Transmitter and transceiver for a coherent optical system

• US 5,084,779 A
• Filed: 12/15/1988
• Issued: 01/28/1992
• Est. Priority Date: 04/15/1987
• Status: Expired due to Fees

• Current Assignee: British Telecommunications PLC (BT Group PLC)
• Original Assignee: British Telecommunications PLC (BT Group PLC)
• Inventors: Stanley, Ian W.
• Primary Examiner(s): Kuntz, Curtis
• Assistant Examiner(s): Negash, Kinfe-Michael
• Application Number:
  US07/288,253
• Time in Patent Office: 1,139 Days
• Field of Search: 455/617, 455/618, 455/606, 455/607, 455/619, 455/616, 370/3, 370/2
• US Class Current: 398/139
• CPC Class Codes: H04B 10/297 Bidirectional amplification
• CPC Class Codes: H04B 10/40 Transceivers
• CPC Class Codes: H04B 10/63 Homodyne , i.e. coherent receivers where the local oscillator is locked in frequency and phase to the carrier signal
• 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

In a coherent optical system, a transmitter or transceiver having an optical source which feeds a single coherent wave to both a modulator and a bi-direction amplifier. The modulator generates a modulated information signal and the amplifier generates an unmodulated, amplified reference signal. A coupling means combines the modulated and amplified signals for transmission to a remote detector. The detector uses the amplified signal as the reference optical signal in a homodyne or heterodyne system.

Claims

1. An optical transmitter for use in a coherent optical system comprising a single optical source coupled to a modulating means for generating a modulated information signal and to an optical amplifier to provide an amplified, unmodulated reference signal, a coupling means for combining said modulated information signal and said amplified, unmodulated reference signal;

and a wavelength shifting means for shifting the wavelength of said source signal before modulation thereof by said modulating means.

2. An optical transmitter according to claim 1 wherein said optical source comprises a laser and means for tuning said source signal.

3. An optical transceiver for use in a coherent optical system comprising

a single optical source coupled to a modulating means providing a transmitted modulated information signal and to an optical amplifier providing a transmitted amplified, unmodulated reference signal;

said optical amplifier providing bi-directional optical amplification in one direction for said transmitted reference signal and in the other direction both for a received modulated information signal and a received unmodulated reference signal;

a coupling means for combining said transmitted information signal and said transmitted reference signal; and

a receiver including a coherent detection receiver coupled to said amplifier for receiving an amplified input signal comprising said received information signal and said received reference signal.

4. An optical transceiver according to claim 3 wherein said coupling means comprises a directional coupler and an optical isolator located between said optical source and said directional coupler so as to prevent any of the source signal coupling back into said optical source.

5. An optical transceiver according to claim 3 further comprising a second coupling means having a second directional coupler and a second optical isolator located between said second directional coupler and said modulating means so as to prevent said input signal coupling into said modulating means.

6. An optical transceiver according to claim 3 wherein said receiver includes a filter means for selecting said input signal from a plurality of signals.

7. An optical transceiver as in claim 3 further comprising a wavelength shifting means for shifting the wavelength of the signal from said optical source before modulation thereof by said modulating means.

8. A coherent optical system having a transceiver;

said transceiver having an output means for transmitting optical signals having a modulated information component and an amplified, unmodulated reference component, said components being formed from a single input source means of coherent light, said transceiver also including means for receiving optical signals having reference and information components;

said transceiver further comprising a bidirectional amplifier for generating said amplified unmodulated reference component of the signals to be transmitted and for amplifying said reference and information components of received signals.