Abstract:
Systems and apparatus for a wirelessly-powered passive optical power meter device. In one aspect, an optical power meter device comprises a power circuit connected to one or more antennas, the circuit including an RF to DC converter that generates a DC power signal that provides a DC power source for the optical power meter from an RF signal received by the one or more antennas, a photodetector that generates a power measurement signal that measures the power of the optical input signal, and a communication circuit that is connected to the one or more antennas, the photodetector, and the power circuit that when powered by the DC power source generates a modulation signal that is responsive to the power measurement signal and that causes the one of the one or more antennas to convey the power measurement signal to a reader device that is transmitting the RF signal.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation application of, and claims priority to, U.S. patent application Ser. No. 14/301,860, titled “WIRELESSLY POWERED PASSIVE OPTICAL POWER METER,” filed on Jun. 11, 2014. The disclosure of the foregoing application is incorporated herein by reference in its entirety for all purposes. 
    
    
     BACKGROUND 
     Internet usage and network traffic have evolved over the past decade. Networks are often required to support larger file sizes that are continuously transferred across the network. As such traffic continues to grow, demands for better and faster connectivity continues to grow as well. Providers and users have turned to fiber-to-the-Home (or FTTH) networks to support these demands. 
     Fiber-to-the-Home or FTTH connections are fiber optic cable connections that are routed to individual residences. Such connections are capable of transferring larger volumes of digital information at higher speeds and more efficiently than traditional coaxial cables, at a comparable price. Two types of optical networks are active optical network (AON) architectures or passive optical network (PON) architectures. 
     Active optical networks utilize electrical based switches and equipment to route and distribute optical signals. Each signal is routed using the electrical switches and equipment, to its intended user or residency. The electrical and optical hybrid nature of AONs require optical to electrical transformations and electrical to optical transformations. Such transformations require additional resources and contribute to reducing the overall speed of the network. 
     Passive optical networks utilize passive beam splitters to divide the optical signal among a plurality of users or residencies. The passive beam splitters are un-powered devices. The passive beam splitters enable the point to multipoint optical connection between the optical line terminal and a group of users or residencies. 
     SUMMARY 
     This specification relates to passive optical power meter devices. In particular, the specification relates to such a device that is powered wirelessly and provides measurements wirelessly. The subject matter of this application describes systems comprising such a device and their operation. 
     In general, one innovative aspect of the subject matter described in this specification can be embodied in a system including, an optical power meter comprising, one or more antennas; a power circuit connected to one of the one or more antennas, the circuit including an RF to DC converter that generates a DC power signal that provides a DC power source for the optical power meter from an RF signal received by the one or more antennas; an optical input port that receives an optical input signal; a photodetector coupled to the power circuit and when powered by the DC power source generates a power measurement signal that measures the power of the optical input signal; a communication circuit that is connected to the one or more antenna, the photodetector, and the power circuit and when powered by the DC power source generates a modulation signal that is responsive to the power measurement signal and that causes the one of the one or more antennas to convey the power measurement signal to a reader device that is transmitting the RF signal. 
     Another innovative aspect of the subject matter described in this specification can be embodied in an optical power meter comprising, one or more antennas; a power circuit connected to one of the one or more antennas, the circuit including an RF to DC converter that generates a DC power signal that provides a DC power source for the optical power meter from an RF signal received by the one or more antennas; an optical input port that receives an optical input signal; a photodetector that generates a power measurement signal that measures the power of the optical input signal; a communication circuit that is connected to the one or more antenna, the photodetector, and the power circuit and when powered by the DC power source generates a modulation signal that is responsive to the power measurement signal and that causes the one of the one or more antennas to convey the power measurement signal to a reader device that is transmitting the RF signal, wherein the optical power meter comprises a first and a second antenna; wherein the first antenna is connected to the power circuit such that receiving the RF signal by the first antenna causes the power circuit to generate a DC power signal; wherein the second antenna is connected to the communication circuit; and wherein the communication circuit generates and transfers, by the second antenna to the reader device, a modulated signal specifying the power measurement signal to the reader device, in response to being powered by a DC power signal from the power circuit. 
