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Masataka NAKAZAWA Masato YOSHIDA Toshihiko HIROOKA
Ultrahigh-speed fiber lasers operating at up to 40 GHz offer a clean longitudinal comb and a narrow linewidth. This makes them suitable for applications including optical comb generation, ultrahigh-speed optical pulse transmission including PSK, and as opto-microwave oscillators. In this paper, we describe recent progress on ultrafast fiber lasers and their applications to optical metrology.
Yun Jong KIM Hyun-Jeong JO Young Yun CHUN Chang-Soo PARK
We present and demonstrate a novel method of generating a π phase-alternated return-to-zero (RZ) signal together with pulse-amplitude equalization in a rational harmonic mode-locked fiber ring laser, by using a dual-drive Mach-Zehnder modulator. By adjusting the voltages applied to both arms of the modulator, amplitude-equalization and π phase shift can be achieved successfully at a 9.95 GHz repetition rate. The generated alternate-phase RZ signals show enhanced transmission performance in the single-mode fiber (SMF) links without dispersion compensation.
Timing noise of 160 GHz optical pulses has been evaluated over nine decades of Fourier frequency using the optoelectronic harmonic mixing technique. For down-converting the 160 GHz pulse intensity into a low-frequency IF signal, the fourth order modulation sidebands produced by a Mach-Zehnder intensity modulator have been employed. Phase noise power spectral density and timing jitter for 155.552-GHz optical time-division multiplexed pulses and 160.640-GHz passively mode-locked pulses are measured using the time domain demodulation and time interval analysis techniques, respectively.
Nobuhide YAMADA Hiroshi OHTA Seiji NOGIWA
This very useful optical sampling system uses a passively mode-locked fiber laser as an optical sampling pulse source and is based on sum-frequency generation. The optical pulse had a sufficiently short pulse width, and its peak power was very high. In addition, it had a very low timing jitter. We could observe optical signals that were jitter-free in terms of single scanning. The sum-frequency generation conversion efficiency was 1.0 10-4 W-1, and the temporal resolution was 700 fs, when we used a 5-mm-thick KTP crystal. A 320-Gbit/s optical signal could be clearly observed. We have also developed a polarization-insensitive optical sampling system with a two-path configuration based on sum-frequency generation using the type-II phase matching condition in a KTP crystal. The polarization dependency was less than 3.5% (0.15 dB) in the wavelength range from 1520 to 1620 nm.
Kenji SATO Shoichiro KUWAHARA Yutaka MIYAMOTO Koichi MURATA Hiroshi MIYAZAWA
Phase-inversion between neighboring pulses appearing in carrier-suppressed return-to-zero pulses is effective in reducing the signal distortion due to chromatic dispersion and nonlinear effects. A generation method of the anti-phase pulses at 40 GHz is demonstrated by using semiconductor mode-locked lasers integrated with chirped gratings. Operation principle and pulse characteristics are described. Suppression of pulse distortion due to fiber dispersion is confirmed for generated anti-phase pulses. Repeaterless 150-km dispersion-shifted-fiber L-band transmission at 42.7 Gbit/s is demonstrated by using the pulse source.
Recent activities on ultrafast photonic device technology development in the Femtosecond Technology Project sponsored by NEDO are introduced. Topics include management and control of the higher order dispersions of optical fibers, ultrafast mode-locked semiconductor laser, symmetric Mach-Zehnder type all-optical switch, ultrafast serial-to-parallel signal converter and sub-picosecond wavelength switch. Challenges towards novel ultrafast switching material systems are also described.
Masataka NAKAZAWA Takashi YAMAMOTO Koichi Robert TAMURA
Progress on a single wavelength channel OTDM terabit/s transmission is described. In particular, we focus on 1.28 Tbit/s OTDM transmission over 70 km which we realized recently. A pre-chirping technique using a high speed phase modulator is emphasized to simultaneously compensate for third- and fourth-order dispersion. The input pulse width was 380 fs, and the pulse broadening after a 70 km transmission was as small as 20 fs. All 128 channels time-division-demultiplexed to 10 Gbit/s had a bit error rate of less than 110-9, in which we employed a lot of new technique for pulse generation, dispersion compensation and demultiplexing. These techniques help pave the path for OTDM technology of the 21 century.
