Various embodiments relate to an electro-optical device having a small optical window (e.g., with a diameter of less than 40 μm). Various embodiments relate to an electro-optical device having improved coupling characteristics.
As data communication demands increase with respect to both volume and speed, the use of electro-optical devices communicating via fiber optics has become an increasingly popular communication approach. One of the key parameters of an electro-optical device to enable higher speed is the parasitic capacitance. The lower the capacitance the higher the rate possible for the same device. The capacitance of a device is set mainly by the geometry of the device following C=Aε/D where A is the device area, D is the distance between the conductive planes, and ε is the dielectric constant between them. However, decreasing the device area (A) amounts to decreasing the optical window size, which, in turn, increases the coupling loss when connecting to an optical fiber. Therefore, there is a need for more efficiently coupling of electro-optical devices having smaller optical window sizes to optical fibers.
Various embodiments of the present invention provide technical solutions to the technical problems regarding electro-optical device alignment arising from the decrease in optical window size of the electro-optical device. For example, various embodiments provide electro-optical devices (e.g., photodiodes, VCSELs, and/or the like) having small optical windows (e.g., with diameters less than 40 μm) that have improved coupling characteristics. For example, various embodiments provide couplable electro-optical devices (e.g., photodiodes, VCSELs, and/or the like) having an integrated lens. Various embodiments provide a receiver, transmitter, and/or transceiver comprising a couplable electro-optical device. In various embodiments, the lens is a molded lens. In various embodiments, the lens is molded with a wafer having one or more electro-optical devices disposed thereon as the carrier. For example, the lens may be molded directly onto the electro-optical device. In various embodiments, the lens is coated with an anti-reflection coating. In various embodiments, the couplable electro-optical device is a single mode VCSEL that may be coupled to an optical fiber, such as a small core optical fiber (e.g., an optical fiber with a diameter core of approximately 10 μm or less) without the use of expensive and time intensive active alignment techniques. In various embodiments, the optical fiber may be a multi-mode optical fiber or a single mode optical fiber.
According to a first aspect, a couplable electro-optical device with improved coupling characteristics is provided. In an example embodiment, the couplable electro-optical device comprises a raw electro-optical device formed on a substrate and an integrated lens that was molded onto the substrate. An optical window of the raw electro-optical device is aligned with the integrated lens. A focal point of the integrated lens is located at a modeling point of the raw electro-optical device.
In an example embodiment, the couplable electro-optical device further comprises an anti-reflective coating on an outer surface of the integrated lens. In an example embodiment, the integrated lens comprises a spacer portion and a lens portion. In an example embodiment, a depth of the spacer portion and a radius of curvature of the lens portion are determined based on a refractive index of the integrated lens and a location of the modeling point. In an example embodiment, the raw electro-optical device is a photodiode or a vertical cavity surface emitting laser (VCSEL). In an example embodiment, the raw electro-optical device has an optical window that has a diameter less than 40 μm.
According to another aspect, a method for fabricating and/or manufacturing a couplable electro-optical device with improved coupling characteristics is provided. In an example embodiment, the method comprises fabricating at least one raw electro-optical device on a substrate; applying lens material to a working stamp; aligning the substrate and the working stamp; pressing the substrate onto the lens material until the distance between the substrate and the working stamp is a predetermined distance; and curing the lens material to form an integrated lens secured to the at least one electro-optical device on the substrate.
In an example embodiment, applying lens material to the working stamp comprises using a drop dispenser. In an example embodiment, aligning the substrate and the working stamp causes an optical window of the raw electro-optical device to be aligned with the integrated lens. In an example embodiment, aligning the substrate and the working stamp causes a focus point of the integrated lens to be located at a modeling point of the raw electro-optical device. In an example embodiment, the method further comprises applying an anti-reflection coating to an outer surface of the integrated lens. In an example embodiment, the method further comprises removing the working stamp from the couplable electro-optical device. In an example embodiment, the working stamp is removed prior the application of an anti-reflective coating. In an example embodiment, the method further comprises performing a thinning and dicing operation on the substrate. In an example embodiment, the integrated lens comprises a spacer portion and a lens portion. In an example embodiment, a depth of the spacer portion and a radius of curvature of the lens portion are determined based on a refractive index of the integrated lens and a location of the modeling point. In an example embodiment, the raw electro-optical device is a photodiode or a vertical cavity surface emitting laser (VCSEL). In an example embodiment, the raw electro-optical device has an optical window with a diameter that is less than approximately 40 μm (e.g., 30 μm, 20 μm, 12 μm (e.g., in the case of a photodiode), 6 μm (e.g., in the case of a VCSEL), and/or the like). In various embodiments, the couplable electro-optical device has a coupling efficiency greater than −1.25 dB. In various embodiments, the electro-optical device has a coupling efficiency in the range of approximately −1.0 to −0.5 dB.
