A time-domain wavelength distribution femtosecond light source based on sum frequency

Abstract

The application discloses a time-domain wavelength distribution femtosecond light source based on sum frequency. The application is based on a high-repetition-frequency broadband light source, adopts synchronous triggering, time-spectrum coding, adjustable filtering and time-delay components, so that synchronized narrow-band spectrum femtosecond pulse signals and broadband spectrum femtosecond pulse signals with odd multiple repetition frequency relationship generate time-domain wavelength distribution sum frequency pulse signals, space structures are avoided through a fiber type gradient refractive index lens and a small sum frequency crystal, and all-fiber type time-domain wavelength distribution femtosecond pulse output can be realized.

Description

Technical Field

[0001] This invention relates to the field of femtosecond light sources, and particularly to a femtosecond light source based on sum-frequency time-domain wavelength distribution. Background Technology

[0002] Time-domain wavelength distribution laser technology can distribute lasers of different wavelengths in the time domain along with pulses, enabling high-speed data transmission. It has important applications in telecommunications, fiber optic networks, and high-speed data transmission for scientific research.

[0003] There are three typical methods to achieve time-domain wavelength distribution lasers: 1) Multiple lasers with different wavelengths [IEEE Photonics Journal, 2020, 12(6): 1-12]. This method is based on multiple continuous-wave lasers with different wavelengths, combined with a Mach-Zehnder interferometer to form pulses, and uses dispersive fiber to broaden the pulses. The dispersion of the fiber is used to separate the laser pulses of different wavelengths, thereby achieving time-domain wavelength distribution lasers. 2) Multi-wavelength lasers [CLEO, IEEE, 2001: 67-68]. This method uses Fabry-Perrie laser diodes and electro-optic modulators, and through dispersion broadening and dispersion compensation in the cavity, directly generates laser pulse trains with different wavelengths, thereby achieving time-domain wavelength distribution lasers. 3) Wideband mode-locked laser spectral segmentation method [Optics express, 2015, 23(3): 2174-2186]. This method utilizes the stability and ultra-wide spectral bandwidth of mode-locked lasers to generate relative time delays in the time domain through wavelength division multiplexing combined with a delay line, thereby achieving time-domain wavelength distribution lasers. Patent CN102830569B utilizes a wavelength division multiplexer and a tunable optical delay line to realize a time-wavelength interleaved optical sampling clock generation device, but this method requires precise adjustment of the time delay. Summary of the Invention

[0004] The problem this invention aims to solve is to realize a femtosecond light source with time-domain wavelength distribution. Based on a wide-bandwidth mode-locked laser, and employing sum-frequency technology and time-domain-spectral coding technology, this invention provides a femtosecond light source scheme with time-domain wavelength distribution.

[0005] The objective of this invention is achieved by at least one of the following technical solutions.

[0006] A time-domain wavelength distribution femtosecond light source based on sum-frequency includes a high repetition rate broadband femtosecond light source, an optical beam splitter, a signal generator, a frequency downsampling unit, a time-spectral coding unit, a filtering unit, a time delay unit, an optical beam combiner, and a sum-frequency unit;

[0007] A high-repetition-rate broadband femtosecond light source generates femtosecond pulse signals with a high repetition rate and a wide bandwidth spectrum, which are split into two signals by an optical beam splitter.

[0008] The first signal passes through a frequency down-conversion component to reduce its repetition frequency. The frequency down-conversion component modulates the signal with a synchronization signal through a signal generator. The signal generator is synchronously triggered by a high repetition rate broadband femtosecond light source, so that the repetition frequencies of the first signal and the second signal are in an odd multiple relationship. The first signal then passes through a time-spectral encoding component to encode the wide bandwidth spectral information of the signal into the time domain, and the pulses are closely connected but do not overlap in the time domain.

[0009] The second signal is filtered by a filter to produce a narrow bandwidth spectrum with an adjustable center wavelength; the second signal is then delayed by a delay component to adjust the delay amount so that its pulse time domain center is aligned with the pulse time domain center of the first signal with a low repetition frequency.

