Showing papers on "Supercontinuum published in 1999"

Femtosecond spectroscopy of condensed phases with chirped supercontinuum probing

Abstract: Pump--supercontinuum-probe (PSCP) spectroscopy with femtosecond time resolution is developed theoretically and experimentally. The connection to previous theoretical results on nonchirped probing is established. It is experimentally shown that the supercontinuum can be described as a single chirped pulse. A key problem of the technique---the precise time correction of transient spectra---is solved by monitoring the nonresonant electronic response from a pure solvent (liquids) or from a transparent substrate (solid films). This allows for an adequate characterization of the supercontinuum, in particular, for directly measuring the spectral dependence of the pump-probe cross correlation. For 50-fs pump pulses, a theoretical estimate gives an accuracy for the time correction of 10 fs, which is typically \ensuremath{\approx}1/30 of the supercontinuum pulse duration. Hence a time resolution of 10--20 fs can be experimentally realized. Contributions to the nonresonant transient signal from high-frequency Raman excitations and from low-frequency impulsive-stimulated Raman processes are discussed. The PSCP technique is illustrated by results from experiments with fused silica and several common solvents and with a chromophore in solution.

3 Tbit/s (160 Gbit/s × 19 channel) optical TDM and WDM transmission experiment

Abstract: A 3 Tbit/s (160 Gbit/s × 19 channels) optical signal has been successfully transmitted over 40 km of dispersion-shifted fibre Low noise supercontinuum signal pulse sources and 70 nm bandwidth tellurite-based optical amplifiers are used for 3 Tbit/s signal generation and amplification

Time-domain optical sensing

Abstract: A chirped optical supercontinuum is used to map absorption spectra into temporal waveforms. Time-domain spectral measurement of acetylene is demonstrated using a modelocked fibre laser as the source of broadband radiation and a sampling oscilloscope for spectral measurement.

Filamentation and supercontinuum generation during the propagation of powerful ultrashort laser pulses in optical media (white light laser)

Abstract: The fundamental physical mechanism responsible for the self-focussing, filamentation, supercontinuum generation and conical emission of a powerful ultrashort laser pulse in a transparent optical medium is reviewed. The propagation can be described by the model of moving focus modified by the defocussing effect of the self-induced plasma through multiphoton interaction with the medium. Spatial and temporal self-phase modulation in both the neutral Kerr medium and the plasma transform the pulse into a chirped (elongated) and strongly deformed pulse both temporally and spatially. The manifestation of the deformation is supercontinuum generation and conical emission. A new phenomenon of refocussing was observed. It is due to the diffraction of the trailing part of the pulse by the plasma that results in a ring structure of positive index changes surrounding the plasma column. This ring structure refocuses the pulse partially. The measured coherence lengths of the various frequencies components of the supercontinuum are independent of the optical media used and are essentially equal to that of the pump laser pulse when compared to an incoherent white light source. We thus justify that such a deformed pulse with a very broad spectrum could be called a chirped white light laser pulse.

Femtosecond time-resolved Raman spectroscopy using stimulated Raman scattering

Abstract: Femtosecond Raman spectroscopy has been developed to investigate ultrafast photoinduced structural changes of materials. Vibrational modes in the photogenerated transient species are measured by stimulated Raman scattering using a Raman pump pulse with narrow bandwidth and a femtosecond supercontinuum probe pulse. The Raman signal can be measured without slowing the temporal response and broadening the spectrum, because the temporal and spectral resolutions of the present method can be improved independently without the restriction of the transform limit. The transient Raman spectra of the trans- cis photoisomerization process in the DCM (4-dicyanomethylene-2-methyl-6-$p$-dimethylaminostyryl-4H-Pyran) dye solution were observed with the resolutions of 250 fs and $25{\mathrm{cm}}^{\ensuremath{-}1}.$

Stable supercontinuum generation in short lengths of conventional dispersion-shifted fiber

