Optical transmitter unit, optical receiver unit, and optical transceiver unit

Abstract

The optical transmitter includes an array of light sources that transmit visible light having a wavelength between 580 nm and 700 nm along each core of the multi-core fiber optic cable for reception at a corresponding array of photodetectors in the optical receiver unit, and a controller that receives data from a transmitting computer system, encodes the data by modulating the visible light output by the array of light sources, and transmits the data. The optical receiver unit includes a photodetector array for receiving the modulated visible light from the multi-core fiber optic cable; and a controller that receives the output of the photodetectors; decodes the data from the received output, and provides the decoded data to the receiving computer system. The optical transceiver unit includes an optical transmitter and an optical receiver.

Description

[Technical field]

[0001] Field The present disclosure relates to an optical transmitter unit, an optical receiver unit, and an optical transceiver unit. [Background technology]

[0002] background Fiber optic communication involves encoding data as pulses of light transmitted from a transmitter to a receiver over an optical fiber. Fiber optic communication systems are used in a wide variety of contexts to transfer information for telephone and Internet communications as well as for broadcasting television signals. Fiber optic communication systems are also widely used for intra-datacenter connectivity where emerging workloads such as machine learning and resource partitioning are significantly increasing network demands.

[0003] In conventional systems, precise alignment of the optical fiber with the light source and photodetector is essential. Thus, such systems, which require specialist packaging procedures, are expensive to manufacture. Furthermore, expensive light sources and receivers, such as single-mode and multimode lasers and silicon germanium receivers, are commonly used. Given the costs involved in such components, these systems (e.g., systems with bandwidths of 50-100 Gbps per lane) strive to maximize the data bandwidth that can be transmitted per lane (i.e., per transmitting and receiving component). This approach requires expensive and complex digital circuitry to modulate the light source and process the received optical signals.

[0004] In existing systems using light sources in the visible light spectrum, similar approaches have involved complex encoding schemes such as PAM4 (four-level pulse amplitude modulation) or OFDM (orthogonal frequency division multiplexing) employed to maximize the bandwidth offered per lane. Again, these systems require expensive and complex digital circuitry to encode and decode the signals. Further challenges arise due to chromatic dispersion of visible light signals, where different colors of visible light travel at different speeds through the fiber and potentially cause overlap or interference between signals. High speed transmission increases chromatic dispersion and accordingly limits the distance over which signals can be transmitted. It is an object of the present disclosure to address the above-mentioned challenges and any other challenges that will be apparent to one skilled in the art from the disclosure herein. Summary of the Invention

[0005] overview According to one aspect of the present disclosure, there is provided an optical transmitter unit for connection to an optical receiver unit via a multi-core fiber optic cable, the optical transmitter unit including: an array of light sources, each light source configured to transmit visible light along a respective core of the multi-core fiber optic cable for reception at a corresponding photodetector array of the optical receiver unit; and a controller configured to receive data from a transmitting computer system, and to encode and transmit the data by modulating the visible light output by the array of light sources.

[0006] The optical transmitter may include an optical filter configured to reduce chromatic dispersion. Each of the multiple light sources may be configured to form a communication path with a corresponding photodetector of the photodetector array of the optical receiver unit. The controller may be further configured to modulate the visible light output by the array of light sources and to encode and transmit data in parallel across the multiple communication channels. The controller may be further configured to transmit control information on at least one communication channel in parallel with the data. The control information may include clock forwarding information, training sequence information, or redundancy information. The controller may be configured to encode the data by using an on-off keying (OOK) encoding scheme (e.g., a non-return-to-zero encoding scheme).

[0007] Each light source may be configured to transmit visible light between multiple cores of the multi-core fiber optic cable, and each communication channel may include multiple cores of the multi-core fiber optic cable.

[0008] Each light source may be configured to transmit visible light having a wavelength between 500 nm and 700 nm, while optionally excluding wavelengths below 500 nm. Each light source may be configured to transmit visible light having a wavelength between 580 nm and 700 nm, while optionally excluding wavelengths below 580 nm.

[0009] The maximum data rate per communication channel may be 10 Gbps or less (e.g., 5 Gbps or less). The transmitter unit may include at least 50 communication channels. The transmitter may include at least 25 or 75 or 100 communication channels. The array of light sources may include a number of light sources that are not used to form a communication channel.

[0010] The controller may include analog circuitry for encoding and transmitting data. The analog circuitry may include an equalizer. The equalizer may be a feedforward equalizer.

[0011] The optical filter configured to reduce chromatic dispersion may include an optical bandpass filter configured to narrow the pulses of modulated light emitted by the light source. The optical bandpass filter may have an optical bandwidth of less than 50 nm (e.g., 10 nm). The central wavelength of the optical bandpass filter may be matched to the central wavelength of the light source.

