JP2012244073A - Optical transmitter module - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical transmitter module capable of saving power without restricting the number of channels.SOLUTION: In an optical transmitter module 100 for outputting optical signals having a plurality of frequencies, a plurality of laser diodes Ch1 to Ch4 are connected to each other in serial. A first current adjustment circuit 150 is connected to an electric power source 10 connected to anode sides of a plurality of laser diodes (Ch1 to Ch4), and adjusts current from the electric power source 10. A second current adjustment circuit 195 is connected to a plurality of laser diodes Ch1 to Ch4 respectively in parallel, and adjusts current flowing each of a plurality of laser diodes Ch1 to Ch4 among current adjusted by the first current adjustment circuit 150.

Description

  The present invention relates to an optical transmission module.

  In recent years, various techniques for achieving both reduction in size of an optical transceiver module used for optical transmission and an increase in data transmission capacity have been studied. For example, Patent Document 1 describes an optical transmission module that reduces power consumption by simple mounting by connecting a differential current switch to both ends of a laser diode.

  As a technique for increasing the amount of data transmission, a WDM (Wavelength Division Multiplexing) technique for multiplexing and transmitting a plurality of optical channels having different wavelengths is known. For example, 40 GBASE-LR4 that realizes a transmission rate of 40 Gbit / s and 100 GBASE-LR4 that realizes a transmission rate of 100 Gbit / s in one optical transmission / reception module by multiplexing four optical channels of wavelengths around 1300 nm. Optical transmission / reception modules (CFP: 100 Gbit / s and 40 Gbit / s Form-factor Pluggable) are known.

  In order to multiplex an optical channel, a power source is required for each laser diode, which causes a problem of increasing power consumption. For this reason, a technique is known in which, by connecting two laser diodes in series (cascade), the extra power other than the power necessary for causing the laser diode to emit light out of the power consumed by the optical transmission module is known. (Patent Document 2).

JP 2004-193489 A JP 2006-246390 A

  However, the technique of Patent Document 2 is based on the premise that two laser diodes are connected in series, and the two laser diodes constitute one structural unit, so the number of laser diodes must be an even number. That is, the technique of Patent Document 2 has a problem that the number of channels is limited in order to reduce power consumption in the optical transmission module.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide an optical transmission module capable of saving power without limiting the number of channels.

  In order to solve the above problems, an optical transmission module according to the present invention includes an optical transmission module that outputs optical signals having a plurality of wavelengths, and a plurality of laser diodes connected in series, and anodes of the plurality of laser diodes A first current adjustment circuit that is connected in series to a power supply connected to the side and adjusts a current from the power supply, and is connected in parallel to each of the plurality of laser diodes, and is adjusted by the first current adjustment circuit And a second current adjustment circuit for adjusting a current flowing through each of the plurality of laser diodes.

  Further, according to one aspect of the present invention, the optical transmission module further includes an inductor connected to both ends of each of the plurality of laser diodes, and the inductor is connected in parallel to the second current adjustment circuit. It is characterized by that.

  Further, according to one aspect of the present invention, the optical transmission module includes a modulation circuit connected in parallel to each of the plurality of laser diodes, and a connection between the modulation circuit and each of the plurality of laser diodes. And a capacitor.

  Further, according to one aspect of the present invention, the optical transmission module includes a modulation circuit connected in parallel to each of the plurality of laser diodes, and a connection between the modulation circuit and each of the plurality of laser diodes. And a resistor.

  According to the present invention, it is possible to provide an optical transmission module capable of saving power without limiting the number of channels.

It is a block diagram which shows an example of the optical transmission / reception module using WDM. It is a figure which shows an example of a structure of an optical transmission module. It is a wave form diagram which shows a mode that an electrical signal is modulated. It is a figure which shows an example of a structure of the optical transmission module in a modification.

[Embodiment]
DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments according to the present invention will be described in detail based on the drawings.

[Overall configuration of optical transceiver module]
FIG. 1 is a block diagram showing an example of an optical transceiver module using WDM. As shown in FIG. 1, the optical transceiver module 1 includes an optical transmitter module 100 that outputs optical signals having a plurality of wavelengths, and an optical receiver module 200 that receives optical signals having a plurality of wavelengths. . For example, n (n is a natural number; for example, n = 4 or 10) ch electrical signals are input to the optical transmission module 100.

