A semiconductor light-emitting device includes: a stacked structure including a light-emitting layer, a first cladding layer, and a second cladding layer; a first electrode electrically connected with the first cladding layer; a second electrode electrically connected with the second cladding layer; and a third electrode electrically connected with the second cladding layer. The stacked structure includes an optical waveguide. The optical waveguide includes a straight waveguide portion extending from a light exiting portion along a straight line inclined to a normal of a front edge surface of the stacked structure, and a curved waveguide portion including a curved waveguide having a shape with a curvature. The density of current injected into the straight waveguide portion is higher than that of current injected into the curved waveguide portion.

BACKGROUND

1. Technical Field

The present invention relates to a semiconductor light-emitting device, a super luminescent diode, and a projector.

2. Related Art

A super luminescent diode (hereinafter also referred to as “SLD”) is a semiconductor light-emitting device that can provide an output up to about several hundreds of mW with a single device in optical output characteristics similarly to a semiconductor laser while exhibiting incoherent properties and a wideband spectrum shape similarly to an ordinary light-emitting diode.

The SLD is used as, for example, a light source of a projector. For realizing a small and high-luminance projector, it is necessary to improve the luminous efficiency of the light source, reduce loss in an optical system, and reduce the number of components. With the use of the SLD as a light source, a dichroic mirror necessary for a color separation optical system and a rotating diffuser necessary for securing the safety of a semiconductor laser and reducing speckle noise can be eliminated.

For example, JP-A-2012-43950 discloses an SLD including an optical waveguide including a straight waveguide portion and a curved waveguide portion.

In the SLD described above, however, light guided in an active layer is exponentially amplified toward a light exiting portion side (low reflectance side). Therefore, the number of carriers becomes insufficient relative to light on the light exiting portion side. Due to this, gain saturation occurs, so that light output is reduced in some cases.

SUMMARY

An advantage of some aspects of the invention is to provide a semiconductor light-emitting device that can suppress a reduction in light output due to gain saturation. Another advantage of some aspects of the invention is to provide a projector including the semiconductor light-emitting device.

A semiconductor light-emitting device according to an aspect of the invention includes: a stacked structure including a light-emitting layer, a first cladding layer, and a second cladding layer, the first cladding layer and the second cladding layer interposing the light-emitting layer therebetween; a first electrode electrically connected with the first cladding layer; a second electrode electrically connected with the second cladding layer; and a third electrode electrically connected with the second cladding layer and arranged at a position different from that at which the second electrode is arranged, wherein the stacked structure includes an optical waveguide, the optical waveguide includes a straight waveguide portion extending from a light exiting portion along a straight line inclined to a normal of a front edge surface of the stacked structure, the light exiting portion being disposed on the front edge surface of the stacked structure, and a curved waveguide portion continuous with the straight waveguide portion and including a curved waveguide having a shape with a curvature, and the density of current injected into the straight waveguide portion located between the first electrode and the second electrode is higher than that of current injected into the curved waveguide portion located between the first electrode and the third electrode.

According to the semiconductor light-emitting device, a reduction in light output due to gain saturation can be suppressed. Further, according to the semiconductor light-emitting device, the formation of a direct resonator can be prevented, so that laser oscillation of light generated in the optical waveguide can be suppressed. Accordingly, speckle noise can be reduced.

It is noted that, in the descriptions concerning the invention, the phrase “electrically connect” or “electrically connected” may be used, for example, in a manner as “a specific member (hereinafter referred to as “A member”) “electrically connected” to another specific member (hereinafter referred to as “B member”. In the descriptions concerning the invention, in the case of such an example, the phrase “electrically connect” or “electrically connected” is used, while assuming that it includes the case where A member and B member are electrically connected in direct contact with each other, and the case where A member and B member are electrically connected via another member.

In the semiconductor light-emitting device according to the aspect of the invention, the density of current injected into the straight waveguide portion located between the first electrode and the second electrode may be higher than that of current injected into the straight waveguide portion located between the first electrode and the third electrode.

According to the semiconductor light-emitting device with this configuration, a reduction in light output due to gain saturation can be suppressed.

In the semiconductor light-emitting device according to the aspect of the invention, the optical waveguide may be disposed so as to extend from the front edge surface to a rear edge surface of the stacked structure.

According to the semiconductor light-emitting device with this configuration, a reduction in light output due to gain saturation can be suppressed.

In the semiconductor light-emitting device according to the aspect of the invention, the curved waveguide portion may perpendicularly reach the rear edge surface of the stacked structure.

According to the semiconductor light-emitting device with this configuration, light loss at a reflecting portion disposed on the rear edge surface can be reduced.

In the semiconductor light-emitting device according to the aspect of the invention, the curved waveguide portion may be formed closer to the rear edge surface side of the stacked structure than the center of the optical waveguide.

According to the semiconductor light-emitting device with this configuration, light loss in the curved waveguide portion can be reduced.

In the semiconductor light-emitting device according to the aspect of the invention, a high-reflectance film in which a plurality of dielectric films are stacked may be formed on the rear edge surface of the stacked structure.

According to the semiconductor light-emitting device with this configuration, in a wavelength band of light generated in the optical waveguide, the reflectance of the rear edge surface can be made high, so that the semiconductor light-emitting device can include a reflecting portion with a little light loss.

In the semiconductor light-emitting device according to the aspect of the invention, an extremely-low-reflectance film as a single layer or multiple layers of dielectric films may be formed on the front edge surface of the stacked structure.

According to the semiconductor light-emitting device with this configuration, in the wavelength band of the light generated in the optical waveguide, the reflectance of the front edge surface can be made low, so that the semiconductor light-emitting device can include a light exiting portion with a little light loss. Further, according to the semiconductor light-emitting device, the formation of a direct resonator can be prevented, so that laser oscillation of the light generated in the optical waveguide can be suppressed.

A projector according to another aspect of the invention includes: the semiconductor light-emitting device according to the aspect of the invention; a light modulation device modulating, according to image information, light emitted from the semiconductor light-emitting device; and a projection device projecting an image formed by the light modulation device.

According to the projector, it is possible to include the semiconductor light-emitting device that can suppress a reduction in light output due to gain saturation.

A super luminescent diode according to still another aspect of the invention includes: a straight waveguide linearly extending from a light exiting portion; and a curved waveguide continuous with the straight waveguide and having a shape with a curvature, wherein the density of current injected into the straight waveguide is higher than that of current injected into the curved waveguide.

According to the super luminescent diode, a reduction in light output due to gain saturation can be suppressed.

A projector according to yet another aspect of the invention includes: the super luminescent diode according to the aspect of the invention; a light modulation device modulating, according to image information, light emitted from the super luminescent diode; and a projection device projecting an image formed by the light modulation device.

