Patent Application
20240396302
The present invention relates to an aperture for a laser for high-bandwidth communication.
With demand for high-speed and high-volume data communication increasing, communications providers are increasingly adopting optics-based communication solutions. To meet these demands, high-speed transmitters are being developed.
The following presents a simplified summary of one or more embodiments of the present invention, in order to provide a basic understanding of such embodiments. This summary is not an extensive overview of all contemplated embodiments and is intended to neither identify key or critical elements of all embodiments nor delineate the scope of any or all embodiments. This summary presents some concepts of one or more embodiments of the present invention in a simplified form as a prelude to the more detailed description that is presented later.
In one aspect, the present invention is directed to a laser including an active region, an emission surface, and an aperture. The active region may be configured to emit light along and parallel to an optical axis. The emission surface may be spaced from the active region, and the light may be emitted through the emission surface. The aperture may be positioned along the optical axis between the active region and the emission surface and may have a cross-sectional area in a plane perpendicular to the optical axis. The cross-sectional area may define a non-circular shape, where the non-circular shape has at most one axis of symmetry. The aperture may be configured to reduce (i) a spectral bandwidth of the light emitted by the laser and (ii) a relative intensity noise of the laser.
In some embodiments, the non-circular shape may have a centroid and include at least one inwardly-curved portion with respect to the centroid. Additionally, or alternatively, the centroid may be positioned on the optical axis. In some embodiments, a first distance between a first point on the at least one inwardly-curved portion and the centroid is smaller than a second distance between any other point not on the inwardly-curved portion on the non-circular shape and the centroid. For example, the first distance may be at least two times smaller than the second distance between any other point not on the inwardly-curved portion on the non-circular shape and the centroid.
In some embodiments, the non-circular shape may correspond to an ellipse having a concave portion along a minor elliptical axis.
In some embodiments, the aperture may be configured to attenuate a fundamental mode of the light emitted by the laser.
In some embodiments, the non-circular shape may be asymmetrical.
In some embodiments, the non-circular shape may be configured to separate two or more higher-order modes of the light emitted by the laser.
In some embodiments, the aperture may be configured to reduce the relative intensity noise of the laser by shifting intermodal beat notes outside of a frequency band at which the laser is configured to transmit signals.
In some embodiments, the aperture may be configured to laterally confine the light and a current applied to the laser.
In some embodiments, the laser may have a spectral root-mean-square bandwidth of less than 0.6 nanometers.
In some embodiments, the relative intensity noise of the laser is less than about −145 dBc/Hz.
In another aspect, the present invention is directed to a vertical-cavity surface-emitting laser (VCSEL) including an active region, an emission surface, a first mirror region, a second mirror region, and an aperture. The active region may be configured to emit light along and parallel to an optical axis. The emission surface may be spaced from the active region, and the light may be emitted through the emission surface. The first mirror region may be positioned along the optical axis between the active region and the emission surface. The second mirror region may be positioned along the optical axis on an opposite side of the active region from the first mirror region. The aperture may be positioned along the optical axis between the active region and the emission surface. The aperture may have a cross-sectional area in a plane perpendicular to the optical axis, where the cross-sectional area defines a non-circular shape. The non-circular shape may be asymmetrical and may have a centroid. The non-circular shape may include at least one inwardly-curved portion with respect to the centroid. The aperture may be configured to reduce (i) a spectral bandwidth of the light emitted by the VCSEL and (ii) a relative intensity noise of the VCSEL.
In some embodiments, the centroid may be positioned along the optical axis.
In some embodiments, the first mirror region may include a first distributed Bragg reflector, and the second mirror region may include a second distributed Bragg reflector.
In some embodiments, the laser may have a spectral root-mean-square bandwidth of less than 0.6 nanometers.
In some embodiments, the relative intensity noise of the laser may be less than about −145 dBc/Hz.
In yet another aspect, the present invention is directed to a method of manufacturing a vertical-cavity surface-emitting laser (VCSEL). The method may include determining, based on characteristics of a VCSEL, an optimized cross-sectional area for a circular-shaped theoretical aperture for the VCSEL. The method may include selecting, for the VCSEL, a non-circular shape for an actual aperture of the VCSEL having a cross-sectional area that is approximately equal to the optimized cross-sectional area for the circular-shaped theoretical aperture, where the non-circular shape has at most one axis of symmetry. The method may include manufacturing the VCSEL including the actual aperture having the cross-sectional area in a plane perpendicular to an optical axis of the VCSEL, where the aperture has the non-circular shape.
