Multiphoton upconversion luminescence (UL) properties from the Yb3+-sensitized Tm3+ ions in nanocrystalline yttria
host were studied experimentally under 973 nm laser excitation. Bright pure blue luminescence in the visible spectral
region was performed even at low pump excitation level. An interesting chromatic switching behavior was observed for
the near-infrared and blue spectral bands at room temperature, showing a pump intensity-controlled emission wavelength
switcher. The chromatic switching is intrinsically associated with the competition of two-photon UL and three-photon
UL processes. Moreover, the wavelength switching of Stark emission of Tm3+1G4 state took place as the pump intensity
rises enough. This phenomenon is attributed to pump induced photothermal effect changing the distribution of Stark
level populations in Tm3+1G4 energy state.
A self-saturated absorption regime is proposed to theoretically investigate the optical bistability of Tm,Ho:YLF laser.
Based on this bistability regime, the rate equation model of the optical bistability is established. The optical bistability
behaviors of Tm,Ho:YLF laser are obtained by numerical simulating. The relation between laser gain and loss are also
analyzed to confirm the rationality of the bistability mechanism. Furthermore, the time characters of the optical
bistability are investigated. It is found that the high pulse power and the duration of the pre-pump are two major factors
that affect the laser turn-on delay time and their influences on the turn-on delay are analyzed.
Thermal effects have been investigated in the laser diode end-pumped Tm,Ho:YLF solid state laser. Under the condition
that the pump light and the output laser are Gaussian distributions, the continuous wave rate equations of the
Tm,Ho:YLF laser are given which take into energy transfer upconversion and ground state reabsorption effects. The
fractional thermal loading and thermal focal length are obtained for different pump powers by solving the steady state
rate equations. The thermal focal length as a function of pump power is measured by the knife edge method
experimentally. Furthermore, the experimental results are compared with the theoretical results, and it is found that the
theoretical results agree well with the experimental results.
We evaluate the measurement errors induced by various deleterious effects in an optical passive ring-resonator gyro
(OPRG) with a hollow-core photonic bandgap fiber (HC-PBF) sensing coil. The uncertainties in measuring rotation rate
due to Kerr, Shupe, and Faraday effects are found to be reduced respectively by 2~3, 1, and 1~2 orders of magnitude as
compared with an OPRG with a conventional single mode fiber (SMF) sensing coil of similar parameters. The errors due
to shot and coherent backscatter noises are larger for the OPRG made of the current state-of-the-art HC-PBF than for the
OPRG with a conventional SMF coil, but are expected to reduce in future with improved fiber manufacture technologies.
Nonlinear upconversion emission properties in Tm and Yb codoped yttria nanocrystal have been studied under 973 nm
laser excitation. Intrinsic bistability and hysteresis have been observed for the bright blue upconversion luminescence of
Tm3+ ions at room temperature. The mechanism of the Tm3+ bistable emission is mainly related to laser-induced local
thermal effects which cause the enhancement of sequential multi-photon energy transfer upconversion of Yb3+-Tm3+
We demonstrate strong optical bistability in 2μm continuous wave Tm,Ho:YLF laser pumped by a 792nm laser diode
near room temperature. The bistable region is as much as 100mW wide at 283K and can be controlled by the temperature
of the laser crystal. The influence of crystal temperature on the characteristics of optical bistability is obtained. The
influence of the pump-to-mode ratio on the bistable characteristics of the laser is also discussed.
Thermal lensing in an end-pumped Tm,Ho:YLF laser crystal has been investigated with a theoretical model of
continuous-wave (CW) quasi-three-level laser. Under considering energy transfer up-conversion (ETU) and ground state
re-absorption (GSA), the rate equations are given. The influence of ETU on fractional thermal loading is calculated, and
the results show that fractional thermal loading critically depends on the pump-to-mode size ratio. The temperature
distributions of a Tm,Ho:YLF crystal under different pump powers have been analyzed. The output power and the focal
length of the thermal lens as a function of pump power are obtained in experiment. The experimental results are
compared with theoretical results, and the experimental results show that the theoretical results are reasonable.
