JP2011078142A - Optical terminal unit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To simplify the configuration of an optical terminal unit, and reduce costs. <P>SOLUTION: The optical terminal unit 2d has a photodiode 26 receiving a modulation optical signal. A cathode of the photodiode is grounded and its anode is grounded via a resistor 46, thereby operating under a non-bias state. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an optical terminal unit that converts an optical signal transmitted through an optical fiber into an electrical signal.

  For example, a joint reception facility may be configured using optical signals. In this case, it is necessary to convert the optical signal into an electric signal at the subscriber terminal of the joint reception facility. An example of an optical terminal unit used for this conversion is disclosed in Patent Document 1. In this technique, the anode side of the photodiode is grounded via a bias resistor, the cathode side is connected to a positive DC power source via a low-pass filter, and a reverse bias is applied to the photodiode. When the photodiode receives light, the current generated in the photodiode is taken out from the anode side and the cathode side, amplified by an amplifier, and then synthesized.

Japanese Patent Laid-Open No. 2005-51504

  According to the technique disclosed in Patent Document 1, since the photodiode is reverse-biased, the optical terminal unit needs to have a DC power supply for reverse bias. Since this optical terminal unit is often installed outdoors, in order to operate a DC power supply, a power line for supplying commercial AC power to the optical terminal unit is installed, or from the optical terminal unit indoors. It is necessary to superimpose the operating power from a power supply device provided indoors on the installed output transmission cable, which complicates the configuration of the optical terminal unit and increases the cost.

  An object of the present invention is to provide an optical terminal unit that is simple in configuration and low in cost.

  An optical terminal unit according to an aspect of the present invention receives a modulated optical signal obtained by modulating an optical signal with a joint reception signal in an optical transmitter via an optical transmission line. This optical terminal unit has a photodiode that receives the modulated optical signal, and a cathode and an anode of the photodiode are connected in a non-biased state via a load connected in series to the photodiode. Has been.

  In the optical terminal unit of the above aspect, a voltage drop resistor can be connected to the opposite side of the load across the photodiode. In this case, the load, the photodiode, and the voltage drop resistor are connected in series.

  In the optical terminal unit of the above aspect, switching means for switching between the no-bias state and the reverse bias state by the reverse bias circuit between the cathode and the anode of the photodiode can be provided.

  As described above, the configuration of the optical terminal unit according to the present invention can be simplified and the cost can be reduced.

It is a circuit diagram of the optical terminal unit used in the optical joint reception facility of the 1st reference example of this invention. It is a block diagram of the optical joint reception facility of the 1st reference example of this invention. FIG. 2 is a characteristic diagram of optical input level versus high frequency output level of the optical terminal unit of FIG. It is a circuit diagram of the optical terminal unit of the optical joint reception facility of the 2nd reference example of this invention. FIG. 5 is a characteristic diagram of optical input level versus high frequency output level of the optical terminal unit of FIG. It is a circuit diagram of the optical terminal unit of the optical joint reception facility of the 3rd reference example of this invention. It is a circuit diagram of the optical terminal unit of the optical joint reception facility of the 4th reference example of this invention. It is a circuit diagram of the optical terminal unit of the optical joint reception facility of the 1st Embodiment of this invention. It is a circuit diagram of the optical terminal unit of the optical joint reception facility of the 2nd Embodiment of this invention. It is a circuit diagram of the optical terminal unit of the optical joint reception facility of the 5th reference example of this invention.

  The optical terminal unit 2 of the first reference example of the present invention is used in a joint reception facility as shown in FIG. In this joint reception facility, a UHF band terrestrial digital television broadcast signal received by the terrestrial digital broadcast antenna 4 is amplified by a terrestrial digital broadcast reception amplifier 6. Similarly, the FM broadcast signal received by the FM dedicated antenna 8 is amplified by the channel proper amplifier 10. The amplified signals of the two amplifiers 6 and 10 are mixed by the mixer 12, and the mixed output is transmitted to the outdoor U / V optical transmitter 14. The outdoor U / V optical transmitter 14 is also supplied with a satellite broadcast intermediate frequency signal from the converter 16 a of the satellite broadcast receiving antenna 16. The outdoor U / V optical transmitter 14 modulates an optical signal with the supplied terrestrial digital television broadcast signal, FM broadcast signal, and satellite broadcast intermediate frequency signal, and outputs a modulated optical signal.

