JP3306742B2 - Waveguide type optical branching coupling device and optical line using the same - 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 branching / coupling element used for optical communication and an optical line using the same, and more particularly to a waveguide type optical branching / coupling element used for an optical line test. .

[0002]

2. Description of the Related Art In order to diversify and enhance communication services, it is urgently necessary to introduce an optical fiber capable of high-capacity and high-speed communication into a subscriber system instead of a conventional metallic cable. Along with this, a test system for optical fiber lines has been developed for maintenance and operation of communication services (N. Tomita ct al., 'Design and performance o
fa novel automatic fiber line testing system with
OTDR for optical subscriber loop's, Journal of Lig
htwave Technology, Vol. 12. p. 717 (1994)).

In an optical line test system, for example,
A wavelength different from the communication light from the test apparatus, for example, to the optical fiber transmission line communicating with the communication light having the wavelength of 1.3 μm, for example,
A test light having a wavelength of 1.55 μm is introduced through an optical branching / coupling element, and the test light backscattered light and reflected return light generated during propagation through the optical fiber transmission line are taken into the test apparatus again, and the optical fiber transmission line Diagnose faults and ruptures.

[0004] In order to perform an optical line test even during the provision of a communication service, the test light includes the wavelength of the communication light (eg,
Although light having a wavelength (for example, 1.55 μm) different from 1.3 μm is used, it is necessary to test with light having the same wavelength (1.3 μm) as communication light when laying an optical fiber.
Therefore, the optical branching / coupling element for guiding the test light from the test device to the optical fiber transmission line must function at both the wavelength of the communication light (1.3 μm) and the wavelength of the test light (1.55 μm).

There are two types of optical branching / coupling elements: a fiber type manufactured by polishing, fusing and stretching an optical fiber itself, and a waveguide type manufactured on a flat substrate by a photolithography process. Fiber type has low loss, but poor reproducibility,
There is a disadvantage that it is not suitable for mass production and has a large size and it is difficult to integrate it in a small size. On the other hand, the waveguide type is excellent in reproducibility, productivity, and compact integration since the designed optical circuit pattern is manufactured by using a finer technology. Furthermore, by designing using optical circuit theory, it is expected that an optical branching / coupling element that contributes to diversified optical communication services can be provided.

FIGS. 10A and 10B respectively show:
FIG. 4 is a plan view and transmission characteristics of a conventional optical branching coupler for optical line testing constituted by a silica-based waveguide. This device is composed of a Mach-Zehnder interferometer 13 in which two directional couplers 11 and 12 are formed on two optical waveguides 1 and 2.
Two optical waveguides 1, 1 connecting the directional couplers 11, 12
2, an optical waveguide length difference of about 0.6 μm is provided, thereby alleviating the wavelength dependence of the directional coupler. As a result, 1.2
20 ± 2% binding rate from 5 μm to 1.6 μm
Wavelength independent coupler (WINC: Wavelength Insen)
sitive Coupler) (K. Jinguji, 'Mach-
Zhender interferometer type opticalwaveguide coupl
er with wavelength-flattened coupling ratio ', Elec
tronics Letters, Vol. 26, p. 1326 (1990)).

[0007] The "coupling rate" refers to an optical branching / coupling element,
It is the ratio of the optical power incident from one optical waveguide to the other optical waveguide to the elements or circuit elements that branch and couple the optical power, such as an optical coupler, a Mach-Zehnder interferometer, and a directional coupler. The “transmittance” is a ratio at which the optical power incident from an input port having an optical element is transmitted to an output port. In this specification, the value determined by the configuration of the optical circuit is displayed by subtracting the loss of the optical power due to scattering or absorption by the structure or material of the optical waveguide.

In FIG. 10, 1.3 μm communication light from the station is guided to a communication port (input port 1a), and about 80% of the light is emitted from a subscriber port (output port 1b). It is led to a fiber transmission line. On the other hand, 1.55 μm test light from the test apparatus enters from the test port (input port 2a), and is guided from the subscriber port 1b to the subscriber-side optical fiber transmission line via the Mach-Zehnder interferometer 13. The test return light from the optical fiber transmission line on the subscriber side is transmitted from the Mach-Zehnder interferometer 13 through the subscriber port 1b.
Through the test port 2a, and is detected by the test apparatus. WINC exhibits uniform branching and coupling characteristics over a wide band from the 1.3 μm band to the 1.55 μm band, so that the communication light wavelength and the test light wavelength can be selected in a wide range, and various communication and test services can be performed.

[0009]

As described above, WI
NC is 20 ± 2% from 1.25 μm to 1.6 μm
Test port 2a and subscriber port 1
b is about 7 dB (≒ −10 × log ₁₀ (0.
2)), and the test light suffers a loss of about 14 dB in a round trip. Further, about 80% of the test return light passes through the communication port 1a and goes to the station side. Since the mixing of the test light into the station causes deterioration of the communication light during the provision of the communication service, a wavelength filter or the like must be separately inserted into the communication port 1a of the optical waveguide 1 to block the 1.55 μm light. Must. This operation lowers the reliability and productivity, and impairs the advantages of the waveguide-type optical branching / coupling element that can be batch-produced with good reproducibility.

