JPH02106979A - Wavelength demultiplexing photodetector - Google Patents

Abstract

(57) [Abstract] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] [Industrial applications! t] The present invention relates to a wavelength demultiplexing photodetector for optical communication.

[Conventional technology]

In the optical fiber low loss region of the wavelength i, o to 1.7 μm band, a wavelength division multiplexing communication system that transmits light of multiple wavelengths to one optical fiber to increase communication capacity can be used. In order to perform wavelength division multiplexing communication, optical multiplexers and optical demultiplexers have been used for some time, but on the other hand, wavelength multiplexers and optical demultiplexers have been used. By using one functional photodetector, the system can be made more compact, and losses in the optical equipment described above can also be reduced. This photodetector will be explained here.

Figure 3 shows, for example, the Compound Semiconductor Device Handbook (
Published by Science Forum in 1986)
1 is a cross-sectional structural diagram showing a conventional photodetector with a wavelength demultiplexing function; in the figure, 1 is an n-InP substrate; 2 is an n-InP substrate;
I n P buffer layer 3 is an I n P buffer layer that absorbs light of wavelength λ1
A photodiode made of nGaAsP is used, and 3a is n −1n H-maGa xaA ! 1 *-y
a P ya layer, 3 b is p I
n tox*GazaASI-y@Pya layer, 4 is p-I n P layer, 5 is In which absorbs light with wavelength λb
It is a photodiode made of GaAsP, and 5a is p
-1n 1-*bG a *bAsl-ybPybJ
i! , 5b is n In1-xbGa.

As1□bPyb layer, 11 is an n-side terminal for taking out a signal from the photodiode 3, 12 is a common terminal on the p-side of the photodiode 3 and photodiode 5, and 13 is for taking out a signal from the photodiode 5. An n-side terminal, 14 is an n-side electrode formed on the n-1n P substrate 1, 15 is a p-ON electrode formed on the p-I n P layer 4, and 16 is the n-1n Gu
This is an n-side electrode formed on the AsP layer 5b.

In Fig. 4, this photodetector is placed on the substrate 1 side)J0.6~1.
It shows the sensitivity spectrum when light with a wavelength of 6 μm is incident, with the horizontal axis showing the wavelength and the vertical axis showing the quantum efficiency. The spectrum on the left side of the figure shows the output between terminals 11 and 12, that is, the sensitivity spectrum of photo 1 and diode 3, and the spectrum on the right side shows the output between terminals 12 and 13, that is, the sensitivity spectrum of diode 5 and 7. There is.

Next, the operation will be explained.

This structure uses two diodes 3 and 5 with different absorption edge wavelengths, that is, band gaps, along the incident light fI.
The photodiode 3 on the light incident side has a larger bandgap than the other photodiode 5, and works as a photodiode while absorbing only the shorter wavelength λ of the two wavelengths in wavelength multiplexing communication. On the other hand, it also plays the role of a filter that passes long wavelength λb.

In this photodetector, the photodiode 3 has λ, <
The photodiode 5 absorbs short wavelengths of 1.3<λt and <1.53 μm. For example, λ is the wavelength for wavelength division multiplexing communication.
If 1 is 1.0 μm and λ is 1.4 μm, the wavelength λ,
The light is absorbed by the photodiode 3 and sent to the terminal 11-
An electromotive force is generated between 12, and when a load such as a resistor is connected, a current is generated. The quantum efficiency of photoelectric conversion in this case is 1.0 μm
It is about 50% at the wavelength of .

On the other hand, λ, which has a longer wavelength, is transmitted through the photodiode 3 with a large bandgap without being absorbed by the photodiode 3, and is absorbed by the photodiode 5 with a small bandgap, where it is photoelectrically converted in the same way as the photodiode 3, and 1. Even at a wavelength of 4 μm, a quantum efficiency of about 50% can be obtained. In this way, the optical signal of wavelength λ1 is detected from terminals 11-12,
Since the optical signal of wavelength λb is detected from the terminals 12-13, this element operates as a wavelength demultiplexing type monolithic photodetector, and is an effective element as a multiplexed ε photodetector.

