OPTICAL DEVICE, MULTI-CHIP MODULE AND METHOD FOR FORMING AN OPTICAL DEVICE

Abstract

Optical device (100), (202), (302), (402), (502), (602), comprising: a light-emitting structure (104), (204), (504), (604) for emitting light upon application of electricity to the optical device; and an integrated waveguide capacitor (106), (206), (506), (606) formed beneath the light-emitting structure (104), (204), (504), (604) for monitoring the light emitted by the light-emitting structure, wherein the integrated waveguide capacitor comprises a waveguide region (207), (307), (407), (507), (607) that guides at least a portion of the light, and wherein the waveguide region comprises one or more photon absorption sites (226) for absorbing photons of the portion of the light guided in the waveguide region, which cause the generation of free charge carriers relative to an intensity of the light confined in the waveguide region based on the absorbed photons, resulting in a change in a conductivity of the waveguide region that is proportional to the intensity of the portion of the light guided in the waveguide region.

Description

BACKGROUNDOptical systems include optical devices that can generate, process, and / or transmit optical signals from one point to another point. In certain embodiments, optical systems, such as optical communication systems, may facilitate data transmission over longer ranges with higher bandwidth with lower cable width (or diameter) as compared to communication systems with electrical lines. In an optical communication system, the light may be generated from a light source, e.g., a laser. In some optical systems, external light monitoring devices such as photodiodes are used to monitor the light generated by the light source.U.S. Pat. No. 8,937,981 B2 relates generally to a laser system which contains a first electrode, a second and a third electrode.US 2014 / 0 177 994 A1 relate to optical devices having an optical modulator and to methods for their production and / or use.Against this background, the present invention provides an optical device according to independent claim 1, a multi-chip module according to independent claim 13, and a method according to independent claim 19. Embodiments are subject matter of the respective dependent claims.BRIEF DESCRIPTION OF THE DRAWINGSVarious examples will be described below with reference to the following figures. FIG. 1 shows an example of an optical device with a light emitting structure and an integrated waveguide capacitor for monitoring light. FIG. 2 is a cross-sectional view showing an example of an optical device. FIG. 3 is a plan view showing an example of an optical device. FIG. 4 is a plan view showing another example of an optical device. FIG. 5 is a cross-sectional view showing an example of an optical device. FIG. 6 is a cross-sectional view showing another example of an optical device. FIG. 7 is a block diagram showing an example of an optical system including an example of an optical device. FIG. 8 is a block diagram showing an example of a multichip module including an electronic chip and a photonic chip including an example of an optical device. FIG. 9 is a flow chart of an example method for manufacturing an example of an optical device. FIG. 10 is a flow chart of another example method for manufacturing an example of an optical device.It is emphasized that various features are not drawn to scale in the drawings. Rather, the dimensions of the various features in the drawings are arbitrarily increased or decreased for clarity.DETAILED DESCRIPTIONThe following detailed description refers to the accompanying drawings. Wherever possible, the same reference numbers will be used in the drawings and the following description to refer to the same or like parts. It is expressly understood that the drawings are for illustration and description only. Although several examples are described in this document, modifications, adaptations, and other implementations are possible.Optical systems may include various optical devices (e.g., components), such as, but not limited to, light sources (e.g., lasers), optical modulators, optical filters, optical amplifiers, optical couplers, waveguides, optical combiners, optical multiplexers, optical demultiplexers, optical resonators, or photodetectors (e.g., photodiodes). Some optical systems may include light monitoring circuitry that monitors the optical signals included in one or more of these optical components. Such monitoring of the light may be useful to correct certain operating parameters, e.g., bias conditions as the environmental conditions change or aging of the optical devices.One common technique employed in some light monitoring circuits is to extract a small portion of the light from an optical component using one or more optical splitters. The extracted light may be directed to one or more separate photodetectors (e.g., photodiodes) that convert the extracted light into an electrical signal (e.g., electrical current). Such extraction of the light and the transmission of the extracted light to the separate photodetectors may result in a loss of usable optical power. In addition, the photodetectors that convert the light to electrical signals may not be properly calibrated, resulting in inaccurate measurement of the light. Moreover, in an optical system having multiple optical components (e.g., light source, ring resonators, etc., cascaded in a long chain), the use of the above-mentioned light monitoring technique may result in increased optical losses. Moreover, the above-described light monitoring technique may be affected by uncertainties in the splitting ratio between the different splitters used, even if the splitters are of similar construction. Moreover, the light from the splitters can be directed via a chip to the photodetector, which can result in further uncertainties in the power level or unavoidable waveguide crossovers. In some embodiments, the use of additional features such as the separate photodetectors may require additional space, resulting in an increase in the overall footprint of the optical system, and / or may require tradeoffs in the internal structure and / or efficiency of the ring resonator.According to one or more examples provided herein, an optical device, such as an optical light source, is provided that includes on-chip monitoring of photon density within a cavity of the optical device without extracting a portion of the light into a separate detector, thereby reducing losses and adverse effects of light reflections. The footprint of the example optical device is small and compatible with the heterogeneous III-V on silicon.The example of the optical device includes a light emitting structure that emits light upon application of electricity to the optical device. In addition, the optical device includes an integrated waveguide capacitor integrally formed with the structure of the optical device. In particular, the integrated waveguide capacitor may be a metal oxide semiconductor (MOS) capacitor formed under the light emitting structure to monitor the light emitted by the light emitting structure without extracting light from the optical device (e.g., to a separate photodetector downstream of the light emitting structure). In some examples, the integrated waveguide capacitor includes a waveguide region that guides at least a portion of the light emitted from the light emitting structure. The waveguide region has one or more photon absorption sites