JPH10190016A - Semiconductor demultiplexing photodetector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a photodetector having a demultiplexing function without increasing the number of components and the number of alignment processes. SOLUTION: This demultiplexing photodetector is constituted of semiconductor optical waveguides 1 and 1a to which light is made incident and a photodetector having diffraction gratings formed in the waveguides 1 and 1a and a plurality of elements which receive diffracted light radiated into the space from the waveguides 1 and 1a. In the diffracted light radiating region 5 of the waveguides 1 and 1a, a plurality of waveguides are formed in parallel with each other so that the phases of guided light of the waveguides in the region 5 can become coincident with each other.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photodetector having a demultiplexing function used in optical communication and the like, and a wavelength division multiplexing communication network using the same.

[0002]

2. Description of the Related Art Conventionally, as a demultiplexed light detecting device utilizing the fact that the emission angle of diffracted light radiated from an optical waveguide having a diffraction grating to the outside of the waveguide depends on the wavelength, Japanese Patent Application Laid-open No. There is one disclosed in JP-A-130438.

[0003]

SUMMARY OF THE INVENTION In the conventional example,
The change of the inclination angle θ of the diffracted light with respect to the change of the wavelength λ of the incident light is dθ / dλ to −0.4 deg / nm (1). The spread angle θp (far-field pattern (FFP)) of the diffracted light in the direction along the waveguide is very narrow,
p〜0.2 ° or less. Therefore, if the wavelength of the incident light changes by about 1 nm, the radiation angle of the diffracted light changes by about 0.4 ° according to equation (1). Therefore, since the radiation angle of the diffracted light changes about the beam diameter of the diffracted light in the direction along the waveguide, the size of the light receiving surface in the direction along the waveguide of the photodetector is changed to about the beam diameter (θp) of the diffracted light. Then, a wavelength change of about 1 nm can be detected.

However, since the divergence angle (θt) of the diffracted light in the direction crossing the waveguide is as large as about 15 °, the conventional configuration (FIG. 6) requires a space between the waveguide and the photodetector for condensing. In this case, a cylindrical lens is arranged, and the number of components and the number of alignment steps increase.

FIG. 6 is a configuration diagram of the above-mentioned conventional example of a photodetector having an optical waveguide with a diffraction grating and a photodetector array 132. As shown in FIG. In the figure, on an n-GaAs substrate 122, in _{sequence, n-Al x Ga 1-} x As light confinement layer 123, A
l _y Ga _1-y As waveguide layer 124 (0 ≦ y <has a x <1. Thus towards the energy gap of the optical confinement layer 123 is larger than that of the optical waveguide layer 124, the layer 123 refractive index becomes small optical confinement _{functions), p-Al x Ga 1} -x As light confinement layer 12
_{5, p-Al z Ga 1} -z As contact layer 128 (0
<Z <1) is formed. Lateral confinement is carried out in a high-resistance Al x _Ga 1-x _As buried layer 135 are stacked in regrowth after both side etching except the stripe-shaped portion.

An upper p-type electrode 127 having a diffracted light emission window 136 formed thereon is formed on the contact layer 128, and an n-type electrode 12 is formed on the back surface of the n-GaAs substrate 122.
1 is formed. _At a position in the wavelength range from the interior or the waveguide layer 124 of the light Al _{y Ga 1-y} As waveguide layer 124, the diffraction grating (not shown) is formed.
Further, a light detection element array 132 including three elements PD1 to PD3 is arranged right above the diffracted light emission window 136 of the optical waveguide with a diffraction grating. Also, the diffracted light exit window 136
A polarizing plate 138 is disposed directly above the polarizing plate 138 so that the demultiplexing function is not reduced by the polarization state of the incident light.

