CN100392443C - Design Method of Curved Optical Waveguide Structure with Section Correction - Google Patents

Abstract

The design method of the curved optical waveguide structure with cross-section modification is a method to reduce the leakage of the optical waveguide mode by changing the cross-sectional shape of the optical waveguide. That is, the traditional axisymmetric cross-sectional structure is modified, so that the outer dimension of the optical waveguide is increased to accommodate more transmission modes as much as possible, thereby effectively reducing the leakage of the transmission field mode, improving the transmission efficiency, and reducing the light loss. The specific method is that the curved optical waveguide is composed of a core layer (2) and a cladding layer (1), the core layer (2) is located in the cladding layer (1), and the outer core layer (22) of the curved optical waveguide core layer (2) is The thickness or height is greater than that of the inner side (21) of the optical waveguide core layer, or the thickness or height on its curved surface is increased; the refractive index of the core layer (2) is greater than that of the cladding layer (1).

Description

Design Method of Curved Optical Waveguide Structure with Section Correction

technical field

The invention relates to a method for designing a curved optical waveguide structure with section correction, and belongs to the technical field of curved optical waveguide structure design.

Background technique

Optical waveguide is the most basic physical concept in integrated optics, and it is also the most basic structural form of integrated optical devices. Broadly speaking, any physical structure or device capable of transmitting light waves can be called an optical waveguide. Optical waveguide, as the most basic structural form, is widely used in optical communication devices and integrated optical devices. A curved optical waveguide refers to an optical waveguide that is bent geometrically. Bending optical waveguides play an important role in integrated optical devices such as optical path connections, optical resonant rings, optical couplers, and waveguide array gratings (AWG). Bending of an optical waveguide introduces bend loss, which typically results in attenuation of the optical signal. Therefore, effectively reducing the bending loss of the curved optical waveguide and improving the light transmission efficiency is a key issue in the design and fabrication of the curved optical waveguide.

Commonly used optical waveguides include two-dimensional optical waveguides and three-dimensional optical waveguides. A two-dimensional optical waveguide is also called a slab waveguide, and its structure is shown in Figure 1. The middle layer of the optical waveguide is called the core layer, and the upper and lower layers are respectively called the upper cladding layer and the lower cladding layer. Since the refractive index of the core layer is greater than that of the cladding layer, certain modes of light waves are restricted to propagate in the core layer. Three-dimensional optical waveguides are usually prepared as strip or ridge structures. As shown in Fig. 2 and Fig. 3, its cross-sectional shape is rectangle (a square is a kind of rectangle), trapezoid or convex. At present, curved 3D optical waveguides usually only have simple forms such as strips and ridges. However, curved optical waveguides have their particularity compared to straight waveguides. Due to the asymmetry of the geometric scales on the left and right sides, the transmitted light waves have a large mode leakage on the outside of the bend, which is the inherent nature of the bend loss. Therefore, according to the characteristics of the curved optical waveguide, the patent of the present invention proposes a cross-section modified curved optical waveguide structure design method. This method can optimize the cross section of the optical waveguide according to the refractive index of the core layer, the cladding layer and the radius of curvature of the optical waveguide, thereby reducing the leakage of the guided wave mode caused by the bending of the optical waveguide and reducing the loss of the bent optical waveguide. . This method can be applied to the design and manufacture of optical waveguide devices.

Contents of the invention

Technical problem: The purpose of this invention is to propose a design method for a curved optical waveguide structure with cross-section correction, so as to solve the shortcomings of the existing technology such as large optical bending loss.

Technical solution: The technical solution of the present invention is realized in this way. For the straight waveguide, the optical waveguide is designed to have a rectangular, trapezoidal or ridge-shaped cross-section, which has the characteristics of axisymmetric. By designing the structure, size and core layer of the straight waveguide , The refractive index of the cladding can effectively realize the transmission of light waves. For the curved optical waveguide, due to the curvature of the waveguide itself, the leakage of the transmission mode outside the optical waveguide caused by the bending is serious. The present invention proposes to change the cross-sectional shape of the optical waveguide, that is, to modify the traditional axisymmetric cross-sectional structure, so that the outer dimension of the optical waveguide is increased to accommodate more transmission modes as much as possible, thereby effectively reducing the outer dimension of the transmission field mode. Leakage improves transmission efficiency and reduces optical loss. This method is especially effective when the size of the optical waveguide structure is small and there are few conduction modes to be accommodated.

