Tunable Repetition Rate Research Articles

Bismuth (III) Telluride (Bi2Te3) Based Topological Insulator Embedded in PVA as Passive Saturable Absorber in Erbium-Doped Fiber Laser

We demonstrate a passive Q-switched by integrating a Bismuth (III) Telluride (Bi2Te3) dispersed in Polyvinyl Alcohol (PVA) as passive saturable absorber. The experimental works show that the proposed passive saturable absorber operated at input power ranging from 21.69 mW to 126.89 mW with central operating wavelength of 1531 nm. We observe the tunable repetition rate from 40 kHz to 166 kHz with the shortest pulse width of 1.32 μs. The laser produced maximum instantaneous output peak power and pulse energy of 1.62 mW and 11.2 nJ, respectively. The signal to noise ratio was measured at 49 dB which indicates the stability of the generated pulse.

Quantum dot cadmium selenide as a saturable absorber for Q-switched and mode-locked double-clad ytterbium-doped fiber lasers

This paper demonstrates the integration of quantum dot (QD) cadmium selenide (CdSe) nanoparticles, which is embedded into polymethyl methacrylate (PMMA) film into an ytterbium-doped fiber laser (YDFL) cavity to produce Q-switched and mode-locked fiber lasers. The QD CdSe based film functions as a saturable absorber (SA). For Q-switching operation, stable pulse is generated within 970–1200mW pump power, with tunable repetition rate and pulse width of 24.5–40.5kHz and 6.8–3.7µs, respectively. Maximum pulse energy and peak power are obtained about 1.1µJ and 0.28W, respectively. As we tune the polarization state of the laser cavity and use a single QD CdSe film, the mode-locking operation could also be generated within 310–468mW pump power with repetition rate of 14.5MHz and pulse width of 3.5ps. Maximum pulse energy and peak power are obtained about 2nJ and 0.11W, respectively. These results may contribute to continuous research work on laser pulse generation, providing new opportunities of CdSe material in photonics applications.

Simply-integrated dual-comb spectrometer via tunable repetition rates and avoiding self-referencing.

Dual-comb system with simplified integration acts a crucial role in the next stage of field-deployable application. Here we demonstrate a home-made dual-comb spectrometer that meets this requirement based on optically stabilized erbium-fiber frequency combs. The simplified integration and operability are highlighted by the embedded large motion-span automatic optical delay line that resulted in 1.7 MHz of continuous repetition rate tuning range and avoid multiple fiber cutbacks. This relaxes the second similar frequency comb duplication, therefore simplifies dual-comb system integration. The mutual coherence was enhanced by optical phase lock to a common narrow-linewidth reference laser via pump current modulation. We acquired the absorption feature of acetylene 12C2H2 molecule in 1.5 μm region with an apodized instrument linewidth of 0.076 cm-1. The mean signal-to-noise ratio within a spectral bandwidth of 90 cm-1 achieved 280, and the corresponding noise equivalent absorption coefficient was 3.7 × 10-6 cm-1·Hz-1/2 for an absorption path of 7.5 cm and a pressure of 100 Torr. The accuracy of the retrieved spectrum was further confirmed by comparing with HITRAN database.

Bismuth (III) Telluride (Bi2Te3) topological insulator embed in PVA as passive Q-switcher at 2 micron region

