An on-chip tunable femtosecond light source based on an integrated electro-optic frequency comb

Abstract

The present invention belongs to the field of lasers and discloses an on-chip tunable femtosecond light source based on an integrated electro-optical frequency comb. The light source comprises an intensity modulator (9), a first phase modulator (10) and a second phase modulator (11) which are integrated on the same chip and connected in sequence. Three radio frequency drive signals provide radio frequency drive signals to the intensity modulator, the first phase modulator and the second phase modulator respectively. The intensity modulator modulates the intensity of a wavelength-tunable continuous optical signal to generate a flat-top optical pulse sequence. The first phase modulator and the second phase modulator are used to perform quadratic phase modulation on the flat-top optical pulse sequence to generate a broadband electro-optical frequency comb. A dispersive optical fiber is used to perform pulse compression on the electro-optical frequency comb to generate femtosecond optical pulses. Compared with existing femtosecond pulse light source generation systems, the present invention has the advantages of simple structure, high integration, tunable pulse width and repetition frequency, and low cost.

Description

Technical Field

[0001] The present invention belongs to the field of lasers, and more specifically, relates to an on-chip tunable femtosecond light source based on an integrated electro-optical frequency comb. Background Art

[0002] Femtosecond optical pulses, characterized by high temporal resolution and high peak power, have been widely used in optical communications, ultrafast optics, and precision machining. Traditional femtosecond pulse sources are based on mode-locked lasers. While these lasers can produce high-quality femtosecond optical pulses, their systems are often bulky, complex, and consume high power. In contrast, on-chip femtosecond pulse sources offer advantages such as small size, high integration, and low power consumption, and hold broad application prospects in fields such as ultrahigh-speed optical communications.

[0003] Currently reported implementations of on-chip femtosecond pulse light sources include supercontinuum generation based on optical waveguides, soliton optical frequency combs based on microcavities, and semiconductor mode-locked lasers. With the rapid development of low-loss nano-waveguides, broadband supercontinuum across octaves can be achieved with picojoule-level energies. However, this approach requires a pulsed laser as a pump source, and the required system is relatively complex. Continuous light coupled to a high-quality optical microcavity can generate femtosecond optical pulses using a soliton optical frequency comb. However, due to the resonant conditions of the microcavity, the repetition frequency of the optical pulses is difficult to tune. Electrically pumped semiconductor mode-locked lasers have a high degree of integration, but their performance is easily affected by temperature changes, requiring a complex temperature control system. Summary of the Invention

[0004] To address the aforementioned deficiencies or improvements in the prior art, the present invention aims to provide an on-chip tunable femtosecond light source based on an integrated electro-optical frequency comb. This system utilizes a monolithic integrated modulator chip (i.e., an intensity modulator, a first phase modulator, and a second phase modulator integrated on the same chip). Three electro-optical modulators (the intensity modulator, the first phase modulator, and the second phase modulator) are driven by three RF signals to generate an electro-optical frequency comb. This comb then generates femtosecond optical pulses via a dispersive optical fiber. Compared to existing femtosecond pulse source generation systems, this system offers advantages such as a simple structure, high integration, tunable pulse width and repetition rate, and low cost. It addresses the issues of low integration, high cost, and poor tunability associated with femtosecond optical pulse generation technology.

[0005] To achieve the above objectives, according to one aspect of the present invention, an on-chip tunable femtosecond light source based on an integrated electro-optical frequency comb is provided, comprising: a continuous laser, a monolithically integrated modulator chip, a radio frequency signal source, a distribution function module, and a dispersive optical fiber. The monolithically integrated modulator chip comprises an intensity modulator, a first phase modulator, and a second phase modulator, which are integrated on the same chip and connected in sequence.

[0006] The RF signal source is used to generate a RF signal. After being processed by the distribution function module, the RF signal is divided into three RF drive signals. The three RF drive signals have the same frequency and phase, and the power of each RF drive signal can be adjusted. The three RF drive signals provide RF drive signals for the intensity modulator, the first phase modulator, and the second phase modulator, respectively.

[0007] The continuous laser is used to generate a continuous optical signal with tunable wavelength; the intensity modulator is used to perform intensity modulation on the continuous optical signal with tunable wavelength to generate a flat-top optical pulse sequence; the first phase modulator and the second phase modulator are used to perform quadratic phase modulation on the flat-top optical pulse sequence to generate a broadband electro-optical frequency comb; the dispersive optical fiber is used to perform pulse compression on the electro-optical frequency comb to generate femtosecond optical pulses.

