Lateral grounding structure for frequency noise reduction in laser waveguides

A waveguide structure, comprising:

• a substrate;
• a lower cladding layer arranged on the substrate;
• a waveguide core layer arranged on the lower cladding layer, the waveguide core layer configured to generate, guide and amplify laser light;
• a back distributed Bragg reflector (DBR) arranged in the waveguide core layer;
• a front DBR arranged in the waveguide core layer, wherein the back DBR and the front DBR define a laser cavity of the waveguide core layer;
• one or more active regions arranged in the waveguide core layer for light generation and amplification;
• an upper cladding layer arranged on the waveguide core layer, wherein the lower cladding layer, the waveguide core layer, and the upper cladding layer form a waveguide;
• a thermally-controllable heater arranged on the upper cladding layer, the thermally-controllable heater configured to thermally tune a thermally-controllable section of the waveguide core layer;
• a primary waveguide ridge that extends outward from the waveguide core layer in a vertical direction, wherein the primary waveguide ridge is formed by a not-intentionally-doped spacer layer, and a doped layer arranged on the undoped spacer layer,
• wherein the undoped spacer layer is arranged on the waveguide core layer and extends from the waveguide core layer in the vertical direction to form a protrusion that forms a bottom portion of the primary waveguide ridge, and
• wherein the doped layer is arranged on the undoped spacer layer to form an upper portion of the primary waveguide ridge;
• a first secondary ridge laterally displaced from the primary waveguide ridge in a first lateral direction,
• wherein the first secondary ridge is formed by a first protrusion of the upper cladding layer and a first contact layer arranged on the first protrusion of the upper cladding layer;
• and
• a first ground ohmic contact arranged on the first waveguide ridge, the first ground ohmic contact being in contact with the first contact layer.

A method of manufacturing a monolithically-integrated narrow-linewidth tunable semiconductor laser device, the method comprising:

• providing an initial layer stack, comprising:
• a lower cladding layer, the lower cladding layer having a doping of a first conductivity type,
• a waveguide core layer arranged on the lower cladding layer,
• a separation layer arranged on the waveguide core layer, the separation layer being undoped, and
• a not-intentionally-doped setback layer arranged on the separation layer;
• etching the undoped setback layer to form a not-intentionally-doped mesa structure;
• forming an upper cladding layer, the upper cladding layer having a doping of a second conductivity type, wherein forming the upper cladding layer comprises:
• doping the separation layer with dopants of the second conductivity type, where a section of the separation layer underneath the undoped mesa structure remains undoped;
• and
• growing an additional doped layer over the separation layer and over the undoped mesa structure such that the additional doped layer covers peripheral sides and an upper surface of the undoped mesa structure;
• forming a contact layer on the additional doped layer, the contact layer having a doping of a second conductivity type;
• etching the contact layer and the additional doped layer to form a primary waveguide ridge and a plurality of secondary waveguide ridges,
• wherein the primary waveguide ridge includes the undoped mesa structure, a portion of the additional doped layer, and a portion of the contact layer, and
• wherein the portion of the additional doped layer covers the peripheral sides and the upper surface of the undoped mesa structure;
• and
• forming a ground ohmic contact on the portion of the contact layer.

A waveguide structure, comprising:

• a substrate;
• a lower cladding layer arranged on the substrate;
• a waveguide core layer;
• an upper cladding layer arranged on the waveguide core layer, wherein the lower cladding layer, the waveguide core layer, and the upper cladding layer form a waveguide;
• a thermally-controllable heater arranged on the upper cladding layer, the thermally-controllable heater configured to thermally tune a thermally-controllable section of the waveguide core layer;
• a primary waveguide ridge that extends outward from the upper cladding layer in a vertical direction, wherein the primary waveguide ridge is formed by a not-intentionally-doped spacer layer, the upper cladding layer, and a contact layer arranged in a layer stack,
• wherein the undoped spacer layer is arranged on the waveguide core layer and extends from the waveguide core layer in the vertical direction to form a protrusion that forms a partial bottom portion of the primary waveguide ridge,
• wherein the upper cladding layer laterally surrounds and extends over an upper surface of the undoped spacer layer to form peripheral portions and a middle portion of the primary waveguide ridge, and
• the contact layer is arranged on the upper cladding layer to form an upper portion of the primary waveguide ridge;
• and
• a ground ohmic contact arranged on the primary waveguide ridge, the ground ohmic contact being in contact with the contact layer.