According to the projector, it is possible to include the super luminescent diode that can suppress a reduction in light output due to gain saturation.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

Hereinafter, preferred embodiments of the invention will be described in detail with reference to the drawings. The embodiments described below do not unduly limit the contents of the invention set forth in the appended claims. Moreover, not all of the configurations described below are essential elements.

1. First Embodiment

First, a semiconductor light-emitting device according to a first embodiment will be described with reference to the drawings.FIG. 1is a plan view schematically showing a semiconductor light-emitting device100according to the first embodiment.FIG. 2is a cross-sectional view taken along line II-II inFIG. 1, schematically showing the semiconductor light-emitting device100according to the first embodiment.FIG. 3is a cross-sectional view taken along line III-III inFIG. 1, schematically showing the semiconductor light-emitting device100according to the first embodiment.

Hereinafter, the semiconductor light-emitting device100will be described in which the semiconductor light-emitting device100is an SLD formed using nitride semiconductor and outputting blue light at a wavelength of 450 nm. In the SLD, unlike a semiconductor laser, laser oscillation can be prevented by suppressing the formation of a resonator due to edge reflection. Therefore, speckle noise can be reduced.

As shown inFIGS. 1 to 3, the semiconductor light-emitting device100includes a stacked structure102, a first electrode120, a second electrode122, and a third electrode124. Further, the semiconductor light-emitting device100can include a substrate101, insulating layers116and118, an extremely-low-reflectance film140, and a high-reflectance film142.

The substrate101is, for example, a GaN substrate of first conductivity type (for example, n type). In the illustrated example, the planar shape (shape as viewed from a stacked direction of the stacked structure102) of the substrate101is rectangular.

The stacked structure102is formed on the substrate101. In the example shown inFIG. 1, the planar shape of the stacked structure102is rectangular. The stacked structure102includes a front edge surface131, a rear edge surface132, and side edge surfaces133and134. In surfaces of the stacked structure102, the edge surfaces131to134are surfaces that are not in contact with the substrate101, the second electrode122, and the third electrode124in a planar manner. The edge surfaces131to134are, for example, flat surfaces. The edge surfaces131to134may be cleaved surfaces formed by cleavage. The front edge surface131and the rear edge surface132face each other. The side edge surfaces133and134face each other and are connected to the front edge surface131and the rear edge surface132.

On the front edge surface131of the stacked structure102, the extremely-low-reflectance film140as a single layer or multiple layers of dielectric films is formed. On the rear edge surface132of the stacked structure102, the high-reflectance film142in which multiple layers of dielectric films are stacked is formed. With this configuration, in a wavelength band of light generated in an active layer106(in an optical waveguide160), the reflectance of the rear edge surface132can be made higher than that of the front edge surface131. The reflectance of the front edge surface131is desirably 0% or close to 0%. The reflectance of the rear edge surface132is desirably 100% or close to 100%. As the extremely-low-reflectance film140and the high-reflectance film142, for example, a SiO2layer, a Ta2O5layer, an Al2O3layer, a TiN layer, a TiO2layer, a SiON layer, a SiN layer, or a multilayer film of them is used.

The stacked structure102is formed of a plurality of semiconductor layers including the active layer106as a light-emitting layer, and a first cladding layer104and a second cladding layer108interposing the light-emitting layer therebetween. More specifically, the stacked structure102is composed of the first cladding layer104, a first guide layer16, the active layer106, a second guide layer26, a carrier overflow suppression (OFS) layer36, the second cladding layer108, and a contact layer110. The stacked structure102includes the optical waveguide160.

The first cladding layer104is formed on the substrate101. The first cladding layer104is, for example, an n-type AlGaN layer. Although not illustrated, a buffer layer may be formed between the substrate101and the first cladding layer104. The buffer layer is, for example, an n-type GaN layer. The buffer layer can improve the crystallinity of a layer formed thereon.

The first guide layer16is formed on the first cladding layer104. The first guide layer16is, for example, an n-type GaN layer. The first guide layer16can guide light generated in the active layer106.

The active layer106is formed on the first guide layer16. The active layer106has, for example, a multi-quantum well (MQW) structure in which three quantum well structures composed of InGaN well layers and InGaN barrier layers are stacked.

A portion of the active layer106constitutes the optical waveguide160. Specifically, the optical waveguide160is composed of portions of the first cladding layer104, the first guide layer16, the active layer106, the second guide layer26, the OFS layer36, and the second cladding layer108.

The optical waveguide160can guide light. In the illustrated example, the optical waveguide160includes portions that overlap electrodes122and124, in plan view, and a portion that does not overlap the electrodes122and124. The portions of the optical waveguide160overlapping the electrodes122and124are portions into which current is injected through the electrode120and the electrodes122and124.

The portions of the optical waveguide160into which current is injected can generate light. The light that is guided in the optical waveguide160can receive a gain in the portions of the optical waveguide160into which current is injected. Specifically, the portions of the optical waveguide160into which current is injected are portions located between a contact plane103between the substrate101and the first electrode120and contact planes112aand112bbetween the contact layer110and the electrodes122and124.

The optical waveguide160is disposed so as to extend from the front edge surface131to the rear edge surface132of the stacked structure102. The optical waveguide160includes a straight waveguide portion162and a curved waveguide portion164.

The straight waveguide portion162extends from the front edge surface131to the curved waveguide portion164. The straight waveguide portion162has a predetermined width as viewed from the stacked direction of the stacked structure102(hereinafter also referred to as “in plan view”), and has a belt-like linear longitudinal shape along an extending direction of the straight waveguide portion162. The straight waveguide portion162includes a first end surface181disposed at a portion connecting with the front edge surface131. The first end surface181can function as a light exiting portion through which the light guided in the optical waveguide160exits. That is, the straight waveguide portion162linearly extends from the light exiting portion181disposed on the front edge surface131to the curved waveguide portion164. The first end surface181is covered with the extremely-low-reflectance film140.

The extending direction of the straight waveguide portion162is, for example, an extending direction of a straight line passing the center of the first end surface181and the center of a connecting plane between the straight waveguide portion162and the curved waveguide portion164in plan view. Moreover, the extending direction of the straight waveguide portion162may be an extending direction of a border line of the straight waveguide portion162(a border line between the straight waveguide portion162and a portion excluding the straight waveguide portion162).

The straight waveguide portion162is disposed, in plan view, along a straight line (imaginary straight line) L relative to a normal P of the front edge surface131. In the illustrated example, the straight waveguide portion162is inclined at an angle α to the normal P and connected with the front edge surface131. In other words, it can be said that the extending direction of the straight waveguide portion162has the angle α relative to the normal P. The angle α is an acute angle greater than 0° and an angle smaller than a critical angle.

