Optical Phase Modulator

Abstract

To provide an optical phase modulator capable of suppressing occurrence of poor connection.SOLUTION: In a rib part 20, defining one edge in an extension direction is one edge 20a, an edge opposite to the one edge in the extension direction as the other edge 20b, and a part between the one edge 20a and the other edge 20b as a middle part 20c, the one edge 20a is configured to have only a first rib part 21 of a first conductivity type, the other edge 20b is configured to have only a second rib 22 of a second conductivity type, the middle part 20c has a structure in which the first rib part and the second rib part are laminated along in a thickness direction, and a first slab portion 31 is of a first conductivity type and is connected to the first rib part 21 arranged at the one edge, and a second slab portion 32 is of the second conductivity type and is connected to the second rib part 22 placed on the other edge.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an optical phase modulator having a PN junction.

Background Art

[0002] Conventionally, an optical phase modulator having a rib portion has been proposed (see, for example, Patent Document 1). Specifically, in this optical phase modulator, a rib portion extending in one direction as an extending direction, and a first slab portion and a second slab portion disposed on both sides of the rib portion, connected to the rib portion, and having a thickness thinner than that of the rib portion. Note that, when the direction intersecting the extending direction and the thickness direction of the rib portion is defined as the width direction, the length in the width direction is longer than the length in the thickness direction.

[0003] Specifically, in the rib portion, an N-type first rib portion and a P-type second rib portion are laminated in the thickness direction, and a PN junction is formed along the extending direction of the rib portion. For example, in this optical phase modulator, the first rib portion is laminated on the second rib portion. The first slab portion is N-type, and the second slab portion is P-type. The first slab portion and the second slab portion are disposed so as to sandwich the rib portion.

[0004] In addition, the rib portion is configured such that only the upper first rib portion is disposed on one end portion side in the width direction. That is, on one end portion side in the width direction, the first rib portion is disposed so as to cover the second rib portion. The first rib portion is connected to the first slab portion on the one end portion side. The second rib portion is connected to the second slab portion on the other end portion side in the width direction.

[0005] Such an optical phase modulator is configured by using, for example, an SOI substrate (abbreviation for Silicon On Insulator) on which a support substrate, an insulating film, and an active layer are laminated. Then, N-type impurities and P-type impurities are ion-implanted into the active layer using a mask, and the rib portion and the slab portion are partitioned by performing etching or the like using the mask.

Prior Art Documents

Patent Document

[0006]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0007] However, in the optical phase modulator as described above, when mask misalignment or the like occurs, connection failure may occur between the portion located above the rib portion and the slab portion.

[0008] In view of the above points, an object of the present invention is to provide an optical phase modulator capable of suppressing the occurrence of connection failure.

Means for Solving the Problems

[0009] Claim 1 for achieving the above object is an optical phase modulator having a rib portion (20), which is extended in one direction as an extending direction, with the direction intersecting the extending direction and along the surface direction of the rib portion as the width direction, and the direction intersecting the extending direction and the width direction as the thickness direction. The rib portion has a length in the width direction longer than the length in the thickness direction, a first slab portion (31) having a thickness thinner than that of the rib portion and extending in one direction in the width direction in a state of being connected to the rib portion, and a second slab portion (32) having a thickness thinner than that of the rib portion and extending in the other direction in the width direction in a state of being connected to the rib portion. The rib portion is The thickness is made constant in the extending direction,If one end in the extending direction is defined as one end (20a), the end on the side opposite to the one end in the extending direction is defined as the other end (20b), and the portion between the one end and the other end is defined as the intermediate portion (20c), then the one end is configured to have only the first rib portion (21) of the first conductivity type, the other end is configured to have only the second rib portion (22) of the second conductivity type, the intermediate portion is configured such that the first rib portion and the second rib portion are laminated along the thickness direction, the first slab portion is of the first conductivity type and is connected to the first rib portion disposed at the one end, and the second slab portion is of the second conductivity type and is connected to the second rib portion disposed at the other end.

