WO2017217168A1

WO2017217168A1 - Optical element

Info

Publication number: WO2017217168A1
Application number: PCT/JP2017/018331
Authority: WO
Inventors: 聡上野山; 和義廣瀬; 黒坂　剛孝
Original assignee: 浜松ホトニクス株式会社
Priority date: 2016-06-16
Filing date: 2017-05-16
Publication date: 2017-12-21
Also published as: JP6688168B2; JP2017223867A

Abstract

This optical element is provided with: a substrate; a plurality of antenna structures, which are two-dimensionally arrayed on the substrate, and each of which has an n-type semiconductor layer and/or a p-type semiconductor layer for forming an electron flow channel; and electrodes for changing the shape of the electron flow channel by expanding or reducing a depletion layer in each of the antenna structures.

Description

Optical element

The present disclosure relates to an optical element for modulating at least one of the phase, intensity, and polarization of light.

In recent years, metasurfaces have attracted attention as optical elements for modulating at least one of the phase, intensity, and polarization of light (see, for example, Patent Document 1). In the metasurface, for example, a plurality of minute metal structures are two-dimensionally arranged at a pitch smaller than the wavelength of light to be modulated.

U.S. Pat. No. 8,848,273

However, since the metasurface as described above is composed of a static structure such as a plurality of fine metal structures, it is only possible to realize predetermined constant modulation.

Therefore, an object of the present disclosure is to provide an optical element that can dynamically modulate at least one of the phase, intensity, and polarization of light.

An optical element according to an embodiment of the present disclosure includes a substrate and a plurality of antenna structures that are two-dimensionally arranged on the substrate and include at least one of an n-type semiconductor layer and a p-type semiconductor layer for forming an electron channel. And an electrode for changing the shape of the electron flow path by enlarging or reducing the depletion layer in each of the plurality of antenna structures.

In this optical element, when a voltage is applied to the electrodes in each of the plurality of antenna structures arranged in a two-dimensional shape, the depletion layer is expanded or contracted to change the shape of the electron flow path. Therefore, according to this optical element, at least one of the phase, intensity, and polarization of light can be dynamically modulated.

In the optical element according to an embodiment of the present disclosure, the plurality of antenna structures may be arranged two-dimensionally on the substrate or may be arranged two-dimensionally within the substrate.

In the optical element according to an embodiment of the present disclosure, the electrode may be bonded to the n-type semiconductor layer or the p-type semiconductor layer so that the depletion layer expands when a reverse voltage is applied. According to this configuration, the shape of the electron channel can be suitably changed in each of the plurality of antenna structures.

In the optical element according to an embodiment of the present disclosure, the electrode is disposed on the n-type semiconductor layer or the p-type semiconductor layer via the insulating layer so that the depletion layer expands when a reverse voltage is applied. May be. According to this configuration, the shape of the electron channel can be suitably changed in each of the plurality of antenna structures.

In the optical element according to an embodiment of the present disclosure, each of the plurality of antenna structures has an n-type semiconductor layer and a p-type semiconductor layer forming a PN junction, and the electrode is a depletion layer when a forward voltage is applied. May be bonded to the n-type semiconductor layer or the p-type semiconductor layer so as to be reduced. According to this configuration, the shape of the electron channel can be suitably changed in each of the plurality of antenna structures.

In the optical element according to an embodiment of the present disclosure, each of the plurality of antenna structures may be provided with a plurality of electrodes. According to this configuration, it is possible to appropriately change the shape of the electron flow path by selectively applying a voltage to the plurality of electrodes in each of the plurality of antenna structures arranged two-dimensionally.

In the optical element according to an embodiment of the present disclosure, each of the plurality of antenna structures has an annular or C-shape when viewed from the thickness direction of the substrate, and each of the plurality of electrodes has a position different from each other. May be arranged. According to this configuration, each of the plurality of antenna structures can function as, for example, a C-shaped antenna opened in different directions.

In the optical element according to an aspect of the present disclosure, each of the plurality of antenna structures has a plurality of arms arranged radially when viewed from the thickness direction of the substrate, and each of the plurality of electrodes includes a plurality of It may be arranged on each of the arms. According to this configuration, each of the plurality of antenna structures can function as, for example, a V-shaped antenna opened at different angles in different directions.

In the optical element according to an aspect of the present disclosure, each of the plurality of antenna structures has a polygonal shape when viewed from the thickness direction of the substrate, and each of the plurality of electrodes includes at least a plurality of polygonal shapes. You may arrange | position at each of a corner | angular part. According to this configuration, each of the plurality of antenna structures can function as, for example, a C-type antenna or a V-type antenna as described above.

In the optical element according to an embodiment of the present disclosure, each of the plurality of antenna structures may have a side surface extending along the thickness direction of the substrate, and the electrode may be disposed on the side surface. According to this configuration, for example, when light is transmitted along the thickness direction of the substrate, it is possible to suppress the plurality of electrodes from becoming light scattering sources in each of the plurality of antenna structures.

An optical element according to an embodiment of the present disclosure includes a switching element having a control terminal and a pair of current terminals, the electrode being electrically connected to one of the pair of current terminals, and the other of the pair of current terminals being electrically A first wiring connected to the control terminal and a second wiring electrically connected to the control terminal may be further provided. According to this configuration, a voltage signal can be sent to the switching element via the first wiring, and a control signal can be sent to the switching element via the second wiring to switch ON / OFF the voltage application to the electrodes.

