Terumi Chikama

Compensation of chromatic dispersion in a single-mode fiber by optical phase conjugation

The effective compensation of waveform distortion due to chromatic dispersion in a single-mode fiber was demonstrated using an optical phase-conjugate wave generated by nondegenerate forward four-wave mixing in a zero-dispersion single-mode fiber. After transmission of 5- and 6-Gb/s continuous-phase FSK (CPFSK) signal through a dispersive single-mode fiber, distortion compensation was confirmed by measuring bit error rate characteristics and observing heterodyne-detected eye-patterns.<<ETX>>

Modulation and demodulation techniques in optical heterodyne PSK transmission systems

Modulation and demodulation techniques are described for an optical PSK heterodyne transmission system operating at 560 Mb/s and 1.2 Gb/s. Performance limitations affecting the receiver sensitivity in a 1.2-Gb/s DPSK system, such as laser phase noise, phase modulation depth, IF center frequency deviation, and local laser power, are studied. High receiver sensitivities for PSK systems were achieved. The applicability of the Mach-Zehnder modulator as a phase modulator for 1.2-Gb/s DPSK is also demonstrated. A 1.2-Gb/s DPSK transmission of over 100 km, using polarization diversity with novel polarization-insensitive automatic frequency control in an attempt to overcome signal fading caused by polarization fluctuation in the transmitting fiber, is also described. A receiver sensitivity of less than -42.8 dBm and varying within 1.4 dB for all states of polarization was achieved. A multichannel high-definition TV (HDTV) transmission experiment using a DPSK polarization-diversity tunable receiver is described. >

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>>

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. >

Measuring the longitudinal distribution of four-wave mixing efficiency in dispersion-shifted fibers

We measured and analysed four-wave mixing (FWM) efficiency and fluctuation along the actual dispersion-shifted fibers (DSFs). In the short, 1.1-km DSF, our results agreed with theory, and we also obtained zero-dispersion wavelength /spl lambda//sub 0/, zero-dispersion slope dD/d/spl lambda/, and nonlinear refractive index n/sub 2/ simultaneously. In the long, 23-km, DSF, a high FWM efficiency was observed in the wide wavelength region, due to the longitudinal zero-dispersion wavelength distribution. The fluctuation range was about 3.5 nm and the maximum slope about 1.1 km/nm.<<ETX>>

Four 5-Gbit/s WDM transmission over 4760-km straight-line using pre- and post-dispersion compensation and FWM cross talk reduction

Summary form only given. In conclusion, four 5.332-Gbit/s optical WDM signals were successfully transmitted over 4760-km straight-line using pre and post-compensation of group velocity dispersion (GVD) for each channel and the reduction of four wave mixing (FWM) cross talk with high-speed polarization scrambling.

Theoretical and experimental study of self-filtering effect in concatenated erbium-doped fiber amplifiers

This paper describes the self-filtering effect which appears in concatenated erbium-doped fiber amplifier (EDFA) systems. Employing a theoretical model we observed how the self-filtering wavelength is affected by the variation of some EDFA parameters, such as gain, fiber composition, pump wavelength and temperature. By a recirculating loop experiment which simulates a concatenated repeater transmission system, we measured the evolution of the amplified spontaneous emission (ASE) spectra with the number of circulations, and with the loss of the loop. We found a good agreement between the theoretical simulations and the experiments. >

Optical heterodyne image-rejection receiver for high-density optical frequency division multiplexing system

An optical heterodyne image-rejection receiver (IRR) for high-density optical frequency division multiplexing (OFDM) systems is described. The IRR was realized using balanced receivers, which showed more than 18-dB suppression over the 1.5-3.0-GHz IF region. Measured crosstalk penalties in a two-channel 560 Mb/s differential phase-shift keyed (DPSK) heterodyne optical communication system were realized for the first time. The crosstalk penalties in an OFDM system are estimated theoretically with and without the IRR. The required channel spacing and number of channels that can be accommodated in the 10-nm tuning range of the local laser are presented. A particular configuration of the IRR, its operation, and its performance limitations are discussed. The experimental results for image-rejection reception in a two-channel 560-Mb/s DPSK system are also given. Crosstalk penalties are estimated experimentally and compared to the theoretical calculation. Since the conventional configurations of the IRR are very sensitive to the polarization fluctuation of the transmitted signals, polarization-insensitive IRRs are proposed and their features are considered. >

128-Gbit/s WDM transmission of 24 5.3-Gbit/s RZ signals over 7828 km using gain equalization to compensate for asymmetry in EDFA gain characteristics

Erbium-doped fiber amplifiers (EDFAs) with broad signal bandwidth, low NF and high output power, and transmission characteristic improvement using chromatic dispersion management and modulation format are required for long-haul, wavelength-division multiplexing (WDM) transmission systems. We performed a 24 5.3-Gbit/s WDM transmission experiment over 7828 km using gain equalization to compensate for the asymmetry of the EDFA gain characteristics, RZ modulation format, and both pre- and post-compensation of chromatic dispersion.

Optical coherent broad-band transmission for long-haul and distribution systems using subcarrier multiplexing

The system configuration and future possibility of a coherent optical transmission system using subcarrier multiplex- ing (SCM) techniques are described. First, signal multiplexing techniques for coherent optical trans- mission are compared, and appropriate application for coherent SCM system is discussed. By comparing optical modulation meth- ods, optical frequency modulation (FM) using direct modulation of a DFB-LD and a heterodyne detection is shown to be feasible. lkansmission system using a configuration with a local laser in the transmitter is unaffected by polarization and is cost-effective. Phase noise can be suppressed by a phase-noise-canceling circuit (PNC) in a heterodyne receiver. This circuit is also effective for compensating for the frequency instability of light sources. A theoretical simulation of a coherent SCM system showed that a 100 channel of 30-MHz FM signal or a 15 channel of 155-Mb/s signal can be distributed to 10 000 subscribers using single stage or double stage optical amplifiers. To confirm the feasibility of coherent SCM transmission, pre- liminary experiments have been performed with optical FM by 2-channels 560-Mb/s ASK-SCM signal and a heterodyne detection using 3-electrode DFB-LDs. With a local LD setting at the transmitter, a span-loss margin of 40.7 dB was obtained using single stage Er3+-doped fiber amplifier (EDFA), and the system was insensitive to the state of polarization in the transmission fiber. In a subcarrier transmission of 560 Mb/s DPSK signal, the PNC effectively suppressed phase noise and the influence of IF frequency deviation. Finally, application of coherent SCM combined with optical frequency division multiplexing (OFDM) is discussed. A model allocation of optical carriers is proposed and possible receiving channel number is estimated.