Fabrication of waveguide structures

Abstract

To satisfy a need for improved techniques for fabrication of waveguide structures including optical chips and optofluidic chips that are simpler, less difficult, less time-consuming, and less expensive than known techniques.SOLUTION: A method of fabricating a waveguide structure to form a solid-core waveguide from a waveguiding layer is provided, the method capable of comprising etching a fluid channel into the waveguiding layer, and etching a first air-gap and a second air gap into the waveguiding layer, where etching the first and the second air-gaps creates a solid-core waveguide in the waveguiding layer between the first air-gap and the second air-gap.SELECTED DRAWING: Figure 2A

Description

[Technical field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the benefit of U.S. Provisional Application No. 62 / 674,853, filed May 22, 2018, the entire contents of which are incorporated herein by reference.

[0002] The present disclosure relates generally to methods for fabricating waveguides, and more particularly to methods for fabricating two-dimensional waveguide structures such as solid core waveguides, fluid core channels, and / or optofluidic chips having fluid core waveguides. [Background technology]

[0003] Waveguide structures, such as optical and optofluidic chips, are important in modern biomedical research. These waveguide structures may contain solid-core waveguides, fluidic channels, and / or fluid-core waveguides, which may be coplanar with one another and may cross one another in various configurations.

[0004] Known techniques for manufacturing the above structures require multiple manufacturing steps. For example, known techniques for manufacturing a waveguide chip may include six or more lithography steps, multiple etching steps, multiple deposition steps, and a sacrificial core removal process. Summary of the Invention [Problem to be solved by the invention]

[0005] As mentioned above, known techniques for manufacturing waveguide structures, such as optical and optofluidic chips, require multiple steps. These various steps can be difficult, complex, time-consuming and expensive to perform. For example, alignment steps create various opportunities for defects and failures in the waveguide structures due to misalignment. Additionally, the sacrificial core removal process can be very time consuming. Furthermore, in fields utilizing biosensor chips and waveguide structures, there is a need to develop optimized chip and waveguide architectures to improve overall manufacturability, cost, yield and reproducibility, including by reducing the number of steps and processes for fabricating the optimized chips and structures. Thus, there is a need for improved techniques for fabricating waveguide structures, including optical and optofluidic chips, that are simpler, less difficult, less time consuming and less expensive than known techniques. [Means for solving the problem]

[0006] Improved techniques are disclosed herein that can address one or more of the above needs. In some embodiments, a single lithography / etching process followed by a bonding process as described herein can replace the cumbersome and extensive sequence of steps required by previous techniques. The reduction in the overall number of steps can enable faster, more efficient, less complicated, and less expensive production (e.g., manufacturability, cost, yield, repeatability), including on a commercial scale. Eliminating the alignment step can further improve quality control by preventing misalignments and defects that can occur during traditional alignment procedures. For example, these techniques can enable automated alignment and waveguide crossings with much fewer defects than those formed by conformal coating and etching. Additionally, the techniques described herein may require fewer microfabrication steps than known methods, may form automatic alignment of solid core waveguides to fluidic core channels (instead of one mask each), may form monolithic intersections between solid and fluidic cores, may enable direct fluidic integration (e.g., planar chip surfaces may enable bonding techniques and simpler fluidic interconnects), may eliminate the need for time-consuming sacrificial core removal, and may allow a wider variety of materials to choose from, rather than just those compatible with conventional methods.

[0007] In some embodiments, a first method is provided for fabricating a waveguide structure to form at least one solid core waveguide from a waveguide layer, the first method including etching a fluid channel in the waveguide layer; etching a first air gap and a second air gap in the waveguide layer, where the etching of the first air gap and the second air gap creates a solid core waveguide in the waveguide layer between the first air gap and the second air gap; and attaching a cover layer to the waveguide layer to encapsulate the fluid channel.

[0008] In some embodiments of the first method, the waveguide layer includes a first oxide layer and a second oxide layer, the first oxide layer being on a first side of the second oxide layer and having a first refractive index, and the second oxide layer having a second refractive index lower than the first refractive index.

[0009] In some embodiments of the first method, etching the fluid channel includes etching into the second oxide layer and the first oxide layer at once, etching the first air gap includes etching into the second oxide layer and the first oxide layer at once, and etching the second air gap includes etching into the second oxide layer and the first oxide layer at once.

[0010] In some embodiments of the first method, the waveguide layer further includes a third oxide layer on a second side opposite the first side of the second oxide layer, the third oxide layer having a third refractive index lower than the first refractive index, and etching the fluid channel includes etching into the third, second, and first oxide layers at once, etching the first air gap includes etching into the third, second, and first oxide layers at once, and etching the second air gap includes etching into the third, second, and first oxide layers at once.

[0011] In some embodiments of the first method, the first method further includes doping the waveguide layer to create one or more doped regions in the waveguide layer having a doped refractive index lower than the surrounding refractive index, the one or more doped regions being adjacent to the solid core waveguide.

[0012] In some embodiments of the first method, the one or more doped regions are adjacent to the first air gap and the second air gap.

[0013] In some embodiments of the first method, the one or more doped regions are adjacent to the fluid channel.

[0014] In some embodiments of the first method, the first method further includes doping the waveguide layer to create one or more doped regions in the waveguide layer having a doped refractive index higher than the surrounding refractive index, the one or more doped regions forming a solid core waveguide.

[0015] In some embodiments of the first method, the waveguide structure includes an ARROW layer, and etching the fluidic channels includes etching in the waveguide layer without etching in the ARROW layer, etching the first air gap includes etching in the waveguide layer without etching in the ARROW layer, and etching the second air gap includes etching in the waveguide layer without etching in the ARROW layer.

[0016] In some embodiments of the first method, the waveguide structure includes an ARROW layer, the waveguide structure includes an etch stop layer between the ARROW layer and the waveguide layer at a location corresponding to the fluidic channel, etching the fluidic channel includes etching into the waveguide layer without etching into the ARROW layer and dissolving the etch stop layer, etching the first air gap includes etching into the waveguide layer and the ARROW layer at once, and etching the second air gap includes etching into the waveguide layer and the ARROW layer at once.

[0017] In some embodiments of the first method, the waveguide structure includes an ARROW layer, and etching the fluidic channels includes performing a dry etch followed by a wet etch, etching the first air gap includes performing a dry etch followed by a wet etch, and etching the second air gap includes performing a dry etch followed by a wet etch.

[0018] In some embodiments of the first method, the waveguide structure includes an ARROW layer, and etching the fluidic channel includes etching partially into the waveguide layer without etching through the waveguide layer to the ARROW layer, etching the first air gap includes etching into the waveguide layer and the ARROW layer at once, and etching the second air gap includes etching into the waveguide layer and the ARROW layer at once.

[0019] In some embodiments of the first method, etching the first air gap includes etching into the waveguide layer, the ARROW layer, and the substrate layer at once, and etching the second air gap includes etching into the waveguide layer, the ARROW layer, and the substrate layer at once.

[0020] In some embodiments of the first method, the waveguide structure includes an ARROW layer below the waveguide layer, the waveguide structure includes an etch stop layer between the ARROW layer and the waveguide layer extending at locations corresponding to the fluidic channels, the locations corresponding to the first air gap, and the locations corresponding to the second air gap, etching the fluidic channels includes etching into the waveguide layer without etching into the ARROW layer, etching the first air gap includes etching into the waveguide layer without etching into the ARROW layer, and etching the second air gap includes etching into the waveguide layer without etching into the ARROW layer, and the first method further includes dissolving the etch stop layer.

[0021] In some embodiments of the first method, the waveguide structure includes a substrate layer coupled to the waveguide layer, and the method further includes etching into the substrate to form a third air gap adjacent to one or more of the fluidic channels and the solid core waveguide, the third air gap configured to cause internal reflection of light propagating in the one or more of the fluidic channels and the solid core waveguide.

[0022] In some embodiments of the first method, the first method further includes providing a lens element in the third air gap, the lens element configured to collect light that escapes from the fluid channel into the third air gap.

[0023] In some embodiments of the first method, etching into the substrate to form the third air gap includes undercutting one or more of the fluidic channel and the solid core waveguide.

[0024] In some embodiments of the first method, the waveguide structure includes micro-machined fiber alignment features.

[0025] In some embodiments of the first method, the first method further includes doping the waveguide layer from a surface of the waveguide layer where the etching is performed such that the waveguide layer has the highest refractive index gradient near the doped surface.

[0026] In some embodiments of the first method, the first method further includes providing a protective layer on the waveguide layer after doping the waveguide layer and before etching into the waveguide layer, and attaching the cover layer to the waveguide layer includes attaching the cover layer to the protective layer.

[0027] In some embodiments of the first method, etching the fluid channel includes performing a dry etch, etching the first air gap includes performing a dry etch, and etching the second air gap includes performing a dry etch.

[0028] In some embodiments of the first method, the first method further includes etching into the waveguide layer behind the end of the solid core waveguide, thereby forming the end of the solid core waveguide.

[0029] In some embodiments, a first waveguide structure is provided, the first waveguide structure including a waveguide layer including a fluid channel, a first air gap, and a second air gap, the first and second air gaps defining a solid core waveguide in the waveguide layer between the first air gap and the second air gap, and a cover layer attached to the waveguide layer to encapsulate the fluid channel.

