JP5628091B2 - Optical waveguide, optical waveguide interferometer circuit, and phase adjustment method of optical waveguide interferometer circuit - Google Patents

Description

  The present invention relates to an optical waveguide element (optical waveguide circuit) that includes an optical waveguide constituting an interferometer and is used in the field of optical communication or optical information processing, and in particular, an optical waveguide that can adjust a phase difference with high accuracy and permanently. And an optical waveguide interferometer circuit and a phase adjustment method of the optical waveguide interferometer circuit.

Interferometer circuits composed of optical waveguides are used in current optical communication networks. For example, an AWG (Arrayed Waveguide Grating) is a typical device using multi-beam interference, and is an important device that supports WDM (Wavelength Division Multiplexing) transmission.
In addition to AWG, optical waveguide circuits consisting of optical waveguides include optical modulators, phase shifters, polarization splitters (PBS), and polarization beam combiners (PBC) on semiconductor substrates. ) Etc. monolithically integrated, and a Mach-Zehnder interferometer.

  The most difficult point in manufacturing these interferometer circuits is that they are manufactured so that their optical characteristics such as their transmission peaks coincide with the wavelength grid. It must be manufactured by adjusting the transmission spectrum peak to the wavelength (frequency) determined by standards such as ITU-T (International Telecommunication Union Telecommunication Standardization Sector).

In many cases, these optical waveguide interferometer circuits are manufactured by a wafer process. However, due to a manufacturing error or the like, the characteristics do not necessarily become the desired characteristics.
In other words, the optical path length of the optical waveguide interferometer circuit can be obtained by the product of the optical waveguide length and the refractive index of the optical waveguide. In reality, it is unavoidable that a deviation occurs due to a process error during mounting.

  Therefore, there is a trimming technique (characteristic correction technique) that performs inspection after manufacture and changes characteristics irreversibly by some method. That is, there is a technique for adjusting the phase (optical path length) of the optical waveguide, and a conventional example thereof will be described below.

  In the case of an interferometer circuit made of a quartz-based material, a common method that is often used is adjustment by laser irradiation (see Patent Document 1 (Japanese Patent Application Laid-Open No. 2006-243011)). This technique is a method of changing the refractive index by irradiating a part of the optical waveguide with laser light after the optical waveguide is formed.

  The trimming technique by laser irradiation shown in Patent Document 1 is a very effective means for an optical waveguide made of glass. However, in the case of a circuit composed of an optical waveguide made of another semiconductor or the like, the physical phenomenon that may occur due to laser irradiation is different, and trimming may not be possible. In many cases, semiconductors absorb light and are not suitable for adjusting the phase (refractive index) of a semiconductor optical waveguide.

  In the case of an optical waveguide having a low refractive index, it is known that a groove is formed by cutting a part of the optical waveguide and the refractive index is adjusted by filling the groove with a resin having a refractive index different from that of the optical waveguide. (See Patent Document 2 (Japanese Patent Laid-Open No. 2009-163013)).

  The technique disclosed in Patent Document 2 is effective when the relative refractive index difference (the refractive index difference between the clad and the core) that forms the core is relatively small as in a silica-based waveguide. However, in semiconductor optical waveguide circuits where the refractive index difference is large, the radiation loss when crossing a part of the optical path is not negligible, so it can be applied to adjust the phase (refractive index) of the semiconductor optical waveguide. It was not appropriate.

  In the case of a semiconductor optical waveguide, the relative refractive index difference is generally large, and cutting of the optical path results in a very large loss. In order to prevent these, in the case of a semiconductor optical circuit, it has been proposed to replace a part of the optical waveguide as an adjustment region with a different material (see Patent Document 3 (Japanese Patent Laid-Open No. 2006-222305)).

  However, in the first place, the method shown in Patent Document 3 must produce optical waveguides of different materials on the same substrate, and the load applied for adjustment is large, which is applied to the phase (refractive index) adjustment of the semiconductor optical waveguide. It was not appropriate.

In addition, as a method for adjusting the refractive index of an interferometer circuit composed of an optical waveguide, when the propagating light oozes out from a part of the core, the refractive index is changed by dripping and curing a resin or the like on the surface. Attempts to perform phase adjustment have also been proposed.
These are excellent in that the refractive index can be changed and the phase can be adjusted without cutting the optical path, but there are many problems.

