Transverse grounding structure for frequency noise reduction in laser waveguide

Abstract

The present disclosure relates to lateral grounding structures for frequency noise reduction in laser waveguides. A waveguide structure includes a waveguide ridge extending outward in a vertical direction from an upper cladding layer. The waveguide ridge is formed from an unintentionally doped spacer layer, an upper cladding layer, and a contact layer arranged in a layer stack. The undoped spacer layer is arranged on a waveguide core layer and extends from the waveguide core layer in a vertical direction to form a portion of a base portion of the waveguide ridge. The upper cladding layer laterally surrounds and extends over an upper surface of the undoped spacer layer to form a perimeter portion and a middle portion of the waveguide ridge. The contact layer is arranged on the upper cladding layer to form an upper portion of the waveguide ridge. A grounded ohmic contact is arranged on the main waveguide ridge, the grounded ohmic contact being in contact with the contact layer.

Description

Cross-references to related applications

[0001] This patent application claims priority to U.S. Provisional Patent Application No. 63 / 782,119, filed April 2, 2025, entitled "Lateral Grounding Structure for Frequency Noise Reduction". The disclosure of the earlier application is considered part of this patent application and is incorporated herein by reference. Technical Field

[0002] This disclosure generally relates to laser waveguides. Background Technology

[0003] Narrow-linewidth, wide-tunable semiconductor lasers are a special type of laser that emits light with a very small spectral width (narrow linewidth) and can be tuned across a wide wavelength range (wide-tunable). These characteristics make narrow-linewidth, wide-tunable semiconductor lasers ideal for applications requiring high coherence and precise wavelength control. With a narrow linewidth, the laser emits light with very small frequency variations, typically in the kilohertz (kHz) or sub-kHz range, thus achieving high coherence. This high coherence can be used in spectroscopy, coherent optical communication, and sensing applications. With wide-tunability, the output wavelength of the laser can be tuned across a wide spectral range, typically tens of nanometers or more. Wavelength tuning can be achieved through mechanisms such as thermal tuning, current injection, or external cavity design. Narrow-linewidth, wide-tunable semiconductor lasers can be semiconductor-based lasers that use one or more semiconductor gain materials to generate the laser beam. Summary of the Invention

[0004] In some embodiments, the waveguide structure includes: a substrate; a lower cladding disposed on the substrate; a waveguide core disposed on the lower cladding, the waveguide core configured to generate, guide, and amplify laser light; a back-facing distributed Bragg reflector (DBR) disposed in the waveguide core; a forward-facing DBR disposed in the waveguide core, wherein the back-facing DBR and the forward-facing DBR define a laser cavity for the waveguide core; one or more active regions disposed in the waveguide core for generating and amplifying light; an upper cladding disposed on the waveguide core, wherein the lower cladding, the waveguide core, and the upper cladding form a waveguide; and a thermally controllable heater disposed on the upper cladding, the thermally controllable heater being configured to... The waveguide ridge includes a thermally controllable section of the layer for thermal tuning; a main waveguide ridge extending vertically outward from the upper cladding, wherein the main waveguide ridge is formed by unintentionally doped spacer layers, an upper cladding, and a contact layer arranged in a stacked manner, wherein undoped spacer layers are disposed on the waveguide core layer and extend vertically from the waveguide core layer to form protrusions that form a portion of the bottom portion of the main waveguide ridge, wherein the upper cladding laterally surrounds and extends to cover the upper surface of the undoped spacer layers to form a peripheral and intermediate portion of the main waveguide ridge, and a contact layer is disposed on the upper cladding to form the upper portion of the main waveguide ridge; and a ground ohmic contact disposed on the main waveguide ridge, the ground ohmic contact contacting the contact layer.

[0005] In some embodiments, the waveguide structure includes: a substrate; a lower cladding disposed on the substrate; a waveguide core disposed on the lower cladding, the waveguide core configured to generate, guide, and amplify laser light; a back-facing DBR disposed in the waveguide core; a forward-facing DBR disposed in the waveguide core, wherein the back-facing DBR and the forward-facing DBR define a laser cavity in the waveguide core; one or more active regions disposed in the waveguide core for light generation and amplification; an upper cladding disposed on the waveguide core, wherein the lower cladding, the waveguide core, and the upper cladding form a waveguide; a thermally controllable heater disposed on the upper cladding, the thermally controllable heater configured to thermally tune a thermally controllable segment of the waveguide core; and a laser core from the waveguide core. A main waveguide ridge extending outward in a vertical direction, wherein the main waveguide ridge is formed by an undoped spacer layer and a doped layer disposed on an undoped spacer layer, wherein the undoped spacer layer is disposed on a waveguide core layer and extends vertically from the waveguide core layer to form a protrusion forming a bottom portion of the main waveguide ridge, and wherein the doped layer is disposed on the undoped spacer layer to form an upper portion of the main waveguide ridge; a first stage ridge laterally displaced from the main waveguide ridge in a first lateral direction, wherein the first stage ridge is formed by a first protrusion of an upper cladding and a first contact layer disposed on the first protrusion of the upper cladding; and a first ground ohmic contact disposed on the first stage ridge, the first ground ohmic contact contacting the first contact layer.

[0006] In some embodiments, a method of fabricating a monolithically integrated narrow-linewidth tunable semiconductor laser device includes: providing an initial layer stack structure comprising: a lower cladding layer doped with a first conductivity type, a waveguide core layer disposed on the lower cladding layer, an undoped separation layer disposed on the waveguide core layer, and an unintentionally doped retreat layer disposed on the separation layer; etching the undoped retreat layer to form an unintentionally doped mesa structure; and forming an upper cladding layer doped with a second conductivity type, wherein forming the upper cladding layer includes: doping the separation layer with a dopant of the second conductivity type, wherein the undoped mesa structure... The lower separation layer section remains undoped; and an additional doped layer is grown on the separation layer and the undoped mesa structure such that the additional doped layer covers the peripheral side and the upper surface of the undoped mesa structure; a contact layer is formed on the additional doped layer, the contact layer having a second conductivity type doping; the contact layer and the additional doped layer are etched to form a main waveguide ridge and a plurality of secondary ridges, wherein the main waveguide ridge includes portions of the undoped mesa structure, the additional doped layer, and the contact layer, and wherein portions of the additional doped layer cover the peripheral side and the upper surface of the undoped mesa structure; and a ground ohmic contact is formed on portions of the contact layer.

[0007] In some embodiments, the waveguide structure includes: a substrate; a lower cladding disposed on the substrate; a waveguide core layer; an upper cladding layer disposed 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 disposed on the upper cladding layer, the thermally controllable heater being configured to thermally tune a thermally controllable segment of the waveguide core layer; and a main waveguide ridge extending outward in a vertical direction from the upper cladding layer, wherein the main waveguide ridge comprises unintentionally doped spacer layers and the upper cladding layer arranged in a stacked manner. A contact layer is formed, wherein an undoped spacer layer is disposed on the waveguide core layer and extends vertically from the waveguide core layer to form a protrusion that forms a portion of the bottom portion of the main waveguide ridge, wherein an upper cladding laterally surrounds and extends to cover the upper surface of the undoped spacer layer to form a peripheral portion and a middle portion of the main waveguide ridge, and a contact layer is disposed on the upper cladding to form the upper portion of the main waveguide ridge; and a ground ohmic contact is disposed on the main waveguide ridge, the ground ohmic contact contacting the contact layer. Attached Figure Description

[0008] Figure 1 A longitudinal cross-sectional view of a waveguide structure associated with a narrow linewidth, wide-tunable semiconductor laser device according to one or more embodiments is shown, the structure having thermal tuning capability.

[0009] Figure 2 A cross-sectional view of a waveguide structure according to one or more embodiments is shown.

