Manufacturing hollow core photonic crystal fibers

Abstract

Disclosed is a method of manufacturing an optical fiber, the method comprising: providing an optical fiber manufacturing intermediate product comprising: (i) a hollow core rod comprising a first sheath having a hollow interior structure wherein a plurality of capillaries are welded to the first sheath within the hollow interior structure; and (ii) a second sheath surrounding the hollow core rod; roughening an outer surface of the second sheath over a portion (310) of the second sheath; coupling the end of the fiber optic fabrication intermediate product to a pressure connector (402); and drawing the hollow core photonic crystal fiber from the fiber manufacturing intermediate product.

Description

Cross-references to related applications

[0001] This application claims priority to EP application 23188462.8, filed on July 28, 2023, which is incorporated herein by reference in its entirety. Technical Field

[0002] This invention relates to a method for manufacturing hollow core photonic crystal fibers, and intermediate products for manufacturing hollow core photonic crystal fibers. Background Technology

[0003] A lithography apparatus is a machine configured to apply a desired pattern onto a substrate. Lithography apparatuses can be used, for example, in the manufacture of integrated circuits (ICs). A lithography apparatus can project a pattern (often referred to as a “design layout” or “design”) onto a layer of radiation-sensitive material (resist) disposed on a substrate (e.g., a wafer), for example at a patterning apparatus (e.g., a mask).

[0004] To project a pattern onto a substrate, photolithography equipment can use electromagnetic radiation. The wavelength of this radiation determines the minimum size of the feature that can be formed on the substrate. Typical wavelengths currently used are 365 nm (i-line), 248 nm, 193 nm, and 13.5 nm. Compared to photolithography equipment using radiation with a wavelength of, for example, 193 nm, photolithography equipment using extreme ultraviolet (EUV) radiation in the range of 4 nm to 20 nm (e.g., 6.7 nm or 13.5 nm) can be used to form smaller features on the substrate.

[0005] Low-k1 lithography can be used to process features smaller than the classical resolution limit of lithography equipment. In such a process, the resolution formula can be expressed as CD = k1 × λ / NA, where λ is the wavelength of radiation used, NA is the numerical aperture of the projection optics in the lithography equipment, CD is the "critical size" (typically the smallest feature size printed, but in this case, half a pitch), and k1 is an empirical resolution factor. Generally, the smaller k1 is, the more difficult it is to reproduce patterns on the substrate that are similar in shape and size to those planned by the circuit designer for specific electrical functions and performance. To overcome these difficulties, complex fine-tuning steps can be applied to the lithography projection equipment and / or design layout. These include, for example, but not limited to, optimization of NA, customized illumination schemes, the use of phase-shifting patterning apparatus, various optimizations of the design layout (such as optical proximity correction (OPC, sometimes also called "optical process correction")), or other methods generally defined as "resolution enhancement techniques" (RET). Alternatively, a tight control loop used to control the stability of the lithography equipment can be used to improve pattern reproduction at low k1.

[0006] Metrological tools are used in many aspects of the IC manufacturing process, such as alignment tools for properly positioning the substrate before exposure, leveling tools for measuring the surface topology of the substrate, and focus control and scattering tools for inspecting / measuring exposed and / or etched products in process control. In each case, a radiation source is required. Broadband or white light radiation sources are increasingly used in such metrological applications for various reasons, including measurement robustness and accuracy. Improvements to current devices for broadband radiation generation are desired. Among other techniques for white light generation, photonic crystal fibers (PCFs) can be used to convert narrowband input radiation into broadband output radiation via one or more nonlinear optical processes. The output performance of PCF-based radiation sources depends heavily on the quality and properties of the PCF, which are primarily determined by the fiber manufacturing process.

[0007] Hollow core photonic crystal fiber (HC-PCF) is manufactured by assembling glass raw materials and drawing the components (or fiber preforms) down into optical fibers, which typically involves multiple steps.

[0008] Known optical fiber preforms (referred to herein as intermediate products in optical fiber manufacturing) may have: (i) a blank rod comprising a first sheath having a hollow core, wherein a plurality of glass capillaries are fused to the first sheath within the hollow core; and (ii) an outer sheath surrounding the blank rod (in which the first sheath and the capillaries are fitted before being drawn into an optical fiber).

[0009] In the final production step, HC-PCF is drawn in a fiber drawing tower that draws HC-PCF from fiber preforms (i.e., intermediate products in fiber manufacturing). When performing this final production step, a set of directly adjustable process parameters, such as (i) furnace temperature, (ii) glass material feed and drawing speed, and (iii) capillary and core pressure, are used to adjust the fiber structure according to the desired specifications.

[0010] Based on the initial blank structure, the obtained fiber structure can be calculated using the following equation:

[0011] The furnace temperature (i) is derived from the glass viscosity μ(z), the feed and drawing speeds (ii) are incorporated into the position-dependent axial velocity w(z) of the glass, and the pressure difference (iii) between the capillary and the core is Δp. This equation demonstrates that actively adjusted pressure is crucial for the resulting fiber structure and is a necessary process to prevent the capillary from simply collapsing due to the surface tension γ of the glass. In the above equation, r c R represents the inner radius of the capillary. cThis indicates the outer radius of the capillary.

[0012] Pressure is selectively applied to the core and glass capillaries fused to the first sheath via inserted and sealed glass and polymer capillaries, and is adjusted by a high-precision pressure controller during the drawing process. Specifically, glass pressure capillaries are inserted into multiple glass capillaries within the preform, and core polymer pressure capillaries are inserted into the hollow core of the preform. Selective pressure is achieved by cutting the core capillaries to different lengths than the other pressure capillaries and sealing the remaining open areas inside the preform using an adhesive. The low-viscosity adhesive is drawn into the preform structure by capillary force and cured with UV light. The resulting fiber preform can then be selectively pressured during the fiber drawing process, allowing for active control of the final fiber structure. Summary of the Invention

[0013] The inventors have observed that during fiber drawing in a furnace (e.g., at 1800°C or higher), thermal radiation is generated within the glass volume, and this thermal radiation is guided back through the fiber preform via total internal reflection into the sealed preform portion having its pressurized capillary. This causes thermal expansion of the adhesive used to seal the end of the preform with the inserted pressurized capillary. This expansion then damages the glass capillary of the preform and causes capillary collapse in the final fiber. This process is irreversible, and therefore drawing attempts fail. The inventors have observed that, using known techniques, approximately 15% of all drawing attempts fail due to capillary collapse.

[0014] Attempts to address this issue included using Teflon tape to couple out thermal radiation by wrapping the Teflon tape around a 15cm length of the fiber preform sheath (the outer sheath surrounding the blank). This portion of the fiber preform is lost during the drawing process because it cannot be fed into the drawing furnace, as the high drawing temperatures would cause the Teflon to decompose (its residue would contaminate the drawn fiber). The 15cm fiber preform corresponds to an 85m final hollow-core photonic crystal fiber.

[0015] According to a first aspect of the present invention, a method for manufacturing a hollow-core photonic crystal fiber is provided, the method comprising: providing an intermediate product for fiber manufacturing, the intermediate product comprising: (i) a hollow-core blank, the hollow-core blank including a first sheath having a hollow internal structure, wherein a plurality of capillaries are fused to the first sheath within the hollow internal structure; and (ii) a second sheath surrounding the hollow-core blank; roughening an outer surface of the second sheath on a portion thereof; coupling an end of the intermediate product for fiber manufacturing to a pressure connector; and drawing a hollow-core photonic crystal fiber from the intermediate product for fiber manufacturing.

[0016] Compared to existing technologies using Teflon tape, the roughened portion of the second sheath advantageously couples away heat radiation more effectively during the drawing process, thereby reducing the risk of damage to the pressure connector by heat radiation.

[0017] Furthermore, embodiments of this disclosure enable a portion of the fiber preform previously wrapped in Teflon tape to be available and drawn into a hollow-core photonic crystal fiber. Specifically, more efficient heat coupling means that the length of the roughened portion of the intermediate fiber manufacturing product can be significantly smaller than the length of Teflon tape required to couple thermal radiation in known techniques. Therefore, embodiments of this disclosure significantly increase the yield per drawing (i.e., more meters of fiber per successful fiber drawing). Additionally, embodiments of this disclosure reduce the probability of fiber drawing failures, resulting in higher yields.

[0018] Roughening the outer surface of the second sheath may include guiding fluid toward the portion of the second sheath, the fluid comprising abrasive particles.

[0019] The fluid may be a gas. Alternatively, the fluid may include a liquid.

[0020] The abrasive particles may include sand particles.

[0021] Roughening the outer surface of the second sheath may include chemically etching the portion of the second sheath.

[0022] Roughening the outer surface of the second sheath may include plasma etching of the portion of the second sheath.

[0023] Roughening the outer surface of the second sheath may include directing radiation emitted from the radiation source to strike said portion of the second sheath.

[0024] Roughening the outer surface of the second sheath may include applying an abrasive material to the portion of the second sheath.

[0025] The portion of the second sheath can be positioned closer to the end of the optical fiber manufacturing intermediate than the opposite end of the intermediate product.

[0026] The portion of the second sheath can be positioned closer to the end of the optical fiber manufacturing intermediate product than the center of the axial length of the intermediate product.

[0027] The portion of the second sheath can be separated from the end portion of the intermediate product in the optical fiber manufacturing process through another portion of the second sheath.

[0028] The other portion of the second sheath may have a length between 7 cm and 14 cm.

[0029] In some embodiments, the roughening is not performed on the other portion of the second sheath.

[0030] The portion of the second sheath may have a length of less than 10 cm.

[0031] The portion of the second sheath may have a length between 1 cm and 5 cm, and optionally between 2 cm and 4 cm.

[0032] During the drawing process, heat, tension, and pressure can be applied to the intermediate products used in optical fiber manufacturing.

[0033] The hollow internal structure of the hollow core blank can have a polygonal cross-section, such as a hexagonal cross-section.

