Dual-band frequency modulation signal generation device and method

Abstract

The invention discloses a dual-band frequency-modulated signal generating device, which belongs to the technical field of photoelectronics and comprises a short-coupling mutual-injection semiconductor laser, a single-mode fiber, a photoelectric detector and a radio frequency cable which are connected in sequence, an optical signal output by the short-coupling mutual-injection semiconductor laser is transmitted to the photoelectric detector through the single-mode optical fiber, is converted into an electric signal by the photoelectric detector and is output through the radio frequency cable; the short-coupling mutual-injection semiconductor laser comprises a master laser and a slave laser which are integrated on the same substrate, the master laser and the slave laser are mutually injected, the initial working wavelengths of the master laser and the slave laser are different, a driving current signal of the master laser or the slave laser is a modulation signal, and the driving current signal of the master laser or the slave laser is a modulation signal. And generating a dual-band frequency modulation signal by continuously tuning the amplitude of the modulation signal. The device is simple in structure, and the generated dual-band frequency modulation signal is compact in structure, low in cost, high in tunability and stable in performance.

Description

Technical Field

[0001] The invention relates to a dual-band frequency modulation signal generating device and method, belonging to the field of optoelectronic technology. Background Art

[0002] Radar has the ability to detect objects at long distances and identify them with high precision, and has vital applications in battlefield identification, missile guidance, traffic safety, meteorological remote sensing, etc. With the continuous development of modern radar technology, the increasingly complex application environment requires radar sources to have multi-band capabilities.

[0003] However, due to the limitation of "electronic bottleneck", most traditional narrowband radars only work in a single frequency band and can only perform specific functions. To achieve multi-functions, it is inevitable to increase the number of radars, and each band needs to be equipped with a frequency synthesizer and multi-level up and down mixing frequency multiplication links, which makes the system complexity, coordination, software and hardware costs rise sharply, and there is strong electromagnetic interference.

[0004] Using optical methods to achieve dual-band frequency modulation signals is a feasible method, but it mainly relies on the discrete optoelectronic system of the electro-optical modulator, which has obvious disadvantages such as large insertion loss, large size, high power consumption and high cost. Summary of the invention

[0005] The object of the present invention is to provide a dual-band FM signal generating device, which can solve the problems of complex structure, high cost and low integration of the existing dual-band FM signal generating device.

[0006] In order to achieve the above object, the present invention provides the following technical solutions: In a first aspect, the present invention provides a dual-band frequency modulation signal generating device, comprising a short-coupled mutual injection semiconductor laser, a single-mode optical fiber, a photodetector and a radio frequency cable connected in sequence, wherein the optical signal output by the short-coupled mutual injection semiconductor laser is transmitted to the photodetector through the single-mode optical fiber, converted into an electrical signal by the photodetector and output through the radio frequency cable; the short-coupled mutual injection semiconductor laser comprises a master laser and a slave laser integrated on the same substrate, the master laser and the slave laser are injected into each other, the initial operating wavelengths of the master laser and the slave laser are different, the driving current signal of the master laser or the slave laser is a modulation signal, and the dual-band frequency modulation signal is generated by continuously tuning the amplitude of the modulation signal.

[0007] In combination with the first aspect, further, the master laser and the slave laser are distributed feedback semiconductor lasers made by reconstructing equivalent chirp technology; and the grating regions of the master laser and the slave laser are both provided with pi phase shift structures.

[0008] In combination with the first aspect, further, the master laser and the slave laser have the same material epitaxial structure; the material epitaxial structure includes an n-type substrate, an n-type buffer layer, an n-type lower optical confinement layer, a multi-quantum well layer, a p-type upper optical confinement layer, a grating layer, a p-type cladding layer, a p-type ohmic contact layer, a p-type waveguide layer, a positive electrode and a negative electrode; the master laser and the slave laser share a ridge waveguide structure.