In the optical transmission module 100, for example, a plurality of electrical signals (nch electrical signals) are collected by the multiplexer 110 and one signal is output. The output electrical signals are transmitted by kSA (k is a positive number, for example, k = 25) Gbit / s by TOSA (Transmitter Optical Sub-Assembly) 131-134 via laser drivers 121-124. Signal conversion is performed. The TOSAs 131 to 134 include, for example, laser diodes for emitting light having different wavelengths λ _{1 to} λ ₄ . The optical signals converted by each of the TOSAs 131 to 134 are multiplexed by the optical multiplexer 140 and transmitted.

On the other hand, the optical receiving module 200 receives multiplexed optical signals. The optical signal is demultiplexed into optical signals having wavelengths λ ₁ to λ _{4 by} the optical demultiplexer 210. The demultiplexed optical signals are subjected to optical-electrical signal conversion by ROSA (Receiver Optical Sub-Assembly) 221 to 223, respectively. The converted electrical signal is distributed to nch electrical signals by the demultiplexer 230.

  Note that the TOSA 131 to 134 and the ROSA 221 to 223 may be provided on different substrates, respectively, or may be integrated. For example, by integrating elements that perform electrical-optical signal conversion or optical-electrical signal conversion, the configuration of the optical transmission / reception module 1 can be achieved while achieving both an increase in data transmission capacity and a reduction in the size of the optical transmission / reception module 1. Can be simplified.

[Detailed configuration of optical transmission module]
FIG. 2 is a diagram illustrating an example of the configuration of the optical transmission module 100. Here, a circuit for causing a laser diode included in the TOSA 131 to 134 to emit light in the optical transmission module 100 will be described. In the present embodiment, the case where the circuit is configured as a direct modulation type and the number of optical channels used by the optical transceiver module 1 is four will be described. However, the configuration of the optical transceiver module 1 is limited to this. Absent.

As shown in FIG. 2, the optical transmission module 100 includes a plurality of laser diodes Ch1 to Ch4 connected in series. In the present embodiment, since the number of optical channels is four, four laser diodes Ch1 to Ch4 having different wavelengths are arranged. That is, the number of laser diodes corresponding to the number of optical channels is arranged. For example, the laser diodes Ch1 to Ch4 emit light having wavelengths λ _{1 to} λ ₄ , respectively.

  The cathode (cathode) of one laser diode among the laser diodes Ch1 to Ch4 is connected to the anode (anode) of another laser diode, and the anode and the cathode are connected in series. That is, the laser diodes Ch1 to Ch4 are connected in series so that the forward biases of the laser diodes Ch1 to Ch4 are in the same direction.

The optical transmission module 100 is connected in series to a power source 10 connected to the anode side of the plurality of laser diodes Ch1 to Ch4, and adjusts the current (total laser bias current I ₀ ) from the power source 10. 150 (first current adjustment circuit). In other words, among the plurality of laser diodes Ch1 to Ch4, the power source 10 is connected to the anode side of the laser diode whose anode is not connected to the cathode of another laser diode. The overall current adjustment circuit 150 is connected in series with the laser diodes Ch1 to Ch4. The overall laser bias current I ₀ is a current that flows from the power supply 10 to the whole of the plurality of laser diodes Ch1 to Ch4.

  For example, the total current adjusting circuit 150 is connected in series to the anode at one end of the laser diodes Ch1 to Ch4 connected in series (for example, the anode of the laser diode Ch1. That is, the anode on the side to which no other laser diode is connected). Connected. Further, for example, the cathodes at the other ends of the laser diodes Ch1 to Ch4 connected in series (for example, the cathode of the laser diode Ch4. That is, the cathode on the side where no other laser diode is connected) are connected to the ground GND. .

  The configuration of the optical transmission module 100 is not limited to the example of FIG. In addition, for example, the entire current adjustment circuit 150 may be connected to the ground GND side instead of the power supply 10 side. That is, the entire current adjustment circuit 150 may be connected to the cathode side instead of the anode side of the laser diodes Ch1 to Ch4. Therefore, the entire current adjustment circuit 150 may be disposed between the power supply 10 and the laser diodes Ch1 to Ch4, or may be disposed between the laser diodes Ch1 to Ch4 and the ground GND.

