Optical wireless communication receiver with a large photodetection surface, a wide field of view and a wide bandwidth

Abstract

An optical wireless communication (OWC) receiver is presented for receiving an incident optical beam modulated with data and outputting an electrical output signal comprising the modulated data, the receiver comprising: a lens configured to receive the incident optical beam; a plurality of photodiodes positioned at a distance from the lens at or near the focal plane of the lens; and an amplifier. Each of the plurality of photodiodes is configured to receive a portion of the incident optical beam and generate a photocurrent of photons corresponding to the received portion of the incident optical beam. The plurality (N) photodiodes are arranged in a two-dimensional array of (1, ..., M) rows and (1, ..., K) columns (N = M x K). The outputs from columns (1, ..., K) are combined, and the photocurrents from these columns are summed. An amplifier is connected to the combined outputs from columns (1, ..., K) of the two-dimensional array and converts the summed photocurrents into an amplified electrical output signal. The interconnections between each photodiode in the two-dimensional array (M x K) form at least two (1, ..., K; where K >= 2) parallel photodiode branches. Each parallel branch forms a cascade of at least two (1, ..., M; where M >= 2) photodiodes. The two-dimensional array forms a plane of interdigitated photodiodes.

Description

[Technical field]

[0001] The present invention relates generally to optical wireless communications, and more particularly to wireless communications receivers having large photodetector surface areas and wide bandwidths. [Background technology]

[0002] While the use and innovation of radio frequency (RF) based communications is constantly growing, its popularity is causing congestion of the radio spectrum. Optical wireless communication (OWC) is a type of optical communication that uses unguided visible, infrared (IR) or ultraviolet (UV) light to carry signals. OWC is rapidly gaining industrial interest because (visible) light (which lies in the wavelength region of about 400-700 nm) achieves a bandwidth of at least 320 THz, a spectrum that is typically used in long-distance optical fiber communications (1500-1600 nm). These values ​​are higher than what can be achieved by future THz wireless technologies.

[0003] OWC can be used in wireless personal area networks and vehicular networks among other application areas including wireless LAN networks. OWC networks operating in the visible light range are commonly called visible light communication (VLC) systems. The communication data is modulated by pulsing visible light at high speeds without any noticeable effect on the light output or on the human eye. VLC systems may also be piggybacked on LED lighting systems, since the light output of LEDs may be used for data modulation, not just for lighting purposes. However, LEDs are not fundamentally designed for such purposes, so the achievable bandwidth is limited.

[0004] OWC systems operating in the infrared (IR) and near-IR range provide a protocol-transparent link between high data rates. These OWC systems use infrared beams that are directed on-demand to user devices. This allows for the establishment of high-capacity, congestion-free wireless links between devices with high privacy characteristics because these beams are not shared and cannot be accessed by users outside the footprint of the beam.

[0005] OWC has significant advantages over RF-based communication systems. As mentioned above, OWC systems have a large potential bandwidth, but more than that, the optical spectrum is unregulated and does not require licenses. Because light cannot penetrate walls, OWC systems offer greater privacy and security.

[0006] Aside from these advantages, OWC systems present several technical challenges, such as efficiently directing narrow individual light beams and aligning optical receivers towards user devices without the need for delicate and precise positioning that would increase the complexity and cost of the user devices.

[0007] The basic physical law of etendue limits the product of cross-sectional aperture area and solid angle; increasing one reduces the other. For example, a large aperture lens can be used to increase light gathering power, but this lens focuses it onto a small, fast photodetector. This is the approach usually taken when building optical receivers in OWC systems. However, a small angular offset of the incoming light with respect to the lens shifts the focused beam outwards with respect to the tiny detector. This causes losses in received light. This shift is proportional to the focal length of the lens. Large aperture lenses usually have long focal lengths. Thus, the larger the aperture, the smaller the allowed beam angle offset (and therefore the limited field of view (FoV)). Summary of the Invention [Problem to be solved by the invention]

[0008] It is therefore an object of the present disclosure to provide an improved OWC receiver that has a large photodetection surface and a wide viewing angle without narrowing the bandwidth compared to conventional OWC receivers. [Means for solving the problem]