     Another innovative aspect of the subject matter described in this specification can be embodied in an optical power meter comprising, one or more antennas; a power circuit connected to one of the one or more antennas, the circuit including an RF to DC converter that generates a DC power signal that provides a DC power source for the optical power meter from an RF signal received by the one or more antennas; an optical input port that receives an optical input signal; a photodetector that generates a power measurement signal that measures the power of the optical input signal; a communication circuit that is connected to the one or more antenna, the photodetector, and the power circuit and when powered by the DC power source generates a modulation signal that is responsive to the power measurement signal and that causes the one of the one or more antennas to convey the power measurement signal to a reader device that is transmitting the RF signal, wherein the optical power meter comprises a first antenna, the first antenna being connected to the power circuit such that receiving the RF signal by the first antenna causes the power circuit to generate a DC power signal, the first antenna being also connected to the communication circuit; wherein the communication circuit when powered modulates an impedance connected to the antenna such that modulation, in turn, alters a backscattered RF signal, the backscattered RF signal being produced by the RF signal, the RF signal being transmitted from the reader device; wherein the backscattered RF signal is altered to be encoded with data specifying the power measurement signal to the reader device. 
     Another innovative aspect of the subject matter described in this specification can be embodied in a system including, an optical power meter comprising, one or more antennas; a power circuit connected to one of the one or more antennas, the circuit including an RF to DC converter that generates a DC power signal that provides a DC power source for the optical power meter from an RF signal received by the one or more antennas; an optical input port that receives an optical input signal; a photodetector that generates a power measurement signal that measures the power of the optical input signal; a communication circuit that is connected to the one or more antenna, the photodetector, and the power circuit and when powered by the DC power source generates a modulation signal that is responsive to the power measurement signal and that causes the one of the one or more antennas to convey the power measurement signal to a reader device that is transmitting the RF signal, the system further including an optical power reader comprising, a display device; one or more antennas; and a communication circuit that is connected to the one or more antennas and the display device, the communication circuit being a circuit that produces an RF signal for transmission by the one or more antennas to the optical power meter, and also being a circuit that receives an RF signal from the optical power meter and in response to receiving the RF signal from the optical power meter, at the one or more antennas, produces a signal that causes the display device to display data encoded in received RF signal, the data comprising a power measurement signal. 
     Particular embodiments of the subject matter described in this specification can be implemented so as to realize one or more of the following advantages. Power monitoring can be accomplished in a fiber optic network without interrupting service. Because the measurements are obtained in a non-disruptive manner, service time is also reduced. Additionally, power monitoring can be achieved without requiring a dedicated AC or DC power line for operation. 
     Particular embodiments of the subject matter can be installed inside a permanent structure (e.g. underground, inside a wall). Also, power measurements can be obtained without pre-setup procedures. Power measurements can be obtained wirelessly and from a distance. Because of the flexibly described above, the embodiments of the subject matter can support a wide variety of optical networks that are installed in different locations and in different structures. 
     Finally, particular embodiments of the subject matter allow for simultaneous measuring of multiple test points, which in turn contributes to further reducing setup and measurement time. 
     The details of one or more embodiments of the subject matter described in this specification are set forth in the accompanying drawings and the description below. Other features, aspects and advantages of the subject matter will become apparent from the description, the drawings and the claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram of an example environment in which wireless powered passive optical power meters are used. 
         FIG. 2  is a block diagram of an example implementation of a system comprising a wireless powered passive optical power meter comprising two antennas, and a wireless reader. 
         FIG. 3  is a block diagram of an alternative example implementation of a system comprising a wireless powered passive optical power meter comprising two antennas, and a wireless reader. 
         FIG. 4  is a block diagram of an example implementation of a system comprising a wireless powered passive optical power meter comprising a single antenna, and a wireless reader. 
         FIG. 5  is a block diagram of an example implementation of a bidirectional, dual-wavelength wireless powered passive optical power meter comprising two antennas. 
     
    
    
     Like reference numbers and designations in the various drawings indicate like elements. 
     DETAILED DESCRIPTION 
     The subject matter below relates to systems and methods where wirelessly powered passive optical power meters are used in combination with wireless readers to obtain optical power measurements in an optical network. This arrangement allows for obtaining measurements within both AONs and PONs. 
     One maintenance procedure of PONs is the monitoring or measuring particular attributes, such as power, in a particular branch of the network. Active monitoring or measurements within PONs may result in service interruptions for more than one user or residency. Accordingly, an interposed passive device for monitoring and measuring optical attributes of branches of PONs that would not result in service interruptions enhances the network performance and improve the user experience. However, frequently connecting and disconnecting such devices to the network can in itself create service interruptions for more than one user. 
