JP2008228267A - Optical transmitting apparatus and temperature control method used therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical transmitting apparatus for controlling an oscillation wavelength to a desired value while stabilizing the oscillation wavelength under predetermined optical modulation conditions (frequency band conditions). <P>SOLUTION: The bias current of a semiconductor laser 1 is feedback-controlled so that the value of a power monitor PD 9 can be kept constant (optical power constant control 22). An optical waveguide substrate 2 feeds temperature information back to a temperature control element 4 so that the temperature of a temperature monitoring element 3 can be kept at a predetermined temperature to control the temperature to be constant (filter temperature initialization 23). A heater 6 is controlled to be kept constant at a predetermined electric power (electric power constant control 21). The outputs of the power monitor PD 9 and a wavelength monitor PD 10 are fed back to the temperature control element 4 so that the ratio of both the outputs can be kept constant (Δλ constant control 24), thereby controlling the temperature of the optical waveguide substrate 2. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an optical transmission device and a temperature control method used therefor, and more particularly to a temperature control method in an optical transmission device.

  With the progress of optical transmission technology in recent years, various small optical transmission devices have been developed. In these small optical transmitters, high speed and long distance support are major technological innovation directions, and so far, for example, small optical transmitters capable of transmitting a single mode fiber of about 80 km at a bit rate of 10 Gbps have been proposed. Exists. However, with the increase of the bit rate, the chromatic dispersion limit has already been reached in the normal NRZ (Non Return to Zero) modulation method.

  On the other hand, various modulation schemes that exceed the chromatic dispersion limit have been developed. For example, the Duo binary modulation scheme has problems in terms of the size, power consumption, and cost of the optical transmitter. The CML (Chirp Managed Laser) modulation method is effective in these respects, but further size reduction and cost reduction are necessary. This CML modulation method is a technique for improving transmission characteristics by controlling frequency fluctuations during signal modulation.

  As a technique that enables size reduction and cost reduction by this CML modulation method, a structure in which an optical waveguide substrate and a semiconductor laser are mounted in a hybrid manner has been proposed by the present applicant. However, in this configuration, since the hybrid integration is realized, the wavelengths of the semiconductor laser and the wavelength filter cannot be controlled independently. Therefore, WDM (Wavelength Division Multiplexing) which has become mainstream in recent optical transmission systems. : Wavelength division multiplexing) system cannot be supported.

In addition, as a prior art regarding an optical transmitter, there exists a technique of the following patent document 1. FIG.
JP 2006-313309 A

  In the conventional optical transmitter related to the CML described above, the temperature of the optical filter and the semiconductor laser are separately adjusted, and since there are many components of the entire optical system including the monitoring port for the filter transmission characteristics, the size of the device is increased. There is a problem that it ends up.

  In addition, the conventional optical transmitter related to the other CML does not allow independent temperature control of the optical filter and the semiconductor laser. Therefore, when integration is realized, stabilization to a specific wavelength corresponding to the WDM system is realized. There is a problem that can not be done.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to solve the above-mentioned problems and to provide an optical transmitter capable of controlling to a desired oscillation wavelength while stabilizing it to a predetermined optical modulation condition (frequency band condition) and a temperature control method used therefor Is to provide.

An optical transmission device according to the present invention is an optical transmission device including an optical filter, an optical filter transmission light monitoring port, and an optical filter non-transmission light monitoring port,
An optical waveguide substrate on which an optical waveguide including the optical filter and a filter transmission characteristic monitoring port is formed; a semiconductor laser; and a heater capable of independently adjusting a wavelength characteristic of either the optical waveguide or the semiconductor laser; Have
The optical waveguide substrate and the semiconductor laser are integrated together so that the temperature can be adjusted.

A temperature control method according to the present invention is a temperature control method used for an optical transmission device including an optical filter, an optical filter transmitted light monitoring port, and an optical filter non-transmitted light monitoring port,
An optical waveguide substrate on which an optical waveguide including the optical filter and the filter transmission characteristic monitoring port is formed and a semiconductor laser are integrated in a form capable of temperature adjustment at a time, and a heater is provided in one of the optical waveguide and the semiconductor laser. The wavelength characteristics of any one of the optical waveguide and the semiconductor laser can be adjusted independently.

  By adopting the above-described configuration and operation, the present invention provides an effect that the oscillation wavelength can be controlled to a desired value while being stabilized to a predetermined light modulation condition (frequency band condition).

  Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing the overall configuration of the optical transmission apparatus according to the first embodiment of the present invention. In FIG. 1, an optical transmission device 100 includes a semiconductor laser 1, an optical waveguide substrate 2, a temperature monitoring element 3, a temperature control element 4, an optical filter 5, a heater 6, and a power monitor PD (Photo Diode) 9. And a wavelength monitor PD10. An optical waveguide 12 is formed on the optical waveguide substrate 2, and the optical waveguide 12 includes a filter non-passing port 7, a filter passing port 8, and an optical output port 11.

