Patent Description:
Recently, demand for communication using fiber optics has increased significantly due to its superior performance and cost effectiveness. One particular application is the transmission of optical signals with rotating devices. A fiber optic rotary joint (FORJ) is a device that allows the transmission of an optical signal while rotating along the fiber optical axis. A typical FORJ device includes at least two optical fibers each terminated with a collimator on the joint end. One fiber is stationary and the other fiber is rotating.

To minimize signal loss, the axes of the collimators facing each other should be aligned precisely in yaw and pitch angular as well as x and y translational orientations to each other. For both stationary and rotating fibers, this alignment would require adjustments having <NUM> degrees of freedom in total. Such an alignment procedure is time consuming and is undesirable from a manufacturing standpoint.

Thus, there is a need for new optical alignment methods and apparatus to overcome the problems as discussed above.

Prior art can be found e.g. in document <CIT> disclosing a detachable connector for optical fibres comprising two connector portions, wherein each connector portion comprises fixing means, for detachably connecting the connector portions to each other, and at least one rotatable symmetrical housing, a rotationally symmetrical tube, and a ball lens. The housing is provided with a bore, which is coaxial to a central axis of the housing, and with a reference face perpendicular to the central axis on one end. A seat is formed in the bore at the end near the reference face. The seat faces the end of the housing which is remote from the reference face and accommodates the ball lens which is retained there by the tube. The tube bears against the lens by way of a seat formed thereon. At an end which is remote from the seat, the tube is supported by adjusting means secured in the housing. The adjusting means enable an optical axis, of an end of an optical fiber to be accommodated in the tube to be adjusted at least parallel to the central axis of the housing; and in document <CIT> disclosing a two beam optical switch and attenuator and method of use. Further, prior art can be found e.g. in document <CIT> disclosing a compact optical module with adjustable joint for decoupled alignment and in document <CIT> disclosing an apparatus and method for adjusting an optical rotating data transmission device.

In order to overcome at least some of the deficiencies and issues as discussed above, exemplary embodiments are provided herein for optical alignment. Some embodiments provide an apparatus, a method and a non-transitory storage medium according to the respective claims.

Further features of the disclosure will become apparent from the following description of exemplary embodiments with reference to the attached drawings.

<FIG> is a diagram illustrating a fiber-optic rotary joint (FORJ) assembly <NUM>. The diagram shows a side view of the FORJ assembly <NUM>. The FORJ assembly <NUM> includes a first optical component <NUM>, a second optical component <NUM>, first adjustment key <NUM> and second adjustment key <NUM>.

In this exemplary embodiment, the first optical component <NUM> is a rotator or a rotating unit. It includes a first optical axis adjuster <NUM>, a base element <NUM>, and a first key slot <NUM>. The first optical component <NUM> may include more or less than the above components. The first optical axis adjuster <NUM> includes components (e.g., screws) to adjust the pitch and yaw angles and the horizontal (X) and vertical (Y) displacements of a collimator located inside the first optical axis adjuster <NUM>. The base element <NUM> provides support for the first optical axis adjuster <NUM> and the collimator. It has a bottom surface <NUM> and a first flat surface <NUM>. The first flat surface <NUM> stands upright and is perpendicular to the bottom surface <NUM>. The first key slot <NUM> is a hollow or opening region or portion within the base element <NUM>. The first key slot <NUM> is configured to mate with the first adjustment key <NUM>; i.e., the first key slot <NUM> fits the first adjustment key <NUM> with additional clearance to allow the key to move during alignment.

The second optical component <NUM> is a stator or a stationary unit. It includes a second optical axis adjuster <NUM>, a base element <NUM>, and a second key slot <NUM>. The second optical component <NUM> may include more or less than the above components. The second optical axis adjuster <NUM> includes components (e.g., screws) to adjust the pitch and yaw angles of a collimator located inside the second optical axis adjuster <NUM>. The base element <NUM> provides support for the second optical axis adjuster <NUM> and the collimator. It has a bottom surface <NUM> and a second flat surface <NUM>. The second flat surface <NUM> stands upright and is perpendicular to the bottom surface <NUM>. The second key slot <NUM> is a hollow or opening region or portion within the base element <NUM>. The second key slot <NUM> is configured to mate with the second adjustment key <NUM>; i.e., the second key slot <NUM> fits the second adjustment key <NUM> with additional clearance to allow the key to move during alignment.

The first and second optical components <NUM> and <NUM>, respectively, are configured to be compatible with each other for alignment. For example, the first and second flat surfaces <NUM> and <NUM>, respectively, are parallel when they directly face each other. The first and second key slots <NUM> and <NUM>, respectively, are orthogonal with respect to each other. If the first key slot <NUM> is horizontal then the second key slot <NUM> is vertical. If the first key slot <NUM> is vertical then the second key slot <NUM> is horizontal. The first and second adjustment keys <NUM> and <NUM> follow the directions of the corresponding first and second key slots <NUM> and <NUM>, respectively, and joined rigidly together in an orthogonal orientation.

