CN117913654A

CN117913654A - Vertical cavity surface emitting laser with enhanced modulation bandwidth

Info

Publication number: CN117913654A
Application number: CN202310885293.5A
Authority: CN
Inventors: C-Y·鲁; 朱叶雨
Original assignee: Lumentum Operations LLC
Current assignee: Lumentum Operations LLC
Priority date: 2022-10-19
Filing date: 2023-07-18
Publication date: 2024-04-19

Abstract

In some embodiments, a Vertical Cavity Surface Emitting Laser (VCSEL) includes a substrate having a first side and a second side, a first mirror disposed on the first side of the substrate, a second mirror disposed on the first side of the substrate and defining a first optical cavity between the first mirror and the second mirror, an active region between the first mirror and the second mirror, and a third mirror defining a second optical cavity. The VCSEL can be configured to produce a primary optical mode and a secondary optical mode under direct modulation. The second optical cavity may be configured to resonate a secondary optical mode.

Description

Vertical cavity surface emitting laser with enhanced modulation bandwidth

Technical Field

The present disclosure relates generally to Vertical Cavity Surface Emitting Lasers (VCSELs) and vertical cavity surface emitting lasers with enhanced modulation bandwidth. This patent application claims priority from U.S. provisional patent application 63/380,148 entitled "Bandwidth enhanced vertical Cavity surface emitting laser," filed on day 10 and 19 of 2022. The disclosure of this prior application is considered to be part of the present patent application and is incorporated by reference.

Background

A vertical emission laser device such as a VCSEL is a laser in which a light beam is emitted in a direction perpendicular to a surface of a substrate (for example, emitted vertically from a surface of a semiconductor wafer). A plurality of vertical emitter devices may be arranged in an array with a common substrate.

Disclosure of Invention

In some embodiments, a VCSEL includes a substrate having a first side and a second side, a first mirror disposed on the first side of the substrate, a second mirror disposed on the first side of the substrate and defining a first optical cavity between the first mirror and the second mirror, an active region between the first mirror and the second mirror, and a third mirror defining a second optical cavity. The VCSEL can be configured to produce a primary optical mode and a secondary optical mode under direct modulation. The second optical cavity may be configured to resonate a secondary optical mode.

In some embodiments, the emitter includes a first mirror, a second mirror defining a first optical cavity between the first mirror and the second mirror, and a third mirror defining a second optical cavity between the third mirror and the first mirror or the second mirror. The transmitter may be configured to produce the primary optical mode and the secondary optical mode under direct modulation. The second optical cavity may be configured to resonate a secondary optical mode.

In some embodiments, a VCSEL includes a substrate having a first side and a second side, a first mirror disposed on the first side of the substrate, a second mirror disposed on the first side of the substrate and defining a first optical cavity between the first mirror and the second mirror, an active region between the first mirror and the second mirror, and a third mirror defining a second optical cavity. The VCSEL can be configured to produce a primary optical mode and a secondary optical mode under direct modulation. The second optical cavity may be configured to induce at least one of a photon-photon resonance effect or a detuned loading effect in the optical output of the VCSEL.

Drawings

Fig. 1A and 1B are schematic diagrams illustrating a top view of an exemplary emitter and a cross-sectional view of the exemplary emitter along line X-X, respectively.

FIG. 2 is a schematic diagram illustrating an example transmitter;

FIG. 3 is a schematic diagram illustrating an example transmitter;

FIG. 4 is a schematic diagram illustrating an example transmitter;

FIG. 5A shows an example diagram illustrating an optical mode of an emitter;

Fig. 5B shows an example diagram illustrating a small signal modulation response (S21 response);

FIG. 6 shows an exemplary plot of the reflection spectrum of a reflector of an emitter;

Fig. 7 shows an exemplary plot of the reflection spectrum of the reflector of the emitter.

Detailed Description

The following detailed description of example implementations refers to the accompanying drawings. The same reference numbers in different drawings may identify the same or similar elements.

Directly modulated VCSELs are suitable for many applications, such as in data centers for data communications and in three-dimensional (3D) sensing (LIDAR) for optical detection and ranging. In general, directly modulated VCSELs require a large modulation bandwidth. However, current modulation bandwidths of directly modulated VCSELs may be less than 30 gigahertz (GHz).