In the above configuration, when light is input to the waveguide, diffracted light is emitted to the upper surface of the waveguide by the diffraction grating formed in the optical waveguide layer 124 or near the waveguide including the same. As described above, the far-field pattern of the diffracted light emitted from the optical waveguide is very narrow in the direction along the waveguide and has a divergence angle (θ _P ) of 0.2 ° or less, and in the direction crossing the waveguide. Wide, its divergence angle (θ
_t ) is about 15 °. Since the divergence angle in the direction traversing the waveguide is large, the photodetector array 132
Is about several percent of the total amount of radiation.

Therefore, a cylindrical lens 137 is disposed between the optical waveguide and the photodetector array 132 to collect the diffracted light in a direction crossing the waveguide, thereby increasing the amount of light incident on the detector array 132. In addition, the detection is effectively performed even if the light incident on the optical waveguide is weak. However, this has the drawbacks as described above.

Accordingly, it is an object of the present invention to provide a photodetector having a demultiplexing function and the like used in optical communication and the like which has solved the above problems, and a wavelength division multiplexing communication network and the like using the same. It is in.

[0010]

According to the present invention, there are provided a plurality of parallel waveguides in a region which emits diffracted light;
By making all the phases of the respective guided lights coincide, diffracted light is emitted from a wide area including between the waveguides in a direction crossing the waveguide, and the spread angle of the diffracted light in this direction ( θt) can be greatly reduced. This realizes a demultiplexing detection device that does not require a cylindrical lens or the like for condensing light.

When the size of the opening is D, the spread angle of the light emitted from the narrow region can be approximated by a diffraction pattern when the parallel light passes through the slit D. Assuming that the position where / 2 is the spread angle θ, sin θ = 0.52 · λ / Dλ: wavelength of light (2) Therefore, the light wavelength λ is 1.55 μm,
If the width D of the stripe is 2 μm of a normal laser, the divergence angle becomes as large as 24 degrees.

On the other hand, if the stripe width is 20 μm,
The divergence angle is about 1/10 of 2.4 degrees from the above equation (2). However, if the stripe width is wide, it becomes difficult to maintain a uniform light intensity distribution in the stripe. The invention which solves these is each invention demonstrated below.

The invention according to claim 1 of the present application is directed to a method in which a plurality of narrow stripes are arranged in parallel, and the phases of light in each stripe are made to coincide with each other, so that the stripes have the same effect. And a structure in which light can be emitted from a wide area including the above, and the light intensity distribution in the stripe can be maintained uniformly. In detail, a semiconductor optical waveguide into which light is incident, a diffraction grating formed in the waveguide, and a photodetector having a plurality of elements for receiving diffracted light radiated from the waveguide into space are provided. In the wave light detecting device, at least a plurality of waveguides in a region of the semiconductor waveguide that emits diffracted light exist in parallel, and all of the waveguides in the waveguide of the region that emits the diffracted light have the same phase. It is characterized in that it is formed so that

According to the second aspect of the present invention, the guided light is optically coupled to the semiconductor optical waveguide where the light is incident by arranging the stripe waveguides adjacent to each other or by connecting them by a waveguide. The phased array laser is configured so that the phase of the guided light in each stripe is matched and the phased array laser is connected to the waveguide in the region that emits the diffracted light. Thereby, a plurality of waveguides in the semiconductor waveguide in the region emitting the diffracted light exist in parallel, and the phases of the respective guided lights in the waveguides in the region emitting the diffracted light all match. it can. In detail, the portion of the semiconductor optical waveguide on which the light is incident is constituted by a plurality of waveguides, and the plurality of waveguides are so close that they are optically coupled, or It is a phased array laser configuration in which adjacent waveguides are connected by waveguides.

According to a third aspect of the present invention, by providing a plurality of optical amplifiers for compensating for coupling loss and waveguide loss of incident light, it is possible to easily achieve the same phase of each of the guided lights and to reduce the number of light beams within the stripe. By improving the uniformity of the light intensity distribution, the spread angle of the diffracted light in the direction of the resonator is narrowed, and the wavelength resolution is improved. In detail, a plurality of current injection regions for amplifying the guided light are provided in all the waveguides including the semiconductor optical waveguide into which the light is incident.

