Dual-wavelength Operation Research Articles

Simultaneous orthogonally polarized dual-wavelength actively Q-switched Ho:YLF laser at 2063 nm and 2065 nm

The simultaneous and output-balanced orthogonally polarized dual-wavelength actively Q-switched Ho:YLF laser at 2063 nm and 2065 nm was realized for the first time. In the continuous wave orthogonally polarized dual-wavelength operation, the total maximum output power of 4.6 W was achieved. In the actively Q-switching orthogonally polarized dual-wavelength operation, at the pulse repetition frequency of 5 kHz, the total maximum average output power, pulse energy, and peak power were 2.37 W, 0.47mJ, and 4.32 kW, respectively. As far as we know, this is the first simultaneous orthogonally polarized dual-wavelength actively Q-switched 2 μm Ho-doped solid-state laser.

A Tunable and Switchable Multi-Wavelength Erbium-Doped Fiber Ring Laser Enabled by Adjusting the Spectral Fringe Visibility of a Mach-Zehnder Fiber Interferometer

This paper presents a tunable, switchable multi-wavelength emission from an erbium-doped fiber ring laser, enabled by adjusting the spectral fringe visibility of a fiber interferometer filter. The filter is formed with specially designed concatenated tapered fibers to configure a Mach-Zehnder fiber interferometer (MZFI). The laser emission is highly flexible and reconfigurable, allowing for tuning between single- and dual-wavelength operation. The laser can switch sequentially from one up to six wavelengths by fixing the curvature and adjusting the polarization state. The lasing emission is generated over a stable wavelength range between 1559.59 nm and 1563.54 nm, exhibiting an optical signal-to-noise ratio (OSNR) exceeding ~35 dB. The performance of amplitude and wavelength fluctuations were evaluated, indicating an appropriate stability of ~3 dB and a shift less than 0.1 nm within a 45 min period at room temperature. A detailed comparison with the literature is given.

Spectrally narrowband simultaneous dual-wavelength emission from Y-branch DBR diode lasers at 785 nm

Y-branch distributed Bragg reflector (DBR) diode lasers with a stable narrowband emission in simultaneous dual-wavelength operation with spectral distances below 3.2 nm are presented. The Y-branch laser consists of two laser branches with different DBR gratings serving as wavelength-selective rear-side mirrors. Therefore, two emission wavelengths with a spectral distance defined by the DBR grating periods can be generated simultaneously. A Y-coupler combines the two ridge waveguide (RW) branches into a single straight output RW. Devices with a spectral distance of 0.6 nm and 2.0 nm emitting around 785 nm are manufactured. Selecting the operation parameters carefully, stable narrowband emission for both wavelengths is obtained. Resistors serving as heaters implemented next to the DBR gratings allow for wavelength adjustment and a tuning of the spectral distance. At an optical output power of 100 mW, the spectral distance can be shifted from 0 to 1.55 nm (0–0.76 THz) for the former device or from 1.00 to 3.15 nm (0.49–1.54 THz) for the latter device, respectively. This makes the Y-branch DBR diode laser particularly interesting for the generation of THz beat-note signals, needed to generate THz radiation via photo-mixing.

1.645 µm Er:YAG single-mode dual-wavelength emitter for CH4 differential absorption lidar.

We present a hybrid fiber/bulk laser source at 1.645 µm designed for methane (CH4) monitoring using differential absorption lidar (DIAL) measurements in the atmosphere. The emitter is also suited for coherent wind Doppler lidar. It relies on a Q-switched Er:YAG ring cavity pumped by erbium fiber lasers at 1532 nm. The pulsed laser is sequentially seeded by two fiber-coupled CW distributed feedback (DFB) laser diodes in the center of the CH4 line multiplet at 1645.55 nm (ON wavelength) and out of at 1645.30 nm (OFF wavelength). Despite a gain difference in the crystal between the ON and OFF wavelengths, pulses with equal energies and durations (9 mJ/300 ns) are obtained at a rate of 1 kHz. The spectral stability and purity properties in the dual-wavelength operating regime are presented.

