JP2020148826A - Semiconductor optical phase modulator, hybrid modulator, and ssb modulator - Google Patents

Abstract

To make it possible to reduce optical loss even when light to be modulated has a high power.SOLUTION: A semiconductor optical phase modulator 10 converts single-mode light into multi-mode light, and has a first area A1 where a mirror image is formed due to interference of light and a second area A2 where the power density of the light is lower than that in the first area A1. The semiconductor optical phase modulator comprises a multi-mode waveguide 12 for propagating the interfered light, and a pair of channels 14 and 15 provided to face each other so as to sandwich the propagated light with the second area A2 and each having a higher doping concentration than a doping concentration at a peripheral area.SELECTED DRAWING: Figure 1

Description

The present invention relates to a semiconductor optical phase modulator, and a hybrid modulator and an SSB modulator using this semiconductor optical phase modulator.

Conventionally, as an optical phase modulator used in a laser light source of a laser radar detector, an SSB (Single Side Band) modulator, etc., the semiconductor optical modulator described in Patent Document 1 and the optical modulator described in Patent Document 2 It has been known. In the light modulator of Patent Document 1 and the light modulator of Patent Document 2, a semiconductor material such as silicon (Si) is used as a waveguide for propagating light. Hereinafter, the semiconductor optical phase modulator is also simply referred to as a "phase modulator".

In a phase modulator using Si or the like, it is possible to change the phase of the input light and output it by applying the carrier plasma effect in which the refractive index of light in the waveguide changes according to the change in carrier density. Specifically, it is possible to generate the carrier plasma effect by increasing the carrier density by providing a channel for applying an electric field or injecting a current at a specific position in the waveguide. In the case of modulation by the carrier plasma effect, the linearity of the modulation operation can be improved as compared with the case of modulation in which the refractive index is changed by heating the waveguide with a heater or the like.

Japanese Unexamined Patent Publication No. 2013-190492 JP-A-2017-173365

When the phase modulator is used in a device such as LIDAR (Light Detection and Ranging) that requires strong floodlight power, the light input to the phase modulator also depends on the required floodlight power. High output (high power).

Here, when the waveguide of the phase modulator is a single-mode waveguide that propagates light in single mode, the cross section of the waveguide is relatively small, so that the power of light in the waveguide is relatively small. It tends to be dense. When the power density of light becomes high, the influence of non-linear effects such as two-photon absorption becomes large, so that there is a problem that modulation control becomes difficult.

Further, as the carrier density increases, many free carriers are generated, so that the influence of scattering becomes large and the optical loss increases. In particular, if a channel is provided for a portion of light having a high power density such that a mirror image is formed, there is a problem that the carrier density is further increased in combination with the high power density and the optical loss is further increased. is there.

The present invention has been made by paying attention to the above-mentioned problems, and an object of the present invention is to provide a phase modulator, a hybrid modulator, and an SSB modulator that can reduce optical loss even when the modulated light has a high output. And.

In order to solve the above problems, the semiconductor optical phase modulator according to claim 1 converts single-mode light into multi-mode light, and a first place where a mirror image is formed by light interference, and It has a second location where the power density of light is lower than that of the first location, and is provided so as to face each other so that the propagating light is sandwiched between the multimode waveguide that propagates the interfered light and the second location. Each comprises a pair of channels having a doping concentration higher than that of the surrounding region.

In the semiconductor optical phase modulator according to claim 2, the multimode waveguide is a multimode interference waveguide.

In the semiconductor optical phase modulator according to claim 3, the pair of channels are different conductive types from each other, and a portion of the channel close to light has a low-concentration portion having a doping concentration lower than that of the other portions.

In the semiconductor optical phase modulator according to claim 4, the pair of channels are different conductive types from each other, and project to a portion of the channel close to light toward a gap of adjacent multimode light. It has a protrusion provided so as to.

In the semiconductor optical phase modulator according to claim 5, the pair of channels are different conductive types from each other, and the PN junction and the multimode light are joined inside the multimode waveguide so as to overlap each other. ..

In the semiconductor optical phase modulator according to claim 6, the cross-sectional area of the pair of channels when the P-shaped channel is cross-sectionald on a plane orthogonal to the direction of light propagation is N of the pair of channels. Greater than the cross section of the channel of the mold.

In the semiconductor optical phase modulator according to claim 7, a P-type high-concentration portion having a doping concentration higher than that of the surrounding region is provided between the adjacent multimode lights at the second portion. ..