A problem with this method is the area of the resin to be dropped. Although the dripping length (the length of the portion covered with resin) is not controlled, dripping and curing may be performed and the length adjusted by some method (laser ablation, etc.) to be removed. The increase in itself is remarkable.
In addition, there is a method of controlling the dropping length by using an ink jet device or the like with a high-precision amount, but the spread of the resin varies depending on the surface state of the optical circuit to be trimmed no matter how much the dropping amount is controlled. There's a problem.
In addition, a large capital investment burden is required in view of the apparatus itself for controlling the high-precision dropping and the adjustment throughput. In the case of a semiconductor optical circuit, the circuit is very small compared to them because the relative refractive index difference is large and the bending radius is small compared to an optical waveguide made of quartz-based material or lithium niobate crystal. In the case of such a circuit, there arises a problem that the resin is dropped in an unnecessary portion or a direction in which the characteristics are deteriorated, regardless of how the resin dropping amount is controlled.
Therefore, this method is also not suitable for application to the phase (refractive index) adjustment of the semiconductor optical waveguide.

JP 2006-243011 A JP2009-163013 JP 2006-222305 A

  As described above, it has been difficult to adjust the phase of the optical waveguide interferometer circuit including the optical waveguide with high accuracy and permanently. In particular, such a problem is remarkable in an optical waveguide interferometer circuit formed of a semiconductor optical waveguide.

  An object of the present invention is to provide an optical waveguide, an optical waveguide interferometer circuit, and a phase adjustment method for the optical waveguide interferometer circuit that can perform phase adjustment with high accuracy in view of the above-described conventional technology.

The configuration of the optical waveguide of the present invention that solves the above problems is as follows.
In a ridge type or mesa type optical waveguide formed on a substrate, the waveguide width is set so that the propagating light field oozes out of the optical waveguide.
A phase adjustment groove formed in the specific section by filling a portion of the groove formed along the optical waveguide with a material for backfilling except for a specific section along a predetermined longitudinal direction;
Refractive index is different from the material constituting the optical waveguide, and the phase adjusting material filled in the phase adjusting groove for phase adjustment,
Equipped with a,
The phase adjustment groove is formed at a plurality of locations along the longitudinal direction of the groove,
The intervals between the plurality of phase adjustment grooves are unequal .

The configuration of the optical waveguide of the present invention is as follows:
It plurality of said phase adjusting grooves, it is unequal-length length,
Or, more of the phase adjustment grooves are unequal length length, and the refractive index of the phase adjusting material is characterized in that the same or different to be filled in each phase adjustment groove.

The configuration of the optical waveguide of the present invention is as follows:
An outflow prevention groove is formed along and adjacent to the phase adjustment groove.

The configuration of the optical waveguide interferometer circuit of the present invention is as follows:
At least two couplers;
And at least two optical waveguides for connecting the coupler.

The configuration of the optical waveguide interferometer circuit of the present invention is as follows:
In the groove, portions adjacent to each other in the vicinity of the coupler are filled with a structure that separates both grooves.

The configuration of the phase adjustment method of the optical waveguide interferometer circuit of the present invention is as follows:
Adjusting the length and number of the phase adjustment grooves filled with the phase adjustment resin so as to obtain predetermined optical characteristics while measuring the characteristics of the optical waveguide interferometer circuit or after measurement. And

  According to the present invention, the phase adjustment groove is formed along the optical waveguide constituting the optical waveguide interferometer circuit, and the phase adjustment groove having a refractive index different from that of the optical waveguide is filled into the phase adjustment groove. In addition, the phase of the optical waveguide interferometer circuit can be easily adjusted.

It is a figure which shows the optical waveguide interferometer circuit which concerns on Example 1 of this invention, (a) is a top view, (b) is BB sectional drawing of (a), (c) is C- of (a). C sectional drawing, (d) is DD sectional drawing of (a). It is a characteristic view which shows the relationship between a waveguide width and an optical confinement rate. In Example 1, it is a characteristic view which shows the relationship between the wavelength of light, and the transmittance | permeability before filling after filling with the resin for phase adjustment. It is a figure which shows the modification of Example 1, (a) is a top view, (b) is BB sectional drawing of (a), (c) is CC sectional drawing of (a), (d). FIG. 2D is a sectional view taken along the line DD in FIG. In the modification of Example 1, the characteristic view which shows the relationship between the wavelength of light and the transmittance | permeability before filling after filling with the resin for phase adjustment. It is a figure which shows the structure in the middle of manufacture of the optical waveguide interferometer circuit of this invention, (a) is a top view, (b) is BB sectional drawing of (a). It is a figure which shows the structure in the middle of manufacture of the optical waveguide interferometer circuit of this invention, (a) is a top view, (b) is BB sectional drawing of (a), (c) is C- of (a). It is C sectional drawing. It is a figure which shows the optical waveguide interferometer circuit which has arrange | positioned the phase adjustment groove | channel in the curve part, (a) is a top view, (b) is BB sectional drawing of (a), (c) is C of (a). It is -C sectional drawing. It is a characteristic view which shows the relationship between the wavelength of light and the transmittance | permeability in the optical waveguide interferometer circuit which has arrange | positioned the phase adjustment groove | channel in the curve part, (a) is before filling the phase adjustment resin into one phase adjustment groove | channel, Characteristic diagram showing the relationship between the wavelength and transmittance of light after filling, (b) is the relationship between the wavelength and transmittance of light before and after filling the phase adjusting resin in all phase adjusting grooves FIG. It is a figure which shows the optical waveguide interferometer circuit based on Example 2 of this invention, (a) is a top view, (b) is an enlarged view which shows the (gamma) part of (a), (c) is (gamma) of (a) It is an enlarged view which shows the state provided with the resin structure in the part. It is a figure which shows the optical waveguide interferometer circuit which concerns on Example 3 of this invention, (a) is a top view, (b) is BB sectional drawing of (a).