Switchable Dual-Wavelength Fiber Laser with Narrow-Linewidth Output Based on Parity-Time Symmetry System and the Cascaded FBG

In this paper, a dual-wavelength narrow-linewidth fiber laser based on parity-time (PT) symmetry theory is proposed and experimentally demonstrated. The PT-symmetric filter system consists of two optical couplers (OCs), four polarization controllers (PCs), a polarization beam splitter (PBS), and cascaded fiber Bragg gratings (FBGs), enabling stable switchable dual-wavelength output and single longitudinal-mode (SLM) operation. The realization of single-frequency oscillation requires precise tuning of the PCs to match gain, loss, and coupling coefficients to ensure that the PT-broken phase occurs. During single-wavelength operation at 1548.71 nm (λ1) over a 60-min period, power and wavelength fluctuations were observed to be 0.94 dB and 0.01 nm, respectively, while for the other wavelength at 1550.91 nm (λ2), fluctuations were measured at 0.76 dB and 0.01 nm. The linewidths of each wavelength were 1.01 kHz and 0.89 kHz, with a relative intensity noise (RIN) lower than −117 dB/Hz. Under dual-wavelength operation, the maximum wavelength fluctuations for λ1 and λ2 were 0.03 nm and 0.01 nm, respectively, with maximum power fluctuations of 3.23 dB and 2.38 dB. The SLM laser source is suitable for applications in long-distance fiber-optic sensing and coherent LiDAR detection.

Diode-pumped dual-wavelength Nd:YVO4/Nd:CTGAS laser

LD pumped dual-wavelength lasers have great application potential in scientific and technical scopes. In this paper, we reported a novel dual-wavelength laser by combining Nd:YVO4 and Nd:CTGAS crystals. For 1064 nm and 1068 nm dual-wavelength laser operation, the maximum continuous-wave output power was 929 mW, corresponding to an optical conversion efficiency of 38.7 %. With a Cr:YAG crystal as the saturable absorber, the maximum passively Q-switched output power was 239 mW, giving a shortest pulse width of 20.8 ns and an optical conversion efficiency of 17.1 %.

Optical properties of La2MgSnO6: Eu3+/Mn4+ double-perovskite phosphors for multifunctional applications

A series of Eu3+/Mn4+ doped La2MgSnO6 double-perovskite phosphors were successfully synthesized by solid-state method. The crystal structure, optical properties, and temperature sensitivity of the phosphors were investigated systematically. Under excitation at 310 and 394 nm, the La2MgSnO6: Eu3+, Mn4+ phosphor exhibits intense red emission of Mn4+ (2Eg→4A2g) and orange-red emission of Eu3+ (5D0→7F2). Within the temperature range of 298–473 K, Eu3+ exhibits excellent thermal stability, whereas the Mn4+ shows significant thermal quenching behavior. A luminescence thermometer for dual-wavelength operation with high sensitivity was designed based on the fluorescence intensity ratio (FIR) method. The value of maximum relative sensitivity (Sr) was calculated as 1.58 % K−1 at 423 K. Particularly, the wavelength-dependent of La2MgSnO6: Eu3+, Mn4+ phosphor was investigated over a range of 270–340 nm, revealing promising potential with a remarkably high maximum wavelength sensitivity of 18.2 % nm−1 at 300 nm. Subsequently, a prototype LED device was fabricated by integrating the La2MgSnO6: Eu3+, Mn4+ phosphors and a near-UV LED chip, demonstrating significant spectral overlap with the absorption curves of plant pigments. These results suggest that the La2MgSnO6: Eu3+, Mn4+ multifunctional phosphor has promising applications in optical thermometry, wavelength detection, and promoting plant growth.

Spectral programmable mid-infrared optical parametric oscillator

A spectral programmable, continuous-wave mid-infrared (MIR) optical parametric oscillator (OPO), enabled by a self-developed high-power spectral tailorable fiber laser, was proposed and realized. While operating at a single-wavelength, the maximum idler power reached 5.53 W at 3028 nm, with a corresponding pump-to-idler conversion efficiency of 14.7%. The wavelength number switchable output was available from one to three. The single idler was tunable in a range of 528 nm (2852–3380 nm). In a dual-wavelength operation, the interval between two idlers could be flexibly tuned for 470 nm (53–523 nm), and the intensity of each channel was controllable. Triple-wavelength idler emission was realized, meanwhile exhibiting spectral custom-tailored characteristics. Furthermore, we balanced the parametric gain through the pre-modulating broadband multi-peak pump spectra, enabling a 10 dB bandwidth adjustment of the idler emission from 20 to 125 nm. This versatile mid-infrared laser, simultaneously featuring wide tuning, multi-wavelength operation, and broad bandwidth manipulation, has great application potential in composition detection, terahertz generation, and speckle-free imaging.

