Multi-wavelength Laser Research Articles

Melasma treatment with a 1064 nm, picosecond-domain laser with a fractionated multibeam lens array.

Picosecond-domain lasers have been fitted with fractionated optics for dermal remodeling. This study evaluates the safety and efficacy of a multiwavelength picosecond-domain laser, using a 1064 nm multibeam lens array, for improving the appearance of melasma. Twenty adults with a clinical diagnosis of melasma were enrolled and received 4 monthly 1064-nm, 450 ps laser treatments delivered with a 10 × 10 fractional array of 150 µm microbeams. Cosmetic units with melasma were treated with fluences ranging from 1.7 to 2.9 mJ/microbeam with a repetition rate of 6 Hz. Treatment effect was evaluation of digital images by dermatologists blinded as to the treatment conditions, comparing baseline and 3- and 8-month post-treatment images. Modified melasma area and severity index (mMASI) scores were determined by the study investigator based on clinical photography. Subject self-assessment of treatment effects was also recorded. Blinded reviewers correctly identified the post-treatment image in 16 of the 20 image sets (80%). Ratings demonstrated statistically significant (p < 0.001) improvement on an 11-point scale at both the 3- and 8-month timepoints for a mean improvement of 3.7 point (range -8 to 10) or 37% improvement at the 3-month follow-up, and 2.7 (range -8 to 9) or 27% at the 8-month follow-up for all subjects. The average mMASI score showed highly significant reduction at both the 3- and 8-month follow-ups compared to baseline (p < 0.01). Most subjects (90%) were satisfied with the treatment outcome in melasma at both follow-ups, which is consistent with the treatment outcome and mMASI scores. The fractionated, picosecond-domain, 1064 nm laser is safe and effective for improving melasma and should be considered as an adjunct to topical treatment regimens and sun-protection for management of melasma.

Generation of multiwavelength bismuth-doped fiber laser based on all-fiber Lyot filter

A stable multiwavelength fiber laser was proposed and demonstrated using a bismuth-doped fiber together with an all-fiber Lyot filter. The proposed multiwavelength bismuth-doped fiber laser (BDFL) spectrum can generate up to 21 output channels between 1309.88 nm and 1313.69 nm by carefully adjusting two polarization controllers (PCs). The multiwavelength BDFL shows good stability over time with a signal-to-noise ratio (SNR) of 48.69 dB, contributing to the average power fluctuations of 0.6 dB and wavelength drift of less than 0.1 nm in the laser output. In addition, the multiwavelength BDFL exhibits a free spectral range (FSR) of about 0.192 nm and a frequency bandwidth of 33.45 GHz. The characteristics of the multiwavelength BDFL can be observed by varying the pump power of the pump source, lasing output at different lengths of polarization maintaining fiber (PMF), and the generation in multiwavelengths using additional single mode-fiber (SMF).

Spectroscopic properties and discrete multi-wavelength tuning lasers of Nd:GSAG

Spectroscopic properties and discrete multi-wavelength tuning lasers of Nd:GSAG

Effect of Rayleigh backscattering on the multiwavelength random fiber laser bandwidth

We investigated the effect of Rayleigh backscattering on the bandwidth of a multiwavelength random fiber laser (MWRFL). This MWRFL is based on an erbium-doped fiber amplifier (EDFA) as the gain medium and a Lyot filter as the wavelength-selective device. A high number and stable lasing line is generated with the assistance of a nonlinear polarization rotation effect induced by highly nonlinear fiber (HNLF) and optimized by a polarization controller. Longer single-mode fiber (SMF) produces wider multiwavelength bandwidth as compared to shorter SMF lengths, as 10 km, 3 km, and 0.1 km obtained 6.24 nm, 5.76 nm, and 2.75 nm wavelength bandwidth, respectively. When the SMF is removed from the setup, no Rayleigh backscattering is provided in the cavity, which led to a narrower multiwavelength bandwidth of 2.69 nm. Subsequently, the alteration of EDFA power, half-wave plate (HWP) angle, and quarter-wave plate (QWP) angles affected the degradation of multiwavelength performance. The best output spectrum is achieved at an EDFA power of 18 dBm, a HWP angle of 60°, and a QWP angle of 105°. The laser stability over a period of 120 min was excellent with a peak power deviation of 1.33 dB.

