JP2008130805A - External resonator wavelength variable light source - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an external resonator wavelength variable light source which exhibits a high wavelength resolution and which can be easily adjusted. <P>SOLUTION: The external resonator wavelength variable light source 10 is an external resonator wavelength variable optical source of a Littman type and includes a laser diode 11, a collimator lens 12, an adjusting lens 13, a diffraction grating 14 and a planar mirror 15. The adjusting lens 13 is arranged in an optical path between the collimator lens 12 and the diffraction grating 14, can at least either rotate or shake and further can slightly move in the direction along the optical path of parallel light through the collimator lens 12. The incident angle of the parallel light with respect to the diffraction grating 14 through the collimator lens 12 can be varied. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an external resonator type wavelength tunable light source used in the field of optical communication or the field of optical measurement technology.

  As a light source used in optical communication or optical measurement technology, a light source capable of wavelength stability with a single mode oscillation with a narrow spectral line width and a variable wavelength is required. An external resonator type tunable light source has been developed as one of light sources capable of oscillation wavelength. FIG. 6 is a plan view showing an example of a conventional external resonator type wavelength tunable light source. As shown in FIG. 6, the external resonator type wavelength tunable light source 100 includes a laser diode 101, a collimating lens 102, a diffraction grating 103, and a plane mirror 104. The external resonator type wavelength tunable light source shown in FIG. 6 is a Littman type external resonator type wavelength tunable light source.

  The laser diode 101 is a Fabry-Perot type semiconductor laser in which, for example, a lower cladding layer, an active layer, and an upper cladding layer are sequentially formed on a semiconductor substrate, and parallel end surfaces obtained by cleaving the semiconductor substrate are used as resonators. . The laser diode 101 has a non-reflective film (AR coat) 105 formed on one end face forming a resonator. The laser diode 101 is disposed with the end surface on which the antireflective film 105 is formed facing the collimating lens 102 side.

  The collimating lens 102 is positioned with respect to the laser diode 101 so that one focal point is disposed at the laser light emission position on the end surface of the laser diode 101 where the non-reflective film 105 is formed. The collimator lens 102 collimates the laser light emitted from the laser diode 101 and condenses the laser light diffracted by the diffraction grating 103 at the laser light emission position of the laser diode 101. The diffraction grating 103 has a planar diffraction surface 103a in which a grating is formed in a direction orthogonal to the paper surface, and the laser light collimated by the collimating lens 102 and the laser light reflected by the plane mirror 104 are obtained. Diffracts at an angle corresponding to the wavelength. The plane mirror 104 reflects the laser light diffracted by the diffraction grating 103. The flat mirror 104 can move in a plane parallel to the paper surface and can rotate in the same plane.

  FIG. 7 is a diagram showing the positional relationship between the laser diode 101, the diffraction grating 103, and the plane mirror 104 provided in the conventional external resonator type wavelength tunable light source 100. As shown in FIG. In FIG. 7, the collimating lens 102 is not shown. As shown in FIG. 7, the laser beam emission position on the end surface of the laser diode 101 where the non-reflective film 105 is formed is P11, the laser beam incident position on the diffraction grating 103 is P12, and the laser beam incident position on the flat mirror 104 is P13.

Now, as shown in FIG. 7, the incident angle of the laser beam with respect to the diffraction grating 103 is α, the emission angle is β, the wavelength of the laser beam emitted from the external resonator type tunable light source 100 is λ, and the grating of the diffraction grating 103 If the constant is d, the following equation (1) holds. Here, it is assumed that the external resonator type wavelength tunable light source 100 is disposed in the air, and the refractive index with respect to the laser light is “1”.
λ / d = sin α + sin β (1)
Here, the relationship between the change amount δβ of the emission angle of the laser beam with respect to the diffraction grating 103 and the change amount δλ of the wavelength is expressed by the following equation (2).
δλ = d · cosβ · δβ (2)

Further, the wave number in the external resonator type wavelength tunable light source 100 is k, the optical path length between the laser diode 101 and the diffraction grating 103 (the optical path length between the emission position P11 and the incident position P12) is Li, and the diffraction grating. When the optical path length between the optical path 103 and the flat mirror 104 (the optical path length between the incident position P12 and the incident position P13) is Lo, the following expression (3) is established.
(K · λ) / 2 = Li + Lo (3)
Here, the relationship between the change amount δLo of the optical path length Lo and the change amount δλ of the wavelength is expressed by the following equation (4).
δλ = (2 · δLo) / k (4)

