JP2008199233A - Optical reception device and method, and station-side optical terminator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve the incoming transmission efficiency of a PON (Passive Optical Network) system. <P>SOLUTION: An OLT (Optical Line Terminal) control device (48) collects information of delay times corresponding to distances to ONUs (Opitcal Network Unit) (18-1 to 18-n) and intensities of light inputted from ONUs to the OLT control device, during link up processes of respective ONUs and during operation and stores this information in a memory 50. An opto-electric transducer (36) converts an up optical signal to an electric signal. An AGC (Automatic Gain Control) circuit (38) adjusts the amplitude of the electric signal from the opto-electric transducer (36) to a prescribed value. An AGC control device (48a) refers to the memory (50) to preset an initial gain according with the amplitude of an electric signal to be inputted to the AGC circuit (38). <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an optical receiving apparatus and method, and more specifically to an apparatus and method for receiving optical signal sequences having different optical intensities.

  Optical transmission that connects optical terminal equipment OLT (Optical Line Terminal) installed on the center station side and optical terminal equipment ONU (Opitcal Network Unit) at a plurality of user homes via passive elements including optical fibers and optical couplers. The system is generally called a PON (Passive Optical Network) system.

  In the PON system, a time division multiple access method is applied as a method for transmitting an upstream signal from each ONU to the OLT. The OLT controls the transmission timing of each ONU so that upstream optical burst signals transmitted from each ONU do not overlap on the optical coupler.

  The optical fiber length from the optical coupler to each ONU is generally different, and the transmission loss is also different. Further, since there is an individual difference in the optical output from each ONU, the optical intensity of the upstream optical burst signal from each ONU is different for each ONU at the input stage to the OLT. Furthermore, since the frequency or phase of the oscillator that serves as a reference for each ONU to generate the upstream optical burst signal is generally different for each ONU, the oscillators of each ONU are not synchronized with each other.

  In this way, upstream optical burst signal sequences having different optical intensities and clocks are input to the OLT optical receiver. Therefore, the optical receiver of the OLT must adjust the amplitude level of the incoming upstream optical burst signal sequence to a predetermined value, or adjust the threshold value for binary discrimination according to the input signal amplitude. The optical receiver of the OLT needs a time margin for such gain or threshold adjustment. Usually, an automatic gain control (AGC) circuit that aligns the amplitude level of an incoming upstream optical burst signal sequence to a predetermined value, a so-called AGC circuit, is provided.

  The ONU uses direct modulation of the laser diode for cost reduction. An operation of raising the amplitude of the laser output light before the direct modulation and lowering the amplitude of the laser output light after the direct modulation is performed. The OLT AGC needs to be able to follow such transient amplitude fluctuations, and generally has a configuration in which the gain is controlled continuously with respect to the input signal level. This increases the time required for the gain to stabilize.

  Further, since the binary discrimination circuit must establish clock synchronization for each input upstream burst signal, a time margin for synchronizing the clock to the input upstream burst signal is also required.

  In the conventional PON system, a time domain for gain adjustment and clock data recovery (CDR) is prepared in advance before data transmission.

  FIG. 3 shows a waveform change of one optical burst signal. The laser intensity rises to a predetermined value during the laser startup period Ton. In the next synchronization period Tsync, the optical receiver of the OLT completes the AGC and clock regeneration and synchronization. In a data period Tdata following the synchronization period Tsync, a data frame, for example, a MAC frame is transmitted. The laser intensity falls in the laser fall period Toff after the data period Tdata. The laser startup period Ton is usually about 30 ns, and the synchronization period Tsync is about 500 ns.

  FIG. 4 is a schematic diagram of AGC operation in the OLT for optical burst signal trains from three ONUs having different transmission losses. FIG. 4A shows an example of the waveform of an optical burst signal. The light intensity of the second optical burst signal 70B is strong and the light intensity of the third optical burst signal 70C is weaker than the light intensity of the first optical burst signal 70A. 4B shows changes in the gains 72A, 72B, and 72C of the AGC circuit with respect to the optical burst signals 70A, 70B, and 70C shown in FIG. 4A, and FIG. 4C shows the electric signal 74A after AGC. , 74B, 74C.

