A super-stable power and frequency-stabilized high-power faraday laser

Abstract

The present application relates to super-stable power and frequency-stable high-power Faraday laser, comprising high-power Faraday laser light source (101) and fiber beam splitter (103), collimator (104), neutral density filter (105), half-wave plate (106) and polarization beam splitter prism (107) are arranged on the weak light output end light path of fiber beam splitter (103), first high-sensitivity detector (108) and high-speed servo controller (115) are arranged in one output light direction of polarization beam splitter prism (107); high-precision voltage reference source (112) outputs as the reference voltage of high-speed servo controller (115). The high-power Faraday laser of the present application has stable power, wide power stability range, and small laser power loss required for realizing stable power, improves power utilization rate, realizes long-term stable continuous adjustable super-stable power high-power Faraday laser, reduces system complexity and is easy to integrate.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of laser, in particular to a super-stable power and frequency-stable high-power Faraday laser. BACKGROUND

[0002] Laser plays an important role in metrology, and the slight fluctuation of laser power limits the sensitivity of precision measurement. For example, in the fields of atomic clock, optical trap technology, laser cooling, and laser deflection of atomic beam, the high power stability and frequency stability of laser are of great significance.

[0003] Most of the methods for stabilizing laser power can be summarized into two categories: internal control stabilization system and external control stabilization system. The internal control stabilization system establishes a closed-loop system to control the internal factors of laser devices such as driving current, temperature, and cavity length, which has the advantages of simple structure and high efficiency. However, the power fluctuation index of this method can only reach 0.1% to 0.01% at present, and this system is also limited to stabilizing small power mW order output laser due to the limitation of the detected power. More importantly, for conventional external cavity semiconductor lasers such as grating external cavity semiconductor lasers, stabilizing power by the internal control stabilization system will interfere with the frequency of the laser, causing large fluctuations in the laser frequency and affecting the applications with high requirements for frequency stability.

[0004] The external control stabilization system controls the laser power through optical modulation technology, such as using acousto-optic modulator (AOM) and electro-optic modulator (EOM). Although this method does not interfere with the laser frequency, it will cause a large loss of laser power. Among them, the use of AOM to achieve power stabilization can reach 10 -6 order, but the power loss is at least 30%, and it is difficult to prepare high-precision high-power laser. Due to the excessive power loss required to achieve power stabilization and the difficulty in implementing high-end high-power lasers, the existing technology cannot meet the special needs of applications for high-power lasers, such as laser cooling, and the system performance is better with higher laser power. Therefore, how to stabilize the power of high-power laser efficiently and accurately without interfering with the stability of the laser frequency is a practical problem that is difficult to solve at present. SUMMARY

[0005] In order to solve the problems existing in the prior art, the present application proposes a super-stable power and frequency-stable high-power Faraday laser, which aims to realize output of super-stable power and frequency-stable high-power laser with long-term stability.

[0006] The idea of the present application is to use a high proportion beam splitter to divide a high-power Faraday laser into a strong beam and a weak beam, the weak beam is converted into spatial light and detected by a high-sensitivity detector, and the high-speed servo controller is locked to a high-precision voltage reference source with precise temperature control, so that a long-term stable super-stable power and frequency stabilized Faraday laser output is realized at the strong beam end.

[0007] Based on this, the present application provides a super-stable power and frequency stabilized high-power Faraday laser, which comprises a high-power Faraday laser light source 101 and a fiber beam splitter 103, the fiber beam splitter 103 comprises a strong light output end and a weak light output end, a collimator 104, a neutral density filter 105, a half-wave plate 106 and a polarization beam splitter prism 107 are sequentially arranged on the output light path of the weak light output end, a first high-sensitivity detector 108 and a second high-sensitivity detector 109 are arranged on the two output light directions of the polarization beam splitter prism 107 respectively, and a high-speed servo controller 115 is arranged downstream of the first high-sensitivity detector 108;

