JPH11109160A - Optical waveguide design device, its offset quantity designing method, and recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily provide the offset quantity, and improve the response of a computer through the arrangement design and the pattern display of a wave guide by respectively inputting the refractive index of a waveguide core, the equivalent refractive index of the straight waveguide basic mode, the equivalent refractive index of the primary mode of the waveguide, the radius of bend of a curved waveguide and the wavelength of the light in vacuum, and calculating the offset quantity in accordance with the prescribed expression. SOLUTION: In the offset quantity design method of an optical waveguide design device to design the route of an optical waveguide, the refractive index Ncore of a waveguide core, the equivalent refractive indexncq.0 of the basic mode of a straight waveguide, the equivalent refractive indexncq.1 of the primary mode of the straight waveguide, the radius R of bend of a curved waveguide, and the wavelength λ of the light in vacuum are respectively inputted in the optical waveguide design device in order to design the offset quantity δS of a curved part of optical waveguide. The offset quantity δS is calculated in accordance with the expression based on these inputted values in the optical waveguide design device. A program to run the function of the optical waveguide design device by a computer is recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical waveguide designing apparatus for determining the offset amount of an optical waveguide by calculation, a method of designing the offset amount, and a recording medium, in relation to the design of the arrangement and the path of the optical waveguide.

[0002]

2. Description of the Related Art With the development of optical communication technology, a waveguide-type optical integrated device for multiplexing and demultiplexing light using an optical waveguide formed on a substrate has been widely used. In an optical waveguide formed on a substrate, a straight waveguide and a curved waveguide have different electric field intensity distributions on the waveguide cross section. Therefore, at the connection between the straight waveguide and the curved waveguide, the incident light propagating through the straight waveguide in the fundamental mode becomes
Partially convert to the first order mode of the curved waveguide. Light converted to the first-order mode of the curved waveguide becomes noise and degrades device performance (C. van Dam, et. Al. “Elimination of
ghost images in the response of PHASER-demultiple
xers, "ECIO'97, (1997). The conversion can be reduced by shifting the center of the straight waveguide and the center of the curved waveguide. It is generally called "offset" and the amount of shift is called "offset amount" (Katsuyuki Okamoto, "Basics of Optical Waveguides", Chapter 7, Corona, Tokyo, (1992)).

In device fabrication, it is necessary to design an "offset amount" so that incident light propagating in a linear waveguide in a fundamental mode is not converted into a first mode of a curved waveguide. In the present specification, such “offset amount” will be referred to as “appropriate offset amount”.

An element for converting a linear waveguide from a fundamental mode to a first-order mode of a curved waveguide changes depending on a bending radius. Therefore, it is necessary to appropriately set an "offset amount" according to the bending radius. The conversion ratio from the fundamental mode of the straight waveguide to the first mode of the curved waveguide is proportional to the overlap integral of the fundamental mode electric field profile of the straight waveguide and the first mode electric field profile of the curved waveguide. Conventionally, in order to obtain an “offset amount” that does not convert a linear waveguide from a fundamental mode to a primary mode of a curved waveguide, it is necessary to convert the linear waveguide into a fundamental mode electric field profile and a primary mode electric field intensity of the curved waveguide. The profile was obtained, the overlap integral was obtained by shifting the profile, and the shift amount at which the overlap integral became 0 was found (C. van Dam, et. Al. “Eliminatio
n of ghostimages in the response of PHASER-demulti
plexers, "ECIO'97, (1997)).

[0005]

When an optical waveguide designing apparatus utilizing CAD or the like is to be constructed, the conventional offset amount designing method requires the first order of a curved waveguide to obtain an “appropriate offset amount”. It was necessary to calculate the mode field strength profile. Further, for various offset amounts, it is necessary to find an overlap integral between the fundamental mode electric field intensity profile of the linear waveguide and the first mode electric field intensity profile of the curved waveguide, and to find an “appropriate offset amount”. Needed computational complexity.

