JP3275758B2 - Waveguide type optical circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical circuit using a single-mode optical waveguide used in the field of optical communication and the like. The present invention relates to an optical circuit in which correction (trimming) eliminates the need for bias power for compensating an optical path length error during operation of the optical circuit.

[0002]

2. Description of the Related Art In recent years, with the spread of multimedia communication including high bit rate communication of moving images and the like, there is a strong demand for higher capacity and more sophisticated communication networks as well as higher capacity. There is no doubt that optical communication technology will play an important role in this realization, and most of the communication lines in the relay communication network have already been replaced by optical fiber communication. The optical communication network currently laid is point-to-point optical communication that individually connects nodes, but in the future, optical signals will be converted without converting electrical signals between a plurality of nodes including an access network. It has been desired to develop an optical communication network having a network structure that connects as it is.

The key components required for the optical communication system include an optical amplifier, an optical branching / coupling device, an optical multiplexer / demultiplexer, an optical switch, and the like. Among them, an optical switch and an optical multiplexer / demultiplexer are one of important components used in an optical line switching device represented by an optical cross-connect device. Among various types of optical components, waveguide type optical components are expected to be excellent optical components in terms of mass productivity, miniaturization, and the like. Above all, quartz-based optical waveguides fabricated on silicon substrates have features such as low loss, excellent stability, and excellent compatibility with optical fibers, and are the leading optical waveguides constituting practical optical circuits. It is attracting attention as a means of realization.

FIG. 2 shows an example of an object of the present invention.
An example of a × 2 optical switch is shown. 2A is a plan view of the above-described optical circuit, FIG. 2B is a cross-sectional view taken along the line AA ′ of FIG. 2A, and FIG. 2C is B of FIG. 2A. It is sectional drawing which followed the -B 'line. In the figure, 1 is a silicon substrate, 2 is a core portion made of quartz glass embedded in a cladding layer 3, 3
Is a cladding layer made of quartz glass, and 14 and 15 are thin film heaters formed on the surface of the cladding layer 3 above the core portion 2.

The 2 × 2 optical switch is a Mach-Zehnder optical interferometer circuit composed of two 3 dB directional couplers 13 and thin film heaters 14 and 15. Optical path length difference | Δ of two waveguides connecting two directional couplers 13
L _opt | is depending on the application, a zero (| ΔL _opt | = 0) or signal light one-half of a wavelength _{(| L o pt | = λ} / 2) is designed like. FIG. 2A shows a configuration when | ΔL _opt | = 0.

Hereinafter, the switching operation will be described. When the optical path length difference is designed to be zero, and when the thin film heater 14 is not energized (cross state, OFF), the signal light entering from the input waveguide end 11b is output from the output waveguide end 12a by a known interference principle. And the signal light entering from the input waveguide end 11a propagates to the output waveguide end 12b. When one thin-film heater 14 (driving phase shifter) is energized (bar state, ON) and the optical path length difference is changed by half of the signal light wavelength by the thermo-optic effect, the input waveguide Edge 1
1b is guided to the output waveguide end 12b,
The signal light entering from the input waveguide end 11a is output from the output waveguide end 1
2a. When the optical path length difference is designed to be half of the signal light wavelength, the operation is performed with the cross / bar switched.

A 2 × 2 optical switch using this silica-based optical waveguide is manufactured by the method shown in FIG. First, as shown in FIG. 3B, the lower cladding layer 4 and the waveguide core layer 6 are formed on the silicon substrate 1 shown in FIG. 3A by the flame hydrolysis reaction deposition technique. Next, as shown in FIG. 3 (c), only a portion which will later become the waveguide core 2 is left.
Unnecessary portions are removed by a reactive ion etching technique. Subsequently, as shown in FIG. 3D, the upper clad layer 5 is formed again by the flame hydrolysis reaction deposition technique,
Finally, as shown in FIG. 3 (e), the thin film heaters 14 and 15 to be phase shifters (phase adjusters) and the electric wiring are formed on the upper clad by the vacuum evaporation technique and the wet etching technique. Silica optical waveguide is Si
It is manufactured by a known combination of a glass film deposition technique using a hydrolysis reaction of a source gas such as Cl ₄ or GeCl ₄ , a reactive ion etching technique, and wet etching.

