JP2006024876A - Wavelength scanning fiber laser light source - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a wavelength variable fiber laser light source capable of changing making the wavelengths at a high speed. <P>SOLUTION: An optical fiber loop is provided with a gain medium, having gain in an oscillation wavelength by an optical fiber to form a loop. This optical fiber loop is provided with an optical circulator 13. The light extracted by the optical circulator 13 is enlarged by a collimate lens 22, and a polygon mirror 24 is provided on the optical axis. The optical axis reflected by the polygon mirror 24 is formed into parallel light by a lens 25, and a mirror 27 is provided perpendicularly to the optical axis. Moreover, a band path filter 26 for continuously changing the selected wavelength in the scanning direction is provided between the mirror and the lens 25. Thus, the selected wavelength can be changed at a high speed by the rotation of the polygon mirror 24. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a wavelength scanning fiber laser light source that generates single light and periodically scans its emission wavelength.

  Conventionally, a broadband light source is used as a light source of an analysis apparatus that irradiates a measurement object with light and analyzes the measurement object. In the spectroscopic analysis, a method is widely used in which broadband light is projected onto a measurement target, and the reflected light or transmitted light is spatially decomposed into wavelength components by a grating or the like, or is analyzed by Fourier transform into frequency components by an interferometer. It has been. Examples of such a light source include a white light source and an ASE light source using erbium-doped fiber (EDF). However, in such spectroscopic analysis, since the light output intensity density with respect to the wavelength is low, the level of light that can be used in spectroscopy is small. For this reason, even if Fourier transform analysis is performed, the detection light signal is buried in noise, which makes it difficult to analyze.

  There is also a method of using a wavelength-variable light source that changes a single spectrum of a strong level in a desired band as a light source of the analyzer. In this method, the wavelength of light having strong single light is changed to irradiate the measurement object, and light that passes through or reflects the measurement object is received by the light receiving element as it is. In this method, since the light output intensity density with respect to the wavelength of the light source is high, the level of the detection light and the signal-to-noise ratio are sufficiently high, and sufficient measurement accuracy can be realized.

  Conventional wavelength tunable light sources include an external resonator laser and a fiber ring laser. The external resonator type laser uses a gain medium, for example, a semiconductor laser, forms an external resonator between one end face of the semiconductor laser and an external mirror, and a wavelength tunable filter such as a grating in the external resonator. By changing the oscillation wavelength, a wavelength-tunable light source is obtained. In the external resonator type laser light source, the external resonator type length is relatively small, for example, 50 mm, and the longitudinal mode interval is wide, for example, 30 GHz. Therefore, simply changing the wavelength of the tunable filter makes it unstable between the longitudinal modes. For example, discontinuous mode hops may occur between modes, or oscillation may occur in multiple modes. Therefore, in order to continuously change the wavelength in a single mode and stabilize the output, the external resonator length must be delicately controlled using a piezo element or the like, and complicated control is required. . In addition, there is a drawback that it is difficult to change the wavelength at high speed because the wavelength and the external resonator length are controlled in synchronization with the mechanical operation.

Non-Patent Document 1 also proposes a wavelength tunable light source using a ring laser using an erbium-doped fiber. In this method, an erbium-doped fiber (EDF) and a fiber amplifier that excites the erbium-doped fiber are used as a gain medium, and a wavelength-variable band-pass filter is provided between the optical fiber loops to change the wavelength of the band-pass filter. Thus, a tunable light source is obtained. In this case, since the resonator length of the optical fiber loop can be increased to, for example, 30 m, the longitudinal mode interval can be reduced. Therefore, the influence of the mode hop can be eliminated without changing the resonator length. Therefore, although it is not strictly single mode oscillation, it is possible to tune the wavelength continuously in a pseudo manner simply by changing the selected wavelength of the bandpass filter.
YAMASHITA ET AL., IEEE JOURAL ON SELECTED TOPICS IN QUANTUM ELECTRONICS, VOL.7, NO.1 JANUARY / FEBRUARY 2001, PP41 ~ 43

  When using a wavelength tunable light source as a light source for an analyzer, it is necessary to change the wavelength at high speed and to narrow the width of the oscillation spectrum, and characteristics corresponding to this are also required for the bandpass filter. . For example, when high-speed wavelength scanning is available in optical coherent tomography (OCT), dynamic analysis such as high-speed image processing, blood flow observation, and oxygen saturation concentration change can be performed. Is required. However, there has been no wavelength laser light source capable of high-speed scanning that follows the image display frame rate.

