JP2017112292A - Light-emitting element and optical coherence tomograph having the same - Google Patents

Abstract

Kind Code: A1 A light-emitting element is provided that is capable of more reliably detecting the intensity of light emitted from an active layer having a high current density by including a structure capable of detecting the intensity of light emitted from the light-emitting element. A light-emitting element (100) has a laminate (100) including two electrode layers (110, 118) and an active layer (113) provided therebetween, and the laminate (100) emits light in an in-plane direction of the active layer. has a waveguide through which is guided. A third electrode 103 is provided between the first electrode 101 and the second electrode 102 in the surface electrode layer. The third electrode detects (monitors) light generated by current injection into the active layer by the first electrode. [Selection drawing] Fig. 1

Description

  The present invention relates to a light emitting element and an optical coherence tomography having the same.

  As an apparatus for acquiring a tomographic image of an object (subject), there is an optical coherence tomography (hereinafter abbreviated as OCT). In Spectral domain OCT (SD-OCT), which is a kind of OCT, a light-emitting element called a superluminescent diode that emits light having an emission spectrum in a wide wavelength band is used. Hereinafter, a super luminescent diode may be abbreviated as SLD. An SLD has a semiconductor multilayer structure including an active layer. By utilizing inductive amplification that occurs while light propagates through the active layer, light in a wide wavelength band from one end face of the waveguide structure of the multilayer body. Is injected.

  Here, in SD-OCT, the depth resolution of the tomographic image is higher as the wavelength band of the emission spectrum of the light source is wider. Therefore, it is desirable that the light source used for SD-OCT has a wide wavelength band in the emission spectrum. In Non-Patent Document 1, a plurality of electrodes are arranged in series with respect to the waveguide direction of the light emitting element (SLD), and the emission spectrum is controlled by individually controlling the amount of current injected from the electrodes into the active layer. It is what. Specifically, the electrode region for injecting current into the SLD is divided into three in the light guiding direction of the SLD, and current injection is performed at a large current density from the electrode provided in the region closest to the light emission end. To emit light. Adjacent electrodes are configured to inject current at a smaller current density, thereby realizing a broad emission spectrum. This utilizes the fact that light emission in the short wavelength band tends to occur as the current density increases, and light emission in the long wavelength band tends to occur as the current density decreases. That is, light in a short wavelength band is generated by increasing the density of current injected from the electrode closest to the emission end. Then, by injecting a current having a smaller current density from an electrode adjacent thereto, light emission in a long wavelength band is generated, thereby realizing light emission in a wide band as the entire SLD.

JP 2014-120633 A

ELECTRONICS LETTERS 1st February 1996 Vol. 32 No. 3 pp. 255-256

  Here, the present inventors have found that there is a problem with the light emitting element as in Non-Patent Document 1. That is, the active layer into which current is injected with a large current density tends to have a high temperature, and thus the light emission intensity is likely to change. In addition, the active layer in which the current density is high is likely to deteriorate in a short period of time compared to the case where the current density is low. OCT using a light source with a narrow emission wavelength band may cause a problem that the resolution of an obtained tomographic image is lowered.

  Therefore, in a light emitting device using a plurality of electrodes, it is required to measure and monitor the emission intensity from the active layer where the current density increases.

  On the other hand, Patent Document 1 discloses a configuration in which a plurality of photodetectors are installed outside a light waveguide of a light emitting element in a light emitting element (SLD) in which an electrode is divided into a plurality of pieces in a light guiding direction. . According to this configuration, it is possible to detect individual light emission amounts caused by current injection from a plurality of electrodes, but the detected light is spontaneously emitted light leaking from the optical waveguide. There has been a demand for a structure for detecting light more reliably because the emission intensity of spontaneously emitted light leaking from the optical waveguide is small.

  In view of the above problems, an object of the present invention is to provide a light emitting element capable of more reliably detecting light emission intensity from an active layer having a high current density.

The light emitting device according to the present invention has a laminate including two electrode layers and an active layer provided therebetween,
A light emitting element that emits light from an end face in an in-plane direction of the laminate,
At least one of the two electrode layers constitutes an electrode group composed of three or more electrodes provided separately in the in-plane direction, and the light emitting element is disposed on the end face of the electrode group. Injecting current independently into a plurality of different regions in the active layer using at least two electrodes, the first electrode provided at the closest position and the second electrode different from the first electrode. In the electrode group, a third electrode provided between the first electrode and the second electrode in the electrode group is used, and the active is performed by the first electrode. A light emitting device configured to detect light generated by injecting current into a layer.

  According to the light emitting element according to the present invention, the light emission intensity from the active layer having a high current density can be detected more reliably by providing the light emission element with a configuration capable of detecting the light emission intensity.