In the semiconductor optical phase modulator according to claim 8, the multimode waveguide is connected to a phase modulation section and a first input waveguide that is connected to the phase modulation section and whose cross-sectional area increases toward the phase modulation section. The power density of the single mode light input to the phase modulation unit by the first input waveguide is reduced.

In the semiconductor optical phase modulator according to claim 9, the multimode waveguide is connected to a phase modulation section and a second input waveguide that is connected to the phase modulation section and whose cross-sectional area decreases toward the phase modulation section. The power density of the single mode light input to the phase modulation unit by the second input waveguide is reduced.

The semiconductor optical phase modulator according to claim 10 further includes an intermediate region provided by joining each of the pair of channels between the pair of channels, and the pair of channels and the intermediate portion are formed on the pair of channels. It is the same conductive type.

The hybrid modulator according to claim 11 is the semiconductor optical phase modulator according to any one of claims 1 to 10 and a third input waveguide of a dielectric bonded to the semiconductor optical phase modulator. And.

The SSB modulator according to claim 12 includes the semiconductor optical phase modulator according to any one of claims 1 to 10.

According to the phase modulator, hybrid modulator and SSB modulator according to the present invention, optical loss can be reduced even when the modulated light has a high output.

FIG. 1 (A) is a plan view schematically explaining the configuration of the phase modulator according to the embodiment of the present invention, and FIG. 1 (B) is the position of line 1B-1B in FIG. 1 (A). It is sectional drawing which schematically explains the structure of the channel in. It is a top view which schematically explains the structure of the phase modulator which concerns on 1st modification. It is a top view schematically explaining the structure of the phase modulator which concerns on 2nd modification. It is a top view schematically explaining the structure of the phase modulator which concerns on 3rd modification. It is a top view schematically explaining the structure of the phase modulator which concerns on 4th modification. It is a top view schematically explaining the structure of the phase modulator which concerns on 5th modification. FIG. 7A is a plan view schematically explaining the configuration of the phase modulator according to the sixth modification, and FIG. 7B is a schematic view of the configuration of the phase modulator according to the seventh modification. It is a top view to explain. 8 (A) is a plan view schematically explaining the configuration of the phase modulator according to the eighth modification, and FIG. 8 (B) is the position of line 8B-8B in FIG. 8 (A). It is sectional drawing explaining the structure of a channel schematically. FIG. 9A is a plan view schematically explaining another configuration of the phase modulator according to the eighth modification, and FIG. 9B is a further view of the phase modulator according to the eighth modification. It is a top view schematically explaining the structure of. FIG. 10 (A) is a diagram schematically explaining the configuration of the hybrid modulator according to Application Example 1, and FIG. 10 (B) is a plan view illustrating a part of the hybrid modulator. It is a figure explaining the structure of the SSB modulator which concerns on application example 2 schematically.

Embodiments of the present invention will be described below. In the description of the drawings below, the same or similar parts are designated by the same or similar reference numerals. However, it should be noted that the drawings are schematic, and the relationship between the thickness and the plane dimension, the ratio of the thickness of each device and each member, etc. are different from the actual ones. Therefore, the specific thickness and dimensions should be determined in consideration of the following explanation. In addition, there are parts in which the relations and ratios of the dimensions of the drawings are different from each other.

Further, the directions of "left and right" and "up and down" in the following description are merely definitions for convenience of explanation, and do not limit the technical idea of the present invention. Therefore, for example, if the paper surface is rotated 90 degrees, "left and right" and "up and down" are read interchangeably, and if the paper surface is rotated 180 degrees, "left" becomes "right" and "right" becomes "left". Of course it will be.

Further, in the present specification and the accompanying drawings, it means that electrons or holes are a large number of carriers in the regions and layers labeled with N or P, respectively. Further, + and-attached to N and P mean that the impurity concentration is relatively high or low, respectively, as compared with the semiconductor region to which + and-are not added. However, even if the notation indicates the same concentration such as N + and N +, it is not limited to the fact that the impurity concentration is actually the same.

The semiconductor optical phase modulator (phase modulator) 10 according to the embodiment of the present invention is a phase modulator using a semiconductor such as Si, and as shown in FIG. 1 (A), has a multi-mode waveguide 12 and , A pair of channels 14, 15 and the like. The configuration of the phase modulator 10 shown in FIG. 1 is illustrated with some emphasis for convenience of explanation, and includes layers and elements in other semiconductor regions not shown in the figure. However, it can be used as a member constituting a phase modulator.

