High-speed receiver architecture

1. A transceiver for communication over a fiber, the transceiver comprising:

a host interface for receiving digital data, the received digital data in a host format;

a laser driver port for generating an electrical signal modulated by the received digital data in electrical form, the electrical signal suitable for driving a laser driver;

transmit path circuitry coupled between the host interface and the laser driver port; and

receive path circuitry to receive an electrical signal representing an optical signal received from the fiber, and to provide the received electrical signal to the host interface, the receive path circuitry comprising:

an analog-to-digital converter that generates signal samples from the received electrical signal;

a transformation block applying a nonlinear transformation to the signal samples to generate transformed samples, wherein the nonlinear transformation converts non-Gaussian noise in the signal samples to Gaussian or approximately Gaussian noise;

a multiplexer to select between a first input and a second input depending on a mode of the receive path circuitry selectable between a Gaussian mode and a non-Gaussian mode, the first input coupled to receive untransformed samples from the analog-to-digital converter, the second input coupled to receive the transformed samples from the transformation block, the multiplexer selecting the first input when operating in the Gaussian mode, and the multiplexer selecting the second input when operating in the non-Gaussian mode;

an equalizer configured to equalize the selected samples from the multiplexer, the equalizer configured to operate on a Gaussian or approximately Gaussian channel.

2. The transceiver of claim 1 , wherein the multiplexer selects the first input to operate the receive path circuitry in a Gaussian mode responsive to the fiber having predominantly Gaussian noise.

3. The transceiver of claim 1 , wherein the multiplexer selects the second input to operate the receive path circuitry in a non-Gaussian mode responsive to the fiber having predominantly non-Gaussian noise.

4. The transceiver of claim 3 , wherein the predominantly non-Gaussian noise comprises amplified spontaneous emission (ASE) noise.

5. The transceiver of claim 1 , wherein the transformation block implements the function LUT(y n )=sqrt(y n +y ref ) for a sample y n when the sample y n is in an interval between −y ref and +y ref and wherein y ref comprises a reference value.

6. The transceiver of claim 1 , wherein the transformation block implements the function

(

y

+

y

min

)

v

-

(

y

min

)

v

≈

{

α

1

⁢

y

,

y

>

0

α

0

⁢

y

,

y

≤

0

for a sample y where v is a constant and where 0≦v≦1, y min is a predefined offset value, and α 0 and α 1 are constants.

7. A receiver comprising:

an analog-to-digital converter that generates signal samples from a received signal;

a transformation block applying a nonlinear transformation to the signal samples to generate transformed samples, wherein the nonlinear transformation converts non-Gaussian noise in the signal samples to Gaussian or approximately Gaussian noise;

a multiplexer to select between a first input and a second input depending on a mode of the receiver selectable between a Gaussian mode and a non-Gaussian mode, the first input coupled to receive untransformed samples from the analog-to-digital converter, the second input coupled to receive the transformed samples from the transformation block, the multiplexer selecting the first input when operating in the Gaussian mode, and the multiplexer selecting the second input when operating in the non-Gaussian mode;

an equalizer configured to equalize the selected samples from the multiplexer, the equalizer configured to operate on a Gaussian or approximately Gaussian channel.

8. The receiver of claim 7 , wherein the multiplexer selects the first input to operate the receiver in the Gaussian mode responsive to the receiver being coupled to a fiber having predominantly Gaussian noise.

9. The receiver of claim 7 , wherein the multiplexer selects the second input to operate the receiver in the non-Gaussian mode responsive to the receiver being coupled to a fiber having predominantly non-Gaussian noise.

10. The receiver of claim 9 , wherein the predominantly non-Gaussian noise comprises amplified spontaneous emission (ASE) noise.

11. The receiver of claim 7 , wherein the transformation block implements the function LUT(y n )=sqrt(y n +y ref ) for a sample y n when the sample y n is in an interval between −y ref and +y ref and wherein y ref comprises a reference value.

12. The receiver of claim 7 , wherein the transformation block implements the function

(

y

+

y

min

)

v

-

(

y

min

)

v

≈

{

α

1

⁢

y

,

y

>

0

α

0

⁢

y

,

y

≤

0

for a sample y where v is a constant and where 0≦v≦1, y min is a predefined offset value, and α 0 and α 1 are constants.

13. A method for equalizing samples in the presence of noise, the method comprising:

generating, by an analog-to-digital converter, signal samples from a received signal;

applying, by a signal processor, a nonlinear transformation to the signal samples to generate transformed samples, wherein the nonlinear transformation converts noise in the signal samples to Gaussian or approximately Gaussian noise;

selecting between a first input and a second input of a multiplexer of the signal processor depending on a mode of the signal processor selectable between a Gaussian mode and a non-Gaussian mode, the first input coupled to receive untransformed samples from the analog-to-digital converter, the second input coupled to receive the transformed samples from the signal processor, the multiplexer selecting the first input when the signal processor is operating in the Gaussian mode, and the multiplexer selecting the second input when the signal processor is operating in the non-Gaussian mode;

equalizing the selected samples from the multiplexer using an equalizer of the signal processor configured to operate on a Gaussian or approximately Gaussian channel.

14. The method of claim 13 , wherein the multiplexer selects the first input to operate the equalizer in a Gaussian mode responsive to the equalizer being coupled to a fiber having predominantly Gaussian noise.

15. The method of claim 13 , wherein the multiplexer selects the second input to operate the signal processor in a non-Gaussian mode responsive to the signal samples originating from a fiber having predominantly non-Gaussian noise.

16. The method of claim 15 , wherein the predominantly non-Gaussian noise comprises amplified spontaneous emission (ASE) noise.

17. The method of claim 13 , wherein applying the non-linear transformation comprises implementing the function LUT(y n )=sqrt(y n +y ref ) for a sample y n when the sample y n is in an interval between −y ref and +y ref and wherein y ref comprises a reference value.

18. The method of claim 13 , wherein the applying the non-linear transformation comprises implementing the function:

(

y

+

y

min

)

v

-

(

y

min

)

v

≈

{

α

1

⁢

y

,

y

>

0

α

0

⁢

y

,

y

≤

0

for a sample y where v is a constant and where 0≦v≦1, y min is a predefined offset value, and α 0 and α 1 are constants.