Patent ID: 12259561

all arranged in accordance with at least one embodiment described herein.

DETAILED DESCRIPTION OF SOME EXAMPLE EMBODIMENTS

The term “light” as used herein is to be construed broadly as any electromagnetic radiation that may be used for optical communication. Accordingly, light may include electromagnetic radiation in the O-band (˜1261 nanometers (nm) to 1361 nm), the E-band (˜1361 nm to 1461 nm), the S-band (˜1461 nm to 1531 nm), the C-band (1531 nm to 1561 nm), the L-band (1561 nm to 1625 nm), the 850 nm band, or other wavelength bands.

Some embodiments herein relate to a SSC that gradually weakens optical confinement in a waveguide core by down-tapering the waveguide core along a light propagation direction. The gradually weakening optical confinement of the waveguide core allows the optical mode to expand and be released from the waveguide core into a box structure. The waveguide core is surrounded or clad by the box structure. The box structure has a lower refractive index than the waveguide core. In turn, the box structure is surrounded or clad by air or other material with a lower refractive index than the box structure. As such, the optical mode released into the box structure is confined within the box structure.

The SSC supports a first optical mode at a first end of the SSC where the waveguide core has a first cross-sectional area normal to the light propagation direction and a second, smaller, optical mode at a second end of the SSC where the waveguide core has a second, larger, cross-sectional area normal to the light propagation direction. The first optical mode may have a beam diameter of about 10 micrometers (e.g., 3 to 12 micrometers) and the second optical mode may have a beam diameter of about 1.5 micrometers (e.g., 1.2 to 1.8 micrometers). Thus, the SSC may be configured to convert the optical mode of light output by a DML or EML to a larger optical mode that matches the optical mode of a SMF or another waveguide. Two optical modes may be said to match if their profiles overlap by at least 70%, at least 80%, at least 90%, or some other threshold.

The waveguide core of the SSC may be tapered laterally, transversely, or both in the light propagation direction. Alternatively or additionally, the waveguide core may include a grating portion at the first end of the SSC with a duty cycle that gradually increases, e.g., to 90%, in the light propagation direction.

The SSC may be suspended above a substrate by one or more pillars such that a bottom surface of the box structure is clad by air in an air gap between the SSC and the substrate. Alternatively, an index step material layer may be disposed between the bottom surface of the box structure and the substrate and the pillars may be omitted.

In some embodiments, the SSC may be formed on the same substrate as an active optical element, such as a laser or photodiode, to which the SSC is optically coupled in an optical system. Further, the SSC may be formed by at least some of the same processing steps as used to form the active optical element. In an example, the active optical element includes a laser, such as a distributed feedback (DFB) laser. Alternatively or additionally, the DFB laser may include a lateral junction buried heterostructure (BH).

Some embodiments include an optical system with a laser, a SSC as described herein, a silicon (Si) photonic integrated circuit (PIC), and an edge coupler positioned to receive light output by the SSC and couple the light into the Si PIC. Such an optical system may exhibit less optical loss than otherwise similar optical systems that include a conventional SSC, which may reduce required output of the laser, e.g., by 2 decibels (dB) or other amount. The reduced output power may improve reliability of the laser.

Embodiments of the SSC are generally described herein in the context of coupling light out of a laser with spot size conversion to a larger optical mode. Embodiments of the SSC may alternatively or additionally be used in the context of coupling light into a photodiode with spot size conversion to a smaller optical mode.

Reference will now be made to the drawings to describe various aspects of example embodiments of the invention. The drawings are diagrammatic and schematic representations of such example embodiments, and are not limiting of the present invention, nor are they necessarily drawn to scale.

FIG.1Aincludes a perspective view of an example SSC100, arranged in accordance with at least one embodiment described herein. The SSC100may generally include a first waveguide structure102and a second waveguide structure104formed on or spaced apart from a substrate105.

As illustrated, the first waveguide structure102extends longitudinally along a waveguide axis106from a first end108to a second end110of the SSC100. As used herein, terms such as longitudinal, length, and variants refer to the light propagation direction or waveguide axis106. Terms such as transverse, height, thickness, top, bottom, and variants refer to a direction normal to the light propagation direction and normal to a surface105A of the substrate105on or spaced apart from which other layers of the SSC100are formed. Terms such as lateral, width, side, and variants refer to a direction normal to both the light propagation direction and the transverse direction. An arbitrarily defined x-y-z axis is included inFIG.1Afor reference where the z axis is parallel to the longitudinal direction, the y axis is parallel to the transverse direction, and the x axis is parallel to the lateral direction.

