JP4630047B2 - Optical transmission equipment - Google Patents

Description

  The present invention relates to an optical transmission device that converts an electrical signal into an optical signal and transmits the signal, and more particularly to an electrical / optical (E / O) conversion unit.

  In optical transmission, in order to maintain the stability and reliability of signal transmission, it is necessary to keep the optical modulation index (OMI) constant when electrical / optical conversion is performed.

  2. Description of the Related Art Conventionally, an optical transmission apparatus that can control the optical modulation degree of an optical signal converted by E / O to be constant is disclosed in Patent Document 1.

  Patent Document 1 discloses an optical transmission device in which an optical receiving device is connected through an optical transmission line, and an optical signal that has been E / O converted by the optical transmission device is received by the optical receiving device and optical / electrical (O / E) conversion is performed. It is shown.

  The E / O converter, particularly the laser diode (LD), affects the optical modulation factor by the gain of the input high-frequency electrical signal or the temperature change of the LD itself, and the optical modulation factor by the bias current applied to the LD. Therefore, the E / O converter of Patent Document 1 monitors the bias current of the LD, and based on the monitored result, the E / O converted light modulation degree is constant. The gain of the input high-frequency electrical signal is adjusted.

  On the other hand, optical transmission apparatuses are installed in various environments, and required E / O conversion conditions differ depending on the installation location and installation environment. For example, there is a demand to reduce third-order distortion (IM3: 3rd order Inter Modulation) in an optical transmission section or to reduce noise (CNR: Carrier to Noise Ratio). In this case, as in the conventional optical transmission apparatus, the method of uniquely controlling the optical modulation degree when converted by the E / O conversion unit to be constant, for each optical transmission apparatus, installation conditions There is a problem that it must be set manually every time, and is troublesome, and it is difficult to realize optimum E / O conversion conditions for each installation environment.

JP 2002-33705 A

  In view of such circumstances, the present invention provides an optical transmission apparatus that can adjust the light modulation degree and can easily obtain the optimum light modulation degree according to the installation location and the installation environment.

  The present invention includes a laser diode that converts an electrical signal into an optical signal, an optical modulation degree adjusting unit that adjusts an attenuation rate of a signal input to the laser diode, and a bias current detection unit that detects a bias current of the laser diode. And an arithmetic processing unit that controls the attenuation factor of the optical modulation degree adjusting means so that the optical modulation degree is set based on the detected bias current, and a setting value of the optical modulation degree is input to the arithmetic processing unit The present invention relates to an optical transmission apparatus including an OMI setting unit.

  According to the present invention, a laser diode that converts an electrical signal into an optical signal, a light modulation degree adjusting means that adjusts an attenuation rate of a signal input to the laser diode, and a bias current that detects a bias current of the laser diode A detection unit, an arithmetic processing unit for controlling the attenuation factor of the optical modulation degree adjusting means so as to obtain an optical modulation degree set based on the detected bias current, and a set value of the optical modulation degree in the arithmetic processing unit. Since the input OMI setting unit is provided, the light modulation degree can be set according to the installation location and the installation environment, and an excellent effect of obtaining the optimum light modulation degree is exhibited.

  The best mode for carrying out the present invention will be described below with reference to the drawings.

  In the optical transmission apparatus, it is the optical modulation index (OMI) that determines the third-order distortion (IM3: 3rd order Inter Modulation) and noise (CNR: Carrier to Noise Ratio) of the optical section, and the OMI (OMI: Optical Modulation Index). Is defined by the ratio between the modulation amplitude of the light intensity and the average light intensity, and is defined by the following equation (1).

OMI = (modulation amplitude of light intensity / average light intensity)
= (Ppeak-Pave) / Pave
= √ (2PRF / ZLD) / (Ib−Ith) (1)
Where Ppeak: modulation amplitude of light intensity
Pave: Average light intensity
PRF: LD input level per carrier wave
ZLD: LD input impedance
Ib: Bias current
Ith: threshold current

  In the equation (1), ZLD, Ib, and Ith are fixed values for each LD. Therefore, the only parameter that can be changed when examining IM3 and CNR is PRF. Therefore, the OMI increases or decreases with respect to the increase or decrease of the PRF. For example, when the OMI is increased, the input level of the LD, that is, the PRF may be increased.

  Next, IM3, CNR, and gain (Gopt) in the optical transmission section are expressed by the following equations (2), (3), and (4).

