CN115714301A - Line width adjustable laser based on external injection spontaneous radiation - Google Patents
Line width adjustable laser based on external injection spontaneous radiation Download PDFInfo
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Abstract
The invention provides a line width adjustable laser based on external injection spontaneous radiation, which comprises a laser resonant cavity, a gain medium, a pumping source and an external injection spontaneous radiation source, wherein the pumping source is connected with a first input end of the laser resonant cavity; after being input to the laser resonant cavity, the pumping source is transmitted to the gain medium to generate stimulated radiation; the external injection spontaneous radiation source injects spontaneous radiation into the laser resonant cavity so that the coupling of the spontaneous radiation and stimulated radiation in the laser resonant cavity is balanced again, and therefore the laser line width stably output by the laser is adjustable.
Description
Technical Field
The invention belongs to the field of laser line width regulation and control, and particularly relates to a line width adjustable laser based on external injection spontaneous radiation.
Background
The laser has wide application in the fields of distance measurement, industrial production, medical cosmetology and the like. The conventional laser generally comprises a pumping source, a gain medium and a laser resonant cavity, wherein the gain medium can generate spontaneous radiation, and the pumping source provides energy for the gain medium to enable the gain medium to generate stimulated radiation and realize population inversion; the laser resonant cavity provides optical feedback capability, and ensures that output laser has certain directionality and monochromaticity when the coupling of spontaneous radiation and stimulated radiation in the laser resonant cavity is balanced. Taking a fiber laser as an example, the fiber laser is a laser system generally formed by connecting optical active and passive devices with a fiber pigtail by using a doped fiber or a nonlinear effect (stimulated raman scattering, stimulated brillouin scattering) in the fiber as a gain medium. Fig. 1 shows a schematic structural diagram of a ring fiber laser based on traveling wave interference, where the fiber laser includes a pump light source, a wavelength division multiplexer, a gain fiber, an isolator, and a coupler, the pump light source is connected with a first input end of the wavelength division multiplexer, an output end of the wavelength division multiplexer sequentially passes through a gain medium and the isolator to be connected with an input end of the coupler, a first output end of the coupler is connected with a second input end of the wavelength division multiplexer, and a second output end is an output end of the laser. In a traditional laser, when a gain fiber and an input pumping light source are fixed, coupling of spontaneous radiation and stimulated radiation in a laser resonant cavity reaches balance, namely, after a power spectral density ratio of the spontaneous radiation to the stimulated radiation tends to be stable, a laser line width output by the laser tends to be stable, and adjustment cannot be performed. The application field of the traditional laser is limited because the fields of communication, measurement, medicine and the like have different requirements on laser wave bands.
Disclosure of Invention
The invention provides a linewidth adjustable laser based on external injection spontaneous radiation, which aims to solve the problems that the linewidth of laser output by the traditional laser is not adjustable, and the requirements of different wave bands in different application fields are difficult to meet.
According to a first aspect of the embodiments of the present invention, there is provided an external injection spontaneous emission-based line width tunable laser, including a laser resonant cavity, a gain medium, a pump source, and an external injection spontaneous emission source, where the pump source is connected to a first input end of the laser resonant cavity, the external injection spontaneous emission source is connected to a second input end of the laser resonant cavity, and the gain medium is disposed in the laser resonant cavity and used for generating spontaneous emission;
the pumping source is input into the laser resonant cavity and then is transmitted to the gain medium to generate stimulated radiation; and the external injection spontaneous radiation source injects spontaneous radiation into the laser resonant cavity so as to ensure that the coupling of the spontaneous radiation and the stimulated radiation in the laser resonant cavity is balanced again, thereby realizing the adjustable line width of laser stably output by the laser.
In an optional implementation manner, the laser further includes a cycle number regulating and controlling component, configured to determine a cycle transmission number in the laser resonant cavity before the unit amount of stimulated radiation is completely output from the laser resonant cavity, where after the unit amount of stimulated radiation is circularly transmitted in the laser resonant cavity for multiple times and completely output from the laser resonant cavity, coupling of spontaneous radiation and stimulated radiation in the laser resonant cavity reaches balance again, and thus the laser stably outputs laser and completes line width adjustment of the laser;
in each cycle transmission process of the stimulated radiation, along with the increase of the spontaneous emission amount which is injected into the laser resonant cavity and coupled with the stimulated radiation, the random interference degree of the spontaneous emission to the phase of spectral components in the stimulated radiation is enhanced in the cycle transmission process, the line width of the laser output by the laser is increased, and the laser line width when the laser is stably output is the result of the accumulated increase of the line width in each cycle transmission process;
under the condition that the number of the stimulated radiation cyclic transmission times is not changed, along with the increase of the injected spontaneous emission amount in each cyclic transmission process, the laser power is increased when the laser is stably output; along with the increase of the number of the stimulated radiation circulation transmission times, the laser line width and the power of the laser when the laser is stably output are increased.
In another optional implementation manner, at least one of the power of the pump source, the amount of spontaneous radiation injected into the laser resonant cavity and coupled with the stimulated radiation, and the number of times of cyclic transmission of the stimulated radiation is adjusted, so that the laser stably output by the laser meets the corresponding line width and/or power requirement.
