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US 5,477,369 AGranted
Device for optical heterodyne or homodyne detection of an optical signal beam and receiver provided with such a device
AssigneeU.S. Philips Corporation
InventorsMahon, Cathal J., Giok D. Khoe
Life of this patent
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Abstract
A device for optical heterodyne detection is described, using only two adjustable elements influencing the state of polarisation and having a limited control range (51, 52) in order to realize an endless polarisation control. In a first embodiment a temporary loss of signal intensity of at most 3 dB is accepted. This signal loss is avoided if a circuit of non-adjustable optical components (81, 82, 83) is incorporated in the heterodyne detection device.
Claims18
A device for optical heterodyne or homodyne detection of an optical signal beam, which device comprises:
- a) a local oscillator,
- b) an input for receiving the signal beam,
- c) a beam-combining element for combining radiation from the local oscillator with radiation from the signal beam, the beam-combining element supplying combined optical radiation,
- d) at least one opto-electrical converter for converting the combined optical radiation into an electric signal,
- e) no more than two adjustable elements, the adjustable elements being for influencing a state of polarisation of either the radiation from the local oscillator or the radiation from the signal beam or both, the adjustable elements having respective limited control ranges,
- f) a control circuit for adjusting the adjustable elements, so that the adjustable elements provide endless control of the state of polarization, in response to all possible endless variations in the state of polarization of the radiation from the signal beam
- wherein
- a. the adjustable elements are disposed along a radiation path coupled to an input of said beam-combining element;
- and
- further comprising, coupled between the adjustable elements and said beam-combining element:
- b. a polarization sensitive beam splitter, for splitting the radiation path into first and second branches;
- c. a second beam-combining element for combining the first and second branches;
- and
- d. a state of polarization converter, disposed along the first branch, for converting a state of polarization of radiation in the first branch into an orthogonal state of polarization.
11 more elements
A device for optical heterodyne or homodyne detection of an optical signal beam, which device comprises:
- a) a local oscillator,
- b) an input for receiving the signal beam,
- c) a beam-combining element for combining radiation from the local oscillator with radiation from the signal beam, the beam-combining element supplying combined optical radiation,
- d) at least one opto-electrical converter for converting the combined optical radiation into an electric signal,
- e) no more than two adjustable elements, the adjustable elements being for influencing a state of polarisation of either the radiation from the local oscillator or the radiation from the signal beam or both, the adjustable elements having respective limited control ranges,
- f) a control circuit for adjusting the adjustable elements, so that the adjustable elements provide endless control of the state of polarization, in response to all possible endless variations in the state of polarization of the radiation from the signal beam wherein
- when a variation of the state of polarization of the signal beam would require one of the adjustable elements to pass an end of its control range, the control circuit
- adjusts the first and second adjustable elements so that a first beam resulting from any effects of the adjustable elements on the signal beam has a polarization which is at an angle no more than 90.degree. different from a polarization of a second beam resulting from any effects of the adjustable elements on the radiation from the local oscillator, when the polarizations of the first and second beams are represented on a Poincare sphere, whereby the angles of polarization of the first and second beams differ by no more than 45.degree.;
- and
- then adjusts the first and second adjustable elements such that if the state of polarization of one of the first and second beams is represented as a first point on the Poincare sphere, then the state of polarization of the other of the first and second beams follows a circle on the surface of the Poincare sphere, each point of which circle is at the angle from the first point;
- whereby, the one of the adjustable elements is adjusted away from said end with a signal loss of no more than 3 dB.
8 more elements
Dependencies are inferred from the claim text.