JPH01183622A - Optical fiber type polarized light beam splitter - Google Patents

Abstract

PURPOSE:To attenuate an unnecessary polarized wave and to obtain a splitter of a high quenching ratio by constituting the splitter so that in two emitting ports of a coupler, as for one of them, a slow axis is allowed to coincide with a transmission axis of an optical fiber type polarizer, and the other is allowed to be orthogonal to the transmission axis. CONSTITUTION:When a light beam which is polarized in the long axis direction of an elliptical jacket 12 is made incident on an incident port 4 of a direction coupler 1, since the polarized wave of an output port 6 of transmission side coincides with a transmission axis of a polarizer 2, it passes it through at a low loss, and emitted from an emitting port end 8. On the other hand, a polarized wave of an emitting port 7 of a coupling side coincides with a jacket short axis and goes to orthogonal to the transmission axis, therefore, attenuated and not emitted from an emitting end 9. In the same way, when a light beam which is polarized in the short axis direction of the jacket 12 is made incident on the port 4, it is not emitted from the output end 8 but emitted from the output end 9 without being attenuated. In such a way, an unnecessary polarized wave from the emitting port is attenuated and a polarization beam splitter of a high quenching ratio is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical fiber type polarizing beam splitter using a polarization maintaining optical fiber.

[Prior Art] Conventionally, most polarizing beam splitters that separate incident light into two orthogonal polarization components are of the bulk type.

As for the fiber type, as shown in Fig. 6, there is a polarizing beam splitter (Yokohama, et al. [Fiber type polarizing beam splitter J 0QE8
5-15PP, 19-24°1985). This is a fusion-stretched type in which two polarization-maintaining optical fibers 21 are fused and stretched, and the length of the optical coupling part (Taber region part) 22 is adjusted to perform polarization separation. It is. The length of this Taber region portion 22 depends on the mode birefringence B of the polarization maintaining optical fiber 21, and the larger B is, the shorter the length of the Taber region portion 22 is.

[Problems to be Solved by the Invention] Bulk type polarizing beam splitters have problems in coupling with optical fibers. In other words, it is difficult to make the entire system compact because the snout beam must be spread in space using a lens or the like. Furthermore, since a dielectric multilayer film is inserted between two right-angled prisms and bonded together with an optical bond, there is a reliability problem in that the bonding can be removed at high and low temperatures.

A fusion-stretched polarizing beam splitter using a panda-shaped polarization-maintaining optical fiber 21 is a 3D beam splitter with a normal branching ratio of 50%.
Unlike the B coupler, it is necessary to determine the length of the Taber region 22 depending on the mode birefringence B. For this reason, there are problems such as the fact that a normal 3 dB coupler cannot be used and there are difficulties in mass production.

SUMMARY OF THE INVENTION An object of the present invention is to provide a reliable and durable optical fiber polarizing beam splitter.

[Means for Solving Problem 81] In the optical fiber type polarizing beam splitter of the present invention, one of the two output ports of a polishing type directional coupler using a polarization maintaining optical fiber is The output port is connected with its axis aligned with the transmission axis of an optical fiber polarizer using a polarization maintaining optical fiber, and the other output port is connected with its slow axis perpendicular to the transmission axis of the optical fiber polarizer. be.

[Function] Light incident from one of the input ports of a polishing type directional coupler is split into two output ports, one on the transmission side and one on the coupling side of that input port. The axis is aligned with the transmission axis of the optical fiber type polarizer, and the slow axis of the other output port is perpendicular to the transmission axis of the optical fiber type polarizer, so unnecessary polarized waves from each output port are transmitted through the optical fiber type polarizer. It is attenuated by a polarizer and becomes a polarizing beam splitter with a high extinction ratio.

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

FIG. 1 shows the configuration of a polarizing beam splitter using an elliptical jacket type polarization maintaining optical fiber.

The optical fiber type polarizing beam splitter consists of a polishing type directional coupler 1 and optical fiber type polarizers 2.2 connected to its two output ports 6.7, respectively. Reference numeral 3 indicates a connection portion by fusion bonding or the like.

As shown in FIGS. 1 and 2, the polishing type directional coupler 1 includes an elliptical jacket type polarization maintaining optical fiber 11 placed in a curved groove formed in a quartz substrate 10 in the long sleeve direction of the elliptical jacket 12. After inserting and fixing the quartz substrate 10 so that it is perpendicular to the surface of the quartz substrate 10, the quartz substrate 10 is polished to the vicinity of the core 13, and the polished surfaces of the two quartz substrates 10 thus prepared are joined. It is. 4.5 is an input port of the polishing type directional coupler 1, and 6.7 is an output port, which is a normal 3 dB cup with a branching ratio of 50%. The polarization maintaining optical fiber 11 has a four-layer structure including a core 13, a cladding, an elliptical jacket 12, and a support 14, but the cladding is included in the elliptical jacket 12 and omitted to simplify the drawing. Polarization maintaining optical fibers include not only elliptical jacket type fibers but also elliptical clad type fibers.