[0010] The two signals are re-combined by the optical beam combiner and input into the frequency summation unit, ultimately outputting a femtosecond pulse frequency summation signal with a time-domain wavelength distribution.

[0011] Furthermore, the center wavelength λ of the sum-frequency signal SFG Depends on the center wavelength λ of the time-domain overlap between the first and second signals a and λ b ,Right now The center wavelength λ of the second signal b The center wavelength of the time-domain overlap between the first and second signals is adjusted by the filtering component, and the time delay component is used to adjust the time-domain overlap.

[0012] Furthermore, the repetition frequency of the high repetition rate broadband femtosecond pulse signal is f1, the repetition frequency of the first signal after frequency reduction is f2, the repetition frequency of the second signal is f1, and the relationship between the repetition frequencies of the two signals is f1=N*f2, N≥3, where N is a positive odd number.

[0013] Furthermore, the center wavelength of the high-repetition-rate broadband femtosecond pulse signal is λ2, and the spectral bandwidth is Δλ. seed =λ3-λ1, where λ1 is the wavelength of the shortest spectral bandwidth and λ3 is the wavelength of the longest spectral bandwidth;

[0014] The center wavelength of the first signal is λ2, and the spectral bandwidth is Δλ. a =λ3-λ1, mapped in the time domain by the time-spectral coding component, and the pulses are closely connected but do not overlap in the time domain;

[0015] The center wavelength of the second signal is λ b , which is a narrow bandwidth spectrum generated by the filtering component, with an adjustable range of λ1 to λ3.

[0016] Furthermore, a first signal pulse with a low repetition frequency will be summed with N second signal pulses with a high repetition frequency to generate N summed frequency pulses. Finally, the repetition frequency of the time-domain pulse of the summed frequency signal is the same as the repetition frequency of the second signal, which is f1.

[0017] By adjusting the filtering components, when the center wavelength λ of the second signal is made... b When λ = 1, the smallest possible center wavelength λ of the sum-frequency signal is... SFG-min λ is the center wavelength of the first signal. a =λ1 and the second signal λ b =λ1 sum-frequency result when time domain overlap The largest possible center wavelength λ of the sum-frequency signal SFG-max λ is the center wavelength of the first signal. a =λ3 and the center wavelength λ of the second signal b =λ1 sum-frequency result when time domain overlap The wavelength bandwidth of the sum-frequency signal is then...

[0018] When the center wavelength λ of the second signal is made b When λ = 3, the smallest possible center wavelength λ of the sum-frequency signal. SFG-min λ is the center wavelength of the first signal. a =λ1 and the second signal λ b =λ3 sum-frequency results when time domain overlap The largest possible center wavelength λ of the sum-frequency signal SFG-max λ is the center wavelength of the first signal. a =λ3 and the center wavelength λ of the second signal b =λ3 sum-frequency results when time domain overlap The wavelength bandwidth of the sum-frequency signal is then...

[0019] Therefore, by adjusting the filtering components to change the center wavelength of the second signal, the wavelength range and bandwidth of the tunable sum-frequency signal that can be achieved can be deduced in the same way.

[0020] The final sum-frequency signal's time-domain pulses exhibit different wavelength distributions, and the repetition frequency of these wavelength distributions is the same as the repetition frequency of the first signal, which is f2.

[0021] Furthermore, the frequency reduction component is an acousto-optic modulator, which generates a square wave through a synchronously triggered signal generator to reduce the frequency of the first signal. The repetition frequency of the first signal is f2, so the repetition frequencies of the first signal and the second signal are in an odd multiple relationship.

[0022] The time-spectral encoding component is a dispersive fiber; the first signal is then pulse-widened by the dispersive fiber to encode wide-bandwidth spectral information into the time domain, and the pulses are closely connected but do not overlap in the time domain.

[0023] Furthermore, theoretically, the correspondence between the frequency domain and the time domain can be given by the following formula:

[0024]

[0025] Where u(z,T) is the pulse time-domain optical field. Let z be the pulse frequency domain optical field, T be the pulse transmission distance, β2 be the dispersion coefficient of the dispersive fiber, and α be the attenuation coefficient of the dispersive fiber. From the above formula, it can be seen that after passing through a sufficiently long dispersive fiber, the shape of the pulse time domain envelope is similar to the shape of the original spectral envelope, and the time-frequency correspondence satisfies ω=T / β2z.

