Patent Description:
Optical communications use modulated light beams to convey information through optical fibers, free space, or waveguides. Modern optical communication systems can contain a large number of optical fiber interconnections, which can number from thousands to hundreds of thousands, which must be managed. Management of these interconnections create difficulties in planning, deployment, and upgrading communication capacities.

An optical circuit switch (OCS) can be used to manage interconnections in optical communication systems. Functionally, an optical circuit switch may be considered an all-optical, 2D switching matrix that may direct light from any input fiber N to any output fiber M by changing the angles of the mirrors in one or more micro-electromechanical system (MEMS) mirror arrays. The OCS is typically implemented through a mechanical switching mechanism (electro-optical, thermo-optical mechanisms also exist), directing light beams between different ports in free space. Piezoelectric actuator technology can also be used to steer optical beams in free space between different ports. The switch is designed for low insertion loss over a broad wavelength range, so each fiber may carry many wavelengths as well as be bidirectional. The OCS may also be designed for fast, reliable switching by the MEMS mirror arrays. Optical performance requirements and optical signals can be limited by insertion loss, return loss, dynamic optical crosstalk, and static optical crosstalk.

The OCS can also be considered as a patch panel with N input ports and N (or another integer number) output ports. Any input port can be connected with any output port. An OCS can be programmed through software, allowing for fiber interconnections to be made in software, and managed more easily, enabling planning, deployment, and upgrading changes to the communication network more easily.

<CIT> discloses systems and methods for optimizing port usage in an optical circuit switch.

<CIT> discloses systems and methods for characterizing an optical fiber performed in part by an optical node in an optical line system including performing one or more measurements to characterize the optical fiber with one or more components at the optical node.

<CIT> discloses an optical circuit switch that includes a fiber hole array, a plurality of internal optical fibers, a collimating lens array, a MEMS mirror array, and a reflective surface.

Aspects of the disclosed technology enable the implementation of an optical time domain reflectometer (OTDR) or optical return loss (ORL) meter, referred to as a link diagnostic system (LDS), coupled with the OCS system for automated diagnosis of the fiber-optic network fabric insertion loss and return loss.

Aspects of the disclosed technology include an optical links diagnostic system (LDS) and its operation within an optical circuit switch (OCS) for measurement and diagnosis of fiber-optic network fiber performance and quality. The LDS can contain two photodetectors, a laser source, and be coupled to an OCS. Optical circulators can further be linked to the OCS. The LDS can be used both as an optical time domain reflectometer (OTDR) or as an optical return loss (ORL) meter and can automate the diagnosis of the fiber optical network fiber insertion loss and return loss.

Aspects of the disclosed technology enable determination of transmission losses, reflection losses, and other link impairments within specific optical links connected to the OCS or optical pathway within an N x N optical circuit switch.

Aspects of the disclosed technology include a system, the system comprising an optical circuit switch (OCS), an optical circulator having a bidirectional port optically coupled to a port of the second fiber collimator; a first transceiver optically coupled to the optical circulator; a link diagnostic system comprising: a first photodetector and a second photodetector; a light source; an optical coupler or optical circulator, coupling the light source to the second photodetector. The OCS can comprise a first fiber collimator and a second fiber collimator and a core coupling the first and second fiber collimators. The first photodetector can be optically coupled to the optical circulator along a path comprising a fiber input to the first fiber collimator, the core, and the port of the second fiber collimator.

The system can further comprise a plurality of optical circulators optically coupled to a plurality of ports of the first fiber collimator and a plurality of ports of the second fiber collimator. The plurality of the ports of the first fiber collimator can comprise N input ports, the plurality of the ports of the second fiber collimator comprising N output ports, and 2N optical circulators optically coupled and in one to one correspondence with the N input ports and N output ports. The system of claim <NUM> can further comprise a second link diagnostic system, the second link diagnostic system comprising a first photodetector, a second photodetector, a light source, and an optical coupler. The second link diagnostic system can be optically connected to the OCS through the second fiber collimator. The system can further comprise a second optical circulator optically linked to the second link diagnostic system and a second transceiver. The OCS can further comprise microelectromechanical system (MEMS) mirrors. The link diagnostic system can comprise a discrete unit separate from the OCS.