The optical element according to an embodiment of the present disclosure may further include a capacitor electrically connected to one of the pair of current terminals and the ground potential. According to this configuration, a voltage applied to the electrode can be held.

According to the present disclosure, it is possible to provide an optical element that can dynamically modulate at least one of the phase, intensity, and polarization of light.

FIG. 1 is a perspective view of an optical element according to the first embodiment. FIG. 2 is a cross-sectional view of the antenna structure of the optical element according to the first embodiment. FIG. 3A is a cross-sectional view showing a state of a depletion layer when a reverse voltage is applied to one divided electrode in the antenna structure of the optical element of the first embodiment. FIG. 3B is a plan view showing the shape of the electron flow path when a reverse voltage is applied to one of the divided electrodes in the antenna structure of the optical element according to the first embodiment. FIG. 4A is a cross-sectional view showing a state of a depletion layer when a reverse voltage is applied to the other divided electrode in the antenna structure of the optical element of the first embodiment. FIG. 4B is a plan view showing the shape of the electron flow path when a reverse voltage is applied to the other divided electrode in the antenna structure of the optical element of the first embodiment. FIG. 5A is a cross-sectional view showing a state of a depletion layer when a reverse voltage is applied to one divided electrode and the other divided electrode in the antenna structure of the optical element of the first embodiment. FIG. 5B is a plan view showing the shape of the electron flow path when a reverse voltage is applied to one divided electrode and the other divided electrode in the antenna structure of the optical element of the first embodiment. FIG. 6 is a diagram showing the relationship between the electron density of n-type GaAs and the plasma frequency. FIG. 7 is a plan view of a first modification of the optical element of the first embodiment. (A) of FIG. 8 is sectional drawing of the 2nd modification of the optical element of 1st Embodiment. FIG. 8B is a cross-sectional view showing the state of the depletion layer when a reverse voltage is applied to one of the divided electrodes in the antenna structure of the second modified example. (A) of FIG. 9 is sectional drawing of the 3rd modification of the optical element of 1st Embodiment. FIG. 9B is a cross-sectional view showing the state of the depletion layer when a reverse voltage is applied to one of the divided electrodes in the antenna structure according to the third modification. (A) of FIG. 10 is sectional drawing of the 4th modification of the optical element of 1st Embodiment. FIG. 10B is a cross-sectional view showing the state of the depletion layer when a reverse voltage is applied to one of the divided electrodes in the antenna structure according to the fourth modified example. FIG. 11 is a plan view of an antenna structure of a fifth modification of the optical element of the first embodiment. FIG. 12 is a cross-sectional view of a sixth modification of the optical element of the first embodiment. FIG. 13 is a cross-sectional view of the optical element of the second embodiment. FIG. 14A is a cross-sectional view showing a state of a depletion layer when a forward voltage is applied to a plurality of divided electrodes except one of the divided electrodes in the antenna structure of the optical element of the second embodiment. FIG. 14B is a plan view showing the shape of the electron flow path when a forward voltage is applied to a plurality of divided electrodes except one of the divided electrodes in the antenna structure of the optical element of the second embodiment. . FIG. 15A is a cross-sectional view showing a state of a depletion layer when a forward voltage is applied to a plurality of divided electrodes excluding the other divided electrode in the antenna structure of the optical element of the second embodiment. FIG. 15B is a plan view showing the shape of the electron flow path when a forward voltage is applied to a plurality of divided electrodes excluding the other divided electrode in the antenna structure of the optical element of the second embodiment. . FIG. 16 is a plan view of an optical element according to the third embodiment. FIG. 17 is a cross-sectional view of the optical element of the third embodiment. FIG. 18A is a plan view showing the shape of an electron flow path when a reverse voltage is applied to one combination of divided electrodes in the optical element antenna structure of the third embodiment. FIG. 18B is a plan view showing the shape of the electron flow path when a reverse voltage is applied to another combination of divided electrodes in the optical element antenna structure of the third embodiment. FIG. 19 is a plan view of an optical element according to the fourth embodiment. FIG. 20 is a cross-sectional view of the optical element according to the fourth embodiment. FIG. 21A is a plan view showing the shape of the electron flow path when a reverse voltage is applied to one combination of divided electrodes in the antenna structure of the optical element of the fourth embodiment. FIG. 21B is a plan view showing the shape of the electron channel when a reverse voltage is applied to another combination of divided electrodes in the antenna structure of the optical element according to the fourth embodiment. (A) of FIG. 22 is sectional drawing of the 7th modification of the optical element of 1st Embodiment. FIG. 22B is a cross-sectional view showing the state of the depletion layer when a reverse voltage is applied to one of the divided electrodes in the antenna structure according to the seventh modified example. FIG. 23 is a plan view of an eighth modification of the optical element of the first embodiment. FIG. 24 is a cross-sectional view of a ninth modification of the optical element of the first embodiment.

Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. In addition, in each figure, the same code | symbol is attached | subjected to the same or an equivalent part, and the overlapping description is abbreviate | omitted.
[First Embodiment]

As shown in FIG. 1, the optical element 1 A of the first embodiment includes a substrate 2, a plurality of antenna structures 3, and a plurality of divided electrodes (electrodes) 4. The optical element 1A functions as a metasurface for modulating at least one of the phase, intensity, and polarization of light.

The substrate 2 is made of a semiconductor material such as GaAs. The substrate 2 has a rectangular plate shape, for example. The substrate 2 has a front surface 2a and a back surface 2b facing each other in the thickness direction.

