Photonic crystal fiber, preparation method of photonic crystal fiber and supercontinuum light source

Abstract

The present invention relates to a photonic crystal fiber (PCF), a method for preparing the PCF, and a supercontinuum light source comprising such a PCF. The PCF has a longitudinal axis and comprises a core extending along the length of the longitudinal axis and a cladding region surrounding the core. At least the cladding region comprises a plurality of microstructures in the form of inclusions extending along the longitudinal axis of the PCF in at least the microstructure length portion. In at least the anti-degradation length portion of the microstructure length portion, the PCF comprises hydrogen and / or deuterium. In at least the anti-degradation length portion, the PCF further comprises a primary coating surrounding the cladding region, the primary coating being oxidized at a temperature below T h is impermeable to hydrogen and / or deuterium at a temperature of h At least about 50°C, preferably 50°C <T h <250℃.

Description

[0001] This application is a divisional application of the Chinese patent application with application number 201580075601.1 and invention name “Photonic crystal fiber, method for preparing photonic crystal fiber and supercontinuum light source”. Technical Field

[0002] The present invention relates to a photonic crystal fiber (PCF), a method for preparing the PCF, a supercontinuum light source comprising the PCF (microstructure fiber), and an optical supercontinuum radiation source. Background Art

[0003] A photonic crystal fiber, hereinafter referred to as a PCF or microstructured fiber, is an optical fiber having a core surrounded by a cladding region having a plurality of inclusions (sometimes referred to as cladding features or microstructures) arranged in a background material (typically in a regular array). The inclusions may be gas, liquid or solid inclusions. In principle, the inclusions may be pores, but in practice the pores usually contain some gas molecules.

[0004] Optical fibers of this type are well known in the art, for example as described in US2012195554, US8406594, US2011116283 and US2012195554.

[0005] The microstructured fibers may be, for example, silica glass. Other materials may be added to the silica glass to change its refractive index or to provide effects such as light amplification, sensitivity, etc.

[0006] The center-to-center spacing between cladding inclusions is defined as the pitch (Λ). The PCF is typically characterized, at least in part, by the size of the core and the ratio of the size of the inclusions to their spacing or pitch (Λ). By adjusting the size and spacing of the cladding inclusions, the zero dispersion wavelength (ZDW) of the fiber can be tuned.

[0007] Photonic crystal fibers are generally suitable for high-power light sources. The conduction of relatively high powers in optical fibers may be relevant for several commercial applications, such as the conduction of surgical and / or therapeutic light, optical sensing, and material processing. These applications are the transmission of optical energy and the exploitation of the nonlinear effects of optical fibers, which are generally more pronounced with higher optical powers inside the fiber. The optical power may be continuous wave (CW), pulsed wave, or a mixture thereof. High optical powers inside optical fibers may be particularly significant with pulsed light, if high peak powers can be obtained even with relatively modest average powers.

[0008] One limitation on the average power / spectral density carried by an optical fiber is the damage threshold of the optical fiber. Particularly in the case where PCFs are applied to supercontinuum generation, where high power light is fed into the PCF via the emission end (sometimes referred to as the input end) of the PCF, it has been found that the PCF degrades over time, depending on the peak power of the fed light. Furthermore, it has been found that portions of the optical fiber near or adjacent to the emission end are more subject to degradation than portions further away from the emission end.

[0009] US8145023 describes a method of mitigating degradation caused by high power light fed to a PCF by loading the core material and optionally the cladding material with hydrogen and / or deuterium. It was found that such loading resulted in some increase in the fiber lifetime. In US2011116283, the method was further improved by annealing and / or high power irradiation of the PCF after hydrogen and / or deuterium loading. Summary of the invention

[0010] It is an object of the present invention to provide a PCF suitable for supercontinuum generation which is very resistant to degradation.

[0011] In one embodiment, an object is to provide a PCF suitable for supercontinuum generation which has a long lifetime even when used for supercontinuum generation.

[0012] Another object is to provide a supercontinuum light source including a PCF having high anti-degradation performance, and preferred applications of such a supercontinuum light source.

[0013] These and other objects have been solved by the present invention or its embodiments as defined in the claims and described hereinafter.

[0014] It has been discovered that the present invention or its embodiments have many other advantages, which will become apparent to those skilled in the art from the following description.

[0015] The photonic crystal fiber (PCF) of the present invention has a longitudinal axis and includes a core extending along the length of the longitudinal axis and a cladding region surrounding the core. At least the cladding region includes a plurality of microstructures in the form of inclusions extending along the longitudinal axis of the PCF in at least the microstructure length portion. The PCF has a degradation-resistant length portion, which can be the entire length of the PCF or only a portion of its length.

[0016] The term "degradation resistant length portion" is used to denote an optical fiber length portion having a very high resistance to degradation over time relative to other prior art optical fiber length portions.

[0017] The PCF comprises hydrogen and / or deuterium in at least the degradation resistant length portion of the microstructure length portion, and the PCF further comprises a primary coating surrounding the cladding region in at least the degradation resistant length portion, the primary coating being oxidized below Th is impermeable to said hydrogen and / or deuterium at a temperature T h of at least about 50 °C. Advantageously, T h is at least about the maximum expected temperature of the PCF in use. Thus, over time and / or during use, a minimal amount of hydrogen and / or deuterium diffuses to the outside of the optical fiber. T h is preferably as follows: 50 °C < Th < 250 °C. In one embodiment, T h is up to about 150 °C.

[0018] The term "gas-impermeable" as used herein is meant to indicate that any diffusion of hydrogen atoms and / or deuterium atoms through the coating is less than about 1% per day, which is for example measured by: using Raman spectroscopy and at the relevant temperature under atmospheric conditions (i.e., the optical fiber is arranged in air at 1 bar), or by measuring the absorption lines of H2 (or D2) by infrared spectroscopy, H2 at about 1240 nm or about 1870 nm or D2 at about 1715 nm. Preferably, the gas-impermeable coating allows a diffusion of less than 0.5% per day, such as less than about 0.1% per day, such as less than about 0.01% per day.

[0019] The term "inclusion" means an inclusion in the background material, where the inclusion has a refractive index different from that of the surrounding background material. The inclusion can be, for example, a gas inclusion such as air, nitrogen or any other gas; a solid inclusion such as another glass type and / or doping material different from the background material (refractive index-changing materials such as F, Ge, P, B), a vacuum inclusion or any combination thereof. Advantageously, at least some of the inclusions are gas or vacuum inclusions. It has been found that gas inclusions can be used as storage sites for hydrogen and / or deuterium, where the inclusions are enclosed on either side of the anti-degradation length section.

[0020] The wording "radial distance" means the distance determined along the radial direction from the longitudinal axis.

[0021] The term "substantially" as used herein should be considered to encompass the deviations and tolerances of ordinary products.

[0022] It should be noted that the cladding region can have a uniform background material, or it can have several regions with respective background materials that are different from each other. The background material is advantageously silica, optionally doped silica. In one embodiment, the cladding region includes an inner cladding region and an outer cladding region surrounding the inner cladding region, where the background material of the inner cladding region is different from the background material of the outer cladding region, as described in US8600207.

[0023] In one embodiment, the cladding region comprises an inner cladding region and an outer cladding region surrounding the inner cladding region, wherein the background material of the inner cladding region has the same refractive index as the background material of the outer cladding region. In this embodiment, advantageously, the inner cladding region and the outer cladding region have the same background material. The difference between the inner cladding region and the outer cladding region is, for example, a difference in size, type and / or number of inclusions. The cladding region confines light to the core, and advantageously, the inclusions are configured to affect the average refractive index of the confinement that produces the light. This means that the inclusions should be relatively close to the core, and preferably, at least some of the inclusions should have a center-to-center distance from the core of up to about 50 μm, preferably up to about 40 μm, for example up to about 30 μm, for example up to about 15 μm.

