JP2003014958A - Waveguide type optical multiplexer/demultiplexer circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize a waveguide type optical multiplexer/demultiplexer circuit which has an excellent productivity and designability. SOLUTION: A plurality of arm waveguides 801 and 802 of MZI are constructed so as to include each one of arcs. The arc of each arm waveguide has no inflection points and the convex side of each arc is directed in a same direction. Thus, the interval of arms is approximately fixed to the interval of arcs and the productivity is improved. The difference in the optical paths length is given by the length of straight section adjacent to the arcs (refer to Fig. 10) or the difference in the curvature radius of arcs (refer to Fig. 11) and the designability is improved.

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 multiplexing / demultiplexing circuit, and more specifically, in a Mach-Zehnder optical interference type filter composed of a planar optical waveguide, a plurality of arms are all provided with arcs having no inflection point. By including the shape, the circuit size can be reduced and a high yield can be obtained.

[0002]

2. Description of the Related Art At present, an optical wavelength division multiplexing communication system using a plurality of optical wavelengths is actively developed for expanding communication capacity. In this optical wavelength division multiplex communication system, an optical wavelength demultiplexer that multiplexes optical signals of multiple wavelengths on the transmitter side and demultiplexes multiple optical signals in one optical fiber to different ports on the receiver side As a wave circuit, a Mach-Zehnder optical interference type filter (hereinafter abbreviated as MZI) and a lattice filter in which MZI is configured in multiple stages are widely used.

FIG. 1 shows a circuit configuration of a conventional MZI (waveguide type optical multiplexing / demultiplexing circuit). The light incident on the input waveguide 101 is demultiplexed by the first coupler 102 into the two arm waveguides 103 and 104. Optical path length difference between arms ΔL
Therefore, one of the signal lights causes a phase delay. Here, the arm waveguide 103 is composed of a plurality of arcs and has a substantially S-shape with an inflection point. The arm waveguide 104 is composed of a straight line. The input waveguide 101 and the output waveguides 106 and 107 face each other. In particular, the input waveguide 1
01 and the output waveguide 107 directly face each other.

Then, both signal lights are transmitted to the second coupler 10.
By combining and interfering again at 5, the transmission spectrum characteristic shown in FIG. 2 is obtained. That is, the wavelength-multiplexed signal light incident from the input waveguide 101 can be group-demultiplexed at the period (channel interval) Δf of the transmission spectrum characteristic of FIG. Δf can be designed using the following equation (3). Δf = c / (2 · _ng · ΔL) Equation (3) In Equation (3), Δf is the channel spacing, _ng is the group refractive index, and c is
Is the speed of light, and ΔL is the optical path length difference. In the case of multiplexing, for example, the light incident on the output waveguides 106 and 107 is demultiplexed by the second coupler 105 into the two arm waveguides 103 and 104, respectively, and one is divided by the optical path length difference ΔL between the arms. Of the first coupler 1 after both signal lights have a phase delay.
At 02, they will combine and interfere again.

Therefore, the optical path length difference ΔL is an extremely important design parameter in design. For example, the channel spacing Δf
= 50 GHz MZI is designed, ΔL is 2.03
mm, and a long ΔL is required for MZI with a narrow channel spacing. As a result, the circuit size becomes large, and the yield (or yield) at which MZI can be produced from one wafer is reduced.

Further, in the circuit configuration of FIG. 1, the optical path length difference ΔL is given by the following equation (4). ΔL = 4 · R · (θ-sin θ) Equation (4) where R represents the radius of curvature of the arc, θ represents the interior angle of the arc,
It is assumed that the arm waveguide 103 is composed of four arcs having the same curvature radius R and the same internal angle θ, 4 · R · θ is the optical path length of the arm waveguide 103, and 4 · R · sin θ is the arm waveguide 1.
The optical path length is 04.

Therefore, in order to obtain the accurate channel spacing Δf, it is necessary to solve the nonlinear equation of the equation (4) by numerical calculation, which causes difficulty in designing the MZI.

Further, a directional coupler 301 having a structure shown in FIG. 3 is usually used as a coupler forming the MZI. In this directional coupler 301, the light incident on the input waveguide 302 passes through the incident side expansion section 303, passes through the coupling section 304 composed of two adjacent waveguides, and again exits the emission side expansion section 305. It passes through and is output from the output waveguides 306 and 307. The expansion section 303 is provided to guide the input waveguide 302 to the coupling section 304, and the expansion section 305 is provided to guide the coupling section 304 to the output waveguides 306 and 307. FIG. 4 shows the relationship between the length of the coupling section 304 (coupling length) and the coupling rate of the coupler.

As shown in FIG. 4, the coupling ratio of the coupler changes sinusoidally with respect to the coupling length. However, since the y-intercept (coupling rate when the coupling length is zero) does not become zero, the coupling rate is zero even in the directional coupler that includes only the expanding sections 303 and 305 and does not have the coupling section 304. do not become. This means that the expansion sections 303 and 305 provide additional coupling (optical crosstalk). In order to make the intensity distribution of light propagating through the directional coupler in the case where the length of the coupling portion 304 is zero, the beam propagation method was used for calculation in order to clarify it more visually. FIG. 5 shows the calculation result. In FIG. 5, a thick white portion 501 represents a path along which most of the incident light propagates without being demultiplexed, and a thin light white portion 502 partially propagates after demultiplexing the incident light. Indicates a route.

In particular, when designing an MZI having a minute optical path length difference ΔL, as inferred from the circuit configuration of FIG. 1,
The arm spacing also becomes narrower. However, the expansion unit 30 described above
In order to avoid optical crosstalk due to 3, 305 as much as possible, it is necessary to set the arm interval sufficiently large.

