CN221041914U - Annular cavity optical parametric oscillator with four-way pumping in two-way operation - Google Patents
Annular cavity optical parametric oscillator with four-way pumping in two-way operation Download PDFInfo
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Abstract
The utility model relates to a four-way pumping bidirectional running annular cavity optical parametric oscillator, which belongs to the technical field of mid-infrared nonlinear frequency conversion and comprises a pumping laser, a nonlinear crystal, a residual pumping light transmission unit and a parametric light polarization synthesis unit, wherein an annular resonant cavity is formed in the nonlinear crystal, pumping light is led into the nonlinear crystal to carry out reverse transmission gain first, residual pumping light is led into the nonlinear crystal again after being reflected by the residual pumping light transmission unit to carry out forward transmission gain, in the reverse and forward transmission gain processes, the pumping light sequentially passes through the nonlinear crystal twice, and the forward and reverse parametric light after gain conversion is transmitted to the parametric light polarization synthesis unit to be synthesized, so that the power of output parametric light is improved.
Description
Technical Field
The utility model belongs to the technical field of mid-infrared nonlinear frequency conversion, and particularly relates to a four-way pumping bidirectional running annular cavity optical parametric oscillator.
Background
The Optical Parametric Oscillator (OPO) is an important technical means for generating near infrared, middle infrared and far infrared lasers, and the wavelength-tunable laser generated by the nonlinear frequency conversion technology can compensate the limited output wavelength of a direct laser based on energy level transition, plays an important role in national defense safety, medical diagnosis, air pollution monitoring, organic matter analysis, communication and processing, and has great development prospect and commercial value.
In order to increase the utilization rate of pump laser and improve the conversion efficiency of parametric light, a structure of bi-pass back and forth of pump laser is generally adopted, so that the pump laser can generate gain during forward propagation and reverse propagation and is converted into the needed parametric light. Meanwhile, the OPO with the annular cavity structure can reduce adverse effects of reverse conversion effect on conversion efficiency, and is beneficial to improving the beam quality of parametric light, so that the OPO with the annular cavity has been intensively studied and widely applied in recent years. The combined advantages of the two-way pump and the ring cavity OPO are combined, and the infrared parametric light output with high efficiency (high power or large energy) and high beam quality is realized. However, even with the dual-pass pumped OPO, a portion of the remaining pump light is not converted efficiently and is wasted. Unlike a conventional solid-state laser main oscillation amplifier (MOPA), each pass of pump light in OPO also takes into account phase matching issues. In addition, the general ring cavity OPO is composed of a nonlinear crystal and a plurality of cavity mirrors (three, four or more), and the space distance between the nonlinear crystal and the cavity mirrors increases the cavity length of the ring cavity OPO, so that the vibration starting threshold of the OPO is obviously increased, the conversion efficiency is reduced, the probability of crystal damage is increased, and further the performance of the OPO is reduced. Meanwhile, the sensitivity of a resonant light path in the OPO of the annular cavity is high, and any cavity mirror is out of balance to cause the reduction of the output power and the conversion efficiency of the OPO, even the light cannot be emitted, so that the stability and the reliability of the OPO of the annular cavity are poor.
Disclosure of utility model
Aiming at various defects in the prior art, a ring cavity optical parametric oscillator with a four-way pumping bi-directional operation is provided so as to solve the technical problems that pumping light is not fully and effectively converted, output power is low and conversion efficiency is low in the prior art.
In order to achieve the above purpose, the present utility model provides the following technical solutions:
A four-way pumped bi-directionally operated ring cavity optical parametric oscillator comprising:
A pump laser generating pump light;
The nonlinear crystal is internally provided with a ring resonant cavity, the side surfaces of the nonlinear crystal are respectively a pump light incidence surface, a pump light and parameter light reflection surface, a residual pump light output surface and a parameter light output surface, the pump light is led into the nonlinear crystal to perform reverse transmission gain firstly, the pump light passes through the nonlinear crystal twice in sequence in the reverse transmission gain process, and the residual pump light is output through the residual pump light output surface;
The residual pump light transmission unit is arranged corresponding to the residual pump light output surface, the output residual pump light is reflected by the residual pump light transmission unit and then is led into the nonlinear crystal to carry out forward transmission gain, and in the forward transmission gain process, the residual pump light passes through the nonlinear crystal twice in sequence;
And the parametric light polarization synthesis unit is arranged corresponding to the parametric light output surface, and the reverse and forward parametric light after gain conversion is output to the parametric light polarization synthesis unit for synthesis through the parametric light output surface, so that the power of the output parametric light is improved.
