KR100547252B1 - Fabrication of Photonic crystal with Graded-Index distribution and Preparing method for the same - Google Patents

Abstract

The present invention relates to a photonic crystal having a gradual refractive index distribution and a method for manufacturing the same, and more particularly, after forming a polymer layer capable of bulk polymerization on one surface of the cell for polymerization, the polymer layer and After fixing the formed photonic crystal made of a material that does not dissolve in the polymer on one side of the adjacent cell, and then filling the inside of the cell in which the photonic crystal is formed with a mixed solution containing a monomer of the polymer and a refractive index control agent and then gel-polymerized The process takes place.

According to the present invention, an advanced and novel method in which a space composed of interconnected air layers existing between unit particles of photonic crystals having a repeated refractive index corresponding to a wavelength of incident light is filled with a polymer of a polymer having various refractive index distributions according to polymerization conditions Photonic crystals can be prepared, and thus the photonic crystals of the present invention have a continuous optical band interval due to the effective refractive index of the photonic crystals being changed according to their position, unlike conventional photonic crystals having one optical band interval. Since there is no need to apply a separate field at, it has a high possibility of application as a next-generation high density optical integrated optical device.

Photonic crystal, optical band spacing, effective refractive index, optical element

Description

Photonic crystal with Graded-Index distribution and Preparing method for the same}             

Figure 1a is a schematic diagram showing the structure of the photonic crystal having a gradual refractive index distribution to be described in the present invention, Figure 1b is a graph illustrating the refractive index distribution according to the photonic crystal position, Figure 1c has the same refractive index distribution as Figure 1b This is a graph illustrating the distribution of wavelengths of the light band intervals according to the photonic crystal locations.

FIG. 2A is a unit schematic diagram of a colloidal photonic crystal having a three-dimensional face center cubic (FCC) structure in which colloidal particles used in the embodiment are self-assembled, and FIG. 2B is a colloidal photonic crystal of FIG. 2A. This is a unit schematic diagram after removing colloidal particles after filling different materials in nano-sized spaces between unit particles.

3 is a schematic diagram sequentially showing a method of manufacturing a photonic crystal having a gradual refractive index distribution of the present invention.

4A is a scanning electron microscope (Scanning Electron Microscopy, SEM) photograph showing the plane 111 crystal direction of the colloidal photonic crystal used in the embodiment, Figure 4b is a scanning microscope photograph showing a cross section of the colloidal photonic crystal used in the embodiment to be.

5 is an optical microscope image and a real picture before and after gel-polymerization, (a) is an optical micrograph of the colloidal photonic crystals before gel-polymerization, (b) is an optical micrograph of the colloidal photonic crystals after gel-polymerization (c) is a photonic crystal picture in an actual glass cell before gel-polymerization, and (d) is a photonic crystal picture in an actual glass cell filled with a polymer after gel-polymerization.

FIG. 6 is a schematic diagram of measurement equipment used for measuring transmittance of photonic crystals having a gradual refractive index distribution prepared in Examples. FIG.

 7 is a transmission spectrum of photonic crystals before and after gel-polymerization.

 FIG. 8 is a transmission spectrum showing a change in light band spacing depending on a position of a photonic crystal having a gradual refractive index distribution manufactured in the example. FIG.

<Explanation of symbols for the main parts of the drawings>

1: White light source 2: Spectrum analyzer

3: colloidal photonic crystal 4: fiber coupler

5: colloidal particles 6: space between colloidal particles

7: polymer layer 8: polymerized sample glass cell

9: glass substrate 10: silica colloidal photonic crystal

11: monomer, dopant mixed solution 12: single mode optical fiber

13: lens 14: photonic crystal sample

15: multimode fiber

The present invention relates to a photonic crystal having a gradual refractive index distribution and a method for manufacturing the same, and more particularly, after forming a polymer layer capable of bulk polymerization on one surface of the cell for polymerization, the photonic crystal is made of a material that does not dissolve in the polymer Form photonic crystals on one surface of the cell adjacent to the polymer layer, and then fill the inside of the cell in which the photonic crystals are formed with a mixed solution containing monomers of the polymer and a refractive index modifier. It consists of a process of polymerization.