The curved waveguide portion164is continuous with the straight waveguide portion162. The curved waveguide portion164extends from the straight waveguide portion162to the rear edge surface132. The curved waveguide portion164has, in plan view, a predetermined width and includes a curved waveguide165having a shape with a curvature along an extending direction of the curved waveguide portion164. For example, the whole of the curved waveguide portion164may be the curved waveguide165. That is, the curved waveguide portion164may be composed of the curved waveguide165. The curved waveguide portion164includes a second end surface182disposed at a portion connecting with the rear edge surface132. The second end surface182can function as a reflecting portion that reflects light guided in the optical waveguide160. That is, the curved waveguide portion164extends from the straight waveguide portion162to the reflecting portion182disposed on the rear edge surface132. The second end surface182is covered with the high-reflectance film142.

The extending direction of the curved waveguide portion164may be an extending direction of a border line of the curved waveguide portion164(a border line between the curved waveguide portion164and a portion excluding the curved waveguide portion164). The optical waveguide160may have a constant width (size in a direction orthogonal to the extending direction) from the front edge surface131to the rear edge surface132.

The radius of curvature of the curved waveguide165is not particularly limited, and is, for example, 1 mm or more. With this configuration, light loss in the curved waveguide165can be reduced. The entire length (length in the extending direction) of the optical waveguide160is not particularly limited, and is, for example, about 1.5 mm.

The curved waveguide portion164perpendicularly reaches (connects with) the rear edge surface132in plan view. The curved waveguide portion164is formed closer to the rear edge surface132side than a center C of the optical waveguide160. The term “center C of the optical waveguide160” as used herein means the straight line (center line) C bisecting the length of the optical waveguide160in the extending direction and orthogonal to the extending direction of the optical waveguide160in plan view as shown inFIG. 1.

The second guide layer26is formed on the active layer106. The second guide layer26is, for example, an InGaAlP layer of second conductivity type (for example, p type). The second guide layer26can guide light generated in the active layer106.

The OFS layer36is formed on the second guide layer26. The OFS layer36is, for example, a p-type AlGaN layer. The OFS layer36can suppress the overflow of carriers from the active layer106to the second cladding layer108due to, for example, temperature rise.

The second cladding layer108is formed on the OFS layer36. That is, the first cladding layer104and the second cladding layer108interpose therebetween the first guide layer16, the active layer106, the second guide layer26, and the OFS layer36. The second cladding layer108is, for example, a p-type AlGaN layer. Moreover, the second cladding layer108may include a strained superlattice layer formed of a p-type AlGaN layer and a p-type GaN layer.

For example, the p-type second cladding layer108, the active layer106not doped with an impurity, and the n-type first cladding layer104constitute a pin diode. Further, the pin diode may be configured to include also the p-type OFS layer36, the p-type second guide layer26, and the n-type first guide layer16. Each of the first cladding layer104and the second cladding layer108is a layer having a larger forbidden band width and a lower refractive index than those of the active layer106. The active layer106has a function of generating light with current injected through the electrodes120,122, and124and guiding the light while amplifying the light. The first cladding layer104and the second cladding layer108have a function of interposing the active layer106therebetween to confine injected carriers (electrons and holes) and light (a function of suppressing light leakage).

In the semiconductor light-emitting device100, when the forward bias voltage of the pin diode is applied (current is injected) between the electrode120and the electrodes122and124, the optical waveguide160is generated in the active layer106, and the recombination of electrons and holes as carriers occurs in the optical waveguide160. Light emission occurs due to this recombination. With this generated light as a starting point, stimulated emission occurs in a chain reaction manner, so that the intensity of light is amplified in the portions of the optical waveguide160into which current is injected.

For example, as shown inFIG. 1, light10that is generated in the optical waveguide160and directed to the rear edge surface132side is amplified in the portions of the optical waveguide160into which current is injected, and thereafter, the light is reflected at the reflecting portion182and travels in the optical waveguide160toward the light exiting portion181. Then, the light is further amplified in the portions of the optical waveguide160into which current is injected, and then exits as light20through the light exiting portion181. Some of the light generated in the optical waveguide160directly exits as the light20through the light exiting portion181.

The contact layer110is formed on the second cladding layer108. The contact layer110is capable of being in ohmic contact with the electrodes122and124. The contact layer110is, for example, a p-type GaN layer.

The contact layer110and a portion of the second cladding layer108constitute a columnar portion114. The planar shape of the columnar portion114is, for example, the same as that of the optical waveguide160. For example, current paths between the electrode120and the electrodes122and124are determined by the planar shape of the columnar portion114, and as a result, the planar shape of the optical waveguide160is determined. Although not illustrated, a side surface of the columnar portion114may be inclined.

A groove170is disposed in the stacked structure102. In the example shown inFIG. 3, the groove170penetrates through the contact layer110to reach the second cladding layer108. That is, a bottom surface of the groove170is defined by a surface of the second cladding layer108. Although not illustrated, the groove170may not reach the second cladding layer108, and the bottom surface of the groove170may be defined by a surface of the contact layer110. Moreover, the groove170may penetrate through the contact layer110, the second cladding layer108, and the OFS layer36to reach the second guide layer26. In this case, it can be said that the bottom surface of the groove170is defined by an upper surface of the second guide layer26.

The groove170is disposed, in plan view, at a position overlapping the optical waveguide160between the second electrode122and the third electrode124. More specifically, the groove170is disposed, in plan view, between the second electrode122and the third electrode124in the extending direction of the optical waveguide160(a propagation direction of light). In other words, the groove170is disposed, in plan view, between the contact plane112aand the contact plane112b.

The planar shape of the groove170is not particularly limited, and is rectangular in the example shown inFIG. 1. Although not illustrated, the long sides of the groove170having a rectangular planar shape may be orthogonal to the extending direction of the optical waveguide160. The size of the groove170in the extending direction of the optical waveguide160is, for example, equal to or more than half the thickness of the second cladding layer108, and is desirably sufficiently smaller than the entire length of the optical waveguide160. Specifically, the size is from 250 nm to 200 μm. Since the size of the groove170in the extending direction is small as described above, light can be guided in the optical waveguide160with little influence of the groove170.

As shown inFIG. 3, the groove170may be filled with the insulating layer118. The insulating layer118may be, for example, a SiN layer, a SiO2layer, a SiON layer, an Al2O3layer, or a polyimide layer.

