A small and efficient integrated ring optical parametric oscillator / amplifier

Abstract

The application discloses a small-sized and high-efficiency integrated ring-shaped optical parametric oscillator / amplifier, which combines the ring-shaped optical parametric oscillator technology and the optical parametric amplifier technology, amplifies the pump light and the signal light output by the ring-shaped optical parametric oscillator in the optical parametric amplifier, and designs the pump light and the signal light into an integrated ring-shaped structure with a collinear pumping mode, so that the conversion efficiency is remarkably improved and the size of the device is greatly simplified; meanwhile, due to the adoption of the oscillation and amplification technology, the output signal light beam quality of the application is obviously superior to that of a single polycrystal optical parametric oscillator, and the requirements of military laser on size, beam quality and efficiency and the like can be met.

Description

Technical Field

[0001] This invention relates to an optical parametric oscillator and an optical parametric amplifier, and particularly to an integrated ring optical parametric oscillator / amplifier with compact and reliable structure, high conversion efficiency and high beam quality characteristics. Background Technology

[0002] Currently, laser equipment (laser rangefinders, laser target designators, etc.) typically uses Nd:YAG lasers with a wavelength of 1.06μm. However, Nd:YAG laser sources have revealed some drawbacks, including eye safety and poor penetration through battlefield smoke. In light of this, various countries have launched research into next-generation eye-safe laser technologies.

[0003] Optical parametric oscillation (OPO) technology utilizes pump light with a certain power density to act on a nonlinear crystal. When the phase matching condition is met, signal light and idler light are generated. The signal light is then resonantly amplified to obtain the desired signal light output. Therefore, using the 1.06μm laser output from an existing Nd:YAG laser as pump light and converting it into a 1.57μm wavelength laser (signal light) through OPO technology is an effective way to achieve laser output at a wavelength safe for the human eye. However, current OPO technology faces three serious problems in engineering applications: return light problem, conversion efficiency problem, and beam quality problem, which will be discussed in detail below.

[0004] A traditional direct-cavity OPO consists of a pair of parallel input and output mirrors and one or more nonlinear crystals (KTP or KTA). The input mirror is coated with an anti-reflection coating for the pump light. Since the pump light is usually incident perpendicularly to the light-transmitting surfaces of the three mirrors, a small amount of pump light reflected from the optical components can easily return directly to the pump source laser through the input mirror. This returned light severely interferes with the generation of giant pulses during the pump light's Q-switching process, affecting the output stability of the pump light and even creating localized strong points, potentially damaging the optical components in the pump source laser. Currently, there are two main approaches to solving this problem: one is to place an optical isolator between the pump source laser and the OPO; the other is to artificially deviate the optical axis of the OPO from the optical axis of the pump light, so that the returning pump light forms a certain angle with the pump light entering the OPO, preventing it from entering the pump source laser. However, both methods have problems. First, optical isolators are usually large in size and weight, which is unacceptable for military lasers that require small size and portability. At the same time, the temperature characteristics of optical isolators, especially their low-temperature characteristics, are poor, which also makes it difficult to meet the requirements of military lasers to operate normally over a wide temperature range. Second, the method of using the OPO optical axis to deviate from the pump optical axis also comes at the cost of reducing the system conversion efficiency and the signal beam quality, which cannot meet the requirements of military lasers for power consumption and beam quality.

[0005] To completely solve the return light problem of the aforementioned direct-cavity OPO, a ring-shaped OPO has been proposed. A ring-shaped cavity is a resonant cavity that can provide a polygonal oscillation circuit. In a ring-shaped OPO, since all its cavity mirrors are at a certain angle to the pump light, surface-reflected light from any component cannot enter the pump source laser. At the same time, the pump light is pumped along a ring path, and residual pump light will not return to the pump light resonant cavity. Therefore, the return light problem of the direct-cavity OPO is fundamentally solved, and it can be placed directly in front of the pump source, making the overall structure of the device very small and compact.

[0006] However, the single-pass transmission of pump light through the nonlinear crystal in a ring cavity OPO leads to problems such as a high optical parametric oscillation threshold and low conversion efficiency from pump light to signal light, which limits its application in high-conversion-efficiency applications. One effective measure to improve the conversion efficiency of a ring cavity OPO is to increase the number of nonlinear crystals; however, this method degrades the beam quality of the signal light while improving conversion efficiency, which is also undesirable. Therefore, developing a ring cavity OPO with high conversion efficiency while maintaining good beam quality is a pressing issue in the field of OPO engineering applications.