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.

Switchable multi-wavelength fiber lasers based on asymmetric biconical fiber tapers

In this paper, switchable multi-wavelength erbium-doped fiber lasers (MW-EDFLs) are proposed and experimentally demonstrated. An in-fiber Mach–Zehnder interferometer (IFMZI) composed of asymmetric biconical fiber taper (ABFT) pairs is integrated into the all-fiber ring cavity for multi-wavelength filtering. This laser can stably emit single-, dual-, or triple-wavelength outputs by fine-tuning the polarization controller. A high optical signal to noise ratio of 58.5 dB is obtained for the output spectra. The maximum wavelength shift is 0.08 nm and the power fluctuation in all laser emissions is recorded at 1.64 dB.

Tunable Multiwavelength SOA-Based Fiber Laser

Tunable multiwavelength fiber lasers based on semiconductor optical amplifiers (SOA) have received attracting interest due to their wide prospective applications in dense division multiplexing (DWDM) systems and optical sensing. Using an SOA in a nonlinear optical loop mirror (NOLM), we demonstrate up to 13 lasing peaks by controlling the pump current and the polarization controller. At maximum pump current (450 mA), the emitted multiwavelength is between 1550 nm and 1572 nm with a wavelength spacing of 1.87 nm and 3 dB output linewidth of 0.8 nm with an output power of −7 dBm and 27 dB optical signal-to-noise ratio (OSNR). The multiwavelength output power and multiwavelength peak stability are investigated, and it was found that the power fluctuation of each multiwavelength line is less than 0.2 dB. In addition, by adjusting the polarization controllers (PCs) and SOA temperature, we obtained a tunable multiwavelength emission. The proposed fiber laser offers advantages such as simple structure, low loss, and long-time stable and multiwavelength emission.

Transfer-learning-based multi-wavelength laser sensor for high fidelity and real-time monitoring of ambient temperature and humidity.

Multi-wavelength laser absorption spectroscopy has the advantages of superior sensitivity, accuracy, and robustness for gas sensing applications, offering an opportunity for the development of high-performance laser-based hygrothermographs. However, accurate and fast determination of gas parameters from multiple spectral features can be quite challenging in the presence of large numbers of features, measurement noise, and increasing demands for real-time measurements. To address this challenge, we propose a transfer-learning-based multi-wavelength laser absorption sensor for the quantitative and simultaneous measurement of temperature and concentration of water vapor, with a focus on real-time monitoring of ambient temperature and relative humidity (RH). A spectral simulation based on the most-updated HITRAN database was employed as the dataset for model pre-training and transfer learning. The experimental dataset was obtained from absorption measurements using a distributed feedback laser that probed multiple water absorption features within the band of 7179-7186c m -1. To evaluate the sensor performance, mean absolute error, error distribution, and linearity were selected. In the presence of an insufficient experimental dataset for direct data training, the proposed transfer learning approach outperformed the traditional deep learning method with a lower prediction error of 0.14°C and 0.42% for temperature and RH, respectively, as compared to the values of 0.84°C and 0.66% obtained using the traditional deep learning method. Finally, the fast data post-processing performance of the proposed transfer learning approach was demonstrated in a field test against the conventional baseline fitting method.

Plasmonic multi-wavelength random laser by gold nanoparticles doped into glass substrate

Plasmonic multi-wavelength random laser by gold nanoparticles doped into glass substrate

Flatness enhancement of multi-wavelength Brillouin-Raman fiber laser with 10 GHz spacing utilizing Raman pump power distribution.

