Optical data link

The invention provides an optically powered device interface module for operating an external device, and an optically powered data link comprising the same. In one embodiment the device interface module includes an optical interface for receiving optical power and data signals, an electrical USB interface for providing USB compliant electrical data signals and a 5V electrical power signal to an external USB device, a transducer coupled to a signal processor for converting the optical power and data signals into the 5V electrical power signal and the USB-compliant electrical data signals, and a power distribution circuit for providing electrical power obtained from the optical power signal to the device interface module circuitry. The transducer may be embodied using a single photovoltaic power converter for receiving the optical power and for receiving and transmitting optical data signals.

TECHNICAL FIELD

The present invention generally relates to computer systems and devices using the Universal Serial Bus (USB) protocol for communications, and in particular relates to an optical USB link wherein both data and power are transmitted optically.

BACKGROUND OF THE INVENTION

The recent proliferation of computer-controlled devices for performing a wide variety of tasks can be at least partially attributed to the development of powerful and convenient communications interface standards, such as various types of serial bus interfaces. Some of them have conveniently incorporated remote electrical powering to the communication functionality of the interface, so that peripheral devices that do not require excessive electrical power to operate could be powered remotely through the communications interface rather than requiring a built-in or a separate power supply at the device location. One such interface standard that has now become ubiquitous is the Universal Serial Bus (USB).

The USB is a peripheral hub-centric serial bus that is widely used to facilitate coupling of a wide range of simultaneously accessible peripheral devices to a host computer system. The bus allows up to 127 peripheral devices to be attached, configured, used, and detached while the host is in operation. For example, USB printers, scanners, digital cameras, storage devices, card readers, etc. may communicate with a host computer system over USB. USB based systems may require that a USB host controller be present in the host system, and that the operating system (OS) of the host system support USB and USB Mass Storage Class Devices. As compared to other ways of connecting devices to the computer, such as parallel ports, serial ports and custom cards installed inside the computer's case, the USB devices are relatively simple. If the USB device is a new device, the OS auto-detects the USB device and may initiate a dialog with the user to locate a driver for the USB device. If the USB device has already been installed, the computer activates the USB device.

USB devices may communicate with the USB host at low-speed (LS), full-speed (FS), or high-speed (HS). USB Specification version 1.1 supports two different rates for transmitting data: A Low Speed (LS) rate of 1.5 Mega bits (Mbits) per second that is mostly used for low-speed human interface type devices such as keyboards and mice, and a Full-Speed (FS) rate of 12 Mbits/second for most other devices. USB Specification 2.0 adds a High-Speed (HS) rate of 480 Mbps for communications with high speed devices. The USB Specification Revision 2.0, Apr. 27, 2000, which describes the USB 2.0 protocol in detail, is available on-line at http://www.usb.org/developers/docs and is incorporated herein by reference in its entirety.

A connection between the USB device and the USB host is typically established via a four wire interface that is formed by 4-pin USB connectors and a USB cable that includes four wires: two wires for providing a 5V dc power signal and ground, respectively, and a twisted pair of wires to carry data, which are labeled as D+ and D−, and are used for half-duplex differential signaling to combat the effects of electromagnetic noise on longer lines, with the data sent in digital format using a NRZI (Non Return to Zero Invert) encoding scheme.

Advantageously, low-power devices such as mice, video cameras, and/or other devices can draw their power directly from the USB connection. High-power devices such as printers and/or other devices have power supplies and typically draw minimal power from the USB connection. USB devices are hot-swappable, which means that they can be plugged and unplugged at any time. Up to 127 devices can be connected to any one USB bus at any one given time. At system turn-on, the host computer powers up, queries all of the USB devices connected to the bus and assigns an address to each USB device. This process is called enumeration; USB devices are also enumerated when they are connected to the bus in operation. The host computer determines the type of data transfer that the USB device employs, such as an interrupt mode, a bulk transfer mode, or an isochronous mode.

Due to it numerous advantages and ease of operation, the USB protocol is now the prevalent protocol for communication between computers and peripheral devices of different kind. Various sensors, transducers as well as more recently GPS devices and video cameras are now available with a USB interface that provides both power and the entire data transmission between the device and a computer in a digital format. This universality leads to acceptance of the USB protocol as a standard protocol for peripheral communications, as well as the proliferation of digital data transmission for a variety of applications.

However, the traditional USB links involving communications over 4-wire USB cables cannot be longer than 5 meters, therefore limiting possible applications to a desktop type environment. This is in part due to strict limitations that the current USB specification imposes on the cable delay time, which should not exceed 26 ns for a single cable. There is however another important limitation on the maximum length of a traditional USB cable, namely—signal attenuation, which in traditional 4-wire USB cables strongly increases with signal frequency, typically from about 0.7 dB/m at 10 MHz to as high as 5.8 dB/m at 400 MHz. This signal attenuation makes it difficult to impossible to use cables in excess of 5-10 meters at full and, especially, high data transfer speed.

Another limitation of the traditional USB copper-based links is their potential susceptibility to high magnetic, voltage and RF fields, which may induce errors in USB data transmission. Furthermore, the traditional copper-based USB cables can themselves be a source of electromagnetic interference (EMI), and therefore their use can cause undesirable problems in EMI-sensitive environments.

U.S. Pat. No. 6,950,610 issued to Lee and assigned to Opticis Co., LTD, which is incorporated herein by reference, has disclosed an optical communication interface module for connecting USB interfaces through an optical fiber line that employs separate optical fibers to transmit optical signals in each direction. However, the optical communication interface module of Lee only partially solves the above stated problems, since operating a USB device using it will either still require two separate copper lines VCC and GND to remotely power the device, or require an external power supply at the device location, which may be inconvenient or even close to impossible in some applications. The optical communication interface modules of Lee therefore do not provide a fully-functional all-optical alternative to a USB cable, which would be beneficial in applications where conventional copper USB cables cannot be used, such as in EMI sensitive environments.

It is therefore desirable to provide a USB link and USB interface modules that can be used in EMI sensitive environments or in the presence of high magnetic, electrical and RF fields to remotely operate and to power conventional USB devices.

An object of the present invention is to overcome the shortcomings of the prior art by providing an optically powered optical data link and optical interface modules for remotely powering and operating peripheral devices using a desired communications protocol, and to provide an optically powered optical data link and optical interface modules that are capable of operating in EMI sensitive environment or in the presence of strong electrical, magnetic or RF fields.

