PATENT DOCUMENT

Publication Number: US-11956341-B2
Application Number: US-202217830087-A
Country: US
Kind Code: B2

Title: Electronic devices having electro-optical phase-locked loops

Abstract:
An electronic device may include wireless circuitry clocked using an electro-optical phase-locked loop (OPLL) having primary and secondary lasers. A frequency-locked loop (FLL) path and a phase-locked loop (PLL) path may couple an output of the secondary laser to its input. A photodiode may generate a photodiode signal based on the laser output. A digital-to-time converter (DTC) may generate a reference signal. The FLL path may coarsely tune the secondary laser based on the photodiode signal until the secondary laser is frequency locked. Then, the PLL path may finely tune the secondary laser based on the reference signal and the photodiode signal until the phase of the secondary laser is locked to the primary laser. The photodiode signal may be subsampled on the PLL path. This may allow the OPLL to generate optical local oscillator signals with minimal jitter and phase noise.

Claims:
What is claimed is: 
     
       1. An electro-optical phase-locked loop comprising:
 a first light source configured to emit light at a first frequency; 
 a second light source configured to emit light at a second frequency that is offset from the first frequency by an offset frequency of at least 50 GHz; 
 a feedback path that communicably couples an output of the second light source to an input of the second light source; 
 a digital-to-time converter (DTC) configured to generate a reference signal; 
 a phase comparator disposed along the feedback path, wherein the phase comparator is configured to adjust the second light source based at least in part on the reference signal; and 
 a photodiode having an output coupled to an input of the phase comparator. 
 
     
     
       2. The electro-optical phase-locked loop of  claim 1 , further comprising:
 a first optical path that communicably couples an output of the first light source to the photodiode; and 
 a second optical path that communicably couples the output of the second light source to the photodiode, wherein the photodiode is configured to generate a photodiode signal at the offset frequency using at least some of the light emitted by the first light source at the first frequency and at least some of the light emitted by the second light source at the second frequency. 
 
     
     
       3. The electro-optical phase-locked loop of  claim 2 , wherein the photodiode comprises a uni-travelling-carrier photodiode (UTC PD). 
     
     
       4. The electro-optical phase-locked loop of  claim 2 , further comprising:
 a first optical splitter that couples the output of the first light source to the first optical path and to a first output terminal of the electro-optical phase-locked loop; and 
 a second optical splitter that couples the output of the second light source to the second optical path and to a second output terminal of the electro-optical phase-locked loop. 
 
     
     
       5. The electro-optical phase-locked loop of  claim 2 , wherein the phase comparator is configured to adjust the second light source based on a comparison of a phase of the photodiode signal to a phase of the reference signal. 
     
     
       6. The electro-optical phase-locked loop of  claim 5 , further comprising:
 a subsampling mixer that includes the phase comparator, wherein the subsampling mixer is configured to subsample the photodiode signal to produce a subsampled photodiode signal and the phase comparator is configured to adjust the second light source based on a comparison of a phase of the subsampled photodiode signal to the phase of the reference signal. 
 
     
     
       7. The electro-optical phase-locked loop of  claim 2 , further comprising:
 an additional feedback path that communicably couples the output of the second light source to the input of the second light source; and 
 a counter disposed along the additional feedback path, wherein the counter is configured to identify the offset frequency based on the photodiode signal and is configured to adjust the second frequency based at least on the identified offset frequency. 
 
     
     
       8. The electro-optical phase-locked loop of  claim 7 , further comprising:
 a reference oscillator configured to generate a reference oscillator signal, wherein the DTC is configured to generate the reference signal based on the reference oscillator signal and the counter is configured to estimate the offset frequency based on the photodiode signal and the reference oscillator signal, the reference oscillator signal being at a frequency between 5 GHz and 25 GHz. 
 
     
     
       9. The electro-optical phase-locked loop of  claim 1 , further comprising a counter coupled between an output of the photodiode and the second light source. 
     
     
       10. The electro-optical phase-locked loop of  claim 1 , further comprising:
 a reference oscillator configured to generate a reference oscillator signal, wherein the DTC is configured to generate the reference signal based on the reference oscillator signal; 
 an additional feedback path that communicably couples the output of the second light source to the input of the second light source; and 
 a counter disposed along the additional feedback path, wherein the counter is configured to identify the offset frequency based at least in part on the reference oscillator signal and is configured to adjust the second frequency based at least on the identified offset frequency. 
 
     
     
       11. A method of operating an electro-optical phase-locked loop comprising:
 emitting, using a first laser, emitting a first optical local oscillator (LO) signal at a first frequency; 
 emitting, using a second laser, a second optical LO signal at a second frequency that is offset from the first frequency by an offset frequency greater than 50 GHz; 
 coarsely tuning, using a frequency-locked loop (FLL) path communicably coupled between an output of the second laser and an input of the second laser, the second optical LO signal emitted by the second laser until the second frequency is locked; and 
 once the second frequency is locked, finely tuning, using a phase-locked loop (PLL) path communicably coupled between the output of the second laser and the input of the second laser, the second optical LO signal emitted by the second laser until the second optical LO signal is phase-locked with the first optical LO signal. 
 
     
     
       12. The method of  claim 11 , further comprising:
 transmitting the first optical LO signal and the second optical LO signal to a photodiode that uses the first optical LO signal and the second optical LO signal to convey wireless signals at the offset frequency over an antenna radiating element. 
 
     
     
       13. The method of  claim 11 , further comprising:
 generating, using a photodiode disposed along the FLL path and the PLL path, a photodiode signal at the offset frequency using at least some of the first optical LO signal and at least some of the second optical LO signal. 
 
     
     
       14. The method of  claim 13 , further comprising:
 subsampling, using a subsampling mixer disposed along the PLL path, the photodiode signal to generate a subsampled photodiode signal, wherein finely tuning the second optical LO signal includes adjusting, using the subsampling mixer, a phase of the second optical LO signal based at least on a phase of the subsampled photodiode signal. 
 
     
     
       15. The method of  claim 14 , further comprising:
 generating, using a digital-to-analog converter (DTC), a reference signal, wherein finely tuning the second optical LO signal includes adjusting, using the subsampling mixer, the phase of the second optical LO based on a comparison of the phase of the subsampled photodiode signal to a phase of the reference signal. 
 
     
     
       16. The method of  claim 13 , further comprising:
 identifying, using a counter disposed along the FLL path, the offset frequency using the photodiode signal, wherein coarsely tuning the second optical LO signal comprises adjusting the second frequency based at least on the identified offset frequency. 
 
     
     
       17. An electronic device comprising:
 an antenna radiating element; 
 a first photodiode coupled to the antenna radiating element and configured to convey wireless signals at a frequency greater than 100 GHz using the antenna radiating element, a first optical local oscillator (LO) signal, and a second optical LO signal; and 
 optical components configured to generate the first optical LO signal and the second optical LO signal, the optical components including
 a first laser configured to emit the first optical LO signal, 
 a second laser configured to emit the second optical LO signal, 
 a second photodiode configured to generate a photodiode signal based on the first optical LO signal and the second optical LO signal, and 
 a subsampling mixer configured to generate a subsampled photodiode signal based on the photodiode signal and configured to tune the second laser based at least in part on a phase of the subsampled photodiode signal. 
 
 
     
     
       18. The electronic device of  claim 17 , further comprising:
 a counter configured to identify a frequency of the photodiode signal and configured to tune the second laser based at least in part on the identified frequency of the photodiode signal. 
 
     
     
       19. The electronic device of  claim 17 , wherein the first laser comprises a first portion of a resonant cavity and the second laser comprises a second portion of the resonant cavity that is longer than the first portion. 
     
     
       20. The electronic device of  claim 17 , wherein the first photodiode comprises a uni-travelling-carrier photodiode (UTC PD).

Description:
This application claims the benefit of U.S. Provisional Patent Application No. 63/246,747, filed Sep. 21, 2021, which is hereby incorporated by reference herein in its entirety. 
    
