Patent Application
20090316738
The present invention concerns a device for amplitude and phase programming of long light pulses with narrow spectral bands using a modulator of short light pulses with wide spectral bands.
It more particularly concerns the adaptation of a programmable generator of ultra short wide spectral band light pulses, to long narrow spectral band light pulses.
In general, it is known that generators of ultra short wide spectral band laser pulses such as spatial programmable masks or filters (ex: liquid crystals) placed in the focal plane of a zero-dispersion optical delay line and programmable dispersive acousto-optic filters, generate pulses in the spectral domain by modifying, in a programmable way, the amplitude and phase of each frequency (or each wavelength) contained in the spectral band of the pulses. This allows generation over a time scale from a femtosecond to several picoseconds.
As for electro-optic temporal modulators, such as programmable Mach-Zehnder interferometers, realized in integrated optics, they allow one to generate, in time, only long pulses in the vicinity of several nanoseconds with a very narrow spectral band.
For intermediate programming times between approximately 10 picoseconds and 10 nanoseconds, there is no programmable laser pulse generation system, spectral systems not having a sufficient temporal programming excursion and temporal systems not having a sufficient programming bandwidth.
The object of the invention therefore more particularly aims to overcome this gap by proposing a device for adapting a programmable generator of ultra short wide spectral band light pulses, to long narrow spectral band light pulses, the duration of which is between 10 picoseconds and 10 nanoseconds.
The present invention consists of inserting a generator of wide spectral band light pulses between two nonlinear optical mixers, a linear dispersion device being placed upstream from the first mixer and the long, narrow spectral band light pulses, bearing the modulation, in amplitude and in phase, introduced by the aforementioned generator of large spectral band light pulses, being obtained at the outlet of the second nonlinear optical mixer.
To this end, the invention proposes a device to adapt a programmable generator of ultra short wide band spectral light pulses, to long narrow spectral band light pulses, comprising:
Thus, the output signal of said second nonlinear optical mixer is a signal whereof the central frequency is equal to that of said pump laser; the duration of this output signal is equal to the duration of lengthening output from said dispersion device; the spectral band of this output signal is the resulting spectral band given by the spectral band of the aforementioned long pulses coming from the dispersion device modified by the ratio of the durations corresponding on one hand to the duration according to which one can modulate, in amplitude and in phase, a pulse using said generator, and on the other hand the lengthening duration output from said dispersion device.
As a result, this output signal, which is no longer modulated linearly in frequency on the spectral band of the pulses coming from the laser source of short pulses, bears, in the reduced spectral band, previously defined, the modulation, in amplitude and in phase, introduced by said generator of large band light pulses.
The frequency of said second channel emerging from the first nonlinear optical mixer corresponds to the difference or the sum of the frequencies, respectively from said pump laser at quasi-monochromatic frequency and from said laser source of short light pulses.
Indeed, when the frequency of said pump laser is greater than the frequency of the laser source of short pulses, the frequency of the second channel emerging from the first mixer corresponds to the difference in the frequencies of said pump laser at quasi-monochromatic frequency and from said laser source of short light pulses, respectively; in this case, the modulation slope of the long pulses has a sign opposite that of long pulses injected into the first mixer by the laser source of short pulses.
Reciprocally, the frequency of the second channel emerging from the first mixer corresponds to the sum of the frequencies of said pump laser at quasi-monochromatic frequency and from said laser source of short light pulses, respectively, if the frequency of said pump laser is less than the frequency of the laser source of short pulses; in this case, the modulation slope of the long pulses has the same sign as that of the long pulses injected into the first mixer by the laser source of short pulses.
Advantageously, said device for dispersing the ultra-short pulses coming from the laser source may be a dispersive optical fiber or a pair of parallel optical networks.
Advantageously, said generator of wide spectral band light pulses may be a spatial modulator of amplitude and phase placed in the focal plane of a zero dispersion optical delay line 4-f, or it may also be a programmable dispersive acousto-optic filter.
One embodiment of the invention will be described below, as a non-limiting example, in reference to the appended drawings in which:
In the example illustrated in
Thus, output from said second nonlinear optical mixer 6, the output signal is a signal of frequency v2, spectral band B2 and length T2 which is no longer linearly modulated in frequency in the band B1, but bears, in the band B2, the modulation, in amplitude and in phase, introduced by the generator of wide band light pulses.