The optical fiber polarizer 2 is made by winding a polarization-maintaining optical fiber 11 (or an absolutely single polarization-maintaining optical fiber) so that it operates in an absolutely single motion. Only polarized light is transmitted.

At the output port 6, as shown in FIG. ) and connect. On the other hand, at the exit port 7, the length of the elliptical jacket 12 @ (slow axis)
are connected perpendicularly to the long axes (transmission axes) of the elliptical jackets i to 12 of the optical fiber polarizer 2.

As shown in FIG. 3, light (X polarization) polarized in the long axis direction of the elliptical jitocket 1 enters the input port 4 of the directional coupler 1.
When the beam is incident, the X-polarized waves are equally divided into the output ports 6 and 7, respectively. Output port 6 on the transmission side of input port 4
Since the X-polarized wave that came to coincides with the transmission axis of polarizer 2,
The light passes through the polarizer 2 with low loss and is emitted from the output port end 8. On the other hand, the X-polarized wave arriving at the output port 7 on the coupling side of the input port 4 coincides with the short axis of the elliptical jacket of the polarizer 2 and is perpendicular to the transmission axis (long axis of the elliptical jacket), so the polarized light The light is attenuated within the child 2 and is not emitted from the output end 9.

Similarly, as shown in FIG. 4, when light polarized in the short axis direction of the elliptical jacket 12 (Y polarization) enters the input port 4, the Y polarization at the output port 6 is attenuated by the polarizer. However, the Y polarized wave from the output port 7 is hardly attenuated by the polarizer 2 and is output from the output end 9.

Furthermore, as shown in FIG. Depending on the fiber length of the optical fiber 11, the light is circularly polarized or linearly polarized, but the optical fiber polarizer 2,
According to the transmission axis 2, xN waves are emitted from the output end 8, and Y-polarized waves are emitted from the output end 9.

We actually fabricated a prototype polarizing beam splitter using an elliptical jacket type polarization-maintaining optical fiber. Polished directional coupler 1 has an extinction ratio of -20 dB (all ports) and an excess loss of 0.2.
dB, and the optical fiber type polarized light has an extinction ratio of -47 dB.
, the insertion loss is 0.3 dB.

The characteristics of the obtained polarizing beam splitter are that the insertion loss is
Both polarization and Y polarization are 3.5 dB, extinction ratio is 141 dB,
The separation ratio was 1=1 (light output ratio at the output end 8.9 when a 45° linearly polarized wave was incident on the input port 4).

[Effects of invention According to the present invention, the following excellent effects are exhibited.

(1) Since it is an optical fiber type directional coupler using a polarization maintaining optical fiber, it is easy to couple with the optical fiber and a highly reliable polarizing beam splitter can be obtained.

(2) Since a normal 3 dB polished directional coupler can be used, it is suitable for mass production and can reduce cost.

(3) Since unnecessary polarized waves are attenuated by the optical fiber polarizer, a polarizing beam splitter with a high extinction ratio can be obtained. Therefore, it is possible to improve the functionality of a system using this polarizing beam splitter.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram showing an embodiment of the optical fiber type polarizing beam splitter of the present invention, FIG. 2 is an enlarged cross-sectional view of a polishing type directional coupler used in the polarizing beam splitter, and FIG. 4 and 5 show the input port of the polished directional coupler of FIG. 1 at 0° with respect to the long axis of the elliptical jacket. Fig. 6 is a perspective view of a conventional optical fiber type polarizing beam splitter. In the figure, 1 is a polishing type directional coupler. , 2 is an optical fiber type polarizer, 3 is a connection part, 4.5 is an input port, 6.7 is an output port, 8 and 9 are output ends, 10 is a quartz substrate, 11 is a polarization-maintaining optical fiber, and 12 is a polarization-maintaining optical fiber. Oval jacket, 13 is core,
14 is a support, 21 is a polarization maintaining optical fiber, and 22 is a tapered region.

Claims (1)

[Claims] 1. Of the two output ports of a polished directional coupler using a polarization-maintaining optical fiber, one output port has its slow axis aligned with the transmission axis of the optical fiber polarizer using a polarization-maintaining optical fiber. 1. An optical fiber type polarizing beam splitter, characterized in that the other output port is connected with its slow axis orthogonal to the transmission axis of the optical fiber type polarizer.