    
     FIELD 
     This disclosure relates generally to electronic devices and, more particularly, to electronic devices with wireless circuitry. 
     BACKGROUND 
     Electronic devices can be provided with wireless capabilities. An electronic device with wireless capabilities has wireless circuitry that includes one or more antennas. The wireless circuitry is used to perform communications using radio-frequency signals conveyed by the antennas. 
     As software applications on electronic devices become more data-intensive over time, demand has grown for electronic devices that support wireless communications at higher data rates. However, the maximum data rate supported by electronic devices is limited by the frequency of the radio-frequency signals. As communication frequencies increase, it can become difficult to provide low jitter and low phase noise clocking for the wireless circuitry. 
     SUMMARY 
     An electronic device may include wireless circuitry that conveys wireless signals at frequencies greater than 100 GHz. The wireless circuitry or other circuitry in the device may be clocked using an electro-optical phase-locked loop (OPLL). The OPLL may include a primary laser that emits a first optical local oscillator (LO) signal at a fixed first frequency and a secondary laser that emits a second optical LO signal at an adjustable second frequency. The wireless circuitry may, for example, convey the wireless signals using the first and second optical LO signals. 
     A frequency-locked loop (FLL) path and a phase-locked loop (PLL) path may couple an output of the secondary laser to an input of the secondary laser. A photodiode may be interposed on both the FLL path and the PLL path. The photodiode may generate a photodiode signal based on the first and second optical LO signals. The OPLL may include a reference oscillator that generates a reference oscillator signal. The OPLL may include a digital-to-time converter (DTC) that generates a DTC reference signal based on the oscillator signal. 
     The FLL path may coarsely tune the secondary laser based on the reference oscillator signal and the photodiode signal. For example, the FLL path may include a counter that estimates a frequency offset between the first and second optical LO signals. The counter may coarsely tune the secondary laser based on the estimated frequency offset (e.g., until the frequency of the second optical LO signal settles and is locked to a predetermined value). Once the frequency of the second optical LO signal is locked, the PLL path may finely tune the secondary laser based on the DTC reference signal and the photodiode signal. For example, the PLL path may include a subsampling mixer that subsamples the photodiode signal to produce a subsampled photodiode signal. The subsampling mixer may finely tune the secondary laser based on a phase difference between the DTC reference signal and the subsampled photodiode signal (e.g., until the phase of the second optical LO signal settles and is locked with respect to the first optical LO signal). In this way, the first and second optical LO signals may be used to clock portions of device  10  with minimal jitter and phase noise. 
     An aspect of the disclosure provides an electro-optical phase-locked loop. The electro-optical phase-locked loop can include a first light source configured to emit light at a first frequency. The electro-optical phase-locked loop can include a second light source configured to emit light at a second frequency that is offset from the first frequency by an offset frequency of at least 50 GHz. The electro-optical phase-locked loop can include a feedback path that communicably couples an output of the second light source to an input of the second light source. The electro-optical phase-locked loop can include a digital-to-time converter (DTC) configured to generate a reference signal. The electro-optical phase-locked loop can include a phase comparator interposed along the feedback path, wherein the phase comparator is configured to adjust the second light source based at least in part on the reference signal. 
     An aspect of the disclosure provides a method of operating an electro-optical phase-locked loop. The method can include with a first laser, emitting a first optical local oscillator (LO) signal at a first frequency. The method can include with a second laser, emitting a second optical LO signal at a second frequency that is offset from the first frequency by an offset frequency greater than 50 GHz. The method can include with a frequency-locked loop (FLL) path communicably coupled between an output of the second laser and an input of the second laser, coarsely tuning the second optical LO signal emitted by the second laser until the second frequency is locked. The method can include once the second frequency is locked, with a phase-locked loop (PLL) path communicably coupled between the output of the second laser and the input of the second laser, finely tuning the second optical LO signal emitted by the second laser until the second optical LO signal is phase-locked with the first optical LO signal. 
     An aspect of the disclosure provides an electronic device. The electronic device can include an antenna radiating element. The electronic device can include a photodiode coupled to the antenna radiating element and configured to convey wireless signals at a frequency greater than 100 GHz using the antenna radiating element, a first optical local oscillator (LO) signal, and a second optical LO signal. The electronic device can include optical components configured to generate the first optical LO signal and the second optical LO signal. The optical components can include a first laser configured to emit the first optical LO signal. The optical components can include a second laser configured to emit the second optical LO signal. The optical components can include a photodiode configured to generate a photodiode signal based on the first optical LO signal and the second optical LO signal. The optical components can include a subsampling mixer configured to generate a subsampled photodiode signal based on the photodiode signal and configured to tune the second laser based at least in part on a phase of the subsampled photodiode signal. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a block diagram of an illustrative electronic device having wireless circuitry with at least one antenna that conveys wireless signals at frequencies greater than about 100 GHz in accordance with some embodiments. 
         FIG.  2    is a top view of an illustrative antenna that transmits wireless signals at frequencies greater than about 100 GHz based on optical local oscillator (LO) signals in accordance with some embodiments. 
         FIG.  3    is a top view showing how an illustrative antenna of the type shown in  FIG.  2    may convert received wireless signals at frequencies greater than about 100 GHz into intermediate frequency signals based on optical LO signals in accordance with some embodiments. 
         FIG.  4    is a top view showing how multiple antennas of the type shown in  FIGS.  2  and  3    may be stacked to cover multiple polarizations in accordance with some embodiments. 
         FIG.  5    is a top view showing how stacked antennas of the type shown in  FIG.  4    may be integrated into a phased antenna array for conveying wireless signals at frequencies greater than about 100 GHz within a corresponding signal beam. 
         FIG.  6    is a circuit diagram of illustrative wireless circuitry having an antenna that transmits wireless signals at frequencies greater than about 100 GHz and that receives wireless signals at frequencies greater than about 100 GHz for conversion to intermediate frequencies and then to the optical domain in accordance with some embodiments. 
         FIG.  7    is a circuit diagram of an illustrative phased antenna array that conveys wireless signals at frequencies greater than about 100 GHz within a corresponding signal beam in accordance with some embodiments. 
         FIG.  8    is a circuit diagram of an illustrative electro-optical phase-locked loop that may use primary and secondary light sources to emit low jitter and low phase noise optical local oscillator signals in accordance with some embodiments. 
         FIG.  9    is a timing diagram showing how an illustrative digital-to-time converter (DTC) may generate a programmable DTC reference signal for an electro-optical phase-locked loop in accordance with some embodiments. 
         FIG.  10    is a flow chart of illustrative operations involved in using an electro-optical phase-locked loop to emit low jitter and low phase noise optical local oscillator signals in accordance with some embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     Electronic device  10  of  FIG.  1    (sometimes referred to herein as electro-optical device  10 ) may be a computing device such as a laptop computer, a desktop computer, a computer monitor containing an embedded computer, a tablet computer, a cellular telephone, a media player, or other handheld or portable electronic device, a smaller device such as a wristwatch device, a pendant device, a headphone or earpiece device, a device embedded in eyeglasses, goggles, or other equipment worn on a user&#39;s head, or other wearable or miniature device, a television, a computer display that does not contain an embedded computer, a gaming device, a navigation device, an embedded system such as a system in which electronic equipment with a display is mounted in a kiosk or automobile, a wireless internet-connected voice-controlled speaker, a home entertainment device, a remote control device, a gaming controller, a peripheral user input device, a wireless base station or access point, equipment that implements the functionality of two or more of these devices, or other electronic equipment. 
     As shown in the functional block diagram of  FIG.  1   , device  10  may include components located on or within an electronic device housing such as housing  12 . Housing  12 , which may sometimes be referred to as a case, may be formed of plastic, glass, ceramics, fiber composites, metal (e.g., stainless steel, aluminum, metal alloys, etc.), other suitable materials, or a combination of these materials. In some situations, parts or all of housing  12  may be formed from dielectric or other low-conductivity material (e.g., glass, ceramic, plastic, sapphire, etc.). In other situations, housing  12  or at least some of the structures that make up housing  12  may be formed from metal elements. 
     Device  10  may include control circuitry  14 . Control circuitry  14  may include storage such as storage circuitry  16 . Storage circuitry  16  may include hard disk drive storage, nonvolatile memory (e.g., flash memory or other electrically-programmable-read-only memory configured to form a solid-state drive), volatile memory (e.g., static or dynamic random-access-memory), etc. Storage circuitry  16  may include storage that is integrated within device  10  and/or removable storage media. 
     Control circuitry  14  may include processing circuitry such as processing circuitry  18 . Processing circuitry  18  may be used to control the operation of device  10 . Processing circuitry  18  may include on one or more processors, microprocessors, microcontrollers, digital signal processors, host processors, baseband processor integrated circuits, application specific integrated circuits, central processing units (CPUs), graphics processing units (GPUs), etc. Control circuitry  14  may be configured to perform operations in device  10  using hardware (e.g., dedicated hardware or circuitry), firmware, and/or software. Software code for performing operations in device  10  may be stored on storage circuitry  16  (e.g., storage circuitry  16  may include non-transitory (tangible) computer readable storage media that stores the software code). The software code may sometimes be referred to as program instructions, software, data, instructions, or code. Software code stored on storage circuitry  16  may be executed by processing circuitry  18 . 
