We report mid-infrared supercontinuum (SC) generation in a dispersion-engineered step-index indium fluoride fiber pumped by a femtosecond fiber laser near 2 μm. The SC spans 1.8 octaves from 1.25 μm to 4.6 μm with an average output power of 270 mW. The pump source is an all-fiber femtosecond laser that generates sub-100 fs pulses at 50 MHz repetition rate with 570 mW average power. The indium fluoride fiber used for SC generation is designed to have a zerodispersion wavelength close to 1.9 μm. Two fiber lengths of 30 cm and 55 cm are selected for the SC generation experiments based on the numerical modelling results. The measured spectra and the numerical modelling results are presented showing good agreement for both lengths. The femtosecond pumping regime is a key requirement for generating a coherent SC. We show by modelling that the SC is coherent for a pump with the same pulse width and energy as our fiber laser and added quantum-limited noise. The results are promising for the realization of coherent and high-repetition-rate SC sources, two conditions that are critical for spectroscopy applications using FTIR spectrometers. Additionally, the entire SC system is built using optical fibers with similar core diameters, which enables integration into a compact platform.
Tm3+-doped fluoride (ZBLAN) fibers offer amplification and lasing in a wide variety of wavelength ranges, including 810 nm, 1480 nm, 1900 nm, and 2300 nm.1 Amplification and lasing around 1480 nm through the 3H4→3F4 transition is of interest for extending the capacity of WDM transmission systems, as well as developing sources for pumping erbium-doped fiber and fiber Raman amplifiers. The 3H4→3F4 transition, however, poses a challenge due to its self terminating nature. As such, the 3F4 level can be depleted either by colasing at 1900 nm2 or by using upconversion pumping at 1064 nm. High-power 1480 nm Tm3+:ZBLAN fiber lasers with upconversion pumping at 1064 nm have been demonstrated.3-6 Recent research has focused on improving further the power conversion efficiency as well as the development of monolithic fiber lasers, e.g., by incorporating fiber Bragg gratings (FBGs) directly within the Tm3+: ZBLAN fiber gain medium.
Dual-wavelength and multi-wavelength sources can have many applications in instrumentation (e.g., component testing), LIDAR systems, and fiber optics sensing. There have been several reports of dual-wavelength Tm3+-doped fiber lasers. For example, Androz et al. demonstrated operation at 785 nm and 810 nm, corresponding to the 1G4→3H5 and 3H4→3H6
transitions, respectively, with a Tm3+:ZBLAN fiber gain medium.7 Wang et al. obtained dual-wavelength lasing around 2 μm with a tunable wavelength spacing from 1 nm – 40 nm in a Tm3+:silica fiber laser.8 We realized oscillation at 805 nm and 810 nm through the 3H4→3H6 transition in a Tm3+:ZBLAN fiber laser; we also reported wavelength switching capability as well as bistable operation in both single cavity and cascaded cavity configurations.9 In this paper, we
extend our work further and report a dual-wavelength Tm3+:ZBLAN fiber laser operating in the S-band. Wavelength spacings of 11 nm and as narrow as 0.6 nm are achieved in a linear cascaded cavity configuration with bidirectional upconversion pumping at 1064 nm.
Fluoride glasses are the only material that transmit light from ultraviolet to mid-infrared and can be drawn
into industrial optical fibers. The mechanical and optical properties of new indium fluoride glass fibers
have been investigated. Multimode fiber 190 microns, has very high mechanical strength greater than 100
kpsi and optical loss as low as 45 dB/km between 2 and 4 microns. Unlike chalcogenide glass fibers,
indium fluoride fiber has a wide transmission window from 0.3 to 5.5 microns without any absorption peak.
Indium fluoride glass fibers are the technology of choice for all application requiring transmission up to 5
micron such as infrared contour measure (IRCM) and chemical sensing. Furthermore, Indium fluoride
glasses have low phonon energy and can be heavily doped and co-doped whit rare-earth elements.
Therefore they are very promising candidates for infrared fiber lasers.
The availability of high quality optical fibers with transmission window, larger than that of silica fiber,
extends the use of optical fibers and open new application fields. There is increasing demand of optical
fiber with transmission over 2 microns, where silica is opaque, for applications as diverse as sensing, fiber
lasers and amplifiers, defense (IRCM), spectroscopy... No materials can fulfill all applications needs.
Engineers have to make some compromise when choosing the right materials for the right application.
Heavy metal fluoride glass is one of these materials. The glass, under bulk form, has a wide transmission
window from 0.3 up to 8 microns, without any absorption peaks.
Heavy metal fluoride glass fibers are drawn using the preform technique, the same technique used for silica
fiber. This technique has proven to allow good control of fiber dimensions and geometry. Fluoride glass
fibers with different exotics shapes have already been obtained, such as D-shaped, square, of centered fiber,
multi cladding fibers and microstructured fibers....
As far as active fibers are concerned, heavy metal fluoride glasses have low phonon energy and can contain
high concentration of active ions, rare-earth elements. Therefore, new laser lines have been already
demonstrated using fluoride glass fibers. Fiber lasers with output power exceeding 10 w have been
obtained by different groups.
This paper will present the latest development of fluoride glass fiber technology, including fibers optical
and mechanical properties, fiber lasers and power handling.