[0008] As a further preferred embodiment of the present invention, the distribution function module includes a first power distributor, a second power distributor, a first radio frequency amplifier, a second radio frequency amplifier, a first phase shifter, and a second phase shifter;

[0009] The radio frequency signal generated by the radio frequency signal source is divided into a first radio frequency signal and a second radio frequency signal by the first power divider; the first radio frequency signal is input to the intensity modulator through a first radio frequency amplifier to provide a radio frequency driving signal for the intensity modulator;

[0010] The second RF signal is input into the second power divider through the second RF amplifier and is divided into a third RF signal and a fourth RF signal by the second power divider; the third RF signal is phase-shifted by the first phase shifter and input into the first phase modulator to provide an RF drive signal for the first phase modulator; the fourth RF signal is phase-shifted by the second phase shifter and input into the second phase modulator to provide an RF drive signal for the second phase modulator.

[0011] As a further preferred embodiment of the present invention, the intensity modulator, the first phase modulator and the second phase modulator are all thin film lithium niobate electro-optic modulators.

[0012] As a further preferred embodiment of the present invention, the dispersion optical fiber is a single-mode optical fiber, and the pulse width of the generated femtosecond optical pulse can be tuned by changing the length of the dispersion optical fiber.

[0013] According to another aspect of the present invention, a method for using the above-mentioned on-chip tunable femtosecond light source based on the integrated electro-optic frequency comb is provided, by adjusting the power of the three-way RF driving signal, thereby regulating the bandwidth and flatness of the electro-optic frequency comb.

[0014] According to another aspect of the present invention, a method for using the above-mentioned on-chip tunable femtosecond light source based on an integrated electro-optical frequency comb is provided, by changing the frequency of the radio frequency signal generated by the radio frequency signal source, thereby tuning the repetition frequency of the femtosecond light pulses.

[0015] According to another aspect of the present invention, a method for using the above-mentioned on-chip tunable femtosecond light source based on the integrated electro-optical frequency comb is provided, by changing the length of the dispersive optical fiber to tune the pulse width of the generated femtosecond light pulse.

[0016] Compared with the prior art, the above technical solutions proposed by the present invention can achieve the following:

[0017] Beneficial effects:

[0018] 1. The present invention is based on an on-chip tunable femtosecond light source with an integrated electro-optical frequency comb. A continuous laser generates a continuous optical signal with tunable wavelength, which is then transmitted to a modulator chip. The cascaded intensity modulator and phase modulator are driven by radio frequency signals to generate a broadband flat electro-optical frequency comb. Finally, pulse compression is performed through a dispersive optical fiber to achieve femtosecond optical pulse output.

[0019] The present invention integrates three modulators (i.e., an intensity modulator, a first phase modulator, and a second phase modulator) on a single chip and optically and electrically packages the modulator chip, improving device stability and ease of testing. Using three RF signals to drive these three electro-optical modulators produces a broadband electro-optical frequency comb, significantly improving system integration compared to traditional methods. These three RF drive signals have the same frequency and consistent phase, and the bandwidth and flatness of the generated electro-optical frequency comb can be increased by adjusting the power of any RF drive signal.

[0020] The present invention integrates three electro-optic modulators (EOMs)—an intensity modulator, a first phase modulator, and a second phase modulator—on the same chip. Three RF signals are used to drive these three EOMs to generate an EO frequency comb, which is then passed through a dispersive fiber to produce femtosecond optical pulses. This realizes an on-chip tunable femtosecond light source based on an integrated EO frequency comb, offering advantages such as high integration and tunable pulse width and repetition rate. A continuous laser generates a wavelength-tunable EO signal, which is passed through a monolithic integrated modulator chip to produce a broadband flat EO frequency comb. The intensity modulator is used to generate a sequence of narrowband flat-top optical pulses. The first and second phase modulators perform quadratic phase modulation on the optical pulse sequence to produce a broadband flat EO frequency comb. Dispersion compensation is performed using a dispersive fiber, compressing the broadband flat EO frequency comb in the time domain to produce femtosecond optical pulses. The present invention utilizes a monolithic integrated modulator chip to generate a wideband, highly flat, tunable EO frequency comb. Dispersion compensation is then performed through a dispersive fiber to achieve femtosecond optical pulse output. The bandwidth and flatness of the generated electro-optical frequency comb can be improved by optimizing the DC bias point and driving RF signal power of the intensity modulator, and optimizing the driving RF signal power of the first and second phase modulators. The repetition rate of the generated electro-optical frequency comb and femtosecond pulses can be tuned by adjusting the frequency of the RF signal driving the monolithic integrated modulator chip (i.e., the RF signal from the RF signal source).

