KR20190128876A - Optical device including graphene film placed on polymer waveguide and laser pulse apparatus including the same - Google Patents

Abstract

The present invention relates to an optical device including a graphene film placed on a polymer waveguide and a laser pulse apparatus including the same. The laser pulse apparatus comprises: a core layer including a core; a cladding layer surrounding at least a part of the core layer; a substrate surrounding the cladding layer; and a graphene film placed on the core layer, wherein the core layer and the cladding layer are formed of a polymer, thereby generating a high quality laser pulse even when the waveguide is flexible.

Description

TECHNICAL DEVICE INCLUDING GRAPHENE FILM PLACED ON POLYMER WAVEGUIDE AND LASER PULSE APPARATUS INCLUDING THE SAME}

The present invention relates to an optical device including a graphene film located on a polymer waveguide and a laser pulse device including the optical device, and more particularly, to a graphene film located on a flexible polymer waveguide. It relates to an optical element and a laser pulse device for use in generating high quality laser pulses.

Recently, researches for miniaturizing integrated circuits by applying optical interconnects have been actively conducted. Optical interconnects technology is a technology that enables high-capacity transmission, and has advantages of parallel data connection, little electromagnetic interference, and low power consumption and signal loss. Therefore, photonic integrated circuits (PICs) to which optical interconnect technology is applied have high integration density and can realize large scale optical integration.

Silicon (Si) is the most representative material with respect to PIC. Due to the high refractive index of silicon (Si), silicon (Si) based optical devices can obtain a very high degree of degree of integration.

However, silicon (Si) -based optical devices are relatively expensive for lithography techniques such as E-beam or deep-ultraviolet lithography, and are applied to devices requiring flexible functions due to the nature of the material. There is a limit.

Patent Registration No. 10-1028803

According to one aspect of the invention, there is provided an optical device comprising a graphene film located on a polymer waveguide.

In addition, it provides a laser pulse device including the optical element.

According to an aspect of the present invention, an optical device for generating a laser pulse from an input continuous wave laser includes a core layer including a core; A cladding layer surrounding at least a portion of the core layer; A substrate surrounding the cladding layer; And a graphene film positioned on the core layer. Here, the core layer and the cladding layer may be formed of a polymer.

In one embodiment, the cladding layer may be formed of a flexible polymer.

In one embodiment, the cladding layer and the core layer may be formed of the same flexible polymer.

In one embodiment, the core may be a plurality.

In an embodiment, the refractive index of the cladding layer may be 1.45 and the refractive index of the core layer may be 1.455 at a wavelength of 1550 nm.

In one embodiment, the core has a trapezoidal cross-section, the upper surface may be 0.1 to 15um, the height of 0.1 to 15um.

Laser pulse device according to another aspect of the invention the above-described optical element; An amplifier for amplifying the laser transmitted in the laser resonant loop; An isolator presenting the direction of the laser; A polarization controller for controlling polarization of the laser; Single mode optical fiber for controlling chromatic dispersion; And a coupler for branching a laser pulse output from the optical element.

In one embodiment, the laser pulse generated by the laser pulse device has a central wavelength, spectral width, repetition rate and pulse duration of 1553.32 nm, 10.21 nm, It can be 4.18 MHz and 390 fs.

An optical device according to one aspect of the present invention uses a graphene film located on a flexible polymer to generate high quality laser pulses. Therefore, it is possible to generate high-quality laser pulses having flexible characteristics and beyond the limitation of using a rigid silicon (Si) substrate-based optical device, thereby widening the range of the optical device.

In addition, by transferring the graphene film to the optical waveguide that was used only as a passive device, it can be manufactured as an active device, thereby miniaturizing and increasing efficiency.