[0010] According to this, one end of the rib portion is configured to have only the first rib portion, and the other end of the rib portion is configured to have only the second rib portion. Then, the first slab portion is connected to the first rib portion disposed at one end of the rib portion, and the second slab portion is connected to the second rib portion disposed at the other end of the rib portion. Therefore, in the phase modulator of the present embodiment, even if mask misalignment or the like occurs, it is possible to suppress the occurrence of a connection failure between the first rib portion and the first slab portion, and it is possible to suppress the occurrence of a connection failure between the second rib portion and the second slab portion.

[0011] Note that the reference numerals in parentheses attached to each component or the like indicate an example of the correspondence relationship between the component or the like and the specific components or the like described in the embodiments described later.

Brief Description of the Drawings

[0012]

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Embodiments for Carrying Out the Invention

[0013] Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following embodiments, parts that are identical or equivalent to each other are denoted by the same reference numerals for description.

[0014] (First Embodiment) The first embodiment will be described with reference to FIGS. 1 to 5. Note that the optical phase modulator of this embodiment is preferably used for communication devices for optical fibers and the like.

[0015] The optical phase modulator of this embodiment is configured using a semiconductor substrate 10 composed of an SOI substrate on which a support substrate 11, an insulating film 12, and an active layer 13 are laminated. 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 normal direction to the plane direction of the semiconductor substrate 10 is also referred to as the thickness direction. Note that the normal direction to the plane direction of the semiconductor substrate 10 is, in other words, the direction along the lamination direction of the support substrate 11, the insulating film 12, and the active layer 13. Also, in FIG. 1, an interlayer insulating film 60 described later is omitted.

[0016] The active layer 13 has a rib portion 20, a first slab portion 31, a second slab portion 32, a first contact portion 41, a second contact portion 42 doped with impurities, and an undoped portion 50 not doped with impurities.

[0017] The rib portion 20 extends in one direction in the plane direction of the semiconductor substrate 10 as an extension direction. Then, when the direction intersecting the thickness direction and the extension direction is defined as the width direction, the rib portion 20 has a longer length in the width direction than in the thickness direction. In FIGS. 2 and the like, the vertical direction of the paper surface is the thickness direction, and the horizontal direction of the paper surface is the width direction. Also, the width direction is a direction intersecting the extension direction of the rib portion 20 and can also be said to be a direction along the plane direction of the rib portion 20.

[0018] The rib portion 20 is configured by laminating an N-type first rib portion 21 and a P-type second rib portion 22 in the thickness direction, and a PN junction is formed between the first rib portion 21 and the second rib portion 22. In the rib portion 20 of the present embodiment, the first rib portion 21 and the second rib portion 22 are laminated in this order from the side of the insulating film 12. Also, in the present embodiment, the first rib portion 21 and the second rib portion 22 have approximately the same impurity concentration.

[0019] At one end of the rib portion 20 in the extending direction, only the first rib portion 21 is arranged. Also, at the other end of the rib portion 20 in the extending direction, only the second rib portion 22 is arranged. That is, it can be said that the rib portion 20 has a configuration in which the substantially L-shaped first rib portion 21 and the second rib portion 22 are fitted together as shown in FIG. 5 in a cross section along the extending direction. In FIG. 1, one end of the rib portion 20 in the extending direction is the end portion on the lower side of the paper surface, and the other end of the rib portion 20 in the extending direction is the end portion on the upper side of the paper surface. Hereinafter, in the rib portion 20, one end will be referred to as one end portion 20a, the other end will be referred to as the other end portion 20b, and the portion between the one end portion 20a and the other end portion 20b will be referred to as the intermediate portion 20c. That is, in the rib portion 20, only the first rib portion 21 is arranged at the one end portion 20a, only the second rib portion 22 is arranged at the other end portion 20b, and the first rib portion 21 and the second rib portion 22 are laminated at the intermediate portion 20c.

