On-chip tunable femtosecond light source based on integrated electro-optical frequency comb

Abstract

The invention belongs to the field of laser, and discloses an on-chip tunable femtosecond light source based on an integrated electro-optical frequency comb, which comprises an intensity modulator (9), a first phase modulator (10) and a second phase modulator (11) which are integrated on the same chip and are connected in sequence, the three paths of radio frequency driving signals respectively provide radio frequency driving signals for the intensity modulator, the first phase modulator and the second phase modulator; the intensity modulator performs intensity modulation on the wavelength-tunable continuous optical signal to generate a flat-topped optical pulse sequence; the first phase modulator and the second phase modulator are used for performing quadratic phase modulation on the flat-topped optical pulse sequence to generate a broadband electro-optical frequency comb; the dispersion optical fiber is used for carrying out pulse compression on the electro-optical frequency comb so as to generate femtosecond optical pulses. Compared with an existing femtosecond pulse light source generation system, the femtosecond pulse light source generation system has the advantages of being simple in structure, high in integration level, tunable in pulse width and repetition frequency, low in cost and the like.

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 have the characteristics of high temporal resolution and high peak power, and have been widely used in optical communications, ultrafast optics, precision machining and other fields. Traditional femtosecond pulse light sources are based on mode-locked lasers. Although these lasers can produce high-quality femtosecond optical pulses, their systems are often bulky, complex in structure and have high power consumption. In contrast, on-chip femtosecond pulse light sources have the advantages of small size, high integration and low power consumption, and have broad application prospects in ultra-high-speed optical communications and other fields.

[0003] The reported implementation schemes 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-optical waveguides, broadband supercontinuum across octaves can be achieved with picojoule-level energy. However, this scheme requires a pulsed laser as a pump source, and the required system is relatively complex. Continuous light is coupled to a high-quality optical microcavity, and femtosecond optical pulses can be generated through a soliton optical frequency comb. However, due to the resonance conditions of the microcavity, the repetition frequency of the optical pulse 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 and require a complex temperature control system. Summary of the invention

[0004] In view of the above defects or improvement needs of the prior art, the purpose of the present invention is to provide an on-chip tunable femtosecond light source based on an integrated electro-optical frequency comb, using a monolithic integrated modulator chip (i.e., an intensity modulator, a first phase modulator, and a second phase modulator integrated on the same chip), and based on three radio frequency signals, driving the intensity modulator, the first phase modulator, and the second phase modulator to generate an electro-optical frequency comb, and then generating femtosecond optical pulses through a dispersive optical fiber. Compared with the existing femtosecond pulse light source generation system, the present invention has the advantages of simple structure, high integration, tunable pulse width and repetition frequency, and low cost, and solves the problems of low integration, high cost, and poor tunability of femtosecond optical pulse generation technology.

[0005] To achieve the above object, 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 monolithic integrated modulator chip, a radio frequency signal source, a distribution function module, and a dispersive optical fiber, wherein the monolithic 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, wherein:

[0006] The RF signal source is used to generate a RF signal, which is processed by the distribution function module and then 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 through the first power divider; the first radio frequency signal is input to the intensity modulator through the 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 input into the first phase modulator after being phase-shifted by the first phase shifter, and a RF driving signal is provided for the first phase modulator; the fourth RF signal is input into the second phase modulator after being phase-shifted by the second phase shifter, and a RF driving signal is provided 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 dispersive 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 dispersive optical fiber.

[0013] According to another aspect of the present invention, a method for using the 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 RF signal generated by the RF signal source, thereby tuning the repetition frequency of the generated 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 an integrated electro-optical frequency comb is provided, wherein the pulse width of the generated femtosecond light pulse is tuned by changing the length of the dispersive optical fiber.

[0016] Compared with the prior art, the above technical solutions conceived 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-optic 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-optic 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 at the same time, and performs optical and electrical packaging on the modulator chip, thereby improving the stability of the device and the convenience of testing. The three electro-optical modulators are driven by three RF signals to generate a broadband electro-optical frequency comb, which significantly improves the integration of the system compared with the traditional method. The 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 improved by adjusting the power of any RF drive signal.

[0020] The present invention integrates three electro-optic modulators, namely, an intensity modulator, a first phase modulator and a second phase modulator, on the same chip, uses three RF signals to drive the three electro-optic modulators to generate an electro-optic frequency comb, obtains femtosecond optical pulses through dispersive optical fibers, and realizes an on-chip tunable femtosecond light source based on an integrated electro-optic frequency comb, which has the advantages of high integration, tunable pulse width and repetition frequency. A continuous optical signal with tunable wavelength is generated by a continuous laser, and a broadband flat electro-optic frequency comb is generated through a monolithic integrated modulator chip; wherein the intensity modulator is used to generate a narrowband flat-top optical pulse sequence; the first phase modulator and the second phase modulator perform quadratic phase modulation on the optical pulse sequence to generate a broadband flat electro-optic frequency comb; the dispersive optical fiber performs dispersion compensation, compresses the broadband flat electro-optic frequency comb in the time domain, and generates femtosecond optical pulses. The present invention uses a monolithic integrated modulator chip to generate a large bandwidth, high flatness, tunable integrated electro-optic frequency comb, and then performs dispersion compensation through a dispersive optical fiber to realize the output of femtosecond optical pulses. The bandwidth and flatness of the generated electro-optical frequency comb can be improved by optimizing the DC bias point and the driving RF signal power of the intensity modulator and optimizing the driving RF signal power of the first phase modulator and the second phase modulator. The repetition frequency of the generated electro-optical frequency comb and femtosecond pulses can be tuned by adjusting the frequency of the RF signal (i.e., the RF signal from the RF signal source) driving the monolithic integrated modulator chip.