[0021] 2. The on-chip tunable femtosecond pulse light source based on an integrated electro-optical frequency comb provided by the present invention can change the frequency interval of the electro-optical frequency comb by changing the frequency of the radio frequency signal, so that the pulse width and repetition frequency of the generated femtosecond light pulses can be tuned; and by tuning the output wavelength of the continuous laser, the operating band of the femtosecond pulses can be changed, thereby being able to adapt to a variety of complex application requirements.

[0022] 3. The on-chip tunable femtosecond light source based on an integrated electro-optic frequency comb provided by this invention has excellent compatibility and can be seamlessly integrated into existing photonics devices and systems. It can also be combined with other integrated optical components to form complex on-chip optical systems. Furthermore, the on-chip tunable femtosecond optical pulse generation system based on an integrated electro-optic frequency comb is insensitive to temperature changes, eliminating the need for complex temperature control systems.

[0023] The on-chip tunable femtosecond light source based on the integrated electro-optic frequency comb in the present invention can generate broadband electro-optic frequencies by integrating three modulators on the same chip, and has the characteristics of high integration and tunability. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a schematic structural diagram of a tunable on-chip femtosecond pulse light source based on an integrated electro-optical frequency comb according to an embodiment of the present invention.

[0025] Figure 2: This is the electro-optical frequency comb spectrum diagram and femtosecond optical pulse time domain diagram with a repetition frequency of 10 GHz generated in Example 1 of the present invention; wherein, Figure 2 (a) in the figure corresponds to the electro-optical frequency comb spectrum. Figure 2 (b) in the figure corresponds to the time domain diagram of the femtosecond optical pulse.

[0026] Figure 3 This is the electro-optical frequency comb spectrum diagram and femtosecond optical pulse time domain diagram with a repetition frequency of 20 GHz generated in Example 2 of the present invention; wherein, Figure 3 (a) in the figure corresponds to the electro-optical frequency comb spectrum. Figure 3 (b) in the figure corresponds to the time domain diagram of the femtosecond optical pulse.

[0027] Figure 4 This is a time domain diagram of the femtosecond optical pulse generated in Example 3 of the present invention. DETAILED DESCRIPTION

[0028] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely for the purpose of explaining the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.

[0029] The on-chip tunable femtosecond optical pulse generation system based on an integrated electro-optical frequency comb in the present invention loads the radio frequency signal onto a wavelength-tunable optical signal through a monolithic integrated cascade electro-optical modulator, generates a broadband flat electro-optical frequency comb after electro-optical intensity modulation and phase modulation, compensates for its dispersion using a dispersive medium, and compresses it in the time domain to generate tunable femtosecond optical pulses.

[0030] like Figure 1 As shown, the on-chip tunable femtosecond optical pulse generation system based on the integrated electro-optical frequency comb includes: a continuous laser 8, a monolithic integrated modulator chip, a radio frequency signal source 1, a first power divider 2, a first radio frequency amplifier 5, a second radio frequency amplifier 3, a second power divider 4, a first phase shifter 6, a second phase shifter 7, and a dispersive optical fiber 12; wherein the monolithic integrated modulator chip is based on thin-film lithium niobate material and includes an intensity modulator 9, a first phase modulator 10, and a second phase modulator 11 connected in sequence;

[0031] The output end of the radio frequency signal source 1 is connected to the input end of the first power divider 2, and the radio frequency signal source 1 is used to generate a radio frequency signal;

[0032] The first radio frequency signal output by the first power divider 2 is input to the first radio frequency amplifier 5 , and the second radio frequency signal output by the first power divider 2 is input to the second radio frequency amplifier 3 ;

[0033] The output end of the second radio frequency amplifier 3 is connected to the input end of the second power divider 4, and the second radio frequency amplifier 3 amplifies the second radio frequency signal;