In another optional implementation manner, for pump sources of different powers, parameter adjustment data blocks corresponding to the pump sources are constructed, each parameter adjustment data block includes a plurality of stimulated radiation cyclic transmission times allowed to be adjusted, each stimulated radiation cyclic transmission time corresponds to a plurality of spontaneous emission amounts which can be adjusted, and for each stimulated radiation cyclic transmission time, each spontaneous emission amount corresponding to the stimulated radiation cyclic transmission time corresponds to one laser line width and one power group respectively;
according to the following steps, at least one of the power of the pump source, the amount of spontaneous radiation injected into the laser resonant cavity and coupled with the stimulated radiation and the number of stimulated radiation cyclic transmission times is adjusted, so that the laser stably output by the laser meets the corresponding line width and/or power requirements:
step S101, determining a parameter adjusting data block corresponding to the current pump source according to the power of the current pump source, and searching a laser line width and a power group corresponding to a required line width from the determined parameter adjusting data block;
step S102, aiming at each found laser line width and power group, sequentially judging whether the laser line width and the power in the power group are the same as the required power, if so, finding out the spontaneous emission amount corresponding to the laser line width and the power group and the stimulated emission cycle transmission times corresponding to the spontaneous emission amount, and executing step S103, otherwise, executing step S106;
step S103, judging whether the laser line width and the power group are the last one of the searched laser line widths and power groups, if so, executing step S104, otherwise, returning to execute step S102;
step S104, taking the minimum stimulated radiation cyclic transmission frequency in the searched stimulated radiation cyclic transmission frequencies as a stimulated radiation cyclic transmission target frequency, taking the spontaneous emission quantity corresponding to the minimum stimulated radiation cyclic transmission frequency in the searched spontaneous emission quantity as a spontaneous emission target quantity, and executing step S105;
s105, controlling the external injection spontaneous radiation source to inject the target amount of spontaneous radiation into the laser resonant cavity, so that the target amount of spontaneous radiation is coupled with the stimulated radiation in each cycle transmission process of the stimulated radiation; controlling the cycle number regulating and controlling assembly to regulate the cycle transmission number of the stimulated radiation in the laser resonant cavity to the target number, so that the laser linewidth and power meet the corresponding linewidth and power requirements when the laser stably outputs laser, and executing step S107;
step S106, judging whether the maximum stimulated radiation cycle transmission frequency in the determined parameter adjusting data block is smaller than the required power or not according to the laser line width and the power of the power group under the maximum spontaneous emission quantity, if so, taking the next pumping source with larger power as the current pumping source, returning to execute step S101, and if not, taking the last pumping source with smaller power as the current pumping source, returning to execute step S101;
and S107, adjusting the power of the pumping source to the power of the current pumping source.
In another optional implementation manner, parameter adjustment data blocks corresponding to different power pump sources may be stored in a controller in advance, and the controller is connected to the pump source, the external injection spontaneous radiation source, and the cycle number adjustment and control component, so as to control and adjust the power of the pump source, the amount of spontaneous radiation provided by the external injection spontaneous radiation source, and the number of stimulated radiation source cyclic transmission times determined by the cycle number adjustment and control component, respectively.
In another optional implementation manner, the laser resonant cavity includes a wavelength division multiplexer and a coupler, and a first input end of the wavelength division multiplexer is a first input end of the laser resonant cavity and is connected to the pump source; the output end of the wavelength division multiplexer is connected with the first input end of the coupler through the gain medium, the second input end of the coupler is used as the second input end of the laser resonator and is connected with the external injection spontaneous radiation source, the first output end of the coupler is connected with the second input end of the wavelength division multiplexer, and the second output end of the coupler is used as the output end of the laser; the coupler is the cycle number regulating and controlling component, and the coupling degree of the second output end of the coupler determines the cycle transmission number in the laser resonant cavity before unit amount of stimulated radiation is completely output from the laser resonant cavity.
In another optional implementation manner, the laser resonator further includes a band-pass filter, the first output end of the coupler is connected to the second input end of the wavelength division multiplexer through the band-pass filter, and the band-pass filter is used for limiting an effective gain range of laser in the laser resonator, suppressing mode hopping, and realizing single longitudinal mode operation of the laser.
In another optional implementation manner, the laser resonator further includes an isolator, where the isolator is disposed between the first output end of the coupler and the second input end of the wavelength division multiplexer, and the isolator is configured to ensure unidirectional operation of laser in the laser resonator, so as to improve laser output efficiency.
In another optional implementation manner, the laser resonator includes a total reflector and an output reflector that are vertically arranged relatively, the gain medium is disposed between the total reflector and the output reflector, a reflection side of the total reflector faces the gain medium, the gain medium includes an active region, and a P region and an N region that are respectively located on the upper side and the lower side of the active region, the P region between the total reflector and the output reflector is a first input end of the laser resonator and is connected to the pump source; the output reflector is used as a second input end of the laser resonator and is connected with the external injection spontaneous radiation source;
the gain medium is used for generating spontaneous radiation, and the gain medium generates stimulated radiation after receiving the pumping source through the P region; the external injection spontaneous radiation source injects spontaneous radiation into the N region through the output reflector so as to enable coupling of the spontaneous radiation in the laser resonant cavity and the stimulated radiation source to reach balance again.
In another optional implementation manner, the laser gain control device further includes a half-mirror, the half-mirror is used as the cycle number adjusting and controlling component, and is connected to the output mirror, and transmits a part of laser output from the output mirror as output laser of the laser, and returns another part of laser output to the gain medium through the output mirror, and a transmission and reflection ratio of the half-mirror determines the cycle transmission number in the laser resonator before the unit amount of stimulated radiation is completely output from the laser resonator.
