Isolator, light source apparatus, optical transceiver, optical switch, optical amplifier, and data center

An isolator comprising:

• a first waveguide including a first end, a second end, and a port at each of the first end and the second end for input and output of electromagnetic waves;
• and
• a second waveguide with an annular shape positioned along the first waveguide, wherein
• the first waveguide and the second waveguide each are positioned along each other at least at a portion thereof in a direction of extension as a parallel waveguide,
• the second waveguide includes a straight part, at least a portion of the straight part being parallel with the first waveguide as the parallel waveguide,
• the first waveguide and the second waveguide are coupled so that, at any operating frequency of the isolator, a coupling coefficient when electromagnetic waves inputted from the second end propagate towards the first end is greater than a coupling coefficient when electromagnetic waves inputted from the first end propagate towards the second end, and
• a core of the second waveguide includes, in at least a portion of parts being the parallel waveguide, a non-reciprocal member in at least a portion of a cross-section intersecting a direction in which the second waveguide extends.