A simple high flat amplitude multi-wavelength Brillouin-Raman fibre laser (MBRFL) with 10 GHz spacing and excellent optical signal-to-noise ratio (OSNR) in C-Band spectral region is demonstrated. The laser consists of a linear cavity in which 12 km dispersion compensating fiber (DCF) in addition to 49 cm Bismuth-oxide Erbium doped fiber (Bi-EDF) are employed as a gain medium for amplification. The impact of Raman pump power distribution through changes in coupling ratio on amplitude flatness is carried out by comparing the peak power discrepancy between odd- and even-order Brillouin Stoke lines. This is the main property that allows the efficient controlling of gain propagation between lasing lines that is vital for Stokes flattening initiation and other output spectra characteristics. The attainment of MBRFL with outstanding OSNR necessitates the utilizing of Bi-EDF as a noise suppressor. By utilizing a 50/50 coupler, 354 identical channels together with uniform Brillouin Stokes linewidth within only 0.3-dB maximum power difference between adjacent channels is generated. The average OSNR and Stokes power are 28 dB and -5 dBm respectively when the RPP is set at 1300 mW. To date, this is the highest flatness 10 GHz spacing MBRFL with outstanding OSNR attained in MBRFL that incorporate only a single Raman pump unit.

Spectral characteristic of multi-wavelength random fiber laser using a microfiber knot resonator

We demonstrate a U-band multi-wavelength random Raman fiber laser (RRFL) based on a microfiber knot resonator (MKR). The RRFL has a forward-pump half-open cavity, wherein a 10-km single mode fiber provides both Rayleigh backscattering feedback and Raman gain. A MKR with a 0.18 nm free spectral range is used as the broadband comb filter. Up to 40 and 38 wavelength channels within 3 dB bandwidth were achieved from the intracavity and the end of the RRFL, respectively. The laser showed a good stability with maximum 0.38 and 0.1 dB peak power fluctuation within an hour at the two outputs, respectively. The spectral evolution with two envelopes was observed, and the impact of the MKR was discussed. The MKR is a small-size all-fiber and wavelength-insensitive broadband filter, which suits well with the broadband operation of the RRFL. The proposed RRFL has a simple structure and good potential tunability and provides guidance for flexible multi-wavelength lasers in the U-band and other wavebands, which have great potential in applications.

A switchable multi-wavelength mode-locked fiber laser based on a multi-mode interference device

A switchable multi-wavelength, passively mode-locked fiber laser in the 1 μm regime is demonstrated in this paper. The key principles of working include the nonlinear polarization rotation (NPR) mechanism for the mode-locked pulse generation and a single mode-multimode-single mode (SMS) structure as the spectral filter. The SMS structure is coiled on the paddles of a polarization controller (PC). Stable mode-locking operation is achieved at the fundamental repetition rate of 7.97 MHz. The pulse duration is 429 ps at the pump level of 216 mW, with the dual-wavelength laser emitting at 1037.86 nm and 1045.72 nm. By properly tuning the paddles of PCs, multi-wavelength mode-locked laser spectra can be observed switching from triple- to sextuple-wavelength, with the emission bandwidth of 27.6 nm from 1035.6 nm to 1063.2 nm.

Mode-Locking and Noise Characteristics of InAs/InP Quantum Dash/Dot Lasers

The mode-locking and noise characteristics of InP/InAs quantum dash (QDash) and quantum dot (QDot) multi-wavelength lasers, showing identical structural design, operating at the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">C</i> -band, are investigated and compared to each other. The QDash lasers exhibit improved repetition frequency stability with a lower threshold current and cavity loss. On the other hand, the QDot lasers show higher quality repetition frequency tunability with higher internal quantum efficiency, as well as lower average integrated relative intensity noise (RIN) and average optical linewidth. Furthermore, we demonstrate both the QDash and QDot lasers exhibit very clean constellation diagrams at 32 GBaud 16QAM base-band signal, while the QDot lasers' bit-error ratio (BER) performance outperforms the QDashes. This finding highlights the viability of InAs/InP QDash/QDot lasers to be used as a low-cost optical source for large-scale networks.