The beneficial effects of the invention are:
1. according to the invention, by adjusting the spontaneous emission amount injected into the laser resonant cavity and coupled with the stimulated radiation, the line width of the output stable laser can be increased, and the power of the output stable laser can be improved under the condition that the number of stimulated radiation cyclic transmission times is not changed, so that even if the number of stimulated radiation cyclic transmission times is less, under the condition that the injected spontaneous radiation is added, the laser can also meet the output requirement of high-power laser, namely, the high-power laser can be generated more easily and rapidly; by injecting the spontaneous radiation outside the laser resonant cavity, the time coherence of the laser output by the laser can be reduced, and the speckle phenomenon caused by high time coherence is weakened; in addition, the invention can improve the line width and the power of the output stable laser by increasing the number of the stimulated radiation cycle transmission times, and the power is obviously improved; the invention has adjustable line width and power, so the invention has wider application range and can be widely applied to the fields of optical precision measurement, optical communication, optical signal processing and the like;
2. when the line width and/or the power of the laser stably output by the laser are/is adjusted, firstly, under the condition that the power of a pumping source is not changed, the line width and the power requirements are met by adjusting the spontaneous emission and the stimulated emission cyclic transmission times, and when the adjustment of the spontaneous emission and the stimulated emission cyclic transmission times cannot meet the power requirements, the power of the pumping source is changed to enable the laser stably output by the laser to meet the corresponding power requirements, so that the laser line width and the power can be independently adjusted according to any parameter, and the laser output diversity is improved; aiming at the searched laser linewidth and power group which are equal to the required linewidth and the required power, the minimum cycle transmission times are selected as the target times from the stimulated radiation cycle transmission times corresponding to the laser linewidth and power group preferentially, namely the cycle transmission times of the stimulated radiation in the laser resonant cavity are reduced as much as possible on the premise of ensuring that the linewidth and power requirements are met, and therefore the generation speed of stable laser can be ensured;
3. the invention makes the controller respectively connected with the pump source, the external injection spontaneous radiation source and the cycle number regulating and controlling component to respectively control and regulate the power of the pump source, the spontaneous radiation amount provided by the external injection spontaneous radiation source and the cycle number of the stimulated radiation source determined by the cycle number regulating and controlling component, thereby realizing the automatic regulation of the laser line width and the power, and realizing the continuous regulation of the laser line width and the power without interrupting the laser output in the regulating process.
Drawings
FIG. 1 is a schematic structural diagram of one embodiment of a conventional fiber laser;
FIG. 2 is a schematic structural diagram of a line-width tunable laser based on external injection spontaneous emission according to the present invention;
FIG. 3 is a schematic structural diagram of an embodiment of a line-width tunable laser based on external injection spontaneous emission according to the present invention;
fig. 4 is a schematic structural diagram of another embodiment of the linewidth-tunable laser based on external injection spontaneous radiation according to the present invention.
Detailed Description
In order to make the technical solutions in the embodiments of the present invention better understood and make the above objects, features and advantages of the embodiments of the present invention more comprehensible, the technical solutions in the embodiments of the present invention are described in further detail below with reference to the accompanying drawings.
In the description of the present invention, unless otherwise specified and limited, it should be noted that the term "connected" should be interpreted broadly, for example, as being mechanically or electrically connected, or as being interconnected between two elements, directly or indirectly through an intermediate medium, and the specific meaning of the term is understood by those skilled in the art according to the specific situation.
Referring to fig. 2, a schematic structural diagram of an embodiment of the line width tunable laser based on external injection spontaneous emission according to the present invention is shown. The laser with the adjustable line width can comprise a laser resonant cavity, a gain medium, a pumping source and an external injection spontaneous radiation source, wherein the pumping source is connected with a first input end of the laser resonant cavity, the external injection spontaneous radiation source is connected with a second input end of the laser resonant cavity, and the gain medium is arranged in the laser resonant cavity and used for generating spontaneous radiation; the pumping source is input into the laser resonant cavity and then is transmitted to the gain medium to generate stimulated radiation; and the external injection spontaneous radiation source injects spontaneous radiation into the laser resonant cavity so as to ensure that the coupling of the spontaneous radiation and the stimulated radiation in the laser resonant cavity is balanced again, thereby realizing the adjustable line width of laser stably output by the laser.
Although the laser output by the laser may include many spectral components with different wavelengths, only the corresponding wavelength spectral component with a larger light intensity is usually used as the laser output by the laser, and the corresponding wavelength spectral component with a weaker light intensity is negligible. The light intensity of laser output by the laser is mainly determined by stimulated radiation, namely, the gain coefficient of the gain medium and the energy of the pumping source, the influence of spontaneous radiation on the light intensity of the output laser is small and can be ignored, the main effect of the spontaneous radiation is to cause random interference to the phase of the stimulated radiation, and for the spectral components which have the same wavelength but have phases which do not meet interference conditions in the stimulated radiation, when the phase of one spectral component is changed under the interference of the spontaneous radiation, so that the phases of two spectral components meet the interference conditions, the two spectral components will interfere with each other, and the light intensity of the spectral component corresponding to the wavelength is increased.