  In order to flexibly cope with the transient response of the ONU transmission waveform, the AGC circuit continuously changes the gain according to the input light intensity, and the gain and the electric signal amplitude after AGC change gently. By such gain control, it takes time until the gain of the AGC circuit or the amplitude of the output of the AGC circuit converges to a desired value.

  As is well known, the AGC circuit generally has a function of reducing the amplitude of an electric signal having an amplitude larger than a target amplitude. In other words, the AGC circuit has both an amplifier function and an attenuator function.

  For an optical signal of any light intensity, the AGC operation must be continuously functioned to converge the gain within the synchronization period Tsync, and the clock regeneration and synchronization establishment must be achieved for each optical burst signal. Therefore, the synchronization period Tsync must be set to a length sufficient to perform the above-described process.

  The time required for AGC / CDR is overhead when viewed from the data signal. This time is preferably as short as possible, and the uplink transmission efficiency is improved by shortening this time.

  However, high-speed AGC / CDR requires advanced hardware technology and components. Even if the overhead can be reduced by using a high-speed AGC / CDR device, the system becomes very expensive.

  Also, the time required for the AGC gain to stabilize does not depend on the transmission rate. Accordingly, the higher the transmission speed, the greater the overhead occupied by AGC. At high transmission rates, the demands on hardware become severe.

  An object of the present invention is to provide an optical receiving apparatus and method and a station-side optical termination apparatus that reduce AGC overhead and improve uplink transmission efficiency without relying on high-speed AGC hardware.

  An optical receiver according to the present invention is an optical receiver that receives optical signals from a plurality of optical transmitters multiplexed on a time axis, and the optical signals from the plurality of optical transmitters are received by the optical receiver. Measuring means for measuring delay time according to the light intensity at the time of input to the apparatus and the distance to the plurality of optical transmission apparatuses, an optical / electrical converter for converting the optical signal into an electrical signal, and the optical / electrical An AGC circuit that adjusts the gain of the electrical signal from the converter and an initial gain corresponding to the light intensity of the optical signal are set in the AGC circuit at the stage of inputting the electrical signal corresponding to the optical signal. And an AGC control device.

  An optical reception method according to the present invention is an optical reception method for receiving optical signals from a plurality of optical transmission devices multiplexed on a time axis, and the optical signals from the plurality of optical transmission devices are received by the optical reception method. Measuring step for measuring delay time according to light intensity at the time of input to device and distance to said plurality of optical transmitting devices, and optical / electrical converting step for converting said optical signal into electric signal by optical / electrical converter And a gain adjustment step of adjusting the gain of the electric signal from the optical / electrical converter by an AGC circuit, and the gain adjustment step inputs the electric signal corresponding to the optical signal to the AGC circuit. And a gain preset step for setting an initial gain according to the light intensity of the optical signal in the AGC circuit.

  A station-side optical termination device according to the present invention is a station-side optical termination device that is connected to a plurality of user optical termination devices via a passive optical transmission line including an optical fiber and an optical coupler, and the plurality of user optical termination devices Measuring means for measuring the delay time according to the light intensity and the distance to the plurality of optical terminal devices when the optical signal from the optical signal is input to the station side optical terminal device, and converting the optical signal into an electrical signal An optical / electrical converter, an AGC circuit that adjusts the gain of the electrical signal from the optical / electrical converter, and an input of the electrical signal corresponding to the optical signal to the AGC circuit And an AGC control device that sets an initial gain according to the light intensity.

