An external cavity semiconductor chaotic laser

Abstract

The application discloses an external cavity semiconductor chaotic laser, which comprises a driving source, a temperature control unit and an output assembly; the temperature control unit comprises a TEC controller, a TEC refrigerating sheet and a temperature sensor which are located inside a butterfly-shaped package; a semiconductor gain medium, a coupling lens group, an external cavity reflector and a collimating lens group are fixedly installed on the TEC refrigerating sheet in sequence along the outgoing direction of laser; the semiconductor gain medium, the coupling lens group and the external cavity reflector are coupled in sequence to form a laser resonant cavity; the electrodes of the temperature sensor and the TEC refrigerating sheet are connected with the TEC controller through the pins of the butterfly-shaped package respectively; the electrodes of the semiconductor gain medium are connected with the driving source through the pins of the butterfly-shaped package; and the output assembly is located right behind the output end of the collimating lens group. The laser of the application has the advantages of simple structure, low cost, easy operation, good environmental adaptability and stable high-quality chaotic laser output.

Description

Technical Field

[0001] This invention relates to laser devices, specifically an external cavity semiconductor chaotic laser. Background Technology

[0002] Unlike continuous-wave and pulsed lasers, chaotic lasers, with their unpredictable, noise-like wide-spectrum, low-coherence, and high-complexity characteristics, have demonstrated significant application value in several cutting-edge fields. Specifically: in secure communication, their unpredictability provides a natural platform for physical-layer encryption, greatly enhancing the anti-eavesdropping and anti-interference capabilities of optical communication; in high-speed random number generation, chaotic lasers can serve as high-quality entropy sources, generating truly random numbers at rates far exceeding those of electronic methods, serving cryptography and high-performance computing; in radar and detection systems, they can significantly improve range resolution and anti-interference performance, enabling high-precision, low-interception-rate monitoring; in optical sensing and measurement, their wide-spectrum characteristics facilitate higher-sensitivity distributed sensing; furthermore, chaotic lasers also provide potential optical implementation schemes for neuromorphic computing and chaotic computing, driving the development of novel information processing architectures. These advantages make them an important tool for the development of next-generation photonic information technology.

[0003] The core of chaotic laser generation technology lies in controllingly disrupting the stable output of a laser to introduce nonlinear dynamics, thereby obtaining a chaotic light field with a wide spectrum of noise-like characteristics and extreme sensitivity to initial conditions. Current mainstream technologies include two main systems: all-optical feedback and optoelectronic hybrid feedback. Specifically: 1) The all-optical feedback scheme achieves this by constructing an optical path outside the laser to re-inject a portion of the output light into the cavity. This is achieved in two ways: one is based on external mirror feedback and fiber loop feedback; the other is through optical injection locking to generate chaotic lasers, where a stable beam from a master laser is injected into a slave laser. By adjusting the injection power and frequency detuning, the slave laser output enters a wide-bandwidth chaotic state. This scheme generates chaotic signals with bandwidths reaching tens of GHz, making it particularly suitable for... High-speed physical random number generation and other fields with extremely high speed requirements require two highly matched lasers, making the system complex and costly. In short, traditional all-optical lasers rely on precise optical alignment and are susceptible to temperature drift and vibration interference. 2) The optoelectronic hybrid feedback scheme combines flexibility and stability. It converts the laser output into an electrical signal through a photodetector, and after processing by an electrical amplifier, filter or delay line, it directly modulates the laser's drive current or the phase modulator in the cavity, avoiding the optical alignment problem. It can also flexibly design nonlinear functions and multiple delays in the electrical domain, and easily generate highly complex chaotic dynamics. However, the chaotic bandwidth of the system is limited by the response speed of the electrical devices. In addition, the existing mainstream technologies are generally based on discrete components, which are bulky and difficult to replicate and mass-produce.

[0004] In fact, the quality and complexity of chaotic laser output are extremely sensitive to parameter changes. Maintaining a stable and high-performance chaotic state in real-world environments remains a significant challenge. Therefore, without increasing system cost and complexity, it is of great importance to promote the engineering application of chaotic lasers by finding a convenient electronic control method to achieve stable and high-quality chaotic laser output based on the same external cavity semiconductor mode-locked laser. Summary of the Invention

[0005] The purpose of this invention is to provide an external cavity semiconductor chaotic laser, which is not only simple in structure, low in cost, and easy to operate, but also has good environmental adaptability and can achieve stable and high-quality chaotic laser output.

