In Free-Space Optical (FSO) communication, with the increase of bit resolution of M, the required bandwidth of PPM and DPIM increase sharply, and the bandwidth efficiency are extremely low. There is also a clock synchronization problem in the demodulation process of PPM and OOK. We propose a pulsed-laser Pulse-Number Modulation (PNM) method to address the high required bandwidth and low bandwidth efficiency for high-order modulation in FSO communication with traditional modulation methods. The symbol structure, power efficiency and bandwidth properties of PNM are presented. The modulation and demodulation of PNM are simple and easy to implement without complex clock synchronization processing. Additionally, we use the FPGA as the core controller to build an FSO communication system, which realizes accurate modulation and demodulation of data with PNM modulation method under the communication distance of 27 m and the bit rate of 2.5K bps.
We report a close connection between the fluctuation characteristics of the electrical derivative
(ED) initial peaks and the 1/f noise intensities of different samples we found during the investigation of
the 1/f noise origins of InGaAs quantum well high-power semiconductor laser diodes (LDs). We conduct contrast measurements on over fifty samples, where the current 1/f noise is measured under
different bias currents, expressed by power spectrum density (PSD) and the EDs are computed from the
current-voltage (I-V) measurement results. Then the influence of 1/f noise on the ED initial peaks is
presented by comparing these parameters of different samples. The results show a clear pattern
between the noise intensity and the ED initial peak fluctuation, and distinct differences between functional and aged LD devices, showing that ED initial peak can also be a non-destructive testing
method for high power LD cavity damage and surface defects.
In this paper, firstly we established the theoretical model of the relationship between correlation and wavelet vanishing moment of 1/f noise. Then we designed and built the 1/f noise measurement system for semiconductor laser diodes (LDs). Based on this, we introduced the measurement method of low-frequency electrical noise in semiconductor LDs and the extraction process of parameters associated. The wavelet transform decorrelation calculation is applied to the time-domain of the low-frequency noise signals, and the calculation and analysis of the relation between wavelet coefficients variances and scales are completed. The experimental results show that the noise wavelet coefficient correlation E and the vanishing moment N of wavelet function satisfy the decorrelation theoretical model at some scales, which implies that the low-frequency noise signals measured from the LDs belong to 1/f noise. Besides, the wavelet coefficient variance calculation results indicate that the noise measured in the experiments is 1/f noise from another aspect. Finally we theoretically proposed a new idea of semiconductor laser 1/f noise judging based on the methods above.
In this paper, a testing and analyzing system for volt-current and optic-power characteristics of semiconductor laser
diodes (LDs) based on virtual instrumentation is designed and developed by using PCI-6014 DAQ. The design methods
of hardware circuit and software for NI-DAQ are introduced. Some protective methods to LDs, such as driving current
limit, avoiding electrical pulse and delay start-up etc. problems, are completely finished by the software, instead of
mostly considering the resolvent on hardware circuits. The detailed tested data for the function and performance of the
system is presented, and the every tested data of LDs indicates that the whole system is of excellent performance and
stability to obtain the parameters of LDs.
This paper presents a new image mosaic algorithm based on ratio template matching by introducing gradient factor to
enhance the robustness of the template. It corrects the exposure difference in the stitching image, and applies the fade-in
and fade-out method to make the stitched image seamless and smooth. Experimental results testify that this algorithm
improves the reliability and increases the speed of matching and is easier to operate.
The method of screening semiconductor lasers by using electrical derivative technique is described in detail. The nonlinear diffusion equation is applied to denoising of electrical derivative data according to its denoising theory in signal processing. The denoising experiments of electrical derivative data for several dozens semiconductor lasers indicate that the denoising method can effectively reduce the noise in electrical derivative data and the errors of the measured parameters. The farther experiments indicate that the accurate estimate ratio of the devices can be effectively increased by using the measured parameters which have been denoised, to estimate the quality and reliability of semiconductor lasers.
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