Optical phase modulator

Abstract

To provide an optical phase modulator with which it is possible to reduce a change of modulation efficiency.SOLUTION: The optical phase modulator comprises a core part 20, and slab parts 31, 32 arranged across the core part 20 and the length in thickness direction of which is made shorter than the core part 20. The core part 20 includes a first protrusion 21 which is of a first conductive type, and a second protrusion 22 which is of a second conductive type, and the first protrusion 21 and the second protrusion 22 are arranged so as to constitute a PN junction. The slab parts 31, 32 are constituted by an ion injection layer, with the first slab part 31 being made a first conductive type and electrically connected to the first protrusion 21, the second slab 32 being made a second conductive type and electrically connected to the second protrusion, and are arranged so as to include a section constituting the core part 20 and the PN junction. In a region ER2 where a PN junction is constituted between the slab parts 31, 32 and the core part 20, the second protrusion 22 is located in sections of the core part 20 on the slab parts 31, 32 side, so that the core part 20 is sandwiched by the first slab part 31.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] Optical phase modulators having a PN junction have been proposed (see, for example, Patent Document 1). Specifically, this optical phase modulator has a waveguide extending in one direction, and the waveguide includes a core portion through which light propagates, and a first slab portion and a second slab portion that are disposed on both sides of the core portion and are thinner than the core portion.

[0003] More specifically, the core portion has an N-type first protrusion and a P-type second protrusion. The first protrusion has a generally L-shaped planar shape, including a first protrusion-use first portion extending along the extension direction and a first protrusion-use second portion extending from an end of the first protrusion-use first portion along a transverse direction intersecting the extension direction. The second protrusion has a generally L-shaped planar shape, including a second protrusion-use first portion extending along the extension direction and a second protrusion-use second portion extending from an end of the first protrusion-use first portion along a transverse direction intersecting the extension direction. The core portion is in a state in which the first convex portion and the second convex portion, which are approximately L-shaped, are fitted together so that the first portion for the first convex portion and the first portion for the second convex portion are adjacent to each other, the second portion for the first convex portion is connected to the first portion for the second convex portion, and the second portion for the second convex portion is connected to the first portion for the first convex portion.

[0004] The first slab is an N type with a higher impurity concentration than the N type in the core. + The second slab portion is a P type, and is arranged on the opposite side of the first protrusion portion first portion with the second protrusion portion first portion sandwiched therebetween, and is connected to the second protrusion portion first portion and the first protrusion portion second portion. The second slab portion is a P type having a higher impurity concentration than the P type of the core portion. + The first protrusion-use first portion is disposed on the opposite side of the first protrusion-use first portion from the second protrusion-use first portion, and is connected to the first protrusion-use first portion and the second protrusion-use second portion.

[0005] In such an optical phase modulator, the core portion, the first slab portion, and the second slab portion are ion-implanted layers formed by ion implantation. [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] However, in the optical phase modulator described above, the first slab portion and the second slab portion may be misaligned in the intersecting direction relative to the core portion due to mask misalignment during ion implantation, etc. In the optical phase modulator described above, if the first slab portion and the second slab portion are misaligned in the intersecting direction, there is a possibility that the change in the light modulation efficiency will be large.

[0008] An object of the present disclosure is to provide an optical phase modulator that can reduce changes in modulation efficiency. [Means for solving the problem]

[0009] According to one aspect of the present disclosure, an optical phase modulator comprises a core portion (20) extending in one direction as an extension direction, and slab portions (31, 32) arranged on either side of the core portion and having a shorter length in a thickness direction intersecting the extension direction than the core portion, wherein the core portion has a first convex portion (21) of a first conductivity type and a second convex portion (22) of a second conductivity type, the first convex portion and the second convex portion being arranged to form a PN junction, the slab portion being formed of an ion-implanted layer and having a first slab portion (31) of the first conductivity type and electrically connected to the first convex portion, and a second slab portion (32) of the second conductivity type and electrically connected to the second convex portion, and is arranged to include a portion that forms a PN junction with the core portion, and in a region (ER2) where a PN junction is formed between the slab portion and the core portion, the second convex portions are arranged on both sides of the core portion on the slab portion side, and the core portion is sandwiched between the first slab portions.

[0010] According to this, in the region where a PN junction is formed between the core and slab portions, the core portion is sandwiched by the first slabs. Therefore, even if the first slab portion and the second slab portion are misaligned in the direction intersecting the extension direction and the thickness direction, this misalignment can be easily offset. Therefore, a large change in modulation efficiency can be suppressed.