[0020] The first slab portion 31 is of N type and is connected to the first rib portion 21 arranged at one end 20a of the rib portion 20. The second slab portion 32 is of P type and is connected to the second rib portion 22 arranged at the other end 20b of the rib portion 20. The first slab portion 31 and the second slab portion 32 are thinner than the rib portion 20. In this embodiment, the first slab portion 31 and the second slab portion 32 are of the same thickness as the first rib portion 21 arranged at the middle portion 20c of the rib portion 20. In this embodiment, the first slab portion 31 and the second slab portion 32 have the same impurity concentration as the first rib portion 21 and the second rib portion 22. The first slab portion 31 and the second slab portion 32 are arranged so as to protrude to the opposite side across the rib portion 20.

[0021] The first contact portion 41 is an N-type semiconductor having a higher impurity concentration than the first slab portion 31. + The second contact portion 42 is a P type, and is disposed on the opposite side of the rib portion 20 across the first slab portion 31, and is connected to the first slab portion 31. The second contact portion 42 is a P type having a higher impurity concentration than the second slab portion 32. + The first contact portion 41 and the second contact portion 42 are disposed on the opposite side of the second slab portion 32 from the rib portion 20 and are connected to the second slab portion 32. In this embodiment, the first contact portion 41 and the second contact portion 42 have the same thickness as the rib portion 20.

[0022] The undoped portion 50 is disposed in a position of the active layer 13 different from the positions of the rib portion 20, the first slab portion 31, the second slab portion 32, the first contact portion 41, and the second contact portion 42. In other words, the undoped portion 50 is configured in a portion of the active layer 13 different from the portions where the rib 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.

[0023] An interlayer insulating film 60 is disposed on the active layer 13. The interlayer insulating film 60 is formed with a first contact hole 61 that exposes the first contact portion 41 and a second contact hole 62 that exposes the second contact portion 42. On the interlayer insulating film 60, a first electrode 71 connected to the first contact portion 41 through the first contact hole 61 and a second electrode 72 connected to the second contact portion 42 through the second contact hole 62 are formed.

[0024] The above is the configuration of the optical phase modulator in this embodiment. Next, the operation of the optical phase modulator will be briefly described.

[0025] In the optical phase modulator of this embodiment, light mainly propagates along the extending direction of the rib portion 20. In the optical phase modulator, when a voltage higher than that of the second electrode 72 (i.e., a reverse bias voltage) is applied to the first electrode 71, the depletion layer expands at the PN junction and the carrier density decreases. Thereby, the effective refractive index of light can be changed and the phase can be changed. In this case, light is likely to propagate while spreading in an elliptical shape with the width direction as the major axis in a cross section with the propagation direction (i.e., the extending direction of the rib portion 20) as the normal direction. For this reason, the rib portion 20 has a longer length in the width direction than in the thickness direction. Thereby, in the optical phase modulator, it is possible to propagate light while reducing the modulation loss.

[0026] Next, the manufacturing method and effects of the optical phase modulator of this embodiment will be described with reference to FIGS. 6A to 6C, FIG. 7, and FIG. 8. Note that FIGS. 6A to 6C, FIG. 7, and FIG. 8 are diagrams corresponding to the III-III cross section in FIG. 1.

[0027] When manufacturing the optical phase modulator, first, as shown in FIG. 6A, a semiconductor substrate 10 in which a support substrate 11, an insulating film 12, and an active layer 13 are sequentially laminated is prepared.

[0028] Next, as shown in FIG. 6B, a mask (not shown) is disposed to perform partial etching or the like to reduce the thickness of the portions that will become the first slab portion 31, the second slab portion 32, and the undoped portion 50.

[0029] Thereafter, as shown in FIG. 6C, a mask (not shown) is disposed and N-type impurities and P-type impurities are ion-implanted to form the first rib portion 21, the second rib portion 22, the first slab portion 31, the second slab portion 32, the first contact portion 41, and the second contact portion 42. Note that the first slab portion 31, the second slab portion 32, the first contact portion 41, and the second contact portion 42 are formed in a cross-section different from that of FIG. 6C.

