Ultra-narrow linewidth laser based on echo wall optical cavity

Abstract

The invention discloses an ultra-narrow linewidth laser based on an echo wall optical cavity. The ultra-narrow linewidth laser comprises a butterfly laser, an erbium-doped optical fiber amplifier, an optical frequency doubling module and an optical fiber filter, wherein the butterfly laser is used for providing pump light, the erbium-doped optical fiber amplifier is used for amplifying the power of the pump light, the optical frequency doubling module is used for converting laser of 1556nm into laser of 778nm, the optical fiber filter is used for filtering stray light in the laser after frequency doubling, and the laser of 778nm can be obtained through self-injection locking and optical frequency doubling technologies. 1556 nm laser is converted into 778 nm ultra-narrow linewidth laser, the requirements of quantum gravity measurement, atomic clocks and other precision fields for low-noise and high-stability laser are met, the ultra-narrow linewidth laser has higher coherence, errors in measurement can be reduced, and the precision of quantum gravity measurement, atomic clocks and other precision measurement is improved.

Description

TECHNICAL FIELD

[0001] The application relates to the field of laser technology, in particular to an ultra-narrow linewidth laser based on an echo wall optical cavity. BACKGROUND

[0002] Quantum gravity measurement, time-frequency measurement, detection imaging and other information fields have extremely strict requirements on the performance of lasers. In the field of time precision measurement, the Rb 5S 1 / 2 →5D 5 / 2 The optical frequency forbidden transition corresponds to an optical wavelength of 778 nm. Therefore, in the development of a new type of Rb atomic clock, a single-mode narrow linewidth 778 nm tunable semiconductor laser is urgently needed as a pump source to detect and analyze the hyperfine structure of rubidium atoms.

[0003] At present, the commercial DFB chips and their corresponding modules required by the 778 nm tunable semiconductor laser are all imported products from abroad, which are expensive and have been banned by the United States and European countries, which greatly hinders the application of quantum core components to new quantum information equipment in China. Therefore, it is urgent to independently develop a 778 nm band ultra-narrow linewidth tunable semiconductor laser to break through the technical blockade of foreign countries and solve the problem of quantum technology core components in the United States and Europe. In addition, the existing DFB laser has a wide linewidth (usually MHz level), which cannot meet the demand for ultra-narrow linewidth (Hz level) and low phase noise in quantum technology. The application introduces the self-injection locking technology of the echo wall optical cavity to narrow the linewidth to the Hz level. The narrow linewidth tunable laser in this band plays an important role in quantum sensing, remote sensing and other fields. SUMMARY

[0004] The application provides a kind of ultra-narrow linewidth laser based on echo wall optical cavity, utilize the echo wall optical cavity with ultra-high optical quality factor as external feedback module, make 1556nm DFB laser self-injection locking to echo wall mode, narrow the linewidth to Hz level;Subsequently, the wavelength is doubled to 778 nm through an optical frequency doubling module, combining self-injection locking and frequency doubling technology, the advantages of C-band laser are expanded to 778 nm band, realizing ultra-low phase noise, high wavelength stability and compact structure, the linewidth is narrowed by about 6 orders of magnitude, the relative intensity noise is less than or equal to-135dBc / Hz@10kHz, and the wavelength is tunable. Through the self-injection locking and optical frequency doubling technology, the 1556nm laser is converted into a 778nm ultra-narrow linewidth laser, which meets the demand for low noise and high stability laser in quantum gravity measurement, atomic clock and other precision fields. The ultra-narrow linewidth laser has higher coherence, which can reduce the error in measurement and improve the precision of quantum gravity measurement, atomic clock and other precision measurement.

[0005] This application provides an ultra-narrow linewidth laser based on a whispering-gallery optical cavity, comprising: a butterfly laser, an erbium-doped fiber amplifier, an optical frequency doubling module, and a fiber filter; wherein, the butterfly laser is used to provide pump light, the erbium-doped fiber amplifier is used to amplify the pump light power, the optical frequency doubling module is used to convert 1556nm laser light into 778nm laser light, and the fiber filter is a 778nm bandpass filter used to filter out stray light in the frequency-doubled laser light.

