External cavity resonator type turnable light source which can be easily manufactured and which is capable of wavelength sweeping at high speed

• US 20050220162A1
• Filed: 03/21/2005
• Published: 10/06/2005
• Est. Priority Date: 03/30/2004
• Status: Active Grant

• Current Assignee: Anritsu Corporation
• Original Assignee: Anritsu Corporation
• Inventors: Nakamura, Kenichi
• Granted Patent: US 7,496,118 B2
• Time in Patent Office: Days
• US Class Current: 372/92
• CPC Class Codes: H01S 5/02326 Arrangements for relative positioning of laser diodes and optical components, e.g. grooves in the mount to fix optical fibres or lenses
• CPC Class Codes: H01S 5/141 using a wavelength selective device, e.g. a grating or etalon H01S5/146 takes precedence
• CPC Class Codes: H01S 5/143 Littman-Metcalf configuration, e.g. laser - grating - mirror

Abstract

A collimator lens converts light beams emitted from a low reflectance facet of a semiconductor laser into parallel light beams. A diffraction grating receives and diffracts the light beams from the collimator lens at a predetermined incident position and a predetermined angle of a diffraction face on which a diffraction groove is provided. A turnable mirror has a mirror surface which is positioned to be opposed to the diffractance facet of the diffraction grating, make the diffracted light beams incident in a reverse optical path to the diffraction face of the diffraction grating again, and return the incident light beams to the semiconductor laser. A stationary mirror is allocated so as to make the light beams emitted from the semiconductor laser via the collimator lens incident from a predetermined direction to a predetermined position of the diffraction grating at the side of the mirror surface of a virtual plane extending the mirror surface of the turnable mirror and at the side of the diffraction face of a virtual plane extending the diffraction face of the diffraction grating.

Claims

1. An external cavity resonator type tunable light source comprising:

a semiconductor laser, at least one light emission facet of which has low reflectance facet;

a collimator lens which converts light emitted from the low reflectance facet of the semiconductor laser into parallel light beams;

a diffraction grating which receives and diffracts the light beams from the collimator lens at a predetermined incident position on and at a predetermined incident angle to a diffraction face on which a diffraction groove is provided;

a turnable mirror which has a mirror surface positioned to be opposed to the diffraction face of the diffraction grating, the mirror surface being adopted to receive diffracted light beams from the diffraction grating, make the received light beams incident to the diffraction face of the diffraction grating again in a reverse optical path, and return the incident light beams to the semiconductor laser, and which is formed so as to enable the reflection face to be reciprocally turned at a predetermined angle range and around an axis defined as a turning center, which is parallel to the diffraction groove and is on a plane extending the diffraction face of the diffraction grating wherein a resonator length determined depending on an optical path length from an effective end facet of the resonator to the turnable mirror surface via the diffraction grating is changed by turning of the turnable mirror surface to sweep a wavelength of the emitted light beams of the semiconductor laser; and

a stationary mirror allocated so as to make light beams emitted from the semiconductor laser via the collimator lens incident from a predetermined direction to a predetermined position of the diffraction grating at the side of the mirror surface of a virtual plane extending the turnable mirror surface and at the side of the diffraction face of a virtual plane extending the diffraction face of the diffraction grating,

wherein the semiconductor laser and the collimator lens are allocated at the side of the mirror surface of a virtual plane extending the turnable mirror surface, and an optical path length from the effective end facet of the resonator to the collimator lens, the stationary mirror, the predetermined position of the diffraction grating, and the turnable mirror surface is substantially equal to the resonator length.

2. An external cavity resonator type tunable light source according to claim 1, wherein the turnable mirror comprises:

a frame;

a reflection plate which is allocated inside of the frame and which has the mirror surface formed at least at one face side thereof;

a pair of link sections which extend so as to be arranged on one straight line from edge portions opposed to each other, of the frame, to outer edges of the reflection plate to link between the frame and the reflection plate, the link sections enabling torsional deformation along a lengthwise direction thereof; and

drive means for applying an external force to the reflection plate to cause the reflection plate to turn in the predetermined angle range around a line connecting centers of the pair of link sections defined as the turning center.