  In the Littman-type external resonator type wavelength tunable light source 100 shown in FIG. 6, when changing the wavelength while keeping the wave number k constant, the laser beam emission position P11 of the laser diode 101 and the laser beam with respect to the diffraction grating 103 are used. The incident position P12 of the laser beam and the incident position P13 of the laser beam with respect to the flat mirror 104 are respectively arranged on the circumference of a circle R10 indicated by a broken line. At this time, as shown in FIG. 7, the diffraction grating 103 is positioned so that a plane including the diffraction surface 103a and perpendicular to the paper surface passes through the center of the circle R10. Further, if the intersection point located outside the diffraction grating 103 among the two intersection points between the plane including the diffraction surface 103a of the diffraction grating 103a and the plane perpendicular to the paper surface and the circle R10 is C11, the plane mirror 104 has a reflection surface thereof. The laser beam is rotated so that the laser beam incident position P13 is positioned on the circumference of the circle R10, which is included in a plane perpendicular to the paper surface through the intersection C11.

At this time, if the diameter of the circle R10 shown in FIG. 7 is D, Li = D · sin α and Lo = D · sin β are satisfied, and the following equations (5) to (7) are established.
D (sin α + sin β) = Li + Lo (5)
(D · λ) / d = (k · λ) / 2 (6)
D / d = k / 2 (7)

  In the above configuration, the laser light emitted from the laser diode 101 is converted into parallel light by the collimator lens 102, then enters the diffraction surface 103a of the diffraction grating 103, and is diffracted at an angle corresponding to the wavelength. Of the laser light diffracted by the diffraction grating 103, the laser light diffracted in the direction in which the plane mirror 104 is disposed is reflected by the plane mirror 104 and then enters the diffraction surface 103 a of the diffraction grating 103 again. This laser light is again diffracted by the diffraction grating 103 and travels in the reverse direction along the original optical path, and is condensed by the collimating lens 102 and enters the laser diode 101. Part of the laser light incident on the laser diode 101 is reflected by the end face 101a of the laser diode 101, travels in the reverse direction inside the laser diode 101, and is emitted again toward the collimator lens 102, and the rest is emitted from the end face 101a to the laser diode. 101 is injected outside.

  As described above, the conventional external resonator type wavelength tunable light source 100 shown in FIG. 6 has a resonator formed by the end face 101 a of the laser diode 101 and the flat mirror 104 provided outside the laser diode 101. Here, when the plane mirror 104 constituting the resonator is moved in a plane parallel to the paper surface and rotated in the same plane so that the light diffracted by the diffraction grating 103 is vertically incident, the plane mirror 104 enters the plane mirror 104. The wavelength of the laser light emitted from the end face 101a of the laser diode 101 can be varied because the optical path length of the resonator changes as the wavelength of the laser light changes. Specifically, when the plane mirror 104 is moved in the direction indicated by the reference numeral D11 in FIG. 6 and rotated as appropriate, the wavelength of the laser light can be continuously varied to the long wavelength side. When the plane mirror 104 is moved in the direction indicated by the reference numeral D12 and rotated as appropriate, the wavelength of the laser beam can be continuously varied to the short wavelength side.

For details of the conventional external resonator type wavelength tunable light source, see, for example, the following Patent Documents 1 and 2.
JP-A-11-68248 JP 2000-353854 A

  By way of example, when the external resonator type wavelength tunable light source 100 shown in FIG. 6 is used in the field of optical communication, the external resonator type wavelength tunable light source 100 is required to have a wavelength resolution of less than 1 pm. Here, when the wavelength λ = 1550 nm, the incident angle α = 75 ° to the diffraction grating 103, the emission angle β = 25.4 °, and the grating constant d = 1.11 μm, the wavelength resolution required for the wavelength of the laser light. In order to change by 1 pm, if δλ = 1 pm in the above-described equation (2), the change amount δβ of the laser beam emission angle is about 1 μrad. The plane mirror 104 is driven by a mechanical drive device such as a motor or a feed screw, but it is difficult to drive the plane mirror 104 with an accuracy of 1 μrad.

