Multi-wavelength Laser Research Articles

Generation of cylindrical vector beam pulses by using multi-wavelength EDFL with two-mode fiber filter

A multi-wavelength erbium-doped fiber laser (MW-EDFL) operating in the L-band with cylindrical vector beam outputs is proposed and experimentally investigated. The multi-wavelength lasing is realized by exploiting a two-mode fiber filter (TMFF) as the comb filter and a single-mode fiber spool with 2-km in length to suppress the mode competition. The multi-wavelength combs with channel spacing of 0.36 nm, 0.58 nm, and 1.12 nm are achieved by regulating the interference length of the TMFF, and up to 18 lasing channels are obtained with a wavelength spacing of 0.36 nm. Good long-term stability is manifested within a 100-minute duration, as the maximum peak power fluctuation of 1.96 dB and the maximum wavelength shift of 0.03 nm are measured. By adjusting the polarization controller associated with the two-mode long-period grating as a high-efficiency mode converter, radially and azimuthally polarized cylindrical vector beams of high purity are thus generated.

O-band tunable multiwavelength Brillouin-Raman fiber laser based on a wavelength-agile Raman pump.

Multiwavelength Brillouin-Raman fiber laser (MBRFL) features broadband multiwavelength generation with flat-amplitude and high optical signal to noise ratio (OSNR), which has great potential in optical fiber communication applications. Till now, the spectral regions of MBRFLs are mostly concentrated at conventional C- and L-band and the tunability of MBRFL is limited by using the Raman pump with fixed wavelength. Here, by utilizing wavelength-agile random fiber laser which can emit tunable lasing at 1.2 µm band as the Raman pump, we experimentally demonstrate the tunable MBRFL in the O-band for the first time, to the best of our knowledge. At Raman and Brillouin pump powers of 920 mW and -3 dBm, respectively, up to 90 Stokes lines with 0.13 nm wavelength spacing and >13 dB OSNR can be obtained when the Raman and Brillouin pump wavelength are set at 1231 nm and 1300 nm, respectively. Moreover, by tuning the wavelength of Brillouin pump from 1295 nm to 1330 nm, tunable MBRFL can be achieved with similar multiwavelength generation bandwidth by simultaneously tuning the Raman pump wavelength, and the number of Stokes lines are beyond 85 across the tuning range. The bandwidth of the demonstrated O-band MBRFL is also the widest wavelength span ever reported for multiwavelength Brillouin fiber lasers at 1.3 µm band. Our work indicates that the use of wavelength-agile random fiber laser as Raman pump in MBRFL can provide an effective way to extend the spectral regions of MBRFL and also improve the tunability performance of MBRFL.

Tunable spectrally-flat multi-wavelength cylindrical vector beam fiber laser by using a re-circulating frequency shifter loop with two external injections

We experimentally demonstrate a tunable spectrally -flat multi-wavelength cylindrical vector beam (CVB) fiber laser based on a two-mode long-period fiber grating (TM-LPFG) and a re-circulating frequency shifter loop with two external injections. The TM-LPFG is utilized as a mode converter in the re-circulating frequency shifter loop to excite the LP11 mode in the two-mode fiber. By adjusting the wavelength interval of the two injected seed signals, the power of the injected seed signals, and the pump power can produce a flat intensity envelope between the two injected wavelengths. Multi-wavelength CVBs of 12, 18, or 30 channels with a peak-to-peak power variation lower than 2 dB between the two injected wavelengths are obtained with a wavelength spacing of approximately 0.08 nm. The wavelength spacing can be adjusted by changing the frequency of the radio frequency signal. Multi-wavelength CVBs of 14 channels with a peak-to-peak power variation lower than 2 dB between the two injected wavelengths are obtained with a wavelength spacing of approximately 0.2 nm. The purity of the generated multi-wavelength CVBs is higher than 98%. Due to the absence of interference-type filter elements, the multi-wavelength CVB fiber laser exhibits excellent stability. The maximum wavelength deviation of each channel is less than 6.5 pm, and the maximum intensity fluctuation is less than 0.7 dB over a period of one hour.

