Patent Description:
A surface-emitting laser array, in which multiple surface-emitting laser elements (vertical cavity surface emitting lasers (VCSEL)) are arranged two-dimensionally, is used as a laser light source.

Conventionally, a VCSEL array, in which a laminated body including an active layer is formed on a semiconductor substrate and a light emitting window is formed on the back side of the substrate, has been proposed (for example, see Patent Literature <NUM>). <CIT> discloses a vertical cavity surface emitting laser (VCSEL) device containing one VCSEL or an array of VCSELs. Each VCSEL has a corresponding integrated microlens.

<CIT> discloses a semiconductor surface emitting array including VCSEL or RC-LED array and an array of microlens elements to generate a wide range of structured light illumination patterns.

<CIT> discloses laser equipment including: a surface emitting laser for emitting an excitation light; a light converter for outputting an output light by receiving the excitation light; and a lens portion for collimating or concentrating a light.

<CIT> discloses a method for fabricating a VCSEL using wafer bonding. <CIT> discloses a laser device comprising at least one large area VCSEL and at least one optical feedback element providing an angular-selective feedback for laser radiation emitted from the laser. The angular-selective feedback is higher for at least one portion of laser radiation emitted at angles θ > <NUM> to the optical axis of the laser than for laser radiation emitted on said optical axis.

However, in the conventional VCSEL, it is difficult to control a radiation angle of a laser beam emitted from the VCSEL element.

The present invention has been conceived in view of the foregoing situations, and an object is to control a radiation angle of a laser beam emitted from a surface-emitting laser.

According to an aspect of the present invention, there is provided a surface-emitting laser array, detection device, light receiver and laser device as specified in the claims.

According to an embodiment of the present invention, it is possible to control a radiation angle of a laser beam emitted from a surface-emitting laser.

Exemplary embodiments of a surface-emitting laser array, a detection device, and a laser device will be described in detail below with reference to the accompanying drawings. The present invention is not limited by the embodiments below.

<FIG> is a partial lateral cross-sectional view illustrating an example of a configuration of a surface-emitting laser array according to a first example, and <FIG> is a partial bottom view illustrating an example of the configuration of the surface-emitting laser array according to the first example.

A surface-emitting laser array <NUM> includes a plurality of surface-emitting laser elements <NUM> (hereinafter, referred to as light emitting elements) that are arranged on a first surface 10a of a semiconductor substrate <NUM>, a plurality of microlenses <NUM> that are arranged on a second surface 10b, a light shielding member <NUM> that is provided on the second surface 10b, and a surface electrode <NUM>. In the example illustrated in <FIG>, the n-type semiconductor substrate <NUM> is used. Further, the semiconductor substrate <NUM> is made of a material that is transparent to laser beams emitted by the light emitting elements <NUM>.

The light emitting elements <NUM> are elements that emit laser beams in a direction crossing the first surface 10a (in general, in a perpendicular direction). Each of the light emitting elements <NUM> includes a lower reflecting layer <NUM>, a resonator constructing layer <NUM>, an upper reflecting layer <NUM>, a current constriction layer <NUM>, and a protection film <NUM>.

The lower reflecting layer <NUM> is arranged on the semiconductor substrate <NUM> and constructed with a semiconductor multilayer, in which a high refractive index n-type semiconductor film having an optical thickness of λ/<NUM> (here, λ is one wavelength of a laser beam emitted from the light emitting element <NUM>) and a low refractive index n-type semiconductor film having an optical thickness of λ/<NUM> are alternately and repeatedly laminated.

The resonator constructing layer <NUM> is a layer that is arranged between the lower reflecting layer <NUM> and the upper reflecting layer <NUM> and constructs an optical resonator. For example, the resonator constructing layer <NUM> has a structure in which an active region is sandwiched between a lower spacer layer and an upper spacer layer. The lower spacer layer and the upper spacer layer are constructed with, for example, non-doped semiconductor layers. The active region includes a semiconductor material that is selected depending on a wavelength of a laser beam to be emitted. A thickness of the resonator constructing layer <NUM> in a direction perpendicular to the first surface 10a of the semiconductor substrate <NUM> is set to, for example, one wavelength (=λ) of the laser beam emitted from the light emitting element <NUM>. Further, a wavelength that is not absorbed by the semiconductor substrate <NUM> is selected as a wavelength of a laser beam emitted from the resonator constructing layer <NUM>.

The upper reflecting layer <NUM> is arranged on the resonator constructing layer <NUM> and constructed with a semiconductor multilayer, in which a high refractive index p-type semiconductor film having an optical thickness of A /<NUM> and a low refractive index p-type semiconductor film having an optical thickness of A /<NUM> are alternately and repeatedly laminated.

The current constriction layer <NUM> is a layer that is provided inside the upper reflecting layer <NUM> in order to reduce an electric current passage area. The current constriction layer <NUM> includes a current constriction region <NUM> that is provided in a predetermined region including a center of the position at which the light emitting element <NUM> is formed, and an oxidized region <NUM> that is provided on the periphery of the current constriction region <NUM>. By reducing the electric current passage area using the current constriction layer <NUM>, it is possible to reduce a lasing threshold. The current constriction region <NUM> is made of the same material as the semiconductor film that forms the upper reflecting layer <NUM>, and the oxidized region <NUM> is made of a material that is obtained by oxidizing the same semiconductor film as the current constriction region <NUM>.

