KR100837077B1 - Method for forming a dielectric mirror and tuneable filter by use of a dielectric mirror to increase reflection rate - Google Patents

Abstract

The present invention provides a method for forming a dielectric mirror multilayer reflective structure for increasing reflectance and a wider tunable wavelength range of a tunable passband filter using a dielectric mirror and a width of the resonant mode ( The present invention relates to a method of forming a resonator or a passband filter that reduces bandwith. That is, the present invention is to improve the performance of the dielectric mirror using the one-dimensional photonic crystal structure and the transmission filter using the dielectric mirror, according to the refractive index of the medium by adjusting the refractive index and thickness of the outermost dielectric layer adjacent to the medium of the dielectric mirror By improving the reflectivity, this makes it possible to obtain the same reflectance even with fewer layers stacked. Also, in the resonator or passband filter using two dielectric mirrors, the outermost dielectric layer is appropriately selected to reduce the width of the resonator mode. In the wavelength changeable filter using two dielectric mirrors, the innermost outer dielectric layer is used. By appropriately increasing the range of tunable wavelengths is increased.

Description

FIELD OF FORMING A DIELECTRIC MIRROR AND TUNEABLE FILTER BY USE OF A DIELECTRIC MIRROR TO INCREASE REFLECTION RATE}

1 is a diagram illustrating a conventional one-dimensional dielectric mirror structure;

2 is a diagram illustrating a resonator structure using a conventional one-dimensional dielectric mirror;

3 and 4 is a diagram illustrating the refractive index distribution of the dielectric mirror according to the refractive index of the conventional medium,

5 is an exemplary diagram of dielectric mirror reflectance according to an embodiment of the present invention;

6 is a view illustrating a change in reflection phase of a dielectric mirror according to an embodiment of the present invention;

7 to 10 are examples of reflectance of the resonator mode using a dielectric mirror according to an embodiment of the present invention.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to dielectric mirrors and resonators using dielectric mirrors. In particular, dielectric mirrors are provided by selectively adjusting the refractive index and thickness of the outermost dielectric layer adjacent to medium in the dielectric mirror. By adjusting the reflectance and reflection phase shift of, and the refractive index and thickness of the outermost layer in the resonator, the width of the resonance mode and the variable wavelength range of the resonance mode ( To tune a tuning wavelength range.

In general, metal mirrors have reflection characteristics in a wide wavelength band, but the dielectric mirror has reflection characteristics only in a specific wavelength band, and when a suitable material is selected, there is no absorption by the mirror itself. Very high reflectance can be obtained.

Because of these features, current dielectric mirrors are used in photovoltaic devices such as Fabry Ferro interferometers, Vertical Cavity Surface Emitting Laser (VCSEL), coating of terminations of Edge Emitting Laser Diode, Distributed Feeback (DFB) Laser, Distributed Bragg Reflector (DBR) Laser, etc. It is widely used in areas requiring reflection characteristics, and recently, various parts that can be made using a one-dimensional mirror structure have also been manufactured in optical fibers.

Hereinafter, the characteristics of the dielectric mirror will be described in more detail. As shown in FIG. 1, the dielectric mirror has a structure in which two materials having different refractive indices are repeated. This periodicity creates a band in which electromagnetic waves of a specific wavelength are reflected. The ideal dielectric mirror is an infinite number of layers, theoretically showing a "1" reflectance. However, when fabricating a real dielectric mirror, it is impossible to stack an infinite number of layers, so that the amount of reflectance can be obtained as much as necessary. As the number of layers increases, the reflectance becomes closer to "1". So if you can stack the same layer and get the same size of reflectance, you will save time and money.

The dielectric mirror has two outermost dielectric layers 100, 102. What is known so far about the effect of this outermost dielectric layer on the properties of the dielectric mirror is that using a high refractive index material as the outermost dielectric layer results in higher reflectivity when the medium is air.

However, it is not known how to obtain the same high reflectivity when using a material with a lower refractive index as the outermost dielectric layer. Also, when the medium is a material other than air in the dielectric mirror, the selection of the outermost dielectric layer is dependent on the reflectance. Little is known about the effect on reflection phase change.

Also, the influence of the selection of the outermost dielectric layer on the reflection phase shift of the dielectric mirror is not well known, and the reflection phase shift is resonant in a resonator using two dielectric mirrors as shown in FIG. The characteristics of the mode have a great influence on how the outermost outermost dielectric layers 200,208 and innermost outermost dielectric layers 202,206 relate to the width and variable wavelength range of the resonator mode, respectively. Also not well known.

