Dual-wavelength Mode Research Articles

Modularized orthogonal-polarization dual-wavelength microcavity based on light curing gradient-composite multi-dimensional meta-filters

The utilization of a stable orthogonally polarized laser can promote the head-mounted miniature fluorescence microscopy into a powerful tool for real-time intracerebral three-dimensional observation. However, the realization of wearable dual-wavelength polarized light sources has remained an attractive challenge to break through the spatial constraints of transmitting fiber-optic paths. Herein, we have proposed a modularized orthogonal-polarization dual-wavelength microcavity enabled by high reflectance (HR) and output-coupled (OC) gradient-composite multi-dimensional meta-filters, where these printable meta-filters are composed of two nanocomposite metasurfaces (NCMSs). Specifically, based on the Mie surface lattice resonances (Mie-SLR), the designed NCMSs can realize tunable multi-parameter filtering at diverse dimensions (wavelength, polarization, and incident angle) by optimizing the lattice distances. By virtue of the sandwich-type gradient-composite configuration, the proposed meta-filters have integrated orthogonal-polarization filtering of two independent NCMS at 1064 nm and 1320 nm. The stability of the multi-dimensional filtering capabilities of the proposed meta-filters has been enhanced by optimizing the thickness of the resin bonding layers in the gradient-composite structure. Without other nonlinear modulation, orthogonal-polarization dual-wavelength mode oscillations can be developed only by passive multi-dimensional filtering of HR and OC meta-filters in the microcavity. These proposed new-generation gradient-composite multi-dimensional meta-filters will provide novel strategies toward high-robust miniature light sources for wearable optical devices.

Dual-wavelength mode-locked erbium fiber laser utilizing a Ge-PCF saturable absorber

In this work, we demonstrate a mode-locked erbium-doped fiber laser (EDFL) based on germanium-core doped photonic crystal fiber (Ge-PCF) as a passive saturable absorber (SA). The proposed SA was incorporated inside the PCF core during the manufacturing process. The short length of the proposed high nonlinear fiber can achieve a stable mode-locked pulse by controlling the fiber and collapsing lengths. The proposed Ge-PCF has been integrated into an erbium-doped fiber ring laser to establish the desired ultrashort pulse with the merits of a short interaction length (<3cm), enhanced damage threshold, environmental robustness, ease of manufacture, and suitable mass production. The obtained output pulses at FWHM have a pulse width of 800 ps and a repetition rate of ∼19MHz. Furthermore, the EDFL based on Ge-PCF achieved a dual-wavelength output spectrum with narrow bandwidths centered at 1557.27 and 1558.81 nm. The short-pulse capabilities of the proposed fiber laser make it highly suitable for a wide range of photonic applications.

Flexible tunable microwave photonic filter with a dual ultra-narrow passband based on a dual-wavelength Brillouin laser.

This article presents a flexibly tunable microwave photonic filter (MPF) with a dual ultra-narrow passband based on a dual-wavelength and narrow linewidth Brillouin laser. The dual passband of the filter not only exhibits ultra-high frequency selectivity but also allows for flexible and simultaneous tuning of the center frequency and interval of the passbands. In the proposed scheme, the core optical processor of the MPF consists of a dual-ring Brillouin laser resonator, which is composed of a 100-meter main fiber ring cascaded with a 10-meter secondary fiber ring. A dual-tone pump is generated through carrier-suppressed dual sideband modulation and injected into the dual-ring resonator to excite two Brillouin gains, which resonate separately in the dual-ring resonant cavity to generate a dual-wavelength single longitudinal mode Brillouin laser for processing optical RF signals. By selectively amplifying the modulated sideband signal through narrow linewidth Brillouin laser gain, the ultra-narrow dual passband are ultimately demodulated. The resulting dual filtering passband exhibits unparalleled sub-kHz bandwidth and flexible tuning capability. Experimental results demonstrate that the MPF proposed in this paper achieves an ultra-narrow dual passband of 83 Hz with a maximum side-mode suppression ratio of over 28 dB. Within the testing range of vector network analysis, the maximum tuning range of the center frequency is 20 GHz, and the passband interval can be freely tuned from 2-18 GHz. These results highlight the MPF's ability to concurrently filter dual-channel signals with high precision and its significant potential application value in ultrafine microwave frequency spectrum resolution and processing fields, such as instantaneous frequency measurement and microwave photonic sensing.

