mW Of Pump Power Research Articles

Femtosecond all-polarization-maintaining Nd fiber laser at 920 nm mode locked by a biased NALM.

We demonstrate a femtosecond all-polarization-maintaining Nd fiber laser working at 920 nm mode locked by a biased non-linear loop mirror. The broadest spectral width of the pulse is 25.2 nm and the output power is 8 mW with 320 mW pump power. The measured pulse width is 109 fs with extra-cavity compression. The laser configuration of all-polarization-maintaining fiber can directly enhance the environmental stability of generated pulses. The seed pulses of the oscillator were amplified over 400 mW, which served as the light source for a two-photon microscope. To the best of our knowledge, this is the first demonstration of a 920 nm femtosecond Nd polarization-maintaining fiber laser based on a non-linear loop mirror.

Nanosized titanium dioxide saturable absorber for soliton mode-locked thulium-doped fiber laser

We demonstrate the potential of nanosized titanium dioxide (TiO2) in forming ultrashort pulses using a ring cavity thulium-doped fiber laser. A TiO2 polymer composite was transferred onto a microfiber through a spin coating technique to act as a light-absorbing material, saturable absorber (SA). The nonlinear transmission characteristics of this TiO2-SA exhibited 3.8% modulation depth and 17 MW/cm2 saturation intensity at 1.92 µm wavelength. At 1587 mW pump power, the central wavelength, average output power, pulse duration, peak power, and pulse energy were 1925.6 nm, 126.8 mW, 1.5 ps, 6.45 kW, and 11 nJ, respectively. The fabricated TiO2-SA displayed a wide pump power range of fundamental mode-locking at 11.53 MHz without any sign of laser-induced damage threshold or pulse breaking effect. This work has shown the potential use of nanosized TiO2-SA for fabricating broadband nonlinear photonic devices.

Design of Multiwavelength EDF-Raman Lasers Utilizing Mach-Zehnder Interferometer

This paper presents the design of multiwavelength Erbium Doped Fiber (EDF)-Raman fiber laser utilizing Mach-Zehnder Interferometer (MZI) with various cavity structures. A multiwavelength laser employing hybrid gain medium of EDF-Raman amplifier is simulated using OptiSystem software. Three cavity structures of multiwavelength laser such as unidirectional, bidirectional and ring cavity are simulated and analysed. From the simulation result, it is found that ring cavity structure produced the best performance whereas at 1000 mW pump power, up to 19 lasing lines were obtained in the ring cavity, compared to 18, and 16 lasing lines in the unidirectional and bidirectional linear cavity, respectively. All multiwavelength fiber lasers exhibit the same line spacing of 4.9 nm. In addition, at coupling coefficient of 0.9, up to 49.5 dB of side mode suppression ratio (SMSR) were achieved in the ring cavity structure, compared to 49.2 dB, and 30.3 dB of SMSR in the unidirectional and bidirectional linear cavity, respectively. However, bidirectional linear cavity exhibits the highest peak power of 2.07 dBm, compared to -17.4 dBm, and -15.5 dBm of peak power in the unidirectional linear and ring cavity, respectively.

Q-switched Ytterbium-doped fibre laser using an 8 cm long Hafnium bismuth erbium co-doped fibre saturable absorber

In this paper, we present a Q-switched fibre laser at 1069 nm which is induced by an 8 cm long Hafnium bismuth erbium co-doped fibre (HBEDF) saturable absorber (SA). The pulsating laser has a maximum repetition rate of 67 kHz at 175 mW pump power. We obtained the narrowest pulse width of 3.48 μs, the maximum pulse energy of 70.2 nJ, the maximum output power of 4.7 mW and the maximum peak power of 20.1 mW. The Q-switched laser is simple and may found practical applications in medicine and remote sensing.

Hafnium Bismuth Erbium Co-Doped Fiber Based Dark Pulses Generation With Black Phosphorus As Saturable Absorber

A dark pulse generation is demonstrated in a fiber laser configured with a 20 cm long HBEDF and multilayer Black Phosphorus as a gain medium and saturable absorber, respectively. Dark pulses fiber laser at 1.5 µm region was obtained when the pump power exceeds the threshold of 147 mW. Meanwhile, the spectrum of the dark pulse is centred at 1556.40 nm, with the 3 dB bandwidth of 0.12 nm and the separation between adjacent pulses is 1145 ns, corresponding to the cavity length of 211 m. The pulse width was measured to be around 320 ns. The radio-frequency spectrum of the dark pulse, which was measured within the 20 MHz range. More than 17 harmonics were observed within this range, which indicates the mode-locking operation of the laser. The fundamental frequency was obtained at 1.1 MHz, which agreed with the oscilloscope trace. Furthermore, it shows a signal to noise ratio of about 36.58 dB, which indicates good stability. The maximum output power of 0.78 mW and pulse energy of 0.78 nJ were obtained at 187 mW pump power.