Multiwavelength semiconductor lasers facilitate industry applications

The development of multiwavelength lasers could herald a new era of 6G communications and remote sensing.

Development of a compact pulsed time-of-flight LiDAR platform for underwater measurements

The mapping and inspection of underwater topography and infrastructure require precise and robust instrumentation which cannot be completely fulfilled by sonar or camera-based systems. At Fraunhofer IPM we have therefore built a versatile platform that implements all necessary building blocks for various laser scanner configurations targeted at subsea applications. Based on this platform, we present two scanner prototypes: One compact and lightweight multi-wavelength airborne laser scanner for deployment with unmanned aerial vehicles. It is intended for easy and fast shallow water bathymetric and topographic mapping. The second scanner is embedded in a pressure resistant housing and designed for submerged deployment on stationary or moving platforms to facilitate numerous inspection tasks. Initial tests of the scanners have been performed in an excavation pond and on a dedicated underwater measurement range. The resulting point clouds indicate promising performance in terms of resolution, accuracy, and speed. Further work will focus on extensive field tests and software optimization for increased usability.

Monolithic InAs/InP Quantum Dash Mode-Locked Lasers for Millimeter-Wave-Over-Fiber Mobile Fronthaul Systems

Semiconductor monolithic mode-locked lasers (MLLs) are potential solutions for generating high-speed optical pulses in future mobile fronthaul networks in the millimeter-wave (mmW) bands. Our previous studies have investigated using buried heterostructure (BH) quantum dash (QDash) multi-wavelength lasers for photonic mmW applications. Here we present results from monolithic chip-scale ridge waveguide QDash MLLs for generating and transmitting mmW signals. Through optimizing epitaxy growth, waveguide design, and fabrication process, the five-layer ridge waveguide QDash MLL exhibits superior performance with regard to the coherent comb bandwidths, lasing threshold current, output power, and internal quantum efficiency. The generated mmW frequency at 28.36 GHz exhibits excellent frequency stability, with a drift of less than ± 50 kHz. For the first time, we have utilized the free-running five-layer ridge waveguide QDash MLL to implement single- and dual-optical carrier modulation schemes in the millimeter-wave-over-fiber (mmWoF) systems. Both modulation schemes have achieved satisfactory performance achieving error vector magnitude (EVM) performance much lower than the 3GPP requirements (<12.5%) for future networks. In particular, the single-carrier modulation scheme achieves higher conversion efficiency and improved EVM performance. In contrast, the dual-carrier modulation scheme alleviates the path length matching challenges, offering a low-cost and easy-to-implement solution in different usage scenarios.

Integrated multi-wavelength lasers for all-optical processing of ultra-high frequency signals

Semiconductor lasers are nowadays simply unavoidable and essential light sources. While their complexity and dynamical behavior have attracted some attention from a fundamental viewpoint, these special properties remain largely left aside in applications outside the lab. The development of multi-wavelength or multi-color lasers may be a turning point in this regard. On the one hand, multi-color lasers allow for simultaneous emission at multiple and controllable modes, thus adding extra versatility to the lasers. On the other hand, the coupling between the different modes may lead to exciting new functionalities and applications exploiting directly the intrinsic dynamical response of the laser itself. In this perspective letter, we describe the role that multi-wavelength lasers may, in our opinion, play in the future in signal processing applications, especially at the mm-wave and subterahertz frequencies.

Photonic convolutional neural network with robustness against wavelength deviations.

