JPH0348486B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a novel optical coupling device capable of optically coupling optical signals emitted from two laser light sources to an optical transmission line made of a single mode fiber with low insertion loss.

In optical transmission systems using single-mode optical fibers, semiconductors are mainly used as light sources for transmitting optical signals because the spread of the emitted beam is small and the oscillation wavelength is required to be in the low transmission loss wavelength region of the optical fiber. A laser is used. By the way, in the above-mentioned optical transmission system, when the semiconductor laser incorporated in the optical transmitter or the repeater breaks down or reaches the end of its lifespan, for example, the semiconductor laser in the device must be replaced each time, and the replacement time is short. During this period, there was an inconvenience that the optical transmission would naturally be interrupted.Therefore, in order to eliminate this inconvenience, an extra semiconductor laser was installed.
There is a need for a method to provide a standby semiconductor laser, and when one semiconductor laser fails, to immediately switch to the standby semiconductor laser and optically couple the emitted optical signal to the optical fiber with low insertion loss.

The present invention has been made in view of the above-mentioned conventional points, and provides a novel optical coupling device capable of optically coupling optical signals emitted from two laser light sources to a single mode optical fiber with low insertion loss. . That is, the optical coupling device of the present invention has a refractive index for ordinary light.
n _p , where n _e is the refractive index for extraordinary light, n _e ² −
A birefringent prism formed of a birefringent crystal that satisfies n _p ² > 1, each face of which is parallel to the optical axis of the crystal, and one apex angle formed by the two faces forms the Brieuster angle, and the birefringent prism that forms the Brieuster angle. one side of the
first and second 1/2 wavelength plates, which are provided to face each other on surfaces that do not form a Brieuster angle; and first and second lasers, which are provided to face the first and second 1/2 wavelength plates. by making the polarization direction of the light from the first laser light source perpendicular to the optical axis of the crystal by the first half-wave plate; The light is completely transmitted through the prism, and the second
By making the polarization direction from the laser light source parallel to the optical axis of the crystal by the second 1/2 wavelength plate, the light from the second laser light source is made different from the light from the first laser light source. The laser light source is characterized in that it is reflected at the point of incidence so that the optical axes of the first and second laser light sources are aligned so that they are emitted in the same direction.

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

FIG. 1 is a plan view showing an embodiment of the optical coupling device according to the present invention, and 1 is a birefringent prism, which has a refractive index n _p for ordinary light and a refractive index for extraordinary light as shown in FIG. For example, it is made of a rutile (TiO ₂ ) crystal that satisfies n ² _e −n ² _p > 1, where n _e is It is a triangular prism-shaped birefringent prism in which the angle A forms the Brieuster angle, and for example, among the light incident perpendicularly to the 1a plane along the optical axis Q,
The extraordinary light component is totally reflected at point P and emitted toward the optical axis R, and the ordinary light component is completely transmitted through point P and directed toward the optical axis S.
It is possible to emit light in both directions without loss. This embodiment makes use of this principle to rotate and adjust the polarization direction in accordance with the optical axis R direction and the optical axis S direction of the prism 1 as shown in the figure, so that the prism 1 can be rotated around the optical axis. Input optical fibers 6 and 7 are a combination of half-wave plates 2 and 3 supported by the input optical fibers 6 and 7, and lenses 4 and 5 that convert the output light from the input optical fibers 6 and 7 into parallel beams.
(In this case, a single mode fiber is used in which the polarization direction of the laser beam is maintained while being transmitted.) The laser light sources 8 and 9 are arranged via a single mode fiber. Note that 10 is a transmission single mode optical fiber disposed along the optical axis Q direction of the prism, and 11 is a lens for condensing a parallel beam into the single mode optical fiber 10.

