CN110556696B - Injection type optical parametric oscillation device and method - Google Patents
Injection type optical parametric oscillation device and method Download PDFInfo
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- CN110556696B CN110556696B CN201910772948.1A CN201910772948A CN110556696B CN 110556696 B CN110556696 B CN 110556696B CN 201910772948 A CN201910772948 A CN 201910772948A CN 110556696 B CN110556696 B CN 110556696B
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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
- H01S3/05—Construction or shape of optical resonators; Accommodation of active medium therein; Shape of active medium
- H01S3/08—Construction or shape of optical resonators or components thereof
- H01S3/081—Construction or shape of optical resonators or components thereof comprising three or more reflectors
- H01S3/0813—Configuration of resonator
- H01S3/0816—Configuration of resonator having 4 reflectors, e.g. Z-shaped resonators
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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
- H01S3/106—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating by controlling devices placed within the cavity
- H01S3/107—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating by controlling devices placed within the cavity using electro-optic devices, e.g. exhibiting Pockels or Kerr effect
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- H—ELECTRICITY
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- 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
- H01S3/106—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating by controlling devices placed within the cavity
- H01S3/108—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating by controlling devices placed within the cavity using non-linear optical devices, e.g. exhibiting Brillouin or Raman scattering
- H01S3/1083—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating by controlling devices placed within the cavity using non-linear optical devices, e.g. exhibiting Brillouin or Raman scattering using parametric generation
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Abstract
The invention discloses an injection type optical parametric oscillation device and method, which achieve the purpose of adjusting the wavelengths of signal light and idler frequency light by introducing the interaction of seed light and pump light to excite the signal light with the same wavelength as the seed light. The injection type optical parametric oscillation device comprises an optical parametric oscillation cavity and a regulating system, wherein seed light passes through a phase modulation crystal and is injected into the optical parametric oscillation cavity, and the locking of signal light at the wavelength center of the seed light is realized through a phase locking crystal. The invention realizes the wavelength locking of the signal light and the seed light by utilizing the injection type thought, and can reduce the light emitting threshold of the optical parametric oscillator after the seed light is injected; the signal optical wavelength is stably locked relative to the seed optical wavelength for a long time, the wavelength of the seed light can be tuned, the signal optical wavelength and the idler optical wavelength can be tuned, and the large tuning of the signal optical wavelength and the idler optical wavelength is realized. The invention can realize the long-term stable operation of locking, the line width of the signal light after locking is consistent with that of the seed light, and the narrow line width output of optical parametric oscillation is realized.
Description
Technical Field
The invention belongs to the technical field of laser, particularly relates to solid laser control, and particularly relates to an injection type continuous optical parametric oscillation device and method.
Background
Optical parametric oscillation is one of the important methods of the current mid-infrared laser technology, and is widely applied to spectrum detection. The continuous optical parametric oscillation method has great application potential due to the advantages of stable output power, narrow output line width and the like.
In the application of the current optical parametric oscillation method, there are major problems including: the light emitting threshold is high; the wavelength of the emitted light is unstable; the width of the emergent ray is required to be further narrowed. In view of the above problems, an optical cavity locking and narrowing line width technology is proposed in the prior art. The optical cavity locking narrow linewidth technology mainly guides out signal light in an optical parametric oscillator, locks the signal light on a stable external optical cavity, and compensates the change of the optical cavity mode wavelength of the optical parametric oscillator by adjusting the optical cavity length of the optical parametric oscillator. Although the optical cavity locking narrowing line width technology achieves line width narrowing to a certain extent, certain defects also exist, such as: first, the wavelength of the signal light cannot be tuned arbitrarily, limited by the discontinuity of the external optical cavity mode; secondly, the compensation signal is loaded on an optical cavity mirror of the optical parametric oscillator, is limited by bandwidth, cannot realize rapid compensation and is difficult to obtain extremely narrow output optical linewidth; third, the light extraction threshold of the optical parametric oscillator is not lowered.
Therefore, how to solve the problems of the prior art that the wavelengths of the signal light and the idler frequency light cannot be continuously adjusted and the width of the emergent light line is wide, becomes a problem to be solved urgently by those skilled in the art.
Disclosure of Invention
Technical problem to be solved
In view of the above, the present invention provides an injection optical parametric oscillation device and an oscillation method thereof, so as to solve the problem that the wavelengths of the signal light and the idler light cannot be adjusted in the optical parametric oscillation.