In some embodiments, selecting the non-circular shape for the actual aperture may include manipulating a perimeter of the optimized cross-sectional area for the circular-shaped theoretical aperture to include at least one of a perturbation or an inwardly-curved portion to form the non-circular shape for the aperture.
The features, functions, and advantages that have been discussed may be achieved independently in various embodiments of the present invention or may be combined with yet other embodiments, further details of which may be seen with reference to the following description and drawings.
Having thus described embodiments of the invention in general terms, reference will now be made to the accompanying drawings, wherein:
Embodiments of the present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which some, but not all, embodiments of the invention are shown. Indeed, the invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will satisfy applicable legal requirements. Where possible, any terms expressed in the singular form herein are meant to also include the plural form and vice versa, unless explicitly stated otherwise. Also, as used herein, the term “a” and/or “an” shall mean “one or more,” even though the phrase “one or more” is also used herein. Further, 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 “set” is intended to include one or more items (e.g., related items, unrelated items, a combination of related and unrelated items, etc.), and may be used interchangeably with “one or more.” Where only one item is intended, the phrase “only one” or similar language is used. Also, as used herein, the terms “has,” “have,” “having,” or the like are intended to be open-ended terms. Furthermore, when it is said herein that something is “based on” something else, it may be based on one or more other things as well. In other words, unless expressly indicated otherwise, as used herein “based on” means “based at least in part on” or “based at least partially on.” Also, as used herein, the term “or” is intended to be inclusive when used in a series and may be used interchangeably with “and/or,” unless explicitly stated otherwise (e.g., if used in combination with “either” or “only one of”). As used herein, terms such as “top,” “about,” “around,” and/or the like are used for explanatory purposes in the examples provided below to describe the relative position of components or portions of components. As used herein, the terms “substantially” and “approximately” refer to tolerances within manufacturing and/or engineering standards. Like numbers refer to like elements throughout. No element, act, or instruction used herein should be construed as critical or essential unless explicitly described as such.
As noted, demand for high-speed and high-volume data communication is increasing, and communications providers are increasingly adopting optics-based communication solutions. To meet these demands, high-speed transmitters are being developed. Such high-speed transmitters may include different types of lasers, such as top-emitting lasers, bottom-emitting lasers, edge-emitting lasers, GaAs-based lasers, InP-based lasers, directly modulated lasers, distributed-feedback lasers, and/or the like. For example, vertical-cavity surface-emitting lasers (VCSELs) may include oxide apertures for electrical current confinement and optical guiding, which increase the speeds at which VCSEL-based transmitters can operate. Such oxide apertures may be formed by selectively, laterally oxidizing a layer of, for example, AlGaAs in a VCSEL. The shape of the oxide aperture influences the transverse optical guiding, which determines the spectral characteristics of light emitted by the VCSEL. Conventional VCSELs are inherently multimode and emit light at several discrete wavelengths simultaneously. Due to chromatic dispersion in optical fibers that transmit light signals from VCSELs, the multimode nature of conventional VCSELs limits the speeds at which such VCSEL-based transmitters can operate.
Additionally, when two light waves having different frequencies, such as two lateral modes emitted by a VCSEL, interfere with each other and are incident on a photodiode receiver, an electrical signal is generated that has a frequency corresponding to the difference between the frequencies of the light waves. Such electrical signals are referred to as intermodal beat notes. If the difference between the frequencies is low enough to be within the electrical bandwidth of the data signal, the intermodal beat note generates noise, which increases the relative intensity noise (RIN) of the VCSEL. The contribution of intermodal beat notes to RIN is low enough that it does not impact typical data rates. However, to achieve higher data rates, system noise must be reduced to low enough levels that such intermodal beat notes impact performance of transmitter/receiver systems.
Some embodiments of the present invention are directed to an aperture for a laser for high-bandwidth communication. In particular, the aperture may be designed for VCSELs and may include at least one side that is concave. The aperture may be configured to reduce the spectral bandwidth of the light emitted by the laser and the RIN of the laser. In some embodiments, the aperture may have a cross-sectional area in a plane perpendicular to an optical axis of the laser, where the shape of the cross-sectional area has at most one axis of symmetry. The aperture may have a centroid, or geometric center, and at least one side of the aperture may be curved inward toward the centroid. To maintain current flow, the cross-sectional area of the aperture may be configured to have the same cross-sectional area as a conventional circular aperture that would otherwise have been used for the particular application. In some embodiments, the aperture may be configured to slightly attenuate the fundamental mode of the light emitted by the laser (e.g., due to the inwardly curved edge of the aperture). The shape of the aperture may disrupt the X/Y symmetry of the laser such that higher order modes are separated from each other if not fully attenuated and intermodal beat notes are shifted outside of a frequency band at which the laser is configured to transmit signals, thereby reducing the RIN of the laser. By reducing the laser's spectral bandwidth and RIN, the laser is capable of higher bandwidth communication.
