JP2008227407A - External-resonator wavelength variable light source and light source device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an external-resonator wavelength variable light source capable of eliminating various conventionally necessary measures in execution, with a small size and having high wavelength stability. <P>SOLUTION: The external-resonator wavelength variable light source 1 includes a semiconductor laser 11, a collimate lens 12, a reflection mirror 13, a diffractive grating 14, and a planar mirror 15, with a resonator formed by an end face 11b of the semiconductor laser 11 and a reflection surface 15a of the planar mirror 15. A laser beam from the semiconductor laser 11 is reflected by the reflection mirror 13 to be incident to the diffractive grating 14 at a prescribed incident angle. The semiconductor laser 11 is positioned, with an end face 11a, on which a reflection preventive film 16 is applied, arranged toward the reflection mirror 13, so that an optical path length from the end face 11b up to the planar mirror 15 via the reflection mirror 13 and the diffractive grating 14 corresponds to the optical path length of the resonator when the semiconductor laser 11, the diffractive grating 14, and the planar mirror 15 are set in Littman arrangement. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an external resonator type wavelength tunable light source and a light source device 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 that oscillates in a single mode and has a narrow spectral line width, good wavelength stability, and variable wavelength is required. An external resonator type tunable light source has been developed as one of tunable light sources. FIG. 12 is a plan view showing an example of a conventional external resonator type wavelength tunable light source. As shown in FIG. 12, the external resonator type wavelength tunable light source 100 includes a semiconductor laser 101, a collimating lens 102, a diffraction grating 103, and a plane mirror 104. The external resonator type tunable light source 100 shown in FIG. 12 is an external resonator type tunable light source having a Littman arrangement.

  The semiconductor laser 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 semiconductor laser 101 is provided with an antireflection film (AR coat) 105 on one end face forming a resonator. The semiconductor laser 101 is arranged with the end surface provided with the antireflection film 105 facing the collimating lens 102 side. The size of the semiconductor laser 101 is about 0.2 to 1 mm.

  The collimating lens 102 is positioned with respect to the semiconductor laser 101 so that one focal point is disposed at the laser light emission position on the end surface of the semiconductor laser 101 where the antireflection film 105 is applied. The collimator lens 102 collimates the laser light emitted from the semiconductor laser 101 and condenses the laser light diffracted by the diffraction grating 103 at the laser light emission position of the semiconductor laser 101. The semiconductor laser 101 and the collimating lens 12 are accommodated in the case 110.

  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. In addition, the length of the diffraction grating 103 in the direction along the paper surface of the diffraction surface 103a is about several tens of millimeters. The plane mirror 104 reflects the laser light diffracted by the diffraction grating 103 and can rotate (swing) in the rotation directions D101 and D102 along the paper surface.

  Here, as shown in FIG. 12, the optical position of the end face 101a of the semiconductor laser 101 where the antireflection film 105 is not applied to the diffraction grating 103 is P101, the incident position of the laser beam to the diffraction grating 103 is P102, and the plane mirror 104 The incident position of the laser beam with respect to is P103. The length (optical path length) from the optical position P101 of the end face 101a of the semiconductor laser 101 to the incident position P103 with respect to the flat mirror 104 through the incident position P102 with respect to the diffraction grating 103 is about 40 to 50 mm.

  In the external resonator type wavelength tunable light source 100 shown in FIG. 12, in order to change the wavelength while keeping the wave number constant, the optical position P101 of the end face 101a of the semiconductor laser 101, the incident position P102 with respect to the diffraction grating 103, and the plane It is necessary to rotate the plane mirror 104 so that the incident position P103 moves along the circumference of a circle R100 passing through the incident position P103 with respect to the mirror 104. At this time, as shown in FIG. 12, the center of rotation of the plane mirror 104 is a line extending perpendicularly to the optical axis starting from the optical position P101 of the end surface 101a, and a plane including the diffraction surface 103a of the diffraction grating 103. Need to be arranged at a point C101 where.

  In the above configuration, the laser light emitted from the semiconductor laser 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 collimator lens 102 and enters the semiconductor laser 101. Part of the laser light incident on the semiconductor laser 101 is reflected by the end face 101a of the semiconductor laser 101, travels in the reverse direction inside the semiconductor laser 101, and is emitted again toward the collimator lens 102, and the rest is emitted from the end face 101a to the semiconductor laser. 101 is injected outside.

  As described above, the conventional external resonator type wavelength tunable light source 100 shown in FIG. 12 has a resonator formed by the end face 101 a of the semiconductor laser 101 and the plane mirror 104 provided outside the semiconductor laser 101. Here, when the plane mirror 104 constituting the resonator is rotated in the rotation direction D101 around the point C101 in the figure, the wavelength of the laser light can be continuously varied to the long wavelength side, and conversely, the point C101 is centered. As a result, the wavelength of the laser beam can be continuously varied to the short wavelength side. As a result, laser light having a narrow spectral line width and good wavelength stability can be obtained from the external resonator type wavelength tunable light source 100, and the wavelength can be continuously varied without causing mode hops.

For details of the conventional external resonator type wavelength tunable light source, see, for example, Patent Documents 1 to 4 below.
JP 2003-289173 A JP 2000-164980 A Japanese Patent Application Laid-Open No. 2000-164979 Japanese Patent Laid-Open No. 11-126943

  By the way, in the conventional external resonator type wavelength tunable light source 100, in order to rotate the plane mirror 104 in the rotation directions D101 and D102 along the paper surface around the point C101, a predetermined rotation mechanism is required. For example, a rotation mechanism is provided that includes a rotation motor that passes through the point C101 and that has a rotation axis that is perpendicular to the paper surface, and a rotation arm that is attached to the rotation shaft of the rotation motor. The above rotation can be realized by attaching 104.

  However, as shown in FIG. 12, in the conventional external resonator type wavelength tunable light source 100, the optical path of the laser light is positioned between the rotation center (point C 101) of the plane mirror 104 and the plane mirror 104. For this reason, it is necessary to arrange the rotating arm so as to cross the optical path of the laser beam. The optical path of the laser beam is blocked by the rotating arm, or the rotating arm and the case 110 physically interfere with each other, and the wavelength on the long wavelength side. Inconveniences such as restriction of variable bandwidth occur. In order to eliminate such a problem, for example, the rotation surface of the rotation arm is shifted with respect to the plane including the circle R100 that prevents the optical path of the laser beam from being blocked or interferes with the case 110 by making the rotation arm hollow. Therefore, there is a problem that it is necessary to take practical measures such as preventing the interference by arranging them, or devising the shape of the flat mirror 104 to prevent the restriction of the wavelength variable band.

