JP4076623B2 - Tunable light source - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention is configured so that light emitted from a semiconductor laser is incident on a diffraction grating, and the diffracted light of the diffraction grating is reflected to the diffraction grating by a mirror, and the angle of the diffraction grating with respect to the light from the semiconductor laser and the semiconductor laser The present invention relates to a wavelength tunable light source that outputs light having a continuously variable wavelength by varying the external resonator length of the laser.
[0002]
[Prior art]
As a light source for measuring various wavelength-dependent characteristics of optical components, an external resonance type tunable light source has been used conventionally.
[0003]
The Litman-type external resonance type tunable light source is configured so that light emitted from a semiconductor laser is incident on a diffraction grating, and the diffracted light is reflected by a mirror toward the diffraction grating and returned to the semiconductor laser.
[0004]
In this configuration, an external resonator is formed between the mirror and one end face of the semiconductor laser, and when the length of the external resonator is changed, the resonance wavelength emitted from the semiconductor laser is continuously changed. Furthermore, when the incidence of light from the semiconductor laser to the diffraction grating is varied, the selected wavelength of the external resonator changes.
[0005]
Therefore, in order to continuously change the emission wavelength with this external resonance type semiconductor laser, the change in the wavelength of light in a specific resonance mode among the light whose resonance wavelength is changed by changing the external resonator length. It is necessary to vary the angle of the diffraction grating by following the above.
[0006]
Thus, in order to change the angle of the diffraction grating following the change in the external resonator length, the conventional wavelength tunable light source 10 is configured as shown in FIG.
[0007]
The wavelength variable light source 10 is formed on a base 11 having a flat upper surface. A semiconductor laser 12 that emits light in a certain direction along the upper surface of the base is provided at a predetermined position on the base 11. Light emitted from the semiconductor laser 12 is converted into parallel light by the collimator 13.
[0008]
A rectilinear stage 14 is disposed on the opposite side of the semiconductor laser 12 across the collimator 13. The upper surface 14a of the rectilinear stage 14 is formed in parallel with the upper surface 11a of the base 11, and can be moved linearly on the base 11 along the optical axis of the collimator 13 by a guide member (not shown). It is driven by the driving device 15.
[0009]
A rotary stage 16 is provided on the straight stage 14. The rotary stage 16 is supported by the linear stage 14 so as to be rotatable about a rotational axis J that is orthogonal to the upper surface 14 a of the linear stage 14 and intersects the optical axis of the collimator 13.
[0010]
A diffraction grating 17 and a mirror 18 are fixed on the rotary stage 16. The diffraction grating 17 is rotated so that the rotation axis J of the rotary stage 16 passes through the diffraction surface 17 a provided with the score line for diffracting light, and the score line is parallel to the rotation axis J of the rotation stage 16. It is fixed on the stage 16.
[0011]
The mirror 18 is fixed on the periphery of the rotary stage 16 with the reflecting surface 18 a facing the diffraction surface 17 a of the diffraction grating 17.
[0012]
Further, one end side 20 a of the slide bar 20 is fixed to the rotary stage 16. The slide bar 20 is orthogonal to the rotation axis J of the rotary stage 16 and extends in the radial direction of the rotary stage 16 in the same plane as the diffraction surface 17 a of the diffraction grating 17.
[0013]
The other end 20 b side of the slide bar 20 is supported from below by a base portion 21 a of a slide guide 21 erected on the base 11, and the tip thereof is in contact with the guide surface 21 b of the slide guide 21. The guide surface 21b of the slide guide 21 extends in a direction parallel to the rotation axis J of the rotary stage 16 and perpendicular to the moving direction of the linear stage 14, and the guide surface 21b allows the tip of the slide bar 20 to move to the linear stage 14. The sliding guide is in a direction perpendicular to the moving direction.
[0014]
A spring 22 is attached between the rotary stage 16 and the base 11 so as to rotate and urge the slide bar 20 attached to the rotary stage 16 so that the tip of the slide bar 20 is always in contact with the guide surface 21b of the slide guide 21. It has been.
