JP2014165384A - Semiconductor laser module - Google Patents

Abstract

Provided is a semiconductor laser module capable of setting a control wavelength of a laser beam more flexibly while being highly accurate.
A semiconductor laser element and a transmittance corresponding to the transmission characteristics of two or more laser beams having a periodic transmission characteristic in terms of frequency of light and being a part of a laser beam output from the semiconductor laser element. 2 and two or more optical filters 9 and 10, and two or more optical receivers 11, 12, and 13 that receive each laser beam transmitted through the two or more optical filters. Two or more optical filters have a transmission characteristic with a difference period within 1/3 of the period, and the transmission characteristics with respect to two or more laser beams are within a range of 1/3 to 1/5 of one period. Semiconductor laser module 100 arranged so that the phases are different.
[Selection] Figure 1

Description

  The present invention relates to a semiconductor laser module.

  In a wavelength division multiplexing (WDM) communication field in which a plurality of optical signals having different wavelengths are multiplexed and transmitted simultaneously on one optical fiber, optical signals are transmitted at narrower wavelength intervals as the amount of information communication increases. Multiplexing is required. In order to multiplex optical signals at narrower wavelength intervals, it is necessary to control the wavelength of the laser light emitted from the semiconductor laser element as signal light with high accuracy. For this reason, there has been proposed a semiconductor laser module including an etalon filter that selectively transmits laser light emitted from a semiconductor laser element (see Patent Documents 1 and 2).

  In this semiconductor laser module, a part of the laser light emitted from the semiconductor laser element is branched to the etalon filter side, and the temperature of the semiconductor laser element is controlled based on the intensity of the branched light transmitted through the etalon filter. The wavelength of laser light emitted from the laser element is controlled. Since the etalon filter has periodic transmission characteristics with respect to the wavelength of the laser light, the temperature of the semiconductor laser element is controlled so that the intensity of the branched light transmitted through the etalon filter becomes a predetermined value. Thus, the laser beam can be controlled to a predetermined wavelength.

  For more precise wavelength control, the wavelength of the laser beam to be controlled is a frequency region where the transmittance change rate (hereinafter referred to as transmittance change rate) is large with respect to the light frequency in the transmission characteristics of the etalon filter. It is preferable that the wavelength is set.

JP 2007-142110 A JP 2003-110190 A

  Incidentally, in recent years, digital coherent optical communication such as 40 Gbps and 100 Gbps has begun to spread. When realizing such a large-capacity optical communication, the frequency interval of the laser light is also different from the conventional fixed grid method fixed at 25 GHz or 50 GHz for efficient use of the optical transmission wavelength band. A so-called flexible grid system that is mixedly arranged at intervals is about to be introduced.

  However, since the etalon filter has a fixed transmission characteristic, if the wavelength of the laser light to be controlled is a wavelength in the frequency region where the transmittance change rate is small, highly accurate wavelength control is difficult, and the flexible grid method is used. Had a problem that it was difficult to apply. The transmission characteristics of the etalon filter can be controlled to some extent by adjusting the temperature. However, additional temperature adjusting elements must be prepared, and adjustment takes time or the temperature must be changed by nearly 30 ° C. It was difficult.

  The present invention has been made in view of the above, and an object of the present invention is to provide a semiconductor laser module that can set a control wavelength of laser light more flexibly while being highly accurate.

  In order to solve the above-mentioned problems and achieve the object, a semiconductor laser module according to the present invention includes a semiconductor laser element and a laser having a periodic transmission characteristic of light in frequency and output from the semiconductor laser element Two or more optical filters that transmit two or more laser beams, which are part of the light, with a transmittance according to the transmission characteristics, and two or more light receivers that receive the laser beams transmitted through the two or more optical filters And the two or more optical filters have the transmission characteristics with a difference period within 1/3 of one period, and the two or more optical filters have the two or more laser beams with respect to the two or more laser beams. The transmission characteristics are arranged so that the phases are different from each other within a range of 1/3 to 1/5 of one cycle.

