A step frequency pulsed light generating device and method

Abstract

The application belongs to the technical field of photoelectricity, and discloses a step frequency shift type pulsed light generating device and method, which comprises a continuous wave laser (1), a first light beam combiner (2), a first light beam splitter (3), a second light beam splitter (4), a main frequency shifter (5), a first microwave signal source (6), a third light beam splitter (7), a slave frequency shifter (8), a second microwave signal source (9), a second light beam combiner (10), a third light beam combiner (11), an optical amplifier (12), an optical filter (13) and an optical output port (14). The application can generate a light frequency comb signal with step change characteristics, and the time domain and frequency domain characteristics of the signal are special. The signal can be used in application fields such as secret communication, laser target indication, test measurement and other fields requiring special signals as working media. The application has the ability to realize on-chip integration, and the tuning accuracy and working stability of the application will be improved after on-chip integration.

Description

Technical Field

[0001] This invention belongs to the field of optoelectronic technology and relates to a step-frequency shift pulsed light generator and method. Background Technology

[0002] In today's rapidly developing optical technology, optical frequency combs (often simply called optical frequency combs) have become a revolutionary light source tool, demonstrating enormous potential and broad application prospects in various fields such as precision measurement, optical communication, radar, and basic scientific research. Optical frequency combs possess unique spectral characteristics—a series of equally spaced frequency components uniformly distributed along the frequency axis, manifesting in the time domain as a collection of short pulses of light. In recent years, the generation and application technologies of optical frequency combs have been extensively studied. Optical frequency combs have become a bridge connecting radio waves, microwaves, and light waves, greatly promoting the advancement of related technologies in the optoelectronic field.

[0003] Among the many technologies for generating optical frequency combs, cyclic frequency shifting (CFS) technology has attracted much attention due to its simple system structure, high flexibility in output optical frequency combs, and high stability. CFS typically achieves periodic frequency shifting of optical signals in the frequency domain through modulator cascading, phase shifter introduction, and feedback control, thereby generating high-quality optical frequency combs. This technology can not only precisely control the comb tooth spacing and number, but also achieve flexible tuning within a certain frequency range, meeting the needs of different application scenarios. However, traditional CFS lasers based on single-cavity structures are limited by factors such as cavity structure and working principle, resulting in relatively limited tunability. They can generally only control the repetition frequency and spectral width of the output optical frequency comb (pulse light), and cannot flexibly generate optical frequency comb signals with specific characteristics, thus limiting the application range of CFS lasers. Summary of the Invention

[0004] (I) Purpose of the Invention

[0005] To overcome the limitations of existing cyclic frequency shifting technology, this invention proposes a cyclic frequency shifting pulsed light generator with a nested ring cavity structure. This device can generate and tune pulsed light in a multi-dimensional and more flexible manner. It utilizes a multi-level frequency shifting structure to generate a special optical frequency comb signal with step-change characteristics. Its time domain manifestation is a periodic optical pulse train. By controlling various operating parameters of the laser, the repetition frequency, envelope shape, spectral width, center wavelength, and other parameters of the output optical pulse train can be manipulated. This flexible and tunable pulsed light generator is expected to demonstrate application value in civilian, military, and other fields.

[0006] (II) Technical Solution

[0007] To solve the above-mentioned technical problems, the present invention provides a step-frequency shift pulsed light generator, comprising a continuous wave laser 1, a first optical beam combiner 2, a first optical beam splitter 3, a second optical beam splitter 4, a master frequency shifter 5, a first microwave signal source 6, a third optical beam splitter 7, a slave frequency shifter 8, a second microwave signal source 9, a second optical beam combiner 10, a third optical beam combiner 11, an optical amplifier 12, an optical filter 13, and an optical output port 14.