  The optical transmission module 100 includes a modulation circuit (for example, laser drivers 121 to 124) connected in parallel to each of the plurality of laser diodes Ch1 to Ch4.

FIG. 3 is a waveform diagram showing how an electric signal is modulated. As shown in FIG. 3, by adding the amplitude I _mod of the input waveforms of the laser drivers 121 to 124 and the constant currents of the laser diodes Ch1 to Ch4 (currents after the constant current start times t _{1 to} t ₄ ), A modulated waveform in each optical channel can be obtained.

  Returning to FIG. 2, in the present embodiment, a case where capacitors 161a to 164b and resistors 171a to 174b are connected in series between the laser diodes Ch1 to Ch4 and the laser drivers 121 to 124 will be described. . In other words, each of the anodes and cathodes of the laser diodes Ch1 to Ch4 is connected to the modulation circuit via capacitors 161a to 164b and resistors 171a to 174b.

  Since the capacitors 161a to 164b are connected between the laser diodes Ch1 to Ch4 and the laser drivers 121 to 124, voltage changes between the anode and the cathode of the laser diodes Ch1 to Ch4 are absorbed by the capacitors 161a to 164b. Therefore, it is possible to prevent an adverse effect on the output terminals of the laser drivers 121 to 124 due to the voltage change (for example, insufficient driving voltage).

  Further, since the resistors 171a to 174b are connected between the laser diodes Ch1 to Ch4 and the laser drivers 121 to 124, the resistors 171a to 174b serve as damping or termination, thereby suppressing current reflection and modulation. The shape of the optical waveform thus made can be adjusted.

  The optical transmission module 100 includes inductors 181a to 184b connected to both ends of each of the plurality of laser diodes Ch1 to Ch4. That is, the inductors 181a to 184b are disposed at both the anode and cathode nodes of the laser diodes Ch1 to Ch4.

  The inductors 181a to 184b do not vibrate the AC signals input from the laser drivers 121 to 124, so that signals to optical channels other than the laser diodes Ch1 to Ch4 that are directly connected to the inductors 181a to 184b. It is possible to suppress leakage and signal leakage to a circuit through which a bypass current of its own optical channel flows.

The optical transmission module 100 is connected in parallel to each of the plurality of laser diodes Ch1 to Ch4, and the plurality of laser diodes Ch1 to Ch4 out of the current (total laser bias current I ₀ ) adjusted by the overall current adjustment circuit 150. Transistors 191 to 194 (second current adjusting circuit) for adjusting the current flowing through each of the transistors. The inductors 181a to 184b are connected in parallel to the transistors 191 to 194.

Each of transistors 191 to 194 is connected in parallel with each of laser diodes Ch1 to Ch4. The light output control circuit 195 connected to the transistors 191 to 194 is used to control the bypass currents i _{1 to} i ₄ flowing through the transistors 191 to 194. For example, the light output control circuit 195 controls the bypass currents i _{1 to} i ₄ by controlling the voltage between the emitters and the bases of the transistors 191 to 194.

In the optical transmission module 100 according to the present embodiment, the bypass currents i _{1 to} i ₄ flowing through the transistors 191 to 194 are controlled by the optical output control circuit 195, whereby the lasers flowing to the laser diodes Ch1 to Ch4 corresponding to the respective optical channels. The bias currents I _{1 to} I ₄ can be adjusted. For example, the laser bias currents I _{1 to} I ₄ and the bypass currents i _{1 to} i ₄ have the relationship of the following formula 1.
I ₀ = I ₁ + i ₁ = I ₂ + i ₂ = I ₃ + i ₃ = I ₄ + i ₄ (Equation 1)

[Light output setting method]
Next, a method for adjusting the laser bias currents I _{1 to} I ₄ will be described. In order for the optical transceiver module 1 to perform accurate optical communication, the optical output of the laser diodes Ch1 to Ch4 is set within a predetermined range (for example, −4.3 dbm to +4.5 dbm) regulated in advance by various standards. Need to be done.

