KR20080029598A - Optical fiber having diffraction grating, method of fabricating diffraction grating at cutting plane, and optical apparatus using the same fiber - Google Patents

Abstract

An optical fiber having a diffraction grating, a method for fabricating a diffraction grating at a cutting plane, and an optical apparatus using the same fiber are provided to enhance reproducibility of the grating by using a photolithography, a femtosecond laser, and a UV ray. An optical fiber(100) includes a core(110) and a cladding(120). The core is formed to transfer an optical signal. The optical fiber is surrounded by the cladding. A diffraction grating(130) is formed on a sectional surface of the optical fiber in order to separate or select the optical signal according to a wavelength. The diffraction grating is a type of a Frensnel diffraction lens having a linear pattern or a circular pattern. The interval and the depth of the linear pattern or the circular pattern has a constant rate or is increased or decreased in a constant rate in order to be separated or selected according to the wavelength.

Description

Optical fiber having diffraction grating, method of fabricating diffraction grating at cutting plane, and optical apparatus using the same fiber}

1A is a perspective view of an optical fiber having a diffraction grating formed in a cross section according to an embodiment of the present invention.

1B is a perspective view of an optical fiber having a Fresnel diffractive lens formed on a cross section according to another embodiment of the present invention.

2A through 2C are plan views illustrating diffraction grating patterns that may be formed in an optical fiber cross section.

3A to 3C are perspective views schematically showing each optical fiber including a core portion of another type in which a diffraction grating is formed.

<Description of main parts in the drawing>

100,100a, 100b: optical fiber 110,110a, 110b: core

120: cladding 130, 130b: linear diffraction grating

130a: Fresnel diffraction lens

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical device used in an optical communication system, and more particularly, to an optical fiber for transmitting an optical signal, a method of forming a diffraction grating on the optical fiber, and an optical device using the optical fiber.

In the case of an optical component used in an optical communication system in recent years, in addition to the trend to minimize the size, there is a tendency to gradually have a structural feature of simplifying the structure of the optical component. In other words, efforts have been made to reduce the number of components in order to provide optical modules that are suitable for the simplification and low cost of optical components, and until now, many parts of bulk optics have evolved into fiber optics. Attempts have been made to implement many functional devices in the optical fiber itself.

In general, when the optical signal waveguided, i.e., to separate the transmitted optical signal by wavelength, it is placed in the front of the optical signal using a thin film, an AWG (arrayed waveguide grating) device, or a transmission diffraction grating To spatially separate.

When using a thin film form or AWG device, very high diffraction resolution can be obtained. In the case of a thin film form, the resolution is increased in proportion to the number of layers of the overlapping thin film, and the transmission diffraction grating increases in proportion to the number of engraved gratings per unit area. This type of diffraction grating element is necessary in order to diffract the optical signal passing through the optical fiber for each wavelength.

However, when such a diffraction grating device is manufactured separately and packaged with an optical fiber, the size of an optical component increases, and there are technical problems in packaging and reliability problems after packaging. In addition, the high cost of manufacturing has been disadvantageous in terms of price competition of the product.

On the other hand, there is a method of forming a diffraction grating on the optical fiber itself. For example, an optical fiber grating is formed in the optical fiber core in the longitudinal direction of the optical fiber, so that a specific wavelength can be selected or converted into a cladding mode by using reflection characteristics for each wavelength. In addition, there has been a technique of forming a long period grating on an optical fiber core to gain flattening using loss characteristics of certain portions of the spectrum.

However, the method of forming the diffraction grating inside the optical fiber has a technical difficulty because it requires a very precise process, and accordingly, there is an unsuitable problem in mass production of the optical fiber.

Therefore, the technical problem to be achieved by the present invention is to form a diffraction grating in the optical fiber itself, but the optical fiber having a diffraction grating formed into a cross section that can be formed through a relatively simple process, the method of forming the diffraction grating and the optical fiber manufactured using the optical fiber It is to provide a device.

In order to achieve the above technical problem, the present invention is a core (core) through which the optical signal; It includes a cladding surrounding the core, and provides an optical fiber in which a diffraction grating is formed in a cross section so that the optical signal can be separated or selected for each wavelength.

In the present invention, the diffraction grating is formed on the cross section of the core, the diffraction grating may have a straight pattern or a Fresnel diffraction lens of a circular pattern. In addition, the spacing and depth of the linear pattern or the circular pattern may be constant or increase or decrease at a constant rate for separation or selection for each wavelength.