It is the top view (a) and sectional drawing (b) which show the structure of the light emitting element which concerns on embodiment of this invention. It is the top view (a) and perspective view (b) of the light emitting element which concern on Embodiment 1 of this invention. FIG. 2A is a cross-sectional view taken along line a-a ′, a cross-sectional view taken along line b-b ′, and a cross-sectional view taken along line c-c ′. It is a figure which shows the structure of OCT which concerns on Embodiment 2 of this invention. It is the figure (a) which shows the emission spectrum of the light emission area | region corresponding to the 1st electrode of the light emitting element which concerns on Example 1 of this invention, and is the integrated intensity | strength (b) of an emission spectrum. The graph (a) showing the relationship between the current injected into the third electrode and the detected voltage in Example 1 of the present invention, and the emission spectrum (b) obtained when no current is injected into the second electrode. is there. Relationship between the amount of current injected into the first electrode (I ₁ ) and the voltage (V ₃ ) detected at the third electrode of the light emitting device according to Example 1 of the present invention. It is the structure (a) of the light emitting element which concerns on the reference example 1 of this invention, and the graph (b) of the emission spectrum obtained. It is the emission spectrum (a) and gain (b) which are obtained with the light emitting element which concerns on the reference example 1 of this invention. It is a figure which shows the structure (a) of the light emitting element which concerns on Example 2 of this invention, and the structure (b) of the light emitting element which concerns on the reference example 2. FIG. It is a figure which shows the structure (a) of the light emitting element which concerns on Example 3 of this invention, and the structure (b) of the light emitting element which concerns on the reference example 2. FIG. It is a figure which shows the structure (a) of the light emitting element which concerns on Example 4 of this invention, and the structure (b) of the light emitting element which concerns on the reference example 2. FIG.

  Hereinafter, a light-emitting element according to an embodiment of the present invention will be described with reference to FIG. FIG. 1A is a top view of the light emitting device according to this embodiment, and FIG. 1B is a cross-sectional view taken along the α-α ′ cross section of FIG.

(Light emitting element)
The light emitting element in this embodiment includes a stacked body 100 including two electrode layers 110 and 118 and an active layer 113 provided therebetween, and the stacked body 100 emits light in an in-plane direction of the active layer. Has a waveguide to be guided. The waveguide in FIG. 1 is configured by providing the ridge 120 on the active layer, but the waveguide may be configured by a structure other than the ridge structure. The active layer 113 is sandwiched between a lower clad layer 112 and an upper clad layer 114 provided on the substrate 111.

  In the light emitting device according to the present embodiment, when current is injected into the active layer 113 by the two electrode layers 110 and 118, the active layer 113 emits light, and the light is guided through the waveguide. Light is emitted from the end face 105 in the inward direction.

  In the present embodiment, at least one of the two electrode layers constitutes an electrode group composed of three or more electrodes provided separately in the in-plane direction of the waveguide (light guiding direction). FIG. 1 shows an example in which the electrode layer 110 constitutes an electrode group composed of three electrodes 101, 102, and 103. The electrodes 101, 102, 103 are provided on a contact layer 115 provided on the upper cladding layer 114.

  In this electrode group, the first electrode 101 provided at a position closest to the end face 105 on which light is emitted, the second electrode 102 different from the first electrode 101, and the active layer 113 are separated from each other. A current is injected into the active layer 113 with the other electrode layer 118 provided. Note that current injection may be performed using at least two electrodes of the first electrode 101 and the second electrode 102, and in order to inject current into the active layer by using four or more electrodes constituting the electrode group. The number of electrodes can be three or more.

  By using two electrodes, the first electrode 101 and the second electrode 102, current is independently injected into a plurality of different regions in the active layer 113, and light is emitted in different regions of the active layer. These generated lights are induced and amplified when propagating through the active layer 113, and the combined light is configured to be emitted from the end face 105.

By making the current densities injected into the first electrode 101 and the second electrode 102 different from each other, the emission wavelength of the active layer 113 can be made different from each other. Light in the wavelength band can be emitted. However, if the current density of the current injected into the active layer 113 is small, the emission intensity is low and light having a long wavelength is likely to be emitted. If the current density is large, the emission intensity is large and light having a short wavelength is likely to be emitted. Further, when the generated light propagates along the waveguide along the active layer 113, the longer the propagation distance, the greater the emission intensity due to induction amplification. Therefore, the first electrode 101 closest to the light emitting end face 105 of the light emitting element has a large current density of current injected into the active layer, and the second electrode 102 has a small current density. To. With such a configuration, light having a high emission intensity in a short wavelength band (band including λ ₁ ) is generated from the region of the active layer 113 into which current is injected by the first electrode 101. Then, light having a small emission intensity in a long wavelength band (a band including λ ₂ , λ ₁ <λ ₂ ) is generated from the region of the active layer 113 into which current is injected by the second electrode 102. The light in the long wavelength band is inductively amplified before reaching the light emission end face 105 of the light emitting element, and the light emission intensity increases. Finally, light having a high emission intensity can be emitted from a short wavelength to a long wavelength from the end face of the light emitting element. Here, although two examples of electrodes used for light emission in the electrode group have been described, three or more electrodes may be used depending on the wavelength band desired to be emitted by the light emitting element.

In the light emitting device according to this embodiment, a third electrode 103 is provided between the first electrode 101 and the second electrode 102 in the electrode group. The third electrode 103 is configured to detect (monitor) light generated when a current is injected into the active layer 113 by the first electrode 101. The third electrode 103 has a current of 0 kA / cm ² or less so that no current is injected into the active layer 113 or a current (reverse bias current) flows in a direction opposite to that of the first and second electrodes 101 and 102. Make the current density. With such a configuration, light generated in the active layer 113 by current injection by the first electrode 101 reaches the region of the active layer 113 including the region immediately below the third electrode 103, and carriers are generated. Arise. The generated current is detected as a voltage change or a current change by the third electrode 103, and can be calculated back to calculate the light emission intensity generated by the current injection from the first electrode 101. If the voltage of the third electrode 103 is fixed, a current change is detected, and if the voltage is not fixed, a voltage change caused by the generation of carriers is detected.