[0011] The reference symbols in parentheses attached to each component indicate an example of the correspondence between the component and the specific components described in the embodiments described below. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a plan view of an optical phase modulator according to a first embodiment. [Figure 2] FIG. 2 is a cross-sectional view taken along line II-II in FIG. [Figure 3] FIG. 2 is a cross-sectional view taken along line III-III in FIG. [Figure 4] FIG. 4 is a cross-sectional view taken along line IV-IV in FIG. [Figure 5]5A and 5B are schematic diagrams showing the positions of the first slab portion and the second slab portion when misalignment occurs in the optical phase modulator of the comparative example and the optical phase modulator of the first embodiment. [Figure 6] 10 is a diagram showing misalignment between the first slab portion and the second slab portion and the amount of change in phase modulation amount. FIG. [Figure 7] FIG. 10 is a plan view of an optical phase modulator according to a modified example of the first embodiment. [Figure 8] FIG. 10 is a plan view of an optical phase modulator according to a second embodiment. [Figure 9] FIG. 10 is a plan view of an optical phase modulator according to a third embodiment. [Figure 10] FIG. 10 is a cross-sectional view taken along line XX in FIG. [Figure 11] FIG. 10 is a cross-sectional view taken along line XI-XI in FIG. [Figure 12] FIG. 10 is a cross-sectional view taken along line XII-XII in FIG. [Figure 13] FIG. 10 is a cross-sectional view taken along line XIII-XIII in FIG. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings. In the following embodiments, identical or equivalent parts will be denoted by the same reference numerals.

[0014] (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.

[0015] The optical phase modulator of this embodiment is configured using a semiconductor substrate 10 that is configured as an SOI (that is, an abbreviation for 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.

[0016] Hereinafter, one direction in the surface direction of the semiconductor substrate 10 is referred to as the X-axis direction, a direction perpendicular to the X-axis direction and along the surface direction of the semiconductor substrate 10 is referred to as the Y-axis direction, and a direction perpendicular to the X-axis direction and the Y-axis direction is referred to as the Z-axis direction. In FIG. 1 , the left-right direction of the page is referred to as the X-axis direction, the up-down direction of the page is referred to as the Y-axis direction, and the direction perpendicular to the page is referred to as the Z-axis direction. The Z-axis direction is also a direction 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. Furthermore, 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. Hereinafter, the X-axis direction will also be referred to as the width direction, the length in the X-axis direction will simply be referred to as the width, and the length in the Z-axis direction will simply be referred to as the thickness.

[0017] The active layer 13 includes a core portion 20, a first slab portion 31, a second slab portion 32, a first contact portion 41, a second contact portion 42, and the like, which are doped with impurities to form a waveguide. The core portion 20, the first slab portion 31, the second slab portion 32, the first contact portion 41, and the second contact portion 42 are formed as ion-implanted layers into which impurities are ion-implanted. The active layer 13 of this embodiment also includes a non-doped layer 60 that is not doped with impurities. Furthermore, the active layer 13 includes a first electrode portion 51, a second electrode portion 52, and the like, as described below.

[0018] The core portion 20 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 core portion 20, and light propagates along the Y-axis direction.

[0019] The first protrusion 21 is generally T-shaped and has a first protrusion first portion 21a whose width is the same as that of the core portion 20, and a first protrusion second portion 21b extending along the Y-axis direction from approximately the center of the first protrusion first portion 21a in the X-axis direction. The second protrusion 22 is generally U-shaped and has a second protrusion first portion 22a whose width is the same as that of the core portion 20, and a second protrusion second portion 22b extending along the Y-axis direction from both end portions of the second protrusion first portion 22a in the X-axis direction.

[0020] The core portion 20 is configured such that the first protrusion 21 and the second protrusion 22 are arranged to fit together. More specifically, the first protrusion 21 and the second protrusion 22 are fitted together such that the first protrusion-use second portion 21b is sandwiched between the second protrusion-use second portion 22b. The core portion 20 is configured such that the P-type, N-type, and P-type are arranged in this order in the X-axis direction in the portion where the first protrusion-use second portion 21b is sandwiched between the second protrusion-use second portion 22b. In other words, the core portion 20 has both ends in the X-axis direction that are P-type in the portion where the first protrusion-use second portion 21b is sandwiched between the second protrusion-use second portion 22b.