[0009] In a first aspect, an optical wireless communication (OWC) receiver is provided for receiving an incident optical beam modulated with data and outputting an electrical output signal including the modulated data, the OWC receiver comprising: a lens configured to receive an incident light beam; and a number of photodiodes arranged at a distance from a lens, at or near the focal plane of said lens; an amplifier; Equipped with each of the plurality of photodiodes is configured to receive a portion of the incident light beam and generate a photocurrent of photons corresponding to the received portion of the incident light beam; The plurality (N) of photodiodes are arranged in a two-dimensional array (N=M×K) of rows (1, . . . , M) and columns (1, . . . , K); The outputs from the columns (1, ..., K) are combined and the photocurrents from these columns are summed; the amplifier is connected to the combined outputs from columns (1, ..., K) of the two-dimensional array and converts the summed photocurrents into an amplified electrical output signal; the interconnections between each of the photodiodes in the two-dimensional array (M×K) form at least two (1, ..., K; where K >= 2) parallel photodiode branches; each of said parallel branches forming a cascade of at least two (1, ..., M; where M >= 2) photodiodes; The two-dimensional array is characterized in that it forms an interdigitated surface of photodiodes.

[0010] The inventors have realised that the surface of the photodiodes can be enlarged, and therefore the aperture, without narrowing the bandwidth of the receiver. This can be achieved according to a first aspect of the present disclosure by an OWC receiver comprising a lens and a number of photodiodes, the number of photodiodes being arranged at a distance from the lens, at or near the focal plane of the lens (preferably in front of the lens). In particular, each of the number of photodiodes is configured to receive a portion of the incident light beam and generate a photocurrent of photons corresponding to the received portion of the incident light beam. The number (N) of photodiodes are arranged in a two-dimensional array (N=M×K) of rows (1,…,M) and columns (1,…,K). The outputs from the columns (1,…,K) are combined and the photocurrents from these columns are summed. These summed photocurrents are input to an amplifier, in particular a transimpedance amplifier. The amplifier is connected to the combined outputs from the columns (1,…,K) of the two-dimensional array and converts the summed photocurrents into an amplified electrical output signal.

[0011] The inventors have realized that if the interconnections between the photodiodes in a two-dimensional array (M×K) form at least two (1, ..., K; where K≧2) parallel photodiode branches, each of which forms a cascade of at least two (1, ..., M; where M≧2) photodiodes, then a receiver can be obtained in which the photodetection surface and bandwidth can be adjusted by defining the interconnections that define the number of parallel branches and the number of photodiodes per branch. A receiver with a two-dimensional array according to the present disclosure produces an output signal generated by N=M×K photodiodes (hence a combined photodetector with a photodetection surface N times larger than a single photodiode). In this case, at low frequencies, the detected signal is K times larger and the receiver bandwidth is M / K times larger than a receiver with a single photodiode. This will be explained in more detail later.

[0012] It is proposed here to combine several photodiodes in a novel way, which allows to enlarge the light detection surface formed by their connection (or combination) while also achieving an enlarged bandwidth. The resulting large detection surface allows to increase the amount of light received from the incident beam, which is usually much more than in the case of a single photodiode. In addition, in combination with a lens system, the angular aperture (FoV) of the OWC receiver can be increased. The proposed array or matrix of photodiodes, in which the light detection surface, i.e. the active area, of the photodiodes is enlarged, allows to obtain a trade-off between sensitivity and bandwidth of the OWC receiver without the need for complex high-frequency circuits or additional tuning control algorithms.

[0013] The proposed OWC receiver receives an incident light beam modulated with high-speed data and converts it into an electrical output signal. For this purpose, the OWC receiver utilizes a photodiode in front of an electrical amplifier (specifically a transimpedance amplifier, which converts the summed light signals into the amplifier's output signal). The diameter of the beam is typically much larger than the active area of ​​the photodiode. Therefore, to maximize the output signal of the photodiode, the photodiode needs to capture as much of the power of the incident beam as possible. The light beam is first captured by a lens and then illuminated on the photodiode. To maximize the power of the captured light beam and to eliminate the need for precise angular adjustments to the beam, the OWC receiver is proposed to have a large aperture cross-section and a large field of view (FoV, hence a large angular area). Since the photodetection area is formed by combining several individual photodiodes, the individual photodetection active areas are small. This typically requires the OWC to have a large bandwidth.

[0014] By placing several photodiodes in parallel, the collected and generated photocurrent is increased. However, this necessarily adds capacitance, which reduces the overall bandwidth. By placing several photodiodes in series, their capacitance is also placed in series, which increases the bandwidth. However, the photocurrent cannot be increased. This option is usually rejected, since an ideal photodiode acts as a current source, and conventional wisdom is that current sources cannot be placed in series. Now, realizing that a typical photodiode is not a perfect current source, but has a finite parallel resistance, it is possible to propose combining photodiodes placed in series in parallel. Thus, a two-dimensional array or matrix of M x K interconnected photodiodes according to a first aspect is proposed. This array is preferably integrated on a single chip.

[0015] Each photodiode in the array can be represented by an equivalent circuit consisting of a (usually large) resistance to account for leakage current, the capacitance of the reverse-biased photodiode junction, a (usually small) current source for dark current caused by thermal effects, and a current source representing the photocurrent itself (which is a response to the portion of a light beam impinging on the active area of ​​the photodiode).

[0016] By applying the well-known Thévenin and Norton theorems, the entire array of M × K photodiodes can be represented using a single equivalent photodiode circuit with its output current and internal impedance Z tot is expressed as follows, where a m、k ￣ denotes the average fraction of the optical beam power reaching the (m, k)th photodiode.

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[0017] Therefore, (R d >>R s , R p >>Z T / (1+A), the -3 dB bandwidth of a receiver using an M × K photodiode matrix is, to a good approximation, (M / K) times wider than that of a receiver using a single photodiode. With the proposed M × K photodiode matrix, the generated current is i out ≒K·R·a￣·P(t) (ignoring dark current), which is K times larger than the single photodiode case. In particular, if a square M × M photodiode matrix (i.e., M = K) is placed in front of the TIA, the resulting bandwidth is the same as the single photodiode case, but the active area is M 2 2x larger and the output signal is Mx larger. Thus, by adjusting the number of rows and columns of the array, one can obtain an OWC receiver with configurable bandwidth and active area.

[0018] In one example, the number K of parallel branches (1, ..., K) in a two-dimensional array (N=M x K) is greater than the number M of cascades (1, ..., M) in each branch (i.e., M <K)。

[0019] If the matrix is ​​configured with a larger number of parallel branches (i.e., with interconnections between the photodiodes), the collected and generated photocurrent will be larger than in the M=K case, but the number of capacitances will necessarily increase, and as a result the overall bandwidth will be smaller than in the M=K case.

[0020] In one example, the number K of parallel branches (1, ..., K) contained in a two-dimensional array (N=M x K) is less than the number M of cascades (1, ..., M) contained in each branch (i.e., M>K).

[0021] If the matrix is ​​arranged so that each branch contains a larger number of cascades of photodiodes (1, ..., M) (i.e., due to the interconnection between the photodiodes), the capacitance will be in series and therefore the bandwidth will increase. Connecting photodiodes in series is usually considered undesirable, since an ideal photodiode acts as a current source, and current sources cannot be placed in series in theory. The inventors now realize that a typical photodiode is not a perfect current source, but has a limited parallel resistance. They then consider the option of combining photodiodes placed in series in parallel. Thus, what is proposed in this disclosure is a two-dimensional matrix of M x K interconnected photodiodes, preferably integrated on a single chip.

[0022] In one example, the number K of parallel branches (1, ..., K) contained in a two-dimensional array (N=M x K) is equal to the number M of cascades (1, ..., M) contained in each branch (i.e., M=K).

[0023] In one example, a lens illuminates the received light beam onto a surface area larger than the combined surface area of ​​the two-dimensional array of photodiodes.

[0024] In one example, a two-dimensional array (N=M×K) defining the rows and columns of the two-dimensional array of photodiodes includes interconnects of the photodiodes, each of the interconnects defining each row (1, ..., M) also defining each column (1, ..., K).

[0025] In one example, each row of the two-dimensional array further comprises a resistor disposed in parallel with the photodiodes in each row.

[0026] In one example, each of the resistors is positioned external to the two-dimensional array of photodiodes.

[0027] In one example, each of the resistors is integrated within a two-dimensional array of photodiodes.

[0028] In a second aspect, an Optical Wireless Communication (OWC) system is provided, the system comprising an Optical Wireless Communication (OWC) receiver as previously described.

[0029] In a third aspect, an Optical Wireless Communication (OWC) system is used for optical communication using electromagnetic waves at wavelengths in the visible, infrared, near infrared or ultraviolet spectrum.

[0030] In a fourth aspect, the optical wireless communication (OWC) system is used in either a wireless LAN network, a wireless personal network, or a vehicular network.

[0031] Those skilled in the art will appreciate that all examples and advantages of the first aspect of the present disclosure are equally applicable to the second aspect of the present disclosure. [Brief description of the drawings]

[0032] [Figure 1A] 1 shows the half-angle of field of view α of an OWC receiver according to the present disclosure. A light beam passes through a lens of diameter D1 and focal length f and strikes and illuminates a photodiode (PD) of diameter D2 at an angle α. The photodiode is defocused a distance x with respect to the focal plane of the lens. [Figure 1B] Shown is the projection of a beam spot onto a photodiode. A defocused spot of radius Rc = Dc / 2 illuminates a photodiode of radius R2 = D2 / 2. [Figure 2A] The half-angle of field α of the incident light beam is shown as a function of the defocus parameter p, where p is defined as p=x / f. The lens diameter D1=10 mm, the lens focal length f=5 mm, and the photodiode diameter D2 take various values. [Figure 2B] We show the photodetection allocation T of the incident light beam versus the defocus parameter p (p is defined as p=x / f). The lens diameter D1=10 mm, the lens focal length f=5 mm, and the photodiode diameter D2 take various values. [Diagram 3] 1 shows an equivalent circuit of a single photodiode. [Figure 4] 1 shows an optical transimpedance receiver. [Diagram 5] An example of an equivalent circuit for N photodiodes arranged in parallel is shown. [Figure 6] An example of an equivalent circuit for N photodiodes arranged in series is shown below. [Figure 7] The DC bias voltage Vn of each of N photodiodes arranged in series is shown (n=1, . . . , N). [Figure 8] An example of a two-dimensional matrix of photodiodes is shown, with a resistor Rp arranged parallel to each column. [Figure 9] A two-dimensional matrix in which multiple photodiodes are arranged in series / parallel is shown (M photodiodes are arranged in series to form a set, and K sets of these M photodiodes are arranged in parallel). [Figure 10] The frequency characteristics of the OWC receiver (a two-dimensional array of N=M×K photodiodes placed in front of a transimpedance amplifier) ​​are shown. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0033] As shown in Figure 1, the proposed OWC receiver receives an incident light beam modulated with high-speed data and converts it into an electrical output signal. For this purpose, the OWC receiver utilizes a photodiode followed by an electrical amplifier. In general, the diameter of the light beam is much larger than the active area of ​​the photodiode. Therefore, to maximize the signal of the photodiode, it is necessary to capture as much of the power of the incident beam as possible. As shown in Figure 1, the light beam is first captured by a lens and then illuminated on the photodiode. To maximize the power of the captured light beam and to eliminate the need for fine angular adjustments to the beam, the OWC receiver needs to have a large aperture cross-section and a wide field of view (FoV, hence a wide angular range). However, to handle high-speed data, the OWC receiver also needs to have a wide bandwidth. Usually, this must be achieved by a photodiode with a narrow light-detecting active area.