(II) technical scheme
In order to achieve the above object, the present invention provides an injection type optical parametric oscillation device, which comprises an optical parametric oscillation cavity and a modulation system, wherein:
the optical parametric oscillation cavity comprises an optical parametric oscillation crystal 3, a first cavity mirror 4, a second cavity mirror 5, a third cavity mirror 6 and a fourth cavity mirror 7, pump light penetrates through the first cavity mirror 4 and irradiates on the second cavity mirror 5 to form a first light path, the optical parametric oscillation crystal 3 is arranged on the first light path, light in the first light path is reflected to the third cavity mirror 6 by the second cavity mirror 5 to form a second light path, light in the second light path is reflected to the fourth cavity mirror 7 by the third cavity mirror 6 to form a third light path, light on the third light path irradiates to the first cavity mirror 4 through reflection of the fourth cavity mirror 7 to form a fourth light path, and light on the fourth light path returns to the first light path through reflection of the first cavity mirror 4;
the adjusting system comprises a phase modulation crystal 2, a phase locking crystal 1, a control system and a high-speed detector 9, wherein the phase modulation crystal 2 is arranged on the outer side of the optical parametric oscillation cavity and is used for modulating the phase of seed light, and the seed light is modulated by the phase modulation crystal 2, then enters the fourth cavity mirror 7 and enters the optical parametric oscillation cavity; the phase locking crystal 1 is arranged on a third light path of the optical parametric oscillation cavity; the control system is in signal connection with the phase locking crystal 1 and adjusts the optical path of the optical parametric oscillation cavity through the phase locking crystal 1; the high-speed detector 9 is arranged corresponding to the fourth cavity mirror 7 and the optical cavity and is used for obtaining light parameter values in the optical parametric oscillation cavity, and the high-speed detector 9 is in signal connection with the control system.
In an embodiment of the present invention, the adjusting system further includes a light guiding mirror 8, which is disposed on the other side of the phase modulation crystal 2 corresponding to the fourth cavity mirror 7, and is configured to reflect the seed light to the fourth cavity mirror 7 in a manner of overlapping with the fourth optical path and enter the optical parametric oscillation cavity.
In one embodiment of the present invention, the injection optical parametric oscillation device further comprises a color separation mirror 10 for separating the emergent light into a pump light, an idler light and a signal light for separate output.
In one embodiment of the present invention, the first cavity mirror 4 is a plano-concave mirror, and the concave surface of the first cavity mirror 4 is disposed toward the inside of the optical parametric oscillation cavity; the second cavity mirror 5 is a plano-concave lens, and the concave surface of the second cavity mirror 5 faces the inside of the optical parametric oscillation cavity; the third cavity mirror 6 and the fourth cavity mirror 7 are both plane mirror plates.
In one embodiment of the invention, the phase modulation crystal 2 is an electro-optical phase modulation crystal.
In order to achieve the above object, the present invention further provides an injection optical parametric oscillation method, including: modulating the phase of seed light introduced into the optical parametric oscillation cavity by adopting a phase modulation crystal; pump light is incident into the optical parametric oscillation cavity, so that the pump light and the seed light generate nonlinear interaction in an optical parametric oscillation crystal in the optical parametric oscillation cavity to generate signal light and idler frequency light; and adjusting the optical path of the optical parametric oscillation cavity by adopting the phase-locked crystal to ensure that the mode frequency of the optical parametric oscillation cavity is consistent with the frequency of the introduced seed light, thereby forming mode oscillation in which the signal light and the seed light are correlated.
In an embodiment of the present invention, the modulating the phase of the seed light introduced into the optical parametric oscillation cavity by using the phase modulation crystal includes: the polarization direction of the seed light is controlled, so that the included angle between the polarization direction of the seed light and the polarization direction of the signal light is less than or equal to 0.5 degrees.
In an embodiment of the present invention, in the step of adjusting the optical path length of the optical parametric oscillation cavity by using the phase-locked crystal to make the mode frequency of the optical parametric oscillation cavity consistent with the frequency of the introduced seed light, the mode frequency of the optical parametric oscillation cavity is adjusted as follows: the method comprises the steps that the phase modulation crystal is utilized, and before seed light is injected into an optical parametric oscillation cavity, the seed light is subjected to phase modulation; after the seed light is injected into the optical parametric oscillation cavity, the seed light is captured by the high-speed detector, an error signal is obtained through demodulation, and the optical path and the length of the optical parametric oscillation cavity are adjusted by utilizing the phase-locked crystal according to the error signal to complete mode frequency adjustment of the optical parametric oscillation cavity.
In one embodiment of the present invention, the seed light and the signal light circulate in the optical parametric oscillation cavity and are incident into the phase-locked crystal, and the seed light and the signal light are incident into the phase-locked crystal at the brewster angle or the non-brewster angle.
(III) advantageous effects
The injection type optical parametric oscillation device and the injection type optical parametric oscillation method provided by the invention achieve the purpose of adjusting the wavelength of the signal light by introducing the interaction of the seed light and the pump light to excite the signal light with the same wavelength as that of the seed light. The core concept of the invention is as follows: the optical parametric oscillation is obtained by an injection mode, and the specific conception realization method comprises the following steps: the method comprises the steps that external seed light (laser) is injected into an optical parametric oscillation cavity, and mode frequency of the optical parametric oscillation cavity is locked on the seed laser, so that the injected seed laser oscillates in the optical parametric oscillation cavity, oscillation light intensity of the injected seed laser is far greater than mode light intensity of other optical parametric oscillation cavities, and advantageous mode oscillation is formed, and output light (mainly signal light) is related to the seed light. Since the output light (signal light) is associated with the seed light, the output light can be adjusted by adjusting the seed light. The method has the advantages that:
1. the seed light is injected into the outside of the optical parametric oscillation cavity, the light intensity of each mode in the optical parametric oscillation cavity is concentrated on the light intensity of the seed light, and the seed light is associated with the signal light, so that the gain of the signal light can be increased by the mode, and the purpose of reducing the light emitting threshold of the optical parametric oscillation is achieved.
