Optical phase modulator

Abstract

To prevent a reduction in effective refractive index of light, while preventing an increase in modulation loss.SOLUTION: A rib part 20 has a first rib part 21 of an N-type and a second rib part 22 of a P-type in a width direction. A first slab part 31 is of the N-type, and is connected with the first rib part 21 and arranged on the opposite side of the second rib part 22. A second slab part 32 is of the P-type, and is connected with the second rib part 22 and arranged on the opposite side of the first rib part 21. A third slab part 33 is of the P-type, and is connected with the first rib part 21 and arranged on the opposite side of the second rib part 22. A fourth slab part 34 is of the N-type, and is connected with the second rib part 22 and arranged on the opposite side of the first rib part 21. On a cross section in which an extension direction is defined as a normal direction, a PN structure formed of the rib part 20, first slab part 31, and second slab part 32, and a PNPN structure formed of the rib part 20, third slab part 33, and fourth slab part 34 are alternately arranged along the extension direction.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an optical phase modulator having rib sections. [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 has an optical waveguide having a rib portion that extends in one direction, and a first slab portion and a second slab portion arranged on both sides of the rib portion, connected to the rib portion, and having a thinner thickness than the rib portion.

[0003] In the rib section, if the width direction is defined as the direction intersecting the extension direction and thickness direction, then an N-shaped first rib section and a P-shaped second rib section are arranged in the width direction. Furthermore, the first and second rib sections are periodically arranged along the extension direction. The second rib section is fitted between adjacent first rib sections along the extension direction. Similarly, the first rib section is fitted between adjacent second rib sections along the extension direction. In other words, in the planar shape, the rib section of this optical phase modulator is in a state where the roughly L-shaped first rib section and the second rib section are fitted together. For this reason, this optical phase modulator has a configuration with a PN junction in the direction intersecting the extension direction.

[0004] Hereinafter, the first rib section located between adjacent second rib sections along the extension direction will be referred to as the first connecting section, and the first rib section extending along the extension direction will be referred to as the first main section. Similarly, the second rib section located between adjacent first rib sections along the extension direction will be referred to as the second connecting section, and the second rib section extending along the extension direction will be referred to as the second main section. In other words, in the rib section of this optical phase modulator, the first main section and the second connecting section are arranged alternately along the extension direction, and the second main section and the first connecting section are also arranged alternately.

[0005] The first slab section is P-shaped and connected to the first main section and the second connecting section. Therefore, the second main section is connected to the first slab section via the second connecting section. Furthermore, since the first slab section is connected to the first main section, a PN joint is formed between the first rib section (i.e., the first main section) and the first slab section.

[0006] The second slab section is N-shaped and connected to the second main section and the first connecting section. Therefore, the first main section is connected to the second slab section via the first connecting section. Furthermore, since the second slab section is connected to the second main section, a PN joint is formed between the second rib section (i.e., the second main section) and the second slab section.

[0007] In such an optical phase modulator, in addition to the PN junction within the rib section, PN junctions are also formed between the first rib section and the first slab section, and between the second rib section and the second slab section. Therefore, when a reverse bias voltage is applied to the PN junction, a larger area of ​​depletion layer can be created, which is expected to increase the effective refractive index of the light. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] U.S. Patent Application Publication No. 2017 / 0315387 [Overview of the project] [Problems that the invention aims to solve]

[0009] In the optical phase modulator described above, when a reverse bias voltage is applied to the PN junction, there is a possibility that the carriers in the first and second connection points may be completely discharged first. In this case, it becomes difficult to apply a reverse bias voltage to the first and second main sections of the optical phase modulator described above, and it may become impossible to sufficiently discharge the carriers in the first and second main sections. Therefore, in the optical phase modulator described above, it is conceivable that the configuration should be such that when a reverse bias voltage is applied to the PN junction, the carriers in the first and second connection points are not completely discharged first. However, if carriers remain in the first and second connection points when a reverse bias voltage is applied to the PN junction, the remaining carriers will absorb light, resulting in increased modulation loss.

[0010] In view of the above, the present invention aims to provide an optical phase modulator that can suppress a decrease in the effective refractive index of light while suppressing an increase in modulation loss. [Means for solving the problem]

[0011] Claim 1, for achieving the above objective, is an optical phase modulator having a rib portion (20), comprising: a rib portion extending with one direction as the extension direction; and first to fourth slab portions (31 to 34) that are thinner than the rib portion and arranged in a manner connected to the rib portion, wherein the rib portion has an N-shaped first rib portion (21) and a P-shaped second rib portion (22) arranged along the width direction intersecting the extension direction and the thickness direction, and a PN joint is formed between the first rib portion and the second rib portion along the extension direction, and the first slab portion is N-shaped and is connected to the first rib portion and arranged on the opposite side of the first rib portion from the second rib portion. The second slab section is P-shaped and connected to the second rib section, and positioned on the opposite side of the second rib section from the first rib section. The third slab section is P-shaped and connected to the first rib section, and positioned on the opposite side of the first rib section from the second rib section. The fourth slab section is N-shaped and connected to the second rib section, and positioned on the opposite side of the second rib section from the first rib section. In a cross section with the extension direction as the normal direction, a PN structure consisting of the rib section, the first slab section and the second slab section, and a PNPN structure consisting of the rib section, the third slab section and the fourth slab section are alternately arranged along the extension direction.