The design method of the cross-section modified curved optical waveguide structure of the present invention is that the curved optical waveguide is composed of a core layer and a cladding layer, the core layer is located in the cladding layer, and the thickness or height outside the core layer of the curved optical waveguide core layer is greater than that of the optical waveguide core An increase in thickness or height on the outside of a ply, or on its curved face. The refractive index of the core is greater than that of the cladding. When the curved optical waveguide is a planar structure, the cladding layer includes an upper cladding layer and a lower cladding layer, and the core layer is located between the upper cladding layer and the lower cladding layer. On the outside of the curved portion of the core, its thickness increases.

Beneficial effect: compared with the prior art, the present invention has the following advantages:

According to the characteristics of the curved optical waveguide, the present invention abandons the traditional axisymmetric waveguide core layer design idea, and proposes the design idea and method of end surface correction, and uses the increase of the outer dimension of the curved optical waveguide to compensate for the light transmission mode caused by the waveguide bending. Leakage, which solves the problem of excessive bending waveguide loss in the traditional axisymmetric waveguide core layer design.

Description of drawings

Figure 1 is a schematic diagram of a slab waveguide.

Fig. 2 is a schematic diagram of a three-dimensional rectangular bar waveguide.

Fig. 3 is a schematic diagram of the cross-sectional structure of the trapezoidal and ridge waveguide core layers.

Fig. 4 is a schematic cross-sectional view of a curved optical waveguide core layer with cross-section correction.

Fig. 5 is a schematic diagram of various cross-sectional structures of the curved optical waveguide core layer with cross-section correction.

In the above figures, there are an optical waveguide upper cladding layer 1 , an upper cladding layer 11 , a lower cladding layer 12 , a core layer 2 , an inner side 21 of the core layer, and an outer side 22 of the core layer.

Detailed ways

The design method of the present invention is that the thickness or height of the core layer on the outer side of the curved optical waveguide is always greater than that on the inner side of the optical waveguide, or the thickness or height on the curved surface is increased. The refractive index of the core layer 2 is greater than that of the cladding layer 1 . When the curved optical waveguide is a planar structure, the cladding layer 1 includes an upper cladding layer 11 and a lower cladding layer 12, the core layer 2 is located between the upper cladding layer 11 and the lower cladding layer 12, and the refractive index of the core layer 2 is greater than that of the upper cladding layer 11. or the refractive index of the lower cladding layer 12 .

The structural design schematic diagram (Fig. 4) of the above-mentioned cross-sectional correction is only an example to illustrate the design method of the present invention, and cannot exhaust all the graphics designed by this method. In the design of the curved optical waveguide, the method of reducing the leakage of the optical waveguide mode by increasing or optimizing the structural size of the end face is designed and protected by the patent.

The following is a specific implementation of the method for designing a curved optical waveguide structure using section correction.

For the design of the curved optical waveguide, the "axisymmetric cross-section" waveguide such as the curved strip waveguide or the ridge waveguide is designed into a non-axisymmetric cross-sectional shape according to the degree of curvature. The shape is characterized by the outer surface thickness or height of the curved waveguide being greater than inner side to reduce conduction mode leakage due to waveguide bending. When the curved optical waveguide is a planar structure, the cladding layer 1 includes an upper cladding layer 11 and a lower cladding layer 12, and the core layer 2 is located between the upper cladding layer 11 and the lower cladding layer 12, and on the outside of the curved part of the core layer 2, its thickness has increased.

The materials used to make the curved waveguide may include all materials that can be used to make waveguides. That is, the design method itself does not impose special restrictions on the material for preparing the optical waveguide.

Claims (2)

1. A design method of a curved optical waveguide structure with section correction, characterized in that at first this curved optical waveguide is designed to be made of a core (2) and a cladding (1), and the core (2) is positioned at the cladding (1 ), then the thickness of the outer core (22) of the curved optical waveguide core (2) is designed to be greater than the thickness of the inner core (21) of the optical waveguide core; the refractive index of the core (2) is greater than that of the cladding (1) refractive index. 2. The design method of the curved optical waveguide structure according to claim 1, wherein the curved optical waveguide is characterized in that when the curved optical waveguide is a planar structure, the cladding (1) comprises an upper cladding (11) and a lower cladding (12) ), the core layer (2) is located between the upper cladding layer (11) and the lower cladding layer (12), and its thickness increases on the outside of the curved portion of the core layer (2).

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