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• Thulium-doped fiber (TDF) as saturable absorber for ultrashort pulse generation. • 12 cm-long TDF is incorporated into Erbium-doped fiber laser cavity. • The SA has a modulation depth of 3.6% • The mode-locked laser operates at 1568.2 nm with a pulse width of 2.27 ps. • The dark pulse with 220 ns pulse width and 1.85 MHz repetition rate. • The maximum peak power and pulse energy are calculated as 1.75 kW and 3.93 nJ. Generation of ultrashort pulses in an all-fiber Erbium-doped fiber laser (EDFL) cavity with doped fiber saturable absorber (DFSA) is demonstrated for the first time. The doped fiber saturable absorber is fabricated by a single-mode 12 cm-long thulium-doped fiber (TDF). The optical characteristic of TDF indicates a saturable absorption of 3.6 %, which indicates it's capability to function as a mode-locker. Continuous wave, mode-locked and combined-mode operations are observed sequentially with the increase of pump power. The mode-locked erbium-doped fiber laser operates at 1568.2 nm with a pulse width of 2.27 ps. A mode-locked pulse train with a constant repetition rate of 0.99 MHz is obtained as the pump power increased from 96 mW to 178 mW. At the pump power of 178 mW, the maximum peak power and pulse energy are calculated as 1.75 kW and 3.93 nJ, respectively. The obtained pulse train is very robust with a signal-to-noise ratio (SNR) of 63 dB. The experimental results attest that utilizing doped fiber saturable absorber can achieve ultrashort pulses and possess the potentially increasable power of mode-locked operation in all-fiber lasers. [ABSTRACT FROM AUTHOR]

Abstract: Multiple antenna transmission methods are currently being developed all around the world for evolving 3G wireless standards. Space–Time Trellis Code (STTC) has been proven to use transmit diversity efficiently. It effectively exploits the effects of multipath fading to increase the information capacity of the multiple antenna transmission systems. STTC is a channel coding technique that maximises the ‘distance’ between different symbol matrices such that the probability of transmission errors are decreased when transmitting redundant symbol or in other words, to maximise the minimum determinant. Maximising the minimum determinant is equivalent to obtaining optimal generator matrix G. Instead of using state diagrams, optimal generator matrix G discussed in this paper is obtained using an improved algorithm which is based on Lisya tree structure. Optimal generator matrix G in this paper has a minimum determinant of 48 which is the highest coding gain obtained so far. [Copyright &y& Elsevier]

Non-orthogonal multiple access (NOMA) is considered as an important technique to alleviate the spectral scarcity of wireless networks. Cooperative NOMA (C-NOMA) along with simultaneous wireless information and power transfer (SWIPT) pave paths towards energy and spectral efficient communication networks. This paper investigates SWIPT enabled multiple relay C-NOMA network, where dedicated intermediate relays are energy-constrained and harvest energy from the transmitted source signal. New two-stage relay selection (RS) schemes for C-NOMA with fixed power allocation and dynamic power allocation at relay node are proposed. Analytical expressions and asymptotic expressions of outage probability for proposed schemes and partial RS are derived to evaluate the system performance. Simulation results demonstrate that two stage RS provides the maximum performance gain at high SNR regime, while the partial RS is preferable at low SNR. Based on outage probability difference, a hybrid RS scheme which switches between partial and two-stage is introduced. The important insights of analytical results, such as comparative analysis of relay selection schemes, performance gain over SWITP OMA networks, effect of data rates, effect of relay location, and impact of using SWIPT on the outage performance of C-NOMA networks are discussed. [ABSTRACT FROM AUTHOR]

A dual-wavelength Q-switched fiber laser is successfully demonstrated by utilizing an all-fiber configuration based on fiber saturable absorber (SA). An 18 cm-long Tm-doped fiber (TDF) is employed as a fiber SA since it presents an apparent nonlinear optical characteristic at near-infrared wavelength with 180 MW∕cm2 saturable intensity and 2% modulation depth. After splicing the TDF into an Erbium-doped fiber laser (EDFL) cavity, a stable dual-wavelength Q-switched pulses is generated with the aid of polarization controller as an optical wavelength selector. It operates at wavelengths of 1532.6 nm and 1557 nm (with wavelength spacing as wide as 24.4 nm). To the best of our knowledge, this is the dual-wavelength fiber laser with widest wavelength spacing reported so far. Furthermore, single-wavelength Q-switched operations of 1532 nm and 1558 nm are also realized, which can be flexibly switched between the two wavelengths just by merely manipulating the intra-cavity birefringence. The results attest that TDF SA combined with nonlinear polarization rotating technique can provide a simple and practical method for a switchable single/dual-wavelength all-fiber laser. The proposed all-fiber laser could be applied in terahertz communication, manufacturing, laser radar, and so on. • Dual-wavelength Q-switched pulse generation in Erbium-doped fiber laser (EDFL) cavity. • 18 cm-long Tm-doped fiber (TDF) as a passive saturable absorber (SA). • The SA has a saturation intensity of 180 MW/cm2 and a modulation depth of 2%. • A switchable single/dual-wavelength Q-switched fiber laser has been achieved at 1532.6 nm and 1557 nm. [ABSTRACT FROM AUTHOR]

