JP3541862B2 - Optical function element - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an optical functional device used for an optical signal processing system or the like.
[0002]
[Prior art]
Optical communication and optical interconnection using optical signals have attracted attention as a method of realizing a higher signal transmission speed and an increase in transmission capacity. This is a method that enables a dramatic increase in transmission capacity and an increase in speed by focusing on optical multiplexing (wavelength and spatial multiplexing) and parallel transmission.
[0003]
In wavelength division multiplexing transmission utilizing wavelength multiplicity, an optical functional element is used that splits a plurality of wavelength-multiplexed and transmitted signal lights according to the wavelength and receives a specific signal light. As such an optical functional device, for example, there is a device provided with a band-pass filter formed by finely processing a dielectric multilayer film or a semiconductor multilayer film, and as a light-emitting device integrated with such a band-pass filter, For example, a surface emitting laser device disclosed in JP-A-6-244502 is known.
[0004]
For example, as shown in FIG. 6, an optical functional device having a band-pass filter has light receiving portions 29, 30, 31 and light emitting devices 32, 33, 34 formed on a substrate 25 and a spacer (not shown). Bandpass filters 26, 27, 28 are arranged above the respective light receiving sections 29, 30, 31 via the light receiving sections 29, 30, 31. The optical functional element, a plurality of wavelengths _{(e.g., λ 1, λ 2, λ} 3) of the multiplexed signal light to light, for example, a signal light of the wavelength lambda ₁ to the light receiving element 29, the wavelength lambda ₂ of the signal It is used in such a manner that light is given to the light receiving element 30 and signal light of the wavelength λ ₃ is given to the light receiving element 31.
[0005]
[Problems to be solved by the invention]
Incidentally, such as by changing the processing mode changes and processor design, for example, may need to change that want to the light receiving element 29 does not give a signal light having a wavelength of lambda _1. Further, the light emitting element as one, to which should be tied to the three light receiving portions 29, 30, 31, and with the one light emitting element emits light when the wavelength lambda ₁ of the signal light is incident manner And a mode in which the one light emitting element emits light when the signal light of wavelength λ ₂ is incident, and a mode in which the one light emitting element emits light when the signal light of wavelength λ ₃ is incident It is desired to be able to arbitrarily change it at any time in order to improve design flexibility.
[0006]
However, in an optical functional device using a dielectric multilayer film or a semiconductor multilayer film as the above-described bandpass filter, the wavelength selection characteristics are uniquely determined by the design thereof. There is a disadvantage that the optical transmission path cannot be changed.
[0007]
The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an optical functional device that can easily change an optical transmission path and the like.
[0008]
[Means for Solving the Problems]
In order to solve the above-described problems, the optical functional element of the present invention includes a wavelength-splitting optical element that splits a plurality of signal lights that are wavelength-multiplexed and transmitted according to wavelengths, and a light-emitting element that splits each of the split signal lights. It is characterized by comprising a light receiving element provided at a position for receiving light, and a light modulation element formed on the light receiving surface side of the light receiving element and changing light transmission characteristics by electrical control. The light modulation element may change light transmission characteristics by a quantum confined Stark effect generated by application of an electric field.
[0009]
According to the above configuration, the signal light obtained by multiplexing the light beams of a plurality of wavelengths (for example, λ ₁ , λ ₂ , λ ₃ ) is separated, and for example, the signal light of the wavelength λ ₁ is transmitted to the first light receiving element. After producing an optical functional element by a circuit design that gives the signal light of λ ₂ to the second light receiving element and the signal light of the wavelength λ ₃ to the third light receiving element, the first light receiving element Is changed so as not to give the signal light of the wavelength λ ₁ to the first light receiving element by performing electrical control so that the light modulating element provided on the light receiving surface side of the first light receiving element has a characteristic of blocking light. It can be easily realized. Further, three light receiving sections are connected to one light emitting element, and the one light emitting element emits light when the signal light of wavelength λ ₁ is incident, and the signal light of wavelength λ ₂ is incident on the light emitting element. a mode in which the one light emitting element is to emit light when the, and embodiments wherein one of the light emitting element is to emit light when the signal light of the wavelength lambda ₃ is incident, may be arbitrarily changed at any time.
[0010]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1A is a plan view showing an optical functional device according to this embodiment, and FIG. 1B is a side view thereof.
