Optical isolator and optical fiber amplifier

An optical fiber amplifier comprising:

• a lens for converting incident light into collimated light;
• a plurality of pairs of input optical fibers and output optical fibers provided on one end side of said lens;
• a reflecting mirror provided on the other end side of said lens so as to reflect incident rays from said input optical fibers, which passed through said lens, to said output optical fibers which correspond individually to said input optical fibers;
• a birefringent element provided between said lens and said input and output optical fibers so as to resolve light which passes therethrough into an ordinary ray and an extraordinary ray, which are linearly polarized rays at right angles to each other;
• a compensator provided in the optical paths of the incident rays from said input optical fibers between said lens and said birefringent element or in the optical paths of the rays emitted to said output optical fibers so as to rotate 45 degrees the planes of polarization of the rays which pass therethrough;
• a magneto-optical element provided between said lens and said reflecting mirror so as to rotate 22.5 degrees the planes of polarization of the rays which pass therethrough;
• an amplification optical fiber which has one terminal connected to the output optical fiber in one of said pairs and the other terminal connected to the input optical fiber in the other of said pairs via an optical multiplexer;
• and
• an excitation light source for outputting excitation light to said amplification optical fiber via said optical multiplexer,
• said compensator and said magneto-optical element rotating the planes of polarization of the rays emitted from said input optical fibers in the same direction.

An optical fiber amplifier comprising:

• a lens for converting incident light into collimated light;
• a plurality of pairs of input optical fibers and output optical fibers provided on one end side of said lens;
• a polarization-maintaining optical fiber provided on one end side of said lens;
• a reflecting mirror provided on the other end side of said lens so as to reflect incident rays from said input optical fibers, which passed through said lens, to said output optical fibers which correspond individually to said input optical fibers:
• a birefringent element provided between said lens and said input and output optical fibers so as to resolve light which passes therethrough into an ordinary ray and an extraordinary ray, which are linearly polarized rays at right angles to each other;
• a compensator provided in the optical paths of the incident rays from said input optical fibers between said lens and said birefringent element or in the optical paths of the rays emitted to said output optical fibers so as to rotate 45 degrees the planes of polarization of the rays which pass therethrough;
• a magneto-optical element provided between said lens and said reflecting mirror so as to rotate 22.5 degrees the planes of polarization of the rays which pass therethrough;
• an amplification optical fiber which has one terminal connected to the output optical fiber in one of said pairs and the other terminal connected to the input optical fiber in the other of said pairs:
• an excitation light source for outputting excitation light to said polarization-maintaining optical fiber;
• and
• a wavelength selecting filter provided between said lens and said magneto-optical element, which transmits incident rays from said input optical fibers while reflecting the excitation light incident from said polarization-maintaining optical fiber the input optical fiber in the other of said pairs or to the output optical fiber in one of said pairs,
• said compensator and said magneto-optical element rotating the planes of polarization of the rays emitted from said input optical fibers in the same direction.

An optical fiber amplifier comprising:

• a lens for converting incident light into collimated light;
• a plurality of pairs of input optical fibers and output optical fibers provided on one end side of said lens;
• first and second polarization-maintaining optical fibers provided on one end side of said lens;
• a reflecting mirror provided on the other end side of said lens so as to reflect incident rays from said input optical fibers, which passed through said lens, to said output optical fibers which correspond individually to said input optical fibers;
• a birefringent element provided between said lens and said input and output optical fibers so as to resolve light which passes therethrough into an ordinary ray and an extraordinary ray, which are linearly polarized rays at right angles to each other;
• a compensator provided in the optical paths of the incident rays from said input optical fibers between said lens and said birefringent element or in the optical paths of the rays emitted to said output optical fibers so as to rotate 45 degrees the planes of polarization of the rays which pass therethrough;
• a magneto-optical element provided between said lens and said reflecting mirror so as to rotate 22.5 degrees the planes of polarization of the rays which pass therethrough;
• an amplification optical fiber which has one terminal connected to the output optical fiber in one of said pairs and the other terminal connected to the input optical fiber in the other of said pairs;
• an excitation light source for inputting excitation light
• said first and second polarization-maintaining optical fibers:
• and
• a wavelength selecting filter provided between said lens and said magneto-optical element, which transmits incident rays from said input optical fibers while reflecting the excitation light incident from said first polarization-maintaining optical fiber to the input optical fiber in the other of said pairs and reflecting the excitation light incident from said second polarization-maintaining optical fiber to the output optical fiber in one of said pairs,
• said compensator and said magneto-optical element rotating the planes of polarization of the rays emitted from said input optical fibers in the same direction.