  In the conventional filter technology, it is difficult to obtain a high-speed wavelength variable characteristic and a high Q value at the same time. For example, a wavelength tunable filter using the photoacoustic optical effect (AO) has a drawback that the suppression ratio other than the transmission wavelength is not sufficient, and stable oscillation cannot be performed. Further, when a Fabry-Perot etalon is formed using a piezo element as a bandpass filter, there is a problem that the wavelength variable speed is as low as several Hz or less and there is hysteresis. In addition, when a grating is used for the bandpass filter, there is a disadvantage that adjustment of the optical axis is difficult and expensive. Further, although an optical interference filter may be used as a bandpass filter, there is a drawback that the spectrum cannot be narrowed much because the Q of the filter is low only by passing the filter once.

  The present invention has been made in order to eliminate such drawbacks, and an object of the present invention is to provide a wavelength scanning type fiber laser light source capable of scanning the wavelength of a light source having a narrow band spectrum at high speed.

  In order to solve this problem, a wavelength scanning fiber laser light source according to the present invention includes an optical fiber serving as a laser oscillation optical path, a gain medium connected to the optical fiber and having a gain at the oscillation wavelength, and the optical fiber. And a wavelength tunable optical filter that continuously varies the wavelength, wherein the wavelength tunable filter periodically changes the reflection angle of the light beam obtained from the optical fiber within a certain range. , A first optical element that converts light from the light beam deflecting section into parallel scanning light, and a selection wavelength continuously changing along a scanning direction of light emitted from the first optical element And a second optical element that reflects light transmitted through the optical filter in the same direction.

  Here, the optical fiber is formed in a loop shape, and may further include an optical coupler that is connected to the optical fiber and extracts a part of light passing through the optical fiber.

  Here, the gain medium may be an optical fiber amplifier constituting a part of the loop of the optical fiber.

  Here, it has first to third terminals, the first and second terminals are connected to an optical fiber loop, the third terminal is connected to the wavelength tunable filter, and is incident on each terminal. You may make it further have the optical circulator which controls the direction of light.

  Here, the optical fiber loop may include a polarization-preserving optical fiber.

  Here, the gain medium may be connected to one end of the optical fiber, and the wavelength tunable filter may be connected to the other end of the optical fiber.

  Here, the gain medium may be a semiconductor optical amplifier that amplifies light.

  Here, an optical coupler connected to the optical fiber and extracting a part of the light passing through the optical fiber may be further provided.

  Here, the optical fiber may further include a polarization controller that regulates the polarization direction of light passing through the optical fiber in a fixed direction.

  Here, one end of the gain medium may be connected to the optical fiber, and light may be extracted from the other end.

  Here, the light beam deflecting unit of the wavelength tunable filter is disposed on the optical axis emitted from the optical fiber, and includes a polygon mirror having a plurality of reflecting surfaces that change a reflection angle of light by rotation, and the polygon mirror. And a drive unit that rotates to control the reflection angle of light.

  Here, the light beam deflecting unit of the wavelength tunable filter is disposed on the optical axis emitted from the optical fiber, and rotates the flat mirror that changes the reflection angle of light by rotation and the flat mirror within a certain angle range. And a galvanometer to be moved.

  Here, the first optical element of the wavelength tunable filter may be a lens system in which the deflected light from the light deflecting unit is in a certain direction.

  Here, the first optical element of the wavelength tunable filter may be a concave mirror that reflects the deflected light from the light deflecting unit in the same direction.