  The output frequency of the semiconductor laser 1 is modulated by modulating the bias current under appropriate conditions. The semiconductor laser 1 is mounted on the optical waveguide substrate 2 so that the modulated optical signal is coupled to the optical waveguide 12 on the optical waveguide substrate 2. By passing through the optical filter 5, the optical signal is limited to an appropriate frequency component, which becomes a main signal and is output from the optical output port 11.

  By limiting the frequency components as shown here, for example, long-distance transmission of 100 km or more can be realized with a normal single mode fiber in the wavelength band of 1550 nm at a modulation rate of 10 Gbps. Usually, an optical isolator is introduced at the tip of the optical output port 11 and coupled to an optical fiber using a lens or the like (not shown).

  A part of the optical signal of the optical waveguide 12 is output to the filter non-transmission port 7, and the intensity thereof is received by the power monitor PD9. Furthermore, after a part of the optical signal of the optical waveguide 12 passes through the optical filter 5, it is output to the filter transmission port 8, and its intensity is received by the wavelength monitor PD10. Here, Δλ is defined as the difference between the oscillation wavelength λLD of the semiconductor laser 1 and the center wavelength λFilter of the optical filter 5. The power monitor PD9 receives a signal that does not depend on Δλ, and the wavelength monitor PD10 receives a signal that changes depending on Δλ. As described later, by using these monitor signals, Δλ can be controlled to be constant, and stable light modulation characteristics can be obtained.

  The temperature of the optical waveguide substrate 2 can be monitored by the temperature monitoring element 3. Further, the entire optical waveguide substrate 2 is mounted on the temperature control element 4, and the temperature control of the entire substrate can be performed by the temperature control element 4. Furthermore, the center wavelength λFilter of the optical filter 5 can be adjusted by controlling the temperature of the heater 6.

  FIG. 2 is a block diagram showing a control block of the optical transmission apparatus according to the first embodiment of the present invention, and FIGS. 3 and 4 are diagrams showing an outline of the modulation signal in the first embodiment of the present invention. The operation of the optical transmission apparatus 100 according to the first embodiment of the present invention will be described with reference to FIGS.

  As described above, the modulation signal is supplied to the semiconductor laser 1, and the modulation signal is output from the optical output port 11 after the frequency band is limited by the optical filter 5 so as to correspond to the long distance optical transmission. Here, operations related to wavelength control of the semiconductor laser 1 and the optical filter 5 will be described.

  First, the bias current of the semiconductor laser 1 is feedback-controlled so that the value of the power monitor PD9 is constant (optical power constant control 22). The optical waveguide substrate 2 feeds back to the temperature control element 4 so that the temperature of the temperature monitoring element 3 becomes a predetermined temperature, and performs constant temperature control (filter temperature initial setting 23).

  The heater 6 is controlled to be constant at a predetermined power (power constant control 21). Since the heater 6 performs local temperature control, it is difficult to perform appropriate temperature monitoring. Therefore, it is desirable to perform control to make the input power constant.

  In this state, basically stable control is possible. However, in the optical transmission device 100 according to the first embodiment of the present invention, it is necessary to stabilize Δλ defined above with extremely high accuracy. It is necessary to perform a control for detecting a slight deviation of Δλ when a change occurs or after a long-term operation or the like and feeding it back. In order to satisfy this, the output of the power monitor PD9 and the output of the wavelength monitor PD10 are used to feed back to the temperature control element 4 so that the ratio between them is constant (Δλ constant control 24), and the optical waveguide substrate 2 Switch to control the temperature.

  In the case of a system that does not need to be controlled to a predetermined output wavelength, only Δλ needs to be stably controlled, and it is unnecessary to control the oscillation wavelength λLD of the semiconductor laser 1 to a predetermined value. No constant power control is required. This is shown in FIG. The oscillation wavelength λLD of the semiconductor laser 1 changes depending on the center wavelength λFilter of the optical filter 5.

  In the case of a WDM system in which the oscillation wavelength λLD of the semiconductor laser 1 needs to be set to a predetermined value, the oscillation wavelength λLD of the semiconductor laser 1 needs to be adjusted to a specific wavelength grid, so that the center wavelength λFilter of the optical filter 5 is previously set. It is necessary to adjust the value to a constant value. For this purpose, in this embodiment, stability control of the heater 6 that controls the local temperature on the optical filter 5 of the optical waveguide substrate 2 is performed. As a result, as shown in FIG. 4, the oscillation wavelength λLD of the semiconductor laser 1 is stabilized to a predetermined grid wavelength while being stably controlled to a predetermined light output condition.

  As described above, in this embodiment, the temperature of the entire optical waveguide substrate 2 on which the semiconductor laser 1 is mounted is collectively controlled, and local temperature control of the optical filter 5 portion of the optical waveguide 12 is performed independently. The semiconductor laser 1 and the optical filter 5 can be integrated and controlled to a desired oscillation wavelength while being stabilized at a predetermined light modulation condition (frequency band condition).