  Further, in the external resonator type wavelength tunable light source 100 shown in FIG. 12, the semiconductor laser 101 and the collimating lens 102 are housed in the case 110, but in order to reduce the influence of the temperature change and to stabilize it. In addition to the semiconductor laser 101 and the collimating lens 102, it is desirable that the diffraction grating 103 is also housed in the case 110 to keep the temperature of the entire case 110 constant. However, in order to optimize wavelength selectivity and diffraction efficiency, the diffraction grating 103 needs to be disposed so as to be inclined so that the incident angle of the laser light from the semiconductor laser 101 is about 80 °. In order to accommodate 103, the shape of the case 110 is inevitably complicated. Furthermore, as described above, since the distance between the semiconductor laser 101 and the diffraction grating 103 cannot be reduced in order to avoid physical contact between the rotating arm and the case 110, it is difficult to reduce the size of the case 110. Such a complicated or large shape of the case 110 has a problem that it hinders cost reduction and stabilization.

  Further, in the external resonator type wavelength tunable light source 100 of the Littman arrangement, in order to change the wavelength while keeping the wave number constant, as described above, the plane mirror 104 is set in the rotation directions D101 and D102 along the paper surface with the point C101 as the center. Basically it is rotated. In addition to the point C101, there is a point on the straight line (hereinafter referred to as a dead zone line) passing through the point C101 where the wave number shift is not so large. Therefore, if the center of rotation of the plane mirror 104 is moved along the dead zone line, the center of rotation of the plane mirror 104 can be precisely aligned with the point C101. However, since the dead zone line is usually not parallel to the optical axis of the semiconductor laser 101, there is a problem that adjustment takes time.

  The present invention has been made in view of the above circumstances, and does not require various implementation measures that have been required in the past, and is a compact external resonator type wavelength tunable light source having high wavelength stability, and the external resonance. An object of the present invention is to provide a light source device including a model wavelength variable light source.

In order to solve the above problems, an external resonator type wavelength tunable light source of the present invention includes a light source (11) having an antireflection film (16) applied to a first end face (11a) of a pair of end faces, A diffraction grating (14) into which light from a light source is incident with a predetermined incident angle, and a rotatable reflecting mirror (15, 15) that reflects a part of the light diffracted by the diffraction grating toward the diffraction grating. 40), and an external resonator type wavelength tunable light source (1-5, 1'-4 ') in which a second end face (11b) different from the first end face of the light source and the reflecting mirror form a resonator. The light source includes a reflection element (13, 31) that reflects light from the light source and enters the diffraction grating with the predetermined incident angle, and the light source has a first end face on which the antireflection film is applied. Is disposed toward the reflective element, and the anti-reflection The optical path length reaching the reflecting mirror through the element and the diffraction grating is positioned so as to be the optical path length of the resonator when the light source, the diffraction grating, and the reflecting mirror are in a Littman arrangement. It is said.
According to the present invention, the light emitted from the light source is reflected by the reflecting element, is incident on the diffraction grating with a predetermined incident angle, and is diffracted at an angle corresponding to the wavelength. Of the diffracted light diffracted by the diffraction grating, the light diffracted in the direction in which the reflecting mirror is disposed is reflected by the reflecting mirror forming a part of the resonator, and is incident again on the diffraction grating and is diffracted. Of the light diffracted by the diffraction grating, the light diffracted in the direction in which the reflective element is disposed is reflected by the reflective element toward the light source. Of the light that has been diffracted twice by the diffraction grating in this way, the light of the wavelength component that is perpendicularly incident on the reflecting mirror enters the light source from the first end face of the light source and is reflected by the second end face. As described above, laser light is generated as the light from the light source travels along the optical path set to the optical path length of the resonator when the light source, the diffraction grating, and the reflecting mirror are in the Littman arrangement, and laser light is obtained.
In the external resonator type wavelength tunable light source of the present invention, the optical axis of the second end face with respect to the diffraction grating when the rotation center of the reflection mirror is the light source, the diffraction grating, and the reflection mirror is a Littman arrangement. It is characterized in that it is set at the intersection of a line extending perpendicularly to the optical axis starting from the target position (P1, P1 ′) and a plane including the diffraction surface (14a) of the diffraction grating.
In the external resonator type wavelength tunable light source of the present invention, an optical path from the light source to the reflection element passes between the rotation center (C1, C1 ′) of the reflection mirror and the diffraction grating. It is characterized by being positioned as follows.
Moreover, the external resonator type wavelength tunable light source of the present invention is characterized in that an optical path from the light source to the reflective element is parallel to a normal line (PL) of a diffraction surface of the diffraction grating.
In addition, the external resonator type wavelength tunable light source of the present invention includes a case (20-22) for housing the light source, and at least one of the reflective element and the diffraction grating is fixedly held by the case. It is said.
In the external resonator type wavelength tunable light source of the present invention, the reflecting element is an element that reflects part of incident light and transmits the remaining light.
Moreover, the external resonator type wavelength tunable light source of the present invention is characterized in that out of the light incident on the reflective element from the diffraction grating, the light transmitted through the reflective element is output as the output light.
Moreover, the external resonator type wavelength tunable light source of the present invention includes a reflecting member (32) that reflects light transmitted through the reflecting element in a direction along an optical path from the reflecting element to the light source to generate the output light. It is characterized by providing.
Furthermore, in the external resonator type wavelength tunable light source of the present invention, the reflecting mirror has two reflecting surfaces (40a, 40b) orthogonal to each other, and the surface orthogonal to each of the reflecting surfaces is diffracted by the diffraction grating. It is characterized by being a retro-reflector arranged so as to intersect the direction.
A light source device according to the present invention includes a light source device (50) that emits laser light having a variable wavelength, the external resonator type wavelength variable light source according to any one of the above, and the external resonator type wavelength variable light source. A wavelength control unit (55) that controls the amount of rotation of the reflecting mirror to vary the wavelength of the laser light is provided.

  According to the present invention, the light source is arranged at a position different from the Littman arrangement, the reflection element that reflects the light from the light source and enters the diffraction grating with a predetermined incident angle, and the reflection element from the second end face of the light source is provided. Since the light source is positioned so that the optical path length to the reflecting mirror through the diffraction grating becomes the optical path length of the resonator when the light source, the diffraction grating, and the reflecting mirror are in the Littman arrangement, this is conventionally necessary. In addition, it is possible to eliminate the need for various implementation measures, to realize a small and high wavelength stability, and to change the wavelength stably without causing a mode hop. is there.

  Hereinafter, an external resonator type tunable light source and a light source device according to embodiments of the present invention will be described in detail with reference to the drawings.

