KR102397557B1 - Electro-absorption modulated laser - Google Patents

Abstract

A field absorption modulator integrated laser according to an embodiment is disclosed. The field absorption modulator integrated laser includes a substrate; a DFB disposed on the substrate and configured to output an optical signal of a single wavelength; and an EAM disposed on the substrate, including an active layer having at least one of a thickness and a width different from a thickness and width of a partial area of the entire area, and modulating an optical signal output from the DFB through the active layer.

Description

ELECTRO-ABSORPTION MODULATED LASER

Embodiments relate to field absorption modulator integrated lasers.

In general, in a high-speed optical communication network, a signal wave output from a single-wavelength laser (Distributed Feedback; DFB) as its light source is directly modulated, that is, a signal output by applying AC to the active layer of the DFB is directly modulated and used, or Alternatively, the output of the laser is fixed by combining the DFB and an external modulator, but the output light is modulated at a high speed in the required frequency range through an external modulator.

As a device that combines DFB with an external modulator and uses it as a light source for a high-speed optical communication network, there is an Electro-absorption Modulated Laser (EML) with an integrated field absorption modulator.

1 is a view showing a field absorption modulator integrated laser according to the prior art.

Referring to FIG. 1 , the conventional integrated laser field absorption type modulator is a field absorption modulator that modulates the DFB 100 and the signal wave output from the DFB 100 using the difference in absorption according to the electric field of the semiconductor ( Electro-absorption Modulator; EAM (300) is combined.

At this time, among the characteristics of EAM, extinction ratio and modulation speed are important design factors, and there is a trade-off relationship. That is, when the length of the electro-absorptive modulator increases, the light absorption area increases and the extinction ratio increases, but the capacitance increases and the modulation rate decreases.

Therefore, it is not easy to derive an optimal modulator length that satisfies both characteristics.

An embodiment provides a field absorption modulator integrated laser capable of obtaining a desired extinction ratio and modulation rate.

The problem to be solved in the embodiment is not limited thereto, and it will be said that the purpose or effect that can be grasped from the method of solving the problem described below or the embodiment is also included.

A field absorption modulator integrated laser according to an embodiment includes: a substrate; a DFB disposed on the substrate and configured to output an optical signal of a single wavelength; and an EAM disposed on the substrate, including an active layer having at least one of a thickness and a width different from a thickness and width of a partial region of the entire region, and modulating an optical signal output from the DFB through the active layer.

The active layer is divided into a first region having a constant thickness and width, and a second region extending from the first region to receive an optical signal output from the DFB, and at least one of the thickness and width of the second region is determined from the second region. It may be different from area 1.

The second region may be formed to extend from the first region, and may have a tapered structure in which at least one of a thickness and a width increases in at least one direction.

In the second area, at least one of a thickness and a width of a first surface to which the optical signal is input is larger than a second surface through which the optical signal is output, and the thickness and width of the second surface are the same as the first area. can do.

The length of the second region may be less than or equal to that of the first region.

The second region may be formed using a selective area growth (SAG) effect.

The active layer may be formed of a multiple quantum well (MQW).

A field absorption modulator integrated laser according to an embodiment includes a first cladding layer; an active layer disposed on the first cladding layer and modulating an optical signal output from the DFB, wherein at least one of a thickness and a width of a partial region of the entire region is different; a second cladding layer disposed on the active layer; an upper electrode disposed on the second cladding layer; and a lower electrode disposed under the first clad layer.

According to an embodiment, the active layer of the EAM is divided into a first region and a second region, the first region has a constant thickness, and the second region extends from the first region using the SAG effect to gradually increase the thickness By forming it in a tapered structure such as the one with

Various and advantageous advantages and effects of the present invention are not limited to the above, and will be more easily understood in the course of describing specific embodiments of the present invention.

1 is a view showing a field absorption modulator integrated laser according to the prior art.
2 is a diagram illustrating a field absorption modulator integrated laser according to an embodiment of the present invention.
FIG. 3 is a view for explaining the shape of the second active layer shown in FIG. 2 .
4A to 4C are diagrams for comparing and explaining the performance of the second active layer according to the embodiment.
5A to 5B are views illustrating various structures of a second active layer according to an embodiment.
6A to 6B are diagrams for comparatively explaining the field absorption modulator integrated laser.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

However, the technical spirit of the present invention is not limited to some embodiments described, but may be implemented in various different forms, and within the scope of the technical spirit of the present invention, one or more of the components may be selected between the embodiments. It can be used by combining or substituted with .

In addition, terms (including technical and scientific terms) used in the embodiments of the present invention may be generally understood by those of ordinary skill in the art to which the present invention belongs, unless specifically defined and described explicitly. It may be interpreted as a meaning, and generally used terms such as terms defined in advance may be interpreted in consideration of the contextual meaning of the related art.

In addition, the terminology used in the embodiments of the present invention is for describing the embodiments and is not intended to limit the present invention.

In this specification, the singular form may also include the plural form unless otherwise specified in the phrase, and when it is described as “at least one (or more than one) of A and (and) B, C”, it is combined with A, B, and C It may include one or more of all possible combinations.