[0008] The first optical beam combiner 2, the first optical beam splitter 3, the second optical beam splitter 4, the main frequency shifter 5, the third optical beam splitter 7, the slave frequency shifter 8, the second optical beam combiner 10, the third optical beam combiner 11, the optical amplifier 12, and the optical filter 13 are sequentially optically connected to form a frequency shifting loop. The seed light signal emitted by the continuous wave laser 1 is coupled into the frequency shifting loop via the first optical beam combiner 2 and the first optical beam splitter 3. At the second optical beam splitter 4, the optical path is split into a first main optical path A and a first optical branch 1-A. At the third optical beam splitter 7, the optical path is split into a second main optical path B and a second optical branch 1-B. The first main optical path A and the second main optical path B are frequency shifting optical paths, which are part of the frequency shifting loop. The first optical branch 1-A and the second optical branch 1-B are optical direct-through branches, which are branches nested in the frequency shifting loop that directly pass through a portion of the signal light. The optical connections between the components are made of optical fibers.

[0009] The master frequency shifter 5 is electrically connected to the first microwave signal source 6. The first microwave signal source 6 outputs a high-frequency microwave signal to drive the master frequency shifter 5 to generate a large frequency shift of the signal light, typically on the order of GHz. The master frequency shifter 5 is generally a high-speed electro-optic modulator with carrier suppression single-sideband modulation function, such as a dual parallel Mach-Zehnder modulator. The slave frequency shifter 8 is electrically connected to the second microwave signal source 9. The second microwave signal source 9 outputs a low-frequency microwave signal to drive the slave frequency shifter 8 to generate a small frequency shift of the signal light, typically on the order of MHz. The slave frequency shifter 8 is generally an optical modulator that uses physical effects such as acousto-optic effects to cause frequency shift of the signal light, such as an acousto-optic frequency shifter.

[0010] The second optical beam splitter 4 can control the ratio of signal optical power allocated to the first main optical path A and the first optical branch 1-A, and the third optical beam splitter 7 can control the ratio of signal optical power allocated to the second main optical path B and the second optical branch 1-B.

[0011] When the pulsed light generator is working stably, the output signal light is pulsed light. In the frequency domain, the signal is represented by a main frequency component that appears at intervals of the main frequency shift frequency. Near the main frequency component, there are secondary frequency shift components that appear at intervals of the secondary frequency shift frequency. The number of secondary frequency shift components near each main frequency shift component is different, and the change in the number shows an arithmetic sequence relationship. In the time domain, the signal is represented by a pulse train that appears at the main frequency shift frequency. The pulse train exhibits periodic amplitude modulation.

[0012] The pulsed light generator has excellent tuning performance. When it is working stably, the repetition frequency, envelope shape, spectral width, and center wavelength of the output pulsed light can all be controlled and changed by controlling the frequency of the microwave signals output by the first microwave signal source 6 and the second microwave signal source 9, the splitting ratio of the second optical beam splitter 4 and the third optical beam splitter 7, the passband range of the optical filter 13, and the operating wavelength of the continuous wave laser 1.

[0013] During operation, the seed light signal emitted by the continuous wave laser 1 is coupled into the frequency shifting loop via the first optical combiner 2 and the first optical beam splitter 3. The seed light in the main loop cavity is split into two paths by the second optical beam splitter 4. The first main optical path A is the frequency shifting branch, through which the signal light generates a frequency shift signal. The first optical branch 1-A is a direct branch, ensuring that a portion of the signal light participates in the next cycle. The power distribution between the first main optical path A and the first optical branch 1-A can be adjusted by the second optical beam splitter 4. In the first main optical path A, the signal light first passes through the main frequency shifter 5 driven by the first microwave signal source 6, generating a large main frequency shift amount f. p The light is then split into a second main optical path B and a second optical branch 1-B by the third optical beam splitter 7, where the second optical branch 1-B is a direct branch. The signal light on the second main optical path B generates a small slave frequency shift f via the slave frequency shifter 8 driven by the second microwave signal source 9. s The signals on the second main optical path B and the second optical branch 1-B are combined into one path by the second optical combiner 10. Finally, the frequency-shifted signal and the signal light on the first optical branch 1-A are combined into the main ring cavity by the third optical combiner 11. Then, the signal light passes through the optical amplifier 12 and the optical filter 13. Part of the signal light is output through the first optical combiner 2 and the first optical splitter 3, and part of the signal light is coupled into the frequency-shifting ring for the next cycle.

