A fast, electrically controlled 100-picosecond pulse laser

Abstract

The present invention discloses a fast, electrically controllable 100-picosecond pulse laser. The laser includes a resonant cavity, a pump light source, and a radio frequency signal source. The laser's ring resonant cavity includes an integrated device, a gain fiber, a single-mode fiber, a phase modulator, and a polarization controller. The integrated device has the functions of a wavelength division multiplexer, a polarization-independent isolator, and a coupler. The radio frequency signal source is connected to the phase modulator via a radio frequency cable. Electrical modulation of the light field is achieved by inputting an electrical signal into the phase modulator via a signal source. The phase modulator contains a polarizer, and the light intensity at its output end is sensitive to the polarization state of the light field at the input end, so that the phase modulator has the effect of intensity modulation. Combining the polarization controller and the integrated device can achieve nonlinear polarization rotation mode locking. The output light polarization state of the phase modulator is related to the voltage of the electrical signal, which can achieve fast electrical modulation of the light pulse. The present invention can greatly improve the modulation rate of the light pulse and has the advantages of fast and flexible modulation.

Description

Technical Field

[0001] The present invention relates to the technical field of ultrafast fiber lasers, and in particular to a rapidly electrically controllable 100-picosecond pulse laser. Background Art

[0002] Ultrashort optical pulses have attracted widespread attention due to their promising applications in optical communications, biomedicine, spectroscopy, materials processing, and other fields. Mode-locked fiber lasers, as ultrafast pulse light sources with simple structure and excellent performance, have been extensively and intensively studied in recent decades. Typically, the output of a mode-locked laser is a periodic pulse sequence. To embed information into the optical pulses, the pulse sequence must be modulated in some way.

[0003] Currently, the most direct method is to electro-optically modulate the optical pulse sequence outside the laser cavity. This method has the advantages of high stability and ease of use, but suffers from poor flexibility. Modulating the light field within the laser resonant cavity can overcome this disadvantage. Laser mode locking is a dissipative nonlinear process that is extremely complex. Even very weak modulation of the light pulse within the cavity will significantly modulate the intensity of the light pulse within the laser cavity due to nonlinearity, and this intensity modulation often varies significantly with slight changes in the RF signal. Typically, electrically controlled devices such as electrically controlled polarization controllers or electrically controlled attenuators are used within the laser cavity to regulate the light field. However, the response time of these devices is often very long, on the order of milliseconds, which cannot meet the requirements of fast modulation. Therefore, the practical need for fast modulation of light pulses can be met by loading an electro-optical modulator with a suitable RF signal within the laser resonant cavity.

[0004] Ultrashort pulse lasers can be categorized by mode-locking method, either actively or passively. These methods can often generate optical pulses with widths ranging from hundreds of femtoseconds to tens of picoseconds without generating strong chirp. Q-switched lasers can be used to generate pulses exceeding nanoseconds. However, practical applications require optical pulses with widths exceeding hundreds of picoseconds. Therefore, developing pulse lasers with pulse widths in the hundreds of picoseconds range has significant application and commercial value. Summary of the Invention

[0005] In response to the requirements of ultrafast fiber lasers for fast pulse modulation and pulse widths of hundreds of picoseconds, the present invention proposes a fast electrically controllable 100-picosecond pulse laser. The modulation of the intracavity pulse is achieved by controlling the electro-optical characteristics of the phase modulator through radio frequency signals, and the Lyot filtering principle is used to achieve a pulse width of hundreds of picoseconds.

[0006] The technical solutions of the present invention are as follows:

[0007] A fast, electrically controllable 100-picosecond pulse laser comprises a resonant cavity, a pump light source and a radio frequency signal source; the resonant cavity is a ring resonant cavity, comprising an integrated device, a gain fiber, a single-mode fiber, a phase modulator and a polarization controller; the integrated device combines the functions of a wavelength division multiplexer, a polarization-independent isolator and a coupler; the integrated device is connected to the pump light source via a pump input port; and the radio frequency signal source is connected to the phase modulator via a radio frequency cable.

[0008] Furthermore, the phase modulator contains a polarizer. Experimental tests have shown that the light intensity at its output end is sensitive to the polarization state of the input light field. Combining a polarization controller and an integrated device can achieve nonlinear polarization rotation mode locking, and laser mode locking can be achieved by adjusting the polarization controller.

[0009] Furthermore, the pigtails at the input and output ends of the phase modulator are polarization-maintaining fibers.

[0010] Furthermore, the gain fiber is a quartz fiber doped with rare earth ions; the operating band of the integrated device and the phase modulator corresponds to the gain fiber, and the pump light source corresponds to the absorption wavelength of the gain fiber, that is: for erbium-doped fiber, the pump source wavelength is 976 nm, and the operating wavelength of the integrated device and the phase modulator is in the optical communication C band; for ytterbium-doped fiber, the pump source wavelength is 976 nm, and the operating wavelength of the integrated device and the phase modulator is in the 1060 nm band.

