KR20140075404A

KR20140075404A - Graphene photonic devices

Info

Publication number: KR20140075404A
Application number: KR1020120143704A
Authority: KR
Inventors: 김진태; 유영준; 정광효; 최진식; 최춘기
Original assignee: 한국전자통신연구원
Priority date: 2012-12-11
Filing date: 2012-12-11
Publication date: 2014-06-19

Abstract

The present invention discloses a graphene optical element. The optical element includes a clad having a trench, a plurality of optical waveguides extending in a first direction in the clad and separated in the trench, and a plurality of optical waveguides arranged in the trench in a second direction intersecting the first direction And an optical modulation unit for modulating an optical signal inserted and transmitted through the optical waveguides.

Description

Graphene photonic devices < RTI ID = 0.0 >

The present invention relates to an optical element, and more specifically to a graphene optical element.

Planar Lightwave Circuit (PLC) technology is a technology for fabricating optical devices by implementing optical waveguides as optical communication media on flat substrates such as silicon wafers.

A typical optical waveguide type optical device is composed of a quadrangular or circular core dielectric with a high refractive index and a clad dielectric with a low refractive index. Light can be transmitted through the core dielectric. The optical waveguide can change the intensity, polarization, phase or the like of light by the change of the refractive index.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a graphene optical device capable of realizing optical modulation.

A graphene optical device according to an embodiment of the present invention includes: a clad having a trench; A plurality of optical waveguides extending in a first direction in the clad and separated in the trench; And an optical modulation unit inserted in the trench in a second direction intersecting with the first direction to modulate an optical signal transmitted through the optical waveguides.

According to an embodiment of the present invention, the light modulation unit may comprise a first electrode and a second electrode facing each other adjacent to a side wall of the trench, and a first dielectric between the first electrode and the second electrode have.

According to another embodiment of the present invention, the first dielectric layer may include a silica polymer whose refractive index is changed by heat or an electric field.

According to an embodiment of the present invention, any one of the first electrode and the second electrode may include graphene.

According to another embodiment of the present invention, the other one of the first electrode and the second electrode may include a transparent electrode. The transparent electrode may include indium tin oxide (ITO) or indium zinc oxide (IZO).

According to an embodiment of the present invention, a first modulated optical waveguide may be further arranged in the optical waveguides in the first dielectric between the first electrode and the second electrode.

According to an embodiment of the present invention, according to another embodiment of the present invention, the modulated optical waveguide may have a higher refractive index than the first dielectric.

According to an embodiment of the present invention, the modulation optical waveguide may have a rectangular, circular, or polygonal cross section.

According to another embodiment of the present invention, the light modulation unit comprises: a second dielectric disposed between the trench sidewalls and the first electrode; And a third dielectric disposed between the second electrode and the trench sidewall.

According to an embodiment of the present invention, second modulation optical waveguides disposed in the second dielectric and the third dielectric and aligned with the optical waveguides may be further included.

According to another embodiment of the present invention, the light modulation unit comprises: a second dielectric disposed between the trench sidewalls and the first electrode; And a third dielectric disposed between the second electrode and the trench sidewall. The second dielectric and the third dielectric may comprise a silica polymer. The optical waveguides may be respectively connected to the first electrode and the second electrode through the second dielectric and the third dielectric in the trench.

According to an embodiment of the present invention, the optical waveguides may include a metal line optical waveguide. The metal line optical waveguide may have a thickness of 5 nanometers to 200 nanometers and a line width of 2 micrometers to 100 micrometers.

According to another embodiment of the present invention, the optical waveguides may comprise a polymer, silicon oxide, or silicon nitride.

According to an embodiment of the present invention, the clad may include a polymer, a silicon oxide film, quartz, or silicon.

According to another embodiment of the present invention, a substrate below the clad may be further included.