[0024] When describing the materials of the cladding regions, inclusions, and core, the amount of hydrogen and / or deuterium is not considered part of the material.

[0025] In one embodiment, the background material of the cladding region and the core material are substantially pure silica.

[0026] In one embodiment, the background material of the cladding region and the core material is fluorine-doped silicon dioxide.

[0027] It has been found that higher resistance to photo-induced degradation can be achieved where the core material is doped with fluorine in at least the degradation resistant length portion.

[0028] Advantageously, the content of hydrogen and / or deuterium in the form of H2 or D2 in at least the core of the degradation-resistant length portion comprises at least about 0.001 ppm, such as at least about 0.01 ppm, such as about 0.1 to about 10000 ppm. The amount of hydrogen and / or deuterium can be determined, for example, by determining the absorption produced at each hydrogen or deuterium absorption peak as described above.

[0029] The anti-degradation length portion may be of any length. Advantageously, the anti-degradation length portion extends from one end of the PCF. In one embodiment, the anti-degradation length portion extends from an emission end of the PCF. The emission end is the end that is optically coupled to or adapted to be coupled to a pump laser for feeding light to the PCF. Thus, the anti-degradation length portion may be located where high power light is fed to the PCF. It has been observed that the main damage to prior art PFCs occurs near the emission end of the PCF. By ensuring that there is sufficient hydrogen and / or deuterium loading at the emission end of the PCF, the PCF has greatly increased resistance to damage caused by loading stresses, which further extends the service life of the entire PCF.

[0030] In the context of the present application, the expression "inclusion ring" refers to cladding inclusions that are generally at substantially equal distances from the core and aligned in a circular or non-circular ring around the core. Typically, the inclusion ring is not completely circular, but is shaped to have multiple soft angles, such as a hexagonal shape. Preferably, all inclusions of the inclusion ring have substantially the same size and are preferably of the same material.

[0031] In one embodiment, the plurality of inclusions in the cladding region are arranged in a pattern comprising at least two rings of inclusions surrounding the core.

[0032] In order to obtain a PCF that is very favorable for supercontinuum generation, the center-to-center distance (also referred to as the spacing Λ) is advantageously at least about 1 μm, such as about 1.5 μm to about 5 μm or more. The inclusion diameter (d) is advantageously at least about 0.5 μm, such as about 1 μm to about 3 μm. The relative diameter / spacing d / Λ is preferably about 0.4 to about 0.85.

[0033] The inclusion diameter or diameter of an inclusion is also referred to as the characteristic diameter of the inclusion. The expression "characteristic diameter" is a measure of the size of an inclusion (also referred to as a cladding feature). If the cladding feature is circular, the characteristic diameter is the diameter of the circle of the cladding feature. In the case where the cladding feature is not circular, the characteristic diameter is determined in one embodiment as the average of the largest and smallest range of the cladding feature, or in another embodiment, the characteristic diameter is the diameter of a circle having an area corresponding to the calculated or measured area of ​​the cladding feature in question.

[0034] The inclusions may have the same or different diameters, and the inclusion diameters of the various inclusions may be equal or unequal along the length of the optical fiber as described.

[0035] Embodiments of different and preferred combinations of inclusions and their diameters are disclosed in co-pending application DK PA201470146, which is incorporated herein by reference with respect to the structure of the core, cladding region and inclusions. PA201470146 discloses a preferred embodiment of the PCF of the present invention, except that at least one length portion of the PCF disclosed in PA201470146 is modified to be or include an anti-degradation length portion containing hydrogen or deuterium and an impermeable coating, as described herein.

[0036] In one embodiment, the inclusion diameter (d) of each inclusion is equal along the length of the optical fiber. In one embodiment, the inclusion diameter (d) of each inclusion is different along at least a portion of the length of the optical fiber, such as along the tapered portion.

[0037] As mentioned above, inclusions may in principle comprise or consist of any kind of material, typically including materials having a different refractive index than the background material in which the respective inclusion is embedded or contained. Examples of suitable inclusion materials are disclosed above.

[0038] In one embodiment, the inclusions comprise gas inclusions, such as gas pores, such as gas pores with air (atmospheric pressure) at the bottom or around.Preferably, the gas inclusions are closed on both sides of the degradation resistant length portion.

[0039] In one embodiment, the degradation resistant length portion is the entire length of the PCF, optionally excluding the closed end of the PCF.

[0040] By sealing the ends of the PCF, any diffusion of hydrogen and / or deuterium out of the PCF is further reduced, which is found to also improve the resistance to degradation, thereby increasing the lifetime of the entire PCF.

[0041] The ends of the PCF may be closed, for example, by folding the PCF in the short end portions or by fusing short solid silica lengths to the respective ends.

[0042] Advantageously, the closed ends each have a relatively short length along the length of the PCF in order to reduce any risk of losing light. Advantageously, the closed ends each have a length along the length of the PCF of up to about 3 mm, such as up to about 2 mm, such as up to about 1 mm, such as up to about 0.5 mm, such as up to about 0.3 mm, such as up to about 0.2 mm.

[0043] In one embodiment, the plurality of inclusions in the cladding region of at least the degradation resistant length portion comprises an inner cladding region comprising an inner inclusion and an outer cladding region comprising an outer inclusion. It has been found that this embodiment provides a PCF that is very advantageous for supercontinuum generation. Advantageously, the inner inclusion is larger than the outer inclusion. Preferably, the inner inclusion comprises at least one inner inclusion ring, and the outer inclusion comprises at least one outer inclusion ring. In one embodiment, more preferably, the diameter d of the inner inclusion is inner Than the diameter of the outer inclusion d outer The PCF is at least about 15% greater, such as at least about 20%, such as at least about 25%, such as at least about 30%. Thus, a PCF for supercontinuum generation having high stability even in the blue light range is provided. Furthermore, due to the anti-degradation length portion, the PCF will have a long lifetime even when operating at very high powers.

[0044] In one embodiment, d innerPreferably it is at least about 1.5 μm, such as about 1.8 to about 4 μm, such as about 2 to about 2.5 μm.

[0045] In one embodiment, d outer Preferably, it is less than about 2.5 μm, such as about 0.8 to about 2 μm, such as about 1 to about 1.8 μm.

[0046] Advantageously, the background material of the inner cladding region and the background material of the outer cladding region are identical and optionally also identical to the core material. Advantageously, the background material of the inner cladding region and the background material of the outer cladding region and optionally the core material are substantially pure silica or optionally fluorine-doped silica.

[0047] Advantageously, the outer envelope region comprises at least three outer inclusion rings.

[0048] In one embodiment, the structure and configuration of the inclusions are as described in co-pending application DK PA201470146, for example DK PA 201470146. Figure 2 a and 3a, wherein the PCF is modified to be or include a degradation resistant length portion containing hydrogen and / or deuterium and an impermeable coating as described herein.

[0049] In one embodiment, the cladding region in at least the degradation resistant length portion comprises an inner cladding region comprising inclusions and an outer cladding region surrounding the inner cladding region, wherein a radial distance between the outermost inclusions of the inner cladding region and the primary coating is at least about 10 μm. Optionally, the material between the inner cladding region and the primary coating forms a reservoir for hydrogen and / or deuterium.

[0050] By having a relatively large radial distance between the outermost inclusions in the inner cladding region and the primary coating, a large region can form a reservoir of hydrogen and / or deuterium, which can gradually diffuse into the core as hydrogen and / or deuterium is consumed in the core, thereby maintaining a relatively stable and sufficient hydrogen and / or deuterium concentration in the core.

[0051] In one embodiment, the material between the inner cladding region and the primary coating forms a reservoir for hydrogen and / or deuterium, for example, the hydrogen reservoir is porous silicon dioxide.

