JP2986029B2 - Wavelength demultiplexed light detector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wavelength division multiplexing optical detector having a function of demultiplexing an optical signal transmitted by frequency multiplexing and detecting light in a frequency division multiplexing optical transmission system.

[0002]

2. Description of the Related Art Heretofore, there has been an optical device in which a vertical diffraction grating and a waveguide are integrally formed to separate light having a wavelength of 1.48 to 1.56 μm. [Appl. Phys. L
ett. 58 (1991) pp. 1949-1951]

FIG. 4 is a plan view showing a conventional wavelength demultiplexer, wherein 1 is a slab waveguide, 2 is a ridge waveguide, 3 is a vertical diffraction grating, and 4 is input light (λ ₁ , λ ₂ ...). ... λ _n ), 5
Is output light. The frequency-multiplexed input light enters the ridge waveguide 1, spreads in the slab waveguide section 1, is split by the vertical diffraction grating 3, and condenses on different ridge waveguides 2. Since the vertical diffraction grating 3 is on the Rowland circle and the input portion of the ridge waveguide 2 is on the 1/2 Rowland circle, light of each wavelength is focused on a different ridge waveguide 2 without defocus.

[0004]

However, in this conventional example, since the refractive index of the slab waveguide section 1 is fixed, there is no disadvantage that there is no fine adjustment function of the demultiplexing angle, and no photodetector is integrated. Therefore, there is a disadvantage that the optical axis needs to be adjusted with another photodetector.

An object of the present invention is to solve the disadvantage that the photodetector is not monolithically integrated and the disadvantage that the wavelength demultiplexing angle cannot be finely adjusted. Provide a monolithically integrated wavelength demultiplexing photodetector that has the function of optically detecting light of each wavelength and the function of fine-tuning the light wavelength suitable for each photodetector. It is in.

[0006]

In order to achieve this object, a wavelength demultiplexing photodetector according to the present invention is provided with electrodes on a slab waveguide and on a back surface of a substrate so that a voltage can be applied to the slab waveguide, and An arc-shaped vertical diffraction grating is formed at one end of the waveguide, and a plurality of waveguides such as ridge waveguides are provided at the other end of the slab waveguide, and light is detected at the end of the waveguide. A detector is provided, or a plurality of photodetectors are provided directly on the other end surface of the slab waveguide, and the direction of the groove of the diffraction grating is perpendicular to the substrate of the slab waveguide. As a first feature, a second feature is that the waveguide and the photodetector or the photodetector are electrically separated from each other by an etching groove or a butt joint of an insulating layer.

The conventional technique is that the photodetector is monolithically integrated, or a reverse bias voltage is applied to the slab waveguide, and the effective refractive index of the slab waveguide and the light distribution are measured by the electro-optic effect. The difference is that the wave angle can be finely adjusted, that is, the wavelength of light suitable for each photodetector can be finely adjusted.

[0008]

FIG. 1 is a perspective view for explaining a first embodiment of the present invention, wherein 11 is an n-InP substrate, 12 is a vertical diffraction grating, 13 is a slab waveguide portion, 14 is a ridge waveguide, Fifteen
Is a photodetector, 16 is an input ridge waveguide, 17 is a p-electrode, and 18 is an n-electrode. The layer structures of the slab waveguide portion and the ridge waveguide, and the high reflection film are omitted for simplicity. The multiplexed light λ ₁ , λ _2, ... Λ _n incident on the input ridge waveguide 16 spreads laterally in the slab waveguide section 13 and the vertical diffraction grating 1 on the arc of the Rowland circle.
The light is demultiplexed by 2 and condensed on the ridge waveguide 14 according to each wavelength, and is converted into an electric signal by the photodetector 15. When the vertical diffraction grating is on the Rowland circle and the input end of the ridge waveguide is on the 1/2 Rowland circle, light of each wavelength is demultiplexed and condensed without causing defocus, and the ridge waveguide is Enter 14. Next, a mechanism for finely adjusting the branching angle by applying a reverse bias to the slab waveguide 13 will be described.