  Also, in this embodiment, the integration of the semiconductor laser 1 and the optical filter 5 reduces the number of component parts and enables the temperature control of the whole as a whole, thereby reducing the size of the optical transmission device 100. can do.

  FIG. 5 is a block diagram showing a configuration of an optical transmission apparatus according to the second embodiment of the present invention. The second embodiment of the present invention is the same as that shown in FIG. 1 except that the heater 6 is formed on the semiconductor laser 1 instead of forming the heater 6 on the optical filter 5 portion of the optical waveguide substrate 2. The configuration is the same as that of the first embodiment, and the same components are denoted by the same reference numerals. The operation of the same component is the same as that of the first embodiment of the present invention.

  In the present embodiment, as in the first embodiment of the present invention, the temperature of the entire optical waveguide substrate 2 on which the semiconductor laser 1 is mounted is collectively controlled, and the local temperature control of the semiconductor laser 1 portion is independent. Therefore, the semiconductor laser 1 and the optical filter 5 can be integrated and controlled to a desired oscillation wavelength while being stabilized to a predetermined light modulation condition (frequency band condition).

  FIG. 6 is a block diagram showing a control block of the optical transmission apparatus according to the third embodiment of the present invention. The third embodiment of the present invention is the same as the optical transmission apparatus 100 according to the first embodiment of the present invention, except that the control blocks 31 to 34 are different from the above-described first embodiment of the present invention. It has a configuration. The operation of the optical transmission apparatus 100 according to the third embodiment of the present invention will be described with reference to FIG.

  As described above, the modulation signal is supplied to the semiconductor laser 1, and the modulation signal is output from the optical output port 11 after the frequency band is limited by the optical filter 5 so as to correspond to the long distance optical transmission. Here, operations related to wavelength control of the semiconductor laser 1 and the optical filter 5 will be described.

  First, the bias current of the semiconductor laser 1 is feedback-controlled so that the value of the power monitor PD9 is constant (optical power constant control 32). The optical waveguide substrate 2 is fed back to the temperature control element 4 so that the temperature of the temperature monitoring element 3 becomes a predetermined temperature, and temperature control is performed using the temperature monitoring element 3 for initial setting of the filter temperature for performing constant temperature control. A constant temperature control is performed on the element 4 (a constant temperature control 33).

  The heater 6 is controlled to be constant at a predetermined power (filter wavelength initial setting 31). Further, in this embodiment, in order to make the wavelength difference Δλ between the semiconductor laser 1 and the optical filter 5 constant, the input power to the heater 6 is controlled using the output of the power monitor PD9 and the output of the wavelength monitor PD10 ( Switching from temperature control using the temperature monitoring element 3) (Δλ constant control 34).

  Further, in the present embodiment, the set temperature of the temperature monitoring element 3 that monitors the temperature of the temperature control element 4 is adjusted in order to obtain an appropriate output wavelength such as matching with the WDM grid (continuously using the temperature monitoring element 3). Constant temperature control).

  As described above, in this embodiment, the temperature of the entire optical waveguide substrate 2 on which the semiconductor laser 1 is mounted is collectively controlled, and the local temperature control of the optical filter 5 portion of the optical waveguide 12 or the semiconductor laser 1 portion is controlled. Since local temperature control is performed independently, the semiconductor laser 1 and the optical filter 5 can be integrated and controlled to a desired oscillation wavelength while stabilizing to a predetermined optical modulation condition (frequency band condition). .

  In the fourth embodiment of the present invention, the configuration of the optical transmitter is the same as that of the second embodiment of the present invention shown in FIG. 5, and the temperature control is the third embodiment of the present invention shown in FIG. The control is the same as that of the form. As a result, in the fourth embodiment of the present invention, instead of the local temperature control of the optical filter 5 portion of the optical waveguide 12 as shown in the third embodiment of the present invention, the semiconductor laser 1 portion Since local temperature control is performed, the semiconductor laser 1 and the optical filter 5 are integrated and controlled to a desired oscillation wavelength while being stabilized to a predetermined optical modulation condition (frequency band condition) in the same manner as described above. be able to.

  FIG. 7 is a diagram showing the relationship among control parameters, control objects, and monitoring objects in the first to fourth embodiments of the present invention. As shown in FIG. 7, in the present invention, the entire optical waveguide substrate 2 is controlled by the temperature control element 4, and the optical filter 5 portion of the optical waveguide 12 or the semiconductor laser 1 portion is locally controlled by the heater 6. . Therefore, in the present invention, the semiconductor laser 1 and the optical filter 5 can be integrated and controlled to a desired oscillation wavelength while being stabilized at a predetermined optical modulation condition (frequency band condition).

  That is, in the first to fourth embodiments of the present invention, the optical transmission device 100 includes the optical filter 5, the optical filter transmitted light monitoring port (filter passing port 8), and the optical filter non-transmitted light monitoring port (filter Non-passing port 7), optical waveguide substrate 2 on which these are formed, monitor PD (power monitor PD9, wavelength monitor PD10) installed in each monitoring port, semiconductor laser 1, temperature monitoring element 3, optical filter 5 or semiconductor laser 1 The heater 6 and the temperature adjusting element (temperature control element 4) formed above are provided.