  Here, the second optical element of the wavelength tunable filter may be a second mirror having a reflecting surface arranged perpendicular to the optical axis of the light transmitted through the optical filter.

  Here, the second optical element of the wavelength tunable filter may be a prism that reflects light parallel to the optical axis of the light transmitted through the optical filter.

  According to the present invention having such characteristics, the optical path length is increased by using the optical fiber as the optical path length of laser oscillation, and the oscillation wavelength is changed by the wavelength variable filter. The wavelength tunable filter deflects light by the light beam deflecting unit, changes the light into parallel scanning light, and then passes through the optical filter. The wavelength tunable filter forms part of the optical path length by transmitting light in the same direction by the second optical element, and the oscillation wavelength can be determined by the selected wavelength. Accordingly, the wavelength can be varied by continuously changing the selection wavelength of the optical filter, and the laser light passes through the optical filter twice, so that the laser light having a narrow emission spectrum can be oscillated. Then, by making the deflection speed of the light beam deflecting part sufficiently high, an effect that wavelength can be varied at high speed can be obtained.

FIG. 1 is a diagram showing a configuration of a wavelength scanning fiber laser light source according to an embodiment of the present invention. The wavelength scanning fiber laser light source 10 of the present embodiment includes an optical fiber 11 to form a loop. A gain medium 12, an optical circulator 13, an optical coupler 14, and a polarization controller 15 are provided in a part of this loop. The gain medium 12 includes an erbium-doped fiber 16 doped with erbium ions (Er ³⁺ ) provided in a part of an optical fiber loop, and a fiber-pumped semiconductor laser 17 that makes pump light incident on the erbium-doped fiber 16. And a WDM coupler 18. This optical fiber loop is assumed to have a length of 30 to 50 m, for example. The pumping semiconductor laser 17 has a wavelength of 1480 nm or 980 nm, for example, and amplifies the light transmitted through the erbium-doped fiber 16. The optical circulator 13 regulates the direction of light passing through the optical fiber 11 in the direction of the arrow as shown. That is, the input terminals 13a and 13b of the optical circulator 13 are connected to the optical fiber loop, and the light incident from the input terminal 13a is emitted from the terminal 13c of the optical circulator. The light incident from the optical circulator 13c is emitted from the terminal 13b. Light incident from the terminal 13b is emitted from the terminal 13a. The optical coupler 14 extracts a part of the light in the optical fiber loop, and the polarization controller 15 defines the polarization direction of the light transmitted through the optical fiber loop in a certain direction.

  The terminal 13c of the optical circulator 13 is connected to the collimating lens 22 through the optical fiber 21 as illustrated. The collimating lens 22 converts the light from the optical fiber 21 into parallel light, and a polarizer 23 and a polygon mirror 24 are disposed on the optical axis. The polygon mirror 24 reflects parallel light by changing the angle within the range shown in the drawing by rotating it along an axis perpendicular to the paper surface as shown. A cylindrical lens 25, a band pass filter 26, and a mirror 27 are provided on the optical axis of the reflected light. As shown in the figure, the cylindrical lens 25 refracts the reflected light so that it is always in a fixed direction regardless of the rotation angle of the polygon mirror 24. The mirror 27 has a reflecting surface perpendicular to the optical axis emitted from the cylindrical lens 25. The bandpass filter 26 is an optical interference type dielectric multilayer filter in which a large number of dielectric multilayer films are stacked, and the optical film thickness of the multilayer film is changed with respect to the scanning direction of the illustrated light to continuously change the selection wavelength. Configured to let For example, the selected wavelength is in the range of 1500 to 1600 nm. The filter 26 is disposed slightly inclined with respect to the optical axis in order to prevent the reflected light from entering the collimating lens 22 again. The drive unit 28 rotates the polygon mirror 24 at a constant speed. The polarizer 23 defines the polarization direction of light transmitted between the collimating lens and the polygon mirror 24 in a predetermined direction. Here, the polygon mirror 24 and the drive unit 28 constitute a light beam deflecting unit that periodically changes the reflection angle of the light beam obtained from the optical fiber within a certain range. The cylindrical lens is a first optical element that converts deflected light into parallel scanning light, and the mirror 27 is a second optical element that reflects light that passes through the optical filter in the same direction.

