JP3216066B2 - Optical attenuator and manufacturing method thereof - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to optical communication, optical measurement, CA
The present invention relates to an optical attenuator used to attenuate an optical signal by a certain amount in a field such as a TV system and a method of manufacturing the same.

[0002]

2. Description of the Related Art In the field of data transmission and control using an optical signal, such as optical communication and optical measurement, an optical attenuator for amplifying and converting an optical signal and attenuating the optical signal by a certain amount is used. FIG. 2 shows an example of the simplest configuration of such an optical attenuator. This figure is a longitudinal sectional view of a main part of the optical attenuator. In the figure, an optical attenuator 1 has a configuration in which an optical fiber 3 having a function of attenuating an optical signal is inserted into the center of a ferrule 2 such as a metal cylinder.

In this example, the optical fiber 3 contains a dopant that attenuates an optical signal. As a result, the optical signal input to the optical attenuator is attenuated by a fixed amount and is extracted to the output side. Such a technique is described in, for example,
This is introduced in JP-A-3-96506, JP-A-63-96504, and the like. In addition, there is also introduced a technique of providing a material or a structure for reflecting or absorbing an optical signal in the intermediate portion of the optical fiber 3 as described above (Japanese Utility Model Application Laid-Open No. 63-122301, Japanese Utility Model Application Laid-Open No. 63-122301; 63-1307
No. 02, Japanese Utility Model Laid-Open Publication No. 1-38613).

[0004]

However, the above-mentioned conventional optical attenuator has the following problems to be solved. In the optical signal processing circuit, not only light of a single wavelength,
Sending various kinds of optical signals having different wavelengths into an optical fiber is performed. Here, for example, the optical fiber 3 shown in FIG.
It is assumed that an optical attenuator containing a constant optical attenuation dopant is used. However, this kind of dopant usually has a transmission light attenuation characteristic depending on the wavelength of the optical signal. Therefore, even if a signal of a uniform level for all wavelengths is input to the optical attenuator, a level difference occurs between optical signals of each wavelength on the output side.

An attenuator using a light reflection film or the like has an advantage that input light can be attenuated uniformly without depending on the wavelength. However, since a loss of an optical signal occurs in the reflection film portion, it is not suitable as a high-power signal attenuator.

SUMMARY OF THE INVENTION The present invention has been made in view of the above points. In a system containing a dopant, the wavelength dependence is eliminated, and a constant amount of attenuation is provided for optical signals of two or more wavelengths. It is an object of the present invention to provide an optical attenuator to be obtained and a manufacturing method thereof.

[0007]

An optical attenuator according to the present invention has two
An optical fiber for transmitting an optical signal of at least one of different wavelengths, and a bending portion for bending a part of the optical fiber at a set curvature, wherein the optical fiber has a wavelength of the optical signal. Is characterized in that a dopant that attenuates the transmitted light more as the value is shorter is compounded.

Further, the manufacturing method is to reduce the wavelength dependency of the transmitted light attenuation characteristic in the optical fiber caused by bending a part of the optical fiber, and to attenuate the transmitted light more greatly as the wavelength of the optical signal becomes shorter. The present invention is characterized by adjusting the optical attenuation characteristics of the optical fiber with respect to optical signals of two or more different wavelengths in the optical fiber so as to be almost equal to each other by mixing the dopants.

[0009]

When a certain bending is applied to an optical fiber, an optical signal having a longer wavelength has a larger attenuation. When a dopant that attenuates the transmitted light as the wavelength becomes shorter is mixed into the optical fiber, when the optical fiber is viewed as a whole, the optical signal having the shorter wavelength and the optical signal having the longer wavelength are almost uniformly attenuated.

[0010]

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 longitudinal sectional view showing an embodiment of the optical attenuator of the present invention. This optical attenuator 5 has a cylindrical coupling portion 5A.
And has a cavity 5B inside at the center. A bending portion 8 is provided in the cavity 5B. Both ends of the optical fiber 7 are arranged and fitted and fixed at the center of the coupling portion 5A. When an optical signal is inputted from one end of the optical fiber 7, a predetermined attenuation effect is obtained and the signal is outputted to the other end. The bend imparting portion 8 has an arrow 1 in its cavity 5B.
A curvature setting device 11 that moves up and down in two directions is arranged.
The upper surface of the curvature setting device 11 is in contact with the optical fiber 7, and the optical fiber 7 is just pushed upward from the bottom of the figure to bend the optical fiber 7 with an appropriate bending radius. An adjustment screw 13 is provided to move the curvature setter 11 up and down in the direction of arrow 12. The adjusting screw 13 is screwed into the lower wall surface of the bending portion 8 and rotated in the direction of arrow 14 to turn the curvature setting device 11 to the direction of arrow 12.
It can move up and down in the direction. In the present invention, the bending portion 8 including the cavity 5A, the curvature setting device 11, the adjusting screw 13, and the like is called.

