Copper phthalocyanines as a mode-locker in an Er-doped fiber laser.

We demonstrate a mode-locked erbium-doped fiber laser (EDFL) utilizing copper phthalocyanines (CuPc) as a saturable absorber (SA) for the first time, to the best of our knowledge. The investigated SA was prepared using a simple, low-cost and straightforward technique, whereby the CuPc powder was embedded into polyvinyl alcohol (PVA) to form a thin film. The thin film acted as a mode-locker when it was incorporated into the EDFL cavity to produce output pulses at a repetition rate of 1.8 MHz with a pulse duration of 1.98 ps. The frequency spectrum showed a signal-to-noise ratio as high as 55 dB, which indicates the stability of the mode-locking operation. To the best of our knowledge, this is the first work to report using CuPc as a mode-locker.

Sodium carbonate modulated ultrashort mode-locked stretched pulses in an erbium-doped fiber laser.

In this paper, we propose a new, to the best of our knowledge, saturable absorber (SA) based on sodium carbonate (N a 2 C O 3) for producing an ultrafast mode-locked stretched pulse in a passively erbium-doped fiber laser at near-zero dispersion. The solid film of a N a 2 C O 3-SA was fabricated by the drop-casting method using polyvinyl alcohol as a host polymer. The modulation depth of the proposed SA, which was measured by a balanced twin detector technique, was 2.3% with saturation intensity of 181M W/c m 2. The mode-locking operation of the EDFL-based N a 2 C O 3-SA was observed at a pump power of 117 mW. A stable stretched pulse was generated by using the proposed N a 2 C O 3-SA. The laser can generate pulses with a repetition rate and duration of 1.87 MHz and 820 fs, respectively, within a bandwidth of 6.6 nm. The single pulse energy reaches up to 5 nJ, which is equivalent to the average output power of 9.3 mW. Finally, to the best of our knowledge, this is the first report on using the N a 2 C O 3-SA for generating a stretched-pulse mode-locked fiber laser.

Nanosecond Q-switched laser with PEDOT: PSS saturable absorber.

We demonstrate deployment of the nonlinear saturable absorption property of the organic material poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT: PSS) for pulse generation in the near-infrared region. The saturable absorber (SA) film was made using a straightforward process of depositing a layer of the PEDOT: PSS material onto a polyvinyl alcohol (PVA) film. The prepared SA was inserted into an erbium-doped fiber laser cavity as a Q-switcher to produce laser pulses with a maximum pulse rate of 92.75 kHz, minimum pulse duration of 912 ns, and highest pulse energy of 222.83 nJ. Results showed that PEDOT: PSS/PVA SA could become a promising SA for various laser applications. To our knowledge, this is the first time that PEDOT: PSS/PVA has been utilized as a SA to produce a stable Q-switched laser in 1.55 µm.

Self-starting triple-wavelength vector dark soliton with a bismuth-doped fiber saturable absorber.

We report on the generation of a triple-wavelength vector dark soliton in an all-fiber ring cavity of erbium-doped fiber laser mode-locked with a bismuth-doped fiber saturable absorber. The formation of the triple-wavelength vector dark soliton is due to the cross-phase coupling derived from the cavity birefringence. The mode-locked laser operated at a 1.89 MHz repetition rate with a 335 ns pulse width, and its robustness is confirmed.

Nanosecond passively Q-switched fibre laser using a NiS2 based saturable absorber.

Q-switched pulse laser generation is successfully demonstrated in both Erbium-doped fibre laser (EDFL) and Thulium-doped fibre laser (TDFL) cavities by employing Nickel disulfide (NiS2) as a saturable absorber (SA). Q-switched pulse laser operation at 1.55 µm and 2.0 µm is obtained at low pump power levels of 37 mW and 48 mW, respectively. For the EDFL, stable passively Q-switched laser output at a wavelength of 1561.86 nm is achieved, with a minimum pulse duration of 237 ns and a repetition rate of 243.9 kHz. For the TDFL, the centre wavelength of the laser output is 1915.5 nm, with a minimum pulse duration of 505 ns and a repetition rate of 214.68 kHz. NiS2 is used as SA for Q-switched laser generation over a broadband wavelength for the first time.

Nanosecond pulse laser generation at 1.55 and 2 µm regions by integrating a piece of newly developed chromium-doped fiber-based saturable absorber.