[0007] The beam quality of a military laser directly affects the energy density of the laser beam acting on the target surface. Better beam quality means more concentrated energy acting on the target, and vice versa. Therefore, beam quality is a key indicator in laser design. Although using a linear unstable cavity OPO structure can significantly improve the beam quality of the output signal light, it still suffers from the return light problem of the aforementioned linear cavity OPO, making it difficult to apply in military lasers with stringent size and weight constraints. Another way to improve OPO beam quality is to use optical parametric amplification (OPA) technology. This involves amplifying the low-energy signal light (seed light) of the OPO with good beam quality through an OPA. Under the action of the OPA pump light, the signal light energy is multiplied while retaining the good beam quality of the injected signal light. It can be seen that OPA technology can achieve both high conversion efficiency and high beam quality. However, in practical applications, this technology requires the pump light to be split into two beams to pump the OPO and the OPA respectively. The pump light from the OPA and the signal light output from the OPO must be adjusted by time delay line to ensure that the pump light from the OPA and the signal light from the OPO arrive at the nonlinear crystal in the OPA at the same time, resulting in a complex device structure and large size.

[0008] In conclusion, combining ring cavity OPO technology with OPA technology, using the ring cavity OPO design to solve the return light problem, and further utilizing OPA technology to obtain high conversion efficiency and high beam quality is an effective way to truly engineer OPO technology for military applications. Summary of the Invention

[0009] The purpose of this invention is to design a small, efficient, integrated ring optical parametric oscillator / amplifier with compact and reliable structure, high conversion efficiency, and high beam quality characteristics, which can simultaneously meet the requirements of military lasers in terms of size, beam quality, and efficiency.

[0010] The technical solution for implementing this invention is as follows:

[0011] A small, high-efficiency, integrated ring optical parametric oscillator / amplifier (OPO) consists of two total internal reflection right-angle prisms and a 45-degree plane mirror for both incident and exit directions, forming a quadrilateral ring OPO resonant cavity. The pump light's optical axis is parallel to one side of the quadrilateral. It enters the OPO cavity through the plane mirror placed at a 45-degree angle to the pump light's optical axis, undergoes two total internal reflections on the two right-angle faces of one right-angle prism, and one total internal reflection on the bottom face of the other right-angle prism, before returning along the ring path of the quadrilateral to the plane mirror at the point of incidence and exiting the ring OPO from there. The exit direction is perpendicular to the incident direction. Since all reflecting surfaces are at a 45-degree angle to the pump light axis, any reflected light is perpendicular to the incident light and cannot return to the pump laser along its original direction, thus solving the problem of return light.

[0012] In this ring-shaped OPO, a nonlinear crystal (such as KTP) for wavelength conversion can be placed on two sides parallel to the incident optical axis, with the light-transmitting surface perpendicular to the incident pump light. When the pump light intensity reaches a certain value, the signal light is generated and resonates and amplified within the cavity, ultimately exiting through a plane mirror in the same direction as the pump light. The purpose of using a total internal reflection right-angle prism instead of the 45-degree reflector in a conventional ring-shaped OPO in this technical solution is twofold: first, the self-collimating characteristic of the total internal reflection prism greatly simplifies the adjustment and assembly process; second, the principle of total internal reflection simultaneously reflects both the pump light and the signal light, eliminating the need for a relatively complex optical reflective coating and enabling tuning of the output signal wavelength.

[0013] To further improve conversion efficiency, the residual pump light and signal light emitted simultaneously and in the same direction from the plane mirror of the ring OPO are totally reflected (rotated 90 degrees) by the bottom surface of another totally internally reflected right-angle prism and then enter the OPA, which consists of one or two nonlinear crystals (consistent with those in the ring OPO). Under the action of the nonlinear crystal in the OPA, the residual pump light is further converted into signal light while retaining good beam quality. This collinear structure, which directly injects the signal light and residual pump light output from the OPO into the OPA for signal light amplification, ensures that the OPA pump light and signal light are completely coincident in time and space, achieving the best amplification effect and the best beam quality. Moreover, it eliminates the need to adjust the OPA pump light through a time delay line to ensure that the OPA pump light and the signal light output from the OPO arrive at the nonlinear crystal in the OPA simultaneously, greatly simplifying the OPA structure.

[0014] This invention designs a ring-shaped OPO utilizing total internal reflection via prisms and an OPA employing a collinear pumping method. The ring-shaped OPO resonant cavity utilizes the total internal reflection and self-collimation characteristics of the prisms, simplifying the structure while improving device reliability. The OPA, using a collinear pumping method, is placed directly after the ring-shaped OPO, and the two are designed into a compact, reliable, and integrated "e"-shaped optical path through total internal reflection via prisms. This technology solves the OPO return light problem using the ring-shaped OPO while achieving high conversion efficiency and good beam quality using the OPA, making it an OPO device suitable for military engineering applications.

[0015] Compared with the prior art, the present invention has the following advantages and effects:

[0016] 1. This invention adopts a ring-shaped OPO optical path, in which all reflected light is at a 90-degree angle to the incident light, thus preventing it from directly returning to the pump laser. This solves the problem of reflected light in linear cavity OPO and greatly improves the stability of the device.

[0017] 2. The annular OPO resonant cavity of the present invention is composed of a total reflection right-angle prism, which has the advantages of simple structure, easy debugging and assembly, and mechanical stability and reliability, and is also easy to tune the wavelength.

[0018] 3. This invention uses OPA technology to amplify the signal light output by the ring OPO, which significantly improves the conversion efficiency from pump light to signal light compared to a conventional single-stage ring OPO.

[0019] 4. This invention utilizes OPA technology to achieve better signal beam quality, which is significantly improved compared to polycrystalline single-stage ring OPO.

[0020] 5. The OPA part of the present invention adopts a collinear pumping method, which directly injects the signal light emitted from the OPO and the remaining pump light into the OPA, greatly simplifying the structure of the OPA.

[0021] 6. This invention connects the OPO and OPA through a right-angle prism to form a compact and reliable "e"-shaped optical path, which meets the requirements of military lasers in terms of size, beam quality and efficiency. Attached Figure Description

[0022] Figure 1 This is a diagram of a traditional straight-cavity OPO structure;

[0023] Figure 2 This is a diagram of a traditional annular cavity OPO structure;

[0024] Figure 3 This is a traditional OPO-OPA structure diagram;

[0025] Figure 4The present invention provides a structural diagram of a small, integrated ring-shaped OPO-OPA. Detailed Implementation

[0026] The present invention will be further described below with reference to the accompanying drawings and embodiments, but the present invention is not limited to these embodiments.

[0027] Figure 1 The diagram shows the structure of a traditional direct-cavity OPO. The pump laser 10 emits a 1.06 μm wavelength pump light 11 to pump the OPO 12, generating the required 1.57 μm wavelength signal light 16. The OPO 12 consists of two parallel cavity mirrors 13 and 14 and a nonlinear crystal (KTP) 15 placed between them. Since the light-transmitting surfaces of all three are perpendicular to the pump light 11, reflected light from the surfaces is highly likely to return directly to the pump laser 10 along the original path, causing system instability—the so-called return light problem.

[0028] To solve this problem, Figure 2 A ring-shaped OPO structure is adopted. The ring-shaped OPO 22 consists of four cavity mirrors 23, 24, 25, and 26 placed at a 45-degree angle to the pump light 11, and two KTP crystals 27a and 27b. The input cavity mirror 23 is coated with an anti-reflection film for the 1.06μm pump light 11 and a total reflection film for the 1.57μm signal light 16 for pump light input. The output cavity mirror 24 is coated with a total reflection film for the pump light 11 and a partial reflection film (reflectivity R of 10%-90%) for the signal light 16 for signal light output. The other two mirrors 25 and 26 are both coated with total reflection films for both pump light and signal light. Thus, the pump light 11 incident from the input mirror 23 is reflected by cavity mirrors 24, 25, and 26 and ultimately exits from cavity mirror 23, forming the remaining pump light 17, while the signal light 16 is output from the output mirror 24. With this ring structure, the reflected light from all cavity mirrors is at a 90-degree angle to the incident light, and the output direction of the remaining pump light 17 is also perpendicular to the pump light 11, thus solving the problem of return light in a direct-cavity OPO. However, since the pump light 11 only passes through the KTP crystals 27a and 27b once, the conversion efficiency from pump light to signal light is relatively low.

[0029] To further improve the conversion efficiency of OPO, Figure 4 An OPO employing an OPA structure has a pump light 11 split into two beams 11a and 11b by a plane mirror 31. Pump light 11a is then deflected by a total reflection mirror 32 and used for pumping and... Figure 1The OPO12, with a similar structure, outputs signal light 16 which enters OPA35 via beam splitter 34. OPA35 consists of one or more KTP crystals 36 identical to KTP crystal 15. Another pump light beam 11b enters OPA35 after passing through time delay device 37, total reflection mirror 33, and beam splitter 34. In this structure, plane mirrors 31, 32, 33, and 34 are all placed at a 45-degree angle to the direction of pump light 11. Plane mirror 31 is coated with a partial reflection film (reflectivity R is 10%-90%) for pump light 11, plane mirrors 32 and 33 are coated with total reflection films for pump light 11, and beam splitter 34 is coated with a total reflection film for pump light 11 and an anti-reflection film for signal light 16. Because the principle of OPO dictates that signal light 16 can only resonate within cavities 13 and 14 when the intensity of pump light 11a exceeds the OPO threshold, its arrival time at OPA 35 is inevitably delayed compared to pump light 11b. The function of time delay device 37 is to control the arrival time of pump light 11b at OPA 35 to synchronize it with signal light 16, thus achieving optimal signal amplification. It can be seen that although this scheme can achieve high conversion efficiency, it has a relatively complex structure, large size, and requires precise time control.

[0030] Figure 4The structural diagram illustrates the implementation of this invention. This technical solution comprises a ring-shaped OPO47 and an OPA35. The ring-shaped OPO47 consists of a plane mirror 41, two right-angle prisms 42 and 43, and two KTP crystals 48a and 48b. The OPA35 consists of one or more KTP crystals 36. The right-angle prism 44 guides the signal light 16 output from the OPO47 and the remaining pump light 17 together into the OPA35. The plane mirror 41 is coated with an anti-reflection film for the pump light 11 and a partial reflective film for the signal light 16 (reflectivity R is 10%-90%), serving as the input / output mirror for the pump light 11 and the output mirror for the signal light 16. The inclined surface 42c of the right-angle prism 42, the two right-angle surfaces 43b and 43c of the right-angle prism 43, and the two right-angle surfaces 44b and 44c of the right-angle prism 44 are all coated with a dual-wavelength anti-reflection film for both the pump light 11 and the signal light 16. After the pump light enters OPO47 from plane mirror 41, it undergoes two total internal reflections through the two right-angled surfaces 42a and 42b of right-angle prism 42, and one total internal reflection through the inclined surface 43a of right-angle prism 43, before returning to plane mirror 41 and exiting from there, forming residual pump light 17. The signal light 16 generated by OPO47 also exits from plane mirror 41. The residual pump light 17 and signal light 16 exiting from plane mirror 41 in the ring OPO47 undergo total internal reflection through the inclined surface 44a of right-angle prism 44 and simultaneously enter OPA35. In OPA35, the residual pump light 17 is further converted into signal light 16 through the nonlinear effect of the KTP crystal. This OPA method fully utilizes the energy of the residual pump light 17, significantly improving the conversion efficiency from pump light 11 to signal light 16 while preserving the good beam quality of the signal light in the ring OPO47.

[0031] This integrated ring-shaped OPO-OPA is compared to the current ring-shaped OPO ( Figure 2 ) and traditional OPA ( Figure 3 There are three differences: First, two right-angle prisms are used instead of... Figure 2 The three plane mirrors 24, 25, and 26 utilize the total internal reflection characteristic of right-angle prisms, eliminating the need for complex and expensive optical film designs while achieving extremely high stability. Secondly, the collinear design of the signal light 16 and the remaining pump light 17, with their outputs in the same direction, ensures that both enter the OPA35 simultaneously to achieve optimal amplification. This avoids... Figure 3 The OPA scheme shown requires pump light beam splitting and a relatively complex time delay line design. Thirdly, it adopts a small and compact "e"-shaped ring optical path design, which greatly saves space, and the overall device size does not exceed 60mm×50mm×40mm.

Claims

1. A small, high-efficiency, integrated ring optical parametric oscillator / amplifier, characterized in that: It consists of two parts: a ring-shaped OPO and an OPA. The ring-shaped OPO and OPA form a collinear "e" optical path through total internal reflection of a prism. A quadrilateral annular OPO resonant cavity is formed by two total internal reflection right-angle prisms and a 45-degree plane mirror for exit and incident. The optical axis of the pump light is parallel to one side of the quadrilateral. It enters the OPO cavity through the plane mirror placed at a 45-degree angle to its optical axis. After passing through two total internal reflections on the two right-angle faces of one right-angle prism and one total internal reflection on the bottom face of the other right-angle prism, it returns to the plane mirror at the point of incident along the annular path of the quadrilateral and leaves the annular OPO from there. The exit direction is perpendicular to the incident direction. The residual pump light and signal light emitted simultaneously and in the same direction from the ring OPO plane mirror enter the OPA, which is composed of one or two nonlinear crystals, after total reflection from the bottom surface of another total reflection right-angle prism. Inside the OPO cavity, the inclined surface of the right-angle prism through which the pump light first passes, and the two right-angle surfaces of the right-angle prism through which the pump light passes later, are all coated with a dual-wavelength anti-reflection film for both the pump light and the signal light. The ring-shaped OPO consists of a plane mirror, two right-angle prisms, and two KTP crystals; The plane mirror in the ring OPO serves as both the input mirror for the pump light and the output mirror for the signal light and the remaining pump light. The closed loop in the ring-shaped OPO is formed by total internal reflection through a right-angle prism; The residual pump light and signal light emitted from the plane mirror in the ring OPO are reflected by the inclined plane of the right-angle prism and then enter the OPA simultaneously, forming an OPA that uses a collinear pumping method. The dimensions of the ring optical parametric oscillator / amplifier do not exceed 60mm × 50mm × 40mm.

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