In the phase modulator 10, a multi-mode interference (MMI) waveguide is adopted as the multi-mode waveguide 12. The multimode waveguide 12 has a phase modulation section 12A, an input section 18A, and an output section 18B. The phase modulation unit 12A converts the single mode input optical PI input from the lower input unit 18A in FIG. 1 into multi-mode light, and the converted multi-mode light is the phase modulation unit 12A. Propagate while interfering with the inside of. The cross-sectional area of the portion of the phase modulation unit 12A through which light propagates is larger than the cross-sectional area of each of the input unit 18A and the output unit 18B. Hereinafter, unless otherwise specified, the "cross-sectional area" means a cross-sectional area when a cross section is formed on a plane orthogonal to the direction of light propagation (vertical direction in FIG. 1A).

A first portion A1 and a second portion A2 are set inside the phase modulation unit 12A. In FIG. 1 (A), the second portion A2 is illustrated by the area surrounded by the rectangular broken line, and the first portion A1 is three consecutive second portions along the vertical direction. It is located between A2. That is, the first portion A1 and the second portion A2 are located side by side in the light propagation direction.

The first portion A1 is a position where a mirror image is formed due to the interference of light, and the second portion A2 is a position where the power density (electric field density) of light is lower than that of the first portion A1. In addition, "the power density of light in the second place A2 is lower than the power density of light in the first place A1" means that the peak value of the power density of light in the second place A2 is the first place. It means that it is lower than the peak value of the power density of light in A1.

When the input optical PI is input to operate the multimode waveguide 12, the phase modulator 12A generates spatial optical beats in the low-order mode and the high-order mode, so that the optical mode is contracted and expanded. Is formed periodically. That is, the places where the power densities of light are different are repeated. The positions of the first portion A1 and the second portion A2 are arranged according to the magnitude of the power density of light.

In the first portion A1 in FIG. 1 (A), the contraction optical mode PM1 is illustrated by a small ellipse as light whose optical mode is contracted. Further, in the second portion A2, the extended optical mode PM2 is illustrated as an extended optical mode in an elliptical shape larger than the contraction optical mode PM1.

In FIG. 1A, as a configuration of one cycle of repeated multi-mode light, the contraction optical mode PM1 occurs once, the extended optical mode PM2 occurs twice, and then the contraction optical mode PM1 The state in which is generated once is illustrated. Further, a case where one cycle of this light is continuous three times is illustrated. However, the present invention is not limited to this, and the configuration of one cycle and the number of repetitions can be changed as appropriate. Similarly, the positions and numbers of the first location A1 and the second location A2 can be changed as appropriate.

(channel)
The pair of channels 14 and 15 are provided so as to sandwich the propagating multimode light on the left and right sides of the second portion A2 in FIG. 1 (A) so as to face each other. The inner ends of the pair of channels 14 and 15 overlap with the phase modulation section 12A. In the case of the phase modulator 10 illustrated in FIG. 1, the conductive type of the left channel 14 in FIG. 1 (A) is P type (P +), and the conductive type of the right channel 15 is N type (N +). is there.

The pair of channels 14 and 15 have a higher doping concentration around the respective channels 14 and 15 than the doping concentration of the same conductive region. In FIG. 1, the display of the doping concentration in the surrounding region is omitted. The doping concentrations of "P +" and "N +" shown in FIG. 1 are examples, and in the present invention, as long as the doping concentration of channels 14 and 15 is higher than the doping concentration of the region around channels 14 and 15. For example, it may be "P" and "N".

The pair of channels 14 and 15 have base portions 14A and 15A, respectively. As shown in FIG. 1 (B), contact regions 14B and 15B are provided at the outer ends of the upper portions of the base portions 14A and 15A, respectively. The contact areas 14B and 15B are not shown in FIG. 1A for convenience of explanation. Further, electrodes 16A and 16B using, for example, aluminum (Al) are bonded to the contact regions 14B and 15B, respectively.

In the phase modulator 10 according to the embodiment of the present invention, a drive current is injected from the outside of the phase modulator 10 via the electrodes 16A and 16B, so that a current flows between the pair of opposite channels 14 and 15. The carrier plasma effect occurs at the second location A2. Since high-concentration doping is intensively performed in the second location A2, the carrier plasma effect is such that the light is more than the first location A1 instead of the first location A1 where the mirror image is formed and the light power density is high. It occurs at the second location A2 where the power density of the plasma is low. Then, the refractive index of the multimode waveguide 12 at the second portion A2 changes, and the phase of the propagating light is modulated to a desired value. The modulated light is output as output light PO from the upper output unit 18B in FIG.