  The semiconductor laser module according to the present invention has a semiconductor laser element, a branching device for branching the laser beam output from the semiconductor laser element into two or more laser beams, and a periodic transmission characteristic of the light in frequency. An optical filter that transmits the two or more branched laser beams at a transmittance according to the transmission characteristics; and two or more light receivers that receive the laser beams transmitted through the optical filter. Are characterized in that the transmission characteristics of the optical filter with respect to the laser beams are incident on the optical filter at angles that are different from each other in a range of 1/3 to 1/5 of one cycle.

  In the semiconductor laser module according to the present invention as set forth in the invention described above, the optical filter is an etalon filter.

  In the semiconductor laser module according to the present invention as set forth in the invention described above, the optical filter is a ring resonator type filter.

  According to the present invention, the control wavelength of the laser beam can be set more flexibly while being highly accurate.

FIG. 1 is a schematic configuration diagram of the semiconductor laser module according to the first embodiment. FIG. 2 is a diagram illustrating an example of transmission characteristics of the etalon filter. FIG. 3 is a diagram showing the transmission characteristics of the two etalon filters shown in FIG. FIG. 4 is a schematic configuration diagram of the semiconductor laser module according to the second embodiment. FIG. 5 is a schematic configuration diagram of the semiconductor laser module according to the third embodiment. FIG. 6 is a schematic configuration diagram of a semiconductor laser module according to the fourth embodiment. FIG. 7 is a diagram showing the transmission characteristics of the three etalon filters shown in FIG. FIG. 8 is a configuration diagram using a ring resonator type optical filter.

  Hereinafter, embodiments of a semiconductor laser module according to the present invention will be described in detail with reference to the drawings. Note that the present invention is not limited to the embodiments. Moreover, in each drawing, the same code | symbol is attached | subjected suitably to the same or corresponding component. Also, it should be noted that the drawings are schematic, and the thicknesses and ratios of the layers are different from the actual ones. Moreover, the part from which the relationship and ratio of a mutual dimension differ also in between drawings is contained. In the present specification, the semiconductor optical amplification element is a semiconductor element having a laser amplification function, and includes a semiconductor laser element and a semiconductor optical amplifier. The term “semiconductor optical amplifier” means an amplifier that amplifies input light and outputs it.

(Embodiment 1)
FIG. 1 is a schematic configuration diagram of a semiconductor laser module according to Embodiment 1 of the present invention. As shown in FIG. 1, a semiconductor laser module 100 includes a housing 1, bases 2 and 3, a semiconductor laser element 4, a thermistor 5, a collimator lens 6, an optical isolator 7, a beam splitter 8 that is an optical splitter, Etalon filters 9 and 10, three photodiodes (PD) 11, 12 and 13 which are light receivers, a condenser lens 14, and an optical fiber 15 are provided. The semiconductor laser module 100 is connected to the controller C.

  The base 2 is placed on a temperature control element (not shown) in the housing 1. The base 2 mounts an optical isolator 7, a beam splitter 8, etalon filters 9 and 10, PDs 11, 12, and 13 and a base 3. The base 3 is placed on the base 2, and the semiconductor laser element 4, the thermistor 5, and the collimator lens 6 are placed on the base 3. The condenser lens 14 and the optical fiber 15 are attached to the housing 1.

  The temperature adjustment element is, for example, a Peltier element. The temperature adjusting element can cool the semiconductor laser element 4 and adjust its temperature by being supplied with a driving current. The thermistor 5 is disposed in the vicinity of the semiconductor laser element 4 in order to measure the temperature of the semiconductor laser element 4.

  The bases 2 and 3 are made of, for example, aluminum nitride (AlN) having a high thermal conductivity of 170 W / m · K, but are not limited to AlN, and materials having high thermal conductivity such as CuW, silicon carbide (SiC), and diamond. But you can.