[0006] Preferably, the butterfly laser includes a first thermoelectric cooler, a second thermoelectric cooler, a DFB chip, a microlens, a phase shifter, a third thermoelectric cooler, a prism, a whispering-gallery optical microcavity, a piezoelectric ceramic, an isolator, a beam splitter cube, a photodetector, and an optical fiber collimator.

[0007] Preferably, the first thermoelectric cooler, the second thermoelectric cooler, and the third thermoelectric cooler control the operating temperature of the environment, the DFB chip, and the whispering-gallery optical microcavity, respectively; wherein, the third thermoelectric cooler is used for laser thermal tuning.

[0008] Preferably, the whispering-gallery optical microcavity is a crystal whispering-gallery wedge cavity used to narrow the DFB linewidth.

[0009] Preferably, the piezoelectric ceramic is used to fine-tune the laser wavelength using an external modulation signal.

[0010] Preferably, the fiber collimator is a lens type, prism type, or hybrid structure.

[0011] Preferably, the optical frequency doubling module is made of periodically polarized lithium niobate crystal material.

[0012] One or more technical solutions provided in this application have at least the following technical effects or advantages: by using self-injection locking and optical frequency doubling technology, 1556nm laser is converted into 778nm ultra-narrow linewidth laser, which meets the requirements of precision fields such as quantum gravity measurement and atomic clocks for low noise and high stability laser. The ultra-narrow linewidth laser has higher coherence, which can reduce measurement errors and improve the accuracy of precision measurements such as quantum gravity measurement and atomic clocks. Attached Figure Description

[0013] 100. Butterfly laser; 101. First thermoelectric cooler; 102. Second thermoelectric cooler; 103. DFB chip; 104. Microlens; 105. Phase shifter; 106. Third thermoelectric cooler; 107. Prism; 108. Whispering-gallery optical microcavity; 109. Piezoelectric ceramic; 110. Isolator; 111. Beam splitter cube; 112. Photodetector; 113. Fiber collimator; 200. Erbium-doped fiber amplifier; 300. Optical frequency doubling module; 400. Fiber optic filter;

[0014] Figure 1 This is a schematic diagram of the structure of an ultra-narrow linewidth laser based on a whispering-gallery optical cavity according to the present invention;

[0015] Figure 2 This is a schematic diagram of the internal structure of the butterfly laser of the present invention;

[0016] Figure 3 This is a schematic diagram of the structure of the whispering-gallery optical microcavity of the present invention;

[0017] Figure 4 This is a schematic diagram of the phase noise of the present invention;

[0018] Figure 5 This is a schematic diagram of the relative intensity noise (RIN) of the present invention;

[0019] Figure 6 This is a schematic diagram illustrating the long-term wavelength stability of the present invention. Detailed Implementation

[0020] To facilitate understanding of the present invention, a more complete description of this application will be given below with reference to the accompanying drawings, which illustrate preferred embodiments of the invention. However, the invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to enable a more thorough and complete understanding of the disclosure of the present invention.

[0021] It should be noted that the terms "vertical," "horizontal," "up," "down," "left," "right," and similar expressions used in this article are for illustrative purposes only and do not represent the only possible implementation.

[0022] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains; the terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to limit the invention; the term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0023] Example 1: Figure 1This is a schematic diagram of an ultra-narrow linewidth laser based on a whispering-gallery optical cavity according to an embodiment of the present invention, including: a butterfly laser 100, an erbium-doped fiber amplifier 200, an optical frequency doubling module 300, and a fiber filter 400; wherein, the butterfly laser 100 is used to provide pump light, the erbium-doped fiber amplifier 200 is used to amplify the pump light power, the optical frequency doubling module 300 is used to convert 1556nm laser light into 778nm laser light, and the fiber filter 400 is used to filter out stray light in the frequency-doubled laser light. The fiber filter 400 is a 778nm bandpass filter (insertion loss <1dB, passband ±0.1nm).