We experimentally explore the practicality of integrated multiwavelength laser arrays (MLAs) for photonic convolutional neural network (PCNN). MLAs represent excellent performance for PCNN, except for imperfect wavelength spacings due to fabrication variation. Therefore, the performance of PCNN with non-ideal wavelength spacing is investigated experimentally and numerically for the first time. The results show that there exists a certain tolerance for wavelength deviation on the degradation of the structural information of the extracted feature map, leading to the robustness of photonic recognition accuracy under non-ideal wavelength spacing. The results suggest that scalable MLAs could serve as an alternative source for the PCNN, to support low-cost optical computing scenarios. For a benchmark classification task of MNIST handwritten digits, the photonic prediction accuracy of 91.2% for stride 1 × 1 scheme using the testing dataset are experimentally obtained at speeds on the order of tera operations per second, compared to 94.14% on computer. The robust performance, flexible spectral control, low cost, large bandwidth and parallel processing capability of the PCNN driven by scalable MLAs may broaden the application possibilities of photonic neural networks in next generation data computing applications.

L-U-band multiwavelength Brillouin-Raman fiber laser assisted by a broadband pump source

L-U-band multiwavelength Brillouin-Raman fiber laser assisted by a broadband pump source

Curved InGaAs nanowire array lasers grown directly on silicon-on-insulator.

Catalyst-free, selective nano-epitaxy of III-V nanowires provides an excellent materials platform for designing and fabricating ultra-compact, bottom-up photonic crystal lasers. In this work, we propose a new type of photonic crystal laser with a curved cavity formed by InGaAs nanowires grown directly on silicon-on-insulator. This paper investigates the effect of the radius of the curved cavity on the emission wavelength, quality factor as well as laser beam emission angle. We find that the introduction of curvature does not degrade the quality factor of the cavity, thereby offering another degree of freedom when designing low-footprint multiwavelength photonic crystal nanowire lasers. The experimentally demonstrated device shows a lasing threshold of 157 µJ/cm2 at room temperature at telecom O-band wavelengths.

Significant enhancement of multiple resonant sidebands in a soliton fiber laser

Resonant sidebands in soliton fiber lasers have garnered substantial interest in recent years due to their crucial role in understanding soliton propagation and interaction dynamics. However, most previous studies and applications were restricted to focusing on only the first few low-order resonant sidebands because higher-order sidebands usually decay exponentially as their wavelengths shift far away from the soliton center and are negligibly weak. Here we report numerically and experimentally significant enhancement of multiple resonant sidebands in a soliton fiber laser mode-locked by a nonlinear polarization evolution mechanism. The birefringence and the gain profile of the laser cavity were shown to be critical for this phenomenon. Multiple intense resonant sidebands were generated whose maximum intensity was more than 30 dB higher than that of the soliton, which is the highest yet reported, to our knowledge. To accurately predict the wavelengths of all high-order resonant sidebands, an explicit formula was derived by taking the third-order dispersion effect into account. The temporal features of multiple orders of resonant sidebands were characterized, which all exhibit exponentially decaying leading edges. This study provides insight into understanding the properties of high-order resonant sidebands in a soliton laser and opens possibilities for constructing multi-wavelength laser sources.

Synchronous multi-wavelength mode-locked laser at 2-μm based on Mamyshev cavity

In recent years, 2-μm band lasers have developed rapidly due to their wide range of usage. It is a challenging problem to realize the synchronization of multi-wavelength multi-channel ultrashort pulses for many important applications. In this paper, a 2-μm synchronous multi-wavelength fiber laser is proposed. The laser was constructed based on cascaded Mamyshev regenerators. The multi-cascade nonlinear broadening and offset filtering can act as a saturable absorber, enabling mode locking, and resolving the issues of gain competition and synchronous output encountered in traditional multi-wavelength lasers. A stable synchronous multi-wavelength mode-locked laser was realized through numerical simulation. The laser can provide six-channel ultrashort pulses with a wavelength interval of 5 nm (the central wavelengths range from 2000 nm to 2025 nm). The peak power and duration of the output pulses are respectively 0.1–0.25 kW (intracavity peak power 0.4–1.1 kW for coupler ratio is 20:80) and ∼1.1 ps. Design principles and the effects of various parameters such as the filter, the fiber length, etc., on the optimization of the laser are analyzed and discussed.

