Fiber configuration, optical system, and method of operating an optical system - Patents.com

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 fiber configurations, particularly fiber configurations for providing broadband light, preferably in the ultraviolet frequency range, optical systems, and methods for operating optical systems. [Background technology]

[0002] Hollow core optical fibers can be employed to convert input radiation into broadband radiation. The hollow core of such optical fibers 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 an appropriate laser pulse input into the hollow core of the fiber. The output broadband light pulses can have, for example, a spectral width between about 25 nm and about 125 nm and a central wavelength between about 375 nm and about 240 nm. The width of the broadband pulse is typically narrower the smaller the central wavelength of the broadband pulse. The position of the central wavelength of the broadband output pulse depends on the pressure of the fluid in the hollow core. The central wavelength of the broadband output pulse is typically larger the greater the pressure of the fluid in the core. Thus, multiple broadband output pulses with different central wavelengths can be generated using different pressures for the fluid in the core, and these broadband output pulses can cover a wide spectral range in the ultraviolet region, for example with wavelengths between 225 nm and 450 nm. It may be desirable to rapidly vary the spectrum provided by a broadband output pulse and, further, to be able to rapidly sweep across a wide spectral range covered by a plurality of such broadband output pulses. Summary of the Invention [Problem to be solved by the invention]

[0003] It is therefore an object of the present invention to provide a fiber configuration capable of providing laser light pulses, particularly broadband light pulses, allowing, for example, rapid sweeping over a wide spectral range. [Means for solving the problem]

[0004] The object is achieved by a fiber arrangement according to the features of claim 1. Preferred embodiments of the invention are set out 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, the piezoelectric device having a variable length, the chamber being in fluid communication with the hollow core of the fiber such that a change in length of the piezoelectric device causes a change in the size of the hollow core and the volume that the chamber provides for a fluid, such as a gas or mixture of gases.

[0005] The piezoelectric device can change the size of the volume provided for the fluid in the hollow core and chamber of the fiber, and therefore the pressure of the fluid can change correspondingly. 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 temperature in Kelvin, and V is volume) indicates that pressure is proportional to the inverse of volume. Thus, a decrease in the volume available for the fluid in the hollow core and chamber causes a pressure increase, while an increase in volume causes a pressure decrease.

[0006] The change in volume results from a change in the length of the piezoelectric device, which can change very quickly (e.g., on the order of about 10 kHz). Furthermore, piezoelectric devices typically offer long-term reliability, such that the spectrum of a broadband output pulse, e.g., obtained from launching a laser pulse into a fluid-filled hollow-core fiber, can change quickly and reproducibly depending on the length of the piezoelectric device.

[0007] A piezoelectric device may include or be formed from a piezoelectric material that is capable of changing its length in response to an electrical signal provided to the piezoelectric material, as such piezoelectric materials are known in the art.

[0008] The housing is capable of hermetically containing the piezoelectric device in the chamber so that fluid communication between the chamber and the hollow core is hermetic to the environment. The housing may include a through hole having an opening at a first axial end of the housing and an opening at a second axial end of the housing, and the fiber may be inserted into the through hole. The through hole may receive the fiber, and the chamber may be in fluid communication with the through hole. The through hole may hermetically seal the fiber. A diameter of the through hole may correspond to or be slightly larger than an 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 through which the fiber is inserted. The ferrule can be easily fixed to the fiber in a particularly gas-tight manner.

[0010] It should be noted that, according to the present disclosure, in these embodiments where the housing is a ferrule and where the housing is generally a housing (such as a cell or chamber), the piezo device is disposed 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, the present disclosure provides control of the volume of the fluid inside the fiber by controlling the volume and / or length of the housing using a piezo device disposed in the housing, thereby controlling the length of the fiber. Such a particular configuration ensures not only a fast change in the pressure of the gas, but also a very accurate control of the pressure of the gas. Thus, the present disclosure provides a solution for fast and accurate control of the pressure inside the fiber, so that it is possible to generate particularly broadband light pulses very efficiently.

[0011] Prior art such as EP 3705942 A1 typically controls the pressure inside the fiber by controlling the pressure directly. Although the Ideal Gas Law is known in the art, indirectly controlling the pressure in the fiber by controlling the volume has not been done before, since the most obvious and simplest approach is to simply control the pressure in the fiber directly. Furthermore, when the pressure is controlled in the fiber by adjusting the pressure (especially up to high pressures as in EP 3705942) and / or by adjusting the temperature, the housing for the fiber is made very robust against volume changes, and thus the housing is configured to withstand changes in volume. In other words, in the prior art for pressure control of fluids in a fiber, especially for the generation of broadband optical pulses, changing the volume of the housing for the fiber is not an option.

