JP2008153379A - Wavelength detecting device, and wavelength detecting method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a wavelength detecting device and a wavelength detecting method, in which the size of device will not be enlarged even when a minute wavelength over wide range is to be detected. <P>SOLUTION: The wavelength detecting device 1A is equipped with an external resonator type semiconductor laser 10 for emitting the laser light PL (photo luminescence), a wavelength detecting unit 20 which detects the minute change of the wavelength of laser light PL and discriminates the wavelength of the laser light PL over wide range to output a detecting signal SD and a laser control unit 27 which feedbacks a control signal CT produced based on the detecting signal SD to the external resonator type semiconductor laser 10. The wavelength detecting unit 20 comprises a grating 2A which effects the diffraction of one part of the laser light PL or a light beam PR and a light detector 3A which receives the light beam diffracted by the grating 2A and outputs a detecting signal SD. The wavelength detecting unit 20 detects the wavelength of the laser light PL based on a setting of a distance between the grating 2A and the light detector 3A and the setting of the grating pitch of the grating 2A. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a wavelength detection device and a wavelength detection method, and more specifically to a wavelength detection device and a wavelength detection method for stabilizing the oscillation mode of an external cavity semiconductor laser.

  Research and development of hologram recording devices that record data using holography is ongoing. In the hologram recording apparatus, two of modulated signal light and unmodulated reference light are generated from laser light, and these are irradiated to the same location of the hologram recording medium. Thereby, the signal light and the reference light interfere on the hologram recording medium, and a diffraction grating (hologram) is formed at the irradiation point. As a result, data is recorded on the hologram recording medium. When the signal light is modulated, data is superimposed on the signal light.

  By irradiating the recorded hologram recording medium with reference light, diffracted light (reproduced light) is generated from the diffraction grating formed during recording. Since the reproduction light includes data superimposed on the signal light at the time of recording, the recorded signal can be reproduced by receiving the data with a light receiving element.

  A light source for hologram recording / reproduction requires a single-mode laser light source with extremely good coherency, such as a gas laser or SHG (Second Harmonic Generation) laser. Since a normal laser diode is a multimode, it is not sufficient as a light source for hologram recording and reproduction in terms of coherency.

  However, if the laser diode is configured as an external resonance laser, a light source for hologram recording / reproduction with good coherency can be realized. A blue laser diode that is small and power-saving can also be used as a hologram light source by adopting an external resonance type.

  What is important when using laser light for hologram recording is wavelength reproducibility. In particular, when performing wavelength multiplexing for recording information by changing the wavelength, the wavelength of the output light must be controlled to the intended length. When wavelength multiplexing is performed, for example, a wavelength variable type external resonator laser can be used.

  As an external resonator in the external resonator laser, for example, there is a Littrow type. In such an external resonator, first, a laser beam emitted from a laser diode is converted into parallel light by a collimating lens, and is irradiated onto a reflective diffraction grating. The light beam reflected by the diffraction grating is separated into zero-order light and first-order light. The primary light passes through the incoming optical path as it is and returns to the laser diode.

  As described above, the external cavity laser is composed of a laser diode and a reflective diffraction grating. The laser diode oscillates at a wavelength determined by the grating shape of the reflective diffraction grating and the distance between the reflective diffraction grating and the laser diode. A means for detecting the wavelength of such a laser light source is disclosed in Patent Document 1, for example. In Patent Document 1, the wavelength of light is detected using a simplified device. Specifically, it is as follows.

FIG. 13 is a diagram showing a schematic configuration of a conventional semiconductor laser system 100.
Referring to FIG. 13, a conventional semiconductor laser system 100 includes an external resonator type semiconductor laser 50, a wavelength detection unit 101, and a laser control unit 110. The wavelength detection unit 101 includes light detection units 102 and 103. The light detection unit 102 includes an optical wedge 104 and a two-divided photodetector 106. The light detection unit 103 includes an optical wedge 105 and a two-divided light detector 107.

  The external resonator type semiconductor laser 50 outputs laser light PL whose wavelength is controlled to the light detection units 102 and 103. The optical wedge 104 reflects a part of the laser beam PL as a light beam PR1. The optical wedge 105 reflects a part of the laser light PL that has passed through the optical wedge 104 as a light beam PR2. The laser beam PT that has passed through the optical wedge 105 is output to the outside.

  The optical wedges 104 and 105 are made of a glass plate whose angle between both surfaces is several tens of minutes. When the laser light is incident on the optical wedges 104 and 105 with an inclination of about 45 degrees, the light reflected by the front and back surfaces of the glass plate forms interference fringes. The optical wedges 104 and 105 generate interference fringe patterns having different thicknesses on the two-divided photodetectors 106 and 107 with different movement amounts of the fringes with respect to wavelength changes. As a result, as described below, oscillation wavelength detection is performed with different sensitivities and wavelength ranges.