[0021] In the following description of the present embodiment, a region where one first protrusion 21 and one second protrusion 22 are fitted together will be referred to as one cell region SR. The cell region SR also includes a region located in the X-axis direction of the region where one first protrusion 21 and one second protrusion 22 are fitted together, including a first slab portion 31 and a second slab portion 32, which will be described later. The optical phase modulator of the present embodiment is configured such that the cell regions SR are repeatedly arranged in the Y-axis direction. In the description of the present embodiment, a region in the X-axis direction where only the first protrusion 21 is arranged as the core portion 20 will be referred to as a first extended region ER1, a region in the X-axis direction where the first protrusion 21 and the second protrusion 22 are arranged as the core portion 20 will be referred to as a second extended region ER2, and a region in the X-axis direction where only the second protrusion 22 is arranged as the core portion 20 will be referred to as a third extended region ER3. In FIG. 1, the cell region SR is divided into a first extended region ER1, a second extended region ER2, and a third extended region ER3 from the bottom of the page. FIG. 2 is a cross-sectional view of the first extended region ER1, FIG. 3 is a cross-sectional view of the second extended region ER2, and FIG. 4 is a cross-sectional view of the third extended region ER3. In the following, the region located on one side of the core portion 20 in the X-axis direction will be referred to as the first width region WR1, and the region located on the other side of the core portion 20 in the X-axis direction will be referred to as the second width region WR2. In FIG. 1, the portion located on the left side of the core portion 20 in the page will be referred to as the first width region WR1, and the portion located on the right side of the core portion 20 in the page will be referred to as the second width region WR2.

[0022] The first slab portion 31 and the second slab portion 32 are thinner than the core portion 20. Therefore, the first slab portion 31 and the second slab portion 32 can also be said to be recesses of the waveguide.

[0023] The first slab portion 31 is made of N, which has a higher impurity concentration than the first protrusion portion 21 of the core portion 20. + In the first extension region ER1, the first slab portions 31 are arranged in the first width region WR1 and the second width region WR2 with the core portion 20 interposed therebetween, and are connected to the first protrusion first portions 21a in the core portion 20, respectively.

[0024] In the second extended region ER2, the first slab portions 31 are arranged in the first width region WR1 and the second width region WR2, sandwiching the core portion 20 therebetween. That is, in the second extended region ER2, the core portion 20 is sandwiched between first slab portions 31 of a conductivity type (i.e., N-type) different from the conductivity type (i.e., P-type) of both ends in the X-axis direction. In other words, in the second extended region ER2, the N-type first slab portions 31 are arranged so as to form PN junctions with the second protrusion second portions 22b (i.e., P-type layers) arranged on both ends in the X-axis direction of the core portion 20. However, in this embodiment, in consideration of mask misalignment when forming the first slab portions 31 and the like by ion implantation, the first slab portions 31 in the second extended region ER2 are arranged on the opposite side of the core portion 20 with the non-doped layer 60 sandwiched therebetween.

[0025] In the third extended region ER3, the first slab portion 31 is arranged in the first width region WR1 so as to form a PN junction with the second convex first portion 22a. However, in this embodiment, in consideration of mask misalignment when forming the first slab portion 31 etc. by ion implantation, the first slab portion 31 in the third extended region ER3 is arranged on the opposite side of the non-doped layer 60 from the core portion 20.

[0026] The first slab portion 31 formed in the first width region WR1 extends along the Y-axis direction, and the portions formed in the first extended region ER1, the second extended region ER2, and the third extended region ER3 are joined and electrically connected. The first slab portions 31 formed in the first extended region ER1 and the second extended region ER2 of the second width region WR2 are electrically connected to the first slab portion 31 formed in the first width region WR1 via the first protrusion first portion 21a.

[0027] The second slab portion 32 is made of P, which has a higher impurity concentration than the second protrusion portion 22 of the core portion 20. +The second slab portion 32 is disposed in the second width region WR2. Specifically, in the first extension region ER1 and the second extension region ER2, the second slab portion 32 is disposed on the opposite side of the core portion 20 across the first slab portion 31. In the third extension region ER3, the second slab portion 32 is disposed so as to be connected to the second protrusion first portion 22a in the core portion 20.

[0028] The second slab portion 32 formed in the second width region WR2 extends along the Y-axis direction, and the portions formed in the first extension region ER1, the second extension region ER2, and the third extension region ER3 are connected and electrically coupled.

[0029] The first contact portion 41 is made of N-type silicon, and the impurity concentration is higher than that of the first slab portion 31. ++ The first contact portion 41 extends along the Y-axis direction in the first width region WR1, is disposed on the opposite side of the core portion 20 across the first slab portion 31, and is connected to the first slab portion 31.