Some embodiments described in the present disclosure provide directly modulated emitter devices (e.g., VCSELs) that utilize photon-photon resonance (PPR) effects and/or detuned loading effects (e.g., individually or simultaneously) to improve the modulation bandwidth of the emitter device. In some embodiments, the emitter device may include a substrate having a first side (e.g., a top surface) and a second side (e.g., a bottom surface). The first mirror and the second mirror of the emitter device defining the first optical cavity of the emitter device may be arranged at a first side of the substrate. The third mirror of the emitter device may define a second optical cavity with the first mirror or the second mirror. For example, a third mirror may be disposed on the second side of the substrate. However, other configurations may be employed without departing from the scope of the present disclosure.

Direct modulation of the emitter device may produce a primary optical mode and a secondary optical mode in the vicinity of the primary optical mode (i.e., within a frequency range). In some embodiments, the second optical cavity may provide feedback (e.g., passive feedback) and facilitate excitation of the secondary optical mode to cause resonance enhancement of the modulation sidebands in the vicinity of the primary optical mode using the PPR effect. In this way, the PPR effect may enhance the modulation bandwidth of the transmitter device.

Further, the second optical cavity may provide a reflection spectrum associated with different reflectivities (e.g., associated with an on state of the emitter device and an off state of the emitter device) when the emitter device is biased at different current settings. For example, the wavelength of the light output of the emitter device may be shifted (e.g., wavelength chirped) when the emitter device is modulated from an on state to an off state. The offset may move the wavelength away from the peak reflectivity of the second optical cavity, thereby reducing feedback from the second optical cavity. Thus, due to the detuning loading effect, the light output of the emitter device may drop faster than the light output caused by the variation of the drive current alone, providing an enhancement of the modulation bandwidth for the emitter device. For example, the offset may effectively enhance the differential gain, thereby increasing the modulation speed of the transmitter device. In addition, the linewidth enhancement factor may also be reduced due to the detuning loading effect, thereby improving the Relative Intensity Noise (RIN) performance of the transmitter device.

Fig. 1A and 1B are schematic diagrams illustrating a top view of an example of a conventional emitter 100 and a cross-sectional view 150 of the example emitter 100 along line X-X, respectively. As shown in fig. 1A, the emitter 100 may include a set of emitter layers constructed in an emitter structure. In some embodiments, the emitter 100 may correspond to one or more vertical emitting devices described herein.

As shown in fig. 1A, in this example, the emitter 100 may include a circular injection protection layer 102. In some embodiments, the implanted protection layer 102 may have another shape, such as an oval, a polygon, etc. The injection protection layer 102 is defined based on a space between injection material portions (not shown) included in the emitter 100.

As shown in the middle gray and dark gray regions of fig. 1A, the emitter 100 includes an ohmic metal layer 104 (e.g., a P-ohmic metal layer or an N-ohmic metal layer) configured in a partial ring shape (e.g., having an inner radius and an outer radius). The middle gray region shows the region of the ohmic metal layer 104 covered by a protective layer (e.g., a dielectric layer, passivation layer, or dielectric mirror composed of multiple layers) of the emitter 100, and the dark gray region shows the region of the ohmic metal layer 104 exposed by the via 106, as described below. As shown, the ohmic metal layer 104 overlaps the implant protection layer 102. This configuration may be used, for example, in the case of a P-top/top-emitting transmitter 100. In the case of bottom emission transmitter 100, the configuration may be adjusted as desired.

Not shown in fig. 1A, the emitter 100 includes a protective layer in which the via 106 is formed (e.g., etched). The dark gray areas show the areas of the ohmic metal layer 104 exposed by the via 106 (e.g., the shape of the dark gray areas may be the result of the shape of the via 106), while the medium gray areas show the areas of the ohmic metal layer 104 covered by some protective layer. The protective layer may cover all emitters except the through holes. As shown, the via 106 is formed in a partial ring shape (e.g., similar to the ohmic metal layer 104) and is formed on the ohmic metal layer 104 such that the metallization on the protective layer contacts the ohmic metal layer 104. In some embodiments, the via 106 and/or the ohmic metal layer 104 may be formed in another shape, such as a complete ring shape or an open ring shape.

