Dual-wavelength Generation Research Articles

Nonlinear Multimodal Interference as Ultrafast Photonic Device for Dual-Wavelength Domain-Wall Dark Pulse Generation

Abstract In comparison to bright pulses, better stability that is not susceptible to loss makes dark pulses accessible for applications in such fields as signal processing, optics sensing, and quantum communication. Here we investigate the dual-wavelength domain-wall dark pulse generation in a graded-index multimode fiber (GIMF) based anomalous dispersion single-mode fiber (SMF) laser. By optimizing intra-cavity nonlinearity and pulse polarization, the mode-locked states can evolve each other between bright pulses, dark pulses, and bright-dark pulse pairs. The evolution mechanism among them may be relevant to the coherent mode superposition, spectral filtering, and mode selection in SMF-GIMF-SMF hybrid-fiber modulation devices that affect the pulse formation and evolution in temporal, frequency, and space domains. These results provide a valuable reference for promoting further development of nonlinear optics and ultrafast optics, in which ultrafast photonic devices, with low cost, simple manufacture as well as wide adaptability, as novel pulsed generation technique, play a vital role.

Theoretical analysis of the buried heterostructure laser for stable dual-wavelength generation

Stable dual-wavelength emission from a laser is desirable for microwave signal generation using the optical heterodyning method. As both optical wavelengths are generated from the same cavity, the phase noise of the generated microwave signal is minimized. In this work, we exploit the inherent birefringence in the buried heterostructure semiconductor laser to generate dual polarized modes. We carefully analyze the mode competition between various modes in the cavity and propose the desirable gain modification conditions for stable dual mode oscillations when the laser is operating near the threshold. We show that the required asymmetry in the gain for two stable modes can be obtained from the mode confinement factors and facet losses. We also show the applicability of our results to a homogeneously broadened multimode laser.

Dual wavelength signal generation with four wave mixing based on directly modulated laser

Dual wavelength (DW) lasers are crucial for producing petahertz (PHz) signals, which are higher value terahertz (THz) signals. The infrared and visible light sub-bands are valuable frequency range for a number of applications, including networking, multiple access techniques, next-generation mobile networks (6G), future wireless networks, and new PHz communication systems. The importune need to the high frequency signal such as THz and PHz signal for 5 and 6 next generation wireless cellular mobile networks motivate us to design an optical system to provide these signals rather than an electronic circuits. They are also beneficial for a variety of medical testing. The wavelength spacing ranging from 14 nm to 7 nm is proposed and demonstrated a dual-wavelength generation with FWM based on DML is realized at 1554 and 1548 nm. It is essential to make use of the fiber's non-linearity characteristics to ensure synchronization for continuous wave (CW) laser and directly modulated laser (DML) signals and the creation of the four wave mixing (FWM) components. With the help of OptiSystem version 14.0, the system is designed and investigated then, the desired THz signal is created as pulse amplitude modulation. The position of the FWM components within the frequency range between the spectrums of the two lasers affects the synthesis of the required signal. At the DML frequency equal to or below the CW Laser (1520 nm), neither FWM frequency components nor dual wavelength pulses exist. On the other hand, the FWM frequency components and dual wavelength pulses can only be seen when the DML frequency is greater than 1520 nm. The CW laser frequency is the main controlling factor in the generation THz signal. If the CW laser frequency is set at or below 1520 nm, the dual wavelength and THz signal are accessible. Because these frequencies are so far from the reference fiber frequency, it is impossible to produce dual wavelength pulses at frequencies higher than those mentioned above.