The technical scheme is further characterized by further comprising an isolation unit, wherein the isolation unit is positioned between the pump laser and the nonlinear crystal.
The technical scheme is further characterized in that the residual pump light transmission unit comprises an imaging lens and a pump light reflecting mirror, wherein the imaging lens and the pump light reflecting mirror are arranged on the same optical axis, and the imaging lens is arranged corresponding to the residual pump light output surface.
The technical scheme is further that the parametric light polarization synthesis unit comprises a forward parametric light transmission element, a reverse parametric light transmission element and a parametric light polaroid, wherein the forward parametric light transmission element is located on a parametric light forward transmission path, the reverse parametric light transmission element is located on a parametric light reverse transmission path, a parametric light half-wave plate is arranged on the parametric light forward transmission path so as to rotate the polarization state of forward parametric light, and the parametric light polaroid is located at the intersection of the parametric light forward transmission path and the reverse transmission path.
The technical scheme is further characterized by further comprising a power meter, wherein the parametric light synthesized by the polarization of the parametric light polaroid is transmitted to the power meter.
The technical scheme is further characterized in that the cross section of the nonlinear crystal is hexagonal and comprises 2 horizontal planes and 4 inclined planes, the 4 inclined planes form a ring-shaped resonant cavity, and the 4 inclined planes are a pumping light incidence plane, a pumping light and parametric light reflecting plane, a residual pumping light output plane and a parametric light output plane respectively.
The technical scheme is further characterized in that the pump light incidence surface is plated with a pump light antireflection film and a parametric light high reflection film, the residual pump light output surface is plated with a pump light antireflection film and a parametric light high reflection film, the parametric light output surface is plated with a pump light high reflection film and a parametric light partial reflection film, and the pump light and the parametric light reflection surface are plated with a pump light high reflection film and a parametric light high reflection film.
The technical scheme is further characterized in that the 4 inclined planes are symmetrically arranged, and a rectangular resonant circuit or a cross resonant circuit is formed between the 4 inclined planes.
The technical scheme is that the cross section of the nonlinear crystal is trapezoid, 2 side surfaces and the top surface of the nonlinear crystal form a ring-shaped resonant cavity, the 2 side surfaces and the top surface are a pumping light incidence surface, a parametric light output surface, pumping light and a parametric light reflection surface respectively, and the pumping light incidence surface is overlapped with the rest pumping light output surface.
The technical scheme is further characterized in that the pump light incidence surface is plated with a pump light antireflection film and a parametric light high reflection film, the parametric light output surface is plated with a pump light high reflection film and a parametric light partial reflection film, and the pump light and the parametric light reflection surface are plated with the pump light high reflection film and the parametric light high reflection film.
The beneficial effects of the utility model are as follows:
Through setting up surplus pumping light transmission unit, simultaneously, the inside annular resonant cavity that forms of nonlinear crystal, the pumping light is four times to come and go through the reverse and forward two-way operation of annular cavity OPO that forms of same nonlinear crystal, finally forms the common light path output through the mode that the polarization closes the beam, has improved pumping light time, has shortened the chamber length of annular cavity OPO, has reduced the threshold value of light-emitting, is favorable to promoting conversion efficiency and output power/energy, in addition, because OPO resonant cavity and nonlinear crystal are integrated into one piece structure, has improved annular cavity OPO's stability and reliability, has practicality advantages such as small, light in weight.
Drawings
FIG. 1 is a schematic diagram of a four-way pumped bi-directionally operated ring cavity optical parametric oscillator in an embodiment of the present utility model;
FIG. 2 is a schematic diagram of a nonlinear crystal in an embodiment of the utility model;
FIG. 3 is a schematic diagram of another nonlinear crystal in an embodiment of the present utility model;
fig. 4 is a schematic diagram of another nonlinear crystal in an embodiment of the present utility model.