  Hereinafter, embodiments of the present invention will be described in detail based on examples.

In this example, a delay interferometer composed of a Mach-Zehnder interferometer was designed and manufactured, and an optical waveguide interferometer circuit was produced using the element, and trimming was performed.
A schematic diagram of the manufactured optical waveguide interferometer circuit 10 is shown in FIG. In FIG. 1, (a) is a plan view, (b) is a sectional view taken along line BB in (a), (c) is a sectional view taken along line CC in (a), and (d) is (a) It is DD sectional drawing of).

As shown in these drawings, in the optical waveguide interferometer circuit 10 of this embodiment, two MMI (Multimode Interference) type couplers 21 and 22 and an optical waveguide connecting both couplers 21 and 22 are used. The upper arm waveguide 31 and the lower arm waveguide 32, the input optical waveguides 33 and 34, and the output optical waveguides 35 and 36, which form a Mach-Zehnder interferometer.
The upper and lower arm waveguides 31 and 32 are provided with a delay amount on one side (upper arm waveguide 31) so as to form a delay interferometer. When using an interferometer as a filter, add a delay amount. In this embodiment, a delay amount is provided in the interferometer in order to easily obtain the effect of trimming with a wavelength spectrum.

  The upper and lower arm waveguides (optical waveguides) 31 and 32 and the input / output optical waveguides 33 to 36 are high-mesa type in this example, and these optical waveguides 31 to 36 are formed on a substrate 301 with a thin film forming technique. A lower clad 302, a core 303, and an upper clad 304 are formed using a photolithography technique and an etching technique.

In addition, the waveguide widths of the upper and lower arm waveguides (optical waveguides) 31 and 32 are set so that the field of light propagating through the optical waveguides 31 and 32 oozes out of the optical waveguides 31 and 32. .
When the propagating light field is constant, as shown in FIG. 2, as the waveguide width of the optical waveguide becomes narrower, the optical confinement ratio becomes smaller. It is known to ooze out of the waveguide. For this reason, if the waveguide width is defined in consideration of the material characteristics of the optical waveguides 31 and 32, the propagating light field can be oozed out of the optical waveguides 31 and 32.

Further, a groove 41 and a groove 42 are formed along the upper arm waveguide 31, and the upper arm waveguide 31 is sandwiched between the groove 41 and the groove 42. Moreover, the groove 41 is also formed along the side surfaces of the couplers 21 and 22 and the input / output waveguides 33 and 35 by extending both ends thereof.
A groove 43 and a groove 44 are formed along the lower arm waveguide 32, and the lower arm waveguide 32 is sandwiched between the groove 43 and the groove 44. Moreover, the groove 44 is formed along the side surfaces of the couplers 21 and 22 and the input / output waveguides 34 and 36 by extending both ends thereof.
A groove 45 is formed between the input arm waveguide 33 and the input arm waveguide 34, and a groove 46 is formed between the output arm waveguide 35 and the output arm waveguide 36.
These grooves 41 to 46 are formed simultaneously with the formation of the optical waveguide by etching when the optical waveguide is formed.

Of the grooves 41 and 42 formed along the upper arm waveguide 31, a portion along the predetermined longitudinal direction excluding the section α, and among the grooves 43 and 44 formed along the lower arm waveguide 32, A portion along the predetermined longitudinal direction excluding the section β is filled with a backfilling resin (backfilling material) 51. As the backfilling resin 51, for example, polyimide can be used. However, the backfilling material is not limited to polyimide, and other organic materials or inorganic materials may be used.
In this example, the backfilling resin 51 fills the grooves 45 and 46, and further, the upper surfaces of the couplers 21 and 22 and the upper surfaces of the upper and lower arm waveguides 31 and 32 excluding the sections α and β. It is also given to.

  Thus, in order to fill the portion of the grooves 41 to 44 excluding the sections α and β with the backfilling resin 51, the portion of the section α that is not filled with the backfilling resin 51 in the grooves 41 and 42 is a groove. The phase adjustment grooves 41a and 42a are left and the portions of the section β of the grooves 43 and 44 that are not filled with the backfill resin 51 remain as grooves and are formed as phase adjustment grooves 43a and 44a.

