阅读说明：本技术 多包层光纤 (Multi-clad optical fiber ) 是由 马克·泽迪克 罗伯特·斯特格曼 詹姆斯·塔克 让-菲利普·费夫 于 2018-04-20 设计创作，主要内容包括：描述了一种多包层光纤设计,以便在光谱的UV可见光部分中为基本传播模式线性偏振(LP)01模式提供低光损耗、高数值孔径(NA)和高光学增益。光纤设计可以包含掺杂剂,以便同时增加纤芯区域的光学增益,同时避免在光纤制造过程中产生额外的损耗。光纤设计可以掺入稀土掺杂剂以有效地发射激光。另外,光学纤芯中传播模式的模态特性促进高效的非线性混合,从而提供高光束质量(M<Sup>2</Sup><1.5)的发射光输出。(A multi-clad fiber design is described to provide low optical loss, high Numerical Aperture (NA), and high optical gain for the fundamental propagating mode Linear Polarization (LP)01 mode in the UV-visible portion of the spectrum. The fiber design may include dopants to simultaneously increase the optical gain of the core region while avoiding additional losses in the fiber fabrication process. The fiber design can incorporate rare earth dopants to efficiently emit laser light. In addition, the modal characteristics of the propagating modes in the optical core promote efficient nonlinear mixing, providing high beam quality (M) 2 <1.5) emitted light output.)

1. A fused silica-based multi-clad optical fiber comprising:

a core surrounded by a first cladding such that the optical fiber has a high NA; whereby the optical fiber is configured to couple M²>>1.5 conversion of Low Beam quality visible or UV light to M²<1.5 high beam quality light;

a hydrogen dopant, whereby the optical fiber is configured to provide low propagation loss in the visible or UV portion of the spectrum; and the combination of (a) and (b),

the core includes a GRIN structure.

2. The optical fiber of claim 1, wherein the GRIN structure comprises a component selected from the group consisting of: a modifier for silica glass to change the refractive index; a structure comprising silica glass, which alters the effective refractive index; and a modifier to the silica glass to protect the core from UV radiation.

3. The optical fiber of claim 1 or 2, wherein said first cladding is surrounded by a second cladding, and said second cladding is surrounded by an outer cladding, wherein each said cladding comprises fused silica glass.

4. The optical fiber of claim 1 or 2, wherein said first cladding is surrounded by a second cladding and said second cladding is surrounded by an outer cladding, wherein each said cladding comprises fused silica glass with a chemical modifier.

5. The optical fiber of claim 1, wherein the low beam quality light is converted to the high beam quality light by direct laser emission of rare earth ions.

6. The optical fiber of claim 1, wherein the low beam quality light is converted to the high beam quality light by an energy exchange process induced by a nonlinear optical device.

7. The optical fiber of claim 1, wherein the light propagation loss is low in both the visible and UV portions of the spectrum.

8. The optical fiber of claim 1, wherein the GRIN structure comprises a component selected from the group consisting of phosphorous, aluminum, and aluminum and phosphorous.

9. The optical fiber of claim 1, wherein the GRIN structure comprises a component selected from the group consisting of: a material that increases the refractive index of pure fused silica and does not solarize when irradiated with blue light.

10. The optical fiber of claim 9, configured to exhibit the highest nonlinear gain for the fundamental mode of the fiber, LP01 mode.

11. The optical fiber of claim 1, comprising a second cladding surrounding said first cladding, wherein said second cladding has an effective refractive index lower than a refractive index of said first cladding.

12. The optical fiber of claim 11, wherein the second cladding comprises a modifier to the glass matrix to reduce the refractive index of the second cladding to less than the refractive index of the first cladding.

13. The optical fiber of claim 11, wherein the second cladding comprises a non-solid structure, thereby reducing the refractive index of the second cladding to less than the refractive index of the first cladding.

14. The optical fiber of claim 11, wherein the second cladding comprises a low refractive index polymer, thereby lowering the refractive index of the second cladding to less than the refractive index of the first cladding.