3. An external cavity resonator type tunable light source according to claim 2, wherein the drive means apply an external force in a cycle which corresponds to a resonance frequency of the reflection plate of the turnable mirror to cause the reflection plate to be reciprocated at the resonance frequency.

4. An external cavity resonator type tunable light source according to claim 1, wherein a relationship r=(L3+L4−

L2)/sin α

is established among;

a distance “

r”

from the turning center to the predetermined incidence position of the diffraction face of the diffraction grating;

a distance L2 from the turning center to the plane extending the mirror surface;

an optical path length L3 from the effective end facet of the resonator to the stationary mirror;

an optical path length L4 from the stationary mirror to the predetermined incident position of the diffraction face of the diffraction grating; and

a light incidence angle α

from the stationary mirror to the diffraction face of the diffraction grating.

5. An external cavity resonator type tunable light source according to claim 1, wherein the turnable mirror comprises:

a frame formed of an electrically conductive substrate, and formed of a top plate, a bottom plate, and a pair of side plates in a transversely rectangular frame shape;

a transversely rectangular shaped reflection plate which is allocated concentrically inside of the frame, and which has formed thereon a mirror surface for reflecting light beams at least at one face side thereof;

a pair of link sections which extend so as to be vertically arranged on one straight line from inner edge centers opposed to each other, of the top plate and the bottom plate of the frame to an upper edge center and a lower edge center of the reflection plate to link between the top plate or the lower plate of the frame and the reflection plate, the link sections being torsionally deformed to turn the reflection plate; and

drive means for applying an external force to the reflection plate to cause the reflection plate to turn in the predetermined angle range around a line connecting centers of the pair of link sections defined as the turning center.

6. An external cavity resonator type tunable light source according to claim 5, wherein the substrate is a silicon substrate.

7. An external cavity resonator type tunable light source according to claim 5, wherein the drive means include means for generating an electrostatic driving force as an external force applied to the reflection plate.

8. An external cavity resonator type tunable light source according to claim 5, wherein the drive means each include two electrode plates mounted via an insulating spacer on one or both of a pair of side plates of the frame in order to apply an external force to the reflection plate in an electrostatic manner.

9. An external cavity resonator type tunable light source according to claim 8, wherein the drive means each include means for applying signals V1, V2 whose phase are shifted by 180 degrees each other with respect to the two electrode plates while the frame is defined as a reference electric potential, and alternately generating an electrostatic attractive force between the two electrode plates and the end portion of the reflection plate, thereby causing the reflection plate to reciprocally turn.

10. An external cavity resonator type tunable light source according to claim 9, wherein a frequency of the signals V1, V2 is set so as to be substantially equal to the resonance frequency of the reflection plate which is mainly determined depending on a shape or a weight of the reflection plate of the turnable mirror and a torsional spring constant of the pair of link sections.

11. An external cavity resonator type tunable light source according to claim 5, wherein the drive means each include means for electromagnetically applying an external force as an external force applied to the reflection plate.

12. An external cavity resonator type tunable light source according to claim 11, wherein the means for electromagnetically applying an external force each include a combination of a magnetic plate fixed to the reflection plate and a coil which acts an electromagnetical force to the magnetic plate.

13. An external cavity resonator type tunable light source according to claim 11, wherein the means for electromagnetically applying an external force each include a combination of a magnet fixed to the reflection plate and a coil which acts an electromagnetical force to the magnet.

14. An external cavity resonator type tunable light source according to claim 12, wherein the drive means each include means for applying a half wave current in a cycle which is substantially equal to the resonance frequency of the reflection plate to the coil.

15. An external cavity resonator type tunable light source according to claim 13, wherein the drive means each include means for applying a full wave current in a cycle which is substantially equal to the resonance frequency of the reflection plate to the coil.

16. An external cavity resonator type tunable light source according to claim 1, wherein a configuration is provided so that the stationary mirror surface is in parallel to the diffraction groove of the diffraction grating and an optical path from the semiconductor laser to the reflection plate through the collimator lens, the stationary mirror, and the diffraction grating is on an identical plane.

