Chip atomic clock physical light path low-power temperature control system and method

Abstract

The application discloses a chip atomic clock physical light path low-power temperature control system and method, and belongs to the technical field of atomic clock temperature control. The system is based on an LCC base, and comprises a PCB heat resistance network component, a reverse-docking ceramic heating sheet, a temperature feedback module, a copper cesium bubble support, an aluminum nitride heat conduction plate and optical components. The PCB is in a suspended cantilever shape to form an elongated heat conduction path, the heating sheet is provided with a serpentine trace, and heat conduction adopts a double-path parallel structure. The method optimizes structure parameters by constructing a heat-structure collaborative finite element simulation model, increases heat resistance and reduces power consumption based on the Fourier heat conduction law and a heat resistance network model, maintains the laser at 70 DEG C plus or minus 10 DEG C and the cesium bubble support at greater than or equal to 45 DEG C in combination with temperature control closed loop, and realizes optical optimization through polarization adjustment, buffer gas filling and magnetic shielding. The application improves mechanical strength and thermal stability, the total power consumption of the physical light path is 33 mW under vacuum, and the application has low power consumption, high reliability and easy production, and is suitable for portable low-consumption scenes such as satellite navigation.

Description

Technical Field

[0001] This invention relates to the field of atomic clock technology, specifically to a low-power temperature control system and method for the physical optical path of a chip atomic clock. Background Technology

[0002] Chip-Scale Atomic Clocks (CSACs) are miniaturized atomic frequency standards based on the principle of Coherent Population Trapping (CPT). As a new generation of ultra-high precision frequency reference devices, CSACs have achieved revolutionary breakthroughs in size, weight, and power consumption (SWAP) compared to traditional optically pumped rubidium clocks and cesium beam clocks. They have become core basic devices in fields such as anti-jamming of Global Navigation Satellite Systems (GNSS), tactical communication, underwater exploration, time synchronization of financial transactions, and key nodes of the Internet of Things. All of these application scenarios have placed stringent requirements on the portability, low power consumption, and environmental adaptability of the devices.

[0003] The core physical unit (physical package) of a chip atomic clock mainly consists of a vertical cavity surface-emitting laser (VCSEL), an atomic gas cell containing alkali metal atoms such as rubidium and cesium, and a photodetector. Among them, the VCSEL is the core light source, and the frequency and power of the emitted laser are extremely sensitive to temperature changes. The temperature stability of the laser directly determines the overall frequency stability of the chip atomic clock. Therefore, building a highly stable, heat-efficient, and low-power constant-temperature working environment for the VCSEL is a core technical challenge in the design and development of chip atomic clocks, and also a key prerequisite for improving the working performance of atomic clocks and expanding application scenarios.

[0004] Currently, mainstream chip-based atomic clock products in the industry (such as Microchip's SA.45s) generally adopt a cantilever beam heating structure based on polyimide (PI) film to achieve ultra-low power consumption (approximately 125mW) temperature control. This structure fabricates the heating wire on an extremely thin PI film substrate, utilizing the extremely low heat capacity and thermal conductivity of the PI film to achieve the dual effects of rapid temperature control and low power consumption heating. However, this technical solution has several inherent drawbacks: First, the PI film material itself has poor mechanical strength, and the cantilever beam structure cannot withstand standard mechanical shocks, vibrations, and conventional assembly stresses, making it prone to damage during product assembly, transportation, and actual application, raising questions about its long-term reliability. Second, the thermal conductivity characteristics of the PI film substrate are difficult to accurately control, making it difficult to control the uniformity of the thermal field, which cannot provide a stable constant temperature environment for the laser and easily leads to fluctuations in the atomic clock frequency stability. Third, the fabrication process of this structure is complex, requiring high precision in the integration of the heating wire and the PI film, and subsequent debugging is difficult, which not only affects the product yield but also significantly increases the cost of mass production. Summary of the Invention

[0005] To address these issues, this invention provides a low-power temperature control system and method for the physical optical path of a chip atomic clock, solving the problems of poor mechanical strength, poor thermal uniformity, complex process debugging, and low reliability of existing chip atomic clock PI thin film temperature control structures.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a low-power temperature control system for the physical optical path of a chip atomic clock, comprising an LCC base, a thermal resistance network assembly, a heating element, a temperature feedback module, a copper cesium bulb bracket, an aluminum nitride heat-conducting plate, and optical components;

[0007] The thermal resistance network assembly uses the LCC base as the basis for mechanical mounting and electrical interface, and the thermal resistance network assembly is supported above the LCC base by a circuit board bracket and a gasket.

[0008] The heating element is mounted upside down on the free end of the thermal resistance network assembly. The temperature feedback module is integrated into the thermal resistance network assembly and is located adjacent to the VCSEL laser. The aluminum nitride heat-conducting plate is located between the heating element and the VCSEL laser. The copper cesium bubble bracket connects the thermal resistance network assembly and the cesium bubble chamber.

[0009] The optical component is assembled in the optical path, and the support structure of the optical component is thermally coupled to the temperature control system. The optical component includes an attenuator, a quarter-wave plate, and a photodetector (PD).

[0010] As a preferred solution for a low-power temperature control system for the physical optical path of a chip atomic clock, the thermal resistance network component is a rigid PCB thermal resistance network isolation structure, including a laser base circuit board made of FR4 material. One end of the laser base circuit board is fixed to the circuit board bracket, and the other end of the laser base circuit board is suspended in a cantilever shape, forming a slender and restricted heat conduction path. Several solder points are provided at the connection end between the thermal resistance network component and the LCC base as leakage hot spots.

