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1.
In this paper, for a laser scanning imaging system (LSIS) with different operation modes, the relationship between received laser power and the product of the signal noise ratio and the bandwidth of the receiver is derived, and their corresponding curves are given, thus facilitating operation mode comparison and performance determination. Avalanche photodiode direct detection is recommended as the optimum operation mode for a short wavelength LSIS. The conclusion is in good agreement with experimental results. The analyses can also be helpful for the design of optical fibre communication systems and in other applications. 相似文献
2.
Simulation-based comparison of noise effects in wavelength modulation spectroscopy and direct absorption TDLAS 总被引:1,自引:0,他引:1
B. Lins P. Zinn R. Engelbrecht B. Schmauss 《Applied physics. B, Lasers and optics》2010,100(2):367-376
A simulative investigation of noise effects in wavelength modulation spectroscopy (WMS) and direct absorption diode laser
absorption spectroscopy is presented. Special attention is paid to the impact of quantization noise of the analog-to-digital
conversion (ADC) of the photodetector signal in the two detection schemes with the goal of estimating the necessary ADC resolution
for each technique. With laser relative intensity noise (RIN), photodetector shot noise and thermal amplifier noise included,
the strategies used for noise reduction in direct and wavelength modulation spectroscopy are compared by simulating two respective
systems. Results show that because of the combined effects of dithering by RIN and signal averaging, the resolutions required
for the direct absorption setup are only slightly higher than for the WMS setup. Only for small contributions of RIN an increase
in resolution will significantly improve signal quality in the direct scheme. 相似文献
3.
调谐半导体激光吸收光谱自平衡检测方法研究 总被引:12,自引:0,他引:12
可调谐半导体激光吸收光谱技术(TDLAS)是利用半导体激光器的波长调谐特性,扫描待测气体特征吸收线,从而获得待测气体的浓度信息。基于可调谐半导体激光吸收光谱的自平衡检测方法能够有效地消除激光器光强波动等共模噪声和其他同性干扰的影响。实验表明自平衡检测方法可以获得较理想的结果,检测限低于体积比1.2×10-6,与直接吸收光谱法相比降低了一个数量级。自平衡检测电路简单,自带的电子增益补偿机制能够自动进行平衡探测,该方法不用加信号调制和锁相放大器,直接探测待测气体的吸收光谱,从而降低成本,减小系统装置体积,易于集成为便携式痕量气体检测仪。 相似文献
4.
Coherent Beam Combination of Two Polarization Maintaining Ytterbium Fibre Amplifiers 总被引:10,自引:0,他引:10
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We investigate coherent beam combination of fibre laser beams by phase locking. Phase noise of a polarization maintaining ytterbium fibre amplifier is inspected with a fibre interferometer. In a feed back control loop, two fibre polarization maintaining ytterbium amplifiers are phase locked and coherent combined when the phase noise is properly controlled by a LiNO3 phase modulator. 相似文献
5.
For the first time the fibre laser constructed from a polymer optical fibre Bragg grating is reported. The single frequency laser with the peak power of −5 dBm and signal to noise ratio greater than 45 dB has been achieved. Further examination demonstrates the excellent characteristics of the fibre laser. First, the fibre laser can be easily tuned over 35 nm by the simple axial tension method. Second, the fibre laser has the high strain sensitivity of 1.48 pm/με with the dynamic measurement range as large as 2.37%. 相似文献
6.
We consider in this paper the origin and effect of those sources of noise present in optical fibre backscatter systems which employ large-area semiconductor laser diodes and avalanche photodetectors. Source noise due to the filamentary lasing action of the photodiodes is shown to dominate the near-end performance. The clear superiority of two-point processing over boxcar integration in the presence of source noise is demonstrated. 相似文献
7.
E. Weidel 《Optical and Quantum Electronics》1976,8(4):301-307
Two methods of coupling a multimode fibre to a GaAs double-heterostructure laser are investigated: firstly direct coupling into a plane fibre end face, and secondly coupling via a cylindrical glass fibre lens. The power coupled into the fibre was measured for three different lasers (and with one laser as a function of its bias current). The measured coupling efficiency was compared with theoretical considerations. Optical feedback effects due to reflection of the fibre end face have been observed. These cause an oscillation of the coupled power, when the separation between the laser and the fibre end face is varied by only a few tenths of a micron. The alignment tolerances using a fibre lens were, as expected, more critical than for direct coupling. 相似文献
8.