[First Embodiment]
FIG. 1 is a plan view showing a configuration of an external resonator type wavelength tunable light source according to a first embodiment of the present invention. As shown in FIG. 1, the external resonator type wavelength tunable light source 1 according to the present embodiment includes a semiconductor laser 11 (light source), a collimator lens 12, a reflection mirror 13 (reflection element), a diffraction grating 14, and a plane mirror 15 (reflection mirror). ). A resonator is formed by the end face 11 b (second end face) of the semiconductor laser 11 and the reflecting face 15 a of the flat mirror 15.

  The semiconductor laser 11 includes, for example, a lower clad layer, an active layer, and an upper clad layer sequentially formed on a semiconductor substrate, and a pair of parallel end surfaces 11a (first end surfaces) and second end surfaces 11b obtained by cleaving the semiconductor substrate. This is a Fabry-Perot type semiconductor laser having a cavity as a resonator. An antireflection film (AR coating) 16 is provided on the end surface 11 a of the semiconductor laser 11. The semiconductor laser 11 is positioned so that the end surface 11a provided with the antireflection film 16 faces the reflection mirror 13, and a predetermined optical path length condition is satisfied. Details of the optical path length condition will be described later.

  The collimator lens 12 is disposed on the optical path between the semiconductor laser 11 and the reflection mirror 13, and one focal point is disposed at the laser beam emission position on the end surface 11 a on which the antireflection film 16 of the semiconductor laser 11 is applied. It is positioned with respect to the semiconductor laser 11. The collimating lens 12 converts the laser light emitted from the semiconductor laser 11 into parallel light, and the laser light diffracted by the diffraction grating 14 and passed through the reflection mirror 13 is emitted from the end face 11 a of the semiconductor laser 11. Condensed to

  The reflection mirror 13 reflects the laser light emitted from the semiconductor laser 11 and passing through the collimating lens 12 toward the diffraction grating 14 so that a predetermined incident angle condition is satisfied. Specifically, the laser light from the semiconductor laser 11 is reflected toward the diffraction grating 14 so that the laser light from the semiconductor laser 11 enters the diffraction grating 14 with a predetermined incident angle (for example, an incident angle of about 80 °). To do. The reflection mirror 13 reflects the laser light, which is diffracted by the laser light reflected by the flat mirror 15, incident on the diffraction grating 14 toward the collimating lens 12 and the semiconductor laser 11. In the example shown in FIG. 1, the reflection mirror 13 reflects the laser light from the semiconductor laser 11 at a substantially right angle so that the laser light from the semiconductor laser 11 is incident on the diffraction grating 14 at a predetermined angle. .

  The diffraction grating 14 has a planar diffraction surface 14 a in which gratings extending in a direction orthogonal to the paper surface are arranged, and is made parallel by the collimating lens 12, the laser light via the reflection mirror 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, and can be rotated (swinged) in the rotation directions D1 and D2 along the paper surface with the point C1 in the figure as the center of rotation.

  Although not shown in FIG. 1, the external resonator type wavelength tunable light source 1 of the present embodiment is for rotating the plane mirror 15 around the point C1 in the rotation directions D1 and D2 along the paper surface. A predetermined rotation mechanism is provided. The rotation mechanism includes, for example, a rotation motor having a rotation axis that is an axis that passes through the point C1 and is perpendicular to the paper surface, and a rotation arm attached to the rotation shaft of the rotation motor. The plane mirror 15 is attached to the above, thereby realizing the above rotation.

  Next, the arrangement of the semiconductor laser 11, the collimating lens 12, the reflecting mirror 13, the diffraction grating 14, and the plane mirror 15 will be described in detail. The external resonator type wavelength tunable light source 1 of this embodiment is based on the concept of Littman arrangement, and has problems that arise in the case of Littman arrangement while taking advantage of the Littman arrangement (for example, between the rotating arm and the semiconductor laser 11 described above). Interference). For this reason, first, the case where the semiconductor laser 11, the diffraction grating 14, and the reflection mirror 15 are in the Littman arrangement will be considered. That is, consider a case where the semiconductor laser 11 and the collimating lens 12 are respectively disposed at positions Q1 and Q2 in FIG. 1 and the reflection mirror 13 is omitted.

  Here, as shown in FIG. 1, the optical position with respect to the diffraction grating 14 of the end surface of the semiconductor laser (hereinafter referred to as the semiconductor laser 11 ') which is supposed to be arranged at the position Q1 is not applied to the diffraction grating 14. The incident position of the laser beam on the grating 14 is P2, and the incident position of the laser beam on the flat mirror 15 is P3. When the semiconductor laser 11 ', the diffraction grating 14, and the plane mirror 15 are in a Littman arrangement, the optical position P1, the incident position P2, and the incident position P3 are arranged on the circumference of a circle R1 indicated by a broken line. Is done. The point C1, which is the center of rotation of the plane mirror 15, is a point where the line extending perpendicularly to the optical axis starting from the optical position P1 and the plane including the diffraction grating 14 and the diffraction surface 14a intersect. Become.

Now, the incident angle of the laser light emitted from the semiconductor laser 11 ′ to the diffraction grating 14 is α, the emission angle is β, the wavelength of the laser light is λ, the grating constant of the diffraction grating 14 is d, and the diameter of the circle R1 is D. And Further, in the case of the Littman arrangement, the wave number of the laser light in the external resonator type wavelength tunable light source is k, and the optical path length between the semiconductor laser 11 'and the diffraction grating 14 (the optical position P1 and the incident position). Let L _{i be} the distance between P2 and L _o be the optical path length between the diffraction grating 14 and the plane mirror 15 (the distance between the incident position P2 and the incident position P3).

When the semiconductor laser 11 ′, the diffraction grating 14, and the plane mirror 15 are in a Littman arrangement, the following equation (1) is established.

  Next, the diffraction grating 14 and the plane mirror 15 included in the external resonator type wavelength tunable light source 1 of the present embodiment are arranged in the same manner as in the Littman arrangement. The center of rotation of the plane mirror 15 coincides with the point C1 set in the case of the Littman arrangement. The reflection mirror 13 is disposed on the optical path between the Littman-arranged semiconductor laser 11 ′ and the diffraction grating 14, and the semiconductor laser 11 is disposed with the end surface 11 a provided with the antireflection film 16 facing the reflection mirror 13. The The angle of the reflection mirror 13 with respect to the laser beam from the semiconductor laser 11 is set so that the incident angle of the laser beam with respect to the diffraction grating 14 becomes the above-described incident angle α.

The semiconductor laser 11 has an optical path length (L _i + L _o :) when the optical path length from the end face 11b to the plane mirror 15 via the collimating lens 12, the reflecting mirror 13, and the diffraction grating 14 is a Littman arrangement. Positioning is performed so that the optical path length condition of (see (1) above) is satisfied. As described above, the diffraction grating 14 and the plane mirror 15 are arranged in the same manner as in the Littman arrangement. Therefore, the semiconductor laser 11 can be referred to the collimator from the end face 11b lens 12, the optical path length of the optical path to the reflecting mirror 13 and the diffraction grating 14, it is positioned so as to be equal to the above-mentioned optical path length L _i.

