Dual-wavelength Regime Research Articles

Passively mode-locked dual-wavelength Ho-doped fiber laser with noise-like pulse regime

We experimentally and theoretically investigate the noise-like pulse (NLP) generation in a nonlinear polarization rotation-based mode-locked Ho-doped fiber ring laser, which can optionally operate in the dual-wavelength regime. By carefully changing the pump power and polarization state, the dual-wavelength NLP regime at 2041.9 and 2083.3 nm is finally achieved, which corresponds to a pulse energy of 11.84 nJ and a pulse duration of 849 fs. It is believed to be the first report on the dual-wavelength NLP operation from the previously reported Ho-doped fiber lasers.

Dual-wavelength harmonic mode-locked dissipative soliton resonance of Yb fiber laser

Dissipative soliton resonance (DSR) mode-locked fiber lasers have stimulated great interest recent years due to their unique pulse-breaking-free advantage for scaling soliton pulse energy. However, the mechanism accounting for pulse breaking to generate multipulses in DSR fiber lasers has not reached a consensus. Here, we show that harmonic mode-locked DSR 1-μm Yb-doped fiber laser in the dual-wavelength regime can be realized with a semiconductor saturable absorber mirror (SESAM). In the fundamental frequency (3.5 MHz) mode-locked state, the pulse width continuously broadens from 2 to 8.9 ns as the output power increases from 1.26 to 5.1 mW (pulse energy being from 0.36 to 1.46 nJ), while the pulse peak power is clamped at 0.17 W, highlighting the typical characteristics of DSR mode-locking operation. Through simply adjusting the SESAM’s feedback conditions, the DSR fiber laser can transits from the fundamental-frequency mode locking to harmonic mode-locked states. Harmonic states from the 2nd to 9th order have been observed, with pulse repetition rate enhanced from 7 to 31.5 MHz. Under fixed pump power, increasing harmonic orders leads to reduction of the pulse width and pulse energy but does not change the unique quantization feature of the peak power. The status of the SESAM also guarantees the generation of dual wavelengths centered at 1072.5 and 1079.5 nm with spectral widths of 2.7 and 1.9 nm, respectively. This dual-wavelength harmonic mode-locked DSR Yb fiber laser can find applications in various areas.

Single/dual-wavelength switchable and tunable passively Q-switched erbium-doped fiber laser

We demonstrate a passively Q-switched erbium-doped fiber laser (EDFL) with a birefringent Sagnac loop mirror (SLM) that combines the gain spectrum enables the laser to operate in tunable and switchable single/dual-wavelength states. When the pump power is up to 300 mW, the stable Q-switched pulse with the repetition rate and pulse duration of 58.57 kHz and 17.07 μs is achieved by properly adjusting the polarization controller-1 (PC-1) in the cavity. Meanwhile, the tunable and switchable single wavelength and dual wavelength regime is achieved by modulating the PC-2 in SLM, whose tunable ranges of single and dual wavelength are 3.27 nm and 1.69 nm, respectively. The proposed laser may meet the great application demands in nonlinear optics at 1.5 μm band.

Dual-wavelength complementary grayscale imaging by an ultrathin metasurface.

It is important to arbitrarily manipulate optical intensity, an important degree of freedom to light, on microscales, which is a fundamental requirement for integration and miniaturization of optical devices. Metasurfaces have shown unprecedented capabilities for manipulating light in terms of phase, intensity, and polarization. Here, an ultrathin metasurface composed of silver nanorods illuminated by linearly polarized light is demonstrated to manipulate optical intensity in subwavelength scales. By modulating rod orientations, gradient reflectance of light can be achieved on dual-wavelength regimes with contrast reflection intensities. Further, a nanorod metasurface, embedded with a picture of a panda profile, is experimentally designed for grayscale imaging, and the measurements demonstrate that two complementary grayscale images can be displayed at 633 and 900 nm. The grayscale imaging by a proposed ultrathin metasurface with dual-wavelength, complementary, and subwavelength-resolution characteristics provides a simple but efficient way for tailoring optical intensity on subwavelength scales, which is promising for a variety of applications such as encryption and decryption, display, information security, and optical communication.

Dynamic polarization attractors of dissipative solitons from carbon nanotube mode-locked Er-doped laser

Abstract We report experimental observation of polarization attractors in the form of vector dissipative solitons from a carbon nanotube mode locked fiber laser. At a time scale of 14–14,000 roundtrips, the typical polarization locked vector solitons, and other appealing attractors are shown. In addition, we observe the vector dissipative solitons operated in dual-wavelength regime with central wavelength of 1533 and 1557 nm which can be related to a fixed point polarization attractor. The results unveiled complex oscillatory behavior of dissipative solitons in the polarization domain which may help understand laser physics, nonlinear optics. The demonstrated work may underpin a new type of high energy laser source leading to possible applications in nanoparticle manipulation, micromachining, spectroscopy etc.

