Waveform Conversion and Wavelength Multicasting with Pulsewidth Tunability Using Raman Amplification Multiwavelength Pulse Compressor

A combination of nonreturn-to-zero (NRZ)-to-return-to-zero (RZ) waveform conversion and wavelength multicasting with pulsewidth tunability is experimentally demonstrated. A NRZ data signal is injected into a highly nonlinear fiber (HNLF)-based four-wave mixing (FWM) switch with four RZ clocks compressed by a Raman amplification-based multiwavelength pulse compressor (RA-MPC). The NRZ signal is multicast and converted to RZ signals in a continuously wide pulsewidth tuning range between around 12.17 and 4.68 ps by changing the Raman pump power of the RA-MPC. Error-free operations of the converted RZ signals with different pulsewidths are achieved with negative power penalties compared with the back-to-back NRZ signal and the small variation among received powers of RZ output channels at a bit-error-rate (BER) of 10-9. The NRZ-to-RZ waveform conversion and wavelength multicasting without using the RA-MPC are also successfully implemented

光波長多重及び光時分割多重ネットワークにおける光波長マルチキャスティング技術

The capacity of optical communication systems has shown an incredibly thriving growth from their inception to the last several decades. From the observations in traffic demand, the objectives of this thesis are to develop some key functions for improving the flexibility and efficiency of wavelength division multiplexing (WDM) and optical division multiplexing (OTDM) networks by using wavelength multicasting technique. Practically, at a photonic gateway, for the interconnection between WDM and OTDM networks, an nonreturn-to-zero (NRZ)-to-return-to-zero (RZ) waveform conversion is necessary due to the popular utilization of NRZ and RZ formats in WDM and OTDM networks, respectively. Moreover, if the waveform conversion combines with wavelength multicasting, multiple RZ signals will be generated, resulting in an increase of the throughput of network and the flexibility of wavelength assignment. A desirable stage after these conversions is to aggregate the higher bit-rates OTDM signals based on these lower bit-rates multicast RZ signals. The pulsewidth is one of the parameters to determine the bit-rates of OTDM signals. Therefore, to achieve the aggregate OTDM signals with flexible bit-rates adapting to specific network demand, it is necessary to manage the pulsewidth in a wide tuning range. In the first work, a NRZ data signal is injected into an highly nonlinear fiber (HNLF)-based four-wave mixing (FWM) switch with four RZ clocks compressed by a Raman amplification-based multiwavelength pulse compressor (RA-MPC).The pulsewidth of four multicast RZ signals is adjusted in a continuously large range from 12.17 to 4.68 ps by changing Raman pump power of RA-MPC. In addition, the sampling of optical signal waveform is necessary to monitor signals in optical network. The signals can always be analyzed off-line by capture-and-process-later techniques. However, it is challenging that these techniques are not compatible with instantaneous amplitude changes of signals as well as capturing the details and singular manners such as transient events which need real-time processing. Therefore, in the second work, an effort to characterize the waveform of signal in real-time using wavelength multicasting technique with multiwavelength sampling short-width pulses which are on the order of a few picoseconds is implemented. Using the short pulsewidths of the sampling pulses, it is possible to sample the signal precisely because its waveform does not change significantly in the sampling time. An all-optical waveform sampling of NRZ and RZ on-off-keying (OOK) signals is focused. The 4x10 GHz WDM sampling pulses are compressed with the pulsewidth which are less than 3 ps by RA-MPC and then interact with the input signal under test using FWM effect in an HNLF. Four obtained sampled signals result in a sampling rate of 40 GSample/s, therefore, the reconstructed waveforms are well-matched with the input signal waveforms. Moving to the phase-modulated signals, especially RZ-differential phase shift keying (DPSK) signal, it is attractive for RZ-DPSK signal due to its robust tolerance to the effects of some fiber nonlinearities, and the support of high spectral efficiency. Moreover, all-optical pulse compression has been widely investigated as one of the key elements to enable high bit-rate signals overcoming electronics limits. So far, pulse compression has often used before data modulation at the transmitter to generate high bit-rate signals. Our work, on the other hand, implements the pulse compression for RZ-DPSK signal for inline applications. A useful inline application of the data pulse compression is to generate an aggregate high-speed data rate based on optical time multiplexing of many channels with lower-speed data rates. The higher bit-rates of aggregate signals depend on the pulsewidths of lower bit-rate signals. Therefore, the compression of an inline 10 Gb/s RZ-DPSK signal using a distributed Raman amplifier-based compressor (DRA-PC) is done. The RZ-DPSK signal with pulsewidth of 20 ps after 30 km standard single mode fiber (SSMF) transmission is compressed down to in picoseconds duration such as 12, 7.0, and 3.2 ps. The pulse compression of the inline signal is applied in two works. In the first work, a compressed signal with the pulsewidth of 3.2 ps is multiplexed to a 40 Gb/s OTDM signal and then successfully de-multiplexed. The second application is wavelength multicasting of the inline compressed RZ-DPSK signal to get multicast signals with short-pulsewidths for increasing the throughput of network and wavelength resource. The DRA-PC compresses the inline RZ-DPSK signal with the obtained pulsewidths of 12, 7.0, and 3.2 ps which then interact with two continuous waves (CWs) in an HNLF-based FWM switch. Thus, the pulsewidths of the multicast signals were compressed down to 12.5, 7.89, and 4.27 ps. Finally, for networking between OTDM and WDM networks, an OTDM-to-WDM conversion is crucially required. However, it is given that in some cases, different WDM channels are expected to be generated in order to connect to each tributary of OTDM signal. In this work, a 20 Gb/s OTDM RZ-DPSK signal is converted to 4x10 Gb/s WDM RZ channels. One tributary of OTDM signal is converted to 2x10 Gb/s WDM RZ signals at two FWM products.電気通信大学201

Performance of an Inline RZ-DPSK Pulse Compression Using Raman Amplifier and Its Application in OTDM Tributary

We experimentally investigate the performance of a distributed Raman amplifier (DRA)-based pulse compressor for a phase modulated signal. A 10 Gb/s return-to-zero (RZ)-differential phase shift keying (DPSK) signal is compressed to picosecond range after transmission. Pulsewidth is continuously compressed in a wide range from 20 to 3.2 ps by changing the pump power of the DRA while the compressed waveforms are well-matched with sech2 function. Error-free operations at bit-error-rate (BER) of 10-9 are achieved for the compressed signals of various pulsewidths with low power penalties within 2.3 dB compared to the back-to-back. After the compression, the 10 Gb/s signal is used to generate a 40 Gb/s RZ-DPSK optical time division multiplexing (OTDM) signal. This 40 Gb/s OTDM signal is then successfully demultiplexed to 10 Gb/s DPSK signal by using an optical gate based on four-wave mixing (FWM) in a highly nonlinear fiber (HNLF)