INTERFEROMETRIC GAIN LASER DEVICE

Abstract

A laser device configured to emit a coherent optical radiation is provided. The laser device has an amplifier system having a single interferometric optical amplification arrangement or a plurality of interferometric optical amplification arrangements in series, an optical return path of an optical beam emerging from the amplifier system and entering the amplifier system to form an optical ring resonant structure, and a radiation output for extracting a portion of the optical beam emerging from the amplifier system and deliver the extracted portion of the optical beam emerging from the amplifier system as output laser radiation of the laser device.

Claims

1-12. (canceled)

13. A laser device configured to emit a coherent optical radiation, comprising: an amplifier system, comprising a single interferometric optical amplification arrangement or a plurality of interferometric optical amplification arrangements in series, wherein each interferometric optical amplification arrangement comprises input beam splitters adapted to spatially separate an incident optical beam into a first beam portion and a second beam portion, downstream of which an amplification arm of the first beam portion, comprising an active gain region capable of emitting photons coherent with the first beam portion, and a propagation arm without amplification of the second beam portion extend, which meet at an output of the interferometric optical amplification arrangement; beam combining means different from said input beam splitters and adapted to gather the first beam portion amplified in the active gain region and the second beam portion propagated without amplification of the single interferometric optical amplification arrangement or of the last interferometric optical amplification arrangement of the plurality of interferometric optical amplification arrangements, into an optical beam emerging from the amplifier system; a return optical path for the optical beam emerging from the amplifier system, comprising optical reflectors and configured to conduct said optical beam emerging from the amplifier system at an input to the amplifier system forming an optical ring resonant structure therewith; and a radiation output for extracting a portion of the optical beam emerging from the amplifier system and deliver said portion of the optical beam emerging from the amplifier system as output laser radiation of the laser device, wherein power of the first beam portion routed in the amplification arm is less than power of the second beam portion routed in the propagation arm without amplification.

14. The laser device of claim 13, wherein the amplification arm comprises an active gain region of semiconductor material capable of emitting photons coherent with the first beam portion following attainment of a population inversion condition of a population of charge carriers confined therein and consequent radiative recombination, said active gain region being associated with an electrical excitation system configured to alter a thermodynamic equilibrium of the population of charge carriers to determine said population inversion condition.

15. The laser device of claim 13, wherein in the plurality of interferometric optical amplification arrangements the input beam splitters are adapted to spatially separate interfering first beam portion and second beam portion of a preceding interferometric optical amplification arrangement.

16. The laser device of claim 13, wherein each intermediate interferometric optical amplification arrangement of said plurality of interferometric optical amplification arrangements comprises input beam splitters adapted to spatially split only the first beam portion of a preceding interferometric optical amplification arrangement, and not a recombined beam of the preceding interferometric optical amplification arrangement.

17. The laser device of claim 13, wherein said portion of the optical beam emerging from the amplifier system and delivered as output laser radiation of the laser device is a loss beam of said beam combining means adapted to bring together the first beam portion amplified in the active gain region and the second beam portion propagated without amplification into the optical beam emerging from the amplifier system.

18. The laser device of claim 13, wherein said portion of the optical beam emerging from the amplifier system and delivered as output laser radiation of the laser device is a loss beam of one of said optical reflectors of the return optical path.

19. The laser device of claim 13, wherein the amplification arm comprises an input beam coupling stage and an output beam collimation stage coupled to said active gain region, comprising a pair of dioptric systems arranged respectively to focus the first beam portion entering the active gain region and to collimate the first beam portion amplified in the active gain region and exiting the active gain region.

20. The laser device of claim 13, wherein the propagation arm without amplification comprises a catoptric system or a dioptric system configured to control addressing or distribution of transverse power of the second beam portion.

21. The laser device of claim 13, wherein said optical reflectors include a plurality of totally reflective catoptric systems.

22. The laser device of claim 13, wherein said return optical path comprises optical elements configured to shape distribution of transverse power of the beam emerging from the amplifier system.

23. The laser device of claim 13, wherein said optical ring resonant structure comprises an optical isolator configured to allow propagation of a beam in a single predetermined direction.

24. The laser device of claim 13, wherein an optical length of the amplification arm and an optical length of the propagation arm without amplification of each interferometric optical amplification arrangement are equivalent.