[0024] The butterfly laser 100 includes a first thermoelectric cooler 101, a DFB chip 103, a second thermoelectric cooler 102, a microlens 104, a phase shifter 105, a third thermoelectric cooler 106, a prism 107, a whispering-gallery optical microcavity 108, a piezoelectric ceramic 109, an isolator 110, a beam-splitting cube 111, a photodetector 112, and an optical fiber collimator 113. The whispering-gallery optical microcavity 108 is a crystalline whispering-gallery wedge cavity with a quality factor Q ≥ 10^8. Through Rayleigh scattering feedback, it narrows the DFB laser linewidth from the MHz level to approximately 2Hz. Figure 4 As shown, a significant narrowing of the DFB linewidth is achieved. The first thermoelectric cooler 101, the second thermoelectric cooler 102, and the third thermoelectric cooler 106 respectively control the operating temperature of the environment, the DFB chip 103, and the whispering-gallery optical microcavity 108. The piezoelectric ceramic 109 is used to fine-tune the laser wavelength with an external modulation signal. The piezoelectric ceramic 109 and the first thermoelectric cooler 101, the second thermoelectric cooler 102, and the third thermoelectric cooler 106 are used for wavelength tuning: the piezoelectric ceramic achieves rapid modulation, and the thermoelectric coolers achieve mode-skipping-free thermal tuning. Among them, the third thermoelectric cooler 106 can achieve laser thermal tuning by changing its temperature. The DFB chip 103 is mounted on the second thermoelectric cooler 102 and is used for... Temperature control is achieved by focusing the laser emitted from the DFB chip 103 through the microlens 104, followed by a phase shifter 105 and a prism 107. The phase shifter 105 is used to adjust the coupling phase, and the prism 107 guides the laser into the whispering-gallery optical microcavity 108, which is mounted on the third thermoelectric cooler 106. The laser resonates in the whispering-gallery optical microcavity 108, and part of the laser is scattered back to the DFB chip 103 by Rayleigh scattering to complete optical feedback and narrow the laser linewidth. The remaining laser passes through the isolator 110 and then through the beam splitter 111, where a portion of the laser is injected into the photodetector 112 for power monitoring, and the other portion of the laser is collected by the fiber collimator 113 to achieve fiber laser output.

[0025] The laser output from the butterfly laser 100 is connected to the erbium-doped fiber amplifier 200 to amplify the power to the level required for frequency doubling (typical value 100-500mW). The amplified laser is then input into the PPLN frequency doubling module, which generates a 778nm laser through nonlinear effects. The PPLN crystal needs to be preheated to the phase matching temperature (approximately 40-60℃). The frequency-doubled laser contains a residual 1556nm laser component, which is filtered out by a 778nm bandpass filter to ensure output purity. The filter insertion loss needs to be <1dB and the passband width ±0.1nm.

[0026] In this embodiment, the whispering-gallery optical microcavity 108 is a crystal whispering-gallery wedge cavity. Figure 3 This is a schematic diagram of an optical microcavity used in a 778nm ultra-narrow linewidth laser based on a whispering-gallery optical cavity provided in the embodiment. The whispering-gallery optical microcavity 108 is made of calcium fluoride, magnesium fluoride, lithium niobate or lithium tantalate crystal. The whispering-gallery optical microcavity 108 includes any one of crystal microcavity, ring core cavity or micro disk cavity.

[0027] The sounding wall optical microcavity 108 has a diameter of 3-10 mm, a thickness of 0.2-2 mm, and a working surface thickness of 20-200 μm. In specific implementation, the type and material of the optical microcavity can be selected according to the actual situation, and this invention does not limit it.

[0028] The aforementioned whispering-gallery optical microcavity has a quality factor ≥ 10⁸. 8 This allows the DFB linewidth to be effectively narrowed.

[0029] Figure 4 An embodiment provides a schematic diagram of the phase noise of a 778nm ultranarrow linewidth laser based on a whispering-gallery cavity. Figure 3 The whispering wedge cavity in the DFB significantly narrows the linewidth. Using the linewidth-phase noise relationship, the intrinsic linewidth can be calculated to be about 2Hz, which is about 6 orders of magnitude narrower than the intrinsic linewidth of the DFB.

[0030] Figure 5 The embodiment provides a schematic diagram of the relative intensity noise (RIN) of a 778nm ultranarrow linewidth laser based on a whispering-gallery optical cavity. As can be seen from the figure, the RIN noise is ≤-135dBc / Hz@10kHz.

