Method and apparatus for optimizing output characteristics of a tunable external cavity laser

A tunable laser comprising:

• a pumped gain medium having a first and second end for generating a laser light within a given wavelength tuning range, at a given output power and having given gain medium gain and loss coefficients and a given threshold pumping level for each wavelength, the gain medium emitting the laser light out both the first and second end;
• an output coupler for outputting the laser light;
• tuning means for selecting different wavelengths of the laser light emitted from the gain medium, the tuning means controlling which wavelength of laser light is emitted from the output coupler;
• and
• a coating on the output coupler having a spectrally flat reflectance that reflects approximately the same percentage of light independently of the light wavelength and having a reflectance R.sub.oc at each wavelength related to a given expression as follows:
• R.sub.oc R.sub.back Exp [2(.GAMMA.g-.alpha.)L.sub.chip ],
• wherein .GAMMA. is an optical confinement factor, "g" is a gain medium gain coefficient per unit length, .alpha. is a gain medium loss coefficient per unit length including confinement effects, L.sub.chip is a gain medium length and R.sub.back is a power reflectivity from the tuning means including any coupling loss,
• the coating reflectance R.sub.oc varied according to wavelength so that R.sub.oc is large enough to cause the given expression to be greater than or equal to one at each selected wavelength thereby providing at least one of said decreased threshold pumping level and increased tuning range.

A method for varying the output characteristics of a tunable external cavity laser comprising:

• providing a pumped laser gain medium for generating a laser light within a given wavelength tuning range having a given threshold pumping level for each wavelength within the given tuning range;
• providing an output coupler having a reflectance R.sub.oc at each wavelength for outputting the laser light;
• selecting the reflectance R.sub.oc according to wavelength to yield the maximum possible output power from the tunable laser at each wavelength through transmitting the optimal portion of the circulating power thereby increasing at least one of said given tuning range and said output power;
• and
• selecting different wavelengths of the laser light emitted from the gain medium thereby controlling which wavelength of laser light is emitted from the output coupler.

A method for optimizing output characteristics of an external cavity laser comprising:

• providing a pumped gain medium, a wavelength selecting element and a predetermined net gain, yielding a tuning range, the gain medium having a laser pumping threshold varying according to the wavelength of light output from the laser and including an output coupler reflectance R.sub.oc at each wavelength having a given relationship to the output power as follows:
• ##EQU9## wherein P.sub.sat is a circulating saturation power, P.sub.out is the output power, .GAMMA. is an optical confinement factor, "g" is a gain medium gain coefficient per unit length, .alpha. is a gain medium loss coefficient per unit length including confinement effects, L.sub.chip is a gain medium length and R.sub.back is a power reflectivity from the tuning means including any coupling loss,
• calculating a net gain for a given laser pumping level for each wavelength within said tuning range using a set of data derived at the given pumping threshold;
• determining an output coupler reflectance value according to wavelength that maximizes P.sub.out /P.sub.sat at each wavelength within said tuning range using the calculated laser net gain for said given pumping level;
• and
• applying a coating on the output coupler that has a reflectance vs. wavelength relationship that is similar to said determined output coupler reflectivity values.