Triple-wavelength Laser Research Articles

Tunable and stable multi-wavelength erbium-doped fiber laser based on a double Sagnac comb filter with polarization-maintaining fibers

In this paper, a tunable and stable multi-wavelength erbium-doped fiber laser that employs a double polarization-maintaining Sagnac loop comb filter is proposed and experimentally demonstrated. The two nested Sagnac loops are used as the comb filter, which was fabricated using two 3-dB couplers, two polarization controllers (PC), and two sections of polarization-maintaining fibers (PMFs) with lengths of 1.2m and 1.8m, respectively. In the proposed laser, a stable and tunable single-, double-, and triple-wavelength lasing was obtained experimentally in the spectral range of 1528–1564nm, the side mode suppression ratio (SMSR) was higher than 38dB, and the wavelength shifts and power fluctuations were less than 0.04nm and 4.7dB, respectively, for a duration of 10min at a room temperature of 26°C. Furthermore, the laser can emit quadruple-wavelengths through adjustment of the two PCs in the experiment.

Smartphone snapshot mapping of skin chromophores under triple-wavelength laser illumination

Chromophore distribution maps are useful tools for skin malformation severity assessment and for monitoring of skin recovery after burns, surgeries, and other interactions. The chromophore maps can be obtained by processing several spectral images of skin, e.g., captured by hyperspectral or multispectral cameras during seconds or even minutes. To avoid motion artifacts and simplify the procedure, a single-snapshot technique for mapping melanin, oxyhemoglobin, and deoxyhemoglobin of in-vivo skin by a smartphone under simultaneous three-wavelength (448–532–659 nm) laser illumination is proposed and examined. Three monochromatic spectral images related to the illumination wavelengths were extracted from the smartphone camera RGB image data set with respect to crosstalk between the RGB detection bands. Spectral images were further processed accordingly to Beer’s law in a three chromophore approximation. Photon absorption path lengths in skin at the exploited wavelengths were estimated by means of Monte Carlo simulations. The technique was validated clinically on three kinds of skin lesions: nevi, hemangiomas, and seborrheic keratosis. Design of the developed add-on laser illumination system, image-processing details, and the results of clinical measurements are presented and discussed.

Tuneable and stable multi-wavelength thulium-doped ring-cavity fibre laser based on Sagnac loop and Mach–Zehnder filter utilizing thin-core fibre

A multi-wavelength thulium-doped fibre laser based on a Sagnac loop and a Mach–Zehnder filter was designed and experimentally demonstrated. In this ring-cavity fibre laser, the Sagnac loop was composed of 2 m-long polarization-maintaining fibres, and the pigtail fibre core/cladding diameter of all components was 10/125 µm. A 4 m-long thin-core fibre with a 5/130 µm core/cladding diameter was spliced into the cavity to obtain the Mach–Zehnder structure. The wavelength spacings of the comb spectra of the Sagnac loop and the Mach–Zehnder filter were 3.2 nm and 20.3 nm, respectively. When the pump power was 150 mW, single-wavelength lasing occurred with 3 nm-wavelength spacing within the 1857–1897 nm range; the maximum power difference was less than 1.27 dB; the side-mode suppression ratio was greater than 32.68 dB; and the peak power fluctuations, measured over a 10 min interval, were less than 0.2 dB. A tuneable dual-wavelength lasing mode was also realized by adjusting the polarization controllers, with emission occurring simultaneously at 1874 and 1891 nm. In this case, the power fluctuations were less than 1.36 dB and 0.53 dB, respectively. A tuneable triple-wavelength lasing mode was also demonstrated, with a side-mode suppression ratio greater than 34.51 dB.

A 1.8-µm multiwavelength thulium-doped fiber laser based on a hybrid interference filter

ABSTRACTA 1.8-µm tunable multiwavelength thulium-doped fiber laser based on a hybrid filter is proposed. In the designed ring-cavity fiber laser, the filter consists of one Sagnac loop and one dual-pass Mach–Zehnder filter. In the experiment, the lasing threshold is 155 mW, and a continuously tunable and stable single-wavelength laser could be realized with a minimum tuning interval of 2.1 nm within a scope of 22.5 nm. When an 1858-nm laser is obtained, the peak power fluctuation is less than 0.83 dB within 20 minutes at room temperature. By adjusting the polarization controller, stable dual-wavelength lasers are simultaneously achieved, and the peak power shift is less than 1.24 dB within a scan time of 20 minutes at room temperature. By changing the polarization state, stable triple-wavelength lasing is obtained, and the power fluctuation is less than 1.95 nm. In the experiment, the 3-dB linewidth of the laser is less than 0.4 nm.

