JP5208695B2 - Communication control device - Google Patents

Description

  The present invention relates to a communication control apparatus.

  In a communication system (for example, PON (Passive Optical Network)) that can cope with a case where the amplitude of input light is different, a semiconductor optical amplifier (SOA) is used. In this communication system, when input light having a small amplitude is input to the SOA, the SOA amplifies the input light by a predetermined amount and inputs it to a light receiving element for optical / electrical signal conversion.

  When the intensity of the input light is so high that the SOA is unnecessary, it is conceivable to reduce the amplification factor of the SOA to such an extent that the sensitivity of the light receiving element is not saturated. However, the present inventor has found that the signal waveform of the signal light output from the SOA having the amplification degree is distorted.

  That is, when the intensity of the input light to the SOA is unnecessarily high, it can be said that the adverse effect of receiving waveform distortion is caused by the light input to the SOA that is not necessary. Of course, in such a case, a method of bypassing the SOA and coupling the input light directly to the light receiving element is conceivable. However, in order to bypass the SOA, an element such as an optical path switch is required, which is not realistic.

  An object of the present invention is to provide a communication control apparatus that can suppress waveform distortion in an SOA.

  A communication control apparatus according to the present invention provides a semiconductor optical amplifier for a communication apparatus including an optical input unit, a light receiving element, and a semiconductor optical amplifying element disposed between the optical input unit and the light receiving element. A transmission mode control current is supplied so that the input light intensity and the output light intensity of the element itself are substantially the same. In the communication control apparatus according to the present invention, waveform distortion of an optical signal can be suppressed.

  Further, in a state where the transmission mode control current is injected into the semiconductor optical amplifying element, the optical signal input to the optical input unit can be in a state of receiving a loss before reaching the light receiving element.

  The loss may be an optical coupling loss existing between the optical input unit and the light receiving element.

  In addition, it is effective for suppressing the waveform distortion of the optical signal to make the transmission mode control current smaller than the control current for realizing the amplification gain for compensating the optical coupling loss.

  Further, the input / output intensity ratio of the semiconductor optical amplifying element itself can be selected from -0.5 dB to 0.5 dB.

  The communication control device may selectively perform a first control for amplifying the input light by giving a predetermined amplification gain to the semiconductor optical amplifying element and a second control for giving the transmission mode control current. . In this case, if the input light intensity is small, it can be amplified.

  According to the present invention, waveform distortion of input light input to the SOA can be suppressed.

Hereinafter, the best mode for carrying out the present invention will be described.
(First embodiment)
A communication system 100 to which the communication control apparatus 50 according to the first embodiment is applied will be described with reference to FIGS. FIG. 1 is a block diagram showing the overall configuration of the communication system 100. FIG. 2 is a schematic diagram showing details of a semiconductor optical amplification module 20 described later. FIG. 3 is a schematic cross-sectional view of a semiconductor optical amplifier 21 to be described later.

  As shown in FIG. 1, the communication system 100 includes a beam splitter 10, a semiconductor optical amplification module 20, a light receiving element 30, a light receiving element 40, and a communication control device 50. The beam splitter 10 branches the optical signal input to the communication system 100 into two branches. One branched light is input to the semiconductor optical amplification module 20. The other branched light is input to the light receiving element 30. The light receiving element 30 detects the light intensity of the branched light and gives the result to the communication control device 50.

  The communication control device 50 includes a control unit including a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), and the like. The communication control device 50 controls the semiconductor optical amplification module 20 based on the detection result of the light receiving element 30. Thereby, the output light intensity from the semiconductor optical amplification module 20 is controlled. The output light from the semiconductor optical amplification module 20 is received by the light receiving element 40.

  As shown in FIG. 2, the semiconductor optical amplification module 20 has a structure in which, for example, a semiconductor optical amplification element 21 is accommodated in a package 22. An optical fiber 23 through which the optical signal from the beam splitter 10 passes is inserted into the package 22. The optical fiber 23 is optically coupled to the input side of the semiconductor optical amplifier 21. An optical fiber 24 that is optically coupled to the light receiving element 40 is inserted into the package 22. The optical fiber 24 is optically coupled to the output side of the semiconductor optical amplification element 21. An optical component such as a lens may be disposed between the optical fibers 23 and 24 and the semiconductor optical amplifying element 21.

  As shown in FIG. 3A, the semiconductor optical amplifier 21 has a structure in which, for example, a clad layer 62, an active layer 63, and a clad layer 64 are laminated on a substrate 61. The substrate 61 is made of N-type InP. The clad layer 62 is made of N-type InP. The active layer 63 is made of InGaAsP. As shown in FIG. 3B, the active layer 63 has, for example, a height of 100 nm, a width of 2 μm, and a length of 900 μm. The clad layer 64 is made of P-type InP.

  The active layer 63 and the clad layer 64 have a width smaller than that of the clad layer 62 and have a mesa structure extending in a stripe shape. A high resistance buried layer 65 is disposed on both sides of the active layer 63 and the clad layer 64 on the clad layer 62. The high resistance buried layer 65 is made of Fe-doped InP. An N-side electrode 66 is disposed on the lower surface of the substrate 61. A P-side electrode 67 is disposed on the upper surface of the cladding layer 64.

