An injection-locked blue laser system

Abstract

This invention discloses an injection-locked blue laser system, which injects a low-power, narrow-linewidth, and frequency-stable seed light into another high-power, wide-linewidth laser to obtain a high-power, narrow-linewidth, and frequency-stable laser. In this invention, by injecting a 5mW seed light, a 300mW slave light can be locked, and the system has a wavelength adjustment range of 6nm after locking. The main body of the laser system has a volume of 23×22×6cm. 3 After long-distance transport, it only requires adjustment of the internal fiber optic coupler to function normally. The advantages of this invention are: it realizes a portable, tunable 6nm wavelength, 300mW output power, low manufacturing cost, and easy-to-operate 480nm blue laser system. Furthermore, this injection-locking method can also be used in other optical bands, with the output power limited by the performance of the laser diodes within the laser system. This invention provides a new approach for the development of portable high-performance laser systems and has extremely high application value.

Description

Technical Field

[0001] This invention relates to the field of laser light sources, and more specifically to an injection-locked blue laser system. Background Technology

[0002] High-power 480nm blue lasers are fundamental for realizing Rydberg quantum sensing measurements based on rubidium atoms. Precise measurements of the amplitude [Nature Physics 8.11:819-824(2012)], polarization [Physical Review Letters 111.6:063001(2013)], and phase information of microwave electric fields have already been achieved [Applied Physics Letters 114.11:114101(2019)]. Using a high-power blue light source can yield electromagnetically induced transparency (EIT) signals with a high signal-to-noise ratio, enabling weak-field measurements of microwaves.

[0003] Master-slave injection locking refers to the injection of light emitted from one laser into another, thereby altering some operating characteristics of the injected laser. Master-slave injection locking is commonly used to control the beam quality of a high-power laser from a low-power, narrow-linewidth, frequency-stable laser. It can also be used to control the phase or spatial characteristics of laser modes. Compared to optical amplification techniques that achieve the same effect, master-slave injection locking technology offers advantages such as higher power conversion efficiency and simpler equipment.

[0004] While high-power blue lasers are available on the market, they are primarily obtained through frequency-doubling crystals. This makes high-power blue lasers extremely demanding in terms of operating environment, preventing their portability. Furthermore, the wavelength tuning of blue lasers obtained through laser frequency doubling is complex, limiting the practical application of rubidium atom-based quantum sensing. Therefore, designing a portable, tunable, high-power injection-locked blue laser system has become an urgent problem to be solved. Summary of the Invention

[0005] In view of the above problems, the object of the present invention is to provide an injection-locked blue laser system. By injecting a low-power, narrow-linewidth, frequency-stable seed light into another high-power, wide-linewidth laser, a high-power, narrow-linewidth, frequency-stable laser is obtained. The first laser uses a Littrow-type external cavity semiconductor laser structure with a wavelength tuning range of 6 nm, and the main body of the laser system has a volume of 23 × 22 × 6 cm. 3This is a portable blue light source with a maximum output power of 300mW. The 480nm blue laser system described in this invention fully meets the engineering requirements of rubidium atom-based quantum sensing. This structure is also applicable to laser sources in other wavelength bands, with the output power limited by the performance of the laser diodes within the laser system.

[0006] The specific technical solution for achieving the purpose of this invention is as follows:

[0007] An injection-locked blue laser system includes a first laser, a laser beam-shrinking device, a first lens, a first mirror, a second mirror, an optical isolator, a first half-wave plate, a first polarization beam-splitting prism, a first fiber coupler, a single-mode polarization-maintaining fiber, a second fiber coupler, a second half-wave plate, an optical isolator, a third mirror, a fourth mirror, a third half-wave plate, a second lens, a laser shaping device, a second laser, and a fiber port collimator.

[0008] The first laser is a Littrow type external cavity semiconductor laser, which generates a seed light with a center wavelength of 480nm. The seed light passes sequentially through a laser beam-shrinking device, a first lens, a first mirror, a second mirror, an optical isolator, and a first half-wave plate. At the first polarization beam-splitting prism, it is split into two paths. One path is monitored for frequency by a collimator at the fiber optic port, and the other path enters the first fiber coupler and a single-mode polarization-maintaining fiber. It exits through the second fiber coupler and passes sequentially through the second half-wave plate, an optical isolator, a third mirror, a fourth mirror, the third half-wave plate, the second lens, and a laser shaping device before being injected into the second laser for frequency locking.