A graphene optical device according to an embodiment of the present invention may include a clad, optical waveguides, and a light modulation unit. The optical waveguides are placed in the clad. The cladding can have a trench. The optical waveguides can be separated from each other in the first direction in the trench. The light modulation unit can be inserted in the trench in the second direction. The light modulation unit may include a first dielectric, a first electrode, a second dielectric, a second electrode, and a third dielectric. An electric field may be induced between the first electrode and the second electrode by an external power supply voltage. The first electrode and the second electrode may include graphene and a transparent metal, respectively. Graphene may have a light transmittance that varies with the magnitude or direction of the electric field. When an AC voltage is applied between the first electrode and the second electrode of the graphene, an electric field can be induced in the first dielectric and the second dielectric. The refractive index of the first dielectric and the second dielectric may be changed by an electric field. The light can be modulated at the first electrode of the graphene by an alternating voltage. Therefore, the graphene optical device according to the embodiment of the present invention can realize optical modulation.

1 is a perspective view showing a graphene optical device according to a first embodiment of the present invention.
FIGS. 2 and 3 are views showing a flow of light and a guide mode of guiding light along a metal line optical waveguide at the time of transmission of an optical signal.
4 is a perspective view showing the first electrode, the second dielectric, and the second electrode of the optical modulation unit of FIG. 1 in detail.
5 is a graph showing a change in the transmittance of the light 160 of the light modulation unit according to the voltage applied to the graphene.
6 is a perspective view showing a graphene optical device 100 according to a second embodiment of the present invention.
7 is a perspective view and a cross-sectional view showing an application example of the light modulation unit of the present invention.
8 is a cross-sectional view showing another application example of the optical modulation unit of the present invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art can easily carry out the present invention. The present invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein.

In order to clearly illustrate the present invention, parts not related to the description are omitted, and similar parts are denoted by like reference characters throughout the specification.

Throughout the specification and claims, when a section is referred to as "including " an element, it is understood that it does not exclude other elements, but may include other elements, unless specifically stated otherwise.

Whenever a portion of a layer, film, region, plate, or the like is referred to as being "on" another portion, it includes not only the case where it is "directly on" another portion, but also the case where there is another portion in between. Conversely, when a part is "directly over" another part, it means that there is no other part in the middle.

1 is a perspective view showing a graphene optical device 100 according to a first embodiment of the present invention.

1, a graphene optical device 100 according to a first embodiment of the present invention includes a substrate 110, a clad 120, optical waveguides 130, and a light modulation unit 140 .

The clad 120 is disposed on the substrate 110. The substrate 110 and the clad 12 may comprise polymer, glass, quartz, or crystalline silicon. Clad 120 may have a trench 122 on substrate 110. The bottom 126 of the trench 122 may be disposed below the optical waveguides 130. The light modulation unit 140 may be disposed in the trench 122. [ The light modulation unit 140 may be in contact with the sidewall 124 to the trench 122. The clad 120 may have a lower refractive index than the optical waveguides 130.

The optical waveguides 130 may be disposed in the clad 120 in a first direction parallel to the substrate 110. The optical waveguides 130 can be separated in the trenches 122. [ The optical waveguides 130 may include a metal line optical waveguide. The metal line optical waveguide may include gold (Au). The metal line optical waveguide may have a thickness of about tens to hundreds of nanometers and a line width of about several tens of micrometers. The optical transmission of metal optical waveguides can be explained by the theory of long-range surface plasmon polaritons (LR-SPP).

The principle of the optical waveguide of the metal line optical waveguide will be briefly described as follows. The optical signal can be transmitted through the free electron polarizations in the metal line optical waveguide and their mutual coupling. The continuous coupling of these free electrons is called surface plasmon polariton. Long-range optical transmission among surface plasmon polaritons is called long-range surface plasmon polariton.

Surface plasmons (SP) can be vibration files of charge density that are constrained along the interface where the real number terms of the dielectric constant are opposite to each other. Surface charge density oscillations can form longitudinal surface confinement waves. The longitudinal surface confinement wave is a component whose electric field component of the incident wave is perpendicular to the interface. Only the TM mode (Transverse Magnetic Mode) can excite and wave the long-range surface plasmon polariton. For example, the metal line optical waveguide may have a thickness of about 5 nm to 200 nm and a width of about 2 탆 to 100 탆.