Wavelength-tunable mode-locked fiber laser based on a bending strain-controlled filter

Wavelength-tunable mode-locked fiber lasers are highly versatile and find applications in pump–probe measurement, optical communications, optical parametric oscillation, among others. Herein, we introduce a novel approach for tuning carbon nanotube-based passively mode-locked fiber laser using a bending-based mechanism. Our method involves a bending strain controlled multimode interference all-fiber filter. This filter consists of a hybrid structure built from a cascaded seven-core fiber (SCF)-twin-hole twin-core fiber (THDCF)-SCF. It achieves a continuous wavelength tuning range of 25 nm from 1558 nm to 1583 nm with a tuning efficiency of −3.38 nm/m−1. By increasing the pump power, the dual-wavelength locked modes are also achieved at specific curvature. Owing to advantages of simple structure, low cost, and high bending sensitivity, our tunable filter shows promise for efficient wavelength tuning in ultrafast fiber laser.

Passively mode-locked fiber lasers dynamic behavior by multimode fiber polarization controller

Passively mode locked fiber lasers (PML-FLs) can produce a variety of phenomena due to the nonlinear effects. With the introduction of the nonlinear polarization rotation (NPR) and a multimode fiber polarization controller (MMF-PC), we observed nonlinear effects in our erbium-doped mode-locked fiber laser, such as the evolution of the soliton bunch to dissipates soliton resonance (DSR) pulses. In the evolution of the soliton bunch to DSR pulses, the soliton square bunch and the multi-longitudinal mode oscillation also appeared in our experiment with the increasing the pump power. To illustrate the importance of MMF-PC, a control experiment is conducted by replacing the MMF-PC with a single mode fiber PC (SMF-PC). The experimental results indicate that the MMF-PC are crucial for the evolution of soliton pairs to DSR pulses and the generation of soliton pairs. The NPR mode-locked structure is used to achieve dual-wavelength filtering, its strength-dependent non-uniform loss can effectively suppress the mode competition in the gain fibers. The MMF-PC in the mode-locked structure adds a polarization burned hole effect inside the resonator. We achieved dual-wavelength mode locking by adjusting the PC to control the birefringence and loss in the resonator.

Single-Chip Switchable Dual-Wavelength Vertical External-Cavity Surface-Emitting Laser

Dual-wavelength output devices have a wide range of applications in mid-infrared band difference frequency generation, anti-interference lidar, dual-wavelength holographic interferometry, and other applications. Vertical external cavity surface-emitting lasers (VECSELs) are a type of semiconductor laser that can achieve single-chip dual-wavelength output by designing the chip structure. In this paper, we present a single-chip VECSEL that can switch between dual-wavelength and single-wavelength output modes. The VECSEL can simultaneously emit coaxial laser beams at 967 nm and 1013 nm, with a wavelength spacing of about 45 nm. The degree of mismatch between the gain peaks of the two quantum wells in the gain chip and the corresponding cavity modes is different. By adjusting the pump power, the temperature of the active region can be changed, which alters the matching relationship between the gain peaks and the cavity modes and controls the output mode of the VECSEL. The dual-wavelength output mode maintains a stable wavelength spacing at different operating temperatures. The laser output mode can be switched between single-wavelength and dual-wavelength, and the beam divergence angle is less than 8°. The dual-wavelength output power can exceed 400 mW, and the long-wavelength output power can reach up to 700 mW.