If T1 is the time over which one can modulate, in amplitude and in phase, a light pulse of band B1 using a generator of wide band pulses, the number of independent programming points is: N=B1T1.
The quantity of information, and therefore this number of points, being kept in the device illustrated in
This band is much narrower than B1, since T2 is in the vicinity of a nanosecond while T1 is in the vicinity of a picosecond.
The modulation capacity of the generator of short wide band pulses was therefore transferred to long wide band signals.
In the example illustrated in
Thus, the ultra-short wide spectral band light pulses coming from the aforementioned laser source 1 have a frequency v1, a wide spectral band B1, and an ultra-short duration in the vicinity of 1/B1.
The light pulses coming from said dispersion device have a frequency v1, a wide spectral band B1, a lengthened duration T2 and an increasing (or decreasing) modulation slope of the frequency according to time.
The long quasi-monochromatic light pulses from said laser source 3 have a frequency v2 greater than the frequency v1 and a long duration T0 greater than T2.
The light pulses coming from said first optical mixer 4, along the channel V2, have a frequency V3, equal to v2−v1, a wide spectral band B1, and a duration T2.
At the output of said dispersion device, the modulation slope of the optical signal, coming from the laser 1, at the frequency v1, spectral band B1, duration T2 being increasing (or decreasing), the modulation slope of the optical signal coming from the first optical mixer 4 along the channel V2, at the frequency v3, spectral band B1, duration T2, will be decreasing (or increasing)
In the example illustrated in
Thus, output from said second nonlinear optical mixer 6, the output signal is a signal of frequency v2, spectral band B2 and length T2 which is no longer linearly modulated in frequency in the band B1, but bears, in the band B2, the modulation, in amplitude and in phase, introduced by the generator of wide band light pulses.
If T1 is the time over which one can modulate, in amplitude and in phase, a light pulse with band B1 using a generator of wide band pulses, the number of independent programming points is: N=B1T1.
The quantity of information, and therefore this number of points, being kept in the device illustrated in
This band is much narrower than B1, since T2 is in the vicinity of a nanosecond while T1 is in the vicinity of a picosecond.
The modulation capacity of the generator of short wide band pulses was therefore transferred to long narrow band signals.
In the example illustrated in
Thus, the ultra-short wide spectral band light pulses coming from said laser source 1 have a frequency v1, a wide spectral band B1, and an ultra-short duration in the vicinity of 1/B1.
The light pulses coming from said dispersion device have a frequency v1, a wide spectral band B1, a lengthened duration T2 and an increasing (or decreasing) modulation slope of frequency according to time.
The long quasi-monochromatic light pulses coming from said laser source 3 have a frequency v2 less than the frequency v1 and a long duration T0 greater than T2.
The light pulses coming from said first optical mixer 4, along the channel V2, have a frequency v3, equal to v2+v1, a wide spectral band B1, and a duration T2.
At the output of said dispersion device, the modulation slope of the optical signal, coming from the laser 1, at the frequency v1, spectral band B1, duration T2 being increasing (or decreasing), the modulation slope of the optical signal coming from the first optical mixer 4 along the channel V2, at the frequency v3, spectral band B1, duration T2, will also be increasing (or decreasing).
Thus, the output signal of the second nonlinear optical mixer 6 is a signal whereof the central frequency v2 is equivalent to that of the pump laser 3; the duration of this output signal is equal to the lengthening duration T2 output from said dispersion device 2; the spectral band B2 of this output signal is the resulting spectral band given by the spectral band B1 of said long pulses coming form the dispersion device 2 modified by the ratio T1/T2 of the durations corresponding on one hand to the duration T1 according to which one can modulate, in amplitude and in phase, a pulse using the generator 5, and on the other hand to the lengthening duration T2 output from the dispersion device 2.
The modulation capacity of the generator 5 of short wide band pulses was therefore transferred to long narrow band signals.
| Number | Date | Country | Kind |
|---|---|---|---|
| 06 03526 | Apr 2006 | FR | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/FR2007/000621 | 4/12/2007 | WO | 00 | 5/19/2009 |