The signal obtained from the first photodetector can be analyzed in conjunction with a signal obtained at the second photodetector. The light source is configured to generate an optical time domain light signal. A reflection signal can be used to determine the location of a source of signal loss and/or reflection along the path. A reflection signal can be used to determine the amount of signal loss and/or reflection across and/or within the entire optical path. The system can further comprise a memory containing instructions, the instructions when executed configured to control the optical core. The system can contain instructions which can further cause light generated from the light source to take all possible optical paths across the optical core and corresponding paths of the system. The instructions can be further configured to analyze signals to quantify or identify sources of optical losses and/or losses in the system. Instructions can also be sent from an external system to control or interact with the disclosed technology.

Aspects of the disclosed technology include systems, methods, and apparatuses for detecting signal loss in an optical fiber system, which can comprise: forming a path comprising a fiber input to a first fiber collimator, an optical core, and a port of a second fiber collimator; generating, at a first link diagnostic system, a first optical signal; transmitting, the optical signal through at least a portion of the path; receiving a portion of the first optical signal at a circulator connected to a port of the second collimator; receiving at a first photodetector of the first link diagnostic system a reflected portion of the first optical signal; and configuring the first photodetector to be coupled to the optical circulator.

The first optical signal can be a signal of substantially constant amplitude. The first optical signal can be an optical time domain signal.

The first optical signal can be generated by pulsing a light source at the first link diagnostic system. The method can determine the location of a source of signal loss and/or signal reflection along the path. The method can comprise generating calibration values. The method can comprise calculating optical loss values by using the calibration values. The method can further comprise comparing the reflected portion of the first optical signal to the first optical signal. The method can further comprise modifying a path taken by the first optical signal within the optical core. All possible optical paths can be taken by the first optical signal.

An optical circuit switch (OCS) allows for the transmission of data through the use of light and optical fiber. For some applications, such as within a datacenter or any other high interconnect count network, it is desirable to increase switch port count to meet bandwidth and interconnect count demand while maintaining the OCS infrastructure. Increasing switch port count may lead to signal degradation, which may impact performance. As switch port count increases, it is desirable to maintain signal quality and to be able to automatically diagnose signal degradation or performance issues. In that regard, the ability to use high throughput signal processing is impacted by degradation caused by fibers, transceivers, circulators, or other optical components related to the OCS system. In additon to signal degradation which can occur with an OCS due to dust, incorrect alignment, degradation of OCS drivers and electronics over time, temperature variations, dust, other sources of degradation of a signal can be present. Degradation of a signal sent over an OCS system can also be caused by the fibers, transceivers, circulators, or other components connected to the OCS externally, and/or back-reflection within an OCS data path or OCS data link. Aspects of the disclosed technology enable detection of degradation caused by the fibers, transceiver, and circulators connected to the OCS externally.

A link diagnostic system (LDS) can allow the above-mentioned and other sources of noise within an OCS system to be determined. An LDS contains two photodetectors, a laser or other light source, and is coupled to an OCS. Optical circulators are further linked to the OCS. In part, one photodetector acts as a sensor to understand the intensity of light transmitted by the laser, acting as a control for the laser within the LDS system, and the other photodetector measures a percentage of signal being back-transmitted within the OCS system and externally connected components, such as a fiber, circulator, or transceiver.

The LDS can be used both in various modes or configurations. In some examples, the LDS system can be used as an optical time domain reflectometer (OTDR) while in other examples, the LDS system can be used as an optical return loss (ORL) meter. The LDS can also be used as a transmitter and receiver to measure loss along the various paths of the entire optical system.

Further, the LDS system can automate the diagnosis of the fiber optical network fiber insertion loss and return loss. In some examples, the LDS can be controlled in conjunction with the OCS to diagnose a subset of the optical links within an OCS. For example, within an N x M optical switch, N or M links can be diagnosed.

In some examples, the following equations can be referred to or utilized in connection with the analysis, collection, or calculation of various parts of the optical links or each optical link path. <MAT> <MAT> <MAT>.

The following figures illustrate aspects of the disclosed technology. A person of skill in the art will understand that the various disclosed components can be coupled electronically by one or more of the disclosed electronics, processors, and computing devices to perform the methods and techniques disclosed herein. For simplicity and clarity, not every electronic or data link is illustrated or disclosed and a person of skill in the art will appreciate that various sensors, photodetectors, lasers, and other electronics can be controlled collectively and be in data connectivity with one another or one or more computing devices.

