JP2007329212A - Optical transmitter, and optical transmitting method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical transmitter which can suppress interference to an adjacent wavelength on short wave side even if, when the power is turned off, a temperature control circuit is not operated and the operation of a shutter is delayed, and to provide an optical transmitting method. <P>SOLUTION: When the power supply voltage gets lower than some level, it is detected and the supply of forward bias current is promptly intercepted. A power supply voltage detector 10 detects the drop of voltage in power supply 1, and a switch control unit 11 turns off an intercept switch 12 so that the forward bias current is not supplied to an LD3. Since the switch control circuit is configurated by logic only, it can operate more quickly than an analog constant current source 2 and a shutter control circuit 9, and the optical output of shifted wavelength hardly goes out to the outside of a laser diode module 7. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an optical transmitter and an optical transmission method for supplying a forward bias current to a laser diode by a constant current source so that the optical output becomes constant under a condition where the wavelength is controlled to be constant.

  In order to make the oscillation wavelength of the laser diode constant, it is necessary to keep the temperature of the active layer of the laser constant. The fluctuation factors of the active layer temperature are a change in the ambient temperature of the laser diode and a fluctuation in the laser forward bias current. By mounting the laser diode and the thermistor on the same Peltier element and feeding back the voltage of the thermistor, the temperature of the laser diode can be kept constant even if the ambient temperature and the forward bias current change. Further, the wavelength can be controlled with higher accuracy by feeding back the photodiode voltage after passing through the etalon filter mounted in the laser diode module.

  On the other hand, the laser diode can keep the light output constant by feeding back the voltage of the photodiode. Under this condition, when the laser diode is aged, the forward bias current is increased in order to keep the light output constant. This increase in forward bias current results in an increase in the active layer temperature and shifts the wavelength to the longer wavelength side, but this wavelength variation cannot be corrected by temperature control using the thermistor. Conventionally, there are techniques described in Japanese Patent Application Laid-Open No. 11-163462 (Patent Document 1) and US Pat. No. 6,934,063 (Patent Document 2) as a countermeasure for such a wavelength variation.

JP 11-163462 A US Pat. No. 6934063

  Patent Document 1 discloses an optical transmitter that corrects a temperature control target value corresponding to a wavelength fluctuation due to a fluctuation in a forward bias current in order to correct the wavelength fluctuation described above. The temperature control using such a thermistor, the transmitted light of the etalon filter is fed back, the fluctuation of the forward bias current is converted into the wavelength, and the temperature target value is changed as in the case of laser aging. It is effective against slow fluctuations. However, since the time constant of this temperature control is as slow as several seconds, there is a problem that fluctuations with a faster time constant, that is, wavelength fluctuations due to a sudden increase or decrease in forward bias current cannot be corrected.

  Further, in Patent Document 2, an optical transmission that suppresses the influence of wavelength fluctuation by a method in which a shutter is provided inside the laser diode module and the shutter is opened after the wavelength is sufficiently stabilized against an increase in forward bias current. A vessel is disclosed. However, with respect to the decrease in the forward bias current when the power of the optical transmitter is turned off, there is a possibility that the wavelength variation cannot be suppressed by the shutter function. In other words, due to the time constant between the forward bias current supply circuit of the laser and the circuit that controls the shutter, the wavelength toward the short wavelength side when the forward bias current slowly decreases during the shutter opening time. Variation will be observed. Since the power is turned off, the temperature control circuit is not operating, and even if it is operating, this wavelength variation cannot be corrected with a time constant of about several seconds.

  An object of the present invention is to provide an optical transmitter and an optical transmission method that suppress the influence of wavelength fluctuations even when the temperature control circuit is not operating and the shutter operation is sufficiently slow when the power is turned off. And

  In order to solve the above-described problems, the optical transmitter of the present invention detects that the power supply voltage has fallen below a certain level, and promptly shuts off the forward bias current supply circuit.

  ADVANTAGE OF THE INVENTION According to this invention, when the power supply is turned off, the optical transmitter and the optical transmission method which suppressed the interference to the adjacent wavelength of a short wavelength side are realizable.

  Hereinafter, the present invention will be described with reference to examples describing embodiments of the present invention.

  First, an optical transmitter according to an embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a block diagram for explaining the basic configuration of a laser diode of an optical transmitter and its temperature control and optical output control. FIG. 2 is a block diagram of the laser diode of the optical transmitter and its temperature control and optical output control for explaining the first embodiment of the present invention.

