Er-doped Laser Research Articles

783 MHz fundamental repetition rate all-fiber ring laser mode-locked by carbon nanotubes

We demonstrate a 783 MHz fundamental repetition rate mode-locked Er-doped all-fiber ring laser with a pulse width of 623 fs. By using carbon nanotubes saturable absorber, a relatively low self-starting pump threshold of 108 mW is achieved. The laser has a very compact footprint less than 10 cm × 10 cm, benefiting from the all-active-fiber cavity design. The robust mode-locking is confirmed by the low relative intensity noise and a long-term stability test. We propose a new scheme for generating high repetition rate femtosecond optical pulses from a compact and stable all-active-fiber ring oscillator.

Similariton-like Pulse Evolution in an Er-Doped Fiber Laser with Hybrid Mode Locking

An Er-doped all-fiber ultrashort pulse laser with positive total net-cavity group-velocity dispersion is demonstrated based on a hybrid mode-locking mechanism ensured by single-walled carbon–boron–nitrogen nanotubes with coaction of the nonlinear polarization evolution effect. The generation regime with a similariton-like spectrum is obtained. The spectrum width is ~31.5 nm, and the minimal pulse duration is ~294 fs at full width at half maximum. The average output power is ~3.2 mW, corresponding to 0.376 nJ pulse energy and 1.25 kW peak power. The fundamental pulse repetition rate is ~8.5 MHz, with a signal-to-noise ratio of 60 dB. The standard deviation of average output optical power stability, measured for 12 h, is about ~1% RMS, and the maximum level of relative intensity noise (RIN) does not exceed <−120 dBc/Hz in the 30 Hz–1 MHz frequency range. To prove the similariton-like regime generation, we also studied numerically and experimentally the pulse evolution during propagation through a laser resonator and output single-mode fiber with anomalous dispersion.

Microwave-free BOTDA based on a continuous-wave self-sweeping laser.

This Letter presents the first demonstration, to our knowledge, of a Brillouin optical time domain analysis (BOTDA) system based on a self-sweeping fiber laser. The unique feature of such laser sources is the generation of a narrowband tunable radiation with a small (6 MHz) tuning step and a reasonably large tuning range (3 GHz) making self-sweeping lasers extremely attractive for use in BOTDA systems. Since the wavelength tuning occurs solely due to internal processes occurring in the laser cavity, there is no need to use complex current/temperature control and feedback systems. This makes it possible to completely eliminate microwave devices, such as electro-optic modulators, from the BOTDA design. In this work, distributed temperature measurements with sensing line length of 25 km, spatial resolution of 10 m, and sensitivity of 2°C is demonstrated in a BOTDA system based on an Er-doped self-sweeping laser. The described approaches can reduce the complexity and overall cost of the BOTDA systems.

Development of the 2.7 μm to 3 μm Erbium-Doped Laser

The 3 μm wavelength band laser is located on the strong absorption peak of water and the atmospheric transmission window. The 3 μm laser with high single pulse energy is used in medical treatment for cutting soft tissues and bones during surgery. It is used as a pump source for optical parametric oscillators, and Fe lasers can realize 3~5 μm or 8~14 μm laser output, which has an irreplaceable role in certain areas (e.g., optoelectronic countermeasures, LIDAR, atmospheric monitoring, etc.). Commercial semiconductor-pumped Er lasers are capable of achieving 3 μm laser output of 600 mJ with the maturation of a 970 nm semiconductor laser. The conversion efficiency is significantly improved. However, the energy is lower than a flash-lamp-pumped Er laser. There are still serious crystal thermal effects and an inefficient conversion process. In this paper, the energy-level systems of 3 μm Er-doped lasers are discussed. A summary of the current state of research on Er lasers using different matrices and the commercialization of Er-doped lasers with wavelengths ranging from 2.7 μm to 3 μm is also provided. Several technical means are given to enhance laser performance. Furthermore, the development of Er-doped solid-state lasers with wavelengths between 2.7 and 3 μm is envisaged in the near future.

Gain-switched Fe:ZnSe laser pumped by a coupled-cavity Q-switched Er:ZrF4 fiber laser.