[0030] In some embodiments of the first waveguide structure, the waveguide layer includes a first oxide layer and a second oxide layer, the first oxide layer being on a first side of the second oxide layer and having a first refractive index, and the second oxide layer having a second refractive index lower than the first refractive index.

[0031] In some embodiments of the first waveguide structure, one or more of the fluid channel, the first air gap, and the second air gap extend at least partially through the first oxide layer and the second oxide layer.

[0032] In some embodiments of the first waveguide structure, the waveguide layer further includes a third oxide layer on a second side opposite the first side of the second oxide layer, the third oxide layer having a third refractive index lower than the first refractive index, and one or more of the fluid channel, the first air gap, and the second air gap extend at least partially through the first oxide layer, the second oxide layer, and the third oxide layer.

[0033] In some embodiments of the first waveguide structure, the waveguide layer includes one or more doped regions having a doped refractive index lower than the refractive index of the surroundings, and the one or more doped regions are adjacent to the solid core waveguide.

[0034] In some embodiments of the first waveguide structure, the one or more doped regions are adjacent to the first air gap and the second air gap.

[0035] In some embodiments of the first waveguide structure, the one or more doped regions are adjacent to the fluid channel.

[0036] In some embodiments of the first waveguide structure, the waveguide layer includes one or more doped regions having a doped refractive index higher than the refractive index of the surroundings, the one or more doped regions forming a solid core waveguide.

[0037] In some embodiments of the first waveguide structure, the first waveguide structure further includes an ARROW layer, and one or more of the fluid channel, the first air gap, and the second air gap extend at least partially through the waveguide layer without extending into the ARROW layer.

[0038] In some embodiments of the first waveguide structure, the first waveguide structure further includes an ARROW layer, wherein the fluid channels extend at least partially through the waveguide layer without extending into the ARROW layer, and one or more of the first air gap and the second air gap extend at least partially through the waveguide layer and the ARROW layer.

[0039] In some embodiments of the first waveguide structure, the first waveguide structure further includes a substrate layer coupled to the waveguide layer.

[0040] In some embodiments of the first waveguide structure, the substrate layer includes a third air gap adjacent to the one or more fluidic channels and the solid core waveguide, the third air gap configured to cause internal reflection of light propagating in the one or more fluidic channels and the solid core waveguide.

[0041] In some embodiments of the first waveguide structure, the third air gap includes a lens element configured to collect light that escapes from the fluid channel into the third air gap.

[0042] In some embodiments of the first waveguide structure, the third air gap undercuts one or more fluid channels and the solid core waveguide.

[0043] In some embodiments of the first waveguide structure, the first waveguide structure further includes micro-machined fiber alignment features.

[0044] In some embodiments of the first waveguide structure, the waveguide layer has a refractive index gradient.

[0045] In some embodiments of the first waveguide structure, the first waveguide structure further includes a protective layer disposed on the waveguide layer, and one or more of the fluid channel, the first air gap, and the second air gap extend at least partially through the protective layer and the waveguide layer.

[0046] In some embodiments, a second method is provided for fabricating a waveguide structure to form at least one solid core waveguide, the second method including forming a first trench, a second trench, and a third trench in a substrate layer; forming an oxide layer from the machined substrate layer by oxidizing the machined substrate layer; doping the oxide layer to create one or more doped regions having a doped refractive index higher than an original refractive index of the oxide layer, where doping the oxide layer creates a hollow core of a fluid channel at a location corresponding to the first trench and a solid core waveguide portion in the waveguide layer at a location corresponding to a region between the second trench and the third trench; and attaching a cover layer to the doped oxide layer to encapsulate the fluid channel.

[0047] In some embodiments of the second method, the second method further includes depositing a second oxide layer over the doped oxide layer before applying the cover layer.

[0048] In some embodiments of the second method, forming one or more of the first trench, the second trench, and the third trench in the substrate layer includes machining one or more trenches in the substrate layer.

[0049] In some embodiments of the second method, the substrate layer comprises silicon.

[0050] In some embodiments, a second waveguide structure is provided, the second waveguide structure being made by a method including etching a fluid channel into a waveguide layer of the waveguide structure; etching a first air gap and a second air gap into the waveguide layer, where the etching of the first and second air gaps creates a solid core waveguide in the waveguide layer between the first and second air gaps; and attaching a cover layer to the waveguide layer to encapsulate the fluid channel.

[0051] In some embodiments, any one or more of the features of any one or more of the above embodiments can be combined with each other and / or with other features or aspects of any methods, systems, techniques, or devices disclosed herein. [Brief description of the drawings]

[0052] [Figure 1A] 1A-1D show two schematic diagrams of a waveguide structure according to some embodiments. [Figure 1B] 1A-1D show two schematic diagrams of a waveguide structure according to some embodiments. [Figure 2A] 1A-1D show two schematic diagrams of a waveguide structure having a low index layer below a bonded cover layer according to some embodiments. [Figure 2B] 1A-1D show two schematic diagrams of a waveguide structure having a low index layer below a bonded cover layer according to some embodiments. [Figure 3A] 1A-1D show two schematic diagrams of a waveguide structure including low index doped regions defining one or more waveguides, according to some embodiments. [Figure 3B] 1A-1D show two schematic diagrams of a waveguide structure including low index doped regions defining one or more waveguides, according to some embodiments. [Figure 4A] 1A-1D show two schematic diagrams of a waveguide structure including a high index doped region defining a waveguide, according to some embodiments. [Figure 4B] 1A-1D show two schematic diagrams of a waveguide structure including a high index doped region defining a waveguide, according to some embodiments. [Figure 5A] 1A-1D show two schematic diagrams of a waveguide structure including an ARROW layer according to some embodiments. [Figure 5B] 1A-1D show two schematic diagrams of a waveguide structure including an ARROW layer according to some embodiments. [Figure 6A] 1A-1D show two schematic diagrams of a waveguide structure including an ARROW layer and an etch stop layer according to some embodiments. [Figure 6B]1A-1D show two schematic diagrams of a waveguide structure including an ARROW layer and an etch stop layer according to some embodiments. [Figure 7A] 1A-1D show two schematic diagrams of a waveguide structure including an ARROW layer and formed using wet etching finishing techniques, according to some embodiments. [Figure 7B] 1A-1D show two schematic diagrams of a waveguide structure including an ARROW layer and formed using wet etching finishing techniques, according to some embodiments. [Figure 8] 1 shows a schematic diagram of a waveguide structure including an ARROW layer and a variable depth etch according to some embodiments. [Figure 9A] 1A-1C show two schematic diagrams of a waveguide structure including an anti-resonant reflecting optical waveguide (ARROW) layer and an etch stop layer underlying a number of trenches, according to some embodiments. [Figure 9B] 1A-1C show two schematic diagrams of a waveguide structure including an anti-resonant reflecting optical waveguide (ARROW) layer and an etch stop layer underlying a number of trenches, according to some embodiments. [Figure 10A] 1A-1D show two schematic diagrams of a waveguide structure including an air gap formed in a substrate layer according to some embodiments. [Figure 10B] 1A-1D show two schematic diagrams of a waveguide structure including an air gap formed in a substrate layer according to some embodiments. [Figure 11A] 1A-1D show two schematic diagrams of a waveguide structure including an air gap formed in a substrate layer and including a focusing lens according to some embodiments. [Figure 11B] 1A-1D show two schematic diagrams of a waveguide structure including an air gap formed in a substrate layer and including a focusing lens according to some embodiments. [Figure 12A] 1A-1D show two schematic diagrams of a waveguide structure including an undercut air gap formed in a substrate layer according to some embodiments. [Figure 12B] 1A-1D show two schematic diagrams of a waveguide structure including an undercut air gap formed in a substrate layer according to some embodiments. [Figure 13A] 1A-1D show two schematic diagrams of a waveguide structure including fiber alignment features according to some embodiments. [Figure 13B] 1A-1D show two schematic diagrams of a waveguide structure including fiber alignment features according to some embodiments. [Figure 14A] 1A-1D show four schematic views of a waveguide structure during various stages of a CMP-based trench fabrication method according to some embodiments. [Figure 14B] 1A-1D show four schematic views of a waveguide structure during various stages of a CMP-based trench fabrication method according to some embodiments. [Figure 14C] 1A-1D show four schematic views of a waveguide structure during various stages of a CMP-based trench fabrication method according to some embodiments. [Figure 14D] 1A-1D show four schematic views of a waveguide structure during various stages of a CMP-based trench fabrication method according to some embodiments. [Figure 15A] 1A-1D show two schematic diagrams of a waveguide structure including a doped oxide substrate according to some embodiments. [Figure 15B] 1A-1D show two schematic diagrams of a waveguide structure including a doped oxide substrate according to some embodiments. [Figure 16A] 1A-1D show two schematic diagrams of a waveguide structure including a doped oxide substrate and a cap layer below a bonded cover layer according to some embodiments. [Figure 16B] 1A-1D show two schematic diagrams of a waveguide structure including a doped oxide substrate and a cap layer below a bonded cover layer according to some embodiments. [Figure 17A] 1A-1D show two schematic diagrams of a waveguide structure obtained by oxidizing and doping a machined substrate layer to form a waveguide layer according to some embodiments. [Figure 17B] 1A-1D show two schematic diagrams of a waveguide structure obtained by oxidizing and doping a machined substrate layer to form a waveguide layer according to some embodiments. [Figure 18A] 1A-1D show two schematic diagrams of a waveguide structure obtained by oxidizing and doping a machined substrate layer to form a waveguide layer according to some embodiments. [Figure 18B] 1A-1D show two schematic diagrams of a waveguide structure obtained by oxidizing and doping a machined substrate layer to form a waveguide layer according to some embodiments. [Figure 19A] 1A-1C show two schematic diagrams of a waveguide structure including an air gap formed in a substrate layer, including a focusing lens, and including an aperture layer, according to some embodiments. [Figure 19B] 1A-1C show two schematic diagrams of a waveguide structure including an air gap formed in a substrate layer, including a focusing lens, and including an aperture layer, according to some embodiments. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0053] In some embodiments, a single lithography / etching process followed by a bonding process as described herein can replace the cumbersome and extensive sequence of steps required by previous techniques. For example, a waveguide structure (e.g., a two-dimensional waveguide structure) can be formed from a chip including a substrate layer and a waveguide layer overlying the substrate layer. In some embodiments, the substrate layer can be formed of silicon or other suitable material, and the waveguide layer can be formed of one or more oxides, such as low-temperature oxide, phosphorus-doped oxide, silicon oxynitride, or other suitable material. The waveguide layer can be 1 μm, 5 μm, 10 μm, or 20 μm or more thick in some embodiments. The waveguide layer can be 1 μm, 5 μm, 10 μm, or 20 μm or less thick in some embodiments. The material used in the waveguide layer can be selected such that the material effectively transmits light and can form both the solid core of the solid core waveguide and the walls of the fluidic channels and / or the walls of the fluidic core.

