Fiber configuration, optical system, and method of operating the optical system

Abstract

1. A fiber arrangement, in particular a fiber arrangement for providing broadband light, preferably in the ultraviolet frequency range, comprising a hollow core optical fiber (11) and one or more housings (15) having a chamber (27) in which a piezoelectric device (25) is arranged, the piezoelectric device (25) having a variable length, the chamber (27) being in fluid communication with the hollow core (13) of the fiber (11) such that a change in length of the piezoelectric device (25) causes a change in the size of the hollow core (13) and a volume (23) that the chamber (27) provides for a fluid, such as a gas or a mixture of gases.

Description

Technical Field

[0001] The present disclosure relates to a fiber arrangement, particularly a fiber arrangement for providing broadband light, preferably a fiber arrangement for providing broadband light in the ultraviolet frequency range, an optical system, and a method for operating the optical system.

Background Art

[0002] Hollow-core optical fibers can be employed to convert input radiation into broadband radiation. The hollow core of such an optical fiber can be filled with a fluid, particularly a gas. For example, a fluid-filled hollow-core fiber can be used to generate broadband light pulses in the ultraviolet frequency range from the input of suitable laser pulses into the hollow core of the fiber. The output broadband light pulses can, for example, have a spectral width between about 25 nm and about 125 nm, and a center wavelength between about 375 nm and about 240 nm. The width of a broadband pulse typically becomes narrower as the center wavelength of the broadband pulse decreases. The position of the center wavelength of the broadband output pulse depends on the pressure of the fluid in the hollow core. The center wavelength of the broadband output pulse typically increases as the pressure of the fluid in the core increases. Therefore, a plurality of broadband output pulses having various center wavelengths can be generated using various pressures for the fluid in the core, and these broadband output pulses can cover a wide spectral range in the ultraviolet region having wavelengths, for example, between 225 nm and 450 nm. It may be desirable to rapidly vary the spectrum provided by the broadband output pulses. Furthermore, it may be desirable to be able to rapidly sweep across the wide spectral range covered by such a plurality of broadband output pulses.

Summary of Invention

Problems to be Solved by the Invention

[0003] Therefore, an object of the present invention is to provide a fiber configuration that can provide laser light pulses (particularly broadband light pulses), and for example, enables rapid sweeping over a wide spectral range. [Means for solving the problem]

[0004] This objective is achieved by a fiber configuration according to the features of claim 1. Preferred embodiments of the present invention are described in the dependent claims. In some embodiments, a fiber configuration, particularly a fiber configuration for providing broadband light, preferably in the ultraviolet frequency range, comprises a hollow-core optical fiber and one or more housings having a chamber in which a piezoelectric device is located, wherein the piezoelectric device has a variable length, and the chamber is in fluid communication with the hollow core of the fiber such that a change in the length of the piezoelectric device causes a change in the size of the volume that the hollow core and the chamber provide for a fluid such as a gas or a mixture of gases.

[0005] Piezoelectric devices allow for changes in the size of the volume provided for the fluid in the hollow core and chamber of the fiber, thus allowing the fluid pressure to change accordingly. In particular, the ideal gas law P=nRT / V (where P is pressure, n is the number of moles, R is the gas constant, T is the Kelvin temperature, and V is the volume) shows that pressure is inversely proportional to volume. Therefore, a decrease in the volume available for the fluid in the hollow core and chamber leads to an increase in pressure, while an increase in volume leads to a decrease in pressure.

[0006] The change in volume is obtained from the change in the length of the piezoelectric device. The length of the piezoelectric device can be changed very rapidly (e.g., on the order of approximately 10 kHz). Furthermore, piezoelectric devices typically offer long-term reliability. This allows, for example, the spectrum of a broadband output pulse obtained by inputting a laser pulse into a fluid-filled hollow core fiber to change rapidly with high reproducibility depending on the length of the piezoelectric device.

[0007] Piezoelectric devices can contain or be formed from piezoelectric materials. Piezoelectric materials can change their length in response to electrical signals supplied to them. Such piezoelectric materials themselves are known in the prior art.