[0012] The optical transmitter unit may include a lens unit configured to direct light emitted from the array of light sources into the core of the multi-core fiber optic cable. The lens unit may include a single optical axis of symmetry. The lens unit may include a first lens attached to the array of light sources. The lens unit may include a collimator lens configured to receive the light from the first lens and to split the light into a plurality of parallel light beams. The lens unit may include a focusing lens configured to receive the plurality of parallel light beams from the collimator lens and to focus the plurality of parallel light beams into the core of the multi-core fiber optic cable.

[0013] The optical transmitter unit may include a mechanical adapter for direct alignment of the cores of the multi-core fiber optic cable with the light sources of the light source array.

[0014] The array of light sources may include an array of micro LEDs. The light transmitter unit may include a plurality of LED drivers. The controller may encode and transmit data by controlling the LED drivers to modulate the micro LEDs.

[0015] The array of light sources may be disposed on a chiplet.

[0016] According to another aspect of the present disclosure, there is provided an optical receiver unit for connection to an optical transmitter unit via a multi-core fiber optic cable, the optical receiver unit including: a photodetector array, where each photodetector in the photodetector array is configured to receive modulated visible light from an array of light sources of the optical transmitter unit via a respective core of the multi-core fiber optic cable; and a controller configured to receive outputs of the photodetectors; decode data from the received outputs, and provide the decoded data to a receiving computer system.

[0017] Each light detector may be configured to form a communication channel with a corresponding light source. The controller may be further configured to decode data received in parallel across the multiple communication channels. At least one communication channel may include control information received in parallel with the data, and the controller may be configured to decode the data based on the control information. The control information may include clock transfer information, training sequence information, or redundancy information. The controller may be configured to decode the data by using an on-off keying (OOK) encoding scheme (e.g., a non-return-to-zero encoding scheme).

[0018] The photodetector array may include complementary metal-oxide-semiconductor (CMOS) sensors. The photodetector array may be disposed on a chiplet.

[0019] The optical receiver unit may include an optical filter configured to reduce chromatic dispersion. Each optical detector in the optical detector array may include a plurality of photodiodes. Each optical detector in the optical detector array may include a plurality of filters. The photodiodes may each be positioned to receive light from a respective one of the plurality of filters. The optical receiver unit may include a dispersive optical element configured to separate the received modulated visible light into a plurality of optical signals based on wavelength; and to direct each optical signal through a corresponding filter into a different one of the photodiodes. The optical filter configured to reduce chromatic dispersion may include the plurality of filters of the optical detector and the dispersive optical element.

[0020] The optical receiver unit may include a combining circuit configured to combine output charges of multiple photodiodes of the optical detectors in the optical detector array, the combining circuit may be configured to delay one or more of the output charges to compensate for different reception times of the multiple optical signals.

[0021] The optical receiver unit may be configured to receive modulated visible light having a wavelength between 580 nm and 700 nm.

[0022] According to another aspect of the present disclosure, there is provided an optical transceiver unit for connection to another optical transceiver unit via a multi-core fiber optic cable, the optical transceiver unit including: an array of light sources configured to transmit visible light along respective cores of the multi-core fiber optic cable for reception at a corresponding photodetector array of the optical receiver unit; a photodetector array, where each photodetector in the photodetector array is configured to receive modulated visible light from a respective core of the multi-core fiber optic cable; and a controller configured to receive first data from a computer system; and to encode and transmit the first data by modulating the visible light output by the array of micro LEDs; the controller further configured to: receive output of the photodetectors; decode second data from the output, and provide the decoded second data to the computer system.

[0023] Further optional features of the optical transceiver unit are as defined herein with respect to the optical transmitter unit and the optical receiver unit and may be combined in any combination. The present disclosure further extends to a kit of parts including an optical transmitter unit, an optical receiver unit and a multi-core fiber optic cable. A system including the same may also be provided. The present disclosure also extends to a kit of parts including a pair of optical transceiver units and a multi-core fiber optic cable. A system including the same may also be provided.

[0024] The present disclosure also extends to a method of transmitting data by using an optical transmitter unit as defined herein, the method comprising receiving data from a sending computer system, and encoding and transmitting the data by controlling a plurality of LED drivers to modulate visible light output by an array of micro LEDs. The present disclosure also extends to a method of receiving data by using an optical receiver unit as defined herein, the method comprising receiving outputs of a plurality of photodetectors of a photodetector array; decoding data from the received outputs, and providing the decoded data to a receiving computer system.

[0025] According to another aspect of the present disclosure, an optical transceiver system is provided, the optical transceiver system including: a multi-core fiber optic cable; a transmitter unit including an array of micro light emitting diodes (micro LEDs) each configured to transmit visible light along the multi-core fiber optic cable; a receiver unit including a photodetector array configured to receive the transmitted visible light; and a filtering unit disposed between the array of micro LEDs and the photodetector array, the filtering unit configured to reduce chromatic dispersion. The filtering unit may include an optical bandpass filter configured to narrow pulses of modulated light emitted by the micro LEDs.