  In the optical transmission device 100, the substrate (optical waveguide substrate 2) on which the optical waveguide including the optical filter 5 and the filter transmission characteristic monitoring port is formed (the optical waveguide substrate 2) and the semiconductor laser 1 are integrated in a form that allows temperature adjustment in a lump. Alternatively, by adding a heater 6 that allows the wavelength characteristics of the semiconductor laser 1 to be adjusted independently, stabilization to a specific optical output wavelength and frequency band limitation of the semiconductor laser modulation spectrum by optical filtering can be implemented. Thus, long-distance optical fiber transmission at a high bit rate corresponding to the WDM system is possible.

  Note that the optical transmitter of the present invention may have a structure in which the heater 6 formed on the semiconductor laser 1 is not provided, but the heater 6 formed on the optical waveguide substrate 2 serving as a characteristic wavelength adjusting unit of the optical filter 5 is provided.

  In order to apply a modulation scheme related to the present invention to a DWDM (Density Wavelength Division Multiplexing) system, an optical output / light that can suppress the influence on adjacent wavelength channels when the optical transmitter is started up. Wavelength characteristics are required. Specifically, it is necessary to suppress the generation of a light output larger than a specified value at the time of start-up, or to suppress the generation of light output at a wavelength different from the specified value.

  However, in the optical transmission apparatus related to the present invention as described above, the semiconductor laser that is basically the light source of the optical transmission apparatus has a characteristic that the optical output wavelength becomes longer with respect to the increase of the injection current. When the current is increased so that a prescribed optical output can be obtained from zero at the start of startup, optical output wavelength fluctuations occur with the increase of the optical output. Therefore, in the optical transmitter used in the DWDM system, the optical output at startup There is a problem that there is a variation in wavelength, and it becomes difficult to reduce the optical output at a wavelength other than the prescribed optical wavelength, and there is a high possibility that the adjacent optical wavelength channel is adversely affected.

  In addition, in order to solve the above problems, there is a method of mounting a variable optical attenuator or the like on the optical output portion of the optical transmission apparatus in the optical transmission apparatus related to the present invention, but an excessive loss of optical output occurs. At the same time, there is a problem that the size of the apparatus and the control become complicated.

  This is because it is not easy to realize a variable attenuator that can be mounted in a package of a small optical module that is currently used in a general optical transmitter, and the size of the attenuator may increase or be mounted. However, in order to stably control the light output intensity, a part and a control function for monitoring and controlling the light output intensity of the attenuator output are newly required. In addition to the insertion loss of the optical attenuator itself, the occurrence of optical loss in the optical output monitoring system is unavoidable.

  Furthermore, in the optical transmission apparatus related to the present invention, it is very difficult to stably transmit a general optical fiber of 80 km or more at a transmission speed of 10 gigabits / second, for example. The cause of this is that when the modulation rate is increased to 10 gigabits / second, the optical spectrum band output from a general optical transmission device widens greatly, and is affected by chromatic dispersion in the optical fiber, so that the optical transmission signal waveform is This is because it deteriorates.

  In order to solve these problems, in the present invention, in the optical transmission device, the optical output wavelength that is initially set when the optical transmission device is started is set to be longer than the optical output wavelength that is set in the steady state. Thereafter, when the semiconductor laser output is started, it is possible to reach the specified light output and enter the steady operation state without instantaneously generating a light output greatly exceeding the specified value.

  FIG. 8 is a block diagram showing an overall configuration of an optical transmission apparatus according to the fifth embodiment of the present invention. In FIG. 8, the optical transmitter according to the fifth embodiment of the present invention includes a semiconductor laser 1, a wavelength discrimination unit 110, a temperature monitoring element 3, a temperature control element 4, an optical filter 5, and a light intensity monitor. PD 41, wavelength monitor PD 10, CPU (central processing unit) 42, memory 43, laser drive circuit 44, temperature control element drive circuit 45, control switching circuit 46, common monitor / feedback circuit 47, carrier 48. In FIG. 8, 101 is an electric signal input, and 102 is an optical signal output.

  A bias current and a modulation current are applied to the semiconductor laser 1 by a laser drive circuit 44. Here, the laser drive circuit 44 converts a signal corresponding to the electric signal input 101 into a current amplitude designated by the CPU 42. Further, the bias current of the semiconductor laser 1 is controlled from the laser drive circuit 44 so that the photocurrent of the light intensity monitor PD41 in front of the semiconductor laser 1 becomes a value designated by the CPU. By these operations, in this embodiment, a constant modulation signal is obtained with a constant bias.

  The optical output signal 102 from the semiconductor laser 1 passes through the wavelength discrimination unit 110, and at that time, the optical spectrum is limited by the optical filter 5 in the wavelength discrimination unit 110. As a result, in the present embodiment, the spread of the modulation spectrum is suppressed even at a high transmission rate, the wavelength dispersion tolerance is high, and long-distance optical fiber transmission such as 80 km or more is possible.

