Midinfrared (MIR) Supercontinuum (SC) laser has a wide range of applications in environmental monitoring, medical imaging and other fields. In-amplifier MIR SC generation benefits from compact configuration and high conversion efficiency. In this paper, high-power supercontinuum generation based on thulium-doped ZBLAN fiber was achieved, with a spectral range covering 2~3.72 μm and an output power up to 9.04 W.
Mid-infrared supercontinuum has been widely used in biomedicine, spectroscopy and other fields. The past decade has seen tremendous progress in the field of supercontinuum lasers. In this paper, supercontinuum generation based on a thulium-doped ZBLAN fiber amplifier was achieved. A supercontinuum with spectral coverage of 1.9-3.75 μm and an output power of 1.64 W was achieved in a thulium-doped ZBLAN fiber amplifier. In this paper, we also compare the output of supercontinuum laser in silica-fiber-based and fluoride-fiber-based thulium-doped fiber amplifier respectively with the same seed parameters.
Mid-infrared supercontinuum has been widely used in biomedicine, spectroscopy and other fields. With the development of fluoride fiber, the output power of mid-infrared supercontinuum has gradually increased. In this paper, the supercontinuum generation system of InF3 fiber pumped by a supercontinuum laser with a spectral range of 1.9-2.6 μm is presented. By optimizing the cooling device, the supercontinuum laser with an output power of 26.2 W and an output spectral range of 1.95-4.5 μm is realized. To our knowledge, this is the first report of mid-infrared supercontinuum output with an average power exceeding 20 W in InF3 fiber.
An active spectrum tailoring scheme is proposed and demonstrated in this letter to enhance the energy distribution further towards the long wavelength side. By cascading Dy-doped fluoride fiber to the Er-doped ZBLAN fiber, the residual spectral peak at ~2.8 μm was eliminated, and a spectrally-flat, 3.5-W MIR-SC with power ratio beyond 3 μm up to 91.2% was achieved.
In order to distinguish the direction of the moving object, a frequency-shifted laser Doppler velocimetry system was designed using acousto-optic modulation technology. Based on the heterodyne detection method, a fixed frequency is introduced by shifting the frequency of the reference beam, so that the received signal changes about the fixed frequency. In addition, the correlation detection technology is applied to signal processing in order to reduce the signal-to-noise requirements of laser Doppler velocimetry. Finally, the feasibility and speed measurement accuracy of the system are tested by using a turntable as the speed source. The experimental results show that the frequency-shifted laser velocimetry system can discriminate the velocity direction effectively.
In order to discriminate the sense of velocity, this paper proposes a laser Doppler velocimetry system based on the phase shift method. First, the expression for the light intensity of the interference field is derived, and the relationship between the interference fringes in time is obtained. Then two signal reception channels are generated by means of optical methods with a phase difference of π/2 between them. Finally, the direction of velocity is identified according to the change in phase between the two signals caused by the change in the direction of movement of the object. The experimental results show that the direction of velocity can be effectively determined by using the phase discrimination method.
High power supercontinuum (SC) pumped by noise-like pulse (NLP) has become an attractive research topic. In this work, we experimentally demonstrate a high power all-fiber short wavelength infrared SC pumped by amplified 2 μm NLP. The mode-locked structure of NLP seed is based on nonlinear amplifying loop mirror (NALM) with repetition frequency of 6.3 MHz, pulse width of 5.491 ns and maximum output power of 187.2 mW. After amplification of two-stage thulium-doped fiber amplifiers (TDFAs), the obtained SC has spectrum ranging from ~1926 nm to ~2372 nm and the maximum output power of 90 W. As far as we know, this works achieves the highest SC power seeded by 2 μm NLP, demonstrating that the NLP pump has advantages of relatively simple structure and high power in generating SC.