According to still another aspect, a receiver, transmitter, and/or transceiver is provided. In an example embodiment, the receiver, transmitter, and/or transceiver comprises a couplable electro-optical device and an optical fiber, wherein the couplable electro-optical device is coupled to the optical fiber via passive alignment. In an example embodiment, the couplable electro-optical device comprises a raw electro-optical device formed on a substrate; and an integrated lens that was molded onto the substrate. An optical window of the raw electro-optical device is aligned with the integrated lens. A focal point of the integrated lens is located at a modeling point of the raw electro-optical device.
In an example embodiment, the couplable electro-optical device is coupled to the optical fiber via an outer lens. In an example embodiment, the optical fiber has a core that has a diameter less than approximately 10 μm. In an example embodiment, the raw electro-optical device has an optical window with a diameter that is less than 40 μm.
Having thus described the invention in general terms, reference will now be made to the accompanying drawings, which are not necessarily drawn to scale, and wherein:
Various embodiments of the present invention provide technical solutions to the technical problems regarding electro-optical device alignment arising from the decrease in optical window size of the electro-optical device. For example, various embodiments provide electro-optical devices (e.g., photodiodes, VCSELs, and/or the like) having small optical windows (e.g., with diameters less than 40 μm) that have improved coupling characteristics. For example, various embodiments provide couplable electro-optical devices (e.g., photodiodes, VCSELs, and/or the like) having an integrated lens. In various embodiments, the lens is a molded lens. In various embodiments, the lens is molded with a wafer having one or more electro-optical devices disposed thereon as the carrier. For example, the lens may be molded directly onto the electro-optical device. In various embodiments, the lens is coated with an anti-reflection coating.
In an example embodiment, the raw electro-optical device 120 comprises an active area. For example, when the raw electro-optical device 120 is a photodiode or other receiving device, the active area is the surface/location at which signal detection occurs. In another example, when the raw electro-optical device 120 is a VCSEL or other emitting device, the active area is the surface/location from which the light is emitted. In various embodiments, a modeling point 122 may be used to model the active area of the raw electro-optical device 120 as a point. For example, when the focal point 136 of the integrated lens 130 is located at the modeling point 122 of the raw electro-optical device 120, a beam incident on the active region of the raw electro-optical device 120 via the integrated lens 130 will have a beam width such that a significant portion of the beam (e.g., the central portion of the beam within the full width half maximum radius of the beam) incident on the optimal portion of the active area for signal detection. In another example, when the focal point 136 of the integrated lens 130 is located at the modeling point 122 of the raw electro-optical device 120, a beam emitted from the active region and incident on the integrated lens 130 will be emitted from the couplable electro-optical device 100 with an approximately constant beam width (e.g., the beam may be modeled by approximately and/or substantially parallel rays).
In various embodiments, the couplable electro-optical device 100 comprises an integrated lens 130. In various embodiments, the integrated lens comprises a lens portion 134 and a spacer portion 132. In an example embodiment, the lens portion 134 has a radius of curvature R and a thickness T, and the spacer portion 132 has a depth D such that the focal point 136 of the integrated lens 130 is coincident with the modeling point 122. As should be understood by one skilled in the art in light of this disclosure, the radius of curvature R and the depth D are determined based on the modeling point 122 and the refractive index n of the material of the integrated lens 130. In various embodiments, the integrated lens 130 is a molded lens. In various embodiments, the integrated lens 130 is molded onto the raw electro-optical device 120 and/or the substrate 110. In various embodiments, the integrated lens 130 is a molded micro-lens.
In various embodiments, the depth D is in the range of approximately 0.03 mm to 0.05 mm. In various embodiments, the depth D is in the range of approximately 0.035 mm to 0.045 mm. In an example embodiment, the depth D is approximately 0.4 mm. In various embodiments, the radius of curvature R is in the range of approximately 20 to 35 μm. In various embodiments, the radius of curvature R is in the range of approximately 25-30 μm. For example, the radius of curvature R may be in the range of approximately 26-28 μm. In various embodiments, the thickness T is in the range of approximately 5-25 μm. In various embodiments, the thickness T is in the range of approximately 8-16 μm. In an example embodiment, the thickness T is in the range of approximately 10-14 μm.
In various embodiments, the integrated lens 130 is made of a lens material selected for a combination of the mechanical and optical properties of the material. In an example embodiment, the integrated lens 130 is made of a lens material that is a polymeric material. In an example embodiment, the lens material is a cured polymeric material. In an example embodiment, curing the polymeric material to provide the lens material includes heating the polymeric material and/or exposing the polymeric material to UV light. In an example embodiment, the lens material is a polymeric material that requires heat and/or UV curing. For example, the lens material may be a liquid resin that when cured becomes a solid polymeric material. In an example embodiment, the lens material is a hybrid inorganic-organic polymeric material. In various embodiments, the cured lens material has a refractive index n in the range of approximately 1.2 to 1.9. In an example embodiment, the cured lens material has a refractive index n in the range of approximately 1.4 to 1.6. For example, in an example embodiment, the cured lens material has a refractive index n in the range of approximately 1.50 to 1.55. In various embodiments, the cured lens material has a refractive index n in the range of approximately 1.50 to 1.55 in the wavelength range 400-1600 nm. In various embodiments, the cured lens material has a refractive index n in the range of approximately 1.50 to 1.52 in the wavelength range of 700-1600 nm.