  The semiconductor laser element 4 is a DFB laser element or an integrated semiconductor laser element (for example, see Patent Document 1). The semiconductor laser element 4 is supplied with a drive current from the controller C and outputs a laser beam L1. The wavelength of the laser beam L1 is a wavelength within a wavelength band (for example, 1520 nm to 1620 nm) used for optical communication.

  The collimating lens 6 is disposed on the front side, which is the side that outputs the laser light of the semiconductor laser element 4. The collimating lens 6 converts the laser light L1 output from the semiconductor laser element 4 into parallel light.

  The optical isolator 7 transmits the laser light L1 to the beam splitter 8 side and prevents the light from returning from the beam splitter 8 side to the semiconductor laser element 4.

  The beam splitter 8 transmits most of the laser light L1 and outputs it to the condensing lens 14, and branches a part of the laser light L1 (laser light L2, L3, L4). Reflected toward the etalon filters 9 and 10.

  The condensing lens 14 condenses and inputs the laser light L1 output from the beam splitter 8 onto the optical fiber 15. The optical fiber 15 transmits the laser light L1 to a predetermined device or the like.

  On the other hand, the PD 11 detects the intensity of the laser light L2 and outputs a current corresponding to the detected intensity to the controller C.

  The etalon filters 9 and 10 have a periodic transmission characteristic of the light in frequency, and selectively transmit the laser beams L3 and L4 reflected by the beam splitter 8 with a transmittance according to the transmission characteristic. Input to monitor PDs 12 and 13. The PDs 12 and 13 detect the intensities of the laser beams L3 and L4 that have passed through the etalon filters 9 and 10 and output a current having a value corresponding to the detected intensities to the controller C.

  The intensities of the laser beams L2, L3, and L4 detected by the PDs 11, 12, and 13 are used for wavelength lock control (control for setting the laser beam L1 to a desired wavelength and intensity) by the controller C.

  Here, the etalon filters 9 and 10 have transmission characteristics with substantially the same period. However, as shown in FIG. 1, the etalon filter 10 is arranged so that the optical axis thereof is substantially parallel to the traveling direction of the laser light L4, but the etalon filter 9 is disposed in the traveling direction of the laser light L3. In contrast, the optical axis is inclined. The inclination angle is, for example, about 0.7 degrees when the period of the etalon filters 9 and 10 is 50 GHz.

  FIG. 2 is a diagram illustrating an example of transmission characteristics of the etalon filter. The horizontal axis indicates the frequency of light, and the vertical axis indicates the PD current. The PD current on the vertical axis is substantially proportional to the transmittance of the etalon filter. In the case of FIG. 2, for example, in the case of light having a frequency of 191700 GHz (curve valley) or 191750 GHz (curve peak), the transmittance change rate is small, so that highly accurate wavelength control is difficult.

  On the other hand, FIG. 3 is a diagram showing transmission characteristics of the two etalon filters 9 and 10 shown in FIG. A curve C1 is the transmission characteristic of the etalon filter 9, and a curve C2 is the transmission characteristic of the etalon filter 10. Such curves C1 and C2 are also called frequency discrimination curves. As described above, the etalon filter 10 is disposed so that the optical axis is substantially parallel to the traveling direction of the laser light L4, and the etalon filter 9 is inclined with respect to the traveling direction of the laser light L3. As shown in FIG. 3, the etalon filters 9 and 10 have substantially the same period but have different transmission characteristics phases.

  As a result, there is a wider frequency region that can be used for high-accuracy wavelength control with a large transmittance change rate of about 10 μA / GHz shown by the thick line portions of the curves C1 and C2 than in the case shown in FIG. It will be. If the controller can stabilize with an accuracy of 1 μA, the wavelength is controlled with an accuracy of 0.1 GHz. As a result, the control wavelength of the laser beam L1 can be set more flexibly while being highly accurate. Further, there is no need to add a temperature adjusting element for adjusting the transmission characteristics of the etalon filter, and highly accurate and flexible wavelength control can be realized at low cost.

