Extended lifetime and improved performance of microstructured fibers through high temperature loading process

Abstract

To extend the life of a supercontinuum light source. The present invention relates to an optical fiber comprising a core made of a core material and a cladding made of a cladding material, the optical fiber being a nonlinear microstructured optical fiber, which can be obtained by a method comprising a step of loading the core material and, optionally, the cladding material, and the lifetime of the optical fiber can be extended in high pulse applications.

Description

[Technical Field]

[0001] More particularly, the present invention relates to a nonlinear microstructured optical fiber that includes a core made of a core material and a cladding made of a cladding material. [Background technology]

[0002] Recently, optical fibers known as microstructured optical fibers, photonic crystal optical fibers (PCFs), and holey optical fibers have been developed (some of these optical fibers are specifically called photonic bandgap optical fibers (PBGs)). Photonic crystal optical fibers consist of a cladding made of a transparent material with a series of holes embedded along the fiber's length (see Non-Patent Document 1). The holes are typically arranged laterally periodically and are filled with a material having a lower refractive index than the rest of the cladding. The center of the optical fiber typically contains a transparent region that interrupts the periodicity of the cladding. This region often functions as the fiber's core. However, in principle, this region does not have to be located at the center of the cross section. The cross section of an optical fiber typically includes a core region made of core material, surrounded by a cladding region containing holes (optionally filled with air or gas), and solid or liquid microstructured elements embedded in the cladding background material. Both regions extend along the fiber's length. The core typically guides more than 80% of the light at the fiber's operating wavelength. Generally, both the core and cladding are made of pure silica, and the holes are filled with air. A variation of the photonic crystal optical fiber is one in which, instead of holes, rods made of another material are arranged laterally. Such an optical fiber is disclosed, for example, in Patent Document 1. Patent Document 1 also discloses several photonic crystal optical fibers with holes arranged laterally.

[0003] Photonic crystal optical fibers are typically manufactured from rod-shaped units. The rod-shaped units are stacked to form a preform, which is then processed through one or more steps to form the final optical fiber. Non-Patent Document 2 discloses a method for manufacturing a preform from capillary rods formed by stacking tubes. A method for manufacturing photonic crystal optical fibers is also described in Non-Patent Document 3.

[0004] US Patent No. 5,999,623 discloses a method for manufacturing a microstructured optical fiber preform by placing a plurality of elongated elements parallel to one another in a tube, filling at least a portion of the tube with a silica-containing sol, followed by drying and sintering.

[0005] Microstructured optical fibers are a relatively new technology that offers considerable freedom in designing the waveguide properties. These fibers are typically composed of pure silica (often holes or doped glass) with patterns extending along the fiber's length. This design flexibility makes them interesting for applications requiring the inherent nonlinear properties of optical fibers. One such application is supercontinuum generation, which allows the production of broad-spectrum output from optical fiber light sources. Supercontinuum (SC) generation in microstructured optical fibers has been investigated for several years as a source of spatially coherent broadband light (called white light or supercontinuum light). New applications for such sources are continually being discovered, some of which are categorized as fluorescence microscopy, laser precision spectroscopy, and optical coherence tomography (OCT). High-brightness illumination in the visible portion of the spectrum is particularly important for confocal fluorescence microscopy. However, insufficient output power in the shorter wavelength portion of the spectrum has prevented the full potential of supercontinuum sources from being realized in this region. The experiments presented here focused on high-power, visible supercontinuum generation.

[0006] While most research to date has been based on seeding nonlinear optical fibers with femtosecond (fs) lasers, supercontinuum generation using nanosecond and picosecond (ps) lasers has also been demonstrated. The latter significantly reduces the cost and simplifies the system while maintaining high repetition rates and efficient supercontinuum generation. It is also typically possible to produce a spectrally more uniform supercontinuum spectrum in the picosecond regime. In the picosecond regime, more powerful seed sources can be used, resulting in a more powerful supercontinuum while remaining below the damage threshold of the optical fiber. Overall, picosecond systems are often more attractive for real-world applications outside of optical laboratories. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] International Publication No. 00 / 37974 [Patent Document 2] International Publication No. 03 / 078338 [Non-patent literature]