2. The frequency of the output light can be controlled by controlling the frequency of the seed light, and the control of the wavelength of the output light is realized.
3. Because the seed light can have a very narrow line width, and meanwhile, the signal light is related to the seed light, the line width is also very narrow, and the square of the line width of the optical parametric oscillation output is the sum of the square of the line width of the pump light and the square of the line width of the signal light, the optical parametric oscillation output light correspondingly has a narrow line width after the line width of the signal light is narrowed.
Drawings
FIG. 1 is a schematic diagram of the structure of an injection optical parametric oscillation device according to the present invention;
FIG. 2 is a diagram showing the relationship between the idler power and the pump power of the injection optical parametric oscillation device according to the present invention;
fig. 3 is a graph showing the effect of the light emitting frequency of the injection optical parametric oscillation device of the present invention.
In fig. 1, the correspondence between the component names and the reference numerals is:
the phase-locked crystal comprises a phase-locked crystal 1, a phase modulation crystal 2, an optical parametric oscillation crystal 3, a first cavity mirror 4, a second cavity mirror 5, a third cavity mirror 6, a fourth cavity mirror 7, a light guide mirror 8, a high-speed detector 9 and a color separation mirror 10.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to specific embodiments and the accompanying drawings.
The invention provides an injection type optical parametric oscillation device and a method, which achieve the purpose of adjusting the wavelengths of signal light and idler light by introducing the interaction of seed light and pump light to excite the signal light with the same wavelength as the seed light, wherein the frequency of the pump light is equal to the frequency of the signal light plus the frequency of the idler light, and the idler light and the signal light are mainly used in practical application. The injection type optical parametric oscillation device is provided with an optical parametric oscillation cavity, a phase locking crystal and a phase modulation crystal, seed light with adjustable wavelength is continuously injected into the optical parametric oscillation cavity through the phase modulation crystal, and locking of signal light in seed light wavelength is achieved through the phase locking crystal.
Referring to fig. 1 to 3, fig. 1 is a schematic diagram illustrating a structure of an injection optical parametric oscillation device according to the present invention; FIG. 2 is a diagram showing the relationship between the idler power and the pump power of the injection optical parametric oscillation device according to the present invention; fig. 3 is a graph showing the effect of the light emitting frequency of the injection optical parametric oscillation device of the present invention.
The invention provides an injection type optical parametric oscillation device based on the seed light injection type thought, which has the basic principle that the signal light wavelength in the optical parametric oscillation is locked in the seed light wavelength, so that the purpose of low-threshold light emitting is realized, and meanwhile, the output signal light also has the characteristics of easy control of the light emitting wavelength, wide and narrow light emitting rays and the like.
The core technology for realizing locking is that a phase modulation crystal 2 and a phase locking crystal 1 are arranged on the basis of an optical parametric oscillation cavity, the phase modulation crystal 2 is utilized to realize the phase adjustment of seed light, and the seed light with adjustable wavelength can be continuously injected into the optical parametric oscillation cavity through the phase locking crystal 1.
Specifically, the application discloses an injection type optical parametric oscillation device, which comprises a light guide mirror 8, an endoscope, a nonlinear crystal, a high-speed detector 9 and a color separation mirror 10.
The four cavity mirrors are named as a first cavity mirror 4, a second cavity mirror 5, a third cavity mirror 6 and a fourth cavity mirror 7 for structural description, and form a stable and foldable optical parameter oscillation cavity through reasonable structural layout.
The pump light is transmitted into the optical parametric oscillation cavity through the first cavity mirror 4 and irradiates the second cavity mirror 5, and a light path formed between the first cavity mirror 4 and the second cavity mirror 5 is a first light path. A nonlinear crystal, i.e. an optical parametric oscillation crystal 3, is disposed on the first optical path, and a part of the pump light passing through the optical parametric oscillation crystal 3 is divided into signal light and idler light when passing through the first optical path. The light (including the pump light, the signal light, and the idler light) passing through the optical parametric oscillation crystal 3 is partially emitted through the second cavity mirror 5, and the other portion (including only the signal light) is reflected to the third cavity mirror 6 by the second cavity mirror 5. The optical path formed between the second cavity mirror 5 and the third cavity mirror 6 is a second optical path. Third cavity mirror 6 has the reflection function, light on the second light path shines fourth cavity mirror 7 after the reflection of third cavity mirror 6, the light path that forms between third cavity mirror 6 and the fourth cavity mirror 7 is the third light path, be provided with a nonlinear crystal on the third light path, phase locking crystal 1 promptly, utilize phase locking crystal 1 can adjust the optical path of optical parameter oscillation chamber, thereby make the mode frequency of optical parameter oscillation chamber the same with the frequency of seed light, in order to realize the dominant oscillation of seed light in optical parameter oscillation chamber. The light on the third light path is reflected to the first cavity mirror 4 by the fourth cavity mirror 7 to perform next circulation in the optical parametric oscillation cavity.
In the invention, the optical parametric oscillation cavity comprises an endoscope and an optical parametric oscillation crystal 3. The optical parametric oscillation crystal 3 is a nonlinear crystal, one end of the optical parametric oscillation crystal 3 is an incident end and is used for the incidence of pump light, the other end of the optical parametric oscillation crystal 3 is an emergent end, the pump light is incident from the incident end of the optical parametric oscillation crystal 3 and is emitted from the emergent end of the optical parametric oscillation crystal 3, and when passing through the optical parametric oscillation crystal 3, one part of the pump light is divided into signal light and idle frequency light.
