50-W 2-μm Nanosecond All-Fiber-Based Thulium-Doped Fiber Amplifier

Transcription

1 IEEE JOURNAL OF SELECTED TOPICS IN QUANTUM ELECTRONICS, VOL. 20, NO. 5, SEPTEMBER/OCTOBER W 2-μm Nanosecond All-Fiber-Based Thulium-Doped Fiber Amplifier Yulong Tang, Xiaohui Li, Zhiyu Yan, Xia Yu, Ying Zhang, and Qi Jie Wang Abstract We report a two-stage 2-μm Tm 3+ fiber amplifier seeded by an acousto-optic modulator (AOM) modulated narrowbandwidth pulsed laser. Maximum output average power is over 50 W (slope efficiency of 58%) at 50 khz repetition rate, providing record performance in nanosecond 2-μm all-fiber-based amplifiers. The maximum pulse energy and peak power are 1.0 mj and 10 kw, respectively. The pulse width can be tuned from tens of to hundreds of nanosecond through changing the seed s pump power or the modulation repetition rate. This high-power 2-μm Tm 3+ fiber amplifier has an all-fiber-based configuration, providing high-degree stability and robustness. The laser emission wavelength, centered at 1951 nm with a spectral width of 1.4 nm, shows no obvious change with amplified power. Index Terms Acousto-optic Q switched, Tm 3+ fiber amplifier, high average power. I. INTRODUCTION RECENT years, Tm 3+ -doped fiber lasers (TDFLs) at 2 μm have attracted great research interest due to their wide applications in the areas such as polymer material processing [1], pump sources for mid-infrared optical parametric oscillators [2] and supercontiuum generation [3], [4]. By taking advantages of rapid development of diode lasers and the double-cladding fiber pumping technique, continuous wave (CW) mode 2 μm TDFLs have achieved >1 kw power [5]. However, high average Manuscript received November 29, 2013; revised February 18, 2014 and March 17, 2014; accepted March 28, This work was supported by the A STAR SERC Singapore under Grants and , the National Natural Science Foundation of China under Grant , and the Research Fund for the Doctoral Program of Higher Education of China under Grant Y. Tang is with the OPTIMUS, Photonics Centre of Excellence School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore, and also with the Key Laboratory for Laser Plasmas (Ministry of Education) and Department of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai , China ( yulong@sjtu.edu.cn). X. Li and Z. Yan are with the OPTIMUS, Photonics Centre of Excellence School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore ( LIXH@ntu.edu.sg; ZYAN004@e.ntu.edu.sg). X. Yu and Y. Zhang are with the Singapore Institute of Manufacturing Technology, Singapore ( xyu@simtech.a-star.edu.sg; yzhang@simtech.a-star.edu.sg). Q. J. Wang is with the OPTIMUS, Photonics Centre of Excellence, School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore and also with the CDPT, Centre for Disruptive Photonic Technologies, Nanyang Technological University, Singapore ( qjwang@ntu.edu.sg). Color versions of one or more of the figures in this paper are available online at Digital Object Identifier /JSTQE power of pulsed-mode 2 μm TDFLs is still limited due to the presence of nonlinear effects and amplified stimulated emission (ASE). High-peak-power and high-pulse-energy 2 μm TDFLs are highly desired in order to expand their applications. Pulsed 2-μm TDFLs are usually constructed by either Q switching [6], [7] or mode-locking [8], [9]. Graphene (a 2-D material) has also been widely used in mode-locked [10], [11] or Q-switched 2-μm fiber lasers [12] due to its easiness of being integrated to fibers and wide operation wavelength band. However, graphene has a comparatively lower damage threshold (compared with acousto-optic crystals) and the passively Q-switched pulses usually consist of mode-locking-like modulation on the pulse envelop [12]. Acousto-optic (AO) Q-switched 2 μm TDFLs have achieved average power of tens of watts by using high pump ratios [13], and the maximum average power of 33 W was obtained from a large-pitch fiber [14]. However, the use of free-space bulk modulators cannot provide an allfiber configuration, which decreases the system stability, robustness, and can easily damage the fiber facets. Gain-switched TDFLs have been proposed to generate high-energy [15], [16] and high-average-power [17], [18] 2 μm laser pulses, and a pulse energy of 14.7 mj has been obtained [15], but these systems either possess spiky pulses (relaxation) or need a complex gain modulator [19]. Tm 3+ -doped fiber amplifier (TDFA) systems are another alternative to improve