JP2002016308A - Polarized light source device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide two linear polarized light sources wherein beat noise frequency due to interference between output lights can be controlled. SOLUTION: This polarized light source is provided with two light sources outputting linear polarized lights, and a photocoupler which synthesizes the linear polarized lights in such a manner that polarization surfaces of the linear polarized lights are made perpendicular to each other. An optical attenuator is so arranged that intensity of an output light of at least one out of the two light sources is attenuated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser light source whose polarization is controlled, and more particularly to a semiconductor laser-excited solid-state laser light source which emits two linearly polarized lights having slightly different wavelengths and mutually perpendicular polarization planes.

[0002]

2. Description of the Related Art In general, most optical devices used in the field of optical communication and optical measurement have polarization dependence. Therefore, it is preferable to use a polarization maintaining fiber for an optical fiber regardless of the transmission distance. .

However, at least at present, the cost of a polarization maintaining fiber is about ten times the price of a single mode fiber, and especially in a transmission system that requires remote transmission, the cost occupied by the transmission line in the entire system. It is no exaggeration to say that it threatens the existence of the system itself.

On the other hand, when a single-mode fiber is used as the transmission line, fluctuations in the polarization plane cannot be avoided here.
In order to obtain a constant light intensity in a constant polarization direction on the light receiving side, two linearly polarized light sources whose polarization planes are orthogonal to each other are required.

[0005] Against this background, there is a need to pursue economic efficiency, and a method for compensating for the operation disadvantage caused by using a single-mode fiber instead of a polarization-maintaining fiber as an optical transmission line has been studied. Was.

As one of them, a light source as shown in FIG. 2 has been conventionally used (hereinafter, referred to as conventional technology). As shown in FIG. 2, the light sources are two linearly polarized light sources 2.
Polarization maintaining fibers 24 and 25 are provided to connect the optical couplers 1 and 22 and the optical coupler 26, respectively, and light from the optical coupler 26 is guided by a single mode fiber 27.
In FIG. 2, a horizontal arrow indicates light having a horizontal polarization plane, and a vertical arrow indicates light having a vertical polarization plane.

In the light source according to the prior art having such a configuration, the linearly polarized lights emitted from the two linearly polarized light sources 21 and 22 are combined by the optical coupler 26 so that the polarization planes are orthogonal to each other. If an analyzer is added immediately before the optical device connected to the other end of the optical fiber, an effect substantially equivalent to the case where a polarization maintaining fiber is used can be obtained.

FIG. 3 is a diagram showing a schematic configuration of a linearly polarized light source 21 or 22 composed of one semiconductor laser-excited solid-state laser light source constituting the bilinearly polarized light source shown in FIG. The semiconductor laser 8 for excitation, the first optical lens 9 as a convex lens, the optical resonator 14, the second optical lens 13 as a convex lens, and the polarization plane holding fiber 24 or 25 include:
They are provided in order.

The optical resonator 14 is constructed by inserting a solid-state laser crystal as the laser medium 11 between a pair of mirrors 10 and 12 each having a concave surface. That is, this light source is driven by the excitation light of the
In 4, laser oscillation is performed.

Here, the linearly polarized light sources 21 and 22 and the optical coupler 26 and the pair of polarization maintaining fibers 24 and 25 coupled between them are used to convert the outgoing light into two linearly polarized light planes. Since the light is synthesized and emitted so as to be vertical, it may be collectively called a polarized light source device.

[0011]

However, in the case of the light source according to the prior art, it is difficult to control the wavelength of the emitted light of each of the two light sources due to variations in the composition and thickness of the laser medium, and interference occurs between the emitted light. There was a case. In addition, it has been difficult to control the frequency of beat noise due to interference.

An object of the present invention is to solve the above-mentioned problems in the conventional linearly polarized light source and to provide a linearly polarized light source capable of controlling the beat noise frequency due to interference between the emitted lights. is there.

[0013]

In order to solve the above-mentioned problems, a polarized light source device according to the present invention comprises two light sources for emitting linearly polarized light and two linearly polarized light beams emitted from these light sources. A polarized light source device comprising: an optical coupler for vertically combining light, wherein at least one of the two light sources includes a light attenuation mechanism.