<FIG> illustrates an example OCS <NUM>, such as may be used in datacenter. The OCS <NUM> includes a structure such as chassis <NUM> supporting a number of components. In a front of the OCS chassis <NUM> are optical fiber connections, such as fiber management block <NUM>. The OCS <NUM> may further include an optical core <NUM>. The optical core can also be referred to as the OCS internal optical path or OCS internal optical space. The optical core houses MEMS <NUM>, fiber collimators <NUM>, optics <NUM>, cameras <NUM>, and injectors <NUM> and other mechanisms <NUM>. A rear of the OCS <NUM> includes electronics <NUM>, such as high voltage driver boards <NUM> for the MEMS, one or more processors <NUM>, such as a CPU board, one or more memories <NUM> storing executable software, and power supplies <NUM> and fan modules <NUM>. The chassis <NUM> interfaces with OCS control system <NUM>. While a number of components are shown, it should be understood that such components are merely non-limiting examples, and that other components may additionally or alternatively be included.

There may be any number of input fibers and output fibers connected to the front of the OCS chassis <NUM>. Inside the chassis <NUM>, these fiber fanouts are spliced to the fiber collimators <NUM>.

The fiber collimators <NUM> are lensed fiber arrays. Just as one example, the fiber collimators <NUM> may include tens or hundreds or more fiber arrays. The fibers are assembled in a hole array that matches a MEMS array grid pattern, thereby forming a fiber array. The fiber array is attached to a mounting flange. A lens array is aligned and attached to the fiber array. Fiber and lens position errors are very tightly controlled.

The one or more processors <NUM> may be any conventional processors, such as commercially available microprocessors. Alternatively, the one or more processors may be a dedicated device such as an application specific integrated circuit (ASIC) or other hardware-based processor. Although <FIG> functionally illustrates the processor, memory, and other elements of the OCS control system <NUM> as being within the same respective blocks, it will be understood by those of ordinary skill in the art that the processor or memory may actually include multiple processors or memories that may or may not be stored within the same physical housing. Similarly, the memory may be a hard drive or other storage media located in a housing different from that of the OCS control system <NUM>. Accordingly, references to a processor or computing device will be understood to include references to a collection of processors or computing devices or memories that may or may not operate in parallel.

Memory <NUM> may store information that is accessible by the processors <NUM>, including instructions <NUM> that may be executed by the processors <NUM>, and data <NUM>. The memory <NUM> may be of a type of memory operative to store information accessible by the processors <NUM>, including a non-transitory computer-readable medium, or other medium that stores data that may be read with the aid of an electronic device, such as a hard-drive, memory card, read-only memory ("ROM"), random access memory ("RAM"), optical disks, as well as other write-capable and read-only memories. The subject matter disclosed herein may include different combinations of the foregoing, whereby different portions of the instructions <NUM> and data <NUM> are stored on different types of media.

Data <NUM> may be retrieved, stored or modified by processors <NUM> in accordance with the instructions <NUM>. For instance, although the present disclosure is not limited by a particular data structure, the data <NUM> may be stored in computer registers, in a relational database as a table having a plurality of different fields and records, XML documents, or flat files. The data <NUM> may also be formatted in a computer-readable format such as, but not limited to, binary values, ASCII or Unicode. By further way of example only, the data <NUM> may be stored as bitmaps comprised of pixels that are stored in compressed or uncompressed, or various image formats (e.g., JPEG), vector-based formats (e.g., SVG) or computer instructions for drawing graphics. Moreover, the data <NUM> may comprise information sufficient to identify the relevant information, such as numbers, descriptive text, proprietary codes, pointers, references to data stored in other memories (including other network locations) or information that is used by a function to calculate the relevant data.

The instructions <NUM> may be used to control components of the optical circuit switch described herein. It should be understood that the optical circuit switch may include other components which are not shown but may be utilized in execution of the instructions <NUM>.

<FIG> illustrates an example MEMS mirror <NUM>. The MEMS mirror <NUM> may be approximately <NUM> in size and highly reflective. For example, the MEMS mirror <NUM> may be coated with a highly reflective material, such as gold. The mirror <NUM> includes an inner portion <NUM> and an outer portion <NUM>, wherein the inner portion is rotatable about a first axis and the outer portion is rotatable about a second axis. For example, the inner portion may rotate about inner torsion beams <NUM> actuated by a comb drive actuator. The outer portion may rotate about outer torsion beams <NUM> actuated by a comb drive actuator. The comb drive actuators may be high voltage, electro-static vertical comb drives which rotate the mirrors about the torsion beams. For example, the rotation may be approximately +/- <NUM>-<NUM> degrees when a voltage ranging between <NUM> of volts to hundreds of volts is applied across the electrodes.