[0009] In combination with the first aspect, further, the material epitaxial structure is obtained by epitaxially growing the material by metal organic chemical vapor deposition; the epitaxial growth includes: growing an n-type buffer layer doped with indium phosphide on an n-type substrate doped with indium phosphide, growing an n-type lower optical confinement layer doped with InAlGaAs material on the n-type buffer layer doped with indium phosphide, sequentially growing a multiple quantum well layer doped with InAlGaAs material and a p-type upper optical confinement layer doped with InAlGaAs material on the n-type lower optical confinement layer doped with InAlGaAs material, and growing a grating layer doped with InAlGaAs material on the p-type upper optical confinement layer doped with InAlGaAs material; growing a p-type cladding layer doped with indium phosphide on the grating layer, and growing a p-type ohmic contact layer and a p-type waveguide layer doped with InAlGaAs material on the p-type cladding layer doped with indium phosphide, respectively.

[0010] In combination with the first aspect, further, the positive electrode is made by sputtering a metal layer on the p-type ohmic contact layer and the p-type waveguide layer, and the negative electrode is made by annealing the outer surface of the n-type substrate.

[0011] In combination with the first aspect, further, an electrical isolation region is formed between the master laser and the slave laser by etching away the grating layer and the p-type ohmic contact layer through photolithography technology.

[0012] In combination with the first aspect, further, the end faces of the master laser are coated with a high anti-reflection film with a reflectivity less than 1%.

[0013] In combination with the first aspect, further, the master laser and the slave laser use a same heat sink.

[0014] In combination with the first aspect, further, the cavity length of the master laser is greater than the cavity length of the slave laser, and the interval between the free oscillation wavelengths of the master laser and the slave laser is less than 0.4 nm.

[0015] In a second aspect, the present invention provides a dual-band frequency modulation signal generation method, which is used in the dual-band frequency modulation signal generation device described in any one of the first aspects, comprising: The modulation signal is set to a periodic sawtooth wave signal, so that the frequency interval and light injection ratio between the master laser and the slave laser change periodically, and the base frequency and double frequency corresponding to the electrical signal converted by the photodetector also change periodically, thereby realizing the generation of a dual-band frequency modulation signal.

[0016] Compared with the prior art, the present invention has the following beneficial effects: The dual-band frequency modulation signal generating device provided by the present invention has a compact structure, low cost, stable performance, and wideband tunability, which overcomes the shortcomings of traditional dual-band frequency modulation signal generating devices, such as multiple discrete devices, complex structure, low integration, high power consumption, and high cost. The short-coupled mutual injection semiconductor laser is realized at low cost based on the reconstruction equivalent chirp technology. By sampling the uniform grating, the nanometer-level effect can be achieved with a micron-level process. On the basis of improving the wavelength control accuracy, the stringent requirements on manufacturing difficulty and manufacturing cost are greatly reduced, especially in batch realization of short-coupled mutual injection semiconductor lasers and production of large-scale arrays. The present invention controls the master laser or the slave laser with a relatively low-cost, low-repetition-rate periodic sawtooth wave signal to realize broadband tunable dual-band frequency modulation signal generation.

[0017] The dual-band frequency modulation signal generating device provided by the present invention does not require a radio frequency modulation port and is more efficient than a direct current power supply driving a laser with a radio frequency modulation port. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a schematic diagram of the structure of a dual-band frequency modulation signal generating device provided by an embodiment of the present invention; Figure 2 It is a schematic diagram of the structure of a short-coupled mutual injection semiconductor laser provided by an embodiment of the present invention; Figure 3 Schematic diagram of a typical spectrum of a short-coupled mutual injection semiconductor laser in a double-period oscillation state provided by an embodiment of the present invention, wherein (a) is a schematic diagram of the spectrum; (b) is a schematic diagram of the frequency spectrum; Figure 4 Schematic diagram of double-period changes of a short-coupled mutual injection semiconductor laser provided by an embodiment of the present invention, wherein (a) is a schematic diagram of changes in current intensity and time, (b) is a schematic diagram of changes in frequency and current intensity, and (c) is a schematic diagram of changes in frequency and time; Figure 5 It is a practical effect diagram of the dual-band FM signal generating method provided by an embodiment of the present invention; In the figure: 1. master laser; 2. slave laser; 3. single-mode optical fiber; 4. photodetector; 5. RF cable; 6. external low repetition rate voltage control signal source; 7. n-type substrate; 8. n-type buffer layer; 9. n-type lower optical confinement layer; 10. multi-quantum well layer; 11. p-type upper optical confinement layer; 12. grating layer; 13. p-type cladding layer; 14. p-type ohmic contact layer; 15. p-type waveguide layer; 16. master laser positive electrode; 17. slave laser positive electrode; 18. negative electrode. DETAILED DESCRIPTION

[0019] The technical solution of the present application is further described in detail below in conjunction with specific implementation methods.