[0010] Figure 3A cross-sectional view of a waveguide structure according to one or more embodiments is shown.

[0011] Figures 4A-4D The invention illustrates a manufacturing process for fabricating a ridge-top grounded waveguide structure according to one or more embodiments. Detailed Implementation

[0012] The following detailed description of exemplary embodiments is provided with reference to the accompanying drawings. The same reference numerals in different drawings may identify the same or similar elements.

[0013] A vernier-tuned laser structure is a tunable semiconductor laser that utilizes the vernier effect to achieve wide wavelength tuning. A vernier-tuned laser structure can include two or more wavelength selection elements. By co-tuning these two or more wavelength selection elements, the wavelengths at which the transmission peaks of the two or more wavelength selection elements are aligned can be selected, thus allowing for a large tuning range. A vernier-tuned laser structure includes a thermally tunable forward mirror, a thermally tunable back mirror, a thermally tunable phase segment, and a passive waveguide segment connecting the phase segment. The forward and back mirrors together provide supermode selection and enhanced longitudinal mode selection.

[0014] Semiconductor optical amplifiers (SOAs) are optical amplifiers based on semiconductor gain media. Quantum wells are nanoscale thin layers of semiconductor material designed to confine electrons or holes in one dimension (perpendicular to the layer surface) while allowing them to move freely in the other two dimensions. Multiple quantum well (MQW) structures consist of multiple quantum wells separated by thin barrier layers, typically made of a semiconductor material with a wider bandgap than the well material. MQWs are used as the active region in laser diodes, providing optical gain. Vernier-tuned lasers include one or more amplification sections located between a front mirror and a back mirror; these are called gain sections.

[0015] Ideally, vernier-tuned laser structures are transparent to the guided optical modes and tunable via thermo-optical effects (e.g., localized temperature-induced refractive index changes caused by one or more electrically isolated but thermally connected resistive microheaters). In practice, waveguides are formed from semiconductor materials doped with impurities in their electron and valence bands to form pin diodes. Pin diodes enable the injection of current into the laser's active region to generate optical gain through stimulated emission, but are largely unnecessary for thermally tunable or passive waveguides. Furthermore, carrier fluctuations (e.g., the generation and recombination of electron-hole pairs) naturally occur in these nominally transparent semiconductor waveguides. Generation processes include thermal generation and nonlinear optical (two-photon) absorption. Recombination occurs via nonradiative (defect- or trap-assisted), radiative, or Auger recombination. Carrier generation and recombination produce unwanted refractive index fluctuations over time. These fluctuations, in turn, lead to excessive frequency noise (referred to as excessive mid-band frequency noise) in the Fourier frequency range up to approximately ~10-100 MHz, which is related to the time constant of the recombination process itself. This excess noise also adds to the white (Gaussian) noise associated with the instantaneous laser linewidth. When such a laser with excess noise is used as a local oscillator in a coherent transmission system, it will cause degradation in signal recovery, ultimately limiting the laser's transmission distance.

[0016] If the quasi-Fermi levels in the semiconductor material (e.g., InGaAsP) constituting the tuning waveguide section of a vernier-tuned laser structure are maintained at a constant potential, carrier fluctuations can be reduced. These quasi-Fermi levels describe the chemical potentials or particle number statistics for electrons and holes in a pin diode, and these chemical potentials can be fixed by electrically connecting them to an external voltage source. For example, fixing the chemical potentials can be achieved by forming a metal electrode and an ohmic contact to the p-type doped upper cladding of the waveguide, and electrically connecting (grounding) the electrode to the n-type doped lower cladding via a common n-type doped substrate, as shown below. Figure 3 Example 300 is shown in the diagram. In this case, the fixed potential difference is zero volts. This previous method—called Ridge Top Grounding (RTG) because it places the contact vertically on the etched ridge waveguide—increases excessive optical absorption from free carrier absorption in p-type doped InP, interband absorption in the p+InGaAs contact layer, and absorption from the metal ohmic contact. This excessive optical absorption, combined with the intense light propagation beam within the laser cavity, leads to light-induced self-heating, resulting in unintended thermal gradients along the lengths of the forward and backward mirrors of the vernier-tuned laser structure. These unintended thermal gradients generate unwanted chirps that form the gratings of each mirror, thereby reducing the spectral filtering characteristics of the forward and backward mirrors and consequently reducing the spectral purity of the laser.

[0017] Some implementations provide waveguide structures with improved frequency noise characteristics. This waveguide structure can be a portion of a narrow-linewidth, wide-tunable semiconductor laser with improved frequency noise characteristics. The waveguide structure can include a vernier-tuned laser structure for providing wavelength-tunable laser light with a narrow linewidth. The waveguide structure can be configured to mitigate carrier fluctuations in the thermally tunable forward mirror, thermally tunable back mirror, thermally tunable phase section, and passive waveguide section in a manner compatible with the vernier-tuned laser structure. Therefore, techniques can be used to control carrier fluctuations to minimize light absorption in the waveguide. In some implementations, a monolithically integrated narrow-linewidth tunable semiconductor laser is provided for coherent transmission at 800 Gbps and above, with an extended band tuning range (C++, L++). The C++ and L++ bands refer to extended wavelength ranges in fiber optic communication beyond the standard C-band (1530-1565 nm) and L-band (1565-1625 nm). For example, the C++ band includes a wavelength range of 1505-1530 nm in addition to the standard C band, and the L++ band includes a wavelength range of 1625-1675 nm in addition to the standard L band.

[0018] In some implementations, an undoped spacer layer (so-called doped retreat layer or unintentionally doped spacer layer) that has been laterally patterned can be provided. Therefore, the p-type doping in the periphery of the ridge waveguide facilitates electrical grounding without causing excessive optical loss. The undoped spacer layer keeps the evanescent optical field away from the absorption layer. Additionally, the lossy p+-InGaAs contact layer and metal electrodes are moved onto so-called “secondary ridges” that operate parallel to the “primary” (optically active) ridge waveguide. The lateral conductive path between the secondary and primary ridge waveguides provides carrier wave control.

[0019] Figure 1 A cross-section of a waveguide structure 100 associated with a narrow-linewidth, wide-tunable semiconductor laser device is shown, which has thermal tuning capabilities. This cross-section can be taken along the length of the waveguide structure 100 parallel to the output direction of the output laser (e.g., parallel to the propagation direction).

[0020] Waveguide structure 100 can be a vernier-tuned laser structure. The narrow-linewidth, wide-tunable semiconductor laser structure of waveguide structure 100 can be monolithically integrated for coherent transmission at 800 Gbps and above, with extended band tuning range (C++, L++). In some examples, waveguide structure 100 can be referred to as a ridge waveguide structure having one or more waveguide ridges (e.g., a primary waveguide ridge and a secondary waveguide ridge).

[0021] Waveguide structure 100 may include a substrate 102 (e.g., an indium phosphide (InP) substrate); a sacrificial layer 104 disposed on the substrate 102 and defining a thermally insulating section 106 (e.g., an air gap); a lower cladding 108 disposed on the substrate 102 (e.g., disposed on the sacrificial layer 104); a waveguide core layer 110 disposed on the lower cladding 108; and an upper cladding 112 disposed on the waveguide core layer 110. The lower cladding 108, the waveguide core layer 110, and the upper cladding 112 form a waveguide. The waveguide core layer 110 is configured to generate, guide, and amplify laser light. In some examples, the lower cladding 108 may be an n-type doped InP layer (e.g., an n-InP layer), the waveguide core layer 110 may be an InGaAsP layer, and the upper cladding 112 may be a p-type doped InP layer (e.g., a p-InP layer). n-type doping can be referred to as the first conductivity type, and p-type doping can be referred to as the second conductivity type.

