Tunable single longitudinal mode S-band fiber laser using a 3 m length of erbium-doped fiber

In this paper a tunable single-longitudinal mode (SLM), short-wavelength band (S-band) fiber laser using a conventional erbium-doped fiber (EDF) with a length of 3?m and a step index erbium dopant profile as opposed to the commonly used depressed cladding erbium-doped fiber (DC-EDF) is proposed and demonstrated. The proposed SLM fiber laser has a tuning range of 1496 to 1507?nm in a ring configuration using two 0.15?m of EDF which acts as saturable absorbers (SAs). The highest peak power measured is about ?0.6?dBm at a wavelength range of 1502 to 1507?nm. The measured signal-to-noise ratio (SNR) is approximately 74?dB for the same wavelength range. The line-width of the SLM output is measured to be 140?kHz.     

Tunable graphene Q-switched erbium-doped fiber laser with suppressed self-mode locking effect

Self-mode locking effect in a wideband tunable graphene-based passively Q-switched erbium-doped fiber laser has been observed experimentally. Q-switching is achieved by using graphene as a saturable absorber, while a tunable bandpass filter with a narrow bandwidth is used to obtain wideband tunability. We propose to suppress the modulation on each pulse from self-mode locking by introducing three subring resonators constructed with three 3 dB couplers into the laser ring cavity. Moreover, the laser output characteristics with respect to pump power are studied in detail. A stable Q-switched erbium-doped fiber laser with a tunable range from 1522 nm to 1568 nm is demonstrated experimentally.     

非对称光纤反射镜的可调谐光纤激光器

提出一种非对称窄带光纤环形反射镜结构的可调谐掺铒光纤激光器。980nm泵浦光对掺铒有源光纤进行抽运,高双折射光纤、偏振控制器（PC）和光纤耦合器构成窄带光纤反射镜,窄带光纤反射镜和普通光纤反射镜组成激光谐振腔,利用窄带光纤反射镜工作带宽纳米量级的特性得到单纵模激光。调整偏振控制器改变反射镜对不同波长的反射率,实现可变波长的激光输出。实验表明,该激光器的工作带宽为8nm,120mW泵浦光条件下最大输出功率为4mW,3dB带宽（脉冲的半高宽度）小于0．2nm,边模抑制比为20dB以上,在1527nm～1535nm的波长范围内观察到稳定激光输出。     

Tunable passively Q-switched thulium doped fluoride fibre (TDFF) laser using reduced graphene oxide-silver (rGO-Ag) as saturable absorber

A tunable, passively Q-switched thulium doped fluoride fibre (TDFF) laser using a reduced-graphene oxide-silver (rGO-Ag) thin film as a saturable absorber (SA) for S band operation is proposed and its efficacy demonstrated. Over a pump power range of 91.4?mW up to 158.6?mW, passively generated Q-switched pulses are observed with repetition rates from 20 to 34.5?kHz and pulse widths from 3.1 to 7.1?µs. The highest pulse energy observed is 101.2?nJ with a signal to noise ratio of ～42?dB. The proposed laser has a tuning range ～52?nm from 1458 to 1510?nm with a tunable bandpass filter (TBPF) introduced into the cavity.     

Simple system for optical short-pulse generation in both active mode-locking and self-seeding schemes

A simple system that simultaneously supports active mode-locking and self-seeding schemes for wavelength-tunable optical short-pulse generation is proposed. The system consists of a gain-switched Fabry-Perot laser diode, an erbium-doped fiber amplifier, a tunable optical filter, and two circulators. The mode-locked optical pulses exhibit good stability, a high side-mode suppression ratio of more than 31 dB over a wide wavelength tuning range of 42 nm, and a pulse width of around 35 ps at a repetition frequency of approximately 2.8 GHz.     

Passively Q-switched fibre laser utilizing erbium-doped fibre saturable absorber for operation in C-band region

In this paper, a stable and robust all-fibre passively Q-switched erbium-doped fibre laser (EDFL) emitting at 1558?nm is described. The proposed laser utilizes an 11?cm long erbium-doped fibre as saturable absorber (SA). The fibre SA features a linear optical absorption of about 13?dB in the Q-switched EDFL operating regime. By elevating the input pump power from the threshold of 60?mW to the maximum available power of 142?mW, a pulse train with a maximum repetition rate of 86?kHz, minimum pulse width of 3.39?µs, maximum average output power of 10.5?mW, maximum pulse energy of 122?nJ and maximum peak power of 36?mW are obtained. The signal to noise ratio (SNR) of the spectrum is measured to be around 70?dB. This fibre SA is simple, reliable, compact and alignment free. Thus it is suitable for making a portable pulse laser source.     

