JP2010219315A - Wavelength sweeping light source - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a wavelength sweeping light source that can perform high-speed continuous wavelength sweeping of single mode over a wide wavelength range, and emit a plurality of output light beams. <P>SOLUTION: An external resonator type wavelength sweeping light source, employing a Littmann system, that continuously varies the wavelength of light emitted by a semiconductor light-emitting element 22 within a predetermined range by varying a resonator length in accordance with angle variation of a reflecting surface 32a of a rotary mirror 30 includes: a half-mirror 240 which reflects part of the light emitted by the semiconductor light-emitting element 22 toward a predetermined incidence position G of a diffraction grating 25, and reflects part of light returned from the diffraction grating 25 through a reverse optical path toward a low-reflectivity surface 22a of the semiconductor light-emitting element 22 and transmits at least part of the rest; and a first output mirror 241 which emits first output light L<SB>1</SB>to the outside by reflecting the light returned from the diffraction grating 25 through the reverse optical path and transmitted through the half-mirror 240 in a direction not crossing the rotary mirror 30. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a wavelength-swept light source of an external resonator type, and more particularly, to a wavelength-swept light source that is easy to manufacture and capable of performing wavelength sweep at high speed.

  A wavelength-swept light source is widely used as a light source for testing an optical communication line or an optical communication device or an optical fiber sensing light source such as an FBG (Fiber Bragg Grating) sensor. At present, an extremely high-performance light source capable of performing single-mode high-speed continuous wavelength sweeping over a wide wavelength range is realized as an external resonator type wavelength sweeping light source called a Litman type.

  As an example of such a wavelength swept light source, there is a light source provided with a rotating mirror that is significantly reduced in size by a MEMS (Micro Electro Mechanical Systems) technique (see, for example, Patent Document 1).

  In order to realize a mode-hop-free continuous wavelength sweep in such a wavelength-swept light source, in addition to at least one light output for a device to which the light source is applied, in addition to monitoring wavelength information of the light output A separate optical output is required. For this reason, generally, a wavelength swept light source is required to be able to emit a plurality of output lights.

  For example, as a method for extracting light resonating in a resonator in a wavelength swept light source to the outside through a plurality of optical output ports, it has been conventionally performed to arrange an optical demultiplexer in the resonator (for example, Patent Document 2). This method is useful for a light source having a large size and a sufficiently long resonator length as in the conventional type and having a sufficient space for placing an optical demultiplexer inside the resonator.

Japanese Patent No. 4073886 JP-A-9-102645

  However, since the resonator length of the light source disclosed in Patent Document 1 is very short, it is very difficult to secure a spatial space in which the above-described optical demultiplexer is arranged.

  Here, consider a case where the resonator is configured in a vacuum or in air. The refractive index of free space is 1, whereas the refractive index of optical glass, for example, is about 1.5. Accordingly, even if an optical demultiplexer made of optical glass can be arranged in the resonator, the optical path length corresponding to 1.5 times the length of the optical demultiplexer out of the resonator length is Therefore, it becomes impossible to realize a resonator length that guarantees a mode-hop-free continuous wavelength sweep.

  Further, since such a light source is mounted at a high density in order to achieve miniaturization, light is blocked by other optical components simply by placing an optical demultiplexer, and the light is output to the outside. I can't.

  The present invention has been made to solve such a conventional problem, and is capable of single-mode high-speed continuous wavelength sweeping over a wide wavelength range and a wavelength capable of emitting a plurality of output lights. An object is to provide a swept light source.

  The wavelength swept light source of the present invention includes a base, a semiconductor light emitting element that is fixed on the base, and one of the two end faces has a lower reflectivity surface than the other end face, and the base. A collimating lens that is fixed and converts light emitted from the low-reflectance surface of the semiconductor light-emitting element into parallel light; and a diffractive surface in which diffraction grooves for diffracting light are formed in parallel. A diffraction grating fixed on the base in a state where light emitted from a lens is incident on a predetermined incident position at a predetermined incident angle orthogonal to the diffraction groove and non-orthogonal to the diffraction surface; A reflecting plate fixed on the base and facing the diffractive surface of the diffraction grating, and in a plane perpendicular to the diffractive surface about an axis at a specific position parallel to the diffraction groove of the diffraction grating It is formed so that it can be rotated with the collimating lens. Of the diffracted light with respect to the light incident on the diffractive surface of the diffraction grating, the light along the optical path perpendicular to the reflective surface of the reflecting plate is reflected and returned to the diffractive grating by the reverse optical path, and the returned light A rotating mirror that returns the semiconductor light emitting element to the semiconductor light emitting element via the collimating lens in the same optical path as the incident optical path, and from the semiconductor light emitting element to the collimating lens according to a change in the angle of the reflecting surface of the rotating mirror. A Littman-type external resonance that changes the resonator length from the diffraction surface of the diffraction grating to the reflection surface of the rotating mirror and continuously changes the wavelength of light emitted from the semiconductor light emitting element within a predetermined range. And a part of the light emitted from the collimating lens is reflected toward the predetermined incident position of the diffraction grating. A fixed mirror that reflects a part of the light returned from the diffraction grating by a reverse optical path toward the low-reflectance surface of the semiconductor light-emitting element and transmits at least a part of the remaining light-emitting element; The collimating lens, the fixed mirror, and the diffraction grating are arranged on one surface side of the rotating mirror, and an optical path from the semiconductor light emitting element to the diffraction grating via the fixed mirror is non-intersecting with the rotating mirror. A distance r from the rotation center position of the rotation mirror to the predetermined incident position of the diffraction grating, a distance L2 from the rotation center position to a plane extending the reflection surface, an effective resonance end surface of the semiconductor light emitting element The optical path length L3 from the fixed mirror to the fixed mirror, the optical path length L4 from the fixed mirror to the predetermined incident position of the diffraction surface of the diffraction grating, and the diffraction grating from the fixed mirror The relationship r = (L3 + L4-L2) / sin α is established between the light incident angle α on the diffractive surface of the child, and the rotating mirror includes a frame fixed to the base, and the frame The reflection plate is disposed on the inner side of the reflection plate, and the reflection surface is formed on one side of the reflection plate. The torsional deformation connecting the outer edge of the reflection plate and the inner edge of the frame is parallel to the diffraction groove of the diffraction grating. And a pair of connecting portions arranged in a straight line, and a rotation driving means for periodically applying a force for reciprocating rotation to the reflecting plate, the reflecting plate is centered on the connecting portion. A first output for reflecting light that has been returned from the diffraction grating through a reverse optical path and transmitted through the fixed mirror in a direction that does not intersect the rotating mirror; A first output light from the first output mirror It has a configuration to emit.

