Tunable laser based on band gap gradient semiconductor nanowire

Abstract

The invention discloses a tunable laser based on a band gap gradual change semiconductor nanowire. The bottom layer is a Bragg reflector, the middle layer is an air layer supported by supporting columns, the top layer is a silver-plated reflecting layer, and the gradual change nanowire is placed on the Bragg reflector on the bottom layer. The Bragg reflector on the bottom layer and the silver-plated reflecting layer on the top layer serve as two reflecting mirrors of an external Fabry-Perot cavity, and the air layer in the middle serves as a resonant cavity. The invention also provides a spectrum modulation system based on the tunable laser, and by utilizing the high optical gain of the semiconductor nanowire and the proper external Fabry-Porro cavity design, tunable laser emission can be realized at different axial positions of the external laser pumping semiconductor nanowire.

Description

Technical Field

[0001] The invention belongs to the field of lasers, and in particular relates to a tunable laser based on a bandgap gradient semiconductor nanowire. Background Art

[0002] Tunable lasers based on semiconductor nanowires with gradient band gaps are a new type of laser. Compared with traditional large tunable lasers, their miniature and high efficiency advantages play an important role in science, medicine, industry and other fields. The natural Fabry-Perot cavity formed by the smooth end face of the semiconductor nanowire and its own high optical gain can be used to emit lasers under the condition of external laser pumping. The gradient band gap nanowires generated by different semiconductor materials can achieve tunable lasers covering visible light after laser pumping. With the development of technology, nanowire tunable lasers have made breakthrough progress. At present, international research mainly uses its natural structural characteristics, and then assists in the design of some special structures such as resonant rings to enhance the resonance effect in the axial nanowire cavity. However, since specific nanowires need to be selected and finely micro-nano-manipulated during the design process, and the laser does not form a stable packaging structure, it has the disadvantages of complex operation, poor stability, and low tuning rate. Summary of the invention

[0003] To solve the problems in the prior art, the present invention proposes a tunable laser based on bandgap gradient semiconductor nanowires, which realizes tunable laser output from green light to red light after laser pumping at different positions by combining with an externally manufactured Fabry-Perot cavity.

[0004] The technical solution adopted by the present invention to solve the technical problem is:

[0005] The present invention first provides a tunable laser based on a bandgap gradient semiconductor nanowire, comprising a silver-plated reflective layer, a support column and a Bragg reflector;

[0006] The Bragg reflector is arranged at the bottom, and gradient nanowires are arranged on the Bragg reflector; the gradient nanowires are used as gain materials; a plurality of support columns are arranged on the Bragg reflector; the silver-plated reflective layer is arranged on the plurality of support columns; and the gap between the silver-plated reflective layer and the Bragg reflector is an air layer.

[0007] The present invention also provides a spectrum modulation system based on the above-mentioned tunable laser, comprising a nanosecond pulse laser, an optical lens group, a tunable laser, a microscope objective, a spectrometer, a semi-transparent and semi-reflective mirror, and a charge-coupled device; the laser light emitted by the nanosecond pulse laser passes through the optical lens group and irradiates different positions of the gradient nanowire, and the radiated light is resonantly enhanced in the designed Fabry-Perot cavity, and finally the output of the tunable laser is realized; the optical lens group is used to reduce the light spot of the laser light emitted by the nanosecond pulse laser; after the resonance-enhanced tunable laser light passes through the semi-transparent and semi-reflective mirror, a part of the tunable laser light is reflected and enters the spectrometer, and a part of the tunable laser light passes through the semi-transparent and semi-reflective mirror and enters the charge-coupled device; the microscope objective is used to collect the laser light emitted from the tunable laser.