[0006]

In order to achieve the above object, according to the present invention, there is provided an optical waveguide designing apparatus for designing a path of an optical waveguide, wherein an offset amount δ _s of a curved portion of the optical waveguide is provided. The refractive index n of the waveguide core
_core, linear waveguide fundamental mode effective refractive index n _{eq, 0,} straight waveguide 1 equivalent refractive index of the order mode n _{eq, 1,} the bending radius R of the curved waveguide values and light in a vacuum wavelength λ, respectively Based on the input means to be input and the input value,

[0007]

(Equation 3)

According [0008], it is characterized in that comprises an arithmetic processing means for calculating the offset amount [delta] _s.

According to a second aspect of the present invention, there is provided an offset amount designing method of an optical waveguide designing apparatus for designing a path of an optical waveguide, wherein the refractive index of the waveguide core is designed for designing the offset amount δ _s of a curved portion of the optical waveguide. n _core, linear waveguide fundamental mode effective refractive index n _{eq, 0,} the equivalent refractive index n _eq linear waveguide first-order _{mode, 1,} the wavelength λ in vacuum values and light bending radius R of the curved waveguide Each input to the optical waveguide design device, based on the input value,

[0010]

(Equation 4)

In accordance with the present invention, the offset amount δ _s is calculated in the optical waveguide designing apparatus.

A third aspect of the present invention is characterized in that a program for executing the function of the optical waveguide designing apparatus according to the first or second aspect by a computer is recorded.

[0013]

Embodiments of the present invention will be described below in detail with reference to the drawings.

First, the offset design method will be described. The design of “appropriate offset amount” depends on the refractive index of the waveguide core, the equivalent refractive index of the fundamental mode of the linear waveguide, and the linear waveguide 1
This is performed based on the values of the equivalent refractive index of the next mode, the bending radius of the curved waveguide, and the wavelength of light in a vacuum.

When the traveling direction of the waveguide is set to the z direction and the direction perpendicular thereto (the cross-sectional direction of the waveguide) is set to the x direction, the equivalent refractive index n _{eq, i} of the i-th mode of the linear waveguide and the electric field intensity profile ψ _i (x) is

[0016]

(Equation 5)

That is, the wave equation is satisfied. here,
ω is the angular frequency of light, c is the speed of light in vacuum, and n (x) is the refractive index distribution of the waveguide cross section. Here, the center of the waveguide is x
= 0. It is assumed that the electric field intensity profile ψ _i (x) is standardized as follows.

[0018]

(Equation 6)

The integration of equation (6) is performed over the entire region of x (hereinafter, all integrations are the same).

This linear waveguide has the same sectional shape,
When a curved waveguide having a radius R is used, the equivalent refractive index n _{eq, b, i} of the i-th mode of the curved waveguide and the electric field intensity profile η
_i (x) is

[0021]

(Equation 7)

Φ _i (x) that satisfies the wave equation
Using,

[0023]

(Equation 8)

(C. Vassallo,
“Optical Waveguide Concepts”, Chap. 5, Elsevie
r). Here, it is assumed that φ _i (x) is also standardized as follows.

[0025]

(Equation 9)

Usually, the bending radius is much larger than the waveguide width, and 2 × /
R is about one-tenth of a magnitude. Therefore, the solution of Equation 7 can be described by the solution of Equation 5 by the perturbation method. φ ₁ (x) is

[0027]

(Equation 10)

## EQU1 ## Therefore, the electric field intensity profile η _i (x) of the first-order mode of the curved waveguide can be written as follows.

[0029]

[Equation 11]

The linear waveguide fundamental mode is

[0031]

[Outside 1]

[0032]

(Equation 12)

Is given by Here, δ is an offset amount.

R ^1/2 times the overlap integral of the electric field profile of the curved waveguide primary mode and the electric field intensity profile of the offset linear waveguide fundamental mode is:

[0035]

(Equation 13)

Can be calculated.

Since the “appropriate offset amount” is an offset amount δ where the overlap integral is 0, if it is δ _s ,

[0038]

[Equation 14]

## EQU1 ## Since the light is usually confined in the core of the waveguide, the following equation holds with good approximation.