  With this configuration, a single-mode high-speed continuous wavelength sweep is possible over a wide wavelength range, and in addition to the output light from the other end face of the semiconductor light emitting element and the 0th-order diffracted light of the diffraction grating, the first output mirror 1st output light from can be emitted.

  In addition, the wavelength swept light source of the present invention reflects the light returned from the diffraction grating through a reverse optical path and transmitted through the fixed mirror in a non-intersecting direction with respect to the rotating mirror and the first output mirror. And an n-th output mirror (n ≧ 2) that is transmitted toward the light source, and the n-th output light is emitted from the n-th output mirror.

  With this configuration, it is possible to emit the nth output light from the nth output mirror (n ≧ 2).

  Moreover, the wavelength swept light source of the present invention may have a configuration including a reflecting member in which the fixed mirror and the output mirror are integrally formed.

  In the wavelength-swept light source of the present invention, an optical path from the semiconductor light emitting element through the collimating lens to the fixed mirror is parallel to the diffraction groove of the diffraction grating, and an optical path from the fixed mirror to the diffraction grating is The fixed mirror is disposed so as to be perpendicular to the diffraction groove, and the light that has been returned from the diffraction grating through a reverse optical path and transmitted through the fixed mirror is reflected in a direction parallel to the diffraction groove of the diffraction grating. In this way, the first output mirror may be arranged.

  Further, the wavelength swept light source of the present invention includes a base, a semiconductor light emitting element that is fixed on the base, and one of the two end faces has a lower reflectivity surface than the other end face, and the base. A collimating lens that is fixed on the semiconductor light-emitting element and converts the light emitted from the low-reflectance surface of the semiconductor light-emitting element into parallel light; and a diffractive surface in which diffraction grooves for diffracting light are formed in parallel. A diffraction grating fixed on the base in a state where light emitted from the collimating lens is incident on a predetermined incident position at a predetermined incident angle orthogonal to the diffraction groove and non-orthogonal to the diffraction surface And a reflector fixed on the base and facing the diffraction surface of the diffraction grating, and orthogonal to the diffraction surface about an axis at a specific position parallel to the diffraction groove of the diffraction grating The collimating lens is formed so as to be rotatable in a plane. Of the diffracted light with respect to the light emitted from the diffraction grating and incident on the diffraction surface of the diffraction grating, the light along the optical path orthogonal to the reflection surface of the reflector is reflected and returned to the diffraction grating by a reverse optical path. A rotating mirror that returns the reflected light to the semiconductor light emitting element through the collimating lens in the same optical path as the incident optical path, and from the semiconductor light emitting element to the collimator according to an angle change of the reflecting surface of the rotating mirror A Littman method for changing the wavelength of the light emitted from the semiconductor light emitting element continuously within a predetermined range by changing a resonator length from the diffraction surface of the lens and the diffraction grating to the reflection surface of the rotating mirror. In the external resonator type wavelength sweeping light source, when a part of the light that is fixed on the base and emitted from the collimating lens is reflected toward the predetermined incident position of the diffraction grating, In addition, the semiconductor light emitting device includes a fixed mirror that reflects a part of the light returned from the diffraction grating by a reverse optical path toward the low reflectance surface of the semiconductor light emitting element and transmits at least a part of the remaining light. An element, the collimating lens, the fixed mirror, and the diffraction grating are arranged on one surface side of the rotating mirror, and an optical path from the semiconductor light emitting element to the diffraction grating via the fixed mirror is not on the rotating mirror. A distance r from the rotation center position of the rotation mirror to the predetermined incident position of the diffraction grating, a distance L2 from the rotation center position to a plane extending the reflection surface, and the semiconductor light emitting element An optical path length L3 from the effective resonance end surface to the fixed mirror, an optical path length L4 from the fixed mirror to the predetermined incident position of the diffraction surface of the diffraction grating, and the fixed mirror to the The relationship r = (L3 + L4-L2) / sin α is established between the light incident angle α on the diffraction surface of the diffraction grating, and the rotating mirror includes a frame fixed to the base, The reflection plate disposed on the inner side of the frame and having the reflection surface formed on one side thereof, and torsionally deformable connecting the outer edge of the reflection plate and the inner edge of the frame, and parallel to the diffraction grooves of the diffraction grating And a pair of connecting portions arranged in a straight line, and the reflecting plate centering on the connecting portion by a rotation driving means that periodically applies a force for reciprocating rotation to the reflecting plate. The optical path from the semiconductor light emitting element through the collimating lens to the fixed mirror is parallel to the diffraction groove of the diffraction grating and from the fixed mirror to the diffraction grating. The optical path is to the diffraction groove The fixed mirror is arranged so as to be perpendicular, or may have a structure for emitting light transmitted through the fixed mirror back to backlight path from the diffraction grating as an output light.