In a test system using such a WINC, about 80% of 1.3 μm light from the communication port is transmitted to the subscriber port and 1.55 μm from the test port.
A system using a wavelength multiplexer / demultiplexer in which almost all light is transmitted to a subscriber port has also been proposed. FIGS. 11A and 11B are a plan view and transmission characteristics of a conventional optical branching / coupling element using the above-described wavelength multiplexer / demultiplexer. This element also includes a Mach-Zehnder interferometer 13 in which two directional couplers 11 and 12 are connected. Two directional couplers 11, 1
The optical waveguides 1 and 2 have a length difference of 2.7 μm between the optical waveguides 1 and 2.
At 5 μm, the interference is weakened. for that reason,
1.3 μm incident on the communication port (input port 1a)
About 80% of the communication light is used for the subscriber port (output port 2b)
The light can be further emitted and guided to the subscriber-side optical fiber transmission line. Further, 1.55 μm test light can be input from the test port (input port 2a), and almost all of the power can be output from the subscriber port 2b and guided to the subscriber-side optical fiber transmission line. The test return light incident from the subscriber port 2b can be almost completely detected from the test port 2a without leaking to the communication port 1a. That is, when the wavelength multiplexer / demultiplexer having this configuration is used as an optical branching / coupling element, the loss of the 1.55 μm test light is small, and the amount of the 1.55 μm test light leaking to the communication port is also small. However, since the transmittance-wavelength characteristic of the Mach-Zehnder interferometer has a substantially sinusoidal curve,
In the 1.3 μm band, the transmission characteristic between the communication port and the subscriber port is not flat, and the wavelength width at which the transmittance is 80 ± 2% is 2
It was as narrow as 0 nm. Therefore, there is a problem that the number of wavelengths that can be used in the 1.3 μm band is small.

The present invention has been made in view of the above circumstances, and has as its object to reduce loss of test light and mixing of test return light into a communication port, and to function over a wide band in the wavelength band of communication light. An object of the present invention is to provide a waveguide type optical branching / coupling element and an optical line using the same.

[0012]

The structure of the present invention to achieve the above object has the following points. 1) A substrate, two optical waveguides provided on the substrate, and two equal optical couplers sequentially arranged in series from the input side to the output side on the two optical waveguides. The coupling rate of the optical coupler is set to approximately 50% in a first wavelength band and to approximately 0% in a second wavelength band. Between the two optical waveguides, the first wavelength is approximately 0.5 mm.
A waveguide type optical branching / coupling element characterized in that an effective optical path length difference of 18 times or less and greater than 0 is provided. 2) A substrate, two optical waveguides provided on the substrate, and two equal optical couplers sequentially arranged in series from the input side to the output side on the two optical waveguides. Having a coupling rate of the optical coupler,
Is approximately 50% in the 1.3 μm band and approximately 0% in the 1.55 μm band, and approximately 0.3% of 1.3 μm is provided between the two optical waveguides between the two optical couplers.
18 times or less , and cos ² (πΔS / λ) ≒ 0.8 ( λ =
(1.3 μm) , wherein the effective optical path difference ΔS is provided. 3 ) A waveguide type optical branching / coupling element, wherein a wavelength differential coefficient of a coupling rate of the optical coupler is substantially zero at a certain wavelength in the first wavelength band. 4) The waveguide type optical branching / coupling device according to any one of claims 1 to 3, wherein the optical coupler comprises a directional coupler. 5) The waveguide type optical branching / coupling device according to any one of claims 1 to 3, wherein the optical coupler comprises an optical circuit including at least one Mach-Zehnder interferometer. 6) A light source of a first wavelength is installed in a communication port that is one input port of the two optical waveguides of the waveguide-type branch coupling device according to any one of 1) to 5). A light source and a light receiver of the second wavelength are installed at the test port which is the other input port, and a light receiver of the first wavelength and a reflection element of the second wavelength are installed at the subscriber port which is one output port. An optical line characterized by:

[0013]

[0014]

[0015]

[0016]

According to the present invention, in the first wavelength band serving as the communication light, two equal optical couplers having a coupling ratio of approximately 50% are symmetrically positioned with respect to the center from the input side to the output side. By forming a Mach-Zehnder interferometer by connecting them sequentially in series, the branch coupling characteristics in the first wavelength band can be made flat. In addition, in the second wavelength band serving as the test light, the loss of the test light can be eliminated by setting the coupling rate of the optical coupler to 0 to 1%, that is, by making the coupling practically hardly performed. By providing an effective optical path length difference of about 0.18 times or less of the first wavelength to the connection portion of the two optical couplers, the coupling rate of the Mach-Zehnder interferometer can be widened in the first wavelength band. It can be set to a constant value.

As described above, the waveguide type optical branching / coupling element of the present invention exhibits a flat transmission characteristic in a communication light wavelength band (for example, 1.3 μm band) which has not been realized so far, and a test light wavelength band ( For example, it is possible to provide a waveguide type optical branching / coupling element for an optical line test which has a low loss in a 1.55 μm band).