BRIEF DESCRIPTION OF DRAWINGS To describe the technical solutions in the embodiments of the present invention or in the prior art more clearly, the drawings required in the description of the embodiments are briefly introduced below. It is to be understood that the drawings below are for the purpose of describing the embodiments herein and are not intended to be limiting. In addition, some elements to which various modifications, such as exaggeration and omission, may be shown in the following drawings for clarity of explanation.
1 is a conceptual diagram of a laser pulse device for generating a laser pulse according to an embodiment of the present invention.
2 is a conceptual diagram of an optical device according to an embodiment of the present invention.
3 is a conceptual diagram illustrating light absorption characteristics of graphene having a point band gap structure.
4 is a cross-sectional view of an optical device according to an embodiment of the present invention.
5A to 5C are graphs and images showing characteristics of graphene included in an optical device according to an embodiment of the present invention.
6 is a view showing the alignment of a polymer waveguide and a single mode optical fiber using a visible light laser according to an embodiment of the present invention.
7A to 7E are diagrams illustrating characteristics of a laser pulse generated using a laser pulse apparatus according to an embodiment of the present invention.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The singular forms used in the present invention and the appended claims are intended to include the plural forms as well, unless the context clearly indicates otherwise. It is also to be understood that the term "and / or" as used herein includes any or all possible combinations of one or a plurality of related enumerated items.

When a portion is referred to as being "above" another portion, it may be just above the other portion or may be accompanied by another portion in between. In contrast, when a part is mentioned as "directly above" another part, no other part is involved between them.

Terms such as first, second, and third are used to describe various parts, components, regions, layers, and / or sections, but are not limited to these. These terms are only used to distinguish one part, component, region, layer or section from another part, component, region, layer or section. Accordingly, the first portion, component, region, layer or section described below may be referred to as the second portion, component, region, layer or section without departing from the scope of the invention.

The terminology used herein is for reference only to specific embodiments and is not intended to limit the invention. As used herein, the singular forms “a,” “an,” and “the” include plural forms as well, unless the phrases clearly indicate the opposite. As used herein, the meaning of "comprising" embodies a particular characteristic, region, integer, step, operation, element and / or component, and the presence of other characteristics, region, integer, step, operation, element and / or component It does not exclude the addition.

Unless defined otherwise, all terms including technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. Commonly defined terms used are additionally interpreted to have a meaning consistent with the related technical literature and the presently disclosed contents, and are not interpreted in an ideal or very formal sense unless defined.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

1 is a conceptual diagram of a laser pulse device 1 for generating laser pulses according to an embodiment of the present invention.

Referring to FIG. 1, the laser pulse device 1 includes a light source 11, an amplifier 12, an isolator 13, a polarization controller 14, an optical element 15, and Coupler 16. Each component 11, 12, 13, 14, 15, 16 is optically connected to form a laser resonant loop. In one embodiment, the laser pulse device 1 further comprises a single mode fiber (SMF) 17.

The light source 11 is a device for outputting a continuous wave laser and may be referred to as a laser oscillator. Ruby, Nd: YAG (neodymium-doped yttrium aluminum garnet, Nd: Y3Al5O12, Endiyag), Nd: Glass (Neodymium glass) or Ti: Sapphire can be used as the solid state laser used for the light source 11. have. In one embodiment, the light source 11 may be a pump laser diode.

The amplifier 12 amplifies the laser transmitted in the laser resonant loop. The laser pulse device 1 can instantaneously obtain a large laser pulse output while passing through the amplifier 12. In one embodiment, the amplifier 12 may be an Er-doped fiber amplifier (EDFA).

The laser amplified by the amplifier 12 is transmitted to the polarization controller 14 through the isolator 13. The polarization controller 14 controls the polarization of the laser. On the other hand, since the isolator 13 prevents the transmitted laser from flowing backward, the laser flows in only one direction.

2 is a conceptual diagram of an optical element 15 according to an embodiment of the present invention.

The optical element 15 contains a saturable absorption material. Weak intensity light is absorbed by the saturated absorbent material, and strong intensity light passes through the saturated absorbent material. In particular, when the saturable absorbent material is a nanomaterial, it is possible to insert the saturated absorbent material into a desired place in the laser resonator, so that the integration of the system is advantageous and the process can be simplified. In addition, high nonlinear nanomaterials can minimize their pulse size, resulting in high quality pulses.