[0008] The present invention also provides a spectrum modulation method of the spectrum modulation system as described above, comprising the following steps:

[0009] 1) Starting the nanosecond pulse laser, which emits nanosecond pulse laser to the optical mirror assembly;

[0010] 2) The optical lens group reduces the spot size of the incident nanosecond pulse laser;

[0011] 3) After the spot is reduced by an optical lens group, the nanosecond pulse laser irradiates different positions of the gradient nanowire, and the radiated light resonates and strengthens in the designed Fabry-Perot cavity, ultimately achieving the output of tunable laser;

[0012] 4) adjusting the position of the nanosecond pulse laser irradiating the tunable laser with the aid of a microscope objective lens;

[0013] 5) After the resonance-enhanced tunable laser is irradiated onto the semi-transparent and semi-reflective mirror, a portion of the tunable laser is reflected and enters the spectrometer, and a portion of the tunable laser passes through the semi-transparent and semi-reflective mirror and enters the charge-coupled device;

[0014] 6) The spectrometer collects the spectrum of the incoming tunable laser; the charge coupled device images the incoming tunable laser.

[0015] Compared with the prior art, the present invention has the following beneficial effects:

[0016] 1. The present invention provides a tunable laser based on bandgap gradient semiconductor nanowires, which has a simple structure, is easy to manufacture, has a fast tuning rate, and a tunable range covering the green to red light band.

[0017] 2. The present invention provides a tunable laser based on a bandgap gradient semiconductor nanowire, which adds a second vertical resonance structure to the axial resonance cavity structure of the semiconductor nanowire itself, so that the output laser gain is higher. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 A schematic diagram of the structure of a tunable laser based on a bandgap gradient semiconductor nanowire according to the present invention;

[0019] Figure 2 The optical path diagram of the spectrum modulation system based on a tunable laser of the present invention.

[0020] In the figure, 1-quartz plate, 2-silver-coated film, 3-support column, 4-gradient nanowire, 5-Bragg reflector, 6-nanosecond pulse laser, 7-bandpass filter, 8-adjustable attenuation plate, 9-first convex lens, 10-second convex lens with a focal length of 300 mm, 11-silver-coated reflector, 12-third convex lens with a focal length of 25.4 mm, 13-tunable laser, 14-microscope objective, 15-spectrometer, 16-semi-transparent and semi-reflective mirror, 17-charge-coupled device. DETAILED DESCRIPTION

[0021] The present invention is further described and illustrated below in conjunction with specific embodiments. The embodiments are merely exemplary of the present disclosure and do not define the scope of limitation. The technical features of each embodiment of the present invention may be combined accordingly without conflicting with each other.

[0022] The working principle of the present invention is that the laser with a wavelength of 355nm is incident from the bottom of the manufactured laser, reaches the nanowire after passing through the Bragg emission mirror, and by changing the laser focus at different positions of the nanowire, the transition from green light, yellow light to red light excited by the CdS-CdSSe-CdSe material in the nanowire can be realized. The tunable laser excited by the nanowire resonates vertically in the Fabry-Perot cavity composed of the external two-side reflectors and the air layer, and transmits out from the top silver-plated emission layer after the resonance is enhanced.

[0023] like Figure 1 As shown, the tunable laser based on the bandgap gradient nanowire of the present invention comprises a silver-plated reflective layer as a top layer, a support column and a Bragg reflector as a bottom layer;

[0024] The Bragg reflector is provided with a gradient nanowire 4; the gradient nanowire 4 is used as a gain material; a plurality of support pillars are provided on the Bragg reflector 5; a silver-plated reflective layer is provided on the plurality of support pillars; and an air layer is provided in the gap between the silver-plated reflective layer and the Bragg reflector 5. The bottom Bragg reflector and the top silver-plated reflective layer act as two emission mirrors of the external Fabry-Perot cavity, and the air layer in the middle acts as a resonant cavity.

[0025] In a specific embodiment of the present invention, the silver-plated reflective layer is made into a silver-plated film on a quartz plate by a thermal evaporation method. The selected quartz plate has a thickness of 30 nm. At this time, the reflectivity is about 70% and the transmittance is 20%.

[0026] The support column is made of SU-8 2050 photoresist and is used to adjust the cavity thickness of the resonant cavity by changing different photolithography parameters.