[0008] The housing allows for the hermetically sealed containment of the piezo device within the chamber, ensuring that the fluid communication between the chamber and the hollow core is airtight to the environment. The housing may be provided with a through-hole having an opening at the first axial end of the housing and an opening at the second axial end of the housing, and the fiber may be inserted into the through-hole. The through-hole may accommodate the fiber, and the chamber may be in fluid communication with the through-hole. The through-hole may hermetically seal the fiber. The diameter of the through-hole may correspond to the outer diameter of the fiber or be slightly larger than the outer diameter of the fiber.

[0009] In some embodiments, the housing is a ferrule attached to the fiber, the ferrule comprising a tubular body providing the through-hole into which the fiber is inserted. The ferrule can be easily secured to the fiber, particularly airtightly.

[0010] Furthermore, according to this disclosure, in these embodiments where the housing is a ferrule and the housing is generally a housing (such as a cell or chamber), the piezo device is located in the housing. This may mean that when the piezo device is operating and its length changes, then the length of the fiber also changes. In other words, this disclosure provides control of the volume of fluid inside the fiber by controlling the length of the fiber by controlling the volume and / or length of the housing using a piezo device located in the housing. Such particular configuration ensures not only rapid changes in the gas pressure but also very precise control of the gas pressure. Thus, this disclosure provides a solution for rapidly and accurately controlling the pressure inside a fiber, in particular, so that broadband optical pulses can be generated very efficiently.

[0011] Prior art, such as European Patent Application Publication No. 3705942, typically controls the pressure inside a fiber by directly controlling the pressure. While the laws of ideal gases are well known in this field, indirectly controlling the pressure in a fiber by controlling its volume has never been done before, as directly controlling the pressure in the fiber is the most obvious and simplest method. Furthermore, when the pressure in the fiber is controlled by adjusting the pressure (especially to high pressures as in European Patent Application Publication No. 3705942) and / or adjusting the temperature, the housing for the fiber is made very robust to volume changes and is therefore configured to withstand changes in volume. In other words, in the prior art concerning fluid pressure control in a fiber, particularly for the generation of broadband optical pulses, changing the volume of the housing for the fiber is not an option.

[0012] This disclosure now provides new insights into the field of controlling pressure in a fiber, particularly for the generation of broadband optical pulses, using a housing configured to vary its volume.

[0013] A ferrule, as described above, is an embodiment of a housing. Ferrules are known in the field of optical fibers and are therefore known as optical fiber ferrules. An optical fiber ferrule is a mechanical fixture, generally a rigid tube, that can be configured to enclose the stripped end of a fiber or fiber bundle. Optical fiber ferrules can be configured to align and / or polish the optical fiber, for example, to prevent scattering and attenuation of the optical signal. Most optical fiber ferrules are made of metal, such as stainless steel, ceramic, such as alumina or zirconia, or plastic materials. Optical fiber ferrules made of borosilicate glass and glass are also available. Most optical fiber ferrules are manufactured using a direct-draw or redraw process and cut to a predetermined length using a diamond saw blade. To prevent problems such as splice loss and end gaps, these optical fiber ferrules have a hole formed through the center with a diameter slightly larger than the diameter of the fiber cladding. The entry end is then blown, acid etched, or countersunk by drilling.

[0014] In embodiments where the housing is a ferrule, particularly an optical fiber ferrule as described above, the ferrule can serve both to confine the stripped end of the fiber and to control the pressure in the fiber. The pressure in the fiber is controlled via the ferrule and the piezoelectric device, as previously stated. In one embodiment, the ferrule is an optical fiber ferrule configured to hold and center the fiber, and the piezoelectric device is positioned in the ferrule such that the volume of the fiber is controlled via the piezoelectric device and the optical fiber ferrule. In such embodiments, the material of the ferrule can determine its response to volume changes, such as those set by the piezoelectric device. The use of an optical fiber ferrule in combination with a piezoelectric device enables a compact design that can both hold the fiber and fluid and control the pressure of the fluid in the fiber. When the piezoelectric device is positioned in the optical fiber ferrule, the length of the fiber can be controlled with great precision. Thus, the volume inside the fiber, and therefore the pressure, can be controlled with great precision and speed.

[0015] In some embodiments, the housing, in particular the ferrule, is attached to one end of the fiber, or, with respect to at least two housings, in particular the ferrule, one housing is attached to one end of the fiber and the other housing is attached to the other end of the fiber.

[0016] The optical window can close the opening of the through-hole at the first axial end of each housing, and one fiber end can be inserted into the second axial end of the through-hole in the housing. The housing can be used in conjunction with the optical window to seal one end of the fiber.