[0012] According to this, the optical phase modulator has a configuration in which portions forming PN junctions and portions forming PNPN junctions are alternately and repeatedly arranged in the extension direction. When a reverse bias voltage is applied, the depletion layer expands in the PN junctions between the first rib portion and the second rib portion, between the first rib portion and the third slab portion, and between the second rib portion and the fourth slab portion. This suppresses a decrease in the effective refractive index of light.

[0013] Furthermore, the first rib section is electrically connected to the first slab section, which is located on the opposite side of the second rib section across the first rib section. The second rib section is electrically connected to the second slab section, which is located on the opposite side of the first rib section across the second rib section. In this optical phase modulator, there are no PN junctions intersecting the extension direction within the rib section. Therefore, it is possible to suppress the increase in modulation loss due to residual carriers.

[0014] Note that the reference numerals in parentheses attached to each component etc. indicate an example of the correspondence relationship between the component etc. and the specific components etc. described in the embodiments described later.

Brief Description of the Drawings

[0015] [Figure 1] It is a plan view of an optical phase modulator in the first embodiment. [Figure 2] It is a cross-sectional view taken along line II-II in FIG. 1. [Figure 3] It is a cross-sectional view taken along line III-III in FIG. 1. [Figure 4] It is a plan view of an optical phase modulator in the second embodiment. [Figure 5] It is a cross-sectional view taken along line V-V in FIG. 4. [Figure 6] It is a cross-sectional view of an optical phase modulator in the third embodiment. [Figure 7] It is a plan view of an optical phase modulator in the fourth embodiment. [Figure 8] It is a cross-sectional view taken along line VIII-VIII in FIG. 7. [Figure 9] It is a cross-sectional view taken along line IX-IX in FIG. 7. [Figure 10] It is a plan view of an optical phase modulator in the fifth embodiment.

Modes for Carrying Out the Invention

[0016] Hereinafter, embodiments of the present invention will be described based on the drawings. In the following embodiments, parts that are the same or equivalent to each other are denoted by the same reference numerals for description.

[0017] (First Embodiment) The first embodiment will be described with reference to the drawings. The optical phase modulator of this embodiment is preferably used for communication devices for optical fibers and the like.

[0018] As shown in Figures 1 to 3, the optical phase modulator of this embodiment is constructed using a semiconductor substrate 10 made of an SOI (Silicon On Insulator) substrate in 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. Hereinafter, the direction along the direction normal to the plane direction of the semiconductor substrate 10 will also be called the thickness direction, and the direction that intersects the thickness direction (i.e., the orthogonal direction) and is along the plane direction of the semiconductor substrate 10 will also be called the width direction. In other words, the direction normal to the plane direction of the semiconductor substrate 10 is the direction along the stacking direction of the support substrate 11, the insulating film 12, and the active layer 13. Also, in Figure 1, the interlayer insulating film 60, which will be described later, is omitted.

[0019] The active layer 13 has impurity-doped rib portions 20, a first slab portion 31, a second slab portion 32, a third slab portion 33, and a fourth slab portion 34. The active layer 13 also has a first connecting portion 41, a second connecting portion 42, a third connecting portion 43, a fourth connecting portion 44, a first contact portion 51, a second contact portion 52, a third contact portion 53, and a fourth contact portion 54.

[0020] Specifically, the rib portion 20 extends in one direction along the plane of the semiconductor substrate 10 as the extension direction (hereinafter simply referred to as the extension direction). For example, in Figure 1, the vertical direction of the paper is the extension direction. The rib portion 20 is arranged in the width direction as an N-shaped first rib portion 21 and a P-shaped second rib portion 22, and a PN junction is formed between the first rib portion 21 and the second rib portion 22. The first rib portion 21 and the second rib portion 22 are extended without being divided in the extension direction. In this embodiment, the impurity concentrations of the first rib portion 21 and the second rib portion 22 are approximately the same.

[0021] The first slab section 31 is N-shaped and is positioned on the opposite side of the second rib section 22 so as to connect with the first rib section 21. The first slab section 31 has the same impurity concentration as the first rib section 21. The second slab section 32 is P-shaped and is positioned on the opposite side of the first rib section 21 so as to connect with the second rib section 22. The second slab section 32 has the same impurity concentration as the second rib section 22. The first slab section 31 and the second slab section 32 are arranged periodically along the extension direction. In other words, multiple first slab sections 31 and second slab sections 32 are arranged spaced apart in the extension direction.