This paper demonstrated the nanosecond pulse laser operation at 1.55 and 2 µm wavelength regions using a newly develop chromium-doped fiber (CrDF) as a saturable absorber (SA) to convert efficiently continuous-wave laser operation to nanosecond pulse laser operation. The laser uses an erbium-doped fiber (EDF) and thulium-doped fiber as the gain medium. A piece of 10 cm long CrDF was integrated into both laser cavities to generate nanosecond pulse laser operation. In 1.55 region generation, an additional single-mode fiber (SMF) 100 m long was added into the EDF laser cavity. Stable pulse generation occurred at a repetition rate of 1 MHz with a pulse width of 432 ns and a signal-to-noise ratio (SNR) of 66 dB. The highest peak power of 24 mW was obtained at 142 mW pump power. In 2 µm region generation, the obtained repetition rate was 10 MHz with a pulse width and SNR of 59 ns and 41 dB, respectively. The highest peak power was only 8.3 mW. By looking into the findings, the newly developed CrDF SA has a potential to be further enhanced toward better generation of ultrashort pulse fiber lasers.

Ultrashort pulse generation with an erbium-doped fiber laser ring cavity based on a copper oxide saturable absorber.

A soliton mode-locked erbium-doped fiber (EDF) laser has been experimentally demonstrated using copper oxide (CuO) thin film as a saturable absorber (SA). The dispersion of the EDF cavity including the CuO-SA was balanced by a suitable length of single-mode fiber (SMF). The fabricated CuO-SA has 3.5% modulation depth and 3.3 MW/cm2 saturation intensity. The mode-locked train pulses have 1.7 ps pulse width and 983 kHz repetition rate, while the pulse energy and output power are 1.29 nJ and 1.27 mW, respectively, at maximum pump power of 159 mW. These results indicate that the CuO thin film is a good SA candidate for a fiber laser operating at a low pump power. To the best of our knowledge, this is the first demonstration of a CuO-SA-based mode-locked fiber laser.

All-fiber dual wavelength passive Q-switched fiber laser using a dispersion-decreasing taper fiber in a nonlinear loop mirror.

This paper describes a proposal and successful demonstration of a dual wavelength all-fiber passively Q-switched erbium-doped fiber ring laser. The Q-switch operation was realized by using a nonlinear loop mirror that incorporated an unbalanced dispersion-decreasing taper fiber to act as a saturable absorber without additional elements. This setup enabled a fiber ring laser to achieve a performance of 48.7 kHz repetition rate with pulse duration of around 3.2 µs and approximate pulse energy of 20 nJ.

Gain-shift induced by dopant concentration ratio in a Thulium-Bismuth doped fiber amplifier.

This paper details the effect of Thulium and Bismuth concentration ratio on gain-shift at 1800 nm and 1400 nm band in a Thulium-Bismuth Doped Fiber Amplifier (TBDFA). The effect of Thulium and Bismuth's concentration ratio on gain shifting is experimentally established and subsequently numerically modeled. The analysis is carried out via the cross relaxation and energy transfer processes between the two dopants. The energy transfer in this process was studied through experimental and numerical analysis of three samples with different Tm/Bi concentration ratio of 2, 0.5 and 0.2, respectively. The optimized length for the three samples (TBDFA-1, TBDFA-2 and TBDFA-3) was determined and set at 6.5, 4 and 5.5 m, respectively. In addition, the experimental result of Thulium Doped Fiber Amplifier (TDFA) was compared with the earlier TBDFA samples. The gain for TBDFA-1, with the highest Tm/Bi ratio, showed no shift at the 1800 nm region, while TBDFA-2 and TBDFA-3, possessing a lower Tm/Bi concentration ratio, shifted to the region of 1950 and 1960 nm, respectively. The gain shifting from 1460 nm to 1490 nm is also observed. The numerical model demonstrates that the common 3F4 layer for 1460 nm emission (3H4→3F4), and 1800 nm emission (3F4→3H6)inversely affects the 1460 nm and 1800 nm gain shifting.

Domain-wall dark pulse generation with SMF-GIMF-SMF structure as artificial saturable absorber.

We experimentally demonstrated the generation of domain-wall dark pulse in an Erbium-doped fiber laser using the combination of a 10 cm graded index multimode fiber sandwiched by single mode fibers as artificial saturable absorber. The interaction of phase difference in grade index multimode fiber allowed the stable dual-wavelength oscillation in the cavity. The dual-wavelength centered at 1567.2 nm and 1569.4 nm produces the topological defect in temporal domain and achieved a dark pulse formation with repetition rate of 21.5 MHz. The highest average pulse energy is calculated as 769.6 pJ with pulse width of 5 ns. Throughout the operating pump power range, the average pulse energy and output power increase linearly, with R2 of 0.9999 and achieved the laser efficiency of 9.33%. From the measurement in frequency domain, the signal-to-noise ratio is measured as 49 dB. As compared to reported DW dark pulse works, the proposed structure only required a short length of multimode fiber, which allowed the domain-wall dark pulse to achieve higher pulse repetition rate. The venture of domain wall dark pulse is potentially to pave the foundation toward sustainable industrial growth.

