Multiplier for RZ Optical Clock

Phase Difference Control between Adjacent Optical Pulses by Means of Stabilization of Delayed Interferometer and Its Application to an OTDM

Multiplier for RZ Optical Clock

Hiroyuki TODA and Junichi MIYASHITA

(Received January 22, 2009)

Phase difference between adjacent optical pulses is stabilized by means of stabilization of a delayed interferometer (DI), which can be considered as an optical time-division multiplexed (OTDM) multiplexer. A continuous wave (CW) tunable laser, where the wavelength is different from that of the optical pulse, was used to stabilize the DI. We have confirmed that the phase difference of more than 8 was controlled using a piezo-electric transducer and a lock-in amplifier by tuning the CW laser wavelength. Moreover, we investigated an optical clock quadruple multiplier by serially concatenating the OTDM multiplexer. In 40GHz optical clock generation experiment, we have observed the temporal waveforms and optical spectra when in-phase and out-of phase optical clocks were successfully generated, respectively. The undesired optical sidebands were suppressed to be more than 15 dB for both cases.

Keywords: delayed interferometer, stabilizatin of interferometer, optical time-division multiplexing (OTDM), OTDM multiplexer, clock multiplier

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1) R. Ludwig, S. Weisser, C. Schmidt-Langhorst, L.

Raddatz and C. Schubert, "160 Gb/s-DPSK OTDM-transmission over 480 km using 160 km repeater spans and advanced forward-error-correction," Optical Fiber Communication (OFC 2007) and National Fiber Optic Engineers (NFOEC 2007), OWE4 (2007).

2) H. Murai, M. Kagawa, H. Tsuji, K. Fujii,

"EA-Modulator-Based Optical Time Division Multiplexing/Demultiplexing Techniques for 160-Gb/s Optical Signal Transmission," IEEE J. Sel. Top.

Quantum Electron., vol. 13, no. 1, pp. 70-78 (2007).

3) M. Daikoku, T. Miyazaki, I. Morita, H. Tanaka, F.

Kubota, and M. Suzuki, "8x160-Gb/s WDM Field Transmission Experiment With Single-Polarization RZ-DPSK Signals and PMD Compensator," IEEE Photon. Tech. Lett., vol. 18, no. 2, pp. 391-393 (2006).

(a) RZ optical clock

(b) CS-RZ optical clock

Fig. 6. Optical spectra of the generated 40GHz optical clocks by the optical clock quadruple multiplier.

(a) Without stabilization.

(b) With stabilization.

Fig. 7. Waveforms of the generated 40GHz RZ optical clock.ĺ10ps/divĻ

4) T. Hirooka, M. Okazaki, K. Osawa, and M. Nakazawa,

"160 Gbit/s-900 km DPSK transmission with time-domain optical Fourier transformation, European Conference on Optical Communication (ECOC2007), 1.3.3, (2007).

5) ^ža·ä"Ĩ«§Úċ›œ}(+qIX>į

jëx°," 2007mš@˜B-10-18 (2007).

6) ^žaėõ·ä"›œ}Ĩ«§Úċ(+

RZq7ZC74ģnqÅuy—ĬŒĘ," 2008m

šý˜B-10-72 (2008).