PATENT DOCUMENT

Publication Number: US-8577195-B2
Application Number: US-62241709-A
Country: US
Kind Code: B2

Title: Interface accessories with optical and electrical paths

Abstract:
Electronic devices are provided that communicate over cables and other communications paths that include optical and electrical paths. A cable may include wires for forming an electrical path and one or more optical fibers for forming an optical path. Connectors at one or both ends of the cable may include electrical contacts and an optical coupling structure associated with the optical path. Optical paths may be included in connectors such as tip-ring-sleeve connectors and connectors of other types. Interface circuitry may be included in a connector to convert between optical and electrical signaling schemes. Wavelength-division-multiplexing may be used to support bidirectional communications. Breakout boxes and other equipment may be connected using the cables. Digital signals such as digital noise cancellation signals may be conveyed over the optical paths. Power and other electrical signals may be conveyed over the electrical paths.

Claims:
What is claimed is: 
     
       1. A cable, comprising:
 a first connector operable to convey optical and electrical signals, wherein the first connector is operable to be connected to an electronic device that is external to the cable and to receive the optical signals from the electronic device; 
 an optical path coupled to the first connector, wherein the optical signals are conveyed over the optical path; 
 an electrical path coupled to the first connector, wherein the electrical signals from the first connector are conveyed over the electrical path; 
 optical-electrical converter circuitry that receives the optical signals from the first connector over the optical path and that converts the received optical signals to converted electrical signals; and 
 a second connector that receives the converted electrical signals from the optical-electrical converter circuitry and the electrical signals conveyed from the first connector over the electrical path, wherein the cable is an asymmetric cable, wherein the first connector includes two types of external interfaces, and wherein the second connector includes only one type of external interface. 
 
     
     
       2. The cable defined in  claim 1  wherein the cable has first and second ends, wherein the first connector is at the first end, wherein the optical-electrical converter circuitry is at the second end, and wherein the second connector is at the second end. 
     
     
       3. The cable defined in  claim 1  wherein the two types of external interfaces comprise an optical interface and an electrical interface and wherein the one type of external interface comprises an additional electrical interface. 
     
     
       4. A cable, comprising:
 a first connector operable to convey optical and electrical signals, wherein the first connector is operable to be connected to an electronic device and to receive the optical signals from the electronic device; 
 an optical path coupled to the first connector, wherein the optical signals are conveyed over the optical path; 
 an electrical path coupled to the first connector, wherein the electrical signals from the first connector are conveyed over the electrical path; 
 optical-electrical converter circuitry that receives the optical signals from the first connector over the optical path and that converts the received optical signals to converted electrical signals; and 
 a second connector that receives the converted electrical signals from the optical-electrical converter circuitry and the electrical signals conveyed from the first connector over the electrical path, wherein the first connector has a plurality of electrical contacts including a tip contact, at least one ring contact, and a sleeve contact formed on a prong-shaped member and wherein the electrical path is electrically coupled to the electrical contacts. 
 
     
     
       5. The cable defined in  claim 4  further comprising electrical-optical converter circuitry that receives additional electrical signals from the second connector and that transmits corresponding optical signals to the first connector on the optical path. 
     
     
       6. The cable defined in  claim 5  further comprising a wavelength-division-multiplexing filter coupled to the optical path, wherein the optical-electrical converter circuitry comprises a light detector coupled to the wavelength-division-multiplexing filter. 
     
     
       7. The cable defined in  claim 6  wherein the electrical-optical converter circuitry comprises a light source coupled to the wavelength-division-multiplexing filter. 
     
     
       8. The cable defined in  claim 7  wherein the first connector comprises a 3.5 mm plug. 
     
     
       9. The cable defined in  claim 4  wherein the first connector has a transparent insulator portion that separates and isolates a respective pair of the electrical contacts. 
     
     
       10. A cable, comprising:
 a first connector; 
 an optical path coupled to the first connector; 
 an electrical path coupled to the first connector; 
 optical-electrical converter circuitry that receives the optical signals from the first connector over the optical path and that converts the received optical signals to electrical signals; 
 a second connector that receives the electrical signals from the optical-electrical converter circuitry; 
 a wavelength-division-multiplexing filter coupled to the optical path, wherein the optical-electrical converter circuitry comprises a light detector coupled to the wavelength-division-multiplexing filter 
 electrical-optical converter circuitry that receives electrical signals from the second connector and that transmits corresponding optical signals to the first connector on the optical path, wherein the first connector has a plurality of electrical contacts including a tip contact, at least one ring contact, and a sleeve contact formed on a prong-shaped member and wherein the electrical path is electrically coupled to the electrical contacts, wherein the electrical-optical converter circuitry comprises a light source coupled to the wavelength-division-multiplexing filter, wherein the first connector comprises a 3.5 mm plug, and wherein the optical path in the 3.5 mm plug has a transparent insulator portion that separates and isolates a respective pair of the electrical contacts. 
 
     
     
       11. The cable defined in  claim 10  wherein the transparent insulator portion comprises a ring-shaped structure that surrounds the prong-shaped member. 
     
     
       12. A cable, comprising:
 a first connector operable to convey optical and electrical signals, wherein the first connector is operable to be connected to an electronic device that is external to the cable and to receive the optical signals from the electronic device; 
 an optical path coupled to the first connector, wherein the optical signals are conveyed over the optical path; 
 an electrical path coupled to the first connector, wherein the electrical signals from the first connector are conveyed over the electrical path; 
 optical-electrical converter circuitry that receives the optical signals from the first connector over the optical path and that converts the received optical signals to converted electrical signals; and 
 a second connector that receives the converted electrical signals from the optical-electrical converter circuitry and the electrical signals conveyed from the first connector over the electrical path, wherein the second connector comprises an XLR connector. 
 
     
     
       13. A cable, comprising:
 first and second connectors; 
 an optical path coupled to the first connector; 
 an electrical path coupled between the first and second connectors, wherein the electrical path is operable to convey data signals; and 
 optical-electrical converter circuitry that receives optical signals from the first connector over the optical path and that converts the received optical signals to electrical signals, wherein the electrical signals are provided to the second connector by the optical-electrical converter circuitry, wherein the first connector has a plurality of electrical contacts including a tip contact, at least one ring contact, and a sleeve contact formed on a prong-shaped member and wherein the first connector has a transparent insulator portion that separates and isolates a respective pair of the electrical contacts. 
 
     
     
       14. The cable defined in  claim 13  wherein the cable has first and second ends, wherein the first connector is at the first end, wherein the optical-electrical converter circuitry is at the second end, and wherein the second connector is at the second end. 
     
     
       15. The cable defined in  claim 13  further comprising electrical-optical converter circuitry that receives additional electrical signals from the second connector and that transmits corresponding optical signals to the first connector on the optical path.