  In the present invention, since the initial gain of the AGC circuit is preset, the time until convergence of AGC can be shortened, and the synchronization period added to the optical signal for AGC / CDR can be shortened. As a result, optical signals can be more densely arranged on the time axis, and transmission efficiency is improved.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 shows a schematic block diagram of an embodiment of the present invention. The OLT 10 installed in the center station is connected to the optical coupler 14 via the optical fiber 12, and the optical coupler 14 is connected to the ONUs 18-1 to 18- of each user via the individual optical fibers 16-1 to 16-n. connect to n. The ONUs 18-1 to 18-n are installed in each user's home. One or a plurality of computers 20-1 to 20-n can be connected to each ONU 18-1 to 18-n.

  An optical signal transmission mode between the OLT 10 and the ONUs 18-1 to 18-n will be briefly described. The optical coupler 14 divides the downstream optical signal power output from the OLT 10 and input through the optical fiber 12 into n pieces, and outputs the optical signals obtained by the power division to the optical fibers 16-1 to 16-n. Each of the power-divided downstream optical signals propagates through the optical fibers 16-1 to 16-n and is input to the ONUs 18-1 to 18-n. Each ONU 18-1 to 18-n converts the downstream optical signal into an electrical signal, internally processes commands and responses addressed to itself, and transmits data addressed to the computers 20-1 to 20-n to the computers 20-1 to 20-20. Output to -n.

  Each of the ONUs 18-1 to 18-n multiplexes the command and response addressed to the OLT 10 into the upstream data from the computers 20-1 to 20-n, converts the multiplexed signal into an optical signal, and transmits the optical fiber 16-1 to Output to 16-n. The optical signal, that is, the upstream optical signal propagates through the optical fibers 16-1 to 16-n and enters the optical coupler 14. The optical coupler 14 outputs upstream optical signals from the optical fibers 16-1 to 16-n to the optical fiber 12. The upstream optical signal from each user that has propagated through the optical fiber 12 enters the OLT 10.

  The configuration and operation of the OLT 10 will be described. The PON interface 30 includes an electrical / optical (E / O) converter 32, a wavelength-selective optical coupler 34, and an optical / electrical (O / E) converter 36. The E / O converter 32 converts a downstream traffic electrical signal, which will be described later, into an optical signal, that is, a downstream optical signal. The WDM optical coupler 34 supplies the downstream optical signal from the E / O converter 32 to the optical fiber 12 and supplies the upstream optical signal from the optical fiber 12 to the O / E converter 36. In the PON system, the upstream optical signal uses the 1.3 μm band and the downstream optical signal uses the 1.49 μm band. Therefore, the WDM optical coupler 34 causes the upstream optical signal and downstream optical signal to flow as described above. Can be controlled. The O / E converter 36 converts the upstream optical signal from the optical coupler 34 into an electrical signal.

  An AGC (automatic gain control) circuit 38 adjusts the amplitude level of the output electric signal of the O / E converter 36 to a constant value under the control of the OLT control device 48. Once the amplitude level higher than the target level is raised, the limiter may adjust the amplitude level to the target level. The detailed operation of the AGC circuit 38 will be described later. The output electrical signal of the AGC circuit 38 is supplied to the binary discriminating device 40 and the clock recovery device 42.

  The clock recovery device 42 regenerates a clock from the output of the AGC circuit 38 or generates a clock synchronized with the output of the AGC circuit 38 and applies the recovered clock or the generated clock to the binary discriminating device 40. The binary discriminating apparatus 40 discriminates the output signal of the AGC circuit 38 in accordance with the control of the clock from the clock regenerating apparatus 42 and the discrimination threshold from the OLT control apparatus 48.

  The output signal of the binary discriminator 40 is supplied to a demultiplexer (MUX / DEMUX) 44. The demultiplexer 44 supplies a signal (request signal or response signal from the ONU 18-1 to 18-n to the OLT 10) addressed to the OLT 10 among the output signals of the binary discriminator 40 to the OLT controller 48. The other signals are multiplexed with signals to be transmitted by the OLT 10 to the network control device or the like of the upper network, and supplied to the network interface 46 in a predetermined frame format.