We demonstrate a passive Q-switched at 2 um region by integrating Bismuth (III) Telluride (Bi2/Te3) embedded in Polyvinyl Alcohol (PVA). Bi2Te3 was embedded in PVA by solution casting approach to develop a Bi2/Te3-PVA film and integrated in the laser cavity with ring configuration to generate pulse laser. The experimental works show that the proposed passive saturable absorber operates at input pump power ranges from 637 mW to 784 mW with central wavelength of 1957.6 nm. We observed the tunable repetition rate from 12.6 kHz to 26.1 kHz with the shortest pulse width of 2.22 us. The laser produces maximum instantaneous output peak power and pulse energy of 0.42 W and 0.94 uJ, respectively. Full Text: PDF ReferencesC. Zhao, H. Zhang, X. Qi, Y. Chen, Z. Wang, S. Wen, and D. Tang, "Ultra-short pulse generation by a topological insulator based saturable absorber", Appl. Phys. Lett. 101, 211106 (2012). CrossRef Z. C. Luo, M. Liu, H. Liu, X.-W. Zheng, A.-P. Luo, C.-J. Zhao, H. Zhang, S. C. Wen, and W.-C. Xu, "2GHz passively harmonic mode-locked fiber laser by a microfiber-based topological insulator saturable absorber", Opt. Lett. 38, 5212 (2013). CrossRef J. Lee, J. Koo, Y. M. Jhon, and J. H. Lee, "A femtosecond pulse erbium fiber laser incorporating a saturable absorber based on bulk-structured Bi2Te3 topological insulator", Opt. Express 22, 6165 (2014). CrossRef M. Jung, J. Lee, J. Koo, J. Park, Y. W. Song, K. Lee, S. Lee, and J. H. Lee, "A femtosecond pulse fiber laser at 1935 nm using a bulk-structured Bi2Te3 topological insulator", Opt. Express 22, 7865(2014). CrossRef Y. H. Lin, C. Y. Yang, S.-F. Lin, W. H. Tseng, Q. Bao, C. I. Wu, and G.R. Lin, "Soliton compression of the erbium-doped fiber laser weakly started mode-locking by nanoscale p-type Bi2Te3 topological insulator particles", Laser Phys. Lett. 11, 055107(2014). CrossRef J. Lee et al., "All-fiberized, passively Q-switched 1.06 ?m laser using a bulk-structured Bi2Te3 topological insulator", Journal of Optics 16, 085203(2014). CrossRef Y. Chen, et al., "Large Energy, Wavelength Widely Tunable, Topological Insulator Q-Switched Erbium-Doped Fiber Laser", IEEE Journal of Selected Topics in Quantum Electronics 20, 315(2014). CrossRef M. Wu et al., "Nanosecond Q -Switched Erbium-Doped Fiber Laser With Wide Pulse-Repetition-Rate Range Based on Topological Insulator", IEEE Journal of Quantum Electronics 50, 393(2014). CrossRef J. Lee et al., "Dry Etched Waveguide Laser Diode on GeOI", IEEE Journal of Selected Topics in Quantum Electronics 21, 31(2015). CrossRef J. Li et al., "3-?m mid-infrared pulse generation using topological insulator as the saturable absorber ", Optics Letters 40, 3659(2015). CrossRef Z. Luo et al., "Topological-Insulator Passively Q-Switched Double-Clad Fiber Laser at 2 ?m Wavelength", IEEE J. Sel. Topics Quantum Electron 20, 0902708 (2014). CrossRef M. C. Paul, A. Dhar, S. Das, A. A. Latiff,M. T. Ahmad,and S. W. Harun, "Enhanced Erbium?Zirconia?Yttria?Aluminum Co-Doped Fiber Amplifier" IEEE Photonics Journal 7, 7100408 (2015). CrossRef H. Liu et al., "Femtosecond pulse generation from a topological insulator mode-locked fiber laser", Optics Express 22, 6868 (2014). CrossRef Z. Sun, T. Hasan, and A. C. Ferrari, "Ultrafast lasers mode-locked by nanotubes and graphene", Physica E 44, 1082(2012). CrossRef J. Lee, M. Jung, J. Koo, C. Chi, and J. Lee, "Dry Etched Waveguide Laser Diode on GeOI", IEEE Journal of Selected Topics in Quantum Electronics 21, 0900206 (2015). CrossRef H. Ahmad, A. Z. Zulkifli, K. Thambiratnam, and S. W. Harun, "2.0-?m Q-Switched Thulium-Doped Fiber Laser With Graphene Oxide Saturable Absorber", IEEE Photonics Journal5, 1501108(2013). CrossRef

Pulsed Pumping for Pulsewidth Tunable Nanosecond Ytterbium-Doped Fiber Laser

High efficiency, good robustness, and low amplified spontaneous emission are among the key factors of the high power ytterbium-doped pulsed fiber laser. In this letter, we propose an optimized pulsed pumping design for the nanosecond ytterbium-doped fiber laser with tunable pulse repetition rate and pulsewidth. For the pulsed pumping, the pumping power is kept at the maximal reachable power level and the pumping duration is modulated according to the pulsewidth. At each pulsewidth, the pumping duration is fixed for every seeding pulse. The performance of this laser at 130- and 20-ns seeding pulsewidth is experimentally analyzed. Simulation results are provided with the same configuration of the experiments. The results show that better performance of the laser is achieved. This technique is meaningful and strongly recommended for the design of high power nanosecond ytterbium-doped fiber laser.

Nanosecond double-pulse fiber laser with arbitrary sub-pulse combined based on a spectral beam combining system

In order to improve the processing efficiency and quality of nanosecond pulse laser drilling, a new double-pulse technique is put forward. Two single pulse lasers with different pulse duration or different repetition rate are spectrally combined by a home-made polarization-independent multilayer dielectric reflective diffraction grating. The pulse energy of single lasers and the inter-pulse separation can both be set at one's option. Then, double-pulse lasers represent two closely conjoint pulses with tunable pulse duration and tunable repetition rate and tunable pulse energy and tunable inter-pulse separation are obtained.