Description:
BACKGROUND 
     Electronic devices such as computers, media players, and cellular telephones typically contain audio jacks. Accessories such as headsets have mating plugs. A user who desires to use a headset with an electronic device may connect the headset to the electronic device by inserting the headset plug into the mating audio jack on the electronic device. Miniature size (3.5 mm) phone jacks and plugs are commonly used electronic devices such as notebook computers and media players, because audio connectors such as these are relatively compact. Because 3.5 mm phone jacks and plugs are sometimes used to carry video signals, 3.5 mm audio connectors such as these are sometimes referred to as audio-video (A/V) connectors. 
     Headsets and other accessories have speakers that can be used to play back audio for a user. Some accessories have microphones. Microphones can be used to pick up the sound of a user&#39;s voice. This allows an electronic device to be used to record voice memos. Electronic devices with cellular telephone circuitry can use a microphone on an accessory to gather the user&#39;s voice during a telephone call. 
     In some headsets, microphones are used to form part of a noise cancellation circuit. When noise cancellation functions are active, the impact of ambient noise on audio playback can be reduced. Microphones can also be used to implement voice microphone noise cancellation. 
     Noise cancellation operations are generally implemented using analog noise cancellation circuitry. The analog noise cancellation circuitry subtracts a weighted version of the microphone signal from the audio signal. 
     Although conventional noise cancellation circuit arrangements can be satisfactory in some situations, recent advances in headphone quality and audio playback fidelity are placing increasing burdens on conventional noise cancellation circuits. These burdens are making it difficult or impossible to implement desired levels of noise cancellation performance with conventional approaches. 
     Conventional audio-video connector arrangements may also make it difficult or impossible to implement desired functionality in a system. For example, conventional 3.5 mm jacks and plugs and associated cables may not exhibit sufficient bandwidth for conveying large amounts of data. 
     SUMMARY 
     Electronic devices and external equipment such as headsets and other accessories may handle digital signals. These digital signals may include digital audio and digital video data. Audio-video (A/V) connectors, which are sometimes referred to as tip-ring-ring-sleeve (TRRS) connectors, tip-ring-sleeve (TRS) connectors, or audio connectors, may include electrical and optical components. For example, an audio connector may include electrical contacts that are coupled to electrical transceiver circuitry and an optical path that is coupled to optical transceiver circuitry. 
     An electronic device may be provided with audio digital signal processing circuitry. Switching circuitry may be configured to ensure that appropriate sets of electrical signal paths are formed. For example, in configurations in which no optical functions are needed, the switching circuitry can be configured to couple electrical data transceiver circuitry or analog circuitry to the electrical contacts in an audio connector. When optical functionality is desired, the switching circuitry can be configured to route power signals over the electrical paths while optical signals are being used to convey potentially large amounts of digital data. 
     Audio connectors can include conductive contact structures (e.g., tip, ring, and sleeve conductors). These conductors may be separated by insulating structures. For example, a ring of insulator may be located between each of the conductors. Optical functionality can be incorporated into the audio connectors using coaxial optical paths or, when transparent material is used for the insulator that is located between respective conductive contacts in the audio connectors, by conveying light radially through the insulator. 
     Audio connectors with optical and electrical capabilities may be used in electrical devices and cables and in external equipment such as breakout boxes and other accessories. The optical capabilities of the connectors can be used to convey video data, audio data such as noise cancellation data, or other suitable data. 
     Further features of the invention, its nature and various advantages will be more apparent from the accompanying drawings and the following detailed description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram of an illustrative electronic device in communication with an accessory such as a headset, breakout box, or other external equipment in a system in accordance with an embodiment of the present invention. 
         FIG. 2  is a diagram showing how a communications path that includes a tip-ring-sleeve connector can be used to allow equipment to interact in accordance with an embodiment of the present invention. 
         FIG. 3  is a schematic diagram showing illustrative circuitry that may be used in an electronic device to electrically and optically communicate with an accessory and to provide processing and power supply functions in accordance with an embodiment of the present invention. 
         FIG. 4  is a circuit diagram of illustrative circuitry in an accessory that performs processing functions and that electrically and optically communicates with circuitry in an electronic device such as the circuitry of  FIG. 3  in accordance with an embodiment of the present invention. 
         FIG. 5  is a diagram of an illustrative system in which electronic equipment such as a breakout box serves as an interface between an electronic device and other equipment in accordance with an embodiment of the present invention. 
         FIG. 6  is a diagram showing how an electronic device may communicate with external equipment using a cable having connectors with optical and electrical components in accordance with an embodiment of the present invention. 
         FIG. 7  is a diagram showing how an electronic device may communicate with external equipment using a cable with a connector at one end that has optical and electrical components in accordance with an embodiment of the present invention. 
         FIG. 8  is a circuit diagram showing how an electronic device may communicate with external equipment using a cable that contains optical-to-electrical and electrical-to-optical interface circuitry in accordance with an embodiment of the present invention. 
         FIG. 9  is a cross-sectional diagram of an illustrative cable containing four wires and an optical fiber in accordance with an embodiment of the present invention. 
         FIG. 10  is a cross-sectional diagram of an illustrative cable containing four wires and two optical fibers in accordance with an embodiment of the present invention. 
         FIG. 11  is a cross-sectional diagram of an illustrative jack and plug that are coupled to a cable having an optical fiber and wires in accordance with an embodiment of the present invention. 
         FIG. 12  is a diagram of an optical path coupled to a pair of optical transceivers in accordance with an embodiment of the present invention. 
         FIG. 13  is a perspective view of an illustrative pair of audio connectors that have mating engagement features in accordance with an embodiment of the present invention. 
         FIG. 14  is a cross-sectional diagram of an illustrative plug and mating jack of the type shown in  FIG. 13  showing how an optical source and optical detector may be coupled to respective optical fibers in a cable in accordance with an embodiment of the present invention. 
         FIG. 15  is a perspective view of an illustrative plug having annular transparent portions through which light may be conveyed to optical fiber structures in an attached cable in accordance with an embodiment of the present invention. 
         FIG. 16  is a perspective view of a portion of an electronic device containing a jack and associated annular source and detector regions that may mate with the annular transparent jack regions in a jack of the type shown in  FIG. 15  in accordance with an embodiment of the present invention. 
         FIG. 17  is a cross-sectional side view of a system based on a plug of the type shown in  FIG. 15  and jack of the type shown in  FIG. 16  in accordance with an embodiment of the present invention. 
         FIG. 18  is a cross-sectional side view of an illustrative plug-and-jack system in which the plug has transparent ring-shaped insulators and the jack has matching source and detectors in accordance with an embodiment of the present invention. 
         FIG. 19  is a perspective view of an illustrative electronic device and an associated accessory that has a vertically mounted protruding hybrid plug that is received by a hybrid jack in the electronic device in accordance with an embodiment of the present invention. 
         FIG. 20  is a flow chart of illustrative steps involved in configuring and using electrical equipment that has optical and electrical connectors in accordance with an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Electronic components such as electronic devices and other equipment may be interconnected using wired and wireless paths. For example, a wireless path may be used to connect a cellular telephone with a wireless base station. Wired paths may be used to connect electronic devices to equipment such as computer peripherals and audio accessories. As an example, a user may use a wired path to connect a portable music player to a headset. 
     In a typical wired path, wires are used to handle electrical signals. One or more optical fibers may be included in the same wired path as the wires. For example, a cable may contain four wires and one or two optical fibers (as an example). 
     With an arrangement of this type, the optical fiber or fibers in the cable may form an optical path and the wires may form an electrical path that runs in parallel with the optical path. The optical and electrical paths may be used to convey digital data such as audio data, video data, control signal data, etc. If desired, power signals and analog signals can be conveyed over the electrical path. 
     Connectors may be provided in a wired path that contains electrical and optical paths. For example, male and/or female connectors may be provided at one or both ends of a cable or may be used in directly connecting an accessory to an electronic device. 
     Electronic devices that may be connected to external equipment using optical and electrical paths include desktop computers and portable electronic devices. The portable electronic devices that are connected to the external equipment in this way may include tablet computers, laptop computers, and small portable computers of the type that are sometimes referred to as ultraportables. The portable electronic devices may also include somewhat smaller portable electronic devices such as wrist-watch devices, pendant devices, and other wearable and miniature devices. 
     The electronic devices that are connected to external equipment may also be handheld electronic devices such as cellular telephones, media players with wireless communications capabilities, handheld computers (also sometimes called personal digital assistants), remote controllers, global positioning system (GPS) devices, and handheld gaming devices. The electronic devices may be devices that combine the functionality of multiple conventional devices. For example, the electronic devices may be cellular telephones that have media player functionality, gaming devices that have wireless communications capabilities, cellular telephones that include game and email functions, and portable devices that receive email, support mobile telephone calls, have music player functionality, and support web browsing. These are merely illustrative examples. 
     An example of external equipment that may be connected to such an electronic device using optical and electrical paths is an accessory such as a headset. A headset typically includes a pair of speakers that a user can use to play audio from the electronic device. The accessory may have a user control interface such as one or more buttons. When a user supplies input, the input may be conveyed to the electronic device. As an example, when the user presses a button on the accessory, a corresponding signal may be provided to the electronic device to direct the electronic device to take an appropriate action. Because the button is located on the headset rather than on the electronic device, a user may place the electronic device at a remote location such as on a table or in a pocket, while controlling the device using conveniently located headset buttons. 
