JP2008103766A - High-speed wavelength variable distributed feedback semiconductor laser array, and distributed feedback semiconductor laser - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a broadband variable wavelength light source which is fully used for a DWDM system and also carries out high-speed wavelength switching in ms order, while enabling it to establish mass production organization and also utilize a DFB-LD simple in controlling mechanism. <P>SOLUTION: A distributed feedback semiconductor laser array consists of: two or more distributed feedback semiconductor lasers under an identically controlled temperature; and an optical couplers which lead output light from two or more distributed feedback semiconductor lasers to one waveguide. The distributed feedback semiconductor laser array comprises a means for controlling the amount of inflow current of distributed feedback semiconductor lasers 21, and a means for measuring oscillating wavelength, wherein rough control of the wavelength of the distributed feedback semiconductor laser is performed by adjusting temperature, and after the temperature or wavelength of light entering within a desired limit, the trimming of the wavelength is performed by controlling the amount of inflow current by bringing the measured oscillating wavelength close to an oscillating target value. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a broadband wavelength tunable light source capable of high-speed wavelength switching using a semiconductor laser.

  In order to realize a large transmission capacity in an optical communication system, DWDM (High Density Wavelength Division Multiplexing) transmission that multiplexes many wavelength channels with high density at narrow intervals is required, and many wavelength channels are transmitted. A tunable light source is needed. As a wavelength tunable light source necessary for this DWDM transmission, there are a distributed feedback semiconductor laser (DFB-LD), a distributed reflection semiconductor laser (DBR-LD), an external resonant semiconductor laser, a surface emitting laser, and the like. Among them, DFB-LD has an advantage that it transmits in a single longitudinal mode, and is advantageous in that it is easy to manufacture and reliable compared to other lasers, and the wavelength control method is also easy. It is often used in optical communication systems.

  The DFB-LD can control a wavelength of about 3 nm by temperature control. Recently, it has been reported that a plurality of DFB lasers are arranged on an array and used as a broadband wavelength tunable light source (for example, Non-Patent Document 1).

  FIG. 1 shows a configuration diagram of an array using DFB-LD. 10 is an LD current source, 11 is N DFB-LDs, 12 is a thermistor and an LD temperature monitor that monitors the temperature of the DFB-LD 11, 13 is an LD temperature controller that adjusts the temperature of the DFB-LD, and 14 is a Peltier device. An LD temperature control circuit configured to control an LD temperature controller based on a temperature monitored by the LD temperature monitor 12, and an optical coupler configured of an optical coupler configured to multiplex light output from each DFB-LD 11, Reference numeral 16 denotes a gain element, and reference numeral 17 denotes a gain element current source.

  In the above document, 16 DFB-LDs 11 are arranged. The oscillation wavelength of each DFB-LD is set to be shifted by about 3 nm at the same temperature. A current is injected from the LD current source 10 to one DFB-LD 11. The output light of each DFB-LD 11 is guided to one optical waveguide by the optical multiplexer 15. Thereafter, the optical output power is increased by a semiconductor optical amplifier (SOA). The temperature of the DFB-LD 11 is detected by the LD temperature monitor 12 and is usually adjusted to a desired temperature by the LD temperature controller 13 controlled by the LD temperature control circuit 14.

  The oscillation wavelength of the DFB-LD 11 is switched by the following method. This DFB-LD array can change a wavelength of about 47 nm. The wavelength variable range of 47 nm wavelength is divided into 16 to oscillate light having different wavelengths by about 3 nm from the respective DFB-LDs 11. The above-described wavelength change in each DFB-LD 11 is performed by temperature adjustment. By this method, the wavelength variable range of 47 nm can be covered.

  In the above document, since an optical coupler is used for the optical multiplexer 15, a DFB-LD 11 that oscillates light of a desired wavelength is selected and current is injected. Here, in addition to the optical multiplexer 15, a method of selecting one output light from the DFB-LD 11 using an optical selector such as a MEMS-SW (Micro Electro-mechanical system) has been reported (for example, non-patented). Reference 2).

As a method of changing the oscillation wavelength in the DFB-LD, in addition to the method of changing the wavelength by changing the temperature, the method of changing the oscillation wavelength by changing the amount of current injected into the active layer to the DFB-LD. Has been reported. For example, in Patent Document 1, the temperature is adjusted when the oscillation wavelength of the DFB-LD is changed, but the wavelength is changed at a high speed by also using the adjustment of the injection current amount. In Patent Document 2, the amount of injected current is controlled to adjust the oscillation light of the DFB-LD to an acetylene absorption line.
JP 9-331107 A JP-A-11-354877 H. Oohashi, et al, 2001 International Conference on Indium Phosphide and Related Materials Onference Proceedings, FB1-2, 2001 B. Pezeshki, et al, IEEE Photon. Tecnol. Lett., Vol. 14, pp. 1557-1559, 2002

  However, the above wavelength tunable light source has the following problems.