As further shown, the emitter 100 includes an optical aperture 108 in a portion of the emitter 100 within a partially annular inner radius of the ohmic metal layer 104. The emitter 100 emits a laser beam through an optical aperture 108. As further shown, the emitter 100 also includes a current limiting aperture 110 (e.g., an oxide aperture (not shown) formed by the oxide layer of the emitter 100). A current limiting aperture 110 is formed below the optical aperture 108.

As further shown in fig. 1A, the emitter 100 includes a set of trenches 112 (e.g., oxidized trenches) spaced (e.g., equal, unequal) around the circumference of the implanted protection layer 102. How closely the trench 112 can be positioned relative to the optical aperture 108 depends on the application and is generally limited by the implant protection layer 102, the ohmic metal layer 104, the via 106, and manufacturing tolerances.

The number and arrangement of layers shown in fig. 1A is provided as an example. In practice, the emitter 100 may include more layers, fewer layers, different layers, or layers of different arrangements than those shown in FIG. 1A. For example, while the emitter 100 includes a set of six grooves 112 (e.g., the same size or different sizes), in practice, other configurations may be used, such as a compact emitter including five grooves 112, seven grooves 112, or other numbers of grooves. In some embodiments, trench 112 may surround emitter 100 to form mesa structure d _t (shown in fig. 1B). As another example, while the emitter 100 is a circular emitter design, in practice, other designs may be used, such as rectangular emitters, hexagonal emitters, elliptical emitters, and the like. Additionally or alternatively, one set of layers (e.g., one or more layers) of the transmitter 100 may each perform one or more functions described as being performed by another set of layers of the transmitter 100.

It is noted that while the design of the transmitter 100 is described as including a VCSEL, other implementations are also contemplated. For example, the design of the emitter 100 may be applied in the context of another type of optical device, such as a Light Emitting Diode (LED) or another type of vertical-emitting (e.g., top-emitting or bottom-emitting) optical device. Furthermore, the design of the emitter 100 may be applied to emitters of any wavelength, power level and/or emission profile. In other words, the transmitter 100 is not specific to a transmitter having a given performance characteristic.

As shown in fig. 1B, an example cross-sectional view may represent a cross-section through a pair of grooves 112 or emitter 100 between a pair of grooves 112 (e.g., as shown by the line labeled "X-X" in fig. 1A). As shown, the emitter 100 may include a backside cathode layer 128, a base layer 126, a bottom mirror 124, an active region 122, an oxide layer 120, a top mirror 118, an implanted isolation material 116, a protective layer 114 (e.g., a dielectric passivation/mirror layer), and an ohmic metal layer 104. As shown, the emitter 100 may have an overall height of, for example, about 10 micrometers (μm).

The backside cathode layer 128 may include a layer in electrical contact with the base layer 126. For example, the backside cathode layer 128 may include an annealed metallization layer, such as an AuGeNi layer, pdGeAu layers, or the like.

The base layer 126 may include a base layer on which an epitaxial layer is grown. For example, the base layer 126 may include a semiconductor layer, such as a GaAs layer, an InP layer, and/or another type of semiconductor layer.

Bottom mirror 124 may comprise the bottom reflective layer of emitter 100. For example, the bottom mirror 124 may include a Distributed Bragg Reflector (DBR).

Active region 122 may include a layer that confines electrons and defines the emission wavelength of emitter 100. For example, active region 122 may be a quantum well.

The oxide layer 120 may include an oxide layer that provides optical and electrical confinement of the emitter 100. In some embodiments, the oxide layer 120 may be formed as a result of wet oxidation of the epitaxial layer. For example, the oxide layer 120 may be an Al ₂O₃ layer formed due to oxidation of an AlAs or AlGaAs layer. Trench 112 may include a channel that allows oxygen (e.g., dry oxygen, wet oxygen) to enter the epitaxial layers forming oxide layer 120.