[0006] This invention is achieved through the following technical solution: An external cavity semiconductor chaotic laser includes a driver source, a temperature control unit, and an output component; The temperature control unit includes a TEC controller, a TEC cooler and a temperature sensor located inside a butterfly package. A semiconductor gain medium, a coupling lens group, an external cavity reflector and a collimating lens group are sequentially fixed on the TEC cooler along the laser emission direction. The semiconductor gain medium, the coupling lens group and the external cavity reflector are sequentially coupled to form a laser resonant cavity. The electrodes of the temperature sensor and the TEC cooling chip are respectively connected to the TEC controller through the pins of the butterfly package, and the electrodes of the semiconductor gain dielectric are connected to the driving source through the pins of the butterfly package. The output component is located directly behind the output end of the collimating lens group.

[0007] Furthermore, the semiconductor gain medium is a semiconductor gain chip or an on-chip gain waveguide, wherein: when the semiconductor gain medium is a semiconductor gain chip, the driving source is a current source; when the semiconductor gain medium is an on-chip gain waveguide, the driving source is a pump laser source.

[0008] Furthermore, the input end face of the semiconductor gain chip is coated with a high-reflectivity film with a reflectivity of 90%, and the output end face is coated with an anti-reflectivity film with a reflectivity of less than 0.5%. The saturated output power of the semiconductor gain chip is not less than 10 mW, and the small-signal gain is greater than 15 dB.

[0009] Furthermore, the output current of the current source is 100~500 mA, and the fluctuation of the output current is less than 3μA; the output power of the pump laser source is greater than 100 mW.

[0010] Furthermore, the coupling lens group consists of an aspherical lens and a spherical lens, wherein: the aspherical lens is used to shape the mode field of the semiconductor gain medium output in two directions to output approximately collimated light; the spherical lens is used to transform the mode field of the approximately collimated light to be the same as the mode field of the external cavity reflector.

[0011] Furthermore, the external cavity reflector is a wavelength-selective reflector, whose reflected wavelength is within the gain bandwidth range of the semiconductor gain medium, and its reflectivity is 5%~98%; Furthermore, the wavelength-selective reflector is a Bragg grating reflector, which includes a fiber Bragg grating, a bulk Bragg grating, and an on-chip waveguide grating.

[0012] Furthermore, the collimating lens group is a spherical lens.

[0013] Furthermore, the output component includes an optical isolator, a coupling lens, and an output fiber arranged sequentially along the laser emission direction, wherein: the optical isolator is located directly behind the output end of the collimating lens group, and the isolation of the optical isolator is greater than 35 dB; the output fiber is a single-mode polarization-maintaining fiber.

[0014] Furthermore, the temperature sensor is a thermistor sensor.

[0015] The present invention has the following beneficial technical effects: First, the external cavity semiconductor chaotic laser provided by this invention has no external feedback structure, overcoming the problems of complex laser structure and high cost caused by the need to introduce external all-optical feedback and photoelectric hybrid feedback to disrupt the stable output of the laser in traditional chaotic laser generation technology. It has the advantages of simple structure and low cost, and is more suitable for mass production. Second, the core device of the external cavity semiconductor chaotic laser provided by this invention is integrated into the TEC cooler, with a high degree of integration. Moreover, the core component is packaged inside a butterfly package, which has the advantages of compact structure and small size, providing convenient conditions for miniaturization of subsequent ranging, communication and other application systems. Third, by controlling the operating temperature of the laser resonant cavity through the TEC cooler, the stability of the laser working in different environments is increased, and the robustness of the laser system is improved. In summary, the external cavity semiconductor chaotic laser provided by this invention has the advantages of simple structure, compact size, small size, low cost, simple operation and strong environmental adaptability. It can achieve stable and high-quality chaotic laser output, which is of great value for promoting the practical application and industrialization of chaotic laser technology.

