Optical phase modulator

Abstract

To provide an optical phase modulator that enables boosting pressure resistance.SOLUTION: A rib waveguide convex part 20 includes: a first primary part 21a; and a first connection part 21b that is extended along a cross direction crossing an extension direction from an end part in the extension direction in the first primary part 21a. The rib waveguide convex part has: a first convex part 21 that is called N-type; a second primary part 22a that has a boundary with the first primary part 21a and the first connection part 21b; a second connection part 22b that is extended along a cross direction from an end of an extension direction in the second primary part 22a, and has a boundary with the first primary part 21a; and a second convex part 22 that is called P-type. In the extension direction, let a region where the first primary part 21a and the second primary part 22a are arranged be a many-numbers-of-PN junctions depletion layer region MR, and a region where the first connection part 21b, or the second connection part 22b is arranged be a small depletion layer region SR, and then, in a small-numbers-of-PN junctions depletion layer region SR, insulation parts 60 to 62 are arranged in a part on a rib waveguide convex part 20 side of first and second slab parts 31 and 32.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to optical phase modulators. [Background technology]

[0002] Conventionally, optical phase modulators having a PN junction have been proposed (see, for example, Patent Document 1). Specifically, this optical phase modulator includes a convex portion of a rib waveguide extending in one direction, and a first slab portion and a second slab portion that are arranged on both sides of the convex portion of the rib waveguide, are connected to the convex portion of the rib waveguide, and are thinner than the convex portion of the rib waveguide. The first slab portion and the second slab portion can also be said to be recesses of the rib waveguide.

[0003] More specifically, the convex portion of the rib waveguide has a first N-type convex portion and a second P-type convex portion. The first convex portion is substantially L-shaped in plan, having a first main portion extending along the extension direction and a first connection portion extending from an end of the first main portion along a cross direction crossing the extension direction. The second convex portion is substantially L-shaped in plan, having a second main portion extending along the extension direction and a second connection portion extending from an end of the second main portion along a cross direction crossing the extension direction. The convex portion of the rib waveguide is in a state in which the substantially L-shaped first convex portion and the second convex portion are fitted together such that the first main portion and the second main portion are adjacent to each other, and the first connection portion is connected to the second main portion and the second connection portion is connected to the first main portion.

[0004] The first slab portion is N-type, disposed on the opposite side of the second main portion from the first main portion, and connected to the first main portion and the second connection portion. The second slab portion is P-type, disposed on the opposite side of the first main portion from the second main portion, and connected to the second main portion and the first connection portion.

[0005] In such an optical phase modulator, PN junctions are formed between the first main section and the second main section, between the first main section and the second connection section, between the second main section and the first connection section, between the first convex section and the second slab section, and between the second convex section and the first slab section. This is expected to increase the depletion layer that spreads when a reverse bias voltage is applied to the PN junction, improving the amount of phase modulation. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] US Patent Application Publication No. 2017 / 0315387 Summary of the Invention [Problem to be solved by the invention]

[0007] In the optical phase modulator as described above, in the intersecting direction intersecting with the extending direction, the number of PN junctions is different between the portion passing through the first and second main portions and the portion passing through the first or second connecting portion. Specifically, three PN junctions are formed in the portion passing through the first and second main portions, whereas one PN junction is formed in the portion passing through the first or second connecting portion. Hereinafter, in the extending direction, the portion having the first and second main portions is referred to as a multi-depletion layer region, and the portion having the first or second connecting portion is referred to as a low-depletion layer region.

[0008] According to the study by the inventors, it was confirmed that the number of PN junctions is smaller in the low depletion layer region than in the high depletion layer region, and therefore electric field concentration is likely to occur between the convex portion of the rib waveguide and the slab portion. Therefore, the withstand voltage of the optical phase modulator described above may decrease.