     The external equipment that is connected to the electronic device may include equipment such as a tape adapter. A tape adapter may have a plug on one end and a cassette at the other end that slides into a tape deck such as an automobile tape deck. Equipment such as a tape adapter may be used to play music or other audio over the speakers associated with the tape deck. Audio equipment such as the stereo system in a user&#39;s home or automobile may also be connected to an electronic device using optical and electrical paths. As an example, a user may connect a music player to an automobile sound system using a three-pin or four-pin audio connector that includes an optical path. 
     In some situations, it may be desirable to convey relatively large amounts of data between the electronic device and accessory. For example, if the accessory has video playback capabilities (or is coupled to equipment that has video display capabilities), the optical and electrical paths between the electronic device and the accessory may be used to convey relatively large amounts of data (e.g., video data and accompanying soundtrack information, image data, etc.). The data that is conveyed between the electronic device and the accessory may be carried over the optical path and/or the electrical path as digital data. 
     As another example, the data that is conveyed between the electronic device and the accessory may include audio data. For example, digital audio data from a microphone or digital audio data that is being played back from storage may be conveyed over the optical and/or electrical paths. When an optical path between the electronic device and accessory is available, it may be possible to convey larger amounts of data between the electronic device and accessory than would otherwise be possible. For example, an optical path may be used to convey data at data rates of tens of Mbps or more, hundreds of Mbps or more, or a Gbps or more. Optical paths may also be suitable for incorporation into miniature parts such as 3.5 mm TRS connectors. 
     In a typical scenario that involves the transmission of audio data, the electronic device that is connected to the external equipment produces audio signals. These audio signals may be transmitted to the external equipment in the form of analog and digital audio. For example, the electrical path may include wires that convey analog audio to speakers in the accessory. The electrical and optical paths may be used to convey digital audio data (e.g., pulse-code-modulation encoded digital audio data). 
     The external equipment may include a voice microphone. One or more noise cancelling microphones may also be provided. Microphone signals (e.g., analog audio signals corresponding to a user&#39;s voice, ambient noise, or other sounds) may be processed locally in the accessory. Microphone signals may also be conveyed to the electronic device using the electrical and/or optical paths. 
     The communications path between the electronic device and accessory may be used to convey signals such as control signals in addition to audio and video signals. Digital data may be conveyed if desired. In general, data conveyed between the electronic device and accessory may include for example, control signals, audio, video, information to be displayed for a user, etc. 
     Accessories such as headsets are typically connected to electronic devices using plugs (male connectors) and mating jacks (female connectors). Connectors such as these may be provided in a variety of form factors. Most commonly, these connectors take the form of 3.5 mm (⅛″) miniature plugs and jacks. Because audio signals and sometimes video signals are conveyed over 3.5 mm plugs and jacks, 3.5 mm plugs and jacks are sometimes referred to as audio connectors or audio-video (A/V) connectors. The 3.5 mm size is popular for earbuds and other headsets. Other sizes are also sometimes used such as 2.5 mm subminiature connectors and ¼ inch connectors. 
     In the context of accessories such as headsets, these audio connectors and their associated cables can be used to carry analog signals such as audio signals for speakers and microphone signals. Digital data streams may also be used to convey audio signals (e.g., audio output signals such as played-back media or telephone call audio, microphone signals, and noise cancellation audio), control signals (e.g., input-output signals), clock information, and other signals. Video may be conveyed with or without audio (e.g., as digital data). 
     Analog signals such as analog audio signals may be conveyed over electrical paths. Power may also be conveyed using electrical paths. Digital data may be conveyed using electrical and/or optical paths. Optical structures such as optical fibers and transparent windows may be incorporated into a communications path between an electronic device and external equipment. These optical structures may be incorporated into audio connectors (e.g., 3.5 mm jacks and plugs) or other connectors (e.g., digital data connectors such Universal Serial Bus connectors, 30-pin connectors, XLR connectors, etc.). For clarity, the use of optical structures in audio connectors such as 3.5 mm jacks and plugs is sometimes described herein as an example. 
     The audio connectors (audio-video connectors) that are used in connecting an electrical device to external equipment may have any suitable number of electrical terminals. The electrical terminals in a connector are formed from conductive materials such as metal and are typically referred to as contacts. Stereo audio connectors typically have three electrical contacts. The outermost end of an audio plug is typically referred to as the tip. The innermost portion of the plug is typically referred to as the sleeve. A ring contact lies between the tip and the sleeve. When using this terminology, stereo audio connectors such as these are sometimes referred to as tip-ring-sleeve (TRS) connectors. The sleeve can serve as ground. The tip contact can be used in conjunction with the sleeve to handle a left audio channel and the ring contact can be used in conjunction with the sleeve to handle the right channel of audio (as an example). In four-contact audio connectors, an additional ring contact is provided to form a connector of the type that is sometimes referred to as a tip-ring-ring-sleeve (TRRS) connector or simply as a type of TRS connector. Four-contact audio connectors may be used to handle a microphone signal, left and right audio channels, and ground (as an example). If desired, switching circuitry can be used to route different signals to and from the contacts in a connector as needed to implement desired functions. An optical path may be incorporated into an audio connector such as a TRS connector using one or more optical fibers and associated optical structures. 
     Electrical devices and external equipment may be connected in various ways. For example, a user may connect either a pair of stereo headphones or a headset that contains stereo headphones and a microphone to a cellular telephone audio jack. Accessories such as these may include one or more noise cancelling microphones. For example, the voice microphone may have an associated noise cancellation microphone that picks up ambient noise in the vicinity of the voice microphone. The earbuds or other speakers in an accessory may also have noise cancellation microphones. For example, each earbud in a headset may have an external noise cancellation microphone on an outer surface of the earbud. In addition to the external noise cancellation microphone or instead of the external noise cancellation microphone, each earbud may have an internal noise cancellation microphone on an interior surface of the earbud (adjacent to the ear). 
     In accessories with more speakers, more noise cancellation microphones may be used. For example, additional noise cancellation microphones can be provided in earbuds that contain multiple drivers or in surround sound accessories. A surround sound accessory might, for example, have five or six speakers (or more) and might have a noise cancellation microphone that is adjacent to each respective speaker. 
     Electrical devices and external equipment may be operated in various modes. For example, a cellular telephone may be used in a music player mode to play back stereo audio to a user. When operated in telephone mode, the same cellular telephone may be used to play telephone call left and right audio signals to the user while simultaneously processing telephone call microphone signals from the user. Noise cancellation features may be selectively turned on and off as needed. For example, microphone noise cancellation may be activated while earbud noise cancellation features are deactivated (as an example). Noise cancellation functions can also be globally deactivated or globally activated. 
     Electronic devices and external equipment may be provided with switching circuitry or other path configuration circuitry that allows the electronic devices and external equipment to be operated in a variety of different operating modes in a variety of different combinations. When, for example, a user connects one type of accessory to an electronic device, the switching circuitry may be adjusted to form a first set of electrical paths between the electronic device and accessory. When a user connects a different type of accessory, the path configuration circuitry may be adjusted to form a second set of electrical paths between the electronic device and accessory. 
     Consider, as an example, the use of an electronic device that has a four-contact TRS jack with integrated optical structures for supporting optical path communications. When a user of device plugs a conventional stereo headset into the electronic device, switching circuitry in the electronic device can be configured to route left and right analog audio output signals to speakers in the headset through the electrical contacts of the TRS jack. When the user plugs a headset that includes noise cancellation microphones into the device, the switching circuitry can be configured to route power to the headset while the optical path is used to convey digital noise cancellation signals between the headset and the device. Another possible scenario involves the use of video equipment. A user may, for example, plug video equipment into the TRS jack. In this situation, the electrical contacts in the jack may be used to convey control signals or power while the optical path is used to convey audio and video data. 
     Noise cancellation functions may be implemented in the external equipment or in an electronic device. In schemes in which digital audio signals are conveyed from the accessory to the electronic device, the circuit resources of the electronic device may be used to help implement desired functions. This may help reduce the amount of circuitry that is included in a given accessory and may help minimize accessory power consumption. Digital audio processing may also be performed using digital processing circuitry that is primarily or exclusively implemented within an accessory. 
     In configurations in which at least some of the communications between the electronic device and accessory are implemented using digital communications (optical and/or electrical), the capacity of the electronic device and accessory to communicate can be enhanced. For example, digital communications may allow numerous channels of audio to be conveyed between the electronic device and accessory in real time. Control signals and other signals may also be conveyed digitally. At the same time, the electronic device may, if desired, include analog circuitry that produces analog audio signals. When an accessory with digital communications capabilities is connected to the electronic device, the electronic device and accessory can communicate digitally. When an accessory without digital communications capabilities is connected to the electronic device, analog circuitry in the electronic device may supply analog audio signals to the accessory. For example, if a stereo headset with two speakers and no microphone or control capabilities is connected to the electronic device, analog audio circuitry may be used to supply left and right channels of analog audio to the speakers in the stereo headset. When a more advanced accessory is connected to the electronic device, additional features may become available (e.g., digital audio processing for noise reduction, digital control capabilities, additional audio streams for surround sound speakers, etc.). 
     An illustrative system in which an electronic device and external equipment may communicate over a wired communications link that includes optical and electrical paths is shown in  FIG. 1 . As shown in  FIG. 1 , system  10  may include an electronic device such as electronic device  12  and external equipment  14 . External equipment  14  may be equipment such as an automobile with a sound system, consumer electronic equipment such as a television or audio receiver with audio and/or video capabilities, a peer device (e.g., another electronic device such as device  12 ), a breakout box that serves as an interface between a multiple electronic devices  12 , or any other suitable electronic equipment. In a typical scenario, which is sometimes described herein as an example, external equipment  14  may be an accessory that contains speakers such as a headset. External equipment  14  is therefore sometimes referred to as “accessory  14 ” or “headset  14 .” Speakers in accessory  14  may be provided as earbuds or as part of a headset or may be provided as a set of stand-alone powered or unpowered speakers (e.g., desktop speakers). As shown in  FIG. 1 , equipment  14  may include I/O circuitry  32  and storage and processing circuitry  26 . 