  The present invention provides a wavelength swept light source capable of single-mode high-speed continuous wavelength sweeping over a wide wavelength range and emitting a plurality of output lights.

The perspective view which shows the structure of the wavelength sweep light source of the 1st Embodiment of this invention. The top view which shows the structure of the wavelength swept light source of the 1st Embodiment of this invention Sectional drawing which shows the structure of the semiconductor light-emitting device with which the wavelength sweep light source of the 1st Embodiment of this invention is provided. The disassembled perspective view of the rotation mirror with which the wavelength sweep light source of the 1st Embodiment of this invention is provided. Graph showing the relationship between drive signal and wavelength change The schematic diagram for demonstrating the conditions for the wavelength sweep light source of the 1st Embodiment of this invention to sweep a wavelength continuously The perspective view which shows the structure of the wavelength swept light source of the 2nd Embodiment of this invention. The perspective view which shows the structure of the wavelength swept light source of the 3rd Embodiment of this invention. Sectional drawing which shows the structure of the principal part of the wavelength swept light source of the 3rd Embodiment of this invention. Sectional drawing which shows the other structural example of the principal part of the wavelength swept light source of the 3rd Embodiment of this invention.

  Hereinafter, embodiments of a wavelength swept light source according to the present invention will be described with reference to the drawings.

(First embodiment)
Hereinafter, embodiments of a wavelength swept light source according to the present invention will be described with reference to the drawings. 1 is a perspective view of the wavelength swept light source 20, and FIG. 2 is a plan view.

  That is, the wavelength swept light source 20 is fixed on the base 21 having a high step portion 21a and a low step portion 21b whose upper surfaces are parallel to each other, and one end surface of the two end surfaces 22a and 22b. The semiconductor light emitting element 22 in which 22a is a low reflectance surface compared with the other end surface, and the collimating lens fixed on the high step part 21a which converts the emitted light from the low reflectance surface 22a of the semiconductor light emitting element 22 into parallel light 23 and a diffractive surface 25a in which a diffraction groove 25b for diffracting light is formed in parallel, and the light emitted from the collimating lens 23 is orthogonal to the diffraction groove 25b and non-diffracting with respect to the diffractive surface 25a. And a diffraction grating 25 that is vertically fixed to the lower step portion 21b of the base 21 while being incident on the predetermined incident position G at a predetermined incident angle α that is orthogonal.

  Further, the wavelength swept light source 20 has a reflecting plate 32 facing the diffraction surface 25a of the diffraction grating 25, and is a plane orthogonal to the diffraction surface 25a with the axis at a specific position parallel to the diffraction groove 25b of the diffraction grating 25 as the center. Of the diffracted light with respect to the light emitted from the collimating lens 23 and incident on the diffraction surface 25a of the diffraction grating 25, and reflects light along an optical path orthogonal to the reflection surface 32a of the reflection plate 32. A rotating mirror 30 having a MEMS (Micro Electro Mechanical Systems) structure for returning the returned light to the diffraction grating 25 in the reverse optical path and returning the returned light to the semiconductor light emitting element 22 through the collimating lens 23 in the same optical path as the incident optical path; The parallel light emitted from the lens 23 is received by the reflection surface 240a perpendicular to the upper surface of the high step portion 21a, and a part thereof is reflected toward the diffraction surface 25a of the diffraction grating 25, and A half mirror 240 as a fixed mirror that reflects part of the light returned from the folding grating 25 through the reverse optical path toward the low reflectance surface 22a of the semiconductor light emitting element 22 and transmits at least part of the remaining part. .

  By periodically changing the angle of the reflection surface 32a with respect to the diffraction surface 25a of the diffraction grating 25 within a predetermined angle range, the semiconductor light emitting element 22, the collimating lens 23, the reflection surface 240a of the half mirror 240, and the diffraction surface of the diffraction grating 25 are obtained. The resonator length reaching the reflecting surface 32a of the rotating mirror 30 via 25a changes continuously and periodically, and the wavelength of the light emitted from the wavelength sweep light source 20 also changes continuously and periodically.