average power and pulse energy of 2 μm TDFLs. In the nanosecond regime, a 16-W average power ( 1 mj)2-μm TDFA has been reported with an all-fiber-based configuration [20], and high propagation loss for both the laser signal and the pump in the adopted germanate fiber limit its power scaling. In the picosecond region, 2-μm TDFA has realized average power of 120 W [21] and peak power over 100 kw [22]. In the femtosecond regime, 2-μm TDFA has produced the narrowest pulse width of 108 fs [23], and has achieved the highest peak power of >3 MW by using chirped pulse amplification [24]. However, these systems usually have a low-power seed, necessitating multiple-stages and large gain (e.g., >30 db) to realize high-power output. This not only increases the system complexity, but also makes it easy to trigger ASE, limiting further average-power and pulse-energy scaling. In addition, high peak power in picosecond and femtosecond TDFAs makes it easy to stimulate various nonlinear effects. In this paper, based on an acousto-optic modulator (AOM) modulated seed source and two-stage amplifier, we realize highpower Q switched 2-μm TDFAs in an all-fiber-based configuration. The >50 W average power achieved in a repetition-rate tunable regime, are the highest value realized in 2-μm all-fiberbased pulsed lasers in the nanosecond regime. The high peak X 2014 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission. See standards/publications/rights/index.html for more information.

2 IEEE JOURNAL OF SELECTED TOPICS IN QUANTUM ELECTRONICS, VOL. 20, NO. 5, SEPTEMBER/OCTOBER 2014 Fig. 1. Experimental setup of the TDFA. LD: Laser diode; G: Grating; SMF: Single-mode fiber. power ( 10 kw) and pulse energy ( 1.0 mj) are very promising for nonlinear frequency conversion (e.g., supercontinuum generation in mid-infrared fibers). At the 10-kW peak power level, a narrow bandwidth of 1.4 nm is also achieved. II. EXPERIMENTAL SETUP Fig. 1 depicts the schematic setup of the 2-μm Q switched TDFA. In order to achieve high average power, double-cladding pumping technique was adopted for both the seed laser and the two amplifiers. The double-clad Tm 3+ silica fiber [10/130 μm, 0.15/0.46 NA (numerical aperture)] has a Tm 3+ doping concentration of 2 wt.% and cladding absorption of 3 db/mat 793 nm. In the seed laser, the Tm 3+ fiber has a length of 4 m. The pump source was a 35-W 793-nm laser diode (LD) with a 100-μm (0.22 NA) diameter pigtail fiber, and the pump light was launched into the Tm 3+ fiber through a (2 + 1) 1 fiber combiner, with a coupling efficiency of 95%. One end of the Tm 3+ fiber was fusion spliced to the signal fiber (10 μm core with 0.15 NA) of the combiner, and which in turn was spliced to a matched FBG (R = 99.5% at 1951 nm). The other end of the Tm 3+ fiber was connected to an AOM for Q switching, and after the AOM another FBG (R = 10% at 1951 nm) was incorporated. The AOM was a custom-designed high-power allfiber-based one operated at 1.95 μm with operating frequency of 65 MHz (Gooch & Housego Inc.). This pair of FBGs completes the laser cavity. The 10 angle cleaved end of the first FBG is used to suppress parasitic oscillations in the laser cavity due to Fresnel reflection. The output fiber (pigtail of G2) of the seed laser is fusion spliced to 1-m of single mode fiber (SMF-28) to filter the residual 790-nm pump light. Then, an isolator was inserted to maintain single-direction propagation of the laser light. After that, a 2-μm optical circulator was spliced to detect backward reflected light. The first-stage amplifier was also constructed with 10/130 Tm 3+ fiber (with a length of 3.5 or 4.1 m), which was also pumped by a 35-W 793-nm LD through a(2+ 1) 1 fiber combiner. The output from the first-stage amplifier was launched into the second amplifier by direct splicing the output signal fiber to the second stage amplifier. The second stage amplifier was pumped with two LDs through a (2 + 1) 1 fiber combiner. In order to improve the amplified average power and pulse energy while at the same time mitigate nonlinear effects, the signal fiber was changed to a large mode area fiber of 25/250 μm (NA 0.09/0.46) with a length of 3.5 m (cladding absorption is 9.5 db/m at 793 nm). Output end of the gain fiber of the second-stage amplifier was 10 angle cleaved for suppressing parasitic oscillation. All the Tm 3+ fibers were wrapped on 10-cm-diameter copper drums convectively cooled (for the seed laser) or circulating- Fig. 2. Output characteristics