Further, the phase adjustment grooves 43 a and 44 a formed along the lower arm waveguide 32 are filled with a phase adjustment resin (phase adjustment material) 52. In this example, the phase adjusting resin 52 is also applied to the upper surface of the lower arm waveguide 32 located in the section β. As the phase adjusting resin 52, for example, a silicone resin whose refractive index is adjusted with a dopant can be used. The refractive index of the phase adjusting resin 52 is determined by upper and lower arm waveguides (optical waveguides) 31 and 32. This is different from the refractive index of the material constituting the core, particularly the material constituting the core.
Of course, it goes without saying that the phase adjusting grooves 43a and 44a are hollow grooves before the phase adjusting grooves 43a and 44a are filled with the phase adjusting resin 52 and trimmed.
The phase adjusting material is not limited to a silicone resin whose refractive index is adjusted with a dopant, and other organic materials or inorganic materials may be used.
In the example of FIG. 1, the phase adjustment grooves 41 a and 42 a are not filled with the phase adjustment resin 52.

  Thus, by filling the phase adjusting grooves 43a and 44a along the lower arm waveguide 32 with the phase adjusting resin 52, the phase of the lower arm waveguide 32 is adjusted, and the upper arm waveguide 31 and the lower arm waveguide 31 are adjusted. The phase difference of the side arm waveguide can be adjusted.

  In the present embodiment, a high mesa waveguide is assumed as an optical waveguide from which a part of the core is exposed, but the phase of the propagating light is a phase adjustment groove 41a, which is a portion into which a phase adjustment resin is inserted later. As long as it is an optical waveguide that oozes out to 42a, 43a, and 44a, it is not limited to a high mesa structure, and may be an optical waveguide such as a low mesa structure or a ridge structure.

  The principle of the actual trimming method of the optical waveguide interferometer circuit 10 composed of the Mach-Zehnder interferometer having the above configuration will be described.

  The effective refractive index n1 of the optical waveguide where the side surface of the core without resin is exposed and the side surface is air (refractive index 1) is calculated as follows: wavelength: 1.55 μm, waveguide width: 1.5 μm, band gap wavelength: 1.3 μm When the core thickness is 0.3 μm, it is estimated that n1 = 3.20733 considering only the TE polarization.

  On the other hand, when the side surface of a high-mesa optical waveguide having the same optical waveguide width is filled with a phase adjusting resin 52 having a refractive index of 1.60, the effective refractive index n2 is 3.20792 for TE polarization, which is higher than that of air. Rise.

  Consider an interferometer in which the optical waveguide of the upper arm waveguide 31 is longer by ΔL than the optical waveguide of the lower arm waveguide 32. The side surface of the optical waveguide is exposed by the upper and lower arm waveguides 31 and 32 by the length of L0, and the other portions (including ΔL) are already filled with the backfilling resin 51. think of. ΔL is appropriately set, and 96.6 μm ΔL is provided so that the order is equivalent to 200.

At this time, the phase difference Φ0 between the upper and lower arm waveguides 31 and 32 before filling the phase adjusting resin 52 is expressed by the following equation. Here, n1 is an effective refractive index when the core side surface is air, and λ is a design wavelength of 1.55 μm.

Here, only the phase adjusting grooves 43a and 44a of the lower arm waveguide 32 of the filling portion length L1 are filled with the phase adjusting resin 52 having the refractive index n2. It is assumed that L1 = 1313 μm. Then, the phase difference between the upper and lower arm waveguides 31 and 32 is given by the following equation.

In the design wavelength, when all the filling portion lengths L1 of the phase adjusting grooves 43a and 44a of the lower arm waveguide 32 are filled with the phase adjusting resin 52, the second term is approximately π from the above formula. In other words, when viewed on the wavelength spectrum, as shown in FIG. 3, the characteristic that was OFF in the initial state can be changed to the characteristic in the ON state by changing the half-wavelength characteristic.
In FIG. 3, the vertical axis indicates the transmittance (dB) of the interferometer, the horizontal axis indicates the wavelength (μm) of light input to the interferometer, the solid line indicates the characteristics before filling the phase adjusting resin, and the dotted line indicates the phase adjusting resin. The characteristic after filling is shown.

  If adjustment for one period is necessary, the variable range can be expanded by increasing the length of the phase adjustment grooves 43a and 44a. Normally, when a phase change of π or more is necessary, the phase adjusting grooves 41a and 42a of the arm waveguide 31 on the opposite side (upper side) are filled with the phase adjusting resin and adjusted to obtain the desired characteristics. It is possible.