[0022] Furthermore, in this embodiment, the first rib portion 21 and the first slab portion 31, and the second rib portion 22 and the second slab portion 32 are formed symmetrically with respect to the interface between the first rib portion 21 and the second rib portion 22 (i.e., the PN joint surface of the rib portion 20).

[0023] The third slab section 33 is P-shaped and is positioned on the opposite side of the second rib section 22 so as to connect with the first rib section 21. More specifically, the third slab section 33 is positioned between adjacent first slab sections 31 along the extension direction. Furthermore, the third slab section 33 has the same impurity concentration as the second rib section 22.

[0024] The fourth slab section 34 is N-shaped and is positioned on the opposite side of the first rib section 21 so as to connect with the second rib section 22. More specifically, the fourth slab section 34 is positioned between adjacent second slab sections 32 along the extension direction. Furthermore, the fourth slab section 34 has the same impurity concentration as the first rib section 21.

[0025] In this embodiment, the third slab portion 33 and the fourth slab portion 34 are formed symmetrically with respect to the interface between the first rib portion 21 and the second rib portion 22. Also, in this embodiment, the third slab portion 33 and the fourth slab portion 34 are longer in the extension direction than the first slab portion 31 and the second slab portion 32.

[0026] Furthermore, the thickness of the first to fourth slab sections 31 to 34 is thinner than that of the rib section 20.

[0027] In this embodiment, if the rib section 20 and the first to fourth slab sections 31 to 34 constitute an optical waveguide OW, the optical waveguide OW is configured as follows. That is, in a cross section with the extension direction as the normal direction, the optical waveguide OW is configured such that portions where PN joints are formed and portions where PNPN joints are formed are alternately and repeatedly arranged in the extension direction. In other words, in the rib section 20, there are no connecting portions within the first rib section 21 that cross the first rib section 21 and connect to the second rib section 22, and there are no connecting portions within the second rib section 22 that cross the second rib section 22 and connect to the first rib section 21. To put it another way, no PN joints intersecting the extension direction are formed in the rib section 20.

[0028] The first connecting portion 41 has an impurity concentration higher than that of the first slab portion 31. + It is formed as a mold and is positioned on the opposite side of the first rib portion 21, with the first slab portion 31 in between, and is connected to the first slab portion 31. The second connecting portion 42 is made of P with an impurity concentration higher than that of the second slab portion 32. + It is positioned on the opposite side of the second rib section 22, sandwiching the second slab section 32, and is connected to the second slab section 32. In this embodiment, the first and second connecting sections 41 and 42 have the same length and thickness in the extension direction as the first and second slab sections 31 and 32.

[0029] The third connection section 43 is made of P, in which the impurity concentration is higher than that of the third slab section 33. + It is formed as a mold and is positioned on the opposite side of the third slab section 33 from the first rib section 21 and connected to the third slab section 33. The fourth connecting section 44 has an impurity concentration higher than that of the fourth slab section 34. + It is positioned on the opposite side of the second rib section 22, sandwiching the fourth slab section 34, and is connected to the fourth slab section 34. In this embodiment, the third and fourth connecting sections 43 and 44 have the same length and thickness in the extension direction as the third and fourth slab sections 33 and 34.

[0030] The first contact portion 51 is made of N with an impurity concentration higher than that of the first connection portion 41. ++ It is molded and is positioned on the opposite side of the first rib portion 21, with the first connecting portion 41 in between, and is connected to the first connecting portion 41. The second contact portion 52 is made of P with an impurity concentration higher than that of the second connecting portion 42. ++ The first and second contact portions 51 and 52 in this embodiment are positioned on the opposite side of the second rib portion 22, with the second connecting portion 42 in between, and are connected to the second connecting portion 42. Furthermore, the first and second contact portions 51 and 52 in this embodiment have the same length in the extension direction as the first and second slab portions 31 and 32. In addition, the first and second contact portions 51 and 52 in this embodiment have the same thickness as the rib portion 20.

[0031] The third contact portion 53 has a higher impurity concentration than the third connection portion 43. ++ It is molded and is positioned on the opposite side of the first rib portion 21, with the third connecting portion 43 in between, and is connected to the third connecting portion 43. The fourth contact portion 54 is made of N with an impurity concentration higher than that of the fourth connecting portion 44. ++ It is shaped and positioned on the opposite side of the second rib portion 22, with the fourth connecting portion 44 in between, and is connected to the fourth connecting portion 44. Furthermore, the third and fourth contact portions 53 and 54 in this embodiment have the same length in the extension direction as the third and fourth slab portions 33 and 34. In addition, the third and fourth contact portions 53 and 54 in this embodiment have the same thickness as the rib portion 20.