The waveguide type optical branching / coupling element of the present invention cannot be made by directly using the configuration of the conventional Mach-Zehnder interferometer, but has the wavelength characteristics and optical characteristics of the optical coupler constituting the Mach-Zehnder interferometer. It was completed based on the fact that the arrangement of the couplers and the effective optical path length difference between the optical waveguides connecting the optical couplers were studied in detail, and the optical waveguides were successfully operated as intended in a desired wavelength band.

[0020]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a view showing a basic configuration of a waveguide type optical branching / coupling element according to the present invention. Two optical waveguides 1 and 2 are formed from the input end (the left end in FIG. 1) to the output end (the right end in FIG. 1), and different positions on the optical waveguides 1 and 2, ie, the input port and the output Two equal optical couplers 3 and 4 are sequentially arranged in series from the input side to the output side at positions symmetrical with respect to an intermediate position with respect to the port.
It constitutes a Zehnder interferometer. A phase shift region 5 is provided on the optical waveguides 1 and 2 connecting the optical couplers 3 and 4,
An effective optical path length difference ΔS is given.

In the optical branching / coupling element of the present invention, the two equal optical couplers 3 and 4 are arranged symmetrically with respect to each other, so that the phase difference generated between the optical waveguides 1 and 2 when passing through each optical coupler. Cancel each other out. Therefore, the coupling rate K of the optical branching / coupling element of the present invention is the coupling rate K of the optical coupler.
_{Using 1} , K = 4K ₁ (1-K ₁ ) cos ² (π × ΔS / λ) (1) Here, λ is the wavelength of light.

Equation (1) 4K ₁ (1-K ₁ ) on the right side is K ₁
= 0.5 Since (50%) is a parabolic curve having the maximum value 1, approximately 50% of K _1, for example, in the range of 45 to 55%, 4K ₁ (1-K ₁₎ is 0.99 ~ 1 and K ₁
Changes can be compressed and flattened. In the present invention,
Using this property, and bandwidth of the first wavelength band by the coupling ratio K ₁ of the optical coupler to approximately 50% in the vicinity of the first wavelength. Further, when the wavelength derivative of K ₁ is set to substantially 0 in the first wavelength band, the change itself of K ₁ with respect to the wavelength change in the first wavelength band can be reduced, and the flattening of the coupling ratio K can be enhanced. . In this way, 4K ₁ (1−K ₁ ) ≒ 1 over the wide range of the first wavelength band, and K ≒ cos ² (π × ΔS / λ). That is, the coupling ratio K in the first wavelength band is determined by the effective optical path length difference ΔS.

In the present invention, by making the effective optical path length difference ΔS sufficiently smaller than the first wavelength, the change in cos ² (π × ΔS / λ) is made insensitive to the change in wavelength λ, and the first The flat characteristic of K in the wavelength band is maintained.

FIGS. 2A and 2B show this cos^Two(Π ×
FIG. 9 is a diagram illustrating the magnitude of ΔS / λ) and flatness characteristics. Figure
2 (a) is cos with ΔS as a parameter^Two(Π × ΔS /
λ) shows the wavelength dependence, and the wavelength λ on the horizontal axis is the first wavelength.
Wavelength λ₁It has been standardized. The smaller the ΔS, the more cos
^Two(Π × ΔS / λ) approaches 1, and is flat against wavelength change.
Be tan. The curve (a) in FIG. 2B is the effective optical path length difference Δ
S and cos^TwoThe change of (π × ΔS / λ) becomes ± 0.02
The relationship with the wavelength width Δλ is shown, and the curve (b) shows the effective optical path length difference.
ΔS and the first wavelength λ₁Cos in^Two(Π × ΔS / λ₁)When
Shows the relationship. ΔS on the horizontal axis and Δλ on the left vertical axis
Is the first wavelength λ₁It is standardized in. Optical line test system
In the system, communication is performed in, for example, a 1.3 μm band.
In this case, the transmittance was flat over 1.25 to 1.35 μm.
A flat property is required. This is because Δλ is λ ₁= 1.3 μm
It corresponds to about 0.076 times. At this time, the song shown in FIG.
From line (b), ΔS ≒ 0.18λ and cos^Two(Π × ΔS
/ Λ₁) ≒ 0.7. That is, ΔS is about 0.18
λ₁Greater than the required bandwidth for the communication band.
Absent. Conversely, ΔS is about 0.18λ₁Smaller if smaller than
Δλ becomes larger and cos^Two(Π × ΔS / λ) wave
The long characteristic is flattened and widened. At this time,
s^Two(Π × ΔS / λ₁) Is larger than 0.7
As a result, the coupling rate of 80% required for optical line tests can be realized.
You. Thus, in the present invention, ΔS is set to about 0.18λ.₁Yo
Larger wavelength width required for communication band
And the required coupling rate for that communication band at the same time.
Wear.

Further, in the present invention, the characteristic of the coupling ratio K in the second wavelength band is realized by the wavelength dependence of the coupling ratio K ₁ of the optical coupler. Approximately 0% coupling rate K ₁ in the second wavelength band, for example, by a 0 to 1%, 4K
Since _{1 (1-K 1)} is 0 to 4 percent, the coupling rate K of the Mach-Zehnder interferometer almost 0%. Note that the same effect can be obtained even when K ₁ ≒ 1 (100%).
₁ ≒ 0% is based on the fact that a 0% optical coupler is easier to form than an optical coupler with a coupling rate of 100%.