Here, only one phase adjusting groove has been considered for the sake of explanation. However, in actual trimming work, we want to change only a minute phase. Therefore, the phase adjusting groove having the length L1 is divided into dL1 and arranged along the arm waveguide. One phase adjustment groove having a length L1 is divided into M pieces to obtain M phase adjustment grooves having a length dL1, and m pieces of phase adjustment grooves of one arm waveguide are filled with resin. In this case, the phase difference to be given is given by the following equation, and it is possible to perform trimming to approach a desired characteristic although it is discrete.

  As an example, FIG. 4 shows the case where M = 10 and the phase adjustment groove of length L1 is equally divided into 10 (dL = L1 / M). The sum of the lengths of the divided phase adjustment grooves is divided to be equal to the original length.

  That is, in FIG. 4, along the upper arm waveguide 31, for example, ten divided phase adjustment grooves 41a-1 to 41a-10 and, for example, ten divided phase adjustment grooves 42a-1 to 42a-10 are formed. For example, ten divided phase adjusting grooves 43a-1 to 43a-10 and ten divided phase adjusting grooves 44a-1 to 44a-10 are formed along the lower arm waveguide 32. In addition, in this example, the seven phase adjustment grooves 43a-1 to 43a-7 and the seven phase adjustment grooves 44a-1 to 44a-7 of the lower arm waveguide 32 are filled with the phase adjustment resin 52. The other parts are the same as those shown in FIG.

  In this case, it is possible to adjust the phase by 10π% by filling one phase adjustment groove with the phase adjustment resin 52, and one phase adjustment groove while looking at the characteristics so as to approach the desired characteristics. What is necessary is just to fill with the phase adjustment resin 52.

FIG. 5 shows the change from the initial stage when one phase adjustment groove of the lower (short side) arm waveguide is embedded, and it can be seen that a minute change can be obtained. What is necessary is just to repeat these and to obtain a desired characteristic.
If the characteristic goes too far, the characteristic can be restored to the original by filling one phase adjustment groove in the opposite (upper) arm waveguide.
In FIG. 5, the vertical axis indicates the transmittance (dB) of the interferometer, the horizontal axis indicates the wavelength (μm) of the light input to the interferometer, the solid line indicates the characteristics before filling the phase adjusting resin, and the dotted line indicates the phase adjusting resin. The characteristic after filling is shown.

Although the length dL0 of the divided phase adjusting grooves is 133.1 μm and the length of each phase adjusting groove is equal, the length of each phase adjusting groove is not necessarily equal and may be different. .
For example, if the length of the shortest phase adjustment groove is set to dL0min shorter than dL0, the stepwise change can be set more finely. If dL0min = dL0 / 5, 2π% adjustment is possible in this embodiment. Further, a phase adjustment groove twice as long as dL0 and a phase adjustment groove three times as long may be prepared.

  In particular, if the length of each phase adjustment groove (excluding the shortest phase adjustment groove) is set to an integral multiple of the length of the shortest phase adjustment groove, the adjustment work can be saved and the adjustment time can be shortened.

  In actual adjustment, the phase adjustment groove whose length is either dL0min is filled with resin first, and how much characteristic change such as spectrum occurs is observed, and the phase adjustment groove whose length is dL0min is filled up to the target. The necessary amount can be inferred from the amount of phase change.

  For example, if one phase adjustment groove having a length of dL0 min is filled and if a phase change of 14 times the phase change amount is necessary, a phase adjustment groove having a length three times that of the phase adjustment groove having a length of dL0 is required. If one is prepared, the phase adjustment groove is filled, and if one phase adjustment groove having a length of dL0 min in the arm waveguide opposite to the filling is filled, the target phase change amount can be obtained. In other words, if a phase adjustment groove having an integral multiple of the shortest phase adjustment groove is prepared, the adjustment can be completed more quickly than when three dL0s are filled.

The length of each of the other phase adjustment grooves is not limited to an integral multiple of the length of the shortest phase adjustment groove.
In other words, when a large number of phase adjustment grooves of the same length are arranged, a resonator effect is generated in which both ends of the phase adjustment groove are cavities due to refractive index modulation that occurs due to a slight difference in refractive index. The transmission intensity may be degraded by the wavelength.
However, these problems do not occur if the lengths are unevenly spaced.

  Similarly, with respect to the pitch when arranging a plurality of phase adjustment grooves, depending on the pitch, when a large number of phase adjustment grooves are arranged at equal intervals, the pitch operates as LPG (Long Period Grating), and in the wavelength region to be used. Transmission intensity may be deteriorated. That is, when there are several types of length of the phase adjustment groove, there is an effect of increasing the adjustment stage, and the number of times of resin dripping can be reduced, and an effect of improving work efficiency can be obtained. Furthermore, the effect of reducing the transmission intensity deterioration due to the resonator effect in which both ends of the phase adjusting groove are cavities can be obtained. Further, by making the pitch unequal, there is an effect of suppressing transmission intensity deterioration due to the LPG effect.

