In this work, the Q-switched Erbium-doped fiber laser (EDFL) is visualized using Ti 2 SnC as saturable absorber. The thin layer of Ti 2 SnC is mechanically exfoliated from a bulk material and pasted onto a fiber ferrule and integrated into EDFL by sandwiched method. The proposed Q-switched EDFL successfully achieved a stable pulse train, and the smallest pulse width of 1.26 µs and the highest pulse energy of 43.76 nJ are obtained at low operational pump power of 110 mW. The pulse energy obtained is comparable to other metal–ceramic based SA, with relatively low pump power. Owing to the strength of thermal shock resistance and oxidation resistant, the proposed saturable absorber is more feasible to cater the commercialization requirements.

This publisher's note serves to correct an error in Appl. Opt. 58, 3495 (2019)APOPAI0003-693510.1364/AO.58.003495.

This publisher's note serves to correct an error inAppl. Opt. 58, 3495 (2019). (C) 2022 Optica Publishing Group

We propose a simple design of all‐fiber Q‐switched erbium‐doped fiber laser (EDFL). The laser is passively Q‐switched by splicing bismuth‐doped fiber into a ring cavity. The design has been experimentally demonstrated at the emission wavelength of 1560.48 nm. A single‐mode Q‐switched pulse with pulse duration of 1.18 μs and pulse energy of 15.6 nJ was obtained with 980 nm pump power of 178 mW. Stable and typical Q‐switched pulses were achieved at the repetition rate changing from 63.3 to 94.6 kHz. To the best of our knowledge, it is the first time to demonstrate bismuth‐doped fiber as an effective saturable absorber for erbium‐doped fiber laser.

A passively Q-switched ytterbium-doped fiber laser (YDFL) operating at 1062 nm was demonstrated by using a segment of 20 cm titanium dioxide-doped fiber saturable absorber (TiO2DF SA). The Q-switched YDFL emerged stably with tunable repetition rates ranging from 32 kHz to 53 kHz as the pump power rose from 109 mW to 233 mW. Within this range of pump power, a maximum output power of 10.1 mW, maximum peak power of 75 mW, and maximum pulse energy of 191 nJ were obtained. The narrowest pulse width of 2.55 μs was attained at the maximum pump power of 233 mW, while the signal-to-noise ratio of the fundamental frequency was 47 dB. This demonstration reveals that the proposed TiO2DF SA is feasible for constructing a flexible and reliably stable Q-switched pulsed fiber laser in the 1-micrometer region.

We demonstrated and compared picoseconds pulsed fiber lasers based on Titanium dioxide based saturable absorbers (SAs); 20 cm long Titanium dioxide-doped fiber (TiO2DF) and Titanium dioxide PVA film (TiO2PF) in the 1.5-micron region. The laser cavity utilized 2.4 m long Erbium-doped fiber (EDF) as the gain medium. A self-starting pulsed laser with a consistent repetition rate of ∼1 MHz emerged stably with the incorporation of TiO2 based SAs. The TiO2DF SA produced 9.74 ps pulsed laser at a central wavelength of 1553 nm within a pump power range of 106-142 mW. The fiber SA promoted slightly higher slope efficiency and maximum pulse energy of 13.17% and 8.56 nJ, respectively in comparison with the film SA. On the other hand, the TiO2PF SA generated stable 3.89 ps pulsed laser at an operating wavelength of 1560 nm within 86-142 mW pump power range. The film SA also produced slightly greater maximum output power of 12.17 mW and maximum peak power of 3.43 kW, respectively at the maximum pump power. The results confirmed that both TiO2 SAs can be good alternative pulse modulator in the 1.5-micron region.