The first waveguide structure102may include a box structure that includes one or more semiconductor materials or other materials. In an example, the box structure includes undoped indium phosphide (InP). In another example, a portion of the box structure may be n-doped, e.g., in a range of 3×1017cm−3to 5×1017cm−3, which may facilitate monolithic integration of the SSC100with a laser or photodetector. The first waveguide structure102may be configured to support a first optical mode, generally designated at112, at the first end108. The first optical mode112may have a beam diameter of about 10 micrometers, or in a range from 3 to 12 micrometers, or some other beam diameter.

The second waveguide structure104is formed within the first waveguide structure102and may include part of the first waveguide structure102. The second waveguide structure104may extend longitudinally between the first end108and the second end110and may be configured to support a second optical mode, generally designated at114, at the second end110. The second optical mode112has different dimensions than the first optical mode112. For example, the second optical mode112may have a beam diameter of about 1.5 micrometers, or in a range from 1.2 to 1.8 micrometers, or some other beam diameter.

The second waveguide structure104includes a waveguide core116and at least some cladding of the first waveguide structure102that surrounds the waveguide core116. The waveguide core116may extend from the second end110toward the first end108. The waveguide core116may reach the first end108or the waveguide core116may terminate before reaching the first end108as illustrated inFIG.1A. The waveguide core116may have a higher index of refraction than the cladding. The waveguide core116may or may not be visible within the first waveguide structure102and thus the waveguide core116is illustrated with dashed lines.

The waveguide core116is configured to release light from the second waveguide structure104into the first waveguide structure102. Accordingly, a configuration of the waveguide core116may vary along the waveguide axis106such that the optical confinement provided by the second waveguide structure104varies along the waveguide axis106from, e.g., relatively weak or zero confinement at the first end108to relatively strong confinement at the second end110.

In this and other examples, the waveguide core may taper from the first end108to the second end110may inverse taper from the second end110to the first end108. Tapers and inverse tapers are structurally equivalent, the difference being whether a cross-sectional area of the waveguide core116normal to the light propagation direction (e.g., parallel to the x-y plane inFIG.1A) increases or decreases in the light propagation direction. For light that propagates through the second waveguide structure104from the first end108to the second end110such that the cross-sectional area of the waveguide core116increases in the light propagation direction, the waveguide core116has a taper. On the other hand, for light that propagates through the second waveguide structure104from the second end110to the first end108such that the cross-sectional area of the waveguide core116decreases in the light propagation direction, the waveguide core116has an inverse taper. For simplicity herein, the term “taper” and its variants should be broadly construed as a variation of one or both of a lateral or transverse dimension of the waveguide core116along the waveguide axis106. The lateral dimension or the transverse dimension may vary linearly or nonlinearly or in segments of linear and nonlinear variation.

Instead of or in addition to being tapered at the first end108of the SSC100, the waveguide core116may include a grating portion, generally designated at118inFIG.1A, that decreases optical confinement of the waveguide core116along the waveguide axis106moving toward the first end108. The grating portion118may extend nearer to the first end108than a remainder of the waveguide core116. The remainder of the waveguide core116may include a continuous length of core material with a core index of refraction. The grating portion118may include grating lines of core material that alternate with a second material that is different than the core material. The second material has a second index of refraction that is different than the core index of refraction. The second material may include the same material as the cladding of the first waveguide structure102or other material. The grating lines may be arranged at an angle to the waveguide axis106. The angle may be in a range from 20-90 degrees, 30-80 degrees, 40-70 degrees, or in some other range.

Each grating line and alternating section of second material of the grating portion118has a longitudinal dimension along the waveguide axis106. A duty cycle of the grating portion118may be defined as a ratio of the longitudinal dimension of a section of second material to a period of the grating portion118. The period may be defined as the longitudinal distance from one core-to-second material interface through a second material-to-core interface to a next core-to-second material interface. In some embodiments, the duty cycle may gradually increase moving toward the first end108. For example, the duty cycle of the grating portion118of the waveguide core116may gradually increase along the waveguide axis106to 90% at the first end108.

The first waveguide structure102may include the cladding that encapsulates and surrounds the waveguide core116. The cladding of the first waveguide structure102may have opposing transverse surfaces120,122and opposing lateral surfaces124,126. The transverse surfaces120,122may also be referred to as top and bottom surfaces120,122. In some embodiments, one or more of the surfaces120,122,124,126may be clad by air or other material with an index of refraction lower than that of the cladding. In the illustrated example, the top surface120and the lateral surfaces124,126are clad by air, while the bottom surface122is clad by an index step material layer128disposed between the substrate105and the bottom surface122. More generally, some or all of the surfaces120,122,124,126may be clad by air or index step material, or both.

