Showing papers by "Norihiko Nishizawa published in 2002"

Pulse trapping by ultrashort soliton pulses in optical fibers across zero-dispersion wavelength

Abstract: A new phenomenon of pulse trapping by the ultrashort soliton pulse of an optical fiber has been experimentally observed. The trapped pulse in the normal-dispersion region copropagates with the soliton pulse in the anomalous-dispersion region along the fiber, and the wavelength of the trapped pulse is shifted to satisfy the condition of group-velocity matching. The wavelengths of the soliton pulse and the trapped pulse change almost continuously as the power of the soliton pulse is varied. Almost perfect conversion efficiencies are observed for soliton self-frequency shift and pulse trapping.

Characteristics of pulse trapping by ultrashort soliton pulse in optical fibers across zerodispersion wavelength.

Abstract: Characteristics of pulse trapping by ultrashort soliton pulse in optical fibers across zero-dispersion wavelength are analyzed both experimentally and numerically. The spectrogram of pulse trapping is observed using the technique of cross correlation frequency resolved optical gating and the phenomenon of pulse trapping is confirmed directly. The pulse trapping is numerically analyzed using the coupled strict nonlinear Schrodinger equations and the numerical results are well in agreement with the experimental ones. It is clarified that the pulse trapping occurs due to the sequential cross phase modulation by the Raman shifted soliton pulse.

Trapped pulse generation by femtosecond soliton pulse in birefringent optical fibers

Abstract: A novel phenomenon of trapped pulse generation by orthogonally polarized femtosecond soliton pulse is discovered in low birefringent optical fiber. As pulse propagation, wavelengths of soliton pulse and trapped pulse are shifted toward longer wavelength side due to effects of soliton self-frequency shift and pulse trapping. The energy of trapped pulse is increased exponentially through Raman gain of soliton pulse and orthogonally polarized and temporally overlapped two colored femtosecond twin pulses are generated. The spectrogram of output pulses is observed using cross-correlation frequency resolved optical gating technique. The characteristics of this phenomenon are also analyzed numerically and numerical results are almost in agreement with experimental ones.

0.78-0.90-μm wavelength-tunable femtosecond soliton pulse generation using photonic crystal fiber

Abstract: A compact system of 780-900-nm wavelength tunable femtosecond soliton pulse generation is demonstrated for the first time using a fiber laser, periodically poled LiNbO/sub 3/, and a photonic crystal fiber (PCF). The wavelength of the generated soliton pulse can be shifted almost linearly by varying the fiber input power. The temporal width of the generated soliton pulse is as short as 55 fs. The results of numerical analysis suggest that the wavelength of the soliton pulse can be shifted above 1.1 /spl mu/m using much higher power or a longer PCF. This system is constructed with almost all fiber devices and is compact and useful for practical applications.

Squeezed Vacuum Generation Using Symmetric Nonlinear Polarization Interferometer

Abstract: Squeezed vacuum generation is demonstrated using an ultrashort pulse fiber laser and a symmetric nonlinear polarization interferometer (NOPI). In this system, the squeezed vacuum can be generated only by passing the ultrashort pulse along the optical fiber. Noise reduction of -1.7 dB below shot noise level is observed. Considering the effect of quantum efficiency in this system, the corresponding magnitude of squeezing is estimated to be -2.7 dB. The system is constructed with all fiber devices and is compact, stable, and useful for practical applications.

Squeezed Vacuum Generation Using Symmetric Nonlinear Polarization Interferometer : Optics and Quantum Electronics

Abstract: Squeezed vacuum generation is demonstrated using an ultrashort pulse fiber laser and a symmetric nonlinear polarization interferometer (NOPI). In this system, the squeezed vacuum can be generated only by passing the ultrashort pulse along the optical fiber. Noise reduction of -1.7 dB below shot noise level is observed. Considering the effect of quantum efficiency in this system, the corresponding magnitude of squeezing is estimated to be -2.7 dB. The system is constructed with all fiber devices and is compact, stable, and useful for practical applications.

Wideband light spectrum generator and pulse light generator

Abstract: A wideband light spectrum generator (20) comprising an ultrashort pulse fiber laser (22) generating a pulse light having pulse width from pico second to femto second, and an optical fiber (24) connected with the ultrashort pulse fiber laser (22) through a lens (26) and generating a wideband light spectrum having such characteristics as the nonlinear coefficient for the wavelength of pulse light not smaller than 10 [W-1m-1] and the wavelength dispersion not larger than 2.0[ps/km/nm]. Pulse light from the ultrashort pulse fiber laser (22) is subjected to wavelength dispersion at the time of passing through the optical fiber (24) for generating a wideband light spectrum to form a super continuum spreading relatively flatly over a wide range of 1200-2000 nm.

Single shot transition absorption measurement method and single shot transition absorption measurement system using broadband super-continuum ultra-short light pulse

Abstract: PROBLEM TO BE SOLVED: To provide a method and a system for measuring transitional absorption variation of an ultrahigh-speed phenomenon over a wide wavelength band in a substance with a single shot. SOLUTION: A broadband super-continuum ultra-short light pulse 3 is branched into reference light 4 and probe light 5 to input the probe light 5 to an optical fiber 6. A signal light pulse 8 outputted from the optical fiber 6 is entered into a diffraction grating 10. The signal light pulse 8 dispersed by the diffraction grating 10 is subjected to time-space conversion into a frequency distribution 12 by a cylindrical lens 11. The frequency distribution 12 is subjected to spatial frequency filtering by a time-frequency conversion filter 13, and subjected to inverse time-space conversion into a two-dimensional lightwave distribution 15 by a cylindrical lens 14, so that an interference distribution of the lightwave distribution 15 with the lightwave from the reference light 6 is obtained as a light spectrogram 16 representing temporal variation of the frequency distribution of the signal light pulse. COPYRIGHT: (C)2004,JPO

Experimental Analysis of Ultrashort Pulse Propagation along Optical Fibers Using the Technique of Cross-Correlation Frequency Resolved Optical Gating.

Abstract: Characteristics of ultrashort pulse propagation in optical fibers at the wavelength region of 1.55 μm are experimentally analyzed using the cross-correlation frequency resolved optical gating (X-FROG) technique. In the anomalous dispersive fibers, widely wavelength tunable femtosecond soliton pulse is generated. The spectrogram of almost transform limited soliton pulse around 2 μm is observed. In the dispersion shifted fibers, the wavelength tunable soliton pulse and anti-stokes pulse are generated. As the results of X-FROG measurement, it is clarified that the anti-stokes pulse is overlapped with the soliton pulse and trapped by the soliton pulse. In the highly nonlinear optical fibers, 1.2-2.1 μm ultra-widely broadened super continuum and 1.46-1.68 μm linearly chirped one are generated. The spectrograms of generated super continuum are observed. The phenomenon of pulse trapping is also observed in generated super continuum.

Generation and characterization of widely broadened super continuum using highly nonlinear fibers and fiber laser

Abstract: In conclusion, we have demonstrated the generation of 1.18-2.10 /spl mu/m ultra-widely broadened SC and 1.46-1.68 /spl mu/m linearly chirped SC using only 5 m long two different kinds of highly nonlinear fibers and only 600 pJ pulse. This system is constructed with all the fiber devices and it is useful for practical application. The generated SC is experimentally analyzed using X-FROG technique. It is observed that the anti-Stokes pulse is overlapped with the trailing edge of the soliton pulse in PM-HN-DSF. It is considered that, after the a few meter propagation, the soliton pulses are redshifted due to the soliton self-frequency shift and the anti-Stokes components are gradually blueshifted due to the effect of pulse trapping by the soliton pulse in PM-HN-DSF.

Novel phenomenon of pulse trapping by ultrashort soliton pulse across zero-dispersion wavelength

Abstract: Summary form only given. The characteristics of pulse trapping are analyzed both experimentally and numerically. The spectrogram of the trapped pulse and soliton pulse is observed using the crosscorrelation frequency resolved optical gating (X-FROG) technique. The fundamental characteristics of the pulse trapping are analyzed numerically using simultaneous nonlinear Schrodinger equations. In the experiment, the soliton pulse is coupled into polarization maintaining highly nonlinear dispersion shifted fiber (PM-HN-DSF) slightly before signal pulse. The numerical results are well in agreement with the experimental ones. It is considered that the effects of cross-phase modulation and soliton self-frequency shift (SSFS) are the key factors of pulse trapping.

Short pulse light generating device and mutual correlation measurement device

Abstract: PROBLEM TO BE SOLVED: To provide a short pulse light generating device of which the output time of a short pulse light is continuously varied while the optical path of the short pulse light is kept constant and to provide a mutual correlation measurement device in which the short pulse light generating device is used. SOLUTION: The short pulse light generating device 2 is composed of a fiber laser 11, an acoustic and optical modulator 12, a polarized wave maintaining type optical fiber F1, an optical filter 15 or the like. The soliton pulse of each short pulse light outputted from the short pulse light generating device 2 is used as a reference short pulse, superimposed with a short pulse light to be measured on PBS32 and is made incident on an avalanche diode 33. Further, a signal outputted from the avalanche diode 33 is observed on an oscilloscope 34.