JPH049825A - End surface reflection type optical amplifyer - Google Patents

Abstract

PURPOSE:To improve S/N by bringing two waveguides into contact with each other on at least one end surface. CONSTITUTION:When a signal which is inputted to a 1st waveguide is reflected by the end surface and guided to a 2nd waveguide, a natural light emission component generated in the 1st waveguide is transmitted except in a specific wavelength band according to the reflection characteristics of the end surface, so a signal which has excellent S/W is led to the 2nd waveguide. For the purpose, at least two slanting waveguides which cross each other on the end surface are provided, the end surface on their intersection side is coated with a film 11 which has reflection characteristics only to the specific wavelength, and a low-reflecting film 12 is formed on the other end surface. Consequently, the amplified signal which has the excellent S/N is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to the structure of an optical amplification device used in optical networks, broadband optical communications, and the like.

[Conventional technology]

FIG. 2 shows a conventional optical amplification device. This device has one diagonal waveguide 13, and the waveguide 13 is a BH
It has a structure in which the active layer 7 is embedded; 1.
It is used as a 5 μm band or 1.3 μm band optical amplification element. All such devices have n-type I on an InP substrate.
After epitaxially growing the nP buffer layer 4b and the n-type InP cladding layer 4a, and further epitaxially growing the InGaAsP waveguide layer (active layer) 7 and the p-type InP cladding layer 6, mesa etching is performed to cut the cross section of the waveguide into a width of about 0.0mm. This is obtained by forming the film to have a thickness of 8 to 1.3 μm and a thickness of about 0.3 μm. Thereafter, it is buried with p and n InP layers, and electrodes are attached to each of the Pan parts to form a light amplifying element.

This device uses a low reflection film on the end face and a diagonal stripe structure to prevent stimulated emission due to reflection and to obtain amplification characteristics without gain deviation.

On the other hand, in order to obtain single-pass gain, there are methods such as increasing the stripe length, but at the same time the spontaneous luminescence component also increases, resulting in problems such as the inability to improve the S/N ratio.

Note that related devices of this type are disclosed in Japanese Patent Application Laid-open No. 1999-1-
There are 289287.

[Problem to be solved by the invention]

The conventional technology described above has a problem in that when the end face reflectance is not reduced, gain ripples occur due to reflection between end faces, and the S/N ratio deteriorates. The present invention was made for the purpose of improving this S/N ratio.

Another object of the present invention is to provide an optical amplification device with a multi-branching function by guiding light (including a signal) reflected at an end face and returning into the element into a waveguide and amplifying it.

(Means for Solving the Problems) In order to achieve the above first objective, at least two diagonal waveguides are provided that intersect at the end faces, and the end faces on the intersecting side are provided with only one waveguide for a specific wavelength band. It adopts a structure in which a film with reflective properties is coated, and the other end face is coated with a low-reflection film.

In addition, in order to achieve the second objective, a multi-branch optical amplification structure is adopted, which has a desired plurality of the above-mentioned end face crossing diagonal waveguides and sets the end face reflectance to a predetermined amount. .

[Effect]

The effect for the first purpose will be explained.

When a signal input to the first waveguide is reflected at the end face and guided to the second waveguide, the spontaneous luminescence component generated in the first waveguide is caused by the reflection characteristics of the end face (specific wavelength Since wavelengths other than a specific wavelength band are transmitted, a signal with a good S/W ratio is guided to the second waveguide. Therefore, by providing a low reflection film on the end face opposite to the above-mentioned end face, an amplified signal with a good S/N ratio can be obtained from this side.

Next, the effect for the second purpose will be explained. In a multi-branch optical amplification device that has n diagonal waveguides and has a structure in which each waveguide is in contact with each other at the end face, a signal input to the first waveguide is reflected at the end face, and the signal is transferred to the second waveguide. When guided by the second waveguide, the return light P1 returns to the first waveguide.
It is obvious that a large amount of light P2 can be guided to the waveguide. The gain deviation ΔG is ΔG = (1+, 7Gs on page 077)”/ (1-1JomiT
■=-as)2-・a) (where R,, R, is the reflectance of both end faces, and GS is the single pass gain), and the reflectance for the first waveguide is expressed as Although it is necessary to suppress R2 as much as possible, the reflectance R2' to the second waveguide
Then, if R2'·Gs~1, it is possible to obtain the same gain for the second waveguide. Similarly, it is possible to obtain the same gain for n waveguides. The number n is determined by saturation gain and noise characteristics.

〔Example〕

The present invention will be explained in detail below.

<Example 1> FIG. 1(,) is a cross-sectional structural diagram of an optical amplifying device according to an embodiment having two oblique waveguides, and FIG. 1(b) is a plan view thereof. Moreover, the same figure (c) - (h) show the optical characteristic in each part of the said apparatus.

The angles of the oblique waveguides 13 and 14 with respect to the end surface 11 are 84 degrees and -84 degrees, respectively, and the end surface folds are formed so that they intersect at position 16 of the end surface 11. If this angle is symmetrical, reflected light can be effectively extracted, but it is not necessary to make it particularly symmetrical.