The upper reflecting layer <NUM> and the current constriction layer <NUM> are processed into mesa shapes on the resonator constructing layer <NUM>. In other words, the upper reflecting layer <NUM> and the current constriction layer <NUM> are configured so as to be separated from those of the adjacent light emitting elements <NUM>. In the following description, the upper reflecting layer <NUM> and the current constriction layer <NUM> processed into the mesa shapes will be referred to as a mesa structure <NUM>. In the first example, the mesa structures <NUM> are provided so as to be located at lattice points of a square lattice (hereinafter, referred to as a square-lattice shape) on the first surface 10a of the semiconductor substrate <NUM>.

The protection film <NUM> is provided so as to cover side surfaces of the mesa structure <NUM> and the resonator constructing layer <NUM>. In other words, the protection film <NUM> is provided on the resonator constructing layer <NUM>, on which the mesa structure <NUM> is provided, such that a top surface of the mesa structure <NUM> is exposed.

The microlenses <NUM> are provided on the second surface 10b of the semiconductor substrate <NUM> to correspond to arrangement positions of the light emitting elements <NUM>. Because the light emitting elements <NUM> (the mesa structures <NUM>) are arranged in the square-lattice shape, the microlenses <NUM> are also arranged in the square-lattice shape as illustrated in <FIG>. The microlenses <NUM> are optical elements that reduce radiation angles of laser beams emitted from the corresponding light emitting elements <NUM>. By reducing the radiation angles of the laser beams, it is possible to reduce a spot diameter when the laser beams that have passed through the microlenses <NUM> are collected onto a target object via a condenser lens or the like. The microlenses <NUM> are obtained by, for example, processing regions that correspond to the arrangement positions of the light emitting elements <NUM> on the second surface 10b side of the semiconductor substrate <NUM> into convex lens shapes. In this example, the radiation angle means an angle at which <NUM>% of the maximum intensity of a laser beam is obtained.

To control the radiation angle of a laser beam emitted from a surface-emitting laser by using a lens, it is desirable to use a lens with a long focal length. For example, it is desirable to ensure a certain optical length (up to about hundreds micrometers (µm)) between a light emitting unit and a lens. However, if the optical length between the light emitting unit and the lens is increased, a beam diameter is increased until the laser beam reaches the lens part. As a result, the beam diameter at the lens part may exceed a lens diameter and the laser beam may enter a residual portion between the lenses, so that stray light may occur. Therefore, in the first example, the light shielding member <NUM> is arranged on the residual portions to prevent stray light.

As illustrated in <FIG>, the light shielding member <NUM> covers gaps between the microlenses <NUM> on the second surface 10b of the semiconductor substrate <NUM> and has a function to reflect or absorb light emitted from the light emitting elements <NUM>. With this configuration, as illustrated in <FIG>, laser beams B that reach outer peripheries of the microlenses <NUM> among laser beams emitted from the light emitting elements <NUM> are not emitted from the second surface 10b of the semiconductor substrate <NUM>. Further, the light shielding member <NUM> prevents laser beams emitted by the light emitting elements <NUM> corresponding to the adjacent microlenses <NUM> from reaching the subject microlens <NUM>, so that it is possible to largely reduce stray light. As the light shielding member <NUM>, a metal film that reflects laser beams, a semiconductor multilayer reflective film, or a semiconductor film that has a smaller bandgap than the laser beams emitted by the light emitting elements <NUM> and that absorbs the laser beams may be used. The semiconductor multilayer reflective film and the semiconductor film are formed by, for example, epitaxial growth on the second surface 10b side of the semiconductor substrate <NUM>. Meanwhile, the light shielding member <NUM> is not limited to those as described above, and, for example, may be made of a material that can be applied by a spin coating method. Further, while the light shielding member <NUM> in film form is described in this example, the light shielding member <NUM> is not limited to film form and may be in bulk form.

A preferable size of a lens diameter ϕ of the microlens <NUM> (a diameter of the lens) will be described below. When the microlenses <NUM> are formed by performing dry etching on the semiconductor substrate <NUM> using lens-shaped photoresists as masks, the lens diameter ϕ of each of the microlenses <NUM> needs to be smaller than a pitch X between the light emitting elements <NUM> in order to prevent interference between the photoresists. In other words, a gap of X- ϕ is present between the adjacent microlenses <NUM>, and this gap will be referred to as a residual. By coating the residuals with the light shielding member <NUM> that prevents transmission of laser beams, it is possible to prevent stray light and collect light beams with a small beam spot diameter.

The surface electrode <NUM> is provided on the protection films <NUM> of the light emitting elements <NUM>. The protection films <NUM> are not provided on the upper parts of the mesa structures <NUM>, and therefore, the surface electrode <NUM> comes in electrical contact with the upper reflecting layers <NUM>. Further, a back surface electrode is provided on the second surface 10b side of the semiconductor substrate <NUM>. The surface electrode <NUM> and the back surface electrode are provided to cause electrical currents to flow into the active regions of the light emitting elements <NUM>. When the light shielding member <NUM> is made of a conductive material, the light shielding member <NUM> may also function as the back surface electrode.