Here, for example, when a channel is provided corresponding to the first portion A1 where the mirror image is formed to generate the carrier plasma effect, the high power density of the light at the first portion A1 and the input high output In combination with the light of, two-photon absorption easily occurs at the first location A1.

(Action effect)
In the embodiment of the present invention, the generation of two-photon absorption is prevented and the generation of free carriers that cause scattering is suppressed as compared with the case where the carrier plasma effect is generated at the first portion A1 where the mirror image is formed. To. Therefore, even if the modulated light has a high output, the modulated light can be stably output and the optical loss can be reduced.

Further, in the embodiment of the present invention, since the cross-sectional area of the phase modulation unit 12A is larger than the cross-sectional area of the input unit 18A, the power density of the light input to the phase modulation unit 12A can be suppressed low.

Further, in the embodiment of the present invention, since the multimode waveguide 12 is an MMI waveguide, the single mode waveguide 12 and the multimode waveguide 12 are optically discontinuously joined to generate an optical beat. Becomes possible. That is, the optical mode can be expanded by the MMI waveguide alone.

In this respect, it is possible to expand the optical mode by connecting, for example, a forward-tapered or reverse-tapered waveguide to the phase modulation unit 12A without using the MMI waveguide. However, since the size of the entire device including the phase modulator becomes long, the footprint at the time of manufacturing increases, and the manufacturing cost increases. On the other hand, when the multi-mode waveguide 12 is an MMI waveguide, the dimensions of the entire device can be kept short to be compact, and the manufacturing cost can be reduced.

<First modification>
Next, a modification and an application example of the phase modulator according to the embodiment of the present invention will be described. In the following modifications and application examples, a configuration different from that of the phase modulator 10 shown in FIG. 1 will be mainly described, and duplicate explanations will be appropriately given for members equivalent to the members having the same name in the phase modulator 10. Omit.

As shown in FIG. 2, in the phase modulator 10A according to the first modification, the pair of channels 24, 25 are different from each other, as in the pair of channels 14 and 15 of the phase modulator 10 shown in FIG. Is. However, in the first modification, the channels 24 and 25 are provided with low density portions 24C and 25C, respectively, in portions close to the light in the base portions 24A and 25A of the extended optical mode PM2.

The doping concentration of the low concentration portion 24C on the left side in FIG. 2 is "P-", which is lower than that of the base portion 24A, which is the other surrounding portion in the channel 24. Further, the doping concentration of the low concentration portion 25C on the right side in FIG. 2 is “N−”, which is lower than that of the base portion 25A which is another peripheral portion in the channel 25.

Here, as the doping concentration of channels 24 and 25 increases, the optical loss in the phase modulator 10A also increases. Therefore, in the first modification having the low density portions 24C and 25C, the optical loss is reduced by adjusting the portion of the channels 24 and 25 close to the distribution of the extended optical mode PM2 so that the doping concentration is lower than the surroundings. It can be further reduced. Other effects of the phase modulator 10A according to the first modification are the same as those of the phase modulator 10 shown in FIG.

<Second modification>
As shown in FIG. 3, in the phase modulator 10B according to the second modification, the pair of channels 34, 35 are different from each other, like the pair of channels 14 and 15 of the phase modulator 10 shown in FIG. Is. However, in the second modification, the gaps in the extended optical mode PM2 in which the protrusions 34C and 35C are distributed adjacent to the portions of the channels 34 and 35 near the light in the base portions 34 and 35A of the extended optical mode PM2. Each is provided so as to protrude toward.

The left protruding portion 34C in FIG. 3 has the same P + type as the base portion 34A, and the right protruding portion 35C in FIG. 3 has the same N + type as the base portion 35A. The protrusions 34C and 35C are arranged so as to sew a gap in the extended optical mode PM2 at the second portion A2 in a plan view. In other words, the protrusions 34C and 35C are doped and formed so as to avoid the extended optical mode PM2. The protrusions 34C and 35C illustrated in FIG. 3 are formed so as to protrude in a reverse taper shape so that the cross section becomes smaller toward the extended optical mode PM2. In the present invention, the shape of the protruding portion is not limited to that exemplified in FIG. 3 as long as it protrudes toward the gap of the extended optical mode PM2.

According to the second modification, the protrusions 34C and 35C can further enhance the carrier plasma effect of the channels 34 and 35 when the extended optical mode PM2 is energized. Other effects of the phase modulator 10B according to the second modification are the same as those of the phase modulator 10 shown in FIG.