which cause the generation of free charge carriers relative to an intensity of the light enclosed in the waveguide region, which leads to a change in the conductivity of the waveguide region.In some examples, a monitoring circuit may be electrically coupled to the optical device to monitor light trapped in the optical device. In particular, the monitoring circuit may be electrically coupled to the integrated waveguide capacitor(s) at one or more monitoring locations within the optical device to cause the generation of electrical signals representative of the intensities of the light contained in the optical devices at the respective monitoring locations. The monitoring circuit may be configured to determine an optical parameter such as, but not limited to, an efficiency of the optical device using the electrical signals generated via the integrated waveguide capacitor(s). The use of the integrated waveguide capacitor may eliminate the need for separate photodiodes for monitoring the light, resulting in a compact footprint and lower complexity of an optical system using the proposed optical device.Referring now to the drawings, an example of an optical device 100 is illustrated in FIG. 1. The optical device 100 may be a light source, such as a laser, that may be disposed in an optical system (not shown) for generating light and providing light to other optical devices in the optical system. The optical device 100 of FIG. 1 may include electrical contacts 102A, 102B, 102C, a light emitting structure 104, and an integrated waveguide capacitor 106. In the example shown in FIG. 1, three electrical contacts 102A- 102C are shown for illustrative purposes. In other examples, the optical device 100 may include a fewer or greater number of electrical contacts. The optical device 100 may be supplied with electrical power and / or reference monitoring voltages via one or more of the electrical contacts 102A- 102C.Upon application of electrical power to the optical device 100 via one or more of the electrical contacts 102A- 102C, the light emitting structure 104 may emit light. The light emitting structure 104 may be a region of semiconductor material(s) that generates light due to excitation of charge carriers (e.g., electrons) by an electric field generated by the applied electric power at the light emitting structure. The light-emitting structure 104 can be, for example, a diode such as a light-emitting diode. In other examples, the light emitting structure 104 may include a heterogeneous quantum well structure or a quantum dot structure for generating the light. Further details of the light emitting structure 104 will be described in connection with FIGS. 5-6.The integrated waveguide capacitor 106 may be a MOS capacitor formed within the device structure of the optical device 100, unlike photodiodes used in conventional optical devices, which are constructed outside the conventional optical devices and receive light through a drop port. The integrated waveguide capacitor 106 may aid in the detection of the light contained in the optical device 100 without diverting a portion of the light out of the optical device 100. In an example, the integrated waveguide capacitor 106 may include photon absorption sites (see FIG. 2 ) that may cause the generation of free charge carriers relative to the intensity of the optical signal within the optical device 100. As will be appreciated, the generation of free charge carriers may result in a change (e.g., increase) in the conductivity of a particular region (e.g., a waveguide region) of the optical device. The changes in the conductivity of the given region may cause variations in the current flowing through the given region that may be monitored by the monitoring circuit (not shown in FIG. 1, see FIG. 4 ). Further details of an example of an integrated waveguide capacitor, such as the integrated waveguide capacitor 106, will be described with reference to FIG. 2.Referring now to FIG. 2, a cross-sectional view 200 of an example of an optical device 202 is shown. The optical device 202 may be an example of the optical device 100 and may include a light emitting structure 204 and an integrated waveguide capacitor 206. In some examples, the optical device 202 may include a waveguide region 207, a first buffer semiconductor region 208, and an insulating layer 210. The waveguide region 207, the first buffer semiconductor region 208 and the insulating layer 210 together form a metal oxide semiconductor (MOS) capacitor, also referred to herein as an integrated waveguide capacitor 206. In particular, the waveguide region 207 constitutes a part of the integrated waveguide capacitor 206. The insulating layer 210 may be formed between the waveguide region 207 and the first buffer semiconductor region 208, such that the insulating layer 210 may act as an electrical insulator between two electrically conductive regions, for example the waveguide region 207 and the first buffer semiconductor region 208.The optical device 202 may be formed using a substrate 212. In some examples, the substrate 212 may be a silicon-on-insulator (SOI) substrate, which may include a base substrate layer 216, a base oxide layer 214, and a device layer 218. The base substrate layer 216 may be made of a semiconductor material, e.g., silicon (Si). Other examples of materials that may be used to form the base substrate layer 216 are III-V semiconductors such as indium phosphide (InP), germanium (Ge), gallium arsenide (GaAs), aluminum gallium arsenide (AlGaAs), indium gallium arsenide (InGaAs), indium arsenide (InAs), or combinations thereof. As shown in FIG. 2, the substrate 212 may also include a base oxide layer 214 disposed on an underlying base substrate layer 216. The base oxide layer 214 may be formed by oxidation of the substrate 212, for example. In the embodiment of FIG. 2, the base oxide layer 214 for the base substrate layer 216 made of silicon may comprise silicon dioxide (SiO 2) which may be formed in the presence of oxygen at a temperature in the range of 900° C. to 1380° C. In some examples, the base oxide layer 214 may be a buried oxide layer (BOX) (e.g., the SiO 2 may be buried in the base substrate layer 216). In some examples, a layer of the SiO 2 may be buried in the base substrate layer 216 at a depth of less than 100 nm to several micrometers from the wafer surface, depending on the application. Other examples of the base oxide layer 214 may include, but are not limited to, silicon nitride (Si 3 N 4), aluminum oxide (Al 2 O 3), hafnium dioxide (HfO 2), diamond, silicon carbide (SiC), or combinations thereof.Further, the substrate 212 may include a device layer 218 disposed on the base oxide layer 214. In the embodiment of FIG. 2, device layer 218 is made of silicon. The device layer 218 may be suitably shaped (e.g., by techniques such as photolithography and etching) to form one or more regions, such as the waveguide region 207 and a non-waveguide region 209, isolated by an air trench 219. The waveguide region 207 carries an optical signal during operation of the optical device 202. In some examples, the waveguide region 207 may include a first type doping (e.g., p-doping) or a compensation doping to generate a net first type doping. In an example, the waveguide region 207 may represent a cross-section of an annular optical waveguide (see e.g. FIG. 4 ). In another example, the waveguide region 207 may represent a cross-section of a linear optical waveguide (see e.g. FIG. 3 ). The