  Specifically, in the wavelength lock control, the controller C controls the intensity of the laser light L2 detected by the PD 11 and the laser light L3 or the laser light L3 after passing through the etalon filter 9 or etalon filter 10 detected by the PD 12 or PD 13. Control is performed to change the drive current and temperature of the semiconductor laser element 4 so that the ratio of the intensity of the laser beam L4 to the intensity and wavelength of the laser beam L1 becomes a desired intensity and wavelength. Thereby, the intensity | strength and wavelength of laser beam L1 are controllable to desired intensity | strength and wavelength (lock wavelength).

  As for the detection result of the intensity of the laser light after passing through the etalon filter, which value of PD12 or PD13 is used is determined by the transmission of the etalon filter 9 and the etalon filter 10 at the wavelength to be controlled by the laser light L1. It is preferable to use the detection result of the larger rate change rate. Note that the controller C stores a table indicating the correspondence between the control wavelength and the transmittance change rate in the storage unit to determine which transmittance change rate is large at the wavelength to be controlled, and according to the control wavelength. May be selected as appropriate.

  As the basic period of the etalons 9 and 10, it is desirable to use one having a frequency of about 20 GHz to 150 GHz in view of fixing accuracy and transmittance change rate at the time of manufacture. Regarding the difference in phase of the transmission characteristics of the etalon filters 9 and 10, in the range of 1/3 to 1/5 of one cycle, the frequency region having a large transmittance change rate in the wavelength range of 30 nm or more Since it can distribute over a wavelength range, it is preferable.

  Further, the periods of the etalon filters 9 and 10 are preferably substantially equal to each other. However, if the difference is within 1/3 of one period, a frequency region having a large transmittance change rate can be obtained even if they are different from each other. Since it can distribute over a range, it is preferable and it is still more preferable that it is the same.

  In the semiconductor laser module 100, the etalon filter 10 is arranged so that the optical axis is substantially parallel to the traveling direction of the laser light L4. However, a difference in phase of transmission characteristics from the etalon filter 9 is desired. You may make it incline so that it can set to the value of.

(Embodiment 2)
FIG. 4 is a schematic configuration diagram of a semiconductor laser module according to Embodiment 2 of the present invention. The semiconductor laser module 100A has a configuration in which the beam splitter 8 and the etalon filters 9 and 10 of the semiconductor laser module 100 are replaced with a beat splitter 8A and an etalon filter 9A. Note that the controller C is not shown.

  In this semiconductor laser module 100A, the beads splitter 8A causes the laser beams L3 and L4 to enter the etalon filter 9A so that the angle formed between each other is inclined at a predetermined angle. As a result, the transmission characteristics of the etalon filter 9A with respect to the laser beams L3 and L4 are different from each other in the range of 1/3 to 1/5 of one cycle. As a result, as with the semiconductor laser module 100, the control wavelength of the laser light L1 can be set more flexibly while being highly accurate, with the single etalon filter 9A.

(Embodiment 3)
FIG. 5 is a schematic configuration diagram of a semiconductor laser module according to Embodiment 3 of the present invention. In the semiconductor laser module 100B, the beam splitter 8, the etalon filters 9, 10, PDs 11, 12, and 13 of the semiconductor laser module 100 are arranged behind the semiconductor laser element 4, and the beam splitter 18, PD 19, and collimator lens 20 are further arranged. It has an added configuration. Note that the controller C is not shown.

  In this semiconductor laser module 100B, a part (laser light L5) of the laser light L1 output from the front end side of the semiconductor laser element 4 is branched by the beam splitter 18 and reflected to the PD 19 side. The PD 19 detects the intensity of the laser light L5 and outputs a current corresponding to the detected intensity to the controller C. Thus, the intensity of the laser beam L1 is detected by the PD 19.