[0034] According to another aspect of the present invention, an intermediate product for manufacturing hollow core photonic crystal fibers is provided, the intermediate product comprising: (i) a hollow core blank including a first sheath having a hollow internal structure, wherein a plurality of capillaries are fused to the first sheath within the hollow internal structure; and (ii) a second sheath surrounding the hollow core blank; wherein the outer surface of the second sheath includes a roughened portion. Attached Figure Description

[0035] Embodiments of the invention will now be described by way of example only, with reference to the accompanying schematic diagrams, in which: - Figure 1 A schematic schematic diagram of a photolithography apparatus is depicted; - Figure 2 A schematic schematic diagram of the photolithography unit is depicted; - Figure 3 A schematic representation of overall photolithography is depicted, illustrating the collaboration between three key technologies used to optimize semiconductor manufacturing. - Figure 4 A schematic schematic diagram of the scattering apparatus used as a measuring device is depicted. - Figure 5 A schematic schematic diagram of a horizontal sensor device that may include a radiation source is depicted. - Figure 6 A schematic schematic diagram of an alignment sensor device that may include a radiation source is depicted. - Figure 7 This is a schematic cross-sectional view of a hollow core optical fiber that can form part of a radiation source in a transverse plane (i.e., perpendicular to the axis of the fiber). - Figure 8 A schematic representation of a radiation source used to provide broadband output radiation is depicted. - Figure 9 (a) and Figure 9 (b) A cross-section of an example hollow-core photonic crystal fiber (HC-PCF) design for supercontinuum generation is schematically depicted. - Figure 10 This is a flowchart of a known method for manufacturing hollow-core photonic crystal fibers; - Figure 11 This is a flowchart of a method for manufacturing a hollow core according to an embodiment of the present disclosure; - Figure 12 The diagram shows the cross-section of the hollow core billet. - Figure 13 The illustration shows a cross-section of an intermediate product in optical fiber manufacturing, including a hollow core blank. - Figure 14 The illustration shows the roughened portion of the blank sheath of an intermediate product in optical fiber manufacturing; and - Figure 15 The illustration shows the drawing of HC-PCF from intermediate products in optical fiber manufacturing. Detailed Implementation

[0036] In this document, the terms “radiation” and “beam” are used to cover all types of electromagnetic radiation, including ultraviolet radiation (e.g., wavelengths of 365 nm, 248 nm, 193 nm, 157 nm, or 126 nm) and EUV (extreme ultraviolet radiation, e.g., wavelengths in the range of about 5 nm to 100 nm).

[0037] As used herein, the terms “mask,” “mask,” or “patterning apparatus” can be broadly interpreted to refer to a general-purpose patterning apparatus that can be used to impart a patterned cross-section to an incident radiation beam corresponding to a pattern to be produced in a target portion of a substrate. The term “optical valve” may also be used in this context. Examples of such patterning apparatuses, in addition to classic masks (transmission or reflection masks, binary masks, phase-shifting masks, hybrid masks, etc.), include programmable mirror arrays and programmable LCD arrays.

[0038] Figure 1 A lithography apparatus LA is schematically depicted. The lithography apparatus LA includes: an irradiation system (also called an irradiator) IL configured to modulate a radiation beam B (e.g., UV radiation, DUV radiation, or EUV radiation); a mask support (e.g., a mask stage) MT configured to support a patterning apparatus (e.g., a mask) MA and connected to a first positioner PM configured to accurately position the patterning apparatus MA according to specific parameters; a substrate support (e.g., a wafer stage) WT configured to hold a substrate (e.g., a wafer coated with resist) W and connected to a second positioner PW configured to accurately position the substrate support according to specific parameters; and a projection system (e.g., a refractive projection lens system) PS configured to project a pattern imparted by the radiation beam B by the patterning apparatus MA onto a target portion C (e.g., including one or more dies) of the substrate W.

[0039] In operation, the irradiation system IL receives a radiation beam from the radiation source SO, for example via the beam transmission system BD. The irradiation system IL may include various types of optical components for guiding, shaping, and / or controlling the radiation, such as refractive, reflective, magnetic, electromagnetic, electrostatic, and / or other types of optical components, or any combination thereof. The irradiator IL can be used to adjust the radiation beam B to have a desired spatial and angular intensity distribution in its cross-section at the plane of the pattern forming apparatus MA.

[0040] As used herein, the term "projection system" PS should be interpreted broadly to encompass various types of projection systems, including refractive, reflective, catadioptric, distorting, magnetic, electromagnetic, and / or electrostatic optical systems, or any combination thereof, applicable to the exposure radiation and / or other factors (such as the use of immersion liquids or vacuum). Any use of the term "projection lens" herein may be considered synonymous with the more general term "projection system" PS.

[0041] A lithography apparatus LA can be of the type in which at least a portion of the substrate can be covered by a liquid (e.g., water) with a relatively high refractive index to fill the space between the projection system PS and the substrate W; this is also known as immersion lithography. More information on immersion techniques is given in US6952253 (which, by reference and incorporation herein),

[0042] The lithography equipment LA can also be of the type having two (also known as "dual stage") or more substrate supports WT. In such a "multi-stage" machine, the substrate supports WT can be used in parallel, and / or while subsequent exposure preparation steps for substrate W are performed on substrate W located on one of the substrate supports WT, another substrate W on another substrate support WT is used to expose a pattern on the other substrate W.

[0043] In addition to the substrate support WT, the lithography apparatus LA may include a measurement stage. The measurement stage is arranged to hold sensors and / or cleaning devices. The sensors may be arranged to measure the properties of the projection system PS or the properties of the radiation beam B. The measurement stage may hold multiple sensors. The cleaning devices may be arranged to clean part of the lithography apparatus, such as part of the projection system PS or part of a system providing immersion liquid. The measurement stage may move below the projection system PS as the substrate support WT moves away from the projection system PS.

[0044] In operation, a radiation beam B is incident on a pattern forming apparatus (e.g., a mask) MA held on a mask support MT, and patterned by a pattern (design layout) presented on the pattern forming apparatus MA. After passing through the mask MA, the radiation beam B passes through a projection system PS, which focuses the beam onto a target portion C of the substrate W. With the aid of a second positioner PW and a position measurement system IF, the substrate support WT can be moved precisely, for example, to position different target portions C at focused and aligned positions along the path of the radiation beam B. Similarly, a first positioner PM and possibly another position sensor (which is not in...) Figure 1 (As explicitly shown in the diagram) the pattern forming apparatus MA can be used to accurately position itself relative to the path of the radiation beam B. The pattern forming apparatus MA and the substrate W can be aligned using mask alignment marks M1, M2 and substrate alignment marks P1, P2. Although the substrate alignment marks P1, P2 occupy dedicated target portions, they can be located in the space between the target portions. When the substrate alignment marks P1, P2 are located between the target portions C, they are referred to as scribing alignment marks.

[0045] like Figure 2As shown, a lithography apparatus LA can form part of a lithography unit LC, sometimes also called a lithography unit or (lithography) cluster. The lithography unit LC typically also includes equipment for performing pre-exposure and post-exposure processes on a substrate W. These devices typically include a spin coater SC for depositing a resist layer, a developer DE for developing the exposed resist, a chiller CH, and a baking plate BK, for example, to adjust the temperature of the substrate W, or to adjust the solvent in the resist layer. A substrate transport device (or robot) RO picks up the substrate W from input / output ports I / O1, I / O2, moves the substrate W between different processing devices, and transports the substrate W to the loading stage LB of the lithography apparatus LA. The devices in the lithography unit (often collectively referred to as tracks) are typically controlled by a track control unit TCU, which itself can be controlled by a management control system SCS, which can also control the lithography apparatus LA, for example, via the lithography control unit LACU.

[0046] To ensure accurate and consistent exposure of the substrate W exposed by the lithography apparatus LA, it is desirable to inspect the substrate to measure properties of the patterned structure, such as overlap error between subsequent layers, line thickness, critical dimension (CD), etc. For this purpose, the lithography unit LC may include inspection tools (not shown). If an error is detected, especially if the inspection is performed before exposing or processing other substrates W in the same batch or batch, adjustments can be made, for example, to the exposure of subsequent substrates and / or other processing steps to be performed on the substrate W.

[0047] Inspection equipment (also called measurement equipment) is used to determine the properties of a substrate W, particularly how the properties of different substrates W vary or how the properties associated with different layers of the same substrate W vary between layers. Alternatively, the inspection equipment may be configured to identify defects on the substrate W and may be, for example, part of a photolithography unit LC, or integrated into a photolithography apparatus LA, or even a stand-alone device. The inspection equipment may measure the properties of latent images (images in a resist layer after exposure), or semi-latent images (images in a resist layer after a post-exposure baking (PEB) step), or developed resist images (where the exposed or unexposed portions of the resist have been removed), or even etched images (after a pattern transfer step such as etching).

[0048] Typically, the patterning process in photolithography (LA) equipment is one of the most critical steps in the process of achieving high-precision sizing and placement of structures on a substrate (W). To ensure this high precision, three systems can be combined into a so-called "integrated" control environment, such as... Figure 3The diagram illustrates this schematically. One of these systems is the lithography apparatus LA, which is (in fact) connected to the metrology tool MT (second system) and the computer system CL (third system). The key to this “holistic” environment is optimizing the collaboration between these three systems to enhance the overall process window and providing tight control loops to ensure that the patterning performed by the lithography apparatus LA remains within the process window. The process window defines a range of process parameters (e.g., dose, focus, overlap) within which a particular manufacturing process produces a defined result (e.g., a functional semiconductor device), typically allowing process parameters during the lithography or patterning process to vary within these ranges.

[0049] The computer system CL can use a portion of the design layout to be patterned to predict which resolution enhancement technique to use and perform computational lithography simulations and calculations to determine which mask layouts and lithography equipment settings enable the largest overall process window (within) the patterning process. Figure 3 (Represented by the double arrows in the first scale SC1). Typically, resolution enhancement techniques are arranged to match the patterning possibilities of the lithography apparatus LA. The computer system CL can also be used to detect where the lithography apparatus LA is currently operating within the process window (e.g., by using input from the metrology tool MT) to predict whether defects might exist due to, for example, suboptimal processes (in...). Figure 3 (This is indicated by the arrow pointing to "0" in the second scale SC2).

[0050] The measurement tool MT can provide input to the computer system CL for accurate simulation and prediction, and can provide feedback to the lithography equipment LA to identify possible drifts in, for example, the calibration state of the lithography equipment LA. Figure 3 (represented by multiple arrows in the third scale SC3).

[0051] During photolithography, it is often desirable to measure the resulting structure, for example, for process control and verification. The tools used to perform these measurements are generally called metrology tools (MTs). Different types of metrology tools (MTs) for performing such measurements are known, including scanning electron microscopes or various forms of scatterometer metrology tools (MTs). A scatterometer is a versatile instrument that allows the measurement of parameters of the photolithography process by placing a sensor in the pupil of the scatterometer objective or in a plane conjugate to that pupil; this measurement is generally referred to as pupil-based measurement. Alternatively, the measurement of parameters of the photolithography process can be performed by placing a sensor in the image plane or in a plane conjugate to that image plane; in this case, the measurement is generally referred to as image- or field-based measurement. Such scatterometers and related measurement techniques are further described in patent applications US20100328655, US2011102753A1, US20120044470A, US20110249244, US20110026032, or EP1,628,164A, which are incorporated herein by reference in their entirety. The aforementioned scatterer can measure gratings using light from soft X-rays and visible light to near-IR wavelengths.