3 and 4 show the flow of the optical signal and the guide mode when the optical waveguide 130 is replaced with the metal optical waveguide at the time of transmission of the optical signal.

When a very thin and narrow metal line is inserted into the dielectric, the long-range surface plasmon polaritons excited at the metal-dielectric interface formed above and below the metal line are coupled together to form a circular guide mode around the metal line, . The formed guide mode guides along the metal line as shown in FIG.

When light is incident on the surface of the optical waveguides 130, an electromagnetic surface wave called a surface plasmon is generated. Surface plasmons are generated by the interaction of free electrons with light incident from the outside, which means a vibration wave of charge density traveling along the interface between a substance having free electrons and a dielectric in contact with the substance. When an AC voltage is applied to the optical waveguides 130 and the optical modulation unit 140, the charge density of the first electrode 144 of the optical modulation unit 140 changes. The optical signal can be modulated according to the magnitude of the charge density. (A description thereof will be given in the optical modulation unit 140 described later).

Therefore, the graphene optical device 100 according to the present invention can realize modulation of light.

Referring again to FIG. 1, the light modulation unit 140 may be disposed in a trench 122 of the clad 120 in a second direction perpendicular to the substrate 10. The light modulation unit 140 may include a first dielectric 142, a first electrode 144, a second dielectric 146, a second electrode 148, and a third dielectric 150. The first dielectric 142 and the third dielectric 150 may be in contact with the sidewalls 124 of the trenches 122. The first electrode 144 and the second electrode 148 may be disposed between the first dielectric 142 and the third dielectric 150. The second dielectric 146 may be disposed between the first electrode 144 and the second electrode 148). The refractive index of the first to third dielectrics 142, 146, and 150 may be changed by heat or an electric field at the first and second electrodes 144 and 148. The first to third dielectrics 142, 146, and 150 may include a polymer, glass, quartz, or crystalline silicon. Specifically, the first to third dielectrics 142, 146, and 150 may include a silica polymer.

The first electrode 144 and the second electrode 148 may be electrically connected to the optical waveguides 130. The optical waveguides 130 can be passed through the first dielectric 142 and the third dielectric layer 150 in the trenches 122, respectively. The optical waveguides 130 may be connected to electric lines. A power supply voltage may be applied to the electric wires. The light modulation unit 140 can modulate the light 160 of the input signal 162 into the output signal 164 according to the power supply voltage.

4 is a perspective view showing the first electrode 144, the second dielectric 146, and the second electrode 148 of the light modulation unit 140 of FIG. 1 in detail.

Referring to FIG. 4, the first electrode 144 may include a Graphene. Graphene has electrical properties as a honeycomb thin planar structure of carbon atoms connected together. The carbon atoms are connected together to form a layer of carbon atoms. Graphene can be composed of single or multiple layers of carbon atoms. At this time, the graphene of the single layer may be equal to the thickness of one carbon atom. The carbon atoms have a 6-membered ring as a basic unit, and may be formed of a 5-membered ring or a 7-membered ring. The graphene may be formed through a transferring method or a chemical vapor deposition process. The transferring method is a method of transferring the adhesive tape to the second dielectric material 146 by contacting the graphite source. The second electrode 148 may comprise a transparent metal. The transparent metal may include an indium tin oxide film, or an indium zinc oxide film.

Graphene can change the transmittance of light 160 passing through the graphene layer depending on the change in the charge density of graphene. When an external electric field is applied to the graphene layer 160, the density of charges (electrons or holes) in the graphene layer is changed, and this change contributes to the change in interaction with external light. Using this principle, the transmittance of light passing through the graphene layer can be changed according to the change of the applied external voltage 210 as shown in FIG. 2A.

5 is a graph showing the change in the transmittance of the light 160 according to the voltage applied to the graphene.

