JP3233503B2 - Optical attenuator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical attenuator used for adjusting a signal level on an optical signal transmission line.

[0002]

2. Description of the Related Art An optical attenuator is used in an apparatus for transmitting and processing various kinds of information by an optical signal to adjust the level of the optical signal. As this type of optical attenuator, for example, a device in which a fiber doped with a transition metal or a fiber doped with a high concentration OH group is arranged between an input optical fiber terminal and an output optical fiber terminal is known. (Japanese Utility Model Application Laid-Open No. 63-96506, Japanese Utility Model Application Laid-Open No.
No.).

[0003]

The transition metal-doped fiber attenuates a signal by utilizing light absorption resulting from transition of transition metal ions in the d-orbit. But d
Since the transition in orbit is easily affected by the ligand field, the absorption spectrum width is widened. Therefore, it is not suitable for the purpose of obtaining high attenuation only in a specific wavelength region. Further, in the high-concentration OH group-containing fiber, the light is attenuated by utilizing the absorption of the second and third harmonics of the molecular vibration of the OH group and the combined wave. Therefore, in order to obtain a sufficient attenuation, the length of the fiber used as the optical attenuator needs to be sufficiently long. Therefore, it is not suitable for the purpose of being incorporated in a small optical circuit or the like.

On the other hand, there is known a configuration in which the end faces of an input optical fiber and an output optical fiber are cut obliquely, and a film for light attenuation is deposited on the end faces (Japanese Patent Application Laid-Open No. 60-1985).
-64307). The optical attenuator having such a configuration is relatively practical, and various similar ones have been introduced. However, all of them need to be manufactured with relatively high accuracy and are not suitable for low-priced products.

In the field of optical circuits, specifically, 20
There is a demand to realize an attenuation of 5 to 20 dB with a length of about millimeter. In such a case, doping with a transition metal known for light attenuation requires doping of several thousand ppm or more. As a glass having such a high impurity concentration, a multi-component glass is effective. However, the multi-component glass has a high refractive index, and has a disadvantage that reflection loss increases when it is connected to quartz glass which is usually used for an optical fiber.

On the other hand, when a quartz glass is doped with a high concentration of a transition metal or the like, a so-called cluster is formed,
The transition metal cannot be uniformly dispersed and mixed in the quartz glass. Therefore, the dopant concentration becomes non-uniform in the longitudinal direction of the optical fiber, and it is not possible to provide a stable quality optical attenuator. The present invention has been made in view of the above points, and has an object to provide an optical attenuator having a relatively high optical attenuation effect, and further in which a dopant and quartz are uniformly mixed with each other. is there.

[0007]

Means for Solving the Problems The first invention of the present invention is an input
Between the optical fiber for output and the optical fiber for output.
Is, has a light guiding portion comprising a core and a cladding formed on the core periphery, the core and or cladding,
It contains two or more elements selected from the rare earth element and the transition metal element , and
Field diameter is smaller than that of both input and output optical fibers.
It is characterized by being selected small. According to a second aspect of the present invention, there is provided an optical fiber between an input optical fiber and an output optical fiber.
A light guide portion composed of a core and a clad formed on the outer periphery of the core, wherein the core and / or the clad is one of a rare earth element and a transition metal element. The above elements and the elements uniformly
Aluminum for dispersing and contains
The field diameter is the same as that of the input and output optical fibers.
It is characterized in that it is selected to be slightly smaller.

[0008]

The attenuator body is an optical fiber type consisting of a core and a clad, and one or both of them contains two or more rare earth elements or transition metal elements , or contains aluminum.
To suppress cluster formation, ensure that the dopants are evenly mixed into the fiber , and
The diameter is smaller than that of both input and output optical fibers.
Prevents connection loss with force.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to the embodiments shown in the drawings. FIG. 1 is a sectional view of a main part showing an embodiment of an optical attenuator according to the present invention. As shown in the figure, the optical attenuator 1 is of an optical fiber type and comprises a core 1A and a clad 1B. Optical fibers 4 are connected to both ends of the optical attenuator 1 via connectors 2. The optical attenuator 1 and the connector 2 are housed inside a casing 3. Optical attenuator 1
One or both of the core 1A and the cladding 1B contain two or more elements selected from the rare earth elements and the transition metal elements. The radius of the core or clad of the optical fiber 4 and the optical attenuator 1 is selected as follows so that the connection loss does not affect the optical attenuation by the optical attenuator itself.