IM3 = IM3ref + 40 log (OMI / OMIref) (2)
Here, IM3ref: IM3 when modulated with OMIref
OMIref: Reference OMI, for example 0.2

^{CNR = [(OMI) 2 (} η · Pr) 2/2] / {[RIN · (η · Pr) 2 + 2qηPr + (In) 2] · BW} ... (3)
Here, RIN: Relative intensity noise
η: Photosensitive sensitivity efficiency of photodiode (PD)
Pr: Average light receiving level (for example, if light loss α, Pr = α · Pave)
q: Elementary electric quantity 1.60 × 10 ⁻¹⁹
In: Input equivalent noise current density
BW: Noise bandwidth

Gopt = PRF_OUT−PRF
= (ZPD / 2) (OMI · η · Pr) ² − (ZLD / 2) {OMI · (Ib−Ith)} ² (4)
Where ZPD: PD load resistance

  From the above formulas (2), (3), and (4), it can be seen that increasing the OMI (that is, the input level to the LD) increases the CNR, and decreasing the OMI improves the IM3. Once determined, CNR and IM3 are uniquely determined. In the present invention, the OMI value can be changed so that CNR and IM3 corresponding to the installation location and installation environment can be obtained.

  A first embodiment of the present invention will be described with reference to FIG.

  FIG. 1 shows an electrical / optical conversion unit 1 of an optical transmission apparatus. An electrical signal is input to the electrical / optical conversion unit 1 via an RF amplifier 2. The RF amplifier 2 is adjusted so that an electric signal of a certain level is output to the electric / optical converter 1.

  The electrical / optical converter 1 will be described.

  A first amplifying unit 4 for amplifying an electric signal input to the input terminal 3 of the electric / optical converting unit 1; a first variable attenuating unit 5 which is an OMI adjusting means for absorbing variations in the gain of the laser diode 9; In response to the electric signal, the second variable attenuating unit 6 that absorbs the gain variation, the second amplifying unit 7 that amplifies the electric signal, the detection circuit 8 that cuts noise and prevents over-input to the laser diode A laser diode (LD) 9 which is an electric / optical converter that emits light is sequentially connected, and an optical transmission unit, for example, an optical fiber 11 is connected to the laser diode 9. The laser diode 9 is cooled to a predetermined temperature by a cooling means (not shown) such as a Peltier element during driving.

  A bias current detector 12 is provided for detecting a bias current Ib of the laser diode 9, A / D converting and outputting a bias detection signal Cb. The bias detection signal Cb from the bias current detector 12 is represented by a CPU. Are input to the arithmetic processing unit 13. The arithmetic processing unit 13 outputs a control signal CAT to the first variable attenuation unit 5 based on the detection result from the bias current detection unit 12, and the control signal CAT is passed through the D / A conversion unit 14. The first variable attenuator 5 is inputted as an attenuation control signal VAT.

  The electrical / optical conversion unit 1 includes a storage unit 15. The storage unit 15 stores a control data table 16 as shown in FIG. 2, and the arithmetic processing unit 13 stores the bias. The attenuation control signal VAT is output with reference to the control data table 16 based on the signal from the current detector 12.

  In the control data table 16, the association between the bias current Ib for OMI, the bias detection signal Cb input to the arithmetic processing unit 13, and the control signal CAT output from the arithmetic processing unit 13 is set.

  For example, when the level of the electric signal input to the laser diode 9 is set to OMI1, the bias detection signal Cb11 and the control signal CAT11 are used when the bias current Ib1 is used to maintain the OMI1. Are the bias detection signal Cb12, the control signal CAT12, and so on.

  Further, in order to obtain the relationship shown in FIG. 2, the input signal Vb to the bias current detector 12, the bias detection signal Cb, the control signal CAT, and the attenuation amount control from the D / A converter 14 with respect to the bias current Ib are obtained. The association with the signal VAT is set as shown in the data table 21 of FIG. 3. For example, when the bias current is Ib1, the input signal Vb1, the bias detection signal Cb1, the control signal CAT1, and the attenuation control signal VAT1. The amount of attenuation of the first variable attenuation unit 5 is DAT1.

  Further, an OMI setting signal 17 is input to the arithmetic processing unit 13 from an OMI setting unit (not shown), and the OMI setting signal is the optimum OMI setting signal according to the installation location and installation environment. 17 is input to the arithmetic processing unit 13.

  Hereinafter, the operation of controlling the OMI to be constant in the electrical / optical converter 1 will be described.

  The optimal OMI setting signal 17 according to the installation location and installation environment is input to the arithmetic processing unit 13 from the OMI setting unit (not shown). The arithmetic processing unit 13 controls the attenuation factor of the first variable attenuation unit 5 so that the OMI value corresponding to the input OMI setting signal 17 becomes, for example, OMI1.

  A bias current Ib2 of the laser diode 9 is detected by the bias current detection unit 12, A / D converted, and output to the arithmetic processing unit 13 as a bias detection signal Cb12. The arithmetic processing unit 13 refers to the control data table 16 based on the input bias detection signal Cb12 and outputs a control signal CAT12. The control signal CAT12 is D / A converted by the D / A converter 14 and input to the first variable attenuator 5 as an attenuation control signal VAT12, and the electric signal input to the laser diode 9 becomes constant. In this way, the attenuation is adjusted to DAT12.