[0011] As a preferred solution for a low-power temperature control system for the physical optical path of a chip atomic clock, the heating element consists of at least two ceramic heating elements. The ceramic heating elements are vertically inserted into the slots of the laser base circuit board and soldered together. The heating surface of the ceramic heating elements is in close contact with the heat sink of the VCSEL laser. The interior of the ceramic heating elements uses serpentine wiring to achieve uniform heating and counteract the induced magnetic field.

[0012] As a preferred solution for a low-power temperature control system for the physical optical path of a chip atomic clock, the temperature feedback module includes a thermistor circuit board and a temperature sensor integrated on the thermistor circuit board. The thermistor circuit board is disposed on the thermal resistance network component to realize the coupling between the temperature measuring point and the heat source.

[0013] As a preferred solution for a low-power temperature control system for the physical optical path of a chip atomic clock, the thermal resistance network component adopts an equal-length uniform thermal conduction path structure designed based on Fourier's law of heat conduction and the thermal resistance network model.

[0014] This invention also provides a low-power temperature control method for the physical optical path of a chip atomic clock, applied to the aforementioned low-power temperature control system for the physical optical path of a chip atomic clock, comprising the following steps:

[0015] S1: Construct a thermal-structural co-finite element analysis simulation model of the temperature control system. The simulation model includes a PCB thermal resistance network, a ceramic heating element, a copper cesium bulb support, and optical components. The simulation constraints are set as mechanical natural frequency and thermal uniformity, with the minimum steady-state heating power as the optimization objective.

[0016] S2: Based on the simulation model, optimize the PCB thickness, heating element layout and the geometry of the copper cesium bulb bracket, complete the quantitative structural design of the temperature control system and build the physical system;

[0017] S3: Controls the operation of the ceramic heating element, dividing the heat into two parallel paths for conduction. One path conducts the heat upwards to the VCSEL laser to stabilize the emission wavelength, while the other path conducts the heat radially through the copper cesium bubble support to the cesium bubble chamber to achieve the optimal atomic activity temperature.

[0018] S4: The temperature signal of the VCSEL laser area is collected in real time through the temperature feedback module. The heating power of the ceramic heating element is adjusted according to the temperature signal to maintain the working temperature of the VCSEL laser within the preset temperature range and the temperature of the cesium bulb support not lower than 45℃.

[0019] S5: Optical optimization of the physical optical path to achieve high contrast and narrow linewidth of the CPT signal, and to meet the frequency stability requirements of the chip atomic clock.

[0020] As a preferred method for low-power temperature control of the physical optical path of a chip atomic clock, in step S1, the simulation environment of the simulation model is an ideal vacuum environment, simulating all external surfaces exposed to air, and the convective heat transfer coefficient is set to 10 W·m. -2 ·K -1 and 1W·m -2 ·K -1 The ambient temperature is set to 25℃; in the simulation model, the target temperature of the VCSEL laser base is around 70℃, and the target temperature of the cesium bulb support is above 45℃ to ensure the vapor pressure of cesium atoms. Under vacuum conditions, the steady-state power consumption of the first ceramic heating element is controlled at 20mW, the steady-state power consumption of the second ceramic heating element is controlled at 10mW, and the total power consumption of the physical optical path is controlled at 33mW.

[0021] As a preferred method for low-power temperature control of the physical optical path of a chip atomic clock, in step S3, the two parallel heat conduction paths are:

[0022] Path A heating laser: ceramic heating element - aluminum nitride heat-conducting plate - PCB substrate - silver paste / bonding material - VCSEL laser base / PCB heat sink heat-conducting structure;

[0023] Path B heating cesium bubble chamber: ceramic heating plate - attenuation plate and 1 / 4 wave plate - copper cesium bubble support - glass cesium bubble chamber;

[0024] The heat dissipation / leakage path is: heating zone / thermal resistance network component free end - PCB material - PCB heat sink thermal conduction structure - LCC base - external environment. The main heat leakage is axial conduction at the solder joint at the connection end between the thermal resistance network component and the LCC base.

[0025] As a preferred method for low-power temperature control of the physical optical path of a chip atomic clock, in step S3, the thermal resistance is increased based on Fourier's law of heat conduction and a thermal resistance network model to reduce steady-state heating power consumption. Fourier's law of heat conduction is:

[0026]

[0027] In the formula, For heat flux density, For the thermal conductivity of the material, For temperature gradient;

[0028] The formula for calculating thermal resistance is:

[0029]

[0030] In the formula, For thermal resistance, This is the length of the heat conduction path. This refers to the thermally conductive cross-sectional area.

[0031] The formula for calculating heat flux is:

[0032]

[0033] In the formula, Heat flow is the heating power. This refers to the temperature difference between the heat source and the cold end; the thermal path length of the PCB thermal resistance network is increased. Increase the thermal resistance of the main heat leakage path Reduce heat flow This achieves a reduction in steady-state heating power consumption;

[0034] The VCSEL laser and the cesium bubble chamber heating area, which require maintaining high temperatures, are designated as the heat source end, while the external environment is designated as the cold end. The temperature difference between the heat source end and the cold end is specified. To fix this, the thermal path length of the PCB support structure is increased. Increase the thermal resistance of the main heat leakage path Increase total thermal resistance ,according to Reduce the heat loss from the heating element to the environment. Heating power under steady state Equal to total heat dissipation power ,Right now This reduces heat dissipation power and directly lowers steady-state heating power consumption.

[0035] As a preferred method for low-power temperature control of the physical optical path of a chip atomic clock, the specific steps of optical optimization in step S5 are as follows:

[0036] S51: Adjust the drive current, radio frequency modulation index and quarter-wave plate angle of the VCSEL laser to make the laser that excites the CPT phenomenon circularly polarized.

