Module for simultaneously providing carrier envelope offset frequency detection and super-continuum spectrum output

Abstract

The invention discloses a module for simultaneously providing carrier envelope offset frequency detection and super-continuum spectrum output in the technical field of laser science. The module comprises a mode-locked laser, an optical fiber array, a film lithium niobate chip, a photoelectric detection module and a signal processing circuit, the output end of the mode-locked laser is optically connected with the input end of the thin-film lithium niobate chip through the optical fiber array, and the output end of the thin-film lithium niobate chip is directly spatially output to the photosensitive surface of the photoelectric detection module. The output end of the photoelectric detection module is connected with the signal processing circuit through a signal patch cord, and the photoelectric detection module simultaneously realizes spectrum octave broadening output and high signal-to-noise ratio repetition frequency and carrier envelope offset frequency signal detection of the optical frequency comb under the condition of low pulse energy; and powerful support is provided for developing an optical frequency comb light source which is low in power consumption, small in size, high in stability and fully locked.

Description

Technical Field

[0001] The invention relates to the field of laser science and technology, and in particular to a module which simultaneously provides carrier envelope offset frequency detection and supercontinuum spectrum output. Background Art

[0002] The application of optical frequency combs relies on high-stability frequency locking. Currently, the comb teeth of optical frequency combs are generally stabilized by locking their repetition frequency and carrier-envelope offset frequency. The repetition frequency signal of the optical frequency comb can be directly measured by a high-speed photodetector, while the carrier-envelope offset frequency signal comes from the phase deviation between the carrier and its envelope during pulse propagation. Its detection and locking have always been the core and difficulty of optical comb research.

[0003] In the past two decades, the f-2f self-reference technology is usually used to detect the carrier envelope offset frequency signal, and feedback locking is performed through the digital phase-locked loop technology. If the spectrum broadening satisfies the condition of being greater than one octave, the f can be obtained by detecting the beat frequency between the high and low frequencies in the spectrum. ceo This technology requires phase-coherent cross-octave supercontinuum generation (SCG). The conventional method is to use highly nonlinear optical fiber for waveguide broadening and then use a self-referenced f-2f interferometer for interference detection. However, this method has problems such as difficulty in managing optical fiber dispersion, poor spectrum broadening effect, and bulky and complex detection equipment.

[0004] In recent years, the medium that generates supercontinuum (SC) has shown a trend of evolving from nonlinear optical fiber to nonlinear integrated optical waveguide. Among the many waveguide materials, lithium niobate has excellent second-order and third-order nonlinearity. It can obtain SC output greater than one octave on a waveguide of only centimeters in length, and the energy of the pump pulse only needs tens to hundreds of pJ. Therefore, in highly nonlinear integrated optical waveguides, high peak power can be achieved at x (2) The nonlinear effect enables efficient second harmonic generation (SHG), and sufficient excess pump power is generated by the χ (3) The nonlinear effect realizes cross-octave broadening of the spectrum. By performing SCG and SHG simultaneously and then carrying out an on-chip f-2f self-reference process, the carrier-envelope offset frequency signal can be directly detected to obtain a completely stable frequency comb. This method is simple and efficient, and is expected to solve the problems of high-precision detection and high signal-to-noise ratio locking of the carrier-envelope offset frequency signal of the optical frequency comb.

[0005] In 2021, Ewelina Obrzud and others from the Swiss Center for Electron Microscopy Technology combined Thin Film Lithium Niobate (TFLN) waveguides with silicon photodiodes to build a compact repetition frequency and carrier envelope offset frequency detection module. Low-energy pulses (~140pJ) were injected into the waveguide for direct on-chip f-2f interference, and the resulting frequency comb was completely stable with a high signal-to-noise ratio of 56dB. However, the SC generated by this method was not filtered, and all broadband optical signals entered the detector, which easily caused the detector to saturate. In addition, the SC generated in this scheme was not exported, and an additional SCG device was required for applications such as optical comb spectroscopy and laser frequency reference. In 2023, Scott A. Diddams of the National Institute of Standards and Technology of the United States combined dispersion management and chirped quasi-phase matching on the TFLN waveguide, achieving a spectral coverage range of 330 to 2400nm with a carrier envelope offset frequency intensity of 38dB at a pulse energy of only 90pJ. Although the detection of carrier envelope offset frequency was achieved, the signal-to-noise ratio was low, and frequency signal detection and SC output could not be achieved simultaneously. These research results show that TFLN is a material platform suitable for frequency signal detection and SCG applications in optical frequency combs, and is expected to replace the bulky standard f-2f interferometer for optical frequency comb locking, providing support for optical frequency combs to provide ultra-wide bandwidth spectral output and obtain excellent noise performance. Summary of the invention