Sign reversal of visible to UV photocurrent in core–shell n-InGaN/p-GaN nanowire photodetectors

We demonstrate the change of the sign from negative to positive of the self-powered photovoltaic photocurrent in core–shell n-InGaN/p-GaN nanowire heterojunctions within the visible to UV wavelength range. Such dual-polarity photodetectors are of broad interest to provide extended functionalities for optoelectronic devices, starting with dual-wavelength photodetectors. The physics of the photocurrent sign reversal is understood by a well-balanced selective absorption and photocarrier generation, photocarrier transfer, and thermal excitation paths in the core–shell n-InGaN/p-GaN nanowire functional absorber with different bandgap energies and opposite inner- and surface energy band bendings. The basic dual-wavelength photodetector operation parameters are given.

Continuous-Wave Self-Raman Vanadate Lasers Generating Versatile Visible Wavelengths

In this review, the developments of efficient high-power CW orange-lime-green lasers by using intracavity stimulated Raman Scattering (SRS) in Nd-doped vanadate lasers are systematically discussed. The overall properties of the spontaneous Raman spectra in Nd:YVO4 and Nd:GdVO4 crystals are overviewed. The critical phase matchings of using the lithium triborate (LBO) crystals for sum frequency generation (SFG) and second harmonic generation (SHG) are thoroughly reviewed. We make a detailed review for achieving the individual green-lime-orange emissions from the self-Raman Nd:YVO4 and Nd:GdVO4 lasers with LBO crystals. The following is to review the dual-wavelength operations of the lime-green and orange-green lasers. Finally, the procedure for generating the triple-wavelength operation of orange-lime-green simultaneous emissions is completely described. The present review is expected to be useful for developing compact, efficient, high-power CW visible lasers for applications including medical treatment, biology, spectroscopy, and remote sensing.

Dual-wavelength mid-infrared laser operation at 2.8 μm and 3.6 μm in Er3+ doped fluoride fiber

This study presents a pioneering experimental demonstration of dual-wavelength laser operation at 2.8 μm and 3.6 μm in an Er3+-doped ZrF4-BaF2-YF3-AlF3 double-cladding fluoride glass fiber, fabricated in-house. The achievement is realized through the implementation of a novel dual-wavelength pumping scheme utilizing 980 nm and 1150 nm lasers. This innovative scheme enables the excitation of the lower energy level of the 2.8 μm laser transition (4I11/2) to the upper energy level of the 3.6 μm transition (4F9/2) via an excited state absorption process, resulting in simultaneous emission at 2.8 μm and 3.6 μm. The maximum laser output powers at 2.8 μm and 3.6 μm are measured at 0.96 W and 0.32 W, respectively. This groundbreaking work marks the first experimental realization of dual-wavelength laser operation at 2.8 + 3.6 μm in Er3+-doped fluoride fiber, contributing significantly to the advancement of laser technology in this spectral range.

Mid-infrared dual-wavelength operation of a diode-pumped Tm:YScO3 laser

A simultaneous continuous-wave (CW) dual-wavelength Tm:YScO3 laser using a single birefringent filter (BF) was experimentally demonstrated. We calculated the wavelength-dependent loss property of the BF. By adjusting the BF plate, the spectral intensity ratio of the generated wavelengths can be maintained to be 1:1. A simultaneous CW dual-wavelength Tm:YScO3 laser at 1948 and 2098 nm is experimentally realized. For a pump power of 15.2 W, mid-infrared dual-wavelength laser radiation at 1948 and 2098 nm and 5.9 W of output power using a 5% output coupler could be generated. A slope efficiency of 42.2% with respect to the absorbed pump power and optical-to-optical efficiency of 38.8% for the highest-incident pump power were obtained. To our knowledge, this is the first study that has realized the dual-wavelength in a Tm:YScO3 laser.

Orthogonally polarized dual-wavelength Pr:LiGdF4 lasers in the green range

We demonstrate a diode-pumped continuous-wave tunable orthogonally polarized dual-wavelength Pr:LiGdF4 laser in the green range. The excellent mode matching between the pump and green lasers is achieved under the consideration of thermally induced effects. We analyze the condition of gain-to-loss balance via an uncoated glass etalon to achieve the dual-wavelength operation. At an absorbed pump power of 17.9 W, a dual-wavelength laser operating at 546 nm in π-polarization and 538 nm in σ-polarization with 1.72 W of average output power was obtained. Orthogonally polarized dual-wavelength laser operation at shorter- or longer-wavelength pairs with lower average output power could also be realized for other output-coupling transmissions. To the best of our knowledge, this is the first work realizing orthogonally polarized dual-wavelength operation in Pr:LiGdF4 lasers.

Dual-wavelength synchronously mode-locked Cr:LiSAF laser with a tunable beating frequency and a central wavelength.

We demonstrate a versatile dual-wavelength synchronous mode-locking of a diode-pumped Cr:LiSAF laser for the first time, to our knowledge. A two-color mode-locked operation is achieved by using intracavity birefringent filters (BRFs) or etalons as frequency-selective elements. Using filters with different thicknesses and hence different free spectral ranges (FSRs), wavelength separation in two-color mode-locking could be selected between 1 and 9 nm, with corresponding beating frequencies in the 0.4-3.5 THz range. Moreover, the central wavelength of the two-color output could be tuned smoothly between 840 and 875 nm, only limited by the bandwidth of the semiconductor saturable absorber mirror (SESAM) used for mode-locking. The method, which enables easy adjustment of the central wavelength and beating frequency of a dual-wavelength operation, is suitable for use in other laser gain media as well.

Generation of a switchable and tunable rectangular pulse and multi-pulse with different peak powers at the L-band

A novel, to our knowledge, L-band erbium-doped fiber laser, utilizing a nonlinear optical loop mirror (NOLM) as a mode-locker, is presented in this study. Through precise adjustments of the polarization controllers (PCs), the laser achieves the generation of rectangular pulses with distinct single wavelengths, λ1=1593nm and λ2=1571nm, as well as dual-wavelength operation. The laser’s operational mode can extend further to include harmonic mode-locking (HML). Furthermore, the investigation reveals the emergence of trapezoidal pulses and low-peak-power rectangular pulses within proximity of the conventional rectangular pulses. Notably, the evolutions of these low-peak-power pulses with the pump power also adhere to the peak power clamping (PPC) effect. Remarkably, the relative positioning of these pulses remains consistent across varying pump power levels or harmonic orders. Intriguingly, the evolution of the trapezoidal pulse with respect to pump power stands in stark contrast to that of the h-shaped pulse.

1.94 & 2.04 µm dual-band four-wavelength-switchable single-frequency narrow linewidth fiber laser using a novel fs-laser direct-written polarization-dependent four-channel filter

We present a dual-band four-wavelength-switchable single-frequency thulium-holmium co-doped fiber laser (THDFL) utilizing a novel band-switchable polarization-dependent four-channel filter (BS-PDFCF). The filter incorporates two high-birefringence fiber Bragg gratings (HB-FBGs) and an electrical-controlled optical switch (EC-OS). Specifically designed for operation in the 1.94 μm and 2.04 μm bands, two HB-FBGs are fabricated using femtosecond (fs) laser direct-writing technology in two segments of polarization-maintaining fibers via a point-by-point method. Each HB-FBG features two narrow-band reflection channels with perpendicular polarization directions. The EC-OS switches the operation band of the BS-PDFCF. A 1.2 m long dynamic ultra-narrow-band filter is employed in the THDFL to achieve single-longitudinal-mode oscillation. The THDFL achieves exceptional output performance, including four single-wavelength and two dual-wavelength operations, spectral wavelength and power fluctuations of ≤0.012 nm and ≤0.386 dB, respectively, OSNRs of >76 dB, RINs of ≤−142.48 dB/Hz@≥5 MHz, linewidths of ≤3.59 kHz@1.94 μm band and ≤5.46 kHz@2.04 μm band, and output power fluctuations of ≤0.109 dB in a measurement time span of 30 min.

Nonlinear optical response of strain-mediated gallium arsenide microwire in the near-infrared region.