Monolithic all-fiber repetition-rate tunable gain-switched single-frequency Yb-doped fiber laser.

We report a monolithic gain-switched single-frequency Yb-doped fiber laser with widely tunable repetition rate. The single-frequency laser operation is realized by using an Yb-doped distributed Bragg reflection (DBR) fiber cavity, which is pumped by a commercial-available laser diode (LD) at 974 nm. The LD is electronically modulated by the driving current and the diode output contains both continuous wave (CW) and pulsed components. The CW component is set just below the threshold of the single-frequency fiber laser for reducing the requirement of the pump pulse energy. Above the threshold, the gain-switched oscillation is trigged by the pulsed component of the diode. Single-frequency pulsed laser output is achieved at 1.063 μm with a pulse duration of ~150 ns and a linewidth of 14 MHz. The repetition rate of the laser output can be tuned between 10 kHz and 400 kHz by tuning the electronic trigger signal. This kind of lasers shows potential for the applications in the area of coherent LIDAR etc.

Frequency-time coherence for all-optical sampling without optical pulse source.

Sampling is the first step to convert an analogue optical signal into a digital electrical signal. The latter can be further processed and analysed by well-known electrical signal processing methods. Optical pulse sources like mode-locked lasers are commonly incorporated for all-optical sampling, but have several drawbacks. A novel approach for a simple all-optical sampling is to utilise the frequency-time coherence of each signal. The method is based on only using two coupled modulators driven with an electrical sine wave. Since no optical source is required, a simple integration in appropriate platforms, such as Silicon Photonics might be possible. The presented method grants all-optical sampling with electrically tunable bandwidth, repetition rate and time shift.

Optically stabilized Erbium fiber frequency comb with hybrid mode-locking and a broad tunable range of repetition rate.

We present an optically stabilized Erbium fiber frequency comb with a broad repetition rate tuning range based on a hybrid mode-locked oscillator. We lock two comb modes to narrow-linewidth reference lasers in turn to investigate the best performance of control loops. The control bandwidth of fast and slow piezoelectric transducers reaches 70 kHz, while that of pump current modulation with phase-lead compensation is extended to 32 kHz, exceeding laser intrinsic response. Eventually, simultaneous lock of both loops is realized to totally phase-stabilize the comb, which will facilitate precision dual-comb spectroscopy, laser ranging, and timing distribution. In addition, a 1.8-MHz span of the repetition rate is achieved by an automatic optical delay line that is helpful in manufacturing a secondary comb with a similar repetition rate. The oscillator is housed in a homemade temperature-controlled box with an accuracy of ±0.02 K, which not only keeps high signal-to-noise ratio of the beat notes with reference lasers, but also guarantees self-starting at the same mode-locking every time.

High-Power Single-Frequency 1336 nm Raman Fiber Amplifier

A high power, single frequency, quasi-continuous-wave 1336 nm laser is achieved by Raman amplification of an external cavity diode laser in a variably strained polarization maintaining silica fiber. The pump laser is a 1256 nm Ytterbium-Raman integrated fiber amplifier with a maximum output peak power of 235 W. The 1336 nm amplifier produces square-shaped pulses with tunable repetition rate and duration. The peak power is as high as 53 W, which remains constant during the tuning. A polarization extinction ratio of >25 dB is achieved due to the all polarization maintaining fiber configuration. The laser is locked precisely at 1336.63 nm for future application in laser cooling of <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">27</sup> Al <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> after 8 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</sup> harmonic generation.

Simulation, Design and Fabrication of transverse diode-pumped Nd:YAG Solid-State Laser with 1.08 Beam Quality Factor

In this paper, design and fabrication of a diode pumped Nd:YAG laser using a new design of laser head and high beam quality factor is reported. Appropriate diode lasers are prepared. Driver circuit, which works at quasi continuous wave (QCW) mode is fabricated. This circuit has a tunable pulse repetition rate and input current. Heat distribution in the active material and output beam profile is simulated by LASCAD software. Output pulses with 14 mJ energy, 200 μs time duration, and 1 Hz pulse repetition rate are achieved. High beam quality factor with M2 ≤ 1.08 is obtained.