[0034] The third radio frequency signal output by the second power divider 4 is input to the first phase shifter 6 , and the fourth radio frequency signal output by the second power divider 4 is input to the second phase shifter 7 ;

[0035] The output end of the first radio frequency amplifier 5 is connected to the electrical input end of the intensity modulator 9, and the first radio frequency amplifier 5 amplifies the first radio frequency signal;

[0036] The output end of the first phase shifter 6 is connected to the electrical input end of the phase modulator 10, and the first phase shifter 6 is used to adjust the phase of the radio frequency signal applied to the first phase modulator 10;

[0037] The output end of the second phase shifter 7 is connected to the electrical input end of the second phase modulator 11, and the second phase shifter 7 is used to adjust the phase of the radio frequency signal applied to the second phase modulator 11;

[0038] The continuous laser 8 is connected to the optical input end of the intensity modulator 9, and the continuous laser 8 is used to generate a continuous optical signal with tunable wavelength;

[0039] The optical output end of the intensity modulator 9 is connected to the optical input end of the first phase modulator 10. The intensity modulator 9 performs electro-optical intensity modulation on the wavelength-tunable continuous optical signal to generate a narrow-band flat-top optical pulse sequence.

[0040] The optical output end of the first phase modulator 10 is connected to the optical input end of the second phase modulator 11, and the phase modulator performs quadratic phase modulation on the optical pulse sequence to generate a broadband flat electro-optical frequency comb;

[0041] The optical output end of the second phase modulator 11 is connected to the dispersive optical fiber 12 , which performs dispersion compensation on the broadband flattened electro-optical frequency comb and compresses it in the time domain, thereby generating femtosecond optical pulses.

[0042] The bandwidth and flatness of the generated electro-optical frequency comb can be improved by optimizing the DC bias point and driving RF signal power of the intensity modulator 9 and optimizing the driving RF signal power of the first phase modulator 10 and the second phase modulator 11.

[0043] Example 1

[0044] In this embodiment, continuous laser 8 generates a continuous optical signal with a wavelength of 1550 nm, and RF signal source 1 generates an RF signal with a frequency of 10 GHz. Intensity modulator 9 operates at a quadrature bias point, driving the RF signal power to 23 dBm. The drive signal powers of first phase modulator 10 and second phase modulator 11 are both 36 dBm, and the phases of the three RF drive signals are aligned. Dispersive fiber 12 is a 300 m long single-mode fiber.

[0045] This embodiment uses a 10 GHz radio frequency signal to drive the modulator chip to generate an electro-optical frequency comb (output from the optical output end of the second phase modulator 11) spectrum, such as Figure 2 As shown in (a); the time domain diagram of the femtosecond light pulse finally generated after passing through the dispersion fiber 12, as shown in Figure 2 As shown in (b) in . Figure 2 As shown in (a), a 10 GHz RF signal is loaded onto the optical signal output by the continuous laser 8 through a monolithic integrated modulator chip, generating a flat broadband electro-optical frequency comb with a repetition frequency of 10 GHz. Figure 2 As shown in (b), the obtained electro-optical frequency comb with a repetition frequency of 10 GHz is dispersion compensated by passing through a 300 m long dispersion optical fiber 12, and is compressed in the time domain to generate femtosecond pulses with a pulse width of 919 fs.

[0046] Example 2

[0047] In this embodiment, continuous laser 8 generates a continuous optical signal with a wavelength of 1550 nm, and RF signal source 1 generates an RF signal with a frequency of 20 GHz. Intensity modulator 9 operates at a quadrature bias point, driving the RF signal power to 21 dBm. The drive signal power of first phase modulator 10 and second phase modulator 11 are both 35 dBm, and the phases of the three RF drive signals are aligned. Dispersive fiber 12 is a 150 m long single-mode fiber.

[0048] This embodiment uses a 20 GHz radio frequency signal to drive the modulator chip to generate an electro-optical frequency comb (output from the optical output end of the second phase modulator 11) spectrum, such as Figure 3 As shown in (a); the time domain diagram of the femtosecond light pulse finally generated after passing through the dispersion fiber 12, as shown in Figure 3 As shown in (b) in . Figure 3 As shown in (a), a 20 GHz RF signal is loaded onto the optical signal output by the continuous laser 8 through a monolithic integrated modulator chip, generating a flat broadband electro-optical frequency comb with a repetition frequency of 20 GHz. Figure 3 As shown in (b), the obtained electro-optical frequency comb with a repetition frequency of 20 GHz is dispersion compensated by passing through a 150 m long dispersion optical fiber 12, and is compressed in the time domain to generate femtosecond pulses with a pulse width of 670 fs.