Tunable and switchable thulium-doped fiber laser utilizing Sagnac loops incorporating two-stage polarization maintaining fibers

Abstract A ring cavity thulium-doped fiber laser incorporating a Sagnac loop is proposed and experimentally demonstrated. In the designed fiber laser, a 0.4-m-long thulium-doped fiber is selected as the gain medium; the Sagnac loop is composed of two-stage polarization maintaining fibers of lengths 1 m and 2 m, respectively; and one broadband reflection mirror is used as the wavelength reflector. In the experiment, the lasing threshold is 135 mW, and by adjusting the polarization controller, a tunable and stable single-wavelength laser can be realized. The line interval is less than 3 nm within 1832–1865 nm, the power difference of each line is less than 1.111 dB, and the side-mode suppression ratio is larger than 44.7 dB. When 1848.4 and 1846.4 nm single-wavelength lasers are realized, the peak power fluctuation is less than 0.18 dB and 0.206 dB, respectively, within 10 min of scan time. A tunable and stable dual-wavelength laser can be realized by adjusting polarization controller; the power difference is less than 3.68 dB, and the side-mode suppression ratio is more than 35.04 dB. When 1844 and 1863.2 nm lasers are obtained simultaneously, the power shift is less than 0.6 dB and 0.95 dB, respectively, at room temperature. By changing the polarization state, tunable triple-wavelength lasing can be achieved ultimately, and the side-mode suppression ratio is larger than 41 dB.

Simultaneous triple 914 nm, 1084 nm, and 1086 nm operation of a diode-pumped Nd:YVO4 laser

We report a diode-pumped continuous-wave (cw) triple-wavelength Nd:YVO4 laser operating at 914, 1084, and 1086 nm. A theoretical analysis has been introduced to determine the threshold conditions for simultaneous triple-wavelength laser. Using a T-shaped cavity, we realized an efficient triple-wavelength operation at 4F3/2→4I9/2 and 4F3/2→4I11/2 transitions for Nd:YVO4 crystal, simultaneously. At an absorbed pump power of 16 W (or 25 W of incident pump power), the maximum output power was 2.3 W, which included 914 nm, 1084 nm, and 1086 nm three wavelengths, and the optical conversion efficiency with respect to the absorbed pump power was 14.4%.

Stable and tunable narrow-linewidth erbium-doped fibre laser based on polarization-maintaining fibre ring filter and PM-FBG

A tunable, narrow-linewidth, ring-cavity, erbium-doped fibre laser (EDFL) incorporating a polarization-maintaining fibre ring filter (PMF-FRF) and a polarization-maintaining fibre Bragg grating (PM-FBG) was designed and used in experiments. In the proposed configuration, the PM-FBG was used as a wavelength selector and the PMF-FRF was fabricated by a 3 dB coupler and a 2 m polarization-maintaining fibre. In order to constrain the mode hopping, a 1 m long segment of erbium-doped fibre was inserted between the circulator and the PM-FBG as a saturable absorber. Based on these enhancements, the side-mode suppression was improved and a stable and tunable single-wavelength laser was achieved within the tuning scope of 1534.36–1535.07 nm by adjusting the polarization controller. In the tunable scope, each wavelength space was ≤0.1 nm, the maximum power drift was ≤0.35 dB, and the 3 dB linewidth was ≤0.15 nm. In the experiment, dual- and triple-wavelength laser emissions were also realized by modifying the polarization condition of the cavity. Over a 20 min monitoring period at room temperature, the wavelength shift and power fluctuation of the single-wavelength emission were ≤0.01 nm and 0.11 dB respectively, while wavelength shift and power fluctuation of the dual-wavelength emission of 1534.39 and 1535.07 nm were ≤0.02 nm and 0.7 dB respectively.