Experimental study of an in-fiber acousto-optic tunable bandpass filter for single- and dual-wavelength operation in a thulium-doped fiber laser.

A tunable single- and dual-wavelength thulium-doped all-fiber laser is demonstrated based on the implementation of an in-fiber acousto-optic tunable bandpass filter (AOTBF). The AOTBF is fabricated to be operated in the 1.9 µm region, and takes advantage of the intermodal coupling effect produced by traveling flexural acoustic waves in an optical fiber. It exhibits a 3-dB bandwidth of 2.04 nm with an insertion loss of 4.75 dB. The tuning properties of the AO device allows a continuous-wave operation with characteristics of wide tuning range (211.5 nm), narrow linewidth (50 pm) and high signal-to-noise ratio (60 dB). In the dual-wavelength regime, the laser is capable of independent tuning of each of the laser lines, achieving a tunable dual-wavelength emission that extends from 1802.67 to 1932.75 nm. A controllable wavelength spacing with minimum and maximum separations of 1.04 and 130.08 nm is obtained.

Passively Q-Switched 3-$\mu$ m $\text{Ho}^{3+}$ -Doped Fiber Laser Based on Nonlinear Polarization Rotation

We report a 3- $\mu \text{m}$ -waveband passively Q-switched $\text{Ho}^{\mathbf {3+}}$ -doped ZBLAN fiber laser based on nonlinear polarization rotation (NPR) in the ring cavity for the first time, to the best of our knowledge. The laser can operate in stable single- and dual-wavelength regimes. The stable single-wavelength pulse train is obtained with a ∼104 pm spectral linewidth at 2960.7 nm for 1.064-W launched pump power. By further increasing the launched pump power, the dual-wavelength pulsed laser can be observed, which is caused by the combination of intra-cavity birefringence and polarizer. The resulting dual-wavelength pulse has a narrow spectral linewidth of ∼87 pm and ∼131 pm at the central wavelength of 2966.8 nm and 2971.7 nm, respectively, under the maximum launched pump power of 3.86 W. The corresponding maximum output power and shortest pulse duration are 86.6 mW and $1.6~\mu \text{s}$ , respectively.

Switchable and dual-wavelength self-Q-switched fiber laser based on a homemade Er/Yb double clad fiber and polarization maintaining fiber Bragg grating

We report an experimental study on the self-Q-switched operation of a linear cavity fiber laser based on a homemade Er/Yb double clad fiber as gain medium. The parameters of the self-Q-switched pulses depend on the active fiber length of 2, 3, and 4 m. With a maximum fiber length of 4 m, stable self-Q-switched pulses are obtained for the whole 976 nm pump range, with a minimum pulse duration of 1.24 µs and a maximum repetition rate of 92.57 kHz. When the fiber length is shortened to 2 m, the range of the pump power level, at which the self-Q-switched operation is attained, is significantly diminished. Besides, dual-wavelength and switchable single-wavelength laser operations of the fiber laser are achieved by using a polarization maintaining fiber Bragg grating as spectral filter. Laser wavelengths at 1536.7 and 1537.1 nm with a line-width of 0.4 nm are obtained. The maximum average output power for the Q-switched laser operating in the dual-wavelength regime is 472 mW.

Tunable and switchable C-band and L-band multi-wavelength erbium-doped fiber laser employing a large-core fiber filter

In this paper, we propose and experimentally demonstrate a C- and L-band erbium-doped fiber laser (EDFL) with tunable single-, dual- and triple-wavelength lasing emissions. A tapered structure large-core fiber filter (LCFF) is inserted to serve as tuning component and wavelength selector for tunable and stable multi-wavelength oscillations. Based on the axial strain response of LCFF, two tunable triple-wavelength regimes within the range from 1558.71 to 1579.81 nm are obtained with side mode suppression ratio (SMSR) as high as 55 dB. Moreover, tunable single- and dual-wavelength regimes are also achieved with total tuning range of 11 nm and 6.23 nm, respectively. The tuning step for overall laser regimes is 0.02 nm, and the maximum wavelength sensitivity reaches to 1.87 pm/με. In addition, this proposed versatile EDFL is proved to be very stable since the lasing wavelength shifts and power fluctuations are less than 0.02 nm and 0.78 dB during an hour.