  The wavelength monitor PD10 in the wavelength discrimination unit 110 can monitor the light output wavelength of the semiconductor laser 1 and the relative wavelength of the optical filter 5 under the constant photocurrent condition of the light intensity monitor PD41. By controlling the temperature of the carrier 48 using the common monitor / feedback circuit 47, the temperature control element drive circuit 45, and the temperature control element 4 so that the photocurrent of the optical wavelength monitor PD10 becomes constant, the optical filter 5 The relative wavelength of the light is controlled to be constant, and a stable light output characteristic can be obtained.

  The semiconductor laser 1 used here is a DFB (Distributed FeedBack) laser having a wavelength band of 1550 nm, and the optical filter 5 is made of a quartz material. Assuming a general situation, the temperature characteristics of the semiconductor laser 1 and the optical filter 5 are approximately 0.1 nm / ° C. and 0.01 nm / ° C., respectively, which are ten times different. The wavelength of the semiconductor laser 1 is adjusted with respect to the wavelength of the optical filter 5.

  However, since the temperature control method described above cannot be realized without the light output from the semiconductor laser 1, the temperature control element 4 is controlled using the signal of the temperature monitoring element 3 when the semiconductor laser 1 is turned off. Will do. Thereafter, when the semiconductor laser 1 is turned on and an optical output is obtained, the monitoring signal is switched by the control switching circuit 46, and temperature control using the optical wavelength monitor PD10 is performed. These are performed according to instructions from the CPU 42, and target set values of the temperature monitoring element 4 and the wavelength monitor PD 10 are stored in the memory 43.

  FIG. 9 is a block diagram showing a specific configuration example of the wavelength discrimination unit 110 of FIG. In FIG. 9, since the optical waveguide 12 and the optical filter 5 are formed on the optical waveguide substrate 22, the optical waveguide substrate 2 also serves as the carrier 48.

  Since it is easy to form an optical branch in the optical waveguide 12, it is possible to form the filter non-passing port 7 and the filter passing port 8 and obtain a monitor signal necessary for controlling the semiconductor laser 1 as described above. From the optical output port 11, an optical signal output band-limited by the optical filter 5 is obtained.

  10 and 11 are flowcharts showing the operation of the optical transmission apparatus according to the fifth embodiment of the present invention, and FIG. 12 is a diagram showing the monitor signal output characteristics in the fifth embodiment of the present invention. FIGS. 13 and 14 are diagrams showing optical wavelength / light output characteristics in the fifth embodiment of the present invention, and FIG. 15 is a diagram showing an example of setting the steady operation wavelength in the fifth embodiment of the present invention. It is. The operation of the control method of the optical transmission apparatus according to the fifth embodiment of the present invention will be described with reference to FIGS.

  In the semiconductor laser 1, the bias current is controlled so that the photocurrent (defined as Im-Power) of the light intensity monitor PD41 is constant in the steady state, and the photocurrent (defined as Im-Lambda) of the wavelength monitor PD10 is controlled. The temperature (Tld) of the carrier 48 on which the semiconductor laser 1 is mounted is controlled so as to be constant.

  FIG. 12 shows an overview of the respective photocurrent characteristics and the wavelength dependence of the optical output intensity of the optical transmitter. In FIG. 12, the horizontal axis represents the optical output wavelength, but since this is proportional to the carrier temperature, it may be the carrier temperature. The optical output monitor characteristic can be obtained without wavelength dependence, and the wavelength monitor characteristic and optical output characteristic can be obtained depending on the shape of the optical filter 5.

  In the optical transmission apparatus according to the present embodiment, in order to obtain good optical signal characteristics, the slope is set to a longer wavelength than the peak seen in the optical output characteristics as shown in the steady-state operating wavelength of FIG. It is desirable. Eventually, the carrier temperature is controlled so that the value shown by the Im-Lambda target set value is obtained, and the operating wavelength at the normal time is obtained.

  The start-up operation for starting the output of the semiconductor laser 1 is controlled as shown in the flowchart of FIG. First, since it is necessary to turn off the optical output, the CPU 42 selects a mode for controlling the carrier temperature using the signal of the temperature monitoring element 3 as the temperature monitoring mode (step S1 in FIG. 10). Thereafter, the CPU 42 performs Im-Power setting that is a target value of light output (step S2 in FIG. 10). As an actual operation, the CPU 42 reads the set value from the external memory 43 to which the set value has been input in advance.

  Next, the CPU 42 sets Tld. Here, Tld is set so as to be on the long wave side from the operating point in the steady state as shown in the initial target wavelength of FIG. 12 (FIG. 10). Step S3). Thereafter, the CPU 42 starts the operation of the temperature control element 3 in the temperature monitoring mode (steps S4 and S5 in FIG. 10), and then starts the light output operation in the Im-Power constant mode (step S6 in FIG. 10).