According to the present invention, an advanced and novel method in which a space composed of interconnected air layers existing between unit particles of photonic crystals having a repeated refractive index corresponding to a wavelength of incident light is filled with a polymer of a polymer having various refractive index distributions according to polymerization conditions Photonic crystals can be prepared, and thus the photonic crystals of the present invention have a continuous optical band interval due to the effective refractive index of the photonic crystals being changed according to their position, unlike conventional photonic crystals having one optical band interval. Since there is no need to apply a separate field at, it has a high possibility of application as a next-generation high density optical integrated optical device.

With the advent of the information society and the explosive spread of the Internet, the amount of information and communication data that our society needs is increasing exponentially, and the electronic device industry, which has been a driving force as the foundation of 20th century science and technology, The development has been remarkable through integration and large capacity. However, photons have been proposed as a new information transfer medium due to the large interaction between the media and the limitation of the slow propagation rate due to the mass and charge of electrons themselves.

However, since the existing optical devices are showing limitations in terms of efficiency and space density, the development of new photoelectronic devices is becoming increasingly important in implementing the 21st century ultra-high information society. Accordingly, alternatives that can overcome the limitations of existing optical devices using a material that can freely control photons in a micro space, that is, photonic crystals, have been in the spotlight. Currently, developed countries in the United States, Japan, and Europe are investing intensively by selecting nano photonics as an important part of future nanotechnology as a next-generation strategic research project. Research and development is ongoing. As such, the interest and importance of nano-photonic crystals is gradually increasing, and the ripple effect of the photonic crystal technology is expected to have a very large ripple effect such as semiconductors, electrical and electronic devices, functional devices, and nano-bio.

Photonic crystals are similar in concept to the formation of electronic band gaps in conventional semiconductors. Materials with a crystalline structure have a periodic potential due to the regular arrangement of atoms or molecules that make up the material, which affects the movement of electrons. An important phenomenon is the formation of a band gap. to be. The band gap prevents the progress of electrons with a specific energy, and if the potential energy of the lattice is large enough, it can completely prevent the progress of electrons with all kinds of energy. It is a completely band gap existing between a conduction band and a valence band in a semiconductor.

In 1987, Yablonobitch and John announced that the same concept of band gap can be applied to light [Yablonovitch, E., Phys. Rev. Lett. 58, 2059. (1987)], since the potential acting on light is a dielectric, periodic arrangement of the photonic band gap can lead to selective transmission of electromagnetic waves with a specific wavelength. It could theoretically be prevented by using the Maxwell equation. This proposal was realized in 1989 by the Jablonović group experimentally demonstrating the existence of photon band gaps in two-dimensional photonic crystals [Yablonovitch, E, and T. J. Gmitter, Phys. Rev. Lett. 63, 1950 (1989). Since 1991, the same group has produced three-dimensional photonic crystals in the microwave frequency domain, suggesting the possibility that photonic crystals can be applied to actual devices. Active research has been conducted in various places [Yablonovitch, E, and TJ Gmitter]. , and KM Leung., Phys. Rev. Lett. 67, 2295. (1989).

The theory of the light band spacing is as follows. When light is irradiated, light with a wavelength similar to the lattice size of the photonic crystal is superimposed on the interference between light scattered by each regular lattice center inside the photonic crystal. It cannot pass through the inside of the phosphorus photonic crystal. In other words, the irradiated light must be completely reflected unless the material itself is absorbed.

Photonic crystal is a crystal structure whose structure repeatedly has a dielectric equal to the wavelength of light. The photonic crystal is a structure in which the refractive indices of two different materials are regularly repeated, and the repetition of the dielectric is a medium having a high refractive index (metal , Semiconductors, dielectrics, etc.) are formed by regularly repeating and spatially arranging the air holes. In this case, the difference between the refractive index of the medium and the air, the ratio of the medium and the air, and the arrangement in the structure are important factors for the optical properties of the photonic crystal. The refractive index of air is the lowest as 1, and can be used as a reference material, and it is possible to change the optical properties of the photonic crystal by adjusting the refractive index difference with the medium by filling another material in the air layer space.

Currently known techniques for producing photonic crystals can be classified into two types, one of which is based on nano-microfabrication technology, using photolithography, electron beam lithography, holography, etc. The crystal is a method of processing a crystal, and the other is a method of manufacturing a photonic crystal by periodically arranging and stacking unit particles having a size of several hundred nanometers using a self-assembly method.

