CN109149347B - Wide-spectrum optical time domain shaping device - Google Patents
Wide-spectrum optical time domain shaping device Download PDFInfo
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- CN109149347B CN109149347B CN201811055614.4A CN201811055614A CN109149347B CN 109149347 B CN109149347 B CN 109149347B CN 201811055614 A CN201811055614 A CN 201811055614A CN 109149347 B CN109149347 B CN 109149347B
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
- H01S3/10—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating
- H01S3/11—Mode locking; Q-switching; Other giant-pulse techniques, e.g. cavity dumping
- H01S3/1106—Mode locking
- H01S3/1112—Passive mode locking
- H01S3/1115—Passive mode locking using intracavity saturable absorbers
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
- H01S3/005—Optical devices external to the laser cavity, specially adapted for lasers, e.g. for homogenisation of the beam or for manipulating laser pulses, e.g. pulse shaping
Abstract
A wide-spectrum optical time domain shaping device comprises a pumping source, an adjustable attenuator, an input collimator, a saturable absorber, a small hole and an output collimator; the pump source is a light source system with flexible time domain waveform regulation and control capability, and the output of the pump source is incident to the saturable absorber after the output energy is regulated by the adjustable attenuator; the broad spectrum light is output by collimation of the input collimator, part of the saturable absorber is absorbed by the saturable absorber, and the rest part of the light is transmitted by the saturable absorber and then reaches the output collimator through the small hole for coupling and output. When the pumping source does not output or does not reach the saturable absorber, the transmission type saturable absorber is in an unsaturated state, has a strong absorption effect on wide-spectrum light, and has low transmissivity; when strong pump light with a certain time domain waveform output by the pump source reaches the saturable absorber, the transmission type saturable absorber generates a saturable effect, so that the transmissivity of the transmission type saturable absorber to the broad spectrum light is increased, and the output collimator can receive a broad spectrum shaping pulse within the duration time of the pump light.
Description
Technical Field
The invention belongs to the field of high-power laser and optical communication, and particularly relates to a wide-spectrum optical time domain shaping device.
Background
At present, output light of common wide-spectrum light sources is continuous light, but in many fields, flexible time-domain waveform control needs to be performed on output of incoherent wide-spectrum light sources, for example, pulsed light with a certain repetition frequency is generated. The time domain shaping of the wide-spectrum light source is a difficulty in the large-scale high-power laser field in the optical communication and inertial confinement nuclear fusion technology. On one hand, the envelope of the time domain waveform output by shaping is required to be smooth; on the other hand, the shaping process is required not to change the non-coherence and spectral characteristics of the broad spectrum light source.
In the prior art, both an acousto-optic modulator and an electro-optic intensity modulator can be used for time-domain shaping, but the design principle is based on the interference effect, and the acousto-optic modulator and the electro-optic intensity modulator are generally suitable for narrow-band coherent laser. However, for the partially coherent/incoherent broad spectrum light, irregular modulation occurs at the top of the time domain waveform obtained by shaping by using the traditional time domain shaping method, and the lower the coherence degree of the broad spectrum light is, the deeper the irregular modulation at the top is. The reason is that the acousto-optic modulator realizes modulation by utilizing the interaction of the ultrasonic grating and light, while the electro-optic modulator is based on the principle of a Mach-Zehnder interferometer, and the two intensity modulation processes are realized by utilizing the interference process of light beam superposition, actually, mode selection and coherence degree improvement destroy the non-coherence of the broad-spectrum light; moreover, the two processes introduce strong modulation to the shaped time-domain envelope, and therefore, are not suitable for the time-domain shaping of the partially coherent/incoherent broad-spectrum light source. Although a frequency-time mapping (FTTM) shaping scheme commonly used in the field of communications can achieve flexible control over a wide-spectrum optical time-domain waveform, the scheme is complex and high in cost, and a shaped optical signal is narrow-band at each time, that is, the incoherent characteristic of an original wide-spectrum light source is destroyed. In contrast, the saturable absorber is a device which only responds to the light intensity change, has the advantages of small volume, short relaxation time and the like, and some saturable absorbers also have large transmission bandwidth and are very suitable for performing time-domain shaping on the partially coherent/incoherent broad-spectrum light.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provide a wide-spectrum optical time-domain shaping device which is based on a saturable absorber with wide-spectrum transmission characteristics and utilizes a pump light source with flexible time-domain control capability to realize time-domain shaping on a continuous wide-spectrum light source. The scheme solves the problems of destroying the non-coherence and spectral characteristics of the wide-spectrum light source and the like in the current time domain shaping scheme, is not only suitable for shaping coherent wide-spectrum light, but also can realize flexible time domain shaping of a partially coherent/non-coherent wide-spectrum light source.