To meet the 5G requirements for higher bandwidth, the focus has been shifted to millimeter waves paving the way to radio over fiber (RoF) in order to minimize radio losses. Dual wavelength transmission within RoF for electromagnetic immunity interference (EMI) can be utilized within local area network and long-haul transmission. Health care services will also be able to utilize the technology to transmit health-related data from thousands of patients to the specific destination by connecting to the long-haul fiber optic cable connection. To make dual-wavelength transmission stable and reliable, the formation of the two-wavelength light source is proposed in this paper by means of the double coupled micro-ring resonators. The proposed RoF system will be able to transmit EMI signals of patients over 300 km of optical fiber link and 3 m wireless link without the need for any intermediate signal amplifying device. All the patient's data will be available to any doctor in any hospital securely by integrating with currently available wireless and the internet of things systems.

In this paper, we experimentally demonstrate a stable passively Q-switched fiber laser in the 1-micron regime by incorporating a segment of Ytterbium-doped fiber (YDF, 12 cm) as a saturable absorber (SA) in a ring cavity scheme. The fiber SA exhibits a linear absorption of about 2.44 dB at the Q-switched oscillating regime (1068 nm). The Q-switched pulses started to self-occur as the pump power elevated to its threshold of 151 mW and steadily existed up to the maximum pump power of 233 mW. At the maximum pump power, we obtained a maximum repetition rate of 74.2 kHz, a maximum output power of 3.7 mW, a maximum pulse energy of 49 nJ and a pulse width as short as 1.97 µs. Our results denote that a segment of YDF is possible of generating a reliable Q-switched fiber laser in the 1-micron regime, revealing its potential as another fiber SA candidate.

We propose a segment of 11 cm long Thulium-doped fiber (TDF) as a passive saturable absorber (SA) in generating a stable Q-switched Erbium-doped fiber laser (EDFL). The obtained pulsed laser has a central wavelength of 1560 nm and emerges stably within a repetition rate range of 54.1-106.7 kHz over a pump power range of 35-136 mW. At the maximum pump power of 136 mW, the EDFL produces a maximum output power of 14.3 mW, a maximum pulse energy of 134.7 nJ and a maximum peak power of 41 mW as well as the narrowest pulse width of 3.28 µs. The fundamental frequency of the pulsed laser has a signal to noise ratio (SNR) of approximately 63 dB. The proposed laser would have a good prospect for material processing and medicine.

Microfiber loop resonator (MLR) fabricated by using silica fiber for relative humidity (RH) sensing application is reported. The silica fiber was tapered to achieve waist diameter of 5 mu m using flame brushing technique. The MLR with a 300 mu m diameter loop microfiber was formed by manually twisted the tapered fiber. Initially, the effect of whispering gallery modes (WGMs) on the MLR was observed. Transmission mode spectra were observed to determine the number of resonated wavelength and quality factor (Q-factor). The Q-factor for MLR is observed to be > 10(5) which is a good attribution for sensing application. A significant response to RH from 35% to 85% was observed due to the change of resonating behaviour of MLR across the RH range. The sensing sensitivity increased by a factor of 8.15 in MLR compared to the straight microfiber (SF) structure. As the RH increased, the output power of the MLR decreased linearly from -43.05 dBm to -46.81 dBm with linearity and resolution of 95.91% and 0.153% RH respectively.

We demonstrate a Q-switched all-fiber laser operating at 2-mu m region by adding a piece of 8 cm long holmium doped fiber (HDF) as a fiber saturable absorber (SA) in Thulium doped fiber laser (TDFL) ring cavity. Doping of Ho ions into yttria-alumina silica glass was done through conventional Modified Chemical Vapor Deposition (MCVD) technique in conjunction with solution doping process. The fabricated HDF has a linear absorption of 3 dB with a core diameter and a numerical aperture of 10 mu m and 0.18, respectively. A self-started Q-switching operation begins at 418 mW pump level and continually dominant until 564 mW pump level. As the pump power increases, stable pulse train presence from 30.61 kHz to 38.89 kHz while the pulse width reduces from 3.18 mu s to 2.27 mu s. Both maximum output power and maximum peak power are obtained at 5.05 mW and 57.2 mW, respectively, while the maximum pulse energy is calculated to be 129 nJ. The signal-to-noise ratio (SNR) of the fundamental frequency is 50 dB. Our work may contribute to the discovery of stable, robust, and economic SA for pulse fiber laser generation at 2-mu m region.

