JPS61185707A - Device for connection between semiconductor laser and polarization plane maintaining optical fiber - Google Patents

Abstract

PURPOSE:To obtain a high-quality light source of high extinction ratio by separating and condensing only a linearly polarized light of the oscillated light of a semiconductor laser and connecting this light in accordance with the axis of polarization peculiar to a polarization plane maintaining optical fiber by a lens system including a convex lens consisting of a uniaxial crystal. CONSTITUTION:A polarizer is constituted with a lens 12 consisting of the uniaxial crystal which is so formed that the convex lens function is attained, and an optical axis 13 peculiar to this crystal is set at an angle other than right angles to the optical path of the oscillated light in a plane perpendicular to or parallel with the linearly polarized light of the oscillated light of a semiconductor laser 11, and only ordinary rays are condensed selectively when the optical axis is in the plane perpendicular to the linearly polarized light, and only extraordi nary rays are condensed selectively when the optical axis is in the plane parallel with the linearly polarized light, and thereby, only the linearly polarized light of the oscillated light of the semiconductor laser 11 is connected in accordance with the axis of polarization peculiar to a polarization plane maintaining optical fiber 15 by the lens 12. By this constitution, a high extinction ratio is attained, and the polarizer is made small-sized and low-cost because the lens 12 consisting of the uniaxial crystal is used as the polarizer. Further, this device can be used to obtain a light source of high quality used in optical fiber metrology engineer ing, coherent optical communication, etc.

Description

Detailed Description of the Invention Field of the Invention The present invention relates to a semiconductor laser polarization maintaining optical fiber coupling device for coupling a semiconductor laser to a polarization maintaining optical fiber with good polarization characteristics.

2. Description of the Related Art Conventionally, an optical fiber having a cross-sectional shape as shown in FIG. 3 is called an elliptical jacket type polarization-maintaining optical fiber, and is an example of a polarization-maintaining optical fiber. In FIG. 3, 1 is a core, 2 is a cladding, 3 is an oval jacket, and 4 is a support. In a polarization-maintaining optical fiber having such a configuration, the short axis and long axis of the elliptical gear are called intrinsic polarization axes, and the linearly polarized light components of Ex mode and Ey mode incident in these directions are preserved. To combine the polarization-maintaining optical fiber described above with the linearly polarized light emitted from the semiconductor laser,
It is necessary to align the incident linearly polarized light with the unique polarization axis of the polarization-maintaining optical fiber, and in order to obtain a high extinction ratio of -30 dB or more, it is necessary to precisely align it within about 2 degrees, so the semiconductor laser is fixed. After that, either rotate the polarization preserving optical fiber to align the polarization axis, or
As shown in the figure (=), the oscillation light of the semiconductor laser 5 is focused by a rod lens 6 onto a connector-type polarization-maintaining optical fiber 8 attached to the receptacle. The polarization axis is aligned with high precision by a rotatable and adjustable wavelength plate 9 provided in between, and it is ideal that the oscillation light of the semiconductor laser 6 normally contains only linearly polarized light parallel to the active layer. However, since there is actually a small amount of linearly polarized light perpendicular to the active layer, when coupled to the polarization maintaining optical fiber 8, the extinction ratio deteriorates and the S/N of the signal decreases.
In order to remove the linearly polarized light perpendicular to the linearly polarized light of the oscillation light of the semiconductor laser 6, a polarizer 10 (polarizing beam splitter) is installed between the rod lens 6 and the wavelength plate 9, as shown in FIG. 4(b). In other words, a semiconductor V-the polarization maintaining optical fiber coupling device is provided with a polarization prism (for example, Japanese Patent Laid-Open No. 59-28116).

Problems to be Solved by the Invention However, in the configuration shown in FIG. A semiconductor laser polarization-maintaining optical fiber coupling device that uses the polarizer to remove linearly polarized light perpendicular to the linearly polarized light of the oscillated light of the semiconductor laser, efficiently couples only the linearly polarized light of the oscillated light, and obtains a high extinction ratio. is intended to provide.