According to a fourth aspect of the present invention, by setting the band edge wavelength of the waveguide of the diffracted light radiating section to be shorter than the wavelength of the guided light, the absorption loss of the guided light is reduced, and the waveguide of the diffracted light radiating section is guided. This is to further flatten the wave light intensity distribution and suppress a decrease in wavelength resolution. Specifically, at least the band edge wavelength of the waveguide in the region that emits the diffracted light is shorter than the wavelength of the guided light.

According to a fifth aspect of the present invention, the interval between the waveguides in the region where the diffracted light is radiated can be made wider than the interval between the stripes necessary for the optically coupled state of the guided light. This achieves a narrow divergence angle. Furthermore, by not using the guided light of the adjacent waveguide in the coupled state in the phased array region, the stability of the demultiplexing characteristics is maintained even when the incident light and the opposite-phase guided light are excited in the adjacent waveguide. Is what makes it possible. For details,
A plurality of optically coupled waveguides in a portion of the semiconductor optical waveguide into which the light is incident are alternately connected to waveguides in a region that emits the diffracted light. .

According to a sixth aspect of the present invention, the current injection into the semiconductor optical waveguide into which light is incident and the current injection into the optical amplifier provided adjacent to the waveguide that emits diffracted light are optimized. , A uniform guided light is obtained. More specifically, the present invention is characterized in that the current injection region is independently formed in a portion of the semiconductor optical waveguide where the light is incident and a portion where the number of waveguides is small.

The invention according to claim 7 is characterized in that a guided light absorbing portion for absorbing guided light is provided at an end opposite to a portion of the semiconductor optical waveguide into which the light is incident. Thereby, the reflected light does not adversely affect the diffracted light.

The invention according to claim 8 is characterized in that a diffraction grating is formed only in the vicinity of the waveguide in the region for emitting the diffracted light.

According to a ninth aspect of the present invention, a receiving apparatus comprising the above-described demultiplexed light detecting apparatus is used in a wavelength division multiplexing communication network for performing information communication at a plurality of different wavelengths. Specifically, in a wavelength division multiplexing communication network that performs information communication using a plurality of different wavelengths using an optical fiber, at least one terminal connected to the wavelength division multiplexing communication network has at least a part of the plurality of wavelength signals. In order to receive the signal, the above-described semiconductor demultiplexing light detecting device is provided as a demultiplexing receiving device.

[0022]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1 FIG. 1 is a top view of a waveguide portion which best shows the features of the first embodiment of the present invention. In the figure, current is injected into a phased array laser structure region 2 in which adjacent waveguides 1 are optically coupled (or adjacent waveguides may be connected by a branch waveguide). And the signal light is transmitted from the optical fiber 3 to the phased array laser structure 2.
When the light is incident on the central stripe 1a, the incident light is amplified, and the guided light having the same phase propagates to the adjacent stripe 1. Each guided light is diffracted in the grating coupling region 5 where a diffraction grating (see 210 in FIG. 2) is formed in the vicinity of the waveguide 1, and most of the light is radiated to a space outside the waveguide 1. An electrode 29 for current injection is provided in the signal light incident portion and a part of the waveguide (the optical amplifying portion 4 behind the grating coupling region 5 in this embodiment), and a coupling loss with the optical fiber 3 is provided. And a configuration that compensates for the loss of the waveguide 1. A low-reflection coating 8 is applied to the incident end of the device, and a waveguide light absorbing section 9 is provided at the other end.

FIG. 2 is a partial cross-sectional perspective view showing the configuration of FIG. 1 in detail.
An 80 nm diffraction grating 210 is formed, and its p-
An InGaAsP light guide layer 23 having a band edge wavelength of 1.13 μm formed in a stripe shape on an InP substrate 22;
And a multiple quantum well (MQ) having a band edge wavelength of 1.54 μm.
W) The active layer 24 is laminated.