<Third modification example>
As shown in FIG. 4, in the phase modulator 10C according to the third modification, the pair of channels 44, 45 are different from each other, like the pair of channels 14 and 15 of the phase modulator 10 shown in FIG. Is. However, in the third modification, the pair of channels 44, 45 are joined and provided inside the multimode waveguide 12 so that the PN junction and the multimode light overlap.

The channel 44 on the left side in FIG. 4 has a joint surface forming portion 44C on the right side of the base portion 44A. Further, the channel 45 on the right side in FIG. 4 has a joint surface forming portion 45C on the left side of the base portion 45A. The junction surface forming portion 44C is a P-type semiconductor region having a doping concentration lower than that of the base portion 44A, and the junction surface forming portion 45C is an N-type semiconductor region having a doping concentration lower than that of the base portion 45A.

The pair of junction surface forming portions 44C and 45C are arranged so as to overlap (overlap) with the waveguide of the phase modulation portion 12A, and the junction interface of the pair of junction surface forming portions 44C and 45C forms the PN junction J. .. The PN junction J overlaps the axial center of the multimode waveguide 12. The axial center of the multimode waveguide 12 is located at the center in the left-right direction in FIG. 4 in a plan view.

According to the third modification, since the PN junction J is formed inside the multimode waveguide 12 by the junction surface forming portions 44C and 45C, not only the forward bias but also the reverse bias is applied at the time of driving. It becomes possible to pull out a free carrier. Other effects of the phase modulator 10C according to the third modification are the same as those of the phase modulator 10 shown in FIG.

In FIG. 4, the doping concentration of the joint surface forming portions 44C and 45C was lower than that of the surrounding region, but the present invention is not limited to this, and the doping concentration is changed, for example, to the same extent as the surrounding region. It is also possible to do. However, if the doping concentration of the joint surface forming portions 44C and 45C is set lower than that of the surrounding region as in the third modification, it is advantageous in that the optical loss of the phase modulator 10C can be reduced.

<Fourth modification>
As shown in FIG. 5, in the phase modulator 10D according to the fourth modification, the PN junction J is displaced from the position of the central axis of the multimode waveguide 12 toward the N-type channel 45. However, it is different from the phase modulator 10C according to the third modification shown in FIG. Therefore, in the fourth modification, the cross-sectional area of the P-type channel 44 is larger than the cross-sectional area of the N-type channel 45.

Here, when a drive current is passed through the phase modulator 10D, it is possible to increase the modulation efficiency by varying the hole density at the time of reverse bias. Inside the multimode waveguide 12 of the phase modulator 10D according to the fourth modification, the P-type junction surface forming portion 44C1 is arranged so that the cross-sectional area is larger than that of the N-type junction surface forming portion 45C1. ing. Therefore, the density of more holes can be varied, and the modulation efficiency can be further improved. Other effects of the phase modulator 10D according to the fourth modification are the same as those of the phase modulator 10 shown in FIG. 1 and the phase modulator 10C shown in FIG.

<Fifth modification>
As shown in FIG. 6, in the phase modulator 10E according to the fifth modification, a point that a plurality of high density portions 44D are provided along the central axis of the multimode waveguide 12 is shown in FIG. It is different from the phase modulator 10D according to the fourth modification. The high density portion 44D is a semiconductor region having a doping concentration of P + higher than that of the surrounding region in the P-type joint surface forming portion 44C, and is intermediate between the two extended optical modes PM2 generated along the light propagation direction. It is located in.

Inside the multimode waveguide 12, at a position in the middle of the extended optical mode PM2 distributed adjacently, the power density of the multimode light is lower than that in the surrounding region. The number and arrangement patterns of the extended optical modes PM2 in FIG. 6 are examples, and can be changed as appropriate in the present invention. Similarly, the number and arrangement pattern of the high-concentration portion 44D can be changed as appropriate.

In the fifth modification, the high concentration portion 44D makes it possible to reduce the electrical resistance of the channels 44 and 45. Here, the time constant that determines the frequency characteristic at the time of modulation varies depending on the junction capacitance and the resistance component. Therefore, according to the fifth modification, the frequency characteristics of the phase modulator 10E can be improved by lowering the electrical resistance of the channels 44 and 45. Other effects of the phase modulator 10E according to the fifth modification are the same as those of the phase modulator 10 shown in FIG. 1 and the phase modulator 10D shown in FIG.