SUMMARY OF THE INVENTION

In accordance with the invention, a device interface module is provided for remotely powering and operating an external device, the device interface module comprising: an optical interface for receiving an upstream optical signal from an optical fiber line and for transmitting a downstream optical signal through the optical fiber line; an electrical interface for connecting to the external device, comprising a data port for receiving an input electrical data signal from the external device according to a pre-determined data communications protocol and for providing an output electrical data signal to the device, and an output power port for providing electrical power to the remote device; a transducer optically coupled to the optical interface for converting the upstream optical signal into a received electrical data signal and electrical power, and for generating the downstream optical data signal; a signal processor comprising a receiver circuit operatively connected between the transducer and the electrical data port for producing the output electrical data signal from the received electrical data signal according to the pre-determined data communications protocol, and a transmitter circuit operatively connected between the electrical data port and the transducer, for producing an electrical drive signal from the input electrical data signal for driving the transducer therewith to generate the downstream optical data signal; and, a power distribution circuit for distributing the electrical power obtained from the upstream optical signal for powering the external device, the signal processor and the transducer.

The transducer preferably comprises a multi-segment photovoltaic power converter (MSPPC) that is optically coupled to the optical interface for receiving the upstream optical signal and may further comprise a signal separation circuit for separating power and data components of the detected electrical signal. In one embodiment, the transducer further comprises a bias circuit for forward biasing at least a segment of the MSPPC for generating the downstream optical signal, and may comprise a switching circuit for switching the at least a segment of the MSPPC between a photodetecting mode of operation and a light emitting mode of operation. The device interface module of this embodiment may further comprise a controller for controlling the switching circuit, wherein the controller is operatively connected for monitoring at least one of the received electrical data signal and the output electrical data signal so as to switch the at least a segment of the MSPPC from the photodetecting mode of operation to the light emitting mode of operation upon detecting an end of the upstream transmission, and for monitoring at least one of the electrical drive signal and the input electrical data signal so as to switch the at least a segment of the MSPPC from the light emitting mode of operation to the photodetecting mode of operation upon detecting an end of the downstream transmission. This embodiment of the invention utilizes the MSPPC to generate electrical power from the upstream optical signal for powering the external device and internal circuitry of the device interface module, to receive an upstream optical data signal, and to transmit the downstream optical data signal.

In accordance with another aspect of this invention there is provided an optically powered optical data link comprising the device interface module, a host interface module, and the optical fiber line optically connecting the host interface module to the device interface module. The host interface module comprises an electrical interface electrically coupled to a host controller, and an optical transceiver optically coupled to the optical fiber line, the optical transceiver configured for converting an upstream electrical data signal provided from the host controller into the upstream optical signal, and for converting the downstream optical data signals received from the device interface module into upstream electrical data signals for providing to the host controller.

DETAILED DESCRIPTION

FIG. 1illustrates an optical data link (ODL)5between a host controller10and an external, or peripheral device50according to the present invention. The host controller10, which can be embodied for example as a card in a computer, and the device10preferably support one of standard communication protocols and preferably have standard communication interfaces. The ODL5may be used for operating the peripheral device50, hereinafter referred to as simply the device50, by providing a communication channel between the device50and the host controller10, and by remotely supplying the device with electrical power required for it operation. By way of example, the device50is shown as a video camera and has a USB port. In other embodiment, the device50can be any other device that has a desired functionality, can be externally powered, and has a standard communication interface supporting one or more standard data communication protocols, including but not limited to interfaces which comply with serial bus interface standards such as USB, FireWire, I2C, and RS 232, and video interfaces such as DMV and HDMI. A data communications protocol as used in the current specification is a set of standard rules for representing data with digital electrical signals, which may include rules for representing actual data to be transmitted and signaling rules for supporting the communication between the host and the device, such as signaling a beginning and end of a transmission session, of a packet or a frame.

In the shown embodiment, the host controller10is a USB host controller, and the device50has a standard USB 1.1 or USB 2.0 interface including a 4-pin USB cable61having a VCC line for supplying a 5V power to the device, a ground line GND, and a pair of twisted signaling lines D+ and D− for supporting bi-directional data communications with the host controller10using differential signaling according to the USB protocol.

The ODL5is comprised of a host interface module (HIM)20and a device interface module (DIM)40, which are coupled by an optical line30embodied as a fiber-optic cable. Depending on a particular embodiment, the fiber-optic cable30may have one, two or three optical fibers as described hereinbelow. Data transmission from the host10to the device50is referred to hereinafter as the upstream transmission, while data transmission from the device50to the host10is referred to hereinafter as the downstream transmission.

The device interface module40includes an optical interface41to which a distal end of the fiber-optic cable30is coupled, and an electrical interface51to which the device50is operatively connected by means of the cable61. The electrical interface45, which preferably matches the communication interface of the device50, includes an output power port and a bidirectional data port. In the exemplary embodiments herein described, the electrical interface51may be a standard USB connector having a ground pin GND, a power supply pin VCC for outputting a 5V power signal, and signaling pins D+ and D− for supporting data communications according to the USB protocol. The optical and electrical interfaces41,51are operatively coupled by means of a transceiver circuit42,43,44, which converts optical signal or signals received from the optical line30into electrical power and data signals for providing to the device50, and converts electrical data signals from the device50into optical data signals for sending over the data line30. A transducer42is optically coupled to the optical interface41, and electrically connects to a signal processor circuit44, which in turn connects to the electrical interface51via a bidirectional electrical connection45. A power distribution circuit43has an input that is electrically coupled to a power output port of the transducer42, and one or more outputs that are electrically coupled to the power output port46of the electrical interface51, and also to the signal processor44for supplying electrical power thereto.

The host interface module20has an optical interface27optically coupled to a proximal end of optical line30, and an electrical interface21, which may include a USB connector, that is connected to a matching electrical communications interface28of the host controller10, for example the USB interface. The optical and electrical interfaces27,21of the HIM20are operatively coupled by an optical transceiver23.

In operation, the electrical interface21of the host interface device receives the upstream electrical data signal Supgenerated by the host controller10, and provides them to the optical transceiver23, which converts it into an upstream optical signal Pup24that includes a sequence of optical pulses representing the upstream electrical signal Sup, and transmits said upstream optical signal through the optical interface27and the optical line30to the DIM40.

The optical interface41of the DIM40receives the upstream optical signal Pup, and provides it to the transducer42, which converts the upstream optical signal into a received electrical data signal Srd47and an electrical power signal Sp48. In a preferred embodiment, the transducer42includes a photovoltaic power converter PPC (not shown) for converting the upstream optical signal Pupinto at least the electrical power signal, and preferably also for extracting therefrom the received data signal Srd47. The received electrical data signal Srd47is then provided to the signal processor44, which includes a receiver circuit (nor shown) for producing therefrom an output electrical data signal Soutthat is compliant with the standard communication protocol supported by the device50, in the current example—the USB protocol. The output electrical data signal Soutis then provided to the electrical interface51and thereby to the device50.