  Next, optical amplification in the semiconductor optical amplifier 21 will be described. FIG. 4 is a schematic diagram for explaining optical amplification in the semiconductor optical amplifier 21. FIG. 4A and FIG. 4B are schematic diagrams for explaining the case where light is amplified in the semiconductor optical amplifier 21. When the drive current (hereinafter referred to as SOA current) supplied to the semiconductor optical amplifier 21 is large, the number of electrons increases at a high energy level. In this case, an electron transits to a lower vacant level by interaction with light, and energy corresponding to the difference between the two levels is emitted as light. Thereby, light is amplified.

  The greater the intensity of input light, the stronger the interaction between light and electrons. In this case, there may be a case where the supply of electrons to the upper level is not in time for the transition from the upper level to the lower level. In this case, light amplification is saturated. When a strong light pulse is input, there is sufficient electrons in the upper level in the first part of the pulse, so that light amplification is increased. However, with the passage of time, the supply of electrons to the upper level is not in time, and the amplification factor decreases. In this case, the optical pulse of the output light is distorted, and the rise overshoots. This phenomenon becomes more prominent as the SOA current is smaller or the input light intensity is larger. This phenomenon is a problem when it is desired to attenuate strong input pulsed light without distortion.

  4 (a) and 4 (b) schematically show that the upper level electrons are eliminated, but in reality, the upper level electrons are always supplied by the SOA current. Yes. However, when the light intensity increases, the supply of electrons to the upper level may not be in time for the transition from the upper level to the lower level. In this case, light amplification is saturated.

  FIG. 4C and FIG. 4D are schematic diagrams for explaining the case where light is attenuated in the semiconductor optical amplifier 21. When the SOA current is small, the number of electrons increases at a low energy level. In this case, the electrons transition to a higher vacant level while absorbing energy from the light by interaction with the light. Thereby, the light is attenuated.

  When a strong light pulse is input, since the number of lower level electrons is sufficiently present at the beginning of the pulse, the light absorption rate is increased. However, as time elapses, the number of electrons that have transitioned to higher levels due to light absorption increases and the light absorption rate decreases. In this case, in the second half of the light pulse, the absorptance decreases and a transparency phenomenon occurs. As a result, the light pulse is distorted and the rising edge is smoothed.

  FIGS. 4E and 4F are schematic diagrams for explaining the case where the semiconductor optical amplifier 21 does not amplify or attenuate light. Here, the absorption and emission of light are determined according to the number of electrons in the low energy level and the high energy level. When the number of electrons is such that light absorption and emission are balanced, the input light passes through without being amplified or attenuated. In this case, the number of electrons at each level does not change. Thereby, the light passes through the semiconductor optical amplifying element 21 without depending on the light intensity.

  In the present embodiment, when the input light to the semiconductor optical amplifying element 21 is strong, the communication control device 50 generates a driving current as shown in FIGS. 4 (e) and 4 (f). To supply. In this case, distortion of the drive waveform of the semiconductor optical amplifier 21 can be suppressed.

  FIG. 5 is a flowchart showing an example of the control of the semiconductor optical amplifier 21 by the communication control device 50. As shown in FIG. 5, the communication control device 50 receives the detection result from the light receiving element 30 (step S1). Next, the communication control device 50 determines whether or not the intensity of light received by the light receiving element 30 exceeds a threshold value (step S2).

  If it is determined in step S2 that the light intensity exceeds the threshold value, the communication control device 50 performs semiconductor optical amplification that is smaller than the amplification gain that compensates for the coupling loss with the semiconductor optical amplification element 21 and excludes the coupling loss. A drive current at which the input light intensity and the output light intensity of the element 21 become substantially the same is supplied to the semiconductor optical amplifier element 21 (step S3). Thereafter, the communication control device 50 ends the execution of the flowchart.

  If it is not determined in step S2 that the light intensity exceeds the threshold value, the communication control device 50 supplies the semiconductor optical amplifier 21 with a drive current that realizes a predetermined amplification factor (step S4). Thereafter, the communication control device 50 ends the execution of the flowchart.

  According to the flowchart of FIG. 5, it is possible to suppress the distortion of the driving waveform of the semiconductor optical amplifying element while supplying the driving current to the semiconductor optical amplifying element.

  In the examples, optical amplification was performed using the communication system 100 according to the above embodiment. The structure of the semiconductor optical amplifying element 21 is the same as that described with reference to FIG. FIG. 6 is a diagram showing the relationship among SOA current (mA), output light intensity, and output light intensity / input light intensity. In FIG. 6, the horizontal axis indicates output light intensity (dBm), and the vertical axis indicates output light intensity / input light intensity (dB). The output light intensity and the input light intensity are values at the fiber end, and the output light intensity / input light intensity (dB) includes a coupling loss with the semiconductor optical amplifying element 21.