Graphene can function as a saturated absorbent material that satisfies all of the above conditions. When the saturated absorption characteristic of graphene is implemented, a picosecond laser pulse may be generated. In graphene, carbon atoms are ordered in two dimensions. Since graphene has a point bandgap structure in which the bandgap between energy bands is zero, it can absorb all light without limiting the wavelength. Therefore, the wideband optical signal can be smoothly generated or processed. Hereinafter, the above description will be described in more detail with reference to FIG. 3.

3 is a conceptual diagram illustrating light absorption characteristics of graphene having a point band gap structure. Models M1 and M2 of FIG. 3 represent light absorption linearity of graphene, and model M3 represents saturation absorption nonlinearity of graphene having a point band gap structure. The dark green areas of model M2 and model M3 in FIG. 3 indicate the state of charge of the photons.

When the amount of photons absorbed by the graphene is small, electrons generate holes in the valence electron band and are excited to specific sites in the conduction band corresponding to the wavelength of the photon. The produced Dirac-fermions exchange energy with plasmons or phnons on the graphene surface. As a result, Dirac Fermions satisfy the Fermi-Dirac distribution. Therefore, the holes and electrons generated are gradually charged from the ends of the electron and conduction bands, so that the energy band becomes wider and cannot absorb photons having the same wavelength.

That is, as in the models M1 to M3 of FIG. 3, when the amount of photons is large enough, the generated carriers fill the energy state and the electrons are no longer blocked by the Pauli exclusive principle of occupied carriers (Pauli blocking). ) The energy state becomes a state that is not excited. This explains the saturated absorption by graphene.

4 is a cross-sectional view of an optical element 15, according to an embodiment of the invention. In one embodiment, the optical element 15 comprises a core layer 151 comprising a core, a cladding layer 153 surrounding some and / or all of the core layer, a substrate surrounding the cladding layer and a graphene film ( 155).

Referring back to FIG. 2, the cladding layer 153 is formed such that the laser is transmitted along the core in the direction in which the core extends due to the difference in refractive index between the core layer 151 and the cladding layer 153. For this waveguide function, the refractive index of the cladding layer is formed to be relatively lower than the refractive index of the core. In addition, the core layer 151 and the cladding layer 153 are formed of a flexible polymer so that the optical element 15 has more flexible characteristics. In one embodiment, both core layer 151 and cladding layer 153 are formed of ZPU12-RI. As a result, the polymer refractive index used for the core is higher than that of the polymer used for the cladding. In one embodiment where the laser wavelength of the light source 11 is 1550 nm, the polymer refractive index used for the core is 1.455 and the polymer refractive index used for the cladding is 1.45. As described above, the core layer 151 and the cladding layer 153 are formed of a flexible polymer, and thus, the core layer 151 and the cladding layer 153 may be used as various flexible optical devices.

Additionally, there may be a plurality of cladding layers. For example, if it is difficult to produce a high quality pulse with one cladding layer, an additional cladding layer may be further coated on the cladding layer 153 to have the refractive index and refractive index differences required to produce a high quality pulse. have.

The optical element 15 generates a laser pulse by the interaction of the graphene film with the laser transmitted along the core. In order to prevent the damage of graphene, the nonlinearity of graphene is used by using the loss of laser having a relatively low energy. The cladding layer 153 is formed such that the graphene film interacts with the disappearance of the laser traveling along the core. In one embodiment, the cladding layer 153 is formed to surround a portion of the core except for the portion corresponding to the top of the optical element 15.

In one embodiment, the core layer 151 of the optical element 15 has a thickness of 36um, the core surrounded by the cladding layer 153 may be formed in a trapezoidal shape with a top surface of 0.1 to 15um, 0.1 to 15um in height. have. In one example, the top surface of the core may be 9um wide and 7um high.

