Multi-mode chaotic laser generator based on pump modulation

Abstract

The present invention relates to the field of laser technology, and in particular to a multi-mode chaotic laser generating device based on pump modulation. The device includes a resonant cavity, a 4‑f telescope system, a gain medium, a pinhole aperture and a pump source. The resonant cavity includes a coaxially arranged plane reflector and an output coupling mirror; the 4‑f telescope system is arranged in the resonant cavity, and the 4‑f telescope system includes a coaxially arranged first thin lens and a second thin lens; the gain medium is arranged between the plane reflector and the first thin lens; the pinhole aperture is arranged between the first thin lens and the second thin lens, and the resonant cavity, the 4‑f telescope system, the gain medium and the pinhole aperture are coaxial; the pump source is arranged on the side of the gain medium, and the pump source is used to provide energy for the generation of laser. The present invention combines the multi-transverse mode resonance characteristics of the degenerate cavity and the system instability induced by pump modulation to realize multi-mode laser output from the spatial dimension and chaotic output from the time dimension.

Description

Technical Field

[0001] The invention relates to the field of laser technology, in particular to a multi-mode chaotic laser generating device based on pump modulation. Background Art

[0002] As a typical nonlinear optical phenomenon, chaotic laser has the characteristics of noise-like and wide spectrum, and has been applied in digital communication, random number generation and radar ranging. However, there are still the following problems in the application of chaotic laser: first, because the autocorrelation curve of the traditional external cavity chaotic laser contains obvious time delay characteristics, it is easy to be cracked by the cracker to steal the signal, and the pseudo sidelobe generated in the correlation ranging will interfere with the distance determination, limiting its application in confidential communication and laser ranging scenarios; second, the generated chaotic signal is a single-channel signal, which is difficult to achieve parallel output and cannot meet the future communication system's parallel demand for data transmission and high-speed random bit generation requirements; third, due to the relaxation oscillation limitation of the laser itself, the chaotic laser spectrum is not flat and contains obvious relaxation oscillation characteristics, which limits the information transmission rate of confidential communication.

[0003] Therefore, it is urgent to develop a parallel broadband chaotic laser generating device for application fields such as secure communication, laser ranging, and optical random bit generation. Summary of the invention

[0004] The purpose of the present invention is to provide a multi-mode chaotic laser generating device based on pump modulation in view of the above-mentioned problems and shortcomings, which can effectively solve the problems of relaxation oscillation and time delay label existing in the current chaotic laser technology.

[0005] To achieve the above purpose, the technical solution adopted is:

[0006] The present invention provides a multi-mode chaotic laser generating device based on pump modulation, comprising:

[0007] A resonant cavity comprising a coaxially arranged plane reflector and an output coupling mirror;

[0008] A 4-f telescope system, which is arranged in the resonant cavity, the 4-f telescope system comprising a first thin lens and a second thin lens arranged coaxially;

[0009] A gain medium, which is arranged between the plane reflector and the first thin lens;

[0010] A pinhole stop is disposed between the first thin lens and the second thin lens, and the resonant cavity, the 4-f telescope system, the gain medium and the pinhole stop are coaxial;

[0011] and a pump source, which is arranged on the side of the gain medium, and is used to provide energy for the generation of laser.

[0012] According to the multi-mode chaotic laser generating device based on pump modulation of the present invention, it is further characterized in that the first thin lens and the second thin lens are both circular and are convex lenses.

[0013] According to the multi-mode chaotic laser generating device based on pump modulation of the present invention, it is further characterized in that the back focal plane of the first thin lens and the front focal plane of the second thin lens coincide with each other to form a common focal plane.

[0014] According to the multi-mode chaotic laser generating device based on pump modulation of the present invention, further, the pinhole aperture is arranged at the common focal plane.

[0015] According to the multi-mode chaotic laser generating device based on pump modulation of the present invention, further, the plane reflector is arranged at the front focal plane of the first thin lens.