  Here, as long as the above-described optical path length condition and incident angle condition with respect to the diffraction grating 14 are satisfied, the positions where the semiconductor laser 11 and the collimating lens 12 are positioned are not limited. However, in order to avoid interference with an arm (not shown) for rotating the plane mirror 15, the optical path from the semiconductor laser 11 to the reflection mirror 13 is between the point C1 and the diffraction grating 14, as shown in FIG. It is desirable to position the semiconductor laser 11 and the collimating lens 12 so as to pass.

  Further, the semiconductor laser 11 and the collimator lens 12 may be positioned at a position deviated from the plane including the circle R1 in FIG. 1 as long as the above-described optical path length condition and the incident angle condition with respect to the diffraction grating 14 are satisfied. Is possible. When such positioning is performed, the laser light emitted from the semiconductor laser 11 is incident on the plane including the circle R1 from an oblique direction or a vertical direction. In order to be satisfied, it is necessary to appropriately adjust the reflecting mirror 13 according to the incident direction.

  In the above configuration, the laser light emitted from the semiconductor laser 11 is converted into parallel light by the collimator lens 12, and then travels on the optical path passing between the point C 1 and the diffraction grating 14 and enters the reflection mirror 14. Reflected toward the diffraction surface 14 a of the diffraction grating 14. The laser beam reflected by the reflection mirror 13 is incident on the diffraction surface 14a of the diffraction grating 14 with a predetermined incident angle and is diffracted at an angle corresponding to the wavelength.

  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. This laser light is again diffracted by the diffraction grating 14 and travels in the reverse direction along the original optical path, and is reflected by the reflection mirror 13 toward the collimating lens 12 and the semiconductor laser 11 and passes between the point C 1 and the diffraction grating 14. The light travels in the opposite direction on the road and enters the collimating lens 12, is condensed by the collimating lens 12, and enters the semiconductor laser 11. Part of the laser light incident on the semiconductor laser 11 is reflected by the end surface 11b of the semiconductor laser 11, travels in the reverse direction inside the semiconductor laser 11, and is emitted again to the collimator lens 12, and the rest is transmitted from the end surface 11b to the semiconductor laser. 11 is injected outside.

  Here, when the reflecting mirror 15 is rotated around the point C1 in the direction indicated by the symbol D1 in FIG. 1, the wavelength of the laser beam can be continuously varied to the long wavelength side without changing the wave number. . On the other hand, when the reflecting mirror 15 is rotated around the point C1 in the direction indicated by the symbol D2 in FIG. 1, the wavelength of the laser beam can be continuously varied to the short wavelength side without changing the wave number. .

  As described above, according to the external resonator type wavelength tunable light source 1 of the present embodiment, a laser beam having a narrow spectral line width and good wavelength stability can be obtained, and the wavelength can be continuously varied without causing a mode hop. it can. Further, since the semiconductor laser 11 and the collimating lens 12 are positioned so that the optical path from the semiconductor laser 11 to the reflection mirror 13 passes between the point C1 and the diffraction grating 14, for example, for rotating the plane mirror 15 Various implementation measures that have been conventionally required, such as measures for preventing interference between the rotary arm and the semiconductor laser 11, etc., become unnecessary.

  FIG. 2 is a diagram showing a modification of the external resonator type wavelength tunable light source 1 according to the first embodiment of the present invention. As shown in FIG. 2, the external resonator type wavelength tunable light source 1 ′ includes a semiconductor laser 11, a collimating lens 12, a reflection mirror 13, a diffraction grating 14, and a plane mirror 15. The external resonator type wavelength light source 1 ′ shown in FIG. The configuration is the same as that of the wavelength tunable light source 1. However, these arrangements are different, and the optical path length from the end face 11b of the semiconductor laser 11 to the plane mirror 15 via the collimating lens 12, the reflecting mirror 13, and the diffraction grating 14 is set to a shorter optical path length.

  That is, the semiconductor laser 11 and the collimating lens 12 are arranged at positions Q1 'and Q2' closer to the diffraction grating 14 than the positions Q1 and Q2 shown in FIG. Here, the optical position with respect to the diffraction grating 14 of the end surface of the semiconductor laser (hereinafter referred to as semiconductor laser 11 ″) which is supposed to be arranged at the position Q1 ′ is not defined as P1 ′. In the case where the diffraction grating 14 and the plane mirror 15 are in the Littman arrangement, the optical position P1 ′, the incident position P2, and the incident position P3 are indicated by broken lines smaller than the circle R1 shown in FIG. It arrange | positions on the periphery of circle | round | yen R1 ', respectively. The point C1 ′, which is the center of rotation of the plane mirror 15, intersects the line extending perpendicularly to the optical axis starting from the optical position P1 ′ and the plane including the diffraction grating 14 and the diffraction surface 14a. It becomes a point.

  In the external resonator type wavelength tunable light source 1 ′ shown in FIG. 1, the semiconductor laser 11 has an optical path length from the end face 11 b to the plane mirror 15 via the collimator lens 12, the reflection mirror 13, and the diffraction grating 14. Is positioned so as to be equal to the optical path length from the semiconductor laser 11 ″ to the plane mirror 15 through the diffraction grating 14. The diffraction grating 14 and the plane mirror 15 are shown in the case of the Littman arrangement and FIG. The semiconductor laser 11 has the same optical path length from the end face 11b to the collimating lens 12, the reflecting mirror 13, and the diffraction grating 14 in the optical position described above. It can be said that it is positioned to be equal to the distance between P1 ′ and the incident position P2 of the diffraction grating 14.

  According to the external resonator type tunable light source 1 ′ of this modification, similarly to the external resonator type tunable light source 1 according to the first embodiment, laser light having a narrow spectral line width and good wavelength stability can be obtained. In addition, the wavelength can be continuously varied stably without causing a mode hop. In addition, the external resonator type wavelength tunable light source 1 ′ of this modification can be downsized.

[Second Embodiment]
FIG. 3 is a plan view showing a configuration of an external resonator type wavelength tunable light source according to the second embodiment of the present invention. In FIG. 3, the same components as those shown in FIG. 1 are denoted by the same reference numerals. As shown in FIG. 3, the external resonator type wavelength tunable light source 2 of the present embodiment includes the semiconductor laser 11, the collimating lens 12, the reflection mirror 13, the diffraction grating 14, and the plane mirror 15, and the external resonance shown in FIG. 1. This is the same as the model wavelength variable light source 1. Further, the optical path length from the end face 11b of the semiconductor laser 11 to the incident position P2 of the diffraction grating 14 via the collimating lens 12 and the reflection mirror 13 is the optical position P1 ′ and the incident position P2 of the diffraction grating 14 in FIG. 1 is common to the external resonator type wavelength tunable light source 1 shown in FIG. 1 in that the optical path length condition is satisfied.