[0015]
In the wavelength tunable light source 10 configured in this way, as shown in FIG. 6, for example, as shown in FIG. 6, when the linear stage 14 moves a predetermined distance in the direction approaching the semiconductor laser 12, the tip of the slide bar 20 and the slide guide 21 are moved. The contact position A with the guide surface 21b moves away from the semiconductor laser 12, and the rotary stage 16 rotates clockwise by a predetermined angle against the force of the spring 22. Conversely, when the linear stage 14 moves away from the semiconductor laser 12, the contact position A between the tip of the slide bar 20 and the guide surface 21 b of the slide guide 21 moves in a direction approaching the semiconductor laser 12 by the force of the spring 22. Then, the rotary stage 16 rotates counterclockwise.
[0016]
Here, moving the rectilinear stage 14 changes the external resonator length of the semiconductor laser 12, and therefore the angle of the diffraction grating 17 can be changed following the external resonator length.
[0017]
The distance from the rotation axis J of the rotation stage 16 to the tip of the slide bar 20, the distance from the rotation axis J to the guide surface 21b of the slide guide 21, the distance from the rotation axis J to the semiconductor laser 12, and the rotation axis J to the mirror By setting in advance such that the distance to the 18 reflecting surfaces 18a satisfies a predetermined relationship, light in one resonance mode can be emitted in a state in which the wavelength can be continuously varied.
[0018]
The wavelength-variable light is emitted from the end face opposite to the diffraction grating side of the semiconductor laser 12, as indicated by a broken line in FIGS.
[0019]
[Problems to be solved by the invention]
However, as described above, the conventional wavelength tunable light source in which the diffraction grating 17 and the mirror 18 are arranged on the rotary stage 16 has a problem that the diameter of the rotary stage 16 is increased.
[0020]
In addition, since the mirror 18 is disposed at the peripheral edge on the rotary stage 16, the center of gravity of the rotary stage 16 is separated from the center of rotation by the mirror 18, and the support for supporting the central part of the rotary stage 16 is rotatably supported. Due to the slight backlash of the mechanism, the rotary stage 16 is greatly shaken, and the angle of the engraving of the diffraction surface 17 of the diffraction grating 17 with respect to the optical axis of the semiconductor laser 12 changes due to this shake. There is a problem that the change of the selected wavelength does not follow the change, and the reproducibility of the wavelength of the emitted light with respect to the position of the straight stage is low.
[0021]
An object of the present invention is to provide a wavelength tunable light source that solves this problem.
[0022]
[Means for Solving the Problems]
In order to achieve the above object, a wavelength tunable light source according to claim 1 of the present invention comprises
A base (31);
A semiconductor laser (32) provided on the base and emitting light in a direction along the base surface;
A collimator (33) for converting light emitted from the semiconductor laser into parallel light;
A rectilinear stage (34) formed to be movable on the base along the optical axis of the collimator;
Drive means (35) for moving the linear stage;
A rotary stage (36) that is perpendicular to the stage surface of the linear stage and is rotatably supported on the linear stage around a rotational axis that intersects the optical axis of the collimator;
A diffraction surface provided with a score line for diffracting light from the collimator, the rotation axis of the rotary stage passes through the diffraction surface, and the score line is parallel to the rotation axis of the rotation stage. A diffraction grating (37) fixed on the rotary stage,
A mirror (38) provided on the rectilinear stage so as to face the diffraction surface of the diffraction grating and reflecting diffracted light from the diffraction surface of the diffraction grating to the diffraction surface;
The angle formed by the normal line of the reflecting surface of the mirror and the optical axis of the collimator that is in a plane perpendicular to the rotation axis of the rotation stage and intersects the rotation axis of the rotation stage with respect to the diffraction surface of the diffraction grating. A slide bar (40) of a predetermined length extending in the radial direction of the rotary stage so as to form an angle of 1/2 and having one end fixed to the rotary stage;
A slide guide (41) that slides and guides in a direction perpendicular to the moving direction of the linear stage while the other end of the slide bar is in contact with the slide bar;
The distance from the rotation axis of the rotary stage to the intersection of the plane including the surface in the sliding direction of the slide bar and the optical axis of the collimator is constituted by the optical path between one end face of the semiconductor laser and the mirror It is characterized by being configured to be equal to the effective external resonator length.