[0011]
The optical waveguide 1 and the semiconductor substrate 2 are provided in opposition to each other, and a spacer (not shown) is provided between them so that a predetermined interval is secured between them. The optical waveguide is made of a flat glass substrate or a semiconductor substrate, and the light incident thereon is totally reflected at an interface between the substrate and an atmosphere outside the substrate (for example, the atmosphere) or reflected by a diffraction grating or a reflecting mirror formed on the upper and lower surfaces of the substrate. By repeating this, light is propagated through the substrate and light is output to a predetermined position. The semiconductor substrate 2 is made of, for example, a material such as GaAs, Si, or InP. The material is appropriately selected depending on the wavelength of the light to be propagated. A material suitable for forming a light receiving element for receiving light on a substrate is selected. When the optical waveguide 1 is made of a semiconductor substrate, the substrate is made of a material such as GaAs, Si, InP or the like, and is appropriately selected according to the wavelength of light to be propagated.
[0012]
At the signal light receiving position on the upper surface side of the optical waveguide 1, a wavelength separating optical element 3 (size 2 mm × 2 mm) is formed, and also on the upper surface side, on the propagation path of each of the separated signal light. Are formed with condensing optical elements 4, 5, and 6 (having a diameter of 1 mm to 2 mm).
[0013]
In this embodiment, the wavelength-splitting optical element 3 is a transmission-type diffraction grating, and converts a signal light obtained by multiplexing a plurality of wavelengths of light (for example, λ ₁ , λ ₂ , λ ₃ ) according to the wavelength. The light is split and guided into the optical waveguide 1. The condensing optical elements 4 to 6 are reflection-type diffraction gratings in this embodiment, and condense the signal light that is dispersed and propagated in the optical waveguide 1 and improve the light extraction efficiency from the optical waveguide 1. The light is controlled so as to be guided to light receiving elements 7, 8, and 9 described later. In the present embodiment, the spectroscopic optical element 3 is designed so that the light that has entered the optical waveguide 1 and has been spectrally reflected is totally reflected on the lower surface of the optical waveguide 1, but the reflection condition on the lower surface is not defined as total reflection. For example, a reflecting mirror made of, for example, an Au thin film or an Ag thin film may be formed on the lower surface of the optical waveguide 1. Further, a collimating function portion, a diffraction grating serving as a light extraction portion, or the like may be provided separately at a light extraction position of the optical waveguide 1, or may be provided.
[0014]
On the semiconductor substrate 2, light receiving elements 7, 8, 9 for receiving each signal light and one light emitting element 10 are formed. The light-emitting element 10 is connected to the light-receiving elements 7, 8, and 9 by electric wirings 15, 16, and 17, and outputs light when signal light is input to any of these light-receiving elements. I have. The light receiving element 7 is formed at a position where the signal light of the wavelength λ ₁ reflected by the condensing optical element 4 is incident, and the light receiving element 8 is formed by the condensing optical element 5. The light receiving element 9 is formed at the position where the reflected signal light of the wavelength λ ₂ is incident, and the light receiving element 9 is formed at the position where the signal light of the wavelength λ ₃ reflected by the condensing optical element 6 is incident. ing.
[0015]
On each of the light receiving surfaces of the light receiving elements 7, 8, and 9, light modulation elements 11, 12, and 13 that change light transmission characteristics by electrical control are formed. In this embodiment, each of the light modulating elements 11 (12, 13) has a light transmission characteristic that is changed by a quantum confined Stark effect (QCSE) generated by application of an electric field.
[0016]
FIG. 2 is a cross-sectional view illustrating an example of the light modulation element 100 that changes light transmission characteristics by a quantum confined Stark effect generated by application of an electric field. The light modulation device 100 includes an n-type AlGaAs layer (impurity concentration 7 × 10 ¹⁷ cm ⁻³ , a film thickness of 0.8 μm) 101, an i-type MQW (GaAs (85 °) and Al _0.3 Ga _0.7 As) (A multiple quantum well in which 120 pairs of (80 °) are formed) 102, a p-type AlGaAs layer (impurity concentration 7 × 10 ¹⁷ cm ⁻³ , film thickness 0.4 μm) 103, a p-type GaAs layer (impurity concentration 1 × 10 ¹⁸ cm ⁻³ , a film thickness of 0.2 μm) 104 and a p-type electrode 105 are laminated in this order, and an n-type ground electrode 106 is formed on the n-type AlGaAs layer 101. I have.
[0017]
FIG. 3 is a graph showing wavelength-light absorption characteristics of the light modulation element. This graph shows respective light absorption curves when Vs (reverse bias) = 0, Vs = a, and Vs = b. When Vs = 0, the absorption edge is the position of the _{T 0} in FIG. Then, by changing the Vs, Vs = absorption edge T ₁ of the when the a is shifted to the longer wavelength side than the T _0, the absorption edge T ₂ of the when the Vs = b rather than the absorption edge T ₁ The wavelength shifts to the longer wavelength side.
