Control device

Abstract

A control device (4) comprises a control unit that sets the resistance value of a load resistor (22) connected to a directly modulated laser (21) on the basis of the magnitude of a bias current supplied to the directly modulated laser (21).

Description

control device

[0001] This invention relates to a control device.

[0002] When an electrical signal is converted into an optical signal using a laser diode (LD) and transmitted, lowering the laser bias reduces the damping constant. In this case, the peak in the frequency characteristics of the small-signal response (E / O response) becomes more pronounced when the modulation frequency is near the relaxation oscillation frequency. If the LD modulates a large signal under these conditions, the response near the relaxation oscillation frequency becomes strong in the eye waveform, creating an overshoot structure, which can increase the bit error rate (BER).

[0003] U.S. Patent No. 1,0063032

[0004] Nogawa, Katsurai, Nakamura, Kamitsuna, Otomo, “10 Gbit / s Burst Mode Receiving IC Technology”, NTT Technical Journal, Vol.9, No.3, pp.31-35, 2011.1

[0005] In view of the above circumstances, the present invention aims to provide a technique that can mitigate the peaks in the frequency characteristics of small-signal responses.

[0006] One aspect of the present invention is a control device comprising: a control unit that sets the resistance value of a load resistor connected to a direct-modulation laser based on the magnitude of the bias current supplied to the direct-modulation laser.

[0007] The present invention makes it possible to mitigate the peaks in the frequency characteristics of small-signal responses.

[0008] This figure shows an example configuration of the optical communication system 1 according to the first embodiment. This figure shows an example configuration of the transmitter 2 according to the first embodiment. Gain S of the electro-optical conversion of the direct-modulated laser 21. ２１ This figure shows an example. This is a flowchart of the operation of the control unit 41 according to the first embodiment. This is a flowchart of the operation of the control unit 41 according to the second embodiment. Gain S of the electro-optical conversion of the direct-modulated laser 21. ２１ This figure shows the gain S of the electro-optical conversion of the direct-modulated laser 21. ２１ This figure shows the gain S of the electro-optical conversion of the direct-modulated laser 21. ２１ This is a diagram.

[0009] Embodiments of the present invention will be described below with reference to the drawings. The embodiments described below are merely examples, and the embodiments to which the present invention is applied are not limited to the embodiments described below.

[0010] Figure 1 shows an example configuration of an optical communication system 1 according to the first embodiment. The optical communication system 1 comprises a transmitter 2, a receiver 3, and a control device 4. The transmitter 2 transmits an optical signal to the receiver 3. The control device 4 controls the transmitter 2.

[0011] Figure 2 shows an example configuration of the transmitter 2 and control device 4 according to the first embodiment. The transmitter 2 includes a direct modulation laser 21, a load resistor 22, and a bias current supply 23. The control device 4 includes a control unit 41 and a storage unit 49.

[0012] The direct-modulated laser 21 converts electrical signals into optical signals. When an electrical signal is applied to the direct-modulated laser 21, it oscillates and is converted into an optical signal. The generated optical signal is output to the receiver 3.

[0013] The load resistor 22 is connected to the cathode of the direct-modulated laser 21. The load resistor 22 is connected in series with the electrical resistance of the direct-modulated laser 21. The load resistor 22 is a resistor with a variable resistance value.

[0014] The bias current supplier 23 is connected to the load resistor 22. The bias current supplier 23 supplies bias current to the load resistor 22, thereby supplying bias current to the cathode of the direct-modulated laser 21.

[0015] The anode of the direct-modulated laser 21 is grounded.

[0016] The control unit 41 controls the load resistor 22 and the bias current supplier 23. The control unit 41 controls the load resistor 22 and changes its resistance value. The control unit 41 controls the bias current supplier 23 and changes the magnitude I of the supplied bias current.

[0017] Here, how the operation of the directly modulated laser 21 changes in accordance with changes in the resistance value R of the load resistor 22 and changes in the magnitude I of the supplied bias current will be described. The modulation frequency characteristic of the electro-optical conversion gain (E / O response) of the directly modulated laser 21 is the relaxation oscillation frequency f ｒ It is determined by multiplying the intrinsic response determined by the damping constant Γ by the response caused by delays such as electrical resistance R, capacitance C, and carrier transit time. For example, the electro-optical conversion gain S of the directly modulated laser 21 ２１ is the relaxation oscillation frequency f ｒ , is given by Equation (1) using the damping constant Γ, electrical resistance R, capacitance C, and modulation frequency f. Delays such as carrier transit time are synthetically included in the RC time constant.

