KR20090053510A - Electroabsorption modulator, electroabsorption transceiver and radio antenna unit including the same - Google Patents

Abstract

Field of the Invention The present invention relates to an electroabsorption optical modulator, an electroabsorption transceiver, and a remote antenna device using the same. Specifically, an electroabsorption optical modulator and an electroabsorption transceiver are capable of improving the characteristics as an optical detector without the need for an external bias. And a remote antenna device using the same.

The difference between the wavelength of the input optical signal and the edge wavelength of the light absorption layer is substantially greater than 36 nm and less than 50 nm.

Field Absorption, Transceiver, Picocell, EAM, Optical Modulator, Optical Detector, RAU

Description

ELECTROABSORPTION MODULATOR, ELECTROABSORPTION TRANSCEIVER AND RADIO ANTENNA UNIT INCLUDING THE SAME}

Field of the Invention The present invention relates to an electroabsorption optical modulator, an electroabsorption transceiver, and a remote antenna device using the same. Specifically, an electroabsorption optical modulator and an electroabsorption transceiver are capable of improving the characteristics as an optical detector without the need for an external bias. And a remote antenna device using the same.

In general, a semiconductor laser is used as a light source for optical communication. That is, when a current is applied to the semiconductor laser, light of a monochromatic wavelength is emitted. The optical signal is transmitted by modulating the intensity of light and passing it through the optical fiber. As a method of modulating the intensity of light emitted from a semiconductor laser, there is a method of outputting light of a semiconductor laser at a constant intensity and modulating the intensity of light using another optical device from the outside. An optical device that plays such a role is called an optical modulator, and an electro-absorption modulator (EAM) is a type thereof.

A field absorption optical modulator is an optical device using a phenomenon in which a band gap is reduced when an electric field is applied to a semiconductor. In other words, the optical signal is generated by modulating the light of a constant intensity output from the light source by using a phenomenon in which the light passes through the semiconductor when the electric field is not applied and does not absorb and pass the light when the electric field is applied.

On the other hand, in a network that transmits and receives a lot of data wirelessly, such as next generation mobile communication or broadband convergence network, it is predicted that the cell size will be reduced, and the picocell structure is expected to be used instead of the conventional microcell. In such a picocell structure, since the number of Remote Antenna Units (RAUs) used is greatly increased, it is important to simply configure the structure of the RAU to reduce costs. To this end, Radio-Over-Fiber, a technology that loads data from a central station (CS) on a transmission frequency and transmits it to the RAU by light waves, has attracted much attention. In particular, when the field absorption transceiver is used, the structure of the RAU is dramatically simplified, and the cost can be greatly reduced.

Such an electroabsorption optical modulator can be used as a photodetector, and when it is used to enable both functions at the same time, it is called an electroabsorption transceiver (transceiver), and modulates or absorbs light by using a phenomenon in which light absorption varies depending on an electric field. do.

In general, the field absorption transceiver is designed to optimize the performance as an optical modulator, and the performance as an optical modulator exhibits the maximum efficiency when the external bias is about 1 V and the maximum, resulting in maximum efficiency. The insertion loss is designed to not exceed 10dB.

In order to reduce the insertion loss as described above, the detuning between the wavelength of the light used and the absorption edge wavelength of the field absorbing element absorption blue is 50 nm or more, so that there is little absorption of the light in the absence of external bias.

Korean Patent No. 10-0333482 discloses an 'field absorbing semiconductor optical modulator and a method of manufacturing the same, in which the electrode contact surface can be kept large while the width of the light absorbing layer is kept small to simultaneously reduce capacitance and contact resistance which impede high-speed operation. Korean Patent No. 10-0703367 discloses a radio communication service radius at the same time to improve the low light sensing characteristics of the field absorption modulator in the remote base station to convert the optical signal to a radio frequency for wireless transmission and reception Disclosed is a 'wireless remote base station and a pico-cell system using the same' that can increase the.