High-Pulse-Energy Topological Insulator Bi2Te3-Based Passive Q-Switched Solid-State Laser

Due to the ultralow saturation properties of the topological insulator (TI), stable and high-power TI-based solid state has become an important issue. In this paper, using a folding V-shaped laser cavity to minimize the residual pump to the broadband saturable absorber, passive Q-switched operations with high power not only at 1.06 $\mu\text{m}$ but at 1.34 $\mu\text{m}$ as well were demonstrated. The 1.06- $\mu\text{m}$ laser of 150 mW and the corresponding repetition rate and a pulse duration of 28.57 kHz and 576 ns, respectively, were performed. The pulse energy of 5.24 $\mu\text{J}$ and the corresponding peak power of over 9 W were also estimated. Additionally, the laser at 1.3- $\mu\text{m}$ exhibited a passive Q-switched operation with an average power of as high as 326 mW and a pulse duration of 673 ns. A tunable repetition rate of 75.5 to 116.6 kHz, a pulse energy of 2.8 $\mu\text{J}$ , and the corresponding peak power of 4.2 W were obtained. In addition, the stability of Q-switched pulses was analyzed. The results experimentally extend the promising application of the 2-D material, i.e., exfoliated TI Bi2Te 3, in solid-state lasers.

Efficient high repetition rate electro-optic Q-switched laser with an optically active langasite crystal.

With an optically active langasite (LGS) crystal as the electro-optic Q-switch, we demonstrate an efficient Q-switched laser with a repetition rate of 200 kHz. Based on the theoretical analysis of the interaction between optical activity and electro-optic property, the optical activity of the crystal has no influence on the birefringence during Q-switching if the quarter wave plate used was rotated to align with the polarization direction. With a Nd:LuVO4 crystal possessing a large emission cross-section and a short fluorescence lifetime as the gain medium, a stable LGS Q-switched laser was designed with average output power of 4.39 W, corresponding to a slope efficiency of 29.4% and with a minimum pulse width of 5.1 ns. This work represents the highest repetition rate achieved so far in a LGS Q-switched laser and it can provide a practical Q-switched laser with a tunable high repetition rates for many applications, such as materials processing, laser ranging, medicine, military applications, biomacromolecule materials, remote sensing, etc.

Photonic microwave waveform generation based on phase modulation and tunable dispersion.

Photonic generation of microwave waveforms is currently an interesting topic due to the advantages of large bandwidth and immunity to electromagnetic interference. In this paper, a photonic microwave waveform generator with tunable waveforms and repetition rates is proposed and experimentally demonstrated. A continuous-wave (CW) light is phase modulated by a local oscillator (LO) signal to generate optical sidebands. By locating the phase modulator (PM) in a Sagnac loop, we can control the intensity and phase of the carrier of the phase modulated signal. Then a compact tunable dispersion compensation module is used to introduce phase shifts to the optical sidebands. Thanks to the flexible controlling of the optical signal, the generation of microwave waveforms with tunable shapes and repetition rates can be realized. In the demonstration experiment, full-duty-cycle triangular and square waveforms with repetition rates of 5 and 10 GHz (bandwidths of 15 and 30 GHz) are successfully generated, respectively. The bandwidths are expected to be improved to above 120 GHz if larger-bandwidth measurement instruments are used. In addition to the flexible tunability, the proposed scheme also features the advantages of easy implementation and free from bias drift.

Orange-light passively Q-switched Pr^3+-doped all-fiber lasers with transition-metal dichalcogenide saturable absorbers

We experimentally demonstrated compact orange-light passively Q-switched praseodymium (Pr3+)-doped all-fiber lasers utilizing two-dimensional (2D) transition-metal dichalcogenides (TMDs, WS2 and MoS2) as saturable absorbers (SAs). The filmy TMDs SAs are fabricated by evaporating the composite of TMDs nanosheets and polyvinyl alcohol (PVA), and then inserted into an orange-light Pr3+-doped fiber laser cavity, which is designed by coating dielectric mirrors on fiber ends. Stable passively Q-switched orange lasers at 604 nm are successfully achieved. The passive Q-switching generated the short pulse duration of 435 ns and 602 ns, as well as the tunable repetition rate in the range of 67.3 ~132.2 kHz and 50.8 ~118.4 kHz, respectively. This is, to the best of our knowledge, the shortest-wavelength operation of 2D-material-based pulsed fiber lasers.

Widely Continuous Tunable ps Pulse Train Generation Based on SOA Nonlinear Dynamics

We propose a simple setup based on nonlinear dynamics in a semiconductor optical amplifier (SOA) and solitonic compression for the generation of stable and tunable repetition rate picosecond (ps) optical pulses. A quantum-well SOA is used to amplify electrical-optic-modulated rectangular optical signal, during which the nonlinear amplification process induces front-edge distortion. Due to the non-zero linewidth enhancement factor, the front-edge distortion can be isolated by the optical filtration of the chirped frequency component, which eventually becomes Gaussian-like pulse train of tens of ps FWHM pulsewidth. Following a stage of solitonic compression and a stage of pedestal suppression, we are able to obtain a train of 1-ps high-quality pulses for which the root mean square timing jitter is $C$ -band.