Further, in the MZI (waveguide type optical multiplexing / demultiplexing circuit) having the structure shown in FIG. 6, the heater electrodes 601 and 602 for setting the central wavelength using the thermo-optic effect are provided in the arm waveguide 6.
03 and 604. Each arm waveguide 6
03 and 604 are embedded structures, and each heater electrode 60
It exists just below 1,602. In FIG. 6, the input waveguide 60
5, first coupler 606, arm waveguides 603, 60
4, the second coupler 607 and the output waveguides 608 and 609 are the MZI input waveguide 101, the first coupler 102, the arm waveguides 103 and 104, the second coupler 105, and the output waveguide shown in FIG. 1, respectively. It corresponds to the waveguides 106 and 107.

FIG. 7 shows the heat distribution of the two-dimensional cross section taken along the line segment aa 'perpendicular to the heater electrode 602 of FIG. A large number of white lines are isotherms, and a portion 701 directly below the heater electrode
Is the highest temperature, and the temperature decreases as it goes in the depth direction Y. However, it can be seen from FIG. 7 that the heat distribution diffuses not only in the depth direction Y but also in the lateral direction X (direction toward the adjacent arm waveguide). Therefore, in order to prevent one arm from being affected by the thermal crosstalk from the other arm, it is necessary to set the arm interval sufficiently large.

For the above-mentioned two reasons, the arm spacing of the MZI must be sufficiently separated to avoid optical crosstalk and thermal crosstalk. However, this requirement also limits the circuit size of the MZI, which makes it difficult to reduce the size.

Further, in the conventional MZI shown in FIG. 1, since the optical delay section is composed of the S-shaped arm waveguide 103 and the straight arm waveguide 104, the arm interval is between the couplers 102 and 105. It is not constant, and the arm interval is extremely large in the middle part, and this tendency is remarkable as the optical path length difference ΔL increases, so that it is susceptible to manufacturing deviations such as the refractive index distribution and the in-wafer distribution of the core thickness. I have a problem. This also applies to the MZI shown in FIG.

Furthermore, when connecting an optical fiber to the MZI of FIG. 1, the input waveguide 101 and the output waveguides 106, 1
Since the light beams 07 face each other, when leaked light occurs between the optical fiber and these input / output waveguides, the leaked light causes deterioration of the transmission spectrum characteristic. The same applies to MZI in FIG.

[0016]

As described above, the conventional MZI has various problems to be solved. That is,
One is a large circuit size by avoiding narrow channel spacing or crosstalk, and a consequent deterioration in yield per wafer. Another problem is the difficulty in designing because the optical path length difference ΔL is given by equation (4).
Still another problem is deterioration of transmission spectrum characteristics due to leaked light. Another problem is that it is easily affected by manufacturing deviation. An object of the present invention is to solve these problems and to provide MZI with good manufacturability.

[0017]

In the present invention, the above object is achieved by improving the shape of the arm waveguide in the MZI constituting the waveguide type optical multiplexer / demultiplexer circuit as follows.

A waveguide type optical multiplexer / demultiplexer circuit according to a first aspect of the present invention is configured by using an optical waveguide including a core having a high refractive index on a plane substrate and a clad around the core, and an optical coupler and its optical coupler. In MZI consisting of multiple arms connecting
Each of the arms includes one arc, the arc has a shape without an inflection point, and the convex directions of the arc are the same between the arms.

According to a second aspect of the present invention, in the invention according to the first aspect, the radius of curvature and the interior angle of the arc are equal between the arms, the interval between the arcs between the arms is S, and the interior angle of the arc is θ. In this case, the optical path length difference ΔL is given by ΔL = S · tan (θ / 2) (Equation 1) by the linear waveguide adjacent to the arc.

According to a third aspect of the invention, in the invention according to the first aspect, the radii of curvature of the arcs are different between the arms, the interior angles of the arcs are equal to each other, and the intervals of the arcs between the arms are equal to each other. S, where the internal angle of the arc is θ, the optical path length difference ΔL is given by ΔL = S · θ (Equation (2)).

The invention according to claim 4 is characterized in that, in the invention according to any one of claims 1 to 3, the MZI is configured in multiple stages.

The invention according to claim 5 is characterized in that, in the invention according to any one of claims 1 to 4, the MZI is composed of a silica glass optical waveguide on a silicon substrate.

As described above, in the present invention, attention is paid to the geometrical shape of the circular arc, and the arm waveguide is constituted by the circular arc, whereby the problems in manufacturing and design are solved.

[0024]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.

[First Embodiment] FIG. 8 shows a first embodiment of the present invention.
2 shows a circuit configuration of a waveguide type optical multiplexing / demultiplexing circuit according to the exemplary embodiment. In the waveguide type optical multiplexer / demultiplexer circuit shown in FIG. 8, a plurality (two in the figure) of arm waveguides 801 and 802 of MZI are both configured by arcs. Specifically, each of the arm waveguides 801 and 802 includes one arc, and each arc has a shape without an inflection point, and the convex directions of the arcs are the same in the arms (in the figure, (Upward). The internal angle of the arc connects the two ends of the arc with the arc center point 2
The angle formed by the line segments of the book.

In this case, as shown in FIG. 9A, when a large number of waveguide type optical multiplexing / demultiplexing circuits (MZI) 901 are integrated and manufactured on a plane, one waveguide type optical multiplexing / demultiplexing circuit 901 is directed upward. It is possible to lay out the upward convex arm of another waveguide type optical multiplexer / demultiplexer circuit 901 below the convex convex arm. The waveguide type optical multiplexer / demultiplexer circuit 901 has the circuit configuration shown in FIG. On the contrary, when the arm is downwardly convex, a downward convex arm of another waveguide type optical multiplexer / demultiplexer circuit is woven above the downwardly convex arm of one waveguide type optical multiplexer / demultiplexer circuit. Therefore, a higher degree of integration can be obtained as compared with the conventional waveguide type optical multiplexer / demultiplexer circuit.

FIG. 9B shows a state in which a conventional waveguide type optical multiplexer / demultiplexer circuit 902 is integrated. The waveguide type optical multiplexer / demultiplexer circuit 902 has the circuit configuration shown in FIG. 1, and the linear arm waveguides hinder high integration.