[0052] In one embodiment, the reservoir of hydrogen between the inner blanket region and the primary coating comprises glass or plastic having a higher adsorption capacity for hydrogen and / or deuterium than the material of the inner blanket region background material.

[0053] A person skilled in the art will be able to find suitable materials through several hydrogen and / or deuterium loading tests.

[0054] The core can in principle be of any size. The larger the core, the higher the power that can be fed into the PCF, however, if the core is too large, it may be difficult to broaden the bandwidth to the desired degree. In order to provide a broad and stable supercontinuum light, it is advantageous for the core to have a diameter of at least about 1 μm, preferably at least about 2 μm. Thus, ensuring that the fiber can withstand the power necessary for supercontinuum generation and / or high powers in general.

[0055] In one embodiment, the core in at least the degradation resistant length portion has a core diameter of about 10 μm or less, such as about 8 μm or less, such as about 6 μm or less. In one embodiment, the core diameter is in a range of greater than about 3 μm, such as about 3 μm to about 7 μm.

[0056] In one embodiment, the core is defined by the inclusions, ie, the inclusions surrounding the core have a different refractive index, thereby forming the core.

[0057] Advantageously, the PCF is made of silicon dioxide, optionally doped as described above.

[0058] In one embodiment, the material of the core and / or cladding regions is doped.

[0059] In one embodiment, at least the innermost inclusions in the degradation resistant length portion are less than about 50 μm, preferably less than about 40 μm, such as less than about 30 μm, such as less than about 10 μm, from the center to the center of the core.

[0060] The core is a solid core.

[0061] The term "solid core" means that the core has a solid material that is substantially free of gas (including pores). In one embodiment, the core is a microstructured core.

[0062] Advantageously, the core is a solid core optionally comprising a solid microstructure.

[0063] In one embodiment, the core is substantially pure silica.

[0064] As mentioned above, a very beneficial property of PCF is that the zero dispersion wavelength (ZDW) of the fiber can be tuned by adjusting the size and spacing of the cladding inclusions.

[0065] In one embodiment, the PCF has anomalous dispersion for at least one wavelength between 1000 nm and 1100 nm.Preferably, the PCF has anomalous dispersion at about 1030 nm or 1064 nm.

[0066] In one embodiment, the core of the PCF is single mode at the pump wavelength.

[0067] Advantageously, the core of the PCF is spatially single mode at 1064 nm.

[0068] Spatially single-mode means that for a 2 m long fiber, the loss of the higher-order modes is at least 19.3 dB higher than the loss of the fundamental mode. This can be measured, for example, using the S^2 method, see JW Nicholson et al., "Spatially and spectrally resolved imaging of modal content in large mode-area fibers", Optics Express, Vol. 16, No. 10, p. 7233, 2008.

[0069] In one embodiment, the core of the PCF is single mode at 1030 nm.

[0070] In one embodiment, the core of the PCF is multimode at the pump wavelength, for example at 1064 nm or 1030 nm.

[0071] Advantageously, at least the core of the PCF is substantially free of germanium. It has been found that germanium may cause certain structural defects in the silicon dioxide, so it is desirable that the germanium content is as low as possible. It has been found that hydrogen and / or deuterium also increase resistance to germanium-induced structural defects, so in the case where the PCF contains germanium, the loading of hydrogen and / or deuterium may be increased.

[0072] In one embodiment, the entire PCF is substantially free of germanium. In one embodiment, the entire PCF is substantially undoped silicon dioxide. In one embodiment, at least a portion of the PCF is doped with fluorine, for example, at a doping level of more than 1000 ppm.

[0073] In the context of the present invention, the expression "substantially free of germanium" means that the concentration of germanium is less than about 10 ppm, including zero.

[0074] In the context of the present invention, the expression "substantially undoped" means that the concentration level of refractive index changing dopants such as Ge, B, F, P, Al and / or active materials such as rare earth elements Er or Yb is below 1000 ppm. In one embodiment, the level of dopants is even lower, such as about 1 ppm or less.

[0075] In one embodiment, at least the core of the PCF is substantially free of active materials, such as rare earth ions.

[0076] In one embodiment, the entire PCF is free of active ions.

[0077] In the context of the present invention, the expression "substantially free of active materials" means that the concentration level of active materials, such as rare earth elements Er or Yb, is below 1000 ppm. Preferably, the level of active materials is even lower, such as about 1 ppm or lower.

[0078] The primary coating may be of any material that provides a gas impermeable coating as described above.

[0079] Examples of suitable materials for the primary coating are materials including nitrides (eg, carbon nitride, silicon nitride, boron nitride, silicon nitride, and / or silicon oxynitride), carbon, aluminum, metallic glass, or a combination comprising one or more of the foregoing.

[0080] A particularly preferred material for the primary coating is carbon.

[0081] The thickness of the primary coating depends on the type of material. It is generally desirable to select a primary coating material that is impermeable to air at a relatively low thickness, thereby ensuring high flexibility and bendability of the PCF without incurring any significant risk of crack formation.

[0082] In one embodiment, the primary coating has a thickness of about 5 nm to about 10 μm, such as 10 nm to about 5 μm, such as about 20 nm to about 1 μm.

[0083] In one embodiment, the primary coating has a thickness of about 30 nm.

[0084] For the metallic primary coating, its thickness is advantageously between 15 μm and 60 μm.

[0085] In one embodiment, the primary coating is diffusely open to hydrogen and / or deuterium at temperatures above T0, wherein T0 is greater than T h . Thus, hydrogen and / or deuterium can be loaded into the PCF after the coating has been applied. This provides a preferred embodiment for the preparation of the PCF, since the primary coating protects the optical fiber during mechanical and dust protection handling. Furthermore, a more uniform and precise content of hydrogen and / or deuterium can be loaded. It has been found that after loading a PCF without a primary coating, the loaded hydrogen and / or deuterium will begin to be lost immediately, and in fact an undesirable large amount of hydrogen and / or deuterium may be lost before the primary coating is applied. Therefore, if the primary coating is applied after loading, it is desirable to initially load a larger amount of hydrogen and / or deuterium into the PCF.

[0086] Preferably, T0 is at least about 25°C, preferably T0 is in the interval of about 50°C to about 300°C, such as at least about 70°C, such as at least about 100°C. In one embodiment, T0 is determined at 1 bar. In one embodiment, T0 is determined at 100 bar.

[0087] Generally, it is desirable that T0 is greater than the temperature of the PCF used (or the desired temperature). On the other hand, T0 should advantageously not increase the softening temperature of the material, which would risk deforming the material.

[0088] The PCF may advantageously include one or more additional coatings above or below the primary coating.

[0089] Such additional coatings may provide additional mechanical protection, reduce the risk of any cracks in the primary coating and / or provide an outermost appearance and / or feel.

[0090] The additional coating is preferably a polymer coating, advantageously comprising acrylate, polyimide, polyurethane, silicone or any combination thereof.

[0091] In one embodiment, if the primary coating is carbon, then the additional coating is a metal, such as aluminum, gold, copper, nickel, metallic glass, or a combination or alloy comprising at least one of the foregoing metals.

[0092] In one embodiment, the PCF comprises at least one tapered length section, wherein the core has a core diameter D1 at a first end of the tapered length section, and the core has a core diameter D2 at a second end of the tapered length section, wherein D1 is greater than D2, preferably D2 is up to about 0.95 times D1, such as about 0.1 to about 0.9 times D1. Advantageously, the first end is the emitting end.

[0093] It has been found that the supercontinuum generation properties of a PCF can be increased by tapering the PCF, as described in PCT / DK2014 / 050205. In one embodiment, the PCF differs from that described in PCT / DK2014 / 050205 in that the PCF is modified to be or include a degradation resistant length portion comprising hydrogen and / or deuterium and a gas impermeable coating, as described herein.