  As described above, the light emitting device according to the present embodiment can monitor in real time the light emission intensity from the region of the active layer 113 into which a current having a high current density is injected by the first electrode 101. Therefore, it is possible to detect a change in emission intensity due to a temperature change in the region during driving of the light emitting element. Further, when the emission intensity becomes smaller than a predetermined value, the control unit (not shown) increases the current density of the first electrode 101, and when the emission intensity becomes higher than the predetermined value, the feedback reduces the current density. You can control. In addition, when the active layer in the region is deteriorated and a predetermined light emission intensity cannot be obtained, driving of the light emitting element can be stopped.

  Note that detecting light by the third electrode 103 is not limited to detecting the light emission intensity (light emission amount), and voltage change, current change, etc. detected by the third electrode corresponding to the light emission intensity, There is no particular limitation as long as information on the parameters related to the emission intensity can be acquired.

  Here, when the waveguide of the light emitting element extends to both end faces of the laminate, there are two light exit end faces. In the following, of the end points of the waveguide of the light emitting element, an end face 105 that emits light that is actually used is referred to as an emission end face, and the other end face is referred to as a rear end face 106. The injection end face 105 side may be called the front side, and the rear end 106 side may be called the rear side.

Further, when the light emitting element can emit light and the emission wavelength from the highest level is λ ₁ and the emission wavelength from the next higher level is λ ₂ (λ ₁ <λ ₂ ), the first The electrode 101 and the second electrode 102 are driven so that the gain at λ ₂ is zero or more. Hereinafter, the electrode that performs such driving may be referred to as a light emission driving electrode. The third electrode 103 is preferably driven so that the gain at λ ₂ is less than zero. This is because light having a long wavelength (λ ₂ ) emitted from the second electrode has a wavelength of λ ₂ in the active layer region including the region immediately below the third electrode 103 when the gain at λ ₂ becomes zero or more. This is because light of a wavelength is absorbed. As a result, light having a long wavelength (λ ₂ ) is reduced in the wavelength band of light emitted from the light emitting element.

  The gain can be controlled mainly by the current density of the current injected into each electrode. The first electrode 101 is basically configured so as not to be divided on the waveguide. However, even if the first electrode 101 is divided into a plurality of parts, if the current density of these electrode regions is the same and the amount of light absorption at the part where the electrode is not provided (non-electrode part) is small, this As long as the effect of the invention can be obtained, it may be divided. Here, “the current density is the same” means a range where the difference in the current density of the divided electrode regions is ± 10%, and “the light absorption amount is small” means that the light absorption amount at the non-electrode portion is incident light. The state is less than 50% with respect to the amount of light.

  Hereinafter, the light-emitting element according to the present embodiment will be described in detail by taking a super luminescent diode (hereinafter, abbreviated as SLD) as an example of the light-emitting element as an example.

(Embodiment 1)
(Light emitting element)
Hereinafter, the structure of the light-emitting element according to Embodiment 1 of the present invention will be described with reference to FIG.

  2A and 2B are a top view and a perspective view, respectively, of the light emitting device according to this embodiment. 3 (a), 3 (b), and 3 (c) are cross sections cut along the aa ′, bb ′, and cc ′ sections of FIG. 2 (a), respectively. FIG.

  First, the structure will be described while explaining the manufacturing procedure of the light emitting device according to the present embodiment.

First, n-Al _0.5 GaAs is provided as an n-type cladding layer (lower cladding layer) 212 on the GaAs substrate 211, and InGaAs having an asymmetric multiple quantum well structure is provided as the active layer 213. Further, p-Al _0.5 GaAs is provided as the p-type cladding layer (upper cladding layer) 214, and highly doped p-GaAs is provided as the contact layer 215. Each of these layers can be grown sequentially using, for example, a MOCVD (Metal Organic Chemical Vapor Deposition) method. Here, the asymmetric quantum well structure has a multiple quantum well structure having a plurality of quantum wells, and at least one of the composition and the well width of at least one quantum well among the plurality of quantum wells is It refers to a well structure different from other quantum wells.

The wafer on which the layers are stacked is formed into a waveguide (also referred to as an optical waveguide) by forming a ridge 204 by a general semiconductor lithography method and semiconductor etching. By forming the ridge, light can be confined and guided in the active layer. For example, after forming a dielectric film and SiO ₂ using a sputtering method, a stripe mask for forming an optical waveguide is formed with a photoresist using a semiconductor lithography method. Thereafter, a portion of the semiconductor other than the striped mask is selectively removed using a dry etching method. At this time, the portion to be removed is halfway between the contact layer 215 and the p-type cladding layer 214, and the depth (height of the ridge) is, for example, 0.8 μm. The optical waveguide width w is set to a width of 3 μm so that the light emitted from the light emitting element is in a single mode. In order to suppress reflection at the exit end face 205 and the rear end face 206, the optical waveguide is inclined by about 7 degrees with respect to the normal direction of each end face.

Next, an insulating film 216, for example, SiO ₂ is formed on the semiconductor surface, and the insulating film 216 on the upper portion of the optical waveguide (upper portion of the ridge structure) is partially removed by photolithography and wet etching. Thereafter, the p-electrode 217 is formed using a vacuum deposition method and a lithography method. The p electrode 217 is, for example, Ti / Au, and a plurality of p electrodes 217 are arranged on the optical waveguide in a state of being insulated in series in the waveguide direction. Further, the contact layer 215 in a region where no electrode is provided (hereinafter also referred to as a non-electrode portion) 207 is removed by wet etching using citric acid / hydrogen peroxide to form an electrically insulated region.