In FIG. 8, an MZI (waveguide type optical multiplexer / demultiplexer circuit) itself includes a first coupler (optical coupler) 804 and a second coupler.
The coupler (optical coupler) 805 and the arm waveguides 801 and 802 connecting the couplers 805 to each other are used to form an optical waveguide including a core having a high refractive index on a plane substrate and a clad around the core. The light incident on the input waveguide 803 is transmitted by the first coupler 804 to the two arm waveguides 801 and 802.
Demultiplex into. Due to the optical path length difference ΔL between the arms, one of the signal lights has a phase delay, and both signal lights have the second coupler 8
Group division is performed by combining and interfering again at 05. In the case of multiplexing, for example, the light incident on the output waveguides 806 and 807 is demultiplexed into two arm waveguides 801 and 802 by the second coupler 805, and the optical path length difference Δ between the arms is divided.
After one of the signal lights has a phase delay due to L, both of the signal lights will be combined and interfered again by the first coupler 804.

Here, inflection points can be seen near the front and rear ends of each arm waveguide 801, 802.
1, the part before 802 is the output side expansion part of the first coupler 804, and the part after it is the second coupler 805.
Of the arm waveguides 801, 8
The circular arc 02 is the "shape having no inflection point" in the present invention. The unfolding part of the coupler does not have an optical delay and is not an arm waveguide.

The waveguide type optical multiplexer / demultiplexer circuit shown in FIG. 8 has the following effects in addition to the above-mentioned high integration degree. (1) Since each of the plurality of arm waveguides 801 and 802 includes one arc, each arc has a shape without an inflection point, and the convex directions of the arcs are the same in the arms. , The arm spacing depends on the spacing S between the arcs of the arm waveguides 801 and 802, and the two couplers 804 and 8
It becomes almost constant between 05, and there is no fluctuation that becomes extremely large on the way unlike the conventional case. That is, the arm interval corresponds to the arc interval S. (2) Since the arm spacing does not fluctuate extremely greatly as in the conventional case, even if the arm spacing is increased to narrow the channel spacing or to avoid crosstalk,
The circuit size does not increase as in the past, and the yield per wafer is improved. (3) Since the arm interval is almost constant between the two couplers 802 and 805 and does not fluctuate significantly, it is unlikely to be affected by manufacturing deviations such as the refractive index distribution and the in-plane distribution of the core thickness on the wafer. (4) Since the plurality of arm waveguides 801 and 802 each include one arc, and each arc has a shape without an inflection point, the expression for the optical path length difference ΔL is not the same as the conventional expression (4). It is not a linear equation and simplifies the design. The optical path length difference ΔL of the arm can be obtained by appropriately giving the radius of curvature R of the arc of each of the arm waveguides 801 and 802, the internal angle θ, and the interval S of the arc between the arms, or independently or together therewith. By adjoining a linear waveguide of an appropriate length to
Can be set. (5) Since the plurality of arm waveguides 801 and 802 each include one arc, and the convex directions of the arcs are the same between the arms, the input waveguide 803 and the output waveguide 80
Nos. 6 and 807 do not face each other, and even if leaked light occurs when an optical fiber is connected to them, the transmission spectrum characteristics do not deteriorate.

[Second Embodiment] FIG. 10A shows, as a second embodiment of the present invention, a circuit configuration of an arm waveguide portion in the waveguide type optical multiplexer / demultiplexer circuit shown in FIG. Of the two arm waveguides 1001 and 1002, the arm waveguide 1
001 corresponds to the outer arm waveguide 801 in FIG. 8, which is composed of one circular waveguide 1003 and two linear waveguides 1004 and 1005 that are adjacent to each other in the front and rear and have the same length. The arm waveguide 1002 corresponds to the inner arm waveguide 802 in FIG. 8 and is composed of one arc. Both the inner circular arc waveguide 1002 and the outer circular arc waveguide 1003 have a circular arc shape having no inflection point, and the radius of curvature R of the circular arc and the internal angle θ are equal to each other. Assuming the interval S between the arcs 1003 and 1002, the optical path length difference ΔL of the arm is expressed by the above-mentioned equation (1), that is, ΔL = S
It is given by tan (θ / 2). The arcuate interval S is the deviation of the center positions of the inner arc waveguide 1002 and the outer arc waveguide 1003, and this corresponds to the arm interval. Specifically, the optical path length difference ΔL is given by the lengths of the straight waveguides 1004 and 1005 adjacent to the outer circular waveguide 1003, and the lengths of the straight waveguides 1004 and 1005 are S · ta, respectively.
It is designed to be 1/2 of n (θ / 2).

In order to configure a waveguide type optical multiplexing / demultiplexing circuit with multi-stage MZIs, when the optical path length difference is set in accordance with the stage of MZIs, as shown in FIG. A configuration in which the arc intervals of the waveguides 1002 and 1003 are changed, or a configuration in which the inner angles of the arcs of the inner and outer arc waveguides 1002 and 1003 are changed as shown in FIG. In the configuration shown in FIG.
Compared with (A), the radius of curvature R of the arc and the interior angle θ are the same, only the interval of the arc is changed from S to 2S, and the lengths of the two linear waveguides are respectively set to S · tan (θ / 2). , Optical path length difference 2Δ
L = 2S · tan (θ / 2) is obtained. In the configuration shown in FIG. 10C, the radius of curvature R of the arc is larger than that in FIG.
And the interval S is the same, only the interior angle of the arc is changed from θ to 2θ, and the lengths of the two linear waveguides are respectively S · tan (θ), and the optical path length difference 2ΔL = S · tan (θ) is obtained. ing.

In any of FIGS. 10A, 10B, and 10C, the arm interval is substantially constant at the arc interval S or 2S. Therefore, when manufacturing a waveguide type optical multiplexing / demultiplexing circuit using MZI, there is an advantage that it is unlikely to be affected by manufacturing deviation due to in-plane distribution of the wafer. Further, the optical path length difference is given by the lengths of the linear waveguides 1004 and 1005 adjacent to the circular arc waveguide 1003 of the arm waveguide 1001. Therefore, the calculation is simple, and the design for obtaining the accurate channel spacing Δf is performed. It's easy.