It may be possible to use a GaAs substrate as the semiconductor substrate <NUM>, and use InGaAs as the active layers. When InGaAs is used as the active layers, a peak wavelength of an oscillation spectrum of each of the light emitting elements <NUM> is in a range of about <NUM> to <NUM> nanometers (nm). Further, a wavelength band at around <NUM> that is included in the above-described wavelength band is one of wavelength bands that are absorbed by earth's atmosphere, the spectrum of the sunlight has a relatively low intensity around <NUM>, and if applied to a measurement distance device using a laser beam, it is possible to construct a system with low noise. Furthermore, similarly, the wavelength band of <NUM> is a wavelength band where an absorption coefficient of Yb:YAG (yttrium aluminum garnet) is large, so that it is possible to excite Yb:YAG solid-state laser with high efficiency. Moreover, InGaAs is a material that exhibits compressive strain with respect to GaAs and has a high differential gain when used as an active layer of a semiconductor laser. Therefore, it is possible to realize low threshold oscillation, so that it is possible to provide the surface-emitting laser array <NUM> with high efficiency.

Furthermore, it may be possible to use an InP substrate as the semiconductor substrate <NUM>, and use InGaAs as the active layers. In this case, the peak wavelength of the oscillation spectrum of each of the light emitting elements <NUM> is in a range of <NUM> to <NUM> µm.

It may be possible to use, as the lower reflecting layer <NUM> and the upper reflecting layer <NUM>, a laminate in which multiple pairs of Al(Ga)As films with different aluminum compositions are laminated. It may be possible to use, as the current constriction layer <NUM>, an AlAs film or an AlGaAs film that is a material used for the upper reflecting layer <NUM>. Further, while the semiconductor multilayer reflective films are used as the lower reflecting layer <NUM> and the upper reflecting layer <NUM> in this example, it may be possible to use a dielectric multilayer reflective layer in which a low refractive index dielectric film and a high refractive index dielectric film are alternately and repeatedly laminated. As the dielectric multilayer film as described above, for example, it may be possible to use a laminate in which tantalum pentoxide and silicon dioxide (Ta<NUM>O<NUM>/SiO<NUM> ) are alternately and repeatedly laminated. However, in this case, it is impossible to cause electrical currents to flow into the lower reflecting layer <NUM> and the upper reflecting layer <NUM>, and therefore, it is necessary to form electrodes by adopting an intra-cavity structure.

It may be possible to use AlGaInP, GaInP, AlGaAs, or the like as the lower spacer layers and the upper spacer layers inside the resonator constructing layers <NUM>. Further, it may be possible to use InGaAsP as the active layers.

It may be possible to use, as the surface electrode <NUM>, a multilayer film of Cr/ AuZn/Au or Ti/Pt/Au laminated in this order from the first surface 10a side. When these materials are used as the surface electrode <NUM>, the topmost surface is made of Au that is chemically stable, so that it is possible to obtain high reliability. Further, it may be possible to use a metal capable of realizing Ohmic contact as the material of the back surface electrode. It may be possible to use, as the back surface electrode, a multilayer film of AuGe/Ni/Au laminated in this order from the second surface 10b side.

It may be possible to use a metal material, such as Au, as the light shielding member <NUM>. Meanwhile, when a metal material, such as Au, is used as the light shielding member <NUM>, the light shielding member <NUM> may also function as the back surface electrode.

While the example has been described above in which the n-type semiconductor substrate <NUM> is used, it may be possible to use the p-type semiconductor substrate <NUM>. In this case, the current constriction layer <NUM> is provided on the lower reflecting layer <NUM> side. Further, in this case, it may be possible to use, as the surface electrode <NUM>, a multilayer film of AuGe/Ni/Au laminated in this order from the first surface 10a side. Furthermore, it may be possible to use, as the back surface electrode, a multilayer film of Cr/AuZn/Au or Ti/Pt/Au laminated in this order from the second surface 10b side.

Next, a method of manufacturing the surface-emitting laser array <NUM> configured as above will be described. As a method of manufacturing the light emitting elements <NUM>, a well-known technique is applicable, and therefore, only summary thereof will be described. A method of generating the light shielding member <NUM> will be described with reference to the drawings. <FIG> are cross-sectional views schematically illustrating an example of the flow of the method of generating the light shielding member <NUM> according to the first example. In <FIG>, the semiconductor substrate <NUM> is arranged with the second surface 10b facing upward.

First, semiconductor layers including the lower reflecting layers <NUM>, the resonator constructing layers <NUM> including the active layers, and the upper reflecting layers <NUM> are deposited on the first surface 10a of the semiconductor substrate <NUM>. As a method of forming the semiconductor layers, for example, a metal organic chemical vapor deposition (MOCVD) method, a molecular beam epitaxy (MBE) method, or the like may be used.

Subsequently, photoresists are applied onto the upper reflecting layers <NUM>, and exposure processing based on the lithography technique and developing processing are preformed, so that resist patterns are generated in regions in which the mesa structures <NUM> are formed. Thereafter, etching is performed based on the dry etching technique, such as the reactive ion etching (RIE) method, using the resist patterns as masks until the resonator constructing layers <NUM> are exposed, so that the mesa structures <NUM> are formed. Top surfaces of the mesa structures <NUM> may be formed in, for example, circular shapes, elliptical shapes, square shapes, rectangular shapes, or any other shapes. Further, the mesa structures <NUM> are formed so as to be arranged in the square-lattice shape on the first surface 10a.