Pulse Laser Generation at 2.0 µm Region based on Polyvinyl Alcohol Doped Graphene Nanoplatelets Saturable Absorber

A passive Q-switcher based on graphene nanoplatelets (GnP) doped with polyvinyl alcohol (PVA) is proposed for pulse laser generation at 2.0 µm region. An optimized solution casting approach is adopted in the customized preparation of a 12.04 wt.% weight ratio of GnP to PVA. The fabricated saturable absorber (SA) is characterized using field emission scanning electron microscope (FESEM), which confirmed the embedment of GnP in PVA composite. A 5 m long thulium doped fiber (TDF) is used as a gain medium in the laser cavity measurement. Our characterization demonstrates dual-wavelength Q-switched pulse generation at 1904.0 nm and 1904.9 nm for input power ranging from 644 mW to 698 mW, respectively. The repetition rate is tunable from 69 kHz to 98 kHz with the shortest pulse width of 1.4 µs. The calculated output peak power, pulse energy and signal-to-noise ratio are recorded at 143 mW, 0.21 µJ and 35 dB, respectively. Notably, the present work is the first-ever work of a Q-switcher based on GnP doped with PVA host at 2.0 µm region.

Inter-/intra-pulse dual-wavelength-operated mid-infrared optical parametric oscillator.

We demonstrate a pulsed mid-infrared (MIR) optical parametric oscillator (OPO) with both inter-pulse and intra-pulse dual-wavelength operation capability. A fiber master oscillator power amplifier incorporating an acousto-optic tunable filter (AOTF) was employed as the pump for the OPO. By finely adjusting the drive wave packets for the AOTF, dual-wavelength pump can be realized within each pulse or between two adjacent pulses. These special temporal-spectral behaviors of the pump can be transferred to MIR via an OPO. In the proof-of-principle experiments, two pump wavelengths at ∼1065 and ∼1076 nm were generated and amplified to ∼31.2 W with equivalent spectral intensities for both pulsation modes. At the highest pump power, total idler power of ∼3.5 W was achieved at ∼3.45 and ∼3.55 µm under both pulsation modes. To the best of our knowledge, this is the first demonstration of both inter-pulse and intra-pulse dual-wavelength MIR generation via an OPO with an identical configuration. It is believed that our design may provide a promising solution to many practical applications including differential absorption lidar and tunable terahertz wave generation.

Dual-Wavelength Q-switched Fiber Laser Generation by Incorporating 2D Materials in D-SMS Fiber Structure

We demonstrate a dual-wavelength Q-switched fiber laser generation by inserting a combination of SM-MM-SM fiber and a d-shape structure. This combination is known as D-SMS fiber. By side-polishing an SM fiber with 1-dB loss, the d-shape fiber structure is obtained. Then the d-shape SM fiber is spliced to 25 cm long MM and SM fiber to form a D-SMS fiber structure. After inserting D-SMS fiber, a stable dual-wavelength presence at 1562.8 nm and 1563.8 nm (1 nm wavelength spacing). The pulse train generates once we deposited a graphene oxide solution onto the surface of the d-shape structure. This Q-switching operation mode obtained from 45 mW to 111 mW pump power with a maximum pulse energy of 56 nJ. The repetition rate and pulse width have been recorded from 34 kHz to 55 kHz and from 10.22 µs to 6.47 µs, respectively.

Fiber laser with intracavity parallel Mach-Zehnder interferometers towards Vernier refractive index sensing.

In this paper, dual-wavelength laser emission of an erbium-doped fiber laser (EDFL) with a tunable distinct wavelength selection of the simultaneously produced laser lines was achieved by applying a parallel comb filter configuration based on the optical Vernier effect. The intracavity inserted proposed comb filter consists of two parallel branches to generate the Vernier effect. Each branch is an in-line Mach-Zehnder interferometer (MZI) filter, which is composed of a polarization-maintaining fiber fusion spliced between single-mode fibers with sphere shapes at both ends. The tunability of the selected laser wavelength was realized by submerging the proposed filter in different sodium chloride/water mixtures. The proposed comb filter-based Vernier effect was used to independently achieve the selection of the dual-wavelength EDFL lines and for refractive index (RI) sensing applications. The in-line M Z I 1 and M Z I 2 structures show a wavelength shift sensitivity to RI variations of -88 and 79nm/RIU, respectively. Our proposed MZI structure presents a reliable, straightforward, and low-cost spectral comb filter for separate tunable dual-wavelength laser generation in the c-band region. Furthermore, the proposed filter structure-based Vernier effect presents a new perspective and method in the RI sensing application.