Communication signals generated by the device50in compliance with the selected standard communications protocol are received by the electrical (USB) interface51of the DIM40as input electrical data signals, and are provided through the bi-directional connection to a transmitter circuit (not shown) of the signal processor44, which is operatively connected between the electrical data port45of the electrical interface51and the transducer42. The receiver circuit produces an electrical drive signal Sdrfrom the input electrical data for driving the transducer42therewith to generate a downstream optical data signal Pdwn, which is then transmitted by the transducer42through the optical interface41of the DIM40and the optical fiber line30to the HIM20.

The optical interface27of the HIM20receives the upstream optical data signal Pup, and couples it into a receive port of the transceiver23, which detects and processes the signal to re-produce the upstream electrical data signal Sup, which is then fed to the host controller via the USB interface21.

Advantageously, the ODL5of the present invention enables operating the device50without any additional source of electrical power at the distal end of the link; electrical power required for operation of both the DIM40and the device50is remotely supplied from the HIM20via the fiber line30in the form of optical power, which is then converted by the transducer42into electrical power and used for powering both the internal circuitry of the DIM40, and the device50, so that neither of them requires electrical power supplies.

The upstream optical signal Pupmay be comprised of optical data and power signals Pud, Ppthat are generated separately using dedicated optical sources in the transceiver23at a same or different wavelengths and then delivered to the DIM40using either two separate optical fibers within the fiber line30, or they can be coupled into a single fiber strand. Alternatively, it can be generated by a single optical transmitter such as a high-power laser diode that is modulated to carry the upstream data signal. The transducer42may include a separate photodetector for detecting the optical data signal and the PPC for converting the optical power signal into the electrical power signal, and may also include a light source such as an LED or a VCSEL for generating the downstream optical data signal. A preferred embodiment of the current invention however utilizes a single PPC to convert optical power into electrical power, and to detect the data signal component of the upstream optical signal. Furthermore, some embodiments may utilize the same PPC for transmitting the downstream optical data signal Pdwnto the HIM20via the optical line30, which in this case advantageously includes a single fiber strand both for downstream and upstream optical signals.

FIG. 2illustrates a first embodiment100of the HIM20, which is referred to hereinafter as the HIM100. In this embodiment, the HIM optical transceiver23includes three separate devices for receiving and transmitting light: a modulated optical source (MOS)130for generating a upstream optical data signal Pud, an optical power source (OPS)145for generating the optical power signal Pp, and a photodetector (PD)135for receiving the downstream optical data signal Pdwnand converting it into an electrical signal. Additionally, the HIM transceiver23in this embodiment also includes a power laser driver140and a signal processor144, which in turn includes a transmitter (Tx) circuit120and a receiver (Rx) circuit125.

The MOS130can utilize an LED, an edge-emitting laser diode (LD) or a VCSEL, and may include driver circuitry for drive current modulation as known in the art. The OPS145can be embodied as a high-power laser diode, for example a 980 nm pump laser diode, preferably having a fiber-optic pigtail. An additional power supply110may be used to provide enough electrical power, for example about 1 W or more, to drive the OPS145. The MOS130and the OPS145may emit light at equal or different wavelengths, preferably but not exclusively in the wavelength range between 0.8 nm and 1.55 nm, for which relatively inexpensive compact high-power optical sources and light emitters amiable to direct current modulation are commercially available, and where optical fibers of the optical line30have suitably low optical loss. The PD135can be embodied as PIN or PN diode suitable for detecting the downstream optical data signal, and can include bias circuitry. The OPS145, MOS130, and PD135are each optically coupled, for example using fiber-optic pigtails, to respective fiber-optic connectors141,142and143, which together form the HIM optical interface27, which in turn connect to three optical fibers301-303that form the optical line30in this embodiment of the invention; two of these fibers,301and302, are used for separately transmitting the optical power signal and the optical data signal, while the optical fiber303is used for the downstream optical transmission. The optical fibers301-303can be either single-mode or multimode; some embodiments may include single mode fibers, for example fibers303and302for transmitting optical data signals, and a multimode fiber301for transmitting the optical power signal.

The electrical interface of the HIM100for connecting to the host controller10is embodied as a USB connector108, having a GND ground port114, a VCC power port111providing a 5V power signal, and D+ and D− data ports112,113for receiving and transmitting electrical data signals D+, D−. The host controller10utilizes differential NRZI modulation in accordance with the USB protocol to transmit data packets. In NRZI encoding, a ‘1’ is represented by no change in level and a ‘0’ is represented by a change in level, so that a string of zeros causes the NRZI signal to toggle each bit time. With reference toFIG. 3, the data are transmitted using a differential voltage signal DV=(D+, D−) wherein single-ended voltage signals D+412and D−411vary in counter-phase, so that the D− signal is in a logic “low” state when the D+ signal is in a logic “high” state, and vice versa, for every transmit data bit within a packet. Each packet concludes with an “End Of Packet” (EOP) symbol428, typically of a two-bit duration, when both the D+ and D− signals411,412are in the logical “low” state; this USB EOP signal is referred to hereinbelow as a double-zero signal.

Referring now toFIGS. 2 and 3, the Tx circuit120receives data packets from the electrical USB interface108through a differential line pair112,113in the form of the differential voltage signal pair ‘D+’412and ‘D−’411, and converts it into a single-ended pulsed current or voltage signal421that drives the MOS130. This conversion is performed in such a way that each differential pulse421where, for example, D+ is greater than D−, is converted to a single-ended drive current pulse423of a first amplitude I1that is suitable for causing the MOS130to emit a light pulse433, while each EOP symbol427is converted into a substantially larger current or voltage pulse428having a second amplitude I2that is substantially larger than the first amplitude I1. As a result, the MOS130generates a series of optical pulses431corresponding to the differential USB signal411,412, so that when the differential signal DV has a first polarity, for example when D+ is greater than D−, a light pulse of a first intensity is produced, and when the differential signal DV has a second polarity opposite to the first polarity, for example when D+ is smaller than D−, substantially no light is produced, and when both the D+ and D− signals are in the logic “low” state, a light pulse of a second intensity that is substantially, for example by 50% or more, larger that the first intensity, is produced.

FIG. 4illustrates one possible embodiment of the Tx circuit120. The MOS130may be in the form of an LED, such as 1A299 LED from Zarlink, and is driven by transistors470and420. The sum of the collector currents from these two transistors forms the electrical drive signal in the form of electrical current that is output through a port415and drives the LED130. The D+ and D− signals are received via input ports450and460, and are provided to input ports of an exclusive-NOR (XNOR) logic gate440. An output signal E=XNOR{D+,D−} of the XNOR gate440is a logical “high”, or “1” when D+=D−, and a logical low, or “0” when D+ is either greater or smaller than D−. The output port435of the XNOR gate440is connected to a base of the second transistor420through a base resistor430, so that the second transistor,420, is driven by the XNOR gate signal E=XNOR{D+,D−}. The first transistor470is driven directly by the D+ signal through a connection416and a second base resistor465.