[0016] According to the multi-mode chaotic laser generating device based on pump modulation of the present invention, further, the output coupling mirror is arranged at the back focal plane of the second thin lens.

[0017] According to the multi-mode chaotic laser generating device based on pump modulation of the present invention, further, the calculation equation of the resonant frequency of the eigenmode of the resonant cavity is shown in Formula 1,

[0018]

[0019] The v qmn is the resonant frequency of the eigenmode of the resonant cavity, q is the longitudinal mode number of the eigenmode of the resonant cavity, m is the transverse mode number of the eigenmode of the resonant cavity, n is the other transverse mode number of the eigenmode of the resonant cavity, c is the speed of light in vacuum, L is the optical length of the resonant cavity, A is the linear magnification of the eigenmode of the resonant cavity, and D is the angular magnification of the eigenmode of the resonant cavity.

[0020] According to the multi-mode chaotic laser generating device based on pump modulation of the present invention, further, the transformation matrix of the resonant cavity system is as shown in matrix ①,

[0021]

[0022] Among them, M1 is the system forward transmission transformation matrix from the plane reflector to the output coupling mirror in the resonant cavity, M2 is the reverse transmission transformation matrix from the output coupling mirror to the plane reflector in the resonant cavity, A is the line magnification, B is the transmission length, C is the optical focal length, and D is the angular magnification.

[0023] According to the multi-mode chaotic laser generating device based on pump modulation of the present invention, further, the system forward transmission transformation matrix M1 from the plane reflector to the output coupling mirror in the resonant cavity is as shown in matrix ②,

[0024]

[0025] Among them, A1 is the linear magnification in forward transmission, B1 is the transmission length in forward transmission, C1 is the optical power in forward transmission, and D1 is the angular magnification in forward transmission.

[0026] According to the multi-mode chaotic laser generating device based on pump modulation of the present invention, further, the reverse transmission transformation matrix M2 from the output coupling mirror to the plane reflection mirror in the resonant cavity is as shown in matrix ③,

[0027]

[0028] Among them, A2 is the linear magnification in reverse transmission, B2 is the transmission length in reverse transmission, C2 is the optical power in reverse transmission, and D2 is the angular magnification in reverse transmission.

[0029] The beneficial effects achieved by adopting the above technical solution are:

[0030] The invention has a simple overall structure and an ingenious design. The invention combines the multi-transverse mode resonance characteristics of the degenerate cavity and the system instability induced by pump modulation to achieve multi-mode laser output from the spatial dimension and chaotic output from the temporal dimension. The laser generated by the generating device can be used for secure communication, parallel random bit generation and chaotic laser three-dimensional imaging.

[0031] The present invention starts with the modulation of the pump source, adds a third degree of freedom - modulation current, and controls the chaotic dynamics of the pump system by modulation depth and modulation angular frequency. The mode number is adjusted by using a degenerate cavity structure and a variable aperture diaphragm, and the two together construct a multi-mode chaotic laser, breaking through the shortcomings of the traditional scheme of using optical mode beat frequency parameters to generate chaos with a limited parameter range and difficulty in regulation, and expanding the chaotic dynamics to the field of external electrical parameter regulation, realizing electrical control of chaotic dynamics. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings of the embodiments of the present invention, wherein the drawings are only used to illustrate some embodiments of the present invention, but not to limit all embodiments of the present invention thereto.

[0033] Figure 1 Schematic diagram of the structure of a multi-mode chaotic laser generating device based on pump modulation according to an embodiment of the present invention;

[0034] Figure 2 is the time series of the ith mode output obtained by the simulation of the embodiment of the present invention;

[0035] Figure 3is the Lyapunov index spectrum of the i-th mode obtained by simulation of the embodiment of the present invention;

[0036] Figure 4 is the power spectrum of the i-th mode obtained by simulation of the embodiment of the present invention;

[0037] Figure 5 is the autocorrelation spectrum of the ith mode obtained by simulation in the embodiment of the present invention.