In the whole optical parametric oscillation cavity, the optical parametric oscillation crystal 3 is arranged on a first light path, the cavity mirror arranged corresponding to the incident end of the optical parametric oscillation crystal 3 is a first cavity mirror 4, and the cavity mirror arranged corresponding to the emergent end of the optical parametric oscillation crystal 3 is a second cavity mirror 5.
The pump light is emitted into the optical parametric oscillation crystal 3 from the outside of the optical parametric oscillation cavity through the first cavity mirror 4, and generates signal light and idler frequency light through the optical parametric oscillation crystal 3. The light emitted from the optical parametric oscillation crystal 3 includes pump light, signal light and idler light, the signal light and a part of the pump light emitted from the optical parametric oscillation crystal 3 can be emitted from the second cavity mirror 5, and the other part of the signal light in the light emitted from the optical parametric oscillation crystal 3 continues to circulate in the optical parametric oscillation cavity.
In order to control the wavelength and frequency of the signal light, the present invention introduces seed light from the outside of the optical parametric oscillation cavity, and the seed light can be injected into the optical parametric oscillation cavity. The seed light enters the phase modulation crystal 2 (nonlinear crystal) through the reflection of the light guide mirror 8, and then enters the optical parametric oscillation cavity through the fourth cavity mirror 7. The phase modulation crystal 2 and the light guide mirror 8 form a frequency locking signal stage, a high-speed detector 9 is further arranged in the frequency locking signal stage, and the frequency locking signal stage can generate a frequency locking signal, namely an error signal.
A first optical path is arranged between the first cavity mirror 4 and the second cavity mirror 5, the first cavity mirror 4 and the second cavity mirror 5 form an optical parametric oscillation stage, a nonlinear crystal, namely an optical parametric oscillation crystal 3, is arranged in the optical parametric oscillation stage, the optical parametric oscillation crystal 3 is arranged on the first optical path, the optical parametric oscillation crystal 3 is in phase matching with the pumping light and the seed light, and the pumping light interacts with the seed light to separate out signal light and idle frequency light when passing through the optical parametric oscillation crystal 3.
A third light path is arranged between the third cavity mirror 6 and the fourth cavity mirror 7, and the third cavity mirror 6 and the fourth cavity mirror 7 form an optical parametric oscillation cavity locking stage. A nonlinear crystal, namely a phase locking crystal 1 is arranged in the optical parametric oscillation cavity locking stage, and the phase locking crystal 1 is arranged on a third light path. By adjusting the optical path of the optical parametric oscillation cavity through the phase-locked crystal 1, the mode frequency of the optical parametric oscillation cavity can be locked on the seed laser, so that the power of the seed laser enters the optical parametric oscillation cavity as much as possible, and the phase-locked crystal 1 can realize the phase locking of the optical parametric oscillation cavity and the seed light at the central wavelength of the seed light.
The above-described locking operation for the signal light wavelength is as follows: a modulation signal is added on the phase modulation crystal 2, the seed light carries the modulation signal to act with the optical parametric oscillation cavity and then is detected by the high-speed detector 9, the signal detected by the high-speed detector 9 is demodulated to generate a Pound-Drever-Hall error signal, and the error signal acts on the phase locking crystal 1 through a negative feedback circuit to adjust the optical path of the optical parametric oscillation cavity, so that the optical parametric oscillation cavity and the seed light are locked.
The signal light and the pump light are transmitted in the optical parametric oscillation cavity in a collinear mode, the second cavity mirror 5 is an output light guide mirror of the optical parametric oscillation cavity, the signal light, the pump light and the idler frequency light are led out from the second cavity mirror 5 in a collinear mode, and then the led out collinear light (the signal light, the pump light and the idler frequency light) is divided into the signal light, the pump light and the idler frequency light through the two color separation mirrors 10 and is respectively output.
In the invention, the core concept is as follows: the optical parametric oscillation is obtained by an injection mode, and the specific conception realization method comprises the following steps: the method comprises the steps that external seed light (laser) is injected into an optical parametric oscillation cavity, and mode frequency of the optical parametric oscillation cavity is locked on the seed laser, so that the injected seed laser oscillates in the optical parametric oscillation cavity, oscillation light intensity of the injected seed laser is far greater than mode light intensity of other optical parametric oscillation cavities, and advantageous mode oscillation is formed, and output light (mainly signal light) is related to the seed light. Since the output light (signal light) is associated with the seed light, the output light can be adjusted by adjusting the seed light. The method has the advantages that: 1. the method is characterized in that the light intensity of each mode in the optical parametric oscillation cavity is concentrated on the light intensity of the seed light in a mode of injecting the seed light into the outside of the optical parametric oscillation cavity, and the seed light is related to the signal light, so that the gain of the signal light can be increased in the mode, and the purpose of reducing the light emitting threshold of the optical parametric oscillation is achieved; 2. the frequency of the output light can be controlled by controlling the frequency of the seed light, so that the control of the wavelength of the output light is realized; 3. because the seed light can have a very narrow line width, and meanwhile, the signal light is related to the seed light, the line width is also very narrow, and the square of the line width of the optical parametric oscillation output is the sum of the square of the line width of the pump light and the square of the line width of the signal light, the optical parametric oscillation output light correspondingly has a narrow line width after the line width of the signal light is narrowed.