Double-Brillouin Frequency Spacing Multi-Wavelength Brillouin Erbium Fiber Laser in Double Cavities Configuration

Multi-wavelength fiber laser has great potential for use in dense wavelength-division multiplexing (DWDM) systems, sensors, and microwave photonics. This paper presents a multi-wavelength Brillouin erbium fiber laser (MW-BEFL) with double-frequency Brillouin spacing of approximately 0.176 nm between each adjacent Stokes. The proposed setup utilizes double cavities configuration for odd and even-order Brillouin Stokes to propagate separately in the system. This configuration is flexible as it can be transformed into a single-spacing MW-BEFL by swapping the ports of the circulator; it can also extract the odd-orders Brillouin Stokes by relocating the OSA in the cavity. Up to 25 double-spaced Brillouin Stokes are obtained with a tuning range of 30 nm. The first 8 Stokes have peak power variation within ± 3.7 dB and an average signal-to-noise ratio of 20 dB.

Multi-wavelength fiber laser via evanescent field confinement with Al2O3 nanolaminate-coated thinned fiber

We present the fabrication and analysis of an Erbium-doped optical fiber laser emitting at multiple wavelengths. This is accomplished via a filter constructed from a fiber taper coated with alumina (Al2O3). The taper is created using the flame brushing induction technique with a combination of Butane (25 %) and Oxygen (75 %). The diameter is reduced to a 20 µm waist and 2 mm burner displacement. The thin film of Al2O3 was deposited via atomic layer deposition (ALD), resulting in a 15 nm layer. The coated fiber taper was then inserted into a ring fiber laser cavity functioning as a selector filter. This fiber laser produced an output comprising six simultaneous wavelengths: 1531.14, 1531.79, 1532.45, 1541.85, 1544.45, and 1562.22 nm. Laser signal stability tests were performed for one hour at 25 °C at the six emission wavelengths, resulting in a maximum optical power fluctuation of 0.15 to 0.33 dB, a wavelength shift variation of 0.02 nm, and a signal-to-noise ratio of 31.79 dB in average. The laser lines emitted have an average spectral width of 0.06 nm. Our results show that the typical performance of the fiber laser configuration based on an optical fiber taper was improved by the addition of the Al2O3 layer and can be further improved. Our findings demonstrate that the standard operation of the fiber laser setup, which utilizes an optical fiber taper, was enhanced through the incorporation of an Al2O3 layer and has the potential for further development.

PANDA Fiber Sagnac Interferometer for Temperature Sensor Application

Fiber Sagnac loop mirror has great potential for use in various application such as multi-wavelength laser source, strain and temperature sensors. This paper demonstrates an optical fiber temperature sensor based on two lengths of PANDA polarization maintaining fibers (PMFs) in a fiber Sagnac interferometer. The temperature sensing is based on the change of spectral spacing of the generated optical comb with the temperature difference between two PMFs. The performance of the system was characterized numerically and experimentally by measuring the spectral spacing when raising the temperature of one of the PMFs. A high temperature sensitivity up to 0.36 nm/°C is obtained, with detuning range of 43 nm. This makes it a good candidate for various in-field sensing application.

Tunable Single and Multi-Wavelength Er-Doped Mode-Locked Fiber Laser Based on GIMF-PCF-GIMF

Tunable Single and Multi-Wavelength Er-Doped Mode-Locked Fiber Laser Based on GIMF-PCF-GIMF

Multi-wavelength fiber laser with high-purity LP11 output mode based on a symmetrical fiber mode selective coupler and Sagnac interferometer

In this work, a multi-wavelength fiber laser with a high-purity LP11 output mode was proposed and experimentally demonstrated. More specifically, a novel symmetrical fiber mode selective coupler (MSC) was utilized for mode conversion and a Sagnac interferometer is fabricated as a multi-channel filter for wavelength selection. From the experimental results, it was shown that the laser was able to emit stable single-, dual-, and triple-wavelength outputs both around 1530 nm and 1550 nm, and the purity of the LP11 mode was above 97 % and 98 % at the two bands respectively. In addition, the laser was capable of simultaneous dual-wavelength emission around 1530 nm and 1550 nm, resulting in an overall four-wavelength output with an LP11 mode purity of above 98 %. The proposed high-order mode multi-wavelength fiber laser has potential applications in various fields including optical communications, optical sensing, and materials processing.