[0016] The coupling lens group of the present invention is composed of an aspherical lens and a spherical lens. The aspherical lens is used to shape the output mode field of the semiconductor gain chip, so that the mode field size in the two directions is approximately the same, and the output is approximately collimated light. The spherical lens transforms the collimated light mode field to be the same as the mode field of the external cavity reflector, realizing low-loss coupling between the semiconductor gain medium and the external cavity reflector, and has the advantage of low power consumption. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the external cavity semiconductor chaotic laser of the present invention; Figure 2 This is a schematic diagram of the output component of the external cavity semiconductor chaotic laser of the present invention. Figure 3 This is a spectrum of the chaotic laser output by the external cavity semiconductor laser of the present invention; Figure 4 This is a spectrum diagram of the chaotic laser output by the external cavity semiconductor laser of the present invention; Figure 5 This is a time-domain waveform diagram of the chaotic laser output by the external cavity semiconductor laser of the present invention; Figure 6 This is an autocorrelation curve of the chaotic laser output from the external cavity semiconductor laser of the present invention.

[0018] In the diagram: 1. Driver source; 2. Semiconductor gain medium; 3. Coupled lens group; 4. External cavity reflector; 5. Collimating lens group; 6. Temperature control unit; 7. Output component; 71. Optical isolator; 72. Coupled lens; 73. Output optical fiber; Detailed Implementation The present invention will be further described in detail below with reference to specific embodiments. These descriptions are for explanation purposes only and are not intended to limit the scope of the invention.

[0019] refer to Figure 1 and Figure 2 As shown, an external cavity semiconductor chaotic laser includes a driving source 1, a temperature control unit 6, and an output component 7. The temperature control unit 6 includes a TEC controller, a TEC cooler and a temperature sensor located inside the butterfly package. A semiconductor gain medium 2, a coupling lens group 3, an external cavity reflector 4 and a collimating lens group 5 are sequentially fixed on the TEC cooler along the laser emission direction. The semiconductor gain medium 2, the coupling lens group 3 and the external cavity reflector 4 are sequentially coupled to form a laser resonant cavity. The operating temperature of the laser resonant cavity is controlled by the TEC cooler to increase the stability of the laser operation and improve the robustness of the laser system. The external cavity reflector 4 has filtering capability, realizing the selection and control of the output wavelength of chaotic laser. It reflects part of the laser back to the laser resonant cavity to form laser oscillation, and transmits part of the laser as the output of the laser. The electrodes of the temperature sensor and the TEC cooling chip are connected to the pins of the butterfly package via gold wires, thereby connecting to an external TEC controller. The maximum output current of the TEC controller is 1.2 A. The electrodes of the semiconductor gain medium 2 are connected to the pins of the butterfly package via gold wires, thereby connecting to the external driving source 1, which provides excitation to the semiconductor gain medium 2. The output component 7 includes an optical isolator 71, a coupling lens 72, and an output fiber 73 arranged sequentially along the laser emission direction. The optical isolator 71 is located directly behind the output end of the collimating lens group 5, and the isolation of the optical isolator 71 is greater than 35 dB. It is used to prevent external light signals from being reflected into the laser and thus affecting the normal operation of the laser. The laser transmitted by the collimating lens group 5 is coupled into the output fiber 73 through the coupling lens 72, so as to realize the fiber output of the laser.

[0020] Preferably, the semiconductor gain medium 2 is a semiconductor gain chip or an on-chip gain waveguide, wherein: when the semiconductor gain medium 2 is a semiconductor gain chip, the driving source 1 is a current source; when the semiconductor gain medium 2 is an on-chip gain waveguide, the driving source 1 is a pump laser source. The semiconductor gain chip has an InGaAsP / InP quantum well layer structure, and its input end face is coated with a high-reflectivity film with a reflectivity of 90%, and its output end face is coated with an anti-reflectivity film with a reflectivity of less than 0.5%. Its gain bandwidth is greater than 80nm, the gain center wavelength is 1550nm, and the saturated output power is not less than 10mW. In this embodiment, the preferred saturated output power is greater than 18dBm and the small signal gain is greater than 15dB.