[0038] The meanings of the numbers in the figure are:

[0039] 1. Plane reflector, 2. Gain medium, 3. Pump source, 4. Positive electric wire, 5. Negative electric wire, 6. Modulation current source, 7. First thin lens, 8. Pinhole aperture, 9. Second thin lens, 10. Output coupling mirror. DETAILED DESCRIPTION

[0040] The following will be combined with the drawings of specific embodiments of the present invention to clearly and completely describe the exemplary scheme of the embodiment of the present invention. Unless otherwise defined, the technical terms or scientific terms used in the present invention should be the common meanings understood by people with ordinary skills in the field.

[0041] like Figure 1 As shown, the multi-mode chaotic laser generating device based on pump modulation of this embodiment includes a resonant cavity, a 4-f telescope system, a gain medium 2, a pinhole aperture 8 and a pump source 3. The resonant cavity is coaxially provided with a plane reflector 1 and an output coupling mirror 10; the 4-f telescope system is arranged in the resonant cavity, and the 4-f telescope system includes a first thin lens 7 and a second thin lens 9 which are coaxially arranged; the gain medium is arranged between the plane reflector 1 and the first thin lens 7; the pinhole aperture is arranged between the first thin lens 7 and the second thin lens 9, and the resonant cavity, the 4-f telescope system, the gain medium and the pinhole aperture are coaxially arranged; the pump source 3 is arranged on the side of the gain medium 2, and the pump source 3 is used to provide energy for the generation of the laser.

[0042] The resonant cavity composed of the plane reflector 1 and the output coupling mirror 10 realizes the extension of the working length of the gain medium 2 by reflecting the light in the cavity back and forth.

[0043] The first thin lens 7 and the second thin lens 9 form a 4-f telescope system, so that the light field of the plane reflector 1 can achieve self-reproduction on the output coupling mirror 10 after a single-pass transit, reducing the diffraction loss of high-order modes and enabling the cavity to support multi-transverse mode resonance.

[0044] The pinhole aperture 8 performs loss control on the transverse mode in the frequency spectrum to control the number of transverse modes.

[0045] Gain medium 2 is used to achieve population inversion and increase light energy density, while determining the wavelength of the laser.

[0046] The pump source 3 serves as an energy source, and its function is to emit photons to pump electrons in the gain medium from the ground state energy level to the high energy level to achieve a population inversion.

[0047] The modulation current source 6 generates a modulation current to modulate the output power of the pump source 3 .

[0048] Furthermore, the surface of the plane reflector 1 is coated with a high reflectivity film layer for light of the laser wavelength, and the reflectivity of the high reflectivity film layer is greater than 99.9%.

[0049] Optionally, the laser wavelength is 808 nm, 1064 nm or 1550 nm. Optionally, the plane reflector 1 is a circular reflector with a diameter of 25.4 cm or 50.8 cm.

[0050] Optionally, the gain medium 2 is cylindrical or rectangular.

[0051] Optionally, the gain medium 2 may be made of neodymium-doped yttrium aluminum garnet laser crystal (Nd:YAG), neodymium-doped yttrium lithium fluoride crystal (Nd:YLF), neodymium-doped yttrium vanadate crystal (Nd:YVO4), or other neodymium-doped yttrium aluminum garnet laser crystal (Nd:YAG). 3+ ) solid gain medium, with a concentration of 0.8at%-1.2at% and a thickness of 1-3mm. Alternatively, the gain medium 2 can be selected as a semiconductor quantum well material.

[0052] Optionally, the pump source 3 may be a high-intensity radiation device such as a semiconductor laser, an arc lamp, or a scattered light lamp.

[0053] Optionally, the gain medium 2 and the pump source 3 are arranged as a whole between the thin lens 7 and the pinhole aperture 8, or between the pinhole aperture 8 and the thin lens 9, or between the thin lens 9 and the output coupling mirror 10.