In various embodiments, the integrated lens 130 comprises an anti-reflective coating 140. For example, the outer surface 136 of the integrated lens 130 may be the surface of the integrated lens 130 that faces away from the raw electro-optical device 120. In various embodiments, the outer surface 136 of the integrated lens 130 may have an anti-reflective coating 140 thereon. In various embodiments, the anti-reflective coating 140 may be selected based on the wavelength of light that the raw electro-optical device 120 is configured to receive/detect and/or emit. In an example embodiment, the thickness of the anti-reflective coating 140 is selected based on the wavelength of light that the raw electro-optical device 120 is configured to receive and/or emit.
In various embodiments, the couplable electro-optical device 100 may be coupled to an optical fiber 300. In various embodiments, the couplable electro-optical device 100 is coupled to the optical fiber 300 without the use of active alignment. In various embodiments, the couplable electro-optical device 100 is coupled to the optical fiber 300 via an outer lens 200. In an example embodiment, the optical fiber 300 is a small core optical fiber. For example, the optical fiber 300 may comprise an outer fiber cladding 302 and an optical fiber core 304. In an example embodiment, the optical fiber core 304 has a diameter of approximately 9 μm. For example, the optical fiber core 304 may have a diameter less than 15 μm. For example, the integrated lens 130 may condition the light emitted by the raw electro-optical device 120 (e.g., a VCSEL) such that the light emitted by the couplable electro-optical device 100 is described by a set of substantially parallel rays. The outer lens 200 may then be used to focus the light emitted by the couplable electro-optical device 100 into the core of the optical fiber 300. Thus, the couplable electro-optical device 100 may be efficiently coupled to a small core optical fiber 300 (e.g., having a core 304 diameter of approximately 10 μm or less) without the use of expensive and time intensive active alignment techniques. Rather, a static outer lens 200 may be employed to focus the light emitted by the couplable electro-optical device 100 onto the core 304 of the optical fiber 300 for an efficient coupling.
At block 404, the lens material is applied to a working stamp. In various embodiments, the working stamp is manufactured and/or fabricated using a very accurate photolithography-based process to assure accurate alignment between the raw electro-optical devices populated and/or fabricated on the substrate 110 (e.g., on a wafer) and the resulting integrated lenses 130. In an example embodiment, the lens material applied to the working stamp using a droplet dispenser. For example, a droplet dispenser may dispense the lens material drop by drop into/onto the working stamp. In an example embodiment, the droplet dispenser is used to apply the lens material to the working stamp so that when the raw electro-optical device 120 is pressed onto the lens material within the working stamp, the lens material does not cover the leads of the raw electro-optical device 120 and/or the space between raw electro-optical devices on the substrate 110 that is intended for use during thinning and dicing procedures and/or during wire bonding while assembling the couplable electro-optical device 100 onto an optical cable (e.g., active optical cable (AOC)), transceiver, and/or the like, later in the couplable electro-optical device 120 fabrication and/or assembly process.
The master stamp 452 may be used to make or form the working stamp 454. For example, the working stamp 454 may be a negative of the integrated lens 130. For example, the working stamp 454 may comprise one or more molds 456 for receiving and molding lens material into integrated lenses 130. Each mold 456 may comprise a well comprising a lens mold portion 464 having a radius of curvature R and a thickness T, and a spacer mold portion 462 having a depth 8. For example, the lens mold portion 464 may be a curved surface that approximates and/or is a portion of a sphere, as shown by the dashed circle in
Continuing with block 406 of
For example, in an example embodiment, the first set of alignment marks 114 comprises a plus sign disposed on the substrate 110, as shown in
For example, the raw electro-optical devices 120 on the substrate 110 (e.g., wafer) may be positioned onto the lens material 458 in the working stamp 454. For example, the substrate 110 may be aligned with the working stamp 454 and then the substrate 110 may be pressed onto the lens material 458 within the working stamp 454 until the distance between the substrate and the working stamp is a predetermined distance. In various embodiments, the predetermined distance (e.g., the distance between the substrate 110 and the working stamp 454) is D−δ, such that the resulting spacer portions 132 will have a depth D.
Continuing with
At block 412 of
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Many modifications and other embodiments of the invention set forth herein will come to mind to one skilled in the art to which this invention pertains having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is to be understood that the invention is not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.
Filing Document | Filing Date | Country | Kind |
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PCT/GR2019/000078 | 11/6/2019 | WO |