     PONs rely on un-powered network elements, such as the passive beam splitters discussed above. The un-powered nature of the PON networks provides no power source for powering maintenance devices such as optical power meters. Therefore, maintenance devices need to receive electrical power from an external source. Accordingly, a wirelessly powered passive optical power meter can be implemented in PON networks. This arrangement allows for the advantageous placement of optical meters within the PON network branches, such that service interruptions are eliminated. 
       FIG. 1  is a block diagram of an example environment in which wireless powered passive optical power meters (OPMs) are used. The network  100  is a PON comprising a beam splitter  120  that distributes an optical signal to a plurality of optical network units ( 122 - 124 .) The optical line terminal (OLT)  110  combines various electrical signals into a single optical signal. For example, the OLT can multiplex an electrical Ethernet signal and an electrical video signal for transmission over the PON  100 . The optical signal is divided among the optical network units ( 122 - 124 ) according to a pre-specified ratio via beam splitter  120 . For example, the beam splitter  120  may divide the optical signal equally among the optical network units (ONUs). Alternatively, the beam splitter  120  may divide the signal among optical network units ( 122 - 124 ) such that optical network unit- 3   123  receives a largest portion of the optical signal. The PON may operate at different wavelengths. For example, the PON may operate at 1550 nm wave length. In a different implementation, the PON may utilize wavelength division multiplexing (WDM) to operate at multiple wavelengths simultaneously. 
     In some implementations, optical power meters are interposed between elements of the PON. For example, optical power meter OPM- 1   111  is interposed between the OLT  110  and the beam splitter  120 . OPM- 2  is interposed between the beam splitter  120  and optical network unit- 2 . Similarly OPM- 3  is interposed between the beam splitter  120  and optical network unit- 3 , while OPM-X is interposed between the beam splitter  120  and optical network unit-x. As shown in  FIG. 1 , the separate branches of the PON  100  include different OPMs. Each OPM ( 111 - 114 ) within PON  100  is equipped with a wireless system capable of receiving and transmitting wireless RF signals. The OPMs ( 111 - 114 ) are further configured to receive power via an RF signal wirelessly, such that receiving an RF signal at an OPM causes the OPM to produce an electrical voltage that powers the OPM. The wireless reader  130  is also equipped with a wireless system capable of receiving and transmitting wireless RF signals. 
     In some implementations, each branch of the PON  100  includes an OPM. As discussed above, the OPMs are wirelessly powered. The OPMs are also passive devices that produce an optical output signal that is substantially the same as the optical input signal, except for component losses. For example, an OPM may output 97% of the input optical signal due to tap loss, manufacturing imperfections, dissipation, and noise. In some implementations the losses may be less, while in other implementations the losses may be as high as 10%. This arrangement provides the ability to monitor power and other signals in a PON without interrupting the service. 
     The following example will be discussed with reference to the branch were OPM- 1   111  resides in  FIG. 1 . First, when OPM- 1   111  is not receiving any radio signal, the OPM  111  is not powered. As described above, because the OPM  111  is a passive device, the OPM  111  will output an optical signal that is substantially the same as the input optical signal. Accordingly, the optical signal will be transmitted through OPM- 1   111  from the OLT  110  to the beam splitter  120 . 
     Second, when a reading is required from OPM- 1  the wireless reader  130  generates and transmits an RF signal to the OPM- 1   111 . In turn, the receipt of the RF signal by the OPM  111  results in the powering of the OPM  111 . The RF signal may be further encoded with an ID query requesting that OPM- 1  returns an OPM ID and one or more specific measurements, such as, a power and/or a temperature reading. In response to receiving the RF signal and being powered, the OPM  111  performs various operations that include, for example, measuring the attributes specified in the ID query. For example, OPM- 1   111  may measure the power of the optical signal passing through the meter and the surrounding temperature in response to receiving the RF signal and being powered. After the required measurements are obtained, OPM- 1   111  transmits an RF signal encoded with the measurements and the OPM ID of OPM- 1   111  to the wireless reader  130 . For example, OPM- 1   111  may transmit an RF signal encoded with the power measurement, the temperature measurement, and the OPM ID for OPM- 1   111  back to the wireless reader. In turn, the wireless reader receives the encoded RF signal and decodes the RF signal to extract the encoded measurements and OPM ID. Finally, the measurements along with the OPM ID may be displayed on a display section of the wireless reader. For example, in response to receiving the RF signal from OPM- 1   111  the reader device may display the power measurement, the temperature measurement, and the OPM ID for OPM- 1   111 . Since each OPM is associated with a unique ID and a particular branch, the unique ID specifies that the accompanied measurements correspond to the branch associated with that unique ID. 