[0017] The chamber can have an annular shape and can extend circumferentially around the through-hole of the housing. Therefore, a compact configuration can be obtained.

[0018] The chamber may have a central axis positioned parallel to or at an angle to the central axis of the through-hole in the housing. The central axis of the chamber can determine the direction in which the piezo device can change its length. The direction in which the piezo device can extend its length may be, for example, at a 90° angle with respect to the central axis of the through-hole, and therefore the central axis of the fiber.

[0019] The chamber can be sized to appropriately accommodate the piezo device. The configuration of the chamber can correspond to the configuration of the piezo device, and the dimensions of the chamber can correspond at least approximately to the dimensions of the piezo device.

[0020] In some embodiments, a filler, particularly an airtight filler, a filler made of a deformable material, or both, is placed between the outer surface of the piezo device and the inner surface of the chamber. The piezo device can be buffered in the filler, and the filler can compensate for the decrease in the outer diameter of the piezo device while its length is extended. The filler can seal the area between the outer surface of the piezo device and the inner surface of the chamber.

[0021] In some embodiments, at the maximum extension position of the piezo device, the piezo device extends across the entire length of the chamber in which the piezo device is located.

[0022] In some embodiments, one or more fluid channels extend radially through the housing to fluidly connect the chamber to the through-hole provided in the housing.

[0023] In some embodiments, several fluid channels are arranged at equal intervals around the periphery of the through-hole of the housing. The number can be any number such as 2, 3, 4, 5, 6, etc.

[0024] In some embodiments, four fluid channels are arranged circumferentially around the through-hole, offset by 90° each. In some embodiments, the fiber arrangement is an airtight arrangement.

[0025] The fiber can be an anti-resonant hollow-core fiber or a hollow-core photonic bandgap fiber. In some embodiments, the present invention relates to a fiber arrangement, the fiber arrangement comprising a hollow-core optical fiber and one or more ferrules attached to the fiber. The ferrule comprises a tubular body that provides a through-hole into which the fiber is inserted. The ferrule and the hollow core provide a volume for a fluid such as a gas or a mixture of gases, and a piezo device having a variable length is arranged in the ferrule such that a change in the length of the piezo device causes a change in the size of the volume available for the fluid.

[0026] In some embodiments, the ferrule is attached to one end of the fiber, an optical window is disposed on the first axial end of the ferrule, and one fiber end is inserted into the second axial end of the tubular body. The ferrule is capable of hermetically sealing one fiber end. The optical window can function to couple radiation into the hollow fiber or output broadband radiation from the fiber, depending on whether the ferrule is attached to the input end or the output end of the fiber. Preferably, the fiber arrangement comprises at least two ferrules, one ferrule attached to the input end of the fiber and the other ferrule attached to the output end of the fiber.

[0027] One or more ferrules can be positioned in the middle portion of the fiber. The middle portion of the fiber is the portion of the fiber that is not at the fiber end. Thus, the fiber can protrude through the tubular body of the ferrule. In some embodiments, multiple ferrules are positioned on the middle portion of the fiber, for example, at regular intervals. One or more ferrules positioned on the middle portion of the fiber can help provide a uniform pressure distribution within the hollow core of the fiber, or can help provide a desired pressure gradient along the length of the hollow core of the fiber.

[0028] In some embodiments, the piezo device is housed in a chamber within a ferrule, which is in fluid communication with the interior of a tubular body and a hollow fiber. The ferrule can function as a storage location for housing the piezo device. Electrical wires for supplying electrical signals to the piezo device can be routed out of the ferrule, particularly in an airtight manner.

[0029] In some embodiments, the chamber has an annular shape and is circumferentially arranged around the tubular body of the ferrule. The piezo device may also have a ring shape and can be designed to be fitted into the annular chamber. The central axis of the annular chamber can correspond at least substantially to the central axis of the fiber.

[0030] In some embodiments, the chamber can have a cylindrical shape. When the ferrule is attached to the fiber, the central axis of the cylindrical chamber can be positioned parallel to or at an angle (e.g., 90°) to the central axis of the hollow fiber.

[0031] In some embodiments, the chamber is sized to accommodate the piezo device appropriately. Therefore, the chamber can have a configuration that can accommodate the external shape of the piezo device.