[0014] In the frequency shift loop, the loss of the loop cavity is mainly compensated by the optical amplifier 12. To suppress the spontaneous emission noise introduced by the optical amplifier 12, an optical filter 13 is also used in the frequency shift loop to filter out stray light. The optical filter 13 also controls the number of signal light cycles in the frequency shift loop. The signal light output by the proposed step-frequency shift pulsed light generator is essentially a signal with a comb spectrum, i.e., an optical frequency comb signal, the generation principle of which is shown in the attached figure. Figure 2 As shown, the characteristics of the signal light output by the proposed step-frequency-shifting pulsed light generator are mainly composed of: the splitting rate A, the main frequency shifting frequency f. p Spectrophotometry B, from frequency shift f s The parameters H(ω) and the filtering window determine the process of generating this specific optical frequency comb signal. The following section will provide a theoretical derivation of the process.

[0015] Assume that the angular frequency of the single-frequency seed light emitted by the continuous-wave laser 1 is ω0. In the first cycle, node ① contains only the seed light signal, which can be defined as:

[0016]

[0017] Where E0 is the intensity of the initial light field.

[0018] Subsequently, the seed light signal passes through the second optical beam splitter 4, and A (0≤A≤1) of the signal light is split into the first main optical path A, while the remaining 1-A of the optical power is split into the first optical branch 1-A. The signal light distributed into the first main optical path A undergoes a frequency shift of f by the main frequency shifter 5. p The frequency-shifted signal. At this time, the signal light field at node ② can be expressed as:

[0019]

[0020] Next, the signal E2(t) is split into two paths, the second main optical path B and the second optical branch 1-B, by the third optical beam splitter 7. Signal light of denoted by B (0≤B≤1) is allocated to the second main optical path B, and its frequency is shifted by f by the frequency shifter 8. s The frequency-shifted signal. The signal light from the second main optical path B and the second optical branch 1-B is combined by the second beam combiner 10. The signal light at node ③ after beam combining can be represented as:

[0021]

[0022] For ease of problem analysis, assuming the optical loss of the ring cavity can be completely compensated by optical amplifier 12, the signal light at node ④ can be expressed as:

[0023]

[0024] In the formula, H(ω) is the passband window function of optical filter 13, which determines the maximum number of cycles of the signal light in the cyclic frequency shifter cavity. It should be noted that, to simplify the problem analysis, the evolution of the signal light from node ① to node ④, i.e., the evolution of a complete cycle of the signal, is shown in the derivation, but the phase difference in the optical field caused by the varying path lengths between branches is not considered. The cyclic evolution of the signal light in the frequency shifter cavity can be viewed as a process of multiple nested frequency shifts of the signal light. Here, the cyclic function is defined... for:

[0025]

[0026] Then we can derive the expression for the output signal light field after N complete cycles:

[0027]

[0028] It is easy to see from the above theoretical derivation that the output signal light band after N cycles has obvious periodic characteristics. The generated optical frequency comb has a main period, which is the main frequency shift frequency, and a slave period, which is the slave frequency shift frequency, attached to the main period. The number of slave periods increases linearly with the number of cycles. Its spectral characteristics are shown in the attached figure. Figure 2 As shown.

[0029] (III) Beneficial Effects

[0030] The step-frequency shift pulsed light generator and method provided by the above technical solution have the following beneficial effects:

[0031] (1) The step-frequency shift pulse light generator proposed in this invention has the ability to generate optical frequency comb signals with step-change characteristics. The time domain and frequency domain characteristics of the signal are special, and it can be used in application fields that require special signals as working media, such as secure communication, laser target indication, and test measurement.

