JPH06308428A - In-line type optical isolator - Google Patents

Abstract

PURPOSE:To facilitate assembling, to reduce a connection loss, to enhance a reliability and to ease the miniaturization by integrally constituting the incident side optical parts with an optical element provided with an optical multiplex function, an exciting light source coupling function and a filtering function. CONSTITUTION:This isolator is an in-line type optical isolator for optical amplifier integrating the optical multiplex function, the filtering function, etc., with the in-line type optical isolator. This isolator consists of the incident side optical components consisting of lenses 2a, 2b, 2c, the optical multiplex function consisting of a wavelength selection filter 4, the exciting light source connection function consisting of an exciting light source connecting polarizing beam splitter 3e placed on the optical path of the exciting beams 1b, 1c, and the filtering function consisting of a low pass filter 7. Then, an incident beam 1a and the exciting beams 1b, 1c are multiplexed. The beam 1a with a wavelength lambda1 is totally transmitted, and the beams 1b, 1c with the wavelength lambda2 is reflected by the wavelength selection filter 4 (lambda1>lambda2). The multiplexed beam is made incident on the isolator to arrive at a connection lens 2d in an output part.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polarization-independent optical isolator used in optical communication for removing return light caused by reflection and dispersion of signal light in a network and an optical fiber amplifier.

[0002]

2. Description of the Related Art Conventionally, an optical isolator of this type is used, for example, in a network using an optical fiber in which the polarization direction of transmitted light varies, or between fibers in an optical fiber amplifier as shown in FIG. It is necessary to have a function that does not depend on the polarization characteristics of incident light. Therefore, the normally incident light is separated into two orthogonal components, and the respective lights pass through the Faraday rotator and are merged.
Usually, a birefringent plate such as rutile or a polarization separation element such as a polarization beam splitter is used as an optical element for separating and merging. Also in the optical fiber amplifier, one or two polarization-independent optical isolators are used to remove the return light due to the amplified light. The amplifier module is constructed by assembling an optical multiplexer / demultiplexer, an optical fiber connecting lens, and a bandpass filter in addition to the optical isolator.

[0003]

However, the conventional technique requires an optical multiplexer / demultiplexer, an optical coupler, a low-pass filter or a band-pass filter in addition to the polarization-independent optical isolator, and many components are used. However, there are problems that it is difficult to integrate, it takes time to assemble each component, it is difficult to miniaturize and integrate due to the large number of components, and the connection loss is large because there are many connecting portions.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to solve these problems of the prior art, and an in-line for an optical amplifier in which an in-line type optical isolator is integrated with an optical multiplexing function, a filter function and the like. 3 is an in-line type optical isolator configured to separate polarized light as shown in FIG. 3 in order to provide a type optical isolator, and an incident side optical component including lenses (2a, 2b, 2c) and a wavelength selection filter. The optical multiplexing function consisting of (4) and the pumping light (1
b, 1c) an in-line optical isolator integrated with an optical element having a pumping light source coupling function consisting of a pumping light source coupling polarization beam splitter (3e) and a filtering function consisting of a low-pass filter (7). Is.

[0005]

Embodiments of the present invention will be described below with reference to the drawings. 1 to 3 are schematic views of the configuration of an embodiment of the present invention, in which the same parts are designated by the same reference numerals. FIG. 1 is a schematic diagram showing a partial structure of an in-line type optical isolator according to the present invention, in which an input / output portion of an incident signal light 1a is integrated using a gradient index lens 2a, and polarization separation is performed by a polarization beam splitter 3a. Each Faraday rotator 5a, 5
It is incident on b. The polarization beam splitter used as the polarizer used here transmits P waves,
The light that passes through the upper stage of the in-line type optical isolator is of the type that reflects S waves, and the polarized beam splitter 3
It is reflected by c, is incident on the lower polarization beam splitter 3d as an S wave, and is totally reflected there.

On the other hand, the S wave reflected at the upper stage in the incident side polarization beam splitter 3a is reflected at the lower stage polarization beam splitter 3b and enters the Faraday rotator 5b. Here, the rotation directions of the upper and lower stages are the same. That is,
The magnetic field application directions are the same. Next, the polarization beam splitter 3d
Is transmitted as a P wave and merges with the S wave from the upper stage. That is, on the emission side, one polarization beam splitter 3
d is enough. Here, as shown in FIG. 2, it is preferable that the polarization beam splitter is composed of polarization beam splitters 3c and 3d rotated by 45 ° in the optical axis direction. However,
At this time, the two optical axes joined by the polarization beam splitter 3d are slightly deviated from each other, so that the lens 2d has a slightly larger aperture.

The return light 9 is split into two orthogonal waves by the polarization beam splitter 3d, and the Faraday rotators 5a and 5b.
After passing through 45 ° rotation at, the incident side polarization beam splitter 3
In a and 3b, the incident light and the crossed Nicols condition are established.
It is radiated to the 0 ° orthogonal side. Therefore, the absorber 1 is
Setting 0a and 10b is good for preventing scattering. With such a configuration, a polarization-independent in-line type optical isolator is realized.

FIG. 2 is a diagram showing a configuration of the in-line type optical isolator according to the present invention using the polarization beam splitters 3c and 3d rotated by 45 ° in the optical axis direction, as viewed from the direction A in FIG. Here, two polarization beam splitters 3c and 3d are used as the incident-side polarization separation elements, but other elements having the same function may be used without any problem, and a birefringent plate such as a rutile crystal may be used. . Further, the magnets 6a and 6b of the Faraday rotator may be integrated into one.

FIG. 3 is a schematic diagram of an integrated module for an optical amplifier according to the present invention. The polarization beam splitter section of the in-line type optical isolator of FIG. LD excitation light 1b,
Lenses 2b and 2c for inputting 1c and a polarization beam splitter 3e for coupling an excitation light source are integrally and closely attached. Thereby, the incident signal light 1a and the excitation lights 1b and 1c are multiplexed. Wavelength selection filter 4 functions as wavelength λ1
Of the incident signal light 1a of
1c is reflected and those lights are combined. (Λ1> λ2)
The combined light enters the in-line type optical isolator described with reference to FIG. 1, and passes through the connecting lens 2d of the output section to
It is incident on the r-doped optical fiber 8 and signal light (wavelength λ
2) is amplified.

The return light 9 is emitted to the outside from the incident side polarization beam splitter surface, as described with reference to FIG. The in-line type optical isolator used here is preferably of a type that covers wavelengths λ1 and λ2. With the above configuration, it can be used as a forward excitation type module. On the other hand, in the case of backward pumping, the light is emitted from the optical multiplexing portion in the opposite direction as shown by 4a and is connected to the Er-doped fiber.

[0011]

As described above, according to the structure of the in-line type optical isolator for the optical amplification module of the present invention,
As the number of parts, it consists of an optical multiplexer integrated with an in-line type optical isolator, a polarization separation element, a low-pass filter, and a connecting lens, which is simple, easy to assemble, and has an integrated structure with little connection loss. It is highly reliable and therefore easy to miniaturize.

[Brief description of drawings]

FIG. 1 is a schematic diagram of an in-line type optical isolator according to an embodiment of the present invention.

FIG. 2 is a schematic view of the embodiment of FIG. 1 viewed from the optical axis side.

FIG. 3 is a schematic diagram of an in-line optical isolator for fiber amplification according to the present invention.

FIG. 4 is a schematic view of a conventional optical fiber amplification module.

[Explanation of symbols]

 1a Incident signal light 1b, 1c Excitation light 2a-2d Lens 3a-3e Polarizing beam splitter 4 Wavelength selection filter 5a, 5b Faraday rotator 6a, 6b Magnet 7 Low pass filter 8 Er-doped optical fiber 9 Return light 10A, 10b Absorber

Claims (1)

[Claims] 1. An in-line type optical isolator configured by separating polarized light, which is integrally formed with an incident side optical component and an optical element having an optical multiplexing function, an excitation light source coupling function, and a filtering function. Optical isolator.