Furthermore, the wavelength swept light source 20 reflects the light returned from the diffraction grating 25 through the reverse optical path and transmitted through the half mirror 240 in a direction that does not intersect the rotating mirror 30, whereby the first output light L _{A first} output mirror 241 for emitting ₁ to the outside is provided.

In addition, between the half mirror 240 and the first output mirror 241, the emitted light from the half mirror 240 is transmitted toward the first output mirror 241, and the emitted light is transmitted to the rotating mirror 30. The second output mirror 242 and the Nth output mirror 242 that emit the second output light L ₂ and the Nth output light L _N (N ≧ 3) (not shown) to the outside by reflecting in the non-intersecting direction. Output mirrors (N ≧ 3) (not shown) may be arranged.

Incidentally, a half mirror 240, the transmittance of the output mirror (N ≧ 3) of the second output mirror 242 and the N, the output light L _A from the end face 22b of the semiconductor light emitting element 22, the first output light L ₁ and it may be the value obtained the desired light intensity for each of the output light L _n of the n (n ≧ 2).

  The optical path of the light emitted from the half mirror 240 and reflected by the first output mirror 241, the second output mirror 242, or the Nth output mirror (N ≧ 3) is the optical path of the resonator of the wavelength sweep light source 20. Not included. Accordingly, since the optical path length from the half mirror 240 to the first output mirror 241, the second output mirror 242, or the Nth output mirror (N ≧ 3) is independent of the resonator length, Each optical path length may be an arbitrary length as long as it does not contact the optical component.

  The rotating mirror 30 is fixed to a rotating mirror holder (not shown), and the rotating mirror holder is fixed on the lower step portion 21 b of the base 21. The semiconductor light emitting element 22 is fixed to a chip carrier (not shown), and the chip carrier is fixed on the high step portion 21 a of the base 21. The collimating lens 23, the half mirror 240, the first output mirror 241, the second output mirror 242, and the Nth output mirror (N ≧ 3) are on the high step portion 21a of the base 21, and the diffraction grating 25 is It is fixed on the lower step portion 21b of the base 21 with solder, welding or adhesive. However, in any case, it may be indirectly fixed to the base 21 via another member (for example, a lens holder in the case of a lens).

  As shown in the cross-sectional view taken along the light propagation direction in FIG. 3, the semiconductor light emitting element 22 is formed, for example, on an n-type semiconductor substrate 101 made of n-type InP (indium / phosphorus) on an InGaAsP (indium / phosphorus). An active layer 102 made of gallium, arsenic, and phosphorus (here, the active layer 102 includes MQW and an SCH layer sandwiching it), a p-type InP cladding layer 103, and InGaAs (indium gallium arsenide). In this semiconductor laser, contact layers 104 are sequentially stacked.

  Further, a lower electrode 105 is formed on the lower surface of the n-type semiconductor substrate 101, and an upper electrode 106 is formed on the contact layer 104 by vapor deposition. Further, as already described, the reflectance of one end surface 22a of the two end surfaces 22a, 22b is formed lower than the reflectance of the other end surface 22b.

  As shown in the exploded perspective view of FIG. 4, the rotating mirror 30 is formed by etching or the like on a conductive substrate (for example, a silicon substrate), and is horizontally long by an upper plate 31a, a lower plate 31b, and horizontal plates 31c and 31d. A frame 31 formed in a rectangular frame shape, a horizontally long rectangular reflector 32 arranged concentrically on the inner side of the frame 31 and having a reflecting surface 32a for reflecting light on at least one surface side, The upper plate 31a, the lower plate 31b, and the reflecting plate 31a, the lower plate 31b, and the reflecting plate 32 extend in a straight line from the center of the inner edges of the upper plate 31a and the lower plate 31b facing each other to the center of the upper and lower edges of the reflecting plate 32. And a pair of connecting portions 33 and 34 for rotating the reflecting plate 32 by being twisted and deformed.

  The reflecting surface 32a of the reflecting plate 32 can be formed of, for example, a mirror finish on the material surface, vapor deposition of a metal film exhibiting high reflectivity, or a dielectric multilayer film. Further, when the rotating mirror 30 is made of a material exhibiting a high reflectance with respect to the laser light, the surface of the material can be used as a reflecting surface without providing a reflecting film or a reflecting sheet.

  However, when the rotating mirror 30 does not have conductivity, it is necessary to deposit a conductive metal film as a mirror material in order to ensure electrostatic driving force.

  The widths and lengths of the connecting portions 33 and 34 are set so that the connecting portions 33 and 34 themselves can be twisted and deformed along the longitudinal direction, and a restoring force is generated to return to the original state by the deformation. ing.

  Further, electrode plates 35 and 36 for applying an external force to the reflecting plate 32 are insulated on both surfaces of one of the horizontal plates 31c and 31d (here, the horizontal plate 31c) of the frame 31 of the rotating mirror 30. It attaches via the spacer 37 which has property. The electrode plates 35 and 36 are overlapped with a gap corresponding to the thickness of the spacer 37 formed on both surfaces of one end side (here, the left end side) of the reflection plate 32. Here, the spacer 37 has a vertically long rectangular shape, but the spacer 37 may be formed in a rectangular frame shape that overlaps the frame 31 in order to reinforce the entire frame 31.