[0094] Preferably, the first end of the tapered length portion is at, or up to 5 cm from, the emitting end of the optical fiber, and preferably said first end of the tapered length portion is close to or included in the degradation-resistant length portion.

[0095] Therefore, the PCF is particularly protected against degradation when the peak power is very high.

[0096] In one embodiment, the PCF does not include any splicing.

[0097] In one embodiment, the PCF comprises two or more spliced ​​optical fiber lengths, wherein at least one of the spliced ​​optical fiber lengths is or comprises a degradation resistant length portion.

[0098] In order to provide an optimal supercontinuum, it has been found that an optical fiber comprising fiber length portions having different properties may be advantageous, for example as described in PCT / DK2014 / 050206.

[0099] In one embodiment, the PCF comprises a first length portion and a second length portion spliced ​​to the first length portion, the first length portion comprising or consisting of an anti-degradation length portion, wherein the second length portion has a lower hydrogen and / or deuterium content than the anti-degradation length portion.

[0100] In one embodiment, the PCF includes:

[0101] a first length portion having a first length L1, wherein the inclusions of the optical fiber at least at a first cross-section through the first length portion perpendicular to the longitudinal axis have a first spacing Λ1, a first inclusion diameter d1 and a first relative size d1 / Λ1 of the inclusions,

[0102] a second length portion having a second length L2, wherein the microstructure elements of the optical fiber at least at a second cross section through the second length portion perpendicular to the longitudinal axis have a second spacing Λ2, a second inclusion diameter d2 and a second relative size d2 / Λ2 of the inclusions,

[0103] At least one of the first length L1 and the second length L2 includes or consists of a degradation resistant length portion.

[0104] One or more of the length portions of the optical fiber may be tapered.

[0105] In one embodiment, the PCF of the present invention differs from the PCF disclosed in PCT / DK2014 / 050206 in that at least the length portion of the PCF disclosed in PCT / DK2014 / 050206 is improved to be a degradation-resistant length portion and an airtight coating containing hydrogen and / or deuterium, as described herein.

[0106] In one embodiment, the PCF includes a mode adapter extending along the length of the PCF, the mode adapter being at least in a mode field adaptation length portion extending from the transmitting end of the PCF or extending up to 5 cm from the transmitting end of the PCF. Preferably, the length of the mode field adaptation length portion is at least about 5 cm, such as at least about 10 cm, such as at least about 20 cm. Advantageously, the mode field adaptation length portion is partially or completely contained in the anti-degradation length portion.

[0107] The present invention also includes a method for preparing PCF, comprising:

[0108] · preparing a preform, the preform comprising a preformed structure for the core and cladding regions of the PCF,

[0109] Drawing the preform to obtain the core and cladding regions of the PCF,

[0110] hydrogen and / or deuterium loading of at least the degradation resistant length portion of the PCF, and

[0111] • Applying a primary coating to at least the degradation resistant length portion of the PCF.

[0112] Preferably, the degradation resistant length portion is the entire length of the PCF, optionally except for the closed end of the PCF. Advantageously, the closed end is as described above.

[0113] In one embodiment, the method includes hydrogen and / or deuterium loading the PCF prior to applying the primary coating.

[0114] If hydrogen and / or deuterium loading is performed prior to applying the primary coating, hydrogen and / or deuterium loading comprises placing the PCF in a chamber containing hydrogen and / or deuterium for a duration of at least t1 at a pressure of at least about P1 and a temperature of at least about T1.

[0115] In order to provide a relatively rapid hydrogen and / or deuterium loading, the temperature and optionally the pressure are advantageously increased.

[0116] In one embodiment, T1 is preferably at least 40° C., such as about 50° C. to about 250° C., such as about 100° C. to about 800° C., such as up to about 500° C., such as up to about 200° C. In practice, the material of the PCF sets an upper limit on the temperature T1.

[0117] The loading time t1 is preferably at least about 1 hour, such as about 2 hours to about 200 hours, such as about 24 hours to about 96 hours.

[0118] The loading pressure P1 is preferably greater than about 1 bar, such as from greater than 1 bar to about 250 bar, such as about 50 bar to about 200 bar, such as about 100 bar to about 200 bar.

[0119] In this embodiment, it is desirable to apply the primary coating within a few hours of loading, otherwise a large portion of the loaded hydrogen and / or deuterium may diffuse out of the optical fiber. Preferably, the primary coating is applied to the PCF within about 5 hours, such as about 2 hours, of the end of loading.

[0120] In a preferred embodiment, the method includes hydrogen and / or deuterium loading the PCF after applying the primary coating.

[0121] Thus, the loaded hydrogen and / or deuterium will hardly diffuse out of the PCF after loading, and as described above, the quality of the PCF can be improved. In addition, the amount of loaded hydrogen and / or deuterium may be low, which may result in a shorter loading time.

[0122] Preferably, the method comprises:

[0123] · preparing a preform, the preform comprising a preformed structure for the core and cladding regions of the PCF,

[0124] Drawing the preform to obtain the core and cladding regions of the PCF,

[0125] Applying primary coating to PCF,

[0126] subjecting the PCF to hydrogen and / or deuterium at a temperature of at least about T0, and

[0127] Cool the PCF to T h or lower.

[0128] Cooling may be performed by passive cooling (simply cooling the PCF, e.g., at room temperature) or active cooling (e.g., blowing cold air over the PCF).

[0129] In embodiments where the primary coating is applied prior to loading hydrogen and / or deuterium, loading preferably comprises placing the PCF in a chamber containing hydrogen and / or deuterium for a duration of at least t2, with the chamber having a pressure of at least about P2 and a temperature of at least about T2, T2>T0.

[0130] In one embodiment, T2 is preferably at least 50° C., such as about 75° C. to about 250° C., such as about 100° C. to about 200° C. or more. In practice, the material of the primary coating or any additional coating that may have been applied sets an upper limit on the temperature T2, which means that for certain types of primary coatings, the temperature T2 may be as high as about 500° C., or even as high as about 800° C.

[0131] The loading time T2 is preferably at least about 1 hour, such as about 2 hours to about 200 hours, such as about 24 hours to about 96 hours.

[0132] The loading pressure P2 is preferably greater than about 1 bar, such as from greater than 1 bar to about 250 bar, such as about 50 bar to about 200 bar, such as about 100 bar to about 200 bar.

[0133] If the PCF comprises gas inclusions, then the method of making the PCF preferably comprises enclosing the gas inclusions on either side of the degradation resistant length portion. The method preferably comprises enclosing the gas inclusions at both ends of the PCF.

[0134] In one embodiment, the method includes sealing the gas inclusions prior to hydrogen and / or deuterium loading of the PCF, thereby reducing the risk of hydrogen and / or deuterium diffusing outwardly through the inclusions.

[0135] In one embodiment, the method includes hydrogen and / or deuterium loading of the PCF prior to enclosing the gas inclusions at the fiber end. In one embodiment, loading may include loading through unenclosed gas inclusions followed by enclosing the gas inclusions at the fiber end. In this embodiment, the primary coating may be applied prior to loading.

[0136] The material of the primary coating and its thickness are as described above.

[0137] In one embodiment, the primary coating is applied to the PCF by chemical vapor deposition (CVD) or a similar or improved deposition method.

[0138] In one embodiment, the primary coating is a carbon coating, and the method comprises applying the primary carbon coating by a chemical vapor deposition process. Advantageously, the CVD process comprises drawing the optical fiber through a reactor chamber of a reactor and subjecting the optical fiber in the reactor chamber to a reactor gas having a temperature of at least about 700° C. Preferably, the temperature is in the interval of about 700° C. to about 1100° C., for example about 700° C. to about 900° C. Temperatures above 900° C. may result in the formation of a carbon coating having a diamond-like structure.

[0139] Methods of carbon coating optical fibers may be described, for example, in US5000541.

