KR101094361B1 - Optical waveguide structure - Google Patents

Abstract

An optical waveguide core including an incident surface to which the light wave generated from the light source is incident and an optical waveguide clad covering the optical waveguide core, wherein an angle between the incident light source and the incident surface or the inclined plane inclination angle is determined from Snell's law inside the optical waveguide. It is configured to satisfy the parallel light conditions obtained.

Description

Optical Waveguide Structure

The present invention relates to an optical waveguide structure, and more particularly, a waveguide configured to minimize loss when light waves generated from an external light source are incident on a planar optical waveguide and to propagate the light waves into the inside of the optical waveguide core in a stable mode. It's about structure.

The present invention is derived from research conducted as part of the IT growth engine technology development project of the Ministry of Knowledge Economy. [Task Management No .: 2008-S-008-01, Title: FTTH Advanced Optical Component Technology Development].

 In the 21st century, with the development of optical communication, research is being actively conducted to apply optical communication technology to board-to-board communication of computers, chip-to-chip communication within a board, or communication within a CMOS chip. When the optical signal communication technology is applied to the silicon semiconductor VLSI chip, the problems of the low speed, high resistance, high heat generation, and parasitic capacitance, which are disadvantages of the communication technology using the electrical signal, can be solved. It is expected to be actively studied in the field of semiconductor and information communication.

In optical communication technology, planar optical waveguides have been mainly used in the fabrication of integrated optical devices, and play the same role as optical fibers, which are mediators for directly transmitting optical signal information. Although silica has been used mainly as a material for constituting a planar optical waveguide in which a manufacturing process is established and the propagation loss of light waves is small, in recent years, a polymer having a reduced manufacturing process complexity, a great flexibility, and a low propagation loss characteristic is a planar optical waveguide. It is also used for. Such a planar optical waveguide-outer resonator laser includes a light source coupled and aligned at one end cross section of the planar optical waveguide, and reflective mirrors disposed at outer ends of both ends of the light source and the planar optical waveguide to form a resonant structure. The light waves generated by the light source resonate between these two mirrors and then oscillate with a laser. In a long study of such planar optical waveguide-external resonator lasers, one of the main concerns has been to make the light source and the optical waveguides efficient structures to produce high power lasers.

When the light waves generated by the light source are reflected from the incident surface of the optical waveguide and return to the light source, the resonance characteristics of the light waves may be degraded. In order to solve this problem, a technique has been proposed in which the incident surface of the optical waveguide is inclined in the traveling direction of the optical wave to prevent the light wave reflected from the incident surface from returning to the light source. For example, in the prior art, the incident surface may be formed to have an inclination angle of approximately 8 degrees.

However, since this inclination angle is a conventionally and roughly selected value without a careful examination of the refractive index and thus light propagation characteristics of the media constituting the waveguide, the waveguide characteristics optimized for the optical waveguides of various structures are May not be provided. For example, in the case of polymer optical waveguides, since the traveling light wave vector may not be parallel to the traveling direction of the optical waveguide, a curved section having a predetermined curvature as shown in FIG. May be required for correction. In addition, when the inclination angle is selected approximately, the light waves incident into the waveguide may be lost by repetitive reflection and transmission.

One technical problem to be achieved by the present invention is to provide an optical waveguide structure configured to enable the optical wave to travel parallel to the direction of travel of the optical waveguide.

One object of the present invention is to provide an optical waveguide structure configured to reduce reflection and transmission of light waves generated inside the optical waveguide core.

In order to achieve the above technical problem, the present invention provides an optical waveguide structure having an inclined incident surface. The structure includes an optical waveguide core including an incident surface on which the light waves generated by the light source are incident, and an optical waveguide cladding covering the optical waveguide core, wherein an incident angle of the optical wave incident on the incident surface is a direction in which the optical wave travels. And the traveling direction of the optical waveguide may be substantially parallel to each other.

According to one embodiment, the angle between the incident direction of the light wave and the advancing direction of the optical waveguide may be configured to substantially satisfy the following conditions.