[0030] Here, if a configuration in which the second rib portion 22 and the second slab portion 32 are electrically connected at the intermediate portion 20c in the rib portion 20 is used as the optical phase modulator of the comparative example, the optical phase modulator of the comparative example is as shown in FIG. 7. That is, in the optical phase modulator of the comparative example, the second rib portion 22 is disposed so as to cover the first rib portion 21 at one end in the width direction of the rib portion 20, and this portion is connected to the second slab portion 32. Then, in the phase modulator of the comparative example, when mask misalignment or the like occurs during manufacturing, as shown in FIG. 8, a connection failure between the second rib portion 22 and the second slab portion 32 may occur.

[0031] Therefore, in the present embodiment, one end portion 20a of the rib portion 20 is configured to include only the first rib portion 21, and the other end portion 20b of the rib portion 20 is configured to include only the second rib portion 22. Then, the first slab portion 31 is connected to the first rib portion 21 disposed at one end portion 20a of the rib portion 20, and the second slab portion 32 is connected to the second rib portion 22 disposed at the other end portion 20b of the rib portion 20. Thereby, even if mask misalignment or the like occurs, it is possible to suppress the occurrence of a connection failure between the first rib portion 21 and the first slab portion 31, and it is possible to suppress the occurrence of a connection failure between the second rib portion 22 and the second slab portion 32.

[0032] According to the present embodiment described above, one end portion 20a of the rib portion 20 is configured as only the first rib portion 21, and the other end portion 20b of the rib portion 20 is configured as only the second rib portion 22. Then, the first slab portion 31 is connected to the first rib portion 21 disposed at one end portion 20a of the rib portion 20, and the second slab portion 32 is connected to the second rib portion 22 disposed at the other end portion 20b of the rib portion 20. Therefore, in the phase modulator of the present embodiment, even if mask misalignment or the like occurs, it is possible to suppress the occurrence of a connection failure between the first rib portion 21 and the first slab portion 31, and it is also possible to suppress the occurrence of a connection failure between the second rib portion 22 and the second slab portion 32.

[0033] Further, in order to configure the rib portion 20 as described above, at one end portion in the width direction of the rib portion 20 in the intermediate portion 20c, it is not necessary to arrange the second rib portion 22 disposed in the upper layer so as to cover the first rib portion 21 disposed in the lower layer. Therefore, in the optical phase modulator of the present embodiment, when the length in the width direction of the rib portion 20 is the same as that of the optical phase modulator of the comparative example, in the rib portion 20, the region of the PN junction can be widened. Therefore, the amount of phase change can also be improved.

[0034] (Second Embodiment) The second embodiment will be described. This embodiment is different from the first embodiment in that the configurations of the first slab portion 31 and the second slab portion 32 are changed. Since the other aspects are the same as those of the first embodiment, the description is omitted here.

[0035] In the optical phase modulator of the present embodiment, as shown in FIGS. 9 and 10, the second slab portion 32 is arranged so as to be connected to the second rib portion 22 disposed at the other end portion 20b of the rib portion 20 and the first rib portion 21 disposed in the intermediate portion 20c. That is, in the present embodiment, in the intermediate portion 20c of the rib portion 20, a PN junction is also formed between the first rib portion 21 and the second slab portion 32.

[0036] Further, in the present embodiment, the first slab portion 31 is arranged so as to be connected to the first rib portion 21 disposed at one end portion 20a and the intermediate portion 20c of the rib portion 20.

[0037] The first contact portion 41 is formed such that the length along the extending direction is approximately the same as the length of the first slab portion 31. The second contact portion 42 is formed such that the length along the extending direction is approximately the same as the length of the second slab portion 32.

[0038] According to the present embodiment described above, the first slab portion 31 is connected to the first rib portion 21 disposed at one end portion 20a of the rib portion 20, and the second slab portion 32 is connected to the second rib portion 22 disposed at the other end portion 20b of the rib portion 20. Therefore, the same effects as those of the first embodiment can be obtained.