  Since the laser diodes Ch1 to Ch4 have individual characteristics, the light emission intensity (that is, the light emission efficiency) with respect to the current flowing through the laser diodes Ch1 to Ch4 varies. That is, even if the same current is supplied to the laser diodes Ch1 to Ch4, some of them emit light brightly and some emit light darkly. Therefore, the current flowing through the laser diodes Ch1 to Ch4 is adjusted in accordance with the individual characteristics of the laser diodes Ch1 to Ch4. The adjustment described below may be performed by an engineer or may be performed by software processing using a microcomputer.

First, an overall adjustment method of the laser bias currents I _{1 to} I ₄ will be described.

Under the control of the light output control circuit 195, the base-emitter voltages of the transistors 191 to 194 are set to zero, and the transistors 191 to 194 are set to an off state. Since the transistors 191 to 194 are off, the bypass currents i _{1 to} i ₄ are zero. Therefore, the entire laser bias current I ₀ and the laser bias currents I _{1 to} I ₄ flowing through the laser diodes Ch1 to Ch4 are all set to the same value.

When the current is started to be applied to the overall current adjusting circuit 150 with the transistors 191 to 194 turned off as described above, the overall laser bias current I ₀ starts to flow through the laser diodes Ch1 to Ch4. In this state, technician or microcomputer, by increasing the output of the whole current adjusting circuit 150 gradually, the entire laser bias current I ₀ is increased gradually.

When the laser bias currents I _{1 to} I ₄ (that is, the same value as the total laser bias current I ₀ ) flowing through the laser diodes Ch _{1 to} Ch ₄ exceed the threshold current, the laser diodes Ch 1 to Ch 4 start to emit light. As described above, since there are individual differences in the characteristics of the laser diodes Ch1 to Ch4, the threshold current value also varies.

In the present embodiment, when the light output of the laser diode (for example, laser diode Ch1) having the lowest light emission efficiency among the laser diodes Ch1 to Ch4 is equal to or higher than the lower limit value (for example, −4.3 dBm) of the specified range. The increase in the output of the overall current adjustment circuit 150 is stopped. In other words, the entire laser bias current I ₀ is fixed.

The light emission efficiency is the degree of light output with respect to the laser bias currents I _{1 to} I ₄ . If the light output of the laser diode with the lowest light emission efficiency exceeds the lower limit value of the specified range, the light output of another laser diode with better light emission efficiency than the laser diode is naturally lower than the lower limit value of the specified range. It is getting bigger. Whether or not the optical output exceeds the lower limit value of the specified range is detected by, for example, a tester connected to the optical transmission module 100.

By thus setting the total current regulating circuit 150 is performed, in the least total laser bias current I _0, can be larger than the lower limit of the specified range the light output of all the laser diodes CH1 to CH4. In order of characteristics due to aging or the like of the laser diode CH1 to CH4, the extent no problem in the power consumption, the entire laser bias current I ₀ any larger amount than the current value of the above, the whole current adjusting circuit 150 You may set it.

Next, individual adjustment methods of the laser bias currents I _{1 to} I ₄ will be described.

  When the overall current adjustment circuit 150 is set as described above, the light output of laser diodes other than the laser diode having the lowest light emission efficiency may exceed the upper limit value (for example, 4.5 dbm) of the standard range. In this case, the transistors 191 to 194 are controlled by the light output control circuit 195 so that the light output exceeding the upper limit falls within the standard range.

The optical output control circuit 195 controls a transistor (for example, the transistor 194) connected in parallel to the laser diodes Ch1 to Ch4 (for example, the laser diode Ch4) of the optical channel that exceeds the upper limit value among the transistors 191 to 194. To do. The light output control circuit 195 can increase or decrease the bypass currents i _{1 to} i ₄ by controlling the voltage between the base and the emitter of the transistors 191 to 194.

As shown in equation (1), the light output control circuit 195 controls the transistors 191 to 194 to decrease the laser bias currents I _{1 to} I ₄ as the bypass currents i _{1 to} i ₄ increase. Can do. When the laser bias currents I _{1 to} I ₄ are decreased, the light outputs of the laser diodes Ch _{1 to} Ch ₄ are reduced, so that the light output exceeding the upper limit value of the standard range can be set within the standard range.