In the invention, the cavity mirror is a coated dichroic mirror, and the coating requirements on the cavity mirror are as follows: the film coating film layer has high reflectivity for the signal light and the seed light and high transmissivity for the idler light and the pump light, so that the reflection of the signal light and the seed light in the optical parametric oscillation cavity is realized, and the elimination of the pump light and the idler light in the optical parametric oscillation cavity is realized. The film coating is the reason that the second cavity mirror 5 can reflect the signal light to enable the signal light to enter the circulating transmission, and the pump light and the idler frequency light are directly emitted out of the cavity through the second cavity mirror 5.
Furthermore, the coating film arranged on the cavity mirror is a broadband coating film, and the reflection angle of the broadband coating film is 8 degrees.
The optical parametric oscillation crystal 3 is a component for realizing the phase matching of the seed light, and in this embodiment, the optical parametric oscillation crystal 3 is disposed in a temperature control device (temperature control furnace), and the behavior of the optical parametric oscillation crystal 3 is changed by the temperature, so that the phase matching of the signal light and the pump light is realized by the temperature control. The phase matching of the signal light and the pump light is the phase velocity coincidence of two (e.g., signal light and pump light) or more beams of light everywhere in the crystal.
In the invention, the Pound-Drever-Hall method is adopted for injection light locking, so that in the frequency-locked signal stage, the frequency-locked signal generated by the frequency-locked signal stage is the Pound-Drever-Hall signal.
As a preferred embodiment, the included angle between the polarization direction of the seed light in the frequency-locked signal stage and the polarization direction of the signal light in the optical parametric oscillation stage is less than or equal to 0.5 °
The signal light and the seed light are transmitted out of the phase modulation crystal 2 in a collinear way and captured and detected by a high-speed detector 9, specifically, the phase modulation crystal 2 is a nonlinear crystal with a light-transmitting end coated with a film, and the film is an antireflection film for the signal light and the seed light and is used for generating a frequency-locked signal.
In the optical parametric oscillation cavity locking stage, the phase locking crystal 1 is a non-linear crystal with a coated light-transmitting end, and the film layer is an antireflection film for signal light and seed light.
The invention inserts a nonlinear crystal (phase locking crystal 1) in an optical parametric oscillation cavity for injection locking, and the phase locking crystal 1 is also used for feedback of a frequency locking signal. For phase-locked crystal 1: the characteristics and the length of the nonlinear crystal need to realize that the loss of signal light and seed light in the optical parametric oscillation cavity passing each time is less than 0.4%; the characteristics and the length of the nonlinear crystal need to realize high-speed compensation of the mismatch of the optical parametric oscillation cavity mode wavelength relative to the seed optical wavelength; the phase-locked crystal 1 is arranged in a temperature control device, and the amplitude modulation of signal light by temperature control parameters needs to be less than 0.1%.
In the invention, the light intensity of the seed light needs to be selected, and the light intensity of the seed light needs to realize the leading of the signal light in the optical parametric oscillation cavity, so that the signal light and the seed light have the same wavelength. The light intensity of the seed light needs to be selected to satisfy the following conditions: the light intensity of the seed light needs to be greater than the light intensity of the signal light in the optical parametric oscillation cavity under the non-injection condition.
The invention fully exerts the advantages of injection idea and quick locking of the optical parametric oscillation cavity, and the basic transmission light path is as follows: a stable and foldable optical parametric oscillation cavity is formed by using a dichroic mirror as an endoscope; the pump light enters the optical parametric oscillation cavity through the first cavity mirror 4, propagates along the first optical path, passes through the optical parametric oscillation crystal 3, and generates signal light and idler frequency light with nonlinear action with the seed light in the optical parametric oscillation crystal 3; the seed light is guided into the optical parametric oscillation cavity by the light guide mirror 8 and transmitted with the signal light in a collinear mode; the optical parametric oscillation cavity mode is locked on the seed light to form single-frequency transmission of the seed light, and the seed light, the pump light and the optical parametric oscillation crystal 3 act together to excite the seed light to generate signal light with the frequency height consistent with that of the seed light.
The cavity mirror forming the optical parametric oscillation cavity, namely the coated dichroic mirror, has high reflectivity for the signal light and the seed light and high transmissivity for the idler light and the pumping light, can realize the reflection of the signal light and the seed light in the optical parametric oscillation cavity, and realize the total elimination in the optical parametric oscillation cavity of the pumping light and the idler light. The pump light and the idler frequency light pass through the cavity mirror and the optical parametric oscillation crystal 3 once to realize phase matching, namely the pump light, the signal light and the idler frequency light form phase matching in the optical parametric oscillation crystal 3.
In the frequency-locked signal level, the length and the characteristics of the phase modulation crystal 2 are selected, so that the small transmission loss of the signal light and the seed light in the optical parametric oscillation cavity can be realized, and the large and high-speed compensation is realized on the mode wavelength of the optical parametric oscillation cavity relative to the seed light wavelength mismatch. The temperature control of the phase modulation crystal 2 can realize smaller amplitude modulation of the signal light, and the temperature control of the phase modulation crystal 2 can reduce the amplitude modulation of the signal light in the optical parametric oscillation cavity so as to obtain more stable output power.