Thereafter, the semiconductor films that are exposed on the side surfaces of the mesa structures <NUM> and that serve as the current constriction layers <NUM> are oxidized by being subjected to, for example, high-temperature treatment in a water-vapor atmosphere, so that the oxidized regions <NUM> are formed on the peripheral portions of the semiconductor films. Regions that are not oxidized in the semiconductor films that constitute the current constriction layers <NUM> serve as the current constriction regions <NUM>. Thus, the current constriction layers <NUM> are formed.

Meanwhile, when InGaAs is used for the active layers, because InGaAs is a material that does not contain Al that is chemically active, a small amount of oxygen that is present in a reaction room during crystal growth is less likely to be introduced into the active layers. With this configuration, it is possible to provide the surface-emitting laser array <NUM> with high reliability.

Subsequently, the protection films <NUM> are formed on the entire resonator constructing layers <NUM> having the mesa structures <NUM>. As a method of forming the protection films <NUM>, for example, a plasma CVD method or the like may be used. Thereafter, photoresists are applied onto the protection films <NUM> by a spin coating method or the like, and exposure processing based on the lithography technique and developing processing are preformed, so that resist patterns in which the top surfaces of the mesa structures <NUM> are opened are formed. Then, the protection films <NUM> formed on the top surfaces of the mesa structures <NUM> are removed by the anisotropic etching technique, such as the RIE method, using the resist patterns as masks. With this operation, openings are formed in the protection films <NUM> at positions corresponding to the top surfaces of the mesa structures <NUM>. After the resist patterns are removed, the surface electrode <NUM> is formed on the protection films <NUM>. With this operation, the surface electrode <NUM> is electrically connected to the upper reflecting layers <NUM>.

Thereafter, a photoresist is applied onto the second surface 10b of the semiconductor substrate <NUM>, and, for example, exposure processing based on the gray-tone mask lithography technique and developing processing are preformed, so that a resist pattern in which lens shapes are formed at positions where the microlenses <NUM> are to be formed is formed. Subsequently, etching is performed based on the dry etching technique, such as the RIE method, using the resist pattern as a mask, so that the microlenses <NUM> are formed on the second surface 10b of the semiconductor substrate <NUM>. The microlenses <NUM> are formed in the square-lattice shape to correspond to the light emitting elements <NUM> that are formed on the first surface 10a.

Meanwhile, the method of forming the microlenses <NUM> is not limited to the above-described example. For example, it may be possible to cause epitaxial growth of semiconductor films to occur on the second surface 10b of the semiconductor substrate <NUM>, apply resists on the semiconductor films, and perform patterning such that the resists remain at positions where the microlenses <NUM> are to be formed. Thereafter, resist patterns are formed by deforming the resists into convex lens shapes by reflowing the resists. Then, etching is performed on the epitaxially grown semiconductor films based on the dry etching technique, such as the RIE method, using the resist patterns as masks, so that semiconductor films in the forms of the microlenses <NUM> are formed.

Further, it may be possible to form the microlenses <NUM> by dropping solution of cured resin precursor with optical transparency at the positions where the microlenses <NUM> are to be formed on the second surface 10b of the semiconductor substrate <NUM>, and curing the precursor. Furthermore, it may be possible to form the microlenses <NUM> by methods other than those as described above.

Thereafter, as illustrated in <FIG>, a resist is applied onto the second surface 10b of the semiconductor substrate <NUM> on which the microlenses <NUM> are formed, and exposure processing based on the lithography technique and developing processing are preformed, so that resist patterns <NUM> for liftoff are formed on the microlenses <NUM>.

Subsequently, as illustrated in <FIG>, the light shielding member <NUM> is formed on the second surface 10b on which the resist patterns <NUM> are formed. The light shielding member <NUM> is film-formed by a vacuum evaporation method, a sputtering method, or the like depending on a type of the light shielding member <NUM>. The light shielding member <NUM> is formed on the second surface 10b and the resist patterns <NUM>. Then, as illustrated in <FIG>, the resist patterns <NUM> are lifted off to remove unnecessary portions, so that the light shielding member <NUM> remains in regions other than the microlenses <NUM>. Through the above-described operation, the surface-emitting laser array <NUM> as illustrated in <FIG> is obtained.

Meanwhile, by using a metal material, such as Au, as the light shielding member <NUM>, it is possible to cause the light shielding member <NUM> to also further function as the back surface electrode. With this configuration, it is possible to simultaneously form the light shielding member <NUM> and the back surface electrode, so that it is possible to simplify a manufacturing process. At this time, it is possible to form the back surface electrode in the same manner as described above with reference to <FIG>.

The configuration of the surface-emitting laser is not limited to the configuration as illustrated in <FIG>. <FIG> is a partial cross-sectional view illustrating another example of the configuration of the surface-emitting laser array according to the first embodiment. In <FIG>, the surface-emitting laser array is illustrated upside down as compared to <FIG>, and the surface electrode <NUM> is connected to a heatsink <NUM> via a joint material <NUM>. It may be possible to use an electrode instead of the joint material <NUM>. Meanwhile, the same components as those illustrated in <FIG> are denoted by the same reference symbols, and explanation thereof will be omitted.

With this configuration, a distance between peripheries of the active layers that mainly generate heat at the time of operation and the heatsink <NUM> is reduced, so that radiation performance is improved, and it is possible to improve efficiency of the surface-emitting laser array <NUM>.