In this embodiment, before the external spontaneous emission is not injected into the laser resonant cavity, the spontaneous emission and the stimulated emission generated by the gain medium in the laser resonant cavity are mutually coupled and balanced, and at this time, the laser output by the laser is stable, and the line width is constant. After the external injection spontaneous radiation source injects spontaneous radiation into the laser resonant cavity, the balance between the spontaneous radiation generated by the gain medium in the laser resonant cavity and the stimulated radiation is broken, the injection of the spontaneous radiation can enable the phase random interference of the spontaneous radiation in the laser resonant cavity to the stimulated radiation to be strengthened, the strengthening of the phase random interference can enable the probability that spectral components with the same wavelength but the phases which do not meet interference conditions in the stimulated radiation interfere to be increased, the spectral components with increased light intensity are increased, and the line width of laser output by the laser is widened. Generally, before unit amount of stimulated emission is completely output from the laser resonant cavity, cyclic transmission may be performed multiple times in the laser resonant cavity, so the laser of the present invention may further include a cycle number adjusting component for determining the number of cyclic transmission in the laser resonant cavity before unit amount of stimulated emission is completely output from the laser resonant cavity, wherein when unit amount of stimulated emission is cyclically transmitted multiple times in the laser resonant cavity and is completely output from the laser resonant cavity, coupling of spontaneous emission and stimulated emission in the laser resonant cavity is balanced again, so that the laser stably outputs laser and completes line width adjustment of laser.
In addition, the laser stably outputs the Linewidth and the spontaneous emission power spectral density I of the laser 0 Total power of stimulated radiation in cavity I 2, total of The relationship between can be expressed as:
wherein τ represents a group velocity, and when the external injection spontaneous radiation source injects spontaneous radiation into the laser resonator, a power spectral density of the spontaneous radiation in the laser resonator increases, and correspondingly, a line width of laser output by the laser also increases. Power spectral density refers to the power per unit frequency interval. It can be seen from the above formula that reducing the total stimulated emission power can also increase the output laser linewidth. The total stimulated radiation power can be reduced by reducing the power of the pump source.
When the total power of the stimulated radiation is reduced, in the process of the stimulated radiation in the circulating transmission of the laser resonant cavity, the light intensity value increased by the spectral components in the stimulated radiation is smaller when the spectral components interfere once, and even if the corresponding spectral components in the stimulated radiation interfere in the circulating transmission once, the difference between the light intensity of the spectral components and the light intensity of the spectral components which do not interfere is still small, so that the requirement on high-power laser output of a laser cannot be met. In this case, if the number of times of cyclic transfer of the excitation radiation is increased, the power of the laser stably outputting the laser light can be increased, but the stable laser light generation speed is decreased by the cyclic transfer of a plurality of times. Therefore, when the total power of the stimulated radiation is reduced to increase the line width of the output laser, the laser stably output by the laser cannot meet the high-power requirement, and when the power of the stable laser is improved by increasing the number of stimulated radiation cycles, the problem of low laser generation speed exists.
When the line width of the output laser is increased, the line width of the output laser is realized by injecting spontaneous radiation from the outside and increasing the power spectral density of the spontaneous radiation, when the line width of the stimulated radiation is not changed, in each cyclic transmission process of the stimulated radiation, along with the increase of the amount of the spontaneous radiation which is injected into the laser resonant cavity and is coupled with the stimulated radiation, the random interference degree of the spontaneous radiation on the phase of the spectral components in the stimulated radiation is enhanced in the cyclic transmission process, the number of the spectral components which interfere in each cyclic transmission is more, so that the line width of the output laser of the laser is increased, and the line width of the output laser when the laser is stably output is the result of the accumulated increase of the line width in each cyclic transmission process.
The probability that the spontaneous emission is coupled with the stimulated emission in the laser resonant cavity is increased, the random interference of the spontaneous emission on the phase of the stimulated emission can be enhanced, the probability that the phase of each spectral component in the stimulated emission is interfered is improved, the probability that each spectral component in the stimulated emission is interfered is improved, in each cycle transmission process of the stimulated emission, the interference of the spontaneous emission on the phase of the stimulated emission is random and independent, the probability that the spectral components are interfered in each cycle transmission process is equal and improved, therefore, in the whole cycle transmission process, the probability that the light intensity of the spectral components is accumulated to be a large value can be improved, and the laser can generate high-power laser more easily. That is, under the condition that the number of times of the cyclic transfer of the stimulated emission is not changed, the laser power when the laser stably outputs the laser is increased along with the increase of the amount of the spontaneous emission injected in each cyclic transfer process. Because the probability of interference of the spectral components in each cyclic transmission process is improved, the laser line width and the power average rate when the laser stably outputs the laser are increased and the power is obviously increased along with the increase of the number of the cyclic transmission times of the stimulated radiation, and after the number of the cyclic transmission times is increased to the corresponding number, the power value increased by the laser after injecting the spontaneous radiation is larger than the power value increased by the laser when not injecting the spontaneous radiation.
It can be seen from the above embodiments that, by adjusting the amount of spontaneous emission injected into the laser resonator and coupled with the stimulated emission, the invention can not only increase the linewidth of the output stable laser, but also improve the power of the output stable laser under the condition that the number of times of the stimulated emission cyclic transmission is not changed, so that even if the number of times of the stimulated emission cyclic transmission is small, the laser can meet the output requirement of the high-power laser under the hold of the injected spontaneous emission, that is, the invention can generate the high-power laser more easily and quickly; in addition, the invention can improve the linewidth and power of the output stable laser by increasing the number of the stimulated radiation cycle transmission times, and the power is obviously improved.
In addition, the relationship between the laser line width Δ v and the coherence time Δ t can be expressed as:
when the line width of the laser is increased, the time coherence of the laser is correspondingly reduced, so that the time coherence of the laser output by the laser can be reduced by injecting the spontaneous radiation outside the laser resonant cavity, and the speckle phenomenon caused by high time coherence is weakened. The invention has adjustable line width and power, so the invention has wide application range and can be widely applied to the fields of optical precision measurement, optical communication, optical signal processing and the like.