The linear diffraction grating refracts a signal of a specific wavelength among the incident optical signals at a predetermined angle, and the diffraction grating of the Fresnel diffractive lens type focuses a signal of a specific wavelength among optical signals as a point. Can be.

The linear diffraction grating has a two-dimensional diffraction grating form by vertically overlapping a linear pattern in one direction and a linear pattern in another direction, and focusing an optical signal to a point according to a wavelength or several points using the two-dimensional diffraction grating. You can focus by dividing it into points.

The optical fiber may be any one of a single mode optical fiber, a multimode optical fiber, and a thermal expanded core (TEC) fiber in which a core portion of the cross section is enlarged, and the optical fiber may be used in an optical transmission and reception device or an optical display device.

The present invention also provides a method for forming a diffraction grating to form a diffraction grating on the cross section of the optical fiber in order to achieve the above technical problem.

In the present invention, the diffraction grating is a method of forming a grating directly on the cross section of the optical fiber with a photolithography or femtosecond laser, or by forming UV light by irradiating the cross section of the optical fiber through an interference or phase mask to change the refractive index. Can be formed.

Furthermore, the present invention provides an optical device manufactured using the optical fiber in order to achieve the above technical problem.

In the present invention, the optical device may include various optical components such as an optical transmission and reception device and an optical display device.

The optical fiber according to the present invention does not need to package the diffraction grating element by forming the diffraction grating on the optical fiber cross section, and thus the reliability problem can be solved to some extent. In addition, since the diffraction grating can be formed using a photolithography process, the manufacturing cost can be reduced, and the spacing, depth, etc. of the diffraction grating pattern can be freely adjusted, and thus the diffraction grating production reproducibility is excellent. Furthermore, since the diffraction grating is formed on the cross section, the aging phenomenon due to the stress caused by the heterogeneous materials may be greatly reduced.

Hereinafter, with reference to the accompanying drawings will be described a preferred embodiment of the present invention; In the following description, when a component is described as being on top of another component, it may be directly on top of another component, and a third component may be interposed therebetween. In addition, in the drawings, the thickness or size of each component is exaggerated for convenience and clarity of description, and parts irrelevant to the description are omitted. Like numbers refer to like elements in the figures. On the other hand, the terms used are used only for the purpose of illustrating the present invention and are not used to limit the scope of the invention described in the meaning or claims.

1A is a perspective view of an optical fiber having a diffraction grating formed in a cross section according to an embodiment of the present invention.

Referring to FIG. 1A, the optical fiber 100 of the present invention has a linear diffraction grating 130 formed in a cross section. The diffraction grating 130 is formed on the cross section of the core 110 constituting the optical fiber 100. In some cases, the diffraction grating is formed on the entire optical fiber cross section including the cladding 120 for the optical signal guided in the cladding mode. It may be.

The diffraction grating 130 may be formed by forming micro grooves having a fine concavo-convex shape through a dry etching method or a wet etching method using a photolithography process. The arrangement of these microgrooves causes diffraction of the light, which leads to different angles of refraction depending on the wavelength.

For example, the linear diffraction grating 130 functions to separate or select an optical signal having a specific wavelength among optical signals incident on the optical fiber. That is, by outputting only the optical signal of a specific wavelength at a specific angle when outputted out of the optical fiber, it is possible to function to enable the detection or transmission of only the optical signal of the specific wavelength. Therefore, the pattern shape of the linear diffraction grating, the spacing or depth of the pattern, etc. should be appropriately manufactured in consideration of the wavelength of the optical signal used and the characteristics of the wavelength to be separated or selected. In particular, it is desirable to increase the diffraction efficiency by making the depth of the refractive index change evenly depending on the position of the center and the edge of the optical fiber cross-section by paying close attention when forming the diffraction grating 130.

Since the optical fiber of the present invention forms a diffraction grating in the cross section by using a photolithography process, it has the advantage of being able to form the diffraction grating at a low cost and easily forming the shape of the required pattern. In addition, since the diffraction grating is formed in the cross section, the aging phenomenon due to the time caused by the stress between the heterogeneous materials can be significantly reduced.

Meanwhile, the diffraction grating 130 may directly etch the cross section of the optical fiber 100 by using a femtosecond laser having a very small focus. It may also be formed through a change in refractive index induced by ultraviolet (UV) light. That is, in the case of a photosensitive optical fiber, UV light is irradiated to the end face of the optical fiber by using a phase mask, or two UV light are irradiated to alternately construct the reinforcement interference and the extinction interference at the optical fiber end face, thereby alternating the refractive index of the optical fiber itself. The diffraction grating can be formed by a method of changing to.