[0009] An object of the present disclosure is to provide an optical phase modulator that can increase the withstand voltage. [Means for solving the problem]

[0010] According to one aspect of the present disclosure, an optical phase modulator having a convex portion (20) of a rib waveguide includes the convex portion of the rib waveguide extending in one direction as an extension direction, and a first slab portion (31) and a second slab portion (32) that are thinner than the convex portion of the rib waveguide and are arranged in a state of being connected to the convex portion of the rib waveguide, the convex portion of the rib waveguide including a first main portion (21a) extending along the extension direction and a first connection portion (21b) extending from an end of the first main portion in the extension direction along a cross direction that crosses the extension direction, and the first convex portion (21) is N-type, a second main portion (22a) extending along the extension direction and having a boundary between the first main portion and the first connection portion, and a second main portion (22b) extending from an end of the second main portion in the extension direction along the cross direction, the first main portion and a second convex portion (22) of P type, the first slab portion being of N type, disposed on the opposite side of the first main portion to the second main portion across the first main portion, and connected to the second main portion and the first connection portion, and the second slab portion being of P type, disposed on the opposite side of the first main portion to the second main portion across the first main portion, and connected to the first main portion and the second connection portion, and in the extension direction, a region in which the first main portion and the second main portion are disposed is defined as a multi-depletion layer region (MR) and a region in which the first connection portion or the second connection portion is disposed is defined as a small-depletion layer region (SR), and in the small-depletion layer region, insulating portions (60-62) are disposed in a portion of the first slab portion on the convex portion side of the rib waveguide and a portion of the second slab portion on the convex portion side of the rib waveguide.

[0011] According to this, an insulating portion is arranged in the small depletion layer region. Therefore, when a reverse bias voltage is applied, the reverse bias voltage is divided between the depletion layer and the insulating portion in the small depletion layer region. Therefore, electric field concentration in the small depletion layer region can be suppressed, and the breakdown voltage can be improved.

[0012] The reference symbols in parentheses attached to each component indicate an example of the correspondence between the component and specific components described in the embodiments described below. [Brief description of the drawings]

[0013] [Figure 1]FIG. 2 is a plan view of the optical phase modulator according to the first embodiment. [Diagram 2] FIG. 2 is a cross-sectional view taken along line II-II in FIG. [Diagram 3] FIG. 2 is a cross-sectional view taken along line III-III in FIG. [Figure 4] FIG. 2 is a cross-sectional view taken along line IV-IV in FIG. [Diagram 5] FIG. 11 is a plan view of an optical phase modulator in a comparative example. [Figure 6] 11 is a diagram for explaining an electric field when a reverse bias voltage is applied to a small depletion layer region in an optical phase modulator of a comparative example. FIG. [Figure 7] 4 is a diagram for explaining an electric field when a reverse bias voltage is applied to a small depletion layer region of the optical phase modulator in the first embodiment. FIG. [Figure 8] FIG. 13 is a diagram showing the relationship between reverse bias voltage and leakage current. [Figure 9] FIG. 13 is a diagram showing the results of investigating the characteristics of an optical phase modulator when the length of a small depletion layer region is 2 μm. [Figure 10] FIG. 10 is a diagram showing the relationship between the ratio of the I layer length to the length of the small depletion layer region in FIG. 9, the withstand voltage, and the phase modulation ratio. [Figure 11] FIG. 13 is a diagram showing the results of investigating the characteristics of an optical phase modulator when the length of a small depletion layer region is 3 μm. [Figure 12] 12 is a diagram showing the relationship between the ratio of the length of the I layer to the length of the small depletion layer region in FIG. 11, the withstand voltage, and the phase modulation ratio. FIG. [Figure 13] FIG. 13 is a diagram showing the results of an investigation into the relationship between the arrangement of the I layer and the withstand voltage. [Figure 14] FIG. 13 is a diagram showing the results of an investigation into the relationship between the arrangement of the I layer and the withstand voltage. [Figure 15] FIG. 11 is a cross-sectional view of an optical phase modulator according to a second embodiment. [Figure 16] FIG. 11 is a cross-sectional view of an optical phase modulator according to a modified example of the second embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. In the following embodiments, parts that are the same or equivalent to each other will be denoted by the same reference numerals.