[0037] S52: Fill the cesium bubble chamber with a set ratio of buffer gas to narrow the CPT signal linewidth and suppress temperature frequency shift;

[0038] S53: Apply an external magnetic field to the temperature control system, set up a magnetic shielding structure, stabilize the quantized axis, and isolate external electromagnetic interference.

[0039] The present invention has the following advantages:

[0040] First, this invention uses a rigid PCB instead of a fragile PI film as the main body of the thermal resistance network, forming a stable hard support structure that can withstand standard mechanical impacts, vibrations, and conventional assembly stresses. This completely solves the defects of traditional structures that are easily damaged during assembly and transportation, and improves the product's environmental adaptability and long-term working reliability.

[0041] Second, the thermal control stability and uniformity are significantly optimized. By forming a slender heat conduction path through the PCB thermal resistance network, directional heating with inverted heating elements, and thermal diffusion design of the aluminum nitride heat conduction plate, the thermal field uniformity ΔT<0.1℃ is achieved, providing a stable constant temperature environment for the VCSEL laser that is resistant to external interference, and ensuring the frequency stability of the atomic clock from a thermal perspective.

[0042] Third, the low power consumption characteristics are maintained and optimized. The heat conduction structure is designed based on Fourier's heat conduction law and thermal resistance network model. The heat dissipation thermal resistance is actively increased to reduce steady-state heat loss. The total power consumption of the physical optical path in vacuum is only 33mW. While improving performance in many aspects, the power consumption is controlled at a highly competitive level.

[0043] Fourth, it achieves efficient single-point heating and global temperature control. The single-point heat source design of the inverted ceramic heating element provides heat to the laser and cesium bubble chamber simultaneously through dual parallel heat conduction paths. The laser heating has a higher priority, which greatly reduces the frequency lock-in time of the optical path power-on start-up and meets the short-time lock-in requirements of quantum frequency standard under MEMS process.

[0044] Fifth, the production and debugging difficulties are significantly reduced. The PCB structure prepared using standard electronic processes is easy to assemble and has good performance consistency. It replaces the complex PI film cantilever beam structure, effectively improving product yield and reducing mass production costs and subsequent debugging difficulties.

[0045] Sixth, the system has strong integration and adaptability. The optical components, temperature feedback module and heat conduction structure of the temperature control system are integrated into the design. The optical component support structure is thermally coupled to the temperature control system. The temperature sensor is tightly coupled to the heat source, realizing high-precision and fast response of the temperature control closed loop, which is adapted to the development needs of miniaturization and integration of chip atomic clocks. Attached Figure Description

[0046] To more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings in the following description are merely exemplary, and those skilled in the art can derive other embodiments based on the provided drawings without creative effort.

[0047] The structures, proportions, sizes, etc. illustrated in this specification are only for the purpose of assisting those skilled in the art in understanding and reading the content disclosed herein, and are not intended to limit the conditions under which the present invention can be implemented. Therefore, they have no substantial technical significance. Any modifications to the structure, changes in the proportions, or adjustments to the size, without affecting the effects and objectives that the present invention can produce, should still fall within the scope of the technical content disclosed in the present invention.

[0048] Figure 1 This is an exploded view of the low-power temperature control system for the physical optical path of the chip atomic clock provided in an embodiment of the present invention;

[0049] Figure 2 This is a flowchart of a low-power temperature control method for the physical optical path of a chip atomic clock provided in an embodiment of the present invention.

[0050] Figure 3 This is a thermal simulation diagram of the low-power temperature control structure with rigid support of thermal resistance network provided in the embodiments of the present invention.

[0051] Figure 4 This is a design analysis diagram of the physical optical path PCB chassis heat conduction structure provided in the embodiments of the present invention;

[0052] Figure 5 This is a schematic diagram illustrating the frequency stability of the low-power temperature control structure of the solid rigid support thermal resistance network provided in this embodiment of the invention. Detailed Implementation

[0053] The following specific embodiments illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0054] See Figure 1 This invention provides a low-power temperature control system for the physical optical path of a chip atomic clock, including an LCC base, a thermal resistance network (RTN) assembly, a heating element, a temperature feedback module, a copper cesium bulb support, an aluminum nitride heat-conducting plate, and optical components. The RTN assembly uses the LCC base as the mechanical mounting and electrical interface foundation, and is supported above the LCC base by a circuit board bracket and a gasket. The heating element is mounted upside down on the free end of the RTN assembly. The temperature feedback module is integrated into the RTN assembly and is located adjacent to the VCSEL laser. The aluminum nitride heat-conducting plate is located between the heating element and the VCSEL laser. The copper cesium bulb support connects the RTN assembly and the cesium bulb chamber. The optical components are assembled in the optical path, and the support structure of the optical components is thermally coupled to the temperature control system. The optical components include an attenuator, a quarter-wave plate, and a photodetector (PD).

[0055] The LCC base serves as the fundamental load-bearing structure, providing a reference for the mechanical fixation and electrical connection of the entire temperature control system, preventing foundation vibration from affecting the stability of the thermal field and optical path. Placing the heating element close to the VCSEL laser achieves close coupling between the heat source and the core temperature control object, reducing heat transfer loss. The aluminum nitride heat-conducting plate utilizes its high thermal conductivity (170-230W / mk) to achieve uniform heat diffusion, preventing localized overheating of the laser. The copper cesium bulb support leverages copper's high thermal conductivity (401W / mk) to achieve efficient heat conduction. The optical component support structure is thermally coupled to the temperature control system, preventing deformation of optical components due to temperature differences and ensuring the stability of the CPT optical path.

[0056] In this embodiment, the thermal resistance network component is a rigid PCB thermal resistance network isolation structure, including a laser base circuit board made of FR4 material. One end of the laser base circuit board is fixed to the circuit board bracket, and the other end of the laser base circuit board is suspended in a cantilever shape, forming a slender and restricted heat conduction path. Several solder joints are provided at the connection end between the thermal resistance network component and the LCC base as leakage hot spots.