[0009] The laser beam-shrinking device includes a third lens and a fourth lens, which are placed after the first laser to shrink the seed light.

[0010] The first lens is placed after the laser beam-concentrating device to focus the seed light;

[0011] The first and second reflecting mirrors are placed after the first lens to reflect the focused seed light;

[0012] The optical isolator is placed after the second reflector to reduce the impact of reflected light on the first laser.

[0013] The first half-wave plate and the first polarizing beam splitter are placed after the optical isolator to split the seed light into two paths. One path is used for injection locking of the laser system, and the other path is used to monitor the frequency of the first laser through the fiber optic port collimator.

[0014] The first fiber coupler and the single-mode polarization-maintaining fiber are placed after the first polarization beam splitter to couple and transmit the seed light, and to perform spot shaping on the seed light.

[0015] The second laser generates slave light with a center wavelength of 480nm. The slave light passes sequentially through the laser shaping device, the second lens, the third half-wave plate, the fourth mirror, and the third mirror, and is reflected out of the laser system at the optical isolation device.

[0016] The laser shaping device includes a first cylindrical mirror and a second cylindrical mirror, which are placed after the second laser to shape the elliptical light spot emitted from the second laser into a circular light spot.

[0017] The second lens, positioned after the laser shaping device, focuses the subordinate light;

[0018] The third half-wave plate is placed after the second lens to adjust the polarization of the subordinate light so that the subordinate light enters the optical isolation device with horizontal polarization.

[0019] The third and fourth reflecting mirrors are placed behind the third half-wave plate to reflect the focused subordinate light;

[0020] The optical isolation device is placed after the third reflecting mirror. By changing the polarization of the seed light and the slave light, the seed light can pass through with low loss, and the slave light can be reflected out of the laser system.

[0021] The second half-wave plate is placed after the optical isolation device to adjust the polarization of the seed light so that the seed light enters the optical isolation device with horizontal polarization.

[0022] The second fiber coupling head is placed after the second half-wave plate to match the spot patterns of the seed light and the slave light, thereby improving the injection efficiency of the seed light.

[0023] The first laser includes a laser diode, a collimating lens, a blazed grating, a piezoelectric ceramic plate, and a small mirror. The light emitted from the laser diode is collimated by the collimating lens and then incident on the blazed grating. The first-order diffracted light returns along the same path as the feedback light, and the zero-order diffracted light is reflected by the small mirror as the seed light of the laser system. The piezoelectric ceramic plate is placed on the back of the blazed grating. By changing the voltage of the piezoelectric ceramic plate, the angle of the blazed grating can be changed, thereby changing the wavelength of the seed light emitted by the first laser.

[0024] The optical isolation device includes: a second polarizing beam splitter prism, a rotator, a fourth half-wave plate, and a third polarizing beam splitter prism;

[0025] For the seed light, it passes through the second polarizing beam splitter prism, the optical rotator, the fourth half-wave plate and the third polarizing beam splitter in sequence. By adjusting the second half-wave plate, the seed light entering the optical isolation device is horizontally polarized. After passing through the optical rotator and the fourth half-wave plate, the seed light is still horizontally polarized and passes through the third polarizing beam splitter with low loss.

[0026] For the slave light, it passes sequentially through the third polarizing beam splitter prism, the fourth half-wave plate, the optical rotator, and the second polarizing beam splitter prism. By adjusting the third half-wave plate, the slave light entering the optical isolation device becomes horizontally polarized light. After passing through the fourth half-wave plate and the optical rotator, the slave light becomes vertically polarized light, and then it is reflected out of the laser system by the second polarizing beam splitter prism.

[0027] Compared to existing blue lasers, the advantages of this invention are:

[0028] 1. This invention is a low-cost, simple-to-operate, and easy-to-implement portable laser system, which provides a portable light source for portable quantum sensing and offers ideas for the practical application of quantum microwave measurement based on Rydberg atoms;

[0029] 2. The wavelength of the laser system realized by the present invention is easy to adjust, and a wavelength adjustment range of 6nm can be achieved, covering most of the Rydberg states of rubidium atoms;

[0030] 3. This invention provides a high-power injection-locked laser technology, which outputs 300mW at 480nm after locking. This injection-locked laser system can also be applied to other laser bands. Attached Figure Description

[0031] Figure 1 This is a schematic diagram of the structure of the present invention;

[0032] Figure 2 This is a schematic diagram of the Littrow type external cavity semiconductor laser structure used in the first laser of this invention;

[0033] Figure 3 Power spectra of laser system output light measured at different injection powers in embodiments of the present invention;

[0034] Figure 4 This is a schematic diagram showing the maximum non-mode-skipping range of the laser system scanning frequency under different injection powers as measured in an embodiment of the present invention. Detailed Implementation

[0035] This invention realizes an injection-locked blue laser system. The implementation of the invention will be described below through specific embodiments and accompanying drawings. The methods described are only some implementations of the invention, and the invention can also be verified through other different specific embodiments. The details in this specification can also be modified and improved based on different experimental backgrounds without departing from the spirit of the invention.