KEYWORDS: Signal attenuation, Signal processing, Signal detection, Time metrology, Data acquisition, Computing systems, Fourier transforms, Signal to noise ratio, Thin films, Spectroscopy
As a parameter of the process of an event, the measurement of decay time constant has been widely used in many fields such as electronic information, economy, chemistry and biology. How to quickly and accurately obtain the decay time constant of various kinds of decay signals has always been a hot issue in the field of testing technology. In this paper, research and carding are carried out on the fast and accurate decay acquisition method of time constant of single exponential decay signal. The main purpose is to comprehensively grasp the main methods adopted in current engineering technology and scientific research, and on this basis, a set of fast and accurate acquisition scheme of attenuation time constant based on ZYNQ system is proposed, It lays a foundation for the development of cavity ring down loss measurement and spectrum measurement system.
KEYWORDS: Filtering (signal processing), Particles, Electronic filtering, Signal processing, Optical filters, Optical tweezers, Systems modeling, Motion models, Interference (communication), Signal to noise ratio
The cooling and quantum control of the optically trapped particles is a hot topic in quantum frontier research. One of the key steps is using Kalman filter to extract the particle’s motion from noisy signals. Time delays of the Kalman filters are found in the process of signal extraction. Here the particle displacements based on the parameters of actual optical trapping systems are simulated, and the time delays of the Kalman filtering process are observed by changing the oscillation periods and the relaxation time for stabilization. The results indicate that Kalman filtering can effectively compress the noises in the displacement signal and thus improve the signal-to-noise ratio. Furthermore, as smaller the signal frequency is, larger time delays are observed in the process. It shows that the time delays should be noticed and compensated. Meanwhile, it is shown that the consuming time for signal stabilizations in the filtering process and the phase of the original signal, neither of which affects the filtering effect. These simulation results are our initial explorations for the cooling of optically trapped particles in vacuum. It would provide possible help to deal with the delay mismatch resulted from Kalman filtering and for the cooling of the optically trapped particles.
Optical tweezers (OTs) are an important tool for the viscosity measurements in microrheology, and passive techniques have the features of being simple and need no external force generations. Current passive methods using OT always first calibrate the potential stiffness and then do parameter fittings to obtain the viscosity. Here, we introduced and demonstrated a passive viscosity estimation method for low-viscous microfluids using OTs without stiffness calibration and parameter fitting. By Brownian trajectory tracking of single trapped bead, the viscosity coefficients of water and NaCl solutions are quickly obtained with small deviations (typical <10 % ) from the reference values. Besides, we introduce estimations for the commonly used voltage-to-displacement conversion factor, and the consistency check between the estimations and calibrations is used to represent the estimation quality. The whole process is very convenient for automatic processing. Further matrix operations are proposed and tested, which are expected to be integrated with holographic OTs and optical fiber traps for distributed multidimensional measurement.
We present a precise passive frequency difference stabilization scheme for the Y-shaped cavity dual-frequency laser. A two-stage thermostat and a precision steady current circuit were designed to stabilize the temperature and discharge current of the laser. The laser relative frequency difference drift rate is stabilized within 0.011% at room temperature. The result shows an improvement of two orders of magnitude over the stress-induced birefringence closed-loop control method. This scheme will further improve the accuracy of acceleration and precision force measurement. Moreover, the scheme shows the great potential in industrial applications because of the low cost and good environmental adaptability. In addition to the temperature change, we found that the mode repulsion also affects the stability of the frequency difference.
We propose a compact all fiber Yb-doped rectangular burst-mode laser with high inter-burst repetition rate (~MHz) and high intra-burst repetition rate (~GHz). In this burst-mode fiber laser, the dissipative soliton resonance (DSR) passive mode-locked laser is employed to generate tunable rectangular burst-mode pulse while combining with active modulator (Electro-Optic Modulator, EOM). Tunable burst-mode pulse is achieved includes 5-10 ns of tunable burst duration, 0.8- 1.5 GHz of adjustable intra-burst repetition rate and tunable intra-burst duty cycle. The inter-burst repetition rate is 1.58 MHz. This system combing with such parameters can be employed to generate ultra-high repetition rate microwave signal at high frequency band.
