JP2010050641A - Optical receiver, optical transceiver, and method for optical reception - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical receiver, optical transceiver, and method for optical reception, capable of easily adjusting a tap coefficient to the suitable one even when dispersion characteristic changes comparatively significantly in accordance with replacement of transmission media. <P>SOLUTION: A controller 4 outputs a reset signal K to a dispersion equalization part 6 when intensity of an optical signal deviates from a predetermined range based on output of an optical detection circuit 7 which detects change of the intensity of the optical signal to be input in an ROSA (Receiver Optical Sub-Assembly) 5. On receiving the reset signal K, the dispersion equalization part 6 sets the tap coefficient to a predetermined initial value. After that, the dispersion equalization part 6 adjusts the tap coefficient. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an optical receiver, an optical transceiver, and an optical receiving method.

In recent years, devices called electronic dispersion equalization circuits have been developed for the purpose of correcting the propagation delay time between modes in a multimode fiber. An example of such an electronic dispersion equalization circuit is described in Non-Patent Document 1 and Non-Patent Document 2. For example, an electronic dispersion equalization circuit described in Non-Patent Document 1 includes a transversal filter for compensating for dispersion caused by transmission of an optical signal through an optical fiber. The transversal filter sequentially delays and outputs an electrical signal photoelectrically converted from an optical signal, and multiplies each of the plurality of signals output from the plurality of delay circuits by the respective tap coefficients and outputs the result. A plurality of multipliers, and a summation circuit for summing a plurality of signals after multiplication.
P. Pepeljugoski, J. Schaub, J. Tierno, J. Kash, S. Gowda, B. Wilson, H. Wu, A. hajimiri, “Improved Performance of 10 Gb / s Multimode Fiber Optic Link Using Equalization”, Technical Digest of Optical Fiber Conference, 2003, ThG4 Jack H. Winters, Richard D. Gitlin, “Electrical Signal Processing Techniques in Long-Haul Fiber-Optic System”, IEEE Transaction On Communications, 1990, vol. 38, No. 9, p.1439-1453.

  The dispersion characteristics of a transmission medium including an optical fiber vary depending on factors such as vibration of the transmission medium. For this reason, the electronic dispersion equalization circuit adjusts the tap coefficient according to the varying dispersion characteristic. However, when the transmission medium is replaced with another transmission medium and the dispersion characteristic changes relatively greatly, or when the dispersion characteristic changes relatively due to a change in the laying state of the transmission medium, the conventional method is used. Then, adjustment of the tap coefficient becomes difficult. Accordingly, an object of the present invention is to provide an optical receiver that can be easily adjusted to a suitable tap coefficient even when the dispersion characteristic varies relatively greatly with the replacement of the transmission medium or the change in the laying state of the transmission medium, An optical transceiver and an optical receiving method are provided.

  The optical receiver of the present invention converts an optical signal into a photocurrent and outputs it, amplifies the output photocurrent and outputs it as an electrical signal, and dispersion of the optical signal using the electrical signal A dispersion equalization unit for performing equalization processing, and a control unit for controlling the dispersion equalization unit, the distribution equalization unit having a transversal filter for performing distributed equalization processing, and transversal Each tap coefficient of the plurality of taps of the filter is adjustable, and the control unit measures the intensity of the optical signal based on the photocurrent, and when the measured intensity of the optical signal is out of a predetermined range, A reset signal for setting each tap coefficient to a predetermined initial value is output to the dispersion equalization unit, and the dispersion equalization unit sets each tap coefficient to a predetermined initial value according to the reset signal input from the control unit. Set to

  The optical transceiver of the present invention is an optical transceiver including an optical receiver that receives an optical signal, and the optical receiver converts the optical signal into a photocurrent and outputs it, and amplifies the output photocurrent. An optical receiving subassembly for outputting as an electrical signal, a dispersion equalization unit for performing dispersion equalization processing of the optical signal using the electrical signal, and a control unit for controlling the dispersion equalization unit, such as dispersion The conversion unit has a transversal filter for performing dispersion equalization processing, each tap coefficient of a plurality of taps of the transversal filter can be adjusted, and the control unit adjusts the intensity of the optical signal based on the photocurrent. When the intensity of the measured optical signal is out of a predetermined range, the reset signal for setting each tap coefficient to a predetermined initial value is output to the dispersion equalization unit. The relay input from the control unit Depending on Tsu preparative signal sets each tap coefficient to a predetermined initial value, wherein the.

