We report on diode-end-pumped a-cut Nd:YLF laser on F43/2→I411/2 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.
We demonstrate a 1484-nm two-cascaded Raman mode-locked fiber laser based on the intermode-beating mode-locking (IBML) technique. Through the two-cascaded Raman shifts of P2O5 in a phosphosilicate fiber, the continuous-wave (CW) 1064-nm Raman pump can be transferred to the 1484-nm second-order Stokes. When the intermode-beating frequency of the 1064-nm pump source matches with the 1484-nm Raman-cavity frequency, the IBML condition is satisfied, and the harmonic mode-locking at 1484-nm occurs to stably emit nanosecond pulse trains. By properly adjusting the 1484 nm Raman-cavity length, we have further realized the tuning of the mode-locking harmonic order. The 472nd- and 757th-order harmonic mode-locking operations with repetition rates of 72.728 and 116.292 MHz have been obtained, respectively. The IBML operation is stable with a radio-frequency (RF) supermode suppression ratio of 33.9 dB and RF signal-to-noise ratio of 51.8 dB.
Label-free biosensor based on the dynamic distributed feedback (DFB) laser emission is proposed. The sensitivity of the
sensor is substantially realized by the refractive index of the cladding layer that influences the effective refractive index
(neff) of the whole waveguide structure. The designed multilayer structure consists of the substrate (n=1.51), the low
refractive index mesoporous silica film (n=1.1~1.3), the dye-doped gain layer (n=1.58) and the high refractive index
TiO2 (n=2.1) thin film. We used the finite difference time domain (FDTD) algorithm to simulate the influence of the
mesoporous silica film and the TiO2 layer to the neff of the fundamental transverse electric (TE0) mode and the sensitivity
in the DFB structure. It was found that the increase of refractive index of the mesoporous silica and the thickness of TiO2
layer can slightly increase the neff of the structure. And the sensitivity of the sensor can be enhanced not only by the introduction of mesoporous silica, but also by a thicker TiO2 layer.
We investigate a high-pumping-efficiency and linewidth-broadening, L-band, erbium-doped, superfluorescent fiber source (SFS) using a cascaded dual-backward-pumped configuration. With optimized structural parameters, the design provides an L-band SFS with a mean wavelength of 1578.2 nm, an output power of 132.8 mW, and a spectral linewidth of 52.6 nm without using any external spectral filters under 265-mW pump power. The high pumping efficiency of 50.1% is achieved experimentally. The design relaxes the danger in resonant lasing while enhancing the pumping efficiency and broadening the linewidth.
The laser performances of silica microspheres functionalized by neodymium doped gadolinium oxide nanocrystals
are investigated. First, we have developed a new method to identify and selectively excite small mode volume
WGMs using a tapered fiber coupler. The electromagnetic-field distribution ofWGMs is mapped by the excitation
efficiency, providing a measurement of the near field intensity. Moreover a method to characterize the ultra-low
threshold microlaser is presented here, which relies on the use of the thermal bistability effect: the thermal drift
of the resonance line which slows down the power scanning help us to detect the onset of laser effect on the
emitted light. Finally, a single mode lasing at 1088.2 nm with threshold as low as 65 nW is achieved, for a
quality factor at lasing wavelength of 1.4 × 108.
We first demonstrate that by inserting an appropriate section of unpumped erbium-doped fiber (EDF) in an erbium-doped superfluorescent fiber source (SFS) of double-pass backward configuration, a stable L-band SFS can be achieved. The fiber-length arrangement of unpumped fiber are shown to have significant effects on the output properties of the L-band SFS. The spectral linewidth is broadened, and the variation of mean wavelength versus pump power is eliminated to achieve a wideband and mean wavelength stable L-band SFS by optimizing the fiber-length ratio of the pumped fiber length to the total fiber length. For a 19-m-long total EDF with fiber-length ratio of 0.84, a mean wavelength stable L-band SFS with a spectral linewidth of 49.6 nm, an output power of 46.3 mW, and a mean wavelength of 1583.20 nm was experimentally achieved.
An approximate explicit solution for Raman fiber lasers with arbitrary cascades is obtained. The solution is deduced
without using depleted pump approximation. The proposed analytical solution shows excellent agreement with numerical
simulation. Furthermore, optimal design of the cascaded Raman fiber lasers is carried out analytically. The optimal
values of fiber length, reflectivity of output fiber Bragg grating and power conversion efficiency are obtained under
different pump power. The optimal fiber length and reflectivity of output FBG decrease with increasing pump power.
There exists a certain tolerance of the optimal cavity parameters, in which the conversion efficiency decreases only
slightly. In addition, by the proposed solution one can readily determine whether pump power is depleted.