  The OLT control device 48 controls the OLT 10 and the entire PON system, and includes an AGC control device 48a and a DBA control device 48b. The AGC control device 48a can preset the initial gain at the start of the AGC operation in the AGC circuit 38, and can instruct the start timing of the AGC operation. The AGC control device 48a also monitors the gain in the AGC circuit 38. The DBA controller 48b dynamically manages and determines the upstream signal band of each ONU 18-1 to 18-n.

  The memory 50 stores information on the subordinate ONUs 18-1 to 18-n, in particular, information on the delay time corresponding to the light intensity and distance input to the OLT 10. Of course, other information necessary for managing the ONUs 18-1 to 18-n, for example, identification information of the logical links that have been set and information such as service levels are also stored in the memory 50. The OLT controller 48 collects these ONU information not only during the link-up process of each ONU but also during operation. The optical intensity of the upstream optical signal input to the OLT 10 varies depending on the light output fluctuation of the laser mounted on the ONUs 18-1 to 18-n, and the delay time varies depending on the optical path length change according to the environmental change. The OLT control device 48 refers to the ONU information in the memory 50 and controls the initial gain and AGC operation of the AGC circuit 38.

  The network interface 46 sends the upstream signal from the demultiplexer 44 to the upper network. Further, the network interface 46 outputs to the demultiplexing device 52 from the upper network. The demultiplexer 52 separates the signal from the network interface 40 into data to be transferred to any one of the lower users and commands and responses to the OLT 10, and supplies the former to the E / O converter 32, and the latter Is supplied to the OLT control device 48. The OLT control device 48 processes the command and response from the demultiplexing device 52 according to the contents. The OLT control device 48 also outputs a control signal addressed to each ONU 18-1 to 18-n to the demultiplexing device 52. Such a control signal includes a Gate message indicating the transmission band determined by the DBA controller 48b. The demultiplexer 52 multiplexes the control signal from the OLT controller 48 with the data signal addressed to each user and supplies the multiplexed signal to the E / O converter 32.

  The E / O converter 32 converts the electrical signal from the demultiplexer 52 into an optical signal and applies it to the WDM optical coupler 34 as a downstream optical signal. This downstream optical signal enters all the ONUs 18-1 to 18-n through the optical fiber 12, the optical coupler 14, and the optical fibers 16-1 to 16-n. As described above, each ONU 18-1 to 18-n takes in only a frame addressed to itself in the downstream signal and ignores other frames. Thereby, the data and control signal for a specific user reach the ONU of the user. Each ONU 18-1 to 18-n transmits uplink data within the transmission band assigned by the Gate message of the received control signal.

  A control operation of the AGC circuit 38, which is a characteristic operation of this embodiment, will be described. FIG. 2 shows a timing chart of the present embodiment for optical burst signal sequences from three ONUs having different transmission losses. FIG. 2A shows an example of the waveform of an optical burst signal sequence incident on the optical / electrical converter 36 of the OLT 10. Similar to the conventional example shown in FIG. 4A, the optical intensity of the second optical burst signal 60B is higher than the optical intensity of the first optical burst signal 60A, and the optical intensity of the third optical burst signal 60C. Is weak. 2B shows changes in gains 62A, 62B, and 62C of the AGC circuit 38 with respect to the optical burst signals 60A, 60B, and 60C shown in FIG. 2A, and FIG. 2C shows the electrical signals after AGC. The amplitudes of 64A, 64B, and 64C are shown.

