Dual-wavelength Operation Research Articles

Dual-Wavelength Holmium-Doped Fiber Laser Pumped by Thulium–Ytterbium Co-Doped Fiber Laser

We present an all-fiber dual-wavelength holmium-doped fiber laser operating in 2μm region using a newly developed holmium-doped fiber (HDF) as a gain medium. The proposed fiber laser is constructed by using a hybrid gain medium, i.e., a thulium–ytterbium co-doped fiber (TYDF) and an HDF in conjunction with a simple half-opened linear cavity, which is formed by a broadband mirror and an output coupler reflector. Without the HDF, the TYDF laser operates at wavelengths of 1991 and 1999 nm with a signal-to-noise ratio of more than 34 dB and the slope efficiency of 26.16 %. With the HDF, dual-wavelength output lines are obtained at 2075 and 2083nm with signal-to-noise ratios of more than 17dB, 3 dB bandwidth of less than 0.2 nm and the power difference between the two peaks of less than 1 dB at the TYDF laser pump power of 320 mW.

Compact dual-wavelength thulium-doped fiber laser employing a double-ring filter

In this paper, we report on stable dual-wavelength operation of a thulium-doped compact all-fiber laser using a double-ring filter as the wavelength selective element. Simultaneously lasing at 2014.4 and 2018.4nm has been obtained via tuning the polarization controllers to adjust the relative gain and loss of the laser cavity. The side mode suppression ratios are greater than 52dB and the output power difference between the two lasing lines is less than 0.08dB under 2.6W of incident pump power.

Dual-Wavelength Emission From a Serially Connected Two-Chip VECSEL

We present a compact two-chip vertical-external-cavity surface-emitting laser design, which provides dual-wavelength emission with a wavelength separation of 10 nm. The design is ideal for type-I frequency conversion, since the two wavelengths exhibit the same polarization, and over 600-W intracavity power is generated. Dual-wavelength operation with other desirable wavelength difference can be achieved in this flexible cavity, by using different chip combinations and suitable filters.

Diode End Pumped Continuous Wave and Graphene Q-Switched Tm:LGGG Lasers

A detailed investigation was conducted on continuous wave, wavelength tunable, and graphene passively Q-switched (PQS) lasers of Tm:LGGG crystal. In continuous wave operation, a maximum average output power of 2.26 W at 2003 nm was obtained under the absorbed power of 12.1 W, giving an optical-to-optical conversion efficiency of 18.7% and a slope efficiency of 23.6%. By using a quartz plate, the emission spectrum could be tuned from 1907.5 to 2055.9 nm, corresponding to a full-width at half-maximum (FWHM) of 83 nm. Dual-wavelength operation could be obtained by rotating the quartz plate at an appropriate angle. In graphene PQS regime, the Tm:LGGG laser produced a 1.29- $\mu \text{s}$ pulse under the pulse repetition frequency of 43.9 kHz, corresponding to a pulse energy of 3.19 $\mu \text{J}$ .

Dual-wavelength mode-locked operation on a novel Nd^3+,Gd^3+:SrF_2 crystal laser

We report on efficient continuous-wave (CW) and dual-wavelength mode-locked operations on a novel Nd3+,Gd3+:SrF2 crystal laser for the first time. Codping Gd3+ in the Nd3+:SrF2 crystal significantly increased the fluorescence intensity and aroused and inhomogeneously broadened the emission spectrum. A CW operation with an output power of 992 mW and corresponding slope efficiency as high as 42.7% was obtained. We also obtained dual-wavelength synchronously mode-locked operation, with pulse duration of 1.9 ps. The mode-locked spectrum separated distinctly at 1052.2 nm and 1059.4 nm. Autocorrelation trace clearly showed a 417 fs beating period, and 1.94 THz repetition rate.