Q-switched Erbium-doped fiber laser at 1600 nm for photoacoustic imaging application.

We present a nanosecond Q-switched Erbium-doped fiber (EDF) laser system operating at 1600 nm with a tunable repetition rate from 100 kHz to 1 MHz. A compact fiber coupled, acousto-optic modulator-based EDF ring cavity was used to generate a nanosecond seed laser at 1600 nm, and a double-cladding EDF based power amplifier was applied to achieve the maximum average power of 250 mW. In addition, 12 ns laser pulses with the maximum pulse energy of 2.4 μJ were obtained at 100 kHz. Furthermore, the Stokes shift by Raman scattering over a 25 km long fiber was measured, indicating that the laser can be potentially used to generate the high repetition rate pulses at the 1.7 μm region. Finally, we detected the photoacoustic signal from a human hair at 200 kHz repetition rate with a pulse energy of 1.2 μJ, which demonstrates that a Q-switched Er-doped fiber laser can be a promising light source for the high speed functional photoacoustic imaging.

Bi2Se3as a saturable absorber for ultrafast photonic applications of Yb-doped fiber lasers

We experimentally demonstrated a Q-switched mode-locked (QML) and a continuous-wave mode-locked (CWML) ytterbium-doped fiber lasers with topological insulator: Bi2Se3 as saturable absorber (SA) in all normal dispersion regime. The Bi2Se3-SA is conventionally composited by embedding Bi2Se3 nanoplatelets into polyvinyl alcohol thin film, which provides a modulation depth of 7.6% and a saturation intensity of 38.9 MW/cm2. Based on this SA, with different cavity length, ytterbium-doped fiber laser can be operated at QML and CWML state, respectively. In the QML operation, a Q-switched envelope has the shortest pulse width of 1.12 μs and the tunable repetition rate from 96 to 175 kHz. The largest pulse envelope energy is 39.6 nJ, corresponding to average output power of 6.93 mW. In the CWML operation, an environmentally stable dissipative soliton laser pulse with pulse duration of ∼210 ps is obtained. The single pulse energy is 0.83 nJ with the repetition rate of 11.38 MHz at the wavelength of 1037 nm.

Investigation on quadrupling triangular-shaped pulses generator with flexible repetition rate tunability

An optical triangular-shaped pulses generation structure using quadrupling RF modulation and active polarization control is proposed. The ultimate goal is to make the expression of optical intensity approximately equal to the Fourier expansion of ideal triangular-shaped waveform. In the proposal, the dual-parallel Mach–Zehnder modulator (DP-MZM) is operated at quadrupling RF modulation. Thus, repetition rate of the generated pulse train is four times of the driving frequency. By tuning the driving frequency of local oscillator, continuous tunability of the repetition rate (20, 30, 40 and 60 GHz) is obtained. Numerical simulations show that the finite extinction ratio and the bias drift of the DP-MZM should be within a range respectively to obtain triangular-shaped pulses. The merit of this proposal is that it can generate high order frequency-multiplexed optical pulses train with less complex parameter alignment.

Harmonically mode-locked femtosecond fiber laser using non-uniform, WS2-particle deposited side-polished fiber

We investigated the feasibility of using a WS2-deposited side-polished fiber as a harmonic mode-locker to produce a femtosecond fiber laser with a frequency of 1.51 GHz. Our work focuses on using a side-polished fiber platform with non-uniform WS2 particles prepared through liquid phase exfoliation method without centrifugation. Femtosecond optical pulses were generated from an all-fiberized erbium-doped fiber-based ring cavity by increasing the pump power to achieve a tunable pulse repetition rate from 14.57 MHz to 1.51 GHz (104th harmonic). The characteristics of the output pulse were systematically investigated to analyze the pulse repetition rate, harmonic order, average output power, pulse energy, and pulse width as a function of the pump power. The output performance of the laser was compared to that of a laser based on a microfiber-based WS2 film SA described in (Yan et al 2015 Opt. Mater. Express 5 479–89). This experimental demonstration reaffirms that a side-polished fiber is an effective platform to implement an ultrafast harmonic mode-locker, and non-uniform WS2 particles prepared via simple liquid phase exfoliation method without centrifugation provide a suitable saturable absorption response at 1.55 μm.