[0032] In some embodiments, a filler, particularly an airtight filler, a filler made of a deformable material, or both, is placed between the outer surface of the piezoelectric device and the inner surface of the chamber. The piezoelectric device can be buffered in the filler. The filler can compensate for the decrease in the outer diameter of the piezoelectric device while its length is being extended. The filler can particularly seal the region between the outer surface of the piezoelectric element and the inner surface of the chamber facing the outer surface of the piezoelectric element. This prevents fluid from flowing into the space that may be available for the extension of the piezoelectric device's length, thus allowing the outer diameter of the piezoelectric element to decrease in the region between the outer surface of the piezoelectric element and the inner surface of the chamber. Rather, the piezoelectric device can function as a piston capable of pushing fluid out of the chamber when its length is being extended.

[0033] In some embodiments, the length of the piezo device can be varied between a maximum extension position and a minimum extension position. Correspondingly, the volume can be varied between a minimum volume when the piezo device is in its maximum extension position and a maximum volume when the piezo device is in its minimum extension position.

[0034] In some embodiments, at its maximum extension position, the piezo device can extend along the entire length of the chamber in which it is located. In some embodiments, one or more fluid channels extend radially through the tubular body, fluidly connecting the chamber to the interior of the tubular body. In some embodiments, several fluid channels are arranged at equal intervals around the periphery of the tubular body. The number of fluid channels can be any number, such as 2, 3, 4, 5, etc. In some embodiments, four fluid channels are arranged circumferentially, offset by 90° each.

[0035] This disclosure also relates to optical systems, optical systems for providing optical pulses (such as broadband optical pulses). The optical system comprises a fiber configuration according to the present invention, a pulsed laser source for providing laser pulses to the fiber configuration, and one or more piezo drivers for driving the piezo devices located in one or more housings (particularly ferrules) of the fiber configuration.

[0036] In some embodiments, the one or more piezo drive units are configured to drive the one or more piezo devices in accordance with the pulse repetition rate of the laser pulses. In some embodiments, the fiber configuration comprises two or more housings, particularly ferrules, arranged at a certain distance from each other along the fiber, and one or more piezo drivers are configured to drive the piezo devices in the two or more housings (particularly ferrules) to generate a desired pressure distribution in the hollow core of the fiber. In particular, it is possible to generate a uniform pressure distribution or pressure gradient along the length of the hollow core of the fiber.

[0037] In some embodiments, the fiber configuration comprises one or more housings, particularly ferrules, at each fiber end, and optionally, one or more housings, particularly ferrules, on the intermediate portion of the fiber.

[0038] This disclosure also relates to a method for generating optical pulses, particularly broadband optical pulses, and especially broadband optical pulses in the ultraviolet frequency range, using an optical system according to the present invention. In some embodiments, the method comprises an input step of inputting a laser pulse into the fiber configuration to generate an optical pulse, particularly a broadband optical pulse, output by the fiber configuration; and, during the input step, controlling one or more piezo devices located in one or more housings (particularly ferrules) to generate the optical pulse having a desired frequency spectrum, or to generate the pulses such that different pulses contain different frequency spectra. The generated pulses can be particularly broadband optical pulses. One or more piezo devices make it possible to control the fluid pressure distribution in the hollow core of the fiber. As a result, the spectral range covered by the generated broadband output pulse can be controlled depending on the length of one or more piezo devices. One or more piezo devices can be particularly controlled so that the generated output pulse covers a desired spectral range. In other embodiments, one or more piezo devices can be controlled so that the pulses of a series of broadband output pulses are swept over a larger spectral range.

[0039] The generated output pulse can have wavelengths in the ultraviolet wavelength region (e.g., less than 380 nm). The present invention also relates to fiber configurations, particularly fiber configurations for providing optical pulses (such as broadband optical pulses), preferably in the ultraviolet frequency range. The fiber configuration comprises a hollow-core optical fiber having a hollow core and a volume for a fluid (such as a gas or a mixture of gases), and a variable-length piezoelectric device arranged such that a change in the length of the piezoelectric device causes a change in the density or pressure of the fluid in the volume of the fluid.

[0040] The apparatus and methods described can be employed to tune nonlinear effects that may occur in hollow fibers and depend on the fluid pressure in the hollow core. Thus, a piezoelectric device can change or adjust the fluid density in the hollow core of the fiber, thereby influencing any nonlinear effects that depend on the fluid density, and can be used accordingly to generate optical pulses in the fiber.

