Optical waveguide multimode to single mode transformer

An external cavity solid state laser comprising:

• a solid state laser coupled to output a divergent beam, multimode optical signal, including a fundamental mode, to an optical waveguide mode transformer, said solid state laser and said optical waveguide mode transformer having anti-reflective coated neighboring end surfaces;
• said solid state laser and said optical waveguide mode transformer each having a low reflectivity coated opposite end surface;
• said optical waveguide mode transformer comprising a substrate supporting low refractive index cladding material on either side of a high refractive index core layer;
• said core layer including a lengthwise extending localized region of increased thickness defining a ridge upstanding from a surface of said core layer and spaced from opposite lateral edges of said core layer, said ridge having a height relative to the core layer thickness such that the ridge defines lateral waveguiding boundaries of at least said input and intermediate waveguide sections, said lengthwise extending ridge having a width that functionally changes along its length to accept said multimode optical signal output from said solid state laser and to transform said fundamental mode of said multimode optical signal to a single fundamental mode optical signal, without significant loss of intensity of said fundamental mode signal, to an output section of said optical waveguide mode transformer which supports single mode propagation of said fundamental mode optical signal.

An optical system comprising:

• a solid state laser coupled to output a divergent beam, multimode optical signal, including a fundamental mode,
• an optical waveguide mode transformer, and
• a cylindrical lens intermediate said solid state laser and said optical waveguide mode transformer,
• said solid state laser and said optical waveguide mode transformer having anti-reflective coated end surfaces;
• said solid state laser and said optical waveguide mode transformer each having a reflective coated opposite end surface, the reflective coating of said mode transformer opposite surface having a low reflectivity;
• said waveguide mode transformer comprising:
• an optical waveguide structure including a substrate supporting a high refractive index core layer between lower refractive index cladding layers, said core layer including a localized region of increased thickness defining a ridge upstanding from a surface of said core layer and spaced from opposite lateral edges of said core layer, said core layer including an input waveguide section having a wide ridge coupled by an intermediate waveguide section including a tapered ridge to an output waveguide ridge section;
• said input waveguide section ridge having a width to accept a multimode, including a fundamental mode, light input,
• said output waveguide section having a ridge width to support a single mode light output comprising said fundamental mode, and
• said tapered ridge section having a taper length enabling adiabatic transfer of said fundamental mode of said multimode light from said wide input waveguide section ridge to said output waveguide section ridge;
• said cylindrical lens positioned to receive said optical signal output by said solid state laser and to direct said signal to the wide input waveguide section of said optical waveguide mode transformer;
• and
• said antireflective coated end surface of the optical waveguide mode transformer being inclined at an angle to the antireflective coated end surface of said solid state laser.

An external cavity solid state laser comprising;

• a solid state laser coupled to output a divergent beam, multimode optical signal, including a fundamental mode, to a first optical waveguide mode transformer;
• said solid state laser and said optical waveguide mode transformer having anti-reflective coated neighboring front and back end surfaces, respectively;
• said solid state laser and said optical waveguide mode transformer each having a reflective coated opposite back and front end surfaces, respectively;
• and a second, feedback optical waveguide mode transformer device coupled to said solid state laser at said back end surface of the solid state laser;
• said first optical waveguide mode transformer comprising a substrate supporting low refractive index cladding material on either side of a high refractive index core layer;
• said core layer having a lengthwise extending ridge having a width that functionally changes along its length from a wide input section to accept said multimode optical signal output from said solid state laser and to transform said fundamental mode of said multimode optical signal to a single fundamental mode optical signal, without significant loss of intensity of said fundamental mode signal, to a narrow output section of said core layer that supports single mode propagation of said fundamental mode optical signal;
• said narrow output section perpendicularly intersecting said front end surface of the first optical waveguide mode transformer;
• and said wide input section intercepting said back end surface of the first optical waveguide transformer at a non-perpendicular angle;
• said solid state laser including an active region extending between and tilted at a non-perpendicular angle with respect to said front and back end surfaces of the solid state laser;
• said second, feedback optical waveguide transformer comprising a substrate supporting low refractive index cladding material on either side of a high refractive index core layer;
• said core layer having a lengthwise extending ridge having a width that functionally changes along its length from a wide input section to accept a multimode optical signal output from said back end surface of said solid state laser and to transform said fundamental mode of said multimode optical signal to a single fundamental mode optical signal, without significant loss of intensity of said fundamental mode signal, to a narrow output section of said core layer that supports single mode propagation of said fundamental mode optical signal;
• said narrow output section perpendicularly intersecting said reflective coated back end surface of the second optical waveguide mode transformer;
• and said wide input section intercepting the front end surface of the second optical waveguide transformer at a non-perpendicular angle;
• in each of said first and second optical waveguide mode transformers, said core layer including a localized region of increased thickness defining a ridge upstanding from a surface of said core layer and spaced from opposite edges of said core layer;
• the active region of said solid state laser lengthwise aligned with the wide input sections of the core layers of both said first and second optical waveguide mode transformers.

An optical waveguide multiplexer comprising:

• a pair of solid state lasers each coupled to output a divergent beam, multimode optical signal, including a fundamental mode, to respective first and second optical waveguide mode transformers;
• each of said lasers outputting a different wavelength optical signal within the gain-wavelength characteristic of both lasers;
• each of said first and second optical waveguide mode transformers comprising a substrate supporting a high refractive index core layer disposed between low refractive index cladding layers;
• said core layer of each of said first and second optical waveguide mode transformers including a localized region of increased thickness defining a lengthwise extending ridge upstanding from a surface of said core layer and spaced from opposite outer edges of said core layer, said lengthwise extending ridge having a width that functionally changes along its length to accept said multimode optical signal output from the solid state laser to which it is coupled and to transform the fundamental mode of said multimode optical signal to a single, fundamental mode optical signal, without significant loss of intensity of said fundamental mode signal;
• a Mach-Zehnder Interferometer structure comprising first and second waveguide sections coupled to receive said fundamental mode optical signals from the first and second optical waveguide mode transformers, respectively;
• each of said first and second waveguide sections comprising a high refractive index core layer disposed between low refractive index cladding layers to support single mode propagation of the fundamental mode optical signal received from the first and second mode transformers, said core layer of each of said first and second waveguide sections including a localized region of increased thickness defining a ridge upstanding from a surface of said core layer and spaced from opposite outer edges of said core layer;
• said first and second waveguide sections including spaced apart 3 db couplings, one of the first and second waveguide sections being longer than the other waveguide section in the region between the 3 db couplings to define a phase loop introducing effective to interleave said different wavelength fundamental mode, optical signals;
• and
• wherein one of said first and second waveguide sections is coupled to transfer said interleaved optical signals to an optical waveguide output section comprising a high refractive index core layer disposed between low refractive index cladding layers, said core layer of each of the first and second optical waveguide output sections including a localized region of increased thickness defining a ridge upstanding from a surface of said core layer and spaced from opposite outer edges of said core layer, said optical waveguide output section supporting single mode propagation of said interleaved fundamental mode optical signals.