By way of example, collector resistors465and430are such that the first transistor470contributes 25 mA to the total LED current when D+ is a ‘1’. If the D+ signal is a ‘0’, then no current is driven by the first transistor470. The contribution to the total LED current from the second transistor420is 50 mA when D+=D−, and zero when D+NOT=D−. Accordingly, four possible states of the differential signal (D+,D−) result in four values of the total LED current flowing through the LED130:

One advantage of the Tx circuit ofFIG. 4is that it provides two special optical signals, one being the EOP and a reserved second signal, to be sent optically through the same fiber channel in addition to the optical pulses corresponding to regular differential high-low USB data signals.

Referring back toFIG. 2, the optical pulses produced in this by the LED130are then transmitted by the MOS130via the optical fiber302as the upstream optical data signal Pud.

The downstream optical data signal Pdwn, in the form of a sequence of optical pulses is coupled from the optical fiber303to the PD135, which converts them into single-ended electrical pulse signals, which are then provided to the Rx circuit125that converts them into differential USB voltage signals. The Rx circuit performs an operation that is substantially a reverse of the operation performed by the Tx circuit120, as described herein below with reference to a Rx circuit of a DIM200shown inFIG. 5.

The optical power signal Ppgenerated by the OPS145preferably provides at least 0.5 W of electrical power, i.e. one unit load of 100 mA at 5V, at the DIM located upstream from the HIM100. A power conversion efficiency as high as 50% can be realized using a multi-segmented PPC, such as those described in concurrent US patent applications entitled “Photovoltaic power converter” and “Multi-segment photovoltaic power converter with a center portion” filed by the applicant of the present application. Thus, the OPS145should emit at least 1 W of optical power, and preferably about or greater than 1.5 W of optical power, accounting for the need to power electrical and optical conversion circuitry of the upstream DIM. Such high-power laser diodes emitting up to 4 W of optical power in a multi-mode fiber at wavelengths in the 900-980 nm range are commercially available, for example, from JDSU Inc.

Since such high-power lasers can present significant safety issues, for example in case of a fiber brake, a laser safety control circuit111may be incorporated in the HIM100, as illustrated inFIG. 2; this circuit shuts down laser power supply110when the USB “hand-shake” protocol is not established, i.e. a handshake packet is not received by the HIM100within a pre-determined time interval after the host controller10initiates communications with the external device, for example within a fraction of a second. In addition, this safety feature may be monitoring the presence of the received data signals, and in their eventual absence also command an immediate shut off of the laser driver140and/or laser power supply110, so that to shut off the OPS145. The shut-off operation can be activated by an ASCII command sent by the laser safety control circuit111via an RS 232 interface to the laser driver140and/or laser power supply110.

FIG. 5illustrates an embodiment200of the DIM40, which is referred to hereinafter as the DIM200and is suitable for operating with the HIM100according to the first embodiment of the invention. In operation, the DIM200receives the optical power signal Ppand the upstream optical data signal Pudfrom the optical fibers301,302of the optical line30. Similarly to the HIM100, the optical interface of the DIM200includes fiber-optic connectors250,255and260, to which the fibers301,302and303are coupled. The DIM transducer42includes in this embodiment a PD230that is coupled to the connector255for receiving the upstream optical signal Pud, and a PPC245coupled to the connector250for receiving the optical power signal Ppand converting it into an electrical power signal. The transducer42further includes a MOS235, such as an LED or a VCSEL, for generating the downstream optical data signal Pdwn, in a same way as the MOS130of the HIM100is used to generate the upstream optical signal Pud. Electrical ports of the PD230and the MOS235are connected to single-ended ports of the DIM signal processor44, which performs same functions and have a substantially same structure as the HIM signal processor144, with the Rx circuit220and the Tx circuit225of the DIM200corresponding to the Rx circuit125and the Tx circuit120of the HIM100, and the Tx circuit120embodied as shown inFIG. 4.

The PPC245is preferably a multi-segment device such as that described in U.S. Pat. No. 5,342,451, or most preferably a multi-segment PPC such as one of the PPC devices disclosed in the co-pending U.S. patent applications entitled “Photovoltaic power converter” and “Multi-segment photovoltaic power converter with a center portion” that are assigned to the assignee of the current application, which are capable of converting the optical power signal Ppinto an electrical power signal Sphaving a voltage component of 5V or greater with power conversion efficiency in excess of 50%, so that a 100 mA, 5V power signal can be obtained from 1 W of optical power coupled into the PPC245. This electrical power signal Spis then provided to the power distributor circuit43for powering the peripheral device50through the power port211of the electrical interface208embodied as a conventional 4-port USB connector, and for powering the signal processor44and the bias circuits of the transducer42. By way of example, power distributor43provides a 5V power signal at the power port VCC211of the USB interface208through a 5V feed line228and can drive up to 100 mA of electrical current therethrough, thereby providing up to 500 mW of power to operate the external device50, and provides up to 200 mW of electrical power though the 3.3V electrical feed229to the DIM200circuitry44,42, for a total electrical power of 700 mW provided by the PPC245by converting the optical power signal Ppcarrying about 1.4 W of optical power.

The upstream optical data signal Pudis converted by the PD230into a received electrical data signal Srd, which may be in the form of a pulsed photocurrent or pulsed voltage. This received electrical data signal Srdis provided to the Rx circuit220, which converts it into a differential USB-compliant output data signal Soutthat reproduces the upstream data signal Supwhich was generated by the host controller10and converted by the HIM100into the upstream optical data signal Pud.

One embodiment of the Rx circuit220is shown inFIG. 6. This embodiment of the Rx circuit220assumes that the PD230includes a current-to-voltage converter such as a trans-impedance amplifier (TIA), so that the Srdsignal is a voltage signal consisting of a sequence of voltage pulses corresponding to the optical pulses431ofFIG. 3, with each data pulse resulting from the optical data pulses433having a peak voltage exceeding a first reference voltage V1but below a second reference voltage V2>V1, and each EOP voltage pulse, i.e. voltage pulse in the received Srdsignal corresponding to the optical EOP pulse438, having a peak voltage exceeding V2.

The Rx circuit ofFIG. 6includes an input single-ended port550, which provides the received single-ended data signal Srdin the form of the voltage pulse sequence from the PD135to positive inputs of each of two dual voltage comparators555and540, which negative inputs are connected to a source505of the reference voltage V2and to a source545of the reference voltage V1, respectively. By way of example V1=2 Volt, and V2=3 Volt, so that the source505provides a 3V reference voltage, while the source545provides a 2 Volt reference voltage to the negative inputs of respective comparators555and545. The 2V and 3V reference voltages are sourced from the 3.3V voltage feed of the power distributor43, which drives a pair of dividing resistors (not shown) to each comparator minus input. The pair of dividing resistors forms a voltage divider, dividing down the 3.3V to both 2V and 3V reference values.