<6th modification>
As shown in FIG. 7A, the phase modulator 10F according to the sixth modification includes a multimode waveguide 22 and a pair of channels 14 and 15. The multimode waveguide 22 has a phase modulation unit 12A, a first input waveguide 52A, and a first output waveguide 52B. Although not shown, channels 14 and 15 are provided corresponding to the positions of the extended optical mode PM2. The first input waveguide 52A is provided in place of the input unit 18A in the phase modulator 10 shown in FIG. 1, and the first output waveguide 52B is provided in place of the output unit 18B in the phase modulator 10. Has been done.

The first input waveguide 52A has a forward taper shape in which the cross section increases toward the phase modulation unit 12A from the outside. Since the light beam of the input light PI to the multimode waveguide 22 expands adiabatically by passing through the first input waveguide 52A having a forward taper shape, the power density of the single mode input light PI decreases. .. In the sixth modification, the first input waveguide 52A reduces the power density of the input optical PI in the single mode, so that it is not necessary to use the MMI waveguide as in the phase modulator 10 shown in FIG. ..

The first output waveguide 52B has an inverse taper shape symmetrically with the first input waveguide 52A, and the light passing through the phase modulation unit 12A is reduced by the first output waveguide 52B, and the output light PO Is output as.

According to the sixth modification, the forward-tapered first input waveguide 52A makes it possible to reduce the power density of the input light PI to the multimode waveguide 22, so that the scattering of free electrons is suppressed. To. Therefore, as in the case of the phase modulator 10 shown in FIG. 1, the optical loss can be reduced even if the modulated light has a high output.

<7th modification>
Even if a second input waveguide 54A having a reverse taper shape, in which the cross section decreases toward the phase modulation unit 12A, is used as in the phase modulator 10G according to the seventh modification shown in FIG. 7B. Good. In the seventh modification, when the light beam of the input light PI to the multimode waveguide 22 passes through the second input waveguide 54A having a reverse taper shape, it partially leaks from the waveguide and expands, so that it is single. The power density of the input light PI of the mode decreases. Further, a second output waveguide 54B, which has a forward taper shape symmetrically with the first input waveguide 52A, is provided in the phase modulation section 12A. The light that has passed through the phase modulation unit 12A passes through the second output waveguide 54B and is output as output light PO.

According to the seventh modification, the reverse-tapered second input waveguide 54A makes it possible to reduce the power density of the input light PI to the multimode waveguide 22, so that the scattering of free electrons is suppressed. To. Therefore, as in the case of the phase modulator 10 shown in FIG. 1, the optical loss can be reduced even if the modulated light has a high output.

<8th modification>
As shown in FIG. 8 (A), the phase modulator 10H according to the eighth modification is an intermediate provided between the multimode waveguide 12, the pair of channels 14, 14 and the pair of channels 14, 14. A unit 56 is provided. The intermediate portion 56 is joined to each of the pair of channels 14 and 14. That is, in the eighth modification, the pair of channels 14 and 14 are of the same conductive type, and as shown in FIG. 8B, an intermediate portion 56 is further provided so as to fill the gap between the pair of channels 14 and 14. The point is different from the phase modulator 10 shown in FIG.

In the eighth modification, the pair of channels 14, 14 and the conductive type of the intermediate portion 56 are integrated as a P type channel. When an electric field is applied to the pair of channels 14, 14, the pair of channels 14, 14 and the intermediate portion 56 are heated by Joule heat generation. In the eighth modification, the refractive index of the waveguide is not changed by using the carrier plasma effect as in the phase modulators 10, 10A to 10G shown in FIGS. 1 to 7, but the thermo-optical effect by Joule heat generation is obtained. Use to change the index of refraction.

In the phase modulator 10H shown in FIG. 8, the MMI waveguide was used as the multimode waveguide 12, but as shown in FIG. 9A, the phase modulator 10I was used without using the MMI waveguide. It can also be realized. Specifically, the forward-tapered first input waveguide 52A and the reverse-tapered first output waveguide 52B described in the sixth modification are connected to the phase modulation unit 12A. Further, as shown in FIG. 9B, the reverse-tapered second input waveguide 54A and the forward-tapered second output waveguide 54B described in the seventh modification are connected to the phase modulation unit 12A. By doing so, the phase modulator 10J may be realized.

As in the eighth modification, in the present invention, not only the current injection type but also the electric field application type phase modulators 10H to 10J can reduce the optical loss even if the modulated light has a high output. Can be done. In FIGS. 8 and 9, the case where the conductive type of the pair of channels 14 and 14 and the intermediate portion 56 is P type is exemplified, but the present invention is not limited to this, and the pair of N type channels and the N type are used. Joule heat generation may be generated by using the intermediate portion. Further, the notation of the concentration in the semiconductor region is not limited to "P-", and may be, for example, "P" or the like.