[0032] (2) The step-frequency shift pulse light generator proposed in this invention has excellent tunability. The repetition frequency, slow-varying envelope shape, spectral width, center wavelength and other parameters of the output pulse light can be flexibly controlled by adjusting the working state of the relevant components in the system.

[0033] (3) The step-frequency shift pulse light generator proposed in this invention has the ability to achieve on-chip integration. After the on-chip integration is completed, its tuning accuracy and working stability will be improved. Attached Figure Description

[0034] Figure 1 This is a structural diagram of a step-frequency-shifting pulsed light generator proposed in this invention;

[0035] Figure 2 This is a schematic diagram of the principle of a stepping frequency shifting pulse light generator that produces a stepping optical frequency comb, as proposed in this invention.

[0036] Figure 3 The output signal light simulation results of the step-frequency shift pulse light generator proposed in this invention are shown. Detailed Implementation

[0037] To make the objectives, contents, and advantages of the present invention clearer, the specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings and examples.

[0038] In this embodiment, the frequency-shifting ring cavity structure of the step-frequency-shifting pulsed light generator is made of optical fiber, and all functional components used are connected by optical fiber.

[0039] See appendix Figure 1 and Figure 2As shown, in this embodiment of the step-shift pulsed light generator, the continuous wave laser (1) uses a distributed feedback (DFB) laser, and its output narrow-linewidth, linearly polarized laser signal is used as seed light input into the frequency shifting loop; the first optical beam combiner (2), the first optical beam splitter (3), the second optical beam combiner (10), and the third optical beam combiner (11) all use a one-to-two optical coupler; the second optical beam splitter (4) and the third optical beam splitter (7) both use polarized beam splitters, which, in conjunction with a polarization controller, enable... The optical power distribution control can be realized on the first main optical path (A) and the first optical branch (1-A), the second main optical path (B) and the second optical branch (1-B); the main frequency shifter (5) adopts a dual parallel Mach-Zehnder modulator (DPMZM) which is biased in a carrier-suppressed single-sideband modulation state; the slave frequency shifter (8) uses an acousto-optic frequency shifter (AOFS); the optical amplifier (12) uses an erbium-doped fiber amplifier (EDFA); and the optical filter (13) uses a bandpass optical filter with a controllable passband window.

[0040] To determine the technical features of the step-frequency-shift pulsed light generator provided in this application, numerical modeling and simulation are used for principle verification and analysis. (See attached diagram.) Figure 3 This is a simulation result of the output signal of a step-frequency shift pulsed light generator in the embodiment. In the simulation, the operating wavelength of the continuous wave laser (1) is set to 1550nm; the splitting ratio of the second optical beam splitter (4) and the third optical beam splitter (7) is configured to be 1:1, i.e., A=B=0.5; the output microwave signal frequency f of the first microwave signal source (6) is set to be... p =5GHz, the second microwave signal source (9) outputs a microwave signal frequency f s =70MHz; Configure the passband window of the optical filter (13) so that the number of cycles N of the frequency-shifted signal is 20. Appendix Figure 3 (a) and appendix Figure 3 (b) The time-domain waveform and spectrum of the output signal light obtained from the simulation are shown. The simulation results show that the generated signal has obvious periodic characteristics. Its signal light in the time domain is a periodic pulse train; its signal light in the frequency domain is a specific frequency component that appears every 5 GHz, forming a master frequency comb. Near the master frequency comb, there are also slave frequency combs with an interval of 70 MHz. As the interval of the master frequency increases, the number of teeth of the slave frequency combs attached to the master frequency comb will also increase linearly, which is consistent with the theoretical derivation and analysis results.