는 상기 입사면의 법선과 상기 광도파로 코어의 진행 방향 사이의 각도이고, a는 상기 광도파로 코어의 굴절률에 대한 상기 입사면과 접촉하는 매질의 굴절률 사이의 비율이다. Here, x is an angle between the incident direction of the light wave and the advancing direction of the optical waveguide,

Is an angle between the normal of the incident surface and the advancing direction of the optical waveguide core, and a is the ratio between the refractive index of the medium in contact with the incident surface to the refractive index of the optical waveguide core.

According to one embodiment, when the angle x is 0 degrees, the incident surface may be configured such that the angle between its normal and the advancing direction of the optical waveguide core has an inclination angle that substantially satisfies the following conditions.

Where b is the ratio of the refractive index of the optical waveguide clad to the refractive index of the optical waveguide core.

According to an embodiment, at least one grating structure may be further formed in the optical waveguide core. In addition, the optical waveguide core may constitute a planar optical waveguide, and the light source may constitute a resonator laser.

In order to achieve the above technical problem, the present invention may include an optical waveguide core including an incident surface on which the light wave generated by the light source is incident, and an optical waveguide cladding covering the optical waveguide core. In this case, the incident surface may be configured such that the light waves are totally reflected inside the optical waveguide core.

According to one embodiment, the incident surface is an optical waveguide structure, characterized in that the angle between its normal and the advancing direction of the optical waveguide core has an inclination angle that substantially meets the following conditions.

Where a is the ratio of the refractive index of the optical waveguide core to the refractive index of the medium in contact with the incident surface, and b is the ratio of the refractive index of the optical waveguide clad to the refractive index of the optical waveguide core.

According to an embodiment of the present invention, the light source has an angle given by Equation 2 or 4 below with respect to the incident surface of the core so that the light waves passing through the incident surface of the core may travel parallel to the direction of travel of the optical waveguide. Is placed. According to another embodiment of the present invention, the incident surface of the core is formed at an angle given by Equation 11 below so that total reflection can occur inside the waveguide. Accordingly, it is possible to prevent or reduce the loss of light waves due to reflection or transmission inside the waveguide.

Objects, other objects, features and advantages of the present invention will be readily understood through the following preferred embodiments associated with the accompanying drawings. However, the present invention is not limited to the embodiments described herein but may be embodied in other forms. Rather, the embodiments introduced herein are provided so that the disclosure may be made thorough and complete, and to fully convey the spirit of the invention to those skilled in the art.

In this specification, when it is mentioned that a film is on another film or substrate, it means that it may be formed directly on another film or substrate, or a third film may be interposed therebetween. Further, in the drawings, the thicknesses of the films and regions are exaggerated for an effective explanation of the technical content. Also, while the terms first, second, third, etc. in various embodiments of the present disclosure are used to describe various regions, films, etc., these regions and films should not be limited by these terms . These terms are only used to distinguish any given region or film from another region or film. Thus, the membrane referred to as the first membrane in one embodiment may be referred to as the second membrane in another embodiment.

A planar optical waveguide structure according to an embodiment of the present invention will be briefly described with reference to the accompanying drawings. However, the following embodiments are provided to those skilled in the art to fully understand the present invention can be modified in various forms, the scope of the present invention is described below It is not limited to.

1 is a plan view showing a schematic structure of a planar optical waveguide according to an embodiment of the present invention.

Referring to FIG. 1, the planar optical waveguide may include a core M1 and a cladding M2 covering the core M1, and may be formed of polymer materials having a relatively easy process and controlling refractive index. have. The polymer optical waveguide includes a tapered section R1 for collecting incident light waves, a first stable section R2 for adapting the light waves from the tapered section R1 to a planar optical waveguide, and a curved section disposed at a rear end of the optical waveguide ( R3), a second stable section R4 for adapting the light waves from the curved section R2 back to the planar optical waveguide, and a grating section R5 serving as a mirror of the resonator. The curved section R3 may be configured such that the traveling direction of the light wave and the traveling direction of the optical waveguide are parallel to each other.