     Control circuitry  14  may be used to run software on device  10  such as satellite navigation applications, internet browsing applications, voice-over-internet-protocol (VOIP) telephone call applications, email applications, media playback applications, operating system functions, etc. To support interactions with external equipment, control circuitry  14  may be used in implementing communications protocols. Communications protocols that may be implemented using control circuitry  14  include internet protocols, wireless local area network (WLAN) protocols (e.g., IEEE 802.11 protocols—sometimes referred to as Wi-Fi®), protocols for other short-range wireless communications links such as the Bluetooth® protocol or other wireless personal area network (WPAN) protocols, IEEE 802.11ad protocols (e.g., ultra-wideband protocols), cellular telephone protocols (e.g., 3G protocols, 4G (LTE) protocols, 3GPP Fifth Generation (5G) New Radio (NR) protocols, Sixth Generation (6G) protocols, sub-THz protocols, THz protocols, etc.), antenna diversity protocols, satellite navigation system protocols (e.g., global positioning system (GPS) protocols, global navigation satellite system (GLONASS) protocols, etc.), antenna-based spatial ranging protocols, optical communications protocols, or any other desired communications protocols. Each communications protocol may be associated with a corresponding radio access technology (RAT) that specifies the physical connection methodology used in implementing the protocol. 
     Device  10  may include input-output circuitry  20 . Input-output circuitry  20  may include input-output devices  22 . Input-output devices  22  may be used to allow data to be supplied to device  10  and to allow data to be provided from device  10  to external devices. Input-output devices  22  may include user interface devices, data port devices, and other input-output components. For example, input-output devices  22  may include touch sensors, displays (e.g., touch-sensitive and/or force-sensitive displays), light-emitting components such as displays without touch sensor capabilities, buttons (mechanical, capacitive, optical, etc.), scrolling wheels, touch pads, key pads, keyboards, microphones, cameras, buttons, speakers, status indicators, audio jacks and other audio port components, digital data port devices, motion sensors (accelerometers, gyroscopes, and/or compasses that detect motion), capacitance sensors, proximity sensors, magnetic sensors, force sensors (e.g., force sensors coupled to a display to detect pressure applied to the display), temperature sensors, etc. In some configurations, keyboards, headphones, displays, pointing devices such as trackpads, mice, and joysticks, and other input-output devices may be coupled to device  10  using wired or wireless connections (e.g., some of input-output devices  22  may be peripherals that are coupled to a main processing unit or other portion of device  10  via a wired or wireless link). 
     Input-output circuitry  20  may include wireless circuitry  24  to support wireless communications. Wireless circuitry  24  (sometimes referred to herein as wireless communications circuitry  24 ) may include one or more antennas  30 . 
     Wireless circuitry  24  may also include transceiver circuitry  26 . Transceiver circuitry  26  may include transmitter circuitry, receiver circuitry, modulator circuitry, demodulator circuitry (e.g., one or more modems), radio-frequency circuitry, one or more radios, intermediate frequency circuitry, optical transmitter circuitry, optical receiver circuitry, optical light sources, other optical components, baseband circuitry (e.g., one or more baseband processors), amplifier circuitry, clocking circuitry such as one or more local oscillators and/or phase-locked loops, memory, one or more registers, filter circuitry, switching circuitry, analog-to-digital converter (ADC) circuitry, digital-to-analog converter (DAC) circuitry, radio-frequency transmission lines, optical fibers, and/or any other circuitry for transmitting and/or receiving wireless signals using antennas  30 . The components of transceiver circuitry  26  may be implemented on one integrated circuit, chip, system-on-chip (SOC), die, printed circuit board, substrate, or package, or the components of transceiver circuitry  26  may be distributed across two or more integrated circuits, chips, SOCs, printed circuit boards, substrates, and/or packages. 
     The example of  FIG.  1    is merely illustrative. While control circuitry  14  is shown separately from wireless circuitry  24  in the example of  FIG.  1    for the sake of clarity, wireless circuitry  24  may include processing circuitry (e.g., one or more processors) that forms a part of processing circuitry  18  and/or storage circuitry that forms a part of storage circuitry  16  of control circuitry  14  (e.g., portions of control circuitry  14  may be implemented on wireless circuitry  24 ). As an example, control circuitry  14  may include baseband circuitry (e.g., one or more baseband processors), digital control circuitry, analog control circuitry, and/or other control circuitry that forms part of wireless circuitry  24 . The baseband circuitry may, for example, access a communication protocol stack on control circuitry  14  (e.g., storage circuitry  20 ) to: perform user plane functions at a PHY layer, MAC layer, RLC layer, PDCP layer, SDAP layer, and/or PDU layer, and/or to perform control plane functions at the PHY layer, MAC layer, RLC layer, PDCP layer, RRC, layer, and/or non-access stratum layer. 
     Transceiver circuitry  26  may be coupled to each antenna  30  in wireless circuitry  24  over a respective signal path  28 . Each signal path  28  may include one or more radio-frequency transmission lines, waveguides, optical fibers, and/or any other desired lines/paths for conveying wireless signals between transceiver circuitry  26  and antenna  30 . Antennas  30  may be formed using any desired antenna structures for conveying wireless signals. For example, antennas  30  may include antennas with resonating elements that are formed from dipole antenna structures, planar dipole antenna structures (e.g., bowtie antenna structures), slot antenna structures, loop antenna structures, patch antenna structures, inverted-F antenna structures, planar inverted-F antenna structures, helical antenna structures, monopole antennas, dipoles, hybrids of these designs, etc. Filter circuitry, switching circuitry, impedance matching circuitry, and/or other antenna tuning components may be adjusted to adjust the frequency response and wireless performance of antennas  30  over time. 
     If desired, two or more of antennas  30  may be integrated into a phased antenna array (sometimes referred to herein as a phased array antenna) in which each of the antennas conveys wireless signals with a respective phase and magnitude that is adjusted over time so the wireless signals constructively and destructively interfere to produce (form) a signal beam in a given pointing direction. The term “convey wireless signals” as used herein means the transmission and/or reception of the wireless signals (e.g., for performing unidirectional and/or bidirectional wireless communications with external wireless communications equipment). Antennas  30  may transmit the wireless signals by radiating the signals into free space (or to free space through intervening device structures such as a dielectric cover layer). Antennas  30  may additionally or alternatively receive the wireless signals from free space (e.g., through intervening devices structures such as a dielectric cover layer). The transmission and reception of wireless signals by antennas  30  each involve the excitation or resonance of antenna currents on an antenna resonating (radiating) element in the antenna by the wireless signals within the frequency band(s) of operation of the antenna. 
     Transceiver circuitry  26  may use antenna(s)  30  to transmit and/or receive wireless signals that convey wireless communications data between device  10  and external wireless communications equipment (e.g., one or more other devices such as device  10 , a wireless access point or base station, etc.). The wireless communications data may be conveyed bidirectionally or unidirectionally. The wireless communications data may, for example, include data that has been encoded into corresponding data packets such as wireless data associated with a telephone call, streaming media content, internet browsing, wireless data associated with software applications running on device  10 , email messages, etc. 
     Additionally or alternatively, wireless circuitry  24  may use antenna(s)  30  to perform wireless sensing operations. The sensing operations may allow device  10  to detect (e.g., sense or identify) the presence, location, orientation, and/or velocity (motion) of objects external to device  10 . Control circuitry  14  may use the detected presence, location, orientation, and/or velocity of the external objects to perform any desired device operations. As examples, control circuitry  14  may use the detected presence, location, orientation, and/or velocity of the external objects to identify a corresponding user input for one or more software applications running on device  10  such as a gesture input performed by the user&#39;s hand(s) or other body parts or performed by an external stylus, gaming controller, head-mounted device, or other peripheral devices or accessories, to determine when one or more antennas  30  needs to be disabled or provided with a reduced maximum transmit power level (e.g., for satisfying regulatory limits on radio-frequency exposure), to determine how to steer (form) a radio-frequency signal beam produced by antennas  30  for wireless circuitry  24  (e.g., in scenarios where antennas  30  include a phased array of antennas  30 ), to map or model the environment around device  10  (e.g., to produce a software model of the room where device  10  is located for use by an augmented reality application, gaming application, map application, home design application, engineering application, etc.), to detect the presence of obstacles in the vicinity of (e.g., around) device  10  or in the direction of motion of the user of device  10 , etc. 
     Wireless circuitry  24  may transmit and/or receive wireless signals within corresponding frequency bands of the electromagnetic spectrum (sometimes referred to herein as communications bands or simply as “bands”). The frequency bands handled by communications circuitry  26  may include wireless local area network (WLAN) frequency bands (e.g., Wi-Fi® (IEEE 802.11) or other WLAN communications bands) such as a 2.4 GHz WLAN band (e.g., from 2400 to 2480 MHz), a 5 GHz WLAN band (e.g., from 5180 to 5825 MHz), a Wi-Fi® 6E band (e.g., from 5925-7125 MHz), and/or other Wi-Fi® bands (e.g., from 1875-5160 MHz), wireless personal area network (WPAN) frequency bands such as the 2.4 GHz Bluetooth® band or other WPAN communications bands, cellular telephone frequency bands (e.g., bands from about 600 MHz to about 5 GHz, 3G bands, 4G LTE bands, 5G New Radio Frequency Range 1 (FR1) bands below 10 GHz, 5G New Radio Frequency Range 2 (FR2) bands between 20 and 60 GHz, etc.), other centimeter or millimeter wave frequency bands between 10-100 GHz, near-field communications frequency bands (e.g., at 13.56 MHz), satellite navigation frequency bands (e.g., a GPS band from 1565 to 1610 MHz, a Global Navigation Satellite System (GLONASS) band, a BeiDou Navigation Satellite System (BDS) band, etc.), ultra-wideband (UWB) frequency bands that operate under the IEEE 802.15.4 protocol and/or other ultra-wideband communications protocols, communications bands under the family of 3GPP wireless communications standards, communications bands under the IEEE 802.XX family of standards, and/or any other desired frequency bands of interest. 
     Over time, software applications on electronic devices such as device  10  have become more and more data intensive. Wireless circuitry on the electronic devices therefore needs to support data transfer at higher and higher data rates. In general, the data rates supported by the wireless circuitry are proportional to the frequency of the wireless signals conveyed by the wireless circuitry (e.g., higher frequencies can support higher data rates than lower frequencies). Wireless circuitry  24  may convey centimeter and millimeter wave signals to support relatively high data rates (e.g., because centimeter and millimeter wave signals are at relatively high frequencies between around 10 GHz and 100 GHz). However, the data rates supported by centimeter and millimeter wave signals may still be insufficient to meet all the data transfer needs of device  10 . To support even higher data rates such as data rates up to 5-10 Gbps or higher, wireless circuitry  24  may convey wireless signals at frequencies greater than 100 GHz. 