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

[0013] A ferrule, as described above, is one embodiment of a housing. Ferrules are known in the field of optical fibers and are therefore known as fiber optic ferrules. Fiber optic ferrules are mechanical fixtures, typically rigid tubes, that can be configured to confine the stripped end of a fiber or fiber bundle. Fiber optic ferrules can be configured to align and / or polish the optical fiber, for example, to prevent scattering and attenuation of the optical signal. Most fiber optic ferrules are made of metals, such as stainless steel, ceramics, such as alumina or zirconia, or plastic materials. Borosilicate and glass fiber ferrules are also available. Most fiber optic ferrules are manufactured using a direct-draw or redraw process and cut to length using a diamond saw blade. To prevent issues such as splice losses and end gaps, the fiber optic ferrules have a hole drilled through the center with a diameter slightly larger than the diameter of the fiber cladding. The lead-in is then blown, acid etched, or countersunk with a drill.

[0014] In embodiments where the housing is a ferrule, particularly a fiber optic ferrule as described above, the ferrule can serve both to confine the stripped end of the fiber and to control the pressure on the fiber. The pressure on the fiber is controlled via the ferrule and the piezo device as described above. In one embodiment, the ferrule is a fiber optic ferrule configured to hold and align the fiber, and the piezo device is disposed in the ferrule such that the volume of the fiber is controlled via the piezo device and the fiber optic ferrule. The material of the ferrule, in such an embodiment, can determine the reaction to the volume change as set by the piezo device. The use of a fiber optic ferrule in combination with a piezo device allows for a compact design that can both hold the fiber and fluid and control the pressure of the fluid on the fiber. When a piezo device is disposed in the fiber optic ferrule, the length of the fiber can be controlled very accurately. Thus, the volume inside the fiber, and therefore the pressure, can be controlled very accurately and quickly.

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

[0016] An optical window may close the opening of the through hole at the first axial end of each of the housings, and a fiber end may be inserted into the second axial end of the through hole of the housing, and the housing together with the optical window may be used to seal one end of a fiber.

[0017] The chamber may have an annular shape and may extend circumferentially around the through hole of the housing, so that a compact arrangement may be obtained.

[0018] The chamber may have a central axis that is arranged parallel or at an angle to the central axis of the through hole of the housing. The central axis of the chamber may 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 an angle of 90° to the central axis of the through hole and thus to the central axis of the fiber.

[0019] The chamber can be dimensioned such that the piezoelectric device is properly accommodated in the chamber, the geometry of the chamber can correspond to the geometry of the piezoelectric device, and the dimensions of the chamber can correspond at least approximately to the dimensions of the piezoelectric device.

[0020] In some embodiments, a filler, in particular a gas-tight filler, a filler of a deformable material, or both, is disposed between the outer surface of the piezoelectric device and the inner surface of the chamber. The piezoelectric device can be cushioned in the filler, and the filler can compensate for the reduction in the outer diameter of the piezoelectric device while the length of the piezoelectric device is extended. The filler can seal the area between the outer surface of the piezoelectric device and the inner surface of the chamber.

[0021] In some embodiments, at a maximum extended position of the piezoelectric device, the piezoelectric device extends the entire length of the chamber in which it is disposed.

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

[0023] In some embodiments, several fluid channels are equally spaced around the circumference of the through hole in the housing, which can be any number such as 2, 3, 4, 5, 6, etc.

[0024] In some embodiments, four fluid channels are circumferentially arranged around the through-hole, staggered by 90 degrees. In some embodiments, the fiber configuration is an airtight configuration.

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

[0026] In some embodiments, a ferrule is attached to one end of the fiber, an optical window is disposed on a first axial end of the ferrule, and one fiber end is inserted into the second axial end of the tubular body. The ferrule can hermetically seal 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 or output end of the fiber. Preferably, the fiber configuration comprises at least two ferrules, one ferrule attached to the input end of the fiber and another ferrule attached to the output end of the fiber.