Accordingly, an object of the present invention is to appropriately select the refractive index and thickness of the outermost dielectric layer adjacent to the medium according to the refractive index of the medium to improve the reflectivity of the dielectric mirror and to adjust the reflection phase change, thereby stacking fewer layers. The present invention provides a method for forming a dielectric mirror that makes it possible to obtain the same reflectance.

Another object of the present invention is to reduce the width of the resonant mode in the resonator by selecting the refractive index and thickness of the four outermost dielectric layers in the resonator using two dielectric mirrors, and in the tunable filter When the length of the cavity is changed, more wavelengths are changed, thereby providing a method for forming a wavelength conversion filter having a wider tuning range.

In accordance with another aspect of the present invention, there is provided a method for forming a reflecting dielectric mirror, the method comprising: (a) comparing a refractive index of a medium with refractive indices of dielectric layers constituting the dielectric mirror, and (b) Inspecting the refractive index of the dielectric layer to be laminated to the outer dielectric layer; and (c) a dielectric layer having a refractive index lower than that of the dielectric layer having the lowest refractive index among the dielectric layers, and having a high refractive index at the outermost dielectric layer. If desired, laminating a dielectric layer having a high refractive index on the outermost dielectric layer, (d) after the outermost dielectric layer, repeatedly laminating dielectric layers having different refractive indices to form a dielectric mirror, Characterized in that it comprises a.

In addition, the present invention provides a method of forming a passband filter having a small resonance mode width using a dielectric mirror, wherein (a ') the refractive index of the medium in contact with the outermost outer dielectric layer is the refractive index of the two dielectric layers forming the dielectric mirror. (B ') examining the refractive index of the dielectric layer to be laminated to the outermost outermost dielectric layer, and (c') the refractive index of the medium is the lower of the dielectric layers forming the dielectric mirror. Stacking a dielectric layer having a high refractive index on the outermost outermost dielectric layer when the dielectric layer having a refractive index lower than the refractive index of the dielectric layer having a high refractive index is required for the outermost dielectric layer, and (d ') After the outermost dielectric layer, repeatedly stacking dielectric layers having different refractive indices to form a passband filter using a dielectric mirror; Characterized in that it comprises a.

In addition, the present invention relates to a method of forming a frequency changeable filter having a wide frequency variation in resonance mode, wherein the refractive index of the medium in contact with the innermost outermost dielectric layer is compared with the refractive indices of the two dielectric layers forming the dielectric mirror. (B ") examining a refractive index of the dielectric layer to be laminated to said innermost outermost dielectric layer; and (c") a dielectric layer having a lower refractive index among the dielectric layers in which the refractive index of said medium forms said dielectric mirror. Stacking a dielectric layer having a high refractive index on the innermost outermost dielectric layer, and (d ") after the innermost outermost dielectric layer if a dielectric layer having a refractive index lower than and having a high refractive index is required for the outermost dielectric layer. And repeatedly laminating dielectric layers of different refractive indices to form a dielectric mirror.

Hereinafter, with reference to the accompanying drawings will be described in detail the operation of the preferred embodiment according to the present invention.

Table 1 below shows the refractive index and the thickness of the outermost dielectric layer adjacent to the medium to have an optimal reflectance according to the refractive index of the medium in the embodiment of the present invention.

TABLE 1

Occation Outermost dielectric layer n _m > n _H L (refractive index: n _L , thickness: d _L ) 2 * H (refractive index: n _H , thickness: 2 * d _H ) n _m < n _L H (refractive index: n _H , thickness: d _H ) 2 * L (refractive index: n _L , thickness: 2 * d _L )

₀/4/n _H, d _L=

₀/4/n _L와 같이 결정된다.

₀은 유전체 거울의 반사 파장 대역의 중심 파장이다.: H, L is the dielectric refers to two high refractive index layer (H) of the type of layer and the lower layer (L) constituting a mirror, _{respectively, n m, n H, n} L are each medium, H layer, L layer The refractive index value of is shown. d _H and d _L represent the thicknesses of the H layer and the L layer, respectively, and are determined by quarter wave conditions. d _H =

_0/4 / n _H , d _L =

_Is determined as _0/4 / n _L.

₀ is the center wavelength of the reflection wavelength band of the dielectric mirror.