The present invention adopts the thought of continuous seed laser injection, is applied to a continuous optical parametric oscillation device, and the thought and the technology can also be applied to a pulse type optical parametric oscillation device.
The optical parametric oscillation device provided by the invention specifically comprises an optical guide mirror 8, an endoscope, a nonlinear crystal, a color separation mirror 10 and a high-speed detector 9, wherein the nonlinear crystal is further divided into an optical parametric oscillation crystal 3, a phase modulation crystal 2 and a phase locking crystal 1, the phase locking crystal 1 can completely replace piezoelectric ceramics, and the piezoelectric ceramics can be omitted to avoid complication. The optical parametric oscillation cavity is composed of an optical parametric oscillation crystal 3 and a cavity mirror, wherein the optical parametric oscillation crystal 3 is taken as a reference in the optical parametric oscillation cavity, and the cavity mirror is divided into a first cavity mirror 4, a second cavity mirror 5, a third cavity mirror 6 and a fourth cavity mirror 7.
In the above-described components, the light guide mirror 8 functions to guide the seed light into the optical parametric oscillation cavity, and the seed light and the optical parametric oscillation cavity perform mode matching, so that the mode frequency of the optical parametric oscillation is made to coincide with the frequency of the seed laser.
The four cavity mirrors form a ring cavity structure, wherein the first cavity mirror 4 and the second cavity mirror 5 are plano-concave lenses, the concave surface points to the inside of the ring cavity structure, the third cavity mirror 6 and the fourth cavity mirror 7 are plane lenses, and the four cavity mirrors form a stable optical parametric oscillation cavity for seed light and signal light.
Among the four cavity mirrors, the substrates of the cavity mirror are all made of materials with high transmission to the pumping light and the idler frequency light, wherein the inner side coating of the first cavity mirror 4, the second cavity mirror 5 and the third cavity mirror 6 is required to show extremely high reflectivity (> 99.9%) to the wave bands of the seed light and the signal light, and show high transmission to the wave bands of the pumping light and the idler frequency light. The coating of the outer sides of the first cavity mirror 4, the second cavity mirror 5 and the third cavity mirror 6 requires high transmittance for the seed light, the signal light, the pump light and the idler frequency light wave bands. For the fourth cavity mirror 7, the inner side coating of the fourth cavity mirror 7 is required to have a high reflectivity (> 97%) for the seed light and signal light bands, a high transmittance for the pump light and idler light bands, and the outer side coating is required to have a high transmittance for the seed light and signal light, the pump light and idler light bands.
The four cavity mirrors form a ring cavity structure, and the function of the ring cavity structure is to enable seed light and signal light to be stably resonated and amplified in the cavity.
The phase modulation crystal 2 is an electro-optical phase modulation crystal, the phase of light passing through the crystal is changed by loading an electric field, the phase modulation crystal 2 has the function of carrying out phase modulation on seed light entering an optical parametric oscillation cavity, and a Pound-Drever-Hall signal is generated by matching with a high-speed detector 9. The high-speed detector 9 is a photoelectric detector having high-speed correspondence to the seed light and signal light wave bands, and has the functions of detecting the Pound-Drever-Hall signal, generating a control signal according to a detection structure, and modulating the seed light by using the phase modulation crystal 2 through a control system.
The phase-locked crystal 1 is an electro-optical crystal which is required to have high transmittance for the seed light and the signal light and to be capable of modulating the refractive index thereof by an electrical signal. The phase-locked crystal 1 is used for feedback control of Pound-Drever-Hall frequency locking. The phase-locked crystal 1 can be coated with a film, so that the seed light and the signal light in the optical parametric oscillation cavity are normally incident into the phase-locked crystal 1, and high transmittance of the seed light and the signal light is realized.
Alternatively, the phase-locked crystal 1 may adopt an appropriate cut angle so that the seed light and the signal light in the optical parametric oscillation cavity can be incident on the crystal at brewster's angle, achieving high transmittance of the seed light and the signal light, and the seed light and the signal light having proper polarization will pass through the crystal without loss when incident at brewster's angle. In other embodiments, the seed light and the signal light may also be incident into the phase-locked crystal at a non-Brewster angle.
In an alternative embodiment of the present invention, the phase-locked crystal 1 may be placed in a temperature control device, and the purpose of reducing the variation of the optical path of the seed light and the signal light in the cavity is achieved by stabilizing the temperature of the crystal.
The optical parametric oscillation crystal 3 is required to have a sufficiently large nonlinear coefficient, and simultaneously satisfies the requirement of enabling the pump light and the seed light and the signal light to realize quasi-phase in a collinear manner, and has the function of enabling the pump light and the seed light and the signal light to generate nonlinear interaction so as to convert and generate idler frequency light.
The color separation mirror 10 is a separation mirror for pump light and idler light, and the two color separation mirrors 10 are a first color separation mirror and a second color separation mirror.
For the first color separation mirror, it is used for separating the pump light, the substrate of the first color separation mirror is a flat plate, the material is required to have higher transmittance (more than 85%) to the idler frequency light, and the coating film is required to have high transmittance to the 45 ° incident idler frequency light and high reflectance to the 45 ° incident pump light.