     A path such as path  16  may be used to connect electronic device  12  and accessory  14 . In a typical arrangement, path  16  includes one or more audio connectors such as 3.5 mm plugs and jacks or audio connectors of other suitable sizes. Conductive lines in path  16  may be used to convey electrical signals over path  16 . These lines may be, for example, copper wires covered with plastic insulation. An optical path in path  16  may be used to convey optical signals (i.e., light). The optical path may be formed using one or more optical fibers. 
     There may, in general, be any suitable number of conductive lines and optical fibers in path  16 . For example, there may be two, three, four, five, or more than five separate lines and one, two, or more than two optical fibers. These lines and fibers may be part of one or more cables. Cables may include solid wire, stranded wire, shielding, single ground structures, multi-ground structures, twisted pair structures, or any other suitable electrical cabling structures. The cables may also include plastic fiber, glass fiber, multimode fiber, single mode fiber, and other suitable optical path structures. 
     Extension cord and adapter arrangements may be used as part of path  16  if desired. In an adapter arrangement, some of the features of accessory  14  such as user interface and communications functions may be provided in the form of an adapter accessory with which an auxiliary accessory such as a headset may be connected to device  12 . Adapter functions may also be incorporated into a cable. This type of arrangement may be used, for example, in a cable that has both electrical and optical capabilities at one end, but that has only electrical capabilities at its other end. 
     Electronic device  12  may be a desktop or portable computer, a portable electronic device such as a handheld electronic device that has wireless capabilities, equipment such as a television or audio receiver, or any other suitable electronic equipment. Electronic device  12  may be provided in the form of stand-alone equipment (e.g., a handheld device that is carried in the pocket of a user) or may be provided as an embedded system. Examples of systems in which device  12  may be embedded include automobiles, boats, airplanes, homes, security systems, media distribution systems for commercial and home applications, display equipment (e.g., computer monitors and televisions), etc. 
     Device  12  may include input-output circuitry  28  and storage and processing circuitry  30 . Input-output circuitry  28  of device  12  and input-output circuitry  32  of equipment  14  may include buttons, touch-sensitive components such as touch screens and touch pads, microphones, sensors, and other components for gathering input from a user. Input-output circuitry  32  and  28  may also include speakers, status inductors such as light-emitting diodes, displays, and other components for providing output to users. Circuitry  32  and  28  may also include digital and analog communications circuitry for supporting electrical and optical communications over path  16  and for supporting wireless communications. Storage and processing circuitry  26  and  30  may be based on microprocessors, application-specific integrated circuits, audio chips (codecs), video integrated circuits, microcontrollers, digital signal processors, memory devices such as solid state storage, volatile memory, and hard disk drives, etc. 
     Device  12  may communicate with network equipment such as equipment  18  over path  22 . Path  22  may be, for example, a cellular telephone wireless path. Equipment  18  may be, for example, a cellular telephone network. Device  12  and network equipment  18  may communicate over path  22  when it is desired to connect device  12  to a cellular telephone network (e.g., to handle voice telephone calls to transfer data over cellular telephone links, etc.). 
     Device  12  may also communicate with equipment such as computing equipment  20  over path  24 . Path  24  may be a wired (electrical and/or optical) or wireless path. Computing equipment  20  may be a computer, a set-top box, audio-visual equipment such as a receiver or television, a disc player or other media player, a game console, a network extender box, or any other suitable equipment. 
     In a typical scenario, device  12  may be, as an example, a handheld device that has media player and cellular telephone capabilities (sometimes referred to collectively as a cellular telephone). Accessory  14  may be a headset with a microphone and a user input interface such as a button-based interface for gathering user input. Path  16  may be a four or five conductor audio cable with an embedded optical path that is connected to devices  12  and  14  using 3.5 mm audio jacks and plugs (as an example). Computing equipment  20  may be a computer with which device  12  communicates (e.g., to synchronize a list of contacts, media files, etc.). 
     Paths such as path  24  and  16  may be based on commonly available digital connectors such as USB or IEEE 1394 connectors, XLR connectors, audio connectors, etc. These connectors may include electrical and optical paths. An advantage of using communications paths that are compatible with commonly-used audio connectors such as the 3.5 mm audio connectors is that this type of arrangement may maintain compatibility with a user&#39;s existing collection of headsets and other legacy equipment. Arrangements in which the communications paths of system  10  are implemented using audio connectors with a 3.5 mm form factor or other arrangement that is compatible with conventional audio connectors are therefore sometimes described herein as an example. This is merely illustrative. In general, the communications paths and connectors that are used in system  10  may include electrical and optical paths and coupling structures of any suitable type. 
     In system  10 , electronic device  12  and accessory  14  may include switching circuitry (also sometimes referred to as adjustable path configuration circuitry) that can be used to selectively interconnect various circuits to the contacts in the audio connectors of path  16 . The switching circuitry may be adjusted to support different modes of operation. These different modes of operation may result from different combinations of accessories and electronic devices, scenarios in which different device applications are active, etc. The switching circuitry may be formed from one or more transistor-based switches. If desired, the switching circuitry may include hybrid circuits that can be selectively switched into use. When the hybrid circuits are not actively used, the electrical communications path and associated connector contacts to which they are connected may be used for unidirectional communications. When the hybrid circuits are switched into active use, the same electrical communications path and connector contacts may be used to support bidirectional signals (e.g., an outgoing left or right audio channel in one direction and an incoming microphone signal in the opposite direction). Bidirectionality may also be supported using time multiplexing protocols. 
     Illustrative circuitry that may be associated with path  16  is shown in  FIG. 2 . Switching circuitry  160  may be provided in electronic device  12  and switching circuitry  162  may be provided in accessory  14  or other external equipment. Wired path  16  may be used to connect electronic device  12  and accessory  14 . Path  16  may include audio connectors such as audio connectors  34  and  38 . 
     The audio connectors of path  16  may include an audio plug such as plug  34  (i.e., a male audio connector). Plug  34  may have a prong-shaped member that allows plug  34  to mate with a corresponding audio jack such as audio jack (i.e., a female audio connector). Jack  38  may include electrical contacts that surround a cylindrical opening that receives plug  34 . These contacts may be formed from rings of metal, spring-loaded conductive structures, etc. Connectors  34  and  38  may be used at any suitable location or locations within path  16 . For example, audio jacks such as jack  38  can be formed within the housing of device  12  and plugs such as plug  34  can be formed on the end of a cable such as cable  70  that is associated with a headset or other accessory  14 . As shown in  FIG. 2 , cable  70  may be connected to audio plug  34  via strain-relief plug structure  66 . Structures such as structure  66  may be formed with an external insulator such as plastic (as an example). 
     Audio plug  34  is an example of a four-contact plug. A four-contact plug has four conductive regions that mate with four corresponding conductive regions in a four-contact jack such as jack  38 . As shown in  FIG. 2 , these regions may include a tip region such as region  48 , ring regions such as rings  50  and  52 , and a sleeve region such as region  54 . These regions surround the cylindrical surface of plug  34  and are separated by insulating regions  56 . When plug  34  is inserted in mating jack  38 , tip region  48  may make electrical contact with jack tip contact  74 , rings  50  and  52  may mate with respective ring regions  76  and  78 , and sleeve  54  may make contact with sleeve terminal  80 . Insulating regions  56  may separate the contacts in jack  38 . In a typical configuration, there are four wires  88  in cable  70 , each of which is electrically connected to a respective contact in plug  34 . 
     Cable  70  may also include optical path  200 . Optical path  200  may be formed from one or more optical fibers. In the example of  FIG. 2 , path  200  is formed from a single optical fiber. As shown in  FIG. 2 , path  200  extends through the central core of plug  34  and mates with a corresponding optical path  206  in jack  38 . Path  206  may be located in electronic device  12  ( FIG. 1 ) and may be used to convey optical signals between optical transceiver  208  in device  12  and optical path  200 . In this capacity, path  206  may be considered to form a part of path  200 . 
     Transceiver  202  may be located in accessory  14 . During optical communications between device  12  and accessory  14 , optical transceivers  208  and  202  may communicate optically over path  200 . 
     Switching circuitry  160  may receive analog signals via path  170 . For example, switching circuitry  160  may receive analog audio output signals on path  170  and may switch these signals onto lines  168  when operating in an analog output mode to support legacy analog accessories. Path  170  may also be used to route power supply signals to appropriate contacts in jack  38 . Switching circuitry  160  may handle digital electrical signals using path  172 . For example, when operating in a digital audio mode to support a digital-ready headset, switching circuitry  160  may switch digital audio streams that are received on path  172  onto lines  168 . 
     In electronic device  12 , signals (e.g., digital signals) that are conveyed over path  200  optically can be handled using input-output path  210 . During data transmission operations from device  12 , data from processing circuitry within electronic device  12  may be provided to path  210 . Data that is received at path  210  may be converted into optical signals using transceiver  208  and may be routed to path  200  via path  206 . In accessory  14 , optical signals from path  200  may be received by transceiver  202 . Transceiver  202  may convert received optical signals to electrical signals that are provided on input-output path  204 . Processing circuitry within the accessory may receive and process the signals on path  204 . 
     Accessory  14  can transmit optical data using transceiver  202 . Processing circuitry within accessory  14  can provide data to input-output path  204 . Transceiver  202  may convert the electrical signals that are received at path  204  to optical signals. The optical signals can be transmitted to electronic device  12  using path  200 . In device  12 , optical signals from path  200  may be conveyed to transceiver  208  via path  206 . Transceiver  208  may convert received optical signals to electrical signals that are provided at path  210 . 
     Transceivers  208  and  202  may include light sources and detectors. For example, each transceiver may include one or more light emitting diodes, one or more laser diodes, or other sources of light. These sources may operate at a single wavelength or wavelength division multiplexing arrangements can be supported using multiple wavelengths of light. Each transceiver may also include photodetectors such as p-i-n diodes, p-n junction diodes, photodiode arrays, etc. 
