US 6,326,910 B1Granted

Photonic analog-to-digital conversion using light absorbers

AssigneeThe United States of America as represented by the Secretary of the Air Force

InventorsMichael J. Hayduk, Rebecca J. Bussjager, Mark A. Getbehead, Paul M. Payson, James P. Theimer

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Abstract

Apparatus and method for high-speed analog-to-digital conversion employs photonic circuits with variable light-absorption. A coherent light source is clocked to produce a stream of coherent light pulses onto which is modulated an analog signal to be converted to digital form. An optical splitter divides the stream of pulses into a number of streams that is proportional to the resolution sought. A passive photonic quantizer absorbs, to a predetermined degree, the light energy of the incident pulse streams. The output of a fully absorbed pulse does not trigger a comparator. Pulse streams of sufficient intensity pass through the light absorbers, and their output does trigger the comparator. The output state of the comparators may be read into a digital memory to form a digital word that represents the analog signal during any discrete clock interval. Most of the elements of the apparatus can be fabricated on a substrate of photonic semiconducting material.

Claims20

Dependent claims

A photonic analog-to-digital converter, comprising:

a source of coherent light;
a sampling clock, effective for converting said coherent light into a first stream of coherent light pulses;
an electro-optic modulator, effective for receiving as inputs said first stream and an analog signal, the output of said modulator being a second stream of modulated coherent light pulses;
an optical splitter, effective for splitting said second stream into a plurality of streams, each of said streams comprising modulated coherent light pulses;
a passive photonic quantizer, effective for quantizing said plurality of streams, said quantizer further comprising a plurality of light absorbers;
a plurality of optical delay lines, effective for aligning a quantized plurality of streams to a discrete instant at which each member of said plurality of streams was sampled from said analog signal;
a plurality of optical detectors, effective for converting said quantized plurality of streams into a plurality of detected voltages;
a plurality of comparators for comparing said plurality of detected voltages to a reference voltage, whereby a logical “1” is produced if said detected voltage is at least equal to a reference voltage and a logical “0” is produced if said detected voltage is less than said reference voltage;
and
a digital device, effective for storing a plurality of logical “1” and logical “0” as a digital word synchronous with said sampling clock.

7 more elements

A photonic analog-to-digital converter, comprising:

generating coherent light;
generating a clock waveform;
sampling said coherent light with said clock waveform to produce a first stream of coherent light pulses;
modulating an input analog signal onto said first stream to produce a second stream of modulated coherent light pulses;
splitting said second stream into a plurality of streams, each comprising modulated coherent light pulses;
passively quantizing said plurality of streams by absorbing said pulses in a like plurality of light absorbers;
adjusting in a predetermined fashion an absorption characteristic of each of said plurality of light absorbers;
absorbing said plurality of streams in varying degree, whereby some pulses are passed and other pulses are fully absorbed;
aligning a quantized plurality of streams to the same instant relative to the time at which they were sampled from said analog signal;
detecting each of said quantized plurality of streams, thereby producing a proportional voltage;
comparing, within the period of said clock waveform, said proportional voltage to a reference voltage, thereby producing a logical “1” if said proportional voltage is at least equal to said reference voltage and producing a logical “0” if said proportional voltage is less than said reference voltage;
and
storing said logical “1” and said logical “0” in a digital device.

10 more elements

Dependencies are inferred from the claim text.