Referring to FIGS. 4 and 5, graphene has a transmittance of about 0.9 or more at a voltage of about -20 V to -5 V, and a transmittance of about 0.5 or less at a voltage of about 10 V to 20 V. Therefore, the light modulation unit 140 can modulate the light 160 according to an alternating current electrical signal applied from the outside. When an external electric field is applied to the graphene, the density of its internal charge (electrons or holes) can be changed. Based on this principle, the light 160 may travel from one of the optical waveguides 130 to the first electrode 144 of the graphene.

When an AC voltage is applied between the first electrode 144 and the second electrode 148, the charge density in the first electrode 144 may be changed. The degree of loss of the light by the first electrode 144 of the graphene changes according to the magnitude of the charge density. Such a change in loss can induce a modulation effect of the optical signal intensity at the output end of the optical waveguides 130. Therefore, the graphene optical device 100 according to the first embodiment of the present invention can realize the light modulation effect.

In addition, when an AC voltage is applied between the first electrode 144 and the second electrode 148, the refractive index of the second dielectric 146 may be changed. The change in the refractive index can correspond to the change in the coupling efficiency of the TM mode or TE mode light in the first electrode 144. [ The light 160 can adjust the polarization of the TM mode or the polarization of the TE mode by changing the coupling efficiency.

6 is a perspective view showing a graphene optical device 100 according to a second embodiment of the present invention.

4 and 6, the optical waveguides 130 of the second embodiment of the present invention are different from those of the first embodiment in that the first electrode 144 and the second electrode 148 of the light modulation unit 140, As shown in FIG. The first electrode 144 and the second electrode 148 may be connected to external electric wires, respectively. An AC voltage may be applied to the electric wires.

The optical waveguides 130 may extend in the clad 120 in the first direction. The clad 120 and the optical waveguides 130 may have different refractive indices. The input signal 162 and the output signal 164 of the light 160 can be transmitted through a medium having a high refractive index. Therefore, the optical waveguides 130 may have a refractive index higher than that of the clad 120. The optical waveguides 130 may include at least one of a polymer, silicon oxide, or silicon nitride. The clad 120 may be disposed on the substrate 110. The substrate 110 and the clad 120 may comprise polymer, glass, quartz, or crystalline silicon. The clad 120 may have a trench 122.

The light modulation unit 140 can be inserted in the trench 122 in the second direction. The first dielectric 142 and the third dielectric 150 of the light modulation unit 140 may be in contact with the side walls 124 of the trenches 122. [ The first electrode 144 and the second electrode 148 may be disposed between the first dielectric 142 and the third dielectric 150. A second dielectric 146 may be disposed between the first electrode 144 and the second electrode 148. The first to third dielectrics 142, 146, and 150 may include a polymer, glass, quartz, or crystalline silicon. Specifically, the first to third dielectrics 142, 146, and 150 may include a silica polymer. The first electrode 144 and the second electrode 148 may each include graphene and a transparent metal. The first electrode 144 and the second electrode 148 may be spaced from the optical waveguides 130 by the first dielectric 142 and the third dielectric 150. A first dielectric 142 is disposed between the first electrode 144 and one of the optical waveguides 130. The third dielectric 150 is disposed between the second electrode 148 and the other one of the optical waveguides 130. The input signal 162 and the output signal 164 may pass through the first dielectric 142 and the third dielectric 150, respectively.

Graphene can change the transmittance of light 160 passing through the graphene layer depending on the change in the charge density of graphene. When an external electric field is applied to the graphene layer 160, the density of charges (electrons or holes) in the graphene layer is changed, and this change contributes to the change in interaction with external light. Using this principle, the transmittance of light passing through the graphene layer can be changed according to the change of the applied external voltage 210 as shown in FIG. 2A. When an AC voltage is applied to the first electrode 144 and the second electrode 148, the charge density in the first electrode 144 is changed. The optical signal can be modulated according to the magnitude of the charge density.

Accordingly, the graphene optical device according to the second embodiment of the present invention can realize light modulation.

7A and 7B are a perspective view and a cross-sectional view showing an application example of the light modulation unit 140 of FIG.