The plurality of antenna structures 3 are two-dimensionally arranged on the surface 2a of the substrate 2 (in the optical element 1A, in a matrix shape). Each antenna structure 3 includes an n-type semiconductor layer 31 made of an n-type semiconductor material such as n-type GaAs. Each antenna structure 3 has an annular shape when viewed from the thickness direction of the substrate 2. The size of each antenna structure 3 and the distance between adjacent antenna structures 3 are smaller than the wavelength of light to be modulated.

The plurality of divided electrodes 4 are arranged at different positions in each antenna structure 3. In the optical element 1 A, the pair of divided electrodes 4 are disposed at positions facing each other across the center of the antenna structure 3 when viewed from the thickness direction of the substrate 2. Each divided electrode 4 is made of, for example, a metal material.

As shown in FIG. 2, each of the pair of divided electrodes 4 is formed on the surface 3 a opposite to the substrate 2 side in the antenna structure 3, and is joined to the n-type semiconductor layer 31. More specifically, each divided electrode 4 is connected to the divided electrode 4 in the n-type semiconductor layer 31 when a reverse voltage (positive voltage with respect to the joint surface with the n-type semiconductor layer 31) is applied. It is joined to the n-type semiconductor layer 31 so that a depletion layer appears at the junction and expands (in other words, forms a Schottky junction). In FIG. 2, the

wirings

5a and 5b are omitted (the same applies to FIGS. 3 to 5 and 8 to 22).

As shown in FIG. 1, one divided electrode 4 provided in each antenna structure 3 is electrically connected to a gate electrode 6a through a wiring 5a. The other divided electrode 4 provided in each antenna structure 3 is electrically connected to the gate electrode 6b through the wiring 5b. Each

gate electrode

6a, 6b is electrically connected to an external power source. The external power supply applies a voltage between the

gate electrodes

6 a and 6 b and the ohmic electrode 7. Each antenna structure 3, each

wiring

5a, 5b, and each

gate electrode

6a, 6b are formed on the surface 2a of the substrate 2 via an insulating film made of SiO ₂ , Si ₃ N ₄ , Si ₃ C ₄ or the like. . The ohmic electrode 7 is formed on the surface 2 a of the substrate 2 so as to form an ohmic junction with the substrate 2. Each

wiring

5a, 5b, each

gate electrode

6a, 6b, and ohmic electrode 7 consists of metal materials, for example.

In the optical element 1A configured as described above, as shown in FIG. 3A, a reverse voltage is applied to one divided electrode 4 (the right divided electrode 4 in FIG. 3), and the other divided electrode. 4 (the left divided electrode 4 in FIG. 3), when no voltage is applied, the depletion layer D appears and expands only at the junction with the one divided electrode 4 in the n-type semiconductor layer 31. As a result, as shown in FIG. 3B, the portion of the n-type semiconductor layer 31 excluding the junction with one of the divided electrodes 4 has an electron flow path F (an electron-filled region that can cause light scattering). ) Therefore, the antenna structure 3 in this case functions as a C-type antenna opened on one side (the right side in FIG. 3).

Also, as shown in FIG. 4A, a reverse voltage is applied to the other divided electrode 4 (left divided electrode 4 in FIG. 4), and one divided electrode 4 (right divided electrode 4 in FIG. 4). ), No depletion layer D appears and expands only at the junction of the n-type semiconductor layer 31 with the other divided electrode 4. Thereby, as shown in FIG. 4B, the portion of the n-type semiconductor layer 31 excluding the junction with the other divided electrode 4 becomes the electron flow path F. Therefore, the antenna structure 3 in this case functions as a C-type antenna opened on the other side (left side in FIG. 4).

Further, as shown in FIG. 5A, a reverse voltage is applied to one divided electrode 4 (right divided electrode 4 in FIG. 5) and the other divided electrode 4 (left divided electrode 4 in FIG. 5). Then, the depletion layer D appears and expands only at the junction with the one divided electrode 4 and the junction with the other divided electrode 4 in the n-type semiconductor layer 31. As a result, as shown in FIG. 5B, the portion of the n-type semiconductor layer 31 excluding the junction with the one divided electrode 4 and the junction with the other divided electrode 4 is the electron flow path F. Become.

As described above, in the optical element 1A of the first embodiment, a voltage is selectively applied to the plurality of divided electrodes 4 in each of the plurality of antenna structures 3 arranged two-dimensionally. The depletion layer D is expanded and the shape of the electron flow path F is changed. Therefore, the optical element 1A can dynamically modulate at least one of the phase, intensity, and polarization of light.

More specifically, each divided electrode 4 is joined to the n-type semiconductor layer 31 so that the depletion layer D expands when a reverse voltage is applied. According to this configuration, the shape of the electron flow path F can be suitably changed in each antenna structure 3.

Further, each antenna structure 3 has an annular shape when viewed from the thickness direction of the substrate 2, and the divided electrodes 4 are arranged at different positions. According to this configuration, each antenna structure 3 can function as, for example, a C-shaped antenna that is opened in different directions.