[0027] In a specific embodiment of the present invention, the gradient nanowire is a cadmium sulfide selenide (CdSSe) nanowire, which is grown by controlling temperature, pressure, time and other parameters by the solid-liquid-gas (VLS) method, and has a diameter of about 1 μm and a length of 100-200 μm. One end of the nanowire is pure cadmium sulfide (CdS), the other end is pure cadmium selenide (CdSe), and the middle is the CdSSe transition region from CdS to CdSe.

[0028] like Figure 2 As shown, the spectrum modulation system of the tunable laser of the present invention comprises a nanosecond pulse laser 6, an optical lens group, a tunable laser, a microscope objective 14, a spectrometer 15, a semi-transparent and semi-reflective mirror 16 and a charge coupled device 17; the laser light emitted by the nanosecond pulse laser 6 is irradiated to different positions of the gradient nanowire after passing through the optical lens group, and the radiated light is resonantly enhanced in the designed Fabry-Perot cavity, and finally the output of the tunable laser is realized; the optical lens group is used to reduce the spot of the laser light emitted by the nanosecond pulse laser 6; after the resonance-enhanced tunable laser light passes through the semi-transparent and semi-reflective mirror 16, a part of the tunable laser light is reflected and enters the spectrometer 15, and a part of the tunable laser light passes through the semi-transparent and semi-reflective mirror 16 and enters the charge coupled device 17; the microscope objective 14 is used to collect the laser light emitted from the tunable laser. The optical lens group includes a bandpass filter 7, an adjustable attenuation plate 8, a first convex lens 9, a second convex lens 10, a silver-coated reflector 11, and a third convex lens 12; the bandpass filter 7 is used to filter the nanosecond pulse laser, and the adjustable attenuation plate 8 is used to control the intensity of the nanosecond pulse laser after filtering by the bandpass filter 7; the first convex lens 9 is used to expand the nanosecond pulse laser, the second convex lens 10 is used to collimate the nanosecond pulse laser after expansion, and the third convex lens 12 is used to focus the nanosecond pulse laser; the silver-coated reflector 11 is used to change the direction of light on the optical path.

[0029] In a specific embodiment of the present invention, the 355nm laser emitted by the nanosecond pulse laser 6 is first filtered by a 340-360nm bandpass filter, and then attenuated by an adjustable attenuation plate 8. The laser is then expanded and collimated by a first convex lens 9 and a second convex lens 10. The reflector 11 causes the laser to reach the position of the nanowire laser after reflection, and finally the laser spot is reduced to 10-20μm by a third convex lens 12. With the help of a microscope objective 14, a displacement platform is used to make the 355nm laser excite different positions of the nanowire. After the laser excited by the nanowire passes through a semi-transparent and semi-reflective mirror 16, the reflected light enters the spectrometer 15, and the transmitted light enters the charge-coupled device 17. Among them, the focal length of the first convex lens 9 is 30mm, the focal length of the second convex lens 10 is 300mm, and the focal length of the third convex lens is 25.4mm; the distance between the first convex lens 9 and the second convex lens 10 is 330mm, the sum of their focal lengths. In order to achieve a better laser spot focusing effect, the optical path length of the second convex lens 10 and the second convex lens 12 is greater than the sum of their focal lengths. After multiple reflections by the reflector, the experimental distance is 1500mm.

[0030] The device of the present invention adds a second vertical resonance structure on the basis of the axial resonance cavity structure of the semiconductor nanowire itself, so as to make the output laser gain higher. By changing the laser focus at different positions of the nanowire, the transition from green light, yellow light to red light excited by the CdS-CdSSe-CdSe material in the nanowire can be realized. The device has simple operation, high stability and high tuning rate.

[0031] The above-mentioned embodiments only express several implementation methods of the present invention, and the description is relatively specific and detailed, but it cannot be understood as limiting the scope of the present invention. For ordinary technicians in this field, several modifications and improvements can be made without departing from the concept of the present invention, which all belong to the protection scope of the present invention.

