摘要 |
A waveguide, approximately Y-shaped in plan view, provides coupling between first and second optical fibers, each attached to an end of the waveguide on the branched portion of the Y, and a third fiber attached to the single end of the Y. A fourth fiber, smaller in cross section than the waveguide on the single-ended portion of the Y and placed with its adjacent end therein between the junction of the Y and the third fiber, and bent gradually to one side, extends away from the waveguide before reaching the end to which the third fiber is attached. Typically the first fiber directs light from an emitter into the waveguide, the second fiber directs light away from the waveguide to a detector, the third fiber directs light away from the waveguide to a reference detector, and the fourth fiber directs light away from the waveguide to a sensor and back from the sensor into the waveguide.
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