[0052] In the first embodiment, the scatterer MT is an angle-resolved scatterer. In such a scatterer, reconstruction methods can be applied to the measurement signal to reconstruct or calculate the properties of the grating. For example, this reconstruction can be obtained by simulating the interaction between the scattered radiation and a mathematical model of the target structure and comparing the simulation results with the measurement results. The parameters of the mathematical model are adjusted until the simulated interaction produces a diffraction pattern similar to that observed from a real target.

[0053] In the second embodiment, the scatterer MT is a spectroscopic scatterer MT. In such a spectroscopic scatterer MT, radiation emitted by a radiation source is directed to the target, and radiation reflected or scattered from the target is directed to a spectroscopic detector that measures the spectrum of the specularly reflected radiation (i.e., the intensity as a function of wavelength). Based on this data, the structure or profile of the target that generated the detected spectrum can be reconstructed, for example, through rigorous coupled-wave analysis and nonlinear regression or by comparison with a simulated spectral library.

[0054] In the third embodiment, the scatterer MT is an elliptically polarized scatterer. An elliptically polarized scatterer allows the determination of parameters of the photolithography process by measuring the scattered radiation for each polarization state. This measurement device emits polarized light (e.g., linear, circular, or elliptical) by, for example, using a suitable polarization filter in the illumination portion of the measurement device. A source suitable for the measurement device can also provide polarized radiation. Various embodiments of existing elliptically polarized scatterers are described in U.S. Patent Applications 11 / 451,599, 11 / 708,678, 12 / 256,780, 12 / 486,449, 12 / 920,968, 12 / 922,587, 13 / 000,229, 13 / 033,135, 13 / 533,110, and 13 / 891,410, the entire contents of which are incorporated herein by reference.

[0055] In one embodiment of a scattering instrument (MT), the scattering instrument MT is adapted to measure the overlap of two misaligned gratings or periodic structures by measuring the reflectance spectrum and / or detecting asymmetry in the configuration, the asymmetry being related to the degree of overlap. The two (typically overlapping) grating structures can be applied to two different layers (not necessarily consecutive layers) and can be formed substantially at the same location on a wafer. The scattering instrument can have a symmetrical detection configuration, for example, described in common patent application EP1,628,164A, such that any asymmetry can be clearly distinguished. This provides a direct method for measuring grating misalignment. Other examples of measuring the overlap error between two layers comprising a periodic structure when measuring a target by means of asymmetry in a periodic structure can be found in PCT patent application publication WO 2011 / 012624 or U.S. patent application US 20160161863, the entire contents of which are incorporated herein by reference.

[0056] Other parameters of interest may be focus and dose. Focus and dose can be determined simultaneously by a scatterometer (or alternatively by a scanning electron microscope), as described in U.S. Patent Application US2011-0249244, the entire contents of which are incorporated herein by reference. A single structure with a unique combination of critical dimensions and sidewall angle measurements for each point in the focus energy matrix (FEM – also known as the focus exposure matrix) can be used. If these unique combinations of critical dimensions and sidewall angles are available, the focus and dose values ​​can be uniquely determined based on these measurements.

[0057] The measurement target can be a set of composite gratings formed mostly in the resist during the photolithography process, but also, for example, after the etching process. Typically, the pitch and linewidth of the structures in the gratings are largely dependent on the measurement optics (especially the NA of the optics) to be able to capture the diffraction order from the measurement target. As previously mentioned, the diffraction signal can be used to determine the drift (also known as "overlap") between two layers, or it can be used to reconstruct at least a portion of the original grating produced by the photolithography process. This reconstruction can be used to provide guidance on the quality of the photolithography process and can be used to control at least a portion of the photolithography process. The target can have smaller sub-segments configured to simulate the dimensions of functional portions of the design layout in the target. Due to these sub-segments, the behavior of the target will be more similar to the functional portions of the design layout, thus making the overall process parameter measurements better similar to the functional portions of the design layout. The target can be measured in either an unfilled mode or an overfilled mode. In the unfilled mode, the spot produced by the measurement beam is smaller than the entire target. In the overfilled mode, the spot produced by the measurement beam is larger than the entire target. In this overfilled mode, different targets can also be measured simultaneously, thereby simultaneously determining different processing parameters.

[0058] The overall measurement quality of a lithography parameter used for a specific target is determined at least in part by the measurement configuration used to measure that lithography parameter. The term "substrate measurement configuration" can include one or more parameters of the measurement itself, one or more parameters of one or more measured patterns, or both. For example, if the measurement used in the substrate measurement configuration is a diffraction-based optical measurement, the one or more measured parameters can include the wavelength of the radiation, the polarization of the radiation, the angle of incidence of the radiation relative to the substrate, the orientation of the radiation relative to the pattern on the substrate, etc. For example, one criterion for selecting a measurement configuration could be the sensitivity of one of the measurement parameters to processing variations. Further examples are described in U.S. Patent Application US2016-0161863 and U.S. Patent Application US2016 / 0370717A1, the entire contents of which are incorporated herein by reference.

[0059] Figure 4 A measuring device, such as a scattering instrument, is described. The measuring device includes a broadband (white light) radiation projector 2, which projects radiation onto a substrate 6. The reflected or scattered radiation is transmitted to a spectrometer 4, which measures the spectrum 10 of the specularly reflected radiation (i.e., a measurement of intensity as a function of wavelength). Based on this data, for example by means of... Figure 3As shown at the bottom, through rigorous coupled-wave analysis and nonlinear regression, or by comparison with a simulated spectral library, the processing unit (PU) can reconstruct the structure or profile that produced the detected spectrum. Typically, for reconstruction, the general form of the structure is known, and some parameters are assumed based on knowledge of the process that forms the structure; therefore, only a few parameters of the structure need to be determined from the scattering measurements. This scatterometer can be configured as a normal-incident or oblique-incident scatterometer.

[0060] The overall measurement quality of lithographic parameters measured on a target is determined at least in part by the measurement scheme used to measure those lithographic parameters. The term "substrate measurement scheme" can include one or more parameters of the measurement itself, one or more parameters of one or more measured patterns, or both. For example, if the measurement used in the substrate measurement scheme is a diffraction-based optical measurement, the one or more measured parameters can include the wavelength of the radiation, the polarization of the radiation, the angle of incidence of the radiation relative to the substrate, the orientation of the radiation relative to the pattern on the substrate, etc. For example, one of the criteria for selecting a measurement scheme could be the sensitivity of one of the measurement parameters to processing variations. Further examples are described in U.S. Patent Application US2016 / 0161863 and U.S. Patent Application US2016 / 0370717A1, the entire contents of which are incorporated herein by reference.

[0061] Another type of metrology tool used in IC manufacturing is a topography measurement system, a level sensor, or a height sensor. These tools can be integrated into photolithography equipment to measure the topography of the top surface of a substrate (or wafer). A topography map of the substrate (also called a height map) can be generated from these measurements, which indicate the height of the substrate as a function of its position on the substrate. This height map can then be used to correct the substrate's position during pattern transfer onto the substrate, providing a spatial image of the patterning apparatus at the appropriate focal point on the substrate. It will be understood that, in this context, "height" refers to a dimension relative to the substrate that is significantly outside a plane (also known as the Z-axis). Typically, the level sensor or height sensor performs measurements at a fixed location (relative to its own optical system), and the relative motion between the substrate and the optical system of the level sensor or height sensor produces height measurements at multiple locations across the substrate.

[0062] Figure 5An example of a level sensor or height sensor LS known in the art is illustrated schematically, illustrating only the principle of operation. In this example, the level sensor includes an optical system comprising a projection unit LSP and a detection unit LSD. The projection unit LSP includes a radiation source LSO that provides a radiation beam LSB imparted by a projection grating PGR of the projection unit LSP. The radiation source LSO can be, for example, a narrowband or broadband light source, such as a supercontinuum light source, a polarized or unpolarized radiation source, a pulsed or continuous radiation source, such as a polarized or unpolarized laser beam. The radiation source LSO can include multiple radiation sources with different colors or wavelength ranges, such as multiple LEDs. The radiation source LSO of the level sensor LS is not limited to visible radiation, but can additionally or alternatively cover UV and / or IR radiation and any wavelength range suitable for reflection from the surface of the substrate.

[0063] The projection grating (PGR) is a periodic grating comprising a periodic structure that generates a radiation beam BE1 with periodically varying intensity. The radiation beam BE1 with periodically varying intensity is guided toward a measurement position MLO on the substrate W, the radiation beam BE1 having an incident angle ANG relative to an axis (Z-axis) perpendicular to the surface of the incident substrate, the incident angle ANG being between 0 and 90 degrees, typically between 70 and 80 degrees. At the measurement position MLO, the patterned radiation beam BE1 is reflected by the substrate W (indicated by arrow BE2) and guided toward the detection unit LSD.

[0064] To determine the height level at the measurement location MLO, the level sensor also includes a detection system comprising a detection grating DGR, a detector DET, and a processing unit (not shown) for processing the output signal of the detector DET. The detection grating DGR may be equivalent to a projection grating PGR. The detector DET generates a detector output signal indicating the received light, such as a detector output signal indicating the intensity of the received light (e.g., a photodetector), or a detector output signal representing the spatial distribution of the received intensity (e.g., a camera). The detector DET may include any combination of one or more detector types.

[0065] The height level at the measurement location MLO can be determined using triangulation techniques. The detected height level is typically related to the signal strength measured by the detector DET, which exhibits periodicity, particularly dependent on the design of the projection grating PGR and the (tilted) incident angle ANG.

[0066] The projection unit LSP and / or the detection unit LSD may include other optical elements, such as lenses and / or mirrors, along the path of the patterned radiation beam between the projection grating PGR and the detection grating DGR (not shown).

[0067] In one embodiment, the detection grating DGR can be omitted, and the detector DET can be placed at the location of the detection grating DGR. This configuration provides more direct detection of the image of the projection grating PGR.

[0068] In order to effectively cover the surface of the substrate W, the horizontal sensor LS can be configured to project an array of measurement beams BE1 onto the surface of the substrate W, thereby producing an array of measurement regions MLO or spots that cover a larger measurement range.

[0069] Various general-purpose height sensors are disclosed, for example, in US7265364 and US7646471, both of which are incorporated herein by reference. A height sensor that uses UV radiation instead of visible or infrared radiation is disclosed in US2010233600A1, which is incorporated herein by reference. In WO2016102127A1, which is incorporated by reference, a compact height sensor is described that uses a multi-element detector to detect and identify the position of a grating image without requiring the detection of the grating itself.

