Patent Description:
Fiber optic cables typically comprise a core, a cladding, and a buffer (a protective outer coating), in which the cladding guides the light along the core using the physical principle of total internal reflection. The core of the fiber-optic cable is made of a material, such as high quality silica or plastic, which has a higher refractive index than the cladding. Consequently, light rays which enter the fiber-optic cable at an angle below the critical angle reflect off the cladding and are guided down the cable. However, light rays which enter at above the critical angle partially reflect and partially refract each time the light ray encounters a boundary between the core and the cladding. As result, the light's intensity, and thus the signal carried by the light, becomes attenuated and is eventually lost. Alignment methods for aligning the coupling positions between fibres, focusing lenses, and emitters are known from e.g. <CIT>, <CIT>, <CIT>, and <CIT>.

The present invention is illustrated by way of examples, and not by way of limitation, in the figures of the accompanying drawings and in which like reference numerals refer to similar elements and in which:.

Techniques for coupling light from a waveguide array to a single mode fiber array are described.

Embodiments are described herein according to the following outline:.

A method for performing active alignment is presented. In an embodiment according to independent claim <NUM>, the method comprises measuring an intensity of light passing through a lens holder sub-assembly. The lens holder sub-assembly coupling a plurality of focusing lenses to a plurality of optical fiber ferrules. In response to a determination that the intensity of light exceeds a particular threshold, locking the lens holder sub-assembly in place. In response to a determination that the intensity of light does not exceed the particular threshold, adjusting the degree of tilt of the lens holder sub-assembly.

The method is performed by one or more computing devices.

An apparatus for coupling light is described. In an embodiment according to independent claim <NUM>, the apparatus comprises a transmitter configured to emit modulated light upon which data is encoded; a plurality of focusing lenses configured to focus the modulated light into a plurality of optical fiber ferrules; and a lens holder sub-assembly, tilted with respect to a propagation axis of the modulated light, that couples the focusing lenses to the optical fiber ferrules.

The foregoing and other features and aspects of the disclosure will become more readily apparent from the following detailed description of various embodiments.

At present, there are two common types of fiber-optic cables, multimode fiber-optic cable and single mode fiber-optic cable. The primary difference between multimode and single mode fiber-optic cable is the size of the core, which is one of the factors that determines how many modes of light the cable can support. A mode of light may be termed a path through which a light ray can travel down a fiber-optic cable, although this term is merely an approximation of the actual physical phenomenon.

Multimode fiber-optic cables typically have a core that is <NUM>-<NUM> microns in diameter and thus are capable of supporting light rays which take multiple paths down the cable. For example, light traveling in the lowest mode travels down the center of the cable and reaches the end without bouncing off the cladding. Light following subsequent modes travel by bouncing off the cladding, with light rays entering the cable at progressively steeper angles traveling in increasingly higher modes and, as a result, bouncing more often during the transmission.

Due to supporting light rays which follow multiple paths, multimode fiber optic cables suffer from modal dispersion, in which a signal represented in the light rays is spread in time because the propagation velocity of the optical signal is not the same for all modes. In simpler terms, paths which bounce less often are traversed more quickly, thus there is a time difference between when light traveling in the lowest mode reaches the end of the cable and when light traveling in the highest mode reaches the end of the cable. This time delay, and thus the modal dispersion, is more pronounced when the cable length is longer. As a result, multimode fiber-optic cables are typically limited in both data transfer rate and the length of the fiber-optic connection. Consequently, multimode fiber-optic cables are primarily used for communication over short distances, such as within a building or across a campus.

Single mode fiber-optic cables resolve the modal dispersion issue by supporting only a single (lowest) mode of light. As a result, single mode fiber-optic cables are capable of transmitting data at faster rates and over longer distances than multimode fiber-optic cable. However, in order to support only a single mode of light, the core of a single mode fiber-optic cable is significantly smaller than the core of a multimode fiber-optic cable. In most cases, single mode fiber-optic cables are designed with a core that is approximately <NUM>-<NUM> microns in diameter. Consequently, the aperture at which light must enter the single mode fiber-optic cable is narrow and extreme precision is required in aligning light from the transmitter to the fiber-optic cable, a process referred to as coupling. As a result, the equipment required to perform the delicate calibrations for coupling light into a single mode fiber-optic cable can be very expensive compared to the equipment for coupling light into a multimode fiber-optic cable.