[0006] The purpose of the present invention is to provide a module that simultaneously provides carrier envelope offset frequency detection and supercontinuum spectrum output, so as to solve the technical problems that the repetition frequency and carrier envelope offset frequency detection devices of the existing optical frequency combs are complex in structure, low in detection signal strength, high in cost, and cannot be directly applied to wide-spectrum output, and to simultaneously realize the spectral octave broadening output of the optical frequency comb and the high signal-to-noise ratio repetition frequency and carrier envelope offset frequency signal detection under low pulse energy conditions, so as to provide strong support for the development of low-power, small-volume, highly stable, fully-locked optical frequency comb light sources.

[0007] In order to achieve the above object, the technical solution of the present invention is as follows:

[0008] The present invention provides a module that simultaneously provides carrier envelope offset frequency detection and supercontinuum spectrum output, comprising a mode-locked laser, an optical fiber array, a thin-film lithium niobate chip, a photoelectric detection module and a signal processing circuit; the output end of the mode-locked laser is optically connected to the input end of the thin-film lithium niobate chip through the optical fiber array, the output end of the thin-film lithium niobate chip is directly spatially output to the photosensitive surface of the photoelectric detection module, and the output end of the photoelectric detection module is connected to the signal processing circuit through a signal adapter line to realize the detection and filtering output of the repetition frequency and the carrier envelope offset frequency.

[0009] As one aspect of a module that simultaneously provides carrier envelope offset frequency detection and supercontinuum output of the present invention, the optical fiber array is two polarization-maintaining optical fibers or a tapered lens optical fiber array that are arranged at equal intervals.

[0010] As one aspect of a module that simultaneously provides carrier envelope offset frequency detection and supercontinuum spectrum output according to the present invention, the optical fiber array includes a core, a sleeve disposed outside the core, and a coating layer disposed on the core.

[0011] As one aspect of a module of the present invention that simultaneously provides carrier envelope frequency deviation detection and supercontinuum spectrum output, the thin-film lithium niobate chip is provided with an optical connection end and a free space output end, the optical connection end is an inverted cone structure, and the coupling loss between the end face of the optical connection end and the optical fiber array is ≤6dB.

[0012] As one aspect of a module that simultaneously provides carrier envelope offset frequency detection and supercontinuum spectrum output of the present invention, the thin film lithium niobate chip includes a silicon dielectric layer, a silicon dioxide substrate support layer and a TFLN waveguide layer from bottom to top; the cross-section of the TFLN waveguide layer is trapezoidal or rectangular.

[0013] As one aspect of a module that simultaneously provides carrier envelope offset frequency detection and supercontinuum spectrum output according to the present invention, the TFLN waveguide layer is provided with an asymmetric optical waveguide coupler, and the asymmetric optical waveguide coupler is a TFLN waveguide with an asymmetric waveguide width design.

[0014] As one aspect of a module of the present invention that simultaneously provides carrier envelope frequency deviation detection and supercontinuum spectrum output, the TFLN waveguide includes a straight waveguide and a bent waveguide; the input end of the straight waveguide is connected to the core of an optical fiber of the optical fiber array, and the input end of the bent waveguide is connected to the core of another optical fiber of the optical fiber array.

[0015] As one aspect of a module of the present invention that simultaneously provides carrier envelope offset frequency detection and supercontinuum spectrum output, the photoelectric detection module uses a Si-PIN detector or a Si-APD detector to detect the repetition frequency of light pulses and the carrier envelope offset frequency; the bandwidth of the photoelectric detection module is between 100 MHz and 4 GHz, and the size of the photosensitive surface of the photoelectric detection module is 100 μm to 5 mm.