[0018]
Such an optical modulator is disclosed in Applied physics letters vol. 145 pp. 13 (1984), Applied physics letters vol. 150 pp. 1119 (1984).
[0019]
Here, assuming that T ₁ <λ ₂ <T ₂ , for example, when the reverse bias applied to the optical modulation element 12 provided at the position for receiving the signal light of the wavelength λ ₂ is Vs = a, the optical modulation element 12 becomes possible to transmit the signal light of the wavelength lambda _2, when a reverse bias was Vs = b is the optical modulation element 12 will be impermeable to the signal light of the wavelength lambda _2. That is, by adjusting the reverse bias voltage, the optical transmission path can be changed.
[0020]
Note that a liquid crystal element that transmits and blocks light by electrical control may be used as the light modulation element, but a liquid crystal element that changes light transmission characteristics by the quantum confined Stark effect generated by application of an electric field described above is used. Is desirable. This is because such a light modulation element can be formed by stacking semiconductor films, so that it can be integrally formed with a light receiving element and a light emitting element, thereby facilitating the manufacturing process of such an optical function element. An example of this integrated formation will be described below.
[0021]
FIG. 4 is a partial cross-sectional view showing an example of a structure in which each light receiving element, light modulation element, and light emitting element are integrally formed on a semiconductor substrate. This structure is a reflection type structure. An n-electrode 200 is formed on the lower surface side of an n-type GaAs semiconductor substrate 201 which is the semiconductor substrate 2, and an n-type GaAs layer (impurity concentration 1 × 10 ¹⁷ cm ⁻³ , film thickness of 3000 °) 202, p is formed on the upper surface side Type GaAs layer (impurity concentration 1 × 10 ¹⁸ cm ⁻³ , thickness 2500 °) 203 and n-type Al _0.35 Ga _0.65 As layer (impurity concentration 1 × 10 ¹⁶ cm ⁻³ , thickness 5000 °) 204 are formed in this order.
[0022]
The n-type GaAs layer 202 functions as an emitter, the p-type GaAs layer 203 functions as a base, and the n-type Al _0.35 Ga _0.65 As layer 204 functions as a collector. A phototransistor 151 as a light receiving element is formed by the two layers.
[0023]
Then, on the n-type Al _0.35 Ga _0.65 As layer 204, a light emitting device 100 and a surface emitting semiconductor laser 150 as the light emitting device 10 are formed. The light modulation element 100 has the structure shown in FIG. 2 and is formed via a high-resistance layer (for example, AlAs or AlGaAs) 205. The surface-emitting type semiconductor laser 150 includes an n-type reflecting mirror 206 made of an n-type semiconductor multilayer film, an active region 207, and a p-type reflecting mirror 208 made of a p-type semiconductor multilayer film.
[0024]
The n-type reflecting mirror 206, the active region 207, and the p-type reflecting mirror 208 will be described by taking as an example the case where the surface emitting semiconductor laser 150 is a GaAs surface emitting semiconductor laser.
[0025]
The n-type reflecting mirror 206 is formed of a multilayer film in which 25.5 layers of Al _0.15 Ga _0.85 As / AlAs each having a thickness of λ / 4n and doped with Si are formed. The Al composition and thickness are designed to be λ / 4n depending on the oscillation wavelength λ and the refractive index n of the material used. The range of available materials, _generally, Al _0.15 Ga 0.85 As / besides _{AlAs Al X Ga 1-x As} (0 ≦ x ≦ 0.2) / Al y Ga 1-y As (0 .6 ≦ y ≦ 1) is used.
[0026]
The p-type reflecting mirror 208 is composed of a Be-doped multilayer film in which 20 pairs of Al _0.15 Ga _0.85 As / AlAs each having a thickness of λ / 4n are formed. Note that the p-type reflector 208, and in some cases forming _{Al z Ga 1-z As (} x ≦ z ≦ y) between the films of the multilayer film as an intermediate layer for reducing electric resistance.
[0027]
The active region 207 has a quantum well structure in which four well layers of GaAs (about 100 °) are used, and a barrier layer of Al _0.3 Ga _0.8 As is a spacer layer of Al _0.4 Ga _0.6 As. One having a double hetero structure including an active layer GaAs and Al _0.1 Ga _0.9 As sandwiched between p-type and n-type cladding layers (Al _0.4 Ga _0.6 As). Are used.
[0028]
An Au / Sn / Cr alloy film is used as the n-type electrode, and an Au / Cr alloy film or Au / Zn / Au alloy film is used as the p-type electrode.
