A laser device includes: a laser unit that outputs laser light; an output end that launches the laser light; a first fusion splice portion; and a second fusion splice portion. In each of the first fusion splice portion and the second fusion splice portion, two multi-mode fibers are fusion-spliced. Each of the two multi-mode fibers include a core through which the laser light propagates and a cladding that surrounds the core. The first fusion splice portion is disposed closer to the laser unit than is the second fusion splice portion. At least a part of the core in the first fusion splice portion contains a dopant that is the same type as a dopant contained in the cladding in the first fusion splice portion for decreasing a refractive index.

A device providing efficient transformation between an initial optical mode and a second optical mode includes first, second and third elements fabricated on a common substrate. The first element includes first and second active sub-layers supporting initial and final optical modes with efficient mode transformation therebetween. The second element includes a passive waveguide structure supporting a second optical mode. The third element, at least partly butt-coupled to the first element, includes an intermediate waveguide structure supporting an intermediate optical mode. If the final optical mode differs from the second optical mode by more than a predetermined amount, a tapered waveguide structure in the second or third elements facilitates efficient transformation between the intermediate optical mode and the second optical mode. Precise alignment of sub-elements formed in one of the elements, relative to sub-elements formed in another one of the elements, is defined using lithographic alignment marks.

A device providing efficient transformation between an initial optical mode and a second optical mode includes first, second and third elements fabricated on a common substrate. The first element includes first and second active sub-layers supporting initial and final optical modes with efficient mode transformation therebetween. The second element includes a passive waveguide structure supporting a second optical mode. The third element, at least partly butt-coupled to the first element, includes an intermediate waveguide structure supporting an intermediate optical mode. If the final optical mode differs from the second optical mode by more than a predetermined amount, a tapered waveguide structure in the second or third elements facilitates efficient transformation between the intermediate optical mode and the second optical mode. Precise alignment of sub-elements formed in one of the elements, relative to sub-elements formed in another one of the elements, is defined using lithographic alignment marks.

A splitter. In some embodiments, the splitter includes an input waveguide; a first output waveguide; a second output waveguide; a first internal waveguide, connected to the input waveguide and to the first output waveguide, and a second internal waveguide, coupled to the first internal waveguide and connected to the second output waveguide. The splitter may be configured, when fed, at the input waveguide, power in a fundamental mode of the input waveguide or power in a first order spatial mode of the input waveguide: to transmit at least 80% of the power in the fundamental mode to the first output waveguide, and to transmit at least 80% of the power in the first order spatial mode to the second output waveguide.

A splitter. In some embodiments, the splitter includes an input waveguide; a first output waveguide; a second output waveguide; a first internal waveguide, connected to the input waveguide and to the first output waveguide, and a second internal waveguide, coupled to the first internal waveguide and connected to the second output waveguide. The splitter may be configured, when fed, at the input waveguide, power in a fundamental mode of the input waveguide or power in a first order spatial mode of the input waveguide: to transmit at least 80% of the power in the fundamental mode to the first output waveguide, and to transmit at least 80% of the power in the first order spatial mode to the second output waveguide.

An optical waveguide device has a function of removing or suppressing a higher-order mode component of propagating light. The optical waveguide device includes a curved waveguide having a curved shape where a curvature continuously changes. A first waveguide is coupled to one end of the curved waveguide and a second waveguide is coupled to the other end of the curved waveguide. A curvature of the first waveguide and the curvature of the curved. waveguide are equal to each other in a coupling point in which the first waveguide is coupled to the curved waveguide, and a curvature of the second waveguide and the curvature of the curved waveguide are equal to each other in a coupling point in which the second waveguide is coupled to the curved waveguide.

A process fiber including a core extending along a central axis and a clad covering a circumference of the core includes an outer edge portion constituting an outer edge of a core cross section obtained by vertically cutting the core. The outer edge portion includes seven sides and seven corner portions respectively connecting the sides adjacent to each other. Each of the corner portions has an R shape along a circumscribed circle circumscribed to the outer edge portion. When a diameter of the circumscribed circle is O, a diameter of an inscribed circle inscribed to the outer edge portion is I, and the number of the corner portions is n (n is an odd number), a diameter ratio α, which is a ratio between the diameter O of the circumscribed circle and the diameter I of the inscribed circle, fulfills a predetermined condition.

An optical coupling system for coupling a light source to a photonic integrated circuit (PIC) comprises a multimode coupler configured to receive an input optical signal of a first mode. The multimode coupler triggers one or more higher-order modes from the input optical signal of the first mode. The optical coupling system also includes a mode de-multiplexer and an optical combiner. The mode de-multiplexer transfers the input optical signal of the first mode and one or more optical signals of the triggered one or more higher-order modes to respective output optical signals of the first mode. The optical combiner combines the respective output optical signals to produce a single output signal of the first mode.

An optical delay device includes a multi-mode waveguide for propagating first light through at least a portion of the multi-mode waveguide. The multi-mode waveguide has a first width. The optical delay device also includes a first waveguide having a second width that is less than the first width and a first coupler connected to the multi-mode waveguide and the first waveguide for coupling the first light from the multi-mode waveguide to the first waveguide. The first waveguide includes a first portion connected to the first coupler for receiving the first light from the first coupler; and a second portion connected to the first portion for receiving the first light from the first portion and positioned adjacent to the multi-mode waveguide for coupling of the first light to the multi-mode waveguide as second light so that the second light propagates through at least the portion of the multi-mode waveguide.

An optical delay device includes a multi-mode waveguide for propagating first light through at least a portion of the multi-mode waveguide. The multi-mode waveguide has a first width. The optical delay device also includes a first waveguide having a second width that is less than the first width and a first coupler connected to the multi-mode waveguide and the first waveguide for coupling the first light from the multi-mode waveguide to the first waveguide. The first waveguide includes a first portion connected to the first coupler for receiving the first light from the first coupler; and a second portion connected to the first portion for receiving the first light from the first portion and positioned adjacent to the multi-mode waveguide for coupling of the first light to the multi-mode waveguide as second light so that the second light propagates through at least the portion of the multi-mode waveguide.