In the invention, the linewidth and the power of the output laser can be simultaneously improved by adjusting the spontaneous radiation quantity injected from the outside, the linewidth and the power of the output laser can be influenced by the cycle transmission frequency of the stimulated radiation in the laser resonant cavity, and the power of the pump source can influence the power of the output laser. Therefore, the laser device can adjust at least one of the power of the pump source, the amount of spontaneous radiation injected into the laser resonant cavity and coupled with the stimulated radiation and the number of stimulated radiation cyclic transmission times, so that the laser stably output by the laser device meets the corresponding line width and/or power requirements. Firstly, parameter adjusting data blocks corresponding to the pump sources with different powers can be constructed, each parameter adjusting data block comprises a plurality of stimulated radiation cyclic transmission times allowed to be adjusted, the stimulated radiation cyclic transmission times included in each parameter adjusting data block are the same, each stimulated radiation cyclic transmission time corresponds to a plurality of adjustable spontaneous emission quantities, and the spontaneous emission quantity corresponding to each stimulated radiation cyclic transmission time is the same. And aiming at each stimulated radiation cycle transmission frequency, each spontaneous emission amount corresponding to the stimulated radiation cycle frequency respectively corresponds to one laser line width and one laser power group.
In the parameter adjustment data block corresponding to the same power pumping source, aiming at each spontaneous emission quantity corresponding to the same stimulated radiation cycle transmission frequency, along with the increase of the spontaneous emission quantity, the line width and the power of the laser line width and the power group corresponding to the spontaneous emission quantity are increased; aiming at different stimulated radiation cycle transmission times with the same spontaneous emission amount, along with the increase of the stimulated radiation cycle times, the line width and the power of the different stimulated radiation cycle transmission times are increased in the laser line width and the power group corresponding to the spontaneous emission amount. Specifically, at least one of the power of the pump source, the amount of spontaneous emission injected into the laser resonant cavity and coupled with the stimulated radiation, and the number of times of cyclic transmission of the stimulated radiation may be adjusted according to the following steps, so that the laser stably output by the laser meets the corresponding line width and/or power requirements:
step S101, determining a parameter adjusting data block corresponding to the current pumping source according to the power of the current pumping source, and searching a laser line width and a power group corresponding to a required line width from the determined parameter adjusting data block;
step S102, aiming at each found laser line width and power group, sequentially judging whether the laser line width and the power in the power group are the same as the required power, if so, finding out the spontaneous emission amount corresponding to the laser line width and the power group and the stimulated emission cycle transmission times corresponding to the spontaneous emission amount, executing step S103, and if not, executing step S106;
step S103, judging whether the laser line width and the power group are the last one of the searched laser line widths and power groups, if so, executing step S104, otherwise, returning to execute step S102;
step S104, taking the minimum stimulated radiation cycle transmission frequency in the searched stimulated radiation cycle transmission frequencies as the stimulated radiation cycle transmission target frequency, taking the spontaneous emission quantity corresponding to the minimum stimulated radiation cycle transmission frequency in the searched spontaneous emission quantity as the spontaneous emission target quantity, and executing step S105;
s105, controlling the external injection spontaneous radiation source to inject the target amount of spontaneous radiation into the laser resonant cavity, so that the target amount of spontaneous radiation is coupled with the stimulated radiation in each cycle transmission process of the stimulated radiation; and controlling the cycle number regulating and controlling assembly, regulating the cycle transmission number of the stimulated radiation in the laser resonant cavity to the target number, so that the laser linewidth and the power meet the corresponding linewidth and power requirements when the laser stably outputs laser, and executing the step S107. Aiming at the searched laser linewidth and power group which are equal to the required linewidth and the required power, the minimum cycle transmission times are selected as the target times from the stimulated radiation cycle transmission times corresponding to the laser linewidth and the power group preferentially, namely, the cycle transmission times of the stimulated radiation in the laser resonant cavity are reduced as much as possible on the premise of ensuring that the linewidth and the power requirements are met, and therefore, the generation speed of the stable laser can be ensured.
And S106, judging whether the laser line width and the power of the power group corresponding to the maximum stimulated radiation circulating transmission frequency under the maximum spontaneous emission quantity in the determined parameter adjusting data block are smaller than the required power, if so, taking the next pumping source with higher power as the current pumping source, returning to execute the step S101, and otherwise, taking the last pumping source with lower power as the current pumping source, and returning to execute the step S101.
And S107, adjusting the power of the pumping source to the power of the current pumping source.
When the invention is used for adjusting the line width and/or the power of the laser stably output by the laser, firstly, under the condition that the power of the pumping source is not changed, the line width and the power requirements are met by adjusting the spontaneous emission and the stimulated emission cycle transmission times, and when the adjustment of the spontaneous emission and the stimulated emission cycle transmission times cannot meet the power requirements, the power of the pumping source is changed to enable the laser stably output by the laser to meet the corresponding power requirements, so that the invention can realize the independent adjustment of any parameter of the line width and the power of the laser and improve the diversity of the laser output. It is to be noted that, when the amount of spontaneous emission is adjusted, it can be achieved by adjusting the output frequency or wavelength of the spontaneous emission.