Here, materials used for the antenna structure 3 will be described. FIG. 6 is a diagram showing the relationship between the electron density of n-type GaAs and the plasma frequency (where the vertical axis is the wavelength). As shown in FIG. 6, when n-type GaAs is used as the material for the antenna structure 3, the light source of light to be modulated can be obtained by increasing the electron density to about 1.3 × 10 ¹⁸ / cm ³ or more. For example, QCL (quantum cascade laser) that outputs laser light having a wavelength of 7.75 μm can be used. Further, if the electron density is increased to about 9.3 × 10 ²⁰ / cm ³ or more, for example, a PCSEL (photonic crystal laser) that outputs laser light having a wavelength of 0.94 μm is used as a light source of light to be modulated. be able to. Further, when GZO (ZnO to which gallium is added), AZO (ZnO to which Al is added) or ITO (In ₂ O ₃ to which Sn is added) is used as a material for the antenna structure 3, a modulation target is used. For example, QCL that outputs laser light having a wavelength of 7.75 μm can be used as the light source. In the example shown in FIG. 6, GZO is ZnO to which 4% by weight of gallium is added, AZO is ZnO to which 2% by weight of Al is added, and ITO is InO to which 10% by weight of Sn is added. ₂ O ₃ . Note that in a material having a plasma frequency higher than the frequency of the external electric field (lower side in FIG. 6), internal electrons are vibrated (followed), and light scattering occurs.

Next, an example of a method for manufacturing the optical element 1A when n-type GaAs is used as the material for the antenna structure 3 will be described.

First, a substrate 2 made of GaAs is prepared. Subsequently, in order to generate a potential difference in the portion corresponding to each divided electrode 4 in the n-type semiconductor layer 31, the portion excluding the portion corresponding to the ohmic electrode 7 in the surface 2 a of the substrate 2 is insulated by plasma CVD. A film is formed. Subsequently, an electron beam resist is formed on the surface 2a of the substrate 2 by spin coating. Subsequently, patterns corresponding to the plurality of antenna structures 3 are formed by electron beam drawing and development on the electron beam resist. Here, the diameter of the antenna structure 3 is 1 μm, the width of the antenna structure 3 is 0.2 μm, and the distance between adjacent antenna structures 3 is 2 μm. Subsequently, n-type GaAs is deposited by a molecular beam epitaxy method to form a plurality of antenna structures 3 made of n-type GaAs. Here, the thickness of the antenna structure 3 is 50 nm. Subsequently, the electron beam resist is removed from the surface 2 a of the substrate 2.

Subsequently, an electron beam resist is formed again on the surface 2a of the substrate 2 by spin coating. Subsequently, a pattern corresponding to the plurality of divided electrodes 4, the plurality of

wirings

5a and 5b, the pair of

gate electrodes

6a and 6b, and the ohmic electrode 7 is formed. Subsequently, Ti is vapor-deposited by electron beam vapor deposition, and Au is further deposited to form a plurality of divided electrodes 4, a plurality of

wirings

5a and 5b, a pair of

gate electrodes

6a and 6b, and an ohmic electrode 7. Here, the thickness of the Ti layer as the adhesion layer is 5 nm, and the thickness of the Au layer is 50 to 150 nm. Finally, the electron beam resist is removed from the surface 2a of the substrate 2 to obtain the optical element 1A.

Next, a modified example of the optical element 1A of the first embodiment will be described. First, three or more divided electrodes 4 may be arranged on one antenna structure 3. As shown in FIG. 7, the optical element 1A includes a switching element 10 having a control terminal and a pair of current terminals, a voltage supply line (first wiring) 8 for sending a voltage signal to the switching element 10, and a switching element. And a switch line (second wiring) 9 for sending a control signal to 10. In that case, the divided electrode 4 is electrically connected to one of the pair of current terminals, the voltage supply line 8 is electrically connected to the other of the pair of current terminals, and the switch line 9 is electrically connected to the control terminal. Connected to. As an example, the switching element 10 is a transistor. In that case, the control terminal is a gate electrode, and the pair of current terminals are a drain electrode and a source electrode. This configuration can be applied to each of the divided electrodes 4 with respect to the plurality of antenna structures 3. According to this configuration, a voltage signal is sent to the switching element 10 via the voltage supply line 8, and a control signal is sent to the switching element 10 via the switch line 9 to turn on / off voltage application to the divided electrode 4. Can be switched. That is, according to this configuration, it is possible to apply a voltage to the desired divided electrode 4 via the switching element 10 for each antenna structure 3. Further, as shown in FIG. 23, the optical element 1A may further include a capacitor 11 that is electrically connected to one of a pair of current terminals in the switching element 10 and a ground potential. According to this configuration, the voltage applied to the divided electrode 4 can be held.

Further, each antenna structure 3 may have a p-type semiconductor layer instead of the n-type semiconductor layer 31. In that case, when a reverse voltage (negative voltage with respect to the junction surface with the p-type semiconductor layer) is applied to the divided electrode 4, the depletion layer D is applied only to the junction portion with the divided electrode 4 in the p-type semiconductor layer. Appears and expands.

Further, as shown in FIGS. 8A and 9A, the divided electrode 4 may be disposed on the side surface 3 b of the antenna structure 3. Also in this case, when a reverse voltage is applied to the divided electrode 4, as shown in FIG. 8B and FIG. 9B, the junction between the n-type semiconductor layer 31 and the divided electrode 4 is applied. Since the depletion layer D appears and expands, the shape of the electron flow path F can be changed suitably.