17. An external cavity resonator type tunable light source according to claim 2, wherein the semiconductor laser and the collimator lens are allocated at an arbitrary position in a space in which the diffraction grating is included, from among two spaces partitioned by a plane extending the reflection face of the reflection plate, and a direction of the stationary mirror surface is set in accordance with the allocation position of the semiconductor laser and the collimator lens.

18. An external cavity resonator type tunable light source according to claim 17, wherein the semiconductor laser, the collimator lens and the stationary mirror are supported by a support member after being allocated to be vertically arranged with respect to a base so that optical axes thereof are parallel to the diffraction groove of the diffraction grating, light beams from the collimator lens are received on the stationary mirror surface which forms an angle of 45 degrees with respect to a top face of the base, and the received light beams are made incident to the diffraction face of the diffraction grating.

19. An external cavity resonator type tunable light source according to claim 2, wherein the frame of the turnable mirror is supported by a pair of support members stood at both ends of the top part of a flat base;

the diffraction grating is supported by another support member stood on the top part of the substrate;

the semiconductor laser, the collimator lens, and the stationary mirror are supported by a still another support member stood in the vicinity of the another support member.

20. An external cavity resonator type tunable light source according to claim 18, wherein, also at the other end side of the reflection plate, another semiconductor laser, another collimator lens, and another stationary mirror are supported by the another support members and the still another support member, thereby providing a configuration such that wavelength variable light beams can be emitted in a dual system manner.

21. An external cavity resonator type tunable light source according to claim 2, wherein the reflection plate is formed symmetrically on the left and right with respect to the pair of link sections, one end side of which is used as a light reflecting section, and the other end side is adopted to receive an external force.

22. An external cavity resonator type tunable light source according to claim 2, wherein the reflection plate of the turnable mirror reduces a length in a transverse direction at the other end side and increase a width corresponding to a length in a vertical direction thereof to ensure that left and right rotation moments are well balanced.

23. An external cavity resonator type tunable light source according to claim 2, wherein the drive means include means for generating an electrostatic driving force as an external force applied to the reflection plate.

24. An external cavity resonator type tunable light source according to claim 2, wherein the drive means each include two electrode plates mounted via an insulating spacer on one or both of a pair of side plates of the frame in order to apply an external force to the reflection plate in an electrostatic manner.

25. An external cavity resonator type tunable light source according to claim 24, wherein the drive means each include means for applying signals V1, V2 whose phase are shifted by 180 degrees each other with respect to the two electrode plates while the frame is defined as a reference electric potential, and alternately generating an electrostatic attractive force between the two electrode plates and the end portion of the reflection plate, thereby causing the reflection plate to reciprocally turn.

26. An external cavity resonator type tunable light source according to claim 25, wherein a frequency of the signals V1, V2 is set so as to be substantially equal to the resonance frequency of the reflection plate which is mainly determined depending on a shape or a weight of the reflection plate of the turnable mirror and a torsional spring constant of the pair of link sections.

27. An external cavity resonator type tunable light source according to claim 2, wherein the drive means each include means for electromagnetically applying an external force as an external force applied to the reflection plate.

28. An external cavity resonator type tunable light source according to claim 27, wherein the means for electromagnetically applying an external force each include a combination of a magnetic plate fixed to the reflection plate and a coil which acts an electromagnetic force to the magnetic plate.

29. An external cavity resonator type tunable light source according to claim 27, wherein the means for electromagnetically applying an external force each include a combination of a magnet fixed to the reflection plate and a coil which acts an electromagnetical force to the magnet.

30. An external cavity resonator type tunable light source according to claim 28, wherein the drive means each include means for applying a half wave current in a cycle which is substantially equal to the number of resonance frequency of the reflection plate to the coil.

31. An external cavity resonator type tunable light source according to claim 29, wherein the drive means each include means for applying a full wave current in a cycle which is substantially equal to the resonance frequency of the reflection plate to the coil.

32. An external cavity resonator type tunable light source according to claim 2, wherein the diffraction grating and the tunable mirror are structured to be stood on a base.