The optical element 15 may have a single core having one core or a multi core having a plurality of cores.

However, the number and cross-sectional shape of the cores are exemplary and not limited thereto, and the cores may be variously formed according to the pattern in which the polymer serving as the cladding is etched.

The graphene film 155 is formed on the core layer 151. In order to extend the evanescent field of the laser propagating into the waveguide core out of the waveguide, the effective refractive index around the core must be lowered. For this purpose, the core is filled on the etched cladding during the optical waveguide fabrication. The periphery of the core is made to be an air layer having a refractive index of 1. As a result, the desired vanishing field extends outward and the interaction with the device located in the area of the extended field is enhanced.

In one embodiment, the graphene film 155 used in the optical element 15 is formed to be transferred onto the core layer 151 after being synthesized by CVD on a copper foil (Cu foil).

5A through 5B are graphs and images showing characteristics of graphene included in the optical device 15 according to an embodiment of the present invention. Nonlinearity of the optical element 15 is determined according to the quality of the graphene film 155.

Referring to Figure 5a, the spectral optical element obtained from the graphene film 155 included in the (15) shows a peak in the 2D peak G, ~ 2700cm ^-1 in the D peak, ~ 1580cm ^-1 at ~ 1350cm ^-1. Based on the spectrum showing a 2D peak that is very sharp and symmetric at 2697 cm ⁻¹ , it can be seen that there are few defects of graphene included in the optical element 15.

The ID / IG peak intensity ratio is directly related to the diameter of the crystalline clusters of graphene, indicating the crystallinity of the film. As shown in FIG. 5A, the ID / IG peak intensity ratio of the graphene included in the optical element 15 is measured to be 0.07, indicating that the graphene has excellent quality with almost no defects of the graphene.

Detailed structure and composition analysis of the graphene film 155 is performed using XPS as shown in FIG. 5B. The C1s spectrum of FIG. 5B shows a single peak with maximum intensity at the binding energy (28.46 eV) of the sp ² hybridized carbon (C) bond. The relative area percentage of sp2 hybridized carbon (C) bonds is 73.96%, which accounts for most of the graphene layer. Thus, graphene included in the optical element 15 may provide sufficient nonlinearity.

The laser pulse device 1 may include a graphene film 155 having a very small number (eg, 5 or less) of graphene layer structures. In one embodiment, the graphene film 155 may have a monolayer structure.

5C is a photograph obtained through transmission electron microscopy (TEM) analysis of the graphene film 155 having the characteristics of FIGS. 5A to 5B. 5C, the graphene film 155 included in the laser pulse apparatus 1 may be visually confirmed to be of high quality.

Referring again to FIG. 1, the laser pulse output from the optical element 15 branches through the coupler 16.

In one embodiment, the laser pulse device 1 may further comprise a single mode fiber. In the course of the laser pulse propagating along the optical fibers connecting the components 11 to 16 of the laser pulse device 1 to each other, the refractive index of glass, which is the optical fiber material, is caused to be different depending on the wavelength of the laser pulse that proceeds. Time difference occurs and the laser pulse spreads. This is called chromatic dispersion, and the laser pulse device 1 can control chromatic dispersion through a single mode optical fiber (SMF), thereby generating a higher quality laser pulse.

FIG. 6 shows the results of alignment of a polymer waveguide with a single mode optical fiber using a visible light laser, according to one embodiment of the invention. As shown in the right side of FIG. 6, even though the graphene film 155 is present on the flexible polymer waveguide, scattering exists at the edge of the graphene, but alignment may be well performed.

7A to 7E are diagrams showing characteristics of laser pulses generated using the laser pulse device 1 according to one embodiment of the present invention.

FIG. 7A is an optical spectrum of an output pulse output from the laser pulse device 1. The central wavelength of the hyperbolic secant pulse is 1553.32 nm and the full width half maximum (FWHN) of the spectral width is 10.21 nm.

FIG. 7B is a graph showing a laser pulse spectrum measured using an oscilloscope, and FIG. 7C is a diagram showing autocorrelation traces of the laser pulse of FIG. 7B.