  Up to this point, it is a case where only a resin having a refractive index of n2 = 3.20785 is used as a phase adjusting resin. If necessary, N types (a plurality of types) of phase adjusting resins having different refractive indexes may be prepared. In addition to the above-mentioned M-stage phase adjustment, N × M-stage phase adjustment is possible, and the discrete adjustment can be made finer.

For example, in the above example, when one of the phase adjustment grooves whose lower arm waveguide length is dL is filled with a phase adjustment resin having a refractive index n2 = 1.45, 6.8π% Phase adjustment is possible.
If a phase adjustment resin with a refractive index of 1.60 is put in the phase adjustment groove of the upper arm waveguide and a phase adjustment resin with a refractive index of 1.45 is filled in the phase adjustment groove of the lower arm waveguide, the phase difference (1.60-1.45) dL / λ is generated, and phase adjustment of 3.2π% is possible. In other words, if several types of phase adjusting resins are prepared even if they are discrete, almost stepless refractive index modulation is possible.

  In this way, by using different phase adjusting resins having a plurality of refractive indexes, there is an advantage that phase adjustment with more adjustment steps is possible.

  In this embodiment, an asymmetric Mach-Zehnder interferometer provided with a delay amount is taken up. However, this is the same even in an isometric Mach-Zehnder interferometer with no delay amount, which is provided with an initial phase difference φ0. It is possible to adjust as follows.

Such an interferometer can be manufactured as follows.
On the InP substrate, InGaAsP having a composition adjusted so that the bandgap wavelength was 1.3 μm was grown by 0.3 μm, and on the substrate, InP serving as an overcladding was grown by 1.5 μm. For these crystal growths, MOCVD metal organic chemical vapor deposition (Metal Organic Chemical Vapor Deposition) was used.

After that, SiO ₂ as an etching mask material is formed using a sputtering method, a resist is applied on the substrate formed with SiO _2, and an optical circuit pattern is formed using a standard photolithography technique using a photomask. Was transcribed. Thereafter, the pattern was once transferred to SiO ₂ using RIE reactive ion etching (RIE). Next, the semiconductor was etched using the processed SiO ₂ pattern as a mask to produce an interferometer.

FIG. 6 shows an outline of the circuit at this time, (a) is a plan view, and (b) is a cross-sectional view taken along the line BB of (a).
As shown in this figure, by etching by RIE, grooves 41, 42, 43, and 44 are formed on both sides of optical waveguides (upper and lower arm waveguides) 31 and 32 that form interference paths. At the same time as forming 31 and 32, grooves 41, 42, 43 and 44 into which resin will enter later are formed simultaneously. In this embodiment, the optical waveguides 31 and 32 are formed with a width of 1.5 μm and an etching width of the waveguide side surface of 10 μm. The width of the optical waveguides 31 and 32 is preferably a size that allows propagating light to propagate in a single mode, but the size is not limited to this.

  Thereafter, a photosensitive polyimide serving as a resin for backfilling is applied onto the substrate on which the semiconductor has been processed as described above, and is patterned using a photolithography technique to obtain a device shape as shown in FIG. 7A is a plan view, FIG. 7B is a sectional view taken along the line BB in FIG. 7A, and FIG. 7C is a sectional view taken along the line CC in FIG.

  Here, photosensitive polyimide is used. However, after filling the grooves 41, 42, 43, and 44 with non-photosensitive polyimide or BCB (benzocyclobutene), a part using photolithography technology and RIE technology is used. May be removed.

If necessary, an inorganic substance such as SiO ₂ or Si ₃ N ₄ may be coated immediately after the semiconductor etching and immediately after the polyimide film is formed. In that case, the portion of the window where the optical waveguide is to be exposed may be protected again with a resist and the like, and the inorganic material formed on the semiconductor side surface may be removed using hydrogen fluoride or the like. If not removed, the semiconductor optical waveguide has a high confinement factor, so even if the resin is filled after production, a sufficient refractive index change cannot be obtained.

  In the present embodiment, for the sake of clarity, the case where the phase adjustment grooves 41a, 42a, 43a, and 44a are formed in a straight line portion different from the portion that gives the delay amount has been described. However, the element size is prevented from becoming large. Therefore, by arranging the phase adjusting grooves 41a, 42a, 43a, 44a in the curved portion as shown in FIG. 8, it is possible to prevent the element itself from becoming large. 8A is a plan view, FIG. 8B is a sectional view taken along line BB in FIG. 8A, and FIG. 8C is a sectional view taken along line CC in FIG.