[Problem to be solved by the invention]

The conventional wavelength demultiplexing photodetector is as described above! +'4, so if the short wavelength λ is not sufficiently absorbed by the photodiode 3 and reaches the 7th first diode 5, the 7th first diode 5 will absorb the wavelengths λ1 and λ. , and both optical signals are detected, which has the disadvantage of increasing crosstalk. The area where the left and right spectra overlap shown in FIG. 4 shows this. Therefore, if the wavelength λ is 1.2 μm and the wavelength λb is 1.4 μm and multiplex communication is performed, the photodiode 5 will have strong sensitivity to the wavelength λ that should originally be detected by the photodiode 3. There were drawbacks such as:

The present invention was made to solve the above-mentioned problems, and an object of the present invention is to obtain a wavelength division type photodetector with low crosstalk in wavelength division multiplex communication.

[Means to solve the problem]

The wavelength demultiplexing photodetector according to the present invention has a diffraction grating inserted between each of a plurality of photodiodes, the grating spacing of which is determined according to the wavelength of light to be demultiplexed.

[Effect]

The wavelength demultiplexing photodetector of the present invention has a diffraction grating between a plurality of photodiodes with a grating interval determined according to the wavelength of light to be demultiplexed. Since the incident light is selectively demultiplexed, crosstalk between the plurality of photodetectors is reduced.

〔Example〕

Hereinafter, examples of the fruitful colors of this invention will be explained with reference to the drawings.

FIG. 1 is a sectional view of a wavelength division type photodetector showing an embodiment of the present invention. In FIG. 1, the same reference numerals as in FIG. 3 indicate the same groove portions, 8 is a slope having an angle of θ with respect to the surface of the substrate 1, and 9 is a diffraction beam formed on the slope 8.
The 8th element, 17, is 5i0211Q formed at the light incidence part.

FIG. 2 does not show the sensitivity spectrum of the wavelength division type photodetector according to the present invention, and the explanation regarding FIG. 2 is as shown in the conventional example.

Next, the manufacturing method will be explained.

n -I n P uneven layer 2 on n -1n P substrate 1 , 11 I n 1-1@G n
zaA S +-yaPya layer 3 a X pI
The crystals of the n+-*aG a xaA S 1-yaP ya layer 3b are sequentially grown. Thereafter, the inclined surface 8 is formed by densely forming triangular grooves having an angle of .theta. with respect to the growth surface using photolithography and etching techniques. The angle θ at this time can be easily manufactured by using the crystal plane. Next, a thin resist is applied onto the slope 8 of this triangular groove, interference fringes are transferred by a two-beam interference exposure method, and a wavy diffraction grating 9 is formed by etching.

Note that the pitch d of this diffraction grating 9 is θ with respect to the slope 8.
The conditions are set so that light with a wavelength of λ, which is incident at an incident angle of λ, is Bragg-reflected (here, ^1 is 1.
2 μm, and θ and d are set so that light with this wavelength λ is Bragg-reflected. Next, In is applied only to the light incident part.
Although a material with a much lower refractive index than P or InGaAsP is formed, S i O* 111A17 is used here. As the second crystal growth, p −1n P
Layer 4. p-In1-xb G axb As 1-yb
PybNI5 (1,n I nl-HbG az
The hAS I-ybP yb layers 5b are sequentially grown, but since it is impossible to directly grow crystals on the 5iOzllIA 17, the portion where the 5ins film 17 is not formed, that is, the p-InGaAsP layer 3b, is used as a growth nucleus. The photodiode 5 is crystal-grown on the 5ift film 17 by lateral growth. As the growth method in this case, it is desirable to use a liquid phase growth method that facilitates lateral growth.

Finally, by forming the electrodes 14, 15, and 18 in the same manner as in the conventional example, the fabrication of the wavelength division type photodetector is completed.

Next, the operation will be explained.

This invention can be applied to the 7 first diodes 3 and 5 shown in the conventional example.
[Optics using Bragg reflection by diffraction grating 9 between]
, f router inserted (7).

Two wavelengths for multiplex communication, λ1. When λb is incident from the substrate 1 side, the shorter wavelength λ is absorbed by the first diode 3. The light of the wavelength ^ which is not sufficiently absorbed here is Bragg-reflected by the diffraction grating 9 and is further absorbed by the photodiode 3. On the other hand, the light λ is transmitted without being absorbed by the photodiode 3, and is not Bragg-reflected by the diffraction grating 9, so it reaches the photodiode 5 and is absorbed there. Therefore, in the sensitivity spectrum of this element, as shown in Fig. 2, the effect of the filter using reflection on the diffraction grating 9 appears in the vicinity of 1.2 μm, and the output between terminals 11 and 12 (stronger Terminal 1
The output between 1 and 12 will be weakened. In this way, even in the wavelength range where crosstalk is large in the conventional element structure, it is possible to obtain a wavelength range with small crosstalk due to the filter effect of this structure.
Even when multiplex communication is performed using light with a wavelength of μm, crosstalk can be reduced compared to conventional elements.

In the above embodiment, an InGaAsP/InP material is used, but other materials such as AjGaAs/GaAs may be used, and the same effects as in the above embodiment can be obtained.

In addition, in the above embodiment, a two-wavelength splitting type was shown in which two photodiodes 3.5 and one diffraction grating 9 were inserted between them, but three photodiodes and two diffraction gratings were inserted between each photodiode. It can also be applied as a multi-wavelength demultiplexing type photodetector, such as a 3-wavelength demultiplexing type with a grating inserted, or a 4-wavelength demultiplexing type with three diffraction gratings inserted between four photodiodes.

〔Effect of the invention〕

As explained above, in this invention, a diffraction grating is provided between each of a plurality of photodiodes, and the grating spacing is determined according to the wavelength of the light to be demultiplexed. This is made possible by the detector and has the advantage of having low crosstalk.

[Brief explanation of the drawing]

Fig. 1 is a sectional view showing a wavelength division type photodetector according to an embodiment of the invention as shown in Fig. 2, Fig. 2 is a diagram without showing the sensitivity spectrum of the invention, and Fig. 3 is a diagram showing a conventional photodetector. The cross-sectional view, FIG. 4, is a diagram showing the sensitivity spectrum of a conventional photodetector. In the figure, 1 is an n-InP substrate, 2 is an n-In
P buffer layer 3 is InGnA that absorbs light with wavelength λ
A photodiode consisting of sP, 3a is n I nl
-Xa G ax, As 5-ya r'ya FIJ
s 3 b is p-I nt-xa GaXAAsl-y
@p, layer 4 is p-InPM, 5 is fnGaAsP that absorbs light with wavelength λb, 7 O+-diode, 5a is pI n 1-xb G a xb A s
5-yb P xb layer, 5 b 11. t nI n
1-xb G a xb As1-yk Pyb Hz
8 is a slope, 9 is a diffraction grating, 11 is a photodiode 1:
12 is the common terminal on the p side, 13 is the n side terminal that takes out the signal from the photodiode.
side terminals, 14 and 16 are 1 side electrodes, 15 is p61 electrode,
17 is a Si0g film, and λ, , λb are wavelengths. Note that the same reference numerals in each figure indicate the same or corresponding parts. Agent Masuo Oiwa (2 others) Figure 1 Figure 2 One wavelength (mm) Figure 3

Claims (1)

[Claims] A photodetector in which a plurality of photodiode structures are stacked on a substrate and detects a signal by wavelength demultiplexing a plurality of optical signals having a plurality of wavelengths incident in a direction perpendicular to the stacking surface, wherein the plurality of photodiode structures are stacked on a substrate. A wavelength demultiplexing photodetector characterized in that a diffraction grating is provided between each of the photodiodes, the grating spacing of which is determined according to the wavelength of light to be demultiplexed.