[0039] (1) In the present embodiment, the second slab portion 32 is connected to the first rib portion 21 disposed at the intermediate portion 20c. Therefore, at the intermediate portion 20c of the rib portion 20, a PN junction is also formed between the first rib portion 21 and the second slab portion 32. Thus, when a reverse bias voltage is applied, the depletion layer can be widened even at the PN junction between the first rib portion 21 and the second slab portion 32, and the amount of phase change can be increased.

[0040] Specifically, in the optical phase modulator of the first embodiment, the electron concentration becomes as shown in FIGS. 11A and 11B. In the optical phase modulator of the present embodiment, the electron concentration becomes as shown in FIGS. 12A and 12B. FIGS. 11A and 11B show the simulation results of the cross section along the line XIA-XIA in FIG. 1. FIGS. 12A and 12B show the simulation results of the cross section corresponding to FIG. 10.

[0041] That is, in the optical phase modulator of the first embodiment, when a reverse bias voltage is applied, it is confirmed that electrons remain at the end portion of the first rib portion 21 on the side opposite to the first slab portion 31. On the other hand, in the optical phase modulator of the present embodiment, since a PN junction is also formed at the intermediate portion 20c of the rib portion 20, it is confirmed that it is difficult for electrons to remain at the end portion of the first rib portion 21 on the side opposite to the first slab portion 31 when a reverse bias voltage is applied.

[0042] And, as shown in Fig. 13, the relationship between the reverse bias voltage and the amount of phase change is larger in the second embodiment because carriers can be sufficiently discharged. In the present embodiment, since the first slab portion 31 and the second slab portion 32 are arranged on both sides of the rib portion 20, when light propagates through the intermediate portion 20c of the rib portion 20, light also enters the first slab portion 31 and the second slab portion 32. For this reason, as shown in Fig. 14, when the reverse bias voltage is low, the modulation loss is larger in the second embodiment than in the first embodiment. However, when the reverse bias voltage is increased, the amount of carrier discharge becomes larger in the optical phase modulator of the second embodiment, and the modulation loss can also be reduced.

[0043] (2) In the present embodiment, the first slab portion 31 is also connected to the first rib portion 21 at the intermediate portion 20c. For this reason, the potential of the first rib portion 21 arranged at the intermediate portion 20c can be stabilized.

[0044] (Third Embodiment) The third embodiment will be described. This embodiment is different from the second embodiment in that the impurity concentrations of the first rib portion 21, the second rib portion 22, and the second slab portion 32 are changed. Since the other aspects are the same as those of the first embodiment, the description is omitted here.

[0045] As shown in Figs. 15 to 18, the optical phase modulator of the present embodiment has the same basic configuration as that of the second embodiment. In the present embodiment, the second rib portion 22 has a higher impurity concentration than the first rib portion 21. However, the first rib portion 21 and the second rib portion 22 have an impurity concentration such that the first rib portion 21 can be depleted when a reverse bias voltage is applied. Also, the second slab portion 32 is a P + type having a higher impurity concentration than the second rib portion 22. However, the second slab portion 32 has a lower impurity concentration than the second contact portion 42. In Figs. 15 to 17, for easy understanding, the second contact portion 42 is shown as a P ++ type. Also, the first slab portion 31 has the same impurity concentration as the first rib portion 21.

[0046] Furthermore, in the second rib portion 22 disposed at the other end portion 20b of the rib portion 20, the impurity concentration of the connection portion 22a connected to the first rib portion 21 is higher than that of the second rib portion 22 disposed in the intermediate portion 20c or the like. In other words, the connection portion 22a can also be said to be the lower layer portion of the second rib portion 22 disposed at the other end portion 20b of the rib portion 20.

[0047] Next, the operation and effects of the optical phase modulator of the present embodiment will be described.