Intrinsic optical bistability and dynamic hysteresis phenomenon, induced by nonlinear excitation and energy level
coupling, are predicted theoretically in single Tm-doped laser crystal pumped at 648nm avalanche wavelength. Taking
into account the dominant energy transfer processes including excited state absorption, cross relaxation, energy transfer
up-conversion and decay of the metastable level Tm3+3F4, the analytical formula of avalanche threshold condition are
deduced in the steady-state approximation. Based on the theory of microscopic coupled rate equations, intrinsic optical
bistability and influence of system parameters on hysteresis loop are studied numerically in detail by using a four-order
Runge-Kutta technique. The numerical results predict that intrinsic optical bistability of near 2 micrometer fluorescence
emission relevant to Tm 3F4→3H6 transition is achievable experimentally in single Tm-doped laser crystal. For
realization of low threshold optical bistability and notable bistable hysteresis loop, it is beneficial to properly increase
Tm3+-doped concentration and suppress energy transfer up-conversion. Furthermore, the interesting results obtained
numerically show that laser-induced thermal effect is not the indispensable factor for occurrences of intrinsic optical
bistability in rear-earth-doped crystal. Cooperation of nonliear excitation and energy level coupling can essentially lead
to intrinsic optical bistability in rear-earth-doped system.
Under considering energy transfer up-conversion (ETU) and ground state re-absorption (GSA), the rate equations of the Tm,Ho:YLF laser are given. The influence of ETU on fractional thermal loading is calculated for the continuous wave and Q-switched Tm,Ho:YLF lasers and the results show that the fractional thermal loading critically depends on the pump-to-mode size ratio. Furthermore, the fractional thermal loading depends on the pulse repetition frequency for a Q-switched laser. The temperature distributions of a Tm,Ho:YLF crystal under different pump powers have been analyzed. The thermal focal length as a function of pump power is calculated.
Microring resonator-coupled Mach-Zehnder interferometer (MRCMZI) is attractive for its applications in the field of
all-optical switch, with low threshold, fast response speed and compact scale suitable for integration. The paper provides
analytically and numerically investigation on optical pulse transmission characteristics of MRCMZI. The analytical
formulations of dynamic process are derived in an easy-understood method of light beam tracing. These formulations
can degenerate gradually to steady-state response when incident pulse becomes quasi-continuous wave (CW) or
adequately broad with duration much more than cavity lifetime. For the coupled-microresonator system, several
interesting signal processing tasks, such as optical differentiation, integration, pulse compression and trigger pulse
generation, can be realized. Because of the complementarity between two output ports of MZI, the optical pulse
differentiation and integration operations can be carried out synchronously at two output ports through optical
interference between the reference light of direct-bus and the modulated light of coupled-microresonator bus. The
interesting functions related to optical pulse shaping have potential applications in future all-optical communication.
The influence of energy-transfer up-conversion (ETU) on diode-end-pumped actively Q-switched Tm,Ho:YLF lasers is
investigated by the rate equation analysis. The theoretical results show that the energy-transfer up-conversion reduces not
only pulse energy but also effective upper level life. The practical example of the diode-end-pumped Q-switched
Tm,Ho:YLF laser has been used to verify the present model.
One of the major challenges in realizing practical all-optical switching devices is the need for strong and fast material
nonlinearity. The use of resonance-enhanced nonlinear effects in optical cavities has been explored as a promising way to
lower the switching power. This paper provides numerically investigation of resonator-enhanced Mach-Zehnder
interferometer all-optical switch by employing a nonlinear ratio-variable coupler with the merits of easy fabrication and
excellent nonlinear optical controllability. This performs nonlinear optical switching with advantages of hundreds tW
low switching threshold, steady switch ON/OFF states and a wide wavelength range by combining the high nonlinearity
of ring and adjustable coupling ratio of RVC. Resonator finesse is controllable by incident power with potential
applications in controllable photonic devices. Some undesirable effects involving attenuation, group delay and partial
coherence lead to increase of switching power and low extinction ratio. Optical bistability and instability do not limit
practical applications in optical switch. A desired tradeoff between response time and switching power can be achieved
by controlling finesse. Picosecond ultrafast all-optical switch is predicted.
A room-temperature Tm,Ho:YLF laser is constructed with a 2.5-mm-long Tm(6%) and Ho(0.4%) co-doped yttrium lithium fluoride crystal pumped by a laser diode operating at 792nm. The output power as a function incident pump power at different output coupler transmission values is given. At room temperature, the laser operates on a single transverse mode (TEM00) at 2.066μm, the laser threshold pump power is 55mW, and its maximum output power and optical-to-optical conversion efficiency are 388mW and 14.1% respectively. At the same time, the output power and optical-to-optical conversion efficiency as a function of incident pump power at different temperatures are obtained. Furthermore, the experimental results are explained reasonably.