[0030] The second contact portion 42 is made of P ++ The second contact portion 42 extends along the Y-axis direction in the second width region WR2, is disposed on the opposite side of the core portion 20 with the second slab portion 32 in between, and is connected to the second slab portion 32.

[0031] In this embodiment, the first contact portion 41 and the second contact portion 42 have the same thickness as the core portion 20.

[0032] The first electrode portion 51 is disposed on the first contact portion 41 and electrically connected to the first contact portion 41, and extends along the Y-axis direction similar to the first contact portion 41. The second electrode portion 52 is disposed on the second contact portion 42 and electrically connected to the second contact portion 42, and extends along the Y-axis direction similar to the second contact portion 42.

[0033] The above is the basic configuration of the optical phase modulator in this embodiment. In this embodiment, N type corresponds to the first conductivity type, and P type corresponds to the second conductivity type. Next, the operation and effects of the optical phase modulator will be described.

[0034] In the optical phase modulator of this embodiment, in the second extended region ER2, PN junctions are formed between the second convex portion second region 22b and the first slab portion 31 of the first width region WR1, and between the second convex portion second region 22b and the first slab portion 31 of the second width region WR2. Also, in the second extended region ER2, PN junctions are formed between the first convex portion second region 21b and each of the two second convex portion second regions 22b. In the third extended region, PN junctions are formed between the second convex portion first region 22a and the first slab portion 31 of the first width region WR1.

[0035] In an optical phase modulator such as that of this embodiment, light propagates along the extension direction of the core portion 20 (i.e., the Y-axis direction). At this time, when a higher voltage is applied to the first contact portion 41 than to the second contact portion 42, a depletion layer expands at each PN junction, and the carrier density decreases, thereby modulating the phase of the light. Hereinafter, applying a higher voltage to the first contact portion 41 than to the second contact portion 42 (i.e., applying a higher voltage to the first convex portion 21 than to the second convex portion 22) will also be simply referred to as application of a reverse bias voltage.

[0036] The optical phase modulator of this embodiment is manufactured as follows.

[0037] First, the semiconductor substrate 10, which is an SOI substrate, is prepared. Next, etching or the like is performed using a mask to thin the portions of the active layer 13 that form the first slab portion 31 and the second slab portion 32. Then, N-type impurities and P-type impurities are appropriately ion-implanted using a mask to form the core portion 20 having the first protrusion portion 21 and the second protrusion portion 22 configured as described above. Next, N-type impurities and P-type impurities are appropriately ion-implanted to form the first slab portion 31 and the second slab portion 32 configured as described above.

[0038] Thereafter, N-type impurities and P-type impurities are appropriately ion-implanted to form the first contact portion 41 and the second contact portion 42, and the first electrode portion 51, the second electrode portion 52, etc. are appropriately formed, thereby manufacturing the above-mentioned optical phase modulator.

[0039] When forming the first slab portion 31 and the second slab portion 32, there is a possibility that the first slab portion 31 and the second slab portion 32 may be misaligned in the X-axis direction due to mask misalignment, etc. However, in this embodiment, because the optical phase modulator is configured as described above, even if the first slab portion 31 and the second slab portion 32 are misaligned in the X-axis direction, the misalignment is easily offset in the second extended region ER2, and therefore, a large change in modulation efficiency can be suppressed.

[0040] The change in modulation efficiency will be described in detail below, in comparison with an optical phase modulator of a comparative example. Note that the following description will be given taking the optical phase modulator of the comparative example shown in FIG. 5 as an example of the optical phase modulator of the comparative example. The cross-sectional view of the optical phase modulator of FIG. 5 shows a cross-sectional view of a portion corresponding to the second extended region ER2 of this embodiment. Furthermore, in the optical phase modulator of the comparative example and the optical phase modulator of this embodiment shown in FIG. 5, the support substrate 11, the insulating film 12, etc. are omitted.

[0041] 5, the optical phase modulator of the comparative example has a core portion 20 formed by arranging an N-type first convex portion 21 and a P-type second convex portion 22 side by side in the X-axis direction. Also, in this optical phase modulator of the comparative example, a P-type first convex portion 21 is sandwiched between the first convex portion 21 and the second convex portion 22. + The second slab portion 32 of the mold is disposed, and the second protrusion 22 is sandwiched between the second protrusion 22 and the first protrusion 21. + 5, the first slab portion 31 of the mold is arranged. In the optical phase modulator of the comparative example, the first convex portion 21 and the first slab portion 31 are electrically connected, and the second convex portion 22 and the second slab portion 32 are electrically connected, in a cross section different from that of FIG.