In addition, parameter adjustment data blocks corresponding to different power pump sources can be stored in a controller in advance, and the controller is connected with the pump sources, the external injection spontaneous radiation sources and the cycle number adjusting and controlling assembly respectively to control and adjust the power of the pump sources, the spontaneous radiation quantity provided by the external injection spontaneous radiation sources and the cycle transmission number of the stimulated radiation sources determined by the cycle number adjusting and controlling assembly respectively, so that the automatic adjustment of the laser line width and the power can be realized, the laser output does not need to be interrupted in the adjusting process, and the continuous adjustment of the laser line width and the power is realized.
Referring to fig. 3, a schematic structural diagram of an embodiment of the linewidth tunable laser based on external injection spontaneous emission according to the present invention is shown. In this embodiment, a fiber laser is taken as an example, and fig. 3 differs from the embodiment shown in fig. 2 in that the laser resonant cavity may include a wavelength division multiplexer and a coupler, where a first input end of the wavelength division multiplexer is a first input end of the laser resonant cavity and is connected to the pump source; the output end of the wavelength division multiplexer is connected with the first input end of the coupler through the gain medium, the second input end of the coupler is used as the second input end of the laser resonator and is connected with the external injection spontaneous radiation source, the first output end of the coupler is connected with the second input end of the wavelength division multiplexer, and the second output end of the coupler is used as the output end of the laser; the coupler is the cycle number regulating and controlling component, and the coupling degree of the second output end of the coupler determines the cycle transmission number in the laser resonant cavity before unit quantity of stimulated radiation is completely output from the laser resonant cavity. The pumping source is input to the wavelength division multiplexer and then transmitted to the gain medium, particle number inversion is achieved at the gain medium, the pumping process is completed, stimulated radiation is generated, the external injection spontaneous radiation source injects spontaneous radiation into the coupler, the coupling of the spontaneous radiation and the stimulated radiation reaches balance again at the coupler, and the number of times of the stimulated radiation circulation transmission can be adjusted by adjusting the coupling degree of the second output end of the coupler. In this embodiment, the pump source and the external injection spontaneous emission source may be light sources, that is, the pump light and the external injection spontaneous emission light, respectively, and the gain medium may be an erbium-doped fiber.
Fig. 3 differs from the embodiment shown in fig. 2 in that the laser resonator may further include a band-pass filter and an isolator, the first output end of the coupler is connected to the second input end of the wavelength division multiplexer through the band-pass filter, and the band-pass filter is configured to limit an effective gain range of laser light in the laser resonator, suppress mode hopping, and implement single longitudinal mode operation of the laser; the isolator is arranged between the first output end of the coupler and the second input end of the wavelength division multiplexer, and is used for ensuring unidirectional operation of laser in the laser resonant cavity and improving the laser output efficiency.
It can be seen from the above embodiments that, by adjusting the amount of spontaneous emission injected into the laser resonant cavity to couple with the stimulated emission, the invention can not only increase the line width of the output stable laser, but also improve the power of the output stable laser under the condition of unchanged stimulated emission cycle transmission frequency, so that even if the stimulated emission cycle transmission frequency is less, the laser can meet the output requirement of high-power laser under the influence of the injected spontaneous emission, that is, the invention can generate high-power laser more easily and quickly; by injecting the spontaneous radiation outside the laser resonant cavity, the time coherence of the laser output by the laser can be reduced, and the speckle phenomenon caused by high time coherence is weakened; in addition, the invention can improve the line width and the power of the output stable laser by increasing the number of the stimulated radiation cycle transmission times, and the power is obviously improved. The invention has adjustable line width and power, so the invention has wide application range and can be widely applied to the fields of optical precision measurement, optical communication, optical signal processing and the like.
Referring to fig. 4, it is a schematic structural diagram of another embodiment of the line width tunable laser based on external injection spontaneous emission according to the present invention. In this embodiment, a semiconductor laser is taken as an example, and the difference between the embodiment shown in fig. 4 and the embodiment shown in fig. 2 is that the laser resonant cavity may include a total reflector and an output reflector which are vertically arranged relatively, the gain medium is disposed between the total reflector and the output reflector, a reflection side of the total reflector faces the gain medium, the gain medium includes an active region, and a P region and an N region (the P region and the N region may be formed on the upper and lower sides of the active region in a deposition manner) which are respectively located on the upper and lower sides of the active region, and the P region between the total reflector and the output reflector is a first input end of the laser resonant cavity and is connected with the pump source; the output reflector is used as a second input end of the laser resonator and is connected with the external injection spontaneous radiation source; the gain medium is used for generating spontaneous radiation, and after the gain medium receives the pumping source through the P region, population inversion is realized at the gain medium, the pumping process is completed, and stimulated radiation is generated; the external injection spontaneous radiation source injects spontaneous radiation into the N region through the output reflector so as to enable coupling of the spontaneous radiation in the laser resonant cavity and the stimulated radiation source to reach balance again. The reflectivity of the total reflector is 100%, the output reflector is a partial transmission mirror, which transmits out a part of laser generated by the gain medium, and the other part of laser reflects back to the gain medium to continue to multiply photons in the laser resonant cavity.
Fig. 4 is different from the embodiment shown in fig. 2 in that a half mirror is included as the cycle number adjustment and control component, and is connected to the output mirror, so that a part of the laser output from the output mirror is transmitted as the output laser of the laser, and another part of the laser is returned to the gain medium through the output mirror, and the transmission and reflection ratio of the half mirror determines the cycle transmission number in the laser resonator before the unit amount of the stimulated radiation is completely output from the laser resonator, and the cycle transmission number of the stimulated radiation can be adjusted by adjusting the transmission and reflection ratio of the half mirror. In this embodiment, the pump source and the external injection spontaneous radiation source may be currents, that is, the pump current and the external injection spontaneous radiation current, the gain medium may be a direct band gap semiconductor, such as a semiconductor material of GaAs (gallium arsenide), alGaAs (aluminum gallium arsenic), and the like, one surface of the half mirror is provided with an antireflection film, and the other surface is provided with a reflection film, and the transmission and reflection ratio of the incident laser light can be changed by plating the half reflection film on the optical glass.