  Here, since the bias current of the semiconductor laser 1 increases from zero to a specified value, the optical output increases and the optical output wavelength fluctuates. However, in this embodiment, since the initial setting wavelength is set on the long wave side from the stationary time, it does not pass through the filter peak when the optical output wavelength fluctuates, and passes near the bottom of the filter, The light output is suppressed near zero level.

  Then, the CPU 42 switches from the temperature monitoring mode to the wavelength monitoring mode (step S7 in FIG. 10), so that the operating wavelength is adjusted from the vicinity of the filter bottom to the steady-state operating point near the filter slope. The optical output increases only near the optical wavelength of the operating point and reaches a specified value. An outline of the change in the light output / light wavelength at this time is shown in FIG.

  If the initial setting wavelength is the same as that in the steady operation, the light wavelength passes through the filter peak after the semiconductor laser 1 is turned on, and the light output during the steady operation is increased as shown in FIG. The light output exceeding it will generate | occur | produce. This may hinder the stable start-up operation of the optical transmission device on which the optical transmission device is mounted, and an operation method that does not generate this large optical output is required.

  The operation for turning off the optical output of the optical transmission apparatus, such as when an alarm occurs in the optical transmission system, is controlled as shown in the flowchart of FIG. First, the CPU 42 switches from the wavelength monitoring mode to the temperature monitoring mode (step S11 in FIG. 11), and stops the optical output (step S12 in FIG. 11). If the optical output is stopped in the wavelength monitoring mode, there is no monitoring signal for temperature control, and the temperature control element 4 cannot be controlled.

  As described above, in this embodiment, the optical filter 5 for limiting the optical spectrum band is mounted and the optical output can be obtained only in the vicinity of the prescribed optical wavelength, so that the DWDM (High Density Wavelength Division Multiplexing) system is used. In the optical transmitter used, the optical output at startup can be obtained only near the specified operating wavelength, that is, the optical output can be reduced at other than the specified optical wavelength, and the influence on the adjacent optical wavelength channel is suppressed. can do.

  In the present embodiment, the wavelength set at the initial stage is set to be longer than the operating wavelength at the time of steady operation, so that the light output at the start-up passes near the bottom of the filter, which is near the zero level. Since the light intensity is suppressed, in the light output characteristics at the time of start-up, it can be suppressed that a light output larger than a specified value is instantaneously generated.

  Furthermore, in the present embodiment, the optical filter 5 can limit the optical spectrum band at the time of modulation and suppress waveform degradation due to the influence of chromatic dispersion in the optical fiber. An optical transmission device that stably realizes transmission can be realized.

  Furthermore, in the present embodiment, the optical filter 5 that stabilizes the characteristics of the optical output signal can also be used to stabilize the optical wavelength / optical output characteristics at the time of start-up. Since it is not necessary to install an attenuator or an optical output monitoring element for controlling the optical attenuator, the optical transmitter has a high transmission capability as described above, and suppresses the influence on adjacent wavelength channels at startup. Can be realized.

  In the present embodiment, a general DFB laser is assumed as the semiconductor laser 1 in the above description. At that time, when the modulation signal corresponds to “0” to “1”, there is an adiabatic chirp effect that the wavelength is shifted from the long wavelength to the short wavelength, and the optical spectrum of the portion corresponding to “0” among them A good optical transmission waveform can be obtained by setting the wavelength of the semiconductor laser 1 in the middle of the long-wave slope of the optical filter 5 so as to cut off.

  It has been described that when the semiconductor laser 1 is started, the wavelength is shifted to the longer wavelength side in accordance with current injection. That is, there is a characteristic that the direction of wavelength shift is reversed depending on the operating frequency. This may cause problems when trying to transmit lower-frequency signals, and as a means to avoid this, the wavelength change when changing from “0” to “1” even during high-speed modulation. It is conceivable to apply a red chirped semiconductor laser in which the direction is from a short wavelength to a long wavelength.

  In this case, in order to remove “0” on the short wavelength side, as shown in FIG. 15, the slope on the short wavelength side of the filter peak is set as the steady operating wavelength. When this red chirped semiconductor laser is used, basically the same effect as that of the first embodiment of the present invention described so far can be obtained. It is set not on the long wavelength side of the wavelength but on the short wavelength side of the steady operating wavelength or the same as the steady operating wavelength. As a result, it is possible to obtain appropriate optical output / optical wavelength characteristics when the optical transmitter is started up.

  FIG. 16 is a block diagram showing an overall configuration of an optical transmission apparatus according to the sixth embodiment of the present invention. 16, the optical transmission apparatus according to the sixth embodiment of the present invention is the same as that shown in FIG. 8 except that a current monitor feedback circuit 49 and a temperature monitor / feedback circuit 50 are provided instead of the common monitor / feedback circuit 47. The configuration is the same as that of the optical transmission apparatus according to the fifth embodiment of the present invention, and the same components are denoted by the same reference numerals.