[0049] Example 3

[0050] The difference between Example 3 and Example 2 is that the length of the dispersion optical fiber 12 is 100m. The generated femtosecond optical pulse time domain diagram is as follows: Figure 4 As shown, the pulse width of the femtosecond light pulse generated in this example is 753 fs.

[0051] The above embodiment takes a monolithic integrated modulator chip based on thin film lithium niobate as an example. In addition to thin film lithium niobate materials, other optoelectronic materials with similar functions can also be used to form a monolithic integrated modulator chip.

[0052] It will be easily understood by those skilled in the art that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. An on-chip tunable femtosecond light source based on an integrated electro-optical frequency comb, characterized in that: include: A continuous laser (8), a monolithic integrated modulator chip, a radio frequency signal source (1), a distribution function module, and a dispersion optical fiber (12), wherein the monolithic integrated modulator chip includes an intensity modulator (9), a first phase modulator (10), and a second phase modulator (11) integrated on the same chip and connected in sequence, wherein: The distribution function module includes a first power distributor (2), a second power distributor (4), a first radio frequency amplifier (5), a second radio frequency amplifier (3), a first phase shifter (6), and a second phase shifter (7); the radio frequency signal generated by the radio frequency signal source (1) is divided into a first radio frequency signal and a second radio frequency signal through the first power distributor (2); the first radio frequency signal is input to the intensity modulator (9) through the first radio frequency amplifier (5), and provides a radio frequency driving signal for the intensity modulator (9); the second radio frequency signal is input to the second power distributor (4) through the second radio frequency amplifier (3), and is divided into a third radio frequency signal and a fourth radio frequency signal by the second power distributor (4); the third radio frequency signal is phase-shifted by the first phase shifter (6) and input to the first phase modulator (10), and provides a radio frequency driving signal for the first phase modulator (10); The fourth radio frequency signal is phase-shifted by the second phase shifter (7) and then inputted into the second phase modulator (11), providing a radio frequency drive signal for the second phase modulator (11); the three radio frequency drive signals have the same frequency and phase, and the power of each radio frequency drive signal can be adjusted; The continuous laser (8) is used to generate a wavelength-tunable continuous optical signal; the intensity modulator (9) is used to perform intensity modulation on the wavelength-tunable continuous optical signal to generate a flat-top optical pulse sequence; the first phase modulator (10) and the second phase modulator (11) are used to perform quadratic phase modulation on the flat-top optical pulse sequence to generate a broadband electro-optical frequency comb; the dispersive optical fiber (12) is used to perform pulse compression on the electro-optical frequency comb to generate femtosecond optical pulses.

2. The on-chip tunable femtosecond light source based on an integrated electro-optical frequency comb according to claim 1, characterized in that: The intensity modulator (9), the first phase modulator (10) and the second phase modulator (11) are all thin-film lithium niobate electro-optical modulators.

3. The on-chip tunable femtosecond light source based on an integrated electro-optical frequency comb according to claim 1, characterized in that: The dispersion optical fiber (12) is a single-mode optical fiber, and the pulse width of the generated femtosecond light pulse can be tuned by changing the length of the dispersion optical fiber (12).

4. The method for using the on-chip tunable femtosecond light source based on the integrated electro-optical frequency comb according to any one of claims 1 to 3, characterized in that: By adjusting the power of the three RF drive signals, the bandwidth and flatness of the electro-optical frequency comb can be controlled.

5. The method for using the on-chip tunable femtosecond light source based on the integrated electro-optical frequency comb according to any one of claims 1 to 3, characterized in that: The repetition frequency of the femtosecond optical pulse is tuned and generated by changing the frequency of the radio frequency signal generated by the radio frequency signal source.

6. The method for using the on-chip tunable femtosecond light source based on the integrated electro-optical frequency comb according to claim 3, characterized in that: By changing the length of the dispersion optical fiber (12), the pulse width of the generated femtosecond optical pulse is tuned.

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