As mentioned above, the reflective characteristic of dielectric mirrors is due to the periodic reflection of electromagnetic waves passing through the structure in which the refractive index changes periodically. The periodicity determining these reflection characteristics is the periodicity of the change of the reflection phase and the periodicity of the optical thickness. If either of these is broken, the reflectance drops.

As shown in Table 1 above, when the refractive index of the medium ( n _m ) is higher than the refractive index ( n _L ) of the dielectric layer L having the low refractive index among the dielectric layers, the outermost part of the dielectric adjacent to the medium is shown. By forming the dielectric layer with a high refractive index dielectric layer (H) to ensure the periodicity of the refractive index of the dielectric layer from the medium, the reflection phase change at the interface between the medium and the outermost dielectric layer as shown in FIG. It can preserve the periodicity of. Alternatively, the outermost dielectric layer is formed of a dielectric layer L having a high refractive index, and the thickness thereof is twice that of the periodic layer so that the periodicity of the reflection phase change is broken as shown in FIG. It may be offset by an increase and consequently conserve periodicity.

In this case, as shown in FIG. 5, the reflectance when the outermost dielectric layer is formed is higher than that when the outermost dielectric layer is formed, as shown in the above embodiment. By stacking a number of layers, it is possible to fabricate a dielectric mirror having the same reflectance. Also, as shown in FIG. 6, when the outermost dielectric layer is formed, the reflection phase change according to the wavelength near the center wavelength of the reflection band (980 nm) is small. This property is changed in the resonator to be described below. It serves to widen the wavelength range.

As shown in [Table 1], when the refractive index of the medium ( n _m ) is higher than the refractive index ( n _H ) of the dielectric layer (H) having the high refractive index among the dielectric layers, the maximum value of the dielectric adjacent to the medium is shown. The outer dielectric layer may be formed of a high refractive index dielectric layer L so that the periodicity of the refractive index of the dielectric layer is established from the medium to preserve the periodicity of the reflection phase change at the interface between the medium and the outermost dielectric layer. Alternatively, the outermost dielectric layer may be formed of a dielectric layer (H) having a high refractive index, but the thickness thereof may be double the periodic layer, thereby canceling the periodicity of the reflection phase change by the increase in the optical thickness, thereby conserving the periodicity. have. In this way, when the outermost dielectric layer is selected, the reflectance is higher and the change of the wavelength of the reflection phase change is smaller than that of the other selection.

In the case of the resonator, if the outermost outermost dielectric layers 200 and 208 of FIG. 2 are selected to satisfy the conditions of Table 1, the bandwidth of the resonant mode is significantly reduced. This is because, when the condition is satisfied, the reflectivity of both mirrors of the resonator increases to increase the number of photons stored in the entire structure. On the other hand, whether the innermost outermost dielectric layers 202 and 206 satisfy the condition of Table 1 does not affect the width of the resonance mode.

In addition, when the innermost outermost dielectric layers 202 and 206 of FIG. 2 satisfy the conditions of Table 1, the wavelength of the resonance mode is changed as the length of the space 204 is changed. Changes more. This is because the change in reflection phase is small when the condition is satisfied, so the effective cavity length is short.

On the other hand, whether the outermost outermost dielectric layers 200 and 208 satisfy the conditions of Table 1 does not affect the effective space length. That is, it does not affect the change of the wavelength of the resonance mode according to the change of the length of space.

As described above, in the present invention, the width of the resonance mode can be reduced in the resonator by appropriately selecting the refractive index and thickness of the outermost outer dielectric layer in the resonator in which the two dielectric mirrors are used. Dielectric mirrors can be used to achieve the desired transmission band width.

In addition, by selecting the refractive index and thickness of the innermost outer dielectric layer in the resonator using two dielectric mirrors, it is possible to increase the wavelength change of the resonance mode according to the change of the length of the space, through which MEMS or piezoelectric is used. It is possible to improve the tunable wavelength range of the tunable passband filter or to improve the tuning speed.

In addition, since the width of the resonance mode is influenced only by the outermost outer dielectric layer, and the change of the wavelength of the resonance mode according to the change of the length of the space is affected only by the innermost outer dielectric layer, , 8, 9, and 10, the width of the resonance mode is narrow and the wavelength change of the resonance mode is large, the width of the resonance mode is narrow, the wavelength change of the resonance mode is small, or the width of the resonance mode is wide and the resonance mode is It is possible to make four structures having a large wavelength change or a wide resonance mode and a small wavelength change in the resonance mode.