The change in the refractive index due to the electro-optic effect is given by the following equation. Here, Δn is a change in refractive index, n is a refractive index, E is an applied electric field, and r ₄₁ is an electro-optic coefficient of approximately 1.6 × 10 ⁻¹² m.
/ V. 0.5 total thickness of undoped layer
If μm = 5 × 10 ⁻⁷ m, E =
It becomes 10 ⁸ V / m. Assuming that n ≒ 3.3, Δn ≒ 2.
9 × 10 ^-3, and the shift of the compatible optical wavelength to an optical detector is 1.55μm band is about [Delta] [lambda] ≒ 14 Å. The resolution of the diffraction grating is given by the following equation. Δλ = λ / (hNn _ett ) (2) where h is the order of diffraction, N is the number of diffraction gratings, _nett is the effective refractive index, and λ is the wavelength. If the slab waveguide portion is made sufficiently long, the number N of the diffraction gratings becomes large, and the slab waveguide portion can be used sufficiently for the frequency division multiplexing system. Further, by making the shape of the diffraction grating into a saw shape and adding a high reflection film, the diffraction efficiency can be made about 85 to 95%.

FIG. 2 is a sectional view showing a coupling portion between the photodetector and the ridge waveguide of the wavelength demultiplexing detector according to the first embodiment, wherein 21 is an n-InP substrate and 22 is an n-InP layer. , 23
Represents an undoped InGaAsP layer (λg = 1.3 μm).
m), 24 is an undoped InP layer, 25 is p-InP
Layer, 26 is a p-InGaAsP layer, 27 is an n-electrode, 28
Is a p-electrode, 29 is an n-InP layer, 30 is n-InGaAs
s layer, 31 is an undoped InGaAs layer, 32 is p-I
nP layer, 33 is a p-InGaAsP layer, 34 is a non-reflective film, 35 is an etching groove, 36 is a ridge waveguide portion, 37
Denotes a photodetector unit. With such a structure, the slab waveguide section 13 for applying a reverse bias and the photodetector are electrically separated.

FIG. 3 is a sectional view for explaining a coupling portion between the photodetector and the ridge waveguide of the wavelength spectrophotometer of the second embodiment. 41 is an n-InP layer, 42 is an n-InP layer, 43 is an undoped InGaAsP layer (λg = 1.3 μm), 4
4 is an undoped InP layer; 45 is a p-InP layer; 46 is a p-InGaAsP layer; 47 is an n-InP layer;
-InGaAs layer, 49 is an undoped InGaAs layer,
50 is a p-InP layer, 51 is a p-InGaAsP layer, 5
2 is an insulating Si-InP layer, 53 is an insulating Si-InG
aAsP layer (λg = 1.3 μm), 54 is insulating Si—
InP, 57 is a ridge waveguide portion, 58 is a photodetector portion, 5
9 is an insulating layer part. The insulating layer portion is formed by butt bonding. With such a structure, the slab waveguide section for applying a reverse bias and the photodetector section are electrically separated.

Also, proton (H ⁺ ) injection can be used for electrical separation between the photodetector and the slab waveguide.
Further, although the embodiment has described the InGaAsP / InP-based crystal, it may be made of an AlGaAs / GaAs-based crystal. Also, for example, undoped I
A superlattice layer of nGaAs / InAlAs may be used. When such a superlattice layer is used, the electro-optic coefficient can be increased. As is apparent from this result, the point that the photodetector is monolithically integrated and the demultiplexing angle, that is, the light wavelength suitable for each photodetector can be finely adjusted, as compared with the conventional technology. There was an improvement.

[0013]

As described above, according to the present invention, the electrodes are provided on the slab waveguide and on the back surface of the substrate, and one end of the slab waveguide has a vertical diffraction effect in the form of an arc of a Rowland circle. In addition, a waveguide such as a plurality of ridge waveguides is provided on the other end surface of the slab waveguide, and a photodetector is provided at an end of the same waveguide, or a plurality of photodetectors are directly provided. Since the waveguide is provided and the waveguide and the photodetector or the photodetector are electrically separated from each other, the light transmitted by frequency division multiplexing can be separated and detected. By applying a reverse bias to the slab waveguide, there is an advantage that the electro-optic effect allows fine adjustment of the effective refractive index and the wavelength demultiplexing angle, that is, the wavelength suitable for each photodetector.

[Brief description of the drawings]

FIG. 1 is a perspective view of a wavelength splitter photodetector according to a first embodiment of the present invention.