Description

[0034] Further features and advantages of the invention will be presented in greater detail in the following detailed description of an embodiment thereof, given by way of non-limiting example, with reference to the accompanying drawings, wherein:

[0035] FIG. 1 is a general diagram of a laser device according to the invention;

[0036] FIG. 2 is a first schematic embodiment of a laser device according to the invention having a single interferometric optical amplification arrangement, in a free-space embodiment;

[0037] FIG. 3 shows a variant embodiment of the laser device of FIG. 2;

[0038] FIG. 4 is a simulation diagram of the behavior of the laser device of FIG. 3;

[0039] FIG. 5 shows the variant embodiment of the laser device of FIG. 3 with two cascaded interferometric optical amplification arrangements;

[0040] FIG. 6 is a second schematic embodiment of a laser device according to the invention having a single interferometric optical amplification arrangement, in a free-space embodiment;

[0041] FIG. 7 is a simulation diagram of the behavior of the laser device of FIG. 6;

[0042] FIG. 8 shows the second embodiment of the laser device of FIG. 6 with two cascaded interferometric optical amplification arrangements;

[0043] FIG. 9 shows a third embodiment of a laser device according to the invention having a single interferometric optical amplification arrangement, in a free-space embodiment; and

[0044] FIG. 10 shows the third embodiment of the laser device of FIG. 9 with a plurality of cascaded interferometric optical amplification arrangements.

[0045] FIG. 1 schematically shows in the essential aspects a laser device according to the invention, indicated collectively with 10. It comprises an amplifier system 12 of an incident optical beam B.sub.i, an optical return path 14 of an optical beam B.sub.o emerging from the amplifier system 12 adapted to carry the optical beam B.sub.o to the input of the amplifier system 12 as an incident optical beam B.sub.i and forming an optical resonant structure with the amplifier system 12, and means 16 for the output of a coherent optical radiation from the laser device adapted to extract a portion of the beam emerging from the amplifier system—or, alternatively (represented by a dashed line), a portion of the incident beam entering the amplifier system—and emitting said beam portion as output laser radiation B.sub.L.

[0046] The amplifier system 12 comprises a single interferometric optical amplification arrangement 20 or a plurality of interferometric optical amplification arrangements 20 in series or cascade, as schematically represented in the block 12. Each interferometric optical amplification arrangement 20 includes input beam splitting means, adapted to spatially split the incident optical beam in a first beam portion B.sub.1 and a second beam portion B.sub.2, downstream of which the first beam portion B.sub.1 is directed into an amplification arm 20a and the second beam portion B.sub.2 is directed into a non-amplifying propagation arm 20b. Beam combining means, different from the input beam splitting means, are adapted to bring together the first portion of the amplified beam coming from the amplification arm 20a and the second portion of the beam propagated without amplification coming from the propagation arm 20b of each interferometric optical amplification arrangement 20, thus substantially forming a Mach Zehnder interferometric arrangement, and the combining means of the last optical interferometric amplification arrangement of the series form the optical beam B.sub.o emerging from the amplifier system 12.

[0047] The amplification arm 20a includes an active region or gain region G capable of emitting photons coherent with the first portion of the beam B.sub.1 by stimulated emission following the excitation obtained, for example, by means of optical or electrical pumping.

[0048] In a currently preferred embodiment, the active region includes a semiconductor material, and an electrical excitation system is associated therewith, adapted to alter the thermodynamic equilibrium of the charge carrier populations confined therein, in order to determine an inversion condition of the charge carrier population and consequent radiative recombination.

[0049] In an alternative embodiment, the active region may include another material capable of supporting a stimulated emission of photons following optical or electrical excitation.

[0050] FIG. 2 shows a first schematic embodiment of a laser device according to the invention having a single interferometric optical amplification arrangement 20, in a free-space embodiment.

[0051] The interferometric optical amplification arrangement 20 includes at the input means BS for splitting the incident beam B.sub.i in the first beam portion B.sub.1 and in the second beam portion B.sub.2, and at the output combining means BC of the first beam portion B.sub.1 amplified in the active gain region G and the second beam portion B.sub.2. The combined optical beam B.sub.o emerging from the interferometric optical amplification arrangement 20 is returned at the input to the same interferometric optical amplification arrangement 20 through an optical return path 14 forming an optical resonant ring structure, comprising optical reflector means, in the non-limiting example, four flat mirrors M1-M4.