[0021] 2. The on-chip tunable femtosecond pulse light source based on the integrated electro-optic frequency comb provided by the present invention can change the frequency interval of the electro-optic frequency comb by changing the frequency of the radio frequency signal, so that the pulse width and repetition frequency of the generated femtosecond light pulse are tunable; and by tuning the output wavelength of the continuous laser, the working band of the femtosecond pulse 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 the integrated electro-optical frequency comb provided by the present invention has good compatibility, can be seamlessly integrated into existing photonic devices and systems, and can be combined with other integrated optical components to form a complex on-chip optical system. In addition, the on-chip tunable femtosecond light pulse generation system based on the integrated electro-optical frequency comb of the present invention is insensitive to temperature changes and does not require a complex temperature control system.

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

[0026] Figure 3 It 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) corresponds to the electro-optic frequency comb spectrum. Figure 3 (b) in the figure corresponds to the time domain diagram of the femtosecond light 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 purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain 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 can 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-optic frequency comb in the present invention loads the radio frequency signal onto a wavelength-tunable optical signal through a monolithic integrated cascade electro-optic modulator, generates a broadband flat electro-optic frequency comb after electro-optic intensity modulation and phase modulation, performs dispersion compensation on the comb using a dispersive medium, and compresses the comb 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 a 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 RF signal output by the first power divider 2 is input to the first RF amplifier 5, and the second RF signal output by the first power divider 2 is input to the second RF 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, and 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 flat 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, the continuous laser 8 generates a continuous optical signal with a wavelength of 1550nm, and the radio frequency signal source 1 generates a radio frequency signal with a frequency of 10GHz. The intensity modulator 9 operates at an orthogonal bias point, and the driving radio frequency signal power is 23dBm. The driving signal power of the first phase modulator 10 and the second phase modulator 11 are both 36dBm, and the phases of the three radio frequency driving signals are consistent. The dispersion optical fiber 12 is a single-mode optical fiber with a length of 300m.

[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 optical pulse finally generated after passing through the dispersion optical 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 through a 300 m long dispersion optical fiber 12, compressed in the time domain, and generates femtosecond pulses with a pulse width of 919 fs.

[0046] Example 2

[0047] In this embodiment, the continuous laser 8 generates a continuous optical signal with a wavelength of 1550nm, and the radio frequency signal source 1 generates a radio frequency signal with a frequency of 20GHz. The intensity modulator 9 operates at an orthogonal bias point, and the driving radio frequency signal power is 21dBm. The driving signal powers of the first phase modulator 10 and the second phase modulator 11 are both 35dBm, and the phases of the three radio frequency driving signals are consistent. The dispersion optical fiber 12 is a single-mode optical fiber with a length of 150m.

[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 optical pulse finally generated after passing through the dispersion optical 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 100 m. The time domain diagram of the generated femtosecond optical pulse is as follows: Figure 4 As shown, the pulse width of the femtosecond light pulse generated in this example is 753fs.

[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 only 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 protection scope of the present invention.

Claims

1. An on-chip tunable femtosecond light source based on an integrated electro-optic 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 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, wherein: The radio frequency signal source (1) is used to generate a radio frequency signal, and the radio frequency signal is processed by the distribution function module and is divided into three radio frequency drive signals; 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 three radio frequency drive signals provide radio frequency drive signals for the intensity modulator (9), the first phase modulator (10), and the second phase modulator (11), respectively; 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 as claimed in claim 1, characterized in that: The distribution function module comprises 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 by the first power divider (2); The first radio frequency signal is input into the intensity modulator (9) via a first radio frequency amplifier (5), so as to provide a radio frequency driving signal for the intensity modulator (9); The second radio frequency signal is input into 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 input into the first phase modulator (10) after being phase-shifted by the first phase shifter (6), and provides a radio frequency driving signal for the first phase modulator (10); The fourth radio frequency signal is input into the second phase modulator (11) after being phase-shifted by the second phase shifter (7), thereby providing a radio frequency driving signal for the second phase modulator (11).

3. The on-chip tunable femtosecond light source based on an integrated electro-optical frequency comb as claimed in 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-optic modulators.

4. The on-chip tunable femtosecond light source based on an integrated electro-optical frequency comb as claimed in claim 1, characterized in that: The dispersion optical fiber (12) 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 (12).

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 4, characterized in that: The bandwidth and flatness of the electro-optical frequency comb are regulated by adjusting the power of the three-way radio frequency driving signal.

6. 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 4, 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.

7. The method for using the on-chip tunable femtosecond light source based on the integrated electro-optical frequency comb as claimed in claim 4, characterized in that: The pulse width of the generated femtosecond optical pulse is tuned by changing the length of the dispersion optical fiber (12).

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