[0008] The laser also comprises a laser controller 116 and a first temperature controller 117 for controlling the high-power Faraday laser light source 101; the laser controller 116 provides a driving current to the high-power Faraday laser light source 101, and the first temperature controller 117 controls the working temperature of the laser;

[0009] The laser also comprises a high-precision voltage reference source 112 installed in a constant temperature mechanism 113, and the output of the high-precision voltage reference source 112 is used as the reference voltage of the high-speed servo controller 115;

[0010] In operation, the laser output by the high-power Faraday laser light source 101 is divided into a strong beam and a weak beam by the fiber beam splitter 103, the strong beam is directly output as the system output, and the weak beam is collimated by the collimator 104 and then output as parallel light, the parallel light is power-adjusted by the neutral density filter 105, and then passes through the half-wave plate 106 and the polarization beam splitter prism 107 to be divided into two beams, which enter the first high-sensitivity detector 108 and the second high-sensitivity detector 109 respectively; the output signal of the first high-sensitivity detector 108 and the output signal of the high-precision voltage reference source 112 are simultaneously input into the high-speed servo controller 115, a servo signal with a center at zero point is obtained by adjusting the direct current voltage bias of the high-speed servo controller 115, the servo signal is input into the current modulation port of the laser controller 116, and finally a high-power continuous adjustable super-stable power and frequency stabilized Faraday laser is realized by controlling the current of the laser.

[0011] According to a preferred embodiment, in order to improve the output voltage stability of the high-precision voltage reference source 112, the laser system further comprises a thermostat mechanism 113, and the high-precision voltage reference source 112 is installed in the thermostat mechanism 113, so as to ensure that the high-precision voltage reference source itself is in a temperature-constant environment, and the interference of temperature on the output is minimized. As an implementation, the thermostat mechanism 113 comprises a shell made of heat preservation material and a second temperature controller 114 for constant temperature of the inside of the shell. This design is conducive to stabilizing the ambient temperature of the high-precision voltage reference source 112, improving the output voltage stability thereof, and thus plays a role in improving the power stability of the high-power Faraday laser.

[0012] Further, the high-precision voltage reference source 112 can use a voltage stabilizing chip based on LM399 model for voltage stabilization, and can output a voltage reference signal with a high stability of 10 -6 orders of magnitude, which can ensure the long-term stability of the reference source.

[0013] In the present application, the power of the weak laser beam can be doubly adjusted and compensated through the combination of the neutral density filter, the half-wave plate and the polarization beam splitter prism, so that the signal of the first high-sensitivity detector 118 approaches the signal of the high-precision voltage reference source, thereby obtaining a better power stabilization effect. Alternatively, when the signal of the first high-sensitivity detector 108 does not approach the signal of the high-precision voltage reference source 112, the high-speed servo controller 115 can also add a direct current voltage so that the values of the two are close to each other, and the difference approaches 0, and the direct current voltage can be up to ±10V at the maximum.

[0014] In the present application, the temperature of the precision voltage source in the heat preservation shell is stabilized within ±0.01℃ by the second temperature controller 114.

[0015] According to a preferred embodiment, the laser system of the present application further comprises a fiber adapter flange 102 arranged between the high-power Faraday laser light source 101 and the fiber beam splitter 103.

[0016] In the present application, preferably, a six-and-a-half digit digital multimeter 110 and a laser power reading device 111 are arranged downstream of the light path of the second high-sensitivity detector 109. The six-and-a-half digit digital multimeter 110 measures the voltage signal converted by the detector from the optical power signal, and the laser power reading device 111 is used to obtain the data before and after the laser power stabilization in the laser system ring, which can usually be realized by a general-purpose computer in cooperation with appropriate software.

[0017] In the present application, the minimum splitting ratio of the high-proportion fiber beam splitter 103 is less than 1:99, i.e. the minimum power of the strong laser beam is greater than 99% of the total power of the laser output by the high-power Faraday laser light source 101, and thus the power loss required for power stabilization is less than 1%.