     As shown in  FIG.  1   , wireless circuitry  24  may transmit wireless signals  32  and may receive wireless signals  34  at frequencies greater than around 100 GHz. Wireless signals  32  and  34  may sometimes be referred to herein as tremendously high frequency (THF) signals  32  and  34 , sub-THz signals  32  and  34 , THz signals  32  and  34 , or sub-millimeter wave signals  32  and  34 . THF signals  32  and  34  may be at sub-THz or THz frequencies such as frequencies between 100 GHz and 1 THz, between 100 GHz and 10 THz, between 100 GHz and 2 THz, between 200 GHz and 1 THz, between 300 GHz and 1 THz, between 300 GHz and 2 THz, between 300 GHz and 10 THz, between 100 GHz and 800 GHz, between 200 GHz and 1.5 THz, etc. (e.g., within a sub-THz, THz, THF, or sub-millimeter frequency band such as a 6G frequency band). The high data rates supported by these frequencies may be leveraged by device  10  to perform cellular telephone voice and/or data communications (e.g., while supporting spatial multiplexing to provide further data bandwidth), to perform spatial ranging operations such as radar operations to detect the presence, location, and/or velocity of objects external to device  10 , to perform automotive sensing (e.g., with enhanced security), to perform health/body monitoring on a user of device  10  or another person, to perform gas or chemical detection, to form a high data rate wireless connection between device  10  and another device or peripheral device (e.g., to form a high data rate connection between a display driver on device  10  and a display that displays ultra-high resolution video), to form a remote radio head (e.g., a flexible high data rate connection), to form a THF chip-to-chip connection within device  10  that supports high data rates (e.g., where one antenna  30  on a first chip in device  10  transmits THF signals  32  to another antenna  30  on a second chip in device  10 ), and/or to perform any other desired high data rate operations. 
     Space is at a premium within electronic devices such as device  10 . In some scenarios, different antennas  30  are used to transmit THF signals  32  than are used to receive THF signals  34 . However, handling transmission of THF signals  32  and reception of THF signals  34  using different antennas  30  can consume an excessive amount of space and other resources within device  10  because two antennas  30  and signal paths  28  would be required to handle both transmission and reception. To minimize space and resource consumption within device  10 , the same antenna  30  and signal path  28  may be used to both transmit THF signals  32  and to receive THF signals  34 . If desired, multiple antennas  30  in wireless circuitry  24  may transmit THF signals  32  and may receive THF signals  34 . The antennas may be integrated into a phased antenna array that transmits THF signals  32  and that receives THF signals  34  within a corresponding signal beam oriented in a selected beam pointing direction. 
     It can be challenging to incorporate components into wireless circuitry  24  that support wireless communications at these high frequencies. If desired, transceiver circuitry  26  and signal paths  28  may include optical components that convey optical signals to support the transmission of THF signals  32  and the reception of THF signals  34  in a space and resource-efficient manner. The optical signals may be used in transmitting THF signals  32  at THF frequencies and in receiving THF signals  34  at THF frequencies. 
       FIG.  2    is a diagram of an illustrative antenna  30  that may be used to both transmit THF signals  32  and to receive THF signals  34  using optical signals. Antenna  30  may include one or more antenna radiating (resonating) elements such as radiating (resonating) element arms  36 . In the example of  FIG.  2   , antenna  30  is a planar dipole antenna (sometimes referred to as a “bowtie” antenna) having two opposing radiating element arms  36  (e.g., bowtie arms or dipole arms). This is merely illustrative and, in general, antenna  30  may be any type of antenna having any desired antenna radiating element architecture. 
     As shown in  FIG.  2   , antenna  30  includes a photodiode (PD)  42  coupled between radiating element arms  36 . Electronic devices that include antennas  30  with photodiodes  42  such as device  10  may sometimes also be referred to as electro-optical devices (e.g., electro-optical device  10 ). Photodiode  42  may be a programmable photodiode. An example in which photodiode  42  is a programmable uni-travelling-carrier photodiode (UTC PD) is described herein as an example. Photodiode  42  may therefore sometimes be referred to herein as UTC PD  42  or programmable UTC PD  42 . This is merely illustrative and, in general, photodiode  42  may include any desired type of adjustable/programmable photodiode or component that converts electromagnetic energy (e.g., light or light energy) at optical frequencies (e.g., infrared, visible, and/or ultraviolet frequencies) to current at THF frequencies on radiating element arms  36  and/or vice versa. Each radiating element arm  36  may, for example, have a first edge at UTC PD  42  and a second edge opposite the first edge that is wider than the first edge (e.g., in implementations where antenna  30  is a bowtie antenna). Other radiating elements may be used if desired. 
     UTC PD  42  may have a bias terminal  38  that receives one or more control signals V BIAS . Control signals V BIAS  may include bias voltages provided at one or more voltage levels and/or other control signals for controlling the operation of UTC PD  42  such as impedance adjustment control signals for adjusting the output impedance of UTC PD  42 . Control circuitry  14  ( FIG.  1   ) may provide (e.g., apply, supply, assert, etc.) control signals V BIAS  at different settings (e.g., values, magnitudes, etc.) to dynamically control (e.g., program or adjust) the operation of UTC PD  42  over time. For example, control signals V BIAS  may be used to control whether antenna  30  transmits THF signals  32  or receives THF signals  34 . When control signals V BIAS  include a bias voltage asserted at a first level or magnitude, antenna  30  may be configured to transmit THF signals  32 . When control signals V BIAS  include a bias voltage asserted at a second level or magnitude, antenna  30  may be configured to receive THF signals  34 . In the example of  FIG.  2   , control signals V BIAS  include the bias voltage asserted at the first level to configure antenna  30  to transmit THF signals  32 . If desired, control signals V BIAS  may also be adjusted to control the waveform of the THF signals (e.g., as a squaring function that preserves the modulation of incident optical signals, a linear function, etc.), to perform gain control on the signals conveyed by antenna  30 , and/or to adjust the output impedance of UTC PD  42 . 
     As shown in  FIG.  2   , UTC PD  42  may be optically coupled to optical path  40 . Optical path  40  may include one or more optical fibers or waveguides. UTC PD  42  may receive optical signals from transceiver circuitry  26  ( FIG.  1   ) over optical path  40 . The optical signals may include a first optical local oscillator (LO) signal LO 1  and a second optical local oscillator signal LO 2 . Optical local oscillator signals LO 1  and LO 2  may be generated by light sources in transceiver circuitry  26  ( FIG.  1   ). Optical local oscillator signals LO 1  and LO 2  may be at optical wavelengths (e.g., between 400 nm and 700 nm), ultra-violet wavelengths (e.g., near-ultra-violet or extreme ultraviolet wavelengths), and/or infrared wavelengths (e.g., near-infrared wavelengths, mid-infrared wavelengths, or far-infrared wavelengths). Optical local oscillator signal LO 2  may be offset in wavelength from optical local oscillator signal LO 1  by a wavelength offset X. Wavelength offset X may be equal to the wavelength of the THF signals conveyed by antenna  30  (e.g., between 100 GHz and 1 THz (1000 GHz), between 100 GHz and 2 THz, between 300 GHz and 800 GHz, between 300 GHz and 1 THz, between 300 and 400 GHz, etc.). 
     During signal transmission, wireless data (e.g., wireless data packets, symbols, frames, etc.) may be modulated onto optical local oscillator signal LO 2  to produce modulated optical local oscillator signal LO 2 ′. If desired, optical local oscillator signal LO 1  may be provided with an optical phase shift S. Optical path  40  may illuminate UTC PD  42  with optical local oscillator signal LO 1  (plus the optical phase shift S when applied) and modulated optical local oscillator signal LO 2 ′. If desired, lenses or other optical components may be interposed between optical path  40  and UTC PD  42  to help focus the optical local oscillator signals onto UTC PD  42 . 
     UTC PD  42  may convert optical local oscillator signal LO 1  and modulated local oscillator signal LO 2 ′ (e.g., beats between the two optical local oscillator signals) into antenna currents that run along the perimeter of radiating element arms  36 . The frequency of the antenna currents is equal to the frequency difference between local oscillator signal LO 1  and modulated local oscillator signal LO 2 ′. The antenna currents may radiate (transmit) THF signals  32  into free space. Control signal V BIAS  may control UTC PD  42  to convert the optical local oscillator signals into antenna currents on radiating element arms  36  while preserving the modulation and thus the wireless data on modulated local oscillator signal LO 2 ′ (e.g., by applying a squaring function to the signals). THF signals  32  will thereby carry the modulated wireless data for reception and demodulation by external wireless communications equipment. 
       FIG.  3    is a diagram showing how antenna  30  may receive THF signals  34  (e.g., after changing the setting of control signals V BIAS  into a reception state from the transmission state of  FIG.  2   ). As shown in  FIG.  3   , THF signals  34  may be incident upon antenna radiating element arms  36 . The incident THF signals  34  may produce antenna currents that flow around the perimeter of radiating element arms  36 . UTC PD  42  may use optical local oscillator signal LO 1  (plus the optical phase shift S when applied), optical local oscillator signal LO 2  (e.g., without modulation), and control signals V BIAS  (e.g., a bias voltage asserted at the second level) to convert the received THF signals  34  into intermediate frequency signals SIGIF that are output onto intermediate frequency signal path  44 . 
     The frequency of intermediate frequency signals SIGIF may be equal to the frequency of THF signals  34  minus the difference between the frequency of optical local oscillator signal LO 1  and the frequency of optical local oscillator signal LO 2 . As an example, intermediate frequency signals SIGIF may be at lower frequencies than THF signals  32  and  34  such as centimeter or millimeter wave frequencies between 10 GHz and 100 GHz, between 30 GHz and 80 GHz, around 60 GHz, etc. If desired, transceiver circuitry  26  ( FIG.  1   ) may change the frequency of optical local oscillator signal LO 1  and/or optical local oscillator signal LO 2  when switching from transmission to reception or vice versa. UTC PD  42  may preserve the data modulation of THF signals  34  in intermediate signals SIGIF. A receiver in transceiver circuitry  26  ( FIG.  1   ) may demodulate intermediate frequency signals SIGIF (e.g., after further down conversion) to recover the wireless data from THF signals  34 . In another example, wireless circuitry  24  may convert intermediate frequency signals SIGIF to the optical domain before recovering the wireless data. In yet another example, intermediate frequency signal path  44  may be omitted and UTC PD  42  may convert THF signals  34  into the optical domain for subsequent demodulation and data recovery (e.g., in a sideband of the optical signal). 
     The antenna  30  of  FIGS.  2  and  3    may support transmission of THF signals  32  and reception of THF signals  34  with a given polarization (e.g., a linear polarization such as a vertical polarization). If desired, wireless circuitry  24  ( FIG.  1   ) may include multiple antennas  30  for covering different polarizations.  FIG.  4    is a diagram showing one example of how wireless circuitry  24  may include multiple antennas  30  for covering different polarizations. 