Next, an effect of the first example will be described in comparison with a comparative example in which the light shielding member <NUM> is not provided on the second surface 10b of the semiconductor substrate <NUM>. <FIG> is a partial cross-sectional view illustrating an example of a configuration of a surface-emitting laser array according to the comparative example. Meanwhile, the same components as those illustrated in <FIG> are denoted by the same reference symbols, and explanation thereof will be omitted. Specifically, in a surface-emitting laser array 1C of the comparative example, the light shielding member <NUM> is not provided in a region other than the positions where the microlenses <NUM> are formed on the second surface 10b of the semiconductor substrate <NUM>.

Laser beams that oscillate from a light-emitting region <NUM> inside the resonator constructing layer <NUM> of each of the light emitting elements <NUM> pass through the semiconductor substrate <NUM> and are output to the outside via the microlens <NUM>. At this time, laser beams A that pass through the inside of the microlens <NUM> directly enter a condenser lens. However, laser beams B that are output from the outside of the microlens <NUM>, that is, from the residuals between the microlenses <NUM> on the second surface 10b, become stray light. Then, the stray light may increase the spot diameter when the laser beams are collected via the condenser lens or the like.

In the first example, the laser beams A that pass through the inside of the microlens <NUM> among the laser beams that oscillate from the light-emitting region <NUM> inside the resonator constructing layer <NUM> of each of the light emitting elements <NUM> directly enter a condenser lens, similarly to the comparative example. In contrast, the laser beams B that reach the residuals outside the microlens <NUM> are reflected or absorbed by the light shielding member <NUM>. Further, unexpected laser beams that are incident from the other light-emitting regions <NUM> onto the microlens <NUM> are also reflected or absorbed by the light shielding member <NUM>. As a result, it is possible to largely reduce stray light that is output from the residual portions to the outside of the surface-emitting laser array <NUM>. By largely reducing the stray light, it is possible to control radiation angles of laser beams emitted from the surface-emitting lasers, so that it is possible to reduce the radiation angles at the time the laser beams emitted from the light-emitting regions <NUM> pass through the microlenses <NUM>. Therefore, it is possible to reduce a size of a target object, such as a reflecting mirror, that is for performing laser beam scanning, so that it is possible to reduce the size of the device as compared to the comparative example.

Further, the microlenses <NUM> are formed on the second surface 10b of the semiconductor substrate <NUM> by performing etching on the semiconductor substrate <NUM> or curing resin that is transparent to laser beams. Therefore, it is not necessary to manufacture the microlenses <NUM> from silica, glass, or the like and then mount the microlenses <NUM>, so that it is possible to reduce the number of components and manufacturing processes, enabling to manufacture the surface-emitting laser array <NUM> at low costs.

<FIG> is a partial bottom view illustrating an example of a configuration of a surface-emitting laser array according to a second example. <FIG> is a diagram of the surface-emitting laser array <NUM> viewed from the second surface 10b side of the semi- conductor substrate <NUM>. In the first example, the microlenses <NUM> are arranged in the square-lattice shape in accordance with the arrangement positions of the light emitting elements <NUM>. In contrast, in the second example, the light emitting elements <NUM> and the microlens <NUM> are provided so as to be located at all of corners and centers of regular hexagons. Other configurations are the same as those of the first example, and therefore explanation thereof will be omitted.

In the second example, the light emitting elements <NUM> and the microlens <NUM> are provided so as to be located at all of corners and centers of regular hexagons, so that when the light emitting elements <NUM> are arranged at equal intervals, it is possible to arrange the light emitting elements <NUM> in a most densely manner. As a result, to obtain the same laser beam output, it is possible to reduce a chip size as compared to the arrangement of the first example illustrated in <FIG>.

<FIG> is a partial lateral cross-sectional view illustrating an example of a configuration of a surface-emitting laser array according to a first embodiment, and <FIG> is a partial bottom view illustrating an example of the configuration of the surface-emitting laser array according to the first embodiment. In the surface-emitting laser array <NUM> according to the first embodiment, the light shielding member <NUM> provided on the second surface 10b side of the semiconductor substrate <NUM> covers not only the residual portions but also peripheral portions in a predetermined range from outer edges of the microlenses <NUM>. Meanwhile, the same components as those of the first example will be denoted by the same reference symbols, and explanation thereof will be omitted.

As described above, to reduce the radiation angles (divergence angles) of the laser beams emitted from the light emitting elements <NUM>, it is necessary to increase the thickness of the semiconductor substrate <NUM> and collect the laser beams by the microlenses <NUM> with increased focal lengths. However, if the thickness of the semiconductor substrate <NUM> is increased, laser beams from a certain light emitting element enter the microlenses <NUM> corresponding to the adjacent light emitting elements, in particular, enter the peripheral portions of the microlenses <NUM>, due to divergence of the laser beams inside the semiconductor substrate <NUM>, so that stray light may occur. Therefore, by providing the light shielding member <NUM> so as to cover the peripheral portions from the outer edges of the microlenses <NUM> as in the first embodiment, it is possible to reduce the radiation angles of the emitted laser beams while preventing stray light caused by the laser beams B emitted from the adjacent light emitting elements <NUM>, so that it is possible to further reduce a light condensing spot dimeter.