Claims

1. A tunable laser based on a bandgap gradient semiconductor nanowire, characterized in that: It includes a silver-plated reflective layer, a support column and a Bragg reflector (5); The Bragg reflector (5) is arranged at the bottom, and a gradient nanowire (4) is arranged on the Bragg reflector; the gradient nanowire (4) is used as a gain material; a plurality of support columns are arranged on the Bragg reflector (5); the silver-plated reflective layer is arranged on the plurality of support columns; and the gap between the silver-plated reflective layer and the Bragg reflector (5) is an air layer.

2. The tunable laser according to claim 1, characterized in that: The Bragg reflector (5) has high transmittance for narrow-band light around 340nm-360nm wavelength and high reflectivity for visible light band, and is parallel to the silver-plated reflective layer as a whole.

3. The tunable laser according to claim 1, characterized in that: The silver-plated reflective layer is made on a quartz sheet by a thermal evaporation method.

4. The tunable laser according to claim 1, characterized in that: The gradient nanowire is a cadmium sulfide selenide (CdSSe) nanowire, which is grown by controlling parameters such as temperature, pressure, and time through a solid-liquid-gas (VLS) method, with a diameter of 0.5-1 μm and a length of 100-200 μm. One end of the nanowire is pure cadmium sulfide (CdS), and the other end is pure cadmium selenide (CdSe), with a CdSSe transition region from CdS to CdSe in the middle.

5. A spectrum modulation system based on the tunable laser according to claim 1, characterized in that: The invention comprises a nanosecond pulse laser (6), an optical lens group, a tunable laser, a microscope objective lens (14), a spectrometer (15), a semi-transparent and semi-reflective mirror (16), and a charge coupled device (17); the laser light emitted by the nanosecond pulse laser (6) passes through the optical lens group and irradiates different positions of the gradient nanowire, and the radiated light is resonated and enhanced in the designed Fabry-Perot cavity, thereby finally realizing the output of tunable laser light; the optical lens group is used to reduce the spot of the laser light emitted by the nanosecond pulse laser (6); After the resonance-enhanced tunable laser passes through a semi-transparent and semi-reflective mirror (16), a portion of the tunable laser is reflected and enters a spectrometer (15), and a portion of the tunable laser passes through the semi-transparent and semi-reflective mirror (16) and enters a charge coupled device (17); the microscope objective lens (14) is used to collect the laser light emitted from the tunable laser.

6. The spectrum modulation system according to claim 5, characterized in that: The optical lens group comprises a bandpass filter (7), an adjustable attenuation plate (8), a first convex lens (9), a second convex lens (10), a silver-plated reflector (11), and a third convex lens (12); the bandpass filter (7) is used to filter nanosecond pulse laser light, and the adjustable attenuation plate (8) is used to control the intensity of the nanosecond pulse laser light after being filtered by the bandpass filter (7); the first convex lens (9) is used to expand the nanosecond pulse laser light, the second convex lens (10) is used to collimate the nanosecond pulse laser light after the expansion, and the third convex lens (12) is used to focus the nanosecond pulse laser light; and the silver-plated reflector (11) is used to change the direction of light on the optical path.

7. A spectrum modulation method of the spectrum modulation system according to claim 5, characterized in that: The following steps are involved: 1) Starting the nanosecond pulse laser, which emits nanosecond pulse laser to the optical mirror assembly; 2) The optical lens group reduces the spot size of the incident nanosecond pulse laser; 3) After the spot is reduced by an optical lens group, the nanosecond pulse laser is irradiated to different positions of the gradient nanowire. The radiated light is resonated and enhanced in the designed Fabry-Perot cavity, and finally the output of tunable laser is realized; 4) adjusting the position of the nanosecond pulse laser irradiating the tunable laser with the aid of a microscope objective lens; 5) After the resonance-enhanced tunable laser is irradiated onto the semi-transparent and semi-reflective mirror (16), a portion of the tunable laser is reflected and enters the spectrometer (15), and a portion of the tunable laser passes through the semi-transparent and semi-reflective mirror (16) and enters the charge coupled device (17); 6) The spectrometer (15) collects the spectrum of the incoming tunable laser light; the charge coupled device (17) images the incoming tunable laser light.

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