[0054] After the waveguide layer is provided (e.g., placed or deposited) on the substrate layer, one or more etching steps may be performed to form one or more solid core waveguides and one or more fluidic channels (which in some embodiments may also be fluidic core waveguides). To form the fluidic channels, the hollow cores of the channels may be etched away from the waveguide layer.

[0055] In some embodiments, the dimensions of the fluid channel can be varied to affect the flow rate of the fluid through the fluid channel. In some embodiments, the flow of the fluid through the fluid channel can be induced by one or more of vacuum, positive pressure, electroosmosis, and / or electrophoresis. In some embodiments, the geometry of the fluid channel can be configured to induce flow focusing by sheath flow. In some embodiments, the height and / or width of the channel fluid channel can be 0.25 μm, 0.5 μm, 1 μm, 5 μm, 10 μm, 25 μm, 50 μm, 100 μm, 250 μm, 500 μm, or 1000 μm or less. In some embodiments, the height and / or width of the channel fluid channel can be 0.25 μm, 0.5 μm, 1 μm, 5 μm, 10 μm, 25 μm, 50 μm, 100 μm, 250 μm, 500 μm, or 1000 μm or more. In some embodiments, the flow rate through the fluidic channels may be less than or equal to 0.005 μL / min, 0.01 μL / min, 0.1 μL / min, 1 μL / min, 10 μL / min, 100 μL / min, or 500 μL / min. In some embodiments, the flow rate through the fluidic channels may be greater than or equal to 0.005 μL / min, 0.01 μL / min, 0.1 μL / min, 1 μL / min, 10 μL / min, 100 μL / min, or 500 μL / min.

[0056] To form the solid core waveguide, air gaps may be etched away from the waveguide layer on each side of the solid core waveguide such that the solid core waveguide is formed from the remaining material of the waveguide layer left between the air gaps. In some embodiments, the etching step may include a dry etch, such as reactive ion etching, deep reactive ion etching, and / or neutral loop discharge etching, and in some embodiments, the etching step may include a wet etch, such as etching with buffered hydrofluoric acid. In some embodiments, in addition to etching the air gaps to define regions on each side of the solid core waveguide, the etching process may also include etching regions at the ends of the solid core waveguide, thereby forming ends of the optical waveguide (e.g., optical facets) through which light may be coupled.

[0057] After etching into the waveguide layer to form the solid core waveguide and fluidic channels, a cover layer can be applied over the waveguide layer to encapsulate the open top side of the fluidic channels and / or encapsulate one or more air gaps. In some embodiments, the cover layer may comprise a bonding glass, an ARROW layer, or a total internal reflection coated material (e.g., a low refractive index material such as TEFLON AF), or a metal coated material. In some embodiments, the cover layer may be 1 μm, 5 μm, 10 μm, 50 μm, 100 μm, 150 μm, or 200 μm, 300 μm, or 500 μm or less in thickness. In some embodiments, the cover layer may be 1 μm, 5 μm, or 10 μm, 50 μm, 100 μm, 150 μm, or 200 μm, 300 μm, or 500 μm or more in thickness. In some embodiments, the cover layer may be attached to the waveguide layer (or another layer of a waveguide structure, discussed further below) by permanent or non-permanent bonding, adhesive gluing, or other suitable means.

[0058] After etching and attachment of the cover layer is complete, the fluidic channel may be filled with a fluid (e.g., gas and / or liquid), such as a gas or liquid containing an analyte that propagates along the solid core waveguide and is excited by the excitation light incident on the fluidic channel. In some embodiments, emission from an analyte in the fluidic channel may be collected out-of-plane (e.g., above or below a photodetector) or in-plane (e.g., by guiding by the fluidic channel to an in-plane photodetector when the fluidic channel is a fluidic core waveguide, or by capturing such emission by a solid core waveguide structure without the use of a fluidic core waveguide).

[0059] In some embodiments, the performance of a fluidic channel as a fluidic core waveguide (e.g., for in-plane detection of emitted light) can be increased by reducing the wall thickness, by reducing the average refractive index of the cladding material, or by etching away portions of the substrate layer beneath the channel, as discussed further below.

[0060] Figures 1A and 1B show two schematic views of a waveguide structure 100, according to some embodiments. Figure 1A shows cross-sectional views of the waveguide structure 100 from two angles, with the two views separated by a dotted line showing the 90° corner 102. Figure 1B shows a top view of the waveguide structure 100.

[0061] 1A, the waveguide layer 104 may be formed from one or more oxide layers. In some embodiments, a low index oxide layer 106 may be provided on a substrate (e.g., silicon) layer 108, and a high index oxide layer 110 may be provided on the low index oxide layer 106. The two oxide layers may together form the waveguide layer 104. As light 112 propagates through the high index oxide layer 110, it may be internally reflected back along the solid core waveguide 114 by the air gap 116 and / or the low index oxide layer 106. In some embodiments, both the low index oxide layer 106 and the substrate layer 108 may be replaced by a low index substrate layer.

[0062] As shown in FIG. 1A, the etching steps forming the air gaps 116 and the fluid channels 118 can be performed such that the high-index oxide layer 110 and the low-index oxide layer 106 are simultaneously etched into and / or through them. That is, rather than etching the oxide layers separately and then aligning the gaps / channels etched in each layer, the etching can be performed after the layers are already bonded together, thereby achieving self-alignment. As shown in the example of FIG. 1, the channels 118 and / or the air gaps 116 can be formed in some embodiments by etching completely through the high-index oxide layer 110 from above and partially into the low-index oxide layer 106 from above. In some embodiments, the waveguide structure 100 can include a cover layer 120 that can be applied over the waveguide layer 104 to encapsulate the open top side of the fluid channels 118 and / or to encapsulate one or more air gaps 116.

[0063] In some embodiments of any of the waveguide structures disclosed herein, one or more of the waveguide layers may be disposed or deposited on top of another layer. In some embodiments, one or more of the layers may be deposited by sputtering, spin-on, plasma enhanced chemical vapor deposition (PECVD), low pressure chemical vapor deposition (LPCVD), electron beam evaporation, and / or any other deposition method.

[0064] Using this method, it can be very easy to fabricate more complex waveguide structures and expose individual dies (e.g., e-beam defined features) for this process, since there is only one lithography step. Furthermore, this workflow does not require the alignment of masks between manufacturing steps.

[0065] In some embodiments of the waveguide structure 100 and / or other waveguide structures discussed herein, the refractive index of the high index oxide (e.g., layer 110) may be less than or equal to 1, 2, 3, or 4. In some embodiments of FIG. 1 and / or other waveguide structures discussed herein, the refractive index of the high index oxide (e.g., layer 110) may be greater than or equal to 1, 2, 3, or 4.

[0066] In some embodiments of the waveguide structure 100 and / or other waveguide structures discussed herein, the refractive index of the low index oxide (e.g., layer 106) may be less than or equal to 1, 2, 3, or 4. In some embodiments of FIG. 1 and / or other waveguide structures discussed herein, the refractive index of the low index oxide (e.g., layer 106) may be greater than or equal to 1, 2, 3, or 4.

[0067] In some embodiments of the waveguide structure 100 and / or other waveguide structures discussed herein (see, e.g., Figures 15 and 16 below), the refractive index of the doped oxide may be less than or equal to 1, 2, 3, or 4. In some embodiments of Figure 1 and / or other waveguide structures discussed herein, the refractive index of the doped oxide may be greater than or equal to 1, 2, 3, or 4.