  For DBR-LD, high-speed wavelength switching can be realized, but it is necessary to simultaneously control the current injected into the reflection region and the phase region in addition to the active layer region. is there. For external resonant semiconductor lasers and surface-emitting lasers, a wavelength switching mechanism using MEMS has been proposed as means for performing wavelength switching at high speed, but the wavelength switching speed is limited to several tens to several hundreds of ms.

  Although it is a DFB-LD array in which a plurality of DFB-LDs are mounted, since wavelength adjustment is performed by adjusting the temperature of the DFB-LD, several tens of seconds are required for wavelength switching time.

  In the method of adjusting the wavelength by controlling the injection current, the wavelength can be changed at high speed. However, the wavelength range that can be controlled by the injection current amount is limited to the order of sub-nm, so a broadband wavelength tunable light source. Cannot be used as

  The object of the present invention is to establish a mass production system and use a DFB-LD with a simple control mechanism, which can be sufficiently used for a DWDM system, and is capable of high-speed wavelength switching on the order of ms. An object of the present invention is to provide a tunable light source having a wide bandwidth.

In the present invention, in order to achieve the above object, in claim 1, after adjusting the wavelength range that cannot be controlled by the injection current in the DFB-LD array by temperature adjustment, after the wavelength converges within the range that can be controlled by the injection current, By adjusting the wavelength by adjusting the injection current , high-speed wavelength switching and a broadband wavelength tunable light source are realized. Faster wavelength switching can be realized than the DFB-LD array, which currently performs wavelength adjustment for all temperatures.

  The measurement result of the change Δf in the oscillation frequency (wavelength) when the injection current is changed by ΔI by the DFB-LD is as follows.

  In this equation, the first term on the right side is the amount by which the refractive index of the active layer is changed by the amount of injected current, and the oscillation wavelength changes at a high speed of the order of ms or less. The second term on the right side shows the change in the oscillation wavelength corresponding to the temperature change by changing the temperature of the DFB-LD by changing the injection current amount. Since this term is via temperature change, it changes in sec order. Although the amount of wavelength change varies somewhat depending on the structure of the DFB-LD, Patent Document 1 reports that the coefficient of the first term is −1 GHz / mA, and the wavelength can be changed at high speed by changing the injection current. I can confirm that I can do it.

In the DFB-LD array according to the second aspect, the response speed for controlling the injection current amount is made faster than the response speed for adjusting the temperature, thereby satisfying a plurality of negative feedback controls.

In the DFB-LD array according to claims 1 and 2 , since the injection current amount is controlled so that the oscillation wavelength becomes a desired wavelength, the oscillation wavelength can match the target wavelength when the injection current amount is large or small. There is sex. When the amount of injected current is large, there are disadvantages in that power consumption is large and device deterioration is accelerated. On the other hand, when the amount of injected current is small, there is a drawback that the optical SN characteristic is deteriorated. For this reason, it is better to fix the injection current amount to a certain moderate value. According to the third aspect of the present invention, this is realized by adjusting the DFB-LD temperature in order to adjust the injection current amount to a certain value.

In the DFB-LD array according to claims 1 to 3 , the output power from the wavelength tunable light source also changes in order to change the injection current. According to the fourth aspect of the present invention, a gain element is inserted in the output from the wavelength tunable light source, and the gain is controlled so that the output power becomes constant. Gain control is realized by performing control at a faster response speed than injection current control.

In the fifth aspect , instead of the gain element according to the fourth aspect, an element whose gain depends on the input power is used. By using a gain element with a small gain when the input power is large, fluctuations in the optical output power due to changes in the amount of injected current are suppressed. Compared with the fourth aspect of the present invention , the gain element control circuit is simpler than necessary and the output power of the wavelength tunable light source becomes constant.

In the sixth aspect , a single DFB-LD performs the same wavelength control method as in the first to fifth aspects. High-speed wavelength switching can be realized compared to a single DFB-LD that is currently adjusting the wavelength at the temperature.

According to DFB-LD array 請 Motomeko 1, a wavelength range that can not be controlled by the injection current for controlling the temperature control, a wider range, besides, can achieve high-speed wavelength switchable wavelength-tunable light source. Furthermore, since the wavelength can be adjusted at high speed by controlling the injection current, the operating temperature of each DFB-LD may vary, and the difficulty of manufacturing the DFB-LD can be reduced and inexpensively. A DFB-LD array can be realized.