As shown in FIGS. 8 and 9, when the divided electrode 4 is disposed on the side surface 3 b extending along the thickness direction of the substrate 2, for example, light is transmitted along the thickness direction of the substrate 2. In this case, it is possible to suppress the plurality of divided electrodes 4 from becoming light scattering sources in each antenna structure 3. In particular, when the insulating layer 12 is disposed between the divided electrode 4 and the substrate 2, it is possible to more reliably suppress the plurality of divided electrodes 4 from becoming light scattering sources in each antenna structure 3. . Furthermore, as shown in FIG. 9, if the side surface 3b is inclined by etching or the like, the divisional electrode 4 can be easily and reliably formed by vapor deposition or the like. 9 extends in a direction perpendicular to the thickness direction of the substrate 2, but also extends in a direction parallel to the thickness direction of the substrate 2. The side surface 3b shown in FIG. Such a side surface 3 b is also included in the side surface extending along the thickness direction of the substrate 2.

Further, as shown in FIGS. 10A and 10B, the divided electrode 4 has an n-type semiconductor layer through the insulating layer 12 so that the depletion layer D expands when a reverse voltage is applied. 31 may be arranged. Also with this configuration (so-called MIS structure), the shape of the electron flow path F can be suitably changed in each antenna structure 3. Also in this case, each antenna structure 3 may have a p-type semiconductor layer instead of the n-type semiconductor layer 31. That is, the divided electrode 4 may be disposed on the p-type semiconductor layer via the insulating layer 12 so that the depletion layer D expands when a reverse voltage is applied.

In addition, as shown in FIG. 11, the plurality of divided electrodes 4 may be arranged in a part of the antenna structure 3 having an annular shape (a quarter in this modification). Good. Also in this case, the shape of the electron flow path F can be appropriately changed by selectively applying a voltage to one or a plurality (including all) of the divided electrodes 4. In addition, the some division | segmentation electrode 4 may be arrange | positioned at all the parts of the antenna structure 3 which exhibits an annular | circular shape.

Further, as shown in FIG. 12, a mirror 13 may be disposed on the surface 3 a of the antenna structure 3. In this case, the modulated light can be extracted as reflected light by causing the light to be modulated to enter from the back surface 2 b side of the substrate 2. Further, as shown in FIG. 24, a mirror 13 may be disposed between the surface 2 a of the substrate 2 and the antenna structure 3. In this case, the modulated light can be extracted as reflected light by causing the light to be modulated to enter from the surface 2a side of the substrate 2.

In addition, each antenna structure 3 may have an annular shape other than an annular shape or a C-shape when viewed from the thickness direction of the substrate 2. As an annular shape other than the annular shape, a polygon, an ellipse and the like can be exemplified.
[Second Embodiment]

As shown in FIG. 13, the optical element 1B of the second embodiment is mainly different from the optical element 1A of the first embodiment in the layer structure of the antenna structure 3 and the arrangement of the plurality of divided electrodes 4. . In the optical element 1 B, each antenna structure 3 includes an n-type semiconductor layer 31 and a p-type semiconductor layer 32. The n-type semiconductor layer 31 is formed on the surface 2 a of the substrate 2. The p-type semiconductor layer 32 is formed on the n-type semiconductor layer 31. The n-type semiconductor layer 31 and the p-type semiconductor layer 32 form a PN junction, and a depletion layer D is formed at the junction between the n-type semiconductor layer 31 and the p-type semiconductor layer 32.

Each antenna structure 3 has a plurality of divided electrodes 4 arranged in a ring shape. Each divided electrode 4 is formed on the surface 3 a of the antenna structure 3 and is joined to the p-type semiconductor layer 32. More specifically, each divided electrode 4 is applied to the n-type semiconductor layer 31 and the p-type semiconductor layer 32 when a forward voltage (positive voltage with respect to the junction surface with the p-type semiconductor layer 32) is applied. The depletion layer D is bonded to the p-type semiconductor layer 32 so that the depletion layer D is reduced in a portion located immediately below the divided electrode 4 in the bonding portion. Note that the gap between the adjacent divided electrodes 4 is narrowed to such a width that electrical insulation between the adjacent divided electrodes 4 can be maintained.

In the optical element 1B configured as described above, as shown in FIG. 14A, a forward voltage is applied to the plurality of divided electrodes 4 except for one divided electrode 4 (the right divided electrode 4 in FIG. 14). When applied, the depletion layer D shrinks and disappears at the portion of the junction between the n-type semiconductor layer 31 and the p-type semiconductor layer 32 located immediately below the plurality of divided electrodes 4 to which the forward voltage is applied. As a result, as shown in FIG. 14B, a portion (that is, a depletion layer D is formed immediately below one of the divided electrodes 4 in the junction portion of the n-type semiconductor layer 31 and the p-type semiconductor layer 32). A portion excluding the portion that is formed becomes an electron flow path F (an electron-filled region that can cause light scattering). Therefore, the antenna structure 3 in this case functions as a C-type antenna opened on one side (right side in FIG. 14).

Further, as shown in FIG. 15A, when a forward voltage is applied to a plurality of divided electrodes 4 excluding the other divided electrode 4 (left divided electrode 4 in FIG. 15), the n-type semiconductor layer 31 is applied. In addition, the depletion layer D shrinks and disappears in a portion located immediately below the plurality of divided electrodes 4 to which the forward voltage is applied in the junction portion of the p-type semiconductor layer 32. As a result, as shown in FIG. 15B, a portion (that is, a depletion layer D formed immediately below the other divided electrode 4) in the junction portion of the n-type semiconductor layer 31 and the p-type semiconductor layer 32 is formed. The portion excluding the portion that is formed becomes the electron flow path F. Therefore, the antenna structure 3 in this case functions as a C-type antenna opened on the other side (left side in FIG. 15).

