短波长上转换发光的光谱分析：Tm掺杂光纤研究

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"这篇研究论文探讨了Tm3+掺杂的ZrF4-BaF2-LaF3-AlF3-NaF (ZBLAN)光纤中的短波长发射的光谱分析，特别是通过上转换过程。研究了荧光在Tm3+离子中的演变，并着重关注了在紫外到红外区域的放大自发辐射，特别是350nm、365nm和450nm的波段。作者分析了单线泵浦和双线泵浦对紫外蓝光信号产生的效率，并估计了该区域内放大所需的最优光纤长度。" 在本文中，作者M.Juárez-Hernández和E.B.Mejía对Tm3+离子掺杂的ZBLAN光纤进行了深入的研究，这种光纤被用于短波长发射的光谱分析，特别是在上转换过程中。上转换是一种非线性光学现象，它允许低能量的光子（通常在红外区域）结合，转化为高能量的光子（如紫外或蓝光）。这项研究对于理解和优化光纤激光器和放大器的设计至关重要。研究发现，当使用687nm和/或645nm的双线泵浦时，紫外蓝光信号的产生效率显著提高，而且所需光纤长度显著缩短，大约只需20cm，而单线泵浦则需要超过50cm的光纤。这一结果揭示了双线泵浦中一个虚拟循环的存在，在这个循环中，泵浦光源互相增强彼此的吸收，从而提高了转换效率。关键词包括非线性光学、光纤和上转换，表明研究的核心在于理解并利用非线性光学效应在光纤介质中的作用，尤其是上转换过程，以实现更高效、紧凑的光子能量转换系统。这种转化对于开发新型的光通信技术、生物成像、激光手术等领域有潜在的应用价值。这项研究不仅提供了关于Tm3+掺杂ZBLAN光纤中上转换机制的新见解，还为设计更高效的短波长光源提供了理论基础和实验数据，有助于推动光纤技术和非线性光学领域的发展。

Spectral analysis of short-wavelength emission

by up-conversion in a Tm

:ZBLAN

dual-diode-pumped optical fiber

M. Juárez-Hernández

1,2,

* and E. B. Mejía

Centro de Investigaciones en Óptica, A.C., 37150 Guanajuato, México

División de Ciencias e Ingenierías, Universidad de Guanajuato, 37150 Guanajuato, México

*Corresponding author: mjuarezh@fisica.ugto.mx

Received January 17, 2020; accepted April 3, 2020; posted online May 26, 2020

The fluorescence evolution along Tm

-doped ZrF

–BaF

–LaF

–AlF

–NaF (ZBLAN) optical fibers, as well as

amplified spontaneous emission in the UV-IR region with emphasis on 350 nm, 365 nm, and 450 nm, is studied,

estimating optimal fiber lengths for amplification within the region. The fibers were diode-pumped with single

and double lines (687 and/or 645 nm). Double-line pumping presents a quite superior efficiency for producing

UV-blue signals with the benefit of requiring very short fibers, around 20 cm, compared to single-line pumping

requiring more than 50 cm. A virtual cycle in which the pumps enhance each other’s absorption is the key to these

systems.

Keywords: nonlinear optics; fiber; up-conversion; fluorescence and luminescence.

doi: 10.3788/COL202018.071901.

The need for obtaining short-wavelength operation sources

is constantly increasing. These types of light sources are

already highly used in an ample range of disciplines and

applications such as interferometry, laser microscopy, bio-

medicine, photolithography, optical data storage, pump

sources, laser projection displays, among others. As a gen-

eral rule, shorter-wavelength sources focus on smaller spots

and resolve finer structures in imaging applications.

These sources are often obtained from frequency

doubling or tripling lasers emitting around 600–1100 nm.

The most common lasers used for this purpose are

Nd∶Y

(Nd:YAG) (946 nm to obtain 473 nm

and 1064 nm to get 355 nm)

[1]

,Nd∶YVO

(914 nm to

obtain 457 nm and 1064 nm to obtain 532 nm)

[2]

Nd∶GdAl

ðBO

(Nd:GAB) (1062 nm to get 531 nm)

[3]

and Nd∶YAlO

(930 nm to get 465 nm)

[4]

. Nevertheless,

these kinds of lasers are usually bulky and hence usually

require external cooling systems. Their short absorption

lengths translate into low efficiencies. All of these qualities

together make them expensive with relatively complicated

operation and maintenance.

As an alternative to the bulk solid-state laser systems,

the up-conversion fiber lasers doped with rare-earth ions

are excellent candidates. They have many properties that

make them suitable for generating short wavelengths in

the visible (VIS) and the ultraviolet (UV) regions. At

moderated powers (up to some watts), they do not usually

present thermal issues and have superior conversion effi-

ciencies. Among the rare-earth ions, thulium (Tm

3þ

)asa

dopant in ZrF

–BaF

–LaF

–AIF

–NaF (ZBLAN) glass is

capable to convert low-energy infrared (IR) photons into

high energy photons (in the VIS and UV regions); the

reason is that fluorozirconate glasses based on ZBLAN

have more metastable levels compared to silica glasses,

expanding in this way the number of radiative transitions

for most rare-earth dop ants.

Since the first report of VIS up-conversion lasing in fluo-

ride glass fibers

[5,6]

, short-wavelength laser operation in

3þ

:ZBLAN has been demonstrated by many groups

in the past, usually obtaining 480 nm pumped by IR laser

sources (generally at 1064 nm with Nd:YAG lasers)

[7–10]

Also, wavelengths in the UV region (284 nm, 293 nm,

351 nm, and 360 nm) have been achieved by pumping with

solid-state lasers such as Nd:YAG at 1064 nm

[11]

, with an

laser at 485 nm and a dye laser at 585 nm

[12]

. However,

these systems often require absorption of three photons,

which often have a tradeoff between ground-state absorp-

tion (GSA) and excited-state absorption (ESA) in addition

to having small absorption [less than 5 dB/(km·ppm)

(ppm, parts per million) at 1064 nm and 10 dB/(km·ppm)

for 485 nm]. They also present a factor that may reduce the

efficiency of their systems; when being pumped with IR

sources, it may produce a photodarkening effect

[13,14]

An alternative arrangement for obtaining short-

wavelength emission in Tm

:ZBLAN is pumping with a

dual-wavelength configuration

[15,16]

. Since the strongest

absorption band of thulium-doped fluorozirconate is

centered at around 690 nm (

→

transition), we

proposed to use this wavelength as GSA

[17]

. Using this

wavelength, we can expect an optimal absorption

[≥35 dB∕ðkm·ppmÞ]

[18]

; this represents a factor of

3.5 to 7 better than that of IR and some other VIS

(485 nm or 585 nm) pump sources. Additionally, using

∼645 nm (

→

) as ESA, it is then possible to

obtain a variety of radiative transitions in the UV

(360 nm from

→

) and in the blue-VIS region

(450nm from

→

and 475 nm from

→

An additional advantage is that these kinds of pump

COL 18(7), 071901(2020) CHINESE OPTICS LETTERS July 2020

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短波长上转换发光的光谱分析：Tm掺杂光纤研究

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