[0011] Furthermore, the frequency of the RF signal source does not exceed 20 kHz, the peak-to-peak voltage does not exceed 5 Vpp, and the response time of the signal control is greater than or equal to 50 microseconds.

[0012] Furthermore, the pulse width of the pulse laser is 100 ps-300 ps.

[0013] Furthermore, the pigtails at the input and output ends of the phase modulator are polarization-maintaining fibers. When the laser passes through the modulator, its power transmittance varies with wavelength, allowing the phase modulator to act as a Lyot filter. After filtering, the optical pulse width becomes narrower, and the pulse width correspondingly increases to hundreds of picoseconds.

[0014] Furthermore, experimental testing revealed that, when an RF signal is input to the phase modulator's RF input, not only does the phase of the optical field undergo modulation, but the polarization state of the optical field at the output undergoes a slight, rapid change in response to the RF signal. Furthermore, as the optical field at the output of the phase modulator propagates within the resonant cavity to the modulator's input, its polarization state is also modulated by the RF signal. Therefore, the phase modulator can modulate the intensity within the laser cavity under the action of the RF signal.

[0015] The present invention also provides a method for rapidly electrically controlling the generation of 100-picosecond pulsed lasers. After the phase modulator passes through the polarization-maintaining optical fiber at the output end, its power transmittance changes with the wavelength, so that the phase modulator can function as a Lyot filter. After filtering, the pulse width of the optical pulse reaches the order of 100 picoseconds. After the radio frequency signal is input into the phase modulator, not only is the phase of the optical field modulated, but the polarization state of the optical field at the output end also changes rapidly and weakly with the radio frequency electrical signal. That is, the phase modulator can modulate the intensity in the laser cavity under the action of the radio frequency signal.

[0016] The advantages of the present invention are as follows:

[0017] 1. The fast electrically controllable 100-picosecond pulse laser of the present invention has a phase modulator with a shorter response time than commonly used electrically controlled polarization controllers and electrically controlled attenuators, thereby enabling faster pulse modulation.

[0018] 2. The electrically controlled picosecond laser can be modulated by any electrical signal, and the pulse evolution can be modulated by various signals, making the operation very flexible.

[0019] 3. The electrically controlled 100-picosecond laser has a simple structure. The resonant cavity consists only of integrated devices, polarization controllers, phase modulators and optical fibers, and has a compact structure.

[0020] 4. This electrically controlled 100-picosecond laser does not require any filters. It can achieve filtering through a section of polarization-maintaining fiber to make the pulse width reach hundreds of picoseconds, which greatly simplifies the laser structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 Schematic diagram of the 100-picosecond pulse laser that can be rapidly electrically controlled according to the present invention;

[0022] Figure 2 A diagram of a test device for a phase modulator according to the present invention;

[0023] Figure 3 for Figure 2 The output waveform of the test device under sinusoidal RF signal modulation;

[0024] Figure 4 The pulse sequence output by the laser of the present invention under a 10 kHz radio frequency signal;

[0025] Figure 5 for Figure 4 Pulse distribution at corresponding time.

[0026] In the figure, 101 is a pump light source, 102 is an integrated device, 103 is a gain fiber, 104 is a polarization controller, 105 is a phase modulator, 106 is a signal source, 107 is a polarization-maintaining fiber, 108 is a single-mode fiber, 201 is a test continuous light source, 202 is a polarization-dependent isolator, 203 is a photodetector, and 204 is an oscilloscope. DETAILED DESCRIPTION

[0027] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0028] like Figure 1 As shown, the present invention provides a rapidly electrically controllable 100-picosecond pulse laser. The laser resonator uses a 976nm single-mode semiconductor laser 101 as a pump light source. The intracavity components include an integrated device 102, a gain fiber 103, a squeezed polarization controller 104, a phase modulator 105, a polarization-maintaining fiber 107, and a single-mode fiber 108. The integrated device combines the functions of a wavelength division multiplexer, a coupler, and an isolator, with a coupling output ratio of 20%. The polarization controller is clamped to the single-mode fiber and applies stress to the fiber by rotating, squeezing, and twisting it, thereby regulating the birefringence effect within the laser. The gain fiber uses a high-gain erbium-doped fiber, model ER110-4 / 125 (LIEKKI), with a length of 0.8 m. The total length of the single-mode fiber is 12.5 m, and the dispersion parameter is 22.1 ps. 2 / km, and the nonlinear coefficient is 1.3 W -1 ×km -1 The polarization-maintaining fiber is the pigtail of the phase modulator and is 2.5 m long. The phase modulator has an RF port connected to the signal source 106 via an RF cable. A 10 kHz RF signal is input to the RF input port. The total length of the laser resonator is 15.8 m, corresponding to a repetition rate of 12.96 MHz.