  In the rotation mirror 30, the rotation center position of the reflection plate 32 (a line connecting the centers of the coupling portions 33 and 34) is on a surface extending from the diffraction surface 25a of the diffraction grating 25 and parallel to the diffraction groove 25b. In the state, it is fixed on the base 21.

  The rotating mirror 30 includes the electrode plates 35 and 36 and the spacer 37, and is formed by etching the silicon substrate as described above. However, the manufacturing method is arbitrary.

  For example, the frame 31, the reflecting plate 32, and the connecting portions 33 and 34 of the rotating mirror 30 are formed by etching on a single layer substrate, and the spacer 37 and the electrode plates 35 and 36 are formed on another substrate, and these are bonded together. Or a three-layer substrate such as an SOI substrate, the frame 31 of the rotating mirror 30, the reflection plate 32, and the connecting portions 33 and 34 are etched on the upper layer substrate, and the spacer 37 is formed on the lower layer substrate. Can be manufactured by various methods such as forming one electrode by attaching the electrode plate 35 manufactured in another process.

  Further, as shown in FIG. 2, the rotating mirror 30 applies an external force to the reflecting plate 32, and the reflecting plate 32 is centered on the rotating center position O that is a line connecting the centers of the pair of connecting portions 33 and 34. It has a mirror driving device 40 as a rotation driving means for reciprocating rotation within a predetermined angle range.

  The mirror driving device 40 uses a frame 31 of the rotating mirror 30 as a reference potential, for example, a driving signal whose phase is shifted by 180 degrees with respect to the two electrode plates 35 and 36 as shown in FIGS. By applying V1 and V2, an electrostatic attractive force is alternately generated between the electrode plates 35 and 36 and the end of the reflecting plate 32, and the reflecting plate 32 is reciprocally rotated.

  The frequencies of the drive signals V1 and V2 are set to be equal to the natural frequency of the reflector 32 determined by the shape and weight of the reflector 32 of the rotating mirror 30 and the torsion spring constant of the coupling portions 33 and 34. Therefore, the reflecting plate 32 can be reciprocated at a large angle with a small driving power.

  By the reciprocating rotation of the reflecting plate 32, the effective optical path length in the wavelength swept light source 20 and the angle of the reflecting surface 32 a of the reflecting plate 32 with respect to the diffracting surface 25 a of the diffraction grating 25 are changed, and output from the semiconductor light emitting element 22. The wavelength of the emitted laser light changes continuously and periodically as shown in FIG.

  However, in the case of a simplified structure in which the reflecting plate 32 itself having the reflecting surface 32a formed on one surface side is rotated like the wavelength swept light source 20, the rotation center is the connecting portions 33, 34. Is not on the line connecting the centers of the two, i.e., inside the reflecting plate 32 and on the surface extending the reflecting surface 32a, and does not satisfy the conditions of the conventional Litman method.

  Therefore, in the wavelength swept light source 20 of this embodiment, the wavelength is continuously varied by applying the technique disclosed in Japanese Patent No. 3069643.

That is, the wavelength swept light source 20 includes a half mirror 240, a first output mirror 241, a second output mirror 242, and an Nth output mirror (N ≧ 3) (not shown) as shown by the dotted line in FIG. In a hypothetical arrangement in which laser light is transmitted through the reflector 32 without being used, a plane obtained by extending the diffraction surface 25a of the diffraction grating 25 is H1, and an effective resonance end surface 22c considering the refractive index inside the semiconductor light emitting element 22 is used. When the extended plane is H2, the plane extending the reflection surface 32a of the reflection plate 32 is H3, and the plane H1 and the plane H3 intersect at a position between the rotation center position O of the reflection plate 32 and the diffraction grating 25, The distance from the rotation center position O to the predetermined incident position G of the diffraction grating 25 is r, the effective optical path length from the predetermined incident position G to the effective resonance end face 22c of the semiconductor light emitting element 22 is L1, and the rotation center position O to the plane H3. Until When the distance is L2 and the incident angle of light with respect to the diffraction grating 25 is α, the following equation is satisfied, so that the wavelength can be continuously varied in a single mode without generating a mode hop. is there.
r = (L1-L2) / sin α (1)

  However, when the optical path from the semiconductor light emitting element 22 to the diffraction grating 25 is bent via the half mirror 240 as in this embodiment, the effective optical path length L1 from the predetermined incident position G to the effective resonance end face 22c of the semiconductor light emitting element 22 is obtained. Is represented by the sum of the optical path length L3 from the effective resonance end face 22c of the semiconductor light emitting element 22 to the half mirror 240 and the optical path length L4 from the half mirror 240 to the predetermined incident position G (L1 = L3 + L4).

Therefore, by arranging each part so that the following equation holds, continuous wavelength sweep without mode hopping can be performed as shown in FIG.
r = (L3 + L4-L2) / sin α (2)

  That is, the wavelength swept light source 20 makes light incident on the diffraction grating 25 through the half mirror 240, and the semiconductor light emitting element 22, the collimating lens 23, the half mirror 240, the first output mirror 241, and the second output mirror 242. Since the Nth output mirror (N ≧ 3) and the diffraction grating 25 are arranged on one surface side of the reflection plate 32 so that the reflection plate 32 and the optical path do not cross each other, the reflection plate 32 has a hole for passing light, etc. There is no need to provide. For this reason, deformation due to a decrease in rigidity does not occur, and even a thin plate can perform high-speed wavelength sweeping that is stable and highly reproducible.