[0008] [Non-Patent Document 1] JCKnight et al., "Opt. Lett. 21", 1996, p. 1547: "Errata: Opt. Lett. 22", 1997, p. 484 [Non-patent document 2] TABirks et al., “2D Photonic band gap structures in fiber form”, Photonic Band Gap Materials, Kluwer, 1996, [Non-patent document 3] Bjarklev, Broeng, Bjarklev, "Photonic crystal fibers (Chapter 4)", Kluwer Academic Press, 2003, pp. 115-130. Summary of the Invention [Problem to be solved by the invention]

[0009] The average power and spectral density of a supercontinuum source, as well as the width of the supercontinuum, are limited by the damage threshold of the nonlinear optical fiber. If the maximum power or pulse energy is greater than the bulk glass or glass-to-air interface damage threshold, the input facet or the first few millimeters of the optical fiber can collapse, causing catastrophic failure of the system. The inventors have observed that when the maximum power or pulse energy is below this threshold, nonlinear microstructured optical fibers can degrade over time. This degradation is typically observed as a decrease in visible power output over time. For commercial applications, a long lifetime for a supercontinuum source is important, and such degradation of the optical fiber is typically unacceptable. [Means for solving the problem]

[0010] It is an object of the present invention to provide a nonlinear microstructured optical fiber in which the above degradation is eliminated or reduced to an acceptable level. The objects of the present invention are achieved by the invention as defined in the appended claims and as described below.

[0011] The object of the present invention as defined in claim 1 is achieved by an optical fiber comprising a core made of a core material and a cladding made of a cladding material, said optical fiber being a nonlinear microstructured optical fiber, said microstructured optical fiber being obtained by a manufacturing method including a loading step of loading said core material and optionally said cladding material with at least one of hydrogen and deuterium. Such an optical fiber may have properties suitable for a long lifetime in applications for guiding pulses at high peak powers.

[0012] Deuterium loading is sometimes applied in the art to overcome absorption due to the so-called water-band, which increases when an optical fiber is placed in a hydrogen-rich environment, such as found in undersea communication cables. This problem is different from the problem described herein. Thus, in one embodiment, the optical fiber contains less than 5 atomic percent (at%), or alternatively less than 1 at%, less than 0.1 at%, less than 0.01 at%, or less than 0.001 at% H ions and H + The ion is applied to an environment in which the ion is placed in a medium containing at least one of the ions.

[0013] In one embodiment, the nonlinear optical fiber has a wavelength of at least λ min ~λ max and has a nonlinearity parameter γ, and over at least a portion of the range, the product γ×λ is 4×10 -9 W -1 or more, or 5 x 10 -9 W -1 That's it, 6 x 10 -9 W -1 That's it, 7 x 10 -9 W -1 That's it, 8 x 10 -9 W -1 That's it, 10 x 10 -9 W -1 That's it, 20 x 10 -9 W -1 or more, or 40 x 10 -9 W -1 The nonlinear parameter γ is defined by the following equation:

[0014]

number

[0015] where n2 is the nonlinear refractive index of the optical fiber material, A eff is the practical mode area of ​​the optical fiber. Typically, for silica glass, n2 is approximately 2.6 × 10 -20 m 2 / W. In one embodiment, the nonlinear optical fiber has a nonlinear parameter γ when guiding a wavelength of 1550 nm, and the nonlinear parameter γ is 3×10 -3 (Wm) -1 or more, or 5 x 10 -3 (Wm) -1 That's it, 10 x 10 -3 (Wm) -1 That's it, 15 x 10 -3 (Wm) -1 That's it, 20 x 10 -3 (Wm) -1 That's it, 30 x 10 -3 (Wm) -1 That's it, 40 x 10 -3 (Wm) -1 or more, or 50 x 10 -3 (Wm) -1 This means an optical fiber that satisfies the above requirements.

[0016] In one embodiment, the nonlinear optical fiber has a nonlinear parameter γ when guiding a wavelength of 1064 nm, and the nonlinear parameter γ is 5×10 -3 (Wm) -1 or more, or 10 x 10 -3 (Wm) -1 That's it, 15 x 10 -3 (Wm) -1 That's it, 20 x 10 -3 (Wm) -1 That's it, 30 x 10 -3 (Wm) -1 That's it, 40 x 10 -3 (Wm) -1 or more, or 50 x 10 -3 (Wm) -1 This means an optical fiber that satisfies the above requirements.