waveguide region 207 may be undoped, resulting in improved sensitivity to a variable reference voltage applied by the monitoring circuit, e.g., the monitoring circuit 108 shown in FIG. 1.As shown in an enlarged view 222 of a portion 224 of the waveguide region 207, the waveguide region 207 may include one or more photon absorption sites 226. As used herein, the term "photon absorption sites" may refer to crystal imperfections or defects in the bulk of the material of the waveguide region 207, surface imperfections at the boundaries of the waveguide region 207, or both. In some examples, the photon absorption sites may have been caused by imperfections in the manufacturing process. In some examples, some photon absorption sites may be intentionally created. The photon absorption sites 226 may absorb photons and cause the generation of free charge carriers relative to the intensity of the optical signal impinging thereon within the waveguide region 207. The conductivity of the waveguide region 207 depends on the amount of free charge carriers, so that an increase of the optical signal causes an increase of the conductivity of the waveguide region 207.The insulating layer 210 is disposed over the waveguide region 207 and / or the non-waveguide region 209. Specifically, the insulating layer 210 is formed such that the insulating layer 210 is disposed between the waveguide region 207 and the first buffer semiconductor region 208. The insulating layer 210 may be formed of one or more dielectric materials including, but not limited to, native oxides of the materials of the waveguide region 207 or the first buffer semiconductor region 208, or both, or of external dielectric materials such as high-k dielectrics or polymers which may be formed by deposition, oxidation, wafer bonding, or other dielectric coating methods. Other non-limiting examples of dielectric materials that may be used to form the insulating layer 210 include SiO 2, Si 3 N 4, Al 2 O 3, HfO 2, polyimide, benzocyclobutene (BCB), or combinations thereof.Moreover, the first buffer semiconductor region 208 may be made of a semiconductor material, e.g., a III-V semiconductor material. Examples of III-V semiconductor materials that may be used to form the first buffer semiconductor region 208 include GaAs, gallium nitride (GaN), or indium nitride (InN). The first buffer semiconductor region 208 may be formed over the insulating layer 210 using techniques such as, but not limited to, deposition, wafer bonding, monolithic growth, or other fabrication techniques. In some examples, the first buffer semiconductor region 208 may have a second type of doping (e.g., n-doping) different than the first type of doping.The light emitting structure 204 may represent an example of the light emitting structure 104 and is capable of generating light based on excitation of charge carriers (e.g., electrons) due to an electric field generated at the light emitting structure 204 by the electric energy applied via metal contacts (as described later). The light-emitting structure 204 may be, for example, a diode such as a light-emitting diode. In other examples, the light emitting structure 204 may include a heterogeneous quantum well structure (see FIG. 5 ) or a quantum dot structure (see FIG. 6 ) for generating the light.The light emitting structure 204 may be formed over at least a portion of the first buffer semiconductor region 208. In particular, the light emitting structure 204 may be formed on a surface of the first buffer semiconductor region 208 above the waveguide region 207. The light emitting structure 204 may include an optical amplification region 236 and a second buffer semiconductor region 238. The optical gain region 236 may be formed over the integrated waveguide capacitor 206, in particular on the surface of the first buffer semiconductor region 208 above the waveguide region 207. The second buffer semiconductor region 238 may be formed over the optical gain region 236. The second buffer semiconductor region 238 may be made of a semiconductor material, e.g., III-V semiconductor materials such as GaAs, GaN, or InN. In some examples, the second buffer semiconductor region 238 may have a different doping type compared to the first buffer semiconductor region 208. In particular, the second buffer semiconductor region 238 may have the first type (e.g. p-type) doping if the first buffer semiconductor region has a second type (e.g. n-type) doping. Forming the buffer semiconductor regions 208 and 238 with such different doping types may reduce the optical propagation loss within the optical device 202.Moreover, in some examples, the optical device 202 may include a first contact region 228, a second contact region 230, and a third contact region 231. For illustrative purposes, in FIG. 2, contact regions 228, 230, and 231 are shown as being made of silicon. In other examples, the contact regions 228 and 230 may be made of other semiconductor materials including, but not limited to, InP, Ge, GaAs, AlGaAs, InGaAs, or combinations thereof. The first contact region 228 may comprise the first type doping and is arranged in contact with the waveguide region 207. Furthermore, the second contact region 230 may comprise the second type doping and is arranged in contact with the first buffer semiconductor region 208. The third contact region 231 may comprise the first type doping and is arranged in contact with the second buffer semiconductor region 238. In particular, in some examples, the third contact region 231 may be formed over the second buffer semiconductor region 238.Moreover, in some examples, the optical device 202 may include metal contacts, such as a first metal contact 232, a second metal contact 234, and a third metal contact 235 (collectively referred to herein as metal contacts 232- 235). As shown in FIG. 2, the first metal contact 232 and the second metal contact 234 are each disposed in electrical contact (e.g., in direct physical contact or via an intervening electrically conductive material) with the first contact region 228 and the second contact region 230. The third metal contact 235 is arranged in electrical contact with the third contact region 231. In some examples, the metal contacts 232, 234, and 235 may be formed on (i.e., vertically above) the first contact region 228, the second contact region 230, and the third metal contact 235, respectively. Examples of materials used to form the metal contacts 232 and 234 include copper (Cu), gold (Au), aluminum, and / or platinum (Pt). In an example, in an optical system (see, e.g., FIG. 7 ), a monitoring circuit may be electrically connected to the contact regions 228 and 230 via the respective metal contacts 232 and 234. Further, in order for the optical device 202 to generate light, an operating electrical power may be applied to the optical device 202 via the metal contacts 234 and 235.For example, during operation, electrical energy (e.g., operating voltage) may be applied to the optical device 202 via the metal contacts 234 and 235. Application of the operating voltage may cause generation of light through the optical gain region 236. At least a portion of the generated light may be included in the waveguide region 207, the first buffer semiconductor region 208, and the optical gain region 236. Such confinement of the light in the waveguide region 207 (also referred to as modal overlap) allows efficient coupling into passive regions where the first buffer semiconductor region 208 is etched