A tunable laser based on bandgap-graded semiconductor nanowires

Abstract

The application discloses a tunable laser based on a band gap gradient semiconductor nanowire, a bottom layer is a Bragg reflector, a middle layer is an air layer supported by a support column, and a top layer is a silver-coated reflective layer; the gradient nanowire is placed on the bottom layer Bragg reflector; the bottom layer Bragg reflector and the top layer silver-coated reflective layer serve as two emitting mirrors of an external Fabry-Perot cavity, and the middle layer air layer serves as a resonant cavity. The application also provides a spectrum modulation system based on the tunable laser, utilizes high optical gain of the semiconductor nanowire, and realizes tunable laser emission when an external laser pump is applied to different positions of the semiconductor nanowire in the axial direction through proper design of the external Fabry-Perot cavity.

Description

Technical Field

[0001] This invention belongs to the field of lasers, specifically relating to a tunable laser based on bandgap graded semiconductor nanowires. Background Technology

[0002] Tunable lasers based on bandgap-gradient semiconductor nanowires are a novel type of laser. Compared to traditional large-scale tunable lasers, their miniaturization and high efficiency play a crucial role in science, medicine, and industry. Utilizing the natural Fabry-Poirot cavity formed by the smooth, flat end faces of semiconductor nanowires, along with their inherent high optical gain, laser emission can be achieved under external laser pumping. Furthermore, bandgap-gradient nanowires made from different semiconductor materials can achieve tunable lasers covering visible light after laser pumping. With technological advancements, nanowire tunable lasers have made significant progress. Current international research primarily leverages their natural structural characteristics, further enhanced by designing special structures such as resonant rings to improve the resonance effect within the axial nanowire cavity. However, due to the need to select specific nanowires and perform precise micro / nano manipulations during the design process, and the lack of a stable encapsulation structure for the laser, drawbacks include complex operation, poor stability, and low tuning rates. Summary of the Invention

[0003] To address the problems in the prior art, this invention proposes a tunable laser based on bandgap graded semiconductor nanowires. By combining an externally fabricated Fabry-Poirot cavity, tunable laser output from green to red light is achieved after laser pumping at different positions.

[0004] The technical solution adopted by this invention to solve its technical problem is as follows:

[0005] This invention first provides a tunable laser based on bandgap graded semiconductor nanowires, including a silver-plated reflective layer, a support pillar, and a Bragg mirror;

[0006] The Bragg reflector is located at the bottom, and gradient nanowires are disposed on the Bragg reflector; the gradient nanowires are used as gain materials; multiple support pillars are disposed on the Bragg reflector; the silver-plated reflective layer is disposed on the multiple support pillars; the gap between the silver-plated reflective layer and the Bragg reflector is an air layer.

[0007] This invention also provides a spectral modulation system based on the aforementioned tunable laser, comprising a nanosecond pulsed laser, an optical mirror group, a tunable laser, a microscope objective, a spectrometer, a semi-transparent mirror, and a charge-coupled device (CCD). The laser emitted by the nanosecond pulsed laser, after passing through the optical mirror group, illuminates different positions of a graded nanowire. The emitted light resonates and intensifies in a designed Fabry-Poirot cavity, ultimately achieving the output of the tunable laser. The optical mirror group is used to reduce the beam size of the laser emitted by the nanosecond pulsed laser. After the resonantly intensified tunable laser passes through the semi-transparent mirror, a portion of the tunable laser is reflected and enters the spectrometer, while another portion passes through the semi-transparent mirror and enters the CCD. The microscope objective is used to collect the laser emitted from the tunable laser.

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

[0009] 1) Start the nanosecond pulse laser, which emits nanosecond pulse laser light towards 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 size is reduced by the optical mirror group, the nanosecond pulsed laser irradiates different positions of the graded nanowire. The emitted light resonates and is enhanced in the designed Fabry-Polo cavity, and finally the output of tunable laser is realized.

[0012] 4) The position of the nanosecond pulsed laser irradiating the tunable laser is adjusted with the aid of a microscope objective;

[0013] 5) After the resonant-enhanced tunable laser irradiates the semi-transparent mirror, part of the tunable laser is reflected and enters the spectrometer, while part of the tunable laser passes through the semi-transparent mirror and enters the charge-coupled device.

[0014] 6) The spectrometer acquires the spectrum of the incoming tunable laser; the charge-coupled device (CCD) 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 graded semiconductor nanowires, which has a simple structure, is easy to manufacture, has a fast tuning rate, and can be tuned to cover the green to red light band.