[0017] In one embodiment, the nonlinear optical fiber has a wavelength of at least λ min ~λ max and the mode field diameter MFD of the fundamental mode is at least a portion of said range, and the ratio of MFD / λ is 5 or less, alternatively 4 or less, 3 or less, 2 or less, or 1 or less.

[0018] In one embodiment, nonlinear optical fiber refers to an optical fiber having a mode field diameter MFD of 10 μm or less, alternatively 8 μm or less, 6 μm or less, 5 μm or less, 4 μm or less, 3 μm or less, 2 μm or less, or 1 μm or less when guiding a wavelength of 1550 nm.

[0019] In one embodiment, nonlinear optical fiber refers to an optical fiber having a mode field diameter MFD of 6 μm or less, alternatively 5 μm or less, 4 μm or less, 3 μm or less, 2 μm or less, or 1 μm or less when guiding a wavelength of 1064 nm.

[0020] In the various embodiments described above, the wavelength λ min ~λ max The range may be one selected from the group consisting of 350 nm to 2000 nm, 980 nm to 1550 nm, 1100 nm to 1550 nm, and 1300 nm to 1450 nm. In one embodiment, when the optical fiber is single-mode, the wavelength λ min ~λ max The range of is chosen to limit consideration to a range of wavelengths.

[0021] In a preferred embodiment, the optical fiber is a silica fiber, and at least a portion of the core is silica. Preferably, at least the entire core is silica, i.e., the entire core and some or all of the cladding. Because microstructured optical fibers are guided by holes extending within the cladding, the optical fiber is often entirely composed of undoped silica (i.e., both the core and cladding are composed of silica). This differs from, for example, standard single-mode telecommunications optical fibers, whose cores are typically doped with germanium to modify their refractive index. Thus, in one embodiment, the core of the optical fiber contains 10 at.% or less germanium, or alternatively, less than 5 at.%, less than 3 at.%, less than 2 at.%, less than 0.1 at.%, less than 0.01 at.%, or less than 0.001 at.% germanium.

[0022] In one embodiment, the present invention provides an optical system including the optical fiber of the present invention and a supply section, the supply section having a power output of 100 W / μm2 or more than 500W / μm 2 More than 1000W / μm 2 More than 2500W / μm 2 More than 5000W / μm 2 More than 7500W / μm 2 or more than 10000W / μm 2 The present invention relates to an optical system configured to supply the optical fiber with pulses of maximum power density within the optical fiber, pulses producing such power densities in the optical fiber being referred to in this application as high pulse applications.

[0023] The supply is typically a pump light source and may comprise one or more amplifiers. The supply may in principle be an optical system that supplies pulses to an optical fiber with a specific power density within the optical fiber.

[0024] Due to exposure to high peak powers, the optical fiber of the present invention experiences little or no degradation, which may extend the operating life of the system. In one embodiment, the present invention relates to a supercontinuum light source comprising a pulsed pump light source and an optical fiber of the present invention. The pump light source has an output of 100 W / μm 2 or more than 500W / μm 2 More than 1kW / μm 2 More than 2.5kW / μm 2 More than 5kW / μm 2 More than 7.5kW / μm 2 More than 10kW / μm 2 More than 15kW / μm 2 or more, or 20kW / μm 2 The pump and optical fiber are configured to provide pulses at a maximum power density within the optical fiber, and / or the pump and optical fiber are configured to provide a power span of at least one octave at at least 10 μW / nm, and / or the pump and optical fiber are configured to provide a maximum modulation instability gain Ω max is configured to exceed 20 or 40.

[0025] Maximum modulation instability gain Ω max is obtained by the following formula:

[0026]

number

[0027] where β2 is the group velocity at the pump wavelength, P peak is the maximum pump power, and γ is a nonlinear parameter related to the pump wavelength. In one embodiment, a span of more than one octave is achieved with the nonlinear optical fiber SC-5.0-1040 available from the Danish company Crystal Fiber A / S. Using this optical fiber with a maximum output power of 200 W pumped at 1064 nm, Ω max =22 (a maximum output of 200 W can be obtained with, for example, a 50 MHz, 100 mW input signal and a 10 picosecond pulse).