)는 상기 입사면(IS)으로부터 반사되는 광파가 상기 외부 광원(S)으로 되돌아가는 현상을 방지할 수 있는 범위(이하, 제 1 각도 범위) 내에서 선택될 수 있다. 하지만, 본 발명에 따르면, 광파의 진행 방향과 코어의 진행 방향 사이의 평행을 위해 추가적으로 부가되는 조건 또는 코어-클래딩 경계면에서의 전반사를 위해 부가되는 조건에 의해, 상기 입사면의 경사각(

)는 상기 제1각도범위보다 좁은 범위 또는 다른 범위로 한정될 수 있다. 이러한 부가적인 조건들은 도 3 및 도 5를 참조하여 보다 상세하게 설명될 것이다. The core M1 may include an incident surface IS formed at an angle inclined to a traveling direction of the core M1 (hereinafter, referred to as a central axis A _co ). When the light wave generated by the external light source S is incident on the incident surface IS of the core M1, a part of the light waves is reflected at the incident surface IS and the other part passes through the incident surface IS. Incident to the core M1. According to the prior art, the angle between the normal line (N) of the incident surface and the advancing direction (A _co ) of the core (

) May be selected within a range (hereinafter, referred to as a first angular range) to prevent a phenomenon in which the light wave reflected from the incident surface IS is returned to the external light source S. However, according to the present invention, the angle of inclination of the incidence plane (by

) May be limited to a narrower range or other range than the first angle range. These additional conditions will be described in more detail with reference to FIGS. 3 and 5.

A lens Ls may be further disposed between the external light source S and the incident surface IS to collect the light waves, and the medium between the incident surface IS and the lens may be air or vacuum. have. The first stable section R2 may be configured to have a travel direction parallel to a travel direction of the light wave vector of the transmitted light. The transmitted light may travel along the core M1 and be reflected in the grating section to return to the light source. The light waves reciprocating between the mirror formed in the light source and the grating section may be resonated to form a laser.

2 is a plan view showing a schematic structure of a linear planar optical waveguide according to another embodiment of the present invention. Since this embodiment is similar to the embodiment described with reference to FIG. 1 except that it does not include a curved section, a description of overlapping technical features for brevity may be omitted below.

Referring to FIG. 2, the core M1 of the optical waveguide may include a mode stable section R2 and a grating R5 section. According to a modified embodiment, a tapered section R1 for collecting incident light waves may be further formed between the mode stable section R2 and the lens LS. Silica optical waveguides can typically be formed in a straight line with a straight sidewall of the core, as shown in FIG. 2, because silica is not easy to precisely form curved sidewalls unlike polymers.

)를 갖도록 형성될 수 있다. 하지만, 도 1 의 실시예와 유사하게, 광파의 진행 방향과 코어의 진행 방향 사이의 평행을 위해 추가적으로 부가되는 조건 또는 코어-클래딩 경계면에서의 전반사를 위해 부가되는 조건에 의해, 상기 제1각도는 상기 제1각도범위보다 좁은 범위로 한정될 수 있다. 이러한 부가적인 조건들은 도 3 및 도 5를 참조하여 보다 상세하게 설명될 것이다. In addition, similar to the previous embodiment, the incident surface IS of the core is in the traveling direction of the core M1 so that the light reflected therefrom can be prevented from being returned to the light source S. Inclined angle (

It can be formed to have). However, similarly to the embodiment of FIG. 1, the first angle is determined by conditions additionally added for parallelism between the propagation direction of the light wave and the propagation direction of the core or for the total reflection at the core-cladding interface. It may be limited to a narrower range than the first angle range. These additional conditions will be described in more detail with reference to FIGS. 3 and 5.

3 is a view for explaining the technical idea of the present invention in a planar optical waveguide-external resonator laser. Hereinafter, referring to FIG. 3, the conditions required for the transmitted light of the incident light wave to travel parallel to the central axis of the core will be described.