In some embodiments, index step material includes the same material as the cladding with one or more added dopants such that the index step material has a different index of refraction than the cladding. As an example, the cladding may include InP and the index step material layer128may include doped InP. As another example, lower cladding, e.g., a portion of the cladding that is generally beneath the waveguide core116, may be n-doped, e.g., in a range of 3×1017cm−3to 5×1017cm−3, and the index step material layer128may also be n-doped but to a greater degree than the lower cladding, e.g., in a range of 2×1018cm−3to 5×1018cm−3. In embodiments described herein, the index step material layer128may have a lower index of refraction than the cladding of the first waveguide structure102.

FIG.1Bincludes an end view of the SSC100ofFIG.1A, arranged in accordance with at least one embodiment described herein. In particular,FIG.1Bincludes a view of the first end108of the SSC100.

FIG.1Cincludes a simulated optical mode130at the first end108of the SSC100, arranged in accordance with at least one embodiment described herein. It can be seen from the simulated optical mode130ofFIG.1Cthat the optical mode is confined within the first waveguide structure102at the first end108and is not confined, or is only weakly confined, by the second waveguide structure104(not visible inFIG.1C).

FIGS.2A-2Binclude end views of another example SSC200, arranged in accordance with at least one embodiment described herein. The SSC200may include, be included in, or correspond to other SSCs described herein.FIG.2Aincludes an end view of a first end202of the SSC200that may be the same as or similar to the first end108of the SSC100ofFIGS.1A-1C.FIG.2Bincludes an end view of a second end204of the SSC200that may be the same as or similar to the second end110of the SSC100ofFIGS.1A-1C.

The SSC200ofFIGS.2A-2B, similar to the SSC100, may include a first waveguide structure206that includes cladding and a second waveguide structure208formed within the first waveguide structure206, the second waveguide structure208including a waveguide core210surrounded by the cladding of the first waveguide structure206. A cross-sectional area of the waveguide core210normal to the light propagation direction is greater at the second end204than the first end202. The cross-sectional area of the waveguide core210may gradually decrease from the second end204to the first end202. Alternatively or additionally, the waveguide core210may include a grating portion at or near the first end202that is nearer to the first end202than a remainder of the waveguide core210.

The cladding of the first waveguide structure208has opposing transverse surfaces212,214and opposing lateral surfaces216,218. The transverse surfaces212,214may also be referred to as top and bottom surfaces212,214. In the illustrated example, all of the surfaces212,214,216,218are clad by air.

FIGS.2A and2Badditionally included simulated optical modes of the SSC200. In particular,FIG.2Aincludes a simulated optical mode220at the first end202of the SSC200andFIG.2Bincludes a simulated optical mode220at the second end204of the SSC200. It can be seen from the simulated optical mode222ofFIG.2Bthat the optical mode is strongly confined within the second waveguide structure208at the second end204. It can be seen from the simulated optical mode220ofFIG.2Athat the optical mode is confined within the first waveguide structure206at the first end202and is not confined, or is weakly confined, by the second waveguide structure208.

FIG.3Aincludes a perspective view of an example optical system300(hereinafter “system300”) that includes a SSC302, arranged in accordance with at least one embodiment described herein.FIG.3Aadditionally includes example cross-sectional views304A,304B,304C (collectively “cross-sectional views304”) of the SSC302at different axial locations of the SSC302and in planes normal to a waveguide axis306of the SSC302. The locations of the cross-sections are generally indicated by arrows from the cross-sectional views304. The cross-sectional view304A is from a location at or near a first end308of the SSC302. The cross-sectional view304C is from a location at or near a second end310of the SSC302. The cross-sectional view304B is from a location between the first and second ends308,310.

The SSC302may include, be included in, or correspond to other SSCs described herein. For example, as illustrated in the cross-sectional views304, the SSC302may generally include first and second waveguide structures312,314that extend between the first and second ends308,310. The first waveguide structure312includes cladding. The second waveguide structure314is formed within the first waveguide structure312and includes a waveguide core316. It can be seen from the cross-sectional views304that a cross-sectional area of the waveguide core316normal to the waveguide axis306increases in the direction from the first end308to the second end310. Alternatively or additionally, the waveguide core316may include a grating portion at or near the first end308. The SSC302may include a first optical mode at the first end308, generally designated at318. The first optical mode318may be larger than a second optical mode (not shown) of the SSC302at the second end310.