  When the OLT control device 48 of the OLT 10 assigns logical links to the ONUs 18-1 to 18-n, the delay time according to the distance to each ONU 18-1 to 18-n, more specifically, the OLT 10 The round trip time (RTT) to each ONU 18-1 to 18-n and the light intensity input to the OLT 10 are measured and stored in the memory 50 as ONU information. RTT is a reference parameter that determines transmission timing by TDMA. The light intensity can be acquired from the AGC circuit 38. In other words, the AGC control device 48a of the OLT control device 48 monitors the gain in the AGC circuit 38, and the monitoring result indicates the light intensity of the upstream optical signal from each ONU 18-1 to 18-n continuously or intermittently. Recognize. The OLT control device 48 corresponds to measurement means defined in the claims, that is, measurement means for measuring the light intensity and delay time of the optical signals from the plurality of optical transmission devices.

  In this embodiment, the OLT control device 48 presets an initial gain corresponding to the amplitude of the upstream signal in the AGC circuit 38 immediately before the upstream signal from each ONU 18-1 to 1-n enters the AGC circuit 38. . The OLT control device 48 instructs the AGC circuit 38 to start the AGC operation almost simultaneously with the start of the laser rising period Ton of the upstream signal. As shown in FIG. 2B, changes in the gains 62A, 62B, and 62C of the AGC circuit 38 due to the AGC operation are extremely less than those of the conventional example (gains 72A, 72B, and 72C in FIG. 4B). . Thereby, in the present embodiment, the signal amplitude rises rapidly at the output stage of the AGC circuit 38 and converges to the target level as shown by the waveforms 64A, 64B, and 64C shown in FIG.

  Thus, in this embodiment, since the gain of the AGC circuit 38 converges in a short time, the clock synchronization of the clock recovery device 42 can be realized at the initial stage of the synchronization period Tsync. That is, the synchronization period Tsync can be shortened as compared with the prior art, and each optical burst signal can be arranged densely on the time axis. Overall, upstream transmission efficiency is improved.

  The AGC controller 48a also stores the converged gain value of the AGC circuit 38 or the loss value corresponding to the gain value in the memory 50 in preparation for the next reception. Then, the AGC controller 48a reads the gain value or the loss value from the memory 50 for the next upstream optical burst signal from the same ONU, and presets it in the AGC circuit 38 as an initial gain.

  The convergence gain value in the previous upstream optical burst signal from the same ONU may be used as it is as the initial gain value or convergence gain value of the next optical burst signal. Thereby, the convergence process of continuous AGC can be omitted completely, and the time related to the clock synchronization of the clock recovery device 42 can be directly used as the synchronization period Tsync.

  The gain adjustment loop of the AGC circuit 38 may include a bit error rate (BER) measured by the binary discrimination device 40. That is, the gain of the AGC circuit 38 is feedback-controlled so that the BER in the binary discriminating device 40 is reduced.

  The AGC circuit 38 also has a function of lowering the amplitude of an electric signal having an amplitude larger than the target amplitude, like a conventional AGC amplifier. In other words, the AGC circuit 38 has both an amplifier function (positive gain) and an attenuator function (negative gain).

  Although the invention has been described with reference to specific illustrative embodiments, various modifications and alterations may be made to the above-described embodiments without departing from the scope of the invention as defined in the claims. This is obvious to an engineer in the field to which the present invention belongs, and such changes and modifications are also included in the technical scope of the present invention.

It is a schematic block diagram of one Example of this invention. It is a timing chart of a present Example, (a) shows the waveform example of the optical burst signal sequence which injects into OLT10, (b) shows the gain change of an AGC circuit, (c) shows the electric signal amplitude after AGC. Show. It is an example of a waveform of an upstream optical burst signal. It is a timing chart of a prior art example, (a) shows the waveform example of the optical burst signal sequence which injects into OLT, (b) shows the gain change of an AGC circuit, (c) shows the electric signal amplitude after AGC. .