  The optical receiving method of the present invention converts an optical signal into a photocurrent and outputs it, amplifies the output photocurrent and outputs it as an electrical signal, and dispersion of the optical signal using the electrical signal An optical reception method using an optical receiver including a dispersion equalization unit having a transversal filter for performing equalization processing and a control unit for controlling the dispersion equalization unit, wherein the control unit A measurement step for measuring the intensity of the optical signal based on the measurement signal, and when the intensity of the optical signal measured in the measurement step is out of a predetermined range, the control unit determines the tap coefficients of the plurality of taps of the transversal filter. An output step for outputting a reset signal for setting to an initial value of the output to the dispersion equalization unit, and the dispersion equalization unit performs each tap according to the reset signal output from the control unit in the output step. It has a setting step of setting the number to a predetermined initial value, and wherein the.

  According to the optical receiver, the optical transceiver, and the optical reception method, for example, when a transmission medium including an optical fiber is replaced and the intensity of an optical signal input from the transmission medium to the optical reception subassembly suddenly decreases, When the intensity of the optical signal input to the optical receiving subassembly suddenly increases due to a change in the laying state of the transmission medium, the control unit detects a decrease or increase in the intensity of the optical signal, and the dispersion equalization unit The dispersion equalization unit outputs a reset signal for resetting the tap coefficient to a predetermined initial value, and the distribution equalization unit receives the reset signal and sets the tap coefficient to a predetermined initial value. Thereafter, the tap coefficient is adjusted. In adjusting the tap coefficient, resetting the tap coefficient has the same effect as restarting the optical receiver. Therefore, even when the transmission medium is exchanged and the dispersion characteristic of the transmission medium changes relatively large, it is possible to easily adjust to a suitable tap coefficient. Therefore, suitable dispersion equalization processing can be performed on the optical signal.

  Optical receiver, optical transceiver, and optical receiving method that can be easily adjusted to a suitable tap coefficient even when dispersion characteristics change relatively greatly due to exchange of transmission media or changes in the laying state of transmission media Can be provided.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. In the description of the drawings, if possible, the same elements are denoted by the same reference numerals, and redundant description is omitted.

  FIG. 1 is a diagram illustrating a configuration of an optical transceiver according to an embodiment. The optical transceiver 1 includes a receiver 2 (optical receiver) and a transmitter 3.

  The receiver 2 includes a controller 4, a ROSA 5 (ROSA: Receiver Optical Sub-Assembly), a dispersion equalization unit 6, a light detection circuit 7, and a CDR unit 8 (CDR: Clock Data Recovery). The ROSA 5 is a semiconductor light receiving element (not shown) that converts an optical signal input from a transmission medium (not shown) including an optical fiber into a photocurrent and outputs it to the photodetection circuit 7, and amplifies and amplifies the photocurrent. And an amplification unit (not shown) that outputs the photocurrent as an electrical signal to the dispersion equalization unit 6. The controller 4 and the light detection circuit 7 constitute a control unit that cooperates to control the dispersion equalization unit 6. The photodetection circuit 7 monitors the value of the photocurrent and detects the intensity of the input optical signal, and the controller 4 outputs a reset signal K to the dispersion equalization unit 6 according to the detection result. Further, the controller 4 has functions such as processing of a supervisory control signal between the host side device on which the optical transceiver 1 is mounted and the optical transceiver 1, and control of optical output and extinction ratio on the transmitter 3 side.