As described above, according to the optical transceiver module 1 of the present embodiment, the overall current adjustment circuit 150 roughly adjusts the laser bias currents I _{1 to} I ₄ by adjusting the overall laser bias current I ₀ , The output control circuit 195 adjusts the bypass currents i _{1 to} i ₄ , so that the laser bias currents I _{1 to} I ₄ can be finely adjusted. Further, since the laser diodes Ch1 to Ch4 are connected in series, the laser diodes Ch1 to Ch4 can be mounted without limitation on the number of channels.

  Further, in the configuration in which the power supplies are individually connected to the laser diodes Ch1 to Ch4 as in the prior art, a current adjustment circuit is required for each of the laser diodes Ch1 to Ch4. Since the current adjustment circuit is integrated into one, the necessary voltage can be kept to a minimum, and the power can be saved.

  Specifically, for example, when a power supply of 3.3 V is connected to each of the four laser diodes, if the current flowing through each laser diode is 0.2 (A), 3.3 (V) * 0 .2 (A) * 4 = 2.64 (W) of power is consumed. On the other hand, in the present embodiment, when the voltage applied to each laser diode is 1.5 (V) and the current flowing through each laser diode is 0.25 (A) (for example, the laser diode having the lowest luminous efficiency flows). Current is 0.25 (A), and the current flowing through the laser diode with the best luminous efficiency is 0.2 (A).) 1.5 (V) * 0.25 (A) * 4 = The power consumption can be reduced to 1.5 (W).

Note that the same processing as described above is performed when laser diodes Ch1 to Ch4 other than the laser diodes Ch1 to Ch4 that output light exceeding the upper limit value of the standard range are adjusted. That is, by the light output control circuit 195 controls the transistor 191 to 194, to change the bypass current _i 1 through i _4, it is possible to control the laser bias current _I 1 ~I ₄ flowing through the laser diode Ch1~Ch4 . For example, the laser bias currents I _{1 to} I ₄ may be adjusted so that the optical outputs of all the laser diodes Ch 1 to Ch ₄ approach the lower limit value of the standard range.

[Light output cutoff function]
Next, the light output cutoff function of the laser diodes Ch1 to Ch4 will be described. A general optical transceiver module is required to have an optical output cutoff function for all optical channels mainly for the purpose of safety and the like. In addition, for the purpose of various tests such as individual light emission tests of the laser diodes Ch1 to Ch4, it is also required to have an individual light output cutoff function for each of the laser diodes Ch1 to Ch4.

  For example, the current flowing through each of the laser diodes Ch1 to Ch4 can be reduced to zero by turning off the outputs of the laser drivers 121 to 124 or turning off the overall current adjusting circuit 150. The optical output cutoff function of the channel can be realized. However, in this method, since the current flowing through all the laser diodes Ch1 to Ch4 becomes zero, the light output of the individual laser diodes Ch1 to Ch4 cannot be cut off.

  In the optical transmission module 100 of the present embodiment, the optical output control circuit 195 controls the transistors 191 to 194, whereby the optical output of the individual laser diodes Ch1 to Ch4 can be cut off. Here, as an example, the case where only the laser diode Ch1 is turned off will be described as an example.

First, the output of the laser driver 121 corresponding to the laser diode Ch1 to be turned off is turned off. Then, the light output control circuit 195 turns on the transistor 191 corresponding to the laser diode Ch1 completely. Thus, the transistor 191 is therefore in a state of being substantially short-circuit, and the laser bias current I ₁ of the laser diode Ch1 to zero, can be any whole laser bias current I ₀ and the bypass current i _1.

  That is, the current flowing through the laser diode Ch1 can be made zero, and the light output cutoff function of the laser diode Ch1 can be realized. Similarly, with respect to the other laser diodes, the individual light output cutoff function can be realized by setting the transistors connected in parallel to the laser diodes whose light output is turned off to be completely turned on.

[Modification]
The present invention is not limited to the embodiment described above, and can be appropriately changed without departing from the spirit of the present invention. For example, the configuration of the optical transmission module 100 is not limited to the example of the first embodiment, and may be realized by using another modulator.