  Thus, in the wavelength swept light source 20 of the present embodiment, the rotation is performed in a space sandwiched between a plane obtained by extending the reflection surface 32a of the reflection plate 32 and a surface obtained by extending the diffraction surface 25a in the rotation center position O direction. A half mirror 240 is disposed between the center position O and the predetermined incident position G of the diffractive surface 25a, and two spaces separated by a surface obtained by extending the reflecting surface 32a of the reflecting plate 32 of the rotating mirror 30 are provided. The semiconductor light emitting element 22, the collimating lens 23, the half mirror 240, the first output mirror 241, the second output mirror 242, and the Nth output mirror (N ≧ 3) are arranged in the space including the diffraction grating 25. Light is incident on the half mirror 240 from the semiconductor light emitting element 22 through the collimator lens 23, and the reflected light is incident on a predetermined incident position G of the diffraction surface 25a of the diffraction grating 25.

  Therefore, regardless of the optical path, the rotating mirror can be configured with a very simple structure in which the reflecting plate 32 itself having the reflecting surface 32a is reciprocally rotated, and the wavelength can be tuned at high speed and with high accuracy.

The wavelength swept light source 20 of the present embodiment configured as described above has a half mirror 240, a first output mirror 241, a second output mirror 242, and an Nth as an optical demultiplexing means instead of the conventional optical demultiplexer. Since the output mirror (N ≧ 3) is provided, not only can the mode hop-free wavelength sweep satisfying Equation (2) be achieved even with a very small resonator length, but also other optical components. A plurality of output lights (the output light L _A from the end face 22 b of the semiconductor light emitting element 22, the output light L _B as the 0th-order diffracted light of the diffraction grating 25, and the first output from the first output mirror 241 without being blocked by the components) The output light L ₁ , the second output light L ₂ from the second output mirror 242, and the Nth output light L _N from the Nth output mirror (N ≧ 3) can be emitted to the outside.

  Further, in the wavelength swept light source 20 of the present embodiment, since all the optical components are fixed, it is not easily affected by vibrations from the outside, and moreover, a complicated mode hop suppression control means like a conventional light source is provided. Even if it is not used, a very stable mode hop-free wavelength sweep can be realized.

(Second Embodiment)
A second embodiment of the wavelength swept light source according to the present invention will be described with reference to the drawings. The description of the same configuration as that of the first embodiment is omitted.

  As shown in FIG. 7, the wavelength swept light source 50 of the present embodiment includes a reflecting member 24 in which a half mirror 240 and a first output mirror 241 are integrally formed. Such a reflecting member 24 can be realized, for example, by preparing optical glass having two end faces parallel to each other and applying a dielectric multilayer coating or mirror coating to each end face. Further, an nth output mirror (n ≧ 2) (not shown) may be further formed inside the reflecting member 24.

  The optical path of light emitted from the half mirror 240 and transmitted through the reflecting member 24 and reflected by the first output mirror 241 is not included in the optical path of the resonator of the wavelength sweep light source 50. Therefore, unlike the conventional optical demultiplexer, the length of the reflecting member 24 in the optical waveguide direction is independent of the resonator length, so that the length of the reflecting member 24 is arbitrary as long as the reflecting member 24 does not contact other optical components. Good.

  In the wavelength swept light source of the present embodiment configured as described above, since the half mirror 240 and the first output mirror 241 are integrally formed, the optical axis alignment between the optical components in the manufacturing process is simplified. .

(Third embodiment)
A third embodiment of the wavelength swept light source according to the present invention will be described with reference to the drawings. The description of the same configuration as in the first and second embodiments is omitted.

  In the first and second embodiments, the reflecting surface 240 a of the half mirror 240 is parallel to the diffraction groove 25 b of the diffraction grating 25, and is reflected from the semiconductor light emitting element 22 through the collimator lens 23, the half mirror 240, and the diffraction grating 25. However, this is not intended to limit the present invention, and the semiconductor light emitting element 22 and the collimating lens 23 are planes obtained by extending the reflecting surface 32a of the reflecting plate 32. As long as the space including the diffraction grating 25 is included in the two spaces separated by 1, it can be arranged at an arbitrary position, and the direction of the reflection surface 240 a of the half mirror 240 is set according to the position. Good.

  For example, as shown in FIG. 8 and FIG. 9 which is a sectional view taken along line AA, the semiconductor light emitting element 22 and the collimating lens 23 are arranged so that the optical axis thereof is parallel to the diffraction groove 25b of the diffraction grating 25. The light from the collimating lens 23 is received by a reflecting member 44 having a half mirror 240 that forms an angle of 45 degrees with respect to the upper surface of the base 21, and is diffracted by the diffraction grating 25. The light may enter the surface 25a.

  As shown in FIG. 9, the reflecting member 44 is integrally formed so that the half mirror 240 and the first output mirror 241 intersect with each other at an angle of 90 degrees.