The current confinement is performed by a known method, p-InP.
This is performed by the current blocking layer of the layer 25 and the n-InP layer 26. Further, an n-InP upper clad layer 27, an n-InGaAs contact layer 28, and a metal electrode 29 are laminated on these layers, and a metal electrode 21 is formed on the back surface of the substrate 22. These layer configurations are basically the same through the phased array laser structure 2, the grating coupling region (diffraction light output unit) 5, the optical amplification unit 4, and the guided light absorption unit 9.

In the diffracted light output section 5, the n-InGaAs 28 and the metal electrode 29, which hinder the diffracted light from being emitted into space, are removed. Although not shown in FIG. 2, a low-reflection coating 8 is applied to the end face on which the signal light is incident.

The operation of this embodiment will be described. In FIG. 2, the phased array laser structure region 2 is in a current injection state that does not oscillate, and an optical signal having a wavelength of 1.55 μm is incident on one stripe waveguide 1 a from the optical fiber 3. In the phased array laser structure region 2, the distance between adjacent waveguides is close to about 4 μm, which is in an optically coupled state, and is in a current injection state, so that incident light is amplified and the adjacent waveguides are amplified. The same optical signal having the same phase is successively guided, and the guided light of all the stripe waveguides 1 in the phased array laser structure region 2 becomes the same optical signal having the same phase.

When these guided lights reach the diffracted light output section 5, the diffracted light is radiated by the diffraction grating 210 into a space substantially in the vertical direction. At this time, a current is injected into the phased array laser structure region 2 and the optical amplifier 4 to compensate for the attenuation of the guided light over substantially the entire length of the diffracted light output unit 5. The uniformity of the light intensity in the stripe is improved, and the intensity distribution of the diffracted light is also improved, so that accurate detection of the split light can be realized.

The tilt angle φ of the diffracted light from the vertical direction depends on the pitch の of the diffraction grating 210 and the wavelength λ of the incident light, and the diffracted light is emitted at a wavelength-dependent tilt angle according to the following relational expression. sinφ = neff-λ / Λ neff: Equivalent refractive index of the waveguide (3) In other words, since diffracted light is emitted at different inclination angles for each wavelength, each diffracted light must be received by a separate photodetector. As a result, the wavelength division multiplexed signal is separated into individual wavelength signals.

The spread angle of the diffracted light in the direction crossing the waveguide 1 is determined by the distance between the farthest stripes of the diffracted light output section 5 (see FIG. 1). In this embodiment, since the width of each stripe waveguide is set to 2 μm and the distance between stripes is set to 4 μm, the distance between the farthest stripes in the configuration of FIG. 1 is 26 μm, and the diffracted light crosses the waveguide 1. According to equation (3), the angle spreading in the direction is greatly reduced to about 1.8 degrees from about 24 degrees in the case of one stripe having a width of 2 μm.

FIG. 3 is a schematic configuration diagram of a demultiplexed light detecting device using the waveguide type diffraction grating demultiplexer of FIG. The width and length of the diffracted light output unit 5 include the wavelength interval of the wavelength multiplexed signal, the distance to the photodetector array 30, the size of the light receiving unit of each detection element,
Also, the optimum value is determined from the pitch of the light receiving unit.

In FIG. 3, the length of the diffracted light output section 5 is 130
μm, the width is 26 μm, and the photodetector array 30 is arranged approximately 110 mm vertically above the diffracted light output unit 5.
Each detection element of the photodetector array 30 is 150 × 200 μ
It has m light receiving sections, and has a pitch of 370 μm, and 20 elements are arranged in the traveling direction of the guided light facing the diffracted light output section 5.

Assuming that the wavelength division multiplexed signal is multiplexed in 20 wavelengths at a wavelength interval of 1 nm in a wavelength region of 1.5 μm, the spread of the diffracted light in the waveguide direction has a wavelength dependence of the radiation angle of −0. .4 deg / nm, the wavelength interval (Δ
λ) １1 nm light is spatially separated by ３370 μm on the light receiving surface of the photodetector located 110 mm away from the waveguide. Therefore, since the pitch matches the pitch of each detection element of the photodetector array 30 to 370 μm, one element receives one split wavelength and converts it into an electric signal. On the other hand, the spread in the direction crossing the waveguide 1 (the intensity of the diffracted light is 1
/ 2), since the width of the diffracted light output portion 5 is 26 μm, the divergence angle is about 1.8 degrees from the above equation (2), and the diffracted light intensity is smaller than that of the conventional 2 μm stripe. More than 13 times. Therefore, sufficient diffracted light can be received without using a condensing means in a direction crossing the waveguide, which is indispensable in the past.