Investigation of low-power comb generation in silicon microresonators from dual pumps

Here, the influence of pump powers for silicon microresonator-based Kerr comb generation (KCG) was investigated theoretically and experimentally in two types of dual-pumped KCG. One employs dual pumps at different free spectral range (FSR) spacings of the resonator for broadband comb spectrum and the other to produce comb lines at one FSR spacing for low pump powers. The KCG is modeled by including nonlinear absorption and mode interaction into the Lugiato–Lefever equation. Both the theoretical and the experimental results indicate that the KCG with pump powers inside the ring of tens of milliwatts would be limited by high nonlinear absorption even with a 25 V reverse bias to deplete free carriers. The most efficient comb spectrum occurs with recirculating pump power in the ring cavity of 13 mW (0.3 mW pump power in the bus waveguide) at 25 V reverse bias. Generally, for silicon KCG at the telecom wavelengths, the use of low pump powers and reverse bias is essential. At 25 V reverse bias, increasing the stored pump power in the ring to 160 mW would suppress the KCG and produce a similar number of comb lines as 1 mW recirculating pump power. This work advances our understandings of silicon KCG in the telecom band.

Comparison of 1480 nm and 980 nm-pumped Gallium-Erbium fiber amplifier.

Background: One way to reduce the length of the gain medium in Erbium-Doped Fiber Amplifier (EDFA) is by doping the fiber core with a high concentration of Erbium. However, this method caused ion clustering effects, which limits the EDFA's efficiency. In this research, the use of Gallium as a new co-dopant in erbium-doped silica fiber is explored. Methods: The new fiber, namely Gallium co-doped Erbium fiber (Ga-EDF), is used as a gain medium in an optical fiber amplifier setup. A 2-meter length of the Ga-EDF fiber was used in a single pass configuration with a forward pumping scheme at 150 mW pump power. The Ga-EDF amplifier's gain and noise figure while pumping at 980 nm and 1480 nm were compared. The amplifier's performance was evaluated as the input signal power varied between -30 dBm to 3 dBm, over the wavelength range of 1520 nm to 1580 nm. Results: The 980 nm-pumped Ga-EDF amplifier achieved the maximum small-signal gain of 22.45 dB and the corresponding noise figure of 5.71 dB at the input signal wavelength of 1535 nm. Meanwhile, the 1480 nm-pumped Ga-EDF amplifier attained the maximum small-signal gain of 20.83 dB and the corresponding noise figure of 5.09 dB at the input signal wavelength of 1550 nm. At the input signal power below -20 dBm and the wavelength range 1520 nm to 1547 nm, the Ga-EDF performs better when pumped at 980 nm. Their performance is comparable at the input signal wavelength range between 1547 nm to 1580 nm. At the input signal power above -20 dBm, the 1480 nm-pumped Ga-EDF outperformed the 980 nm-pumped amplifier. Conclusions: The overall performance indicates that the gain saturation point of the 1480 nm-pumped amplifier is higher than the 980 nm-pumped.

Multi-wavelength switchable random fibre laser based on double Sagnac-loop filter

A multi-wavelength switchable random fibre laser based on a double Sagnac-loop filter is proposed. The threshold of laser is 27 mW and the slope efficiency of the total power output to pump power is about 0.04%. In the experiment, stable and switchable laser outputs of single-, dual-, tri- and quad-wavelength channels are obtained by adjusting the polarization controller at room temperature. The wavelength positions are tuneable within the range of 1556–1564 nm and intervals are switchable between 2.5, 5 and 7.5 nm. Under 300 mW pump power, average power intensity of −24dBm is achieved. Furthermore, the output of fibre laser is relatively stable with less than 0.2 nm wavelength drift and less than 1.5 dBm power fluctuation within one hour. The proposed random fibre laser has promising application prospects for distributed sensing systems and biomedical imaging.