       FIG. 1  shows a single wireless reader  130 ; however, multiple wireless readers may operate simultaneously. For example, while wireless reader  130  is obtaining measurements from OPM- 1   111 , a second reader (not shown) may obtain measurements from OPM- 2   112 . Because OPMs are passive devices, each OPM ( 111 - 124 ) will output an optical signal that is substantially the same as the input optical signal when the OPMs are powered or un-powered. Therefore, obtaining measurements from the OPMs does not interrupt the PON operation. 
       FIG. 2  is a block diagram of an example implementation of a system comprising a wireless powered passive optical power meter comprising two antennas, and a wireless reader. In one implementation, the system  200  includes a wireless powered passive optical power meter OPM  220  that is configured to operate in conjunction with the reader  210 . 
     The OPM  220  includes an optical input port  232  and an output optical port  233 . The optical input port  232  receives an optical input to the OPM  220 . Tap  222  is designed to tap the fiber between input port  232  and output port  233 . In some implementations, using a beam splitter, the tap  222  diverts a small amount of the input to the photodetector  222 , while the rest of the input is routed to output port  233 . The sensitivity of the photodetector  222  dictates how much of the input signal has to be diverted to the photodetector. For example, a sensitive photodetector may require only 1% of the input signal, while a photodetectors with low sensitivity may require 5% of the input signal. In one implementation, the tap  222  utilizes the stress properties of fiber, to create stress in the fiber, and arrange the photodetectors such that the leakage of the input signal due to the introduced stress is measured by the photodetectors. Other methods to tap the input to the OPM  220  may be used such that the OPM  220  remains substantially passive. 
     Photodetectors are commonly used to convert optical signals into electrical signals. In some implementations, the photodetector operates by converting light signals to either electrical voltage or current. The photodetectors is designed to absorb photons. The result of the absorption of photons is the creation of electron-hole pairs in a semiconductor&#39;s depletion region. In some implementations photodetectors are photodiodes. In different implementations the photodetectors are phototransistors. Alternatively, other optical devices similar to photodetectors may be used. 
     In one implementation the DC electrical output of the photodetector  224  is directly transferred to an RF modulator  226 . In one implementation communication circuitry includes RF modulator  226 . The RF modulator  226  receives a signal either encoded with the power measurement directly from the photodetector  224 , or encoded with the power measurement. The RF modulator modulates the received signal for wireless transmission to the reader  210  via antenna  234 . 
     The OPM  220  includes an antenna  235  connected to power circuitry. The power circuitry is configured to power the OPM  220  in response to receiving an RF signal from reader  210 . The power circuitry includes an RF-to-DC converter  228  that is connected to antenna  235 . The RF signal received by the antenna  235  is transmitted to the RF-to-DC converter  228 , which in turn produces a DC voltage. The RF-to-DC converter  228  is also connected to a DC regulator  229 . The DC voltage is transmitted to the DC regulator to ensure that the DC voltage is modified to provide appropriate voltage to each of the elements of the OMP  220 . For example, the voltage may be converted to a higher voltage level. The DC regulator is connected, directly or indirectly, to each element of the OPM  220  that requires power. This configuration allows the components of OPM  220  to be powered wirelessly in response to receiving an RF signal at antenna  235 . For example, the output of DC regulator  229  powers the photodetector  224 , and RF modulator  226 , and in some implementations the MCU  235 . Therefore the operations described above regarding the photodetectors, and communication circuitry occurs in response to the OPM being powered by an RF signal from the reader  210 . 
     In some implementations, simple electrical circuit elements may be interposed between the elements shown in  FIG. 2 . For example, a capacitor (not shown) may be placed between the RF-to-DC converter and the DC regulator to further regulate the DC signal. Other electrical circuit elements include, but are not limited to, resistors, transistors, inductors and switches. 
     The reader  210  of  FIG. 2  provides multiple functions that include providing power to the OPM  220 , receiving and demodulating RF signals from OPM  220 , and displaying measurements corresponding to signals received from OPM  220 . In some implementations the reader  210  is a portable wireless device that is internally powered by, for example, one or more batteries. In different implementations, the reader  210  is a stationary device that, for example, resides at a maintenance station and is in communication with one or more OPMs, such as OPM  220 . 
