Methods, systems, and apparatus, for an external cavity FP laser. In one aspect, an apparatus is provided that includes a FP laser diode; a Faraday rotator (FR) coupled to receive an optical output of the FP laser diode and that rotates a polarization of the optical output; an optical fiber coupled at a first end to receive the output of the FR; a WDM filter coupled to a second end of the optical fiber to receive the optical signal from the optical fiber; and a FRM coupled directly or indirectly to an output of the WDM filter, wherein an optical output of the WDM filter is partially reflected by the FRM such that the polarization of a reflected beam is rotated, and wherein the reflected optical signal then passes through the FR with its polarization being rotated by the FR before it is injected back into the FP laser diode.

A fiber laser device (1) includes an amplification optical fiber (10) having a core (11) doped with an active element, a first FBG (35) reflecting at least a part of light emitted from the active element, and a second FBG (45) reflecting the light reflected off the first FBG (35) at a reflectance lower than the reflectance of the first FBG (35). The wavelength of a fundamental-mode light beam reflected off the first FBG (35) and the wavelength of a fundamental-mode light beam reflected off the second FBG (45) are matched with each other. The wavelengths of higher-mode light beams reflected off the first FBG (35) and the wavelengths of higher-mode light beams reflected off the second FBG are unmatched with each other.

There is provided a semiconductor device that comprises a layered structure configured by layering a first compound semiconductor layer, an active layer, and a second compound semiconductor layer. The semiconductor device further includes a substrate, a first light reflecting layer arranged on the first surface side of the first compound semiconductor layer, and a second light reflecting layer arranged on the second surface side of the second compound semiconductor layer. Further, the second light reflecting layer has a flat shape, a concave surface portion is formed on a substrate surface, the first light reflecting layer is formed on at least the concave surface portion, the first compound semiconductor layer is formed to extend from the substrate surface onto the concave surface portion, and a cavity is present between the first light reflecting layer and the first compound semiconductor layer.

Methods, systems, and apparatus, for an external cavity FP laser. In one aspect, an apparatus is provided that includes a FP laser diode; a Faraday rotator (FR) coupled to receive an optical output of the FP laser diode and that rotates a polarization of the optical output; an optical fiber coupled at a first end to receive the output of the FR; a WDM filter coupled to a second end of the optical fiber to receive the optical signal from the optical fiber; and a FRM coupled directly or indirectly to an output of the WDM filter, wherein an optical output of the WDM filter is partially reflected by the FRM such that the polarization of a reflected beam is rotated, and wherein the reflected optical signal then passes through the FR with its polarization being rotated by the FR before it is injected back into the FP laser diode.

A laser diode has a first gain section having a first length and a second gain section having a second length and aligned with the first gain section. The second gain section is aligned with and coupled to the first gain section along a light output direction. The second length is an integer multiple m of the first length, where m is greater than one.

The invention relates to an edge-emitting semiconductor laser diode, having: a semiconductor layer sequence, which comprises a bottom surface, a ridge waveguide on a top surface facing away from the bottom surface, and a side surface which is arranged transverse to the top surface, and a first recess, which extends from the bottom surface to the top surface, wherein a first region of the semiconductor layer sequence is removed from the side surface in the region of the first recess. The invention further relates to a method for producing a plurality of edge-emitting semiconductor laser diodes.

A surface emitting laser element includes a lower Bragg reflection mirror; an upper Bragg reflection mirror; and a resonator region formed between the lower Bragg reflection mirror and the upper Bragg reflection mirror, and including an active layer. A wavelength adjustment region is formed in the lower Bragg reflection mirror or the upper Bragg reflection mirror, and includes a second phase adjustment layer, a wavelength adjustment layer and a first phase adjustment layer, arranged in this order from a side where the resonator region is formed. An optical thickness of the wavelength adjustment region is approximately (2N+1)/4, and the wavelength adjustment layer is formed at a position where an optical distance from an end of the wavelength adjustment region on the side of the resonator region is approximately M/2, where is a wavelength of emitted light, M and N are positive integers, and M is N or less.

A technique relates to a superchannel. Laser cavities include a first laser cavity, a next laser cavity, through a last laser cavity. Modulators include a first modulator, a next modulator, through a last modulator, each having a direct input, an add port, and an output. A concatenated arrangement of the laser cavities is configured to form the superchannel, which includes the last laser cavity coupled to the direct input of the last modulator, and the output of the last modulator coupled to the add port of the next modulator. The arrangement includes the next laser cavity coupled to direct input of the next modulator, and the output of the next modulator coupled to add port of first modulator, along with the first laser cavity coupled to direct input of the first modulator, and the output of first modulator coupled to input of a multiplexer, thus forming the superchannel into multiplexer.

A surface-emitting, single mode laser includes a gain medium and a photonic structure. The gain medium is configured to emit an electromagnetic wave. The photonic structure is electromagnetically coupled to the gain medium and has a cavity mode-dependent scaling of losses so that higher order modes are coupled to more lossy bands and a fundamental mode, at a high symmetry point, is coupled to a less lossy band of the photonic structure.

A laser element includes a light-transmitting substrate with a light emission surface at its back, a first semiconductor layer including a photonic crystal layer, an active layer, a second semiconductor layer, and a light reflection layer with a reflection surface. The photonic crystal layer includes air holes with two-dimensional periodicity in a plane parallel to the active layer and has a diffraction surface that is a wave source when standing light is diffracted in a direction orthogonal to the photonic crystal layer. A distance between the diffraction surface and the reflecting surface is provided such that light intensity of interference light generated by interference between first diffracted light diffracted from the diffraction surface to the light emission surface side and second diffracted light diffracted from the diffraction surface to the light reflection layer side and reflected on the reflecting surface is smaller than light intensity of the first diffracted light.