15. The optical fiber of claim 1, comprising a third cladding and said second cladding, wherein an effective refractive index of said third cladding is higher than an effective refractive index of said second cladding.

16. The optical fiber of claim 11, comprising a third cladding, wherein an effective refractive index of the third cladding is higher than an effective refractive index of the second cladding.

17. The optical fiber of claim 11 or 15, wherein one or more of the first, second and third claddings comprises a chemical modifier to protect the first cladding and the core from UV radiation.

18. The optical fiber of claim 11, comprising a third cladding, wherein an effective refractive index of the third cladding is lower than an effective refractive index of the second cladding.

Technical Field

Embodiments of the present invention relate generally to optical fibers and, more particularly, to multi-clad high power optical fibers having a high numerical aperture for incident light and a high beam quality factor for output light operating in the visible region.

Background

The fiber has, among other functions, the ability to deliver low beam quality (e.g., M)²>>1.5) conversion of input light to high beam quality (e.g., M)²<1.5) potential for outputting light. However, it is believed that this potential is essentially only achieved in the IR (infrared) spectrum, and then only in the 900nm to 2000nm range.

It is believed that existing methods for multi-clad optical fibers that convert low beam quality laser diode light to high beam quality light have several disadvantages, including among others the inability to provide or suggest light output in the visible region.

It is believed that existing methods of converting low beam quality light in multi-clad optical fibers to high beam quality light have several disadvantages, including, among other things, their inability to address the problem of efficient nonlinear conversion of visible light (e.g., blue light) using non-solarized fiber material (non-solarized fiber material).

Therefore, it is believed that prior to the present invention, among other features, fiber configurations having multi-clad structures for high power operation, laser diode pumping of optical fibers, and mode conversion processes utilizing rare earth-doped ions or stimulated raman scattering, as well as other features and properties of the present invention, have never been achieved.

Due to the long interaction length of the optical fibers, low propagation loss is desirable for high efficiency. When using third-order nonlinear tensor elements (especially raman tensor elements) in optical glass, low propagation loss is of paramount importance. Chemically and mechanically stable glass compositions have been disclosed which require low optical loss and a wider transparent window compared to pure fused silica. However, it is believed that all chemically and mechanically stable glass compositions reported to date have higher optical losses in the visible and UV portions of the spectrum than pure fused silica. Thus, it is believed that these prior compositions do not meet the long felt need for low transmission losses, particularly for silica substitutes that have lower transmission losses for visible and UV light than silica.

In order to fabricate an optical fiber that guides light in the core via total internal reflection, the refractive index of the core must be greater than the refractive index of the surrounding cladding region. The use of aluminum in silica cores with silica cladding is known in the visible and UV portions of the spectrum, however this approach has a number of drawbacks, and in particular, it is believed to have the side effect of increasing propagation losses in the visible and UV portions of the spectrum.

Another way to further reduce optical loss in fused silica fibers is to introduce excess hydrogen atoms into the pure fused silica glass matrix to reduce losses in the visible and UV portions of the spectrum. This method has several drawbacks, and it is believed that it does not improve the light propagation loss of blue light when the fused silica glass is doped with other materials (e.g., aluminum or phosphorous), among other drawbacks.

As used herein, unless otherwise expressly specified, "UV," "ultra violet," "UV spectrum," and "UV portion of the spectrum" and similar terms shall be given their broadest meaning and include light having wavelengths of from about 10nm to about 400nm, and from 10nm to 400 nm.

As used herein, unless otherwise expressly specified, the terms "visible", "visible spectrum" and "visible portion of the spectrum" and similar terms are to be given their broadest meaning and include light having a wavelength of from about 380nm to about 750nm, and 400nm to 700 nm.

As used herein, unless otherwise expressly specified, the terms "blue laser beam," "blue laser," and "blue" shall be given their broadest meaning and generally refer to systems that provide a laser beam, laser source, such as lasers and diode lasers that provide, for example, a propagating laser beam or light having a wavelength of about 400nm to about 500 nm.