As described above, a waveguide-type optical branching / coupling element which can be provided to an optical line test system and exhibits broadband branching / coupling characteristics in the wavelength band of communication light and transmits with low loss in the wavelength band of test light is provided. Can be configured.

Embodiment 1 FIGS. 3 (a) and 3 (b) show a first embodiment of a waveguide type optical branching / coupling device according to the present invention, in which the transmittance from the communication port to the subscriber port is 1.31 μm. The configuration of a waveguide-type optical branching / coupling element having 80 ± 2% over 150 nm in the center and 96 to 100% in a range of 40 nm centering on a wavelength of 1.55 μm from a test port to a subscriber port is shown. FIG. 3 is a plan view and a plan view of a directional coupler 8 that is the optical couplers 3 and 4 constituting the waveguide type optical branching / coupling element.

FIGS. 4 (a), (b), (c) and (d)
Are line segments AA ', BB', and C in the plan view of FIG.
It is an expanded sectional view showing the section along C 'and DD'.

Here, a silicon substrate was used as the substrate 6, and a quartz optical waveguide formed of a quartz glass material on the silicon substrate 6 was used as the optical waveguides 1 and 2. This waveguide type optical branching / coupling element has a linear pattern and a curvature radius of 40.
A Mach-Zehnder interferometer is constituted by a combination with an arc pattern of mm. Optical couplers 3 and 4 are
The optical waveguides 1 and 2 are constituted by a directional coupler 8 in which the optical waveguides 1 and 2 are brought close to each other while changing the waveguide width, and a phase shift that gives an effective optical path length difference ΔS between the optical waveguides 1 and 2 between the optical couplers 3 and 4. There is a region 5.

Each of the optical waveguides 1 and 2 has a width of about 7.5 to 8.5 μm and a height of about 0.8 μm buried in a cladding layer 7 of SiO ₂ glass having a thickness of about 50 μm.
Consists of a core portion made of _2- GeO ₂ glass (hereinafter, referred to as “core portion”).
“The width of the core portion of the optical waveguide” is abbreviated as “the width of the optical waveguide”. The relative refractive index obtained by dividing the refractive index difference between the core and the cladding layer by the refractive index of the core is 0.3%. Such quartz optical waveguides 1 and 2 can be formed by a known combination of a glass film deposition technique using a flame hydrolysis reaction of silicon tetrachloride or germanium tetrachloride and a fine processing technique by reactive ion etching.

The distance between the input ports 1a and 2a and the distance between the output ports 2b and 2b were made wider than the outer diameter of the optical fiber, 0.125 mm, and 0.25 mm for connection with a single mode optical fiber. (FIG. 4 (a)).

Each of the optical couplers 3 and 4 comprises a directional coupler 8. As shown in FIG. 3B, the directional coupler 8 includes an interaction unit 8a in which two optical waveguides are brought close to each other so that light interacts to transmit and receive optical power. It is composed of expanded portions 8b and 8c for guiding the two optical waveguides to a sufficiently distant position. In order for light to interact, the distance between the two optical waveguides is set smaller than the width of the optical waveguide. In the optical branching / coupling device of this embodiment, the width of each of the optical waveguides 1 and 2 of the optical coupler 3 is 8.5.
μm and 7.5 μm, and the interval between the optical waveguides 1 and 2 at the interaction section 8a is 5.5 μm (FIG. 4B).
The optical coupler 4 is different from the directional coupler 8 shown in FIG.
It is arranged rotated by degrees. That is, the optical couplers 3 and 4
Are arranged in a point-symmetric relationship. Therefore, in the optical coupler 4, the widths of the optical waveguides 1 and 2 are 7.5 μm and 8.
It is 5 μm (FIG. 4D). The width of the two optical waveguides of the directional coupler 8 and the distance between the interaction parts are appropriately set so that the optical couplers 3 and 4 have desired coupling ratio characteristics, as described later.

In the phase shift region 5, the widths of the optical waveguides 1 and 2 are both equal to 8 μm. The distance between the optical waveguides 1 and 2 was set sufficiently larger than the width of 8 μm so that light did not interact with each other, and was 0.1 mm at the maximum (FIG. 4C). The optical waveguide 1 is composed of an S-shaped curved optical waveguide, the optical waveguide 2 is composed of a straight optical waveguide, and the optical waveguide 1 is longer than the optical waveguide 2 by ΔL to provide an effective optical path difference ΔS. 1.31μ wavelength
m, the effective optical path length difference ΔS (= n × ΔL) is 1.31 in order to make the coupling rate of the present branch coupling element about 80%.
0.144 times μm, that is, 0.19 μm. Since the effective refractive index n of the optical waveguide is about 1.45, ΔL is set to 0.13 μm. This ΔL
By appropriately designing the shape of the S-shaped curve of the optical waveguide 1, it can be accurately set by ordinary photolithography technology.