  However, the semiconductor laser 11 and the collimating lens 12 are positioned so that the optical path from the semiconductor laser 11 to the reflection mirror 13 is parallel to the normal line PL of the diffraction surface 14a of the diffraction grating 14, and the incident angle The difference is that the angle of the reflection mirror 13 with respect to the optical path is adjusted in order to satisfy the conditions. By making the optical path from the semiconductor laser 11 to the reflecting mirror 13 parallel to the normal line PL of the diffraction surface 14a of the diffraction grating 14, adjustments such as optical axis alignment can be easily performed.

  FIG. 4 is a view showing a modification of the external resonator type wavelength tunable light source 2 according to the second embodiment of the present invention. The external resonator type wavelength tunable light source 2 ′ shown in FIG. 4 extends from the semiconductor laser 11 to the reflection mirror 13 in the modification 1 ′ of the external resonator type wavelength tunable light source 1 according to the second embodiment shown in FIG. The semiconductor laser 11 and the collimating lens 12 are positioned so that the optical path is parallel to the normal line PL of the diffraction surface 14a of the diffraction grating 14, and the same components as those shown in FIG. It is.

  The external resonator type wavelength tunable light source 2 ′ shown in FIG. 4 includes a semiconductor laser 11, a collimating lens 12, and a reflection mirror 13, and includes a case 20 that is kept constant by a temperature control device (not shown). The case 20 houses a rectangular parallelepiped main body 20 a that houses the semiconductor laser 11 and the collimating lens 12, and a reflection mirror 13. The case 20 protrudes from the main body 20 a in a direction from the semiconductor laser 11 toward the reflection mirror 13. And a rectangular parallelepiped protrusion 20b. The main body 20a and the protrusion 20b communicate with each other, and an opening (not shown) through which laser light is input and output is formed on the surface of the protrusion 20b facing the diffraction grating 14.

  In the case 20, the surface on which the protruding portion 20 b is provided and the surface opposite to the surface are perpendicular to the optical path between the semiconductor laser 11 and the reflection mirror 13, and the other surfaces are reflected from the semiconductor laser 11. The semiconductor laser 11, the collimating lens 12, and the reflection mirror 13 are accommodated so as to be parallel to the optical path between the mirror 13. In addition, the diffraction grating 14 is fixedly held on the surface of the main body 20a where the protrusion 20b is provided.

  With the above configuration, the semiconductor laser 11, the collimating lens 12, and the reflection mirror 13 can be accommodated inside the case 20 and the diffraction grating 14 can be fixedly held on the case 20. Can be. In addition, such a configuration makes it easier to keep the case 20 at a constant temperature, thereby further improving the wavelength stability. Further, since the optical path from the semiconductor laser 11 to the reflection mirror 13 and the normal line PL of the diffraction surface 14a of the diffraction grating 14 are parallel, adjustment can be easily performed.

[Third Embodiment]
FIG. 5 is a plan view showing a configuration of an external resonator type wavelength tunable light source according to the third embodiment of the present invention. In FIG. 5, the same components as those shown in FIG. As shown in FIG. 5, the external resonator type wavelength tunable light source 3 of this embodiment also includes a semiconductor laser 11, a collimating lens 12, a reflection mirror 13, a diffraction grating 14, and a plane mirror 15, and the optical path length condition is as follows. It is common with the external resonator type wavelength tunable light source 1 shown in FIG.

  However, in the present embodiment, the optical path from the semiconductor laser 11 to the reflection mirror 13 is substantially the same with respect to the dead band SL where there is a point where the deviation of the wave number does not increase so much even if the rotation center of the plane mirror 15 is deviated from the point C1. The semiconductor laser 11 and the collimating lens 12 are positioned so as to be vertical, and the angle of the reflection mirror 13 with respect to the optical path is adjusted in order to satisfy the incident angle condition. By making the optical path from the semiconductor laser 11 to the reflection mirror 13 substantially perpendicular to the dead zone line SL, adjustments such as optical axis alignment can be easily performed.

Next, the dead zone line SL will be described. FIG. 6 is a diagram for explaining the dead zone line SL. Here, for simplicity of explanation, a case where the semiconductor laser 11, the diffraction grating 14, and the plane mirror 15 are in a Littman arrangement is considered. As shown in FIG. 6A, the optical position P1 of the end face of the semiconductor laser that is not provided with the antireflection film, the optical position P1 with respect to the diffraction grating 14, the incident position P2 of the laser light with respect to the diffraction grating 14, and the laser light with respect to the plane mirror 15 incident position P3 (position P11, P12) is to be arranged on the circumference of the diameter _{D 1.}

When the rotation center of the plane mirror 15 coincides with the point C1, the optical path length (distance) between the optical position P1 and the incident position P2 is represented by D ₁ · sin α ₁ . Further, when the plane mirror 15 is disposed at the position P11 in the drawing in order to set the wavelength of the laser beam to λ _S , the optical path length between the incident position P2 of the diffraction grating 14 and the position P11 of the plane mirror 15 is shown. (Distance) is represented by D ₁ · sin β _S1 . Further, in order to set the wavelength of the laser beam to λ _L , when the plane mirror 15 is arranged at the position P12 in the figure, the optical path length between the incident position P2 of the diffraction grating 14 and the position P12 of the plane mirror 15 (Distance) is represented by D ₁ · sin β _L1 . Since the wave number in the external resonator type wavelength tunable light source does not change regardless of whether the plane mirror 15 is disposed at the positions P11 and P12, the following equation (2) is established.

Next, consider the case where the center of rotation of the plane mirror 15 is set at a point C2 that is deviated from the point C1. As shown in FIG. 6 (b), and the straight line connecting the points C1 and incident position P2 of the diffraction grating 14, the angle of a straight line connecting the point C2 and the incident position P2 of the diffraction grating 14 and theta _1. Further, the incident position of the laser beam P3 (position P13, P14) are disposed on the circumference of diameter _{D 2} with respect to the incident position of the laser beam P2 and a plane mirror 15, with respect to the diffraction grating 14. Now, assuming that the number of grooves per unit length of the diffraction grating 14 is N and the order (diffraction order) is m, each angle shown in FIG. 6A and each angle shown in FIG. ) Expression.

When the plane mirror 15 is rotated around the point C2 without changing the relative positional relationship between the semiconductor laser 11 and the diffraction grating 14 and the incident angle of the laser beam on the diffraction grating 14, the external resonator wavelength In order that the wave number does not change in the variable light source, the following expression (4) needs to be satisfied.