As used herein, unless otherwise expressly specified, the terms "green laser beam," "green laser," and "green" shall be given their broadest meaning and generally refer to a system that provides a laser beam, a laser source, e.g., a laser and a diode laser that provides, for example, a propagating laser beam or light having a wavelength of about 500nm to about 575 nm.

Generally, unless otherwise specified, the term "about" as used herein is meant to include variations or ranges of ± 10%, experimental or instrumental errors associated with obtaining the stated values, and preferably, the larger of these.

The background of the invention section is intended to introduce various aspects of art, which may be associated with embodiments of the present invention. The preceding discussion in this section therefore provides a framework for a better understanding of the present invention and should not be taken as an admission of prior art.

Disclosure of Invention

Thus, there has long been an unmet need for optical fibers with low loss, high power, multiple cladding, and high beam quality for visible light (including and particularly for blue, blue-green, and green wavelengths). The present invention meets these needs by providing, inter alia, the articles, devices, and methods taught and disclosed herein.

Accordingly, a multi-clad, fused silica-based optical fiber is provided that operates at high power in the visible portion of the spectrum, particularly the blue portion, to convert low-brightness, high-power light from a blue laser diode to high-power, high-brightness blue light from the fiber output.

An optical fiber and a method of converting a laser beam in one or more or all of visible, UV and blue wavelengths into higher beam quality and lower transmission loss using the same are provided, the fused silica based multi-clad optical fiber having: a core surrounded by a first cladding-said optical fiber thereby having a high NA; whereby the optical fiber is configured to couple M²>>1.5 conversion of Low Beam quality visible or UV light to M²<1.5 high beam quality light; a hydrogen dopant, whereby the optical fiber is configured to provide low propagation loss in the visible or UV portion of the spectrum; and the core has a GRIN structure.

In addition, such fibers and methods are provided having one or more of the following characteristics: wherein the GRIN structure has a composition selected from the group consisting of: a modifier for silica glass to alter the refractive index, including structures of silica glass that alter the effective refractive index, and a modifier for silica glass to protect the core from UV radiation; wherein the first cladding is surrounded by a second cladding, the second cladding being surrounded by an outer cladding, wherein each cladding has fused silica glass; wherein the first cladding is surrounded by a second cladding, the second cladding being surrounded by an outer cladding, wherein each cladding has fused silica glass containing a chemical modifier; wherein light of low beam quality is converted to light of high beam quality by direct laser emission (lasing) of rare earth ions; wherein light of low beam quality is converted to light of high beam quality by an energy exchange process induced by the non-linear optics; where the light propagation losses are low in both the visible and UV portions of the spectrum; wherein the GRIN structure has a composition selected from the group consisting of phosphorous, aluminum, and aluminum and phosphorous; wherein the GRIN structure has a composition selected from materials that increase the refractive index of pure fused silica and do not solarize when illuminated by blue light, configured to exhibit the highest nonlinear gain for the fundamental LP01 mode of the fiber; a second cladding layer surrounding the first cladding layer, wherein the effective refractive index of the second cladding layer is lower than the refractive index of the first cladding layer; wherein the second cladding layer has a modifier to the glass matrix to reduce the refractive index of the second cladding layer to less than the refractive index of the first cladding layer; wherein the second cladding has a non-solid structure, thereby reducing the refractive index of the second cladding to less than the refractive index of the first cladding; wherein the second cladding has a low refractive index polymer to reduce the refractive index of the second cladding to less than the refractive index of the first cladding; having a third cladding and a second cladding, wherein the third cladding has an effective refractive index higher than that of the second cladding; having a third cladding, wherein the effective refractive index of the third cladding is higher than the effective refractive index of the second cladding; a third cladding layer, wherein the effective refractive index of the third cladding layer is lower than the effective refractive index of the second cladding layer; and wherein one or more of the first cladding, the second cladding, and the third cladding have a chemical modifier to protect the first cladding and the core from UV radiation.