In a 2 × 2 switch actually manufactured, the optical path length difference between the two waveguides does not become a desired value due to a manufacturing error, but is slightly changed, that is, there is an optical path length error.

Until recently, power (bias power) was slightly applied to the thin film heater 14 or 15 even at the time of OFF to compensate for this. However, such bias power application had the following problems. . First, since the bias power needs to be set in accordance with the amount of shift of each switch, the driving circuit becomes complicated. In addition, when the number of switches in the OFF state is larger than the number of switches in the ON state, such as a matrix switch, although the bias power is small, the total consumption of the bias power is ignored in the total power consumption. Become too large.

As a means for permanently correcting the optical path length error, a thin film heater (trimming phase shifter) has recently been used.
Method of using a phenomenon in which the effective refractive index of the waveguide is permanently changed by locally heating the waveguide at a high temperature with relatively large power (about 5 W in the case of a thin film heater of 4 mm × 40 μm) using No. 15. Has been developed (for example,
-42538). By using this optical path length trimming method, the above optical path length error can be compensated, and operation with no bias power becomes possible.

[0011]

However, in the optical path length trimming method for a 2 × 2 optical circuit as described above,
There were the following problems. The variation of the optical path length is basically random, and the optical path length difference ΔL _opt (= [optical path length of the waveguide on the driving phase shifter 14 side] − [optical path length of the waveguide on the trimming phase shifter 15 side] ) May be larger or smaller than the design value.

In the optical path length trimming method, the optical path length is increased.
ΔL _optIs more than the design value
When it becomes smaller, the drive phase shifter 14
Will be performed. As mentioned above, the optical path length Trimin
In the method, several times more power than normal driving power is applied.
The heater used for trimming is easy to break.
You. Therefore, the drive phase shifter 14 is trimmed.
There is a problem from the viewpoint of long-term reliability.

As one method for avoiding this, as shown in FIG. 4, it is conceivable to separately provide a trimming heater 15a in addition to the driving phase shifter 14a on the waveguide on the driving phase shifter side. Similarly, the trimming phase shifter 15 is placed on the waveguide on the trimming phase shifter side.
In addition to b, a drive phase shifter 14b is provided. However, in this case, as apparent from FIG. 4, there is a problem that the total circuit length is increased by the provision of the trimming heater. The present invention has been made in view of the above prior art, and has as its object to provide a high-phase-precision optical circuit that avoids performing a trimming process with the driving phase shifter 14 and has excellent long-term reliability. Is what you do.

[0014]

According to a first aspect of the present invention, there is provided a light emitting device comprising: a substrate formed by using an optical waveguide;
In a waveguide type optical circuit including a two-input two-output Mach-Zehnder interferometer composed of two directional couplers and a phase shifter, two waveguides linking the two directional couplers are provided. One of the waveguides is loaded with a driving phase shifter, and the other waveguide is locally heated to obtain an effective refractive index of the waveguide.
And a trimming phase shifter for permanently correcting the optical path length error caused by the manufacturing error is loaded, and the optical path length of the waveguide on which the driving phase shifter is loaded is adjusted from a desired value to a manufacturing error. Is designed to be longer by the amount of variation of the optical path length error caused by the above, and the effective refractive index of the waveguide on the side where the trimming phase shifter is loaded is permanently increased by the trimming phase shifter to reduce the optical path length difference to a desired value. Value.

Further, the Mach-Zehnder interferometer is 2 ×
A two-optical switch, wherein the driving phase shifter is a switching phase shifter. Further, the core portion and the cladding layer in the optical waveguide are made of SiO _2.
Characterized by being made of quartz-based glass whose main component is
Before SL phase shifter for trimming, characterized in that a thin film heater.

[Operation] According to the present invention, the waveguide loaded with the driving phase shifter is compared with the waveguide loaded with the trimming phase shifter, and the variation in the optical path length error caused by the manufacturing error from the desired optical path length. Since the optical path length is set to be large, even if an optical path length error occurs due to a manufacturing error, the waveguide loaded with the driving phase shifter always has a value larger than a desired optical path length. Therefore, it is possible to avoid performing the trimming process with the driving phase shifter.