  Further, as described above, the collimating lens 102 is positioned with respect to the laser diode 101 so that one focal point is disposed at the laser light emission position on the end surface of the laser diode 101 where the non-reflective film 105 is formed. However, in the external resonator type wavelength tunable light source 100, in order to ensure a wide wavelength tunable range (for example, about 200 nm), the positioning accuracy of the collimating lens 102 is extremely important. For example, when the focal length of the collimating lens 102 is 2 mm, the positioning error of the collimating lens 102 needs to be 1 μm or less in order to ensure a wide wavelength variable range. High accuracy is required for positioning the collimating lens 102, and adjustment is extremely difficult.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide an external resonator type wavelength tunable light source having high wavelength resolution and easy adjustment.

In order to solve the above-described problems, an external resonator type wavelength tunable light source according to the present invention includes a light source (11, 21) having an anti-reflective film (16, 25) formed on one end face, and the non-reflective of the light source. External resonator type wavelength comprising lenses (12, 22) arranged on the end face side on which the film is formed and wavelength selection elements (14, 24, 30) for selecting a predetermined wavelength from light via the lens In a variable light source (10, 20), an optical element (13, 23) disposed on an optical path between the lens and the wavelength selection element and configured to vary an incident angle of the light via the lens with respect to the wavelength selection element. It is characterized by having.
According to this invention, the laser light emitted from the end face on which the antireflection film of the light source is formed enters the optical element via the lens, and the incident angle with respect to the wavelength selection element is varied and enters the wavelength selection element.
Also, the external resonator type wavelength tunable light source of the present invention is characterized in that the optical element is capable of at least one of rotation and oscillation.
The external resonator type wavelength tunable light source of the present invention is characterized in that the optical element is movable in a direction along an optical path between the lens and the wavelength selection element.
The external resonator type wavelength tunable light source of the present invention is characterized in that the optical element is a refractive element.
Here, in the external resonator type wavelength tunable light source of the present invention, the refractive element is preferably one of a lens and a prism.
Further, in the external resonator type wavelength tunable light source of the present invention, the wavelength selection element is a diffraction grating that diffracts light through a lens disposed on an end face side of the light source at an angle corresponding to the wavelength. It is a feature.
Alternatively, the external resonator type wavelength tunable light source according to the present invention is a dielectric multilayer film in which the wavelength selection element reflects light having a wavelength corresponding to an incident angle of light through a lens disposed on an end face side of the light source. It is characterized by being.
Furthermore, the external resonator type wavelength tunable light source of the present invention includes a movable reflecting mirror (15) for reflecting a part of the light diffracted by the diffraction grating toward the diffraction grating. Yes.

  According to the present invention, since the optical element that varies the incident angle with respect to the wavelength selection element is provided between the lens and the wavelength selection element, the wavelength can be varied with high accuracy and the wavelength resolution can be increased. There is an effect that can be done. In addition, since this optical element can move in the direction along the optical path between the lens and the wavelength selection element, the positioning error of the lens with respect to the light source can be compensated by adjusting the position of the optical element. There is an effect that is easy. As a result, a wide wavelength variable range (for example, about 200 nm) can be ensured.

  Hereinafter, an external resonator type wavelength tunable light source according to an embodiment of the present invention will be described in detail with reference to the drawings. FIG. 1 is a plan view showing a configuration of an external resonator type tunable light source according to an embodiment of the present invention. As shown in FIG. 1, the external resonator type wavelength tunable light source 10 according to the present embodiment includes a laser diode 11 (light source), a collimator lens 12, an adjustment lens 13 (optical element, a refractive element), and a diffraction grating 14 (wavelength selection element). ) And a plane mirror 15 (reflecting mirror). The external resonator type wavelength tunable light source shown in FIG. 1 is a Littman type external resonator type wavelength tunable light source.

  The laser diode 11 is a Fabry-Perot type semiconductor laser in which, for example, a lower clad layer, an active layer, and an upper clad layer are sequentially formed on a semiconductor substrate, and parallel end surfaces obtained by cleaving the semiconductor substrate are used as resonators. . The laser diode 11 is formed with a non-reflective film (AR coat) 16 on one of end faces forming a resonator. The laser diode 11 is arranged with the end surface on which the antireflective film 16 is formed facing the collimating lens 12 side.