[0068] In some embodiments, the thickness of the oxide layer adjacent to the substrate layer (e.g., low index oxide layer 106) may be 0.05 μm, 0.1 μm, 0.5 μm, 1 μm, 5 μm, 10 μm, or 50 μm or less. In some embodiments, the thickness of the oxide layer adjacent to the substrate layer (e.g., low index oxide layer 106) may be 0.05 μm, 0.1 μm, 0.5 μm, 1 μm, 5 μm, 10 μm, or 50 μm or more. In some embodiments, the oxide layer adjacent to the substrate layer (e.g., low index oxide layer 106) may improve the waveguiding properties of the waveguide and / or reduce background photoluminescence from the adjacent silicon / substrate material.

[0069] In some embodiments, the thickness of the core oxide layer (e.g., high refractive index oxide layer 110) may be 0.5 μm, 1 μm, 2.5 μm, 5 μm, 7.5 μm, 10 μm, or 15 μm or less. In some embodiments, the thickness of the core oxide layer (e.g., high refractive index oxide layer 110) may be 0.5 μm, 1 μm, 2.5 μm, 5 μm, 7.5 μm, 10 μm, or 15 μm or more.

[0070] Figures 2A and 2B show two schematic views of a waveguide structure 200 having a low index layer 206 below a bonded cover layer 220, according to some embodiments. Figure 2A shows cross-sectional views of the waveguide structure 200 from two angles, with the two views separated by a dotted line showing the 90° corner 202. Figure 2B shows a top view of the waveguide structure 200.

[0071] The waveguide structure 200 shown in FIG. 2 may share any one or more characteristics in common with the waveguide structure 100 shown in FIG. 1 and may differ from the structure 100 shown in FIG. 1 in that the waveguide layer 204 of the structure of FIG. 2 may include an additional low index oxide layer 222 above the high index oxide layer 210 and below the cover layer 220. In some embodiments, the second low index oxide layer 222 may be provided (e.g., provided or deposited) on top of the other oxide layer subsequent to the other oxide layer being provided (e.g., provided or deposited). As the light 212 propagates through the high index oxide layer 210, the air gap 216, the low index oxide layer 206, and / or the additional low index oxide layer 222 may cause internal reflection along the solid core waveguide 214.

[0072] In some embodiments, the thickness of the second low refractive index oxide layer 122 may be less than or equal to 0.5 μm, 1 μm, 2.5 μm, 5 μm, 7.5 μm, 10 μm, or 15 μm. In some embodiments, the thickness of the second low refractive index oxide layer 122 may be greater than or equal to 0.5 μm, 1 μm, 2.5 μm, 5 μm, 7.5 μm, 10 μm, or 15 μm.

[0073] In some embodiments, the etching steps forming the air gap 216 and the fluid channel 218 can be performed to simultaneously etch into and / or through the high index oxide layer 210 and the two low index oxide layers 206, 222. That is, rather than etching the oxide layers separately and then aligning the gaps / channels etched in each layer, the etching can be performed after the layers are already bonded together, thereby achieving automatic alignment. As shown in the example of the waveguide structure 200, the channel 218 and / or the air gap 216 can be formed in some embodiments by etching completely through the top low index oxide layer 222 from above, etching completely through the high index oxide layer 210 from above, and etching partially into the low index oxide layer 206 from above. In some embodiments, the etch forming the fluid channel 218 can cut completely through the waveguide layer 204 and partially into the substrate layer 208 (as shown by the dashed profile 224).

[0074] The presence of the bottom 206 and top low index layers 222 (or alternatively ARROW layers) may create a well-defined waveguide, and the cover layer 220 may allow for the use of any type of material to seal the liquid channel 218 without significantly interfering with the optical properties required for waveguiding in the solid core waveguide 214 and, in some embodiments, the fluid core waveguide.

[0075] Figures 3A and 3B show two schematic views of a waveguide structure 300 including low index doped regions 326 that define one or more waveguides, according to some embodiments. Figure 3A shows cross-sectional views of the waveguide structure 300 from two angles, with the two views separated by a dotted line showing the 90° corner 302. Figure 3B shows a top view of the waveguide structure 300.

[0076] The waveguide structure 300 shown in FIG. 3 may share any one or more characteristics in common with the waveguide structure 100 shown in FIG. 1 and may differ from the structure 100 shown in FIG. 1 in that instead of or in addition to defining the solid core waveguide 314 and / or fluid core waveguide by etching the air gap 316, dopant diffusion through a photomask may be used to define regions 326 in the waveguide layer 304 that have a lower refractive index than elsewhere in the waveguide layer 304.

[0077] In some embodiments, dopant diffusion may include ion diffusion, ion exchange, and / or ion implantation. In some embodiments, ions used for dopant diffusion may include He+, N+, O+, Si+, P+, Ti+, Ge+, or any one or more of the ions listed in Righini, GC & Chiappini, A. Glass optical waveguides: a review of fabrication techniques, OE, OPEGAR 53, 071819 (2014), Penia-Rodri'guez, O. et al., Optical Waveguides Fabricated by Ion Implantation / Irradiation: A Review. Ion implantation (InTech, 2012), and / or Chen, F., Wang, X.-L. & Wang, K.-M., Development of ion-implanted optical waveguides in optical materials: A review. Optical Materials 29, 1523-1542 (2007). 3B, the solid core waveguide 314 may be defined by the region between the two doped regions 326. In some embodiments, the use of dopants to define the waveguide may produce a structure 300 that refracts and scatters less light 312 compared to structures that rely on etching to form the solid core waveguide 314, which may reduce the background signal of the chip.

[0078] In some embodiments, dopant diffusion in the waveguide layer 304 may also be used to define regions on the sides, bottom, and / or top of the waveguide, including the solid core waveguide 314 and / or the fluid core waveguide. In some embodiments, the waveguide layer 304 includes a low index oxide layer 306 and a high index oxide layer 310. The low index oxide layer 306 may be provided on a substrate (e.g., silicon) layer 308, and the high index oxide layer 310 may be provided on the low index oxide layer 306. In some embodiments, additional doped regions 328 may be included to define specific modes of the waveguide or to produce other optical phenomena. The additional doped regions 328 may be provided in the low index oxide layer 306 (located on the substrate layer 308) and / or in the high index oxide layer 310 (provided below the cover layer 320).

[0079] In some embodiments, the dopant diffusion may be performed before one or more etching steps, and in some embodiments, it may be performed after one or more etching steps.

[0080] Figures 4A and 4B show two schematic views of a waveguide structure 400 including high index doped regions defining a waveguide, according to some embodiments. Figure 4A shows cross-sectional views of the waveguide structure 400 from two angles, with the two views separated by a dotted line showing the 90° corner 402. Figure 4B shows a top view of the waveguide structure 400.

[0081] The waveguide structure 400 of FIG. 4 may share any one or more characteristics in common with the waveguide structure 300 shown in FIG. 3. Similar to the waveguide structure 300 shown in FIG. 3, the waveguide structure 400 shown in FIG. 4 may include one or more waveguides created and defined by dopant diffusion, such as dopant diffusion through a photomask. While the structure 300 shown in FIG. 3 may be created using dopant diffusion that defines a doped region 326 having a lower refractive index than the surrounding regions, the structure 400 shown in FIG. 4 may instead be created using dopant diffusion that defines a doped region having a higher refractive index than the surrounding regions. In some embodiments, germanium or other suitable ions, such as one or more of those listed above, may be used to create high refractive index regions by doping. It should be noted that in some embodiments, the refractive index variation created by doping the waveguide layer 404 may include an instantaneous spatial change (e.g., a step change) in refractive index and / or may include a gradual spatial increase or decrease in refractive index.

[0082] Thus, as shown in the top view of FIG. 4B, the solid core waveguide 414 may be defined by the doped region itself, which may have a higher refractive index than the undoped oxide in the waveguide layer 404. In some embodiments, the use of dopants to define the waveguide may create a structure 400 that refracts and scatters less light 412 compared to structures that form the solid core waveguide 414 by etching, thereby reducing the background signal of the chip. In some embodiments, the waveguide layer 404 may include an oxide layer 406 disposed over a substrate layer 408. The waveguide layer 404 may also include an air gap 416, and a fluidic channel 418. In some embodiments, a cover layer 420 may be provided over the waveguide layer 404.

[0083] In some embodiments, the dopant diffusion may be performed before one or more etching steps, and in some embodiments, it may be performed after one or more etching steps.

[0084] Figures 5A and 5B show two schematic views of a waveguide structure 500 including an ARROW layer 530, according to some embodiments. Figure 5A shows cross-sectional views of the waveguide structure 500 from two angles, with the two views separated by a dotted line showing the 90° corner 502. Figure 5B shows a top view of the waveguide structure 500.

[0085] The waveguide structure 500 shown in Figure 5 may share any one or more characteristics in common with the waveguide structure 100 shown in Figure 1 and may differ from the structure 100 shown in Figure 1 in that the structure 500 further includes an ARROW layer 530 above the substrate 508 and below the waveguide layer 504. The ARROW layer 530 may, in some embodiments, be provided (e.g., provided or deposited) on the substrate layer 508, and the waveguide layer 504 may then be provided (e.g., provided or deposited) on the ARROW layer 530. In some embodiments in which the ARROW layer 530 is used below the waveguide layer 504, the waveguide layer 504 may have a constant refractive index from top to bottom, rather than being composed of multiple different oxide layers with different refractive indices.

