Optical element array, optical module, and optical transmission device

To provide a optical element array in which a plurality of optical elements can be monolithically integrated, and each of the optical elements can be independently driven. A optical element array in accordance with the present invention includes a plurality of optical elements having light emitting sections formed above a substrate and photodetecting sections formed above the light emitting sections; and an element isolation section that is formed between the optical elements, for electrically isolating each of the optical element from the other, wherein the substrate is dielectric or semi-dielectric, the light emitting section includes a first semiconductor layer, an active layer, and a second semiconductor layer, the photodetecting section includes a first contact layer, a photoabsorption layer, and a second contact layer, the optical element has a first electrode that is electrically connected to the first semiconductor layer, and a second electrode that is electrically connected to the second semiconductor layer, the first electrodes are electrically isolated one from the other between the optical elements, and the second electrodes define a common electrode for driving the light emitting section and the photodetecting section.

BACKGROUND

The present invention relates to optical element arrays, optical modules, and optical transmission devices.

A surface-emitting type semiconductor laser has characteristics in which its light output varies depending on ambient temperatures. For this reason, there may be cases where an optical module that uses a surface-emitting type semiconductor laser may be equipped with a photodetecting function that detects a part of laser light emitted from the surface-emitting type semiconductor laser to thereby monitor light output values. For example, a photodetecting element such as a photodiode or the like may be provided on a surface-emitting type semiconductor laser, such that a part of laser light emitted from the surface-emitting type semiconductor laser can be monitored within the same device (for example, seed Patent Document 1).

This element has a common electrode for driving the surface-emitting type semiconductor laser and the photodetecting element. For example, the photodetecting element is operated by applying a constant reverse bias thereto. In other words, a constant bias is applied between the common electrode described above and another electrode of the photodetecting element for driving. For this reason, in order to modulate the surface-emitting type semiconductor laser, a modulation signal would be implied to the other electrode of the surface-emitting type semiconductor laser, not to the common electrode described above.

SUMMARY

It is an object of the present invention to provide a optical element array in which a plurality of optical elements can be monolithically integrated, and each of the optical elements can be independently driven.

Also, it is an object of the present invention to provide an optical module including the optical element array, and an optical transmission device including the optical module.

A optical element array in accordance with the present invention includes:

a plurality of optical elements having a substrate, light emitting sections formed above the substrate and photodetecting sections formed above the light emitting sections; and

an element isolation section that is formed between the optical elements, for electrically isolating the optical elements from one another,

wherein the substrate is dielectric or semi-dielectric,

the light emitting section includes a first semiconductor layer, an active layer, and a second semiconductor layer,

the photodetecting section includes a first contact layer, a photoabsorption layer, and a second contact layer,

the optical element has a first electrode that is electrically connected to the first semiconductor layer, and a second electrode that is electrically connected to the second semiconductor layer,

the first electrodes are electrically isolated one from the other between the optical elements, and

the second electrodes define a common electrode for driving the light emitting section and the photodetecting section.

In a optical element array in accordance with the present invention, the case where another specific element (hereafter referred to as “B”) is formed above a specific element (hereafter referred to as “A”), includes a case where B is formed directly on A, and a case where B is formed through another element above A. This similarly applies to a method for manufacturing a optical element array in accordance with the present invention.

In the optical element array, each of the photodetecting elements is electrically isolated from others by each of the element isolation sections. In particular, each of the first electrodes in each of the photodetecting elements is electrically isolated from others by the element isolation section. For example, by transmitting different modulation signals to the first electrodes in the respective optical elements, respectively, the optical elements can be operated differently. Accordingly, in the optical element array, although the second electrodes define a common electrode for driving the light emitting sections and the photodetector sections, each of the optical elements can be driven independently.

In the optical element array in accordance with the present invention, the element isolation section can be a groove.

In the optical element array in accordance with the present invention, the groove can be embedded with dielectric resin.

In the optical element array in accordance with the present invention, the element isolation section can be an impurity layer formed by ion injection.

In the optical element array in accordance with the present invention, the optical element can have a third electrode that is electrically connected to the second contact layer.

In the optical element array in accordance with the present invention,

the first contact layer concurrently defines an uppermost layer of the second semiconductor layer, and

the second electrode can be formed to be in contact with the first contact layer.

In the optical element array in accordance with the present invention, the optical element can have a fourth electrode that is electrically connected to the first contact layer.

In the optical element array in accordance with the present invention, the fourth electrode can be electrically connected to the second electrode.

In the optical element array in accordance with the present invention,

the light emitting section can function as a light emitting diode,

the first semiconductor layer can be a first conductive type, and

the second semiconductor layer can be a second conductive type.

In the optical element array in accordance with the present invention,

the light emitting section can function as a surface-emitting type semiconductor laser,

the first semiconductor layer can be a first mirror, and

the second semiconductor layer can be a second mirror.

In the optical element array in accordance with the present invention, the optical element can have an optical member that functions as a lens above the photodetecting section.

An optical module in accordance with the present invention can include the optical element array described above, and an optical waveguide.

An optical transmission device in accordance with the present invention can include the optical module described above.

DETAILED DESCRIPTION OF EMBODIMENTS

1. First Embodiment

1-1. Structure of Optical Element Array

FIG. 1is a cross-sectional view schematically showing a optical element array100in accordance with a first embodiment of the present invention. Also,FIG. 2is a plan view schematically showing the optical element array100shown inFIG. 1. It is noted thatFIG. 1is a view showing a cross section taken along a line I—I inFIG. 2.

The optical element array100in accordance with the present embodiment includes, as shown inFIG. 1, two optical elements200, an element isolation section20. The optical element200includes a light emitting section140, and a photodetecting section120. The present embodiment shows a case in which the light emitting section140functions as a surface-emitting type semiconductor laser, and the photodetecting section120functions as a photodetector.

The overall structure of the light emitting section140, the photodetecting section120, and the optical element200, and the element isolation section20are described below.

The light emitting section140is provided on a semiconductor substrate101. The light emitting section140includes a vertical resonator. Also, the light emitting section140can include a columnar semiconductor deposition body (hereafter referred to as a “columnar section”)130.

