Investigation On All-optical Buffer For A Large Dynamic Delay Range

Buffering is an effective method to solve the packet contention in optical domain without the conversion of 'optical-electronic-optical(O/E/O)' and all-optical buffer becomes the key component in optical switching node.The dynamic delay range and the minimum delay granularity are very important to improve the all-optical networks' throughput and flexibility.This dissertation focuses on the dynamic delay range and the application of the double loop optical buffer(DLOB). These conclusions can also be applicable for all the other SOA based re-circular all-optical buffers.What I have done during the PHD period are as follows:1.We analyze the signal impairment of the output packets from the DLOB according to the transmmision equation for SOA for the first time.The simulation results indicate that the number of buffered cycles of packets in DLOB is no more the 10 due to serious signals impairment under the condition of little power for control light.When the power of control light is far more than the power of signals light,the waveform distortion fiom SON's nonlinear gain can be neglected.So we establish a simple cascade SOA model for DLOB to analyze the signal-noise ratio(SNR), extinction rate(ER),the output power and the "leak" for the buffered packets for the first time.The results indicate that the number of buffered cycles is limited to 20-30 because of the accumulation of the SON's ASE.In order to improve the buffered cycles,we proposed a new control process:by inserting amplifying process in an interval of about 10 cycles.The experiment demonstrates that the buffered cycles can be improved from 20 to 60.2.We propose a new optical buffer configuration based on cascade DLOB,if the delays of the sections are T,10T,...,10^kT respectively and the numbers of the cycles is controlled to change from 0～9,a decimal optical buffer is achieved.By 4-cascaded DLOB,the buffer can provide large variable delay range of 1-9999 times of the basic delay unit,and the adjustable delay resolution is 25ns.Thus fine granularity,large variable delay,high adjustable delay resolution and compactness can be achieved simultaneously in this new cascaded DLOB.The simulation indicates that SNR and ER are improved 7dB and 2dB,and the output power of the signals light is improved 7dB at least,after the packets are bufferd in four buffers with different fiber length 9 cycles respectively.We set up a 4-stage experimental system and realize a large variable delay range of 1～9999 times of basic delay unit for the first time.The output waveforms are perfect,the eye diagragms are clear and open,and the bit error rate(BER) is less then 10^-9.In order to decrease the time when the packets aren't buffered and pass by the loop.3.NOLM+DLOB and 2×2 coupler+DLOB are proposed.The passing-by times are decrease to 2μs and 8ns in the two proposed buffers.4.In order to eliminate the crosstalk,leak,and unequalizing output power in the NOLM loop and polarization switch based on SOA,we proposed that the conventional SOA is replaced by gain transparent SOA(GT-SOA).We set up an experimental system and demonstrate that the "leak" power in the new NOLM loop is less 20～30 times than it in the conventional NOLM loop and output power for two states is equalized in polarization switch based on GT-SOA.The DLOB based on GT-SOA is also proposed.The theoretical analysis and the experimental results indicate that the "leak" is eliminated and the buffer is erased thoroughly.The packets are only buffered in the DLOB based on GT-SOA 4cycles because the GT-SOA has a large loss to the signals light.In order to improve the power of the buffered packets,an EDFA is added into the loop.Although the power is compensated partly;the loop is resonant when the packets propagate 4 cycles along the loop.5.The optical packets compression or decompression,time-slot multiplexing or de-multiplexing,parallel to serial conversion(PSC) or serial to parallel(SPC), time-slot switch or re-assignment according to the priority are realized by single DLOB or cascaded DLOB with a large variable delay range.The compression ratio or decompression ratio is 9999:1 or 1:9999.