[0041] Preferred embodiments of the present invention can be described by reference to the accompanying drawings, merely as examples. [Brief explanation of the drawing]

[0042] [Figure 1] A schematic cross-sectional view of a fiber configuration known from prior art. [Figure 2] A schematic cross-sectional view of one embodiment of the fiber configuration according to the present invention. [Figure 3] Schematic cross-sectional view of the fiber configuration shown in Figure 2. [Figure 4] Figure 2 shows a further schematic cross-sectional view of the fiber configuration. [Figure 5] A schematic cross-sectional view of a further embodiment of the fiber configuration according to the present invention. [Figure 6] A schematic cross-sectional view of a further embodiment of the fiber configuration. [Figure 7] A schematic cross-sectional view of a further embodiment of the fiber configuration according to the present invention. [Figure 8] A schematic diagram illustrating an optical system according to the present invention. [Modes for carrying out the invention]

[0043] The fiber configuration shown in Figure 1 comprises an optical fiber 11 having a hollow core 13. The core 13 extends along the length of the fiber, forming the central portion of the fiber 11. The core 13 is surrounded by one or more cladding layers of the fiber. Since the core 13 is hollow, it can be filled with a fluid (e.g., a gas or a mixture of gases).

[0044] The fiber configuration 11 comprises a housing 15, which in the described example is a ferrule. The ferrule 15 has a tubular body 17 that provides a through-hole for inserting the fiber 11. The through-hole of the tubular body 17 is open at one axial end. One end of the fiber 11 is inserted into the open end of the through-hole of the tubular body 17, as shown in Figure 1. The other axial end of the through-hole in the ferrule 15 is closed using an optical window 19, which can function as an incident window for laser pulses input into the optical fiber 11.

[0045] Furthermore, the housing can be another element other than the ferrule; for example, it can be a material block (not shown) that provides a chamber for the piezo device and a through-hole for inserting the fiber 11.

[0046] The optical cone 21 of the focused laser pulse is shown in Figure 1. The fiber end of fiber 11 is away from the optical window 19. Therefore, even within the length of the ferrule 15, the laser pulse can be focused to a cross-sectional spot size smaller than the diameter of the fiber core 13. This makes it possible to avoid ablation of the cladding material of fiber 11. A typical cladding material is silica. The ablation threshold for the silica surface is typically about 3 J / mc² for femtosecond pulses. 2 An example value for the diameter of the fiber core 13 is 27 μm.

[0047] A corresponding ferrule 15 can be positioned at the opposite end of the fiber 11 (not shown), and the optical window 19 of such ferrule can function as an output window for broadband optical pulses generated in the fiber 11 from the input laser pulse. Both ferrules (i.e., ferrule 15 at the first fiber end and the other ferrule at the second fiber end) can hermetically close the fiber ends.

[0048] The volume 23 provided inside the tubular body 17 of the ferrule 15 and in the hollow core 13 can be filled with a fluid such as a gas or a mixture of gases. The fluid can interact with the input laser pulse to form broadband optical pulses or even supercontinuous optical pulses, for example, through a nonlinear process that occurs during the interaction between the input optical pulse and the fluid.

[0049] Figures 2 to 4 show one embodiment of a fiber configuration according to the present invention. The fiber configuration comprises a piezo device 25 located in a ferrule 15. More specifically, the piezo device 25 is located in a chamber 27 of the ferrule 15. The chamber 27 is in fluid communication with the inside of the tubular body 17 and the core 13 of the hollow fiber 11.

[0050] In the embodiments shown in Figures 2 to 4, one or more fluid channels 29 extend radially through the tubular body 17 from the chamber 27 into the interior of the tubular body 17. Thus, the volume available for the fluid is expanded by the volume of the chamber 27.

[0051] As shown in Figure 4, in the embodiment described, four fluid channels 29 are arranged offset by 90° with respect to the circumferential direction C, extending radially through the tubular body 17, and providing fluid connections between the chamber 27, the interior of the tubular body 17, and the hollow core 13.

[0052] As shown in Figures 2 and 3, the length of the piezoelectric device 25 is variable. A change in the length of the piezoelectric device 25 causes a change in the size of the volume available for the fluid. As a result, the pressure of the fluid in volume 23 can be varied depending on the length of the piezoelectric device 25, for example, as is evident from the law of ideal gases.