The substrate101is dielectric or semi-dielectric. As a dielectric substrate101, sapphire, glass or the like can be used. As a semi-dielectric substrate101, GaAs undoped or with CrO added therein, InP with Fe added therein or the like can be used. In the present embodiment, an example in which a GaAs substrate with CrO added therein is described.

The light emitting section140is formed from, for example, a distributed reflection type multilayer mirror of 40 pairs of alternately laminated n-type Al0.9Ga0.1As layers and n-type Al0.15Ga0.85As layers (hereafter called a “first mirror”)102, an active layer103composed of GaAs well layers and Al0.3Ga0.7As barrier layers in which the well layers include a quantum well structure composed of three layers, and a distributed reflection type multilayer mirror of 25 pairs of alternately laminated p-type Al0.9Ga0.1As layers and p-type Al0.15Ga0.85As layers (hereafter called a “second mirror”)104, which are successively stacked in layers. It is noted that the composition of each of the layers and the number of the layers forming the first mirror102, the active layer103and the second mirror104are not particularly limited to the above.

The second mirror104is formed to be p-type by, for example, doping carbon (C), and the first mirror102is formed to be n-type by, for example, doping silicon (Si). Accordingly, the p-type second mirror104, the active layer103in which no impurity is doped, and the n-type first mirror102form a pin diode. It is noted here that an uppermost layer of the second mirror104may preferably be formed to have a high carrier density such that ohmic contact can be readily made with an electrode (second electrode109). Also, the uppermost layer of the second mirror104concurrently defines a first contact layer111of the photodetecting section120to be described below.

Among the light emitting section140, a portion extending from the second mirror104(first contact layer111) toward an intermediate portion of the first mirror102is etched in a circular shape, thereby forming a first columnar section130, as viewed from the side of an upper surface111aof the light emitting section140(first contact layer111). It is noted that, although the plane configuration of the first columnar section130in accordance with the present embodiment is formed to be circular, this can be in any configuration.

Furthermore, a current constricting layer105, that is obtained by oxidizing the AlGaAs layer from its side surface, is formed in a region near the active layer103among layers composing the second mirror104. The current constricting layer105is formed in a ring shape. In other words, the current constricting layer105has a cross section, when cut in a plane parallel with a surface101aof the substrate101shown inFIG. 1, which is a circular ring shape concentric with a circle of the plane configuration of the columnar section130.

Also, the light emitting section140is provided with a first electrode107and a second electrode109. The first electrode107and the second electrode109are used to drive the light emitting section140. Also the second electrode109is also used to drive the photodetecting section120, as described below. In other words, the second electrode109serves as a common electrode for driving the light emitting section140and the photodetecting section120.

More specifically, as shown inFIG. 1, the first electrode107is provided on an upper surface102aof the first mirror102. The first electrode107, as shown inFIG. 1andFIG. 2, is provided in a manner to surround mainly the first columnar section130. Stated otherwise, the first columnar section130is provided inside the first electrode107.

The second electrode109is provided on an upper surface111aof the light emitting section140(first contact layer111). The second electrode109, as shown inFIG. 2, has a connection section109ahaving a plane configuration in a ring shape, a lead-out section109bhaving a plane configuration in a linear shape, and a pad section109chaving a plane configuration in a quadrangle shape. The second electrode109is electrically connected to the second mirror104at the connection section109a. The lead-out section109bof the second electrode109connects the connection section109aand the pad section109c. The pad section109cof the second electrode109can be used as an electrode pad. The connection section109aof the second electrode109is provided in a manner to surround mainly a second columnar section132to be described below, as shown inFIG. 1andFIG. 2. Stated otherwise, the second columnar section132is provided inside the second electrode109.

The first electrode107is composed of a laminated film of an alloy of gold (Au) and germanium (Ge), and gold (Au), for example. The second electrode109is composed of a laminated film of platinum (Pt), titanium (Ti) and gold (Au), for example. Electric current is injected in the active layer103by the first electrode107and the second electrode109. It is noted that the materials for forming the first electrode107and the second electrode109are not limited to those described above, but, for example, an alloy of gold (Au) and zinc (Zn) can be used.

In the optical element200in accordance with the present embodiment, a first insulation layer30is formed in a manner to surround mainly the first columnar section130. The first insulation layer30is formed on the first mirror102. Further, the first insulation layer30is formed below the lead-out section109band the pad section109cof the second electrode109.

It is noted that although a case in which the light emitting section140functions as a surface-emitting type semiconductor laser is described above, the present invention is also applicable to other light emitting elements besides the surface-emitting type semiconductor laser. For example, a semiconductor light emitting diode can be enumerated as a light emitting element to which the present invention can be applied. This can be similarly applied to light emitting sections in second through fourth embodiments to be described below.

The photodetecting element120is provided on the light emitting section140. In the optical element200of the present embodiment, the upper surface of the photodetecting element120includes an emission surface108of laser light.

Also, the photodetecting element120includes the first contact layer111, a photoabsorption layer112, and a second contact layer113. The first contact layer111concurrently defines an upper surface of the second mirror104of the light emitting section140. The photoabsorption layer112is provided on the first contact layer111, and the second contact layer113is provided on the photoabsorption layer112. The photoabsorption layer112and the second contact layer113compose a columnar semiconductor deposition body (a “second columnar section”)132.

The first contact layer111concurrently defines the uppermost layer of the second mirror104of the light emitting section140described above, and may be composed of, for example, a p-type GaAs layer. Also, the photoabsorption layer112may be composed of, for example, a GaAs layer with no impurity being introduced, and the second contact layer113may be composed of, for example, an n-type GaAs layer. More specifically, the first contact layer111is made to be p-type by doping, for example, carbon (C), and the second contact layer113is made to be n-type by doping, for example, silicon (Si). Accordingly, the p-type first contact layer111, the photoabsorption layer112without an impurity being doped, and the n-type second contact layer113form a pin diode.

The photodetecting element120is provided with a second electrode109and a third electrode110. The second electrode109and the third electrode110are used to drive the photodetecting element120. As described above, the second electrode109is also used for driving the light emitting section140. In other words, the second electrode109is a common electrode for driving the light emitting section140and the photodetecting section120.