We report on a gain-switched operation of single-crystal Fe2+:ZnSe pumped by a coupled-cavity Q-switched Er3+:ZrF4 fiber laser. With this approach, we use a continuous wave Er-doped ZrF4 fiber laser whose cavity is coupled with the Fe:ZnSe laser cavity. A stable Q switching operation of the Er-doped fiber laser was achieved in this case and, as a result, a gain-switched operation of the Fe:ZnSe laser was obtained. The highest repetition rate was 79 kHz, the pulse duration of the pump Er-doped laser was ∼1.6 μs, and the pulse duration of the Fe:ZnSe was 62 ns. The maximum output power achieved from gain-switched Fe:ZnSe was 63 mW.

Growth and spectroscopic properties investigation of Er-doped BGSO single crystal: A potential gain medium for eye-safe laser

Erbium-doped crystals are well-suited for eye-safe solid-state laser systems around 1.5 μm. Broadband and high-gain Er-doped laser crystals can achieve high-power tunable laser output, which plays a great role in promoting commercial eye-safe laser research. Herein, the 2 at% Er-doped bismuth germanium silicate (BGSO) laser crystal is successfully grown by the vertical Bridgman method. The X-ray Rietveld refinement was used to obtain the structural parameters. The spectroscopic parameters of Er ions in BGSO crystal are calculated and analyzed with Judd-Ofelt theory. Furthermore, the broadband luminescence is observed in the wavelength range of 1450–1600 nm. The stimulated emission cross-section is calculated around 1500 nm, which largest value is 5.31 × 10−20 cm2 at 1543 nm. Meanwhile, the luminous efficiency of BGSO crystal in the eye-safe band is further characterized and explored by studying the energy transfer process and anomalous thermal quenching in the 550 nm and 660 nm bands. All results indicate that the Er: BGSO crystal is a promising broadband eye-safe laser material.

Generation of widely tunable single- and dual-wavelength in a figure-eight mode-locked fiber laser

We report a single- and dual-wavelength tuning at the C + L band in a nonlinear amplifying loop mirror (NALM) mode-locked Er-doped all-fiber laser. The single-wavelength tuning range is 52 nm, and the dual-wavelength can vary from 1558 nm and 1581 nm to 1581 nm and 1606 nm, accompanied by a slight change in the spacing of the wavelengths. To our knowledge, this is the widest dual-wavelength tuning range achieved in an Er-doped mode-locked fiber laser. The optical spectrum of the dual wavelengths has no significant variation within 60 min, which indicates potential for applications such as dual-comb. Our work provides a compact and low-cost dual-wavelength all-fiber laser, which may facilitate the design and application of dual-wavelength sources.

CrTe2 as a new saturable absorber for a passive mode-locking Er-doped laser

A 1T-CrTe2 nanoparticle SPF SA-based EDF mode-locking laser with a pulse duration of 586 fs has been obtained for the first time.

Linear-cavity Er-doped fiber mode-locked laser with large wavelength tunability.

A linear-type wavelength-tunable all-polarization-maintaining fiber mode-locked laser is proposed for the first time, to our knowledge, and is implemented with an Er-doped fiber and polarization-maintaining fiber components. The tuning range of the center wavelength is from 1533.7nm to 1565.6nm. The linear-type configuration makes the proposed laser simpler and more compact, allowing it to achieve the highest repetition rate of 126.5MHz among C-band wavelength-tunable mode-locked lasers due to its short cavity length. Also, its polarization-maintaining fiber components provide reliable operating robustness. The significant wavelength tunability and high repetition rate of the proposed laser can be expected to make it an attractive resource for various applications, including optical communications, broadband spectroscopic LIDAR, and high-precision ranging.

Femtosecond Er-Doped All-Fiber Laser with High-Density Well-Aligned Carbon-Nanotube-Based Thin-Film Saturable Absorber.