[0052] In an embodiment wherein the active gain region G of the amplification branch is formed by an optical semiconductor amplifier, it is expedient to associate thereto an input beam coupling stage 22 and an output beam collimation stage 24, which may alternatively be obtained by: [0053] a pair of aspherical lenses, respectively a first lens adapted to focus the beam entering the amplification region and a second lens adapted to collimate the beam exiting the amplification region; [0054] a pair of aspherical lenses and a pair of cylindrical lenses to circularize the beam, respectively first lenses adapted to focus and circularize the beam entering the amplification region and second lenses adapted to circularize and collimate the beam exiting the amplification region; [0055] a pair of spherical lenses and a pair of anamorphic prisms, respectively entering the amplification region and exiting the amplification region; [0056] an aspherical lens for focusing the beam entering the amplification region and a pair of cylindrical lenses to collimate and circularize the beam exiting the amplification region; [0057] a pair of micro-lenses, respectively for focusing and collimating the beam entering the amplification region and exiting the amplification region; [0058] a micro-lens for focusing the beam entering the amplification region and a pair of micro-lenses to collimate the beam exiting the amplification region both in the slow axis and in the fast axis.

[0059] The propagation arm 20b may comprise one or more reflecting or refracting optical elements (not shown), respectively for controlling the optical length of the propagation path and for controlling the spatial shape of the beam.

[0060] The combining means BC at the output of the interferometric amplification arrangement 20 further form the output means 16 of the coherent optical radiation from the laser device (B.sub.L) by extracting a portion of the beam B.sub.o emerging from the arrangement 20 as a loss beam of said combining means.

[0061] FIG. 3 shows a variant embodiment of the laser device of FIG. 2 wherein the return optical path 14 comprises four flat mirrors M1-M4 and two curved mirrors M5, M6 for folding and shaping the beam.

[0062] The figure also shows an optical isolator 26 downstream of the active region G, adapted to allow the propagation of the first portion of the amplified beam in a single predetermined direction. The isolator 26 may be present in any other embodiment described and arranged at any point of the resonant structure. However, since the gain means G emits from both directions, for simplicity of alignment the isolator is advantageously arranged at the output of the active amplification region.

[0063] FIG. 4 is a simulation diagram of the behavior of the laser device of FIG. 3, which shows its output power as a function of the spectral window with respect to the origin of the graph. Specifically, the graph shows the result due to the interference between the two beams (amplified and unperturbed). The fringes are due to the interference between the first beam portion B.sub.1 amplified in the active gain region G of the arm 20a and the second beam portion B.sub.2 propagated without amplification in the arm 20b. The spacing between the fringes depends on the optical path. The dashed line indicates the average power, while the dotted line indicates the maximum power that may be extracted from a resonant structure having the same dimensions, but without interferometric arrangement of the propagation branch.

[0064] In the interference maximum the device of the invention shows better performances than a standard laser diode without interferometric arrangement. However, given the difficulty of balancing an interferometric arrangement, i.e., given the impossibility of making the optical paths in the two branches equal, the resulting output power is the average value of that which is shown in the graph.

[0065] FIG. 5 shows the variant embodiment of the laser device of FIG. 3 with two cascaded interferometric optical amplification arrangements 20, 20′, connected by beam splitting means BS' which actuate both the recombination of the beams of the interferometric amplification arrangement 20 upstream and the separation of the beams in the interferometric amplification arrangement 20′ downstream. This variant embodiment makes it possible to adopt interferometric amplification arrangements in each of which the difference in optical length of the amplification and propagation arms 20a, 20b (20a′, 20b′ respectively) may be minimized, or such optical lengths made equivalent.

[0066] FIG. 6 is a second schematic embodiment of a laser device according to the invention having a single interferometric optical amplification arrangement, in a free-space embodiment. It shows a more compact structure wherein the beam splitting means BS and the beam combining means BC—different from the beam splitting means BS—are substantially aligned with the input paths of the incident beam B.sub.i and the output paths of the emerging beam B.sub.o, to the detriment of the interference control between the first beam portion B.sub.1 amplified in the active gain region G of the arm 20a and the second beam portion B.sub.2 propagated without amplification in the arm 20b, the two arms 20a, 20b showing a significant difference in optical length.

[0067] FIG. 7 is a simulation diagram of the behavior of the laser device of FIG. 6, which shows its output power as a function of the spectral window with respect to the origin of the graph. Specifically, the graph shows the result due to the interference between the two beams (amplified and unperturbed). The fringes are due to the interference between the amplified beam and the unperturbed beam. The spacing between the interference fringes between the first beam portion B.sub.1, amplified in the active gain region G of the arm 20a, and the second beam portion B.sub.2, propagated without amplification in the arm 20b, depends on the optical path and is different with respect to the spacing between the fringes of the graph in FIG. 4 because the optical path is different: the narrower fringes correspond to a greater difference in the optical path traveled by the beams. The dashed line indicates the average power, while the dotted line indicates the maximum power that may be extracted from a resonant structure having the same dimensions, but without interferometric arrangement of the propagation branch.