The input ports 1a and 2a connect to the optical coupler 3.
The width of each of the optical waveguides 1 and 2 from 8 μm
8.5 μm and continuous sliding from 8 μm to 7.5 μm
0.1mm length tapered optical waveguide 1 changing to crab₁And 2
₁Light radiation loss due to changes in the width of the optical waveguide
Has been suppressed. Then, the phase shift area is output from the optical coupler 3.
Each of the optical waveguides 1 and 2 connected to the region 5 has a width of 8.
Continuous from 5 μm to 8 μm and 7.5 μm to 8 μm
0.1mm length tapered optical waveguide 1 that changes smoothly_TwoYou
And 2_TwoIs provided. Similarly, the optical coupler 4 and the phase shifter
Tapered on the optical waveguides 1 and 2 connecting the
Optical waveguide 1_Three, 2_ThreeAnd the optical coupler 4 and the output port 1
tapered on optical waveguides 1 and 2 connecting b and 2b, respectively
Optical waveguide 1 _Four, 2_FourIs provided.

FIG. 5 is a diagram for explaining the transmission characteristics of the optical branching / coupling element of this embodiment. Here, the curve (a)
And (b) show the transmittance between the test port (input port 2a) and the subscriber port (output port 2b) and the communication port (input port 1) of the optical branching / coupling device of this embodiment, respectively.
a) and the transmittance between the subscriber ports 2b (equal to the coupling rate of the optical branching / coupling element of the present embodiment), and the curve (c) is the directional coupler 8 which is the optical couplers 3 and 4 of the constituent elements. Is the coupling rate.

As described above, the directional coupler 8 is provided with an interaction section for bringing two linear optical waveguides close to each other to transmit and receive optical power, and a distance from the interaction section to a position sufficiently separated from the two optical waveguides. And a deployment unit for guiding. In general, to approximate two optical waveguides having different widths, the coupling ratio K _c of the configuration the directional coupler arranged parallel to ^{_{K c = F × sin 2 (}} θ) (2) θ = q × 1 c + θ e (3) is represented by Here, 1 _c represents the length of the optical waveguide in the interaction section, and θ _e represents the contribution of the expansion section to the coupling of the curved optical waveguide. Further, F and q are represented by the following equations, respectively.

F = κ ² / (δ ² + κ ² ) (4) q = √ (δ ² + κ ² ) (5) where δ is the difference between the propagation constants of the optical waveguides 1 and 2,
Is a coupling coefficient representing the strength of optical coupling between the optical waveguides 1 and 2. As the wavelength is longer and the interval between the optical waveguides is smaller, κ and θ _e have the property of increasing. Further, as the difference between the widths of the two optical waveguides is larger, δ and θ
_e has the property of increasing.

In this embodiment, the characteristics of δ, κ and θ _e are examined, and the two optical waveguides in the optical coupler are 8.5 μm and 7.5 μm in width, 5.5 μm in interval, and 1 μm in length. _c
Was set to 2 mm. With such a configuration, the coupling coefficient κ and the propagation constant difference δ are substantially equal near the wavelength of 1.3 μm. Further, δ, κ and θ _e are θ = 1.2 around a wavelength of 1.3 μm when the optical waveguide length 1 _c is 2 mm.
It is set to satisfy θ = 2π at 5π and a wavelength of 1.55 μm. As a result, as shown by the curve (c) in FIG. 5, the coupling rate characteristic of the optical coupler of this embodiment is 1.31 in wavelength.
The maximum value is 55% at μm, and 0% at a wavelength of 1.55 μm.

By configuring the waveguide type optical branching / coupling element as described above, the transmittance between the communication port 1a and the subscriber port 2b becomes 1.25 μm as shown in the curve (b).
11 is maintained at 80 ± 2% over 1.4 μm from FIG.
The broadband of about 7 times is achieved as compared with the conventional optical branching / coupling device using the wavelength multiplexer / demultiplexer shown in FIG. On the other hand, as shown in the curve (a), the test port 2a and the subscriber port 2
The transmittance between b is 40 nm centered on a wavelength of 1.55 μm.
, The transmittance becomes 96 to 100% (loss 0.2 dB or less), and almost all of the 1.55 μm test light entering the test port 2a is emitted from the subscriber port 2b.
Then, almost all of the test return light entering the subscriber port 2b returns to the test port 2a, and hardly leaks to the communication port 1a.

Embodiment 2 FIGS. 6A and 6B show a second embodiment of a waveguide type optical branching / coupling element according to the present invention. FIG. 2 is a plan view and branch cross-sectional enlarged views of a phase shift region 5 along a line CC ′ on the plan view of the branch coupling elements having characteristics and different configurations.