As shown inFIG. 3, the third electrode110has a connection section having a plane configuration in a ring shape, a lead-out section110bhaving a plane configuration in a linear shape, and a pad section110chaving a plane configuration in a quadrangle shape. The third electrode110is electrically connected to the second contact layer113at the connection section110a. The lead-out section110bof the third electrode110connects the connection section110aand the pad section110c. The pad section110cof the third electrode110can be used as an electrode pad. The third electrode110is provided on an upper surface of the photodetecting section120(on the second contact layer113). The third electrode110defines an opening section114, and a part of the upper surface of the second conductive layer113is exposed through the opening section114. The exposed surface defines an emission surface108of laser light. Accordingly, by appropriately setting the plane configuration and the size of the opening section114, the configuration and the size of the emission surface108can be appropriately set. In the present embodiment, as shown inFIG. 2, a case in which the emission surface108is in a circular shape is indicated.

Also, in the optical element200in accordance with the present embodiment, the third electrode110can be formed with the same material as that of the first electrode107.

In the optical element200in accordance with the present embodiment, a second insulation layer32is formed in a manner to mainly surround the second columnar section132. The second insulation layer32is formed on the second mirror104, as shown inFIG. 1andFIG. 2. Further, the second insulation layer40is formed below the lead-out section110band the pad section110cof the third electrode110.

1-4. Overall Structure of Optical Element200

In the optical element200in accordance with the present embodiment, the n-type first mirror102and the p-type second mirror104of the surface-emitting type semiconductor laser140, and the p-type first contact layer111and the n-type second contact layer113of the photodetecting element120form a npn structure as a whole.

The photodetecting section120has a function to monitor outputs of light generated by the light emitting section140. More specifically, the photodetecting element120converts light generated by the light emitting section140into electric current. With values of the electric current, outputs of light generated by the light emitting section140can be detected.

More specifically, in the photodetecting element120, a part of light generated by the light emitting section140is absorbed by the photoabsorption layer112, and photoexcitation is caused by the absorbed light in the photoabsorption layer112, and electrons and holes are generated. Then, by an electric field that is applied from an outside element, the holes move to the second electrode109, and the electrons move to the third electrode110, respectively. As a result, a current is generated in the direction from the second contact layer113to the first contact layer111in the photodetecting element120.

Also, light output of the light emitting section140is determined mainly by a bias voltage applied to the light emitting section140. In particular, light output of the light emitting section140greatly changes depending on the ambient temperature of the light emitting section140and the service life of the light emitting section140. For this reason, it is necessary for the light emitting section140to maintain a predetermined level of light output.

In the optical element200in accordance with the present embodiment, light output of the light emitting section140is monitored, and the value of a voltage to be applied to the light emitting section140is adjusted based on the value of a current generated by the photodetecting element120, whereby the value of a current flowing within the light emitting section140can be adjusted. Accordingly, a predetermined level of light output can be maintained in the light emitting section140. The control to feed back the light output of the light emitting section140to the value of a voltage to be applied to the light emitting section140can be performed by using an external electronic circuit (a drive circuit not shown).

In the optical element array100in accordance with the present embodiment, the element isolation section20is formed between the two optical elements200. More specifically, as shown inFIG. 1andFIG. 2, the element isolation section20is a groove that is formed in the first mirror102and the substrate101. As shown inFIG. 2, the element isolation section20has a plane configuration in a linear shape.

The two optical elements200are electrically isolated from each other by the element isolation section20. More specifically, the element isolation section20penetrates the first mirror102. Then the two optical elements200are connected to each other by the connection section22of the substrate101. As described above, the substrate101is dielectric or semi-dielectric. In other words, current does not flow, or is difficult to flow in the substrate101. Naturally, current does not flow, or is difficult to flow in the connection section22of the substrate101. Accordingly, current does not flow, or is difficult to flow in the connection section22that connects the two optical elements200, such that the two optical elements200can be electrically isolated from one another.

1-6. Operation of Optical Element200

General operations of the optical element200of the present embodiment are described below. It is noted that the following method for driving the optical element200is described as an example, and various changes can be made without departing from the subject matter of the present invention.

First, when a voltage in a forward direction is applied to the pin diode across the first electrode107and the second electrode109, recombination of electrons and holes occur in the active layer103of the light emitting section140, thereby causing emission of light due to the recombination. Stimulated emission occurs during the period the generated light reciprocates between the second mirror104and the first mirror102, whereby the light intensity is amplified. When the optical gain exceeds the optical loss, laser oscillation occurs, whereby laser light is emitted from the upper surface104aof the second mirror104. Then, the laser light enters the first contact layer111of the light emitting section120.

Next, the laser light that has entered the first contact layer111of the photodetector element120, enters the photoabsorption layer112. As a result of a part of the incident light being absorbed by the photoabsorption layer112, photoexcitation is caused in the photoabsorption layer112, and electrons and holes are generated. Then, by an electric field that is applied from an outside element, the holes move to the second electrode109and the electrons move to the third electrode110, respectively. As a result, an electric current (photoelectric current) is generated in the direction from the second contact layer113to the first contact layer111in the photodetecting element120. By measuring the value of the electric current, light output of the light emitting section140can be detected.

1-7. Method for Manufacturing Optical Element Array100

Next, one example of a method for manufacturing the optical element array100in accordance with an embodiment of the present invention is described, using FIG.3–FIG. 9. FIG.3–FIG. 9are cross-sectional views schematically showing a process of manufacturing optical element array100shown inFIG. 1andFIG. 2, and correspond to the cross-sectional view shown inFIG. 1, respectively.