  The semiconductor light emitting element 22, the collimating lens 23, and the reflecting member 44 are supported by a support member 41 fixed on the base 21. Similar to the first embodiment, the semiconductor light emitting element 22 is fixed to a chip carrier (not shown), and the chip carrier is fixed to the side surface of the support member 41. The collimating lens 23 and the reflecting member 44 are fixed to the side surface of the support member 41, and the diffraction grating 25 is fixed to the base 21 by soldering, welding, or adhesive. However, in any case, the support member 41 or the base 21 may be indirectly fixed via another member (for example, a lens holder in the case of a lens).

The support member 41 and the base 21 are formed with through holes 41 a and 21 c for outputting the _first output light L ₁ from the first output mirror 241 to the outside, respectively.

Since the wavelength swept light source 60 of the present embodiment configured as described above includes the reflecting member 44 having the half mirror 240 and the first output mirror 241 instead of the conventional optical demultiplexer, other optical components are used. A total of three output lights (output light L _A from the end face 22 b of the semiconductor light emitting element 22, output light L _B as the 0th-order diffracted light of the diffraction grating 25, and first light from the first output mirror 241 without being blocked) The output light L ₁ ) can be output in two directions perpendicular to the base 21 and in one direction parallel to the base 21.

As shown in the sectional view of FIG. 10, the wavelength swept light source of the present invention includes the reflecting member 54 having the reflecting mirror 240, and returns the light L ₀ that is returned from the diffraction grating 25 through the reverse optical path and transmitted through the half mirror 240. May be formed in the support member 41 through the through hole 41b. The wavelength-swept light source configured in this way has a total of three output lights (output light L _A from the end face 22b of the semiconductor light emitting element 22 and zero-order diffracted light of the diffraction grating 25 without being blocked by other optical components). The output light L _B and the transmitted light L ₀ from the half mirror 240 can be output in one direction perpendicular to the base 21 and in two directions parallel to the base 21. Also, the traveling direction of the transmitted light L _0, i.e. the take-out direction of the transmitted light L ₀ is may be varied in any direction such as a reflective plate if necessary.

20, 50, 60 Wavelength swept light source 21 Base 21a High step portion 21b Low step portion 22 Semiconductor light emitting element 22a End face (low reflectivity surface)
22b End face 22c Effective resonance end face 23 Collimating lens 24, 44, 54 Reflective member 25 Diffraction grating 25a Diffraction face 25b Diffraction groove 30 Rotating mirror 31 Frame 32 Reflecting plate 32a Reflecting face 33, 34 Connecting portion 40 Mirror drive device (rotation drive) means)
240 half mirror (fixed mirror)
240a Reflecting surface 241 First output mirror 242 Second output mirror

Claims (5)