Means for solving the problem The technical means of the present invention for solving the above problem is to configure the polarizer with a lens made of a uniaxial crystal having a shape that provides a convex lens function, and to adjust the optical axis unique to this crystal. is set at an angle that is not perpendicular to the optical path of the oscillated light in a plane perpendicular or parallel to the linearly polarized light of the oscillated light of the semiconductor laser, and when the optical axis is in the perpendicular plane, only the ordinary light is transmitted. By selectively focusing only the extraordinary light when it is in parallel planes, only the linearly polarized light of the semiconductor laser's oscillation light is coupled with the lens system in alignment with the unique polarization axis of the polarization-maintaining optical fiber. .

According to the above-described configuration, the present invention uses a lens system including a convex lens made of uniaxial crystal to separate and focus only the linearly polarized light of the oscillated light of the semiconductor laser, and combines the linearly polarized light of the oscillated light of the semiconductor laser in alignment with the inherent polarization axis of the polarization-maintaining optical fiber. This makes it possible to obtain a high extinction ratio, and since the polarizer is a lens made of uniaxial crystal, it is small and inexpensive.

Embodiment FIG. 1 is a diagram showing the basic configuration of an embodiment of a semiconductor laser polarization-maintaining optical fiber coupling device of the present invention. In FIG. 1, 11 is a semiconductor laser, 12 is a ball lens made of uniaxial crystal, and 13 is a ball lens 12 made of uniaxial crystal.
14 is a rod lens, and 15 is a polarization maintaining optical fiber.

FIG. 2 is an explanatory diagram of a uniaxial crystal. 16 is a light source,
17 is a parallel plate uniaxial crystal, 1st is the optical axis of the uniaxial crystal 17, 19 is ordinary light, and 20 is extraordinary light. First, using FIG. 2, the ordinary light 19 and the extraordinary light 2 due to the uniaxial crystal 17 are
The separation of o will be explained. Optical axis 1 of uniaxial crystal 17
If 8 is within the plane of the figure and is tilted by θ with respect to the optical path of the light emitted from the light source 16, the polarized light component (marked with ○ in the figure) perpendicular to the plane of the paper of the light emitted from the light source 16 becomes ordinary light 19 and travels straight. The parallel polarization component (marked 1 in the figure) is abnormal H.

Then, in the uniaxial crystal 17, the light is emitted as parallel light that is tilted by α with respect to the incident plane and separated by d as shown in the following equation.

Here, t is the thickness of the uniaxial crystal 17 in the optical path direction, and n
o, n, l″i are the ordinary lights of the uniaxial crystal 17, respectively.

This is the refractive index for extraordinary light. For example, if a rutile crystal (T 102 ) is used as the uniaxial crystal, d=100 μm for light with a wavelength of 1.3−1 at t=1 yas and θ=48°.

Next, the principle of the semiconductor laser polarization-maintaining optical fiber coupling device shown in FIG. 1 in which the uniaxial crystal 17 is used as the ball lens 12 will be explained. Here, it is assumed that the linearly polarized light of the semiconductor laser 11 is perpendicular to the plane of the paper. When using a uniaxial crystal ball lens, assuming that the optical axis 13 is within the plane of the paper in Figure 1 as in Figure 2, the positional deviation d between the ordinary and extraordinary rays is more complicated than equation (1) in the case of a parallel plate. This is comparable to the case of a parallel plate having the same thickness as the diameter of the ball lens 12. Moreover, since it is a spherical lens, the ordinary light and extraordinary light of the light emitted from the uniaxial crystal ball lens 12 are not parallel as shown in FIG. When θ = 48° with a 1-diameter spherical lens made of rutile crystal, the positional deviation and angular deviation of the ordinary and extraordinary rays are each approximately 1o.
○μm, approximately several degrees. Since the linearly polarized light of the oscillated light from the semiconductor laser 11 is perpendicular to the entire paper surface, the linearly polarized light of the oscillated light becomes ordinary light as shown in FIG. 2 and is coupled to the polarization-maintaining optical fiber 16 through the rod lens 14. .