  The length of the optical fiber loop needs to be selected such that a plurality of longitudinal modes are included in the full width at half maximum of the bandpass filter 26. The number of longitudinal modes is preferably 10 or more, more preferably 100 or more, and the greater the number. However, in order to increase the longitudinal mode, it is necessary to lengthen the optical fiber, and an optical fiber having a length of several tens of meters is practically used.

  Next, the operation of this embodiment will be described. In this embodiment, the above-described pumping semiconductor laser 17 is driven to pump the optical fiber loop through the WDM coupler 18. FIG. 2A shows the gain of the gain medium 12. In this way, light added from the terminal 13 a by the action of the optical circulator 13 enters the optical fiber 21 from the terminal 13 c and becomes parallel light by the collimating lens 22. Then, the light is reflected at a position shown by a solid line in FIG. 1 according to the rotational position of the polygon mirror 24 and converted into an optical axis perpendicular to the reflecting surface of the mirror 27 by the cylindrical lens 25. Light having a wavelength that passes through the bandpass filter 26 enters the mirror 27, is reflected by the mirror 27, and is added to the collimating lens 22 via the bandpass filter 26, the cylindrical lens 25, and the polygon mirror 24 again. Further, the light is added to the optical fiber loop from the optical circulator 13 through the collimator lens 22. The polarization controller 15 adjusts the polarization of light transmitted through the optical fiber loop in a certain direction. FIG. 2B shows the external resonance longitudinal mode determined according to the optical length determined by the length of the optical fiber loop and the refractive index of the optical fiber. For example, when the optical length is 30 m, there are longitudinal modes with an interval of about 10 MHz. Here, the curve A in FIG. 3 is a diagram showing the transmission characteristics of the band-pass filter 26 once, and the curve B is a diagram showing the characteristics of the band-pass filter narrowed by two transmissions. FIG. 2 (c) shows the filter characteristic B1 due to the two transmissions. The wavelength selected by transmitting through the filter includes a plurality of longitudinal modes as shown in FIG. 2 (d). Mode oscillation occurs. The oscillation wavelength is, for example, 1500 nm. A part of the laser light oscillated in the optical fiber loop in this way, for example, light having a level of 90% of the laser light is extracted through the optical coupler 14. Optical signals in multimode oscillation are a problem when transmitted by optical wavelength division multiplexing. However, in spectral analysis, optical fiber sensing, optical component evaluation, etc., the oscillation line width (strictly, in multimode oscillation) If the half-value width of the envelope of the spectrum is sufficiently narrower than the resolution of the object to be measured, this is not a problem. The length of the optical fiber 11 is selected so that a plurality of modes, preferably at least 10 or more, and more preferably 100 or more modes can stand within the full width at half maximum of the optical filter.

  Then, the polygon mirror 24 is rotated by the drive unit 28. In this way, the reflected light from the polygon mirror 24 is scanned to the center of the cylindrical lens 25 as indicated by the broken line in FIG. 1, and further to the position indicated by the arrow. As a result, the transmission wavelength of the band-pass filter 26 changes as B1 to B2 to B3 in FIG. By rotating the polygon mirror 24, the selected wavelength can be changed at a scanning speed of several KHz within a range of 100 nm, for example. For example, when the rotational speed of the polygon mirror 24 is 30,000 rpm and the number of reflection surfaces of the polygon mirror 24 is 12, the oscillation wavelength of the fiber laser light source can be changed at a scanning speed of 15.4 KHz. FIG. 4 is a graph showing temporal changes in the oscillation wavelength, where the oscillation wavelength changes in a sawtooth shape.

  In the case of the oscillation according to this embodiment, the oscillation is in a multimode state as shown in FIG. However, as shown in FIG. 2B, since the longitudinal mode interval is extremely narrow and the mode hop is fast and fast, there is no adverse effect associated with the mode hop as in the case of an external cavity semiconductor laser, and the oscillation wavelength can be changed. Can do. Further, by using the polygon mirror, an effect that the fiber laser light source can be put into practical use at a relatively low cost can be obtained.

  Here, as shown in FIG. 1, the optical axis between the cylindrical lens 25 and the mirror 27 is shifted left and right by the rotation of the polygon mirror 24. However, the light reflected by the mirror 27 passes through the same optical path through the band pass filter 26 and is reflected by the polygon mirror 24 and enters the collimating lens 22. Therefore, in this embodiment, since the band-pass filter 26 is transmitted twice, the wavelength selectivity is improved. Furthermore, the light emitted from the optical fiber 21 and the light incident on the optical fiber 21 have the same optical axis. Therefore, even if the angle of the polygon mirror 24 changes, the coupling loss does not change, and the loss can be flattened over the entire wavelength range. Therefore, the gain band of the gain medium can be used more effectively and the output wavelength range can be widened. For this reason, there is no change in the output level accompanying a change in the angle of the bandpass filter.

  On the other hand, FIG. 5 shows a wavelength scanning fiber laser light source shown as a comparative example of the present embodiment. In this comparative example, a band pass filter 33 is inserted directly into the optical fiber loop via the collimating lenses 31 and 32 instead of the circulator. Other configurations are the same as those of the present embodiment. FIG. 6 is a diagram showing changes in the optical axes of the collimating lenses 31 and 32 and the bandpass filter 33 in this case. When the bandpass filter 33 is rotated by the galvanometer 34 and the selected wavelength is changed, the optical axis fluctuates left and right depending on the angle of the filter as shown in FIG. 6, so the level of light incident on the optical fiber changes. Therefore, there is a problem that the loss in the resonator fluctuates over the wavelength change region and the output level changes according to the wavelength. In contrast, this embodiment can eliminate such a problem.

  In this embodiment, the cylindrical lens 25 is used as the lens. However, an fθ lens having a telecentric function for converting the rotation angle vertically in proportion to the angle can be used. When this fθ lens is used and a bandpass filter whose wavelength changes in a curve according to the scanning axis of light is used as the optical bandpass filter, as shown in FIG. 4, the change in wavelength with respect to time is linear and Sawtooth can be wavy.

  FIG. 7 is a diagram showing a wavelength scanning fiber laser light source according to the second embodiment of the present invention. In this embodiment, a semiconductor optical amplifier (SOA) 41 is used as a gain medium in a part of the optical fiber loop. In the fiber loop, a loop is formed only by the ordinary optical fiber 11. Further, 15a and 15b are inserted as polarization controllers. Other configurations are the same as those of the first embodiment. The semiconductor optical amplifier 41 has output surfaces at both ends, and amplifies light by injecting current. However, there is no specific resonance wavelength, and an optical fiber is connected to both ends as in the present embodiment. As a result, the external resonance mode shown in FIG. 2B is obtained. Similarly to the first embodiment, a polygon mirror 24, a lens 25, a band pass filter 26, and the like are connected through the optical circulator 13. In this way, oscillation can be obtained at the wavelength of the bandpass filter 26 as in the above-described embodiment. By rotating the polygon mirror 24, the oscillation wavelength can be changed at high speed.

  FIG. 8 shows a wavelength scanning fiber laser light source according to the third embodiment of the present invention. In this embodiment, a fiber laser light source loop is formed by using a polarization-maintaining optical fiber 42 in the optical fiber loop. In this embodiment as well, the semiconductor optical amplifier 41 is used as a gain medium, as in the second embodiment. Also, the use of the optical circulator 13 and the optical coupler 14 is the same as in the above-described embodiment. In this embodiment, since the polarization plane preserving optical fiber 42 is used, the polarization plane of light oscillating around the loop is constant in a predetermined direction. Other configurations are the same as those of the above-described embodiment, and similar effects can be obtained with a relatively simple configuration.