Referring to FIG. 3, the condition for transmitting the transmitted light parallel to the center line A _co of the core may be expressed by Equation 1 below by Snell's law.

는 상기 입사면의 법선(N)과 상기 코어의 중심축(A_co) 사이의 각도이다. Here, n _ai and n _co are the refractive indices of the air and the core, respectively, x is the angle between the propagation direction of the light wave incident from the lens LS and the centerline A _co of the core,

Is an angle between the normal line N of the incident surface and the central axis A _co of the core.

From the above equation, the angle x can be expressed as Equation 2 below.

, 0<a<1)을 나타내는 파라미터이다. Where a is the relative index of refraction of air and the core (i.e.

, 0 <a <1).

Using trigonometric identities below and Equation 2 above,

By solving Equation 1 again, sin x given by Equation 3 below can be obtained.

The angle x of Equation 2 may be rewritten from Equation 3 as Equation 4 below.

The equation (2) and 4, the incident surface (IS) transmitted light is desired, the central axis of the incident direction of the light wave and the core is to proceed in parallel with the central axis (A _co) of the core passing through the (A _co) Prescribe conditions for the angle between. That is, when light waves are incident on the incidence plane IS so as to meet the conditions given by Equations 2 and 4, the light waves travel inside the core while maintaining a state parallel to the central axis A _co of the core. Can be. In addition, the light waves reflected from the grating section R5 and returned to the incident surface IS are also refracted at an angle given by Equations 2 and 4 at the incident surface IS to be focused on the lens LS. Can be. Accordingly, the propagation loss of the light wave generated by the light wave reflected or transmitted to the outside of the optical waveguide can be minimized. In the embodiments described with reference to FIGS. 1 and 2, the arrangement between the light source S and the planar waveguide may be formed to substantially satisfy the conditions given by Equation 2 or 4 above.

) 및 굴절률 비율(a) 사이의 관계를 예시적으로 보여준다. 표 1을 참조하면, 굴절률 비율(a)가 1/1.39, 1/1.50 및 1/2.00의 값을 갖는 경우들이 고려되었다. 각각의 경우들에 있어서, 입사면의 경사각

는 5도, 8도 및 10도일 때, 광파의 입사 각도 x는 각각 2.0도, 3.2도 및 4.0도로 바뀌었다. 즉, 주어진 a에 대해서,

가 증가하면 x도 증가하였다. 또한, 주어진

에 대해서 a가 증가하면 x는 감소하였다. Table 1 below shows the angles (x,

) And the refractive index ratio (a) are shown by way of example. Referring to Table 1, cases in which the refractive index ratio a had values of 1 / 1.39, 1 / 1.50 and 1 / 2.00 were considered. In each case, the inclination angle of the incident surface

When 5 degrees, 8 degrees, and 10 degrees, the incident angles x of the light waves were changed to 2.0 degrees, 3.2 degrees, and 4.0 degrees, respectively. That is, for a given a

As x increased, x increased. Also, given

X decreased as a increased.

a 1 / 1.39 1 / 1.5 1 / 2.0

(degree)

(degree) 5 8 10 5 8 10 5 8 10 x (degree) 2.0 3.2 4.0 2.5 4.0 5.1 5.0 8.2 10.3

의 함수로서 그려진(plot) 각도 x의 3차원 그래프이다. 일부 영역은 관계식

에 의해 그려지지 않았다. 4 shows the refractive index ratio a and the inclination angle of the incident surface.

A three-dimensional graph of plotted angle x as a function of. Some areas are relational

Not drawn by

일 경우, 광파의 입사 각도 x는

이었고,

인 점을 기준으로 a가 감소하거나

가 증가하면, x도 증가하였다. 이때,

가

보다 컸다. Referring to Figure 4,

If the incident angle of light waves x

Was

A decreases relative to

When increased, x also increased. At this time,

end

Was greater than

5 is a view for explaining the technical idea of the present invention in a planar optical waveguide-external resonator laser. Hereinafter, with reference to FIG. 5, the inclination angle condition of the incident surface required for the light wave having a traveling direction parallel to the central axis (A _co ) of the core is totally reflected at the core-cladding interface.