[0086] 5A, the channels 518 and / or air gaps 516 may in some embodiments be formed by etching partially into the waveguide layer 504 without etching all the way through to avoid etching into the ARROW layer 530 and compromising its optical properties. In some embodiments, the solid core waveguide 514 may be defined by etching. In some embodiments, a cover layer 520 may be provided over the waveguide layer 504.

[0087] In some embodiments, the total thickness (e.g., total stack thickness) of the ARROW layers 530 may be less than or equal to 0.1 μm, 0.2 μm, 0.5 μm, 1 μm, 5 μm, 10 μm, or 15 μm. In some embodiments, the total thickness (e.g., total stack thickness) of the ARROW layers 530 may be greater than or equal to 0.1 μm, 0.2 μm, 0.5 μm, 1 μm, 5 μm, 10 μm, or 15 μm. The total thickness of the ARROW layers 530 may vary depending on the number of alternating layers and / or the desired waveguiding properties for, for example, the guided light 512.

[0088] Figures 6A and 6B show two schematic views of a waveguide structure 600 including an ARROW layer 630 and an etch stop layer 632, according to some embodiments. Figure 6A shows cross-sectional views of the waveguide structure 600 from two angles, with the two views separated by a dotted line showing the 90° corner 602. Figure 6B shows a top view of the waveguide structure 600.

[0089] The waveguide structure 600 shown in FIG. 6 may differ from the structure 500 shown in FIG. 5 in that the structure 600 further includes an etch stop layer 632 above the ARROW layer 630 and below the waveguide layer 604. In some embodiments, the etch stop layer 632 may be a localized etch stop layer located below the areas that are etched away to form the fluidic channels 618. By this means, the etching step forming the air gaps 616 can etch through the waveguide layer 604, into and / or through the ARROW layer 630, and all the way to the substrate layer 608, but the etching step forming the fluidic channels 618 is prevented by the etch stop layer 632 from etching into or through the ARROW layer 630. Thus, the ARROW layer 630 can be protected and preserved in locations below the fluidic channels 618, while the ARROW layer 630 in other locations of the structure 600 may be etched through.

[0090] In some embodiments, following the step of etching the fluid channels 618, the localized etch stop layer 632 may be dissolved, such as by wet etching, or otherwise removed such that the hollow cores of the fluid channels 618 are directly adjacent the ARROW layer 630. In some embodiments, such as when the etch stop layer 632 is compatible with the desired optical properties of the ARROW layer 630, the etch stop layer 632 may be left in place.

[0091] In some embodiments, the etch stop layer 632 may include a metal, a dielectric material, a polycrystalline material, and / or other suitable material. In some embodiments, the material for the etch stop layer 632 may be selected such that the material has a sufficiently different etch rate when compared to the etch rate of one or more materials of the waveguide layer 604.

[0092] In some embodiments, the thickness of the etch stop layer 632 may be less than or equal to 0.05 μm, 0.1 μm, 0.5 μm, 1 μm, 2.5 μm, 5 μm, or 10 μm. In some embodiments, the thickness of the etch stop layer 632 may be greater than or equal to 0.05 μm, 0.1 μm, 0.5 μm, 1 μm, 2.5 μm, 5 μm, or 10 μm.

[0093] Figures 7A and 7B show two schematic views of a waveguide structure 700 including an ARROW layer 730 and formed using wet etching finishing techniques, according to some embodiments. Figure 7A shows cross-sectional views of the waveguide structure 700 from two angles, with the two views separated by a dotted line showing the 90° corner 702. Figure 7B shows a top view of the waveguide structure 700.

[0094] The waveguide structure 700 shown in FIG. 7 may share any one or more characteristics in common with the waveguide structure 500 shown in FIG. 5 and may differ from the structure 500 shown in FIG. 5 in that following a first etching step (e.g., a rough deep etching step), a second etching step may be performed for each of the air gaps 716 and the fluidic channels 718 to etch all the way through the waveguide layer 704 and to (but not into) the ARROW layer 730. In some embodiments, the first etching step may be a deep etch and the second etching step may be a wet etch. In some embodiments, the second etching step may be used to etch further down and / or further to the sides 734 of the etched gaps 716 or channels 718. In some embodiments, the outermost (e.g., top or bottom) layer of the ARROW layer 730 may be an etch stop ARROW layer configured to prevent the wet etching step from damaging the ARROW layer 730 by etching into the ARROW layer 730. By selecting the outermost ARROW layer as an effective etch stop for an etching process such as a wet etch, and applying a subsequent wet etch after the deep etch, it is possible to achieve an intact ARROW layer 730 directly beneath the fluidic channel 718.

[0095] In some embodiments, to achieve relatively vertical sidewalls of the channels 718 and / or air gaps 716, etching can be performed to a substantial depth such that the tops of the profiles of the channels 718 and / or air gaps 716 are relatively vertical.

[0096] 8 shows a schematic diagram of a waveguide structure 800 including an ARROW layer 830 and variable depth etching, according to some embodiments. FIG. 8 shows cross-sectional views of the waveguide structure 800 from two angles, with the two views separated by a dotted line showing the 90° corner 802.

[0097] The waveguide structure 800 shown in Figure 8 may share any one or more characteristics in common with the waveguide structure 600 shown in Figure 6, and may differ from the structure 600 shown in Figure 6 in that the structure 800 of Figure 8 does not have a localized etch stop layer (or any etch stop layer, e.g., layer 632). Thus, during etching, the etch that forms the liquid channels 818 may stop short of cutting all the way through the waveguide layer 804 into the ARROW layer 830, even if the etch is not stopped by an etch stop layer (e.g., layer 632).

[0098] 9A and 9B show two schematic diagrams of a waveguide structure 900 including an ARROW layer 930 and an etch stop layer 932 underlying a number of trenches, according to some embodiments. Fig. 9A shows a cross-sectional view. Fig. 9B shows a top view of the waveguide structure 900.

[0099] The waveguide structure 900 shown in Figure 9 may share any one or more characteristics in common with the waveguide structure 600 shown in Figure 6 and may differ from the structure 600 shown in Figure 6 in that the structure 900 includes an etch stop layer 932 that is not confined to only locations corresponding to the fluidic channels 918. Instead, the etch stop layer 932 may extend to areas under one or more other etches, such as one or more air gaps 916 etched from the waveguide layer 904. Thus, the non-confined etch stop layer 932 may prevent the etch forming the fluidic channels 918 and the etch forming the one or more air gaps 916 from extending into the ARROW layer 930.

[0100] In some embodiments, the etch stop layer 932 may be completely or partially dissolved or otherwise removed after one or more etching steps. In some embodiments, the etch stop layer 932 may remain present under the solid core waveguide 914 (e.g., even if the etch stop layer 932 is removed from the areas where etching occurs in the fluidic channels 918 and air gaps 916) and therefore may be transparent so as not to block the propagation of the light 912 in the solid core waveguide 914 into the ARROW layer 930. In some embodiments, the transparent etch stop layer 932 may include one or more oxides (in some embodiments, the opaque etch stop layer 932 may include one or more metals, which in some embodiments may be removed from the waveguide structure 900 using a secondary process step, such as an additional etching step).

[0101] In some embodiments, the transparent etch stop layer 932 may have a thickness of 0.5 μm, 1 μm, 2.5 μm, 5 μm, 7.5 μm, 10 μm, or 15 μm or less. In some embodiments, the transparent etch stop layer 932 may have a thickness of 0.5 μm, 1 μm, 2.5 μm, 5 μm, 7.5 μm, 10 μm, or 15 μm or more.

[0102] 10A and 10B show two schematic views of a waveguide structure 1000 including an air gap 1036 formed in a substrate layer 1008, according to some embodiments. Fig. 10A shows cross-sectional views of the waveguide structure 1000 from two angles, with the two views separated by a dotted line showing the 90° corner 1002. Fig. 10B shows a top view of the waveguide structure 1000.

[0103] The waveguide structure 1000 shown in FIG. 10 may share any one or more characteristics in common with the waveguide structure 100 shown in FIG. 1 and may differ from the structure 100 shown in FIG. 1 in that in addition to the top-down etching performed to create the fluid channels 1018 and solid core waveguide 1014 in the waveguide layer 1004, a bottom-up etch may also be performed to remove a portion of the substrate layer 1008 and expose the underside of the waveguide layer 1004 to one or more air gaps 1036 below the fluid channels 1018 and / or solid core waveguide 1014. By forming one or more air gaps 1036 below the fluidic channels 1018 and / or solid core waveguides 1014, the light 1012 within the solid core waveguides 1014 and / or fluidic channels 1018 (which may function as fluidic core waveguides) can be prevented from leaking downward out of the waveguides 1014 / channels 1018, such that the air gaps 1036 cut out of the substrate layer 1008 themselves can eliminate the need for an ARROW layer (e.g., layer 930) or a low refractive index oxide layer.