[0015] (First embodiment) The configuration of the optical phase modulator of the first embodiment will be described with reference to Figures 1 to 4. The optical phase modulator of this embodiment is suitable for use in, for example, communication devices for optical fibers.

[0016] The optical phase modulator of this embodiment is configured using a semiconductor substrate 10 that is an SOI (that is, an abbreviation of Silicon On Insulator) substrate on which a support substrate 11, an insulating film 12, and an active layer 13 are stacked. In this embodiment, the support substrate 11 is made of silicon or the like, the insulating film 12 is made of an oxide film or the like, and the active layer 13 is made of silicon or the like.

[0017] In the following description, one direction in the surface direction of the semiconductor substrate 10 is defined as the X-axis direction, a direction perpendicular to the X-axis direction and along the surface direction of the semiconductor substrate 10 is defined as the Y-axis direction, and a direction perpendicular to the X-axis direction and the Y-axis direction is defined as the Z-axis direction. The Z-axis direction is also a direction along a normal to the surface direction of the semiconductor substrate 10, and can also be referred to as the thickness direction of the semiconductor substrate 10. The Z-axis direction can also be referred to as a direction along the stacking direction of the support substrate 11, the insulating film 12, and the active layer 13.

[0018] The active layer 13 has a protruding portion 20 of a rib waveguide doped with impurities, a first slab portion 31, a second slab portion 32, a first connecting portion 41, a second connecting portion 42, a first contact portion 51, and a second contact portion 52. The active layer 13 also has an I (that is, an abbreviation of intrinsic) layer 60 which is a non-doped layer that is not doped with impurities.

[0019] Specifically, the protrusion 20 of the rib waveguide extends along the Y-axis direction in the surface direction of the semiconductor substrate 10, and has an N-type first protrusion 21 and a P-type second protrusion 22. In this embodiment, the first protrusion 21 and the second protrusion 22 have approximately the same impurity concentration. In this embodiment, the Y-axis direction corresponds to the extension direction of the protrusion 20 of the rib waveguide.

[0020] The first protrusion 21 has a first main portion 21a extending along the Y-axis direction and a first connecting portion 21b provided at one end of the first main portion 21a in the Y-axis direction and extending in the X-axis direction, and is generally L-shaped in plan. The second protrusion 22 has a second main portion 22a and a second connecting portion 22b, and is generally L-shaped in plan. In detail, the second main portion 22a extends along the Y-axis direction and is disposed so as to have a boundary with the first main portion 21a of the first protrusion 21 and a boundary with the first connecting portion 21b of the first protrusion 21. The second connecting portion 22b extends in the X-axis direction from the other end of the second main portion 22a in the Y-axis direction and is disposed so as to have a boundary with the first main portion 21a. That is, the first connecting portion 21b and the second connecting portion 22b extend in opposite directions with respect to the main portions 21a and 22a. The protrusion 20 of the rib waveguide is arranged so that the first protrusion 21 and the second protrusion 22 are fitted together, and as a whole, the protrusion 20 has a generally rectangular shape in plan view with the Y-axis direction as the extension direction. In Fig. 1, the upper side of the paper surface is one end side, and the lower side of the paper surface is the other end side. In addition, being arranged to have a boundary can be said to be arranged adjacent to each other.

[0021] The first slab portion 31, the second slab portion 32, the first connecting portion 41, the second connecting portion 42, the first contact portion 51, and the second contact portion 52 each extend along the Y-axis direction.

[0022] The first slab portion 31 is N-shaped, and is disposed on the opposite side of the second main portion 22a to the first main portion 21a, and is connected to the second convex portion 22 and the first connecting portion 21b of the first convex portion 21. Therefore, the first main portion 21a of the first convex portion 21 is connected to the first slab portion 31 via the first connecting portion 21b.