<FIG> illustrates additional aspects of MEMS mirror <NUM>. <FIG> illustrates the centroid of MEMS mirror <NUM>, centroid <NUM>. Centroid <NUM> may correspond with the center of mass of MEMS mirror <NUM>. For example, when the density of the MEMS mirror is uniform, the center of mass and the centroid <NUM> would be at the same location. <FIG> also illustrates a first axis <NUM> of rotation, such as an x-axis. Similarly, <FIG> illustrates a second axis <NUM> of rotation, such as a y-axis. Rotation of the MEMS mirror about either axis <NUM> or axis <NUM> may be achieved through rotating torsion beam <NUM> or torsion beam <NUM> respectively. By actuation of all torsion beams attached to MEMS mirror <NUM>, it is possible to move MEMS mirror <NUM> in a direction perpendicular to the plane formed by the two axes of rotation, axis <NUM> and axis <NUM>, such as a z-axis. Thus, the MEMS mirror may be moved in at least three independent directions. The movement of the MEMS mirror in these three independent directions may also be referred to as tip, tilt, and piston actuation of the MEMS mirror. The amount of movement of the MEMS mirror may be tracked by the movement of centroid <NUM> with respect to three independent axes, such as an x- axis, y-axis, and z-axis.

In some examples, it may be necessary to adjust the positioning of one or more MEMS mirrors, such as MEMS mirror <NUM>. As an example, it may be necessary to remove a MEMS mirror out of the path of a light beam. As another example, it may be necessary to remove one of the MEMS mirrors out of the field of view of a particular camera. Removing a MEMS mirror from the camera field of view may be referred to as "parking" of the MEMS mirror. Parking may be achieved by applying voltages to the driver elements capable of moving a MEMS mirror. However, the high voltage required to park a MEMS mirror may damage the driver elements associated with the MEMS mirror through more stress on electronic components and aging, increasing the likelihood of failure in the future. Additional methods and apparatuses to prevent the interference caused by an unwanted light beam are discussed below.

<FIG> illustrates an example die <NUM> including an array of MEMS mirrors <NUM>. Accordingly to some examples, the MEMS die packages include MEMS mirror arrays, but in other examples any number of MEMS mirrors may be included. The die may be hermetically sealed inside a package with a window in its lid. Not all of the mirrors may be needed or used at a same time. For example, only the best mirrors and fibers in a MEMS mirror array may be selected to make an optical switch, which may be divided as a number of ports + several spares.

<FIG> provides an example of a data optical path and a monitor optical path included in the optical core, also referred to as an optical link In some examples, the optical link can refer to the entire path light takes, including external fiber, transceivers, and circulators. On data path <NUM>, traffic comes in as light input to fiber collimator A. All of the optics in the data path <NUM> may be designed for very low loss over a variety of wavelengths. The light travels along this path <NUM>, and is reflected from MEMSA, then from MEMSB, then is coupled to output fiber collimator B. MEMS A and MEMS B may be just two MEMS mirrors of a larger array, such as illustrated in <FIG> and explained above. By rotating the mirrors in the array, light from any input fiber may be coupled to any output fiber. The injectors shine small laser beams on the MEMS. The cameras image the beams reflected from the MEMS to measure the mirror positions.

Monitor path <NUM> does not carry data, but provides information to a mirror control system about the positions of the mirrors. This may be done using, for example, an injector to shine small beams on each of the MEMS mirrors, and a camera to view the positions of the beams reflected from the MEMS. There may be a camera/injector pair for each MEMS.

<FIG> illustrates an example mirror control loop. The OCS control system <NUM> tells the OCS what configuration it should be in. The mirror control loop handles the MEMS mirror control and movement algorithms based on the monitor path data, and then tells the high voltage drivers to move the mirrors.

<FIG> illustrates a schematic of an N by N optical circuit switch (OCS) <NUM> switch according to aspects of this disclosure. <FIG> illustrates a number of ports, such as input ports <NUM>-<NUM> and output ports <NUM>-<NUM>. In some examples, the input ports of <FIG> may be considered to be part of fiber collimator A of <FIG> while the output ports of <FIG> may be considered to be part of fiber collimator B - though these two diagrams do not necessarily need to be related. Although only a few ports are illustrated for clarity, an OCS switch can have an arbitrary integer number of ports, such as N input ports and M output ports. Each input port can be optically linked to any output port through an optical pathway, and vice versa. For clarity, a subset of the N by N optical links are illustrated in unlabeled dashed lines. These dashed lines can correspond to space within an OCS switch where light beams pass through. Although reference is given with input ports and output ports, a person of skill in the art will understand that the ports and signals transmitted through OCS <NUM> can be transmitted from output ports to input ports. Each port can be paired with an optical transceiver which is capable of both transmitting and receiving optical signals.

