Yasuhiro Okamura

Simultaneous detection of 10-Gbit/s QPSK × 2-ch. Fourier-encoded synchronous OCDM signals with digital coherent receiver

We experimentally demonstrate the simultaneous detection of 10-Gbit/s quadrature phase shift keying (QPSK) × 2-channel Fourier-encoded synchronous optical code division multiplexing (FE-SOCDM) signals using a digital coherent receiver, for the first time. First, we analytically verify that simultaneous detection can be achieved with an N-point discrete Fourier transform (DFT) using digital signal processing (DSP) because the N-channel Fourier encoding corresponds to an N × N inverse DFT, then the operation is experimentally confirmed. Simultaneous detection of 10-Gbit/s QPSK × 2-channel FE-SOCDM signals is evaluated. The proposed scheme dramatically expands the capability of OCDM systems.

All-Optical Generation of Optical BPSK/QPSK Signals Interleaved With Reference Light

In this letter, all-optical generation of multilevel modulated signals interleaved with reference light is proposed and experimentally demonstrated. Four Gbaud BPSK and QPSK signals interleaved with reference light are generated using a based 22 optical switch, and the generated signals are demodulated by self-homodyne detection using an optical delay interferometer and a single photodetector. Moreover, we obtained negligible difference of error vector magnitude values between an external cavity laser with 100-kHz linewidth and a distributed-feedback laser with 6-MHz linewidth.

Optical pump phase locking to a carrier wave extracted from phase-conjugated twin waves for phase-sensitive optical amplifier repeaters

In this paper, an optical phase-locked loop assisted by sum-frequency and second-harmonic generation (SS-OPLL) for frequency nondegenerate optical parametric phase-sensitive amplifier repeaters is experimentally demonstrated. First, theoretical derivations show that carrier extraction from phase-conjugated twin waves (PCTWs) and reference light generation are achieved by sum-frequency generation; therefore, the SS-OPLL circuit enables optical phase locking between PCTWs and a pump wave by a simple architecture based on a balanced OPLL. Then, optical phase locking between 20-Gbit/s quadrature phase-shift keying PCTWs and an individual pump source is experimentally demonstrated. Experimental results indicate that phase errors were reduced during the SS-OPLL operation.

Experimental demonstration of optical concatenated coding enabling channel grouping on OCDM networks

Concatenated optical coding provides channel grouping ability on OCDM networks. With the 16-chip optical code concatenating two 4-chip Fourier codes, selection of a channel in sixteen or a code group in four is experimentally demonstrated.

Pump phase-locking method dependence of ND-PSA repeaters on multi-span transmission of QPSK-PCTWs in dispersion compensated links

Pump phase-locking method dependence of non-degenerate phase-sensitive optical amplifier (ND-PSA) repeaters on phase-conjugated twin waves transmission is investigated. Simulation results show ND-PSAs with an optical phase-locked loop method can extend a transmission distance compared to the case of an optical injection locking method in dispersion compensated links.

Noise characteristics of non-degenerate optical parametric phase-sensitive amplifier with gain saturation and distributed loss in gain medium

Noise characteristics of non-degenerate optical parametric phase sensitive amplifiers are theoretically investigated using numerical simulation. Quantum properties of noise are taken into account by adding random amplitude to signal as vacuum noise. Amplitude noise suppression owing to gain saturation and its mitigation due to distributed loss in a gain medium are shown.

Optical phase-locking among phase-conjugated twin waves and free-running pump by using sum-frequency and second harmonic generation assisted OPLL for ND-PSA repeaters

Optical phase-locking among 5-Gbit/s BPSK phase-conjugated twin waves and a free-funning pump is experimentally demonstrated. A sum-frequency and second harmonic generation assisted OPLL circuit compensates error signals between the PCTWs and the pump successfully.

Influence of chromatic dispersion on optical transmission of 16QAM signals interleaved with reference light

We numerically investigated influence of chromatic dispersion on an optical transmission of 16 quadrature amplitude modulation (QAM) signals interleaved with reference light. Simulation results showed that values of dispersion tolerance, satisfying 3-dB eye opening penalty, of 5-, 10-, and 20-Gbaud interleaved 16QAM were 630-, 156-, and 38-ps/nm, respectively.

Degradation of signal quality due to pump-phase fluctuation on non-degenerated fiber parametric phase-sensitive amplifier repeaters

Degradation of phase-conjugated twin waves on non-degenerated fiber parametric phase-sensitive amplifier repeaters due to pump-phase fluctuation is numerically investigated. From simulation results, an acceptable phase error on pump-phase locking is clarified.

Optical phase lock loop circuit for non-degenerate optical parametric phase sensitive amplifiers with wide signal-idler optical frequency spacing

Optical phase lock loop circuit for non-degenerate parametric phase sensitive amplifiers with wide signal-idler light frequency spacing is proposed. The proof-of-principle experiment is successfully demonstrated for 40-GHz spaced signal-idler lights using 5-GHz beat signals.