Fluoride glasses are very unique materials that transmit light continually from the UV to mid-infrared (0.3
to 9 μm) without any absorption peaks, and can be drawn into high quality optical fibers. They have been
discovered at Rennes University in the mid-seventies, and have experienced an extraordinary and intensive
development for more than 25 years for their outstanding optical properties. They have been first
intensively developed for long haut telecommunication applications due to their ultra low theoretical
optical loss (0.01 to 0.001 dB/km). After many years of intensive research, unfortunately, this goal has not
been reached yet and remains a challenge. In the late nineties, the research activities around fluorides
glasses and fibers have slowed down and only a few laboratories continue to have some ongoing activity
focusing mainly on applications such as fiber lasers, Supercontinuum, spectroscopy and laser power
Fluoride glasses are the only materials that transmit light in a continuous fashion from ultraviolet up to 8 μm in the mid-infrared
region, and can be drawn into high quality optical fibers. In fact fluoride glass fiber technology is the second
most mature, beside silica based fiber technology.
Fluoride glasses have experienced extraordinary development for more than 25 years. This development was motivated
in the beginning by their outstanding optical properties, especially the minimum theoretical attenuation which is 0.01
dB/km between 2 and 3 μm.
High quality optical fibers are now commercially available, with attenuation ranging from 5 to 30 dB/km, and
mechanical strength ranging from 50 to 100 kpsi depending on fiber diameter.
The fluoride glass transmission window is from 0.25 μm to 8 μm without any absorption peaks, while the resulting fiber
transmission window can be from 0.3 μm to 4.5 μm for standard fiber and from 0.3 μm to 6 μm for the extended window
In this paper we will present mechanical and optical properties of current fluoride glasses and fibers, as well as high
power transmission results.
This presentation will review and compare different purification processes of starting materials and
different synthesis processes developed so far to prepare high purity rare-earth doped and un-doped
Discovered in 1975 at Rennes University and intensively developed for more than 25 years, fluoride
glasses have experienced an extraordinary development, due to their broad transmission spectrum and their
low optical loss. With a theoretical optical loss of 0.001 dB| km fluoride at 2.6 micron, fluoride glass have
been considered as material of choice for repeater less communication link. Since this goal wasn't easy to
achieve the intensive development ended in early nineties. However, the technology is quite mature to
provide high purity bulk glass, lenses and fibers for short and medium-length application. Single and multimode
fibers with optical loss lower than 10 dB|km are routinely prepared.
Furthermore, compared to silica and chalcogenide glasses, fluoride glasses can be doped with high
concentration of rare-earth element required for different applications such as, fiber laser, fiber amplifier.
They can also be prepared with lower rare earth and transition metals ions required for laser cooling
Compared to other transparent infrared fiber materials, ZBLAN fluoride glasses promise to be best suited for laser power
delivery in the 3μm wavelength region due to their high transmission and excellent mechanical flexibility. These claims
were demonstrated in a series of power handling tests of both straight and coiled fibers using an Er,Cr:YSGG laser
emitting a train of pulses of 150 μs duration at a repetition frequency of 20 Hz producing 7.5 W average power. Large
core fibers (450/510μm 0,2NA) are characterized by an attenuation of 0.02dB/m at 3μm and stay within 0.5°C from
ambient temperature when carrying full laser power. A 2-m fiber length prepared with bare cleaves has been tested for
over 23 hours, cumulating 1,140,000 shots of 1530 J/cm2 fluence while maintaining 90% transmission without any
measurable degradation. Coiling the fiber to 11 cm radius did not have an impact on power handling reliability. These
results show the potential of these highly transparent fibers in surgical laser delivery applications.
Fiber lasers offer several advantages over bulk solid-state lasers because they can achieve both high efficiency and fair output power. Still, the use of those silica fiber lasers is limited to very few particular applications like broadband ASE source and pulsed fiber lasers. But, since non-oxide fibers open a broad wavelength range not accessible via rare-earth doped silica fiber nor semiconductor lasers, several niches should be available. In this paper, a comparative study of performances and commercial readiness of both oxide and non- oxide fiber lasers will be done. Effectively, non-oxide fiber laser developers are confronted to several fundamental (photo- induced loss) and technical challenges (splicing, moisture, handling in general). For example, the availability of the right pump laser wavelength lags behind any serious commercial applications. Fortunately, efficient up-conversion process helps access visible to UV wavelength range with commercial IR and near-IR pumps. Also, optimization and prediction of the performance must rely almost solely on experimental validation because the numerical simulation of non-oxide glass is very complex. In particular, for up-conversion lasers, one must consider and more important, know both the emission and absorption cross-sections of 5 to 10 energy levels. Nevertheless, we will review some promising applications coming from sensors system, RGB visible sources, telecommunication applications and some special LIDAR systems that can use double-clad fiber geometry for more efficient pumping and higher power output.
The prospect of using optical fiber amplifiers made of rare- earth doped glasses other than the very familiar silica glass opens new applications and new amplifications windows. A literature survey has been conducted in order to assess the current situation in regards to these alternative technologies. Clearly, despite the amount of efforts, the 1.3 micrometers spectral region is still looking for a more efficient candidate. So far, Pr3+-doped ZBLAN is the technology of choice, offering quantum efficiencies of about 1.5 percent only. On the other hand, the current 1.55 micrometers fiber amplifiers offer nearly unbeatable performances. Other than rare-earth silica fiber amplifiers, only fluoride and tellurite glasses rare-earth doped fiber amplifiers applications is currently in a prospective state, although the potential of these technologies is undeniable. In these cases, the huge step between bulk glass and fiber fabrication remains to be made and/or optimized.