In the accompanying drawings: the device comprises a 1-pump laser, a 2-isolation unit, a 3-pump light turning mirror, a 4-pump light guiding mirror, a 5-nonlinear crystal, a 6-imaging lens, a 7-pump light reflecting mirror, an 8-first parametric light reflecting mirror, a 9-parametric light half-wave plate, a 10-second parametric light reflecting mirror, an 11-parametric light spectroscope, a 12-parametric light polaroid and a 13-power meter.
Detailed Description
In order to make the technical solution of the present utility model better understood by those skilled in the art, the technical solution of the present utility model will be clearly and completely described in the following with reference to the accompanying drawings, and based on the embodiments of the present utility model, other similar embodiments obtained by those skilled in the art without making any inventive effort should be included in the scope of protection of the present utility model. In addition, directional words such as "upper", "lower", "left", "right", and the like, as used in the following embodiments are merely directions with reference to the drawings, and thus, the directional words used are intended to illustrate, not to limit, the utility model.
According to an embodiment of the present utility model, referring to fig. 1, there is provided a four-way pumping bidirectional operation ring cavity optical parametric oscillator, including a pump laser 1, a nonlinear crystal 5, a residual pump light transmission unit and a parametric light polarization synthesis unit;
Wherein the pump laser 1 generates pump light; the nonlinear crystal 5 is internally provided with a ring resonant cavity, the side surfaces of the ring resonant cavity are a pumping light incidence surface, a pumping light and parameter light reflection surface, a residual pumping light output surface and a parameter light output surface respectively, the pumping light is led into the nonlinear crystal 5 to carry out reverse transmission gain firstly, and in the reverse transmission gain process, the pumping light passes through the nonlinear crystal 5 twice successively, and the residual pumping light is output through the residual pumping light output surface; the residual pump light transmission unit is arranged corresponding to the residual pump light output surface, the output residual pump light is reflected by the residual pump light transmission unit and then is led into the nonlinear crystal 5 to carry out forward transmission gain, and in the forward transmission gain process, the residual pump light passes through the nonlinear crystal 5 twice in sequence; the parametric light polarization synthesis unit is arranged corresponding to the parametric light output surface, and the reverse and forward parametric light after gain conversion is output to the parametric light polarization synthesis unit for synthesis through the parametric light output surface, so that the power of the output parametric light is improved.
Meanwhile, an annular resonant cavity is formed in the nonlinear crystal 5, pump light passes through the same nonlinear crystal 5 in four round trips to form reverse and forward bidirectional operation of the annular cavity OPO, and finally common-path output is formed in a polarization beam combining mode, so that the pass of the pump light is improved, the cavity length of the annular cavity OPO is shortened, the light-emitting threshold is reduced, conversion efficiency and output power/energy are improved, and in addition, the OPO resonant cavity and the nonlinear crystal 5 are of an integrated structure, so that stability and reliability of the annular cavity OPO are improved, and the optical fiber has the advantages of small volume, light weight and the like.
In the ring cavity optical parametric oscillator with the four-way pumping bi-directional operation of the present embodiment, referring to fig. 1, the ring cavity optical parametric oscillator further includes an isolation unit 2, where the isolation unit 2 is located between the pump laser 1 and the nonlinear crystal 5, and the isolation unit 2 can prevent the influence of subsequent return light on the pump laser 1.
In the ring cavity optical parametric oscillator with four-way pumping and two-way operation in this embodiment, referring to fig. 1, linearly polarized pump light is collimated and output from the pump laser 1 after beam shaping, and then is incident to the pump light turning mirror 3 through the isolation unit 2, the pump light turning mirror 3 reflects the pump light to the pump light introducing mirror 4, and the combined function of the pump light turning mirror 3 and the pump light introducing mirror 4 is to enter the pump light into the nonlinear crystal 5 at a specific angle.