The current confinement holes 110 may include optically active holes defined by the oxide layer 120. The size of the current limiting aperture 110 may be in the range of, for example, from about 4 μm to about 20 μm. In some embodiments, the size of the current limiting aperture 110 may depend on the distance between the trenches 112 surrounding the emitter 100. For example, trench 112 may be etched to expose the epitaxial layer forming oxide layer 120. Here, before the protective layer 114 is formed (e.g., deposited), oxidation of the epitaxial layer may occur a certain distance (e.g., identified as d ₀ in fig. 1B) toward the center of the emitter 100, thereby forming the oxide layer 120 and the current limiting aperture 110. In some embodiments, the current limiting aperture 110 may include an oxide aperture. Additionally or alternatively, the current confinement holes 110 may include holes associated with another type of current confinement technique, such as etched mesas, regions without ion implantation, lithographically defined intra-cavity mesas, regrowth, and the like.

The top mirror 118 may include a top reflective layer of the emitter 100. For example, the top mirror 118 may include a DBR.

The implant isolation material 116 may include a material that provides electrical insulation. For example, the implant isolation material 116 may include an ion implant material, such as a hydrogen/proton implant material or similar implant element, to reduce conductivity. In some embodiments, the implant isolation material 116 may define the implant protection layer 102.

The protective layer 114 may include a layer that acts as a protective passivation layer and may act as an additional DBR. For example, protective layer 114 may include one or more sub-layers (e.g., dielectric passivation and/or mirror layers, siO ₂ layers, si ₃N₄ layers, al ₂O₃ layers, or other layers) deposited (e.g., by chemical vapor deposition, atomic layer deposition, or other techniques) on one or more other layers of emitter 100.

As shown, the protective layer 114 may include one or more vias 106 that provide electrical communication to the ohmic metal layer 104. For example, the through-hole 106 may be formed as an etched portion of the protective layer 114 or a peeled portion of the protective layer 114. The optical aperture 108 may include a portion of the protective layer 114 over the current confinement aperture 110 through which light may be emitted.

Ohmic metal layer 104 may include a layer that forms an electrical contact through which an electrical current may flow. For example, the ohmic metal layer 104 may include Ti and Au layers, ti and Pt layers, and/or Au layers, etc., through which current may flow (e.g., by contacting pads (not shown) of the ohmic metal layer 104 via the via 106). The ohmic metal layer 104 may be P-ohmic, N-ohmic, or other forms known in the art. The choice of the particular type of ohmic metal layer 104 may depend on the structure of the emitter and is within the knowledge of one skilled in the art. The ohmic metal layer 104 may provide an ohmic contact between the metal and the semiconductor, may provide a non-rectifying electrical junction, and/or may provide a low resistance contact. In some embodiments, the emitter 100 may be manufactured using a series of steps. For example, bottom mirror 124, active region 122, oxide layer 120, and top mirror 118 may be epitaxially grown on base layer 126, after which ohmic metal layer 104 may be deposited on top mirror 118. Next, trench 112 may be etched to expose oxide layer 120 for oxidation. The implanted isolation material 116 may be created by ion implantation, after which the protective layer 114 may be deposited. A via 106 may be etched in the protective layer 114 (e.g., exposing the ohmic metal layer 104 for contact). Electroplating, seeding, and etching may be performed, after which the base layer 126 may be thinned and/or ground to a target thickness. Finally, a backside cathode layer 128 may be deposited on the bottom side of the substrate layer 126.

The number, arrangement, thickness, order, symmetry, etc. of layers shown in fig. 1B are provided as examples. In practice, the transmitter 100 may include more layers, fewer layers, different configurations of layers, or different arrangements of layers than shown in FIG. 1B. Additionally or alternatively, a set of layers (e.g., one or more layers) of the transmitter 100 may perform one or more functions described as being performed by another set of layers of the transmitter 100, and any layer may include more than one layer.

Fig. 2 is a schematic diagram illustrating an example transmitter 200. The transmitter 200 may be a VCSEL. As shown in fig. 2, the emitter 200 may be a bottom emission structure.

The transmitter 200 may be configured for direct modulation. For example, a device or system including the transmitter 200 may provide direct modulation of the transmitter 200. The transmitter 200 may be configured to produce a primary optical mode and a secondary optical mode under direct modulation.