[0140] The reactor gas may advantageously comprise a carbon-containing compound, preferably an alkyne (C n H 2n-2 ), and / or olefins (C n H 2n+2 ), wherein n is 2 to 10, for example 2 to 4. Preferably, the reactor gas is substantially free of oxygen.

[0141] It has been found that it is very effective to apply the primary carbon coating immediately after the optical fiber is drawn in the draw tower. It is thus ensured that the surface of the optical fiber is not contaminated before the primary coating is applied, and it has also been found that by applying the primary carbon coating immediately after the optical fiber is drawn and not cooling the optical fiber below the reaction temperature of the reactor gases before applying the carbon coating, the optical fiber does not need to be reheated before carbon coating. In an alternative embodiment, the optical fiber is reheated to the reaction temperature. The reaction temperature in the reaction chamber is advantageously at least about 700°C, for example about 800°C to about 1100°C.

[0142] Advantageously, the reactor is an integrated part of the draw tower, preferably so that the optical fiber is drawn through the reactor chamber to apply the carbon coating prior to winding, ie in an in-line process.

[0143] In one embodiment, the method comprises applying an additional coating on the carbon coating. The additional coating is preferably a polymer coating or a metal coating as described above. Preferably, the additional coating is applied to the carbon coating in a draw tower before winding the optical fiber.

[0144] In one embodiment, the primary coating is a metallic coating and the method comprises applying the primary metallic coating by drawing the optical fiber through a liquid metal melt, wherein the temperature of the optical fiber when entering the melt is lower than the temperature of the metal melt.

[0145] The temperature of the metal melt depends on the type of metal.In one embodiment, the metal coating is applied to the optical fiber in a draw tower after the optical fiber is submerged and at least partially cooled, preferably in an in-line process before winding the optical fiber.

[0146] In one embodiment, the method includes applying at least one additional coating, for example, external to the primary coating.

[0147] The present invention also includes a supercontinuum light source comprising a PCF as described above and a pump source configured to feed a pump pulse to an emission end of the PCF.

[0148] In one embodiment, the PCF is configured to generate supercontinuum light having a bandwidth wider than a bandwidth of the pump pulses.

[0149] Advantageously, the PCF is configured to generate supercontinuum light having a bandwidth broadened by at least about 100%, such as at least about 200%, relative to a bandwidth of the pump pulses.

[0150] In one embodiment, the supercontinuum generated has a bandwidth spanning at least one octave.

[0151] The pump source may be any type of pump source capable of providing pump pulses of sufficiently high energy, for example a mode-locked pump source, such as a MOPA with or without a pulse picker (gating component).

[0152] The pump pulses preferably have relatively high peak power. In one embodiment, the pump pulses generated by the pulse source are high peak power pulses having a peak power of at least about 5 kW, such as at least about 10 kW, such as at least about 15 kW, such as at least about 20 kW at the transmitting end of the PCF.

[0153] In one embodiment, the pulse duration of the pump pulses generated by the pulse source is up to about 200 ps, ​​such as up to about 100 ps, ​​such as up to about 50 ps, ​​such as up to about 30 ps, ​​such as up to about 10 ps, ​​such as up to about 8 ps, such as up to about 5 ps, such as up to about 3 ps, such as up to about 1 ps.

[0154] Advantageously, the pump pulses generated by the pulse source have a pulse duration of at least about 200 fs, such as at least about 1 ps, such as at least about 5 ps.

[0155] Preferably, the repetition rate of the pump pulses generated by the pulse source is at least about 100 kHz, such as at least about 10 kHz, such as at least about 1 MHz, and the repetition rate is preferably tunable, for example using an EOM (electro-optic modulator), an AOM (acousto-optic modulator) or an AOTF (acousto-optic tunable filter) that also acts as a filter.

[0156] In one embodiment, the pump pulses generated by the pulse source have a wavelength of about 900 nm to about 1100 nm, such as about 1030 or about 1064 nm.

[0157] In one embodiment, the average output power of the supercontinuum light source is at least about 1 W, such as at least about 5 W, such as at least about 10 W, such as at least about 20 W, such as at least about 50 W, such as at least about 100 W or even at least about 500 W. In general, it has been found that due to the degradation-resistant length portion of the PCF of the present invention, a high-power supercontinuum light source with a desired high output power while having a surprisingly long lifetime can be provided.

[0158] In one embodiment, the output of the supercontinuum light source includes a wavelength less than about 600nm, such as less than about 550nm, such as less than about 450nm, such as less than about 420nm, such as less than about 410nm, such as less than about 400nm, such as less than about 380nm, such as less than about 360nm.

[0159] In one embodiment, the output of the supercontinuum light source includes wavelengths greater than about 1800 nm, such as greater than about 2000 nm, such as greater than about 2200 nm.

[0160] In one embodiment, the supercontinuum light source further comprises a spectral filtering unit configured to filter the output of the supercontinuum source into a filtered SC output having a central wavelength λ1 and an output bandwidth BW1, wherein at least one of the central wavelength λ1 and the output bandwidth BW1 is tunable. The output bandwidth BW1 is advantageously (at least in one tuning) less than about 5 nm. The spectral filtering unit comprises, for example, an AOTF.

[0161] The invention also relates to an illumination source, comprising a supercontinuum light source as described above. Preferably, the illumination source is adapted for stimulated emission depletion.

[0162] In one embodiment, the illumination source is suitable for fluorescence imaging, fluorescence lifetime imaging (FLIM), total internal reflection fluorescence (TIRF) microscopy, fluorescence resonance energy transfer (FRET), broadband spectroscopy, nanophotonics, flow cytometry, industrial detection such as metrology, ring-down spectroscopy such as gas sensing, analytical spectroscopy such as hyperspectral spectroscopy and yield and time-of-flight spectroscopy (TCSPC), single molecule imaging, and / or combinations thereof.

[0163] In one embodiment, the microscope is preferably an optical fluorescence microscope, such as one based on fluorescence lifetime imaging (FLIM), total internal reflection fluorescence (TIRF) microscopy.

[0164] In one embodiment, the spectrometer is preferably a broadband spectrometer.

[0165] The invention also relates to an optical coherence tomography apparatus for optical coherence tomography (OCT), wherein the tomography apparatus comprises an illumination source as described above.

[0166] The invention also relates to industrial inspection comprising an illumination source as described above.

[0167] All features of the invention and embodiments of the invention described above, including ranges and preferred ranges, may be combined in various ways within the scope of the invention, unless there is a specific reason why these features cannot be combined. BRIEF DESCRIPTION OF THE DRAWINGS

[0168] The above and / or other objects, features and advantages of the present invention will be further clarified through the following illustrative and non-limiting description of the embodiments of the present invention with reference to the accompanying drawings.

[0169] Figure 1 is a cross-sectional view of a PCF according to an embodiment of the present invention.

[0170] Figure 2 is a cross-sectional view of a PCF according to another embodiment of the present invention.

[0171] Figure 3 is a cross-sectional view of a PCF according to yet another embodiment of the present invention.

[0172] Figure 4a , 4b 4c show a side view of a PCF according to an embodiment of the present invention, and a cross-section through its first and second length portions, respectively.

[0173] Figure 5 is a schematic diagram of an embodiment of a supercontinuum radiation source according to the present invention.

[0174] Figure 6 is a schematic diagram of a drawing tower in which a primary coating and an additional coating are applied in an in-line process and the drawing tower includes a coating station including a reactor for applying a carbon coating.

[0175] Figure 7 is a schematic diagram of a drawing tower in which a primary coating and an additional coating are applied in an in-line process and the drawing tower includes a coating station for applying the metallic coating.