of the seed fiber laser. water cooled with a temperature of 20 C (for the amplifiers). At the output end, a dichroic mirror (R > 99.9%@793 nm, 0 ) was used to filter residual pump light. The laser output power was measured with an OPHIR power meter (F150 A-SH, OPHIR OPTRONICS LTD.) and the laser spectrum was recorded with a triple-grating spectrometer (Zolix Co.) with a spectral resolution of 0.2 nm. The laser pulsing dynamics were measured with a 500 MHz Agilent oscilloscope (DSO5054 A) combined with an InGaAs detector (15 MHz bandwidth). III. RESULTS AND DISCUSSION Increasing the 793-nm pump power to over 3.5 W, pulsing laser oscillation occurs (detected on the oscilloscope) and the output power shows an abrupt increase (detected with power meter). The output features of the seed laser at two repetition rates (10 khz and 50 khz) are shown in Fig. 2. The maximum output is slightly over 0.5 W, which is finally limited by the damage threshold of the fiber-based AOM. The tolerable average power incident on the acousto-optic crystal (TeO2) is 2 W, constraining the maximum output power of the seed laser to be 0.6 W after taking into account the 5 db transmission loss of the AOM. The output power at 50 khz is slightly higher than that at 10 khz frequency. Linear fitting of the output at 50 khz gives a slope efficiency of 8.3% with respect to launched pump power. The comparatively lower efficiency of the seed laser mainly originated from the comparatively high transmission loss of the AOM (5.3 db). Slightly high reflection coefficient of the output FBG (10%) and non-optimized fiber length also contribute to the low slope efficiency. Pulsing characteristics of the seed fiber laser are shown in Fig. 3 at two repetition rates (10 and 50 khz). For either repetition rate, higher pump power leads to narrower pulse width, which is a typical sign of actively Q switched lasers. At 50 khz, the pulse full width at half maximum (FWHM) was estimated from the envelop fitting to be 460 ns at 0.55 W output. However, the pulse is not clean, showing multiple peaks on the pulse envelope. The period of the peaks on the pulse envelop corresponds exactly to the round-trip time of the cavity, showing that some kind of modulation occurs in the laser cavity. This multipeak phenomenon has been explained as originating

3 TANG et al.: 50-W 2-μm NANOSECOND ALL-FIBER-BASED THULIUM-DOPED FIBER AMPLIFIER Fig. 3. Pulse shapes at different power levels of the AOM modulated fiber laser at two different repetition rates. Fig. 5. Amplified output of the TDFA in the second stage with a fiber length of 3.5 m. Fig. 4. Amplified output of the TDFA in the first stage at several repetition rates with two different fiber lengths. The seed power is 0.2 W. The amplification slope efficiency is also indicated. from injection of an ASE pulse by fast Q switching [25]. Our AOM has a rise time of 30 ns, thus is indeed a fast Q switch (compared to the 80 ns cavity round-trip time). Therefore, the multipeak phenomenon here can be attributed to periodic ASE perturbation initiated by fast Q switching. Compared with 50 khz, low repetition rate (10 khz) can provide much narrower pulse width at nearly identical pump levels. The narrowest pulse width achieved at 10 khz can be near 40 ns (at 0.5 W power level). In addition, the pulse shows nearly a single pulse shape (with just two very weak sub peaks). After choosing a certain power and pulse shape of the seed laser, we increased the pump power of the first-stage amplifier and the second-stage amplifier to scale the average power of the system. The output from the first-stage amplifier and that from the second-stage amplifier are shown in Figs. 4 and 5. The seed power of 0.55 W (50 khz) and 0.52 W (10 khz) decreased to 0.2 W after propagating through the SMF-28 fiber, the isolator, and the circulator. However, for consistence consideration, we still use 0.55 W (50 khz) and 0.52 W (10 khz) as the seed power in the following amplification. In the first-stage amplifier, the maximum amplified output power (16.2 W) was restricted by two factors. At comparatively high repetition rates (e.g., 50 khz), the limiting factor is the launched pump power. When we increased the pump power by incorporating another LD into the combiner, the output power can be improved to over 30 W (not shown here). However, at this power level (30 W), the system became unstable and heavy nonlinear effects occurred, limiting further power scaling. At comparatively