[0042] In addition, in FIG. 5, the case where the non-doped layer 60 having a desired width is disposed between the core 20 and the first slab 31 and second slab 32 is shown as having an alignment deviation of 0 (ie, no deviation).

[0043] 5, in the optical phase modulator of the comparative example, a case of zero misalignment is used as a reference, and the case where the first slab portion 31 and the second slab portion 32 are misaligned toward the core portion 20 by the width of the non-doped layer 60 is shown as Min misalignment. That is, in the modulator of the comparative example, the Min misalignment is shown as a case where the first slab portion 31 is misaligned to the second convex portion 22 and the second slab portion 32 is misaligned to the first convex portion 21. Note that in FIG. 5, the Min misalignment case refers to a case where the first slab portion 31 is misaligned to the right side of the paper and the second slab portion 32 is misaligned to the left side of the paper in the optical phase modulator of the comparative example. In the column for the optical phase modulator of this embodiment, the case where the first slab portion 31 and the second slab portion 32 are misaligned in the same direction as the case where the first slab portion 31 and the second slab portion 32 of the optical phase modulator of the comparative example are misaligned to the Min misalignment is shown. That is, in the column for the optical phase modulator of this embodiment, the case where the first slab portion 31 is misaligned to the right on the paper surface and the second slab portion 32 is misaligned to the left on the paper surface is shown as the Min misalignment.

[0044] 5, in the optical phase modulator of the comparative example, a case where the misalignment is 0 is used as a reference, and the case where the first slab portion 31 and the second slab portion 32 are misaligned by the width of the non-doped layer 60 toward the opposite side of the core portion 20 is shown as misalignment Max. Note that in FIG. 5, the case of misalignment Max refers to the case where the first slab portion 31 is misaligned to the left side of the paper and the second slab portion 32 is misaligned to the right side of the paper in the optical phase modulator of the comparative example. In the column for the optical phase modulator of this embodiment, the misalignment Max refers to the case where the first slab portion 31 and the second slab portion 32 are misaligned in the same direction as the case where the first slab portion 31 and the second slab portion 32 of the optical phase modulator of the comparative example are misaligned to the Max. That is, in the column for the optical phase modulator of this embodiment, the case where the first slab portion 31 is misaligned to the left side of the paper and the second slab portion 32 is misaligned to the right side of the paper is shown as misalignment Max.

[0045] The inventors then conducted extensive research into the phase modulation amount VΠ when misalignment occurs as shown in FIG. 5 for the optical phase modulator of the comparative example and the optical phase modulator of this embodiment, and obtained the results shown in FIG. 6.

[0046] 6, if the phase modulation amount VΠ when the misalignment is 0 is taken as the reference (i.e., the change in the phase modulation amount VΠ is 1), it is confirmed that in the optical phase modulator of the comparative example, the phase modulation amount VΠ changes significantly due to misalignment. Note that the phase modulation amount VΠ is the applied voltage required to change the phase of light by 180°, and the smaller the value, the more preferable it is.

[0047] That is, in the optical phase modulator of the comparative example, when the misalignment is minimum, the first slab portion 31 and the second slab portion 32 approach the core portion 20, and it is confirmed that the phase modulation amount VΠ is smaller than the reference value. However, in the optical phase modulator of the comparative example, when the misalignment is maximum, it is confirmed that the phase modulation amount VΠ is larger than the reference value. That is, it is confirmed that in the optical phase modulator of the comparative example, the phase modulation amount VΠ changes significantly between when the misalignment is minimum and when it is maximum.

[0048] On the other hand, in the optical phase modulator of this embodiment, first slab portions 31 of the same conductivity type are arranged to sandwich the core portion 20. Therefore, in the optical phase modulator of this embodiment, when the alignment misalignment is Min, the first slab portion 31 in the first width region WR1 is misaligned in the direction toward the core portion 20, but the first slab portion 31 in the second width region WR2 is misaligned in the direction away from the core portion 20, as shown in Fig. 5. Therefore, the misalignment of the first slab portion 31 in the first width region WR1 and the misalignment of the first slab portion 31 in the second width region WR2 cancel each other out.