[0036] like Figure 1As shown, the first laser 1 is a Littrow-type external cavity semiconductor laser with a center wavelength of 480nm. Internally, it uses a NICHIANDSA116T laser diode, which is an antireflection coated laser diode with a maximum output power of 30mW. A schematic diagram of the laser structure is shown below. Figure 2 As shown, the laser diode 101 emits laser light under the action of the pump source. The laser light is collimated by the collimating lens 102 and incident on the surface of the blazed grating 103 (2400 lines / mm). The first-order diffracted light returns to the laser diode 101 as the feedback light. The zero-order diffracted light is reflected by the small mirror 105 and serves as the seed light of the laser system. An external cavity is formed between the laser diode 101 and the blazed grating 103 to select the output mode of the laser diode 101. The piezoelectric ceramic plate 104 is placed on the back of the blazed grating 103. By changing the voltage of the piezoelectric ceramic plate 104, the angle of the blazed grating 103 can be changed, thereby changing the wavelength of the seed light emitted by the first laser 1.

[0037] The seed light emitted from the first laser 1 passes sequentially through the laser beam-shrinking device 2, the first lens 3, the first reflector 4, the second reflector 5, the optical isolator 6, and the first half-wave plate 7. At the first polarization beam-splitting prism 8, it is split into two paths. One path passes through the fiber optic port collimator 20 for frequency monitoring of the first laser 1. The other path enters the first fiber coupler 9 and the single-mode polarization-maintaining fiber 10, exits through the second fiber coupler 11, and passes sequentially through the second half-wave plate 12, the optical isolator 13, the third reflector 14, the fourth reflector 15, the third half-wave plate 16, the second lens 17, and the laser shaping device 18 before being injected into the second laser 19. To save space, the laser beam-shrinking device 2 uses a Galilean beam-shrinking system. The focal length of the third lens 201 is f1 = 50 mm, and the focal length of the fourth lens 202 is f2 = -25 mm. The first lens 3, positioned after the laser beam-shrinking device 2, has a focal length of f3 = 125 mm to focus the seed light, ensuring high coupling efficiency at the first fiber coupler 9. The first reflector 4 and the second reflector 5 ensure that the overall size of the laser system is small by reflecting the focused seed light. The optical isolator 6 is placed after the second reflector 5 to prevent the seed light and slave light from being reflected into the first laser 1.

[0038] The second laser 19 contains only a laser diode and an aspherical collimating lens. The laser diode is a NICHIANDA4216, a type of FP-cavity laser diode with a maximum output power of 300mW. The slave light emitted from the second laser 19 passes sequentially through the laser shaping device 18, the second lens 17, the third half-wave plate 16, the third reflector 15, the fourth reflector 14, and is finally reflected out of the laser system by the second polarizing beam splitter prism 131 inside the optical isolation device 13. In this invention, cylindrical mirrors are used to shape the slave light spot. Although they occupy more space than shaping prisms, they have higher transmittance and lower optical loss. The focal length of the first cylindrical mirror 181 is f4 = 75mm, the focal length of the second cylindrical mirror 182 is f5 = -25mm, and the second lens 17, placed after the laser shaping device 18, has a focal length of f6 = 125mm to focus the slave light and ensure high coupling efficiency at the second fiber coupler 11. The third and fourth mirrors 14 and 15 ensure that the laser system has a small overall size by reflecting the focused slave light.

[0039] The optical isolation device 13 ensures that the seed light can pass through with minimal loss, while the slave light is reflected by the second polarizing beam splitter 131 as the output light of the laser system. For the seed light, the second half-wave plate 12 is adjusted to make the seed light entering the optical isolation device 13 horizontally polarized. After passing through the optical rotator 132 and the fourth half-wave plate 133, the seed light remains horizontally polarized and then passes through the third polarizing beam splitter 134 with minimal loss. For the slave light, the third half-wave plate 16 is adjusted to make the slave light entering the optical isolation device 13 horizontally polarized. After passing through the fourth half-wave plate 133 and the optical rotator 132, the slave light becomes vertically polarized and is then reflected by the second polarizing beam splitter 131 out of the laser system.