In the four-way pumping bidirectional running ring cavity optical parametric oscillator of this embodiment, referring to fig. 1, the residual pumping light transmission unit includes an imaging lens 6 and a pumping light reflector 7, where the imaging lens 6 and the pumping light reflector 7 are coaxially disposed, and the imaging lens 6 is disposed corresponding to the residual pumping light output surface.
The surplus pump light output from the surplus pump light output surface is incident on the pump light reflecting mirror 7 after passing through the imaging lens 6, and the reflected surplus pump light is re-introduced into the nonlinear crystal 5 from the surplus pump light output surface. The function of the imaging lens 6 is to adjust the spot size and divergence angle of the remaining pump light so that it achieves a high efficiency conversion when the nonlinear crystal 5 is forward pumped.
Referring to fig. 1, the parametric optical polarization synthesis unit of the ring cavity optical parametric oscillator with the four-way pumping bi-directional operation in this embodiment includes a forward parametric optical transmission element, a reverse parametric optical transmission element and a parametric optical polarizer 12, where the forward parametric optical transmission element is located on a forward parametric optical transmission path, the reverse parametric optical transmission element is located on a reverse parametric optical transmission path, and a parametric optical half-wave plate is disposed on the forward parametric optical transmission path to rotate the polarization state of the forward parametric light, and the parametric optical polarizer 12 is located at the intersection of the forward parametric optical transmission path and the reverse parametric optical transmission path.
The four-way pumping bidirectional running annular cavity optical parametric oscillator in the embodiment, referring to fig. 1, further comprises a power meter 13, and the parametric light synthesized by the polarization of the parametric light polarizer 12 is transmitted to the power meter 13.
The parametric light polarizer 12 performs polarization beam combination on parametric light generated by the reverse annular cavity OPO (indicated by a black dotted arrow in fig. 1) and parametric light generated by the forward annular cavity OPO after spin-polarization (indicated by a gray dotted arrow in fig. 1), and forms a common optical path to be incident on the power meter 13.
Referring to fig. 1 and 2, the cross section of the nonlinear crystal 5 of the ring cavity optical parametric oscillator of the four-way pumping bidirectional operation in this embodiment is hexagonal, and the nonlinear crystal comprises 2 horizontal planes and 4 inclined planes, the 4 inclined planes form a ring resonator, and the 4 inclined planes are a pumping light incident plane (S1), a parametric light output plane (S2), a pumping light and parametric light reflecting plane (S3), and a residual pumping light output plane (S4) in sequence.
Specifically, the pump light incidence surface (S1) is plated with a pump light antireflection film and a parametric light high reflection film, the residual pump light output surface (S4) is plated with a pump light antireflection film and a parametric light high reflection film, the parametric light output surface (S2) is plated with a pump light high reflection film and a parametric light partial reflection film, and the pump light and parametric light reflection surface (S3) is plated with a pump light high reflection film and a parametric light high reflection film.
In the ring cavity optical parametric oscillator with the four-way pumping bidirectional operation in the embodiment, referring to fig. 1 and 2,4 inclined planes are symmetrically arranged, and a rectangular resonant circuit is formed between the 4 inclined planes.