[0048] When a reverse bias voltage is applied to the PN junction as described above, the carrier density decreases and the effective refractive index of light changes in the optical phase modulator. Here, holes and electrons as carriers existing in the rib portion 20 have a lower light absorption rate for holes than for electrons. Therefore, in the present embodiment, the impurity concentration of the second rib portion 22 is made higher than that of the first rib portion 21 so that there are more holes than electrons in the rib portion 20. As a result, compared with an optical phase modulator in which the amounts of holes and electrons are the same and the total amount of carriers existing in the rib portion 20 is the same, the modulation loss can be reduced while the amount of phase change can be made equivalent.

[0049] Also, in the present embodiment, the impurity concentration of the second slab portion 32 is made higher than that of the second rib portion 22. As a result, it becomes easier to discharge electrons as carriers, and it is possible to further suppress the remaining of electrons at the end portion of the first rib portion 21 on the side opposite to the first slab portion 31.

[0050] Similarly, in the present embodiment, the second rib portion 22 disposed at the other end portion 20b of the rib portion 20 has a higher impurity concentration in the connection portion 22a connected to the first rib portion 21 than in the second rib portion 22 disposed in the intermediate portion 20c or the like. Therefore, it becomes easier to discharge electrons as carriers from the connection portion 22a, and it is possible to further suppress the remaining of carriers in the first rib portion 21.

[0051] According to the present embodiment described above, the first slab portion 31 is connected to the first rib portion 21 disposed at one end portion 20a of the rib portion 20, and the second slab portion 32 is connected to the second rib portion 22 disposed at the other end portion 20b of the rib portion 20. Therefore, the same effects as those of the first embodiment can be obtained.

[0052] (1) In the present embodiment, the impurity concentration of the second rib portion 22 is made higher than the impurity concentration of the first rib portion 21 so that the number of holes in the rib portion 20 becomes larger than the number of electrons. Therefore, compared with an optical phase modulator in which the amounts of holes and electrons are the same and the total amount of carriers present in the rib portion 20 is the same, the modulation loss can be reduced while the amount of phase change can be made equivalent.

[0053] (2) In the present embodiment, the impurity concentration of the second slab portion 32 is made higher than the impurity concentration of the second rib portion 22. As a result, it becomes easier to discharge electrons as carriers, and it is possible to further suppress the remaining of electrons on the side opposite to the first slab portion 31 in the first rib portion 21.

[0054] (3) In the present embodiment, the second rib portion 22 disposed at the other end portion 20b of the rib portion 20 has a higher impurity concentration than the second rib portion 22 in which the connection portion 22a connected to the first rib portion 21 is disposed in the intermediate portion 20c or the like. Therefore, it becomes easier to discharge electrons as carriers also from the connection portion 22a, and it is possible to further suppress the remaining of carriers in the first rib portion 21.

[0055] (Other Embodiments) Although the present disclosure has been described in accordance with the embodiments, it is understood that the present disclosure is not limited to the embodiments and structures. The present disclosure includes various modifications and modifications within the equivalent scope. In addition, various combinations and forms, and further, other combinations and forms including only one element, more, or less thereof, fall within the scope and spirit of the present disclosure.