  Before forming the n-electrode 218, the GaAs substrate 211 is thinned to a thickness of about 100 μm by polishing. By doing so, cleavage on the facet surface is facilitated. Then, the n electrode 218 is formed by a vacuum evaporation method. The n electrode 218 is, for example, AuGe / Ni / Au. In order to obtain good electrical characteristics, annealing is performed in a high-temperature nitrogen atmosphere to alloy both electrodes and the semiconductor. Finally, the light emitting element is completed by exposing facet surfaces to the emission end face 205 and the rear end face 206 by cleavage.

(Measurement method of luminescence intensity)
Next, how the light absorption amount is actually obtained and used from the injection current amount at the third electrode (absorption drive electrode) and the detected voltage value will be described below.

  First, the first electrode 201 is driven as a light emission drive electrode, and the third electrode 203 is driven as an absorption drive electrode. Further, a table having information on the relationship between the emission intensity from the active layer obtained by injecting current from the first electrode 201 and the injection current amount in the third electrode 203 region at that time and the detected voltage value is provided. Store in advance. Then, when driving, the driving state (current injection amount) in each electrode region is adjusted with reference to the table. Alternatively, instead of the table, an arithmetic expression representing the relationship between the two may be prepared, and the driving state may be adjusted based on the arithmetic expression. The table may be created at the time of initial driving. Moreover, you may have a memory which memorize | stores a table and an arithmetic expression. Note that the intensity of light emission using the first electrode is calculated using the voltage value of the third electrode and the current value of the third electrode. If the current value is known, only the voltage value is used. It is also possible to calculate.

  For the driving state actually used in the first electrode 201, a range is set for the injection current amount and the detected voltage value in the third electrode 203, so that the value falls within the determined range. The driving state of the first electrode 201 is adjusted based on a table or an arithmetic expression. For example, when there is a change in the injection current amount and the detected voltage value in the third electrode 202 region, the deterioration with time in the active layer region immediately below the first electrode 201 reduces the amount of light emitted from the higher level. It may be connected. Therefore, by increasing the current density in the first electrode 201 region, it is possible to return the higher-level light emission amount to the original level again.

  Further, since the change in the light emission intensity of the light emitting element is monitored in real time, the light emission characteristics of the light emitting element can be corrected at any time while the information related to the tomography of the object is acquired in the OCT.

  If it is not necessary to monitor the light emission amount in real time, an active layer region into which current is injected by the first electrode 201, a driving mode, and a monitoring driving mode are prepared. It is good also as a structure which switches a mode alternately. With such a configuration, an operation for setting a driving state necessary for the current conditions and environment may be performed.

  The formation method, semiconductor material, electrode material, dielectric material, and the like are not limited to those disclosed in the embodiment, and other methods and materials can be used as long as they do not depart from the spirit of the present invention. It is. For example, a p-type substrate may be used as the substrate, and in that case, the conductivity type of each semiconductor layer can be changed according to the conductivity type of the substrate.

(Active layer)
In this embodiment, the active layer is shown as an asymmetric quantum well structure (asymmetric multiple quantum well structure). A structure may be used. Further, the material is not limited to this, and a light emitting material such as GaAs, GaInP, AlGaInN, AlGaInAsP, and AlGaAsSb may be used.

  The active layer has a single thickness and a single composition in the waveguide direction, but is not limited to this as long as the effects of the present invention can be obtained.

(Waveguide)
In this embodiment, the waveguide has a linear shape and a shape with which a constant width and refractive index can be obtained. However, the waveguide shape may be bent or branched, and the waveguide width and refractive index may be guided. It may be configured to change in the wave direction. Further, the waveguide width w is preferably configured so that light emitted from the light emitting element is in a single mode. This is because single-mode light tends to gather in the center at a portion with high intensity in the light spot.

  Further, in order to obtain a single mode, the waveguide width w is 3 μm. However, the waveguide width w may be set so that multimode light emission occurs. Furthermore, the waveguide may not have a configuration extending to the end face.

  In this embodiment, an example of a ridge type optical waveguide is adopted as the waveguide. However, for example, a stripe type active layer or a current blocking layer may be introduced to confine light.

  In order to widen the emission wavelength band of the light emitting element, it is preferable that the light emitting element has a configuration that hardly causes laser oscillation. In order to make it difficult to oscillate the laser, it is necessary to suppress reflection at the exit end 205 and the rear end 206, which are the end of the waveguide. Therefore, although the waveguide is inclined about 7 degrees with respect to the normal direction of each end face, the angle can be appropriately changed. In order to suppress reflection at the end face, an anti-reflection (AR) film may be formed on each end face. In order to suppress the concentration of light and current at each end face, a region (window region) where current injection is not performed may be formed near each end face. The window region can be provided by extending the electrode to a position that does not reach the end face.

(Electrode layer)
As for the electrode layer in this embodiment, an example in which a plurality of p electrodes 217 are arranged in series with respect to the waveguide direction is shown, but the n electrode 218 or both of them are arranged in the waveguide direction. A configuration in which a plurality of electrodes are arranged in series may be used.

  In the present embodiment, three p electrodes 217 are arranged in series with respect to the waveguide direction, and a ridge 204 is formed to form a waveguide. A portion between two adjacent electrodes is a non-electrode portion 207, which is a region where current is not injected. In the non-electrode portion 207, the electrical resistance is increased by removing the contact layer 215 together with the p-electrode 217 for the purpose of preventing current leakage to the adjacent electrode region. Although not shown, all the electrodes are connected to current injection means for injecting current into the electrodes. That is, a mechanism capable of controlling the injection current amount in the light emission drive electrode (first electrode 201, second electrode 202), and a mechanism capable of detecting the injection current amount and voltage value in the absorption drive electrode (third electrode 203). (Control unit). Note that the absorption drive electrode for monitoring in the present embodiment is a third electrode.