[0041] To further verify the tuning performance of the proposed step-frequency-shift pulsed light generator, simulations were performed with different operating parameters. In the simulations, the microwave signal frequency f output from the first microwave signal source (6) was... p Modified to 11GHz, the second microwave signal source (9) outputs a microwave signal frequency f.s The frequency was changed to 50 MHz, and the simulated spectrum is shown in the attached image. Figure 3 As shown in (c), with the attached Figure 3 The simulated spectrum comparison in (b) reveals that the comb tooth spacing of the cyclic frequency-shifting optical comb, generated by changing the frequency shifting frequency, changes significantly. The periodicity of the output signal can be adjusted by controlling the operating frequency of the microwave signal source. By changing the passband window of the optical filter (13), the number of cycles of the frequency-shifting signal N = 40 is obtained from the simulation. Figure 3 The spectrum shown in (d) shows that the spectral width is positively correlated with the number of cycles, and can be adjusted by controlling the passband window of the optical filter (13). The splitting ratios of the second optical beam splitter (4) and the third optical beam splitter (7) are modified to [A=0.1, B=0.5] and [A=0.1, B=0.1] respectively. The simulation results show the attached spectrum. Figure 3 As shown in (e), the time-domain waveform diagram shows that the output pulse train envelope shape can be controlled by changing the splitting ratio of the optical beam splitter (4) and the optical beam splitter (7).

[0042] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A step-frequency shift pulsed light generator, characterized in that, include: A continuous wave laser (1), a first optical beam combiner (2), a first optical beam splitter (3), a second optical beam splitter (4), a master frequency shifter (5), a first microwave signal source (6), a third optical beam splitter (7), a slave frequency shifter (8), a second microwave signal source (9), a second optical beam combiner (10), a third optical beam combiner (11), an optical amplifier (12), an optical filter (13), and an optical output port (14) are sequentially optically connected to form a frequency shifting loop; The seed light signal emitted by the continuous wave laser (1) is coupled into the frequency shifting ring through the first optical beam combiner (2) and the first optical beam splitter (3); at the second optical beam splitter (4), the optical path is divided into the first main optical path (A) and the first optical branch (1-A), and at the third optical beam splitter (7), the optical path is divided into the second main optical path (B) and the second optical branch (1-B). The first main optical path (A) and the second main optical path (B) are frequency shifting optical paths, which are part of the frequency shifting ring. The first optical branch (1-A) and the second optical branch (1-B) are optical direct-through branches, which are branches nested in the frequency shifting ring that directly pass through a part of the signal light. The main frequency shifter (5) is electrically connected to the first microwave signal source (6), and the secondary frequency shifter (8) is electrically connected to the second microwave signal source (9). On the first main optical path (A), the signal light first passes through the main frequency shifter (5) driven by the first microwave signal source (6), generating a large main frequency shift amount. f p The light is then split into a second main optical path (B) and a second optical branch (1-B) by a third optical beam splitter (7). The second optical branch (1-B) is a direct branch. The signal light on the second main optical path (B) is converted into a small slave frequency shift by a slave frequency shifter (8) driven by a second microwave signal source (9). f s The signals on the second main optical path (B) and the second optical branch (1-B) are combined into one path by the second optical combiner (10). Finally, the frequency-shifted signal and the signal light on the first optical branch (1-A) are combined into the main ring cavity by the third optical combiner (11). Then, the signal light passes through the optical amplifier (12) and the optical filter (13). Part of the signal light is output through the first optical combiner (2) and the first optical splitter (3), and part of the signal light is coupled into the frequency shifting ring for the next cycle.

2. The step-frequency-shifting pulsed light generator as described in claim 1, characterized in that, The optical path for the optical connection between the components in the frequency shift ring is an optical fiber.