[0018] When the magnitude I of the bias current supplied to the directly modulated laser 21 is reduced, the damping constant Γ is reduced. At this time, the electro-optical conversion gain S of the directly modulated laser 21 given by Equation (1) ２１ , the amount of change in gain per amount of change in frequency increases when the modulation frequency f is in the vicinity of the relaxation oscillation frequency f ｒ . That is, when the modulation frequency f is plotted on the horizontal axis, the electro-optical conversion gain S of the directly modulated laser 21 ２１ is plotted on the vertical axis, the change in the gain S ２１ becomes steep. At this time, by increasing the resistance value of the load resistor 22, the RC response causes the modulation frequency f to shift to the relaxation oscillation frequency f ｒ when it is in the vicinity of the gain S ２１ can be prevented from changing steeply.

[0019] Figure 3 shows the electro-optical conversion gain S of the directly modulated laser 21 ２１ is a diagram showing an example. In FIG. 3, the vertical axis represents the electro-optical conversion gain S of the directly modulated laser 21 ２１ , and the horizontal axis represents the modulation frequency f. In the case where no load resistor is connected to the directly modulated laser 21 and there is no RC response (Without RC response), the gain S ２１The gain S when the load resistor is directly connected to the modulated laser 21 and there is an RC response (With RC response) is given by the following: ２１ Comparing the two, the gain S is greater when there is an RC response than when there is no RC response. ２１ We can see that the sharp changes have been reduced.

[0020] The control unit 41 sets the emission intensity of the optical signal output from the direct-modulating laser 21 based on the transmission loss α of the optical signal output from the transmitter 2 and received by the receiver 3. The emission intensity of the optical signal set here is set such that, for example, the emission intensity of the optical signal received by the receiver 3 is equal to or greater than the minimum receiving sensitivity. Since the emission intensity of the optical signal output from the direct-modulating laser 21 changes depending on the magnitude I of the bias current, the control unit 41 sets the emission intensity of the optical signal output from the direct-modulating laser 21 by setting the magnitude I of the bias current supplied from the bias current supplier 23 based on the transmission loss α of the optical signal output from the transmitter 2 and received by the receiver 3.

[0021] For example, the memory unit 49 stores information indicating the correspondence between the transmission loss α of the optical signal and the magnitude I of the bias current, and the control unit 41 uses the correspondence between the transmission loss α of the optical signal and the magnitude I of the bias current stored in the memory unit 49 to set the magnitude I of the bias current to a magnitude corresponding to the transmission loss α of the optical signal.

[0022] The transmission loss α of the optical signal is calculated, for example, by subtracting the emission intensity of the optical signal received by the receiver 3 from the emission intensity of the optical signal output from the transmitter 2. Information on the transmission loss α is acquired by the control unit 41, for example, by inputting it into an input device connected to the transmitter 2 by the user.

[0023] The transmission loss α of the optical signal output from transmitter 2 and received by receiver 3 may be calculated based on the distance L between transmitter 2 and receiver 3. The control unit 41 may calculate the transmission loss α based on the information of the distance L between transmitter 2 and receiver 3. In this case, the information of the distance L between transmitter 2 and receiver 3 may be obtained by inputting it into an input device connected to transmitter 2 by the user, or it may be obtained from a measuring device that measures the distance L between transmitter 2 and receiver 3. Alternatively, the storage unit 49 may store information showing the correspondence between the distance L between transmitter 2 and receiver 3 and the magnitude I of the bias current, and the control unit 41 may use the correspondence between the distance L between transmitter 2 and receiver 3 and the magnitude I of the bias current stored in the storage unit 49 to set the magnitude I of the bias current to a magnitude corresponding to the distance L between transmitter 2 and receiver 3.

[0024] The control unit 41 sets the resistance value of the load resistor 22 based on the magnitude I of the bias current. The control unit 41 uses, for example, the correspondence between the magnitude I of the bias current and the resistance value R of the load resistor 22 stored in the memory unit 49 to set the resistance value R of the load resistor 22 to the resistance value corresponding to the magnitude I of the bias current.

[0025] The relationship between the magnitude I of the bias current and the resistance R of the load resistor 22 is given by the gain S. ２１ The frequency variation is arbitrarily determined so that it is gradual. The relationship between the magnitude of the bias current I and the resistance value of the load resistor 22 is such that, in particular, the modulation frequency f is the relaxation oscillation frequency f ｒ Gain S when located in the neighborhood ２１ The frequency is determined so that the change is gradual.