[0040] The function of the second fiber optic coupler 11 is to enable the seed light and the slave light to achieve spot pattern matching. The principle is based on the reversibility of the optical path. The higher the coupling efficiency of the slave light at the second fiber optic coupler 11, the higher the injection efficiency of the seed light. That is, the two beams achieve a good spot pattern matching degree. In this invention, the coupling efficiency of the slave light at the second fiber optic coupler 11 is required to be no less than 60%.

[0041] The laser system housing of this invention is a hollow aluminum block. Each optical element is fixed to a specially designed frame. The positions of each optical element are determined by simulating the optical path using optical software. The final volume of the main body of the laser system is determined to be 23 × 22 × 6 cm. 3 It is a portable 480nm blue light source.

[0042] To verify the performance of the injection-locked blue laser system, a spectrometer was used to observe the relationship between the injection power and the output optical power spectral density of the laser system, such as... Figure 3 The figures show the power spectra of the laser system's output light when no seed light is injected, when 0.5 mW seed light is injected, and when 8.1 mW seed light is injected, respectively. In free operation (without seed light), the slave light power spectrum is relatively broad. As the injected power increases, the slave light power spectrum linewidth gradually decreases, indicating that the monochromaticity of the laser system's output light is better at this time. It can be concluded that injection locking can narrow the linewidth of the laser system, and the higher the injected power, the more significant the narrowing effect, and the higher the power at a specific wavelength.

[0043] To achieve a larger dynamic range for spectral measurements in experiments, the laser system, while having a narrow linewidth, must simultaneously possess a large mode-hopping-free frequency scanning range. For example... Figure 4 As shown, the relationship between injected optical power and the mode-hopping-free frequency scanning range of the laser system was measured. It is important to emphasize that the laser system's tuning range of 6nm refers to the fact that the output wavelength of the laser system can be tuned to 6nm by adjusting the angle of the blazed grating 103 inside the first laser 1 and the current value of the second laser 19. The mode-hopping-free frequency scanning range of the laser system is the maximum mode-hopping-free frequency scanning range of the emitted light when only the voltage of the piezoelectric ceramic plate 104 is scanned. Measurements show that the mode-hopping-free frequency scanning range is 4.8GHz, which fully meets the design requirements. The mode-hopping-free frequency scanning range of the laser system can also be increased by increasing the seed light power or improving the spot mode matching degree between the seed light and the slave light.

[0044] In summary, this invention realizes a portable, tunable, high-power 480nm injection-locked blue laser system with advantages such as high output power (300mW), broadband tuning (6nm), a mode-hopping-free frequency scanning range of 4.8GHz, and portability. This invention is low-cost, easy to operate, and is a readily implementable portable laser system. It provides a mobile light source for portable quantum sensing, offers insights for Rydberg microwave measurement applications based on rubidium atoms, and can also be applied to laser sources in other wavelength bands, representing a general-purpose injection-locked laser system design.

[0045] The above-described embodiments of the present invention provide a further detailed explanation of the technical features and design concepts of the present invention. It should be understood that the scope of the invention is not limited to the specific embodiment described above. Any modifications, substitutions, or other operations made within the spirit and scope of the present invention should be within the protection scope of the present invention. The essence of the present invention is defined by the claims, not by the specific description of the embodiments.