(1) First, on a surface101aof a semiconductor substrate101composed of an i-type GaAs layer, a semiconductor multilayer film150shown inFIG. 3is formed by epitaxial growth while modifying its composition. It is noted here that the semiconductor multilayer film150is formed from, for example, a first mirror102of 40 pairs of alternately laminated n-type Al0.9Ga0.1As layers and n-type Al0.15Ga0.85As layers, an active layer103composed of GaAs well layers and Al0.3Ga0.7As barrier layers in which the well layers include a quantum well structure composed of three layers, a second mirror104of 25 pairs of alternately laminated p-type Al0.9Ga0.1As layers and p-type Al0.15Ga0.85As layers, a first contact layer111composed of a p-type GaAs layer, and concurrently defines an uppermost layer of the second mirror104, a photoabsorption layer112composed of a GaAs layer without impurity being doped, and a second contact layer composed of an n-type GaAs layer. These layers are successively stacked in layers on the semiconductor substrate101, thereby forming the semiconductor multilayer film150.

It is noted that, when the second mirror104is grown, at least one layer thereof near the active layer103can be formed to be a AlAs layer or a AlGaAs layer that is later oxidized and becomes an insulation layer for current constriction105. The Al composition of the AlGaAs layer that becomes to be the insulation layer105is, for example, 0.95 or greater. Also, the first contact layer111and the second contact layer113may preferably be formed to have a high carrier density, such that ohmic contact can be readily made with an electrode (second electrode109and third electrode110).

The temperature at which the epitaxial growth is conducted is appropriately decided depending on the growth method, the kind of raw material, the type of the semiconductor substrate101, and the kind, thickness and carrier density of the semiconductor multilayer film150to be formed, and in general may preferably be 450° C.–800° C. Also, the time required for conducting the epitaxial growth is appropriately decided like the temperature. Also, a metal-organic chemical vapor deposition (MOVPE: Metal-Organic Vapor Phase Epitaxy) method, a MBE method (Molecular Beam Epitaxy) method or a LPE (Liquid Phase Epitaxy) method can be used as a method for the epitaxial growth.

(2) Next, a second columnar section132is formed (seeFIG. 4). First, resist (not shown) is coated on the semiconductor multilayer film150, and then the resist is patterned by a lithography method, thereby forming a resist layer R1having a specified pattern.

Then, by using the resist layer R1as a mask, the second contact layer113and the photoabsorption layer112are etched by, for example, a dry etching method. By this, the second contact layer113and the photoabsorption layer112having the same plane configuration as that of the resist layer R1are formed. In other words, the second columnar section132is formed. Then, the resist layer R1is removed.

(3) Then, a light emitting section140including a first columnar section130is formed by patterning (seeFIG. 5). More specifically, first, resist (not shown) is coated on the first contact layer111, and then the resist is patterned by a lithography method, thereby forming a resist layer R2having a specified pattern. Then, by using the resist layer R2as a mask, the first contact layer111, the second mirror104, the active layer103, and a part of the first mirror102are etched by, for example, a dry etching method. By this, as shown inFIG. 5, the first columnar section130is formed.

By the steps described above, a vertical resonator (light emitting section140) including the first columnar section130is formed on the substrate101. In other words, a stacked layered body of the light emitting section140and the photodetecting section120is formed. Then, the resist layer R2is removed.

It is noted that, in the present embodiment described above, the description is made as to a case in which the second columnar section132is formed first, and then the first columnar section130is formed. However, the first columnar section130may be formed first, and then the second columnar section132may be formed.

(4) Then, an element isolation section20is formed by patterning (seeFIG. 6). More specifically, first, resist (not shown) is coated on an upper surface102aof the first mirror102, the resist is patterned by a lithography method, thereby forming a resist layer R3having a specified pattern. Then, by using the resist layer R3as a mask, the first mirror102and a part of the substrate101are etched by, for example, a dry etching method. Thus, a groove is formed in the first mirror102and a part of the substrate101. This groove is formed in a manner to penetrate the first mirror102. This groove is formed in a manner not to penetrate the substrate101. The width of the groove is appropriately set depending on the layout of the two optical elements200. By this, the element isolation section20is formed, as shown inFIG. 6. Then, the resist layer R3is removed.

It is noted that, in the present embodiment described above, the description is made as to a case in which the element isolation section20is formed after the second columnar section132and the first columnar section130are formed first. However, the order of the step of forming the element isolation section20and other steps is not particularly limited. For example, it is also possible that the second columnar section132and the first columnar section130can be formed after the element isolation section20has been formed.

Then, by placing the semiconductor substrate101on which the first columnar section130is formed through the aforementioned steps in a water vapor atmosphere at about 400° C., for example, a layer having a high Al composition provided in the second mirror104is oxidized from its side surface, thereby forming a current constricting layer105(seeFIG. 7).

The oxidation rate depends on the temperature of the furnace, the amount of water vapor supply, and the Al composition and the film thickness of the layer to be oxidized. In a surface-emitting type laser equipped with a current constricting layer that is formed by oxidation, when it is driven, a current flows only in a portion where the current constricting layer is not formed (a portion that is not oxidized). Accordingly, in the process for forming the current constricting layer by oxidation, the range of the current constricting layer105to be formed may be controlled, whereby the current density can be controlled.

Also, the diameter of the current constricting layer105may preferably be adjusted such that a major portion of light that is emitted from the light emitting section140enters the first contact layer111.

(6) Next, as shown inFIG. 8, a first insulation layer30is formed on the first mirror102, and around the first columnar section130, and a second insulation layer32is formed on the second mirror, and around the second columnar section312.

For example, the first insulation layer30and the second insulation layer32can use layers that may be obtained by hardening liquid material settable by energy, such as, heat, light or the like (for example, a precursor of ultraviolet setting type resin or thermosetting type resin). As the ultraviolet setting type resin, for example, an acrylic resin, an epoxy resin or the like that is an ultraviolet setting type can be enumerated. Also, as the thermosetting type resin, a polyimide resin or the like that is a thermosetting type can be enumerated. Also, the first insulation layer30and the second insulation layer32can use an inorganic dielectric film, such as, for example, a silicon oxide film, silicon nitride film or the like. Also, the first insulation layer30and the second insulation layer32can be made to be a laminated film using a plurality of the materials described above.

Here, the case where a precursor of polyimide resin is used as the material for forming the first insulation layer30and the second insulation layer32is described. First, for example, by using a spin coat method, the precursor (precursor of polyimide resin) is coated on the semiconductor substrate101, thereby forming a precursor layer. It is noted that, as the method for forming the precursor layer, besides the aforementioned spin coat method, another known technique, such as, a dipping method, a spray coat method, a droplet ejection method or the like can be used.