[0026] The direct-modulated laser 21 has an intrinsic relaxation oscillation frequency f ｒ It has capacitance C. Therefore, from equation (1), the gain S of the direct-modulated laser 21's electro-optical conversion is ２１ The damping constant Γ and resistance R change, and since the damping constant Γ changes with the bias current, the modulation frequency response of the direct-modulating laser 21 changes depending on the magnitude of the bias current R and the resistance value R of the load resistor 22. Therefore, the gain S ２１By storing the correspondence between the magnitude I of the bias current, which can moderate the change due to frequency, and the resistance value R of the load resistor 22, the resistance value R of the load resistor 22 can be set according to the magnitude I of the bias current.

[0027] Information on the correspondence between the magnitude I of the bias current and the resistance value R of the load resistor 22 is stored in the storage unit 49, for example, by being input by a user to an input device connected to the transmitter 2.

[0028] Note that the modulation current or modulation voltage of the directly modulated laser 21 is set based on a coefficient (S11 coefficient) indicating the ratio of a signal reflected with respect to an input signal. Since the S11 coefficient is a value that changes depending on the resistance value R of the load resistor 22, the modulation current or modulation voltage of the directly modulated laser 21 may be set based on the resistance value R of the load resistor 22.

[0029] FIG. 4 is a flowchart showing the operation of the control unit 41 according to the first embodiment. The control unit 41 acquires information on the transmission loss α of an optical signal output from the transmitter 2 and received by the receiver 3 (step S11). The control unit 41 sets the magnitude I of the bias current supplied from the bias current supplier 23 to the directly modulated laser 21 based on the transmission loss α of the optical signal (step S12). The control unit 41 sets the resistance value R of the load resistor 22 based on the set magnitude I of the bias current (step S13). As described above, in the first embodiment, the magnitude I of the bias current supplied to the directly modulated laser 21 and the resistance value R of the load resistor 22 connected to the directly modulated laser 21 are set, so that the electro-optical conversion gain S of the directly modulated laser 21 ２１ can moderate the modulation frequency characteristic of.

[0030] Note that although increasing the resistance value R of the load resistor 22 increases power consumption here, the magnitude I of the bias current decreases, so the overall power consumption of the directly modulated laser 21 can be reduced.

[0031] Hereinafter, a second embodiment will be described. In the second embodiment, in addition to the first embodiment, the control unit 41 acquires information on the temperature T of the direct modulation laser 21. The temperature T of the direct modulation laser 21 is measured, for example, by a temperature sensor disposed around the direct modulation laser 21, and the control unit 41 acquires information on the temperature T from the temperature sensor. The information on the temperature T of the direct modulation laser 21 may be acquired by input to an input device connected to the transmitter 2 by a user.

[0032] The control unit 41 may set the magnitude I of the bias current supplied from the bias current supplier 23 based on the temperature T of the direct modulation laser 21, in addition to the transmission loss α of the optical signal output from the transmitter 2 and received by the receiver 3. The emission intensity of the optical signal output from the direct modulation laser 21 is affected by the temperature T of the direct modulation laser 21.

[0033] For example, information indicating the correspondence between the combination of the transmission loss α of the optical signal, the temperature T of the direct modulation laser 21 and the magnitude I of the bias current is stored in the storage unit 49, and the control unit 41 uses the correspondence between the combination of the transmission loss α of the optical signal, the temperature of the direct modulation laser 21 and the magnitude I of the bias current stored in the storage unit 49 to set the magnitude I of the bias current to a magnitude corresponding to the combination of the transmission loss α of the optical signal and the temperature of the direct modulation laser 21.

[0034] Information indicating the correspondence between the combination of the distance L between the transmitter 2 and the receiver 3, the temperature of the direct modulation laser 21 and the magnitude I of the bias current is stored in the storage unit 49, and the control unit 41 may use the correspondence between the combination of the distance L and the temperature T and the magnitude I of the bias current stored in the storage unit 49 to set the magnitude I of the bias current to a magnitude corresponding to the combination of the distance L and the temperature T.