  In the block diagram shown in FIG. 1, a forward bias current is supplied to a laser diode (hereinafter LD: Laser Diode) 3 by a constant current source 2. In order to keep the light output constant, the photodiode and the control circuit are collectively expressed as a constant current source 2. By monitoring the temperature of the LD 3 with the thermistor 5 and supplying a heating or cooling current to the Peltier element 6 with the temperature control circuit 8, the temperature of the LD 3 is kept constant. Although the temperature control circuit and the illustration are omitted, if the shutter 4 is opened by the shutter control circuit 9 in a state where the wavelength is controlled with high accuracy by the etalon filter, the photodiode for detecting the transmitted light, and the control circuit, Light is emitted to the outside of the laser diode module 7.

  In the block diagram shown in FIG. 2, the description of the part described in FIG. 1 is omitted. In FIG. 2, a control signal is sent to the switch control unit 11 according to the state of the power supply voltage detection unit 10 that detects the voltage of the power supply 1, and the cutoff switch 12 of the forward bias current supply circuit is switched. That is, in the normal operation state, the cutoff switch 12 is in an ON state, and a forward bias current is supplied to the LD 3. However, when the voltage of the power supply 1 decreases and exceeds the threshold value of the power supply voltage detection unit 10, the switch control unit 11. Quickly turns off the shutoff switch 12.

  In FIG. 1, when the voltage of the power source 1 is lowered, the constant current source 2 and the shutter operation circuit 9 are turned off at the respective time constants, so the constant current source 2 supplies the LD 3 before the shutter 4 is closed. When the current gradually decreases, light whose wavelength is shifted to the short wavelength side is emitted to the outside of the laser diode module 7.

  On the other hand, in FIG. 2, if the power supply voltage detection unit 10 detects that the voltage of the power supply 1 has decreased and the switch control unit 11 turns off the cutoff switch 12, the forward bias current is not supplied to the LD 3. Since this switch control circuit can be composed only of logic, it can operate sufficiently faster than the analog constant current source 2 and the shutter control circuit 9, and the optical output whose wavelength is shifted does not go out of the laser diode module 7. .

  Another example of the optical transmitter according to the embodiment of the present invention will be described with reference to FIG. Here, FIG. 3 is a block diagram of the laser diode of the optical transmitter and its temperature control and optical output control for explaining the second embodiment of the present invention. In the block diagram shown in FIG. 3, detailed description of the parts described in FIG. 1 or FIG. 2 is omitted.

  In the optical transmitter of this embodiment, the power supply voltage detection unit 10 detects the power supply voltage of the power supply 1 and the switch control unit 11 switches the forward bias current supply circuit bypass switch 13. That is, in the normal operation state, the bypass switch 13 is in an OFF state, and a forward bias current is supplied to the LD 3. However, when the voltage of the power source 1 drops and exceeds the threshold value of the power source voltage detector 10, the switch controller 11. Quickly turns on the bypass switch 13. Since the forward bias current flows to the GND via the bypass switch 13, the forward bias current is not supplied to the LD 3, and the optical output whose wavelength is shifted does not come out of the laser diode module 7.

  As shown in the first and second embodiments, the effect of quickly turning off the forward bias current of the LD 3 is not only shortening the wavelength variation time determined by the time constant of the circuit. By quickly turning off the forward bias current, the FM modulation efficiency of the laser is lowered, so dλ / dI (the wavelength fluctuation relative to the bias current fluctuation) is lowered. Therefore, it can be explained that it is acting in the direction of suppressing the wavelength fluctuation.

  Another example of the optical transmitter according to the embodiment of the present invention will be described with reference to FIG. FIG. 4 is a block diagram of an optical transmitter for explaining the third embodiment of the present invention. The optical transmitter of the present embodiment is obtained by adding other circuit blocks of the optical transmitter to the block diagram of the laser diode of the first embodiment and its temperature control and optical output control. The detailed description of the part described in the above is omitted.

  The optical transmitter 100 in FIG. 4 converts a signal processing circuit 16 that multiplexes 16 pairs of 622 MHz input signals, and converts a 10 Gbit / s signal multiplexed by the signal processing circuit 16 into a drive signal for the external modulator 14. And a laser diode module 7, a temperature and light output control circuit of the laser diode module 7, and optical components such as a lens (not shown).

  The optical transmitter according to the present embodiment is short-circuited by quickly turning off the forward bias current cutoff switch 12 of the LD 3 by the switch control unit 11 when the power supply voltage detection unit 10 detects a decrease in the power supply voltage. The light whose wavelength is shifted to the wavelength side does not come out of the optical transmitter 100.