Then, the semiconductor substrate101is heated by using, for example, a hot plate or the like, thereby removing the solvent, and then is placed in a furnace at, for example, about 350° C. to thereby imidize the precursor layer, thereby forming a polyimide resin layer that is almost completely set. Then, as shown inFIG. 8, the polyimide resin layer is patterned by using a known lithography technique, thereby forming the first insulation layer30and the second insulation layer32. As the etching method used for patterning, a dry etching method or the like can be used. Dry etching can be conducted with, for example, oxygen or argon plasma.

In the method for forming the first insulation layer30and the second insulation layer32described above, an example is presented in which a precursor layer of polyimide resin is set, and then patterning is conducted. However, patterning may be conducted before the precursor layer of polyimide resin is set. As the etching method used for this patterning, a wet etching method or the like can be used. The wet etching can be conducted with, for example, an alkaline solution or an organic solution.

(7) Then, a first electrode107is formed on an upper surface102aof the first mirror102, and a third electrode110is formed on an upper surface (upper surface113aof the second contact layer113) of the photodetecting section120(seeFIG. 9).

First, before the first electrode107and the third electrode110are formed, the upper surface102aof the first mirror102and the upper surface113aof the second contact layer113may be washed by using a plasma processing method or the like, if needed. By so doing, an element with more stable characteristics can be formed.

Next, a laminated film (not shown) of an alloy of gold (Au) and germanium (Ge), and gold (Au), for example, is formed by, for example, a vacuum deposition method. Then, the first electrode107and the third electrode110are formed by removing the laminated film other than specified positions by a lift-off method. In this instance, a portion where the above-mentioned laminated film is not formed is formed on the upper surface113aof the second contact layer113. This portion becomes an opening section114, and a portion of the upper surface113aof the second contact layer113is exposed through the opening section114. The exposed surface defines an emission surface108of laser light.

It is noted that, instead of the lift-off method, a dry etching method or a wet etching method can also be used. Also, in the aforementioned step, a sputter method can be used, instead of the vacuum vapor deposition method. Also, in the aforementioned step, the first electrode107and the third electrode110are patterned at the same time, but the first electrode107and the third electrode110may be formed independently.

(8) Next, by a similar method, a laminated film of platinum (Pt), titanium (Ti), and gold (Au), for example, is patterned, whereby a second electrode109is formed on the second mirror104of the light emitting section140(seeFIG. 1andFIG. 2).

(9) Next, an annealing treatment is conducted. The temperature of the annealing treatment depends on the electrode material. This is usually conducted at about 400° C. for the electrode material used in the present embodiment. Through the steps described above, the first-third electrodes107,109and110are formed.

By the steps described above, the optical element array100in accordance with the present embodiment shown inFIG. 1andFIG. 2can be obtained.

1-8. Actions and Effects

In the optical element array100, the two optical elements200are electrically isolated from each other by the element isolation section20. In particular, each of the first electrodes109in each of the optical elements200is electrically isolated from the other by the element isolation section20. For example, by transmitting different modulation signals to the first electrodes109in the respective optical elements200, respectively, the two optical elements200can be operated differently. Accordingly, in the optical element array100in accordance with the present embodiment, although the second electrode109defines a common electrode for driving the light emitting section140and the photodetecting section120, the two optical elements200can be driven independently.

According to the optical element array100in accordance with the present embodiment, because a portion of light output of the light emitting section140is monitored by the photodetecting section120and fed back to the driving circuit, output fluctuations due to temperatures or the like can be corrected, and therefore stable light outputs can be obtained.

1-9. Modified Examples

In the optical element array100shown inFIG. 1andFIG. 2, the description is made as to the case in which the element isolation section20is a groove. However, as shown inFIG. 10, the groove described above can be embedded with insulating resin. By this, the mechanical strength can be improved, compared to the case where the element isolation section20is a groove. In other words, when the element isolation section20is a groove, the substrate101would likely be cleaved along the groove, but it would become difficult to be cleaved because the groove is embedded with resin. As the insulating resin, for example, the same material as that of the first insulation layer30or the second insulation layer32can be used. It is noted thatFIG. 10is a cross-sectional view schematically showing a optical element array300in this case, and corresponds to the cross-sectional view ofFIG. 1.

In the optical element array100shown inFIG. 1andFIG. 2, the description is made as to the case in which the element isolation section20is a groove. However, as shown inFIG. 1, the groove described above can be an impurity layer that is formed by ion injection. The element isolation section20in this case is formed in a forming region of the element isolation section20of the first mirror102and the substrate101by injecting ions by using a known ion injection technique. The element isolation section20in this case can be formed over the entire region other than the forming region of the two optical elements200, as viewed in a plan view. As the ions to be injected, for example, H+, B+, O+or Cr+ions can be used. By injecting these ions, the first mirror102and the substrate101can be formed to have a high resistance. In other words, the element isolation section20that electrically isolates the two optical elements200from each other can be formed.

By a optical element array400shown inFIG. 11, the mechanical strength can be improved, compared to the case where the element isolation section20is a groove. In other words, when the element isolation section20is a groove, the substrate101would likely be cleaved along the groove, but it would become difficult to be cleaved because the element isolation section20is an impurity layer. It is noted thatFIG. 11is a cross-sectional view schematically showing the optical element array400in this case, and corresponds to the cross-sectional view ofFIG. 1.

Also, as shown inFIG. 12, for example, optical members50may be formed on upper surfaces of the photodetecting sections120. The optical member50functions as, for example, a lens. In this case, light generated by the light emitting section140can be emitted from the emission surface108, and then condensed by the optical member50, and irradiated outside. It is noted thatFIG. 12is a cross-sectional view schematically showing a optical element array500in this case, and corresponds to the cross-sectional view ofFIG. 1.

The optical member50can be formed, for example, by hardening liquid material settable by energy, such as, heat, light or the like (for example, a precursor of ultraviolet setting type resin or thermosetting type resin). As the ultraviolet setting type resin, for example, an acrylic resin, an epoxy resin or the like that is an ultraviolet setting type can be enumerated. Also, as the thermosetting type resin, a polyimide resin or the like that is a thermosetting type can be enumerated.