[0026] Furthermore, the sum-frequency component consists of a pair of fiber-optic gradient refractive index lenses and a sum-frequency crystal. The fiber-optic lenses focus the two sum-frequency signal lights into the sum-frequency crystal and then couple them into the fiber. The sum-frequency crystal is fixed in a ceramic ferrule that can be used for fiber end-to-end splicing.

[0027] Compared with the prior art, the advantages of this invention are:

[0028] This invention is based on a high repetition rate broadband light source and employs synchronous triggering down-frequency reduction, time-spectral encoding, adjustable filtering, and time delay components to generate a sum-frequency pulse signal with a time-domain wavelength distribution from synchronous narrow-bandwidth spectral femtosecond pulse signals with odd-multiple repetition frequency relationships and wide-bandwidth spectral femtosecond pulse signals. By using fiber-optic gradient variable refractive index lenses and small sum-frequency crystals, spatial structures are avoided, enabling all-fiber time-domain wavelength distribution femtosecond pulse output. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the femtosecond light source structure based on sum-frequency time-domain wavelength distribution in an embodiment of the present invention;

[0030] Figure 2 This is a schematic diagram of the system principle spectral information in an embodiment of the present invention;

[0031] Figure 3 This is a schematic diagram of the system principle time domain information in an embodiment of the present invention. Detailed Implementation

[0032] The technical solutions are illustrated in the following description with specific figures to provide a full understanding of this application. However, this application can be implemented in many other ways different from those described herein, and similar extended embodiments made by those skilled in the art without inventive effort are all within the scope of protection of this invention.

[0033] The terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to be limiting of this specification. The singular forms “a,” “described,” and “the” as used in one or more embodiments of this specification and in the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise. It should also be understood that the term “and / or” as used in one or more embodiments of this specification refers to and includes any or all possible combinations of one or more associated listed items.

[0034] Example:

[0035] The sum-frequency-based time-domain wavelength distribution femtosecond light source of this invention employs, as follows: Figure 1 The system structure shown is used for specific implementation. The system includes a high-repetition-rate broadband femtosecond light source 1, an optical beam splitter 2, a signal generator 3, a frequency reduction component 4, a time-spectral encoding component 5, a filtering component 6, a time delay component 7, an optical beam combiner 8, and a sum-frequency component 9. The output of the high-repetition-rate broadband femtosecond light source 1 is connected to the input of the optical beam splitter 2. One output of the optical beam splitter 2 is sequentially connected to the frequency reduction component 4 and the time-spectral encoding component 5. The other output of the high-repetition-rate broadband femtosecond light source 1 is connected to the input of the signal generator 3. The output of the signal generator 3 is connected to the electrical signal terminal of the frequency reduction component 4. The other output of the optical beam splitter 2 is sequentially connected to the filtering component 6 and the time delay component 7. The outputs of the time-spectral encoding component 5 and the time delay component 7 are respectively connected to the two inputs of the optical beam combiner 8. The output of the optical beam combiner 8 is connected to the input of the sum-frequency component 9. The output of the sum-frequency component 9 is the output of the sum-frequency-based time-domain wavelength distribution femtosecond light source of this invention.

[0036] Figure 2 and Figure 3 These are schematic diagrams illustrating the system's spectral and temporal information, respectively.

[0037] In one specific embodiment, the high repetition rate broadband femtosecond source is a 1.5 μm erbium-doped fiber mode-locked laser with a repetition rate of f1 = 60 MHz, a center wavelength of λ2 = 1550 nm, and a spectral bandwidth of Δλ. seed =λ3-λ1=1600nm-1500nm=100nm, spectral and time-domain information as follows Figure 2 Figure a in the middle and Figure 3 As shown in Figure a.

[0038] The laser signal is split into two paths after passing through an optical beam splitter, which is a 1*2 port 50:50 fiber optic coupler.

