KR100405968B1 - ode cunversion based Fiber Gratings coupling system - Google Patents

Abstract

Disclosed is an optical coupling system using a mode conversion in which a portion of wavelength components is optically coupled from one optical waveguide to another using a grating having a narrow mode conversion bandwidth and a grating having a wide mode conversion bandwidth. The optical coupling system using the mode conversion of the present invention forms a first grating having a narrow mode conversion bandwidth for reflecting a wavelength component of a part of the incident optical signal of the first mode into a second mode to reflect the second optical waveguide. A first optical waveguide; And a second optical waveguide forming a second grating having a wide mode conversion band for transmitting the second optical waveguide by converting the reflected second mode into a third mode adjacent to the first optical waveguide. It is done. According to the present invention, the present invention is expected to contribute to the development of the optical communication industry and optical technology by being easy to manufacture and inexpensive compared to the conventional optical coupling system, and its wide application range.

Description

Optical coupling system using mode conversion {ode cunversion based Fiber Gratings coupling system}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical coupling system using mode conversion. In particular, an optical waveguide including a grating having a narrow mode conversion bandwidth and an optical waveguide including a grating having a wide mode conversion bandwidth are brought into close proximity to each other. An optical coupling system using mode conversion for optically coupling some wavelength components.

A grating is an optical device having a form in which the refractive index of the optical waveguide changes periodically. The grating is divided into a short period grating having a period of several μm and a long period grating having a period of several hundred μm or more according to the grating period. In the case of the short-period grating, the narrow band is converted to the opposite direction of the propagation direction by modulating the narrow band among the optical signals of the waveguide. Guide in the same direction.

The present invention proposes a system for optically combining a wavelength component of a part of an optical signal proceeding using two kinds of gratings having different characteristics from one optical waveguide to another.

Conventional methods for optically coupling a portion of wavelength components of a traveling optical signal from one optical waveguide to another optical waveguide include a directional optical coupler using optical waveguides having different characteristics. In general, a directional optical coupler is composed of a directional optical coupler using two optical waveguides having the same characteristics, but in this case, not only certain specific wavelength components but also several other wavelength components of the incident optical signal are generated because optical coupling occurs over a wide band. Coupling will occur. On the other hand, when the directional optical coupler is composed of two different optical waveguides having the same propagation constant only at a specific wavelength, optical coupling occurs only in a narrow band of specific wavelength components. However, this method is not only difficult to design and fabricate the directional optical coupler, but also requires the manufacture of two different optical waveguides that satisfy the design conditions.

Another method of combining the wavelength components of some of the traveling optical signals from one optical waveguide to another is to insert a short period grating into the coupling region of the directional optical coupler. In this method, since a single period grating is used, it is easy to optically couple some specific wavelength components to another optical waveguide, but it is not easy to insert the grating into the coupling region of the directional optical coupler, and the light depends on the insertion position of the grating. The disadvantage is that the binding efficiency of the bond is severely affected.

Another method of optically combining or extracting a wavelength component of a part of an optical signal from one optical waveguide to another is to use an optical rotor and a short period grating and an interferometer. However, since the rotor used is expensive, the manufacturing cost of the system increases, and in the latter case, the operation of the system is sensitive to the external environment.

Accordingly, an object of the present invention is to solve the above-mentioned problems and widen the application range of the device, and does not require easy fabrication and additional equipment, and also provides an optical coupling system using mode conversion that can reduce manufacturing cost. To provide.

1 is a view showing a method of optically combining a signal having a specific wavelength by using a first grating having a narrow mode conversion bandwidth and a second grating having a wide mode conversion bandwidth;

2A to 2D are diagrams illustrating first gratings having different structures according to grating slopes and grating periods of the first grating used in FIG. 1;

FIG. 2E illustrates a transmission spectrum of the first grating of FIG. 1;

3a and 3b are views showing a second grating having a different structure according to the grating slope of the second grating used in FIG.

3C is a diagram illustrating a transmission spectrum of a second grating of FIG. 1;

4A is a view illustrating a structure in which a wavelength tunable function is added to the structure of FIG. 1 by installing a wavelength variator for changing a lattice period in the first grating of FIG.

4B is a diagram illustrating a transmission spectrum of a wavelength grating and a second grating of FIG. 4A.

5 is a view showing an application example of an optical coupler for dispersion compensation using a first grating whose period of the grating is aperiodic;

6 is a view showing an application example of a multi-wavelength optical coupler using one or more first gratings having different wavelengths from each other;

7 is a view showing an application example of the addition / extraction wavelength multiplexing system using the optical coupler of the present invention, and

8 is a view showing an optical path specifying optical coupling system using an optical coupler of the present invention.