One technique for coupling light into a multimode fiber-optic cable involves a dual lens design (sometimes known as a "PRIZM" coupler). In the PRIZM coupler design, light emitted by the transmitter is collimated using a first lens array. The collimated light is then directed towards a lens holder sub-assembly by a mirror or turning prism. The lens holder sub-assembly contains a second array of lenses that focuses the light into ferrules where a fiber-optic cable can be placed to receive the light.

Extending the "PRIZM" coupler for use with single mode fiber optic cable is problematic because the single mode fiber core is only <NUM>-<NUM> microns in diameter verses the <NUM>-<NUM> micron core of a multimode fiber-optic cable. As a result, the tolerances required to transition from multimode to single mode fiber require at least a fivefold greater accuracy when aligning the second lens array to the ferrules. Equipment to produce the aforementioned accuracy requirements can be very expensive and/or difficult to acquire.

For example, the lens holder sub-assembly is typically created by aligning the second array of lenses to the ferrules and epoxying the second array of lenses in place onto the lens holder sub-assembly. However, as the epoxy hardens, typically through ultraviolet or thermal curing, the resulting stresses may cause the second lens array and the ferrules to shift slightly out of alignment. For multimode fiber optical cables, the tolerance is great enough that the shift has a negligible effect on the resulting signal strength. Signal strength for single mode fiber-optic cables, on the other hand, can be greatly affected by even minor misalignments within the lens holder sub-assembly. Consequently, lens holder subassemblies that are manufactured with all but the most nominal amount of misalignment would ordinarily be unusable for the purpose of coupling single mode fiber-optic cable.

The techniques described herein may be used to relax the tolerance and thus the accuracy requirements needed to couple light into a single-mode fiber optic cable. As a result, the cost of coupling can be greatly reduced since cheaper and more readily available equipment can be used to perform the coupling effectively.

In an embodiment, misalignment within the lens holder sub-assembly is compensated by tilting the lens holder sub-assembly with respect to the propagation axis of the collimated light. With tilt axis control, there is little to no excess loss due to the misalignment between the second lens array and the ferrules within the lens holder sub-assembly, which increases the allowed tolerance and thus reduces cost. Since the amount of tilt can be adjusted according to the degree of lateral misalignment, lens holder sub-assembles manufactured with varying degrees of misalignment may still be utilized to couple light into a single mode fiber-optic cable. In addition, the same technique can be used to compensate for other defects as well, such as angular errors (e.g. manufacturing or placement) of the turning mirror or prism used to direct light into the lens holder sub-assembly.

In other examples not according to the invention, rather than using the dual lens PRIZM design, coupling is performed using a single lens. In the single-lens design, instead of collimating light using a first array of lenses, the transmitter emits light onto the turning mirror/prism, which directs the light onto the lens holder sub-assembly. Because the light is not collimated, the light falls upon the lens holder sub-assembly at many different angles. As a result, compensation for misalignment within the lens holder sub-assembly can be accomplished by adjusting the lens holder sub-assembly laterally without the need for tilt access control. In addition, the same technique can be used to correct other defects, such as angular errors of the turning mirror or prism used to direct the divergent light toward the lens holder sub-assembly.

<FIG>, <FIG>, <FIG>, <FIG> illustrate an example optical networking device <NUM>. <FIG> depicts a side view of the optical networking device <NUM>. <FIG> depicts a view of an interposer <NUM> with a lens holder sub-assembly <NUM> removed. <FIG> depicts a top-down view of the lens holder sub-assembly <NUM>. <FIG> depicts a bottom-up view of the lens holder sub-assembly <NUM>.