[0049] Similarly, when the alignment misalignment is Max, the first slab portion 31 in the first width region WR1 is misaligned in a direction away from the core portion 20, but the first slab portion 31 in the second width region WR2 is misaligned in a direction toward the core portion 20. Therefore, the misalignment of the first slab portion 31 in the first width region WR1 and the misalignment of the first slab portion 31 in the second width region WR2 cancel each other out.

[0050] Therefore, in the optical phase modulator of this embodiment, regardless of the direction in the X-axis direction in which misalignment occurs, the phase modulation amount VΠ decreases in both cases. Therefore, in the optical phase modulator of this embodiment, as shown in FIG. 6, large changes in the phase modulation amount VΠ due to misalignment are suppressed.

[0051] In the optical phase modulator of this embodiment, when the misalignment is Min, the misalignment between the first slab portion 31 and the second slab portion 32 is reversed in the second width region WR2, and the width of the first slab portion 31 or the second slab portion 32 is shortened. Similarly, when the misalignment is Max, the misalignment between the first slab portion 31 and the second slab portion 32 is reversed in the second width region WR2, and the non-doped layer 60 is formed between the first slab portion 31 and the second slab portion 32. However, because these portions are not the portions through which light mainly propagates, slight changes in the configuration do not have a significant effect on modulation efficiency.

[0052] Furthermore, in the optical phase modulator of this embodiment, the impurity concentration of the first slab portion 31 is higher than the impurity concentration of the first convex portion 21. Therefore, if misalignment causes the first slab portion 31 to reach the inside of the core portion 20, optical loss will increase. Therefore, it is preferable that the width of the non-doped layer 60 of the first slab portion 31 is adjusted so that it does not reach the inside of the core portion 20 even if misalignment occurs.

[0053] According to the present embodiment described above, in the second extended region ER2 where a PN junction is formed between the core portion 20 and the slab portions 31 and 32, the core portion 20 is sandwiched between the first slab portion 31. Therefore, even if the first slab portion 31 and the second slab portion 32 are misaligned in the X-axis direction, this misalignment can be easily offset, and therefore, a large change in modulation efficiency can be suppressed.

[0054] (1) In this embodiment, in the second extended region ER2, the core portion 20 has the first convex portion 21 sandwiched between the second convex portion 22 in the X-axis direction, and a PN junction is formed between each of the first convex portion 21 and the second convex portion 22. This allows the number of PN junctions to be increased, thereby improving modulation efficiency.

[0055] (2) In this embodiment, the core region 20, the first slab region 31, and the second slab region 32 are repeatedly extended in the Y-axis direction. That is, in this embodiment, the cell region SR is repeatedly extended in the Y-axis direction. This makes it easier to uniformly expand the depletion layer in the core region 20, thereby improving modulation efficiency.

[0056] (Modification of the first embodiment) In the first embodiment, an example was described in which P-type, N-type, and P-type are arranged in the X-axis direction in the second extended region ER2 of the core portion 20. However, as shown in FIG. 7 , the optical phase modulator may be configured such that N-type, P-type, and N-type are arranged in the second extended region ER2. That is, in the first embodiment, the first protrusion 21, the first slab portion 31, and the first contact portion 41 may be P-type, and the second protrusion 22, the second slab portion 32, and the second contact portion 42 may be N-type. In other words, the first protrusion 21, the first slab portion 31, and the first contact portion 41 in the first embodiment may be reversed with the second protrusion 22, the second slab portion 32, and the second contact portion 42. In this configuration, a higher voltage than that applied to the first contact portion 41 may be applied to the second contact portion 42. In this configuration, the P type is the first conductivity type, and the N type is the second conductivity type.

[0057] (Second embodiment) A second embodiment will be described. In this embodiment, the number of PN junctions in the second extended region ER2 is increased compared to the first embodiment. As the rest of the configuration is the same as the first embodiment, a description thereof will be omitted here.

[0058] 8, in the optical phase modulator of this embodiment, the first convex portion 21 has a first convex portion first portion 21a and two first convex portion second portions 21b extending from the first convex portion first portion 21a along the Y-axis direction. The two first convex portion second portions 21b are spaced apart in the X-axis direction.

[0059] The second protrusion 22 has a second protrusion first portion 22a and three second protrusion second portions 22b extending from the second protrusion first portion 22a along the Y-axis direction. The three second protrusion second portions 22b are spaced apart in the X-axis direction.

[0060] The first protrusion 21 and the second protrusion 22 are arranged such that two first protrusion second portions 21b and three second protrusion second portions 22b interlock with each other. Therefore, in the core portion 20 of the second extended region ER2, P-type, N-type, P-type, N-type, and P-type are arranged in the X-axis direction. Compared to the first embodiment, the number of PN junctions increases, resulting in an increase in the number of depletion layers. This improves modulation efficiency.