FIG. 2 is a sectional view of a coupling portion between a photodetector and a ridge waveguide of the wavelength division photodetector according to the first embodiment of the present invention.

FIG. 3 is a sectional view of a coupling portion between a photodetector and a ridge waveguide of a wavelength division photodetector according to a second embodiment of the present invention.

FIG. 4 is a plan view of a conventional wavelength demultiplexer.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 slab waveguide section 2 ridge waveguide section 3 vertical diffraction grating 4 input light (λ ₁ , λ ₂ ... Λ _n ) 5 output light 11 n-InP substrate 12 vertical diffraction grating 13 slab waveguide section 14 ridge waveguide ( (Light receiving side waveguide) 15 Photodetector 16 Input ridge waveguide 17 p electrode 18 n electrode 21 n-InP substrate 22 n-InP 23 u-InGaAsP (λg = 1.3 μm) 24 u-InP 25 p-InP 26 p -InGaAsP 27 n-electrode 28 p-electrode 29 n-InP 30 n-InGaAs 31 u-InGaAs 32 p-InP 33 p-InGaAsP 34 Antireflection film 35 Etching groove 36 Ridge waveguide (light receiving side waveguide) 37 Photodetector section 41 n-InP substrate 42 n-InP 43 u-InGaAsP (λg = 1.3 μm) 44 u-InP 45 p- nP 46 p-InGaAsP 47 n-InP 48 n-InGaAs 49 u-InGaAs 50 p-InP 51 p-InGaAsP 52 Si-InP 53 Si-InGaAsP (λg = 1.3 μm) 54 Si-InP 55 n electrode 56 n 57 Ridge waveguide part (light receiving side waveguide) 58 Light detection part 59 Insulating layer part

Continuation of the front page (56) References JP-A-3-171115 (JP, A) JP-A-4-367819 (JP, A) Japanese Translation of PCT Publication No. 3-50101065 (JP, A) Appl. Phys. Lett. , Vol. 58 No. 18 pp. 1949-1951 (6 May 1991) Electronics Letters, Vol. 27 No. 2 pp. 132-134 (17th January 1991) (58) Fields investigated (Int. Cl. ⁶ , DB name) H01L 31/10 G02F 1/00-1/055 505 G02F 1/29-1/313 G02B 6 / 12-6/14

Claims (5)

(57) [Claims] An electrode is provided on the slab waveguide and on the back surface of the substrate, an arc-shaped vertical diffraction grating is formed on one end face of the slab waveguide, and a plurality of light-receiving side guides are provided on the other end face of the slab waveguide. A light detector is provided at the end of the light-receiving side waveguide with a waveguide, or a plurality of light detectors are provided directly on the other end surface of the slab waveguide, and the direction of the groove of the diffraction grating is The waveguide is perpendicular to the substrate of the slab waveguide, and the waveguide and the photodetector or the plurality of photodetectors are electrically separated from each other by a butt junction of an etching groove or an insulating layer. A wavelength demultiplexed photodetector configured to be on a Rowland circle and the light receiving side waveguide or the incident portion of the photodetector be on a 1/2 Rowland circle. 2. The vertical diffraction grating is formed in a saw-tooth shape so as to increase diffraction efficiency, so that incident light and diffracted light have a substantially regular reflection relationship with respect to a groove surface of the diffraction grating. The wavelength demultiplexed photodetector according to claim 1, wherein: 3. The wavelength-demultiplexed light according to claim 1, wherein a high-reflection film made of an insulating film and a metal film is formed on an end face of the vertical diffraction grating in order to increase diffraction efficiency. Detector. 4. The slab waveguide is an n-type InP substrate, n
-Type InP cladding layer, undoped InGaAsP core layer, undoped InP layer, p-type InP layer, p-type InGa
4. The wavelength demultiplexed photodetector according to claim 1, wherein the photodetector is made of an AsP layer and configured to apply a reverse bias voltage. 5. The slab waveguide is an n-type InP substrate, n
Type InP cladding layer, undoped InGaAs / InA
lAs superlattice core layer, undoped InP layer, p-type InP
4. The wavelength demultiplexed photodetector according to claim 1, wherein the photodetector is composed of a p-type InGaAsP layer and a reverse bias voltage.