The present optical branching / coupling element differs from the waveguide type optical branching / coupling element described in the first embodiment in the phase shift region 5 and the tapered optical waveguide connected thereto. In the present embodiment, the optical waveguides 1 and 2 of the phase shift region 5 are each formed of a linear waveguide having a width equal to the width of the optical waveguides 1 and 2 of the optical coupler 3 and a length L. Further, no tapered optical waveguide is provided between the optical coupler 3 and the phase shift region 5. The effective optical path length difference ΔS in the phase shift region 5 is given by the product of the effective refractive index difference Δn generated between optical waveguides having different widths and the optical waveguide length L. Between the phase shift region 5 and the optical coupler 4, 7.5 [mu] m tapered waveguide 1 ₄ for converting the width is on the optical waveguide 1 from 8.5μm to 7.5 [mu] m is, the width is on the optical waveguide 2
Tapered waveguide 2 ₄ to be converted to 8.5μm are arranged from are both 0.2mm length. Since the tapered waveguide 1 _4, 2 ₄ shapes are equal, there is no phase difference between both the tapered waveguide.

Optical waveguides 1 and 2 in phase shift region 5
Are 8.5 μm and 9.5 μm, respectively, so the difference Δn in the effective refractive index between the two optical waveguides is about 0.00026
Becomes At a wavelength of 1.31 μm, the effective optical path length difference ΔS (=
(Δn × L) = 0.19 μm, the optical waveguide length L was set to 0.731 mm.

Embodiment 3 FIGS. 7A and 7B show a third embodiment of the waveguide type optical branching / coupling element according to the present invention, in which the transmittance from the communication port 1a to the subscriber port 2b is 1.0. 100 around 31 μm
FIG. 2 is a plan view showing a configuration of a waveguide type optical branching / coupling element in which the transmittance from the test port 2a to the subscriber port 2b is 96 to 100% over a wavelength of 100 nm centering on a wavelength of 1.55 μm. FIG. 4 is a plan view of a Mach-Zehnder interferometer 9 which becomes optical couplers 3 and 4 constituting the waveguide type optical branching / coupling element.

In the waveguide type optical branching / coupling element of this embodiment, a silicon substrate is used as the substrate 6, and a quartz optical waveguide formed of a quartz glass material on the silicon substrate 6 is used as the optical waveguides 1 and 2. . This waveguide type optical branching / coupling element is configured by a combination of a linear pattern and an arc pattern having a radius of curvature of 15 mm. Core dimensions are 7 in all areas
μm × 7 μm, and the relative refractive index difference between the core and the clad was 0.45%.

The optical couplers 3 and 4 comprise a Mach-Zehnder interferometer 9 in which two equal directional couplers 10a and 10b are connected in two stages. Two directional couplers 10
Between a and 10b, one optical waveguide is an S-shaped curved optical waveguide and the other is a straight optical waveguide, and an optical waveguide length difference ΔL ₂ is given. In the optical coupler 3, the optical waveguide 1 is an S-curve optical waveguide, and in the optical coupler 4, the optical waveguide 2 is an S-curve optical waveguide so that the optical couplers 3 and 4 have a point-symmetric relationship with each other. I have.

FIG. 8 is a diagram for explaining the transmission characteristics of the optical branching / coupling element of this embodiment. Here, the curve (a)
And (b) show the transmittance between the test port (input port 2a) and the subscriber port (output port 2b) and the communication port (input port 1) of the optical branching / coupling device of this embodiment, respectively.
a) and the transmittance between the subscriber port 2b (equal to the coupling rate of the optical branching / coupling element of the present embodiment), and the curve (c) is a Mach-Zehnder interferometer which becomes the optical couplers 3 and 4 as constituent elements. 9
The curve (d) shows the coupling rate of the directional couplers 10a and 10b constituting the Mach-Zehnder interferometer 9.

The coupling ratio characteristics (curve (c)) of the optical coupler of the optical branching / coupling element of this embodiment are shown by directional couplers 10a and 10a.
This is achieved by appropriately designing the coupling ratio characteristic (curve (b)) of b and the interference characteristic of the Mach-Zehnder interferometer 9.

The coupling rate K ₁ of the Mach-Zehnder interferometer 9 functioning as the optical couplers 3 and 4 is as follows: K ₁ = 4K ₂ (1−K ₂ ) cos ² (π × ΔS ₂ / λ) (6) expressed. Here, K ₂ is the Mach-Zehnder interferometer 9
Is the coupling ratio of the directional couplers 10a and 10b, and ΔS ₂ is the effective optical path length difference between the waveguides 1 and 2 connecting the two directional couplers 10a and 10b.

In this embodiment, cos ^{2 in the} wavelength band of 1.55 μm is used.
(Π × ΔS ₂ / λ) ≒ 0 so that the effective optical path length difference Δ
S ₂ (= n × ΔL ₂ ) is set to approximately 3.5 at a wavelength of 1.55 μm.
It is set to double. Since the effective refractive index n of the optical waveguide at a wavelength of 1.55 μm is about 1.446, ΔL ₂ is 3.7
μm. Furthermore, as is almost 100% coupling rate K ₂ of the directional coupler at the wavelength _{1.55μm, 4K 2 (1-K} 2) at 1.55 .mu.m band ≒
It is set to 0. The two effects, K ₁ 1.55
It is 1% or less in a wide band in the μm band.