Further, according to the DFB-LD21 array of the second aspect, by making the response speed for controlling the injection current amount faster than the response speed for adjusting the temperature, it is possible to achieve a plurality of negative feedback controls.

In addition, according to the DFB-LD21 array according to claim 3, high-speed wavelength switching can be realized by controlling the wavelength with the injection current, but the injection current amount is adjusted to a certain amount on a long time scale. Therefore, the power consumption of the DFB-LD array can be reduced, the element deterioration can be suppressed, and the optical characteristics can be improved.

Further, according to the DFB-LD array of the fourth aspect , since the optical output power can be made constant, a light source suitable for the optical communication system can be realized.

Further, according to the DFB-LD array of the fifth aspect , since the optical output power can be made constant, a light source suitable for an optical communication system can be realized.

Further, according to the DFB-LD of the sixth aspect , since the fine adjustment of the wavelength is controlled by the injection current, the wavelength switching can be performed faster than the current DFB-LD.

Hereinafter, the present onset Akira will be described with reference to the accompanying drawings.

FIG. 2 shows a first reference example of the present invention. In FIG. 2, 20 is an LD current source, 21 is N DFB-LDs, 22 is an LD temperature monitor for monitoring the temperature of the DFB-LD 21, 23 is an LD temperature controller for adjusting the temperature of the DFB-LD 21, and 24 is An LD temperature control circuit that controls the LD temperature controller 23 based on the temperature monitored by the LD temperature monitor 22, 25 is an optical multiplexer that multiplexes the light output from each DFB-LD 21, 26 is an optical demultiplexer, 27 Is a wavelength monitor that monitors the wavelength of the optical demultiplexer 26, and 28 is an LD current control circuit that controls the LD current source 20.

  The DFB-LD 21 is a semiconductor laser in which a diffraction grating is formed in an active layer region, and is a laser that can emit light in a single longitudinal mode by injecting a current into the active layer. When transmitting light in the 1.5 μm band, an InGaAsP semiconductor is used. The optical multiplexer 25 is an element that collects light output from a plurality of paths into one path, and an optical coupler, an AWG (Array Waveguide Grating), or the like can be used. The optical demultiplexer 26 is an element that branches light input from one path into a plurality of paths, and an optical coupler, a half mirror, a beam splitter, or the like is used. The wavelength monitor 27 is a device or element that measures the wavelength of input light. The light path between the DFB-LD 21, the optical multiplexer 25, the optical demultiplexer 26, and the wavelength monitor 27 transmits an optical waveguide, an optical fiber, a spatial system, and the like. The LD temperature controller 23 is an element or device that adjusts the temperature of the DFB-LD 21, and a Peltier element or the like is used. In FIG. 2, the range in which the temperature is adjusted by the LD temperature controller 23 is the portion of the DFB-LD 21. There is also. The LD temperature monitor 22 is an element or device for measuring the temperature of the DFB-LD 21 adjusted by the LD temperature controller 23, and a thermistor or the like is used. A temperature controller different from the LD temperature controller 23 may be used for the optical demultiplexer 26 and the wavelength monitor 27. The DFB-LD 21, the optical multiplexer 25, the LD temperature controller 23, and the LD temperature monitor 22 are often mounted in one case. Further, the optical demultiplexer 26 and the wavelength monitor 27 may be included in the same case. The LD current source 20 is a device that supplies current to the DFB-LD 21 and injects current into one selected DFB-LD 21. The LD current control circuit 28 is a device that controls the amount of current that the LD current source 20 injects into the DFB-LD 21, and injects an amount of current calculated from the wavelength of the oscillation light detected by the wavelength monitor 27. The LD temperature control circuit 24 is a device that controls the LD temperature controller.