  FIG. 9 is a diagram showing a wavelength scanning fiber laser light source according to the fourth embodiment of the present invention. In this embodiment, instead of the polygon mirror of the first embodiment, a flat mirror 43 is used as shown in FIG. The galvanometer 44 is a drive unit that rotates the mirror 43. In this case as well, the light reflected by the mirror 43 is converted into parallel light regardless of the scanning direction by the cylindrical lens 25 and reflected by the second mirror 27 via the band pass filter 26. Other configurations are the same as those of the first embodiment. In this case, the wavelength changes depending on the driving angle of the flat mirror 43 by the galvanometer 44. Therefore, a triangular wave-like wavelength change can be obtained instead of the sawtooth waveform shown in FIG.

  FIG. 10 shows a wavelength scanning fiber laser light source according to the fifth embodiment of the present invention. In this embodiment, a concave mirror 51 is used as the first optical element as shown in FIG. 10 in place of the fθ lens of the first embodiment. Other configurations are the same as those of the first embodiment. Also in this case, as in the first embodiment, the light reflected by the mirror 51 is converted into parallel light regardless of the scanning direction, and reflected by the second mirror 27 via the bandpass filter 26. Also in this case, the reflection angle of the light is changed by rotating the polygon mirror 24 and converted into light scanned in the same direction by the mirror 51. By so doing, it is possible to oscillate at a wavelength selected by the bandpass filter 26.

  FIG. 11 is a perspective view of a wavelength tunable optical filter portion of a wavelength scanning fiber laser light source according to a sixth embodiment of the present invention. The description of the same parts as those of the first embodiment described above is omitted in the description, and the wavelength variable filter part is different as shown. In this embodiment, collimating lenses 61 and 62 are connected to both ends of the filter loop without using an optical circulator. The collimating lenses 61 and 62 are arranged in parallel toward the polygon mirror 24. The collimating lens 61 irradiates the polygon mirror 24 with light incident from the optical fiber 11 as parallel light. The polygon mirror 24 is driven by the drive unit 28. At this time, the reflected light of the polygon mirror 24 is refracted by the cylindrical lens 25 and is incident on the band pass filter 26 and the triangular prism 63. The prism 63 is a second optical element that reflects light transmitted through the optical filter in the same direction, and is arranged in parallel with the bandpass filter 26. The light reflected by the prism 63 is vertically shifted from the scanning direction indicated by the arrow, and is added to the polygon mirror 24 again through the band pass filter 26 and the cylindrical lens 25 in parallel with the incident light. Then, the reflected light enters the collimating lens 62 through an isolator (not shown), and further returns to the optical fiber loop through the collimating lens 62.

  In this way, laser light can be emitted at a wavelength selected by the bandpass filter 26. By rotating the polygon mirror 24, the reflected light deflected from the polygon mirror 24 becomes parallel scanning light by the cylindrical lens as shown in the figure, and the oscillation wavelength can be changed. In this way, as described above, the incoming and outgoing light can be separated without using an optical circulator, and high-speed wavelength scanning can be performed at low cost.

  Next, a seventh embodiment of the present invention will be described with reference to FIGS. In this embodiment, the optical fiber is not in a loop shape, and an optical resonator is configured by using a gain medium, an optical fiber, and a wavelength tunable filter unit. As the gain medium 71, a semiconductor optical amplifier (SOA), a Fabry-Perot semiconductor laser (FPLD), a super luminescent laser diode (SLD), or the like is used as shown in FIG. Then, one surface 71a of the gain medium 71 is a high reflection film, for example, a reflection film having a reflectance of about 80 to 100%, the other surface 71b is a low reflection film, and light transmitted through the surface 71b is passed through the collimating lens 72. To the optical fiber 73. A polarization controller 74 is connected to the optical fiber 73, and the wavelength tunable filter unit 76 of any of the above-described embodiments is provided at the other end. The wavelength tunable filter unit 76 may be configured by the polygon mirror 24, the cylindrical lens 25, the band pass filter 26, and the mirror 27 as in the first embodiment. Further, as in the fourth embodiment, a galvano mirror 43 may be used in place of the polygon mirror 24, and a concave mirror 51 is used in place of the cylindrical lens as in the fifth embodiment. It may be. An optical coupler 75 is attached to the optical fiber 73 so that a part of the laser light is emitted to the outside. Here, the optical fiber 73 is used for sufficiently increasing the optical path length. It is necessary to select the length of the optical fiber 73 such that a plurality of longitudinal modes are included in the full width at half maximum of the bandpass filter 26. The number of longitudinal modes is preferably 10 or more, more preferably 100 or more, and the greater the number. However, in order to increase the longitudinal mode, it is necessary to lengthen the optical fiber, and an optical fiber having a length of several tens of meters is practically used.