Passively harmonic dissipative soliton generation in normal dispersion erbium-doped fiber laser using SMS fiber as artificial saturable absorber.

Passively harmonic mode-locking has been experimentally demonstrated in an erbium-doped fiber laser with large normal dispersion using single-multi-single mode structure as artificial saturable absorber. By increasing the pump power under the same polarization setting, the mode-locking operation can switch from fundamental mode-locked to 5th order harmonic mode-locked. Highest repetition rate of 4.26 MHz (5th order harmonic) is observed, with pulse width and pulse energy ascertained at 290 fs and 3.0 nJ, respectively. Excellent signal-to-noise ratio (SNR) of above 50 dB is observed for all harmonic orders. The findings validated that SMS structure can be used to generate stable and switchable high order of harmonic mode-locked. The low-cost SMS fiber for harmonic mode-locked generation technique could lay the groundwork for future sustainable industrial growth.

S-band multiwavelength Brillouin/Raman distributed Bragg reflector fiber lasers.

A multiwavelength Brillouin/Raman distributed Bragg reflector fiber laser operating in the S-band region is proposed and demonstrated. The laser uses a 7.7 km long dispersion-shifted fiber with an effective mode area of 15 µm(2) as the Brillouin and Raman gain media simultaneously. Two 1420 nm laser diodes with a combined power of 372 mW are used as pump sources, while a fiber Bragg grating with a center wavelength of 1500 nm is used as a reflector in the cavity. The setup is capable of generating 6 clearly defined Stokes lines at the highest pump power, spanning from 1499.8 to 1500.3 nm with the even Stokes having relatively higher peak powers, between 1.4 and 3.5 dBm as compared to the odd Stokes, which have peak powers between -4.7 and -5.0 dBm. The output of the laser is very stable and shows little to no fluctuations over a monitoring period of 50 min.

Highly stable graphene-assisted tunable dual-wavelength erbium-doped fiber laser.

A highly stable tunable dual-wavelength fiber laser (TDWFL) using graphene as a means to generate a highly stable output is proposed and generated. The TDWFL comprises a 1 m long, highly doped erbium-doped fiber (EDF) acting as the linear gain medium, with a 24-channel arrayed waveguide grating acting as a wavelength slicer as well as a tuning mechanism to generate different wavelength pairs. The tuned wavelength pairs can range from 0.8 to 18.2 nm. A few layers of graphene are incorporated into the laser cavity to induce the four-wave-mixing effect, which stabilizes the dual-wavelength output by suppressing the mode competition that arises as a result of homogenous broadening in the EDF.

Temperature-insensitive bend sensor using entirely centered Erbium doping in the fiber core.

A fiber based bend sensor using a uniquely designed Bend-Sensitive Erbium Doped Fiber (BSEDF) is proposed and demonstrated. The BSEDF has two core regions, namely an undoped outer region with a diameter of about 9.38 µm encompassing a doped, inner core region with a diameter of 4.00 µm. The doped core region has about 400 ppm of an Er2O3 dopant. Pumping the BSEDF with a conventional 980 nm laser diode gives an Amplified Spontaneous Emission (ASE) spectrum spanning from 1,510 nm to over 1,560 nm at the output power level of about -58 dBm. The ASE spectrum has a peak power of -52 dBm at a central wavelength of 1,533 nm when not spooled. Spooling the BSEDF with diameters of 10 cm to 2 cm yields decreasing peak powers from -57.0 dBm to -61.8 dBm, while the central wavelength remains unchanged. The output is highly stable over time, with a low temperature sensitivity of around ~0.005 dBm/°C, thus allowing for the development of a highly stable sensor system based in the change of the peak power alone.

Single and Bunch Soliton Generation in Optical Fiber Lasers Using Bismuth Selenide Topological Insulator Saturable Absorber.

In this work, we present the generation of two distinct types of soliton pulses using a Bismuth Selenide (Bi2Se3) saturable absorber (SA) synthesized in our laboratory. The soliton pulses were generated in two different laser cavity configurations, resulting in two types of solitons: a soliton pulse with Kelly sidebands and a bunched soliton pulse with peak-dip sidebands. Both solitons operated at the fundamental repetition rate-23.3 MHz (for the soliton with Kelly sidebands) and 13 MHz (for the bunched soliton with peak-dip sidebands). We observed that the accumulation of nonlinear phase shift from the added single mode fiber (SMF) split the single soliton pulse into 44 pulses in a bunched oscillation envelope. At the same time, peak-dip sidebands were imposed on the bunched soliton spectrum due to constructive and destructive interferences between soliton pulse and dispersive waves. The measured pulse width for both solitons were 0.63 ps (for the soliton with Kelly sidebands) and 1.52 ps (for the bunched soliton with peak-dip sidebands), respectively. Our results demonstrate the potential of Bi2Se3 SAs in generating different types of soliton pulses, which could have potential applications in various areas of optical communication and spectroscopy.