As shown in fig. 2, the emitter 200 may include a substrate 202 in a manner similar to that described in connection with fig. 1A-1B. The substrate 202 can have a first side (e.g., a top surface) and a second side (e.g., a bottom surface) opposite the first side, which defines a thickness of the substrate 202. In some embodiments, the thickness of the substrate 202 may be about 100 μm. Similar to those epitaxial layers described in connection with fig. 1A-1B, a set of epitaxial layers 204 may be disposed on (e.g., formed on) a first side of the substrate 202. The set of epitaxial layers 204 may include a first mirror 206 (i.e., a first DBR) and a second mirror 208 (i.e., a second DBR). In other words, the first mirror 206 may be disposed on a first side of the substrate 202 (i.e., disposed on a first side of the substrate 202), and the second mirror 208 may be disposed on a first side of the substrate 202 (i.e., disposed on a first side of the substrate 202). A first optical cavity (e.g., an optical resonator) may be defined between the first mirror 206 and the second mirror 208. The set of epitaxial layers 204 can include an active region 210 (e.g., a quantum well) between the first mirror 206 and the second mirror 208 (e.g., in the first optical cavity). That is, the first optical cavity may be active. Emitter 200 may include an electrical contact layer 212 (e.g., an ohmic metal layer) electrically connected to the set of epitaxial layers 204.

The emitter 200 may include a third mirror 214. In some embodiments, the third mirror 214 may be disposed on a second side of the substrate 202 (e.g., on a second side of the substrate 202), as shown. In some embodiments, the third mirror 214 may be disposed on a first side of the substrate 202 between the bottom 202 and the first mirror 206 (e.g., the third mirror 214 may be in the epitaxial layer set 204). Here, a semiconductor layer (not shown) similar to the substrate 202 may be disposed between the third mirror 214 and the first mirror 206. In some implementations, the third mirror 214 can be disposed on a first side of the substrate 202 between the first mirror 206 and the second mirror 208 (e.g., the third mirror 214 can be in the epitaxial layer group 204). In some embodiments, the third mirror 214 may be disposed on a first side of the substrate 202 (e.g., the third mirror 214 may be in the epitaxial layer group 204), and the second mirror 208 may be between the first mirror 206 and the third mirror 214.

The third mirror can define a second optical cavity (e.g., an optical resonator) between the third mirror 214 and the first mirror 206 or the second mirror 208. For example, the second optical cavity may be between the third mirror 214 and the first mirror 206. As another example, the second optical cavity may be between the third mirror 214 and the second mirror 208. In some implementations (e.g., when the third mirror 214 is disposed on the second side of the substrate 202), the substrate 202 can be in the second optical cavity. The second optical cavity may be inactive (e.g., there may be no gain medium in the second optical cavity). In some embodiments, the second optical cavity may be an optical cavity external to the main structure of the emitter 200, defined by the epitaxial layer group 204, and integrated into the main structure.

In some implementations, the third mirror 214 can include a plurality of dielectric layers (e.g., dielectric films) having alternating refractive indices. For example, the dielectric layer may include alternating higher and lower refractive index layers (e.g., the difference between the higher and lower refractive indices may be from about 0.1 to about 2). In some implementations, the third mirror 214 can include a DBR, as described herein. In some embodiments, the third mirror 214 may be configured to provide less than 10% optical power reflection, such as about 5% or less or about 3% or less. In this way, the output power of the transmitter 200 is not significantly reduced.

In some implementations, the second optical cavity may be configured as a resonant secondary optical mode that may be generated by the emitter 200 under direct modulation. For example, the second optical cavity may be tuned (e.g., the third mirror 214 may be tuned) to resonate at the frequency of the second optical mode. In some implementations, the emitter 200 can be configured for thermal tuning of the first optical cavity and/or the second optical cavity (e.g., for thermal tuning of the first mirror 206, the second mirror 208, and/or the third mirror 214). For example, the emitter 200 may include one or more heating elements for thermal tuning. In some implementations, the first optical cavity can be tuned to align the primary optical mode and the secondary optical mode (e.g., the primary optical mode can be biased on the longer wavelength side of the first mirror 206 and/or the second mirror 208).

As described herein, the second optical cavity may be configured to cause at least one of PPR effects or detuning loading effects in the optical output of the emitter 200 (e.g., PPR effects and detuning loading effects in the optical output of the emitter 200). For example, the second optical cavity may be configured to cause PPR effects and/or detuned loading effects under direct modulation of the emitter 200. By resonating the secondary optical mode, the second optical cavity may provide PPR, thereby improving the response time and modulation bandwidth of the transmitter 200. In addition, modulation of the emitter 200 from the on state to the off state may cause the wavelength to deviate from the peak reflectivity of the second optical cavity, thereby rapidly reducing feedback from the second optical cavity and increasing the modulation bandwidth of the emitter 200.