Thulium-doped multi-wavelength and mode-locked fiber laser based on multimode interference

We demonstrate a thulium-doped multi-wavelength mode-locked fiber laser with a single-mode-gradient refractive index multimode-single-mode fiber (SMF-GIMF-SMF) structure which acts as both a filter and a saturable absorber. Based on the multimode interference effect (MMI) filtering, wavelength-tunable operation with a tunable range of up to 15.69 nm can be obtained in the fiber laser. Moreover, tunable multi-wavelength continuous wave (CW) laser output of up to four wavelengths can be obtained by properly adjusting the pump power and polarization controller. Owing to mode interference and phase modulation, the SMS structure also plays a role as a saturable absorber (SA), which leads to the multi-wavelength output of the fiber laser accompanied by mode-locking. The state of dual-wavelength mode locking and the state of coexistence of continuous wave and mode-locking pulses at different wavelengths were observed in the laser. These results suggest that the all-fiber SMF-GIMF-SMF structure is a key device for fiber lasers to achieve multi-wavelength and mode-locked pulse output, which may find potential applications in nonlinear microscopy, biodegradable material processing, and terahertz spectroscopy.

Widely tunable continuous-wave visible and mid-infrared light generation based on a dual-wavelength switchable and tunable random Raman fiber laser

Nonlinear frequency conversion of wavelength agile and high-power random fiber lasers can provide a promising way to generate continuous-wave (CW) visible and mid-infrared (MIR) light with unique properties such as the continuous modeless spectrum, low temporal/spatial coherence, and high temporal stability. Here, we report a dual-wavelength switchable and tunable random Raman fiber laser (RRFL) based on a phosphosilicate fiber that has two Raman gain peaks for the first time and demonstrate its superior capability to generate widely tunable CW visible and mid-infrared light via nonlinear frequency conversions. By using the combination of a tunable pump and two tunable gratings in Littrow configuration that can provide separated point feedback for the two Stokes wavelengths corresponding to silica- and phosphorus-related Raman peaks, the spectrum of an RRFL can be flexibly manipulated for the aim of nonlinear frequency conversions, including single-wavelength tunable emission at the 1.1 μm or 1.2 μm band for second-harmonic generation (SHG), dual-wavelength simultaneously tunable emission at the 1.1 μm and 1.2 μm bands for the sum-frequency generation (SFG), and dual-wavelength separation tunable emission for difference-frequency generation (DFG). As a result, with the combination of SHG and SFG in a periodically poled lithium niobate crystal array, we experimentally demonstrate the broadest tuning range (560–630 nm) of visible light generated from an RRFL, to the best of our knowledge. The tunable MIR light in the range of 10.7–12.3 μm is also demonstrated through DFG of an RRFL operating in separation tunable dual-wavelength emission mode in a BaGa4Se7 (BGSe) crystal, which is the first realization of >10 μm CW DFG in the BGSe crystal. We believe the developed dual-wavelength switchable and tunable RRFL can provide a new compact, robust, and cost-effective platform to realize broadly tunable light in both the visible and MIR regions, which can also find potential applications in imaging, sensing, and temporal ghost imaging in various spectral bands.

946/1030 nm Dual-Wavelength Laguerre-Gaussian (LG01) Mode Vortex Laser Based on Intracavity Cascade Pumped Resonator

In this paper, the 946/1030 nm dual-wavelength LG01 mode vortex laser is obtained by applying the intracavity cascade pumped structure and annular-beam end-pumped method, an innovative and pioneering exploration of the transverse mode of the dual-wavelength laser. First, we demonstrate the oscillation characteristic theoretical model of the dual-wavelength LG01 mode laser, considering the reabsorption effect. Then the length of the laser crystal and the transmittance of the output mirror are simulated and analyzed, respectively, related to the oscillation characteristics of the 946 and 1030 nm LG01 mode vortex lasers. Finally, a 946/1030 nm LG01 mode vortex laser with the same handedness is successfully achieved in our experiment. With 20 W of annular-beam pump power, the output power of 946 and 1030 nm LG01 mode vortex lasers is 0.404 and 0.510 W, the slope efficiency is 3.6% and 6.2%, and the total optical-optical conversion efficiency is 4.6%. At the maximum output power, the fluctuations of output power within 1 h are 4.02% and 4.23%, and the beam quality factors M2 are 2.32 and 2.27, respectively, for 946 and 1030 nm LG01 mode vortex lasers. The wavefront phase exp(iϕ) of the 946/1030 nm dual-wavelength is also proved by the self-interference method.