In some examples, mechanisms which can be used to control or operate OCS <NUM> can be similar to the systems and apparatus described in reference to <FIG>, such as OCS <NUM>. Similarly, OCS <NUM> can be programmable as described above. In some examples, other mechanical switching mechanisms can be used to control the operation of OCS <NUM> and the particular optical pathway being used at a particular time, such as mechanical switching methods, including electro-optical and thermo-optical mechanism. One particular example, which has been described above with respect to MEMS mirror, uses an array of silicon mirrors which are tilted by applying a control signal or voltage signal to deflect optical beams in free space to different ports. Other examples can include piezoelectric actuator technology, which can be used to steer optical beams in free space between different ports.

OCS <NUM> can include any combination of components to improve the quality and performance of optical signals and reduce the amount of noise through an optical link. Non-limiting examples of components or techniques which can be used include the use of low return loss connector technologies at optical connection points and ports, ultra physical contact connectors, and angled physical contact connectors.

OCS <NUM> can also transmit optical signals encoded in various protocols or methods. One example of a protocol which can be used with OCS <NUM> includes pulse amplitude modulation (PAM). Pulse-amplitude modulation is a method of signal modulation where information is encoded in the amplitude of a series of signal pulses. The duration of the pulses can be adjusted to encode additional information in a shorter period of time. Varieties of PAM include single polarity PAM and double polarity PAM. A person of skill in the art will appreciate that several techniques and protocols can be used in connection with the disclosed technology.

Illustrated in <FIG> is circulator <NUM> having a dedicated first port or a unidirectional output port <NUM> and dedicated second port or unidirectional inputport <NUM>, and a third port or bidirectional port <NUM>. Circulator <NUM> can be an optical circulator, which is a three port device, which has cyclical connectivity. An input into the first port <NUM> is directed to the third port <NUM>, an input into the third port <NUM> is directed to the second port <NUM>. In this manner, optical circulator <NUM> can allow bi-directional transmission over a single fiber or a single optical path by propagating a signal received at the first port <NUM> through the third port <NUM>, and from the third port <NUM> to the second port <NUM>. Circulator <NUM> can contain optical polarizers, magneto-optical materials, and other optical components to achieve the functionality described with respect to circulator <NUM>. Although <FIG> is described with reference to a first, second, and third port, any variation of the principles described with respect to optical circulator <NUM> can be used.

<FIG> illustrates an N by N optical circuit switch (OCS) <NUM> coupled with circulators on ports of the N by N optical circuit switch. OCS <NUM> can be similar to OCS <NUM>. <FIG> illustrates a number of ports, such as input ports <NUM>-<NUM> and output ports <NUM>-<NUM>. Although only a few ports are illustrated for clarity, an OCS switch can have an arbitrary integer number of ports, such as N input ports and M output ports. Coupled to each port of OCS <NUM> can be a fiber-optic cable, represented by an unlabeled bidirectional arrow. One end of the fiber-optic cable can be optically linked to a circulator, such as circulator <NUM> illustrated in <FIG>. These circulators are illustrated but unlabeled in <FIG> for clarity.

As OCS switch <NUM> implements a passive optical path between the input and output port, this single path must be bidirectional or reciprocal, meaning light can pass in both directions along the path in a symmetric, similar manner. More specifically, changes in amplitude and phase of the light signal are the same going from the input port to the output port or from the output port to the input port.

Given the symmetry described above, circulators can be combined with OCS <NUM>. By the use of a circulator with each input and output port of OCS <NUM>, each input and output port becomes a bidirectional port, which can double the number of ports in OCS <NUM> from N to 2N, creating the equivalent of a 2N by 2N optical switch. Although reference is given with respect to an N by N switch, a person of skill in the art will understand that the optical switches described herein can be any arbitrary number of integer switches.