[0070] Another type of metrology tool used in IC manufacturing is the alignment sensor. Therefore, a key aspect of the performance of a lithography apparatus is its ability (using the same or different lithography equipment) to correctly and accurately align the applied pattern relative to features laid in the previous layer. For this purpose, the substrate is provided with one or more sets of marks or targets. Each mark is a structure whose position can be measured later using a position sensor (usually an optical position sensor). The position sensor can be called an "alignment sensor," and the mark can be called an "alignment mark."

[0071] Photolithography apparatuses may include one or more alignment sensors that can accurately measure the position of alignment marks formed on a substrate. Alignment sensors (or position sensors) can use optical phenomena such as diffraction and interference to obtain positional information from alignment marks formed on the substrate. Examples of alignment sensors used in current photolithography apparatuses are based on self-reference interferometers as described in US6961116. Various enhancements and modifications of position sensors have been developed, for example, as disclosed in US2015261097A1. All of these disclosures are incorporated herein by reference.

[0072] Figure 6This is a schematic block diagram of an embodiment of a known alignment sensor AS (such as the alignment sensor described, for example, in US6961116, which is incorporated by reference). A radiation source RSO provides a radiation beam RB of one or more wavelengths, which is directed by a steering optics element onto a marker (such as a marker AM located on a substrate W) as an illumination spot SP. In this example, the steering optics element includes a spot mirror SM and an objective lens OL. The diameter of the illumination spot SP used to illuminate the marker AM may be slightly smaller than the width of the marker itself.

[0073] The radiation diffracted by the alignment mark AM is collimated (in this example via the objective lens OL) into an information-carrying beam IB. The term "diffraction" is intended to include zero-order diffraction from the mark (which may be referred to as reflection). A self-reference interferometer SRI (such as the type disclosed in US6961116 mentioned above) causes the beam IB to interfere with itself, after which the beam is received by a photodetector PD. In cases where more than one wavelength is generated by the radiation source RSO, additional optics (not shown) may be included to provide a separate beam. If desired, the photodetector may be a single element, or it may include multiple pixels. The photodetector may include a sensor array.

[0074] In this example, the steering optics that include the speckled mirror SM can also be used to block the zero-order radiation reflected from the marker, so that the information-carrying beam IB only includes higher-order diffraction radiation from the marker AM (this is not necessary for the measurement, but it improves the signal-to-noise ratio).

[0075] The intensity signal SI is provided to the processing unit PU. Through a combination of optical processing in the block SRI and computational processing in the unit PU, the values ​​of the X and Y positions on the substrate relative to the reference frame are output.

[0076] A single measurement of this type fixes the mark's position within a specific range corresponding to one pitch of the mark. This is combined with coarse measurement techniques to identify which period of the sine wave includes the mark's position. The same process can be repeated at coarser or finer levels at different wavelengths to improve accuracy and / or robustly detect the mark, regardless of its material or the materials placed on or under it. Wavelengths can be optically multiplexed and demultiplexed for simultaneous processing, and / or multiplexed via time-division or frequency-division multiplexing.

[0077] In this example, the alignment sensor and the spot SP remain stationary, while the substrate W moves. Therefore, the alignment sensor can be fixed and accurately mounted to the reference frame while effectively scanning the mark AM in the direction opposite to the direction of movement of the substrate W. The substrate W is controlled during this movement by mounting it on a substrate support and by a substrate positioning system that controls the movement of the substrate support. A substrate support position sensor (e.g., an interferometer) measures the position of the substrate support (not shown). In one embodiment, one or more (alignment) marks are provided on the substrate support. Measuring the position of the marks provided on the substrate support allows for calibration of the position of the substrate support determined by the position sensor (e.g., calibration relative to the frame to which the alignment system is attached). Measuring the position of the alignment marks provided on the substrate allows for determination of the position of the substrate relative to the substrate support.

[0078] Measurement tools (MTs) such as scatterometers, topography measurement systems, or position measurement systems described above can perform measurements using radiation originating from a radiation source. The nature of the radiation used by the measurement tool can affect the type and quality of the measurements that may be performed. For some applications, it may be advantageous to use multiple radiation frequencies to measure the substrate, for example, broadband radiation can be used. Multiple different frequencies can propagate, illuminate, and scatter the measurement target with minimal or no interference from other frequencies. Therefore, for example, more measurement data can be obtained simultaneously using different frequencies. Different radiation frequencies can also enable the querying and discovery of different properties of the measurement target. Broadband radiation can be used in measurement systems (MTs) such as, for example, level sensors, alignment mark measurement systems, scattering measurement tools, or inspection tools. Broadband radiation sources can be supercontinuum sources.

[0079] Generating high-quality broadband radiation (e.g., supercontinuum radiation) can be challenging. One approach to generating broadband radiation is, for example, to broaden high-power narrowband or single-frequency input or pump radiation using nonlinear, higher-order effects. The input radiation (which can be generated using a laser) can be referred to as pump radiation. Alternatively, the input radiation can be called seed radiation. To obtain high-power radiation for the broadening effect, the radiation can be confined to a small region, achieving locally enhanced high-intensity radiation. In these regions, the radiation can interact with broadening structures and / or materials that form a nonlinear medium, thereby generating broadband output radiation. In high-intensity radiation regions, different materials and / or structures can be used to achieve and / or improve radiation broadening by setting a suitable nonlinear medium.

[0080] In some implementations, broadband output radiation is generated in a photonic crystal fiber (PCF). In several embodiments, such a PCF has microstructures around its fiber core, which helps to confine radiation traversing the fiber within the fiber core. The fiber core can be made of a solid material with nonlinear properties, and broadband radiation can be generated when high-intensity pump radiation propagates through the fiber core. While generating broadband radiation in a solid-core PCF is feasible, using a solid material can have some drawbacks. For example, if UV radiation is generated in a solid core, this radiation may not appear in the fiber's output spectrum because it would be absorbed by most solid materials.

[0081] In some implementations, see the following references. Figure 8 Further discussion reveals that methods and apparatus for broadening input radiation can utilize optical fibers to confine and broaden the input radiation to output broadband radiation. The optical fiber can be a hollow-core fiber and may include internal structures for effectively guiding and confining radiation within the fiber. The fiber may be a hollow-core photonic crystal fiber (HC-PCF), which is particularly suitable for strong radiation confinement primarily within the hollow core of the fiber, thereby achieving high radiation intensity. The hollow core of the fiber may be filled with a gas serving as a broadening medium for broadening the input radiation. This fiber and gas arrangement can be used to generate a supercontinuum radiation source. The radiation input to the fiber can be electromagnetic radiation, such as radiation from one or more of the infrared, visible, UV, and extreme UV spectra. The output radiation may consist of or include broadband radiation, which may be referred to herein as white light.

[0082] Some embodiments relate to novel designs of such broadband radiation sources comprising optical fibers. The optical fiber is a hollow-core photonic crystal fiber (HC-PCF). Specifically, the optical fiber can be a type of hollow-core photonic crystal fiber including an anti-resonant structure for confining radiation. Such fibers including anti-resonant structures are known in the art as anti-resonant fibers, tubular fibers, single-loop fibers, negative curvature fibers, or suppression-coupled fibers. Various different designs of such fibers are known in the art. Alternatively, the optical fiber can be a photonic bandgap fiber (HC-PBF, such as Kagome fiber).

[0083] Various types of HC-PCFs can be designed based on different physical guidance mechanisms. Two such HC-PCFs include: hollow core photonic bandgap fiber (HC-PBF) and hollow core anti-resonant reflective fiber (HC-ARF). Details regarding the design and manufacture of HC PCFs can be found in US Patent US2004 / 015085A1 (for HC PBF) and International PCT Patent Application WO2017 / 032454A1 (for hollow core anti-resonant reflective fiber), which are incorporated herein by reference. Figure 9 (a) shows a Kagome optical fiber including a Kagome lattice structure.

[0084] Now for reference Figure 7 Describe an example of the optical fiber used in a radiation source. Figure 7 This is a schematic cross-sectional view of the optical fiber (OF) in the transverse plane. WO2017 / 0324541 discloses a similar view. Figure 7 Other embodiments similar to the actual examples of optical fibers.

[0085] An optical fiber (OF) includes an elongated body that is longer in one dimension than the other two. This longer dimension may be referred to as the axial direction and defines the axis of the optical fiber. The other two dimensions define planes that may be referred to as transverse planes. Figure 7 A cross-sectional view of the optical fiber OF in a transverse plane (i.e., perpendicular to the axis) is shown, which is labeled the xy plane. The transverse section of the optical fiber OF can be substantially consistent along the fiber axis.

[0086] It will be understood that optical fiber (OF) has a degree of flexibility, therefore the direction of the axis will generally be inconsistent along the length of the optical fiber. Terms such as optical axis and cross-section will be understood to refer to local optical axis, local cross-section, etc. Furthermore, when components are described as cylindrical or tubular, these terms will be interpreted to encompass this shape, which may have been deformed when the optical fiber (OF) is bent.

[0087] Optical fiber OF can be of any length, and it will be understood that the length of optical fiber OF can depend on the application. The length of optical fiber OF can be between 1 centimeter (cm) and 10 meters (m), for example, the length of optical fiber OF can be between 10cm and 100cm.

[0088] An optical fiber (OF) comprises: a hollow core (HC); a cladding portion surrounding the hollow core (HC); and a support portion (SP) surrounding and supporting the cladding portion. An optical fiber (OF) can be considered to include a body (including the cladding portion and the support portion SP) having the hollow core (HC). The cladding portion includes multiple anti-resonant elements or capillary CAPs for guiding radiation through the hollow core (HC). Specifically, the multiple anti-resonant elements are arranged to confine radiation propagating through the optical fiber (OF) primarily within the hollow core (HC) and to guide radiation along the optical fiber (OF). The hollow core (HC) of the optical fiber (OF) can be substantially located in the central region of the optical fiber (OF) such that the axis of the optical fiber (OF) can also define the axis of the hollow core (HC).

[0089] The cladding portion includes multiple anti-resonant elements for guiding radiation propagation through the optical fiber (OF). Specifically, in this embodiment, the cladding portion includes a single ring having six tubular capillary CAPs. Each tubular capillary CAP serves as an anti-resonant element.

[0090] A capillary CAP can also be referred to as a tube. The cross-section of a capillary CAP can be circular or may have other shapes. Each capillary CAP includes a generally cylindrical wall portion WP that at least partially defines the hollow core HC of the optical fiber OF and separates the hollow core HC from the capillary cavity CC. It will be understood that the wall portion WP can serve as an anti-reflection Fabry-Perot resonator for radiation propagating through the hollow core HC (and which may be incident on the wall portion WP at a grazing angle of incidence). The thickness of the wall portion WP can be adapted to ensure that reflections returning to the hollow core HC are generally enhanced, while transmission into the capillary cavity CC is generally suppressed.