This work reports on the use of the holmium oxide (Ho2O3) polymer film as a saturable absorber (SA) for generating stable Q-switching pulses operating in a 2-mu m region in a thulium-doped fiber laser cavity. The SA is prepared by diluting a commercial Ho3O2 powder and then mixing it with polyvinyl alcohol (PVA) solution to form a Ho2O3-PVA film. A tiny part of the film about 1 mmx 1 mm in size is sandwiched between two fiber ferrules with the help of index matching gel. When incorporated in a laser cavity driven by a 1552-nm pump, stable Q-switching pulses are observed at 1955 nm within the pump power range of 363-491 mW. As the pump power increases within this range, the repetition rate rises from 26 kHz to 39 kHz, as the pulse width drops from 4.22 mu s to 2.57 mu s. The laser operates with a signal-to-noise ratio of 47 dB, and the maximum output power and the pulse energy obtained are 2.67 mW and 69 nJ, respectively. Our results successfully demonstrate that the Ho2O3 film can be used as a passive SA to generate a 2-mu m pulse laser.

A new Erbium–Zirconia–Yttria–Aluminum co-doped fiber amplifier (Zr-EDFA) with improved gain and noise figure characteristics is successfully demonstrated using a newly developed Erbium–Zirconia–Yttria–Aluminum Co-Doped fiber (Zr-EDF) as the gain medium. The fiber consists of Er2O3-doped ZrO2 rich nano-crystalline particles and thus it has a high erbium doping concentration with absorption pump power around 80.0 dB/m at 980 nm. Compared to the conventional silica based Erbium-doped fiber amplifier (Si-EDFA), the gain of the proposed Zr-EDFA is more efficient especially at longer wavelength region. At input signal of −10 dBm, a flat gain of 19.5 dB is obtained for the single-pass Zr-EDFA with gain variation of less than 1 dB within a wavelength region from 1530 to 1570 nm. In double-pass configuration, the measured gain varies from 17.5 dB to 21.3 dB within the wavelength region from 1525 to 1565 nm, where the noise figure is maintained at below 10 dB. The double-pass Zr-EDFA gain is also maintained above 12 dB within a wavelength region from 1520 to 1600 nm. These results indicate that the Zr-EDFA can achieve even better flat-gain value and bandwidth as well as lower noise figure than the conventional Si-EDFA

We report a passively Q-switched fiber laser operating at 1900nm region using the newly developed thulium bismuth co-doped lithium-alumino-germano-silicate fiber (TBF) as a gain medium in conjunction with a multiwall carbon nanotubes (MWCNTs) based saturable absorber (SA). The TBF and MWCNTs are fabricated and prepared in-house. By increasing the 802nm pump power from 106.6 to 160mW, stable generation of Q-switched TBFL has been obtained at 1857.8nm wavelength. The pulse repetition rate varies from 12.84 to 29.48kHz while pulse width is increased from 9.6 to 6.1µs. The performance of the laser is also compared with the Q-switched TDFL, which was obtained using a similar MWCNTs SA and pump wavelength. The Q-switched TDFL generates an optical pulse train with a repetition rate increasing from 3.8 to 4.6kHz and pulse width reducing from 22.1 to 18.3μs when the pump power is tuned from 187.3 to 194.2mW. This shows that the TBFL performs better than the TDFL in terms of threshold pump power, repetition rate and pulse width.

In the recent years, femtocell technology has received a considerable attention due to the ability to provide an efficient indoor wireless coverage as well as enhanced capacity. However, under the spectrum sharing between femtocell user equipment (FUEs) and the owner of spectrum macrocell user equipment (MUEs), both may experience higher uplink interference to each other. This paper proposes a novel distributed power control algorithm for the interference management in two-tier femtocell networks. Due to the assignment of licensed radio frequency to the outdoor macrocell users, the access priority of MUEs should be higher than FUEs. In addition, the quality of service (QoS) of MUEs that is expressed in the target signal-to-interference-plus-noise ratio (SINR) must always be achieved. On the other hand, we consider an efficient QoS provisioning cost function for the low-tier FUEs. The proposed algorithm requires only local information and converges even in cases where the frontiers of available power serve the target SINRs impossible. The advantage of the algorithm is the ability to implement in a distributed manner. Simulation results show that the proposed algorithm based on our cost function provides effective resource allocation and substantial power saving as compared to the traditional algorithms.

In this paper, the problem of distributed power control is investigated and analyzed for two-tiered femtocell networks that share the same frequency band with the central macrocell. Femtocell users are associated with a proper utility function via pricing, which represents the ratio of user's signal-to-interference-noise ratio (SINR) and the exponential price of power consumed. Assuming a femtocell user seeks selfishly to maximize its utility function under the imposed constraints, a femtocell non-cooperative power control game (FNPC) is formulated. We prove the existence and uniqueness of the Nash Equilibrium output for the game model of power control algorithm. Numerical results show the effectiveness of pricing parameters in the penalty function to the speed of convergence and power consumed.

This paper demonstrates the achievable performance enhancement in a multi-user network using optical unique code sequences. The study is conducted in a four-user Metropolitan Area Network (MAN) with a transmission rate of 10 Gbps. This paper investigates the feasibility of implementing Differential Phase Shift Keying (DPSK) and Differential Quadrature Phase Shift Keying (DQPSK) technique to replace conventional techniques such as On-Off Keying (OOK) and Amplitude Shift Keying (ASK). The performance of the integrated formulation of optical unique code sequenceswith DPSK and DQPSKtechnique is evaluated by determining the Bit Error Rate (BER) for various configurations and transmission distances up to 100 km.

We demonstrate an efficient fiber laser operating at 1901.6 nm using a new Thulium Bismuth co-doped fiber (TBF) under 802 nm pumping. The TBF was fabricated using modified chemical vapor deposition process associated with optimized solution doping techniques. The TBF lasers at 1901.6 nm are obtained at a noticeably low threshold pump power of 75-92 mW using two fiber Bragg gratings in a Fabry-Perot cavity. The highest efficiency of 42.2% is achieved using a 0.4 m long TBF fiber with a core dopant concentrations (in wt%) of 0.35 Bi2O3, 0.9 Tm2O3, 3.0 Al2O3 and 4.0 GeO2. Compared to the laser from a commercially available Thulium-doped fiber, the proposed laser has a significantly higher efficiency and lower threshold pump power. This is attributed to the incorporation of Bi ions in the gain medium which helps to increase the F-3(4) population through energy transfer processes. The maximum output power of 52.7m W is achieved at the pump power of 195 mW.

The Cross-Entropy-based (CE-based) stopping criteria advantage is able to terminate early in the high signal-to-noise ratio (SNR) while maintain the bit error rate (BER) performance. Unfortunately, the criteria fails to cope with low SNR region and make the decoder iterates until maximum or infinite iteration. This paper proposed an early termination technique at low SNR for the CE-based stopping criteria using the decoding threshold derived by the measurement of reliability (MOR) at low SNR. In the simulation results and analysis, we compare the average iteration number (AIN) and the bit-error rate (BER) performance between the proposed combination methods with the existing CE-based stopping criteria. From the results, the combination method capable to reduce the AIN at low SNR with minimum one AIN while maintaining the AIN at high SNR as the traditional method. This significant reduction could reduce delay and complexity of existing CE-based stopping criteria while maintaining the BER performances.