All-optical wavelength conversion of NRZ signal by SOA-MZI with bidirectional data injection is numerically studied. The numerical results showed good agreement with experimental results.
Optical 3R regeneration is of great interest due to its ability to enhance the system margins in photonic network, because it enables to reset transmission impairments induced by channel interaction distortion, accumulation of amplified spontaneous emission (ASE) noise, chromatic dispersion and non-linearities of optical fibers and so forth. In comparison to electrical 3R regenerators, optical 3R regenerators are expected to be less complex and require less high-speed electronic components owing to simple optical signal processing, leading to small footprint, low power consumption and low cost. In this paper, we describe an optical 3R regenerator operable with carrier-suppressed return-to-zero (CS-RZ) modulation format which will be employed in dense WDM (DWDM) network to increase the efficiency of bandwidth utilization. We have demonstrated 3R regenerative transmission using 100 GHz-spacing 40 Gbit/s 5 WDM CS-RZ signals so as to confirm that a DWDM filtering effect can be drastically mitigated by the 3R regenerator.
GMPLS-controlled photonic network utilizing optical cross-connect in conjunction with WDM equipment will soon be realized in core network to partly eliminate OEO terminations in cut-through traffic. In the next step, all photonic end-to-end connection/switching is emerging technology for realizing higher bit-rate transmission with finer datum granularity, and reducing both size and power consumption of network nodes to establish truly transparent and flexible network. In this presentation, all optical signal processing devices as wavelength converters and regenerators for such future all photonic networks will be reviewed.
All-optical wavelength conversion is one of the key technologies in future wavelength division multiplexed (WDM) transparent photonic network. An electro-absorption modulator (EAM) is one of promising candidates for optical nonlinear element to realize optical wavelength conversion due that it has fast absorption recovery in comparison to slow gain recovery of a semiconductor optical amplifier while it has moderate conversion efficiency in comparison to silica fibers or electro-optic dielectric materials. In this paper, cross-absorption modulation (XAM) and cross-phase modulation (XPM) characteristics as well as absorption recovery time of EAM having multiple quantum well (MQW) absorption layer was quantitatively analyzed. Absorption recovery time less than 10 ps were achieved for the MQW EAM due to fast sweep-out of photogenerated carriers by the external electric field. The phase shift induced by 1.5 pJ pulse injection was about 0.2. All-optical 2R type wavelength converter using the MQW EAM in conjunction with delayed-interferometer was tested at bit-rate of 100 Gbit/s. Error-free conversion was successfully confirmed. The operable wavelength bandwidth was investigated at 40 Gbit/s. The bandwidth of 30 nm covering almost full C-band was confirmed. An electro-optical 3R type wavelength converter utilizing rf-driven EAM was also proposed and demonstrated. The intentionally added timing jitter onto the input signal was reduced with simultaneous contrast ratio improvement after the 3R wavelength conversion due to periodical gate closing by the rf-clock drive. These results show that EAM is suitable for optical wavelength conversion at bit-rate range of 40-100 Gbit/s with a reasonable conversion efficiency.
All optical regenerations or wavelength conversions using SOA-based polarization discriminated switch injected by a transparent assist light are reviewed. First, the reduction of a gain recovery time in SOA by injection of a transparent assist light wass discussed. A simple measurement technique of cross gain modulation (XGM) and cross phase modulation (XPM) in SOA was shown to confirm that the injection of transparent cw assist light reduced a gain recovery time without significant reduction in the amount of XGM and XPM. All optical regeneration operation 40Gbit/s as well as bit-rate tunable operation from 10Gbit/s to 80Gbit/s were presented. Simultaneous demultiplexing from 80Gbit/s to 2 channels of 40Gbit/s signals with little loss was also demonstrated. Finally, tolerance to amplitude noise and timing jitter was discussed. Those results indicate that the SOA-based polarization discriminated switch is a promising candidate for all-optical regenerator from the practical point of view.
We have developed high power and highly reliable single-mode 980 nm laser diodes (LDs) as an excitation light source for erbium doped fiber amplifiers (EDFAs) for practical communication usage. We designed buried-stripe type 980 nm LDs with a weakly index guided structure to maintain a stable single transverse mode even in high power output operation. Regarding the typical initial device characteristics, a kink level of 315 plus or minus 15 mW was realized and the devices showed maximum light output powers of over 550 mW at 25 degrees Celsius and complete thermal rollover characteristics measured at temperatures up to 150 degrees Celsius with 800 mA current injection. In electrostatic discharge (ESD) tests, no significant change of light output and/or voltage versus current characteristics after forward bias discharges typically up to about plus 12 kV and reverse up to -30 kV (equipment limitation) was found. Regarding the reliability, we carried out long-term aging tests at 120 mW light output power at 50 degrees Celsius. In the tests, we confirmed no sudden failure and very stable spectral characteristics. In addition, we obtained similar degradation rates over different device groups. Furthermore, 150 - 250 mW light output aging tests also showed stable operation. The characteristics of these devices make them suitable for practical communication applications.
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