[0091] It will be understood that, as used herein, the term cladding portion refers to the portion of an optical fiber OF used to guide radiation propagation through the optical fiber OF (i.e., the capillary CAP that confines the radiation within the hollow core HC). The radiation can be confined to propagate along the fiber axis in a lateral mode.

[0092] The support portion is typically tubular, and the support cladding portion has six capillary CAPs. If it is an inner support portion SP, the six capillary CAPs are evenly distributed around the inner surface. The six capillary CAPs can be described as being arranged in a roughly hexagonal shape.

[0093] The capillary CAPs are arranged such that each capillary does not contact any other capillary CAP. Each capillary CAP contacts the inner support portion SP and is spaced apart from adjacent capillary CAPs in the annular structure. This arrangement can be advantageous because it can increase the transmission bandwidth of the optical fiber OF (e.g., relative to an arrangement where capillaries are in contact with each other). Alternatively, in some embodiments, each capillary CAP may contact adjacent capillary CAPs in the annular structure.

[0094] The cladding portion has six capillary CAPs arranged in a ring structure around the hollow core HC. The inner surface of the ring structure of the capillary CAPs at least partially defines the hollow core HC of the optical fiber OF. The diameter D of the hollow core HC (which can be defined as the minimum dimension between opposing capillaries, indicated by arrow d) can be between 10µm and 1000µm. The diameter D of the hollow core HC can affect the mode field diameter, impulse loss, dispersion, mode number, and nonlinear properties of the hollow core HC optical fiber OF.

[0095] The other dimensions shown are the pitch Λ of adjacent capillaries, the gap δ between adjacent capillaries, and the inner radius r of the capillary. c Capillary outer radius R c Capillary wall thickness t=R c -r c The radius r of the hollow region j and the radius R of the optical fiber j .

[0096] In this embodiment, the cladding portion comprises a single-ring arrangement of capillary CAPs (which serve as anti-resonant elements). Therefore, no line in any radial direction from the center of the hollow core HC to the outside of the optical fiber OF will pass through more than one capillary CAP.

[0097] It will be understood that other embodiments may have different arrangements of anti-resonant elements. These may include multi-ring arrangements of anti-resonant elements and arrangements with nested anti-resonant elements. Figure 9 (a) An embodiment of an HC-PCF is shown, comprising three capillary CAPs stacked on top of each other in a radial direction. In this embodiment, each capillary CAP contacts other capillaries in the same ring and other capillaries in different rings. Furthermore, although Figure 7 The illustrated embodiment includes a ring of six capillaries, but in other embodiments, one or more rings may be provided in the cladding portion, the one or more rings including any number of anti-resonant elements (e.g., 4, 5, 6, 7, 8, 9, 10, 11 or 12 capillaries).

[0098] Figure 9(b) illustrates a modified embodiment of the HC-PCF described above, which has a single-ring tubular capillary. Figure 9 In example (b), there is a tubular capillary 21 with two coaxial rings. To maintain the inner and outer rings of the tubular capillary 21, a support tube ST may be included in the HC-PCF. The support tube may be made of silica.

[0099] Figure 7 as well as Figure 9 (a) and Figure 9 The tubular capillary in example (b) can have a circular cross-sectional shape. Tubular capillaries can also be other shapes, such as elliptical or polygonal cross-sections. Additionally, Figure 7 as well as Figure 9 (a) and Figure 9 (b) The solid material of the tubular capillary in the example may include plastic materials such as PMA, glass, silica-like material or soft glass.

[0100] Figure 8 A radiation source RDS for providing broadband output radiation is described. The radiation source RDS includes a pulse-pumped radiation source PRS, or any other type of source capable of generating short pulses with desired length and energy levels; an optical fiber OF with a hollow core HC (e.g., Figure 7 The type shown); and the working medium WM (e.g., gas) disposed within the hollow core HC. Although in Figure 8 In this context, the radiation source RDS includes Figure 7 The optical fiber OF shown is an example, but in alternative embodiments, other types of hollow core HC optical fiber OF can be used.

[0101] A pulse-pumped radiation source (PRS) is configured to provide an input radiation IRD. The hollow core (HC) of the optical fiber (OF) is arranged to receive the input radiation IRD from the PRS and widen the input radiation IRD to provide an output radiation ORD. The operating medium (WM) is capable of widening the frequency range of the received input radiation IRD to provide a broadband output radiation ORD.

[0102] The radiation source RDS also includes a storage unit RSV. An optical fiber OF is disposed within the storage unit RSV. The storage unit RSV may also be referred to as a housing, container, or gas cell. The storage unit RSV is configured to contain a working medium WM. The storage unit RSV may include one or more features known in the art for controlling, regulating, and / or monitoring the composition of the working medium WM (which may be a gas) within the storage unit RSV. The storage unit RSV may include a first transparent window TW1. In use, the optical fiber OF is disposed within the storage unit RSV such that the first transparent window TW1 is located near the input end IE of the optical fiber OF. The first transparent window TW1 may form part of the wall of the storage unit RSV. The first transparent window TW1 may be transparent at least to the received input radiation frequency, such that the received input radiation IRD (or at least a majority thereof) can be coupled into the optical fiber OF located within the storage unit RSV. It will be understood that optics (not shown) may be provided to couple the input radiation IRD into the optical fiber OF.

[0103] The storage unit RSV includes a second transparent window TW2, which forms part of the wall of the storage unit RSV. In use, when the optical fiber OF is placed inside the storage unit RSV, the second transparent window TW2 is located near the output end OE of the optical fiber OF. The second transparent window TW2 can be transparent at least to the frequency of the broadband output radiation ORD of the device 120.

[0104] Alternatively, in another embodiment, the two opposite ends of the optical fiber OF can be housed within different repositories. The optical fiber OF may include a first end portion configured to receive an input radiation IRD and a second end portion configured to output a broadband output radiation ORD. The first end portion may be housed within a first repositories comprising a working medium WM. The second end portion may be housed within a second repositories, wherein the second repositories may also comprise the working medium WM. The repositories may function as described above regarding... Figure 8The first reservoir may include a first transparent window configured to be transparent to the input radiation IRD. The second reservoir may include a second transparent window configured to be transparent to the broadband output radiation ORD. Both the first and second reservoirs may also include sealable openings to allow the optical fiber OF to be partially placed inside and partially outside the reservoir, so that the gas can be sealed inside the reservoir. The optical fiber OF may also include an intermediate portion not included inside the reservoir. This arrangement of using two separate gas reservoirs may be particularly convenient for embodiments of relatively long optical fiber OFs (e.g., when the length is greater than 1 m). It will be understood that, for this arrangement using two separate gas reservoirs, the two reservoirs (which may include one or more features known in the art for controlling, regulating, and / or monitoring the composition of the gas inside the two reservoirs) can be considered to be provided with means for supplying the working medium WM into the hollow core HC of the optical fiber OF.

[0105] In this context, the window may be transparent to the frequency if at least 50%, 75%, 85%, 90%, 95%, or 99% of incident radiation of a frequency incident on the window is transmitted through the window.

[0106] Both the first transparent window TW1 and the second transparent window TW2 can form an airtight seal within the wall of the reservoir RSV, allowing the working medium WM (which can be a gas) to be contained within the reservoir RSV. It will be understood that the gas WM can be contained within the reservoir RSV at a pressure different from the ambient pressure of the reservoir RSV.

[0107] The working medium WM can include inert gases (such as argon, krypton, and xenon), Raman-active gases (such as hydrogen, deuterium, and nitrogen), or gas mixtures (such as argon / hydrogen mixtures, xenon / deuterium mixtures, krypton / nitrogen mixtures, or nitrogen / hydrogen mixtures). Depending on the type of filling gas, nonlinear optical processes can include modulation instabilities (MI), soliton self-compression, soliton fission, Kerr effect, Raman effect, and dispersive wave generation (DWG), details of which are described in WO2018 / 127266A1 and US9160137B1 (both incorporated herein by reference). Since the dispersion of the filling gas can be tuned by varying the pressure of the working medium WM (i.e., the gas chamber pressure) in the reservoir RSR, the resulting broadband pulse dynamics and associated spectral broadening characteristics can be adjusted to optimize frequency conversion.

[0108] In one implementation, at least during the process of receiving input radiation IRD to generate broadband output radiation ORD, the working medium WM can be disposed within the hollow core HC. It will be understood that when the optical fiber OF does not receive input radiation IRD to generate broadband output radiation, the gas WM may be completely or partially absent from the hollow core HC.

[0109] To achieve frequency broadening, high-intensity radiation may be required. The advantage of hollow-core HC fiber OF (Hollow Core Optical Fiber) lies in its ability to achieve high-intensity radiation, resulting in locally high radiation intensity, through strong spatial confinement of radiation propagating through the fiber OF. For example, the internal radiation intensity of the fiber OF can be high due to the high intensity of received input radiation and / or the strong spatial confinement of radiation within the fiber OF. The advantage of hollow-core fibers is that they can guide radiation with a wider wavelength range than solid-core fibers, and in particular, hollow-core fibers can guide radiation in the ultraviolet and infrared ranges.

[0110] The advantage of using hollow core HC fiber OF is that most of the radiation guided inside the fiber OF is confined to the hollow core HC. Therefore, the main interaction of radiation inside the fiber OF is with the working medium WM, which is disposed inside the hollow core HC of the fiber OF. Thus, the broadening effect of the working medium WM on radiation can be increased.

[0111] The received input radiation IRD can be electromagnetic radiation. The input radiation IRD can be received as pulsed radiation. For example, the input radiation IRD can include, for example, ultrafast pulses generated by a laser.

[0112] The input radiation IRD can be coherent radiation. The input radiation IRD can also be collimated radiation, which has the advantage of promoting and improving the efficiency of coupling the input radiation IRD to the fiber OF. The input radiation IRD can include a single frequency or a narrow frequency range. The input radiation IRD can be generated by a laser. Similarly, the output radiation ORD can be collimated radiation and / or coherent radiation.

[0113] The broadband range of an output radiation ORD can be a continuous range, including a continuous range of radiation frequencies. An output radiation ORD can include supercontinuum radiation. Using continuous radiation can be advantageous in many applications, such as measurement applications. For example, a continuous range of frequencies can be used to query a large number of properties. For example, a continuous range of frequencies can be used to determine and / or eliminate the frequency dependence of the measured property. For example, a supercontinuum output radiation ORD can include electromagnetic radiation with wavelengths ranging from 100 nm to 4000 nm. For example, the frequency range of a broadband output radiation ORD can be 400 nm to 900 nm, 500 nm to 900 nm, or 200 nm to 2000 nm. A supercontinuum output radiation ORD can include white light.