away to produce laser mirrors (not shown) or into other devices in a photonic integrated circuit that are entirely made of silicon, such as waveguides, modulators, detectors, multiplexers, demultiplexers, etc.The integrated waveguide capacitor 206 helps to monitor the light confined within the waveguide region 207 without the need to use external photodiodes or other devices such as splitters. In order to monitor the light emitted by the light emitting structure 204, a reference voltage is applied to the second contact region 230 and a current flowing through the first contact region is measured. As mentioned above, the photon absorption sites 226 may absorb photons and cause the generation of free charge carriers relative to the intensity of the optical signal incident thereon within the waveguide region 207. The conductivity of the waveguide region 207 depends on the amount of free charge carriers, so that an increase of the optical signal causes an increase of the conductivity of the waveguide region 207. Consequently, the current flowing through the integrated waveguide capacitor 206 may vary. The variation of the current is proportional to the change in conductivity of the waveguide region, thereby indicating the light emitted from the light emitting structure. As can be appreciated, the use of an integrated waveguide capacitor, such as the integrated waveguide capacitor 206, may aid in the detection of light within the optical device without having to direct a portion of the light out of the waveguide region 207. Moreover, in some examples, the use of the integrated waveguide capacitor may eliminate the need for separate photodiodes to monitor the light, resulting in a compact footprint and lower complexity of the proposed optical system. Moreover, in some examples, by using the integrated waveguide capacitors in the optical components and a common monitoring circuit, tasks such as operation monitoring and debugging can be easily performed in the proposed optical system.In FIG. 3, a top view 300 is depicted on an example of an optical device 302. The optical device 302 is a linear light source (e.g., a laser). The optical device 302 may be an example of the optical device 202 and may include one or more material regions similar to those described for the optical device 202 in FIG. 2, although not all such regions are depicted in FIG. 3 for simplicity. In some examples, instead of a continuous contact region, such as contact region 228, along the perimeter of waveguide region 207 of FIG. 2, the contact region may be divided into a plurality of sections to enable monitoring of light intensities at corresponding locations within optical device 302. For example, the optical device 302 may include contact regions such as the contact regions 304, 306 and the contact region portions 308A, 308B, and 308C. For the purpose of illustration, the contact regions 304, 306, a waveguide region 307 and the contact region sections 308A, 308B and 308C are illustrated in the plan view 300 from FIG. 3. Although the optical device 302 is shown as including three contact area portions 308A- 308C, it is contemplated that fewer or greater numbers of contact area portions may be used within the scope of the present disclosure. The optical device 302 may have the same cross-section as shown in FIG. 2 at multiple locations along the length "L" of the optical device 302, in particular at the locations of the contact region portions 308A, 308B, and 308C. For example, a cross-section of the optical device 302 at example 3- 3 along the contact region portion 308B may look similar to the cross-sectional view 200 illustrated in FIG. 2. Additionally, the optical device 302 may include metal contacts (not shown) disposed in contact with each of the contact regions 304, 306 and the contact region portions 308A- 308C.The contact regions 304 and 306 are examples representative of the contact regions 230 and 231 of FIG. 2 and are arranged similar to the contact regions 228 and 231. In particular, the contact region 304 is arranged in contact with the first buffer semiconductor region (not shown) of an integrated waveguide capacitor of the optical device 302 along the length of the optical device 302. The contact region 306 is disposed over a second buffer semiconductor region (similar to the second buffer semiconductor region 238, not shown) of a light emitting structure of the optical device 302. Further, the contact area portions 308A- 308C are representative of the contact area 228 of FIG. 2.In one example, to measure the light inside the optical device 302, a sinusoidal reference voltage may be applied to the contact region 304, and the electrical current flowing through one or more portions of the contact region 308A- 308C may be monitored via a monitoring circuit (not shown). As already mentioned, changes in the light intensities within the waveguide region 307, similar to those described with respect to the waveguide region 207, may also cause changes in the conductivity of the waveguide region 307. Consequently, the current flowing through the integrated waveguide capacitor of the optical device 302 may vary. The variation of the current is proportional to the change in the conductivity of the waveguide region 307, thereby indicating the light emitted from the light emitting structure. The measurement of the electric current through the portions 308A- 308C of the contact region may be an indicator of the light intensities inside the waveguide region at the location of the respective portions of the contact region.FIG. 4 shows a plan view 400 of an example of an optical device 402. The optical device 402 may be an annular light source (e.g., a ring laser). The optical device 402 may be an example of the optical device 202, and may include one or more material regions similar to those described for the optical device 202 in FIG. 2, although not all such regions are depicted in FIG. 4 for simplicity. In the embodiment shown in FIG. 4, the optical device 402 comprises a coupling waveguide 401 and a ring laser waveguide 403. The coupling waveguide 401 can be arranged next to the ring laser waveguide 403 and is evanescently coupled thereto. The coupling waveguide 401 may have output ports 405A and 405B. The light generated in the ring laser waveguide 403 may be coupled into the coupling waveguide 401 and supplied to other optical devices (not shown) via one or both output ports 405A and 405B. In some examples, the ring laser waveguide 403 may include an integrated waveguide capacitor, such as the integrated waveguide capacitor 206 shown in FIG. 2, to sense the light intensity within the ring laser waveguide 403. In some examples, both the coupling waveguide 401 and the ring laser waveguide 403 may include integrated waveguide capacitors.Similar to that described in FIG. 3, in the optical device 402, one or more of the contact regions may be divided into a plurality of sections to enable monitoring of light intensities at corresponding locations within the optical device 402. For example, the optical device 402 may include contact regions such as the contact regions 404, 406 and the contact region portions 408A, 408B, and 408C. Instead of a single contact region, such as contact region 228 along the perimeter of waveguide region 207 of FIG. 2, optical device 402 includes contact region portions 408A, 408B, and 408C. For illustrative purposes, the top view 400 of FIG. 4 shows the contact regions 404, 406, a waveguide region 