In addition, in describing the components of the embodiment of the present invention, terms such as first, second, A, B, (a), (b), etc. may be used.

These terms are only for distinguishing the component from other components, and are not limited to the essence, order, or order of the component by the term.

And, when it is described that a component is 'connected', 'coupled' or 'connected' to another component, the component is not only directly connected, coupled or connected to the other component, but also with the component It may also include a case of 'connected', 'coupled' or 'connected' due to another element between the other elements.

In addition, when it is described as being formed or disposed on “above (above) or under (below)” of each component, the top (above) or bottom (below) is one as well as when two components are in direct contact with each other. Also includes a case in which another component as described above is formed or disposed between two components. In addition, when expressed as “upper (upper) or lower (lower)”, the meaning of not only the upward direction but also the downward direction based on one component may be included.

In the embodiment, the active layer of the EAM is divided into a first region and a second region, the first region has a constant thickness, and the second region extends from the first region using the SAG effect to gradually increase the thickness. A new EML structure is proposed to be formed in a tapered structure.

2 is a diagram illustrating a field absorption modulator integrated laser according to an embodiment of the present invention.

Referring to FIG. 2 , the field absorption modulator integrated laser according to an embodiment of the present invention includes a DFB 100 and an EAM 300 , but includes a lower electrode 10 , a first cladding layer 20 , and a grid layer. (grating layer) 30 , first active layer 40 , second active layer 50 , first waveguide 60 , second waveguide 62 , second cladding layer 70 , first upper electrode 80 ), the second upper electrode 90 may be included.

The first active layer 40 of the DFB 100 and the second active layer 50 of the EAM 300 are formed on the first clad layer 20 which becomes the substrate, and the first active layer 40 and the second active layer A first waveguide 60 may be formed between 50 .

The DFB 100 may output an optical signal of a single wavelength. The DFB 100 may include a lower electrode 10 , a first clad layer 20 , a grid layer 30 , a first active layer 40 , a second cladding layer 70 , and a first upper electrode 80 . can

A lower electrode 10, which is an n-type electrode, is disposed below the first clad layer 20, which is an n-type cladding layer made of n-InP, and a grid layer 30, a second One active layer 40 may be disposed.

The grating layer 30 is formed only in the region of the DFB 100 , and may provide a single wavelength, for example, 1.55 μm. The first active layer 40 may be formed of a multiple quantum well (MQW).

A second cladding layer 70 that is a p-type cladding layer made of P-InP is disposed on the first active layer 40 , and a first upper electrode 80 that is a p-type electrode is disposed on the second clad layer 70 . can be

In this case, a contact layer may be disposed on the second cladding layer 70 , and the first upper electrode 80 may be disposed on the contact layer.

When a forward voltage is applied to the lower electrode 10, which is an n-type electrode, and the first upper electrode 80, which is a p-type electrode, the DFB 100 generates light of a single wavelength by the grating layer 30 and the first active layer 40. signal can be output.

The EAM 300 may modulate an optical signal output from the DFB 100 . The EAM 300 may include a lower electrode 10 , a first clad layer 20 , a second active layer 50 , a second clad layer 70 , and a second upper electrode 90 .

A lower electrode 10, which is an n-type electrode, is disposed below the first clad layer 20, which is an n-type cladding layer made of n-InP, and a second active layer 50 is disposed on the first clad layer 20. can be placed.

The second active layer 50 may be formed of a multiple quantum well (MQW) having a shorter wavelength than the first active layer 40 . The second active layer 50 is divided into a first region 51 and a second region 52 , the first region 51 has a constant thickness, and the second region 52 is the first region 51 . ) and may be formed as a tapered structure in which the thickness is gradually increased.

In this case, the second region 52 may be formed using a selective area growth (SAG) effect.

In other words, in general, according to the principle of integrating optical devices having different functions, for example, DFB and EAM, semiconductor devices having different bandgap energies should be able to be grown on the same substrate. In addition, the materials forming the thin film must be smoothly connected at the coupling portion between the different semiconductor devices so that the optical signal can be propagated without attenuation or scattering.

At this time, the butt growth technique is used to partially etch and remove the semiconductor layer and then re-grow another semiconductor layer. At this time, a dielectric film mask is present on the first active layer, and a selective area growth (SAG) effect occurs in the second active layer by the mask. That is, the growth material does not grow in the dielectric film mask on the first active layer and moves toward the second active layer, so that the boundary portion of the second active layer is grown relatively thickly.

It is known that the SAG effect is mainly determined by the following conditions: growth temperature, growth pressure, V/III ratio, and shape of a mask pattern. Therefore, in order to obtain good characteristics of the growth layer, it is necessary to grow the growth layer by well combining the above conditions.

A second cladding layer 70 that is a p-type cladding layer made of P-InP is disposed on the second active layer 50 , and a second upper electrode 90 that is a p-type electrode is disposed on the second clad layer 70 . can be

In this case, a contact layer may be disposed on the second cladding layer 70 , and the second upper electrode 90 may be disposed on the contact layer.