[0023]
The tunable light source according to claim 2 of the present invention is the tunable light source according to claim 1,
Mirror moving means (51) for moving the mirror in the normal direction of the reflecting surface is provided on the rectilinear stage.
[0024]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows a configuration of a wavelength tunable light source 30 according to an embodiment of the present invention.
[0025]
The wavelength tunable light source 30 is formed on a base 31 having a flat upper surface, and a semiconductor laser 32 that emits light in a fixed direction along the upper surface of the base is provided at a predetermined position on the base 31. The light emitted from 32 is converted into parallel light by the collimator 33.
[0026]
A rectilinear stage 34 is disposed on the opposite side of the semiconductor laser 32 across the collimator 33, and the upper surface 34 a of the rectilinear stage 34 is formed in parallel with the upper surface 31 a of the base 31. The linear stage 34 is linearly movable on the base 31 along the optical axis of the collimator 33 by a guide member (not shown), and is driven by a driving device 35 such as a motor.
[0027]
A rotation stage 36 is provided on the rectilinear stage 34. The rotary stage 36 is supported by the linear stage 34 so as to be rotatable about a rotational axis J perpendicular to the upper surface 34 a of the linear stage 34 and intersecting the optical axis of the collimator 33.
[0028]
A diffraction grating 37 is fixed on the rotary stage 36. The diffraction grating 37 is rotated so that the rotation axis J of the rotary stage 36 passes through the diffraction surface 37 a provided with the score line for diffracting light, and the score line is parallel to the rotation axis J of the rotation stage 36. It is fixed on the stage 36.
[0029]
On the other hand, the mirror 38 for reflecting the diffracted light from the diffraction grating 37 to the diffraction surface faces the diffraction surface 37a of the diffraction grating 37 with the normal passing through the center of the reflection surface 38a orthogonal to the rotation axis J. ing. The mirror 38 is a plane mirror or a corner mirror.
[0030]
In addition, one end 40 a side of the slide bar 40 is fixed to the rotary stage 36. The slide bar 40 is perpendicular to the rotation axis J of the rotation stage 36 and intersects the rotation surface J of the rotation stage 36 with respect to the diffraction surface 37 a of the diffraction grating 37, and the optical axis of the collimator 33. Is extended in the radial direction of the rotary stage 36 so as to form an angle γ that is ½ of the angle 2γ formed by.
[0031]
The other end 40 b side of the slide bar 40 is supported from below by a base portion 41 a of a slide guide 41 erected on the base 31, and its tip abuts against the guide portion 41 b of the slide guide 41. The guide part 41 b of the slide guide 41 extends in a direction parallel to the base 31 and perpendicular to the moving direction of the rectilinear stage 34, and the rotary stage 36 from the intersection of the extension line of the guide part 41 b and the optical axis of the collimator 33. Is set to be equal to the effective external resonator length of the external resonator. The leading end of the slide bar 40 is slidably guided in a direction orthogonal to the moving direction of the linear stage 34 by the guide portion 41b.
[0032]
A spring 42 is attached between the rotary stage 36 and the base 31 so as to rotate and urge the slide bar 40 attached to the rotary stage 36 so that the tip of the slide bar 40 is always in contact with the guide portion 41b of the slide guide 41. It has been.
[0033]
The light whose wavelength has been varied is extracted from the end surface of the semiconductor laser 32 opposite to the diffraction grating.
[0034]
In the wavelength tunable light source 30 configured in this way, the other end of the slide bar 40 is moved by the drive device 35 when the rectilinear stage 34 moves a predetermined distance in the direction approaching the semiconductor laser 32 as shown in FIG. The contact position between 40b and the guide portion 41b of the slide guide 41 moves away from the semiconductor laser 32, the rotation stage 36 rotates clockwise by a predetermined angle against the force of the spring 42, and the diffraction grating 37 also It rotates at the same angle in the same direction as the rotary stage 36.
[0035]
As shown in FIG. 2B, when the linear stage 34 moves away from the semiconductor laser 32, the force of the spring 42 causes the other end 40b of the slide bar 40 and the guide portion 41b of the slide guide 41 to contact each other. The contact position moves in a direction approaching the semiconductor laser 32, the rotation stage 36 rotates counterclockwise, and the diffraction grating 37 also rotates in the same direction as the rotation stage 36 by the same angle.