[0027] One or more ferrules can be disposed on the mid-portion of the fiber. The mid-portion of the fiber is the portion of the fiber that is not the fiber end. Thus, the fiber can protrude through the tubular body of the ferrule. In some embodiments, multiple ferrules are disposed on the mid-portion of the fiber, for example at regular intervals. The one or more ferrules disposed on the mid-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 piezoelectric device is disposed in a chamber of the ferrule, the chamber being in fluid communication with the interior of the tubular body and the hollow fiber. The ferrule can serve as a storage location for housing the piezoelectric device. Electrical lines for providing electrical signals to the piezoelectric device can be led out of the ferrule in a particularly gas-tight manner.

[0029] In some embodiments, the chamber has an annular configuration and is circumferentially disposed around the tubular body of the ferrule. The piezoelectric device can also have a ring-shaped configuration and be designed to fit within the annular chamber. A central axis of the annular chamber can at least approximately correspond to a central axis of a fiber.

[0030] In some embodiments, the chamber can have a cylindrical configuration. The central axis of the cylindrical chamber can be disposed parallel or at an angle (e.g., 90°) to the central axis of the hollow fiber when the ferrule is mounted onto the fiber.

[0031] In some embodiments, the chamber is dimensioned such that the piezoelectric device is properly accommodated in the chamber, and thus the chamber can have a configuration that can accommodate the geometry of the piezoelectric device.

[0032] In some embodiments, a filler, in particular an airtight filler, a filler of a deformable material, or both, is arranged 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 reduction in the outer diameter of the piezoelectric device during the extension of the length of the piezoelectric device. The filler can in particular seal the area between the outer surface of the piezoelectric element and the inner surface of the chamber facing the outer surface of the piezoelectric element. Thereby, fluid cannot flow into the space that may be available for the extension of the length of the piezoelectric device, so that the outer diameter of the piezoelectric element can decrease in the area between the outer surface of the piezoelectric element and the inner surface of the chamber. Rather, the piezoelectric device can function as a piston that can push fluid out of the chamber when the length of the piezoelectric device is extended.

[0033] In some embodiments, the length of the piezoelectric device can be variable between a maximum and minimum extended position, and correspondingly, the volume can be variable between a minimum volume when the piezoelectric device is in a maximum extended position and a maximum volume when the piezoelectric device is in a minimum extended position.

[0034] In some embodiments, in a fully extended position, the piezoelectric device can extend the entire length of the chamber in which it is disposed. In some embodiments, one or more fluid channels extend radially through the tubular body to fluidly connect the chamber with the interior of the tubular body. In some embodiments, several fluid channels are equally spaced around the circumference 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 staggered 90° in the circumferential direction.

[0035] The present disclosure also relates to an optical system for providing optical pulses, such as broadband optical pulses, comprising a fiber arrangement according to the invention, a pulsed laser source for providing laser pulses to said fiber arrangement, and one or more piezo drivers for driving said piezo devices arranged in one or more housings, in particular ferrules, of said fiber arrangement.

[0036] In some embodiments, the one or more piezo drivers are configured to drive the one or more piezo devices in response to a pulse repetition rate of the laser pulses. In some embodiments, the fiber arrangement comprises two or more housings, in particular ferrules, arranged at a distance from each other along the fiber, and the one or more piezo actuators are configured to drive the piezo devices in the two or more housings (in particular ferrules) to generate a desired pressure distribution in the hollow core of the fiber. In particular, a uniform pressure distribution or pressure gradient along the length of the hollow core of the fiber can be generated.

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

[0038] The present disclosure also relates to a method of generating light pulses, in particular broadband light pulses, in particular broadband light pulses in the ultraviolet frequency range, using an optical system according to the invention. In some embodiments, the method comprises a step of inputting laser pulses into the fiber arrangement to generate light pulses, in particular broadband light pulses, output by the fiber arrangement, and a step of controlling, during the inputting step, the one or more piezo devices arranged in the one or more housings, in particular ferrules, to generate the light pulses with a desired frequency spectrum or to generate the pulses such that different pulses include different frequency spectra. The generated pulses can in particular be broadband light pulses. The one or more piezo devices make it possible to control the pressure distribution of the fluid in the hollow core of the fiber. As a result, the spectral range covered by the generated broadband output pulses can be controlled depending on the length of the one or more piezo devices. The one or more piezo devices can be specifically controlled such that the generated output pulses cover a desired spectral range. In other embodiments, the one or more piezo devices can be controlled such that the pulses of the series of broadband output pulses are swept over a larger spectral range.