Abstract: By propagating 500-fs pulses through 2.5 m of standard fiber followed by 2 m of dispersion-shifted fiber, we generated >200 nm of spectral continuum between 1430 and 1630 nm, which is flat to less than ±0.5 dB over more than 60 nm. Pulses obtained by filtering the continuum show no increase in timing jitter over the source laser and are pedestal free to >28 dB, indicating excellent stability and coherence. We show that the second- and third-order dispersions of the continuum fiber and self-phase modulation are primarily responsible for the continuum generation and spectral shaping and found close agreement between simulations and experiments.

The White Light Supercontinuum Is Indeed an Ultrafast White Light Laser

Abstract: We identify the white light supercontinuum generated by femtosecond Ti-sapphire laser pulses as an ultrafast white light laser because the relative coherence lengths of all the wavelength components of the supercontinuum are essentially the same as that of the laser pulse when compared to an incoherent white light source.

Analyses of coherence-maintained ultrashort optical pulse trains and supercontinuum generation in the presence of soliton–amplified spontaneous-emission interaction

Abstract: Coherence degradation in the soliton pulse-compression process and supercontinuum generation in the presence of amplified spontaneous emission are studied with numerical simulations. We have developed a new simulation method to study the quality of a pulse train and use numerical simulations to present three ways to suppress its coherence degradation. We point out that a simple measurement of the pulse train’s power spectrum does not fully represent the quality of the pulse train because it does not contain detailed information on noise.

Photoionization of silicate glasses exposed to IR femtosecond pulses

Abstract: Photoionization of alkali-silicate, boro-silicate, lead-silicate and photosensitive multi-component silicate glasses has been studied under exposure to infrared femtosecond laser pulses at irradiance below the thresholds of laser-induced damage and catastrophic self-focusing. It is proved that the supercontinuum that is generated in all glasses studied as a result of the femtosecond laser pulses spectral broadening extends up to the short-wavelength part of the ultraviolet region of spectrum even if the glass is opaque in this region. It is shown that photoionization results from absorption of the short-wavelength component of this supercontinuum generated by infrared radiation. This ionization leads to the color center formation and luminescence in the bulk of glasses studied. Photoionization of photosensitive multi-component glasses leads to the creation of latent image and to the refractive index changing in exposed area after thermodevelopment. Fused silica exhibits the same spectral broadening too but color center formation in the visible was not recorded at irradiance up to the laser damage threshold.

3 Tbit/s (160 Gbit/s/spl times/19 ch) OTDM/WDM transmission experiment

Abstract: 3 Tbit/s (160 Gbit/s/spl times/19 channels) optical signal is successfully transmitted over 40 km dispersion-shifted fiber. Low noise supercontinuum signal pulse sources and 70 nm bandwidth tellurite-based optical amplifiers are used for 3 Tbit/s signal generation and amplification.

Nondispersive wavelength-division sampling.

Abstract: We propose and demonstrate a new wavelength-division-sampling technique with high temporal resolution. A discrete-time true-time delay generates multiwavelength near-transform-limited pulses from a supercontinuum source. Pulses sample the analog signal in an electro-optic modulator and are subsequently demultiplexed in a wavelength-division-multiplexing filter. A 100-Gsample/s experimental demonstration of this concept is presented.

1.4 W saturated output power from a fibre Raman amplifier

Abstract: Fiber Raman amplifiers with high output power and a 50% net pump to signal conversion efficiency are reported. A 100-nm supercontinuum based upon a 10-GHz, 8-ps pulse source was generated strong nonlinear interaction in the amplifier.