[0036]
Therefore, the diffraction grating 37 on the rotary stage 36 rotates following the movement of the linear stage 34, and moving the linear stage 34 changes the external resonator length of the semiconductor laser 32. Therefore, the angle of the diffraction grating 37 can be varied following the external resonator length.
[0037]
Next, conditions for enabling the wavelength variable light source 30 to continuously change the wavelength will be described.
[0038]
As shown in FIG. 3, in this wavelength tunable light source 30, the optical path length La between the diffraction grating 37 and the mirror 38 is constant regardless of the movement of the linear stage 34 or the rotation of the rotary stage 36. The sum of the optical path length La and the optical path length Lb between the semiconductor laser 32 and the diffraction grating 37 is the external resonator length.
[0039]
Since the refractive index in the semiconductor laser 37 is larger than the outside, the actual optical path length Lb is at a position C ′ farther from the reflecting surface side than the semiconductor laser 32 as viewed from the diffraction grating 37, as shown in FIG. The distance between this position C ′ and the intersection position C between the extension line of the guide portion 41 b of the slide guide 41 and the extension line of the optical axis of the semiconductor laser 32 is the optical path between the diffraction grating 37 and the mirror 38. It is preset to be equal to the length La.
[0040]
Further, as described above, the angle formed by the incident optical axis of the light from the semiconductor laser 32 to the diffraction grating 37 and the diffraction optical axis is twice the angle γ formed by the diffraction surface 37 a of the diffraction grating 37 and the slide bar 40. It is set to 2γ.
[0041]
Assuming that light with an oscillation wavelength λ ₀ is emitted from the semiconductor laser in this state, the conditions under which the light with the wavelength λ ₀ is diffracted by the diffraction grating 37 are expressed by the following equations (1) and (2). .
[0042]
λ ₀ = X · sin θ ₀ (1)
However, X = (2 · d · cos γ) / m, where m is the diffraction order, d is the grating constant of the diffraction grating 37, and θ ₀ is the incident optical axis of the diffraction grating 37 as shown in FIG. And the bisector I of the angle formed by the diffraction optical axis and the normal H of the diffraction grating 37, where β is the diffraction angle of the diffraction grating 37 and i is the angle of incidence on the diffraction grating 37. θ ₀ = (β + i) / 2, and γ is a constant represented by (β−i) / 2.
[0043]
q ₀ · λ ₀ = 2L ₀ (2)
However, q ₀ is the external resonance mode order, and L ₀ is the effective resonator length of the external resonator.
[0044]
Here, the effective resonator length L ₀ of the external resonator is expressed by the following equation (3).
L ₀ = Ls · sin (ζ ₀ ) (3)
However, Ls is a distance from the rotation axis J to the tip of the slide bar 40 and the contact position A of the slide guide 41, and ζ ₀ is an angle formed by the slide bar 40 and the guide portion 41b of the slide guide 41.
[0045]
Next, consider the case of wavelength (λ), ζ = ζ ₀ + Δζ, and θ = θ ₀ + Δθ.
ζ = ζ ₀ + Δζ and θ = θ ₀ + Δθ are equal from the following relationship.
(Ζ ₀ + Δζ) + α = 90 °, (θ ₀ + Δθ) + α = 90 °
Here, α is an angle formed by the slide bar 40 and the optical axis of the semiconductor laser 32.
[0046]
Therefore, the wavelength (λ) selected by the angle (θ ₀ + Δθ) of the diffraction grating 37 is
λ = X · sin (θ ₀ + Δθ)
The external resonator length (L) at this time is
L = Ls · sin (ζ ₀ + Δζ) = Ls · λ / X
It becomes.
[0047]
Therefore, the resonance mode order q is
q = 2 · L / λ = 2 · Ls / X
Thus, since Ls and X are constants, q is also constant, and the wavelength can be continuously varied while maintaining one resonance mode order.
[0048]
As an actual numerical example, the number of engravings of the diffraction grating 37 is 1000 / mm, the angle γ formed by the diffraction surface of the diffraction grating 37 and the slide bar 40 is 22.5 °, and the incident angle and the emission angle of the diffraction grating 37. Is 45 °, θ = ζ = 57 ° at a wavelength of 1.55 μm, and the incident angle i = 79.5 ° to the diffraction grating.