[0057] Specifically, FR4 epoxy board (thermal conductivity 0.25-0.35W / mk) is selected as the material for the laser base circuit board, combining rigid mechanical properties with low thermal conductivity. The rigid structure can withstand standard mechanical impacts, vibrations, and assembly stresses, solving the problem of poor mechanical strength of traditional PI films. The cantilevered design makes the heat conduction path long and restricted. According to Fourier's law of heat conduction and the thermal resistance network model, the longer the heat conduction path, the greater the thermal resistance and the smaller the heat flow, which can significantly increase the heat dissipation thermal resistance from the heating area to the environment and reduce steady-state heat loss. The solder joints at the connection end are the main leakage hotspots. By controlling the number of solder joints, the number of parallel heat leakage paths is reduced, avoiding a significant decrease in the total thermal resistance. At the same time, concentrating the leakage hotspots at the fixed end makes the thermal field of the heating area more stable and reduces the interference of heat leakage on the laser temperature.

[0058] In this embodiment, the heating element is at least two ceramic heating elements. The ceramic heating elements are vertically inserted into the slots of the laser base circuit board and soldered. The heating surface of the ceramic heating elements is in close contact with the heat sink of the VCSEL laser. The ceramic heating elements have serpentine wiring inside to achieve uniform heating and counteract the induced magnetic field.

[0059] Specifically, the ceramic heating element possesses high temperature resistance and good thermal stability. Its vertical insertion and welding method achieves mechanical fixation and thermal tight coupling with the PCB structure, reducing heat contact loss. The heating surface is in close contact with the laser heat sink, allowing heat to be directly conducted to the laser, improving heat transfer efficiency. Using at least two heating elements enables graded power adjustment, adapting to the different temperature control requirements of the laser and the cesium bubble chamber. The internal serpentine wiring ensures uniform distribution of the heating area, guaranteeing consistent heating surface temperature and providing a uniform thermal environment for the laser, thus meeting thermal uniformity requirements. On the one hand, the current directions of the serpentine circuit cancel each other out, which can eliminate the induced magnetic field generated during the heating process, avoid magnetic field interference with the quantum axis of the atomic clock, and ensure the stable excitation of the CPT phenomenon.

[0060] In this embodiment, the temperature feedback module includes a thermistor circuit board and a temperature sensor integrated on the thermistor circuit board. The thermistor circuit board is disposed on the thermal resistance network component to realize the coupling between the temperature measuring point and the heat source.

[0061] Specifically, by placing the thermistor circuit board on the thermal resistance network assembly and achieving tight coupling between the temperature sensing point and the heat source, the temperature sensor can acquire the real temperature near the laser in real time, reducing the temperature difference between the sensing point and the heat source and improving the accuracy of temperature detection. The close coupling also shortens the temperature signal transmission path, making the temperature control loop respond faster. When the laser temperature fluctuates slightly, the temperature feedback module can quickly capture and transmit the signal, providing a basis for timely adjustment of the heating power, ensuring the stability of the laser's operating temperature, and thus maintaining the stability of the laser frequency and power.

[0062] In this embodiment, the thermal conductivity structure of the thermal resistance network component adopts an equal-length uniform thermal conductivity path structure designed based on Fourier's law of heat conduction and the thermal resistance network model.

[0063] Specifically, Fourier's law of heat conduction This indicates that heat flux density is proportional to temperature gradient, and the thermal resistance in the thermal resistance network model... Heat flow The uniform heat conduction path structure ensures that the heat conduction path of the laser is of consistent length and has a uniform cross-sectional area, ensuring that the thermal resistance of each path is the same. This prevents heat from concentrating locally or dissipating too quickly during conduction, thus avoiding uneven thermal field. At the same time, this design avoids the thermal resistance "short circuit" problem caused by inconsistent path lengths in traditional heat conduction structures, ensuring the effectiveness of the thermal resistance network design. This allows the design intention of increasing thermal resistance and reducing power consumption by increasing the length of the heat conduction path to be realized. In addition, the uniform heat conduction path can improve the mechanical stability of the structure and avoid structural deformation caused by uneven stress.

[0064] See Figure 2 This invention also provides a low-power temperature control method for the physical optical path of a chip atomic clock, applied to the aforementioned low-power temperature control system for the physical optical path of a chip atomic clock, comprising the following steps:

[0065] S1: Construct a thermal-structural co-factor finite element analysis simulation model of the temperature control system. The simulation model includes a PCB thermal resistance network, a ceramic heating element, a copper cesium bulb support, and optical components. The simulation constraints are set as the mechanical natural frequency and thermal uniformity, with the minimum steady-state heating power as the optimization objective.

[0066] Constructing a thermal-structural synergistic finite element analysis model can simultaneously simulate the system's thermal conduction and mechanical structural characteristics, achieving synergistic optimization of thermal and mechanical properties. This avoids the problems of insufficient mechanical strength due to single thermal optimization or reduced thermal control efficiency due to single mechanical optimization. Incorporating core components such as the PCB thermal resistance network and ceramic heating element into the model can recreate the heat transfer and mechanical stress conditions of the actual temperature control system; setting the mechanical natural frequency (>2000Hz) and thermal uniformity (… To ensure the system has sufficient vibration resistance to withstand vibrations and shocks during transportation and application, and to provide a stable and uniform constant temperature environment for the laser, the minimum steady-state heating power is the core requirement for the low-power design of the chip atomic clock. Simulation can quantitatively optimize the parameters of each component, replacing traditional empirical design and achieving predictable and optimizable design.

[0067] S2: Based on the simulation model, optimize the PCB thickness, heating element layout, and the geometry of the copper cesium bulb support to complete the quantitative structural design of the temperature control system and build the physical system.