[0031] Figure 6 The embodiment provides a schematic diagram of the long-term wavelength stability of a 778nm ultranarrow linewidth laser based on a whispering-gallery cavity. The diagram shows that the wavelength drift does not exceed 1pm during a test lasting up to 12 hours.

[0032] Ideally, narrow-linewidth laser sources exhibit a single-frequency spectrum, with intracavity carrier fluctuations, optical phase, and photon density all in an absolutely stable state, characterized by low relative intensity noise and low frequency noise. However, due to the unavoidable spontaneous emission in the active region, practical lasers introduce phase and intensity perturbations in stimulated emission mode, leading to intrinsic broadening of the single laser frequency spectral line in the Lorentz pattern. These small fluctuations are easily affected by technical noise in the external environment, causing greater perturbations and further broadening the laser linewidth. This application addresses this issue based on the self-injection locking principle. By introducing an external high-quality factor optical microcavity as a feedback unit, filtering and passive optical feedback are achieved, ultimately narrowing the laser linewidth. The DFB laser output light is coupled into the WGR, and due to Rayleigh scattering caused by inhomogeneities inside and on the surface of the microcavity, some light is reflected back to the laser. When the laser output light approaches the resonant frequency of the WGR and the feedback light is in a suitable phase, a self-injection locking mechanism is established. Due to the frequency pulling effect, the locked laser frequency is mainly determined by the WGR resonant frequency, which effectively suppresses the frequency drift caused by the DFB laser current fluctuation and narrows the laser linewidth.

[0033] The technical solutions described in the above embodiments of this application have at least the following technical effects or advantages: by using self-injection locking and optical frequency doubling technology, 1556nm laser is converted into 778nm ultra-narrow linewidth laser, which meets the requirements of precision fields such as quantum gravity measurement and atomic clocks for low noise and high stability lasers. Ultra-narrow linewidth lasers have higher coherence, which can reduce measurement errors and improve the accuracy of precision measurements such as quantum gravity measurement and atomic clocks.

[0034] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. For those skilled in the art, the present invention can have various modifications and variations. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. An ultra-narrow linewidth laser based on a whispering-gallery optical cavity, characterized in that, include: The system comprises a butterfly laser (100), an erbium-doped fiber amplifier (200), an optical frequency doubling module (300), and a fiber filter (400); wherein the butterfly laser (100) is used to provide pump light, the erbium-doped fiber amplifier (200) is used to amplify the pump light power, the optical frequency doubling module (300) is used to convert 1556nm laser into 778nm laser, and the fiber filter (400) is a 778nm bandpass filter used to filter out stray light in the frequency-doubled laser.

2. The ultra-narrow linewidth laser based on a whispering-gallery cavity as described in claim 1, characterized in that, The butterfly laser (100) includes a first thermoelectric cooler (101), a second thermoelectric cooler (102), a DFB chip (103), a microlens (104), a phase shifter (105), a third thermoelectric cooler (106), a prism (107), a whispering-gallery optical microcavity (108), a piezoelectric ceramic (109), an isolator (110), a beam splitter cube (111), a photodetector (112), and an optical fiber collimator (113).

3. The ultra-narrow linewidth laser based on a whispering-gallery cavity as described in claim 2, characterized in that, The first thermoelectric cooler (101), the second thermoelectric cooler (102), and the third thermoelectric cooler (106) control the operating temperature of the environment, the DFB chip (103), and the whispering-gallery optical microcavity (108), respectively; wherein, the third thermoelectric cooler (106) is used for laser thermal tuning.

4. The ultra-narrow linewidth laser based on a whispering-gallery cavity as described in claim 3, characterized in that, The whispering-gallery optical microcavity (108) adopts a crystal whispering-gallery wedge cavity to narrow the DFB linewidth.

5. The ultra-narrow linewidth laser based on a whispering-gallery cavity as described in claim 4, characterized in that, The piezoelectric ceramic (109) is used to fine-tune the laser wavelength using an external modulation signal.

6. The ultra-narrow linewidth laser based on a whispering-gallery cavity as described in claim 5, characterized in that, The fiber collimator (113) is a lens type, prism type or hybrid structure.

7. The ultra-narrow linewidth laser based on a whispering-gallery cavity as described in claim 5, characterized in that, The optical frequency doubling module (300) is made of periodically polarized lithium niobate crystal material.

Images