As shown in
In some embodiments, the first mirror region 106 (e.g., an n-type mirror region) and the second mirror region 108 (e.g., a p-type mirror region) may include distributed Bragg reflectors formed of multiple alternating semiconductor layers (e.g., of GaAs and AlGaAs), and they may vertically confine light generated in the active region 104. In this regard, the active region 104 may define an active region plane (e.g., a horizontal plane in the orientation of
As shown in
As will be appreciated by one of ordinary skill in the art in light of this disclosure, the laser 100 may include other elements, such as metal contacts, one or more trenches, one or more coatings (e.g., an anti-reflective coating and/or the like), one or more insulators, one or more lenses, and/or the like. Although the laser 100 depicted in
As shown in
As shown in
As will be appreciated by one of ordinary skill in the art in view of this disclosure, the inwardly-curved portion 102y may be considered a concave portion of the non-circular shape due to its inward curve toward the centroid 102x. In this regard, each of the apertures 102b and 102c may be referred to as a concave aperture because of its non-circular shape having a concave portion.
As shown in
As shown in
In some embodiments, the non-circular shape may have at most one axis of symmetry (e.g., one axis of symmetry or fewer). In this regard, the non-circular shape may correspond to a circular shape that has one or more perturbations, where the perturbations break at least one axis of symmetry of the circular shape. For example, the aperture 102b of
In some embodiments, each of the non-circular shapes of the apertures 102b and 102c may be configured to reduce a spectral bandwidth of the light emitted by the laser and a relative intensity noise of the laser. In this regard, each of the non-circular shapes of the apertures 102b and 102c may suppress, decrease, and/or separate power in lateral modes (e.g., two or more higher-order modes) supported by an optical cavity of the laser, which reduces spectral flatness and the spectral bandwidth of the light emitted by the laser. For example, the inwardly-curved portion 102y and/or the perturbation 102z may inhibit development of the lateral modes. Additionally, the lack of symmetry in the non-circular shape of the aperture 102b and/or the single axis of symmetry in the non-circular shape of the aperture 102c may split any degeneracies between the modes that may be supported by the optical cavity of the laser. Splitting such degeneracies may reduce the likelihood of the formation of intermodal beat notes and/or shift any intermodal beat notes outside of a frequency band at which the laser is configured to transmit signals. By suppressing the lateral modes and splitting any degeneracies between supported modes, the non-circular shape of the aperture 102b may reduce spectral width and relative intensity noise of light emitted by the laser, which improves the laser's suitability for high data rate communication.
In some embodiments, the inwardly-curved portion 102y and/or the perturbation 102z may attenuate a fundamental mode of the light emitted by the laser. For example, the distance d between the inwardly-curved portion 102y and the centroid 102x may be selected to be small enough to attenuate the fundamental mode of the light emitted by the laser. Attenuating the fundamental mode in this manner may also reduce spectral bandwidth of the laser.
As will be appreciated by one of ordinary skill in the art in view of this disclosure, the apertures 102b and 102c are examples of apertures having cross-sectional areas defining non-circular shapes that have at most one axis of symmetry (e.g., one axis of symmetry or fewer). Other embodiments of apertures in accordance with the present invention may have cross-sectional areas defining other non-circular shapes that have at most one axis of symmetry. For example, an aperture may have a cross-sectional area defining a non-circular shape that corresponds to an ellipse having an inwardly-curved portion that is not positioned along either a major axis or a minor axis, an ellipse having one or more inwardly-curved portions, an ellipse that has one or more inwardly-curved portions and one or more perturbations (e.g., similar to the perturbation 102z of
As noted, the non-circular shapes of concave apertures may be configured to reduce a spectral bandwidth of light emitted by lasers that include such concave apertures. In this regard, the graph 200 includes plot 202 showing relative spectral RMSBDW values for the first set of lasers having circular apertures and plot 204 showing relative spectral RMSBDW values for the first set of lasers having concave apertures. As shown by the plots 202 and 204, on average the lasers having concave apertures have lower spectral RMSBDW values as compared to the lasers having circular apertures. In particular, the lasers having concave apertures may have spectral RMSBDW values that are at least ten percent less than the spectral RMSBDW values of the lasers having circular apertures on average.