However, the conventional electroabsorption optical modulator as described above has a problem in that the performance is improved only by applying an external bias, and the performance is greatly reduced when the external bias is not applied. In order to solve this problem, a method of increasing the length of the waveguide has been proposed. However, increasing the length of the waveguide increases the capacitance of the device, thereby decreasing the modulation / detection speed of the device.

In addition, when a field absorption transceiver according to the prior art is used in a passive pico-cell system that does not use a power source, there is a problem in that the performance of the device as an optical modulator and a light detector are both degraded.

Some embodiments of the present invention provide an electroabsorption transceiver capable of improving the characteristics as an optical detector while maintaining the characteristics as an optical modulator without an external bias.

As a technical means for achieving the above-described technical problem, the first aspect of the present invention is an electric field absorption optical modulator, the difference between the wavelength of the input optical signal and the edge wavelength of the light absorption layer substantially greater than 36nm and less than 50nm Provide an absorbing light modulator.

The wavelength of the input optical signal may be substantially 1536 nm to 1550 nm, and the edge wavelength of the light absorption layer may be substantially 1500 nm.

As a technical means for achieving the above-described technical problem, the second aspect of the present invention, in the method for manufacturing the field absorption optical modulator, forming a first polarizing optical waveguide layer on the substrate, substantially the wavelength of the input optical signal Growing a light absorbing layer such that a difference in wavelength greater than 36 nm and smaller than 50 nm occurs; sequentially stacking a second polarizing optical waveguide layer, a second polarizing clad layer, and a second polarizing ohmic contact layer; Etching the waveguide layer, the light absorbing layer, the second polarizing optical waveguide layer, the second polarizing cladding layer, and the second polarizing ohmic contact layer to have a predetermined width, and the first polarizing optical waveguide layer, the light absorbing layer, and the second polarizing light. Forming a dielectric thin film on the waveguide layer, the second polar clad layer and the second polar ohmic contact layer, and the second polar electrode and the first polar electrode on the upper part of the second polar ohmic contact layer and the lower part of the substrate. It provides a method for producing an electric field absorption optical modulator, comprising the step of forming each.

As a technical means for achieving the above technical problem, the third aspect of the present invention is a field absorption transceiver for converting a downlink optical signal to a downlink RF frequency and an uplink RF frequency to an uplink optical signal and wireless transmission of the downlink RF frequency And a remote antenna device configured to output the wirelessly received uplink RF frequency to the field absorption transceiver, wherein the field absorption transceiver has a difference between an edge of an input optical signal and a light absorption layer substantially greater than 36 nm and less than 50 nm. Provided is a remote antenna device which is an electroabsorption light modulator.

According to one of the problem solving means of the present invention described above, by changing the detuning (smaller) than the existing value, the field absorption can be improved while maintaining the characteristics as an optical modulator without an external bias It can provide a transceiver.

According to another one of the above-mentioned means for solving the problems of the present invention, the structure of the radio antenna unit (RAU) is simplified by using the field absorption transceiver that can improve the characteristics as the optical detector while maintaining the characteristics as the optical modulator. Can be reduced.

DETAILED DESCRIPTION Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art may easily implement the present invention. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention. In the drawings, parts irrelevant to the description are omitted in order to clearly describe the present invention, and like reference numerals designate like parts throughout the specification.

Throughout the specification, when a part is "connected" to another part, this includes not only "directly connected" but also "electrically connected" with another element in between. . In addition, when a part is said to "include" a certain component, which means that it may further include other components, except to exclude other components unless otherwise stated.

DETAILED DESCRIPTION Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art may easily implement the present invention. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention. In the drawings, parts irrelevant to the description are omitted in order to clearly describe the present invention, and like reference numerals designate like parts throughout the specification.

Throughout the specification, when a part is "connected" to another part, this includes not only "directly connected" but also "electrically connected" with another element in between. . In addition, when a part is said to "include" a certain component, which means that it may further include other components, except to exclude other components unless otherwise stated.

Hereinafter, an electric field absorption transceiver according to an embodiment of the present invention will be described with reference to FIGS. 1 to 3.