[0032] An interlayer insulating film 60 is disposed on the active layer 13. The interlayer insulating film 60 has a first contact hole 61 that exposes the first contact portion 51, and a second contact hole 62 that exposes the second contact portion 52. The interlayer insulating film 60 also has a third contact hole 63 that exposes the third contact portion 53, and a fourth contact hole 64 that exposes the fourth contact portion 54.

[0033] On the interlayer insulating film 60, a first electrode 71 connected to the first contact portion 51 through the first contact hole 61 and a second electrode 72 connected to the second contact portion 52 through the second contact hole 62 are formed. On the interlayer insulating film 60, a third electrode 73 connected to the third contact portion 53 through the third contact hole 63 and a fourth electrode 74 connected to the fourth contact portion 54 through the fourth contact hole 64 are formed.

[0034] The above is the configuration of the optical phase modulator in this embodiment. Next, the operation of the optical phase modulator will be described.

[0035] In the optical phase modulator of this embodiment, light mainly propagates along the extending direction of the rib portion 20. Then, when a higher voltage (i.e., reverse bias voltage) than that of the second and third electrodes 72 and 73 is applied to the first and fourth electrodes 71 and 74, the depletion layer expands at the PN junction and the carrier density decreases. At this time, in this embodiment, the depletion layer expands at the PN junctions between the first rib portion 21 and the second rib portion 22, between the first rib portion 21 and the third slab portion 33, and between the second rib portion 22 and the fourth slab portion 34. Therefore, the change in the effective refractive index of light can be increased. FIGS. 1 to 3 show the state when a reverse bias voltage is applied, and as the state where a higher voltage than that of the second and third electrodes 72 and 73 is applied to the first and fourth electrodes 71 and 74, voltage V + and voltage V - are shown. And in each corresponding figure described later, the same voltage V + and voltage V - are shown.

[0037] Furthermore, in this embodiment, the rib portion 20 does not have a connection portion that crosses the first rib portion 21 and connects to the second rib portion 22 within the first rib portion 21, nor does it have a connection portion that crosses the second rib portion 22 and connects to the first rib portion 21 within the second rib portion 22. Therefore, it is possible to suppress an increase in modulation loss. Here, the phase modulator of the comparative example is one in which a connection portion that crosses the first rib portion 21 and connects to the second rib portion 22 is arranged within the first rib portion 21, and a connection portion that crosses the second rib portion 22 and connects to the first rib portion 21 is arranged within the second rib portion 22. In other words, the phase modulator of the comparative example is one in which a PN junction along a direction intersecting the extension direction is arranged within the rib portion 20.

[0037] In this case, the phase modulator of the comparative example is configured such that carriers remain at each connection point when a reverse bias voltage is applied to the PN junction, as described above. As a result, the modulation loss increases due to the absorption of light by the residual carriers. Therefore, the modulation loss increases as the number of interfaces (i.e., PN junctions) that intersect the extension direction of the rib portion 20 increases. In contrast, in the optical phase modulator of this embodiment, since there are no interfaces intersecting the extension direction within the rib portion 20, the increase in modulation loss due to residual carriers can be suppressed.

[0038] According to the embodiment described above, the optical waveguide OW has a configuration in which portions where PN junctions are formed and portions where PNPN junctions are formed are alternately and repeatedly arranged in the extension direction in a cross section with the extension direction as the normal direction. When a reverse bias voltage is applied, the depletion layer expands at the PN junctions between the first rib portion 21 and the second rib portion 22, between the first rib portion 21 and the third slab portion 33, and between the second rib portion 22 and the fourth slab portion 34. As a result, it is possible to suppress a decrease in the effective refractive index of light and to suppress a decrease in the amount of phase change.

[0039] Furthermore, according to this embodiment, the first rib portion 21 is electrically connected to the first slab portion 31, which is located on the opposite side of the first rib portion 21 from the second rib portion 22. The second rib portion 22 is electrically connected to the second slab portion 32, which is located on the opposite side of the second rib portion 22 from the first rib portion 21. Therefore, in the optical phase modulator of this embodiment, there is no interface within the rib portion 20 that intersects the extension direction. As a result, it is possible to suppress the increase in modulation loss due to residual carriers.

[0040] (1) In this embodiment, the first rib portion 21 and the first slab portion 31, and the second rib portion 22 and the second slab portion 32 are formed symmetrically with respect to the interface between the first rib portion 21 and the second rib portion 22. Therefore, when a reverse bias voltage is applied to the PN junction, it is possible to suppress uneven spreading of the depletion layer between the first rib portion 21 and the second rib portion 22, and to suppress an increase in modulation loss.

[0041] (2) In this embodiment, the third slab portion 33 and the fourth slab portion 34 are formed symmetrically with respect to the interface between the first rib portion 21 and the second rib portion 22. Therefore, when a reverse bias voltage is applied to the PN junction, it is possible to suppress uneven spreading of the depletion layer between the first rib portion 21 and the third slab portion 33, and between the second rib portion 22 and the fourth slab portion 34, thereby suppressing an increase in modulation loss.