All-fiber laser simultaneously delivering multi-wavelength solitons

All-fiber triple-wavelength laser mode-locked by a nonlinear amplifier loop mirror is proposed and demonstrated experimentally for the first time to author׳s best knowledge. By means of chirped fiber Bragg gratings in the intra-cavity and extra-cavity, three kinds of solitons with different wavelengths are simultaneously delivered from the proposed laser. The central wavelengths of solitons are 1539.5, 1549.5, and 1559.5nm with the pulse durations of 6.2, 4.2, and 5ps and the spectral bandwidths of 0.4, 0.7, and 0.5nm, respectively. The experimental observations show that the all-fiber triple-wavelength laser is very stable in the long-term operation and is convenient for practical applications.

Switchable multi-wavelength fiber ring laser using a side-leakage photonic crystal fiber based filter

A switchable multi-wavelength fiber ring laser is proposed and experimentally demonstrated with a novel side-leakage photonic crystal fiber (SLPCF) based filter incorporated into the ring cavity at room temperature. Stable multi-wavelength laser operations can be achieved due to the spatial mode beating, polarization hole burning and spectral hole burning effects. By adjusting the polarization controller appropriately, the laser can be switched among the single-, dual- and triple-wavelength lasing oscillations whose signal-to-noise ratio is up to 50 dB. In addition, the lasing wavelength can be also tuned and switched by applying the strain to the filter.

Switchable multiwavelength erbium-doped fiber laser employing wavelength-dependent loss

A novel switchable multiwavelength erbium-doped fiber laser (EDFL) is proposed and demonstrated based on two comb filters. One comb filter is used to define the wavelength spacing, the other filter with a very narrow wavelength spacing is used to induce wavelength-dependent loss (WDL) effect to suppress the mode competition caused by homogeneous gain broadening of the erbium-doped fiber (EDF). As a result, triple-wavelength lasing operation with wavelength spacing of 0.8 nm has been achieved. Wavelength switching operation of the laser was also obtained by adjustment of a polarization controller (PC) in the cavity. The measured power fluctuation of each wavelength is less than 0.4 dB.

High-resolution laser beam induced current measurements on Cd0.9Zn0.1S/ CdTe solar cells

An assessment of Cd0.9Zn0.1S window layer thickness and its impact on photoresponse uniformity in CdTe thin film photovoltaic (PV) devices is presented. A triple-wavelength laser beam induced current (LBIC) system provided a spatially resolved photocurrent mapping technique. Three diode lasers; λ = 405, 658, 810 nm gave photon absorption and carrier generation characteristics over the spectral range of the Cd0.9Zn0.1S/ CdTe devices. Two contrasting device structures were grown by metal-organic chemical vapour deposition (MOCVD), where the uniformity of the Cd0.9Zn0.1S window layer was known to vary: 1. uniform 240 nm Cd0.9Zn0.1S/ 2 μm CdTe and 2. a poorly nucleated 40 - 300 nm Cd0.9Zn0.1S/ 2 μm CdTe. Calculated photon penetration depths, δp allowed for the separation of identified defects within the device cross-section. Cd0.9Zn0.1S pin holes were identified in 240 nm Cd0.9Zn0.1S/ 2 μm CdTe where 405 nm photon ‘punch-through’ into the absorber material was observed. These pin holes also led to a localised reduction in photoresponse at λ = 658 and 810 nm. In the device structure where the Cd0.9Zn0.1S window layer thickness was known to vary from 40 to 300 nm, CdTe pin holes were identified where localised ∼ 50 μm regions of reduced photoresponse, at all wavelengths were observed. Local variations in both Cd0.9Zn0.1S and CdTe thickness were also identified where variable absorption led to a distribution of LBIC photoresponse. It was demonstrated that reduced photoresponse uniformity at all incident wavelengths was related to reduced device shunt resistance, Rsh and open-circuit voltage, Voc.