[0018] As an alternative embodiment, the second high-sensitivity detector 109 can not be provided, and a three-way adapter is used to connect the signal of the first high-sensitivity detector 108 to the six-half digital multimeter 110, and then the data before and after the laser power in the ring is obtained through the laser power reading device 111.

[0019] The super-stable power and frequency-stable high-power Faraday laser of the present application first splits the light through a high-proportion beam splitter, and the weak laser beam split out is used to adjust and compensate the power in the ring through a spatial light path, so that the strong laser beam as the output can realize power stability and will not disturb the laser frequency at the same time. At the same time, the best current working point can be selected without affecting the system composition, so that the output laser has the optimal power stability and frequency stability.

[0020] In terms of power loss, the power of the weak laser beam split out is less than 1% of the total output power, i.e. the power loss required to realize stable power is less than 1%, which is significantly better than the power loss generated by the external control and stabilization system realized by the acousto-optic modulator (AOM) or electro-optic modulator (EOM) in the prior art.

[0021] The high-precision voltage reference source used in the present application has a stability of 10 -6 orders of magnitude, and the current of the laser controller can be modulated through a high-speed servo controller to accurately lock the laser power to the reference voltage, realizing a high-power continuous adjustable super-stable power laser system with a stability of 10 -6 orders of magnitude, which solves the problems of the existing laser power stabilization system, such as disturbing the output frequency, poor stability, inability to continuously adjust, large loss and inability to realize power stabilization of a high-power laser.

[0022] The present application realizes high-precision locking of the power in the ring by combining a high-proportion beam splitter, an in-ring spatial light path, a high-precision voltage reference source and a high-speed servo controller, and in combination with the characteristics of the output frequency of a high-power Faraday laser being immune to current, the servo signal adjusts the current while ensuring that the frequency is not disturbed, thereby realizing a high-power super-stable power and frequency-stable Faraday laser system. The laser of the present application has high power stability and frequency stability, and can be applied to atomic clocks, optical trap technology, laser cooling and other applications, reduces system complexity and is easy to integrate, and meets the application requirements of high-precision equipment such as atomic clocks.

[0023] Although the existing technology has a loss of about 30%, it does not disturb the frequency, and although the existing internal control has a loss of about 1%, it feeds back the current of the laser, and in the field, changing the current will inevitably change the frequency, so the frequency must be locked to be used in applications requiring frequency stability.

[0024] The present invention uses a Faraday laser source as input. Since the Faraday laser itself is immune to frequency, changing the current will not change the frequency, which can achieve the beneficial effect of stabilizing power without interfering with the frequency. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the structure of a high-power Faraday laser with ultra-stable power and frequency stability in an embodiment of the present invention;

[0026] Figure 2 This is a comparison of power fluctuation data before and after power stabilization of high-power Faraday lasers with ultra-stable power and frequency stabilization in this embodiment of the invention;

[0027] Figure 3 This invention presents a comparison of the power stability of high-power Faraday lasers before and after power stabilization, including ultra-stable power and frequency-stabilized models.

[0028] Figure 4 This invention provides a comparison of the output voltages of a high-power Faraday laser with and without temperature control using a high-precision voltage source in an ultra-stable power and frequency-stabilized high-power voltage source.

[0029] Figure 5 This illustrates the variation of the output wavelength of a high-power Faraday laser with current in an embodiment of the present invention.

[0030] Figure 6 The output wavelength of a conventional vertical cavity surface-emitting semiconductor laser (a) and a grating external cavity semiconductor laser (b) varies with current.