[0026] According to another aspect of the present disclosure, an optical receiver unit for connection to an optical transmitter unit via a multi-core fiber optic cable is provided, the optical receiver unit including: a photodetector array including a plurality of photodiodes configured to receive visible light from an array of micro light emitting diodes (micro LEDs) of the optical transmitter unit via the multi-core fiber optic cable, where each photodetector in the photodetector array includes a plurality of filters and a plurality of corresponding photodiodes, each photodetector including a plurality of filters and a plurality of corresponding photodiodes, each photodiode positioned to receive light from a respective one of the plurality of filters; and a dispersive optical element configured to separate the received visible light into a plurality of optical signals based on wavelength; and to direct each optical signal through a corresponding filter and into a different one of the photodiodes.

[0027] According to another aspect of the present disclosure, there is provided an optical transmitter unit for connection to an optical receiver unit via a multi-core fiber optic cable, the optical transmitter unit including: an array of micro light emitting diodes (micro LEDs), each configured to transmit visible light along a respective core of the multi-core fiber optic cable for reception at a corresponding photodetector array of the optical receiver unit; and a lens unit configured to direct light emitted from the micro LED array into a core of the multi-core fiber optic cable, the lens unit including a single optical axis of symmetry.

[0028] This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter. The claimed subject matter is also not limited to implementations that solve any and all of the disadvantages described herein.

[0029] BRIEF DESCRIPTION OF THE DRAWINGS For a better understanding of the present invention, and to show how the same may be put into practice, reference will now be made, by way of example, to the accompanying drawings in which: [Brief description of the drawings]

[0030] [Figure 1] FIG. 1 is a perspective view of an exemplary optical transceiver system. [Figure 2A] 1 is a schematic cross-sectional view of an exemplary optical transceiver unit. [Figure 2B] FIG. 2 is a schematic plan view of an exemplary optical transceiver unit. [Diagram 3] 1 is a schematic block diagram of an exemplary optical transceiver unit. [Figure 4] FIG. 1 is a schematic diagram of a communication channel formed between a micro-LED array and a photodetector array. [Figure 5A]2 is a schematic diagram of an exemplary filtering unit of an exemplary optical transceiver system. [Figure 5B] FIG. 1 is a schematic diagram showing filtering of a light source. [Figure 6A] 1 is a schematic diagram of another exemplary filtering unit of an exemplary optical transceiver system. [Figure 6B] FIG. 1 is a schematic diagram showing filtering of a light source. [Figure 6C] 4 is a schematic timing diagram illustrating signals generated by photodiodes of a photodetector array. [Figure 6D] 6B is a schematic diagram illustrating filtering of an exemplary combining circuit of the optical transceiver system of FIG. 6A. [Figure 7A] 1 is a schematic diagram of an exemplary lens unit of an optical transceiver system. [Figure 7B] FIG. 7B is a schematic diagram showing the mounting of a first lens of the example lens unit of FIG. 7A. [Figure 8] 1 is a schematic diagram of a mechanical adapter for directing light into a multicore fiber optic cable. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0031] Detailed Description In summary, some examples of the present disclosure provide an optical transmitter unit including an array of micro light emitting diodes (micro LEDs) that transmits modulated visible light along a multi-core fiber optic cable. The modulated light is received by a photodetector array at a receiver unit. In some examples, communication channels are formed between the micro LEDs and corresponding photodetectors, and data is transmitted in parallel over multiple communication channels. Data may be transmitted at a relatively low speed (e.g., 2 Gbps) but over a relatively large number of channels (e.g., 100 or 200 channels). Transmitting over a large number of parallel channels at a slow speed may enable the use of cost-effective, off-the-shelf components such as CMOS sensors and polymer optical fibre (POF) cables, avoid the need for complex digital signal processing, and ease challenges associated with chromatic dispersion.

[0032] 1 shows an optical transceiver system 1. The transceiver system 1 includes a first transceiver unit 100A, a second transceiver unit 100B, and a connection cable 50 extending between the two transceiver units 100.

[0033] Each transceiver unit 100 is connectable to a respective computer system (C, see FIG. 3), such as a data center server, to enable data transfer between the two computer systems via a connecting cable. In other examples, one or both of the transceiver units 100 may be connected to suitable network hardware, such as a switch.

[0034] Each transceiver unit 100 includes a housing 101 that may hold the other components of the transceiver unit. A connecting component 102 may be formed on an exterior surface of the housing 101 that may connect with a corresponding connecting component of a computer system. The connecting component 102 may form a detachable connection with the computer system (e.g., via a plug and socket type arrangement). Data may be provided to and from the computer system via the connecting component 102.

[0035] Each transceiver unit 100 also includes a cable housing 103 in which a connecting cable 50 is attached. The connecting cable 50 may be removable from the cable housing 103, for example to allow replacement of a defective cable 50 or to allow a selection of cables of different lengths. In the example shown, the cable housing 103 is at the opposite end of the housing 101 to the connecting piece 102, although in other examples various configurations of the housing 101 are possible.