[0068] PCB thickness directly affects its mechanical strength and thermal resistance. Increasing thickness improves mechanical strength but alters the thermal conductivity cross-sectional area, thus impacting thermal resistance. Simulation can help find the optimal balance between mechanical strength and thermal resistance. The heating element layout determines the location of the heat source; optimizing the layout allows for more precise heat transfer to the laser and cesium bulb chamber, reducing heat loss. The geometry of the copper cesium bulb support affects the length and cross-sectional area of ​​the heat transfer path; optimization improves heat transfer efficiency, enabling "single-point heating and global temperature control." Simulation enables quantitative design of various parameters, ensuring the performance of the physical system matches the design goals, improving product performance consistency, reducing debugging difficulty, and providing accurate process parameters for mass production.

[0069] S3: Controls the operation of the ceramic heating element, which divides the heat into two parallel paths. One path is conducted upward to the VCSEL laser to stabilize the emission wavelength, and the other path is conducted radially through the copper cesium bubble support to the cesium bubble chamber to achieve the optimal atomic activity temperature.

[0070] The emission frequency and power of VCSEL lasers are extremely sensitive to temperature. Temperature fluctuations can cause laser wavelength shifts, making it impossible to effectively excite the CPT phenomenon. Therefore, heat must be preferentially conducted to the laser to stabilize its operating temperature and ensure stable laser wavelength. The cesium bubble chamber needs to reach above 45°C to generate sufficient vapor pressure for cesium atoms, ensuring coherent interactions between atoms and achieving stable CPT signal output. A dual-parallel conduction method can simultaneously meet the temperature control requirements of both the laser and the cesium bubble chamber, avoiding the complexity and mutual interference of a dual-temperature zone system. Simultaneously, the high thermal conductivity of the copper support enables rapid heating of the cesium bubble chamber, shortening the frequency lock-in time after optical path startup. This single-point heating method concentrates the heat source, reducing power loss from multiple heat sources and ensuring low-power temperature control.

[0071] S4: The temperature feedback module collects the temperature signal of the VCSEL laser area in real time, and adjusts the heating power of the ceramic heating element according to the temperature signal to maintain the working temperature of the VCSEL laser within the preset temperature range and the temperature of the cesium bulb support not lower than 45℃.

[0072] Establishing a closed-loop temperature control system is crucial for maintaining temperature stability. The temperature feedback module collects temperature signals in real-time, serving as the basis for adjustment. When the laser temperature exceeds the preset range, the heating element power is reduced to decrease heat input. When the temperature falls below the preset range, the heating element power is increased to replenish heat, ensuring the laser always operates within the optimal temperature range of 70℃±10℃, guaranteeing stable laser performance. Maintaining a cesium bulb support temperature of no less than 45℃ is the minimum requirement to ensure cesium atomic vapor pressure. Due to the thermal conductivity of the copper support, the stable temperature of the laser region can provide continuous heat to the cesium bulb support through thermal conduction. Therefore, the temperature of the cesium bulb support can be indirectly maintained simply by adjusting the laser temperature, simplifying the temperature control logic and improving efficiency.

[0073] S5: Optical optimization of the physical optical path to achieve high contrast and narrow linewidth of the CPT signal, and to meet the frequency stability requirements of the chip atomic clock.

[0074] The optical characteristics of the optical path directly affect the excitation effect of the CPT phenomenon. Optical optimization can eliminate interference factors in the optical path, enabling the laser to stably and coherently interact with cesium atoms, thus improving the quality of the CPT signal. A high-contrast CPT signal can improve the frequency locking accuracy of the atomic clock, while a narrow linewidth can reduce frequency errors caused by signal fluctuations. Ultimately, this achieves the short-term and long-term frequency stability requirements of the chip atomic clock, meeting the requirement of stable operation for thousands of seconds. Performance metrics on a scale of magnitude.

[0075] See Figure 3 In this embodiment, in step S1, the simulation environment of the simulation model is an ideal vacuum environment, simulating all external surfaces exposed to air, and the convective heat transfer coefficient is set to 10 W·m. -2 ·K -1 and 1W·m -2 ·K -1 The ambient temperature is set to 25℃; in the simulation model, the target temperature of the VCSEL laser base is around 70℃, and the target temperature of the cesium bulb support is above 45℃ to ensure the vapor pressure of cesium atoms. Under vacuum conditions, the steady-state power consumption of the first ceramic heating element is controlled at 20mW, the steady-state power consumption of the second ceramic heating element is controlled at 10mW, and the total power consumption of the physical optical path is controlled at 33mW.

[0076] Specifically, the physical package of a chip atomic clock is typically located in a vacuum environment. Simulating an ideal vacuum environment can accurately reproduce the heat transfer mechanism in actual working scenarios (there is no convection heat transfer in a vacuum; heat dissipation occurs only through heat conduction and radiation). Setting two convection heat transfer coefficients can simulate the slight convection effects under different vacuum levels, improving the comprehensiveness of the simulation. The ambient temperature is set to 25℃ as the standard value for normal operating conditions, serving as the cold-end reference temperature for the thermal control system. The laser base's target temperature of around 70℃ is its optimal operating temperature, at which the laser's frequency and power are most stable. Cesium has a melting point of 39℃, and temperatures above 45℃ ensure sufficient vaporization of cesium atoms to generate enough vapor pressure to meet the atomic concentration requirements for the CPT phenomenon. Through simulation, the steady-state power consumption of the heating element was controlled to 20mW and 10mW respectively, resulting in a total heating power consumption of 30mW. Adding the laser's own 3mW power consumption, the total power consumption is 33mW, achieving an ultra-low power design, far superior to the 125mW of traditional PI thin-film structures. Furthermore, it still meets the temperature requirements of the dual-temperature-controlled object under low power consumption, verifying the effectiveness of the thermal resistance network design.