[0029]
In addition, as an optical functional element in which a light receiving unit is integrated, Applied physics letters vol. 58 (21) pp. 2342 (1991), Electronics letters vol. 27, no. 3, pp. 216 (1991), Applied physics letters vol. 60 (13) pp. 1541 (1992).
[0030]
FIG. 5 is also a partial cross-sectional view showing an example of a structure in which each light receiving element, light modulation element, and light emitting element are integrally formed on a semiconductor substrate. This structure is a transmission type structure. An n-electrode 300 is formed on the lower surface side of an n-type GaAs semiconductor substrate 301 which is the semiconductor substrate 2, and a light incident surface is formed on the n-electrode 300 side. On the upper surface side of the n-type GaAs semiconductor substrate 301, an n-type _Al 0.3 _{Ga 0.7} As layer 302, an i-type MQW layer 303, p-type _Al 0.3 _{Ga 0.7} As layer 304 Are formed.
[0031]
The phototransistors 151 serving as the light receiving elements 7, 8, and 9 are formed on the light modulation element 100 via a high-resistance layer (for example, AlAs or AlGaAs) 305. The phototransistor 151 includes an n-type Al _0.3 Ga _0.7 As layer (impurity concentration 1 × 10 ¹⁷ cm ⁻³ , a film thickness of 5000 °: functioning as an emitter) 306 and a p-type GaAs layer (impurity concentration 1 × 10 ¹⁸ cm ⁻³ , thickness 2500 °: function as base) 307, and n-type GaAs layer (impurity concentration 1 × 10 ¹⁶ cm ⁻³ , thickness 5000 °: function as collector) 308. A p-type ground electrode 312 of the light modulation element 100 is formed on the p-type Al _0.3 Ga _0.7 As layer 304, and is formed on the n-type Al _0.3 Ga _0.7 As layer 306. Is formed with an n-type ground electrode 313 of the phototransistor 151.
[0032]
On the phototransistor 151 serving as the light receiving elements 7, 8, and 9, a surface emitting semiconductor laser 150 serving as the light emitting element 10 is formed. The surface emitting semiconductor laser 150 includes an n-type reflecting mirror 309 made of an n-type semiconductor multilayer film, an active region 310, and a p-type reflecting mirror 311 made of a p-type semiconductor multilayer film.
[0033]
As described above, the wavelength of the light received by the light receiving element can be changed arbitrarily and at any time by controlling the electric signal applied to the light modulation element, and the light emitting element can be driven by the light of the desired wavelength. it can. That is, by providing an optical element for wavelength spectroscopy and an optical modulation element capable of selecting a wavelength by an electrical method, an optical function element capable of changing the wavelength of received light can be realized, and a signal transmission path can be reconfigured (connected). Can be easily performed, and the degree of freedom in system design can be greatly improved.
[0034]
In the above example, a phototransistor is shown as a light receiving element. However, the present invention is not limited to this, and a photodiode may be used. Alternatively, the condensing optical element may be of a transmission type, and may be formed on the lower surface side of the optical waveguide 1.
[0035]
【The invention's effect】
As described above, according to the present invention, it is possible to easily reconfigure the signal transmission path (change the connection), and it is possible to significantly improve the degree of freedom in system design.
[Brief description of the drawings]
FIG. 1A is a plan view of an optical functional device of the present invention, and FIG. 1B is a side view thereof.
FIG. 2 is a cross-sectional view showing a light modulation device of the present invention.
FIG. 3 is a graph showing characteristics of the light modulation device of the present invention.
FIG. 4 is a cross-sectional view showing an example in which a light modulation element, a light receiving element, and a light emitting element of the present invention are integrally formed.
FIG. 5 is a cross-sectional view showing an example in which a light modulation element, a light receiving element, and a light emitting element of the present invention are integrally formed.
FIG. 6A is a plan view of a conventional optical functional device, and FIG. 6B is a side view thereof.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Optical waveguide 2 Semiconductor substrate 3 Wavelength spectroscopic optical elements 4, 5, 6 Condensing optical elements 7, 8, 9 Light receiving element 10 Light emitting elements 11, 12, 13 Light modulation element

Claims (2)

A wavelength splitting optical element for splitting a plurality of wavelength-multiplexed and transmitted signal lights according to wavelength, a light receiving element provided at a position for receiving the split signal light, and a light receiving surface of the light receiving element A light modulation element formed on the side and changing light transmission characteristics by electrical control. The optical function device according to claim 1, wherein the light modulation device changes light transmission characteristics by a quantum confined Stark effect generated by application of an electric field.

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