  As obvious from the first and second embodiments, even if the bypass bias 13 in the block diagram of FIG. 3 is used instead of the cutoff switch 12, the supply of the forward bias current to the LD 3 is cut off. Good. In this embodiment, a modulator is provided outside the LD, but the same applies to a modulator integrated laser diode in which the LD and the modulator are integrated.

  An example of an optical transceiver according to another embodiment of the present invention will be described with reference to FIG. Here, FIG. 5 is a block diagram of an optical transceiver for explaining the fourth embodiment of the present invention. The optical transceiver according to the present embodiment is obtained by adding another circuit block of the optical receiver to the block diagram of the optical transmitter according to the third embodiment. The detailed explanation is omitted.

  The optical transceiver 200 of FIG. 5 converts a signal processing circuit 16 that multiplexes 16 pairs of 622 MHz input signals, and converts a 10 Gbit / s signal multiplexed by the signal processing circuit 16 into a drive signal for the external modulator 14. Modulator driving circuit 15, laser diode module 7, temperature and light output control circuit of laser diode module 7, and light receiving element 17 that converts an optical signal of 10 Gbit / s transmitted from the transmission path into an electrical signal, The amplifier circuit 18 amplifies the converted electric signal, the signal processing circuit 19 separates the amplified signal into 16 pairs of 622 MHz signals, and an optical component such as a lens (not shown).

  The optical transceiver according to the present embodiment is short-circuited by quickly turning off the forward bias current cutoff switch 12 of the LD 3 by the switch control unit 11 when the power supply voltage detection unit 10 detects a decrease in the power supply voltage. The light whose wavelength is shifted to the wavelength side does not come out of the optical transmitter 100.

  As obvious from the first and second embodiments, even if the bypass bias 13 in the block diagram of FIG. 3 is used instead of the cutoff switch 12, the supply of the forward bias current to the LD 3 is cut off. Good. In this embodiment, a modulator is provided outside the LD, but the same applies to a modulator integrated laser diode in which the LD and the modulator are integrated.

  Although the shutters are illustrated in the first to fourth embodiments, it goes without saying that the necessity of the present invention is further increased in the case where there is no shutter. Also, the present invention is naturally effective for a circuit that does not include a temperature control circuit and an etalon filter, but the wavelength control under discussion is premised on temperature control conditions, and is not shown.

  The effect of the present invention will be specifically described with reference to FIGS. 6 and 7 using the optical transceiver shown in the fourth embodiment. FIG. 6 is a block diagram of a measurement system for confirming the effect of the present invention using the optical transceiver according to the fourth embodiment of the present invention. FIG. 7 is an example of an experimental result obtained by the optical spectrum analyzer shown in the block diagram of FIG.

  In the block diagram shown in FIG. 6, an electrical signal of 10 Gbit / s is output from the pulse pattern generator 20 and input to the electrical module 22 mounted on the jig 24. This electric signal is input to a reference optical transceiver (abbreviated as REF.TRV) 300 through the jig 24. REF. A signal modulated at 10 Gbit / s is output from the TRV 300 to the optical fiber.

  The center wavelength at this time is set to 1559.794 nm. This optical output signal is divided into two by a splitter 23, one of which passes through an EDFA 26, an attenuator 27, a photocoupler 30, and a filter 28, and REF. It is input to the receiver of TRV300. This signal is input to the electric jig 22 as an electric signal through the jig 24, and a bit error rate (abbreviated as BER) is measured by the error detector 21 as an output of the electric module 22.

  On the other hand, the other optical signal divided by the splitter 23 is input to an optical transceiver (abbreviated as DUT) 400 via the attenuator 25. The electric signal output from the DUT 400 is turned back on the jig 29 and enters the DUT 400 again. This signal is output from the transmitter of the DUT 400 as an optical signal having a center wavelength of 1560.194 nm, and is superimposed on the optical signal of REF.TRV300 via the photocoupler 30. The spectrum of this optical signal was observed with an optical spectrum analyzer 31.

  The purpose of performing the measurement of FIG. 6 is to check the error by the error detector 21 when there is interference between two types of wavelength components having a 400 pm wavelength difference corresponding to a 50 GHz grid. Wavelength meters and optical spectrum analyzers have a slow data sampling period, so there is a possibility that wavelength interference cannot be monitored in a very short time. On the other hand, since the measurement system of FIG. 6 is an error count for transmission at 10 Gbit / s, wavelength interference in the nanosecond order can be monitored.