As shown inFIG. 2, the insulating layer116is formed on the second cladding layer108and lateral to the columnar portion114(around the columnar portion114in plan view). The insulating layer116is in contact with the side surface of the columnar portion114. An upper surface of the insulating layer116is, for example, continuous with an upper surface112of the contact layer110.

The insulating layer116is, for example, a SiN layer, a SiO2layer, a SiON layer, an Al2O3layer, or a polyimide layer. When the material described above is used as the insulating layer116, current between the electrode120and the electrodes122and124can flow through the columnar portion114interposed between the electrode120and the electrodes122and124while avoiding the insulating layer116.

The insulating layer116can have a refractive index lower than that of the active layer106. In this case, the effective refractive index in a vertical cross-section of a portion at which the insulating layer116is formed is lower than that in a vertical cross-section of a portion at which the insulating layer116is not formed, that is, a portion at which the columnar portion114is formed. Due to this, in a planar direction (direction orthogonal to the up-and-down direction), light can be efficiently confined in the optical waveguide160. Although not illustrated, the insulating layer116may not be disposed. That is, the insulating layer116may be an air layer.

The first electrode120is formed on the entire lower surface of the substrate101. More specifically, the first electrode120is formed to be in contact with a lower surface (the contact plane)103of a layer (the substrate101in the illustrated example) that is in ohmic contact with the first electrode120. The first electrode120is electrically connected with the first cladding layer104via the substrate101. The first electrode120is one of electrodes for driving the semiconductor light-emitting device100. As the first electrode120, for example, an electrode obtained by stacking a Ti layer, a Pt layer, and an Au layer in this order from the substrate101side is used.

It is also possible that a second contact layer (not shown) is disposed between the first cladding layer104and the substrate101, the second contact layer is exposed on the side opposite to the substrate101by dry etching or the like from the side opposite to the substrate101, and thus the first electrode120is disposed on the second contact layer. With this configuration, a single-sided electrode structure can be obtained. This form is particularly effective when the substrate101is insulating.

The second electrode122is formed on the contact layer110at a position overlapping the straight waveguide portion162in plan view. The second electrode122is an electrode located on the front edge surface131side of the third electrode124in the extending direction of the optical waveguide160.

The second electrode122has a shape extending along the extending direction of the optical waveguide160in plan view. The straight waveguide portion162includes a portion overlapping the second electrode122, in plan view, and a portion not overlapping the second electrode122. Into the portion of the straight waveguide portion162overlapping the second electrode122, current is injected through the electrodes120and122.

The third electrode124is formed on the contact layer110at a position overlapping the curved waveguide portion164in plan view. The third electrode124is arranged at a position different from that at which the second electrode122is arranged. In the illustrated example, the third electrode124is further formed at a position overlapping the straight waveguide portion162in plan view. The third electrode124is an electrode located on the rear edge surface132side of the second electrode122in the extending direction of the optical waveguide160.

The third electrode124has a shape extending along the extending direction of the optical waveguide160in plan view. Into the portion of the straight waveguide portion162overlapping the third electrode124, in plan view, and the portion of the curved waveguide portion164overlapping the third electrode124, current is injected through the electrodes120and124.

The second electrode122and the third electrode124are spaced apart from each other. That is, it can be said that the electrode formed on the contact layer110is divided into plural electrodes. A gap between the second electrode122and the third electrode124is disposed at a position overlapping the straight waveguide portion162in plan view.

The size of a portion of the straight waveguide portion162not overlapping the second electrode122and the third electrode124(the size in the extending direction of the straight waveguide portion162) is sufficiently smaller than that of portions of the straight waveguide portion162overlapping the second electrode122and the third electrode124(the size in the extending direction of the straight waveguide portion162). Therefore, the straight waveguide portion162can guide light also in the portion not overlapping the second electrode122and the third electrode124. Specifically, the size of the portion of the straight waveguide portion162not overlapping the second electrode122and the third electrode124is, for example, from 250 nm to 200 μm.

The current density of the straight waveguide portion162into which current is injected through the first electrode120and the second electrode122is higher than that of the curved waveguide portion164into which current is injected through the first electrode120and the third electrode124. That is, the density of current injected into the straight waveguide portion162located between the first electrode120and the second electrode122is higher than that of current injected into the curved waveguide portion164located between the first electrode120and the third electrode124. Further, the density of current injected into the straight waveguide portion162located between the first electrode120and the second electrode122is higher than that of current injected into the straight waveguide portion162located between the first electrode120and the third electrode124. The term “current density” or “density of current” as used herein means the quantity of electricity (charge, that is, carrier) flowing in a direction perpendicular to a unit area in a unit time. Accordingly, the carrier density of the straight waveguide portion162into which carriers are injected through the electrodes120and122is higher than that of the curved waveguide portion164into which carriers are injected through the electrodes120and124.

Although not illustrated, the semiconductor light-emitting device100may include a control unit that controls the density of current injected through the first electrode120and the second electrode122and the density of current injected through the first electrode120and the third electrode124. The control unit can perform control such that the current density of the straight waveguide portion162into which current is injected through the electrodes120and122is higher than that of the curved waveguide portion164into which current is injected through the electrodes120and124.

The second electrode122and the third electrode124are electrically connected with the second cladding layer108via the contact layer110. The electrodes122and124are the other electrodes for driving the semiconductor light-emitting device100. As the electrodes122and124, for example, an electrode obtained by stacking a Pd layer and a Pt layer in this order from the contact layer110side, or the like can be used. Moreover, the electrodes122and124may include a pad electrode on the electrode structure described above. As the pad electrode, for example, an electrode obtained by stacking a Ti layer, a Pt layer, and an Au layer in this order from the contact layer110side, or the like can be used.

As the semiconductor light-emitting device100according to the first embodiment, the SLD formed using nitride semiconductor and outputting blue light at a wavelength of 450 nm has been described so far. However, for the semiconductor light-emitting device according to the invention, any material system capable of forming an optical waveguide can be used. In the case of a semiconductor material, for example, an AlGaInP-based, GaAs-based, AlGaAs-based, InGaAs-based, InGaAsP-based, InP-based, GaP-based, AlGaP-based, or ZnCdSe-based semiconductor material can be used.

In the above, the semiconductor light-emitting device100according to the first embodiment has been described as of so-called refractive index-guiding type in which a refractive index difference is provided for confining light between an area where the insulating layer116is formed and an area where the insulating layer116is not formed, that is, an area where the columnar portion114is formed. Although not illustrated, the semiconductor light-emitting device according to the invention may be of so-called gain-guiding type in which a refractive index difference is not provided due to the formation of the columnar portion114and the optical waveguide160serves as it is as a waveguide area.

