George Ishikawa

Compensation of pulse shape distortion due to chromatic dispersion and Kerr effect by optical phase conjugation

Pulse shape distortion due to chromatic dispersion and self-phase modulation in a single-mode fiber was effectively compensated for by using an optical phase-conjugate wave generated by nondegenerate forward four-wave mixing in a zero-dispersion single-mode fiber. Using optical phase conjugation at the midpoint of a 100-km standard single-mode fiber compensates for the distortion of 10-Gb/s intensity-modulated NRZ pulse at an input power level exceeding +10 dBm with a resultant power penalty of less than 1.2 dB.<<ETX>>

40-Gb/s WDM transmission with virtually imaged phased array (VIPA) variable dispersion compensators

We have demonstrated variable dispersion compensation by using a virtually imaged phased array (VIPA) to overcome the small dispersion tolerance in 40-Gb/s dense wavelength-division multiplexing (WDM) transmission systems. By utilizing the periodical characteristics of VIPA compensators, we performed simultaneous dispersion compensation in a 1.28-Tb/s (40-Gb/s/spl times/32 ch; C band) short-haul transmission and confirmed that only two VIPA compensators and one fixed dispersion-compensating fiber are required for a large transmission range of 80 km. This performance can greatly reduce the cost, size, and number of compensator menus in a 40-Gb/s WDM short-haul transmission system. In addition, we achieved 3.5-Tb/s (43-Gb/s/spl times/88 ch; C and L bands) transmission over a 600-km nonzero dispersion-shifted fiber by using VIPA compensators. Although channel-by-channel dispersion compensation is required due to the larger residual dispersion slope in long-haul transmission, the periodical characteristics of the VIPA compensators offer the advantage of considerably reducing the number of different modules required to cover the whole C (or L) band. An adequate optical signal-to-noise ratio, which was the same for all channels, was-obtained by using distributed Raman amplification, a gain equalizer, and a preemphasis technique. We achieved a Q-factor of more than 11.8 dB; (BER<10/sup -17/ with forward-error correction) for all 88 channels.

Polarization-mode dispersion sensitivity and monitoring in 40-Gbit/s OTDM and 10-Gbit/s NRZ transmission experiments

Summary form only given. We established guidelines for the 40-Gbit/s system design with optimum dispersion compensation and optical power against chromatic dispersion and self-phase modulation (SPM). The signal distortion due to PMD remains a major limitation on transmission distance. This paper describes our experimental evaluation of PMD sensitivity in 40-Gbit/s OTDM transmission using a PMD emulator. We also found that the 40-GHz frequency component in the baseband signal is sensitive to waveform distortion due to PMD, and can be used for PMD monitoring. We also investigated PMD sensitivity and monitoring in 10-Gbit/s nonreturn to zero (NRZ) transmission experiments.

Generation of optical phase-conjugate waves and compensation for pulse shape distortion in a single-mode fiber

The generation of optical phase-conjugate waves and the application of optical phase conjugation (OPC) to optical communication systems is described. The method of pulse shape distortion compensation by OPC is outlined including distortion due to both fiber dispersion and the optical Kerr effect. The generation of a forward-going phase-conjugate wave in a third-order nonlinear medium is discussed and that by a nondegenerate forward four-wave mixing in a zero-dispersion single-mode fiber (SMF) is investigated. Suppressing the stimulated Brillouin scattering (SBS) of a pump wave in the fiber prevents saturation of the generation efficiency of the phase-conjugate wave even when the pump power exceeds the SBS threshold. In transmission experiments through a 200-km standard SMF with a 16-Gb/s intensity-modulated signal and a 5-Gb/s continuous-phase FSK (CPFSK) modulated signal, it is shown the applicability of OPC is modulation independent and that OPC effectively compensates for both chromatic dispersion and the optical Kerr effect. >

Automatic polarization-mode dispersion compensation in 40-Gbit/s transmission

We believe we demonstrated automatic polarization-mode dispersion (PMD) compensation in 40-Gbit/s NRZ transmission for the first time. By the feedback control of an optical PMD compensator to maximize the 20-GHz intensity of received baseband signals, we more than doubled the allowable PMD from 11 to 23 ps.

Demonstration of automatic dispersion equalization in 40 Gbit/s OTDM transmission

We demonstrated automatic dispersion equalization in a 10-Gbit/s OTDM transmission along 100-km of dispersion shifted fibre (DSF) using a tunable laser as a light source. We used the intensity of the 40-GHz frequency component extracted from the baseband signal to monitor the dispersion in the transmission fiber.

Automatic compensation of polarization-mode dispersion for 40 Gb/s transmission systems

We present an automatic compensator that effectively mitigates signal distortion due to polarization-mode dispersion (PMD). Accurate compensation is achieved by utilizing a degree of polarization (DOP) monitor with a measurement uncertainty of better than 1% achieved by applying a self-dependent precalibration procedure. The compensation performance at 43 Gb/s was evaluated systematically with respect to both first- and second-order PMD by using a crystal-optical PMD emulator. The compensator extended the tolerable differential group-delay (DGD) limit from 8 to 28 ps, while maintaining the Q penalty below 1 dB. In terms of the average of a Maxwellian-distributed DGD, the PMD compensator enabled transmission for up to 8 ps, or about three times higher than the level tolerated in the uncompensated case. In addition to the compensation performance, we demonstrate successful operation, even for distorted signals with high chromatic dispersion. We believe this capability will be a key enabler for a combined operation with adaptive chromatic dispersion compensators.

Technology-oriented review and vision of 40-Gb/s-based optical transport networks

Research and development of 40-Gb/s-based technologies are very significant for not only increasing the total capacity of wavelength-division multiplexing transmission systems but also providing higher speed interfaces to routers and Ethernet devices in order to create new services in the twenty-first century. The technologies of digital and analog integrated circuits are progressing steadily, and the LiNbO/sub 3/ Mach-Zehnder external modulator has already reached the performance level required for practical use. Adaptive, intelligent compensation for problems such as chromatic dispersion and polarization-mode dispersion can make the design of optical transport networks more flexible. As an example, we achieved 3.5-Tb/s (43 Gb/s/spl times/88 ch) transmission over a 600-km nonzero dispersion-shifted fiber by using LiNbO/sub 3/ modulators and virtually imaged phased array variable-dispersion compensators.

Transmission Characteristics of 43 Gb/s Single-Polarization and Dual-Polarization RZ-DQPSK Signals with Co-propagating 11.1 Gb/s NRZ Channels over NZ-DSF

XPM impairments on 43 Gb/s single-polarization and dual-polarization RZ-DQPSK signals were compared under co-propagation of 11.1 Gb/s NRZ channels with direct-detection. The higher symbol rate, single-polarization format, showed a larger tolerance than the dual-polarization case.

Optimum system parameters for multigigabit CPFSK optical heterodyne detection systems

To obtain a multigigabit continuous-phase frequency-shift-keying (CPFSK) system with a high receiver sensitivity, we theoretically and experimentally investigated the optimum modulation index parameter and IF center frequency, considering the modulation and demodulation baseband widths and the IF bandwidth. In a 6-Gb/s CPFSK experiment, we achieved a receiver sensitivity of -41.6 dBm, or 89 photons/bit. To use the 4- to 13-GHz IF band efficiently, we set the IF center frequency f/sub IF/ to 8.7 GHz, or 1.45 times the bit rate. To compensate for the insufficient 5-GHz FM-modulation bandwidth in the transmitter, we set the modulation index parameter /spl beta/ to 1.38, that is, a modulation index m of 0.8. >