[0053] In the embodiments shown in Figures 2 to 4, the chamber 27 is located in a housing section 31 that has an annular shape and extends in the circumferential direction C around the tubular body 17 of the ferrule 15. The housing section 31 and the tubular body 17 preferably form a single piece. Furthermore, preferably, the chamber 27 is sized such that the piezo device 25 is properly accommodated within the chamber 27. Thus, the piezo device 25 can fill the chamber 27. In particular, as shown in Figure 3, when the piezo device 25 reaches its maximum extension position, the piezo device 25 extends along the entire length of the chamber 27.

[0054] The piezo device can have, for example, an outer diameter of 8 mm, an inner diameter of 4 mm, and an axial length of 36 mm. The axial length can be varied by 25 μm using modulation up to a resonant frequency of 40 kHz. Such an actuator can have a 0.9 mm 3 It is possible to adjust the volume up to a certain point.

[0055] In some embodiments, two or more of these piezo devices 25 can be arranged in series behind each other and placed in the same chamber 27, thereby enabling even greater volume adjustment.

[0056] The fiber configuration embodiment shown in Figure 5 differs from the embodiments described in Figures 2 to 4 in that the piezo device 25 comprises a piezo element 33 having an annular shape and an end plate 35 fixed to one end of the piezo element 33, as shown in Figure 5. The end plate 35 faces the volume 23 available for the fluid in the chamber 27. The end plate 35 has an annular shape. The cross-sectional size of the end plate 35, when viewed radially, is approximately equivalent to the cross-sectional size of the chamber 27.

[0057] The piezoelectric element 33 can be controlled, in particular by using a piezoelectric controller (not shown in Figure 5) connected to the piezoelectric element 33, so that its axial length can be extended or retracted. The piezoelectric element 33 and the end plate 35 can function as a piston that can push fluid out of the chamber 27 when the piezoelectric element 35 is extended, or draw fluid into the chamber 27 when the piezoelectric element 35 is retracted.

[0058] The packing material 37 is positioned between the outer surface 39 of the piezoelectric element 33 and the inner surface 41 of the housing section 31. In the embodiment shown in Figure 5, the inner surface 41 is the surface of a guide ring 43 that supports the piezoelectric element 33. The guide ring 43 is arranged concentrically on the radially inner and radially outer sides of the piezoelectric element 33, allowing it to hold the piezoelectric element 33 and the packing material 37 in place and to support changes in the length of the piezoelectric element 33.

[0059] The filler 37 can also extend between the radial outer surface of the end plate 35 and the opposing inner surfaces of the housing section 31. The filler 37 can be made of a deformable material. The filler 37 can seal the chamber 27 in the space occupied by the piezo device 25 in the housing section 31. In particular, the filler 37 can form a seal in the region between the radial outer surface of the end plate 35 and the inner surface of the housing section 31.

[0060] Referring again to the embodiments in Figures 2 to 4, it is also possible to include a filler 37 between the radially outer inner surface of the piezo device 25 and the opposing surfaces of the housing section 31 and the tubular body 17. The filler functions as an airtight seal and can compensate for the reduction in the width of the piezo device 25 caused by the lengthening of the piezo device 25.

[0061] In the fiber configuration of Figure 6, the piezo device 25 is located in a chamber 27 provided by a housing section 31 positioned outside the tubular body 17. The central axis B of the housing 31 extends at a 90° angle with respect to the central axis A of the tubular body 17 and the hollow fiber 11 of the ferrule 15. The housing section 31 can have any shape (e.g., cylindrical, square, or rectangular).

[0062] A filler 37 is placed between the inner surface of the housing section 31 and the piezo device 25. The filler 37 is made of a flexible material and can also function as a seal. The volume 23 can extend into the chamber 27 so that the material of the tubular body 17 covered by the housing section 31 is completely removed. In other words, the fluid channel through the tubular body 17 is formed by a considerably large side wall in the tubular body 17, which has a cross-sectional area approximately corresponding to the cross-sectional area of ​​the chamber 27.