The optical networking device <NUM> possesses a base for an interposer <NUM>, through which the optical networking device <NUM> may communicate with other devices or circuit board components. Transmitter <NUM>, turning mirror <NUM>, lens holder sub-assembly <NUM>, and receiver <NUM> are mounted onto the base for interposer <NUM>. Transmitter <NUM> emits light modulated to carry information for fiber-optic communication. In addition, the transmitter <NUM> is aligned with a collimating lens array <NUM> used to parallelize the emitted light. Once parallelized by the collimating lens array <NUM>, the emitted light is reflected off turning mirror <NUM> towards the focusing lens array <NUM> held by the lens holder sub-assembly <NUM>. The focusing lens array <NUM> focuses the emitted light into one or more fiber-optic cable ferrules <NUM> dedicated to optical fibers used for transmitting data. The remaining fiber-optic cable ferrules <NUM> are dedicated to optical fibers used for receiving data. Light received through the remaining fiber-optic cable ferrules <NUM> is focused through focusing lens array <NUM> onto the receiver <NUM>, which translates the incoming light pulses into electrical signals. The fiber-optic cable ferrules <NUM> are aligned with guide pins <NUM> that are used to guide and hold an array of optical fibers in place.

The exact design of the example optical networking device <NUM> is not critical to the techniques described herein. The design of the optical networking device <NUM> may vary greatly from the depictions of <FIG>, <FIG>, <FIG>, <FIG>. For example, instead of using turning mirror <NUM> to direct the light emitted from the transmitter <NUM> to the focusing lens array <NUM>, the optical networking device <NUM> may have the transmitter <NUM> in line with the focusing lens array <NUM>, thus allowing the turning mirror <NUM> to be omitted. As another example, which will be discussed in more detail in later sections, the optical networking device <NUM> may use a single-lens design by omitting the collimating lens array <NUM>, thus allowing divergent light from the transmitter <NUM> to reach the focusing lens array <NUM>.

Furthermore, the design of the example optical networking device <NUM> allows for coupling light into an array of optical fibers, but the design could also be scaled down to couple light into a single optical fiber, as opposed to an array. In addition, the example optical networking device <NUM> possesses both a transmitter <NUM> and a receiver <NUM>, and is thus capable of both transmitting and receiving data. The optical networking device <NUM> may be designed to perform one function, but not the other. As a result, an alternative design may omit the transmitter <NUM> or the receiver <NUM> and dedicate the fiber-optic cable ferrules <NUM> to serve only the remaining function.

An interposer <NUM> is an electrical interface routing between one socket or connection to another. Through the interposer <NUM>, the optical networking device <NUM> may communicate with other devices or circuit board components. For example, electrical signals produced by the receiver <NUM> as a result of receiving incoming light pulses may be rerouted to another circuit component or device configured to perform signal processing. As another example, a circuit board component or device configured to send data may interface with the transmitter <NUM> through interposer <NUM> to convert the data into modulated light pulses. However, the exact interface mechanism used for this purpose is not critical to the techniques described herein, and the interposer <NUM> may be replaced with a different type of interface.

Transmitter <NUM> is any component capable of emitting modulated light pulses upon which data is encoded for fiber-optic communication. For example, the transmitter <NUM> may represent one or more light-emitting diodes (LEDs) vertical-cavity surface-emitting lasers (VCSELs), or laser diodes. However, transmitter <NUM> is not limited to components which create the modulated light pulses. Transmitter <NUM> may represent waveguides, such as one or more optical fibers, which carry modulated light pulses created by other sources.

Collimating lens array <NUM> is an array of lenses configured to parallelize light emitted by the transmitter <NUM>. To achieve the aforementioned parallelization, the collimating lens array <NUM> is set a distance from the transmitter <NUM> equal to the focal length of the collimating lens array <NUM>. As a result, the divergent light from the transmitter <NUM> bends through the collimating lens array <NUM> and is transformed into approximately parallel rays of light. In some cases, the transmitter <NUM> may emit light, such as certain types of laser light, which is already heavily collimated. Thus, the collimating lens array <NUM> may be omitted from the optical networking device <NUM> if further collimation would not significantly increase the parallelization of the light.