[0049]
As described above, in this wavelength tunable light source 30, only the diffraction grating 37 is supported by the rotary stage 36 at the substantially central portion, and the mirror 38 is provided on the linear stage 34. It can be made as small as necessary to support it. In addition, since the axis of the rotary stage due to the mirror 38 does not occur, the resonator length and the selected wavelength are always tuned, and the wavelength of the emitted light can be changed with high reproducibility with respect to the change of the position of the straight stage. .
[0050]
In the above embodiment, the mirror 38 is fixed on the rectilinear stage 34. However, like the variable wavelength light source 50 shown in FIG. 4, the mirror 38 is formed on the reflecting surface 38a by the mirror moving means 51 such as a piezoelectric element. You may comprise so that it can move to a normal line direction. In such a configuration, the shift of the resonator length and the rotation angle of the diffraction grating 37 can be corrected by the movement of the mirror 38 by the mirror moving means 51.
[0051]
【The invention's effect】
As described above, the wavelength tunable light source of the present invention has only the diffraction grating disposed on the rotary stage on the straight stage, and the mirror is provided on the straight stage. Since the rotation stage does not shake, the resonator length and the selected wavelength are always tuned, and the wavelength of the emitted light can be changed with high reproducibility with respect to the change in the position of the straight stage.
[0052]
In addition, the wavelength tunable light source provided with the moving means in the mirror can correct the deviation of the resonator length and the rotation angle of the diffraction grating by moving the mirror by the mirror moving means, and continuously tunes the wavelength with higher stability. be able to.
[Brief description of the drawings]
FIG. 1 is a diagram showing the configuration of an embodiment of the present invention. FIG. 2 is a diagram for explaining the operation of the embodiment. FIG. 3 is a diagram for examining conditions for continuously changing the wavelength. FIG. 5 is a diagram showing the configuration of another embodiment of the present invention. FIG. 5 is a diagram showing the configuration of a conventional light source. FIG. 6 is a diagram for explaining the operation of the conventional light source.
30 Wavelength variable light source 31 Base 32 Semiconductor laser 33 Collimator 34 Linear stage 35 Driving means 36 Rotating stage 37 Diffraction grating 38 Mirror 40 Slide bar 41 Slide guide 42 Spring

Claims (2)

A base (31);
A semiconductor laser (32) provided on the base and emitting light in a direction along the base surface;
A collimator (33) for converting light emitted from the semiconductor laser into parallel light;
A rectilinear stage (34) formed to be movable on the base along the optical axis of the collimator;
Drive means (35) for moving the linear stage;
A rotary stage (36) that is perpendicular to the stage surface of the linear stage and is rotatably supported on the linear stage around a rotational axis that intersects the optical axis of the collimator;
A diffraction surface provided with a score line for diffracting light from the collimator, the rotation axis of the rotary stage passes through the diffraction surface, and the score line is parallel to the rotation axis of the rotation stage. A diffraction grating (37) fixed on the rotary stage,
A mirror (38) provided on the rectilinear stage so as to face the diffraction surface of the diffraction grating and reflecting diffracted light from the diffraction surface of the diffraction grating to the diffraction surface;
The angle formed by the normal line of the reflecting surface of the mirror and the optical axis of the collimator that is in a plane perpendicular to the rotation axis of the rotation stage and intersects the rotation axis of the rotation stage with respect to the diffraction surface of the diffraction grating. A slide bar (40) of a predetermined length extending in the radial direction of the rotary stage so as to form an angle of 1/2 and having one end fixed to the rotary stage;
A slide guide (41) that slides and guides in a direction perpendicular to the moving direction of the linear stage while the other end of the slide bar is in contact with the slide bar;
The distance from the rotation axis of the rotary stage to the intersection of the plane including the sliding direction surface of the slide bar and the optical axis of the collimator is constituted by the optical path between one end surface of the semiconductor laser and the mirror The wavelength tunable light source is configured to be equal to the effective external resonator length. The wavelength tunable light source according to claim 1, wherein mirror moving means (51) for moving the mirror in the normal direction of the reflecting surface is provided on the rectilinear stage.

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