Abrupt-tapered fiber filter arrangement for a switchable multi-wavelength and tunable Tm-doped fiber laser.

A switchable and tunable multi-wavelength Tm-doped fiber laser is successfully demonstrated using a filter constructed with two tapered fiber elements in the cavity. The proposed system design uses a low-cost simple filter that allows stable dual, triple, quadruple, and quintuple-wavelength emission operation in the region around 1.9 μm. In the dual wavelength regime, the laser is capable of independently tuning each wavelength. For switching and tuning, a curvature is applied to the tapered fibers.

Tunable and switchable dual-wavelength mode-locked Tm3+-doped fiber laser based on a fiber taper.

We demonstrate a self-starting dual-wavelength mode-locked fiber laser at a 2 μm spectral region by using a fiber taper in a Tm3+-doped ring fiber cavity. The fiber taper fabricated with a flame brushing technique was used as a periodic filter with a modulation depth of ~3.61 dB and a modulation period of ~7.3 nm, respectively. Diverse dual-wavelength regimes including continuous wave (CW)/multi-soliton, soliton/multi-soliton, and soliton/soliton regimes were obtained by adjusting pump power. Wavelength tuning for the dual-wavelength was also precisely controllable through stretching the fiber taper carefully. The tuning range was ~7 nm which was limited by the modulation period of the taper. By inserting a 10.0 m dispersion compensation fiber (DCF) into the fiber cavity, a stable dual-wavelength dissipative-soliton operation was obtained at 2 μm spectral region for the first time.

Orthogonally polarized dual-wavelength Yb:KGW laser induced by thermal lensing

Simultaneous dual-wavelength laser oscillation with orthogonal polarizations has been observed and analyzed in a continuous wave N g-cut Yb:KGW oscillator. Without inserting any optical elements for polarization control, the N m- and N p-polarized modes, each of which possessed a distinct wavelength, coexisted and switched twice in two power regimes as the pump power was varied. The two wavelengths and their separation slightly depended on output coupling level. The wavelength switching and coexistence was studied and explained by considering the thermal and spectral anisotropy of the Yb:KGW crystals, which led to polarization-dependent reabsorption loss in the unpumped regions of the crystal. The maximum average output power obtained in the dual-wavelength regime was 4.6 W.

Switchable dual-wavelength CNT-based Q-switched using arrayed waveguide gratings (AWG)

In this paper, a dual-wavelength synchronously pulsed fiber laser Q-switched by carbon nanotube-based saturable absorber with switchable wavelength spacing enabled using arrayed waveguide grating (AWG) is proposed and demonstrated. By just switching the channels of the AWG, discrete tuning in wavelength spacing of the dual-wavelength Q-switched laser operation can be attained over several nanometers, ranging from 1.6 to 4.0 nm in a stable dual-wavelength regime without employing any modulation technique or intracavity spectral filters. Our experimental results show that the fiber laser can generate Q-switched microsecond pulses with a wide repetition rate range, starting from 12.0 kHz to a maximum value of 54.9 kHz. This proposed system is also reasonably simple to realize at low cost.

Formation and evolution of passively mode-locked fiber soliton lasers operating in a dual-wavelength regime

The formation and evolution of dual-wavelength solitons in passively mode-locked fiber soliton lasers are investigated both numerically and experimentally. By solving the Ginzburg–Landau equation and taking the gain profile into account, mode-locked soliton emissions at 1532 and 1555 nm are achieved simultaneously. Numerical results show that the two solitons exhibit the same intensity and duration, indicating that the dual-wavelength pulses possess the soliton energy quantization effect. In the process of pulse–pulse collisions, two solitons pass through each other and maintain their properties, qualitatively distinct from single-wavelength solitons that never overlap each other. The dual-wavelength mode-locked operation evolves into single-wavelength mode locking with the decrease of the pumping strength. The dual-peak gain spectrum of erbium-doped fiber and the birefringence-induced cavity filtering effect play crucial roles in the formation of dual-wavelength solitons. Numerical results agree well with analytical solutions and experimental observations. Our study provides an optional method of measuring the fiber dispersion by means of the dual-wavelength solitons.

Synchronization effects in a dual-wavelength class-B laser with modulated losses.

Different types of synchronization: in-phase, antiphase, phase, and lag synchronization, as well as amplitude death have been found theoretically in a dual-wavelength class-B laser with modulated losses in one of the channels. Depending on the laser parameters, oscillations in master and slave channels can be either completely or partially synchronized. The conditions for the dual-wavelength regime have been established. The analysis has been performed on the basis of transfer functions of the master and slave channels.