     In some implementations, the OPM  220  includes a continuous wave signal generator or a CW generator  212 . The CW generator  212  generates a continuous RF signal, in response to user instructions to reader  210 . For example, CW generator  212  may generate a 915 MHz RF signal in response to a user pushing a button (not shown) on reader  210 , the button being for activating and obtaining measurements from OPM  220 . The CW generator  212  is connected to RF transmitter or RF TX  219 . RF TX  219  prepares the RF signals for transmission via antenna  237 , which is also connected to RF TX  219 . For example, the signal generated by CW generator  212  is received by RF TX  219 , and in turn, transmitted through antenna  237  to antenna  235  of the OPM  220 . As discussed above, the signal received at antenna  235  from antenna  237 , provides power through power circuitry to OPM  220 . 
     Also as discussed above, a signal encoded with, at least, a power measurement is transmitted from antenna  234  of OPM  220  to antenna  236  of reader  210 . The antenna  236  is connected to an RF receiver RF RX  218 . RF RX  218  is also connected to RF demodulator  216 . The receiver RF RX  218  receives the signal encoded with the power measurement via antenna  236  and provides the signal to RF demodulator  216  for demodulation. The RF demodulator  216  demodulates the received signal to extract information from the received signal, such as, the power measurement. The RF demodulator  216  is also connected to MCU  214 . The demodulated signal is provided to MCU  214 . An analogue to digital converter (not shown) may be interposed between the MCU and the demodulator, to prepare the electrical output signal for the MCU input. MCU  214  is connected to display device  212 . In some implementations the display device  212  is an LCD display. The MCU  214  is responsible for communicating with the RF demodulator  216  or the analogue to digital converter and the display device  212 , in order to display the power measurement on the display device  212  based on the signal provided by the RF demodulator  216 . Additionally, the MCU may be responsible for providing a graphical user interface to allow the user to issue particular instructions to OPMs. For example, the reader  212  may be equipped by a touch screen LCD display  212 . 
       FIG. 3  is a block diagram of an alternative example implementation of a system comprising a wireless powered passive optical power meter comprising two antennas, and a wireless reader. The system of  FIG. 3  is similar to the system of  FIG. 2 , however the system of  FIG. 3  allows reader  310  and OPM  420  to send and receive OPM identification data. In some implementations, the OPM identification data is a unique power meter ID. This system allows the reader to send an OPM ID query to a particular OPM requesting specific measurement. For example, reader  310  may send a query to OPM  320  requesting a power measurement, a temperature measurement, and an OPM ID from OPM  320 . This allows the reader  410  to request measurements from specific OPMs in particular branches of a network, such as, the network discussed with respect to  FIG. 1 . It also allows the reader  410  to request measurements from a particular group of OPMs or all OPMs in the range that the RF signal can reach. 
     The OPM  320  includes an optical input port  332  and an output optical port  333 . The optical input port  332  receives an optical input to the OPM  320 . Tap  322  is designed to tap the fiber between input port  332  and output port  333 . In some implementations, using a beam splitter, the tap  322  diverts a small amount of the input to the photodetector  322 , while the rest of the input is routed to output port  333 . 
     In the implementation shown in  FIG. 3 , the output of the photodetector is transferred to a microcontroller unit MCU  325 . An analogue to digital converter (not shown) may be interposed between the MCU and the photodetectors, to prepare the electrical output signal for the MCU input. Other devices may be attached to the MCU  325  to take measurements other than power. For example, a temperature measuring device may be connected to the MCU  325  to obtain temperature measurements. Similarly, other environmental factors or hazards to the network may be measured and monitored using the OPM. For example, humidity measurements may be obtained by connecting a humidity measuring device to the MCU  325 . 
     In this implementation, the communication circuitry includes RF modulator  326  and MCU  325 . The RF modulator  326  receives a signal encoded with the power measurement and the additional information provided by the other systems connected to the MCU. The RF modulator modulates the received signal for wireless transmission to the reader  310  via antenna  334 . 