Turning mirror <NUM> represents a reflective surface angled to direct light towards the focusing lens array <NUM>. Turning mirror <NUM> is coated in a reflective material (e.g. gold or aluminum) in order to create the reflective surface. Components other than a mirror, such as a prism, may be used for the same purpose by bending light in the direction of the focusing lens array <NUM>. In addition, although the examples depicted by <FIG>, <FIG>, <FIG>, <FIG> mounts the turning mirror <NUM> onto the interposer <NUM>, other examples may instead mount the turning mirror <NUM> directly onto the transmitter <NUM>.

Receiver <NUM> contains a photodetector (e.g. p-n photodiodes, pi-n photodiodes, avalanche photodiodes, etc.), which converts light into electricity using the photoelectric effect. Receiver <NUM> is coupled with a transimpedance amplifier and/or a limiting amplifier to produce a digital signal in the electrical domain from the incoming optical signal. In some cases, the digital signal may, during transport, become attenuated and distorted. As a result, receiver <NUM> may perform preliminary signal processing (e.g. clock recovery performed by a phased-locked loop), before the digital signal is transmitted through the interposer <NUM> to other components or devices.

Lens holder sub-assembly <NUM> comprises a housing to hold the focusing lens array <NUM> in alignment with the fiber-optic cable ferrules <NUM>. The focusing lens array <NUM> is held to the lens holder sub-assembly <NUM> with epoxy or other adhesive. However, alternative holding mechanisms may also be employed for the same purpose.

The focusing lens array <NUM> is positioned onto the lens holder sub-assembly <NUM> by aligning the focusing lens array <NUM> with the guide pins <NUM> or other fiduciary marker. In other examples the focusing lens array <NUM> is positioned onto the lens holder sub-assembly <NUM> by active alignment. For example, light such as that emitted by transmitter <NUM> can be directed through the focusing lens array <NUM> and out of the fiber-optic cable ferrules <NUM> onto a measuring device that detects the light's intensity. The position of the focusing lens array <NUM> can then be moved about incrementally until an optimal or threshold intensity reading is detected by the measuring device before being locked into place.

In embodiments, lens holder sub-assembly <NUM> is formed to interface with a Multiple-Fiber Push-On (MPO) connector, that is used to align an array of optical fibers with the fiber-optic cable ferrules <NUM>.

<FIG> illustrates an example MPO connector <NUM>. The MPO connector <NUM> of <FIG> acts as an interface for an array of optical fibers contained within fiber-optic cable <NUM>. The guide pin holes <NUM> of the MPO connector <NUM> serve as an attachment mechanism that aids to align the fiber-optic cable apertures <NUM> when interfacing with another device. In some embodiments, the fiber-optic cable <NUM> houses an array of single mode optical fibers. However, the techniques described herein are not limited to single mode optical fibers, and may also be applied to lower the tolerance requirements for multimode fiber-optic cables.

In an embodiment, the MPO connector <NUM> of <FIG> interfaces with the lens holder sub-assembly <NUM> of <FIG> by inserting the guide pins <NUM> into the guide pin holes <NUM>, thus aligning the fiber-optic cable apertures <NUM> to the fiber-optic cable ferrules <NUM>. As a result, light emitted by the transmitter <NUM> carrying outgoing data enters one or more optical fibers of the fiber-optic cable <NUM> that are dedicated to transmitting data. Similarly, light carrying incoming data exits one of more optical fibers of the fiber-optic cable <NUM> dedicated to receiving data and is directed towards the receiver <NUM>. In some embodiments, the other end of the fiber-optic cable <NUM> is connected to another optical networking device <NUM>, such as the optical networking device <NUM> depicted in <FIG>, <FIG>, <FIG>, <FIG>. However, in other embodiments, the other end of the fiber-optic cable <NUM> may be connected to a different type of optical networking device <NUM>.

As mentioned above, when the focusing lens array <NUM> is mounted onto the lens holder sub-assembly <NUM> the manufacturing process often leaves a misalignment between the focusing lens array <NUM> and the fiber-optic cable ferrules <NUM>, resulting in attenuation or loss of the light (and thus the optical signal) that enters the fiber-optic cable <NUM>.