In this embodiment, the effective stripe width of the diffracted light output section 5 is set to 26 μm.
If m, most of the diffracted light can be received without changing other configurations.

FIG. 4 is a schematic configuration diagram when the device of the present invention is used as a demultiplexer for wavelength division multiplexing communication.
In the figure, signals of different wavelengths (λ1,
λ2,..., λn) are wavelength-multiplexed by the merger 41 and input to one optical fiber 40. On the receiving side, the wavelength division multiplexed signal is separated into each wavelength by the demultiplexing receiver 42 of the present invention, and the electric signals (S1, S2,..., Sn) are separated.
And are input to the terminals 1 to n via electric wires.

Embodiment 2 FIG. 5 shows a second embodiment of the present invention. The difference from FIG. 1 is that a current is injected into the phased array laser structure region 52 by a grating coupling region (diffraction light output portion) 55. Can be controlled independently of the current injection into the optical amplification unit 54 provided before and after that, and every other stripe waveguide 51 in the phased array laser structure region 52 has the diffracted light output unit 55 and the optical amplification unit 54. This is a point connected to the stripe 55.

The spacing between the stripes 51 in the phased array laser structure region 52 is difficult to greatly increase because the adjacent stripes 51 must be in an optically coupled state. On the other hand, in the diffracted light output unit 55, as long as the phases match, a stripe interval of 2 to 3 times that of the first embodiment is sufficient. Further, since the power consumption of the optical amplifier 54 is proportional to the number of the stripes 51, the power consumption can be reduced by the reduction in the number of the stripes 51.

Further, the phased array laser structure region 5
By not using the guided light of the second adjacent waveguide, it is possible to maintain the stability of the demultiplexing characteristic even when the opposite waveguide is excited in the adjacent waveguide. When the light whose phase is inverted is excited in the adjacent waveguide, the diffracted light is split into two, and the accuracy of detecting the demultiplexed light is deteriorated.

In the second embodiment, the stripes 51 of the diffracted light output section 55 and the light amplification section 54 are alternately arranged in the phased array laser structure area 52. The number of the diffracted light emitting portions 55 is reduced from 26
It extends from μm to 38 μm. Accordingly, the power consumption is 4/5 that of the first embodiment, and the angle at which the diffracted light spreads in the direction crossing the waveguide 51 is increased from about 1.8 degrees to about 1.2 degrees, which further improves the characteristics. In FIG. 5, reference numeral 53 denotes an optical fiber 3 for inputting signal light to the central stripe 51a of the phased array laser structure 52, 58 denotes a low reflection coating, 59 denotes a guided light absorbing unit, 6
Reference numeral 9 denotes a current injection electrode, and reference numeral 70 denotes a groove that separates the electrode 69 of the phased array structure region 52 from the electrode 69 of the optical amplifier 54.

The use of the demultiplexed light detecting device of the present invention is not limited to the case where the demultiplexed light detecting device is used as a demultiplexing receiver for wavelength division multiplexing communication as described above. It can also be used as a photodetector having a wavelength tracking function that can be detected by light detection.

[0040]

As described above, the present invention comprises a semiconductor optical waveguide, a diffraction grating formed on the waveguide, and a plurality of photodetectors for receiving diffracted light radiated from the waveguide into space. In the demultiplexed light detection device, a plurality of waveguides in a region that emits diffracted light exist in parallel, and by making all the phases of the respective guided lights coincide, the angle at which the diffracted light spreads in the direction crossing the waveguides Is greatly reduced, and a conventionally required cylindrical lens for condensing light is not required. The reduction in the number of components and the number of alignment steps at the time of assembly reduced the size and cost of the apparatus.

[Brief description of the drawings]

FIG. 1 is a schematic top view of a first embodiment of a demultiplexed light detecting device provided with a plurality of semiconductor waveguides having a phased array laser structure region according to the present invention.

FIG. 2 is a partial sectional perspective view of FIG. 1 showing a detailed structure.

FIG. 3 is a diagram for explaining a demultiplexing reception operation of the device of the present invention.

FIG. 4 is a conceptual diagram of wavelength division multiplexing communication using the demultiplexing receiver according to the present invention.

FIG. 5 is a schematic top view showing another embodiment of the demultiplexed light detecting device of the present invention.

FIG. 6 is a perspective view showing a conventional example by the present inventor.

[Explanation of symbols]

 1, 51 Striped waveguide 1a, 51a Striped waveguide on which light enters 2, 52 Phased array laser structure region 3, 40, 53 Optical fiber 4, 54 Optical amplification unit 5, 55 Grating coupling region (diffracted light output unit) 8 , 58 Low-reflection coating 9, 59 Guided light absorption part 21 p-side common electrode 22 p-InP substrate 23 InGaAsP light guide layer 24 MQW active layer 25, 26 Current block layer 27 n-InP light confinement layer 28 n-InGaAs contact layer 29, 69 n-side electrode 30 photodetector array 41 combiner 42 demultiplexing receiver of the present invention 70 groove for electrode separation 210 diffraction grating

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[Submission date] April 10, 1997

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Claims (9)

[Claims] 1. A photodetector having a semiconductor optical waveguide on which light is incident, a diffraction grating formed on the waveguide, and a plurality of elements for receiving diffracted light emitted from the waveguide into space. In the demultiplexed light detection device, at least a plurality of waveguides in a region of the semiconductor waveguide that emits diffracted light exist in parallel, and the phases of the respective guided lights of the waveguides in the region that emit the diffracted light are all different. A semiconductor demultiplexed light detection device characterized by being formed so as to match. 2. The semiconductor optical waveguide portion, into which the light is incident, comprises a plurality of waveguides, and the plurality of waveguides are so close that they are optically coupled to each other.
2. The semiconductor demultiplexed light detecting device according to claim 1, wherein a phased array laser configuration in which adjacent waveguides are connected by a waveguide. 3. The semiconductor device according to claim 1, wherein a plurality of current injection regions for amplifying the guided light are provided in all the waveguides including the semiconductor optical waveguide into which the light is incident. Semiconductor demultiplexed light detection device. 4. The semiconductor branched light detection according to claim 1, wherein at least the band edge wavelength of the waveguide in the region that emits the diffracted light is shorter than the wavelength of the guided light. apparatus. 5. The semiconductor optical waveguide according to claim 5, wherein a plurality of waveguides in a portion of the semiconductor optical waveguide into which the light is incident are connected to waveguides in a region for emitting the diffracted light. 1
5. The semiconductor demultiplexed light detection device according to any one of claims 4 to 4. 6. The semiconductor split-light detection according to claim 5, wherein the current injection region is formed independently in a portion of the semiconductor optical waveguide where the light is incident and a portion where the number of the waveguides is small. apparatus. 7. A waveguide light absorbing portion for absorbing guided light is provided at an end opposite to a portion of the semiconductor optical waveguide on which the light is incident. Or the semiconductor demultiplexed light detection device. 8. The apparatus according to claim 1, wherein a diffraction grating is formed only in the vicinity of the waveguide in a region where the diffracted light is emitted. 9. A wavelength division multiplexing communication network for performing information communication at a plurality of different wavelengths using an optical fiber,
The at least one terminal connected to the wavelength division multiplexing communication network receives the semiconductor demultiplexed light detection device according to claim 1 in order to receive at least a part of the plurality of wavelength signals. A wavelength division multiplexing communication network provided as a wave receiving device.