  In the present embodiment, the number of electrodes of the plurality of electrodes is not limited to this as long as the number of electrodes (three or more) satisfies the requirement for obtaining the effects of the present invention.

  The width of the non-electrode portion 207 is not particularly limited as long as the effect of the present invention is obtained.

(Embodiment 2)
In the second embodiment of the present invention, an optical coherence tomography (hereinafter referred to as an optical coherence tomography, which may be hereinafter abbreviated as an OCT or OCT apparatus) provided with the light emitting element according to the above embodiment will be described below with reference to FIG.

  The OCT according to the present embodiment is configured such that light emitted from the light emitting element 601 is collected by a condenser lens 602 and propagates to an interference optical system (demultiplexing unit) 611 that divides the light into reference light and irradiation light. ing. The light demultiplexed by the demultiplexing unit 611 is configured to propagate to the reference optical system 603 and the irradiation optical system 605 for irradiating the object (object) 604 to be measured. Furthermore, the OCT in the present embodiment is obtained by the interference unit 607 and the interference unit 607 that cause the reference light reflected by the reflecting mirror 614 of the reference optical system 603 to interfere with the reflected light (backscattered light) from the object 604. A light detection unit 608 that detects interference light is included. Then, an interference signal is output based on the interference light detected by the light detection unit 608, an acquisition unit 609 that acquires information (tomographic image) regarding a tomogram of the object 604, and a display unit that displays information (tomographic image) regarding the tomography 610.

  The OCT according to the present embodiment will be described in more detail. In this embodiment, the light emitting element (SLD) according to the above embodiment is used as the light emitting element 601.

  The light wave unit 611 demultiplexes the reference light and the irradiation light via the optical fiber, and part of the demultiplexed light enters the reference optical system 603. Here, the light wave unit 611 and the interference unit 607 use the same fiber coupler.

  The reference optical system 603 includes collimator lenses 612 and 613 and a reflecting mirror 614, which is reflected by the reflecting mirror 614 and enters the optical fiber again. Irradiation light which is the other light demultiplexed by the demultiplexing unit 602 from the optical fiber enters the irradiation optical system 605. The irradiation optical system 605 includes collimator lenses 615 and 616, a reflecting mirror 617 for bending the optical path by 90 °, and a polarization controller 606 for aligning the polarization of the reflected (backscattered) light from the object. The irradiation optical system 605 serves to enter the incident light into the object 604 to be measured and to couple the reflected light to the optical fiber again.

  Each light returned from the reference optical system 603 and the irradiation optical system becomes interference light in the interference unit 607 and enters the light detection unit 608. The light detection unit 608 includes collimator lenses 618 and 619 and a line sensor 621 for obtaining information on light dispersed by the wavelength dispersion unit (spectrometer) 620. The spectroscope 620 uses a grating. The light detection unit 608 is configured to obtain information on light incident thereon.

  When the light detection unit 608 interference light is received, an interference signal is sent to the acquisition unit 609, and the acquisition unit 609 converts it into information about the tomography. Finally, information about a fault (information about a tomographic image) is obtained. This is displayed as information (tomographic image) about the tomography on the display unit 610 constituted by a display screen of a personal computer or the like.

  The light emitting element 601 according to Embodiment 1 is used. That is, the OCT in the present embodiment has a control unit 650 that detects the light emission intensity generated using the electrode closest to the emission end and controls the amount of current injected from the electrode for causing light emission. High-power and broadband light is emitted stably. This is because a mechanism for detecting (monitoring) the light emission intensity generated using the electrode closest to the emission end is provided, and feedback control can be performed so that a predetermined output is produced as necessary.

  Therefore, it is possible to stably acquire tomographic image information with high resolution of depth.

  The OCT in this embodiment is useful for tomographic imaging in industrial applications such as ophthalmology, dentistry, dermatology, and inspection of semiconductor chips.

Example 1
A light emitting device according to an example of the present invention will be described. The light-emitting element according to this example has a structure (FIGS. 1 and 2) similar to that of the light-emitting element (SLD) described in Embodiment 1, and is manufactured using the same materials and procedures.

In the light emitting element in this embodiment, the length L ₁ of the first electrode 201 is 0.28 mm, the length L ₃ of the third electrode 203 is 0.10 mm, and the length L ₂ of the second electrode 202 is 0. .10 mm, the optical waveguide width w is 3 μm, and the measurement temperature is 15 ° C. The center wavelength (λ ₁ ) of the emission wavelength from the active layer region into which current is injected by the first electrode 201 is 825 nm, and the center wavelength of the emission wavelength from the active layer region into which current is injected by the second electrode 202 ( λ ₂ ) was 870 nm.