As described above, in the optical element 1B of the second embodiment, a voltage is selectively applied to the plurality of divided electrodes 4 in each of the plurality of antenna structures 3 arranged two-dimensionally. The depletion layer D is reduced and the shape of the electron flow path F is changed. Therefore, the optical element 1B can dynamically modulate at least one of the phase, intensity, and polarization of light.

More specifically, each antenna structure 3 has an n-type semiconductor layer 31 and a p-type semiconductor layer 32 forming a PN junction, and each depletion electrode 4 has a depletion layer D when a forward voltage is applied. The p-type semiconductor layer 32 is joined so as to be reduced. According to this configuration, the shape of the electron flow path F can be suitably changed in each antenna structure 3.

Note that the optical element 1B of the second embodiment also sends a voltage signal to the switching element 10 via the voltage supply line 8 and the switching element 10 via the switch line 9 in the same manner as the optical element 1A of the first embodiment. It may be configured so that a control signal can be sent to and ON / OFF of voltage application to the divided electrode 4 can be switched (see FIGS. 7 and 23). Further, the p-type semiconductor layer 32 may be formed on the surface 2 a of the substrate 2, and the n-type semiconductor layer 31 may be formed on the p-type semiconductor layer 32. In that case, when a forward voltage (negative voltage with respect to the junction surface with the n-type semiconductor layer 31) is applied to the divided electrode 4, the division of the junction portion between the p-type semiconductor layer 32 and the n-type semiconductor layer 31 is performed. The depletion layer D shrinks and disappears at a portion located directly below the electrode 4. Further, the mirror 13 may be disposed on the surface 3a of the antenna structure 3 (see FIG. 12). Further, a mirror 13 may be disposed between the surface 2a of the substrate 2 and the antenna structure 3 (see FIG. 24). In addition, each antenna structure 3 may have an annular shape other than an annular shape or a C-shape when viewed from the thickness direction of the substrate 2.
[Third Embodiment]

As shown in FIG. 16, the optical element 1C of the third embodiment is mainly different from the optical element 1A of the first embodiment in the shape of the antenna structure 3 and the arrangement of the plurality of divided electrodes 4. Yes. In the optical element 1 C, each antenna structure 3 has a plurality of arms 33 arranged radially when viewed from the thickness direction of the substrate 2. More specifically, the plurality of arms 33 are connected to each other at the base end portion 33a, and are arranged radially, for example, at intervals of 45 degrees. In each antenna structure 3, each divided electrode 4 is formed on the surface 3 a of the antenna structure 3 for each arm 33, and is joined to the n-type semiconductor layer 31 as shown in FIG. 17. More specifically, each divided electrode 4 has a depletion layer that appears and expands at the junction with the divided electrode 4 in the n-type semiconductor layer 31 when a reverse voltage is applied (in other words, , So as to form a Schottky junction).

In the optical element 1C configured as described above, as shown in FIGS. 18A and 18B, a pair of appropriately selected divided electrodes 4 (in FIGS. 18A and 18B). When a reverse voltage is applied to a plurality of divided electrodes 4 (divided electrodes 4 indicated by two-dot chain lines in FIGS. 18A and 18B) excluding the divided electrodes 4 indicated by solid lines, an n-type The depletion layer D appears and expands only at the junctions with the plurality of divided electrodes 4 excluding the pair of appropriately selected divided electrodes 4 in the semiconductor layer 31. Thereby, the junction part with a pair of division | segmentation electrode 4 selected suitably among the n-type semiconductor layers 31 becomes the electron flow path F (electron filling area | region which can produce scattering of light). Therefore, the antenna structure 3 shown in FIG. 18A functions as a C-type antenna that is opened at an angle of 90 degrees in the direction of 45 degrees from the upper side in FIG. The antenna structure 3 shown in FIG. 18 functions as a C-shaped antenna opened at an angle of 45 degrees in the direction of 135 degrees from the upper side in FIG.

As described above, in the optical element 1C of the third embodiment, a voltage is selectively applied to the plurality of divided electrodes 4 in each of the plurality of antenna structures 3 arranged two-dimensionally. The depletion layer D is expanded and the shape of the electron flow path F is changed. Therefore, according to the optical element 1C, it is possible to dynamically modulate at least one of the phase, intensity, and polarization of light.

Each antenna structure 3 has a plurality of arms 33 arranged radially when viewed from the thickness direction of the substrate 2, and each divided electrode 4 is disposed on each arm 33. According to this configuration, each antenna structure 3 can function as, for example, a V-shaped antenna opened at different angles in different directions.

In the optical element 1 C of the third embodiment, a plurality of divided electrodes 4 may be arranged on one arm 33. According to this configuration, in addition to the opening direction and angle of the V-shaped antenna, the length of each arm of the V-shaped antenna can be changed. The optical element 1C of the third embodiment also sends a voltage signal to the switching element 10 via the voltage supply line 8 and also the switching element 10 via the switch line 9 in the same manner as the optical element 1A of the first embodiment. It may be configured so that a control signal can be sent to and ON / OFF of voltage application to the divided electrode 4 can be switched (see FIGS. 7 and 23). Each antenna structure 3 may have a p-type semiconductor layer instead of the n-type semiconductor layer 31. In that case, when a reverse voltage is applied to the divided electrode 4, the depletion layer D appears and expands only at the junction with the divided electrode 4 in the p-type semiconductor layer. Moreover, the division | segmentation electrode 4 may be arrange | positioned at the side surface 3b of the antenna structure 3 (refer FIG.8 and FIG.9). Further, the mirror 13 may be disposed on the surface 3a of the antenna structure 3 (see FIG. 12). Further, a mirror 13 may be disposed between the surface 2a of the substrate 2 and the antenna structure 3 (see FIG. 24). In addition, each antenna structure 3 may have an annular shape other than an annular shape or a C-shape when viewed from the thickness direction of the substrate 2.