[0039] The output pulses generated can have a wavelength in the ultraviolet wavelength region (eg, less than 380 nm). The invention also relates to a fiber configuration, in particular a fiber configuration for providing light pulses (such as broadband light pulses), preferably in the ultraviolet frequency range, comprising 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 piezoelectric device of variable length 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 fluid.

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

[0041] Preferred embodiments of the present invention may be described, by way of example only, with reference to the accompanying drawings, in which: [Brief description of the drawings]

[0042] [Figure 1] 1 is a schematic cross-sectional view of a fiber configuration known from the prior art; [Diagram 2] 1 is a schematic cross-sectional view of one embodiment of a fiber configuration according to the present invention. [Diagram 3] FIG. 3 is a schematic cross-sectional view of the fiber configuration of FIG. 2. [Figure 4] FIG. 3 is a further schematic cross-sectional view of the fiber configuration of FIG. 2; [Diagram 5] 3A-3C are schematic cross-sectional views of further embodiments of fiber configurations according to the invention; [Figure 6] 13A-13C are schematic cross-sectional views of further embodiments of fiber configurations; [Figure 7] 3A-3C are schematic cross-sectional views of further embodiments of fiber configurations according to the invention; [Figure 8] 1 shows a schematic diagram of an optical system according to the present invention; DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[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, where it forms a central portion of the fiber 11. The core 13 is surrounded by one or more claddings of the fiber. Because the core 13 is hollow, it can be filled with a fluid (e.g., a gas or mixture of gases).

[0044] The fiber arrangement 11 comprises a housing 15, which in the illustrated example is a ferrule. The ferrule 15 has a tubular body 17 providing 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 FIG. 1. The other axial end of the through-hole in the ferrule 15 is closed with an optical window 19, which can serve as an entrance window for the laser pulses to be input into the optical fiber 11.

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

[0046] The light cone 21 of the focused laser pulse is shown in FIG. 1. The fiber end of the fiber 11 is away from the optical window 19. Hence, 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. Thereby, ablation of the cladding material of the fiber 11 can be avoided. A typical material for the cladding is silica. The ablation threshold for a silica surface is typically around 3 J / mc for femtosecond pulses. 2 An exemplary value for the diameter of the fiber core 13 is 27 μm.

[0047] A corresponding ferrule 15 can be disposed at the opposite end of the fiber 11 (not shown), and an optical window 19 of such ferrule can serve as an output window for broadband optical pulses generated in the fiber 11 from the input laser pulses. Both ferrules (i.e., the 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 within 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, which can interact with the input laser pulse to form, for example, a broadband or even a supercontinuum optical pulse by nonlinear processes occurring during the interaction between the input optical pulse and the fluid.

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

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

[0051] As shown in FIG. 4, in the described embodiment, four fluid channels 29 are arranged at 90° intervals relative to the circumferential direction C and extend radially through the tubular body 17 to fluidly connect the chamber 27 and the interior of the tubular body 17 and the hollow core 13.

[0052] 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 fluid. As a result, the pressure of the fluid in the volume 23 can vary depending on the length of the piezoelectric device 25, as evident from, for example, the ideal gas law.

[0053] In the embodiment of Figures 2-4, the chamber 27 has an annular form and is disposed in a housing section 31 that 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 dimensioned such that the piezoelectric device 25 is properly accommodated in the chamber 27. Thus, the piezoelectric device 25 is able to fill the chamber 27. In particular, as shown in Figure 3, when the piezoelectric device 25 reaches its maximum extended position, the piezoelectric device 25 extends over the entire length of the chamber 27.

[0054] A piezo device may 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 may be varied by 25 μm with modulation up to a resonant frequency of 40 kHz. Such an actuator may have a displacement of 0.9 mm. 3 It is possible to adjust the volume up to

[0055] In some embodiments, two or more such piezo devices 25 can be placed in series behind each other and in the same chamber 27, so that even greater volumetric adjustment can be achieved.

[0056] The embodiment of the fiber configuration shown in Fig. 5 differs from the previous embodiment of Figs. 2 to 4 in that, as shown in Fig. 5, the piezoelectric device 25 comprises a piezoelectric element 33 having an annular form and an end plate 35 fixed to one end of the piezoelectric element 33. The end plate 35 faces the volume 23 available for fluid in the chamber 27. The end plate 35 has an annular form. The cross-sectional size of the end plate 35 corresponds approximately to the cross-sectional size of the chamber 27 when viewed in the radial direction.