In general, one of the most important characteristics of the analog optical link used in the passive picocell system is the ratio of the RF signal restored by the optical detector to the RF signal input to the optical modulator, that is, the RF gain.

In particular, the RF gain in the optical modulator is closely related to the insertion efficiency of the optical signal and the slope efficiency of the optical modulator. That is, in an optical modulator, the RF gain is proportional to the square of the output optical power and proportional to the slope of the transfer function of the optical modulator. Thus, analog light modulators operate at large input optical power and require a large slope of the transfer function.

The RF gain G of the analog optical link can be calculated by Equation 1.

는 입사하는 광의 세기,

는 바이어스

에서 전달 함수의 기울기,

은 전계흡수 소자의 전송 요소(transmission factor, 삽입 손실이

으로 주어짐),

는 0V에서 광 섬유의 전송 요소,

는 광 검출기의 반응도(responsivity),

는 소스 신호 발생기(source signal generator)의 저항 값,

은 부하(load)의 저항 값을 나타낸다. here,

Is the intensity of incident light,

The bias

Slope of the transfer function,

The transmission factor (insertion loss) of the

),

Transmission element of optical fiber, at 0V

Is the responsivity of the photodetector,

Is the resistance value of the source signal generator,

Represents the resistance value of the load.

뿐만 아니라

의 영향을 받음을 알 수 있다. 따라서, 디튜닝(detuning)을 감소시키더라도 광 링크의 RF 이득(G)은

과

의 곱에 의존하므로 큰 변화가 없게 된다. 즉, 디튜닝(detuning) 값을 감소시키면

이 감소(삽입 손실 증가)하여 소자의 광 변조기로서의 특성은 큰 변화가 없다. 하지만, 디튜닝(detuning)을 감소시키면 광 흡수가 늘어나서 소자의 광 검출기로서의 특성은 크게 향상된다. 이러한 특성에 대한 실험적 데이터는 도 1 내지 도 2를 참조하여 후술한다. As shown in Equation 1, the RF gain (G) of the optical link is

As well as

It is influenced by. Therefore, even if the detuning is reduced, the RF gain (G) of the optical link remains

and

Since it depends on the product of, there is no big change. In other words, if you decrease the detuning value

With this reduction (insertion loss increase), the characteristics of the device as an optical modulator do not change significantly. However, reducing detuning increases light absorption, greatly improving the device's characteristics as a photodetector. Experimental data on these characteristics are described below with reference to FIGS.

As described above, the detuning value of the field absorbing element is set to a value smaller than the existing value (50 nm) (36 nm or more and 50 nm or less), thereby maintaining the characteristics as an optical modulator without an external bias while maintaining the characteristics as an optical detector. Can provide a field absorption transceiver which can be improved.

1 is a view for explaining a method for improving the zero bias operation of an EAM according to an embodiment of the present invention. At this time, the wavelength of the input optical signal used is 1536nm, the edge wavelength of the light absorption layer of the field absorbing element is 1500nm, the detuning value is 36nm.

As shown in FIG. 1, the field absorption optical modulator (EAM) according to the embodiment of the present invention reduces the detuning value of a field absorption element of more than 50 nm to 36 nm in zero-bias. The slope efficiency of the modulator can be increased. In this case, the responsiveness of the detector can be increased by about 3 dB, and this 3 dB increase in optical detection performance can increase the RF gain of the link by about 6 dB, and increase the RF gain when using a high power optical transmission signal. Can increase.

2 is a view for explaining the characteristics of the transfer function of the field absorption light modulator according to an embodiment of the present invention.

As shown in FIG. 2, it can be seen that the field absorption optical modulator according to the exemplary embodiment of the present invention has a zero-bias, that is, the slope of the transfer function becomes maximum when the external bias voltage is 0V.

As described above, the wavelength of the input optical signal is set to 1536 nm, the absorption edge wavelength of the light absorbing layer of the field absorbing element is set to 1500 nm, and the detuning value is reduced to 36 nm, thereby maintaining the characteristics as an optical modulator without maintaining an external bias. Characteristics can provide an improved field absorption transceiver.