Here, in FIG. 10, two straight waveguides 1004 and 1005 having the same length are provided before and after the circular arc waveguide 1003.
Are adjacent to each other to form the arm waveguide 1001.
The lengths of the two linear waveguides 1004 and 1005 may be different, or the linear waveguides may be adjacent to only one of the front and rear sides of the circular arc waveguide 1003. Two straight waveguides 10 of the same length are provided before and after the arc waveguide 1003.
The distance between the arms 04 and 1005 is closer to be substantially constant, but the point is that the optical path difference should be given by the straight waveguide adjacent to the arc waveguide 1003.

[Third Embodiment] FIG. 11A shows, as a third embodiment of the present invention, a circuit configuration of an arm waveguide portion in the waveguide type optical multiplexing / demultiplexing circuit shown in FIG. Of the two arm waveguides 1101 and 1102, the arm waveguide 1
Reference numeral 101 corresponds to the outer arm waveguide 801 in FIG. 8, which is composed of only one circular arc 1103. The arm waveguide 1102 corresponds to the inner arm waveguide 802 in FIG. 8 and is also composed of only one arc 1104. The arc 1103 of the outer arm waveguide 1101 and the arc 1104 of the inner arm waveguide 1102 both have a shape without an inflection point. The radius of curvature of the outer arc 1103 is R + S, the radius of curvature of the outer arc 1104 is R,
Although different from each other, each interior angle is θ, and they are equal to each other. The interval between the arcs 1103 and 1104 is S
(= R + S−R), the optical path length difference ΔL of the arm
Is given by the above equation (2), that is, ΔL = S · θ.
That is, the optical path length difference ΔL is equal to the two inner and outer arcs 1003 and 10
It is proportional to the difference in the radius of curvature of 04. The interval S between the arcs corresponds to the arm interval.

In order to configure a waveguide type optical multiplexing / demultiplexing circuit with multi-stage MZIs, when the optical path length difference is set in accordance with the stage of MZIs, as shown in FIG. A configuration in which the inner angles of the arcs of the waveguides 1101 and 1102 are changed, or a configuration in which the arc intervals of the inner and outer arm waveguides 1101 and 1102 are changed as shown in FIG. 11C can be considered. In the configuration shown in FIG.
Compared to (A), the radius of curvature R + S of the outer arc, the radius of curvature R of the inner arc, and the interval S of the inner and outer arcs are the same,
Only the inner angles of the inner and outer arcs are changed from θ to 2θ, and the optical path length difference 2Δ
L = 2Sθ is obtained. In the configuration shown in FIG. 11C,
Compared to FIG. 11 (A), the radius of curvature R + S of the outer arc,
The radius of curvature R of the inner arc and the inner angle θ of the inner and outer arcs are the same, only the interval between the inner and outer arcs is changed from S to 2S, and the optical path length difference 2ΔL = 2Sθ is obtained.

In any of FIGS. 11A, 11B and 11C, the arm interval is substantially constant at the arc interval S or 2S. Therefore, when manufacturing a waveguide type optical multiplexing / demultiplexing circuit using MZI, there is an advantage that it is unlikely to be affected by manufacturing deviation due to in-plane distribution of the wafer. In addition, the optical path length difference is the arc 1103 of the arm waveguide 1101 and the arm waveguide 1102.
Since it is given by the difference in the curvature relation of the arc 1104 and the internal angle, the calculation is simple and the design for obtaining the accurate channel spacing Δf is easy.

FIG. 12 shows the relationship between the circuit length of the waveguide type optical multiplexing / demultiplexing circuit and the optical path length difference ΔL. Here, "Structure 1" represents the waveguide type optical multiplexer / demultiplexer circuit of the second embodiment shown in FIG. 10, and "Structure 2" is the waveguide type optical multiplexer / demultiplexer of the third embodiment shown in FIG. 1 shows a wave circuit, and "conventional example" means the conventional waveguide type optical multiplexing / demultiplexing circuit shown in FIG. In either case, the minimum arm spacing is 250 μm and the radius of curvature R is 5 m.
m. From FIG. 12, it is possible to shorten the circuit length of the “Structure 1” and the “Structure 2” of the present invention to ½ or less as compared with the “conventional example”.

FIG. 13 shows the relationship between the yield of the waveguide type optical multiplexing / demultiplexing circuit and the optical path length difference ΔL. Here, the waveguide type optical multiplexer / demultiplexer circuit of the second embodiment, the waveguide type optical multiplexer / demultiplexer circuit of the third embodiment, and the conventional waveguide type optical multiplexer / demultiplexer circuit shown in FIG. It was integrated as shown in FIG. At that time, the minimum distance between the arms and the minimum distance between the circuits are set to 250.
μm, and the radius of curvature R was 5 mm. The yield was standardized by setting the yield by the conventional waveguide type optical multiplexing / demultiplexing circuit shown in FIG. 1 to 1. The relationship between the yield and the optical path length difference ΔL of the waveguide type optical multiplexing / demultiplexing circuits of the second embodiment and the third embodiment is the same. It can be seen from FIG. 13 that the yield of the structure of the present invention is higher than that of the conventional example. In particular, the channel spacing is 1
In the DWDM region of 00 GHz, ΔL is a value longer than the value shown in FIG. 13, so that the superiority of the present invention with respect to the yield becomes more remarkable.

[Fourth Embodiment] FIG. 14 shows a circuit configuration of a waveguide type optical multiplexer / demultiplexer circuit according to a fourth embodiment of the present invention. In this embodiment, a waveguide type optical multiplexing / demultiplexing circuit using a lattice filter in which MZIs are configured in multiple stages is designed based on the above-mentioned equation (2), that is, ΔL = S · θ.