  Here, in the example shown in FIG. 8, the signals of the temperature monitoring element 3 and the wavelength monitor PD10 are selected by the control switching circuit 46 and then introduced into the common monitor / feedback circuit 47. In the example shown in FIG. As described above, the signals of the temperature monitoring element 3 and the wavelength monitor PD 10 are received independently by the temperature monitor / feedback circuit 50 and the current monitor feedback circuit 49, respectively, and the control signal output to the temperature control element drive circuit 45 is controlled by the control switching circuit. A method of switching at 46 may be used.

  In the optical output control method of the present invention, the optical transmission device increases the chromatic dispersion tolerance by limiting the band of the modulation spectrum of the direct modulation semiconductor laser 1 and the optical modulation signal, and the optical output required for wavelength stabilization control. A wavelength discriminating unit 110 for providing a monitor signal and a wavelength monitor signal, and a temperature monitoring element 3 are mounted on a carrier 48 on the temperature control element 4, and further, a temperature control state and a wavelength monitor using the temperature monitoring element 3 A common monitor / feedback circuit 47 that enables switching between temperature control states using signals, a control switching circuit 46, a temperature control element 4, a laser drive circuit 44, a CPU 42, and a memory 43. It is composed.

  In the optical output control method of the present invention, in this optical transmission device, by setting the optical output wavelength that is initially set when the optical transmission device is started to be longer than the optical output wavelength that is set in a steady state, When the semiconductor laser 1 starts the output, it is possible to reach the specified light output and enter the steady operation state without instantaneously generating a light output that greatly exceeds the specified value.

  The output optical spectrum of the optical transmission device is limited in band by the bandpass filter in the wavelength discrimination unit 110 even at a modulation rate of 10 gigabits / second, for example, and the influence of chromatic dispersion can be reduced. Thus, it becomes possible to stably transmit a general optical fiber of 80 km or more.

  Further, in the present embodiment, due to the effect of the bandpass filter, the optical wavelength at which the optical output is obtained when the semiconductor laser 1 starts output is limited to the vicinity of the optical wavelength during steady operation. It is possible to suppress the influence on the adjacent channel.

  Furthermore, in the present embodiment, by the method of initially setting the light wavelength to the long wave side from the stationary time, when the semiconductor laser 1 starts output, light output that greatly exceeds the specified value is not generated instantaneously. It becomes possible to reach a specified light output and enter a steady operation state.

  The present invention can also be applied to an optical transmission / reception module in an optical transmission device or a network device.

1 is a block diagram showing an overall configuration of an optical transmission apparatus according to a first embodiment of the present invention. It is a block diagram which shows the control block of the optical transmitter by the 1st Example of this invention. It is a figure which shows the outline | summary of the modulation signal in 1st Example of this invention. It is a figure which shows the outline | summary of the modulation signal in 1st Example of this invention. It is a block diagram which shows the structure of the optical transmitter by the 2nd Example of this invention. It is a block diagram which shows the control block of the optical transmitter by the 3rd Example of this invention. It is a figure which shows the relationship between the control parameter in 1st-4th Example of this invention, a control object, and a monitoring object. It is a block diagram which shows the whole structure of the optical transmitter by the 5th Embodiment of this invention. It is a block diagram which shows the specific structural example of the wavelength discrimination unit 110 of FIG. It is a flowchart which shows operation | movement of the optical transmission apparatus by the 5th Embodiment of this invention. It is a flowchart which shows operation | movement of the optical transmission apparatus by the 5th Embodiment of this invention. It is a figure which shows the monitor signal output characteristic in the 5th Embodiment of this invention. It is a figure which shows the optical wavelength / light output characteristic in the 5th Embodiment of this invention. It is a figure which shows the optical wavelength / light output characteristic in the 5th Embodiment of this invention. It is a figure which shows the example of a setting of the steady operation wavelength in the 5th Embodiment of this invention. It is a block diagram which shows the whole structure of the optical transmitter by the 6th Embodiment of this invention.

Explanation of symbols

1 Semiconductor laser
2 Optical waveguide substrate
3 Temperature monitoring element
4 Temperature control element
5 Optical filter
6 Heater
7 Filter non-passing port
8 Filter passing port
9 Power monitor PD
10 Wavelength monitor PD
11 Optical output port 12 Optical waveguide 21 Constant power control 22, 32 Constant optical power control 23 Initial filter temperature setting 24, 34 Constant Δλ control 31 Initial filter wavelength setting 33 Constant temperature control 41 Optical intensity monitor PD
42 CPU
43 Memory 44 Laser Drive Circuit 45 Temperature Control Element Drive Circuit 46 Control Switching Circuit 47 Common Monitor / Feedback Circuit 48 Carrier 49 Current Monitor Feedback Circuit 50 Temperature Monitor / Feedback Circuit 100 Optical Transmitter 110 Wavelength Discrimination Unit

Claims (20)