As mentioned above, fig. 2 is provided as an example. Other examples may differ from that described with respect to fig. 2.

Fig. 3 is a schematic diagram illustrating an example transmitter 300. The transmitter 300 may be a VCSEL. As shown in fig. 3, the emitter 300 may be a bottom emission structure. The emitter 300 may include a substrate 302 having a first side (e.g., a top surface) and a second side (e.g., a bottom surface) opposite the first side, and a set of epitaxial layers 304 disposed on the first side of the substrate 302, the epitaxial layers 304 including a first mirror 306, a second mirror 308, and an active region 310 between the first mirror 306 and the second mirror 308 in a manner similar to that described in connection with fig. 2. Emitter 300 may include an electrical contact layer 312 electrically connected to the set of epitaxial layers 304 in a manner similar to that described in connection with fig. 2.

As shown, the optical element 316 may be integrated into a second side (e.g., bottom surface) of the substrate 302. For example, the optical element 316 may be a lens. The emitter 300 may include a third mirror 314 disposed on a second side of the substrate 302 (i.e., disposed on a bottom surface of the substrate 302); however, other configurations of the third mirror 314 may be utilized in a similar manner as described in connection with FIG. 2. For example, the third mirror 314 may be disposed on the optical element 316. Thus, the third mirror 314 may correspond in shape to the second side of the substrate 302 of the integrated optical element 316. For example, as shown, the third mirror 314 may be convex, concave, or other non-planar shape.

As described above, fig. 3 is provided as an example. Other examples may differ from that described with respect to fig. 3.

Fig. 4 is a schematic diagram illustrating an example transmitter 400. The emitter 400 may be a VCSEL. As shown in fig. 4, the emitter 400 may be a top-emitting structure. The emitter 400 may include a substrate 402 having a first side (e.g., a top surface) and a second side (e.g., a bottom surface) opposite the first side, and a set of epitaxial layers 404 disposed on the first side of the substrate 402, the epitaxial layers 404 including a first mirror 406, a second mirror 408, and an active region 410 between the first mirror 406 and the second mirror 408 in a manner similar to that described in connection with fig. 2. Emitter 400 may include an electrical contact layer 412 electrically connected to epitaxial layer group 404 in a manner similar to that described in connection with fig. 2. As shown in fig. 4, the electrical contact layer 412 may be annular or partially annular to facilitate top emission of the emitter 400. The emitter 400 may include a third mirror 414 disposed on a second side of the substrate 402 (i.e., disposed on a bottom surface of the substrate 402); however, other configurations of the third mirror 414 may be utilized in a similar manner as described in connection with FIG. 2.

As described above, fig. 4 is provided as an example. Other examples may differ from that described with respect to fig. 4.

The emitters described herein (e.g., emitter 200, 300, or 400) may include oxide-confined emitter devices, implant-only emitter devices, mesa-type emitter devices, top-emitter devices, bottom-emitter devices, multi-junction emitter devices (e.g., emitters with multiple active regions 210 included within epitaxial layer 204), and/or another emitter device. The emitters may be configured to emit light associated with one or more wavelength ranges, such as 800 nanometers (nm) to 1550 nm, and/or may utilize different material systems, such as those including GaAs substrates or InP substrates. The emitters may include any number, any size, and/or arrangement of emitters in any array shape, among other examples. The emitter may employ circular oxide holes or other shaped oxide holes, such as oval, rectangular, etc. As described herein, the transmitters may be VCSELs.

Some embodiments provide a method of manufacturing the emitter 200, 300, or 400. In some embodiments, the method may include forming a first mirror (e.g., first mirror 206, 306, or 406) on a first side of a substrate (e.g., substrate 202, 302, or 402). The method may include forming an active region (e.g., active region 210, 310, or 410) on the first mirror. The method may include forming a second mirror (e.g., second mirror 208, 308, or 408) over the active region. As described herein, the method may include forming a third mirror (e.g., third mirror 214, 314, or 414) on the second side of the substrate or the first side of the substrate.