Comparison of 1480 nm and 980 nm-pumped Gallium-Erbium fiber amplifier

Background: One way to reduce the length of the gain medium in Erbium-Doped Fiber Amplifier (EDFA) is by doping the fiber core with a high concentration of Erbium. However, this method caused ion clustering effects, which limits the EDFA’s efficiency. In this research, the use of Gallium as a new co-dopant in erbium-doped silica fiber is explored. Methods: The new fiber, namely Gallium co-doped Erbium fiber (Ga-EDF), is used as a gain medium in an optical fiber amplifier setup. A 2-meter length of the Ga-EDF fiber was used in a single pass configuration with a forward pumping scheme at 150 mW pump power. The Ga-EDF amplifier's gain and noise figure while pumping at 980 nm and 1480 nm were compared. The amplifier's performance was evaluated as the input signal power varied between -30 dBm to 3 dB, over the wavelength range of 1520 nm to 1580 nm. Results: The 980 nm-pumped Ga-EDF amplifier achieved the maximum small-signal gain of 22.45 dB and the corresponding noise figure of 5.71 dB at the input signal wavelength of 1535 nm. Meanwhile, the 1480 nm-pumped Ga-EDF amplifier attained the maximum small-signal gain of 20.83 dB and the corresponding noise figure of 5.09 dB at the input signal wavelength of 1550 nm. At the input signal power below -20 dBm and the wavelength range 1520 nm to 1547 nm, the Ga-EDF performs better when pumped at 980 nm. Their performance is comparable at the input signal wavelength range between 1547 nm to 1580 nm. At the input signal power above -20 dBm, the 1480 nm-pumped Ga-EDF outperformed the 980 nm-pumped amplifier. Conclusions: The overall performance indicates that the gain saturation point of the 1480 nm-pumped amplifier is higher than the 980 nm-pumped.

Proposal for noise-free visible-telecom quantum frequency conversion through third-order sum and difference frequency generation.

Quantum frequency conversion (QFC) between the visible and telecom is a key to connect quantum memories in fiber-based quantum networks. Current methods for linking such widely separated frequencies, such as sum/difference frequency generation and four-wave mixing Bragg scattering, are prone to broadband noise generated by the pump laser(s). To address this issue, we propose to use third-order sum/difference frequency generation (TSFG/TDFG) for an upconversion/downconversion QFC interface. In this process, two long wavelength pump photons combine their energy and momentum to mediate frequency conversion across the large spectral gap between the visible and telecom bands, which is particularly beneficial from the noise perspective. We show that waveguide-coupled silicon nitride microring resonators can be designed for efficient QFC between 606 and 1550 nm via a 1990 nm pump through TSFG/TDFG. We simulate the device dispersion and coupling, and from the simulated parameters, estimate that the frequency conversion can be efficient (${\gt}80 \%$) at 50 mW pump power. Our results suggest that microresonator TSFG/TDFG is promising for compact, scalable, and low-power QFC across large spectral gaps.

A Passively Q-Switched Holmium-Doped Fiber Laser with Graphene Oxide at 2058 nm

This study reports a Q-switching-based, 2058-nm holmium (Ho) fiber laser incorporating a saturable absorber (SA) based on graphene oxide (GO). The SA was prepared with a side-polished fiber, while GO particles were deposited onto the fiber-polished surface to realize an all-fiber SA. A continuous-wave thulium-doped all-fiber laser, which was configured with a master-oscillator power-amplifier (MOPA) structure, was constructed as a pumping source. By inserting the fabricated SA into an all-fiber ring resonator based on 1-m length of Ho-doped fiber, Q-switched pulses could readily be obtained at a wavelength of 2058 nm. The pulse width was observed to vary from 2.01 to 1.56 μs as the pump power was adjusted from ~759 to 1072 mW, while the repetition rate was tunable from 45.56 to 56.12 kHz. The maximum values of average optical power and pulse energy were measured as ~11.61 mW and 207.05 nJ, respectively, at a ~1072 mW pump power.

Four-wave-mixing assisted multi-wavelength short pulse generation in an erbium-doped-fiber laser based tellurium nanorod saturable absorber

We report on tellurium nanorods as a new type of saturable absorber (SA)-induced four-wave-mixing to construct an all-fiber multi-wavelength passively Q-switched erbium-doped-fiber laser. This proposed material is prepared via a green method of nanorod synthesis. The results show that the SA device simultaneously generates seven wavelengths within 1592.4–1599.6 nm waveband and mode spacing of 1.2 nm. Meanwhile, the Q-switched operation is attained with the minimum pulse width of 2.85 μs, maximum repetition rate is 44 kHz and maximum pulse energy of 50 nJ at 275 mW pump power. The number of the generated multi-wavelength lasing lines and the performance of Q-switched pulse fiber lasers have significant value for understanding the dynamics of laser physics and also have potential applications in different fields of photonics such as sensing, optical communication, optical metrology and spectroscopy.

