JPS59100411A - Device for reducing coherence in fiber - Google Patents

Abstract

PURPOSE:To reduce the coherence of output light and to reduce modal noises and distortion during the analog modulation of a light source, by coupling numbers of optical fibers which differ in length between the light source and an output optical fiber and generating delay difference. CONSTITUTION:Light from an LD1 is incident to input terminals L1IN-LnIN of respective optical fibers forming a fiber bundle 5 while diverged from a bundling part L01 into light beams L1, L2-Ln through the lens 2. Those light beams are converged at a bundling part L02 again and projected dispersedly to output terminals L1OUT-LnOUT, entering a lens 3. The projected light from the lens 3 is coupled with an output optical fiber 4 and transmitted. In this case, respective optical fibers L1-Ln are slightly different in length, so the projected light beams are slightly out of phase with one another; even when the emitted light of the LD1 has good coherence, the light incident to the optical fiber 4 has no coherence.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field of the Invention The present invention relates to a fiber optic that can reduce the coherence of light transmitted within an optical fiber when transmitting light generated by a laser diode (hereinafter referred to as LI) to an optical fiber. The present invention relates to a coherence reduction device within.

Conventional technology and problems When modulating the light of a light source to generate modulated light and using it for purposes such as communication, an analyzer 1 that changes the light intensity according to the signal strength
Although there are a cog modulation force type and a digital modulation type that changes the light intensity in a binary manner, the analog modulation type has a simple device and is suitable for use in simple communication devices.

As a light source for generating modulated light in analog modulation method,
There are light emitting diodes (hereinafter referred to as LEDs) and laser diodes (hereinafter referred to as LDs), but LI) has the advantage of being able to modulate at a higher speed than LEDs, and has a higher light intensity and can also be transmitted over long distances. has.

Further, optical fibers used as optical signal transmission lines include multimode optical fibers and single mode optical fibers, but multimode optical fibers are exclusively used for subscriber system transmission lines. In the case of a multimode optical fiber, if the coherence of the transmitted light is good, interference will occur between the low-order mode light and the high-order mode light, resulting in a partial intensity distribution of the transmitted light within the fiber core cross section. This generates a so-called speckle pattern, which causes noise, that is, modal 7 noise, to the analog-modulated light, and also causes distortion.

On the other hand, it is known that the LD used as a light source for generating modulated light generates light with good 1-heherence.
In the analog modulation multimode optical fiber transmission line using D as a light source, it is difficult to prevent the occurrence of modal noise and distortion based on the speckle pattern as described above.

Purpose of the Invention The present invention solves the problems of the prior art such as -)
The purpose is to provide a device that can reduce the occurrence of modal noise and distortion in an analog modulation multimode optical fiber transmission line using an LD as a light source. .

Composition of the invention In order to achieve the above object, the present invention provides a light source glue.

A large number of different bundles are provided between D and the output optical fiber -C:? 1. Optical fiber transmission line when C analog modulation is performed using LD. This is designed to reduce the occurrence of modal 7 noise and distortion.

EMBODIMENT OF THE INVENTION The figure shows the configuration of an embodiment of the in-fiber coherence reducing device of the present invention. In the figure, 1 is I, D,
2 is a first lens, 3 is a second lens, and 4 is an output optical core. LI +L2 +-+Ln are optical fibers having different lengths, and these form a fiber bundle 5, 141 IN +1.21
N+"'+I, nlN and L fUT' L 2),
, T'"" Ln+, + are respectively optical core Shiba L
1. L2. −1Ln input and output terminals, Lol,
Lo2 is a collection part of optical fibers.

In the figure, the light beam L D 10 is generated and passes through the lens 2 to the input end LI of each optical core 1° C forming the fiber bundle 5.
INI L21N+"'+Ln Input into IN. Each input terminal 1, l IN I 1.+ 2 IN! -"
+'Ln 1h+ is disposed at an angle suitable for receiving and receiving the incident light from the convergence part LoI and from the lens 2, so that the light from lens 2 is efficiently transmitted to each optical fiber L, , L2,−,l,n, and are distributed and transmitted. The light that has been distributed and transmitted to each optical fiber is collected at the collecting section Lo2, and then is returned to each output "I"'OUT' 26..1+ "' + Ln5
The light is dispersed into the ur, exits, and enters the lens 3. Each output end of the optical fiber is arranged at an angle suitable for inputting the respective output light into the lens 3. Therefore, the output light of each optical fiber is efficiently coupled to the lens 3, and the output light of the lens 3 is is coupled to and transmitted to the output optical fiber 4.

At this time, each of the optical fibers I and +12 +-In is configured to have slightly different lengths, so that the light incident on each input end Ll+11+L2n++'-'In IN becomes an output Ha' l lli'T ＋”
2117 +-' + L n When outputting to luT, the respective phases are slightly different.

Therefore, even if the coherence of the light generated by the LDI, which is the light source, is good, the output terminal L + bvT + L 2ovv
-+ The light that enters the lens 3 from Lnour has received different delays, and these lights enter the lens 3.
When the transmitted light is transmitted to the optical core IHA 4, the transmitted light has no coherence. In addition, optical fiber L+
1121-, Ln may be simply bundled together at the collecting parts Lo11 LO2 to form a handle fiber, or may be integrated to form a single core at each collecting part to form a star coupler. (The configuration between the input and output terminals is free.

DETAILED DESCRIPTION OF THE INVENTION As described in detail, the in-fiber ':1 Heellen reduction device of the present invention provides a plurality of different lengths between a laser diode and an output optical fiber that transmits the output light of the laser diode. Since a fiber bundle is provided, which is a collection of optical fibers, even if the light generated by the light source has good coherence, the coherence in the output light can be reduced. It is extremely effective because it is possible to prevent the occurrence of distortion and distortion due to the formation of a speckle pattern in the fiber when transmitting to the fiber.

[Brief explanation of drawings]

The figure is a diagram showing the configuration of an embodiment of the in-fiber coherence reducing device of the present invention. 1: Laser diode (1, D), 2: First lens,
3: Second lens, 4: Output optical fiber, 5-fiber bundle, 1.112 + ”-+I-n: Optical fiber patent applicant Fujitsu Limited representative Patent attorney Gobe Tamamushi (13 people in the evening) 53-

Claims (1)

[Claims] A fiber bundle made up of a large number of optical fibers having different lengths is provided between the L. A device for reducing coherence within a fiber, characterized in that output light entering an input end of the fiber bundle and exiting from an output end is combined and transmitted to an output optical fiber.