     As shown in  FIG.  4   , the wireless circuitry may include a first antenna  30  such as antenna  30 V for covering a first polarization (e.g., a first linear polarization such as a vertical polarization) and may include a second antenna  30  such as antenna  3011  for covering a second polarization different from or orthogonal to the first polarization (e.g., a second linear polarization such as a horizontal polarization). Antenna  30 V may have a UTC PD  42  such as UTC PD  42 V coupled between a corresponding pair of radiating element arms  36 . Antenna  30 H may have a UTC PD  42  such as UTC PD  42 H coupled between a corresponding pair of radiating element arms  36  oriented non-parallel (e.g., orthogonal) to the radiating element arms  36  in antenna  30 V. This may allow antennas  30 V and  30 H to transmit THF signals  32  with respective (orthogonal) polarizations and may allow antennas  30 V and  30 H to receive THF signals  32  with respective (orthogonal) polarizations. 
     To minimize space within device  10 , antenna  30 V may be vertically stacked over or under antenna  30 H (e.g., where UTC PD  42 V partially or completely overlaps UTC PD  42 H). In this example, antennas  30 V and  30 H may both be formed on the same substrate such as a rigid or flexible printed circuit board. The substrate may include multiple stacked dielectric layers (e.g., layers of ceramic, epoxy, flexible printed circuit board material, rigid printed circuit board material, etc.). The radiating element arms  36  in antenna  30 V may be formed on a separate layer of the substrate than the radiating element arms  36  in antenna  30 H or the radiating element arms  36  in antenna  30 V may be formed on the same layer of the substrate as the radiating element arms  36  in antenna  30 H. UTC PD  42 V may be formed on the same layer of the substrate as UTC PD  4211  or UTC PD  42 V may be formed on a separate layer of the substrate than UTC PD  42 H. UTC PD  42 V may be formed on the same layer of the substrate as the radiating element arms  36  in antenna  30 V or may be formed on a separate layer of the substrate as the radiating element arms  36  in antenna  30 V. UTC PD  42 H may be formed on the same layer of the substrate as the radiating element arms  36  in antenna  30 H or may be formed on a separate layer of the substrate as the radiating element arms  36  in antenna  30 H. 
     If desired, antennas  30  or antennas  30 H and  30 V of  FIG.  4    may be integrated within a phased antenna array.  FIG.  5    is a diagram showing one example of how antennas  30 H and  30 V may be integrated within a phased antenna array. As shown in  FIG.  5   , device  10  may include a phased antenna array  46  of stacked antennas  30 H and  30 V arranged in a rectangular grid of rows and columns. Each of the antennas in phased antenna array  46  may be formed on the same substrate. This is merely illustrative. In general, phased antenna array  46  (sometimes referred to as a phased array antenna) may include any desired number of antennas  30 V and  30 H (or non-stacked antennas  30 ) arranged in any desired pattern. Each of the antennas in phased antenna array  46  may be provided with a respective optical phase shift S ( FIGS.  2  and  3   ) that configures the antennas to collectively transmit THF signals  32  and/or receive THF signals  34  that sum to form a signal beam of THF signals in a desired beam pointing direction. The beam pointing direction may be selected to point the signal beam towards external communications equipment, towards a desired external object, away from an external object, etc. 
     Phased antenna array  46  may occupy relatively little space within device  10 . For example, each antenna  30 V/ 30 H may have a length  48  (e.g., as measured from the end of one radiating element arm to the opposing end of the opposite radiating element arm). Length  48  may be approximately equal to one-half the wavelength of THF signals  32  and  34 . For example, length  48  may be as small as 0.5 mm or less. Each UTC-PD  42  in phased antenna array  46  may occupy a lateral area of 100 square microns or less. This may allow phased antenna array  46  to occupy very little area within device  10 , thereby allowing the phased antenna array to be integrated within different portions of device  10  while still allowing other space for device components. The examples of  FIGS.  2 - 5    are merely illustrative and, in general, each antenna may have any desired antenna radiating element architecture. 
       FIG.  6    is a circuit diagram showing how a given antenna  30  and signal path  28  ( FIG.  1   ) may be used to both transmit THF signals  32  and receive THF signals  34  based on optical local oscillator signals. In the example of  FIG.  6   , UTC PD  42  converts received THF signals  34  into intermediate frequency signals SIGIF that are then converted to the optical domain for recovering the wireless data from the received THF signals. 
     As shown in  FIG.  6   , wireless circuitry  24  may include transceiver circuitry  26  coupled to antenna  30  over signal path  28  (e.g., an optical signal path sometimes referred to herein as optical signal path  28 ). UTC PD  42  may be coupled between the radiating element arm(s)  36  of antenna  30  and signal path  28 . Transceiver circuitry  26  may include optical components  68 , amplifier circuitry such as power amplifier  76 , and digital-to-analog converter (DAC)  74 . Optical components  68  may include an optical receiver such as optical receiver  72  and optical local oscillator (LO) light sources (emitters)  70 . LO light sources  70  may include two or more light sources (e.g., sources of electromagnetic energy, light, or light energy) such as laser light sources, laser diodes, optical phase locked loops, or other optical emitters that emit light (e.g., electromagnetic energy, light, or light energy that includes optical local oscillator signals LO 1  and LO 2 ) at respective wavelengths (e.g., visible, infrared, and/or ultraviolet wavelengths). If desired, LO light sources  70  may include a single light source and may include optical components for splitting the light emitted by the light source into different wavelengths. Signal path  28  may be coupled to optical components  68  over optical path  66 . Optical path  66  may include one or more optical fibers and/or waveguides. 
     Signal path  28  may include an optical splitter such as optical splitter (OS)  54 , optical paths such as optical path  64  and optical path  62 , an optical combiner such as optical combiner (OC)  52 , and optical path  40 . Optical path  62  may be an optical fiber or waveguide. Optical path  64  may be an optical fiber or waveguide. Optical splitter  54  may have a first (e.g., input) port coupled to optical path  66 , a second (e.g., output) port coupled to optical path  62 , and a third (e.g., output) port coupled to optical path  64 . Optical path  64  may couple optical splitter  54  to a first (e.g., input) port of optical combiner  52 . Optical path  62  may couple optical splitter  54  to a second (e.g., input) port of optical combiner  52 . Optical combiner  52  may have a third (e.g., output) port coupled to optical path  40 . 
     An optical phase shifter such as optical phase shifter  80  may be (optically) interposed on or along optical path  64 . An optical modulator such as optical modulator  56  may be (optically) interposed on or along optical path  62 . Optical modulator  56  may be, for example, a Mach-Zehnder modulator (MZM) and may therefore sometimes be referred to herein as MZM  56 . MZM  56  includes a first optical arm (branch)  60  and a second optical arm (branch)  58  interposed in parallel along optical path  62 . Propagating optical local oscillator signal LO 2  along arms  60  and  58  of MZM  56  may, in the presence of a voltage signal applied to one or both arms, allow different optical phase shifts to be imparted on each arm before recombining the signal at the output of the MZM (e.g., where optical phase modulations produced on the arms are converted to intensity modulations at the output of MZM  56 ). When the voltage applied to MZM  56  includes wireless data, MZM  56  may modulate the wireless data onto optical local oscillator signal LO 2 . If desired, the phase shifting performed at MZM  56  may be used to perform beam forming/steering in addition to or instead of optical phase shifter  80 . MZM  56  may receive one or more bias voltages W BIAS  (sometimes referred to herein as bias signals W BIAS ) applied to one or both of arms  58  and  60 . Control circuitry  14  ( FIG.  1   ) may provide bias voltage W BIAS  with different magnitudes to place MZM  56  into different operating modes (e.g., operating modes that suppress optical carrier signals, operating modes that do not suppress optical carrier signals, etc.). 
     Intermediate frequency signal path  44  may couple UTC PD  42  to MZM  56  (e.g., arm  60 ). An amplifier such as low noise amplifier  82  may be interposed on intermediate frequency signal path  44 . Intermediate frequency signal path  44  may be used to pass intermediate frequency signals SIGIF from UTC PD  42  to MZM  56 . DAC  74  may have an input coupled to up-conversion circuitry, modulator circuitry, and/or baseband circuitry in a transmitter of transceiver circuitry  26 . DAC  74  may receive digital data to transmit over antenna  30  and may convert the digital data to the analog domain (e g, as data DAT). DAC  74  may have an output coupled to transmit data path  78 . Transmit data path  78  may couple DAC  74  to MZM  56  (e.g., arm  60 ). Each of the components along signal path  28  may allow the same antenna  30  to both transmit THF signals  32  and receive THF signals  34  (e.g., using the same components along signal path  28 ), thereby minimizing space and resource consumption within device  10 . 
     LO light sources  70  may produce (emit) optical local oscillator signals LO 1  and LO 2  (e.g., at different wavelengths that are separated by the wavelength of THF signals  32 / 34 ). Optical components  68  may include lenses, waveguides, optical couplers, optical fibers, and/or other optical components that direct the emitted optical local oscillator signals LO 1  and LO 2  towards optical splitter  54  via optical path  66 . Optical splitter  54  may split the optical signals on optical path  66  (e.g., by wavelength) to output optical local oscillator signal LO 1  onto optical path  64  while outputting optical local oscillator signal LO 2  onto optical path  62 . 
     Control circuitry  14  ( FIG.  1   ) may provide phase control signals CTRL to optical phase shifter  80 . Phase control signals CTRL may control optical phase shifter  80  to apply optical phase shift S to the optical local oscillator signal LO 1  on optical path  64 . Phase shift S may be selected to steer a signal beam of THF signals  32 / 34  in a desired pointing direction. Optical phase shifter  80  may pass the phase-shifted optical local oscillator signal LO 1  (denoted as LO 1 +S) to optical combiner  52 . Signal beam steering is performed in the optical domain (e.g., using optical phase shifter  80 ) rather than in the THF domain because there are no satisfactory phase shifting circuit components that operate at frequencies as high as the frequencies of THF signals  32  and  34 . Optical combiner  52  may receive optical local oscillator signal LO 2  over optical path  62 . Optical combiner  52  may combine optical local oscillator signals LO 1  and LO 2  onto optical path  40 , which directs the optical local oscillator signals onto UTC PD  42  for use during signal transmission or reception. 
     During transmission of THF signals  32 , DAC  74  may receive digital wireless data (e.g., data packets, frames, symbols, etc.) for transmission over THF signals  32 . DAC  74  may convert the digital wireless data to the analog domain and may output (transmit) the data onto transmit data path  78  as data DAT (e.g., for transmission via antenna  30 ). Power amplifier  76  may amplify data DAT. Transmit data path  78  may pass data DAT to MZM  56  (e.g., arm  60 ). MZM  56  may modulate data DAT onto optical local oscillator signal LO 2  to produce modulated optical local oscillator signal LO 2 ′ (e.g., an optical local oscillator signal at the frequency/wavelength of optical local oscillator signal LO 2  but that is modulated to include the data identified by data DAT). Optical combiner  52  may combine optical local oscillator signal LO 1  with modulated optical local oscillator signal LO 2 ′ at optical path  40 . 