Thus, an input to the input port of a circulator can be transmitted to a bidirectional port, which is in turn connected to an input port of OCS <NUM>. Similarly, an output port of OCS <NUM> can be connected with the bidirectional port of a circulator, allowing an optical signal to travel from the output port of OCS <NUM>, through an optical link, through the bidirectional port of a connected circulator, and through the output port of the circulator.

The bidirectional link described above can suffer from noise signals which are superimposed on top of the desired or intended transmitted optical signal. As one example of a source of noise are reflections in the optical path due to the optical links now being bidirectional. Other sources of noise, particularly within a commercial or typical use setting of OCS, can include fiber contamination, particulate matter, and dust on OCS reflectors or connector ends.

<FIG> illustrates an example link diagnostic system, <NUM>, coupled to an OCS <NUM>. LDS <NUM> consists of a laser <NUM>, two photodetectors, photodetectors <NUM> and <NUM>, a coupler <NUM>, and a port <NUM>. Coupler <NUM> can be a <NUM> by <NUM> coupler.

Laser <NUM> can be any light source, including but not limited to any combination of lasers, specially designed semiconductors. As one example, laser <NUM> can be a distributed feedback laser. Laser <NUM> can output a <NUM> wavelength. The light generated by laser <NUM> can be optically linked to other components of LDS <NUM> as described below.

A photodetector, such as photodetectors <NUM> and <NUM>, can be a semiconductor device that converts light into an electrical current. The photodetector can generate a current which is proportional to the number of photons hitting the surface. As electrical current is generated when photons are absorbed in the photodetector, the photodetector can act as a sensor for light. The photodetector can be any device which is capable of sensing intensities and/or wavelengths of light. Photodetectors <NUM> and <NUM> can be a photodiode or a photosensor. In some examples, a photodetector can be chosen to be more sensitive to specific wavelengths of light. Additional circuitry, calibration, or electronics can be incorporated into photodetectors <NUM> and <NUM> to ensure a better signal to noise ratio and reduce the effect of ambient light or noise.

Coupler <NUM> can couple <NUM> optical links or fibers within LDS <NUM>. In some examples, the coupler can couple two chosen fibers or links. The coupler can help split the amount of light or percentage of signal between pathways within LDS <NUM>, as illustrated in <FIG>. In some examples, an optical circulator can be used in lieu of or in conjunction with coupler <NUM>.

Photodetector <NUM> is a "return power monitor" which monitors a signal returned from an optical path, as further explained with reference to <FIG>. Photodetector <NUM> is a "laser forward power monitor" signal which monitors the power of a laser as transmitted in the forward direction.

Port <NUM> can be a port of an OCS, such as OCS <NUM> or OCS <NUM>. Laser light transmitted to port <NUM> and returned from port <NUM> can arrive at the photodiode <NUM> and be used to monitor a path. In some examples, port <NUM> can be part of a collimator of an OCS system, such as an optical link or optical fiber linking to a collimator.

<FIG> illustrates a schematic view of a system <NUM>. System <NUM> can be an optical time domain reflectometer (OTDR) meter or optical return loss (ORL) meter coupled with the OCS system for automated diagnosis of the fiber-optic network fabric loss and return loss.

System <NUM> includes an OCS <NUM>, including collimators <NUM> and <NUM>, link diagnostic systems (LDS) <NUM> and <NUM>, and a OCS front panel <NUM>. Collimators <NUM> and <NUM> can be similar to those described with reference to <FIG>. Collimators <NUM> and <NUM> can be optically or data connected with LDS <NUM> and LDS <NUM> respectively. Collimators <NUM> and <NUM> are connected to one another through an internal optical path such as that described in <FIG>. Each collimator can be connected through an OCS front panel <NUM> to input and output ports. OCS front panel <NUM> can contain a number of input ports and output ports, similar to input ports <NUM>-<NUM> and output ports <NUM>-<NUM> described with reference to <FIG>. LDS <NUM> and LDS <NUM> can be similar to LDS <NUM>.

Each input and output port can be connected to an optical circulator, such as circulators <NUM> and <NUM>, through the optical circulator's bidirectional port. Circulator <NUM> and <NUM> can be similar to circulator <NUM>. The unidirectional input and output port of circulators <NUM> and <NUM> are connected to a transceiver, such as transceivers <NUM> and <NUM>. In some examples, the transceiver can have a dedicated transmitter connected to the input port of a circulator and a dedicated receiver, connected to the output port of a circulator. Although examples are given with respect to an optical circulator, other functionally equivalent optical components such as a splitter/combiner or a device with equivalent functionality can be used. In other examples, the use of a circulator can be avoided and a connection to two OCS ports can be used,.