Low energy, enhanced supercontinuum generation in high nonlinearity dispersion-shifted fibers

Abstract: Summary form only given We generate >420 nm of supercontinuum (SC) by propagating pulses with energies <100 pJ through less than 2 m of dispersion-shifted fiber (DSF) in which the nonlinearity is enhanced by a factor of 45X over conventional DSF By using high nonlinearity (Hi-NL) fiber, we reduce required pulse energies by 56% while simultaneously increasing the bandwidth by 86 nm compared with SC generated in conventional DSF of the same length and dispersion We study the SC evolution as a function of pulse energy, fiber length and nonlinearity to find optimal conditions for maximum broadening without spectral distortion Fiber-based SC has been demonstrated as a promising candidate for TDM/WDM sources and is generated typically in several kilometers of dispersion-tailored fiber By generating the SC in a fiber shorter by three orders of magnitude, we obtain very stable pulses from the continuum and are able to accurately model the SC generation process The short fiber length, however, requires high average power sources at OC-192 repetition rates We reduce the average power required from a 10 Gb/s or OC-192 source to <550 mW by using 2 m of Hi-NL fiber

Broadcast-and-select OCDM/WDM network using 10 Gbit/s spectrum-sliced supercontinuum BPSK pulse code sequences

Abstract: Broadcast-and-select optical code division multiplexing (OCDM) and a WDM hybrid network are presented, in which 10 Gbit/s spectrum-sliced supercontinuum (SC) binary phase shift keying (BPSK) pulse code sequences are used as multi-wavelength optical BPSK code sources.

Stable 200 nm TDM/WDM source based on continuum generation in 2 m of fiber

Abstract: By propagating 500-fs pulses through 2 m of standard fiber followed by 2 m of dispersion-shifted fiber, we generate >200 nm of supercontinuum between 1430 nm and 1630 nm. The supercontinuum is flat to

Observation of phase conservation in multiwavelength binary phase shift-keying pulse-sequence generation at 10 Gbits/s by use of a spectrum-sliced supercontinuum in an optical fiber.

Abstract: Phase conservation in multiwavelength binary phase shift-keying (BPSK) pulse-sequence generation by slicing of a supercontinuum spectrum with a dispersion-flattened normal-dispersion fiber is experimentally observed. A 10-Gbit/s BPSK pulse sequence with a bit-error rate of <10(-10) is successfully generated over a 20-nm-wide wavelength range 1540-1560 nm.

Analysis and measurement of root-mean-squared bandwidth of cross-phase-modulation-induced spectral broadening

Abstract: The root-mean-squared bandwidth of spectral broadening induced by cross-phase modulation is derived analytically for a two-channel system consisting of a pump and probe channel. The pump channel is randomly modulated by binary data and the probe channel is a weak continuous-wave channel. The analytical expression is verified by experiments.

Self-action of femtosecond pulses with continuum spectrum

Abstract: On the basis of the analysis of the wave equations for an electrical field of radiation and without use of slowly varying envelope approximation the self-action of femtosecond light pulses in transparent media is investigated. The results of numerical simulation of spectral supercontinuum evolution, accompanying temporary broadening of intensive pulses with a spectrum in the range of normal groupdispersion ofmedium both with only electronic nonlinearity, and with simultaneous electronic and electronic-vibrational nonlinearities are presented. The opportunity of compression of pulses with supercontinuum spectrum in light formations consisting of one cycle of anelectric field is predicted. It is shown that spectral superbroadening of the elliptically polarized radiation is accompanied by nonuniform rotation of a polarization ellipse.Keywords: extremely ultra-short pulses, electric field equations, self-action, supercontinuum spectrum, polarization ellipse. 1. INTRODUCTIONThe development of laser engineering of ultrashort pulses has resulted in creation of laser systems generating femtosecondpulses, which consist of several cycles of a light field'. The width of a spectrum of such extremely short pulses (ESP) becomes

Quantum Efficiency of InP/InGaAs Uni-Traveling-Carrier Photodiodes at 1.55–1.7 µm Measured Using Supercontinuum Generation in Optical Fiber

