Tunable optically-pumped semiconductor laser including a polarizing resonator mirror

A mirror for reflecting and transmitting light at first and second different wavelengths, the second wavelength being shorter than the first wavelength, the mirror comprising:

• a membrane of a material having a refractive index greater than about 1.6 said membrane being peripherally supported on a substrate over an aperture therein;
• said membrane having first and second opposite surfaces, said first surface including a grating and said second surface being a plane surface, said grating including a regular array of parallel grooves defining spaced-apart parallel strips surmounting a uniform thickness portion of said membrane, said grating strips having a width and a height and said grating having a grating period defined as the distance between adjacent ones of said parallel strips, said grating period being less than the second wavelength, said membrane material, the width and height of the grating, the ratio between said grating width and period, and the thickness of said uniform thickness portion of said membrane being selected such that;
• a. first wavelength light that is normally incident on the mirror has first and second specular reflectivities for normally incident light in first and second polarization planes oriented respectively perpendicular and parallel to said grating strips, said first specular reflectivity being between about 90% and 99% and said second specular reflectivity being at least about 1 percent less than said first specular reflectivity;
• and
• b. the mirror has greater than 50 percent transmissivity for the second-wavelength light in any one of said polarization plane orientations.

A mirror for reflecting and transmitting light at first and second different wavelengths, the second wavelength being shorter than the first wavelength, the mirror comprising:

• a membrane peripherally supported on a substrate over an aperture therein;
• said membrane including a grating, said grating including a regular array of spaced-apart parallel strips of first material having a first refractive index surmounting a uniform thickness portion of said first material, said grating strips having a width and a height and said grating having a grating period defined as the distance between adjacent ones of said parallel strips, said grating period being less than the second wavelength;
• said grating surmounting first, second, third and fourth uniform-thickness layers, numbered sequentially beginning with the layer adjacent said uniform thickness portion of said grating, said first and third layers being layers of a second material having a second refractive index different from said first refractive index, and said second and fourth layers being layers of said first material, wherein the composition of said materials forming the membrane and the first and second layers, the width and height of the grating, the ratio between said grating width and period, the thickness of said uniform thickness portion of said membrane and the thicknesses of said first, second, third, and fourth layers are selected such that:
• a. first wavelength light that is normally incident on the mirror has first and second specular reflectivities in first and second polarization planes oriented respectively perpendicular and parallel to said grating strips, said second specular reflectivity being between about 90% and 99% and said first specular reflectivity being at least about 1 percent less than said first specular reflectivity;
• and
• b. the mirror has greater than 50 percent transmissivity for the second-wavelength light in any one of said polarization plane orientations.

A tunable laser, comprising:

• a multilayer structure including a first mirror surmounted by a multilayer semiconductor gain-structure said gain-structure having a gain-bandwidth and being energized by pump light having a pump-light wavelength;
• a second mirror in the form of a membrane peripherally supported on a semiconductor substrate having an aperture therein, said second mirror being spaced apart from said first mirror to form a laser resonator therebetween, said pump light being directed into said gain structure through said second mirror;
• said laser resonator having a longitudinal axis and said gain-structure being included in said laser resonator, the optical spacing between said first and second mirrors being selected such that said laser resonant cavity supports only a single lasing mode having a wavelength within the gain-bandwidth of said gain-structure;
• said second mirror including a grating on a surface thereof facing said gain structure, said grating including a regular array of spaced-apart parallel strips of a first material surmounting at least one optical interference layer of uniform thickness, said grating strips having a width and a height and said grating having a grating period defined as the distance between adjacent ones of said parallel strips, said grating period being less than said pump-light wavelength, wherein the composition and thickness of said first material and said interference layer, the width and height of the grating, and the ratio between said grating width and period are selected such that:
• a. said second mirror has a sufficiently different reflectivity in polarization planes oriented parallel and perpendicular to said grating strips, for light having the lasing mode wavelength, that said lasing mode is plane polarized in the plane for which said reflectivity is highest, and
• b. said second mirror has a transmissivity greater than about 0.50 at said pump-light wavelength in any polarization plane orientation;
• and
• wherein a portion of said second mirror is electrically conductive and is electrically isolated from said substrate, and wherein electrical contacts are provided on said mirror and said substrate for establishing an electrical potential therebetween such that said electrical potential determines the spacing between said first and second mirrors, thereby determining said lasing mode wavelength.