The technical scheme of the device is as follows:
a wide-spectrum optical time domain shaping device is characterized by comprising a pumping source, an adjustable attenuator, an input collimator, a saturable absorber, a small hole and an output collimator; the output of the pump source is adjusted by the adjustable attenuator to output energy and then is incident on the saturable absorber to form a pump light spot; the wide-spectrum light to be shaped is input into the collimator to be collimated and then is incident on the saturable absorber to form a wide-spectrum light spot, one part of the collimated wide-spectrum light is absorbed by the saturable absorber, and the rest part of the collimated wide-spectrum light is transmitted by the saturable absorber and then reaches the output collimator through the small hole to be coupled and output.
The wide-spectrum light spot is superposed with the pump light spot, and the area of the pump light spot is larger than that of the wide-spectrum light spot.
The pump source is a light source system with flexible time domain waveform regulation and control capability, and the intensity of output light of the pump source is higher than the saturable threshold of the saturable absorber and lower than the damage threshold of the saturable absorber.
The wide-spectrum light to be shaped is output by a wide-spectrum light source system with the bandwidth of hundreds of nanometers, and the output energy of the wide-spectrum light is lower than the saturable threshold of the saturable absorber.
The diameter of the small hole is larger than that of the collimated broad spectrum light.
The saturable absorber has a uniform transmittance for different wavelengths within the spectral bandwidth of the broad spectrum light to be shaped.
The working process of the broad spectrum optical time domain shaping device is as follows:
the pump light source outputs pump light, and the energy of the pump light is adjusted through the attenuation sheet, so that the energy of the pump light reaches the saturation threshold of the saturable absorber but does not exceed the damage threshold of the saturable absorber. It should be noted that since the pump light usually uses high-energy laser and the output fundamental mode spot is gaussian, when considering the energy flux here, the energy flux within 85% of the height of the gaussian beam is considered rather than the total energy flux of the whole beam. The pump light source should be a light source system with flexible time domain waveform regulation and control capability, and the time domain waveform of the pump light determines the time domain waveform of the partially coherent/incoherent broad spectrum light output by shaping. The positions of the pumping light spots and the wide-spectrum light spots on the transmission-type saturable absorber are accurately adjusted, so that the two light spots are superposed, and the pumping light spots completely cover the wide-spectrum light spots. When the pumping source does not output or does not reach the saturable absorber, the transmission type saturable absorber is in an unsaturated state, has a strong absorption effect on wide-spectrum light, and has low transmissivity; when strong pump light with a certain time domain waveform output by the pump source reaches the saturable absorber, the transmission type saturable absorber generates a saturable effect, so that the transmissivity of the transmission type saturable absorber to the wide-spectrum light is increased, and the output collimator can receive a wide-spectrum shaping pulse within the duration time of the pump light.