  On the other hand, the semiconductor laser element 4 outputs the laser beam L1a from the rear end side. The laser beam L1a is a laser beam oscillated inside the semiconductor laser element 4 similarly to the laser beam L1, and has the same wavelength as the laser beam L1 and a light intensity proportional to the laser beam L1.

  The collimator lens 20 converts the laser light L1a output from the semiconductor laser element 4 into parallel light.

  The beam splitter 8 reflects part of the laser beam L1a (laser beams L2a, L3a, and L4a) toward the PD 11 and the etalon filters 9 and 10, respectively.

  The PD 11 detects the intensity of the laser light L2a and outputs a current corresponding to the detected intensity to the controller.

  The etalon filters 9 and 10 selectively transmit the laser beams L3a and L4a reflected by the beam splitter 8 and transmit them to the wavelength monitoring PDs 12 and 13 with a transmittance according to the transmission characteristics. The PDs 12 and 13 detect the intensities of the laser beams L3a and L4a that have passed through the etalon filters 9 and 10, and output a current having a value corresponding to the detected intensities to the controller.

  The intensities of the laser beams L2a, L3a, and L4a detected by the PDs 11, 12, and 13 are used for wavelength lock control by the controller as in the case of the semiconductor laser module 100. As a result, the control wavelength of the laser beam L1 can be set more flexibly while being highly accurate.

(Embodiment 4)
FIG. 6 is a schematic configuration diagram of a semiconductor laser module according to Embodiment 4 of the present invention. The semiconductor laser module 100C has a configuration in which the beam splitter 8 of the semiconductor laser module 100 is replaced with a beam splitter 8C, and an etalon filter 21 and a PD 22 are further added.

  The beam splitter 8C transmits most of the laser light L1 and inputs the laser light L1 to the condenser lens 14, and part of the laser light L1 (laser light L2, L3, L4, L6) is supplied to the power monitor PD 11, Reflected toward the etalon filters 9, 10, 21.

  The etalon filter 21 has a periodic transmission characteristic of the light in frequency, and selectively transmits the laser light L6 reflected by the beam splitter 8C with a transmittance according to the transmission characteristic, and the PD 22 for wavelength monitoring. To enter.

  The intensities of the laser beams L2, L3, L4, and L6 detected by the PDs 11, 12, 13, and 22 are used for wavelength lock control by the controller.

  Here, the etalon filter 21 has transmission characteristics with substantially the same period as the etalon filters 9 and 10, but is arranged with the optical axis inclined with respect to the traveling direction of the laser light L 6. The inclination angle is smaller than the inclination angle of the optical axis of the etalon filter 9 with respect to the traveling direction of the laser light L3. For example, when the period of the etalon filters 9, 10, and 21 is 50 GHz, it is, for example, about 0.35 degrees.

  FIG. 7 is a diagram showing the transmission characteristics of the three etalon filters 9, 10, and 21 shown in FIG. A curve C1 is the transmission characteristic of the etalon filter 9, and a curve C2 is the transmission characteristic of the etalon filter 10. A curve C3 is the transmission characteristic of the etalon filter 21. As described above, the etalon filter 21 tilts the optical axis at a tilt angle smaller than that of the etalon filter 9 with respect to the traveling direction of the laser light L6. Therefore, as shown in FIG. 10 and 21 have substantially the same period, but the phases of the transmission characteristics are different from each other. Furthermore, the curve C3 that is the frequency discrimination curve of the etalon filter 21 is located between the curve C1 and the curve C2. That is, the phase difference between the curve C1 and the curve C3 is smaller than the phase difference between the curve C1 and the curve C2, and is about ½ of the phase difference between the curve C1 and the curve C2, for example.

  As a result, the frequency region having a large transmittance change rate indicated by the thick line portions of the curves C1, C2, and C3 exists in a wider range than the case shown in FIG. As a result, the control wavelength of the laser beam L1 can be set more flexibly while being highly accurate. Thus, the number of etalon filters is not particularly limited as long as it is two or more.

  In the above embodiment, an etalon filter is used as the optical filter. However, other types of optical filters having periodic transmission characteristics of light may be used.