[0056] In each of the above embodiments, an example in which the rib portion 20 is configured by arranging the second rib portion 22 on the first rib portion 21 has been described. However, the rib portion 20 may be configured by arranging the N-type first rib portion 21 on the P-type second rib portion 22. In this configuration, the first conductivity type is P-type and the second conductivity type is N-type. In this case, in the third embodiment, by making the impurity concentration of the N-type first slab portion 31 higher than the impurity concentration of the first rib portion 21, the same effect as that of the third embodiment can be obtained. Further, in the third embodiment, by making the impurity concentration of the connection portion connected to the second rib portion 22 at the end of the rib portion 20 in the first rib portion 21 higher than the impurity concentration of the first rib portion 21 arranged in the intermediate portion 20c or the like, the same effect as that of the third embodiment can be obtained. (Features of the present invention) [Claim 1] An optical phase modulator having a rib portion (20), When extending in one direction as an extending direction, taking the direction intersecting the extending direction and along the plane direction of the rib portion as a width direction, and taking the direction intersecting the extending direction and the width direction as a thickness direction, the rib portion having a length in the width direction longer than the length in the thickness direction, A first slab portion (31) having a thickness thinner than that of the rib portion and extending in one direction in the width direction in a state of being connected to the rib portion, A second slab portion (32) having a thickness thinner than that of the rib portion and extending in the other direction in the width direction in a state of being connected to the rib portion, and comprising, One end in the extending direction of the rib portion is an end portion (20a), the end portion on the side opposite to the one end in the extending direction is the other end portion (20b), and when the middle portion between the one end portion and the other end portion is the intermediate portion (20c), the one end portion has a configuration having only the first rib portion (21) of the first conductivity type, the other end portion has a configuration having only the second rib portion (22) of the second conductivity type, and the intermediate portion has a configuration in which the first rib portion and the second rib portion are laminated along the thickness direction, The first slab portion has the first conductivity type and is connected to the first rib portion arranged at the one end portion, The second slab portion is of a second conductivity type and is connected to the second rib portion disposed at the other end, and is an optical phase modulator. [Claim 2] The first rib portion and the second rib portion are such that the second rib portion is laminated on the first rib portion at the intermediate portion. The optical phase modulator according to claim 1, wherein the second slab portion is also connected to the first rib portion disposed at the intermediate portion. [Claim 3] The first conductivity type is an N type, and the second conductivity type is a P type. The optical phase modulator according to claim 1 or 2, wherein the second rib portion has a higher impurity concentration than the first rib portion. [Claim 4] The optical phase modulator according to claim 2 or 3, wherein the second slab portion has a higher impurity concentration than the second rib portion. [Claim 5] In the second rib portion at the other end, the impurity concentration of the connection portion (22a) connected to the first rib portion disposed at the intermediate portion is higher than the impurity concentration of the second rib portion disposed at the intermediate portion. The optical phase modulator according to any one of claims 2 to 4.

Explanation of reference numerals

[0057] 20 Rib portion 20a One end portion 20b The other end portion 20c Intermediate portion 21 First rib portion 22 Second rib portion 31 First slab portion 32 Second slab portion

Claims

1. An optical phase modulator having a rib portion (20), When extended in one direction as the extending direction, with the direction intersecting the extending direction and along the plane direction of the rib portion as the width direction, and the direction intersecting the extending direction and the width direction as the thickness direction, the rib portion having a length in the width direction longer than the length in the thickness direction, A first slab portion (31) having a thickness thinner than that of the rib portion and extending in one direction in the width direction in a state of being connected to the rib portion, A second slab portion (32) having a thickness thinner than that of the rib portion and extending in the other direction in the width direction in a state of being connected to the rib portion, and comprising, The rib portion has a constant thickness in the extending direction, with one end in the extending direction as one end (20a) and the end opposite to one end in the extending direction as the other end (20b), and the portion between one end and the other end as the intermediate portion (20c). Then, one end has a configuration having only a first rib portion (21) of a first conductivity type, the other end has a configuration having only a second rib portion (22) of a second conductivity type, and the intermediate portion has a configuration in which the first rib portion and the second rib portion are laminated along the thickness direction, The first slab portion has a first conductivity type and is connected to the first rib portion disposed at one end, The second slab portion has a second conductivity type and is connected to the second rib portion disposed at the other end. An optical phase modulator.

2. In the intermediate portion, the second rib portion is laminated on the first rib portion for the first rib portion and the second rib portion, The optical phase modulator according to claim 1, wherein the second slab portion is also connected to the first rib portion disposed in the intermediate portion.

3. The first conductivity type is N-type, and the second conductivity type is P-type, The optical phase modulator according to claim 1 or 2, wherein the second rib portion has a higher impurity concentration than the first rib portion.

4. The optical phase modulator according to claim 2, wherein the second slab portion has a higher impurity concentration than the second rib portion.

5. For the second rib portion at the other end, the impurity concentration of the connection portion (22a) connected to the first rib portion disposed in the intermediate portion is higher than the impurity concentration of the second rib portion disposed in the intermediate portion. The optical phase modulator according to claim 2.

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