Preferably, the pump laser 1 is a Nd-doped or Yb-doped 1 μm pulse or continuous linear polarization laser, can be in a single resonant cavity mode or a multi-stage amplification Mode (MOPA), and the gain module can be a rod-shaped side pump, a block-shaped end pump or a strip-shaped side pump. The pump light is collimated and output after being regulated to a proper light spot size by a coupling system formed by lenses so as to meet the requirement of the subsequent OPO on the optimal pump power density. For example, the wavelength of the pumping light is 1.064 μm, the repetition frequency is 10kHz, the pulse width is 50-100 ns, the average power is >100W, the beam quality M2<1.5, the light spot size is 2mm, and the linear polarization output is realized. The isolation unit 2 consists of a1 μm polarizer, a 1/4 wave plate, a Faraday rotator and a second polarizer, and aims to make pump light travel along one direction, and return light of a subsequent system cannot return to the pump laser 1, so that performance change or damage of devices is caused. The pump light turning mirror 3 is a plane mirror and is plated with a high reflection film of 1 mu m at 45 degrees. The pump light guide mirror 4 is a plane mirror, is plated with a1 mu m high-reflection film suitable for a large range of angles, and realizes the change of the incident angle of the pump light entering the pump light incident surface (S1) of the nonlinear crystal 5 by adjusting the angle of the high-reflection film so as to be matched with the resonant light path of the OPO of the annular cavity. The nonlinear crystal 5 is a MgO-doped PPLN or PPLT crystal, and the crystal configuration and size are shown in fig. 2. The polarization period varies according to the wavelength of the desired parametric light, for example, when the polarization period is 31.2 μm, the ring cavity OPO process can be realized as follows: the process of the OPO of the annular cavity can be realized when the polarization period is 29.8 mu m and the polarization period is 1 mu m to 1.6 mu m+2.7 to 3.0 mu m: the nonlinear crystal 5 is placed in a temperature control furnace, and the adjustment of the wavelength range (1-5 mu m) of parametric light output wavelength can be realized according to different phase matching conditions, wherein the wavelength range is 1 mu m to 1.5 mu m plus 3.7-4.0 mu m. As shown in FIG. 2, the 4 inclined surfaces (i.e., light passing surfaces) of the nonlinear crystal 5 were each cut at an angle of 45℃and the PPLN/PPLT crystal was 50mm in length (20 mm without unpolarized regions), 20mm in width and 5mm in thickness.
The optical path history is briefly described as follows: s1 is coated with a 1-mu m antireflection film and a parametric light (comprising near infrared signal light and mid infrared idler light) high reflection film, pump light enters a nonlinear crystal 5 from S1, S2 is coated with a 1-mu m high reflection film and a parametric light partial reflection film (such as R=60%), parametric light generated by an OPO of an annular cavity is output from S2, S3 is coated with a 1-mu m high reflection film and a parametric light high reflection film, S4 is coated with a 1-mu m antireflection film and a parametric light high reflection film, and the rest unconverted 1-mu m pump light is emitted from S4.
When S2 is plated with a partial reflection film of near infrared signal light and an antireflection film of intermediate infrared idler frequency light, the annular cavity OPO is of a signal light single resonance structure; when S2 is plated with a partial reflection film of the intermediate infrared idler frequency light and an antireflection film of the near infrared signal light, the annular cavity OPO is in an idler frequency light single resonance structure; when the S2 surface is plated with partial reflection films of the intermediate infrared idler light and the near infrared signal light, the annular cavity OPO is of a double-resonance structure.
After the remaining unconverted 1 μm pump light is emitted from S4 of the nonlinear crystal 5, the pump light is re-incident from S4 through the imaging lens 6 with focal length f=100 mm and the pump light reflector 7 (coated with 1 μm high reflection film), forming a forward circulating ring cavity OPO, and the generated parametric light is outputted downwards from S2 of the nonlinear crystal 5. The parametric light output from S2 generally contains both mid-infrared idler light and near-infrared signal light, which can be split by the first parametric light mirror 8 and the parametric light splitter 11. For example, the first parametric light reflector 8 is coated with a high reflection film of the mid-infrared idler light and an anti-reflection film of the near-infrared signal, while the parametric light spectroscope 11 is coated with an anti-reflection film of the mid-infrared idler light and a high reflection film of the near-infrared signal, and the beam is the mid-infrared laser beam which is combined by the parametric light polarizer 12 at this time, and the power meter 13 measures the power of the mid-infrared laser beam. Correspondingly, the parametric light half-wave plate 9 is aimed at the wavelength of the mid-infrared idler, the polarization state of the mid-infrared idler is rotated by 90 degrees, the second parametric light reflector 10 is high in reflection of the mid-infrared idler, the parametric light polaroid 12 is high in reflection of the S-polarized mid-infrared idler, and the P-polarized mid-infrared idler is high in transmission.