  The collimator lens 12 is positioned with respect to the laser diode 11 so that one focal point is disposed at the laser light emission position on the end surface of the laser diode 11 where the antireflective film 16 is formed. The collimating lens 12 collimates the laser light emitted from the laser diode 11 and collects the laser light diffracted by the diffraction grating 14 and passing through the adjustment lens 13 at the laser light emission position of the laser diode 11. Shine.

  The adjustment lens 13 is movably disposed on the optical path between the collimating lens 12 and the diffraction grating 14, and changes the incident angle of the parallel light converted by the collimating lens 12 with respect to the diffraction grating 14. . Specifically, the adjustment lens 13 is configured to be capable of at least one of rotation and swing, and when the adjustment lens 13 itself performs at least one of rotation and swing, the adjustment lens 13 is parallel to the collimator lens 12. The optical axis of the light is tilted, whereby the incident angle of the parallel light with respect to the diffraction grating 14 is varied.

  FIG. 2 is a view for explaining the rotation and swing of the adjustment lens 13. As shown in FIG. 2A, when the rotation axis X1 is set at a position that is orthogonal to the optical axis of the laser beam and passes through the adjustment amount lens 13, the adjustment lens 13 is rotated around the rotation axis X1. Rotate with. On the other hand, as shown in FIG. 2 (b), when the rotation axis X2 is set at a position orthogonal to the optical axis of the laser light and outside the adjustment amount lens 13, the adjustment lens 13 has the rotation axis. Rotate (ie, swing) around X2. These rotation axes X1 and X2 are set along the longitudinal direction of the grating formed in the diffraction grating 14. Note that both the rotation axis X1 shown in FIG. 2A and the rotation axis X2 shown in FIG. 2B may be set so that the adjustment lens 13 can swing and rotate.

  The adjustment lens 13 is a plano-convex lens having a low power (refractive power), for example, and is arranged with the plane facing the collimator lens 12 and the convex surface facing the diffraction grating 14. When the adjusting lens 13 is rotated, for example, in the direction indicated by reference numeral D1 in FIG. 1, the parallel light from the collimating lens 12 enters the diffraction grating 14 through the optical path L1 in the figure. On the contrary, when the adjustment lens 13 is rotated in the direction denoted by reference numeral D2 in FIG. 1, the parallel light from the collimating lens 12 enters the diffraction grating 14 through the optical path L2 in the figure. As is clear from FIG. 1, when the adjustment lens 13 is rotated, the incident angle of the parallel light with respect to the diffraction grating 14 changes.

  The adjustment lens 13 is configured to be movable (finely movable) in the optical axis direction of parallel light (direction along the optical path of parallel light). As described above, the laser diode 11 is positioned with respect to the laser diode 11 such that one focal point is positioned at the laser light emission position on the end surface of the laser diode 11 where the antireflective film 16 is formed. And the wavelength variable range becomes narrow. By making the adjustment lens 13 movable in the optical axis direction of the parallel light, when the collimating lens 12 and the adjustment lens 13 are viewed as one lens, the positioning error of the collimating lens 12 can be compensated. A wide wavelength range can be secured.

  The diffraction grating 14 has a planar diffraction surface 14 a in which a grating is formed in a direction perpendicular to the paper surface, and is made parallel by the collimating lens 12, parallel light via the adjustment lens 13, and the plane mirror 15. The laser beam reflected by is diffracted at an angle corresponding to the wavelength. The plane mirror 15 reflects the laser light diffracted by the diffraction grating 14. The flat mirror 15 can move in a plane parallel to the paper surface and can rotate in the same plane. Specifically, it can be moved in the direction indicated by reference signs D3 and D4 in FIG.

  In the above configuration, the laser light emitted from the laser diode 11 is converted into parallel light by the collimator lens 12, and then enters the diffraction surface 14a of the diffraction grating 14 via the adjustment lens 13, and is an angle corresponding to the wavelength. It is diffracted by. Of the laser light diffracted by the diffraction grating 14, the laser light diffracted in the direction in which the plane mirror 15 is arranged is reflected by the plane mirror 15 and then enters the diffraction surface 14 a of the diffraction grating 14 again. The laser light is again diffracted by the diffraction grating 14 and travels in the reverse direction along the original optical path, enters the collimating lens 12 through the adjustment lens 13, is condensed by the collimating lens 12, and enters the laser diode 11. Part of the laser light incident on the laser diode 11 is reflected by the end face 11a of the laser diode 11, travels in the reverse direction inside the laser diode 11 and is emitted again toward the collimator lens 12, and the rest is emitted from the end face 11a to the laser diode. 11 is injected outside.