For the second color separating mirror, the substrate of the second color separating mirror is a flat plate, and the material is required to have higher transmittance (more than 85%) for the idler, and the coating film is required to have high transmittance for the 45-degree incident idler and high reflectance for the 45-degree incident signal light.
The optical parametric oscillation device provided by the invention has the general process of optical path transmission, feedback and output as follows: the injected seed light and the signal light are subjected to mode matching through the light guide mirror, are subjected to phase modulation through the phase modulation crystal 2 and then enter an annular optical parametric oscillation cavity formed by cavity mirrors (a first cavity mirror 4, a second cavity mirror 5, a third cavity mirror 6 and a fourth cavity mirror 7), and particularly enter from the fourth cavity mirror 7; after passing through the phase modulation crystal 2, the seed light generates a Pound-Drever-Hall signal, the Pound-Drever-Hall signal is detected by a high-speed detector 9, and the resonance transmission peak of the optical parametric oscillation cavity is phase-locked on the seed light and the signal light by PID control feedback piezoelectric ceramic and the phase locking crystal 1. The PID control flow is as follows: when the cavity length of the optical parametric oscillation cavity changes, the mode frequency of the optical parametric oscillation cavity deviates from the frequency of the seed light, the amplitude of an error signal obtained by demodulating a signal detected on the high-speed detector 9 changes, and the amplitude change quantity is amplified by corresponding times to serve as a control parameter and is sent to the phase-locked crystal 1, so that the cavity length change of the optical parametric oscillation cavity is compensated, and the cavity length control is realized. Because the time response of the phase-locked crystal 1 is fast enough, the mode frequency of the optical parametric oscillation cavity can be firmly locked on the seed light to form the synchronization of the optical parametric oscillation cavity and the seed light, and the signal light of the optical parametric oscillation cavity is completely consistent with the seed light and can not be distinguished. The seed light realizes nonlinear interaction with the pump light in the optical parametric oscillation crystal 3 through resonance amplification of the optical parametric oscillation cavity to generate signal light and idler frequency light, and the signal light is subjected to resonance amplification in the optical parametric oscillation cavity; the idler light is transmitted out of the optical parametric oscillation cavity by the third cavity mirror 6, and the pump light and the signal light which are collinear with the idler light are separated by the first color separation mirror 10 and the second color separation mirror 10, so that signal light output with narrow line width is obtained. The frequency of the idler frequency light is the frequency difference between the pump light and the seed light and the signal light.
In the invention, 1064nm laser is taken as pump light, 1566nm laser is taken as seed light, the relationship between the idler frequency light power and the pump light power is shown in figure 2, and by comparison, the threshold power of the pump light of the injection type optical parametric oscillation device is reduced by 20 percent compared with that of the traditional optical parametric oscillation device without injection
The invention takes 1064nm laser as pump light and 1566nm laser as seed light as an example, and the light-emitting frequency effect is as shown in fig. 3.
Compared with the prior art, the injection type optical parametric oscillation concept provided by the invention has the following advantages: the wavelength locking of the signal light and the seed light is realized by utilizing the injection type thought, and the light emitting threshold value of the optical parametric oscillator can be reduced after the seed light is injected; the signal optical wavelength is stably locked for a long time relative to the seed optical wavelength, and the wavelength of the seed light can be tuned to the signal optical wavelength and the idle frequency optical wavelength, so that the signal optical wavelength is greatly tuned; the mode frequency of the optical parametric oscillation cavity is locked on the frequency of seed light, a compensation signal (the compensation signal is obtained by demodulating a signal loaded on a frequency modulation crystal 2 by a signal detected on a high-speed detector 9 to obtain an error signal, the error signal is amplified and then fed back to a phase locking crystal 1, and the mode frequency of the optical parametric oscillation cavity can be adjusted by using the phase locking crystal 1) is loaded on the phase locking crystal 1 in the optical parametric oscillation cavity locking stage, the compensation bandwidth is greatly increased, the locked long-term stable operation is realized, the optical line width of the locked signal is consistent with that of the seed light, and the narrow line width output of the optical parametric oscillation is realized.
The phase-locked crystal 1 is an electro-optic crystal, and has a large time response bandwidth, so that the compensation signal can be responded at a high speed, the mode frequency of the optical parametric oscillation cavity can be firmly locked on the seed light to form synchronization of the optical parametric oscillation cavity and the seed light, the signal light of the optical parametric oscillation cavity is completely consistent with the seed light and can not be distinguished, and the line width of the signal light of the optical parametric oscillation cavity is the same as the line width of the seed light.