A base (21);
A semiconductor light emitting element (22) fixed on the base and having one end face of the two end faces (22a, 22b) having a lower reflectivity than the other end face;
A collimator lens (23) fixed on the base and converting the emitted light from the low reflectance surface of the semiconductor light emitting element into parallel light;
A diffraction groove (25b) for diffracting light has a diffraction surface (25a) formed in parallel, and the light emitted from the collimating lens is orthogonal to the diffraction groove and to the diffraction surface A diffraction grating (25) fixed on the base in a state of being incident on a predetermined incident position at a predetermined incident angle that is non-orthogonal;
A reflecting plate (32) fixed on the base and facing the diffraction surface of the diffraction grating, and orthogonal to the diffraction surface about an axis at a specific position parallel to the diffraction groove of the diffraction grating Of the diffracted light with respect to the light emitted from the collimating lens and incident on the diffractive surface of the diffraction grating, along an optical path perpendicular to the reflective surface (32a) of the reflector. A rotating mirror (30) that reflects light and returns it to the diffraction grating in a reverse optical path, and returns the returned light to the semiconductor light emitting element through the collimator lens in the same optical path as the incident optical path;
According to the change in angle of the reflecting surface of the rotating mirror, the resonator length from the semiconductor light emitting element to the reflecting surface of the rotating mirror through the collimating lens and the diffraction surface of the diffraction grating is changed, In a wavelength sweep light source of a Littman external resonator type that continuously changes the wavelength of light emitted from the semiconductor light emitting element within a predetermined range,
A part of the light fixed on the base and reflected from the collimating lens is reflected toward the predetermined incident position of the diffraction grating, and a part of the light returned from the diffraction grating by a reverse optical path is reflected. A fixed mirror (240) that reflects toward the low reflectivity surface of the semiconductor light emitting element and transmits at least a portion of the remaining surface;
The semiconductor light emitting element, the collimating lens, the fixed mirror, and the diffraction grating are arranged on one surface side of the rotating mirror, and an optical path from the semiconductor light emitting element to the diffraction grating through the fixed mirror is the rotating Non-intersecting with the mirror,
A distance r from the rotation center position of the rotation mirror to the predetermined incident position of the diffraction grating, a distance L2 from the rotation center position to a plane extending the reflection surface, an effective resonance end surface of the semiconductor light emitting element ( 22c) to the fixed mirror, the optical path length L3 from the fixed mirror to the predetermined incident position of the diffraction surface of the diffraction grating, and the light incident angle from the fixed mirror to the diffraction surface of the diffraction grating. Between α and
The relationship r = (L3 + L4-L2) / sin α is established,
The rotating mirror is
A frame (31) fixed to the base;
The reflecting plate disposed inside the frame and having the reflecting surface formed on one side thereof;
A pair of connecting portions (33, 34) that are torsionally deformable and connect between the outer edge of the reflector and the inner edge of the frame and that are aligned in a straight line parallel to the diffraction groove of the diffraction grating. And
It has a structure in which the reflection plate is reciprocally rotated around the connecting portion by rotation driving means (40) that periodically applies a force for reciprocating rotation to the reflection plate,
further,
A first output mirror (241) for reflecting light returned from the diffraction grating by a reverse optical path and transmitted through the fixed mirror in a direction that does not intersect the rotating mirror; A wavelength-swept light source that emits the first output light from.   The nth output mirror that reflects the light returned from the diffraction grating through the reverse optical path and transmitted through the fixed mirror in a direction that does not intersect the rotating mirror and transmits the light toward the first output mirror. 2. The wavelength-swept light source according to claim 1, further comprising (n ≧ 2) (242), wherein the n-th output light is emitted from the n-th output mirror.   The wavelength swept light source according to claim 1, further comprising a reflecting member in which the fixed mirror and the output mirror are integrally formed. An optical path from the semiconductor light emitting element through the collimating lens to the fixed mirror is parallel to the diffraction groove of the diffraction grating, and an optical path from the fixed mirror to the diffraction grating is perpendicular to the diffraction groove. The fixed mirror is arranged in
The first output mirror is disposed so as to reflect light returned from the diffraction grating through a reverse optical path and transmitted through the fixed mirror in a direction parallel to the diffraction groove of the diffraction grating. Item 4. The wavelength-swept light source according to Item 3. A base (21);
A semiconductor light emitting element (22) fixed on the base and having one end face of the two end faces (22a, 22b) having a lower reflectivity than the other end face;
A collimator lens (23) fixed on the base and converting the emitted light from the low reflectance surface of the semiconductor light emitting element into parallel light;
A diffraction groove (25b) for diffracting light has a diffraction surface (25a) formed in parallel, and the light emitted from the collimating lens is orthogonal to the diffraction groove and to the diffraction surface A diffraction grating (25) fixed on the base in a state of being incident on a predetermined incident position at a predetermined incident angle that is non-orthogonal;
A reflecting plate (32) fixed on the base and facing the diffraction surface of the diffraction grating, and orthogonal to the diffraction surface about an axis at a specific position parallel to the diffraction groove of the diffraction grating Of the diffracted light with respect to the light emitted from the collimating lens and incident on the diffractive surface of the diffraction grating, along an optical path perpendicular to the reflective surface (32a) of the reflector. A rotating mirror (30) that reflects light and returns it to the diffraction grating in a reverse optical path, and returns the returned light to the semiconductor light emitting element through the collimator lens in the same optical path as the incident optical path;
According to the change in angle of the reflecting surface of the rotating mirror, the resonator length from the semiconductor light emitting element to the reflecting surface of the rotating mirror through the collimating lens and the diffraction surface of the diffraction grating is changed, In a wavelength sweep light source of a Littman external resonator type that continuously changes the wavelength of light emitted from the semiconductor light emitting element within a predetermined range,
A part of the light fixed on the base and reflected from the collimating lens is reflected toward the predetermined incident position of the diffraction grating, and a part of the light returned from the diffraction grating by a reverse optical path is reflected. A fixed mirror (240) that reflects toward the low reflectivity surface of the semiconductor light emitting element and transmits at least a portion of the remaining surface;
The semiconductor light emitting element, the collimating lens, the fixed mirror, and the diffraction grating are arranged on one surface side of the rotating mirror, and an optical path from the semiconductor light emitting element to the diffraction grating through the fixed mirror is the rotating Non-intersecting with the mirror,
A distance r from the rotation center position of the rotation mirror to the predetermined incident position of the diffraction grating, a distance L2 from the rotation center position to a plane extending the reflection surface, an effective resonance end surface of the semiconductor light emitting element ( 22c) to the fixed mirror, the optical path length L3 from the fixed mirror to the predetermined incident position of the diffraction surface of the diffraction grating, and the light incident angle from the fixed mirror to the diffraction surface of the diffraction grating. Between α and
The relationship r = (L3 + L4-L2) / sin α is established,
The rotating mirror is
A frame (31) fixed to the base;
The reflecting plate disposed inside the frame and having the reflecting surface formed on one side thereof;
A pair of connecting portions (33, 34) that are torsionally deformable and connect between the outer edge of the reflector and the inner edge of the frame and that are aligned in a straight line parallel to the diffraction groove of the diffraction grating. And
It has a structure in which the reflection plate is reciprocally rotated around the connecting portion by rotation driving means (40) that periodically applies a force for reciprocating rotation to the reflection plate,
An optical path from the semiconductor light emitting element through the collimating lens to the fixed mirror is parallel to the diffraction groove of the diffraction grating, and an optical path from the fixed mirror to the diffraction grating is perpendicular to the diffraction groove. The fixed mirror is arranged in
2. A wavelength swept light source, characterized in that light that has been returned from the diffraction grating through a reverse optical path and transmitted through the fixed mirror is emitted as output light.

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