     The OPM  320  includes an antenna  335  connected to power circuitry, the power circuitry being configured to power the OPM  320  in response to receiving an RF signal from reader  310 . The power circuitry includes an RF-to-DC converter  328  that is connected to antenna  335 . The RF signal received by the antenna  335  is transmitted to the RF-to-DC converter  328 , which in turn produces a DC voltage. The RF-to-DC converter  328  is also connected to a DC regulator  329 . The DC voltage is transmitted to the DC regulator to ensure that the DC voltage is modified to provide appropriate voltage to each of the elements of the OMP  320 . For example, the DC voltage may be converted to a higher voltage level. The DC regulator is connected, directly or indirectly, to each element of the OPM  320  that requires power. This configuration allows the components of OPM  320  to be powered wirelessly in response to receiving an RF signal at antenna  335 . For example, the output of DC regulator  329  powers the photodetector  324 , and RF modulator  326 , and the MCU  325 . Therefore, the operations described above regarding the photodetectors and communication circuitry occur in response to the OPM being powered by an RF signal from the reader  310 . 
     The antenna  335  is also connected to RF RX  327 . A portion of the signal received at antenna  335  is diverted to RF RX  327 . The RF RX  327  provides the received signal encoded with the OPM ID query discussed above to MCU  325 . The MCU may demodulate the received signal to extract the encoded ID query information. Alternatively, a demodulator (not shown) may be interposed between RF RX  327  and MCU  325  to perform the same function. In turn, the MCU obtains the measurements specified with by the query, and the identification data for OPM  320 . For example, the MCU  325  may obtain the power measurement, temperature measurement, and a unique ID for OPM  320 . The MCU  325  provides this data to RF modulator  326  for transmission to reader  310  via antenna  334  as discussed above. 
     The reader  310  of  FIG. 3  provides multiple functions that include providing power and an ID query to the OPM  320 , receiving and demodulating RF signals from the OPM  320 , as well as displaying measurements corresponding to signals received from OPM  320 . In some implementations the reader  310  is a portable wireless device that is internally powered by, for example, one or more batteries. In different implementations, the reader  310  is a stationary device that, for example, resides at a maintenance station and is in communication with one or more OPMs, such as OPM  320 . 
     The OPM  320  includes an RF modulator  317  for modulating a signal into an RF signal. RF modulator  317  is connected to MCU  314  and antenna  336 . The MCU  314  provides a signal containing information representing the ID query to the RF modulator  317 . The RF modulator  317  modulates the signal from the MCU  314  to generate an RF signal modulated with the ID query information. The modulated signal is transferred to antenna  337 , which in turn, transfers the signal to antenna  335 . As discussed above, the signal received at antenna  335  from antenna  334  provides power through power circuitry to OPM  320 . 
     In this implementation, the signal encoded with measurements and the OPM ID, is received at antenna  336 . This RF signal from OPM  320  is transmitted from antenna  334  of OPM  320  to antenna  335  of reader  310 . RF RX  418  is connected to RF demodulator  316  and antenna  336 . The receiver RF RX  318  receives the signal encoded with the measurements and the OPM ID via antenna  336  and provides the signal to RF demodulator  316  for demodulation. The RF demodulator  316  demodulates the received signal to extract information from the received signal, such as, the measurements and the OPM ID for OPM  320 . The RF demodulator  316  is also connected to MCU  314 . The demodulated signal is provided to MCU  314 . MCU  314  is connected to display device  312 . In some implementations the display device  312  is an LCD display. The MCU  314  is responsible for communicating with the RF demodulator  316  and the display device  312 , in order to display the measurements and the OPM ID for OPM  320  on the display device  312  based on the signal provided by the RF demodulator  316 . Additionally, the MCU  325  may be responsible for providing a graphical user interface to allow the user to issue particular instructions to OPMs. For example, the reader  310  may be equipped by a touch screen LCD display  312 . 
     In some implementations, the MCU  314  may compare the received ID of a particular OPM to the ID of the requested OPM. Naturally, if the ID is not matching, MCU  314  may disregard the received measurements. 
       FIG. 4  shows an alternative implementation of a system comprising a wireless OPM and a reader. This particular implementation relies on backscatter effect instead of direct transmission. Backscattering is the phenomena where waves, or a portion of waves, are reflected back toward a point from which they originate. This alternative implementation utilizes only one antenna for each of OPM  420  and reader  410 . 