Compared with the prior art, the invention has the following beneficial effects:
1) the device skillfully utilizes the property that the saturable absorber only responds to the change of light intensity, thereby avoiding the reduction of time domain waveform modulation and non-coherence caused by the mode selection interference effect of the traditional electro-optic modulator;
2) the device has the same response to each wavelength in the bandwidth of the broad spectrum light to be shaped, avoids the frequency-selecting filtering action caused by the acousto-optic effect of the traditional acousto-optic modulator, and further avoids the time domain waveform modulation caused by the effect;
3) the principle and the structure are simple, and the device is not easily interfered by the external environment. In addition, the preparation and performance exploration of all devices used by the device are mature, and the saturable absorber of the shaping key device can be prepared on various substrates and even the end face of an optical fiber, so that the device also has the advantages of low cost and easiness in integration.
Drawings
Fig. 1 is a schematic structural diagram of the broad spectrum optical time domain shaping device of the present invention.
In the figure, 1-pump source, 2-adjustable attenuator, 3-wide spectrum light source, 4-input collimator, 5-saturable absorber, 6-pinhole and 7-output collimator.
Fig. 2 is a pump light pulse time domain waveform.
Fig. 3 is a wide spectrum optical time domain waveform obtained by shaping when the attenuator is adjusted to make the peak power of the pump light just reach the saturation threshold of the saturable absorber.
FIG. 4 is a diagram of a wide-spectrum optical time-domain waveform obtained by shaping when the attenuator is adjusted so that the peak power of the pump light is much higher than the saturation threshold of the saturable absorber.
FIG. 5 is a comparison graph of time-domain shaping using an acousto-optic modulator.
Detailed Description
The embodiments of the present invention will be described in detail below with reference to the accompanying drawings: the present embodiment is implemented on the premise of the technical solution of the present invention, and a specific implementation method is given, but the scope of the present invention is not limited to the following embodiments.
Referring to fig. 1, fig. 1 is a wide spectrum optical time domain shaping device, as shown, which is composed of the following parts:
the pump source 1: in the embodiment, the pump source is a single-frequency narrow-band laser with a central wavelength of 1053nm, an acousto-optic modulator and an electro-optic modulator are used in the pump source system to combine with an arbitrary waveform generator to perform time-domain modulation on continuous laser, and the pump source system has high-precision time-domain waveform control capability (the control precision can reach 40 ps). In this embodiment, the pump source outputs a 6ns slant-top pulse, and the output beam is a 3mm fundamental mode Gaussian beam.
The adjustable attenuator 2: in this embodiment, an absorptive attenuation sheet is used;
broad spectrum light to be shaped 3: in this embodiment, the amplified spontaneous emission light of the ytterbium-doped fiber is used as a partially coherent wide-spectrum light source, and the output end is fiber output, which outputs continuous light with a bandwidth of about 60 nm.
Input collimator 4: in the embodiment, the collimator is provided with a tail fiber, and the bottom width of an output light spot after collimation is about 300 mu m;
saturable absorber 5: the saturable absorber used in this embodiment is two pieces of four layers of accumulated graphene deposited on a quartz substrate, and the operation mode is a transmission mode. In an experiment, the position of the graphene saturable absorber is accurately adjusted to be just at the position where the pumping light spot is superposed with a part of related wide-spectrum light spot;
small hole 6: in the embodiment, the small hole is used for preventing the pump light reflected by the saturable absorber from interfering the detection result;
output collimator 7: the tail fiber of the output collimator is connected with a photoelectric tube with the bandwidth of 5GHz, and the shaped output pulse form is observed through an oscilloscope.
Fig. 2 is a time-domain waveform of a pump light pulse, and it can be seen from the figure that the pulse width of the pump light pulse is 6ns, the front and rear edges are steep, and the top is an oblique top, so as to test the response characteristics of the saturable absorber to different pump energies.