[0054] Optionally, the pinhole aperture 8 may be a circular aperture, a square aperture or the like, and its aperture is continuously adjustable within the range of 0 mm to 10 mm.

[0055] like Figure 1 As shown, the first thin lens 7 and the second thin lens 9 are both circular and convex lenses.

[0056] Further, the focal length of the convex lens is 20 cm or 30 cm, the diameter is 25.4 cm or 50.8 cm, and the surface of the convex lens is coated with a high transmittance film layer for laser wavelength light. Further, the wavelength range here is 800nm ​​to 1600nm.

[0057] Optionally, the laser wavelength is 808 nm, 1064 nm or 1550 nm.

[0058] Optionally, the first thin lens 7 and the second thin lens 9 are both plano-convex lenses or bi-convex lenses.

[0059] The rear focal plane of the first thin lens 7 and the front focal plane of the second thin lens 9 coincide with each other to form a common focal plane, and the pinhole stop is arranged at the common focal plane.

[0060] like Figure 1 As shown, the plane reflector 1 is arranged at the front focal plane of the first thin lens 7 , and the output coupling mirror 10 is arranged at the back focal plane of the second thin lens 9 .

[0061] Optionally, the reflection: transmission splitting ratio of the output coupling mirror 10 can be selected as 5:5 or 6:4 or 7:3, etc., and the surface of the output coupling mirror 10 is coated with a reflective film layer and a transmissive film layer for the laser wavelength. Further, the wavelength range here is 800nm ​​to 1600nm.

[0062] Optionally, the laser wavelength is 808 nm, 1064 nm or 1550 nm.

[0063] Optionally, the output coupling mirror 10 is a circular member with a diameter of 25.4 cm or 50.8 cm.

[0064] like Figure 1 As shown, the pump source 3 is connected to the modulation current source 6 via the positive electrode electrical conductor 4 and the negative electrode electrical conductor 5. Thus, an electrical connection circuit is formed to realize the modulation current source 6 supplying power to the pump source 3.

[0065] In this application, the system forward transmission transformation matrix calculation equation from the plane reflector to the output coupling mirror in the resonant cavity is shown in Formula 1,

[0066]

[0067] v qmn is the resonant frequency of the eigenmode of the resonant cavity, q is the longitudinal mode number of the eigenmode of the resonant cavity, m is the transverse mode number of one eigenmode of the resonant cavity, n is the other transverse mode number of the eigenmode of the resonant cavity, c is the speed of light in vacuum, L is the optical length of the resonant cavity, A is the linear magnification of the eigenmode of the resonant cavity, and D is the angular magnification of the eigenmode of the resonant cavity.

[0068] The loop transformation matrix of the resonant cavity system is shown in matrix ①.

[0069]

[0070] Among them, A is the linear magnification of the resonant cavity eigenmode, B is the transmission length of the resonant cavity eigenmode, C is the optical focal length of the resonant cavity eigenmode, and D is the angular magnification of the resonant cavity eigenmode.

[0071] The system forward transmission transformation matrix M1 from the plane reflector to the output coupling mirror in the resonant cavity is shown in matrix ②.

[0072]

[0073] Among them, A1 is the linear magnification in forward transmission, B1 is the transmission length in forward transmission, C1 is the optical power in forward transmission, and D1 is the angular magnification in forward transmission.

[0074] The system forward and reverse transmission transformation matrix M2 from the output coupling mirror to the plane reflector in the resonant cavity is shown in matrix ③.

[0075]

[0076] Among them, A2 is the linear magnification in reverse transmission, B2 is the transmission length in reverse transmission, C2 is the optical power in reverse transmission, and D2 is the angular magnification in reverse transmission.