Fig. 5A shows an example diagram 500 illustrating an optical mode of an emitter. As described herein, the emitter may have a first optical cavity and a second optical cavity (e.g., emitter 200, 300, or 400). As shown, the emitter may use the second optical cavity under direct modulation to facilitate excitation of the primary and secondary optical modes. The secondary optical mode may have a frequency separation from the primary optical mode. For example, the primary optical mode and the secondary optical mode may be separated in frequency by approximately 50GHz. Fig. 5B shows an example graph 550 illustrating a small signal modulation response (S21 response). In particular, graph 550 shows the S21 response (solid line) of an emitter (e.g., VCSEL) comprising a single optical cavity, and the S21 response (dashed line) of an emitter (e.g., emitter 200, 300, or 400) having a first optical cavity and a second optical cavity, as described herein. As shown, the emitter with the first and second optical cavities may exhibit a peak in the S21 response (e.g., about 50 GHz) due to the PPR effect. Thus, the PPR effect can increase the modulation bandwidth of the transmitter beyond that achievable by a transmitter with a single optical cavity.

As described above, fig. 5A-5B are provided as examples. Other examples may differ from that described with respect to fig. 5A-5B.

Fig. 6 shows an example plot 600 of the reflectance spectrum of a mirror (e.g., reflector) of an emitter. As described herein, the emitter may have a first optical cavity and a second optical cavity (e.g., emitter 200, 300, or 400). When the emitter is biased to a first current setting associated with an on state (shown biased at "1"), the primary optical mode of the emitter may be at a first wavelength. As shown, transitioning from the on state to a second current setting (shown biased at "0") associated with biasing the emitter to the off state may result in the wavelength of the primary optical mode being shifted to a second wavelength. As further shown, the reflectivity of the mirror of the primary optical mode may be different when the emitter is biased at different current settings. For example, the optical power reflection of the mirror of the primary optical mode at the first wavelength may be greater than the optical power reflection of the mirror of the primary optical mode at the second wavelength. Thus, the detuned loading effect associated with wavelength shifting may enhance the differential gain, thereby increasing the modulation speed of the transmitter.

As described above, fig. 6 is provided as an example. Other examples may differ from that described with respect to fig. 6.

Fig. 7 shows an example plot 700 of the reflectance spectrum of a mirror (e.g., reflector) of an emitter. As described herein, the emitter may have a first optical cavity and a second optical cavity (e.g., emitter 200, 300, or 400). As shown, the optical power reflection of the mirror associated with the primary optical mode of the first wavelength may be different from the optical power reflection of the mirror associated with the secondary optical mode of the second wavelength. By using thermal tuning, the primary optical mode can be biased on the longer wavelength side of the mirror. Further, by using thermal tuning, a secondary optical mode (e.g., in a modulation sideband) for achieving the PPR effect described herein can be obtained. In particular, the PPR effect exploits the presence of secondary optical modes in the vicinity of the primary optical mode.

As described above, fig. 7 is provided as an example. Other examples may differ from that described with respect to fig. 7.

The foregoing disclosure provides illustration and description, but is not intended to be exhaustive or to limit the embodiments to the precise form disclosed. Modifications and variations are possible in light of the above disclosure or may be acquired from practice of the implementations. Moreover, any implementation described herein can be combined unless the foregoing disclosure explicitly provides a reason why one or more implementations may not be combined.

Even though particular combinations of features are recited in the claims and/or disclosed in the specification, these combinations are not intended to limit the disclosure of the various embodiments. Indeed, many of these features may be combined in ways not specifically set forth in the claims and/or disclosed in the specification. Although each of the dependent claims listed below may depend directly on only one claim, the disclosure of various embodiments includes a combination of each dependent claim with each other claim in the claim set. As used herein, a phrase referring to "at least one" of a series of items refers to any combination of those items, including individual members. For example, "at least one of a, b, or c" is intended to encompass a, b, c, a-b, a-c, b-c, and a-b-c, as well as any combination of multiple like items.

