Katsuhiro Shimizu

NRZ-OOK-to-RZ-BPSK modulation-format conversion using SOA-MZI wavelength converter

A novel all-optical modulation-format conversion from nonreturn-to-zero on-off keying (NRZ-OOK) to return-to-zero binary phase-shift keying (RZ-BPSK) is proposed. A Mach-Zehnder interferometric (MZI) wavelength converter consisting of integrated semiconductor optical amplifiers (SOAs) is utilized to implement the proposed format conversion. Error-free operation at a bit rate of 10.7 Gb/s is experimentally demonstrated in order to show the feasibility of the proposed scheme. The received sensitivity of the converted signal is improved by 2.9 dB compared with a back-to-back NRZ-OOK signal at BER=10 -9. In addition, a reasonable dispersion tolerance of the converted signal up to plusmn500 ps/nm is observed. The numerical simulation based upon the carrier-rate equation verifies the experimental results

Continuous-wave fiber optical parametric wavelength converter with +40-dB conversion efficiency and a 3.8-dB noise figure

We have obtained 40 dB of internal (on-off) conversion gain and a sub-4-dB noise figure (NF) with a continuous-wave (cw) fiber optical parametric wavelength converter. To our knowledge, this is the lowest NF reported for any cw wavelength converter. We have also investigated the properties of NF versus signal input power and pump power.

All-optical modulation format conversion from NRZ-OOK to RZ-QPSK using parallel SOA-MZI OOK/BPSK converters

A novel all-optical modulation format conversion from non-return-to-zero on-off-keying (NRZ-OOK) to return-to-zero quadrature-phase-shift-keying (RZ-QPSK) is proposed and experimentally demonstrated. The proposed format conversion scheme is based on parallel Mach-Zehnder interferometric (MZI) OOK/binary-PSK (BPSK) converters, consisting of integrated semiconductor optical amplifiers (SOAs). We experimentally demonstrate that in both decoded channels of the converted RZ-QPSK signal bit error rate (BER) curves show almost the same receiver sensitivity at a symbol-rate of 10.7 Gsymbol/s. In addition, a reasonable dispersion tolerance of the converted signal up to +295 ps/nm is observed. The numerical simulation based upon carrier rate equation verifies the experimental results.

Continuous-wave fiber optical parametric amplifier with 60-dB gain using a novel two-segment design

We have obtained 60 dB of internal (ON-OFF) gain with a continuous-wave fiber optical parametric amplifier by using an isolator between two fiber segments to increase the pump stimulated Brillouin scattering threshold. Subdecibel penalties were measured for transmission of 10-Gb/s signals, with 35 dB of gain.We have obtained 60 dB of internal (ON-OFF) gain with a continuous-wave fiber optical parametric amplifier by using an isolator between two fiber segments to increase the pump stimulated Brillouin scattering threshold. Subdecibel penalties were measured for transmission of 10-Gb/s signals, with 35 dB of gain.

Interferometric crosstalk-free optical add/drop multiplexer using Mach-Zehnder-based fiber gratings

Mach-Zehnder interferometers with fiber Bragg gratings (MZ-FG) are investigated as promising devices for wavelength-selectable optical add-and-drop multiplexers (OADM). A wavelength reused OADM performance is demonstrated for the first time to our knowledge in a six-channel, 10 Gb/s WDM experiment using a single-stage MZ-FG. We discuss both theoretically and experimentally the interferometric crosstalk induced by imperfect Bragg-reflectivity. Two methods are proposed to solve the interferometric crosstalk issues. The first one is wavelength offset scheme. It is experimentally confirmed that there is no interference when the wavelength of crosstalk is away from that of the signal at least two times of bit-rate. In order to separate each wavelength, the master-slave wavelength control method is proposed with Fabry-Perot interferometer made of a set of fiber gratings. The second one is a cascaded MZ-FG scheme eliminating the crosstalk itself. The calculation indicates that a Bragg-reflectivity of only 93% can suppress the crosstalk to be -35 dB. Cascaded MZ-FGs have been fabricated to show that the interferometric crosstalk can be successfully reduced to -50 dB for the add signal, and -71 dB for the drop signal, respectively. The eight-wavelength 10 Gb/s OADM experiment is carried out to demonstrate the low interferometric crosstalk performance.

A channel-number insensitive erbium-doped fiber amplifier with automatic gain and power regulation function

The design scheme for an erbium-doped fiber amplifier (EDFA) with automatic channel-by-channel gain and power regulation function is discussed with much emphasis on the pump power control scheme and the requirement for feedback circuitry. Based on both wavelength and time-resolved simulation technique, an amplifier repeater employing novel high-speed automatic gain control (AGC) and automatic level control (ALC) functions is designed and implemented. The AGC and ALC scheme can suppress the transient power fluctuation of a surviving channel caused by adding or dropping all other channels less than 0.45 dB and keep output power constant over 9-dB input power range.

4-level direct-detection polarization shift-keying (DD-PolSK) system with phase modulators

We propose and demonstrate a novel 4-level DD-PolSK system with LiNbO/sub 3/-based phase modulator and alternative allocation of constellations, which lead to a greatly simplified transceiver architecture. A 5 Gb/s (2.5 GS/s) testbed has been build to demonstrate the feasibility of the 4-PolSK transceiver.

43 Gb/s DQPSK pre-equalization employing 6-bit, 43GS/s DAC integrated LSI for cascaded ROADM filtering

Electronic pre-equalization for 43 Gb/s DQPSK has been demonstrated for the first time. Waveform distortion caused by bandwidth narrowing to 18.1 GHz by cascaded 10 Gb/s ROADMs has been adequately pre-equalized by a SiGe-BiCMOS LSI with 6-bit, 43 GS/s digital-to-analog converters.

A study on automatic bias control for arbitrary optical signal generation by dual-parallel Mach-Zehnder modulator

A novel automatic bias control (ABC) is proposed to generate arbitrary signals with a dualparallel Mach-Zehnder modulator. We demonstrated the practical generation of arbitrary modulated signals using the proposed scheme.

Soft decision LSI operating at 32 Gsample/s for LDPC FEC-based optical transmission systems

We have developed a 2-bit 32 Gsample/s soft decision LSI for low-density parity-check code FEC at 100 Gb/s in 0.13 mum SiGe-BiCMOS which generates confidence bit with 25 mVpp sensitivity.