Optical analog PPM demodulator
AssigneeHRL Laboratories, LLC
InventorsDaniel Yap, Monica Minden
Life of this patent
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Abstract
The invention is a Demodulator for an Optical Analog Pulse Position Modulated signal suitable for inclusion in receivers for Free Space Optical communication systems. In one embodiment the Demodulator may use the pulse position modulated optical information signal and the clock signal with different wavelengths. By proper biasing of a Semiconductor Optical Amplifier and selection of wavelengths for the information signal and the clock signal, the performance of the Demodulator is made insensitive to noise in the received signals.
Claims20
A Demodulator for optical pulse position modulated signals comprising:
- a splitter having an input receiving an optical signal pulse and an optical clock pulse separated in time by a time difference and generating a first output from the optical signal pulse and a second output from the optical clock pulse;
- a semiconductor optical amplifier (SOA) operating at a bias current, receiving the optical signal pulse, the optical clock pulse and generating an amplified optical clock pulse;
- wherein the semiconductor optical amplifier has a transparency wavelength, the optical signal pulse has a signal wavelength, the optical clock pulse has a optical wavelength, and wherein the transparency wavelength is shorter than or equal to the signal wavelength, and the signal wavelength is shorter than or equal to the clock pulse wavelength;
- wherein the bias current is selected such that the optical signal pulse resets a gain of the semiconductor optical amplifier;
- and the optical clock pulse experiences the gain of the semiconductor optical amplifier proportional to the time difference;
- a photodetector receiving the amplified optical clock pulse and generating an electrical current.
A method of demodulating a pulse position modulated optical signal comprising:
- receiving a pulse position modulated signal comprising an optical signal pulse and an optical clock pulse separated in time by a time difference,
- separating the optical signal pulse and the optical clock pulse from the pulse position modulated signal;
- supplying the optical signal pulse and the optical clock pulse to a semiconductor optical amplifier (SOA) with a wavelength of transparency;
- wherein the wavelength of transparency is less than a wavelength of the optical signal pulse and the wavelength of the optical signal pulse is less than a wavelength of the optical clock pulse;
- and
- converting an output of the semiconductor optical amplifier to an electrical signal with a photodetector.
A Demodulator for optical pulse position modulated signals comprising:
- means for receiving a pulse position modulated signal comprising an optical signal pulse and an optical clock pulse wherein the optical signal pulse and the optical clock pulse are separated in time by a time separation;
- means for separating the optical signal pulse and the optical clock pulse from the pulse position modulated signal;
- means for amplifying the optical clock pulse by a gain proportional to the time separation;
- wherein the gain of the means for amplifying depends on a wavelength of transparency of the means for amplifying, a first wavelength of the optical signal pulse and a second wavelength of the optical clock pulse;
- the wavelength of transparency is less than the first wavelength and the first wavelength is less than or equal to the second wavelength;
- means converting an output of the means for amplifying to an electrical signal.
Dependencies are inferred from the claim text.