  Here, when the adjustment lens 13 is rotated in the direction indicated by the symbol D1 in FIG. 1, the parallel light from the collimating lens 12 enters the diffraction grating 14 through the optical path L1 in the drawing. At this time, the incident angle α of the parallel light with respect to the diffraction grating 14 increases, and laser light having a longer wavelength is diffracted in the direction in which the plane mirror 15 is disposed. Further, the incident angle α of the parallel light with respect to the diffraction grating 14 is increased, and the optical path length between the laser diode 11 and the diffraction grating 14 and the optical path length between the diffraction grating 14 and the plane mirror 15 are increased, thereby causing resonance. Conditions change. For this reason, among the laser beams diffracted by the diffraction grating 14, the laser beam having a wavelength that satisfies the changed resonance condition is amplified.

  Contrary to the above, when the adjustment lens 13 is rotated in the direction indicated by the symbol D2 in FIG. 1, the parallel light from the collimating lens 12 enters the diffraction grating 14 through the optical path L2 in the drawing. At this time, the incident angle α of the parallel light with respect to the diffraction grating 14 becomes small, and the laser light having a shorter wavelength is diffracted in the direction in which the plane mirror 15 is arranged. In addition, the incident angle α of the parallel light with respect to the diffraction grating 14 is reduced, and the optical path length between the laser diode 11 and the diffraction grating 14 and the optical path length between the diffraction grating 14 and the plane mirror 15 are shortened, thereby causing resonance. Conditions change. For this reason, among the laser beams diffracted by the diffraction grating 14, the laser beam having a wavelength satisfying the changed resonance condition is amplified.

  Thus, by rotating the adjustment lens 13 or the like, the wavelength of the laser light emitted from the external resonator type wavelength variable light source 10 can be varied with high accuracy. When the adjustment lens 13 is moved in the optical axis direction of the parallel light in FIG. 1, the focal position on the laser diode 11 side when the collimating lens 12 and the adjustment lens 13 are viewed as one lens is finely adjusted. The Thereby, even if there is a positioning error of the collimating lens 12, one focal point of the collimating lens 12 can be arranged at the laser light emission position on the end surface of the laser diode 11 where the non-reflective film 16 is formed. .

  FIG. 3 is a graph showing an example of the relationship between the rotation angle of the adjustment lens 13 and the amount of change in wavelength and resonator length. In the graph shown in FIG. 3, an aspheric lens having a focal length of 1.8 mm is used as the collimating lens 12, and a convex lens having a focal length of 28.5 mm is used as the adjustment lens 13. The distance between the collimating lens 12 and the adjustment lens 13 is 4 mm, and the distance from the collimating lens 12 to the rotation axis of the adjustment lens 13 is 5.3 mm. Further, a diffraction grating 13 having a grating constant of 1/900 mm is used, and the incident angle of laser light (parallel light) to the diffraction grating 14 is set to 75 °.

  As shown in FIG. 3, when the wavelength of the laser light emitted from the external resonator type wavelength tunable light source 10 is 1550 nm, the rotation angle of the adjustment lens 13 is 0 °. The resonator length at this time is about 37.3338 mm. When the wavelength of the laser beam emitted from the external resonator type tunable light source 10 is set to 1550.1 nm which is longer by 0.1 nm (100 pm), the rotation angle of the adjustment lens 13 is about −0.9 °. On the other hand, in the case of 1549.9 nm which is shorter by 0.1 nm (100 pm), the rotation angle of the adjustment lens 13 may be set to about + 0.9 °. When the wavelength is 1550.1 nm, the resonator length is about 37.3365 mm, and when the wavelength is 1549.9 nm, the resonator length is about 37.3313 mm.