[0042] (3) In this embodiment, the third slab portion 33 and the fourth slab portion 34 are longer in length along the extension direction than the first slab portion 31 and the second slab portion 32. Therefore, compared to the case where the third slab portion 33 and the fourth slab portion 34 are shorter in length along the extension direction than the first slab portion 31 and the second slab portion 32, the area of ​​the PN junction formed between them and the rib portion 20 can be made larger. Therefore, the effective refractive index of light can be made larger and the amount of phase change can be made larger.

[0043] (Second Embodiment) A second embodiment will now be described. This embodiment is similar to the first embodiment in that a separate region is added. Other aspects are the same as the first embodiment, so a detailed explanation will be omitted here.

[0044] In the optical phase modulator of this embodiment, as shown in Figures 4 and 5, a first undoped layer 81, composed of an active layer 13 and not doped with impurities, is placed between the first slab portion 31 and the third slab portion 33. In this embodiment, the first undoped layer 81 is placed not only between the first slab portion 31 and the third slab portion 33, but also between the first connection portion 41 and the third connection portion 43, and between the first contact portion 51 and the third contact portion 53.

[0045] Furthermore, a second undoped layer 82, composed of an active layer 13 and undoped with impurities, is placed between the second slab portion 32 and the fourth slab portion 34. In this embodiment, the second undoped layer 82 is placed not only between the second slab portion 32 and the fourth slab portion 34, but also between the second connecting portion 42 and the fourth connecting portion 44, and between the second contact portion 52 and the fourth contact portion 54. In this embodiment, the first undoped layer 81 and the second undoped layer 82 correspond to separation regions.

[0046] According to the embodiment described above, the optical waveguide OW has a configuration in which portions where a PN junction is formed and portions where a PNPN junction is formed are alternately and repeatedly arranged in the direction of extension in a cross section with the extension direction as the normal direction. Therefore, the same effects as in the first embodiment can be obtained.

[0047] (1) In an optical phase modulator like this embodiment, light mainly propagates through the rib section 20, but also leaks into the first to fourth slab sections 31 to 34. In this embodiment, a first undoped layer 81 is placed between the first slab section 31 and the third slab section 33, and a second undoped layer 82 is placed between the second slab section 32 and the fourth slab section 34. As a result, PN junctions are not formed between each of the slab sections 31 to 34. In other words, PN junctions are not formed in the first to fourth slab sections 31 to 34 in the direction intersecting the extension direction. Therefore, modulation loss can be further reduced. In addition, since PN junctions are not formed between each of the slab sections 31 to 34, capacitance that may occur at the interface of the PN junction can be reduced, and responsiveness can be improved.

[0048] (Third embodiment) A third embodiment will now be described. This embodiment is a modification of the second embodiment in which the configuration of the separation region is changed. Other aspects are the same as in the second embodiment, so a detailed explanation will be omitted here.

[0049] In the optical phase modulator of this embodiment, as shown in Figure 6, compared to the second embodiment, the first insulating film 91 is placed in the area where the first undoped layer 81 was placed, and the second insulating film 92 is placed in the area where the second undoped layer 82 was placed. Note that Figure 6 is a cross-sectional view corresponding to the VV line in Figure 4. In this embodiment, the first insulating film 91 and the second insulating film 92 correspond to the separation region. Furthermore, the first insulating film 91 and the second insulating film 92 in this embodiment are made of the same material as the interlayer insulating film 60.

[0050] The above describes the configuration of the optical phase modulator in this embodiment. Next, the manufacturing methods for each part 21, 22, 31-34, 41-44, and 51-54 of the active layer 13 in the optical phase modulator of this embodiment will be described.

[0051] First, a semiconductor substrate 10 is prepared in which a support substrate 11, an insulating film 12, and an active layer 13 are stacked in that order. Next, using a mask, N-type impurities are ion-implanted into the parts constituting the first rib portion 21, the first slab portion 31, the fourth slab portion 34, the first connection portion 41, the fourth connection portion 44, the first contact portion 51, and the fourth contact portion 54. Then, using another mask, P-type impurities are ion-implanted into the parts constituting the second rib portion 22, the second slab portion 32, the third slab portion 33, the second connection portion 42, the third connection portion 43, the second contact portion 52, and the third contact portion 53.

[0052] Next, partial etching is performed to reduce the thickness of the first to fourth slab portions 31 to 34 and the first to fourth connecting portions 41 to 44. Then, etching is performed to remove the active layer 13 in the portion where the first insulating film 91 and the second insulating film 92 will be placed. After that, the first insulating film 91 and the second insulating film 92 are placed in the portion where the active layer 13 was removed. In this embodiment, when placing the interlayer insulating film 60 on the active layer 13, the first insulating film 91 and the second insulating film 92 are placed in the same process.