The diameter D ₂ of a circle equation (4) is satisfied is represented by (4) deformed by the following equation (5) the formula.

Based on the above equation (5), an angle θ _X formed by a straight line connecting the optical position P1 of the end face of the semiconductor laser and the incident position P2 of the diffraction grating 14 and the dead band SL is expressed by the following equation (6). Is done.

Here, the number N of grooves per unit length of the diffraction grating 14 is N = 1000 / mm, the order is m = 1, the incident angle α ₁ of the laser light with respect to the diffraction grating 14 is α ₁ = 80 °, the wavelength λ _{s is} 1500 nm on the short wavelength side, If the wavelength λ _L on the long wavelength side is 1600 nm, the angle θ _X of the dead zone line SL is approximately 17.6 ° from the above equation (6). The angle θ _X of the dead band SL is determined by the number N of grooves of the diffraction grating 14 and the incident angle α ₁ of the laser light with respect to the diffraction grating 14, but slightly changes depending on the wavelength of the laser light. For this reason, even if it says that the rotation center of the plane mirror 15 is arrange | positioned on the dead zone line SL, it is thought that the variation | change_quantity according to the change of a wavelength becomes large as it deviates from the point C1. Therefore, it is desirable to set the rotation center of the plane mirror 15 as close as possible to the point C1.

  FIG. 7 is a view showing a modification of the external resonator type wavelength tunable light source 3 according to the third embodiment of the present invention. The external resonator type wavelength tunable light source 3 ′ shown in FIG. 7 extends from the semiconductor laser 11 to the reflection mirror 13 in the modification 1 ′ of the external resonator type wavelength tunable light source 1 according to the second embodiment shown in FIG. The semiconductor laser 11 and the collimator lens 12 are positioned so that the optical path is substantially perpendicular to the dead zone line SL, and the semiconductor laser 11 and the collimator are parallel to the normal line PL of the diffraction surface 14a of the diffraction grating 14. The lens 12 is positioned, and the same components as those shown in FIG.

  An external resonator type wavelength tunable light source 3 ′ shown in FIG. 7 includes a semiconductor laser 11, a collimating lens 12, and a reflection mirror 13, and includes a substantially rectangular parallelepiped case 21 that is kept constant by a temperature control device (not shown). . In this case 21, a recess 21a is formed on one side surface where the reflecting mirror 13 is close. A diffraction grating 14 is fixedly held in the recess 21a, and an opening (not shown) through which laser light is input and output is formed on the surface facing the diffraction grating 14.

  The case 21 has a surface facing the surface on which the recess 21a is formed perpendicular to the optical path between the semiconductor laser 11 and the reflection mirror 13, and four surfaces orthogonal to the surface on which the recess 21a is formed are semiconductors. The semiconductor laser 11, the collimating lens 12, and the reflection mirror 13 are accommodated so as to be parallel to the optical path between the laser 11 and the reflection mirror 13. The diffraction grating 14 is fixed to the recess 21a at a predetermined angle with respect to the optical path between the semiconductor laser 11 and the reflection mirror 13 so that the laser beam reflected by the reflection mirror 13 is incident at a predetermined incident angle. Retained.

  With the above configuration, the semiconductor laser 11, the collimating lens 12, and the reflection mirror 13 can be accommodated in the case 21, and the diffraction grating 14 can be fixedly held on the case 21, so that the configuration is small and simple. Can be. Further, such a configuration makes it easy to keep the case 21 at a constant temperature, thereby further improving the wavelength stability. Further, since the optical path from the semiconductor laser 11 to the reflection mirror 13 is set at a substantially right angle to the dead zone line SL, and the side surface of the case 21 is perpendicular or parallel to the dead zone line SL, adjustment is performed very easily in a short time. be able to.

  That is, by making the side surface of the case 21 perpendicular or parallel to the dead zone line SL, adjustment can be performed simply by moving the case 21 in two orthogonal directions d1 and d2 parallel to the side surface of the case 21. In addition, since only the direction d2 requires high accuracy for adjustment, and the direction d1 does not require high accuracy, the cost of the adjustment mechanism can be reduced.

[Fourth Embodiment]
FIG. 8 is a plan view showing a configuration of an external resonator type wavelength tunable light source according to the fourth embodiment of the present invention. In FIG. 8, the same components as those shown in FIG. 3 are denoted by the same reference numerals. As shown in FIG. 8, the external resonator type wavelength tunable light source 4 of the present embodiment is different in that a beam splitter 31 is provided instead of the reflection mirror 13 shown in FIG. Note that the above-described optical path length condition and incident angle condition with respect to the diffraction grating 14 are satisfied, and the optical path from the semiconductor laser 11 to the beam splitter 31 is the normal line PL of the diffraction surface 14 a of the diffraction grating 14. The semiconductor laser 11 and the collimating lens 12 are positioned so as to be parallel to each other, similar to the external resonator type wavelength tunable light source 2 shown in FIG.

  The beam splitter 31 reflects a part of the incident light and transmits the rest, thereby branching the incident light at a predetermined branching ratio. Here, from the viewpoint of preventing a decrease in oscillation efficiency, the beam splitter 31 desirably has a reflectance of about 80 to 90% and a transmittance of about 10 to 20%. If the shape of the beam splitter 31 is a parallel plate shape, multiple reflections may occur inside the beam splitter 30 and noise and mode hops may occur. For this reason, it is desirable that the beam splitter 31 has a wedge shape.

  When laser light emitted from the semiconductor laser 11 enters the beam splitter 31, a part of the laser light is reflected by the beam splitter 31 and the rest passes through the beam splitter 31. The laser beam reflected by the beam splitter 31 enters the diffraction grating 14 at a predetermined incident angle and is diffracted at an angle corresponding to the wavelength. 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, travels in the opposite direction along the original optical path, and enters the beam splitter 31. A part of the laser light is reflected by the beam splitter 31 and reflected toward the collimating lens 12 and the semiconductor laser 11. The On the other hand, the remaining laser light transmitted through the beam splitter 31 is emitted to the outside as output light.

  If the laser light emitted from the end face 11b of the semiconductor laser 11 that is not provided with the antireflection film 16 is used as output light, spontaneous emission light generated by the semiconductor laser 11 is also emitted as output light, and the spectral line width is increased. Concerned. However, since the external resonator type wavelength tunable light source 4 of the present embodiment uses laser light that has passed through the beam splitter 31 (laser light that has been wavelength-selected by being diffracted by the diffraction grating 14) as output light. A narrow laser beam can be obtained. Further, the adjustment can be easily performed as in the external resonator type wavelength tunable light source 4 shown in FIG. A half mirror can be used instead of the beam splitter 31 described above.