  As shown in FIG. 6, when the SOA current is large, the output light intensity / input light intensity (dB) increases, and when the SOA current is small, the output light intensity / input light intensity (dB) decreases. On the other hand, when the SOA current was 20 mA, the output light intensity / input light intensity did not change much even when the output light intensity increased. In this case, the semiconductor optical amplifier 21 is transparent. In this case, the reason why the output light intensity / input light intensity (dB) shows a negative value is that a coupling loss occurs between the semiconductor optical amplifier 21 and the optical fibers 23 and 24.

  Hereinafter, the relationship between the SOA current and the modulation waveform output from the semiconductor optical amplifier 21 will be described with reference to FIGS. First, FIG. 7A shows an example of the waveform of the input light. In FIG. 7A, almost no distortion is seen in the waveform of the input light.

  FIG. 7B shows a modulation waveform when the SOA current is increased and the input light with a small intensity is amplified. FIG. 7B shows a case where the average light intensity of the input light is −20.62 dBm, the SOA current is 300 mA, and the average light intensity of the output light is 1.75 dBm. In this case, since the SOA current is large, it is considered that the distortion in the modulation waveform is suppressed.

  On the other hand, in FIG. 8, the modulation in the case where the light intensity passing through the input-side optical fiber and the light intensity passing through the output-side optical fiber are substantially the same for large-intensity input light. Waveform is shown. FIG. 8 shows a case where the average intensity of input light is 0 dBm, the SOA current is 30 mA, and the average intensity of output light is 0 dBm. In this case, the SOA current was adjusted to compensate for the coupling loss.

  In this case, in the first part of the pulse, electrons are sufficiently present in the upper level, so that the light amplification factor is increased. As time passes, the supply of electrons to the upper level is not in time, and the amplification factor decreases. As a result, as shown in FIG. 8, the optical pulse of the output light is distorted and the rise overshoots.

  On the other hand, FIG. 9 shows a modulation waveform when the intensity of input light having a large intensity is attenuated while the SOA current is controlled to a predetermined value. This shows a case where the SOA current is 20 mA, the input light average intensity is 9.3 dBm, and the output light average intensity is 3.5 dBm. In FIG. 9, the current is such that the input light intensity and the output light intensity of the semiconductor optical amplifying element 21 are smaller than the amplification gain that compensates for the coupling loss with the semiconductor optical amplifying element 21 and the coupling optical loss is substantially the same. Was supplied to the semiconductor optical amplifier 21. As shown in FIG. 9, the distortion in the output waveform of the semiconductor optical amplifier 21 was suppressed. This is presumably because the distortion of the optical pulse is suppressed because the semiconductor optical amplifier 21 is substantially transparent.

  In order to obtain a good communication state, it is desirable to suppress the deformation of the modulation waveform due to overshoot as shown in FIG. 8 to 10% or less. For that purpose, it is useful that the allowable range of the ratio between the output light intensity and the input light intensity in FIG. 6 falls within −0.5 dB to 0.5 dB. In this case, since the ratio of the output light intensity to the semiconductor optical amplifying element 21 and the input light intensity is set to 0 dB, the semiconductor optical amplifying element 21 is in a range of −0.5 dB to 0.5 dB. The current may be controlled.

  As described above, it was confirmed that the distortion of the optical pulse can be suppressed by making the semiconductor optical amplifier 21 substantially transparent when the input light intensity is high.

It is a block diagram which shows the whole structure of a communication system. It is a schematic diagram which shows the detail of a semiconductor optical amplification module. It is a typical sectional view of a semiconductor optical amplification element. It is a schematic diagram for demonstrating the optical amplification in a semiconductor optical amplifier element. It is a flowchart which shows an example of control of the semiconductor optical amplification element by a communication control apparatus. It is a figure which shows the relationship between SOA electric current, output light intensity, and output light intensity / input light intensity. It is a figure for demonstrating the relationship between SOA electric current and an input optical waveform. It is a figure for demonstrating the relationship between SOA electric current and an input optical waveform. It is a figure for demonstrating the relationship between SOA electric current and an input optical waveform.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Beam splitter 20 Semiconductor optical amplification module 21 Semiconductor optical amplification element 22 Package 23, 24 Optical fiber 30, 40 Light receiving element 50 Communication control apparatus 100 Communication system

Claims (6)

  An input light intensity and output light of the semiconductor light amplifying element itself for a communication device comprising a light input part, a light receiving element, and a semiconductor light amplifying element disposed between the light input part and the light receiving element. A communication control device that supplies a transmission mode control current having substantially the same intensity.   2. The optical signal input to the optical input unit in a state where the transmission mode control current is injected into the semiconductor optical amplifying element is lost before reaching the light receiving element. Communication control device.   The communication control apparatus according to claim 2, wherein the loss is an optical coupling loss existing between the optical input unit and the light receiving element.   4. The communication control apparatus according to claim 3, wherein the transmission mode control current is smaller than a control current for realizing an amplification gain that compensates for the optical coupling loss.   2. The communication control apparatus according to claim 1, wherein the input / output intensity ratio of the semiconductor optical amplifier element itself is -0.5 dB to 0.5 dB.   The communication control device selectively performs a first control for amplifying input light by giving a predetermined amplification gain to the semiconductor optical amplifying element and a second control for giving the transmission mode control current. The communication control device according to claim 1.

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