[0176] The accompanying drawings are schematic and may be simplified for clarity. Throughout, the same reference numerals are used for the same or corresponding parts. DETAILED DESCRIPTION

[0177] According to the description given below, the further application scope of the present invention will become apparent. However, it should be understood that although the detailed description and specific examples are given only in an illustrative manner when describing the preferred embodiments of the present invention, various changes and improvements within the spirit and scope of the present invention will be apparent to those skilled in the art based on the detailed description.

[0178] Figure 1 The PCF shown has a core 1 and cladding regions 2, 3 surrounding the core 1. The PCF has a length not shown and a longitudinal axis that coincides with the central axis of the core in the embodiment shown. The cladding region includes an inner cladding region 2 and an outer cladding region 3. The inner cladding region includes a plurality of microstructures in the form of inclusions extending along the longitudinal axis of the PCF. As described above, the inclusions may include any material, but are advantageously gas inclusions, such as air inclusions. Advantageously, the inclusions are folded at one or more locations along the length of the optical fiber, such as at each end of an anti-degradation length portion, which in one embodiment is substantially the entire length of the PCF described above.

[0179] As can be seen, the cross-sectional view of the PCF is a cross-sectional view in a degradation resistant length portion of the PCF, which, as described above, may include the entire length of the PCF or only a portion of the length of the PCF.

[0180] The PCF is loaded with hydrogen and / or deuterium (not shown), preferably in the form of hydrogen molecules and / or deuterium molecules (H2 / D2). The hydrogen and / or deuterium are usually present in both the core 1 and the cladding regions 2, 3. The PCF includes a h A primary coating 4 which is impermeable to hydrogen and / or deuterium at temperatures of 1000 Å to 2000 Å. Different types of preferred primary coatings are described above.

[0181] The PCF comprises an additional coating 5 for mechanical protection and optionally to provide the PCF with a desired appearance and / or texture.

[0182] In use, when the PCF is subjected to high peak power light as described above, the light may cause defects in the core material. This effect (thought to be caused by a different chemical reaction) is sometimes referred to as photo-induced degradation or photo-blackening. It has been found that hydrogen and / or deuterium mitigate degradation by binding to the material to, for example, terminate free radicals.

[0183] As hydrogen and / or deuterium in the core 1 is consumed, fresh hydrogen and / or deuterium migrates from the cladding regions 2, 3 to the core 1. Since the primary coating 4 is impermeable to hydrogen and / or deuterium when the PCF is in use or when stored prior to use, the required amount of hydrogen and / or deuterium can be relatively low and / or the PCF is protected from excessive degradation for a long time, e.g. up to several years, e.g. 3, 4 or even 5 years or more.

[0184] The PCF is advantageously silicon dioxide, for example doped as described above.

[0185] Figure 2 The PCF shown has a core 11 and a cladding region 12 surrounding the core 11. The PCF has a length not shown and a longitudinal axis that coincides with the central axis of the core 11 in the embodiment shown. The cladding region 12 includes a plurality of microstructures 12a in the form of inclusions in a cladding background material 12b. The inclusions 12a extend along the longitudinal axis of the PCF. As described above, the inclusions may include any material, but are advantageously gas inclusions, such as air inclusions. Advantageously, the inclusions are folded at one or more locations along the length of the optical fiber, such as at each end of an anti-degradation length portion, which in one embodiment is substantially the entire length of the PCF as described above.

[0186] A plurality of inclusions 12a are arranged in the cladding region in a pattern comprising a plurality of inclusion rings surrounding the core. The innermost inclusion ring surrounding the core is marked by a dashed ring 12c.

[0187] As can be seen, the cross-sectional view of the PCF is a cross-sectional view in a degradation resistant length portion of the PCF, which, as described above, may include the entire length of the PCF or only a portion of the length of the PCF.

[0188] PCF includes below T h A primary coating 14 that is impermeable to hydrogen and / or deuterium at temperatures of 1.40°C. Different types of preferred primary coatings are described above.

[0189] The PCF comprises an additional material layer 16 sufficiently far from the core 11 that it has no effect as a cladding (ie the refractive index of the material of the material layer 16 does not affect the light conduction of the core).

[0190] The radial distance 17 between the outermost layer of the inclusions 12a in the cladding region and the primary coating 14 is at least about 10 μm.

[0191] The additional material layer 16 may be of the same or different material than the cladding background material 12b. Advantageously, the additional material layer 16 is selected to have a high capacity for hydrogen and / or deuterium, thereby acting as a reservoir for hydrogen and / or deuterium.

[0192] As mentioned above, the PCF is loaded with hydrogen and / or deuterium, not shown. The hydrogen and / or deuterium are usually in the core 11 and the cladding region 12 and the additional material layer 16.

[0193] In use, when the PCF is subjected to high peak power light as described above, and when hydrogen and / or deuterium in the core 11 is consumed, fresh hydrogen and / or deuterium migrates from the cladding region 12 and the material layer 16 to the core 11. Since the primary coating 14 is impermeable to hydrogen and / or deuterium when the PCF is in use or is stored prior to use, the required amount of hydrogen and / or deuterium can be relatively low and / or the PCF is protected from excessive degradation for a long time, such as up to several years, such as 3, 4 or even 5 years or longer.

[0194] The PCF is advantageously silicon dioxide, for example doped as described above.

[0195] Figure 3 The PCF shown has a core 21 and cladding regions 22, 23 surrounding the core 21. The PCF has a length not shown and a longitudinal axis which coincides with the central axis of the core 21 in the embodiment shown.

[0196] The cladding region includes an inner cladding region 22 and an outer cladding region 23. The inner cladding region 22 includes inner inclusions 22a in an inner cladding background material 22b. The outer cladding region 23 includes outer inclusions 23a in an outer cladding background material 22b.

[0197] Inner inclusions 22a include two rings of inner inclusions, and outer inclusions 23a include five rings of outer inclusions.

[0198] The inclusions 22a, 23a extend along the longitudinal axis of the PCF. As described above, the inclusions may comprise any material, but are advantageously gas inclusions, such as air inclusions. Advantageously, the inclusions are folded at one or more locations along the length of the optical fiber, such as at each end of a degradation resistant length portion, which in one embodiment is substantially the entire length of the PCF as described above.

[0199] The background material 22b of the inner cladding region 22 and the background material 23b of the outer cladding region 23 and optionally the core material advantageously have the same material, for example silicon dioxide optionally doped with fluorine.

[0200] As can be seen, the cross-sectional view of the PCF is a cross-sectional view in a degradation resistant length portion of the PCF, which, as described above, may include the entire length of the PCF or only a portion of the length of the PCF.

[0201] PCF includes below T h A primary coating 24 that is impermeable to hydrogen and / or deuterium at temperatures of 100°C is provided. Different types of preferred primary coatings are described above.

[0202] The PCF comprises an additional layer 26 of material sufficiently distant from the core 21 that it has any effect as a cladding.

[0203] In this embodiment, the additional material layer 26 may be the same as the cladding background material 23b.

[0204] The radial distance 27 between the outermost layer of the inner inclusion 22a of the inner cladding region and the primary coating 24 is at least about 10 μm.

[0205] As mentioned above, the PCF is loaded with hydrogen and / or deuterium, not shown. The hydrogen and / or deuterium are typically in the core 21 and the cladding regions 22, 23 and the additional material layer 26.

[0206] In use, when the PCF is subjected to high peak power light as described above, and when hydrogen and / or deuterium in the core 21 is consumed, fresh hydrogen and / or deuterium migrates to the core 21 from the cladding regions 22 , 23 and the material layer 26 .

[0207] Figure 4a , 4b 4c show an embodiment of a PCF 30 comprising two spliced ​​optical fiber lengths, wherein at least one of the spliced ​​optical fiber lengths is or comprises a degradation resistant length as described above. This type of optical fiber is also known as a spliced ​​cascade optical fiber. Figure 4b is a cross-sectional view of the first length portion 31, and Figure 4c is a cross-sectional view of a second length portion 32 spliced ​​to a first length portion. Preferably, at least the first length portion 31 of the PCF is a degradation resistant length portion as described above.