3. The step-frequency shift pulsed light generator as described in claim 2, characterized in that, The first microwave signal source (6) outputs a microwave signal with a frequency exceeding a set threshold to drive the main frequency shifter (5) to generate a large frequency shift of the signal light, which is on the order of GHz. The main frequency shifter (5) is a high-speed electro-optic modulator with carrier suppression single-sideband modulation function.

4. The step-frequency-shifting pulsed light generator as described in claim 3, characterized in that, The second microwave signal source (9) outputs a microwave signal with a frequency lower than the set value to drive the frequency shifter (8) to generate a small frequency shift of the signal light, which is on the order of MHz. The frequency shifter (8) is an optical modulator that uses physical effects such as acoustic-optical effects to make the signal light frequency shift.

5. The step-frequency-shifting pulsed light generator as described in claim 4, characterized in that, The second optical beam splitter (4) controls the ratio of the signal optical power allocated to the first main optical path (A) and the first optical branch (1-A), and the third optical beam splitter (7) controls the ratio of the signal optical power allocated to the second main optical path (B) and the second optical branch (1-B).

6. The step-frequency-shifting pulsed light generator as described in claim 5, characterized in that, During the operation of the pulsed light generator, the seed light signal emitted by the continuous wave laser (1) is coupled into the frequency shifting ring through the first optical combiner (2) and the first optical splitter (3). The seed light in the main ring cavity is split into two paths by the second optical splitter (4). The first main optical path (A) is the frequency shifting branch signal light that generates the frequency shifting signal through this path. The first optical branch (1-A) is a direct branch, which ensures that a portion of the signal light participates in the next cycle. The optical power distribution on the first main optical path (A) and the first optical branch (1-A) is adjusted by the second optical splitter (4).

7. The step-frequency-shifting pulsed light generator as described in claim 6, characterized in that, In the frequency shifting loop, the loss of the loop cavity is compensated by the optical amplifier (12), and the optical filter (13) is used in the frequency shifting loop to filter out stray light. The optical filter (13) also controls the number of signal light cycles in the frequency shifting loop.

8. A method for generating pulsed light using a step-frequency-shifting pulsed light device based on the step-frequency-shifting pulsed light generator of claim 7, characterized in that, The characteristics of the signal light output by the pulsed light generator include: spectral splitting rate. A Main frequency shift f p Spectrophotometry B From frequency shift f s Filter window H ( ω The process of generating the optical frequency comb signal is set as follows: Let the angular frequency of the single-frequency seed light emitted by the continuous-wave laser (1) be . ω 0. In the first cycle, node ① contains only the seed light signal, which is defined as: in, E 0 represents the intensity of the initial light field; Subsequently, the seed light signal passes through the second optical beam splitter (4) and has A The signal light is split into the first main optical path, and the rest are 1- A The optical power is distributed to the first optical branch, and the signal light distributed to the first main optical path undergoes a frequency shift of 1 / 2 by the main frequency shifter (5). f p Frequency-shifted signal; 0≤ A ≤1; The signal light field at node ② is represented as follows: Next, after the signal E 2( t It is then divided into a second main optical path and a second optical branch by the third optical beam splitter (7). B The signal light is distributed onto the second main optical path, and its frequency shift is generated by the frequency shifter (8). f s Frequency-shifted signal, 0≤ B ≤1; The signal beams from the second main optical path and the second optical branch are combined by the second optical combiner (10). The signal beam at node ③ after beam combining is represented as follows: Assuming the optical loss of the ring cavity is completely compensated by the optical amplifier (12), the signal light at node ④ is represented as: In the formula, H ( ω ) is the passband window function of the optical filter (13), which determines the maximum number of cycles of the signal light in the cyclic frequency shift cavity; The cyclic evolution of the signal light in the frequency-shifting cavity can be viewed as a process of multiple nested frequency shifts of the signal light, and a cyclic function is defined. for: Then export the process N The expression for the output signal light field after a complete loop: 。 9. An application of the step-frequency shift pulsed light generation method according to claim 8 in optoelectronic technology.

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