[0104] In some embodiments, etching into the substrate layer 1008 may additionally or alternatively be used to form one or more fluid channels and / or other structures for fluid routing through the substrate layer 1008, such as by etching into the side of the substrate layer 1008 opposite the waveguide layer 1004 as shown in FIG. 10 .

[0105] In some embodiments, etching into the substrate layer 1008 may additionally or alternatively be used to form structures on the waveguide structure 1000 for use in physically positioning the waveguide structure 1000, such as by etching into the side of the substrate layer 1008 opposite the waveguide layer 1004 as shown in FIG. 10. In some embodiments, micromachining of the substrate 1008 may be used to form one or more kinematic structures. In some embodiments, one or more structures formed by etching into the substrate layer 1008 may be used to physically position and / or attach to and / or physically interact with an alignment system. In some embodiments, one or more structures formed by etching into the substrate layer 1008 may be filled with, contain, and / or otherwise attach to a magnetic material and / or one or more magnetic components for use in a kinematic application.

[0106] 11A and 11B show two schematic views of a waveguide structure 1100 including an air gap 1136 formed in a substrate layer 1108 and including a focusing lens 1138, according to some embodiments. Figure 11A shows cross-sectional views of the waveguide structure 1100 from two angles, with the two views separated by a dotted line showing the 90° corner 1102. Figure 11B shows a top view of the waveguide structure 1100.

[0107] The waveguide structure 1100 shown in FIG. 11 may share any one or more characteristics in common with the waveguide structure 1000 shown in FIG. 10 and may differ from the structure 1000 shown in FIG. 10 in that the structure 1100 may further include one or more lenses, for example, for use in out-of-plane excitation light collection. As shown, one or more lenses, such as lens 1138, may be included or attached to the cover layer 1120, such as by adhesive gluing, permanent or non-permanent bonding, or by fabrication within the cover layer 1120 itself, for top-side collection of excitation light 1112 from the fluidic channel 1118. Alternatively or additionally, one or more lenses, such as lens 1140, may be attached below the fluidic channel 1118 following etching of a lower air gap 1136 from the substrate 1108, for bottom-side collection of excitation light 1112 from the fluidic channel 1118. In some embodiments, the one or more lenses 1138, 1140 may be formed from a polymeric material, a dielectric material, glass, or any other suitable material.

[0108] 12A and 12B show two schematic views of a waveguide structure 1200 including an undercut air gap 1242 formed in a substrate layer 1208, according to some embodiments. Figure 12A shows cross-sectional views of the waveguide structure 1200 from two angles, with the two views separated by a dotted line showing the 90° corner 1202. Figure 12B shows a top view of the waveguide structure 1200.

[0109] The waveguide structure 1200 shown in Figure 12 may share any one or more characteristics in common with the waveguide structure 1000 shown in Figure 10, and may differ from the structure 1000 shown in Figure 10 in that the air gaps 1242 below the fluidic channels 1218 and / or solid core waveguides 1214 may be formed not by etching the substrate layer 1208 from below, but by performing an under-etch (e.g., a potassium hydroxide (KOH) etch) to cut from the air gaps 1216 initially etched in the waveguide layer 1204 into and below the solid core waveguide 1214 and / or below the fluidic channels 1218. In some embodiments, the under-etch can be performed in bridged sections, for example, to prevent collapse of the suspended structure.

[0110] 13A and 13B show two schematic views of a waveguide structure 1300 including a fiber alignment feature 1344, according to some embodiments. Figure 13A shows cross-sectional views of the waveguide structure 1300 from two angles, with the two views separated by a dotted line showing the 90° corner 1302. Figure 13B shows a top view of the waveguide structure 1300.

[0111] The waveguide structure 1300 shown in Figures 13A and 13B may share any one or more characteristics in common with the waveguide structure 100 shown in Figure 1 and may differ from the structure 100 shown in Figure 1 in that the structure 1300 may incorporate one or more conventional optical fibers, for example, for use in guiding the excitation light 1312. For example, instead of creating a solid core waveguide by etching an air gap in the waveguide layer 1304, an optical fiber 1346 may be used to guide the light 1312 to the fluidic channel 1318 (which may be formed in the same manner as discussed elsewhere herein). In some embodiments, the optical fiber 1346 may be used to guide the excitation light 1312 to a solid core waveguide formed as discussed elsewhere herein.

[0112] 14A-D show four schematic views of a waveguide structure 1400 during various stages of a CMP (Chemical Mechanical Polishing) based trench fabrication method, according to some embodiments. The waveguide structure 1400 shown in FIG. 14 can share any one or more characteristics in common with the waveguide structure 100 shown in FIG. 1. Unlike some other embodiments discussed herein, the technique shown in FIG. 14 can rely heavily on machining one or more features into a silicon substrate 1408 (or other non-oxide substrate) in addition to or instead of etching into one or more oxides. In some embodiments, a waveguide structure fabrication technique that relies on machining into silicon or other substrate material can be simpler, faster, more efficient and less expensive than a technique that relies primarily or exclusively on etching into oxide, since machining silicon can be a simpler and more standardized process than etching into oxide.

[0113] As shown in FIG. 14A, a silicon substrate 1408 can be machined (e.g., micromachined) to form two intersecting trenches (one 1448 shown to the right of the 90° corner and the other 1450 shown to the left of the 90° corner 1402). One or more oxides can then be deposited onto the machined silicon substrate 1408 such that the machined trenches 1448, 1450 can be filled with an oxide 1406. After the oxide 1406 is provided (e.g., deposited or placed), a fluid channel 1418 can be etched into the oxide 1406 shown to the right of the 90° corner 1402 (alternatively, in some embodiments, the oxide portion that forms the fluid channel 1418 can be formed by oxidation of the etched silicon trench 1448, e.g., as discussed below with reference to FIGS. 17 and 18).

[0114] 14B, the oxide 1406 provided (e.g., deposited or placed) on the substrate 1408 that is not inside one of the trenches 1448 or 1450 machined in the substrate 1406 may then be removed. In some embodiments, the oxide 1406 may be removed by CMP, while in some embodiments, the oxide 1406 may be lifted off.

[0115] 14C, the silicon substrate 1408 surrounding the trench 1448 in which the fluid channel 1418 was etched may then be removed, for example, by a KOH etch. In some embodiments, the substrate 1408 may be etched away (e.g., by an underetch) in area 1442, which may include one or both sides and a portion of the area under the oxide 1406 that forms the fluid channel 1418.

[0116] 14D, the silicon substrate 1408 surrounding the oxide-filled trench 1450 to the left of the 90° corner 1402 may then be removed, for example, by a KOH etch. In some embodiments, the substrate 1408 may be etched away (e.g., by an underetch) in area 1452, which may include one or both sides and a portion of the area under the oxide 1406 that forms the oxide-filled trench 1450.

[0117] 14D, a cover layer 1420 can be added to encapsulate the fluidic channel 1418. The cover layer 1420 can share any one or more properties with the other cover layers discussed elsewhere herein (e.g., cover layer 120).

[0118] Thus, the oxide 1454 shown to the left of the 90° corner 1402 can function as a solid core waveguide for the light 1412, and the etched away oxide 1456 shown to the right of the 90° corner can function as a fluid channel 1418 and / or a fluid core waveguide (e.g., oxide 1454) that intersects with the solid core waveguide.

[0119] Figures 15A and 15B show two schematic views of a waveguide structure 1500 including a doped oxide substrate 1508, according to some embodiments. Figure 15A shows cross-sectional views of the waveguide structure 1500 from two angles, with the two views separated by a dotted line showing the 90° corner 1502. Figure 15B shows a top view of the waveguide structure 1500.

[0120] The waveguide structure 1500 shown in FIG. 15 may share any one or more characteristics in common with the waveguide structure 100 shown in FIG. 1, and may differ from the waveguide structure 100 shown in FIG. 1, and other waveguide structures shown herein (e.g., structures 200-1400), in that rather than including a substrate (e.g., silicon) layer (e.g., layer 108) distinct from the waveguide (e.g., oxide) layer (e.g., layer 104), the structure may be formed from a monolithic oxide substrate 1508 (e.g., a fused silica wafer, borofloat, BK7, fused silica, or single crystal quartz). In some embodiments, the oxide substrate 1508 may be doped with ions near a surface (e.g., top surface 1558) of the substrate 1508 to form a refractive index gradient in the oxide such that the refractive index of the oxide substrate 1508 is higher near the doped (e.g., top surface 1558) surface than at locations further from the doped surface (e.g., top surface 1558) (see, e.g., the description of ion doping above). In some embodiments, the entire surface (e.g., top surface 1558) of the oxide substrate 1508 may be blanket doped rather than doping only certain areas using a mask. An etching step, as discussed elsewhere herein, may then be performed by etching into the doped surface (e.g., top surface 1558) of the oxide substrate 1508 to form the fluidic channels 1518 and the air gaps 1516. The refractive index gradient can prevent excitation light 1512 in a fluid core waveguide (e.g., fluid channel 1518) defined between etched air gaps from leaking downward into a lower refractive index portion of the oxide substrate 1508. Although a refractive index gradient is described above, in some embodiments the refractive index can vary with one or more spatial step functions, according to one or more spatial curves and / or according to one or more spatial gradients.

