Coherent light generators – Particular beam control device – Modulation
Reexamination Certificate
2002-06-13
2004-11-30
Scott, Jr., Leon (Department: 2828)
Coherent light generators
Particular beam control device
Modulation
C372S006000, C372S022000, C372S023000, C372S031000, C372S043010, C372S098000, C372S101000
Reexamination Certificate
active
06826209
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an ultra-broadband, variable and multiple wavelength, pulse waveform shaping apparatus for use in an optical pulse generator for generating light pulses variable and multiple in wavelength over an ultra-broad bandwidth, i.e., a pulse waveform shaping apparatus for shaping light pulses variable and multiple in wavelength over an ultra-broad bandwidth, in which an ultra-broadband light pulse is produced and is then subjected to two-dimensional modulations both In amplitude and phase effected in a beam of the light pulse.
BACKGROUND ART
Light pulse waveform shaping has hitherto been performed by passing a light pulse having a single preselected center wavelength through either a one-dimensional spatial phase modulator or a one-dimensional spatial amplitude modulator or a combination of the two, or passing a light pulse having a single preselected center wavelength through a two-dimensional spatial phase modulator.
Light pulse waveform shaping of this type is designed to shape the waveform of a light pulse having a single preselected center wavelength by using a dispersing element to spatially expand the light pulse in dependence on its wavelengths and to effect a phase or an amplitude modulation for each of its wavelength components.
As the literature for the case of using a one-dimensional spatial phase modulator and for the case of using a one-dimensional spatial amplitude modulator, here may be cited “A. M. Weiner, J. P. Heritage and E. M. Kirschner, J. Opt. Soc. Am. B5, 1563 (1988)”.
Also, as the literature for the case of using both of them, here can be cited “M. M. Wefers and K. A. Nelson, Opt. Lett. 18, 2032 (1993)”.
Further, as the literature for the case of using a two-dimensional spatial phase modulator, here may be cited “M. M. Wefers, K. A. Nelson and A. M. M. Weiners, Opt. Lett. 21, 746 (1996)”.
In the instances shown in the past literature cited above, however, the use of either a one-dimensional spatial phase modulator or a one-dimensional spatial amplitude modulator or even the use of both of them permitted only light pulses of the single center wavelength shaped in waveform to be obtained.
On the other hand, the instance of using a two-dimensional spatial phase modulator made it possible to obtain light pulses varying in waveform with their spatial positions but having the same one wavelength, and thus again permitted only light pulses of the single center wavelength shaped in waveform to be obtained.
In view of the problem noted above, the present invention is aimed to provide an ultra-broadband, variable and multiple wavelength, waveform shaping apparatus that excels with the ability to yield light pulses shaped in waveform, variable and multiple in wavelength over an ultra-broad bandwidth, the pulses being as short as in the order of pico-seconds or less, or even in the order of femto-seconds.
DISCLOSURE THE INVENTION
In order to achieve the object mentioned above, the present invention provides as set forth in the appended claims an ultra-broadband, variable and multiple wavelength, pulse waveform shaping apparatus, characterized in that it comprises: an ultra-broadband light pulse producing means for receiving a fundamental wave light pulse having a bandwidth and broadening the bandwidth of said fundamental wave light pulse into an ultra-broadband range to produce an ultra-broadband light pulse in the form of a beam thereof; a beam expander means comprising a cylindrical lens for expanding the cross section of the said beam of ultra-broad band light pulse in one direction (say along a y-axis) to form an expanded beam of ultra-broadband light pulse and a diffraction grating or the like for dispersing wavelengths of the ultra-broadband light pulse of the said expanded beam in a direction orthogonal to the y-axis (say in a direction of an x-axis) to produce a beam of ultra-broadband light pulse with its cross section thus expanded two-dimensionally; a two-dimensional spatial amplitude modulator for applying amplitude modulation to the said two-dimensionally expanded ultra-broadband light pulse for each, independent of another, of rows each extending in the direction (along the x-axis) of such wavelength dispersion (y-rows: y
1
, y
2
, y
3
and y
4
) to take out thereof, light pulse components having their mutually independent center wavelengths (&lgr;
1
, &lgr;
2
, &lgr;
3
, and &lgr;
4
) for those respective rows; a two-dimensional spatial phase modulator for applying phase modulation to the said light pulse components having their mutually independent center wavelengths (&lgr;
1
, &lgr;
2
, &lgr;
3
, and &lgr;
4
) for each of such rows, independent of another; and a cylindrical lens or a cylindrical mirror and a diffraction grating or a prism for reducing, and condensing into the direction of the said x-axis, the said light pulse components modulated by the said two-dimensional spatial amplitude modulator and the said two-dimensional spatial phase modulator, whereby a plurality of pulses shaped in waveform and controlled in amplitude and phase independently for each of said center wavelengths ensue at different positions on an output screen.
In the makeup mentioned above, the ultra-broadband light pulse generating means enables a fundamental wave light pulse to bring about a self-phase modulation effect and thereby to result in an expanded spectrum, or to bring about an induced phase modulation effect between such a fundamental wave pulse and a pulse generated by a nonlinear phenomenon that takes place using the fundamental wave pulse and thereby to result in an expanded spectrum and to produce an ultra-broadband light pulse. Compared with dispersing the wavelengths of a fundamental wave light pulse, dispersing the wavelength of an ultra-broadband light pulse enables the wavelengths in an ultra-broadband that contains wavelengths in an extremely wide range to be dispersed. Applying amplitude modulations with a selected pattern to given rows, each of which extends in the direction of wavelength dispersion, in the 2-dimensional amplitude modulator to establish amplitudes permits light components with their respective, preselected center wavelengths to be cut out over the broad range of wavelengths. Also, with the ability to apply amplitude modulations to all of the rows in the 2-dimensional amplitude modulator independently of one another, it is possible to cut out light components varying in center wavelength by the number of the rows. Then, applying phase modulations with a selected pattern to the rows in the 2-dimensional phase modulator which correspond to the given rows in the 2-dimensional amplitude modulator permits a particular phase that realizes the temporal waveform of a desired particular pulse train to be added to each of those different rows, independently of one another. The beam reducing and waveform shaping means designed to reduce the beam cross section selectively in the direction of wavelength dispersion, thereby to reshape the beam allows a light pulse outgoing from the 2-dimensional phase modulator to be reduced in cross section only in the direction in which each of the rows extends, namely in the direction of wavelength, thus permitting the shaped light pulse waveforms to appear at positions on the output screen which vary corresponding to the positions of those rows.
The ultra-broadband, variable and multiple wavelength, pulse waveform shaping apparatus set forth in the appended claims may, as set forth in the appended claims, further be characterized in that the said fundamental wave light pulse is an ultra-short pulse of pico-seconds or less generated by a laser light source.
The ultra-broadband, variable and multiple wavelength, pulse waveform shaping apparatus set forth in the appended claims may, as set forth in the appended claims, further be characterized in that the said light source for generating the said fundamental wave light pulse is any one of a solid state laser, a fiber laser, a semiconductor laser, a dye laser and an optical parametric laser, or a combination thereof wit
Morita Ryuji
Morokawa Shigeru
Suguru Akira
Yamashita Mikio
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