  Hereinafter, the details of components and the principle of operation will be described. In order to realize an N-channel variable wavelength light source, N DFB-LDs 21 are used. The oscillation wavelength of each DFB-LD corresponds to the wavelength of each channel. At this time, the DFB-LD 21 is mounted so that each DFB-LD 21 can oscillate a desired channel wavelength at the same temperature as much as possible. There is only one DFB-LD 21 that oscillates among the plurality of DFB-LDs 21. The DFB-LD 21 to be oscillated from the LD current source 20 is selected and an injection current is allowed to flow. After the oscillation light of the DFB-LD 21 is collected into one path by the multiplexer 25, a part of the oscillation light is branched by the optical demultiplexer 26. The branched light is used for wavelength measurement by the wavelength monitor 27. In this wavelength monitor 27, it is necessary to measure the wavelengths of all channels, and it is necessary to have a mechanism capable of measuring the wavelengths even if the optical power is different. The wavelength of light used for optical communication is determined by the ITU grid, and the intervals are 50 GHz, 100 GHz, and 200 GHz. Therefore, a method using a Fabry-Perot etalon filter as the wavelength monitor 27 is an example. The method of the wavelength monitor 27 using the Fabry-Perot etalon filter is as follows: a method of detecting the ratio of the total optical power and the transmission power of the Fabry-Perot etalon filter; and the transmission output of two types of Fabry-Perot etalon filters having different transmission center wavelengths. There are methods for detecting the difference. Here, a deviation between the wavelength of the actually oscillating light and the target wavelength to be oscillated is detected, and the deviation is controlled by changing the amount of injected current by negative feedback control. Here, the relationship between the injection current amount and the wavelength shift amount is as shown in the equation (1), and the oscillation wavelength can be adjusted by adjusting the injection current amount.

  FIG. 2 shows a configuration in which a part of the oscillation light is branched and wavelength detection is performed by the duplexer 26 for measurement of the oscillation wavelength. As a method for measuring the oscillation wavelength, in addition to FIG. 2, an N × 2 optical coupler is used instead of the optical multiplexer, and an optical demultiplexer 26 is inserted between the DFB-LD 21 and the optical multiplexer to extract the oscillation light. And a method of emitting oscillation light on the side opposite to the multiplexer 25 in the DFB-LD 21 and measuring the wavelength of the light. In the latter two cases, N wavelength monitors 27 are prepared, or N monitoring paths are bundled into one to use the same wavelength monitor as in FIG. When N wavelength monitors 27 are prepared, a wavelength monitor that can detect a specific wavelength may be used.

  The temperature adjustment of the DFB-LD 21 is performed by the LD temperature monitor 22, the LD temperature controller 23, and the LD temperature control circuit 24. The LD temperature monitor 22 uses a thermistor or the like, and the temperature of the DFB-LD 21 can be measured by detecting the resistance value of the thermistor. For the LD temperature controller 23, a Peltier device or the like is used. The temperature of the DFB-LD 21 can be adjusted by changing the applied voltage or applied current to the Peltier element. The LD temperature control circuit 24 is a device that controls the DFB-LD temperature through the LD temperature regulator 23, and controls the application of a constant voltage to the LD temperature regulator 23 (constant voltage control), or measures with the LD temperature monitor 22. The negative feedback control is performed from the measured temperature and the control to maintain the constant temperature (constant temperature control) is performed.

  The negative feedback control performs both the LD temperature control and the LD injection current control. In order to make these multiple negative feedback controls compatible, the response speed of each negative feedback control is set to the settling time of the LD temperature control. If (Tt) and the LD current control settling time (Ti) are set, Tt> Ti is set. Here, the settling time refers to the time required for the step response to settle within the range of ± 5% of the steady value, and is a parameter indicating both rapid response and convergence. While the settling time for temperature control by the Peltier element is on the order of sec, the settling time for injection current control can be set on the order of msec.

  When negative feedback control of the LD injection current is started, the oscillation wavelength can be instantaneously adjusted to a desired wavelength in the order of msec based on the wavelength detected by the wavelength monitor. However, according to equation (1), the LD temperature also slowly changes in the order of seconds by changing the injection current value. The temperature of the DFB-LD 21 is somewhat controlled by the LD temperature monitor 22 and the LD temperature controller 23. However, since the response speed is slow, the temperature cannot be fully controlled. Change occurs. With respect to the change of the oscillation wavelength due to the temperature change of the DFB-LD 21, since the negative feedback control is performed from the wavelength monitor 27 to the injection current at a high speed on the order of msec, the wavelength is always adjusted to a desired wavelength. become. With the above mechanism, high-speed wavelength switching can be realized.

  There is also a configuration in which a channel is selected using an optical selector instead of the optical multiplexer 25 as shown in FIG. The optical selector uses an N × 1 optical switch, which is based on PLC-TOSW (a switch fabricated on an optical waveguide substrate using a refractive index change due to a thermo-optic effect), and MEMS (Micro electro-Mechanical System). A switch or the like can be used. At this time, the current may be injected only into one DFB-LD 21 or may be injected into all DFB-LDs 21.