1B is a perspective view of an optical fiber having a Fresnel diffractive lens formed on a cross section according to another embodiment of the present invention.

Referring to FIG. 1B, a diffraction grating in the form of a Fresnel diffraction lens (130a) having a circular pattern is formed in the cross section of the core 110 in the optical fiber of the present embodiment. The Fresnel diffraction lens 130a may also be formed through a refractive index change using photolithography, femtosecond laser, or UV light.

On the other hand, unlike the linear diffraction grating, Fresnel diffraction lens (130a) is preferably performed to align the light when forming the grating in order to accurately match the central axis of the circular pattern. The Fresnel diffraction lens 130a may function to focus the light of a specific wavelength passing through the optical fiber to a point, thereby increasing the transmission or reception efficiency of the specific wavelength optical signal.

2A through 2C are plan views illustrating diffraction grating patterns that may be formed in an optical fiber cross section.

Referring to FIG. 2A, the diffraction grating 130 shows a linear pattern. The spacing or depth of these patterns should be appropriately formed according to the characteristics of the wavelength to be detected as described above. In general, such a pattern follows an average value of wavelengths, but assuming that an optical signal usually corresponds to a wavelength of 1550 nm, the interval of the pattern may be formed to a size of about 1 μm or less.

Referring to FIG. 2B, the diffraction grating 130b may be formed in a two-dimensional shape by vertically overlapping linear patterns in one direction and linear patterns in another direction. The two-dimensional diffraction grating may focus the optical signal at one point according to the wavelength or divide the optical signal into several points.

The two-dimensional diffraction grating may also be formed through a refractive index change using photolithography, femtosecond laser, or UV light, and may be appropriately formed in accordance with characteristics of an optical signal of a specific wavelength to be transmitted or received.

Referring to FIG. 2C, the diffraction grating is formed in the form of a Fresnel diffractive lens 130a having a circular pattern. The Fresnel diffraction lens 130a focuses an optical signal having a specific wavelength that fits the diffraction grating width and moves an optical signal of other wavelengths that do not fit the diffraction grating width away from the focal point to separate or select light according to the wavelength. Function The pattern of such Fresnel diffractive lens may be formed at uniform intervals or at irregular intervals and sizes depending on the wavelength.

3A to 3C are perspective views schematically showing each optical fiber including a core portion of another type in which a diffraction grating is formed.

FIG. 3A shows the communication single mode optical fiber 100a. In the case of the communication single mode optical fiber 100a, since the size of the core 110a portion is small, a more precise method for forming a diffraction grating in the cross section of the core 110a is achieved. Process is required.

3B shows a communication multimode optical fiber 100. Since the core 110 of the multimode optical fiber 100 is considerably larger than the single mode optical fiber 100a, it is relatively easy to form a diffraction grating. Thus, by the various methods described above, a diffraction grating can be formed, and in particular, it is possible to easily form the shape of the diffraction grating required through a photolithography process.

FIG. 3C shows a Thermal Expanded Core (TEC) optical fiber 100b which is heated by heating the core of the cross section. In general, since the diameter of the core portion is difficult to form a diffraction grating in the case of a single mode optical fiber, the diffraction grating may be formed on the cross section of the core 110b by using a TEC optical fiber having an enlarged core diameter of the cross section.

In more detail, in order to obtain high diffraction efficiency of the diffraction grating, a diffraction grating having an appropriate structure must be formed in the core or cladding portion of the optical fiber through which the optical signal travels. However, in the case of single-mode optical fiber, the core diameter is relatively small, and the number of diffraction gratings that can be leaked is limited. If the number of gratings is small, the diffraction phenomenon may be degraded. In order to compensate for this, it is desirable to form the core part largely like the TEC optical fiber, thereby increasing the number of diffraction gratings engraved into the core cross section as much as possible.