<First application example>
As shown in FIG. 10A, the hybrid modulator 60 according to Application Example 1 includes a phase modulator 10H according to an eighth modification, a third input waveguide 62 connected to the phase modulator 10H, and the like. It includes a third output waveguide 64 connected to the phase modulator 10. In FIG. 10A, one upper end of the third input waveguide 62 is branched in a Y shape, and each of the branched portions of the third input waveguide 62 and the input portion of the two phase modulators 10H are used. The case where and is connected is illustrated. Further, in FIG. 10A, one end of the lower side of the third output waveguide 64 is branched in a Y shape, and each of the branched portions of the third output waveguide 64 and two phase modulators 10 Is connected to the output section of.

The third input waveguide 62 and the third output waveguide 64 are single-mode waveguides using a dielectric such as SiN or SiO ₂ . In FIG. 10A, a case where SiN is used is illustrated. The third input waveguide 62 and the third output waveguide 64 are equivalent members to each other, and can function in the same manner even if they are replaced with each other.

The third input waveguide 62 is optically coupled to the phase modulator 10 and has a reverse taper shape in which the cross section decreases as it approaches the phase modulator 10H, as shown in FIG. 10B. Further, the third output waveguide 64 is also optically coupled to the phase modulator 10 like the third input waveguide 62, and has a forward taper shape in which the cross section increases as the distance from the phase modulator 10H increases.

Here, the dielectric waveguide has an advantage that non-linear effects such as two-photon absorption are less likely to occur even when high-power light is passed through, as compared with the case of a semiconductor waveguide such as Si. On the other hand, when manufacturing an active element (device) such as a phase modulator, it is currently difficult to avoid the use of semiconductors such as Si and materials such as lithium niobate (lithium niobate, LiNbO ₃ ).

In Application Example 1 of the embodiment of the present invention, the third output waveguide 64 and the third input waveguide 62 of the single-mode waveguide, which are passive element components, are made of a dielectric material. Further, the phase modulator which is an active element component is the phase modulator 10H according to the eighth modification of the embodiment of the present invention, and the phase modulator 10H is made of a semiconductor such as Si. That is, in Application Example 1, an effective hybrid modulator 60 is realized by combining a waveguide using a dielectric and an active element using a semiconductor. Further, not only the phase modulator 10H according to the eighth modification, but also other phase modulators 10, 10A to 10G, 10I, 10J according to the embodiment of the present invention can be used to obtain an effective hybrid modulator 60. It can be configured in the same way.

According to the phase modulators 10, 10A to 10J according to the embodiment of the present invention, the optical loss due to free carrier scattering can be reduced even if high output light is input. Therefore, according to Application Example 1 using the phase modulators 10 and 10A to 10J, a monolithic optical integrated circuit can be configured, a strong projection power is required like LIDAR, and a modulator is used. Is especially advantageous when is essential. For example, in the lidar to which the application example 1 is applied, the output of the transmitted light can be increased to improve the sensitivity.

<Application example 2>
As shown in FIG. 11, the SSB modulator 70 according to Application Example 2 includes a carrier signal source 72, a 90-degree phaser 74, an inverting phaser 76, and a phase modulator 10 shown in FIG. The carrier signal source 72 generates a carrier signal. The 90-degree phase device 74 is connected to the carrier signal source 72 and modulates the phase of the carrier signal generated by the carrier signal source 72 by 90 degrees.

In the phase modulator 10, two sets are connected in parallel, and a set of two connected in parallel is further connected in parallel. A trimming heater 78 as a 90-degree phase controller is arranged at a predetermined position in the waveguide connecting the four phase modulators 10A to 10D.

The inverting phase device 76 has one input unit 76A and two output units 76B and 76C. The two output units 76B and 76C include a first output unit 76B that outputs the input signal as it is without phase modulation, and a second output unit 76C that inverts the phase of the input signal and outputs the signal. Has.

Of the two inverting phase units 76, the input unit 76A of the upper inverting phase unit 76 in FIG. 11 is connected to the output side of the carrier signal source 72, and the two output units 76B, 76C of the inverting phase unit 76 are connected. Are connected corresponding to the two phase modulators 10 and 10 connected in parallel, respectively.