407, and the contact region sections 408A, 408B, and 408C. Although the optical device 302 is shown as including three contact area portions 408A- 408C, it is contemplated that fewer or greater numbers of contact area portions may be used within the scope of the present disclosure. The optical device 402 may also have the same cross section at multiple locations along the ring of the ring laser waveguide 403 as shown in FIG. 2, in particular at the locations of the contact region portions 408A, 408B, and 408C. For example, a cross-section of the optical device 402 at example 4- 4 along the contact region portion 408B may look similar to the cross-sectional view 200 shown in FIG. 2. Additionally, the optical device 402 may include metal contacts (not shown) disposed in contact with each of the contact regions 404, 406 and the contact region portions 408A- 408C.The contact regions 404 and 406 represent examples of the contact regions 230 and 231 of FIG. 2, and are arranged similarly to the contact regions 230 and 231. In particular, the contact region 404 is arranged in contact with the first buffer semiconductor region (not shown) of an integrated waveguide capacitor of the optical device 402 along the ring of the optical device 402. Further, the contact region 406 is arranged over a second buffer semiconductor region (similar to the buffer semiconductor region 238, not shown) of a light emitting structure of the optical device 402. Further, the contact area portions 408A- 408C represent examples of the contact area 228 of FIG. 2. In particular, the contact area portions 408A- 408C are physically isolated from each other and disposed over the waveguide region 407 along the perimeter of the waveguide region 407.In one example, to measure the light inside the optical device 402, a sinusoidal reference voltage may be applied to the contact region 404 and the electrical current through one or more of the contact region portions 408A- 408C may be monitored via a monitoring circuit (not shown). As already mentioned, similar to that described with respect to the waveguide region 207, changes in the light intensities within the waveguide region 407 may also cause changes in the conductivity of the waveguide region 407. Consequently, the current flowing through the integrated waveguide capacitor of the optical device 402 may vary. The variation of the current is proportional to the change in conductivity of the waveguide region, thereby indicating the light emitted from the light emitting structure. The measurement of the electric current through the contact area portions 408A- 408C may indicate light intensities included within the waveguide region at the location of the respective contact area portions.FIG. 5 shows a cross-sectional view 500 of an optical device 502 according to an example. The optical device 502 of FIG. 5 may represent an example of the optical device 202 of FIG. 2, and may include one or more structural elements similar in one or more aspects to those described in FIG. 2 -- the description of which is not repeated here for brevity. For example, in FIG. 5, the optical device 502 is shown to include a light emitting structure 504, an integrated waveguide capacitor 506, a waveguide region 507, a first buffer semiconductor region 508, an insulating layer 510, a substrate 512 having a base substrate layer 516, a base oxide layer 514, and a device layer 518, a non-waveguide region 509, contact regions 528, 530, and metal contacts 532, 534.Further, the light emitting structure 504 may include an optical amplification region 536, a second buffer semiconductor region 538, a contact region 531 and a metal contact 535. The waveguide region 507 and the non-waveguide region 509 are formed in the device layer 518 of the substrate 512. The waveguide region 507 includes photon absorption sites (not shown) similar to the photon absorption sites 226 shown in FIG. 2. The insulating layer 510 is disposed over the waveguide region 507 and / or the non-waveguide region 509. Further, the first buffer semiconductor region 508 is formed over the insulating layer 510. The light emitting structure 504 may be formed over at least a portion of the first buffer semiconductor region 508. In particular, the light emitting structure 504 may be formed on a surface of the first buffer semiconductor region 508 above the waveguide region 507.In the example of FIG. 5, the optical gain region 536 in the light emitting structure 504 has a quantum well structure. In FIG. 5, the optical gain region 536 is shown to include a quantum well region 540. In particular, the quantum well region 540 is comprised of multiple III-V layers of different composition and doping to ensure lateral charge carrier confinement (electrons and holes) and is also referred to as heterostructures with separate confinement (SCH) and quantum wells (QW) or as an active region. In quantum well region 540, the charge carriers are confined in one dimension, but may move in the other two dimensions. The carrier distribution in quantum well region 540 caused by current flow through optical gain region 536 facilitates light generation or optical gain at a wavelength near the band gap of the material of which quantum well region 540 is made.FIG. 6 shows a cross-sectional view 600 of an example of an optical device 602. The optical device 602 of FIG. 6 may represent an example of the optical device 202 of FIG. 2, and may include one or more structural elements similar in one or more aspects to those described in FIG. 2 -- the description of which is not repeated herein for brevity. For example, in FIG. 6, the optical device 602 is shown to include a light emitting structure 604, an integrated waveguide capacitor 606, a waveguide region 607, a first buffer semiconductor region 608, an insulating layer 610, a substrate 612 having a base substrate layer 616, a base oxide layer 614 and a device layer 618, a non-waveguide region 609, contact regions 628, 630, and metal contacts 632, 634. The light emitting structure 604 may include an optical gain region 636, a second buffer semiconductor region 638, a contact region 631, and a metal contact 635. The waveguide region 607 and the non-waveguide region 609 are formed in the device layer 618 of the substrate 612. The waveguide region 607 may include photon absorption sites (not shown) similar to the photon absorption sites shown in FIG. 2. The insulating layer 610 is disposed over the waveguide region 607 and / or the non-waveguide region 609. Further, the first buffer semiconductor region 608 is formed over the insulating layer 610. The light emitting structure 604 may be formed over at least a portion of the first buffer semiconductor region 608.In particular, the light emitting structure 604 may be formed on a surface of the first buffer semiconductor region 608 above the waveguide region 607.In the example of FIG. 6, the optical gain region 636 in the light emitting structure 604 comprises a quantum dot structure. In FIG. 3, the optical gain region 636 is shown to include a quantum dot region 640. The quantum dot region 640 is comprised of multiple III-V layers of different composition and doping to ensure lateral charge carrier confinement (electrons and holes), and is also referred to as SCH, quantum dots, or active region. In particular, the quantum dot region 640 is bounded in three dimensions and has a discrete energy spectrum, such as an atom. The carrier distribution in the quantum dot region 640 caused