Cavity-enhanced optical pumping of solid-state ring laser gyroscope

Abstract

The present invention is entitled "Cavity Enhanced Optical Pumping of a Solid-State Ring Laser Gyroscope". The present disclosure provides a ring laser gyroscope. A light source is configured to generate light of a first wavelength. A plurality of main cavity mirrors are configured to route light of a second wavelength around the main cavity to a readout device. One of the plurality of main cavity mirrors includes a gain medium. A pump mirror and a main cavity mirror including the gain medium are positioned and configured to reflect light of a first wavelength back and forth through the gain medium in a pump cavity, wherein the light of the first wavelength excites the gain medium to generate light of a second wavelength, which is reflected around the main cavity to a readout device.

Description

Background Art

[0001] Ring laser gyroscopes (RLGs) are used in the field of inertial navigation to measure angular motion or rotation. Traditionally, RLGs utilize low-pressure helium-neon gas discharge as the active gain medium. Although existing helium-neon gas discharge RLGs perform well in inertial navigation and other measurement fields, these helium-neon gas discharge RLGs may have a limited lifespan and are expensive to manufacture.

[0002] RLGs utilizing solid-state gain media instead of the helium-neon gas mixture are currently viewed as viable options. From a manufacturing perspective, solid-state gain medium RLGs can offer significant savings in labor and manufacturing costs over helium-neon gas discharge RLGs. Moreover, such solid-state gain medium RLGs can offer technical advantages over helium-neon gas discharge RLGs in terms of increased lifetime.

[0003] An example of a solid-state gain medium for cavity gain of a solid-state RLG is a layer of neodymium-doped silicon dioxide (Nd-doped SiO2). This Nd-doped silicon dioxide layer can be deposited onto the top layer or can be incorporated into the layers of a highly reflective multilayer dielectric mirror in the RLG cavity. Summary of the invention

[0004] The following summary is made by way of example and not by way of limitation. The purpose of providing the summary is merely to help the reader understand some aspects of the subject matter. Embodiments provide an RLG that implements a pump cavity in an efficient, effective, and compact configuration.

[0005] In one embodiment, a ring laser gyroscope is provided, which includes a light source, a plurality of main cavity mirrors, and a pump mirror. The light source is configured to generate light of a first wavelength. The plurality of main cavity mirrors are configured to route light of a second wavelength around the main cavity to a readout device. One of the plurality of main cavity mirrors includes a gain medium. The pump mirror and one of the main cavity mirrors including the gain medium are positioned and configured to reflect light of a first wavelength back and forth through the gain medium in the pump cavity, wherein the light of the first wavelength excites the gain medium to generate light of a second wavelength, and the light of the second wavelength is reflected around the main cavity to the readout device.

[0006] In another exemplary embodiment, an enhanced optical solid-state optical pumping system is provided. The system includes a light source, a plurality of main cavity reflectors, and a pump reflector. The light source is configured to generate light of a first wavelength. The plurality of main cavity reflectors are configured to route light of a second wavelength through the main cavity. A main cavity reflector of the plurality of reflectors includes a gain medium, a first portion, and a second portion. The first portion is configured to reflect light of a first wavelength. The second portion is configured to reflect light of a second wavelength. The pump reflector and a main cavity reflector including a gain medium are positioned and configured to reflect light of a first wavelength back and forth in a pump cavity, wherein the light of the first wavelength excites the gain medium to generate light of a second wavelength, and the light of the second wavelength is routed through the main cavity.

[0007] In yet another embodiment, a method of operating a laser ring gyroscope is provided. The method includes: directing light of a first wavelength into a pump cavity including a pump mirror and a first main mirror, wherein the pump mirror and the first main mirror are configured and positioned to reflect the light of the first wavelength back and forth; exciting a gain medium associated with the first main mirror with the light of the first wavelength to generate light of a second wavelength; directing the generated light of the second wavelength around the main cavity in an opposite direction using at least the first main mirror; reading at least a portion of the light of the second wavelength that passes through a measurement mirror in the main cavity; and determining a rotation based on the reading of the light of the second wavelength. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] The embodiments may be more readily understood and further advantages and uses of the embodiments will become more apparent when considered in light of the detailed description and the following drawings, in which:

[0009] Figure 1 is a diagram of a ring laser gyroscope according to an exemplary embodiment;

[0010] Figure 2 is a flow chart of forming a ring laser gyroscope according to an exemplary embodiment; and

[0011] Figure 3 is a flow chart of ring laser gyroscope operation according to an exemplary embodiment.

[0012] As is common practice, the various described features are not drawn to scale, but rather are drawn to emphasize specific features relevant to the subject matter described. Reference characters denote similar elements throughout the drawings and text. DETAILED DESCRIPTION

[0013] In the following specific embodiments, reference is made to the accompanying drawings, which form a part of the specific embodiments, and in which specific embodiments that can implement the present invention are shown by way of illustration. These embodiments are described in sufficient detail to enable those skilled in the art to implement these various embodiments, and it should be understood that other embodiments can be utilized and can be changed without departing from the spirit and scope of the present invention. Therefore, the following specific embodiments are not restrictive, and the scope of the present invention is limited only by the claims and their equivalents.

[0014] Embodiments provide a laser assembly with enhanced optical pumping, comprising a pump cavity formed in part with a reflector for a main cavity. Thus, embodiments include a main cavity and a pump cavity. Further, embodiments employ a thin layer of gain medium deposited on a common reflector used to form the pump cavity. In at least one embodiment, the pump cavity is located within the outline of the main cavity to reduce the overall size of the system. If the pump cavity (or gain cavity) is in resonance, the intracavity power generated by the pump cavity at the gain medium is much greater than the original pump laser power achieved.

[0015] Figure 1 An example of an embodiment of a ring laser gyroscope (RLG) 100 is shown. The gyroscope 100 is a solid-state ring laser gyroscope including a pump cavity that passes light of a first wavelength λ1 through a gain medium to excite atoms in the gain medium into excited states, thereby generating light of a second wavelength λ2 that passes through the main cavity. Figure 1 The RLG 100 includes three main cavity mirrors 110-1, 110-2, and 110-3 that reflect light of a second wavelength λ2 around the main cavity 150 in a closed loop path. In this example, the closed path is shown as being substantially triangular, with the main cavity mirrors 110-1, 110-2, and 110-3 positioned at respective corners. This configuration is a non-limiting example. In other examples, closed paths of other shapes may be formed with any number of mirrors required to direct light through the main (or primary) cavity.

[0016] In one embodiment, the main cavity mirrors 110-1, 110-2 and 110-3 are highly reflective multilayer mirrors positioned to reflect light having a second wavelength λ2 to a third mirror 110-3 (a measuring mirror), wherein at least a portion of the counter-propagating second wavelengths λ'2 and λ"2 that pass through the measuring mirror 110-3 is read by a readout device 140. As discussed below, in an RLG embodiment, light of the second wavelength λ2 is reflected in opposite directions around the main cavity 150 via the mirrors 110-1 to 110-3. The readout device 140 may include one or more photodetectors that are optically connected to a closed-loop path of the main cavity via the mirror 110-3. The readout device 140 is communicatively coupled to a processing unit 130 that processes the signals to measure angular motion or rotation.

[0017] In an embodiment, a pump cavity 125 and a gain medium 128 in combination with a reflector such as the main cavity reflector 110-1 are used to create the RLG 100. A light source 120 (which may be a laser source in some embodiments) generates light at a first wavelength λ1. In one embodiment, the fourth reflector 118 (pump reflector) is partially reflective to allow light at the first wavelength λ1 to pass through the fourth reflector 118 (pump reflector) into the pump cavity 125. In such an embodiment, the pump cavity 125 is configured as a "resonant cavity" with passage control. In another embodiment, the light source 120 is positioned to provide light at the first wavelength λ1 in an off-axis orientation onto the fourth reflector 118 using the coating 111a of the reflector 110-1, thereby reflecting the light at the first wavelength λ1 from the light source 120 to the reflector 118 to ensure multiple passes. Further, in another embodiment, at least one hole in the coating or through the fourth reflector 118 provides a path for emitting light at the first wavelength λ1 into the pump cavity 125. In this embodiment, the pump cavity 125 is located within the inner boundary of the main cavity 150 including the shared reflector 110-1. The positioning of the pump cavity 125 and the fourth reflector 118 and the laser source 120 with the inner boundary of the main cavity 150 allows the RLG 100 to have a compact overall size. In addition, the use of the main cavity reflector 110-1 reduces the number of reflectors required for the RLG 100 to utilize the pump cavity 125.

[0018] The gain medium 128 includes a rare earth doped gain medium. In an exemplary embodiment, the gain medium 128 is several wavelengths thick. In other embodiments, the layer can be thicker. In one embodiment, the gain medium can be formed as a thin amorphous film of a rare earth doped glassy material. Further, the gain medium 128 layer can include a plurality of gain medium 128 layers or sublayers having desired properties. In some embodiments, the gain medium 128 is formed on the reflector via deposition. Further, in one embodiment, the gain medium 128 is combined by a lamination process. Further, also in some embodiments, the gain medium 128 is formed within the reflector 110-1. Therefore, the embodiments are not limited to a specific location or type of gain medium 128 formed in combination with the reflector 110-1.

[0019] The shared reflector 110-1 in the exemplary embodiment is shown to include a first portion 111a and a second portion 111b. The first portion 111a and the second portion 111b may be made of a plurality of layers. The first portion 111a is designed to reflect one of the light of the first wavelength λ1 or the second wavelength λ2, while the second portion 111b is designed to reflect the other of the light of the first wavelength λ1 or the second wavelength λ2. For example, the first portion 111a of the reflector 110-1 may be designed to reflect the light of the first wavelength λ1, while the second portion 111b of the reflector 110-1 is designed to reflect the light of the second wavelength λ2.

[0020] Light of the first wavelength λ1 within the pump cavity 125 is reflected back and forth between the first portion 111a of the reflector 110-1 and the fourth reflector 118. This back and forth pumping of light provides a greater chance that the light of the first wavelength λ1 excites ions in the solid-state gain medium 128 into an excited state that produces light of a second wavelength (laser beam), which travels around the main cavity 150 via the reflectors 110-1 to 110-3. The generated light of the second wavelength λ2 travels in two directions around the main cavity 150, as discussed above, with at least a portion of the counter-propagating light of the second wavelengths λ'2 and λ"2 passing through the measuring mirror 110-3 where it is read by the readout device 140.

[0021] Thus, the reflector 110-1 of the embodiment is being used in two different cavities, namely the main cavity 150 and the pump cavity 125. One of the benefits of using this configuration with the pump cavity 125 is that less optical power is required from the light source 120 because the highly reflective mirrors 118 and 110-1 create a reflective cavity that confines the light beam within the cavity 125 at the first wavelength λ1, thereby achieving multiple reflections. This configuration is more efficient in exciting ions in the solid-state gain medium 128. For example, by using the pump cavity configuration of the embodiment, the power of the light source 120 can be reduced by a factor of ten.

[0022] An example of a suitable gain medium 128 dopant is neodymium. Other suitable rare earth dopants that may be used to form the gain medium include, but are not limited to, cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu). Non-limiting examples of glassy host materials that may be used to form the gain layer 230 include silicon dioxide, titanium dioxide, tantalum oxide (Ta2O5), aluminum oxide (Al2O3), zirconium oxide (ZrO2), silicate glass, phosphate glass, fluorosilicate glass, non-oxide glass such as fluoride glass, and the like. Other glassy host materials suitable for ion beam sputtering deposition may also be used.

[0023] Figure 2 An RLG formation flow chart 200 of an exemplary embodiment is shown. The RLG formation flow chart 200 is provided in sequential blocks. Other embodiments may include additional blocks and blocks in different sequential orders. Therefore, the embodiments are not limited to Figure 2 The boxes and box order given in .

[0024] The RLG formation flow chart 200 begins at box (202) where the main cavity 150 and pump cavity 125 of the RLG 100 are formed. As discussed above, in one embodiment, the pump cavity 125 is positioned within (or within the outline of) the main cavity 150. At box (204), a reflector is selected to be used in the main cavity 150. The main cavity reflector (generally designated as 110) is selected to reflect light of the second wavelength λ2 around the main cavity 150. In some embodiments, the number of main cavity reflectors 110 used is three or more. At box (206), the main cavity reflector 110 is positioned to direct light of the second wavelength λ2 around the main cavity 150. At box (208), one main cavity reflector 100-1 is further positioned and configured to create the pump cavity 125 with the pump reflector 118.

[0025] As discussed above, Figure 1The main cavity mirror 110-1 in the example of includes a gain medium 128. The gain medium 128 is selected so that light of a first wavelength λ1 excites atoms of the gain medium 128 to produce (emit) photons of a second wavelength λ2, which are guided in opposite directions around the main cavity 150. Specifically, the light of the first wavelength λ1 generated by the light source 120 excites (or pumps) the atoms in the gain medium 128 from a lower energy state to an excited energy state (by absorption). When the excited atoms return to their normal or ground state, they emit photons (of the second wavelength λ2). The main cavity mirror 110 guides the photons of the second wavelength λ2 to bounce around a path (a ring configuration in the exemplary embodiment) in the main cavity 150. As the photons of the second wavelength λ2 continuously pass through the pump gain medium 128, as they bounce around the main cavity 150, amplification is created by stimulated emission of radiation (laser) that produces a laser beam. The photons of the laser beam have a single wavelength λ2 (monochromatic) and travel in phase with each other. Reflecting the pump light of the first wavelength λ1 back and forth through the gain medium helps to excite more atoms and emit more photons (of the second wavelength λ2), which are guided around the main cavity 150 (laser cavity) to create a laser beam.

[0026] See also Figure 3 , shows a flow chart of RLG operation of one embodiment. RLG operation flow chart 300 is provided in sequential blocks. Other embodiments may include additional blocks and blocks in different sequential orders. Therefore, the embodiments are not limited to Figure 3 The boxes and box order given in .

[0027] The RLG operation flow chart begins at box (302) by generating light (laser beam) of a first wavelength λ1. At box (304), the light of the first wavelength λ1 is directed into the pump cavity 125. Once in the pump cavity 125, the light of the first wavelength λ1 is reflected back and forth between the pump mirror 118 and the first portion 111a of the mirror 110-1 (306). The light of the first wavelength λ1 excites atoms in the gain medium of the mirror 110-1 as it reflects back and forth in the pump cavity 125. The excited atoms in the gain medium generate (emit) light of a second wavelength λ2 as indicated at box (308). At box (310), the second portion 111b of the mirror 110-1 reflects and directs the generated light (photons) of the second wavelength λ2 in opposite directions around the main cavity 150. As discussed above, the light of the second wavelength λ2 (photons of the second wavelength λ2) creates a laser beam of the second wavelength λ2 in the main cavity 150. At step (312), at least part of the counter-propagating light of the second wavelength λ'2 and λ"2 that passes through the measuring mirror 110-3 is read by the readout device 140. At step (314), based on the readings, the processing unit 130 determines the angular motion or rotation.

[0028] Although the above embodiments are described as being applicable to RLGs, any type of device requiring an efficient system for generating a laser signal of a specific wavelength using a low power laser beam generating source may implement a pump cavity as described above.

[0029] Exemplary embodiments

[0030] Embodiment 1 includes a ring laser gyroscope, which includes a light source, a plurality of main cavity mirrors, and a pump mirror. The light source is configured to generate light of a first wavelength. The plurality of main cavity mirrors are configured to route light of a second wavelength around the main cavity to a readout device. One of the plurality of main cavity mirrors includes a gain medium. The pump mirror and one of the main cavity mirrors including the gain medium are positioned and configured to reflect light of a first wavelength back and forth through the gain medium in the pump cavity, wherein the light of the first wavelength excites the gain medium to generate light of a second wavelength, which is reflected around the main cavity to the readout device.

[0031] Embodiment 2 includes the ring laser gyro of embodiment 1, wherein the pump cavity is located within the contour of the main cavity.

[0032] Embodiment 3 includes the ring laser gyro of any one of embodiments 1-2, wherein the gain medium includes neodymium.

[0033] Embodiment 4 includes a ring laser gyro according to any one of embodiments 1 to 2, wherein the gain medium includes a dopant of at least one of cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb) and lutetium (Lu).

[0034] Embodiment 5 includes the ring laser gyro of any one of embodiments 1 to 4, wherein the gain medium includes a gain medium layer having a glassy host material.

[0035] Embodiment 6 includes a ring laser gyroscope according to embodiment 5, wherein the glassy host material includes at least one of silicon dioxide, titanium dioxide, tantalum oxide (Ta2O5), aluminum oxide (Al2O3), zirconium oxide (ZrO2), silicate glass, phosphate glass, fluorosilicate glass and non-oxide glass such as fluoride glass.

[0036] Embodiment 7 includes the ring laser gyro according to any one of embodiments 1 to 6, wherein the number of primary cavity mirrors is at least three.

[0037] Embodiment 8 includes the ring laser gyro according to any one of embodiments 1 to 7, wherein the gain medium is a rare earth doped gain medium layer at least two wavelengths thick.

[0038] Embodiment 9 includes the ring laser gyro according to any one of embodiments 1 to 8, wherein one of the plurality of main cavity mirrors including the gain medium further includes a first portion and a second portion. The first portion is configured to reflect light of a first wavelength, and the second portion is configured to reflect light of a second wavelength.

[0039] Embodiment 10 includes the ring laser gyro of any one of embodiments 1 to 9, wherein the plurality of main cavity mirrors includes a measurement mirror configured to allow at least a portion of light at the second wavelength to pass through to the readout device.

[0040] Embodiment 11 includes the ring laser gyro of any one of embodiments 1 to 10, further comprising a processing unit communicatively coupled to the readout device, the processing unit configured to determine angular motion based on an output of the readout device.

[0041] Embodiment 12 includes an enhanced optical solid-state optical pumping system. The system includes a light source, a plurality of main cavity mirrors, and a pump mirror. The light source is configured to generate light of a first wavelength. The plurality of main cavity mirrors are configured to route light of a second wavelength through the main cavity. A main cavity mirror of the plurality of mirrors includes a gain medium, a first portion, and a second portion. The first portion is configured to reflect light of a first wavelength. The second portion is configured to reflect light of a second wavelength. The pump mirror and a main cavity mirror including a gain medium are positioned and configured to reflect light of a first wavelength back and forth in a pump cavity, wherein the light of the first wavelength excites the gain medium to generate light of a second wavelength, which is routed through the main cavity.

[0042] Embodiment 13 includes the system of embodiment 12, wherein the pump cavity is located within the outline of the main cavity.

[0043] Embodiment 14 includes the system of any one of embodiments 12-13, wherein the gain medium is a rare earth doped gain medium layer at least two wavelengths thick.

[0044] Embodiment 15 includes a system according to any one of embodiments 12 to 14, wherein the gain medium includes a dopant of at least one of cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu).

[0045] Embodiment 16 includes a system according to any one of embodiments 12 to 16, wherein the gain medium includes at least one glassy host material, the glassy host material including at least one of silicon dioxide, titanium dioxide, tantalum oxide (Ta2O5), aluminum oxide (Al2O3), zirconium oxide (ZrO2), silicate glass, phosphate glass, fluorosilicate glass, and non-oxide glass such as fluoride glass.

[0046] Embodiment 17 includes a method of operating a laser ring gyroscope. The method includes: directing light of a first wavelength into a pump cavity including a pump mirror and a first primary mirror, wherein the pump mirror and the first primary mirror are configured and positioned to reflect the light of the first wavelength back and forth; exciting a gain medium associated with the first primary mirror with the light of the first wavelength to generate light of a second wavelength; directing the generated light of the second wavelength around the primary cavity in an opposite direction using at least the first primary mirror; reading at least a portion of the light of the second wavelength that passes through a measurement mirror in the primary cavity; and determining a rotation based on the reading of the light of the second wavelength.

[0047] Embodiment 18 includes the method of Embodiment 17, wherein the pump cavity is located within the outline of the main cavity.

[0048] Embodiment 19 includes a method according to any one of Embodiments 17 to 18, wherein generating light of a second wavelength around the main cavity in an opposite direction using at least the first main reflector also includes reflecting the light of the second wavelength away from a first portion of the first main reflector that is configured to reflect the light of the second wavelength.

[0049] Embodiment 20 includes the method of any one of Embodiments 17 to 19, wherein directing light of the first wavelength into the pump cavity further comprises directing light of the first wavelength through a pump mirror.

[0050] Although specific embodiments have been illustrated and described herein, one of ordinary skill in the art will recognize that any arrangement calculated to achieve the same purpose may be substituted for the specific embodiments shown. This application is intended to cover any modifications or variations of the present invention. Therefore, it is apparent that the present invention is limited only by the claims and their equivalents.

Claims

1. A ring laser gyroscope, comprising: a light generating source (120) configured to generate light of a first wavelength; a plurality of main cavity mirrors (110) configured to route light of a second wavelength around a main cavity (150) to a readout device (140), one of the plurality of main cavity mirrors (110) comprising a gain medium (128); and A pump mirror (118), wherein the pump mirror (118) and the one main cavity mirror including the gain medium (128) are positioned and configured to reflect light of the first wavelength back and forth in the pump cavity (125) through the gain medium (128), wherein the light of the first wavelength excites the gain medium (128) to produce light of the second wavelength, and the light of the second wavelength is reflected around the main cavity (150) to the readout device (140).

2. The ring laser gyroscope according to claim 1, wherein the pump cavity (125) is located within the contour of the main cavity (150).

3. A method of operating a laser ring gyroscope, the method comprising: directing light at a first wavelength into a pump cavity (125) comprising a pump mirror (118) and a first primary mirror, wherein the pump mirror (118) and the first primary mirror are configured and positioned to reflect light at the first wavelength back and forth; exciting a gain medium (128) associated with the first primary reflector with light at the first wavelength to generate light at a second wavelength; directing the generated light at the second wavelength in opposite directions around the main cavity (150) using at least the first primary reflector; reading at least a portion of the light of the second wavelength that passes through a measurement reflector (110-3) in the main cavity (150); as well as The rotation is determined based on a reading of the light of the second wavelength passing through the measuring reflector (110-3).

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