Few-mode erbium-doped fiber amplifier based on a multi-inclusions core optical fiber.

In this work, we demonstrate and evaluate a new design of micro-structured core erbium-doped few-mode fiber to be used as optical amplifier in the context of mode-division multiplexing. This concept is proposed so as to better control the distribution of the Er3+ ions in the core area, thus permitting to adjust the overall differential modal gains between the different signal modes. The design presented here consists of 19 erbium-doped inclusions embedded in a pedestal geometry guiding 10 modes in the C-band. It has been optimized numerically so as to reach the equalized amplification of all the signal modes. The fiber has been realized and combined with custom-made dual-wavelength mode multiplexers based on multi-plane light conversion to shape the signal and pump beams. Amplification properties have finally been evaluated experimentally.

Effective linewidth compression of a single-longitudinal-mode fiber laser with randomly distributed high scattering centers in the fiber induced by femtosecond laser pulses.

Femtosecond lasers can be used to create many functional devices in silica optical fibers with high designability. In this work, a femtosecond laser-induced high scattering fiber (HSF) with randomly distributed high scattering centers is used to effectively compress the linewidth of a fiber laser for the first time. A dual-wavelength, single-longitudinal-mode (SLM) erbium-doped fiber laser (EDFL) is constructed for the demonstration, which is capable of switching among two single-wavelength operations and one dual-wavelength operation. We find that the delayed self-heterodyne beating linewidth of the laser can be reduced from >1 kHz to <150 Hz when the length of the HSF in the laser cavity increases from 0 m to 20 m. We also find that the intrinsic Lorentzian linewidth of the laser can be compressed to several Hz using the HSF. The efficiency and effectiveness of linewidth reduction are also validated for the case that the laser operates in simultaneous dual-wavelength lasing mode. In addition to the linewidth compression, the EDFL shows outstanding overall performance after the HSF is incorporated. In particular, the optical spectrum and SLM lasing state are stable over long periods of time. The relative intensity noise is as low as <-150 dB/Hz@>3 MHz, which is very close to the shot noise limit. The optical signal-to-noise ratios of >85 dB for single-wavelength operation and >83 dB for dual-wavelength operation are unprecedented over numerous SLM fiber lasers reported previously. This novel method for laser linewidth reduction is applicable across gain-medium-type fiber lasers, which enables low-cost, high-performance, ultra-narrow linewidth fiber laser sources for many applications.

Orthogonally polarized dual-wavelength single longitudinal mode Pr:YLF laser at 607 nm and 604 nm

We demonstrate a diode-pumped orthogonally polarized dual-wavelength single-longitudinal-mode Pr:YLF laser output at 607 nm and 604 nm by using combined F-P etalons. The experimental results show that switchable single and dual-wavelength single-longitudinal-mode laser output can be realized by selectively combining the F-P etalons with 0.3 mm and 1 mm thickness. We obtained the maximum output power of the orthogonally polarized dual-wavelength single-longitudinal-mode laser at π-polarized 607 nm and σ-polarized 604 nm is reaches 79 mW, corresponding to a slope efficiency of 6.2%. The measured spectral line-widths are 115.4 MHz and 133.3 MHz respectively. The maximum output power of the single wavelength single-longitudinal-mode laser at 607 nm and 604 nm are 201 mW and 81 mW respectively, corresponding to a slope efficiency of 11.5% and 6%. The measured spectral line-widths are 52.3 MHz and 111.3 MHz respectively. To the best of our knowledge, it is the first time to investigate the orthogonally polarized dual-wavelength single-longitudinal-mode CW Pr:YLF laser.

Polarization-maintaining all-fiber tunable mode-locked laser based on a thermally controlled Lyot filter.

We propose and demonstrate for the first time, to the best of our knowledge, a thermally controlled all polarization-maintaining (PM) fiber Lyot filter. This filter is implemented in an all-PM mode-locked fiber laser to achieve wavelength tunability. When operating in the single-wavelength tunable mode, the center wavelength can be tuned across a range from 1546 nm to 1571 nm. Furthermore, the laser can also operate in a dual-wavelength mode with center wavelengths at 1545 nm and 1571 nm. The temperature sensitivity achieved in our all-PM fiber Lyot filter is 0.602 nm/°C, which is over 46 times higher than other fiber-based filters such as a fiber Bragg grating filter (0.013 nm/°C). This highly stable and versatile wavelength-tunable all-PM fiber mode-locked laser is a promising source for various applications requiring wavelength tunability and/or dual-wavelength output, such as coherent Raman microscopy and dual-comb spectroscopy.

Dual-wavelength hybrid Tamm plasmonic laser.

Miniature lasers emitting dual-wavelength modes have diverse applications alongside the more explored single-mode counterparts. However, having dual-wavelength modes originating from a plasmonic-photonic hybrid laser is still a relatively new area for research. Compared to the amount of literature devoted to the physics of such hybrid cavities, only a few have analyzed their role in lasing applications. Notably, the role of hybrid cavities in dual-wavelength lasing is still unexplored. In this work, the properties of one-dimensional distributed Bragg reflectors and thin metal nanohole arrays come together to create a hybrid dual-mode plasmonic laser. The similar energy distribution characteristics of photonic and plasmonic lasers make hybrid structures a viable choice for efficient dual-mode lasing. In this work, the lasing cavity simultaneously excites photonic and Tamm plasmonic modes to generate dual-mode lasing. Consequently, the proposed laser shows high emission output with narrow linewidth and a clear and tunable mode separation.

Single-fiber optical tweezers for particle trapping and axial reciprocating motion using dual wavelength and dual mode

The manipulation of particles is of great significance in the fields of biology, physics, and chemistry. We injected laser sources with wavelengths of 650 nm and 980 nm in a single-mode fiber, so that the LP01 mode beam and the LP11 mode beam in this single-mode fiber were excited separately. Then we constructed a flat-facet fiber probe and built a simulation model for it, and we used it to carry out particle trapping experiments. Experimental results show that this fiber probe enables two laser beams to achieve focus separation after passing through it. It can achieve stable trap at two focal points separately. In addition, it can achieve the axial reciprocating transfer of particles between two focal points without moving the fiber. The experimental results are supported by our numerical simulations. This structure makes it possible for multi-wavelength excitation and the use of multi-mode beams for particle manipulation.

(INVITED)A diverse set of soliton molecules generation in a passively mode-locked Er-doped fiber laser with a saturable absorber of WSe2 nanofilm

WSe2, an intriguing transition metal dichalcogenides (TMDs) material with high-performance electronic and optoelectronics property, is emerging as next-generation photoelectronic devices. In this contribution, by applying WSe2 nanofilm as a saturable absorber in an Er-doped fiber laser, versatile mode-locked operations of conventional soliton, soliton molecules and dual-wavelength mode locked state can be experimentally observed. By properly setting the state of the polarization controller and pump power, the phase difference and pulse separation of soliton molecules can be adjusted. The soliton molecule with four steady phase difference (0, ±π/2, π) are realized in the fiber laser with TMDs based SA for the first time, to our knowledge. Meanwhile, a novel dual-wavelength mode-locked state with a soliton singlet and a soliton molecule is also obtained. Experiments results show that WSe2 is a suitable SA for vector soliton and soliton molecules generation.

Sinusoidal Spectral Filtering-Based Soliton Dynamics in Mode-Locked Fiber Lasers

Sinusoidal spectral filtering (SSF) plays an essential role in dual- and multi-wavelength operations in mode-locked fiber lasers. However, the impact of SSF on the underlying soliton dynamics has not been systematically revealed so far. Herein, we investigate numerically the SSF-based soliton dynamics in mode-locked fiber lasers. SSF could facilitate the formation of dual-wavelength mode locking, and the generation of dual-comb solitons with slightly different group velocities. Pulse shaping based on SSF and gain filtering leads to the non-monotonic relationship between both solitons' group velocity difference and the cavity gain. In addition, dual-comb soliton mode locking exhibits threshold feature and multi-pulse instability to soliton annihilation and diverse soliton coexistences. Our investigations could shade new light on the SSF-based soliton dynamics and might bring new insights into the laser design and applications.

