Optical isolator and polarization splitter therefor

An optical isolator having no dependence on a plane of polarization, which comprises in the following sequence beginning from an input side to an output side:

• one or more parallel linear input optical waveguides;
• a first birefringent crystal plate arranged obliquely with respect to the linear optical waveguides;
• parallel intermediate optical waveguides one more greater in number than the at least one input optical waveguide and in alignment with said at least one input optical waveguide;
• a half wave plate and a Faraday rotator inserted in an oblique groove formed in said intermediate optical waveguides;
• a second birefringent crystal plate arranged obliquely with respect to the intermediate optical waveguides;
• and
• one or more parallel output waveguides in alignment with said intermediate optical waveguides;
• wherein a plane formed by said optical waveguides is parallel to a vector normal to the incident surface of each of said birefringent crystal plates, the optical axes of said birefringent crystal plates are also parallel to said plane, and the following relationship is substantially satisfied:
• tan .theta..sub.in =A/[.sqroot.B(n.sub.in -.sqroot.B)]
• where
• A=(n.sub.o.sup.2 -n.sub.E.sup.2) cos .theta..sub.c sin .theta..sub.c
• B=.sub.E.sup.2 sin.sup.2 .theta..sub.c +n.sub.O.sup.2 cos .theta..sub.c
• n.sub.in :
• Refractive index of the optical waveguides
• n.sub.o :
• Refractive index of the birefringent crystal plates for ordinary light
• n.sub.E :
• Refractive index of the birefringent crystal plates for extraordinary light
• .theta..sub.in :
• Angle between axes of the optical waveguides and the vector normal to the incident surface of each of the birefringent crystal plates
• .theta..sub.c :
• Angle between axes of the optical waveguides and the optical axis of each of the birefringent crystal plates (side opposite to .theta..sub.in is deemed positive).

A polarization splitter comprising at least two parallel optical waveguides, and a birefringent crystal plate inserted in a groove formed obliquely in said optical waveguides, wherein a plane formed by said two optical waveguides is parallel to a vector normal to the incident surface of said birefringent crystal plate, the optical axis of said birefringent crystal plate is also parallel to said plane, and the following relationship is substantially satisfied:

• tan .theta..sub.in =A/[.sqroot.B(n.sub.in -.sqroot.B)]
• where
• A=(n.sub.O.sup.2 -n.sub.E.sup.2) cos .theta..sub.C sin .theta..sub.C
• B=n.sub.E.sup.2 sin.sup.2 .theta..sub.C +n.sub.o.sup.2 cos .theta..sub.C
• n.sub.in :
• Refractive index of the optical waveguides
• n.sub.o :
• Refractive index of the birefringent crystal plate for ordinary light
• n.sub.E :
• Refractive index of the birefringent plate for extraordinary light
• .theta..sub.in :
• Angle between axes of the optical waveguides and the vector normal to the incident surface of each of the birefringent crystal plates
• .theta..sub.c :
• Angle between axes of the optical waveguides and the optical axis of the birefringent crystal plate (side opposite to .theta..sub.in is deemed positive).

A polarization splitter comprising one or more input optical waveguides on an incident side and parallel output optical waveguides on an exit side larger in number than said input optical waveguides and in alignment with said input optical waveguides, and a birefringent crystal plate inserted obliquely between said input and output optical waveguides, wherein a plane formed by said optical waveguides is parallel to a vector normal to the incident surface of said birefringent crystal plate, the optical axis of said birefringent crystal plate is also parallel to said plane, and the following relationship is substantially satisfied:

• tan .theta..sub.in =A/[.sqroot.B(n.sub.in -.sqroot.B)]
• where
• A=(n.sub.O.sup.2 -n.sub.E.sup.2) cos .theta..sub.C sin .theta..sub.C
• B=n.sub.E.sup.2 sin.sup.2 .theta..sub.C +n.sub.O.sup.2 cos .theta..sub.C
• n.sub.in :
• Refractive index of the optical waveguides
• n.sub.O :
• Refractive index of the birefringent crystal plate for ordinary light
• n.sub.E :
• Refractive index of the birefringent crystal plate for extraordinary light
• .theta..sub.in :
• Angle between axes of the optical waveguides and the vector normal to the incident surface of the birefringent crystal plates
• .theta..sub.C :
• Angle between axes of the optical waveguides and the optical axis of the birefringent crystal plate (side opposite to .theta..sub.in is deemed positive).