[0023] The second slab portion 32 is P-shaped, is disposed on the opposite side of the first main portion 21a to the second main portion 22a, and is connected to the first convex portion 21 and the second connecting portion 22b of the second convex portion 22. Therefore, the second main portion 22a of the second convex portion 22 is connected to the second slab portion 32 via the second connecting portion 22b.

[0024] The first slab portion 31 and the second slab portion 32 have the same impurity concentration as the first convex portion 21 and the second convex portion 22. The first slab portion 31 and the second slab portion 32 have a length in the Z-axis direction (i.e., a thickness) shorter than the convex portion 20 of the rib waveguide. For this reason, the first slab portion 31 and the second slab portion 32 can also be said to be a concave portion of the rib waveguide.

[0025] The first joint portion 41 is made of N, which has a higher impurity concentration than the first slab portion 31. + The second connecting portion 42 is a P type, and is disposed on the opposite side of the first slab portion 31 from the protruding portion 20 of the rib waveguide, and is connected to the first slab portion 31. The second connecting portion 42 is a P + The first connecting portion 41 and the second connecting portion 42 are arranged on the opposite side of the protrusion 20 of the rib waveguide across the second slab portion 32 and are connected to the second slab portion 32. The first connecting portion 41 and the second connecting portion 42 have the same length in the Z-axis direction (i.e., thickness) as the first slab portion 31 and the second slab portion 32.

[0026] The first contact portion 51 is an N-type semiconductor having a higher impurity concentration than the first connection portion 41. ++ The second contact portion 52 is a P type contact portion having a higher impurity concentration than the second contact portion 42, and is disposed on the opposite side of the first contact portion 41 from the protruding portion 20 of the rib waveguide. ++The first contact portion 51 and the second contact portion 52 are of a type that is disposed on the opposite side of the second connecting portion 42 from the protrusion 20 of the rib waveguide, and are connected to the second connecting portion 42. Although not shown in the figure, the first contact portion 51 and the second contact portion 52 are connected to electrodes and a predetermined voltage is applied. The first contact portion 51 and the second contact portion 52 have the same length in the Z-axis direction (i.e., thickness) as the protrusion 20 of the rib waveguide.

[0027] 1, in the Y-axis direction, a region where the first main portion 21a and the second main portion 22a are arranged is referred to as a multiple depletion layer region MR, and a region where the first connecting portion 21b and the second connecting portion 22b are arranged is referred to as a minimal depletion layer region SR. In other words, a region where a virtual line along the X-axis direction passes through the first main portion 21a and the second main portion 22a is referred to as a multiple depletion layer region MR, and a region where a virtual line along the X-axis direction passes through the first connecting portion 21b or the second connecting portion 22b is referred to as a minimal depletion layer region SR.

[0028] The I layer 60 is composed of a non-doped layer of the active layer 13, and is disposed in the low-depletion-layer region SR. Specifically, the I layer 60 is disposed in a portion of the first slab portion 31 on the convex portion 20 side of the rib waveguide, and in a portion of the second slab portion 32 on the convex portion 20 side of the rib waveguide, in the low-depletion-layer region SR.

[0029] The above is the basic configuration of the optical phase modulator in this embodiment. Next, the operation and effects of the optical phase modulator will be described, and the configuration will be described in more detail.

[0030] In the optical phase modulator of this embodiment, a PN junction is formed between the first main portion 21a of the first convex portion 21 and the second main portion 22a of the second convex portion 22. In addition, in such an optical phase modulator, a PN junction is formed between the first main portion 21a of the first convex portion 21 and the second connection portion 22b of the second convex portion 22, and a PN junction is formed between the second main portion 22a of the second convex portion 22 and the first connection portion 21b of the first convex portion 21. In addition, in such an optical phase modulator, PN junctions are also formed between the first convex portion 21 and the first slab portion 31, and between the second convex portion 22 and the second slab portion 32.