  Here, an allowable range of deviation of the oscillation wavelength from the target oscillation wavelength under the same temperature of each DFB-LD 21 mounted on the DFB-LD array will be described. Even if the oscillation wavelength under the same temperature is deviated from the target oscillation wavelength, the wavelength can be adjusted at high speed by adjusting the injection current. When about 50 mA can be controlled by the amount of injected current, high-speed wavelength adjustment in the order of msec is possible within a range of about 40 GHz. Therefore, the allowable amount of deviation of the oscillation wavelength of the DFB-LD 21 mounted on the DFB-LD array from the target oscillation wavelength can be as large as ± 20 GHz. If the allowable range of deviation from the target oscillation wavelength of the wavelength tunable light source used for DWDM is within ± 2.5 GHz, a DFB-LD within ± 2.5 GHz must be mounted without injection current control. By combining control, the allowable range is greatly expanded within ± 20 GHz. By drastically improving the allowable range of the oscillation wavelength of the DFB-LD, the burden of light source production can be reduced, and a wavelength tunable light source can be manufactured at low cost.

  As described above, with the configuration shown in FIG. 2, an N-channel tunable light source capable of switching wavelengths at high speed in the order of msec can be realized. N channels can be selected at 100 GHz intervals or 200 GHz intervals, and any channel on the ITU grid can be selected at unequal intervals. Furthermore, the configuration of FIG. 2 can simplify the production of the wavelength tunable light source.

FIG. 3 shows a second reference example of the present invention. From N DFB-LD 21, optical multiplexer 25, optical demultiplexer 26, wavelength monitor 27, LD temperature monitor 22, LD temperature controller 23, LD current source 20, LD current control circuit 28, and LD temperature control circuit 34 Composed. The LD temperature control circuit is different from FIG. 2 for explaining the first reference example of the present invention, and the LD temperature control circuit 34 is different in that the amount of injected current is taken into consideration.

In the first reference example , control is performed so that the LD temperature becomes constant or a constant voltage is applied to the LD temperature controller 23. In FIG. 3, the temperature of the LD portion is adjusted so that the injection current amount subjected to negative feedback control from the wavelength approaches a certain value (target value of the injection current amount). Here, the negative feedback control performs both the LD temperature control and the LD injection current control. In order to make these plural negative feedback controls compatible, the settling time of each negative feedback control is set to the LD temperature control. If the settling time (Tt) and the LD injection current control settling time (Ti) are set, control is performed so that Tt> Ti. While the settling time for temperature control of the Peltier element is on the order of sec, negative feedback control of both is realized by setting the settling time for injection current control on the order of msec.

  The advantage of controlling the LD temperature so that the injection current value becomes the target value is as follows. When the wavelength is controlled by the injection current, there is a possibility that the target wavelength is converged when the injection current is too large or too small. If the injection current is too large, not only the power consumption is large, but also the deterioration of the element is accelerated. On the other hand, if the injection current is too small, the optical output power is weak and the optical SN characteristics are also deteriorated. Therefore, when using for a long time, it is better to adjust the injection current to an appropriate amount. With the configuration of FIG. 3, even if the injected current amount is converged to the target wavelength when the injected current amount is large or small, the injected current amount is adjusted to a certain value on a long time scale by adjusting the LD temperature. Therefore, power consumption, element deterioration can be suppressed, and good optical characteristics can be obtained.

FIG. 4 shows a third reference example of the present invention. N DFB-LDs 21, optical multiplexer 25, optical demultiplexer 26, wavelength monitor 27, LD temperature monitor 22, LD temperature controller 23, LD current source 20, LD current control circuit 28, LD temperature control circuit 24, A gain element 40, a gain element control circuit 43, a gain element current source 42, and a power monitor 41 are included.

2 is different from FIG. 2 showing the first reference example of the present invention in that a gain element 40, a gain element control circuit 43, a gain element current source 42, and a power monitor 41 are added. The gain element 40 is an element that amplifies or attenuates the light oscillated from the DFB-LD 21, and a semiconductor optical amplifier (SOA), an optical attenuator, or the like is used. The gain element 40 operates by supplying a current, and a gain element that can change the gain amount by changing the current amount is used. A gain element current source 42 supplies current to the gain element 40. If the gain element 40 is an element that operates by voltage supply, a gain voltage source is used instead of the gain element current source 42. The gain element control circuit 43 adjusts the amount of current supplied from the gain element current source 42. The power monitor 41 is an element or device that measures the power of the light separated by the optical demultiplexer 26 and can be measured by a photodiode (PD) or the like.