Further, a fiber and a method of using the fiber to convert a laser beam in one or more or all of visible, UV and blue wavelengths to higher beam quality and lower propagation loss are provided, the fused silica based multi-clad fiber comprising the following: one or more cladding layers to produce a high NA; light (M) of low beam quality²>>1.5) into light (M) of high beam quality²<1.5) ability; low propagation losses in the visible and UV part of the spectrum are achieved by hydrogen doping; a gradient index (GRIN) structure in the optical core; a modifier for silica glass to change the refractive index; a structure comprising silica glass, which alters the effective refractive index; a modifier to silica glass to protect the core from UV radiation.

Additionally, these fibers and methods are provided having one or more of the following features: comprising a core, an inner cladding, a second inner cladding and an outer cladding, all based on fused silica glass or fused silica glass with a chemical modifier; direct laser emission of rare earth ions to deliver low beam quality light (M)²>>1.5) into light (M) of high beam quality²<1.5); low beam quality light (M) by energy exchange process induced by nonlinear optics²>>1.5) into light (M) of high beam quality²<1.5); due to the hydrogen doping of the silica-based glass, there is lower light transmission loss in the UV and visible part of the spectrum; including a gradient index (GRIN) structure in the optical core by adding a modifying agent to the glass matrix; incorporating a gradient index (GRIN) structure in the optical core by adding phosphorus, aluminum, or some combination of aluminum and phosphorus; wherein the modifier is purity-enhancingAny element or molecule of refractive index of fused silica that does not solarize when illuminated by blue light; exhibits the highest nonlinear gain for the fundamental LP01 mode of the fiber; a second cladding having an effective refractive index lower than that of the inner cladding; using a chemical modifier to the glass matrix to reduce the refractive index of the second cladding; using a non-solid structure to reduce the refractive index of the second cladding; using a low refractive index polymer to reduce the refractive index of the second cladding; a third cladding layer having an effective refractive index higher than that of the second cladding layer; and chemical modifiers to protect the inner cladding and core of the optical fiber from UV radiation.

Drawings

FIG. 1 is a graph of an example of a refractive index profile of an optical fiber according to the present invention.

Detailed Description

Embodiments of the present invention relate to configurations of optical fibers with low propagation losses, multi-clad optical fibers, and optical fibers for high power and high brightness light.

One embodiment of the present invention is a multi-clad optical fiber. The multi-clad fiber incorporates several advances to produce high power, high brightness light from high power, low brightness light in the visible portion of the spectrum. Thus, this embodiment comprises a plurality of cladding layers, e.g., 2, 3, 4, 5 or more, to receive incident light defined as a high NA (e.g., 0.2> NA >0.8) and convert it to light exiting the fiber at a low NA (e.g., 0.02< NA < 0.1). The core is made of pure fused silica, incorporating a graded index structure made of phosphorus and/or aluminum, and the cladding may be made of, for example, pure fused silica, fluorine-doped fused silica, fluorine germanium-doped pure fused silica, or photonic crystal structures made of pure fused silica.

The table below lists the relative refractive indices of one embodiment of the optical fiber.

Region in optical fiber	Relative refractive index
		GRIN core	2.5x 10-3>Δn>0 (parabola type)
Inner cladding	0
		Intermediate cladding	-2.5x 10-2
Outer cladding	0
		Polymer encapsulation	2.5x 10-3

Relative to fused silica at the operating wavelength

In one embodiment of the multiple clad structure, the core material is a fused silica-based matrix that, in combination with a graded index structure made of phosphorus and/or aluminum modified by hydrogen doping of the glass, reduces propagation losses in the visible and UV portions of the spectrum.

In embodiments that provide a small effective area for converting low brightness light to high brightness light, the center or interior of the fiber is a gradient index ("GRIN") structure. The GRIN structure is fabricated by adding dopants to the inner cladding structure so that for a circularly symmetric fiber only the innermost cladding can be doped. The dopant can be any non-solarization, chemically and mechanically stable material element that does not significantly increase optical loss, preferably phosphorus or aluminum, or both. In this manner, the GRIN structure forms the optical core of the optical fiber.

A high NA for accepting incident light is created by additional dopants and/or silica-based structures to lower the effective refractive index in the region surrounding the inner cladding region. Light can also be confined by low index coatings (e.g., low index polymers) on the outside of the fiber.