Abstract: The input wavelength dependence of the external quantum efficiency for InP/InGaAs uni-traveling-carrier photodiodes (UTC-PDs) was examined. A supercontinuum generated in the optical fiber was used as the monochromatic optical source with the wavelength ranging from 1.55 to 1.7 µm. The observed flatness of the efficiency shows the applicability of UTC-PDs to wide bandwidth transmission systems in which the bandwidths of the optical fiber and amplifier are fully utilized. It was also found that a UTC-PD with an acceptor doping density of 2.5×1018 cm-3 in the photo-absorption layer has a larger external quantum efficiency than a UTC-PD with a lower doping density at a wavelength around 1.7 µm. The mechanism of this enhancement is discussed based on the absorption coefficient and pulse responses measured at various input wavelengths.

Apparatus for measurement of an optical pulse shape

Abstract: An apparatus for measurement of an optical pulse shape intended to measure the temporal waveform of an ultrashort single optical pulse is disclosed. The present invention comprises a linearly chirped supercontinuum light source that is synchronized with an optical pulse to be measured; a nonlinear optical interferometer to transform the temporal waveform of an incident optical pulse into a spectrum using an incident light from said supercontinuum light source; and an optical spectrum analyzer to measure the wavelength of the light passing through the nonlinear interferometer so that it can measure the temporal waveform of a single optical pulse. The present invention employs the method that transforms the temporal waveform of an incident optical pulse into a spectrum and measures the wavelength using a linearly chirped supercontinuum light source, a nonlinear optical interferometer, and an optical spectrum analyzer. The present invention provides an apparatus for measurement of an optical pulse shape that is able to measure the waveform not with the repeated measurements but with a single shot measurement.

Pulsed light generator

Abstract: PROBLEM TO BE SOLVED: To make a pulsed light generator generate optical pulses with an extremely narrow time width. SOLUTION: An arrayed waveguide grating 202 for demultiplexing selectively transmits spectral component composing supercontinuum light made incident on an optical input port 201 for separation. An intensity of each separated spectral component is independently adjusted to be constant respectively by variable attenuators 203-1-203-k. The phase differences between each spectral component are adjusted to 0 by variable attenuators 204-1-204-k. Each spectral component adjusted is multiplexed by an array waveguide grating 205 for multiplexing and outputted from an optical output port 206.

High-intensity coherent supercontinuum radiation from optical channeling

Abstract: An intense VUV-IR coherent light source based on the both spatial and temporal phase modulation in rare gas media induced by tera-watt laser field is presented. A spectra intensity of 1 GW/nm has been obtained from the UV to IR regions. An up-conversion broadband optical parametric amplifier based on the four-wave-mixing in a non- birefringence nonlinear materials has also been demonstrated for time gated spectra measurements with the ultra-broadband light source.

Wideband and flat supercontinuum generation from optical fibers and its applications

Abstract: Recent progress in supercontinuum (SC) generation from optical fibers in the 1550 nm band has exploited its attractive applications to a spectral-slicing pulse source used in WDM systems and an ultra-short pulse source used in OTDM systems. We discuss how wideband and flat SC can be generated from optical fibers, and then describe applications of such SC to optical communication systems.

Transformation of strong picosecond pulses in radiation with an extended quasirotational spectrum during self-focusing in high-pressure hydrogen

Abstract: Radiation with a spectrum representing a discrete analog of the extended spectrum observed in the generation of a supercontinuum in gases is generated in the self-focusing of 30-ps pulses with a wavelength of 1.06 μ]m in hydrogen at pressures up to 120 atm. The spectrum contains lines with similar intensities, an average frequency spacing approximately equal to the rotational transition frequency in hydrogen (587 cm−1), and a smooth spatial profile. The lines consist of several vibrational-rotational components. As the pressure is increased, the spectral lines are transformed so that at a pressure above 60 atm each line in the spectrum contains one or two components formed as a result of the smaller number of cascade (rotational and vibrational) processes. Self-focusing is manifested in the occurrence of a radiating channel up to 12 cm in length. The formation of a channel of this length is associated mainly with the variation of the refractive index in vibrational excitation of the hydrogen molecules by electrons heated in the pump field.