  The operation method will be described below. A part of the light output from the DFB-LD array is extracted by the optical demultiplexer 26, and the power of the light output from the DFB-LD array is measured. The gain element control circuit 43 performs negative feedback control on the current amount of the gain element 40 so that the measured optical power approaches the target value. In the configuration of FIG. 4, since the wavelength is adjusted by controlling the amount of current injected into the DFB-LD 21, the output power from the DFB-LD 21 is always maintained by operating the gain element 40 with constant output power control. It becomes constant.

  Here, gain element control, temperature control, LD injection current control, and three negative feedback controls are performed. Since these negative feedback controls need to be performed without affecting each other, the settling time of each negative feedback control is set as the gain element control settling time (Ta), the LD temperature control settling time (Tt), and the LD injection. Assuming that the current control settling time (Ti) is satisfied, control is performed so that Tt> Ti> Ta. The temperature control settling time of the Peltier element must be on the order of sec, the injection current control settling time on the order of msec, and the gain element control settling time on the order of sub msec or less.

  FIG. 4 shows a configuration in which a part of the oscillation light is branched by the branching filter 26 to measure the power for measuring the optical power. As an optical power measurement method, in addition to FIG. 4, an optical demultiplexer 26 is inserted between the DFB-LD 21 and the optical multiplexer 25 to extract oscillation light, and N × 2 instead of the optical multiplexer 25 is used. There is a method using an optical coupler and a method of emitting oscillation light on the opposite side of the multiplexer 25 in the DFB-LD 21 and measuring the power of the light. In any case, when the optical power is measured before the optical power is controlled by the gain element 40, it is necessary to calculate the necessary gain from the input optical power and control the gain element current source 42.

  The configuration of FIG. 4 has the following advantages. 2 and 3, since the wavelength is controlled by changing the amount of injected current, the optical output power also changes according to the amount of injected current. However, the optical output power needs to be constant for use in DWDM transmission for optical communication. By performing as shown in FIG. 4, a constant optical output power can be obtained.

FIG. 5 shows a fourth reference example of the present invention. N DFB-LDs 21, optical multiplexer 25, optical demultiplexer 26, wavelength monitor 27, LD temperature monitor 22, LD temperature controller 23, LD current source 20, LD current control circuit 28, LD temperature control circuit 24, It comprises a saturation characteristic gain element 50 and a gain element current source 51. 2 is different from FIG. 2 showing the first reference example in that a saturation characteristic gain element 51 and a gain element current source 51 are added. The saturation characteristic gain element 50 is an element whose gain changes depending on the intensity of the input light. The gain amount is small when the input light intensity is large, and the gain amount is large when the input light intensity is small. Such saturation characteristics are exhibited when the optical semiconductor amplifier (SOA) is operated in the gain saturation region. The gain element current source 51 is a current source for driving the saturation characteristic gain element 50 and is driven by constant current control.

  Since the optical output power is determined by the amount of injected current, the optical power varies at the speed of injection current control. The saturation characteristic gain element 50 exhibiting saturation characteristics must follow the optical power that fluctuates at a high speed, and the response speed needs to be faster than the injection current control. The optical amplifier can be used for this because the response speed is as high as nS order.

The configuration shown in FIG. 5 has the following advantages. Advantages similar to the present invention the third reference example, can amount injected current be varied to obtain a constant optical output power. Further, as shown in FIG. 4, since the negative feedback control of the gain element 51 is not required, there is an advantage that can be realized with a simpler configuration than that of FIG.

Next, a DFB-LD array capable of performing a high-speed wavelength change in the fifth reference example will be described.

FIG. 6 shows the relationship between the amount of injected current and the oscillation wavelength in order to explain this reference example . In FIG. 2 showing the first reference example of the present invention, N DFB-LDs 21 are used to realize an N-channel wavelength variable light source. FIG. 6A shows the relationship between the injected current amount and the oscillation wavelength in each DFB-LD 21. However, when the injection current amount can be controlled by about 100 mA, the wavelength variable range that can be controlled by the injection current is about 80 GHz. Therefore, when realizing a wavelength variable light source with an interval of 50 GHz, it is possible to oscillate two channels per DFB-LD 21 by controlling the injection current.

  FIG. 6B shows the relationship between the amount of injected current and the oscillation wavelength in each DFB-LD 21 when this method is used. By using such a method, it is possible to construct a wavelength tunable light source that can oscillate more channels with a smaller number of DFB-LDs 21.