  As described above, the adjustment lens 13 may be rotated by about 0.9 ° in order to vary the wavelength of the laser light emitted from the external resonator type wavelength tunable light source 10 by 100 pm. Therefore, in order to obtain a wavelength resolution of 1 pm, it is necessary to rotate the adjustment lens 13 by 0.009 ° (≈157 μrad). This accuracy can be sufficiently obtained even when the adjustment lens 13 is driven by a mechanical drive device, and a high wavelength resolution can be realized.

  As described above, the external resonator type wavelength tunable light source 10 according to the embodiment of the present invention is incident on the diffraction grating 14 of the parallel light via the collimator lens 12 on the optical path between the collimator lens 12 and the diffraction grating 14. An adjustment lens 13 for changing the angle is disposed. For this reason, the wavelength of the laser beam emitted from the external resonator type wavelength tunable light source 10 can be varied with high accuracy only by rotating the adjustment lens 13 without moving the plane mirror 15. Of course, if the plane mirror 15 is moved, it goes without saying that the wavelength of the laser light emitted from the external resonator type wavelength tunable light source 10 can be greatly varied.

  The adjustment lens 13 is movable in a direction along the optical path of the parallel light via the collimating lens 12. For this reason, the focal position on the laser diode 11 side when the collimating lens 12 and the adjustment lens 13 are viewed as one lens can be finely adjusted. Thereby, even if there is a positioning error of the collimating lens 12, one focal point of the collimating lens 12 can be arranged at the laser light emission position on the end surface of the laser diode 11 where the non-reflective film 16 is formed. . As a result, it is possible to ensure a wide wavelength range.

  As described above, the external resonator type wavelength tunable light source according to the embodiment of the present invention has been described, but the present invention is not limited to the above embodiment, and can be freely changed within the scope of the present invention. For example, in the above-described embodiment, the Littman type external resonator type tunable light source has been described as an example. However, the present invention can also be applied to a Littrow type external resonator type tunable light source. FIG. 4 is a plan view showing the configuration of an external resonator type wavelength tunable light source according to another embodiment of the present invention.

  As shown in FIG. 4, an external resonator type wavelength tunable light source 20 according to another embodiment of the present invention includes a Littrow partial resonator type including a laser diode 21, a collimating lens 22, an adjustment lens 23, and a diffraction grating 24. It is a wavelength variable light source. The laser diode 21, the collimating lens 22, and the adjustment lens 23 shown in FIG. 4 are the same as the laser diode 11, the collimating lens 12, and the adjustment lens 13 shown in FIG. An antireflective film 25 is formed on one end face of the laser diode 21. A diffraction grating 24 provided in the external resonator type wavelength tunable light source 20 shown in FIG. 4 has a planar diffraction surface 24 a in which a grating is formed in a direction perpendicular to the paper surface, and is made parallel by a collimating lens 22. The laser light that has passed through the adjustment lens 23 is diffracted at an angle corresponding to the wavelength. The diffraction grating 24 can move in a plane parallel to the paper surface and can rotate in the same plane.

  In the above configuration, the laser light emitted from the laser diode 21 is converted into parallel light by the collimator lens 22, then enters the diffraction grating 24 through the adjustment lens 23, and is diffracted at an angle corresponding to the wavelength. Of the laser light diffracted by the diffraction grating 24, the laser light traveling in the reverse direction on the original optical path is condensed by the collimator lens 22 via the adjustment lens 23 and enters the laser diode 21. A part of the laser light incident on the laser diode 21 is reflected by the end face 21a of the laser diode 21, travels in the reverse direction inside the laser diode 21 and is emitted again to the collimating lens 22 side, and the rest is emitted from the end face 21a to the laser diode 21. It is injected outside.

  The external resonator type wavelength tunable light source 20 shown in FIG. 4 also diffracts parallel light from the collimator lens 22 by rotating the adjustment lens 23 or the like, similarly to the external resonator type wavelength tunable light source 10 shown in FIG. The incident angle with respect to the grating 24 can be varied, and the wavelength can be varied with high accuracy. Of course, when the diffraction grating 24 is moved in the direction indicated by the symbol D5 in FIG. 4 and rotated as appropriate, the wavelength of the laser beam can be varied continuously to the long wavelength side, and conversely the symbol D6. When the diffraction grating 24 is moved in the direction indicated by and rotated as appropriate, the wavelength of the laser light can be greatly varied continuously toward the short wavelength side. Further, by moving (finely moving) in the direction along the optical path of the parallel light, the focal position on the laser diode 21 side when the collimating lens 22 and the adjusting lens 23 are viewed as one lens can be finely adjusted.