Further, in a general microlens formation method, it is difficult to form even the peripheral portions of the microlenses <NUM> into desired shapes. Therefore, in some cases, curvatures of the peripheral portions of the microlenses <NUM> may be deviated from the curvatures of the central portions of the microlenses <NUM>. If a microlens array configured as above is used, light that enters the peripheral portions in which target curvatures are not obtained may become stray light even when the light is emitted from the light emitting units that correspond to the lenses.

In the first embodiment, the light shielding member <NUM> covers not only the residual portions but also the peripheral portions of the microlenses <NUM>, so that it is possible to prevent stray light that may occur due to the laser beams emitted from the light emitting unit corresponding to the lens.

A desirable range of the peripheral portions of the microlenses <NUM> to be covered by the light shielding member <NUM> will be described below. As described above, in general, it is difficult to manufacture peripheral portions of a microlens array with desired curvatures. Portions outside the effective ranges of the peripheral portions may have sizes of <NUM>% of the lens diameters ϕ (<NUM>% from outer circumferences of the lenses) at a maximum, depending on manufacturing methods.

In contrast, if the light shielding member <NUM> is provided in the effective ranges of the lenses, laser beams that are expected to be subjected to desired beam shaping are blocked, so that output from the surface-emitting laser is reduced. Therefore, it is desirable to appropriately select, depending on profiles, a range of the peripheral portions of the microlenses <NUM> in which the light shielding member <NUM> is to be provided, within a range of <NUM> to ϕ /<NUM> from the outer circumferences of the lenses.

A coated width h of the light shielding member <NUM> from the outer edge of the microlens <NUM> falls in a range of <NUM> ≦<NUM> ≦ϕ/<NUM>, as illustrated in <FIG>. In this manner, the light shielding member <NUM> is provided on the residual portions between the microlenses <NUM> and the peripheral portions with the coated widths h in the range of <NUM> ≦<NUM>≦ ϕ /<NUM> from the outer edges of the microlenses <NUM>.

Next, a desirable thickness of the semiconductor substrate <NUM> will be described. As described above, if the thickness of the semiconductor substrate <NUM> is increased, it is possible to collect emitted laser beams with a smaller beam spot diameter. However, the beam diameters inside the semiconductor substrate <NUM> are increased, and the laser beams enter the adjacent microlenses <NUM>, so that stray light occurs. A beam diameter D that is obtained when a laser beam emitted from each of the light emitting elements <NUM> enters the microlens <NUM> arranged on the semiconductor substrate <NUM> is represented by Expression (<NUM>) below, where the size of the light-emitting region <NUM> of the light emitting element <NUM> (the maximum opening length of the current constriction region <NUM>) is denoted by a, the radiation angle of the laser beam inside the semiconductor substrate <NUM> is denoted by θ , and a distance from the light emitting unit to a lens emission surface is denoted by t. Here, a lens height is very small as compared to the substrate thickness, and therefore, t is regarded as constant over the entire emission surface.

It is not preferable that light from the light emitting element <NUM> enters the microlens <NUM> (<NUM>-<NUM>) that is adjacent to the subject microlens <NUM> (<NUM>-<NUM>) across the light shielding member of the adjacent microlens <NUM> (<NUM>-<NUM>). Therefore, it is preferable to satisfy Expression (<NUM>) with respect to the beam diameter D of the laser beam that enters the microlens <NUM> such that "a pitch X between the microlenses <NUM> + the width <NUM> of the light shielding member + a residual X - the lens diameter ϕ".

Based on Expressions (<NUM>) and (<NUM>), the thickness t of the semiconductor substrate <NUM> is set to a value that satisfies Expression (<NUM>) with respect to the inter-element pitch X and the width <NUM> of the light shielding member.

In particular, when <NUM>% of the lens diameter ϕ is to be covered by the light shielding member, <NUM> = ϕ/<NUM>, so that Expression (<NUM>) is represented as Expression (<NUM>).

To generate the light shielding member <NUM> in the surface-emitting laser array <NUM> as described above, in the process in <FIG>, the resist patterns <NUM> are formed on the microlenses <NUM> so as to preferably have smaller sizes in the in-plane direction of the substrate as compared to the first example. For example, the sizes of the resist patterns <NUM> may be set to <NUM>% of the lens diameters ϕ of the microlenses <NUM>. With this configuration, when the light shielding member <NUM> is formed on the second surface of the semiconductor substrate <NUM> in <FIG>, it is possible to cover regions equal to or smaller than <NUM>% of the lens diameters ϕ in the peripheral portions of the microlenses <NUM>.

Next, a result of simulation performed on the surface-emitting laser of the third embodiment will be described. A surface-emitting laser subjected to the simulation is configured as follows: the size a of the light-emitting region <NUM> of each of the light emitting elements <NUM> is <NUM> µm, the radiation angle θ of the laser beam inside the semiconductor substrate <NUM> is <NUM> degrees, a semiconductor layer from the light emitting unit to the substrate (mainly, a lower DBR) is <NUM> µm, the substrate thickness is <NUM> µm, the pitch of the light emitting element and the lens is <NUM> µm, the lens diameter is <NUM> µm, and the inter-lens residual is <NUM> µm.

<FIG> is a diagram illustrating an intensity distribution of light that has passed through the microlens which is the above-described surface-emitting laser and in which the light shielding member <NUM> is not provided. Light (A) emitted from the lens corresponding to the light emitting element, light (B) emitted from the residual portion between the lenses, and light (C) emitted from the adjacent lens are observed.

<FIG> is a diagram illustrating an intensity distribution of light that has passed through the microlens which is the above-described surface-emitting laser and in which the light shielding member <NUM> is provided on only the residual portion. As compared to <FIG>, it is possible to suppress the light (B) emitted from the residual portion between the lenses. In contrast, the light (C) emitted from the adjacent lens are observed similarly to <FIG>.

<FIG> is a diagram illustrating an intensity distribution of light that has passed through the microlens which is the above-described surface-emitting laser and in which the light shielding member <NUM> is provided on the residual portion and the peripheral portion of the lens. In this example, the region covered by the light shielding member is set to <NUM>% of the lens diameter. As compared to <FIG>, it is possible to suppress even the light (C) emitted from the adjacent lens.

<FIG> is a cross-sectional view illustrating an example of a configuration of a microlens part of a surface-emitting laser array. In the second embodiment, a case will be described in which a transparent conductive material is used for a back surface electrode <NUM>, and the back surface electrode <NUM> is formed on the entire second surface 10b of the semiconductor substrate <NUM>. As the transparent conductive material, for example, In<NUM>O<NUM>:Sn, SnO<NUM>:F, ZnO:Al, ZnO:Ga, graphene, or the like may be used. Other configurations are the same as those described in the first or second example or first embodiment.

As a method of manufacturing the surface-emitting laser array <NUM> configured as above, it is preferable to form the light shielding member <NUM> on the residual portions between the microlenses <NUM> as in the first example or form the light shielding member <NUM> on the peripheral portions of the microlenses <NUM> in addition to the residual portions as in the first embodiment, and thereafter form the back surface electrode <NUM> made of the transparent conductive material on the second surface 10b of the semiconductor substrate <NUM>.

In the second embodiment, because the transparent conductive material is used for the back surface electrode <NUM>, it is possible to form the back surface electrode <NUM> on the entire second surface 10b of the semiconductor substrate <NUM> on which the microlenses <NUM> and the light shielding member <NUM> are formed. With this configuration, it is possible to bring the back surface electrode <NUM> in close contact with the surfaces of the mi- crolenses <NUM>, so that it is possible to reduce resistance.

In a third embodiment, a case will be described in which the surface-emitting laser array <NUM> described in the first or second example or first or second embodiment is applied to a detection device. Here, a light detection and ranging or laser imaging detection and ranging (LiDAR) device <NUM>, which measures a distance to a target object and performs shape mapping using laser beams will be described as an example of the detection device.

<FIG> is a schematic diagram illustrating an example of a configuration of the LiDAR device according to the third embodiment. The LiDAR device <NUM> is one example of a distance measuring device that optically measures a distance. The LiDAR device <NUM> includes a projecting unit <NUM> that projects a laser beam, a light receiving unit <NUM> that receives reflected light Lref from a target object <NUM>, and a control/signal processing unit <NUM> that performs distance calculation based on the control of the projecting unit <NUM> and the received reflected light.

The projecting unit <NUM> includes a laser light source <NUM>, a projecting lens <NUM>, and a movable mirror <NUM> serving as a scanning unit. The surface-emitting laser array <NUM> described in the first or second example or first or second embodiment is used as the laser light source <NUM>.

The movable mirror <NUM> scans a desired scanning range <NUM> with a laser beam that is emitted from the projecting lens <NUM>.

The light receiving unit <NUM> includes a condensing optical system <NUM>, an optical filter <NUM>, and a light receiving element <NUM>. The condensing optical system <NUM> collects the reflected light Lref from the target object <NUM>, and causes the reflected light Lref to enter the light receiving element <NUM> via the optical filter <NUM>. The optical filter <NUM> is a filter that transmits only wavelengths in a predetermined range near the oscillation wavelength of the laser light source. By cutting wavelengths different from the oscillation wavelength, it is possible to improve a signal-to-noise (S/N) ratio of light that enters the light receiving element <NUM>. The light receiving element <NUM> converts the light that has transmitted through the optical filter <NUM> into an electrical signal.

The control/signal processing unit <NUM> includes a laser light source driving circuit <NUM> that drives the laser light source <NUM>, a control circuit <NUM> that controls movement (or a deflection angle) of the movable mirror <NUM>, and a signal processing circuit <NUM> that calculates a distance of the target object <NUM>. The laser light source driving circuit <NUM> controls a light emission timing and a light emission intensity of the laser light source <NUM>.

Operation of the LiDAR device <NUM> will be described. Light emitted from the laser light source <NUM> is guided to the movable mirror <NUM> by the projecting lens <NUM>, and applied, as scanning light Lscan, to the target object <NUM> present in the scanning range <NUM> by the movable mirror <NUM>. The reflected light Lref reflected by the target object <NUM> is received by the light receiving element <NUM> via the condensing optical system <NUM> and the optical filter <NUM>. The light receiving element <NUM> outputs, as a detection signal, photocurrent corresponding to the amount of incident light. The signal processing circuit <NUM> performs a distance calculation based on a time lag between a light emission timing signal supplied from the laser light source driving circuit <NUM> and the detection signal, and calculates a distance from the target object <NUM>.

In the third embodiment, the surface-emitting laser array <NUM> described in the first or second example or first or second embodiment, in which laser beams emitted from the microlenses <NUM> can be collected with a small beam spot diameter, is used as the laser light source <NUM>.