[0031] In the figure, 101 is a high-power Faraday laser source, 102 is a flange, 103 is an optical fiber beam splitter, 104 is a collimator, 105 is a neutral density filter, 106 is a half-wave plate, 107 is a polarizing beam splitter, 108 is a first high-sensitivity detector, 109 is a second high-sensitivity detector, 110 is a six-and-a-half-digit multimeter, 111 is a laser power reading device, 112 is a high-precision voltage reference source, 113 is a temperature control mechanism, 114 is a second temperature controller, 115 is a high-speed servo controller, 116 is a laser controller, and 117 is a first temperature controller. Detailed Implementation

[0032] The technical solution of the present invention will be explained in a non-limiting manner with reference to the accompanying drawings.

[0033] Example 1

[0034] like Figure 1 The laser system shown includes a high-power Faraday laser source 101 and a high-ratio fiber beam splitter 103 connected by optical fibers. The fiber beam splitter 103 outputs a strong laser beam and a weak laser beam, with the strong laser beam serving as the system output.

[0035] A collimator 104, a neutral density filter 105, a half-wave plate 106, and a polarization beam splitter prism 107 are sequentially arranged on the light path of the weak laser beam. A first high-sensitivity detector 108 and a second high-sensitivity detector 109 are arranged on the two output light directions of the polarization beam splitter prism 107, respectively. A high-speed servo controller 115 is arranged downstream of the first high-sensitivity detector 108. The output signal of the high-speed servo controller 115 is used as the servo signal of a laser controller 116. A high-precision voltage reference source 112 is used as the input signal of the high-speed servo controller 115, and the high-precision voltage reference source 112 is installed in a thermostat mechanism 113 and is temperature-controlled by a second temperature controller 114.

[0036] In this embodiment, the high-power Faraday laser light source 101 uses an 852 nm wavelength high-power Faraday laser disclosed in Chinese invention patent application CN 114498296A, and the light intensity can reach 300 mW / mm 2 After passing through a high-proportion beam splitter of 1:99, the power of the strong laser beam can be as low as 297 mW / mm 2 , and the power of the weak light beam can be as low as 3 mW / mm 2 .

[0037] The high-precision voltage reference source 112 generates a voltage reference signal through a voltage stabilizing chip of model LM399, is placed in a heat preservation shell made of heat preservation material, and the temperature in the heat preservation shell is kept constant by the second temperature controller 114. By selecting an existing temperature control chip, the temperature control accuracy can be 0.01℃. The constant temperature of the environment is conducive to improving the output stability of the high-precision voltage reference source 112, and the voltage stability can reach 10 -6 orders of magnitude.

[0038] The first high-sensitivity detector 108 and the second high-sensitivity detector 109 both use devices of model PDA100A2 of the American thorlabs company, and the gain can be adjusted to 60 dB, which is high in sensitivity.

[0039] The high-speed servo controller 115 is a high-speed servo controller of model LB1005 of the New Focus company. By adjusting the direct current voltage bias, the maximum adjustable range is ±10V. Even if the voltages of the first high-sensitivity detector 108 and the high-precision voltage reference source 112 are inconsistent, the error signal can also be adjusted to close to 0, greatly widening the stable power range.

[0040] When adjustment is needed, the neutral density filter 105 and the half-wave plate 106 can be rotated to adjust the power of the two beams split by the polarization beam splitter prism 107, so that voltage saturation does not occur after entering the first high-sensitivity detector 108 and the second high-sensitivity detector 109.

[0041] The output signal of the second high-sensitivity detector 109 is recorded by a computer after passing through a six-and-a-half digit digital multimeter 110, and the laser power is obtained. The precision of the six-and-a-half digit digital multimeter can reach 0.00001, so that the power fluctuation data can be accurately collected and the system performance can be monitored. Then, according to the fluctuation of the data, the gain and bandwidth of the high-speed servo controller 115 are optimized, and the stable power effect is improved.

[0042] The working principle of the spatial stable power loop of the laser system is as follows: after the laser emits high-power laser, the weak light beam output by the high-proportion fiber beam splitter passes through the collimator 104 to output parallel light, the parallel light passes through the neutral density filter 105 for power adjustment, and then passes through the half-wave plate 106 and the polarization beam splitter prism 107 to be divided into two beams (the splitting proportion can be adjusted for the second time by rotating the half-wave plate), and the two beams enter the first high-sensitivity detector 108 and the second high-sensitivity detector 109 respectively.