In the example ofFIG.3A, opposing transverse surfaces and opposing lateral surfaces of the first waveguide structure312of the SSC302are clad by air. Accordingly, the SSC302may include one or more supports to support the first waveguide structure312spaced apart from a substrate320on which the SSC302is formed. For example, the SSC302may include a first support322that supports the first end308of the SSC302spaced apart from the substrate320. Alternatively or additionally, the SSC302may include a second support324that supports the second end310spaced apart from the substrate320.

Each of the supports322,324may include any suitable component, material, or structure. In an example, each of the supports322,324includes one or more epitaxial layers formed on the substrate320. Alternatively or additionally, the first and second waveguide structures312,314of the SSC302may include one or more of the same epitaxial layers of the supports322,324that are etched or otherwise processed to form the first and second waveguide structures312,314spaced apart from the substrate320with an air gap326between the substrate and a surface e.g., a bottom surface, of the first waveguide structure312that is spaced apart from and faces the substrate320.

The system300may additionally include an active optical element328with an active layer configured to convert electrical current to light or to convert light to electrical current. For example, the active optical element328may include a laser with a multiple quantum well (MQW) gain layer that converts electrical current to light or a positive-intrinsic-negative (PIN) photodiode with a stack of positive, intrinsic, and negative layers that convert light to electrical current. As illustrated, the SSC302and the active optical element328share the substrate320. In some embodiments, the SSC302and the active optical element328may be formed from one or more of the same epitaxial layers or in one or more of the same epitaxial processing steps. Accordingly, the system300may be or include a monolithically formed active optical element and SSC, a monolithically formed laser and SSC, or a monolithically formed photodiode and SSC.

The SSC302is generally configured to convert the optical mode of an optical beam traveling in the direction of the waveguide axis306from, e.g., the second optical mode at the second end310to the first optical mode318at the first end308(or vice versa). The first support322may be implemented to support the first end308without undue distortion of the emitted optical beam. In this and other embodiments, the first support322may have a length of 4-10 micrometers. It can be seen fromFIG.3Athat the first support322is wider in the lateral dimension than the first waveguide structure312and extends to the substrate320. This configuration of the first support322“releases” both the lateral waveguiding (due to the wider lateral dimension of the first support322than the first waveguide structure312) and the vertical waveguiding lower boundary (due to the first support322extending to the substrate320), over the 4-10 micrometer length of the first support322. However, at the first end308of the SSC302, the optical mode of the optical beam essentially fills the first waveguide structure312(e.g., has the first optical mode318) and is large enough to be well collimated. As such, the optical beam does not diffract rapidly along the length of the first support322where the lateral boundaries and the lower vertical boundary of the first waveguide structure312are briefly removed and is therefore not unduly distorted by the first support322.

FIG.3Bincludes a perspective view of another example optical system350(hereinafter “system350”) that includes a SSC352, arranged in accordance with at least one embodiment described herein.FIG.3Badditionally includes example cross-sectional views354A,354B,354C (collectively “cross-sectional views354”) of the SSC352at different axial locations of the SSC352and in planes normal to a waveguide axis356of the SSC352. The locations of the cross-sections are generally indicated by arrows from the cross-sectional views354. The cross-sectional view354A is from a location at or near a first end358of the SSC352. The cross-sectional view354C is from a location at or near a second end360of the SSC352. The cross-sectional view354B is from a location between the first and second ends358,360.

The SSC352may include, be included in, or correspond to other SSCs described herein. For example, as illustrated in the cross-sectional views354, the SSC352may generally include first and second waveguide structures362,364that extend between the first and second ends358,360. The first waveguide structure362includes cladding. The second waveguide structure364is formed within the first waveguide structure362and includes a waveguide core366. It can be seen from the cross-sectional views354that a cross-sectional area of the waveguide core366normal to the waveguide axis356increases in the direction from the first end358to the second end360. Alternatively or additionally, the waveguide core366may include a grating portion at or near the first end358. The SSC352may include a first optical mode at the first end358, generally designated at368. The first optical mode368may be larger than a second optical mode (not shown) of the SSC352at the second end360.