[0077] In this embodiment, in step S3, the two parallel heat conduction paths are as follows:

[0078] Path A heating laser: ceramic heating element - aluminum nitride heat-conducting plate - PCB substrate - silver paste / bonding material - VCSEL laser base / PCB heat sink heat-conducting structure;

[0079] Path B heating cesium bubble chamber: ceramic heating plate - attenuation plate and 1 / 4 wave plate - copper cesium bubble support - glass cesium bubble chamber;

[0080] The heat dissipation / leakage path is: heating zone / thermal resistance network component free end - PCB material - PCB heat sink thermal conduction structure - LCC base - external environment. The main heat leakage is axial conduction at the solder joint at the connection end between the thermal resistance network component and the LCC base.

[0081] The thermal conductivity of commonly used optical path materials selected for the comprehensive simulation of the temperature control structure is shown in Table 1 below:

[0082] Table 1 Thermal conductivity of commonly used optical path materials selected for comprehensive simulation of temperature control structure

[0083]

[0084] In path A, the aluminum nitride heat sink first evenly diffuses the concentrated heat from the ceramic heating element, then transfers it to the laser base via the PCB substrate and silver paste. The silver paste acts as a bonding material, simultaneously achieving mechanical fixation and heat conduction. The heat sink structure absorbs the small residual heat during laser operation, ensuring no local temperature fluctuations in the laser. In path B, the support structure of the attenuator and quarter-wave plate is thermally coupled to the temperature control system. Heat can be transferred through it to the copper cesium bulb support. The high thermal conductivity of copper quickly conducts heat to the glass cesium bulb chamber. The low thermal conductivity of glass (0.8-1.1 W / mk) reduces heat exchange between the chamber and the outside environment, maintaining a stable chamber temperature. The heat dissipation / heat leakage path is the only main path from the heating area to the environment. Heat leakage is concentrated at the solder joint at the connection between the thermal resistance network component and the LCC base. By designing a slender PCB heat conduction path, the thermal resistance of this path is increased, reducing heat leakage power. At the same time, thermal field disorder caused by the dispersion of heat leakage path is avoided, ensuring the temperature stability of the heating area and realizing the low power consumption design concept of "active heat control and passive heat insulation".

[0085] The main heat leakage points are the eight critical solder joints in the PCB thermal resistance network structure connected to the external CLCC base. Heat is conducted from the heated area (the free end of the thermal resistance network structure) through the PCB material itself, along the length of the thermal resistance network structure, to the PCB heat sink structure, and finally dissipated into the larger CLCC base and the external environment. The PCB thermal resistance network structure is not only a load-bearing structure and circuit carrier, but also a deliberately designed heat conduction path of a certain length. The heating element is located at the free end of the thermal resistance network structure, while the heat leakage point is located at the fixed end (root) of the thermal resistance network structure.

[0086] The fabrication and thermal optimization of the physical optical path PCB base heat conduction structure require optimization of the thermal resistance network structure and the thermal resistance network connecting to the base. A specific design scheme is attached. Figure 4 As shown:

[0087] Figure 4 The demonstration showcased three heat dissipation solutions using left, center, and right PCB chassis heat dissipation structures:

[0088] Left-side solution: The thermal resistance is evenly distributed across the pad and base to complete the thermal conduction structure. However, it does not consider the problem of "short-circuiting" and reducing the thermal resistance design after the area of ​​the pad itself is combined with the thermal conduction structure, which leads to the thermal conduction path following the shortest path. At the same time, although the thermal conduction path is long enough, the support structure is not stable enough and is prone to shaking in actual applications.

[0089] The middle path solution considers the placement of the pad. The thermal resistance of the laser is uniform and of equal length, but the thermal resistance network is simple and the path is relatively short. Further design optimization is needed.

[0090] Right-path solution: This solution fully integrates Fourier's law of heat conduction and the thermal resistance network model. The laser's heat conduction path is uniform and of equal length, and the thermal resistance network is rationally and uniformly designed, which is beneficial for low-power temperature control integration. This invention patent adopts the right-path solution as its application.

[0091] In step S3, the thermal resistance is increased based on Fourier's law of heat conduction and a thermal resistance network model to reduce steady-state heating power consumption. Fourier's law of heat conduction is:

[0092]

[0093] In the formula, For heat flux density, For the thermal conductivity of the material, For temperature gradient;

[0094] The formula for calculating thermal resistance is:

[0095]

[0096] In the formula, For thermal resistance, This is the length of the heat conduction path. This refers to the thermally conductive cross-sectional area.

[0097] The formula for calculating heat flux is:

[0098]

[0099] In the formula, Heat flow is the heating power. This refers to the temperature difference between the heat source and the cold end; the thermal path length of the PCB thermal resistance network is increased. Increase the thermal resistance of the main heat leakage path Reduce heat flow This reduces steady-state heating power consumption.

[0100] In this design, the VCSEL laser and the cesium bubble chamber heating area, which require maintaining high temperatures, are designated as the heat source end, while the external environment is designated as the cold end. The temperature difference between the heat source end and the cold end is specified. To fix this, the thermal path length of the PCB support structure is increased. Increase the thermal resistance of the main heat leakage path Increase total thermal resistance ,according to Reduce the heat loss from the heating element to the environment. Heating power under steady state Equal to total heat dissipation power ,Right now This reduces heat dissipation power and directly lowers steady-state heating power consumption.