An optical transmission device including an optical filter, an optical filter transmission light monitoring port, and an optical filter non-transmission light monitoring port,
An optical waveguide substrate on which an optical waveguide including the optical filter and a filter transmission characteristic monitoring port is formed; a semiconductor laser; and a heater capable of independently adjusting a wavelength characteristic of either the optical waveguide or the semiconductor laser; Have
An optical transmission device, wherein the optical waveguide substrate and the semiconductor laser are integrated in a form capable of temperature adjustment at once.   The optical transmission device according to claim 1, further comprising a temperature control element that collectively adjusts the temperature of the optical waveguide substrate and the semiconductor laser. A wavelength monitor PD (Photo Diode) is installed at the monitoring port of the optical filter transmitted light,
A power monitor PD is installed in the monitoring port of the optical filter non-transmitted light;
3. The optical transmission device according to claim 2, wherein temperature adjustment by the temperature control element is controlled so that a ratio between an output of the wavelength monitor PD and an output of the power monitor PD is constant.   4. The optical transmission device according to claim 1, wherein the heater is controlled to be constant at a predetermined power.   4. The optical transmission apparatus according to claim 3, wherein the input power to the heater is controlled using outputs of the wavelength monitor PD and the power monitor PD. The semiconductor laser is directly modulated,
3. The optical transmission according to claim 1, further comprising control means for setting the optical output wavelength of the semiconductor laser that is initially set when the device is started to a longer wavelength side than the optical output wavelength that is set in a steady state. apparatus.   A wavelength discrimination unit is provided, which limits a modulation spectrum band of an optical modulation signal to increase chromatic dispersion tolerance and provides an optical output monitor signal and a wavelength monitor signal necessary for wavelength stabilization control. 6. The optical transmission device according to 6.   2. The wavelength discrimination unit, wherein a wavelength monitor PD (Photo Diode) is installed in the monitoring port of the optical filter transmitted light, and a light intensity monitor PD is installed in the monitoring port of the optical filter non-transmitted light. 8. The optical transmission device according to 7.   9. The optical transmission device according to claim 7, further comprising a feedback circuit that switches between a temperature control state using the temperature monitoring element and a temperature control state using the wavelength monitor signal.   The control means sets the optical output wavelength of the semiconductor laser to a longer wavelength side than the optical output wavelength set in a steady state in a temperature control state using the temperature monitoring element at the time of startup of the own apparatus, and then the wavelength monitor signal 10. The optical transmission device according to claim 9, wherein the temperature of the optical waveguide substrate and the semiconductor laser is collectively adjusted in a temperature control state using a laser. A temperature control method used for an optical transmission device including an optical filter, an optical filter transmission light monitoring port, and an optical filter non-transmission light monitoring port,
An optical waveguide substrate on which an optical waveguide including the optical filter and the filter transmission characteristic monitoring port is formed and a semiconductor laser are integrated in a form capable of temperature adjustment at a time, and a heater is provided in one of the optical waveguide and the semiconductor laser. A temperature control method characterized in that the wavelength characteristic of any one of the optical waveguide and the semiconductor laser can be adjusted independently.   12. The temperature control method according to claim 11, wherein the temperature of the optical waveguide substrate and the semiconductor laser is collectively adjusted by a temperature control element. A wavelength monitor PD (Photo Diode) is installed at the monitoring port of the optical filter transmitted light,
A power monitor PD is installed in the monitoring port of the optical filter non-transmitted light;
13. The temperature control method according to claim 12, wherein the temperature adjustment by the temperature control element is controlled so that a ratio between the output of the wavelength monitor PD and the output of the power monitor PD is constant.   The temperature control method according to any one of claims 11 to 13, wherein the heater is controlled to be constant at a predetermined electric power.   The temperature control method according to claim 13, wherein the input power to the heater is controlled using outputs of the wavelength monitor PD and the power monitor PD. The semiconductor laser is directly modulated,
13. The control process according to claim 11 or 12, further comprising a control process for setting an optical output wavelength of the semiconductor laser that is initially set when the optical transmitter is activated to a longer wavelength side than an optical output wavelength that is set in a steady state. Temperature control method.   A wavelength discriminating unit for providing an optical output monitor signal and a wavelength monitor signal necessary for wavelength stabilization control is provided while limiting the modulation spectrum band of the optical modulation signal to increase the chromatic dispersion tolerance. The temperature control method according to claim 16.   2. The wavelength discrimination unit, wherein a wavelength monitor PD (Photo Diode) is installed in the monitoring port of the optical filter transmitted light, and a light intensity monitor PD is installed in the monitoring port of the optical filter non-transmitted light. 18. The temperature control method according to 17.   The temperature control method according to claim 17 or 18, wherein a temperature control state using the temperature monitoring element and a temperature control state using the wavelength monitor signal are switched.   In the control process, the optical output wavelength of the semiconductor laser is set to a longer wavelength side than the optical output wavelength set in a steady state in a temperature control state using the temperature monitoring element when the optical transmission device is started, and then the wavelength 20. The temperature control method according to claim 19, wherein the temperature of the optical waveguide substrate and the semiconductor laser is collectively adjusted in a temperature control state using a monitor signal.

Images