Further, the two light sources may be solid-state lasers excited by a semiconductor laser.

Further, even when the values of the drive currents of the pumping semiconductor lasers in the two light sources are set to be different from each other, the intensities of the two linearly polarized light beams having mutually perpendicular polarization planes emitted from the optical coupler are different from each other. It is preferable that the damping amount of the damping mechanism can be set to be equal.

[0016]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows a basic configuration of a polarized light source device according to an embodiment of the present invention. This polarized light source device comprises two linearly polarized light sources 1 and 2 that emit linearly polarized light perpendicular to each other.
And an optical coupler 6 for combining the two linearly polarized lights from the linearly polarized light sources 1 and 2 with their polarization planes perpendicular to each other.
(Attenuation: 0.5 dB), and are coupled by a relatively short polarization maintaining fiber 4, while the linearly polarized light source 2 and the optical coupler 6 are relatively short polarization maintaining fibers without an optical attenuator. 5 are connected. The configuration of the two linearly polarized light sources 1 and 2 is a semiconductor laser pumped solid-state laser, and is the same as that described with reference to FIG. 3 as a conventional example.

In this polarized light source device, the intensity ratio of each polarization axis emitted from the optical coupler 6, that is, the intensity ratio between two polarized lights having polarization planes perpendicular to each other, is made equal by the driving current of the semiconductor laser. Was adjusted.

A single-mode optical fiber of 1 km is connected to the semiconductor laser-excited solid-state laser light source manufactured according to the present embodiment, an analyzer is added to an optical output unit, and the optical output fluctuation with respect to the polarization fluctuation during fiber transmission is measured. After doing
0.5 dB or less, and an effect substantially equivalent to the use of the polarization maintaining fiber was obtained. The beat noise frequency due to the interference between the emitted lights at this time was 1.6 GHz.

Further, the attenuation of the optical attenuator 3 is set to 1 dB,
When adjusted by the drive current of the semiconductor laser to make the intensity ratio of the polarization axes equal, the beat noise frequency due to the interference between the emitted lights is 4.5 GHz.

As described above, the polarized light source device according to the present invention changes the driving wavelength (10 GHz / A) of one of the pumping semiconductor lasers to change the oscillation wavelength,
That is, the beat noise frequency can be easily controlled.

[0022]

As described above, according to the present invention,
In a linearly polarized light source device whose wavelengths are slightly different and whose polarization planes are perpendicular to each other, it is possible to easily control the beat noise frequency, and to easily realize a linearly polarized light source device that can offset the laser medium and thickness variations. Can be manufactured. As a result, it is possible to provide a bilinearly polarized light source capable of controlling the beat noise frequency due to interference between the emitted lights.

[Brief description of the drawings]

FIG. 1 is a diagram showing a basic configuration of a polarized light source device according to one embodiment of the present invention.

FIG. 2 is a diagram showing a configuration of a conventional polarized light source device.

FIG. 3 is a diagram showing a schematic configuration of a linearly polarized light source.

[Explanation of symbols]

 1,2,21,22 Linearly polarized light source 3 Optical attenuator 4,5,24,25 Polarization maintaining fiber 6,26 Optical coupler 7,27 Single mode optical fiber 8 Pumping semiconductor laser 9,13 Optical lens 10, 12 cavity mirror 11 laser medium 14 optical cavity

Claims (3)

[Claims] 1. A polarized light source device comprising: two light sources that emit linearly polarized light; and an optical coupler that combines two linearly polarized light beams emitted from these light sources such that their polarization planes are perpendicular to each other. A polarized light source device, wherein at least one of the two light sources has a light attenuation mechanism. 2. The polarized light source device according to claim 1, wherein said two light sources are semiconductor laser pumped solid-state lasers. 3. When the values of the drive currents of the pumping semiconductor lasers in the two light sources are set differently, the intensities of the two linearly polarized light beams emitted from the optical coupler and whose polarization planes are perpendicular to each other are equal. 3. The polarized light source device according to claim 2, wherein the amount of attenuation of the attenuation mechanism can be set such that the amount of attenuation is adjusted.