  FIG. 9 is a view showing a modification of the external resonator type wavelength tunable light source 4 according to the fourth embodiment of the present invention. The external resonator type wavelength tunable light source 4 ′ shown in FIG. 9 is the same as that of the modification 2 ′ of the external resonator type wavelength tunable light source 2 according to the second embodiment shown in FIG. A beam splitter 31 is provided, a case 22 is provided instead of the case 20, and a reflecting mirror 32 (reflecting member), a condensing lens 33, and an optical fiber 34 are further provided. The configuration is the same as that shown in FIG. Are given the same reference numerals.

  The case 22 accommodates the incident end of the reflecting mirror 32, the condensing lens 33, and the optical fiber 34 in addition to the semiconductor laser 11, the collimating lens 12, and the beam splitter 31, and is kept at a constant temperature by a temperature control device (not shown). The The case 22 houses a rectangular parallelepiped main body 22 a that houses the semiconductor laser 11, the collimating lens 12, the condenser lens 33, and the incident end of the optical fiber 34, a beam splitter 31, and a reflection mirror 32. It consists of a rectangular parallelepiped protruding portion 22 b provided protruding from the main body portion 22 a in the direction toward the beam splitter 31. The main body 22a and the protrusion 22b communicate with each other, and an opening (not shown) through which laser light is input and output is formed on the surface of the protrusion 22b that faces the diffraction grating 14.

  In the case 22, the surface on which the protruding portion 22 b is provided and the surface facing the surface are perpendicular to the optical path between the semiconductor laser 11 and the beam splitter 31, and the other surfaces are the same as the semiconductor laser 11 and the beam. The semiconductor laser 11, the collimating lens 12, and the beam splitter 31 are accommodated so as to be parallel to the optical path between the splitter 31. In addition, the diffraction grating 14 is fixedly held on the surface of the main body 22a where the protrusion 22b is provided.

  Inside the case 22, the reflection mirror 32 is disposed on the optical path along which the laser light diffracted by the diffraction grating 14 and transmitted through the beam splitter 31 travels. The light transmitted through the beam splitter 31 is transmitted from the beam splitter 31. The angle is adjusted and positioned so as to reflect in the direction along the optical path to the semiconductor laser 11. The condensing lens 33 is disposed on the optical path along which the laser light reflected by the reflecting mirror 32 travels, and condenses the laser light on the incident end of the optical fiber 34. The optical fiber 34 guides the laser beam condensed by the condenser lens 33 to the outside of the external resonator type wavelength variable light source 4 '.

  As described above, in the external resonator type wavelength tunable light source 4 ′, the laser beam transmitted through the beam splitter 31 is reflected by the reflection mirror 32 in the direction along the optical path from the beam splitter 31 to the semiconductor laser 11. The rotation of a rotating arm (not shown) that rotates 15 can be prevented from being hindered, and the shape of the case 22 can be made small and simple. Further, similarly to the external resonator type wavelength tunable light source 4 shown in FIG. 8, laser light having a narrow spectral line width can be obtained.

  In addition, it is also possible to provide a half mirror in place of the beam splitter 31 as in the external resonator type wavelength tunable light source 4 shown in FIG. Further, a condensing lens that condenses laser light emitted from the end surface 11b of the semiconductor laser 11 on which the antireflection film 16 is not applied or zero-order light diffracted by the diffraction grating 14, and a condensing lens. It is configured to include an optical fiber that guides the emitted laser light to the outside, and the laser light guided to the outside by the optical fiber is used as secondary output light or as monitor light for wavelength stabilization. Also good.

[Fifth Embodiment]
FIG. 10 is a perspective view showing a main configuration of an external resonator type wavelength tunable light source according to the fifth embodiment of the present invention. The external resonator type wavelength tunable light source 5 of the present embodiment includes a semiconductor laser 11, a collimator lens 12, a reflection mirror 13, and a diffraction grating 14, similarly to the external resonator type wavelength tunable light source 1 of the first embodiment. The difference is that a retro-reflector 40 is provided instead of the plane mirror 15. Note that the optical path length condition and the incident angle condition with respect to the diffraction grating 14 are satisfied in the same manner as in the external resonator type wavelength tunable light source 1 of the first embodiment.

  The retroreflector 40 includes two reflecting surfaces 40a and 40b orthogonal to each other, and a surface (orthogonal surface) orthogonal to each of the reflecting surfaces 40a and 40b is a diffraction direction of the diffraction grating 14 (a direction along the diffraction surface 14a). In the direction in which the grids are arranged). As the retroreflector 40, for example, a right triangular prism or an orthogonal dihedral mirror can be used. In the retro reflector 40, the length in the direction orthogonal to the orthogonal plane is set to a predetermined length or less in order to increase the wavelength resolution of the external resonator type tunable light source 5, and the plane mirror 15 shown in FIG. In the same manner as described above, it can be rotated around a point C1 in FIG. 1 by a rotating arm (not shown) or the like.

  In the external resonator type wavelength tunable light source 1 including the plane mirror 15, in order to maximize the resonance efficiency of the resonator constituted by the end surface 11 b of the semiconductor laser 11 and the reflection surface 15 a of the plane mirror 15, It is necessary to strictly adjust the tilt. On the other hand, since the retroreflector 40 has the property of accurately reflecting incident light in the opposite direction, strict adjustment when the plane mirror 15 is provided is unnecessary, and the resonance of the resonator can be easily performed with simple adjustment. Efficiency can be maximized. The retro-reflector 40 is not only applicable to the external resonator type wavelength tunable light source 1 according to the first embodiment shown in FIG. 1, but can also be applied to the second to fourth embodiments and modifications thereof. .

  As described above, according to the external resonator type wavelength tunable light source of the first to fifth embodiments, a laser beam having a narrow spectral line width and good wavelength stability can be obtained, and the wavelength is continuously generated without causing a mode hop. In addition to being variable, downsizing can be realized. In addition, it is possible to eliminate the various practical measures required in the past, such as measures for preventing interference between the rotating arm for rotating the flat mirror 15 and the retroreflector 40 and the semiconductor laser 11.

  Next, a light source device including the external resonator type wavelength tunable light source according to the embodiment described above will be described. FIG. 11 is a block diagram showing a configuration of a light source device according to an embodiment of the present invention. As shown in FIG. 11, the light source device 50 of the present embodiment includes a wavelength variable light source 51, a beam splitter 52, a light receiver 53, an LD drive circuit 54, a rotation mechanism drive circuit 55 (wavelength variable unit), a temperature control circuit 56, and A CPU (central processing unit) 57 is provided.

  The wavelength tunable light source 51 is any one of the external resonator type wavelength tunable light sources 1 to 5 according to the first to fifth embodiments described above and external resonator type wavelength tunable light sources 1 ′ to 4 ′ according to modifications thereof. The beam splitter 52 reflects a part (for example, about several percent) of the laser light L0 emitted from the wavelength variable light source 51 and transmits the rest. The laser beam L1 that has passed through the beam splitter 52 is output from the light source device 50 to the outside.