     Optical path  40  may illuminate UTC PD  42  with (using) optical local oscillator signal LO 1  (e.g., with the phase shift S applied by optical phase shifter  80 ) and modulated optical local oscillator signal LO 2 ′. Control circuitry  14  ( FIG.  1   ) may apply a control signal V BIAS  to UTC PD  42  that configures antenna  30  for the transmission of THF signals  32 . UTC PD  42  may convert optical local oscillator signal LO 1  and modulated optical local oscillator signal LO 2 ′ into antenna currents on radiating element arm(s)  36  at the frequency of THF signals  32  (e.g., while programmed for transmission using control signal V BIAS ). The antenna currents on radiating element arm(s)  36  may radiate THF signals  32 . The frequency of THF signals  32  is given by the difference in frequency between optical local oscillator signal LO 1  and modulated optical local oscillator signal LO 2 ′. Control signals V BIAS  may control UTC PD  42  to preserve the modulation from modulated optical local oscillator signal LO 2 ′ in the radiated THF signals  32 . External equipment that receives THF signals  32  will thereby be able to extract data DAT from the THF signals  32  transmitted by antenna  30 . 
     During reception of THF signals  34 , MZM  56  does not modulate any data onto optical local oscillator signal LO 2 . Optical path  40  therefore illuminates UTC PD  42  with optical local oscillator signal LO 1  (e.g., with phase shift S) and optical local oscillator signal LO 2 . Control circuitry  14  ( FIG.  1   ) may apply a control signal V BIAS  (e.g., a bias voltage) to UTC PD  42  that configures antenna  30  for the receipt of THF signals  32 . UTC PD  42  may use optical local oscillator signals LO 1  and LO 2  to convert the received THF signals  34  into intermediate frequency signals SIGIF output onto intermediate frequency signal path  44  (e.g., while programmed for reception using bias voltage V BIAS ) Intermediate frequency signals SIGIF may include the modulated data from the received THF signals  34 . Low noise amplifier  82  may amplify intermediate frequency signals SIGIF, which are then provided to MZM  56  (e.g., arm  60 ). MZM  56  may convert intermediate frequency signals SIGIF to the optical domain as optical signals LOrx (e.g., by modulating the data in intermediate frequency signals SIGIF onto one of the optical local oscillator signals) and may pass the optical signals to optical receiver  72  in optical components  68 , as shown by arrow  63  (e.g., via optical paths  62  and  66  or other optical paths). Control circuitry  14  ( FIG.  1   ) may use optical receiver  72  to convert optical signals LOrx to other formats and to recover (demodulate) the data carried by THF signals  34  from the optical signals. In this way, the same antenna  30  and signal path  28  may be used for both the transmission and reception of THF signals while also performing beam steering operations. 
     The example of  FIG.  6    in which intermediate frequency signals SIGIF are converted to the optical domain is merely illustrative. If desired, transceiver circuitry  26  may receive and demodulate intermediate frequency signals SIGIF without first passing the signals to the optical domain. For example, transceiver circuitry  26  may include an analog-to-digital converter (ADC), intermediate frequency signal path  44  may be coupled to an input of the ADC rather than to MZM  56 , and the ADC may convert intermediate frequency signals SIGIF to the digital domain. As another example, intermediate frequency signal path  44  may be omitted and control signals V BIAS  may control UTC PD  42  to directly sample THF signals  34  with optical local oscillator signals LO 1  and LO 2  to the optical domain. As an example, UTC PD  42  may use the received THF signals  34  and control signals V BIAS  to produce an optical signal on optical path  40 . The optical signal may have an optical carrier with sidebands that are separated from the optical carrier by a fixed frequency offset (e.g., 30-100 GHz, 60 GHz, 50-70 GHz, 10-100 GHz, etc.). The sidebands may be used to carry the modulated data from the received THF signals  34 . Signal path  28  may direct (propagate) the optical signal produced by UTC PD  42  to optical receiver  72  in optical components  68  (e.g., via optical paths  40 ,  64 ,  62 ,  66 ,  63 , and/or other optical paths). Control circuitry  14  ( FIG.  1   ) may use optical receiver  72  to convert the optical signal to other formats and to recover (demodulate) the data carried by THF signals  34  from the optical signal (e.g., from the sidebands of the optical signal). 
     If desired, optical components  68  may include clocking circuitry such as one or more electro-optical phase-locked loops. As shown in  FIG.  6   , optical components  68  may include an electro-optical phase-locked loop (OPLL) circuit such as OPLL  75  (sometimes referred to herein as an opto-electrical phase-locked loop). OPLL  75  may be used to control and clock LO light sources  70  and/or to clock any other desired hardware in device  10  (e.g., OPLL  75  need not be located in transceiver  26  and may, in general, be located elsewhere in device  10 ). LO light sources  70  may, for example, generate optical LO signals that are phase-locked and frequency-locked with respect to each other using OPLL  75 . 
       FIG.  7    is a circuit diagram showing one example of how multiple antennas  30  may be integrated into a phased antenna array  88  that conveys THF signals over a corresponding signal beam. In the example of  FIG.  7   , MZMs  56 , intermediate frequency signal paths  44 , data paths  78 , and optical receiver  72  of  FIG.  6    have been omitted for the sake of clarity. Each of the antennas in phased antenna array  88  may alternatively sample received THF signals directly into the optical domain or may pass intermediate frequency signals SIGIF to ADCs in transceiver circuitry  26 . 
     As shown in  FIG.  7   , phased antenna array  88  includes N antennas  30  such as a first antenna  30 - 0 , a second antenna  30 - 1 , and an Nth antenna  30 -(N−1). Each of the antennas  30  in phased antenna array  88  may be coupled to optical components  68  via a respective optical signal path (e.g., optical signal path  28  of  FIG.  6   ). Each of the N signal paths may include a respective optical combiner  52  coupled to the UTC PD  42  of the corresponding antenna  30  (e.g., the UTC PD  42  in antenna  30 - 0  may be coupled to optical combiner  52 - 0 , the UTC PD  42  in antenna  30 - 1  may be coupled to optical combiner  52 - 1 , the UTC PD  42  in antenna  30 -(N−1) may be coupled to optical combiner  52 -(N−1), etc.). Each of the N signal paths may also include a respective optical path  62  and a respective optical path  64  coupled to the corresponding optical combiner  52  (e.g., optical paths  64 - 0  and  62 - 0  may be coupled to optical combiner  52 - 0 , optical paths  64 - 1  and  62 - 1  may be coupled to optical combiner  52 - 1 , optical paths  64 -(N−1) and  62 -(N−1) may be coupled to optical combiner  52 -(N−1), etc.). 
     Optical components  68  may include LO light sources  70  such as a first LO light source  70 A and a second LO light source  70 B. The optical signal paths for each of the antennas  30  in phased antenna array  88  may share one or more optical splitters  54  such as a first optical splitter  54 A and a second optical splitter  54 B. LO light source  70 A may generate (e.g., produce, emit, transmit, etc.) first optical local oscillator signal LO 1  and may provide first optical local oscillator signal LO 1  to optical splitter  54 A via optical path  66 A. Optical splitter  54 A may distribute first optical local oscillator signal LO 1  to each of the UTC PDs  42  in phased antenna array  88  over optical paths  64  (e.g., optical paths  64 - 0 ,  64 - 1 ,  64 -(N−1), etc.). Similarly, LO light source  70 B may generate (e.g., produce, emit, transmit, etc.) second optical local oscillator signal LO 2  and may provide second optical local oscillator signal LO 2  to optical splitter  54 B via optical path  66 B. Optical splitter  54 B may distribute second optical local oscillator signal LO 2  to each of the UTC PDs  42  in phased antenna array  88  over optical paths  62  (e.g., optical paths  62 - 0 ,  62 - 1 ,  62 -(N−1), etc.). 
     A respective optical phase shifter  80  may be interposed along (on) each optical path  64  (e.g., a first optical phase shifter  80 - 0  may be interposed along optical path  64 - 0 , a second optical phase shifter  80 - 1  may be interposed along optical path  64 - 1 , an Nth optical phase shifter  80 -(N−1) may be interposed along optical path  64 -(N−1), etc.). Each optical phase shifter  80  may receive a control signal CTRL that controls the phase S provided to optical local oscillator signal LO 1  by that optical phase shifter (e.g., first optical phase shifter  80 - 0  may impart an optical phase shift of zero degrees/radians to the optical local oscillator signal LO 1  provided to antenna  30 - 0 , second optical phase shifter  80 - 1  may impart an optical phase shift of Δϕ to the optical local oscillator signal LO 1  provided to antenna  30 - 1 , Nth optical phase shifter  80 -(N−1) may impart an optical phase shift of (N−1)Δϕ to the optical local oscillator signal LO 1  provided to antenna  30 -(N−1), etc.). By adjusting the phase S imparted by each of the N optical phase shifters  80 , control circuitry  14  ( FIG.  1   ) may control each of the antennas  30  in phased antenna array  88  to transmit THF signals  32  and/or to receive THF signals  34  within a formed signal beam  83 . Signal beam  83  may be oriented in a particular beam pointing direction (angle)  84  (e.g., the direction of peak gain of signal beam  83 ). The THF signals conveyed by phased antenna array  88  may have wavefronts  86  that are orthogonal to beam pointing direction  84 . Control circuitry  14  may adjust beam pointing direction  84  over time to point towards external communications equipment or an external object or to point away from external objects, as examples. 
     Phased antenna array  88  may be operable in an active mode in which the array transmits and/or receives THF signals using optical local oscillator signals LO 1  and LO 2  (e.g., using phase shifts provided to each antenna element to steer signal beam  83 ). If desired, phased antenna array  88  may also be operable in a passive mode in which the array does not transmit or receive THF signals. Instead, in the passive mode, phased antenna array  88  may be configured to form a passive reflector that reflects THF signals or other electromagnetic waves incident upon device  10 . In the passive mode, the UTC PDs  42  in phased antenna array  88  are not illuminated by optical local oscillator signals LO 1  and LO 2  and transceiver circuitry  26  performs no modulation/demodulation, mixing, filtering, detection, modulation, and/or amplifying of the incident THF signals. 
     Devices with processing capabilities include clocking circuitry such as phase-locked loops (PLLs) that generate clock signals. Devices with THF signaling capabilities such as device  10  are particularly sensitive to jitter (deviations from perfect periodicity) and phase noise frequency generation in clock signals (e.g., because the clocking circuitry consumes a relatively high amount of power and chip area for THF frequencies). To minimize clock jitter, processing operations in device  10  may be clocked using an electro-optical PLL (OPLL) such as OPLL  75  of  FIG.  6   . Examples in which THF communications using transceiver  26  ( FIG.  1   ) are clocked using OPLL  75  are described herein as an example. This is merely illustrative and, in general, OPLL  75  may be used to clock any desired processing operations in device  10  (e.g., high speed digital interface operations, processor computations, sensing, automotive, input/output operations, communications at frequencies lower than 100 GHz such as millimeter/centimeter wave frequencies or frequencies less than 10 GHz, etc.). 