Co-Existence of Watt-Level Dissipative Solitons and Synchronous Dual-Wavelength Mode-Locked Pulses in Yb Fiber Laser

We present a high-average-power laser configuration to simultaneously generate both dissipative solitons (DSs) and synchronous dual-wavelength mode-locked (ML) pulses using large-mode-area (LMA) fibers in combination with a birefringence-based chirped-pulse spectral filter. DSs with average power as high as 5.8 W and pulse width as short as 178 fs are obtained at the output port. Meanwhile, up to 1.5 W average power in synchronous dual-wavelength ML pulsed operation is also obtained at the rejected port with central wavelengths located at 1029.7 nm and 1046.1 nm respectively. To our knowledge, observation of such behavior with both DSs and synchronous dual-wavelength pulse generation simultaneously has not been yet realized in watt-level fiber lasers.

Mode-modulation-induced high power dual-wavelength generation in a random distributed feedback Raman fiber laser.

An all-fiberized random distributed feedback Raman fiber laser (RRFL) with mode-modulation-induced wavelength manipulation and dual-wavelength generation has been demonstrated, where an electrically controlled intra-cavity acoustically-induced fiber grating (AIFG) is employed to adjust the input modal content at the signal wavelength. The wavelength agility of both the Raman effect and the Rayleigh backscattering in RRFL benefits on broadband laser output in case of broadband pumping. The feedback modal content at different wavelengths can be adjusted by AIFG, and then the output spectral manipulation can be ultimately manifested through the mode competition in RRFL. Under the efficient mode modulation, the output spectrum can be continuously tuned from 1124.3 nm to 1133.8 nm with single wavelength, while ulteriorly the dual-wavelength spectrum can be formed at 1124.1 nm and 1134.7 nm with a signal-noise-ratio of 45 dB. Throughout, the power is beyond 47 W with good stability and repeatability. To the best of our knowledge, this is the first dual-wavelength fiber laser based on mode modulation and the highest output power ever reported for an all-fiberized continuous wave dual-wavelength fiber laser.

Experimental and theoretical investigation of a cryogenically cooled Nd:YAG laser with dual-wavelength at 946 and 1061 nm

A diode-end-pumped cryogenically cooled Nd:YAG laser is demonstrated with dual-wavelengths at 946 nm and 1061 nm. As temperature varies from 300 K to 190 K, a transition occur from single-wavelength at 946 nm to dual-wavelength at 946 nm and 1061 nm. Only the line at 1061 nm oscillated for the temperature less than 180 K. Moreover, a theoretical simulation of oscillation condition at cryogenic temperatures is implemented, leading a deep insight into the physical mechanism of dual-wavelength generation.

Diode-pumped continuous-wave laser of a self-frequency-doubling Yb:La2CaB10O19 crystal.

We report the first, to the best of our knowledge, laser operation of acentric Yb3+-doped La2CaB10O19 (Yb:LCB) crystal since its discovery in 1998. The polarized absorption and emission cross-section spectra of Yb:LCB were calculated at room temperature. Using a fiber-coupled 976 nm laser diode (LD) as the pump source, we realized effective dual-wavelength laser generation at around 1030 and 1040 nm. The highest slope efficiency of 50.1% was obtained in the Y-cut Yb:LCB crystal. In addition, via resonant cavity design on a phase-matching crystal, a compact self-frequency-doubling (SFD) green laser at 521 nm was also realized in a single Yb:LCB crystal with an output power of 152 mW. These results promote Yb:LCB as a competitive multifunctional laser crystal, especially for highly integrated microchip laser devices ranging from the visible to the near-infrared regime.

532 nm pumped visible emission from Ho3+-doped fiber lasers

We report a green fiber laser based on an in-band pumping process for the first time. The impact of the pumping mechanism on output characteristics is addressed, and a new pumping strategy to improve the output performance of visible fiber lasers is presented. We demonstrate the highest power of 0.52 W green fiber laser output using a single-wavelength 532 nm solid-state laser as the pump source, and we also exhibit dual-wavelength excitation with a maximum power output of 0.72 W. Simultaneously, we investigate the reasons of visible dual-wavelength generation and modulation approaches in Ho3+-doped fluoride fibers. This method efficiently tackles the problem of visible light generation in Ho3+-doped fibers being limited, as well as pave the way for more efficient and powerful visible fiber lasers.

Black Arsenic-Phosphorus Nanosheets for Highly Responsive Photodetection and Dual-Wavelength Ultrafast Pulse Generation at Telecommunication Bands.

Black arsenic-phosphorus (b-AsP), an alloy containing black phosphorus and arsenic in the form of b-AsxP1-x, has a broadly tunable band gap changing with the chemical ratios of As and P. Although mid-infrared photodetectors and mode-locked or Q-switched pulse lasers based on b-AsP (mostly b-As0.83P0.17) are investigated, the potential of this family of materials for near-infrared photonic and optoelectronic applications at telecommunication bands is not fully explored. Here, we have verified a multifunctional fiber device based on b-As0.4P0.6 nanosheets for highly responsive photodetection and dual-wavelength ultrafast pulse generation at around 1550 nm. The fiber laser with a saturable absorber (SA) based on b-As0.4P0.6 nanosheets can output dual-wavelength mode-locking pulses with a larger bandwidth and spectral separation than those based on other two-dimensional (2D) materials. Remarkably, it is found that the b-As0.4P0.6-based photodetector can achieve a high responsivity of 10,200 A/W at 1550 nm and a peak responsivity of 2.29 × 105 A/W at 980 nm. Our work suggests that b-As0.4P0.6 shows great potential in ultrafast photonics, dual-comb spectroscopy, and infrared signal detection.

Dual wavelength generation and wavelength tunability in Yb-doped mode-locked laser using few-mode fiber as a saturable absorber

In this research, we demonstrate wavelength tunability and dual wavelength generation in all-fiber ytterbium (Yb)-doped mode-locked laser using a single mode–few-mode–single mode fiber (SMF–FMF–SMF) combination act as a saturable absorber (SA). The all-fiber SA exhibits high modulation depth of 34.53% and a saturation intensity of 9.17 MW/cm2. The SMF–FMF–SMF structure encompasses an inherent filtering along with SA property. By combining the tunable intra-cavity birefringence of the laser with the SA features result in dual-wavelength generation and wavelength tunability. Thus, the tuning of center wavelength of output spectrum from 1028.88 through 1076.18 nm, with the compressed pulse widths from 319 to 324 fs respectively, is achieved. Besides, the generated dual-wavelength is switched from 1033.32/1058.2 nm to 1049.7/1075.7 nm, respectively. These results indicate that an all-fiber SMF–FMF–SMF structure is a potential SA element for wavelength tunability and dual-wavelength mode-locking in Yb-doped fiber lasers, which can be used for nonlinear microscopy, bio-degradable material processing and terahertz spectroscopy.

Flexible dual-wavelength second-harmonic generation in nested quasi-periodic optical superlattice

Flexible dual-wavelength second-harmonic generation in nested quasi-periodic optical superlattice

Dual-Wavelength Mode-Locked Oscillation with Graphene Nanoplatelet Saturable Absorber in Erbium-Doped Fiber Laser

In this work, we demonstrate a dual-wavelength passively mode-locked erbium-doped fiber laser employing graphene nanoplatelet as saturable absorber. The dual-wavelength laser is generated in ~1530 nm and ~1550 nm wavelength regions by splitting the main signal into two separate laser oscillations via a red/blue wavelength division multiplexer. Both the unidirectional and bidirectional dual-wavelength oscillation scheme are investigated, and it is found that the latter is advantageous in providing narrower pulse widths of 890 fs and 980 fs for the respective wavelength region, on top of boosting the pulse energy to the maximum value of 139 pJ and 155 pJ, respectively. It is believed that the bidirectional dual-wavelength oscillation scheme can minimize the overlapping effect between the neighboring pulses that cause pulse distortion as well as signal attenuation compared with unidirectional dual-wavelength oscillation. This work expands the dynamics of cavity structure design for synchronized dual-wavelength mode-locked fiber laser generation.

