US 5,416,629 AGranted

Intensity modulated digital optical communications using a frequency modulated signal laser

AssigneeGeneral Instrument Corporation

InventorDavid R. Huber

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Abstract

In long distance digital and frequency modulation systems that use optical sources having optical frequency chirp, degradation due to optical dispersion in the transmission fiber is overcome by filtering the laser wavelength representative of one of the binary levels (e.g., binary "0"). An optical source such as a DFB laser is directly frequency modulated by a digital data stream. A first digital level is represented by a first intensity of the modulated carrier corresponding to a carrier wavelength .lambda..sub.1 and a second digital level is represented by a second intensity of the modulated carrier corresponding to a carrier wavelength .lambda..sub.2. A wavelength selective reflector is used to filter the wavelength .lambda..sub.1 from the modulated carrier. The modulated carrier, from which wavelength .lambda..sub.1 has been filtered, is then coupled to an optical communication path for transmission. In one embodiment the wavelength selective reflector is coupled to the laser output using an optical circulator. In another embodiment, a directional coupler is used.

Claims14

Dependent claims

Apparatus for use in transmitting an optical signal carrying digital data over an optical communication path, comprising:

an optical source for generating an optical carrier that is frequency modulated by a digital data stream, wherein a first digital level is represented by a first intensity of the modulated carrier corresponding to a carrier wavelength .lambda..sub.1 and a second digital level is represented by a second intensity of the modulated carrier corresponding to a carrier wavelength .lambda..sub.2, the wavelengths .lambda..sub.1 and .lambda..sub.2 being close enough together to effectively reduce the degradation of said optical signal due to optical dispersion along said path;
wavelength selective reflector means coupled to an output of said optical source, for filtering said wavelength .lambda..sub.1 from said modulated carrier to increase the extinction ratio of said first and second digital levels in the modulated carrier prior to the communication thereof via said optical communication path;
and
means for coupling said modulated carrier with the wavelength .lambda..sub.1 filtered therefrom to said optical communication path for communication to a receiver.

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Dependencies are inferred from the claim text.