[0034] If the photodiode is completely covered by the unfocused spot of the beam, D c In this case, the displacement Δ of the spot center relative to the photodiode center must satisfy the following (defocus parameter p=x / f, where 0≦p≦1):

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[0035] Spot P spot The optical power P incident on the photodiode is the total optical power in the det is expressed as follows:

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[0036] For the viewing half angle α, the following holds:

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[0037] As shown in FIG. 2A, the FoV half angle α increases with increasing defocus parameter p. That is, a photodiode with diameter D2=0.2 mm is shown by curve 211, a photodiode with diameter 0.4 mm is shown by curve 212, a photodiode with diameter 0.8 mm is shown by curve 213, and a photodiode with diameter 1.0 mm is shown by curve 214. The FoV decreases slightly with increasing photodiode diameter. On the other hand, as shown in FIG. 2B, the photodetected power increases significantly with increasing photodiode diameter. In FIG. 2B, the proportion T of the incident light beam that is photodetected is shown against the defocus parameter p, where p is defined as p=x / f. Here, the lens diameter D1 is D1=1 mm, and the lens focal length f is f=5 mm. With respect to the diameter D2 of the photodiode, the case where D2=1.0 mm is shown by curve 221, the case where D2=0.8 mm is shown by curve 222, the case where D2=0.4 mm is shown by curve 223, and the case where D2=0.2 mm is shown by curve 224.

[0038] [Single photodiode] Figure 3 (left side) shows the electrical circuit of a single photodiode, which includes a series resistor R s and parallel resistance R d and capacitance C d and the dark current i d (t) and the photocurrent i s Typically, a pin photodiode is biased with a reverse voltage across the intrinsic region. When a photon passes through this region, electron-hole pairs are generated. These migrate to the anode and cathode terminals of the photodiode, respectively, due to the electric field. Thus, a photocurrent i s (t) is generated. A (usually small) parallel resistor R d includes the bond wire to the photodiode chip. The (large) parallel resistor R d includes leakage current. (small) dark current i d (t) is generated by thermal effects. The photocurrent is i s(t)=R·a·P(t), where R is the sensitivity of the photodiode in A / W, and a is the fraction of the instantaneous power of the light beam that is detected by the active area of ​​the photodiode.

[0039] Applying Thevenin's theorem, the photodiode can be represented as an equivalent circuit with a voltage source e(t) and a series impedance Z, as shown in Figure 3 (center). Alternatively, applying Norton's theorem, the photodiode can be represented as an equivalent circuit with a current source i tot (t) and the same impedance Z tot =Z in parallel can be shown as an equivalent circuit.

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[0040] [Optical receiver] To process the signal after photodetection, an electronic high-frequency low-noise amplifier is applied after the photodiode. A well-known typical example of this is the transimpedance amplifier (TIA). Figure 4 shows a schematic of its circuit configuration (A is the open-loop gain of the amplifier. Z t is the feedback impedance). Amplification is achieved by the transimpedance Z T It is expressed as follows:

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[0041] [Multiple photodiodes in parallel] To increase the active area, we can also connect N photodiodes in parallel. Figure 5 shows the circuit model for such a parallel arrangement. The current source model of a single photodiode in Figure 3 (right side) is extended to N of them connected in parallel. This means we simply add the currents and divide the impedance by N.

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[0042] From this analysis, the equivalent capacitance is C eq ≒N·C d and the generated photocurrent is i tot (t) ≒ N a ￣ R P(t). At this time, each photodiode receives a fraction a of the beam power. n It is irradiated with a￣=(1 / N)Σ n=1 N a n represents the average fraction of the beam power incident on a single photodiode. The photocurrent generated is therefore N times the average current generated by an individual photodiode.

[0043] When N parallel photodiodes are applied to a transimpedance amplifier, the transimpedance is given by:

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[0044] Therefore the low frequency receive gain and -3dB receiver bandwidth are respectively:

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[0045] For a single photodiode receiver, the photocurrent generated is multiplied by N. Hence, the reference transimpedance Z T,,ref This means that the output signal v is generated by the average photogenerated current per photodiode â·R·P(t).out Represents (t).

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[0046] Thus, the output signal produced by a receiver with N photodiodes in parallel will be N times larger than that produced by a receiver with a single photodiode, but the receiver bandwidth will be N times smaller.

[0047] [Multiple photodiodes in series] Alternatively, the active area can be increased by connecting N individual photodiodes in series. Figure 6 shows an equivalent circuit for such a cascade of photodiodes. Applying a current source equivalent to the single photodiode case of Figure 3 (center), this cascade is shown in Figure 6 (left side). The nth photodiode receives a fraction a of the beam power P(t) n Therefore, the photocurrent is i s,n (t)=a n Therefore, Thévenin again (as in Figure 3 (middle)) considers a voltage source e with a series impedance Z. n As shown in Figure 6 (center), the series connection and impedance of this voltage source can be summed up to a single voltage source e tot (t) and a single series impedance N×Z. Following Norton, this can be expressed as a single current source i tot (t) and the same impedance Z tot =Z can be expressed in parallel. The relationship is expressed as follows:

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[0048] Applying the series connection of photodiodes in a transimpedance amplifier scheme results in the following:

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[0049] Therefore, the low frequency receive gain and -3 dB receiver bandwidth are, respectively,

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[0050] The photocurrent generated is equal to that of a single photodiode receiver. Therefore, the reference transimpedance Z T,ref It is possible to define: which represents the output signal as being generated by the average signal.

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[0051] To achieve sufficient detection and bandwidth performance, each photodiode must be biased with a sufficient reverse voltage. Therefore, the reverse voltage V of n photodiodes connected in series is n(n=1, ..., N) needs to be evaluated. This involves some asymmetry in terms of sensitivity depending on the photodiode characteristics and the photocurrent generated.

[0052] Incident light energizes photodiode n, which has a voltage V n The DC current I generated in the active region of the n becomes:

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[0053] Figure 7 shows N photodiodes connected in series and a bias voltage V applied to the entire series connection. b Here, the resistor R connected in parallel to the photodiode is d and resistor R in series s (See also Figure 3).

[0054] For the current I generated by the series-connected photodiodes,

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[0055] Therefore, the following equation holds:

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[0056] Therefore, the total bias voltage V b is distributed equally to the N photodiodes. Therefore, the bias voltage of each photodiode is V b / N. Here, a voltage deviation may occur in each photodiode n. This is called the parallel resistance R d " and "The dark current I on and the product R n P n By integrating all the photodiodes on the same chip, these differences will be reduced (e.g. by connecting an external resistor in parallel with each diode). d By lowering the resistor R, each bias voltage deviation can be reduced (if necessary for adequate performance). This can be seen in Figure 8 by adding a resistor R outside each diode row in the matrix. p is shown by being connected.

[0057] [Series / parallel multiple photodiodes in a two-dimensional matrix] We propose to arrange the photodiodes in a two-dimensional matrix of M × K. As shown in Figure 9, this corresponds to K sets of M photodiodes connected in series in parallel.

[0058] In the Thevenin equivalent circuit, current source i tot and impedance Z tot The relationship that determines (using the analysis of the series and parallel connected 1D photodiode structures discussed above) is:

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[0059] The low frequency receive gain and -3dB receiver bandwidth are as follows:

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[0060] Thus, a receiver with a two-dimensional matrix of N=M×N photodiodes (whose total light detection area is N times larger than that of a single photodiode) will generate an output signal that is K times larger at low frequencies than a receiver with a single photodiode, and the reception bandwidth will be M / K times larger.

[0061] FIG. 10 shows the behavior of frequency characteristics 901, 902, 903, and 904 of an OWC receiver (consisting of a two-dimensional array of N=M×N photodiodes). Z T,ref =v out (t) / i PD (t) is the ratio of the output voltage v out (t) of the transimpedance amplifier and the average photocurrent i PD (t)=a￣·R·P(t) generated for each photodiode. This behavior is shown on a log-log scale in FIG. 10. That is, both the vertical axis and the horizontal axis are logarithmic axes. As shown in the figure, when K = M, the bandwidth is the same as that of a single photodiode (N = 1).

[0062] Compared with a single photodiode 905, if the number of photodiodes is constant and K > M (see curve 902), the bandwidth becomes M / K times smaller and the gain becomes K times larger. Conversely, if N is constant and K < N (see curve 904), the bandwidth increases but the gain decreases.

[0063] Compared with a single photodiode 905, by applying a two-dimensional array of photodiodes with K = M (see curve 903), the active area of the photodiode can be expanded. On the other hand, at this time, the bandwidth remains unchanged and the output signal of the OWC becomes stronger. In the case of K > M (see curve 902), compared with the case of K = M (see curve 903), the output voltage further increases and the bandwidth decreases. Conversely, in the case of K < M (see curve 904), the output voltage decreases and the bandwidth increases.

[0064] As described above, the present invention has been described according to several embodiments. These are for illustrative purposes and not for limiting purposes. Therefore, the present invention can be greatly modified in detailed implementation, which can be conceived by those skilled in the art from this specification. All such modifications are within the scope of the present invention and the idea defined by the claims and their legal equivalents.

Claims

1. 1. An optical wireless communication (OWC) receiver for receiving an incident light beam modulated with data and outputting an electrical output signal containing the modulated data, comprising: a lens configured to receive an incoming light beam; a number of photodiodes arranged at a distance from a lens, in or near the focal plane of said lens; - an amplifier; Equipped with each of the plurality of photodiodes is configured to receive a portion of the incident light beam and generate a photocurrent of photons corresponding to the received portion of the incident light beam; The plurality (N) of photodiodes are arranged in a two-dimensional array (N=M×K) of rows (1, . . . ,M; where M≧2) and columns (1, . . . ,K; where K≧2); The outputs from the columns (1, ..., K) are combined and the photocurrents from these columns are summed; the amplifier is connected to the combined outputs from columns (1, ..., K) of the two-dimensional array and converts the summed photocurrents into an amplified electrical output signal; the interconnections between each of the photodiodes in the two-dimensional array (M×K) form at least two parallel photodiode branches; each of said parallel branches forming a cascade of at least two photodiodes; An optical wireless communication (OWC) receiver, wherein the two-dimensional array forms an interdigitated surface of photodiodes.

2. 2. The optical wireless communication (OWC) receiver of claim 1, wherein the number K of parallel branches (1, ..., K) included in the two-dimensional array (N=M x K) is greater than the number M of cascades (1, ..., M) included in each of the branches (i.e., M<K).

3. 2. The optical wireless communication (OWC) receiver of claim 1, wherein the number K of parallel branches (1, ..., K) included in the two-dimensional array (N=M x K) is smaller than the number M of cascades (1, ..., M) included in each of the branches (i.e., M>K).

4. 2. The optical wireless communication (OWC) receiver of claim 1, wherein the number K of parallel branches (1, ..., K) included in the two-dimensional array (N=M x K) is equal to the number M of cascades (1, ..., M) included in each of the branches (i.e., M=K).

5. 5. An optical wireless communication (OWC) receiver according to claim 1, wherein the lens projects the received light beam onto a surface area larger than the surface area of ​​the combined photodiode.

6. a two-dimensional array (N=M×K) defining rows and columns of the two-dimensional array of photodiodes, including interconnections of the photodiodes; 6. An optical wireless communication (OWC) receiver as claimed in any one of claims 1 to 5, characterized in that each of the interconnects defining each row (1, ..., M) is also an interconnect defining each column (1, ..., K).

7. 7. The optical wireless communication (OWC) receiver of claim 1, wherein each row of the two-dimensional array further comprises a resistor arranged in parallel with the photodiodes of each row.

8. 8. The optical wireless communication (OWC) receiver of claim 7, wherein each of the resistors is located external to the two-dimensional array of photodiodes.

9. 8. The optical wireless communication (OWC) receiver of claim 7, wherein each of said resistors is integrated within said two-dimensional array of photodiodes.

10. An optical wireless communication (OWC) system comprising an optical wireless communication (OWC) receiver according to any one of claims 1 to 9.

11. An optical wireless communication (OWC) system according to claim 10, comprising a plurality of optical wireless communication (OWC) receivers according to any one of claims 1 to 9.

12. An optical wireless communication (OWC) system comprising an optical wireless communication (OWC) receiver according to any one of claims 1 to 9, Optical wireless communication (OWC) systems are used for optical communication using electromagnetic waves with wavelengths in the visible, infrared, near infrared or ultraviolet spectrum.

13. An optical wireless communication (OWC) system comprising an optical wireless communication (OWC) receiver according to any one of claims 1 to 9, Optical wireless communication (OWC) systems used for either wireless LAN networks, wireless personal networks or vehicular networks.

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