[0035] Figure 5 is a flowchart showing the operation of the control unit 41 according to the second embodiment. The control unit 41 acquires information on the transmission loss α of the optical signal output from the transmitter 2 and received by the receiver 3, and the temperature T of the direct modulation laser 21 (step S21). Based on the transmission loss α of the optical signal and the temperature T of the direct modulation laser 21, the control unit 41 sets the magnitude I of the bias current supplied from the bias current supplier 23 to the direct modulation laser 21 (step S22). Based on the set magnitude I of the bias current, the control unit 41 sets the resistance value R of the load resistor 22 (step S23).

[0036] In the second embodiment, the magnitude of the bias current I is set based on the transmission loss α of the optical signal and the temperature T of the direct-modulation laser 21. This makes it possible to set the magnitude of the bias current I while taking into account the change in the emission intensity of the output optical signal due to the change in temperature T of the direct-modulation laser 21.

[0037] (Experimental Examples) The following describes experimental examples. Figures 6-8 show the gain S of the electro-to-optical conversion of the direct-modulated laser 21. ２１ This figure shows the result. In the examples shown in Figures 6 to 8, the capacitance C was set to 0.3 pF, referring to Patent Document 1. In the example shown in Figure 6, the resistance R was set to 20 Ω, in the example shown in Figure 7, the resistance R was set to 70 Ω, and in the example shown in Figure 8, the resistance R was set to 100 Ω. In Figures 6 to 8, the gain S is when the load resistor is not directly connected to the modulated laser 21 and there is no RC response (Without RC response). ２１ The gain S when the load resistor is directly connected to the modulated laser 21 and there is an RC response (With RC response) is given by the following: ２１ This shows the gain of the RC response.

[0038] Gain S when the load resistor is not directly connected to the modulated laser 21 and there is no RC response. ２１ The gain S is near 13 GHz. ２１ The voltage changes sharply, and a peak is observed. When the resistance R is 70Ω, the RC cutoff frequency is 7.6GHz, and the gain S ２１A correction is applied, and the sharp change near 13 GHz becomes a relatively gradual change. Similarly, when the resistance R is 70 Ω, the sharp change near 13 GHz becomes a relatively gradual change.

[0039] While embodiments of this invention have been described in detail above with reference to the drawings, the specific configuration is not limited to these embodiments and includes designs and the like that do not depart from the spirit of this invention.

[0040] In the embodiment described above, the control device 4 is located outside the transmitter 2, but it may also be located inside. In other words, the transmitter 2 may include a control unit 41 and a storage unit 49.

[0041] The processing of the control unit 41 in the above-described embodiment may be implemented by a computer using software. In that case, the program for implementing this function may be recorded on a computer-readable recording medium, and the program recorded on this recording medium may be loaded into a computer system and executed. Here, "computer system" includes hardware such as the OS and peripheral devices. Furthermore, "computer-readable recording medium" refers to portable media such as flexible disks, magneto-optical disks, ROMs, CD-ROMs, and storage devices such as hard disks built into a computer system. Moreover, "computer-readable recording medium" may also include those that dynamically hold programs for a short period of time, such as communication lines used when transmitting programs via networks such as the Internet or communication lines such as telephone lines, and those that hold programs for a certain period of time, such as volatile memory inside a computer system that acts as a server or client in such cases. Furthermore, the above-mentioned program may be for implementing a part of the above-mentioned function, or it may be a program that can implement the above-mentioned function in combination with a program already recorded in the computer system, or it may be implemented using a programmable logic device such as an FPGA (Field Programmable Gate Array).

[0042] In the embodiment described above, the storage unit 49 is a cloud, and the control unit 41 may access information by accessing the storage unit 49, which is the cloud.

[0043] 1 Optical communication system, 2 Transmitter, 21 Direct modulation laser, 22 Load resistor, 23 Bias current supplier, 3 Receiver, 4 Control device, 41 Control unit, 49 Memory unit

Claims

1. A control device comprising: a control unit that sets the resistance value of a load resistor connected to a direct-modulation laser based on the magnitude of the bias current supplied to the direct-modulation laser; and 2. The control device according to claim 1, wherein the control unit sets the magnitude of the bias current based on the transmission loss of the optical signal output by the direct-modulated laser and received by the receiver.

3. The control device according to claim 1 or 2, wherein the control unit sets the resistance value of the load resistor based on the correspondence between the magnitude of the bias current and the resistance value of the load resistor, which can slow down the frequency-dependent change in the gain of the electro-optical conversion of the direct-modulated laser.

4. The control device according to claim 1 or 2, wherein the control unit further sets the resistance value of the load resistor based on the temperature of the direct modulation laser.

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