[0057] The piezo element 33 can be controlled by using a piezo controller (not shown in FIG. 5) specifically connected to the piezo element 33 such that the axial length of the piezo element 33 can be extended or extended. The piezo element 33 and end plate 35 can function as a piston that can push fluid out of the chamber 27 when the piezo element 35 is extended or draw fluid into the chamber 27 when the piezo element 35 is contracted.

[0058] A filler 37 is disposed between an outer surface 39 of the piezoelectric element 33 and an inner surface 41 of the housing section 31. In the embodiment of Figure 5, the inner surface 41 is a surface of a guide ring 43 that supports the piezoelectric element 33. The guide ring 43 is concentrically disposed radially inward and outward of the piezoelectric element 33 to hold the piezoelectric element 33 and filler 37 in place and to support changes in the length of the piezoelectric element 33.

[0059] The filler 37 may also extend between a radially outer surface of the end plate 35 and an opposing inner surface of the housing section 31. The filler 37 may be made of a deformable material. The filler 37 may seal the chamber 27 against the space occupied by the piezoelectric device 25 in the housing section 31. In particular, the filler 37 may form a seal in the area between the radially outer surface of the end plate 35 and the inner surface of the housing section 31.

[0060] 2-4, it may also include a filler 37 between the inner radially outer end surface of the piezoelectric device 25 and the opposing surfaces of the housing section 31 and the tubular body 17. The filler may act as an airtight seal and compensate for the reduction in width of the piezoelectric device 25 caused by the elongation of its length.

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

[0062] A filler 37 is disposed 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 such 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 substantially larger sidewall of the tubular body 17 having a cross-sectional area that corresponds approximately to the cross-sectional area of ​​the chamber 27.

[0063] The fiber configuration shown in Figure 7 is based on the design of the embodiment of Figures 2-4. However, the ferrule 15 of the fiber configuration of Figure 7 does not include an optical window 19. Instead, both ends of the tubular body 17 are open-ended and the fiber 11 protrudes through the tubular body 17. In other words, the ferrule 15 is disposed at the mid-section of the fiber 11 and a fluid channel 29 extends radially through the tubular body 17 and the fiber 11 to fluidly connect the chamber 27 and the hollow core 13 of the fiber 11.

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

[0065] FIG. 8 shows a schematic of an optical system for providing broadband light (particularly supercontinuum light), comprising a pulsed laser source 45 for providing laser pulses to a fiber arrangement 47, and a piezo driver 49.

[0066] The fiber arrangement 47 comprises an optical fiber 11 having a hollow core 13 as previously described. As shown in FIG. 8, a ferrule 15a is disposed at a first end of the fiber 11, and a ferrule 15b is disposed at a second end of the fiber 11. The ferrules 15a, 15b may particularly correspond to the ferrules as previously described with respect to FIGS. 2-6. Optionally, the fiber arrangement may further comprise a ferrule 15c disposed at an intermediate portion of the fiber 11. The ferrule 15c may particularly correspond to the ferrule 15 as described with respect to FIG. 7.

[0067] The piezoelectric actuator 19 is connected to the piezoelectric devices 25 (see FIGS. 2 to 7) in the ferrules 15a, 15b, and 15c, and is configured to drive each of the piezoelectric devices 25 individually.

[0068] In operation, for example, the piezo drivers 49 can drive the piezo devices 25 in phase. Then, all the piezo devices 25 reach their maximum and minimum extension lengths at the same time. In another example, the piezo devices 25 are operating out of phase. Different piezo devices 25 thus reach their maximum extension lengths at different times.

[0069] Moreover, in some embodiments, each piezoelectric device 25 can be controlled so that its length changes over time according to a predetermined profile, which is particularly possible because the piezoelectric devices 25 can be individually controlled.

[0070] In some embodiments, the piezoelectric device 25 is controlled to obtain a desired uniform pressure distribution along the length of the hollow core 13 of the fiber 11 . In other embodiments, the piezoelectric 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 piezo device can be adjusted at a steady frequency over a period of time. In one such embodiment, a pulsed laser is focused into the 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 piezo modulation corresponds to the frequency of the laser pulses or an integer fraction of the frequency of the laser pulses (e.g., 1 / 2, 1 / 3, 1 / 4...1 / n). In one such embodiment, the delay or phase shift between the frequency of the laser pulses and the frequency of the piezo modulation can be further controlled.