The following table lists the dopant concentrations and dimensions of the preferred embodiments of the disclosed optical fibers.

The region begins at the end of the previous region and ends at the beginning of the next region

**H₂/O₂Flame, H₂Excess, preforming temperature-1000 deg.C, lasting 6.2 days

V (gas flow or gas flow through bubbler) V-GeCL₄/V-SiCl₄:0.359

V-SF₆/V-SiCl₄:0.072

V-O₂excess/V-SiCl₄:6.12

The following table lists dopant concentration ranges and size ranges for additional embodiments of the disclosed optical fibers.

The region begins at the end of the previous region and ends at the beginning of the next region

**H₂/O₂Flame, H₂Excess, preforming temperature-1000 deg.C, lasting for 1-20 days

V (gas flow or gas flow through bubbler) V-GeCL₄/V-SiCl₄:0.2-0.5

V-SF₆/V-SiCl₄:0.01-0.3

V-O₂excess/V-SiCl₄:0.5-15

Solarization of the dopants in the GRIN optical core is prevented by adding additional dopants to the outer cladding. A preferred dopant is germanium, which may be combined with fluorine to reduce refractive index disturbances in the outer cladding. These additional dopants protect the dopants in the core from UV radiation from the environment and from the fiber manufacturing process.

Multi-clad optical fibers provide a method of converting high power, low brightness light into high power, high brightness light via direct laser emission transition of rare earth ions or via frequency shifting of nonlinear optics. Small mode effective area (e.g., 200 μm)²Or less) and a long interaction length (e.g., 50 meters or less) enable efficient generation of high brightness light. Attention is mainly focused on the near infrared part of the spectrum, where optical fiber propagation, semiconductor pump lasers are readily available, and rare earth ions have appropriate absorption and emission bands. In addition, low propagation losses can lead to efficient nonlinear optical processes, even providing modest nonlinearity through silica-based glasses.

Embodiments of the present invention allow the use of optical fibers in the visible and UV portions of the spectrum to generate high power when converting low brightness light to high brightness light. However, in the visible and UV portions of the spectrum, few rare earth ions have substantial absorption and emission cross-sections with long upper state lifetimes, and thus there is also teaching that effective operation is generally not performed using nonlinear optics. Advantageously, most nonlinearities increase as a function of 1/λ according to Miller's Law, where λ is the wavelength of light. Thus, the nonlinear coefficients are higher in the visible and UV portions of the spectrum compared to the near infrared portion of the spectrum. However, the loss due to Rayleigh scattering is a function of 1/λ⁴So that optical losses quickly prevent the appearance of effective nonlinear optics. In addition, the trailing edge of the electron absorption band edge of many materials extends from the UV portion of the spectrum to the visible portion.

One embodiment of the present invention includes combining reducing optical losses in the UV and visible portions of the spectrum and incorporating a multi-clad fiber design to increase the effective nonlinearity of the fiber. The result is an efficient means of converting low brightness light to high brightness light in the visible portion of the spectrum in an optical fiber.

Optical fiber for coupling low beam quality (M)²>>1.5) light transmission and conversion to high beam quality (M)²<1.5) of light. M of low quality laser beams, in particular low quality blue, green and blue-green laser beams, converted by the system of the invention²Values of about 1.55 to about 10, about 2 to about 5, about 1.6 to about 15, and greater, as well as all values within these ranges, are possible. M of high quality laser beams provided by converting these low quality laser beams (including low quality blue laser beams)²Can be about 1.5 to about 1.1, less than 1.5, less than 1.4, less than 1.3, theoretically 1, and all values within these ranges. In addition, M of the converted laser beam provided by embodiments of the system of the present invention²M of a value greater than the initial or low quality laser beam²Values may be increased by at least about 20%, at least about 30%, at least about 40%, at least about 50%, and at least about 5% to about 50%.