In the above, as the semiconductor light-emitting device100according to the first embodiment, an example has been described in which the plurality of electrodes122and124electrically connected with the second cladding layer108are included and each of the electrodes122and124is formed along the optical waveguide160. However, the semiconductor light-emitting device according to the invention may include a plurality of electrodes electrically connected with the first cladding layer104in which the electrodes are formed along the optical waveguide160.

In the above, as the semiconductor light-emitting device100according to the first embodiment, an example has been described in which the two electrodes122and124electrically connected with the second cladding layer108and disposed along the optical waveguide160are included. However, the semiconductor light-emitting device according to the invention may include three or more electrodes electrically connected with the second cladding layer108in which the three or more electrodes are spaced apart from one another and disposed along the optical waveguide160.

The semiconductor light-emitting device100according to the first embodiment is applied to, for example, alight source of a projector, a display, an illuminating device, a measuring device, or the like.

The semiconductor light-emitting device100has, for example, the following features.

According to the semiconductor light-emitting device100, the current density of the straight waveguide portion162into which current is injected through the first electrode120and the second electrode122is higher than that of the curved waveguide portion164into which current is injected through the first electrode120and the third electrode124. That is, the carrier density of the straight waveguide portion162into which carriers are injected through the electrodes120and122is higher than that of the curved waveguide portion164into which carriers are injected through the electrodes120and124. Further, the straight waveguide portion162extends from the light exiting portion181. Therefore, in the semiconductor light-emitting device100, a reduction in light output due to gain saturation can be suppressed. The reasons will be specifically described below.

FIGS. 4A and 5Aare graphs schematically showing the relation between the position in an extending direction of an optical waveguide and the light density.FIGS. 4B and 5Bare graphs schematically showing the relation between the position in the extending direction of the optical waveguide and the injected current density.FIGS. 4A and 4Bshow the case where the injected current density in the extending direction of the optical waveguide is constant.FIGS. 5A and 5Bshow the case where the injected current density in the extending direction of the optical waveguide is varied. The term “light density” as used herein means the number of photons passing per unit area of a cross-section perpendicular to the extending direction of the optical waveguide per unit time at the position in the extending direction of the optical waveguide.

InFIGS. 4A and 4BandFIGS. 5A and 5B, it is assumed that the optical waveguide has a constant width (size in a direction orthogonal to the extending direction of the optical waveguide). Moreover, inFIGS. 4A and 4BandFIGS. 5A and 5B, only light directed from the position 0 on the horizontal axis toward the arrow direction is considered. For example, it may be conceivable that the position 0 is the rear edge surface132.

In the SLD, light is exponentially amplified toward the light exiting portion (low reflectance side) through which the light exits. Therefore, as shown inFIGS. 4A and 4B, the light density has a non-uniform distribution in the extending direction of the optical waveguide, and gain saturation occurs on the light exiting portion side where the light density is high. That is, when the injected current density (that is, carrier density) is constant in the extending direction of the optical waveguide, the number of carriers is insufficient relative to light (to photons) on the light exiting portion side. That is, when light is to be amplified, the number of carriers that are converted into light is insufficient. As a result, gain saturation occurs, and a light output is reduced corresponding to the amount of gain saturation.

At the portion where the light density is low (the side opposite to the light exiting portion side), there are many carriers compared with that of the light exiting portion side. Therefore, carriers are not sufficiently converted into light, and there are excess carriers. As shown inFIGS. 5A and 5B, the excess carriers are injected into the light exiting portion side where the number of carriers is insufficient, so that high-output and highly efficient driving can be performed. That is, by varying the current density, gain saturation is reduced while maintaining the magnitude of injected current of the entire optical waveguide constant, so that a final light output can be increased.

In the semiconductor light-emitting device100, as described above, the current density (carrier density) of the straight waveguide portion162including the light exiting portion181is made higher than that of the curved waveguide portion164, so that a reduction in light output due to gain saturation can be suppressed while maintaining the magnitude of current injected into the entire optical waveguide160constant. That is, in the semiconductor light-emitting device100, even when the magnitude of current injected into the entire optical waveguide160is made the same as that of current injected into the entire optical waveguide whose current density is constant in the extending direction of the optical waveguide, higher output can be achieved. As a result, in the semiconductor light-emitting device100, high-output and highly efficient driving can be performed.

Further, in the semiconductor light-emitting device100, the current density of the straight waveguide portion162is made higher than that of the curved waveguide portion164, so that light loss in the curved waveguide portion164can be reduced. For example, when the current density of a curved waveguide portion having a shape with a curvature is made higher than that of a straight waveguide portion, light loss in the curved waveguide portion is increased, failing in some cases to achieve higher efficiency.

Further, in the semiconductor light-emitting device100, the straight waveguide portion162is inclined to the normal P of the front edge surface131. Therefore, in the semiconductor light-emitting device100, direct multiple reflection of light generated in the optical waveguide160can be reduced between the first end surface181and the second end surface182. Due to this, the formation of a direct resonator can be prevented, so that laser oscillation of the light generated in the optical waveguide160can be suppressed. Accordingly, in the semiconductor light-emitting device100, speckle noise can be reduced.

According to the semiconductor light-emitting device100, the curved waveguide portion164perpendicularly reaches the rear edge surface132. Therefore, light loss at the reflecting portion182can be reduced.

According to the semiconductor light-emitting device100, the curved waveguide portion164is formed closer to the rear edge surface132side of the stacked structure102than the center C of the optical waveguide160. In the semiconductor light-emitting device100, for example, the reflectance of the rear edge surface132is high, while the reflectance of the front edge surface131is extremely low. Therefore, a very large difference in light intensity exists between the front edge surface131and the rear edge surface132. By forming the curved waveguide portion164in this low light-intensity area, light loss in the curved waveguide portion164can be reduced. The light intensity is a light intensity at a certain point in the waveguide direction (extending direction) in the optical waveguide. To be exact, the light intensity is an integration of a light distribution over a waveguide surface and a light density in view of the waveguide surface distribution.

According to the semiconductor light-emitting device100, the high-reflectance film142in which a plurality of dielectric films are stacked is formed on the rear edge surface132. Therefore, in a wavelength band of light generated in the optical waveguide160, the reflectance of the rear edge surface132can be made high, so that the semiconductor light-emitting device100can include the reflecting portion182with a little light loss.

According to the semiconductor light-emitting device100, the extremely-low-reflectance film140as a single layer or multiple layers of dielectric films is formed on the front edge surface131. Therefore, in the wavelength band of the light generated in the optical waveguide160, the reflectance of the front edge surface131can be made low, so that the semiconductor light-emitting device100can include the light exiting portion181with a little light loss. Further, due to the extremely-low-reflectance film140, direct multiple reflection of the light generated in the optical waveguide160can be reduced between the first end surface181and the second end surface182. Due to this, the formation of a direct resonator can be prevented, so that laser oscillation of the light generated in the optical waveguide160can be suppressed.