Tunable and switchable multiwavelength fiber laser incorporating tapered few-mode fiber Bragg gratings

A tunable and switchable multiwavelength Erbium-doped fiber laser (MWFL) is proposed and demonstrated based on tapered few-mode fiber Bragg gratings (TFMFBG). Optical modes inside TFMFBG have extensive evanescent tails that are sensitive to changes in the external medium. The MWFL can be tuned in the 1.5 µm wavelength region when temperature and refractive index variations are applied to the TFMFBG. The temperature and refractive index sensitivities range from 11.5 pm/⁰C to 14.6 pm/⁰C and 3.10 nm/RIU to 3.93 nm/RIU, respectively. Additionally, due to the polarization dependency of TFMFBG, single-, dual-, and triple-wavelength lasing lines can be switched within the MWFL cavity. The stable triple-wavelength lasing was generated at peak wavelengths of 1533.04 nm, 1532.35 nm, and 1531.71 nm for λ1, λ2, and λ3, respectively. The developed triple-wavelength laser corresponded to a specific guided mode inside the few-mode FBG, including fundamental LP01 mode, higher-order LP11 mode, and mode coupling between LP01 and LP11 (LP01-LP11).

A Bioinspired Bilevel Metamaterial for Multispectral Manipulation toward Visible, Multi-Wavelength Detection Lasers and Mid-Infrared Selective Radiation.

Manipulation of the electromagnetic signature in multiple wavebands is necessary and effective in civil and industrial applications. However, the integration of multispectral requirements, particularly for the bands with comparable wavelengths, challenges the design and fabrication of current compatible metamaterials. Here, a bioinspired bilevel metamaterial is proposed for multispectral manipulation involving visible, multi-wavelength detection lasers and mid-infrared (MIR), along with radiative cooling. The metamaterial, consisting of dual-deck Pt disks and a SiO2 intermediate layer, is inspired by the broadband reflection splitting effect found in butterfly scales and achieves ultralow specular reflectance (average of 0.013) over the entire 0.8-1.6µm with large scattering angles. Meanwhile, tunable visible reflection and selective dual absorption peaks in MIR can be simultaneously realized, providing structural color, effective radiative thermal dissipation at 5-8µm and 10.6µm laser absorption. The metamaterial is fabricated by a low-cost colloidal lithography method combined with two patterning processes. Multispectral manipulation performances are experimentally demonstrated and a significant apparent temperature drop (maximum of 15.7°C) compared to the reference is observed under a thermal imager. This work achieves optical response in multiple wavebands and provides a valuable way to effectively design multifunctional metamaterials inspired by nature.

Tunable and switchable multi-wavelength pulsed fiber laser based on a nonlinear optical loop mirror and an improved Sagnac filter.

We propose and experimentally demonstrate a tunable and switchable multi-wavelength erbium-doped fiber ring pulsed laser based on a nonlinear optical loop mirror (NOLM) and an improved Sagnac filter. To achieve multi-wavelength pulsed laser output, we adopt a NOLM as a quasi-saturable absorber and an improved Sagnac loop as a wavelength selected filter. The constructed laser has a maximum output wavelength number of five with a pulse repetition frequency of 40.45kHz and pulse duration of 108ns. The laser can output single-wavelength and dual-wavelength pulsed lasers within a certain wavelength tuning range and a five-wavelength pulsed laser with a constant wavelength interval of 3nm by adjusting the polarization controller. Dual-wavelength, three-wavelength, and four-wavelength pulsed lasers with various wavelength intervals are also obtained. The output performance of the constructed laser is tested with a maximum average output power of 127.45µW and minimum pulse duration of 52ns, and the stability of the laser output is also tested with a maximum power fluctuation of 0.62dB and minimum wavelength drift of 0.51nm with pump power of 350mW.