The Rx circuit ofFIG. 6outputs the differential data signal Soutthrough a differential output port (535,525) that is comprised of a single-ended ‘OUT−’ port535and a single-ended ‘OUT+’ port525.

The comparator540, which uses termination resistors530and520, serves as a data output driver: with an input signal Srdless than 2V, it provides a logical ‘1’ at the ‘OUT−’ port535, and a logical ‘0’ at the ‘OUT+-port525, thereby generating a differential USB signal ‘0’; with an input signal Srdbetween 2V and 3V, it provides a logical ‘0’ at the ‘OUT−’ port535, and a logical ‘1’ at the ‘OUT+’ port525, thereby generating a differential USB signal ‘1’. When the input Srdsignal is higher than 3V, the second comparator555drives the base of the transistor515through a resistor510, and saturates the transistor, causing the signal at the ‘OUT+’ port525to be driven to ‘0’, over-riding the positive output of the comparator540.

The resulting output differential electrical data signal Soutis in a USB protocol compliant form, and is provided to the D+ and D− ports211,213of the USB interface208for communicating to a USB interface of the external device50.

Downstream data packets generated by the external device50are received by the DIM200as an input electrical data signal Sin=(D+, D−) in the form of differential voltage pulses through the bi-directional D+ and D− ports112,113of the electrical interface208. This differential data signal is provided to the Tx circuit225, which may be embodied as shown inFIG. 4and operates as described hereinabove with reference to the Tx circuit120of the HIM100, producing a single-ended drive signal Sdrin the form of pulsed current that drives the MOS235, resulting in the generation of the downstream optical data signal Pup.

The aforedescribed first embodiment of the invention utilizes two different optical receivers, the PD230and the PPC245, to receive optical power and data signals.FIG. 7illustrates a DIM300according to a second embodiment of the present invention, wherein both these functions are performed by the PPC245. Note thatFIGS. 7 and 5use like reference numerals to refer to like features. In this second embodiment, the transducer42consists of two rather than three opto-electronic devices: a single light receiving device, i.e. the PPC245, and the MOS235, and both the upstream optical data and optical power signals Pud, Ppare delivered as a single upstream optical signal Pup=Pud+Ppusing the single strand of optical fiber301, thus enabling to eliminate one strand of optical fiber in the optical cable30and one photodetector compared to the DIM200.

In operation, the PPC245converts the upstream optical signal Pupinto a received optical signal Sr, which is then passed to a signal separation circuit (SSC)223, which separates is into the electrical power signal Spand the received electrical data signal Srd, which may be in the form of a single-ended pulsed voltage signal. These signals are then passed to the power distribution circuit43and the Rx circuit220of the signal processor44, respectively, which are then processed as described hereinabove with reference toFIG. 5.

With reference toFIG. 8, one embodiment of the SSC223includes a power extraction circuit630and a signal extraction circuit635which are both connected at their respected inputs to the anode terminal of the PPC245. A received electrical signal Srgenerated at the anode terminal of the PPC245, which has a voltage component of at least 5V or greater, is coupled into the power extraction circuit630, which obtains therefrom the electrical power signal Spby means of a Schottky diode rectifier605and a shunting capacitor620, and provides the power signal Spto the power distribution circuit43via a power output port615. An optional super-capacitor625at the output of the power extraction circuit630functions as an electrical power accumulator to provide electrical power to the DIM circuitry and the external device50during time intervals when no electrical power is provided by the PPC245. In a preferred embodiment, the PPC245generates at least 5.5V at its anode terminal from the upstream optical signal Pup.

The signal extraction circuit635includes a transistor655acting as a switch, with the collector voltage of the transistor655provided to the Rx circuit220as the received data signal Srdvia a data output port670. The received electrical signal Sris coupled from the anode of the PPC245into the base of the transistor655through a parallel R-C circuit650. When the PPC245receives an optical pulse, an electrical current flows in the base circuit of the transistor655, saturating said transistor and causing the collector voltage to be substantially zero, corresponding to a logic ‘0’ to be generated at the output data port670. In-between optical pulses when the PPC245receives substantially no light, the current in the base circuit of the transistor655is shut off, forcing the transistor655into a cut-off and halting the flow of current through the collector. This allows a collector resistor R2to pull up the collector voltage close to 3.3V, thereby generating a logic ‘1’ at the output data port670.

With reference toFIG. 9, a HIM400is shown that can operate with the DIM300ofFIG. 7to form the ODL5of the present invention in the second embodiment thereof. The HIM400differs from the HIM100in that an optical multiplexer is used to combine the upstream optical data signal Pudgenerated by the MOS135and the optical power signal Ppgenerated by the high-power laser145into a single optical beam, which is the coupled into the optical fiber301. The optical multiplexer may be embodied as a wavelength multiplexer in embodiments wherein the optical power signal Ppand the upstream optical signal Pudare separated in wavelength, for example, if the MOS135is a directly modulated VCSEL operating at a 1.3 μm, and the OPS145is a 980 nm pump laser diode. Alternatively, for example in embodiments wherein the OPS145and the MOS135operate at a substantially same wavelength, the multiplexer550can be a polarization multiplexer.

In another embodiment, both the MOS135and the optical multiplexer550can be eliminated, and the output signal from the Tx circuit125is used to modulate the drive current of the OPS140, as schematically shown by dashed line640. When the OSP140is embodied as a 980 nm pump laser diode emitting 1 W of power, such direct current modulation can be effective at modulation rates up to at least 1.5 Mbps or higher.

With reference toFIG. 10, a DIM500is shown according to a third embodiment of the present invention. In this embodiment, a transducer445of the DIM500utilizes the PPC245as a single opto-electronic converter, both to receive the upstream optical signal Pupthat carries optical power and data, and to generate the downstream optical data signal Pup. The optical line30connecting the DIM500with an downstream HIM consists in this embodiment of a single optical fiber301which supports the transmission of both the upstream and downstream optical signals; accordingly, the optical interface of the DIM500includes a single fiber-optic port/connector250to which the optical fiber301is coupled. The transducer445, which serves herein as the transducer42ofFIG. 1, includes the PPC245and may include additional circuitry such as a PPC bias control circuit and a signal-separation circuit, as described hereinbelow.

With reference toFIG. 11, an embodiment445aof the transducer445includes a bias and signal switching circuit (BSS)720for switching the PPC245from a photodetecting mode of operation to a light emitting mode of operation, and the SSC223for separating the power and data components of the received electrical signal Srwhen the PPC245operates in the photodetecting mode. The PPC245is preferably a monolithic multilayer semiconductor device that includes a plurality of P/N or PIN junctions that are connected in series, such as a multi-segment semiconductor power receiver described in U.S. Pat. No. 5,342,451 or, more preferably, as described in the co-pending patent applications entitled “Photovoltaic power converter” and “Multi-segment photovoltaic power converter with a center portion”.