Shin ARAHIRA Yukio KATOH Daisuke KUNIMATSU Yoh OGAWA
A 160 GHz colliding-pulse mode-locked laser diode (CPM-LD) was stabilized by injection of a stable master laser pulse train repeated at a 16th-subharmonic-frequency (9.873 GHz) of the CPM-LD's mode-locking frequency. Synchroscan steak camera measurements revealed a clear pulse train with 16-times repetition frequency of the master laser pulse train for the stabilized CPM-LD output, indicating that CPM-LD output was synchronized to the master laser and that the timing jitter was also reduced. The timing jitter of the stabilized CPM-LD was quantitatively evaluated by an all-optical down converting technique using the nonlinearity of optical fiber. This technique is simple and has a wider bandwidth in comparison to a conventional technique, making it possible to accurately measure the phase noise of ultrafast optical pulse train when its repetition frequency exceeds 100 GHz. The electrical power spectra measurements indicated that the CPM-LD's mode-locking frequency was exactly locked by the injection of the master laser pulse train and that the timing jitter decreased as the injection power increased. The timing jitter was reduced from 2.2 ps in free running operation to 0.26 ps at an injection power of 57 mW, comparable to that of the master laser (0.21 ps).
Kenji SATO Isamu KOTAKA Yasuhiro KONDO Mitsuo YAMAMOTO
This paper describes short pulse generation at over 40 GHz using monolithic mode-locked lasers integrated with electroabsorption modulators. The electroabsorption modulator using strained-InGaAsP multiquantum wells provides a pulse shortening gate at a high-repetition frequency. Pulse generation around 4 ps has been realized at a repetition frequency of 43. 5 GHz. Pulse compression using a 1. 3 µm single mode fiber is performed and a 0. 87 ps pulse is obtained.
Hidehiko TAKARA Satoki KAWANISHI Masatoshi SARUWATARI
We investigate the relaxation oscillation characteristics of an actively mode-locked fiber laser and a novel stabilizing method of the laser theoretically and experimentally. The stabilizing method controls cavity length to suppress the rf power of the relaxation oscillation frequency of the laser output, and can directly monitor the stability of the laser to ensure the most stable operation. With this method, the rf power ratio between mode-locking frequency and the background noise can be kept to more than 70 dB, and highly stable transform-limited pulse generation is achieved. Bit-error-free operation at 6. 3 GHz over 10 hours is successfully demonstrated. The stability of the center wavelength of the laser output and the required accuracy of cavity control for high-speed laser operation are also discussed.
Yoshitada KATAGIRI Atsushi TAKADA Shigendo NISHI Hiroshi ABE Yuji UENISHI Shinji NAGAOKA
We propose a mechanically tunable passively mode-locked semiconductor laser with a high repetition rate using a simple configuration with a moving mirror located very close to a laser facet. This scheme is demonstrated for the first time by a novel micromechanical laser consisting of an InGaAsP/InP multisegment laser with a monolithic moving micro-mirror driven by an electrostatic comb structure. The main advantage of this laser is the capability of generating high-quality mode-locked pulses stabilized by a phase-locked loop (PLL) with low residual phase noise in a wide repetition-rate tuning range. This paper describes the basic concept and tuning performances utilizing the micromechanical passively mode-locked laser in 22-GHz fundamental mode-locking and in its second-harmonic mode-locking.
Kenji TORIZUKA Hideyuki TAKADA Kenzo MIYAZAKI
Self-modelocking of Ti:sapphire laser has obtained with less than 2 W of argon-ion laser pumping. Two independent lasers with 36 fsec and 63 fsec in pulse duration were operated by a 6 W pump laser. In the low-threshold lasers, not only an ordinary mode-locking but also a double-pulse mode-locking, where two pulses circulating in the cavity, was stable.
Akimasa KANEKO Akira ITO Osamu FURUKAWA Tatsuo WADA Hiroyuki SASABE Keisuke SASAKI
We report the dispersion of two-photon absorption (TPA) coefficient, (β), in polydiacetylene (12, 8) thin film waveguides in the wavelength range less than the one-photon band-gap with a 100 femtosecond mode-locked Ti: Sapphire laser pulses. The TPA coefficient was found to be 4 cm/GW for TE polarization at 900 nm (1.38 eV) by taking into account a Gaussian intensity distribution as well as a temporal pulse shape. We observed a sharp resonance in β above the first one-photon allowed transition with a full width at half maximum (FWHM) of 90 meV.
Akimasa KANEKO Takashi KUWABARA Tatsuo WADA Hiroyuki SASABE Keisuke SASAKI
Optical Kerr effect were applied to all-optical switching devices in the form of nonlinear waveguide directional couplers. The nonlinear waveguide directional coupler consists of a quartz thin gap between two Corning 7059 guided layers on a pyrex substrate with ion-milled grating and organic thin film as a top layer. The vacuum-deposited polydiacetylene (12, 8) film was used as an organic nonlinear material. Power-dependent switching phenomenon in this asymmetrical nonlinear directional coupler was observed by 100 fs pulse duration of mode-locked Ti: Sapphire laser.
Satoki KAWANISHI Masatoshi SARUWATARI
Recent progress on the ultrahigh-speed optical transmission experiments are reviewed including the ultrashort pulse generation, high-speed timing extraction, all-optical multi/demultiplexing. Also discussed are the latest 100 Gbit/s experiments and a scope to higher bit-rate, longer distance optical transmission.