First, for the light-emitting element in this example, current was injected only into the first electrode 201, and the emission intensity when the injection current amount was changed was measured to obtain the wavelength dependence (emission spectrum) of the emission intensity. The results are shown in FIG. According to FIG. 5 (a), the following amount of the injection current increases, gradually more since higher levels of luminescence (emission of short wavelength) is likely to occur, a light emission of lambda ₁ is dominant. Further, FIG. 5B shows the result of calculating the integrated intensity (integrated value of the intensity of light output from the light emitting element) from the emission spectrum of each injected current amount. Note that the optical characteristics when only the first electrode is driven in the SLD having a plurality of electrodes are obtained when the SLD including only the electrode having the electrode length equal to the length L1 of the _first electrode is caused to emit light. You may think that it is equal to the optical characteristics of

Next, FIG. 6A shows the result of measuring the voltage value detected by the third electrode 203 when current is injected into the first electrode 201 and the second electrode 202. It can be seen that the voltage value V ₃ detected at the third electrode increases as the current value I ₁ injected into the first electrode 201 increases.

Here, the relationship between the current value I ₁ injected by the first electrode 201 and the intensity of light emission obtained by injecting the current I ₁ can be seen from FIG. Therefore, the relationship between the voltage value V ₃ detected by the third electrode and the emission intensity (P ₁ ) obtained by the first electrode can be understood. The relationship between V ₃ and P ₁ can be stored in advance in a memory as a table. By using this table, from the voltage value V ₃ detected by the third electrode, it is possible to calculate the light absorption in the electrode region. That is, the emission intensity of light generated by injecting current from the first electrode 201 can be detected.

  Further, the current density injected by the first electrode can be controlled based on the emission intensity detected using the third electrode. For example, when the light emission intensity detected using the third electrode is smaller than the first predetermined value, the amount of current injected into the active layer by the first electrode is increased, so that the desired light emitting element can be obtained. The emission spectrum of can be maintained.

  Moreover, when it is further smaller than the second predetermined value smaller than the first predetermined value, control for stopping the light emission of the light emitting element may be performed.

(Light emission from the rear side of the third electrode)
Here, in the light emitting element of this embodiment, the light emission intensity detected using the third electrode is strictly light emission by the second electrode in addition to light emission by using the first electrode. it is conceivable that. Actually, how much the light emission by the second electrode has an influence was measured. First, in the light-emitting element, an emission spectrum in the case where the first electrode 201 and the second electrode 202 are driven as a light emission drive electrode and the third electrode 203 as an absorption drive electrode is shown in FIG. The amount of current injected into each electrode region at this time is 125 mA for the _first electrode 201 (I ₁ ), 0 mA for the third electrode 203 (I ₃ ), and 17 mA for the second electrode 202 (I ₂ ). At this time, the voltage (V ₃ ) at the third electrode 203 was 1.52V. In this driving state, the full width at half maximum of the emission spectrum of the light-emitting element is 85 nm, and a broadband emission spectrum is obtained as the SLD.

Next, each value of the x-intercept in FIG. 6A, that is, the relationship when the horizontal axis is I ₁ and the vertical axis is I ₃ (0 mA) is V ₃ is as shown in FIG. 7A. . From FIG. 7A, the integrated intensity of the emission spectrum where V ₃ is 1.52 V is 9.21E + 07 (2.58 mW as the optical output). That is, the emission intensity generated at the first electrode 201 is estimated to be 9.21E + 07 as the integrated intensity of the emission spectrum.

FIG. 7B shows a light emission spectrum when the first electrode 201 is driven as a light emission drive electrode and the third electrode 203 is driven as an absorption drive electrode. Amount of injected current to each electrode region to obtain the optical properties are _{I 1} is 125 mA, _{I 2} is 0 mA, _{I 3} is 0 mA, this time, _{V 3} was 1.53V. From FIG. 7A, the integrated intensity of the emission spectrum where V ₃ is 1.53 V is 9.93E + 07 (2.77 mW in terms of light output).

  Therefore, the result was estimated to be about 5% smaller when the light was emitted using the second electrode and when it was not emitted. This 5% is a difference in error level, and is not so large as to have a particularly large effect even when it is incorporated into a system or the like and actually used.

  The reason for the difference of about 5% is that the light absorbed by the third electrode 203 region, that is, the second electrode 202 is absorbed, although the light absorption amount at the absorption drive electrode is more conspicuous as the light has a shorter wavelength. Is considered to be the main cause.

(Reference Example 1)
Here, as shown in FIG. 8A, a sample in which each electrode length L of the light emitting element having two electrodes was 0.3 mm was manufactured. Next, current injection was performed only in the first electrode 301 region to obtain an emission spectrum (P ₀ (λ)). At this time, both λ ₁ and λ ₂ were driven to emit light (light emission drive). The injection current density of the first electrode 301 was 20.4 kA / cm ² , and the injection current density of the third electrode 303 region was 0 kA / cm ² . The emission spectrum (P ₀ (λ)) obtained at that time is shown in FIG. Subsequently, the injection current density in the third electrode 303 region is made the same as the injection current density in the first electrode 301 region, the amount of injection current in the first electrode 301 region is changed, and the emission spectrum ( P ₁ (λ)) is created. In this example, the injection current density of the first electrode 301 region is −1.0 to 3.5 kA / cm ² while the injection current density of the third electrode 303 region is 20.4 kA / cm ² . Changed. The emission spectrum (P ₁ (λ)) obtained at that time is shown in FIG. Finally, the gain (g (λ)) at each wavelength and each injection current density is calculated from the following equation.

この例の場合における利得を算出した結果を図９（ｂ）に示す。

FIG. 9B shows the result of calculating the gain in this example.

In the active layer of this example, when the current density of the injected current is 3.5 kA / cm ² or more, the gain at λ ₂ becomes zero or more, so that light emission driving is performed. When the injection current density is 1.3 kA / cm ² or less, the gain at λ ₂ is less than zero, so that the absorption driving state is set.

