Broad linewidth lasers for optical fiber communication systems

Apparatus for use in communicating information over an optical fiber comprising:

• a laser for providing an output signal with a mode at a frequency .nu..sub.0 ;
• means for directly modulating said laser by a periodic function to increase the linewidth of said mode and thereby provide a broadened optical signal generally centered around .nu..sub.0, said periodic function having a frequency that is high enough to avoid sidebands thereof from interfering with an information signal carried on said broadened optical signal;
• external modulator means coupled to receive the broadened optical signal, for modulating said broadened optical signal with an information signal;
• and
• means for coupling the broadened optical signal modulated with said information signal from said external modulator means to an optical transmission path.

A method for increasing the linewidth of a longitudinal mode of a laser comprising the steps of:

• providing a laser cavity for outputting an optical signal having a longitudinal mode;
• pumping an active medium with a pump laser to provide a source of spontaneous emission at or near the lasing wavelength of said laser cavity;
• and
• simultaneously pumping said laser cavity with said pump laser while injecting spontaneous emission from said source into said laser cavity to increase the linewidth of said mode.

Laser apparatus for providing an optical carrier having a broad linewidth comprising:

• a laser cavity for outputting an optical signal having a longitudinal mode;
• an active medium having an output coupled to said laser cavity;
• and
• a pump laser coupled to pump said active medium to inject spontaneous emission at or near the wavelength of said mode into said laser cavity while simultaneously pumping said laser cavity to produce said optical signal;
• wherein said spontaneous emission in said laser cavity increases the effective linewidth of said mode.

Laser apparatus for providing an output signal with a broad linewidth comprising:

• a laser cavity for outputting an optical signal to a first port of an optical circulator;
• spontaneous emission means, having an output coupled to a second port of said optical circulator, for injecting spontaneous emissions at or near the wavelength of a longitudinal mode of said optical signal into said laser cavity via the first port of said optical circulator;
• and
• a third port on said optical circulator for outputting said optical signal with the effective linewidth of said mode increased by said spontaneous emission.

Laser apparatus for providing an output signal with a broad linewidth comprising:

• a semiconductor laser for outputting an optical signal having a longitudinal mode of a first linewidth;
• and
• an optical amplifier coupled in series with an output of said laser for amplifying said optical signal, said amplifier including means for generating spontaneous emissions at or near the wavelength of said longitudinal mode of said optical signal and injecting said spontaneous emissions into said laser output;
• wherein said spontaneous emission injected into said laser increase said first linewidth to a second broader linewidth.

Laser apparatus for providing an output signal with a broad linewidth comprising:

• a laser responsive to pump energy for outputting an optical signal;
• means for generating spontaneous emissions at or near the wavelength of a longitudinal mode of said optical signal;
• and
• means external of said laser for combining spontaneous emission output from said generating means with said pump energy for input to said laser;
• wherein the spontaneous emission input to said laser increase the effective linewidth of said mode.

A spontaneous emission source having a high spectral density at a desired wavelength comprising:

• an optical fiber providing a guided wave optical path;
• a grating within said optical path;
• an active medium within said optical path;
• and
• means for passing optical energy across said grating and active medium within said optical path;
• wherein said optical energy excites said active medium without lasing to output spontaneous emissions from said optical path at a wavelength established by said grating.