[0017] 2. The present invention provides a tunable laser based on a bandgap graded semiconductor nanowire, which adds a second vertical resonant structure to the axial resonant cavity structure of the semiconductor nanowire itself, thereby increasing the output laser gain. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the structure of a tunable laser based on bandgap graded semiconductor nanowires according to the present invention;

[0019] Figure 2 This is an optical path diagram of a spectral modulation system based on a tunable laser according to the present invention.

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

[0021] The present invention will be further described and illustrated below with reference to specific embodiments. The embodiments described are merely examples of the content of this disclosure and do not limit the scope of the invention. The technical features of each embodiment in the present invention can be combined accordingly, provided that there is no mutual conflict.

[0022] The working principle of this invention is as follows: a 355nm wavelength laser is incident from the bottom of the fabricated laser, passes through a Bragg emitting mirror, and reaches the nanowire. By changing the laser's focus on different positions within the nanowire, the transition from green to yellow to red light excited by the CdS-CdSSe-CdSe material in the nanowire can be achieved. The tunable laser excited by the nanowire resonates vertically in the Fabry-Polo cavity formed by the external mirrors and air layer. After the resonance is enhanced, it is transmitted through the top silver-plated emitting layer.

[0023] like Figure 1 As shown, the tunable laser based on bandgap graded nanowires of the present invention includes a silver-plated reflective layer as the top layer, a support pillar, and a Bragg reflector as the bottom layer.

[0024] A graded nanowire 4 is disposed on the Bragg reflector; the graded nanowire 4 serves as a gain material; multiple support pillars are disposed on the Bragg reflector 5; a silver-plated reflective layer is disposed on the multiple support pillars; the gap between the silver-plated reflective layer and the Bragg reflector 5 is an air layer. The bottom Bragg reflector and the top silver-plated reflective layer serve as the two emitting mirrors of the external Fabry-Poirot cavity, and the air layer in the middle serves as the resonant cavity.

[0025] In one specific embodiment of the present invention, the silver-plated reflective layer is formed on a quartz sheet by thermal evaporation. The selected quartz sheet is 30 nm thick, at which point the reflectivity is about 70% and the transmittance is 20%.

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

[0027] In one specific embodiment of the present invention, the graded nanowires are cadmium sulfide selenide (CdSSe) nanowires, grown by controlling parameters such as temperature, pressure, and time using a vapor-liquid-gas (VLS) method. They have a diameter of approximately 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 section is a CdSSe transition region from CdS to CdSe.

[0028] like Figure 2 The diagram shows the spectral modulation system of the tunable laser of the present invention, including a nanosecond pulsed laser 6, an optical mirror group, a tunable laser, a microscope objective 14, a spectrometer 15, a semi-transparent mirror 16, and a charge-coupled device 17. The laser emitted by the nanosecond pulsed laser 6 passes through the optical mirror group and irradiates different positions on a graded nanowire. The emitted light resonates and is enhanced in a designed Fabry-Poirot cavity, ultimately achieving the output of a tunable laser. The optical mirror group is used to reduce the beam size of the laser emitted by the nanosecond pulsed laser 6. After the resonant and enhanced tunable laser passes through the semi-transparent mirror 16, a portion of the tunable laser is reflected and enters the spectrometer 15, while a portion passes through the semi-transparent mirror 16 and enters the charge-coupled device 17. The microscope objective 14 is used to collect the laser emitted from the tunable laser. The optical lens assembly includes a bandpass filter 7, an adjustable attenuator 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 attenuator 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 beam, the second convex lens 10 is used to collimate the expanded nanosecond pulse laser light beam, and the third convex lens 12 is used to focus the nanosecond pulse laser light beam. The silver-plated reflector 11 is used to change the direction of light rays in the optical path.

[0029] In one specific embodiment of the present invention, the 355nm laser emitted from the nanosecond pulsed laser 6 is first filtered by a 340-360nm bandpass filter, and then attenuated by an adjustable attenuator 8. Subsequently, the laser beam is expanded and collimated by a first convex lens 9 and a second convex lens 10. A reflector 11 reflects the laser beam to the nanowire laser position. Finally, a third convex lens 12 reduces the laser spot size to 10-20μm. With the aid of a microscope objective 14, a displacement platform is used to excite the nanowire at different positions using the 355nm laser. After passing through a semi-transparent mirror 16, the reflected light enters the spectrometer 15, and the transmitted light enters the charge-coupled device 17. 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 the sum of their focal lengths, which is 330mm. 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 mirror, the experimental distance is 1500mm.