Explanation of symbols on the main parts of the drawings

2, 2a, 2b, ... 2N: first grid with narrow mode conversion bandwidth

4, 4a, 4b: second grid with wide mode conversion bandwidth

6, 6a, 6b: optical coupling system

10: first optical waveguide 12: second optical waveguide

14: third optical waveguide 20: first mode incident light

22: second mode reflected light 30: effective refractive index matching layer

40: third mode reflected light 50: wavelength variable

60: exit light

100, 102, 104, 106: input signal

200, 202, 206, 304, 306, 406: output signal

204: extraction signal

404: additional signal

The optical coupling system using the mode conversion for achieving the above object of the present invention, the mode conversion bandwidth for reflecting the wavelength component of a part of the optical signal of the incident first mode to the second optical waveguide to be changed to the second mode A first optical waveguide forming this narrow first grating; And a second optical waveguide forming a second grating having a wide mode conversion band for transmitting the second optical waveguide by converting the reflected second mode into a third mode adjacent to the first optical waveguide. It is done.

In this case, the third mode converted by the second grating may be the same as the first mode, and in the grating, the grating period of the first grating is preferably shorter than the grating period of the second grating. The lattice period of the gratings may be formed periodically or may be formed aperiodically. The gratings may be formed at any angle with respect to the optical waveguide propagation direction axis.

Further, a narrow mode conversion band on the first optical waveguide may be used to selectively couple an optical signal having an arbitrary wavelength among the optical signals of the first mode incident on the first optical waveguide to the second optical waveguide. The wavelength grating of the first grating is varied to attach the wavelength variator to the first grating to vary the wavelength converted from the first mode to the second mode.

Meanwhile, as an application example of the present invention, in order to compensate for dispersion of the optical signal, different positions of the first grating are provided by the first grating having the grating period of the first mode optical signal incident on the first optical waveguide. The optical coupling system may be configured to be converted into a second mode, reflected to an adjacent second optical waveguide, and converted into a first mode by the second grating and transmitted to the second optical waveguide.

Further, in order to perform multi-wavelength optical coupling to the optical signal, the optical signal of the first mode of the multi-wavelength incident on the first optical waveguide is generated by one or more first gratings formed on the first optical waveguide. The optical coupling system may be configured to be converted into two modes and converted into a first mode by a second grating having a wide mode conversion bandwidth on an adjacent second optical waveguide and transmitted to the second optical waveguide.

In order to perform the addition / extraction wavelength multiplexing optical coupling of the optical signal, a wavelength component of a part of the optical signal of the first wavelength of the multi-wavelength incident on the first optical waveguide is converted into the second mode by the first grating. An extraction stage which is reflected by an adjacent second optical waveguide, and the optical signal of the converted second mode is reduced to the first mode by the first second grating on the second optical waveguide, and is extracted and transmitted to the second optical waveguide; An optical coupling system comprising an additional stage in which an optical signal having the same wavelength as that of the extracted optical signal is transmitted from the first mode to the second mode by a second second grating on the second optical waveguide and then transmitted to the first optical waveguide It can also be configured.

Finally, a wavelength component of a portion of the incident first optical signal is converted to a second mode in order to designate an optical path that couples or splits the incident multi-wavelength optical signal to an arbitrary optical waveguide according to the wavelength. An optical coupler comprising a first grating or one or more first gratings for converting to a second grating, and a second grating between any two waveguides for reducing the converted second optical signal to the first mode. You can also configure the system.

Looking at the configuration and operation principle of the present invention as follows.

In this embodiment, the optical waveguide includes both an optical fiber and a planar waveguide. The configuration of the optical coupling system using the mode conversion proposed in the present invention is largely a specific wavelength component of a part of the optical signal of the first mode incident on the first optical waveguide. ) Is a short-period grating having a narrow mode conversion bandwidth for converting the second mode into a second optical waveguide adjacent to the first optical waveguide, and converting the converted second mode into a third mode to transmit the second optical waveguide. It consists of a long-period grid with wide mode conversion bandwidth. Here, the first optical waveguide represents an optical waveguide into which an optical signal is incident, and the second optical waveguide represents a specific wavelength component after optical coupling. ) Represents the optical waveguide output.

The short period grating on the first optical waveguide having a narrow mode conversion bandwidth is called a first grating, and the long period grating having a wide mode conversion bandwidth on a second optical waveguide is called a second grating. In addition, the third mode converted by the second grating may or may not be the same as the first mode. The specific wavelength component causing the mode conversion by the first grating may be approximately expressed by Equation 1, and the wavelength component that is mode-converted by the second grating may be expressed by Equation 2.

[Equation 1]

[Formula 2]

here, Represents the specific wavelength component that causes the mode conversion, Is the effective refractive index of the first mode of the optical waveguide, Represents the effective refractive index of the second mode of the optical waveguide. And and Denotes the lattice periods of the first and second gratings, respectively. The first mode of the optical waveguide generally represents the lowest order mode or the core mode, and the second mode represents the higher order mode or the cladding mode. As can be seen from Equations 1 and 2, the wavelength at which the mode conversion takes place , Can be adjusted by end It has a much larger value than.

The operating principle is that a specific wavelength satisfying [Equation 1] ) Is incident on the first optical waveguide, A first grating having a grating period of is converted from the first mode to the second mode and reflected by the second optical waveguide adjacent to the first optical waveguide. The specific wavelength component of this reflected second mode ( ) Is the lattice period (Equation 2) Is converted into the third mode by the second grating having?) And is transmitted to the second optical waveguide. In this case, the thickness of the effective refractive index matching layer positioned between the adjacent first optical waveguide and the second optical waveguide may be several μm or less to reduce the loss upon optical coupling.

Hereinafter, with reference to the accompanying drawings will be described in detail the present invention.

Here, unless otherwise specified, the same reference numerals are used for components that perform the same function used in the present embodiment.

FIG. 1 is a view illustrating a method of optically combining a signal having a specific wavelength by using a first grating having a narrow mode conversion bandwidth and a second grating having a wide mode conversion bandwidth. As shown in FIG. 1, the first optical waveguide 10 including the first grating 2 having a narrow mode conversion bandwidth and the second optical waveguide including the second grating 4 having a wide mode conversion bandwidth ( 12) and an effective refractive index matching layer 30. The principle of operation is that the optical signal 20 of the first mode enters and guides the first optical waveguide 10, and the specific wavelength component satisfying [Equation 1] ( ) Is mode-shifted by the first grating 2 from the first mode to the second mode, and is reflected to the second optical waveguide 12 adjacent to the first optical waveguide 10 and thus reflects the second mode 22. Wavelength component ( ) Is converted into the third mode 4 by the second grating 4 and transmitted to the second optical waveguide 12. On the other hand, among the optical signals 20 of the first mode incident on the first optical waveguide 10, the wavelength component 60 that does not satisfy Equation 1 is not changed by the first grating 2 without being mode-converted. It is guided by one optical waveguide 12.

2A through 2D are diagrams illustrating first gratings having different structures according to grating slopes and grating periods of the first grating used in FIG. 1. 2A and 2B show a grating period ( Is a periodic grating 2, and FIG. 2A shows the grating slope ( ) Is 0 °, and FIG. 2B shows the grid slope ( ) Represents an arbitrary value other than 0 °. 2C and 2D show grating periods ( ) Shows an aperiodic first grating 2, FIG. 2C shows a grating slope ( ) Is 0 °, and FIG. 2D shows the slope of the grid ( ) Is an example of the case where the value has a random value other than 0 °. According to the type of the first mode, the second mode, and the third mode, the slope of the preferred grid is approximately equal to [Equation 3]. The first, second and third modes include the fiber core mode, the fiber cladding mode, the radiation mode, and the TE and TM modes of the waveguide [Ref. Kyung S. Lee and T. Erdogan, "Fiber Mode Coupling in Tilted Fiber Gratings, "Applied Optics., Vol. 39, No. 9, 2000.].

[Equation 3]

FIG. 2E is a diagram illustrating a transmission spectrum of the first grating of FIG. 1. Referring to FIG. 2E, the first grating 2 has a specific wavelength component of Equation 1 It can be seen that it has a narrow mode conversion bandwidth with

3A and 3B are diagrams illustrating second gratings having different structures according to grating slopes of the second grating used in FIG. 1. 3a shows the slope of the grating ( Is an example showing the second grating 4 when 0 °, and FIG. 3B shows the slope of the grating ( Is an example showing the second grating 4 when () has any value other than 0 °. The slope of the grid ( ) May have any value other than 0 ° or 0 ° according to the mode conversion efficiency, and the preferred grating slope according to the type of the first mode, the second mode, and the third mode is as shown in [Equation 4].

[Equation 4]

However, Equations 3 and 4 are established only when the azimuth orders of the first mode and the second mode are different, and mode conversion is possible without necessarily tilting the angle.

3C is a diagram illustrating a transmission spectrum of the second grating of FIG. 1. Referring to FIG. 3C, the second grating 4 has a specific wavelength component of [Equation 2] We can see that it has a wide mode conversion bandwidth around

FIG. 4A is a view illustrating a structure in which a wavelength tunable function is added to the structure of FIG. 1 by installing a wavelength variable that changes a lattice period in the first grating of FIG. 1. FIG. 4B is a diagram illustrating a transmission spectrum of the first grating and a transmission spectrum of the second grating of which the wavelength is variable in FIG. 4A. As shown in FIGS. 4A and 4B, the wavelength of the mode conversion from the first mode to the second mode is changed by changing the period of the grating in the first grating 2 having the narrow mode conversion band on the first optical waveguide 10. FIG. 1 is a diagram illustrating a structure in which a wavelength tunable function is added to the optical coupling system of FIG. 1 by installing a tunable wavelength tunable device 50. Only the components having a specific wavelength satisfying [Equation 1] among the optical signals 20 of the first mode incident on the first optical waveguide 10 are converted into modes by the first grating 2 from the first mode to the second mode. The second optical waveguide 12 adjacent to the first optical waveguide 10 is reflected by the lattice period of the first grating 2 using the wavelength variator 50. ), The wavelength (mode conversion from the first mode to the second mode ( )of or Can be changed to The wavelength of the second mode selected by the wavelength variator ( or or ) Is converted into the third mode 40 by the second grating 4 having the wide mode conversion bandwidth on the second optical waveguide 12 and transmitted to the second optical waveguide 12.

As shown in FIG. 4B, since the mode conversion band of the second grating 4 is wider than the mode conversion band of the first grating 2, the first grating 2 is controlled by the first grating 2 using the wavelength variator 50. Even if the wavelength which is mode-converted from the mode to the second mode is varied, the mode conversion from the second mode to the third mode is possible by the second grating 4.

FIG. 5 is a diagram illustrating an application example of an optical coupler for dispersion compensation using a first grating whose period of the grating is aperiodic. As illustrated in FIG. 5, the optical signal 100 of the first mode incident on the first optical waveguide 10 has a fast wavelength component due to the first grating 2 having a non-periodic grating period. ) At the rear of the first grating 2, the slow wavelength component ( In the front of the first grating 2, each mode is converted into the second mode and reflected by the second optical waveguide 12 to compensate for dispersion. Converted to the second mode and The wavelength component of is reduced by the second grating 4 to the first mode 200 and transmitted to the second optical waveguide 12. In general, short wavelength components are faster than long wavelength components at 1300 nm or more in general silica optical fibers.

FIG. 6 is a diagram illustrating an application example of a multi-wavelength optical coupler using one or more first gratings having different wavelengths. As shown in FIG. 6, one or more first gratings 2a, 2b, ..., 2N having different grating periods are disposed on the first optical waveguide 10 to configure a multi-wavelength optical coupling system. Yes. The optical signals 102 of the first mode incident on the first optical waveguide 10 are N gratings of different wavelengths on the first optical waveguide 10 (2a, 2b, ..., 2N). Is converted from the first mode to the second mode and reflected by the second optical waveguide 12, and is converted into the first mode by the second grating 4 and transmitted to the second optical waveguide 12.

7 is a view showing an application example of the addition / extraction wavelength multiplexing optical coupling system using the optical coupler of the present invention. As shown in FIG. 7, two first gratings 4a and 4b are installed on the first optical waveguide 10 and two second gratings 4a and 4b on the second optical waveguide 12. This is an example of constructing an extraction wavelength multiplexing optical coupling system. The multi-wavelength optical signal 104 of the first mode incident on the first optical waveguide 10 has a specific wavelength component satisfying [Equation 1] ( ) Is converted by the first grating 2 from the first mode to the second mode and reflected by the second optical waveguide 12 and again by the first second grating 4a on the second optical waveguide 12. The first mode 204 is converted and extracted. When the wavelength component 404 of the same first mode as the extracted wavelength component is incident on the additional end of the second optical waveguide 12, the second second grating 4b performs mode conversion from the first mode to the second mode. The first grating 2 is transmitted through the first optical waveguide 10 and is converted back to the first mode by the first grating 2 on the first optical waveguide 10 and reflected to the output terminal on the first optical waveguide 10. ) Is output 304 to the first optical waveguide 10 together with the signals of the first mode that are not mode converted.

8 is a view showing an optical path specifying optical coupling system using an optical coupler of the present invention. As shown in FIG. 8, a first grating or one or more first gratings and a converted second mode to a first mode convert the wavelength component of a part of the optical signal of the incident first mode into the second mode. An optical coupler 6 composed of a second grating to be arranged between any two waveguides is an example of an optical coupling system for assigning a light distribution or an optical path to an optical waveguide of an incident multiwavelength. The multi-wavelength optical signals 106 incident on the first optical waveguide 10 may include an optical coupler 6a positioned between the first optical waveguide 10 and the second optical waveguide 12. , By) and The wavelength of is reflected by the second optical waveguide 12, Is output 306 as it is to the first optical waveguide 10 without being affected by the optical coupler 6a. Reflected by the second optical waveguide 12 and Wavelength of the optical waveguide 12 is guided to the second optical waveguide 12 and is located between the second optical waveguide 12 and the third optical waveguide 14, By) And is reflected to the third optical waveguide 14 and output 406 Is output 206 to the second optical waveguide 12 as it is.

As described above, the optical coupling system using the mode conversion according to the present invention is not only easy to manufacture and cheaper than conventional optical coupling systems, but also has a wide range of applications and developments in the optical communication industry and optical technology. It is expected to contribute to Specifically, it can be applied to dispersion compensation optical coupling system, multi-wavelength light extraction system, addition / extraction wavelength multiplexing optical coupling system and routed optical coupling system, and is expected to contribute to the development of optical communication industry and optical technology. In addition, in the situation where the WDM optical communication related market is greatly activated and expanded domestically and internationally, the present invention is expected to have a large ripple effect in various applications because it is a technology that can be directly applied to WDM optical communication systems or devices.

The present invention is not limited to the above-described embodiment, and it will be apparent that many modifications are possible by those skilled in the art within the technical spirit of the present invention.

Claims (11)

A first optical waveguide in which a first grating having a narrow mode conversion bandwidth for reflecting a wavelength component of a part of the incident first optical signal into a second optical waveguide to be changed to a second mode; And A second optical waveguide in which a second grating having a wide mode conversion band for transmitting the second optical waveguide by converting the reflected second mode into a third mode adjacent to the first optical waveguide Optical coupling system using a mode conversion, characterized in that consisting of. The optical coupling system of claim 1, wherein the third mode converted by the second grating is the same as the first mode. The optical coupling system of claim 1, wherein the lattice period of the first grating is shorter than that of the second grating. The optical coupling system of claim 1, wherein the lattice periods of the gratings are formed periodically. The optical coupling system of claim 1, wherein the lattice periods of the gratings are formed aperiodically. 6. The optical coupling system according to any one of claims 3 to 5, wherein the gratings are formed at an arbitrary angle with respect to the optical waveguide propagation direction axis. 2. The mode conversion on the first optical waveguide according to claim 1, wherein an optical signal having an arbitrary wavelength among the optical signals of the first mode incident on the first optical waveguide can be selectively optically coupled to the second optical waveguide. An optical coupling system using a mode conversion, wherein the wavelength grating of the first grating having a narrow band is changed to attach a wavelength variator to the first grating to change the wavelength converted from the first mode to the second mode. The second mode optical signal of claim 1, wherein the optical signal of the first mode incident on the first optical waveguide is disposed at different positions of the first grating by a first grating having a non-periodic grating period. The optical coupling system using the mode conversion, characterized in that the conversion to the mode is reflected to the adjacent second optical waveguide, the second grating is converted back to the first mode and transmitted to the second optical waveguide. 2. The at least one first grating of claim 1, wherein an optical signal of a first wavelength of multiple wavelengths incident on the first optical waveguide is formed on the first optical waveguide so as to perform multi-wavelength optical coupling to the optical signal. To the second mode, and the mode conversion bandwidth on the adjacent second optical waveguide is converted to the first mode by the second grating having a wider optical waveguide. . The method of claim 1, wherein the wavelength component of a part of the optical signal of the first wavelength of the multi-wavelength incident on the first optical waveguide is performed by the first grating to perform the addition / extraction wavelength multiplexing optical coupling of the optical signal. Is converted to a mode and reflected by an adjacent second optical waveguide, and the optical signal of the converted second mode is reduced to the first mode by the first second grating on the second optical waveguide, and extracted and transmitted to the second optical waveguide Sweets; And an additional stage in which an optical signal having the same wavelength as the extracted optical signal is transmitted from the first mode to the second mode by a second second grating on the second optical waveguide and transmitted to the first optical waveguide. Optical coupling system using a mode conversion. The method of claim 1, wherein the wavelength component of a portion of the optical signal of the incident first mode for the optical path designation that optically couples or splits the incident multi-wavelength optical signal according to the wavelength. An optical coupler comprising a first grating or one or more first gratings for converting to the second mode and a second grating for reducing the optical signal of the converted second mode to the first mode, between any two waveguides Optical coupling system using a mode conversion, characterized in that made.