We successfully generated short pulse in an erbium-doped fiber laser (EDFL) cavity utilizing a new saturable absorber (SA) based on chromium gallium carbide (Cr 2 GaC). The SA film was prepared by implanting the Cr 2 GaC compound into a polyvinyl alcohol (PVA) matrix. Upon integration into the laser's cavity, we achieved a stable mode-locked laser centered at 1558.24 nm. This stability was maintained within a pump power range of 53.7–95.2 mW. Operating at a fixed repetition rate of 1.82, matching the cavity length, the laser consistently delivered pulses with a duration of 3.04 picoseconds. At its peak performance with a pump power of 95.2 mW, the laser exhibited an average power output of 6.81 mW, a peak power of 1.08 W, and a pulse envelope energy of 3.74 nJ. A noteworthy aspect of our study is the exceptional stability demonstrated by the laser. This stability is evidenced by a signal-to-noise ratio of 71.7 dB for the fundamental frequency. Importantly, this research represents a significant milestone as it marks the first instance of achieving soliton pulses in a laser cavity utilizing Cr 2 GaC as a SA. [ABSTRACT FROM AUTHOR]

• Generation of soliton dark pulses using a Molybdenum Aluminium Boride (MoAlB) as saturable absorber (SA). • MoAlB was coated onto side-polished fiber to improve the birefringence and nonlinearity. • The dark pulses are generated based on cubic-quintic nonlinear Schrödinger equation mechanism. • The SA has a modulation depth of 6.5 %, a saturation intensity of 100 MW/cm2 and non-saturable loss of 50%. • The laser operated at 1560.6 nm with a pulse duration of 152 ns and repetition rate of 1.87 MHz. We demonstrate the generation of dark pulses from an Erbium-doped fiber laser (EDFL) using a Molybdenum Aluminium Boride (MoAlB) as a saturable absorber for the first time. Molybdenum Aluminium Boride (MoAlB) was coated onto side-polished fiber (SPF) to improve the birefringence and nonlinearity inside the EDFL cavity with net anomalous dispersion. The soliton dark pulses are obtained from the laser cavity based on cubic-quintic nonlinear Schrödinger equation (CQNLSE) mechanism. The laser operated at 1560.6 nm with a pulse duration of 152 ns and repetition rate of 1.87 MHz as the pump power is set within 200 mW to 370 mW. At the maximum pump power, the average output power and pulse energy are recorded at 6.93 mW and 3.77 nJ, respectively. We think that this research is the first to show MoAlB 's potential for dark pulse generation. [ABSTRACT FROM AUTHOR]

We successfully demonstrated a stable Q-switched erbium-doped fiber laser (EDFL) using Molybdenum Aluminum Boride (MoAIB), a metal ceramic-based material as saturable absorber (SA). The thin layer of MoAIB was obtained by mechanical exfoliation method and acquired onto the end surface of a standard FC/PC fiber connector to function as SA. The features of MoAIB-SA are experimentally evaluated in two output coupling ratios, which are 50:50 and 95:5. From the experimental results, MoAIB-SA is well-functioning as SA to modulate the CW lasing into Q-switching operation. The 95:5 coupler setup presented better pulse quality, in term of pulse repetition rate and pulse width. Additionally, 50:50 coupler setup allows higher pump power and pulse energy to extract from the fiber laser system. [ABSTRACT FROM AUTHOR]

• WGMs based humidity sensor by integrating microsphere resonator on the ZnO nanorods coated glass surface. • Solve issues pertaining to complicated handling of microfiber during the coating process. • ZnO nanorods growth using hydrothermal method and microfiber fabrication using flame brushing technique. • Superiority in term of ultra-high Q factor of microsphere which enhanced interactions between the light and the external environment. A humidity sensor is proposed by integrating a microsphere resonator onto ZnO nanorods coated glass surface. The glass substrate was coated with ZnO nanorods for 12 h using the hydrothermal method and the microsphere was set at a diameter of 234 µm. The proposed sensor produced sensitivity of 0.0748 dBm/%RH and 0.0142 nm/%RH when exposed to humidity level ranging from 35 %RH to 85 %RH. Standard deviation and resolution of the proposed sensor improve by a factor of 1.7 and 2.4 respectively as compared to the straight microfiber laid on the ZnO nanorods coated glass. It utilized the ultra-high Q factor of microsphere and the changeable refractive index of the ZnO nanorods coated glass. Combination of these elements enhanced the interaction between the whispering gallery mode evanescent components with surrounds analyte. It also solves the issues pertaining to the complicated handling of microfibers during the coating process. The proposed sensor has shown exceptional experiment results for humidity sensing applications. [ABSTRACT FROM AUTHOR]

• Humidity sensor based on microfiber laid on a ZnO nanorods coated glass surface. • Employs the evanescent wave coupling between the microfiber and the ZnO nanorods coated glass. • ZnO nanorods growth using hydrothermal method and microfiber fabrication using flame brushing technique. • Reduced the hassle to access the interaction of the ZnO coating layer and the evanescent wave. In this paper, a proposed humidity sensor is fabricated by integrating the microfiber and the glass surface coated with Zinc Oxide (ZnO) nanorods. The silica fiber diameter was reduced to 6 μm using the flame brushing technique, and the glass surface was coated with ZnO nanorods using a hydrothermal method. A significant response to humidity level concentration ranging from 35 %RH to 85 %RH has been observed. The proposed sensor's output power has decreased linearly from -16.32 dB m to -18.68 dB m with a linearity of 95.87 %. The sensitivity and the resolution of the ZnO coated glass improved by a factor of 2.8 and 7.5, respectively, as compared to the uncoated glass substrate. The proposed humidity sensor successfully employs the interaction between the ZnO nanorods surface and the microfiber's evanescent field from the microfiber, which reduce the striving effort in handling the microfiber during the synthesis process. The proposed sensor has shown an excellent sensing performance as a humidity sensor based on the experimental results. [ABSTRACT FROM AUTHOR]