Example 1: adjusting the attenuator to enable the peak power of the pump light to just reach the saturation threshold of the saturable absorber, wherein the pump light energy is just at the starting point of the linear descending region of the absorption characteristic curve, and then within a certain range, the absorption rate of the saturable absorber is linearly reduced along with the increase of the pump light energy. The resulting shaped broad spectrum optical time domain waveform is shown in fig. 3. As can be seen from the figure, since the peak power of the pump light just reaches the saturation threshold of the saturable absorber, the transmittance of the saturable absorber gradually decreases as the optical power of the top-inclined portion gradually decreases, so that the shaped broad-spectrum optical pulse can well replicate the shape of the pump pulse, and the output is also a top-inclined pulse.
Example 2: when the attenuator is adjusted to make the peak power of the pump light far higher than the saturation threshold of the saturable absorber, the shaped wide-spectrum optical time-domain waveform is as shown in fig. 4. As can be seen from the figure, since the peak power of the pump light is much higher than the saturation threshold of the saturable absorber, although the optical power of the top portion of the oblique portion is gradually reduced, the saturable absorber is always in a fully saturated state during the whole pulse duration, and the transmittance does not change, so that the shaped wide-spectrum optical pulse is almost in a square waveform shape, and the pulse width is the same as the pulse width of the pump light. The output pulse shaped in time domain by using the acousto-optic modulator is shown in fig. 5, and it can be seen from the figure that the top of the pulse has strong irregular modulation.
Finally, it should be noted that the above embodiments are only for illustrating the technical solutions of the present invention and not for limiting, and although the present invention has been described in detail with reference to the preferred embodiments, it should be understood by those skilled in the art that modifications or equivalent substitutions may be made on the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, which should be covered by the claims of the present invention.
Claims (4)
1. A wide-spectrum optical time-domain shaping device is characterized by comprising a pumping source (1), an adjustable attenuator (2), an input collimator (4), a saturable absorber (5), a small hole (6) and an output collimator (7); the output of the pump source (1) is adjusted by the adjustable attenuator (2) to output energy and then is incident on the saturable absorber (5) to form a pump light spot; the wide-spectrum light (3) to be shaped is collimated by the input collimator (4) and then enters the saturable absorber (5) to form a wide-spectrum light spot, one part of the collimated wide-spectrum light is absorbed by the saturable absorber (5), and the rest part of the collimated wide-spectrum light is transmitted by the saturable absorber (5) and then reaches the output collimator (7) through the small hole (6) for coupling and output;
the wide-spectrum light spot is superposed with the pump light spot, and the area of the pump light spot is larger than that of the wide-spectrum light spot;
the pump source (1) is a light source system with flexible time domain waveform regulation and control capability, and the intensity of output light of the pump source system is higher than the saturable threshold of the saturable absorber (5) and lower than the damage threshold of the saturable absorber.
2. The broad spectrum optical time domain shaping device of claim 1, wherein: the wide-spectrum light (3) to be shaped is output by a wide-spectrum light source system with the bandwidth of hundreds of nanometers, and the output energy of the wide-spectrum light is lower than the saturable threshold of the saturable absorber (5).
3. The broad spectrum optical time domain shaping device of claim 1, wherein: the diameter of the small hole (6) is larger than that of the collimated broad spectrum light.
4. The broad spectrum optical time domain shaping device of claim 1, wherein: the saturable absorber (5) has a uniform transmission of different wavelengths within the spectral bandwidth of the broad spectrum light to be shaped.
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| CN114284852B (en) * | 2021-12-01 | 2024-03-01 | 中国科学院上海光学精密机械研究所 | Wide-spectrum low-coherence light source device with arbitrary time shaping capability |
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| JP4306990B2 (en) * | 2001-10-18 | 2009-08-05 | 独立行政法人産業技術総合研究所 | Nonlinear optical element |
| CN106711748B (en) * | 2016-12-23 | 2020-06-02 | 电子科技大学 | High-energy rectangular laser pulse generation system and method of all-fiber structure |
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| CN102053239A (en) * | 2010-11-05 | 2011-05-11 | 西南交通大学 | Triangular pulse generation method based on spectral structure |
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