  In the above description, the case where the external resonator type wavelength tunable light sources 10 and 20 are provided with the diffraction gratings 14 and 24 has been described as an example. However, it is not always necessary to provide the diffraction grating. What is necessary is just to provide the wavelength selection element which selects a specific wavelength. FIG. 5 is a diagram illustrating an example of the wavelength selection element. In FIG. 5, the dielectric multilayer film 30 is illustrated as a wavelength selection element. The dielectric multilayer film 30 is formed by alternately laminating a dielectric film having a refractive index of n1 and a dielectric film having a refractive index of n2, for example, and reflects light having a wavelength corresponding to the incident angle of light. Is. Therefore, if the incident angle of the laser light with respect to the dielectric multilayer film 30 changes, the wavelength of the reflected light also changes. For example, it can be provided instead of the diffraction grating 14 shown in FIG.

  In the above-described embodiment, the case where the adjustment lenses 12 and 22 are planoconvex lenses has been described as an example. However, the adjustment lenses 12 and 22 may be concave lenses. By the way, the adjustment lenses 12 and 22 described in the above embodiment can change the incident angle of the parallel light converted by the collimator lens 12 with respect to the diffraction grating 14. Need not be. For example, a refractive element such as a prism can be provided instead of the adjustment lenses 12 and 22, and an optical element such as a deflecting element other than the refractive element can be further provided.

It is a top view which shows the structure of the external resonator type | mold wavelength variable light source by one Embodiment of this invention. It is a figure for demonstrating rotation and rocking | fluctuation of the adjustment lens. It is a graph which shows an example of the relationship between the rotation angle of the adjustment lens 13, and the variation | change_quantity of a wavelength and resonator length. It is a top view which shows the structure of the external resonator type | mold wavelength variable light source by other embodiment of this invention. It is a figure which shows an example of a wavelength selection element. It is a top view which shows an example of the conventional external resonator type | mold wavelength variable light source. It is a figure which shows the laser diode 101 with which the conventional external resonator type | mold wavelength variable light source 100 is equipped, the diffraction grating 103, and the plane mirror 104 positional relationship.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 External resonator type wavelength variable light source 11 Laser diode 12 Collimating lens 13 Adjustment lens 14 Diffraction grating 15 Plane mirror 16 Non-reflective film 20 External resonator type wavelength variable light source 21 Laser diode 22 Collimating lens 23 Adjustment lens 24 Diffraction grating 25 Nonreflective film 30 Dielectric multilayer film

Claims (8)

A light source having an antireflective film formed on one end face, a lens disposed on the end face side of the light source on which the antireflective film is formed, and a wavelength selection element that selects a predetermined wavelength from light passing through the lens In an external resonator type tunable light source comprising:
An external resonator type wavelength tunable light source, comprising: an optical element that is disposed on an optical path between the lens and the wavelength selection element, and that varies an incident angle of the light passing through the lens with respect to the wavelength selection element. .   2. The external resonator type wavelength tunable light source according to claim 1, wherein the optical element is capable of at least one of rotation and swinging.   3. The external resonator type wavelength tunable light source according to claim 1, wherein the optical element is movable in a direction along an optical path between the lens and the wavelength selection element.   The external resonator type wavelength tunable light source according to any one of claims 1 to 3, wherein the optical element is a refractive element.   5. The external resonator type wavelength tunable light source according to claim 4, wherein the refractive element is one of a lens and a prism.   The said wavelength selection element is a diffraction grating which diffracts the light which passed through the lens arrange | positioned at the end surface side of the said light source by the angle according to the wavelength. The external resonator type wavelength tunable light source according to the item.   The said wavelength selection element is a dielectric multilayer film which reflects the light of the wavelength according to the incident angle of the light through the lens arrange | positioned at the end surface side of the said light source. The external resonator type wavelength tunable light source according to any one of the above.   7. The external resonator type wavelength tunable light source according to claim 6, further comprising a movable reflecting mirror that reflects a part of the light diffracted by the diffraction grating toward the diffraction grating.

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