FIG. 3 is a view for explaining the shape of the second active layer shown in FIG. 2 , and FIGS. 4A to 4C are views for explaining and comparing the performance of the second active layer according to the embodiment.

Referring to FIG. 3 , the second active layer 50 according to the embodiment may be divided into a first region 51 and a second region 52 . The first region 51 may be formed with a constant thickness t1 , and the second region 52 may have a tapered structure extending from the first region 51 and gradually increasing in thickness.

The length L2 of the second region may be less than or equal to the length L1 of the first region.

In the second region 52 , the thickness of the first surface S1 on which the optical signal is incident is t2 , and the thickness of the second surface S2 on which the optical signal is output is the same as the thickness of the first region 51 . t1 may be formed.

Referring to FIG. 4A , since the EAM including the second active layer 50 according to the embodiment absorbs a lot of light at a portion where an optical signal is incident, a desired extinction ratio can be obtained only with a short modulator length and the length of the modulator is minimized. Thus, the modulation speed may be improved.

Referring to FIG. 4B , the EAM having the same length as the EAM of FIG. 4A but including the second active layer having a constant thickness may have a lower extinction ratio because light is relatively less absorbed.

Referring to FIG. 4C , like the EAM of FIG. 4B , an EAM including a second active layer having a constant thickness but a long length may obtain a desired extinction ratio, but may decrease the modulation rate.

Since the EAM according to the embodiment of FIG. 4A absorbs a lot of incident light because the thickness of the second region to which the optical signal is incident is large, it is not necessary to have a relatively increased thickness in the first region. Accordingly, in the first region, there is no need to increase the length as well as the thickness, so that the length of the entire device decreases as the length of the EAM according to the embodiment decreases.

5A to 5B are views illustrating various structures of a second active layer according to an embodiment.

Referring to FIG. 5A , the second region of the second active layer according to the embodiment may be formed such that the thickness gradually increases from the first region, but in the eleventh direction on the first axis, for example, in the upper direction. .

Referring to FIG. 5B , the thickness of the second region of the second active layer according to the embodiment gradually increases from the first region, and the thickness of the second region on the second axis increases in the eleventh direction on the first axis, for example, in the upward direction. Widths in the 21st and 22nd directions, for example, in the left and right directions, may also be formed to gradually increase through photolithography and etching.

Here, the case where the thickness of the second region of the second active layer increases in the upward direction or the width increases in the left and right directions as the thickness increases in the upward direction is described as an example, but it is not necessarily limited thereto, and at least one of the thickness and the width is can grow

6A to 6B are diagrams for comparatively explaining the field absorption modulator integrated laser.

6A to 6B , in the field absorption modulator integrated laser according to the embodiment, since the length of the EAM is minimized by forming a portion of the active layer in a tapered structure as shown in FIG. 6B, when configuring the active layer as shown in FIG. 6A The overall length may be further reduced.

Even if the overall length is reduced as shown in FIG. 6B , when the active layer is configured, a desired extinction ratio can be obtained, and the length of the modulator is minimized, so that the modulation speed can be improved.

Although the above has been described with reference to the preferred embodiment of the present invention, those skilled in the art can variously modify and change the present invention within the scope without departing from the spirit and scope of the present invention as described in the claims below. You will understand that it can be done.

100: DFB
300: EAM
10: lower electrode
20: first cladding layer
30: grid layer
40: first active layer
50: second active layer
60: first waveguide
62: second waveguide
70: second cladding layer
80: first upper electrode
90: second upper electrode

Claims (12)

Board;
a DFB disposed on the substrate and including a first active layer for outputting an optical signal of a single wavelength; and
an EAM disposed on the substrate, including a second active layer formed with different thicknesses and widths of some regions of the entire region, and modulating an optical signal output from the DFB through the second active layer;
The DFB is
a grid layer formed on the substrate;
a first active layer formed on the grid layer; and
a first upper electrode formed on the first active layer;
The EAM is
a second active layer disposed on the substrate and spaced apart from the first active layer; and
a second upper electrode formed on the second active layer;
A first waveguide is formed between the first surface to which the optical signal of the first active layer and the second active layer is input;
and a second waveguide is formed on a second surface of the second active layer through which an optical signal is output. According to claim 1,
The second active layer,
It is divided into a first region having a constant thickness and width and a second region extending from the first region to receive an optical signal output from the DFB,
and a thickness and a width of the second region are both different from those of the first region. 3. The method of claim 2,
The second area is
The field absorption modulator integrated laser is formed to extend from the first region and has a tapered structure in which both thickness and width increase in at least one direction. 4. The method of claim 3,
The second area is
Both a thickness and a width of the first surface to which the optical signal is input are formed to be larger than the second surface to which the optical signal is output,
and the thickness and width of the second surface are the same as those of the first area. 3. The method of claim 2,
and the length of the second region is less than or equal to the length of the first region. 3. The method of claim 2,
The second area is
A field-absorption modulator integrated laser formed using the Selective Area Growth (SAG) effect. According to claim 1,
The active layer is
Field Absorption Modulator Integrated Laser with Multiple Quantum Wells (MQW). delete delete delete delete delete

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