       FIG.  8    is a circuit diagram of OPLL  75 . As shown in  FIG.  8   , OPLL  75  may include an oscillator such as reference oscillator  90 , digital-to-time converter circuitry such as digital-to-time converter (DTC)  92 , counter circuitry such as counter  98 , a mixer such as subsampling mixer  122 , filter circuitry such as loop filter  126 , a first light source such as primary laser  116 , a second light source such as secondary laser  102 , optical splitters such as optical splitter (OS)  104  and optical splitter  112 , and a photodiode such as UTC PD  118 . 
     Reference oscillator  90  may have an output coupled to the input of DTC  92  over path  94 . The output of reference oscillator  90  may also be coupled to an input of counter  98  over path  94 . Counter  98  may have an output coupled to a control input of secondary laser  102  over path  100 . DTC  92  may have an output coupled to an input of subsampling mixer  122  over path  96 . The output of subsampling mixer  122  may be coupled to a control input of secondary laser  102  over path  124 . Loop filter  126  may be interposed along path  124  between subsampling mixer  122  and secondary laser  102 . Secondary laser  102  may have an output coupled to optical splitter  104 . Optical splitter  104  may couple secondary laser  102  to UTC PD  118  over optical path  106  (e.g., one or more optical fibers, waveguides, etc.) and may couple secondary laser  102  to output terminal  108  of OPLL  75 . 
     Primary laser  116  may have an output coupled to optical splitter  112 . Optical splitter  112  may couple primary laser  116  to UTC PD  118  over optical path  114  (e.g., one or more optical fibers, waveguides, etc.) and may couple primary laser  116  to output terminal  110  of OPLL  75 . If desired, optical paths  106  and  104  may be combined into a single optical path and/or optical splitters  104  and  112  may be combined into a single optical splitter. UTC PD  118  may have an output coupled to an input of counter  98  and coupled to an input of subsampling mixer  122  over path  120  (e.g., one or more radio-frequency transmission lines). Output terminals  108  and  110  may provide optical LO signals that are used to clock other components in device  10 . In implementations where OPLL  75  is used to clock THF communications using transceiver  26  ( FIG.  1   ), terminal  108  may be coupled to optical path  62  and terminal  110  may be coupled to optical path  64  of  FIG.  6   , for example. 
     OPLL  75  may include a PLL nested within a frequency-locked loop (FLL). For example, UTC PD  118 , a portion of path  120 , counter  98 , path  100 , secondary laser  102 , optical splitter  104 , and optical path  106  may form an FLL as shown by FLL path  130 . On the other hand, UTC PD  118 , a portion of path  120 , sub-sampling mixer  122 , path  124 , loop filter  126 , secondary laser  102 , optical splitter  104 , and optical path  106  may form a PLL nested within FLL path  130 , as shown by PLL path  128 . FLL path  130  and PLL path  128  may be feedback paths for secondary laser  102  (e.g., feedback paths that communicably couple the output of secondary laser  102  to the (control) input of secondary laser  102 , where subsampling mixer  122  and a phase comparator therein are interposed along the feedback path formed from PLL path  128  and where counter  98  and a comparator therein are interposed along the feedback path formed from FLL path  130 ). OPLL  75  may produce (e.g., generate, output, emit, etc.) optical local oscillator signal LO 1  on output terminal  110  and may produce optical oscillator signal LO 2  on output terminal  108 . The FLL may be used to coarsely adjust (tune) secondary laser  102  until secondary laser  102  is frequency locked with primary laser  116  (e.g., until optical local oscillator signal LO 1  is frequency locked with optical local oscillator signal LO 2  such that there is a selected/predetermined stable frequency difference between the two optical local oscillators). The PLL may be used to finely adjust (tune) secondary laser  102  until secondary laser  102  is phase locked with primary laser  116  (e.g., until optical local oscillator signal LO 1  is phase locked with optical local oscillator signal LO 2 ). The frequency and phase locked optical local oscillator signals may be used to clock other components in device  10  (e.g., wireless circuitry  24  for the transmission and/or reception of THF signals) with very low jitter and with very low phase noise. 
     While described herein as lasers, primary laser  116  and secondary laser  102  may be any desired light sources/emitters. Lasers  116  and  102  may form LO light sources  70  of  FIG.  7    and/or may respectively form LO light sources  70 A and  70 B of  FIG.  7   , for example. Primary laser  116  may sometimes also be referred to as a leader laser whereas secondary laser  102  is sometimes also referred to as a follower laser. Primary laser  116  may emit optical local oscillator signal LO 1 ′ at a fixed frequency/wavelength (e.g., primary laser  116  may be a fixed (non-adjustable) laser having a fixed frequency). On the other hand, secondary laser  102  may emit optical local oscillator signal LO 2 ′ at an adjustable/programmable frequency/wavelength (e.g., secondary laser  102  may be an adjustable/programmable laser). Control signals received by secondary laser  102  over paths  124  and  100  may be used to adjust/program the frequency of optical local oscillator signal LO 2 ′. The wavelength of optical local oscillator signal LO 2 ′ may be offset from the wavelength of optical local oscillator signal LO 1 ′ by a selected wavelength offset X (e.g., the frequencies of the THF signals to be transmitted and/or received using optical local oscillator signals LO 1  and LO 2 ). 
     Optical splitter  104  may transmit a first amount of power from optical local oscillator signal LO 2 ′ to UTC PD  118  over optical path  106  as optical local oscillator signal LO 2 ″. Optical splitter  104  may transmit a second amount of power from optical local oscillator signal LO 2 ′ to output terminal  108  as optical local oscillator signal LO 2  (e.g., where the second amount of power is greater than the first amount). As an example, optical splitter  104  may provide 10% of the power of optical local oscillator signal LO 2 ′ to UTC PD  118  as optical local oscillator signal LO 2 ″ and may provide 90% of the power of optical local oscillator signal LO 2 ′ to output terminal  108  as optical local oscillator signal LO 2 . 
     At the same time, optical splitter  104  may transmit a first amount of power from optical local oscillator signal LO 1 ′ to UTC PD  118  over optical path  114  as optical local oscillator signal LO 1 ″. Optical splitter  112  may transmit a second amount of power from optical local oscillator signal LO 1 ′ to output terminal  110  as optical local oscillator signal LO 1  (e.g., where the second amount of power is greater than the first amount). As an example, optical splitter  112  may provide 10% of the power of optical local oscillator signal LO 1 ′ to UTC PD  118  as optical local oscillator signal LO 1 ″ and may provide 90% of the power of optical local oscillator signal LO 1 ′ to output terminal  110  as optical local oscillator signal LO 1 . Optical local oscillator signals LO 2 ″ and LO 1 ″ may be processed by the FLL and the PLL in OPLL  75  to frequency lock and phase lock optical local oscillator signals LO 1  and LO 2 . 
     Optical path  106  may illuminate UTC PD  118  with optical local oscillator signal LO 2 ″. Optical path  114  may illuminate UTC PD  118  with optical local oscillator signal LO 1 ″. UTC PD  118  of  FIG.  8    need not be a UTC PD and may, in general, be an adjustable/programmable photodiode or component that converts electromagnetic energy (e.g., light or light energy) at optical frequencies (e.g., ultraviolet frequencies, visible frequencies, and/or infrared frequencies) to current at THF frequencies on path  120  (e.g., the same type of component used to produce current on antenna radiating element arms  36  using optical local oscillator signals LO 1  and LO 2  of  FIG.  6   ). 
     UTC PD  118  may generate and output photodiode signal PD_SIG on path  120  based on the optical local oscillator signals LO 2 ″ and LO 1 ″ received over optical paths  106  and  114 . Photodiode signal PD_SIG may be at a frequency given by the difference between the frequency of optical local oscillator signal LO 2 ″ and the frequency of optical local oscillator signal LO 1 ″ (e.g., the frequency of THF signals  32 / 34  of  FIG.  6   ). Path  120  may convey photodiode signal PD_SIG to counter  98  in FLL loop path  130 . 
     As shown in  FIG.  8   , reference oscillator  90  may generate reference oscillator signal osc. Reference oscillator  90  may, for example, be a microelectromechanical systems (MEMS) oscillator, a crystal oscillator, or any other fixed or slightly tunable stable oscillator. Reference oscillator signal osc may be produced at a fixed radio frequency such as a frequency between around 5-25 GHz. Reference oscillator  90  may provide reference oscillator signal osc to DTC  92  and counter  98  over path  94 . 
     Counter  98  may measure (e.g., determine, identify, generate, compute, estimate calculate, etc.) the frequency of the photodiode signal PD_SIG received over path  120  using reference oscillator signal osc. For example, counter  98  may count the number of pulses in photodiode signal PD_SIG using reference oscillator signal osc as a reference and then may estimate the frequency of photodiode signal PD_SIG using the counted number of pulses. Counter  98  may also compare the measured frequency of photodiode signal PD_SIG to the expected difference in frequency between optical local oscillator signals LO 2 ″ and LO 1 ″ (e.g., the expected frequency of THF signals  32 / 34  of  FIG.  6   ). If the difference between the frequency of photodiode signal PD_SIG and the expected frequency exceeds a threshold value, counter  98  may provide a coarse tuning control signal FLL_CTRL (e.g., a frequency error signal) to secondary laser  102  over path  100  that coarsely adjusts secondary laser  102  to begin outputting optical local oscillator signals LO 2 ′ at a different frequency. Coarse tuning control signal FLL_CTRL may coarsely tune the frequency of secondary laser  102  using piezoelectric adjustments, mirror shifts, etc. 
     Counter  98  may then continue re-measuring photodiode signal PD_SIG and coarsely adjusting secondary laser  102  until the difference between the frequency of photodiode signal PD_SIG and the expected frequency is less than the threshold value (e.g., until the actual frequency produced by secondary laser  102  has settled and is sufficiently close to the desired frequency). Once this occurs, OPLL  75  may lock (freeze) the frequency of secondary laser  102  in place. PLL path  128  may then finely adjust secondary laser  102  to phase lock optical local oscillator signal LO 2  to optical local oscillator signal LO 1 . 
     Once OPLL  75  has locked the frequency of secondary laser  102  (e.g., once coarse tuning has been completed), subsampling mixer  122  may process photodiode signal PD_SIG. DTC  92  may generate DTC reference signal DTC_REF based on reference oscillator signal osc. DTC  92  may, for example, generate DTC reference signal DTC_REF by programming the edges of a signal pulse to have a selected timing. DTC  92  may also set (program) the frequency, delay, duty cycle, and/or per-clock interval of the signal pulse. DTC  92  is an open loop system and may generate DTC reference signal DTC_REF very rapidly and without using inductive coils, thereby minimizing the chip area required to produce DTC reference signal DTC_REF. DTC  92  may generate signal ramps instead of signal pulses if desired (e.g., DTC reference signal DTC_REF may include signal pulses or signal ramps). DTC  92  may generate DTC reference signal DTC_REF more rapidly than analog components, for example. DTC  92  may generate DTC reference signal DTC_REF at any desired frequency using reference oscillator signal osc. DTC reference signal DTC_REF may be, for example, at a frequency between 5 GHz and 25 GHz. 
