Single-photodiode optical heterodyne mixers

• US 4,697,284 A
• Filed: 05/08/1986
• Issued: 09/29/1987
• Est. Priority Date: 05/08/1986
• Status: Expired due to Term

• Current Assignee: American Telephone & Telegraph Company (AT&T, Inc.)
• Original Assignee: American Telephone & Telegraph Company (AT&T, Inc.)
• Inventors: Glance, Bernard
• Primary Examiner(s): Orsino, Jr., Joseph A.
• Application Number:
  US06/860,822
• Time in Patent Office: 509 Days
• Field of Search: 455/609, 455/616, 455/617, 455/619, 370/2, 329/144, 356/349, 356/351
• US Class Current: 398/204
• CPC Class Codes: G01J 9/04 by beating two waves of a same source but of different frequency and measuring the phase shift of the lower frequency obtained
• CPC Class Codes: H04B 10/60 Receivers
• CPC Class Codes: H04B 10/614 comprising one or more polarization beam splitters, e.g. polarization multiplexed [PolMux] X-PSK coherent receivers, polarization diversity heterodyne coherent receivers H04J14/06 takes precedence
• CPC Class Codes: H04B 10/64 Heterodyne , i.e. coherent receivers where, after the opto-electronic conversion, an electrical signal at an intermediate frequency [IF] is obtained

Abstract

The present invention relates to a single-photodiode optical mixer for heterodyne detection of optical signals. In the present optical mixer, a received optical signal and an optical local oscillator signal, which are each polarized along one direction of a polarizing beam-splitter, are directed at a 3 dB beam-splitter. Equal portions of the received signal and local oscillator signal are directed along first and second paths by the beam-splitter for arrival at a polarizing beam-splitter. One of the paths between the two beam-splitters comprises a 90 degree polarization rotator for rotating the polarization of the signal passing therethrough by π/2 radians. The output from the polarizing beam-splitter comprises the signal from the first path including a first polarization direction and the signal from the second path including a second polarization direction, which two signals are detected independently by a single photodetector to generate an IF signal which is the sum of the two IF currents.

Claims

1. An optical heterodyne mixer comprising:

a first and a second input terminal for receiving an optical signal and an optical local oscillator signal, respectively, each optical signal comprising a same direction of polarization;

means for both (a) combining the signals received at the first and second input terminals and (b) directing first and second substantially equal portions of the combined signals along first and second output paths, respectively;

means disposed in one of the output paths from the combining and directing means for rotating the direction of polarization of the portion of the combined signals propagating in the one output path by π

/2 radians;

a polarizing beam-splitter disposed to receive the combined signals propagating in the first and second output paths from the combining and directing means for coaxially aligning both (a) the first combined signal portion with a first polarization direction propagating in the first output path and (b) the second combined signal portion with a second polarization direction propagating in the second output path into an output beam directed along a predetermined path; and

a photo detector disposed to receive the coaxially aligned signals in tbe output beam from the polarizing beam-splitter for independently detecting each of the first and second combined signal portions and generating an output current which is the sum of the two combined signal portions at an output of the mixer.

2. An optical heterodyne mixer according to claim 1 wherein the combining and directing means comprises an optical 3 dB beam-splitter.

3. An optical heterodyne mixer according to claims 1 or 2 wherein the rotating means comprises:

a π

/2 polarization rotator for rotating the direction of polarization of signals traversing therethrough.

4. An optical heterodyne mixer according to claim 1 wherein the mixer further includes

redirecting means disposed in one of the output paths comprising a first and a second mirror disposed to, in combination, redirect the associated output path from the combining and directing means to intersect the other output path substantially normal thereto.

5. An optical heterodyne mixer according to claims 1, 2, or 4 wherein signals received at the first and second input terminals each comprise a horizontal polarization direction.

6. An optical heterodyne mixer according to claims 1, 2, or 4 wherein signals received at the first and second input terminals each comprise a vertical polarization direction.

7. An optical heterodyne mixer according to claim 3, wherein signals received at the first and second input terminals each comprise a horizontal polarization direction.

8. An optical heterodyne mixer according to claim 3, wherein signals received at the first and second input terminals each comprise a vertical polarization direction.