(Example 2)
A light-emitting device according to Example 2 of the present invention will be described with reference to FIG.

  Since the present embodiment is the same as the first embodiment except for the electrode configuration and the driving state, only the difference from the first embodiment will be described below. FIG. 10A is a top view of the light emitting device according to this example.

  In the light-emitting element in this embodiment, the first electrode 301 and the second electrode 302 are used as a light emission drive electrode, the third electrode 303 is used as an absorption drive electrode, and the non-electrode between the third electrode 303 and the second electrode 302 is used. The electrode part 304 is configured to be longer than the non-electrode part of the first embodiment. With such a configuration, light having mainly short wavelength components incident on the third electrode 303 region from the rear end face side can be reduced when passing through the non-electrode portion 304 and is detected by the third electrode 303. Can be brought close to the light amount from only the first electrode 301.

  Usually, the length of the non-electrode portion is set to a length (about 10 μm) that prevents current leakage to the adjacent electrode region. In this embodiment, the length between the third electrode 303 and the second electrode 302 is set. The effect can be obtained by setting the length of the non-electrode portion 304 longer than that.

The current injection density in the non-electrode portion 304 is 0 mA / cm ² . Therefore, from FIG. 9B, the gain of λ ₁ is −360 / cm, and by setting the length of the non-electrode portion 304 to 20 μm, the intensity of the light of λ ₁ after passing through the non-electrode portion is The strength can be reduced to 50% or less before passing through the non-electrode portion. Thereby, since the ratio of the light emission amount from the first electrode 301 region in the light absorption amount in the third electrode 303 increases, the light emission amount in the first electrode 301 region can be monitored more accurately. Therefore, the length of the non-electrode portion, that is, the length in the waveguide direction between the second electrode and the third electrode is preferably larger than 10 μm, and more preferably 20 μm or more.

From the viewpoint of reducing the intensity of the light of λ ₁ incident on the detection region, it is desirable that the length of the non-electrode portion is long. On the other hand, if the non-electrode portion is too long, the intensity of the light of λ ₂ becomes small, so that there is a possibility that the intensity of the light of λ ₂ desired to be output as a light emitting element cannot be obtained.

Considering similarly from FIG. 9B, the gain of λ ₂ is −180 / cm, and the light emission amount of λ ₂ is reduced by 90% or more by setting the length of the non-electrode portion 304 to 128 μm.

  As described above, the length of the non-electrode portion 304 in the waveguide direction is desirably 20 μm or more and 128 μm or less.

(Reference Example 2)
As shown in FIG. 10B, the following conditions are satisfied by satisfying the following conditions. Here, the length of the non-electrode portion 314 between the third electrode 313 and the region 312 including the second electrode is L ₀ , and the gain of λ ₁ when the injection current density is ₀ kA / cm ² is g The gain of λ ₂ when ₀ (λ ₁ ) and the injection current density is ₀ kA / cm ² is g ₀ (λ ₂ ).

なお、３１１は第一の電極である。

Reference numeral 311 denotes a first electrode.

(Example 3)
A light emitting device according to Example 3 of the present invention will be described with reference to FIG. Since the present embodiment is the same as the first embodiment except for the electrode configuration and the driving state, only the difference from the first embodiment will be described here.

  FIG. 11A is a top view of the light emitting device according to this example. The difference from the second embodiment is that an absorption drive electrode is newly provided instead of lengthening the non-electrode portion in the waveguide direction. With this configuration, the same effects as those of the second embodiment can be obtained, and the amount of light absorption can be increased as compared with the second embodiment, so that the length of the light emitting element in the waveguide direction can be shortened.

  In the light-emitting element in this embodiment, the first electrode 401 and the second electrode 402 are used as the light emission drive electrodes, and the third electrode 403 and the fourth electrode 404 are used as the absorption drive electrodes. Further, the absorption drive electrode for monitoring in this embodiment is the third electrode 403. With such a configuration, the third electrode 403 is injected with the intensity of mainly short-wavelength light incident from the rear end face of the light-emitting element, and the reverse bias current is injected by the fourth electrode 404. It can be reduced by passing through the region. As a result, the detection value of the light intensity detected by the third electrode 403 can be brought close to the detection value of only the light emission intensity from the first electrode 401.

When the current injection density at the second electrode 402 is −1.0 mA / cm ² , the gain of λ ₁ is −430 / cm from FIG. 9B and the length of the second electrode 402 is 17 μm. By doing so, it is possible to reduce the light emission amount of λ ₁ by 50% or more. Thereby, since the ratio of the light emission amount from the first electrode 401 in the light absorption amount in the third electrode 403 increases, the light emission amount in the first electrode 401 region can be monitored more accurately.

As in Example 2, it is not desirable that the emission amount of λ ₂ is greatly reduced because it becomes difficult to control the emission spectrum. When the injection current density in the second electrode 402 region is −1.0 mA / cm ² , the gain of λ ₂ is −350 / cm from FIG. By setting the value to 66 μm, the light emission amount of λ ₂ is reduced by 90% or more.
From the above, when the injection current density in the second electrode 402 region is −1.0 mA / cm ² , the length of the second electrode 402 is desirably 17 μm or more and 66 μm or less. Note that the desired electrode length changes by changing the injection current density in the second electrode 402 region.