[0028] A phase spanning (i.e., spanning) at least one octave at at least a particular power value (per nm wavelength) means, in this invention, that the output light spectrum from the light source spans at least one octave, with the particular power value defining the outer limits of the spectrum. While the spectrum may have multiple holes, it is assumed that more than 25% of the spanned spectrum has at least the particular power value. In one embodiment, at least 30%, or at least 40%, 60%, 80%, 99%, or 99.9% of the spanned spectrum has at least the particular power value.

[0029] In one embodiment, the power is at least 50 μW / nm, or 500 μW / nm or more, 1 mW / nm or more, 5 mW / nm or more, or 10 mW / nm or more, spanning at least one octave. Depending on the power limits selected, an embodiment may span 0.5 octaves or more, 1.5 octaves or more, or 2 octaves or more.

[0030] In one aspect, the present invention provides a method for manufacturing a microstructured optical fiber comprising a core made of a core material and a cladding made of a cladding material, the optical fiber having an extended lifetime in high pulse applications, the method comprising: a) loading the core material, and optionally the cladding material, with at least one of hydrogen and deuterium; and b) heating the core material and optionally the cladding material at a temperature T anneal At time t anneal and optionally annealing during this period.

[0031] Such manufacturing methods may be advantageously applied to the manufacture of the optical fiber of the present invention, and the properties described with respect to the optical fiber properties may be applied, mutatis mutandis, to the method of manufacturing the optical fiber.

[0032] In one embodiment, the loading step is performed by appropriately placing the optical fiber material in at least one of hydrogen and deuterium under loading conditions so as to chemically bond the at least one of the hydrogen and deuterium to the at least one of the core material and the cladding material, the loading conditions preferably including at least one of a) elevated temperature T; b) elevated pressure P; and c) subsequent irradiation.

[0033] In one embodiment, the present invention relates to an optical fiber of the present invention, an optical system of the present invention, a light source of the present invention, and / or a device comprising an optical fiber manufactured according to the present invention, which device may comprise various forms of systems such as fluorescence microscopy, laser precision spectroscopy, optical coherence tomography (OCT), and the like.

[0034] It has been found that deteriorated optical fibers can be regenerated, typically with an extended lifetime compared to a virgin or unloaded homogeneous optical fiber. Thus, in one embodiment, the present invention relates to a method for regenerating a microstructured optical fiber comprising a core made of a core material and a cladding made of a cladding material. The optical fiber is pulsed in a high-pulse application, thereby increasing its absorption in the visible. The regeneration method may include a loading step of loading at least one of hydrogen and deuterium into the optical fiber.

[0035] As used herein, the words "comprise" and "consist" specify a stated feature, integer, step, or component and do not exclude the presence or addition of at least one of other stated features, integers, steps, components, or groups thereof. [Brief explanation of the drawings]

[0036] [Figure 1] Typical supercontinuum spectra observed in a conventional microstructured optical fiber during initial operation (A) and after 35 hours of operation (B). The reduction in the visible spectrum indicates degradation of the optical fiber. [Figure 2] Figure 1 shows the attenuation of a conventional nonlinear optical fiber after 35 hours of operation as a function of the position in the optical fiber. [Figure 3] Absorption at 633 nm as a function of position in a nonlinear optical fiber. [Figure 4] Supercontinuum spectra shown at the beginning of the experiment (A), after 35 hours when a visible drop was observed (B), and after reheating the optical fiber to 250°C (C). [Figure 5] Supercontinuum spectra after 35 hours (A) when a visible drop was observed, after heating the optical fiber to 250 °C (B), and after loading deuterium into the optical fiber (C). [Figure 6]Figure 1 shows the visible output measured as a function of time for a nonlinear optical fiber with deuterium loading at 160°C (A), with deuterium loading at 80°C (B), and without deuterium loading (C). [Figure 7] Diagram showing extracted lifetimes as a function of three different deuterium loading temperatures (A) and exponential fit to measurements (B). [Figure 8] Figure 1 shows the measured spectra of a deuterium-loaded nonlinear optical fiber after 0 hours (A), 188 hours (B), 260 hours (C), 305 hours (D), and 450 hours (E). [Figure 9] FIG. 1 shows the measured visible output as a function of time for a nonlinear optical fiber with low glass impurities. DETAILED DESCRIPTION OF THE INVENTION

[0037] The present invention is explained more fully below by preferred embodiments and drawings. The figures are schematic and simplified for clarity, showing only the details essential for understanding the invention and omitting other details.