[0029] The working principle of the present invention is as follows:

[0030] The pulsed laser mode-locking method employed in this invention is nonlinear polarization rotation technology. The phase modulator includes an analyzer, and the light intensity at its output is sensitive to the polarization state of the input light field. Combined with a polarization controller and integrated devices, nonlinear polarization rotation mode-locking can be achieved. The principle behind achieving 100-picosecond optical pulse output is that when the polarization direction of the light field is inconsistent with the principal axis of the polarization-maintaining fiber, light of different wavelengths transmits through the polarization-maintaining fiber with different polarization states. Through the phase modulator, its power transmittance varies with wavelength, allowing the phase modulator to function as a Lyot filter. After filtering, the optical pulse width is narrowed, resulting in pulse widths reaching hundreds of picoseconds.

[0031] The principle of light field intensity modulation by phase modulator is as follows Figure 2 As shown. The wavelength of the test continuous light source 201 is a continuous laser of 1550 nm. When a 10 kHz RF signal is input to the RF input end of the modulator, not only the phase of the light field is modulated, but also the polarization state of the light field at the output end changes slightly and rapidly with the RF electrical signal. Therefore, after the modulated light field passes through the polarization-dependent isolator 202, the intensity of the output laser is also modulated. The output light is converted into an electrical signal by the photodetector 203 and measured by the oscilloscope 204. The measured light field intensity changes with time as shown in Figure 3 shown.

[0032] The experimental results of the present invention are as follows:

[0033] When the pump power is 215 mW, the bias controller can be adjusted to achieve mode locking. At this time, a sinusoidal RF signal with a peak-to-peak voltage of 3.5 Vpp and a frequency of 10 kHz is applied to the phase modulator, and the following can be obtained: Figure 4 The pulse sequence shown in Figure 1 shows that the period of change in the pulse peak intensity is consistent with the period of the RF signal. By changing the waveform of the RF signal, pulse sequences of other modulation types can be obtained.

[0034] Figure 4 The specific time distribution of the pulse sequence in the experiment was also measured. The time domain measurement used the bandwidth of a real-time oscilloscope with a bandwidth of 33 GHz and a sampling rate of 100 Gsa / s. Figure 5 Given Figure 4 The pulse distribution at three corresponding times is shown in the figure. The pulse widths of the three pulses of different intensities are 160 ps, ​​150 ps, ​​and 120 ps, ​​respectively.

[0035] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art will be able to modify the technical solutions described in the aforementioned embodiments or replace some of the technical features therein with equivalents. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A fast electrically controllable 100-picosecond pulse laser, characterized in that: The device comprises a resonant cavity, a pump light source and a radio frequency signal source; the resonant cavity is a ring resonant cavity, comprising an integrated device, a gain fiber, a single-mode fiber, a phase modulator and a polarization controller; the integrated device has the functions of a wavelength division multiplexer, a polarization-independent isolator and a coupler; the integrated device is connected to the pump light source via a pump input port; the radio frequency signal source is connected to the phase modulator via a radio frequency cable; The phase modulator includes a polarizer, the light intensity at its output end is sensitive to the polarization state of the light field at the input end, and nonlinear polarization rotation mode locking can be achieved by combining the polarization controller and the integrated device; The pigtails at the input and output ends of the phase modulator are polarization-maintaining optical fibers.

2. The fast electrically controllable 100-picosecond pulse laser according to claim 1, characterized in that: The gain fiber is a quartz fiber doped with rare earth ions; the operating wavelength bands of the integrated device and the phase modulator correspond to the gain fiber, and the pump light source corresponds to the absorption wavelength of the gain fiber.

3. The fast electrically controllable 100-picosecond pulse laser according to claim 1, characterized in that: The frequency of the radio frequency signal source does not exceed 20kHz, the peak-to-peak voltage does not exceed 5Vpp, and the response time of the signal control is greater than or equal to 50 microseconds.

4. A rapidly electrically controllable 100-picosecond pulse laser according to any one of claims 1 to 3, characterized in that: The pulse width of the pulse laser is 100 ps-300 ps.

5. A method for rapidly electrically generating a hundred-picosecond pulse laser, characterized in that: Using the rapidly electrically controllable 100-picosecond pulse laser as described in claim 1, after the phase modulator passes through the polarization-maintaining optical fiber at the output end, its power transmittance changes with the wavelength, so that the phase modulator can act as a Lyot filter, and the pulse width of the optical pulse reaches the order of 100 picoseconds after filtering; after the radio frequency signal is input into the phase modulator, not only the phase of the optical field is modulated, but also the polarization state of the optical field at the output end changes weakly and rapidly with the radio frequency electrical signal, that is, the phase modulator can modulate the intensity in the laser cavity under the action of the radio frequency signal.

Images