[0101] Specifically, the heat source needs to be maintained at around 70°C (laser) and above 45°C (cesium bubble chamber), while the cold end requires an external environment of 25°C. Therefore, the temperature difference... This is a fixed value (the temperature difference between the laser and the environment is approximately 45°C). The PCB support structure is the main heat leakage path from the heat source to the cold end, and its thermal resistance... Total thermal resistance As a core component, increasing the length L of the PCB support structure can directly increase... This increases the total thermal resistance. According to the heat flow formula, fixed Down, The larger the heat transfer rate, the greater the heat loss. The smaller the value; under thermal steady-state conditions, the heating power of the heating element... The heat dissipation power lost to the environment must be fully compensated. ,Right now ,therefore The reduction in thermal resistance directly leads to a reduction in heating power. This design achieves low power consumption by actively increasing thermal resistance, which differs from the traditional approach of achieving low power consumption by reducing heat capacity. It ensures mechanical strength and thermal stability while maintaining low power consumption.

[0102] In this embodiment, the specific steps of optical optimization in step S5 are as follows:

[0103] S51: Adjusting the drive current, RF modulation index, and quarter-wave plate angle of the VCSEL laser ensures that the laser exciting the CPT phenomenon possesses circular polarization. Excitation of the CPT phenomenon requires the laser to have good circular polarization. Circularly polarized lasers can interact efficiently and coherently with the energy levels of alkali metal atoms, improving the contrast of the CPT signal. The drive current of the VCSEL laser determines the laser power and frequency, while the RF modulation index affects the laser's modulation characteristics. Coordinated adjustment of these two factors ensures precise frequency and stable power. The quarter-wave plate converts linearly polarized light into circularly polarized light; adjusting its angle precisely controls the polarization state conversion effect, ensuring that the output laser is standard circularly polarized light and avoiding CPT signal attenuation or distortion caused by polarization state deviation.

[0104] S52: A buffer gas with a predetermined ratio is filled into the cesium bubble chamber to narrow the CPT signal linewidth and suppress temperature frequency shift. Cesium atoms undergo thermal motion in their free state, causing the CPT signal linewidth to broaden and affecting the frequency stability of the atomic clock. Filling the chamber with a specific ratio of buffer gas restricts the thermal motion of cesium atoms, reducing collisions between atoms, thereby narrowing the CPT signal linewidth, improving signal sharpness, and making the atomic clock frequency lock more accurate. Simultaneously, the buffer gas reduces the temperature sensitivity of cesium atom energy levels, suppressing CPT signal frequency shifts caused by temperature changes, reducing the impact of temperature fluctuations on the atomic clock frequency stability, and working synergistically with the thermal control system to further improve overall stability.

[0105] S53: An external magnetic field is applied to the temperature control system, and a magnetic shielding structure is set up to stabilize the quantization axis and isolate external electromagnetic interference. The quantization axis of alkali metal atoms is easily deflected by magnetic fields, leading to disorder in the CPT coherent interaction. Applying an external C field (a constant weak magnetic field) can fix the quantization axis of the atoms, keeping them in the optimal coherent interaction state and ensuring the stability of the CPT signal. The application scenarios of chip atomic clocks involve complex external electromagnetic interference. The magnetic shielding structure can effectively isolate external magnetic fields and electromagnetic signals, preventing them from interfering with the coherent interaction of atoms and the working performance of the laser; at the same time, the magnetic shielding structure can also block the weak magnetic field generated inside the temperature control system, achieving dual isolation of internal and external magnetic fields and providing a stable magnetic environment for the excitation of the CPT phenomenon.

[0106] In this embodiment, the frequency stability (Allen variance) achievable through comprehensive testing of the chip-level atomic clock is shown in the attached figure. Figure 5 As shown, by Figure 5 It can be seen that the second stability of an atomic clock system is about 3.93E-11, the hundred-second stability is about 1.38E-11, the thousand-second stability is about 6.65E-12, and the long-term stability can reach 9.77E-12@10000s. This shows that after the optoelectronic integration of the system design of this invention is completed, it can work stably and reliably for a long time.

[0107] Although the present invention has been described in detail above with general descriptions and specific embodiments, modifications or improvements can be made to it, which will be obvious to those skilled in the art. Therefore, all such modifications or improvements made without departing from the spirit of the present invention fall within the scope of protection claimed by the present invention.

Claims

1. A low-power temperature control system for the physical optical path of a chip atomic clock, characterized in that, Includes LCC base, thermal resistance network assembly, heating element, temperature feedback module, copper cesium bulb bracket, aluminum nitride heat-conducting plate and optical components; The thermal resistance network assembly uses the LCC base as the basis for mechanical mounting and electrical interface, and the thermal resistance network assembly is supported above the LCC base by a circuit board bracket and a gasket. The heating element is mounted upside down on the free end of the thermal resistance network assembly. The temperature feedback module is integrated into the thermal resistance network assembly and is located adjacent to the VCSEL laser. The aluminum nitride heat-conducting plate is located between the heating element and the VCSEL laser. The copper cesium bubble bracket connects the thermal resistance network assembly and the cesium bubble chamber. The optical component is assembled in the optical path, and the support structure of the optical component is thermally coupled to the temperature control system. The optical component includes an attenuator, a quarter-wave plate, and a photodetector (PD).

2. The low-power temperature control system for the physical optical path of the chip atomic clock according to claim 1, characterized in that, The thermal resistance network assembly is a rigid PCB thermal resistance network isolation structure, including a laser base circuit board made of FR4 material. One end of the laser base circuit board is fixed to the circuit board bracket, and the other end of the laser base circuit board is suspended in a cantilever shape, forming a slender and restricted heat conduction path. Several solder points are provided at the connection end between the thermal resistance network assembly and the LCC base as leakage hot spots.