[0016] As one aspect of a module that simultaneously provides carrier envelope offset frequency detection and supercontinuum spectrum output according to the present invention, the bandwidth of the signal processing circuit is greater than the repetition frequency of the optical frequency comb pulse.

[0017] By adopting the above technical solution, the present invention has the following advantages:

[0018] The present invention provides a module that simultaneously provides carrier envelope offset frequency detection and supercontinuum spectrum output. By structurally designing a TFLN chip waveguide, the present invention solves the technical problems of complex structure, low detection signal intensity, high cost and inability to directly apply wide-spectrum output to the repetition frequency and carrier envelope offset frequency detection devices of the existing optical frequency comb, and realizes the generation of supercontinuum spectrum with a spectral range exceeding an octave under low pulse energy, and simultaneously performs second harmonic generation and supercontinuum spectrum generation on a single chip, realizes high-precision detection and high signal-to-noise ratio locking of carrier envelope offset frequency signals, and simultaneously provides ultra-wideband mid-infrared supercontinuum spectrum output, simplifies system links and locking difficulty, has the advantages of integration, small size, light weight, high reliability, high stability and the like, and can provide strong support for the development of low-power, small-size, highly stable and fully locked optical frequency comb light sources. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 A block diagram of a module for simultaneously providing carrier envelope offset frequency detection and supercontinuum spectrum output according to the present invention;

[0020] Figure 2 An embodiment of a module for simultaneously providing carrier envelope offset frequency detection and supercontinuum spectrum output according to the present invention;

[0021] Figure 3 Schematic diagram of the cross-sectional structure of the TFLN waveguide layer in an embodiment of the present invention;

[0022] Figure 4 This is a schematic diagram of the structure of a thin-film lithium niobate chip in an embodiment of the present invention;

[0023] Figure 5 is a repetition frequency spectrum diagram in an embodiment of the invention;

[0024] Figure 6 A carrier envelope offset frequency spectrum diagram according to an embodiment of the present invention;

[0025] Figure 7 This is a spectrum diagram of the ultra-wideband mid-infrared supercontinuum in an embodiment of the present invention. DETAILED DESCRIPTION

[0026] The technical solution of the present invention is described in detail below in conjunction with the drawings in the specification. It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprises" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device.

[0027] A module that simultaneously provides carrier envelope offset frequency detection and supercontinuum spectrum output can be used to simultaneously provide repetition frequency and carrier envelope offset frequency detection for a femtosecond optical frequency comb with a central wavelength of 1530 to 1600 nm, and realize ultra-wideband infrared supercontinuum spectrum output. The module that generates optical frequency comb repetition frequency, carrier envelope offset frequency detection and supercontinuum spectrum output includes a mode-locked laser 1, an optical fiber array 2, a thin film lithium niobate chip 3 (TFLN chip), a photoelectric detection module 4 and a signal processing circuit 5. Figure 1 , Figure 2 As shown. The output end of the mode-locked laser 1 is optically connected to the input end of the thin-film lithium niobate chip 3 through the optical fiber array 2, and the optical fiber array 2 provides femtosecond optical frequency comb pulse input and ultra-wide bandwidth infrared supercontinuum output. The output end of the thin-film lithium niobate chip 3 is directly spatially output to the photosensitive surface of the photoelectric detection module 4, and the output end of the photoelectric detection module 4 is connected to the signal processing circuit 5 through the signal adapter to realize the detection and filtering output of the repetition frequency and the carrier envelope offset frequency.

[0028] In addition, the module size that provides carrier envelope offset frequency detection and supercontinuum spectrum output at the same time is within 50mm*30mm*5mm. The optical fiber array 2 is two PM2000 polarization-maintaining optical fibers or tapered lens optical fiber arrays arranged at equal intervals. The fiber spacing between the two polarization-maintaining optical fibers is 125-130μm; the optical mode field size of the polarization-maintaining optical fiber is 1-10μm; the micro-lens at the front end of the tapered lens optical fiber has the functions of focusing and collimation, and the output light spot mode field size is 1-10μm. The optical fiber array is specifically as follows Figure 2 As shown, it includes a fiber core 23, a sleeve 21 arranged outside the fiber core 23, and a coating layer 22 arranged on the fiber core.