low repetition rates, such as 10 khz or even lower, the main limiting factors will be stimulated Raman scattering (SRS) and ASE. While integrating a narrow-band-pass filter can efficiently suppress ASE for improving output power, mitigating SRS needs increasing fiber core cross section or shortening fiber length. The 50 khz repetition rate can provide an average power more than two times than that at the 10 khz repetition rate. As also shown in Fig. 4, the 3.5 m fiber length is much closer to the optimized fiber length for this fiber amplifier configuration, which gives an output increase of >30% compared to that with the 4.1 m fiber length. With this fiber length (3.5 m), the slope efficiency of the amplification is about 44.5%, which is somewhat lower than that (59%) from the multi-mode fiber amplifier [21]. Based on the first-stage amplifier (0.55 W seed and 3.5 m fiber length), the second-stage amplifier was constructed with a high-power fiber combiner, and the output power is shown in Fig. 5. Here, the first-stage amplifier was operated at the maximum output power of 16.2 W, which decreased to 15.4 W after the combiner 3 and to 12.6 W after the Tm fiber in the second-stage amplifier without pumping. The maximum amplified power of the second-stage amplifier is 52.3 W, which is just limited by the launched pump power. The linear increase of the output power (as well as the clean spectral shape observed from the spectrometer) shows that the average power can be further scaled just by increasing the pump power. The slope efficiency is 58.3%, nearly the same as that achieved with picosecond pulse amplification [21]. To the best of our knowledge, this is the first time to achieve over 50 W (in the ns regime) operation in all-fiber-based 2-μm pulsed fiber lasers. With two more LDs incorporated into the second-stage amplifier with a (6 + 1) 1

4 IEEE JOURNAL OF SELECTED TOPICS IN QUANTUM ELECTRONICS, VOL. 20, NO. 5, SEPTEMBER/OCTOBER 2014 Fig. 6. Pulse train of the TDFA at two repetition rates. fiber combiner (which is readily available currently), the output power can be steadily scaled to over 100 W. At the repetition rate of 10 khz, second-stage amplifier can provide a maximum output average power over 18 W when the first-stage power was kept at 4 W (not shown here). The laser pulse trains measured at two repetition rates are shown in Fig. 6. At the comparatively lower repetition rate (10 khz), the pulsing has high intensity stability. However, the intensity stability will decrease to some extent at the higher repetition rate (50 khz). Such intensity instability is an intrinsic feature of Q switched lasers due to that every pulse is originated from random ASE noise. When the seed laser operating at higher repetition rates (e.g., 50 or 100 khz), the recovery time between consecutive pulses becomes shorter. After each pulse output, the pump strength cannot completely recover the depleted population inversion, leading to enlarged instability at higher repetition rates. The instability of the seed laser will finally be transferred to the amplified output. The pulse shape characteristics of the TDFA measured at 50 and 10 khz are shown in Figs. 7 and 8, respectively. For the 50 khz amplification, the seed laser was kept at 0.55 W with a pulse width of 460 ns [as shown in Fig. 3(c)]. While for the 10 khz amplification, the seed laser was kept at 0.52 W with a pulse width of 42 ns [as shown in Fig. 3(f)], and the firststage power was maintained at 4 W. As shown in Fig. 7, with increasing amplification, the pulse width (here, the pulse width is the Gaussian fitting to the pulse envelop) increases significantly, from 460 ns to 1.25 μs at the output power of 25 W. Further increasing the amplification, the pulse width decreases. At the maximum output level (52 W), the pulse width is around 822 ns, corresponding to a pulse energy of 1.04 mj and peak power of 1.27 kw. The pulse broadening at higher output power is attributed to amplification of more sub pulses which cannot obtain enough gain under lower pump levels (see also Fig. 3). The pulse narrowing when the output is over 25 W can be due to the depletion of population inversion at high amplification levels. At the repetition rate of 10 khz, the pulse number (sub pulses) increases with amplification, and four sub pulses are clear at the Fig. 7. Fig. 8. Pulse evolution of the TDFA at the repetition rate of 50 khz. Pulse evolution of the TDFA at the repetition rate of 10 khz.