  The light receiver 53 receives the laser beam L2 reflected by the beam splitter 52 and outputs a monitor signal S1 corresponding to the intensity of the laser beam L2. The LD drive circuit 54 drives the semiconductor laser 11 included in the wavelength tunable light source 51 using the monitor signal S1 from the light receiver 53 under the control of the CPU 57. The semiconductor laser 11 is feedback controlled by the LD drive circuit 54.

  The rotation mechanism drive circuit 55 rotates to rotate the flat mirror 15 (see FIGS. 1 to 5 and FIGS. 7 to 9) or the retroreflector 40 (see FIG. 10) included in the variable wavelength light source 51 under the control of the CPU 57. A mechanism (not shown) is driven to vary the wavelength of the laser light L0 emitted from the wavelength variable light source 51. The temperature control circuit 56 controls the temperature control device (not shown) under the control of the CPU 57 to keep the temperature of the cases 20 to 22 (see FIGS. 4, 7, and 9) accommodating the semiconductor laser 11 and the like. .

  The CPU 57 comprehensively controls the LD drive circuit 54, the rotation mechanism drive circuit 55, and the temperature control circuit 56 described above to emit laser light with a narrow spectral line width and good wavelength stability, and the wavelength of the laser light is continuously increased. Variable. The light source device 50 described above is used, for example, as a light source for performing optical communication or a light source used in optical measurement technology, but can also be used in various fields where the wavelength needs to be varied.

  As described above, the external resonator type wavelength tunable light source and the light source device according to the embodiment of the present invention have been described. However, 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 example shown in FIGS. 4, 7, and 9, the reflection mirror 13 is accommodated in the cases 20 and 21 and the beam splitter 31 is accommodated in the case 22. May be fixedly held outside the case. In these drawings, the diffraction grating 14 is fixedly held in the cases 20 to 23. However, the diffraction grating 14 may be arranged separately from the case. However, considering the ease of adjustment and miniaturization, it is desirable to hold the diffraction grating 14 fixed to the case.

It is a top view which shows the structure of the external resonator type | mold wavelength variable light source by 1st Embodiment of this invention. It is a figure which shows the modification of the external resonator type | mold wavelength variable light source 1 by 1st Embodiment of this invention. It is a top view which shows the structure of the external resonator type | mold wavelength variable light source by 2nd Embodiment of this invention. It is a figure which shows the modification of the external resonator type | mold wavelength variable light source 2 by 2nd Embodiment of this invention. It is a top view which shows the structure of the external resonator type | mold wavelength variable light source by 3rd Embodiment of this invention. It is a figure for demonstrating a dead zone line SL. It is a figure which shows the modification of the external resonator type | mold wavelength variable light source 3 by 3rd Embodiment of this invention. It is a top view which shows the structure of the external resonator type | mold wavelength variable light source by 4th Embodiment of this invention. It is a figure which shows the modification of the external resonator type | mold wavelength variable light source 4 by 4th Embodiment of this invention. It is a perspective view which shows the principal part structure of the external resonator type | mold wavelength variable light source by 5th Embodiment of this invention. It is a block diagram which shows the structure of the light source device by one Embodiment of this invention. It is a top view which shows an example of the conventional external resonator type | mold wavelength variable light source.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1-5 External resonator type | mold wavelength-tunable light source 1'-4 'External resonator type | mold wavelength variable light source 11 Semiconductor laser 11a, 11b End surface 13 Reflection mirror 14 Diffraction grating 14a Diffraction surface 15 Planar mirror 16 Antireflection film 20-22 Case 31 Beam splitter 32 Reflecting mirror 40 Retro reflector 40a, 40b Reflecting surface 50 Light source device 55 Rotating mechanism drive circuit C1, C1 'Point P1, P1' Optical position PL Normal line

Claims (10)

One of a light source having an antireflection film applied to a first end surface of a pair of end surfaces, a diffraction grating on which light from the light source is incident at a predetermined incident angle, and light diffracted by the diffraction grating An external resonator-type wavelength tunable light source including a rotatable reflecting mirror that reflects a portion toward the diffraction grating, and a second end face different from the first end face of the light source and the reflecting mirror. ,
A reflection element that reflects light from the light source and makes the diffraction grating enter the diffraction grating at the predetermined incident angle;
The light source is disposed with the first end face provided with the antireflection film facing the reflection element, and the optical path length from the second end face to the reflection mirror via the reflection element and the diffraction grating is, An external resonator type wavelength tunable light source, wherein the light source, the diffraction grating, and the reflecting mirror are positioned so as to have an optical path length of a resonator when the Littman arrangement is employed.   The rotation center of the reflecting mirror extends perpendicular to the optical axis starting from the optical position of the second end face with respect to the diffraction grating when the light source, the diffraction grating, and the reflecting mirror are in a Littman arrangement. The external resonator type wavelength tunable light source according to claim 1, wherein the external resonator type wavelength tunable light source is set at an intersection of a line and a plane including a diffraction plane of the diffraction grating.   3. The external resonator type wavelength according to claim 2, wherein the light source is positioned so that an optical path from the light source to the reflecting element passes between a rotation center of the reflecting mirror and the diffraction grating. Variable light source.   4. An external resonator type wavelength tunable light source according to claim 3, wherein an optical path from the light source to the reflection element is parallel to a normal line of a diffraction surface of the diffraction grating. A case for accommodating the light source;
5. The external resonator type wavelength tunable light source according to claim 1, wherein at least one of the reflection element and the diffraction grating is fixedly held on the case. 6.   6. The external resonance according to claim 1, wherein the reflection element is an element that reflects a part of incident light and transmits the remaining light. 6. Type wavelength tunable light source.   7. The external resonator type wavelength tunable light source according to claim 6, wherein out of light incident on the reflective element from the diffraction grating, light transmitted through the reflective element is output as output light.   8. The external resonator type wavelength tunable according to claim 7, further comprising: a reflecting member that reflects light transmitted through the reflecting element into the output light in a direction along an optical path from the reflecting element to the light source. light source.   The reflecting mirror is a retro-reflector having two reflecting surfaces orthogonal to each other and arranged so that a surface orthogonal to each of the reflecting surfaces intersects the diffraction direction of the diffraction grating. The external resonator type wavelength tunable light source according to any one of claims 1 to 8. In a light source device that emits laser light having a variable wavelength,
An external resonator type wavelength tunable light source according to any one of claims 1 to 9,
A light source device comprising: a wavelength control unit that controls a rotation amount of the reflecting mirror included in the external resonator type wavelength tunable light source to vary a wavelength of the laser light.

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