We have studied the ultrafast saturation behavior of a high-density well-aligned single-walled carbon nanotubes saturable absorber (HDWA-SWCNT SA), obtained by a high-pressure and high-temperature treatment of commercially available single-wall carbon nanotubes (SWCNTs) and related it to femtosecond erbium-doped fiber laser performance. We have observed the polarization dependence of a nonlinear optical saturation, along with a low saturation energy level of <1 fJ, limited to the detector threshold used, and the ultrafast response time of <250 fs, while the modulation depth was approximately 12%. We have obtained the generation of ultrashort stretched pulses with a low mode-locking launching threshold of ~100 mW and an average output power of 12.5 mW in an erbium-doped ring laser with the hybrid mode-locking of a VDVA-SWNT SA in combination with the effects of nonlinear polarization evolution. Dechirped pulses with a duration of 180 fs were generated, with a repetition rate of about 42.22 MHz. The average output power standard deviation was about 0.06% RMS during 3 h of measurement.

Ti3C2Tx as Saturable Absorber for Highly Stable All Fiber Er-Doped Q-Switched Laser

We report on a Q-switched Er-doped all-fiber laser based on a solution-processed Ti <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> saturable absorber (SA). Ti <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> is transferred to the fiber core region by optical deposition process through thermal effect. The Ti <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> SA is clamped between two optical fiber connectors, which is flexible to integrate into the laser oscillator. The modulation depth and saturation incident fluence are measured to be ~3% and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\sim 53.31~\mu \text{J}$ </tex-math></inline-formula> /cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> at 1550 nm wavelength region, respectively. At a threshold pump power of 190mW, we get self-started stable Q-switched operation with single-pulse energy of 22.17 nJ and pulse duration of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\sim 7.07~\mu \text{s}$ </tex-math></inline-formula> . With the pump power varing from 190 to 280 mW, the repetition frequency (RF) changes from 52.8 kHz to 62.79 kHz. The maximum average output power is 2.14 mW, which corresponds to the single-pulse energy of 34.03 nJ. The short-term stability is obtained by measuring the RF and temporal sequences of output pulse for 12 hours. Moreover, the long-term stability is demonstrated by measuring the output power and repetition rate for one week, showing the highly stable operation of the Ti <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> fiber laser, for the first time as far as we know.

Simple Design of Double-Layer Antireflection Coating for Er-Doped Glass Laser Application

In an Erbium-doped glass laser resonator, parasitic light oscillations (yielding a lowering of the output laser beam power) may be avoided by deposition of well-adapted antireflection coatings on the edges of the active glass medium. However, towards laser application, efficient double-layers are scarce in literature. Here, we propose a simple design of double-layer (total thickness &lt; 490nm) composed of thin films of MgF2 and Al2O3, materials that are easy to deposit by electron beam evaporation. Such coating design allows a calculated reflectance to be lower than 0.01% in the considered 1530-1570nm Near-Infrared range.

Thermal evaporated group IV Ge(Sn)-on-Si terahertz photoconductive antenna.

We have experimentally demonstrated thermal evaporated group IV Ge1-xSnx-on-Si terahertz (THz) photoconductive antennas (PCA) pumped by an Er-doped femtosecond laser for broadband THz generation. The Ge1-xSnx THz PCAs, free from material epitaxial growth methods, can offer comparable material properties in photocarrier generation, transportation, recombination, and the collection as group III-V THz PCAs. At the optical pumping power of 90 mW and a bias voltage of 40V, the Ge1-xSnx THz PCAs have achieved a broadband spectrum over 1.5 THz with a 40 dB signal-to-noise ratio (SNR). This CMOS-compatible group IV THz source can be monolithically integrated on the Si photonic platform, paving the way toward THz system-on-chip (SoC) for many on-site applications in the non-destructive evaluation, biomedical imaging, and industrial inspections.

All fiber spatiotemporal mode-locked fiber laser at 1.55 μm delivering multimode conventional solitons or bound solitons

In this letter, we report the experimental realization of the spatiotemporal mode-locked (STML) operation in a hybrid all-fiber Er-doped laser cavity composing of both the single-mode (SM) and multimode (MM) fiber segments. In such a hybrid cavity, the locking of the longitudinal or transverse modes is realized by changing the state of polarization controller (PC) or the MMF segment. By adjusting the PC, three different kinds of multimode solitons at ∼ 1560 nm are generated, including the conventional solitons, loosely bound solitons, and tightly bound solitons. Moreover, the evolution of mode distribution for different soliton states are investigated and it is found that the beam profiles are exactly determined by the state of MMF segment, which are quite different from the previous researches in the full-MM fiber system where the beam profile can be affected by the operating states. The obtained results are beneficial for the further exploring the spatiotemporal nonlinear dynamics. And this all-fiber STML laser with flexible outputs have high potential for applications in telecommunications and fiber laser sources.