7A and 7B, the light modulation unit 140 may include a modulated optical waveguide 190 disposed in a second dielectric 146 between the first electrode 144 and the second electrode 148 have. The cross section of the modulated optical waveguide 190 may have a rectangular, circular or polygonal shape. The modulated optical waveguide 190 may have a higher refractive index than the second dielectric layer 146. The modulation optical waveguide 190 can guide light between the first electrode 144 and the second electrode 148. [ Although not shown, the optical waveguides 130 may be aligned with the modulation optical waveguide 190. [

8 is a cross-sectional view showing another application example of the light modulation unit 140 of FIG.

8, the modulated optical waveguides 190 of the light modulation unit 140 may be disposed within the first dielectric 142, the second dielectric 146, and the third dielectric 150. [ Likewise, the cross section of the modulated optical waveguides 190 may have a rectangular, circular or polygonal shape. The modulated optical waveguides 190 may direct light within the first dielectric 142, the second dielectric 146, and the third dielectric 150 of the light modulation unit 140. The optical waveguides 130 may be aligned with the modulation optical waveguides 190. [

The present invention has been described with reference to the preferred embodiments. It will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims. Therefore, the disclosed embodiments should be considered in an illustrative rather than a restrictive sense. The scope of the present invention is defined by the appended claims rather than by the foregoing description, and all differences within the scope of equivalents thereof should be construed as being included in the present invention.

110: substrate 120: clad
122: trench 124: side wall
126: bottom 130: optical waveguides
140: optical modulation unit 142: first dielectric
144: first electrode 146: second dielectric
148: second electrode 150: third dielectric
160: light 162: input signal
164: Output signal

Claims

A clad having a trench;
A plurality of optical waveguides extending in a first direction in the clad and separated in the trench; And
And a light modulation unit inserted in the trench in a second direction crossing the first direction to modulate an optical signal transmitted through the optical waveguides.

The method according to claim 1,
Wherein the light modulating unit comprises a first electrode and a second electrode facing the sidewalls of the trench and a first dielectric between the first electrode and the second electrode.

3. The method of claim 2,
Wherein the first dielectric layer comprises a silica polymer whose refractive index is changed by heat or an electric field.

3. The method of claim 2,
Wherein one of the first electrode and the second electrode comprises graphene.

5. The method of claim 4,
And the other of the first electrode and the second electrode includes a transparent electrode.

6. The method of claim 5,
Wherein the transparent electrode comprises indium tin oxide (ITO) or indium zinc oxide (IZO).

3. The method of claim 2,
And a first modulated optical waveguide aligned with the optical waveguides in the first dielectric between the first electrode and the second electrode.

8. The method of claim 7,
Wherein the modulated optical waveguide has a higher refractive index than the first dielectric.

8. The method of claim 7,
Wherein the modulated optical waveguide has a rectangular, circular or polygonal cross section.

3. The method of claim 2,
Wherein the light modulation unit comprises: a second dielectric disposed between the trench sidewalls and the first electrode; And
And a third dielectric disposed between the second electrode and the sidewall of the trench.

11. The method of claim 10,
And second modulated optical waveguides disposed in the second dielectric and the third dielectric, the second modulated optical waveguides being aligned with the optical waveguides.

11. The method of claim 10,
Wherein the second dielectric and the third dielectric comprise a silica polymer.

11. The method of claim 10,
Wherein the optical waveguides pass through the second dielectric and the third dielectric in the trench and are connected to the first electrode and the second electrode, respectively.

14. The method of claim 13,
Wherein the optical waveguides include a metal wire optical waveguide.

15. The method of claim 14,
Wherein the metal line optical waveguide has a thickness of 5 nanometers to 200 nanometers and a line width of 2 micrometers to 100 micrometers.

The method according to claim 1,
Wherein the optical waveguides comprise a polymer, silicon oxide, or silicon nitride.

The method according to claim 1,
Wherein the clad comprises a polymer, a silicon oxide film, quartz, or silicon.

The method according to claim 1,
And a substrate under the clad.