Embodiments of the optical fiber of the present invention have NA's of about 0.1 to 0.8, about 0.2 to about 0.8, equal to or greater than about 0.22, equal to or greater than 0.25, about 0.22, about 0.3, about 0.4 to about 0.5, about 0.5 to about 0.8, and greater or lesser NA's, particularly for blue, blue-green, and green wavelengths, and all values within these ranges. High NA, as used herein, is NA greater than 0.22 within this range.

Embodiments of the optical fiber provide low propagation losses, particularly for blue, blue-green, and green wavelengths, from about 10dB/km to about 40dB/km, from about 10dB/km to about 30dB/km, from about 20dB/km to about 40dB/km, greater than about 15dB/km, greater than about 10dB/km, and greater and lesser values, as well as all values within these ranges.

Turning to FIG. 1, FIG. 1 is a graph illustrating an embodiment of a relative refractive index profile from the center to the outer radius of the core of an embodiment of an optical fiber. In this embodiment, the refractive index profile exhibits the radial symmetry of the disclosed optical fiber. The dashed line represents the refractive index of pure fused silica for the desired wavelength or operation. Values above this dashed line represent refractive indices higher than the refractive index of pure fused silica at the expected operating wavelength. Values below this dashed line represent refractive indices lower than that of pure fused silica at the expected operating wavelength.

In this embodiment, the optical fiber has a core with a radius of 20 μm, a first cladding with a thickness of 11.25 μm, a second cladding with a thickness of 6.25 μm and a third (and outer) cladding with a thickness of 25 μm, and an outer coating formed of polyimide or acrylate and having a thickness of 60 μm. Dashed line 1 shows the baseline refractive index of pure fused silica at the operating wavelength. Starting from the center of the core of the fiber, the GRIN region 2 shows an increase in refractive index relative to the inner cladding region 3. The second cladding region 4 has a lower refractive index than the inner cladding region 3, resulting in a large numerical aperture. The outer cladding region 5 is the final glass portion of the fiber, which has a slightly higher refractive index than pure fused silica due to the addition of the UV absorbing modifier near the outer edge of the second cladding region 4.

The refractive index of the modifying agent contained in the GRIN core 2 of the optical fiber is higher than that of pure fused silica, and a positive refractive index difference is generated between the GRIN core 2 and the inner cladding 3. The positive index difference acts as a constant lens inside the fiber, forcing the effective area of the low order modes to be small. During irradiance-dependent nonlinear optical processes, the smaller effective area results in greater energy exchange, such as four-wave mixing, stimulated brillouin scattering, and stimulated raman scattering. The modifier is selected so that it does not cause additional losses when illuminated by visible light, which excludes elements such as germanium. In a preferred embodiment, this limitation allows the use of aluminum and/or phosphorus.

The modifier is also selected so that the non-linearity coefficient to be used during the energy exchange is increased relative to the inner cladding, i.e. the chi for four-wave mixing⁽³⁾Electron contribution of tensor, chi to stimulated raman scattering⁽³⁾Tensor electron vibration contribution to chi of stimulated brillouin scattering⁽³⁾Electrostrictive contribution of the tensor. In a preferred embodiment, the modifier is selected to be phosphorus because of its efficient coupling and increase in the raman gain curve of pure fused silica.

Type and amount of modifier

The purpose of the inner cladding (3) and the second cladding (4) is to provide a maximum refractive index difference. High foldThe index difference allows light within the defined cone volume to couple to the inner cladding of the fiber. The NA of an optical fiber is defined as the sine of the maximum angle of an incident ray with respect to the fiber axis that will be guided into the fiber inner cladding. When coupling light from air into an optical fiber, NA is defined as NA ═ n_{Inner cladding} ²–n_{Outer cladding} ²)^0.5Wherein n is_{Inner cladding}Is the refractive index of the inner cladding (3), n_{Outer cladding}The refractive index of the second cladding (4).

To obtain a high NA a second cladding (4) having a lower refractive index relative to the inner cladding region (3) must be used. To minimize optical losses, a preferred embodiment of the inner cladding region is to use pure fused silica. Modifiers for fused silica glass may be used in order to reduce the refractive index. In preferred embodiments, the modifying agent in the second cladding layer (4) is fluorine, boron or a combination of fluorine or boron.