In this paper, a simple single-backward configuration with a section of un-pump fiber is presented to achieve a stable
L-band superfluorescent fiber source (SFS). The effects of the structural parameters on the output characteristics of the
L-band SFS in terms of output spectrum, mean wavelength, and linewidth are theoretically examined. By selecting
suitable structure parameters, an L-band SFS with mean wavelength insensitive to pump power is achieved under a
pump power of 190mW, corresponding to a mean wavelength of 1583.20nm, an output power of 47mW, and a spectral
linewidth of 49.6nm. The proposed L-band SFS design shows its tremendous advantages as simple structure and good
performances that make it be useful in WDM system, fiber optic gyroscopes and fiber sensor systems applications.
Based on an external cavity using Littrow configuration, a high-power, narrow-linewidth and broadband-tunable Yb3+-doped double-clad fiber (YDCF) laser was demonstrated. Numerical simulations were performed to optimize the design
of the laser. A wide wavelength tuning range from 1046 nm to 1121 nm was achieved. The 3-dB linewidth of the laser
was up to 0.5 nm. An output power of over 20W at 1089 nm with a slope efficiency of 60% was achieved.
We have experimentally investigated a new two-stage C+L-band (1525 to 1605-nm) amplified spontaneous emission (ASE) fiber source using a dual forward pumping configuration. The proposed source offers a high pumping efficiency of 24.6%, output power of about 52 mW, and a wide bandwidth of 80 nm. Without using any external spectral filters, the source has a low spectral ripple between 2.4 and 2.9 dB for different pumping power levels. This designed configuration is also suitable for high-efficiency L-band ASE. The obtained source will be useful in characteristic measurement for wavelength-division multiplexing components and spectrum-sliced multiwavelength fiber sources for local access networks.
Theoretical design optimization of the first-order P-doped fiber Raman laser (FRL) by an explicit approach was
investigated. The authors derived an explicit expression for the output power of the laser without using the depleted-pump
approximation. The proposed solution shows excellent agreement with numerical simulation. According to the
explicit solution, one can clearly know the effects of fiber length, reflectivity of output fiber Bragg grating (FBG),
Raman gain and loss of the P-doped fiber and extra losses on the output power. The solution also present a criteria by
which one can determine whether the depleted-pump approximation is valid or not. It is very fast and convenient to
optimize the output power of the FRL using the proposed explicit solution. The optimal values of fiber length,
reflectivity of output FBG and conversion efficiency are obtained under different pump power. While increasing pump
power, the optimal fiber length and reflectivity of output FBG decrease and the optimal conversion efficiency increase.
There exists a certain tolerance of the optimal parameters, in which the conversion efficiency decreases only slightly.
The results provide us an intuitive physical understanding to the laser and are instructive to experimental design of the
laser.
Feedback characteristics in single planar waveguide-coupled square microcavity are investigated by using the two-dimensional
finite-difference time-domain method. A square microcavity with refractive index of 3.5 and side length of
2.2μm plays as a wavelength selective feedback element, and a single planar waveguide with width of 0.2μm is used to
input and output light in the simulation. Simulation results show that most of the on-resonance extinction in transmitted
optical power through the planar waveguide can be reflected. The highest reflection observed is more than 92% of the
incident power at the resonance wavelength. For better understanding the high reflection phenomenon, the steady field
patterns of single waveguide coupled square microcavity has also been obtained. The influence of coupling gap between
the cavity and waveguide, on the resonance wavelength, reflection efficiency and the linewidth of reflection peak has
been studied. With increasing gap, the resonance position shifts to the longer wavelength, and the linewidth narrows. The
results also show that an optimized gap exits for the highest optical power reflection.
We present a two-stage dual-forward pumped configuration to achieve a wavelength stable L-band amplified
spontaneous emission (ASE) source. The effects of EDF length and pump power arrangements on the characteristics of
L-band ASE spectrum, output power, and mean wavelength are investigated. The results show that not only the pumping
conversion efficiency can be improved largely but also the pump power independent mean wavelength operation can be
achieved by optimizing the fiber length ratio and pump ratio of the dual-forward pumped configuration as comparing to
that of the conventional double-pass forward configuration.
Two kinds of configurations of L-band amplified spontaneous emission (ASE) source with two-stage EDF and dual
forward pumps are suggested for generating a high power L-band ASE spectrum. The characteristics are theoretically
compared in terms of the output power, pumping conversion efficiency, bandwidth, and mean wavelength stability for
these two configurations. The EDF length and pump power allotment are also optimized. An L-band ASE source of
76mW output power with about 36.2% pumping conversion efficiency are experimentally obtained.