No element, act, or instruction used herein should be construed as critical or essential unless explicitly described as such. 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" and, as used herein, the article "the" is intended to include one or more items associated with the article "the" and may be used interchangeably with "the one or more" and, as used herein, the term "set" is intended to include one or more items (e.g., related items, unrelated items, or a combination of related and unrelated items), and the phrase "only one" or similar language may be used interchangeably with "one or more" if only one item is referred to. Furthermore, as used herein, the terms "having," "with," and the like are intended to be open ended terms. Furthermore, the phrase "based on" is intended to mean "based, at least in part, on" unless explicitly stated otherwise. Furthermore, as used herein, the term "or" is inclusive in a series of uses and may be used interchangeably with "and/or" unless otherwise specifically indicated (e.g., if used in conjunction with "either" or "only one"). Furthermore, spatially relative terms, such as "lower," "upper," "top," "bottom," and the like, may be used herein for ease of description to describe one element or feature's relationship to another element or feature as illustrated in the figures. Spatially relative terms are intended to encompass different orientations of the device, apparatus and/or element in use or operation in addition to the orientation depicted in the figures. The device may be otherwise oriented (rotated 90 degrees or other directions) and the spatially relative descriptors used herein interpreted accordingly.

Claims

1. A Vertical Cavity Surface Emitting Laser (VCSEL) comprising:

A substrate having a first side and a second side;

a first mirror disposed on a first side of the substrate;

A second mirror disposed on the first side of the substrate and defining a first optical cavity between the first mirror and the second mirror;

An active region between the first mirror and the second mirror; and

A third mirror defining a second optical cavity,

Wherein the VCSEL generates a primary optical mode and a secondary optical mode under direct modulation, an

Wherein the second optical cavity is configured to resonate the secondary optical mode.

2. The vcl of claim 1, wherein the third mirror is disposed on the second side of the substrate.

3. The vcl of claim 1, wherein the third mirror is disposed on a first side of the substrate between the substrate and the first mirror.

4. The vcl of claim 1, wherein a third mirror is disposed on the first side of the substrate between the first and second mirrors.

5. The vcl of claim 1, wherein the third mirror is disposed on a first side of the substrate, and wherein the second mirror is between the first mirror and the third mirror.

6. The vertical cavity surface emitting laser of claim 1, wherein the second optical cavity is configured to induce at least one of a photon-photon resonance effect or a detuned loading effect in an optical output of the VCSEL.

7. The vcl of claim 1, wherein the optical element is integrated on the second side of the substrate.

8. The vcl of claim 7, wherein the third mirror is disposed on the optical element.

9. A transmitter, comprising:

A first mirror;

A second mirror defining a first optical cavity between the first mirror and the second mirror; and

A third mirror defining a second optical cavity between the third mirror and either the first mirror or the second mirror,

Wherein the transmitter generates a primary optical mode and a secondary optical mode under direct modulation, an

10. The emitter of claim 9, wherein the first mirror and the second mirror are disposed on a first side of a substrate, and wherein a third mirror is disposed on a second side of the substrate.

11. The transmitter of claim 9, wherein the third mirror is configured to provide less than 10% optical power reflection.

12. The emitter of claim 9, wherein the second optical cavity is configured to induce at least one of a photon-photon resonance effect or a detuned loading effect in an optical output of the emitter.

13. The emitter of claim 9, wherein said third mirror comprises a plurality of dielectric layers having alternating refractive indices.

14. The transmitter of claim 9, wherein the third mirror comprises a distributed bragg reflector.

15. A Vertical Cavity Surface Emitting Laser (VCSEL) comprising:

A substrate having a first side and a second side;

a first mirror disposed on a first side of the substrate;

An active region between the first mirror and the second mirror; and

A third mirror defining a second optical cavity,

Wherein the second optical cavity is configured to induce at least one of a photon-photon resonance effect or a detuned loading effect in the light output of the vertical cavity surface emitting laser.

16. The vcl of claim 15, wherein the third mirror is disposed on the second side of the substrate.

17. The vcl of claim 15, wherein the second optical cavity is located between the third mirror and the first mirror.

18. The vcl of claim 15, wherein the second optical cavity is located between the third mirror and the second mirror.

19. The vcl of claim 15, wherein the second optical cavity is tuned to resonate at a frequency of a secondary optical mode.

20. The vcl of claim 15, wherein the first optical cavity is tuned to align a primary optical mode with a secondary optical mode.