As the method for forming the optical member50, more specifically, droplets composed of liquid material are ejected against an upper surface of the photodetecting section120by a droplet ejection method or the like, thereby forming an optical member precursor. Then, the optical member precursor is set, thereby obtaining the optical member50.

Also, the optical member50is in a cut-circular globe shape. Because the optical member50is in a cut-circular globe shape, the optical member50can be used as a lens or a deflection element. For example, by forming the upper surface of the photodetecting section120in a circular shape, the three-dimensional configuration of the optical member50can be formed into a cut-circular globe shape. Alternatively, by forming the upper surface of the photodetecting section120in an oval shape, the three-dimensional configuration of the optical member50can be formed into a cut-elliptical globe shape.

It is noted here that the “cut-circular globe shape” means a configuration obtained by cutting a globe in one plane, and the circular globe includes not only a perfect circular globe, but also a configuration approximate to a circular globe. Also, the “cut-elliptical globe shape” means a configuration obtained by cutting an elliptical globe in one plane, and the elliptical globe not only includes a perfect elliptical globe but also a configuration approximate to an elliptical globe.

Because the optical member50is provided on the upper surface of the photodetecting section120, the radiation angle of light generated by the light emitting section140is adjusted, and then the light can be irradiated. For example, because the optical member50is provided, the radiation angle of light generated by the light emitting section140can be narrowed. By this, when light emitted from the optical element200in accordance with the present embodiment is to be introduced in an optical waveguide, such as, for example, an optical fiber or the like, introduction of the light into the optical waveguide becomes easy.

Also, in the optical element200shown inFIG. 12, the photodetecting section120can absorb light coming from outside, and convert the same to electric current. In this case, light from outside first enters the optical member50, and then enters the photodetecting section120through the light incident surface (emission surface)108. The light is absorbed by the photoabsorption layer112, and converted into electric current. Based on the current value obtained here, the amount of light entered from outside can be detected. By the optical element200shown inFIG. 12, light in a wide range can be entered into the light incident surface (emission surface)108because the optical member50is provided on the upper surface of the photodetecting section120.

2. Second Embodiment

FIG. 13is a view schematically showing an optical module600in accordance with a second embodiment of the present invention. The optical module600includes two optical element arrays100(seeFIG. 1andFIG. 2), semiconductor chips70, and optical waveguides (optical fibers)72. The optical module600includes four optical elements200(a first optical element200a, a second optical element200b, a third optical element200c, and a fourth optical element200d). In the optical element200, a photodetecting section320has a function to convert light that enters the photodetecting section320from a light emitting section340into electric current, and has a function to convert light that enters a light incident surface (emission surface)308from an optical member360. Structures and functions common to the first–fourth optical elements200a,200b,200cand200dare described by generally referring to the “optical element200.”

It is noted that, in the optical module600of the present embodiment, the use of any one of the other optical element arrays in accordance with the first embodiment instead of the optical element array100can provide similar actions and effects. This similarly applies to third and fourth embodiments to be described below.

2-1. Structure of Optical Module

In the optical module600, as shown inFIG. 13, the first–fourth optical elements200a,200b,200cand200dare provided at end surfaces72a,72b,72cand72dof optical fibers72, respectively. The first–fourth optical elements200a,200b,200cand200dhave the same structure. Each of the first–fourth optical elements200a,200b,200cand200dincludes a light emitting section340and a photodetecting section320. Each of the layers composing the light emitting section340and the photodetecting section320has generally the same composition as that of the light emitting section140and the photodetecting section120of the optical element200shown inFIG. 1andFIG. 2except the positions of electrodes provided. It is noted thatFIG. 13omits illustration of each of the layers composing the light emitting section340and the photodetecting section320.

In the optical element200shown inFIG. 13, a first electrode307and a second electrode309function to drive the light emitting section340, and the second electrode309and a third electrode310function to drive the photodetecting section320. Also, an opening section314is provided in a part of the third electrode310in a region positioned above the photodetecting section320. A bottom surface of the opening section314defines an emission surface (incident surface)308.

Furthermore, an optical member360is provided on the emission surface (incident surface)308. The optical member360is composed of a material similar to that of the optical member50of the optical element array500shown inFIG. 12, and can be formed by a similar method. The first-third electrodes307,309and310have portions that are provided on an insulation layer306. The insulation layer306may preferably be composed of a resin, such as, for example, a polyimide resin, fluorine resin, acrylic resin, epoxy resin or the like, or an insulation material, such as, for example, silicon nitride, silicon oxide, oxide nitride silicon or the like.

Each of the first–fourth optical elements200a,200b,200cand200dfunctions as a photodetecting element or a light emitting element. The optical module600is capable of two-way parallel communications. For example, when the first optical element200afunctions as a light emitting element, and the second optical element200bfunctions as a photodetecting element, light generated at the light emitting section340of the first optical element200ais emitted from the emission surface (incident surface)308, and enters the optical member360, and then the light is condensed by the optical member360. Thereafter, the light emitted from the optical member360enters the end surface72aof the optical fiber72. The incident light propagates within the optical fiber72, and is emitted from the end surface72b, enters the incident surface (emission surface)308of the second optical element200bthrough the optical member360, and is absorbed by the photodetecting section320of the second optical element200b.

Alternatively, for example, when the first optical element200afunctions as a photodetecting element, and the second optical element200bfunctions as a light emitting section, light generated at the light emitting section340of the second optical element200bis emitted from the emission surface (incident surface)308, and then the light is condensed by the optical member360. Thereafter, the light emitted from the optical member360enters the end surface72bof the optical fiber72. The incident light propagates within the optical fiber72, and is emitted from the end surface72a, enters the incident surface (emission surface)308of the first optical element200athrough the optical member360, and is absorbed by the photodetecting section320of the second optical element200a.

It is noted that although the functions of the first optical element200aand the second optical element200bare described above, the third optical element200cand the fourth optical element200dhave similar functions.