[0031] In the optical phase modulator of this embodiment, as shown in Fig. 2 to Fig. 4, light PL propagates mainly along the extension direction of the convex portion 20 of the rib waveguide. At this time, a depletion layer spreads at each PN junction by applying a voltage higher than that of the second contact portion 52 to the first contact portion 51, and the carrier density decreases, thereby modulating the phase of the light. Hereinafter, application of a voltage higher than that of the second contact portion 52 to the first contact portion 51 (i.e., application of a voltage higher than that of the second convex portion 22 to the first convex portion 21) is also simply referred to as application of a reverse bias voltage.

[0032] Here, an optical phase modulator in which the I layer 60 is not arranged in contrast to the optical phase modulator of this embodiment is taken as an optical phase modulator for comparison. First, the reason why electric field concentration is likely to occur in the small depletion layer region SR in the optical phase modulator of the comparative example will be described.

[0033] In the optical phase modulator of the comparative example, as shown in FIG. 5, in the X-axis direction, one depletion layer 70 is formed in each of the few depletion layer regions SR, and three depletion layers 70 are formed in the many depletion layer regions MR. In the optical phase modulator of the comparative example, when a reverse bias voltage is applied, the voltage is applied to each depletion layer 70. In this case, in the many depletion layer regions MR, the reverse bias voltage is divided by the three depletion layers 70, but in each of the few depletion layer regions SR, the reverse bias voltage is applied to one depletion layer 70. For this reason, electric field concentration is likely to occur in the few depletion layer regions SR. For example, when a reverse bias voltage is applied to the boundary between the first connection portion 21b and the second slab portion 32, the electric field distribution is as shown in FIG. 6. The maximum value of the reverse bias voltage that can be applied until the allowable electric field strength in the configuration is reached becomes the withstand voltage, and when the maximum value of the electric field strength exceeds the allowable electric field strength, an avalanche breakdown occurs. In FIG. 6, the area of ​​the hatched portion represents the applied voltage, and the applied width depends on the width of the depletion layer 70.

[0034] For this reason, in this embodiment, the I layer 60 is disposed in the small depletion layer region SR as described above. As a result, as shown in Fig. 7, the reverse bias voltage is also applied to the I layer 60, so the applied width becomes longer, and the reverse bias voltage is divided between the depletion layer 70 and the I layer 60. Therefore, the reverse bias voltage required to reach the allowable electric field intensity can be increased, and the breakdown voltage can be improved.

[0035] Here, as shown in FIG. 1, the length of the first connection portion 21b and the second connection portion 22b along the Y-axis direction is defined as the low-depletion layer region length d1, the length of the I-layer 60 along the Y-axis direction is defined as the I-layer length d2, and the length of the convex portion 20 of the rib waveguide along the Y-axis direction is defined as the phase shifter length L.

[0036] The inventors then investigated the relationship between the leakage current and the reverse bias voltage when the small depletion layer region length d1 was set to 2 μm, the I layer length d2 was set to 5 μm, and the phase shifter length L was set to 100 μm, and obtained the results shown in FIG. 8. As shown in FIG. 8, for example, when the leakage current is 1×10 -8 The reverse bias voltage at A is 6.3 V in the optical phase modulator of the comparative example, but is 6.6 V in the optical phase modulator of this embodiment. In other words, it is confirmed that the optical phase modulator of this embodiment can withstand a higher voltage than the optical phase modulator of the comparative example.

[0037] The inventors further conducted extensive research into the I layer length d2 and obtained the results shown in Figures 9 and 10. Figures 9 and 10 show the results when the small depletion layer region length d1 was set to 2 μm and the phase shifter length L was set to 100 μm.

[0038] As shown in Fig. 9 and Fig. 10, when the ratio of the I-layer length d2 to the small depletion layer region length d1 is the first length ratio d2 / d1, it is confirmed that the breakdown voltage increases steeply as the first length ratio d2 / d1 increases in a range where the first length ratio d2 / d1 is less than 50%. However, the breakdown voltage becomes almost constant when the first length ratio d2 / d1 is 50% or more. For this reason, it is preferable that the first length ratio d2 / d1 is 50% or more. This allows a sufficient improvement in the breakdown voltage. And, since the optical phase modulator can apply a large reverse bias voltage that increases the breakdown voltage, the depletion layer can be easily expanded and the phase modulation amount can be easily increased.

