JP2009081321A - Wavelength stabilized laser apparatus, method for the same, and raman amplifier equipped with wavelength stabilized laser apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To stabilize the wavelength of radiated laser beams. <P>SOLUTION: A thin-film resistor for heating the diffraction grating of semiconductor laser is arranged. The thin-film resistor is heated to a predetermined temperature before laser beams are radiated by the semiconductor laser, and as a result, the diffraction grating is heated to a predetermined temperature (Step 51). Beams radiated by the semiconductor laser enter two photo detectors whose photosensitive properties are different. Based on the current values of the two photo detectors, it is detected whether the wavelength of the laser beam is longer or shorter than a predetermined wavelength (Step 54). When it is detected that the wavelength of the laser beam is longer than the predetermined wavelength, heating the thin-film resistor is weakened (Step 55). When it is detected that the wavelength of the laser beam is shorter than the predetermined wavelength, heating the thin-film resistor is strengthened (Step 56). <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a wavelength-stabilized laser device and method for stabilizing the wavelength of laser light emitted from a semiconductor laser to a desired wavelength, and a Raman amplifier including the wavelength-stabilized laser device.

Patent Documents 1 and 2 disclose tunable semiconductor lasers provided with heating means (resistive film) for heating a diffraction grating. By changing the temperature of the heating means (resistive film), the temperature of the diffraction grating is changed, and thereby the wavelength of the laser beam emitted from the semiconductor laser can be varied.
Japanese Patent No. 3064118 Japanese Patent No. 3152424

  In Patent Documents 1 and 2, heating by a heating means (resistive film) is used to change the wavelength of laser light emitted from a semiconductor laser. However, some devices and systems that use semiconductor lasers require semiconductor lasers that the wavelength of the laser light emitted from the semiconductor laser does not fluctuate, that is, that laser light having a constant wavelength is always emitted. There are also things.

  For example, a Raman amplifier is an example. In a Raman amplifier, laser light emitted from a semiconductor laser is incident on an amplification optical fiber as excitation light. Stimulated Raman scattering occurs in the amplification optical fiber, and a gain is generated on the longer wavelength side by about 100 nm from the wavelength of the laser light (excitation light wavelength). When the signal light enters the amplification optical fiber, the signal light is amplified by the gain generated in the amplification optical fiber. In the Raman amplifier, when the wavelength of the pumping light from the semiconductor laser fluctuates, the gain of the signal light amplified in the amplifying optical fiber fluctuates, and the amplification factor at the wavelength to be amplified decreases or increases. .

  An object of the present invention is to stabilize the wavelength of laser light emitted from a semiconductor laser.

  Another object of the present invention is to stabilize the power of laser light emitted from a semiconductor laser.

  A wavelength-stabilized laser device according to the present invention includes a diffraction grating, a semiconductor laser provided with a heating element for heating the diffraction grating, and the wavelength of laser light emitted from the semiconductor laser is longer than a predetermined wavelength. A wavelength shift detecting means for detecting shortness and shortness, and a heating control means for controlling the heating of the heating element, wherein the heating control means heats the heating element, and the wavelength shift detection means causes a laser beam to be emitted. The heating element is weakened when it is detected that the wavelength is longer than a predetermined wavelength, and the heating of the heating element is increased when it is detected that the wavelength is shorter than the predetermined wavelength. It is characterized by controlling heating to the body. The semiconductor laser is a Bragg reflection type (DBR (Distributed Bragg Reflector) type) in which an active layer and a diffraction grating are connected in the direction of the laser resonance axis, but a distributed feedback type in which a diffraction grating is formed above or below the active layer. (DFB (Distributed FeedBack) type) may be used. The semiconductor laser may be a semiconductor laser that performs single mode oscillation or a semiconductor laser that performs multimode oscillation. In one embodiment, the semiconductor laser and the wavelength shift detecting means are packaged in a single housing (semiconductor laser module), and the semiconductor laser module and the heating control means are electrically connected.

  The wavelength stabilization method according to the present invention is a method for stabilizing the wavelength of a laser beam emitted from a semiconductor laser including a diffraction grating and provided with a heating element for heating the diffraction grating. And detecting that the wavelength of the laser light emitted from the semiconductor laser is longer or shorter than a predetermined wavelength, and if the wavelength of the laser light is detected to be longer than the predetermined wavelength, the heat generation The heating of the body is weakened, and when it is detected that the length is shorter than the predetermined wavelength, the heating of the heating element is increased.

  The semiconductor laser is provided with a heating element for heating the diffraction grating. By supplying electric power to the heating element (by supplying a current to the heating element), the heating element generates heat (heats).

  When the heating element generates heat, the heat of the heating element is conducted to the diffraction grating and the diffraction grating is heated. In this state, driving of the semiconductor laser is started (laser light is emitted from the semiconductor laser).