[0121] In some embodiments of FIG. 15 and / or other waveguide structures discussed herein, the refractive index of the doped oxide (e.g., layer 1508) may be less than or equal to 1, 2, 3, or 4. In some embodiments of FIG. 15 and / or other waveguide structures discussed herein, the refractive index of the doped oxide (e.g., layer 1508) may be greater than or equal to 1, 2, 3, or 4.

[0122] In some embodiments, the deposition steps can be minimized and background can be reduced from using pure waveguide material by using blanket doping techniques over the oxide substrate 1508. Additionally, in some embodiments, the use of dopants to define the waveguide (e.g., solid core waveguide 1514) can result in less refraction and scattering of light 1512, which can be advantageous in reducing the background signal of the chip.

[0123] In some embodiments, the light 1512 in the fluidic channel 1518 may escape the channel and descend into the oxide substrate 1508, so that the fluidic channel 1518 functions only as a channel and not as a fluidic core waveguide. However, in some embodiments, a deep etch may be performed (or an undercut etch may be performed) on the underside of the substrate 1508 to form an air gap below the fluidic channel 1518 and allow the fluidic channel 1518 to function as a fluidic core waveguide.

[0124] 16A and 16B show two schematic views of a waveguide structure 1600 including a doped oxide substrate 1608 and a cap layer 1660 below a bonded cover layer 1620 according to some embodiments. Fig. 16A shows cross-sectional views of the waveguide structure 1600 from two angles, with the two views separated by a dotted line showing the 90° corner 1602. Fig. 16B shows a top view of the waveguide structure 1600.

[0125] The waveguide structure 1600 shown in FIG. 16 may share any one or more characteristics in common with the waveguide structure 1500 shown in FIG. 15 and may differ from the structure 1500 shown in FIG. 15 in that the structure 1600 may further include a cap layer 1660 on the monolithic oxide substrate 1608 and below the cover layer 1620 that may optically protect the waveguides (e.g., solid core waveguide 1614, fluid core waveguide 1618) formed in the monolithic oxide substrate 1608. The protective layer 1660 may be provided (e.g., deposited or placed) on the oxide substrate 1608 after doping of the oxide substrate 1608 has been performed. In some embodiments, the protective layer 1660 may include one or more oxides. The protective layer 1660 and the oxide substrate 1608 may then be simultaneously etched into and / or through.

[0126] In some embodiments of FIG. 16 and / or other waveguide structures discussed herein, the refractive index of the doped oxide (e.g., layer 1608) may be less than or equal to 1, 2, 3, or 4. In some embodiments of FIG. 16 and / or other waveguide structures discussed herein, the refractive index of the doped oxide (e.g., layer 1608) may be greater than or equal to 1, 2, 3, or 4.

[0127] Figures 17A and 17B show two schematic views of a waveguide structure 1700 obtained by oxidizing and doping a machined substrate layer 1708 to form a waveguide layer XXX, according to some embodiments. Figure 17A shows cross-sectional views of the waveguide structure 1700 from two angles, with the two views separated by a dotted line showing the 90° corner 1702. Figure 17B shows a top view of the waveguide structure.

[0128] The waveguide structure 1700 shown in Figure 17 can share any one or more characteristics in common with the waveguide structure 100 shown in Figure 1. Unlike some other embodiments discussed herein, the technique shown in Figure 17 may rely heavily on machining one or more features into a silicon substrate 1708 (or other non-oxide substrate) in addition to or instead of etching into one or more oxides. In some embodiments, a waveguide structure fabrication technique that relies on machining into silicon or other substrate material 1708 may be simpler, faster, more efficient, and less expensive than a technique that relies primarily or exclusively on etching into an oxide, because machining silicon may be a simpler and more standardized process than etching into an oxide.

[0129] In some embodiments, trenches corresponding to the fluidic channels 1718 can be machined (e.g., micromachined) out of the substrate 1708, and trenches corresponding to the air gaps 1716 surrounding the fluidic channels 1718 and the intersecting solid core waveguides 1714 can be machined (e.g., micromachined) out of the substrate 1708. Thus, the geometry of the fluidic channels 118 and air gaps 116 etched in the oxides 106, 110 shown in Figure 1 can be replicated, except that the geometry may be formed in a substrate 1708, such as a silicon wafer, rather than in a waveguide layer 104, such as an oxide.

[0130] Following the formation of this geometry in the substrate 1708 by machining, a portion 1762 of the machined substrate 1708 (e.g., a portion near the top surface and / or a portion near a surface exposed to the machined trench, channel, or gap) may then be converted (e.g., transformed) into a waveguide material to form an oxide 1706 (e.g., silicon dioxide) for the waveguide layer 1704 from the portion 1762 of the substrate layer 1708. In some embodiments, the portion 1762 of the machined substrate 1708 may be converted by oxidation (e.g., thermal oxidation) to convert silicon to silicon dioxide, thereby forming the silicon dioxide 1706 for the waveguide layer 1704 in the portion 1762 of what was previously the machined silicon substrate 1708. The silicon dioxide 1706 formed from the substrate may mimic the geometry of the machined substrate 1708. Thus, the silicon dioxide material 1706 for forming the waveguide layer 1704 may be formed from a machined substrate layer 1708 and may include fluid channels 1718 and air gaps 1716 formed from respective machined trenches in the substrate layer 1708.

[0131] Following the formation of the silicon dioxide material 1706 on the waveguide layer 1704 (e.g., by oxidizing portion 1762 of a silicon substrate 1708 to form a silicon dioxide waveguide layer 1704), the waveguide layer 1704 may be ion doped (e.g., see the discussion of ion doping above) near a surface (e.g., top surface 1758) of the waveguide layer 1704 to create one or more regions of high refractive index oxide 1710 near the doped surface (e.g., top surface 1758) and thereby complete the formation of the waveguide layer 1704. In this manner, the refractive index may be higher near the doped surface (e.g., top surface 1758) than at locations further from the doped surface (e.g., top surface 1758). In some embodiments, the entire surface of the waveguide layer 1704 may be blanket doped, and thus the doped features 1710 defined in the waveguide layer 1704 by formation from the machined substrate 1708 may define a solid core waveguide 1714 and / or a waveguide fluid channel 1718. In some embodiments, the solid core waveguide 1714 is formed as shown by the doped protruding portion of the oxide 1706 to the left of the 90° corner 1702. In some embodiments, the waveguide fluid channel 1718 is formed as shown by the space between the two doped protruding channel wall oxide portions 1766 to the right of the 90° corner 1702. The high refractive index may prevent the excitation light 1712 in the fluid core waveguide 1718 defined between the doped wall portions 1766 between the air gaps 1716 from leaking outward and / or downward.

[0132] In some embodiments, doping of oxide layer 1706 can be used to form a refractive index gradient in all or a portion of oxide layer 1706, while in some embodiments the refractive index can vary with one or more spatial step functions, according to one or more spatial curves and / or according to one or more spatial gradients.

[0133] In some embodiments, a protective layer (not shown in FIG. 17A, but which in some embodiments may include one or more oxides) may be provided (e.g., deposited or placed) on the oxide layer 1706 after doping of layer 1706 has been performed.

[0134] Finally, a cover layer 1720 can be added to encapsulate the fluidic channel 1718. The cover layer 1720 can share any one or more properties with other cover layers described elsewhere herein (e.g., cover layer 120).

[0135] 18A and 18B show two schematic views of a waveguide structure 1800 obtained by oxidizing and doping a machined substrate layer 1801 to form a waveguide layer 1804, according to some embodiments. Fig. 18A shows cross-sectional views of the waveguide structure 1800 from two angles, with the two views separated by a dotted line showing the 90° corner 1802. Fig. 18B shows a top view of the waveguide structure 1800.

[0136] The waveguide structure 1800 shown in FIG. 18 may share any one or more characteristics in common with the waveguide structure 1700 shown in FIG. 17 and may differ from the waveguide structure 1700 described above with respect to FIG. 17 in that, following doping the silicon dioxide portion of the waveguide layer 1804 with oxide 1806 to create one or more regions of oxide 1810 having a higher refractive index, a second oxide layer 1868 may be provided (e.g., deposited or placed) on the doped high refractive index oxide layer 1810 before adding the cover layer 1820. The second oxide layer 1868 may be deposited, for example, by conformal coating. In some embodiments, the second oxide layer 1868 may have a lower refractive index than the doped portion 1810 of the first layer of oxide 1806. In some embodiments, the waveguiding properties of the first oxide layer 1806 may be preserved by adding the second layer of oxide 1868.

[0137] Following deposition of the second oxide layer 1868, a cover layer 1820 can then be added to encapsulate the fluidic channel 1818. The cover layer 1820 can be bonded or attached directly to the top oxide layer (e.g., layer 1868) and may share any one or more properties with the other cover layers discussed elsewhere herein (e.g., cover layer 1720).

[0138] Figure 19 shows two schematic views of a waveguide structure 1900 including an air gap 1916 formed in a substrate layer 1908, including focusing lenses 1938 and 1940, and including an aperture layer 1970, according to some embodiments. Figure 19A shows cross-sectional views of the waveguide structure 1900 from two angles, with the two views separated by a dotted line showing the 90° corner 1902. Figure 19B shows a top view of the waveguide structure.

