We present an intensity-balanced dual-frequency laser (DFL) based on an Nd: GdVO4 microchip crystal. The intensity balance ratio tuning mechanism of the DFL, which is governed by the heat sink temperature Tc of the laser crystal, is experimentally studied. The experimental results indicate that keeping a balanced intensity condition, when the pumping power of the DFL increases, the heat sink temperature Tc of the laser crystal must be lowered to rebalance the DFL signal intensities. The Tc versus pumping power slope is experimentally measured to be −17.95 ° C / W. By fixing the pumping power at 5.6 W, an intensity-balanced microchip DFL with output power up to 103 mW and frequency separation up to 61 GHz is achieved, whose slope efficiency is 9%.
The intensity balance ratio (IBR) tuning mechanism of Nd:GdVO4 monolithic microchip dual-frequency laser (DFL) is presented. The intensity balanced DFL signals are obtained by precisely controlling the heat sink temperature of the Nd:GdVO4 crystal. In experiments, the DFL signal with frequency separation at 64 GHz and IBR above 0.99 is realized with the temperature at 47.6 °C. The other balanced intensity distribution can be reached at -0.9 °C before mode hopping. Moreover, utilizing the fluorescence spectrum and the intensity balance points of Nd:GdVO4 DFL, we obtain the temperature difference between internal and external of Nd:GdVO4 crystal ΔT = 24.0 °C.
In practical multi-granularity WDM optical networks, optical signals will be degraded due to impairments mainly
introduced by a number of multi-granularity optical cross-connects (MG-OXC) and fiber links. Even worse,
transmission impairments will make the bit-error rate to be unacceptable. We investigate the impact of transmission
impairments on optical signal quality in multi-granularity WDM optical networks. A novel dynamic impairment-aware
RWA algorithm is proposed based on the presented transmission impairments model. We also evaluate the proposed
algorithm in the serial cascaded MG-OXCs network and the interconnecting MG-OXCs network by simulations.
Multi-granularity optical cross-connects (MG-OXC) is proposed as a promising technique to reduce the cost of the optical nodes in the wavelength division multiplexing (WDM) optical networks. In this paper, we use the on-line Maximize the Number of Waveband Route (MNWR) algorithm to evaluate the performance and optimize the design of multi-granularity optical WDM networks based on two different MG-OXCs: the serial MG-OXCs and the interconnecting MG-OXCs. The numerical results show that our optimal design can significantly reduce the network complexity and the blocking probability.
In this paper, a short polarization-maintaining Er:Yb co-doped fiber laser is experimented. A pair of FBGs are
written in the Er:Yb co-doped sensitive fiber using UV beams. A 976nm pumping laser diode is used, and output
wavelength is selected by two FBGs. The PM Er:Yb co-doped fiber is used to main the orthogonal polarizations SM
lasing stability. The SM operation in each wavelength has been verified. On the basis of previous short cavity fiber,
a simple DBR dual wavelength fiber laser array has been designed and experimented. Two sections of short Er:Yb
co-doped fiber cavities are pumped by a 976nm LD simultaneously. The pump laser is splitted to pump each Er:Yb
co-doped fiber. It used a WDM coupler at 1550nm to connect the output port of two DBR fiber laser, an isolator is
spliced to the common arm of the WDM and used as the output port. The dual wavelength spacing is 0.31nm. The
output power reaches 6mW with the optical signal to noise ratio of greater than 30dB. A 12.5Gb/s codes rate is used
in the fiber laser transmission experiment. A nice optical eye diagram is recieved after long distance single-mode
communications fiber transmission.
In this paper, a tunable single-frequency fiber laser is designed. For narrow linewidth and single frequency
operation, a length of 2.75m unpumped EDF as a saturable absorber is used. The FBG combined with the unpumped
EDF provides narrow frequency selection. Counter propagating beams in the unpumped EDF form a standing wave
that results in periodic spatial hole burning. This creates a narrower bandwidth absorption grating than the FBG. The
output laser wavelength can be changed from 1530nm to 1570nm by the FBG. The 3dB spectrum width of output
laser is 0.08nm and the side mode suppression ratio is 55dB. The maximum output power exceeds 12mW, and the
stability is less than ±0.005dB. A nice single-frequency laser is observed. From the relationship of the pump power
and output power, it is obvious that the optical bistability switchable phenomena is showed in output characteristics.
The bistability switchable phenomena is caused by the saturable absorber in the ring cavity. A 10Gb/s codes rate is
used in the fiber laser transmission experiment. The high speed optical signal is transmitted in long distance without
regeneration. The eye diagrams of optical transmission are measured, the performance of long haul transmission
with high speed modulation is perfect.
In the past few years, wavelet-domain hidden Markov models have proven to be useful tools for statistical signal and image processing. The hidden Markov tree (HMT) model captures the key features of the joint probability density of the wavelet coefficients of real-world data. One potential drawback to the HMT framework is the deficiency for taking account of intrascale correlations that exist among neighboring wavelet coefficients. In this paper, we propose to develop a joint hidden Markov model by fusing the wavelet Bayesian denoising technique with an image regularization procedure based on HMT and Markov random field (MRF). The Expectation Maximization algorithm is used to estimate hyperparameters and specify the mixture model. The noise-free wavelet coefficients are finally estimated by a shrinkage function based on local weighted averaging of the Bayesian estimator. It is shown that the joint method outperforms lee filter and standard HMT techniques in terms of the integrative measure of the equivalent number of looks (ENL) and Pratt's figure of merit(FOM), especially when dealing with speckle noise in large variance.