JP2005277219A - Photonic crystal laser - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a laser apparatus capable of scanning a target with a high output laser beam at a high speed without using a mechanical scanning mechanism. <P>SOLUTION: In a photonic crystal laser constituted of forming an active layer 21 and a two-dimensional (2D) photonic crystal layer 23 between upper electrodes 33 and a lower electrode 27, a plurality of upper electrodes 33 are linearly arranged. A current is led from one or a plurality of adjacent upper electrodes 33. When light is generated from the active layer 21 and the generated light is strengthened by diffraction in the 2D photonic crystal layer 23, strong laser light is generated from the periphery of the upper electrodes 33 from which the current is led to the outside. When the upper electrodes from which a current is led are successively switched, a target can be scanned with laser beams in the array direction of the upper electrodes. Since the upper electrodes 33 can be electrically switched, the target can be scanned with laser beams at a high speed without using the mechanical scanning mechanism. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a laser element and a laser apparatus that can be suitably used for various apparatuses that need to scan laser light, such as a laser printer and a barcode reader.

  Laser printers, barcode readers, and the like scan laser light for printing and reading. Here, a laser scanning device in a conventional laser printer will be described with reference to FIG.

  Laser light output from the semiconductor laser 11 is reflected on the side surface of the rotating polygon mirror 12, passes through the f-θ lens 13, and irradiates the photosensitive drum 14. While one side surface of the polygon mirror 12 is irradiated with laser light, the laser light irradiation point (laser light spot) is changed from one end 151 of the photosensitive drum 14 to the other end 152 by the rotation of the polygon mirror 12. Move continuously. When the laser beam spot reaches the other end 152, the reflection position of the laser beam on the polygon mirror 12 is exactly the side edge. Then, at the next moment, the reflection position of the laser beam becomes the start end of the next side surface, whereby the laser beam spot on the photosensitive drum 14 also returns to the one end 151. In this way, laser light is irradiated onto the photosensitive drum 14 while being repeatedly scanned, and during that time, the laser light is turned ON / OFF to print characters and images.

  In order to increase the printing speed of the laser printer, it is necessary to increase the scanning speed of the laser beam spot on the photosensitive drum. According to the above configuration, the speed of the laser beam spot that scans on the photosensitive drum 14 is determined by the rotational speed of the polygon mirror. However, since there is a limit to increasing the speed of such mechanical movement, it is difficult to increase the printing speed with the configuration of FIG.

  Patent Document 1 describes a configuration using a laser light source in which a plurality of surface emitting vertical cavity semiconductor lasers (VCSEL) are arranged in an array as a configuration for further increasing the scanning speed. In this configuration, the scanning speed is increased by simultaneously irradiating laser light from a plurality of VCSELs. However, it is difficult to give the VCSEL itself the ability to move the beam, a polygon mirror is essential for scanning, and the output of the single mode VCSEL is limited to about 3 mW.

On the other hand, in recent years, a new type of laser using a photonic crystal has been developed. A photonic crystal is obtained by artificially forming a periodic structure in a dielectric. The periodic structure is generally formed by periodically providing a region having a refractive index different from that of the dielectric body in the body. Due to the periodic structure, Bragg diffraction occurs in the crystal, and an energy band gap is formed with respect to the energy of light.
Patent Document 2 describes a laser light source using a two-dimensional photonic crystal. This laser light source has an active layer containing a light emitting material between two electrodes (conductive semiconductor layers), and a two-dimensional photonic crystal is formed above the active layer. This two-dimensional photonic crystal is obtained by providing a plate-like member (slab) with a two-dimensional periodic refractive index distribution. Light emission from the active layer is caused by the injection of carriers from the electrode, and this light is intensified by diffraction by the periodic structure of the two-dimensional photonic crystal, thereby causing laser oscillation. When the period of this periodic structure coincides with the wavelength in the medium, light is emitted in a direction perpendicular to the slab surface. With this laser light source, it is possible to obtain light emission with a higher output than VCSEL.