     The OPM  420  includes an optical input port  432  and an output optical port  433 . The optical input port  432  receives an optical input to the OPM  420 . Tap  422  is designed to tap the fiber between input port  432  and output port  433 . In some implementations, using a beam splitter, the tap  422  diverts a small amount of the input to the photodetector  422 , while the rest of the input is routed to output port  433 . 
     In this alternative implementation communication circuitry includes MCU  425 , and switch SW  427 . MCU  425  is connected to photodetector  424 , SW  427 , and RF RX  426 . The MCU  425  receives a signal corresponding to a power measurement from photodetector  424 . The MCU  425  is also connected to, and controls operation of SW  427 . The SW  427  is connected to antenna  434 . The SW  427  is also connected to an electrical ground, either directly or indirectly through an impedance load (not shown.) For example, a resistor and a capacitor (not shown) may be connected between SW  427  and the electrical ground. Since MCU  425  controls the operation of SW  427 , MCU  427  can control the impedance load of antenna  434 . Altering the impedance load of antenna  434 , in turn, alters backscattering that occurs at antenna  434 . Accordingly, this enables MCU  425  to encode information into backscattered signals by altering the backscattered signals. For example, MCU  425  can encode the power measurements from photodetector  424  on to a backscattered signal antenna  434 . Similar to the discussions above with respect to  FIG. 3 , in some implementations, the MCU  425  may further encode the backscattered signal at antenna  434 , with additional information such as temperature measurements, and other environmental measurements. 
     The antenna  434  is connected to power circuitry that is configured to power the OPM  420  in response to receiving an RF signal from reader  410 . The power circuitry includes an RF-to-DC converter  428  that is connected to antenna  234 . The RF signal received by the antenna  434  is transmitted to the RF-to-DC converter  428 , which in turn produces a DC signal. The RF-to-DC converter  428  is also connected to a DC regulator  429 . The DC signal is transmitted to the DC regulator to ensure that the DC signal is modified to provide appropriate power to each of the elements of the OMP  220 . For example, the signal may be attenuated to reduce the power level of the DC signal. The DC regulator is connected, directly or in directly, to each element of the OPM  420  that requires power. This configuration allows the components of OPM  420  to be powered wirelessly in response to receiving an RF signal at antenna  434 . For example, the output of DC regulator  429  powers the photodetector  424  and MCU  425 . Therefore the operations described above regarding the photodetectors and communication circuitry occur in response to the OPM being powered by an RF signal from the reader  410 . 
     In this alternative implementation, the RF signal from the reader  410  is further encoded with an ID query. The ID query is a query that requests measurements and an ID to be returned from a specific OPM. For example, an ID query may request power from OPM  420 . As the RF signal for powering the OPM  420  is received by antenna  434 , a first portion of the signal is routed to RF RX  426  and a second portion is routed to RF-to-DC converter  428 . The RF RX  426  is connected to antenna  434  and MCU  425 . The MCU  425  may demodulate the received signal to extract the encoded ID query information. Alternatively, a demodulator (not shown) may be interposed between RF RX  426  and MCU  425  to perform the same function. The MCU  425  receives an ID query from RF RX  426  or the demodulator (not shown), and in response encodes the OPM ID of OPM  420  along with the power measurement on to the backscattered signal at antenna  434 . 
     The reader  410  of  FIG. 4  provides multiple functions that include providing power and an ID query to the OPM  420  and displaying measurements corresponding to signals received from OPM  420 . In some implementations the reader  410  is a portable wireless device that is internally powered by, for example, one or more batteries. In different implementations, the reader  410  is a stationary device that, for example, resides at a maintenance station and is in communication with one or more OPMs, such as OPM  420 . 
     The OPM  420  includes an RF modulator  417  for modulating a signal into an RF signal. RF modulator  417  is connected to MCU  414  and RF circulator  436 . The MCU  414  provides a signal containing information representing the ID query to the RF modulator  417 . The RF modulator  417  modulates the signal from the MCU  414  to generate an RF signal modulated with the ID query information. The modulated signal is transferred to the RF circulator  436 , which in turn, transfers the signal to antenna  435 . As discussed above, the signal received at antenna  435  from antenna  434 , provides power through power circuitry to OPM  420 . In this implementation, the antenna  435  is the source of the signal that is backscattered at antenna  434 . 