[0038] The scope of the present invention will become apparent from the detailed description set forth hereinafter. The detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from the detailed description.

[0039] Based on the measured data, the invention is described below, and the conclusions drawn from it should not be construed as being limited by the details of the underlying experiments, but should be understood as illustrative of the results possible with the invention.

[0040] Measurement data obtained with a supercontinuum source containing a pump light source and a nonlinear microstructured silica fiber are described below. The fiber was pumped with 8 ps pulses at 1064 nm at a repetition rate of 80 MHz, giving an average power output of 15 W (maximum: 23 kW). The fiber had a mode field diameter of 3.5 μm and a length of approximately 7 m.

[0041] The length of the optical fiber is preferably short to maintain consumption, and is preferably long enough to obtain the desired spectrum through the supercontinuum-based nonlinear process, but is also the minimum length. Typically, the length of the optical fiber is determined by the shape of the pulse, so that a short optical fiber is sufficient for a short pulse. In one embodiment, the length of the nonlinear optical fiber is 1 cm or more, or 10 cm or more, 1 m or more, 5 m or more, 8 m or more, or 10 m or more.

[0042] In one embodiment, the nonlinear microstructure optical fiber is 50 m or less, alternatively 30 m or less, or alternatively 10 m or less. Figure 1 shows typical supercontinuum spectra of a conventional microstructured optical fiber during initial operation (A) and after 35 hours of operation (B). The decrease in the visible portion of the spectrum, from approximately 450 nm to approximately 750 nm, indicates fiber degradation. This decrease was investigated in more detail in the experiment shown in Figure 2. Figure 2 shows the attenuation of a conventional nonlinear optical fiber after 35 hours of operation as a function of fiber position. A was measured in the first 3 m of the nonlinear optical fiber (NL optical fiber), B was measured from 3 m to 4 m, C was measured from 4 m to 5 m, and D was measured from 5 m to 7 m. This curve was obtained by subtracting a 7-m-long reference nonlinear optical fiber. Significant absorption was observed in the visible portion of the spectrum due to fiber degradation. The dips at 900 nm and 1400 nm are attributed to the single-mode cutoff of the nonlinear optical fiber and the difference in the OH maximum absorption between the nonlinear optical fiber and the reference optical fiber. To support the hypothesis that degradation occurs due to interaction with the relatively high-power pump pulse, absorption closer to the pump is required. This trend is evident in the decrease in absorption in fiber sections taken at greater distances from the pump. This trend is also evident in Figure 3, which shows the measured absorption at 633 nm as a function of distance from the index-matched section.

[0043] Figure 4 shows the supercontinuum at the beginning of the experiment (A), after 35 hours when a visible drop was observed (B), and after reheating the optical fiber to 250°C (C). It appears that heating partially regenerates the optical fiber. We hypothesize that regeneration of the optical fiber may be an indication of the pump pulse altering the structure of at least some of the glass. By allowing the glass to reach a high temperature, the glass can again reach a steady state and the optical fiber will at least partially regenerate.

[0044] Figure 5 shows the supercontinuum spectra 35 hours after a visible dip was observed, after heating the optical fiber to 250°C, and after loading deuterium into the optical fiber and subsequent annealing. Loading with deuterium clearly regenerated the optical fiber. The spectrum lacked a visible dip and was similar to the initial spectrum (see Figure 4).

[0045] In this embodiment, it is preferred to load the optical fiber with deuterium because hydrogen and oxygen can combine in the optical fiber to form O-H bonds, which are known to have an absorption maximum near 1400 nm. Such absorption is not preferred in this embodiment, but is preferred in applications where such absorption is insignificant or desirable, especially when hydrogen is less expensive than deuterium.

[0046] Figure 6 shows the results of deuterium loading under different conditions. The visible output power was measured as a function of time for three homogeneous nonlinear optical fibers loaded with deuterium under different conditions. The lifetime of the deuterium-loaded optical fibers was significantly extended compared to the unloaded optical fibers. All optical fibers were loaded with approximately 100% deuterium at a pressure of 100 bar (1 bar = 100,000 Pa). The loading of the optical fibers is preferably performed by placing the optical fiber in a high partial pressure of deuterium or hydrogen at a specific temperature for a certain length of time.