[0039] However, when the I layer length L2 is increased, the I layer 60 is also disposed in the multiple depletion layer region MR. Specifically, when the first length ratio d2 / d1 is greater than 100%, the I layer 60 is also disposed in the multiple depletion layer region MR.

[0040] In this case, in the multiple depletion layer region MR, the reverse bias voltage applied to the depletion layer 70 between the first and second main portions 21a, 22a and the first and second slab portions 31, 32 is also applied to the I layer 60. For this reason, when the length d2 of the I layer 60 is lengthened and the I layer 60 reaches the multiple depletion layer region MR, the reverse bias voltage applied to the depletion layer 70 becomes smaller in the multiple depletion layer region MR, and the depletion layer 70 becomes difficult to spread, and the phase modulation amount tends to become smaller. In other words, when the length d2 of the I layer 60 is lengthened and the I layer 60 reaches the multiple depletion layer region MR, a contradictory phenomenon occurs in which the withstand voltage can be increased to increase the phase modulation amount, and the depletion layer 70 becomes difficult to spread in the multiple depletion layer region MR to decrease the phase modulation amount.

[0041] If the phase modulation amount in the optical phase modulator of the comparative example is taken as a reference phase modulation amount, the ratio of the phase modulation amount to the reference phase modulation amount (hereinafter also simply referred to as the phase modulation ratio) is 1 or more when the first length ratio d2 / d1 is 254% or less. In other words, if the phase modulation ratio is defined by the second length ratio d2 / L of the I layer length d2 to the phase shifter length L, it is 1 or more when the first length ratio d2 / d1 is 100% or more and the second length ratio is 5% or less. The withstand voltage is approximately constant when the second length ratio d2 / L is 1% or more.

[0042] For this reason, the first length ratio d2 / d1 is preferably 50% or more and 254% or less. Also, the second length ratio d2 / L is preferably 1% or more and 5% or less. This allows the phase modulation ratio to be increased while improving the breakdown voltage. Note that, since the reverse bias voltage applied to the depletion layer 70 is reduced by providing the I layer 60, the modulation efficiency Vπ increases and deteriorates as the I layer length d2 increases.

[0043] The inventors further changed the small depletion layer region length d1 for further investigation, and obtained the results shown in Figures 11 and 12. Figures 11 and 12 show the results when the small depletion layer region length d1 is set to 3 μm.

[0044] 11 and 12, even if the small depletion layer region length d1 is changed to 3 μm, it is confirmed that the breakdown voltage increases steeply as the first length ratio d2 / d1 increases in a range where the first length ratio d2 / d1 is less than 50%. It is also confirmed that the breakdown voltage becomes almost constant when the first length ratio d2 / d1 is 50% or more. In other words, it is confirmed that the breakdown voltage can be determined by the first length ratio d2 / d2, not by the direct length of the small depletion layer region length d1.

[0045] Furthermore, the inventors investigated the breakdown voltage by changing the arrangement of the I layer 60 relative to the small depletion layer region SR, and obtained the results shown in Fig. 13. Note that Fig. 13 shows the I layer 60 arranged in the second slab portion 32, but the I layer 60 arranged in the first slab portion 31 is similar. Fig. 13 also shows the results when the small depletion layer region length d1 is set to 2 µm and the I layer length d2 is set to 1 µm.

[0046] 13, in Example 1, the I layer 60 is disposed at the end of the scarce depletion layer region SR opposite to the multi-depletion layer region MR. In Example 2, the I layer 60 is disposed at the center of the scarce depletion layer region SR. In Example 3, the I layer 60 is disposed at the boundary between the scarce depletion layer region SR and the multi-depletion layer region MR. It is confirmed that the breakdown voltage is the same at 6.60 V in Examples 1 to 3. In other words, it is confirmed that the breakdown voltage does not change depending on the position of the I layer 60.