[0043] The output signal of the first high-sensitivity detector 108 is connected to the output signal of the high-precision voltage reference source 112 and enters the high-speed servo controller 115, which is used to adjust the direct current voltage bias of the high-speed servo controller 115, so that the error signal output by the high-speed servo controller 115 is close to zero, and then the fast servo control signal output by the high-speed servo controller 115 is input to the current modulation port of the laser controller 116, so that the high-power continuous adjustable ultra-stable power laser system is realized by controlling the current of the laser.

[0044] The output of the second high-sensitivity detector 109 is used to collect power fluctuation data and monitor system performance.

[0045] The strong light beam output by the high-proportion fiber beam splitter is used as the system output.

[0046] Figure 2 For the data comparison of the power fluctuation of the ultra-stable power laser system of the embodiment before and after power stabilization for 24 hours, it can be seen from the figure that the power fluctuation (the vertical axis in the figure is the voltage fluctuation signal converted by the detector) before power stabilization is greater than 10%, and the power fluctuation is greatly reduced after power stabilization. After calculation, the power fluctuation after stabilization is less than 0.003%.

[0047] Figure 3 For the power stability comparison of the ultra-stable power laser system of the embodiment before and after power stabilization, it can be seen from the figure that the power stability is improved by more than 2 orders of magnitude compared with before and after stabilization. The power second-level stability is improved from 10 -3 orders of magnitude to 10 -6 orders of magnitude, and the second-level stability after power stabilization is 3.3×10 -6 .

[0048] Figure 4The output voltage of the high-precision voltage source in the super-stable power laser system of the embodiment is compared with the output voltage without temperature control. As can be seen from the figure, in the temperature control stage within 0-3 hours, the output voltage fluctuation is very small, and is stabilized at 7.739-7.740 V. The temperature control is turned off at 3-4.5 hours, the output voltage curve is concave downward, and the fluctuation range is obviously larger, reaching 7.737 V at the lowest. At 4.5-6 hours, the temperature control loop is turned on again, and the output voltage is stabilized at 7.739-7.740 V.

[0049] Figure 5 The output wavelength of the Faraday laser changes with the current. As can be seen from the figure, in the current change range of 60-130 m, the output wavelength fluctuation range of the laser is less than 0.005 nm, which proves that the power stabilization through the internal control stabilization system does not change the laser frequency.

[0050] Figure 6 The output wavelength of the traditional vertical cavity surface emitting semiconductor laser (a) and the grating external cavity semiconductor (b) changes with the current. As can be seen from Figure 6 (a), in the current change range of 0-200 mA, the laser wavelength change range is 120 nm, and as can be seen from Figure 6 (b), in the voltage change range of 0-18 V, the laser wavelength change range is 25 nm.

[0051] Therefore, compared with the traditional laser, the output wavelength of the Faraday laser is affected by the current by 4-5 orders of magnitude smaller than the traditional semiconductor laser, and is not easily disturbed by the current change.

[0052] As a comparison, James Keaveney et al. realized a laser (A single-mode external cavity diode laser using an intra-cavity atomic Faraday filter with short-term linewidth, Rev. Sci. Instrum. 87, 095111 (2016)) in 2016, which finally realized a laser with a short-term linewidth <400 kHz and a long-term stability <1 mHz, but did not verify the power stability of the laser.

[0053] Similarly, Chinese invention patent application CN 112542757A discloses another Faraday laser with a similar structure of resonant cavity cavity film locking. This document achieves the reduction of power noise and frequency noise by locking the resonant cavity cavity film. However, the power loss, frequency fluctuation amplitude, voltage fluctuation amplitude or power fluctuation amplitude that the laser can ultimately achieve are not recorded in this document. The inventors verified the stability of the Faraday laser of this document in a laboratory environment, and ultimately only achieved a power fluctuation index of 0.1% to 0.01%.