  The modulated optical signal is transmitted through an optical transmission line, for example, an optical fiber. In the middle of the optical fiber, optical distributors, for example, optical coupler closures 18a, 18b, 18c, and the like are provided, respectively. The signal is distributed and transmitted to each terminal, for example, each home 20.

  An optical terminal unit 2 is provided outside each home 20, and an optical modulation signal transmitted through an optical fiber is supplied to the optical terminal unit 2. The optical terminal unit 2 converts the optical modulation signal into a high-frequency signal, for example, a terrestrial digital television broadcast signal, an FM broadcast signal, and a satellite broadcast intermediate frequency signal, and supplies the signal to the indoor signal processing device 22. The signal processing device 22 demodulates the terrestrial digital television broadcast signal, the FM broadcast signal, and the satellite broadcast intermediate frequency signal so that they can be viewed on the television receiver 24.

  As shown in FIG. 1, the optical terminal unit 2 has a photodiode 26. The photodiode 26 receives the light modulation signal transmitted by the optical fiber.

  The anode and the cathode are connected between a primary winding 28p of a load, for example, a transformer, for example, a high frequency transformer 28. The primary winding 28p has an intermediate tap 28t, and the intermediate tap 28t is connected to a reference potential, for example, a ground potential. The anode of the photodiode 26 is connected to the ground potential via the high frequency blocking coil 30. As a result, the anode is not grounded in terms of high frequency.

  One end of the secondary winding 28 s of the high-frequency transformer 28 is grounded, and the other end is connected to the output terminal 34 via the capacitor 32. The output terminal 34 is supplied to the signal processing device 22 via a transmission line (not shown), for example, a coaxial cable.

  In the optical terminal unit 2, no bias is supplied to the photodiode 26, and the photodiode 26 is used in an unbiased state.

  In the optical terminal unit 2 configured as described above, when the photodiode 26 receives the modulated optical signal, a current flows through the primary winding 28p of the high-frequency transformer 28, and a voltage (terrestrial digital television broadcast signal) flows through the secondary winding 28s. , A voltage corresponding to the FM broadcast signal and the satellite broadcast intermediate frequency signal) is induced, and this is supplied to the signal processing device 22 via the capacitor 32 and the output terminal 34. Moreover, as shown in FIG. 3, as the level of the light modulation signal input to the photodiode 26 increases, the level output from the secondary winding 28s increases. Therefore, even if the input level of the light modulation signal is increased, the digital terrestrial television broadcast signal, FM broadcast signal and satellite broadcast intermediate frequency signal supplied to the signal processing device 22 can be increased, and the maximum light input level is defined. It is effective when possible, and can be used without problems at a light input level of 0 dBm or less that is normally used.

  FIG. 4 shows an optical terminal unit 2a according to a second reference example of the present invention. In this optical terminal unit 2a, the cathode of a photodiode 26 is grounded via a voltage drop element, for example, a resistor 36, and the cathode is connected to one end of a primary winding 28p of a high-frequency transformer 28 via a capacitor 38. is there. Since other configurations are the same as those of the optical terminal unit 2 of the first embodiment, the same portions are denoted by the same reference numerals, and description thereof is omitted.

  In the optical terminal unit 2 of the first reference example, if the input level of the light modulation signal to the photodiode 26 becomes too high, the digital terrestrial television broadcast signal, FM broadcast signal, and satellite broadcast intermediate signal output from the output terminal 34 will be described. The level of the frequency signal becomes too high, and there is a high possibility that distortion will increase in the signal processing device 22. Therefore, in the optical terminal unit 2a of the second embodiment, when the current generated in the photodiode 26 exceeds a predetermined value, the current flowing through the resistor 36 increases, and the voltage generated between the resistors 36 is increased. Increases, the voltage supplied to the primary winding 28p of the high-frequency transformer 28 decreases, and the input level of the optical modulation signal increases, the digital terrestrial television broadcast signal and FM broadcast signal output from the output terminal 34 The level of the satellite broadcast intermediate frequency signal does not increase as shown in FIG.