FIG. 7 shows a sixth reference example of the present invention. It is composed of N DFB-LDs 21, an optical multiplexer 25, an LD temperature monitor 22, an LD temperature controller 23, an LD current source 21, an LD temperature control circuit 24, and an LD current value recording device 70. FIG. 7 omits from FIG. 2 illustrating the first reference example of the present invention a portion where negative feedback control is performed using the oscillation wavelength detected by the wavelength monitor as an injection current amount, and an LD current value recording device 70 is added instead. Different points. In FIG. 7, the injection current value for oscillating each channel in each DFB-LD 21 is measured in advance, and the injection current amount is stored in the LD current value recording device 70. When switching the channel, the current value is read out from the stored injection current value, and the value is sent to the LD current source 21 to inject the current amount of that value into the DFB-LD 21. In this configuration, the negative feedback control circuit of the injection current can be omitted, and a high-speed wavelength variable light source can be realized with a simple configuration.

  In the configuration of FIG. 7, the allowable range of deviation of the oscillation wavelength of each DFB-LD 21 from the target wavelength under the same temperature is further narrowed, and the allowable range of deviation of the actually oscillated light from the target wavelength is widened. This makes it possible to set the same injection current amount for each DFB-LD.

FIG. 8 shows a first embodiment of the present invention. N DFB-LDs 21, optical multiplexer 25, optical demultiplexer 26, wavelength monitor 27, LD temperature monitor 22, LD temperature controller 23, LD current source 20, LD current control circuit 28, LD temperature control circuit 24, The determination circuit 80 is configured.

The difference from FIG. 2 for explaining the first reference example of the present invention is that FIG. 2 uses only injection current control for wavelength adjustment, whereas FIG. 8 uses temperature adjustment for coarse adjustment in wavelength adjustment. The difference is that adjustment by injection current is used for fine adjustment. The newly added discriminating circuit 80 in FIG. 8 is a circuit that discriminates whether or not to switch from coarse adjustment to fine adjustment.

Details of the configuration of FIG. 8 will be described. Each DFB-LD 21 is mounted at intervals of about 400 GHz. The DFB-LD 21 can be adjusted by temperature control in the range of 400 GHz. When adjusting to a desired wavelength, first, the temperature of the DFB-LD is adjusted by the LD temperature controller 23, and the wavelength is roughly adjusted. At this time, either a method of adjusting while detecting the temperature of the DFB-LD 21 by the LD temperature monitor 22 or a method of adjusting while detecting the wavelength of the output light by the wavelength monitor 27 may be used. FIG. 8 shows a method of adjusting while detecting the temperature of the DFB-LD 21 from the temperature monitor 22. Usually, the settling time of the Peltier device takes several seconds, but it can be improved to a sub-sec order settling time by PI control or the like. The determination circuit 80 determines whether the temperature is within the target temperature range of the LD temperature monitor or within the target wavelength range of the wavelength monitor 27. When the temperature of the DFB-LD 21 is detected and controlled by the LD temperature monitor 22, the operating temperature for oscillating a desired wavelength is measured in advance, and the value or the target temperature range for coarse adjustment is recorded on the recording medium. Save to. When the determination circuit 80 determines that the temperature has converged to the target temperature range or the target wavelength range, the injection current control is started. The injection current control is a method of controlling the wavelength only by adjusting the injection current while fixing the temperature as described in the first reference example , or the wavelength control by adjusting the injection current as described in the second reference example. At the same time, the injection current is brought close to the target value over a long time span by adjusting the temperature. Whichever method is used, after switching to the injection current control, the target wavelength can be instantaneously adjusted in the order of msec. This is an example of a temperature range that is a condition for switching from coarse adjustment to fine adjustment. If the wavelength range that can be adjusted by the amount of injected current is about ± 400 GHz, the target temperature is within ± 4 ° C. Normally, temperature control using a Peltier device or the like has a settling time of the order of sec, but it can be realized in a sub-sec order to converge within a range of ± 4 ° C. If the temperature converges within the above temperature range, the wavelength can be adjusted to the target value in ms order by switching to injection current control.

  A method for determining the switching from the coarse adjustment to the fine adjustment will be described. In the temperature control in the coarse adjustment, when adjusting to the target temperature, it is necessary to design the response speed as fast as possible, but it is desirable to keep the overshoot within the target temperature range of the coarse adjustment. In this case, it is only necessary to determine whether or not the temperature detected by the LD temperature monitor 22 is within the target temperature range in the determination of switching from the coarse adjustment to the fine adjustment, and the determination method becomes simple. Conversely, when the overshoot falls outside the target range for coarse adjustment, a switching mechanism for returning from fine adjustment to coarse adjustment is required. Since the rough adjustment target range of ± 4 ° C. in the above example is a relatively wide target range, the control circuit can be easily designed. The same applies when performing coarse adjustment using the wavelength monitor 27.