Japanese Unexamined Patent Publication No. 2000-020995 ([0012], FIG. 2) JP 2000-332351 A ([0037] to [0056], FIG. 1)

  The problem to be solved by the present invention is to provide a laser element and a laser apparatus that can scan a beam of high-power laser light at high speed without using a mechanical scanning mechanism.

The photonic crystal laser device according to the first aspect of the present invention, which has been made to solve the above problems,
a) an active layer that generates light of a predetermined wavelength by charge injection;
b) a two-dimensional photonic crystal provided above the active layer and having a periodic structure corresponding to the predetermined wavelength;
c) a plurality of upper electrodes arranged above the two-dimensional photonic crystal;
d) a lower electrode provided under the active layer;
It is characterized by having.

The photonic crystal laser device according to the second aspect of the present invention is
a) an active layer that generates light of a predetermined wavelength by charge injection;
b) a two-dimensional photonic crystal provided above the active layer and having a periodic structure corresponding to the predetermined wavelength;
c) an upper electrode provided on the upper side of the two-dimensional photonic crystal;
d) a plurality of lower electrodes arranged below the active layer;
It is characterized by having.

  The photonic crystal laser device according to the present invention includes the photonic crystal laser element, voltage applying means for applying a voltage between the upper electrode and the lower electrode, and an applied voltage for each of the upper electrode or the lower electrode arranged in a plurality. And a control means for controlling ON / OFF.

  Here, the directionality with the active layer down and the two-dimensional photonic crystal up is used, but this is only used for convenience of expression, and both and other layers are in the order. Can be arranged in any direction as long as it is as described above.

Embodiments and effects of the invention

  The photonic crystal laser element according to the present invention has an active layer and a two-dimensional photonic crystal. This is the same as the laser disclosed in Patent Document 2. Here, the active layer and the two-dimensional photonic crystal do not need to be in direct contact with each other, and a sufficient feedback effect can be obtained even if a layer such as a spacer is interposed between the active layer and the two-dimensional photonic crystal. The size of the light emitting region can be adjusted by adjusting the distance between the active layer and the two-dimensional photonic crystal by interposing such a layer. The active layer generates light having a predetermined wavelength by injection of electric charges. As the material of the active layer, for example, the same material as that conventionally used for a Fabry-Perot type laser light source can be used. In general, a two-dimensional photonic crystal is formed by periodically arranging a large number of regions having the same shape having a different refractive index from a slab base material. This period includes a triangular lattice shape, a square lattice shape, a hexagonal lattice shape, and the like. The period is set according to the wavelength of light emission in the active layer. The period is usually the same as the emission wavelength, but laser oscillation is possible in other cases (for example, a period having a length of 1/2 of the emission wavelength).

A lower electrode and an upper electrode are provided so as to sandwich the active layer and the two-dimensional photonic crystal. Another layer may be interposed between the active layer and the lower electrode.
In the photonic crystal laser element of the first aspect, a plurality of separate upper electrodes are arranged on the upper side of the two-dimensional photonic crystal. The arrangement of the upper electrodes may be linear (one-dimensional), or may be two-dimensionally arranged such as a square lattice or a triangular lattice. Note that another layer may be interposed between the two-dimensional photonic crystal and the upper electrode. For example, a layered member may be disposed between two-dimensional photonic crystals, and an upper electrode may be placed thereon.

  A plurality of lower electrodes provided on the lower side of the active layer may be provided corresponding to the upper electrode, but one common lower electrode may be provided for the plurality of upper electrodes. Another layer may be interposed between the lower electrode and the active layer. It is desirable that the lower electrode or the intervening layer reflects this light so that light generated in the active layer does not leak outside from the lower electrode side.

  A photonic crystal laser device is configured by providing a voltage applying unit and a control unit in the element configured as described above. The voltage applying means applies a voltage between the upper electrode and the lower electrode, and a normal DC power supply can be used. The control means controls ON / OFF of the applied voltage for each upper electrode. The ON / OFF timing of each upper electrode may be appropriately determined according to the use of the photonic crystal laser as in the example shown later.