Energy-transfer controlled dual-wavelength visible laser generation based on parallel nonlinear frequency up-conversions

A compact frequency up-conversion scheme is demonstrated for dual-wavelength visible laser generation. The parallel sum-frequency generation (SFG) and second-harmonic generation (SHG) processes are simultaneously phase-matched and integrated in a well-designed periodically poled MgO:LiNbO3 crystal. Concurrent nonlinear up-conversions of the coupled SFG and SHG are thus realized. In the proof-of-principle experiment, two near-IR lasers at wavelengths of 800 nm and 1180 nm were used as independent fundamental beams. As a result, the generation of blue light at ∼477 nm by SFG (800 nm + 1180 nm → 477 nm) and the orange light at ∼590 nm by SHG of 1180 nm (1180 nm + 1180 nm → 590 nm) was simultaneously achieved. Finally, it is proved the relative strength of these two coupled nonlinear interactions and consequently the relative power of the blue and orange light could be freely controlled by changing the pump intensities of the fundamental beams, and a maximum photon conversion efficiency (∼25%) comparable to that of the separated SHG process was observed for this simultaneous dual-up-conversion device. This result provides a promising strategy for developing high-efficiency multi-wavelength visible laser systems. Combined with an engineered QPM crystal with different poling periods in sequence, more prospective nonlinear applications may be realized based a series of cascaded single- and dual-QPM nonlinear processes.

PbS Quantum Dots Saturable Absorber for Dual-Wavelength Solitons Generation.

PbS quantum dots (QDs), a representative zero-dimensional material, have attracted great interest due to their unique optical, electronic, and chemical characteristics. Compared to one- and two-dimensional materials, PbS QDs possess strong absorption and an adjustable bandgap, which are particularly fascinating in near-infrared applications. Here, fiber-based PbS QDs as a saturable absorber (SA) are studied for dual-wavelength ultrafast pulses generation for the first time to our knowledge. By introducing PbS QDs SA into an erbium-doped fiber laser, the laser can simultaneously generate dual-wavelength conventional solitons with central wavelengths of 1532 and 1559 nm and 3 dB bandwidths of 2.8 and 2.5 nm, respectively. The results show that PbS QDs as broadband SAs have potential application prospects for the generation of ultrafast lasers.

Laser wavelength shift and dual-wavelength generation in continuous-wave operation of Ho:YAG laser pumped by thulium-doped fiber laser

We present the output coupler transmission and radii of curvature (ROC)-dependent spectral analysis of a Ho:YAG laser, under continuous-wave operation, resonantly end-pumped by a thulium-doped fiber laser. At room temperature, with a 20.2% output coupling transmittance, 100 mm ROC, and 20.3 W incident pump power, the maximum output power is 14.43 W, corresponding to a slope and optical-to-optical conversion efficiency of 76.5% and 71.1%, respectively. For different output coupler transmissions, the laser emits at 2090, 2096, 2121, or 2128 nm along with simultaneous emission at two wavelengths. At a 19.43 W incident pump power, dual-wavelength laser generation, with the same amplitude, was obtained at 2096.73 and 2121.53 nm with good stability, and a signal-to-noise ratio of more than 35 dB at room temperature. A nearly perfect Gaussian beam profile for simultaneous lasing emission at two wavelengths with a beam quality factor of M2 not higher than 1.12 was measured.

Theory and experiments of a power-ratio tunable dual-wavelength Nd:YVO4/Nd:GdVO4 laser by varying the pump wavelength

We demonstrate the theory and experiments of a power-ratio tunable dual-wavelength laser with coaxial diode end-pumping configuration by varying the pump wavelength, which is realized by controlling the working temperature of the pump laser diode (LD). Composite laser gain media containing an Nd : YVO4 crystal and an Nd : GdVO4 crystal was used for example. The dynamics of the dual-wavelength laser generation based on practical input operating parameters were simulated, and in the experiment, a total power of 3.72 W was obtained under the maximum LD pump power of 8 W, corresponding to the optical–optical conversion efficiency of 46.5%. The characteristics of the power-ratio tuning and output power agreed well with the theoretical predictions.