JPH01167722A - Optical isolator type optical demultiplexer - Google Patents

Abstract

PURPOSE:To demultiplex light beams which have the same wavelength and deviate slightly from center wavelength by projecting an incident polarized wave which is perpendicular to the carrying direction of a polarization beam splitter at right angles to incident light, and scattering or absorbing this projection light and performing operation as a polarizer. CONSTITUTION:Light which is incident from a point (a) enters the polarization beam splitter 8, which passes only polarized light in a constant direction from the incident light, e.g. vertical polarized light selectively. Then its projection light is incident on a Faraday rotator FR to generate projection light whose polarization direction rotates by 45 deg.. When the light which rotates by 45 deg. is incident on the Faraday rotator FR from a point (b), the projection light of the Faraday rotator FR for the 45 deg. rotation of the plane of polarization becomes perpendicular to the polarizing direction of the polarization beam splitter 8 because of the relation between a magnetizing direction and the Faraday rotator, and the light is projected at right angles to the direction of transmitted polarized light. Consequently, this demultiplexer functions to demultiplex light beams which have the same wavelength and deviate slightly from the center wavelength.

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention is an optical system that has the function of separating light propagating in opposite directions on the same optical path in bidirectional optical communication or when light propagates in both directions. This invention relates to an isolator-type optical demultiplexer.

[Conventional technology]

Bidirectional optical communication using a single optical fiber is currently carried out using light having significantly different wavelengths on the transmitting and receiving sides.

FIG. 4 shows an example of the basic configuration of a conventional optical multiplexer/demultiplexer. The optical multiplexer/demultiplexer in the same figure is an electrostatic multilayer filter 1.
, 3.4 and a prism 2.

The 1.2μ- input light from a passes through the 1.2μ- bandpass filter 1, passes through the prism 2, and is output in the direction b as a common output. When light of 1.3 μm is incident on prism 2 from direction b, it is reflected by 1.2 μm band pass filter 1, and even with low pass filter 3 of 0.8 μm, [t
L, 1.3μ of the light passes through the bandpass filter 4 and is output in the c direction, where the light is demultiplexed.

[Problem that the invention seeks to solve]

However, the dielectric filter described above has a narrow wavelength range and can only separate light with significantly different wavelengths, so there is a problem that it cannot separate light of the same wavelength or light slightly shifted from the center wavelength.

The purpose of the present invention is to provide an optical fisolator-type optical demultiplexer that has the functions of two-way coherent optical communication and an optical demultiplexer and optical isolator that demultiplexes light having the same wavelength or a slight deviation from the center wavelength. It is to provide.

[Means for solving problems]

In order to achieve the above object, the present invention has a J or 7T Rade single rotor disposed in the center of a hollow magnet magnetized in the direction of propagation of light, and a polarizing beam splitter disposed on the incident side of the light. or a configuration including a polarizer and an analyzer consisting of a polarizing beam splitter placed on both sides of a Faraday beam splitter, and one of the optical axes in the transmitted polarization direction of each polarizing beam splitter on the incident side is One of the end faces of the polarization beam splitter in the direction in which polarized light perpendicular to the transmitted polarized light is separated, that is, the direction perpendicular to the transmitted polarized light optical axis, is used as the input end face and is used as the reverse light output side.

FIG. 5 shows an example of the configuration of a conventional optical fisulator.

In the figure, light incident from point a is converted into parallel light by a lens 5, and then enters a polarizer P1. The polarizer P selectively passes only polarized light in a certain direction, for example, vertically polarized light, from the incident light.

The light emitted from the polarizer P1 is Y I G (Y so x-F
7 Alade per rotation 1,000 FH made by applying a magnetic field to a single crystal such as an oxide whose main component is
, and produces an output light whose polarization direction is rotated by 45 degrees.

Normally, in a 7-Alade single rotor FH, YIG is placed at the center of a cylindrical magnet 7 magnetized in the rotation direction as shown in the figure, and is magnetized in a direction substantially parallel to the YIG.

The emitted light from the 7-Alade single rotator FR enters the analyzer P2, but the polarization direction of the analyzer P2 is tilted by 45 degrees from the vertical direction.

Therefore, the light incident from the 772D single rotator FR passes through the analyzer P2 as it is and exits, and passes through the lens X6 and then b
Produces output converged to a point.

Therefore, for example, by placing the end of the optical 7-eyeper at point b, it is possible to couple the light incident from point a to the optical fiber.