Since the optical waveguide length difference ΔL ₂ is 3.7 μm, cos ² (π × ΔS ₂ /λ)=1.31 μm.
0.91. Therefore, at a wavelength of 1.31 μm, K ₁ is about 5
To a 0%, and the K ₂ and about 82%. Furthermore, K ₂
Is approximately 0.2% / nm, and cos ² (π × Δ
Wavelength to cancel the wavelength dependence of the S ₂ / λ) 1.31μm
To make the wavelength derivative of K ₁ almost zero, and the wavelength is 1.31 μm
The broadband characteristics in the vicinity have been enhanced.

The directional coupler 1 designed as described above
0a and 10b were achieved by setting the interval between the optical waveguides to 2.5 μm and the length of the interaction portion to 0.6 mm. The coupling rate K ₁ of the Mach-Zehnder interferometer 9 shown by the curve (b) in FIG. 8 has a maximum value of 55% at a wavelength of 1.31 μm and is 1% or less at a wavelength of 1.51 μm to 1.59. . For this reason, as shown by the curve (b), the optical branching / coupling element of this example has a coupling ratio of 80 ± 2% over a wavelength of 1.31 μm over 100 nm and over a wavelength of 1.55 μm over 100 nm. A waveguide-type branch coupling device for optical line testing having a coupling ratio of 4% or less and operating in a wide band in both wavelength bands has been obtained.

As described above, the embodiment of the present invention has been described with respect to the branch coupling device for testing an optical line. As another application example of the present invention, the coupling ratio is 50 ± 2% over a wavelength of 1.31 μm and 80 nm. FIG. 9 shows the transmission characteristics of the waveguide type optical branching / coupling element, which is 4% or less in the range of 100 nm centered on the wavelength 1.55 μm. The configuration of the branch coupling device of this application example is the same as that of the waveguide type optical branch coupling device of the third embodiment (FIG. 7).
(A) and (b)) are almost the same except that the optical waveguide length difference in the phase shift region 5 is different. In this application example, the effective optical path length difference ΔS (= n × ΔL) is used to set the coupling rate of the present branch coupling element to about 50% at a wavelength of 1.31 μm.
Is about 0.25 times the wavelength of 1.31 μm, that is, 0.32
8 μm. Therefore, the optical waveguide length difference ΔL is set to 0.22
It was set to 5 μm.

The curves (a) and (b) in FIG. 9 respectively show the coupling rate of the optical branching / coupling element of this application example and the coupling rate of the Mach-Zehnder interferometer 9 serving as the optical couplers 3 and 4 of the components. It is. The present branch coupling element has a first wavelength band of 1.3.
An optical signal can be equally distributed over a wide band in the μm band, and at the same time, an optical signal can be transmitted to one output port with almost no loss over a wide band in the 1.55 μm band, which is the second wavelength band.

In the above embodiment, the optical branching / coupling element is constituted by the quartz (SiO ₂ —GeO ₂ ) optical waveguide on the silicon substrate. However, such a substrate is not limited to the silicon substrate, and is not limited to the silicon substrate. It is also possible to change to a substrate or the like. Further, as a dopant added to the core portion to increase the refractive index, titanium (Ti) or boron (B) can be used instead of germanium (Ge). Further, the present invention is not limited to a silica-based waveguide, but can be applied to other optical waveguide materials, for example, a multi-component glass optical waveguide system and a lithium niobate optical waveguide system.

Further, in the embodiment, an example is shown for an optical line test system in which the 1.3 μm wavelength band is used as the communication light and the test light in the 1.55 μm band is used, but the applicable wavelength is the 1.3 μm band. It is not limited to the 1.55 μm band, but by changing the configuration of the optical coupler, for example,
1.55 μm or the like is used as communication light for the 1.4 μm band or 1.6
The present invention can also be applied to an optical line test system using the μm band as test light.

[0057]

As described above, according to the present invention, in the first wavelength band, the light is coupled to the output port in a wide band at a constant coupling ratio, and is transmitted to the output port with almost no loss in the second wavelength band. Can be provided. Such a waveguide-type optical branching / coupling element is expected to be able to construct an optical line test system with low loss and low crosstalk in the second wavelength band while maintaining the optical communication service provided in the first wide wavelength band. Is done. In addition, this waveguide type optical branching / coupling element
The present invention is not limited to the optical line test system, and can be applied to, for example, an application in which an optical signal is transmitted with a low loss in the second wavelength band and an optical signal is distributed and monitored in the first wavelength band.
It is expected to contribute to the construction of optical communication systems that are becoming more sophisticated.

Further, according to the optical line of the present invention, only the test light can be returned to the test port with high efficiency without deteriorating the communication light during the communication service.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing a basic configuration of a waveguide type branch coupling element of the present invention.

FIGS. 2A and 2B are explanatory diagrams showing the magnitude and flatness of cos ² (π × ΔS / λ) for determining the coupling rate of the waveguide type optical branching / coupling element of the present invention, and FIG. Is a parameter, and the wavelength dependence of cos ² (π × ΔS / λ) is shown. (B) is the effective optical path length difference ΔS, the wavelength width Δλ, and cos ² (π × ΔS / λ).
₁ ) The relationship.

FIGS. 3A and 3B are configuration diagrams of a first embodiment of a waveguide-type branch coupling device according to the present invention, wherein FIG. 3A is an overall plan view and FIG. 3B is an enlarged plan view of an optical coupler.