[0029] The thin film lithium niobate chip (TFLN chip) 3 has a length of 1 to 30 mm and a width of 1 to 30 mm, and includes a silicon dielectric layer, a silicon dioxide substrate support layer and a TFLN waveguide layer from bottom to top, wherein the silicon dioxide substrate support layer is used to protect the TFLN waveguide layer; the cross section of the TFLN waveguide layer is a trapezoid or a rectangle, as shown in FIG. Figure 3As shown, the TFLN waveguide layer is etched to form an optical waveguide, wherein the waveguide width w is 500-3000nm, the etching depth h is 200-400nm, and the waveguide inclination angle θ is 45-90°. The excellent linear electro-optical effect of lithium niobate material and the high refractive index difference of the TFLN platform are used to perform SCG and SHG simultaneously; the TFLN waveguide layer is provided with an asymmetric optical waveguide coupler, which is a TFLN waveguide with an asymmetric waveguide width design, and is used to realize wavelength division processing of high-frequency and low-frequency energy of supercontinuum. The wavelength range of the waveguide direct light is 700-900nm, which can realize the spatial direct output of the optical signal in the band, and the cross-coupling of the optical signal in the 900-2500nm band.

[0030] The thin-film lithium niobate chip 3 is provided with an optical connection end and a free space output end. The optical connection end is an inverted cone structure. The coupling loss between the end face of the optical connection end and the optical fiber array is ≤6dB.

[0031] The TFLN waveguide includes a straight waveguide and a curved waveguide; the input end of the straight waveguide is connected to the core 23 of one optical fiber of the optical fiber array 2, and the input end of the curved waveguide is connected to the core 23 of another optical fiber of the optical fiber array 2. The straight waveguide of the TFLN chip can generate a supercontinuum output of 700 to 2500 nm under pulse pumping with a pulse energy of less than 100 pJ and a pulse width of 100 fs.

[0032] The photoelectric detection module 4 uses a Si-PIN detector or a Si-APD detector to detect the repetition frequency of the light pulse and the carrier envelope offset frequency; the bandwidth of the photoelectric detection module is between 100MHz and 4GHz, and the photosensitive surface size of the photoelectric detection module 4 is 100μm to 5mm.

[0033] The signal processing circuit 5 is used to amplify and filter the carrier envelope offset frequency and repetition frequency signals. The bandwidth of the signal processing circuit 5 is greater than the repetition frequency of the optical frequency comb pulse.

[0034] The working principle of a module that provides both carrier envelope offset frequency detection and supercontinuum spectrum output is as follows:

[0035] The output end of the mode-locked laser 1 is connected to the input end of the thin-film lithium niobate chip 3 through an optical fiber array, the core 23 of one optical fiber of the optical fiber array 2 is connected to the input end 31 of the straight waveguide of the thin-film lithium niobate chip 3, the core 23 of another optical fiber of the optical fiber array 2 is connected to the input end 32 of the curved waveguide of the thin-film lithium niobate chip 3 at one end, and the other end is connected to an optical instrument such as a spectrometer for analyzing the received supercontinuum optical frequency components. An asymmetric optical waveguide coupler is designed on the TFLN chip 3, and light is spatially coupled into the waveguide from the input end 31 of the straight waveguide, a part of which is directly spatially output from the output end 34 through the straight waveguide, and the other part is coupled into the curved waveguide at the coupling connection 33 of the asymmetric optical waveguide coupler, and is spatially output from the other end 32 of the curved waveguide. Figure 4 The straight waveguide output end 34 of the TFLN chip 3 directly outputs and is aligned to the photodetector 4 through spatial coupling, and the output end of the photodetector 4 is connected to the signal processing circuit 5 through a signal adapter to achieve frequency division, filtering, amplification and locking of the repetition frequency and carrier envelope offset frequency signals.