As described above, in the photonic crystal, the repetitive period of the dielectric constituting the crystal must correspond to the wavelength of light, and thus a manufacturing method based on processing technology requires high precision and expensive processing equipment. Therefore, nano-processing technology can produce hundreds of nanometer sized photonic crystals that can operate at frequencies in the optical communication range, but since the optical properties of photonic crystals are very sensitive to structure, continuous research on more precise processing technology need. On the other hand, the method of manufacturing photonic crystals by the self-assembly method is easy to obtain photonic crystals at a relatively low cost because of the naturally occurring method, but it is difficult to produce perfect photonic crystals without defects.

On the other hand, various attempts have been reported to control the optical band spacing of photonic crystals, and such optical band spacing engineering controls the size of the optical band spacing or changes the wavelength of the optical band spacing by a specific field such as a tunable optical filter or an optical switch. Attempts have been made to temporarily eliminate the band gap.

Existing methods have largely designed various photonic crystal structures to change the optical band spacing of the photonic crystals according to the structure, or as shown in FIG. Separate external fields, in particular electric fields [Ozake, M .; Shimoda, Y .; Kasano, M .; Yoshino, K. Adv. Mater. 2002, 14, 514, magnetic field [Xu, X .; Friedman, G .; Humfeld, K. D .; Majetich, S. A., Asher, S. A., Adv. Mater. 2001, 13, 1681], ultraviolet light [Gu, Z. Z, Fujishima, A., Sato, O., J. Am. Chem. Soc. 2000, 122, 12387], thermal energy [Debord, J. D., Lyon, L. A., J. Phy. Chem. B. 2000 14, 6327] have attempted to control the band gap with a change in the effective refractive index difference between the photonic crystal and these materials.

Another approach is to fill a photonic crystal with an elastic material and apply physical pressure from outside to change the lattice spacing of the photonic crystal [Iwayama, Y .; Yamanaka, J .; Takiguchi, Y .; Takasaka, M .; Ito, K .; Shinohara, T .; Sawada, T .; Yonese, M .; Langmuir. 2003, 19, 977] pH change [Alexeev, V. L., Sharma, A. C., Goponeko, A. V., Das, S., Lednev, L. K., Wilcox, C. S., Finegold, D. N., Asher, S. A., Anal. Chem. 1998, 70, 780] Attempts have been made to control light band spacing by introducing light-sensitive materials into photonic crystals in aqueous solutions and by changing the lattice spacing of photonic crystals with changes in electrostatic attraction due to changes in acidity of aqueous solutions. come.

However, the photonic crystals produced by the various methods as described above still have one photonic crystal gap, so when the photonic crystals are to be used in a plurality of wavelengths, the same type of wavelength is used as the photonic crystals. The number of photonic crystals should be used, which is an important factor that cannot increase optical coherence in optical device applications using multi-wavelength splitting.

Accordingly, the inventors of the present invention, as a result of research efforts to solve the problems described above, after forming a photonic crystal as a material that is not dissolved in the polymer, forming a polymer layer, and includes a monomer and a refractive index regulator of the polymer. When the gel-polymerization reaction is performed by filling the mixed solution, the space composed of interconnected air layers existing between the unit particles of the photonic crystal is filled with the polymer and the overall spatial and gradual refractive index is increased by the gel effect. It has been found that photonic crystals having a distribution can be produced to complete the present invention.                         

Accordingly, the present invention has a high possibility of application as a next-generation high-density photo-integrated optical element because the photonic crystal itself has an effective refractive index that changes with its position and thus has a continuous light band interval, and does not need to apply a separate field from the outside. The object of the present invention is to provide a photonic crystal having a progressive and novel gradual refractive index distribution and a method of manufacturing the same.

The present invention provides a gradual refractive index distribution filled with a distributed polymer polymer in a space composed of interconnected air layers existing between unit particles of photonic crystals having a repeated refractive index corresponding to the wavelength of incident light. Characterized by photonic crystals.

In another aspect, the present invention is the first step of forming a polymer layer on one surface of the polymerization cell, the second step of forming a photonic crystal on one surface of the cell adjacent to the polymer layer while being separated from the cell formed with the polymer layer, and the polymer monomer It includes a method for producing a photonic crystal having a gradual refractive index distribution comprising the step of filling the cell in which the photonic crystal is formed with a mixed solution containing a refractive index control agent and then gel-polymerize.

The present invention will be described in detail as follows.

The present invention forms a polymer layer, and filling the space between the unit particles of the photonic crystal with a mixed solution containing a monomer and a refractive index regulator of the polymer in the photonic crystal prepared by various methods on the adjacent side of the polymer layer By polymerizing together with the layers, a space filled with polymers of polymers having various refractive index distributions depending on the polymerization conditions is a space consisting of interconnected air layers existing between unit particles of photonic crystals having a repeating refractive index corresponding to the wavelength of the incident light. And new photonic crystals can be produced.

Hereinafter, the present invention will be described in detail with reference to a manufacturing method.

The photonic crystal having a gradual refractive index distribution of the present invention is prepared by introducing a gel-effect known in the art for producing a graded-index plastic optical fiber base material into photonic crystal production. The gel-effect is a method of incorporating an additive into a plastic precursor to naturally change the refractive index due to the difference in solubility in the polymerization process to achieve a refractive index distribution [Japanese Patent Laid-Open No. H08-262240]. Since the reactivity of the monomer present in the resulting gel layer is higher than other monomers, the refractive index regulator having a high refractive index is pushed out of the polymer layer produced during the polymerization process to generate a progressive refractive index.

In the case of colloidal photonic crystals having a progressive refractive index, the optical characteristic of the photonic crystal can be predicted because the wavelength of the band gap is a function of the refractive index shown in Equation 1 below. This equation corresponds to the case where colloidal photonic crystals are face-centered cubic structure (FCC), the most stable structure by self-assembly, and the incident light is incident perpendicularly to the sample.

In Reaction Scheme 1, λ _max is a wavelength corresponding to the photoband spacing of the photonic crystal, d ₁₁₁ is the spacing between planes in the (111) crystal direction, n _p is the refractive index of the colloidal particles forming the photonic crystal, n _b is the particle Is the refractive index when air or other materials are filled in the void space between them, n _eff is the effectivc index, D is the diameter of the colloidal particles, f is the volume fraction of the colloidal particles, In the case of 0.74.

In the present invention, by spatially varying the value of n _b in the above reaction scheme _{1 n b = f (x)} , that is, with a function called the refractive index of the material of the blank spaces in the photonic crystal where x, according to the position of the photonic crystal It is intended to produce a photonic crystal having a change in wavelength of the light band interval.

First, a first step of forming a polymer layer on one surface of the polymerization cell.

Referring to FIG. 3, the polymer layer 7 is formed on one portion of the glass cell 8 for polymerization having an appropriate size as shown in FIG. 3. In this case, the polymer may be used to select most polymer monomers capable of bulk polymerization, and specifically, for example, a polymer selected from ethylene, vinyl chloride, butadiene, styrene, methyl methacrylate, and vinyl acetate monomer may be used. In particular, it is useful for the production of photonic crystals having better optical properties when a polymer having excellent transparency, such as an acrylic polymer or a styrene polymer, is used.

Next, the second step of positioning the photonic crystal formed on one surface of the cell adjacent to the polymer layer while being distinguished from the cell in which the polymer layer is formed.

That is, the colloidal particles prepared by using a material that is insoluble in the polymer monomer constituting the polymer layer 7 on the other side of the adjacent cell while being separated from the cell on which the polymer layer 7 is formed as shown in FIG. The photonic crystal 10 is prepared by self-assembly on the glass substrate 9 and placed adjacent to the polymer layer 7 in the polymerization cell 8 previously made by bulk polymerization. The photonic crystal may be made of various materials such as an organic material or an inorganic material, but a polymer monomer and a refractive index dispersing agent or a polymerization initiator or a chain transfer agent are injected into empty spaces formed by unit particles constituting the photonic crystal. Select and use according to the type of additive.

The photonic crystals can be prepared by various conventional methods. Specifically, for example, it can be produced by a colloid method, a self-assembly method, a photolithography method, an electron beam lithography method, a holography method, a stereo lithography method, or the like. have.

In the present invention, for the sake of convenience, an example of manufacturing a photonic crystal having a gradual refractive index distribution using colloidal photonic crystal by self-assembly is given, but the empty space formed by the unit particles of the photonic crystal is interconnected to the entire photonic crystal. Any structure can be applied. Therefore, in order to ensure that the regular air layers in the photonic crystals are connected to each other, nanofabrication techniques requiring considerable precision have to be developed. In order to manufacture a photonic crystal having a gradual refractive index distribution intended in the present invention, the nano-sized space formed in the photonic crystal itself should be minimized or minimized at the time of photonic crystal formation. Optimum polymerization conditions should be established to fill the voids of the polymer with the polymer monomer and the refractive index control agent and to have the desired refractive index distribution.

The photonic crystals may be manufactured to have one, two, and three dimensional structures, and the refractive index may be distributed according to the structure of unit particles of photonic crystals such as simple cubic, face-centered cubic, body-centered cubic, and diamond structures. Since it will be different, it can be produced by selecting the structure of the photonic crystal as described above.

In the embodiment of the present invention, the colloidal crystals prepared by the self-assembly method, that is, the opal structure, which is a three-dimensional photonic crystal self-assembly of the colloidal spheres of several tens to hundreds of nanometers produced by the chemical method was used.

Finally, the third step of filling the inside of the cell in which the photonic crystal is formed with a mixed solution containing the polymer monomer and the refractive index regulator is followed by gel-polymerization.

That is, in the colloidal photonic crystals, there is a nano-sized microspace existing between the crystallized colloidal particles, which forms a repeating period of the dielectric in the photonic crystals, and the monomer and the refractive index of the polymer into the nano-sized voids. The regulator is charged and the gel-effect polymerization forms a photonic crystal with progressive refractive index. That is, the nano-sized void spaces formed in the photonic crystals are connected to each other as shown in FIG. 2B, and the refractive index regulators are diffused through the gel-effect polymerization through the mutually connected channels. The distribution is determined and a photonic crystal having a refractive index distribution is realized.

And, by appropriately controlling the rate of polymerization using this gel-effect, it is possible to form a refractive index gradient having a gradual or sudden change. At this time, the photonic crystal may be melted using selective solubility between the photonic crystal material and the polymer used in the gel-effect polymerization to reverse the photonic crystal structure as shown in FIG. 2B, and repetitive manipulation thereof may also be performed.

Into the polymerization cell in which the photonic crystal of the second step is prepared, a mixed solution containing the monomer and the refractive index regulator of the polymer constituting the polymer layer used in the first step is filled and polymerized, wherein the unit particles of the photonic crystal The empty space formed is filled with a polymer having a different refractive index gradually.

The principle of gel-polymerization is a gel layer formed at the interface between the polymer and the monomer. The monomer molecules are easily diffused, whereas the refractive index regulator having a high refractive index is quite large in molecular structure and difficult to diffuse into the gel layer. In other words, as the polymerization proceeds due to the formation of the gel, the refractive index control agent is pushed in the opposite direction of the polymer layer. Thus, the distribution of the refractive index control agent in the photonic crystals means a gradual refractive index distribution. It is possible to produce photonic crystals having a gradual refractive index distribution.

Therefore, the refractive index distribution ideally forms a moderate refractive index distribution in the opposite direction of the polymer layer formed before gel-polymerization if there is no temperature gradient throughout the polymerization cell and the mixed solution of the monomer and the refractive index regulator is perfectly uniformly mixed. .

The type and concentration of the polymer monomer and the refractive index regulator and the organic additives that may be additionally included therein and the temperature applied to the gel-polymerization are important parameters for determining the refractive index distribution during the gel-polymerization. The composition of the polymer monomer and the refractive index regulator and the organic additive that may be additionally included may be optimized according to the desired use under the following conditions.

The larger the amount of the refractive index control agent in the monomer can increase the difference in the refractive index distribution in the photonic crystal, but the thermal property may be significantly lowered since the refractive index regulator itself serves as a plasticizer by remaining in the polymer after polymerization.

In this case, the refractive index control agent should be selected to have a higher refractive index than the polymer used, and phase separation should not occur with the monomer of the polymer, and it is difficult to enter into the gel layer formed at the interface between the polymer layer formed and the polymer monomer added. The molecular size should be selected to be large enough. That is, the monomer of the polymer can enter well into the gel layer, and the refractive index regulator should be excluded by the gel layer, so that the refractive index regulator molecules are gradually pushed out as the polymer layer grows by the gel layer, thereby achieving a gradual refractive index distribution.

Such refractive index regulators include organic materials such as phthalate, phosphate, phosphate, phosphate, phosphate, phenyl, aryl, benzyl, and benzoyl groups such as substituted or unsubstituted phenyl, aryl, benzyl and benzoyl groups. Metric sized quantum dots and metal nanoparticles may be selected and used. Specific examples of the organic materials include benzyl n-butyl phthalate, benzyl benzoate, diphenyl sulfate, triphenyl phosphate and diphenyl phthalate. Can be used.

In the embodiment of the present invention, in consideration of the above matters, the amount of the refractive index regulator and the polymer monomer is limited to 30: 70% by volume, but the above limitation is limited to the case of the polymer monomer and the refractive index regulator used in the examples. The present invention is not applicable to all the scopes of the present invention, and can be easily used by those skilled in the art depending on the material of the polymer and the photonic crystal.

 Organic additives that can be selectively added as needed include a polymerization initiator, a chain transfer agent, and the like, and their selection depends on the polymer used and the material of the photonic crystal. In other words, if the rate of gel-polymerization occurs quickly, the polymerization rate is increased and a thick gel layer is formed rapidly, which causes the refractive index regulator to be pushed out all at once, resulting in a problem of forming a refractive index distribution like a step shape. Therefore, in order to maintain the gentle growth by controlling the rate of gel-polymerization to gradually cause the growth of the gel layer, a polymerization initiator or a chain transfer agent is optionally used in addition to the polymer monomer and the refractive index regulator as necessary.

As the polymerization initiator, peroxide-based, azo-based, disulfide-based and tetragen-based thermal initiators may be used, and specifically, benzoyl peroxide (BPO), dibenzoyl peroxide (DBPO), tertiary butyl peroxide, etc. Alkyl peroxide, cumyl hydroperoxide, tertiary butyl perbenzoate, azobisisobutylone nitrile (AIBN), and the like, and may use acetophenone series photopolymerization initiator, specifically, diethoxyaceto Phenone, saogenton series and the like can be used. In addition, if the growth of the gel layer also gradually occurs by slowly and slowly maintaining the polymerization rate, a more gradual refractive index distribution can be obtained, so that the amount of the polymerization initiator can be adjusted appropriately, and generally about 0.00 to 0.04% by weight can be used. .

In addition, if the molecular weight of the polymer is too large, it is difficult to disperse the heat during polymerization, so as necessary, a chain transfer agent is added as needed to obtain a high quality transparent polymer by controlling the molecular weight of the polymer.

The gel-polymerization may be a method such as heat treatment, ultraviolet irradiation, microwave irradiation, etc., wherein the polymerization temperature is different depending on the type of polymer used. If the polymerization temperature is too high, the reaction proceeds rapidly. As a result, it is not possible to obtain a gradual refractive index distribution, and it may be difficult to obtain a high quality transparent polymer, such as bubbles, due to the difficulty of thermal dispersion, which is a disadvantage of bulk polymerization.

This gel-effect method is characterized in that it is easy to implement a photonic crystal structure having various refractive index distributions by appropriately adjusting the spatial structure or polymerization conditions of the polymer layer to be initially formed. This feature can be emphasized once again with respect to the excellence of the present invention in view of the fact that the change of the spatial refractive index of the photonic crystal, that is, the different size of the empty space, requires tremendous effort and cost with other existing nano-machining techniques. It works.

The optical properties of the photonic crystals having a gradual refractive index distribution prepared according to the present invention can be obtained by measuring the transmittance according to the position (see FIG. 6). As a light source, light having a wavelength of 600 to 1800 nm is transmitted through a single mode optical fiber, and light emitted from the end of the optical fiber is collected by a lens, and the sample is positioned vertically and the light is collected while passing through the sample. The light enters the spectral spectrometer through the multimode optical fiber and analyzes the transmittance according to the wavelength. Among the white light source injected into the photonic crystal, the wavelength corresponding to the optical band interval which cannot exist in the photonic crystal is reflected, so when measuring the transmittance, only the specific wavelength corresponding to the optical band interval is filtered out.

In the photonic crystal having a gradual refractive index distribution of the present invention, the sample is fixed perpendicularly to the direction of light propagation between the light source and the light receiving element, and the micro stage is constructed to move in the longitudinal direction or the height direction of the photonic crystal. The optical band spacing characteristic was measured (see FIG. 6).

The advantage of the present invention over the known art is that the photonic crystal itself does not need to apply an external specific field because the light band interval varies depending on the position. In addition, since photonic crystals having spatially varying refractive index distributions within the photonic crystals can be easily manufactured, various optical band gap engineering can be attempted.

Research and development of photonic crystals having the characteristics described above can be widely applied to the application fields of various optical devices that are expected to contribute greatly to the next generation high density photo-integration. Specific examples of the optical devices include active devices including photonic crystal lasers and photonic crystal light emitting devices, passive devices such as photonic crystal optical waveguides and photonic crystal optical fibers, optical filters, optical splitters, and high refractive prism.

Hereinafter, the present invention will be described in detail with reference to Examples, but the present invention is not limited by the following Examples.

Example

First step: preparation of the polymer layer

99.8% by weight of a methylmethacrylic acid monomer and 0.1% by weight of a polymerization initiator in a glass cell for polymerization having a size of horizontal, vertical, and thickness (7 mm × 30 mm × 1 mm) as shown in FIG. 3 (a). (Benzoylperoxide) and 0.1 wt% of a chain transfer agent (normal butylmercaptan) were polymerized in a convection oven at 80 ° C. to form a polymethyl methacrylate (PMMA) polymer layer.

Second step: photonic crystal manufacturing by self-assembly

The silica colloid particles having a uniform diameter of 500 nm and dispersed in an aqueous dispersion medium (distilled water: ethanol = 1: 1 (w / w)) were crystallized by appropriate evaporation of the dispersion medium. The silica colloidal particles do not dissolve in methacrylate, which is a monomer that will later be filled into colloidal photonic crystals for gel-polymerization, and due to the stiffness of the silica material itself, nano-sized voids in the colloidal crystals are filled or become smaller during crystal formation. It was chosen because it was significantly less.

Silica colloidal photonic crystals having a size of 700 μm × 20 mm × 41 μm were obtained on a glass plate through self-assembly using electrostatic attraction and gravity of the crystallized colloid particles. Figure 5 (c) shows the photo-realization of the colloidal photonic crystal formed on the glass substrate, and an optical micrograph with an iridescent opal color reflected by reflecting light of different wavelengths of visible light according to the incident angle of light is shown in FIG. (A) [scale bar 100 micrometer] of each is shown.

4A and 4B show an enlarged electron scanning micrograph of the photonic crystal, and it was confirmed that a colloidal photonic crystal having a good quality face-centered cubic structure close to about 100 layers was obtained in a fairly large area. In addition, the optical band spacing characteristics of the silica colloidal crystal are shown in the solid line of FIG. 7, and it is confirmed that the optical band gap has about -12 에서 at a wavelength of 1052 nm, thereby obtaining a colloidal photonic crystal having excellent optical properties that almost no light passes through the optical band interval wavelength. It was confirmed.

Third Step: Preparation of Photonic Crystals with Gradual Refractive Index Distributions

The colloidal photonic crystal prepared in the second step was placed in a glass cell for polymerization adjacent to the polymer layer prepared in the first step (Fig. 3b), and 69.02% by weight of methyl methacrylate monomer, 0.04% by weight of polymerization A mixed solution of an initiator (benzoyl peroxide), 0.1% by weight of a chain transfer agent (normal butyl mercaptan) and 29.58% by weight of a refractive index regulator (diphenyl sulfide) containing colloidal photonic crystals prepared in the second step is contained. After injection into a glass cell for polymerization, the cell was sealed, polymerized in a convection oven at 80 ° C. under a nitrogen gas atmosphere, and gel-polymerized to obtain a photonic crystal having a gradual refractive index distribution of the present invention.

The photomicrograph of the sample cell after completion of the above-mentioned gel-polymerization is shown in FIG. 5D by an optical micrograph (scale bar 200 µm), and the optical band gap characteristics of the colloidal photonic crystals before and after gel-polymerization are shown in FIG. 7.

As the polymer with the refractive index control agent distributed in the photonic crystal is filled, the band gap wavelength is changed by the change of the effective refractive index of the photonic crystal, and accordingly, the color of the opal is changed due to the change of the wavelength reflected in the visible region along the crystal direction. It was confirmed that the change was compared with before the polymerization (FIG. 5A). FIG broken line in 7-gel due to the increase in the effective refractive index in a transmission spectrum measured at any point after polymerization photonic crystal was confirmed that the band gap wavelength is moving in a long wavelength to 1174 ㎚ in 1052 ㎚, as in the photonic crystal n _p It was observed that the optical filter characteristic was lowered by decreasing the difference in refractive index of n _b . In addition, it was observed that the decrease in the interval of the optical band interval due to the low refractive index narrows the width of the transmission curve (Full Width Half Maximum) from 47.3 nm to 43.1 nm.