According to the semiconductor light-emitting device100, the groove170is disposed, in plan view, at a position overlapping the optical waveguide160between the second electrode122and the third electrode124(between the contact plane112aand the contact plane112b). With this configuration, the insulating property between the second electrode122and the third electrode124can be enhanced. Moreover, due to a difference in carrier density between the straight waveguide portion162and the curved waveguide portion164, the movement of carriers can be suppressed. As a result, a reduction in light output can be suppressed.

1.2. Method for Manufacturing Semiconductor Light-Emitting Device

Next, a method for manufacturing the semiconductor light-emitting device according to the first embodiment will be described with reference to the drawings.FIGS. 6 to 8are cross-sectional views schematically showing manufacturing steps of the semiconductor light-emitting device100according to the first embodiment, corresponding toFIG. 2.

As shown inFIG. 6, the first cladding layer104, the first guide layer16, the active layer106, the second guide layer26, the OFS layer36, the second cladding layer108, and the contact layer110are epitaxially grown in this order on the substrate101. As the method of epitaxial growth, for example, a metal organic chemical vapor deposition (MOCVD) method or a molecular beam epitaxy (MBE) method is used.

As shown inFIG. 7, the contact layer110and the second cladding layer108are patterned. The patterning is performed using, for example, photolithography and etching. Through this step, the columnar portion114can be formed. Moreover, in this step, the groove170(refer toFIG. 3) can be formed. The step of forming the columnar portion114and the step of forming the groove170may be performed in separate steps.

As shown inFIG. 8, the insulating layer116is formed so as to cover the side surface of the columnar portion114. Specifically, for example, an insulating member (not shown) is first deposited on the second cladding layer108(also on the contact layer110) by a chemical vapor deposition (CVD) method, a coating method, or the like. Next, the upper surface112of the contact layer110is exposed by, for example, etching. Through the step described above, the insulating layer116can be formed. Moreover, in this step, the insulating layer118(refer toFIG. 3) can be formed in the groove170. The step of forming the insulating layer116and the step of forming the insulating layer118may be performed in separate steps.

As shown inFIGS. 1 and 2, the electrodes122and124are formed on the contact layer110. The electrodes122and124are formed by, for example, a vacuum evaporation method. The electrodes122and124may be formed by forming a predetermined shaped mask layer (not shown), depositing an electrode layer thereon, and then removing the mask layer (lift-off). Thereafter, heat treatment for alloying may be performed. Moreover, the formation of the electrodes122and124may include a step of forming a pad electrode. The pad electrode may be formed by, for example, a vacuum evaporation method. When the forming step of the pad electrode is included, the order of the heat treatment step for alloying and the forming step of the pad electrode is not particularly limited. That is, the forming step of the pad electrode may be performed after the heat treatment step for alloying.

Next, the first electrode120is formed on the lower surface of the substrate101. Before forming the first electrode120, the substrate101may be thinned by polishing the lower surface of the substrate101. The first electrode120is formed by, for example, a vacuum evaporation method. After the deposition using a vacuum evaporation method, heat treatment for alloying may be performed. The order of the step of forming the electrode120and the step of forming the electrodes122and124is not particularly limited.

As shown inFIG. 1, the edge surfaces131,132,133, and134of the stacked structure102are exposed by, for example, cleavage. Next, the extremely-low-reflectance film140is formed on the front edge surface131, and the high-reflectance film142is formed on the rear edge surface132. The extremely-low-reflectance film140and the high-reflectance film142are formed by, for example, a CVD method. The order of the step of forming the extremely-low-reflectance film140and the step of forming the high-reflectance film142is not particularly limited.

Through the steps described above, the semiconductor light-emitting device100can be manufactured.

According to the method for manufacturing the semiconductor light-emitting device100, it is possible to obtain the semiconductor light-emitting device100that can suppress a reduction in light output due to gain saturation.

1.3. Modified Examples of Semiconductor Light-Emitting Device

1.3.1. First Modified Example

Next, a semiconductor light-emitting device according to a first modified example of the first embodiment will be described with reference to the drawing.FIG. 9is a plan view schematically showing a semiconductor light-emitting device200according to the first modified example of the first embodiment.

Hereinafter, in the semiconductor light-emitting device200according to the first modified example of the first embodiment, members having functions similar to those of the constituent members of the semiconductor light-emitting device100according to the first embodiment are denoted by the same reference numerals and signs, and the detailed description thereof is omitted. The same applies to semiconductor light-emitting devices300and400, which will be shown below, according to modified examples of the first embodiment.

In the semiconductor light-emitting device100, as shown inFIG. 1, the gap between the second electrode122and the third electrode124is disposed, in plan view, at the position overlapping the straight waveguide portion162. That is, the straight waveguide portion162includes the portion into which current is injected through the electrodes120and122and the portion into which current is injected through the electrodes120and124.

In contrast to this, in the semiconductor light-emitting device200as shown inFIG. 9, the gap between the second electrode122and the third electrode124is disposed, in plan view, at a position overlapping a border line A between the straight waveguide portion162and the curved waveguide portion164. In the illustrated example, the groove170is also disposed at the position overlapping the border line A. In the semiconductor light-emitting device200, current is injected into the straight waveguide portion162only through the electrodes120and122. Current is injected into the curved waveguide portion164only through the electrodes120and124. For example, the curved waveguide portion164may be composed of the curved waveguide165, and the border line A may be arranged at an end of the curved waveguide165.

In the semiconductor light-emitting device200, a reduction in light output due to gain saturation can be suppressed similarly to the semiconductor light-emitting device100.

1.3.2. Second Modified Example

Next, a semiconductor light-emitting device according to a second modified example of the first embodiment will be described with reference to the drawing.FIG. 10is a plan view schematically showing the semiconductor light-emitting device300according to the second modified example of the first embodiment.

In the semiconductor light-emitting device100, as shown inFIG. 1, the gap between the second electrode122and the third electrode124is disposed, in plan view, at the position overlapping the straight waveguide portion162. That is, the straight waveguide portion162includes the portion into which current is injected through the electrodes120and122and the portion into which current is injected through the electrodes120and124.

In contrast to this, in the semiconductor light-emitting device300as shown inFIG. 10, the gap between the second electrode122and the third electrode124is disposed, in plan view, at a position overlapping the curved waveguide165. In the illustrated example, the groove170is also disposed at the position overlapping the curved waveguide165. In the semiconductor light-emitting device300, current is injected into the straight waveguide portion162only through the electrodes120and122. The curved waveguide portion164includes a portion into which current is injected through the electrodes120and122and a portion into which current is injected through the electrodes120and124. For example, the curved waveguide portion164may be composed of the curved waveguide165.