In summary, the utility model can realize the ring cavity OPO with four-way pumping bi-directional operation, the cavity length is 160mm, and the total equivalent gain length of the PPLN crystal is 100mm (reverse loop) +100mm (forward loop) when the pumping light passes back and forth in the horizontal direction, so the oscillation starting threshold of the ring cavity OPO can be reduced, and the conversion efficiency of the pumping light can be improved. The nonlinear crystal 5 (PPLN crystal) and the ring cavity OPO are the same, so that the device is beneficial to realizing miniaturization, the space envelope is smaller than 70mm multiplied by 20mm multiplied by 5mm, and the actual volume is only 6cm 3. The four light-passing surfaces of the nonlinear crystal 5 (PPLN crystal) ensure the surface shape, the perpendicularity, the parallelism and the angle accuracy of the nonlinear crystal by high-precision optical processing so as to ensure the closed loop of the oscillation light path of the OPO of the annular cavity, and the purpose of debugging-free is also achieved. The reduction of parametric light performance caused by displacement or detuning of a cavity mirror in the traditional annular cavity OPO is avoided, and the annular cavity OPO is realized by the light passing surface of the nonlinear crystal 5, so that the reliability and stability of the system are remarkably improved.
In addition, the parametric light output in different directions generated by the OPO of the annular cavity during bidirectional resonance is realized, one path of the parametric light output is subjected to polarization synthesis with the other path after the polarization state of the parametric light half-wave plate 9 is rotated, and finally the common-path output is realized. Therefore, the utility model improves the power or energy of the infrared laser through polarization beam combination while improving the conversion efficiency of the pump light. The nonlinear crystal 5 is not limited to only nonlinear crystals (such as KTP, KTA, etc.) with non-critical phase matching, but also nonlinear crystals with quasi-phase matching (such as PPLN, PPLT, etc.) may be used. When quasi-phase matching is adopted, very long crystals can be selected to further reduce the threshold value of the OPO of the annular cavity, and the method is suitable for continuous laser and pulse laser pumping, and has the advantages of large effective nonlinear coefficient, strong adaptability of pumping light wavelength, insensitivity of pumping light directivity, convenience in tuning output wavelength and the like.
In the ring cavity optical parametric oscillator with four-way pumping and two-way operation in this embodiment, referring to fig. 3, the 4 inclined planes are symmetrically arranged, and a cross resonant circuit is formed between the 4 inclined planes, at this time, S1 is used as a pumping light incident plane and the remaining pumping light output plane, S2 is used as a parametric light output plane, and S3 and S4 are used as pumping light and parametric light reflecting planes.
The optical path history shown in fig. 3 is briefly described as follows: the 1 μm pump light is incident from S1 of the nonlinear crystal 5, horizontally transmitted to S2 to the right, reflected to S4 at a small angle (e.g., 22.5 °) by S2, then horizontally transmitted to S3 to the right and reflected to S1 output, as indicated by the black arrow in fig. 3. Then, the light is re-incident from S1 through the imaging lens 6 and the pump light reflecting mirror 7, and is output from S1 after being reflected by S3, S4 and S2 in sequence, as shown by gray arrows in FIG. 3.
The polarization period of the cross-shaped annular cavity OPO on the horizontal optical path under the phase matching condition is Λ1, and the following conditions are satisfied: n1/λ1=n2/λ2+n3/λ3+1/Λ1, where n1, n2, n3 represent refractive indexes of the pump light, the signal light, and the idler light, respectively, λ1, λ2, and λ3 represent wavelengths of the pump light, the signal light, and the idler light, respectively, and when on an oblique optical path, an equivalent polarization period under a phase matching condition is Λ2=Λ1×arcos (θ), and θ is an angle between the pump light and a polarization period, satisfying the following conditions: n1/λ1=n4/λ4+n5/λ5+1/Λ2, where n4 and n5 represent refractive indices of the signal light and the idler light generated by the inclined optical path, respectively, and λ4 and λ5 represent wavelengths of the signal light and the idler light generated by the inclined optical path, respectively. Therefore, the method can generate the parameter light wavelength matching under two conditions, can output parameter light with four wavelengths, and can realize the tuning of the four parameter light wavelengths by changing the working temperature of the PPLN crystal.