[0068] FIG. 8 shows the second embodiment of the laser device of FIG. 6 with two cascaded interferometric optical amplification arrangements. With respect to the configuration of FIG. 5, this configuration is more compact in a free-space embodiment.

[0069] FIG. 9 shows a third embodiment of a laser device according to the invention having a single interferometric optical amplification arrangement, in a free-space embodiment.

[0070] Unlike the first and second embodiments, the means 16 for the output of the coherent optical radiation from the laser device are arranged to extract a portion of the beam conducted along the optical return path entering the amplifier system and to emit said beam portion as laser radiation at the output.

[0071] FIG. 10 shows the configuration of FIG. 9 with a plurality of cascaded interferometric optical amplification arrangements 20, 20′, . . . , 20′. The first interferometric optical amplification arrangement is substantially analogous to the interferometric optical amplification arrangement which characterizes the embodiments described above, except for the interposition of beam splitting means BS.sub.i along the amplification arm, adapted to extract a smaller portion of the amplified beam to direct it toward the amplification arm of the subsequent downstream interferometric amplification arrangement, separately from a greater portion of the amplified beam directed toward the combiner means BC. Each intermediate interferometric optical amplification arrangement thus has at its input beam splitter means BS.sub.i that act exclusively on the beam of the amplification arm 20a of the preceding interferometric stage, and not on the recombined beam of the preceding interferometric stage. The combining means BC of each interferometric optical amplification arrangement, different from the beam splitting means BS.sub.i, brings together, and passes on to the next stage, the residual beam portion B.sub.1′ amplified in the active gain region G, which is not transmitted to the amplification arm of the downstream arrangement, and the beam portion B.sub.2 propagated without amplification. The combining means BC of each interferometric amplification arrangement may have a relative loss beam which is advantageously directed toward optical beam detector means D (for example, a photodiode) adapted to monitor the intensity and phase of the beam intermediate in the amplification chain.

[0072] The optical combined beam B.sub.o emerging from the series of cascaded interferometric optical amplification arrangements of the amplification system is returned to the input of the first interferometric optical amplification arrangement of the amplification system through an optical return path 14 forming an optical ring resonant structure.

[0073] The laser device according to the invention offers various advantages with respect to the solutions offered by the state of the art. With respect to currently adopted incoherent beam combination techniques, the described device shows the advantages of a coherent combination technique. With respect to techniques for wavelength beam combination, it allows an increase in power to be obtained while maintaining the spectral quality of said laser. With respect to coherent beam combining architectures, it offers a robust tool that avoids the use of active real-time phase control algorithms for each laser-emitting device, making manufacturing and industrial adoption easier.

[0074] Furthermore, the implementation of a single resonant structure external to all the amplifier stages offers the possibility of controlling the spatial shape of the beam directly in the cavity.

[0075] From a theoretical point of view, the only limit on the number of cascaded interferometric amplification arrangements is given by the gain saturation law of the single optical amplifiers of the amplification branches.

[0076] It should be noted that the embodiment proposed for this invention in the foregoing discussion is purely by way of non-limiting example of this invention. A person skilled in the art will easily be able to implement this invention in different embodiments which do not however depart from the principles set forth herein and are therefore encompassed in this patent.

[0077] This is particularly true with regard to the possibility of constructing the beam splitting and combining means, the gain means and the resonant structure according to techniques or configurations different from those described or referred to above. For example, although the interferometric amplification arrangements have been shown with the amplification arm arranged along the direction of transmission of the incident beam on the beam splitting means and the non-amplifying propagation arm arranged along a direction of reflection or coupling of the incident beam on the beam splitting means, it is possible to invert the arrangements of the amplification and propagation arms with respect to the beam splitting means as long as the condition is respected that most of the optical power incident on the beam splitting means is directed toward the non-amplifying propagation branch.

[0078] A free-space embodiment of the device with a large number of gain means requires particular attention in the optical alignment of the components, and more expediently the device of the invention may be obtained—in part or in its entirety—with guided optics, including optical fiber systems or systems with semiconductor integrated optics or another platform (for example glass).

[0079] Naturally, without prejudice to the principle of the invention, the embodiments and the details of execution may vary widely with respect to that which has been described and illustrated purely by way of non-limiting example, without thereby departing from the scope of protection of the invention defined by the appended claims.