  The configuration shown in FIG. 8 has the following advantages. Since one DFB-LD 21 can oscillate in a wavelength range of 400 GHz, by using a plurality of DFB-LDs 21, it is possible to oscillate in a very wide wavelength range or in a very large number of wavelength channels. Furthermore, the wavelength adjustment takes a very long time of about several seconds with only the temperature adjustment, whereas only the coarse adjustment is performed with the temperature adjustment, and the fine adjustment is performed with the injection current control, so that the wavelength switching speed on the order of sub-sec. And can make improvements.

FIG. 9 shows a second embodiment of the present invention. In FIG. 9, one DFB-LD 21, an optical demultiplexer 26, a wavelength monitor 27, an LD temperature monitor 22, an LD temperature adjuster 23, an LD current source 20, an LD current control circuit 28, an LD temperature control circuit 24, and a discrimination circuit. 80. 8 differs from FIG. 8 showing the first embodiment of the present invention in that there is one DFB-LD 21 and there is no optical multiplexer 25.

The wavelength switching method is the same as in the first embodiment. First, the temperature is adjusted by the LD temperature controller 23 for coarse wavelength adjustment. Thereafter, when the temperature or wavelength of the DFB-LD is converged within a certain range, it is confirmed by the discrimination circuit 80 that fine adjustment by injection current control is started. With the same mechanism as in the first embodiment, the wavelength switching time in the range of about 400 GHz can be improved to the sub-sec order in the single DFB-LD 21.

Configuration diagram showing a conventional DFB-LD array Configuration diagram of DFB-LD array of first reference example Configuration diagram of DFB-LD array of second reference example Configuration diagram of DFB-LD array of third reference example Configuration diagram of DFB-LD array of fourth reference example (A) The figure which showed the relationship between the injection current amount and oscillation wavelength in a 1st reference example (b) The figure which showed the relationship between the injection current amount and oscillation wavelength in a 5th reference example Configuration diagram of DFB-LD array of sixth reference example Configuration diagram of the DFB-LD array of the first embodiment Configuration diagram of DFB-LD of second embodiment

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10, 20 ... LD current source 11, 21 ... DFB-LD, 12, 22 ... LD temperature monitor, 13, 23 ... LD temperature controller, 14, 24 ... LD temperature control circuit, 15, 25 ... Optical multiplexer, DESCRIPTION OF SYMBOLS 16, 40 ... Gain element 17, 42, 51 ... Gain element current source, 26 ... Optical demultiplexer, 27 ... Wavelength monitor, 28 ... LD current control circuit, 34 ... LD temperature control circuit, 41 ... Power monitor, 43 ... gain element control circuit, 50 ... saturation characteristic gain element, 70 ... LD current value recording device, 80 ... discrimination circuit.

Claims (6)

In a distributed feedback semiconductor laser array composed of a plurality of distributed feedback semiconductor lasers under the same temperature control and an optical multiplexer that guides output light from the plurality of distributed feedback semiconductor lasers to one waveguide,
Means for controlling the amount of injected current of the distributed feedback semiconductor laser, and means for measuring the oscillation wavelength;
Rough adjustment of the wavelength of the distributed feedback semiconductor laser is performed by adjusting the temperature.After the temperature or light wavelength falls within a certain range, the amount of injected current is adjusted so that the measured oscillation wavelength approaches the oscillation target value. A distributed feedback semiconductor laser array, wherein the wavelength is finely adjusted by controlling . The response speed for controlling the injection current amount is set to be faster than the response speed for adjusting the temperature.
2. The distributed feedback semiconductor laser array according to claim 1, wherein: The temperature of the distributed feedback semiconductor laser is controlled so that the injection current amount controlled to bring the wavelength of the oscillation light closer to the target value in the fine adjustment of the wavelength is made closer to the target value of the injection current amount. The distributed feedback semiconductor laser array according to claim 1 or 2 . Means for controlling the optical output power, and means for measuring the optical output power,
Distributed feedback semiconductor laser array according to claim 1 to 3 any one of claims to this and features at a higher response speed than the response speed for controlling the optical output power to keep the optical output power constant to control the injection current. The gain depends on the optical input power with respect to the input light, and the gain decreases as the optical input power increases, and therefore means for suppressing fluctuations in the optical output power due to changes in the amount of injected current is provided. 4. The distributed feedback semiconductor laser array according to any one of 1 to 3 . Distributed feedback semiconductor laser array distributed feedback semiconductor laser according to claim 1 to 5 any one of claims, characterized by using a distributed feedback semiconductor laser of a single instead of a.

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