Practical sub-picosecond pulse generation at 1.55 /spl mu/m by means of a pulse compressor featuring a highly-nonlinear dispersion-shifted fiber

Abstract: Sub-picosecond optical pulse trains at a high repetition rate in the 1.55 /spl mu/m region are necessary for future ultra-high-speed optical fiber communication systems. For generation of such short pulses, the following two pulse compression scheme are usually employed. One is the adiabatic soliton compression using a dispersion-decreasing fiber (DDF) in the anomalous dispersion region. The other is the supercontinuum-based pulse compression method. In this method, the supercontinuum (SC) spectrum is first generated from initial pulses by the interplay of self-phase modulation (SPM) and normal group-velocity dispersion (GVD) of optical fibers. Such pulses are then compressed linearly by a proper amount of anomalous GVD, because they have the linear up-chirp across the entire pulse width. In these pulse compressors using optical fibers, the third-order dispersion (TOD) of fibers limits the achievable pulse width. Therefore, the dispersion-flattened DDF is strongly desired for the soliton compressor. Also, in the SC-based compression method, the fiber used for SC generation should be a dispersion-flattened fiber with a small normal GVD. We demonstrate a more practical SC-based pulse compressor featuring a highly-nonlinear dispersion-shifted fiber (HNL-DSP). Because of high nonlinearity of such fiber, we may use a relatively large normal GVD for SC generation, which, in turn, diminishes the harmful effect from TOD.

Time domain optical sensing

Abstract: We have demonstrated a simple yet effective spectrometer. It uses chirped supercontinuum pulses as a broadband source and a sampling oscilloscope or A/D converter for spectral analysis. Distinct advantages for this system include the absence of an optical spectrometer, the broad spectral bandwidth available from the supercontinuum source, and the possibility of real time spectral analysis. A passively mode locked erbium doped fiber laser with a pulse compression stage was used as the supercontinuum source.

Apparatus for measurement of an optical pulse shape

Abstract: An apparatus for measurement of an optical pulse shape intended to measure the temporal waveform of an ultrashort single optical pulse is disclosed. The present invention comprises a linearly chirped supercontinuum light source that is synchronized with an optical pulse to be measured; a nonlinear optical interferometer to transform the temporal waveform of an incident optical pulse into a spectrum using an incident light from said supercontinuum light source; and an optical spectrum analyzer to measure the wavelength of the light passing through the nonlinear interferometer so that it can measure the temporal waveform of a single optical pulse. The present invention employs the method that transforms the temporal waveform of an incident optical pulse into a spectrum and measures the wavelength using a linearly chirped supercontinuum light source, a nonlinear optical interferometer, and an optical spectrum analyzer. The present invention provides an apparatus for measurement of an optical pulse shape that is able to measure the waveform not with the repeated measurements but with a single shot measurement.

Numerical analysis of supercontinuum generation in a dispersion flattened /decreasing fiber

Abstract: A flat and broad-band supercontinuum spectrum of soliton pulses in an optical fiber with dispersion flattened and dispersion decreasing characteristic along the axis was numerically analyzed using a split-step Fourier method and confirmed experimentally

Ultrafast transient white-light absorption spectroscopy of novel materials for optical limiting

Abstract: The excited state absorption of lead phthalocyanine is investigated using ultrafast transient white light absorption spectroscopy. Singlet state absorption features are identified on the basis of time. Increases in optical density up to 1 in the near infrared region of 900 nm to 1.1 micrometers are observed by pumping at 800 nm. In addition, several artifacts of this technique are discussed, with an aim towards improvements. In particular, self-pumping of the sample via the supercontinuum probe is observed and investigated.© (1999) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.