Furthermore, the graph 200 of
As noted, the non-circular shapes of concave apertures may be configured to reduce the RIN of lasers that include such concave apertures. In this regard, the graph 300 includes plot 302 showing RIN values for the first set of lasers having circular apertures and plot 304 showing RIN values for the first set of lasers having concave apertures. As shown by the plots 302 and 304, on average the lasers having concave apertures have lower RIN values as compared to the lasers having circular apertures with the same cross-sectional area of the concave apertures. In particular, the lasers having concave apertures may have RIN values that are about 5 dB/Hz less than the RIN values of the lasers having circular apertures on average. In some embodiments, the lasers having concave apertures may have RIN values that are less than about −145 dBc/Hz.
Furthermore, the graph 300 of
As noted, the non-circular shapes of concave apertures may be configured to reduce a spectral bandwidth of light emitted by lasers that include such concave apertures. In this regard, the graph 400 includes plot 402 showing relative spectral RMSBDW values for the second set of lasers having circular apertures and plot 404 showing relative spectral RMSBDW values for the second set of lasers having concave apertures. As shown by the plots 402 and 404, on average the lasers having concave apertures have lower spectral RMSBDW values as compared to the lasers having circular apertures. In particular, the lasers having concave apertures may have spectral RMSBDW values that are at least twenty percent less than the spectral RMSBDW values of the lasers having circular apertures on average.
Furthermore, the graph 400 of
As noted, the non-circular shapes of concave apertures may be configured to reduce the RIN of lasers that include such concave apertures. In this regard, the graph 500 includes plot 502 showing relative RIN values for the second set of lasers having circular apertures and plot 504 showing relative RIN values for the second set of lasers having concave apertures. As shown by the plots 502 and 504, on average the lasers having concave apertures have lower RIN values as compared to the lasers having circular apertures with the same cross-sectional area of the concave apertures. In particular, the lasers having concave apertures may have median RIN values that are about 4-5 dB/Hz less than the RIN values of the lasers having circular apertures on average. In some embodiments, the lasers having concave apertures may have RIN values that are less than about −145 dBc/Hz.
Furthermore, the graph 500 of
As shown in block 602, the method 600 may include determining, based on characteristics of a VCSEL, an optimized cross-sectional area for a circular-shaped theoretical aperture for the VCSEL. For example, the optimized cross-sectional area for a circular-shaped theoretical aperture may be determined based on a desired current density for the VCSEL, a desired voltage drop across the VCSEL, and/or the like.
As shown in block 604, the method 600 may include selecting, for the VCSEL, a non-circular shape for an actual aperture of the VCSEL having a cross-sectional area that is approximately equal to the optimized cross-sectional area for the circular-shaped theoretical aperture, where the non-circular shape has at most one axis of symmetry. For example, the method 600 may include manipulating a perimeter of a circular cross-sectional area of a circular aperture such that the perimeter has one or more perturbations, inwardly-curved portions, concave portions, and/or the like to form the non-circular shape for the aperture. In some embodiments, the method 600 may include selecting a non-circular shape similar to the non-circular shapes of the apertures 102b and 102c shown and described herein with respect to
As shown in block 606, the method 600 may include manufacturing the VCSEL comprising the actual aperture having the cross-sectional area in a plane perpendicular to an optical axis of the VCSEL, where the actual aperture has the non-circular shape. For example, the method 600 may include selectively oxidizing a mirror layer of the VCSEL to form the actual aperture having the non-circular shape. As another example, the method 600 may include adjusting a mesa shape of the VCSEL and/or the oxidation time to achieve the actual aperture having the non-circular shape.
The method 600 may include additional embodiments, such as any single embodiment or any combination of embodiments described herein. Although
As will be appreciated by one of ordinary skill in the art in view of this disclosure, the present invention may include and/or be embodied as an apparatus (including, for example, a photodetector, a device, and/or the like), as a method (including, for example, a manufacturing method, a computer-implemented process, and/or the like), or as any combination of the foregoing.
Although many embodiments of the present invention have just been described above, the present invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will satisfy applicable legal requirements. Also, it will be understood that, where possible, any of the advantages, features, functions, devices, and/or operational aspects of any of the embodiments of the present invention described and/or contemplated herein may be included in any of the other embodiments of the present invention described and/or contemplated herein, and/or vice versa.
While certain exemplary embodiments have been described and shown in the accompanying drawings, it is to be understood that such embodiments are merely illustrative of and not restrictive on the broad invention and that this invention is not to be limited to the specific constructions and arrangements shown and described, as various other changes, combinations, omissions, modifications and substitutions, in addition to those set forth in the above paragraphs, are possible. In light of this disclosure, those skilled in the art will appreciate that various adaptations, modifications, and combinations of the just described embodiments may be configured without departing from the scope and spirit of the invention. Therefore, it is to be understood that, within the scope of the appended claims, the invention may be practiced other than as specifically described herein.