Meanwhile, in the above description of the present invention, specific embodiments have been described, but various modifications may be made without departing from the scope of the present invention. Therefore, the scope of the invention should be determined by the claims rather than by the described embodiments.

As described above, the present invention improves the performance of a dielectric mirror using a one-dimensional photonic crystal structure by adjusting the refractive index and thickness of the outermost dielectric layer adjacent to the medium according to the refractive index of the medium. By improving, this has the advantage that it is possible to obtain the same reflectance even if fewer layers are stacked.

In addition, by properly selecting the refractive index and thickness of the outermost outer dielectric layer in the resonator in which two dielectric mirrors are used, the width of the resonant mode in the resonator can be reduced. Transmissive band width of size can be obtained, and in the resonator in which two dielectric mirrors are used, the wavelength variation of the resonance mode can be increased by changing the refractive index and the thickness of the innermost outer dielectric layer appropriately. There is an advantage.

Claims (18)

In the method of forming a dielectric mirror to increase the reflectance, (a) comparing the refractive index of the medium with the refractive indices of the dielectric layers constituting the dielectric mirror, (b) examining the refractive index of the dielectric layer to be laminated to the outermost dielectric layer of the dielectric layers; (c) in accordance with the determination of steps (a) and (b), When the refractive index of the medium is lower than that of the dielectric layer having the lower refractive index among the dielectric layers, and the dielectric layer having the high refractive index is required in the outermost dielectric layer, the dielectric layer having the high refractive index in the outermost dielectric layer is 1 Laminated to a thickness satisfying the / 4 wavelength condition, If the refractive index of the medium is lower than that of the dielectric layer having the lower refractive index among the dielectric layers, and the dielectric layer having the low refractive index is required for the outermost dielectric layer, the dielectric layer having the low refractive index is provided for the outermost dielectric layer. Stacking to twice the thickness to satisfy the / 4 wavelength condition, (d) after the outermost dielectric layer, repeatedly stacking dielectric layers having different refractive indices to form a dielectric mirror, Dielectric mirror forming method comprising a. delete delete delete The method of claim 1, In the step (c), when the refractive index of the medium is higher than the refractive index of the dielectric layer having the highest refractive index among the dielectric layers, and the outermost dielectric layer requires a dielectric layer having a low refractive index, (g) depositing a dielectric layer having a low refractive index having a thickness satisfying a quarter wavelength condition on the outermost dielectric layer; (h) after the outermost dielectric layer, repeatedly stacking dielectric layers having different refractive indices to form a dielectric mirror, Dielectric mirror forming method further comprising. The method of claim 1, In the step (c), if the refractive index of the medium is higher than the refractive index of the dielectric layer having the highest refractive index among the dielectric layers, the outermost dielectric layer requires a dielectric layer having a high refractive index, (i) depositing a dielectric layer having a high refractive index on the outermost dielectric layer to be twice the thickness satisfying a quarter wavelength condition; (j) forming a dielectric mirror by repeatedly stacking dielectric layers having different refractive indices after the outermost dielectric layer, Dielectric mirror forming method further comprising. In the method of forming a passband filter having a small width of the resonance mode, (a ') comparing the refractive index of the medium in contact with the outermost outermost dielectric layer with the refractive indices of the two dielectric layers forming the dielectric mirror, (b ') examining a refractive index of the dielectric layer to be laminated to the outermost outermost dielectric layer, (c ') the refractive index of the medium is lower than the refractive index of the dielectric layer having the lower refractive index among the dielectric layers forming the dielectric mirror, the outermost outermost outer layer, if the dielectric layer having a high refractive index is required Stacking a dielectric layer having a high refractive index on the dielectric layer; (d ') forming a passband filter using a dielectric mirror by repeatedly stacking dielectric layers having different refractive indices after the outermost outer dielectric layer, A passband filter forming method using a dielectric mirror comprising a. The method of claim 7, wherein A method of forming a passband filter using a dielectric mirror, wherein the high refractive index dielectric layer laminated on the outermost dielectric layer in step (c ') is formed to a thickness satisfying a quarter wavelength condition. The method of claim 7, wherein In the step (c '), when a dielectric layer having a low refractive index is required for the outermost outermost dielectric layer, (e ') laminating a dielectric layer having a low refractive index on the outermost outer dielectric layer; (f ') forming a passband filter using a dielectric mirror by repeatedly stacking dielectric