(Reference Example 3)
Consider a configuration in which an absorption drive electrode 413 and a non-electrode portion 414 are provided between regions including the absorption drive electrode 413 and the second light emission drive electrode 412 as shown in FIG. In this configuration, the lengths of L ₁ , L ₂ ,..., L _n , and λ ₁ are gains of g ₁ (λ ₁ ), g ₂ (λ ₁ ),. Assume that the gains of _n (λ ₁ ) and λ ₂ are g ₁ (λ ₂ ), g ₂ (λ ₂ ),..., g _n (λ ₂ ). At this time, by providing a region satisfying the following conditions between the absorption drive electrode region and the second light emission drive electrode region, an embodiment that satisfies the requirements of this example is obtained.

かつ

And

したがって、第三の吸収駆動電極４１３の後方に設ける吸収駆動電極は１つに限定する必要はなく、複数の電極領域によって上記条件を満たす構成としてもかまわない。また、実施例２の形態と組み合わせて上記条件を満たす構成としてもかまわない。なお、４１１は、第一の発光駆動電極である。

Therefore, the number of absorption drive electrodes provided behind the third absorption drive electrode 413 need not be limited to one, and the above condition may be satisfied by a plurality of electrode regions. In addition, a configuration that satisfies the above conditions may be combined with the mode of the second embodiment. Reference numeral 411 denotes a first light emission drive electrode.

Example 4
A light-emitting element according to Example 4 of the present invention will be described with reference to FIG. Since the present embodiment is the same as the first embodiment except for the electrode configuration and the driving state, only the difference from the first embodiment will be described here.

  In the light emitting device according to this example, the first electrode 501 and the second electrode 502 are used as the light emission drive electrode, the third electrode 503 is used as the absorption drive electrode, and the current injection density of the second electrode 502 is set to the first electrode. The current injection density is smaller than 501. Also, the absorption drive electrode for monitoring in this embodiment is the third electrode 503. By doing so, it is possible to reduce the amount of light emitted mainly from the short wavelength component incident on the third electrode 503 region from behind, and to reduce the amount of light absorption in the third electrode 503 region from the first electrode 501 region. The amount of light emission can be approached.

  The difference between the present embodiment and the second and third embodiments is that there is no structure that mainly absorbs the light emission amount of the short wavelength component behind the third electrode, and the effect that the sample length can be shortened compared to the third embodiment. In addition, there is an advantage that the degree of freedom of electrode configuration can be increased at the design stage.

(Reference Example 4)
Drive state of the second electrode 502 to meet the present embodiment, from 8 injection starts out emission lambda ₁ in (a) current density and FIG. 9 (b), the injection current density of at least 3.5 or more 11. It will be satisfied if it is within the range of 9 kA / cm ² or less.

  An embodiment that satisfies the requirements of this example is shown in FIG. 12B, and the effects of this example can be obtained by adopting this electrode configuration and driving state.

DESCRIPTION OF SYMBOLS 100 Light emitting element 101 1st electrode 102 2nd electrode 103 3rd electrode 105 Outgoing end face 106 Rear end face 110 Electrode layer 111 Substrate 112 Lower clad layer 113 Active layer 114 Upper clad layer 118 Electrode layer 120 Ridge

Claims (12)

Having a laminate comprising two electrode layers and an active layer provided therebetween,
A light emitting element that emits light from an end face in an in-plane direction of the laminate,
At least one of the two electrode layers is
Constituting an electrode group consisting of three or more electrodes provided separated in the in-plane direction;
The light-emitting element includes a first electrode provided at a position closest to the end face in the electrode group;
Using at least two electrodes of a second electrode different from the first electrode,
It is configured to emit light by injecting current independently into a plurality of different regions in the active layer,
This occurs when a current is injected into the active layer by the first electrode using a third electrode provided between the first electrode and the second electrode in the electrode group. A light emitting device configured to detect light.   The light emitting device according to claim 1, configured to control a current density injected by the first electrode based on a light emission intensity detected using the third electrode.   The intensity of light generated by injecting current into the active layer by the first electrode is calculated from a voltage value using the third electrode. Light emitting element.   2. The device is configured to increase an amount of current injected into the active layer by the first electrode when light emission intensity detected using the third electrode is smaller than a predetermined value. The light emitting element as described in any one of thru | or 3. A current density greater than 0 kA / cm ² is injected into the first electrode and the second electrode,
5. The light emitting device according to claim 1, wherein a current having a current density of 0 kA / cm ² or less is injected into the third electrode.   The light emitting device according to any one of claims 1 to 5, wherein the active layer has a single thickness and a single composition in the in-plane direction.   The light emitting device according to claim 1, wherein a length in the in-plane direction between the second electrode and the third electrode is 20 μm or more.   The light emitting element according to claim 1, wherein a length in the in-plane direction between the second electrode and the third electrode is 128 μm or less.   A fourth electrode is provided between the second electrode and the third electrode, and current is injected into the active layer by the second electrode using the fourth electrode. The light emitting device according to claim 1, wherein the light emitting device is configured to absorb a part of the generated light.   The light emitting device according to claim 9, wherein a length of the fourth electrode in the in-plane direction is 17 μm or more.   The light emitting device according to claim 9 or 10, wherein a length of the fourth electrode in the in-plane direction is 66 µm or less.   A light-emitting device according to any one of claims 1 to 11, a light beam that is emitted from the light-emitting device and irradiated light that irradiates an object and a reference light, and a reflected light of the light that is irradiated to the object; An interference optical system that generates interference light by the reference light, a wavelength dispersion unit that wavelength-disperses the interference light, a light detection unit that receives the wavelength-dispersed interference light, and the intensity of the received interference light An optical coherence tomometer comprising: an acquisition unit that acquires information on the object based on

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