The specific parameters are designed as follows: the nonlinear crystal 5 is a PPLN crystal doped with MgO, and has a lateral length of 50mm, a polarization period Λ=29 μm, S1 is coated with an antireflection film of 1 μm pump light, a high reflection film of 1.4 to 1.8 μm for signal light, a high reflection film of 2.7 to 4 μm for idler light, S2 is coated with a high reflection film of 1 μm pump light, a partial reflection film (r=50 to 80%) of 1.4 to 1.8 μm for signal light, an antireflection film of 2.7 to 4 μm for idler light, and S3 and S4 are coated with a high reflection film of 1 μm pump light, a high reflection film of 1.4 to 1.8 μm for signal light, and a high reflection film of 2.7 to 4 μm for idler light. When the pump light of 1 μm passes back and forth horizontally, the equivalent polarization period of the PPLN crystal is 29 μm, and when the working temperature is 120 ℃, the OPO phase matching process is as follows: 1 μm to 1.46 μm+3.9 μm; when 1 μm pump light propagates at an angle of 22.5 °, the equivalent polarization period of the PPLN crystal is 31.4 μm, and when the operating temperature is 120 ℃, the inclined OPO phase matching process is: 1 μm to 1.72 μm+2.8 μm; the ring cavity OPO at this time realizes a phase matching process of two wavelengths, so that laser light containing four wavelengths of 1.46 μm+3.9 μm and 1.72 μm+2.8 μm output from the PPLN crystal S2 can be further split and combined in polarization by a spectroscope according to laser light of a desired wavelength (refer to a parametric light polarization synthesis unit structure in fig. 1).
In the ring cavity optical parametric oscillator with the four-way pumping bi-directional operation in this embodiment, referring to fig. 4, the cross section of the nonlinear crystal 5 is trapezoidal, 2 sides and a top surface thereof form a ring resonator, the 2 sides and the top surface are respectively a pumping light incident surface (S1), a parametric light output surface (S2) and pumping light and parametric light reflecting surfaces (S3), the pumping light incident surface (S1) coincides with the remaining pumping light output surface, and the remaining pumping light is reintroduced into the nonlinear crystal 5 through the imaging lens 6 and the pumping light reflecting mirror 7 via the pumping light input surface (S1).
Specifically, the pump light incidence surface (S1) is plated with a pump light antireflection film and a parametric light high reflection film, the parametric light output surface (S2) is plated with a pump light high reflection film and a parametric light partial reflection film, and the pump light and parametric light reflection surface (S3) is plated with a pump light high reflection film and a parametric light high reflection film.
Preferably, three surfaces of the nonlinear crystal 5 (PPLN crystal) form a triangular ring cavity OPO. At this time, 1 μm pump light is incident from S1, horizontally propagates to S2, is reflected to S3, and is reflected to S1 for output through S3. The parametric light generated by the triangular ring cavity OPO is output from S2. The remaining 1 μm pump light output from S1 is incident again from S1 through imaging lens 6 and pump light reflector 7, and is output from S1 after being reflected by S3 and S2 in turn, to form a forward OPO loop. Because the pump light with the diameter of 1 mu m still forms a certain included angle with the polarization period of the PPLN crystal during non-horizontal transmission, the equivalent polarization period also changes along with the polarization period, so that two kinds of phase matching can be realized, and laser output with four wavelengths can be generated.
The four-way pumping bidirectional running annular cavity optical parametric oscillator of the embodiment selects laser with the pumping wavelength of not 1 mu m, and can be Nd-doped laser with the wavelength of-1.3 mu m, er-doped laser with the wavelength of-1.6 mu m, tm-doped laser with the wavelength of-1.9 mu m, ho-doped laser with the wavelength of-2 mu m, er-doped laser with the wavelength of-2.9 mu m and the like. The polarization period of the PPLN nonlinear crystal should be specifically designed according to the phase matching conditions caused by different pump light.
The foregoing detailed description of the utility model has been presented for purposes of illustration and description, but is not intended to limit the scope of the utility model, i.e., the utility model is not limited to the details shown and described.