  The two-split photodetector 106 detects an interference fringe pattern by the light beam PR1 and outputs a detection signal S1. The two-divided photodetector 106 detects a wavelength variation of a minute wavelength change (a range of about 0.01 nm) due to a laser power variation. The fluctuation of the laser power is caused by the mode hop of the laser chip, for example. The two-split photodetector 107 detects an interference fringe pattern by the light beam PR2 and outputs a detection signal S2. The two-divided photodetector 107 performs wavelength detection in a relatively wide range of the oscillating wavelength range (several nm) of the external cavity semiconductor laser 50. The functions of the two-split photodetectors 106 and 107 may be reversed.

  The laser control unit 110 receives the detection signals S <b> 1 and S <b> 2 and feeds back the control signal CT to the external resonator type semiconductor laser 50. As described above, the semiconductor laser system 100 detects the oscillation wavelength of the external cavity semiconductor laser 50 and performs wavelength feedback and wavelength control by the laser control unit 110. Next, a specific configuration and operation of the external cavity semiconductor laser 50 will be described.

  FIG. 14 is a diagram showing a schematic configuration of an external resonator type semiconductor laser 50 in the conventional semiconductor laser system 100.

  Referring to FIG. 14, external resonator type semiconductor laser 50 includes a laser diode 51, a collimating lens 52, a wavelength controlling diffraction grating 53, and a diffraction grating rotating mechanism 54. The laser diode 51 emits multimode laser light, for example, blue laser light of about 405 nm. The collimating lens 52 makes the laser beam PA emitted from the laser diode 51 parallel light.

  The wavelength control diffraction grating 53 receives the laser beam PA and generates primary light in different directions for each wavelength. The angle with respect to the laser diode 51 is set so that the primary light having a specific wavelength (for example, 405 nm) returns to the laser diode 51. Thereby, only the wavelength component is amplified in the laser diode 51, and the laser beam PA becomes a single mode.

  The diffraction grating rotating mechanism 54 controls the oscillation wavelength of the laser diode 51 by adjusting the angle of the wavelength control diffraction grating 53. The zero-order light (reflected light) PL of the wavelength controlling diffraction grating 53 is emitted from the external resonator type semiconductor laser 50 as output light.

  FIG. 15 is a diagram showing the relationship between the laser power and wavelength of the laser beam PT output from the semiconductor laser system 100 of FIG.

  In FIG. 15, the horizontal axis of the graph indicates laser power (mW), and the horizontal axis of the graph indicates wavelength (nm). As shown in FIG. 15, as the laser power of the laser beam PT increases, the wavelength of the laser beam PT shows a substantially sawtooth change.

  In the semiconductor laser system 100, an external cavity mode hop region in which the wavelength of the laser beam PT gradually increases as the laser power increases, and a laser in which the wavelength of the laser beam PT rapidly decreases when the laser power increases. There is a chip mode hop region. As the two mode hop regions coexist in this way, the wavelength of the laser beam PT changes discretely to some extent as the laser power increases as shown in FIG.

  Since the mode hop by the laser chip is about 0.04 nm, good hologram recording is impossible. Therefore, in the semiconductor laser system 100, as described with reference to FIG. 13, the wavelength detection unit 101 having two detection systems detects the wavelength in the range of several tens of pm to several nm to stabilize the oscillation wavelength. ing.

The laser light source device of Patent Document 2 uses optical wedge interference light for detecting minute wavelength changes (in the range of about 0.01 nm) as in Patent Document 1, and wavelength control for detecting wavelength changes of several nm. The incident position of the reflected light of the diffraction grating for use is detected.
JP 2006-10499 A JP 2006-114183 A

  The conventional semiconductor laser system 100 described with reference to FIGS. 13 to 15 detects the wavelength of the laser beam PT with two detection systems. Specifically, an optical wedge having a thickness of about several hundred μm is used to detect a wavelength variation of a minute wavelength change (a range of about 0.01 nm). On the other hand, an optical wedge having a thickness of about several μm, which is about 1/100 of the optical wedge, is required for detecting a relatively large wavelength change, for example, a wavelength variation in the range of 4 nm, which is 100 times 0.04 nm.

  As described above, an optical wedge having a very thin thickness may be deteriorated in durability and is not practical. Patent Document 1 also proposes a plan in which two pieces of glass that are tilted and stacked are used as a substitute. However, it is necessary to construct the two glasses so as to have an interval of several μm and an angle of about 0.01 degrees, which is difficult to manufacture.

  In addition, two types of optical wedges are required, at least three of which are one for detection in a minute wavelength range and two in a wide wavelength detection range. In this case, there is a problem that the number of members constituting the semiconductor laser system 100 increases and the apparatus becomes large.

  On the other hand, the laser light source device proposed in Patent Document 2 requires separate detection systems for minute wavelength changes (in the range of about 0.04 nm) and wavelength detection in a relatively wide several nm range. After all, the number of components increases and the optical system becomes larger. This causes an increase in the size and cost of the external cavity semiconductor laser system.

  SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a wavelength detection device and a wavelength detection method that do not increase the size of the device even when detecting a wide range of minute wavelengths.

  The present invention is a wavelength detection device that detects the wavelength of a light beam, a laser light source that emits the light beam, and a wavelength detection unit that detects a minute change in the wavelength of the light beam and distinguishes the wavelength of the light beam over a wide range With. The wavelength detection unit includes a diffraction grating that diffracts a part of the light beam and a photodetector that receives the light beam diffracted by the diffraction grating. The wavelength detector detects the wavelength of the light beam based on the setting of the distance between the diffraction grating and the photodetector and the setting of the grating pitch of the diffraction grating.

  Preferably, the diffraction grating includes a first diffraction region that divides a part of the light beam into at least a zero-order diffracted light and a first first-order diffracted light. The photodetector includes first and second light receiving elements that detect a light amount distribution of interference fringes by the 0th-order diffracted light and the first 1st-order diffracted light. The wavelength detector detects a minute change in the wavelength of the light beam based on the differential outputs of the first and second light receiving elements.

  Preferably, the boundary line between the first light receiving element and the second light receiving element is at a position that is ½ of the maximum value of the intensity of the interference fringes incident on the photodetector during single mode oscillation of the laser light source. Is provided.

  Preferably, the diffraction grating has a second diffraction region that divides a part of the light beam into at least a second first-order diffracted light, and a third diffraction that divides a part of the light beam into at least a third first-order diffracted light. Area. The photodetector includes third and fourth light receiving elements that receive the second first-order diffracted light, and fifth and sixth light-receiving elements that receive the third first-order diffracted light. The wavelength detector determines the wavelength of the light beam over a wide range based on the sum of the differential signals of the third and fourth light receiving elements and the differential signals of the fifth and sixth light receiving elements.

  Preferably, the boundary line between the third light receiving element and the fourth light receiving element is provided at a position where the second first-order diffracted light is incident upon the set wavelength of the light beam. The boundary line between the fifth light receiving element and the sixth light receiving element is provided at a position where the third first-order diffracted light is incident upon the set wavelength of the light beam.

  Preferably, the diffraction grating includes a first diffraction region that divides a part of the light beam into at least a zero-order diffracted light and a first first-order diffracted light, and a part of the light beam at least a zero-order diffracted light and a second primary order. And a second diffraction region having a grating pitch larger than that of the first diffraction region, which is divided into folded light. The photodetector includes first and second light receiving elements that detect a light amount distribution of interference fringes by the zeroth-order diffracted light and the first first-order diffracted light, and interference fringes by the zeroth-order diffracted light and the second first-order diffracted light. 3rd and 4th light receiving element which detects light quantity distribution. The wavelength detection unit detects a minute change in the wavelength of the light beam based on the differential outputs of the first and second light receiving elements, and detects the light beam based on the differential outputs of the third and fourth light receiving elements. Distinguish wavelength over a wide range.

Preferably, the laser light source is an external resonator type laser.
According to another aspect of the present invention, there is provided a wavelength detection method for detecting the wavelength of a light beam emitted from a laser light source, the step of diffracting a part of the light beam with a diffraction grating, Based on the step of receiving the light beam with the light detector, the setting of the distance between the diffraction grating and the light detector, and the setting of the grating pitch of the diffraction grating, and detecting the minute change in the wavelength of the light beam Discriminating the wavelength of the light beam over a wide range.

  According to the present invention, the apparatus does not increase in size even when detecting a wide and minute wavelength.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals and description thereof will not be repeated.

[Embodiment 1]
FIG. 1 is a diagram showing a schematic configuration of a wavelength detector 1A according to Embodiment 1 of the present invention.

  Referring to FIG. 1, the wavelength detection device 1 </ b> A of the first embodiment includes an external resonator type semiconductor laser 10, a wavelength detection unit 20, and a laser control unit 27. The wavelength detector 20 includes a diffraction grating 2A, a photodetector 3A, and a half mirror 11.

  FIG. 2 is a diagram showing a schematic configuration of the external resonator type semiconductor laser 10 in the wavelength detector 1A of FIG.

  Referring to FIG. 2, external resonator type semiconductor laser 10 includes a laser diode 21, a collimator lens 22, a wavelength control diffraction grating 23, and a diffraction grating rotating mechanism 24, as in FIG. The laser diode 21 emits multimode laser light, for example, blue laser light of about 405 nm. The collimating lens 22 makes the laser beam PA emitted from the laser diode 21 parallel light.

  The wavelength control diffraction grating 23 receives the laser beam PA and generates primary light in different directions for each wavelength. The angle with respect to the laser diode 21 is set so that the primary light having a specific wavelength (for example, 405 nm) returns to the laser diode 21. Thereby, only the wavelength component is amplified in the laser diode 21, and the laser beam PA becomes a single mode.

  The diffraction grating rotating mechanism 24 controls the oscillation wavelength of the laser diode 21 by adjusting the angle of the wavelength control diffraction grating 23. The zero-order light (reflected light) PL of the wavelength control diffraction grating 23 is emitted from the external resonator type semiconductor laser 10 as output light.

  Returning to FIG. 1, the external cavity semiconductor laser 10 outputs the laser light PL whose wavelength is controlled to the wavelength detector 20. The laser beam PL is a blue laser beam of about 405 nm, for example. The half mirror 11 reflects a part of the laser beam PL as a light beam PR in the direction of the diffraction grating 2A. The diffraction grating 2A diffracts the incident light beam PR and makes it fall on a desired position on the photodetector 3A. The photodetector 3A receives the diffracted light from the diffraction grating 2A and outputs a detection signal SD. The laser control unit 27 feeds back the control signal CT generated based on the detection signal SD to the external resonator type semiconductor laser 10.

  FIG. 3 is a diagram showing a schematic configuration of the diffraction grating 2A in the wavelength detector 1A of FIG. The diffraction grating 2A is divided into three diffraction regions 2a to 2c.

  FIG. 4 is a diagram showing a schematic configuration of the photodetector 3A in the wavelength detection apparatus 1A of FIG. As shown in FIG. 4, the photodetector 3A includes light receiving elements 3a1, 3a2, 3b1, 3b2, 3c1, and 3c2. A photodetector, CCD (Charge Coupled Device), PSD (Position Sensing Detector), etc. can be used for these light receiving elements.

  3 and 4, the light beam PR incident on the diffraction grating 2A is diffracted in each of the diffraction regions 2a to 2c. The diffraction regions 2a to 2c generate a common zero-order diffracted light P0.

  The light beam PR incident on the diffraction region 2a is divided into 0th-order diffracted light P0 and 1st-order diffracted light Pa1. On the photodetector 3A, interference fringes are formed in the Y direction perpendicular to the X direction, which is the diffraction direction of the first order diffracted light Pa1, in the portion where the 0th order diffracted light P0 and the first order diffracted light Pa1 overlap. The light receiving elements 3a1 and 3a2 are arranged at positions where the interference fringes are incident and detect the light quantity distribution of the interference fringes.

  The light beam PR incident on the diffraction region 2b is split into 0th-order diffracted light P0 and 1st-order diffracted light Pb. The first-order diffracted light Pb is condensed between the light receiving elements 3b1 and 3b2 at the set wavelength (405 nm). Further, the light beam PR incident on the diffraction region 2c is split into 0th order diffracted light P0 and 1st order diffracted light Pc. The first-order diffracted light Pc is condensed between the light receiving elements 3c1 and 3c2 at the same set wavelength as described above.

  With the configuration as described above, the wavelength detection device 1A performs high-sensitivity and wide-range wavelength detection in parallel. Specifically, highly sensitive wavelength detection of the mode hop (wavelength change of about 0.01 nm) of the laser chip is performed by the outputs of the light receiving elements 3a1 and 3a2. Further, a wide range of wavelength detection of about several nanometers is performed by the outputs of the light receiving elements 3b1, 3b2, 3c1, and 3c2. Next, these wavelength detection principles will be described in detail.

  FIG. 5 is a diagram showing changes and interference of beam spots on the light receiving elements 3a1, 3a2, 3b1, 3b2, 3c1, and 3c2 when the wavelength of the laser beam PL is changed.

  As shown in FIG. 5, when the wavelength of the laser beam PL is changed in the increasing direction, the spot shapes and the incident positions of the first-order diffracted lights Pb and Pc at the set wavelength are changed as the first-order diffracted lights Pb + and Pc +, respectively. On the other hand, when the wavelength of the laser beam PL changes in the decreasing direction, the spot shape and the incident position of the first-order diffracted light Pb and Pc at the set wavelength change as the first-order diffracted lights Pb− and Pc−.

  As described above, when the wavelength of the laser beam PL changes, the diffraction angle of the diffraction grating 2A changes, and the diffraction angle increases as the wavelength increases. Assuming that the signals output from the light receiving elements 3b1, 3b2, 3c1, and 3c2 are Sb1, Sb2, Sc1, and Sc2, respectively, the wavelength signal Sλ that is a part of the detection signal SD is expressed by the following equation.

Sλ = (Sb2-Sb1) + (Sc2-Sc1)
The wavelength signal Sλ is 0 when the wavelength of the laser light PL is the set wavelength (405 nm), and changes in the ± direction according to the size of the wavelength. Therefore, the wavelength detection apparatus 1A can perform wavelength detection by calculating the wavelength signal Sλ. In wavelength detection using the wavelength signal Sλ, wavelength detection in the range of several nm is possible. However, in this detection system, it is difficult to perform highly sensitive wavelength detection of about 0.01 nm necessary for detecting minute wavelength changes due to mode hops of the laser chip.

  Next, a method for performing highly sensitive wavelength detection using the light receiving elements 3a1 and 3a2 will be described. As described in FIGS. 3 and 4, the diffraction direction of the diffraction region 2a is the Y direction. At this time, as shown in FIG. 5, the intensity distribution of interference fringes between the 0th-order diffracted light Pa0 and the 1st-order diffracted light Pa1 in the diffraction region 2a is not changed in the X direction and is diffracted in the Y direction. A light / dark pattern having a period determined by the grating pitch of the grating 2A is formed.

  FIG. 6 is a diagram showing the intensity distribution of interference fringes between the 0th-order diffracted light Pa0 and the 1st-order diffracted light Pa1 detected on the light receiving elements 3a1 and 3a2.

  In FIG. 6, the horizontal axis indicates the position in the Y direction, and the vertical axis indicates the light intensity. Here, it is assumed that the light beam PR incident on the diffraction grating 2A is parallel light, and the diffraction grating 2A and the light receiving elements 3a1 and 3a2 are arranged in parallel. At this time, as shown in FIG. 6, the distance T from the bright part of the interference fringe to the next bright part or the dark part to the next dark part coincides with the grating pitch Tp.

  FIG. 7 is a diagram showing a change in interference fringes when a mode hop occurs and the laser light PL having a set wavelength of 405 nm is changed to 405.04 nm with a wavelength difference of 0.04 nm.

  In FIG. 7, the intensity distributions of interference fringes when the wavelengths of the laser light PL are 405 nm and 405.04 nm are represented by P405 and P405.04, respectively. The relationship between the light / dark position of the intensity distribution P405 and the light / dark position of the intensity distribution P405.04 depends on the optical path difference at each position on the light receiving elements 3a1 and 3a2 of the 0th-order diffracted light Pa0 and the 1st-order diffracted light Pa1 at each wavelength. Determined. That is, the positional relationship between the two is determined by the distance in the Z direction between the diffraction grating 2A and the photodetector 3A and the grating pitch of the diffraction grating 2A.

  In the first embodiment, it is assumed that the distance in the Z direction between the diffraction grating 2A and the photodetector 3A is 100 mm and the grating pitch of the diffraction grating 2A is 3.5 μm. At this time, as shown in FIG. 7, the light / dark pattern of the interference fringes is shifted by 1/2 period between the light / dark position of the intensity distribution P405 and the light / dark position of the intensity distribution P405.04. Next, a method for generating the wavelength discrimination signal Smh that is a part of the detection signal SD from the change in the interference fringes will be described.

  FIG. 8 is a diagram showing the relationship between the interference fringe intensity distribution shown in FIG. 6 and the arrangement of the light receiving elements 3a1 and 3a2.

  In FIG. 8, it is assumed that the light receiving elements 3a1 and 3a2 have the same width in the X direction. The widths Wt in the Y direction of the light receiving elements 3a1 and 3a2 are also equal and are expressed by the following equations.

Wt = (m + (1/2)) T (m = 0, 1, 2,...)
As shown in FIG. 8, the boundary line between the light receiving elements 3a1 and 3a2 is provided at a position that is ½ of the maximum value of the interference fringes during single mode oscillation. Specifically, the outputs (Sa1-Sa2) of the light receiving elements 3a1, 3a2 are observed and positioned at the position where the maximum value is obtained. By positioning in this way, the output (Sa1-Sa2) is greatly deviated from 0 when the laser beam PL reaches the set wavelength (405 nm).

  In the above setting, when a mode hop of the laser chip occurs, the bright / dark pattern of the interference fringes is shifted by 1/2 period as described with reference to FIG. As a result, the value of the wavelength discrimination signal Smh = Sa1−Sa2 which is the differential output of the light receiving elements 3a1 and 3a2 also decreases. By detecting this wavelength discrimination signal Smh, it is possible to detect a wavelength variation in a minute range of about -0.04 nm to 0.04 nm.

  In the first embodiment, low-sensitivity wavelength detection with a wide wavelength detection range has been described as a few nm range, and high-sensitivity wavelength detection has been described as a range of about -0.04 nm to 0.04 nm. It is not limited to.

  In the first embodiment, the wavelength detection device 1A is used for wavelength detection of the external resonant semiconductor laser. However, the present invention is not limited to this, and the wavelength of a laser light source other than the external resonant semiconductor laser is used. It can also be used for detection.

  As described above, the wavelength detection device 1A according to the first embodiment has the wavelength signal Sλ in a relatively wide range (for example, several nanometers) and a minute change (for example, 0. 0 nm) by the output of each light receiving element of the photodetector 3A. A wavelength discrimination signal Smh at about 01 nm is generated. Thereby, the oscillation wavelength of the external cavity semiconductor laser 10 can be controlled to a desired wavelength, and stable operation can be realized. As a result, it is possible to realize a small and low-cost external resonator type semiconductor laser device with a simple configuration with a small number of members.

  The wavelength detection apparatus 1A according to the first embodiment includes a diffracting unit that diffracts laser light and a light detecting unit that receives the diffracted light beam. The diffracting means has at least first and second diffraction regions, and detects the first and second wavelength discrimination signals by diffracted light from each diffraction region. As a result, a small-sized and low-cost wavelength detection device can be realized with a small number of components such as one diffraction grating and one photodetector.

  Further, in the wavelength detection device 1A according to the first embodiment, in the configuration described above, the light detection unit includes a first light receiving element group that receives diffracted light from the first diffraction region, and a second diffraction region. And a second light receiving element group for receiving diffracted light. Thereby, the light detection means can be realized with a simple configuration of the first and second diffraction regions.

  In the wavelength detector 1A according to the first embodiment, in the above configuration, the laser beam incident on the first diffraction region is divided into a plurality of beams, and the first light reception is performed at a position where the plurality of beams are superimposed. An element group is arranged, and a first wavelength discrimination signal for detecting the wavelength of the laser beam is generated by the differential output of the first light receiving element group. Thereby, a grating pattern for generating interference light can be formed in the first diffraction region of the diffraction grating, and diffracted light for generating a first wavelength discrimination signal can be generated. Further, the diffraction grating for generating the first wavelength discrimination signal can be created by a simple manufacturing process by collective patterning.

  Preferably, the wavelength detection apparatus 1A according to the first embodiment is configured so that the first wavelength discrimination signal changes more sensitively to the change in the wavelength of the laser light than the second wavelength discrimination signal in the above configuration. Features. Thereby, a minute wavelength change (for example, about 0.01 nm) of the laser light source can be detected using the first wavelength discrimination signal.

  Preferably, the wavelength detection apparatus 1A according to the first embodiment is characterized in that, in the above configuration, the first wavelength discrimination signal has a narrower wavelength detection range of the laser light than the second wavelength discrimination signal. Thereby, the wavelength of the laser light source can be detected over a relatively wide range (for example, about several nm) using the second wavelength discrimination signal.

[Embodiment 2]
FIG. 9 is a diagram showing a schematic configuration of a wavelength detection device 1B according to Embodiment 2 of the present invention.

  Referring to FIG. 9, the wavelength detection device 1B according to the second embodiment is the same as the wavelength detection device according to the first embodiment in that the diffraction grating 2A and the photodetector 3A are replaced with the diffraction grating 2B and the photodetector 3B. Different from 1A. Since other configurations are the same as those of the first embodiment, the description of the overlapping portions will not be repeated here.

  FIG. 10 is a diagram showing a schematic configuration of the diffraction grating 2B in the wavelength detector 1B of FIG. The diffraction grating 2B is divided into two diffraction regions 4a and 4b, and their grating pitches are different from each other.

  FIG. 11 is a diagram showing a schematic configuration of the photodetector 3B in the wavelength detector 1B of FIG. As shown in FIG. 11, the photodetector 3B includes light receiving elements 5a1, 5a2, 5b1, and 5b2. For these light receiving elements, for example, a photodetector, CCD, or PSD can be used.

  Referring to FIGS. 10 and 11, the light beam PR incident on the diffraction grating 2B is diffracted by each of the diffraction regions 4a and 4b. The diffraction regions 4a and 4b generate a common zero-order diffracted light P0.

  The light beam PR incident on the diffraction region 4a is divided into 0th-order diffracted light P0 and 1st-order diffracted light Pa1. On the photodetector 3B, interference fringes are formed in the Y direction perpendicular to the X direction, which is the diffraction direction of the first order diffracted light Pa1, in the portion where the 0th order diffracted light P0 and the first order diffracted light Pa1 overlap. In the second embodiment, it is assumed that the distance in the Z direction between the diffraction grating 2B and the photodetector 3B is 100 mm, and the grating pitch of the diffraction region 4a in the diffraction grating 2B is 2.1 μm.

  The light receiving elements 5a1 and 5a2 are arranged at positions where the interference fringes are incident and detect the light quantity distribution of the interference fringes. Thereby, the mode hop of the laser chip can be detected as in the light receiving elements 3a1 and 3a2 of the first embodiment.

  The light beam PR incident on the diffraction region 4b is split into 0th-order diffracted light P0 and 1st-order diffracted light Pb1. On the photodetector 3B, the portion where the 0th-order diffracted light P0 and the 1st-order diffracted light Pb1 overlap with each other on the light receiving elements 5a1 and 5a2 in the Y direction perpendicular to the X direction that is the diffraction direction of the 1st-order diffracted light Pb1. Interference fringes with different pitches are formed. The light receiving elements 5b1 and 5b2 are arranged at positions where the interference fringes are incident and detect the light quantity distribution of the interference fringes.

  FIG. 12 is a diagram for explaining the principle of detecting the wavelength of the laser beam PL using the interference fringes on the light receiving elements 5b1 and 5b2 by the diffraction region 4b.

  In FIG. 12, the horizontal axis represents the grating pitch of the diffraction region 4b of the diffraction grating 2B, and the vertical axis represents the amount of misalignment of the interference fringes normalized by the period of the interference fringes. The amount of positional deviation of the interference fringes at the wavelength difference of 0.04 nm corresponding to the wavelength variation due to the mode hop of the laser chip is represented by 0.04T, and the amount of positional deviation of the interference fringes at the wavelength difference of 5 nm is represented by 5T.

