High power, ultra-broadband supercontinuum source based on highly GeO2 doped silica fiber

We demonstrate a 74 mol % GeO2 doped fiber for mid-infrared supercontinuum generation. Experiments ensure a highest output power for a broadest spectrum from 700nm to 3200nm from this fiber, while being pumped by a broadband 4 stage Erbium fiber based MOPA. The effect of repetition rate of pump source and length of Germania-doped fiber has also been investigated. Further, Germania doped fiber has been pumped by conventional Silica based photonic crystal fiber supercontinuum source. At low power, a considerable broadening of 200-300nm was observed. Further broadening of spectrum was limited due to limited power of pump source. Our investigations reveal the unexploited potential of Germania doped fiber for mid-infrared supercontinuum generation. This measurement ensures a possibility of Germania based photonic crystal fiber or a step-index fiber supercontinuum source for high power ultra-broad band emission being pumped a 1060nm or a 1550nm laser source. To the best of our knowledge, this is the record power, ultra-broadband, and all-fiberized SC light source based on Silica and Germania fiber ever demonstrated to the date

Mid‐IR supercontinuum noise reduction using a short piece of normal dispersion fiber ‐ a general mechanism

Mid-infrared (IR) supercontinuum (SC) lasers are important in applications such as pollution detection, stand-off detection, and non-destructive testing. The performance in many applications is limited by the noise level of the supercontinuum laser. High noise typically results in low sensitivities or a need for long integration times. In this paper, a simple technique to reduce the noise of high noise soliton-based SC sources is introduced by adding a short piece of normal dispersion fiber to force the spectrally distributed solitons to spectrally broaden through self-phase modulation and thereby overlap to average out the noise. The noise reduction is demonstrated experimentally and numerically using a ZBLAN fiber based mid-IR SC source and adding a short piece of highly nonlinear arsenic-sulfide fiber. However, the method is generally applicable to any soliton-based near-IR or mid-IR SC source. Its efficiency is underlined by experimentally comparing it to SC generation in fibers in which a second zero-dispersion wavelength provides the spectral alignment noise reduction mechanism

Investigation into interferometric sub-wavelength periodic feature fabrication and their applications

Fabrication of sub-wavelength periodic structures requires advanced lithographic techniques so as to achieve uniform, large area patterns. Novel interference lithographic concepts/methodologies are proposed theoretically followed by experimental validation to fabricate uniform large area sub-wavelength periodic features. Further a multifaceted prism based zero path interferometer, for large area sub-micron patterning and immersion based interferometer for high resolution nano-scale patterning, is proposed and validated. Fabrication of complex features by interference lithography is one of the thrust research areas that were not fully researched. In this context, effect of the polarization states of individual beams in a multiple beam interference lithography was analyzed which led to the realization of a range of structures in 1D and 2D patterning. It is also found that body centered tetragonal, woodpile, β-tin type and diamond like structures can be obtained using multiple beam interference. Sub-wavelength periodic features are found to be very useful in various areas of nano photonics. Enhancing SPP propagation is explored using a periodic mask based near field lithography and with dye based gain medium. As one of the potential future applications, improving light absorption in thin film solar cell was also explored using the developed structures and proposed concepts.DOCTOR OF PHILOSOPHY (MAE

Periodic feature patterning by lens based solid immersion multiple beam laser interference lithography

In this paper, we report a novel concept and methodology to fabricate high resolution periodic features using i-line laser source and multiple converging lenses. This configuration reduces the number of optical elements by employing a converging two-lens system to direct the beams on to the sample instead of conventional multiple mirror assembly that is normally associated with multiple beam interference configurations. A simple optical configuration using a 60° prism, 364 nm laser source and two converging lenses are employed to implement immersion lithography concept to achieve four beam interference. Square lattice patterns with pitch size of 210±8 and 240±6 nm are recorded on a positive photo resist using this technique

Sub-60 nm periodic grating feature patterning by immersion based 364 nm laser interference

In this paper, we report a methodology to fabricate high resolution periodic grating features using high index prism based interferometer and i-line laser source. Features with sub-60 nm half pitch size were fabricated on i-line resist in an immersion medium using a prism of high index 1.939

Short-wave IR ultrafast fiber laser systems : current challenges and prospective applications

Ultrashort pulse generation at the short-wave infrared (SWIR) wavelength ranges from 1.6 to 2.5μm and together with benefits of the all-fiber design has transformed lasers into an essential tool for industrial, technological, scientific, environmental, and medical applications. With the development of pumping sources and fiber components, ultrafast SWIR fiber lasers have drawn exceptional research and industrial attention over the last decade, resulting in the achievement of comparable performance or even surpassing well-established near-IR sources. Exceptionally compact, highly stable, cost-effective, and maintenance-free ultrafast fiber lasers operating at the SWIR range are currently well on the way to be commercially employed. This invited Perspective article gives a comprehensive overview of the most significant achievements enabling ultrafast generation at SWIR, including up-to-date gain fibers and saturable absorbers, nonlinear process, and laser architectures. This article highlights the perspectives and strategies for further maturing of the field of SWIR fiber lasers and pathways for the improvement of the performance, overcoming existing bottlenecks and challenges toward reducing pulse durations, tunability of repetition rate, and power upscaling. The advancement of the ultrafast SWIR laser development is projected until the landscape of existing technologies, driven by these ultimate sources, and potential applications, emerging on the horizon.Economic Development Board (EDB)Ministry of Education (MOE)Published versionS.Y. is grateful for the support by the Academic Research Fund Tier 1, Ministry of Education (Singapore) under Project Grant No. 2018-T1-001-148 (RG 84/18) and the Economic Development Board—Singapore (EDB) under Grant No. S16-1257-IPP COY-15-IPP/160006 in association with Sintec Optronics Pte. Ltd

Bendable large-mode-area fiber with a non-circular core

We investigate mode-area-scaling and bending performances of a Yb-doped large-mode-area fiber with an elongated non-circular core. Such fiber can be bent in the plane of its short axis to suppress bending effects, such as mode area reduction and mode profile distortion. Meanwhile, the other orthogonal axis can be stretched for mode area scaling. Calculations show that for fibers with the same mode area, the higher the aspect ratio between the long axis and short axis, the less sensitive the fiber will be to bending effects. However, mode area scaling is limited by the increased beat length (BL) between the fundamental mode (FM) and the second-order mode, leading to mode degeneracy at higher aspect ratios. Within the 100 mm BL, the FM area is scalable to 3000 μm2 in a bent fiber. To facilitate FM operation, we study mode-selective gain through confined doping. Thanks to the small bending distortions, the confined-doping approach works well in the bent large-mode-area fiber. In addition, the advantage of tandem pumping is also discussed in terms of preferential modal gain. A noncircular core fiber with a 41 μm short axis and 120 μm long axis was fabricated in-house. We evaluated the fiber in a linear laser cavity pumped by a 975 nm laser diode. The maximum output power obtained was 191 W, with slope efficiency of approximately 67% with respect to launched pump power. The output signal has good beam qualities with M2 of ∼1.5 and ∼3.1, respectively, along the short and long axis.See also:  Publishers' note- Applied Optics 57(29) 8518  (2018)https://doi.org/10.1364/AO.57.00851

Investigation of core compositions for efficient 976 nm lasing from step index large-mode-area fiber

We present an efficient 976 nm fiber laser achieved in a step index large-mode-area (LMA) fiber by 915 nm diode pumping. The 976 nm lasing was enabled using spectroscopic engineering in a fiber design that helps suppress the competing 1030 nm gain. Our study shows, alumino-phospho-silicate (Al:P) is advantageous for shaping a gain spectrum in favor of 976 nm compared to other widely used compositions, hence facilitating otherwise the challenging 976 nm lasing. In addition, a germanium (Ge)-cladding was introduced to achieve LMA and low numerical aperture step-index fiber, permitting a wavelength selective bending technique. By applying the bending technique, an efficient 976 nm lasing was achieved with up to 15 W output power (pump power limited) with 28% slope efficiency in the step-index LMA fiber.This work was supported in part by Taihan Fiberoptics Company Ltd

Ultra-short wavelength operation of thulium doped fibre amplifier in the 1628-1655nm waveband

We present a silica-based thulium-doped fibre amplifier in the 1628-1655nm waveband based on Tm/Ge co-doped fibre. Up to 19dB external small signal gain and a noise figure of 4.4dB are achieved at 1655nm