In the photodetecting mode of operation, which is hereinafter referred to as the PD mode, the PPC245is either zero biased or reverse biased, so that an electrical field in the P/N junctions separates photogenerated electrons and holes, resulting in the creation of a potential difference between the anode and cathode terminals of the PPC245, or a positive photo-induced voltage at the anode terminal if the cathode terminal is grounded as in the shown embodiment. In the light-emitting mode of operation, which is hereinafter referred to as the LED mode, the PPC245is forward-biased, so that electrons and holes are injected in the P/N junction and recombine therein generating photons, and the PPC operates as an LED.

Turning now toFIG. 12, a HIM600is illustrated that can operate with the DIM500to form the ODL5of the present invention in the third embodiment thereof. The HIM600differs from the HIM400mainly in two aspects: first, the OPS145is utilized to generate both the optical power signal Ppand the upstream optical data signal Pup; for that purpose, the output of the Tx circuit125of the signal processor144is coupled to a driver circuit640of the OPS145for modulating the drive current of the OPS145, so that the OPS145produces optical pulses carrying the upstream data signal generated by the host controller. The upstream optical signal Pupcarrying both the optical data and optical power is then provided to an optical circulator650, which couples it into the optical fiber301for transmitting to the DIM500. The same circulator650couples the downstream optical signal Pupreceived through the fiber301from the DIM500into the PD130for converting it into an electrical data signal as described hereinabove with reference to the HIM100.

The host controller10via the USB interface108of the HIM600may initiate communications with the external device50connected to the USB interface208of the DIM500by generating a PING packet. Upon receiving this packet, the HIM600generates the upstream optical signal Pupcarrying the PING packet in the form of optical pulses as described hereinabove with reference to HIM100, which is transmitted to the DIM500over the optical fiber301.

Referring back toFIG. 1, the upstream optical signal is received at the DIM500by the PPC245, which by default operates in the PD mode wherein it is either zero-biased or reverse-biased. In this mode of operation, the PPC245first converts the upstream optical signal Pupinto the received electrical signal, which is coupled to the SSC223. The SSC223obtains therefrom the electrical power signal Sp, with preferably a voltage component of at least 5V, which is then passed to the power distributor43shown inFIG. 10. The power distributor43provides 3.3V voltage to the signal extraction circuit635of the SSC223, which powers up and extracts the received electrical data signal Srdfrom the received electrical signal Sr, as described hereinabove with reference toFIGS. 7 and 8. The received electrical data signal Srdis provided to the Rx circuit220, which converts it back into the differential signal Soutaccording to the USB signaling format, reproducing thereby the USB ‘PING’ data packet that was initially generated by the host controller.

Once the output differential signal Soutcarrying the PING packet is generated, the BSS720may be switched for forward biasing of the PPC250and for modulating the PPC245with the drive signal Sdr.

Upon receiving the output differential USB signal Soutcarrying the PING packet, the external device50generates a USB handshake packet in the form of a differential USB signal Sin=(D+, D−), and sends it over the D+ and D− signaling ports212,213of the USB interface208back to the DIM500, where it is received by the Rx circuit220of the signal processor44and converted into the single-ended electrical drive signal Sdr, which may be then provided to the PPC245of the transducer445in the form of a sequence of current pulses. The downstream optical signal Pup, which is generated by the forward-biased PPC245in response to the electrical drive signal Sdr, is coupled by the optical interface connector250into the optical fiber301, which transmits it to the HIM600where it is received by the Rx circuit102of the signal processor144.

FIG. 13shows one possible implementation of the transducer circuit445aofFIG. 11in further detail. The anode terminal of the PPC245is connected to the SSC223which is described hereinabove, and to the BSS720, which includes three switches773,774, and775, with the switch774connected in series with a parallel combination of switches773and775between the PPC anode and a −5V feed provided by the power distributor43. The switches773and775are referred to hereinafter as the EOP switch and the data switch, respectively, while the774switch is referred to as the bias switch, as it has to be closed to enable the LED mode of operation. The switches773and774are controlled by a controller771, which is preferably embodied as a low-power microcontroller, such as the ATtiny13 microcontroller from Atmel Corp., but can also be embodied using other types of logic devices as would be known to those skilled in the art, examples of which include a microprocessor, an FPGA, and the like. A control interface of the data switch773is coupled to the Tx circuit225as illustrated by a control line787, and receives a single-ended USB data signal D+ therefrom. Control interfaces of switches775and774are coupled to controller output ports PB4and PB3, respectively.

FIG. 14illustrates an embodiment225aof the Tx circuit225, which is suitable for operating with the transducer445aofFIG. 13. The Tx circuit225ais substantially an input portion of the Tx circuit shown inFIG. 4that includes the XNOR gate440, but without the corresponding transistors470and420. Two output ports416and435of the Tx circuit225aofFIG. 14are connected to input ports PB0and PB1of the controller771for providing the D+ signal and the E=XNOR (D+,D−) signal, respectively. A third input port PB2of the controller771is coupled to the data output port670of the SSC223.

In the PD mode of operation, when the PPC245receives the upstream optical signal Pd, the switches773-775are all open, so that no current flows through the BSS720, and the PPC245is substantially zero biased. The received signal Sr generated by the PPC245in the PD mode is provided to the SSC223for extracting the power and data signals Sp, Srdas described hereinabove. The controller771is programmed to monitor the received data signal Srdwhich is provided at the controller's PB2port, and to control the bias switch774depending on said Srdsignal. Once the upstream transmission is ended, the controller771closes the switch774, for example by generating a control signal XMIT ENABLE at the port PB3. The end of the upstream transmission and of the PD mode of operation may be signified by the absence of the Srdsignal for a pre-determined time interval, or by identifying a specific “End Of Transmission” (EOT) signal, such as a specific pulse or sequence of pulses, in the Srdsignal.

The closing of the bias switch774enables the LED mode of operation. In this mode, the data switch773operates as a shutter and is controlled directly by the D+ signal from the Tx circuit225a. For example, a logical “1” received through the control line787may cause the switch773to close, while receiving a logical “0” may cause the switch773to open. When both switches773and774are closed, the PPC245is forward-biased so that, for example, a 25 mA electrical current is drawn through the PPC245and the R3resistor784, causing the PPC245to emit light of a first intensity I1, thereby optically transmitting a logical “1” downstream to an associated HIM. When the switch773is open, the PPC is disconnected from the −5V feed and no light is emitted by the PPC, which may correspond to transmitting a logical “0” downstream through the fiber301.

Note that a negative polarity at the anode of the PPC245in the LED mode during the transmission of the logical ‘1’ drives the transistor655and the Schottky diode605into cut-off, so that no signal is generated at the outputs of the SSC223. The Schottky diode605also acts to switch off the stored supercap power from the PPC245, so that the power stored in the supercap625is provided to the power distributor43which supplies all of the circuitry for up to 250 msec. Switching just one side of the PPC between GND and −5V, effectively isolates the PPC from both the SSC223and the Power Distributor43and reduces the number of transistor switches required.

The controller771is further programmed to monitor the E and optionally D+ signals from the Tx circuit225a, and to generate therefrom a EOP—1 signal at the PB4port that opens or closes the EOP switch775. In one embodiment, the controller is programmed to generate a first EOP—1 signal, for example a logical “1”, which closes the EOP switch775when E is a logical “1”, and to generate a second EOP—1 signal, for example a logical “0”, which opens the EOP switch775when E is a logical “1”. Accordingly, during the transmission of the EOP signal the data switch773is open while the EOP switch775is closed, so that, for example a 50 mA electrical current is drawn through the PPC245and the R4resistor783, causing the PPC245to emit light of a second intensity I2that is substantially, preferably by at least 50%, larger than the first intensity I1, thereby optically transmitting the EOP symbol downstream to the associated HIM.

FIG. 15shows an exemplary embodiment of the power distributor circuit43. As shown, the circuit converts the electrical power signal Sp received at an input port801in the form of a dc voltage, into the regulated voltages +5V, +3.3V, and −5V at output ports821,822and823respectively, which are used by the DIM500. The electrical power signal Spdrives two low dropout (LDO) regulators that are directly connected to the input port801, a +5V LDO810which generates +5V at the output port821, and a 3.3V reference LDO regulator820, which generates +3.3V at the output port822. Both regulators810and820are controlled by an “ENABLE” signal so as to keep the regulators810,820turned off until the Sp voltage rises to a high enough value, for example to 4.3V, in order to assure the PPC stability during a power up phase when the capacitor620and the optional super-capacitor625of the power extraction circuit630are charging up from zero volts. A supervisor/threshold detector805keeps the voltage regulator810turned off with a zero volt signal to its “ENABLE” pin until the voltage component of the power signal Sp rises to a few volts in order to start the PPC before applying the load which will assure a stable and successful start up. When the PPC voltage rises above approximately 4.5V, the supervisor/threshold detector805switches the enable signal to “high” after a delay of about 140 milliseconds. The LDO regulators810and820are then enabled and the outputs are turned on to +5V and +3.3V respectively. The steady-state PPC voltage may be approximately between 5.5V and 6.2V.

Capacitors C2, C3, C4, C6, C7, and C8are provided for stability and noise reduction of the circuitry of the power distributor43. An optional −5V regulator815is connected to the +5V output of the LDO regulator810, from which it receives the regulated 5V signal. This regulator, together with it associated capacitors C1and C5, converts the +5V signal to −5V signal for use with embodiments of a transducer445operating in the LED mode as described herein with reference toFIGS. 13,19.

In the embodiment ofFIGS. 11 and 13, the PPC245does not supply power to the DIM500in the LED mode of operation. In one embodiment, the electrical power required for operation of the DIM in the LED mode is supplied by the super-capacitor625, which by way of example may have a value of 0.1 Farad. The duration of the Tx mode of the transducer445amay be limited to a time interval T1, for example 250 milliseconds, during which this capacitor is only partially drained of charge so that the voltage at the output of the power distributor43does not drop by more than 0.5V.

Once the maximum duration of the LED mode is reached, the transducer445ais switched back to the PD mode of operation by the controller771, for example by opening the bias switch774, wherein it receives optical power from the downstream HIM. The switching to the PD mode can also be caused by the controller771when it identifies an EOT signal in the data signals received from the Tx225a.

In one embodiment, the data signals D+ and E received from the Tx circuit225aare first buffered by the controller771, and then applied to the data and EOP switches773,775during the LED mode of operation. This data buffering enables the DIM400to simultaneously receive the electrical downstream data from the device50, and the optical upstream signal from the HIM500.

Advantageously, the DIM500of the third embodiment of the present invention utilizes a single PPC device to perform three functions—detection of upstream optical data signals, generation of downstream optical data signals, and conversion of optical power into electrical power for powering the DIM500and the device50. In the embodiment described hereinabove with reference toFIG. 11, the PPC245as a whole is switched between the Rx mode and the Tx mode, so that when the PPC245is in the Tx mode, incoming light is not converted to electricity.

The co-pending US patent application entitled “Multi-segment photovoltaic power converter with a center portion” describes a PPC which has independently biased portions, or sections, so that, for example, one section of the PPC can operate as a light transmitter, while the rest of the PPC operates as a light detector and/or photovoltaic power converter. An exemplary embodiment700of such PPC is illustrated inFIG. 16, which shows a face of the device that receives light. The PPC700includes five segments701-705shaped as ring fragments that are positioned outside of a central circular segment722; the five ring segments701-705will be referred to herein collectively as the ring section.

The segments701-705and724are separated by trenches730, and each of them includes a semiconductor heterostructure that includes a p-n junction, with p and n layers parallel to the plane of the figure. The central portion may include two p-n junctions, one on top of the other. In one embodiment, the five p-n junctions of the ring segments701-705are electrically connected in series by metallic interconnecting bridges coupling a p layer of one ring segment to an n layer of an adjacent ring segment, so that when the device receives light, voltages generated across each of the p-n junctions in the ring section are summed to provide a higher PPC voltage VPPCbetween contact pads722and723. P and n layers of a p-n junction of the central section724are separately electrically coupled to another two contact pads, which are not shown.

Advantageously, a portion of the PPC700, i.e. the p-n junction of the central segment724, or one of the pn junctions if the central segment724has two or more pn junctions, can be biased independently from the serially connected pn junctions of the ring segments701-705; for example, the central portion725of the PPC700can be forward-biased to emit light, while the ring segments701-705can be either zero-biased or reversed biased to detect light and convert it into an electrical signal. Note that other segment combinations are possible, wherein the p-n junctions of the PPC segments are connected so as to form two electrically isolated device portions or sections that can be biased independently.

Referring now toFIG. 17, an embodiment445bof the transducer445utilizes the PPC700ofFIG. 16as the PPC245. The electrically isolated device portions of the PPC700are schematically shown with diode symbols labeled with reference numerals745and740, respectively. By way of example, the first device portion740, which will also be referred to herein as the receive portion, corresponds to the serially connected ring segments701-705, while the second portion745, which will also be referred to herein as the transmit portion, corresponds to the central segment724of the PPC700. The transmit portion745of the PPC700is directly independently of the receive portion740thereof by the current drive signal Sdr, which is generated by the Tx circuit225embodied for example as the Tx circuit shown inFIG. 4.

The DIM500operates in this embodiments in substantially the same way as the DIM300that is described hereinabove with reference toFIG. 7, except that both the power and data components of the upstream optical signal Pupare now received through a single optical fiber301. When the upstream optical signal Pupimpinges upon the PPC700, the receive portion740, which in this embodiment is substantially zero biased, converts it into the received electrical signal Sr. The received electrical signal Sris then passed onto the SSC223, which produces therefrom the electrical power signal Spand the received data signal Srd, as described hereinabove.