[0039] The frequency reduction component is an acousto-optic modulator, which generates a square wave through a synchronously triggered signal generator to reduce the frequency of the first signal. The repetition frequency of the first signal is f2 = 20MHz, so the repetition frequencies of the first and second signals are odd multiples of each other. The time-spectral encoding component is a dispersive optical fiber. The first signal is then pulse-widened by the dispersive optical fiber, encoding the wide bandwidth spectral information into the time domain, and the pulses are closely connected but do not overlap in the time domain.

[0040] Theoretically, the correspondence between the frequency domain and the time domain can be given by the following formula:

[0041]

[0042] Where u(z,T) is the pulse time-domain optical field. Let z be the pulse frequency domain optical field, T be the pulse transmission distance, β2 be the dispersion coefficient of the dispersive fiber, and α be the attenuation coefficient of the dispersive fiber. From the above formula, it can be seen that after passing through a sufficiently long dispersive fiber, the shape of the pulse time domain envelope is similar to the shape of the original spectral envelope, and the time-frequency correspondence satisfies ω=T / β2z.

[0043] The spectral and temporal information of the first signal are as follows: Figure 2 Figure b in the middle and Figure 3 As shown in Figure b, its spectral information is the same as that of the high repetition rate broadband femtosecond light source. However, after its time-domain information is processed by the time-spectral coding component, its broadband spectral information is mapped onto the time domain. The spectral component at the leading edge of the pulse is λ1, the spectral component at the center of the pulse is λ2, and the spectral component at the trailing edge of the pulse is λ3. Its pulse shape is consistent with its spectral shape.

[0044] The second signal is filtered by a filter to produce a narrow bandwidth spectrum with an adjustable center wavelength. The center wavelength λ of the filtered narrow bandwidth spectrum is... b The adjustable range is λ1 to λ3; the second signal then undergoes a time delay adjustment component to align its pulse time domain center with the pulse time domain center of the first signal with a lower repetition frequency. The spectral and time domain information of the second signal is as follows: Figure 2 As shown in Figure c, the solid curve represents the center wavelength λ of the narrow bandwidth spectrum. b The spectrum when λ = 1, the dashed curve represents the center wavelength λ of the narrow bandwidth spectrum. b The spectrum when λ = 3. Assume the center wavelength λ of the narrow bandwidth spectrum of the second signal is... b When λ = 1, its time-domain information is as follows: Figure 3 As shown in Figure c.

[0045] The two signals are then combined into the sum-frequency unit via an optical combiner, which is a 1*2 port 50:50 fiber optic coupler.

[0046] The sum-frequency component consists of a pair of fiber-optic gradient refractive index lenses and a miniature sum-frequency crystal. The fiber-optic lenses focus the two sum-frequency signal beams onto the miniature sum-frequency crystal before coupling them into the optical fiber. The miniature sum-frequency crystal is fixed in a ceramic ferrule that can be used for fiber end-to-end splicing, avoiding spatial structures and resulting in a compact overall structure.

[0047] The center wavelength λ of the sum-frequency signal SFG Depends on the center wavelength λ of the time-domain overlap between the first and second signals a and λ b ,Right now The center wavelength λ of the second signal b The center wavelength of the time-domain overlap between the first and second signals is adjusted by the filtering component, and the time delay component is used to adjust the time-domain overlap.

[0048] In the frequency summing component, if the repetition frequency of the high repetition rate broadband femtosecond pulse signal is f1, the repetition frequency of the first signal after frequency reduction is f2, and the repetition frequency of the second signal is f1, the relationship between the repetition frequencies of the two signals is f1 = N * f2, where N ≥ 3, and N is a positive odd number. In this embodiment, N = 3, then a low repetition frequency first signal pulse will be summed with three high repetition frequency second signal pulses to generate three summed pulses. The repetition frequency of the final summed signal's time-domain pulse is the same as the repetition frequency of the second signal, which is 60MHz.

[0049] In one specific embodiment, by adjusting the filtering component, when the center wavelength λ of the second signal is made... b When λ1 = 1500nm, the smallest possible center wavelength λ of the sum-frequency signal is... SFG-min The center wavelength λ of the first signal a =λ1=1500nm and the second signal λ b =Sum-frequency result when λ1 = 1500nm time-domain overlap The largest possible center wavelength λ of the sum-frequency signal SFG-max The center wavelength λ of the first signal a =λ3=1600nm and the second signal λ b =Sum-frequency result when λ1 = 1500nm time-domain overlap The wavelength bandwidth of the sum-frequency signal is then...