[0047] Figure 6 shows the measured visible output as a function of time for three homogeneous nonlinear optical fibers: (A) loaded with deuterium at 160°C, (B) loaded with deuterium at 80°C, and (C) unloaded with deuterium. The lifetime of the deuterium-loaded optical fibers was at least two times greater than that of the unloaded optical fibers. All optical fibers were loaded with approximately 100% deuterium at a pressure of 100 bar.

[0048] Figure 7 shows the lifetimes shown in Figure 6 as a function of three different deuterium loading temperatures (A) and exponential agreement to the measurements (B). In this example, lifetime is defined as a 30% decrease in visible light output. Depending on the application, lifetime may be defined as a decrease in visible light absorption of more than 40%, or even more than 50%, 70%, 80%, or 90%. Visible light may be defined as an integer value in the range of 500 nm to 700 nm. Alternatively, one or more wavelength values ​​may be specified as absorption at 650 nm and / or 633 nm. Measurements of hydrogen loading as a function of temperature clearly show an exponential increase in lifetime with loading temperature. Based on this temperature dependence, it is inferred that the increase in optical fiber lifetime is due to deuterium bonding to the material (in this case, silica glass) and that temperature plays a role in providing the activation energy required for this to occur. Alternatively, sufficiently high pressures may be generated if such a chemical process is induced. Finally, activation by irradiation, either simultaneously with or subsequent to deuterium diffusion into the material, is also believed to enable deuterium bonding. Thus, in a preferred embodiment, the optical fiber is loaded by subjecting the optical fiber to hydrogen and / or deuterium under loading conditions suitable for chemically bonding the hydrogen and / or deuterium to at least one of the core and cladding materials of the optical fiber material. The loading conditions preferably include at least one of a) elevated temperature T, b) elevated pressure P, and / or c) subsequent irradiation. Thus, in one embodiment, the optical fiber contains increased amounts of hydrogen and / or deuterium such that the loaded material contains greater than 0.1 atomic percent (at%), or greater than 1%, 5%, 10%, 20%, or 50% bound hydrogen and / or deuterium.

[0049] In one embodiment, the temperature T is raised to 80°C or higher to allow for such bonding, or the temperature T is raised to 100°C or higher, 120°C or higher, 140°C or higher, 160°C or higher, 180°C or higher, 200°C or higher, 220°C or higher, 240°C or higher, 260°C or higher, 280°C or higher, 300°C or higher, 350°C or higher, 400°C or higher, 450°C or higher, or 500°C or higher.

[0050] The nonlinear optical fiber may or may not include a polymer coating on the cladding. If the nonlinear optical fiber includes a polymer coating, the loading temperature for loading deuterium and / or hydrogen is preferably maintained below the melting point or softening point of the polymer. The upper limit for the deuterium loading temperature increase may be determined by the optical fiber coating. High-temperature coatings allow deuterium loading temperatures of 250°C or higher, thereby significantly improving lifetime. Alternatively, optical fiber can be manufactured without a coating, allowing for much higher loading temperatures (e.g., up to or above 500°C). Alternatively, the loading step for loading the core material (and optionally the cladding material) may occur before or during the optical fiber forming process (i.e., before coating). In principle, these are also applicable to other coatings.

[0051] The chemical reaction time is expected to be temperature and / or pressure dependent, but the loading time is preferably at least long enough for thermal equilibrium to occur. Similarly for the temperature, in one embodiment the pressure P is 10 bar or more, alternatively 25 bar or more, 50 bar or more, 75 bar or more, 90 bar or more, 120 bar or more, 160 bar or more, 200 bar or more, 500 bar or more, 1000 bar or more, or 2000 bar or more.

[0052] The irradiation can in principle be any irradiation suitable for providing a large activation energy. In a preferred embodiment, pulses suitable for supercontinuum generation (e.g., those described in the "Summary of the Invention") are applied to hydrogen or deuterium bonds in the optical fiber. In one embodiment, the optical fiber is cooled after loading and optional annealing to prevent any remaining unbound hydrogen or deuterium from diffusing out of the optical fiber before use. The optical fiber is preferably cooled during storage, or at least part of the storage period, before use. Once in use, it is estimated that pumping the optical fiber in supercontinuum light generation will provide sufficient energy to bond at least some of the remaining hydrogen or deuterium.