In some examples, LDS <NUM> or <NUM> can be attached through input ports or output ports on the front panel. However, this can increase certain types of noise due to connector insertion or return loss, leading to more variability in performance and calibration.

As one example, such as in an optical return loss (ORL) meter, a laser within LDS <NUM> or <NUM> generates light which is transmitted through coupler <NUM>, to collimator A or B, through an OCS core, through OCS front panel <NUM>, and through circulators <NUM> or <NUM> and to transceivers <NUM> or <NUM>. A portion of the light generated by the LDS <NUM> or <NUM> will be reflected backwards along the optical path, causing the light to be transmitted in the reverse direction from the point at which the reflection occurred. Within the LDS, the forward photodiode is used to monitor the power of the laser, which can vary over time, while the reverse photodiode is used to monitor the amount of signal which is received through reflections along the path. The transmitted portion of transceiver <NUM> and <NUM> can be turned off to avoid additional signal from interfering as it will mask reflection signals. In other examples, a small calibration signal can first be sent from the transceiver to ensure that the photodiodes and system are properly calibrated or to measure insertion loss along an optical path, such as from a transceiver to an LDS, as described herein.

In another example, such as in an OTDR implementation, the LDS used can be similar as described above, but the circuit driving a laser within an LDS would be pulsed and the reverse photodiode receiver circuit would require waveform capture capability to analyze time dependent reflections as compared to only a direct current (DC) signal measurement in the ORL meter described above. The additional time dependent information allows accurate determination of reflection location in addition to amplitude, facilitating subsequent repairs and maintenance.

In addition to ORL measurement, LDS <NUM> or LDS <NUM> can allow for measurement of insertion loss along the various paths from an OCS to the receiver of a transceiver and from the transmitter of a transceiver to the OCS. For measurement of transmit path loss, the transmitter of transceiver <NUM> or transceiver <NUM> would be turned ON, with light propagating through a circulator, through the fiber-optic cable, through the OCS core, to a reverse photodiode of the an LDS where the received power is measured. As most modern-day optical transceivers feature monitoring of the transmitter power at the transceiver, known as transmit power monitoring (TPM), the difference between received power at the reverse photodiode and TPM would indicate path loss. The excess loss of the LDS and OCS can be calibrated out of the mentioned path loss for higher accuracy. For the measurement of "receive" path loss, the transceiver transmitter would be turned OFF to eliminate reflection signals and the LDS laser would be turned ON. LDS laser light can then propagate through an OCS core, to the external environment, and reach the receiver of the transceiver.

Analogously, optical receivers feature monitoring of the receiver power at the transceiver, known as receive signal strength indicator (RSSI), with the difference between transceiver received power and LDS laser power indicating the receive path loss. The excess loss of the LDS and OCS can be calibrated out of the aforementioned difference for higher accuracy.

Once the above return/transmit path/receive path loss characterization is done, the OCS internal path would then be switched to a different link/path for its characterization. This step can be achieved through the use of processors described above with reference to <FIG>. Characterization of multiple paths could be done in parallel with multiple LDS units.

In some examples, multiple LDS can be used at various points within an OCS to allow for redundancy, parallelism, increased data sources, and for faster system diagnosis and measurements. In some examples, multiple LDS systems can be used in parallel depending on the size of the OCS front panel.

<FIG> illustrates a schematic diagram of a computing system <NUM> in data connectivity with various components, such as transceivers <NUM> and <NUM>, LDS <NUM>, LDS <NUM>, and optical core. A computing system can be any computer, processing unit, laptop, desktop, server, or other specially designed hardware to perform computations, store data, and enable connectivity between other computing devices and electronic components. Computing system <NUM> can contain any of the functionality described with respect to <FIG>, such as without limitation, OCS control system <NUM>, processors <NUM>, memory <NUM>, instructions <NUM>, and data <NUM>. Computing system <NUM> can be used to automate diagnosis of an OCS system according to aspects of the disclosed technology. Computing system <NUM> can also contain communication interfaces, such as Bluetooth, internet, infrared, wireless, NFC, serial port, or wired data connection to communicate amongst and between electronic components and other computing devices.