     Accessories may have fixed operating modes or adjustable operating modes. For example, a legacy analog headset may only operate in an analog audio mode. As another example, a digital-capable headset may operate in both analog and digital modes. This type of multimode operation may allow a digital-capable headset to revert to an analog audio mode when used with a legacy music player. To accommodate multiple operating modes, accessory  14  may control the configuration of the switches in switching circuitry  164 . When operating in analog audio mode, analog signals that are being conveyed between device  12  and accessory  14  can be routed through analog lines  174 . When operating in digital audio mode, switching circuitry  164  can be configured to switch digital path  176  into use and/or to use transceiver  202  to handle digital optical signals. These configurations need not be mutually exclusive. For example, switching circuitry  160  and  164  may, if desired, be placed into configurations in which a mixture of analog and digital signals are conveyed over path  16  while optical signals are being conveyed over path  200 . A typical mixture of signals over path  16  might include power signals, optical and/or electrical control signals, optical and/or electrical audio signals, and optical and/or electrical video signals. Switching circuitry  164  may, if desired, be used to switch an ultrasonic tone generation circuit into use (e.g., to send electrical ultrasonic tone codes from accessory  14  to device  12  that correspond to button press events or other user input). 
     The signal assignments that are used in the audio connectors of path  16  depend on the type of electronic device and accessory being used and the active operating mode for the system. For example, when operating in a legacy analog mode, ring contact  52  may serve as ground (and may therefore sometimes be referred to as the G contact of plug  34 ), tip  48  may be associated with left channel audio (and may therefore sometimes be referred to as the L contact of plug  34 ), ring  50  may be associated with right channel audio (and may therefore sometimes be referred to as the R contact of plug  34 ), and sleeve  54  may be associated with microphone signals (and may therefore sometimes be referred to as the M contact of plug  34 ). The mating contacts of jack  38  may have corresponding signal assignments. 
     As shown in  FIG. 3 , electronic device  12  may contain video, audio, communications, and control circuitry  180 . Video circuitry in circuit  180  may be used to generate video signals or to receive and process video signals. Audio circuit  182 , which is sometimes referred to as a codec or audio codec, may be used to generate audio signals or to receive and process audio signals. Audio circuit  182  may include analog-to-digital (A/D) converter circuitry  184  and digital-to-analog (D/A) converter circuitry  186 . Analog-to-digital converter circuitry in device  12  may be used to digitize analog signals such as analog audio signals. For example, analog-to-digital converter circuitry  184  may be used to digitize one or more analog microphone signals. These microphone signals may be received from accessory  14  over path  16  or may be received from microphone equipment in device  12 . Digital-to-analog converter circuitry  186  may be used to generate analog output signals. For example, digital-to-analog converter circuitry  186  may receive digital signals corresponding to the audio portion of a media playback event, audio for a telephone call, noise cancellation signals, an alert tone or signal (e.g., a beep or ring), or any other digital information. Based on this digital information, digital-to-analog converter circuitry  186  may produce corresponding analog signals (e.g., analog audio). 
     Audio digital signal processor  188  may be used to perform digital signal processing on digitized audio signals. For example, if operating accessory  14  in a voice microphone noise cancellation mode, digital noise cancellation signals from a voice microphone noise cancellation microphone in accessory  14  may be conveyed over path  16  to audio digital signal processor  188 . Audio digital signal processor  188  may also receive digital audio voice signals from the voice microphone in accessory  14  and digital noise cancellation signals from speaker noise cancellation microphones. Using the processing capabilities of audio digital signal processor  188 , the digital noise cancellation microphone signals from accessory  14  can be digitally removed from the digital audio voice signal and from digital speaker signals. Use of the processing power of device  12  in this way may help to reduce the processing burden that is placed on accessory  14 . This may allow accessory  14  to be constructed from less costly and less complex circuitry. Power consumption efficiency and audio performance may also be enhanced. If desired, digital audio processing circuitry in accessory  14  can be used to supplement or replace the audio processing functions of audio digital signal processor  188 . For example, digital noise cancellation circuitry in accessory  14  may be used in cancelling noise for the speakers of accessory  14 . 
     Electrical transceiver  190  may be used to support unidirectional or bidirectional electrical digital communications with a corresponding electrical transceiver in accessory  14  over path  16 . Optical transceiver  210  may be used to support unidirectional or bidirectional optical digital communications with a corresponding optical transceiver in accessory  14  over path  16 . Optical transceiver  210  may have an optical transmitter  212  and an optical receiver  216 . Transmitter  212  may include a light source such as light source  214 . Light source  214  may be a light-emitting diode (LED), a laser diode, or any other suitable source of light. The light is produced by light source  214  may be visible light, infrared light, or may have other suitable wavelengths. Detector  218  may be used by receiver  216  to convert incoming light signals from optical path  206  (which is an extension of path  200  of path  16 ) to electrical signals. During optical data transmissions, light from source  214  may be conveyed to optical path  200  of path  16  using optical path  206 . 
     Any suitable communications protocol may be used by transceivers  190  and  210 . For example, a protocol may be used that includes functions such as error correction functions. Data may be sent in packets or other suitable data structures. A clock that is produced by circuitry  180  of  FIG. 3  (e.g., by circuitry in transceiver  190 ) may be transmitted with the data. For example, transceiver  190  and/or transceiver  210  may embed a variable clock in a transmitted digital data stream. 
     Power supply circuitry  220  may be used in providing power to the electrical contacts in connector  38  (e.g., from a battery in device  12 ). 
     Switching circuitry such as switching circuitry  160  of  FIG. 2  may be used to selectively connect the contacts of audio connector  38  to the circuits of video, audio, communications, and control circuitry  180 , power supply circuitry  220 , and other circuitry in device  12 . For example, when it is desired to supply analog audio output signals from codec  182  to connector  38 , the switching circuitry can be adjusted accordingly by the control and processing circuitry of device  12 . When it is desired to route electrical digital signals to the audio contacts of audio connector  38 , the switching circuitry can be used to connect transceiver  190  to audio connector  38 . Power signals and other signals can also be selectively routed to connector  38  by switching circuitry  160 . Optical path  206  and associated optical path  200  of  FIG. 2  may be used in conveying optical signals to and from device  12 . 
     Illustrative circuitry that may be used to handle signal processing tasks for accessory  14  is shown in  FIG. 4 . As shown in  FIG. 4 , accessory  14  may include components and processing circuitry  192 . Circuitry  192  may include components such as a battery, switches, a display, a touch screen, a keyboard, integrated circuits, discrete components, etc. Circuitry  192  may also include components such as microphones and speakers. In the example of  FIG. 4 , accessory  14  includes microphones  222 ,  226 ,  230 , and  231  and includes speakers  224  and  228  (shown separately in the FIG.). Speakers  224  and  228  may be, for example, left and right speakers in a pair of earbuds or left and right speakers in other external equipment. Microphones  222  and  226  may be noise cancellation microphones that are used to gather ambient noise signals associated with speakers  224  and  228 , respectively. Using noise cancellation techniques, the ambient noise signals can be used to reduce noise in the audio being played through speakers  224  and  228 . Noise cancellation techniques can also be implemented for microphones. For example, microphone  230  may be a voice microphone that is used to gather the user&#39;s voice during telephone calls or that is used to record audio clips. Microphone  231  may be used to gather ambient noise signals associated with the use of microphone  230  and may therefore serve as a noise cancellation microphone for microphone  230 . 
     Noise cancellation operations may be performed using analog circuitry or using digital processing techniques. Digital audio processing operations for implementing noise cancellation and for implementing other functions can be performed locally in accessory  14  or can be performed remotely in device  12 . As shown in  FIG. 4 , circuitry  192  may include audio processing circuitry  232 . Circuitry  232  may include analog-to-digital converter circuitry  234  (e.g., for digitizing analog audio signals from the microphone in accessory  14 ) and digital-to-analog converter circuitry  236  (e.g., to convert digital signals to analog signals that are played back through the speakers of accessory  14 ). 
     As described in connection with  FIG. 2 , accessory  14  may communicate with device  12  over path  16 . Path  16  may include wires that are connected to respective electrical contacts in connector  34  and thereby electrical interface  238 . Path  16  may also include an optical path (shown as path  200 ) that is connected to optical interface  252 . Electrical interface  238  may include switching circuitry (e.g., switching circuitry  164  of  FIG. 2 ) and electrical transceiver circuitry  241  such as transmitter  240  and receiver  242 . Transmitter  240  and receiver  242  may be used to support electrical communications with corresponding receiver and transmitter circuits in electrical transceiver  190  ( FIG. 3 ). Switching circuitry  164  ( FIG. 2 ) may be used to adjust the electrical paths in accessory  14  to support a desired mode of operation. In particular, circuitry  164  of  FIG. 2  may be used to connect microphone contact M, left and right channel contacts L and R, and ground contact G to appropriate circuits in accessory  14  while switching circuitry  160  in device  12  is used to connect the corresponding contacts in connector  38  to appropriate circuits in device  12 . 
     Optical communications over path  16  may be supported using optical transceiver  202  of optical communications interface circuitry  252 . Transmitter  244  may contain an optical source such as source  246 . Source  246  may contain one or more laser diodes, light-emitting diodes, etc. Receiver  248  may include a detector such as detector circuitry  250 . Detector  250  may include one or more photodetectors for receiving light signals that have been transmitted over optical path  200  from device  12 . 
     Circuitry  192  may use electrical interface  238  to support electrical communications with device  12  over path  16 . Circuitry  192  may use optical interface  252  to support optical communications with device  12  over path  16 . 
     Circuitry  232  may be used to locally implement noise cancellation functions. In a typical local noise cancellation arrangement using digital processing techniques, analog microphone signals are digitized using analog-to-digital circuitry  234 . Processing circuitry  232  receives audio signals (e.g., played back music) from device  12  over path  16  in digital form (optical or electrical). Audio processing circuitry  232  may then use digital processing techniques to cancel noise from the played back audio. The resulting audio signal may be converted to analog for speakers  224  and  228  using digital-to-analog converter circuitry  236 . 