Highly Efficient Amplitude Modulation of Terahertz Fano Resonance Based on Si Photoactive Substrate by Low Power Continuous Wave

AbstractIt is one of the effective methods to modulate Fano resonance intensity by adding the thin photoactive material in the Fano metadevice and then light pumping them. However, most photoactive materials not only depend on high power femtosecond pulse, but also violently destroy the initial Fano resonance, thus deteriorating the modulated amplitude range (less than 0.35 in previous reports). This study introduces a terahertz (THz) Fano resonator based on Si photoactive substrate (SPS) which is modulated by low power 1064 nm continuous wave without additional photoactive materials. 90% modulation depth and the 0.45 modulated amplitude range are obtained by this device with only 2 mW (0.064 W cm−2) pump power. Meanwhile, this study also perfectly solves a long‐neglected problem, i.e., the Fano resonance amplitude of the whole sample seriously deviates from the Au metasurface. At first, the influence of SPS thickness on Fano resonance is investigated, which reveals that SPS thickness low to 3–0.5 µm is required in order to achieve basically the same between Fano resonance of the whole sample and the Au metasurface. And this device shows sharper initial Fano resonance and obtains a higher modulation amplitude range of 0.65 at this time.

Switchable multi-wavelength erbium-doped random distributed feedback fiber laser incorporating two-stage Sagnac filter

A low-threshold and simple structure switchable multi-wavelength fiber laser based on random distributed feedback (RDFB) is presented. The experiment setup incorporates a two-stage Sagnac fiber loop mirror, an 8 m long erbium-doped fiber (EDF), and a 25 km long single-mode fiber (SMF). The SMF provides RDFB via Rayleigh scattering. Due to the implementation of the half-open cavity structure and the gain generated by the EDF, the laser threshold can be significantly suppressed to 60 mW, and the slope efficiency of output lasing power against pump power is ∼0.9%. By adjusting the polarization controllers of the proposed two-stage Sagnac loop mirror, single-, double-, triple-, and quadruple-wavelength lasing channels in the range of 1527–1534 nm are achieved. In the case of quadruple-wavelength channel lasing, the optical signal noise ratio is up to 33 dB under the 180 mW pump power. The proposed random fiber laser can be applied in distributed sensing systems and biomedical imaging.

Wavelength scanning Q-switched fiber-ring laser intra-cavity QEPAS using a standard 32.76 kHz quartz tuning fork for acetylene detection

A novel fiber-ring laser intra-cavity quartz-enhanced photoacoustic spectroscopy (FLI-QEPAS) gas sensor utilizing wavelength scanning Q-switched technique is reported for acetylene detection. The system uses erbium-doped fiber as the gain medium for laser generation and a custom-made fiber Bragg grating attached to a piezoelectric transducer for wavelength scanning to cover the C2H2 absorption line at 1531.58 nm. A standard quartz tuning fork (QTF) operating at 32.76 kHz is placed inside the fiber-ring cavity to fully utilize intra-cavity optical power, realizing an ultra-short absorption path of 10 mm. Acousto-optic Q-switched working mode is employed to enable the fiber-ring laser working in high frequency enough for standard QTF excitation, up to ≃3 W intra-cavity peak power is achieved with 650 mW pump power at 980 nm. In acetylene detection experiments, the system realizes a noise equivalent concentration of 26 ppbv at 50 ms integration time, and Allan deviation shows the minimum detection limit can be improved to 2.8 ppbv at 51 s integration time. A linear dynamic range up to 10,000 ppmv is validated and the stability performance is also analyzed.

Generation of widely wavelength tunable Q-switched pulses in an ytterbium doped all-fiber laser

We report an all-fiber, broadband wavelength-tunable, acousto-optic Q-switched ytterbium-doped fiber laser. The tunable lasing operation was achieved by fiber-based acousto-optic tunable filter with a wavelength range spanning to more than 70 nm from 1008.6–1080.3 nm. Pulse shortening is achieved by spectral filtering and reducing the duty cycle of the acousto-optic modulator (AOM) used for Q-switching. At a 345 mW pump power and 1030 nm laser operation, the duration of Q-switched pulses is reduced from 110 ns (without spectral filtering) to 65 ns with 2.2 μJ pulse energy at a 10 kHz repetition rate and 10% duty cycle of AOM. The Q-switched pulse duration is further shortened to ∼10 ns by reducing the duty cycle of AOM to 0.12%. We believe that this all-fiber integrated Q-switched laser system with wide wavelength tunability and shorter duration pulses will be useful in many scientific applications.