A LD-single-end-pumped Nd:YVO4 CW all-solid-state laser with maximum output power 12.5W at 1064nm was
designed to pump the cascaded phosphosilicate fiber Raman laser. The Nd:YVO4 laser is lower in cost than Yb-doped
cladding fiber laser which is usually used as a pump for Raman fiber laser. However, it is inefficient to couple pump
beam into single mode fiber (SMF). The coupling efficiency from pump beam to SMF is largely affected by the beam
quality. Thus, a high coupling efficiency requires maintaining laser's operation in the TEM00 mode while scaling the
power. The beam quality and maximum output power of the Nd:YVO4 laser is restricted by the thermal lens and fracture
within the gain medium under high pump intensity conditions. The thermal effects was decreased by using a 3×3×
10mm3 Nd:YVO4 crystal with a low neodymium-doped concentration (0.3at%). Furthermore, a plane-plane resonant
cavity with large mode volume and a large pump size was also used to reduce the effects. The Nd:YVO4 laser with
maximum output power 12.5W and M2<1.2 was obtained. More power than 4W was injected into cascaded Raman
cavity at the maximum pump power and about 1W coherent second-order Stokes radiation at 1484nm was achieved.
In this paper, we investigate the 1480nm pumped L-band erbium doped fiber amplified spontaneous emission source of three major configurations: one-stage double-pass forward pump configuration,
two-stage with C-band ASE injection configuration, one-stage double- pass bi-directional pump configuration. The characteristics are compared in terms of the output power, pumping conversion efficiency, bandwidth, and mean wavelength stability. It is shown that the one- stage double-pass bi-directional pump configuration has a better performance than the other two configurations.
A fabricating system of fiber tapers using a CO2 laser as its heat source has been developed. According to the self-regulating effect of the CO2 laser in the process of melt-drawn fiber, the relation between the required CO2 laser power and the moving distance of the motorized stage in the fabrication process of fiber taper is found. The dependence of the required laser power and the moving distance of one motorized stage running is of approximately linear increment, which largely simplifies the computer control. With the relation plus regulating the other parameters, a 1.3 μm diameter fiber taper is fabricated. The tapers fabricated by our system have good shape and size for optical device applications.
A new kind of Erbium doped heavy fluoride glass Er:ZBLALiP has
been studied. Microspheres were fabricated with this fluoride
glass. Whispering Gallery Mode laser spectra around 1550 nm
were analyzed for different sphere diameters and Erbium
concentrations (from 0.01% to 0.2% by mole) under pumping by a fiber taper at 1480 nm. Red-shift effect on the frequencies of both fluorescence and laser spectra is experimentally observed when the pump power is increased, originating from thermal effects. A spectroscopic technique based on the green
upconversion fluorescence is used to compute a loading effective
temperature for the Er:ZBLALiP microsphere and this further allows
us to calibrate the properties of the microsphere laser in terms
of the thermal expansion as well as the variation of the
refractive index.
A new kind of Erbium-doped heavy fluoride glass Er:ZBLALiP was elaborated, and microspheres were fabricated with this fluoride glass. Thermal properties and spectroscopic properties of Er:ZBLALiP excited at 805 nm were investigated. Based on this thermalization effects between upper levels of green fluorescence in Er:ZBLALiP, we proposed an optical temperature sensing using micrometer-sized spherical cavity. The sphere temperature is scaled by the ratio of green emission intensities at 522 and 547 nm. A wide dynamic temperature ranging from 100 K to 850 K can be utilized by this type of point temperature sensor.
Er:ZBLALiP microsphere laser has been studied under pumping by a fiber taper at 1480 nm. Whispering Gallery Mode laser spectra were analyzed for different sphere diameters and Erbium concentrations (from 0.01 % to 0.2% by mole). The gain spectrum is calculated for the transition 4I13/2->4I15/2 around 1550 nm. Red-shift effect on the frequencies of both fluorescence and laser spectra is experimentally observed when the pump power is increased, originating from thermal effects. Temperature inside the microsphere cavity and thermal expansion coefficient were determined by employing the intensity ratio of two green up- conversion emission centered at 526 and 550 nm respectively which quantitatively explain this red-shift.
Two sorts of microchip laser materials, such as Nd:YVO4 and Er/Yb:Cr phosphate Kigre glass, are used to perform the experimental study of pump absorption saturation. A spatial- dependent rate equation model has been developed for the simulation, and hence the corresponding absorption saturation intensities are determined, the pump saturation intensity is 840 W/cm2 in the (pi) -polarization, and 2200 W/cm2 in the (sigma) -polarization for the 3% a-cut Nd:YVO4 crystal for the 810 nm pump wavelength, and 130 kW/cm2 for Er/Yb:Cr phosphate Kigre glass for the 975 nm pump wavelength. Based on this nonlinear absorption effect, a high performance LD end-pumped Nd:YVO4 microchip laser was obtained with a low pump threshold of 3 mW and a high slope efficiency of 50%, while for Er/Yb:Cr phosphate Kigre glass laser, a low pump threshold of 5 mW and 20% slope efficiency was obtained when pumped by a Ti:Sapphire laser. All the laser operated in a single transverse mode, and the 1.535 micrometers laser operated at a single longitudinal mode. This study gives a useful guideline to design and to optimize the pump beam radius of LD end-pumped microchip lasers.
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