[0021] Preferably, the semiconductor gain chip has a length of 1 mm, a small signal gain of 30 dB, and an output waveguide that adopts a polarization-maintaining ridge waveguide, with a horizontal divergence angle of 18° and a vertical divergence angle of 29° for its output mode field.

[0022] Preferably, the current source is a low-noise current source with an output current of 100~500 mA and an output current fluctuation of less than 3μA. The current source is controlled by a digital circuit, and the output current of the current source is controlled by sending instructions to the digital circuit through software loaded on the host computer, thereby having an adjustment accuracy of better than 5 mA.

[0023] Preferably, the output power of the pump laser source is greater than 100 mW, and the output laser wavelength depends on the doping ions of the on-chip gain waveguide. For example, when the doping ions of the on-chip gain waveguide are erbium, the output laser wavelength of the pump laser source is 980 nm.

[0024] Preferably, the coupling lens group 3 consists of an aspherical lens and a spherical lens, wherein: the aspherical lens is used to shape the mode field of the semiconductor gain medium 2 in two directions so that the mode field size in the two directions is approximately the same, thereby outputting approximately collimated light; the spherical lens is used to transform the mode field of the approximately collimated light to be the same as the mode field of the external cavity reflector 4, thereby realizing low-loss coupling between the semiconductor gain medium 2 and the external cavity reflector 4.

[0025] Preferably, the external cavity reflector 4 is a wavelength selective reflector, whose reflection wavelength is within the gain bandwidth range of the semiconductor gain medium 2, and its reflectivity is 5%~98%.

[0026] Preferably, the wavelength selective reflector is a Bragg grating reflector, which includes a fiber Bragg grating, a bulk Bragg grating, and an on-chip waveguide grating.

[0027] Preferably, the fiber Bragg grating is made of polarization-maintaining fiber with a center wavelength of 1550 nm, a reflection bandwidth of 0.2 nm, and a reflectivity of 80%. The polarization-maintaining fiber is preferably a single-mode polarization-maintaining fiber.

[0028] Preferably, the collimating lens group 5 is a spherical lens that collimates the laser output from the external cavity reflector 4, thereby achieving low-loss coupling of the laser to the optical fiber.

[0029] Preferably, the temperature sensor is a 10 kΩ thermistor sensor.

[0030] Preferably, the output optical fiber 73 is a single-mode polarization-maintaining fiber.

[0031] Taking an external cavity semiconductor chaotic laser with driver source 1 as the current source and semiconductor gain medium 2 as the semiconductor gain chip as an example, its performance is tested and its working principle is explained: The output current of driver 1 is set by the host computer software. By adjusting the driving current, the net gain, nonlinear phase shift, external cavity phase, and detuning state of the gain peak and fiber Bragg grating (FBG) are simultaneously changed, thereby affecting the carrier concentration, refractive index, and gain saturation. By increasing the output current, the external cavity semiconductor chaotic laser is made to operate in a chaotic laser state. In this process, the following nonlinear mechanisms work together: First, the intensity-phase coupling caused by carrier-photon relaxation oscillation and strong α factor constitutes the basic instability source; Second, spatial hole burning (SHB) and four-wave mixing (FWM) effects promote complex coupling between longitudinal modes; Third, mode competition and polarization competition caused by narrowband FBG are intertwined with the delayed optical feedback of the composite cavity. These nonlinear mechanisms together cause the laser to start from a stable mode-locked state. When the changes in parameters such as current cross the nonlinear threshold, the original phase lock is broken. Then, through bifurcation paths including period doubling and quasi-period, it evolves into a high-dimensional chaotic state with unpredictable fluctuations in intensity and phase, that is, chaotic laser output is generated. When the output current of driver source 1 is 420 mA, the chaotic laser spectrum output by the laser is as follows: Figure 3 As shown, the frequency of the response is as follows Figure 4 As shown, the time-domain waveform and autocorrelation function curve of the chaotic laser are respectively as follows: Figure 5 and Figure 6 As shown, where: from Figure 3 It can be seen that the laser has left the stable single-mode operating region and entered a chaotic laser state; from Figure 4 It can be seen that the spectral bandwidth of the laser can reach over 10 GHz; from Figure 5 It can be seen that the light intensity output by the laser exhibits irregular fluctuations in the time domain; from Figure 6 It can be seen that the baseline of the autocorrelation function is very close to 0, and the deviation is no more than 0.01, which is much lower than the deviation of 0.1 of existing chaotic lasers, indicating that the laser in this embodiment has entered a high-quality chaotic state.