<FIG> is a block diagram that illustrates light traveling through the optical networking device <NUM> when no misalignment is present between the focusing lens array <NUM> and the fiber-optic cable ferrules <NUM>. As depicted in <FIG>, emitted light <NUM> emanates from the transmitter <NUM>, becomes parallelized by the collimating lens array <NUM>, and reflects off the turning mirror <NUM> towards the focusing lens array <NUM> mounted to the lens holder sub-assembly <NUM>. The focusing lens array <NUM> then directs the light into the fiber-optic cable ferrules <NUM>. Similarly, received light <NUM> entering through the fiber-optic cable ferrules <NUM> falls upon the focusing lens array <NUM>, which directs the received light <NUM> to the receiver <NUM>.

<FIG> is a block diagram that illustrates light traveling through the optical networking device <NUM> when lateral misalignment is present between the focusing lens array <NUM> and the fiber-optic cable ferrules <NUM>. Since the focusing lens array <NUM> is laterally misaligned with the fiber-optic cable ferrules <NUM>, at least some of the emitted light <NUM> misses the fiber-optic cable ferrules <NUM>. Similarly, at least some of the received light <NUM> becomes blocked from reaching the focusing lens-array <NUM>. As a result, the optical signal in both directions becomes attenuated or lost.

<FIG> is a block diagram illustrating an embodiment that compensates for the misalignment by tilting the lens holder sub-assembly <NUM> of the optical networking device <NUM>. In <FIG>, the lens holder sub-assembly <NUM> is tilted with respect to the propagation axis in order to allow the emitted light <NUM> and received light <NUM> to pass through the lens holder sub-assembly despite the lateral misalignment.

Assuming that the degree of lateral misalignment and the distance between the focusing lens array <NUM> and the fiber-optic cable ferrules <NUM> is known, the position and angle needed to compensate for the misalignment can be computed using trigonometry. However, because the lateral misalignment is on the order of microns, or even sub-microns, measuring the misalignment may be difficult using conventional tools. As a result, active alignment is performed to determine an optimal (or acceptable) configuration of the lens holder sub-assembly <NUM>.

In an embodiment, active alignment is achieved by passing light (e.g. laser light) through or from the optical networking device <NUM> and onto a measuring device, such as an optical power meter. For example, the measuring device may be mounted onto the lens holder sub-assembly <NUM> using the guide pins <NUM> or attached to the other end of the fiber-optic cable <NUM>. The position and angle of the lens holder sub-assembly <NUM> is then incrementally adjusted until an optimal or threshold intensity of light is detected by the measuring device. In embodiments, the position and angle of the lens holder sub-assembly <NUM> is calibrated by one or more actuators configured to micron or sub-micron accuracy. In an embodiment, the one or more actuators are controlled by a computing device, such as the computing device described below in the "Hardware Overview", that has been configured to adjust the sub-assembly <NUM> based on input received from the optical power meter.

In some cases, active alignment may be modeled as an optimization problem, where the independent variables are represented by linear variables x, y, z (lateral and vertical movement) and angular variables θx, θy, θz (roll, pitch, yaw) with the independent variable being maximized, L, representing the intensity of the recorded light. However, other embodiments may omit one or more of the independent variables should the actuators performing the calibrations support less than six degrees of freedom.

In an embodiment, a computing device performs active alignment by maximizing the intensity of the recorded light with respect to one degree of freedom at a time until the measured light intensity is above a particular threshold.

<FIG> is a block diagram illustrating a computing device performing active alignment.

At block <NUM> the computing device selects an initial degree of freedom. In an embodiment, the computing devices selects from x, y, z (lateral and vertical movement) and angular variables θx, θy, θz (roll, pitch, yaw). However, the computing device may only be able to adjust a subset of the aforementioned degrees of freedom, and therefore selects from a reduced set. The computing device starts with lateral and vertical movement degrees of freedom. In other examples, the computing device starts with angular variables.

At block <NUM> the computing device searches for the maximum (or near maximum) light intensity with respect to the current degree of freedom. The computing device adjusts the degree of freedom incrementally (positively or negatively) while taking a light intensity measurement after each adjustment. The computer device continues the adjustment until the measured light intensity reaches a local maximum.