  It is detected that the wavelength of the laser light emitted from the semiconductor laser is longer or shorter than the predetermined wavelength (wavelength shift).

  When it is detected that the wavelength of the laser beam is longer than the predetermined wavelength, the heating to the heating element is weakened. As a result, the temperature of the diffraction grating is lowered, and the wavelength of the laser light emitted from the semiconductor laser is shortened. Conversely, when it is detected that the wavelength of the laser beam is shorter than the predetermined wavelength, the heating of the heating element is increased. As a result, the temperature of the diffraction grating is increased, and the wavelength of the laser light emitted from the semiconductor laser becomes longer. According to the present invention, the laser beam emitted from the semiconductor laser can be controlled by controlling the heating of the heating element regardless of whether the laser beam emitted from the semiconductor laser is longer or shorter than the predetermined wavelength. The wavelength of the light can be matched with or close to the predetermined wavelength, and the wavelength of the laser light emitted from the semiconductor laser can be kept (stabilized) at the predetermined wavelength.

  In one embodiment, the wavelength shift (lengthening or shortening of the laser beam) is a light receiver that receives light emitted from the semiconductor laser and outputs a current corresponding to the wavelength of the received light. The detection can be made by using the first and second light receivers having different light receiving sensitivity characteristics. For example, the light receiving sensitivity characteristics of the first and second light receivers are such that the light receiving sensitivity of the first light receiver is higher than the light receiving sensitivity of the second light receiver with respect to light having a wavelength longer than the predetermined wavelength. The light receiving sensitivity of the second light receiver may be larger than the light receiving sensitivity of the first light receiver with respect to light having a wavelength that is large and shorter than the predetermined wavelength. Since the light receiving sensitivity of the first light receiver is larger than the light receiving sensitivity of the second light receiver with respect to light having a wavelength longer than the predetermined wavelength, light having a wavelength longer than the set wavelength is the first and second light. The light receiving current output from the first light receiving device becomes larger than the light receiving current output from the second light receiving device. On the contrary, for light having a wavelength shorter than the predetermined wavelength, the light receiving sensitivity of the second light receiver is larger than the light receiving sensitivity of the first light receiver, so that light having a wavelength longer than the set wavelength is the first. When incident on the first and second light receivers, the current value of the light receiving current output from the second light receiver becomes larger than the current value of the light receiving current output from the first light receiver. In either case, it is detected that the wavelength of the laser beam emitted from the semiconductor laser is shorter or longer than the predetermined wavelength by comparing the current values of the light receiving currents output from the first and second light receivers. can do.

  In one embodiment, power fluctuation detection means for detecting that the power of the laser light emitted from the semiconductor laser is larger or smaller than a predetermined power, and driving current control for controlling the driving current supplied to the semiconductor laser Means are further provided. For example, the semiconductor laser, the wavelength shift detection means, and the power fluctuation detection means are packaged in a single housing (semiconductor laser module), the semiconductor laser module, the heating control means, and the drive current control means, Are electrically connected.

  The drive current control means increases the drive current supplied to the semiconductor laser when the power fluctuation detection means detects that the power of the laser beam is larger than the predetermined power, and is smaller than the predetermined power. When detected, the drive current is controlled so as to decrease the drive current supplied to the semiconductor laser. Not only the wavelength of the laser beam but also the power of the laser beam can be stabilized. The power fluctuation detecting means may be a light receiver that receives light emitted from the semiconductor laser and outputs a current having a value corresponding to the power of the received light. You may use the 1st, 2nd light receiver used in order to detect the shift | offset | difference of the wavelength mentioned above also in order to detect the fluctuation | variation of a power.

  Preferably, the wavelength stabilization laser device includes a first power supply circuit that supplies power for heating (generating heat) the heating element, and a first current that supplies a driving current for emitting laser light from the semiconductor laser. Two power supply circuits, and the first power supply circuit and the second power supply circuit are controlled separately. By controlling the power supplied from the first power supply circuit, heating of the heating element is reduced and further heating (increasing heating) of the heating element is performed. By controlling the drive current supplied from the second power supply circuit, the power (intensity) of the laser beam emitted from the semiconductor laser is controlled.

  The wavelength-stabilized laser device according to the present invention can stably emit laser light having a desired wavelength, and thus is suitable for use as a light source for excitation light in a Raman amplifier. The present invention also relates to the above-described wavelength stabilized laser device and a Raman amplifier including an optical fiber in which laser light emitted from a semiconductor laser included in the wavelength stabilized laser device is incident as excitation light and causes stimulated Raman amplification. providing.

  FIG. 1 shows a block diagram of a wavelength / output stabilizing laser device. 2 shows the appearance of the semiconductor laser module 2 used in the wavelength / output stabilizing laser device, and FIG. 3 shows the internal configuration of the semiconductor laser module 2.

