Optical signal transmitter apparatus and method

Abstract

An optical communication transmitter apparatus comprising: a plurality of semiconductor light devices each semiconductor light device comprising one or more aperture elements for emitting light, wherein the plurality of semiconductor light device are configured to be driven by driving signals to produce modulated optical communication signals; driving circuitry comprising a plurality of driving devices for said plurality of semiconductor light emitting devices, wherein the number of semiconductor light devices is greater than the number of driving devices; one or more input connections for receiving one or more input signals representing input data, wherein the number of driving devices is greater or equal to the number of input connections; signal dividing circuitry between the one or more input connections and the plurality of driving devices configured to divide the plurality of input signals to produce a plurality of divided signals representing said input data, wherein the driving circuitry is configured to produce driving signals in response to receiving said divided signals; wherein the transmitter further comprises signal delivery circuitry configured to selectively deliver driving signals produced by the plurality of driving devices to one or more groups of one or more the plurality of semiconductor light devices.

Description

[0001] Optical Signal Transmitter Apparatus and Method

[0002] Field

[0003] The present invention relates to an optical signal transmitter apparatus, for example an optical wireless communication transmitter, and associated method.

[0004] Background

[0005] It is known to provide wireless data communications using light instead of radio frequencies to transmit and receive data wirelessly between devices. Data may be transmitted using light by modulating at least one property of the light, for example the intensity of the light. Methods that use light to transmit data wirelessly may be referred to as optical wireless communications (OWC) or light communications (LC). LiFi is one form of optical wireless communication.

[0006] In Optical Wireless Communication systems (for example, LiFi systems), usually a number of Access Points (APs) communicate with a number of Stations (STAs). Both the Access Points and the Stations may be, for example, simplex, half duplex or full duplex devices, capable of transmitting and receiving communication data at the same time.

[0007] At high speed, optical detectors may be relatively small, due to the inverse-relationship between detector size and its speed. Due to the small detector size, a high optical emission power may be required at the transmitter. However, high power Vertical-cavity surface-emitting laser (VCSEL) sources may be relatively slow because speed is inversely proportional to emitted optical power. Therefore, there is a need for a high power and high bandwidth emitter solution.

[0008] Electrical to optical energy conversion efficiency does not usually exceed 20% in widely available LASERS. Therefore, the use of high power optical sources results in high power consumption. There is also a need to reduce power consumption for high speed OWC solutions.

[0009] In addition, although high optical power is beneficial, there is a limit on how much optical power an emitter can produce when considering eye and skin safety. The available communication resources in OWC are typically shared between users within the coverage area. Reducing the coverage area can result in increasing the throughput per unit area.

[0010] Summary

[0011] In a first aspect, there is provided an optical communication transmitter apparatus comprising: a plurality of semiconductor laser light devices each semiconductor light device comprising one or more aperture elements for emitting light, wherein the plurality of semiconductor light device are configured to be driven by driving signals to produce modulated optical communication signals wherein each semiconductor light device comprises a plurality of aperture elements configured to emit light; driving circuitry comprising a plurality of driving devices for said plurality of semiconductor light emitting devices, wherein the number of semiconductor laser light devices is greater or equal than the number of driving devices such that each driving device is configured to produce a drive signal for driving a corresponding group of one or more semiconductor laser devices thereby to produce modulated optical communication signals; one or more input connections for receiving one or more input signals representing input data, wherein the number of driving devices is greater or equal to the number of input connections; signal dividing circuitry between the one or more input connections and the plurality of driving devices configured to divide the plurality of input signals to produce a plurality of divided signals representing said input data, wherein the driving circuitry is configured to produce driving signals in response to receiving said divided signals; wherein the transmitter further comprises signal delivery circuitry configured to selectively deliver driving signals produced by the plurality of driving devices to one or more groups of one or more the plurality of semiconductor light devices.

[0012] The semiconductor light devices may comprise a VSCEL (Vertical-cavity surfaceemitting laser) device and wherein each aperture element comprises an aperture of the VCSEL device. Each semiconductor device may comprise a multiple aperture VCSEL device. The one or more input signals may represent one or more data streams.

[0013] Dividing the plurality of input signals comprises multiplexing and / or distributing the input signals.

[0014] Each aperture element may comprise an aperture and / or window that allows light to pass through. Each aperture element may comprise one or more connectors or terminals for example, a cathode and anode. The one or more connectors may be configured to receive a signal, for example, a driving signal.

[0015] Each of the driving devices may be characterised by an impedance or other electrical property and wherein the plurality of semiconductor light devices and / or the aperture elements of each group of semiconductor light devices are connected in an arrangement to substantially match the impedance or other electrical property of each group to the corresponding driving device.

[0016] Each of the driving devices may be characterized by a first impedance and wherein each semiconductor light device and / or respective aperture element is characterized by a second, lower impedance.

[0017] The semiconductor emitter devices may comprise semi-conductor lasers. The semiconductor emitter device may comprise light emitting diodes.

[0018] Each semiconductor device of a group may be connected in a series arrangement. Each aperture element of each semiconductor light device of a group may be connected in a series arrangement. Each semiconductor device may be connected in a parallel arrangement, wherein each semiconductor device comprises multiple apertures elements connected in a series arrangement.

[0019] Each driving device may be suitable and / or intended for use with a single aperture semiconductor laser. The output impedance of each driving device may be in the range 10 to 120 Ohms, optionally substantially 50, further optionally substantially about 60.

[0020] The semiconductor light devices may comprise at least one shared connection, for example, an anode, between the aperture elements. Each group of semiconductor light devices may comprise a shared connection. The shared connection may be for receiving a driving signal.

[0021] The impedance of the semiconductor light devices may be in dependence on the number of aperture elements of the semiconductor light device. The impedance of the semiconductor light devices may be in dependence on the properties of the aperture elements. Each of the semiconductor light devices may comprise a monolithic structure, wherein each of the semiconductor light devices comprise monolithically integrated VCSELs

[0022] Each aperture element may comprise a corresponding connection configured to receive at least part of a driving signal, wherein the aperture element is configured to emit light in the form of a modulated optical signal in response to receiving said driving signal.

[0023] The semiconductor light devices and / or aperture elements may comprise low power light sources. The semiconductor light devices and / or aperture elements may comprise low power light sources having power under 300 mW, optionally under 5 mW, optionally under 3 mW. The light emitted from one or more of said semiconductor light devices may optically combine in free space to transmit signals across a larger signal coverage area.

[0024] The plurality of semiconductor light devices may be arranged in a plurality of addressable groups, wherein each driving device is configured to drive one or more semiconductor light devices, optionally all, semiconductor light devices of an addressable group.

[0025] The driving signal delivery circuitry may be configured to selectively deliver the driving signals from the plurality of driving devices to one or more groups of the semiconductor laser devices in accordance with a pre-determined procedure.

[0026] The pre-determined procedure may comprise a beam selection and / or based on user and / or object tracking.

[0027] The apparatus of any preceding claim, wherein the driving signal delivery circuitry is configured to selectively deliver driving signals to the plurality of semiconductor devices subject to the constraint that only aperture elements separated by a minimum distance apart are driven at substantially the same time.

[0028] The minimum distance may be selected based on an eye-safety requirements, for example, the pre-determined distance may be at least 7mm. The pre-determined procedure may comprise an algorithm or other set of instructions. The beam selection algorithm may comprise beam activation and / or user tracking algorithm. The beam selection algorithm may use or be based on a machine learning algorithm.