  The distributed equalization unit 6 is connected to the controller 4, the ROSA 5, and the CDR unit 8. The dispersion equalization unit 6 processes the electrical signal input from the ROSA 5 (waveform shaping process) so as to compensate for the dispersion of the optical signal input to the ROSA 5, and sends the processed electrical signal to the CDR unit 8. This is an electronic dispersion equalization circuit (Equalizer) for output.

As shown in FIG. 2, the dispersion equalization unit 6 includes a transversal filter 60 used for dispersion equalization processing of an optical signal input to the ROSA 5 and a tap coefficient setting circuit 68. The transversal filter 60 has a plurality of taps P _{C0 to} P _Cm , P _{D0 to} P _Dn , and tap coefficients c _{0 to} c _m , d of the plurality of taps P _{C0 to} P _Cm and P _{D0 to} P _{Dn. 0} to d _n is adjustably configured. Dispersion equalization unit 6, in response to the reset signal K inputted from the controller 4 sets the tap coefficient _{c 0 ~c m, d 0 ~d} n predetermined initial value (hereinafter referred to as the initial value V). For example, the tap coefficient _{c 0} is 1, the initial value V is considered another tap coefficients _c 1 to c _m and the tap coefficients _d 0 to d _n is zero. Tap coefficient setting circuit 68 of the dispersion equalization unit 6, the value is calculated the set tap coefficients dispersed start the operation from the initial value V is minimized _{c 0 ~c m, d 0 ~d} n Make adjustments to maintain.

The light detection circuit 7 is connected to the ROSA 5 and the controller 4. The photodetection circuit 7 measures the intensity of the optical signal input to the ROSA 5 based on the value of the photocurrent input from the semiconductor light receiving element of the ROSA 5 and outputs it to the controller 4. Controller 4, when the intensity of the measured optical signal is out of a predetermined range (hereinafter referred to as range E), the tap coefficient c ₀ of the dispersion equalization unit 6 to c _m, the initial value d ₀ to d _n A reset signal K for setting V is output to the dispersion equalization unit 6. As the lower limit value of the range E, in the case of conforming to the 10GBASE-LRM standard, a value equal to or lower than the minimum reception level defined in the specification is preferable. For example, −20 dBm, which is considered to completely lose the data communication function, may be set as the lower limit value, and the upper limit value may not be provided. Tap coefficient setting circuit 68 of the dispersion equalization unit 6 receives a reset signal K inputted from the controller 4, the tap coefficients _c 0 _{to c m,} the d 0 to d _n once set to an initial value V. Tap coefficient setting circuit 68 the tap coefficients _c 0 _{to c} m of dispersion equalization unit _6, d 0 to d _n temporarily, after setting the initial value V, the tap coefficients _c 0 _{to c} m where dispersion is minimized, to resume the calculation of d ₀ ~d _n, to adjust the tap coefficients. The reset signal K may be output from the light detection circuit 7 to the dispersion equalization unit 6. In this case, the photodetection circuit 7 measures the intensity of the optical signal input to the ROSA 5, and resets to the tap coefficient setting circuit 68 of the dispersion equalization unit 6 when the measured intensity of the optical signal is out of the range E. The signal K is output. The CDR unit 8 restores the electrical signal data input from the dispersion equalization unit 6 and outputs the electrical signal after the data restoration.

  The transmitter 3 includes a CDR unit 9, an LDD 10 (LDD: Laser-Diode Driver), and a TOSA 11 (TOSA: Transmitter Optical Sub-Assembly). The CDR unit 9 restores the data of the input electric signal and outputs the electric signal after the data restoration to the LDD 10. The LDD 10 generates an electrical signal for driving a semiconductor light emitting element (not shown) included in the TOSA 11 based on the electrical signal input from the CDR unit 9, and outputs the generated electrical signal to the TOSA 11. The semiconductor light emitting element of the TOSA 11 generates an optical signal based on the electric signal input from the LDD 10 and outputs the generated optical signal.