Experimental and theoretical study on the dissipative soliton energy quantization effect in the negative dispersion regime

We present experimental and simulation results on the dissipative soliton energy quantization effect in the negative dispersion regime of an all-fiber Er-doped ring laser. A fiber filter is inserted into the cavity to facilitate the energy flow out of the cavity under net negative dispersion value conditions, and a single-dissipative soliton operation with the maximum pulse energy of 0.135 nJ is achieved. The dissipative soliton splitting occurred when the pump power is increased by dual-pulse, triple-pulse, and four-pulse operations. Simulations based on the extended nonlinear Schrödinger equation have been performed to confirm the multiple-dissipative soliton generation and soliton energy quantization in a net negative dispersion mode-locked fiber laser. These experimental and simulation results will help to improve the pulse energy in the negative dispersion regime and provide a more unified theory for the understanding of the mode-locking regimes in negative dispersion lasers.

Power-scalable two-wavelength pumped Er:YAP laser at 2.9 [formula omitted

A method of scaling the output power of a 3 μm Er-doped solid-state laser with two pump wavelengths at 976 nm and 1.7 μm is proposed. Compared with the typical scheme with a single 976 nm pump wavelength, the second 1.7 μm pump wavelength promotes the excited-state absorption and thus increases the effective pump rate and quantum efficiency. A proof-of-principle experiment has been conducted in a 2.9 μm Er:YAP laser with two pump sources, showing a power improvement of 227% at the threshold and 5.8% at 9.3 W of 976 nm absorbed pump power.

Research Progress of LD-Pumped 3 μm Er-Doped Solid-State Lasers

Research Progress of LD-Pumped 3 μm Er-Doped Solid-State Lasers

Generation of 64-fs L-band stretched pulses from an all-fibre Er-doped laser.

We demonstrate an L-band all-fibre erbium-doped laser mode locked by nonlinear polarisation rotation and working in the stretched-pulse regime. The use of a single segment of gain fibre with appropriate length and dispersion and a Brewster fibre grating optimised for the L band as an in-fibre polariser enables the generation of pulses at 1.59-μm central wavelength, which can be linearly compressed to 64-fs duration. Numerical simulations of the laser model support our experimental findings. Our laser design gives a route towards low-cost and low-complexity fibre-integrated laser sources for applications requiring L-band ultrashort pulses.

114 nm broadband all-fiber nonlinear polarization rotation mode locked-laser and time-stretch optical coherence tomography.

We propose and demonstrate an all-fiber Er-doped mode-locked laser with a 3-dB spectrum of 114 nm by using nonlinear polarization rotation (NPR), which to the best of our knowledge is the first realization to date of such a broad spectrum without any spatial optical devices. The repetition rate and pulse width of the laser are 183.6 MHz and 3.7 ps, respectively. Such an all-fiber NPR mode-locked laser is then applied in time-stretch optical coherence tomography. The axial resolution is 12.1 µm. The all-fiber high speed broadband swept laser based on the time stretching technique has compact structure and high stability, which is a promising source for frequency metrology and high resolution optical coherence tomography.

Properties of Scalable Chirped-Pulse Optical Comb in Erbium-Doped Ultrafast All-Fiber Ring Laser

We report on a scalable chirped-pulse Er-doped all-fiber laser, passively mode-locked by single-wall carbon nitride nanotubes. The average output power is ~15 mW, which corresponds to a peak power of ~77 W, and pulse energy of ~1.9 nJ and was achieved using a single amplification stage. We observed chirped-pulse generation with a duration of ~24.6 ps at a relatively low repetition rate of ~7.9 MHz, with a signal-to-noise ratio of ~69 dB. To characterize the short-term stability of the obtained regime, we have measured the relative intensity noise of the laser, which is &lt;−107 dBc/Hz in the range of 3 Hz–1000 kHz. It should be noted that the standard deviation of root mean square of average power does not exceed a magnitude of 0.9% for 3 h of measurement.