인 코어의 입사면(IS)으로 입사될 경우, 입사면(IS)을 통과한 광파(즉, 투과광)의 광축과 입사면의 법선(N) 사이의 각도

는 스넬의 법칙에 의해 아래 수학식 5에 의해 주어진다. Referring to FIG. 5, the light wave having a traveling direction parallel to the central axis A _co of the core has an inclination angle.

When incident on the incident surface IS of the in-core, the angle between the optical axis of the light wave (that is, transmitted light) passing through the incident surface IS and the normal line N of the incident surface

Is given by Equation 5 below by Snell's law.

In this case, since the transmitted light is not parallel to the central axis A _co of the core, the transmitted light may be reflected and transmitted at the interface between the core and the cladding. This process can likewise be described by Equation 6 below by Snell's law.

는 코어-클래딩의 경계면을 통과하여 클래딩 내부로 진행하는 광파(이하, 누설광)의 진행 각도이고, 각도

는 도면에 도시된 것처런

와 같다. Where angle

Is the propagation angle of light waves (hereinafter referred to as “leakage light”) passing through the core-cladding interface and into the cladding.

Is as shown in the drawings.

Same as

의 조건에 의해 기술될 수 있다. 이러한 전반사의 조건을 위 수학식 6에 적용하면, 아래의 수학식 7을 얻을 수 있다. Since total reflection is a phenomenon in which the traveling direction of the leaked light proceeds in parallel with the central axis A _co of the core, total reflection

Can be described by the condition of. Applying this total reflection condition to Equation 6 above, Equation 7 below can be obtained.

는, 위 식으로부터, 아래의 수학식 8에 의해 표현될 수 있다. Here, b is a parameter representing the relative refractive index (0 <b <1) of the core and the cladding. Angle

Can be expressed by Equation 8 below.

를 수학식 5에 대입하면, 아래의 수학식 9를 얻을 수 있고, 수학식 9를 정리하면, 아래의 수학식 10을 얻을 수 있다. Angle given by the above equation

By substituting Equation 5 into Equation 5, Equation 9 below can be obtained, and by arranging Equation 9, Equation 10 below can be obtained.

)은 아래와 같이 주어질 수 있다. From Equation 10 above, the inclination angle of the incidence plane for total reflection expressed as a function of the relative refractive indices a and b

) Can be given as

)이 결정될 수 있다. 이에 더하여, 코어 및 클래딩의 물질을 합성하는 과정에서 그들의 상대 굴절률을 조절할 수 있는 경우, 주어진 입사면의 경사각(

)에 대해, 코어-클래딩의 경계면에서 전반사 조건을 충족하도록 상기 코어 및 클래딩의 굴절률(n_co, n_cl)을 조절할 수 있다. 도 1 및 도 2를 참조하여 설명된 실시예들에서, 상기 코어의 입사면(IS)의 경사각(

)은 위 식 11에 의해 주어지는 조건을 실질적으로 충족시키도록 형성될 수 있다.According to Equation 11 above, when the relative refractive indices are known, the inclination angle of the incidence plane, which enables the transmitted light to be totally reflected at the interface of the core-cladding,

) Can be determined. In addition, if the relative refractive indices can be adjusted during the synthesis of the core and cladding materials,

), The refractive indices n _co , n _cl of the core and the cladding can be adjusted to meet the total reflection conditions at the interface of the core-cladding. In the embodiments described with reference to FIGS. 1 and 2, the inclination angle of the incident surface IS of the core (

) May be formed to substantially satisfy the conditions given by Eq.

의 3차원 그래프이다. 도 6을 참조하면, 경사각

는 a=b인 직선 상에서 최대값을 갖고,

이고

인 점 또는

이고

인 점에서 최소값을 갖는다.6 is the inclination angle plotted as a function of the refractive index ratios a and b

Is a three-dimensional graph. 6, the inclination angle

Has a maximum on a straight line a = b,

ego

Point or

ego

Has the minimum value at.