While described above as first and second flat surfaces <NUM> and <NUM>, in some embodiments, the first and second flat surfaces <NUM> and <NUM> are precision flat surfaces. In some other embodiments there are first and second surfaces that are precision surfaces that are not necessarily flat, as long as they are adapted for sliding relative motion (e.g., they both can be spherical surfaces or cylindrical surfaces).

<FIG> is a diagram illustrating an alignment fixture <NUM> having a mount stage at a proximal position. The alignment fixture <NUM> includes a base <NUM>, a straight rail <NUM>, and a mount stage <NUM>. The base <NUM> provides support for the entire alignment process. It has a precision flat surface on which the mount stage is moved. The straight rail <NUM> provides a guide for the mount stage <NUM> to move in a straight line from the proximal position to the distal position. The proximal and the distal positions refer to the positions at the two ends of the alignment fixture <NUM>. The proximal position is the position closest to the first or second optical components <NUM> or <NUM> when it is clamped to the alignment fixture <NUM>. The distal position is the position farthest to the first or second optical components <NUM> or <NUM> when it is clamped to the alignment fixture <NUM>.

The mount stage <NUM> provides a mechanism to hold the first and second optical components <NUM> and <NUM> in place during the alignment procedure. It also provides a means to decompose a single alignment procedure based on <NUM> degrees of freedom into three sequential alignment procedures each with much less degrees of freedom. The mount stage <NUM> includes a mount base <NUM>, a stopper <NUM>, a slider <NUM>, and a position sensitive detector (PSD) <NUM>. The mount stage <NUM> may include more or less than the above components.

The mount base <NUM> provides support for the slider <NUM> and interface to the bottom and side movements. It has a bottom surface that faces the surface of the base <NUM> to allow a precision movement of the mount stage <NUM> between the proximal and distal positions. It also has a side surface that mates with the straight rail <NUM> so that it can move between the proximal and distal positions in a straight line. The stopper <NUM> has a precision flat surface <NUM> which is perpendicular to the horizontal or bottom surface. The precision flat surface <NUM> is a mating surface for the first and second optical components <NUM> and <NUM> during the first two steps of the optical alignment. During the alignment of the first optical component and the alignment of the second optical component, the stopper <NUM> is secured in place. The slider <NUM> slides horizontally to accommodate the different clearances of the surfaces of the first and second optical components as will be explained later. The PSD <NUM> is attached to the upright surface of the slider <NUM>. It is used to record the positions of the spots of the light incident on its surface. As will be explained later, these spot positions will be used to determine the angles between the first optical axis and the first flat surface during alignment.

<FIG> is a diagram illustrating the alignment fixture <NUM> having the mount stage <NUM> at the distal position. <FIG> shows the same components as in <FIG> and therefore their descriptions will be omitted. The difference between <FIG> is the mount stage <NUM> (except the stopper <NUM>) is moved from the proximal position (in <FIG>) to the distal position (in <FIG>).

The movement of the mount stage <NUM> from the proximal position to the distal position is to allow the PSD <NUM> to record the spot positions of a collimated light through the optical component, which in turn gives measurement data to calculate the angle formed by the optical axis with the flat surface.

The overall optical alignment includes three steps. In the first step, the first optical axis of the first optical component <NUM> is caused to be at a first angle with respect to the first flat surface <NUM> of the first optical component <NUM>. In this step, the optical axis of the rotational unit should be aligned coincident with its axis of rotation.

In the second step, a second optical axis of the second optical component <NUM> is aligned to be at a second angle to the second flat surface <NUM> of the second optical component <NUM>. In one embodiment, this angle may range from <NUM> degrees to <NUM> degrees.

After the first two steps, the two optical axes of the two optical components <NUM> and <NUM> have been aligned to be parallel with each other, leaving only the horizontal and vertical translational alignments to be performed. This is performed in the third step.

In the third step, the first and second flat surfaces are brought to directly face each other to allow only sliding motion between them. Thereafter, the sliding motion between the first and second flat surfaces is performed until the first and second optical axes are sufficiently collinear. At the end of the third step, the entire optical alignment of the FORJ assembly <NUM> is completed.

<FIG> is a diagram illustrating alignment <NUM> of the first optical component <NUM> at the proximal position in the first step. The stopper <NUM> is secured at a position that accommodates the placement of the first optical component <NUM>. The first optical component <NUM> is placed at the position of the stopper <NUM> such that the first flat surface <NUM> is placed against the surface <NUM> of the stopper <NUM>. At this position, the first optical axis adjuster <NUM> points directly to the PSD <NUM>. The goal of this first step is to align the first optical axis of a collimated beam, to its actual axis of rotation in both transverse (horizontal and vertical) and both angular (pitch and yaw) directions. This can be achieved by emitting light through the collimator in the adjuster <NUM> and recording the spot positions of the incident light on the PSD <NUM> as the mount stage <NUM> (and the PSD <NUM>) is moved from the proximal position to the distal position while the fiber is rotated a full revolution. This full revolution corresponds to the translational alignment.

<FIG> shows how the angle is determined in the first step as discussed above. At the proximal position the PSD <NUM> is translated within stage <NUM> in a plane perpendicular to the optical axis to bring the rotational center C to the coordinate center point O (<NUM>,<NUM>) bringing to V=o and H=o. The goal of adjustment in this position is to minimize radius R, where R is the radius of the trace of the spots positions on the PSD as the collimator is rotated. Ideally, the adjustment brings R to, or substantially to o.

<FIG> is a diagram illustrating alignment <NUM> of the first optical component <NUM> at the distal position. The entire mount stage <NUM> is moved to the distal position along the precision rail <NUM> without readjusting position of the PSD <NUM> on it. The goal of adjustment in this position is again to minimize radius R, ideally bringing it to R=o. After that measurements of H and V may be taken which define the first angle with respect to the precision flat surface <NUM>.

<FIG> is a diagram illustrating alignment <NUM> of the second optical component at the proximal position. <FIG> is similar to <FIG> except that instead of the first optical component <NUM> is clamped to the alignment fixture, the second optical component <NUM> is used. The second flat surface <NUM> is placed to face directly the surface <NUM> of the stopper <NUM>. Note that the geometries of the first and second optical components may be different, for example, the length of the first optical component <NUM> may be longer than the length of the second optical component <NUM>. Therefore, in order the second optical axis adjuster <NUM> to directly face the PSD <NUM> at the proximal position, the slider <NUM> has to be moved toward the second optical component <NUM> until the PSD <NUM> touches the second optical axis adjuster <NUM>.

<FIG> is a diagram illustrating alignment <NUM> of the second optical component at the distal position. <FIG> is similar to <FIG> except that instead of the first optical component <NUM>, the second component <NUM> is secured to the alignment fixture. At the start of this alignment step the PSD <NUM> should be positioned to preferably yield beam spot at <NUM>, <NUM> position at the proximal sensor potion and then the collimator <NUM> adjusted to H, -V at the distal sensor position.

<FIG> is a diagram illustrating a spot position recorded by a Position Sensitive Detector (PSD).

The PSD <NUM> is a two-dimensional PSD and therefore it records the spot positions in two dimensional space. The center C of the PSD <NUM> is at coordinates (<NUM>,<NUM>). As the PSD <NUM> is moved to the distal position, the center of rotation C is moved to coordinates (H, V) where H refers to the horizontal coordinate and V refers to vertical coordinate. The angular displacements of the rotational axis with respect to the precision flat surface <NUM> may be determined as: <MAT> <MAT> where L is the distance between the PSD <NUM> at the distal position to the collimator inside the optical axis adjuster <NUM>.

<FIG> is a diagram illustrating alignment <NUM> of the first and second optical axes in the third step. In the third step, the first and second optical components are clamped together such that their precision flat surfaces <NUM> and <NUM> directly face each other. These two surfaces are moved relative to each other on their surfaces in a sliding movement until the two optical axes are sufficiently collinear.

The first adjustment key <NUM> is inserted into the first key slot <NUM> and the second adjustment key <NUM> is inserted into the second key slot <NUM>. The adjustments may be performed using fine pitch alignment screws.

<FIG> is a diagram illustrating a system <NUM> with controller for optical alignment of fiber-optic rotary joint assembly. The system <NUM> illustrates an alignment controller to control the alignment procedure shown in <FIG>, <FIG>, and <FIG>.

The system <NUM> includes a central processing unit (CPU) or a processor <NUM>, a platform controller hub (PCH) <NUM>, and a bus <NUM>. The PCH <NUM> may include an input/output (I/O) controller <NUM>, a memory controller <NUM>, a graphic display controller (GDC) <NUM>, and a mass storage controller <NUM>. The processing unit <NUM> may include more or less than the above components. In addition, a component may be integrated into another component. As shown in <FIG>, all the controllers <NUM>, <NUM>, and <NUM> are integrated in the PCH <NUM>. The integration may be partial and/or overlapped. For example, the GDC <NUM> may be integrated into the CPU <NUM>, the I/O controller <NUM> and the memory controller <NUM> may be integrated into one single controller, etc..

The CPU or processor <NUM> is a programmable device that may execute a program or a collection of instructions to carry out a task. It may be a general-purpose processor, a digital signal processor, a microcontroller, or a specially designed processor such as one design from Applications Specific Integrated Circuit (ASIC). It may include a single core or multiple cores. Each core may have multi-way multi-threading. The CPU <NUM> may have simultaneous multithreading feature to further exploit the parallelism due to multiple threads across the multiple cores. In addition, the CPU <NUM> may have internal caches at multiple levels.

The bus <NUM> may be any suitable bus connecting the CPU <NUM> to other devices, including the PCH <NUM>. For example, the bus <NUM> may be a Direct Media Interface (DMI).

The PCH <NUM> in a highly integrated chipset that includes many functionalities to provide interface to several devices such as memory devices, input/output devices, storage devices, network devices, etc..

The I/O controller <NUM> controls input devices (e.g., stylus, keyboard, and mouse, microphone, image sensor) and output devices (e.g., audio devices, speaker, scanner, printer). It also has interface to a network interface card which provides interface to a network and wireless controller (not shown).

The memory controller <NUM> controls memory devices such as the random access memory (RAM) <NUM>, the read-only memory (ROM) <NUM>, and other types of memory such as the cache memory and flash memory. The RAM <NUM> may store instructions or programs, loaded from a mass storage device, that, when executed by the CPU <NUM>, cause the CPU <NUM> to perform operations as described above, such as aligning operations. It may also store data used in the operations, including the PSD spot positions data. The ROM <NUM> may include instructions, programs, constants, or data that are maintained whether it is powered or not.

The GDC <NUM> controls a display device and provides graphical operations. It may be integrated inside the CPU <NUM>. It typically has a graphical user interface (GUI) to allow interactions with a user who may send a command or activate a function.

The mass storage controller <NUM> controls the mass storage devices such as CD-ROM and hard disk.

The I/O controller <NUM> includes a motor controller <NUM> and an optical controller <NUM>. The motor controller <NUM> may be a stepper motor controller or any controller that can control movement of a device such as the mount stage <NUM> of the alignment fixture <NUM>. It may also control the optical axis adjusters <NUM> and <NUM>, or the screws or the adjustment keys <NUM> and <NUM>. The optical controller <NUM> performs control functions related to the optical components, such as emitting light from a light source to the collimator, moving the PSD <NUM>, recording the spot positions, performing calculations of the angles in equations (<NUM>) and (<NUM>), etc..

Additional devices or bus interfaces may be available for interconnections and/or expansion. Some examples may include the Peripheral Component Interconnect Express (PCIe) bus, the Universal Serial Bus (USB), etc..

All or part of an embodiment may be implemented by various means depending on applications according to particular features, functions. These means may include hardware, software, or firmware, or any combination thereof. A hardware, software, or firmware element may have several modules coupled to one another. A hardware module is coupled to another module by mechanical, electrical, optical, electromagnetic or any physical connections. A software module is coupled to another module by a function, procedure, method, subprogram, or subroutine call, a jump, a link, a parameter, variable, and argument passing, a function return, etc. A software module is coupled to another module to receive variables, parameters, arguments, pointers, etc. and/or to generate or pass results, updated variables, pointers, etc. A firmware module is coupled to another module by any combination of hardware and software coupling methods above. A hardware, software, or firmware module may be coupled to any one of another hardware, software, or firmware module. A module may also be a software driver or interface to interact with the operating system running on the platform. A module may also be a hardware driver to configure, set up, initialize, send and receive data to and from a hardware device. An apparatus may include any combination of hardware, software, and firmware modules.

Claim 1:
A fiber optic rotary joint assembly comprising:
a first optical component (<NUM>) having a first optical axis, a first optical axis adjuster, and a first base element having a first precision surface (<NUM>); and
a second optical component (<NUM>) having a second optical axis, a second optical axis adjuster, and a second base element having a second precision surface (<NUM>) adapted to mate slidingly with the first precision surface with a predetermined range of motion,
wherein the first optical component is a rotating unit and the second optical component is a stationary component;
wherein the first optical axis adjuster is adapted to adjust at least one of the pitch and yaw angles and the translational displacements of a collimator inside the first optical axis adjuster for the first optical axis to assume a first specific geometric relationship with the first precision surface such that the first optical component rotates around the first optical axis,
wherein the second optical axis adjuster is adapted to adjust at least one of the pitch and yaw angles of a collimator inside the second optical axis adjuster for the second optical axis to assume a second specific geometric relationship with the second precision surface such that, if the first optical element and second optical element are combined into an assembly, the first optical axis is parallel with the second optical axis, and
wherein after the first optical axis and second optical axis have each been adjusted to be parallel with one another, the second base element is adapted to slidingly mate with the first base element by movement of the second precision surface in a single plane to combine the first optical component and second optical component into the assembly such that the first optical axis and second optical axis are sufficiently collinear.