High speed pulse slicer/demultiplexer with gain for use in solid state regenerative amplifier systems

A mode-locked solid state laser is disclosed for generating ultrashort optical pulses from a semiconductor type laser. A semiconductor pulse slicer/demultiplexer/modulator with gain amplification is used to modulate and amplify a generated optical beam whether or not the beam is pulsed, continuous wave, q-switched, or modelocked. Alternatively, the semiconductor pulse slicer/demultiplexer/modulator with gain amplification is used to gate a generated optical beam whether or not the beam is pulsed, continuous wave, q-switched, or modelocked. Alternatively, the semiconductor pulse slicer/demultiplexer/modulator with gain amplification is used to demultiplex a generated optical beam whether or not the beam is pulsed, continuous wave, q-switched, or modelocked. The invention uses only semiconductor type materials such as Titanium Saphire, Gallium Arsenide, Aluminum Gallium Arsenide (GaAs/AlGaAs) as both the pulse slicer/demultiplexer/modulator with gain amplification, and the mode-locked laser itself.

This invention relates to lasers, and in particular to a pulse slicer and 
demultiplexer which shows for the combined use of semiconductor laser 
oscillators to be used in conjunction with high power solid stare 
regenerative amplifier systems. 
BACKGROUND AND PRIOR ART 
Solid stare lasers have been used to generate ultrashort optical pulses. 
However, them are problems inherent with these lasers. The techniques 
utilized to generate these pulses have generally relied on sophisticated 
electro-optic modulation techniques or passive techniques which use 
organic dyes to initiate the pulse generation process. These active and 
passive techniques add complexity and potential hazards to the operation 
because of the additional components added to the system and the chemical 
dangers of organic dyes. 
Existing starting mechanisms for passive mode-locked lasers have cost 
approximately $5,000. These staring devices have required spaces of 
approximately one foot per side for the space needed. External power 
supplies such as RF power and mechanically actuated pumps have generally 
been needed for these mechanisms. 
Mode-locked diode lasers have may applications of which the inventors of 
this invention, specifically Dr. Peter Delfyett have well documented. U.S. 
patent Ser. No. 08/241,620 entitled "Self Starting Femtosecond Ti Saphire 
Laser with Intracavity Multiquantum Well Absorber" filed on May 12, 1994, 
by inventor Peter J. Delfyett now U.S. Pat. No. 5,434,873, and U.S. patent 
Ser. No. 08/236,373 entitled "Mode Locked Laser Diode in a High Power 
Solid Siam Regenerative Amplifier and Mount Mechanism" filed on May 2, 
1994, and assigned to the same assignees as this invention, both of which 
are incorporated by reference describe applicable laser applications Dr. 
Delfyett has other "mode-locked" laser inventions which includes U.S. Pat. 
No. 5,265,107, issued on Nov. 23, 1993. 
Current compact modelocked ultrafast lasers suffer from the necessity of 
requiring a fixed cavity length. This necessity prevents the user from 
having the flexibility of choosing an optimum pulse repetition frequency 
for a specific application. 
The pulse repetition frequency of compact diode lasers tend to be large, 
typically on the order of 100 megahertz to several gigahertz, owing to the 
fast gain recovery time of semiconductor diode lasers. Thus, applications 
which require an ultrashort pulse laser source operating at a lower pulse 
repetition rate are required to rely on large, expensive ultrafast laser 
systems. 
Methods for reducing the pulse repetition rate of modelocked ultrafast 
laser systems typically rely on electro-optic materials for producing a 
"Pockel's Cell" which acts as a fast shutter or optical gate. This device 
is relatively large (approximately 1 cubic foot) and requires large 
electric fields (voltages in order to operate. 
In addition, some optical pulse slicers have a limited clear aperature, 
which increases the insertion loss of the device. 
For integrated optic applications, i.e. incorporating a laser device, such 
as a semiconductor laser, with a dielectric optical gate is costly and 
cumbersome owing to the material mismatch employed with current dielectric 
optical gates or modulators. Modulating of data signals has been 
accomplished in the prior art. U.S. Pat. No. 5,136,598 to Weller et al. 
describes where an optical beam from a laser is modulated. However, Weller 
requires multiple components to operate, where the optical beam is first 
modulated by a dielectric material and then subsequently amplified with a 
semiconductor source. The subject invention does not require, or need 
dielectric materials to operate. 
