JP3149088B2 - Optical waveguide circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a single-mode optical waveguide used in the field of optical communication and the like, and more particularly, to minimizing a loading effect generated in a single-mode optical waveguide having different structures around the waveguide. The present invention relates to a single-mode optical waveguide manufactured in a limited size.

[0002]

2. Description of the Related Art In recent years, optical fiber has been widely used in communication networks due to high performance and low cost of optical fibers and light receiving / emitting elements, and most of communication lines in relay networks have already been replaced by optical fiber communication. . Further, the optical communication network is changed from a point-to-point optical communication connecting individual nodes to an optical communication network having a network structure in which a plurality of nodes including an access network are connected as optical signals without being converted into electric signals. It is time to develop, and there is an urgent need to develop various optical components such as optical branching couplers, optical multiplexers / demultiplexers, and optical switches required for this.

Various forms of optical components have been considered so far. Among them, the waveguide type is excellent in mass productivity and miniaturization, and is expected as a future type optical component. Have been. Conventionally, optical waveguides have been manufactured using various material systems. Among them, quartz optical waveguides manufactured on a silicon substrate have low loss, excellent stability, and excellent matching with an optical fiber. It is promising as the most promising means of realizing optical waveguides having features and constituting practical optical circuits.

FIG. 2 shows an example of a conventional optical circuit composed of, for example, a silica-based optical waveguide. The figure of the switch array which integrated two or more 2x2 optical switches is shown. FIG. 2A is a plan view of the above-described optical circuit, and FIG. 2B is a plan view of FIG.
2C is a sectional view taken along the line CC ′ of FIG.
It is sectional drawing along the DD 'line of (a). 1 is a silicon substrate, 2 is a cladding layer made of quartz glass, 3 is a core portion made of quartz glass embedded in the cladding layer 2, and 14 is a thin film heater formed on the surface of the cladding layer 2 above the core portion 3. (Phase shifter). Also, here, 2
1, 2 and 23 are 2 × 2 optical switches having the same specifications. Reference numeral 30 denotes a slab waveguide, which is not always necessary here.

That is, these 2 × 2 optical switches are:
It is a Mach-Zehnder optical interferometer circuit composed of two directional couplers 13 and a phase shifter 14. These directional couplers 13 have a structure in which some of the two optical waveguides are close to each other, and the optical coupling ratio is set to target 50% at the signal light wavelength. The difference between the optical path lengths of the two waveguides connecting the two directional couplers 13 is OF
In the F state (the thin-film heater is not energized), for example, it is set to zero. A thin film heater 14 for changing the optical path length using a so-called thermo-optic effect is mounted on at least one of the two waveguides as a phase shifter.

These 2 × 2 optical switches operate by changing the interference condition by energizing one of the thin film heaters 14. In the OFF state, the difference in optical path length between the two optical waveguides connecting the two directional couplers 13 of the Mach-Zehnder optical interferometer circuit is zero. The signal light entering from the input waveguide end 11a propagates to the output waveguide end 12a, and the signal light entering from the input waveguide end 11a propagates to the output waveguide end 12b. In the ON state, that is, when the optical path length difference is changed to one half of the signal wavelength by energizing one of the thin film heaters 14, the signal light entering from the input waveguide end 11b receives the output waveguide. The signal light guided to the end 12b and entering from the input waveguide end 11a is guided to the output waveguide end 12a.

