Mohammed Saad

Fluoride glass fiber: state of the art

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 fiber. In this paper we will present mechanical and optical properties of current fluoride glasses and fibers, as well as high power transmission results.

Mid-infrared supercontinuum generation spanning 1.8 octaves using step-index indium fluoride fiber pumped by a femtosecond fiber laser near 2 µm.

A nearly two-octave wide coherent mid-infrared supercontinuum is demonstrated in a dispersion-engineered step-index indium fluoride fiber pumped near 2 µm. The pump source is an all-fiber femtosecond laser with 100 fs pulse width, 570 mW average power and 50 MHz repetition rate. The supercontinuum spectrum spans from 1.25 µm to 4.6 µm. Numerical modelling of the supercontinuum spectra show good agreement with the measurements. The coherence of the supercontinuum is calculated using a numerical model and shows a high degree of coherence across the generated bandwidth allowing it to be used for frequency comb applications.

Quantification of different water species in acetone using a NIR-triple-wavelength fiber laser

A fiber laser using a thulium-doped ZBLAN gain medium was used to generate laser radiation simultaneously at 1461, 1505 and 1874 nm, with > 5 mW output power at each of the wavelengths. The laser was used to quantify the near-infrared absorption of liquid water in acetone. Additionally, near-infrared spectra were recorded using a broad band source and were interpreted using parallel factor (PARAFAC) analysis to rationalize the concentration-dependent peak shifts.

Indium fluoride glass fibers

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.

Passively synchronized Q-switched and mode-locked dual-band Tm 3+ :ZBLAN fiber lasers using a common graphene saturable absorber

Dual-band fiber lasers are emerging as a promising technology to penetrate new industrial and medical applications from their dual-band properties, in addition to providing compactness and environmental robustness from the waveguide structure. Here, we demonstrate the use of a common graphene saturable absorber and a single gain medium (Tm3+:ZBLAN fiber) to implement (1) a dual-band fiber ring laser with synchronized Q-switched pulses at wavelengths of 1480 nm and 1840 nm, and (2) a dual-band fiber linear laser with synchronized mode-locked pulses at wavelengths of 1480 nm and 1845 nm. Q-switched operation at 1480 nm and 1840 nm is achieved with a synchronized repetition rate from 20 kHz to 40.5 kHz. For synchronous mode-locked operation, pulses with full-width at half maximum durations of 610 fs and 1.68 ps at wavelengths of 1480 nm and 1845 nm, respectively, are obtained at a repetition rate of 12.3 MHz. These dual-band pulsed sources with an ultra-broadband wavelength separation of ~360 nm will add new capabilities in applications including optical sensing, spectroscopy, and communications.

Multi-wavelength S-band Tm:ZBLAN fiber lasers

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 glass fiber for reliable Er :YAG and Er,Cr :YSGG laser power delivery

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.

Future of nonoxide fiber lasers: searching for the commercial application

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.

Mid-infrared supercontinuum generation up to 4.6 µm using step-index indium fluoride fiber pumped by a femtosecond fiber laser near 2 µm

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.

Indium Fluoride Glass Fibers for Mid-Infrared applications

Abstract: Indium fluoride fibers have a wide transmission window from 0.3 to 5.5 micron. This opens the door to new applications, in aerospace, supercontinuum sources, and spectroscopy and fiber lasers. We report multimode and single mode indium fluoride glass fibers with good optical attenuation.