by a current flow through the optical gain region 636 facilitates light generation or optical gain at a wavelength near the band gap of the material of which the quantum dot region 640 is made.FIG. 7 shows an example of an optical system 700. The optical system 700 may include an optical device, such as the optical device 202, capable of generating light and a monitoring circuit 702 for monitoring the light inside the optical device 100. In some examples, the optical system 700 may include more than one optical device without limiting the scope of the present disclosure.As already mentioned, the optical device 202 comprises the light emitting structure 204 that generates light and the integrated waveguide capacitor 206 that helps to sense the light intensity within the optical device 202 without extracting the light from the waveguide region 207. Upon application of a voltage across the integrated waveguide capacitor 206, the photon absorption sites 226 may cause generation of free charge carriers relative to the intensity of the optical signal within the optical device. As will be appreciated, the generation of free charge carriers may result in a change (e.g., increase) in the conductivity of a particular region (e.g., a waveguide region 207) within the respective optical components. The changes in conductivity of the given region may cause variations in the current flowing through the given region that may be monitored by the monitoring circuit 702.The monitoring circuit 702 may be electrically connected to the integrated waveguide capacitor 206 at one or more monitoring locations. In some examples, the monitoring circuit 702 may cause the integrated waveguide capacitor 206 to generate electrical signals indicative of the intensities of light at the monitoring location. To effect the generation of the electrical signals, monitoring circuit 702 may include a lock-in amplifier 708 and a preamplifier 710 in some examples. In some examples, the lock-in amplifier 708 may generate a variable reference voltage signal, e.g., a sinusoidal signal. For a given integrated waveguide capacitor, the lock-in amplifier 708 may determine a frequency of the variable reference voltage signal based on the conductivity of a waveguide region in the given integrated waveguide capacitor and a capacitance of the given integrated waveguide capacitor. In an example, the lock-in amplifier 708 may determine the frequency (F 0) of the variable reference voltage signal based on an example relationship of equation (1), where G WG represents the conductivity of the waveguide region 207 in the given integrated waveguide capacitor and C represents the capacitance of the given integrated waveguide capacitor 206. In certain other examples, the frequency (F 0) of the variable reference voltage signal may be set to any value greater thanThe monitoring circuit 702 may apply a variable reference voltage signal at frequency F 0 to the integrated waveguide capacitor 206. As already mentioned, the conductivity of the waveguide region 207 may change depending on the intensity of the optical signal therein. Consequently, the current flowing through the waveguide region 207 may also vary. In particular, the magnitude of the electric current generated by the integrated waveguide capacitor 206 may be influenced by the light intensity in the waveguide region 207, since the conductivity of the waveguide region at the monitoring location changes due to the presence of free charge carriers which arise due to the absorption of photons at the photon absorption locations 226.The monitoring circuit 702 may measure the electrical signals (e.g., electrical currents) through the integrated waveguide capacitor 206, which in turn are representative of the intensity of the light contained in the waveguide region 207. In some examples, the electrical current that monitoring circuit 702 receives from integrated waveguide capacitor 206 may be weak. Preamplifier 710 may amplify the electrical currents for further processing by lock-in amplifier 708.FIG. 8 shows a block diagram of an example of a multi-chip module 800. In some examples, the multi-chip module 800 is implemented as a subsystem within an electronic system, e.g., computers (fixed or portable), servers, storage systems, wireless access points, network switches, routers, docking stations, printers, or scanners. Such electronic systems can be offered as independent products or as packet solutions and can be used by a one-time purchase of the entire product or the entire solution or by payment per use or consumption. In an example implementation, the multi-chip module may include at least one electronic chip, e.g., an electronic chip 802, and at least one photonic chip, e.g., a photonic chip 804, mounted on a printed circuit board 806. The circuit board 806 may be a printed circuit board (PCB) including a plurality of electrically conductive traces (not shown) to connect the electronic chip 802 and the photonic chip 804 to each other and to other components disposed on or outside the circuit board 806. Non-limiting examples of the electronic chip 802 may be IC chips such as an application specific integrated circuit (ASIC), a field programmable gate array (FPGA) chip, a processor chip (e.g., a central processing unit and / or a graphics processing unit), a memory chip, a wireless communication module chip, power supply chips or modules, electronic devices such as capacitors, inductors, resistors, or the like, without being limited thereto. In an example, the electronic chip 802 may be configured to operate as a photonics controller. During operation of the multichip module 800, the electronic chip 802 may be configured to transmit and receive data and / or control signals to the photonic chip 804.The photonic chip 804 may include one or more optical devices, such as, but not limited to, optical detectors, optical filters, optical cables, waveguides, optical modulators, light sources (e.g., lasers), and the like. The photonic chip 804 may function as an optical receiver, optical transmitter, optical transceiver, optical communication and / or processing medium for the data and control signals received from the electronic chip. In some examples, the photonic chip 804 may include an optical device 202, such as is shown in FIG. 2, and the description of which is not repeated here for brevity. The use of other optical devices such as optical devices 102, 302, 402, 502 or 602 in photonic chip 804 is also conceivable within the scope of the present disclosure. Moreover, in some examples, the electronic chip 802 may also function as monitoring circuitry, such as monitoring circuitry 702 described in FIG. 7, to monitor the light within the optical device 202 of the photonic chip 804. In certain other examples, the multi-chip module 800 may include additional electronic chip or circuitry that functions as monitoring circuit 702.FIG. 9 shows an example of a method 900 for forming an optical device such as the optical device 100 of FIG. 1 For purposes of illustration, the method 900 is described in conjunction with FIG. 1, however, the method steps described herein may apply to other optical devices described above.In block 902, a substrate is provided. The substrate may be an SOI substrate in one example. Further, at block 904, an integrated waveguide capacitor, such as the integrated waveguide capacitor 106, may be formed using the substrate, wherein the integrated waveguide capacitor may include a waveguide