5 TANG et al.: 50-W 2-μm NANOSECOND ALL-FIBER-BASED THULIUM-DOPED FIBER AMPLIFIER Fig. 10. scale). Spectral evolution of the TDFA at the repetition rate of 10 khz (linear Fig. 9. scale). Spectral evolution of the TDFA at the repetition rate of 50 khz (linear amplification power of 18 W. At >10-W power levels, the noisy feature of the spectra shows that time- and amplitude jitter exist. Clean spectrum could be measured at 10 W power level, giving pulse energy of 1.0 mj. Based on area integration, the pulse peak power is estimated to be 10 kw (at 8-W average power). Another intriguing point is that with increasing pulse energy and peak power, the pulse number increases (at 10 khz repetition rate), but the single pulse width is still maintained at 42 ns. Then single narrow pulse ( 40 ns) can be easily obtained by incorporating a time gate into this fiber laser system. The repetition rate can be tuned from several khz to over 100 khz through changing the AOM modulation rate. However, it was found that too low or too high repetition rates (<5 khz or >100 khz) will greatly decrease the stability of the pulsing operation due to the intrinsic features of the AOM. Too low repetition rates make the AOM cannot be completely turned off due to high gain of fiber lasers. On the contrary, comparatively long pulse build-up time limits the laser to operate at high repetition rates (>100 khz). Other modulation techniques should be adopted if lower or higher repetition-rate pulsing are required. The spectral characteristics of the TDFA measured at 50 khz (with seed power of 0.55 W) and 10 khz (with seed power of 0.52 W) are shown in Figs. 9 and 10, respectively. Under both repetition rates, the spectral FWHM of the seed laser was 1.5 nm. At 50 khz, the spectrum shows no obvious change upon amplification, even up to 52 W output. At the maximum output power level, the optical signal-to-noise ratio (SNR) is Fig. 11. Radio-frequency spectra of the TDFA at the fundamental repetition rate of (a) 50 khz and (b) 10 khz. over 20 db. The spectrum is mainly dictated by the designed FBG at nm with a FWHM of 1.4 nm. Therefore, under such a peak power level, the spectral characteristics can be effectively determined by the FBG and no other measures are necessary. However, under the repetition rate of 10 khz, the spectrum shows slight broadening and some new components in the longer wavelength region. The presence of new spectral components was probably due to parasitic oscillations and ASE. Under either repetition rate, no obvious pump dependence of the center wavelength was observed. The radio frequency spectra of the TDFA at the output power of 52 W (50 khz) and 18 W (10 khz) were measured and are shown in Fig. 11. At both repetition rates, the peak-to-

6 IEEE JOURNAL OF SELECTED TOPICS IN QUANTUM ELECTRONICS, VOL. 20, NO. 5, SEPTEMBER/OCTOBER 2014 background SNR is larger than 25 db, indicating good stability of the fiber amplifier system. The output beam quality is determined by the second-stage Tm 3+ fiber, which has a 25 μm(na= 0.09) core, giving a normalized frequency of 5.3, much larger than the single-mode condition of V = Therefore, the fiber laser operates in the multi-mode situation. IV. CONCLUSION A high-power 2-μm TDFA based on an AOM modulated seed source is reported with 52 W output power in an all-fiber-based configuration for the first time. This kind of actively modulated TDFA can provide stable high repetition rate (>50 khz), >1 mj pulse energy and 10 kw peak power, and will find wide applications in frequency conversion, range finding, marking, gas detecting, etc. Understanding the limitation of power scaling of 2-μmTm 3+ - doped fiber lasers in various pulse width regimes (e.g., nanosecond, picosecond, and femtosecond) will not only increase our understanding of the intrinsic dynamics of this fiber laser system, but also provide new developing routines for mid-infrared fiber lasers. Scaling the average power and pulse energy of 2-μm Tm 3+ -doped fiber lasers will greatly improve their performance and utility. Further average-power and pulse-energy scaling need circumventing detrimental nonlinear effects and improving the damage threshold of related fiber-based elements. One application example of such high-power pulsed 2-μm laser system is for high-power mid-infrared supercontinuum generation in our future work. 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Richardson, 100 kw peak power picosecond thulium-doped fiber amplifier system seeded by a gain-switched diode laser at 2 μm, Opt. Lett., vol. 38, no. 10, pp , [23] G. Imeshev and M. E. Fermann, 230-kW peak power femtosecond pulses from a high power tunable source based on amplification in Tm-doped fiber, Opt. Exp., vol. 13, no. 19, pp , [24] R. A. Sims, P. Kadwani, A. S. L. Shah, and M. Richardson, 1μJ, sub- 500 fs chirped pulse amplification in a Tm-doped fiber system, Opt. Lett., vol. 38, no. 2, pp , [25] Y. Wang and C. Q. Xu, Understanding multipeak phenomena in actively Q-switched fiber lasers, Opt. Lett.,vol.29,no.10,pp ,2004. Yulong Tang received the Ph.D. degree in optical engineering from the Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Shanghai, China, in From 2008 to 2011, he was a Research Assistant at the Shanghai Institute of Optics and Fine Mechanics, where he was involved in the development of mid-ir solid-state lasers. From 2011 to now, he was working in Shanghai Jiao Tong University, China, as an Assistant Professor, involved in research upon high-power fiber lasers and solidstate lasers, and application of laser technologies. His current research interests include mid-ir laser sources and nonlinear optic dynamics. Xiaohui Li received the B.S. degree in science from Northwest University, Xi an, China, in 2006 and the Ph.D. degree from the Xi an Institute of Optics and Precision Mechanics, Chinese Academy of Sciences and Xi an Jiaotong University in He is currently a Research Fellow at Nanyang Technology University, Singapore. His current research interests include passively modelocked fiber laser, high power fiber laser, and solitons in fiber.

7 TANG et al.: 50-W 2-μm NANOSECOND ALL-FIBER-BASED THULIUM-DOPED FIBER AMPLIFIER Zhiyu Yan was born in Yunnan, China, in She received B.Sc. degree in electronics information and technology from Beijing Normal University, Beijing, China, in 2010 and the M.Sc. degree in electronics from Nanyang Technological University, Singapore, in She is currently working toward the Ph.D. degree in Nanyang Technological University. Her research interest include fiber laser, supercontinuum generation. Ying Zhang received the B.Eng., M.Eng., and Ph.D. degrees from Southeast University, China, in 1989, 1992, and 1995, respectively. From 1996 to 1997, he was a Postdoctoral Fellow with Nanyang Technological University, Singapore. Since 1998, he has been working with Singapore Institute of Manufacturing Technology, now as a Senior Scientist, Group Manager of Precision Measurements Group, Division Director of Manufacturing Automation Division, and Director of Research Liaison Office of SIMTech. His current research interests include optical measurements, near-field optics, adaptive control and signal processing, image processing, X-ray optics, and ultra-fast lasers. Xia Yu received the B.Eng. and Ph.D. degrees from the School of Electrical and Electronic Engineering (EEE), Nanyang Technological University (NTU), Singapore, in 2003 and 2007, respectively. From June 2006 to September 2008, she worked as a Postdoctoral Researcher in the School of EEE, NTU. She is currently a Scientist in the Precision Measurements Group, Singapore Institute of Manufacturing Technology (SIMTech), Agency for Science Technology and Research (A STAR). Her research interests include microstructured optics and nonlinear optics. Qi Jie Wang received the Ph.D. degree in electrical and electronic engineering from Nanyang Technological University (NTU), Singapore, in After completing his Ph.D. degree, he worked in NTU. From 2007 to 2009, he joined the School of Engineering and Applied Science, Harvard University, in Prof. Federico Capasso s group as a Postdoctoral Researcher. In October 2009, he was assigned as a joint Nanyang Assistant Professor at the School of Electrical and Electronic Engineering (Microelectronics Division) and the School of Physical and Mathematical Sciences (Physics and Applied Physics Division). His current research interests are to explore theoretically and experimentally nano-structured semiconductor and fiber-based materials, and nanophotonic devices (nanoplasmonics, photonic crystals and metamaterials) with an emphasis on investigating the fundamental properties (optical and electrical) of semiconductor and high power fiber lasers, and nanophotonic devices in the infrared frequency regimes.