  When the bias current detector 12 detects the bias current Ib1 of the laser diode 9, it is A / D converted and output to the arithmetic processor 13 as a bias detection signal Cb11. The arithmetic processing unit 13 outputs the control signal CAT11 with reference to the control data table 16 so that the OMI setting signal 17 becomes OMI1 based on the input bias detection signal Cb11.

  The control signal CAT11 is D / A converted by the D / A converter 14 and input to the first variable attenuator 5 as the attenuation control signal VAT11, and the electric signal input to the laser diode 9 becomes constant. In this way, the attenuation amount DAT11 is adjusted. The attenuation amount DAT is controlled, the variation in gain of the laser diode 9 is absorbed, and the OMI input to the laser diode 9 is held at a set value.

  Thus, a desired OMI value is realized by inputting the OMI value to the CPU by an external signal.

  FIG. 4 shows a second embodiment of the present invention. In FIG. 4, the same components as those shown in FIG. 1 are denoted by the same reference numerals.

  The second embodiment basically has the same configuration as that of the first embodiment, and a third variable attenuation unit 18 is provided in the preceding stage of the first variable attenuation unit 5. The arithmetic processing unit 13 issues a command signal 19 to the third variable attenuation unit 18 via the D / A conversion unit 20.

  When the OMI setting signal 17 is input to the arithmetic processing unit 13, the arithmetic processing unit 13 issues a command signal 19 to the third variable attenuation unit 18 via the D / A conversion unit 20, and The three variable attenuation unit 18 sets an attenuation rate such that the output signal becomes an OMI corresponding to the command signal 19 from the arithmetic processing unit 13.

  The control data table 16 stored in the storage unit 15 in the second embodiment is shown in FIG. The first variable attenuation unit 5 has a data table 21 shown in FIG. 3, and this data table is fixed regardless of the OMI value.

  When the OMI value (OMI) is OMI1, the CPU output value (COMIAT) is COMIAT1, and COMIAT1 is converted to VOMIAT1 by the D / A converter 20 (DAC output voltage value VOMIAT). The amount of attenuation (DOMIAT) is controlled by DOMIAT1. The OMI value is arbitrarily input from the user via the OMI setting unit in each environment of the installation location, so that a CPU output value corresponding to each OMI value is output, and the attenuation amount of the third variable attenuation unit 18 Is controlled.

  In the second embodiment, when the attenuation amount of the first variable attenuating unit 5 is adjusted, the bias value of τ-LD is monitored, and the gain is set so that the E / O converted light modulation degree becomes constant. The third variable attenuator 18 changes the gain by changing the attenuation factor corresponding to the optical modulation factor when the optical modulation factor is changed. Therefore, in the second embodiment, the adjustment for making the optical modulation degree of the LD constant and the adjustment for changing the optical modulation degree can be performed separately, so that the data table of the CPU is simplified and the adjustment is simplified. ,Stabilize. Further, since the light modulation degree is adjusted by the first variable attenuating unit 5 and the third variable attenuating unit 18, the width of the light modulation variable is increased.

  As described above, according to the present invention, the LD bias value is monitored in the electric / optical converter 1, and the gain of the electric / optical converter 1 is automatically adjusted so that the OMI becomes a constant value according to the LD bias value. It is possible to adjust and further change the OMI in each environment, and realize the optimum IM3 · CNR of the optical transmission apparatus.

It is a schematic block diagram which shows the 1st Embodiment of this invention. It is a figure which shows the data table used by this 1st Embodiment. It is a figure which shows the relationship of the signal of each site | part in this 1st Embodiment. It is a schematic block diagram which shows the 2nd Embodiment of this invention. It is a figure which shows the data table used by this 2nd Embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Electrical / optical conversion part 2 RF amplifier 5 1st variable attenuation part 6 2nd variable attenuation part 9 Laser diode 13 Arithmetic processing part 14 D / A conversion part 15 Memory | storage part 16 Control data table 17 OMI setting signal

Claims (1)

A laser diode for converting an electrical signal into an optical signal, a first light modulation factor adjustment means and the second optical modulation index adjusting means for adjusting the attenuation amount of the signal input to the laser diode, the bias of the laser diode a bias current detecting unit for outputting a detection bias detection signal current, outputs a control signal to the first optical modulation index adjusting means and the second optical modulation adjusting means so as to be set to the optical modulation index an arithmetic processing unit which controls the attenuation amount is, the association of the OMI setting unit for inputting the optical modulation index set value to the arithmetic processing unit, the bias detection signal and the set value and the control signal is set and a storage unit in which the control data table is stored, reduction of the first optical modulation factor adjustment means the arithmetic processing unit by said control signal obtained by referring to the control data table based on the set value Controls the amount, the optical transmission apparatus characterized by controlling the attenuation amount of the reference by said control signal obtained by the second optical modulation index adjusting means said control data table based on the bias detection signal .

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