A structure includes a base; a first mask layer disposed on the base, where the first mask layer has a first channel exposing the base, the first channel comprises a first open end and a second open end, the second open end is close to a surface of the base, the first open end is away from the surface of the base, and an area of an orthographic projection of the first open end in a plane where the base is located is smaller than an area of an orthographic projection of the first channel in the plane; and a second mask layer disposed on the first mask layer, where the second mask layer has a second channel exposing the first mask layer, and the second channel is connected to the first channel.

A group-III nitride semiconductor laser device includes a GaN substrate, and an active layer provided on the GaN substrate, in which the GaN substrate has an oxygen concentration of 510.sup.19 cm.sup.3 or more, and an absorption coefficient of the GaN substrate with respect to an oscillation wavelength of the active layer is greater than an absorption coefficient of the active layer with respect to the oscillation wavelength.

A corrected mesa structure for a VCSEL device is particularly configured to compensate for variations in the shape of the created oxide aperture that result from anisotropic oxidation. In particular, a corrected mesa shape is derived by determining the shape of an as-created aperture formed by oxidizing a circular mesa structure, and then ascertaining the compensation required to convert the as-created shape into a desired (target) shaped aperture opening. The compensation value is then used to modify the shape of the mesa itself such that a following anisotropic oxidation yields a target-shaped oxide aperture.

In some implementations, a vertical cavity surface emitting laser (VCSEL) device includes a substrate layer and a first set of epitaxial layers for a bottom-emitting VCSEL disposed on the substrate layer. The first set of epitaxial layers may include a first set of mirrors and at least one first active layer. The VCSEL device may include a second set of epitaxial layers for a top-emitting VCSEL disposed on the first set of epitaxial layers for the bottom-emitting VCSEL. The second set of epitaxial layers may include a second set of mirrors and at least one second active layer. The top-emitting VCSEL and the bottom-emitting VCSEL may be configured to emit light in opposite light emission directions.

A ridge structure (9) having a ridge lower part (6), a ridge upper part (8) above the ridge lower part (6) and having a larger width than the ridge lower part (6), is formed on a semiconductor substrate (1). A recess (11) of the ridge structure (9), where the ridge lower part (6) is laterally set back from the ridge upper part (8) due to a difference in width between the ridge upper part (8) and the ridge lower part t (6), is completely filled with an insulating film (10) by an atomic layer deposition method to form a protrusion (19) from the semiconductor substrate (1), the ridge structure (9), and the insulating film (10) without any step in a side face of the protrusion (19).

A front facet of the semiconductor laser device includes a resonator facet portion containing an end of an active layer, and a protruding portion which protrudes beyond the resonator facet portion in a resonator length direction by a predetermined protrusion amount and has a stepped bottom surface portion. The resonator facet portion and the stepped bottom surface portion are connected to each other to form a corner portion. The distance from a thickness center position of the active layer to the stepped bottom surface portion is defined by a bottom surface portion depth. The bottom surface portion depth is set to be equal to a predetermined specific depth or deeper than the specific depth.

Methods, systems, and apparatus, including a laser including a layer having first and second regions, the first region including a void; a mirror section provided on the layer, the mirror section including a waveguide core, at least part of the waveguide core is provided over at least a portion of the void; a first grating provided on the waveguide core; a first cladding layer provided between the layer and the waveguide core and supported by the second region of the layer; a second cladding layer provided on the waveguide core; and a heat source configured to change a temperature of at least one of the waveguide core and the grating, where an optical mode propagating in the waveguide core of the mirror section does not incur substantial loss due to interaction with portions of the mirror section above and below the waveguide core.

A backside Vertical Cavity Surface Emitting Laser (VCSEL) has a substrate. A first mirror device is formed on the substrate. An active region is formed on the first mirror device. A second mirror device is formed on the active region. A pillar is formed by directional Inductive Coupled Plasma-Reactive Ion Etcher (ICP-RIE). The pillar exposes a portion of the first mirror device, the active region and the second mirror device. A first metal contact is formed over a top section of the pillar. A second metal contact is formed on the substrate. An opening formed in the second metal contact and aligned with the pillar.

A VCSEG-DFB laser, fully compatible with MGVI design and manufacturing methodologies, for single growth monolithic integration in multi-functional PICs is presented. It comprises a laser PIN structure, in mesa form, etched from upper emitter layer top surface through the active, presumably MQW, gain region, down to the top surface of the lower emitter. Lower electrical contacts sit adjacent the mesa disposed on the lower emitter layer with upper strip contacts disposed atop the upper emitter layer on the mesa top. An SEG is defined/etched from mesa top surface, between the upper strip contacts, through upper emitter layer down to or into the SCH layers. Vertical confinement is provided by the SCH structure and the lateral profile in the bottom portion of the mesa provides lateral confinement. The guided mode interacts with the SEG by the vertical tail penetrating the SEG and evanescent field coupling to the SEG.

Methods, systems, and apparatus, including an optical receiver including an optical source, including a substrate; a laser provided on the substrate, the laser having first and second sides and outputting first light from the first side and second light from the second side, the first light output from the first side of the laser has a first power and the second light output from the second side has a second power; and a first modulator that receives the first light and a second modulator that receives the second light, such that the power of the first light at an input of the first modulator is substantially equal to the power of the second light at an input of the second modulator.