[0208] The PCF 30 is configured to generate supercontinuum light when light having a first wavelength λ1, for example, from about 900 nm to about 1100 nm, is fed to an emission end 34 of the PCF 30 .

[0209] Along its length, the optical fiber 30 comprises a first length portion 31, a second length portion 32 and a splice 33 between the first and second length portions 32, 33. The optical fiber 30 may optionally include an end cap, not shown, to enclose the contents.

[0210] The first length portion 31 has a core 41a having a first core diameter W1 and a cladding region 32a having a first spacing Λ1, a first inclusion diameter d1, and a first relative size Λ1 / d1 of the inclusions. The first length portion includes a portion below T h The primary coating 44a is impermeable to hydrogen and / or deuterium at a temperature of 100°C. The preferred primary coatings of different types are described above. At least the first length portion is loaded with hydrogen and / or deuterium.

[0211] The second length portion 32 has a core 41b having a second core diameter W2 and a cladding region 42b having a second pitch Λ2, a second inclusion diameter d2, and a second relative size Λ2 / d2 of the inclusions.

[0212] Advantageously, at least one of the first core diameter W1, the first spacing Λ1, the first inclusion diameter d1 and the first relative size Λ1 / d1 of the inclusions is different from the corresponding sizes of the second core diameter W2, the second spacing Λ2, the second inclusion diameter d2 and the second relative size Λ2 / d2 of the inclusions of the second length portion 32.

[0213] Throughout the first length portion 31 the dimensions of the optical fiber are substantially constant, and throughout the second length portion 32 the dimensions of the optical fiber are substantially constant.

[0214] In this embodiment, the respective lengths of the first length portion 31 and the second length portion 32 are 1-10 m and 10 μm, respectively. However, it should be understood that these lengths are given as examples only and that the optical fiber length portions may in principle have any other lengths.

[0215] Figure 5 Schematic diagram of a supercontinuum light source. The supercontinuum light source 50 includes a PCF 54 including an anti-degradation length portion as described above and a pump source 52. The PCF has two ends: an emission end 55 and an output end 56. Figure 5 In the embodiment, the transmitting end 55 of the PCF 54 has a mode adapter 58 or is optically connected to the mode adapter 58 to adapt the mode of the pump pulses from the pump source 52. Figure 5 In the figure, the mode adapter 58 is shown as if it is larger than the optical fiber 54; however, this is for illustration purposes only, and in fact, the mode adapter can have any suitable external dimensions, such as external dimensions similar to the external dimensions of the optical fiber 54. Although the output end 56 of the optical fiber 54 is shown as if it is a free end, the output end can have an end cap or can be spliced ​​to another device.

[0216] Pump light source 52 has an output 53 configured to feed light into PCF 54 via delivery fiber 57 and mode adapter 58, and a supercontinuum is generated in the PCF and output from PCF output 56. Delivery fiber 57 may, for example, be omitted or replaced by an optical element such as a lens.

[0217] Figure 6The drawing tower is shown drawing PCF 63 from a preform 63a. The preform is enclosed in a pressure control chamber 61, which includes one or more pressure chambers for controlling the pressure of the gas content in the PCF. The bottom extends into a furnace 62, where the bottom of the preform is heated to enable the PCF 63 to be drawn. The speed of the PCF, and thus the diameter of the PCF, is controlled by a drawing wheel 69, which pulls the PCF through the various stations of the drawing tower. The speed of the PCF 63 is adjustable, and by adjusting the temperature of the furnace 62 and the speed of the PCF 63, the diameter of the optical fiber can be adjusted. The PCF passes through a monitoring station 67a, where the diameter of the PCF from the furnace 62 is monitored online.

[0218] From the monitoring station 67a, the PCF 63 is transferred to the coating station for application of the primary carbon coating.

[0219] PCF 63 passes through the reactor chamber of reactor 64 and is introduced and withdrawn from the reaction in a continuous flow as indicated by the arrows to maintain a substantially constant amount of fresh gas in the reactor.

[0220] To ensure that PCF 63 has a sufficiently high temperature when entering reactor 64, it is desirable that the reactor be relatively close to where PCF 63 leaves furnace 62. Alternatively, an oven may be placed before the reactor to preheat PCF 63, but this latter alternative is not preferred due to the additional cost of the oven.

[0221] The thickness of the carbon layer can be adjusted, for example, by adjusting the concentration of the reactive carbon-containing gas in the reactive gas or by changing the PCF speed.

[0222] The carbon coated PCF is transferred from the reactor to another coating station for application of an additional coating, which in the illustrated embodiment is a polymer coating station 65. From the coating station the coated PCF is transferred to a concentricity monitor 67b and further to a curing station 66 where the polymer coating is photocured.

[0223] The coated PCF 63 is further transferred from the curing station 66 to another monitor 67c for monitoring the optical fiber diameter. The coated PCF 63 is transferred from the drawing wheel 69 to be wound onto the reel 68.

[0224] Advantageously, the coated PCF 63 may be hydrogen or deuterium loaded on the reel by placing the coated PCF on the reel 68 in hydrogen and / or deuterium in a loading chamber.

[0225] Figure 7The drawing tower is shown drawing PCF 73 from a preform 73a. The preform is enclosed in a pressure control chamber 71, which includes one or more pressure chambers for controlling the pressure of the gas content in the PCF. The bottom extends into a furnace 72, where the bottom of the preform is heated and the optical fiber 73 is drawn to the desired thickness. The speed of the optical fiber is controlled by a drawing wheel 79, which pulls the PCF 73 through the various stations of the drawing tower. The optical fiber is conveyed from the furnace 72 through a monitoring station 77a, where the diameter of the optical fiber is monitored online.

[0226] From the monitoring station 77a, the PCF 73 is transferred to the coating station 74 for application of the primary metal coating.

[0227] The coating station 74 includes a liquid metal melt at a relatively high temperature, but to ensure a uniform coating, the temperature of the optical fiber should be lower than that of the melt. A blower or similar cooling device may be applied before the coating station 74 to blow cold air 70 to cool the PCF 73 .

[0228] Suitable melt temperatures are listed in Table 1

[0229]

[0230]

[0231] Table 1

[0232] PCF 73 passes through the metal melt at a desired speed equal to the fiber drawing speed. The thickness of the metal coating can be adjusted, for example, by adjusting the amount of melt in the melt chamber of the coating station 74 or the fiber speed.

[0233] The metal coated PCF is further transferred from coating station 74 to a further coating station 75 for application of an additional coating, which in the illustrated embodiment is a polymer coating station 75. The coated PCF is transferred from coating station 75 to a concentricity monitor 77b and further to a curing station 76 where the polymer coating is light cured.

[0234] The coated PCF is further transferred from the curing station 76 to another monitor 77c for monitoring the optical fiber diameter. The coated PCF is transferred from the drawing wheel 79 to be wound onto the reel 78.

Claims

1. A supercontinuum light source comprising a microstructured optical fiber (MSF) and a pump source configured to feed a pump pulse to an emission end of the MSF, the MSF comprising a solid core extending along a length of a longitudinal axis and a cladding region surrounding the core, wherein: At least the cladding region comprises a plurality of microstructures in the form of inclusions extending along the longitudinal axis of the MSF in at least a microstructure length portion, wherein the MSF comprises hydrogen and / or deuterium in at least a degradation resistant length portion of the microstructure length portion, and comprises a coating surrounding the cladding region, wherein the coating is resistant to degradation at a depth below T h is impermeable to hydrogen and / or deuterium at a temperature of h of at least about 50° C., wherein the MSF further comprises an additional coating, wherein the additional coating is a polymer coating, wherein at least the cladding region in the degradation-resistant length portion comprises an inner cladding region comprising the inclusions and an outer cladding region surrounding the inner cladding region, wherein a radial distance between the outermost inclusions of the inner cladding region and the coating is at least about 10 μm, and wherein the material between the inner cladding region and the coating comprises silicon dioxide and forms a reservoir for hydrogen and / or deuterium.