In the optical attenuator of the present invention, as shown in this figure, the optical fiber 7 contains a dopant for attenuating a signal, which will be described later, while the optical fiber 7 is bent at a constant curvature. FIG. 3 is a graph illustrating the attenuation characteristics of the optical signal according to the type of the dopant. The horizontal axis of this graph represents wavelength in [nm], and the vertical axis represents loss in [dB / Km].
It is represented by Usually, as shown in this figure, a transition metal or a rare earth metal is suitable as a dopant for an optical fiber composed of synthetic quartz. All of these increase the loss of an optical signal when contained in an optical fiber. However, the loss of the optical signal has its own wavelength dependency as shown in the figure.

In the present invention, in consideration of such wavelength dependence, for example, in the above embodiment, vanadium V shown in FIG. 3 is used as a dopant. The loss per unit length of the vanadium V gradually decreases as the wavelength increases from 800 nm to a longer wavelength. That is, this dopant has the characteristic that the shorter the wavelength of the optical signal, the greater the attenuation of transmitted light.

On the other hand, FIG. 4 shows the loss when the optical fiber is bent in accordance with the wavelength. In FIG. 4, the horizontal axis represents wavelength [nm], and the vertical axis represents loss [dB /
Km]. As can be seen from the figure, the characteristic shown by the central curve K1 indicates that when a bend is applied to an optical fiber, a longer signal wavelength is more strongly attenuated than a shorter wavelength signal. I have. The curve K1 shifts toward the curve K2 when the bending is increased, and shifts toward the curve K3 when the bending is reduced. However, in each case, the characteristic is such that the longer the wavelength, the more the transmitted light is attenuated.

As can be seen from FIGS. 3 and 4, the wavelength dependences when vanadium V is contained as a dopant in the optical fiber and when the optical fiber is bent are opposite to each other. . Therefore, by combining the two, it is possible to set the optical signal attenuation characteristics to be substantially the same for both short wavelength light and long wavelength light. For this reason, vanadium V is contained as a dopant in the optical fiber 7 shown in FIG. 1, and two types of optical signals having different wavelengths are inputted from one end thereof, and the adjusting screw 13 is adjusted so that the output levels of the two become substantially equal. Manipulate. Specifically, an optical signal having a wavelength of 1.3 μm and an optical signal having a wavelength of 1.55 μm are input,
Light attenuation 5dB, 10dB, 15dB, 20dB, 2
With respect to the 6 types of 5 dB and 30 dB, the difference in attenuation amount could be kept within a range of about 1 dB or less.

FIG. 5 shows the relationship between the wavelength of the optical signal and the amount of attenuation by the optical attenuator. The attenuation of the optical attenuator is determined mainly by the content of the dopant. By sequentially adding the dopant to the optical fiber without bending, and manufacturing a high content of the dopant, as shown in this figure,
An optical attenuator with a small amount of dopant and a small amount of attenuation has a relatively small wavelength dependence, whereas an optical attenuator with a large amount of dopant and a high attenuation shows a large wavelength dependence. That is, within the range of the straight line K4 in the figure, an optical attenuator having the same attenuation for two or more types of optical signals can be realized with the optical fiber containing the dopant as it is. However, when the wavelength dependency increases as shown by the straight lines K5 and K6 in the drawing, the required standard is no longer satisfied. When the optical fiber is bent to cancel the wavelength dependence as in the present invention, the straight lines K7, K7,
As indicated by K8, the optical signal having the wavelength of 1.3 μm and the optical signal having the wavelength of 1.55 μm have substantially the same attenuation.

In particular, in an optical fiber communication network or the like, an optical attenuator is widely used for adjusting the optical power level on the receiving side. In this case, for example, an optical attenuator that obtains substantially the same level of attenuation for optical signals having wavelengths of 1.3 μm and 1.55 μm is required. In this case, the difference in attenuation is required to be about ± 1.5 dB. Therefore, the optical attenuator of the present invention as described above is suitable for meeting these requirements.