[0063] The fiber configuration shown in Figure 7 is based on the design of the embodiments shown in Figures 2 to 4. However, the ferrule 15 in the fiber configuration of Figure 7 does not have an optical window 19. Instead, both ends of the tubular body 17 are open ends, and the fiber 11 protrudes through the tubular body 17. In other words, the ferrule 15 is positioned in the middle portion of the fiber 11, and the fluid channel 29 extends radially through the tubular body 17 and the fiber 11, fluidly connecting the chamber 27 and the hollow core 13 of the fiber 11.

[0064] Depending on the length of the fiber 11, multiple ferrules 15 can be placed on the fiber 11 (not shown). For example, the ferrules 15 can be placed on the fiber 11 at regular intervals.

[0065] Figure 8 schematically shows an optical system for providing broadband light (particularly supercontinuum light), which comprises a pulsed laser source 45 for supplying laser pulses to a fiber configuration 47 and a piezoelectric drive 49.

[0066] As described above, the fiber configuration 47 includes an optical fiber 11 having a hollow core 13. As shown in Figure 8, a ferrule 15a is located at the first end of the fiber 11, and a ferrule 15b is located at the second end of the fiber 11. Ferrules 15a and 15b can particularly correspond to the ferrules described above with respect to Figures 2 to 6. Optionally, the fiber configuration may further include a ferrule 15c located in the middle portion of the fiber 11. Ferrule 15c can particularly correspond to a ferrule 15 as described with respect to Figure 7.

[0067] The piezo drive unit 19 is connected to the piezo devices 25 (see Figures 2 to 7) in the ferrules 15a, 15b, and 15c, and is configured to drive each piezo device 25 individually.

[0068] During operation, for example, the piezo drive 49 can drive the piezo devices 25 in phase. Then, all the piezo devices 25 reach their maximum and minimum extension lengths simultaneously. In another example, the piezo devices 25 are operating in different phases. Different piezo devices 25 therefore reach their maximum extension lengths at different times.

[0069] Furthermore, in some embodiments, each piezo device 25 can be controlled so that its length changes over time according to a predetermined profile. This is particularly possible because each piezo device 25 can be controlled individually.

[0070] In some embodiments, the piezo device 25 is controlled so that a desired uniform pressure distribution is obtained along the length of the hollow core 13 of the fiber 11. In other embodiments, the piezo device 25 is controlled so that a desired pressure gradient is obtained along the length of the hollow core 13 of the fiber 11.

[0071] In one embodiment, the length change of the piezoelectric device can be adjusted to a steady frequency over a period of time. In one such embodiment, a pulsed laser is focused in a hollow fiber, and the pulses of the laser reach a second steady frequency at the same time interval. In one such embodiment, the frequency of the piezoelectric modulation corresponds to the frequency of the laser pulse or an integer fraction of the frequency of the laser pulse (e.g., 1 / 2, 1 / 3, 1 / 4...1 / n). In one such embodiment, it is possible to further control the delay or phase shift between the frequency of the laser pulse and the frequency of the piezoelectric modulation.

[0072] In some embodiments, the entire sealed volume, essentially formed by the fiber core 13, the volume 23, and the volume of the chamber 27, can be changed by approximately three times by changing the length of the piezo device 25. This, in turn, can change the fluid pressure and density by approximately three times.

[0073] In some embodiments, the change in fluid density or pressure is greater than 50%, 60%, 70%, 80%, or 90%. In some embodiments, the change in fluid density or pressure is greater than 10%, for example greater than 20%, for example greater than 25%, for example greater than 30%, for example greater than 40%, for example greater than 50%, for example greater than 75%, for example a coefficient or 1:2, for example a coefficient or 1:3, for example a coefficient or 1:4, for example a coefficient or 1:5, for example a coefficient or 1:7.5, for example a coefficient or 1:10.

[0074] Reference Code List 11 Optical Fiber 13 Hollow core 15 ferrules, housings 15a ferrule 15b ferrule 15c ferrule 17 Tubular body 19 Optical window 21 Light cone 23 Volume 25 Piezo devices 27 Chambers 29 Fluid Channels 31 Housing Section 33 Piezo elements 35 End plate 37 Filling 39 Exterior 41 Inner self 43 Guide Ring 45. Pulse laser source 47 Fiber Configuration 49 Piezoelectric drive A center axis B Center axis C circumferential direction

Claims

1. Fiber configuration, A hollow core optical fiber (11) and The invention comprises one or more housings (15) having a chamber (27) in which a piezo device (25) is located, wherein the piezo device (25) has a variable length, and the chamber (27) is in fluid communication with the hollow core (13) of the fiber (11) such that a change in the length of the piezo device (25) causes a change in the size of the hollow core (13) and the fluid volume (23) that the chamber (27) provides for a fluid such as a gas or a mixture of gases. The housing (15) hermetically seals the end of the fiber (11), A fiber configuration in which the fluid pressure in the hollow core (13) is controlled by the change in the size of the fluid volume (23).