[0020] The embodiments of the present application are described in detail below, and examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements with the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present application, and should not be construed as limitations on the present application. In the absence of conflict, the embodiments of the present application and the technical features in the embodiments may be combined with each other.

[0021] The present application embodiment provides a dual-band frequency modulation signal generating device, such as Figure 1 As shown, it includes a short-coupled mutual injection semiconductor laser, a single-mode optical fiber 3, a photodetector 4, and a radio frequency cable 5.

[0022] In this embodiment, the optical signal output by the short-coupled mutual injection semiconductor laser is transmitted to the photodetector 4 through the single-mode optical fiber 3, converted into an electrical signal by the photodetector 4 and output through the radio frequency cable 5; the short-coupled mutual injection semiconductor laser includes a master laser 1 and a slave laser 2 integrated on the same substrate, the master laser 1 and the slave laser 2 are injected into each other, the initial working wavelengths of the master laser 1 and the slave laser 2 are different, the driving current signal of the master laser 1 or the slave laser 2 is a modulation signal, and a dual-band frequency modulation signal is generated by continuously tuning the amplitude of the modulation signal.

[0023] In one possible embodiment, Figure 1 As shown, the dual-band FM signal generating device further includes an external low repetition rate voltage control signal source 6, and the corresponding driving current is obtained through the voltage control signal output by the external low repetition rate voltage control signal source 6.

[0024] It should be noted that in order to enable the dual-band FM signal generating device of the present application to operate in a dual-period oscillation state, the cavity length of the master laser 1 is greater than the cavity length of the slave laser 2, and the free oscillation wavelength interval between the master laser 1 and the slave laser 2 is less than 0.4nm.

[0025] In this application, "double-cycle oscillation state" refers to an oscillation state that the master laser 1 and the slave laser 2 jointly enter under the condition of mutual light injection. The generated double-cycle oscillation optical signal is similar to frequency modulation on the wavelength of the master oscillation light of the two lasers from the spectrum, and the modulation frequency is the double-cycle oscillation frequency, corresponding to half of the frequency difference of the two laser lasing modes in this state. Generally, the microwave signal generated by the beat frequency of the photodetector contains a double-cycle oscillation frequency component and its double frequency component (the frequency difference between the master laser 1 and the slave laser 2). When the DC bias of the master laser 1 or the slave laser 2 changes, the base frequency and double frequency signal of the generated double-cycle oscillation signal will also change, with a large bandwidth tuning range. Therefore, when the driving signal of the master laser 1 or the slave laser 2 is changed to a sawtooth wave signal, the generation of a dual-band frequency modulation signal can be achieved.

[0026] like Figure 2 As shown, the master laser 1 and the slave laser 2 share the same ridge waveguide structure. The master laser 1 and the slave laser 2 have the same epitaxial material and structure. The material epitaxial structure is obtained by epitaxial growth of the material by conventional metal organic chemical vapor deposition method, and the material epitaxial structure includes an n-type substrate 7, an n-type buffer layer 8, an n-type lower optical confinement layer 9, a multi-quantum well layer 10, a p-type upper optical confinement layer 11, a grating layer 12, a p-type cladding layer 13, a p-type ohmic contact layer 14, a p-type waveguide layer 15, a positive electrode and a negative electrode 18.

[0027] Slave laser 2 is integrated on the right side of master laser 1. The light from master laser 1 is injected into slave laser 2, and the light from slave laser 2 is injected into master laser 1. The two lasers are injected into each other, thereby changing the physical properties of the two lasers (increasing the modulation bandwidth, reducing the threshold current, and enhancing the electro-optical conversion efficiency).