In FIG. 14, 1401 is an input waveguide,
1402, 1403 and 1404 are couplers and 1
405 and 1406 are arm waveguides of the first stage MZI, 14
Reference numerals 07 and 1408 denote arm waveguides of the latter MZI, 140
Reference numeral 9 indicates an output waveguide cross port (# 1), and 1410 indicates an output waveguide through port (# 2). In this lattice filter, the optical path length difference of the first stage MZI is ΔL and the latter stage MZI is M
The optical path length difference of ZI is 2ΔL. The arm waveguides 1407 and 1408 in the latter stage are configured by doubling the internal angle of the arc as compared with the former stage, as described in the description of FIGS. 10 and 11. Also, the couplers 1402, 1
The coupling rates of 403 and 1404 are 50%, 25%,
It was designed as 6.7%. The coupler 1403 is the first stage MZ
It is shared by I and MZI in the latter stage.

For example, the optical path length difference ΔL of the first stage MZI is
The optical path length difference 2ΔL of the latter MZI set by the configuration described in the description of FIG. 11 (A) is, as described in the description of FIG. 11 (B), the inner angle of the arc compared to the former MZI. It is configured by doubling. In addition, MZI of the latter stage
The optical path length difference 2ΔL is compared with the MZI of the preceding stage as described in the description of FIG. 11C, and the arc interval is from S to 2S.
It may be configured by doubling.

Specifically, the first-stage arm waveguide 140
5, 1406, the arm waveguide 1405 is shown in FIG.
11A corresponds to the outer arm waveguide 1101 (one arc having a shape without an inflection point), and the arm waveguide 1406 corresponds to the inner arm waveguide 1102 in FIG. 11A (shape without an inflection point). Of one arc). The convex directions of the two arm waveguides 1405 and 1406 are the same.

Further, the arm waveguides 1407, 14 at the latter stage
08, the arm waveguide 1407 corresponds to the outer arm waveguide 1101 (one arc having a shape without an inflection point) in FIG. 11B, and the arm waveguide 1408 is illustrated in FIG.
This corresponds to the inner arm waveguide 1102 (one circular arc having a shape without an inflection point) in (B). Two arm waveguide 1
The convex directions of 407 and 1408 are the same.

Input waveguide 1401 and output waveguide 140
The arrangements of 9 and 1410 are not arranged because the arm waveguides of each stage all include one arc.

As can be seen from FIG. Since the distance between the first-stage arm waveguides 1405 and 1406 and the distance between the second-stage arm waveguides 1407 and 1408 are both constant (S in FIG. 11), they are less affected by the manufacturing deviation due to the in-plane distribution of the wafer. . Further, since the input waveguide 1401 and the output waveguides 1409 and 1410 are arranged so as not to face each other, there is no characteristic deterioration due to leaked light when the optical fiber is connected.

Next, a method of manufacturing the waveguide type optical multiplexing / demultiplexing circuit of this embodiment will be described with reference to FIG. (1) First, by a flame deposition method on a silicon substrate 1501,
Lower glass clad soot 150 mainly composed of SiO ₂
2 and a core glass soot 1503 added with GeO ₂ are deposited (see FIG. 15A). (2) After that, the glass is made transparent at a high temperature of 1000 ° C. or higher. At this time, glass is deposited so that the lower clad glass layer 1504 has a thickness of 30 μm and the core glass 1505 has a thickness of 7 μm (see FIG. 15B). (3) Subsequently, an etching mask 1506 is formed on the core glass 1505 by photolithography (see FIG. 15C), and the core glass 1505 is patterned by reactive ion etching (FIG. 15).
(D)). Etching mask 150 used at this time
6 is a mask corresponding to the circuit configuration shown in FIG.
Therefore, the pattern of the core glass 1505 also corresponds to the circuit configuration shown in FIG. (4) Then, after removing the etching mask 1506, the upper clad glass 1507 is formed again by the flame deposition method. At that time, the upper clad glass 1507 has B ₂
Each of the patterned core glasses 1 having a glass transition temperature lowered by adding a dopant such as O ₃ or P ₂ O ₅ 1
The upper clad glass 1507 is surely inserted into a narrow gap between the core glass 505 and the core glass 1505 (see FIG. 15E).

FIG. 16 shows the transmission spectrum characteristic of this embodiment shown in FIG.
09 (# 1) and the output waveguide through port 1410 (#
It can be seen that the waves are grouped in 2). As shown in FIG. 16, in this embodiment, the channel spacing Δf = 1250.
A flat and low-loss transmission region of GHz (wavelength interval: 10 nm) was obtained, and low crosstalk of 30 dB or more was obtained in the stop region. As shown here, the filter that performs group branching at the cross port 1409 and the through port 1410 is hereinafter referred to as an interleave filter.

Here, in the circuit configuration of FIG. 14, the first stage MZ
I, and the convex directions of the arm waveguides 1405 and 1406 in I, and the arm waveguides 1407 and 14 in the latter MZI.
Although the convex direction of 08 is different, there is no problem as long as the convex directions of the arm waveguides in the individual stages are the same.

When designing on the basis of the above equation (2) where ΔL = S · θ, the optical path length difference 2ΔL of the MZI in the subsequent stage is
As described in the description of FIG. 11C, the interval of the circular arc can be doubled from θ to 2θ as compared with the MZI in the preceding stage.

[Fifth Embodiment] FIG. 17 shows a circuit configuration of a waveguide type optical multiplexer / demultiplexer circuit according to a fifth embodiment of the present invention. In the present embodiment, the above-described interleave filter is configured in multiple stages to form a waveguide type optical multiplexing / demultiplexing circuit, which is designed based on the above equation (2), that is, ΔL = S · θ.

In FIG. 17, reference numeral 1701 denotes an input waveguide,
1702 is a first stage interleave filter with a channel spacing of 20 nm, 1703 and 1704 are output waveguides of the first stage interleave filter, 1705 and 1706 are latter stage interleave filters with a channel spacing of 40 nm, and 1707 and 1708 are latter stage interleave filters.
Output waveguides of filter 1705, 1709 and 1710
Indicates the output waveguide of the post-interleave filter 1706.

Each interleave filter 1702, 1
As described in the description of FIGS. 10 and 11, 705 and 1706 are designed to change the internal angle of the arc of the arm waveguide between the multiple stages of MZIs forming each interleave filter.