[0047] The inventors also investigated the cases where the I layer 60 is formed continuously and where it is formed in parts, and obtained the results shown in Fig. 14. Note that Fig. 14 shows the I layer 60 disposed in the second slab portion 32, but the I layer 60 disposed in the first slab portion 31 is similar. Fig. 14 also shows the results when the small depletion layer region length d1 is set to 2 µm and the I layer length d2 is set to 1 µm.

[0048] As shown in FIG. 14, in Example 1, the I layer 60 is disposed continuously. In Example 2, the I layer 60 is disposed in two parts. However, in Examples 1 and 2, the overall I layer length d2 is set to 1 μm. It is confirmed that the breakdown voltage is the same at 6.60 V in Examples 1 and 2. That is, it is confirmed that the breakdown voltage does not change depending on how the I layer 60 is disposed. Note that since the I layer 60 is surrounded by the convex portion 20 of the rib waveguide doped with impurities and the first and second slab portions 31 and 32, it is preferable that the I layer 60 be formed in a continuous shape in order to simplify the manufacturing process.

[0049] According to the present embodiment described above, the I layer 60 is disposed in the small depletion layer region SR. Therefore, when a reverse bias voltage is applied, in the small depletion layer region SR, the reverse bias voltage is divided between the depletion layer 70 and the I layer 60. Therefore, electric field concentration in the small depletion layer region SR can be suppressed, and the breakdown voltage can be improved.

[0050] (1) In the present embodiment, the first length ratio d2 / d1 is set to be equal to or greater than 50%, which makes it possible to sufficiently improve the withstand voltage.

[0051] (2) In the present embodiment, the first length ratio d2 / d1 is 100% or more, and the second length ratio d2 / L is 5% or less. Therefore, compared to the optical phase modulator of the comparative example not including the I layer 60, the phase modulation amount can be increased.

[0052] (3) In this embodiment, the I layer 60 is formed in a shape that is continuously connected along the Y-axis direction, which can simplify the manufacturing process.

[0053] (4) In this embodiment, the insulating portion is formed of the I layer 60. Therefore, the active layer 13 can be effectively utilized.

[0054] Second embodiment A second embodiment will be described. This embodiment is different from the first embodiment in that the configuration of the insulating portion is changed. As the rest is the same as the first embodiment, the description will be omitted here.

[0055] In the optical phase modulator of this embodiment, as shown in Fig. 15, a gap 61 is formed as an insulating portion instead of the I layer 60. Note that Fig. 15 corresponds to a cross-sectional view taken along the line II-II in Fig. 1.

[0056] Such an optical phase modulator is manufactured by ion-implanting impurities that constitute the convex portion 20 of the rib waveguide and the first and second slab portions 31, 32, etc., and then removing the portions that will become the voids 61 by etching or the like. Therefore, compared to the case where the insulating portion is constituted by the I layer 60 as in the first embodiment, the portions that will become the voids 61 are removed, and therefore accurate alignment is not required when ion-implanting P-type impurities and N-type impurities into the portions adjacent to the portions that will become the voids 61. This makes it possible to simplify the manufacturing process.

[0057] According to the present embodiment described above, the gap 61 serving as an insulating portion is disposed in the low depletion layer region SR, and therefore, the same effects as those of the first embodiment can be obtained.

[0058] (1) In this embodiment, the insulating portion is formed of the gap 61. This can simplify the manufacturing process.

[0059] (Modification of the second embodiment) A modified example of the second embodiment will be described. In the second embodiment, an insulating film 62 may be embedded in the gap as shown in FIG. 16. In such a configuration, the insulating film 62 corresponds to the insulating portion. The insulating film 62 is, for example, a silicon oxide film. Since there is no gap 61, when an interlayer film is disposed on the protrusion 20 of the rib waveguide or the first and second slab portions 31 and 32, it is not necessary to consider the embedding of the gap, and the degree of freedom in designing the protrusion 20 of the rib waveguide can be improved.