The present invention is not limited to the above embodiment. The optical attenuator shown in FIG. 1 has a configuration in which a bend is given to the center of an optical fiber and the amount of the bend can be adjusted. The optical fiber may be inserted along a guide from which a certain amount of bending is given from the beginning, and the optical attenuator may be completed as it is. In this case, since an adjusting mechanism is not required, cost can be reduced. Further, the bending applied to the optical fiber may be not only at one location but also at two or more locations, or may be provided at the center or at the end of the optical fiber. Further, the dopant has been described by taking vanadium as an example. However, as long as the wavelength of light is shorter, transmitted light is attenuated to a greater extent by one or two kinds.
It is possible to select and contain more than one kind. Further, the attenuation characteristic required for two or more kinds of optical signals of interest may be shown, and it is not necessary to show uniform characteristics for other wavelengths.

[0018]

According to the optical attenuator and the method of manufacturing the same according to the present invention described above, an optical fiber for transmitting two or more kinds of optical signals having different wavelengths and a part of the optical fiber are set. And a bending imparting portion that bends at a curved curvature.
In the optical fiber, a dopant that attenuates the transmitted light greatly as the wavelength of the optical signal becomes shorter is compounded, so that the wavelength dependence of the attenuation characteristic of the optical fiber is canceled out, and two or more kinds of optical signals having different wavelengths are used. Light attenuation characteristics can be made substantially equal. This makes it possible to provide an optical attenuator having a constant attenuation characteristic for an arbitrary wavelength. In addition, since the optical fiber has a structure in which a certain dopant is contained, there is an effect that the optical fiber is stable in characteristics and easily manufactured, and the cost can be easily reduced by mass production.

[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 conventional general optical attenuator.

FIG. 3 is a graph showing a relationship between wavelength and loss of various dopants.

FIG. 4 is a graph showing a relationship between wavelength and loss when an optical fiber is bent.

FIG. 5 is a graph showing the relationship between the wavelength of an optical fiber and the amount of attenuation when the dopant concentration is changed.

[Explanation of symbols]

 5 Optical attenuator 7 Optical fiber 8 Bending section 11 Curvature setting device 13 Adjustment screw

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Kazunori Kanayama 1-1-6 Uchisaiwaicho, Chiyoda-ku, Tokyo Nippon Telegraph and Telephone Corporation (72) Ryo Nagase 1-1-6 Uchisaiwaicho, Chiyoda-ku, Tokyo Japan Within Telegraph and Telephone Co., Ltd. (72) Inventor Kazunari Sugi 2-1-1, Sakae Oda, Kawasaki-ku, Kawasaki-shi, Kanagawa Prefecture Inside Showa Electric Wire & Cable Co., Ltd. No. 1 Inside Showa Electric Wire & Cable Co., Ltd. (72) Inventor Kenichi Muta 2-1-1 Oda Sakae, Kawasaki-ku, Kawasaki City, Kanagawa Prefecture Inside In Showa Electric Wire & Cable Co., Ltd. 2-1-1 Oda Sakae Showa Electric Wire & Cable Co., Ltd. (72) Inventor Yumi Ariga 2-1-1 Oda Ei, Kawasaki-ku, Kawasaki-ku, Kawasaki-shi, Kanagawa (72) Inventor Asa Kumagai 2-1-1, Sakae Oda, Kawasaki-ku, Kawasaki City, Kanagawa Prefecture, Japan Showa Electric Cable Co., Ltd. (56) References JP-A-61-28917 (JP, A) JP-A-5-264816 (JP, A) JP-A-54-2754 (JP, A) JP-A-54-138452 (JP, A) JP-A-5-15002 (JP, U) JP-A 62-125213 (JP, A) JP, U) Japanese Utility Model 63-96506 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) G02B 6/00

Claims (2)

(57) [Claims] 1. An optical fiber for transmitting two or more kinds of optical signals having different wavelengths, and a bending portion for bending a part of the optical fiber at a set curvature, wherein the optical fiber has Is an optical attenuator characterized by incorporating a dopant that attenuates transmitted light more greatly as the wavelength of the optical signal becomes shorter. 2. The method according to claim 1, wherein the wavelength dependence of the transmitted light attenuation characteristic in the optical fiber, which is caused by bending a part of the optical fiber, is determined by blending a dopant that attenuates the transmitted light more as the wavelength of the optical signal becomes shorter. A method of manufacturing an optical attenuator, wherein the optical attenuation characteristics of two or more optical signals having different wavelengths in the optical fiber are adjusted to be substantially equal.