Optoelectronic equalizer circuit

Patent metadata

Field	Value
Publication number	US-9496964-B2
Application number	US-201514658415-A
Country	US
Kind code	B2
Filing date	Mar 16, 2015
Priority date	Mar 16, 2015
Publication date	Nov 15, 2016
Grant date	Nov 15, 2016

Abstract

We disclose an optoelectronic circuit that is configurable to operate as an FIR filter, in which the tapping and the weighting of the signal that is being equalized are performed in the optical domain, whereas the summation of the weighted signals is performed in the electrical domain after the corresponding optical signals are converted into electrical form using an array of photodetectors. Photodetectors in the array are arranged such that some of them contribute to the equalized electrical signal with a positive polarity and the others contribute to the equalized electrical signal with a negative polarity. As a result, at least some of the tap weights used in the FIR filter can be made variable between a positive value and a negative value.

First claim

What is claimed is:

1. An apparatus comprising:
an array of photodetectors;
an optical splitter having an optical input port and a plurality of optical output ports, with each of the optical output ports being connected to illuminate a respective one of the photodetectors in the array of photodetectors;
a bank of optical delay elements, with each of the optical delay elements being coupled between a respective one of the optical output ports and the respective one of the photodetectors such that light of each of the optical output ports passes through a respective one of the optical delay elements; and
an array of variable optical-gain elements coupled between the optical splitter and the array of photodetectors such that, for at least some of the optical output ports, the light also passes through a respective one of the variable optical-gain elements;
wherein each photodetector in the array of photodetectors is configured to convert received light into a respective electrical signal;
wherein the apparatus further comprises an electrical signal combiner configured to combine the respective electrical signals to generate an electrical output signal in a manner that causes a first subset of the photodetectors and a second subset of the photodetectors to contribute the respective electrical signals to the electrical output signal with opposite polarities; and
wherein the apparatus further comprises an electronic controller operatively coupled to the bank of optical delay elements and configured to cause at least one optical delay element in the bank of optical delay elements to change a respective delay time.

2. The apparatus of claim 1 , wherein the array of variable optical-gain elements comprises one or more variable optical attenuators or one or more variable-gain optical amplifiers.

3. The apparatus of claim 1 , wherein the array of photodetectors comprises three photodiodes.

4. The apparatus of claim 1 , wherein the optical splitter is an optical power splitter configured to split light applied to the optical input port into a plurality of optical beams of substantially equal intensities and output each of said optical beams through a respective one of the optical output ports.

5. The apparatus of claim 1 , wherein the optical splitter and the array of variable optical-gain elements are implemented as an optical circuit that comprises two or more Mach-Zehnder interferometers.

6. The apparatus of claim 5 , wherein two Mach-Zehnder interferometers of the two or more Mach-Zehnder interferometers are serially connected with one another.

7. The apparatus of claim 5 , wherein two Mach-Zehnder interferometers of the two or more Mach-Zehnder interferometers are connected in parallel with one another.

8. The apparatus of claim 1 , wherein the electronic controller is further operatively coupled to the array of variable optical-gain elements and further configured to cause at least one of the variable optical-gain elements to change an amount of light amplification therein.

9. The apparatus of claim 1 , wherein the bank of optical delay elements includes a first optical delay element and a second optical delay element that are configured to delay the light by respective delay times that are nominally identical to one another.

10. The apparatus of claim 9 ,
wherein the array of photodetectors comprises a first photodetector coupled to receive light through the first optical delay element and a second photodetector coupled to receive light through the second optical delay element; and
wherein the first photodetector belongs to the first subset of the photodetectors, and the second photodetector belongs to the second subset of the photodetectors.

11. The apparatus of claim 1 , wherein each of the optical delay elements is configured to delay the light by a respective delay time, wherein a set of the respective delay times has at least three different values.

12. The apparatus of claim 11 , wherein the set of the respective delay times includes the following values:
τ n =τ 1 +( n− 1)τ 0 ,

where τ n is the respective delay time of an n-th delay element in the bank of optical delay elements; and τ 1 and τ 0 are constants.

13. The apparatus of claim 1 , wherein the apparatus is configured to operate as a finite-impulse-response filter that is configured to:
variously delay two or more copies of an optical input signal received at the optical input port using the bank of optical delay elements to generate a plurality of filter-tap signals;
individually weight the filter-tap signals using the array of variable optical-gain elements to generate a plurality of weighted signals; and
sum the weighted signals using the electrical signal combiner to generate the electrical output signal.

14. The apparatus of claim 13 , wherein at least one of a plurality of tap coefficients applied to weight the filter-tap signals is positive, and at least one of the plurality of tap coefficients applied to weight the filter-tap signals is negative.

15. The apparatus of claim 13 , wherein at least one of a plurality of tap coefficients applied to weight the filter-tap signals is variable between a positive value and a negative value.

16. The apparatus of claim 13 , wherein the bank of optical delay elements is configured to cause the finite-impulse-response filter to have equally spaced taps.

17. An apparatus comprising:
an array of photodetectors;
an optical splitter having an optical input port and a plurality of optical output ports, with each of the optical output ports being connected to illuminate a respective one of the photodetectors in the array of photodetectors;
a bank of optical delay elements, with each of the optical delay elements being coupled between a respective one of the optical output ports and the respective one of the photodetectors such that light of each of the optical output ports passes through a respective one of the optical delay elements; and
an array of variable optical-gain elements coupled between the optical splitter and the array of photodetectors such that, for at least some of the optical output ports, the light also passes through a respective one of the variable optical-gain elements;
wherein each photodetector in the array of photodetectors is configured to convert received light into a respective electrical signal;
wherein the apparatus further comprises an electrical signal combiner configured to combine the respective electrical signals to generate an electrical output signal in a manner that causes a first subset of the photodetectors and a second subset of the photodetectors to contribute the respective electrical signals to the electrical output signal with opposite polarities; and
wherein the optical splitter and the array of variable optical-gain elements are implemented as an optical circuit that comprises two or more Mach-Zehnder interferometers.

18. The apparatus of claim 17 , wherein two Mach-Zehnder interferometers of the two or more Mach-Zehnder interferometers are serially connected with one another.

19. The apparatus of claim 17 , wherein two Mach-Zehnder interferometers of the two or more Mach-Zehnder interferometers are connected in parallel with one another.

20. An apparatus comprising:
an array of photodetectors;
an optical splitter having an optical input port and a plurality of optical output ports, with each of the optical output ports being connected to illuminate a respective one of the photodetectors in the array of photodetectors;
a bank of optical delay eleme

Assignees

• Alcatel Lucent Usa Inc

Inventors

• Sinsky Jeffrey H
• Chang Chia-Ming

Classifications

• H04B10/615 Primary

  Arrangements affecting the optical part of the receiver · CPC title

• H04B10/674 Primary

  using a variable optical attenuator · CPC title

• H04B10/673

  using an optical preamplifier · CPC title