General optical pulse compression technology can be broadly divided into a pulse compression technique using an optical fiber and a pair of diffraction gratings (first conventional technique) and a pulse compression technique based on soliton effect using a dispersion-decreasing fiber (second conventional technique).
When a strong optical pulse is launched into a fiber, the first conventional technique converts the pulse into a broadband rectangular pulse having a linear chirp by normal dispersion and non-linearity (self-phase modulation effect) of the fiber. Then, the linearly chirped pulse is dispersion-compensated through anomalous dispersion realized artificially by the pair of diffraction gratings, and the width of the input pulse is greatly reduced (non-patent documents 1 and 2). Non-patent document 2 reports an example of compressing an optical pulse train having a repetition frequency of 10 GHz and a pulse width of 7.1 ps to 720 fs at a wavelength of 1548 nm.
The second conventional technique compresses a soliton pulse width by decreasing the anomalous dispersion value of the fiber adiabatically while maintaining the soliton property along the direction of propagation (by changing the dispersion gradually). The principle used here is that a soliton keeps a constant level of energy by automatically varying the pulse width with a change in dispersion (non-patent documents 3 and 4). Non-patent document 4 reports an example of compressing, with the use of a dispersion-decreasing fiber, an optical pulse train having a repetition frequency of 10 GHz and a pulse width of 3 ps to 170 fs at a wavelength of 1550 nm.
Conventional optical function generators and optical pulse shapers (third conventional technique) use a lens and a diffraction grating or an arrayed waveguide grating to change the amplitude and phase of each frequency component of the pulse independently (non-patent documents 5 and 6). Letting the input time waveform be u(t) and its spectrum be U(ω), the output time waveform be v(t) and its spectrum be V(ω), and the transfer function of pulse shaping in the time domain be g(t) and the transfer function of pulse shaping on the spectrum be G(ω), the relationship in the frequency domain can be expressed as follows:V(ω)=G(ω)U(ω)The relationship in the time domain can be expressed as follows:
      v    ⁡          (      t      )        =            ∫              -        ∞            1        ⁢                  g        ⁡                  (                      t            -            τ                    )                    ⁢              u        ⁡                  (          τ          )                    ⁢                          ⁢              ⅆ        τ            Non-patent Document 1W. J. Tomlinson, R. J. Stolen, and C. V. Shank, “Compression of optical pulses chirped by self-phase modulation in fibers,” J. Opt. Soc. Am. B, Vol. 1, pp. 139-149, 1984Non-patent Document 2K. Tamura, T. Komukai, T. Yamamoto, T. Imai, E. Yoshida, and M. Nakazawa, “High energy, sub-picosecond pulse compression at 10 GHz using a fiber/fiber-grating pulse compressor,” Electron. Lett. Vol. 31, pp. 2194-2195, 1995Non-patent Document 3S. V. Chernikov, D. J. Richardson, E. M. Dianov, and D. N. Payne, “Picosecond soliton pulse compressor based on dispersion decreasing fiber,” Electron. Lett. Vol. 28, pp. 1842-1844, 1992Non-patent Document 4M. Nakazawa, E. Yoshida, K. Kubota, and Y. Kimura, “Generation of 170 fs, 10 GHz transform-limited pulse train at 1.55 μm using a dispersion-decreasing, erbium-doped active soliton compressor,” Electron. Lett. Vol. 30, pp. 2038-2040, 1994Non-patent Document 5A. M. Weiner, J. P. Heritage, and E. M. Kirschner, “High-resolution femtosecond pulse shaping,” J. Opt. Soc. Am. B, Vol. 5, pp. 1563-1572, 1988Non-patent Document 6K. Okamoto, T. Kominato, H. Yamada, and T. Goh, “Fabrication of frequency spectrum synthesizer consisting of arrayed-waveguide grating pair and thermo-optic amplitude and phase controllers,” Electron. Lett. Vol. 35, pp. 733-734, 1999
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