Also in the optical element 1C of the third embodiment, each antenna structure 3 has an n-type semiconductor layer 31 and a p-type semiconductor layer 32 forming a PN junction, as in the optical element 1B of the second embodiment. Each divided electrode 4 may be joined to the n-type semiconductor layer 31 or the p-type semiconductor layer 32. In this case, when a forward voltage is applied only to a pair of appropriately selected divided electrodes 4 (divided electrodes 4 indicated by solid lines in FIGS. 18A and 18B), the n-type semiconductor layer 31 and The depletion layer D shrinks and disappears only at the portion of the junction portion of the p-type semiconductor layer 32 located immediately below the pair of divided electrodes 4. As a result, a portion of the junction portion between the n-type semiconductor layer 31 and the p-type semiconductor layer 32 that is located immediately below the pair of divided electrodes 4 can function as the electron flow path F.
[Fourth Embodiment]

As shown in FIG. 19, the optical element 1D of the fourth embodiment is mainly different from the optical element 1A of the first embodiment in the shape of the antenna structure 3. In the optical element 1D, each antenna structure 3 has a square shape when viewed from the thickness direction of the substrate 2. In each antenna structure 3, each divided electrode 4 has a shape of an isosceles right-angled isosceles triangle that divides the square into eight when viewed from the thickness direction of the substrate 2. It arrange | positions at each of the part 34. FIG. In each antenna structure 3, each divided electrode 4 is formed on the surface 3a of the antenna structure 3, and is joined to the n-type semiconductor layer 31 as shown in FIG. More specifically, each divided electrode 4 has a depletion layer that appears and expands at the junction with the divided electrode 4 in the n-type semiconductor layer 31 when a reverse voltage is applied (in other words, , So as to form a Schottky junction). Note that the gap between the adjacent divided electrodes 4 is narrowed to such a width that electrical insulation between the adjacent divided electrodes 4 can be maintained.

In the optical element 1D configured as described above, as shown in FIGS. 21A and 21B, a pair of appropriately selected divided electrodes 4 (in FIGS. 21A and 21B). When a reverse voltage is applied only to the divided electrode 4) indicated by the two-dot chain line, the depletion layer D appears only at the junction between the n-type semiconductor layer 31 and the appropriately selected pair of divided electrodes 4. To enlarge. Thereby, a plurality of divided electrodes 4 (divided electrodes 4 indicated by solid lines in FIGS. 21A and 21B) excluding a pair of appropriately selected divided electrodes 4 in the n-type semiconductor layer 31. The joint portion becomes an electron flow path F (an electron filling region that can cause light scattering). Therefore, the antenna structure 3 shown in FIG. 21A functions as a C-type antenna or a V-type antenna opened to the right side in FIG. 21A, and the antenna structure shown in FIG. The body 3 functions as a C-type antenna or a V-type antenna that opens downward in FIG.

As described above, in the optical element 1D of the fourth embodiment, a voltage is selectively applied to the plurality of divided electrodes 4 in each of the plurality of antenna structures 3 arranged two-dimensionally. The depletion layer D is expanded and the shape of the electron flow path F is changed. Thus, according to the optical element 1D, at least one of the phase, intensity, and polarization of light can be dynamically modulated.

Further, each antenna structure 3 has a square shape when viewed from the thickness direction of the substrate 2, and each divided electrode 4 is disposed at each of a plurality of corner portions 34 in the square. According to this configuration, each antenna structure 3 can function as, for example, a C-type antenna or a V-type antenna as described above.

Note that the optical element 1D of the fourth embodiment also sends a voltage signal to the switching element 10 via the voltage supply line 8 and the switching element 10 via the switch line 9 in the same manner as the optical element 1A of the first embodiment. It may be configured so that a control signal can be sent to and ON / OFF of voltage application to the divided electrode 4 can be switched (see FIGS. 7 and 23). Each antenna structure 3 may have a p-type semiconductor layer instead of the n-type semiconductor layer 31. In that case, when a reverse voltage is applied to the divided electrode 4, the depletion layer D appears and expands only at the junction with the divided electrode 4 in the p-type semiconductor layer. Further, the mirror 13 may be disposed on the surface 3a of the antenna structure 3 (see FIG. 12). Further, a mirror 13 may be disposed between the surface 2a of the substrate 2 and the antenna structure 3 (see FIG. 24). Each antenna structure 3 may have a polygonal shape other than a square when viewed from the thickness direction of the substrate 2. Examples of polygonal shapes other than squares include rectangles, pentagons, hexagons, and the like. At this time, each divided electrode 4 should just be arrange | positioned at each corner | angular part 34 in the said square at least.

Also in the optical element 1D of the fourth embodiment, each antenna structure 3 includes an n-type semiconductor layer 31 and a p-type semiconductor layer 32 forming a PN junction, as in the optical element 1B of the second embodiment. Each divided electrode 4 may be joined to the n-type semiconductor layer 31 or the p-type semiconductor layer 32. In this case, when a forward voltage is applied only to a plurality of divided electrodes 4 (a divided electrode 4 indicated by a solid line in FIGS. 21A and 21B) excluding a pair of appropriately selected divided electrodes 4. The depletion layer D shrinks and disappears only at the portion of the junction between the n-type semiconductor layer 31 and the p-type semiconductor layer 32 that is located immediately below the plurality of divided electrodes 4 excluding the pair of divided electrodes 4. Thereby, the part located just under the some division | segmentation electrode 4 except a pair of division | segmentation electrode 4 among the junction parts of the n-type semiconductor layer 31 and the p-type semiconductor layer 32 can be functioned as the electron flow path F. FIG.