[0114] The input radiation IRD provided by the pulsed-pumped radiation source (PRS) can be pulsed. The input radiation IRD can include electromagnetic radiation at one or more frequencies between 200 nm and 2 µm. For example, the input radiation IRD can include electromagnetic radiation with a wavelength of 1.03 µm. The repetition rate of the pulsed radiation IRD can be on the order of 1 kHz to 100 MHz. The pulse energy can be on the order of 0.1 µJ to 100 µJ, for example, 1 µJ to 10 µJ. The pulse duration of the input radiation IRD can be between 10 fs and 10 ps, ​​for example, 300 fs. The average power of the input radiation IRD can be between 100 mW and several hundred W. For example, the average power of the input radiation IRD can be between 20 W and 50 W.

[0115] The pulsed pump source (PRS) can be a laser. By adjusting the (pump) laser parameters, the working component (WM) variation, and the fiber (OF) parameters, the spatiotemporal propagation characteristics (e.g., its spectral amplitude and phase) of this laser pulse propagating along the fiber (OF) can be altered and tuned. These spatiotemporal propagation characteristics can include one or more of the following: output power, output mode distribution, output time distribution, width of the output time distribution (or output pulse width), output spectral distribution, and bandwidth of the output spectral distribution (or output spectral bandwidth). The PRS parameters can include one or more of the following: pump wavelength, pump pulse energy, pump pulse width, and pump pulse repetition rate. The OF parameters can include one or more of the following: fiber length, size and shape of the hollow core (HC), size and shape of the capillary, and thickness of the capillary wall surrounding the hollow core (HC). The WM (e.g., filled gas) parameters can include one or more of the following: gas type, gas pressure, and gas temperature.

[0116] The broadband output radiation ORD provided by the radiation source RDS can have an average output power of at least 1W. The average output power can be at least 5W. The average output power can be at least 10W. The broadband output radiation ORD can be a pulsed broadband output radiation ORD. The power spectral density of the output radiation across the entire wavelength band of the broadband output radiation ORD can be at least 0.01mW / nm. The power spectral density of the broadband output radiation across the entire wavelength band can be at least 3mW / nm.

[0117] Figure 10 This is a flowchart of a known method for manufacturing hollow core PCF (HC-PCF). At step 1000, initial raw materials are obtained. These initial raw materials may include glass tubes having a length of, for example, about one meter or longer. At step 1005, at least some of these tubes may be drawn downwards to form capillaries. This step is illustrated in Figure 1032, which shows glass tubes 1035 being heated by a heat source or furnace (e.g., a graphite resistance furnace) 1045 to, for example, above 1000 degrees Celsius, above 1500 degrees Celsius, or to about 2000 degrees Celsius, and drawn into capillaries 1040. Each tube 1035 may have a diameter, for example, more than 1 cm, for example, between 1 cm and 3 cm. The outer diameter of the drawn capillary 1040 may be, for example, between 100 µm and 1500 µm or between 100 µm and 1000 µm.

[0118] At step 1010, the PCF preform can be assembled. According to an example method (so-called stacking and drawing technique), the drawn preform capillary 1040 is stacked together with spacers to form a stacked assembly. The stacked assembly can be inserted into a large sheath tube (e.g., having a diameter of several centimeters) to form the preform. The gap between the stacked assembly and the sheath tube can be filled with, for example, silica rods having various outer diameters. The outer diameter of the preform can be, for example, between 10 mm and 100 mm, and the length can be, for example, between 0.3 m and 2 m (e.g., about 1 m).

[0119] Figure 10 A cross-sectional image 1065 of the example preform is also shown. As shown, the example preform is formed by inserting a stacked assembly comprising seven (or other numbers) preform capillary tubes CAP-1 and other elements such as spacers (not shown) into the sheath tube JT. In some cases, the spacers may be in the form of rods or columns. In some cases, the spacers may be made of the same material as the preform capillary tubes.

[0120] According to another example method, instead of inserting the stack of prefabricated capillaries into the sheath tube JT, the prefabricated capillaries CAP-1 are inserted individually and sequentially into the sheath tube JT. In this example method, the sheath tube JT is held horizontally. Each of the prefabricated capillaries CAP-1 is inserted into the sheath tube JT via one of its ends. Once inserted, the prefabricated capillaries CAP-1 are located at the bottom of the sheath tube JT. The prefabricated capillaries CAP-1 are then secured to the inner wall of the sheath tube JT, for example, by welding or fusion. The sheath tube JT is then rotated by a predetermined angle (e.g., 60°) to allow the next prefabricated capillary CAP-1 to be inserted into the bottom of the sheath tube JT. This insertion, securing, and rotation process is repeated until all prefabricated capillaries are inserted and secured to the inner wall of the sheath tube JT.

[0121] At step 1015, a cane is drawn from the preform. This step is illustrated in Figure 1038, which shows the preform 1050, including the capillary 1040, being drawn into a cane 1055. The preform 1050 can be held at the top of a conventional fiber drawing tower (not shown), where the preform is fed downwards into a furnace 1045 to heat the lower section of the preform. The heated section of the preform softens and elongates, forming teardrop-shaped droplets that pull the fiber downwards (also known as dropping). Additional pulling and tension control is used to ensure that the preform is drawn into a cane 1055. Typically, a one-meter-long preform can be drawn into a cane 10m to 1000m long. This long cane is then cut into shorter pieces, each with a length, for example, between 0.5m and 2m (e.g., about 1m).

[0122] A cross-sectional image of an example billet drawn via step 1015 is also shown. The example billet comprises seven capillary tubes CAP-2 surrounding a hollow core HC-2 and supported by support portions SP-2. Although the example billet looks more like the final HC-PCF (or target HC-PCF), the billet is rigid, and its physical dimensions (e.g., capillary dimensions, support portion diameters) are larger than those of the final HC-PCF. At the end of step 1015, the billet may have an outer diameter, for example, between 0.5 mm and 10 mm, and the billet capillary tubes CAP-2 surrounding the hollow core HC may each have an outer diameter, for example, between 100 µm and 1500 µm or between 100 µm and 1000 µm, and a wall portion thickness, for example, between 1.5 µm and 100 µm.

[0123] The preform preparation step 1020 prepares a preform 1055 for the fiber drawing step 1025. This preform preparation step 1020 may include connecting a pressure tube to a preform capillary 1040'. In this way, the preform can be connected to a pressure supply for pressurizing the internal structure of the preform during the fiber drawing step 1025, so that each capillary expands in a desired and controlled manner.

[0124] The fiber drawing step 1025 is illustrated in Figure 1042. In this step, a blank 1055 is mounted in another drawing tower (e.g., suitably configured to draw HC-PCF) and heated within a furnace 1045. The blank 1055 is drawn into the final fiber or HC-PCF 1060, such that the HC-PCF 1060 comprises the target dimensions. Typically, a one-meter-long blank can be drawn into hundreds of meters of fiber in a continuous manner. In the final form of the HC-PCF, the outer diameter of the HC-PCF can be reduced to, for example, between 100µm and 300µm. By carefully tuning the relative pressure between different parts of the blank's internal structure (e.g., the capillary cavity CC and the hollow core HC), the blank capillaries CAP-2 are expanded, and thereby their outer diameter is increased relative to the inner diameter of the support portion SP-2. This effect is evident by comparing two cross-sectional images 1070 and 1075, where the drawn fiber shown in image 1075 has a higher ratio of the outer diameter of each capillary CAP-3 to the inner diameter of the support portion SP-3. At the end of step 1025, the outer diameter of the capillary CAP-3 can be increased, for example, to between 10 µm and 50 µm, and correspondingly, the thickness of the capillary wall portion WP can be reduced, for example, to between 0.05 µm and 0.2 µm. The positive pressure difference between each capillary cavity CC and the hollow core HC can range from 1 mbar to 1000 mbar.

[0125] Finally, step 1030 includes an optional rewinding step, for example, in which the drawn optical fiber 1060 is rewound from a larger spool to a smaller spool.

[0126] Figure 11 This is a flowchart of a method for manufacturing a hollow core PCF (HC-PCF) based on the concepts disclosed herein.

[0127] At step S1102, an intermediate product 202 for optical fiber manufacturing is provided. The techniques used to obtain the intermediate product 202 are outside the scope of this disclosure. However, it should be understood that the intermediate product 202 for optical fiber manufacturing can be obtained by performing the procedures described above. Figure 10 The optical fiber is prepared using steps 1000, 1005, 1010, and 1015 as described. The intermediate product 202 for optical fiber manufacturing includes a hollow core blank 102, such as... Figure 12As shown.

[0128] The hollow core blank 102 includes an elongated body that is longer in one dimension than the other two dimensions of the hollow core blank. This longer dimension (shown as the z-axis) may be referred to as the axial direction and may define the axis of the hollow core blank 102. The other two dimensions define planes that may be referred to as transverse planes. Figure 12 A cross-section of the hollow core blank 102 is shown in the transverse plane (i.e., perpendicular to the axis), which is labeled as the xy plane.

[0129] The hollow core blank 102 includes a first sheath 104 to which one or more capillaries 105 are fused. The first sheath 104 may include silica or soft glass (e.g., heavy metal oxides, fluorides, chalcogenides, borosilicates, etc.).

[0130] like Figure 12 As shown, one or more walls 112 define the hollow internal structure 110 of the hollow core blank rod 102. Figure 12 A hollow internal structure 110 with a hexagonal cross-section is shown; however, it should be understood that this is merely an example. In some embodiments, the hollow internal structure 110 has a cylindrical cross-section. In other embodiments, the hollow internal structure 110 has a non-cylindrical cross-section. For example, the hollow internal structure may have a polygonal cross-section (e.g., pentagonal, hexagonal, heptagonal, etc.).

[0131] The hollow core blank 102 may have an outer diameter (d) between, for example, 1 mm and 10 mm. cane The blank capillaries 105 surrounding the hollow internal structure 110 of the blank can each have an outer diameter, for example, between 100 μm and 1500 μm or between 100 μm and 1000 μm, and a wall portion thickness, for example, between 1.5 μm and 100 μm. One or more capillaries 105 include an intermediate horizontal (e.g., blank horizontal) dimension between the size of the capillaries in the preform from which the hollow core blank 102 is drawn and the size of the capillaries in the final HC-PCF. The hollow core blank 102 can have a length, for example, between 0.5 m and 2 m (e.g., about 1 m).