region having one or more photon absorption sites. The photon absorption sites may be imperfections in the bulk of the material of the waveguide region, surface imperfections at the boundaries of the waveguide region, or both. In some examples, the photon absorption sites may have been caused by imperfections in the manufacturing process. In some examples, photon absorption sites may be intentionally created. Further, in block 906, a light emitting structure, such as light emitting structure 104, may be formed over the integrated waveguide capacitor, the light emitting structure emitting light upon application of electricity to the optical device. Further details of the formation of the integrated waveguide capacitor and the light emitting structure will be described in conjunction with FIG. 10. The waveguide region contains at least a portion of the light generated by the light emitting structure, and the photon absorption sites cause the generation of free charge carriers relative to an intensity of the light confined in the waveguide region, resulting in a change in the conductivity of the waveguide region.FIG. 10 shows an example method 1000 for forming an optical device such as the optical device 202 of FIG. 2 For purposes of illustration, the method 1000 is described in connection with FIG. 2, however, the method steps described herein may apply to other optical devices described above.In block 1002, a substrate, e.g., the substrate 212, may be provided. The substrate 212 may be an SOI substrate including the base substrate layer 216, the base oxide layer 214, and the device layer 218. Further, in block 1004, an integrated waveguide capacitor, such as integrated waveguide capacitor 206, may be formed using substrate 212. In an example, forming the integrated waveguide capacitor 206 in the block 1006 may include forming the waveguide region 207 and the non-waveguide region 209 in the block 1006 into the substrate 212. As mentioned above, in some examples, imperfections are intentionally formed in the waveguide region 207 to provide photon absorption sites such as the photon absorption sites 226. In some cases, the photon absorption sites 226 are caused by imperfections in the manufacturing processes. Further, in some examples, the waveguide region 207 may be lightly doped to achieve a first type doping. In particular, the waveguide region 207 and the non-waveguide region 209 may be formed by photolithographic definition and masking of the regions for the waveguide region 207 and the non-waveguide region 209 and subsequent chemical and / or mechanical etching of the non-masked regions. Further, in block 1008, forming the integrated waveguide capacitor 206 may include forming the insulating layer 210 over the waveguide region 207 and the non-waveguide region 209. The insulating layer 210 may be formed by thermal growth techniques and / or by deposition techniques such as chemical vapor deposition (CVD). Moreover, the formation of the integrated waveguide capacitor 206 in block 1010 may include the formation of a first buffer semiconductor region 208 over the insulating layer 210 using thermal growth techniques and / or using deposition techniques such as CVD or wafer bonding.Moreover, in some examples, the method 1000 may include forming, at block 1012, the light emitting structure, such as the light emitting structure 204, over the integrated waveguide capacitor 206. The light emitting structure 204 may be formed by forming an optical gain region such as the optical gain region 236 and a second buffer semiconductor region such as the buffer semiconductor region 238. For example, in block 1014, the optical gain region 236 may be formed over the first buffer semiconductor region 208. As already described, the optical gain region 236 may comprise a quantum well structure (see FIG. 5 ) or a quantum dot structure (see FIG. 6 ). In particular, in some examples, the optical gain region 236 may be formed on the top surface of the first buffer semiconductor region 208 above the waveguide region 207 using techniques such as, but not limited to, thermal growth or CVD, wafer bonding, molecular beam epitaxy (MBE). Further, in block 1016, the second buffer semiconductor region 238 may be formed over the optical gain region 236 using techniques similar to those used to form the first buffer semiconductor region 208.Moreover, in some examples, at block 1018, one or more contact regions, such as contact regions 228, 230, and 231, may be formed. The contact regions 228, 230, and 231 may be formed by techniques such as, but not limited to, thermal growth and / or CVD, wafer bonding, MBE, and doping with corresponding impurities. For example, contact regions 228 and 231 are doped to have a first type of doping and contact region 230 is doped to have a second type of doping. Further, in some examples, in block 1020, metal contacts such as metal contacts 232, 234, and 235 are formed over contact regions 228, 230, and 231, respectively.The terminology used herein is for the purpose of describing particular examples and is not to be taken as limiting. As used herein, the singular forms "a(s)" and "the / s" also include the plural forms, unless the context clearly indicates otherwise. As used herein, the term "another" is defined as at least a second or more. The term "coupled to" as used herein is defined as being joined, either directly without intervening elements or indirectly with at least one intervening element, unless otherwise indicated. For example, two elements may be mechanically, electrically, optically, or communicatively coupled to one another via a communication channel, path, network, or system. Moreover, as used herein, the term "and / or" refers to and encompasses all possible combinations of the listed elements. It should be noted that, although the terms "first", "second", "third", etc. are used herein to describe various elements, these elements are not to be limited by these terms, as these terms are only used to distinguish one element from another unless stated otherwise or the context indicates otherwise.The term "comprises" as used herein means including, but not limited to, the term "including" means including, but not limited to. The term "based on" means based at least in part on.Although certain implementations have been shown and described above, various changes in form and details may be made. For example, some features and / or functions described with respect to an implementation and / or process may also apply to other implementations. In other words, processes, features, components, and / or characteristics described with respect to an implementation may also be useful in other implementations. Moreover, it should be appreciated that the systems and methods described herein may include various combinations and / or sub-combinations of the components and / or features of the various implementations described. Moreover, the process blocks described in the various methods may be performed serially, in parallel, or in a combination thereof. Furthermore, the method blocks can also be executed in a different sequence than shown in the flowcharts.Moreover, in the foregoing description, numerous details are set forth in order to facilitate understanding of the subject matter disclosed herein. Other implementations may include modifications, combinations, and variations of the details described above. It is intended that the following claims cover such modifications and variations.