Thus, this invention reduces the problems inherent with current mechanisms. 
SUMMARY OF THE INVENTION 
The first object of this invention is to provide an efficient starting 
mechanism for the generation of ultrashort optical pulse trains in 
mode-locked lasers. 
The fourth object of this invention is to provide a low cost starting 
mechanism for the generation of ultrashort optical pulses trains in 
mode-locked lasers. 
The second object of this invention is to provide a fixed repetition rate 
compact ultrafast modelocked laser with the flexibility of obtaining an 
adjustable pulse repetition frequency. 
The third object of this invention is to provide for 
demodulation/demultiplexing in a mode-locked laser. 
The fourth object of this invention is to for optical gain and 
amplification of the light output in a mode-locked laser. 
The fifth object of this invention is to provide a method of generating a 
variable pulsed output from a continuously pulsed laser. 
The sixth object of this invention is to provide a device to modulate the 
output of a pulsed laser source. 
The seventh object of this invention is to reduce the repetition rate of a 
modelocked laser source. 
The eighth object of this invention is provide gain to a modulated laser 
beam. 
The ninth object of this invention is to simultaneously provide a 
modulation capability and optical amplification with a single device. 
The tenth object of this invention is to reduce the repetition rate of high 
pulse repetition rate lasers. 
The eleventh object of this invention is to provide an adjustable pulse 
repetition rate from a compact modelocked laser source to allow the laser 
to be used for a low repetition rate application. 
The twelfth object of this invention is to adjust the repetition rate of a 
modelocked laser so that the laser can be used with a high power laser 
amplifier system, e.g. a regenerative amplifier or single/multipass 
amplifier. 
This invention further avoids the problems of the prior art, because the 
novel pulse slicer: 
(1) Can operate at high pulse repetition frequencies which allow ultrafast 
laser applications to utilize compact and efficient semiconductor laser 
sources. 
(2) The operating voltages of the subject invention is typically about 5 
volts. 
(3) The invention provides optical gain or amplification, thus eliminating 
insertion losses. 
(4) The invention is made of semiconductor material which facilitates 
integrating both the laser and pulse slicer/modulator on a single device 
structure. 
The invention can be used with the new starting mechanism for the 
generation of ultrashort optical pulse trains in mode-locked lasers 
discussed in U.S. patent Ser. No. 08/241,620 entitled "Self Starting 
Femtosecond Ti Saphire Laser with Intracavity Multiquantum Well Absorber" 
filed on May 12, 1994, by inventor Peter J. Delfyett; and can be used with 
the invention disclosed in U.S. patent Ser. No. 08/236,373 entitled "Mode 
Locked Laser Diode in a High Power Solid State Regenerative Amplifier and 
Mount Mechanism" filed on May 2, 1994, and assigned to the same assignees 
as this invention, both of which are incorporated by reference. This 
invention helps to reduce the cost of previous methods of starting 
mechanisms for passive mode-locked lasers by 90% from approximately $5,000 
to $500. The starting mechanism of the invention can be as small as 0.1 
inch on a side as compared to 1 foot on a side for prior mechanisms. The 
invention requires no external power supplies to operate. The generated 
optical pulses can be used in a wide variety of applications such as 
diagnostic testing, communications, computers, medicine and automotive 
applications. 
This invention can be used as a new pulse slicer/demodulator/demultiplexer 
or optical gate for changing the pulse repetition frequency of pulsed 
laser sources to optimize the pulse repetition rate for specific 
applications. This invention reduces the cost of previous methods for 
changing the pulse repetition rate of pulsed laser systems from 
approximately $5,000 to approximately $1,000. The gating device is 
typically a few hundred microns per side or less, demonstrating it small 
size, in comparison to present methodologies which use devices of one foot 
per side. This invention requires low voltages(approximately 5 volts) and 
a few tenths of an ampere of current. 
Further objects and advantages of this invention will be apparent from the 
following detailed description of a presently preferred embodiment which 
is illustrated schematically in the accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Before explaining the disclosed embodiment of the present invention in 
detail it is to be understood that the invention is not limited in its 
application to the details of the particular arrangement shown since the 
invention is capable of other embodiments. Also, the terminology used 
herein is for the purpose of description and not of limitation. 