The first stage interleave filter 1702 is composed of four stages of MZI, and the arm waveguide in all stages has a shape including one circular arc having no inflection point. The convex direction of the arm is upward in all of the MZIs from the first stage to the third stage, and is downward in the MZI of the fourth stage.

FIG. 18 shows the transmission spectrum characteristic of the interleave filter 1702 at the first stage. Similar to the case shown in FIG. 16, the two output waveguides 1703 and 1704 are grouped into an even channel and an odd channel, respectively. The distance between the even channel and the odd channel is 20 nm.

Two post-stage interleave filters 17
Reference numerals 05 and 1706 are both composed of three stages of MZI, and in all stages, the arm waveguide has a shape including one circular arc having no inflection point. The convex direction of the arm is upward in all MZIs.

FIG. 19 shows the transmission spectrum characteristics of the interleave filters 1705 and 1706 at the latter stage. These two subsequent interleave filters 1705, 1
It can be seen that 706 has the same transmission spectrum characteristics, and performs group branching with a channel spacing of 40 nm, which is double that of the first-stage interleave filter 1702.

That is, the output waveguides 1707 (# 1) and 1708 (# of the interleave filter 1705 in the subsequent stage are included.
From 3), the first stage interleave filter 1702
Of the even channels from the output waveguide 1703 that have been demultiplexed by (the output waveguide cross port 17
07) and group division into odd-numbered channels (output waveguide through port 1708).

Similarly, the output waveguides 1709 (# 2) and 1710 (# of the interleave filter 1706 in the subsequent stage are also described.
For 4), the first stage interleave filter 170
Of the odd channels from the output waveguide 1704 that are demultiplexed in 2, the signals are group-demultiplexed into an even-numbered channel (output waveguide cross port 1709) and an odd-numbered channel (output waveguide through port 1710).

FIG. 20 shows the transmission spectrum characteristic of the fifth embodiment as a whole. As described above, the channel spacing 20
It can be seen that the nm demultiplexing circuit has been realized. # 1
Is the demultiplexing characteristic of the output waveguide cross port 1707 of the post-interleave filter 1705, # 2 is the demultiplexing characteristic of the output waveguide through port 1708 of the post-interleave filter 1705, and # 3 is the post-interleave filter. The demultiplexing characteristic of the output waveguide cross port 1709 of 1706, # 4 is the output waveguide through port 17 of the post-interleave filter 1706.
10 shows the demultiplexing characteristic in 10.

[Sixth Embodiment] FIG. 21 shows a sixth embodiment of the present invention.
2 shows a circuit configuration of a waveguide type optical multiplexing / demultiplexing circuit in the embodiment of FIG. The present embodiment is a lattice / multi-stage structure of MZI.
A waveguide type optical multiplexing / demultiplexing circuit using a filter is designed based on the above-mentioned formula (1), that is, ΔL = S · tan (θ / 2).

In FIG. 21, reference numeral 2101 denotes an input waveguide,
2102, 2103 and 2104 are couplers, 2 respectively
105 and 2106 are arm waveguides of the first stage MZI, 21
07 and 2108 are arm waveguides of the latter MZI, 210
Reference numeral 9 indicates an output waveguide cross port (# 1), and 2110 indicates an output waveguide through port (# 2). In this lattice filter, the optical path length difference of the first stage MZI is ΔL and the latter stage MZI is M
The optical path length difference of ZI is 2ΔL. As described in the description of FIGS. 10 and 11, the arm waveguides 2107 and 2108 in the latter stage are configured by doubling the interval between arcs as compared with the former stage. Also, the couplers 2102, 2
The coupling ratios of 103 and 2104 are 50%, 25%,
It was designed as 6.7%. The coupler 2103 is the first stage MZ
It is shared by I and MZI in the latter stage.

That is, the optical path length difference ΔL of the first stage MZI is
The optical path length difference 2ΔL of the MZI in the latter stage, which is set by the configuration described in the description of FIG. 10 (A), has a circular arc interval as compared with the MZI in the former stage, as described in the description of FIG. 10 (B). It is configured by doubling from S to 2S, and the entire circuit is configured to have a Z shape. The optical path length difference 2ΔL of the latter stage MZI is configured by doubling the internal angle of the arc from θ to 2θ as compared with the former stage MZI, as described in the description of FIG. 10C. May be.

Specifically, the first-stage arm waveguide 210
5 and 2106, the arm waveguide 2105 is shown in FIG.
The inner arm waveguide 2106 corresponds to the outer arm waveguide 1001 of FIG. 10A (one circular arc having no inflection point and a straight waveguide adjacent to it), and the inner arm waveguide 2106 is the inner arm waveguide 1002 of FIG. It corresponds to (one circular arc having no inflection point). Two arm waveguides 2105, 210
The convex direction of 6 is the same rightward. Further, of the arm waveguides 2107 and 2108 in the latter stage, the arm waveguide 2107
10B corresponds to the outer arm waveguide 1001 of FIG. 10B (one circular arc having a shape without an inflection point and a straight waveguide adjacent to it), and the arm waveguide 2108 is the inner arm guide of FIG. 10B. Waveguide 1002 (shape 1 without inflection point
Two arcs). Two arm waveguides 1407,
The convex direction of 1408 is the same leftward.

Input waveguide 2101 and output waveguide 210
The arrangements of 9 and 2110 do not face each other because the arm waveguides of each stage all include one arc.

As can be seen from FIG. 21, the interval between the arm waveguides 2105 and 2106 of the first stage MZI and the interval between the arm waveguides 2107 and 2108 of the latter stage MZI are constant (S and 2S in FIG. 10). Therefore, it is unlikely to be affected by the manufacturing deviation due to the in-plane distribution of the wafer. Further, since the input waveguide 2101 and the output waveguides 2109 and 2110 are arranged so as not to face each other, there is no characteristic deterioration due to leaked light when connecting the optical fibers.

FIG. 22 shows the transmission spectrum characteristic of this embodiment shown in FIG. 21, and shows the output waveguide cross port 210.
9 (# 1) and the output waveguide through port 2110 (#
Each group is divided into 2). As shown in FIG. 22, in the present embodiment, a flat and low-loss transmission region with a channel interval Δf = 200 GHz is obtained, and in the stop region, 30 d.
Low crosstalk of B or more is obtained.