Claims

1. An injection-locked blue laser system, characterized in that, The system includes a first laser (1), a laser beam-shrinking device (2), a first lens (3), a first reflector (4), a second reflector (5), an optical isolator (6), a first half-wave plate (7), a first polarization beam-splitting prism (8), a first fiber optic coupler (9), a single-mode polarization-maintaining fiber (10), a second fiber optic coupler (11), a second half-wave plate (12), an optical isolator (13), a third reflector (14), a fourth reflector (15), a third half-wave plate (16), a second lens (17), a laser shaping device (18), a second laser (19), and a fiber optic port collimator (20), wherein: The first laser (1) is a Littrow type external cavity semiconductor laser that generates a seed light with a center wavelength of 480nm. The seed light passes through the laser beam shrinking device (2), the first lens (3), the first reflector (4), the second reflector (5), the optical isolator (6), and the first half-wave plate (7) in sequence. It is split into two paths at the first polarization beam splitter (8). One path is used to monitor the frequency of the first laser (1) through the fiber port collimator (20), and the other path enters the first fiber coupler (9) and the single-mode polarization-maintaining fiber (10). It is emitted through the second fiber coupler (11) and passes through the second half-wave plate (12), the optical isolator (13), the third reflector (14), the fourth reflector (15), the third half-wave plate (16), the second lens (17), and the laser shaping device (18) in sequence before being injected into the second laser (19) for frequency locking. The laser beam-shrinking device (2) includes a third lens (201) and a fourth lens (202), which are placed after the first laser (1) to shrink the seed light. The first lens (3) is placed after the laser beam-concentrating device (2) to focus the seed light; The first reflector (4) and the second reflector (5) are placed after the first lens (3) to reflect the focused seed light; The optical isolator (6) is placed after the second reflector (5) to reduce the influence of reflected light on the first laser (1); The first half-wave plate (7) and the first polarizing beam splitter (8) are placed after the optical isolator (6) to split the seed light into two paths. One path is used for injection locking of the laser system, and the other path is used to monitor the frequency of the first laser (1) through the fiber optic port collimator (20). The first fiber coupler (9) and the single-mode polarization-maintaining fiber (10) are placed after the first polarization beam splitter (8) to couple and transmit seed light, and to perform spot shaping on the seed light; The second laser (19) generates slave light with a center wavelength of 480nm. The slave light passes sequentially through the laser shaping device (18), the second lens (17), the third half-wave plate (16), the fourth reflector (15), and the third reflector (14), and is reflected out of the laser system at the optical isolation device (13). The laser shaping device (18) includes: a first cylindrical mirror (181) and a second cylindrical mirror (182), which are placed after the second laser (19) to shape the elliptical light spot emitted by the second laser (19) into a circular light spot; The second lens (17) is placed after the laser shaping device (18) to focus the subordinate light; The third half-wave plate (16) is placed after the second lens (17) to adjust the polarization of the subordinate light so that the subordinate light enters the optical isolation device (13) with horizontal polarization. The third mirror (14) and the fourth mirror (15) are placed behind the third half-wave plate (16) to reflect the focused subordinate light; The optical isolation device (13) is placed after the third reflector (14). By changing the polarization of the seed light and the slave light, the seed light passes through with low loss, and the slave light is reflected out of the laser system. The second half-wave plate (12) is placed after the optical isolation device (13) to adjust the polarization of the seed light so that the seed light enters the optical isolation device (13) with horizontal polarization. The second fiber coupling head (11) is placed after the second half-wave plate (12) to match the spot patterns of the seed light and the subordinate light, thereby improving the injection efficiency of the seed light.

2. The injection-locked blue laser system according to claim 1, characterized in that, The first laser (1) includes: a laser diode (101), a collimating lens (102), a blazed grating (103), a piezoelectric ceramic sheet (104), and a small mirror (105); the light emitted from the laser diode (101) is collimated by the collimating lens (102) and then incident on the blazed grating (103). The first-order diffracted light returns along the original path as the feedback light, and the zero-order diffracted light is reflected by the small mirror (105) and then used as the seed light of the laser system; A piezoelectric ceramic sheet (104) is placed on the back of a blazed grating (103). By changing the voltage of the piezoelectric ceramic sheet (104), the angle of the blazed grating (103) can be changed, thereby changing the wavelength of the seed light emitted by the first laser (1).

3. The injection-locked blue laser system according to claim 1, characterized in that, The optical isolation device (13) includes: a second polarizing beam splitter prism (131), a rotator (132), a fourth half-wave plate (133), and a third polarizing beam splitter prism (134). For the seed light, it passes through the second polarizing beam splitter prism (131), the optical rotator (132), the fourth half-wave plate (133) and the third polarizing beam splitter prism (134) in sequence. By adjusting the second half-wave plate (12), the seed light entering the optical isolation device (13) is horizontally polarized. After passing through the optical rotator (132) and the fourth half-wave plate (133), the seed light is still horizontally polarized and passes through the third polarizing beam splitter prism (134) with low loss. For the slave light, it passes through the third polarizing beam splitter prism (134), the fourth half-wave plate (133), the optical rotator (132), and the second polarizing beam splitter prism (131) in sequence. By adjusting the third half-wave plate (16), the slave light entering the optical isolation device (13) becomes horizontally polarized light. After passing through the fourth half-wave plate (133) and the optical rotator (132), the slave light becomes vertically polarized light and is then reflected out of the laser system by the second polarizing beam splitter prism (131).

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