At block <NUM> the computing device determines whether the measured light intensity exceeds a particular threshold. In response to a determination that the measured light does not exceed the particular threshold, the computing device selects the next degree of freedom at block <NUM>. Otherwise, the computing device completes active alignment at block <NUM>. The computing device may instead determine whether the measured light intensity meets or falls below a particular threshold at block <NUM>.

The selection of the next degree of freedom at block <NUM> loops back around to the initial degree of freedom until the computing device detects an acceptable light intensity measurement. However, the computing device may put a limit on the number of times the selection and adjustment of the degrees of freedom can loop around, thus putting a cap on the number of adjustments performed during active alignment.

Instead of comparing the measured light intensity to a threshold at block <NUM>, the computing device may instead adjust each degree of freedom until the amount of improvement obtained after finding the local maximum of each degree of freedom falls below a minimum threshold.

Once the measuring device has detected an acceptable light intensity, the lens holder sub-assembly <NUM> is fixed in place. For example, the active alignment may be performed before the lens holder sub-assembly <NUM> is attached to the interposer <NUM> base. As a result, the lens holder sub-assembly <NUM> may, for example, be soldered or epoxied onto the interposer <NUM> in response to the measuring device detecting an acceptable light intensity. The lens holder sub-assembly <NUM> may be configured to adjust the position and angle of the focusing lens array <NUM> and the fiber-optic cable ferrules <NUM> after being mounted onto the interposer <NUM>.

The optical networking device <NUM> may use a single-lens design by omitting the collimating lens array <NUM>, thus allowing divergent light from the transmitter <NUM> to reach the focusing lens array <NUM>.

<FIG> illustrates the effect of lens holder sub-assembly <NUM> misalignment on an embodiment single-lens design of the optical networking device <NUM>. In order to provide a clear illustration, <FIG> has been limited to depicting only one focusing lens <NUM> of the focusing lens array <NUM> and one fiber-optic cable ferrule <NUM> of the fiber-optic ferrules <NUM>. Although the focusing lens <NUM> and fiber-optic cable ferrule <NUM> pair chosen for the following example is used to transmit data, the following techniques are also applicable to lens/ferrule pairs that receive data, provided that light received from the remote source is divergent. For mixed cases, where the light from the transmitter <NUM> is divergent and light destined for receiver <NUM> is collimated, or the converse, the double-lens compensation techniques discussed above may still be utilized to perform the coupling. The design of the optical networking device <NUM> may be modified so that the lenses of the focusing lens array <NUM> and the ferrules of the fiber-optic cable ferrules <NUM> used for transmitting data are adjustable independently from those used for receiving data.

In <FIG>, the collimating lens array <NUM> of the optical networking device <NUM> has been omitted. As a result, divergent light <NUM> emitted from the transmitter <NUM> fans out at many different angles before reaching the lens holder sub-assembly <NUM>. Due to the misalignment between the focusing lens <NUM> and the fiber-optic cable ferrule <NUM>, light which enters at an angle sufficient to strike the focusing lens <NUM> fails to reach the fiber-optic cable ferrule <NUM>. In some respects, <FIG> depicts a worst case scenario where the misalignment is large to the point where the divergent light <NUM> is unable pass through the lens holder sub-assembly <NUM> at all. However, even with a lesser degree of misalignment, the optical signal still becomes attenuated due to divergent light <NUM> becoming blocked that would otherwise pass through the lens holder sub-assembly <NUM> assuming the misalignment was not present.

<FIG> illustrates an example that corrects lens holder sub-assembly <NUM> misalignment for the single lens design. In <FIG>, the lens holder sub-assembly <NUM> has been moved laterally compared to the position of the lens holder sub-assembly <NUM> in <FIG>. As a result, the focusing lens <NUM> is moved into a position to catch the rays of divergent light <NUM> that travel at an angle sufficient to compensate for the misalignment. Thus, in the single-lens design, one may take advantage of the property that the divergent light <NUM> already falls upon the lens holder sub-assembly <NUM> at many different angles. As a result, instead of tilting the lens holder sub-assembly <NUM>, as in the double lens techniques discussed above, the lens holder sub-assembly <NUM> can be moved laterally to catch the rays of divergent light <NUM> traveling at the proper angle.