  As shown in FIG. 12, in order to make the interference fringe displacement amount 0.5 (1/2 period) when the wavelength difference is 0.04 nm, from the intersection with the displacement amount 0.04T. It can be seen that the grating pitch of the diffraction region 4b may be 3.5 μm. In this case, by detecting the differential output of the light receiving elements 5b1 and 5b2, it is possible to detect the wavelength of a minute change such as a mode hop of the laser chip.

  Further, in order to detect the wavelength fluctuation in the range of ± 5 nm, it is only necessary that the amount of displacement of the interference fringes is 0.5 (1/2 period) when the wavelength difference is 5 nm. In this case, the grating pitch of the diffraction region 4b is 38.7 μm from the intersection with the displacement amount 5T. In this case, a wide range of wavelength detection of about several nanometers can be performed by detecting the differential output of the light receiving elements 5b1 and 5b2.

  In the second embodiment, low-sensitivity wavelength detection with a wide wavelength detection range is described as a few nm range, and high-sensitivity wavelength detection is described as a range of about −0.04 nm to 0.04 nm. It is not limited to.

  In the second embodiment, the example in which the wavelength detection device 1B is used for the wavelength detection of the external resonance type semiconductor laser is shown. However, the present invention is not limited to this, and the wavelength of the laser light source other than the external resonance type semiconductor laser is used. It can also be used for detection.

  As described above, the wavelength detection device 1B according to the second embodiment divides the diffraction grating 2B into the diffraction areas 4a and 4b, and sets the grating pitches of the diffraction areas 4a and 4b to different values, thereby making the laser mode hop. Along with detection (for example, about 0.04 nm), it is possible to detect wavelength changes in the range of several nm. As a result, it is possible to realize a small and low-cost external resonator type semiconductor laser device with a simple configuration with a small number of members.

  The wavelength detection device 1B according to the second embodiment includes a diffracting unit that diffracts laser light and a light detecting unit that receives the diffracted light beam. The diffracting means has at least first and second diffraction regions, and detects the first and second wavelength discrimination signals by diffracted light from each diffraction region. As a result, a small-sized and low-cost wavelength detection device can be realized with a small number of components such as one diffraction grating and one photodetector.

  In the wavelength detection device 1B of the second embodiment, the second light receiving element group includes at least one two-divided light receiving element in the above configuration. The second diffraction region of the diffraction grating is characterized in that a grating shape is formed so that incident laser light is diffracted and condensed on a dividing line of the two-divided light receiving element. As a result, a grating pattern (beam focusing pattern) different from the first diffraction area can be formed in the second diffraction area of the diffraction grating, and diffracted light for generating the second wavelength discrimination signal is generated. be able to. Since the diffraction grating can simultaneously form the first and second diffraction regions by batch patterning, a diffraction grating for generating the second wavelength discrimination signal can be created by a simple manufacturing process.

  Further, in the wavelength detection device 1B according to the second embodiment, in the configuration described above, the second light reception is performed at a position where the laser light incident on the second diffraction region is divided into a plurality of beams and the plurality of beams are superimposed. An element group is arranged. A second wavelength discrimination signal for detecting the wavelength of the laser beam is generated by the differential output of the second light receiving element group. As a result, a pattern having a grating pitch different from that of the first diffraction region can be formed in the second diffraction region of the diffraction grating, and diffracted light for generating the second wavelength discrimination signal can be generated. Since the diffraction grating can simultaneously form the first and second diffraction regions by batch patterning, a diffraction grating for generating the second wavelength discrimination signal can be created by a simple manufacturing process.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is shown not by the above description of the embodiments but by the scope of claims for patent, and is intended to include meanings equivalent to the scope of claims for patent and all modifications within the scope.

It is the figure which showed schematic structure of 1 A of wavelength detection apparatuses by Embodiment 1 of this invention. It is the figure which showed schematic structure of the external resonator type semiconductor laser 10 in the wavelength detection apparatus 1A of FIG. It is the figure which showed the schematic structure of the diffraction grating 2A in the wavelength detection apparatus 1A of FIG. It is the figure which showed schematic structure of 3 A of photodetectors in the wavelength detection apparatus 1A of FIG. It is the figure which showed the change and interference of the beam spot on light receiving element 3a1, 3a2, 3b1, 3b2, 3c1, 3c2 when the wavelength of the laser beam PL changed. It is the figure which showed the intensity distribution of the interference fringe of 0th-order diffracted light Pa0 detected on light receiving element 3a1, 3a2 and 1st-order diffracted light Pa1. It is the figure which showed the change of the interference fringe when mode hop generate | occur | produces and the laser beam PL of setting wavelength 405nm changes to 405.04nm of wavelength difference 0.04nm. It is the figure which showed the relationship between intensity distribution of the interference fringe shown in FIG. 6, and arrangement | positioning of light receiving element 3a1, 3a2. It is the figure which showed schematic structure of the wavelength detection apparatus 1B by Embodiment 2 of this invention. It is the figure which showed the schematic structure of the diffraction grating 2B in the wavelength detection apparatus 1B of FIG. It is the figure which showed schematic structure of the photodetector 3B in the wavelength detection apparatus 1B of FIG. It is a figure for demonstrating the principle which detects the wavelength of the laser beam PL using the interference fringe on the light receiving elements 5b1 and 5b2 by the diffraction area | region 4b. 1 is a diagram showing a schematic configuration of a conventional semiconductor laser system 100. FIG. FIG. 6 is a diagram showing a schematic configuration of an external resonator type semiconductor laser 50 in a conventional semiconductor laser system 100. It is the figure which showed the relationship between the laser power of the laser beam PT output from the semiconductor laser system 100 of FIG. 13, and a wavelength.