[0132] One or more capillaries 105 extend along the axis of the hollow core blank 102 from a first end of the hollow core blank 102 to an opposite second end. The one or more capillaries 105 may comprise silica or soft glass (e.g., heavy metal oxides, fluorides, chalcogenides, borosilicates, etc.). The diameter of the capillaries 105 (before drawing HC-PCF) may be 1 mm to 7 mm, optionally 1 mm to 5 mm. The capillaries 105 are hollow. The cross-section of the capillaries 105 may be circular, or may have another cross-sectional shape (e.g., an elliptical or polygonal cross-section).

[0133] like Figure 13 As shown, the intermediate product 202 for optical fiber manufacturing additionally includes a blank sheath 204 (referred to herein as a second sheath), in which the first sheath 104 and the capillary are fitted before being drawn into an optical fiber.

[0134] The billet sleeve 204 may comprise silica or soft glass (e.g., heavy metal oxides, fluorides, chalcogenides, borosilicates, etc.). The billet sleeve 202 may have an outer diameter (d) between, for example, 2 mm and 12 mm. canejacket This outer diameter corresponds to the diameter of the intermediate product 202 in optical fiber manufacturing. The blank sheath 204 has an outer surface 206.

[0135] exist Figure 12 and Figure 13 In the example, the hollow core blank 102 includes six capillaries; however, it should be understood that the embodiments of this disclosure are not limited thereto, and the hollow core blank 102 may include a number of capillaries other than six.

[0136] In step S1104, the outer surface 206 of the billet sleeve 204 is roughened on a portion 310 of the billet sleeve 204. Figure 14 The roughening portion 310 is illustrated in the figure. In the example method, the intermediate fiber manufacturing product 202 is held horizontally while roughening is performed; however, this is merely an example. The roughened portion may extend partially or completely around the circumference of the blank sheath 204.

[0137] One or more different techniques can be used to roughen part 310 of the billet sleeve 204.

[0138] In one embodiment, roughening the outer surface 206 of the billet sleeve 204 includes guiding fluid, comprising abrasive particles, toward said portion 310 of the billet sleeve 204. In some examples, the fluid comprises a gas. For example, compressed air can be used to propel abrasive particles toward the outer surface 206 of the billet sleeve 204 to form the roughened portion 310. In these examples, the abrasive particles may include sand particles. That is, roughening the outer surface 206 of the billet sleeve 204 may include sandblasting said portion 310. Sandblasting is a particularly effective method for roughening the outer surface 206 of the billet sleeve 204 using this readily available tool. It should be understood that additional types and / or alternative types of abrasive particles other than sand can be propelled by gas. In other examples, the fluid comprises a liquid. For example, water (or any other liquid) can be used to propel abrasive particles toward the outer surface 206 of the billet sleeve 204 to form the roughened portion 310.

[0139] Alternatively or additionally, roughening of the outer surface 206 of the billet sleeve 204 includes chemically etching the portion 310 of the billet sleeve 204. Specifically, a chemical etchant is directed and incident onto the portion 310 of the billet sleeve 204 to roughen the outer surface 206.

[0140] Alternatively or additionally, roughening of the outer surface 206 of the billet sheath 204 includes plasma etching of said portion 310 of the billet sheath 204. Specifically, said portion 310 of the billet sheath 204 is exposed to one or more reactive gases, which are then ionized to form plasma.

[0141] Alternatively or additionally, roughening the outer surface 206 of the billet sheath 204 includes directing radiation emitted from a radiation source to incident on said portion 310 of the billet sheath 204 to roughen the outer surface 206. The radiation source may be a laser. The radiation source may be a continuous wave source or a pulsed wave source (e.g., a pulsed laser source). For a continuous wave source, the radiation emitted from the radiation source may have wavelengths in the lower UV range (e.g., in the range of 10 nm to 200 nm) and wavelengths above the infrared range (e.g., greater than 1 mm) to couple the radiation into the billet sheath 204 and allow it to be absorbed. For a pulsed wave source, the entire spectrum from UV (e.g., approximately 355 nm) to infrared is available to couple the radiation into the billet sheath 204 and allow it to be absorbed. For example, an infrared CO2 far-infrared laser (with a wavelength of approximately 10600 nm) can be used.

[0142] Alternatively or additionally, roughening the outer surface 206 of the billet sleeve 204 includes applying an abrasive material to the portion 310 of the billet sleeve 204. That is, the abrasive material (e.g., abrasive paper) is physically brought into contact with the portion 310 and moved across the outer surface 206 of the portion 310 one or more times to roughen the outer surface 206 of the portion 310.

[0143] At step S1104, the outer surface 206 of the billet sleeve 204 may be roughened on the portion 310 of the billet sleeve 204 such that the portion 310 has a root mean square (RMS) height (Sq) defined by the ISO 25178 standard, in the range of 40 nm to 120 nm, optionally in the range of 60 nm to 100 nm.

[0144] At step S1104, the outer surface 206 of the billet sleeve 204 may be roughened on the portion 310 of the billet sleeve 204 such that the portion 310 has an arithmetic mean height (Sa) defined by the ISO 25178 standard, in the range of 25 nm to 105 nm, optionally in the range of 45 nm to 85 nm.

[0145] In step S1104, the outer surface 206 of the billet sleeve 204 may be roughened on the portion 310 of the billet sleeve 204 such that the portion 310 has a maximum height (Sz) defined by the ISO 25178 standard, in the range of 285 nm to 365 nm, optionally in the range of 305 nm to 345 nm. The maximum height (Sz) is the sum of the maximum peak height value and the maximum pit depth value within the region of the portion 310.

[0146] like Figure 14 As shown, the fiber optic manufacturing intermediate product 202 includes an elongated body that is longer in one dimension than the other two dimensions of the fiber optic manufacturing intermediate product 202. As described above, this longer dimension (shown as the z-axis) can be referred to as the axial direction and can define the axis of the fiber optic manufacturing intermediate product 202. The other two dimensions define planes that can be referred to as transverse planes. Figure 14 The length of the fiber manufacturing intermediate product 202 extending in the axial direction is shown.

[0147] The intermediate product 202 in optical fiber manufacturing has a first end 304 and a second end 306. For example... Figure 14 As shown, the hollow core blank 102 of the intermediate product 202 extends from a first end 304 to an opposite second end 306 within the intermediate product 202. It should be understood that... Figure 14Used to illustrate the concepts described herein and not to scale. As will be described later, the first end 304 is coupled to a pressure connector before the hollow core photonic crystal fiber is drawn from the fiber manufacturing intermediate 202.

[0148] In some embodiments, the roughened portion 310 of the blank sheath 204 is positioned closer to the first end 304 of the fiber manufacturing intermediate product 202 than to the opposite second end 306 of the fiber manufacturing intermediate product 202.

[0149] In some embodiments, the roughened portion 310 of the blank sheath 204 is positioned closer to the first end 304 of the fiber manufacturing intermediate product than the center of the axial length (length in the axial direction) of the fiber manufacturing intermediate product 202.

[0150] The axial length (d) of the roughened portion 310 of the billet sleeve 204 rough The length (d) of the roughened portion 310 of the billet sleeve 204 can be less than 10cm. rough The range of the diameter can be, for example, between 1 cm and 5 cm, and optionally between 2 cm and 4 cm. This is advantageously significantly smaller than the approximately 15 cm length of Teflon tape required in known technologies, and allows for more efficient coupling of thermal radiation away from the fiber manufacturing intermediate 202 during the drawing process due to the roughened portion 310.

[0151] In some embodiments, the roughened portion 310 extends from the first end 304 of the fiber manufacturing intermediate product 202 along the axial length of the fiber manufacturing intermediate product 202.

[0152] In other embodiments, the roughened portion 310 is separated from the first end 304 of the optical fiber manufacturing intermediate product 202 by another portion 308 of the blank sheath 204. This is in Figure 14 As shown in the diagram. The roughening performed in step S1104 is not applied to the other portion 308 (referred to herein as the "smooth" portion because roughening is not applied to this portion) or the rest of the billet sheath 204. That is, the roughening performed in step S1104 is applied only to said portion 310 of the billet sheath 204. Therefore, once step S1104 has been performed, said portion 310 has a rougher surface than all the rest of the outer surface 206 of the fiber manufacturing intermediate product 202. By roughening said portion 310, which is separated from the first end 304 of the fiber manufacturing intermediate product 202 by the other portion 308 of the billet sheath 204, this reduces the risk of damaging the fiber manufacturing intermediate product 202.

[0153] The axial length (d) of the smooth portion 308 of the billet sleeve 204smooth The range of ) can be, for example, between 5 cm and 15 cm, and optionally between 7 cm and 14 cm. Advantageously, this reduces the axial length (d) of the smooth portion 308. smooth This reduces the amount of fiber manufacturing intermediate 202 "lost" when drawing HC-PCF from the fiber manufacturing intermediate 202 (i.e., the amount that cannot be drawn into HC-PCF). Specifically, near the end of fiber drawing, when the roughened portion enters the furnace, the fiber structure and / or tension of this roughened portion changes due to the roughness, therefore this roughened portion cannot be drawn into a usable fiber with the target dimensions presented by the rest of the fiber. The smooth portion 308 extends beyond the roughened portion and therefore cannot be drawn into HC-PCF either.

[0154] In step S1106, the end of the intermediate fiber manufacturing product 202 is coupled to the pressure connector 402. Specifically, the first end 304 of the intermediate fiber manufacturing product 202 is coupled to the pressure connector 402. Therefore, the roughened portion 310 is arranged close to or adjacent to the pressure connector 402.

[0155] In an embodiment where the roughened portion 310 extends from the first end 304 of the fiber manufacturing intermediate product 202 along the axial length of the fiber manufacturing intermediate product 202, the pressure connector 402 is coupled (e.g., clamped) to the roughened portion 310.

[0156] In an embodiment where the roughened portion 310 is separated from the first end 304 of the fiber manufacturing intermediate 202 by the smooth portion 308, a pressure connector 402 is coupled (e.g., clamped) to the smooth portion 308. The pressure connector 402 may be clamped onto the smooth portion 308 by O-rings (or other forms of sealing devices). These O-rings within the pressure connector 402 are used to compress the smooth portion 308 to prevent the fiber manufacturing intermediate 202 from slipping. The roughened portion 310 is a damaged surface and is therefore generally more brittle and thus more fragile. By coupling (e.g., clamping) the pressure connector 402 to the smooth portion 308, any risk of breakage of the fiber manufacturing intermediate 202 when it is coupled to the pressure connector 402 at step S1106 is reduced.