[0077] According to matrices ①, ② and ③, we can get:

[0078]

[0079] From this we can get: A = D = 1. Substituting this result into formula (1) we can get: It can be seen from this that the resonant frequency v of the eigenmode of the resonant cavity in this application is qmn It is only related to the speed of light c in vacuum, the optical length L of the resonant cavity, and the longitudinal mode number q, but has nothing to do with the two transverse mode numbers m and n. This shows that the resonant cavity supports independent oscillation of high-order and low-order transverse modes in the same longitudinal mode. By adjusting the aperture size of the small hole diaphragm, the loss of the mode can be adjusted, and the number of modes can be adjusted.

[0080] Under the modulation of pump source 2, the dynamic equation of the i-th mode in the multimode laser is shown in Formula 2

[0081]

[0082] Among them, E i and G i represent the complex amplitude and population gain of the ith laser mode, τ c is the round trip time in the laser field cavity, τ f represents the fluorescence time of the gain medium, ω i represents the detuning amount between the ith laser mode and the center frequency, p i is the pump coefficient of the ith laser mode, α iis the mode loss coefficient of the ith laser mode, M is the pump modulation depth, and Ω is the modulation angular frequency. The difference between the modes is that the frequency detuning, gain, and loss are different. The frequency detuning is determined by the matching degree of the gain curve of the resonant cavity and the gain medium, and the gain and loss are determined by the mode field area and divergence angle of the mode.

[0083] Therefore, the third degree of freedom, the modulation current, is added by modulating the pump coefficient of pump source 2. This makes the system originally described by amplitude and population gain unstable, forming the basis for the generation of chaotic dynamics.

[0084] Furthermore, for the degenerate state, when the round trip transformation matrix M of the resonant cavity system satisfies A+D=u, and u is an integer or an irreducible fraction, the resonant cavity mode still satisfies the degenerate condition, and multi-mode chaotic laser can still be generated through pump modulation.

[0085] According to the actual physical system parameters, the normalized pump coefficient p is taken i =0.02, round trip time τ c =4ns, fluorescence time τ f =240μs,ω i = 0, normalized mode loss coefficient α i =0.01, modulation depth M = 0.95, modulation angular frequency Ω = 1.4 × 10 5 rad / s, the simulation is performed on the i-th mode, and the results are as follows Figure 2-Figure 5 shown.

[0086] The time series output by the i-th mode is as follows Figure 2 As shown, the time series exhibits obvious noise-like characteristics.

[0087] The Lyapunov exponent spectrum of the i-th mode is Figure 3 As shown, where λ1>0, it indicates that the system output time series is a chaotic series.

[0088] The power spectrum of the i-th mode output is as follows: Figure 4 As shown, the power spectrum exhibits a broad spectrum characteristic and does not contain obvious relaxation oscillation features.

[0089] The autocorrelation spectrum of the ith mode output is as follows: Figure 5 As shown, due to the use of pump modulation, the autocorrelation spectrum does not contain time delay features.

[0090] The technical solution of the present invention is described above in combination with the accompanying drawings. It is obvious that the specific implementation of the present invention is not limited to the above-mentioned method. As long as various non-substantial improvements are made using the method concept and technical solution of the present invention, or the concept and technical solution of the invention are directly applied to other occasions without improvement, they are all within the protection scope of the present invention.

[0091] In the description of the present invention, it should be understood that the expressions “first” and “second” are used to describe the various elements of the present invention and do not represent any limitation of order, quantity or importance, but are only used to distinguish one component from another.

[0092] It should be noted that when one element is “connected”, “coupled” or “connected” to another element, it may mean that they are directly connected, coupled or connected, but it should be understood that there may be intermediate elements between the two; that is, the positional relationships of direct connection and indirect connection are covered.

[0093] It should be noted that the use of "a" or "an" and similar words does not necessarily indicate a quantitative limitation. "Include" or "comprising" and similar words mean that the elements or objects preceding the word include the elements or objects listed after the word and their equivalents, but do not exclude other elements or objects.

[0094] It should be noted that terms such as "up", "down", "left" and "right" indicating orientation or positional relationship are only used to indicate relative positional relationship. This is for the convenience of describing the present invention and does not mean that the device or element must have a specific orientation, be constructed and operated in a specific orientation. When the absolute position of the object being described changes, the relative positional relationship may also change accordingly.