Claims

An optical device (100), (202), (302), (402), (502), (602) comprising: a light emitting structure (104), (204), (504), (604) for emitting light upon application of electricity to the optical device; An integrated waveguide capacitor (106), (206), (506), (606) formed under the light emitting structure (104), (204), (504), (604) for monitoring the light emitted by the light emitting structure, wherein the integrated waveguide capacitor comprises a waveguide region (207), (307), (407), (507), (607) guiding at least a portion of the light, and wherein the waveguide region comprises one or more photon absorption sites (226) for absorbing photons of the portion of the light guided in the waveguide region that cause generation of free charge carriers relative to an intensity of the light enclosed in the waveguide region based on the absorbed photons, resulting in a change in a conductivity of the waveguide region that is proportional to the intensity of the portion of the light guided in the waveguide region.The optical device of claim 1, wherein the integrated waveguide capacitor further comprises a first contact region (228) comprising a first type dopant and disposed in contact with the waveguide region.The optical device of claim 2, wherein the integrated waveguide capacitor further comprises a first buffer semiconductor region. (208), (508), (608), and an insulating layer (210), (510), (610) disposed between the waveguide region and the first buffer semiconductor region.The optical device of claim 3, wherein the waveguide region comprises a first type dopant and the first buffer semiconductor region comprises a second type dopant.The optical device of claim 3, wherein the integrated waveguide capacitor further comprises a second contact region (230) comprising a second type dopant and arranged in contact with the first buffer semiconductor region.The optical device of claim 5, wherein to monitor the light emitted from the light emitting structure without extraction of the light from the optical device, a reference voltage is applied to the second contact region and a current flowing through the first contact region is measured, wherein a variation of the current is proportional to the change in conductivity of the waveguide region, thereby indicating the light emitted from the light emitting structure.The optical device of claim 1, wherein the integrated waveguide capacitor further comprises a plurality of physically isolated contact region portions (308A-308C), (408A-408C) disposed in contact with the waveguide region.The optical device of claim 1, wherein the light emitting structure comprises: an optical gain region (236), (536), (636) formed over the integrated waveguide capacitor; and a second buffer semiconductor region (238), (538), (638) formed over the optical gain region.The optical device of claim 8, wherein the optical gain region comprises a quantum well structure.The optical device of claim 8, wherein the optical gain region comprises a quantum dot structure.The optical device of claim 1, further comprising: a monitoring circuit (108), (702) configured to monitor the intensity of light emitted from the light emitting structure without extracting the light from the optical device, wherein the monitoring circuit is configured to apply a reference voltage to the integrated waveguide capacitor and the waveguide region and measure a current flowing through the waveguide region, wherein a change in the current is proportional to the change in the conductivity of the waveguide region that is indicative of the intensity of the light included in the waveguide region.The optical device of claim 1, wherein the one or more photon absorption sites comprise imperfections in a material of the waveguide region, defects in the material of the waveguide region, and / or surface imperfections at boundaries of the waveguide region.A multichip module (800) comprising: an electronic chip (802); and a photonic chip (804) coupled to the electronic chip and communicating with the electronic chip, the photonic chip comprising an optical device (100), (202), (302), (402), (502), (602) comprising: a light emitting structure (104), (204), (504), (604) having an optical gain region (236), (536), (636) for emitting light upon application of electricity to the optical device; and an integrated waveguide capacitor (106), (206), (506), (606) formed under the light emitting structure to monitor the light emitted by the light emitting structure, the integrated waveguide capacitor comprising: a waveguide region (207), (307), (407), (507), (607) guiding at least a portion of the light, a first buffer semiconductor region (208), (508), (608) and an insulating layer (210), (510), (610) disposed between the waveguide region and the first buffer semiconductor region, the waveguide region comprising one or more photon absorption sites (226) causing the generation of free charge carriers relative to an intensity of the light confined in the waveguide region resulting in a change in the conductivity of the waveguide region.The multichip module of claim 13, wherein the integrated waveguide capacitor further comprises: a first contact region (228) having a first type of doping and disposed over the waveguide region; and a second contact region (230) having a second type of doping and disposed over the first buffer semiconductor region.The multichip module of claim 13, wherein the integrated waveguide capacitor further comprises: a plurality of physically isolated contact region portions (308A-308C), (408A-408C), the first contact region having a first type of doping and disposed over the waveguide region; and a second contact region (230) having a second type of doping and disposed over the first buffer semiconductor region.The multichip module of claim 13, wherein the optical gain region comprises a quantum well structure or a quantum dot structure.The multichip module of claim 13, wherein the light emitting structure further comprises a second buffer semiconductor region (238), (538), (638) formed over the optical gain region.The multichip module of claim 13 further comprising monitoring circuitry (108), (702) coupled to the photonic chip for monitoring light intensity within the optical device without diverting a portion of the light out of the waveguide region.A method of forming an optical device (100), (202), (302), (502), (602) comprising: providing a substrate (212), (512), (612); forming an integrated waveguide capacitor (106), (206), (506), (606) using the substrate, wherein the integrated waveguide capacitor comprises a waveguide region (207), (307), (407), (507), (607) comprising one or more photon absorption sites (226); forming a light emitting structure (104), (204), (504), (604) over the integrated waveguide capacitor, the light emitting structure being operable to emit light upon application of electricity to the optical device, wherein the waveguide region contains at least a portion of the light generated by the light emitting structure and the one or more photon absorption sites absorb photons of the portion of the light guided in the waveguide region and cause generation of free charge carriers relative to an intensity of the light confined in the waveguide region based on the absorbed photons, resulting in a change in the conductivity of the waveguide region that is proportional to the intensity of the portion of the light guided in the waveguide region.The method of claim 19, wherein forming the integrated waveguide capacitor comprises: forming the waveguide region into the substrate; forming an insulating layer (210), (510), (610) over the waveguide region; and forming a first buffer semiconductor region (208), (508), (608) over the insulating layer.The method of claim 20, wherein forming the light emitting structure over the integrated waveguide capacitor comprises: forming an optical gain region (236), (536), (636) over the first buffer semiconductor region; and forming a second buffer semiconductor region (238), (538), (638) over the optical gain region.The method of claim 21, wherein the optical gain region comprises a quantum well structure or a quantum dot structure.

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