  FIG. 6 shows an optical terminal unit 2b of the optical reference reception facility of the third reference example. In this optical terminal unit 2b, the resistor 36 of the optical terminal unit 2a of the second reference example is removed, the contact 40a of the changeover switch 40 is connected to the connection point of the capacitor 38 and the cathode of the photodiode 26, and the contact is made. A contact 40b that can be contacted by the child 40a is grounded, and a reverse bias power source, for example, the positive electrode of the battery 44 is connected to the contact 40c that can also be contacted by the contact 40a through the resistor 42, and the negative electrode of the battery 44 is grounded. It is. That is, a state in which the reverse bias circuit including the resistor 42 and the battery 44 is connected to the photodiode 26 and a non-bias state of the photodiode 26 can be switched by operating the changeover switch 40. In addition, since the other structure is the same as that of the optical terminal unit 2a of the 2nd reference example, the same code | symbol is attached | subjected to the same part and the description is abbreviate | omitted.

  In the optical terminal unit 2 of the first reference example, when the level of the optical modulation signal input to the photodiode increases, the terrestrial digital television broadcast signals, the FM broadcast signals, and the satellite broadcast intermediate frequency signals or the ground There is a possibility that mutual distortion occurs between the digital television broadcast signal, the FM broadcast signal, and the satellite broadcast intermediate frequency signal, thereby degrading the transmission signal quality. Therefore, when the level of the light modulation signal input to the photodiode is large, the selector switch 40 is operated to apply a reverse bias to the photodiode 26 from the reverse bias circuit. In this case, since only the photodiode 26 is used as an active element, a battery 44 such as a dry battery can be used as a DC power source, and wiring for supplying commercial AC power is not necessary. Thus, manufacturing is facilitated and costs can be reduced.

  FIG. 7 shows an optical terminal unit 2c of the optical joint reception facility of the fourth reference example. This optical terminal unit 2c is provided with a changeover switch 40 and a battery 44 in the optical terminal unit 2a of the second reference example, and is used as a component of the optical terminal units 2a and 2b of the second and third reference examples. Corresponding portions are denoted by the same reference numerals, and description thereof is omitted. In the optical terminal unit 2c, similarly to the optical terminal unit 2a of the second reference example, in the non-bias state, even if the input level of the optical modulation signal is increased, the terrestrial digital television broadcast output from the output terminal 34 is provided. The level of the signal, the FM broadcast signal, and the satellite broadcast intermediate frequency signal can be prevented from increasing, and a reverse bias can be applied, thereby preventing mutual distortion.

  FIG. 8 shows an optical terminal unit 2d according to the first embodiment of the present invention. This optical terminal unit 2d has a resistor 46 as a load. The resistor 46 is connected between the anode of the photodiode 26 and the ground potential, and the connection point between the anode of the photodiode 26 and the resistor 46 is connected to the output terminal 34 via the capacitor 32. The cathode is grounded. In this configuration, the resistor 46 is used as a load, and the high-frequency transformer 28 is not used. Therefore, the configuration can be made at a lower cost.

  FIG. 9 shows an optical terminal unit 2e of the second embodiment. This optical terminal unit 2e is provided with a changeover switch 40 and a battery 44 in the optical terminal unit 2d of the first embodiment so that a reverse bias can be supplied to the photodiode 26 as in the second reference example. A reverse bias voltage drop resistor 48 is connected between the contact 40 a of the changeover switch 40 and the cathode of the photodiode 26. The cathode is grounded via a capacitor 50.

  FIG. 10 shows an optical terminal unit 2f of the fifth reference example. This optical terminal unit 2f is obtained by replacing the high-frequency transformer 28 of the optical terminal unit 2c of the fourth reference example with a high-frequency coil 52 with a tap, and taking out the output from this tap.

  In each of the above embodiments, the optical modulation signal is a signal modulated by an optical signal using a terrestrial digital television broadcast signal, an FM broadcast signal, and a satellite broadcast intermediate frequency signal. In addition to this, data used on the Internet or the like is used. It is also possible to use a communication signal obtained by modulating an optical signal.

2d 2e Optical terminal unit 26 Photodiode 46 Resistor (load)

Claims (3)

An optical terminal unit that receives a modulated optical signal obtained by modulating an optical signal with a joint reception signal in an optical transmitter via an optical transmission line,
An optical terminal unit including a photodiode that receives the modulated optical signal, and a cathode and an anode of the photodiode connected via a load connected in series to the photodiode and in a non-biased state. .   2. The optical terminal unit according to claim 1, wherein a voltage drop resistor is connected to the opposite side of the load across the photodiode, and the load, the photodiode, and the voltage drop resistor are connected in series. Optical terminal unit.   2. The optical terminal unit according to claim 1, further comprising switching means for switching between a cathode and an anode of the photodiode of the photodiode to one of the no-bias state and a reverse bias state by a reverse bias circuit. Terminal unit.

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