  FIG. 2 is a diagram illustrating the configuration of the dispersion equalization unit 6. The dispersion equalization unit 6 includes a transversal filter 60 and a tap coefficient setting circuit 68. The transversal filter 60 includes an FFE unit 61 (FFE: Feed Forward Equalizer), a DFE unit 62 (DFE: Decision Feed-back Equalizer), a sum circuit 64, and a slicer 66. The transversal filter 60 performs a process (waveform shaping process) for electrically compensating the electrical signal from the ROSA 5 so as to compensate for the dispersion of the optical signal input to the ROSA 5. The transversal filter 60 outputs the processed signal to the CDR unit 8.

The FFE unit 61 includes a delay circuit T _C1 to a delay circuit T _Cm (m is an integer _{equal to} or greater than 1), and a multiplier C ₀ to a multiplier C _m , which include a plurality of taps P _C0 to taps. constitute the P _Cm. The DFE unit 62 includes a delay circuit T _D0 to a delay circuit T _Dn (n is an integer equal to or greater than 1) and a multiplier D ₀ to a multiplier D _n , which are a plurality of taps P _D0 to taps. P _Dn is configured.

Tap P _C0 includes a multiplier C ₀ . The tap P _Ck (k is an integer of ₁ to m) includes a delay circuit T _Ck and a multiplier C _k , and the tap P _Dj (j is an integer of 0 to n) is a delay circuit T _Dj and a multiplier D _j. Including.

The delay circuit T _Ck delays the input signal by 1 bit and outputs the delayed signal to the multiplier C _k and the delay circuit TC _{(k + 1) at the} subsequent stage. The delay circuit T _Dj outputs the input signal by 1 bit. And output to the multiplier D _j and the delay circuit T _{D (j + 1) at the} subsequent stage. For example, (the case of k = 1) delay circuits _T C1 is a signal input from ROSA5 delayed by 1bit minute, and output to the multiplier _{C 1} and subsequent delay circuits _{T C2,} the delay circuit _{T D0} ( In the case of j = 0), the signal input from the slicer 66 is delayed by 1 bit and output to the multiplier D ₀ and the delay circuit T _{D1 at} the subsequent stage.

Multiplier C ₀ multiplies the signal input from ROSA ₅ by tap coefficient c ₀ and outputs the result to sum circuit 64. Multiplier C _k multiplies the signal input from delay circuit T _Ck by tap coefficient _ck and outputs the result to sum circuit 64. The multiplier D _j multiplies the signal input from the delay circuit T _Dj by the tap coefficient d _j and outputs the result to the sum circuit 64.

sum circuit 64 sums the signals input from the multiplier _{C 0} ~ multiplier _{C m,} and outputs to the CDR unit 8 by summing the signals input from the multiplier _{D 0} ~ multiplier _{D n.} The slicer 66 determines “1” or “0” based on the signal input from the sum circuit 64, and outputs a signal indicating the determination result (“1” or “0”) to the delay circuit T _D0 . The difference signal indicating the difference between the signal input to the slicer 66 and the signal output from the slicer 66 is an analog signal (sum) reproduced from the output signal of the sum circuit 64 (that is, the output signal of the dispersion equalization unit 6). The difference from the digital signal based on the analog signal is shown and output to the tap coefficient setting circuit 68.

Tap coefficient setting circuit 68, based on the difference signal, the signal and the tap coefficient c ₀ as this by reducing the difference is equal to or less than a predetermined amount of the reference difference between the signal outputted from the Slicer66 _~ tap input to Slicer66 adjusting the coefficients _{c m} and the tap coefficients _{d 0} ~ tap coefficients _{d n.} If the difference indicated by the difference signal converges, the tap coefficients _{c 0} ~ tap coefficients _{c m} and the tap coefficients _{d 0} ~ tap coefficients _{d n} also converges. The tap coefficient setting circuit 68 transmits the adjustment result to the multipliers C ₀ to C _m and the multipliers D ₀ to D _n . Multipliers C ₀ -multiplier C _m and multipliers D ₀ -multiplier D _n are connected to tap coefficient c ₀ -tap coefficient _cm and tap coefficient d ₀ -tap based on the adjustment result by tap coefficient setting circuit 68. setting the coefficient _{d n.} As a result, the transversal filter 60 can perform optimum waveform shaping (electrical dispersion compensation) on the output signal of the ROSA 5.