[0029] The pre-determined procedure may be dependent on an output from a further sensor, for example, a proximity or presence sensor. The further sensor may comprise a global positioning sensor. The pre-determined procedure may be dependent on an output from a further processing resource.

[0030] The signal dividing circuitry may comprise one or more dividing stages, optionally two or more, wherein each signal dividing stage is configured to divide one input signal into more than one signal. The signal dividing stage may divide the signal for the subsequent stage. The signal dividing stage may divide the power and / or current and / or voltage of the received signals for the subsequent stage and / or the driving circuitry such that the output signals from each stage have a lower power, current and / or voltage than the input signals to each stage.

[0031] The input data signals may be representative of a plurality of data streams, and wherein the plurality of the semiconductor light devices comprise a plurality of groups of semiconductor light devices, wherein each group of semiconductor light devices is configured to selectively transmit optical signals representing a corresponding data stream.

[0032] The dividing circuitry may comprise a plurality of signal and / or power divider devices arranged into a plurality of dividing stages, wherein each input stage is configured to receive a plurality of input signals and output a greater number of output signals for the subsequent stage and / or for the driving circuitry

[0033] The divider devices may comprise at least one of wideband dividers, resistive divider, power divider, Wilkinson divider. The driving devices may comprise a low power and high bandwidth driving device. Each driving device may be configured to be operated with a power under 300 mW, optionally under 5 mW, optionally under 3 mW. Each driving device may have a bandwidth in the range of at least 100 MHz and up to 3 GHz, optionally up to 5 Ghz, optionally, up to 30 GHz. The apparatus may comprise by-pass circuitry provided between the input connections and the driving circuitry, wherein the by-pass circuitry is operable to provide the input signals to the driving circuitry thereby to by-pass the dividing circuitry.

[0034] The signal dividing and / or the driving circuitry and / or the driving signal delivery circuitry may comprise linking components, wherein the linking components comprise amplifier and / or other RF components

[0035] The dividing circuitry and / or the driving circuitry may be provided in a plurality of stages and wherein pre and / or post amplifiers or other RF components are provided between each stage.

[0036] The aperture elements of each semiconductor light device may be arranged in a first spatial arrangement, such that, when the semiconductor light devices are arrayed or otherwise arranged together the aperture elements form a second spatial arrangement, wherein the second spatial arrangement comprises a non-uniform arrangement and / or shape.

[0037] The shape may comprises a regular polygon shape. The regular polygon shape may comprise a regular polygon having N sides, wherein N is at least 3. The regular polygon shape may comprise a hexagonal shape. The regular polygon shape may approximate a circle and / or may comprise a circle-like shape.

[0038] The first spatial arrangement may comprises an arrangement in which the apertures are at one or more corner and / or edge regions of the device and the second spatial arrangement comprises an arrangement in which corner and / or edge regions of two or more light devices are adjacent to each other.

[0039] The non-uniform arrangement may comprise a first region having a first density of aperture elements and a second region having a higher density of aperture elements, optionally wherein the higher density region is surrounded by the lesser density region.

[0040] In accordance with a second aspect there is provided a method of producing modulated optical communication signals for a plurality of semiconductor light devices wherein the plurality of semiconductor light devices comprise one or more apertures for emitting light, the method comprising: receiving, at one or more input connections, one or more input signal representing input data; dividing, by signal dividing circuitry, said input signal into a plurality of divided signals representing said input data; producing, by driving circuitry, a plurality of driving signals in response to receiving said divided signal, wherein the driving circuitry driving comprising a plurality of driving devices and wherein the number of semiconductor light devices is greater than the number of driving devices and wherein the number of driving devices is greater or equal to the number of input connections; selectively delivering said driving signals produced by the plurality of driving devices to one or more groups of one or more of a plurality of semiconductor light devices; producing modulated optical communication signals by the semiconductor light devices in response to receiving said driving signals.

[0041] In accordance with a further aspect, there is provided a segmented monolithically integrated VCSEL chip system activators wherein two or more apertures (multi apertures) on the same monolithic emitter chip are connected in a series. The system may comprise multiple arrays of multi-aperture VCSELs (arrays of arrays) in-series. The system may be configured to produce one or more selective beams. The system may also comprise a user tracking system.

[0042] The two or more apertures may be arranged in two or more adjacent shaped segments wherein multi-apertures are positioned at the edges. The shaped sections may be quadrants wherein the multi-apertures are positioned in a quadrant corner, especially the inner most corner of each quadrant. The multiple apertures of the segments may form a hexagonal arrangement. The hexagonal arrangement may optimal for a circular illumination profile and / or coupling to a fibre optic.

[0043] Each quadrant may have four apertures that are connected in-series.

[0044] The arrangement may make it easier to drive with a better matching to the driving electronics. The architecture may solve the problem of driving high power and high speed directly modulated lasers.

[0045] A plurality of segments may be enabled at the same time to deliver a higher irradiance. This may have the effect of higher signal to noise ratio.

[0046] An eye-safe system may be achieved by proving spacing between the activated multisegment beams exceeding 5mm to 100mm, preferably > 7 mm. The advantage of the multi segmented multi aperture array may be an eye-safe high optical power may be emitted from the emitter. A single emitter system may not be able to achieve this sort of eye safety.

[0047] The system may include a GPS, algorithm, artificial intelligence and machine learning to help locate and track a use.

[0048] The architecture may allow few current drivers to drive few segmented arrays within the VCSEL emitter array.

[0049] The multi-segments array may have multiple segments enabled at the same time to deliver a higher irradiance (translates to a higher signal to noise ratio). An eye-safe approach may be achieved by enabling a larger spacing between the activated multisegment beams exceeding > 7 mm. In such approach, any eye-safe high optical power may be emitted from the emitter array that would have been non-eye safe if it was emitted by a single emitter source. Therefore, the emitter architecture may offer an additional feature related to eye-safety optical wireless transmission.

[0050] Therefore, the emitter architecture may provide eye-safe optical wireless transmission.

[0051] The device is configured to produce one or more selective beams. The device may comprise a user tracking system.

[0052] The two or more apertures may be arranged in two or more adjacent shaped segments wherein multi-apertures are positioned at the edges.

[0053] Preferably the shaped sections are quadrants wherein the multi-apertures are positioned in a quadrant corner, especially the inner most corner of each quadrant.

[0054] Most preferably the multi- apertures form a hexagonal arrangement.

[0055] The hexagonal arrangement is optimal for a circular illumination profile or coupling to a fibre optic.

[0056] Preferably each quadrant would have four apertures that are connected in-series. This arrangement makes it easier to drive with a better matching to the driving electronics.

[0057] This architecture solves the problem of driving high power and high speed directly modulated lasers.

[0058] A plurality of segments may be enabled at the same time to deliver a higher irradiance.

[0059] This may have the effect of higher signal to noise ratio. An eye-safe system may be achieved by proving spacing between the activated multisegment beams exceeding 5mm to 100mm, preferably > 7 mm.

[0060] The advantage of the multi segmented multi aperture array is particularly an eye-safe high optical power may be emitted from the emitter.

[0061] A single emitter system would not be able to achieve this sort of eye safety.

[0062] The system may include a GPS, algorithm, artificial intelligence and machine learning to help locate and track a use.

[0063] The system may provide an architecture allowing few current drivers to drive few segmented arrays within the VCSEL emitter array, and the configurations that would create

[0064] The multi-segments array can have multiple segments enabled at the same time to deliver a higher irradiance (translates to a higher signal to noise ratio). An eye-safe approach can be achieved by enabling a larger spacing between the activated multisegment beams exceeding, in some embodiments, 7 mm. In such approach, any eyesafe high optical power can be emitted from the emitter array that would have been noneye safe if it was emitted by a single emitter source. Therefore, the emitter architecture may offer an additional feature related to eye-safety optical wireless transmission.

[0065] Therefore, the emitter architecture may provide eye-safety optical wireless transmission.

[0066] Features of any one aspect may be provided as feature of any other aspect. For example, apparatus features may be provided as method features or vice versa.

[0067] Brief Description of the Figures

[0068] Various aspects of the invention will now be described by way of example only, and with reference to the accompanying drawings, of which:

[0069] Figure 1 is a block diagram of a transmitter device in accordance with embodiments;

[0070] Figure 2 is a schematic diagram illustrating an array of VCSEL devices according to an embodiment;

[0071] Figure 3 is a schematic diagram illustrating an array of VCSEL devices according to an embodiment;

[0072] Figure 4 is a schematic diagram of an apparatus according to an embodiment;

[0073] Figure 5 shows networks of resistive dividers according to an embodiment;

[0074] Figure 6 comprises two schematic diagrams of resistive divider networks; Figure 7 is a schematic diagram of an apparatus according to an embodiment;

[0075] Figure 8 is an image of the field-of-view of an OWC emitter; and

[0076] Figure 9 comprises images of emitter arrays with focusing lenses according to an embodiment;

[0077] Figure 10 is a block diagram of a transmitter apparatus and a further device illustrating the principle of optical wireless communication.

[0078] Detailed Description

[0079] The term light herein may be used, for example, to refer to electromagnetic waves with wavelengths in a range 1 nm to 2360 nm, which includes ultraviolet, visible light and near-infrared wavelengths.

[0080] The present embodiments relate to transmitter devices that have a plurality of semiconductor laser devices, in particular VCSEL devices, for example, arranged in an array. It will be understood that the driving electronics of VCSEL arrays are non-trivial. Known VCSEL driver devices may be based on fibre communication applications. As such, those drivers are assuming that a single aperture VCSEL is being used as an emitter and therefore, their output impedance may be expecting a load of ~50 Ohm to ~60 Ohm. However, known multi-aperture VCSEL devices are either addressed individually or based on shared anode technology. Examples, are provided in Warren, Mial E., et al. "Low-divergence high-power VCSEL arrays for lidar application." Vertical- Cavity Surface-Emitting Lasers XXII. Vol. 10552. SPIE, 2018.

[0081] Those of which are addressed individually require a single driver per aperture, whereas those connected in-parallel introduce a challenge to the driving electronics. This is because the impedance of the multi-aperture VCSEL array is much lower than 50 Ohm, depending on the number of apertures (linear scale). While the following embodiments relate to arrays of VCSEL devices as semiconductor laser devices, it will be understood that, in other embodiments, alternative multi aperture element semiconductor laser devices may be suitable.

[0082] It will be understood that VCSEL arrays typically comprise multi-apertures that are connected in parallel, and their main use-case is in LIDAR applications where high pulsed optical power is needed. It is known to connect multiple dies (arrays of VCSELs configured in parallel) in series, in which the dies or VCSEL array chips are connected in parallel, rather than the actual apertures. In contrast, in the following, embodiments are described in which apertures within a single VCSEL array die or chip are connected in series.

[0083] It is known to use multi aperture VCSEL devices in LIDAR applications where the problem of low impedance is solved by driving an array in-series with a resistor. In those devices, the multiple aperture VCSEL devices are connected in parallel. The same solution can be used for data communication single aperture VCSEL devices to improve the signal quality (represented using an eye-diagram) and to achieve a better match to the current driver circuitry. However, this solution may be inefficient in power consumption as a large proportion of the power is supplied to the resistor, which makes it undesirable for mobile-held consumer devices.

[0084] Embodiments described below are described in terms of optical wireless communication systems, for example Li Fi systems (for example, an OWC system such as that described with reference to Figure 10). It will be understood that the transmitter may also be used in other optical communication systems, such a fibre optic or alternative systems.

[0085] Figure 1 is a schematic diagram of a transmitter apparatus 10, also referred to as a transmitter, in accordance with an embodiment. The transmitter 10 has a plurality of input connections 12, for example, forming part of an input interface, signal dividing circuitry 14, driving circuitry 16 and driving signal delivery circuitry 18. As described in the following the driving signal delivery circuitry may include routing circuitry and / or a switching network. The transmitter 10 has a plurality of VCSEL devices provided as a VCSEL array 20. The transmitter device 10 is configured to receive input signals that represent input data, for example, communication data. The input signal may correspond to one or more data streams via the input connection.

[0086] The transmitter apparatus may also include a controller for controlling one or more components of the apparatus. In some embodiments, the controller is provided as part of the transmitter apparatus, for example, as part of the driving signal delivery circuitry 18 or is configured to control operation of the driving signal delivery circuitry. In some embodiments, the transmitter is configured to receive control signals from a separate controller.

[0087] As described with reference to the following embodiments, the array of VCSEL devices are provided as described with reference to Figure 2. The driving circuitry 16 includes a plurality of driver devices. The signal dividing circuity 14 includes a number of signal dividing stages. The driving circuitry is connected to the array of VCSEL device and configured to drive groups of the VCSEL devices in the array. Each group of VCSEL devices may be referred to as a segment of the array.

[0088] The architecture of the transmitter apparatus described in the following may allow a plurality of current drivers to drive a plurality of segmented arrays (i.e. a plurality of groups of VCSELs) within the VCSEL array. The internal configuration, such as the connections between multi-aperture VCSELs and the connections between apertures within multiaperture VCSELs may provide the flexibility to allow better impedance matching between the current drivers and the VCSEL arrays. The transmitter apparatus may, for example, allow such an emitter array to produce higher optical power than conventional optical sources.

[0089] Simultaneously high-power and high-speed lasers are not known and the embodiments described in the following may address a need for light sources having such properties. The embodiments described, may rely on driving multiple low-power laser emitters whose optical illumination combines spatially in a medium (such as free space) to cover specific regions within a coverage area. The specific region in the coverage area may be a user location or the location of a remote device. A reduction in power consumption may be achieved by activating selected beams therefore targeting smaller coverage areas which results in an increase in the communication capacity per unit area.

[0090] A further advantage of the above architecture may be the ability to produce high optical power without being limited by eye-safety thresholds. For example, a multi-segment array can have multiple segments (i.e. groups of VCSEL devices) enabled at the same time. This may deliver a higher irradiance and signal to noise ratio. By controlling a spacing between the activated groups of VCSEL devices, for example, to be larger than a predetermined distance, a configuration that avoids unsafe levels of irradiance and damage to eyes may be achieved. Such control can be achieved either via a beam selection algorithm or through spatial configuration of the VCSEL aperture elements. In some embodiments the minimum distance corresponds to a safe distance of 7 millimeters between activated multi-segment beams. In other embodiments, the spacing may be in a range between 5mm to 100mm. Eye safety limits can be derived from BS EN 60825-1 : 2014. Safety of laser products: Part 1. Equipment classification and requirements and M. Dehghani Soltani et al., "Safety Analysis for Laser-Based Optical Wireless Communications: A Tutorial," in Proceedings of the IEEE, vol. 110, no. 8, pp. 1045-1072, Aug. 2022, doi: 10.1109 / JPROC.2022.3181968. In such an approach, any eye-safe high optical power can be emitted from the emitter array that would have been non-eye safe if it was emitted by a single emitter source. Therefore, the emitter architecture may therefore offer additional benefits related to eyesafety in optical wireless transmission.

[0091] Figure 2 shows an array of VCSEL devices. In this embodiment, the VCSEL devices are multi-aperture VCSEL devices, for example, first VCSEL device 202. Each VCSEL device in the present embodiment has multiple aperture elements. The aperture elements may alternatively be referred to as aperture devices. The aperture elements will be understood as comprising at least an aperture or other opening or window for allowing light to be emitted and associated connectors or terminals. For brevity, the VCSEL devices may be referred to as multi-aperture VCSELs. For clarity a single aperture 204 of VCSEL device 202 is indicated on Figure 2. In Figure 2 the multiple apertures of each VCSEL device are shown as connected in a series arrangement.

[0092] The series arrangement is described as follows. In the present embodiment, each aperture of a VCSEL is considered as part of an aperture element that includes a window or other opening that allow light to pass through. Each aperture element also connecting terminals including an anode and a cathode. In Figure 2, the aperture elements are connected in a series arrangement such an anode of the first aperture element is connected to the cathode of the second in-series aperture element. Such a connection may be made during the semi-conductor manufacturing process. In the following, connection of apertures should be understood as connection of associated terminals of aperture elements. VCSEL

[0093] Each multi-aperture VCSEL 202 in Figure 2 has nine VCSEL apertures 204. However, it will be understood that, in other embodiments, each multi-aperture VCSEL may have more or fewer than nine apertures. For example, Figure 3 depicts VCSEL devices having four apertures. It will be understood that the number of apertures and / or the location of the apertures in the VCSEL device may be controlled during fabrication of a multiaperture VCSEL 202. The nine apertures of each VCSEL device are arranged in a square array configuration (3 by 3). As described in further detail in the following, each of the multi-aperture VCSEL devices may be individually addressable such that a drive signal provided to the VCSEL device may be controlled. In the following embodiments, the VCSEL devices are individually addressable, in that each the drive signal to each VCSEL device may be controlled by the controller or routing network. As such, each individual VCSEL device is capable of being controlled to produce an optical signal.

[0094] As depicted in Figure 2, the plurality of apertures 204 are connected in series within each multi-aperture VCSEL 202. It will be understood that the plurality of apertures 204 may alternatively be connected in parallel.

[0095] Multiple apertures within the same device in-series may result in increasing the impedance of the device and therefore improving their match to the current drivers. Alternatively, it may be possible to connect multiple arrays of multi-aperture VCSEL devices (i.e. arrays of arrays) in-series for this particular application. Impedance matching may be achieved because the output impedance of the laser driver is assuming an impedance of 10-60 Ohm.

[0096] In embodiments, power is provided to the VCSEL devices via a driver. The detail of the driving signal is dependent on the type of light emitting device. For example, for directly modulated devices, such as directly modulated lasers, each driver provides a driving signal that has a DC bias and an AC modulated signal for a directly modulated laser (DML). For devices that are externally modulated (i.e. the light output from the laser is modulated by an external modulator) such as an externally modulated laser, the driver provides only a DC bias for the device and provides an AC signal to the semiconductorbased external modulator. In some embodiments, an array of externally modulated lasers is provided and the drivers are configured to provide a modulation signal to the external modulation.

[0097] VCSEL arrays are typically configured to have multi-apertures that are connected in parallel, and their main use-case is in LIDAR applications where high pulsed optical power is needed. It is known also to connect multiple dies (arrays of VCSELs configured in parallel) in series. It is known to connect between VCSEL dies (VCSEL array chips), and not the actual apertures. In contrast to known devices, in the following, series connection of apertures within a single VCSEL array die is proposed.

[0098] Figure 3 shows an array of four multi-aperture VCSEL devices (302a, 302b, 302c, 302d) in a square configuration. The square configuration can be considered to have four quadrants with a VCSEL device in each quadrant, i.e. first VCSEL device 302a in a first quadrant and second VCSEL device 304b in a second quadrant etc. Each VCSEL device corresponds closely to the multi-aperture VCSEL device described with reference to Figure 3, however, with each VCSEL device four apertures arranged in a non-square configuration. For clarity, only a single aperture 304, forming part of the first VCSEL device, is depicted. The arrangement of VCSELs in Figure 3 may be referred to as a segmented array in that array may be operable such that groups of VCSELs, corresponding to segments, are activated at a given time. As described with reference to Figure 3, each of the multi-aperture VCSELs 302 may be individually addressable. It will be understood that the 2x2 square array depicted in Figure 3 is provided as an example, and that larger arrays may be formed in accordance with embodiments. In addition, in the depicted example, a four aperture device is depicted, however, it will be understood that the number of apertures can vary, and in some embodiments, the array is formed from VCSEL devices having at least one aperture.

[0099] The layout of Figure 3 is an addressable multi-aperture array of four quadrants (segments). The multi-apertures are positioned in the corner of the quadrant in order to create a hexagonal layout which is more desired for creating a circular illumination profile or coupling to a fibre optic. In such array, each quadrant has four apertures that are connected in-series. The arrangement may make it easier to drive with better matching to driving electronics.

[0100] The VCSEL apertures of each VCSEL device are shown positioned at an inner corner region of each quadrant. For example, the apertures of the first VCSEL device 302a are positioned in a triangle type configuration at a lower right hand corner of the first VCSEL device. When arrays together in the square configuration, the apertures of the four VCSEL devices form a hexagonal profile or arrangement for the apertures. The hexagonal profile of the apertures 304 results may be beneficial for generating a circular illumination profile and for coupling the configuration to an optic fibre.

[0101] In the array of Figure 3, each VCSEL device of each quadrant has four apertures that are connected in series. As such, the combined resistance is approximately four times the impedance of a single aperture VCSEL. As described in further detail in the following, the ability to control the input impedance of the device with the number of apertures and the configuration of their internal connection may improve impedance matching between driving circuitry and VCSEL devices.

[0102] In the array of Figure 3, each VCSEL device has a shared connector, in this embodiment, cathode pad 306. For clarity, the cathode pad 306 of the first VCSEL device 302a is labelled, and it will be understood that each VCSEL device has a corresponding cathode pad. The cathode pads are provided in an opposing corner to the apertures (i.e. the cathode pad of the first VCSEL device is provided in the top left corner and the apertures are provided generally at the bottom right corner. The cathode pad provide an input for each VCSEL device and receive a driving signal from the driving circuitry.

[0103] The array of Figure 3 is a 2x2 array. In some embodiments, each VCSEL device may be connected in parallel to driving circuitry, therefore allowing each VCSEL device to be individually selected to receive a drive signal. In some embodiments, groups of the VCSEL device may be connected in series. In further embodiments, all VCSEL devices of an array are connected in series.

[0104] In alternative embodiments, a group or all of the multiple-aperture VCSEL devices are connected in series (the number being ‘Ns’) and within each VCSEL device, the apertures themselves are connected in parallel (the number of apertures per segment or group is ‘Np’). The input impedance for this configuration may be expressed as: where ZVCSELis the input impedance of a single-aperture VCSEL device. The impedance calculated above may include parasitic capacitance which may be subtracted out for a more accurate value. Careful design of the layout of the circuit on-chip may help to keep parasitic capacitance low.

[0105] In some embodiments, the connection of apertures in series or parallel may be performed during manufacturing of the semi-conductor device. For example, the apertures may be formed in the device in a series or parallel arrangement during the manufacturing of the device. Alternatively, the VCSEL devices themselves can be connected in series by shorting (connecting) together their respective anodes.

[0106] Figure 3 illustrates an example of a non-uniform spatial arrangement. In the embodiment of Figure 3, the apertures of each VCSEL device are arranged in a first spatial arrangement in which the apertures are arranged in a corner region, opposing the cathode. The VCSEL devices are then arranged together, in this embodiment, in a square array, such that four devices form a second spatial arrangement of apertures. In particular, the corner regions that contain the apertures are adjacent to each other. The second spatial arrangement, in this embodiment, includes a regular hexagon at a central region of the four device array. It will be understood that, in other embodiment, other regular polygon shapes may be suitable. The arrangement of Figure 3 provides an example of a non-uniform arrangement of apertures in which the density of apertures varies across the array. As such, the array has a first region of first density (the hexagon shape) and a second region of a second density surround the first region. In alternative embodiments, alternative non-uniform spatial arrangements and shapes may be used.

[0107] Figure 4 will be understood as a diagram showing a proposed architecture, in accordance with embodiments. In this diagram, multiple inputs can be used to transmit multiple data streams from a single emitter array or a plurality of arrays using single current driver or a plurality of drivers. In some embodiments, the number of inputs may be equal or higher than the number of expected users within the coverage area of an OWC Access point. In some embodiments, the number of individually addressable VCSEL arrays M is higher or equal to the number of drivers, M > D > N, where D is the number of low current high bandwidth drivers (LCBHD), and N is the number of input data streams. The control signals may be governed by the beam selection algorithm which will determine which addressable arrays are required to be active at the same time.

[0108] This architecture may solve the problem of driving high power and high speed directly modulated lasers. Instead of developing a solution to drive a high-power high-speed lase the current invention drives multiple low power emitters that combine spatially in the optical domain to cover specific regions within the coverage areas targeting user location. Thus, achieving a reduction in power consumption by only activating beams targeting smaller coverage areas, and an increase in the communication capacity per unit area.

[0109] Figure 4 depicts a transmitter apparatus 400 in accordance with an embodiment. The apparatus 400 has a plurality of input connections 412, signal dividing circuitry 414, driving circuitry 416 and driving signal delivery circuitry 418. The driving signal delivery circuitry may be alternatively referred to as signal routing circuitry. The transmitter apparatus 400 has a plurality of VCSEL devices provided as a VCSEL array 420. The plurality of input connections 412, dividing circuitry 414, driver circuitry 416 and driving signal delivery circuitry 418 together from part an associated circuitry 430 for the plurality of VCSEL devices. The signal delivery circuitry 418 is coupled to the plurality of VCSEL devices by a number of output connections 422 via which driving signals are delivered to the VCSEL devices. The driver circuitry include a plurality of drivers or driver devices including a first driving device 416a. The VCSEL devices of the VCSEL array are arranged into addressable groups of VCSEL devices. In this embodiment, these groups correspond to rows of the VCSEL devices. However, it will be understood that the VCSEL array may be divided into alternative addressable groups. In the embodiment of Figure 4, each of the M arrays of VCSEL devices is provided in an arrangement in which each device of the array is connected in series. In such an arrangement each array is configured to be driven by a dingle driving signal.

[0110] The associated circuitry 430 is configured to receive a plurality of input signals representative of a plurality of input data streams via the plurality of input connections 412, one or more control signals from a controller via the control signal input 424, and generate a plurality of driving signals for the plurality of VCSEL devices 420. The delivery of the plurality of driving signals by the signal delivery circuitry 418 is based on the control signals. The delivery of the driving signals to the VCSEL devices is controlled by control signals provided by a controller that may or may not form part of the apparatus, in various embodiments.

[0111] The apparatus 400 has multiple input connections 412 in the form of an input interface for receiving multiple input data streams. The apparatus 400 has dividing circuitry 414 in the form of a plurality of driving devices. In the present embodiment, a plurality of low- current high-bandwidth drivers (LCHBD) are provided. A single LCHBD driver 415 is labelled in Figure 4.

[0112] In some embodiments, the low current high bandwidth drivers can be considered to be drivers configured to be operated with, for example, a power under 30 mW, optionally under 5 mW, further optionally under 3 mW. The bandwidth of the drivers may, in some embodiments, be in the range of 100 MHz up to 3 or 5 Ghz, optionally, up to 30 GHz.

[0113] In the embodiment of Figure 4, between the input connections 412 and the dividing circuitry 414, a plurality of amplifiers are provided. A plurality of amplifiers are also provided between each of the plurality of dividers and the connected drivers of the driving circuitry. Pre-amplifiers or post amplifiers can be used before or after each dividing or multiplexing stage. The pre-amplifier and / or post-amplifier may be provided as part of the input interface, the signal dividing circuitry, the driving circuitry and / or the driving signal delivery circuitry. As is described with reference to Figure 6 the network of dividers of the dividing circuitry can be resistive networks, or any other power dividers. The outputs from the plurality of the drivers are then used to drive at least one VCSEL array of multi-apertures or a plurality of arrays of multi-apertures. The signal delivery circuitry, which in this embodiment is a network of switches is governed by the control signals from a controller is based on a beam selection algorithm. This determines which VCSEL array is required to be ON based on the estimated location of a user within the coverage area.

[0114] For the purpose of illustrating the operation of the apparatus of Figure 4, the operation of a chain of components for processing the first input data stream for transmission is described. It will be understood that respective chains are provided for each data stream and these chains form part of the dividing, driving and routing circuitry.

[0115] In operation, a first input data signal 432a is received at a first input data connection 412a. The first input data signal represents a first data stream. The first input data signal proceeds to an initial pre-amplifier 434 before the amplified signal is passed to a first divider of the dividing circuitry. The first divider divides the signal into two divided signals, and the two divided signals and each passed to a subsequent dividerwhich divides these into further divided signals. Each input signal to the dividing circuitry is therefore divided into four signals, in the embodiment of Figure 4. Each of the four divided signals represents the data represented by the first input data signal. The four divided signals are passed to four corresponding driving devices via four respective amplifiers. Each driving device is configured to perform a modulation or encoding process to generate a driving signal that represents the data signal. As a result, four driving signal are generated (labelled Inc1 , ... ,lnc4). These driving signals are referred to as input driving signals as they are input to the routing circuitry 418 and selectively routed, in accordance with one or more control signals received via control signal input 424, to provide output driving signals for any of the addressable groups of VCSEL devices, as controlled by the control signal.

[0116] In total, N input signals are received, the dividing and driving circuitry generates D driving signals (corresponding to the number of driver devices) for the signal delivery circuitry 418. The signal delivery circuitry then delivers these driving signals via M outputs, where M is the number of addressable groups of the VCSEL device array. In the embodiment, of Figure 4, there are M addressable groups corresponding to M rows of VCSEL arrays. However, it will be understood that there each VCSEL device may be individually addressable or may be otherwise grouped.

[0117] The transmitter array 400 is configured to transmit multiple data streams from a single emitter array or a plurality of arrays using single low-current high-bandwidth driver (LCHBD) or a plurality of LCHBDs. The number of input connections or input data streams can be equal to or higher than the number of expected users within the coverage area of the emitter array. The relationship between the number of individually addressable VCSEL groups or arrays (M), the number of low-current high-bandwidth drivers (D) and the number of input data streams (N) can be represented as below:

[0118] M > D > N

[0119] As described above, the routing circuitry 418 is configured to selectively route driving signals from the plurality of drivers of the driving circuitry to groups of the VCSEL devices of the VCSEL array. Figure 4 also shows a control signal input 424. One or more control signals can be provided to the routing network 418 via the control signal input. The controller is configured to transmit control signals and thus control the routing of the driving signals in accordance with a pre-determined beam selection algorithm. The beam selection algorithm determines which addressable VCSEL devices or groups of devices arrays are required to be active at the same time. The controller may be configured to receive signals from a sensor, for example, a presence or proximity sensor and produce control signals for activating groups of VCSEL devices based on a detected proximity. In some embodiments, the controller and / or sensor form part of the transmitter apparatus.

[0120] The architecture contains low power driving circuitry to keep the signal SNR high enough for the targeted modulation along the circuit path from the divider to the switching network, operating preferably at lower power levels for better efficiency, but high enough to have some SNR safety margins. The “operating level" would set the overall efficiency of the multi aperture driver: meaning lower SNR requirements could have higher efficiency drivers by operating at lower power levels along the divider / switch chain. In further detail, the operating level is determined by how much optical power is required to deliver to a corresponding receiver. If a low SNR can be accepted then a low current driver can be achieved by using lower number of stages of dividers and switches. Figure 5 shows an example of signal delivery circuitry, in accordance with an embodiment. The signal delivery circuitry includes signal routing circuitry 518 together with a controller 550. The routing circuitry 518 includes a switching network that is formed form a plurality of switching modules 552a, 552b, ... , 552D. In this embodiment, each driver of the driving circuitry provides a driving signal to a corresponding switching module such that for D drivers there are D switching modules. Accordingly, D driving signals are generated by the drivers and each driving signal is provided to a corresponding switching module.

[0121] Each switching module has a number of switches, in this embodiment, corresponding to the number of addressable VCSEL groups (M). This allows each driving signal to be provided to any one of the addressable groups. In effect, the associated circuitry of the device is capable of transmitting light representing any of the input data streams from any of the addressable groups the VCSEL array.

[0122] In further detail, each switching module has a number of controllable switches equal to the number of addressable groups of the VCSEL array and receives corresponding control signals to turn the switches on or off. Each switch therefore corresponds to VCSEL group and when switched on permits the driving signal provided to that module to pass to the VCSEL group. It will be understood that more than one switch may be on at any one time.

[0123] The switching network routes output from the driving circuitry (not shown) to the VCSEL device array (not shown) to drive the at least one multiple-aperture VCSEL or an array of multiple-aperture VCSELs.

[0124] The switching network is controlled by a control signal from the beam selection algorithm. In the embodiment of Figure 5, the controller is configured to operate in accordance with a beam selection algorithm. The beam selection algorithm determines a configuration that comprises decisions on which multi-aperture VCSEL needs to be powered on at any given time and which multi-aperture VCSEL needs to be powered off at any given times. The controller 550 thus controls the delivery of current to the at least one multi-aperture VCSELs to achieve the configuration determined by the beam selection algorithm. Since M > D there may be as many multi-aperture VCSELs as the number of LCHBDs. It may also be possible for one LCHBD to drive more than one multi-aperture VCSEL. The configuration determined by the beam selection algorithm may be determined based on the estimated location of a user or users in the coverage area. In some embodiments, the beam selection algorithm is based on received input from a sensor for example, a proximity or presence sensor.

[0125] As described above, a network of dividers is used to multiplex the input data stream N to D LCBHDs, where D > N. The network of dividers can be resistive networks, or any other power dividers, as shown in Figure 4. Pre-amplifiers or post amplifiers can be used before or after each dividing or multiplexing stage. The LCBHDs outputs is then used to drive at least one VCSEL array of multi-apertures or a plurality of arrays of multiapertures, as shown in Figure 5. The switches network is governed by the control signal which is based on beam selection algorithm. This determines which VCSEL array is required to be ON based on the estimated location of the User within the coverage area.

[0126] Driving multiple low power emitters that combine spatially in the optical domain may have the technical effects of 1) covering specific regions within the coverage areas 2) enabling the targeting of a user’s location, 3) achieving a reduction in power consumption by only activating beams targeting smaller coverage areas, and 4) an increase in the communication capacity per unit area.

[0127] Other advantages may include a minimal number of current drivers to drive a minimal number of segmented arrays within the VCSEL emitter array, improved impedance matching between these current drivers and the respective arrays, and enabling the emitter array to produce higher optical power than conventional optical sources without it being limited by eye-safety thresholds.

[0128] As described above, the dividing circuit may be formed from a network of resistive dividers. Figure 6(a) shows a part of a resistive divider network with a first resistor 78a, a second resistor 78b and a third resistor 78c. The part of the resistive divider network has a pre-amplifiers 72a and a first post-amplifiers 74 and a second post amplifier 76.

[0129] Figure 6(b) shows part of a resistive divider network without amplifiers. The part of the resistive divider network has a first resistor 79a, a second resistor 79b and a third resistor 79c. The resistors of Figure 6(a) and 6(b) may have different resistance values.

[0130] In other embodiments, the power divider network may not be a resistive network. Resistive dividers may offer the advantage of being wideband. Other lossy structures that are wideband include transformers which may be used as dividers. In further embodiments, lower loss structures like multiple-stage Wilkinson dividers may be used as power dividers, in place of modulation schemes are used wherein a DC response is not essential,

[0131] Figure 7 shows a transmitter apparatus 700 in accordance with a further embodiment. The apparatus 700 has a plurality of input connections 712, in this embodiment a first input connection 712a and a second input connection 712b, signal dividing circuitry 714, driving circuitry 716 and driving signal delivery circuitry 718. The transmitter apparatus 700 has four VCSEL device sub-arrays (first, second, third and fourth VCSEL sub-arrays) provided together as a single VCSEL array 720. The plurality of input connections 712, dividing circuitry 714, driver circuitry 716 and routing circuitry 718 together from part an associated circuitry 730 for the plurality of VCSEL devices 720. The signal delivery circuitry 718 is coupled to the plurality of VCSEL devices by a number of output connections 722 via which driving signals are delivered to the VCSEL devices. In the embodiment of Figure 7, the signal delivery circuity 718 includes a first switches network and a second switches network. Each switches network is served by control signals via a first and second control signal input 724a, 724b.

[0132] Each VCSEL device in the embodiment of the Figure 7 is individually addressable, in that a driving signal may be delivered to each individual VCSEL device of the array by the driving signal delivery circuitry. The multiple aperture VCSEL devices of Figure 7 are provided in a parallel arrangement.

[0133] In the embodiment of Figure 7, there are two input data streams (N =2) provided at first input 712a and second input 712b, respectively. The driving circuitry 716 includes eight driver devices in the form of low cost high bandwidth drivers (D=8). Each of the four VCSEL device sub-arrays are a 2 by 2 array of multi-aperture VCSEL devices. In total, sixteen multi-aperture VCSEL devices (N=16) are provided in the array 720.

[0134] Control signals provided from a controller (not shown in Figure 7) are provided at first and second control inputs 724a, 724b. As described with reference to Figure 4, input signals representing data streams are passed through the dividing circuitry 714 for division, followed by driving circuitry 716 and then signal delivery circuitry 718. Amplifiers are provided as part of the various circuitries and / or between stages. In this embodiment, a first amplifier 734a is provided at the first input connection 712a and a second amplifier 734 is provided at the second input connection 714b. Further amplifiers are provided between the dividers of the dividing circuitry and the drivers of the driving circuitry 716.

[0135] In this embodiment, the dividing circuitry 714 includes two divider networks, one for each input connection, and the driving circuitry includes two sets of four driver devices. Each input also has a corresponding switching network forming part of the routing circuitry. The associated circuitry 730 may be considered to include two processing chains, each chain including a divider network, four drivers and a switches network, together with intermediate amplifiers.

[0136] In the embodiment of Figure 7, the transmitter array includes a number of bypass switching devices. The bypass switching devices are controllable to bypass the signal dividing circuity and provide the data signal directly to the drivers. The by-pass switching devices are controlled by the controller. Switches may be used to bypass dividers in certain circumstances, for example, when only a small number of apertures are to be driven. In further detail, the by-pass switching devices comprises switches provided between the input and the driving devices. When these switches are open, the input signals are divided, as described above. When these switches are closed, input signals by-pass the dividing circuitry and are provided directed to the drivers.

[0137] The two switches network interface with the array of multi-aperture VCSELs 720. In this way multiple low power multi-aperture VCSEL emitters are driven using fewer multiple current drivers based on each input signal.

[0138] It will be understood that, in further embodiments, some of the stages may be based on switches instead of dividers. This may limit the flexibility of the arrangement in terms of the ability to drive all apertures but it would allow for a smaller number of dividers and lead to better efficiency.

[0139] In some embodiments, the spatial configuration of the apertures may be non-uniform, for example, the apertures may be arranged in a desired shape.

[0140] Figure 8 shows the field of view of an optical wireless communication emitter 96 which may comprise one or more multiple-aperture VCSELs. Position A 94 is a location in the centre of the field-of-view cone, on the axis of the OWC emitter 96. Position B 92 is a location at the edge of the field-of-view cone. Figure 8 shows that the distance between the OWC emitter 96 and position B 92 is greater than the distance between the OWC emitter 96 and position A 94. If the coverage area of the OWC emitter 96 is large, the difference in the distances is also large and can lead to lower received signal strength at position B 92 in comparison to position A 94. Figure 8 shows that OWC transmitter and / or transceiver fields of view extend away from the access points in cones with vertical axes perpendicular to, and vertices located on the plane in which the access points are located. Typically, the plane would be the plane of the circuit board that the light transmitters and receivers are mounted on. A lower signal at coverage edges is therefore expected.

[0141] Figure 9(a) shows a uniformly spaced array of VCSELs 102. The radiation from the VCSELs 102 is focused with a simple convex lens 104 and produces a square coverage area (not shown). Following the principle described with reference to Figure 9, as the coverage area increases, the edges of the coverage area will experience a lower received signal strength and will appear ‘dimmer’.

[0142] Figure 9(b) shows a non-uniformly spaced array of VCSELs. In the embodiment of Figure 9(b), the VCSELs 102 in Figure 9(b) are shown packed more tightly towards the edges of the array than in the centre. This leads to more power being radiated near the edge of the array than at its centre. When the radiated power is focused by a lens 104, the edges of the coverage area will experience a similar received signal strength as the centre of the coverage area.

[0143] A simple lens in conjunction with an array may illuminate an area that has the same shape as the array. By changing the spacing and positions of each emitter an intensity profile of the incident signal at a given plane. One benefit of doing this is to flatten the received signal across the plane with more signal sent to the edges of the field-of-view than the centre.

[0144] In some embodiments, the array of VCSELs can assume any other shape based on the required shape of coverage area. For example, a circular profile for the VCSEL array will result in a circular coverage area which may be useful for some applications.

[0145] By driving multiple low power emitters that combine spatially in the optical domain, a number of advantages may be achieved. For example the beams may cover specific regions within the coverage areas. Additionally, a targeting of a user’s location may be enabled. Additionally, there may be a reduction in power consumption by only activating beams targeting smaller coverage areas and an increase in the communication capacity per unit area.

[0146] In the context of providing a device operable in accordance with a beam selection algorithm, embodiments may also offer advantages such as a reduction in the number of current drivers required to drive a minimal number of segmented arrays within the VCSEL emitter array. In addition, embodiments may offer improved impedance matching between current drivers and the respective VCSEL arrays. Additionally, the embodiments may enable an emitter array to produce higher optical power than conventional optical sources without it being limited by eye-safety thresholds.

[0147] In the above-described embodiments, connection of apertures may be performed during manufacture, by connecting an anode of a first aperture element to the cathode of a second in-series aperture. In further embodiments, discrete VCSEL devices may be connected in series.

[0148] Figure 10 is a block diagram illustrating a system 1000 configured to perform optical wireless communication (OWC). Figure 10 shows a transmitter apparatus 1002 and a receiver apparatus 1004. The transmitter apparatus 1002 is configured to send OWC signals in which information is encoded through an optical communication channel 1006 to the receiver apparatus 1004. The transmitter apparatus corresponds to the transmitter apparatus described above in accordance with embodiments.

[0149] The optical communication channel 1006 may be a free-space communication channel. The optical communication channel 1006 may have a characteristic wavelength. Free space communication channels include transmission of optical signals through air, space, vacuum, liquid such as water or similar.

[0150] It will be understood that even though Figure 10 illustrates a transmitter and receiver pair, transmitters and receivers may be provided on the same devices. The receiver may form part of a remote device that may provide access to a further network, for example the internet. In some embodiments the transmitter apparatus 1002 may form part of a transceiver or may form part of an Access Point device. Data connectivity may be via network connection, wireless connection, PLC connection, PoE connection OWC connection or other known data connections. The transmitter and / or receiver may be provided as part of a portable or fixed device. Without limitation, examples of remote device include personal computers, desktops, laptops and smart devices, including mobile devices (for example, mobile phones, tablets or digital book readers). The remote device may be powered by its own battery resource.

[0151] An OWC device may provide data transmission to and / or from a wired network or a WiFi or other wireless network and / or other optical wireless communications network, optionally a LiFi network. Any suitable modulation scheme may be used. For example, orthogonal frequency division multiplexing (OFDM) modulation schemes are used in some embodiments, and the demodulation uses the OFDM demodulation scheme. In further embodiments and without limitation, other modulation schemes may be used, for example on-off keying (00K), phase shift keying (PSK), M-ary pulse amplitude modulation (M-PAM), M-ary quadrature amplitude modulation (M-QAM), Discrete Hartley transformation, Wavelet packet division multiplexing (WPDM), Hadamard coded modulation (HOM), pulse-position modulation (PPM), Colour shift keying (CSK), carrierless amplitude and phase (CAP), or discrete multi-tone (DMT). The light may be modulated at a modulation rate between 1 kHz and 1 PHz, for example at a modulation rate between 1 MHz and 100 GHz. The modulation scheme may form part of an OWC communication protocol, such that the optical signal is produced according to the OWC communication protocol. The OWC communication protocol may be packet-based.

[0152] In the above described embodiments, the impedance of each driving device as being about 50 Ohms or 60 Ohms. It will be understood that this value may vary, and may be in the range may be in the range 10 to 120 Ohms, optionally substantially 50, further optionally substantially about 60.

[0153] A skilled person will appreciate that variations of the described embodiments are possible without departing from the invention. Accordingly, the above description of specific embodiments is provided by way of example only and not for the purposes of limitation. It will be clear to the skilled person that modifications may be made to the embodiments without departing from the scope of the invention.

Claims

CLAIMS:1 . An optical communication transmitter apparatus comprising: a plurality of semiconductor light devices each semiconductor light device comprising one or more aperture elements for emitting light, wherein the plurality of semiconductor light device are configured to be driven by driving signals to produce modulated optical communication signals; driving circuitry comprising a plurality of driving devices for said plurality of semiconductor light emitting devices, wherein the number of semiconductor light devices is greater than the number of driving devices; one or more input connections for receiving one or more input signals representing input data, wherein the number of driving devices is greater or equal to the number of input connections; signal dividing circuitry between the one or more input connections and the plurality of driving devices configured to divide the plurality of input signals to produce a plurality of divided signals representing said input data, wherein the driving circuitry is configured to produce driving signals in response to receiving said divided signals; wherein the transmitter further comprises signal delivery circuitry configured to selectively deliver driving signals produced by the plurality of driving devices to one or more groups of one or more the plurality of semiconductor light devices.

2. The apparatus of claim 1 , wherein the semiconductor light devices comprises a VCSEL device and wherein each aperture element comprises an aperture of the VCSEL device.

3. The apparatus of any preceding claim, wherein each of the driving devices is characterised by an impedance or other electrical property and wherein the plurality of semiconductor light devices and / or the aperture elements of each group of semiconductor light devices are connected in an arrangement to match the impedance or other electrical property of each group to the corresponding driving device.

4. The apparatus of claim 3, wherein each of the driving devices is characterized by a first impedance and wherein each semiconductor light device and / or respective aperture element is characterized by a second, lower impedance.

5. The apparatus of claims 3 or 4, wherein the arrangement comprises at least one of: a) each semiconductor device of a group connected in a series arrangement; b) each aperture element of each semiconductor light device of a group connected in a series arrangement. c) each semiconductor device connected in a parallel arrangement, wherein each semiconductor device comprises multiple apertures elements connected in a series arrangement.

6. The apparatus of any preceding claim wherein: a) each driving device is suitable and / or intended for use with a single aperture semiconductor laser and / or b) the impedance of each driving device is in the range 10 to 120 Ohms, optionally substantially 50, further optionally substantially about 60.

7. The apparatus of any preceding claim, wherein the semiconductor light devices comprise at least one shared anode between the aperture elemnets and / or wherein each group of semiconductor light devices comprise a shared connection.

8. The apparatus of any preceding claim, wherein the plurality of semiconductor light devices are arranged in a plurality of addressable groups, wherein each driving device is configured and / or controllable to drive one or more semiconductor light devices, optionally all semiconductor light devices of an addressable group.

9. The apparatus of any preceding claim wherein the driving signal delivery circuitry is configured to selectively deliver the driving signals from the plurality of driving devices to one or more groups of the semiconductor laser devices in accordance with a predetermined procedure.

10. The apparatus of claim 9, wherein the pre-determined procedure comprise a beam selection procedure and / or is based on user and / or object tracking.11 . The apparatus of any preceding claim, wherein the driving signal delivery circuitry is configured to selectively deliver driving signals to the plurality of semiconductordevices subject to the constraint that only aperture elements separated by a minimum distance apart are driven at substantially the same time.

12. The apparatus of claim 11 , wherein the minimum distance is selected based on eye-safety requirements, for example, the minimum distance may be at least 7mm.

13. The apparatus of any preceding claim, wherein the pre-determined procedure is dependent on an output from a sensor, for example, a proximity or presence sensor or a further processing resource.

14. The apparatus of any preceding claim, wherein the signal dividing circuitry comprises two or more dividing stages, wherein each signal dividing stage is configured to reduce the power and / or current and / or voltage of the received signals for the subsequent stage and / or the driving circuitry such that the output signals from each stage have a lower power, current and / or voltage than the input signals to each stage.

15. The apparatus of any preceding claim, wherein the input data signals are representative of a plurality of data streams, and wherein the plurality of the semiconductor light devices comprise a plurality of groups of semiconductor light devices, wherein each group of semiconductor light devices is configured to selectively transmit optical signals representing a corresponding data stream.

16. The apparatus of any preceding claim, wherein the dividing circuitry comprises a plurality of signal and / or power divider devices arranged into a plurality of dividing stages, wherein each input stage is configured to receive a plurality of input signals and output a greater number of output signals for the subsequent stage and / or for the driving circuitry17. The apparatus of claim 16, wherein the divider devices comprise at least one of wideband dividers, resistive divider, power divider, Wilkinson divider and / or wherein each driving device comprises a low power and high bandwidth driving device.

18. The apparatus of any preceding claim, wherein the apparatus comprises by-pass circuitry provided between the input connections and the driving circuitry, wherein theby-pass circuitry is configured to provide the input signals to the driving circuitry and bypass the dividing circuitry.

19. The apparatus of any preceding claim, wherein the signal dividing and / or the driving circuitry and / or the driving signal delivery circuitry comprises linking components, wherein the linking components comprise amplifier and / or other RF components20. The apparatus of any preceding claim, wherein the dividing circuitry and / or the driving circuitry is provided in a plurality of stages and wherein pre and / or post amplifiers or other RF components are provided between each stage21 . The apparatus according to any preceding claim, wherein the aperture elements of each semiconductor light device are arranged in a first spatial arrangement, such that, when the semiconductor light devices are arrayed or otherwise arranged together the aperture elements form a second spatial arrangement, wherein the second spatial arrangement comprises a non-uniform arrangement and / or shape.

22. The apparatus according to claim 21 , wherein the desired shape comprises a regular polygon shape.

23. The apparatus according to any preceding claim, wherein the first spatial arrangement comprises an arrangement in which the apertures are at one or more corner and / or edge regions of the device and the second spatial arrangement comprises an arrangement in which corner and / or edge regions of two or more light devices are adjacent to each other.

24. The apparatus as claimed in any preceding claim, wherein the non-uniform arrangement comprises a first region having a first density of aperture elements and a second region having a higher density of aperture elements, optionally wherein the higher density region is surrounded by the lesser density region.

25. A method of producing modulated optical communication signals for a plurality of semiconductor light devices wherein the plurality of semiconductor light devices comprise one or more apertures for emitting light, the method comprising: receiving, at one or more input connections, one or more input signal representing input data;dividing, by signal dividing circuitry, said input signal into a plurality of divided signals representing said input data; producing, by driving circuitry, a plurality of driving signals in response to receiving said divided signal, wherein the driving circuitry driving comprising a plurality of driving devices and wherein the number of semiconductor light devices is greater than the number of driving devices and wherein the number of driving devices is greater or equal to the number of input connections; selectively delivering said driving signals produced by the plurality of driving devices to one or more groups of one or more of a plurality of semiconductor light devices, producing modulated optical communication signals by the semiconductor light devices in response to receiving said driving signals.

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