  The wavelength / output stabilizing laser device 1 is a device for stabilizing the wavelength and output (power) of laser light emitted from the semiconductor laser 10. The wavelength / output stabilizing laser device 1 includes a semiconductor laser module 2, a control circuit 3, a heater power supply circuit 4, and a laser power supply circuit 5. The semiconductor laser module 2 includes a semiconductor laser 10 that emits laser light, a lens 21 for condensing and collimating, an optical isolator 22 that prevents the laser light from reversing, two light receivers 23 and 24, and a semiconductor laser. A part of the optical fiber 25 into which the laser beam emitted from 10 enters is packaged.

  Referring to FIGS. 2 and 3, the semiconductor laser module 2 in this embodiment is called a butterfly type, and connector pins 41 penetrating from the inside of the package (housing) 2a to the outside are provided in the package 2a. There are 14 in total, 7 on each side. In FIG. 3, pin numbers are shown in the vicinity of the connector pins 41. A cylindrical ferrule 42 penetrating from the inside of the package 2a to the outside is further provided at one end surface of the package 2a, and an optical fiber 25 passes through the ferrule 42.

  A Peltier element 20 for cooling the inside of the semiconductor laser module 2 is fixed to the bottom surface in the package 2a of the semiconductor laser module 2. A substrate 26 is fixed on the Peltier element 20, the semiconductor laser 10 is fixed on the substrate 26 via a sub-mount 47, and a lens 21, an optical isolator 22, and two light receivers 23 and 24 are fixed. ing. The lens 21 and the optical isolator 22 are located on the emission end face 10 a side of the semiconductor laser 10, and the two light receivers 23 and 24 are located on the rear end face 10 b side of the semiconductor laser 10.

  As will be described in detail later, a diffraction grating is formed inside the semiconductor laser 10 of this embodiment, and a thin film resistor (heater) 18 for heating the diffraction grating is provided on the upper surface of the semiconductor laser 10. Yes. The thin film resistor 18 is connected to the 12th and 13th pins by wires, and the power (current) from the heater power supply circuit 4 is supplied to the thin film resistor 18 through the 12th and 13th pins. The thin film resistor 18 generates heat (heats) by the power supplied from the heater power supply circuit 4. The heat generated by the thin film resistor 18 is transmitted to the semiconductor laser 10 to heat the diffraction grating.

  The electrode on the upper surface of the semiconductor laser 10 is connected to the 11th pin, and the electrode on the lower surface is connected to the 10th pin via a sub-mount 47 by a wire. When the current from the laser power supply circuit 5 is supplied to the semiconductor laser 10 through the 10th pin and the 11th pin, laser light is emitted from the semiconductor laser 10. The laser light is guided to the optical fiber 25 through the lens 21 and the optical isolator 22 described above.

  The light receivers 23 and 24 receive light slightly emitted from the rear end face 10b of the semiconductor laser 10 and output a current having a current value corresponding to the wavelength of the received light. As will be described later, the light receivers 23 and 24 have different light receiving sensitivity characteristics, and the wavelength variation of the laser light emitted from the semiconductor laser 10 is based on the current value of the current output from the light receivers 23 and 24. And fluctuations in output power are detected. The two electrodes of the light receiver 23 are connected to the 3rd and 4th pins, and the two electrodes of the light receiver 24 are connected to the 8th and 9th pins by wires. Electrical signals (current values) from the light receivers 23 and 24 are supplied to the control circuit 3 through the third and fourth pins and the eighth and ninth pins. The control circuit 3 controls the heating of the thin film resistor 18 so that the wavelength of the laser beam becomes a predetermined wavelength, and the driving current supplied to the semiconductor laser 10 so that the output power of the detected laser beam becomes a predetermined power. To control. Details of the light receiving sensitivity characteristics of the light receivers 23 and 24 and the processing of the control circuit 3 will be described later.

  The two electrodes of the Peltier element 20 are connected to the 1st pin and the 14th pin. The Peltier element 20 is driven as a cooling element by a current applied to the first pin and the 14th pin (a power supply circuit for supplying a current to the Peltier element 20 is omitted in FIG. 1).

  4A is a plan view of the semiconductor laser 10, and FIG. 4B is a cross-sectional view of the semiconductor laser 10 taken along line BB in FIG. 4A. In FIG. 4B, illustration of hatching is omitted. 4A and 4B, the width of an active layer 12 to be described later, the thickness of a semiconductor layer, and the like are drawn with considerable emphasis for easy understanding.

  In the semiconductor laser 10, a light emitting region 10A and a DBR (Distributed Bragg Reflector) region 10B are formed continuously in the optical resonance axis direction. In the light emitting region 10A, an active layer 12 is stacked in a stripe shape on an n-type InP (indium-phosphorus) substrate 11. On the other hand, in the DBR region 10B, a diffraction grating 14 having a predetermined pitch is formed in a stripe shape on the n-type InP substrate 1, and an InGaAsP (indium-gallium-arsenic-phosphorus) guide layer 15 is laminated in the stripe shape. . The optical axis of the active layer 12 and the optical axis of the guide layer 15 coincide. Further, a p-type InP cladding layer 13 is laminated on the active layer 12 and the guide layer 15, and current blocking layers (not shown) made of p-type InP and n-type InP are laminated on both sides of the active layer 12 and the guide layer 15. Has been.

A p-type electrode 16 is provided on the upper surface of the p-type InP cladding layer 13, and an n-type electrode 19 is provided on the lower surface of the substrate 11. A SiO ₂ insulating film 17 and a thin film resistor 18 are further provided in this order on the p-type electrode 16 in the range of the DBR region 10B. The thin film resistor 18 includes a linear portion 18c formed along the range where the diffraction grating 14 is formed, and the wire bonding pad 18a, which is continuous with the linear portion 18c, at both ends of the linear portion 18c. 18b is formed. The material of the thin film resistor 18 can be tantalum nitride, platinum, gold, or the like.

  An antireflection film 31 is provided on the light emitting end face 10a of the semiconductor laser 10, and a reflecting film 32 is provided on the rear end face 10b.

  When a current is passed through the p-type electrode 16 provided on the upper surface of the semiconductor laser 10 and the n-type electrode 19 provided on the lower surface, light is generated in the active layer 12 formed in the light emitting region 10A. The light generated in the active layer 12 travels along the active layer 12 and the guide layer 15 and is reflected between the rear end face 10b (reflective film 32) of the semiconductor laser 10 and the diffraction grating 14, thereby resonating the light. The laser beam is emitted from the light emitting end face 10a through the guide layer 15. In this embodiment, the active layer 12 and the diffraction grating 14 are designed so that the semiconductor laser 10 emits laser light having a wavelength of 1450 nm.

  In general, a semiconductor laser is configured by laminating a plurality of semiconductor layers having different compositions, types and amounts of impurities on a semiconductor substrate. The active layer 12 and the guide layer 15 are formed in a form capable of confining light in one or a plurality of layers. The diffraction grating 14 may be formed on the semiconductor substrate 11 as described above, or may be formed on a semiconductor layer different from the semiconductor substrate 11.

  FIG. 5 shows a cross section of the semiconductor laser 10 and shows the positions of the active layer 12, the diffraction grating 14, and the thin film resistor 18 more accurately. As shown in FIG. 5, in the semiconductor laser 10, the active layer 12 and the diffraction grating 14 are located in a portion close to the upper surface of the semiconductor laser 10 (a depth of about 2 μm to 4 μm from the upper surface of the thin film resistor 18). The resistor 18 is located near the diffraction grating 14. For this reason, when the thin film resistor 18 generates heat, the diffraction grating 14 located nearby is locally heated, but the amount of heat transmitted to the active layer 12, the semiconductor substrate 11 and the like located relatively far from the thin film resistor 18 is small. In addition, the cooling effect by the Peltier element 20 (see FIG. 3) located below the semiconductor laser 10 described above covers almost the entire semiconductor laser 10 including the active layer 12, but when heating by the thin film resistor 18 is performed, The cooling effect by the Peltier element 20 does not reach the vicinity of the thin film resistor 18 including the diffraction grating 14.

  As described above, light is emitted slightly from the rear end face 10b of the semiconductor laser 10. The light emitted from the rear end face 10b has the same wavelength as the laser light emitted from the output end face 10a. The power of the light emitted from the rear end face 10b and the power of the laser light emitted from the output end face 10a have a proportional relationship. Light emitted from the rear end face 10b of the semiconductor laser 10 is received by the two light receivers 23 and 24 (see FIGS. 1 and 3).

  The light receivers 23 and 24 are obtained by coating a light-receiving surface of a photo diode (photoelectric conversion element) with a dielectric multilayer film (bandpass filter), and a dielectric multilayer film coated on the light receiver 23, The dielectric multilayer films coated on the light receiver 24 have different layer thicknesses. For this reason, the light receivers 23 and 24 have different light receiving sensitivity characteristics and light receiving current (output current) characteristics.

  FIG. 6 shows the light receiving sensitivity characteristics of the light receiver 23 (hereinafter referred to as the first light receiver 23) and the light receiver 24 (hereinafter referred to as the second light receiver 24) (relation between the light receiving sensitivity and the wavelength of the received light). It is a graph which shows. FIG. 7 shows the relationship between the light receiving current (output current) characteristics (light receiving current (output current) and the wavelength of the received light when light of a predetermined power is incident on the first light receiver 23 and the second light receiver 24. ). 6 and 7, the light receiving sensitivity characteristic and the light receiving current characteristic of the first light receiver 23 are indicated by a thick solid line, and the light receiving sensitivity characteristic and the light receiving current characteristic of the second light receiver 24 are indicated by a thin solid line, respectively.

  Referring to FIG. 6, the first light receiver 23 and the second light receiver 24 both change in light reception sensitivity according to the wavelength of incident light (wavelength dependence of light reception sensitivity characteristics). Both the graph of the light receiving sensitivity characteristic of the first light receiver 23 (thick line) and the graph of the light receiving sensitivity characteristic of the second light receiver 24 (thin line) draw an upwardly convex parabolic curve, but the light receiving sensitivity is maximized. The wavelength is different. That is, the wavelength at which the light receiving sensitivity of the first light receiver 23 is maximized is longer than the set wavelength 1450 nm of the laser light emitted from the semiconductor laser 10. On the other hand, the wavelength at which the light receiving sensitivity of the second light receiver 24 is maximum is shorter than 1450 nm. The first photoreceiver 23 and the second photoreceiver 24 have the same photosensitivity corresponding to the set wavelength 1450 nm of the semiconductor laser 10, and accordingly, the graph (thick line) of the photosensitivity characteristics of the first photoreceiver 23 and The graph (thin line) of the light receiving sensitivity characteristic of the second light receiver 24 intersects at the light receiving sensitivity corresponding to the set wavelength 1450 nm.

  The graph (FIG. 7) showing the light receiving current (output current) characteristics when light of a predetermined power is incident on the first light receiving device 23 and the second light receiving device 24 is also a graph showing the light receiving sensitivity characteristics shown in FIG. Draw a similar upwardly convex parabola.

  Referring to the graph showing the light receiving sensitivity characteristic shown in FIG. 6 and the graph showing the light receiving current (output current) characteristic shown in FIG. 7, the first and second light receivers 23 emitted from the rear end face 10b of the semiconductor laser 10 are shown. , 24 (which is equal to the wavelength of the laser light emitted from the emitting end face 10a of the semiconductor laser 10) is shorter than the predetermined wavelength of 1450 nm, the light receiving sensitivity of the second light receiver 24 is The light receiving sensitivity of the first light receiver 23 is always larger than that of the first light receiver 23 (FIG. 6). Therefore, the current value of the light receiving current output from the second light receiver 24 is the current of the light receiving current output from the first light receiver 23. It is always larger than the value (FIG. 7). On the other hand, when the wavelength of the light emitted from the rear end face 10b of the semiconductor laser 10 and incident on the first and second light receiving elements 23, 24 is longer than the predetermined wavelength of 1450 nm, the first light receiving device 23 is used. Is always larger than the light receiving sensitivity of the second light receiving device 24 (FIG. 6), and the current value of the light receiving current output from the first light receiving device 23 is the light receiving current output from the second light receiving device 24. Is always larger than the current value (FIG. 7). Therefore, by comparing the light receiving currents output from the first light receiver 23 and the second light receiver 24, the wavelength of the laser light emitted from the semiconductor laser 10 is longer than the predetermined wavelength and shorter. It is possible to detect the wavelength (wavelength shift).

  Furthermore, when the wavelength of the laser light emitted from the semiconductor laser 10 is a predetermined wavelength and the power of the laser light is a predetermined power, the first and first light received from the rear end face 10b of the semiconductor laser 10 are received. The current values of the light receiving currents output from the two light receivers 23 and 24 both indicate the same predetermined value (FIG. 7). When the power of the laser light is larger than the predetermined power, the current value of the light receiving current output from the first and second light receivers 23 and 24 indicates a value larger than the predetermined value, and conversely, the power of the laser light is predetermined. When the power is smaller than the power, the current value of the light receiving current output from the first and second light receivers 23 and 24 indicates a value smaller than a predetermined value. Therefore, based on the light receiving current output from the first light receiver 23 and the second light receiver 24, it is detected that the power of the laser light emitted from the semiconductor laser 10 is larger or smaller than the predetermined power. You can also.

  FIG. 8 and FIG. 9 are flowcharts showing the operation flow of the control circuit 3 of the wavelength / output stabilizing laser device 1.

  First, the control circuit 3 instructs the heater power supply circuit 4 to output the heater heating power (current). When power from the heater power supply circuit 4 is supplied to the thin film resistor 18 (when a current is passed between the pads 18a and 18b), the thin film resistor 18 generates heat. That is, before the laser beam is emitted from the semiconductor laser 10, the thin film resistor 18 is heated to a predetermined temperature, for example, 60 ° C. The relationship between the temperature of the thin film resistor 18 and the power supplied to the thin film resistor 18 is measured in advance, and the temperature of the thin film resistor 18 can be grasped according to the amount of power supplied. As described above, the thin film resistor 18 is provided on the upper surface of the semiconductor laser 10, and the diffraction grating 14 exists in the vicinity of the thin film resistor 18 (see FIGS. 4A, 4B, and 5). Therefore, when the thin film resistor 18 generates heat, the diffraction grating 14 is heated to a predetermined temperature by heat conduction (step 51).

  A drive current output instruction is given from the control circuit 3 to the laser power supply circuit 5. A predetermined drive current is supplied from the laser power supply circuit 5 to the semiconductor laser 10 (step 52). Laser light having a predetermined output power is emitted from the light emitting surface 10 a of the semiconductor laser 10.

  As described above, the light slightly emitted from the rear end face 10 b of the semiconductor laser 10 enters the first and second light receivers 23 and 24. Light receiving currents (output currents) from the first and second light receivers 23 and 24 are supplied to the control circuit 3.

  Based on the light reception current values from the first and second light receivers 23 and 24, the control circuit 3 operates as follows.

(1) When a light-receiving current beta ₁ of the first light-receiving unit 23, light-receiving current beta ₂ of the second light receiver 24 do not match (Yes in step 53)

When the laser light emitted from the semiconductor laser 10 has a set wavelength (1450 nm), the first light receiver 23 and the second light receiver 24 output the same current (FIG. 7). In contrast, if the received current value beta ₂ of the light-receiving current beta ₁ and the second light receiver 24 of the first light receiver 23 does not match the wavelength of the laser light is emitted is set from the semiconductor laser 10 It can be seen that the wavelength is not a wavelength, that is, the wavelength of the laser beam is shifted to the long wavelength side or the short wavelength side. The wavelength shift of the laser light is caused by the use environment (ambient temperature, etc.) of the semiconductor laser 10 (semiconductor laser module 2), heat generation of the semiconductor laser 10 (particularly the active layer 12), deterioration of the semiconductor laser 10, and the like.

Referring to FIG. 10, when the wavelength of the laser beam is shifted to the short wavelength side (laser beam wavelength α ₁ <1450 nm), the received light current value β ₂ of the _second light receiver 24 is the first light receiver 23. The received light current value β ₂ becomes larger. That is, by detecting that the light receiving current value β ₂ of the _second light receiver 24 is larger than the light receiving current value β ₁ of the first light receiver 23, the wavelength of the laser light emitted from the semiconductor laser 10 is changed. It can be determined that the wavelength is shifted to the short wavelength side (β ₂ > β _{1 in} step 54).

  When it is determined that the wavelength of the laser beam is shifted to the short wavelength side, the control circuit 3 sets the heater power supply circuit 4 so that the power supplied from the heater power supply circuit 4 to the thin film resistor 18 increases. Control. This intensifies the heat generation of the thin film resistor 18 and raises the temperature of the diffraction grating 14 (step 55). As the temperature of the diffraction grating 14 rises, the oscillation wavelength of the light reflected and oscillated by the diffraction grating 14 shifts to the longer wavelength side (the oscillation wavelength becomes longer). As a result, the wavelength of the laser light emitted from the semiconductor laser 10 approaches the set wavelength.

Referring to FIG. 11, when the wavelength of the laser beam is shifted to the longer wavelength side (laser beam wavelength α ₂ > 1450 nm), the received light current value β ₁ of the _first light receiver 23 is the second light receiver 24. The received light current value β ₂ becomes larger. That is, the wavelength of the laser beam is shifted to the longer wavelength side by detecting that the light reception current value β ₁ of the _first light receiver 23 is larger than the light reception current value β ₂ of the second light receiver 24. (Β ₂ <β _{1 in} step 54).

  When it is determined that the wavelength of the laser beam is shifted to the long wavelength side, the control circuit 3 turns off the heater power supply circuit 4 so that the power supplied from the heater power supply circuit 4 to the thin film resistor 18 decreases. Control. As a result, the heat generation of the thin film resistor 18 is weakened and the temperature of the diffraction grating 14 is lowered (step 56). As the temperature of the diffraction grating 14 decreases, the oscillation wavelength of the light reflected and oscillated by the diffraction grating 14 shifts to the short wavelength side (the oscillation wavelength becomes shorter). For this reason, the wavelength of the laser light emitted from the semiconductor laser 10 approaches the set wavelength.

Receiving current beta ₁ and comparison of the light-receiving current beta ₂ of the second photodetector 24 of the first light receiver 23, and by adjusting the power supplied to the thin film resistor 18 is repeated (step 53-56), The wavelength of the laser light emitted from the semiconductor laser 10 matches the set wavelength. Laser light having a stable wavelength can be emitted from the semiconductor laser 10.

(2) receiving the current value beta ₂ of the light-receiving current beta ₁ and the second light receiver 24 of the first light receiver 23 are matched, if the value is not the predetermined value (NO in step 53, step 57 NO)

As described above, if the wavelength of the laser light emitted from the semiconductor laser 10 is the set wavelength, the first and second light receivers 23 and 24 both output the same value of current. Furthermore, the semiconductor laser 10 is long and emits a laser beam of a predetermined (preset) power, light current value of the light reception current beta ₁ and the second light receiver 24 of the first light receiver 23 beta ₂ Indicates the same predetermined current value γ (see FIG. 7, YES in step 57). However, the semiconductor laser 10 may not emit laser light with a predetermined output power even if a predetermined drive current is supplied to the semiconductor laser 10 due to fluctuations in the ambient temperature, deterioration of the semiconductor laser 10 over time, or the like.

Although the light-receiving current beta ₂ of the light-receiving current beta ₁ and the second light receiver 24 of the first light receiver 23 are matched, if not the predetermined current value gamma (NO at step 57), the semiconductor laser 10 It can be seen that laser light with a predetermined power is not emitted, that is, the power of the laser light is larger or smaller than the predetermined power.

Referring to FIGS. 9 and 12, when the output power of the laser beam is larger than the predetermined power, the light receiving current values β ₁ and β ₂ of the first and second light receivers 23 and 24 correspond to the predetermined power. The current value γ ₁ exceeding the current value γ is indicated. That is, by detecting that the light receiving current values β ₁ and β _{2 of} the first and second light receivers 23 and 24 indicate a current value γ ₁ exceeding a predetermined current value γ, the light is emitted from the semiconductor laser 10. It can be seen that the output power of the laser beam being applied is greater than the predetermined power (β ₁ = β ₂ > γ in step 58). The current value γ corresponding to the predetermined power is set as a control value in the control circuit 3, and the set current value γ is the received light current value β _{1 of} the first and second light receivers 23, 24, Used for comparison with β ₂ .

  When it is determined that the output power of the laser light is greater than the predetermined power, the control circuit 3 turns off the laser power supply circuit 5 so that the drive current supplied from the laser power supply circuit 5 to the semiconductor laser 10 is reduced. Control (step 59). As a result, the power of the laser light emitted from the semiconductor laser 10 decreases and approaches a predetermined power.

Conversely, when the output power of the laser beam is smaller than the predetermined power, the received light current values β ₁ and β ₂ of the first and second light receivers 23 and 24 are smaller than the current value γ corresponding to the predetermined power. . That is, by detecting that the light receiving current values β ₁ and β _{2 of} the first and second light receivers 23 and 24 indicate a current value γ ₂ smaller than the current value γ, the output power of the laser light is reduced. It can be seen that the power is smaller than the predetermined power (β ₁ = β ₂ <γ in step 58).

  When it is determined that the output power of the laser beam is smaller than the predetermined power, the control circuit 3 controls the laser power supply circuit 5 so that the drive current supplied from the laser power supply circuit 5 to the semiconductor laser 10 increases. (Step 60). As a result, the power of the laser light emitted from the semiconductor laser 10 increases and approaches a predetermined power.

By repeatedly comparing the received light current values β ₁ and β _{2 of} the first and second light receivers 23 and 24 with the current value γ corresponding to a predetermined power and adjusting the drive current to the semiconductor laser 10 (step) 57-60), the output power of the laser light emitted from the semiconductor laser 10 becomes a predetermined power. Laser light having a stable output power can be emitted from the semiconductor laser 10.

  The embodiment according to the present invention is not limited to the block diagram of FIG. 1, and the control circuit 3 may include a memory for storing data (for example, the above-described current value γ).

  In the above-described embodiment, the first and second light receivers 23 and 24 are used to detect the variation in the wavelength of the laser beam and the variation in the output power of the laser beam. May be detected using a light receiver (third light receiver) different from the first and second light receivers 23 and 24 (dedicated for detecting fluctuations in the output power of the laser beam). .

  FIG. 13 is a block diagram showing a Raman amplifier including the wavelength / output stabilizing laser device 1 described above.

  In the Raman amplifier 70, laser light output from the semiconductor laser 10 included in the wavelength / output stabilizing laser device 1 is input to the amplification optical fiber 71 through the coupler 72 as excitation light. Stimulated Raman scattering occurs in the amplification optical fiber 71, and a gain is generated on the longer wavelength side by about 100 nm from the wavelength of the laser light (excitation light wavelength). When the signal light is input to the amplification optical fiber 71, the signal light is amplified by the gain generated in the amplification optical fiber 71 (Raman amplification). The wavelength / output stabilizing laser device 1 emits laser light having a stable wavelength and output power, and this laser light is used as pumping light. Therefore, the wavelength band of the signal light amplified in the Raman amplifier 70 is accurately controlled. can do. When the wavelength / output stabilizing laser device 1 is used for the Raman amplifier 70, it is preferable to use a semiconductor laser that performs multimode oscillation as the semiconductor laser 10.

It is a block diagram which shows the structure of a wavelength / output stabilization laser apparatus. It is a perspective view which shows the external appearance of a semiconductor laser module. The internal structure of a semiconductor laser module is shown. (A) is a plan view of the semiconductor laser, and (B) is a cross-sectional view of the semiconductor laser along the line BB in (A). 1 shows a cross-sectional view of a semiconductor laser. The light reception sensitivity characteristics of the first and second light receivers are shown. The photocurrent characteristic of the 1st and 2nd light receiver is shown. It is a flowchart which shows the flow of operation | movement of the control circuit of a wavelength / output stabilization laser apparatus. It is a flowchart which shows the flow of operation | movement of the control circuit of a wavelength / output stabilization laser apparatus. The light receiving currents of the first and second light receivers when the wavelength of the laser light is shifted to the short wavelength side are shown. The light receiving currents of the first and second light receivers when the wavelength of the laser light is shifted to the long wavelength side are shown. The light receiving currents of the first and second light receivers when the power of the laser light increases and decreases are shown. It is a block diagram of a Raman amplifier.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Wavelength / output stabilization laser apparatus 2 Semiconductor laser module 3 Control circuit 4 Heater power circuit 5 Laser power circuit
10 Semiconductor laser
12 Active layer
14 Diffraction grating
18 Thin film resistor
23 First receiver
24 Second receiver
70 Raman amplifier

Claims (8)

A semiconductor laser including a diffraction grating and provided with a heating element for heating the diffraction grating;
A wavelength shift detecting means for detecting that the wavelength of the laser light emitted from the semiconductor laser is longer and shorter than a predetermined wavelength, and a heating control means for controlling the heating of the heating element,
The heating control means includes
Heating the heating element;
When the wavelength shift detecting means detects that the wavelength of the laser beam is longer than a predetermined wavelength, the heating of the heating element is weakened, and when it is detected that the wavelength is shorter than the predetermined wavelength, the heating element is not heated. Control the heating of the heating element to increase the heating,
Wavelength stabilized laser device. The wavelength shift detector includes first and second light receivers that receive light emitted from the semiconductor laser and output a current according to the wavelength of the received light.
The light receiving sensitivity characteristics of the first and second light receivers are different from each other,
The light receiving sensitivity characteristics of the first and second light receivers are such that the light receiving sensitivity of the first light receiver is larger than the light receiving sensitivity of the second light receiver with respect to light having a wavelength longer than the predetermined wavelength. The light receiving sensitivity of the second light receiver is greater than the light receiving sensitivity of the first light receiver for light having a wavelength shorter than the predetermined wavelength.
The wavelength-stabilized laser device according to claim 1. Power fluctuation detecting means for detecting that the power of the laser light emitted from the semiconductor laser is greater than or less than a predetermined power, and drive current control means for controlling the drive current supplied to the semiconductor laser,
The drive current control means includes
The drive current supplied to the semiconductor laser is increased when the power fluctuation detecting means detects that the power of the laser beam is larger than the predetermined power, and the semiconductor when the power fluctuation is detected to be smaller than the predetermined power. Controlling the drive current so as to reduce the drive current supplied to the laser;
The wavelength stabilization laser device according to claim 1 or 2. The semiconductor laser module including the semiconductor laser and the wavelength shift detecting means and the heating control means are electrically connected.
The wavelength stabilization laser device according to claim 1 or 2. The semiconductor laser, the semiconductor laser module provided with the wavelength shift detection means and the power fluctuation detection means, and the heating control means and the drive current control means are electrically connected.
The wavelength-stabilized laser device according to claim 3. A first power supply circuit for supplying electric power for heating the heating element; and a second power supply circuit for supplying a drive current for emitting laser light from the semiconductor laser, the first power supply circuit, The second power circuit is controlled separately,
The wavelength stabilization laser apparatus as described in any one of Claim 1 to 5. The wavelength-stabilized laser device according to any one of claims 1 to 6, and a laser beam emitted from the semiconductor laser included in the wavelength-stabilized laser device is incident as excitation light to generate stimulated Raman amplification. Optical fiber,
Raman amplifier equipped with. A method for stabilizing the wavelength of laser light emitted from a semiconductor laser including a diffraction grating and provided with a heating element for heating the diffraction grating,
Heating the heating element;
Detecting that the wavelength of laser light emitted from the semiconductor laser is longer and shorter than a predetermined wavelength,
When it is detected that the wavelength of the laser beam is longer than the predetermined wavelength, the heating of the heating element is weakened, and when it is detected that the wavelength of the laser light is shorter than the predetermined wavelength, the heating of the heating element is increased.
Wavelength stabilization method.

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