The multi-functionality of microwave links based on remote heterodyne detection of signals from a dual-frequency laser transmitter is discussed and experimentally demonstrated in this paper. Typically, direct detection in conjunction with optical intensity modulation is used to implement fibre-optic microwave links. The resulting links are inherently transparent and mainly used for signal transmission. As opposed to direct detection links, remote heterodyne detection links can directly perform functionalities such as modulation, frequency conversion, and transparent signal recovery in addition to signal transmission. All three functionalities are presented and experimentally demonstrated with a remote heterodyne detection link based on a dual-frequency laser transmitter with two offset phase locked semiconductor lasers. In the modulating link a 1Gbit/s baseband signal is QPSK modulated onto a 9GHz RF carrier. The frequency converting link demonstrates up-conversion of a 100Mbit/s PSK signal from a 2GHz carrier to a 9GHz carrier with penalty-free transmission over 25km of optical fibre. Finally, the transparent signal recovering link transmits a standard FM video 7.6GHz radio-link signal over 25km of optical fibre without measurable distortion. 相似文献
9.
10.
基于新型长周期光纤光栅的掺铒光纤放大器 总被引:10,自引:8,他引:2
报道了基于高频CO2激光脉冲写入的新型长周期光纤光栅的低噪音掺铒光纤放大器,这种新型长周期光纤光栅是用大约几千Hz的高频CO2激光脉冲对光纤玻璃热冲击作用而形成的.在铒纤中插入一个长周期光纤光栅,会明显减少掺铒光纤放大器的放大自发辐射(ASE)噪音.报道了两种低噪音掺铒光纤放大器,作为前置放大器和线路放大器,它们的ASE噪音指数分别从4.0 dB减少到3.5 dB和从4.8 dB减少到4.3 dB,并且在作为线放时,其小信号增益从30 dB提高到37 dB,降噪及提高增益效应十分显著. 相似文献
11.
The recent progress of coherent optical fibre communication systems is reviewed. System constituent technologies, such as coherent optical modulation-demodulation, optical direct amplification for repeaters and single polarization fibre transmission are outlined. Several important optical device technologies, such as frequency stabilization of semiconductor lasers, AM and FM quantum noise and their reduction, and integrated opto-electronic devices, are also described. Finally, on the basis of the current state of the art in these technological areas, the expected system performance and future problems are discussed. 相似文献
12.
Laurent J Mosset A Arcizet O Chevrier J Huant S Sellier H 《Physical review letters》2011,107(5):050801
Interferometric detection of mirror displacements is intrinsically limited by laser shot noise. In practice, however, it is often limited by thermal noise. Here we report on an experiment performed at the liquid helium temperature to overcome the thermal noise limitation and investigate the effect of classical laser noise on a microlever that forms a Fabry-Perot cavity with an optical fiber. The spectral noise densities show a region of "negative" contribution of the backaction noise close to the resonance frequency. We interpret this noise reduction as a coherent coupling of the microlever to the laser intensity noise. This optomechanical effect could be used to improve the detection sensitivity as discussed in proposals going beyond the standard quantum limit. 相似文献
13.
A modal noise model is presented that combines many features of previous theories such as varying fibre contrast, exponential noise p.d.f. and Gaussian noise p.d.f. The model also includes a new feature: the ability to treat multiple lossy connectors in the same link. This model is verified through extensive experimentation and is shown to be conservative, i.e. predicted noise penalties are larger than those observed. Using the model, modal noise penalties are predicted for a number of different link configurations, and laser parameters that result in acceptable amounts of modal noise are identified. The model is also demonstrated as a design tool for determining laser parameters that result in acceptable amounts of modal noise in typical links. 相似文献
14.
We point out the influence of the different noise sources which occur in the detection of the fluorescence signal induced by a laser in an atomic beam. We have developed a theoretical model which takes account of the atomic shot noise, photon noise, laser-frequency noise and a partition noise linked to the imperfect detection of the fluorescence photons. The calculations have been performed for two- and three-level atomic systems. We detail the own contribution of each noise source and give some predictions concerning the value of the fluorescence signal to noise ratio. We determine predominance domains of each noise source which depend on the values of key parameters such as the atomic flux intensity and the laser spectral linewidth. We particularly show that the laser-frequency noise, which induces a coupling between the emission of fluorescence photons by various atoms, leads to a saturation of the S/N ratio for intense atomic fluxes. Moreover, we point out that the optical pumping process associated with a three level atomic system leads to an interesting laser-noise filtering effect. 相似文献
15.