[0050] The final sum-frequency signal exhibits different wavelength distributions in its time-domain pulses, with the repetition frequency of these wavelength distributions being the same as that of the first signal, at 20MHz. The spectral and time-domain information of the output sum-frequency signal is as follows: Figure 2 d-graph and Figure 3 As shown in Figure d.

[0051] In one specific embodiment, by adjusting the filtering component, when the center wavelength λ of the second signal is made... b When λ3 = 1600nm, the smallest possible center wavelength λ of the sum-frequency signal can be achieved. SFG-min The center wavelength λ of the first signal a =λ1=1500nm and the second signal λ b Sum-frequency results when λ3 = 1600nm time-domain overlap The largest possible center wavelength λ of the sum-frequency signal SFG -max is the center wavelength λ of the first signal. a =λ3=1600nm and the second signal λ b Sum-frequency results when λ3 = 1600nm time-domain overlap The wavelength bandwidth of the sum-frequency signal is then...

[0052] Therefore, by adjusting the filtering components to change the center wavelength of the second signal, the wavelength range and bandwidth of the adjustable sum-frequency signal that can be achieved can be obtained in the same way.

[0053] A femtosecond laser output based on sum-frequency time-domain wavelength distribution was achieved.

[0054] The above embodiments are one of the implementation methods of the present invention, but the implementation methods of the present invention are not limited to the embodiments and test examples. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A femtosecond light source based on sum-frequency time-domain wavelength distribution, characterized in that, It includes a high repetition rate broadband femtosecond light source, optical beam splitting components, signal generator, frequency downsampling components, time-spectral coding components, filtering components, time delay components, optical beam combining components, and frequency summing components; A high-repetition-rate broadband femtosecond light source generates femtosecond pulse signals with a high repetition rate and a wide bandwidth spectrum, which are split into two signals by an optical beam splitter. The first signal passes through a frequency down-conversion component to reduce its repetition frequency. The frequency down-conversion component modulates the signal with a synchronization signal through a signal generator. The signal generator is synchronously triggered by a high repetition rate broadband femtosecond light source, so that the repetition frequencies of the first signal and the second signal are in an odd multiple relationship. The first signal then passes through a time-spectral encoding component to encode the wide bandwidth spectral information of the signal into the time domain, and the pulses are closely connected but do not overlap in the time domain. The second signal is filtered by a filter to produce a narrow bandwidth spectrum with an adjustable center wavelength; the second signal is then delayed by a delay component to adjust the delay amount so that its pulse time domain center is aligned with the pulse time domain center of the first signal with a low repetition frequency. The two signals are re-combined by the optical beam combiner and input into the frequency summation unit, ultimately outputting a femtosecond pulse frequency summation signal with a time-domain wavelength distribution.

2. The femtosecond light source based on sum-frequency time-domain wavelength distribution according to claim 1, characterized in that... The center wavelength λ of the sum-frequency signal SFG Depends on the center wavelength λ of the time-domain overlap between the first and second signals a and λ b ,Right now The center wavelength λ of the second signal b The center wavelength of the time-domain overlap between the first and second signals is adjusted by the filtering component, and the time delay component is used to adjust the time-domain overlap.

3. The femtosecond light source based on sum-frequency time-domain wavelength distribution according to claim 2, characterized in that: The repetition frequency of the high repetition rate broadband femtosecond pulse signal is f1, the repetition frequency of the first signal after frequency reduction is f2, the repetition frequency of the second signal is f1, and the relationship between the repetition frequencies of the two signals is f1=N*f2, N≥3, where N is a positive odd number.