[0028] In addition, a pi phase shift structure is added to the center of the grating structure of the master laser 1 and the slave laser 2, which can effectively improve the single-mode performance of the master laser 1 and the slave laser 2. During the manufacturing process, the wavelength of the light emitted by the master laser 1 in the free oscillation state is made smaller than the wavelength of the light emitted by the slave laser 2 in the free oscillation state, which is more conducive to the injection locking of the monolithic integrated laser. The monolithic integrated laser is packaged in a standard butterfly shape with a total of 7 pins, which respectively control the temperature of the integrated laser and the current of the two laser zones and the phase zone. During the packaging process, the chip of the monolithic integrated laser is dissociated, and a high-reflection film and an anti-reflection film are coated on both sides of the integrated laser (i.e., the left side of the master laser 1 and the right side of the slave laser 2), so as to feed back more light to the side of the slave laser and improve the power of the output light of the monolithic integrated laser. In this integrated laser, the output light will eventually be output from the output port of the slave laser 2.

[0029] In a possible embodiment, the master laser 1 and the slave laser 2 are distributed feedback semiconductor lasers made by reconstructing equivalent chirp technology. The grating structure and ohmic contact layer in the connection area between the master laser 1 and the slave laser 2 are etched away by electron beam etching technology, thereby ensuring that each area has good electrical isolation, reducing interference, and realizing independent current tuning.

[0030] The monolithic integrated three-segment laser includes in terms of material structure: an n-type substrate 7; an n-type buffer layer 8; an n-type lower optical confinement layer 9; a multi-quantum well layer 10; a p-type upper optical confinement layer 11; a grating layer 12; a p-type cladding layer 13; a p-type ohmic contact layer 14; a p-type waveguide layer 15; a master laser positive electrode 16; a slave laser positive electrode 17; and a negative electrode 18.

[0031] In a possible embodiment, the material epitaxial structure is obtained by epitaxially growing the material by metal organic chemical vapor deposition method; the epitaxial growth includes: growing an n-type buffer layer doped with indium phosphide on an n-type substrate doped with indium phosphide, growing an n-type lower optical confinement layer doped with InAlGaAs material on the n-type buffer layer doped with indium phosphide, sequentially growing a multiple quantum well layer doped with InAlGaAs material and a p-type upper optical confinement layer doped with InAlGaAs material on the n-type lower optical confinement layer doped with InAlGaAs material, and growing a grating layer doped with InAlGaAs material on the p-type upper optical confinement layer doped with InAlGaAs material; growing a p-type cladding layer doped with indium phosphide on the grating layer, and growing a p-type ohmic contact layer and a p-type waveguide layer doped with InAlGaAs material on the p-type cladding layer doped with indium phosphide, respectively.

[0032] The positive electrode is made by sputtering a metal layer on the p-type ohmic contact layer and the p-type waveguide layer, and the negative electrode is made by annealing the outer surface of the n-type substrate.

[0033] In one possible embodiment, the master laser and the slave laser use the same heat sink.

[0034] It should be noted that in the dual-band FM signal generating device of any embodiment of the present application, the two end faces of the integrated laser chip after cutting, and the end faces of the main laser 1 are coated with a high anti-reflection film with a reflectivity of less than 1%, thereby reducing the FP cavity effect of the laser.

[0035] like Figure 3 As shown, f m is the main oscillator mode of the main laser, f s is the main oscillator mode of the slave laser, f p2 is a dual-periodic oscillation light mode, and its optical signal frequency is half of the sum of the frequencies of the master and slave oscillation light modes. Therefore, when the frequency difference between the dual-periodic oscillation light mode and the master and slave oscillation light modes is defined as f baseWhen the frequency difference between the master laser 1 and the slave laser 2 is 2f base ; Dual-frequency signal generation can be achieved by using the photodetector 4 beat frequency (such as Figure 3 As shown in b); when the bias current of the master laser 1 or the slave laser 2 is changed, the frequency of the microwave signal obtained by the beat frequency will change accordingly, thereby realizing the generation of a tunable dual-frequency microwave signal source. The red curve and the green curve in the figure represent two different lasing scenarios under the dual-cycle oscillation state with different bias current systems; the oscillation light signal generated by the short-coupled mutual injection semiconductor laser in the dual-cycle oscillation state is similar to the multi-level optical sidebands generated by frequency modulation at the main oscillation mode of the master laser 1 and the slave laser 2, and the modulation frequency is the dual-cycle oscillation frequency f base . Figure 3 In, f base1 represents the double-period oscillation frequency corresponding to state 1, f base2 Indicates the double-period oscillation frequency corresponding to state 2.