[0036] The transceiver unit 100 is configured to transmit and receive data as discussed in detail below. However, in other examples, a transmitter unit configured to transmit data but not receive data may be provided. Similarly, in other examples, a receiver unit configured to receive data but not transmit data may be provided.

[0037] Cable 50 is a multi-core fiber optic cable. As such, cable 50 includes a plurality of fiber optic cores (51, see FIG. 4) disposed therein. In one example, cable 50 is a polymer optical fiber (POF) cable. In one example, cable 50 includes 200 cores. In other examples, cable 50 may include more than 200 cores.

[0038] In another example, cable 50 is a multi-core fiber optic cable that includes a bundle (i.e., a plurality) of imaging fibers. The bundle may include thousands or tens of thousands of imaging fibers. Each imaging fiber may be thin (e.g., less than 100 microns or less than 10 microns).

[0039] 2A and 2B show a schematic of the transceiver unit without the housing 101. The transceiver unit 100 includes a board (e.g., an interposer board) 111 on which the other components of the transceiver unit 100 are disposed and which provides electrical connections between the components.

[0040] The connection piece 102 is formed on one end of the interposer board 111 and may be, for example, integral thereto.

[0041] The transceiver unit 100 further includes a micro LED array 120. The micro LED array 120 is electrically connected to a number of LED drivers 130 that drive the micro LEDs in the micro LED array 120. In one example, one driver 130 is provided for each LED in the array 120.

[0042] The micro LED array 120 is above the driver 130 in the example shown. Thus, the driver 130 is discrete and separate from the micro LEDs. However, in other examples, the driver 130 may be co-packaged or stacked with the micro LEDs. The driver 130 drives the micro LED array 120 to generate modulated visible light that is transmitted along the cable 50.

[0043] The micro LED array 120 is one example of an array of light sources configured to generate visible light. In other examples, other types of LEDs or vertical-cavity surface-emitting lasers (VCSELs) may be employed to generate the visible light.

[0044] The transceiver unit 100 further includes a photodetector array 150 including a plurality of photodetectors. The photodetector array 150 may include an image sensor such as a complementary metal oxide semiconductor (CMOS) sensor, a charge-coupled device (CCD), etc. The photodetector array 150 receives modulated visible light from the micro LED array 120 of another transceiver unit 100 via the cable 50 and generates an electrical signal therefrom. Like the micro LED array 120, the photodetector array 150 may be disposed above the driver 130.

[0045] The transceiver unit 100 further includes a controller 140. The controller 140 is configured to receive data from a computer system via the connecting component 102. The controller 140 controls the LED driver 130 to modulate the visible light output by the array of micro LEDs 120, thereby encoding the data and transmitting it along the cable 50.

[0046] The controller 140 is also configured to receive and decode the electrical signals from the photodetector array 150. The decoded signals contain the data transmitted by the separate transceiver unit 100. The controller 140 then provides the data via the connecting component 102 to the connected computer system.

[0047] In one example, an On-Off Keying (OOK) encoding scheme may be used to encode the data. In an OOK encoding scheme, a simple two-level signal is employed where a high value represents a binary "1" and a low value represents a binary "0". Alternatively, a high value may represent a "0" and a low value may represent a "1". For example, the OOK encoding scheme may be a Non-Return to Zero (NRZ) encoding scheme. In NRZ, the emitted light may only have a high or low value without any other value representing a neutral or quiescent state.

[0048] The controller 140 may include analog circuitry for encoding the signals and / or for controlling the LED driver 130. The controller 140 may include analog circuitry for decoding the electrical signals received from the photodetector array 150. In some examples, the controller 140 may not include any digital circuitry for processing the signals.

[0049] For example, controller 140 may include one or more equalizers implemented with analog circuitry. Controller 140 may include a feed forward equalizer (FFE) that forms part of the analog circuitry for encoding the signal or for decoding the signal. Controller 140 may include a decision feedback equalizer (DFE) that may form part of the analog circuitry for decoding the signal.

[0050] The micro LED array 120 may be optically connected to the cable 50 by an LED cabling unit, generally designated by reference numeral 121. The LED cabling unit 121 may include one or more lenses for directing light emitted by the micro LED array 120 into the cable 50 and / or one or more filters for filtering the emitted light. The lenses and filters of the cabling unit 121 will be discussed in detail below. The LED cabling unit 121 may further include any suitable hardware for constraining and positioning the cable 50 or its fibers.

[0051] Similarly, photodetector array 150 may be optically connected to cable 50 by photodetector cable connection unit 151. Connection unit 151 may include one or more lenses for directing received light through cable 50 to photodetector array 150 and / or one or more filters for filtering the received light. The lenses and filters of cable connection unit 151 will be discussed in detail below.

[0052] 2B shows diagrammatically two connecting cables 50: one connected to the micro-LED array 120 for transmitting signals and another connected to the photodetector array 150 for receiving signals. However, the transceiver units 100 may instead be connected by a single connecting cable 50 having multiple cores or fibers, with some fibers or cores of the cable 50 being used for transmission by the transceiver unit 100 and other fibers or cores being used for reception of signals by the transceiver unit 100.

[0053] FIG. 3 illustrates a schematic of an exemplary transceiver unit 100. In addition to the components described above, FIG. 3 illustrates that a number of amplifiers 160 may be connected between the photodetector array 150 and the controller 140. The amplifiers 160 may amplify the output of the photodetector array 150 so that a usable voltage is provided to the controller 140. The amplifiers 160 may include a number of discrete transimpedance amplifiers (TIAs). In another example, the amplifiers 160 may be integrated into the photodetector array 150. That is, the amplifiers 160 and the photodetectors 150 may be located on the same die.

[0054] 3 also shows that the transceiver unit 100 includes a transmitter section 100T and a receiver section 100R. The controller 140 and the transmitter section 100T may form a transmitter unit. The controller 140 and the receiver section 100R may form a receiver unit. In some examples, one of the transmitter section 100T or the receiver section 100R may be omitted to provide a device that includes only a receiver unit or only a transmitter unit. In such examples, the controller 140 may include circuitry for only transmitting or only receiving.

[0055] In some examples, components of transceiver unit 100 may be implemented as one or more chiplets. A chiplet is a small integrated circuit (i.e., a single die) designed to be combined with other chiplets on an interposer substrate to form a package. For example, the chiplets may communicate with each other by using a suitable communication protocol, such as the Universal Chiplet Interconnect Express (UCIe) protocol.

[0056] In particular, the transceiver unit 100 may include a first chiplet that includes a micro LED array 120. The transceiver unit 100 may also include a second chiplet that includes a photosensor array 120. The second chiplet may also include an amplifier 160. In another example, the transceiver unit 100 includes a chiplet that includes a micro LED array 120 and a photosensor array 120.

[0057] By locating some or all of the transmitter or receiver components on a chiplet, these aspects of the transceiver unit 100 are advantageously modular, facilitating easy construction of receiving units, transmitting units, and transceiver units having various numbers of transmitter sections 100T and / or receiver sections 100R.

[0058] 4, there is shown an arrangement of channels provided by the micro LED array 120 and the photodetector array 150. In particular, FIG. 4 shows that the micro LED array includes a plurality of communication channels 200, where each communication channel 200 is formed between an LED 122 and a photodetector 152 of the micro LED array 150. For simplicity in the figure, only some of the communication channels 200, LEDs 122, photodetectors 152 and cores 51 have been labeled.

[0059] In one example, each communication channel 200 corresponds to a single core 51 of the cable 50. That is, the LED 122 and corresponding photodetector 152 may communicate along exactly one core 51. However, in other examples, each communication channel 200 may include multiple cores 51. A core 51 may receive light from a single LED 122 or multiple LEDs 122. For example, if a cable 50 that includes imaging fibers is used, multiple imaging fibers may be used per channel 200.

[0060] Thus, the number of available communication channels 200 provided is defined by the number of LEDs 122 and corresponding photodetectors 152. In the example shown, the micro LED array is a 10×10 array and the photodetector array 150 is a 10×10 array. Thus, 100 communication channels 200 may be available between the micro LED array 120 and the photodetector array 150. In other examples, other sizes of micro LED arrays 120 and photodetector arrays 150 (e.g., 20×20 or 30×30) may be provided to provide more communication channels.

[0061] In one example, the micro LEDs 122 are configured to emit longer wavelength light in the visible spectrum while not transmitting shorter wavelength light. For example, the LEDs 122 may emit yellow or red light. In other words, visible light having a wavelength in the range of 580-700 nanometers (nm), excluding wavelengths below 80 nm. In another example, the wavelength range may be 500-700 nm. The use of longer wavelength visible light may reduce chromatic dispersion.

[0062] The maximum data rate on each communication channel 200 depends on the rate at which the LEDs 122 are modulated by the controller 140. In one example, the maximum data rate per channel 200 is 500 Megabits per second (Mbps). In another example, the maximum data rate per channel 200 is 2 Gigabits per second (Gbps). In other examples, the data rate per channel 200 is less than 10 Gbps (e.g., less than 8 Gbps, less than 7 Gbps, less than 6 Gbps, less than 5 Gbps, less than 4 Gbps, or less than 3 Gbps). In one example, the micro LED array 120 is a micro LED array 120 manufactured by Lumiode, Inc. or Lumileds Holding BV, which can be modulated at a sufficiently high rate to enable data transfer.

[0063] These maximum data rates may be relatively slow compared to other optical transmission systems that employ laser light sources or complex encoding schemes. However, the large number of available channels 200 allows the controller 140 to transmit data on multiple channels 200 in parallel. For example, a transceiver system 1 with 100 channels 200 at a 2 Gbps transfer rate provides a bandwidth of 200 Gbps. Larger bandwidths can easily be provided by providing larger arrays 120 and 150 or more cables 50. The use of commodity components such as visible micro-LEDs and CMOS photodetector arrays allows for cost-effective deployment of a large number of channels 200.

[0064] One or more of the communication channels 200 may be a control channel 201 used by the controller 140 to transmit control signals instead of data. For example, the control channel 201 may carry clock transfer information, training sequence information, or redundancy information. Similarly, the controller 140 may use the control signals received on the control channel 201 to decode the received signals. For example, the controller 140 may use the control signals in clock data recovery, forward error correction, or equalization.

[0065] In one example, not all of the LEDs 122 and photodetectors 152 are used as a communication channel 200. For example, it may be desirable to provide more LEDs 122 than are required for a communication channel 200. This may be referred to as "over-populating" the LEDs 122. Thus, in the event of a failure of an LED 122, another LED 122 may be used to form a replacement communication channel. Over-populating the LEDs 122 may also aid in alignment of the LEDs 122 with the core of the cable 50. For example, a misaligned LED 122 may not be used as a communication channel 200 in view of the large number of other available LEDs 122. In another example, multiple LEDs 122 may be provided for use in a single communication channel 200. Thus, even if some of the multiple LEDs 122 used for a communication channel 200 are misaligned or in a failed state, other of the LEDs 122 assigned to that channel will be aligned and / or in proper operation.

[0066] 5A and 5B show an exemplary filtering unit 170 configured to filter light emitted from the micro-LEDs 122.

[0067] As discussed above, chromatic dispersion poses challenges in optical communications. Specifically, it can limit the bandwidth-distance product (i.e., how much data can be transmitted over how far with a reasonable error rate). This is because each wavelength of light travels through the medium of the core 51 of the cable 50 at a different speed, thereby spreading out the signal pulse as it travels along the cable 50. This can reduce signal fidelity and can be a particular challenge with wide linewidth light sources, including LEDs, and also with POF cables.

[0068] 5A shows a filtering unit 170 (e.g., as part of the LED cabling unit 121) positioned between the micro LEDs 122 and the cable 50. The LED cabling unit 121 may additionally include a lens unit 180 (e.g., disposed between the filtering unit 170 and the micro LEDs 122). In addition, the photodetector cabling unit 151 may include another lens unit 181.

[0069] The filtering unit 170 includes an optical filter that reshapes the light pulses emitted by the micro LEDs 122. The resulting line pulses may have a narrow linewidth or a narrow full width at half maximum. The optical filter may be a bandpass filter.

[0070] Figure 5B illustrates the function of the filtering unit 170. The top graph G1 in Figure 5B shows a broad pulse emitted by the micro LED 122. The middle graph G2 illustrates the spectral filtering provided by the filtering unit 170, which filters out light that does not fall within a particular wavelength range. The bottom graph G3 shows the broad pulse of graph G1 filtered by the filtering unit 170. The resulting pulse is significantly narrower than the pulse emitted by the micro LED 122, and is therefore less vulnerable to chromatic dispersion.

[0071] In one example, the bandpass filter has an optical bandwidth of 10 nm. In other examples, the optical bandwidth may be wider or narrower (e.g., 5 nm, 15 nm, 20 nm, 30 nm, 40 nm, or 50 nm). The central wavelength of the optical filter may match the central wavelength of the micro LEDs 122.

[0072] 5A shows filtering unit 170 disposed after lens unit 180, it will be understood that filtering unit 170 may be disposed elsewhere. For example, filtering unit 170 may be in front of the lens unit. In other examples, filtering unit 170 may be disposed within photodetector cable connection unit 151 or elsewhere within receiver section 100R to filter light received from cable 50.

[0073] 6A and 6B show an alternative filtering unit 170-1 that resides between the cable and the photodetector 152 and includes a dispersive optical element 172 and a number of filters 173a,b,c.

[0074] The dispersive optical element 172 separates the received light by wavelength. In the example shown, the dispersive optical element 172 is a lens. However, one or more lenses, prisms, or zone plates may be employed to separate the light.

[0075] Each wavelength range of the separated light is then directed to a different filter 173a,b,c. The filters 173 may take the form of a filter coating formed on the photodetector 152. In one example, the photodetector 152 includes multiple photodiodes (153, see FIG. 6C), each corresponding to a filter 173. For example, the photodetector 152 may have red, green, and blue photodiodes.

[0076] 6B illustrates the function of the filtering unit 170-1. The top graph G4 shows a broad pulse emitted by the micro LED 122. The middle graph G5 shows that the dispersive optics 172 and filter 173 disperse or filter the light into multiple wavelength ranges. The bottom graph G5 shows that the broad pulse of graph G4 is filtered into multiple narrower wavelength ranges.

[0077] The filtering unit 170-1 separates the light of different wavelengths so that the light of different wavelengths can be separately detected by the photodetector 152. Thus, chromatic dispersion can be avoided or mitigated.

[0078] In the example shown, the light is dispersed into three wavelength ranges, which are then directed to three filter coatings 173. In other examples, the light may be dispersed into more or fewer wavelength ranges for reception at a corresponding number of filter coatings.

[0079] As noted above, different wavelengths of light will travel at different speeds through cable 50. Thus, a single light pulse will result in different separated wavelengths output from dispersive optic 172 arriving at respective photodiodes 153 at different times.

[0080] FIG. 6C shows on a timing diagram the output of three photodiodes 153 receiving light at different times and therefore producing output at different times.

[0081] 6D shows a combining circuit 154 for combining the signals received at the various photodiodes 153 of the photodetector 152. The combining circuit 154 combines the output charges from the photodiodes 153 with a deterministic timing delay (e.g., by using transistors).

[0082] For example, it may be found that light having a certain wavelength will have a certain delay in traversing a particular cable 50. For example, there may be approximately a 150 ns delay for 450 nm-455 nm light traversing 30 m of plastic PMMA. Similar known delays may be calculated for other wavelengths of light. Thus, circuitry 154 may delay the output charge received from photodiode 153 to resynchronize and provide a summed or compared output.

[0083] 7A and 7B show an exemplary lens unit 180. The lens unit 180 is configured to guide light emitted from the micro LED array 120 through the waveguide 52 into the core 51 of the cable 50. In some examples, an array of micro lenses is used to focus the output of each of the LEDs 122 of the micro LED array 120. In such examples, each micro lens in the array has its own axis of symmetry. In other words, there is one optical axis of symmetry per lens such that a micro lens array has multiple optical axes of symmetry. However, micro lens arrays may require precise alignment and therefore may be expensive to manufacture. In contrast, the lens unit 180 provides a single optical axis of symmetry for the micro LED array 120.

[0084] The lens unit 180 includes a first lens 181 that receives light from the micro LED array 120. In other words, the lens unit 180 includes a single lens 181 having a single optical axis of symmetry, and the single lens 181 receives light from all of the micro LEDs 122.

[0085] 7B, the lens 181 may be attached to the micro LED array 122. For example, the lens 181 may be bonded to the interposer 111 or another substrate that supports the micro LED array 122. This allows the lens 181 to capture substantially all of the light from the micro LED array 122 while minimizing total internal reflection losses.

[0086] The lens unit 180 further includes a collimator lens 182 that receives light from the first lens 181 and separates the received light into multiple parallel beams B. Each beam corresponds to the output of a separate micro-LED 122 and thus represents a separate channel 200.

[0087] Lens unit 180 further includes a focusing lens 183 that receives the parallel light beams from collimator lens 182 and focuses them onto the cable waveguide 52 .

[0088] 8 illustrates, in schematic form, another exemplary mechanism for directing light emitted from the micro LED array 120 into the core 51 of the cable 50. In FIG. 8 , a mechanical adapter 190 receives the core 51 of the cable 50 or a corresponding waveguide 52. The mechanical adapter 190 directly aligns each waveguide 52 with a respective micro LED 122. In other words, the mechanical adapter 190 holds the core 51 such that no intervening lens is required to direct light emitted by the micro LED 122 into the core 51.

[0089] The systems described herein may enable the use of commodity electronic components in optical communications. The use of such components allows for cost-effective installation of multiple parallel data transmission channels and allows redundancy to be built into the transmitter. The systems described herein avoid the need for complex encoding schemes and associated digital signal processing hardware. Additionally, the systems described herein provide a cost-effective method of mitigating chromatic dispersion to enable the installation of high bandwidth communications over longer distances.

[0090] It will be understood that the controller or processor or processing system or circuitry referred to herein may in fact be provided by a single chip, or integrated circuit, or multiple chips or integrated circuits, optionally provided as a chipset, an application specific integrated circuit (ASIC), a field programmable gate array (FPGA), a digital signal processor (DSP), a graphic processing unit (GPU), etc. A chip or chips may include circuitry (and possibly firmware) for embodying at least one or more of a data processor or processors, a digital signal processor or processors, baseband circuitry, and radio frequency circuitry that are configurable to operate according to exemplary embodiments. In this regard, exemplary embodiments may be implemented at least in part by computer software stored in a (non-transitory) memory and executable by a processor, or by hardware, or by a combination of tangibly stored software and hardware (as well as tangibly stored firmware). It will be understood that the controllers described herein may include both digital and analog circuitry. Reference to a particular functionality provided by analog circuitry does not exclude the possibility of the controller performing other functions using digital circuitry.

[0091] Although at least some aspects of some embodiments described herein with reference to the accompanying drawings include computer processes carried out in a processing system or processor, the invention also extends to computer programs (particularly computer programs on or in a carrier) adapted to realize the invention. The computer programs may be in the form of non-transitory source code, object code, code intermediate source and object code (such as in specially compiled form) or any other non-transitory form suitable for use in the implementation of the process according to the invention. The carrier may be any entity or device capable of carrying a program. For example, the carrier may include a storage medium such as a solid state drive (SSD) or other semiconductor-based RAM; ROM (e.g. CD ROM, semiconductor ROM); magnetic recording medium (e.g. floppy disk or hard disk); optical memory devices in general; and so on.

[0092] The examples described herein should be understood as illustrative examples of embodiments of the present invention. Further embodiments and examples are envisioned. Any feature described with respect to any one example or embodiment may be used alone or in combination with other features. In addition, any feature described with respect to any one example or embodiment may also be used in combination with one or more features of any other of the examples or embodiments, or in any combination of any other of the examples or embodiments. Furthermore, equivalents and modifications not described herein may also be employed within the scope of the present invention, as defined in the claims.

Claims

1. 1. A system including an optical transmitter unit connected to an optical receiver unit via a multi-core optical fiber cable, the optical transmitter unit comprising: an array of light sources, each light source configured to transmit visible light having a wavelength between 580 nm and 700 nm along a respective core of the multi-core fiber optic cable for reception at a corresponding array of photodetectors of the optical receiver unit; and a transmitter controller configured to receive data from a transmitting computer system and to encode and transmit the data by modulating the visible light output by the array of light sources; the optical receiver unit includes a photodetector array, each photodetector in the photodetector array configured to receive modulated visible light from the array of light sources of the optical transmitter unit via each respective core of the multi-core optical fiber cable; A receiver controller configured to receive the output of the photodetector, decode data from the received output, and provide the decoded data to a receiving computer system.

2. each of the plurality of light sources is configured to form a communication channel with a corresponding light detector in the light detector array of the optical receiver unit; the transmitter controller is further configured to modulate the visible light output by the array of light sources to encode the data for transmission in parallel across multiple communication channels; Optionally, the controller is further configured to transmit control information over at least one communication channel in parallel with the data.

3. The system of claim 2 , wherein the maximum data rate per communication channel is less than or equal to 5 Gbps and / or the optical transmitter unit includes at least 50 communication channels.

4. The system of claim 2 , wherein the array of light sources includes a plurality of light sources that are not used to form a communication channel.

5. 10. The system of claim 1, wherein the optical transmitter controller includes analog circuitry for encoding and transmitting the data.

6. The system of claim 1 , wherein the optical transmitter includes an optical bandpass filter configured to narrow the pulses of modulated light emitted by the light source.

7. The optical transmitter includes a lens unit configured to direct light emitted from the array of light sources into the cores of the multi-core optical fiber cable, the lens unit including a single optical axis of symmetry. The lens unit optionally comprises: a first lens attached to the array of light sources; a collimator lens configured to receive light from the first lens and separate the light into a plurality of parallel light beams; 2. The system of claim 1, further comprising a focusing lens configured to receive the plurality of collimated light beams from the collimator lens and focus the plurality of collimated light beams into the cores of the multi-core fiber optic cable.

8. The system of claim 1 , wherein the optical transmitter includes a mechanical adapter for directly aligning cores of the multi-core fiber optic cable with light sources of the array of light sources.

9. The system of claim 1 , wherein the array of light sources is an array of micro LEDs.

10. The system of claim 1 , wherein the array of light sources is disposed on a chiplet.

11. The system of claim 1 , wherein the visible light excludes wavelengths below 590 nm.

12. each photodetector configured to form a communication channel with a corresponding light source; 2. The system of claim 1, wherein the receiver controller is further configured to decode data received in parallel across multiple communication channels, optionally at least one communication channel including control information received in parallel with the data, and wherein the controller is configured to decode the data based on the control information.

13. The system of claim 1 , wherein the photodetector array comprises a complementary metal oxide semiconductor, CMOS, sensor optionally disposed on a chiplet.

14. each photodetector in the photodetector array includes a plurality of filters and a plurality of corresponding photodiodes each positioned to receive light from a respective one of the plurality of filters; The optical receiver unit further includes a dispersive optical element, the dispersive optical element comprising: Separating the received modulated visible light into a plurality of optical signals based on wavelength; configured to direct each optical signal through a corresponding filter into a different one of the photodiodes; the optical receiver unit optionally further comprises a combining circuit configured to combine output charges of the plurality of photodiodes of the optical detectors in the optical detector array; The system of claim 1 , wherein the combining circuit is configured to delay one or more of the output charges to compensate for different reception times of the multiple optical signals.

15. An optical transceiver unit connected to another optical transceiver unit via a multi-core optical fiber cable, wherein each optical transceiver unit comprises: an array of light sources configured to transmit visible light having a wavelength between 580 nm and 700 nm along each core of the multi-core optical fiber cable for reception at a corresponding array of photodetectors in other optical transceiver units; a photodetector array, each photodetector in the photodetector array configured to receive modulated visible light from a respective core of the multi-core fiber optic cable; and a controller configured to receive first data from a computer system and encode and transmit the first data by modulating the visible light output by the array of light sources; the controller is further configured to receive the output of the photodetector, decode second data from the output, and provide the decoded second data to the computer system.

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