Efficient and Compact Diode-Pumped Nd:YAG Lasers at 1073 and 1078 nm

We report on the efficient diode-pumped continuous-wave laser operation of a Nd:YAG crystal at several wavelengths by using a simple and compact two-mirror laser cavity and an undoped YAG thin plate acting as a Fabry-Perot (F-P) etalon. We thus obtain a high-power single-wavelength laser operation at about 1073 nm with a maximum output power of 5.58 W and a laser slope efficiency of about 36.6%, with respect to absorbed pump power, which is believed to be the highest output power ever obtained with Nd:YAG at 1073 nm. We also achieve dual-wavelength laser operation at 1064 and 1078 nm, with a maximum output power of 1.57 W, and triwavelength laser operation at 1061, 1064, and 1078 nm, with a maximum output power of 2.16 W. This is the first demonstration, to the best of our knowledge, of a diode-pumped Nd:YAG laser at 1078 nm.

High-power continuous-wave dual-wavelength operation of a diode-pumped Yb:KGW laser.

High-power dual-wavelength diode-pumped Yb:KGW laser using a single birefringent filter plate was demonstrated. Two oscillating wavelengths maintained the same polarization and stable dual-wavelength operation at 1014.6 and 1041.3 nm (7.57 THz of frequency offset) with 3.4 W of average output power and a diffraction-limited beam profile was obtained. Dual-wavelength laser operation at shorter- or longer-wavelength pairs with lower average output power could also be realized for other output-coupling transmissions.

Tailoring the output laser wavelength of fiber lasers by the intra-cavity inscription of LPFGs

Tailoring of the output laser spectral characteristics of an Erbium-doped fiber laser (EDFL) by the intra-cavity inscription of long-period fiber gratings (LPFGs) is experimentally demonstrated. The intra-cavity fabrication allows the accurate positioning of the LPFG notch bands in order to tailor the laser wavelength and at the same time suppress the side modes on the output laser spectrum. The red tail of the LPFG notch band is used as an edge filter to modify the gain spectrum, since its shape or slope is modified as the LPFG strength grows. As few as three periods are enough to tailor the laser wavelengths to a single laser line operation, with a side mode suppression ratio (SMSR) of 34.2 dB; while at six periods 37.79 dB of SMSR in a dual wavelength operation is demonstrated. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:1430–1433, 2016

Single-/dual-wavelength switchable and tunable compound-cavity erbium-doped fiber laser with super-narrow linewidth

A single-/dual-wavelength switchable and tunable erbium-doped fiber laser (EDFL) with super-narrow linewidth has been proposed and experimentally demonstrated at room temperature. The fiber laser is based on a compound cavity simply composed of a ring main cavity and a two-ring subring cavity (TR-SC). Regardless of single- or dual-wavelength operation, the EDFL could always work well in single-longitudinal-mode (SLM) state at every oscillating wavelength. In dual-wavelength operation, the spacing could be tuned from 0 nm to 4.83 nm. In single-wavelength operation, the EDFL could lase at a fixed wavelength of 1 543.65 nm or another wavelength with a tunable range of 4.83 nm. The super-narrow linewidths of 550 Hz and 600 Hz for two wavelengths are obtained. The proposed EDFL has potential applications in microwave/terahertz-wave generation and high-precision distributed fiber optical sensing.

Continuous-wave dual-wavelength Nd:YVO4 laser at 1066.4 nm and 1083.8 nm

A LD end-pumped continuous-wave (CW) Nd:YVO4 laser with synchronous dual-wavelength operation at 1066.4nm and 1083.8nm is demonstrated. The threshold at 1083.8nm is only 0.75W due to the high Nd3+-doping-concentration of a Nd:YVO4 gain crystal. At a pump power of 3.9W, the maximum CW total output power of 480mW is obtained. The full width at half maximum (FWHM) at 1066.4 and 1083.8nm are 2.2nm and 2.1nm, respectively.

Highly stable and tunable narrow-spacing dual-wavelength ytterbium-doped fiber using a microfiber Mach–Zehnder interferometer

We describe a successful demonstration of highly stable and narrowly spaced dual-wavelength output via an ytterbium-doped fiber laser. A microfiber-based Mach-Zehnder interferometer and a tunable bandpass filter were both placed into the laser ring cavity for the purpose of ensuring a stable and narrowly spaced dual-wavelength output. Experimental results comprised three sets of dual-wavelength lasing output with wavelength spacing of 0.06, 0.09, and 0.22 nm, respectively, and side-mode suppression ratio of ∼50 dBm. A subsequent stability test provided evidence that maximum power and wavelength fluctuation were less than 0.8 dB and 0.01 nm, respectively, and thus, the obtained output was considered to be highly stable in dual-wavelength operation. The proposed system offers advantages of flexibility in dual-wavelength laser generation in addition to excellent reliability.