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

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

[0074] Reference List 11 Optical Fiber 13 Hollow Core 15 Ferrule, housing 15a ferrule 15b ferrule 15c ferrule 17 Tubular body 19 Optical window 21 Light Cone 23 Volume 25 Piezo Devices 27 Chamber 29 Fluid Channels 31 Housing Section 33 Piezo element 35 End plate 37 Filling 39 Exterior 41 Inside 43 Guide Ring 45 Pulsed Laser Source 47 Fiber Configuration 49 Piezo actuator A center axis B Center axis C circumferential direction

Claims

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 disposed, 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 the volume (23) that the chamber (27) provides for a fluid, such as a gas or a mixture of gases.

2. 2. The fiber configuration of claim 1, wherein the housing (15) has a through hole having an opening at a first axial end of the housing (15) and an opening at a 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 arrangement of claim 2 , wherein the ferrule (15) comprises a tubular body (17) providing the through hole through which the fiber (11) is inserted.

4. 2. The fiber arrangement of claim 1, wherein the housing, in particular the ferrule (15), is attached to one end of the fiber (11) or, for at least two housings, in particular the ferrules (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. 3. The fiber configuration of 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. 2. The fiber arrangement of claim 1, wherein the chamber (27) has an annular shape and is circumferentially (C) disposed around the through hole of the housing (15).

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

8. 4. The fiber configuration of claim 3, wherein the ferrule (15) is an optical fiber ferrule (15) configured to hold and align the fiber (11), and the piezoelectric device (25) is disposed in the ferrule (15) such that the volume of the fiber (11) is controlled via the piezoelectric device (25) and the optical fiber ferrule (15).

9. 2. The fiber arrangement according to claim 1, wherein a filling (37), in particular an airtight filling, a filling of a deformable material, or both, is arranged between an outer surface (39) of the piezoelectric device (25) and an inner surface (41) of the chamber (27).

10. 2. The fiber arrangement of claim 1, wherein in a maximum extended position, the piezoelectric device (25) extends the entire length of the chamber (27) in which the piezoelectric device (25) is located.

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

12. Several fluid channels (29) are equally spaced around the circumference of the through hole, or 12. A fiber arrangement according to claim 11, wherein four fluid channels (29) are arranged around the through hole in a circumferential direction (C) at 90[deg.] intervals.

13. The fiber arrangement of claim 1 , wherein the fiber arrangement is airtight.

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

15. 1. An optical system, in particular an optical system for providing broadband light, comprising: A fiber arrangement according to any one of claims 1 to 14, a pulsed laser source for providing laser pulses to the fiber arrangement; and one or more piezo drivers for driving the piezo devices (25) disposed in the one or more housings (15) of the fiber arrangement.

16. 16. The optical system of claim 15, wherein the one or more piezoelectric drivers are configured to drive the piezoelectric device (25) in response to a pulse repetition rate of the laser pulses, or a change in the length of the piezoelectric device (25) results in a change in density or pressure of the fluid of greater than 50%, or both.

17. 16. The optical system of claim 15, wherein the fiber arrangement comprises two or more housings, in particular ferrules (15), arranged at a fixed distance from each other along the fiber (11), and the one or more piezo drivers are configured to drive the piezo devices (25) of the two or more housings (15) to generate a desired pressure distribution in the hollow core (13) of the fiber (11), in particular a uniform pressure distribution or a pressure gradient in the hollow core (13) of the fiber (11).

18. 16. The optical system of claim 15, wherein the fiber arrangement comprises one or more housings, in particular ferrules (15a, 15b), at each fiber end and optionally one or more housings, in particular ferrules (15c), on an intermediate portion of the fiber (11).

19. A method for generating light, in particular broadband light, in particular in the UV frequency range, with an optical system according to claim 15, comprising the steps of: - injecting a laser pulse into said fiber arrangement to generate a pulse, in particular a broadband pulse, output by said fiber arrangement; and controlling, during the inputting step, the piezoelectric device (25) arranged in the one or more housings (15) to generate the pulses having a desired frequency spectrum, in particular broadband pulses, or to generate the pulses such that different pulses comprise different frequency spectra.

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