2. The supercontinuum light source according to claim 1, wherein: The additional coating is external to the coating.

3. The supercontinuum light source according to claim 1, wherein: The coating includes nitride, carbon, aluminum, gold, copper, nickel, metallic glass, or a combination or alloy comprising one or more of the foregoing.

4. The supercontinuum light source according to claim 1, wherein: The plurality of inclusions in the cladding region are arranged in a pattern comprising at least two rings of inclusions surrounding the core.

5. The supercontinuum light source according to claim 1, wherein: The inclusions include gas inclusions that are enclosed on both sides of the degradation resistant length portion.

6. The supercontinuum light source according to claim 1, further comprising outer inclusions contained in the outer cladding region, wherein the inclusions contained in the inner cladding region are larger than the outer inclusions contained in the outer cladding region.

7. The supercontinuum light source according to claim 6, wherein: The inclusions contained in the inner cladding region include at least one inner inclusion ring, and the outer inclusions contained in the outer cladding region include at least one outer inclusion ring.

8. The supercontinuum light source according to claim 6, wherein: The inclusion contained in the inner cladding region has a diameter d inner , which is smaller than the diameter d of the outer inclusions contained in the outer cladding region outer At least about 15% greater.

9. The supercontinuum light source according to claim 1, wherein: In at least the degradation resistant length portion, the innermost inclusions are less than about 50 μm center-to-center from the core.

10. The supercontinuum light source according to claim 1, wherein: At least the core of the MSF is substantially free of germanium and / or is substantially undoped silicon dioxide or fluorine-doped silicon dioxide.

11. The supercontinuum light source according to claim 1, wherein: At least the core of the MSF is substantially free of active material.

12. The supercontinuum light source according to claim 1, wherein: The MSF includes at least one tapered length portion, wherein the core has a core diameter D1 at a first end of the tapered length portion, and the core has a core diameter D2 at a second end of the tapered length portion, wherein D1 is greater than D2.

13. The supercontinuum light source according to claim 1, wherein: The MSF comprises at least two spliced ​​optical fiber length sections, wherein at least one spliced ​​optical fiber length section is or comprises the degradation-resistant length section.

14. The supercontinuum light source according to claim 1, wherein: The MSF includes a mode adapter extending along the length of the MSF, the mode adapter at least in a mode field adaptation length portion extending from an emission end of the MSF or extending up to 5 cm from the emission end of the MSF, wherein the length of the mode field adaptation length portion is at least about 5 cm.

15. The supercontinuum light source according to claim 1, wherein: The MSF is configured to generate supercontinuum light having a bandwidth wider than a bandwidth of the pump pulse.

16. The supercontinuum light source according to claim 1, wherein: The pump pulses generated by the pulse source are high peak power pulses having a peak power of at least about 5 kW at the transmit end of the MSF.

17. The supercontinuum light source according to claim 1, wherein: The pulse duration of the pump pulses generated by the pulse source is up to about 200 ps.

18. The supercontinuum light source according to claim 1, wherein: The supercontinuum light source has an average output power of at least about 1 W.

19. The supercontinuum light source according to claim 1, wherein: The output of the supercontinuum light source includes wavelengths less than about 600 nm.

20. The supercontinuum light source according to claim 1, wherein: The supercontinuum light source also includes a spectral filtering unit, which is configured to filter the output of the supercontinuum source into a filtered supercontinuum output having a central wavelength λ1 and an output bandwidth BW1, wherein at least one of the central wavelength λ1 and the output bandwidth BW1 is tunable, and the output bandwidth BW1 is less than about 5 nm.

21. The supercontinuum light source according to claim 1, wherein: 50℃<T h <250℃。 22. The supercontinuum light source according to claim 1, wherein: The coating is open to the diffusion of hydrogen and / or deuterium at a temperature above T0, wherein T0 is greater than T h .

23. A microstructured optical fiber (MSF) for a supercontinuum light source, the MSF comprising a solid core extending along the length of a longitudinal axis and a cladding region surrounding the core, wherein: At least the cladding region comprises a plurality of microstructures in the form of inclusions extending along the longitudinal axis of the MSF in at least a microstructure length portion, wherein the MSF comprises hydrogen and / or deuterium in at least a degradation resistant length portion of the microstructure length portion, and the MSF further comprises a coating surrounding the cladding region in at least the degradation resistant length portion, wherein the coating is formed below T h is impermeable to hydrogen and / or deuterium at a temperature of h of at least about 50° C., wherein the MSF further comprises an additional coating, wherein the additional coating is a polymer coating, wherein at least the cladding region in the degradation-resistant length portion comprises an inner cladding region comprising the inclusions and an outer cladding region surrounding the inner cladding region, wherein a radial distance between the outermost inclusions of the inner cladding region and the coating is at least about 10 μm, and wherein the material between the inner cladding region and the coating comprises silicon dioxide and forms a reservoir for hydrogen and / or deuterium.

24. The microstructured optical fiber (MSF) according to claim 23, wherein: The additional coating is external to the coating.

25. The microstructured optical fiber (MSF) according to claim 23, wherein: The inclusions include gas inclusions that are enclosed on both sides of the degradation resistant length portion.

26. The microstructured optical fiber (MSF) of claim 23, further comprising outer inclusions contained in the outer cladding region, wherein the inclusions contained in the inner cladding region are larger than the outer inclusions contained in the outer cladding region.

27. The microstructured optical fiber (MSF) according to claim 26, wherein: The inclusions contained in the inner cladding region include at least one inner inclusion ring, and the outer inclusions contained in the outer cladding region include at least one outer inclusion ring.

28. The microstructured optical fiber (MSF) according to claim 26, wherein: The inclusion contained in the inner cladding region has a diameter d inner , which is smaller than the diameter d of the outer inclusions contained in the outer cladding region outer At least about 15% greater.

29. The microstructured optical fiber (MSF) of claim 23, wherein: In at least the degradation resistant length portion, the innermost inclusions are less than about 50 μm center-to-center from the core.

30. The microstructured optical fiber (MSF) of claim 23, wherein: At least the core of the MSF is substantially free of germanium and / or is substantially undoped silicon dioxide or fluorine-doped silicon dioxide.

31. The microstructured optical fiber (MSF) of claim 23, wherein: At least the core of the MSF is substantially free of active material.

32. The microstructured optical fiber (MSF) of claim 23, wherein: The MSF includes at least one tapered length portion, wherein the core has a core diameter D1 at a first end of the tapered length portion, and the core has a core diameter D2 at a second end of the tapered length portion, wherein D1 is greater than D2.

33. The microstructured optical fiber (MSF) of claim 23, wherein: The MSF comprises at least two spliced ​​optical fiber length sections, wherein at least one spliced ​​optical fiber length section is or comprises the degradation-resistant length section.

34. The microstructured optical fiber (MSF) of claim 23, wherein: The coating includes nitride, carbon, aluminum, gold, copper, nickel, metallic glass, or a combination or alloy comprising one or more of the foregoing.

35. The microstructured optical fiber (MSF) of claim 23, wherein: Hydrogen and / or deuterium can pass through the coating at a temperature above T0, wherein T0 is greater than T h .

36. The microstructured optical fiber (MSF) of claim 23, wherein: The plurality of inclusions in the cladding region are arranged in a pattern comprising at least two rings of inclusions surrounding the core.

37. The microstructured optical fiber (MSF) of claim 23, wherein: Diffusion of hydrogen and / or deuterium through the gas impermeable coating is less than 1% per day.

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