In the optical fiber according to the present invention, the wavelength dependent diffraction grating is directly formed on the optical fiber cross-section, so that the optical fiber itself can be resolved according to the wavelength without adding new components. Accordingly, there is an advantage that wavelength multiplexing or demultiplexing is possible. In addition, by providing a diffraction grating function to the optical fiber itself without an additional diffraction grating or focusing lens, it is possible to reduce the cost of optical components and optical packaging costs accordingly. Recently, optical communication has been required based on time division multiplexing (TDM) and large capacity communication based on wavelength division multiplexing (WDM). Due to enhanced security functions, there is an increasing demand for optical monitoring devices or functional components. It can meet these demands. That is, the optical fiber in which the diffraction grating is formed in the cross section of the present invention can be usefully used in optical devices of optical communication systems such as optical transmitting and receiving devices and optical sensors.

For example, when the arrayed photodiode is positioned in front of the diffraction grating formed in the optical fiber cross section, the intensity of the optical signal according to the wavelength can be differentially detected. As described above, the optical fiber of the present invention can be applied to an optical receiver as a WDM communication device, particularly a CWDM (coarse wavelength division multiplex) communication device. It can also be used in various optical sensors for detecting optical signals.

On the other hand, as a special application, when the input wavelength is changed using the diffraction grating, that is, when the input wavelength is rapidly changed, the optical path is changed through the diffraction grating to be used for a new type of display device. It may be.

So far, the present invention has been described with reference to the embodiments shown in the drawings, which are merely exemplary, and those skilled in the art will understand that various modifications and equivalent other embodiments are possible therefrom. will be. Therefore, the true technical protection scope of the present invention will be defined by the technical spirit of the appended claims.

As described in detail above, the optical fiber in which the diffraction grating is formed in the cross section according to the present invention does not need to package the diffraction element because the grating is formed on the optical fiber itself, thereby solving the reliability problem according to the packaging.

In addition, by using photolithography, femtosecond laser, or UV light, the diffraction grating can be fabricated with excellent reproducibility and easily formed at low cost, thereby significantly lowering the packaging manufacturing cost.

On the other hand, by using such an optical fiber in an optical device of an optical communication system such as an optical transmission / reception device or an optical sensor, it is possible to suitably meet the trends such as low cost, miniaturization, and simplification of the optical device.

Claims (15)

A core through which the optical signal travels; And cladding surrounding the core; An optical fiber having a diffraction grating formed in a cross section to separate or select the optical signal for each wavelength. According to claim 1, The diffraction grating has a straight pattern or a Fresnel diffraction lens in the form of a circular pattern. The method of claim 2, The spacing and depth of the linear pattern or the circular pattern is constant or is increased or decreased at a constant rate for separation or selection by the wavelength. The method of claim 2, The linear diffraction grating refracts a signal having a specific wavelength among the incident optical signals at a predetermined angle, The diffraction grating in the form of Fresnel diffractive lens is characterized in that for focusing the signal of a specific wavelength of the optical signal to a point. The method of claim 2, The linear diffraction grating has a two-dimensional diffraction grating form by vertically overlapping the linear patterns in one direction and the linear patterns in the other direction. And focusing the optical signal to one point according to the wavelength or dividing into several points using the two-dimensional diffraction grating. According to claim 1, The diffraction grating is formed on the optical fiber cross section by a photolithography or femtosecond laser, or is formed by changing the refractive index by irradiating ultraviolet (UV) light to the optical fiber cross section through an interference or phase mask. Optical fiber. According to claim 1, The diffraction grating is formed in the core cross section, or the optical fiber, characterized in that formed over the entire optical fiber cross section including the cladding. According to claim 1, The optical fiber is any one of a single-mode optical fiber, a multi-mode optical fiber and a thermal expanded core (TEC) optical fiber that extends the core portion of the cross section. According to claim 1, The optical fiber is used in an optical transmitting and receiving device or an optical display device. A diffraction grating forming method for forming a diffraction grating on the cross section of the optical fiber of claim 1. The method of claim 10, The diffraction grating is a method of forming a grating directly on the cross section of the optical fiber with a photolithography or femtosecond laser, A method of forming a diffraction grating, characterized in that formed by changing the refractive index by irradiating UV light to the cross section of the optical fiber through an interference or phase mask. The method of claim 10, The diffraction grating is formed in the form of a Fresnel diffraction lens of a linear pattern or a circular pattern (Drench diffraction grating) characterized in that the form. The method of claim 12, The linear diffraction grating is a method of forming a diffraction grating, characterized in that the linear pattern in one direction and the linear pattern in the other direction is vertically overlapping to have a two-dimensional diffraction grating form. An optical device manufactured using the optical fiber of claim 1. The method of claim 14, The optical device comprises an optical transmission and reception device and an optical display device.

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