Claims (10)
1. A four-way pumped bi-directionally operated ring cavity optical parametric oscillator, comprising:
A pump laser generating pump light;
The nonlinear crystal is internally provided with a ring resonant cavity, the side surfaces of the nonlinear crystal are respectively a pump light incidence surface, a pump light and parameter light reflection surface, a residual pump light output surface and a parameter light output surface, the pump light is led into the nonlinear crystal to perform reverse transmission gain firstly, the pump light passes through the nonlinear crystal twice in sequence in the reverse transmission gain process, and the residual pump light is output through the residual pump light output surface;
The residual pump light transmission unit is arranged corresponding to the residual pump light output surface, the output residual pump light is reflected by the residual pump light transmission unit and then is led into the nonlinear crystal to carry out forward transmission gain, and in the forward transmission gain process, the residual pump light passes through the nonlinear crystal twice in sequence;
And the parametric light polarization synthesis unit is arranged corresponding to the parametric light output surface, and the reverse and forward parametric light after gain conversion is output to the parametric light polarization synthesis unit for synthesis through the parametric light output surface, so that the power of the output parametric light is improved.
2. The four-way pumped bi-directionally operated ring cavity optical parametric oscillator of claim 1, further comprising an isolation unit positioned between the pump laser and the nonlinear crystal.
3. The four-way pumping bi-directional operation ring cavity optical parametric oscillator according to claim 1, wherein the residual pumping light transmission unit comprises an imaging lens and a pumping light reflector, the imaging lens and the pumping light reflector are arranged coaxially, and the imaging lens is arranged corresponding to the residual pumping light output surface.
4. The four-way pumping bi-directional operation ring cavity optical parametric oscillator according to claim 1, wherein the parametric optical polarization synthesis unit comprises a forward parametric optical transmission element, a reverse parametric optical transmission element and a parametric optical polarizer, the forward parametric optical transmission element is located on a parametric optical forward transmission path, the reverse parametric optical transmission element is located on a parametric optical reverse transmission path, and a parametric optical half-wave plate is disposed on the parametric optical forward transmission path to rotate the polarization state of the forward parametric light, and the parametric optical polarizer is located at the intersection of the parametric optical forward transmission path and the reverse transmission path.
5. The four-way pumped bi-directionally operating ring cavity optical parametric oscillator of claim 4, further comprising a power meter to which the parametric light synthesized by the parametric light polarizer polarization is transmitted.
6. The four-way pumping bi-directional operation ring cavity optical parametric oscillator according to claim 1, wherein the cross section of the nonlinear crystal is hexagonal and comprises 2 horizontal planes and 4 inclined planes, the 4 inclined planes form a ring resonator, and the 4 inclined planes are a pumping light incident plane, a pumping light and parametric light reflecting plane, a residual pumping light output plane and a parametric light output plane in sequence.
7. The four-way pumping bi-directional operation ring cavity optical parametric oscillator according to claim 6, wherein the pumping light incident surface is coated with a pumping light anti-reflection film and a parametric light high reflection film, the remaining pumping light output surface is coated with a pumping light anti-reflection film and a parametric light high reflection film, the parametric light output surface is coated with a pumping light high reflection film and a parametric light partial reflection film, and the pumping light and the parametric light reflection surfaces are coated with a pumping light high reflection film and a parametric light high reflection film.
8. The four-way pumping bi-directional operation ring cavity optical parametric oscillator of claim 7, wherein the 4 inclined planes are symmetrically arranged, and a rectangular resonant circuit or a cross resonant circuit is formed between the 4 inclined planes.
9. The four-way pumping bi-directional operation ring cavity optical parametric oscillator according to claim 1, wherein the cross section of the nonlinear crystal is trapezoid, 2 side surfaces and a top surface of the nonlinear crystal form a ring resonator, the 2 side surfaces and the top surface are respectively a pumping light incident surface, a parametric light output surface and pumping light and parametric light reflecting surfaces, and the pumping light incident surface coincides with the remaining pumping light output surface.
10. The four-way pumping bi-directional operation ring cavity optical parametric oscillator according to claim 9, wherein the pumping light incident surface is coated with a pumping light anti-reflection film and a parametric light high reflection film, the parametric light output surface is coated with a pumping light high reflection film and a parametric light partial reflection film, and the pumping light and the parametric light reflection surfaces are coated with a pumping light high reflection film and a parametric light high reflection film.
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