[0036] In a possible embodiment, in the dual-band frequency modulation signal generating device, when the bias current control signal of the master laser 1 or the slave laser 2 is changed from a constant current to a sawtooth wave driving signal, as Figure 4 As shown, the input current at time t is I1, and the corresponding frequency is f1. After period T, the current becomes I2, and the corresponding frequency becomes f2.

[0037] By changing the bias current control signal of the master laser 1 or the slave laser 2 from a constant current to a sawtooth wave drive signal, the dual-band frequency modulation signal can be generated. If there are other requirements for the generated dual-band frequency modulation signal, such as a triangular frequency modulation signal, it is only necessary to change the sawtooth wave drive signal to a triangular signal; if the dual-band frequency modulation signal is required to have good linearity, it can be achieved by performing reverse fitting on the bias current control signal initially injected into the master laser 1 or the slave laser 2.

[0038] It should be noted that the control driving signal only needs to be injected into one of the master laser 1 or the slave laser 2 at a time, and the other components remain unchanged. If the bandwidth of the dual-band frequency modulation signal generated needs to be further tuned, it can be achieved by changing the DC bias of the master laser 1 or the slave laser 2 area or the amplitude of the pre-added sawtooth wave signal. If the repetition period of the dual-band frequency modulation signal needs to be changed, it can be achieved by changing the period of the sawtooth wave signal.

[0039] The present application embodiment provides a dual-band frequency modulation signal generation method, which is used in the dual-band frequency modulation signal generation device provided in any embodiment of the present application, and comprises the following steps: Step 1: adjusting the DC bias current of the master laser 1 and the slave laser 2, changing the coupling strength, detuning frequency, and coupling phase between the master laser 1 and the slave laser 2, so that the dual-band frequency modulation signal generating device operates in a dual-cycle oscillation state; In step 1, the master laser 1 and the slave laser 2 are designed and manufactured by using the reconstruction equivalent chirp technology, so as to realize the precise control of the working wavelength of the monolithic integrated laser.

[0040] Step 2: When the DC bias of one of the master laser 1 or the slave laser 2 is changed to change the constant current into a sawtooth wave driving signal, and in each cycle, the current amplitude is close to the aforementioned constant current, the dual-band FM signal generation can be achieved.

[0041] The actual effect of the dual-band FM signal generation method provided by the embodiment of the present application is as follows: Figure 5 As shown, a sawtooth wave signal is input and f1~f2 and 2f1~2f2 dual-band FM signals are output.

[0042] For example, the sawtooth wave signal can be loaded on the master laser 1 or the slave laser 2. It should be noted that in the present application, the sawtooth wave signal used for direct modulation on the short-coupled mutual injection semiconductor laser has a repetition period equal to the repetition period of the generated dual-band frequency modulation signal. The larger the sawtooth wave amplitude range, the larger the bandwidth of the corresponding dual-band frequency modulation signal, the stronger the broadband performance, and the higher precision detection can be achieved.

[0043] The present application provides a dual-band frequency modulation signal generating device with compact structure and stable performance and its implementation method, and the short-coupled mutual injection semiconductor laser used is implemented at low cost. The present application uses a monolithic integration method to realize the dual-period oscillation of the distributed feedback semiconductor laser, overcoming the shortcomings of the traditional multiple discrete devices, large injection system volume, complex structure, poor stability, etc.

[0044] In the embodiments of the present application, the grating of the short-coupled mutual injection semiconductor laser is made by reconstructing the equivalent chirp technology. The wavelengths of the two lasers can be accurately controlled by controlling the sampling grating period in the micron range, thereby improving the detuned frequency control accuracy of the mutual injection semiconductor laser, thereby improving the producibility and yield of the dual-period oscillation state of the short-coupled mutual injection semiconductor laser, and reducing the manufacturing difficulty and manufacturing cost.