In the semiconductor light-emitting device300, a reduction in light output due to gain saturation can be suppressed similarly to the semiconductor light-emitting device100.

1.3.3. Third Modified Example

Next, a semiconductor light-emitting device according to a third modified example of the first embodiment will be described with reference to the drawing.FIG. 11is a plan view schematically showing the semiconductor light-emitting device400according to the third modified example of the first embodiment.

In the semiconductor light-emitting device100, as shown inFIG. 1, one optical waveguide160is disposed. In contrast to this, in the semiconductor light-emitting device400as shown inFIG. 11, a plurality of optical waveguides160are disposed. In the illustrated example, four optical waveguides160are disposed. However, the number of optical waveguides is not particularly limited as long as the number is two or more. The plurality of optical waveguides160are arrayed in a direction orthogonal to the normal P of the front edge surface131. In the illustrated example, a plurality of light exiting portions181are aligned at equal intervals.

According to the semiconductor light-emitting device400, higher output can be achieved compared with the example of the semiconductor light-emitting device100.

2. Second Embodiment

Next, a semiconductor light-emitting device according to a second embodiment will be described with reference to the drawing.FIG. 12is a plan view schematically showing a semiconductor light-emitting device500according to the second embodiment.

Hereinafter, in the semiconductor light-emitting device500according to the second embodiment, members having functions similar to those of the constituent members of the semiconductor light-emitting device100according to the first embodiment are denoted by the same reference numerals and signs, and the detailed description thereof is omitted.

In the semiconductor light-emitting device100, as shown inFIG. 1, one straight waveguide portion162is disposed, and one light exiting portion181is disposed. In contrast to this, in the semiconductor light-emitting device500as shown inFIG. 12, two straight waveguide portions162are disposed, and two light exiting portions181are disposed.

An extending direction of one straight waveguide portion162aof the two straight waveguide portions162is parallel to an extending direction of the other straight waveguide portion162b. Due to this, the light20that exits through the first end surface181of the straight waveguide portion162acan exit in the same direction as the light20that exits through the first end surface181of the straight waveguide portion162b. A gap D between the first end surface181of the straight waveguide portion162aand the first end surface181of the straight waveguide portion162bis, for example, from several hundreds μm to 1 mm. The extending direction of the straight waveguide portion162amay not be parallel to the extending direction of the straight waveguide portion162b.

The sentence “the extending direction of the straight waveguide portion162ais parallel to the extending direction of the other straight waveguide portion162b” as used herein means that in view of manufacturing variations or the like, an inclination angle of the extending direction of the straight waveguide portion162bto the extending direction of the straight waveguide portion162ais within ±1° in plan view.

The curved waveguide portion164is composed of the curved waveguide165that connects the straight waveguide portion162awith the straight waveguide portion162b. The curved waveguide portion164is disposed spaced apart from the rear edge surface132. The curved waveguide portion164does not include a reflecting portion, and a high-reflectance film is not disposed on the rear edge surface132. The radius of curvature of the curved waveguide165is appropriately determined by the gap between the straight waveguide portion162aand the straight waveguide portion162b, and is, for example, about 1 mm. The entire length (length in the extending direction) of the optical waveguide160is not particularly limited, and is, for example, about 3 mm.

In the illustrated example, the straight waveguide portions162aand162bare inclined at the angle c to the normal P of the front edge surface131and connected with the front edge surface131. However, the straight waveguide portions162aand162bmay be orthogonal to the front edge surface131. That is, the extending direction of the straight waveguide portions162aand162bmay be parallel to the normal P. Also in such a form, since the extremely-low-reflectance film140is formed on the front edge surface131, direct multiple reflection of light generated in the optical waveguide160can be reduced between the first end surface181of the straight waveguide portion162aand the first end surface181of the straight waveguide portion162bin the semiconductor light-emitting device500. Due to this, the formation of a direct resonator can be prevented, so that laser oscillation of the light generated in the optical waveguide160can be suppressed.

In the semiconductor light-emitting device500, two second electrodes122are disposed corresponding to the straight waveguide portions162. In the illustrated example, a second electrode122ais disposed at a position overlapping the straight waveguide portion162a, and a second electrode122bis disposed at a position overlapping the straight waveguide portion162b.

In the semiconductor light-emitting device500, the density of current injected through the second electrode122amay be the same in magnitude as that of current injected through the second electrode122b. Due to this, compared with the case where the density of current injected through the second electrode122ais different in magnitude from that of current injected through the second electrode122b, current control in driving can be easily performed. Moreover, the second electrode122aand the second electrode122bmay be electrically connected. Further, the second electrode122aand the second electrode122bmay be composed of a common electrode.

According to the semiconductor light-emitting device500, a reduction in light output due to gain saturation can be suppressed similarly to the semiconductor light-emitting device100.

According to the semiconductor light-emitting device500, since the curved waveguide portion164does not include a reflecting portion, light loss at the reflecting portion can be eliminated.

2.2. Method for Manufacturing Semiconductor Light-Emitting Device

Next, a method for manufacturing the semiconductor light-emitting device according to the second embodiment will be described. The method for manufacturing the semiconductor light-emitting device according to the second embodiment is basically the same as that of the semiconductor light-emitting device100according to the first embodiment, excepting that the high-reflectance film142is not formed on the rear edge surface132. Therefore, the detailed description thereof is omitted.

2.3. Modified Examples of Semiconductor Light-Emitting Device

2.3.1. First Modified Example

Next, a semiconductor light-emitting device according to a first modified example of the second embodiment will be described with reference to the drawing.FIG. 13is a plan view schematically showing a semiconductor light-emitting device600according to the first modified example of the second embodiment.

Hereinafter, in the semiconductor light-emitting device600according to the first modified example of the second embodiment, members having functions similar to those of the constituent members of the semiconductor light-emitting device100according to the first embodiment and the semiconductor light-emitting device500according to the second embodiment are denoted by the same reference numerals and signs, and the detailed description thereof is omitted. The same applies to a semiconductor light-emitting device700, which will be shown below, according to a second modified example of the second embodiment.

In the semiconductor light-emitting device500, as shown inFIG. 12, each of the gaps between the second electrodes122and the third electrode124is disposed, in plan view, at the position overlapping the straight waveguide portion162. That is, each of the straight waveguide portions162includes a portion into which current is injected through the electrodes120and122and a portion into which current is injected through the electrodes120and124.