The above-mentioned embodiments are intended to illustrate the objects, technical solutions and advantages of the present invention in further detail, and it should be understood that the above-mentioned embodiments are only exemplary embodiments of the present invention, and are not intended to limit the present invention, and any modifications, equivalents, improvements and the like made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (10)
1. An injection optical parametric oscillation device comprising an optical parametric oscillation cavity and a conditioning system, wherein:
the optical parameter oscillation cavity comprises an optical parameter oscillation crystal (3), a first cavity mirror (4), a second cavity mirror (5), a third cavity mirror (6) and a fourth cavity mirror (7), pump light penetrates through the first cavity mirror (4) and irradiates on the second cavity mirror (5) to form a first light path, the optical parameter oscillation crystal (3) is arranged on the first light path, light in the first light path is reflected to the third cavity mirror (6) by the second cavity mirror (5) to form a second light path, light in the second light path is reflected to the fourth cavity mirror (7) by the third cavity mirror (6) to form a third light path, light on the third light path irradiates on the first cavity mirror (4) through reflection of the fourth cavity mirror (7) to form a fourth light path, and light on the fourth light path returns to the first light path through reflection of the first cavity mirror (4);
the adjusting system comprises a phase modulation crystal (2), a phase locking crystal (1), a control system and a high-speed detector (9), wherein the phase modulation crystal (2) is arranged on the outer side of the optical parametric oscillation cavity and used for modulating the phase of seed light, and the seed light is modulated by the phase modulation crystal (2) and then enters a fourth cavity mirror (7) and enters the optical parametric oscillation cavity; the phase locking crystal (1) is arranged on a third light path of the optical parametric oscillation cavity; the control system is in signal connection with the phase locking crystal (1) and adjusts the optical path of the optical parametric oscillation cavity through the phase locking crystal (1); the high-speed detector (9) is arranged corresponding to the fourth cavity mirror (7) and the optical cavity and is used for acquiring light parameter values in the optical parametric oscillation cavity, and the high-speed detector (9) is in signal connection with the control system;
the optical parametric oscillation device is an injection type continuous optical parametric oscillation device, injected light and output light are continuous laser, the phase modulation crystal (2) is utilized to realize the phase adjustment of seed light, and the seed light with adjustable wavelength is continuously injected into the optical parametric oscillation cavity through the phase locking crystal (1); the first to fourth cavity mirrors in the optical parametric oscillation cavity adopt coated dichroic mirrors, have high reflectivity for signal light and seed light and high transmissivity for idler light and pumping light, are used for realizing the reflection of the signal light and the seed light in the optical parametric oscillation cavity and realizing the total elimination in the optical parametric oscillation cavity of the pumping light and the idler light.
2. An injection optical parametric oscillation device according to claim 1, wherein the modulation system further comprises a light guide mirror (8) disposed on the other side of the phase modulation crystal (2) corresponding to the fourth cavity mirror (7) for reflecting the seed light to the fourth cavity mirror (7) and into the optical parametric oscillation cavity in a manner of being superposed on the fourth optical path.
3. An injection optical parametric oscillation device according to claim 1, further comprising a color separation mirror (10) for separating the outgoing light into individual outputs of the pump light, the idler light, and the signal light.
4. An injection optical parametric oscillation device according to claim 1,
the first cavity mirror (4) is a plano-concave lens, and the concave surface of the first cavity mirror (4) faces the inside of the optical parametric oscillation cavity;
the second cavity mirror (5) is a plano-concave lens, and the concave surface of the second cavity mirror (5) faces the inside of the optical parametric oscillation cavity;
the third cavity mirror (6) and the fourth cavity mirror (7) are both plane mirror lenses.
5. An injection optical parametric oscillation device according to claim 1,
the phase modulation crystal (2) is an electro-optic phase modulation crystal.
6. An injection optical parametric oscillation method applied to the injection optical parametric oscillation device according to any one of claims 1 to 5, the method comprising:
modulating the phase of seed light introduced into the optical parametric oscillation cavity by adopting a phase modulation crystal;
pump light is incident into the optical parametric oscillation cavity, so that the pump light and the seed light generate nonlinear interaction in an optical parametric oscillation crystal in the optical parametric oscillation cavity to generate signal light and idler frequency light; and
and adjusting the optical path of the optical parametric oscillation cavity by adopting the phase-locked crystal to ensure that the mode frequency of the optical parametric oscillation cavity is consistent with the frequency of the introduced seed light, thereby forming mode oscillation in which the signal light and the seed light are correlated.
7. An injection optical parametric oscillation method according to claim 6, wherein modulating the phase of the seed light introduced into the optical parametric oscillation cavity with the phase modulation crystal comprises:
the polarization direction of the seed light is controlled, so that the included angle between the polarization direction of the seed light and the polarization direction of the signal light is less than or equal to 0.5 degrees.
8. An injection optical parametric oscillation method according to claim 6, wherein in the step of adjusting the optical path length of the optical parametric oscillation cavity by using the phase-locked crystal to make the mode frequency of the optical parametric oscillation cavity consistent with the frequency of the introduced seed light, the mode frequency of the optical parametric oscillation cavity is adjusted in the following manner:
the method comprises the steps that the phase modulation crystal is utilized, and before seed light is injected into an optical parametric oscillation cavity, the seed light is subjected to phase modulation; and
after the seed light is injected into the optical parametric oscillation cavity, the seed light is captured by the high-speed detector, an error signal is obtained through demodulation, and the mode frequency adjustment of the optical parametric oscillation cavity is completed by adjusting the optical path of the optical parametric oscillation cavity through the phase-locked crystal according to the error signal.
9. An injection optical parametric oscillation method according to claim 6,
the seed light and the signal light circulate in the optical parametric oscillation cavity and are incident into the phase-locked crystal.
10. The method of claim 9, wherein the seed light and the signal light are incident into the phase-locked crystal at brewster's angle or at non-brewster's angle.
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