[0045] The above are only preferred implementations of the present application. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present application. These improvements and modifications should also be regarded as the scope of protection of the present application.

Claims

1. A dual-band frequency modulation signal generating device, characterized in that: It comprises a short-coupled mutually-injected semiconductor laser, a single-mode optical fiber, a photodetector and a radio frequency cable connected in sequence, wherein the optical signal output by the short-coupled mutually-injected semiconductor laser is transmitted to the photodetector through the single-mode optical fiber, converted into an electrical signal by the photodetector and output through the radio frequency cable; The short-coupled mutual injection semiconductor laser comprises a master laser and a slave laser integrated on the same substrate. The master laser and the slave laser are mutually injected. The master laser and the slave laser have different initial working wavelengths. The driving current signal of the master laser or the slave laser is a modulation signal. A dual-band frequency modulation signal is generated by continuously tuning the amplitude of the modulation signal.

2. The dual-band FM signal generating device according to claim 1, characterized in that: The master laser and the slave laser are distributed feedback semiconductor lasers made by reconstructing equivalent chirp technology; the grating regions of the master laser and the slave laser are both provided with pi phase shift structures.

3. The dual-band FM signal generating device according to claim 1, characterized in that: The master laser and the slave laser have the same material epitaxial structure; the material epitaxial structure includes an n-type substrate, an n-type buffer layer, an n-type lower optical confinement layer, a multi-quantum well layer, a p-type upper optical confinement layer, a grating layer, a p-type cladding layer, a p-type ohmic contact layer, a p-type waveguide layer, a positive electrode and a negative electrode; the master laser and the slave laser share a ridge waveguide structure.

4. The dual-band FM signal generating device according to claim 3, characterized in that: The material epitaxial structure is obtained by epitaxially growing the material by a metal organic chemical vapor deposition method; the epitaxial growth comprises: growing an n-type buffer layer doped with indium phosphide on an n-type substrate doped with indium phosphide, growing an n-type lower optical confinement layer doped with InAlGaAs material on the n-type buffer layer doped with indium phosphide, sequentially growing a multi-quantum well layer doped with InAlGaAs material and a p-type upper optical confinement layer doped with InAlGaAs material on the n-type lower optical confinement layer doped with InAlGaAs material, growing a grating layer doped with InAlGaAs material on the p-type upper optical confinement layer doped with InAlGaAs material; growing an indium phosphide doped p-type cladding layer on the grating layer, and respectively growing a p-type ohmic contact layer doped with InAlGaAs material and a p-type waveguide layer on the indium phosphide doped p-type cladding layer.

5. The dual-band FM signal generating device according to claim 3, characterized in that: The positive electrode is made by sputtering a metal layer on a p-type ohmic contact layer and a p-type waveguide layer, and the negative electrode is made by annealing an outer surface of an n-type substrate.

6. The dual-band FM signal generating device according to claim 3, characterized in that: The grating layer and the p-type ohmic contact layer are etched away by photolithography technology to form an electrical isolation region between the master laser and the slave laser.

7. The dual-band FM signal generating device according to claim 1, characterized in that: The end faces of the master laser are all plated with a high anti-reflection film with a reflectivity of less than 1%.

8. The dual-band FM signal generating device according to claim 1, characterized in that: The master laser and the slave laser use the same heat sink.

9. The dual-band FM signal generating device according to claim 1, characterized in that: The cavity length of the master laser is greater than that of the slave laser, and the interval between the free oscillation wavelengths of the master laser and the slave laser is less than 0.4 nm.

10. A method for generating a dual-band frequency modulation signal, used in the dual-band frequency modulation signal generating device according to any one of claims 1 to 9, characterized in that: include: The modulation signal is set to a periodic sawtooth wave signal, so that the frequency interval and light injection ratio between the master laser and the slave laser change periodically, and the base frequency and double frequency corresponding to the electrical signal converted by the photodetector also change periodically, thereby realizing the generation of a dual-band frequency modulation signal.

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