  FIG. 8 is a configuration diagram using a ring resonator type optical filter. In this configuration, a planar lightwave circuit (PLC) 30 includes an optical branching unit 31, a linear optical waveguide 32, an optical waveguide 33 having a ring resonator type optical filter 33a, and a ring resonator type light. And an optical waveguide 34 having a filter 34a.

  The ring resonator type optical filters 33a and 34a have transmission characteristics with a period of difference within 1/3 of one period.

  The beam splitter 29 reflects a part of the laser beam L1 (laser beam L7) toward the PLC 30. In the PLC 30, the light branching unit 31 branches the laser beam L7 into laser beams L8, L9, and L10.

  The optical waveguide 32 guides the laser light L8 to the PD 11. The optical waveguides 33 and 34 guide the laser beams L9 and L10 to the PDs 12 and 13, respectively.

  Here, the ring resonator type optical filters 33a and 34a are arranged so that the transmission characteristics with respect to the corresponding laser beams L9 and L10 are different from each other in a range of 1/3 to 1/5 of one cycle. As a result, as in the case of using the etalon filters 9 and 10, the intensities of the laser beams L8, L9 and L10 detected by the PDs 11, 12, and 13 can be used for wavelength lock control by the controller. The control wavelength of L1 can be set more flexibly while being highly accurate.

  The present invention is not limited to the above embodiment. What was comprised combining each component mentioned above suitably is also contained in this invention. For example, in the second embodiment, three or more laser beams are incident on the etalon filter so that the angle formed by each other is inclined at a predetermined angle, and three or more frequency discrimination curves are obtained as in the fourth embodiment. It is good also as a structure provided with. Further effects and modifications can be easily derived by those skilled in the art. Therefore, the broader aspect of the present invention is not limited to the above-described embodiment, and various modifications can be made.

DESCRIPTION OF SYMBOLS 1 Case 2, 3 Base 4 Semiconductor laser element 5 Thermistor 6 Collimator lens 7 Optical isolator 8, 8A, 8C, 18, 29 Beam splitter 9, 9A, 10, 21 Etalon filter 11, 12, 13, 19, 22 PD
14 Condensing lens 15 Optical fiber 20 Collimator lens 29 Beam splitter 30 PLC
31 Optical branching unit 32, 33, 34 Optical waveguide 33a Ring resonator type optical filter 34a Ring resonator type optical filter 100, 100A, 100B, 100C Semiconductor laser module C Controller C1, C2, C3 Curves L1, L1a, L2, L2a, L3, L3a, L4, L5, L6, L7, L8, L9 Laser light

Claims (4)

A semiconductor laser element;
Two or more optical filters having a periodic transmission characteristic of light and transmitting two or more laser beams that are part of the laser beam output from the semiconductor laser element with a transmittance according to the transmission characteristics When,
Two or more light receivers for receiving each laser beam transmitted through the two or more optical filters;
With
The two or more optical filters have the transmission characteristics with a difference period within 1/3 of one period, and the two or more optical filters have the transmission characteristics for the two or more laser beams of 1 A semiconductor laser module, which is arranged so that phases thereof are different from each other in a range of 1/3 to 1/5 of a cycle. A semiconductor laser element;
A branching device for branching the laser beam output from the semiconductor laser element into two or more laser beams;
An optical filter having a periodic transmission characteristic of light in frequency, and transmitting the two or more branched laser beams at a transmittance according to the transmission characteristic;
Two or more light receivers for receiving each laser beam transmitted through the optical filter;
With
Each laser beam is incident on the optical filter at an angle such that the transmission characteristics of the optical filter with respect to the laser beam are different from each other in a range of 1/3 to 1/5 of one cycle. A semiconductor laser module.   The semiconductor laser module according to claim 1, wherein the optical filter is an etalon filter.   2. The semiconductor laser module according to claim 1, wherein the optical filter is a ring resonator type filter.

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