In the downstream path, one or more USB packets generated by the device50in response to the host-generated signals, for example the handshake packet, are again converted by the Tx circuit225into the drive signal Sdr, which drives the second, i.e. transmit portion745. The transmit portion745is forward-biased, so that it emits the downstream optical signal Pupin the form of a sequence of optical pulses, wherein each optical pulse corresponds to either a ‘high’ state of one of the D+ or D− USB signals received from the device50, or to the “double-zero” EOP symbol indicating the end of a packet, in which case the respective optical pulse has a larger magnitude as described hereinabove.

Advantageously, the transducer445bis capable of generating electrical power both when it receives the downstream optical data and when it generates the upstream optical data, provided that the optical power signal Ppis continuously generated by the OPS145of the downstream HIM600, and does not require switching between forward and reverse biasing of either the first or second portions740,745of the PPC700.

With reference toFIG. 18, another embodiment445cof the transducer445is shown that also utilizes the multi-segment PPC700, but in a different way that combines features of the445aand445btransducers. In this embodiment, the first portion740of the PPC700provides electrical power signal Sp, while the independently biased second portion745of the PPC700is switched between the PD mode of operation wherein it is zero- or reverse-biased and receives the upstream optical data signal, and the LED mode of operation wherein it is forward biased and transmits the downstream optical data signal. Advantageously, the first portion of the PPC700is zero or reversed biased during both the PD and LED modes of operation, and therefore uninterruptedly provides electrical power to the DIM500and the device50as long as the optical power signal is provided by the downstream HIM. A bias switch765and an signal switch775are utilized to switch the second portion745of the PPC700from a PD mode of operation when it is reversed or zero biased to an LED mode of operation when it is forward biased.

Turning now toFIG. 19, one possible implementation of the circuit ofFIG. 18is shown wherein the bias switch765and the signal switch775are embodied as a double pole, double throw (DPDT) switch801controlled by a controller820, which can be embodied as described hereinabove with reference to the controller771. The DPDT switch801is shown inFIG. 19in a first state corresponding to the LED mode of operation, wherein the LED/PD portion745of the PPC700is forward biased and is driven by the Sdrcurrent signal from the Tx circuit225, which can be again embodied as the circuit120ofFIG. 4. The controller820may monitor the D+ and E signals from the Tx circuit225to detect the end of the downstream transmission, and ones the transmission end is detected, generates a control signal XMIT ENABLE at its PB3pin for switching the DPDT switch801to a second state corresponding to the PD mode of operation.

In this second state, the LED/PD portion745of the PPC700is reversed biased and converts received upstream optical data signal Pudinto photocurrent, which is converted into a voltage signal by a trans-impedance amplifier (TIA) circuit822, which includes a TIA810and an optional post-amplifier unit815. The TIA circuit822generates at it output port825the received electrical data signal Srdin the form of a sequence of voltage pulses, which are then passed to the Rx circuit220for converting the Srdsignal into the differential USB format as described hereinabove. The Srdsignal is also provided to a PB2pin of the controller820, which monitors it to detect an end of the upstream transmission, which can be signified for example by the absence of the Srdsignal, or said signal being below a pre-defined threshold, for a predefined time interval. Once the end of upstream transmission is detected, the controller820may switch the DPDT switch801to the first state corresponding to the LED mode of operation, when the DIM500transmits the downstream optical signal Pup.

During both the LED and PD modes of operation, the first portion740of the PPC700may convert received light into the electrical power signal Spwhich is then provided to the power distributor43for powering the external device50and the DIM500circuitry. An optional capacitor803at the anode of the first portion740of the PPC700provides stability to the power signal Spgenerated by the PPC portion740.

With reference toFIG. 20, a HIM800is shown according to another embodiment of the present invention, which can operate with the DIM500. In this embodiment, the upstream optical data signal Pudis generated by the MOS135, and is then combined with the optical power signal Ppby the multiplexer550to form the upstream optical signal Pup, which is then coupled into the optical fiber301by the circulator650, which also couples the downstream optical data signal Pup into the PD130. Advantageously, this embodiment enables to utilize a higher upstream data transmission rate by using a MOS135that has a higher modulation bandwidth than the high-power OPS145. This embodiment also enables to use different wavelengths for the upstream optical data and power signals, which in turn enables to increase a power conversion efficiency at the upstream DIM by using a multi-segment PPC, for example as the PPC700in the transducer445cofFIG. 18, wherein the second portion has two p-n junctions.

By way of example, the OPS145emits the optical power signal Ppat a first wavelength λp, which may be 980 nm, while the MOS135emits the upstream optical data signal Pupat a second wavelength λd, which may be 1.3 μm. Referring now back toFIG. 16, each of the ring segments701-705and the central segment724of the PPC700includes a first p-n junction formed in a first semiconductor material that has a bandgap suitable for absorbing light at the first wavelength λp, while the central segment724has also a second p-n junction formed in a second semiconductor material that has a bandgap suitable for absorbing light at the second wavelength λd. The first p-n junctions of the ring segments701-705and optionally the central segment724are connected in series to form the first portion740of the PPC700, which is independently electrically addressable and is electrically coupled to the power distributor43as shown inFIG. 18. The second p-n junction of the central segment724of the PPC700forms the second portion745of the PPC700as shown inFIG. 18, which is also independently electrically addressable and is electrically coupled to the Rx circuit225and may also be coupled to the Tx circuit220through the signal switch775as shown inFIGS. 18,19. Advantageously, this enables to maximize the optical power conversion efficiency of the PPC700by utilizing all its segments to convert the optical power signal Ppinto the electrical power signal Sp, with the optical power conversion efficiency of the PPC defined herein as the ratio Sp/Pp.

The present invention has been described hereinbefore with reference to exemplary embodiments thereof and in particular with reference to devices and modules that utilize a USB protocol and USB interfaces. However, those skilled in the art would appreciate that aspects of the invention are also applicable to optically powered optical data link which utilize alternative communications interfaces and alternative data communications protocols associated therewith, a non-exclusive list of which includes the FireWire, RS232, I2C, SPI, DVI and Ethernet. Adopting the DIM and HIM of the present invention to these standards may require alternative embodiments of the signal processor circuits and may also require the use of additional photodetectors and LEDs at the respective device an host interface modules. Also, some embodiments may include a DIM incorporating a hub such as a USB hub and having more than one electrical interface for operating more than one external device at a time.

Note that the particular embodiments of the system and method of the present invention described hereinabove may utilize portions of other embodiments and are by way of example only, and alternative embodiments of many elements and steps can be employed in particular applications of the invention as would be evident for those skilled in the art.

Of course numerous other embodiments may be envisioned without departing from the spirit and scope of the invention.