[0036] The repetition frequency spectrum diagram of the present invention is as follows Figure 5 As shown, the repetition frequency detected by the photoelectric detector and the signal processing circuit is 125MHz, and the signal-to-noise ratio is greater than 70dB. Figure 6 As shown, the repetition frequency range detected by the photodetector and the signal processing circuit is 0-125MHz, and the signal-to-noise ratio is greater than 35dB. Figure 7 As shown, the spectrum broadening range is 900~2500nm.

[0037] Finally, it should be pointed out that although the present invention has been described with reference to the current specific embodiments, ordinary technicians in this technical field should realize that the above embodiments are only used to illustrate the present invention and are not used as a limitation of the present invention. Various equivalent changes or substitutions can be made without departing from the concept of the present invention. Therefore, as long as the changes and modifications to the above embodiments are within the essential spirit of the present invention, they will fall within the scope of the claims of the present invention.

Claims

1. A module that simultaneously provides carrier envelope offset frequency detection and supercontinuum spectrum output, characterized in that: It includes a mode-locked laser, an optical fiber array, a thin-film lithium niobate chip, a photoelectric detection module and a signal processing circuit; the output end of the mode-locked laser is optically connected to the input end of the thin-film lithium niobate chip through the optical fiber array, the output end of the thin-film lithium niobate chip is directly output to the photosensitive surface of the photoelectric detection module in space, and the output end of the photoelectric detection module is connected to the signal processing circuit through a signal adapter to realize the detection and filtering output of the repetition frequency and the carrier envelope offset frequency.

2. A module for simultaneously providing carrier envelope frequency deviation detection and supercontinuum spectrum output according to claim 1, characterized in that: The optical fiber array is two polarization-maintaining optical fibers or a tapered lens optical fiber array arranged at equal intervals.

3. A module for simultaneously providing carrier envelope frequency deviation detection and supercontinuum spectrum output according to claim 2, characterized in that: The optical fiber array includes a fiber core, a sleeve arranged outside the fiber core, and a coating layer arranged on the fiber core.

4. The module for simultaneously providing carrier envelope frequency deviation detection and supercontinuum spectrum output according to claim 3, characterized in that: The thin-film lithium niobate chip is provided with an optical connection end and a free space output end, the optical connection end is an inverted cone structure, and the coupling loss between the end face of the optical connection end and the optical fiber array is ≤6dB.

5. The module for simultaneously providing carrier envelope frequency deviation detection and supercontinuum spectrum output according to claim 4, characterized in that: The thin-film lithium niobate chip comprises a silicon dielectric layer, a silicon dioxide substrate support layer and a TFLN waveguide layer from bottom to top; the cross section of the TFLN waveguide layer is a trapezoid or a rectangle.

6. The module for simultaneously providing carrier envelope frequency deviation detection and supercontinuum spectrum output according to claim 5, characterized in that: The TFLN waveguide layer is provided with an asymmetric optical waveguide coupler, and the asymmetric optical waveguide coupler is a TFLN waveguide with an asymmetric waveguide width design.

7. The module for simultaneously providing carrier envelope frequency deviation detection and supercontinuum spectrum output according to claim 6, characterized in that: The TFLN waveguide includes a straight waveguide and a bent waveguide; the input end of the straight waveguide is connected to the core of an optical fiber of the optical fiber array, and the input end of the bent waveguide is connected to the core of another optical fiber of the optical fiber array.

8. The module for simultaneously providing carrier envelope frequency deviation detection and supercontinuum spectrum output according to claim 5, characterized in that: The photoelectric detection module adopts a Si-PIN detector or a Si-APD detector for detecting the repetition frequency of light pulses and the carrier envelope offset frequency; the bandwidth of the photoelectric detection module is between 100MHz and 4GHz, and the size of the photosensitive surface of the photoelectric detection module is 100μm to 5mm.

9. The module for simultaneously providing carrier envelope frequency deviation detection and supercontinuum spectrum output according to claim 1, characterized in that: The bandwidth of the signal processing circuit is greater than the repetition frequency of the optical frequency comb pulse.

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