An implementation of orthogonal frequency division multiplexing (OFDM) multimode fiber communication system test
bed developed in simulink is proposed in this paper. The system design and implementation is discussed. Based on the
simulation system, the effect of different fiber lengths, various numbers of the OFDM subcarriers and transmission data
rates on this system has been considered. The simulation results show that with the increase of fiber lengths, the systems
bit error rate (BER) increase as follow. In addition, even though using a large number of subcarriers can reduce the
amplitude variation cause by the magnitude response of the multimode fiber since the bit rate per subcarrier signal is
small, the BER from the system with large number of subcarriers is not always better than the BER from the system with
small number of subcarriers. The simulation system test bed is useful to make the following studies more convenient,
and also is helpful to establish a practical system.
By placing the semiconductor lasers in series or parallel with different resistances, the effects of series and parallel resistances on noise level of devices are studied. The effects of serial and parallel resistances on device quality and the correlations between the noise level and reliability of semiconductor lasers are also discussed. The results indicate that the noise level does not change obviously when the devices are placed with serial resistance. At the bias current of 5mA, the parallel resistance also has no obviously effect on noise level. But, when the bias current is 20μA, the parallel resistance makes noise level of devices decrease evidently. The devices with lower noise may also be unreliabile.
The g-r noise in semiconductor lasers and its relation with device quality and reliability are studied. The results indicated that g-r noise has close relation with semiconductor defects, the devices with g-r noise degrade rapidly during electric aging, the P-I characteristics of the devices evidently become bad, or the devices have failed after aging. By measuring g-r noise in semiconductor lasers, the devices quality and reliability can be estimated, which is an effective and non-destructive method.
High power fiber laser was demonstrated by using Yb-doped double-clad fiber based on laser cavity consisted of both fiber Bragg gratings spliced onto fiber ends, which pumped by a fiber-coupled multimode laser diode (FMLD) with 970nm central wavelength. In our experiment star-shape double clad Ytterbium-doped fiber was used, the MAX output
power and center wavelength is 6W cw and central wavelength of 1100nm respectively, FWHM is about 0.66nm, the slope efficiency is about 51%.
One of the most important technological challenges in the manufacture of high power lasers is to determine device quality and reliability without damaging the device itself. The low-frequency electrical noise has shown potential as a sensitive non-destructive indicator of device quality and reliability. In this paper, the noise levels in semiconductor lasers (LDs) operating in both unconducting state (Svl) and conducting state (Sv2) are measured. From our investigation, the device reliability is associated with not only Sv1 but also Sv2, if one of them is higher, the device is usually reliable. When the noise is used to estimate device reliability, both Sv1 and Sv2 should be measured and considered.
We present a novel, non-destructive technique which the low- frequency terminal electrical noise (TEN) is used to study facet stability of semiconductor lasers. We do different treatments for the facet and measure the changes of TEN before and after treatments. The results indicate that TEN level at low injection shows facet stability and can be used to predict facet stability of the device.
The low frequency electrical noise and electric derivative (IdV/dI-I) are measured at different conditions. The correlation between the noise and device quality is discussed, the results indicate that the low frequency electrical noise of 808 nm high power semiconductor laser is mainly 1/f noise and has good relation with device quality.