[0022] The waveguide structure 100 may further include a back-facing distributed Bragg reflector (DBR) 114 disposed in the waveguide core layer 110, a forward DBR 116 disposed in the waveguide core layer 110, a first active region 118 disposed in the waveguide core layer 110 for light generation and amplification, a phase control segment 120 disposed in the waveguide core layer 110, and a second active region 122 disposed in the waveguide core layer 110 for light amplification. The back-facing DBR 114 and the forward DBR 116 define a laser cavity in the waveguide core layer 110, in which the first active region 118 and the phase control segment 120 are disposed. The first active region 118 includes an optical gain medium for generating and amplifying light based on stimulated emission. Intracavity light is reflected back and forth between the back-facing DBR 114 and the forward DBR 116 within the laser cavity, and some of the intracavity light eventually exits the laser cavity as laser light. The phase control section 120 can be thermally controlled (e.g., thermally tunable) to adjust the round-trip phase of the light within the cavity. The second active region 122 includes an optical gain medium for amplifying the light exiting the laser cavity before it exits from the waveguide structure 100. The second active region 122 can form an SOA and therefore can be provided in the SOA section of the waveguide structure 100.

[0023] The waveguide structure 100 may further include a bottom electrode 124 and a plurality of top electrodes 126-1 and 126-2. The top electrodes 126-1 and 126-2 may each be arranged over a corresponding active region to pump current through their respective active regions for inducing stimulated emission in those regions. Current flows from the top electrodes 126-1 and 126-2 through their respective active regions to the bottom electrode 124, or vice versa. Therefore, the top electrode 126-1 may be arranged over a first active region 118, and the top electrode 126-2 may be arranged over a second active region 122.

[0024] The waveguide structure 100 may also include a plurality of thermally controllable heaters (e.g., microheaters) above the non-active region of the waveguide core layer 110. Therefore, a plurality of thermally controllable heaters may be arranged on the upper cladding 112. Each of the plurality of thermally controllable heaters can thermally tune a corresponding thermally controllable segment of the waveguide core layer 110. The plurality of thermally controllable heaters can be controlled to apply thermally controllable heat to their respective thermally controllable segments. For example, the plurality of thermally controllable heaters may include a first thermally controllable heater 128-1 arranged above the forward DBR 116 for thermally tuning the forward DBR 116. Additionally, the plurality of thermally controllable heaters may include a second thermally controllable heater 128-2 arranged above the phase control segment 120 for thermally tuning the phase control segment 120. Furthermore, the plurality of thermally controllable heaters may include a third thermally controllable heater 128-3 arranged above the backward DBR 114 for thermally tuning the backward DBR 114.

[0025] The back-facing DBR 114 and forward-facing DBR 116, acting as wavelength selection elements, can be thermally tuned to adjust the wavelength of the laser output from the laser cavity. Due to the thermo-optic effect, temperature affects the refractive index of the semiconductor material. Thermal tuning of the back-facing DBR 114 and forward-facing DBR 116 causes a thermo-optic shift in their reflectivity peaks, altering the wavelength aligned with these peaks. Consequently, the wavelength of the laser output from the laser cavity changes. This type of wavelength tuning is called "vernier-based tuning." Therefore, the forward-facing DBR 116 and back-facing DBR 114 form a wavelength-selective filter, allowing the laser to be generated within a narrow wavelength range. Furthermore, by using the thermo-optic effect to change the refractive index in the phase control section 120, the round-trip phase of the intracavity light can be adjusted, thereby fine-tuning the wavelength that resonates with the cavity and is least attenuated by the DBR filtering effect.

[0026] The sacrificial layer 104 can provide structural support to the lower cladding 108. In some cases, the sacrificial layer 104 can provide a thermal path between multiple thermally controllable heaters and the substrate 102.

[0027] The gain section corresponding to the first active region 118 and the SOA section corresponding to the second active region 122 can be referred to as non-thermally controllable sections because these sections are not thermally controlled or tuned by thermally controllable heaters (e.g., on-chip heater sections). In contrast, the back-facing DBR 114, the forward-facing DBR 116, and the phase control section 120 can be referred to as thermally controllable sections because these sections are thermally controlled or tuned by thermally controllable heaters. It should be noted that the gain section and the SOA section can be thermally controlled in other ways. For example, the gain section and the SOA section can be cooled by separate mechanisms, such as by mounting the entire chip on a thermoelectric cooler (TEC), to manage temperature.

[0028] As mentioned above, Figure 1 Provided as an example. Other examples may be related to... Figure 1 The descriptions are different. Figure 1 The number and arrangement of the devices and components shown are provided as examples. In reality, there may be more. Figure 1 Additional equipment or components, more or fewer equipment or components, different equipment or components, or equipment or components arranged differently from those components shown.

[0029] Figure 2 A cross-section of a waveguide structure 200 according to one or more embodiments is shown. The waveguide structure 200 can be incorporated into... Figure 1 The waveguide structure 100 described in the text. For example, Figure 2 The cross section shown can be cut along the width direction of the waveguide structure 100, which is transverse to the output direction of the output laser (e.g., perpendicular to the propagation direction). Figure 2 The cross-section shown can be cut across the thermally controllable section of waveguide structure 100. For example, Figure 2 The cross section shown can be cut across the back-facing DBR 114, the forward-facing DBR 116, or the phase control section 120. Therefore, the waveguide structure 200 can be part of a vernier-tuned laser structure with a monolithically integrated narrow-linewidth, wide-tunable semiconductor laser structure for coherent transmission at 800 Gbps and above, with an extended band tuning range (C++, L++).

[0030] Waveguide structure 200 includes a waveguide formed by a lower cladding 108, a waveguide core layer 110, and an upper cladding 112, as described above. Figure 1 The waveguide core layer 110 may include a mode guiding region in which light is guided for propagation. A thermally controllable heater 128 is disposed on the upper cladding 112. The thermally controllable heater 128 is configured as a thermally controllable segment of the thermally tuned waveguide core layer 110.

[0031] Waveguide structure 200 includes a main waveguide ridge 202 extending outward in a vertical direction from the upper cladding 112. Additionally, waveguide structure 200 may include secondary waveguide ridges laterally displaced from the main waveguide ridge 202. For example, waveguide structure 200 may include a first-stage waveguide ridge 204-1 laterally displaced from the main waveguide ridge 202 in a first lateral direction (e.g., on the left lateral side), and a second-stage waveguide ridge 204-2 laterally displaced from the main waveguide ridge 202 in a second lateral direction opposite to the first lateral direction (e.g., on the right lateral side). One of the thermally controllable heaters 128 is laterally arranged between the main waveguide ridge 202 and the first-stage waveguide ridge 204-1, and the other of the thermally controllable heaters 128 is laterally arranged between the main waveguide ridge 202 and the second-stage waveguide ridge 204-2.

[0032] The main waveguide ridge 202 is formed by a spacer layer 206, an upper cladding layer 112, and a contact layer 208 arranged in a stacked manner. The spacer layer 206 may be referred to as a doped spacer layer or an unintentionally doped layer (some unintentional doping may occur during the processing). Therefore, the spacer layer 206 may be undoped, or may have some unintentional doping that occurs during the processing. The spacer layer 206 may be disposed on the waveguide core layer 110 and may extend vertically from the waveguide core layer 110 to form a protrusion that forms part of the bottom portion of the main waveguide ridge 202.

[0033] The main waveguide ridge 202 is also formed by an upper cladding 112. Here, the doped upper cladding 112 laterally surrounds and extends to cover the upper surface of the spacer layer 206 to form the peripheral and central portions of the main waveguide ridge 202.

[0034] A contact layer 208 (e.g., a p-InGaAs layer) can be arranged in the main waveguide ridge 202 on the upper cladding 112 to form the upper portion of the main waveguide ridge 202.