The operation of the photonic crystal laser device of the present invention will be described.
First, the mechanism of laser light emission in this laser device will be described. When a voltage is applied between one of the upper electrodes and the lower electrode, carriers are injected into a portion of the active layer sandwiched between the upper electrode and the lower electrode, and a predetermined value determined by the material from the active layer. Wavelength light is generated. This light is also introduced into the two-dimensional photonic crystal and is diffracted by the periodic structure of the crystal corresponding to the wavelength. As a result, light of this wavelength is amplified and laser oscillation occurs. This laser light is emitted in a plane from the inside of a certain range (light emitting region) around the upper electrode to the outside on the upper electrode side. The generated laser beam can be taken out from the side surface of the element by confining the generated laser beam in the vertical direction.

  In the photonic crystal laser element and the laser light source of the present invention, since a plurality of upper electrodes are provided, an operation that is not found in a conventional laser can be realized. First, the light emission region is switched by controlling ON / OFF of the applied voltage for each upper electrode by the control means, whereby the laser beam can be apparently moved.

  Next, when the size (diameter) of the light emitting region around one upper electrode is d, a large number of arrays are arranged with the distance between the upper electrodes being smaller than d, and a voltage is applied simultaneously to a predetermined number of adjacent upper electrodes. Is applied (turned on), one light emitting region (wide light emitting region) is formed by the whole upper electrode. By switching ON / OFF of the upper electrode one by one or sequentially by a predetermined number, this wide light emitting region can be moved little by little or stepwise. According to the former method, the light emitting region can be moved smoothly, and according to the latter method, the light emitting region can be moved quickly. In any case, since the light emitting area is wide, high output laser light can be generated.

  Normally, the same value of current flows through a plurality of electrodes that are simultaneously flowing with current, but the shape of the beam can be controlled by changing the current value that flows through the electrodes.

  In the laser element according to the present invention, in order to extract laser light from the upper electrode side, it is desirable to use a material that is transparent to light of that wavelength for the upper electrode.

  In the photonic crystal laser element configured as described above, since the laser light is radiated to the outside almost perpendicularly from the light emitting region, the emission range of the laser light is only within the full length (or full width) of the element. Therefore, when it is desired to radiate to a wider range, it is desirable to provide means (deflecting means) for changing the direction of the laser light output from the vicinity of each upper electrode on the upper electrode. Examples of the deflecting means include a lens that covers the entire element, a prism provided for each element, and the like.

  Up to this point, the photonic crystal laser element and laser device of the first aspect in which a plurality of upper electrodes are arranged side by side have been described, but a plurality of lower electrodes may be arranged in place of the upper electrode. This is the photonic crystal laser element and laser device of the second embodiment. In this case, it is sufficient to provide one upper electrode in common for a plurality of or all lower electrodes. When a voltage is applied between each lower electrode and the upper electrode, the laser beam is emitted from the upper electrode to the outside just above a certain range around the lower electrode. The operations of the photonic crystal laser element and laser device of the second aspect are the same as those of the first aspect.

  In the photonic crystal, light having a wavelength corresponding to the periodic structure of the photonic crystal is amplified. Therefore, by changing the periodic structure in the photonic crystal depending on the position in the crystal, the wavelength of the laser light is increased. Can be tuned.

  In the photonic crystal laser device of the present invention, laser light can be scanned by ON / OFF of a voltage applied to a plurality of upper electrodes or lower electrodes arranged without using a mechanical scanning mechanism. Since the scanning speed of the laser beam is not limited by the speed of the mechanical scanning mechanism, it can be made faster than before. In addition, since a photonic crystal laser capable of emitting light with high output is used, the intensity of the obtained laser light can be sufficiently increased.

  Since the photonic crystal laser of the present invention has such a feature, it can be suitably used for a laser beam scanning device in a laser printer, a barcode reader, or the like. In addition, since the configuration of the present invention can be applied to photonic crystal lasers of various wavelengths, for example, by attaching two-dimensional electrodes to the three primary colors of blue, green, and red, and scanning each light on a screen or the like. Application to full-color displays is also possible.