  As a result, when the optical transceiver according to Example 4 of the present invention was used as the DUT 400, transmission errors when the power was turned off were not counted. On the other hand, when an optical transceiver modified so that the cutoff switch 12 is always ON among the optical transceivers of the fourth embodiment of the present invention is used as the DUT 400, a transmission error of 1000 to 10000 counts was observed. .

  This error count at 10 Gbit / s corresponds to the order of microseconds, and is a level of wavelength interference that cannot be observed with a wavelength meter or an optical spectrum analyzer. Of course, in the wavelength tunable optical transceiver, interference with adjacent wavelengths is not allowed, and the effect of the present invention was shown.

  In the waveform of the optical spectrum analyzer 31 shown in FIG. 7, the locus of the wavelength fluctuation described above could not be confirmed. However, as an interpretation of the phenomenon, the effect of the present invention is that the movement of the spectrum when the power is turned off is in the direction of arrow A. Instead, it can be explained as moving in the direction of arrow B.

It is a block diagram explaining the basic composition of the laser diode of an optical transmitter, its temperature control, and optical output control. 1 is a block diagram of a laser diode of an optical transmitter, temperature control, and optical output control for explaining an embodiment 1 of the present invention. FIG. FIG. 5 is a block diagram of a laser diode of an optical transmitter, temperature control, and optical output control for explaining an embodiment 2 of the present invention. It is a block diagram of the optical transmitter explaining Example 3 of this invention. It is a block diagram of the optical transmitter / receiver explaining Example 4 of this invention. It is a block diagram which shows the measurement system of the experiment which confirms the effect of this invention. It is an example of the experimental result which confirms the effect of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Power source, 2 ... Constant current source, 3 ... Light emitting element, 4 ... Shutter, 5 ... Thermistor, 6 ... Peltier element, 7 ... Laser diode module, 8 ..Temperature control circuit, 9 ... Shutter control circuit, 10 ... Power supply voltage detection unit, 11 ... Switch control unit, 12 ... Laser forward bias current cutoff switch, 13 ... Laser order Direction bias current bypass switch, 14 ... modulator, 15 ... modulator drive circuit, 16 ... signal processing circuit, 17 ... light receiving element, 18 ... amplification circuit, 19 ... signal Processing circuit, 20 ... Pulse pattern generator, 21 ... Error detector, 22 ... Electric module, 23 ... Splitter, 24 ... Electric jig, 25 ... Attenuator, 26 ... EDFA 2 DESCRIPTION OF SYMBOLS 7 ... Attenuator, 28 ... Filter, 29 ... Electric jig, 30 ... Photocoupler, 31 ... Optical spectrum analyzer, 100 ... Optical transmitter, 200 ... Optical transceiver , 300 ... Reference optical transceiver, 400 ... Optical transceiver

Claims (5)

  An optical transmitter having a laser diode mounted on a Peltier element, a temperature control circuit for keeping the temperature of the laser diode constant, and a constant current source for supplying a forward bias current to the laser diode, wherein the power supply voltage An optical transmitter having a detection unit, a switch for cutting off a laser bias current supply circuit, and a control unit for controlling the switch.   An optical transmitter having a laser diode mounted on a Peltier element, a temperature control circuit for keeping the temperature of the laser diode constant, and a constant current source for supplying a forward bias current to the laser diode, wherein the power supply voltage An optical transmitter having a detection unit, a switch for bypassing the laser bias current supply circuit to GND, and a control unit for controlling the switch.   3. The optical transmitter according to claim 1, further comprising: a shutter existing between optical fibers for coupling an output end of the laser diode to an outside of the laser diode module; and a control circuit for the shutter. An optical transmission method for modulating an output light from a laser diode mounted on a Peltier element and transmitting an optical signal,
A switch for detecting the power supply voltage of the laser diode and turning off the switch for cutting off the forward bias current supply circuit if the power supply voltage is lower than the threshold, and for cutting off the forward bias current supply circuit if the power supply voltage is higher than the threshold. The optical transmission method characterized by turning on. An optical transmission method for modulating an output light from a laser diode mounted on a Peltier element and transmitting an optical signal,
The power supply voltage of the laser diode is detected. If the power supply voltage is equal to or lower than the threshold, a switch that bypasses the forward bias current supply circuit and GND is turned on. If the power supply voltage is equal to or higher than the threshold, the forward bias current supply circuit is An optical transmission method comprising: turning off a switch that bypasses GND.

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