An optical circuit using such a silica-based optical waveguide is manufactured by a method called a convex process shown in FIG.
It is manufactured by a method called a concave process shown in FIG. In the convex process, first, [FIG. 3A] a lower clad layer 6 and a waveguide core layer 8 are formed on a silicon substrate 1 by a flame hydrolysis reaction deposition technique [FIG. 3B]. Next, only portions that will later become the waveguide cores 4 and 5 are left, and unnecessary portions are removed by a reactive ion etching technique [FIG.
(C)]. Again, the upper cladding layer 7 is formed by the flame hydrolysis reaction deposition technique [FIG. 3 (d)]. Finally, the thin film heater (phase shifter) 14 serving as a phase adjuster and the electric Wiring is formed on the upper clad [FIG. 3 (e)]. In the concave process,
[FIG. 4 (a)] A lower cladding layer 6 is formed on a silicon substrate 1 by a flame hydrolysis reaction deposition technique [FIG.
(B)]. Next, a portion 9 to be a waveguide core later is dug out by a reactive ion etching technique [FIG. 4 (c)].
Thereupon, a waveguide core layer 8 serving as a waveguide core is formed by a flame hydrolysis reaction deposition technique [FIG. 4 (d)]. And
The excess waveguide core layer is etched over the entire surface, leaving only the portions 4 and 5 that become the net waveguide core [FIG.
(E)]. Again, the upper cladding layer 7 is formed by the flame hydrolysis reaction deposition technique [FIG. 4 (f)], and finally, the thin film heater (phase shifter) 14 serving as a phase adjuster and the electric Wiring is formed on the upper clad [FIG. 4 (g)]. As described above, the manufacturing procedure is slightly different, but any of the methods is based on SiCl ₄ or GeC.
It is produced by known combinations of deposition techniques and reactive ion etching techniques and wet etching of the glass film using hydrolysis reaction of raw material gas such as l _4.

[0008]

However, a switch array in which a plurality of 2 × 2 optical switches are integrated as described above has the following problems.

In the case of the convex step, when forming the upper cladding layer 7 as shown in FIG. 3D, the glass fine particles deposited by the flame hydrolysis reaction are sintered at a high temperature. At this time, the glass fine particles sinter while flowing to some extent. If there is a difference in the distribution of the structure around the circuit, the flow will have directionality. Also, during sintering, the viscosity of the glass in the portions of the waveguide cores 4 and 5 that have already been formed also decreases to some extent. Therefore, the waveguide cores 4 and 4
5 is deformed, and in some cases, its position is slightly shifted. The deformation of the waveguide cores 4 and 5 causes a shift in the effective refractive index of the waveguide, and the positional shift causes a shift in the waveguide length, and as a result, a shift in the optical path length appears.

In the case of the concave process, when forming the waveguide core layer 8 as shown in FIG. 4D, the glass fine particles deposited by the flame hydrolysis reaction sinter while flowing to some extent. Instead of being a perfect plane, irregularities occur due to the shape of the etched lower cladding layer 6. That is, a portion having a high waveguide density is concave (thin), and a portion having a low waveguide density is convex (thick). Therefore, FIG.
As shown in (c), even after the entire waveguide core layer 8 that is excessively stacked is etched to form the waveguide cores 4 and 5, this effect remains. The height of the waveguide core is slightly smaller than that of the small portion. This difference in the core size causes a difference in the effective refractive index of the waveguide, and as a result, a difference in the optical path length appears.

Of the 2 × 2 optical switches shown in FIG.
The middle 2 × 2 optical switch 22 has 2 × 2 optical switches of the same layout on both sides, but the top 2 × 2 optical switch 22 has the same layout.
The optical switch 21 has a slab waveguide 30 at the top here, and conversely, the lowermost 2 × 2 optical switch 23 does not exist at all. As described above, the state of the structure around the 2 × 2 optical switch is different in each 2 × 2 optical switch. Therefore, in the design, even if the difference in the optical path lengths of the two waveguides connecting the two directional couplers 13 is set to zero when each 2 × 2 optical switch is in the OFF state, the actual reason is as described above. In the completed optical circuit, the difference between the optical path lengths does not become zero, and a deviation occurs due to a surrounding circuit pattern. As described above, even if the optical circuit pattern itself is the same, if the surrounding patterns are different, there is a problem that the characteristics are shifted.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned prior art, and has an optical circuit layout for minimizing the influence of a pattern around the optical circuit in order to manufacture an optical circuit having desired characteristics. It is intended to provide.

[0013]

SUMMARY OF THE INVENTION The present invention provides such an eye.
In order to achieve the target, the optical waveguide circuit formed on the substrate
In some cases, the number of rows of optical interferometers
An optical waveguide circuit comprising at least one optical interferometer array,
Around the optical interferometer located at both ends of the optical interferometer
Dummy waveguide pattern with equal row and waveguide pattern density
It is characterized by having.

According to the first aspect of the present invention,
The dummy having the same optical interferometer array and waveguide pattern density
The waveguide pattern is the same as or the same as the optical interferometer array
It is characterized by having a similar shape.

Further, in the invention according to claim 2,
Serial optical interferometer, a Mach-Zehnder interferometer type 2 × 2 optical switch composed of two directional couplers and optical phase shifter
It is characterized by being.

Further , according to the invention of claim 1, 2 or 3,
In the optical waveguide, the core portion and the cladding layer
It is characterized by being made of quartz glass containing O ₂ as a main component.
Is what you do.

Further , according to the invention of claim 1, 2 or 3,
In addition, after forming the lower clad layer and subsequently the core layer on the substrate, removing the core layer other than the waveguide core through which light propagates, and a configuration manufactured by further forming an upper clad layer Is characterized by
You.

Further, according to the invention of claim 1, 2 or 3,
After the lower clad is formed on the substrate, a groove serving as a waveguide core for transmitting light is formed in the lower clad, the waveguide core is filled in the groove, and an upper clad layer is formed. It is characterized by having been configured .

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A dummy waveguide or the like (an optical waveguide pattern having no input / output end, etc. is referred to as a "dummy waveguide or the like" for convenience of description below) is used in the above means. With circuit layout design, the optical circuit patterns near the periphery of all optical circuits are almost the same, and the density of the waveguides is also almost uniform, so that the influence of the patterns around the optical circuits that occur during fabrication is reduced as much as possible. be able to.

[0020]

Embodiments of the present invention will be described below in detail with reference to the drawings. In the following embodiments, an optical circuit realized by a quartz single-mode optical waveguide formed on a silicon substrate as an optical waveguide will be described. This is because the optical waveguide of this combination is stable with low loss and has excellent matching with the silica-based optical fiber. However, the invention is not limited to these combinations.

[Embodiment 1] FIG. 1 is a conceptual diagram showing a configuration of a switch array optical circuit in which a plurality of 2 × 2 optical switches according to a first embodiment are integrated as an example of the present invention. FIG.
FIG. 1A is a plan view of this embodiment, and FIG.
FIG. 1A is a cross-sectional view along the line AA ′, and FIG. 1C is a cross-sectional view along the line BB ′ in FIG. 1 is a silicon substrate, 3 is a cladding layer made of quartz glass, 2 is a core portion made of quartz glass embedded in the cladding layer 3, and 14 is a thin film heater formed on the surface of the cladding layer 3 above the core portion 2. (Phase shifter). Also, here, 2
1, 2 and 23 are 2 × 2 optical switches having the same specifications. Reference numeral 30 denotes a slab waveguide, which has been written following a conventional example, and is not always necessary here.
Reference numeral 24 denotes a dummy 2 × 2 optical switch. Here, 2
In the × 2 optical switch 24, the optical waveguide is not drawn to the edge of the substrate but is cut off in the middle. This is to clearly show that the 2 × 2 optical switch is a dummy element. And the 2 × 2 optical switches 21 and 2 to be used.
A configuration similar to that of 2 or 23 may be used.

As is apparent from a comparison between FIG. 1 and FIG. 2, in this embodiment, dummy 2 × 2 optical switches 21 The switch 24 is arranged, and any 2 × 2 optical switch 21, 22, 2
3 also differs greatly from the conventional configuration in that the structure around the periphery is the same.

As described above, if the circuit layout design using the dummy waveguides and the like shown in the above means is made, the optical circuit patterns near the periphery become almost the same in all the optical circuits and the waveguide density becomes almost one. As a result, the influence of the pattern around the optical circuit generated at the time of fabrication could be reduced as much as possible.

A switch array optical circuit in which a plurality of 2 × 2 optical switches according to the present embodiment are integrated has a thickness of 1
On a silicon substrate having a diameter of 4 inches, a quartz-based waveguide is manufactured by a combination of a deposition technique of a quartz-based glass film using a hydrolysis reaction of a raw material gas such as SiCl ₄ or GeCl ₄ and a reactive ion etching technique, A thin film heater was manufactured by a vacuum deposition method and chemical etching. The cross-sectional dimension of the core is 6 μm square, and the relative refractive index difference between the core and the clad is 0.75%. The size of the thin film heater is
The thickness is 0.1 μm, the width is 40 μm, and the length is 4 mm. The 2 × 2 optical switch and the dummy 2 × 2 optical switch used in the present embodiment are arranged between two waveguides connecting two directional couplers 13 constituting a Mach-Zehnder interferometer circuit. Was 250 μm. The interval between each 2 × 2 optical switch and dummy 2 × 2 optical switch was also set to 250 μm.
The effective optical path length difference between the two waveguides was set to be exactly zero in the OFF state (the thin film heater was not energized) (that is, a symmetric Mach-Zehnder interferometer circuit was used). A chip on which a switch array optical circuit in which a plurality of 2 × 2 optical switches are integrated is cut out by dicing, and a heat sink is provided below the silicon substrate.
A single-mode fiber array was connected to the input / output waveguide, a power supply lead was connected to the thin-film heater, and a switch array optical circuit module in which a plurality of 2 × 2 optical switches were integrated was completed.

The switching operation of each 2 × 2 optical switch was confirmed by appropriately selecting the thin film heater to be supplied with power. In the OFF state (the thin-film heater is not energized), the effective optical path length difference between the two waveguides connecting the two directional couplers of each 2 × 2 optical switch is the current operating wavelength of 1.55 μm.
The deviation was less than 1% of m. In the case of the conventional layout circuit shown in FIG. 2 where no dummy element is arranged, the middle 2 × 2 optical switch 22 has the same layout on both sides.
In a two-optical switch, the effective optical path difference is 1.55 μm, which is 1
%, But in the uppermost 2 × 2 optical switch 21, the effective optical path difference of the upper waveguide is 1.55 μm, which is 100% longer than that of the lower waveguide. In the lowermost 2 × 2 optical switch 23, the effective optical path length difference of the upper waveguide where nothing is present is about 50% longer than that of the lower waveguide by 1.55 μm. Therefore, a switch array optical circuit in which a plurality of 2 × 2 optical switches each including the dummy switch according to the present invention are integrated as compared with the conventional type can obtain desired characteristics and greatly suppress the deviation of the optical path length. did it.

The point of the present invention is to make the pattern density of the waveguide uniform in the waveguide circuit. Therefore, it is preferable that the dummy circuit disposed around the waveguide circuit is completely the same as a real waveguide circuit used by propagating light. However, the dummy circuit does not necessarily have to have the exact same configuration. A configuration according to a real waveguide circuit as shown in FIG. 5A may be used, and a pattern having a very simple shape as shown in FIG. 5B may be used.

In the optical switch array in which a plurality of 2 × 2 optical switches of this embodiment are integrated, one dummy element is arranged on each side. Instead of using one dummy element, only a part of the dummy element is used). Although the number of dummy waveguides does not exceed a large number, the size of the entire chip becomes large.
The size was determined in consideration of the size of the (two-optical switch) and the range of influence of the circuit element on the periphery during the manufacturing process.

In this embodiment, the effect has been demonstrated with an optical switch having a simple configuration. This optical switch is, for example, a cross-type 2 × 2 switch that is strong against manufacturing errors and can stably obtain an optical extinction ratio. But of course it is good.

Further this time, 2 × 2 is an optical switch described <br/> as an example, the 2 × 2 optical switch a plurality integrated to constituted optical switch, for example, matrix light N × M It is obvious that the present invention can be applied to switches (N and M are positive integers) as they are. Further, a circuit using optical interference, for example, an asymmetric MZ interferometer, a ring interferometer,
It goes without saying that the present invention is similarly effective for a waveguide grating, an arrayed waveguide grating, and the like.

In the above embodiment, the optical switch has been described based on quartz-based glass on a silicon substrate. However, the uniformity can be improved with other materials and other manufacturing methods (diffusion method, low-temperature film manufacturing method). It is clear from the above description that the present invention is essential as a means for achieving this. Therefore, it is obvious that the present invention can be applied to, for example, a plastic optical waveguide, an ion diffusion type waveguide, and a lithium niobate-based optical waveguide provided with an optical phase shifter using an electro-optic effect.

[0031]

As described above in detail with reference to the embodiments, the optical waveguide circuit formed on the substrate is partially
At least one array of optical interferometers arranged in parallel
In the optical waveguide circuit equipped with
Around the optical interferometer, the optical interferometer array and the waveguide pattern density
, The influence of the pattern around the optical circuit that occurs during fabrication can be reduced as much as possible by the circuit layout using the dummy waveguide pattern of the present invention, and the optical path length difference is reduced. it can.

As a result, the present invention can produce a waveguide type optical interferometer circuit with an accurate optical path length, which is extremely effective for practical use.

[Brief description of the drawings]

FIG. 1 is a diagram showing a structure of an optical switch array in which a plurality of 2 × 2 optical switches according to a first embodiment of the present invention are integrated.

FIG. 2 is a diagram showing a structure of a conventional optical switch array in which a plurality of 2 × 2 optical switches are integrated.

FIG. 3 is a diagram illustrating a convex process which is one of the optical waveguide circuit processes.

FIG. 4 is a diagram illustrating a concave process which is one of the optical waveguide circuit processes.

FIG. 5 is a diagram showing a structure of an optical switch array in which a plurality of modified 2 × 2 optical switches according to the first embodiment of the present invention are integrated.

[Explanation of symbols]

 Reference Signs List 1 silicon substrate 2 waveguide core 3 cladding 4 channel waveguide core 5 slab waveguide core 6 lower cladding layer 7 upper cladding layer 8 waveguide core layer 11a, 11b input waveguide ends 12a, 12b output waveguide end 13 directional coupling 14 Thin film heater (phase shifter) 21, 22, 23 2 × 2 optical switch 24 Dummy 2 × 2 optical switch 25 Dummy waveguide circuit based on 2 × 2 optical switch 26 Simplifies 2 × 2 optical switch Dummy waveguide circuit 30 slab waveguide

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Akio Sugita 3-19-2 Nishi Shinjuku, Shinjuku-ku, Tokyo Japan Telegraph and Telephone Corporation (56) References JP-A-6-67041 (JP, A) JP-A-3-265802 (JP, A) JP-A-7-63934 (JP, A) JP-A-5-93813 (JP, A) JP-A-7-56032 (JP, A) (58) Int.Cl. ⁷ , DB name) G02B 6/12-6/14

Claims (6)

(57) [Claims] 1. A part of an optical waveguide circuit formed on a substrate
The number of optical interferometer rows in which optical interferometers are
The optical interferometer array,
Around the optical interferometer located at the end, the optical interferometer row
A dummy waveguide pattern with the same waveguide pattern density is provided.
Optical waveguide circuit, wherein a was e. 2. An optical interferometer array and a waveguide pattern density
The same dummy waveguide pattern is equal to the optical interferometer row.
Contractors characterized by having the same or similar shape
The optical waveguide circuit according to claim 1. Wherein the optical interferometer, the serial that the two directional couplers and Mach-Zehnder interferometer type 2 × 2 optical switch composed of optical phase shifters to claim 2, wherein
On-board optical waveguide circuit. 4. The optical waveguide circuits of claim 1, 2 or 3 in which the core portion and the cladding layer is characterized by comprising the silica based glass comprised mainly of SiO ₂ in the optical waveguide. 5. A method in which a lower clad layer and a core layer are formed on a substrate, the core layer other than a waveguide core through which light propagates is removed, and an upper clad layer is further formed. optical waveguide circuits according to claim 1, 2 or 3, characterized in that it is configured. 6. After forming a lower clad on a substrate, forming a groove serving as a waveguide core through which light propagates in the lower clad, filling the groove with the waveguide core, and further forming an upper clad layer. optical waveguide circuits according to claim 1, 2 or 3, characterized in that has a fabricated structure by.