[0054] In comparison, the high-power ultra-stable power laser system of the present application stabilizes the laser power while maintaining the frequency stability of the laser, solves the problem of mutual contradiction between laser power stabilization and frequency stabilization in the existing internal control stabilization system, realizes ultra-stable power and frequency Faraday laser output, and can be used in the fields of precision measurement and atomic clocks.

[0055] The present application realizes power stabilization of a high-power Faraday laser, and the power stabilization range is wide, which can be stabilized in the power range of several hundred mW to 2W. Compared with the prior art, the laser of the present application significantly reduces the laser power loss required to achieve stable power, realizes precise temperature control and high stability output of high-precision voltage source, improves power utilization rate, and overcomes the limitation that the detector is easy to saturate, realizes a long-term stable continuous adjustable ultra-stable power high-power Faraday laser, reduces system complexity and is easy to integrate, makes stable high-power laser a reality, solves the problem of poor power stability of the existing high-precision high-power Faraday laser, and solves the problem of laser frequency interference in the stable power system, realizing a high-power laser with ultra-stable power and frequency.

[0056] The above only describes the preferred embodiments of the present application, and it should be noted that for ordinary skilled persons in the art, without departing from the technical principles of the present application, a number of improvements and modifications can be made, and these improvements and modifications should also be considered as the protection scope of the present application.

Claims

1. A super-stable power and frequency stabilized high power Faraday laser, characterized in that The laser comprises a high-power Faraday laser light source (101) and a fiber beam splitter (103) connected in sequence by an optical fiber, the fiber beam splitter (103) comprises a strong light output end and a weak light output end, a collimator (104), a neutral density filter (105), a half-wave plate (106) and a polarization beam splitter prism (107) are sequentially arranged on the output light path of the weak light output end, a first high-sensitivity detector (108) and a second high-sensitivity detector (109) are respectively arranged on the two output light directions of the polarization beam splitter prism (107), and a high-speed servo controller (115) is arranged downstream of the first high-sensitivity detector (108); The laser further comprises a laser controller (116) and a first temperature controller (117) for controlling the high-power Faraday laser light source (101); The laser further comprises a high-precision voltage reference source (112) installed in a constant temperature mechanism (113), and an output of the high-precision voltage reference source (112) is used as a reference voltage of the high-speed servo controller (115); In operation, laser output by the high-power Faraday laser light source (101) is divided into two beams of strong and weak laser by the fiber beam splitter (103), the strong laser beam is directly output, and the weak laser beam is collimated by the collimator (104) to output parallel light, the parallel light is power-adjusted by the neutral density filter (105), and then is divided into two beams of light by the half-wave plate (106) and the polarization beam splitter prism (107), the two beams of light enter the first high-sensitivity detector (108) and the second high-sensitivity detector (109) respectively; output signals of the first high-sensitivity detector (108) and the high-precision voltage reference source (112) are simultaneously input into the high-speed servo controller (115), a servo signal with a center at zero point is obtained by adjusting a direct-current voltage bias of the high-speed servo controller (115), the servo signal is input into a current modulation port of the laser controller (116), and power stability is realized by controlling a laser current.

2. The laser of claim 1, wherein The constant temperature mechanism (113) comprises a housing made of a heat preservation material and a second temperature controller (114) for keeping the temperature inside the housing constant.

3. The laser of claim 1, wherein The laser further comprises a flange (102) arranged between the high-power Faraday laser light source (101) and the fiber beam splitter (103).

4. The laser of claim 1, wherein A six-bit half-digital multimeter (110) and a laser power reading device (111) are arranged downstream of the light path of the second high-sensitivity detector (109).

5. The laser of claim 1, wherein The minimum light splitting ratio of the high-proportion fiber beam splitter (103) is less than 1:99.

Images