The first optical element200ais in a state in which its relative position with respect to the end surface72aof the optical fiber72is fixed, the second optical element200bis in a state in which its relative position with respect to the end surface72bof the optical fiber72is fixed, the third optical element200cis in a state in which its relative position with respect to the end surface72cof the optical fiber72is fixed, and the fourth optical element200dis in a state in which its relative position with respect to the end surface72dof the optical fiber72is fixed. Also, the emission surface (incident surface)308of the first optical element200ais opposite to the end surface72aof the optical fiber72, the emission surface (incident surface)308of the second optical element200bis opposite to the end surface72bof the optical fiber72, the emission surface (incident surface)308of the third optical element200cis opposite to the end surface72cof the optical fiber72, and the emission surface (incident surface)308of the fourth optical element200dis opposite to the end surface72dof the optical fiber72.

The semiconductor chips70are provided for driving the optical elements200. In other words, the semiconductor chips70have circuits built therein for driving the optical elements200. A plurality of wiring patterns24,34and64that are electrically connected to the internal circuits are provided on the semiconductor chips70.

The semiconductor chip70is electrically connected to the optical element200. For example, the first electrode307and the wiring pattern24are electrically connected to each other through solder26. Also, the second electrode309and the wiring pattern64are electrically connected to each other through solder26. Further, the third electrode310and the wiring pattern34are electrically connected to each other through solder26.

The optical element200can be face-down mounted on the semiconductor chip70. By so doing, the electrical connection can be made through the solder26, and the optical element200and the semiconductor chip70can be affixed together. It is noted that wires or conductive paste may be used for connecting the electrodes and the wiring patterns described above, instead of using the solder26.

Also, as shown inFIG. 13, the optical element200and the semiconductor chip70can be affixed together by using resin56. In other words, the resin56has a function to retain the bonding state between the optical element200and the semiconductor chip70. In this case, as shown inFIG. 13, the resin56does not cover the optical member360, such that the difference in the index of refraction between the optical member360and its surrounding can be secured. By this, the light condensing function of the optical member360can be secured. It is noted that, when the optical member360is not provided, the resin56can be formed as so-called underfill entirely between the optical element200and the semiconductor chip70.

The semiconductor chip70is provided with apertures (for example, through holes)28. The optical fibers72are inserted in the apertures28. The apertures28are formed extending from the surface where the wiring patterns24,34and64of the semiconductor chip70are formed to the opposite surface, while avoiding the internal circuit. It is noted that a taper (not shown) may preferably be formed at at least one of open edge sections of the aperture28. By forming the taper, the optical fiber70can be readily inserted in the aperture28.

It is noted that, when a multi-core fiber or the like is used as the optical waveguide, the pitch of the optical elements200in the optical element array100can be designed to match with the pitch of the fibers. By this, a plurality of the optical elements200and the multi-core fiber can be optically connected in a single alignment.

2-2. Optical Module Driving Method

Next, a method for driving the optical member600shown inFIG. 13is described with reference toFIG. 14.FIG. 14is a view schematically showing one example of a driving circuit (its main part) of the optical element200shown inFIG. 13.

In the optical member600shown inFIG. 13, for example, the first optical element200aand the second optical element200bmay be controlled such that optical transmission and optical reception between them are switched by time division. As described above, when the first optical element200afunctions as a light emitting element, it is controlled such that light generated at the first optical element200ais received by the second optical element200b, and when the second optical element200bfunctions as a light emitting element, it is controlled such that light generated at the second optical element200bis received by the first optical element200a. Also, the time division is controlled by clocks54and55that are inputted in a driver IC40and a switching circuit42, respectively.

The driving circuit of the optical element200includes, as shown inFIG. 14, the driver IC40, the switching circuit42, and a trans-impedance amplifier (TIA)44. The driving circuit shown inFIG. 14is provided for each of the optical elements200. Also, in the optical element200, biases in opposite directions can be applied to the light emitting section340and the photodetecting section320.

The driver IC40is electrically connected to one of the electrodes of the light emitting section340of the optical element200, and the switching circuit42is electrically connected to one of the electrodes of the photodetecting section320of the optical element200. On the other hand, as shown inFIG. 14, the other electrode of the light emitting section340and the other electrode of the photodetecting section320are grounded. Furthermore, a reverse bias is applied to one of the electrodes of the photodetecting section320. The TIA44is electrically connected to the switching circuit42.

The driver IC40is provided for driving the light emitting section340of the optical element200. More specifically, while a transmission signal58is inputted in the driver IC40, light generated at the light emitting section340is emitted. Also, while the light emitting section340is being driven, the photodetecting section320can monitor outputs of the light generated at the light emitting section340. Referring toFIG. 14, operations of the circuit at the time of driving the light emitting section340are described more concretely. First, when the transmission signal58is inputted in the driver IC40, the driver IC starts driving the light emitting section340. Then, while the transmission signal58is being inputted in the driver IC40, the photodetecting section320detects a light output generated by the light emitting section340. The detected light output is inputted by the switching circuit42in the driver IC40as an APC input52.

On the other hand, while the transmission signal58is not inputted in the driver IC40, light emitted from the end surface72aof the optical fiber72enters the incident surface (emission surface)308of the optical element200through the optical member360. More specifically, while the transmission signal58is not inputted in the optical element200, the switching circuit42is switched to the TIA44side (seeFIG. 14). The TIA44has a function to amplify a reception signal51.

As described above, in the optical member600in accordance with the present embodiment, the first and second optical elements200aand200bcan be controlled by time division such that, when the first optical element200ais in a light emitting state, the second optical element200bbecomes to be in a photodetecting state, and when the first optical element200ais in a photodetecting state, the second optical element200bbecomes to be in a light emitting state.

It is noted that, although the control of the first optical element200aand the second optical element200bis described above, the third optical element200cand the fourth optical element200dcan be similarly controlled.

FIG. 15is a view schematically showing optical transmission devices in accordance with a third embodiment of the present invention. The optical transmission devices90mutually connect electronic devices92such as a computer, display device, storage device, printer and the like. The electronic devices92may be data communication devices. The optical transmission device90may include a cable94and plugs96provided on both sides thereof. The cable94includes an optical fiber72(seeFIG. 13). The plug96includes on its inside the optical element200(200a,200b,200cand200d) and the semiconductor chip70. It is noted that, because the optical fiber72is provided inside the cable94, and the optical element200and the semiconductor chip70are provided inside the plug96, they are not shown inFIG. 15. The optical fiber72and the optical element200are attached in a manner described in the second embodiment.