We reported the first erbium-doped ZBLAN fiber MOPA system centered at 2789 nm. The master oscillator was a passively mode-locked ZBLAN fiber laser based on a semiconductor saturable absorber mirror in a linear cavity. The pulse repetition rate was measured as 15.3 MHz with a signal-to-noise ratio of 62 dB, which indicating stable mode-locking operation. Then a one-stage Er3+-doped ZBLAN fiber amplifier was used to boost the average output power after a polarization dependent isolator. The maximum output power of 0.7 W was measured at the end of the amplifier with a slope efficiency of 25%. And the width of 3 dB spectrum was 4.5 nm from 2787.5 nm to 2792 nm.
For pulsed fiber amplifiers with repetition rate of tens of kHz, inter-pulse amplified spontaneous emission (ASE) is easy to build up and makes it difficult to amplify the weak signal effectively. Besides, amplified pulse shape of several tens of nanosecond would distort because of the dynamic gain saturation effect. In this paper, we demonstrate a polarization-maintained fiber laser system with three-stage amplifiers delivering pulse energy up to 70 μJ. The whole system is seeded by a semiconductor diode laser with central wavelength of 1063.9 nm and pulse repetition rate of 10 kHz which is driven directly by an arbitrary waveform electrical signal. We experimentally optimized the gain fiber length of the first-stage amplifier based on the reabsorption effect. The signal amplification efficiency and ASE proportion with different pump schemes in the first amplifier were investigated and compared in detail. Finally, an amplified pulse with 70 μJ energy accompanying with serious shape distortion was experimentally demonstrated. The signal to ASE ratio is as high as 54 dB from spectrum and the overall energy gain is 30 dB. Furthermore, a rectangular pulse with energy of 50 μJ was achieved by pre-compensating the shape distortion using the stochastic parallel gradient descent (SPGD) algorithm and the total energy gain is 28.5 dB.
A strictly-all-fiberized 2 to 5 μm supercontinuum (SC) laser source with high conversion efficiency is demonstrated. A broadband thulium-doped fiber amplifier with spectral coverage of 2-2.7 μm is used to pump a piece of single-mode fluoroindate (InF3) fiber. A fusion spliced joint with loss down to 0.07 dB is achieved between a piece of silica fiber and the InF3 fiber, which keeps all-fiber structure and efficient pump power coupling. A 1.35-W SC with spectral coverage of 1.5-5.2 μm is obtained with a record power conversion efficiency of 59.5%. This research, to the best of the authors' knowledge, demonstrates the first all-fiber-integrated of InF3-fiber-based MIR-SC laser sources to date.
An all-fiber midinfrared supercontinuum with 20-dB spectral coverage from 1.9 to 4.6 μm is demonstrated with a record power ratio beyond 3.8 μm. The supercontinuum is generated in a piece of single-mode ZBLAN (ZrF4-BaF2-LaF3-AlF3-NaF) fiber pumped by a broadband, single-mode thulium-doped fiber amplifier. Under the optimized pulse repetition rate and ZBLAN fiber length, the output spectrum has a good flatness. The power ratio beyond 3.8 μm is measured to be over 30% when the average output power reaches 1.11 W. Based on the all-fiber configuration, we have provided a compact, reliable, and promising supercontinuum source for further spectral extension into the midinfrared region where a high long-wavelength ratio is preferred.
In this letter we have demonstrated, an all-fiber Ho-doped fiber laser working on the noise-like pulse regime based on nonlinear polarization rotation (NPR). The 18.3 nm spectral bandwidth was obtained at the central wavelength of 2133 nm, with the maximum output power of 68.6 mW. To the best of our knowledge, it is the first Ho-doped fiber laser working in noise-like pulse regime. The evolvement among different pulse regimes was also investigated in this experiment.