     In a typical remote noise cancellation technique, circuitry, analog-to-digital converter circuitry  234  may be used to digitize ambient noise signals from noise cancellation microphones in accessory  14  such as microphone  222 , microphone  226 , and microphone  231 . Electrical interface  238  and/or optical interface  252  may be used to transmit these signals to accessory  14 . An advantage of using optical path  200  to convey digital audio signals from accessory  14  to device  12  is that optical path  200  is generally not subject to electrical interference and may be able to support signals with relatively large data rates. Device  12  may receive the digital noise cancellation signals from the noise cancellation microphone using transceiver  190  and/or transceiver  210  ( FIG. 3 ). Audio digital signal processor  188  may then be used to perform noise cancellation operations. The resulting noise-cancelled audio signal can be returned to accessory  14  over path  14  (e.g., using analog output from codec  182 , electrical digital signals from transceiver  190 , or optical digital signals from transceiver  210 ). In accessory  14 , analog signals may be routed to speakers  224  and  228 . If the noise-cancelled audio is provided in digital form, electrical interface  238  and/or optical interface  252  can provide these signals to circuitry  232 . Digital-to-analog converter circuitry  236  may then convert the digital audio to analog audio to play back on speakers  224  and  228 . 
     If desired, other features may be implemented locally and/or remotely. For example, accessory  14  may use circuitry  192  to locally process user input data such as button actuation data, video, images, or sensor data. These signals may also be processed remotely by conveying local signals to device  12  over path  16  using electrical interface  238  and/or optical interface  252 . The use of audio processing circuitry  232  to implement local and remote processing operations is merely illustrative. 
     If desired, device  12  may be coupled to external equipment that serves as an interface between multiple devices. This type of arrangement is shown in  FIG. 5 . 
     As shown in  FIG. 5 , system  10  includes electronic device  12 . Electronic device  12  includes electrical interface circuitry (transceiver)  190  and optical interface circuitry (transceiver)  210 . Path  16 A may include electrical path  88 A and optical path  200 A. Path  16 A may be used to connect electronic device  12  to electronic equipment  14 A. Equipment  14 A may use electrical interface circuitry  238 A (electrical transceiver circuitry) to communicate with device  12  over electrical path  88 A. Equipment  14 A may use optical interface circuitry  252 A (optical transceiver circuitry) to communicate with device  12  over optical path  200 A. 
     Equipment  14 A may serve as an interface (sometimes referred to as a breakout box) between device  12  and one or more additional pieces of equipment  14 B. The devices that are interconnected in system  10  of  FIG. 5  can be, for example, consumer electronics devices such as receivers, set-top boxes, and televisions. The interconnected devices may also include computers, audio equipment (e.g., musical instruments, studio monitors, sound effects boxes, etc.), video equipment (e.g., displays, video processors, etc.), printers and other peripherals, communications equipment, etc. 
     As shown in  FIG. 5 , equipment  14 A may use electrical interface circuitry  238 A to communicate with corresponding electrical interface circuitry  238 B (transceiver circuitry) in one or more pieces of equipment  14 B using electrical paths  88 B in paths  16 B. This allows power and/or electrical data signals to be distributed to equipment  14 B using equipment  14 A. The power and/or data signals may originate in device  12  or may originate in equipment  14 B. Equipment  14 A may also use optical interface circuitry  252 A to communicate with corresponding optical interface circuitry  252 B (transceiver circuitry) in one or more pieces of equipment  14 B using optical paths  200 B in paths  16 B. This allows optical signals from device  12  or one of devices  14 B to be distributed to other equipment in system  10 . 
     Consider, as an example, the use of equipment  14 B as an audio breakout box. In this type of arrangement, equipment (device)  12  may be a computer with one or more audio and video cards. These cards may be coupled to equipment  14 A using path  16 A. Equipment  14 B may include musical instrument equipment such as guitars, synthesizers, studio monitors, voice microphone, instrument microphones, etc. In equipment  14 B, optical interface circuitry  252 B may be used to carry digital optical data such as digital audio data. For example, in a synthesizer, the optical path between the synthesizer and breakout box  14 A may be used to carry musical instrument digital interface (MIDI) data and/or digital audio. In a guitar, the optical path between the guitar and breakout box  14 A may be used to carry digital audio data from pickups or on-board effects circuitry in the guitar. Microphones and studio monitors may use the optical paths to carry digital audio data. 
     To support legacy cables and to enhance compatibility with equipment that does not necessarily contain optical paths, the hybrid optical-electrical connectors that are used in system  10  may use a variety of form factors. For example, the connectors on one or both ends of the cables in paths  16 A and  16 B may be USB connectors, audio connectors such as 3.5 mm jacks and plugs or quarter-inch jacks and plugs, male and female XLR connectors, other connectors, or combinations of these connectors. A cable may have, as an example, a hybrid electrical-optical connector on one end and a larger or smaller audio connector or other connector on the other end. The hybrid connector in this type of arrangement may be based on a USB form factor, an XLR form factor, an audio connector form factor (e.g., 3.5 mm or quarter inch, etc.), a connector that is based on an XLR-¼″ audio connector hybrid, etc. The connector on the other end may have conventional electrical capabilities and may be based on a USB form factor, an XLR form factor, an audio connector form factor (e.g., 3.5 mm or quarter inch, etc.), a connector that is based on an XLR-¼″ audio connector hybrid, etc. Circuitry in the cable or elsewhere in the system may be used to convert between optical and electrical signaling formats. The electrical paths in the cables may be balanced or unbalanced. Each piece of equipment in system  10  may have mating connectors that receive the connectors at the ends of the cables. 
     As shown in  FIG. 6 , path  16  may be provided with hybrid optical-electrical connectors at both ends. Device  12  may have a connector such as connector  254  that contains both electrical (“E”) and optical (“O”) interfaces (transceivers). Cable  70  may have a pair of optical-electrical connectors. Optical-electrical connector  256  may have an optical path and electrical contacts that mate with a corresponding optical path and electrical contacts in connector  254  of device  12 . Optical-electrical connector  258  may mate with optical-electrical connector  260  in device  14 . Devices  12  and  14  may be cellular telephones or other electrical devices, accessories such as headphones or other electrical equipment, etc. Device  14  may have optional additional connectors such as optical-electrical connector  262  for interfacing with additional components (e.g., as described in connection with  FIG. 5 ). Device  12  may also have more than one optical-electrical connector if desired. 
     An arrangement of the type shown in  FIG. 6  may be satisfactory when it is desired to interconnect pieces of equipment that each contain a connector for receiving a mating cable connector. In some situations, it may be desirable to use a hardwired cable connection in place of or in combination with a connector-type arrangement. For example, a headset may have a cable pigtail that has a connector. In this situation, the cable in path  16  may have one end that has a connector and one end that is connected directly to circuitry in a device without using a connector. A configuration of this type is shown in  FIG. 7 . As shown in  FIG. 7 , device  12  may have an optical-electrical connector  254 . Cable  70  in path  16  may have a connector at one end such as connector  256 . Connector  256  may mate with connector  254  to support optical and electrical communications. In device  14 , the wires and optical path in cable  70  may be hardwired to electrical and optical interface circuitry without using a connector (shown as hardwired connection  264  in  FIG. 7 ). Device  14  in  FIG. 7  may have connectors such as optical-electrical connector  262  to interface with additional equipment (e.g., as described in connection with  FIG. 5 ). 
     Cable  70  may contain optical-electrical interface circuitry. An arrangement of this type is shown in  FIG. 8 . As shown in the  FIG. 8  example, cable  70  may contain interface circuitry  266 . At one end, cable  70  may have an optical-electrical connector (connector  256 ) that mates with optical-electrical connector  254  of device  12 . Optical-electrical connector  256  may have an optical path formed from a fiber and/or other optical coupling structure and electrical contacts. The optical path and electrical contacts of connector  256  may mate with a corresponding optical path and electrical contacts in connector  254  of device  12 . At its other end, cable  70  may have an electrical connector (connector  268 ) having electrical contacts that mate with electrical contacts in corresponding electrical connector  270  of device  14 . An electrical path may be formed directly between the electrical contacts of connector  256  and connector  268  and/or wires in the electrical path that originate at the electrical contacts of connector  256  may terminate at electrical terminals associated with interface circuitry  266 . When electrical signals from connector  256  are received by interface circuitry  266 , interface circuitry  266  may retransmit these electrical signals on some or all of the electrical contacts in connector  268  and vice versa. 
     Device  14  of  FIG. 8  may have other ports (e.g., ports formed by electrical connectors  276 ) to support connections with additional equipment. Interface circuitry  266  may contain optical-to-electrical converter circuitry  272  and electrical-to-optical converter circuitry  274 . Circuits  272  and  274  may include optical transceiver circuitry to send and receive optical signals and electrical transceiver circuitry to send and receive electrical signals. For example, optical-to-electrical converter circuitry  272  may include a photodetector. Electrical-to-optical converter circuitry  274  may include a light source. During operation, device  14  may use a light source to transmit optical signals through the optical path in connectors  254 ,  256 , and cable  70 . Circuitry  272  may receive the optical signals from the optical path in cable  70  that have been transmitted by device  12  and, using the photodetector, may produce corresponding electrical signals that are supplied to device  14  using electrical connector  268  and mating electrical connector  270 . Circuitry  266  may receive electrical signals from device  14  via connector  270  and connector  268  and may use the light source of electrical-to-optical circuitry  274  to produce corresponding optical signals. These optical signals may be conveyed to device  12  using the optical path in cable  70 . 
     In arrangements of the type shown in  FIGS. 6 ,  7 , and  8 , the electrical-optical connectors and electrical connectors may be implemented as 3.5 mm TRS audio connectors or other audio connectors, may be implemented as XLR connectors, or may use other suitable form factors. The optical paths in cable  70  may be formed form a single optical fiber that is coupled to wavelength-division-multiplexing filters and corresponding sources and detectors. For example, a single fiber may be used in the arrangement of  FIG. 8  to convey optical signals from connector  256  to optical-electrical interface circuitry  272 . In interface  266 , a wavelength-division-multiplexing filter may be used to route light from the optical path of cable  70  that has a first wavelength to the photodetector in circuitry  272  and may be used to route light that has a second wavelength from the light source in circuitry  274  to the optical path of cable  70 . 
     A cross-sectional side view of an illustrative cable such as cable  70  is shown in  FIG. 9 . In the example of  FIG. 9 , cable  70  has four wires  278  and a single optical fiber (fiber  280 ). Wires  278  and fiber  280  may be encased in jacket  282 . Additional components may be included in cable  70  if desired (e.g., strands of strengthening fiber, dielectric filler, metal braids or foils (e.g., for electromagnetic shielding), etc. Wires  278  may be formed from a solid conductor (e.g., solid copper wire) or from stranded wire. A plastic coating or other insulator may surround each wire to prevent short circuits. Fiber  280  may be formed from a material that is transparent to light (e.g., to infrared or visible light). Suitable materials for fiber  280  include plastic and glass. Fiber  280  may be a multimode fiber or may be a single mode fiber. One or more layers (e.g., a core layer, a cladding layer, strengthening layers, etc.) may be included in fiber  280 . 