Review of Microbottle Resonators for Sensing Applications.

Microbottle resonators (MBR) are bottle-like structures fabricated by varying the radius of an optical fiber. MBRs can support whispering gallery modes (WGM) by the total internal reflection of the light coupled into the MBRs. MBRs have a significant advantage in sensing and other advanced optical applications due to their light confinement abilities in a relatively small mode volume and having high Q factors. This review starts with an introduction to MBRs' optical properties, coupling methods, and sensing mechanisms. The sensing principle and sensing parameters of MBRs are discussed here as well. Then, practical MBRs fabrication methods and sensing applications are presented.

Dissipative Soliton Mode-Locked Erbium-Doped Fiber Laser Using Nb2AlC Nanomaterial Saturable Absorber.

We report the fabrication of an erbium-doped fiber-based saturable absorber (SA) of niobium aluminium carbide (Nb2AlC) nanomaterial that can generate a dissipative soliton mode-locked pulse. Stable mode-locked pulses operating at 1530 nm with repetition rates of 1 MHz and pulse widths of 6.375 ps were produced using polyvinyl alcohol (PVA) and the Nb2AlC nanomaterial. A peak pulse energy of 7.43 nJ was measured at 175.87 mW pump power. In addition to providing some useful design suggestions for manufacturing SAs based on MAX phase materials, this work shows the MAX phase materials' immense potential for making ultra-short laser pulses.

Nanosecond soliton pulse generation by mode-locked erbium-doped fiber laser using single-walled carbon-nanotube-based saturable absorber.

We demonstrate a simple and low cost mode-locked erbium-doped fiber laser (EDFL) operating in the nanosecond region using a single-walled carbon nanotube (SWCNT)-based saturable absorber (SA). A droplet of SWCNT solution is applied on the end of a fiber ferrule, which is then mated to another clean connector ferrule to construct an SA. Then the SA is integrated into a ring EDFL cavity for nanosecond pulse generation. The EDFL operates at around 1570.4 nm, with a soliton-like spectrum with small Kelly sidebands, which confirms the attainment of the anomalous dispersion. It produces a soliton pulse train with a 332 ns width, repetition rate of 909.1 kHz, an average output power of 0.31 mW, and energy of 0.34 nJ at the maximum pump power of 130.8 mW.

Direct airborne acoustic wave modulation of Fabry-Perot fiber laser (FPFL) over 100 kHz of operating bandwidth.

The idea of applying a simple Fabry-Perot fiber laser (FPFL) set-up in a free-running condition as an acoustic sensing medium is proposed. Conventional optical microphone requires a stringently aligned diaphragm to mediate the acoustic impedance mismatch between air and silica fiber. Motivated by the difficulty of optical sensing of airborne acoustic waves, a new sensing method is proposed to sense acoustic waves without the assistance of a diaphragm as transducer. By studying the output power fluctuation of the FPFL, the operating bandwidth and sensitivity of the proposed sensing method are determined. The tunability of the resonant frequency from 5 kHz to 85 kHz allows sensing of acoustic waves in the range of 100 Hz to 100 kHz. Tuning of the resonant frequency can be performed by changing the optical pumping power from as low as 10 mW to 68.5 mW or higher.

Skin lesion classification using multi-resolution empirical mode decomposition and local binary pattern.

Skin cancer is the most common type of cancer in many parts of the world. As skin cancers start as skin lesions, it is important to identify precancerous skin lesions early. In this paper we propose an image based skin lesion identification to classify seven different classes of skin lesions. First, Multi Resolution Empirical Mode Decomposition (MREMD) is used to decompose each skin lesion image into a few Bidimensional intrinsic mode functions (BIMF). MREMD is a simplified bidimensional empirical mode decomposition (BEMD) that employs downsampling and upsampling (interpolation) in the upper and lower envelope formation to speed up the decomposition process. A few BIMFs are extracted from the image using MREMD. The next step is to locate the lesion or the region of interest (ROI) in the image using active contour. Then Local Binary Pattern (LBP) is applied to the ROI of the image and its first BIMF to extract a total of 512 texture features from the lesion area. In the training phase, texture features of seven different classes of skin lesions are used to train an Artificial Neural Network (ANN) classifier. Altogether, 490 images from HAM10000 dataset are used to train the ANN. Then the accuracy of the approach is evaluated using 315 test images that are different from the training images. The test images are taken from the same dataset and each test image contains one type of lesion from the seven types that are classified. From each test image, 512 texture features are extracted from the lesion area and introduced to the classifier to determine its class. The proposed method achieves an overall classification rate of 98.9%.