In conclusion, in the progressive refractive index distribution manufactured in FIG. 8, it was observed that the wavelength of the light band gap gradually changed according to the photonic crystal position.

In addition, since the refractive index distribution described in the present invention is formed in the vertical direction of the initially formed polymer layer, various refractive index distributions may be implemented according to the structure of the initially formed polymer. That is, in the case of the three-dimensional colloidal photonic crystal shown in the above embodiment, the refractive index distribution can be applied in a specific crystal direction, that is, in various directions such as (111) (-110) (11-2) (100) of the FCC.

In addition, by forming the desired refractive index distribution according to the crystal direction or structure of the photonic crystal, it is possible to implement a photonic crystal having a variety of refractive index distribution. This means that by applying various distributions of refractive index to the photonic crystal, it is possible to induce optical characteristics of various photonic crystals, and thus, a wide range of applications can be expected in the implementation of related optical devices.

As described above, the conventional photonic crystals have one light band interval in the entire crystal, whereas the photonic crystals produced by the manufacturing method of the present invention have various refractive index distributions that bring about continuous changes in the light band intervals according to their positions. As a progressive and novel photonic crystal with a conventional optical system, it solves the inefficiency due to the low spatial density of the critical limitations that only a combination of a light source, a passive and active functional optical system, and a light receiving element must work. It is expected to play an important role in high density optical integrated systems.

According to the method of the present invention, photonic crystals having various crystal structures of one, two, and three dimensions can be manufactured, so that the face-centered cubic structure (fcc), the body-centered cubic structure (bcc), and the simple cubic structure (sc) of the photonic crystals can be produced. It can be applied in various crystal directions according to the unit structure consisting of) and diamond structure.

In addition, the photonic crystal manufactured according to the present invention can change the effective refractive index according to its spatial position, so that even if the existing photonic crystal device has one optical band interval under the external field member in the entire device, there is no external field. Since the photonic crystal element has a large number of optical band spacing wavelengths, it is incomparable in terms of spatial efficiency.

In particular, it is useful as an ultra-compact optical filter, and since it can give various refractive index distributions in photonic crystals, it can be said that the application range is very wide in optical elements for information materials, so it plays a very important role in the highly integrated optical communication information system in the next generation information society. It is expected to do.

Claims (7)

Gradual refractive index distribution characterized in that the polymer layer is filled with a gradually increasing or decreasing refractive index in a space composed of interconnected air layers existing between the unit particles of the photonic crystal having a repeated refractive index corresponding to the wavelength of the incident light. Photonic crystal with. A first step of forming a polymer layer on one surface of the polymerization cell, A second step of forming a photonic crystal on one surface of a cell adjacent to the polymer layer while being separated from the cell on which the polymer layer is formed; and Process of filling the inside of the cell in which the photonic crystal is formed with a mixed solution containing the polymer monomer and the refractive index control agent and then gel-polymerized Method for producing a photonic crystal having a gradual refractive index distribution comprising a. The method of claim 2, wherein the polymer is one capable of bulk polymerization. 3. The method of claim 2, wherein the photonic crystal of the second step is made of a material that does not dissolve in the polymer monomer. The photonic crystal of claim 2, wherein the photonic crystal of the second step is manufactured by a method selected from among colloid, self-assembly, photolithography, e-beam lithography, and holography. A method for producing a photonic crystal having a gradual refractive index distribution. The method of claim 2, wherein the refractive index adjusting agent is substituted or unsubstituted phenyl group, aryl group, benzyl group, phthalate-based, benzoate-based, sulfide-based, sulfate-based and phosphate-based organic material, with or without a benzoyl group, nano A method of manufacturing a photonic crystal having a gradual refractive index distribution, characterized in that it is selected from quantum dots of the size and nano-sized metal particles. 3. The method of claim 2, wherein the gel-polymerization is carried out by a method selected from heat treatment, ultraviolet irradiation and microwave irradiation.

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