     Wires  278  may be used in forming an electrical path in path  16 . Fiber  280  may be used in forming an optical path. Although four wires and a single optical fiber are shown in the illustrative cross-sectional view of  FIG. 9 , this is merely an example. Cable  70  may contain fewer than four wires or more than four wires and may contain one, two, or more than two optical fibers. For example, cable  70  may contain two optical fibers  280 , as shown in  FIG. 10 . 
     When path  16  contains a single optical fiber, optical signals may be sent in one direction. For example, a transmitter in device  12  may transmit optical signals to a corresponding receiver in equipment  14  or a transmitter in equipment  14  may transmit optical signals to a corresponding receiver in device  12 . Bidirectional communications may also be supported. With one suitable arrangement, a time division multiplexing scheme may be used to support bidirectional communications. In a time division multiplexing scheme, device  12  and equipment  14  may take turns in using the optical path. During certain time periods, device  12  can transmit optical signals to equipment  14 . During other time periods, equipment  14  can transmit optical signals to equipment  12 . 
     Simultaneous bidirectional communications over a single fiber may also be supported. For example, multiple wavelengths of light may be used in the system. Electronic device  12  may transmit upstream data using light at a first wavelength while equipment  14  is simultaneously transmitting downstream data using light at a second wavelength. When cables contain multiple fibers (as with the illustrative cable of  FIG. 10 ), one fiber may be used for upstream communications while the other fiber is being used for downstream communications. Each fiber in a multi-fiber cable may also be used for bidirectional communications using time-division or wavelength-division multiplexing techniques. 
     In cable  70 , the optical fiber that makes up the optical path may be located in the center of the cable (i.e., running along its longitudinal axis in a coaxial fashion) or may be located in other suitable portions of the cable (e.g., near the plastic jacket or intertwined with other strands of material). In the optical-electrical connectors, the optical fiber can be coupled to transparent structures that help guide light to and from the optical fiber. These transparent structures may include coaxial lengths of fiber, annular (ring-shaped) transparent insulators (e.g., insulators that serve both as transparent conduits for light and as electrical insulators that isolate electrical contacts in the connectors from each other), etc. 
     An illustrative configuration that may be used for an optical-electrical audio plug and a mating optical-electrical audio jack is shown in  FIG. 11 . As shown in  FIG. 11 , audio connector  38  (e.g., a TRS audio jack) may contain electrical contacts  74 ,  76 ,  78 , and  80  (labeled T, R 1 , R 2 , and S, respectively) and may have an associated optical transceiver  208 . The diagram of  FIG. 11  shows plug  34  partially inserted into jack  38 . When plug  34  is fully plugged into jack  38 , electrical contacts  48 ,  50 ,  52 , and  54  (labeled T, R 1 , R 2 , and S, respectively) form respective electrical connections with mating contacts  74 ,  76 ,  78 , and  80 . Optical path  200  may be placed in contact with transceiver  208  or may be placed sufficiently close to transceiver  208  that optical signals (light) may be coupled between transceiver  208  and path  200 . If desired, jack  38  may include an optical member such as member  206  of  FIG. 2  that is interposed in optical path  200  to help convey optical signals between input-output port  286  of transceiver  208  and tip  284  of optical path  200 . In this type of configuration, the optical member (which may be, for example, a short length of optical fiber) may serve as an extending portion of path  200 . 
     In configurations of the type shown in  FIG. 11 , there may be only a single optical fiber in cable  70  and in connector  34 . It may therefore be desirable to use wavelength-division multiplexing techniques to support bidirectional communications over the optical fiber. Wavelength division multiplexing may be implemented using wavelength division multiplexing (WDM) optical filters. As shown in  FIG. 12 , for example, a respective WDM filter may be coupled to each end of path  16 . In device  12 , source  212  may be coupled to an input port of WDM filter  288  by optical path  290  (e.g., an optical fiber). Detector  218  may be coupled to an output port of WDM filter  288  by optical path  292  (e.g., an optical fiber). Path  200  (e.g., an optical fiber) may be coupled to an input-output port of WDM filter  288  (either by direct connection or via an optical path extension such as optical path extension  206  of  FIG. 2 ). In device  14 , WDM filter  294  may have an input-output port that is coupled to path  200 , an output port that is coupled to detector  250  (e.g., by optical path  296 ), and an input port that is coupled to source  246  (e.g., by optical path  298 ). 
     WDM filters  294  and  288  combine and separate light by wavelength. For example, outgoing light from source  212  at a first wavelength may be routed to path  200  by WDM filter  288 . In device  14 , WDM filter  294  may route light at this first wavelength to the input of detector  250 . Source  246  in device  14  may transmit light at a second wavelength that is different than the first wavelength. WDM filter  294  may route this second wavelength of light onto path  200 . In device  12 , WDM filter  288  may route light at the second wavelength to the input of detector  218 . WDM filters  288  and  294  may be implemented using gratings, coupled waveguides, etc. If more than two wavelengths are desired in a wavelength division multiplexing scheme, additional WDM filters or filters with additional ports may be used to accommodate additional sources and detectors. WDM filter configurations of the type shown in  FIG. 12  may, if desired, be used in systems of the type described in connection with  FIGS. 6 ,  7 , and  8  (as an example). 
     In arrangements of the type shown in  FIG. 11 , optical path  200  may be formed using a coaxial fiber (i.e., a fiber that runs along the central longitudinal axis of cable  70  and connectors  34  and  38 ). Audio connectors  34  and  38  in this type of arrangement need not be placed in a particular rotational orientation to ensure adequate optical coupling between path  200  and transceiver  208 , because connectors  34  and  38  in the  FIG. 11  arrangement are radially symmetric. 
     If desired, however, connectors  34  and  38  may be provided with alignment features that help these connectors maintain a particular desired rotational orientation when mated. This type of arrangement is shown in  FIG. 13 . As shown in  FIG. 13 , plug  34  and jack  38  may be aligned along longitudinal axis  304 . Plug  34  may have one or more engagement features such as engagement feature  300  (e.g., a protrusion). Jack  38  may have one or more mating engagement features such as engagement feature  302  (e.g., an indentation or other recess). When a user desires to insert plug  34  into jack  38  along axis  304 , the user may rotate plug  34  about axis  304  in direction  306 . Once the engagement features are properly aligned (i.e., once features  300  and  302  are in rotational alignment), plug  34  may be completely inserted into jack  38 . 
     When rotational alignment features of the type show in  FIG. 13  are used in the audio connectors, a desired rotational alignment between plug  34  and jack  38  may be ensured. As a result, source  212  and detector  218  may be located at particular known positions in device  12 , as shown in  FIG. 14 . In the  FIG. 14  example, path  200  includes first fiber  280 A and a second fiber  280 B. In device  14 , fiber  280 A is coupled to detector  250  and fiber  280 B is coupled to source  246 . When plug  34  is connected to jack  38 , alignment features  300  and  302  ( FIG. 13 ) engage and thereby ensure that fiber  280 A will be properly aligned with source  212  and that fiber  280 B will be properly aligned with detector  218  (or, in configurations that use WDM filters, that the single fiber in path  200  is aligned with the input-output port of the WDM filter). 
     In systems that do not use alignment features, it may be desirable to provide plug  34  and jack  38  with radially-symmetric optical coupling structures. Consider, as an example, the plug configuration of  FIG. 15 . As shown in  FIG. 15 , plug  34  may be provided with annular optical structure  310  and concentric annular optical structure  308 . Structures  310  and  308  may be ring-shaped transparent members that are optically coupled to respective optical fibers in cable  70  and that surround the prong (elongated prong-shaped member  309 ) on which the tip contact, ring contacts, and sleeve contact of the plug are formed. Structures  310  and  308  may be formed from clear plastic, glass, or other suitable transparent substances (e.g., for infrared or visible light). The example of  FIG. 15  includes two annular optical coupling structures, but arrangements with only a single optical coupling structure may be used if desired (e.g., when a WDM arrangement of the type described in connection with  FIG. 12  is used). 
     Because optical coupling structures such as optical coupling structures  310  and  308  are radially symmetric, use of arrangements of the type shown in  FIG. 15  help ensure that there is adequate optical coupling between the audio connectors (e.g., optical coupling between optical path  200  and transceiver  208 ) regardless of the rotational orientation between plug  34  and jack  38 . If desired, one or more annular optical coupling structures may be included in jack  38 , as shown in  FIG. 16 . In this type of arrangement, coupling structure  308  has a diameter that is greater than the diameter of the circular opening of the cylindrical cavity that forms the interior portion of jack  38  and coupling structure  310  has a diameter greater than that of coupling structure  308 . Coupling structure  308  may be used to route incoming light from optical coupling structure  308  of plug  34  to a detector in device  14 . Coupling structure  310  of jack  38  may be used to route transmitted light from the source in device  12  to optical coupling structure  310  in plug  34  ( FIG. 15 ). The ring-shaped optical coupling structures in jack  38  and plug  34  may be used to mate with each other or may be used to mate with sources, detectors, or optical fibers that have fixed positions within their connectors, but that do not completely surround the connector. For example, annular optical coupling structures in plug  34  may be coupled with a source and detector of the type shown in  FIG. 14  or annular optical coupling structures in jack  38  may be coupled with optical fibers such as optical fibers  280 A and  280 B in plug  34 . 
     A cross-sectional side view of a plug and jack where the ring-shaped optical coupling structures of plug  34  are used to mate with a source and detector in jack  38  is shown in  FIG. 17 . As shown in  FIG. 17 , outer annular optical coupling structure  308  may be coupled to optical fiber  280 A and inner annular optical coupling structure  310  may be coupled to optical fiber  280 B. Annular optical coupling structure  308  will optically couple fiber  280 A to source  212 , regardless of the rotational orientation of plug  34  within jack  38 . Similarly, optical coupling structure  310  will optically couple fiber  280 B to detector  218 , regardless of the rotational orientation between plug  34  and jack  38 . 
     If desired, light can be transmitted through transparent optical coupling structures that are formed between the electrical contacts in plug  34  and jack  38 . Each of the electrical contacts in plug  34  and jack  38  (i.e., the tip, ring, and sleeve contacts) may be electrically insulated from adjacent electrical contacts using ring-shaped transparent dielectric structures (e.g., glass, plastic, or other dielectric materials that are transparent in the infrared or visible portions of the spectrum and that are electrically insulating). These structures can therefore serve dual purposes. Electrically, the dielectric structures are insulators that block the flow of current between adjacent electrical connectors. This prevents the electrical contacts from becoming shorted to each other. Optically, at least some of the dielectric structures are transparent to the optical signals on path  200 . This allows the optical signals to be coupled between the optical transceiver and optical path  200 . 
     A connector arrangement in which transparent dielectric structures are formed between respective electrical contacts in plug  34  and jack  38  is shown in  FIG. 18 . As shown in  FIG. 18 , plug  34  may have contacts  48 ,  50 ,  52 , and  54  that mate with respective contacts  74 ,  76 ,  78 , and  80  in jack  38 . Contacts  48 ,  50 ,  52 , and  54  of  FIG. 18  are ring shaped. Mating contacts  74 ,  76 ,  78 , and  80  may be formed using hollow rings, spring metal tabs that protrude inwards and make electrical contact with the contacts of plug  34 , or other suitable electrical contacts. In a typical configuration, the contacts of plug  34  are separated by dielectric (see, e.g., dielectric band  56 , which isolates tip contact  48  from ring contact  50 ). 