[0035] The lower cladding 108, upper cladding 112, and spacer layer 206 may be indium phosphide (InP) layers, the waveguide core layer 110 may be an InGaAsP layer, and the contact layer 208 may be an indium gallium arsenide (InGaAs) layer. Additionally, the lower cladding 108 may have a first conductivity type (e.g., n-type), and the upper cladding 112 and contact layer 208 may have a second conductivity type (e.g., p-type). Furthermore, in some embodiments, the main waveguide ridge 202 may include a diffusion barrier layer 210 disposed on the upper surface of the spacer layer 206, between the spacer layer 206 and the upper cladding 112 within the main waveguide ridge 202. The diffusion barrier layer 210 may be a silicon-doped diffusion barrier layer. In some examples, the diffusion barrier layer 210 may be an n-type diffusion barrier layer configured to block the diffusion of a second conductivity type (e.g., p-type) dopant.

[0036] The waveguide structure 200 may also include a grounding ohmic contact 212 disposed on the main waveguide ridge 202, which contacts the contact layer 208. Therefore, the main waveguide ridge 202 can be referred to as a ridge-top grounding structure. The peripheral and central portions of the main waveguide ridge 202 formed by the upper cladding 112 are configured to facilitate electrical grounding without causing excessive optical loss. For example, the p-InP portion formed by the upper cladding 112 within the main waveguide ridge 202 adds p-type doping to the periphery of the main waveguide ridge 202. In this region, the overlap of the p-type doping with the optical mode field minimizes the disruption to the optical mode, while the p-type doping helps maintain a constant potential.

[0037] The waveguide structure 200 may also include a dielectric layer 214 disposed on the upper cladding 112, the main waveguide ridge 202, the first-stage waveguide ridge 204-1, and the second-stage waveguide ridge 204-2. The dielectric layer 214 is disposed between the upper cladding 112 and the thermally controlled heater 128. Furthermore, the dielectric layer 214 conforms to the shape of the main waveguide ridge 202, the first-stage waveguide ridge 204-1, and the second-stage waveguide ridge 204-2. The dielectric layer 214 provides electrical isolation to the waveguide.

[0038] The first-stage waveguide ridge 204-1 can be formed by a first protrusion 112-1 of the upper cladding 112 and a first ground contact layer 216-1 (e.g., a p-InGaAs layer) disposed on the first protrusion 112-1. The second-stage waveguide ridge 204-2 can be formed by a second protrusion 112-2 of the upper cladding 112 and a second ground contact layer 216-2 (e.g., a p-InGaAs layer) disposed on the second protrusion 112-2.

[0039] The main waveguide ridge 202 forms stripes at the top of the waveguide structure 200 along the upper cladding 112 in the longitudinal direction. Similarly, the first-stage ridge 204-1 and the second-stage ridge 204-2 form stripes at the top of the waveguide structure 200 along the upper cladding 112 in the longitudinal direction. The first-stage ridge 204-1 and the second-stage ridge 204-2 extend parallel to the main waveguide ridge 202 in the longitudinal direction of the waveguide structure 200. Thermo-controllable heater 128 extends parallel to the main waveguide ridge 202 at the top of the waveguide structure 200 along the upper cladding 112 in the longitudinal direction.

[0040] Additionally, the waveguide of waveguide structure 200 includes one or more non-thermally controllable segments, each of which includes an active region. Spacer layer 206 is provided at each thermally controllable segment of the waveguide, but not at the non-thermally controllable segments. In other words, the longitudinal segment of the main waveguide ridge 202 arranged within the gain segment of waveguide structure 200 does not include spacer layer 206, while the longitudinal segment of the main waveguide ridge 202 arranged within the thermally controllable segment of waveguide structure 200 does include spacer layer 206. Here, "non-thermally controllable segment" refers to a segment that is not thermally controlled or tuned by a thermally controllable heater, while "thermally controllable segment" refers to a segment that is thermally controlled or tuned by a thermally controllable heater. It should be noted that non-thermally controllable segments may be thermally controlled in other ways. For example, the gain segment and SOA segment may be cooled by separate mechanisms, such as by mounting the entire chip on a thermoelectric cooler (TEC), to manage temperature.

[0041] As mentioned above, Figure 2 Provided as an example. Other examples may be related to... Figure 2 The descriptions are different.

[0042] Figure 3 A cross-section of a waveguide structure 300 according to one or more embodiments is shown. The waveguide structure 300 can be incorporated into... Figure 1 The waveguide structure 100 described in the text. For example, Figure 3 The cross section can be cut vertically along the width direction of the waveguide structure 100, which is transverse to the output direction of the output laser (e.g., vertical to the propagation direction). Figure 3 The cross-section shown can be cut across the thermally controllable section of waveguide structure 100. For example, Figure 3 The cross section shown can be cut across the back-facing DBR 114, the forward-facing DBR 116, or the phase control section 120. Therefore, the waveguide structure 300 can be part of a narrow-linewidth, wide-tuning-range, monolithically integrated vernier-tuned laser structure with extended band tuning range (C++, L++) for coherent transmission at 800 Gbps and above.

[0043] Waveguide structure 300 includes a waveguide formed by a lower cladding 108, a waveguide core layer 110, and an upper cladding 112, as described above. Figure 1 The waveguide core 110 may include an optical mode field guiding region in which light is guided for propagation. A thermally controllable heater 128 is disposed on the upper cladding 112. The thermally controllable heater 128 is configured to thermally tune a thermally controllable segment of the waveguide core 110.

[0044] The waveguide structure 300 includes a main waveguide ridge 302 extending outward in a vertical direction from the waveguide core layer 110. Additionally, the waveguide structure 300 includes secondary ridges laterally displaced from the main waveguide ridge 302. For example, the waveguide structure 300 may include a first secondary ridge 304-1 laterally displaced from the main waveguide ridge 302 in a first lateral direction (e.g., on the left lateral side), and a second secondary ridge 304-2 laterally displaced from the main waveguide ridge 302 in a second lateral direction opposite to the first lateral direction (e.g., on the right lateral side). One of the thermally controllable heaters 128 is laterally arranged between the main waveguide ridge 302 and the first secondary ridge 304-1, and the other of the thermally controllable heaters 128 is laterally arranged between the main waveguide ridge 302 and the second secondary ridge 304-2.

[0045] The main waveguide ridge 302 can be formed by a spacer layer 306 (e.g., an InP layer) and a doped layer 308 (e.g., a p-InP layer) disposed on the spacer layer 306. The spacer layer 306 can be referred to as a doped spacer layer or an unintentionally doped layer (some unintentional doping may occur during the processing). Therefore, the spacer layer 306 can be undoped or may have some unintentional doping that occurs during the processing. The spacer layer 306 can be disposed on the waveguide core layer 110 and can extend vertically from the waveguide core layer 110 to form a protrusion that forms the bottom portion of the main waveguide ridge 302. The doped layer 308 can be disposed on the spacer layer 306 to form the upper portion of the main waveguide ridge 302. An upper cladding layer 112 extends laterally from the spacer layer 306.

[0046] Additionally, the main waveguide ridge 302 may include a diffusion barrier layer 310 disposed between the spacer layer 306 and the doped layer 308. The diffusion barrier layer 310 may be a silicon-doped diffusion barrier layer. In some examples, the diffusion barrier layer 310 may be an n-type diffusion barrier layer configured to block the diffusion of a second conductivity type (e.g., p-type) dopant. The spacer layer 306 and the doped layer 308 extend laterally across the entire lateral dimension of the main waveguide ridge 302. If a diffusion barrier layer 310 is present, it may also extend laterally across the entire lateral dimension of the main waveguide ridge 302. The lower cladding layer 108, the upper cladding layer 112, the spacer layer 306, and the doped layer 308 may be indium phosphide (InP) layers, wherein the lower cladding layer has a first conductivity type (e.g., n-type), while the upper cladding layer 112 and the doped layer 308 have a second conductivity type (e.g., p-type).

[0047] The first stage ridge 304-1 is formed by a first protrusion 112-1 of the upper cladding 112 and a first contact layer 312-1 (e.g., a p-InGaAs layer) disposed on the first protrusion 112-1. The second stage ridge 304-2 is formed by a second protrusion 112-2 of the upper cladding 112 and a second contact layer 312-2 (e.g., a p-InGaAs layer) disposed on the second protrusion 112-2. Therefore, the first and second contact layers can be indium gallium arsenide (InGaAs) layers and can have a second conductivity type.

[0048] The waveguide structure 300 may further include a first ground ohmic contact 314-1 disposed on the primary waveguide ridge 304-1, which contacts the first contact layer 312-1. Additionally, the waveguide structure 300 may further include a second ground ohmic contact 314-2 disposed on the secondary waveguide ridge 304-2, which contacts the second contact layer 312-2. Therefore, the primary waveguide ridge 304-1 and the secondary waveguide ridge 304-2 can be referred to as a ridge-top grounding structure. In this way, the optically destructive InGaAs and metal ohmic contact layers are removed from the primary waveguide ridge 302 and moved to the secondary ridges 304-1 and 304-2, which have lower absorption capabilities for light scattered from the grating, and optical self-heating is minimized. In addition, the lateral conductive paths between the first-stage ridge 304-1 and the main waveguide ridge 302, as well as the lateral conductive paths between the second-stage waveguide ridge 304-2 and the main waveguide ridge 302, provide carrier wave control.

[0049] The waveguide structure 300 may further include a dielectric layer 316 disposed on the upper cladding 112, the main waveguide ridge 302, the first-stage waveguide ridge 304-1, and the second-stage waveguide ridge 304-2. The dielectric layer 316 is disposed between the upper cladding 112 and the thermally controllable heater 128. Furthermore, the dielectric layer 316 conforms to the shape of the main waveguide ridge 302, the first-stage ridge 304-1, and the second-stage ridge 304-2. The dielectric layer 316 provides electrical isolation to the waveguide.

[0050] As mentioned above, Figure 3 Provided as an example. Other examples may be related to... Figure 3 The descriptions are different.

[0051] Figures 4A-4D A manufacturing process for producing an RTG waveguide structure is illustrated according to one or more embodiments. For example, this manufacturing process can be used to manufacture a combination of... Figure 2 The waveguide structure described is 200.

[0052] Figure 4AA process stage 400A according to one or more embodiments of a fabrication process is illustrated. Process stage 400A may include forming (e.g., via epitaxial layer growth) an initial layer stack comprising an n-InP lower cladding 401, an undoped InGaAsP waveguide core layer 402, an undoped separator layer 403, an undoped InGaAsP ridge etch stop layer 404, and an undoped InP retreat layer 405. In some examples, an n-InP diffusion barrier layer may be formed on the undoped InP retreat layer 405. Additionally, a dielectric mask 407 may be formed on the undoped InP spacer layer 405 (or, if present, on the n-InP diffusion barrier layer 406) at a location corresponding to the main waveguide ridge to be formed. The undoped layers referenced above may be unintentionally doped layers.

[0053] Figure 4B A process stage 400B according to one or more embodiments of a manufacturing process is illustrated. Process stage 400B may include etching an undoped InP retreat layer 405 to form an undoped mesa structure 408 (or an unintentionally doped mesa structure) including the remainder of the undoped InP retreat layer 405. If present, the remainder of an n-InP diffusion barrier layer 406 may be provided on top of the undoped mesa structure 408. The undoped mesa structure 408 may form the substrate of the main waveguide ridge.

[0054] Figure 4C A process stage 400C according to one or more embodiments of a manufacturing process is illustrated. Process stage 400C may include the overgrowth of a p-doped InP upper cladding layer 409 and a p+InGaAs contact layer 410 on an InGaAsP ridge etch stop layer 404. The overgrowth of the p-doped InP upper cladding layer 409, together with the undoped separator layer 403 and the undoped InGaAsP ridge etch stop layer 404, may form an upper cladding layer 411 with a second conductivity type (e.g., p-type) doping. For example, forming the upper cladding layer 411 may include doping the undoped separator layer 403 and the undoped InGaAsP ridge etch stop layer 404 with a dopant of the second conductivity type to form a p-InP separator layer and a p-doped ridge etch stop layer, wherein the undoped separator layer 403 and the undoped ridge etch stop layer 404 remain undoped in a segment 412 below the undoped mesa structure 408. The undoped separation layer 403 and the undoped ridge etch stop layer 404, along with the undoped mesa structure 408, form the undoped spacer layer (or unintentionally doped spacer layer) of the main waveguide ridge.

[0055] Forming the upper cladding 411 may also include overgrowing a p-doped InP upper cladding 409 as an additional doped layer (e.g., p-InP) over the separation layer 403 (e.g., above the ridge etch stop layer 404) and over the undoped mesa structure 408, such that the additional doped layer covers the peripheral side and upper surface of the undoped mesa structure 408. Once the additional doped layer is formed, process stage 400C may include forming a contact layer 410 having a second conductivity type of doping on the p-doped InP upper cladding (e.g., on the additional doped layer).

[0056] Figure 4D A process stage 400D according to one or more embodiments of a manufacturing process is illustrated. Process stage 400D may include etching a contact layer 410 and a p-doped InP upper cladding (e.g., an additional doped layer) to form a primary waveguide ridge and a plurality of secondary waveguide ridges (e.g., two secondary waveguide ridges). The primary waveguide ridge includes an undoped mesa structure 408, a portion of the p-doped InP upper cladding 409, and a portion of the contact layer 410. This portion of the p-doped InP upper cladding 409 covers the peripheral side and upper surface of the undoped mesa structure 408.

[0057] Additionally, a ground ohmic contact (e.g., ground ohmic contact 212) may be deposited or otherwise formed on this portion of the contact layer 410 of the main waveguide ridge. For example, after the main waveguide ridge and the secondary waveguide ridge are formed, the fabrication process may include passivation dielectric deposition, contact window opening, and P-type ohmic metallization.

[0058] As mentioned above, Figures 4A-4D This is provided as an example. Other examples may differ from those provided. Figures 4A-4D The description. In some cases, the combination can be modified. Figures 4A-4D The described manufacturing process combines manufacturing processes. Figure 3 The waveguide structure described is 300.

[0059] The following provides an overview of some aspects of this disclosure:

[0060] Aspect 1: A waveguide structure comprising: a substrate; a lower cladding disposed on the substrate; a waveguide core disposed on the lower cladding, the waveguide core being configured to generate, guide, and amplify laser light; a back-facing DBR disposed in the waveguide core; a forward-facing DBR disposed in the waveguide core, wherein the back-facing DBR and the forward-facing DBR define a laser cavity of the waveguide core; one or more active regions disposed in the waveguide core for generating and amplifying light; an upper cladding disposed on the waveguide core, wherein the lower cladding, the waveguide core, and the upper cladding form a waveguide; and a thermally controllable heater disposed on the upper cladding, the thermally controllable heater being configured to thermally controllable regions of the waveguide core. The waveguide ridge is thermally tuned; a main waveguide ridge extends vertically outward from the upper cladding, wherein the main waveguide ridge is formed by an unintentionally doped spacer layer, an upper cladding, and a contact layer arranged in a stacked manner, wherein an undoped spacer layer is disposed on the waveguide core layer and extends vertically from the waveguide core layer to form a protrusion that forms a portion of the bottom portion of the main waveguide ridge, wherein the upper cladding laterally surrounds and extends to cover the upper surface of the undoped spacer layer to form a peripheral portion and a middle portion of the main waveguide ridge, and a contact layer is disposed on the upper cladding to form the upper portion of the main waveguide ridge; and a ground ohmic contact is disposed on the main waveguide ridge, which contacts the contact layer.

[0061] Aspect 2: The waveguide structure according to Aspect 1, wherein the waveguide includes a non-thermally controllable segment of an active region in one or more active regions, and wherein an undoped spacer layer is disposed on the thermally controllable segment of the waveguide and is not present on the non-thermally controllable segment of the waveguide.

[0062] Aspect 3: The waveguide structure according to any one of Aspects 1-2, wherein the peripheral and intermediate portions of the main waveguide ridge formed by the upper cladding are configured to facilitate electrical grounding without causing excessive optical loss.

[0063] Aspect 4: The waveguide structure according to any one of Aspects 1-3, wherein the lower cladding has a first conductivity type, and wherein the upper cladding and the contact layer have a second conductivity type.

[0064] Aspect 5: The waveguide structure according to aspect 4, wherein the main waveguide ridge includes a diffusion barrier layer disposed on the upper surface of the undoped spacer layer and between the undoped spacer layer and the upper cladding layer, wherein the diffusion barrier layer is configured to block the diffusion of a dopant of a second conductivity type.

[0065] Aspect 6: The waveguide structure according to aspect 4, wherein the first conductivity type is n-type and the second conductivity type is p-type.

[0066] Aspect 7: The waveguide structure according to aspect 4, wherein the lower cladding, upper cladding and undoped spacer layer are made of indium phosphide, and wherein the contact layer is made of indium gallium arsenide.

[0067] Aspect 8: The waveguide structure according to any one of Aspects 1-7 further includes: a first-stage waveguide ridge laterally displaced from the main waveguide ridge in a first lateral direction; and a second-stage waveguide ridge laterally displaced from the main waveguide ridge in a second lateral direction opposite to the first lateral direction, wherein the first-stage waveguide ridge is formed by a first protrusion of the upper cladding and a first ground contact layer disposed on the first protrusion of the upper cladding, and wherein the second-stage waveguide ridge is formed by a second protrusion of the upper cladding and a second ground contact layer disposed on the second protrusion of the upper cladding.

[0068] Aspect 9: According to the waveguide structure described in aspect 8, the thermally controllable heater is laterally arranged between the main waveguide ridge and the first-stage waveguide ridge, or laterally arranged between the main waveguide ridge and the second-stage waveguide ridge.

[0069] Aspect 10: The waveguide structure according to any one of Aspects 1-9 further includes: a dielectric layer disposed on the upper cladding and the main waveguide ridge, wherein the dielectric layer is disposed between the upper cladding and the thermally controllable heater, and wherein the dielectric layer conforms to the shape of the main waveguide ridge.

[0070] Aspect 11: The waveguide structure according to any one of Aspects 1-10 further includes: a sacrificial layer disposed between the substrate and the lower cladding, wherein the removed portion of the sacrificial layer defines one or more thermally insulating regions between the substrate and the lower cladding.

[0071] Aspect 12: The waveguide structure according to any one of Aspects 1-11, wherein the thermally controllable heater is configured to thermally tune the phase control segment of the back-facing DBR, the forward-facing DBR, or the waveguide core layer.

[0072] Aspect 13: A waveguide structure according to any one of Aspects 1-12, wherein a main waveguide ridge forms a stripe along the top of the upper cladding, and wherein a thermally controllable heater extends parallel to the main waveguide ridge along the top of the upper cladding.

[0073] Aspect 14: The waveguide structure according to any one of Aspects 1-13, wherein the main waveguide ridge is a ridge-top grounded structure.

[0074] Aspect 15: A waveguide structure according to any one of Aspects 1-14, wherein the forward DBR and the backward DBR form a wavelength selective filter, such that laser light is generated in a narrow wavelength band.

[0075] Aspect 16: A waveguide structure comprising: a substrate; a lower cladding disposed on the substrate; a waveguide core disposed on the lower cladding, the waveguide core being configured to generate, guide, and amplify laser light; a back-facing DBR disposed in the waveguide core; a forward-facing DBR disposed in the waveguide core, wherein the back-facing DBR and the forward-facing DBR define a laser cavity of the waveguide core; one or more active regions disposed in the waveguide core for generating and amplifying light; an upper cladding disposed on the waveguide core, wherein the lower cladding, the waveguide core, and the upper cladding form a waveguide; a thermally controllable heater disposed on the upper cladding, the thermally controllable heater being configured to thermally tune a thermally controllable segment of the waveguide core; and a main waveguide ridge extending vertically from the waveguide core. Extending outward in a direction, the main waveguide ridge is formed by an unintentionally doped spacer layer and a doped layer disposed on the unintentionally doped spacer layer, wherein the unintentionally doped spacer layer is disposed on the waveguide core layer and extends vertically from the waveguide core layer to form a protrusion forming the bottom portion of the main waveguide ridge, and wherein the doped layer is disposed on the unintentionally doped spacer layer to form the upper portion of the main waveguide ridge; a first-stage waveguide ridge, which is laterally displaced from the main waveguide ridge in a first lateral direction, wherein the first-stage waveguide ridge is formed by a first protrusion of the upper cladding and a first contact layer disposed on the first protrusion of the upper cladding; and a first ground ohmic contact disposed on the first-stage waveguide ridge, the first ground ohmic contact contacting the first contact layer.

[0076] Aspect 17: The waveguide structure according to aspect 16, wherein the upper cladding extends to both sides from the unintentionally doped spacer layer.

[0077] Aspect 18: The waveguide structure according to any one of Aspects 16-17, wherein the unintentionally doped spacer layer and the doped layer extend laterally over the entire lateral dimension of the main waveguide ridge.

[0078] Aspect 19: The waveguide structure according to any one of Aspects 16-18 further includes: a second-stage waveguide ridge that is laterally displaced from the main waveguide ridge in a second lateral direction, the second lateral direction being opposite to the first lateral direction, wherein the second-stage waveguide ridge is formed by a second protrusion of the upper cladding and a second contact layer disposed on the second protrusion of the upper cladding; and a second ground ohmic contact disposed on the second-stage waveguide ridge, the second ground ohmic contact contacting the second contact layer.

[0079] Aspect 20: The waveguide structure according to aspect 19, wherein the lower cladding has a first conductivity type, and wherein the upper cladding, doped layer, first contact layer and second contact layer have a second conductivity type.

[0080] Aspect 21: The waveguide structure according to aspect 20, wherein the main waveguide ridge includes a diffusion barrier layer disposed between an unintentionally doped spacer layer and a doped layer, wherein the diffusion barrier layer is configured to block the diffusion of a dopant of a second conductivity type.

[0081] Aspect 22: The waveguide structure according to aspect 20, wherein the first conductivity type is n-type and the second conductivity type is p-type.

[0082] Aspect 23: The waveguide structure according to aspect 20, wherein the lower cladding, upper cladding, unintentionally doped spacer layer and doped layer are made of indium phosphide, and wherein the first contact layer and the second contact layer are made of indium gallium arsenide.

[0083] Aspect 24: A waveguide structure according to any one of Aspects 16-23, wherein a transverse conductive path between the first-stage waveguide ridge and the main waveguide ridge provides carrier wave control.

[0084] Aspect 25: A method for manufacturing a monolithically integrated narrow-linewidth tunable semiconductor laser, the method comprising: providing an initial layer stack including: a lower cladding layer having dopant of a first conductivity type, a waveguide core layer disposed on the lower cladding layer, a separation layer disposed on the waveguide core layer, the separation layer being undoped, and an unintentionally doped spacer layer disposed on the separation layer; etching the unintentionally doped spacer layer to form an unintentionally doped mesa structure; forming an upper cladding layer having dopant of a second conductivity type, wherein forming the upper cladding layer comprises: doping the separation layer with a dopant of the second conductivity type, wherein the separation layer below the unintentionally doped mesa structure is doped. The layer portion remains undoped; and an additional doped layer is grown on the separation layer and the unintentionally doped mesa structure such that the additional doped layer covers the peripheral side and the upper surface of the unintentionally doped mesa structure; a contact layer is formed on the additional doped layer, the contact layer having a second conductivity type of doping; the contact layer and the additional doped layer are etched to form a main waveguide ridge and a plurality of secondary waveguide ridges, wherein the main waveguide ridge includes the unintentionally doped mesa structure, portions of the additional doped layer and portions of the contact layer, and wherein portions of the additional doped layer cover the peripheral side and the upper surface of the unintentionally doped mesa structure; and a ground ohmic contact is formed on portions of the contact layer.

[0085] Aspect 26: A waveguide structure comprising: a substrate; a lower cladding disposed on the substrate; a waveguide core layer; an upper cladding disposed on the waveguide core layer, wherein the lower cladding, the waveguide core layer, and the upper cladding form a waveguide; a thermally controllable heater disposed on the upper cladding, the thermally controllable heater being configured to thermally tune a thermally controllable segment of the waveguide core layer; and a main waveguide ridge extending vertically outward from the upper cladding, wherein the main waveguide ridge comprises an unintentionally doped spacer layer, the upper cladding layer, and a contact layer arranged in a stacked manner. A layer is formed, wherein an unintentionally doped spacer layer is disposed on and extends vertically from the waveguide core layer to form a protrusion that forms a portion of the bottom portion of the main waveguide ridge, wherein an upper cladding laterally surrounds and extends to cover the upper surface of the unintentionally doped spacer layer to form a peripheral and intermediate portion of the main waveguide ridge, and a contact layer is disposed on the upper cladding to form the upper portion of the main waveguide ridge; and a ground ohmic contact is disposed on the main waveguide ridge, the ground ohmic contact contacting the contact layer.

[0086] Aspect 27: A system configured to perform one or more operations described in one or more of aspects 1-26.

[0087] Aspect 28: Equipment comprising a component for performing one or more operations described in one or more aspects 1-26.

[0088] The foregoing disclosure provides illustrations and descriptions, but is not intended to be exhaustive or to limit the embodiments to the precise forms disclosed. Modifications and variations can be obtained based on the foregoing disclosure or from practice of the embodiments. Furthermore, unless the foregoing disclosure expressly provides a reason why one or more embodiments cannot be combined, any embodiments described herein can be combined.

[0089] Even though specific combinations of features are recited and / or disclosed in the claims and / or specification, these combinations are not intended to limit the disclosure of various embodiments. In fact, many of these features can be combined in ways not specifically recited and / or disclosed in the claims and / or specification. Although each dependent claim listed below may directly depend on only one claim, the disclosure of various embodiments includes combinations of each dependent claim with each other claim in the claim set. As used herein, the phrase “at least one” referring to the list of items means any combination of these items, including single members. For example, “at least one of a, b, or c” is intended to cover a, b, c, ab, ac, bc, and abc, as well as any combination including multiple identical items.

[0090] When a component or one or more components (e.g., a laser emitter or one or more laser emitters) is described or claimed (within a single claim or across multiple claims) to perform or be configured to perform multiple operations, this language is intended to broadly cover a wide range of architectures and contexts. For example, unless explicitly required otherwise (e.g., by using “first component” and “second component” or other language distinguishing components in a claim), this language is intended to cover a single component performing or configured to perform all operations, a group of components collectively performing or configured to perform all operations, a first component performing or configured to perform a first operation and a second component performing or configured to perform a second operation, or any combination of components performing or configured to perform these operations. For example, when a claim has the form “one or more components are configured to: perform X; perform Y; and perform Z,” the claim should be interpreted as “one or more components configured to perform X; one or more (possibly different) components configured to perform Y; and one or more (possibly different) components configured to perform Z.”

[0091] Unless explicitly described as critical or necessary, no element, action, or instruction used herein should be construed as critical or necessary. Furthermore, as used herein, the articles “a” and “an” are intended to include one or more items and may be used interchangeably with “one or more.” Additionally, as used herein, the article “the” is intended to include one or more items referenced in connection with the article “the” and may be used interchangeably with “the one or more.” Furthermore, as used herein, the term “collection” is intended to include one or more items (e.g., related items, unrelated items, or a combination of related and unrelated items) and may be used interchangeably with “one or more.” When referring to only one item, the phrase “only one” or similar language is used. Similarly, as used herein, the terms “has,” “have,” “having,” etc., are intended to be open-ended terms. Furthermore, the phrase “based on” is intended to mean “at least partially based on” unless otherwise explicitly stated. Similarly, as used herein, the term “or” is intended to be inclusive when used in series and may be used interchangeably with “and / or” unless otherwise explicitly stated (e.g., if used in conjunction with “any” or “only one”). Furthermore, spatially relative terms, such as “below,” “lower,” “above,” “upper,” etc., may be used herein for ease of description to describe the relationship of one element or feature to one or more other elements or features, as illustrated in the figures. Spatially relative terms are intended to cover different orientations of devices, apparatuses, and / or elements in use or operation other than those depicted in the figures. The apparatus may be oriented in other ways (rotated 90 degrees or otherwise), and the spatially relative descriptors used herein should be interpreted accordingly.

Claims

1. A waveguide structure, comprising: Substrate; The lower cladding layer is disposed on the substrate; A waveguide core layer is disposed on the lower cladding, and the waveguide core layer is configured to generate, guide and amplify laser light. The distributed Bragg reflector (DBR) is arranged in the waveguide core layer, facing away from the DBR. A forward DBR is disposed in the waveguide core layer, wherein the backward DBR and the forward DBR define the laser cavity of the waveguide core layer; One or more active regions are arranged in the waveguide core layer for light generation and amplification; An upper cladding layer is disposed 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 is disposed on the upper cladding, and the thermally controllable heater is configured to thermally tune a thermally controllable section of the waveguide core. A main waveguide ridge extends vertically outward from the upper cladding, wherein the main waveguide ridge is formed by unintentionally doped spacer layers, the upper cladding, and contact layers arranged in a stacked manner. The undoped spacer layer is disposed on the waveguide core layer and extends from the waveguide core layer in the vertical direction to form a protrusion, the protrusion forming a portion of the bottom of the main waveguide ridge. The upper cladding laterally surrounds and extends to cover the upper surface of the undoped spacer layer to form the peripheral and central portions of the main waveguide ridge. The contact layer is disposed on the upper cladding to form the upper portion of the main waveguide ridge; as well as A grounding ohmic contact is arranged on the main waveguide ridge, and the grounding ohmic contact is in contact with the contact layer.

2. The waveguide structure according to claim 1, wherein the waveguide includes a non-thermally controllable segment, the non-thermally controllable segment including an active region among the one or more active regions, and The undoped spacer layer is provided on the thermally controllable section of the waveguide and is not present on the non-thermally controllable section of the waveguide.

3. The waveguide structure according to claim 1, wherein the peripheral portion and the middle portion of the main waveguide ridge formed by the upper cladding are configured to facilitate electrical grounding without causing excessive optical loss.

4. The waveguide structure according to claim 1, wherein the lower cladding has a first conductivity type. The upper cladding and the contact layer have a second conductivity type.