[0053] In principle, it is contemplated that loading materials may occur at any point during the optical fiber fabrication process. However, consideration must be given to ensuring that the ultimate extended optical fiber life is not affected by subsequent processing steps. Thus, in one embodiment, loading of the core material and, optionally, the cladding material occurs before, during, or after the optical fiber fabrication. Also, as shown in FIG. 5, in one embodiment, the optical fiber may be at least partially regenerated such that loading occurs after use.

[0054] The water bands described above can be disadvantageous in some applications, and therefore, in one embodiment, it is preferable to load as little hydrogen as possible into the optical fiber so that the loaded optical fiber contains 1% or more (atomic) bound deuterium relative to bound hydrogen (and / or corresponding ions), or 10% or more, 100% or more, or 10,000% or more.

[0055] After loading with deuterium or hydrogen, the optical fiber is preferably annealed to enhance the diffusion of unbound deuterium or hydrogen within the optical fiber. Annealing the optical fiber is preferably performed at moderate temperatures so as not to impart enough energy to reunbind the hydrogen or deuterium. In the figures shown above, the optical fiber was annealed at 80°C. If the optical fiber is stored at room temperature, the unbound hydrogen or deuterium may outdiffuse within two to three months. Annealing allows the optical fiber to be spliced ​​to another optical fiber (by plasma heating the hydrogen or deuterium; for example, this splice may explode if melted). These molecules also reduce the photosensitivity added by the annealing. Very high annealing temperatures, above approximately 1000°C, are generally undesirable because they may outdiffuse the unbound hydrogen or deuterium. Therefore, in one embodiment, the method for manufacturing an optical fiber includes a step of annealing the loaded material after the loading step.

[0056] Figure 8 shows the measured spectra of a deuterium-loaded nonlinear optical fiber after 0 hours (A), 188 hours (B), 260 hours (C), 305 hours (D), and 450 hours (E). For the unloaded nonlinear optical fiber, no significant decline was observed in the visible spectrum from 500 nm to 700 nm. Additionally, when increasing the lifetime of the nonlinear optical fiber, deuterium loading significantly alters the spectral behavior of the optical fiber during operation compared to the unloaded optical fiber. Compared to the unloaded optical fiber, degradation was observed not as a decline in the visible spectrum but as a gradual decrease in the visible output. Only the short wavelength range appears to change significantly over time.

[0057] In one embodiment, the lifetime of the optical fiber is increased by 50% or more, or 100% or more, or 200% or more, or 500% or more, or 1000% or more, or 10,000% or more, compared to the lifetime of an otherwise identical optical fiber not loaded with deuterium and hydrogen. The absolute lifetime of an optical fiber not treated with pulses suitable for supercontinuum generation may vary depending on the application and, speculatively, the particular material of the optical fiber core. Thus, in one embodiment, the lifetime is greater than 100 operating hours, or greater than 200 operating hours, or 2,000 operating hours, or 20,000 operating hours, or 50,000 operating hours.

[0058] Figure 9 shows the measured visible output as a function of time for a nonlinear optical fiber with low glass impurities. The impurity level, particularly the amount of chlorine (Cl) atoms in the glass, appears to affect the optical fiber's lifetime. At least to some extent, lower chlorine content appears to result in longer lifetimes. The lifetime is significantly longer than in Figure 5, indicating that the damage threshold is determined by the glass impurity level. However, the lifetime of the deuterium-loaded optical fiber (A) is still significantly increased compared to the unloaded optical fiber (B). The increase in output power seen after 750 hours for the deuterium-loaded optical fiber is due to increased pump power.

[0059] It is believed that the lifetime is extended by the proportion of bound deuterium or hydrogen relative to the total number of impurities in the core and, depending on the application, the cladding material. Thus, in one embodiment, the core of the optical fiber is a solid core (preferably silica) and the proportion of bound hydrogen and / or bound deuterium relative to the total number of impurities is 10% or more, or alternatively 20% or more, 30% or more, 40% or more, 50% or more, 60% or more, 70% or more, 80% or more, 90% or more, 99% or more, or 99.9% or more.

[0060] The invention is defined by the features of the independent claims. Preferred embodiments are defined in the dependent claims. Reference signs in the claims do not limit the scope of the claims.

[0061] While some preferred embodiments have been set forth above, it is emphasized that the present invention is not limited thereto and may be embodied in other ways within the scope of the subject matter defined in the following claims. In particular, while the present invention is described by applying it to the application of nonlinear microstructured optical fibers, it should be understood that the present invention is also applicable to other applications of nonlinear microstructured optical fibers where transmission in the visible is important for high-pulse applications.