Therefore, it is possible to reduce a size of an optical component that receives laser beams emitted from the laser light source <NUM>, so that it is possible to reduce the size of the detection device itself.

In a fourth embodiment, a case will be described in which the surface-emitting laser array <NUM> described in the first or second example or first or second embodiment is applied to a laser device.

<FIG> is a schematic diagram illustrating an example of a configuration of a laser device according to the fourth embodiment. A laser device <NUM> includes a laser light source <NUM>, a first condensing optical system <NUM>, an optical fiber <NUM>, a second condensing optical system <NUM>, a laser resonator <NUM>, and an emitting optical system <NUM>. In <FIG>, the XYZ three-dimensional orthogonal coordinates is used, and explanation will be given based on the assumption that a light emission direction from the laser light source <NUM> corresponds to the positive Z direction.

The laser light source <NUM> is an excitation light source and includes a plurality of light emitting units. The surface-emitting laser array <NUM> described in the first or second example or first or second embodiment is used as the laser light source <NUM>. When the laser light source <NUM> emits light, the plurality of light emitting units emit light simultaneously.

Meanwhile, a surface-emitting laser array is a light source in which wavelength deviation due to temperature can hardly occur, and therefore is favorable for exciting Q switch laser whose characteristics are largely changed due to wavelength deviation. Therefore, using the surface-emitting laser array as an excitation light source is favorable for simplifying operation of controlling an environmental temperature.

The first condensing optical system <NUM> is a condenser lens and collects light emitted from the laser light source <NUM>. Meanwhile, the first condensing optical system <NUM> may include a plurality of optical elements.

The optical fiber <NUM> is arranged such that a center of an end surface of a core on the negative Z side is located at a position at which the first condensing optical system <NUM> collects light. By providing the optical fiber <NUM>, it is possible to arrange the laser light source <NUM> at a position separated from the laser resonator <NUM>. Light that has entered the optical fiber <NUM> propagates inside the core, and is output from an end surface of the core on the positive Z side.

The second condensing optical system <NUM> is a condenser lens, is arranged on an optical path of light emitted from the optical fiber <NUM>, and collects the light. Meanwhile, a plurality of optical elements may be used as the second condensing optical system <NUM> depending on the quality of light or the like. Light that is collected by the second condensing optical system <NUM> enters the laser resonator <NUM>.

The laser resonator <NUM> is Q switch laser that causes laser beams emitted from the second condensing optical system <NUM> to resonate and amplifies the laser beams. The laser resonator <NUM> includes, for example, a solid-state laser medium 206a and a saturable absorber 206b. For example, it may be possible to use Yb:YAG crystal as the solid-state laser medium 206a. For example, it may be possible to use Cr:YAG crystal as the saturable absorber 206b. In the laser resonator <NUM>, the solid-state laser medium 206a and the saturable absorber 206b are bonded together.

Light emitted from the second condensing optical system <NUM> enters the solid-state laser medium 206a. In other words, the solid-state laser medium 206a is excited by the light emitted from the second condensing optical system <NUM>. Meanwhile, it is desirable that a peak wavelength of light emitted from the laser light source <NUM> falls in a range of <NUM> to <NUM> where absorption efficiency of Yb:YAG crystal is the highest. Then, the saturable absorber 206b performs operation as a Q switch.

A surface <NUM> of the solid-state laser medium 206a on the incident side (negative Z side) and a surface <NUM> of the saturable absorber 206b on the emission side (positive Z side) are subjected to an optical polishing process, and function as mirrors. In the following descriptions, for the sake of convenience, the surface <NUM> of the solid-state laser medium 206a on the incident side may be referred to as a "first surface", and the surface <NUM> of the saturable absorber 206b on the emission side may be referred to as a "second surface".

Further, the first surface <NUM> and the second surface <NUM> are coated with dielectric multilayer films corresponding to the wavelength of light emitted from the laser light source <NUM> and the wavelength of light emitted from the laser resonator <NUM>.

Specifically, the first surface <NUM> is coated with a material that has adequately high transmittance with respect to light with the wavelength of <NUM> to <NUM> and adequately high reflectance with respect to light with the wavelength of <NUM>. Further, the second surface <NUM> is coated with a material that has reflectance that is selected so as to obtain a desired threshold with respect to light with the wavelength of <NUM>. With this configuration, light resonates and is amplified inside the laser resonator <NUM>.

The emission optical system <NUM> collects laser pulses emitted from the laser resonator <NUM> and outputs the laser pulses to the outside.

The laser device configured as above is used as, for example, an ignition system of an internal combustion, a laser processing machine, a laser peening device, a terahertz generator, and the like.

Claim 1:
A surface-emitting laser array (<NUM>) comprising:
a plurality of surface-emitting laser elements (<NUM>) arranged on a first surface (10a) of a substrate (<NUM>) and configured to emit light in a direction crossing the first surface (10a);
a plurality of optical elements arranged on a second surface (10b) opposite to the first surface (10a) of the substrate (<NUM>) to correspond to the surface-emitting laser elements (<NUM>) and configured to change a radiation angle of the light; and
a light shielding member (<NUM>) arranged in a region between the optical elements on the second surface (10b) of the substrate;
characterised in that the light shielding member (<NUM>) covers peripheral portions of the optical elements, the peripheral portion being a part of the optical element.