FIG. 1 illustrates a schematic for the preferred location of the invention 
in a mode-locked diode laser. The components of FIG. 1 along with their 
respective functions will now be described. Component 2 is a compact, 
modelocked laser source, such as a modelocked semiconductor laser or other 
compact laser source, e.g. fiber laser, micro chip laser, vertical cavity 
semiconductor laser, and the like. This device provides an input optical 
signal to the semiconductor pulse slicer. 3 illustrates the output of the 
said laser source. In this illustration, the output of the said laser 
source is pulsed. However, the output may also be a steady continuous 
beam. The output from said laser source is directed towards and injected 
into the semiconductor pulse slicer. 4 designates the new device described 
in this patent. It is comprised of semiconductor material and is 
controlled by an electrical signal. The end result of this device is to 
gate or slice a portion of the output of the said laser source, resulting 
in a modulated, or modified optical output. In addition to gating or 
slicing a portion of the output of said laser, the device also amplifies 
the sliced or gated portion of the optical signal, providing both a 
slicing/gating/modulating function with an amplification function. 
Component 5 designates the controlling signal applied to the semiconductor 
gating device. This control pulse is electrical in the present embodiment. 
However, the controlling signal may also be optical in nature, such as but 
not limited to an optical control beam or optical control pulse. 6 
designates the output of the semiconductor gating device. The output can 
be one of several types. One, the output 6 can be a modulated signal 
suitable for carrying information in a communication environment. Two, 
output 6 can be a selected optical pulse that is subsequently injected 
into and amplified in an alternate optical amplifier. Three, output 6, can 
be an optical signal or pulse train that can be generated for applications 
that require an optimized optical pulse repetition frequency. 
FIG. 2 shows a preferred embodiment of using the invention used as 
demultiplexer in a mode-locked diode laser. Each of the components of FIG. 
2 along with their respective function will now be described. 10 refers to 
a specific embodiment of using the semiconductor pulse 
slicer/gate/modulator/demultiplexer with a laser system, whose general 
purpose is to create and generate an optical signal. Component 14 is a 
laser source, which can alternatively be pulsed, gain switched, 
q-switched, modelocked or continuous wave. The purpose of source 14 is to 
generate an optical beam/signal 10. Numeral 16 refers to the optical 
signal, which can be a continuous beam, pulsed, gain switched, q-switched 
or modelocked according the respective source 14 that is used. The purpose 
of signal 16 is to supply an optical signal 10 to the semiconductor 
pulse/slicer/optical gate/modulator 18. Element 12 refers to an electrical 
signal generator whose characteristic is to generate an electrical signal 
of a varying nature, such as but not limited to an electrical pulse, or an 
electrical sinusoidal current. Generator 12 can be alternatively embodied 
as an electrical signal generator, a pulse generator or a frequency 
synthesizer whose purpose is to provide an electric timing signal to the 
laser 14 and to the electrical signal processor 26. Component 18 refers to 
the semiconductor pulse slicer/demultiplexer/modulator with gain whose 
purpose is to modulate an optical beam whether the beam is pulsed, 
continuous wave, q-switched, modelocked and the like. Alternatively, 18 
can gate an optical beam whether the beam is pulsed, continuous wave, 
q-switched, modelocked and the like. Alternatively, 18 can be used to 
demultiplex an optical beam whether or not the beam is pulsed, continuous 
wave, q-switched, modelocked and the like. Component 20 can be an 
electrical signal generator that is used to generate an electrical signal 
of varying nature such as but not limited to an electrical pulse, an 
electrical sinusoidal current and the like. Generator 20 can alternatively 
be embodied as a pulse generator or frequency synthesizer whose purpose is 
to provide an electric timing signal to component 18. Element 22 refers to 
an electric timing signal that is generated by generator 20. Signal 22 can 
be pulsed, sinusoidal, or carrying information in a data format depending 
on the type of generator 20 that is utilized. Signal 22 is applied to and 
is used to control component 18 in order to either modulate,gate or slice 
optical beam 16. Component 24 is an electrical trigger or synchronizing 
signal, which can be pulsed or sinusoidal. The purpose of signal 24 is to 
provide a timing or synchronizing signal to the pulse generator 20. This 
timing signal controls the pulse generator 20 and allows the pulse 
generator to provide an electric timing signal 22 semiconductor gate 18. 