[0157] The pressure connector 402 is used to pressurize the internal structure of the intermediate product 202 of optical fiber manufacturing during the optical fiber drawing step (described in more detail below) so that each of the capillaries 105 expands in a desired and controlled manner.

[0158] The pressure connector 402 can be used to pressurize (i) the hollow internal structure 110, (ii) each of one or more capillaries 105, and (iii) one or more spaces between the first sheath 104 and the billet sheath 204.

[0159] To prepare the intermediate product 202 for optical fiber manufacturing 202 for optical fiber drawing, a pressure capillary (see above reference) can be used. Figure 10 A pressurized capillary tube (referred to as a "pressure tube") is inserted into each of one or more capillaries 105 and the hollow internal structure 110 and sealed with adhesive. In these embodiments, when the fiber optic manufacturing intermediate 202 is coupled to the pressure connector 402, the pressurized capillary tube inserted into the hollow internal structure 110 can extend into the internal core pressure chamber of the pressure connector 402, which is in fluid communication with a first pressure connector 404 that allows pressure to be applied to and selectively controlled within the hollow internal structure 110. In these embodiments, when the fiber optic manufacturing intermediate 202 is coupled to the pressure connector 402, a pressurized capillary tube inserted into each of one or more capillaries 105 can extend into the internal capillary pressure chamber of the pressure connector 402, which is in fluid communication with a second pressure connector 406 that allows pressure to be applied to any space between the first sheath 104 and the blank sheath 204 and selectively controlled (e.g., for creating a vacuum). The pressure connector 402 may include an internal sheath pressure chamber in fluid communication with a third pressure connector 408, which allows pressure to be applied to one or more capillaries and to be selectively controlled.

[0160] In step S1108, HC-PCF is drawn from the optical fiber manufacturing intermediate product 202.

[0161] In step S1108, the intermediate fiber manufacturing product 202 is installed in a drawing tower (e.g., properly assembled for drawing HC-PCF) and heated in a furnace 410, which in Figure 15 As shown in the diagram. Furnace 410 can be maintained at a temperature of at least 1800°C, for example, at least 2000°C. The intermediate fiber manufacturing product 202 is drawn into HC-PCF such that the HC-PCF includes the target dimensions. Typically, a one-meter-long intermediate fiber manufacturing product 202 can be drawn into hundreds of meters of fiber in a continuous manner. In the final form of the HC-PCF, the outer diameter of the HC-PCF can be reduced to, for example, between 100 μm and 300 μm.

[0162] By carefully tuning the relative pressure between different parts of the internal structure of the intermediate product 202 in optical fiber manufacturing (e.g., the capillary lumen and the hollow core), the capillary 105 is expanded, thereby increasing its outer diameter. At the end of the optical fiber drawing process, the outer diameter of the capillary can be increased to, for example, between 10 µm and 50 µm, and correspondingly, the thickness of the capillary wall portion can be reduced to, for example, between 0.05 µm and 0.2 µm. The positive pressure difference between each capillary lumen and the hollow core can range from 1 mbar to 1000 mbar.

[0163] During step S1108, a pulling force (or tension τ) is applied when HC-PCF is drawn from the fiber manufacturing intermediate product 202. Therefore, HC-PCF is drawn from the fiber manufacturing intermediate product 202 while heat, pulling tension, and (multiple) controlled pressures are applied to it.

[0164] Finally, an optional rewinding step can be performed, for example, in which the drawn optical fiber is rewound from a larger spool to a smaller spool.

[0165] While specific references are made to the use of lithography equipment in IC manufacturing in this document, it should be understood that the lithography equipment described herein can have other applications. Possible other applications include manufacturing integrated optical systems, guiding and detecting patterns for magnetic domain memories, flat panel displays, liquid crystal displays (LCDs), thin-film magnetic heads, etc.

[0166] Other embodiments have been disclosed in the list of items numbered below: 1. A method for manufacturing a hollow-core photonic crystal fiber, the method comprising: Provide intermediate products for optical fiber manufacturing, the intermediate products for optical fiber manufacturing comprising: (i) a hollow core blank rod, the hollow core blank rod comprising a first sheath having a hollow internal structure, wherein a plurality of capillaries are fused to the first sheath within the hollow internal structure; and (ii) a second sheath surrounding the hollow core blank rod; Roughen the outer surface of the second sheath on a portion of the second sheath; Couple the end of the intermediate product in the optical fiber manufacturing process to a pressure connector; and Hollow-core photonic crystal fibers are drawn from the intermediate products of optical fiber manufacturing. 2. The method according to claim 1, wherein roughening the outer surface of the second sheath comprises: guiding fluid toward the portion of the second sheath, the fluid comprising abrasive particles. 3. The method according to clause 2, wherein the fluid comprises a gas. 4. The method according to clause 2, wherein the fluid comprises a liquid. 5. The method according to any one of clauses 2 to 4, wherein the abrasive particles comprise sand particles. 6. The method according to any one of the preceding clauses, wherein roughening the outer surface of the second sheath comprises: chemically etching said portion of the second sheath. 7. The method according to any one of the preceding clauses, wherein roughening the outer surface of the second sheath comprises: plasma etching of said portion of the second sheath. 8. The method according to any one of the preceding clauses, wherein roughening the outer surface of the second sheath comprises: directing radiation emitted from a radiation source to incident on said portion of the second sheath. 9. The method according to any one of the preceding clauses, wherein roughening the outer surface of the second sheath comprises: applying an abrasive material to said portion of the second sheath. 10. The method according to any one of the preceding clauses, wherein the portion of the second sheath is positioned closer to the end of the optical fiber manufacturing intermediate than the opposite end of the intermediate product. 11. The method according to any one of the preceding clauses, wherein the portion of the second sheath is positioned closer to the end of the optical fiber manufacturing intermediate product than the center of the axial length of the intermediate product. 12. The method according to any one of the preceding clauses, wherein the portion of the second sheath is separated from the end portion of the intermediate product of the optical fiber manufacturing via another portion of the second sheath. 13. The method according to clause 12, wherein the other portion of the second sheath has a length between 7 cm and 14 cm. 14. The method according to items 11 to 13, wherein the roughening is not performed on the other portion of the second sheath. 15. The method according to any one of the preceding clauses, wherein the portion of the second sheath has a length of less than 10 cm. 16. The method according to any one of the preceding clauses, wherein the portion of the second sheath has a length between 1 cm and 5 cm, and optionally a length between 2 cm and 4 cm. 17. The method according to any one of the preceding clauses, wherein heat, tension and pressure are applied to the intermediate product of optical fiber manufacturing during the drawing process. 18. The method according to any one of the preceding clauses, wherein the hollow internal structure of the hollow core blank has a polygonal cross-section. 19. The method according to clause 18, wherein the hollow internal structure of the hollow core blank has a hexagonal cross-section. 20. An intermediate product for manufacturing hollow core photonic crystal fibers, the intermediate product comprising: (i) a hollow core blank including a first sheath having a hollow internal structure, wherein a plurality of capillaries are fused to the first sheath within the hollow internal structure; and (ii) a second sheath surrounding the hollow core blank; wherein the outer surface of the second sheath includes a roughened portion.

[0167] Although embodiments of the invention may be specifically referred to herein in the context of lithography equipment, embodiments of the invention can be used in other equipment. Embodiments of the invention can be formed by mask inspection equipment, metrology equipment, or any equipment that measures or processes objects such as wafers (or other substrates) or masks (or other patterning apparatuses). These devices are generally referred to as lithography tools. Such lithography tools can use vacuum conditions or ambient (non-vacuum) conditions.

[0168] Although the use of embodiments of the invention may have been specifically referenced above in the context of optical lithography, it should be understood that the invention is not limited to optical lithography and may be used in other applications, such as imprint lithography, where the context permits.

[0169] Although specific embodiments of the invention have been described above, it should be understood that the invention can be practiced in ways other than those described. The above description is intended to be illustrative and not restrictive. Therefore, it will be apparent to those skilled in the art that modifications can be made to the described invention without departing from the scope of the claims set forth below.

Claims

1. A method for manufacturing a hollow-core photonic crystal fiber, the method comprising: Provide intermediate products for optical fiber manufacturing, the intermediate products for optical fiber manufacturing comprising: (i) a hollow core blank rod, the hollow core blank rod comprising a first sheath having a hollow internal structure, wherein a plurality of capillaries are fused to the first sheath within the hollow internal structure; and (ii) a second sheath surrounding the hollow core blank rod; Roughen the outer surface of the second sheath on a portion of the second sheath; Couple the end of the intermediate product in the optical fiber manufacturing process to a pressure connector; and Hollow-core photonic crystal fibers are drawn from the intermediate products of optical fiber manufacturing.

2. The method according to claim 1, wherein, Roughening the outer surface of the second sheath includes guiding fluid toward the portion of the second sheath, the fluid comprising abrasive particles.

3. The method according to claim 2, wherein, The fluid includes gas.

4. The method according to claim 2, wherein, The fluid includes liquids.

5. The method according to any one of claims 2 to 4, wherein, The abrasive particles include sand particles.

6. The method according to any one of the preceding claims, wherein, Roughening the outer surface of the second sheath includes chemically etching the portion of the second sheath.

7. The method according to any one of the preceding claims, wherein, Roughening the outer surface of the second sheath includes plasma etching of the portion of the second sheath.

8. The method according to any one of the preceding claims, wherein, Roughening the outer surface of the second sheath includes guiding radiation emitted from the radiation source to strike said portion of the second sheath.

9. The method according to any one of the preceding claims, wherein, Roughening the outer surface of the second sheath includes applying an abrasive material to the portion of the second sheath.

10. The method according to any one of the preceding claims, wherein, The portion of the second sheath is positioned closer to the end of the optical fiber manufacturing intermediate than the opposite end of the intermediate product.

11. The method according to any one of the preceding claims, wherein, The portion of the second sheath is positioned closer to the end of the optical fiber manufacturing intermediate product than the center of the axial length of the intermediate product.

12. The method according to any one of the preceding claims, wherein, The portion of the second sheath separates from the end portion of the intermediate product in the optical fiber manufacturing process through another portion of the second sheath.

13. The method according to claim 12, wherein, The other portion of the second sheath has a length between 7 cm and 14 cm.

14. The method according to any one of the preceding claims, wherein, During the drawing process, heat, tension, and pressure are applied to the intermediate products used in optical fiber manufacturing.

15. An intermediate product for manufacturing hollow core photonic crystal fibers, the intermediate product comprising: (i) A hollow core blank rod, the hollow core blank rod including a first sheath having a hollow internal structure, wherein a plurality of capillaries are fused to the first sheath within the hollow internal structure; and (ii) a second sheath surrounding the hollow core blank rod; The outer surface of the second sheath includes a roughened portion.

Images