layers having different refractive indices after the outermost outermost dielectric layer, Passband filter forming method using a dielectric mirror, characterized in that it further comprises. The method of claim 9, Forming a passband filter using a dielectric mirror characterized in that the low refractive index dielectric layer laminated on the outermost dielectric layer in step (e ') is formed to be twice the thickness satisfying the quarter wavelength condition. Way. The method of claim 7, wherein In the step (c '), when the refractive index of the medium is higher than the refractive index of the dielectric layer having the highest refractive index among the dielectric layers, and the outermost outer dielectric layer requires the dielectric layer having the low refractive index, (g ') laminating a dielectric layer having a low refractive index having a thickness satisfying a quarter wavelength condition on the outermost outer dielectric layer; (h ') forming a dielectric mirror by repeatedly stacking dielectric layers having different refractive indices after the outermost outermost dielectric layer, Passband filter forming method using a dielectric mirror, characterized in that it further comprises. The method of claim 7, wherein In the step (c '), when the refractive index of the medium is higher than the refractive index of the dielectric layer having the highest refractive index among the dielectric layers, and the outermost outer dielectric layer requires the dielectric layer having the high refractive index, (i ') stacking a dielectric layer having a high refractive index on the outermost outermost dielectric layer to be twice the thickness satisfying a quarter wavelength condition; (j ') forming a dielectric mirror by repeatedly stacking dielectric layers having different refractive indices after the outermost outermost dielectric layer, Passband filter forming method using a dielectric mirror, characterized in that it further comprises. In the method of forming a frequency changeable filter having a wide frequency change range in the resonance mode, (a ") comparing the refractive index of the medium in contact with the innermost outermost dielectric layer with the refractive indices of the two dielectric layers forming the dielectric mirror, (b ") examining a refractive index of the dielectric layer to be laminated to said innermost outermost dielectric layer, (c ") the inner outermost dielectric layer, if the refractive index of the medium is lower than the refractive index of the low refractive index dielectric layer among the dielectric layers forming the dielectric mirror, and the outermost dielectric layer requires a high refractive index dielectric layer Laminating a dielectric layer having a high index of refraction to (d ") after the innermost outermost dielectric layer, repeatedly stacking dielectric layers having different refractive indices to form a dielectric mirror, A method of forming a frequency changeable filter having a wide frequency change range using a dielectric mirror comprising a. The method of claim 13, A high refractive index dielectric layer laminated on the innermost outer dielectric layer in the step (c ") is formed to a thickness satisfying a quarter wavelength condition. Possible filter formation method. The method of claim 13, In the step (c ″), if a dielectric layer having a low refractive index is required for the innermost outermost dielectric layer, (e ") stacking a dielectric layer having a low refractive index on the innermost outermost dielectric layer, (f ″) after the innermost outermost dielectric layer, repeatedly stacking dielectric layers having different refractive indices to form a dielectric mirror, A method of forming a frequency changeable filter having a wide frequency change range using a dielectric mirror further comprising a. The method of claim 15, The low refractive index dielectric layer laminated on the outermost dielectric layer in the step (e ") is formed so as to be twice the thickness satisfying the quarter wavelength condition. Frequency changeable filter formation method. The method of claim 13, In the step (c ″), when the refractive index of the medium is higher than the refractive index of the dielectric layer having the highest refractive index among the dielectric layers, and the innermost outer dielectric layer requires the dielectric layer having the low refractive index, (g ") depositing a dielectric layer having a low refractive index having a thickness satisfying a quarter wavelength condition on the innermost outer dielectric layer; (h ") repeatedly stacking dielectric layers of different refractive indices after the innermost outermost dielectric layer to form a dielectric mirror, A method of forming a frequency changeable filter having a wide frequency change range using a dielectric mirror further comprising a. The method of claim 13, In the step (c ″), when the refractive index of the medium is higher than the refractive index of the dielectric layer having the highest refractive index among the dielectric layers, and the innermost outermost dielectric layer requires the dielectric layer having the high refractive index, (i ") laminating a dielectric layer having a high refractive index on the innermost outermost dielectric layer to be twice the thickness that satisfies a quarter wavelength condition; (j ") after the innermost outermost dielectric layer, repeatedly stacking dielectric layers having different refractive indices to form a dielectric mirror, A method of forming a frequency changeable filter having a wide frequency change range using a dielectric mirror further comprising a.

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