It can be seen from the above embodiments that, by adjusting the amount of spontaneous emission injected into the laser resonant cavity to couple with the stimulated emission, the invention can not only increase the line width of the output stable laser, but also improve the power of the output stable laser under the condition of unchanged stimulated emission cycle transmission frequency, so that even if the stimulated emission cycle transmission frequency is less, the laser can meet the output requirement of high-power laser under the influence of the injected spontaneous emission, that is, the invention can generate high-power laser more easily and quickly; by injecting the spontaneous radiation outside the laser resonant cavity, the time coherence of the laser output by the laser can be reduced, and the speckle phenomenon caused by high time coherence is weakened; in addition, the invention can improve the line width and the power of the output stable laser by increasing the number of the stimulated radiation cycle transmission times, and the power is obviously improved. The invention has adjustable line width and power, so the invention has wide application range and can be widely applied to the fields of optical precision measurement, optical communication, optical signal processing and the like.
It should be noted that, the laser generated by the conventional laser usually has jitter, and since the invention injects the external spontaneous emission into the laser resonant cavity, and the phase of the stimulated emission is changed by adjusting the external spontaneous emission, the external injected spontaneous emission and the pump source have the same clock reference, and the jitter of the laser generated by the laser is suppressed.
Other embodiments of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. This application is intended to cover any variations, uses, or adaptations of the invention following, in general, the principles of the invention and including such departures from the present disclosure as come within known or customary practice within the art to which the invention pertains. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the invention being indicated by the following claims.
It will be understood that the invention is not limited to the precise arrangements described above and shown in the drawings and that various modifications and changes may be made without departing from the scope thereof. The scope of the invention is to be controlled solely by the appended claims.
Claims (10)
1. A line width adjustable laser based on external injection spontaneous radiation comprises a laser resonant cavity, a gain medium and a pumping source, and is characterized by further comprising an external injection spontaneous radiation source, wherein the pumping source is connected with a first input end of the laser resonant cavity, the external injection spontaneous radiation source is connected with a second input end of the laser resonant cavity, and the gain medium is arranged in the laser resonant cavity and used for generating spontaneous radiation;
the pumping source is input into the laser resonant cavity and then transmitted to the gain medium to generate stimulated radiation; and the external injection spontaneous radiation source injects spontaneous radiation into the laser resonant cavity so as to balance the coupling of the spontaneous radiation and the stimulated radiation in the laser resonant cavity again, thereby realizing the adjustable laser line width stably output by the laser.
2. The linewidth tunable laser based on external injection spontaneous emission of claim 1, further comprising a cycle number adjusting and controlling component for determining the number of times of cycle transmission in the laser resonator before the unit amount of stimulated emission is completely outputted from the laser resonator, wherein when the unit amount of stimulated emission is circularly transmitted in the laser resonator for multiple times and is completely outputted from the laser resonator, the coupling of spontaneous emission and stimulated emission in the laser resonator reaches balance again, so that the laser stably outputs laser and the linewidth tuning of the laser is completed;
in each cycle transmission process of the stimulated radiation, along with the increase of the amount of spontaneous radiation which is injected into the laser resonant cavity and coupled with the stimulated radiation, the random interference degree of the spontaneous radiation on the phase of a spectrum component in the stimulated radiation is strengthened in the cycle transmission process, the line width of the laser output by the laser is also increased, and the line width of the laser when the laser is stably output by the laser is the result of the accumulated increase of the line width in each cycle transmission process;
under the condition that the number of the stimulated radiation cyclic transmission times is not changed, along with the increase of the injected spontaneous emission amount in each cyclic transmission process, the laser power is increased when the laser is stably output; along with the increase of the number of the stimulated radiation circulation transmission times, the laser line width and the power of the laser when the laser is stably output are increased.
3. The linewidth tunable laser based on external injection spontaneous emission of claim 2, wherein at least one of the power of the pump source, the amount of spontaneous emission injected into the laser resonator to couple with the stimulated emission, and the number of cyclic transmission of the stimulated emission is adjusted, so that the laser output stably by the laser meets the corresponding linewidth and/or power requirements.