The first and second optical elements200aand200bare provided at both ends of the optical fiber72, respectively. When the first optical element200athat is provided at one of the ends of the optical fiber72functions as a photodetecting element, a light signal is converted into an electrical signal by the photodetecting section320of the first optical element200a, and then the electrical signal is inputted in the electronic device92. In this case, the second optical element200bthat is provided at the other end of the optical fiber72functions as a light emitting element. In other words, an electrical signal outputted from the electronic device92is converted into an optical signal by the light emitting section340of the second optical element200b. The optical signal is transmitted through the optical fiber72, and enters the first optical element200athat functions as a photodetecting element. It is noted that, although the first optical element200aand the second optical element200bare described above, the description similarly applies to the third optical element200cand the fourth optical element200d.

As described above, by the optical transmission device90of the present embodiment, information can be transmitted among the electronic devices92by optical signals.

FIG. 16is a view schematically showing a usage configuration of optical transmission devices in accordance with a fourth embodiment of the present invention. Optical transmission devices90connect electronic devices80. The electronic devices80include, for example, liquid crystal display monitors, digital CRTs (which may be used in the fields of finance, mail order, medical treatment, and education), liquid crystal projectors, plasma display panels (PDP), digital TVs, cash registers of retail stores (for POS (Point of Sale Scanning), videos, tuners, gaming devices, printers and the like.

Preferred embodiments of the present invention are described above. However, the present invention is not limited to the embodiments described above, and many modifications can be made. For example, interchanging the p-type and n-type characteristics of each of the semiconductor layers in the above described embodiments does not deviate from the subject matter of the present invention. In this case, the p-type first mirror102and the n-type second mirror104of the light emitting section140, and the n-type first contact layer111and the p-type second contact layer113of the photodetecting section120can compose a pnp structure as a whole.

Also, as shown inFIG. 17, for example, by interchanging the p-type and n-type characteristics of each of the layers in either the light emitting section140or the photodetecting section120, the light emitting section140and the photodetecting section120can have a npnp structure or a pnpn structure as a whole. It is noted thatFIG. 17is a cross-sectional view schematically showing a optical element array700in this case, and corresponds to the cross-sectional view ofFIG. 1.

It is noted in this case that, as shown inFIG. 17, the plane configuration of the first contact layer111can be formed to be greater than the plane configuration of the photoabsorption layer112and the second contact layer113, and smaller than the plane configuration of the second mirror104. Also, a fourth electrode116is formed on the first contact layer111and the second electrode109. The first contact layer111contacts the second electrode109and the fourth electrode116. The fourth electrode116is formed with a portion thereof on the second electrode109. In other words, the first contact layer111contacts the second electrode109at its side surface, and contacts the fourth electrode116at its upper surface. Also, the fourth electrode116is electrically connected to the second electrode109.

In this case, the third electrode110and the fourth electrode116are used for driving the photodetecting section120. For example, the fourth electrode116can be formed with the same material as that of the first electrode107.

In the optical element array700shown inFIG. 17, a forward bias to be applied to the light emitting section140and a reverse bias to be applied to the photodetecting section120can be supplied from power supplies of the same polarity. More specifically, for example, the second electrode109and the fourth electrode116are grounded, a forward bias to be applied to the light emitting section140can be supplied from a positive power supply, and a reverse bias to be applied to the photodetecting section120can be supplied from another positive power supply. Alternatively, for example, the second electrode109and the fourth electrode116are grounded, a forward bias to be applied to the light emitting section140can be supplied from a negative power supply, and a reverse bias to be applied to the photodetecting section120can be supplied from another negative power supply.

Also, for example, as the optical elements in the embodiments described above, a case in which the light emitting section has one columnar section is described. However, the embodiments of the present invention are not harmed even when a plurality of columnar sections are provided in a light emitting section.

Also, for example, in the optical element array in the embodiments described above, a case in which two optical elements are formed into an array is described. However, even when three or more optical elements are formed into an array, similar actions and effects can be obtained. For example, FIG.18–FIG. 21show cases in which four optical elements200are formed into an array. FIG.18–FIG. 21are plan views schematically showing optical element arrays800,810,820and830in the cases described above, respectively. It is noted that FIG.18–FIG. 21each show first columnar sections130, second columnar sections132, first mirrors102, first electrodes107, and element isolation sections20, and omit illustrations of other members.

In the optical element array800shown inFIG. 18, four optical elements200are electrically isolated from one another by an element isolation section200having a plane configuration in a linear cross shape.

In the optical element array810shown inFIG. 19, each of optical elements200is surrounded by an element isolation section20having a plane configuration in a rectangular ring shape. Because each of the optical elements200is surrounded by the element isolation section20, the four optical elements200are electrically isolated from one another.

In the optical element array820shown inFIG. 20, each of optical elements200is surrounded by an element isolation section20having a plane configuration in a circular ring shape. Because each of the optical elements200is surrounded by the element isolation section20, the four optical elements200are electrically isolated from one another.

In the optical element array830shown inFIG. 21, each of optical elements200is surrounded by an element isolation section20. The element isolation section20has a plane configuration in which portions of circular rings are in linear shapes. The linear shaped portions of the element isolation sections20in the plane configuration are shared by adjacent ones of the optical elements200as element isolation sections20, respectively. Because each of the optical elements200is surrounded by the element isolation section20, the four optical elements200are electrically isolated from one another.

It is noted that the plane configuration of the element isolation section20may be in any shape as long as it can electrically isolate the optical elements200from one another, and is not limited to the plane configurations described above.

Also, for example, in the above described embodiments, the description is made as to an AlGaAs type, but depending on the oscillation wavelength, other materials, such as, for example, GaInP type, ZnSSe type, InGaN type, AlGaN type, InGaAs type, GaInNAs type, GaAsSb type, and like semiconductor materials can be used.