  The surface 71a of the gain medium 71 may also be a low reflection film, and a total reflection mirror may be provided on the outside thereof. In this case, the optical path is configured by the total reflection mirror and the wavelength variable filter unit 76.

  Next, an eighth embodiment will be described with reference to FIGS. In this embodiment, as shown in FIG. 15, the reflectance of one surface 81a of the gain medium 81 is lowered, and the light of the gain medium 81 is extracted from one end thereof. A collimating lens 82 and an output optical fiber 83 are provided on the surface 81a of the gain medium. For this reason, the optical coupler for taking out light becomes unnecessary. Other configurations are the same as those of the seventh embodiment.

  In each of the above-described embodiments, a polygon mirror or a galvanometer mirror is used as the light beam deflecting unit. However, it is only necessary to change the reflection angle at high speed, and the present invention is not limited to these configurations. Further, the lens used in the present embodiment may be configured by a lens system (system lens) including a plurality of lenses, instead of a single lens.

  The present invention can change the wavelength at high speed while improving the wavelength selection characteristic of the optical filter. Further, since no grating is used, it can be realized at a relatively low cost. Therefore, the present invention can be applied to medical analysis equipment, for example, a high resolution medical image diagnostic apparatus for the epidermis layer. When measuring strain using a fiber grating sensor, the wavelength scanning fiber laser light source of the present invention can be used as a light source.

It is the schematic which shows the wavelength scanning fiber laser light source by the 1st Embodiment of this invention. It is a graph which shows the gain of the gain medium of the optical fiber laser light source of this Embodiment, an oscillation mode, a band pass filter, and an oscillation output. It is a graph which shows the characteristic of the band pass filter of this Embodiment. It is a graph which shows the time change of the oscillation wavelength of this Embodiment. It is the schematic of the wavelength scanning fiber laser light source by a comparative example. It is a figure which shows the angle of the band pass filter by a comparative example, and the change of an optical axis. It is the schematic which shows the wavelength scanning fiber laser light source by the 2nd Embodiment of this invention. It is the schematic which shows the wavelength scanning fiber laser light source by the 3rd Embodiment of this invention. It is the schematic which shows the wavelength scanning fiber laser light source by the 4th Embodiment of this invention. It is the schematic which shows the wavelength scanning fiber laser light source by the 5th Embodiment of this invention. It is a perspective view which shows the structure of the filter part of the wavelength scanning fiber laser light source by this Embodiment. It is the schematic which shows the wavelength scanning fiber laser light source by the 7th Embodiment of this invention. It is a figure which shows the detail of the gain medium by this Embodiment. It is the schematic which shows the wavelength scanning fiber laser light source by the 8th Embodiment of this invention. It is a figure which shows the structure of the gain medium by this Embodiment, and its peripheral part.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Wavelength scanning fiber laser light source 11,73 Optical fiber 12,71,81 Gain medium 13 Optical circulator 14 Coupler 15,74 Polarization controller 16 Erbium doped fiber 17 Semiconductor laser 18 WDM coupler 21 Optical fiber 22,61,62 Collimate Lens 23 Polarizer 24 Polygon mirror 25 Cylindrical lens 26 Band pass filter 27, 51 Mirror 28 Drive unit 41 Semiconductor optical amplifier 42 Polarization plane preserving optical fiber 43 Mirror 44 Galvanometer 63 Prism 76 Wavelength variable filter unit

