Analog transmitter using an external cavity laser (ECL)

A method of controlling the width of the temperature region over which a distortion dip occurs and an operating point within that width in a temperature-controlled external cavity laser where said distortion dip defines a relative minimum in distortion, said laser comprising a light source within an optical feedback cavity wherein one end of said optical feedback cavity is a partially-reflective grating, said method comprising

• a) applying two radio frequency pilot signals having different frequencies and a fixed phase difference to said external cavity laser, thereby producing in the optical output of said laser a distortion signal at the frequency difference of said pilot signals;
• and,
• b) extracting in-phase and quadrature component information of the two pilot signals from said distortion signal;
• and,
• c) generating an error signal from said in-phase and quadrature component information;
• and
• d) adjusting the temperature of the external cavity laser within the width of the temperature region and wherein the width of the temperature range is controlled by at least one of:
• a) applying stress to said grating wherein said stress is thermal stress, mechanical stress or both;
• and,
• b) employing a non-chirped grating having transmission bandwidth in the range from approximately 100 picometers to approximately 400 picometers full-width at half-maximum as said partially-reflective grating;
• and,
• c) employing a chirped grating as said partially-reflective grating;
• and,
• d) employing a grating having a knee-shaped reflectivity profile as said partially-reflective grating.

A method of distortion locking a temperature-controlled external cavity laser operating within a distortion dip comprising:

• a) applying two radio frequency pilot signals having different frequencies and a fixed phase difference to said external cavity laser, thereby producing in the optical output of said laser a distortion signal at the frequency difference of said pilot signals;
• and,
• b) extracting in-phase and quadrature component information of the two pilot signals from said distortion signal;
• and,
• c) generating an error signal from said in-phase and quadrature component information;
• and,
• d) adjusting the temperature of said temperature-controlled external cavity laser so as to reduce said error signal to a value near zero within the distortion dip where said distortion dip defines a relative minimum in distortion.

A method of distortion locking a temperature-controlled external cavity laser comprising:

• a) applying two radio frequency pilot signals having different frequencies and a fixed phase difference to said external cavity laser, thereby producing in the optical output of said laser a distortion signal at the frequency difference of said pilot signals;
• and,
• b) extracting in-phase and quadrature component information of the two pilot signals from said distortion signal;
• and,
• c) generating an error signal from said in-phase quadrature component information;
• and,
• using the generated error signal, a thermal electrical cooler and a temperature sensor forming a thermal control loop whereby the operating temperature of the external cavity of said external cavity laser is maintained substantially at a value whereby the output signal of said laser is locked simultaneously at an enhanced distortion dip and at an emission wavelength substantially at a wavelength of the standard grid for wavelength division multiplexed systems where said enhanced distortion dip defines a relative minimum in distortion.

An application-specific analog transmitter for broadcast and narrowcast transmission, said transmitter operating at a wavelength substantially at a wavelength of the standard grid for wavelength division multiplexed systems, said transmitter comprising:

• a temperature-controlled external cavity laser;
• two radio frequency pilot signals having different frequencies and a fixed phase difference applied to said external cavity laser, thereby producing in the optical output of said laser a distortion signal at the frequency difference of said pilot signals;
• and,
• in-phase and quadrature component information of the two pilot signals extracted from said distortion signal;
• and,
• an error signal generated from said in-phase and quadrature component information;
• wherein the temperature-controlled external cavity laser is locked to simultaneously operate substantially at an enhanced distortion dip and at a pre-determined chirp in response to the error signal where said enhanced distortion dip defines a relative minimum in distortion.