Explanation of symbols

10: OLT
12: Optical fiber 14: Optical couplers 16-1 to 16-n: Optical fibers 18-1 to 18-n: ONU
20-1 to 20-n: computer 30: PON interface 32: electrical / optical (E / O) converter 34: wavelength selective optical coupler 36: optical / electrical (O / E) converter 38: AGC (automatic gain) Control) circuit 40: binary discriminator 42: clock regenerator 44: demultiplexer (MUX / DEMUX)
44: Demultiplexer 46: Network interface 48: OLT controller 48a: AGC controller 48b: DBA controller 50: Memory (ONU information)
52: Demultiplexers 60A, 60B, 60C: Optical burst signals 62A, 62B, 62C: Gains 64A, 64B, 64C: Electrical signals 70A, 70B, 70C after AGC: Optical burst signals 72A, 72B, 72C: Gains 74A, 74B, 74C: Electrical signal after AGC

Claims (9)

An optical receiver that receives optical signals from a plurality of optical transmitters (18-1 to 18-n) multiplexed on a time axis,
A measuring means (48) for measuring a delay time according to a light intensity when the optical signals from the plurality of optical transmission devices are input to the optical reception device and a distance to the plurality of optical transmission devices;
An optical / electrical converter (36) for converting the optical signal into an electrical signal;
An AGC circuit (38) for adjusting the gain of the electrical signal from the optical / electrical converter;
An AGC control device (48a) that sets an initial gain according to the light intensity of the optical signal in the AGC circuit (38) at the stage when the electrical signal corresponding to the optical signal is input.
An optical receiver characterized by comprising:   2. The optical receiver according to claim 1, wherein the AGC control device controls an AGC operation of the AGC circuit in accordance with an arrival time of the optical signal calculated from the delay time. Furthermore,
Storage means for storing information relating to the light intensity;
Update means (48) for updating the information on the light intensity stored in the storage means to a value corresponding to the converged gain of the AGC circuit (38).
The optical receiver according to claim 1, further comprising: An optical reception method for receiving optical signals from a plurality of optical transmission devices (18-1 to 18-n) multiplexed on a time axis,
A measurement step (48) for measuring a delay time according to a light intensity when the optical signals from the plurality of optical transmission devices are input to the optical reception device and a distance to the plurality of optical transmission devices;
An optical / electrical conversion step of converting the optical signal into an electrical signal by the optical / electrical converter (36);
A gain adjustment step of adjusting the gain of the electrical signal from the optical / electrical converter by an AGC circuit (38),
The gain adjustment step sets an initial gain corresponding to the light intensity of the optical signal in the AGC circuit (38) when the electrical signal corresponding to the optical signal is input to the AGC circuit (38). An optical receiving method comprising a gain preset step.   5. The optical receiving method according to claim 4, wherein the gain adjusting step controls an AGC operation of the AGC circuit according to the arrival time of the optical signal. The measurement step stores information on the measured light intensity in the storage means (50),
The optical reception method further includes an update step (48) for updating the information on the light intensity stored in the storage means to a value corresponding to the converged gain of the AGC circuit (38). The optical receiving method according to claim 4 or 5. A station side optical terminator connected to a plurality of user optical terminators (18-1 to 18-n) via a passive optical transmission line composed of an optical fiber and an optical coupler,
Measuring means (48) for measuring a delay time corresponding to the light intensity when the optical signals from the plurality of user optical terminal devices are input to the station side optical terminal device and the distances to the plurality of optical terminal devices; ,
An optical / electrical converter (36) for converting the optical signal into an electrical signal;
An AGC circuit (38) for adjusting the gain of an electric signal from the optical / electrical converter;
An AGC control device (48a) that sets an initial gain according to the light intensity of the optical signal in the AGC circuit (38) when the electrical signal corresponding to the optical signal is input.
A station-side optical terminal device.   The said AGC control apparatus controls the AGC operation | movement of the said AGC circuit according to the said arrival time of the said optical signal, The station side optical termination apparatus of Claim 7 characterized by the above-mentioned. Furthermore,
Storage means for storing information relating to the transmission loss;
Update means (48) for updating the information on the light intensity stored in the storage means to a value corresponding to the converged gain of the AGC circuit (38).
The station side optical termination device according to claim 7 or 8, characterized by comprising:

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