Dual-wavelength high-power Yb-doped double-clad fiber laser based on a few-mode fiber Bragg grating

We report a high-power dual-wavelength Yb-doped double-clad fiber laser based on a few-mode fiber Bragg grating (FMFBG). The FMFBG was fabricated by using a piece of fiber in a length of fiber with a cutoff wavelength of 1225 nm, which supported two modes at 1060 nm. The laser was pumped by a fiber pigtailed laser diode working at 915 nm. Single-wavelength, dual-wavelength and triple-wavelength laser oscillations were observed when the fiber laser operated under different low pump powers. However, stable dual-wavelength operation was achieved at higher pump power of 3.9 W and remained unchanged until the output power reached 5.67 W under the maximum available pump power of 10.7 W. The laser wavelengths were centered at 1059.12 and 1060.80 nm with a full-width at half-maximum of 37 and 43 pm, respectively. The signal-to-noise-ratio was greater than 50 dB and the beam quality factor ( M 2) was about 1.9.

Switchable multi-wavelength fiber ring laser based on a compact in-fiber Mach-Zehnder interferometer with photonic crystal fiber

Switchable multi-wavelength fiber ring laser with an in-fiber Mach-Zehnder interferometer incorporated into the ring cavity serving as wavelength-selective filter at room temperature is demonstrated. The filter is formed by splicing a section of few-mode photonic crystal fiber (PCF) and two segments of single mode fiber (SMF) with the air-holes on the both sides of PCF intentionally collapsed in the vicinity of the splices. By adjusting the states of the polarization controller (PC) appropriately, the laser can be switched among the stable single-, dual- and triple-wavelength lasing operations by exploiting polarization hole burning (PHB) effect.

基于啁啾莫尔光栅和半导体光放大器的多波长光纤激光器

A simple and cost-effective multi-wavelength fiber ring laser based on a chirped Moire fiber grating (CMFG) and a semiconductor optical amplifier (SOA) is proposed. Stable triple-wavelength lasing oscillations at room temperature are experimentally demonstrated. The measured optical signal-to-noise ratio (SNR) reaches the highest value of 50 dB and the power fluctuation of each wavelength is less than 0.2 dB within a 1-h period. To serve as a wavelength selective element, the CMFG possesses excellent comb-like filtering characteristics including stable wavelength interval and ultra-narrow passband, and its fabrication method is easy and flexible. The lasing oscillation shows a narrower bandwidth than SOA-based multi-wavelength fiber lasers utilizing some other kinds of wavelength selective components. Methods to optimize the laser performance are also discussed.

Switchable triple-wavelength erbium-doped fiber laser using a single fiber Bragg grating in polarization-maintaining fiber

A stable and narrow wavelength spacing multiwavelength erbium-doped fiber laser is proposed and demonstrated. The laser can produce simultaneous dual- and triple-wavelength lasing oscillations with a narrow wavelength spacing of less than 0.1 nm via using a single fiber Bragg gratings written in polarization-maintaining (PM) fiber. By adjusting polarization controller, the wavelength spacing of dual-wavelength lasing oscillations can be tuned to as small as 0.032 nm. The maximum amplitude variation for every lasing wavelength is less than 0.5 dB. The room-temperature operation principle is based on the polarization hole burning and deeply saturated effect in an ordinary erbium-doped fiber ring laser (EDFRL). The laser has the advantages of simple all-fiber configuration, low cost, high stability and operating at room temperature.

Triple-wavelength switchable Erbium doped fiber laser with cascaded asymmetric exposure long-period fiber gratings

The cascaded asymmetric exposure long-period fiber gratings are fabricated by CO(2) laser, which provide multi-wavelength filters with anisotropic transmission spectrum under different states of polarization. Inserting this device in the ring cavity of an erbium-doped fiber laser, a triple-wavelength switchable lasing laser with equal spacing of 2.6 nm has been obtained. Owing to the polarization dependent loss of the new cascaded long-period fiber grating, the wavelength switching of random combination of C(1) (3), C (2) (3), and C(3) (3) is demonstrated through the polarization controlling. We derive the wavelength switch to the polarization characteristic of cascaded asymmetric exposure long-period fiber gratings.

A widely tunable narrow-linewidth triple-wavelength erbium-doped fiber ring laser

A widely tunable narrow-linewidth simultaneous triple-wavelength oscillation erbium-doped fiber ring laser (EDFRL) is investigated in detail. The EDFRL can produce double-wavelength oscillations with the same polarization output, as well as another widely tunable wavelength oscillation with orthogonal polarization in both the C-band and the L-band. By preventing two polarization-mode competitions, we have achieved a stable single-longitudinal-mode triple-wavelength lasing output along with a minimum side-mode suppression ratio of 40 dB.