Optical analog-to-digital converter

An optical analog-to-digital converter for converting an input optical signal into an output digital electrical signal, the optical analog-to-digital converter comprising:

• a first optical analog-to-digital converter stage having a first photodetector, a first comparator, and a first optical switch, wherein:
• the first photodetector converts a first portion of the input optical signal into a first analog electrical signal,
• the first comparator generates a first digital electrical signal by comparing the first analog electrical signal and a first reference analog electrical signal, and
• the first optical switch outputs a first output optical signal based on the first digital electrical signal;
• a second optical analog-to-digital converter stage having a second photodetector, a second comparator, and a second optical switch, wherein:
• the second photodetector generates a second analog electrical signal based on a difference between a second portion of the input optical signal and the first output optical signal,
• the second comparator generates a second digital electrical signal by comparing the second analog electrical signal and a second reference analog electrical signal,
• the second optical switch outputs a second output optical signal based on the second digital electrical signal;
• and
• wherein the output digital electrical signal is an N-bit digital signal, the first digital electrical signal is a k bit of the N-bit digital signal, the second digital electrical signal is a (k+1) bit of the N-bit digital signal, N and k are integers, N is greater than one, and k is less than N.

A method for converting an input optical signal into an output digital electrical signal, the method comprising:

• converting, by a first optical-to-electrical conversion circuit of an optical analog-to-digital converter, a first optical signal into a first analog electrical signal, wherein the first optical signal is a portion of the input optical signal;
• converting, by a second optical-to-electrical conversion circuit of the optical analog-to-digital converter, a second optical signal into a second analog electrical signal, wherein the second optical signal is a portion of a first reference optical signal;
• generating, by a comparator circuit of the optical analog-to-digital converter coupled to the first optical-to-electrical conversion circuit and the second optical-to-electrical conversion circuit, a digital electrical signal by comparing the first analog electrical signal and the second analog electrical signal;
• and
• generating, by an optical output circuit of the optical analog-to-digital converter coupled to the comparator circuit, an output optical signal by modulating a second reference optical signal based on the digital electrical signal.