A plastic-clad optical fibre system has been examined as a delivery system of pulsed laser energy for the generation of ultrasound. The onset of significant optical damage caused by the laser has been investigated. By using multimode fibres of 1 m length with 600 μm core size, it was found that laser power densities from the fibre were sufficient to produce ultrasonic waveforms corresponding to both the thermoelastic and plasma generation regimes. Out-of-plane acoustic displacements of >250 pm can be achieved through 2.5 cm thick aluminium test samples, showing that fibre optical delivery systems may be considered in systems using laser-generated ultrasound for non-destructive testing applications. 相似文献
16.
M. Schmidt M. Prevedelli A. Giorgini G. M. Tino A. Peters 《Applied physics. B, Lasers and optics》2011,102(1):11-18
We present a modular rack-mounted laser system for the cooling and manipulation of neutral rubidium atoms which has been developed
for a portable gravimeter based on atom interferometry that will be capable of performing high-precision gravity measurements
directly at sites of geophysical interest. This laser system is constructed in a compact and mobile design so that it can
be transported to different locations, yet it still offers improvements over many conventional laboratory-based laser systems.
Our system is contained in a standard 19″ rack and emits light at five different frequencies simultaneously on up to 12 fibre
ports at a total output power of 800 mW. These frequencies can be changed and switched between ports in less than a microsecond.
The setup includes two phase-locked diode lasers with a phase noise spectral density of less than 1 μrad/Hz1/2 in the frequency range in which our gravimeter is most sensitive to noise. We characterise this laser system and evaluate
the performance limits it imposes on an interferometer. 相似文献
17.
A sapphire fibre thermal probe with Cr3+ ion-doped end is developed by
using the laser heated pedestal growth method. The fluorescence thermal
probe offers advantages of compact structure, high performance and ability
to withstand high temperature in a detection range from room temperature to
450℃. Based on the fast Fourier transform (FFT), the fluorescence
lifetime is obtained from the tangent function of phase angle of the
non-zeroth terms in the FFT result. This method has advantages such as quick
calculation, high accuracy and immunity to the background noise. This FFT
method is compared with other traditional fitting methods, indicating that
the standard deviation of the FFT method is about half of that of the Prony
method and about 1/6 of that of the log-fit method. And the FFT method is immune
to the background noise involved in a signal. So,
the FFT method is an excellent way of processing signals. In addition,
a phase-lock amplifier can effectively suppress the noise. 相似文献
18.
Numerical and experimental study on coherent beam combining of fibre amplifiers using simulated annealing algorithm
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We present the numerical and experimental study on
the coherent beam combining of fibre amplifiers by means of simulated
annealing (SA) algorithm. The feasibility is validated by the Monte
Carlo simulation of correcting static phase distortion using SA
algorithm. The performance of SA algorithm under time-varying phase
noise is numerically studied by dynamic simulation. It is revealed
that the influence of phase noise on the performance of SA algorithm
gets stronger with an increase in amplitude or frequency of phase
noise; and the laser array that contains more lasers will be more
affected from phase noise. The performance of SA
algorithm for coherent beam combining is also compared with a widely
used stochastic optimization algorithm, i.e., the stochastic
parallel gradient descent (SPGD) algorithm. In a proof-of-concept
experiment we demonstrate the coherent beam combining of two 1083~nm
fibre amplifiers with a total output power of 12~W and 93%
combining efficiency. The contrast of the far-field coherently
combined beam profiles is calculated to be as high as 95%. 相似文献
19.
Performance of gain-clamped erbium-doped fibre amplifier with different optical feedback schemes has been studied as a function of lasing wavelength. An inverse relation of the signal gains with the amplified spontaneous emission spectrum is observed for the entire laser tuning range as a result of the population variation caused by the different strength of the oscillating laser. The noise figure also shows a feature of the lasing wavelength dependence. However, co-feedback scheme exhibits behaviour opposite to that of the counter-feedback. 相似文献
20.
By using two 1320 nm diode-pumped Nd:YAG lasers and an external modulator, the receiver sensitivity improvement of as much as 17.6 dB over direct detection has been stabilized in a 565 Mb/s ASK optical heterodyne detection of a 100 km transmission experiment. Negligible dispersion penalty and 3.9 dB sensitivity penalty away from the shot noise limit are observed after a 100 km transmission. Furthermore, system performance and sensitivity penalty induced by thermal and laser intensity noise and nonideal filtering have been considered for two different receivers. The results agree with theoretical analysis of system performance. 相似文献