[0095] The preferred embodiments for implementing the present invention have been described in detail above, but it should be understood that the role of these embodiments is only to exemplify, and is not intended to limit the scope, applicability or configuration of the present invention in any way. The protection scope of the present invention is defined by the attached claims and their equivalents. A person of ordinary skill in the art can make many changes to the above embodiments under the guidance of the present invention, and these changes all fall within the protection scope of the present invention.

Claims

1. A multi-mode chaotic laser generating device based on pump modulation, characterized in that: include: A resonant cavity comprising a coaxially arranged plane reflector and an output coupling mirror; A 4-f telescope system, which is arranged in the resonant cavity, the 4-f telescope system comprising a first thin lens and a second thin lens arranged coaxially; A gain medium, which is arranged between the plane reflector and the first thin lens; A pinhole stop is disposed between the first thin lens and the second thin lens, and the resonant cavity, the 4-f telescope system, the gain medium and the pinhole stop are coaxial; and a pump source, which is arranged on the side of the gain medium, and is used to provide energy for the generation of laser.

2. The multi-mode chaotic laser generating device based on pump modulation according to claim 1, characterized in that: The first thin lens and the second thin lens are both circular and convex lenses.

3. The multi-mode chaotic laser generating device based on pump modulation according to claim 2, characterized in that: The back focal plane of the first thin lens and the front focal plane of the second thin lens coincide with each other to form a common focal plane.

4. The multi-mode chaotic laser generator based on pump modulation according to claim 3, characterized in that: The pinhole stop is arranged at the common focal plane.

5. The multi-mode chaotic laser generating device based on pump modulation according to claim 2, characterized in that: The plane reflector is arranged at the front focal plane of the first thin lens.

6. The multi-mode chaotic laser generating device based on pump modulation according to claim 5, characterized in that: The output coupling mirror is arranged at the back focal plane of the second thin lens.

7. The multi-mode chaotic laser generating device based on pump modulation according to claim 1, characterized in that: The calculation equation of the resonant frequency of the eigenmode of the resonant cavity is shown in Formula 1, The v qmn is the resonant frequency of the eigenmode of the resonant cavity, q is the longitudinal mode number of the eigenmode of the resonant cavity, m is the transverse mode number of the eigenmode of the resonant cavity, n is the other transverse mode number of the eigenmode of the resonant cavity, c is the speed of light in a vacuum, L is the optical length of the resonant cavity, A is the linear magnification of the resonant cavity round-trip transformation matrix, and D is the angular magnification of the resonant cavity round-trip transformation matrix.

8. The multi-mode chaotic laser generator based on pump modulation according to claim 8, characterized in that: The loop transformation matrix of the resonant cavity system is shown in matrix ①. Among them, M1 is the system forward transmission transformation matrix from the plane reflector to the output coupling mirror in the resonant cavity, M2 is the reverse transmission transformation matrix from the output coupling mirror to the plane reflector in the resonant cavity, A is the line magnification, B is the transmission length, C is the optical focal length, and D is the angular magnification.

9. The multi-mode chaotic laser generator based on pump modulation according to claim 9, characterized in that: The system forward transmission transformation matrix M1 from the plane reflector to the output coupling mirror in the resonant cavity is shown as matrix ②, Among them, A1 is the forward transmission line magnification, B1 is the forward transmission transmission length, C1 is the forward transmission optical power, and D1 is the forward transmission angular magnification.

10. The multi-mode chaotic laser generating device based on pump modulation according to claim 9, characterized in that: The reverse transmission transformation matrix M2 from the output coupling mirror to the plane reflector in the resonant cavity is shown in matrix ③. Among them, A2 is the linear magnification in reverse transmission, B2 is the transmission length in reverse transmission, C2 is the optical power in reverse transmission, and D2 is the angular magnification in reverse transmission.

Images