Another preferred embodiment of the second cladding region 4 is the use of a Photonic Crystal Fiber (PCF) structure. The PCF structure is designed such that the effective refractive index of the second cladding is lower than the inner cladding and may be lower than the refractive index that would be possible by using modifiers such as fluorine, boron or a combination of fluorine and boron in the silica glass.

The table below lists the relevant parameters and dimensions of the PCF structure to be used as the second cladding region.

PCF structure parameter	Size (mum)
		Pore diameter	0.5≤d≤5
Wall thickness of air hole	0.1≤t≤0.5

A further preferred embodiment of the second cladding region 4 is the use of a UV curable low refractive index polymer. The polymer is selected to have minimal absorption in the blue region and to have a low refractive index. Examples of proposed optical fibers are given in the following table:

the region begins at the end of the previous region and ends at the beginning of the next region

**H₂/O₂Flame, H₂Excess, preforming temperature-1000 deg.C, lasting for 1-20 days

The outer cladding 5 is not intended to guide any visible light but provides two functions. First, it prevents visible light from interacting with the mechanically robust outer coating 6, which is typically placed outside the outer cladding. The overcoat layer 6 may be metallic, organic or inorganic. Secondly, the outer cladding contains a modifier that absorbs UV light to prevent interaction with the inner cladding 3, 4 and the core 2 of the optical fiber.

Another blue fiber laser embodiment is a configuration in which the light guiding coating on the fiber is composed of a low index polymer for confining the pump light inside the optical core. An example of such a polymer is the low refractive index polymer LUVANTIX PC 373. This material has a very high numerical aperture, i.e. a very steep light input cone, the light being subsequently guided by total internal reflection. These polymers have good resistance to optical damage by high power light. The high Numerical Aperture (NA) created with the polymer coating exceeds the input angle created by doping only the clad glass to create a total internal reflection surface. In a preferred embodiment, the NA fiber produced by using the polymer coating has a NA greater than 0.22. In this embodiment, the optical core may contain the GRIN structures previously described, and may or may not have an inner cladding, i.e., the outer coating may serve as the primary or secondary confinement surface for the pump light.

For blue fiber lasers, another embodiment is where the optical core is asymmetric with the pump guiding portion of the fiber, as in the case of a D-core or elliptical core. In these cases, the purpose of the asymmetric core is to optimize the extraction of the pump modes.

During the optical fiber manufacturing process, the outer coating (6) is applied in liquid form and exposed to UV light to harden the liquid to a solid, thereby forming a mechanical protection layer for the glass optical fiber. UV exposure to the modifiers in the core can lead to other loss mechanisms such as color center defects. The inclusion of one or more modifiers in the outer cladding absorbs UV light during fiber fabrication and prevents UV light from interacting with the modifiers in the GRIN core and the second cladding (if present). In a preferred embodiment, the modifier in the outer cladding is germanium.

In one embodiment, a multi-clad fiber design is described to provide low optical loss, high Numerical Aperture (NA), and high optical gain for the fundamental propagation mode, the Linear Polarization (LP)01 mode, in the UV and visible portions of the spectrum. The fiber design may contain dopants to simultaneously increase the optical gain of the core region while avoiding additional losses in the fiber fabrication process. The fiber design can incorporate rare earth dopants to efficiently emit laser light. In addition, the modal characteristics of the propagating modes in the optical core may promote efficient nonlinear mixing, providing high beam quality (M) of the emitted light²<1.5) output.

The following table provides ranges for fiber length, optical power input, optical power output, beam quality input, and beam quality output.

Parameter(s)	Unit of	Range of
			Input power	Watt	5–2000
Output power	Watt	0.1–1500
			Light beam quality input (M)2)	N/A	3–100
Beam quality output (M)2)	N/A	1–2

The following examples are provided to illustrate various embodiments of the laser system of the present invention, and in particular, the blue laser system for welding components including in electronic storage devices, and the operation. These examples are for illustrative purposes only and should not be construed as, and do not otherwise limit the scope of the present invention.