polarization independent optical isolator

Here, the magnetic garnet single crystal constituting the Faraday rotator hardly involves problems in the near-infrared wavelength region, in particular, around a wavelength region (1.2 μm to 1.7 μm) used for optical communications. The optical isolator functions in such a manner. Hence, light exiting from the first wedge-shaped birefringent crystal plate is not parallel, and is not coupled with the core of the optical fiber. After rotated by the Faraday rotator by 45 degrees, the ordinary ray is incident on the first wedge-shaped birefringent crystal plate as an extraordinary ray, and the extraordinary ray is incident thereon as an ordinary ray. Light traveling in the reverse direction is separated into an ordinary ray and an extraordinary ray by the second wedge-shaped birefringent crystal plate. Then, the rays exit as parallel light from the second wedge-shaped birefringent crystal plate, and are coupled with an optical fiber by a collimator lens. Since the Faraday rotator rotates the polarization by 45 degrees, and since the optic axis of a second wedge-shaped birefringent crystal plate is shifted from that of the first wedge-shaped birefringent crystal plate by 45 degrees, the ordinary ray is incident on the second wedge-shaped birefringent crystal plate as an ordinary ray, and the extraordinary ray is incident thereon as an extraordinary ray. Light incident on a first wedge-shaped birefringent crystal plate in the forward direction is separated into an ordinary ray and an extraordinary ray by the first wedge-shaped birefringent crystal plate. Note that an optical element unit including the polarizers and the Faraday rotator is referred to as a non-reciprocal unit. Here, the Faraday rotator has a crystal thickness adjusted so that the Faraday rotator can rotate the polarization by 45 degrees, and the two wedge-shaped birefringent crystal plates are placed such that the directions of the optic axes thereof are shifted from each other by 45 degrees.

In a general polarization independent optical isolator, two wedge-shaped birefringent crystal plates made of rutile, YVO 4, LiNbO 3, or the like are used as polarizers, and a flat plate made of a magnetic garnet single crystal, is placed, as a Faraday rotator, between the two wedge-shaped birefringent crystal plates (see Patent Document 1: U.S. Optical isolators can be broadly classified into polarization dependent optical isolators such as those used for semiconductor laser modules, and polarization independent optical isolators such as those used in front of and behind optical fiber amplifiers.

For example, an optical isolator is used in an optical communication system using a semiconductor laser as a light source in order to prevent oscillation of the semiconductor laser from being unstable due to returning of a reflected optical signal to the light source side.

The present invention relates to a polarization independent optical isolator using a Faraday rotator made of a magnetic garnet single crystal, and two wedge-shaped birefringent crystal plates, and more particularly to improvement of a polarization independent optical isolator, which prevents deterioration in characteristics and breakage of a magnetic garnet single crystal associated with rise in temperature due to light absorption by the magnetic garnet single crystal.Īn optical isolator is a non-reciprocal optical device having a function of allowing an optical signal to pass therethrough in the forward direction and preventing an optical signal from passing therethrough in the reverse direction.

Polarization independent optical isolator