3. The low-power temperature control system for the physical optical path of the chip atomic clock according to claim 2, characterized in that, The heating element consists of at least two ceramic heating elements, which are vertically inserted into the slots of the laser base circuit board and soldered together. The heating surface of the ceramic heating element is in close contact with the heat sink of the VCSEL laser. The interior of the ceramic heating element uses serpentine wiring to achieve uniform heating and counteract the induced magnetic field.

4. The low-power temperature control system for the physical optical path of the chip atomic clock according to claim 1, characterized in that, The temperature feedback module includes a thermistor circuit board and a temperature sensor integrated on the thermistor circuit board. The thermistor circuit board is disposed on the thermal resistance network component to realize the coupling between the temperature measuring point and the heat source.

5. The low-power temperature control system for the physical optical path of the chip atomic clock according to claim 1, characterized in that, The thermal resistance network component adopts an equal-length uniform thermal conduction path structure designed based on Fourier's law of heat conduction and the thermal resistance network model.

6. A low-power temperature control method for the physical optical path of a chip atomic clock, applied to the low-power temperature control system for the physical optical path of a chip atomic clock as described in any one of claims 1-5, characterized in that, Includes the following steps: S1: Construct a thermal-structural co-finite element analysis simulation model of the temperature control system. The simulation model includes a PCB thermal resistance network, a ceramic heating element, a copper cesium bulb support, and optical components. The simulation constraints are set as mechanical natural frequency and thermal uniformity, with the minimum steady-state heating power as the optimization objective. S2: Based on the simulation model, optimize the PCB thickness, heating element layout and the geometry of the copper cesium bulb bracket, complete the quantitative structural design of the temperature control system and build the physical system; S3: Controls the operation of the ceramic heating element, dividing the heat into two parallel paths for conduction. One path conducts the heat upwards to the VCSEL laser to stabilize the emission wavelength, while the other path conducts the heat radially through the copper cesium bubble support to the cesium bubble chamber to achieve the optimal atomic activity temperature. S4: The temperature signal of the VCSEL laser area is collected in real time through the temperature feedback module. The heating power of the ceramic heating element is adjusted according to the temperature signal to maintain the working temperature of the VCSEL laser within the preset temperature range and the temperature of the cesium bulb support not lower than 45℃. S5: Optical optimization of the physical optical path to achieve high contrast and narrow linewidth of the CPT signal, and to meet the frequency stability requirements of the chip atomic clock.

7. The low-power temperature control method for the physical optical path of a chip atomic clock according to claim 6, characterized in that, In step S1, the simulation environment of the simulation model is an ideal vacuum environment, simulating all external surfaces exposed to air, and the convective heat transfer coefficient is set to 10 W·m. -2 ·K -1 and 1W·m -2 ·K -1 The ambient temperature is set to 25℃; in the simulation model, the target temperature of the VCSEL laser base is around 70℃, and the target temperature of the cesium bulb support is above 45℃ to ensure the vapor pressure of cesium atoms. Under vacuum conditions, the steady-state power consumption of the first ceramic heating element is controlled at 20mW, the steady-state power consumption of the second ceramic heating element is controlled at 10mW, and the total power consumption of the physical optical path is controlled at 33mW.

8. The low-power temperature control method for the physical optical path of a chip atomic clock according to claim 7, characterized in that, In step S3, the two parallel heat conduction paths are as follows: Path A heating laser: ceramic heating element - aluminum nitride heat-conducting plate - PCB substrate - silver paste / bonding material - VCSEL laser base / PCB heat sink heat-conducting structure; Path B heating cesium bubble chamber: ceramic heating plate - attenuation plate and 1 / 4 wave plate - copper cesium bubble support - glass cesium bubble chamber; The heat dissipation / leakage path is: heating zone / thermal resistance network component free end - PCB material - PCB heat sink thermal conduction structure - LCC base - external environment. The main heat leakage is axial conduction at the solder joint at the connection end between the thermal resistance network component and the LCC base.

9. The low-power temperature control method for the physical optical path of a chip atomic clock according to claim 8, characterized in that, In step S3, based on Fourier's law of heat conduction and the thermal resistance network model, the thermal resistance is increased to reduce steady-state heating power consumption. Fourier's law of heat conduction is: In the formula, For heat flux density, For the thermal conductivity of the material, For temperature gradient; The formula for calculating thermal resistance is: In the formula, For thermal resistance, This is the length of the heat conduction path. This refers to the thermally conductive cross-sectional area. The formula for calculating heat flux is: In the formula, Heat flow is the heating power. This refers to the temperature difference between the heat source and the cold end; the thermal path length of the PCB thermal resistance network is increased. Increase the thermal resistance of the main heat leakage path Reduce heat flow This achieves a reduction in steady-state heating power consumption; The VCSEL laser and the cesium bubble chamber heating area, which require maintaining high temperatures, are designated as the heat source end, while the external environment is designated as the cold end. The temperature difference between the heat source end and the cold end is... To fix this, the thermal path length of the PCB support structure is increased. Increase the thermal resistance of the main heat leakage path Increase total thermal resistance ,according to Reduce the heat loss from the heating element to the environment. Heating power under steady state Equal to total heat dissipation power ,Right now This reduces heat dissipation power and directly lowers steady-state heating power consumption.

10. The low-power temperature control method for the physical optical path of a chip atomic clock according to claim 6, characterized in that, In step S5, the specific steps of the optical optimization are as follows: S51: Adjust the drive current, radio frequency modulation index and quarter-wave plate angle of the VCSEL laser to make the laser that excites the CPT phenomenon circularly polarized. S52: Fill the cesium bubble chamber with a set ratio of buffer gas to narrow the CPT signal linewidth and suppress temperature frequency shift; S53: Apply an external magnetic field to the temperature control system, set up a magnetic shielding structure, stabilize the quantized axis, and isolate external electromagnetic interference.

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