JP3229965B2 - Asymmetric optical coupler - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an asymmetric optical coupler in a linear optical data bus for realizing multi-terminals for use in flight control, for example, and more particularly to an asymmetric optical coupler suitable for a laser light source. It relates to an optical coupler.

[0002]

2. Description of the Related Art There are various types of data buses using optical fibers. Typically, point-to-point
There are an optical data bus using a star coupler (a simple connection between two points), a linear optical data bus, and the like.

FIG. 1 shows the configuration of a linear optical data bus. This linear optical data bus is an asymmetric type optical data bus for transferring an optical signal between each device 1 and the main bus 2 on a main bus 2 for transmitting an optical signal between the devices 1 using the bus. The optical coupler 3 is attached. This form is a bus form corresponding to the electric linear bus shown in FIG. 2 such as MIL-STD-1553B. In FIG. 2, 1 is a device using a bus, 2 is a main bus, and 3 'is a coupler.

The linear optical data bus is different from the electric linear bus in that it employs a system in which the optical power flowing through the main bus 2 is distributed little by little to each terminal using an asymmetric optical coupler 3. There is a weak point that the transmitted optical power decreases as the number of the asymmetric optical couplers 3 between the terminals that exchange the optical signals increases.

[0005] Therefore, in order to increase the number of terminals in a linear optical data bus, two measures of reducing the loss of the asymmetric optical coupler 3 and increasing the output of the optical signal source are considered. There is a need to. Among them, for the latter increase in light source output, there is a method of using an LD (laser diode) instead of an LED (light emitting diode) conventionally used. The LD can be expected to have an optical output of about -3 to 0 dBm, and an output several dB higher than that of the LED can be obtained.

However, when an LD and an asymmetric optical coupler are combined, slight variations in the use conditions of the optical coupler cause
It has been found that the loss characteristics of the optical coupler fluctuate unstablely. LD has a narrower spectrum than LED,
Also, the luminous flux is very thin. Therefore, light incident from the LD into the fiber is small amount of higher order propagation modes than the LED, by utilizing a difference in different light path propagation modes in an asymmetric optical coupler for branching the light from LD Entering
Use conditions of optical coupler such as difference in launch angle and slight deviation of optical axis
Optical signal caused by a slight shift in
It is considered that there are cases where the optical signal can be branched properly and cases where the optical signal cannot be branched depending on the difference in the condition of whether or not the optical signal is included.

[0007]

SUMMARY OF THE INVENTION Accordingly, the present invention provides an LD
To make a linear optical data bus using
Even if there are differences in the conditions of whether or not the optical signal contains many higher-order propagation modes , the optical signal can be branched without fail even if there is a difference , and a linear optical data bus with stable transfer characteristics can be obtained. It is an object of the present invention to provide an asymmetric optical coupler described above.

[0008]

The asymmetric optical coupler according to the present invention for solving the above-mentioned problems incorporates an element for converting a part of light of a low-order propagation mode into a high-order propagation mode at an input terminal.
It is characterized by the fact that The element for converting a part of the light in the lower-order propagation mode to the higher-order propagation mode is a device in which an optical fiber on the input side of an optical coupler is looped and fused and stretched at an intersection to form a tapered portion. Is preferred.

As described above, the asymmetric optical coupler of the present invention incorporates, at the input end, an element for converting a part of the light of the lower-order propagation mode to the higher-order propagation mode. In the case where the tapered portion is formed, the light input from the LD causes various angles of reflection that are not present in a simple fiber at this portion, and a part of the light in the lower- order propagation mode is changed to the higher-order propagation mode . Since the light is converted, the light contains more light in the higher-order propagation mode than immediately after the input from the LD. Therefore, the condition for determining whether an optical signal contains many high-order propagation modes is
Even if there is a difference , the optical signal can be surely branched, and a linear optical data bus having stable transmission characteristics can be obtained.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the asymmetric optical coupler according to the present invention will be described. In the linear optical data bus shown in FIG. -Each device 1 attached to the bus 2
As shown in FIG. 3, an asymmetric optical coupler 3 for passing an optical signal between the optical bus 3 and the main bus 2 has an element 5 for converting a part of light in a low-order propagation mode to a high-order propagation mode at an input terminal 4. Is incorporated.

As the element 5 for converting a part of the light of the low-order propagation mode to the high-order propagation mode, there is a taper portion formed by fusing and stretching an optical fiber included in the asymmetric optical coupler 3. As an example, as shown in FIG. 4, an optical fiber 6 on the input side of the optical coupler 3 is looped and fused and stretched at an intersection 7 to form a tapered portion 8 as shown in FIG.

As described above, the asymmetric optical coupler 3 of the embodiment incorporates the element 5 for converting a part of the light of the lower-order propagation mode into the higher-order propagation mode at the input terminal 4, and as shown in FIG. In the case where the optical fiber 6 is looped and fused and stretched at the intersection 7 to form the tapered portion 8 as shown in FIG.
The light input from the LD causes various angles of reflection at this part that are not present in a simple fiber, and a part of the light in the low- order propagation mode is converted to the high-order propagation mode. The light contains a larger amount of light in the higher-order propagation mode . Therefore, whether the optical signal contains many higher-order propagation modes
The optical signal can be reliably branched even if the above conditions are different , and a linear optical data bus having stable transmission characteristics can be obtained.

[0013]

As can be seen from the above description, the asymmetric optical coupler of the present invention incorporates an element for converting a part of the light of the lower-order propagation mode into the higher-order propagation mode at the input end.
The light input from D causes various angles of reflection that are not present in a simple fiber in this part, and a part of the light in the low- order propagation mode is converted to the high-order propagation mode. The light contains a larger amount of light in the higher-order propagation mode .
Therefore, it is necessary to determine whether an optical signal contains many higher-order propagation modes.
Even if there is a difference in the conditions , the optical signal can be branched without fail, and a linear optical data bus having stable transmission characteristics can be obtained.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a linear optical data bus.

FIG. 2 is a diagram showing a configuration of an electric linear bus.

FIG. 3 is a conceptual diagram of an asymmetric optical coupler of the present invention.

4 is a schematic diagram showing an example of an element for converting a part of light in a low-order propagation mode into a high-order propagation mode in the asymmetric optical coupler of FIG.

FIG. 5 is an enlarged view of a main part of FIG. 4;

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Device using bus 2 Main bus 3 Asymmetric optical coupler 3 'coupler 4 Input terminal 5 Element which converts a part of light of low order propagation mode to higher order propagation mode 6 Optical fiber on the input side of optical coupler 7 Intersection 8 Taper

Continuing from the front page (72) Inventor Satoshi Nakata 627-5 Gakuen Higashi-cho, Kodaira-shi, Tokyo No. 3 Kodaira-jukusha (72) Inventor Motonori Ishikawa 1 Kawasaki-cho, Kakamigahara-shi, Gifu Kawasaki Heavy Industries, Ltd. 72) Inventor Naoki Sudo 1 Kawasaki-cho, Kakamigahara-shi, Gifu Pref. In the Gifu factory of Kawasaki Heavy Industries, Ltd. (56) References JP-A-7-174932 (JP, A) JP-A-61-272704 (JP, A) Kaihei 1-227108 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) G02B 6/28-6/293 JICST file (JOIS)

Claims (2)

(57) [Claims] 1. An asymmetric optical coupler, wherein an element for converting a part of light in a low-order propagation mode into a high-order propagation mode is incorporated at an input end. 2. A device in which an element for converting a part of light in a low-order propagation mode to a high-order propagation mode is formed by looping an optical fiber on an input side of an optical coupler and fusing and stretching at an intersection to form a tapered portion. The asymmetric optical coupler according to claim 1, wherein