Wavelength switchable graphene Q-switched fiber laser with cascaded fiber Bragg gratings

We have demonstrated a wavelength switchable graphene Q-switched fiber laser with two cascaded fiber Bragg gratings. Stable Q-switching operation with central wavelength 1542.9nm (1543.7nm), repetition rate 28.4kHz (22.58kHz), and pulse duration 2.16μs (2.65μs) can be obtained by adjusting the intra-cavity birefringence. Moreover, stable dual-wavelength operation with wavelength spacing 0.8nm can also be observed. The cascaded fiber gratings combined with the graphene saturable absorber provide a simple and feasible way to get versatile pulsed fiber laser.

Dual-wavelength laser operation in a-cut Nd:MgO:LiNbO3

Diode-pumped dual-wavelength a-cut Nd:MgO:LiNbO3 lasers near 1085 and 1093nm were experimentally and theoretically investigated. The simultaneous dual-wavelength emitting was mainly attributed to the Boltzmann distribution of the occupation in the Stark-split energy-levels in manifold 4I11/2. Under an absorbed pump power of 7.45W, a maximum continuous wave (CW) output power of 1.23W was obtained, giving a slope efficiency of 21.2%. Using Cr:YAG as saturable absorber, the shortest pulse duration of 28ns was obtained with a repetition rate of 24kHz, resulting in a peak power of 729W.

Frequency domain near-infrared multiwavelength imager design using high-speed, direct analog-to-digital conversion.

Frequency domain near-infrared spectroscopy (FD-NIRS) has proven to be a reliable method for quantification of tissue absolute optical properties. We present a full-sampling direct analog-to-digital conversion FD-NIR imager. While we developed this instrument with a focus on high-speed optical breast tomographic imaging, the proposed design is suitable for a wide-range of biophotonic applications where fast, accurate quantification of absolute optical properties is needed. Simultaneous dual wavelength operation at 685 and 830 nm is achieved by concurrent 67.5 and 75 MHz frequency modulation of each laser source, respectively, followed by digitization using a high-speed (180 MS/s) 16-bit A/D converter and hybrid FPGA-assisted demodulation. The instrument supports 25 source locations and features 20 concurrently operating detectors. The noise floor of the instrument was measured at <1.4 pW/√Hz, and a dynamic range of 115+ dB, corresponding to nearly six orders of magnitude, has been demonstrated. Titration experiments consisting of 200 different absorption and scattering values were conducted to demonstrate accurate optical property quantification over the entire range of physiologically expected values.

1.31 and 1.32 μm dual-wavelength Nd:LuLiF4 laser

We demonstrate the operation of Nd:LuLiF4 laser with efficient 1.31 and 1.32μm dual-wavelength. Maximum continuous-wave output power of 1.63W is obtained at an incident pump power of 9.97W and 8% transmission of output coupler (OC), giving a slope efficiency of 17.9%. When monolayer graphene is employed as saturable absorber, stable passively Q-switched 1.31 and 1.32μm dual-wavelength laser operation still remains. The maximum average output power of 1.33W, the largest pulse energy of 17.3μJ and the highest peak power of 111.6W are achieved with the 8% OC. Meanwhile, the shortest pulse duration of 133ns and the highest repetition rate of 91kHz are rendered by the 3.8% OC cavity.