In the case of a 1.5 μm band optical amplification element, n
Type 1nP buffer layer 4b and n-type InP cladding layer 4a
is epitaxially grown, and further I n Ga A
After epitaxially growing the sP waveguide layer (active layer) 7 and the p-type InP cladding layer 6, mesa etching is performed to form a cross section of the waveguide layer 7 with a width of approximately 0.8 μm and a thickness of 0.3 μm.
A BH buried structure is adopted in which the conductive layer is formed to have a thickness of 50 m and is filled with p-type InP5b and n-type InP5a. In addition, p-type electrode 1
is Cu-Au, and n-type electrode 2 is AuGeNi-Pd-Au.
It is a structure. Here, a low reflection coating film is formed on the end face 12, and the reflectance at a wavelength of 1.55 μm is 0.1.
% and 50n on the center is 1% or less, and has the characteristics as shown in FIG. 1 (h). On the other hand, the end face 11 has a reflectance of about 5% at a wavelength of 1.55 μm and a center ±10 n. m or more ±11
A reflective film having a reflectance within 00n of 0.05% to 0.5% and having characteristics as shown in FIG. 1(e) is formed.

Next, the operation will be explained. The input signal has a waveform as shown in figure a, enters from the direction 18, and is taken into the waveguide 13 at the position 15. The light is amplified while passing through the waveguide 13, and when it reaches the intersection 16, the waveform becomes as shown in FIG. 1(d).

The reflection characteristics of the end face coating film 11 are as shown in FIG. 1(e), and the waveform reflected at the end face 11 and taken into the waveguide 14 is as shown in FIG. 1(f). In other words, by matching the wavelength of the input signal and the reflection peak value of the end face coating film 11, it is possible to suppress the reflection of other natural light emission components compared to the reflection of the input signal, improving the noise characteristics by 10 to 20 dB. can do.

The light that has been amplified in two stages as described above becomes as shown in Figure 1 (g), which improves the noise characteristics by 10 to 20 dB compared to the case where conventional elements are simply connected in cascade.
There is no extra coupling loss due to the stage connection. In the present invention, the element length is 600 μm, and the internal gain at the − stage is approximately 30 dB, and due to end face reflection, the internal gain is approximately 14 dB.
Although there is a loss of B, a total gain of 46 dB can be obtained.

<Example 2> FIG. 3 shows a plan view of a second embodiment of the invention.

The cross-sectional structure is the same as that in FIG. 2(a). However, the waveguide is n
The length of the element is correspondingly longer. Also, Figure 2 (
Similarly to a), the angle of the oblique waveguide is 84 degrees and -84 degrees, respectively, with respect to the end surface lid, and the angles of the oblique waveguide are 84 degrees and -84 degrees, respectively, with respect to the end surface 11 except for both ends of the waveguide.
It intersects at a and 12a. The width of the end face was 600 μm.

Reflectance R of the film coated on the end surfaces 11a and 12a
1 and R2 each used a low reflection film of about 0.1%.

In the structure of this example, the single pass gain Gs in one waveguide is about 30clB, so J[=17.05~
1, and the gain obtained from each output terminal p1, p2...Pn was approximately 30 dB. The gain deviation at this time was about 1.5 dB. This is because the waveguide is oblique, so there is less reflected return light.

The spontaneous luminescence component increases as the number of amplification stages increases, but this can be removed by an external filter.

〔Effect of the invention〕

As described in Example 1, the first new feature of the present invention is that the gain can be increased to 40 dB or more using two-stage waveguide amplification, and that the noise characteristics can be improved by suppressing the spontaneous luminescence component by using reflection characteristics. This is something that can be improved. As a result, the performance is significantly improved compared to the conventional one, and since it can be manufactured monolithically, it is also possible to improve the economy compared to the conventional one.

Further, according to the configuration described in the second embodiment, it is possible to obtain an optical amplification element having a multi-branching function, and it is possible to distribute signals in transmissions such as subscriber systems, which is economically advantageous.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional structural diagram, a plan view, and an optical characteristic diagram of each part of an optical amplification device showing a first embodiment of the present invention, and FIG. 2 is a cross-sectional view, a plan view, and a diagram of a conventional optical amplification device. FIG. 3 is a plan view of an optical amplification device showing a second embodiment of the present invention. 1...P sliding electrode layer, 2...D type electrode layer, 3...n
Type InP substrate. 4a・=n-type InP cladding layer, 4b・
- n-type 1nP buffer layer, 5a... n-type InP buried layer, 5b... p-type InP buried layer, 6... p-type InP cladding layer, 7... waveguide (active M), 11...Specific wavelength reflective film. 12 Low reflection film, 13... First diagonal stripe type waveguide, 14... Second diagonal stripe type waveguide, 15... Signal input section, 16... Signal reflection section, 17
... Signal power section, 18... Input signal light, 19... Output signal <e) ■ Figure

Claims (1)

[Scope of Claims] 1. An end-face reflection type amplifier device having an oblique waveguide with respect to the end face, characterized in that two waveguides are in contact with each other on at least one end face. 2. A reflective film is provided on the end face of the side where the two waveguides are in contact, which is characterized by setting the reflectance of the input signal higher than that of other wavelengths, so that the signal passing through the waveguide on the input side is 2. The end-reflection type optical amplification device according to claim 1, wherein the light is guided to the other waveguide after being reflected by the reflective film. 3. The edge reflection type optical amplification device according to item 1 above, which has a plurality of the waveguides in one device, and has an edge reflectance that is at least enough to cancel out the gain obtained by one waveguide.