An embodiment of the photonic crystal laser element according to the present invention will be described with reference to FIG.
A two-dimensional photonic crystal 23 is provided on an active layer 21 made of indium gallium arsenide (InGaAs) / gallium arsenide (GaAs) and having a multiple-quantum well (MQW) via a lower spacer 22. . The two-dimensional photonic crystal 23 is formed by periodically arranging holes 24 in a square lattice pattern in a plate material made of GaAs. In this embodiment, the lower spacer 22 and the two-dimensional photonic crystal 23 are formed as one layer, and a hole 24 is formed only in the upper part to function as the two-dimensional photonic crystal 23. The portion functions as the lower spacer 22. Under the active layer 21, a confinement layer 25 made of GaAs, a lower cladding layer 26 made of n-type aluminum gallium arsenide (AlGaAs), and a lower substrate made of n-type GaAs are provided in order from the side closer to this layer. . After mechanically polishing the lower substrate to a thickness of about 50 to 100 microns, gold, germanium, and nickel are deposited and heated to about 400 ° C. to form an alloy, thereby forming the lower electrode 27. On the upper side of the two-dimensional photonic crystal 23, an upper spacer 28 made of GaAs, an upper clad layer 29 made of p-type AlGaAs, and a contact layer 30 made of p-type GaAs are provided in order from the side closer to this layer. Each of these layers can be manufactured by a method similar to the method described in Patent Document 2.

  A large number of upper electrodes 33 are arranged in a straight line on the contact layer 30. In the present embodiment, the planar shape of the upper electrode 33 is a rectangle that is long in the direction perpendicular to the arrangement direction. For example, gold can be used as the material of the upper electrode 33. An electrode using gold can minimize current loss and can be easily manufactured by, for example, a vapor deposition method. Alternatively, the upper electrode 33 may be a transparent electrode made of zinc oxide (ZnO) doped with carriers. By using such a transparent electrode, a larger amount of light can be extracted to the outside.

  As shown in FIG. 3, the lower electrode 27 and each upper electrode 33 are connected in parallel to a DC power source, and a switch 34 composed of a transistor or the like is provided for each upper electrode 33. And the control part 35 for controlling ON / OFF of these switches 34 is provided. As described above, the photonic crystal laser device is configured.

  The operation of the photonic crystal laser device of this example will be described with reference to FIG. First, among the many arranged upper electrodes 33, four electrodes 331 to 334 at one end are taken as one set, and a voltage is applied between these and the lower electrodes to introduce a current. As a result, carriers are injected into the active layer 21 directly below and around these four upper electrodes 331 to 334, and light is generated in that region. This light is also introduced into the two-dimensional photonic crystal 23, where it is diffracted and amplified to cause laser oscillation. The two-dimensional photonic crystal 23 is formed inside the region 42. This laser light is emitted in a direction perpendicular to the surface of the photonic crystal 23 and emitted from the contact layer 30 to the outside. At this time, as shown in FIG. 4A, the periphery of the four upper electrodes 331 to 334 into which the current is introduced becomes the light emitting region 411. In this embodiment, the upper electrodes 331 to 334 are arranged in the arrangement direction. Since the rectangular shape is long in the vertical direction and the region into which the current is introduced has a shape close to a square, the light emitting region 411 has a shape close to a square.

  Next, the current introduction to the leftmost upper electrode 331 among the four electrodes is turned OFF, and at the same time, the current is introduced to the upper electrode 335 adjacent to the right side thereof (FIG. 4 (b)). . As a result, the light emitting region moves from 411 to 412. In this way, by controlling the switches of the upper electrodes by the control unit 35 and sequentially switching the upper electrodes to which current is introduced, the light emitting region can be moved in the arrangement direction of the upper electrodes 33.