Single- and multi-wavelength Nd:YAlO3 lasers at 1328, 1339 and 1364 nm

We report on the diode-pumped continuous-wave (CW) and passively Q-switched laser operation of a c-cut Nd:YAlO3 (YAP) laser crystal. CW laser operation is demonstrated for the first time with 0.61W output power on a low-gain emission line at 1364nm by using a 0.08-mm glass etalon. Dual-wavelength laser operation is also achieved at 1328 and 1340nm as well as at 1340 and 1364nm with maximum output powers of 0.87 and 0.83W, respectively. Using graphene oxide as saturable absorber, stable Q-switching is obtained at 1339nm with a maximum average output power of 0.43W, a pulse width of 380ns and a repetition rate of 76.9kHz, thus laser pulses with 14.7W peak power and 5.6μJ pulse energy. This work presents the first graphene oxide based Q-switched Nd:YAP laser and shows the effectiveness of graphene oxide as saturable absorber for the generation of 1.3μm laser pulses.

Switchable single-polarization dual-wavelength TDFL using PM Fabry–Perot filter

Abstract A switchable single-polarization (SP), dual-wavelength thulium-doped fiber laser using polarization maintaining (PM) Fabry–Perot (F–P) filter is proposed. A combination of the PM F–P filter, a polarization controller (PC) and a polarizer is used to ensure the SP lasing operation. A stable dual-wavelength lasing operation is obtained at 1941.82 nm and 1942.21 nm. By adjusting the PCs, the proposed laser can achieve SP single-wavelength lasing operation; the polarization extinction ratios are higher than 33 dB. When the pump power is higher than 2.98 W, the optical signal-to-noise ratios of the SP single-wavelength operation can reach 60 dB, and the output power variations are less than 0.32 dB ( X -polarization) and 0.30 dB ( Y -polarization). The slope efficiencies of SP lasing operation are 6.26% ( X -polarization) and 8.79% ( Y -polarization), respectively.

Spectroscopic, thermal and cw dual-wavelength laser characteristics of Nd:LaF3 single crystal

A Nd-doped LaF3 crystal was grown by Czochralski method, and the rocking curves of (002) and (110) diffraction planes show good crystallinity quality of the as-grown crystal. Room-temperature fluorescence spectrum and transmittance spectrum of Nd:LaF3 crystal were investigated, both indicating probable dual-wavelength emissions at ∼1.04μm and ∼1.06μm. The thermal diffusivity and thermal conductivity of Nd:LaF3 crystal were detailed studied. Cw dual-wavelength laser operation of Nd:LaF3 single crystal at 1040nm and around 1065nm with LD pumping was demonstrated. A maximum output power of 302mW was obtained with a slope efficiency of about 18.5% with respect to the pump power. The results of our study indicate the Nd:LaF3 crystal a promising laser crystal.

All fiber tunable- or dual-wavelength Yb-doped fiber laser covering from dissipative soliton to dissipative soliton resonance

In this Letter, a simple and passively mode-locking Yb-doped all fiber laser using a nonlinear polarization rotation technique operating under dissipative soliton (DS) or dissipative soliton resonance (DSR) conditions is proposed. Furthermore, using a combination of a bandpass filter and a Loyt filter, tunable single-wavelength or dual-wavelength operation under two different conditions is realized, respectively. The tunable single-wavelength DS laser has a 5 nm tuning range from 1029 to 1034 nm with a pulse width of 110 ps. The tunable single-wavelength DSR operation laser has a range of 4 nm. In-depth research on the mechanism of the conversion between DS and DSR is carried out. Particularly, under dual-wavelength DSR operation, the obtained step-like pulses consist of two rectangular pulses with different energies. This work could help give a deeper insight into normal dispersion pulses.

Simultaneous dual-wavelength lasing at 1047 and 1053 nm and wavelength tuning to 1072 nm in a diode-pumped a -cut Nd : LiYF4laser

We report on diode-end-pumped a -cut Nd:YLF laser on 4 F 3/2 → 4 I 11/2 transition. In a free-running regime, using an output coupler with a radius of curvature of 1000 mm, we obtain dual-wavelength laser operation at both π -polarized 1047 nm and σ -polarized 1053 nm with maximum output power of about 1.25 W and the highest slope efficiency of about 50.9% at pump power of 5.77 W at room temperature, for the first time to our knowledge. Furthermore, using a 0.1-mm glass plate as a wavelength selector, a dual-wavelength laser at 1047 and 1072 nm can also be yielded with the maximum output power of 0.34 W, which has not been reported before.