A passively Q-switched multi-wavelength erbium-doped fiber laser modulated by 12° tilted fiber Bragg grating

As a promising small-angle TFBG, the 12° tilted fiber Bragg grating (TFBG) has been successfully used in biochemical sensors, fiber optic anemometers, and continuously tunable photon fraction time differentiators. On the other hand, multi-wavelength Q-switched fiber lasers have widely potential and practical applications in various fields, such as laser processing, laser marking, medical diagnosis, military applications, and so on. In this paper, first, a 12° TFBG is prepared by femtosecond laser direct inscription method (FSL-DIM), then, a pulse multi-wavelength erbium-doped fiber laser (EDFL) passively Q-switched by the as-prepared 12° TFBG is exclusively and systematically demonstrated for the first time. When the pump power is raised from 100 mW to 500 mW, the repetition rate is boosted from 51.64 kHz to 149.4 kHz resulting in a repetition rate range about 97.76 kHz, while the pulse duration is compressed from 3.928 μs to 1.033 μs. The average output power monotonically increases up to the maximum value of 6.357 mW corresponding to the maximum pulse energy of 42.55 nJ. The signal-to-noise ratio (SNR) is measured to be 53 dB, which indicates a high stability. The experimental results are comparable to other Q-switched multi-wavelength EDFLs reported so far, and during the experiment, the 12° TFBG exhibits excellent stability and reliability. As far as we can explain, the multi-wavelength Q-switched operation obtained in this paper benefits from the filtering effect and polarization dependent loss (PDL) effect of the 12° TFBG. The work not only provides a reliable reference about the effective-SA performance of 12° TFBG, but also enriches the studies of passively Q-switched lasers based on different kinds of modulators.

Multi-wavelength Multi-direction Laser Light Scattering for Cell Characterization Using Machine Learning-based Methods.

Cell identification and analysis play a crucial role in many biology- and health-related applications. The internal and surface structures of a cell are complex and many of the features are sub-micron in scale. Well-resolved images of these features cannot be obtained using optical microscopy. Previous studies have reported that the single-cell angular laser-light scattering patterns (ALSP) can be used for label-free cell identification and analysis. The ALSP can be affected by cell properties and the wavelength of the probing laser. Two cell properties, cell surface roughness and the number of mitochondria, are investigated in this study. The effects of probing laser wavelengths (blue, green, and red) and the directions of scattered light collection (forward, side, and backward) are studied to determine the optimum conditions for distinguishing the two cell properties. Machine learning (ML) analysis has been applied to ALSP obtained from numerical simulations. The results of ML analysis show that the backward scattering is the best direction for characterizing the surface roughness, while the forward scattering is the best direction for differentiating the number of mitochondria. The laser light having red or green wavelength is found to perform better than that having the blue wavelength in differentiating the surface roughness and the number of mitochondria. This study provides important insights into the effects of probing laser wavelength on gaining information about cells from their ALSP. This article is protected by copyright. All rights reserved.

Low‐Threshold Multiwavelength Plasmonic Nanolasing in an “H”‐Shape Cavity

AbstractMultiwavelength plasmonic nanolasers are central to the quest for ultradense and versatile photonic integrations. However, the insufficient optical feedback and mode selection strategies result in a high lasing threshold and multi‐mode operation with limited spectral purity and stability. Here, a multiwavelength near‐infrared plasmonic nanolaser with high mode purity by leveraging a nontrivial “H”‐shape plasmonic cavity is demonstrated. The nanolaser is constructed by inserting InGaAs/GaAs multi‐quantum‐disk (MQD) nanowires into a metallic Fabry‐Perot cavity consisting of a pair of Ag nanowires positioned on an ultrasmooth Au film. The design is endowed with strong optical feedback to enhance the energy transfer between the exciton and plasmon, rendering a significant reduction of the lasing threshold. More importantly, the “H”‐shape cavity is featured with a large flexibility in tuning the resonance wavelength, where multiwavelength lasing with the virtues of single‐mode is realized at room temperature. The results make a crucial step toward near‐infrared multiwavelength plasmonic nanolasers and open up exciting opportunities for applications such as ultracompact photonic integrated circuits and high‐throughput biochemical sensing.

Tunable and switchable multi-wavelength actively Q-switched random fiber laser based on an electro-optic modulator and Sagnac loop filter.