Here, the part filled in advance with an inorganic substance or resin uses the word "filling", but this "filling" means that the part where the propagating light field has already exuded, This means that the material is filled with another material, and the phase adjusting grooves 41a, 42a, 43a, 44a are not completely filled with another material.
For example, in the case of a high-mesa waveguide, the amount of light that propagates in the lateral direction is only a few hundred nanometers. If deposited in thickness, it will not be affected by the outside. That is, it can be regarded as being filled.

The actual device characteristics are shown.
The measurement method was to cut only one-side TE polarized state by passing 1.55 μm band ASE (Amplified Spontaneous Emission) through fiber-type PBS (Polarization Beamsplitter).
After that, it is led to a tip-end fiber (tip R10μm) made of PMF (Polarization Maintaining Fiber), and is provided on the optical surface plate that holds the PMF on the end face of the sample optical waveguide placed on the sample stage where the Peltier element is installed. The XYZ stage was moved to perform alignment, and the light was guided to the element. At this time, the angle of the PMF fiber is adjusted and adjusted in advance to match the TE mode of the sample.
On the exit side, the tip spherical fiber made of SMF (single-mode fiber) is similarly aligned and aligned with the exit end face of the optical waveguide. The exit fiber was directly introduced into the spectrum analyzer and the spectrum was measured.

FIG. 9A shows the result of actually manufacturing and measuring the structure used in the above calculation. The measurement is performed at a constant temperature by driving the Peltier device on the sample stage so that the measurement temperature is 25 degrees.
In FIG. 9A, the vertical axis represents the transmittance (dB) of the interferometer, the horizontal axis represents the wavelength (μm) of light input to the interferometer, and the dotted line represents the spectrum immediately after fabrication. In this state, a silicone resin prepared by adding a dopant so as to have a refractive index of 1.60 was dropped into one phase adjustment groove (dL = 131 μm) divided into 10 equal parts of the lower arm waveguide. The dropping was performed manually using a micropivet under a microscope.

  Thereafter, the Peltier device on the sample stage was driven, heated to 120 degrees and allowed to stand for about 10 minutes to be cured. Thereafter, the temperature is adjusted so as to reach room temperature again, and the result of measurement is a solid line spectrum.

  When the obtained result was fitted with a theoretical formula and the amount of phase change was determined, a phase change of 9.8π% was recognized in terms of phase. The calculation predicted 10π%, but it is slightly different. This seems to be because the refractive index of the dripping resin slightly deviated from 1.60. However, it can be seen that the spectrum can be moved in the desired direction.

FIG. 9B shows a result obtained by dropping the resin into all of the ten lower phase adjustment grooves prepared by performing the dropping one after another and filling the resin.
It can be seen that the transmission intensity can be maximized after dropping at the wavelength at which the transmission intensity is minimum in the initial characteristics, and the phase can be adjusted by π (pi) as expected by calculation.

  When the groove for forming the high mesa waveguide and the phase adjusting groove are used in combination, the distance between the optical waveguides in the vicinity of the couplers 21 and 22 is shortened, so that the grooves of the upper and lower arm waveguides are connected at this portion. That is, FIG. 10A shows a state in which grooves 41 and 42 are formed along the upper arm waveguide (optical waveguide) 31, and grooves 43 and 44 are formed along the lower arm waveguide 32. FIG. FIG. 10B is an enlarged view of the γ portion of FIG. 10A, and it can be seen from these drawings that the grooves 42 and 43 are connected in the vicinity of the couplers 21 and 22.

  The dropping length is defined by a previously patterned inorganic or organic resin. At this time, when the phase adjusting resin is dropped on the connected portion, the resin does not flow into the opposite arm waveguide side (FIG. 10). (B) Resin structure in which at least a portion where grooves 41 and 42 for forming a high mesa waveguide are connected is formed of an inorganic or organic resin as shown in FIG. 10C. It is necessary to divide the dropping regions of the upper and lower arm waveguides 31 and 32 by the object 53. By separating, it is possible to prevent the resin from flowing into the opposite side.

11A and 11B show an optical waveguide interferometer circuit according to a third embodiment of the present invention, in which FIG. 11A is a plan view and FIG. 11B is a sectional view taken along line BB in FIG.
In this third embodiment, at least inside of each of the optical waveguides constituting the upper and lower arm waveguides forming the Mach-Zehnder interferometer (between the upper and lower arm waveguides) An outflow prevention groove is formed.