  The light emitting region repeats the operation of moving substantially continuously from the left end of the element toward the right end, returning to the left end of the element when reaching the right end of the element, and moving substantially continuously from the left end toward the right end again. . This operation is the same as the laser beam scanning in the laser printer shown in FIG.

  The number of upper electrodes that simultaneously introduce current is not limited to the four shown above. For example, the current may be introduced only to one upper electrode at a time. However, in order to scan the laser beam more smoothly, it is desirable to introduce current into a plurality of upper electrodes at the same time as described above and turn them on / off part by part. In the above example, when the light emitting area reaches the right end, the light emitting area is controlled so that it immediately returns to the left end of the device.However, depending on the application, the light emitting area reaches the right end and then changes from the right end to the left end. You may make it move so that it may return and reverse.

  Further, as shown in FIG. 5, the light emitting region 512 may be formed at a position away from the light emitting region 511 at the same time as forming one light emitting region 511 as described above. Similarly, three or more light emitting regions may be formed simultaneously. By scanning these light emitting regions simultaneously, it is possible to scan within a predetermined region in a shorter time than when scanning one light emitting region.

  The shape of the upper electrode 33 is not limited to a rectangle long in the direction perpendicular to the arrangement direction as described above, and may be, for example, a square. Alternatively, the electrodes may be arranged two-dimensionally, and one or a plurality of beams may be scanned in various directions at the same time.

  FIG. 6 shows an example in which means for changing (deflecting) the direction of the laser beam is provided for each upper electrode 33. In the example of FIG. 6, one lens 61 is provided on the upper side of the photonic crystal laser element so as to cover the entire upper electrode 33. As a result, the radiation range of the laser beam is expanded in the arrangement direction of the upper electrodes 33, and the irradiation range (scanning range) of the laser beam can be widened while downsizing the photonic crystal laser element.

  The photonic crystal laser element and the photonic crystal laser device of the present invention are not limited to the above examples. For example, as shown in FIG. 7, the upper electrode 33 may be two-dimensionally arranged. In this case, the light emitting region can be scanned two-dimensionally by switching the upper electrode 33 that injects current in the order indicated by the arrows in FIG. Further, as shown in FIG. 8B, by switching the upper electrode 33 for injecting current for each column of the upper electrode 33, a plurality of laser beams can be scanned simultaneously.

  Further, as shown in FIG. 9, the upper electrode 33 may be formed as a single sheet, and a plurality of lower electrodes 32 may be formed on the substrate 31. This photonic crystal laser element also operates in the same manner as in the above embodiment.

  FIG. 10 shows an example in which the photonic crystal laser element according to the present invention is used in a light source unit of a laser printer. In the configuration of FIG. 10A, a photonic crystal laser element 71 having the same length as the effective printing width of the photoconductive drum 73 is manufactured and arranged facing the photoconductive drum 73. In this configuration, the number of upper electrodes corresponding to the number of dots in the effective printing width of the photosensitive drum 73 (for example, 12,000 when the effective printing width of the photosensitive drum 73 is 10 inches = 25.4 cm at 1200 dpi) is printed. Although it is necessary to arrange within the effective width, in the photonic crystal laser element according to the present invention, the upper electrode can be made sufficiently small (in the case of the above example, the pitch is about 20 μm), and laser oscillation can be performed. Therefore, such a configuration can be taken.

  In the configuration of FIG. 10B, a photonic crystal laser element 72 that is shorter than the effective printing width of the photosensitive drum 73 but has the same number of upper electrodes is manufactured and arranged facing the photosensitive drum 73. To do. For example, when the size (length) of the photonic crystal laser element 72 is 1/10 of the effective printing width of the photosensitive drum 73 (2.54 cm in the above example), the arrangement pitch of the upper electrodes is about 2 μm. However, this pitch is sufficiently possible if a short wavelength laser is used. In the case of this configuration, in order to emit laser light from a photonic crystal laser element over a wide range, a lens 61 is arranged on the photonic crystal laser element as shown in FIG. 6, or separately from the photonic crystal laser element. A lens 74 is provided between the photonic crystal laser element light source and the photosensitive drum 73.