Further, in the circuit configuration of the sixth embodiment, since the internal angle of the arm arc of the MZI of each stage is set large and the entire circuit is arranged in a Z shape, as shown in FIG. When the waveguide type optical multiplexer / demultiplexer circuit (MZI) 2301 is integrated and manufactured on a plane, another waveguide type optical multiplexer / demultiplexer circuit 2301 is woven into the curved portion of one waveguide type optical multiplexer / demultiplexer circuit 2301. As a result, a high degree of integration can be realized.

In FIG. 23, reference numeral 2301 denotes a waveguide type optical multiplexing / demultiplexing circuit having the circuit configuration shown in FIG. 21, which is provided on the left side of the rightwardly convex arm of one waveguide type optical multiplexing / demultiplexing circuit 2301.
Another waveguide-type optical multiplexer / demultiplexer circuit 2301 is laid out by sequentially weaving convex arms to the right. On the contrary, when the arm is convex to the left, the left convex convex arm of one waveguide type optical multiplexer / demultiplexer circuit is woven into the leftward convex arm of another waveguide type optical multiplexer / demultiplexer circuit. .

[Seventh Embodiment] FIG. 24 shows a seventh embodiment of the present invention.
2 shows a circuit configuration of a waveguide type optical multiplexing / demultiplexing circuit in the embodiment of FIG. In MZI, normally, there are two arm waveguides that connect the optical couplers (see FIG. 8), but three or more MZIs are also conceivable. The waveguide type optical multiplexing / demultiplexing circuit of this embodiment is configured by using MZI having three arm waveguides.

In FIG. 24, 2401, 2402 and 2403 are arm waveguides, 2404 is an input waveguide,
2405 is a first coupler (optical coupler) and 2406 is a second coupler.
Couplers (optical couplers) 2407 and 2408 respectively indicate output waveguides, and three arm waveguides 2401 and 240
2, 2403 connect between the couplers 2405, 2406.

Also in the waveguide type optical multiplexer / demultiplexer circuit shown in FIG. 24, three arm waveguides 2401, 2402, and 2403 are provided.
Are both formed by arcs. That is, each of the arm waveguides 2401, 2402, and 2403 includes one circular arc, and each circular arc has a shape without an inflection point, and the convex directions of the circular arcs are the same in the arms (upward in the figure). ).

The light incident on the input waveguide 2404 is converted into three arm waveguides 2401 and 2 by the first coupler 2405.
It is demultiplexed into 402 and 2403. A phase delay is caused between the three signal lights due to the optical path length difference between the arms, and these signal lights are combined / interfered again by the second coupler 2406, thereby performing group branching. Two types of optical path length differences are set, for example, ΔL between the arm waveguides 2401 and 2402 and 2ΔL between the arm waveguides 2401 and 2403. Also, for the setting of these optical path length differences, the equation (1) of ΔL = S · tan (θ / 2) as in the second embodiment or ΔL = S · θ as in the third embodiment. Equation (2) can be used.

The waveguide type optical multiplexer / demultiplexer circuit shown in FIG. 24 has the same effects as those of the first embodiment except that the number of arm waveguides is different. Furthermore, MZI having three arm waveguides can be configured in multiple stages to configure a waveguide type optical multiplexer / demultiplexer circuit similar to the fourth, fifth, and sixth embodiments.

[Other Embodiments] In the fourth, fifth, and sixth embodiments described above, the multistage MZI, that is, the lattice filter using the silica glass waveguide on the silicon substrate is shown. Waveguide material is polyimide, silicone,
The present invention can be applied to semiconductors, LiNbO _{3, and the} like. Also, the flat substrate is not limited to silicon. The same applies to the waveguide type optical multiplexer / demultiplexer circuit (one of the first to third and seventh embodiments) in which the MZI has one stage. Further, the present invention can be applied to a waveguide type optical multiplexer / demultiplexer circuit in which a heater electrode is loaded on the MZI as shown in FIG.

Further, in the fourth embodiment, the equation (2) of ΔL = S · θ is applied to the setting of the optical path length difference in all stages of MZI, and in the sixth embodiment, the optical path length difference in all stages of MZI is applied. The equation (1) of ΔL = S · tan (θ / 2) is applied to the setting of ΔL = S · tan (θ / 2) for each MZI stage.
A waveguide type optical multiplexer / demultiplexer circuit may be designed by properly using L = S · θ.

In short, the essence of the present invention is to realize a waveguide type optical multiplexing / demultiplexing circuit with good productivity and designability by paying attention to the geometrical shape of an arc and configuring each arm waveguide with an arc. There is something I did. As can be seen by comparing FIG. 8 and FIG. 1, the present invention can be applied to a waveguide type optical multiplexing / demultiplexing circuit in which the difference in optical path length is particularly small.

[0078]

As described above, according to the present invention,
Compared with the prior art, it is possible to obtain effects such as downsizing of a waveguide type optical multiplexing / demultiplexing circuit, improvement of yield from a wafer, relaxation of tolerance against manufacturing deviation, and ease of design.

[Brief description of drawings]

FIG. 1 is a diagram showing a circuit configuration of a conventional waveguide type optical multiplexing / demultiplexing circuit using MZI.

FIG. 2 is a diagram showing a transmission spectrum characteristic of MZI.

FIG. 3 is a diagram showing a circuit configuration of a directional coupler.

FIG. 4 is a diagram showing the relationship between the length of the coupling portion of the directional coupler and the coupling rate.

FIG. 5 is a diagram showing an intensity distribution of light propagating through a directional coupler having a coupling section of zero length.

FIG. 6 is a diagram showing a circuit configuration of a waveguide type optical multiplexing / demultiplexing circuit using a conventional MZI loaded with a heater electrode.

FIG. 7 is a diagram showing heat distribution in a two-dimensional cross section taken along line aa ′ in FIG.