Switchable and tunable thulium-doped fiber laser based on mode interference filter

A cladding pumped thulium-doped fiber laser with tunable and switchable output was demonstrated. The single-mode-multimode-single-mode (SMS) fiber filters with different lengths of multimode fiber were fabricated and the tunability of the laser by axial strain with a sensitivity of ∼ 2.4 pm/με was demonstrated experimentally. Single-wavelength output with an optical signal-to-noise ratio (OSNR) of up to 70 dB and a small tuning range of 2.76 nm was obtained. The fluctuations of the center wavelength and output power within 60 min were less than 0.04 nm and 0.27 dB, respectively, and the tuning sensitivity was ∼ 2.3 pm/με. When the laser was operated in the dual-wavelength output mode, the OSNR reached 60 dB and the fluctuation of the output power was less than 1.53 dB within an observation time of 60 min. Furthermore, the output power was scaled up to 308 mW by changing the output coupling ratio and the different samples of SMS fiber filter were also applied in the fiber laser cavity to obtain different lasing channels. The proposed fiber laser is suitable for applications in sensing and communication systems.

Dual-wavelength Rapid Excitation Raman Difference Spectroscopy System for Direct Detection of Ethanol in Illegal Beverages

A dual-wavelength rapid excitation Raman difference spectroscopy (DWRERDS) system for separation of Raman signals from background interference was developed. In the DWRERDS system, a dual-wavelength diode laser at 784.59 and 785.22 nm with volume Bragg gratings was used as the excitation light source. For each laser line, optical power could reach as high as 550 mW. Under dual-wavelength excitation mode, the DWRERDS system could switch each laser instantaneously and the excitation time of each laser was as short as 1 s. Two Raman spectra were measured with slightly shifted excitation wavelengths and subtracted from each other, resulting in a background-free difference spectrum. The DWRERDS system was applied to complex matrix background suppression, which could improve a very good signal-to-noise ratio (SNR) for Raman spectra. Although ethanol in Coca-Cola could not be detected by conventional Raman spectroscopy, the DWRERDS system could be used for the direct detection of ethanol in illegal alcoholic beverages. The experimental results showed that the limit of detection (LOD) of ethanol in Coca-Cola was volume percentage of 4.76% and the correlation coefficient for the linear regression was as high as 0.984. The DWRERDS system could be used to determine the concentration of ethanol in illegal alcoholic beverages within 1 min without any sample pretreatment.

Three-dimensional Ag2S cubes for switchable multi-wavelength ultrashort pulse application

Three-dimensional (3D) materials are widely used in optoelectronics, thermodynamics and ultrafast fiber lasers because of their excellent nonlinear optical properties. Silver sulfide (Ag2S) is a kind of 3D material with a unique cubic structure and large absorption coefficient. In this paper, a double-balance detection system is used to measure the saturation absorption intensity of Ag2S as 226.6 MW cm−2 and the modulation depth as 13.9%. In the ring fiber laser, Ag2S is used as a saturable absorber (SA) to obtain a stable dual-wavelength mode locking. The center wavelengths of the mode locking are 1536.9 and 1544.5 nm, and the corresponding 3 dB bandwidths are 1.3 and 1.5. nm. By adjusting the polarization controller, a tuning process from two wavelengths to multiple wavelengths is realized, and the tunable width is 13.1 nm. This phenomenon is due to the combined effect of birefringence and nonlinear effects in the cavity. To our knowledge, this is the first report of a multiplexed fiber laser with Ag2S as a SA. The emergence of this result provides a valuable reference information for the multifunctional compact fiber laser, and the formed system can be applied in the fields of fiber sensing, telecommunications and optical communication.