In the example ofFIG.3B, opposing lateral surfaces and a transverse surface (e.g., a top surface) of the first waveguide structure362of the SSC352are clad by air. In addition, the other transverse surface (e.g., a bottom surface) of the first waveguide structure362is clad by an index step material layer370disposed between the first waveguide structure362and a substrate372on which the SSC352is formed. In some examples, the index step material layer370is formed on the substrate372and the first and second waveguide structures362,364are formed on the index step material layer370.

The system350may additionally include an active optical element374with an active layer configured to convert electrical current to light or to convert light to electrical current. For example, the active optical element328may include a laser with a MQW gain layer or photodiode with a stack of positive, intrinsic, and negative layers. As illustrated, the SSC352and the active optical element374share the substrate372. In some embodiments, the SSC352and the active optical element374may be formed from one or more of the same epitaxial layers or in one or more of the same epitaxial processing steps. Accordingly, the system350may be or include a monolithically formed active optical element and SSC, a monolithically formed laser and SSC, or a monolithically formed photodiode and SSC.

FIG.3Cincludes a cross-sectional view376of the SSC352ofFIG.3B, arranged in accordance with at least one embodiment described herein. The cross-sectional view ofFIG.3Cis taken in a plane parallel to a top of the substrate372inFIG.3B.FIG.3Cadditionally includes the cross-sectional views354of the SSC352at locations generally indicated by arrows from the cross-sectional views354.

The cross-sectional view376ofFIG.3Cshows the waveguide core366of the second waveguide structure364formed within the first waveguide structure362. As illustrated inFIG.3C, the waveguide core366includes the grating portion, designated at378inFIG.3C, as well as the remainder portion, designated at380inFIG.3C. The remainder portion378is tapered in the lateral direction. Stated another way, a lateral dimension (e.g., a horizontal dimension inFIG.3C) of the remainder portion378decreases from the second end360moving toward the first end358along the waveguide axis356.

FIG.4Aincludes a perspective view of another example optical system400(hereinafter “system400”) that includes a SSC402and a laser404, arranged in accordance with at least one embodiment described herein.FIG.4Bincludes a cross-sectional view of the system400ofFIG.4A, arranged in accordance with at least one embodiment described herein. The SSC402may include, be included in, or correspond to other SSCs described herein.

Referring toFIGS.4A-4B, the laser404may include a substrate406, a lower cladding408formed on or above the substrate406, a waveguide core410formed on or above the lower cladding408, and an upper cladding412formed on or above the waveguide core410. An active layer410A (FIG.4A) may be included in the laser404within, above, below, or otherwise optically coupled to the waveguide core410.

In some embodiments, the laser404may additionally include two structures413A,413B (FIG.4A) formed in the laser404on opposite lateral sides of the active layer410A. The two structures413A,413B may include a semiconductor material that extends continuously through both the laser404and the SSC402. The semiconductor material may be doped or undoped. In an example, the two structures413A,413B are undoped in the SSC402and are doped in the laser404to be current blocking structures in the laser404.

The SSC402may include the substrate406, a first waveguide structure414(FIG.4B), and a second waveguide structure416(FIG.4B). The first waveguide structure414may extend from the laser404to a facet end418(FIG.4B) and may include the lower cladding408and the upper cladding412, each of which may extend continuously through both the laser404and the SSC402. One or both of the lower cladding408and the upper cladding412may be doped in one or both of the laser404and the SSC402. In an example, the lower cladding408includes n-doped InP and the upper cladding412includes p-doped InP in the laser404, while the lower and upper claddings408,412are undoped in the SSC402. In another example, the lower cladding408includes n-doped InP, e.g., with doping in a range of 3×1017cm−3to 5×1017cm−3, in both the laser404and the SSC402.

The second waveguide structure416may extend from the laser404toward, and in some embodiments to, the facet end418of the SSC402. The second waveguide structure416includes the waveguide core410that is optically coupled to the active layer410A of the laser404. The waveguide core410may be tapered in one or both of the transversal or lateral directions. As such, a cross-sectional area of the waveguide core410normal to a waveguide axis420may decrease along the waveguide axis420from the laser404approaching the facet end418. Alternatively or additionally, the waveguide core410may include a grating portion at or near the facet end418, such as the grating portions118,378described herein.

The facet end418(FIG.4B) may be a cleaved facet. Alternatively or additionally, the facet end418may be angled relative to the waveguide axis420. For example, rather than the facet end418being perpendicular to the waveguide axis420, or a surface normal of the facet end418being parallel to the waveguide axis420, an angle between the surface normal of the facet end418and the waveguide axis420may be in a range from, e.g., 1 degree to 14 degrees. Arranging the facet end418at an angle to the waveguide axis420may reduce reflectivity from the facet end418compared to the facet end418being perpendicular to the waveguide axis420.