On the other hand, the reflected light generated by the aforementioned optical 7 fiper etc.
From point b, the component light passes through lens 6 and enters polarizer P2 (acted as an analyzer last time), and the component light that matches the polarization direction of polarizer P2 passes through polarizer P2 and enters Matsuko FR once in 77 frames. do.

As is well known, in the 77 Alade single rotator FR, the direction of rotation of the plane of polarization changes depending on the relationship between the incident direction of light and the magnetization direction of the 77 F1 rotator material.

In this case, the position of the arrangement 'PIA system is rotated by 45 degrees in the same direction as the incident light, so the polarization direction of the output light of the 7 Alade rotator FR is the analyzer P (acted as a polarizer last time).
perpendicular to the direction of propagation. Therefore, the incident light from the 7-Alade one-shot FR is blocked by the analyzer P and is not propagated to the side a.

Therefore, the reverse intrusion that couples to the semiconductor laser placed at point a is prevented, and deterioration of the S/N in the semiconductor laser is prevented.

When the above polarizer and analyzer are used as a polarizing beam splitter, the incident polarized light in the direction perpendicular to the propagation direction of the polarizing beam splitter is output in the direction perpendicular to the incident light. By scattering or absorbing this emitted light, it acts as a polarizer and becomes an optical fisolator.

〔Example〕

Hereinafter, the present invention will be explained in more detail using Examples.

FIG. 1 shows the basic configuration of the present invention.

In the figure, light incident from point a enters the polarizing beam splitter 8. The polarizing beam splitter 8 selectively passes only polarized light in a certain direction, for example, vertically polarized light, from the incident light. The output light from the polarizing beam splitter 8 is incident on the 7-Alade single rotator FH, producing output light whose polarization direction has been rotated by 45 degrees. The 7-Alade rotor FR is placed at the center of a cylindrical magnet 9 that is magnetized in the direction of the rotation axis as shown in the figure, and is magnetized substantially parallel to the optical path.

When light softened by 45° from point b enters the 77-Fude rotator FH, the polarization plane further rotates by 45° due to the relationship between the magnetization direction and the Faraday rotation.
The emitted light is perpendicular to the polarization direction of the polarization beam splitter 8, and is emitted in a direction perpendicular to the transmitted polarization direction.

In FIG. 1, by setting a to the input side, b to the bidirectional propagation side, and C to the output light side, it operates as an optical demultiplexer depending on the polarization direction.

Since the polarization direction is fixed, the sufficient polarization device of the present invention uses a polarization maintaining fiber on the side b in FIG.
By arranging a polarizer to operate as an optical isolator as shown in the figure, it can have the functions of an optical isolator and an optical demultiplexer.

In addition, in order to obtain the high isolation a required for coherent optical communication, two or more optical isolators are connected in series in the vertical direction as shown in Figure 3 to achieve high isolation and optical demultiplexing. and can be made possible,
Bidirectional communication in coherent optical communication is possible.

〔Effect of the invention〕

According to the present invention, since it is possible to demultiplex the same wavelength or light slightly shifted from the center wavelength, which was insufficient in conventional two-way optical communication, etc., coherent optical communication and two-way communication using the same wavelength can be achieved. can.

[Brief explanation of the drawing]

Figure 1 is a basic configuration diagram of the present invention, Figure 2 and tIS3 are configuration diagrams of embodiments of the present invention, Figure 4 is a basic configuration diagram of a conventional optical multiplexer/demultiplexer, and Figure 15 is a diagram of a conventional optical isolator. FIG. 9, 12, 17, 18: Cylindrical magnet,
8.10, 11, 13.14. ．． 15, 16: Polarizing beam splitter, FR: Faraday rotator Agent Patent attorney Takashi Honma 2 Figure 9, /2 /7. Ill: )”i tube ken senseki 8.
10. //, 13. /J, f5. /6: aK Beams f'Jtsu 9FR: Faraday Painter

Claims (2)

[Claims] (1) A Faraday rotator placed in the center of a hollow magnet magnetized in the direction of the main optical axis, and a polarizing beam splitter placed on both sides or one side of the Faraday rotator, which allows light to be transmitted in one direction along the main optical axis. When the light is incident from the opposite direction, the light is allowed to pass with low loss, and when the light is incident from the opposite direction, it is separated in the direction perpendicular to the main optical axis by at least one of the polarizing beam splitters, and the light is separated in the direction perpendicular to the main optical axis. An optical isolator-type optical demultiplexer characterized by comprising an optical means for guiding separated light as a signal. (2) The optical isolator type optical demultiplexer according to claim 1, characterized in that one or more isolators are provided in the direction of the main optical axis before and after the optical demultiplexer. Isolator type optical demultiplexer.