2. The fiber configuration according to claim 1, wherein the housing (15) has a through hole having an opening at the first axial end of the housing (15) and an opening at the second axial end of the housing (15), and the fiber (11) is inserted into the through hole.

3. The housing is a ferrule (15) attached to the fiber (11), The fiber configuration according to claim 2, wherein the ferrule (15) comprises a tubular body (17) that provides the through-hole into which the fiber (11) is inserted.

4. The fiber configuration according to claim 1, wherein the housing (15) is attached to one end of the fiber (11), or, with respect to at least two housings (15), one housing (15) is attached to one end of the fiber (11) and the other housing is attached to the other end of the fiber (11).

5. The fiber configuration according to claim 2, wherein an optical window (19) closes the opening of the through hole at the first axial end of each of the housings (15), and one fiber end is inserted into the second axial end of the through hole of the housing (15).

6. The fiber configuration according to claim 1, wherein the chamber (27) has an annular shape and is arranged circumferentially (C) around the through hole of the housing (15).

7. The fiber configuration according to claim 1, wherein the chamber (27) has a central axis (B) that is arranged parallel to or at an angle to the central axis (A) of the through hole of the housing (15).

8. The fiber configuration according to claim 3, wherein the ferrule (15) is an optical fiber ferrule (15) configured to hold and center the fiber (11), and the piezo device (25) is arranged on the ferrule (15) such that the fluid volume (23) is controlled via the change in the length of the piezo device (25) and the change in the volume of the optical fiber ferrule (15) resulting from the change in the length of the piezo device (25).

9. The fiber configuration according to claim 1, wherein the packing material (37) is disposed between the outer surface (39) of the piezo device (25) and the inner surface (41) of the chamber (27).

10. The fiber configuration according to claim 1, wherein, at the maximum extension position, the piezo device (25) extends over the entire length of the chamber (27) in which the piezo device (25) is located.

11. The fiber configuration according to claim 2, wherein one or more fluid channels (29) extend radially through the housing (15) to fluidly connect the chamber (27) to the through-hole provided in the housing (15).

12. Some fluid channels (29) are arranged at equal intervals around the periphery of the through hole, The fiber configuration according to claim 11, wherein four fluid channels (29) are arranged around the through hole in the circumferential direction (C) at a 90° offset from each other.

13. The fiber configuration according to claim 1, wherein the fiber configuration is a fiber configuration for providing broadband light.

14. The fiber configuration according to claim 1, wherein the fiber (11) is an anti-resonant hollow core fiber or a hollow core photonic bandgap fiber.

15. An optical system, A fiber configuration according to any one of claims 1 to 14, A pulsed laser source for supplying laser pulses to the aforementioned fiber configuration, An optical system comprising one or more piezo drivers for driving the piezo devices (25) arranged in one or more housings (15) of the fiber configuration.

16. The optical system according to claim 15, wherein the one or more piezo drive members are configured to drive the piezo device (25) in accordance with the pulse repetition rate of the laser pulse, or the change in the fluid density or pressure due to a change in the length of the piezo device (25) is greater than 50%, or both.

17. The optical system according to claim 15, wherein the fiber configuration comprises two or more housings (15) arranged at a certain distance from each other along the fiber (11), and one or more piezo drivers are configured to drive the piezo devices (25) of the two or more housings (15), thereby generating a desired pressure distribution in the hollow core (13) of the fiber (11).

18. The optical system according to claim 15, wherein the fiber configuration comprises one or more housings (15a, 15b) at each fiber end, and optionally, one or more housings (15c) on the intermediate portion of the fiber (11).

19. A method for generating light using the optical system described in claim 15, An input step involves inputting a laser pulse into the fiber configuration to generate a pulse output by the fiber configuration, A method comprising the steps of controlling the piezo device (25) located in one or more housings (15) during the input step to generate the pulse having a desired frequency spectrum, or generating the pulse such that different pulses include different frequency spectra.

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