Further, the input unit 76A of the lower inverting phase unit 76 in FIG. 11 is connected to the output side of the 90 degree phase unit 74, and the two output units 76B and 76C of the inverting phase unit 76 are connected in parallel, respectively. It is connected corresponding to each of the two phase modulators 10 and 10.

Here, for example, in order to perform distance measurement by the FMCW (Frequency-Modulated Continuous Wave) method in LIDAR, it is necessary to phase-modulate or frequency-modulate the transmitted light to be projected. Therefore, according to the SSB modulator 70 according to Application Example 2, the optical loss can be reduced even when the distance is measured by using the FMCW method in LIDAR or even when the input light has a high output. It is advantageous.

<Other embodiments>
Although the present invention has been described by the disclosed embodiments described above, the statements and drawings that form part of this disclosure should not be understood as limiting the invention. It should be considered that this disclosure will reveal to those skilled in the art various alternative embodiments, examples and operational techniques. For example, a phase modulator having a channel having both the low density portions 24C and 25C shown in FIG. 2 and the protruding portions 34C and 35C shown in FIG. 3 may be realized. As described above, the present invention can be configured by combining the configurations included in the phase modulators shown in FIGS. 1 to 11.

The present invention includes various embodiments not described above, and the technical scope of the present invention is defined only by the matters specifying the invention relating to the reasonable claims from the above description. ..

10,10A-10J Semiconductor optical phase modulator (phase modulator)
12 Multimode waveguide 12A Phase modulation section 14 channel 15 channel 16A, 16B Electrode 18A Input section 18B Output section 22 Multimode waveguide 24 channel 24C Low concentration section 25 channel 25C Low concentration section 34 channel 34C Projection section 35 channel 35C Projection section 44 channel 44C, 44C1 junction surface forming part 44D high concentration part 45 channel 45C, 45C1 joining surface forming part 52A first input waveguide 54A second input waveguide 56 intermediate part 60 hybrid modulator 62 third input waveguide 64 Third output waveguide 70 SSB modulator A1 First location A2 Second location JP N junction PI Input light PO Output light PM1 Shrink optical mode PM2 Extended optical mode

Claims (12)

It has a first place where single-mode light is converted into multi-mode light and a mirror image is formed by light interference, and a second place where the power density of light is lower than that of the first place, and interferes. A multi-mode waveguide that propagates the light
A pair of channels that are provided so as to sandwich the propagating light at the second location and each have a doping concentration higher than that of the surrounding region.
A semiconductor optical phase modulator comprising. The multimode waveguide is a multimode interference waveguide.
The semiconductor optical phase modulator according to claim 1. The pair of channels are different conductive types from each other.
A portion of the channel close to light has a low concentration portion with a lower doping concentration than the other portions.
The semiconductor optical phase modulator according to claim 1 or 2. The pair of channels are different conductive types from each other.
A portion of the channel close to light has a protrusion provided to project towards the gap between adjacent multimode lights.
The semiconductor optical phase modulator according to any one of claims 1 to 3. The pair of channels are different conductive types and are joined inside the multimode waveguide so that the PN junction and the multimode light overlap.
The semiconductor optical phase modulator according to any one of claims 1 to 4. The cross-sectional area of the pair of channels when the P-type channel is cross-sectionald in a plane orthogonal to the light propagation direction is larger than the cross-sectional area of the N-type channel of the pair of channels.
The semiconductor optical phase modulator according to claim 5. A P-type high-concentration portion having a higher doping concentration than the surrounding region is provided between the adjacent multi-mode lights in the second portion.
The semiconductor optical phase modulator according to claim 6. The multimode waveguide has a phase modulation section and a first input waveguide connected to the phase modulation section and whose cross-sectional area increases toward the phase modulation section.
The power density of the single mode light input to the phase modulator by the first input waveguide is reduced.
The semiconductor optical phase modulator according to claim 1. The multimode waveguide has a phase modulation section and a second input waveguide connected to the phase modulation section and whose cross-sectional area decreases toward the phase modulation section.
The power density of the single mode light input to the phase modulator by the second input waveguide is reduced.
The semiconductor optical phase modulator according to claim 1. An intermediate portion provided by joining each of the pair of channels is further provided between the pair of channels.
The pair of channels and the intermediate portion are of the same conductive type.
The semiconductor optical phase modulator according to claim 1 or 2. The semiconductor optical phase modulator according to any one of claims 1 to 10.
A third input waveguide of a dielectric bonded to the semiconductor optical phase modulator,
A hybrid modulator equipped with. The semiconductor optical phase modulator according to any one of claims 1 to 10.
SSB modulator comprising.