[0061] In this embodiment, the number of first convex portion second portions 21b and second convex portion second portions 22b can be changed as appropriate. However, if the number of PN junctions is increased too much, the depletion layers may become connected when a reverse bias voltage is applied, potentially reducing the amount of phase modulation. For this reason, it is preferable that the number of PN junctions formed inside the core portion 20 be such that the depletion layers do not come into contact with each other when a reverse bias voltage is applied. For example, if the width of the core portion 20 is approximately 500 nm, it is preferable that four PN junctions (i.e., depletion layers) be formed inside the core portion 20, as in this embodiment.

[0062] According to the present embodiment described above, in the second extended region ER2 where a PN junction is formed between the core portion 20 and the slab portions 31 and 32, the core portion 20 is sandwiched between the first slab portions 31. Therefore, the same effects as those of the first embodiment can be obtained.

[0063] (1) In this embodiment, the second extended region ER2 includes a plurality of first protrusions 21 sandwiched between second protrusions 22. This allows the number of PN junctions to be increased, thereby improving modulation efficiency. However, in such a configuration, it is preferable that the number of PN junctions formed inside the core region 20 is such that the depletion layers are not in contact with each other when a reverse bias voltage is applied.

[0064] (Third embodiment) A third embodiment will be described. This embodiment is different from the first embodiment in that the configuration of the core unit 20 is changed. As the rest is the same as the first embodiment, a description thereof will be omitted here.

[0065] 9 to 13, in the optical phase modulator of this embodiment, the core portion 20 is formed so that a portion having a PN junction is configured in the Z-axis direction. Note that Fig. 13 corresponds to a cross section taken along line XIII-XIII in Fig. 9, and shows the core portion 20 of one cell region SR.

[0066] Specifically, the first protrusion 21 of this embodiment has a first protrusion-use first portion 21a and a first protrusion-use second portion 21b that is thinner than the first protrusion-use first portion 21a and extends in the Y-axis direction. The first protrusion-use second portion 21b has the same width as the first protrusion-use first portion 21a and is configured to be thinner from the insulating film 12 side.

[0067] The second convex portion 22 has the same width as the core portion 20, and a thickness corresponding to the thinner portion of the first convex portion second portion 21b.

[0068] The first protrusion 21 and the second protrusion 22 are arranged so as to form a PN junction in the Z-axis direction (i.e., the XY plane). In this embodiment, in the X-axis direction, a region in which only the first protrusion 21 is arranged as the core portion 20 is referred to as a first extended region ER1. In this embodiment, a region in which the first protrusion 21 and the second protrusion 22 are arranged as the core portion 20 and which is sandwiched by first slab portions 31 as described later is referred to as a second extended region ER2. In this embodiment, a region in which the first protrusion 21 and the second protrusion 22 are arranged as the core portion 20 and which is connected to the second slab portion 32 as described later is referred to as a third extended region ER3. The first protrusion 21 and the second protrusion 22 are arranged so as to form a PN junction in the second extended region ER2 and the third extended region ER3.

[0069] The first slab portion 31 and the second slab portion 32 are arranged in the same manner as in the first embodiment. Therefore, in the second extended region ER2, the N-type first slab portion 31 is arranged in the first width region WR1 and the second width region WR2 so as to form a PN junction with the P-type second protrusion portion 22. That is, in the second extended region ER2, first slab portions 31 of the same conductivity type are arranged to sandwich the core portion 20. Furthermore, in the third extended region ER3, the N-type first slab portion 31 is arranged in the first width region WR1 so as to form a PN junction with the P-type second protrusion portion 22. In the third extended region ER3, the P-type second slab portion 32 is arranged so as to be connected to the P-type second protrusion portion 22. However, the thickness of the first slab portion 31 and the second slab portion 32 is set to be equal to or less than the thickness of the second protrusion portion 22 arranged below the core portion 20.

[0070] In this optical phase modulator, in the second extended region ER2, PN junctions are formed between the second convex portion 22 and the first slab portion 31 of the first width region WR1, and between the second convex portion 22 and the first slab portion 31 of the second width region WR2. Also, in the second extended region ER2, a PN junction is formed between the first convex second portion 21b and the second convex portion 22. In the third extended region ER3, a PN junction is formed between the second convex portion 22 and the first slab portion 31 of the first width region WR1. In the third extended region ER3, a PN junction is formed between the first convex second portion 21b and the second convex portion 22. Therefore, similar to the first embodiment, the phase of light can be modulated by applying a reverse bias voltage.