As illustrated inFIGS.4A-4B, the lower cladding408is spaced apart from the substrate406by an air gap422such that air clads a bottom surface of the lower cladding408in both the laser404and the SSC402. In other embodiments, a step index material layer may be formed between the lower cladding408and the substrate406in one or both of the laser404or the SSC402.

The system400may further include one or more supports424that extend from the substrate406to mechanically support the lower cladding408(and other elements formed above the lower cladding408) suspended above the substrate406with the air gap422therebetween. The system400includes multiple supports424in the illustrated example. The supports424may include pillars of InP, silicon dioxide (SiO2), or other suitable material. Example methods to form a laser suspended above a substrate are disclosed in U.S. Pat. No. 8,236,590, which is incorporated herein by reference. Methods disclosed in the '590 Patent may be adapted to form a laser and SSC suspended above a substrate, such as illustrated inFIGS.4A-4B. An example method is described in greater detail herein.

The SSC402and the laser404share the substrate406. Further, the SSC402and the laser404may be formed from one or more of the same epitaxial layers (e.g., lower and upper claddings408,412, waveguide core410, structures413A,413B) or in one or more of the same epitaxial processing steps. Accordingly, the system400may be or include a monolithically formed laser and SSC.

The system400ofFIGS.4A-4Bmay leverage the detuned-loading effect to improve performance of the system400. Additional details regarding the detuned-loading effect are disclosed in U.S. patent application Ser. No. 16/691,549, filed Nov. 21, 2019 and U.S. Pat. No. 10,461,503, both of which are incorporated herein by reference.

As illustrated, the SSC402is coupled to a front of the laser404. The SSC402may have a length in a range from 100 to 250 micrometers, such as 120 micrometers. The laser404may have a length in a range from 50 to 200 micrometers, or in a range from 80 to 140 micrometers, such as about 100 micrometers.

The active layer410A of the laser404may include a MQW gain layer or other suitable layer configured to convert electrical current to light and the laser404may include a DFB grating426(FIG.4B) formed in, on, or above the active layer410A. The DFB grating426may include first and second grating portions with a phase shift in between. The DFB grating426may have a kappa×length, e.g., κL, in a range from 1.0 to 1.8, or other suitable κL.

A high reflection (HR) mirror428(FIG.4B) is formed at a rear or back, e.g., on a rear facet, of the laser404. The HR mirror428may be coupled to the rear of the laser404. The HR mirror428may have a reflectivity of 30% or more, 50% or more, 70% or more, or even 90% or more. In other embodiments, a DBR mirror with similar reflectivity (e.g., of 30% or more, 50% or more, 70% or more, or even 90% or more) may be substituted for the HR mirror428and may be referred to as an HR DBR mirror. The term “HR mirror” as used herein encompasses HR coatings/mirrors as well as HR DBR mirrors.

A low reflection (LR) mirror430(FIG.4B, omitted fromFIG.4Ato show other components) is formed at a front, e.g., on the facet end418, of the SSC402. The LR mirror430may be coupled to the front of the SSC402. The LR mirror430may have a reflectivity of 15% or less, 10% or less, or even 5% or less, such as 4% or 3%. In some embodiments, the LR mirror430has a reflectivity in a range from 0.5% to 15% or in a range from 3% to 8%. An etalon432is formed between a portion of the DFB grating412at the front of the laser404and the LR mirror430. The system400forms a complex-cavity design consisting of a DFB laser itself, e.g., the laser404, and the etalon432. The etalon432is configured to modify cavity loss dynamically due to frequency chirp as the laser404is modulated. The system400may be referred to as a DFB+R (e.g., DFB plus (weak) reflection) laser400.

The DFB+R laser400may additionally include a modulation contact434and a bias contact436electrically coupled to, respectively, the laser404and the SSC402. A modulation signal438may be provided through the modulation contact434to the laser404to modulate the laser404. A bias440may be provided through the bias contact436to the SSC402. Modulation of the laser404may modulate the cavity loss of the DFB+R laser400and may increase a relaxation oscillation frequency, or Fr, of the DFB+R laser400.

FIG.5includes a perspective view of another example optical system500(hereinafter “system500”) that includes a SSC502and a laser504, arranged in accordance with at least one embodiment described herein. The SSC502and the laser504may respectively include, be included in, or correspond to other SSCs and lasers described herein. The SSC502and the laser504may be formed on or coupled to a substrate506. In some embodiments, the SSC502and the laser504are monolithically formed together. In some embodiments, the SSC502and the laser504are formed as discrete components and subsequently assembled together.