Claims

1. 1. An apparatus comprising: a supercontinuum light source configured to provide at least one of high brightness and high power emission in the visible portion of the spectrum; the supercontinuum light source comprises a pulsed pump light source and an optical fiber; the optical fiber comprises a core made of a core material and a clad made of a clad material, At least a portion of the core is made of silica and contains less than 0.1 at% germanium; the pulsed pump source is configured to provide pulses to the optical fiber; at least one of the core material and the cladding material contains at least one of hydrogen and deuterium to extend the life of the optical fiber; The lifetime is defined as the number of hours of operation at which the reduction in light output in the visible range is 30%. Device.

2. The device is configured to perform one of the following group: fluorescence microscopy, confocal fluorescence microscopy, laser precision spectroscopy, or optical coherence tomography (OCT).

10. The apparatus of claim 1.

3. the pulsed pump light source and the optical fiber are configured to provide an output spanning at least one octave at at least 10 μW / nm; 10. The apparatus of claim 1.

4. the output power is at least 100 μW / nm and spans at least one octave; 4. The apparatus of claim 3.

5. said output power being at least 10 mW / nm and spanning at least one octave; 5. The apparatus of claim 4.

6. the output spans at least 1.5 octaves; 4. The apparatus of claim 3.

7. At least a portion of the core is made of silica and contains less than 0.01 at% germanium.

10. The apparatus of claim 1.

8. At least a portion of the core is made of undoped silica; 10. The apparatus of claim 1.

9. the optical fiber is a nonlinear microstructure optical fiber; 10. The apparatus of claim 1.

10. the pulsed pump source delivers femtosecond pulses to the optical fiber; 10. The apparatus of claim 1.

11. the pulsed pump source delivers picosecond pulses to the optical fiber; 10. The apparatus of claim 1.

12. The life of the optical fiber is extended by 50% or more compared to the life of an optical fiber of the same quality that is not loaded with at least one of deuterium and hydrogen.

10. The apparatus of claim 1.

13. the life of the optical fiber is greater than 200 operating hours; 10. The apparatus of claim 1.

14. 1. A supercontinuum light source configured to provide at least one of high brightness and high power emission in the visible portion of the spectrum, the supercontinuum light source comprises an optical fiber and a supply configured to supply pump pulses to the optical fiber; the optical fiber comprises a core made of a core material and a clad made of a clad material, At least a portion of the core is made of silica and contains less than 0.1 at% germanium; the core material and optionally the cladding material contain at least one of hydrogen and deuterium to extend the lifetime of the optical fiber, the lifetime being defined as the number of hours of operation at which there is a 30% reduction in light output in the visible; the supply and the optical fiber are configured to provide an output spanning at least one octave at at least 10 μW / nm. Supercontinuum light source.

15. the output power is at least 100 μW / nm and spans at least one octave; 15. The supercontinuum light source of claim 14.

16. said output power being at least 10 mW / nm and spanning at least one octave; 15. The supercontinuum light source of claim 14.

17. the output spans at least 1.5 octaves; 15. The supercontinuum light source of claim 14.

18. At least a portion of the core is made of silica and contains less than 0.01 at% germanium.

15. The supercontinuum light source of claim 14.

19. At least a portion of the core is made of undoped silica; 15. The supercontinuum light source of claim 14.

20. the optical fiber is a nonlinear microstructure optical fiber; 15. The supercontinuum light source of claim 14.

21. the supply unit supplies femtosecond pulses to the optical fiber; 15. The supercontinuum light source of claim 14.

22. the supplying unit supplies picosecond pulses to the optical fiber; 15. The supercontinuum light source of claim 14.

23. The life of the optical fiber is extended by 50% or more compared to the life of an optical fiber of the same quality that is not loaded with at least one of deuterium and hydrogen.

15. The supercontinuum light source of claim 14.

24. the life of the optical fiber is greater than 200 operating hours; 15. The supercontinuum light source of claim 14.

25. 1. An apparatus configured to perform one of the group of: fluorescence microscopy, confocal fluorescence microscopy, laser precision spectroscopy, or optical coherence tomography (OCT), comprising: The apparatus comprises a supercontinuum light source according to claim 14. Device.

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