Component 26 is an electrical signal processor, such as an electrical 
frequency divider, whose purpose is to operate and process an electric 
timing signal from the signal generator 12. The output of processor 26 is 
the electric trigger or the synchronizing signal 24 described previously. 
Element 30 is the output from component 18 which is an optical beam which 
was modified from initial optical signal 16. 
FIG. 3 illustrates an oscilloscope trace of the output of a semiconductor 
modelocked laser 14 of FIG. 2 which is plotted versus time. FIG. 3 
establishes an initial optical beam 16 of FIG. 2 which has been generated 
by laser 14. 
FIG. 4 illustrates an oscilloscope trace of the output 30 of FIG. 2 from 
the semiconductor gate/slicer 18 of FIG. 2 which demonstrates a modified 
optical beam, whether gated, modulated, demultiplexed, pulse sliced and 
the like. 
The invention components are compact, efficient and low maintenance. The 
invention can be produced from bandgap engineerable gain media, where the 
semiconductor laser source and semiconductor gate/slicer can be made of 
materials that can be designed to operate desired frequencies. The 
invention can be completely electrically pumped where all power can be 
supplied by electrical energy. No optical power is required to transfer 
energy to or to do work on any device in the application. In the subject 
invention, the power is not supplied by optical beams. The components in 
the invention are potentially integrable, on chip or with optical fiber 
media. Potentially integrable means that the laser and 
gate/demultiplexer/slicer can be constructed in one single device instead 
of two separate devices as noted in the preferred embodiment. Here, the 
laser and the gate/demultiplexer/slicer can be made in a single optical 
fiber or in a single semiconductor device. 
Although, the preferred embodiment can use Titanium Sapphire as the solid 
state media, other types of solid state materials can be used such as but 
not limited to Cr:YAG, Cr:Fosterite, Nd:YAG, Nd:glass, color center 
lasers, semiconductor diode lasers, and optically active fiber lasers. 
Although the preferred embodiment utilizes Gallium Arsenide, Aluminum 
Gallium Arsenide GaAs/AlGaAs) semiconductor materials for the pulse 
slicer/demultiplexer/gate, other solid state and semiconductor materials 
may be used such as but not limited to InP, InGaAlAs, InGaP, GaN, ZnSe, 
CdSe, or any group III-V or II-VII or IV semiconductor compound material, 
or other solid state material such as but not limited to Ti:Saphire, 
Cr:YAG, Nd:YAG, CrFostefite, Nd:YAG, Nd:glass, color center lasers, 
semiconductor diode lasers, optically active fiber lasers, or other active 
solid state materials such as Er:Si or Er:Indium-Tin-Oxide. 
The invention disclosed herein can have wide array of applications. In 
communications, the invention can be used as a transmitter of optical data 
in fiber optic networks. In computers, the invention can be used as a 
transmitter of optical data, as high speed processors of optical data and 
as high speed switches of optical data, and the like. In medical 
applications, the invention can be used for imaging through body tissue. 
In high speed diagnostic applications, the invention can be used to 
measure optical-matter phenomena in condensed matter materials, to measure 
very fast events, processes, mechanisms, interactions and the like. 
Further, the invention can have applicability for initiating or as seed 
pulses in solid state generative amplifier systems. 
Furthermore, this invention can be used to modulate a continuous or pulsed 
optical beam to transmit information. This invention can further be used 
to open or close the optical pathway in an optical fiber to either allow 
light to be transmitted or prevent the light from reaching its 
destination. Furthermore, this invention can be used to operate as a 
nonlinear optical element for gating or switching in an optical 
communication network. 
Additional applications can be for generating ultrashort electrical 
signals, high speed photography, atmospheric, environmental and remote 
sensing and the recording of information for optical data storage systems. 
While the invention has been described, disclosed, illustrated and shown in 
various terms of certain embodiments or modifications which it has 
presumed in practice, the scope of the invention is not intended to be, 
nor should it be deemed to be, limited thereby and such other 
modifications or embodiments as may be suggested by the teachings herein 
are particularly reserved especially as they fall within the breadth and 
scope of the claims here appended.