  Regardless of the configuration, the laser light emission is controlled as described above by ON / OFF control of voltage application to each upper electrode of the photonic crystal laser element light source, and a conventional laser printer is formed on the photosensitive drum 73. Laser beam scanning is performed in the same manner as described above. As described above, since scanning can be performed electronically without using a polygon mirror, very high-speed printing can be performed.

1 is a schematic configuration diagram of a laser scanning device in a conventional laser printer using a polygon mirror. 1 is a perspective view of one embodiment of a photonic crystal laser element according to the present invention. The schematic block diagram which shows the photonic crystal laser apparatus of a present Example. The top view which shows operation | movement of the photonic crystal laser apparatus of a present Example. The top view which shows the example which scans several light emission area | regions (beam of a laser beam) simultaneously. FIG. 4 is a vertical sectional view showing a photonic crystal laser element provided with means for changing the direction of laser light for each upper electrode. The perspective view of the other Example of the photonic crystal laser element based on this invention. The top view for demonstrating operation | movement of the photonic crystal laser element of FIG. The perspective view of the other Example of the photonic crystal laser element based on this invention. 1 is a schematic configuration diagram of a laser scanning device in a laser printer using a photonic crystal laser according to the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 ... Semiconductor laser 12 ... Polygon mirror 13, 74 ... Lens 14, 73 ... Photosensitive drum 21 ... Active layer 22 ... Lower spacer 23 ... Two-dimensional photonic crystal layer 24 ... Hole 25 ... Confinement layer 26 ... Lower cladding layer 27 32 ... Lower electrode 28 ... Upper spacer 29 ... Upper cladding layer 30 ... Contact layers 33, 331, 332, 333, 334, 335 ... Upper electrode 34 ... Switch 35 ... Control units 411, 412, 511, 512 ... Light emitting region 42 ... A region 61 where a two-dimensional photonic crystal is formed ... Microlenses 71, 72 ... Photonic crystal laser element

Claims (10)

a) an active layer that generates light of a predetermined wavelength by charge injection;
b) a two-dimensional photonic crystal provided above the active layer and having a periodic structure corresponding to the predetermined wavelength;
c) a plurality of upper electrodes arranged above the two-dimensional photonic crystal;
d) a lower electrode provided under the active layer;
A photonic crystal laser element comprising: a) an active layer that generates light of a predetermined wavelength by charge injection;
b) a two-dimensional photonic crystal provided above the active layer and having a periodic structure corresponding to the predetermined wavelength;
c) an upper electrode provided on the upper side of the two-dimensional photonic crystal;
d) a plurality of lower electrodes arranged below the active layer;
A photonic crystal laser element comprising:   3. The photonic crystal laser element according to claim 1, wherein the plurality of upper electrodes or lower electrodes arranged in a straight line are arranged linearly.   3. The photonic crystal laser element according to claim 1, wherein the plurality of upper electrodes or lower electrodes arranged in a two-dimensional manner are arranged.   5. The photonic crystal laser element according to claim 1, wherein the upper electrode is made of a material that is transparent to the light having the predetermined wavelength.   6. The photonic crystal laser element according to claim 1, wherein means for deflecting output laser light is provided on the upper electrode.   The photonic crystal laser element according to any one of claims 1 to 6, voltage applying means for applying a voltage between the upper electrode and the lower electrode, and an applied voltage for each of the upper electrode or the lower electrode arranged in plural. And a control means for controlling ON / OFF.   8. The photonic crystal laser device according to claim 7, wherein the control means sequentially turns on and off the applied voltage in the order of arrangement of the plurality of upper electrodes or lower electrodes arranged.   9. The control unit according to claim 8, wherein the control means applies a voltage to a set of a predetermined number of adjacent upper electrodes or lower electrodes arranged in parallel and moves the set. Photonic crystal laser device.   A laser printer comprising the photonic crystal laser device according to claim 7 as a light source.

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