Spectral modulation in an optical wavelength converter

A method for amplitude modulating a laser beam output from an optical wavelength converter responsive to a modulation signal where a source laser beam having a first wavelength is input to the converter and converted to a second wavelength, said method comprising the step of:

• changing the polarization of the first wavelength laser beam responsive to the modulation signal before it is input to the optical wavelength converter;
• wherein said changing polarization of the first wavelength laser beam causes a corresponding change in the amplitude of the second wavelength laser beam output from the optical wavelength converter.

Apparatus for reducing thermal lensing in the crystal of an optical wavelength converter when amplitude modulating a laser beam output from the wavelength converter responsive to a modulation signal, where a source laser beam having a first wavelength is input to the converter and is converted to a second wavelength, said apparatus comprising:

• means for changing the polarization of the first wavelength laser beam before it is input to the optical wavelength converter;
• wherein the total power of the laser beams passing through the wavelength converter remains constant despite the amplitude modulation, thereby providing a constant thermal load that causes constant thermal lensing that can be compensated for.

A method for reducing thermal lensing in the crystal of an optical wavelength converter when amplitude modulating a laser beam output from the wavelength converter responsive to a modulation signal, where a source laser beam having a first wavelength is input to the converter and is converted to a second wavelength, said method comprising:

• changing the polarization of the first wavelength laser beam before it is input to the optical wavelength converter;
• wherein the total power of the laser beams passing through the wavelength converter remains constant despite the amplitude modulation, thereby providing a constant thermal load that causes constant thermal lensing that can be compensated for.