     Subsampling mixer  122  may include a phase detector (e.g., a phase detector that includes digital XOR logic) and/or a frequency detector (e.g., including digital XOR logic and a flip flop). The logic in subsampling mixer  122  (e.g., a phase detector and comparator sometimes referred to herein collectively as a phase comparator) may compare the phase of photodiode signal PD_SIG with the phase of DTC reference signal DTC_REF. In practice, photodiode signal PD_SIG may be at much higher frequencies (e.g., 50-400 GHz) than DTC reference signal DTC_REF (e.g., 5-25 GHz), making phase comparison difficult or impossible. As such, subsampling mixer  122  may subsample photodiode signal PD_SIG to generate a subsampled photodiode signal and may compare the phase of the subsampled photodiode signal to the phase of DTC reference signal DTC_REF (e.g., where the phase of the subsampled photodiode signal is similar to the phase of the original photodiode signal). Subsampling mixer  122  may subsample photodiode signal PD_SIG by only comparing a regularly spaced subset of the samples in photodiode signal PD_SIG to DTC reference signal DTC_REF, for example (e.g., every eighth sample of photodiode signal PD_SIG). 
     Subsampling mixer  122  may compare the difference between the measured phase of photodiode signal PD_SIG (e.g., the subsampled photodiode signal) and the phase of DTC reference signal DTC_REF to a predetermined threshold value. If the difference exceeds the threshold value, subsampling mixer  122  may provide a fine tuning control signal PLL_CTRL to secondary laser  102  over path  124  that finely adjusts secondary laser  102  to begin outputting optical local oscillator signals LO 2 ′ at a different phase. Fine tuning control signal PLL_CTRL may be, for example, an error signal indicative of the phase error in the optical local oscillator produced by secondary laser  102 . Loop filter  126  may filter the error signal (e.g., using a 1-3 MHz filter). Fine tuning control signal PLL_CTRL may finely tune the phase of secondary laser  102  by adjusting the capacitance of a varactor in secondary laser  102 , for example. 
     Subsampling mixer  122  may then continue re-measuring photodiode signal PD_SIG and finely adjusting secondary laser  102  until the difference between the phase of photodiode signal PD_SIG (e.g., the subsampled photodiode signal) and the phase of DTC reference signal DTC_REF is less than the threshold value (e.g., until the phase of secondary laser  102  settles on the desired phase exhibited by DTC reference signal DTC_REF). Once this occurs, OPLL  75  may lock (freeze) the phase of secondary laser  102  in place. 
     The optical local oscillator signals LO 1  and LO 2  subsequently generated by primary laser  116  and secondary laser  102  may thereafter be frequency locked and phase locked. This may allow optical local oscillator signals LO 1  and LO 2  to clock other components in device  10  (e.g., to control UTC PDs  42  in wireless circuitry  24  of  FIGS.  6  and  7    to transmit and/or receive THF signals) with minimal jitter and minimal phase noise. Generating optical local oscillator signals LO 1  and LO 2  using a DTC such as DTC  92  in this way may allow for flexibility in reference clock choice and in clock signal processing. For example, DTC  92  may be used for reference clock modulation, fine frequency tuning, frequency dithering, etc. via the PLL loop, where spurious signals generated by the DTC are filtered out by loop filter  126 . In contrast with comb frequency generation and/or frequency generation using an MZM, OPLL  75  may allow for minimal spurious frequencies with minimal filtering requirements in the optical domain. 
     The example of  FIG.  8    is merely illustrative. If desired, secondary laser  102  and primary laser  116  may share the same resonating cavity (e.g., secondary laser  102  may utilize a longer or shorter portion of the resonating cavity than primary laser  116  to allow for the difference in wavelength between the optical local oscillator signals). Sharing a common resonating cavity between secondary laser  102  and primary laser  116  may cause secondary laser  102  and primary laser  116  to exhibit very similar thermal effects, thereby helping to tightly lock secondary laser  102  to primary laser  116 . Generating optical local oscillator signals LO 1  and LO 2  in a closed-loop manner in this way may minimize phase noise in optical local oscillator signals LO 1  and LO 2 . The components of OPLL  75  may be implemented in hardware (e.g., one or more digital logic gates, digital circuits, analog circuits, one or more processors, etc.) and/or software (e.g., using logical/computational operations executed by one or more processors). 
       FIG.  9    is a timing diagram of an illustrative signal pulse in DTC reference signal DTC_REF of  FIG.  8   . Curve  132  shows one signal pulse  132  that may be produced by DTC  92  and curve  134  shows another pulse that may be produced by DTC  92 . DTC  92  may be programmable to adjust the timing, slope, and/or spacing of leading edge  136  and/or falling edge  138  of the signal pulse. Such adjustments may be extremely precise (e.g., on the scale of picoseconds). The frequency, delay, and/or duty cycle of the signal pulses may also be precisely programed by DTC  92 . The example of  FIG.  9    is merely illustrative. Curves  132  and  134  may have other shapes. DTC reference signal DTC_REF may include signal ramps instead of signal pulses if desired. 
       FIG.  10    is a flow chart of illustrative operations involved in using OPLL  75  of  FIG.  8    to generate optical local oscillator signals LO 1  and LO 2  (e.g., to clock one or more components in device  10  such as wireless circuitry  24  of  FIG.  1   ). At operation  140  of  FIG.  10   , secondary laser  102  and primary laser  116  may begin to illuminate UTC PD  118  using optical local oscillator signals LO 2 ″ and LO 1 ″. UTC PD  188  may generate photodiode signal PD_SIG based on optical local oscillator signals LO 2 ″ and LO 1 ″. 
     At operation  142 , OPLL  75  may use FLL path  130  to coarsely tune secondary laser  102 . For example, at operation  144 , reference oscillator  90  may begin to generate reference oscillator signal osc and may provide reference oscillator signal osc to DTC  92  and counter  98 . 
     At operation  146 , counter  98  may identify the frequency of photodiode signal PD_SIG using reference oscillator signal osc as a reference. Logic in counter  98  (e.g., a comparator and/or other digital logic) may compare the identified frequency to the predetermined/expected/selected frequency of secondary laser  102 . If the identified frequency is excessively far from the expected frequency (e.g., if the difference between the identified frequency and the expected frequency exceeds a threshold), processing may proceed to operation  150  as shown by path  148 . At operation  150 , counter  98  may use coarse tuning control signal FLL_CTRL to coarsely adjust the frequency of secondary laser  102 . Processing may loop back to operation  146  via path  152  until the identified frequency is sufficiently close to the expected frequency. 
     When the identified frequency is sufficiently close to the expected frequency (e.g., when the difference between the identified frequency and the expected frequency is less than the threshold), processing may proceed from operation  146  to operation  156  as shown by path  154 . At operation  156 , OPLL  75  may lock the coarse tuning of secondary laser  102  (e.g., may frequency lock secondary laser  102  and optical local oscillator signal LO 2 ′). Processing may subsequently proceed to operation  160  via path  158 . 
     At operation  160 , OPLL  75  may use PLL path  128  to finely tune secondary laser  102 . For example, at operation  162 , DTC  92  may generate DTC reference signal DTC_REF using reference oscillator signal osc. DTC  92  may generate DTC reference signal DTC_REF at a predetermined/selected/desired phase and frequency (e.g., 5-25 GHz). DTC  92  may provide DTC reference signal DTC_REF to subsampling mixer  122 . 
     At operation  164 , sub-sampling mixer  122  may subsample photodiode signal PD_SIG and may compare the phase of the sub-sampled photodiode signal to the phase of DTC reference signal DTC_REF. If the identified phase of the sub-sampled photodiode signal is excessively far from the phase of DTC reference signal DTC_REF (e.g., if the difference between the identified phase and the phase of DTC reference signal DTC_REF exceeds a threshold), processing may proceed to operation  168  as shown by path  166 . At operation  168 , sub-sampling mixer  122  may use fine tuning control signal PLL_CTRL to finely adjust the phase of secondary laser  102 . Processing may loop back to operation  164  via path  170  until the identified phase is sufficiently close to the phase of DTC reference signal DTC_REF. 
     When the identified phase is sufficiently close to the phase of DTC reference signal DTC_REF (e.g., when the difference between the identified phase and the phase of DTC reference signal DTC_REF is less than the threshold), processing may proceed from operation  164  to operation  174  as shown by path  172 . At operation  174 , OPLL  75  may lock the fine tuning of secondary laser  102  (e.g., may phase lock secondary laser  102  and optical local oscillator signal LO 2 ′). Processing may subsequently proceed to operation  178  via path  176 . 
     At operation  178 , OPLL  75  may clock one or more processing operations in device  10  using optical local oscillator signals LO 1  and LO 2  (e.g., device  10  may perform subsequent processing operations as clocked by optical local oscillator signals LO 1  and LO 2 ). For example, the UTC PDs  42  in device  10  may transmit and/or receive THF signals using the optical local oscillator signals LO 1  and LO 2  produced by OPLL  75 . 
     Device  10  may gather and/or use personally identifiable information. It is well understood that the use of personally identifiable information should follow privacy policies and practices that are generally recognized as meeting or exceeding industry or governmental requirements for maintaining the privacy of users. In particular, personally identifiable information data should be managed and handled so as to minimize risks of unintentional or unauthorized access or use, and the nature of authorized use should be clearly indicated to users. The optical components described herein (e.g., MZM modulator(s), waveguide(s), phase shifter(s), UTC PD(s), etc.) may be implemented in plasmonics technology if desired. 
     The methods and operations described above in connection with  FIGS.  1 - 13    (e.g., the operations of  FIGS.  10  and  13   ) may be performed by the components of device  10  using software, firmware, and/or hardware (e.g., dedicated circuitry or hardware). Software code for performing these operations may be stored on non-transitory computer readable storage media (e.g., tangible computer readable storage media) stored on one or more of the components of device  10  (e.g., storage circuitry  16  of  FIG.  1   ). The software code may sometimes be referred to as software, data, instructions, program instructions, or code. The non-transitory computer readable storage media may include drives, non-volatile memory such as non-volatile random-access memory (NVRAM), removable flash drives or other removable media, other types of random-access memory, etc. Software stored on the non-transitory computer readable storage media may be executed by processing circuitry on one or more of the components of device  10  (e.g., processing circuitry  18  of  FIG.  1   , etc.). The processing circuitry may include microprocessors, central processing units (CPUs), application-specific integrated circuits with processing circuitry, or other processing circuitry. 
     The foregoing is merely illustrative and various modifications can be made to the described embodiments. The foregoing embodiments may be implemented individually or in any combination.

Metadata:
Filing Date: 20220601
Publication Date: 20240409
Grant Date: 20240409
Priority Date: 20210921
Inventors: BOOS, ZDRAVKO
BISMUTO, ALFREDO
GUNZELMANN, Bertram R
Assignee: APPLE INC
CPC Classifications: [{"code": "H04L7/0075", "inventive": true, "first": true, "tree": "[]"}, {"code": "H04B10/11", "inventive": true, "first": false, "tree": "[]"}, {"code": "H03L7/113", "inventive": true, "first": true, "tree": "[]"}, {"code": "H04L7/0075", "inventive": true, "first": true, "tree": "[]"}, {"code": "H03L7/087", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04B10/90", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04B2210/006", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04B10/11", "inventive": true, "first": false, "tree": "[]"}]
Family ID: 82308352