Referring to Figure 7b, it can be seen that the repetition rate (repetition rate) of the pulse is 4.18MHz. 7C, the pulse width to which sech2 fit is applied is 390fs. Thus, the laser pulse device 1 of FIG. 1 supports that it is possible to produce high quality laser pulses having a fairly sharp shape.

In addition, referring to FIG. 7D, the difference in peak-to-noise from the center peak is 76.03 dB in the radio-frequency (RF) spectrum of the laser pulse. As shown in FIG. 7D, the larger the on-off difference of the laser pulses, the cleaner data is obtained, thus supporting the laser pulse device 1 of FIG. 1 capable of generating high quality laser pulses.

FIG. 7E compares the change of the characteristics of the laser pulse when the pump current of the light source 11 is changed from 350 mA to 600 mA. Referring to FIG. 7E, in the laser pulse device 1, when the pump current increases, the output power of the laser pulse increases, while the pulse width is relatively unchanged. In other words, the laser pulse device 1 generates pulses of constant speed.

As a result, even when using the laser pulse device 1 of FIG. 1 including the graphene film 155 positioned on the waveguide formed of polymer, from the continuous wave laser input by the nonlinearity and the loss of action of the graphene, Ultra fast pulses can be generated.

In one embodiment, the laser pulse device 1 comprises a graphene film 155 positioned on a waveguide formed of a polymer, while having a central wavelength, a spectral width, a repetition rate and It is possible to generate high quality ultrafast pulses with pulse durations of 1553.32 nm, 10.21 nm, 4.18 MHz and 390 fs, respectively.

Although the present invention described above has been described with reference to the embodiments illustrated in the drawings, this is merely exemplary, and it will be understood by those skilled in the art that various modifications and variations may be made therefrom. However, such modifications should be considered to be within the technical protection scope of the present invention. Therefore, the true technical protection scope of the present invention will be defined by the technical spirit of the appended claims.

The present invention can be used to convert ordinary continuous wave (CW) lasers into ultra-femtosecond femtosecond lasers using the characteristic of 'saturable absorption', which is a high optical nonlinearity of graphene. This femtosecond laser implementation goes beyond simple graphene device applications, demonstrating that graphene interacts correctly with the laser even when placed on a polymer waveguide.

The laser pulse device developed as described above can be applied to various application inventions that require flexible characteristics in the future for optical elements, and its application is expected to be infinite.

Claims (8)

An optical element for generating a laser pulse from an input continuous wave laser,
A core layer comprising a core;
A cladding layer surrounding at least a portion of the core layer;
A substrate surrounding the cladding layer; And
Including a graphene film located on the core layer,
The core layer and the cladding layer is a laser pulse device, characterized in that formed of a polymer. The method of claim 1,
The cladding layer is a laser pulse device, characterized in that formed of a flexible polymer. The method of claim 2,
The cladding layer and the core layer is a laser pulse device, characterized in that formed of the same flexible polymer. The method of claim 1,
And a plurality of said cores. The method of claim 1,
The refractive index of the cladding layer is 1.45, the refractive index of the core layer is 1.455 at a wavelength of 1550nm. The method of claim 1,
The core has a trapezoidal cross-section, the upper surface of the laser pulse device, characterized in that the width of 0.1 to 15um, the height of 0.1 to 15um. An optical element according to any one of claims 1 to 6;
An amplifier for amplifying the laser transmitted in the laser resonant loop;
An isolator presenting the direction of the laser;
A polarization controller for controlling polarization of the laser;
Single mode optical fiber for controlling chromatic dispersion; And
And a coupler for branching a laser pulse output from the optical element. The method of claim 7, wherein
The laser pulses generated by the laser pulse device have a central wavelength, spectral width, repetition rate and pulse duration of 1553.32 nm, 10.21 nm, 4.18 MHz and 390 fs, respectively. Laser pulse device characterized in that the.

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