 On the other hand, the incidence direction angle of the external light source, the refractive index of the optical waveguide core and cladding, the inclined plane inclination angle, and the like are determined in the method of determining the propagation conditions of the light wave that optimizes the coupling of the optical waveguide and the optical waveguide generated and generated by the external light source. As described for the purpose of one example, various modifications of the invention can be made without departing from the spirit or scope of the invention. In addition, although the structure of the planar optical waveguide in the planar optical waveguide-external resonator laser has been described as an example, the scope of application of the concept and method of the present invention is not limited to the planar optical waveguide-external resonator laser. It is apparent that the method according to the present invention can be applied to the structure of a general planar optical waveguide and can be experimentally applied to produce a planar optical waveguide satisfying the above conditions. Accordingly, the foregoing description of the embodiments according to the present invention will be provided for purposes of illustration only and is not intended to limit the invention, which is only limited by the appended claims and their equivalents.

1 is a plan view showing a schematic structure of a planar optical waveguide according to an embodiment of the present invention.

2 is a plan view showing a schematic structure of a linear planar optical waveguide according to another embodiment of the present invention.

3 is a view for explaining the technical idea of the present invention in a planar optical waveguide-external resonator laser.

의 함수로서 그려진(plot) 각도 x의 3차원 그래프이다. 4 shows the refractive index ratio a and the inclination angle of the incident surface.

A three-dimensional graph of plotted angle x as a function of.

5 is a view for explaining the technical idea of the present invention in a planar optical waveguide-external resonator laser.

의 3차원 그래프이다. 6 is the inclination angle plotted as a function of the refractive index ratios a and b

Is a three-dimensional graph.

Claims (8)

An optical waveguide core including an incident surface on which light waves generated from a light source are incident; And Including an optical waveguide cladding to cover the optical waveguide core, The incident angle of the optical wave incident on the incident surface is configured to be substantially parallel to a central axis of the optical waveguide core, which is a direction in which the optical wave propagates into the optical waveguide and a direction in which the optical waveguide extends. An optical waveguide structure. The method of claim 1, The angle between the direction of incidence of the light wave and the central axis of the optical waveguide core at the incidence plane is configured to substantially satisfy the following conditions, and the method is to adjust the incidence direction of the light wave or to change the inclination angle of the incidence plane. An optical waveguide structure.

(Where x is an angle between the incident direction of the light wave and the advancing direction of the optical waveguide,

Is the angle between the normal of the incident surface and the central axis of the optical waveguide core, and a is the ratio between the refractive index of the medium in contact with the incident surface to the refractive index of the optical waveguide core.) The method according to claim 1 or 2, And at least one grating structure formed in the optical waveguide core. The method according to claim 1 or 2, And the optical waveguide core and clad constitute a planar optical waveguide, and the light source constitutes a resonator laser. An optical waveguide core including an incident surface on which light waves generated from a light source are incident; And Including an optical waveguide cladding to cover the optical waveguide core, The incidence surface is configured to be totally reflected at an interface between the optical waveguide core and the optical waveguide cladding when the optical wave is transmitted through the interior of the optical waveguide, and The incidence surface is configured such that an angle between its normal and the central axis of the optical waveguide core in a direction in which the optical waveguide core extends has an inclination angle such that the following condition substantially satisfies the following conditions: An optical waveguide structure, characterized in that to adjust the ratio of the refractive index of the optical waveguide cladding.

(Where a is the ratio of the refractive index of the optical waveguide core to the refractive index of the medium in contact with the incidence surface, and b is the ratio of the refractive index of the optical waveguide clad to the refractive index of the optical waveguide core.) delete The method of claim 5, The optical waveguide structure of claim 1, wherein the optical wave is incident on the incidence plane while having a traveling direction parallel to the central axis of the optical waveguide core. The method of claim 5, And the optical waveguide core and clad constitute a planar optical waveguide, and the light source constitutes a resonator laser.

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