| 摘要 |
<p>A non-reciprocal optical device interconnects single mode optical fiber waveguides (10A, 10B, 11A, 11B) so that a light beam can pass between input and output fibres in a forward direction but a reverse beam, such as might be caused by unwanted reflections, is displaced so that it does not couple into the input fiber. The device includes a focussing lens unit (14) and at least one non-reciprocal optical element (15; 21) in series between respective ends of an input optical fiber and an output optical fiber. The focussing lens unit has a focal length such that a light beam from the input optical fiber will be focussed onto the end of the output optical fiber. The focussing lens unit may comprise, for example, a half-pitch grin-rod lens. The non-reciprocal device is positioned adjacent one or other of the foci of the focussing lens unit. The focussing lens unit may comprise several lens elements (14A, 14B), for example a pair of quarter pitch collimating lenses, allowing additional optical elements (22), such as filters, to beinterposed. An isolator/wavelength division multiplexing hybrid device is formed by interposing a wavelength-division multiplexing filter and arranging the geometry so that different wavelength light beams are coupled to different output fibers. High isolation and low insertion loss are achieved in a compact device because the non-reciprocal device is placed where the width of the light beams is small.</p> |