[0030] The device of this invention adds a second vertical resonant structure to the axial resonant cavity structure of the semiconductor nanowire itself, which makes the output laser gain higher. By changing the laser focusing position on different positions of the nanowire, the transition from green light and yellow light to red light excited by the CdS-CdSSe-CdSe material in the nanowire can be realized. It is simple to operate, highly stable, and has a high tuning rate.

[0031] The above-described embodiments are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. Those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention.

Claims

1. A spectral modulation system for a tunable laser, characterized in that, It includes a nanosecond pulsed laser (6), an optical mirror assembly, a tunable laser based on bandgap graded semiconductor nanowires, a microscope objective (14), a spectrometer (15), a semi-transparent mirror (16), and a charge-coupled device (17). The tunable laser based on bandgap graded semiconductor nanowires includes a silver-plated reflective layer, support pillars, and a Bragg mirror (5). The Bragg mirror (5) is located at the bottom, and graded nanowires (4) are disposed on the Bragg mirror. The graded nanowires (4) are used as gain materials. The graded nanowires are cadmium sulfide selenide (CdSSe) nanowires, which are grown by controlling parameters such as temperature, pressure, and time through a solid-liquid-gas (VLS) method. The diameter is 0.5-1 μm and the length is 100-200 μm. One end of the nanowire is pure cadmium sulfide (CdS), and the other end is pure cadmium selenide (CdSe). The middle part is a CdSSe transition region from CdS to CdSe. Multiple support pillars are disposed on the Bragg mirror (5). The silver-plated reflective layer is disposed on the multiple support pillars. The gap between the silver-plated reflective layer and the Bragg mirror (5) is an air layer. The laser emitted by the nanosecond pulse laser (6) is irradiated at different positions of the gradient nanowire after passing through the optical mirror group. The emitted light is resonant and enhanced in the designed Fabry-Polo cavity, and finally the output of the tunable laser is realized. The optical mirror group is used to reduce the light spot of the laser emitted by the nanosecond pulse laser (6). After the resonant and enhanced tunable laser passes through the semi-transparent and semi-reflective mirror (16), part of the tunable laser is reflected and enters the spectrometer (15), and part of the tunable laser 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 emitted from the tunable laser.

2. The spectral modulation system for a tunable laser according to claim 1, characterized in that, The Bragg reflector (5) has high transmittance for narrowband light in the wavelength range of 340nm-360nm and high reflectivity for visible light, and is parallel to the silver-plated reflective layer.

3. The spectral modulation system for a tunable laser according to claim 1, characterized in that, The silver-plated reflective layer is fabricated on a quartz plate by thermal evaporation.

4. The spectral modulation system for a tunable laser according to claim 1, characterized in that, The optical lens assembly includes a bandpass filter (7), an adjustable attenuator (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 the nanosecond pulse laser, and the adjustable attenuator (8) is used to control the intensity of the nanosecond pulse laser after being filtered by the bandpass filter (7). The first convex lens (9) is used to expand the nanosecond pulse laser beam, the second convex lens (10) is used to collimate the expanded nanosecond pulse laser beam, and the third convex lens (12) is used to focus the nanosecond pulse laser beam. The silver-plated reflector (11) is used to change the direction of light rays in the optical path.

5. A spectral modulation method for a spectral modulation system of a tunable laser as described in claim 1, characterized in that, Includes the following steps: 1) Start the nanosecond pulse laser, which emits nanosecond pulse laser light towards the optical mirror assembly; 2) The optical lens group reduces the spot size of the incident nanosecond pulse laser; 3) The nanosecond pulsed laser, after being reduced in size by the optical mirror group, is irradiated at different positions of the graded nanowire. The radiated light resonates and is enhanced in the designed Fabry-Porro cavity, ultimately realizing the output of tunable laser. 4) Adjust the position of the nanosecond pulsed laser irradiating the tunable laser with the aid of a microscope objective; 5) After the resonant enhanced tunable laser irradiates the semi-transparent and semi-reflective mirror (16), part of the tunable laser is reflected and enters the spectrometer (15), and part 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; the charge-coupled device (17) images the incoming tunable laser.

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