[0060] (Other embodiments) Although the present disclosure has been described based on the embodiment, it is understood that the present disclosure is not limited to the embodiment or structure. The present disclosure also encompasses various modifications and modifications within the equivalent range. In addition, various combinations and forms, as well as other combinations and forms including only one element, more than one element, or less than one element, are also within the scope and concept of the present disclosure.

[0061] In each of the above embodiments, the impurity concentrations may be different between the first protrusion 21 and the second protrusion 22. Similarly, the impurity concentrations may be different between the first protrusion 21 and the first slab portion 31, and the impurity concentrations may be different between the second protrusion 22 and the second slab portion 32. [Explanation of symbols]

[0062] 20 Rib waveguide protrusion 21 First protrusion 21a First Main Section 21b First connection part 22 Second protrusion 22a Second Main Section 22b Second connection part 61 I layer (insulation part) MR multi-depletion region SR low depletion region

Claims

1. An optical phase modulator having a convex portion (20) of a rib waveguide, a protruding portion of the rib waveguide extending in one direction; a first slab portion (31) and a second slab portion (32) that are thinner than the protruding portion of the rib waveguide and are arranged in a state of being connected to the protruding portion of the rib waveguide; the protrusion of the rib waveguide includes a first protrusion (21) of N type, the first protrusion (21) including a first main portion (21a) extending along the extension direction and a first connection portion (21b) extending from an end of the first main portion in the extension direction along a cross direction crossing the extension direction, the first protrusion (21) including a second main portion (22a) extending along the extension direction and having a boundary with the first main portion and the first connection portion, and the second protrusion (22) including a second connection portion (22b) extending from an end of the second main portion in the extension direction along the cross direction and having a boundary with the first main portion, The first slab portion is an N-type, is disposed on the opposite side of the second main portion from the first main portion, and is connected to the second main portion and the first connection portion, the second slab portion is of P type, is disposed on the opposite side of the first main portion to the second main portion, and is connected to the first main portion and the second connection portion; In the extending direction, a region in which the first main portion and the second main portion are arranged is defined as a high-depletion layer region (MR), and a region in which the first connection portion or the second connection portion is arranged is defined as a low-depletion layer region (SR), an insulating portion (60-62) is disposed in the low-depletion layer region in a portion of the first slab portion on the convex side of the rib waveguide and in a portion of the second slab portion on the convex side of the rib waveguide.

2. 2. The optical phase modulator of claim 1, wherein a length of the low-depletion layer region along the extension direction is defined as a low-depletion layer region length (d1) and a length of the insulating portion along the extension direction is defined as an insulating portion length (d2), and a ratio of the insulating portion length to the low-depletion layer region length is 50% or more.

3. a length of the small depletion layer region along the extension direction is defined as a small depletion layer region length (d1) and a length of the insulating portion along the extension direction is defined as an insulating portion length (d2), the ratio of the insulating portion length to the small depletion layer region length is 100% or more, 2. The optical phase modulator according to claim 1, wherein the length of the rib waveguide along the extension direction of the convex portion is defined as a phase shifter length (L), and the ratio of the length of the insulating portion to the phase shifter length is 5% or less.

4. The optical phase modulator according to claim 1 , wherein the insulating portion is continuously connected along the extending direction.

5. the protruding portion of the rib waveguide, the first slab portion, and the second slab portion are formed of a doped layer doped with an impurity, 5. The optical phase modulator according to claim 1, wherein the insulating portion is made of an I layer (60) which is a non-doped layer.

6. 5. The optical phase modulator according to claim 1, wherein the insulating portion is formed of an air gap (61).

7. 5. The optical phase modulator according to claim 1, wherein the insulating portion is made of an insulating film (62).

Images