[0053] According to the embodiment described above, the optical waveguide OW has a configuration in which portions where a PN junction is formed and portions where a PNPN junction is formed are alternately and repeatedly arranged in the direction of extension in a cross section with the extension direction as the normal direction. Therefore, the same effects as in the first embodiment can be obtained.

[0054] (1) In this embodiment, the isolation region is composed of a first insulating film 91 and a second insulating film 92. When arranging the first insulating film 91 and the second insulating film 92, the active layer 13 is etched and removed before arrangement. Therefore, compared to the case where the isolation region is composed of the active layer 13, variations in the length of the isolation region in the extension direction can be suppressed. That is, when the isolation region is composed of a first undoped layer 81 as in the second embodiment described above, the length of the isolation region in the extension direction depends on the precision of the construction of the first slab portion 31 and the third slab portion 33. Similarly, when the isolation region is composed of a second undoped layer 82, the length of the isolation region in the extension direction depends on the precision of the construction of the second slab portion 32 and the fourth slab portion 34. In other words, in the configuration of the second embodiment described above, two factors influence the length of the isolation region in the extension direction. In contrast, in the configuration of this embodiment, the length of the isolation region in the extension direction depends on the precision of the etching for arranging the first and second insulating films 91 and 92. In other words, in the configuration of this embodiment, one factor influences the length of the separation region in the extension direction. Therefore, according to this embodiment, the factors influencing the length of the separation region in the extension direction can be reduced. Consequently, variations in the length of the separation region in the extension direction can be suppressed, and variations in the length of the first to fourth slab sections 31 to 34 in the extension direction can be suppressed. This makes it possible to suppress changes in the amount of phase change.

[0055] (Fourth Embodiment) A fourth embodiment will now be described. This embodiment specifies the connection method for the first electrode 71 to the fourth electrode 74 compared to the first embodiment. Other aspects are the same as in the first embodiment, so their explanation will be omitted here.

[0056] In the optical phase modulator of this embodiment, as shown in Figure 7, the first and fourth electrodes 71 and 74 are connected to a common first wiring layer 101, and the second and third electrodes 72 and 73 are connected to a common second wiring layer 102.

[0057] Specifically, as shown in Figures 8 and 9, the interlayer insulating film 60 is constructed by stacking the first interlayer insulating film 60a and the second interlayer insulating film 60b in that order from the semiconductor substrate 10 side. The first interlayer insulating film 60a and the second interlayer insulating film 60b are made of the same material. As shown in Figure 8, the first interlayer insulating film 60a and the second interlayer insulating film 60b have first contact holes 61 that expose the first contact portion 51. The first interlayer insulating film 60a has a second contact hole 62 that exposes the second contact portion 52.

[0058] Furthermore, as shown in Figure 9, the first interlayer insulating film 60a and the second interlayer insulating film 60b have a fourth contact hole 64 that exposes the fourth contact portion 54. The first interlayer insulating film 60a has a third contact hole 63 that exposes the third contact portion 53.

[0059] Furthermore, a second electrode 72 is positioned on the first interlayer insulating film 60a, connected to the second contact portion 52 through a second contact hole 62. A third electrode 73 is positioned on the first interlayer insulating film 60a, connected to the third contact portion 53 through a third contact hole 63. In other words, when a reverse bias voltage is applied to the PN junction, the electrode that becomes the negative electrode is positioned on the first interlayer insulating film 60a.

[0060] A first electrode 71 is positioned on the second interlayer insulating film 60b, connected to the first contact portion 51 through a first contact hole 61. A fourth electrode 74 is positioned on the second interlayer insulating film 60b, connected to the fourth contact portion 54 through a fourth contact hole 64. In other words, when a reverse bias voltage is applied to the PN junction, the electrode that becomes the positive electrode is positioned on the second interlayer insulating film 60b.

[0061] The second electrode 72 and the third electrode 73 are routed appropriately on the first interlayer insulating film 60a and electrically connected to a common first wiring layer 101. Similarly, the first electrode 71 and the fourth electrode 74 are routed appropriately on the second interlayer insulating film 60b and electrically connected to a common second wiring layer 102.

[0062] According to the embodiment described above, the optical waveguide OW has a configuration in which portions where a PN junction is formed and portions where a PNPN junction is formed are alternately and repeatedly arranged in the direction of extension in a cross section with the extension direction as the normal direction. Therefore, the same effects as in the first embodiment can be obtained.

[0063] (1) In this embodiment, the second electrode 72 and the third electrode 73 are electrically connected on the first interlayer insulating film 60a, and the first electrode 71 and the fourth electrode 74 are electrically connected on the second interlayer insulating film 60b. Therefore, interference between the first and fourth electrodes 71 and 74 and the second and third electrodes 72 and 73 can be suppressed, and wiring can be easily routed.

[0064] (Fifth embodiment) A fifth embodiment will now be described. This embodiment differs from the second embodiment in that the impurity concentrations of the first to fourth slab sections 31 to 34 are changed. Other aspects are the same as in the second embodiment, so a detailed explanation will be omitted here.

[0065] In this embodiment, as shown in Figure 10, the first slab portion 31 and the fourth slab portion 34 have a higher impurity concentration than the first rib portion 21. + It is considered to be a type. Similarly, the second slab section 32 and the third slab section 33 have a higher impurity concentration than the second rib section 22. + It is considered a type.

[0066] According to the embodiment described above, the optical waveguide OW has a configuration in which portions where a PN junction is formed and portions where a PNPN junction is formed are alternately and repeatedly arranged in the direction of extension in a cross section with the extension direction as the normal direction. Therefore, the same effects as in the first embodiment can be obtained.

[0067] (1) In this embodiment, the impurity concentration in the first to fourth slab sections 31 to 34 is higher than that in the first and second rib sections 21 and 22. Therefore, when a reverse bias voltage is applied, it is easier to extract carriers from the rib section 20, and the amount of phase change can be improved.

[0068] (Other embodiments) This disclosure is described in accordance with embodiments, but it is understood that this disclosure is not limited to such embodiments or structures. This disclosure also includes various modifications and variations within the scope of equivalents. In addition, various combinations and forms, as well as other combinations and forms that include only one, more, or fewer of those elements, fall within the scope and idea of ​​this disclosure.

[0069] For example, in each of the above embodiments, the first rib portion 21 and the first slab portion 31, and the second rib portion 22 and the second slab portion 32 do not have to be formed symmetrically with respect to the interface between the first rib portion 21 and the second rib portion 22. Similarly, the third slab portion 33 and the fourth slab portion 34 do not have to be formed symmetrically with respect to the interface between the first rib portion 21 and the second rib portion 22. Furthermore, the length of the third slab portion 33 and the fourth slab portion 34 in the extension direction does not have to be longer than that of the first slab portion 31 and the second slab portion 32. Even in such an optical phase modulator, the optical waveguide OW is configured such that, in a cross section with the extension direction as the normal direction, portions where a PN junction is formed and portions where a PNPN junction is formed are alternately and repeatedly arranged in the extension direction. Therefore, the same effects as in the first embodiment can be obtained.

[0070] Furthermore, in the third embodiment described above, the manufacturing process for each part 21, 22, 31-34, 41-44, and 51-54 of the active layer 13 can be modified as appropriate. For example, after partially etching to reduce the thickness of the parts that will become the first to fourth slab parts 31-34 and the first to fourth connecting parts 41-44, etching is performed to arrange the first and second insulating films 91 and 92. Next, N-type impurities and P-type impurities are ion-implanted to form each part 21, 22, 31-34, 41-44, and 51-55, and then the first and second insulating films 91 and 92 may be arranged.

[0071] Furthermore, in the fourth embodiment described above, the first and fourth electrodes 71 and 74 may be arranged on the first interlayer insulating film 60a, and the second and third electrodes 72 and 73 may be arranged on the second interlayer insulating film 60b.

[0072] Furthermore, the above embodiments may be combined as appropriate. For example, the fourth embodiment may be combined with the second and third embodiments so that the first and fourth electrodes 71 and 74 are connected to a common first wiring layer 101, and the second and third electrodes 72 and 73 are connected to a common second wiring layer 102. The fifth embodiment may be combined with the first, third, and fourth embodiments so that the impurity concentration in the first to fourth slab portions 31 to 34 is higher than that in the first and second rib portions 21 and 22. (Features of the present invention) [Claim 1] An optical phase modulator having a rib portion (20), The rib portion extends in one direction as the extension direction, It comprises first to fourth slab sections (31 to 34) which are thinner than the rib section and are arranged in a manner connected to the rib section, The rib portion has an N-shaped first rib portion (21) and a P-shaped second rib portion (22) arranged along the width direction intersecting the extension direction and thickness direction, and a PN joint is formed between the first rib portion and the second rib portion along the extension direction. The first slab portion is N-shaped, connected to the first rib portion, and positioned on the opposite side of the first rib portion from the second rib portion. The second slab portion is P-shaped and is connected to the second rib portion, and is positioned on the opposite side of the second rib portion from the first rib portion. The third slab portion is P-shaped, connected to the first rib portion, and positioned on the opposite side of the first rib portion from the second rib portion. The fourth slab section is N-shaped and is connected to the second rib section, and is positioned on the opposite side of the second rib section from the first rib section. In a cross-section where the extension direction is the normal direction, an optical phase modulator is characterized in which a PN structure composed of the rib portion, the first slab portion and the second slab portion, and a PNPN structure composed of the rib portion, the third slab portion and the fourth slab portion are alternately arranged along the extension direction. [Claim 2] The optical phase modulator according to claim 1, wherein the first rib portion and the first slab portion and the second rib portion and the second slab portion are arranged symmetrically with respect to the interface between the first rib portion and the second rib portion. [Claim 3] The optical phase modulator according to claim 1 or 2, wherein the first rib portion and the third slab portion and the second rib portion and the fourth slab portion are arranged symmetrically with respect to the interface between the first rib portion and the second rib portion. [Claim 4] The optical phase modulator according to any one of claims 1 to 3, wherein the third slab portion and the fourth slab portion are longer in length along the extension direction than the first slab portion and the second slab portion. [Claim 5] The optical phase modulator according to any one of claims 1 to 4, wherein impurity-free isolation regions (81, 82, 91, 92) are arranged between the first slab portion and the third slab portion, and between the second slab portion and the fourth slab portion. [Claim 6] The semiconductor substrate (10) has a support substrate (11), an insulating film (12), and an active layer (13) stacked in that order. The rib portion and the first to fourth slab portions are composed of the activated layer, The optical phase modulator according to claim 5, wherein the isolation region is composed of an insulating film. [Claim 7] An interlayer insulating film (60) covering the rib portion and the first to fourth slab portions, A first electrode (71) connected to the first slab portion of the N type, A second electrode (72) connected to the P-shaped second slab portion, A third electrode (73) connected to the P-type third slab portion, It has a fourth electrode (74) connected to the N-type fourth slab portion, The interlayer insulating film is constructed by laminating a first interlayer insulating film (61) and a second interlayer insulating film (62). The optical phase modulator according to any one of claims 1 to 6, wherein the first electrode and the fourth electrode and the second electrode and the third electrode are such that one electrode is placed on the first interlayer insulating film and connected to the other, and the other electrode is placed on the second interlayer insulating film and connected to the other. [Explanation of Symbols]