In contrast to this, in the semiconductor light-emitting device600as shown inFIG. 13, each of the gaps between the second electrodes122and the third electrode124is disposed, in plan view, at a position overlapping the border line A between the straight waveguide portions162and the curved waveguide portion164(the curved waveguide165). In the illustrated example, each of the grooves170is also disposed at the position overlapping the border line A. In the semiconductor light-emitting device600, current is injected into the straight waveguide portions162only through the electrodes120and122. Current is injected into the curved waveguide portion164only through the electrodes120and124.

In the semiconductor light-emitting device600, a reduction in light output due to gain saturation can be suppressed similarly to the semiconductor light-emitting device500.

2.3.2. Second Modified Example

Next, a semiconductor light-emitting device according to the second modified example of the second embodiment will be described with reference to the drawing.FIG. 14is a plan view schematically showing the semiconductor light-emitting device700according to the second modified example of the second embodiment.

In the semiconductor light-emitting device500, as shown inFIG. 12, each of the gaps between the second electrodes122and the third electrode124is disposed, in plan view, at the position overlapping the straight waveguide portion162. That is, each of the straight waveguide portions162includes the portion into which current is injected through the electrodes120and122and the portion into which current is injected through the electrodes120and124.

In contrast to this, in the semiconductor light-emitting device700as shown inFIG. 14, each of the gaps between the second electrodes122and the third electrode124is disposed, in plan view, at a position overlapping the curved waveguide portion164(the curved waveguide165). In the illustrated example, each of the grooves170is also disposed at the position overlapping the curved waveguide portion164(the curved waveguide165). In the semiconductor light-emitting device700, current is injected into the straight waveguide portions162only through the electrodes120and122. The curved waveguide portion164includes a portion into which current is injected through the electrodes120and122and a portion into which current is injected through the electrodes120and124.

In the semiconductor light-emitting device700, a reduction in light output due to gain saturation can be suppressed similarly to the semiconductor light-emitting device500.

Next, a projector according to a third embodiment will be described with reference to the drawings.FIG. 15schematically shows a projector800according to the third embodiment.FIG. 16schematically shows a portion of the projector800according to the third embodiment.

For convenience sake, inFIG. 15, a housing constituting the projector800is omitted, and further, alight source400is shown in a simplified manner. InFIG. 16, for convenience sake, the light source400, a lens array802, and a liquid crystal light valve804are shown, and further, the light source400is shown in a simplified manner.

As shown inFIGS. 15 and 16, the projector800includes a red light source400R, a green light source400G, and a blue light source400B that respectively emit red light, green light, and blue light. The red light source400R, the green light source400G, and the blue light source400B each are the semiconductor light-emitting device according to the invention. Hereinafter, an example will be described in which the semiconductor light-emitting device400is used as the semiconductor light-emitting device according to the invention.

The projector800further includes lens arrays802R,802G, and802B, transmissive liquid crystal light valves (light modulation devices)804R,804G, and804B, and a projection lens (projection device)808.

Lights emitted from the light sources400R,400G, and400B are respectively incident on the lens arrays802R,802G, and802B. As shown inFIG. 16, the lens array802includes, on the light source400side, flat surfaces801on each of which the light20exiting through the light exiting portion181is incident. The plurality of flat surfaces801are disposed corresponding to the plurality of light exiting portions181, and arranged at equal intervals. A normal (not shown) of the flat surface801is inclined to an optical axis of the light20. Accordingly, due to the flat surface801, the optical axis of the light20can be made orthogonal to an irradiated surface805of the liquid crystal light valve804.

The lens array802includes convex curved surfaces803on the liquid crystal light valve804side. The plurality of convex curved surfaces803are disposed corresponding to the plurality of flat surfaces801, and arranged at equal intervals. The lights20whose optical axes are converted on the flat surfaces801are collected or reduced in diffusion angle by the convex curved surfaces803, so that the lights can be superimposed (partially superimposed). Due to this, the liquid crystal light valve804can be irradiated with good uniformity.

As described above, the lens array802can control the optical axes of the lights20emitted from the light source400to thereby collect the lights20.

As shown inFIG. 15, lights collected by the lens arrays802R,802G, and802B are respectively incident on the liquid crystal light valves804R,804G, and804B. Each of the liquid crystal light valves804R,804G, and804B modulates the incident light according to image information. Then, the projection lens808magnifies an image formed by the liquid crystal light valves804R,804G, and804B and projects the image onto a screen (display surface)810.

Moreover, the projector800can include a cross dichroic prism (color light combining unit)806that combines the lights emitted from the liquid crystal light valves804R,804G, and804B and introduces the combined light to the projection lens808.

Three color lights modulated by the respective liquid crystal light valves804R,804G, and804B are incident on the cross dichroic prism806. This prism is formed by bonding four right-angle prisms together, and a dielectric multilayer film that reflects red light and a dielectric multilayer film that reflects blue light are arranged crosswise on its inner surface. With these dielectric multilayer films, the three color lights are combined to form light representing a color image. Then, the combined light is projected onto the screen810through the projection lens808as a projection optical system, so that a magnified image is displayed.

According to the projector800, it is possible to include the semiconductor light-emitting device400that can suppress a reduction in light output due to gain saturation.

According to the projector800, since the projector is of a type (backlight type) in which the light source400is arranged just below the liquid crystal light valve804and light collection and uniform illumination are simultaneously performed using the lens array802, a reduction in the loss of the optical system and a reduction in the number of components can be achieved.

In the example described above, the transmissive liquid crystal light valve is used as a light modulation device. However, a light valve other than that of liquid crystal may be used, or a reflective light valve may be used. Examples of such a light valve include, for example, a reflective liquid crystal light valve and a digital micromirror device. Moreover, the configuration of the projection optical system is appropriately changed depending on the types of a light valve to be used.

Moreover, the light source400can also be applied to a light source device of a scanning type image display device (projector) having a scanning unit as an image forming device in which scanning is performed on a screen with light from the light source400to thereby display a desired size image on a display surface.

The embodiments and modified examples described above are illustrative only, and the invention is not limited to them. For example, each of the embodiments and each of the modified examples can be appropriately combined.

The invention includes a configuration (for example, a configuration having the same function, method, and result, or a configuration having the same advantage and effect) that is substantially the same as those described in the embodiments. Moreover, the invention includes a configuration in which a non-essential portion of the configurations described in the embodiments is replaced. Moreover, the invention includes a configuration providing the same operational effects as those described in the embodiments, or a configuration capable of achieving the same advantages. Moreover, the invention includes a configuration in which a publicly known technique is added to the configurations described in the embodiments.

The entire disclosure of Japanese Patent Application No. 2013-036771, filed Feb. 27, 2013 is expressly incorporated by reference herein.