Tap coefficient setting circuit 68, the reset signal K is inputted, and resets the tap coefficients c _{0 ~} tap coefficients c _m and the tap coefficients d _{0 ~} tap coefficients d _n to the initial value V, this initial value V, tap adjusting the coefficients _{c 0} ~ tap coefficients _{c m} and the tap coefficients _{d 0} ~ tap coefficients _{d n.}

  Next, the operation of the receiver 2 will be described. When the transmission medium including the optical fiber is replaced, the intensity of the optical signal input to the ROSA 5 may decrease. Further, the intensity of the optical signal input to the ROSA 5 may increase due to a change in the laying state of the transmission medium. Here, it is assumed that the transmission medium is replaced with another transmission medium. The semiconductor light receiving element of the ROSA 5 generates a photocurrent from the input optical signal and outputs it to the photodetection circuit 7. The amplification unit of the ROSA 5 amplifies the photocurrent generated by the semiconductor light receiving element of the ROSA 5 and outputs it to the dispersion equalization unit 6 as an electric signal. The light detection circuit 7 measures the intensity of the optical signal input to the ROSA 5 on the basis of the value of the photocurrent generated by the semiconductor light receiving element of the ROSA 5 and outputs it to the controller 4. When the intensity of the measured optical signal is out of the range E, the controller 4 outputs the reset signal K to the tap coefficient setting circuit 68 of the dispersion equalization unit 6. The tap coefficient setting circuit 68 of the dispersion equalization unit 6 receives this reset signal K, sets the tap coefficient to a predetermined initial value, and then adjusts the tap coefficient. In adjusting the tap coefficient, resetting the tap coefficient has the same effect as restarting the optical receiver. Then, the dispersion equalization unit 6 performs dispersion equalization processing of the optical signal input to the ROSA 5 using the adjusted tap coefficient. When the transmission medium is replaced, the dispersion characteristic of the transmission medium changes relatively greatly. According to the configuration of the receiver 2, the tap coefficient can be easily adjusted to a value corresponding to the change of the dispersion characteristic. Can do. The tap coefficient setting circuit 68 has a function of calculating a tap coefficient so that the difference between the input and output of the slicer 66 is equal to or less than a predetermined value and feeding back to the transversal filter 60, and includes a CPU. On the other hand, the controller 4 that performs control related to the entire optical transceiver 1 also includes a CPU. In some cases, the functions of the above two CPUs may be integrated into a single CPU depending on the demand for downsizing and high-density mounting of the optical transceiver 1. That is, the function of the controller 4 and the function of the tap coefficient setting circuit 68 may be included in a one-chip CPU.

FIG. 3 is a diagram showing an eye pattern of an optical signal actually subjected to dispersion equalization processing. FIG. 3A shows an eye pattern of an optical signal obtained by performing dispersion equalization processing on a deteriorated optical signal after 220 m multimode fiber transmission. The tap coefficient is adjusted to a value corresponding to the dispersion characteristic of the fiber. Then, the eye pattern of the optical signal obtained by performing the dispersion equalization process on the deteriorated optical signal after transmission from the 220 m multimode fiber to the 2 m multimode fiber after transmission of this multimode fiber is shown in FIG. Shown in (b). In this case, the tap coefficient before replacement was used at the start of adjustment after replacement without resetting the tap coefficient to the initial value. Since fine adjustment is performed using the tap coefficient before replacement at the start of adjustment after replacement, misconvergence has occurred, and from this state, 1, 0 determination is impossible. On the other hand, FIG. 3C shows an eye pattern of an optical signal that has been subjected to dispersion equalization processing using the receiver 2 according to the present embodiment when the fiber is replaced. Since the eye is satisfactorily open, that the tap coefficients _{c 0 ~c m, d 0 ~d} n is adjusted to a value corresponding to the dispersion characteristics after exchange has suitable dispersion equalization processing is performed Recognize.