4. The linewidth tunable laser based on external injection spontaneous emission of claim 3, wherein for the pump sources with different powers, a parameter adjusting data block corresponding to the pump sources is constructed, each parameter adjusting data block comprises a plurality of stimulated radiation cyclic transmission times allowed to be adjusted, each stimulated radiation cyclic transmission time corresponds to a plurality of tunable spontaneous emission quantities, and each spontaneous emission quantity corresponding to each stimulated radiation cyclic transmission time corresponds to a laser linewidth and a power group respectively;
according to the following steps, at least one of the power of the pump source, the amount of spontaneous radiation injected into the laser resonant cavity and coupled with the stimulated radiation and the number of stimulated radiation cyclic transmission times is adjusted, so that the laser stably output by the laser meets the corresponding line width and/or power requirements:
step S101, determining a parameter adjusting data block corresponding to the current pump source according to the power of the current pump source, and searching a laser line width and a power group corresponding to a required line width from the determined parameter adjusting data block;
step S102, aiming at each found laser line width and power group, sequentially judging whether the laser line width and the power in the power group are the same as the required power, if so, finding out the spontaneous emission amount corresponding to the laser line width and the power group and the stimulated emission cycle transmission times corresponding to the spontaneous emission amount, and executing step S103, otherwise, executing step S106;
step S103, judging whether the laser line width and the power group are the last one of the searched laser line widths and power groups, if so, executing step S104, otherwise, returning to execute step S102;
step S104, taking the minimum stimulated radiation cyclic transmission frequency in the searched stimulated radiation cyclic transmission frequencies as a stimulated radiation cyclic transmission target frequency, taking the spontaneous emission quantity corresponding to the minimum stimulated radiation cyclic transmission frequency in the searched spontaneous emission quantity as a spontaneous emission target quantity, and executing step S105;
s105, controlling the external injection spontaneous radiation source to inject the target amount of spontaneous radiation into the laser resonant cavity, so that the target amount of spontaneous radiation is coupled with the stimulated radiation in each cycle transmission process of the stimulated radiation; controlling the cycle number regulating and controlling assembly to regulate the cycle transmission number of the stimulated radiation in the laser resonant cavity to the target number, so that the laser linewidth and power meet the corresponding linewidth and power requirements when the laser stably outputs laser, and executing step S107;
step S106, judging whether the maximum stimulated radiation cycle transmission frequency in the determined parameter adjusting data block is smaller than the required power or not according to the laser line width and the power of the power group under the maximum spontaneous emission quantity, if so, taking the next pumping source with larger power as the current pumping source, returning to execute step S101, and if not, taking the last pumping source with smaller power as the current pumping source, returning to execute step S101;
and S107, adjusting the power of the pumping source to the power of the current pumping source.
5. The line width tunable laser based on external injection spontaneous emission of claim 4, wherein parameter tuning data blocks corresponding to different power pump sources can be stored in a controller in advance, and the controller is connected to the pump source, the external injection spontaneous emission source, and the cycle number tuning and controlling component, so as to control and tune the power of the pump source, the amount of spontaneous emission provided by the external injection spontaneous emission source, and the cycle transmission number of the stimulated emission source determined by the cycle number tuning and controlling component, respectively.
6. The linewidth tunable laser based on external injection spontaneous radiation according to claim 2, wherein the laser resonator comprises a wavelength division multiplexer and a coupler, and the first input end of the wavelength division multiplexer is the first input end of the laser resonator and is connected to the pump source; the output end of the wavelength division multiplexer is connected with the first input end of the coupler through the gain medium, the second input end of the coupler is used as the second input end of the laser resonator and is connected with the external injection spontaneous radiation source, the first output end of the coupler is connected with the second input end of the wavelength division multiplexer, and the second output end of the coupler is used as the output end of the laser;
the coupler is the cycle number regulating and controlling component, and the coupling degree of the second output end of the coupler determines the cycle transmission number in the laser resonant cavity before unit amount of stimulated radiation is completely output from the laser resonant cavity.
7. The linewidth tunable laser based on external injection spontaneous emission of claim 6, wherein the laser resonator further comprises a band-pass filter, the first output terminal of the coupler is connected to the second input terminal of the wavelength division multiplexer through the band-pass filter, and the band-pass filter is configured to limit an effective gain range of laser light in the laser resonator, suppress mode hopping, and implement single longitudinal mode operation of the laser.
8. The linewidth tunable laser based on external injection spontaneous emission according to claim 6 or 7, wherein the laser resonator further comprises an isolator, the isolator is disposed between the first output end of the coupler and the second input end of the wavelength division multiplexer, and the isolator is configured to ensure unidirectional laser operation in the laser resonator, thereby improving laser output efficiency.
9. The linewidth tunable laser based on external injection spontaneous emission of claim 2, wherein the laser resonator comprises a total reflector and an output reflector which are vertically arranged relatively, the gain medium is disposed between the total reflector and the output reflector, the reflection side of the total reflector faces the gain medium, the gain medium comprises an active region and a P region and an N region respectively located at the upper side and the lower side of the active region, the P region between the total reflector and the output reflector is a first input end of the laser resonator and is connected to the pump source; the output reflector is used as a second input end of the laser resonator and is connected with the external injection spontaneous radiation source;
the gain medium is used for generating spontaneous radiation, and the gain medium generates stimulated radiation after receiving the pumping source through the P region; the external injection spontaneous radiation source injects spontaneous radiation into the N region through the output reflector so as to enable coupling of the spontaneous radiation in the laser resonant cavity and the stimulated radiation source to reach balance again.
10. The linewidth tunable laser according to claim 9, further comprising a half mirror as the cycle number adjusting component, wherein the half mirror is connected to the output mirror, and transmits a part of the laser output from the output mirror as the output laser of the laser, and returns another part of the laser output to the gain medium through the output mirror, and a transmission/reflection ratio of the half mirror determines the cycle number in the laser resonator before the unit amount of the stimulated radiation is completely output from the laser resonator.
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| CN117353148A (en) * | 2023-10-07 | 2024-01-05 | 重庆大学 | Linear Fabry-Perot cavity optical feedback frequency locking device based on asymmetric cavity mirror reflectivity |
| CN117353148B (en) * | 2023-10-07 | 2024-05-03 | 重庆大学 | Linear Fabry-Perot cavity optical feedback frequency locking device based on asymmetric cavity mirror reflectivity |
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