[0139] The waveguide structure 1900 shown in Figure 19 may share any one or more characteristics in common with the waveguide structure 1100 shown in Figure 11, and may differ from the waveguide structure 1100 described above with respect to Figure 11 in that the structure 1900 may further include an aperture layer 1970 configured to allow light from a signal to pass through apertures 1972 for collection while blocking other light. In some embodiments, one or more apertures formed in the aperture layer 1970 are positioned near the fluidic channels 1918 and near the lenses 1940 embedded in the substrate layer 1908 to allow signal light to pass from the fluidic channels 1918 through the aperture layer 1970 to the lenses 1940 in the substrate 1908 for collection, while blocking background light that does not pass through the apertures 1972 and is blocked by opaque portions of the aperture layer 1970.

[0140] In some embodiments, the aperture layer 1970 may include one or more adjacent apertures, apertures of different shapes, multiple apertures forming one or more patterns, and / or spectrally dependent apertures (e.g., the aperture layer 1970 may include a stack of ARROW layers in some embodiments). In some embodiments, one or more apertures in the aperture layer 1970 may be used to spatially filter the excitation light, for example, such that a beam of excitation light incident on the waveguide structure 1900 may pass only through one or more apertures in the aperture layer 1970.

[0141] As shown in Figure 19, the aperture layer 1970 may be provided above a substrate layer 1908 (e.g., a silicon layer) and a lens 1940 embedded in the substrate layer 1908, and may be provided below and adjacent to the fluidic channel 1918. In some embodiments, the aperture layer 1970 may be embedded in a portion of the waveguide layer 1904, such as by being sandwiched between two different low index oxide layers, as shown in the example of Figure 19. In some embodiments, the three-layer stack, including the two low index oxide layers surrounding the aperture layer 1970, may itself be sandwiched between a substrate layer and a high index oxide layer, as shown in Figure 19.

[0142] A further difference between Figure 19 and Figure 11 is that the waveguide layer 1904 of Figure 19 includes both a low index oxide layer (e.g., layer 1906) and a high index oxide layer (e.g., layer 1910). In some embodiments, the aperture layer 1970 can be optically isolated from the waveguides in the waveguide layer 1904 by placing the aperture layer 1970 between two low index oxide layers (and / or suspending the aperture layer in the middle of a single low index oxide layer 1906), thereby preventing the aperture layer 1970 from absorbing light from the waveguides. Furthermore, by placing the aperture layer 1970 between two low index oxide layers (and / or suspending it centrally from a single low index oxide layer 1906), the aperture layer 1970 can be physically separated from the substrate layer 1908 and / or from the top of the waveguide layer (e.g., layer 1910), which allows etching and other post-processing steps to be performed on the substrate layer 1908 and / or on top of the waveguide layer (e.g., layer 1910) without destroying or damaging the aperture layer 1970.

[0143] In some embodiments, the aperture layer 1970 may include chrome, nickel, another metal, one or more ARROW layers (e.g., patterned ARROW layers), and / or another opaque material configured to block background light. In some embodiments, the aperture layer 1970 may be microfabricated such that one or more features of the aperture itself may be formed using microfabrication (e.g., including sputtering, e-beam evaporation, spin coating, and / or one or more coating techniques). In some embodiments, the substrate layer 1908 (e.g., a silicon substrate layer) may be coated with a thick layer (e.g., about 2 μm or more) of optically transparent material that forms a bottom low index oxide layer 1906 (which in some embodiments may have the same or similar dimensions as other bottom low index oxide layers discussed herein). Microfabrication may then be used to form one or more features (e.g., one or more holes) in a thin layer (e.g., about 0.1 μm or less) of patterned absorbing material to form the aperture layer 1970 (which in some embodiments may have the same or similar dimensions as other aperture layers discussed herein). A thick layer (e.g., about 1 μm, 5 μm, or 10 μm or more) of an optically transparent low index material can then be deposited on top of the aperture layer to form another low index oxide layer separating the aperture layers (where the low index oxide layer separating the aperture layers can, in some embodiments, have the same or similar dimensions as other bottom or substrate adjacent low index oxide layers discussed herein). A higher index material may then be deposited on top of the low index oxide layer to form high index regions of the waveguide layer (where the high index regions can have the same or similar thicknesses as other high index oxide layers discussed herein). A single lithography process can then be used to simultaneously define the fluid core and solid core waveguides 1918 and 1914 in the waveguide layer 1904, which can be aligned to the features of the absorbing layer (e.g., aligned such that fluid channels are formed over the apertures of the aperture layer 1970).

[0144] In some embodiments, the substrate 1908 of the waveguide structure 1900 of Figure 19 may include a low index material, such as a low index oxide. In some embodiments, an aperture layer 1970 sharing one or more properties in common with that described with respect to Figure 19 may be incorporated into one or more of any of the other non-axial detection waveguide structures described herein.

[0145] While the disclosure herein has discussed the use of particular oxide materials in the waveguide layers of the waveguide structures, the waveguide layers of the structures disclosed herein, in some embodiments, can be formed (in whole or in part) from one or more alternative or additional materials, including, but not limited to, materials deposited using vapor deposition (e.g., oxides such as titanium dioxide deposited by plasma enhanced chemical vapor deposition (PECVD) or low pressure chemical vapor deposition (LPCVD)), materials formed by thermal oxidation (e.g., silicon dioxide formed from thermal oxidation of silicon), spin-on glass, any one or more other materials that may be selected or configured for background reduction, and / or one or more plastics (e.g., polydimethylsiloxane (PDMS), cyclic olefin copolymer (COC), cyclic olefin polymer (COP)).

[0146] In some embodiments, following fabrication of the waveguide structure by any one or more of the fabrication techniques disclosed herein, one or more additional processes may be performed to further modify the fabricated chip, including, but not limited to, deposition, chemical modification, alteration of surface chemistry, and / or alteration of topology. In some embodiments, these one or more additional processes may be used to modify and / or enhance one or more properties of the fabricated structure, such as the hydrophobicity, smoothness, and / or reactivity of the fabricated structure.

[0147] The foregoing description has been made with reference to specific embodiments for purposes of explanation. However, the exemplary discussion above is not intended to be exhaustive or to limit the invention to the precise form disclosed. Many modifications and variations are possible in light of the above teachings. The embodiments have been chosen and described in order to best explain the basic scheme of the technology and its practical application. This will enable those skilled in the art to best utilize the technology and various embodiments, with various modifications suited to the particular use contemplated.

[0148] Although the disclosure and examples have been fully described with reference to the accompanying drawings, it should be noted that various changes and modifications will become apparent to those skilled in the art. Such changes and modifications should be understood as being included within the scope of the disclosure and examples as defined by the claims. Finally, the entire disclosures of all patents and publications mentioned in this application are incorporated herein by reference.

Claims

1. 1. A method of manufacturing a waveguide structure comprising forming at least one solid core waveguide from a waveguiding layer, the method comprising the steps of: Etching a fluid channel into the waveguiding layer; doping the waveguide layer to form one or more doped regions in the waveguide layer having a doped refractive index different from the refractive index of the surrounding area, the formation of the one or more doped regions forming a solid core waveguide in the waveguide layer; attaching a cover layer to the waveguiding layer to enclose the fluid channel; The method according to claim 1,

2. The method of claim 1 , wherein the doping refractive index is lower than the surrounding refractive index.

3. 2. The method of claim 1 , wherein forming the one or more doped regions comprises forming a first doped region and a second doped region, thereby creating the solid core waveguide between the first doped region and the second doped region.

4. The method of claim 1 , wherein the doping refractive index is higher than the surrounding refractive index.

5. The method of claim 1 , wherein forming the one or more doped regions comprises forming a first doped region that forms the solid core waveguide.

6. The method further comprises doping the waveguiding layer to form one or more additional doped regions configured to define one or more particular modes within the waveguiding layer. The method of claim 1.

7. 7. The method of claim 6, wherein the one or more additional doped regions are formed in a first oxide layer of the waveguiding layer, the first oxide layer adjacent to a second oxide layer, the first oxide layer having a first refractive index and the second oxide layer having a second refractive index, the first refractive index being lower than the second refractive index.

8. 7. The method of claim 6, wherein the one or more additional doped regions are formed in a second oxide layer of the waveguiding layer, the second oxide layer being adjacent to a first oxide layer, the first oxide layer having a first refractive index and the second oxide layer having a second refractive index, the first refractive index being lower than the second refractive index.

9. The method of claim 1 , wherein the waveguide structure comprises a micromachined fiber alignment feature.

10. 2. The method of claim 1, further comprising the step of doping the waveguiding layer such that the waveguiding layer has a spatially varying refractive index that is higher closer to the doped surface and lower further away from the doped surface.

11. The method of claim 10 , wherein the spatially varying refractive index comprises a gradient refractive index.

12. The method further comprises disposing a protective layer over the waveguiding layer after doping the waveguiding layer and before etching into the waveguiding layer; The method of claim 1 , wherein attaching the cover layer to the waveguiding layer comprises fastening the cover layer to the protective layer.

13. The method of claim 1 , wherein the step of etching the fluidic channels comprises performing a dry etch.

14. The method of claim 1 , further comprising the step of etching the waveguiding layer behind an end of the solid core waveguide, thereby forming an end of the solid core waveguide.

Images