[0017]

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,
Moreover, it is because of excellent matching with the quartz optical fiber. However, the invention is not limited to these combinations.

[Embodiment 1] 2 × according to the embodiment of the present invention
A two-optical switch is shown in FIG. In this embodiment, main components such as components and their arrangement are the same as those of the conventional 2 × 2 optical switch shown in FIG.

The difference from the conventional configuration is that a desired optical path length difference ΔL _opt (= [optical path length of the waveguide on the driving phase shifter 14 side] − [optical path length of the waveguide on the trimming phase shifter 15 side]) ), The designed waveguide length difference ΔL is ΔL
= (ΔL _opt + α) / n, and the driving phase shifter 1
The point is that the length of the waveguide on the fourth side is designed and manufactured to be slightly longer. Here, α is a variation amount of an optical path length error caused by a manufacturing error, and n is an effective refractive index of the waveguide.

The 2 × 2 optical switch of this embodiment has a thickness of 1 m.
m and 4 inches in diameter on a silicon substrate. As before, the quartz-based waveguide is fabricated by combining the deposition technique of the quartz-based glass film using the hydrolysis reaction of the raw material gas such as SiCl ₄ and GeCl ₄ with the reactive ion etching technique, and the thin-film heater is vacuum-deposited. It was produced by a 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 heaters 14 and 15 is 0.1 μm in thickness and 40 μm in width.
m, length 4 mm. The interval between the two waveguides connecting the two directional couplers 13 constituting the Mach-Zehnder interferometer circuit was set to 250 μm. Desired optical path length difference Δ
L _opt was set to zero. α was 0.1 μm.

The chip on which the 2 × 2 optical switch is manufactured is cut out by dicing, a heat sink is provided below the silicon substrate, and a single mode fiber is connected to the input / output waveguide. A power supply lead was connected to 15 to make a 2 × 2 optical switch module.
This time, 256 2 × 2 optical switch modules were manufactured.

When the bias power in the cross state in the optical switch module was measured, the actual optical path length difference ΔL _opt was larger than zero in all 256 switch modules.

Next, in the other thin film heater other than the drive phase shifter 14, that is, the trimming phase shifter 15, a power several times as large as the drive power (about 5 W) is applied to locally heat the waveguide. Then, a trimming process was performed. Optical path length error amount to be compensated (for this switch, Δ
L _opt ) varies depending on the switch module, so the heating time was adjusted and selected as appropriate, and the trimming process was performed so that ΔL _opt = 0, which is the desired optical path length difference, could be accurately obtained.

As described above, the optical path length error can be compensated only by the trimming phase shifter 15 without using the driving phase shifter 14, and a 2 × 2 optical switch module with no bias power can be completed. done.

By applying an appropriate power of about 350 mW to the driving phase shifter 14, the switch was switched to a bar state, and a switching operation was confirmed. The ON / OFF extinction ratio at this time was about 25 dB. Further, even in the continuous energizing operation for about 8000 hours, no problem such as disconnection of the driving phase shifter 14 occurred, and it was confirmed that long-term reliability was ensured.

The desired optical path length difference is ΔL _opt = −λ /
In the case of No. 2, it was similarly prepared and measured. in this case,
The waveguide length difference in design was ΔL = (− λ / 2 + α) / n. As a result, as in the case of ΔL _opt = 0, the optical path length error can be compensated only by the trimming phase shifter 15 without using the driving phase shifter 14, and the long-term reliability-free bias power 2 × 2 optical switch module was completed.

In this embodiment, the effect has been demonstrated with a simple 2 × 2 optical switch.
It goes without saying that the same result can be obtained even in a large-scale switch in which a large number of × 2 optical switches are integrated. In this case, the power consumption of the heater can be significantly reduced. Normal,
The bias power at the time of OFF is about 1/7 of the power at the time of ON. Therefore, for example, in the case of an 8 × 8 matrix switch, in the normal operation state, eight switches in the ON state, OF
Since there are 56 switches in the F state, it can be easily understood that the total power consumption for driving the switch heaters is reduced to about half by the trimming process.