Active alignment for the single lens design is performed while taking into account fewer degrees of freedom than those discussed for the double lens design. For example, the active alignment may omit roll, pitch, and/or yaw in order to simplify the optimization process or reduce the number or complexity of the actuators needed to perform adjustments during active alignment.

Angular errors of the turning mirror <NUM> may complicate alignments. For example, the turning mirror <NUM> may possess an inherent defect which causes light to reflect at an improper angle or the turning mirror <NUM> may be placed improperly when mounted onto the interposer <NUM>.

<FIG> illustrates the effect angular errors have on the optical networking device <NUM>, assuming a dual lens design. In order to illustrate a clear example, <FIG> depicts only the lenses of the focusing lens array <NUM> and ferrules of the fiber-optic cable ferrules <NUM> used for transmission. Since the received light carrying incoming data does not pass through turning mirror <NUM>, the received light is not affected by the angular errors of the turning mirror <NUM>. As a result, the following explanations assume that the receiving and transmitting lenses/ferrules are capable of being adjusted independently, or that the optical networking device <NUM> performs only data transmission.

In <FIG>, transmitter <NUM> produces emitted light <NUM> which is parallelized by collimating lens array <NUM>. However, since the turning mirror <NUM> is misaligned, the emitted light <NUM> reflects off the turning mirror <NUM>, but misses the focusing lens array <NUM>. As a result, at least some of the emitted light <NUM> is blocked from reaching the fiber-optic cable ferrules <NUM>.

<FIG> illustrates an example that compensates for the angular errors caused by the misalignment of <FIG>. In <FIG> the lens holder sub-assembly is positioned and tilted to align the emitted light <NUM> reflected from the turning mirror <NUM> to the focusing lens array <NUM> and fiber-optic cable ferrules <NUM>. As a result, the emitted light <NUM> is able to pass through the lens holder sub-assembly <NUM> despite the angular error of the turning mirror <NUM>.

The position and tilt of the lens holder sub-assembly is determined by active alignment, such as the active alignment techniques described earlier in Section <NUM> for dual lens sub-assembly misalignment.

For examples that use the single lens design, the angular error of the turning mirror <NUM> can be compensated by lateral movement using the same techniques described above in Section <NUM> for single lens sub-assembly misalignment.

For example, <FIG> is a block diagram that illustrates a computer system <NUM>.

The techniques herein are performed by computer system <NUM> in response to processor <NUM> executing one or more sequences of one or more instructions contained in main memory <NUM>. Alternatively, hard-wired circuitry may be used in place of or in combination with software instructions.

Claim 1:
An apparatus comprising:
a transmitter (<NUM>) configured to emit modulated light upon which data is encoded;
a plurality of focusing lenses (<NUM>) having an optical axis and being configured to focus the modulated light into respective optical fiber ferrules (<NUM>) configured to receive respective optical fibers along a main direction,
a lens holder sub-assembly (<NUM>) that couples the plurality of focusing lenses (<NUM>) to the respective optical fiber ferrules (<NUM>), and
a connector (<NUM>) coupled to the lens holder sub-assembly (<NUM>) that directs the modulated light into one or more optical fibers, the connector being a Multiple-Fiber Push-On connector (<NUM>),
wherein the optical axis of the plurality of focusing lenses (<NUM>) is parallel to but not aligned with the main direction along which the optical fiber ferrules (<NUM>) are configured to receive the optical fibers; and
wherein the lens holder sub-assembly (<NUM>) is tilted with respect to a propagation axis of the modulated light as it is directed into the plurality of focusing lenses (<NUM>), to an angle enabling the modulated light to pass through the lens holder sub-assembly (<NUM>) despite the optical axis of the plurality of focusing lenses (<NUM>) not being aligned with the main direction along which the optical fiber ferrules (<NUM>) configured to receive the respective optical fibers.