[0040]

(Equation 15)

Here, n _core is the refractive index of the core.

In general, the following relational expression holds between the k-th mode and the first-order mode (k and 1 are different).

[0043]

(Equation 16)

From the above, the “appropriate offset amount” δ _s is

[0045]

[Equation 17]

Is obtained. Here, λ is the wavelength of light in vacuum. Usually, the difference in the equivalent refractive index n _{eq, 1} in the equivalent refractive index n _{eq, 0} and a linear first-order mode of the linear fundamental mode as compared to the value of their own, not more than several%, braces number 17 formula ｛｝
The second term can be ignored. Thus, "appropriate offset amount" [delta] _s is

[0047]

(Equation 18)

Is obtained. In the present embodiment, an appropriate offset amount is designed using Expression (18). Since Expression 18 does not include the electric field intensity profile of the waveguide mode, δ _s can be obtained without performing overlap integration. Further, since the equivalent refractive index of the curved waveguide is not included, it is not necessary to perform the mode analysis on the curved waveguide.

An optical waveguide designing apparatus employing such an offset amount designing method will be described below.

FIG. 1 shows a system configuration of an optical waveguide designing apparatus. In FIG. 1, an information processing device such as a personal computer can be used as the computer 1.
The computer 1 has a CAD (Computer Aided Desig)
n) The component placement design software called is installed.
A keyboard 2 and a mouse 4 are connected to the computer 1 as input devices. The keyboard 2 is used for inputting numerical values of various parameters, and the mouse 4 is used for specifying a position on the display screen.

The display 3 displays the optical waveguides arranged and designed. The user designates the position of the end point of the waveguide to be arranged with the mouse 4 and inputs the parameters of Expression 18 necessary for obtaining the above-mentioned offset amount from the keyboard 2. Although generally known CAD software has a function of drawing an arc or a straight line, it does not have a function of drawing an offset unique to an optical waveguide.

Therefore, a general C waveguide device is used as an optical waveguide design device.
When using AD software, it is necessary to provide an offset drawing function. As a design device exclusively for optical waveguides, the present applicant has disclosed in Japanese Patent Application Nos. 8-280044 and 9-16.
Please refer to it as you propose No. 8414.

When drawing a waveguide in consideration of the offset amount, the computer may execute the following processing.

The case where a waveguide as shown in FIG. 2A is arranged will be described. It is assumed that the values of the parameters used in Expression 18 are given in advance from the keyboard 2 and stored in the memory of the computer 1. The user designates two positions 105 and 106 at the ends of the waveguide with a mouse. Since the radius of curvature of the center of the waveguide is given in advance, the radii of the arcs on the outer and inner circumferences of the waveguide are calculated from the width of the waveguide. The angle and center position of the arc are calculated assuming the end point of the arc. When the angle and center of the arc, and the inner and outer circumferences of the arc are determined, a figure of the outer circumference of the waveguide 102 can be drawn on the memory. At this time, since the offset is not considered, the computer 1 calculates the offset amount (reference numeral 108) according to the above equation (18). Next, when the current waveguide position is moved by the calculated offset amount in the direction of the center of the arc, the position of the waveguide in the curved portion considering the offset is determined. (A) of FIG.
In the example shown in FIG.
01 and exit in direction 110.

When the above processing is executed, the user places the waveguide in consideration of the offset as shown in FIG. 2 (B) only by designating only two points for the waveguide in the curved portion on the display screen. be able to.

In the embodiment described above, an example has been described in which the waveguide arrangement is designed by using CAD which is generally used.
In the optical waveguide design apparatus of Japanese Patent Application No. 9-168414 proposed by the present applicant, when the position and orientation of the arrangement of two optical circuits are specified, the path of the waveguide for connecting the two optical circuits is automatically set. Is determined. In addition, when the path is determined, the position of the waveguide in the curved portion is also automatically determined, so that the position of the curved portion can be automatically designated by this method.