[0032] The external cavity semiconductor chaotic laser in this embodiment is packaged using a butterfly packaging process, which can generate a high-quality broadband chaotic entropy source without the need for a complex external modulator. It has the advantages of simple structure, easy operation, low cost and easy promotion, and has important application value in the fields of chaotic secure optical communication, chaotic lidar, random number generation and other fields.

Claims

1. An external cavity semiconductor chaotic laser, characterized in that, It includes a drive source (1), a temperature control unit (6), and an output component (7). The temperature control unit (6) includes a TEC controller and a TEC cooling chip and a temperature sensor located inside the butterfly package. A semiconductor gain medium (2), a coupling lens group (3), an external cavity reflector (4) and a collimating lens group (5) are sequentially fixed on the TEC cooling chip along the laser emission direction. The semiconductor gain medium (2), the coupling lens group (3) and the external cavity reflector (4) are sequentially coupled to form a laser resonant cavity. The electrodes of the temperature sensor and the TEC cooling chip are respectively connected to the TEC controller through the pins of the butterfly package, and the electrodes of the semiconductor gain medium (2) are connected to the driving source (1) through the pins of the butterfly package. The output component (7) is located directly behind the output end of the collimating lens group (5).

2. The external cavity semiconductor chaotic laser according to claim 1, characterized in that, The semiconductor gain medium (2) is a semiconductor gain chip or an on-chip gain waveguide, wherein: when the semiconductor gain medium (2) is a semiconductor gain chip, the driving source (1) is a current source; when the semiconductor gain medium (2) is an on-chip gain waveguide, the driving source (1) is a pump laser source.

3. The external cavity semiconductor chaotic laser according to claim 2, characterized in that, The input end of the semiconductor gain chip is coated with a high-reflectivity film with a reflectivity of 90%, and the output end is coated with an anti-reflectivity film with a reflectivity of less than 0.5%. The saturated output power of the semiconductor gain chip is not less than 10 mW, and the small-signal gain is greater than 15 dB.

4. The external cavity semiconductor chaotic laser according to claim 2 or 3, characterized in that, The output current of the current source is 100~500 mA, and the fluctuation of the output current is less than 3μA; the output power of the pump laser source is greater than 100 mW.

5. The external cavity semiconductor chaotic laser according to claim 1 or 2, characterized in that, The coupling lens group (3) consists of an aspherical lens and a spherical lens, wherein: the aspherical lens is used to shape the mode field of the semiconductor gain medium (2) in two directions to output approximately collimated light; the spherical lens is used to transform the mode field of the approximately collimated light to be the same as the mode field of the external cavity reflector (4).

6. The external cavity semiconductor chaotic laser according to claim 3, characterized in that, The external cavity reflector (4) is a wavelength selective reflector, whose reflection wavelength is within the gain bandwidth range of the semiconductor gain medium (2), and its reflectivity is 5%~98%.

7. The external cavity semiconductor chaotic laser according to claim 6, characterized in that, The wavelength-selective reflector is a Bragg grating reflector, which includes a fiber Bragg grating, a bulk Bragg grating, and an on-chip waveguide grating.

8. The external cavity semiconductor chaotic laser according to claim 1 or 2, characterized in that, The collimating lens group (5) is a spherical lens.

9. The external cavity semiconductor chaotic laser according to claim 1 or 2, characterized in that, The output component (7) includes an optical isolator (71), a coupling lens (72) and an output fiber (73) arranged sequentially along the laser emission direction, wherein: the optical isolator (71) is located directly behind the output end of the collimating lens group (5), and the isolation of the optical isolator (71) is greater than 35 dB; the output fiber (73) is a single-mode polarization-maintaining fiber.

10. The external cavity semiconductor chaotic laser according to claim 1 or 2, characterized in that, The temperature sensor is a thermistor sensor.

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