incident side end portion P _A to the emission side end portion P _{A of the} 1.31 μm wavelength band light is measured. It can be seen that the insertion loss into _C is much larger in the optical multiplexer / demultiplexer 21 of the first embodiment than in the optical multiplexer / demultiplexer 21 of the second embodiment.

This means that in the optical multiplexer / demultiplexer 21 of the first embodiment, the incident side end portion P _{A of} the first optical waveguide 3 is formed.
Be caused to enter the communication light from the but exit side end most communication light from P _C is not emitted, when the same operation was carried out in the demultiplexer 21 of the second embodiment, the wavelength 1. The insertion loss of the light in the 31 μm band is about 7 to 9 dB, and a part of the communication light is the emission side end portion P _{C of} the first optical waveguide 3.
Is shown to be emitted from. Therefore, when the optical multiplexer / demultiplexer 21 of the second embodiment is used in the optical line test monitoring system of FIG. 2, communication light is transmitted to the terminal P ₀₃ side of the optical multiplexer / demultiplexer as shown by the broken line in FIG. If an optical monitoring device 24 for monitoring is connected, it is possible to monitor communication light at the same time.

FIG. 6 shows a system configuration example of an optical line monitoring system using the waveguide type optical multiplexer / demultiplexer according to the present invention. This optical line test monitoring system is different from the optical line monitoring system shown in FIG. 2 in that the optical filter 12 on the station 18 side is omitted, and optical multiplexers / demultiplexers 22 and 23 are connected in series instead of the optical filter 12. Is provided so that the communication light from the station-side communication device 11 is incident on the terminal P ₀₁ of the optical multiplexer / demultiplexer 21 via the optical multiplexers / demultiplexers 22 and 23. In this system, the optical multiplexers / demultiplexers 22 and 23 are waveguide type optical multiplexers / demultiplexers configured in the same manner as the first embodiment, and the optical multiplexer / demultiplexer 21 is the same as that of the second embodiment. It is a waveguide type optical multiplexer / demultiplexer configured similarly to the optical multiplexer / demultiplexer.

Further, in this system, the test monitoring equipment 14b is connected to the terminal _P03 side of the optical multiplexer / demultiplexer 21,
The test monitoring device 14b has a function of monitoring and monitoring communication light. The terminals P ₁₂ , P _{13 of} the optical multiplexer / demultiplexer 22 are
The terminals P ₂₁ and P _{24 of the} optical multiplexer / demultiplexer 23 are non-reflecting ends.

The optical line monitoring system using this waveguide type optical multiplexer / demultiplexer is configured as described above, and the communication light emitted from the station side communication device 11 passes through the optical multiplexers / demultiplexers 22 and 23. Incident on the optical multiplexer / demultiplexer 21, and at this time, the communication light propagates in the order of terminal P ₁₁ → terminal P ₁₄ → terminal P ₂₂ → terminal P ₂₃ → terminal P _01, and from terminal P _01. Most of the communication light incident on the optical multiplexer / demultiplexer 21 is emitted from the terminal P ₀₄ and is incident on the optical subscriber line 15, and the optical subscriber 19 (not shown in FIG. 6) as in the system of FIG. However, a part of the power of the communication light is emitted from the terminal P ₀₃ side and is incident on the test monitoring equipment 14b. And the communication light is the test monitoring equipment 14
and the communication light is monitored.

On the other hand, the test monitoring light emitted from the test monitoring equipment 14a enters the optical multiplexer / demultiplexer 21 from the terminal P ₀₂ and exits from the terminal P _04, and, as in the system of FIG. Scattering while propagating through the line 15, the return light travels backward in the optical subscriber line 15 and returns to the terminal P ₀₄ of the optical multiplexer / demultiplexer 21, and the terminal P
_The light is emitted from ₀₂ and is incident on the test monitoring equipment 14a, whereby the optical subscriber line 15 is monitored. However, in the return light of the test monitoring light, the coupling efficiency C is completely 0 in the wavelength band of the test monitoring light. Light having a wavelength deviated from the wavelength of 100% is emitted from the terminal P _{01 of} the optical multiplexer / demultiplexer 21.

However, the light emitted from this terminal P ₀₁ uses the conventional optical multiplexer / demultiplexer as in the case of using the optical multiplexer / demultiplexer 21 of the second embodiment in the system of FIG. The intensity of the light is very small compared to when it was in use, and this intensity of weak light is further attenuated when passing through the optical multiplexers / demultiplexers 22 and 23, so that when it enters the station side communication device 11, The light has a sufficiently low intensity so as not to adversely affect the station-side communication device 11. Therefore, it becomes possible to construct an optical line test monitoring system without providing the optical filter 12 for blocking the test monitoring light.
Can be omitted.