Further, the processing procedure for calculating the offset amount and the processing procedure for drawing the waveguide in consideration of the offset are not shown in the flowchart.
Those skilled in the art should understand from the above description,
It would be possible to create a program to be installed on a computer. The language of the program may be appropriately determined according to the type of the computer (CPU). Further, a program for executing the above-described processing includes a floppy disk,
Recorded on various portable recording media such as D-ROM,
It may be installed (implemented) on a storage medium in the computer 1, for example, a hard disk.

[0058]

DESCRIPTION OF THE PREFERRED EMBODIMENTS For a waveguide having a core width of 2.5 μm, a core refractive index of 3.2 and a cladding refractive index of 1.0, a conventional method (a straight-line waveguide was used to calculate the electric field intensity profile of the fundamental mode and the curve of each bending radius). An electric field intensity profile of the first-order mode of the wave path is obtained by modal analysis, and an offset amount at which the overlap integral becomes 0 is searched.) The design value (reference numeral 12) of the appropriate offset amount obtained by the method of the present invention (see FIG. The equivalent refractive index of the fundamental mode and the first-order mode of the linear waveguide is obtained, and the appropriate offset obtained by Expression 18 is used.
FIG. 3 shows the result of comparing the design value of the quantity (reference numeral 11).
In the case where the bending radius is 250 μm or more, which is commonly used, the difference between the two is 2 nm or less, and it can be said that there is almost no difference between the results of the two methods. The method of the present invention, which does not require the mode analysis of the curved waveguide or the calculation of the overlap integral, is useful because the memory space required for the calculation, the calculation time and the labor are small.

[0059]

As described above, according to the first to third aspects, the refractive index of the waveguide core, the equivalent refractive index of the linear waveguide fundamental mode, the equivalent refractive index of the linear waveguide first-order mode, and the curve guide. Since an appropriate offset amount can be designed only from the bending radius of the wave path and the wavelength of light in a vacuum, it is possible to omit the modal analysis and the calculation of the overlap integral for the curved waveguide. Further, if a fixed value such as the refractive index of the waveguide core required for the calculation is given to a computer in advance, the offset amount can be easily obtained. Therefore, the layout design of the waveguide on the display screen and the graphic display of the waveguide are required. Even the computer responds faster. Further, the effect that the memory capacity can be saved can be obtained.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a system configuration according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram for describing a drawing process of a curved waveguide in consideration of an offset.

FIG. 3 is a characteristic diagram showing a comparison result between the present invention and a conventional method.

[Explanation of symbols]

 1 computer 2 keyboard 3 display 4 mouse

Claims (3)

[Claims] 1. An optical waveguide designing apparatus for designing a path of an optical waveguide, wherein the refractive index n _{core of} the waveguide _core and the linear waveguide fundamental mode are equivalent for designing the offset amount δ _s of the curved portion of the optical waveguide. Input means for inputting the refractive index n _{eq, 0} , the equivalent refractive index n _{eq, 1 of the} first-order mode of the linear waveguide, the value of the bending radius R of the curved waveguide, and the wavelength λ of light in vacuum; Based on the value obtained, Accordingly waveguide design apparatus being characterized in that comprises an arithmetic processing means for calculating the offset amount [delta] _s. 2. A offset designing method of the optical waveguide design apparatus for designing a path of the optical waveguide, the refractive index n _core of the waveguide core for the design of the offset amount [delta] _s of curved portion of the optical waveguide, the linear guide equivalent refractive index of the waveguide fundamental mode n _{eq, 0,} straight waveguide 1 equivalent refractive index of the order mode n _{eq, 1,} the optical waveguide each designed wavelength λ in vacuum values and light bending radius R of the curved waveguide Input to the device, and based on the input value, Accordingly offset design method of the optical waveguide design apparatus and calculates the offset amount [delta] _s in the optical waveguide designed device. 3. A recording medium on which is recorded a program for causing a computer to execute the functions of the optical waveguide designing apparatus according to claim 1.