Further, although the optical switch has been described in the present embodiment, it is obvious that the present invention can be applied to optical components of a waveguide type interferometer such as a waveguide type Mach-Zehnder interferometer and a wavelength filter having substantially the same circuit configuration. It is. Although the optical circuit based on quartz glass on the silicon substrate has been described in the above embodiment, other materials and other manufacturing methods (diffusion method,
It is clear from the above description that the present invention is also essentially excellent as a means for separating the phase shifter for trimming and the phase shifter for driving also in the low-temperature film manufacturing method). Therefore, it should be noted that the present invention can be applied to, for example, a plastic optical waveguide, a polymer waveguide, an ion diffusion waveguide, and the like.

[0030]

As described above in detail with reference to the embodiment, the waveguide loaded with the driving phase shifter is compared with the waveguide loaded with the trimming phase shifter.
Since the optical path length error caused by the manufacturing error is set to be larger than the desired optical path length by about the same amount, even if the optical path length error occurs due to the manufacturing error, the waveguide loaded with the driving phase shifter is larger than the desired optical path length. It will always be a large value. Therefore, the optical path length error can be compensated only by the trimming phase shifter without using the driving phase shifter, and a long-term reliable optical circuit module with no bias power can be completed. Therefore, the present invention is extremely effective in putting a small waveguide type optical circuit into practical use.

[Brief description of the drawings]

FIG. 1 is a structural diagram of a 2 × 2 optical switch according to one embodiment of the present invention.

FIG. 2 is a basic structural diagram of a 2 × 2 optical switch which is an example of an object of the present invention.

FIG. 3 is an explanatory view showing a manufacturing process of the optical waveguide.

FIG. 4 is a structural view of a 2 × 2 optical switch in which a switching thin-film heater and a trimming thin-film heater are respectively mounted on both arms of a Mach-Zehnder interferometer.

[Explanation of symbols]

Reference Signs List 1 silicon substrate 2 waveguide core 3 clad 4 lower clad layer 5 upper clad layer 6 waveguide core layer 11a, 11b input waveguide end 12a, 12b output waveguide end 13 directional coupler 14, 14a, 14b thin film heater (drive) Phase shifter) 15, 15a, 15b Thin film heater (trimming phase shifter)

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Yasuyuki Inoue Nippon Telegraph and Telephone Corporation 3-9-1-2 Nishishinjuku, Shinjuku-ku, Tokyo (56) Reference JP-A-4-352133 (JP, A) JP-A-63-182608 (JP, A) JP-A-2-130503 (JP, A) JP-A-3-267902 (JP, A) Patent 3223959 (JP, B2) (58) Fields investigated (Int. Cl. ⁷ , DB name) G02F 1/00-3/00 G02B 6/12-6/14 JICST file (JOIS) WPI (DIALOG)

Claims (4)

(57) [Claims] 1. An optical waveguide formed on a substrate using an optical waveguide.
In a waveguide type optical circuit including a two-input two-output Mach-Zehnder interferometer composed of two directional couplers and a phase shifter, two waveguides linking the two directional couplers are provided. A driving phase shifter is loaded on one of the waveguides, and the other waveguide is locally heated to realize the waveguide.
A trimming phase shifter that increases the effective refractive index and permanently corrects the optical path length error caused by the manufacturing error is loaded, and the optical path length of the waveguide on which the driving phase shifter is loaded is set to a desired value. From the optical path length error caused by the manufacturing error, and the trimming phase shifter permanently increases the effective refractive index of the waveguide on the side where the trimming phase shifter is loaded, thereby reducing the optical path length difference. Is a desired value. 2. The waveguide type optical circuit according to claim 1, wherein the Mach-Zehnder interferometer is a 2 × 2 optical switch, and the driving phase shifter is a switching phase shifter. 3. The waveguide type optical circuit according to claim 1, wherein the core portion and the cladding layer in the optical waveguide are made of silica-based glass containing SiO ₂ as a main component. 4. A phase shifter for the trimming, according to claim 1, 2 or 3 waveguide type optical circuit wherein a formed of a thin film heater.