FIG. 2 is a sectional view of the optical attenuator 1 and the optical fiber 4. (A) is a longitudinal cross-sectional view, and (b) and (c) are cross-sectional views at the abutting surface. As shown in this figure, the cladding diameters of the optical attenuator 1 and the input / output optical fiber 4 are selected to be substantially equal. On the other hand, the core 1 of the optical attenuator 1
The radius of A is selected to be slightly smaller than the radius of the core 4A of the input / output optical fiber 4 connected to both ends. The substantial core diameter of the optical fiber is referred to as a mode field diameter (MFD). For example, the MFD of the input / output optical fiber 4 is set to 9.5 micrometers, and the MFD of the core 1A of the optical attenuator 1 is set to 9.0 micrometers. In this case, as shown in FIGS.
As described above, even if the core 1A and the core 4A are misaligned , the connection loss at the time of inputting the optical signal is about 0.45 dB .
No connection loss occurs at the time of output. Therefore, it is possible to configure an attenuator that hardly affects the amount of attenuation of the optical attenuator 1.

FIG. 3 shows the relationship between the optical attenuation of the optical fiber having the above configuration and the dopant concentration. The material shown in this figure is obtained by cutting a quartz single-mode fiber to a length of 20 mm and forming a casing 3 as shown in FIG.
It is stored in. In this example, the light attenuation was measured so that aluminum was contained at a concentration of 5000 ppm and cobalt was contained at 250 to 1250 ppm as shown in the figure. In this case, as shown in this figure, the light attenuation amount can be freely selected from a range of 5 dB to 20 dB. The optical signal in this case has a wavelength of 1.3 to 1.5 michrome meter.

The aluminum is 5000 to 1000
It is preferable to contain about 0 ppm. The reason for including aluminum in this manner is as follows. In FIG.
The state of Nd clusters inside quartz is illustrated. FIG. 3A shows the state of clusters when Nd is doped at a high concentration in quartz. On the other hand, (b)
Shows a state in which quartz is doped with Nd and aluminum. As shown in this figure, if quartz is doped only with Nd at a high concentration, clusters grow and uniform dispersion becomes impossible.

On the other hand, when aluminum is doped as shown in FIG. 1B, a part of the continuity of the three-dimensional network structure is cut, and the formation of clusters is suppressed. Therefore, Nd
Can be uniformly dispersed. This makes it possible to dope a high concentration of transition metal and obtain a high attenuation. When the light attenuation wavelength is one wavelength, it is preferable to dope aluminum, but when attenuating about two or more wavelengths, a similar effect can be obtained even if a rare earth element or a transition metal element is contained instead of aluminum. .

FIG. 5 shows the relationship between the amount of optical attenuation and the wavelength of a signal when a rare earth or transition metal is doped. As shown in this figure, when two or more kinds of rare earth elements and transition metal elements are contained in quartz, light of the corresponding wavelength can be attenuated. For example, when doping is performed at a ratio of V: Ni = 1: 2, an optical attenuator having a practical attenuation of 1.3 μm and 1.55 μm can be obtained. At the same time, the formation of clusters can be suppressed.

[0015]

According to the optical attenuator of the present invention described above, the light guide portion composed of the core and the clad contains two or more kinds of elements selected from the group consisting of rare earth elements and transition metal elements. Therefore, these elements can be contained at a higher concentration than when one kind of element is contained. Therefore, a high attenuation can be obtained with a relatively short length. In particular, when aluminum, a rare earth element, a transition metal element and the like are contained in combination, a practical optical attenuator having a high attenuation can be obtained.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view showing an optical attenuator according to an embodiment of the present invention.

FIG. 2 is a longitudinal sectional view of a main part showing a coupling state between an optical attenuator and an input / output optical fiber.

FIG. 3 is a graph showing the relationship between the amount of light attenuation and the concentration of a dopant in the optical attenuator of the present invention.

FIG. 4 is an explanatory view showing an effect of preventing cluster formation by aluminum.

FIG. 5 is a graph showing the relationship between the amount of light attenuation by a transition metal and the signal wavelength.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Optical attenuator 1A core 1B clad 2 Connector 3 Casing 4 Optical fiber

Continuation of the front page (56) References JP-A-54-2754 (JP, A) JP-A-3-188687 (JP, A) JP-A-4-291972 (JP, A) JP-A-6-317710 (JP) JP-A-5-88022 (JP, A) JP-A-63-96506 (JP, U) JP-A-55-57706 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB Name) G02B 6/00

Claims (2)

(57) [Claims] 1. An input optical fiber and an output optical fiber.
Arranged aligned between, has a light guiding portion comprising a core and a cladding formed on the core periphery, the core and or cladding, selected from any element of the rare earth elements or transition metal elements Both input and output optical fibers containing two or more elements and having a mode field diameter of the input and output.
An optical attenuator characterized in that it is selected to be slightly smaller than that of the above . 2. An input optical fiber and an output optical fiber.
Arranged aligned between, has a light guiding portion comprising a core and a cladding formed on the core periphery, the core and or cladding, selected from any element of the rare earth elements or transition metal elements One or more elements and aluminum for uniformly dispersing the elements
Both input and output optical fibers having a contained mode field diameter
An optical attenuator characterized in that it is selected to be slightly smaller than that of the above .