The system500ofFIG.5may further include a Si PIC508and an edge coupler510. The Si PIC may include one or more Si or silicon nitride (SiN) waveguides formed therein. Each of the Si or SiN waveguides may include a Si or SiN waveguide core surrounded by cladding of lower refractive index, such as SiO2in this example.FIG.5includes one Si waveguide512for illustration purposes. The Si waveguide512may be optically coupled to one or more other waveguides or passive or active optical devices formed in or coupled to the Si PIC.

The edge coupler510may be positioned to receive light output by the SSC502and couple the light into the Si PIC510, such as into the Si waveguide512. In an example, the edge coupler510may adiabatically couple light into the Si waveguide. Details regarding adiabatic coupling of light into a Si PIC are disclosed in US Patent Publication No. 2018/0156992, which is incorporated herein by reference.

Some embodiments herein may include a laser with a lateral junction buried heterostructure (BH) formed in the laser. Such a laser may be monolithically formed with one or more of the SSCs described herein. Alternatively or additionally, such a laser may be formed separately from the SSC and the two may subsequently be assembled.FIG.6illustrates an example laser600with a lateral junction BH602, arranged in accordance with at least one embodiment described herein. In some embodiments, the laser600is monolithically formed with a SSC.

The laser600includes a ridge structure604that extends lengthwise along a waveguide axis (in and out of the page inFIG.6). The ridge structure604includes an active layer606, such as a MQW gain layer, positioned vertically within the ridge structure604between upper and lower cladding608,610.

The laser600further includes p-doped InP612and n-doped InP614, each of which extends lengthwise parallel to the waveguide axis. The p-doped InP612is positioned laterally adjacent to a first side (e.g., to the left side inFIG.6) of the ridge structure604. The n-doped InP614is positioned laterally adjacent to a second side (e.g., to the right side inFIG.6) of the ridge structure604. The lateral junction BH602includes the ridge structure604with the p-doped and n-doped InP612,614disposed laterally on opposite sides of the ridge structure604.

An anode616may be formed on the p-doped InP612. A cathode618may be formed on the n-doped InP614. Current may be injected into the laser600through the anode616, from which it travels generally laterally through the ridge structure604to the cathode618.

A dielectric layer620, such as SiO2or other suitable material layer, may be formed on the ridge structure604. The dielectric layer620may serve as a passivation layer. The dielectric layer620may have a width in a range from 0.5 micrometers to 2 micrometers in some embodiments, or less than 0.5 or greater than 2 micrometers in other embodiments. The anode616may be spaced apart from the dielectric layer620by a gap622which may extend lengthwise along some or all of a length of the anode616or the dielectric layer620. The gap622may be about 0.5 micrometers or other suitable distance, such as in a range from 0.25 micrometers to 2 micrometers. The cathode618may also be spaced apart from the dielectric layer620by a gap of the same or different distance.

The lateral junction BH602may be formed on a substrate624, such as an InP substrate. In some embodiments, an air gap626is formed between the lower cladding610and the substrate624. The lateral junction BH602(as well as any layers or structures formed in, on, or above it) may be mechanically supported spaced apart from the substrate624by one or more supports, such as one or more pillars of InP. In an example embodiment, such pillars may be formed in the p-doped InP612and the n-doped InP614.

A SSC may be monolithically formed with the laser600that may include, be included in, or correspond to other SSCs described herein. The SSC may have a waveguide core optically coupled to the active layer606, the waveguide core positioned between upper and lower cladding. Alternatively or additionally, the ridge structure604may extend through the SSC with InP positioned on opposite lateral sides of the ridge structure604. Within the SSC, the waveguide core, the upper and lower cladding, the InP, or any combination thereof may include the same semiconductor materials or layers as in the laser600, with the same or different doping characteristics as in the laser600.

FIGS.7A-7Hillustrate an example set of epitaxial processing steps to form the laser600ofFIG.6monolithically with a SSC, arranged in accordance with at least one embodiment described herein. Referring toFIG.7A, at step702, a material stack704may be built up. The Material stack704may include the substrate624, a sacrificial layer708, a lower cladding layer710, an active layer (in the laser) or waveguide core layer (in the SSC)712, and an upper cladding layer714.