5. The waveguide structure of claim 4, wherein the main waveguide ridge includes a diffusion barrier layer disposed on the upper surface of the undoped spacer layer and between the undoped spacer layer and the upper cladding layer. The diffusion barrier layer is configured to block the diffusion of dopants of the second conductivity type.

6. The waveguide structure according to claim 4, wherein the first conductivity type is n-type, and The second conductivity type is p-type.

7. The waveguide structure according to claim 4, wherein the lower cladding, the upper cladding, and the undoped spacer layer are made of indium phosphide (InP), and The contact layer is made of indium gallium arsenide (InGaAs).

8. The waveguide structure according to claim 1, further comprising: The first-stage ridge that is laterally displaced from the main waveguide ridge in the first lateral direction; as well as A second-stage ridge that is laterally displaced from the main waveguide ridge in a second lateral direction, the second lateral direction being opposite to the first lateral direction. The first-stage ridge is formed by a first protrusion of the upper cladding and a first grounding contact layer disposed on the first protrusion of the upper cladding. The second waveguide ridge is formed by a second protrusion of the upper cladding and a second grounding contact layer disposed on the second protrusion of the upper cladding.

9. The waveguide structure according to claim 8, wherein the thermally controllable heater is arranged laterally between the main waveguide ridge and the first-stage ridge, or is arranged laterally between the main waveguide ridge and the second-stage ridge.

10. The waveguide structure according to claim 1, further comprising: The dielectric layer disposed on the upper cladding and the main waveguide ridge, The dielectric layer is disposed between the upper cladding and the thermally controllable heater, and The dielectric layer thereunder conforms to the shape of the main waveguide ridge.

11. The waveguide structure according to claim 1, further comprising: A sacrificial layer disposed between the substrate and the lower cladding, wherein the removed portion of the sacrificial layer defines one or more thermally insulating regions between the substrate and the lower cladding.

12. The waveguide structure of claim 1, wherein the thermally controllable heater is configured to thermally tune the phase control section of the back-facing DBR, the forward-facing DBR, or the waveguide core layer.

13. The waveguide structure of claim 1, wherein the main waveguide ridge forms stripes along the top of the upper cladding, and The thermally controllable heater extends along the top of the upper cladding parallel to the main waveguide ridge.

14. The waveguide structure according to claim 1, wherein the main waveguide ridge is a ridge-top grounded structure.

15. The waveguide structure of claim 1, wherein the forward DBR and the backward DBR form a wavelength selective filter such that the laser is generated within a narrow wavelength band.

16. A waveguide structure, comprising: Substrate; The lower cladding layer is disposed on the substrate; A waveguide core layer is disposed on the lower cladding, and the waveguide core layer is configured to generate, guide and amplify laser light. The distributed Bragg reflector (DBR) is arranged in the waveguide core layer, facing away from the DBR. A forward DBR is disposed in the waveguide core layer, wherein the backward DBR and the forward DBR define the laser cavity of the waveguide core layer; One or more active regions are arranged in the waveguide core layer for light generation and amplification; An upper cladding layer is disposed 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 is disposed on the upper cladding, and the thermally controllable heater is configured to thermally tune a thermally controllable section of the waveguide core. A main waveguide ridge extends vertically outward from the waveguide core layer, wherein the main waveguide ridge is formed by an undoped spacer layer and a doped layer disposed on the undoped spacer layer. The undoped spacer layer is disposed on the waveguide core layer and extends from the waveguide core layer in the vertical direction to form a protrusion, the protrusion forming the bottom portion of the main waveguide ridge, and The doped layer is disposed on the undoped spacer layer to form the upper portion of the main waveguide ridge; The first-stage ridge is laterally displaced from the main waveguide ridge in the first lateral direction. The first primary ridge is formed by a first protrusion of the upper cladding and a first contact layer disposed on the first protrusion of the upper cladding; as well as A first ground ohmic contact is disposed on the first waveguide ridge, and the first ground ohmic contact is in contact with the first contact layer.

17. The waveguide structure of claim 16, wherein the upper cladding extends to both sides from the undoped spacer layer.

18. The waveguide structure of claim 16, wherein the undoped spacer layer and the doped layer extend laterally across the entire lateral dimension of the main waveguide ridge.

19. The waveguide structure according to claim 16, further comprising: A second-stage ridge that is laterally displaced from the main waveguide ridge in a second lateral direction, the second lateral direction being opposite to the first lateral direction. The second-level ridge is formed by a second protrusion of the upper cladding and a second contact layer disposed on the second protrusion of the upper cladding; as well as A second grounding ohmic contact is arranged on the second stage ridge, and the second grounding ohmic contact is in contact with the second contact layer.

20. The waveguide structure of claim 19, wherein the lower cladding has a first conductivity type. The upper cladding, the doped layer, the first contact layer, and the second contact layer have a second conductivity type.

21. The waveguide structure of claim 20, wherein the main waveguide ridge includes a diffusion barrier layer disposed between the undoped spacer layer and the doped layer. The diffusion barrier layer is configured to block the diffusion of dopants of the second conductivity type.

22. The waveguide structure according to claim 20, wherein the first conductivity type is n-type, and The second conductivity type is p-type.

23. The waveguide structure of claim 20, wherein the lower cladding, the upper cladding, the undoped spacer layer, and the doped layer are made of indium phosphide (InP), and The first contact layer and the second contact layer are made of indium gallium arsenide (InGaAs).

24. The waveguide structure of claim 16, wherein the lateral conductive path between the first-stage waveguide ridge and the main waveguide ridge provides carrier wave control.

25. A method for manufacturing a monolithically integrated narrow-linewidth tunable semiconductor laser device, the method comprising: Provide an initial layer stack, the initial layer stack comprising: The lower cladding layer has doping of a first conductivity type. The waveguide core layer arranged on the lower cladding, A separation layer disposed on the waveguide core layer, the separation layer being undoped, and An unintentionally doped retreat layer disposed on the separation layer; The undoped retreat layer is etched to form an unintentionally doped mesa structure; Forming an upper cladding layer, the upper cladding layer having doping of a second conductivity type, wherein forming the upper cladding layer includes: The separation layer is doped with a dopant of the second conductivity type, wherein the section of the separation layer below the undoped mesa structure remains undoped; and An additional doped layer is grown on the separation layer and the undoped mesa structure, such that the additional doped layer covers the peripheral side and the upper surface of the undoped mesa structure. A contact layer is formed on the additional doped layer, the contact layer having a second conductivity type of doping; The contact layer and the additional doped layer are etched to form a primary waveguide ridge and multiple secondary waveguide ridges. The main waveguide ridge includes the undoped mesa structure, a portion of the additional doped layer, and a portion of the contact layer. The portion of the additional doped layer covers the peripheral side and the upper surface of the undoped mesa structure; and A grounding ohmic contact is formed on the portion of the contact layer.

26. A waveguide structure, comprising: Substrate; The lower cladding layer is disposed on the substrate; Waveguide core layer; An upper cladding layer is disposed 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 is disposed on the upper cladding, and the thermally controllable heater is configured to thermally tune a thermally controllable section of the waveguide core. A main waveguide ridge extends vertically outward from the upper cladding, wherein the main waveguide ridge is formed by an unintentionally doped spacer layer, the upper cladding, and a contact layer arranged in a stacked manner. The undoped spacer layer is disposed on the waveguide core layer and extends from the waveguide core layer in the vertical direction to form a protrusion that forms a portion of the bottom portion of the main waveguide ridge. The upper cladding laterally surrounds and extends to cover the upper surface of the undoped spacer layer to form the peripheral and central portions of the main waveguide ridge. The contact layer is disposed on the upper cladding to form the upper portion of the main waveguide ridge; as well as A grounding ohmic contact is arranged on the main waveguide ridge, and the grounding ohmic contact is in contact with the contact layer.

Images