If the optical coupling device is configured as described above, first,
The light emitted from the laser light source 8 propagates through the input optical fiber 6, which is a single mode optical fiber.
After being made into a parallel beam by lens 4, 1/2
The polarization plane is rotated and adjusted by the wavelength plate 2 to match the polarization direction of the incident optical axis of the prism 1, that is, the polarization direction of the optical axis R, for example, the extraordinary light having the polarization direction perpendicular to the plane of the paper, and enters the prism 1. The incident extraordinary light is totally reflected at point P and exits in the optical axis Q direction. Further, the light emitted from the other laser light source 9 is made into a parallel beam by the lens 5 via the input optical fiber 7, and then the polarization plane is rotationally adjusted by the 1/2 wavelength plate 3, and the polarization direction of the light is adjusted. is made incident on the prism 1 with the polarization direction of the incident optical axis of the prism 1, that is, the optical axis S, for example, ordinary light having a polarization direction parallel to the paper surface, and the incident ordinary light is completely transmitted at point P. and emits it in the optical axis Q direction. These lights are emitted from the prism 1 in the same direction, that is, the optical axis Q.
The beams are emitted in a superimposed manner and condensed by a lens 11 into a single mode optical fiber 10 for transmission.
is sent to with low loss. If the configuration is such that the light from the laser light sources 8 and 9 can be input into one transmission single mode optical fiber, for example, the laser light source 8 can be turned on and the other laser light source 9 can be turned off. The output of the laser light source 8 is monitored (for example, in the case of a semiconductor laser, the rear output is monitored). When an abnormality occurs in the laser light source 8, the laser light source 8 is turned off and the other laser light source 9 is turned off. By switching the light source in conjunction with ON, it becomes possible to smoothly switch the light source without momentary interruption.

In addition, in this configuration, in order to prevent the light reflected from each surface of the prism 1 from being returned to the laser light sources 8 and 9 and destabilizing the operation of the laser light sources, for example, even if there is reflected light, it is easy to receive the light. It is desirable to arrange the half-wave plates 2 and 3 with a slight inclination.

As is clear from the above description, the optical coupling device of the present invention uses a prism made of a birefringent crystal to connect optical outputs from two laser light sources to a single transmission single mode optical fiber without using a movable operation. It is highly reliable because it enables switching without instantaneous interruption with low insertion loss, and it can also combine two laser beams with low loss and optically couple them to a transmission optical fiber. Demonstrates excellent effects when applied to optical communication systems.

[Brief explanation of drawings]

FIG. 1 is a plan view conceptually showing an embodiment of the optical coupling device according to the present invention, and FIG. 2 is a plan view illustrating a birefringent prism configured in the optical coupling device of the present invention. In the figure, 1 is a birefringent prism, 2 and 3 are 1/2
A wave plate, 4, 5, and 11 are lenses, 6, 7 are incident optical fibers, 8, 9 are laser light sources, and 10 is a single mode optical fiber for transmission.

Claims (1)

[Claims] 1 It is formed by a birefringent crystal that satisfies n _e ² − _{n p} ² > 1, where n _p is the refractive index for ordinary light and n _e is the refractive index for extraordinary light, and each plane is parallel to the optical axis of the crystal, and two a birefringent prism in which one apex angle formed by a surface forms a Brieustre angle; a first and second birefringent prism provided opposite to one of the surfaces forming the Brieustre angle and a surface not forming the Brieustre angle, respectively; It has a 1/2 wavelength plate and first and second laser light sources provided opposite to the first and second 1/2 wavelength plates, and the polarization direction of the light from the first laser light source is set to the first and second laser light sources. By using a 1/2 wavelength plate perpendicular to the optical axis of the crystal, the light from the first laser light source is completely transmitted through the prism, and the direction of polarization from the second laser light source is changed. By making it parallel to the optical axis of the crystal by the second 1/2 wavelength plate, the light from the second laser light source is reflected at the incident point of the light from the first laser light source, An optical coupling device characterized in that the optical axes of the first and second laser light sources are made to coincide with each other so that they emit light in the same direction.