Explanation of symbols

  1A, 1B wavelength detector, 2A, 2B diffraction grating, 3A, 3B photodetector, 2a-2c, 4a, 4b diffraction region, 3a1, 3a2, 3b1, 3b2, 3c1, 3c2, 5a1, 5a2, 5b1, 5b2 Element 10, 50 External cavity semiconductor laser, 11 Half mirror, 20, 101 Wavelength detection unit, 21, 51 Laser diode, 22, 52 Collimator lens, 23, 53 Wavelength control diffraction grating, 24, 54 Diffraction grating rotation Mechanism, 27 Laser control unit, 100 Semiconductor laser system, 102, 103 Photodetection unit, 104,105 Optical wedge, 106,107 Two-part photodetector, 110 Laser control unit Wavelength detection unit

Claims (8)

A wavelength detector for detecting the wavelength of a light beam,
A laser light source that emits a light beam;
A wavelength detector that detects a minute change in the wavelength of the light beam and discriminates the wavelength of the light beam in a wide range;
The wavelength detector is
A diffraction grating that diffracts a portion of the light beam;
A photodetector for receiving the light beam diffracted by the diffraction grating,
The wavelength detection device detects the wavelength of the light beam based on a setting of a distance between the diffraction grating and the photodetector and a setting of a grating pitch of the diffraction grating. The diffraction grating includes a first diffraction region that divides a part of the light beam into at least a zero-order diffracted light and a first first-order diffracted light,
The photodetector includes first and second light receiving elements for detecting a light amount distribution of interference fringes due to the zero-order diffracted light and the first first-order diffracted light,
The wavelength detection device according to claim 1, wherein the wavelength detection unit detects a minute change in the wavelength of the light beam based on a differential output of the first and second light receiving elements.   The boundary line between the first light receiving element and the second light receiving element is a position that is ½ of the maximum value of the intensity of interference fringes incident on the photodetector during single mode oscillation of the laser light source. The wavelength detection device according to claim 2, wherein the wavelength detection device is provided. The diffraction grating is
A second diffraction region that divides a portion of the light beam into at least a second first-order diffracted light;
A third diffraction region that divides a part of the light beam into at least a third first-order diffracted light,
The photodetector is
Third and fourth light receiving elements for receiving the second first-order diffracted light;
And fifth and sixth light receiving elements for receiving the third first-order diffracted light,
The wavelength detection unit discriminates the wavelength of the light beam over a wide range based on the sum of the differential signals of the third and fourth light receiving elements and the differential signals of the fifth and sixth light receiving elements. The wavelength detection device according to claim 1. A boundary line between the third light receiving element and the fourth light receiving element is provided at a position where the second first-order diffracted light is incident on the set wavelength of the light beam,
The boundary line between the fifth light receiving element and the sixth light receiving element is provided at a position where the third first-order diffracted light is incident upon the set wavelength of the light beam. The wavelength detection apparatus as described. The diffraction grating is
A first diffractive region that divides a portion of the light beam into at least zeroth order diffracted light and first first order diffracted light;
A second diffraction region having a grating pitch larger than that of the first diffraction region, which divides a part of the light beam into at least the 0th-order diffracted light and the second first-order diffracted light,
The photodetector is
First and second light receiving elements for detecting a light amount distribution of interference fringes by the zeroth order diffracted light and the first first order diffracted light;
A third and a fourth light receiving element for detecting a light amount distribution of interference fringes due to the zero-order diffracted light and the second first-order diffracted light;
The wavelength detector detects a minute change in the wavelength of the light beam based on the differential outputs of the first and second light receiving elements, and differential outputs of the third and fourth light receiving elements. The wavelength detection device according to claim 1, wherein the wavelength of the light beam is discriminated in a wide range based on the above.   The wavelength detection device according to claim 1, wherein the laser light source is an external resonator type laser. A wavelength detection method for detecting the wavelength of a light beam emitted from a laser light source,
Diffracting a portion of the light beam with a diffraction grating;
Receiving a light beam diffracted by the diffraction grating with a photodetector;
Based on the setting of the distance between the diffraction grating and the photodetector and the setting of the grating pitch of the diffraction grating, a minute change in the wavelength of the light beam is detected and the wavelength of the light beam is set to a wide range And a step of determining.

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