In this system, in actuality, the loss at the terminal P _{11 of} the optical multiplexer / demultiplexer 22 with respect to the test monitoring light having the wavelength of 1.55 ± 0.02 μm incident from the terminal P ₀₄ of the optical multiplexer / demultiplexer 21.
It was confirmed to be larger than 40 dB, and it was proved that it is possible to construct an optical line test monitoring system without using the optical filter 12.

The present invention is not limited to the above-mentioned embodiments, but can take various modes. For example,
In the above-described embodiment, when configuring the optical line test monitoring system as shown in FIG. 6, instead of the optical filter 12 that blocks the test monitoring light, two optical filters that are configured in the same manner as in the first embodiment are used. The optical multiplexers / demultiplexers 22 and 23 are connected in series to form a series body, but the number of optical multiplexers / demultiplexers included in the series body is not limited to two, and three or more optical multiplexers / demultiplexers are connected. Alternatively, one optical multiplexer / demultiplexer may be provided instead of the serial body.

Further, as described above, the optical multiplexer / demultiplexer for preventing the return light of the test monitoring light from entering the station side communication device 11 is always constructed in the same manner as in the first embodiment. The optical multiplexers / demultiplexers 22 and 23 are not limited to the optical multiplexers / demultiplexers 22 and 23. For example, the optical multiplexer / demultiplexer may have the same configuration as that of the second embodiment. A waveguide type optical multiplexer / demultiplexer having an optical coupling section 13 of an interferometer structure, and of the coupling efficiencies C _DC of the two directional couplers 1 and 2 for the communication wavelength light and the test monitoring wavelength light, It suffices that the coupling efficiencies C _DC with respect to the light of the test monitoring wavelength are at least equal to each other except 50%.

Further, as shown in FIG. 6, when the optical line test monitoring system is constructed without providing an optical filter on the station 18 side, when it is not necessary to monitor the communication light, the optical multiplexer / demultiplexer 21 is used. For example, like the optical multiplexer / demultiplexer of the first embodiment, only the coupling efficiencies C _{DC of the} two directional couplers 1 and 2 with respect to the light of the test monitoring wavelength are equal to each other except 50%. A formed waveguide type optical multiplexer / demultiplexer may be used.

Further, in the above embodiment, the wavelength of communication light in the optical line test monitoring system is 1.31 μm band,
Although the wavelength of the test monitoring light is set to the 1.55 μm band, the wavelengths of the communication light and the test monitoring light are not particularly limited and may be set appropriately.

Further, the materials and dimensions of the first and second optical waveguides 3 and 4 and the cladding 6 which form the waveguide type optical multiplexer / demultiplexer of the present invention are the same as those of the first and second embodiments. It is not necessarily the same as an optical multiplexer / demultiplexer, but the coupling efficiency of two directional couplers forming the optical coupling part of the Mach-Zehnder interferometer structure is equal to each other except at least 50% for the light of the test monitoring wavelength. It is sufficient if it is formed into

[0062]

According to the waveguide type optical multiplexer / demultiplexer of the present invention,
The coupling efficiency of the two directional couplers forming the optical coupling part of the Mach-Zehnder interferometer structure for the light of the test monitoring wavelength is
The return light of the test supervisory light over a wide wavelength band can be obtained by forming the same size other than 50%.
The optical line monitoring system using this waveguide type optical multiplexer / demultiplexer is required for the optical filter etc. necessary to prevent the test monitoring light from entering the communication light source. It becomes possible to relax the blocking characteristic. Therefore, when constructing an optical line monitoring system, it is possible to increase the yield, and it is possible to construct an optical line monitoring system at low cost.

Further , according to the waveguide type optical multiplexer / demultiplexer of the present invention,
If, because the coupling efficiency for the two directional couplers of the communication wavelength light is formed on one another equal magnitude other than 50%, respectively, the demultiplexer when is applied to the optical line monitoring system, etc. , A part of the communication light is emitted from the end of the first optical waveguide without causing all of the communication light incident from the end of the first optical waveguide to be emitted from the end of the emission side of the second optical waveguide. The light can be emitted from the end. Therefore, it is possible to monitor the communication light at the same time by connecting an optical monitoring device or the like for the communication light monitor to the emission side end.

Further, according to the optical line monitoring system of the present invention, the coupling efficiency of the two directional couplers with respect to the communication light and the test monitoring light is provided on the communication light incident side of the waveguide type optical multiplexer / demultiplexer of the present invention. Among these, at least one waveguide type optical multiplexer / demultiplexer that is formed to have the same coupling efficiency with respect to the light of the test and monitoring wavelengths other than 50%, respectively, is connected in series. Type optical multiplexer / demultiplexer attenuates the intensity of the test monitoring light incident on the light source side,
It is possible to prevent the test monitoring light from entering the light source. Therefore, it is possible to omit the filter provided between the light source and the optical multiplexer / demultiplexer in the conventional optical line monitoring system, and by omitting the filter that is difficult to manufacture, the yield is high and the cost is high. A cheap optical line monitoring system can be constructed.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a main part of a waveguide type optical multiplexer / demultiplexer having an optical coupling section of a Mach-Zehnder interferometer structure.