  FIG. 4 is a diagram illustrating an example of a configuration of the optical transmission module 100 according to the modification. In the example illustrated in FIG. 4, a case where the optical transmission module 100 is realized by an electroabsorption modulator will be described. In the optical transmission module 100 of the modified example, each of the laser diodes Ch1 to Ch4 is not directly connected to the laser drivers 121 to 124. Therefore, the current flowing through the laser diodes Ch1 to Ch4 is only a direct current component and is a modulation signal component. Does not flow. Each of the laser diodes Ch1 to Ch4 emits light with steady output light.

  The electroabsorption modulators 301 to 304 generate an optical signal having a modulation component by partially absorbing the steady output light according to the modulated electric signal input to the electroabsorption modulators 301 to 304. It is an element to do.

The setting method of the overall current adjustment circuit 150 in this modification is the same as that of the embodiment. In other words, the overall current adjustment circuit 150 that controls the overall bias current I ₀ is set so that the light output by the laser bias currents I _{1 to} I ₄ flowing through the laser diodes Ch _{1 to} Ch ₄ exceeds the lower limit value of the predetermined range.

Similarly to the embodiment, the transistors 191 to 194 are used to adjust the laser bias currents I _{1 to} I ₄ flowing through the laser diodes Ch _{1 to} Ch ₄ to appropriate values under the control of the light output control circuit 195. The

  In the present modification, as described above, only a direct current flows through each of the laser diodes Ch1 to Ch4, so that no variable current is required. Therefore, as compared with the configuration of the embodiment shown in FIG. 2, the path of the modulation signal is not connected to each of the laser diodes Ch1 to Ch4. In addition, the inductors connected to the anodes and cathodes of the laser diodes are not necessary so as not to affect other circuits of the modulation signal or to suppress the deterioration of the modulation signal itself.

  Note that the optical transmission module 100 may be realized by various modulators in addition to the modulators of the embodiment and the above-described modified example. For example, the optical transmission module 100 may be configured by a Mach-Zehnder modulator. It may be realized.

  As the overall current adjustment circuit 150, various known current adjustment circuits can be applied. For example, the entire current adjustment circuit 150 may be configured to include a transistor and a three-terminal regulator. Similarly, various known transistor control circuits can be applied as the light output control circuit 195.

  DESCRIPTION OF SYMBOLS 1 Optical transmission / reception module, 10 power supplies, 100 optical transmission module, 110 multiplexer, 121,122,123,124 Laser driver, 131,132,133,134 TOSA, 140 Optical multiplexer, 150 Whole current adjustment circuit, 161a, 161b, 162a, 162b, 163a, 163b, 164a, 164b capacitors, 171a, 171b, 172a, 172b, 173a, 173b, 174a, 174b resistors, 181a, 181b, 182a, 182b, 183a, 183b, 184a, 184b inductors, 191, 194b , 193, 194 transistor, 195 optical output control circuit, 200 optical receiver module, 210 optical demultiplexer, 221, 222, 223, 224 ROSA, 230 demultiplexer, 301 , 302, 303, 304 Electroabsorption modulator

Claims (4)

In an optical transmission module that outputs optical signals of a plurality of wavelengths,
A plurality of laser diodes connected in series;
A first current adjusting circuit that is connected in series to a power source connected to the anode side of the plurality of laser diodes and adjusts a current from the power source;
A second current adjustment circuit that is connected in parallel to each of the plurality of laser diodes and that adjusts a current flowing through each of the plurality of laser diodes out of the current adjusted by the first current adjustment circuit;
An optical transmission module comprising: The optical transmission module includes:
An inductor connected to both ends of each of the plurality of laser diodes;
The inductor is connected in parallel to the second current regulation circuit;
The optical transmission module according to claim 1. The optical transmission module includes:
A modulation circuit connected in parallel to each of the plurality of laser diodes;
A capacitor connected between the modulation circuit and each of the plurality of laser diodes;
The optical transmission module according to claim 1, further comprising: The optical transmission module includes:
A modulation circuit connected in parallel to each of the plurality of laser diodes;
A resistor connected between the modulation circuit and each of the plurality of laser diodes;
The optical transmission module according to claim 1, further comprising:

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