Tunable graphene-based Q-switched erbium-doped fiber laser using fiber Bragg grating

A graphene-based Q-switched erbium-doped fiber laser (EDFL) with a tunable fiber Bragg grating (TFBG) acting as a wavelength tuning mechanism is proposed and demonstrated. The proposed setup utilizes a newly-developed ‘ferrule-to-ferrule transfer’ technique to obtain a single graphene layer that allows for Q-switch operation in the EDFL using a highly doped-gain medium. A TFBG is used as a wavelength tuning mechanism with a tuning range of 10 nm, covering the wavelength range from 1547.66 nm to 1557.66 nm. The system has a wide repetition rate range of over 206.613 kHz from 1.387 kHz to 208.000 kHz with pulse durations of between 94.80 μs to 0.412 μs. The laser output is dependent on the pump power, with energy per pulse of 4.56 nJ to 16.26 nJ. The system is stable, with power and wavelength variations of less than 0.47 dBm and 0.067 nm. The output pulse train is free from self-mode locking and pulse jitters.     

Passive mode-locking in erbium-doped fibre laser based on BN-GO saturable absorber

A C-band mode-locked fibre laser incorporating a boron nitride-doped graphene oxide (BN-GO)-based saturable absorber (SA) is proposed and demonstrated. The SA is fabricated by depositing multiple layers of synthesized BN-GO nanoparticles onto the polished surface of a side-polished fibre, which is then inserted into an erbium-doped fibre laser cavity to generate the desired pulsed output. The strong nonlinear optical response and light absorption of the BN-GO nanoparticles induces the generation of a highly stable mode-locked pulse at 1567.32?nm with visible Kelly’s sidebands. The pulses have a measured repetition rate of 13.56?MHz and a pulse width of 1.18?ps at the maximum pump power of 280.5?mW. The pulses have a frequency signal-to-noise ratio of ～53?dB, indicating a highly stable output. The proposed laser would find significant telecommunications applications, particularly for dense wavelength division multiplexing systems.     

Tunable S-band output based on Raman shift in dispersion shifted fiber

A tunable short-wavelength band Raman fiber laser using a dispersion shifted fiber as the nonlinear medium is proposed and demonstrated. This approach provides an alternative to the common method of using depressed-cladding, erbium-doped fibers as the gain medium in S-band fiber lasers. The proposed laser has a tuning range of 1508 to 1534?nm as well as an average peak power of about ?11.3?dBm within the range 1518–1530?nm. A high signal-to-noise ratio of approximately 70 dB is obtained from the system at this range.     

Broadband amplifier and high performance tunable laser with an extinction ratio of higher than 60 dB using bismuth oxide-based erbium-doped fiber

A Bi₂O₃-based erbium-doped fiber (Bi-EDF) ring laser with a 70?nm tunable range is demonstrated with a 49?cm long Bi-EDF in which tuning range can be extended to larger than 100?nm using an optical switch to alter the length of Bi-EDF in the laser cavity. With an extinction ratio of better than 60?dB throughout the entire tuning range, the measured FWHM of laser lines are measured to be 0.09?nm. In addition, the common amplification parameters are measured and studied in detail for various pumping configurations.     

Supercontinuum generation from a sub-megahertz repetition rate femtosecond pulses based on nonlinear polarization rotation technique

A means of supercontinuum (SC) generation is proposed and demonstrated, using femtosecond mode-locked pulses with sub-megahertz repetition rate based on the nonlinear polarization rotation technique. Total cavity length is approximately 522?m, which includes an additional 500?m single mode fiber (SMF) and the fundamental repetition rate obtained is 404.5?kHz. The mode-locked spectrum has a central wavelength of approximately 1600?nm and a 3?dB bandwidth of 16?nm, which falls within the L-band region. The threshold power for the mode-locked operation is achieved at approximately 52?mW. At pump power of 74?mW, the measured pulse width, pulse energy, and average output power are 70?fs, 18.3?nJ and 7.4?mW respectively. The generated pulses are amplified by a 72.44?mW erbium-doped fiber amplifier before being injected into a 100?m long highly non-linear fiber as the nonlinear medium to generate the SC spectrum. The obtained SC spectrum spans from 1250?nm to more than 1700?nm, with bandwidths of 450?nm at a ?70?dBm output power level. For comparison purpose, the 500?m SMF is removed from the setup and similar measurements are then repeated for this case.     

Tungsten tri-oxide (WO3) film absorber for generating Q-switched pulses in erbium laser

ABSTRACT

This paper reports a new type of passive saturable absorber (SA) made of transition metal oxide (TMO) embedded in polyvinyl alcohol (PVA). The Tungsten trioxide (WO₃)-PVA SA is placed in an erbium-doped fibre laser cavity to produce Q-switched pulses operating at 1562.82?nm. The pulse laser starts to manifest at the threshold pump power of 40?mW and continues to exist until the maximum pump power of 195?mW. Within that pump power range, its pulse energy, repetition rate and pulse width vary from 98 to 142.85?nJ, 29.86 to 56.7?kHz and 5.032 to 1.85?µs, respectively. The pulse train is stable with a signal to noise ratio of 70?dB. This is the first demonstration of a Q-switched laser using such a SA.     

All-fibre Mach–Zehnder interferometer based on seven-core and coreless fibres for generating stable wavelength-switchable laser

In order to realize a wavelength-tuneable fibre-laser output, a ring-cavity erbium-doped fibre laser based on an all-fibre Mach–Zehnder interferometer (MZI) is proposed and experimentally tested. The MZI consists of a single-mode fibre, two segments of coreless fibre, and a seven-core fibre. For the proposed fibre laser, the length of the gain medium is 4?m and the lasing threshold is 75?mW. By adjusting the loss of the laser cavity, switchable single-wavelength laser emission is realized across the range of 1527.6–1549.9?nm and the wavelength interval is less than 2.4?nm; the peak power difference of each lasing wavelength is less than 7.9?dB. Tuneable dual- and three-wavelength laser outputs were obtained by adjusting the polarization controller. The 3-dB linewidth was less than 0.57?nm. The single- and dual-wavelength laser output power fluctuations were less than 1.4 and 1.7?dB, respectively, when monitored over a period of 30?min.     

Tm3+-doped fiber master oscillator power amplifier with broad tunability in pulse duration using an acousto-optic external modulator

ABSTRACT

We demonstrate a pulse-duration tunable Tm³⁺-doped pulsed all-fiber master oscillator power amplifier (MOPA) operating at a central wavelength of 1908 nm. By using acousto-optic(AO) external modulation, the amplified laser pulse shows a tuning range having pulse durations from 66.5 ns to 8.0 μs and a repetition rate of 100 kHz-2 MHz. The laser achieved a maximum average power of 28.1 W and a corresponding energy of 28.1 μJ at 1MHz with a 3 dB linewidth of 0.63 nm and a beam quality factor of M_x²=1.25 and M_y²=1.32. The ASE suppression ratio is 50 dB and the corresponding total amplifier gain is 27.5 dB. To the best of our knowledge, it is the highest average output power and slope efficiency (～51.0%) achieved using AO external modulation in a Tm³⁺-doped pulsed fiber amplifier.     

Ultrabroad supercontinuum generation in tellurite equiangular spiral photonic crystal fiber

Simulations are presented of a very broad and flat supercontinuum (SC) in both the normal and anomalous group velocity dispersion regimes of the same equiangular spiral photonic crystal fiber at low pumping powers. For a pump wavelength at 1557?nm and average pump power of 11.2?mW, we obtained a bandwidth >3?μm (970?nm–4100?nm) at 40 dB below the peak spectral power with fiber dispersion ～2.1?ps/km nm at 1557?nm. In the same fiber, at pump wavelength 1930?nm and average pump power of 12?mW the SC bandwidth was more than two octaves (1300?nm–3700?nm) and dispersion was ～1.3?ps/km nm at 1930?nm. This demonstrates the potential use of the fiber for multi-wavelength pumping with commercially available sources at fairly low power.     

10 Gbit/s tunable dual-wavelength nonreturn-to-zero-to-return-to-zero data-format transformer based on a non-direct-current-biased fabry-perot laser diode

We demonstrate the conversion of a nonreturn-to-zero (NRZ)-formatted electrical data stream into a wavelength-tunable return-to-zero (RZ)-formatted optical pulse code by externally seeding a synchronously sinusoidal-modulated Fabry-Perot laser diode (FPLD) with optical pseudorandom binary-sequence data at 10 Gbits/s (Gbps). The FPLD without a dc-biased current was modulated by use of a power-amplified sinusoidal wave signal (approximately 25.6 dBm) as an NRZ-to-RZ data-format transformer, which is regeneratively amplified by a closed-loop erbium-doped fiber amplifier. The gain switching and on-off keying operation of the FPLD is initiated under the seeding of self-feedback and external-injection signals. A maximum wavelength tuning range of 30 nm with a side-mode suppression ratio of greater than 36 dB is obtained. The power penalty of the NRZ-to-RZ data-format conversion at 10 Gbps is 1.5 dB.     

Bismuth-based Brillouin/erbium fiber laser

A multi-wavelength Brillouin/erbium-doped fiber laser (BEFL) operating in the 1573 nm region is proposed and demonstrated. The system employs both linear and nonlinear gain from a bismuth-based erbium-doped fiber (Bi-EDF) approximately 215 cm long and a single mode fiber (SMF) of various lengths to generate an optical comb with a spacing of approximately 0.089 nm. Two 3 dB couplers were used to form a looping arm in the system in order to produce cascaded Brillouin Stokes waves as internal feedback for multi-wavelength operation. A stable output laser comb with 10 lines at more than ??13 dBm was obtained with 4.85 dBm Brillouin pump power and two 140 mW pumps at 1480 nm. The 1480 nm pumps' power and SMF length have a significant effect on the number of wavelengths and on the output power of the generated wavelength comb.     

Wideband-tunable nanotube Q-switched low threshold erbium doped fiber laser

An all-fiber passively wideband-tunable nanotube Q-switched low threshold erbium doped fiber laser is presented. With a low insertion loss carbon nanotube based saturable absorber, C- and L-band tunable Q-switched lasers are achieved by tuning the transmission wavelength of one C-band tunable filter and the other L-band one, respectively. The threshold of the Q-switched operation is only 12.8 mW. The self-mode-locking effect on the Q-switching can be effectively reduced by introducing a spatial hole burning effect with two optical circulators. The tunable wavelength range of the Q-switching laser can be changed by inserting a variable optical attenuator in the laser cavity to tune the gain spectrum.     

Application of macro-bending for flat and broad gain EDFA

Gain flattened C-band erbium-doped fiber amplifier (EDFA) is demonstrated using a macro-bending method. Various bending diameter and length of high concentration aluminosilicate EDFA are theoretically and experimentally analyzed. By varying the bending radius and the length of the doped fiber, the gain saturation effect as well as the energy transfer from shorter wavelength to a longer wavelength can be controlled to obtain a flattened and broadened gain profile in the C-band region. The amplifier uses a 9 m long erbium-doped fiber (EDF) with erbium ion density of 1.6 × 10²⁵ ions m^?3 and bending radius of 6.5 mm as a gain medium. The gain variation of the EDFA is obtained within ±1 dB over 25 nm bandwidth of C-band region.     

A generation of 2 μm Q-switched thulium-doped fibre laser based on anatase titanium(IV) oxide film saturable absorber

We demonstrate a Q-switched thulium-doped fibre laser operating at approximately 1935 nm wavelength using anatase titanium(IV) oxide (TiO₂) embedded in polyvinyl alcohol as the passive newly saturable absorber (SA). The film has absorption loss of 3.5 dB and modulation depth of 33%. It is sandwiched between two fibre ferrules in a ring laser cavity to produce self-started pulse train with a repetition rate that is tuned from 30.12 to 36.96 kHz as the 1552-nm pump power is increased from 289 to 485 mW. At maximum pump power, the laser produced a Q-switching pulse train with pulse duration, output power, pulse energy and peak power of 1.91 μs, 11 mW, 0.3 μJ and 146 mW, respectively. These results show that the TiO₂ is a new potential SA material for pulsed laser applications.