Claims (16)

An optical fiber serving as a laser oscillation optical path;
A gain medium connected to the optical fiber and having a gain at the oscillating wavelength;
A tunable optical filter connected to the optical fiber and continuously tunable in wavelength,
The tunable filter is
A light beam deflecting unit that periodically changes a reflection angle of a light beam obtained from the optical fiber within a certain range;
A first optical element that converts light from the light beam deflection unit into parallel scanning light;
An optical filter disposed so that the selection wavelength continuously changes along the scanning direction of the light emitted from the first optical element;
A wavelength-scanning fiber laser light source, comprising: a second optical element that reflects light transmitted through the optical filter in the same direction. The optical fiber is formed in a loop shape,
2. The wavelength scanning fiber laser light source according to claim 1, further comprising an optical coupler connected to the optical fiber and extracting a part of light passing through the optical fiber.   3. The wavelength scanning fiber laser light source according to claim 2, wherein the gain medium is an optical fiber amplifier constituting a part of a loop of the optical fiber.   Having first to third terminals, the first and second terminals being connected to a loop of an optical fiber, the third terminal being connected to the wavelength tunable filter, and light incident on each terminal 3. The wavelength scanning fiber laser light source according to claim 2, further comprising an optical circulator for controlling a direction.   The wavelength scanning fiber laser light source according to claim 2, wherein the optical fiber loop includes a polarization-preserving optical fiber.   2. The wavelength scanning fiber laser light source according to claim 1, wherein the gain medium is connected to one end of the optical fiber, and the wavelength tunable filter is connected to the other end of the optical fiber.   7. The wavelength scanning fiber laser light source according to claim 1, wherein the gain medium is a semiconductor optical amplifier that amplifies light.   The wavelength scanning fiber laser light source according to any one of claims 1 and 6, further comprising an optical coupler connected to the optical fiber and extracting a part of light passing through the optical fiber.   7. The wavelength scanning fiber according to claim 1, wherein the optical fiber further includes a polarization controller that regulates a polarization direction of light passing through the optical fiber in a fixed direction. Laser light source.   The wavelength scanning fiber laser light source according to claim 6, wherein one end of the gain medium is connected to the optical fiber and light is extracted from the other end. The light beam deflecting portion of the wavelength tunable filter is
A polygon mirror disposed on the optical axis emitted from the optical fiber and having a plurality of reflecting surfaces that change the reflection angle of light by rotation;
The wavelength scanning fiber laser light source according to claim 1, further comprising: a driving unit that controls a reflection angle of light by rotating the polygon mirror. The light beam deflecting portion of the wavelength tunable filter is
A flat mirror that is disposed on the optical axis emitted from the optical fiber and changes a reflection angle of light by rotation;
The wavelength scanning fiber laser light source according to claim 1, further comprising: a galvanometer that rotates the flat mirror within a certain angle range. The first optical element of the wavelength tunable filter is:
2. The wavelength scanning fiber laser light source according to claim 1, wherein the wavelength scanning fiber laser light source is a lens system in which deflected light from the light deflecting unit is in a fixed direction. The first optical element of the wavelength tunable filter is:
2. The wavelength scanning fiber laser light source according to claim 1, wherein the wavelength scanning fiber laser light source is a concave mirror that reflects the deflected light from the light deflecting unit in the same direction. The second optical element of the tunable filter is
2. The wavelength scanning fiber laser light source according to claim 1, wherein the second scanning mirror is a second mirror having a reflecting surface arranged perpendicular to the optical axis of the light transmitted through the optical filter. The second optical element of the tunable filter is
2. The wavelength scanning fiber laser light source according to claim 1, wherein the wavelength scanning fiber laser light source is a prism that reflects light parallel to an optical axis of light transmitted through the optical filter.

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