Furthermore, the linearly polarized light component perpendicular to the linearly polarized light of the oscillated light slightly contained in the oscillated light of the semiconductor laser 11 causes deterioration of the S/N ratio and decrease of the extinction ratio as described in the conventional example, but the uniaxial The crystal ball lens 12 generates extraordinary light, and the core diameter of the polarization-maintaining optical fiber 15 (
The light is focused at a position separated by at least 6 to 10 μm (usually 6 to 10 μm) and is not coupled to the polarization-maintaining optical fiber 16. As can be seen from equation (1), when the optical axis is perpendicular to the optical path in the plane of the paper, θ = 9o0 and d = Q. Both the ordinary light and the extraordinary light travel straight, and the oscillation light of the semiconductor laser 11 is linearly polarized. Both the light beam and the slightly included linearly polarized component perpendicular thereto are coupled to the polarization maintaining optical fiber 16, resulting in deterioration of the S/N ratio and reduction of the extinction ratio.

Furthermore, if the optical axis 13 of the uniaxial crystal lens 12 is set at a position not perpendicular to the optical path of the oscillated light within a plane parallel to the linearly polarized light of the oscillated light of the semiconductor laser 11, the semiconductor laser 11
The linearly polarized light of the oscillated light becomes extraordinary light, and the linearly polarized component perpendicular to it becomes ordinary light.

In this case, the extraordinary light is focused and coupled to a polarization maintaining optical fiber.

The optical axis 13 of the uniaxial crystal ball lens 12 is connected to the semiconductor laser 1
When selectively coupling only the linearly polarized light of the oscillated light by setting it in a plane perpendicular or parallel to the linearly polarized light of the oscillated light of the semiconductor laser 11, the optical path of the oscillated light of the semiconductor laser 11 and the optical axis 13
The angle θ formed by the uniaxial crystal ball lens 12 is determined according to the material and diameter of the uniaxial crystal ball lens 12, the focal length of the rod lens, etc., within a range in which the linearly polarized light component perpendicular to the linearly polarized light of the oscillation light is not coupled to the polarization preserving optical fiber 16. Ru. Here, a spherical lens is used as the convex lens of the uniaxial crystal, but a shape having a convex lens function that can obtain the same effect can also be used. It is also possible to add a final junction with a polarization maintaining optical fiber.

Effects of the Invention As described above, according to the present invention, it is possible to reduce the size and cost, and also improve the phase and polarization of light.

Optical fiber measurement technology using optical interference, high quality,
This makes it possible to create high-quality light sources for use in coherent optical communications, which are expected to provide large-capacity, long-distance transmission.

[Brief Description of the Drawings] Fig. 1 is a diagram showing the basic configuration of a semiconductor laser polarization-maintaining optical fiber coupling device in an embodiment of the present invention, Fig. 2 is a diagram illustrating the function of a uniaxial crystal, FIG. 3 is a cross-sectional view of a general elliptical jacket type polarization-maintaining optical fiber, and FIGS. 4(a) and 4(b) are perspective views showing the schematic structure of a conventional semiconductor laser polarization-maintaining optical fiber coupling device. 11... Semiconductor laser, 12... Uniaxial crystal ball lens, 13... Optical axis, 15...
...Polarization maintaining optical fiber. Name of agent: Patent attorney Toshio Nakao (1st person)
Figure 3 Figure 4 Figure 4

Claims (1)

[Claims] A semiconductor laser and a lens system for coupling linearly polarized light of oscillation light of the semiconductor laser to a polarization maintaining optical fiber include a lens made of a uniaxial crystal having a shape that provides a convex lens function, and the lens made of the uniaxial crystal has a shape that provides a convex lens function. , the optical axis specific to the crystal is located at an angle that is not perpendicular to the optical path of the oscillated light of the semiconductor laser in a plane perpendicular to the direction of linearly polarized light of the oscillated light of the semiconductor laser or in a plane parallel to the direction of the linearly polarized light of the oscillated light of the semiconductor laser. What is claimed is: 1. A semiconductor laser polarization maintaining optical fiber coupling device, characterized in that the device is configured to