4. The femtosecond light source based on sum-frequency time-domain wavelength distribution according to claim 3, characterized in that: The center wavelength of the high-repetition-rate broadband femtosecond pulse signal is λ2, and the spectral bandwidth is Δλ. seed =λ3-λ1, where λ1 is the wavelength of the shortest spectral bandwidth and λ3 is the wavelength of the longest spectral bandwidth; The center wavelength of the first signal is λ2, and the spectral bandwidth is Δλ. a =λ3-λ1, mapped in the time domain by the time-spectral coding component, and the pulses are closely connected but do not overlap in the time domain; The center wavelength of the second signal is λ b , which is a narrow bandwidth spectrum generated by the filtering component, with an adjustable range of λ1 to λ3.

5. The femtosecond light source based on sum-frequency time-domain wavelength distribution according to claim 4, characterized in that, A first signal pulse with a low repetition frequency will be summed with N second signal pulses with a high repetition frequency to generate N summed frequency pulses. The repetition frequency of the time-domain pulse of the final summed frequency signal is the same as the repetition frequency of the second signal, which is f1. By adjusting the filtering components, when the center wavelength λ of the second signal is made... b When λ = 1, the smallest possible center wavelength λ of the sum-frequency signal is... SFG-min λ is the center wavelength of the first signal. a =λ1 and the second signal λ b =λ1 sum-frequency result when time domain overlap The largest possible center wavelength λ of the sum-frequency signal SFG-max λ is the center wavelength of the first signal. a =λ3 and the center wavelength λ of the second signal b =λ1 sum-frequency result when time domain overlap The wavelength bandwidth of the sum-frequency signal is then... When the center wavelength λ of the second signal is made b When λ = 3, the smallest possible center wavelength λ of the sum-frequency signal. SFG-min λ is the center wavelength of the first signal. a =λ1 and the second signal λ b =λ3 sum-frequency results when time domain overlap The largest possible center wavelength λ of the sum-frequency signal SFG-max λ is the center wavelength of the first signal. a =λ3 and the center wavelength λ of the second signal b =λ3 sum-frequency results when time domain overlap The wavelength bandwidth of the sum-frequency signal is then... Therefore, by adjusting the filtering components to change the center wavelength of the second signal, the wavelength range and bandwidth of the tunable sum-frequency signal that can be achieved can be deduced in the same way. The final sum-frequency signal's time-domain pulses exhibit different wavelength distributions, and the repetition frequency of these wavelength distributions is the same as the repetition frequency of the first signal, which is f2.

6. The femtosecond light source based on sum-frequency time-domain wavelength distribution according to claim 1, characterized in that, The frequency reduction component is an acousto-optic modulator, which generates a square wave through a synchronously triggered signal generator to reduce the frequency of the first signal.

7. The femtosecond light source based on sum-frequency time-domain wavelength distribution according to claim 6, characterized in that, In the frequency reduction component, the repetition frequency of the first signal is f2, and the repetition frequencies of the first signal and the second signal are in an odd multiple relationship.

8. The femtosecond light source based on sum-frequency time-domain wavelength distribution according to claim 1, characterized in that, The time-spectral encoding component is a dispersive fiber; the first signal is then pulse-widened by the dispersive fiber to encode wide-bandwidth spectral information into the time domain, and the pulses are closely connected but do not overlap in the time domain.

9. The femtosecond light source based on sum-frequency time-domain wavelength distribution according to claim 1, characterized in that, Theoretically, the correspondence between the frequency domain and the time domain can be given by the following formula: Where u(z,T) is the pulse time-domain optical field. Let z be the pulse frequency domain optical field, T be the pulse transmission distance, β2 be the dispersion coefficient of the dispersive fiber, and α be the attenuation coefficient of the dispersive fiber. From the above formula, it can be seen that after passing through a sufficiently long dispersive fiber, the shape of the pulse time domain envelope is similar to the shape of the original spectral envelope, and the time-frequency correspondence satisfies ω=T / β2z.

10. The femtosecond light source based on sum-frequency time-domain wavelength distribution according to claim 1, characterized in that, The sum-frequency component consists of a pair of fiber-optic gradient refractive index lenses and a sum-frequency crystal. The fiber-optic lenses focus the two sum-frequency signal beams into the sum-frequency crystal and then couple them into the fiber. The sum-frequency crystal is fixed in a ceramic ferrule that can be used for fiber end-to-end splicing.

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