FIG. 2 is a configuration diagram showing an example of an optical line monitoring system using an optical multiplexer / demultiplexer.

FIG. 3 is a graph showing the loss characteristics with respect to the test monitoring wavelength of the first embodiment of the waveguide type optical multiplexer / demultiplexer according to the present invention together with the characteristics of the conventional waveguide type optical multiplexer / demultiplexer.

FIG. 4 is a graph showing a loss characteristic with respect to a communication wavelength of the waveguide type optical multiplexer / demultiplexer according to the first embodiment.

FIG. 5 is a graph showing the loss characteristics with respect to the communication wavelength of the second embodiment of the waveguide type optical multiplexer / demultiplexer according to the present invention.

FIG. 6 is a main part configuration diagram showing an example of an optical line monitoring system using a waveguide type optical multiplexer / demultiplexer according to the present invention.

[Explanation of symbols]

1,2-directional coupler 3 First optical waveguide 4 Second optical waveguide 7 Phase shift section 11 Station side communication device 13 Optical coupling section

Front page continuation (72) Inventor Shoichi Ozawa 2-6-1, Marunouchi, Chiyoda-ku, Tokyo Furukawa Electric Co., Ltd. (72) Inventor Kuji Yanagawa 2-6-1, Marunouchi, Chiyoda-ku, Tokyo Furukawa Electric Co., Ltd. Incorporated (72) Inventor Nobuo Tomita 1-6 Uchisaiwaicho, Chiyoda-ku, Tokyo Within Nippon Telegraph and Telephone Corporation (56) Reference JP-A-2-232631 (JP, A) JP-A-55811 ( JP, A) JP-A-3-213829 (JP, A) 1994 Autumn Meeting of the Institute of Electronics, Information and Communication Engineers, 1994, C-260, p. 261 (58) Fields surveyed (Int.Cl. ⁷ , DB name) G02B 6/12-6/138

Claims (2)

(57) [Claims] 1. A first optical waveguide and a second optical waveguide are arranged in parallel on a substrate with a gap therebetween, and the first optical waveguide and the second optical waveguide are formed in the middle of the first and second optical waveguides. Two directional couplers having the same optical coupling characteristics, which are formed by making the first optical waveguide and the second optical waveguide close to each other, are arranged in series, and the first optical waveguide and the first optical waveguide are provided between these two directional couplers. An optical coupling portion having a Mach-Zehnder interferometer structure in which a phase shift portion having a relatively different length of the second optical waveguide is interposed is provided, and an incident side end portion of the first optical waveguide is a light source. From the communication light, the incident side end of the second optical waveguide is an incident part of test monitoring light having a wavelength different from that of the communication light, and the emission side end of the second optical waveguide is A waveguide type optical multiplexer / demultiplexer which is formed as a connecting portion of an optical line for transmission of the communication light, the coupling effect of the waveguide type optical multiplexer / demultiplexer. The ratio is different between the communication light and the test monitoring light, and the coupling efficiencies of the two directional couplers with respect to the light of the test monitoring wavelength are equal to each other except 50% , and Two-way coupling
The efficiency of coupling each of the communication wavelengths of the devices to 50% or less
A waveguide type optical multiplexer / demultiplexer, which is formed to have the same outer size . 2. A first optical waveguide and a second optical waveguide are arrayed in parallel on a substrate with a space therebetween, and the first optical waveguide and the second optical waveguide are formed in the middle of the first and second optical waveguides. Two directional couplers having the same optical coupling characteristics, which are formed by making the first optical waveguide and the second optical waveguide close to each other, are arranged in series, and the first optical waveguide and the first optical waveguide are provided between these two directional couplers. An optical coupling portion having a Mach-Zehnder interferometer structure in which a phase shift portion having a relatively different length of the second optical waveguide is interposed is provided, and the light of the communication wavelength of the two directional couplers is provided. one or more 請 at least test monitor waveguide multiplexer-demultiplexer coupling efficiency for light having a wavelength is formed on mutually equal magnitude other than 50%, respectively of the coupling efficiency to the light of the test monitoring wavelength
The communication light incident part side of the waveguide type optical multiplexer / demultiplexer according to claim 1 is connected in series, and the communication light from the light source is incident on the communication light incident part via the connected waveguide type optical multiplexer / demultiplexer. An optical line monitoring system using a waveguide type optical multiplexer / demultiplexer having the above configuration.