[0073] 20 Rib section 21 First rib section 22 Second Rib Section 31. First Slab Section 32. Second Slab Section 33 Third Slab Section 34. Section 4 of the slab

Claims

1. An optical phase modulator having a rib portion (20), The rib portion extends in one direction as the extension direction, The system comprises first to fourth slab sections (31 to 34) which are thinner than the rib section and are arranged in a manner connected to the rib section, The rib portion has an N-shaped first rib portion (21) and a P-shaped second rib portion (22) arranged along the width direction intersecting the extension direction and thickness direction, and a PN joint is formed between the first rib portion and the second rib portion along the extension direction. The first slab portion is N-shaped and is connected to the first rib portion and positioned on the opposite side of the first rib portion from the second rib portion. The second slab portion is P-shaped and is connected to the second rib portion, and is positioned on the opposite side of the second rib portion from the first rib portion. The third slab portion is P-shaped and is connected to the first rib portion and positioned on the opposite side of the first rib portion from the second rib portion. The fourth slab portion is N-shaped and is connected to the second rib portion and positioned on the opposite side of the second rib portion from the first rib portion. In a cross-section where the extension direction is the normal direction, an optical phase modulator in which a PN structure composed of the rib portion, the first slab portion and the second slab portion and a PNPN structure composed of the rib portion, the third slab portion and the fourth slab portion are alternately arranged along the extension direction.

2. The optical phase modulator according to claim 1, wherein the first rib portion and the first slab portion and the second rib portion and the second slab portion are arranged symmetrically with respect to the interface between the first rib portion and the second rib portion.

3. The optical phase modulator according to claim 2, wherein the first rib portion and the third slab portion and the second rib portion and the fourth slab portion are arranged symmetrically with respect to the interface between the first rib portion and the second rib portion.

4. The optical phase modulator according to any one of claims 1 to 3, wherein the third slab portion and the fourth slab portion are longer in length along the extension direction than the first slab portion and the second slab portion.

5. The optical phase modulator according to any one of claims 1 to 3, wherein impurity-free isolation regions (81, 82, 91, 92) are arranged between the first slab portion and the third slab portion, and between the second slab portion and the fourth slab portion.

6. The semiconductor substrate (10) has a support substrate (11), an insulating film (12), and an active layer (13) stacked in that order. The rib portion and the first to fourth slab portions are composed of the active layer, The optical phase modulator according to claim 5, wherein the isolation region is composed of an insulating film.

7. An interlayer insulating film (60) covering the rib portion and the first to fourth slab portions, A first electrode (71) connected to the first slab portion of the N type, A second electrode (72) connected to the P-shaped second slab portion, A third electrode (73) connected to the P-shaped third slab portion, It has a fourth electrode (74) connected to the N-type fourth slab portion, The interlayer insulating film is constructed by laminating a first interlayer insulating film (60a) and a second interlayer insulating film (60b). The optical phase modulator according to claim 1, wherein the first electrode and the fourth electrode and the second electrode and the third electrode are such that one electrode is arranged on the first interlayer insulating film and connected to the other, and the other electrode is arranged on the second interlayer insulating film and connected to the other.

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