[0071] Also in an optical phase modulator such as that of this embodiment, when the first slab portion 31 and the second slab portion 32 are formed by ion implantation, there is a possibility that the first slab portion 31 and the second slab portion 32 may be misaligned in the X-axis direction due to mask misalignment or the like. However, in this embodiment, as in the first embodiment, in the second extended region ER2, the core portion 20 (i.e., the second convex portion 22) is sandwiched between the first slab portions 31. Therefore, even if the first slab portion 31 and the second slab portion 32 are misaligned in the X-axis direction, the misalignment can be easily offset, and a large change in modulation efficiency can be suppressed.

[0072] According to the present embodiment described above, in the second extended region ER2 where a PN junction is formed between the core portion 20 and the slab portions 31 and 32, the core portion 20 is sandwiched between the first slab portions 31. Therefore, the same effects as those of the first embodiment can be obtained.

[0073] (1) In this embodiment, a PN junction is formed in the portion where the first protrusion 21 is stacked on the second protrusion 22, and the PN junction is formed in a direction along the XY plane. Here, the core portion 20 in the optical modulator as described above is usually configured so that its width is longer than its thickness. Light tends to spread in the X-axis direction. Therefore, by forming the PN junction in a direction along the XY plane, it is possible to easily improve modulation efficiency.

[0074] (Other embodiments) Although the present disclosure has been described with reference to the embodiments, it is understood that the present disclosure is not limited to the embodiments or structures. The present disclosure also encompasses various modifications and modifications within the scope of equivalents. 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 spirit of the present disclosure.

[0075] For example, in each of the above embodiments, the optical phase modulator may be configured with one cell region SR.

[0076] In each of the above embodiments, the first protrusion 21 and the second protrusion 22 may have different impurity concentrations.

[0077] Furthermore, in each of the above embodiments, when the misalignment is zero, the core region 20 may be in contact with the first slab region 31 and the second slab region 32. However, as described in the first embodiment, if the first slab region 31 or the second slab region 32 reaches the inside of the core region 20 due to misalignment, the loss of light increases. For this reason, it is preferable that the non-doped layer 60 be disposed when the misalignment is zero so that the first slab region 31 or the second slab region 32 does not reach the inside of the core region 20 even if misalignment occurs.

[0078] In the second and third embodiments, similar to the modified example of the first embodiment, the first convex portion 21, the first slab portion 31, and the first contact portion 41 may be P-type, and the second convex portion 22, the second slab portion 32, and the second contact portion 42 may be N-type. [Explanation of symbols]

[0079] 20 Core 31 First Slab Section 32 Second Slab Section ER2 2nd extension area

Claims

1. An optical phase modulator, A core portion (20) extending in one direction; and slab portions (31, 32) arranged on either side of the core portion and having a length in a thickness direction intersecting the extension direction shorter than that of the core portion, The core portion has a first convex portion (21) of a first conductivity type and a second convex portion (22) of a second conductivity type, the first protrusion and the second protrusion are arranged to form a PN junction; the slab portion is formed from an ion-implanted layer, and has a first slab portion (31) of a first conductivity type and electrically connected to the first convex portion, and a second slab portion (32) of a second conductivity type and electrically connected to the second convex portion, and is arranged so as to include a portion that forms a PN junction with the core portion; In a region (ER2) where a PN junction is formed between the slab portion and the core portion, the second convex portions are arranged on both sides of the core portion on the slab portion side, and the core portion is sandwiched between the first slab portions.

2. 2. The optical phase modulator according to claim 1, wherein in the region where a PN junction is formed between the slab portion and the core portion, the first convex portion is arranged between the second convex portion in a width direction intersecting the extension direction and the thickness direction.

3. 3. The optical phase modulator according to claim 2, wherein the core portion has a plurality of first convex portions sandwiched between the second convex portions in the width direction, and depletion layers resulting from PN junctions between the first convex portions and the second convex portions are configured to be non-contact with each other.

4. 2. The optical phase modulator according to claim 1, wherein the first convex portion is disposed on the second convex portion in the region where a PN junction is formed between the slab portion and the core portion.

5. 5. The optical phase modulator according to claim 1, wherein the core portion and the slab portion have the regions where a PN junction is formed between the slab portion and the core portion repeatedly arranged in the extension direction.

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