In the designed reference beam laser Doppler velocimeter (LDV) for the vehicle self-contained navigation system, the reference object is a kind of solid-state surface. This paper expounded the generation mechanism of reference beam laser Doppler signal of this solid-state surface according to the order of the speckle field intensity variation. The expression of reference beam laser Doppler signal intensity of solid-state surface is derived based on the theory of speckle and stochastic process. Results of theory and experiments show that the essence of reference beam laser Doppler signal of solid-state surface is the coherence stack of two speckles. The signal intensity is directly proportional to the diameter of the photosensitive surface of detector and is inversely proportional to the diameter of laser spot on ground.
We report the results of our recent experimental investigation of the modulation frequency detuning effect on the output pulse dynamics in a pulse modulated actively mode-locked ytterbium doped fiber laser. The experimental study shows the existence of five different mode-locking states that mainly depend on the modulation frequency detuning, which are: (a) amplitude-even harmonic/fundamental mode-locking, (b) Q-switched harmonic/fundamental mode-locking, (c) sinusoidal wave modulation mode, (d) pulses bundle state, and (e) noise-like state. A detailed experimental characterization of the output pulses dynamics in each operating mode is presented.
A supercontinuum source with larger than 200 W average power covering 1 μm to beyond 1.7 μm is constructed in a
four-stage master-oscillator power-amplifier (MOPA) configuration. The process of power amplification and spectral
evolution during supercontinuum generation and the influence of pulse duration on this process are investigated. For the
signal light in normal dispersion region, Raman effect plays dominant role in the first phase and the power transfer from
amplified signal light to long wavelength region can be substantially achieved. When the spectrum is extended across the
zero dispersion wavelength, soliton effect becomes the main effect for spectral broadening and the power transfer
efficiency is lower to make the signal light a high peak. With similar average output power, narrower seed pulse leads to
higher peak power and can induce Stokes waves earlier which leaves longer fiber for soliton propagating. Thus the
spectrum can be shifted to longer wavelength. However, the signal light becomes a higher spike. In a word, narrower
seed pulse leads to higher signal peak and wider SC source.
Lasers in the eye-safe 2 μm spectral region are attracting significant interest due to a variety of applications such as atmospheric lidar sensing and medical treatment, which require laser sources matching the absorption lines of various molecules in the 2 μm wavelength region. We demonstrate an all-fiber Tm/Ho-codoped laser operating in the 2 μm wavelength region with a wide wavelength tuning range of more than 300 nm. The Tm/Ho-codoped fiber laser (THFL) was built in a ring cavity configuration with a fiberized grating-based tunable filter to select the operating wavelength. The tunable wavelength range of the THFL was from 1727 nm to 2030 nm. To the best of our knowledge, this is the widest tuning range that has been reported for an all-fiber rare-earth-doped laser to date. Efficient short wavelength operation was also achieved. The output power of the THFL was further scaled up from 1810 nm to 2010 nm by using a stage of Tm/Ho-codoped fiber amplifier (THFA), which exhibited the maximum slope efficiency of 42.6% with output power of 408 mW at 1910 nm.
We generate a flat, polarized and single mode Supercontinuum (SC) spanning at least from 600nm to 1700nm
in a 20m length of highly refringent photonic crystal fibers (PCFs) pumped by a 1064 nm nanosecond microchip laser.
The spectrum and polarization properties of the SC are investigated experimentally. The experimental results and the
analysis provide useful information that helps to optimize and tune the properties of the polarized SC sources.
The dispersion characteristics of Arsenic Trisulfide
As2S3 chalcogenide glass were analyzed and a kind of
As2S3 microstructured optical fiber was designed to shift the zero dispersion wavelength from longer than 4 μm to
around 2 μm. The supercontinuum generation in the designed fiber with selected pump wavelengths and pulse durations
were simulated through numerically solving the Generalized Nonlinear Schrödinger Equation. The results reveal that the
broadest supercontinuum covering 1.1 μm to 5.5 μm can be obtained with pump laser with duration 150 fs centered at
2.0 μm which is slightly longer than the first zero dispersion wavelength. When the pump wavelength is around the zero
dispersion wavelength apparent dispersive waves which are significant for spectral broadening can be observed.
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