     In this implementation, the altered backscattered signal, described above, is received at antenna  435 . The backscattered signal encoded with a power measurement and OPM ID for OPM  420  is transmitted from antenna  434  of OPM  420  to antenna  435  of reader  410 . The RF circulator  436  transfers the backscattered signal from the antenna  435  to RF RX  418 . RF RX  418  is connected to RF demodulator  416 . The receiver RF RX  418  receives the backscattered signal encoded with the power measurement via antenna  436  and provides the signal to RF demodulator  416  for demodulation. The RF demodulator  416  demodulates the received signal to extract information from the received signal, such as, the power measurement and the OPM ID for OPM  420 . The RF demodulator  416  is also connected to MCU  414 . The demodulated signal is provided to MCU  414 . MCU  214  is connected to display device  412 . In some implementations the display device  412  is an LCD display. The MCU  414  is responsible for communicating with the RF demodulator  416  and the display device  412 , in order to display the power measurement and the OPM ID for OPM  420  on the display device  412  based on the signal provided by the RF demodulator  416 . Additionally, the MCU may be responsible for providing a graphical user interface to allow the user to issue particular instructions to OPMs. For example, the reader  410  may be equipped by a touch screen LCD display  412 . 
     In some implementations, the MCU  414  may compare the received ID of a particular OPM to the ID of the requested OPM. Naturally, if the ID is not matching, MCU  414  may disregard the received measurements. 
       FIG. 5  is a block diagram of an example implementation of a bidirectional, dual-wavelength wireless powered passive optical power meter comprising two antennas. The operation of OPM  520  is sustainably similar to the operations of OPM  320  and OPM  220  discussed above. However, the OPM  520  can be configured to operate as a bidirectional OPM or a dual-wavelength OPM. 
     OPM  520  contains two taps, TAP- 1   522  and TAP- 2   521 , which are connected to photodetectors- 1   524  and photodetectors- 2   523  respectively. TAP- 1   522  and TAP- 2  may be configured with opposite alignment such that Tap- 1  taps the signal traveling from port  533  to port  532 , and TAP- 2  taps the signal traveling from port  532  to port  533 . Since each tap is connected to a separate photodetector, each photodetectors connected to MCU  525 , the measurements from both photodetectors is transferred to MCU  525 . This set up allows OPM  520  to obtain measurements from a fiber network, when the terminals  532  and  533  are connected to fiber of the fiber network in a forward or a reverse direction. In other words, terminal  532  and terminal  533  can represent the input to OPM  520  interchangeably. Similarly, terminal  532  and terminal  533  can represent the output to OPM  520  interchangeably. 
     In a different implementation, TAP- 1   522  and TAP- 2   521  can be configured to tap different wavelengths. For example, TAP- 1   522  may be configured to tap a 1550 nm wavelength, while TAP- 2  may be configured to tap a 1330 nm wavelength. This allows OPM  520  to measure two different signals that are traveling simultaneously through the same fiber. As wavelength multiplexing is one of the inherent advantages of optical networks, this dual-wavelength configuration allows for monitoring optical networks that utilize wavelength multiplexing. It is understood that this implementation represents two taps only, however, additional taps can be incorporated to monitor additional wavelength, in a manner similar to the above. It is also understood that the wavelength discussed above is exemplary and not limiting. The invention may operate with a wide variety of wavelength. 
     While this specification contains many specific implementation details, these should not be construed as limitations on the scope of any inventions or of what may be claimed, but rather as descriptions of features specific to particular embodiments of particular inventions. Certain features that are described in this specification in the context of separate embodiments can also be implemented in combination in a single embodiment. Conversely, various features that are described in the context of a single embodiment can also be implemented in multiple embodiments separately or in any suitable subcombination. Moreover, although features may be described above as acting in certain combinations and even initially claimed as such, one or more features from a claimed combination can in some cases be excised from the combination, and the claimed combination may be directed to a subcombination or variation of a subcombination. 
     Similarly, while operations are depicted in the drawings in a particular order, this should not be understood as requiring that such operations be performed in the particular order shown or in sequential order, or that all illustrated operations be performed to achieve desirable results. Moreover, the separation of various system components in the embodiments described above should not be understood as requiring such separation in all embodiments, and it should be understood that the described components and systems can generally be integrated together in a single product. 
     Thus, particular embodiments of the subject matter have been described. Other embodiments are within the scope of the following claims. In some cases, the actions recited in the claims can be performed in a different order and still achieve desirable results. In addition, the processes depicted in the accompanying figures do not necessarily require the particular order shown, or sequential order, to achieve desirable results.