The substrate624may include an InP substrate. The sacrificial layer708may include indium gallium aluminum arsenide (InGaAlAs), indium gallium arsenide (InGaAs), indium aluminum arsenide (InAlAs), or other suitable material. The lower cladding layer710may include doped or undoped InP. The active layer or waveguide core layer712may include a MQW gain layer. The upper cladding layer714may include doped or undoped InP. One or more of the foregoing layers may be doped or otherwise processed differently in the laser than in the SSC, or the same in both the laser and the SSC. The doping or other processing may be implemented as the layers of the material stack704are built up.

Referring toFIG.7B, at step716, a dielectric layer620, such as a layer of SiO2with a thickness of about 0.5 micrometers, may be formed on the upper cladding layer714. The dielectric layer620may have a width in a range from 0.5 micrometers to 2 micrometers or other suitable width. The dielectric layer620is formed where the ridge structure604ofFIG.6is formed in subsequent steps.

Referring toFIG.7C, at step720, a dielectric layer722, such as a layer of SiO2with a thickness of about 0.5 micrometers, may be formed on the upper cladding layer714and the dielectric layer620.

Referring toFIG.7D, at step724, a photoresist726is selectively applied to the thin dielectric layer722.

Referring toFIG.7E, at step728, the material stack704is partially etched in areas not covered by the photoresist726and the photoresist726is removed. The etching in some embodiments may include two or more etching steps to etch partially through the material stack704to different depths in different areas. For example, one etching step may etch through the upper cladding layer714and the active layer or waveguide core layer712in an area730. Another photoresist (not shown) may then be applied to an area732. Finally, a second etching step may etch through the lower cladding layer710and the sacrificial layer708in an area734. After completion of etching the photoresist is removed.

Referring toFIG.7F, at step736, an InP structure738is formed in the area730. The InP structure738may be doped in the laser, such as with n-doping. The InP structure738may be undoped in the SSC.

Referring toFIG.7G, at step740, formation of the ridge structure604is completed with another set of photoresist and etching steps and formation of another InP structure742. This results in formation of the lower cladding610, the active layer606in the laser (or waveguide core layer in the SSC), the upper cladding608, the p-doped InP612in the laser, and the n-doped InP614in the laser. The InP structure742may be doped in the laser, such as with p-doping, to form the p-doped InP612in the laser. The InP structure742may be undoped in the SSC.

In addition, as shown in an overhead view744ofFIG.7G, various dry etched holes745(only some of which are labeled for simplicity) may be formed through portions of the InP structures738/612,742/614and the lower cladding610to remaining sacrificial layer708.

Referring toFIG.7H, at step746, the sacrificial layer708may be exposed to an etchant through the dry etched holes745to etch away the sacrificial layer708beneath the lower cladding610and form the air gap626.

Unless specific arrangements described herein are mutually exclusive with one another, the various implementations described herein can be combined in whole or in part to enhance system functionality or to produce complementary functions. Likewise, aspects of the implementations may be implemented in standalone arrangements. Thus, the above description has been given by way of example only and modification in detail may be made within the scope of the present invention.

With respect to the use of substantially any plural or singular terms herein, those having skill in the art can translate from the plural to the singular or from the singular to the plural as is appropriate to the context or application. The various singular/plural permutations may be expressly set forth herein for sake of clarity. A reference to an element in the singular is not intended to mean “one and only one” unless specifically stated, but rather “one or more.” Moreover, nothing disclosed herein is intended to be dedicated to the public regardless of whether such disclosure is explicitly recited in the above description.

In general, terms used herein, and especially in the appended claims (e.g., bodies of the appended claims) are generally intended as “open” terms (e.g., the term “including” should be interpreted as “including but not limited to,” the term “having” should be interpreted as “having at least,” the term “includes” should be interpreted as “includes but is not limited to,” etc.). Furthermore, in those instances where a convention analogous to “at least one of A, B, and C, etc.” is used, in general, such a construction is intended in the sense one having skill in the art would understand the convention (e.g., “a system having at least one of A, B, and C” would include but not be limited to systems that include A alone, B alone, C alone, A and B together, A and C together, B and C together, or A, B, and C together, etc.). Also, a phrase presenting two or more alternative terms, whether in the description, claims, or drawings, should be understood to include one of the terms, either of the terms, or both terms. For example, the phrase “A or B” will be understood to include the possibilities of “A” or “B” or “A and B.”

The present invention may be embodied in other specific forms without departing from its spirit or essential characteristics. The described embodiments are to be considered in all respects only as illustrative and not restrictive. The scope of the invention is, therefore, indicated by the appended claims rather than by the foregoing description. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope.