Method and assembly for reducing external laser light scattering sources in ring laser gyroscope

Abstract

A method of manufacturing a readout mirror for a ring laser gyroscope, the method comprising: forming an optical substrate component comprising a lower surface, a first upper surface portion substantially parallel to the lower surface, and a second upper surface portion angled relative to the lower surface; roughly polishing the second upper surface part; forming an optical element having a first surface; performing super polishing on the first surface of the optical part; applying a first beam splitter layer to the super-polished first surface of the optical part to create a beam splitter side of the optical part; and bonding the beam splitter side of the optical part to the coarsely polished second upper surface portion of the substrate member using an optical adhesive to produce the reflector member. The reflector member is configured to reduce external cavity light scattering in the ring laser gyroscope.

Description

Background Art

[0001] The performance of various ring laser gyros in terms of noise / angular random walk (ARW) can be affected by external sources of laser beam scattering. A known external source of laser beam scattering is the quality of the back wedge mirror surface from which the laser beam is reflected by the beam splitter coating.

[0002] Currently, some Ring Laser Gyros have difficulty producing sensors with high enough grade / low noise to satisfy users. Given that gyro noise / ARW is affected by external backscatter sources, methods to mitigate this problem are needed. Summary of the invention

[0003] A method of manufacturing a readout mirror for a ring laser gyroscope includes: forming an optical substrate component including a lower surface, a first upper surface portion substantially parallel to the lower surface, and a second upper surface portion angled relative to the lower surface; rough polishing the second upper surface portion of the optical substrate component; forming an optical part having a first surface; super polishing the first surface of the optical part; applying a first beam splitter layer to the super polished first surface of the optical part to produce a beam splitter side of the optical part; and bonding the beam splitter side of the optical part to the rough polished second upper surface portion of the optical substrate component using an optical adhesive to produce a reflector member for the readout mirror. The reflector member is configured to reduce external cavity light scattering in the ring laser gyroscope. BRIEF DESCRIPTION OF THE DRAWINGS

[0004] Features of the present invention will become apparent to those skilled in the art through the following description with reference to the accompanying drawings. Understanding that the drawings depict only typical embodiments and are not therefore to be considered limiting of the scope of the invention, the invention will be described with additional specificity and detail through the use of the accompanying drawings, in which:

[0005] Figure 1 is a flow chart of a method for manufacturing a reflector member for a readout mirror of a ring laser gyroscope according to one specific implementation;

[0006] Figure 2A and Figure 2B is a schematic side view of an exemplary reflector member for a readout mirror of a ring laser gyroscope; and

[0007] Figure 3 is a partial cross-sectional view of a ring laser gyroscope according to one embodiment. DETAILED DESCRIPTION

[0008] In the following specific embodiments, the embodiments are fully described to enable those skilled in the art to practice the present invention. It should be understood that other embodiments may be utilized without departing from the scope of the present invention. Therefore, the following detailed description should not be considered to have a limiting meaning.

[0009] Methods and components for reducing external cavity laser light scatter sources in a ring laser gyroscope are described herein. The method provides a way to minimize external cavity backscatter sources in a cost-effective and practical manner. By reducing external cavity backscatter, the performance of the ring laser gyroscope is improved.

[0010] The ring laser gyroscope generally includes a laser block assembly, which may be triangular in shape, wherein the laser block assembly has a resonant cavity therein, such as a triangular cavity. The ring laser gyroscope also includes a set of multilayer mirrors positioned at respective corners of the laser block assembly. The cavity together with the multilayer mirrors is configured to form a ring-shaped optical path around the laser block assembly. The cavity is filled with a suitable gas mixture, such as helium and neon, which is used to generate a laser beam in the cavity using standard techniques. The laser beam is guided around the optical path by the mirrors so that two counter-propagating beams are produced, which travel in opposite directions relative to each other around the optical path. The ring laser gyroscope includes an optical readout device having a wedge-shaped readout mirror, which couples a portion of the counter-propagating beams out of the resonant cavity and converts the beams into a voltage signal, from which rotation information can be obtained. The wedge-shaped readout mirror includes a multilayer beam splitter coating located on the back wedge angle surface.

[0011] It is known that defects within the beam splitter coating can cause external backscattering. In addition, the polishing condition of the back wedge surface can affect the performance of the beam splitter coating, thereby creating an asymmetric scattering source. It is challenging and / or expensive to achieve a high level of polishing condition on the back wedge surface.

[0012] The present solution works around the current difficulty of achieving a high level of polish on the wedge angle surface of the readout mirror. The present method overcomes the above difficulties by providing an optical part with a flat surface and super polishing the flat surface of the optical part. A high quality beam splitter coating is then applied to the super polished flat surface of the optical part, and a rough polish or other cost effective polish is applied to the wedge angle surface of the readout mirror. The beam splitter coated optical part is then bonded to the wedge angle surface using a refractive index matching optical adhesive. The viscosity of the optical adhesive can be selected so that any substrate polishing defects (such as scratches and gouges on the rough polished wedge angle surface) are filled and smoothed so that unintended beam scattering is minimized.

[0013] While the present approach introduces another component into the ring laser gyroscope, the added component is simpler to manufacture to the extent necessary to mitigate unintended external laser light scattering back into the gyroscope cavity.

[0014] Additional details of various embodiments are described below and with reference to the accompanying drawings.

[0015] Figure 1 is a flow chart of a method 100 for manufacturing a reflector member for a readout mirror of a ring laser gyroscope according to one specific implementation. The method 100 includes forming an optical substrate component including a lower surface, a first upper surface portion substantially parallel to the lower surface, and a second upper surface portion angled relative to the lower surface (block 110). The method 100 also includes: rough polishing the second upper surface portion of the optical substrate component (block 120); forming an optical part having a first surface (block 130); and super polishing the first surface of the optical part (block 140). The method 100 also includes applying a beam splitter layer to the super polished first surface of the optical part to produce a beam splitter side of the optical part (block 150). The method 100 uses an optical adhesive to bond the beam splitter side of the optical part to the rough polished second upper surface portion of the optical substrate component to produce a reflector member configured to reduce external cavity light scattering in a ring laser gyroscope (block 160). The refractive index of the optical adhesive when cured matches the refractive index of the optical part.

[0016] Figure 2A and Figure 2B An exemplary reflector member 200 for a readout mirror of a ring laser gyroscope is shown. Figure 1 The reflector member 200 includes an optical substrate component 202 having a lower surface 204, a first upper surface portion 206 substantially parallel to the lower surface 204, and a second upper surface portion 208 angled relative to the lower surface 204. The optical substrate component 202 is composed of a mechanically and thermally stable material having light transmission properties, such as glass, a glass ceramic material (such as microcrystalline glass), or the like. The optical substrate component 202 may have a substantially wedge-shaped structure or the like.

[0017] An optical bonding layer 210 is located on the second upper surface portion 208 of the optical substrate component 202. An optical component 212 is bonded to the second upper surface portion 208 by the optical bonding layer 210. The optical component may be made of glass, glass-ceramic, or the like. The size of the optical component 212 is set to cover at least a portion of the second upper surface portion 208 of the optical substrate component 202. A first beam splitter layer 214 is located on a surface of the optical component 212 that faces the upper surface portion 208. A second beam splitter layer 218 is located on the lower surface 204 of the optical substrate component 202.

[0018] During manufacture of the reflector member 200, a rough polish is applied to the second upper surface portion 208 of the optical substrate component 202. The rough polish can be applied by a process including a standard optical glass polishing method. In addition, a super polish is applied to the first flat surface of the optical part 212. The super polish can be applied by a process including a standard optical glass polishing method. In some embodiments, the super polish provides an "atomic smooth" surface so that the surface roughness can be measured in angstroms.

[0019] A first beam splitter layer 214 is applied to the super-polished surface of the optical part 212, such as by standard thin film forming techniques, to produce the beam splitter side of the optical part 212. The beam splitter side of the optical part 212 is bonded to the rough-polished second upper surface portion 208 using an optical bonding layer 210 to produce the reflector member 200.

[0020] The optical bonding layer 210 may be made of an optical bonding material, such as an index matching bonding material having a glass index matching property. The optical bonding layer 210 is selected to have a viscosity such that scratches and gouges on the rough-polished second upper surface portion 208 are filled with the optical bonding material. The refractive index of the optical bonding layer 210 when cured matches the refractive index of the optical part 212.

[0021] Figure 2BThe operation of the reflector member 200 when used in a readout mirror for a ring laser gyroscope is shown. A first portion of the laser beam in the cavity of the ring laser gyroscope propagates in a counterclockwise (CCW) direction as a CCW beam 222, and a second portion of the laser beam propagates in a clockwise (CW) direction as a CW beam 224. A portion of the CCW beam 222 is coupled out of the cavity into the reflector member 200 through the second beam splitter layer 218 and travels to the first beam splitter layer 214, which partially reflects the portion of the CCW beam 222 as a reflected CCW beam back to the second beam splitter layer 218, which in turn reflects the reflected CCW beam toward the first upper surface portion 206 used as an output port. In addition, a portion of the CW beam 224 is coupled out of the cavity into the reflector member 200 through the second beam splitter layer 218, so that the portion of the CW beam 224 travels toward the first upper surface portion 206. The reflector member 200 operates such that external cavity laser light scattering is reduced or mitigated as the reflected CCW light beam travels through the optical substrate component 202 .

[0022] Figure 3 3 is a partial cross-sectional view of a ring laser gyroscope 300 according to one embodiment. The ring laser gyroscope 300 includes a laser block assembly 310 having a cavity 312 therein and an optical readout device 320, the optical readout device being in optical communication with the cavity 312. The laser block assembly 310 is constructed of a mechanically and thermally stable material, such as glass-ceramic. In one specific implementation, the laser block assembly 310 has a triangular configuration such that the cavity 312 is a substantially triangular shaped cavity. The cavity 312 is sealed and filled with a suitable gas mixture, such as helium and neon, which is used to generate a laser beam 314 in the cavity 312 according to standard techniques. The cavity 312, together with a set of multilayer mirrors (not shown) and the optical readout device 320, provides an optical path for the laser beam 314 in the laser block assembly 310.

[0023] The optical reading device 320 includes a reflector member 322, which includes an optical substrate component 324, which includes a lower surface 326, a first upper surface portion 328 substantially parallel to the lower surface 326, and a second upper surface portion 330 angled relative to the lower surface 326. The optical substrate component 324 is composed of a mechanically and thermally stable material having light transmission properties, such as glass, microcrystalline glass, or the like. The optical substrate component 324 may have a substantially wedge-shaped structure or the like.

[0024] An optical bonding layer 332 is located on the second upper surface portion 330 of the optical substrate component 324. The optical component 334 is bonded to the second upper surface portion 343 by the optical bonding layer 332. The optical component may be made of glass, microcrystalline glass, or the like. The size of the optical component 334 is set to cover at least a portion of the second upper surface portion 330. A first beam splitter layer 336 is located on the surface of the optical component 334 facing the upper surface portion 330. A second beam splitter layer 338 is located on the lower surface 326 of the optical substrate component 324.

[0025] The first upper surface portion 328 of the optical substrate component 324 is configured as an output port for the optical pickup device 320. The reflector member 322 is configured to reduce light scattering of the laser beam 314 in the cavity 312 of the laser block assembly 310. The optical pickup device 320 also includes an optical detector 340 that is in optical communication with the reflector member 322 through the first upper surface portion 328.

[0026] During operation of the ring laser gyro 300, a first portion of the laser beam 314 in the cavity 312 propagates in the CCW direction as a CCW beam 316 (double arrow), and a second portion of the laser beam 314 propagates in the CW direction as a CW beam 318 (single arrow). A portion of the CCW beam 316 is coupled out of the cavity 312 through the second beam splitter layer 338 into the reflector member 322 and travels to the first beam splitter layer 336, which partially reflects the portion of the CCW beam 316 as a reflected CCW beam (double arrow) back to the second beam splitter layer 338, which in turn reflects the reflected CCW beam toward the first upper surface portion 328, which serves as an output port for the exiting CCW beam. In addition, a portion of the CW beam 318 is coupled out of the cavity 312 into the reflector member 322 through the second beam splitter layer 338, such that the portion of the CW beam 318 travels toward and exits from the first upper surface portion 328. The beam exiting from the first upper surface portion 328 impinges on the optical detector 340 to form an interference pattern or fringes, which is sensed by the optical detector 340 as an indication of the rotation of the ring laser gyroscope about the axis. The reflector member 322 operates such that external cavity laser light scattering is reduced or mitigated in the laser block assembly 310 when the reflected CCW beam travels through the optical substrate component 324.

[0027] Exemplary embodiments

[0028] Embodiment 1 includes a method for manufacturing a readout mirror for a ring laser gyroscope, the method comprising: forming an optical substrate component, the optical substrate component comprising a lower surface, a first upper surface portion substantially parallel to the lower surface, and a second upper surface portion angled relative to the lower surface; rough polishing the second upper surface portion of the optical substrate component; forming an optical part having a first surface; super polishing the first surface of the optical part; applying a first beam splitter layer to the super polished first surface of the optical part to produce a beam splitter side of the optical part; and bonding the beam splitter side of the optical part to the rough polished second upper surface portion of the optical substrate component using an optical adhesive to produce a reflector member for the readout mirror; wherein the reflector member is configured to reduce external cavity light scattering in the ring laser gyroscope.

[0029] Embodiment 2 includes the method according to embodiment 1, wherein the optical substrate component includes a glass or glass ceramic material.

[0030] Embodiment 3 includes the method of any one of embodiments 1 to 2, wherein the optical substrate component has a substantially wedge-shaped structure.

[0031] Embodiment 4 includes the method of any one of embodiments 1 to 3, wherein the optical component includes a glass or glass ceramic material.

[0032] Embodiment 5 includes the method of any one of embodiments 1 to 4, wherein the optical component is sized to cover at least a portion of the second upper surface portion of the optical substrate component.

[0033] Embodiment 6 includes a method according to any one of Embodiments 1 to 5, wherein: the optical adhesive has a viscosity such that scratches and gouges on the rough-polished second upper surface portion are filled by the optical adhesive; and the refractive index of the optical adhesive when cured matches the refractive index of the optical part.

[0034] Embodiment 7 includes the method of any one of embodiments 1 to 6, wherein the optical adhesive has glass index matching properties.

[0035] Embodiment 8 includes the method of any one of embodiments 1 to 7, further comprising forming a second beam splitter layer on the lower surface of the optical substrate component.

[0036] Embodiment 9 includes an optical readout device for a ring laser gyroscope, the optical readout device comprising: a reflector member, the reflector member comprising: an optical substrate component, the optical substrate component comprising a lower surface, a first upper surface portion substantially parallel to the lower surface, and a second upper surface portion angled relative to the lower surface; an optical bonding layer, the optical bonding layer being located on the second upper surface portion of the substrate component; an optical part, the optical part being bonded to the second upper surface portion of the substrate component via the optical bonding layer; and a first beam splitter layer, the first beam splitter layer being located on the surface of the optical part; wherein the reflector member is configured to reduce external cavity light scattering in the ring laser gyroscope.

[0037] Embodiment 10 includes the optical pick-up device according to embodiment 9, wherein the optical substrate component includes a glass or glass ceramic material.

[0038] Embodiment 11 includes the optical pick-up device according to any one of embodiments 9 to 10, wherein the optical substrate component has a substantially wedge-shaped structure.

[0039] Embodiment 12 includes the optical reading device according to any one of embodiments 9 to 11, wherein the optical part comprises a glass or glass ceramic material.

[0040] Embodiment 13 includes the optical readout device according to any one of embodiments 9 to 12, wherein the optical bonding layer has glass refractive index matching properties.

[0041] Embodiment 14 includes the optical pick-up device according to any one of Embodiments 9 to 13, further comprising a second beam splitter layer located on the lower surface of the optical substrate component.

[0042] Embodiment 15 includes a ring laser gyroscope, the ring laser gyroscope comprising: a laser block assembly having a cavity therein; a set of multilayer mirrors, the set of multilayer mirrors being optically connected to the cavity; an optical readout device, the optical readout device being optically connected to the cavity, the optical readout device including a reflector member, the reflector member including: an optical substrate component, the optical substrate component including a lower surface, a first upper surface portion substantially parallel to the lower surface, and a second upper surface portion angled relative to the lower surface; an optical bonding layer, the optical bonding layer being located on the second upper surface portion of the substrate component; an optical The optical component is bonded to the second upper surface portion of the substrate component by the optical bonding layer; a first beam splitter layer, the first beam splitter layer is located on the surface of the optical component; and a second beam splitter layer, the second beam splitter layer is located on the lower surface of the optical substrate component; wherein the cavity together with the multilayer mirror and the optical readout device provides an optical path for the laser beam in the laser block assembly; wherein the first upper surface portion of the optical substrate component is configured as an output port for the optical readout device; and wherein the reflector member is configured to reduce light scattering of the laser beam in the cavity of the laser block assembly.

[0043] Embodiment 16 includes the ring laser gyroscope of embodiment 15, wherein the optical substrate component has a substantially wedge-shaped structure.

[0044] Embodiment 17 includes a ring laser gyroscope according to any one of embodiments 15 to 16, wherein a first portion of the laser beam in the cavity propagates in a counterclockwise (CCW) direction as a CCW beam, and a second portion of the laser beam propagates in a clockwise (CW) direction as a CW beam.

[0045] Embodiment 18 includes a ring laser gyroscope according to embodiment 17, wherein: a portion of the CCW light beam is coupled out of the cavity through the second beam splitter layer into the reflector component and travels to the first beam splitter, the first beam splitter partially reflects the portion of the CCW light beam back to the second beam splitter as a reflected CCW light beam, and the second beam splitter in turn reflects the reflected CCW light beam toward the output port; and a portion of the CW light beam is coupled out of the cavity through the second beam splitter layer into the reflector component, so that the portion of the CW light beam travels toward the output port.

[0046] Embodiment 19 includes the ring laser gyroscope of any one of Embodiments 15 to 18, wherein the multilayer mirror and the optical readout device are positioned at respective corners of the laser block assembly.

[0047] Embodiment 20 includes the ring laser gyroscope of any one of Embodiments 15 to 19, wherein the cavity of the laser block assembly is a substantially triangular shaped cavity.

[0048] The present invention may be embodied in other specific forms without departing from its basic characteristics. The embodiments described are to be considered in all respects as merely illustrative and non-restrictive. Therefore, the scope of the present invention is indicated by the appended claims rather than the foregoing description. All changes within the meaning and scope of the equivalence of the claims will be encompassed within their scope.

Claims

1. A method for manufacturing a readout mirror for a ring laser gyroscope, the method comprising: forming an optical substrate component comprising a lower surface, a first upper surface portion substantially parallel to the lower surface, and a second upper surface portion angled relative to the lower surface; performing rough polishing on the second upper surface portion of the optical substrate component; forming an optical component having a first surface; Super-polishing the first surface of the optical component; applying a first beam splitter layer to the super-polished first surface of the optical part to produce a beam splitter side of the optical part; as well as bonding the beam splitter side of the optical component to a rough-polished second upper surface portion of the optical substrate component using an optical adhesive to produce a reflector member for the readout mirror; The reflector member is configured to reduce external cavity light scattering in the ring laser gyroscope.

2. An optical readout device for a ring laser gyroscope, the optical readout device comprising: A reflector member, the reflector member comprising: an optical substrate component comprising a lower surface, a first upper surface portion substantially parallel to the lower surface, and a second upper surface portion angled relative to the lower surface; an optical bonding layer disposed on the second upper surface portion of the substrate component; an optical component bonded to the second upper surface portion of the substrate member through the optical adhesive layer; and a first beam splitter layer, the first beam splitter layer being located on a surface of the optical component; The reflector member is configured to reduce external cavity light scattering in the ring laser gyroscope.

3. A ring laser gyroscope, comprising: a laser block assembly having a cavity therein; a set of multilayer mirrors in optical communication with the cavity; an optical readout device in optical communication with the cavity, the optical readout device comprising a reflector member, the reflector member comprising: an optical substrate component comprising a lower surface, a first upper surface portion substantially parallel to the lower surface, and a second upper surface portion angled relative to the lower surface; an optical bonding layer disposed on the second upper surface portion of the substrate component; an optical component bonded to the second upper surface portion of the substrate member via the optical adhesive layer; a first beam splitter layer located on a surface of the optical part; and a second beam splitter layer disposed on the lower surface of the optical substrate component; wherein the cavity, together with the multilayer mirror and the optical readout device, provides an optical path for a laser beam in the laser block assembly; wherein the first upper surface portion of the optical substrate component is configured as an output port for the optical pickup device; Wherein the reflector member is configured to reduce light scattering of the laser beam in the cavity of the laser block assembly.

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