3 is a flowchart illustrating a manufacturing process of an electroabsorption light modulator according to an embodiment of the present invention.

Referring to FIG. 3, in step S11, an n-type optical waveguide layer is formed on a semiconductor substrate, and in step S12, incident light used when a remote antenna device of a picocell is configured on the n-type optical waveguide layer. A light absorbing layer that grows in a wavelength of 36 nm to 50 nm smaller than the wavelength is grown. The light absorbing layer is grown by chemical vapor deposition (MOVPE) using an organic metal to have a constant absorbing layer thickness and bandgap wavelength.

In step S13, when the growth of the light absorption layer is completed, the p-type optical waveguide layer, the p-type cladding layer, and the p-type ohmic contact layer are sequentially grown, and in step S14, only the band shape having a predetermined width is left, and the semiconductor is left. Etch to expose the substrate.

In step S15, polyimide is formed, and in step S16, p-type electrodes and n-type electrodes are formed on the upper portion of the p-type ohmic contact layer and the lower portion of the substrate, respectively.

As described above, the field absorption light modulator of the present invention is manufactured by forming a light absorption layer to have a detuning value of 36 nm to 50 nm with respect to the wavelength of incident light.

The foregoing description of the present invention is intended for illustration, and it will be understood by those skilled in the art that the present invention may be easily modified in other specific forms without changing the technical spirit or essential features of the present invention. will be. Therefore, it should be understood that the embodiments described above are exemplary in all respects and not restrictive. For example, each component described as a single type may be implemented in a distributed manner, and similarly, components described as distributed may be implemented in a combined form.

The scope of the present invention is shown by the following claims rather than the above description, and all changes or modifications derived from the meaning and scope of the claims and their equivalents should be construed as being included in the scope of the present invention. do.

1 is a view for explaining a method for improving the zero bias operation of an EAM according to an embodiment of the present invention.

2 is a view for explaining the characteristics of the transfer function of the field absorption light modulator according to an embodiment of the present invention.

3 is a flowchart illustrating a manufacturing process of an electroabsorption light modulator according to an embodiment of the present invention.

Claims (4)

In the field absorption optical modulator, An electroabsorption light modulator having a difference in wavelength between an input optical signal and an edge wavelength of a light absorption layer substantially larger than 36 nm and smaller than 50 nm. The method of claim 1, The wavelength of the input optical signal is substantially 1536nm to 1550nm, the edge wavelength of the light absorption layer is substantially 1500nm. In the manufacturing method of the field absorption light modulator, Forming a first polarizing optical waveguide layer on the substrate, Growing a light absorption layer such that a difference between a wavelength of the input optical signal and a wavelength substantially larger than 36 nm and smaller than 50 nm occurs; Sequentially stacking a second polarized optical waveguide layer, a second polarized clad layer and a second polarized ohmic contact layer; Etching the first polarizing optical waveguide layer, the light absorbing layer, the second polarizing optical waveguide layer, the second polarizing cladding layer and the second polarizing ohmic contact layer to have a predetermined width; Forming a dielectric thin film on the first polarizing optical waveguide layer, the light absorbing layer, the second polarizing optical waveguide layer, the second polarizing cladding layer and the second polarizing ohmic contact layer; Forming a second polarity electrode and a first polarity electrode on an upper portion of the second polar ohmic contact layer and a lower portion of the substrate, respectively; Method of manufacturing a field absorption light modulator comprising a. A field absorbing transceiver for converting a downlink optical signal into a downlink RF frequency and converting an uplink RF frequency into an uplink optical signal, and an antenna for wirelessly transmitting the downlink RF frequency and outputting the wirelessly received uplink RF frequency to the field absorbing transceiver In the remote antenna device, And the field absorption transceiver is an field absorption optical modulator having a difference between an input optical signal and an edge wavelength of the light absorption layer substantially greater than 36 nm and smaller than 50 nm.

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