FIG. 4 is an enlarged sectional view of a first embodiment of the waveguide type optical branching / coupling element according to the present invention, wherein (a), (b), (c) and (d) are whole plan views 3 respectively. A-A 'of (a),
It is an expanded sectional view in BB ', CC', and DD '.

FIG. 5 is a diagram for explaining the transmission characteristics of the first embodiment of the waveguide type optical branching / coupling element of the present invention. Curves (a), (b)
Is the transmittance between the test port and the subscriber port, and the transmittance between the communication port and the subscriber port of the optical branching / coupling element of the present embodiment (equal to the coupling rate of the optical branching / coupling element of the present embodiment). And curve (c) is the coupling ratio of the directional coupler, which is a component optical coupler.

FIGS. 6A and 6B are configuration diagrams of a waveguide type optical branching / coupling element according to a second embodiment of the present invention, wherein FIG. 6A is an overall plan view, and FIG.
It is an expanded sectional view in CC 'of FIG.

FIGS. 7A and 7B are configuration diagrams of a waveguide type optical branching / coupling device according to a third embodiment of the present invention, wherein FIG. 7A is an overall plan view and FIG. 7B is an enlarged plan view of the optical coupler.

FIG. 8 is a diagram for explaining transmission characteristics of a third embodiment of the waveguide type optical branching / coupling element of the present invention. Curves (a) and (b) show the transmittance between the test port and the subscriber port and the transmittance between the communication port and the subscriber port (the optical branch of the present embodiment), respectively, of the optical branching / coupling element of the present embodiment. Curve (c) is the coupling rate of the Mach-Zehnder interferometer, which is the optical coupler of the component, and curve (d) is the directionality of the Mach-Zehnder interferometer. This is the coupling ratio of the coupler.

FIG. 9 is a diagram for explaining transmission characteristics of an application example of the waveguide type optical branching / coupling element of the present invention. The curve (a) shows the coupling rate of the optical branching / coupling element of this application example, and the curve (b) shows the coupling rate of the Mach-Zehnder interferometer, which is an optical coupler as a component.

FIG. 10 is a diagram illustrating transmission characteristics of an optical branching coupling element for optical line testing using a wavelength-independent coupler of a conventional example;
(A) is an overall plan view, and (b) is a transmission characteristic.

11A and 11B are diagrams illustrating transmission characteristics of an optical branching / coupling element for an optical line test using a conventional wavelength multiplexer / demultiplexer, and FIG.
Is an overall plan view, and (b) is a transmission characteristic.

[Explanation of symbols]

1,2 waveguide 1a, 2a input ports 1b, 2b output ports 1 _1, 1 _2, 1 _3, 1 _4, 2 _{1, 2} 2, 2 _3, 2 ₄ tapered waveguide 3,4 optical coupler 5 phase shift Region 6 Silicon substrate 7 Quartz-based glass cladding layer 8 Directional coupler 8a Interaction part 8b, 8c Expansion part 9 Mach-Zehnder interferometer 10a, 10b Directional coupler 11, 12 Directional coupler 13 Mach-Zehnder interferometer

Claims (6)

(57) [Claims] 1. A substrate, two optical waveguides provided on the substrate, and two equal optical couplings sequentially arranged in series from the input side to the output side on the two optical waveguides. A waveguide type optical branching / coupling element having a coupler, wherein the coupling rate of the optical coupler is approximately 5 in the first wavelength band.
0%, approximately 0% in the second wavelength band, and between the two optical waveguides between the two optical couplers, approximately 0.18 times or less of the first wavelength , and 0 %
A waveguide type optical branching / coupling device characterized in that a larger effective optical path length difference is provided. 2. A substrate and two lights provided on the substrate.
A waveguide, and the two optical waveguides are directed from the input side to the output side.
Thus, two equal optical couplers arranged sequentially in series
A coupling type optical coupling device,Is 1.3 μmAlmost 5 in the belt
0%1.55 μmAlmost 0% in the beltAnd Of the two optical waveguides between the two optical couplers
In between, approximately 0.18 times less than 1.3 μmAnd cos
^Two (ΠΔS / λ) ≒ 0.8(λ = 1.3 μm)
Effective optical path length differenceΔSWaveguide type light component characterized by giving
Fork coupling element. Wavelength derivative of the wherein coupling ratio of the optical coupler, waveguide type light according to claim 1 or claim 2, characterized in that substantially is zero at the wavelength of the first wavelength band Branch coupling element. 4. A waveguide type optical branching and coupling device according to any one of claims 1 to 3 wherein the optical coupler is characterized in that it is composed of a directional coupler. Wherein said optical coupler waveguide type optical branching according possible in any one of claims 1 to 3, characterized in that consists of an optical circuit including at least one Mach-Zehnder interferometer Coupling element. 6. A communication port as one input port of one of two optical waveguides of the waveguide-type branch coupling device according to any one of [1] to [ 5 ]. A light source of a second wavelength is installed, a light source of a second wavelength and a receiver are installed in a test port which is the other input port, and a receiver of the first wavelength is installed in a subscriber port which is one output port. An optical line comprising a reflection element having a second wavelength.