The first, second, third, and fourth embodiments of the present disclosure have been described above, but the optical element of the present disclosure is limited to the above-described first, second, third, and fourth embodiments. is not. For example, as the material of the n-type semiconductor layer 31, an n-type semiconductor material such as n-type GaAs, GZO, AZO, or ITO can be used. In addition to the semiconductor material, an insulating material or the like can be used as the material of the substrate 2. Moreover, as a material of the division | segmentation electrode 4, transparent electrode materials, such as ITO other than a metal material, can be used. Alternatively, each of the optical elements 1 of the first, second, third, and fourth embodiments may be stacked on a transmission type PCSEL to constitute a self-luminous phase control element. In addition, each of the optical elements 1 of the first, second, third, and fourth embodiments is not limited to low-order mode scattered light, and can be used for high-order mode scattered light.

Further, as shown in FIG. 22A, a pattern portion is formed with an n-type semiconductor layer 31 by an electron beam lithography method, and then an insulating layer 12 is formed on the surface 2a of the substrate 2, and then an n-type semiconductor is formed. The divided electrode 4 may be formed on the semiconductor layer 31. Also in this case, as shown in FIG. 22B, the voltage is selectively applied to the plurality of divided electrodes 4 in each antenna structure 3, so that the depletion layer D is expanded and electrons are The shape of the flow path F is changed.

In all the embodiments and all the modifications described above, a plurality of antenna structures are formed by forming at least one of the n-type semiconductor layer 31 and the p-type semiconductor layer 32 in the substrate 2 by doping impurities, for example. 3 may be configured. That is, the plurality of antenna structures 3 may be two-dimensionally arranged in the substrate 2.

Further, one divided electrode 4 may be provided for one antenna structure 3. Even in that case, the voltage is applied to the divided electrode 4 in each antenna structure 3, whereby the depletion layer D is expanded or contracted, and the shape of the electron flow path F is changed.

DESCRIPTION OF

SYMBOLS

1A, 1B, 1C, 1D ... Optical element, 2 ... Board | substrate, 2a ... Surface, 3 ... Antenna structure, 3b ... Side surface, 4 ... Divided electrode (electrode), 8 ... Voltage supply line (1st wiring), 9 ... Switch line (second wiring), 10 ... switching element, 11 ... capacitor, 31 ... n-type semiconductor layer, 32 ... p-type semiconductor layer, 33 ... arm, 34 ... corner, D ... depletion layer, F ... electron flow path .

Claims

A substrate,
A plurality of antenna structures that are two-dimensionally arranged on the substrate and have at least one of an n-type semiconductor layer and a p-type semiconductor layer for forming an electron flow path;
An electrode for expanding or reducing a depletion layer in each of the plurality of antenna structures to change the shape of the electron flow path.
2. The optical element according to claim 1, wherein the plurality of antenna structures are two-dimensionally arranged on the substrate.
The optical element according to claim 1, wherein the plurality of antenna structures are two-dimensionally arranged in the substrate.
The electrode according to any one of claims 1 to 3, wherein the electrode is joined to the n-type semiconductor layer or the p-type semiconductor layer such that the depletion layer expands when a reverse voltage is applied. Optical element.
The electrode is disposed on the n-type semiconductor layer or the p-type semiconductor layer via an insulating layer so that the depletion layer expands when a reverse voltage is applied. An optical element according to any one of the above.
Each of the plurality of antenna structures has the n-type semiconductor layer and the p-type semiconductor layer forming a PN junction,
The electrode according to any one of claims 1 to 3, wherein the electrode is joined to the n-type semiconductor layer or the p-type semiconductor layer so that the depletion layer shrinks when a forward voltage is applied. Optical element.
The optical element according to any one of claims 1 to 6, wherein each of the plurality of antenna structures is provided with a plurality of the electrodes.
Each of the plurality of antenna structures has an annular or C-shape when viewed from the thickness direction of the substrate,
The optical element according to claim 7, wherein each of the plurality of electrodes is disposed at a different position.
Each of the plurality of antenna structures has a plurality of arms arranged radially when viewed from the thickness direction of the substrate,
The optical element according to claim 7, wherein each of the plurality of electrodes is disposed on each of the plurality of arms.
Each of the plurality of antenna structures has a polygonal shape when viewed from the thickness direction of the substrate,
The optical element according to claim 7, wherein each of the plurality of electrodes is disposed at least at each of a plurality of corner portions of the polygon.
Each of the plurality of antenna structures has a side surface extending along the thickness direction of the substrate,
The optical element according to any one of claims 1 to 10, wherein the electrode is disposed on the side surface.
A switching element having a control terminal and a pair of current terminals, wherein the electrode is electrically connected to one of the pair of current terminals;
A first wiring electrically connected to the other of the pair of current terminals;
The optical element according to any one of claims 1 to 11, further comprising a second wiring electrically connected to the control terminal.
The optical element according to claim 12, further comprising a capacitor electrically connected to the one of the pair of current terminals and a ground potential.