That is, the optical waveguide interferometer circuit shown in FIG. 11 is provided with the outflow prevention grooves 61, 62, 63, 64 in addition to the optical waveguide interferometer circuit shown in FIG.
More specifically, grooves 41, 42 (41 a, 42 a) are formed on both sides of the upper arm waveguide 31 along the upper arm waveguide 31, and the grooves 41, 42 ( 41a, 42a) are formed with outflow prevention grooves 61, 62 along the grooves 41, 42 (41a, 42a). Similarly, grooves 43 and 44 (43a and 44a) are formed on both sides of the lower arm waveguide 32 along the lower arm waveguide 32. Further, when viewed from the lower arm waveguide 32, the grooves 43 and 44 (43a) are formed. , 44a), outflow prevention grooves 63, 64 are formed along the grooves 43, 44 (43a, 44a).
Eventually, outflow prevention grooves 62 and 63 are formed inside the upper and lower arm waveguides 31 and 32 (between the upper and lower arm waveguides 31 and 32), and the upper and lower arm waveguides are further formed. Outflow prevention grooves 61 and 64 are formed on the outer sides of 31 and 32.
The outflow prevention grooves 61, 62, 63, 64 are formed simultaneously with the formation of the grooves 31-34.

Since the outflow prevention grooves 61, 62, 63, 64 are provided in this way, there is an effect of preventing the dropped phase adjustment resin 51 from flowing into the phase adjustment groove of the adjacent arm waveguide that is not intended. If it drops with an inkjet apparatus etc., it can drop at a more exact position. However, if there are outflow prevention grooves 61, 62, 63, and 64 that accumulate such resin, even if the resin is dripped roughly, it is possible to greatly reduce the movement to the adjacent phase adjustment groove. Even dripping is sufficient. Phase adjustment is possible without using an expensive dripping device, resulting in lower costs.
In addition, this formation may be made in the process of forming the high mesa waveguide, and it can be formed by modifying only the design, and can be realized without an additional process increase.

As in this example, when the outflow prevention grooves 61 and 64 that become a pool of resin are formed outside the grooves 41 and 42, there is an effect of preventing the resin from dripping out of the chip. There is no problem when the chip is dropped in a mounted state (in a fixed state), but when dropping before mounting, if the resin travels along the side surface and wraps around the back surface, it cannot be mounted flat.
Further, it is possible to prevent the heat conduction between the element and the lower mount from being deteriorated, and the characteristics can be maintained. For example, when these circuits are integrated in a laser, heat conduction is very important in terms of characteristics, and they can be maintained.

  The present invention can be used not only for an interferometer circuit made of a semiconductor optical waveguide but also for an interferometer circuit made of a quartz optical waveguide.

DESCRIPTION OF SYMBOLS 10 Optical waveguide interferometer circuit 21,22 Coupler 31 Upper arm waveguide (optical waveguide)
32 Lower arm waveguide (optical waveguide)
33, 34 Optical waveguide for input 35, 36 Optical waveguide for output 41, 42, 43, 44 Groove 41a, 42a, 43a, 44a Phase adjustment groove 51 Resin for backfilling 52 Resin for phase adjustment 53 Resin structure 61, 62, 63, 64 Outflow prevention groove 301 Substrate 302 Lower clad 303 Core 304 Upper clad

Claims (7)

In a ridge type or mesa type optical waveguide formed on a substrate, the waveguide width is set so that the propagating light field oozes out of the optical waveguide.
A phase adjustment groove formed in the specific section by filling a portion of the groove formed along the optical waveguide with a material for backfilling except for a specific section along a predetermined longitudinal direction;
Refractive index is different from the material constituting the optical waveguide, and the phase adjusting material filled in the phase adjusting groove for phase adjustment,
Equipped with a,
The phase adjustment groove is formed at a plurality of locations along the longitudinal direction of the groove,
An optical waveguide characterized in that intervals between the plurality of phase adjustment grooves are unequal . The optical waveguide of claim 1.
A plurality of said phase adjusting groove, the optical waveguide, wherein the length is unequal length. The optical waveguide of claim 1.
A plurality of said phase adjusting groove is unequal length length, and an optical waveguide the refractive index of the phase adjusting material is characterized in that the same or different to be filled in each phase adjustment groove. In the optical waveguide according to any one of claims 1 to 3 ,
An optical waveguide, wherein an outflow prevention groove is formed along and adjacent to the phase adjustment groove. At least two couplers;
An optical waveguide interferometer circuit comprising at least two optical waveguides according to any one of claims 1 to 4 , which connect the coupler. The optical waveguide interferometer circuit of claim 5 ,
In the optical waveguide interferometer circuit, a portion of the groove adjacent to each other in the vicinity of the coupler is filled with a structure that separates both grooves. A method for adjusting the phase of an optical waveguide interferometer circuit according to claim 5 or claim 6 , comprising:
Adjusting the length and number of the phase adjustment grooves filled with the phase adjustment resin so as to obtain predetermined optical characteristics while measuring the characteristics of the optical waveguide interferometer circuit or after measurement. A phase adjustment method for an optical waveguide interferometer circuit.

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