FIG. 8 is a diagram showing a circuit configuration of a first embodiment of the present invention.

9 is a diagram showing a difference in integration degree between the waveguide type optical multiplexing / demultiplexing circuit of FIG. 8 and a conventional waveguide type optical multiplexing / demultiplexing circuit.

FIG. 10 is a diagram showing a circuit configuration of a second embodiment of the present invention (a waveguide type optical multiplexing / demultiplexing circuit in which an optical path length difference ΔL is given by a linear waveguide added to an arc).

FIG. 11 is a diagram showing a circuit configuration of a third embodiment of the present invention (a waveguide type optical multiplexer / demultiplexer circuit in which an optical path length difference ΔL is given by a radius of curvature of an arc).

FIG. 12 is a diagram showing the relationship between the circuit length and the optical path length difference ΔL in each of the waveguide type optical multiplexing / demultiplexing circuits of FIGS. 10, 11 and 1 (conventional).

FIG. 13 shows the relationship between the optical path length difference ΔL and the yield in each of the waveguide type optical multiplexing / demultiplexing circuits of FIGS. 10 and 11, and FIG.
FIG. 6 is a diagram showing each waveguide type optical multiplexing / demultiplexing circuit of FIG.

FIG. 14 is a diagram showing a circuit configuration of a fourth embodiment of the present invention.

FIG. 15 is a diagram showing a manufacturing process of the waveguide type optical multiplexing / demultiplexing circuit of FIG.

16 is a diagram showing transmission spectrum characteristics of the waveguide type optical multiplexing / demultiplexing circuit of FIG.

FIG. 17 is a diagram showing a circuit configuration of a fifth embodiment of the present invention.

FIG. 18 is a diagram showing a transmission spectrum characteristic of the first-stage interleave filter in FIG. 17;

FIG. 19 is a diagram showing a transmission spectrum characteristic of the latter stage interleave filter in FIG. 17;

20 is a diagram showing transmission spectrum characteristics of the entire waveguide type optical multiplexing / demultiplexing circuit of FIG.

FIG. 21 is a diagram showing a circuit configuration of a sixth embodiment of the present invention.

22 is a diagram showing transmission spectrum characteristics of the waveguide type optical multiplexing / demultiplexing circuit of FIG. 21.

23 is a diagram showing a state in which the waveguide type optical multiplexing / demultiplexing circuit of FIG. 21 is integrated.

FIG. 24 is a seventh embodiment of the present invention (the arm waveguide is 3;
The figure which shows the circuit structure of a waveguide type optical multiplexing / demultiplexing circuit).

[Explanation of symbols]

801, 802 Arm waveguide 803 Input waveguide 804, 805 Coupler (optical coupler) 806, 807 Output waveguide 901 Waveguide type optical multiplexing / demultiplexing circuit 1001, 1002 Arm waveguide 1003 Circular arc 1004, 1005 Linear waveguide 1101, 1102 Arm waveguide 1103 Circular arc 1401 Input waveguide 1402, 1403, 1404 Coupler (optical coupler) 1405, 1406 First stage MZI arm waveguide 1407, 1408 Rear stage MZI arm waveguide 1409 Output waveguide (cross port) 1410 Output waveguide (Through port) 1501 Silicon substrate 1502 Lower clad glass soot 1503 Core glass soot 1504 Lower clad glass layer 1505 Core glass 1506 Etching mask 1507 Upper clad glass 1701 Input waveguide 170 2 First-stage interleave filter 1703, 1704 First-stage interleave filter output waveguides 1705, 1706 Second-stage interleave filter 1707, 1708, 1709, 1710 Second-stage interleave filter output waveguide 2101 Input waveguide 2102, 2103, 2104 Coupler (optical) Coupler) 2105, 2106 First stage MZI arm waveguide 2107, 2108 Rear stage MZI arm waveguide 2109 Output waveguide (cross port) 2110 Output waveguide (through port) 2301 Waveguide type optical multiplexer / demultiplexer circuit 2401, 2402, 2403 Arm waveguide 2404 Input waveguide 2405, 2406 Coupler (optical coupler) 2407, 2408 Output waveguide

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Yasuyuki Inoue             2-3-1, Otemachi, Chiyoda-ku, Tokyo             Inside Telegraph and Telephone Corporation (72) Inventor Yoshinori Hibino             2-3-1, Otemachi, Chiyoda-ku, Tokyo             Inside Telegraph and Telephone Corporation F term (reference) 2H047 KA04 KA12 LA12 LA18 PA22                       PA24 QA02 QA03 QA04 QA05                       TA01

Claims (5)

[Claims] 1. A Mach-Zehnder optical interference filter comprising an optical waveguide comprising a core having a high refractive index on a planar substrate and a clad surrounding the optical waveguide and comprising an optical coupler and a plurality of arms connecting the optical coupler. A waveguide type optical multiplexer / demultiplexer circuit characterized in that each of the arms includes one arc, the arc has a shape having no inflection point, and the convex directions of the arc are the same between the arms. . 2. When the radius of curvature and the internal angle of the arc are equal to each other between the arms, the interval between the arcs of the arms is S, and the interior angle of the arc is θ, the optical path is defined by a linear waveguide adjacent to the arc. The waveguide type optical multiplexer / demultiplexer circuit according to claim 1, wherein the length difference ΔL is given by ΔL = S · tan (θ / 2) (Equation 1). 3. The optical path length when the radii of curvature of the arcs are different between the arms, the interior angles of the arcs are equal to each other, and the interval between the arcs between the arms is S and the interior angle of the arcs is θ. The waveguide type optical multiplexer / demultiplexer circuit according to claim 1, wherein the difference ΔL is given by ΔL = S · θ (Equation 2). 4. The Mach-Zehnder optical interference filter is configured in multiple stages.
The waveguide type optical multiplexer / demultiplexer circuit according to any one of claims 1 to 5. 5. The waveguide type optical multiplexer / demultiplexer circuit according to claim 1, wherein the Mach-Zehnder optical interference type filter is constituted by a silica glass optical waveguide on a silicon substrate.