<FIG> illustrates an example method <NUM> which can be used to diagnose and qualify optical links. Arrows between blocks represent example sequences in which blocks can be executed. However, the steps can occur in parallel, or in other sequences and orders. Method <NUM> can occur on processors, such as processor <NUM> or computing system <NUM> described above. As illustrated in <FIG>, a checkmark (✔) can indicate a particular step, test, or block to pass while an "X" can indicate that a particular step, test, or block has not passed or failed. As illustrated in <FIG>, if every test passes, method <NUM> can proceed to "linked passed", indicating that the optical link has been diagnosed and passed.

At block <NUM>, a cable audit can take place. A cable audit can represent a quick check of communication integrity between an optical link. A cable audit can be a process wherein communication is established by sending packets of information in both directions for a short period of time, to check that the link works. At block <NUM>, transmission path losses between two different paths can be measured if the cable audit fails. In some examples, the first path can be formed through a first collimator of an OCS and a second path can be formed through a second collimator of an OCS. Similarly, at block <NUM>, path losses can be measured on both the first path and the second path if the cable audit fails. If the path losses are determined to be high or transmission to be low, a repair may be required of the optical link or OCS system. A repair can occur, after which the cable audit can be repeated. If the cable audit passes, block <NUM> can follow. In some examples, "pass" can be defined as being successful packet communication. In other examples, "pass" can be defined by a particular criterion or set of criteria, such as, for example, one realted to a specific signal quality. For example, the signal quality could be a bit error rate which is to be achieved.

In some examples, a particular repair of the optical system can be established or determined based on the particular problem detected, signature, symptom, or test being performed. In some examples, every possible optical path connected to the LDS can be measured. In this example, a table of data can be generated which can be stored, correlated, and utilized for analysis for each path in the <NUM> x N paths of the OCS.

At block <NUM>, optical return losses can be measured. At this block, return losses for two different paths can be determined. As described above, the first path and the second path can be formed through different fiber collimators.

At block <NUM>, a bit error rate test (BERT) can occur. In some examples, the BERT can be more thorough and a more detailed test than those occurring in block <NUM> and <NUM>.

After block <NUM>, if all the blocks are determined to pass, the link can be determined to pass.

In some examples, blocks <NUM> to <NUM> can be configured to proceed sequentially in an automated manner when a repair is not required. In some examples, both transmission path losses (A and B) can be measured simultaneously. In other examples, a reflection path loss can be excluded from the blocks described with reference to <FIG>. In other examples, a reflection path loss can be included in a particular block after a repair has occurred on a particular segment.

Although method <NUM> is described above with use of the LDS with a fiber-optic network which implements circulators for bidirectional communication, the same methods of diagnosis can be applied to a network with no circulators, such as for example, in a system in which bidirectional communication is achieved through two fiber-optic paths.

While this disclosure contains many specific implementation details, these should not be construed as limitations on the scope of what may be claimed, but rather as descriptions of features specific to particular implementations. Certain features that are described in this specification in the context of separate implementations may also be implemented in combination in a single implementation. Conversely, various features that are described in the context of a single implementation may also be implemented in multiple implementations separately or in any suitable sub-combination. Moreover, although features may be described above as acting in certain combinations and even initially claimed as such, one or more features from a claimed combination may in some cases be excised from the combination, and the claimed combination may be directed to a sub-combination or variation of a sub-combination.

References to "or" may be construed as inclusive so that any terms described using "or" may indicate any of a single, more than one, and all of the described terms. The labels "first," "second," "third," and so forth are not necessarily meant to indicate an ordering and are generally used merely to distinguish between like or similar items or elements.

Claim 1:
A system comprising:
an optical circuit switch, OCS (<NUM>), comprising:
a first fiber collimator (<NUM>) and a second fiber collimator (<NUM>);
a OCS internal optical path (<NUM>) coupling the first and second fiber collimators (<NUM>) an optical circulator (<NUM>) having a bidirectional port optically coupled to a port of the second fiber collimator (<NUM>);
a first transceiver (<NUM>) optically coupled to the optical circulator (<NUM>);
a first link diagnostic system (<NUM>) comprising:
a first photodetector (<NUM>) and a second photodetector (<NUM>);
a light source (<NUM>);
an optical coupler (<NUM>), coupling the light source (<NUM>) to the second photodetector (<NUM>); and
wherein:
the first photodetector (<NUM>) is optically coupled to the optical circulator (<NUM>) along a path comprising a fiber input to the first fiber collimator (<NUM>), the OCS internal optical path (<NUM>), and the port of the second fiber collimator (<NUM>).