     At least some of the dielectric that isolates the electrical contacts in plug  34  may also serve as transparent windows for optical signals. In the  FIG. 18  example, ring-shaped optical band  312  may be formed from a dielectric such as transparent plastic or transparent glass. Optical coupling structure  314  (e.g., one or more transparent plastic or glass members) may be used to optically couple optical band structure  312  to optical path  280 B. Optical structures  312  and  314  are interposed between contacts  50  and  52  and therefore may help to isolate contacts  50  and  52  from each other. Ring-shaped optical band  316  may also be formed from a dielectric such as transparent plastic or transparent glass. Optical coupling structure  318  (e.g., one or more transparent plastic or glass members) may be used to optically couple optical band structure  316  to optical path  280 A. When plug  34  is inserted into jack  38  as shown in  FIG. 18 , structures  312  and  314  may optically couple source  212  to path  280 B and structures  316  and  318  may optically couple detector  218  to path  280 A. 
     With an arrangement of this type, path  280 B may be used by jack  38  to transmit optical signals from device  12  and path  280 A may be used by jack  38  to receive optical signals for device  12 . Other arrangements may be used if desired. For example, jack  38  and plug  34  may be provided with a single optical path rather than multiple optical paths. In this type of arrangement, bidirectional communications may be supported using wavelength-division-multiplexing techniques as described in connection with  FIG. 12  or time-division multiplexing techniques. Moreover, any respective pair of the contacts may be separated by a transparent insulator structure. The separation of the R 1  and R 2  contacts by one such structure and the separation of the R 2  and S contacts by another such structure in the example of  FIG. 18  are merely illustrative. If desired, the transparent insulator structures may be formed as unitary pieces of material. The use of two or more separate pieces of adjacent transparent material (e.g., the two-piece structures such as structure  312 / 314  and structure  316 / 318  of  FIG. 18 ) is shown as an example. 
     As shown in  FIG. 18 , jack  18  may also have transparent insulating structures such as structure  320  and  322  in the gaps between adjacent contacts. These structures may, if desired, help isolate the electrical contacts in jack  38  from each other. Structure  320  may have a fiber shape, a ring shape, or other suitable shape and may be used to guide light from source  212  into structure  312 . Structure  322  may have a fiber shape, a ring shape, or other suitable shape and may be used to guide light from structure  316  into detector  218 . In wavelength-division-multiplexing arrangements, only one of transparent insulator optical coupling structures  320  and  322  need be used. In this type of situation, the optical coupling structure may be coupled to a WDM filter such as filter  288  of  FIG. 12 . 
     Source  212  and detector  218  (or, in WDM configurations, WDM filter  288 ) may be located at a particular rotational orientation around plug  34  (as shown in the  FIG. 18  example) or may be formed at one or more radial locations around plug  34 . In configurations in which only one radial location is used (e.g., the 12:00 position of source  212  and detector  218  that is shown in the  FIG. 18  example), structures  320  and  322  may be used to help concentrate and guide light between that radial location and the radially uniform ring-shaped structures in plug  34  such as structure  312  and  316  or other transparent insulator plug structures. 
     If desired, engagement features such as features  302  and  300  of  FIG. 13  may be used in connection with connectors of the type shown in  FIG. 18 . When engagement features are used, the rotational orientation between plug  34  and jack  38  is known whenever plug  34  and jack  38  are coupled together. As a result, optical coupling structures  314  and  318  may be configured to guide light to and from a particular radial location around plug  34  (e.g., at the 12:00 location of the source and detector of  FIG. 18 ). In this way, the signal strength reductions that might otherwise be associated with spreading out optical signals in a radially uniform fashion can be avoided. 
       FIG. 19  is a perspective view of an illustrative electronic device and an associated accessory. As shown in  FIG. 19 , accessory  14  may have a base  334  from which plug  34  protrudes vertically. Base  334  may serve as a stand that supports an electronic device. Base structure  334  may have a cavity  336 . Cavity  336  may have a size and shape that is configured to receive and support end  338  of device  12 . Cable  330  and connector  332  may be attached to additional equipment such as a computer (see, e.g., computing equipment  20  of  FIG. 1 ). Cable  330  and connector  332  may be used to convey analog signals, power signals, and digital data signals. When a user desires to charge a battery in device  12  or to play audio and video from device  12 , the user may insert device  12  into cavity  336 . In this position, cylindrical plug  34  is received in mating cylindrical jack  38 . Optical and electrical paths through plug  34  and jack  38  may be used to convey data and power between accessory  14  and device  12  (e.g., bidirectionally using time-division multiplexing and/or wavelength division multiplexing techniques). If desired, the electrical contacts of the connectors can distribute power to device  12  while device  12  is conveying digital optical signals to accessory  14  using an optical path through the connectors. Accessory  14  can be provided with speakers or other components that allow accessory  14  to present media to the user. Accessory  14  can also use optical transceiver circuitry and/or electrical transceiver circuitry to relay data to and from the equipment that is attached to cable  330  and connector  332 . 
       FIG. 20  is a flow chart showing illustrative steps involved in conveying electrical and optical signals through communications paths  16  between electrical equipment such as electronic device, accessories, and other equipment. The communications paths typically include both electrical and optical paths. 
     At step  324 , after a user has connected equipment together using paths  16 , the equipment in the system can perform discovery operations. These operations allow the components in the system to determine what other equipment is included in the system and therefore allow components to adjust their settings accordingly. As an example, an electronic device that discovers that a legacy headset that only includes electrical wires has been attached may configure itself to support analog audio playback, whereas an electronic device that discovers that an accessory with optical communications capabilities has been attached may configure itself to use its optical transceiver. 
     One way in which the equipment in system  10  may determine the capabilities of other equipment in the system involves the use of switches. For example, jack  38  may be provided with a mechanically-triggered, electrically-triggered, or optically-triggered switch (e.g., a light sensor such as a light reflection sensor) that changes state whenever an engagement feature such as engagement feature  300  is inserted a mating engagement feature such as engagement feature  302  ( FIG. 13 ). The present of the engagement feature on the audio connector serves as a flag that advertises its capabilities. 
     Another way in which equipment in system  10  may determine the capabilities of other equipment involves the use of communications protocols. Equipment in the system may, for example, broadcast codes that inform other equipment of their capabilities. An electric device or other accessory such as a headset may, for example, transmit optical or electrical information to make other equipment aware of its optical (and electrical) capabilities. Communications protocols may be unidirectional (e.g., equipment may broadcast codes without receiving significant information from other equipment) or may be bidirectional. In a typical bidirectional protocol, equipment in the system may, for example, transmit information that informs other equipment of their capabilities in response to received queries or may exchange capability information as part of a more complex two-way data exchange. 
     During discovery operations  324 , equipment in system  10  may discover information on other equipment such as what type of communications protocols the equipment supports, what type of transceivers the equipment contains, whether the equipment contains an optical transceiver, etc. 
     At step  326 , the equipment in the system may perform link setup operations. For example, the equipment in the system can exchange packets of digital data that inform the other equipment of desired clock rates, desired transmission powers for optical signals, desired communications formats (e.g., whether error correction capabilities will or will not be present, data rate limits, etc.), desired power supply voltages to be conveyed (if any), and other link settings. 
     As an example, consider a situation in which device  12  and equipment  14  each contain a light-emitting-diode (LED) source. Due to the quality of the optical coupling formed when plug  34  is inserted into jack  38  and other variables, the attenuation of optical path  200  may be uncertain. During the operations of step  326 , device  12  and equipment  14  may send test light pulses while making corresponding power measurements with their detectors. Based on these measurements, device  12  and equipment  14  may then negotiate to establish optimal optical signal levels for use in communicating over path  16 . Negotiations may take place using the electrical path and/or using the optical path. By negotiating optimal signal power levels, power consumption can be minimized, thereby enhancing efficiency. 
     A typical optical power negotiation process may initially involve transmission of a test packet from an accessory at an initial power P 1  (e.g., a low or lowest power setting). In response, the electronic device may use its optical transceiver to measure the amount of power in the received optical signal. Once this power level has been measured, the electronic device can respond to the accessory. For example, the electronic device can respond to the accessory using the electrical transceiver in the electronic device. The response of the electronic device may indicate that the power P 1  is an acceptable level for use in future optical communications over the link. If the measured power is low, the response of the electronic device may request that the accessory increase its optical transmission power. This negotiation process may continue until the two devices reach agreement on an acceptable optical power level to use for the link. Optical transmitters in both the electronic device and the accessory may be calibrated in this way. 
     After communications links between the equipment in system  10  have been established at step  326 , the equipment may use these links during normal system operation (step  328 ). For example, the optical and electrical paths in links  16  may be used to convey video data (including audio soundtracks), audio data (e.g., for noise cancellation schemes), control signals, etc. 
     The foregoing is merely illustrative of the principles of this invention and various modifications can be made by those skilled in the art without departing from the scope and spirit of the invention.

Metadata:
Filing Date: 20091119
Publication Date: 20131105
Grant Date: 20131105
Priority Date: 20091119
Inventors: TERLIZZI JEFFREY J.
TISCARENO VICTOR
DOROGUSKER JESSE L.
Assignee: APPLE INC
CPC Classifications: [{"code": "G02B6/3817", "inventive": true, "first": true, "tree": "[]"}, {"code": "H01R24/58", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01R2107/00", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02B6/4246", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02B6/421", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02B6/4292", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B6/3817", "inventive": true, "first": true, "tree": "[]"}, {"code": "H01R24/58", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02B6/4292", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B6/421", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02B6/4246", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01R2107/00", "inventive": false, "first": false, "tree": "[]"}]
Family ID: 44011349