Gallium arsenide (GaAs) semiconductor wires have emerged as potent candidates for nonlinear optical devices, necessitating bandgap engineering for an expanded operational wavelength range. We report the successful growth of strain-mediated GaAs microwires (MWs) with an average diameter of 1.1 μm. The axial tensile strain in these wires, as measured by X-ray diffraction and Raman scattering, ranges from 1.61 % to 1.95 % and from 1.44 % to 2.03 %, respectively. This strain condition significantly reduces the bandgap of GaAs MWs compared to bulk GaAs, enabling a response wavelength extension up to 1.1 μm. Open aperture Z-scan measurements reveal a nonlinear absorption coefficient of -15.9 cm/MW and a third-order magnetic susceptibility of -2.8×10-8 esu at 800 nm for these MWs. I-scan measurements further show that the GaAs saturable absorber has a modulation depth of 7.9 % and a nonsaturation loss of 3.3 % at 1050 nm. In laser applications, GaAs MWs have been effectively used as saturable absorbers for achieving Q-switched and dual-wavelength synchronous mode-locking operations in Yb-bulk lasers. These results not only offer new insights into the use of large diameter semiconductor wires but also expand the potential for applications requiring bandgap tuning.

Dual-wavelength metalens enables Epi-fluorescence detection from single molecules

Single molecule fluorescence spectroscopy is at the heart of molecular biophysics research and the most sensitive biosensing assays. The growing demand for precision medicine and environmental monitoring requires the creation of miniaturized and portable sensing platforms. However, the need for highly sophisticated objective lenses has precluded the development of single molecule detection systems for truly portable devices. Here, we propose a dielectric metalens device of submicrometer thickness to excite and collect light from fluorescent molecules instead of an objective lens. The high numerical aperture, high focusing efficiency, and dual-wavelength operation of the metalens enable the implementation of fluorescence correlation spectroscopy with a single Alexa 647 molecule in the focal volume. Moreover, the metalens enables real-time monitoring of individual fluorescent nanoparticle transitions and identification of hydrodynamic diameters ranging from a few to hundreds of nanometers. This advancement in sensitivity extends the application of the metalens technology to ultracompact single-molecule sensors.

Machine Learning Based Automatic Mode-Locking of a Dual-Wavelength Soliton Fiber Laser

Recent years have witnessed growing research interest in dual-wavelength mode-locked fiber lasers for their pivotal role in diverse applications and the exploration of nonlinear dynamics. Despite notable progress in their development, achieving reliable mode-locked dual-wavelength operation typically necessitates intricate manual adjustments of the cavity’s polarization components. In this article, we present the realization of automatic mode-locking in a dual-wavelength soliton fiber laser. To provide guidance for the algorithm design, we systematically investigated the impact of polarization configurations and initial states on the laser’s operation through numerical simulations and linear scan experiments. The results indicate that operational regimes can be finely adjusted around the wave plate position supporting the mode-locked dual-wavelength solution. Furthermore, the laser exhibits multiple stable states at the mode-locked dual-wavelength point, with critical dependence on the initial conditions. Accordingly, we developed a two-stage genetic algorithm that was demonstrated to be effective for realizing automatic dual-wavelength mode-locking. To further improve the performance of the algorithm, a feedforward neural network was trained and integrated into the algorithm, enabling accurate identification of the dual-wavelength states. This study provides valuable insights into understanding how polarization configurations and initial conditions impact the operational regimes of dual-wavelength mode-locked fiber lasers. The algorithm developed can be extended to optimize other systems with multiple stable states supported at the same parameter point.

Dual-wavelength Nd:CALGO laser based on differential loss of birefringent filter

Continuous-wave dual-wavelength (DW) operation of an a-cut Nd:CALGO (Nd:CaGdAlO4) laser around ∼1.08 μm was demonstrated using a single plate quartz birefringent filter (BRF) with an on-surface optical axis. A wide range of wavelength separations between the two laser lines ranging from sub-nm up to 10 nm was observed with controllable intensity ratios. A new regime of operation of DW laser was also identified where one of the oscillating spectral lines was in the rejection band of the filter. This is in sharp contrast with typical operation of DW lasers with BRF where wavelength separation was limited either to the free spectral range or to the linewidth of a single transmission peak of the used filter. This was enabled by differential loss introduced by a single transmission peak of the BRF. Using this mechanism, generation of a large number of laser wavelength pairs became possible.