  While the principles of the invention have been illustrated and described in the preferred embodiments, it will be appreciated by those skilled in the art that the invention can be modified in arrangement and detail without departing from such principles. The present invention is not limited to the specific configuration disclosed in the present embodiment. We therefore claim all modifications and changes that come within the scope and spirit of the following claims.

It is a figure which shows the structure of the optical transceiver which concerns on embodiment. It is a figure which shows the structure of the dispersion | distribution equalization part which concerns on embodiment. It is a figure which shows the eye pattern of the optical signal after a dispersion | distribution equalization process.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Optical transceiver, 2 ... Receiver, 3 ... Transmitter, 4 ... Controller, 5 ... ROSA, 6 ... Dispersion equalization part, 7 ... Optical detection circuit, 8, 9 ... CDR part, 10 ... LDD, 11 ... TOSA , K ... reset signal, 60 ... transversal filter, 61 ... FFE unit, 62 ... DFE unit, 64 ... sum circuit, 66 ... slicer, 68 ... tap coefficient setting _{circuit, P C0 ~P Cm, P D0} ~P Dn ... _{tap, T C1 ~T Cm, T D0} ~T Dn ... delay _{circuit, C 0 ~C m, D 0} ~D n ... _{multiplier, c 0 ~c m, d 0} ~d n ... tap coefficients

Claims (3)

An optical receiving subassembly that converts an optical signal into a photocurrent and outputs it, amplifies the output photocurrent, and outputs it as an electrical signal;
A dispersion equalization unit for performing dispersion equalization processing of the optical signal using the electrical signal;
A control unit for controlling the distributed equalization unit;
With
The dispersion equalization unit has a transversal filter for performing the dispersion equalization processing,
Each tap coefficient of a plurality of taps of the transversal filter is adjustable,
The control unit measures the intensity of the optical signal based on the photocurrent, and sets each tap coefficient to a predetermined initial value when the measured intensity of the optical signal is out of a predetermined range. A reset signal for output to the distributed equalization unit,
The variance equalization unit sets the tap coefficients to the predetermined initial values according to the reset signal input from the control unit.
An optical receiver. An optical transceiver comprising an optical receiver for receiving an optical signal,
The optical receiver is:
An optical receiver subassembly that converts the optical signal into a photocurrent and outputs the same, amplifies the output photocurrent, and outputs it as an electrical signal;
A dispersion equalization unit for performing dispersion equalization processing of the optical signal using the electrical signal;
A control unit for controlling the distributed equalization unit;
Have
The dispersion equalization unit has a transversal filter for performing the dispersion equalization processing,
Each tap coefficient of a plurality of taps of the transversal filter is adjustable,
The control unit measures the intensity of the optical signal based on the photocurrent, and sets each tap coefficient to a predetermined initial value when the measured intensity of the optical signal is out of a predetermined range. A reset signal for output to the distributed equalization unit,
The variance equalization unit sets the tap coefficients to the predetermined initial values according to the reset signal input from the control unit.
An optical transceiver characterized by that. To convert an optical signal into a photocurrent and output it, amplify the output photocurrent and output it as an electrical signal, and to perform dispersion equalization processing of the optical signal using the electrical signal An optical reception method using an optical receiver including a dispersion equalization unit having a transversal filter and a control unit that controls the dispersion equalization unit,
A measurement step in which the control unit measures the intensity of the optical signal based on the photocurrent;
When the intensity of the optical signal measured in the measurement step is out of a predetermined range, the control unit resets the tap coefficients of the plurality of taps of the transversal filter to be set to a predetermined initial value. An output step of outputting a signal to the dispersion equalization unit;
In accordance with the reset signal output from the control unit in the output step, the dispersion equalization unit sets the tap coefficients to the predetermined initial value,
An optical receiving method characterized by comprising: