JP5083306B2 - Wavelength conversion laser device - Google Patents

Description

  The present invention relates to a wavelength conversion laser device, and more particularly to a wavelength conversion laser device capable of setting a semiconductor laser drive current to a minimum value or a light output intensity to a maximum value even when an environmental temperature varies.

  2. Description of the Related Art Conventionally, a wavelength conversion laser device including a semiconductor laser, a polarization maintaining optical fiber, a wavelength conversion element, and a temperature control unit that controls the temperature of the polarization maintaining optical fiber constant is known (for example, , See Patent Document 1).

JP 2005-181509 A

In the conventional wavelength conversion laser device, the influence of the environmental temperature is suppressed by controlling the temperature of the polarization maintaining optical fiber to be constant.
However, even if the temperature of the polarization maintaining optical fiber is controlled to be constant, the influence of the environmental temperature on the components other than the polarization maintaining optical fiber is not sufficiently suppressed, and the light output intensity ( When P) is controlled to be constant, the semiconductor laser drive current (I) increases due to the influence of the environmental temperature. When the semiconductor laser drive current (I) is controlled to be constant, the light is affected by the influence of the environmental temperature. There has been a problem that the output intensity (P) decreases.
SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a wavelength conversion laser device that can minimize the semiconductor laser drive current (I) or the light output intensity (P) even when the environmental temperature varies. There is.

In a first aspect, the present invention relates to a semiconductor laser that oscillates fundamental light, a polarization-maintaining optical fiber that is optically coupled on the emission side of the semiconductor laser, and an emission side of the polarization-maintaining optical fiber. The wavelength selection element, the wavelength conversion element that converts the wavelength of the light that has passed through the wavelength selection element, the optical branching element that branches the light wavelength-converted by the wavelength conversion element, and the optical branching element that is branched An optical sensor that converts one of the lights into an intensity signal P; and a drive current control unit that controls the drive current I of the semiconductor laser so that the intensity signal P is constant. A part of the wave-maintaining optical fiber is housed in the same housing, the housing and the polarization-maintaining optical fiber are arranged on one substrate, and the driving current I during steady operation is predetermined. Increase over value That when the driving current I is to provide a wavelength conversion laser device characterized by comprising a temperature control means for tuning the temperature of the substrate such that the minimum value.
In the wavelength conversion laser device according to the first aspect, in the state where the drive current I of the semiconductor laser is controlled so that the output light intensity P is constant, the temperature control means monitors the drive current I of the semiconductor laser. If the semiconductor laser and the polarization maintaining optical fiber are partly housed in the housing and the polarization maintaining optical fiber, the semiconductor laser driving current I becomes a minimum value when the value exceeds a predetermined value. Tune the temperature of the placed board. Thereby, even if environmental temperature fluctuates, the semiconductor laser drive current I can be minimized.

In a second aspect, the present invention relates to a semiconductor laser that oscillates fundamental light, a polarization maintaining optical fiber that is optically coupled on the output side of the semiconductor laser, and an output side of the polarization maintaining optical fiber. The wavelength selection element, the wavelength conversion element that converts the wavelength of the light that has passed through the wavelength selection element, the optical branching element that branches the light wavelength-converted by the wavelength conversion element, and the optical branching element that is branched An optical sensor that converts one of the lights into an intensity signal P, and a drive current control unit that controls the drive current I of the semiconductor laser to be constant, and a part of the semiconductor laser and the polarization maintaining optical fiber Are housed in the same housing, the housing and the polarization maintaining optical fiber are arranged on one substrate, and when the intensity signal P during steady operation is reduced to a predetermined value or more, the intensity signal P is the maximum value To provide a wavelength conversion laser device characterized by comprising a temperature control means for tuning the temperature of the substrate such that.
In the wavelength conversion laser device according to the second aspect, in the state where the semiconductor laser drive current I is controlled to be constant, the temperature control means monitors the output light intensity P and exceeds a predetermined value. As the output light intensity P decreases, the temperature tuning of the housing in which the semiconductor laser and a part of the polarization maintaining optical fiber are housed and the substrate on which the polarization maintaining optical fiber is disposed are performed so that the output light intensity P becomes a maximum value. . Thereby, even if environmental temperature changes, the intensity | strength of output light can be made into the maximum value.

In a third aspect, the present invention provides a wavelength conversion laser device characterized in that, in the wavelength conversion laser device according to the first or second aspect, the wavelength selection element is disposed on the substrate.
In the wavelength conversion laser device according to the third aspect, since the wavelength selection element is disposed on the substrate, temperature tuning including the temperature of the wavelength selection element can be performed.

  According to the wavelength conversion laser device of the present invention, the semiconductor laser drive current (I) can be minimized or the light output intensity (P) can be maximized even when the environmental temperature varies.

1 is a configuration explanatory view showing a wavelength conversion laser device according to Example 1. FIG. It is a graph which shows the change of the drive current with respect to the change of the substrate temperature in different environmental temperature. FIG. 5 is a flowchart showing a substrate temperature control process according to the first embodiment. It is explanatory drawing which shows the operation | movement at the time of performing substrate temperature control which concerns on Example 1. FIG. It is explanatory drawing which shows operation | movement at the time of controlling substrate temperature uniformly. FIG. 6 is an explanatory diagram illustrating a wavelength conversion laser device according to a second embodiment. It is a graph which shows the change of output light intensity with respect to the change of the substrate temperature in different environmental temperature. 10 is a flowchart showing a substrate temperature control process according to Embodiment 2. FIG. It is explanatory drawing which shows the operation | movement at the time of performing substrate temperature control which concerns on Example 2. FIG. It is explanatory drawing which shows operation | movement at the time of controlling substrate temperature uniformly.

  Hereinafter, the present invention will be described in more detail with reference to the embodiments shown in the drawings. Note that the present invention is not limited thereby.

Example 1
FIG. 1 is an explanatory diagram illustrating a wavelength conversion laser device 100 according to the first embodiment.
In this wavelength conversion laser device 100, the rear end surface of the semiconductor laser 1 that oscillates fundamental light is provided with a high reflectance coat, and the front end surface is provided with a low reflectance coat.
The light emitted from the front surface of the semiconductor laser 1 is coupled to the polarization maintaining optical fiber 2 in an optimal state.

  The light guides of the semiconductor laser 1 and the polarization maintaining optical fiber 2 are housed in the housing 17, and the polarization maintaining optical fiber 2 is held inside the housing 17.

  The light emitted from the terminal end 3 of the polarization maintaining optical fiber 2 is converted into a desired beam by the lens 4 a and guided to the wavelength selection element 5.

The wavelength selection element 5 selectively reflects part of the light of the first selection wavelength, and this is again fed back to the semiconductor laser 1 through the polarization maintaining optical fiber 2.
By this feedback, the semiconductor laser 1 starts oscillating in the vicinity of the reflection center wavelength of the wavelength selection element 5.

  The light transmitted through the wavelength selection element 5 is converted into a desired beam by the lens 4b, and the wavelength is converted by the wavelength conversion element 6.

  A part of the wavelength-converted light is guided to the optical sensor 9 by the wavelength branching element 8 and converted into an intensity signal P.

  The controller 11 performs control such that the intensity signal P becomes a constant value Po, thereby maintaining the light output of the emitted wavelength converted light at a constant intensity.

  The casing 17, the polarization maintaining optical fiber 2, and the wavelength selection element 5 are disposed on the same substrate 10.

The temperature of the semiconductor laser 1 is controlled by the thermo module 7a.
The controller 11 sets the temperature Ta of the semiconductor laser 1 to a temperature range in which the wavelength selection by the wavelength selection element 5 is stably performed.

The temperature of the substrate 10 is controlled by the thermo module 7b.
The controller 11 sets the temperature Tb of the substrate 10 to a temperature at which the extinction ratio of the polarization plane incident on the wavelength conversion element 5 is maximized, that is, a temperature at which the drive current I is minimized. Then, the driving current I during steady operation is monitored, and when the driving current I increases to a predetermined value ΔI or more, the driving current I is reset to a temperature at which the driving current I becomes a minimum value. This substrate temperature control process will be described later with reference to FIG.

The wavelength conversion element 6 is temperature-controlled by the thermo module 7c.
The controller 11 sets the temperature Tc of the wavelength conversion element 6 to a temperature at which the wavelength of the light having the wavelength selected by the wavelength selection element 5 is most efficiently converted.

Components other than the controller 11 are accommodated in the chassis 18.
Let Ts be the environmental temperature at which the chassis 18 is placed.

FIG. 2A is a graph showing the change in the drive current I with respect to the change in the substrate temperature Tb at the environmental temperature Ts = TA (for example, 0 ° C.).
At the environmental temperature Ts = TA, the drive current I can be set to the minimum value I1 if the substrate temperature Tb = T3 (for example, 30 ° C.).
FIG. 2B is a graph showing a change in the drive current I with respect to a change in the substrate temperature Tb at the environmental temperature Ts = TB (for example, 20 ° C.).
At the environmental temperature Ts = TB, the drive current I can be set to the minimum value I1 if the substrate temperature Tb = T2 (for example, 28 ° C.).
FIG. 2C is a graph showing the change of the drive current I with respect to the change of the substrate temperature Tb at the environmental temperature Ts = TC (for example, 50 ° C.).
At the environmental temperature Ts = TC, the drive current I can be set to the minimum value I1 if the substrate temperature Tb = T1 (for example, 24 ° C.).

FIG. 3 is a flowchart showing the substrate temperature control process.
In Step R1, the controller 11 changes the substrate temperature Tb within a predetermined temperature range (for example, 10 ° C. to 40 ° C.) to set the substrate temperature Tb at which the drive current I becomes a minimum value.
In step R2, the drive current I is stored as a drive current value during steady operation.
In step R3, if the current drive current I increases by ΔI or more than the stored drive current I, the process returns to step R1.

FIG. 4 is an explanatory diagram showing the effect of the substrate temperature control process.
As shown in FIG. 4A, the controller 11 performs control so that the intensity signal P becomes a constant value Po.
Assume that the environmental temperature Ts fluctuates as shown in FIG.

As shown in FIG. 4C, when the environmental temperature Ts = TA, the controller 11 sets the substrate temperature Tb = T3. As shown in FIG. 4B, the drive current I = I1 (steps R1 and R2 in FIG. 2).
When the environmental temperature Ts starts to rise from time t1, the drive current I starts to increase in order to keep the intensity signal P at a constant value Po. When the increase in drive current I reaches ΔI at time t2, the controller 11 resets the substrate temperature Tb so as to return the drive current I to the minimum value I1 (steps R3 and R1 in FIG. 2). The controller 11 frequently resets the substrate temperature Tb while the environmental temperature Ts is changing.
As shown in FIG. 4C, when the ambient temperature Ts = TB is stabilized at time t3, the controller 11 sets the substrate temperature Tb = T2. As shown in FIG. 4B, the drive current I = I1.

Similarly, while the environmental temperature Ts changes from time t4 to t6, the controller 11 frequently resets the substrate temperature Tb. When the ambient temperature Ts = TC is stabilized at time t6, the controller 11 sets the substrate temperature Tb = T1 and the drive current I = I1.
Similarly, while the environmental temperature Ts is changing from time t7 to t9, the controller 11 frequently resets the substrate temperature Tb. When the ambient temperature Ts = TB is stabilized at time t9, the controller 11 sets the substrate temperature Tb = T2 and the drive current I = I1.

According to the wavelength conversion laser device 100 of the first embodiment, the following effects can be obtained.
(1) Since the temperature tuning is performed every time the drive current I increases from the steady value by ΔI or more, the steady value of the drive current I can be minimized. In other words, a decrease in the fundamental wave extinction ratio due to a change in the environmental temperature Ts can be absorbed by temperature tuning, and an increase in the drive current I of the semiconductor laser 1 can be suppressed.
(2) Since the drive current I of the semiconductor laser 1 does not reach the upper limit value Imax, the output is not reduced.

-Comparative Example 1-
FIG. 5 is an explanatory diagram showing a case where control is performed to maintain the substrate temperature Tb = T3 as shown in FIG.
As shown in FIG. 5A, the controller 11 performs control so that the intensity signal P becomes a constant value Po.
Assume that the environmental temperature Ts fluctuates as shown in FIG.

As shown in FIG. 5B, when the environmental temperature Ts = TA, the drive current I = I1.
When the environmental temperature Ts starts to rise from time t1, the drive current I starts to increase in order to keep the intensity signal P at a constant value Po.
When the ambient temperature Ts = TB is stabilized at the time t3, the drive current I = I2.
When the environmental temperature Ts starts to rise from time t4, the drive current I starts to increase in order to keep the intensity signal P at a constant value Po.
At time t5, the drive current I = Imax (upper limit) is reached, and the drive current I cannot be increased beyond this. For this reason, the intensity signal P cannot be maintained at the constant value Po, and the intensity signal P is lowered.
When the environmental temperature Ts decreases from time t7 and reaches time t8, the intensity signal P can be maintained at a constant value Po with the drive current I = Imax.
When the ambient temperature Ts = TB is stabilized at time t9, the drive current I = I2.

In the constant substrate temperature control as in Comparative Example 1, the operation is as follows.
(1) The drive current I of the semiconductor laser 1 increases due to a decrease in the fundamental wave extinction ratio due to a change in the environmental temperature Ts.
(2) Since the drive current I of the semiconductor laser 1 may reach the upper limit value Imax, the output may be reduced.

-Example 2-
FIG. 6 is an explanatory diagram illustrating the wavelength conversion laser device 200 according to the second embodiment.
In this wavelength conversion laser device 200, the rear end surface of the semiconductor laser 1 that oscillates fundamental light is provided with a high reflectance coat, and the front end surface is provided with a low reflectance coat.
The light emitted from the front surface of the semiconductor laser 1 is coupled to the polarization maintaining optical fiber 2 in an optimal state.

  The light guides of the semiconductor laser 1 and the polarization maintaining optical fiber 2 are housed in the housing 17, and the polarization maintaining optical fiber 2 is held inside the housing 17.

  The light emitted from the terminal end 3 of the polarization maintaining optical fiber 2 is converted into a desired beam by the lens 4 a and guided to the wavelength selection element 5.

The wavelength selection element 5 selectively reflects part of the light of the first selection wavelength, and this is again fed back to the semiconductor laser 1 through the polarization maintaining optical fiber 2.
By this feedback, the semiconductor laser 1 starts oscillating in the vicinity of the reflection center wavelength of the wavelength selection element 5.

  The light transmitted through the wavelength selection element 5 is converted into a desired beam by the lens 4b, and the wavelength is converted by the wavelength conversion element 6.

  A part of the wavelength-converted light is guided to the optical sensor 9 by the wavelength branching element 8 and converted into an intensity signal P.

  The controller 11 performs control so that the drive current I of the semiconductor laser 1 becomes a constant value Io.

  The casing 17, the polarization maintaining optical fiber 2, and the wavelength selection element 5 are disposed on the same substrate 10.

The temperature of the semiconductor laser 1 is controlled by the thermo module 7a.
The controller 11 sets the temperature Ta of the semiconductor laser 1 to a temperature range in which the wavelength selection by the wavelength selection element 5 is stably performed.

The temperature of the substrate 10 is controlled by the thermo module 7b.
The controller 11 sets the temperature Tb of the substrate 10 to a temperature at which the extinction ratio of the polarization plane incident on the wavelength conversion element 5 is maximized, that is, a temperature at which the drive current I is minimized. Then, the intensity signal P during steady operation is monitored, and when the intensity signal P decreases to a predetermined value ΔP or more, it is reset to a temperature at which the intensity signal P becomes a maximum value. This substrate temperature control process will be described later with reference to FIG.

The wavelength conversion element 6 is temperature-controlled by the thermo module 7c.
The controller 11 sets the temperature Tc of the wavelength conversion element 6 to a temperature at which the wavelength of the light having the wavelength selected by the wavelength selection element 5 is most efficiently converted.

Components other than the controller 11 are accommodated in the chassis 18.
Let Ts be the environmental temperature at which the chassis 18 is placed.

FIG. 7A is a graph showing the change of the intensity signal P with respect to the change of the substrate temperature Tb at the environmental temperature Ts = TA (for example, 0 ° C.).
At the environmental temperature Ts = TA, the intensity signal P can be set to the maximum value P1 if the substrate temperature Tb = T3 (for example, 30 ° C.).
FIG. 7B is a graph showing the change in the intensity signal P with respect to the change in the substrate temperature Tb at the environmental temperature Ts = TB (for example, 20 ° C.).
At the environmental temperature Ts = TB, the intensity signal P can be set to the maximum value P1 if the substrate temperature Tb = T2 (for example, 28 ° C.).
FIG. 7C is a graph showing the change of the intensity signal P with respect to the change of the substrate temperature Tb at the environmental temperature Ts = TC (for example, 50 ° C.).
At the environmental temperature Ts = TC, the intensity signal P can be set to the maximum value P1 if the substrate temperature Tb = T1 (for example, 24 ° C.).

FIG. 8 is a flowchart showing the substrate temperature control process.
In step S1, the controller 11 changes the substrate temperature Tb within a predetermined temperature range (for example, 10 ° C. to 40 ° C.) to set the substrate temperature Tb at which the intensity signal P becomes a maximum value.
In step S2, the intensity signal P is stored as an intensity signal value during steady operation.
In step S3, if the current intensity signal P decreases by ΔP or more from the stored intensity signal P, the process returns to step S1.

FIG. 9 is an explanatory diagram showing the effect of the substrate temperature control process.
As shown in FIG. 9A, the controller 11 performs control so that the drive current I becomes a constant value Io.
Assume that the environmental temperature Ts fluctuates as shown in FIG.

As shown in FIG. 9C, when the environmental temperature Ts = TA, the controller 11 sets the substrate temperature Tb = T3. As shown in FIG. 9B, the intensity signal P = P1 (steps S1 and S2 in FIG. 8).
When the environmental temperature Ts starts to rise from time t1, the intensity signal P starts to decrease because the drive current I is kept at the constant value Io. When the decrease in the intensity signal P reaches ΔP at time t2, the controller 11 resets the substrate temperature Tb so as to return the intensity signal P to the maximum value P1 (steps S3 and S1 in FIG. 8). The controller 11 frequently resets the substrate temperature Tb while the environmental temperature Ts is changing.
As shown in FIG. 9C, when the ambient temperature Ts = TB is stabilized at time t3, the controller 11 sets the substrate temperature Tb = T2. As shown in FIG. 9B, the intensity signal P = P1.

Similarly, while the environmental temperature Ts changes from time t4 to t6, the controller 11 frequently resets the substrate temperature Tb. When the ambient temperature Ts = TC is stabilized at time t6, the controller 11 sets the substrate temperature Tb = T1, and the intensity signal P = P1.
Similarly, while the environmental temperature Ts is changing from time t7 to t9, the controller 11 frequently resets the substrate temperature Tb. When the ambient temperature Ts = TB is stabilized at time t9, the controller 11 sets the substrate temperature Tb = T2 and the intensity signal P = P1.

According to the wavelength conversion laser device 200 of the second embodiment, the following effects can be obtained.
(1) Since the temperature tuning is performed each time the intensity signal P decreases by ΔP or more from the steady value, the steady value of the intensity signal P can be maximized. In other words, the decrease in the fundamental signal extinction ratio due to the change in the environmental temperature Ts can be absorbed by the temperature tuning, and the decrease in the intensity signal P can be suppressed.

-Comparative Example 2-
FIG. 10 is an explanatory diagram showing a case where control for maintaining the substrate temperature Tb = T3 is performed as shown in FIG.
As shown in FIG. 10A, the controller 11 performs control so that the drive current I becomes a constant value Io.
Assume that the environmental temperature Ts fluctuates as shown in FIG.

As shown in FIG. 10B, when the environmental temperature Ts = TA, the intensity signal P = P1.
When the environmental temperature Ts starts to rise from time t1, the intensity signal P starts to decrease because the drive current I is kept at the constant value Io.
When the ambient temperature Ts = TB is stabilized at the time t3, the intensity signal P = P2.
When the ambient temperature Ts starts to increase from time t4, the intensity signal P starts to decrease because the drive current I is kept at the constant value Io.
When the ambient temperature Ts = TC is stabilized at time t6, the intensity signal P = P3.
When the environmental temperature Ts starts to decrease from time t7, the intensity signal P starts to increase because the drive current I is maintained at the constant value Io.
When the ambient temperature Ts = TB is stabilized at time t9, the intensity signal P = P2.

  In the constant substrate temperature control as in Comparative Example 2, the intensity signal P decreases due to a decrease in the fundamental wave extinction ratio due to a change in the environmental temperature Ts.

Example 3
Similar to the temperature tuning of the substrate 10 in the first and second embodiments, the temperature tuning of the semiconductor laser 1 and the temperature tuning of the wavelength conversion element 6 may be performed.

Example 4
The wavelength selection element 5 may be provided with a dedicated thermo module, and the temperature selection of the wavelength selection element 5 may be performed similarly to the temperature tuning of the substrate 10 in the first and second embodiments.

  The wavelength conversion laser device of the present invention can be used in the bioengineering field and the measurement field.

DESCRIPTION OF SYMBOLS 1 Semiconductor laser 2 Polarization-maintaining optical fiber 5 Wavelength selection element 6 Wavelength conversion element 7a, 7b, 7c Thermo module 8 Optical branching element 9 Optical sensor 10 Substrate 11 Controller 17 Case 18 Chassis 100, 200 Wavelength conversion laser device

Claims (3)

A semiconductor laser that oscillates fundamental light, a polarization maintaining optical fiber optically coupled on the emission side of the semiconductor laser, a wavelength selection element disposed on the emission side of the polarization maintaining optical fiber, and the wavelength selection A wavelength converting element that converts the wavelength of light transmitted through the element, an optical branching element that splits the light converted by the wavelength converting element, and one of the lights branched by the optical branching element is converted into an intensity signal P And a driving current control means for controlling the driving current I of the semiconductor laser so that the intensity signal P is constant, and the semiconductor laser and a part of the polarization maintaining optical fiber are the same. The housing and the polarization maintaining optical fiber are placed on a single substrate, and when the driving current I during steady operation increases to a predetermined value or more, the driving current I Local minimum The wavelength conversion laser device, characterized by comprising a temperature control means for tuning the temperature of the substrate such that. A semiconductor laser that oscillates fundamental light, a polarization maintaining optical fiber optically coupled on the emission side of the semiconductor laser, a wavelength selection element disposed on the emission side of the polarization maintaining optical fiber, and the wavelength selection A wavelength converting element that converts the wavelength of light transmitted through the element, an optical branching element that splits the light converted by the wavelength converting element, and one of the lights branched by the optical branching element is converted into an intensity signal P And a drive current control means for controlling the drive current I of the semiconductor laser to be constant, wherein the semiconductor laser and a part of the polarization maintaining optical fiber are housed in the same housing, And the polarization maintaining optical fiber are arranged on a single substrate, and further, when the intensity signal P during steady operation decreases to a predetermined value or more, the intensity signal P reaches a maximum value. Temperature The wavelength conversion laser device, characterized by comprising a temperature control means for tuning. 3. The wavelength conversion laser device according to claim 1, wherein the wavelength selection element is disposed on the substrate.

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