Investigation of tungsten trioxide as a saturable absorber for mode-locked generation

Low-dimensional materials as saturable absorbers (SA) for pulsed laser applications have gain wide interest due to high nonlinearity and strong light-matter interaction. Various materials have been investigated such as graphene, transition metal oxides (TMO), transition metal dichalcogenides, and topological insulators. Tungsten trioxide (WO3); a cheap and nontoxic type of TMO has not yet been investigated for mode-locked pulsed fiber laser (MLFL) generation despite extensive employment as applications in other fields. WO3 is very attractive with spectral absorption extending in the broad near infra-red region, good mechanical strength, high resistance to photo corrosion, and is one of the few oxides that has high thermal and chemical stability. A tungsten trioxide (WO3) based saturable absorber (SA) fabricated via deposition of WO3 composite on tapered fiber was demonstrated. The WO3 weight percentage was varied from 0.005 to 1.235 wt% to investigate the effect on nonlinear saturable parameters and on mode-locked lasing performance. It was determined that the nonlinear saturable parameters were not dependent on weight percentage within its working range; 0.025 to 1.103 wt%. The generation self-started with 35–70 mW pump power, where the pulse durations and spectral bandwidths fall within the range of 810–940 fs and 8–12 nm, respectively. This experimental investigation provides insight on WO3 as a saturable absorber for mode-locked pulse laser generation. The utilization of this nanomaterial is aimed to cut down the cost the existing SA technology while providing enhanced durability and shelf-life.

Trilayer low-temperature-grown GaAs terahertz emitter and detector device with doped buffer

A low-temperature-grown GaAs (LTG-GaAs) terahertz (THz) photoconductive antenna device with layer structure consisting of doped buffer demonstrated enhanced emission intensity and detection sensitivity. As THz emitter, a 116% increase is exhibited by the LTG-GaAs with doped buffer relative to its undoped counterpart at 9 V bias and 0.8 mW pump power with spectral distribution extending to ∼3 THz. As a THz detector, a dynamic range of 55 dB is obtained at 0.5 THz, which is 5 dB higher than its undoped counterpart. The device proved effective as a THz emitter at low operating bias and pump power while its detection characteristics are acceptable even at low incident THz powers.

High efficiency four wave mixing and optical bistability in amorphous silicon carbide ring resonators

We demonstrate high efficiency wavelength conversion via four wave mixing in amorphous silicon carbide ring resonators with a loaded quality factor of 70 000. Owing to the high quality factor and high nonlinearity of amorphous silicon carbide, −21 dB conversion efficiency is achieved with 15 mW pump power. Moreover, the thermo-optic coefficient (TOC) of amorphous silicon carbide is measured to be 1.4 × 10−4/°C at telecommunication wavelengths. Taking advantage of the high TOC, we demonstrate optical bistability in the silicon carbide ring resonator. This work presents amorphous silicon carbide as a promising platform for applications in optical signal processing.

Thulium oxide film as a passive saturable absorber for pulsed fiber laser generation

Thulium oxide (Tm2O3) film is demonstrated to work as a passive saturable absorber (SA) for stable pulse generation at 1.55-µm region. The Tm2O3 film was fabricated from a commercially available Tm2O3 embedded into polyvinyl alcohol (PVA) as a film host. The obtained Tm2O3 film has an absorption at 1.55-µm region, which corresponds to energy level diagram of thulium. The Tm2O3 film is switched into the all-fibre ring cavity configuration. Self-started Q-switching operation obtained from 84.13 mW until 159.03 mW pump power. The repetition rate increases from 43.82 kHz and stop at 62.70 kHz, while the pulse duration narrowed from 14.00 µs to 9.50 µs. The stability of the pulse train can be confirmed through signal-to-noise ratio (SNR) of fundamental frequency. The maximum output power and pulse energy is 3.90 mW and 6.22 nJ, respectively. As a result, these findings confirm Tm2O3 can be utilised as a potential passive SA to generate laser pulsing at 1.55-µm region.