In-line optical isolator

Abstract

In conventional optical isolators, an optical signal is dispersed by polarization or the characteristics are varied by heat generation in a garnet crystal. According to the invention, the crystal optical axis ( 3 c ) of rutile crystal ( 3 ) is oriented so that the separation directions of the ordinary ray (O) and the extraordinary ray (E) are perpendicular to the plane including the optical axes of optical fibers ( 10, 11 ). Furthermore, the focusing central optical axis ( 6 c ) of a focusing rod lens ( 6 ) is arranged parallel with optical axes of the optical fibers ( 10, 11 ) and at a substantially equal distance from the four rays, i.e. the ordinary ray (O) and the extraordinary ray (E) propagating along the optical axis of the optical fiber ( 10 ) and the ordinary ray (O) and the extraordinary ray (E) propagating along the optical axis of the optical fiber ( 11 ). An air gap ( 7 ) of about 200 [μm] is provided, as a heat insulating means, between the focusing rod lens ( 6 ) and a magnetized garnet crystal ( 8 ).

1 . An in-line optical isolator, comprising:
 an input optical fiber that inputs a forward optical signal in a forward direction and an output optical fiber that outputs a forward optical signal in a reflection direction that is input from said input optical fiber;   a birefringent crystal, which is positioned next to said input fiber and said output fiber and separates said forward optical signal in the forward direction into an ordinary ray and an extraordinary ray, and combines said ordinary ray and said extraordinary ray in the reflection direction into said forward optical signal;   a half-wave plate, which is positioned next to said birefringent crystal and provided along either the optical axes of said ordinary ray and said extraordinary ray of said forward optical signal in the forward direction or the optical axes of said ordinary ray and said extraordinary ray of said forward optical signal in the reflection direction and rotates the polarization directions of said ordinary ray and said extraordinary ray reciprocally;   a lens, which is positioned next to said half-wave plate and collimates said ordinary ray and said extraordinary ray in the forward direction and collects said ordinary ray and extraordinary ray in the reflection direction;   a Faraday rotator, which is positioned next to said lens and rotates the polarization directions of said ordinary rays and said extraordinary rays in both the forward direction and the reflection direction non-reciprocally; and   a reflector, which is positioned next to said Faraday rotator and reflects said ordinary ray and said extraordinary ray from the forward direction to the reflection direction,   wherein the optical axis of said birefringent crystal is oriented so that the separation direction of said ordinary rays and said extraordinary rays are arranged in a plane that is perpendicular to a plane including the optical axes of said input optical fiber and said output optical fiber, and   wherein the optical axes of said ordinary ray and extraordinary ray of the forward optical signal in the forward direction and the ordinary ray and extraordinary ray of the forward optical signal in the reflection direction are arranged at an equal distance from the optical axis of said lens at each point between said lens and said reflector.   
     
     
         2 . An in-line optical isolator according to  claim 1 , further comprising:
 a plurality of individual pairs of an input optical fiber that inputs said forward optical signal in the forward direction and an output optical fiber that outputs said forward optical signal in the reflection direction that is input from said input optical fiber.   
     
     
         3 . An in-line optical isolator according to  claim 1  or  claim 2 , wherein an air gap is provided between said lens and said Faraday rotator and no organic adhesive exists in the optical paths between said lens and said reflector. 
     
     
         4 . An in-line optical isolator according to  claim 1  or  claim 2 , wherein said Faraday rotator is magnetized and magnetically sealed.