In this article, an actively Q-switched multi-wavelength random fiber laser based on a Sagnac loop filter and electro-optic modulator is proposed and demonstrated experimentally. The random distributed feedback media is a section of a 25km long single-mode fiber. When the pump power is 350mW, the polarization angle of the Sagnac loop filter can be adjusted by polarization controller to achieve the switching of a single, double, triple, and quadruple channels laser output. In the case of a single laser channel, dual laser channels, and three laser channels output, multiple laser channels can be tuned simultaneously with a fixed wavelength interval. In addition, by changing the waveform of the external signal source, the light and dark pulses can be switched. Owing to the half-open cavity structure and the high gain of the erbium-doped fiber, the laser threshold was reduced to 25mW, and the light conversion efficiency was 0.67%. The laser is an ideal light source for medical imaging and long-distance sensing.

Investigation on different type of pulses due to strong third order dispersion effect in mode-locked fiber lasers

Here we have numerically investigated the pulse property in a wavelength switchable mode-locked fiber laser which is achieved with a tunable filter. Owing to the strong third-order dispersion (TOD) of dispersion-compensating fiber, the net cavity group velocity dispersion of the proposed fiber laser can be manipulated and exhibits wavelength-dependent feature. Our findings indicate that different types of pulses, including conventional solitons, dispersion-managed solitons, and dissipative solitons, can be achieved, and switched in various wavelengths. The pulse characteristics including pulse width and spectrum bandwidth have been investigated, in addition to with the intracavity dynamics. The influence of the length of dispersion-compensating fiber is also investigated. These results provide an excellent foundation for understanding the formation dynamics of various pulse waveforms in the laser cavity and help the development of a multi-wavelength fiber laser with a strong TOD cavity.

A C-band widely tunable and switchable erbium-doped fiber laser based on a Sagnac-like loop embedded in Lyot filter

In this paper, a new type of widely tunable and switchable multi-wavelength erbium-doped fiber laser based on a Sagnac-like loop embedded in Lyot filter is proposed. The nonlinear polarization rotation effect is obtained by adjusting two polarization controllers (PCs). The polarization-dependent isolator and the Sagnac-like loop are used as the basic structure to realize the wide tuning and wavelength switching in C-band. Compared with the traditional Lyot filter, the Sagnac-like loop is used to replace the segment of polarization-maintaining fiber, and a more uniform comb spectrum can be obtained by this filter. The tunable and switchable wavelengths can be achieved by adjusting the PCs based on the nonlinear effect of the loop. The laser can emit single-, dual-, triple-, quad- and quintuple-wavelengths. The optical signal-to-noise ratios all exceed 43 dB. It can also be adjusted to partial wavelength intervals for quad-wavelength and quintuple-wavelength. The tuning range can reach the full range of the C-band, and the laser efficiency can reach the practical application standard. It can be applied to some precision instruments and equipment.

Surface Vertical Multi-Emission Laser with Distributed Bragg Reflector Feedback from CsPbI3 Quantum Dots.

Quantum dots (QDs) laser has become an important way to solve micro-application problems in many fields. However, single wavelength distributed Bragg reflector (DBR) has many limitations in practical applications, such as signal transmission. How to realize multiwavelength DBR lasing output simply is a challenge. To achieve a stable multi-wavelength quantum dots laser in the near-infrared region, the perovskite CsPbI3 QDs laser with DBR structure is developed in this paper. A tetragonal crystal structure with complete bonding information and no defect is explained by X-ray diffractions (XRD) and Raman spectrum. The cross-section morphology of the DBR laser and the surface morphology of QDs is measured by scanning electron microscope (SEM) and transmission electron microscope (TEM), respectively. An elliptical light propagation field and a double wavelength laser radiation are obtained from the finite-difference time-domain (FDTD) simulation. The output of the three wavelength lasers at 770 nm, 823 nm, and 873 nm is measured. The emission time of a DBR laser is about 2 h, and the average fluorescence quantum yield is 60%. The cavity length selection and energy level model are put in place to clearly see the working mechanism. All the results suggest that an effective and stable CsPbI3 quantum dots DBR laser is realized.