KR102290138B1 - Discrete External Modulated Optical Transmitter - Google Patents

Abstract

The present invention relates to a discrete external modulated optical transmitter, and can provide an optical transmitter which can perform long-distance transmission of a broadband suitable for a 5G communication environment by providing a wide-range wavelength tuning function while increasing production yield, by an external modulator configured by separating an external resonance part which is an unmodulated laser resonance part from an external modulator part which is an optical modulation part.

Description

Discrete External Modulated Optical Transmitter

The present invention relates to an optical transmitter for long-distance high-speed communication, and more particularly, to a separate external modulation optical transmitter.

5G mobile communication (hereinafter referred to as 5G) technology requires an optical communication network (Fronthaul) for wireless base stations that supports a speed of 25 Gbps. Currently, C-band (Conventional band, 1530~1565nm wavelength band), 25Gbps speed, and 20km transmission possible, the optical transmitter is DFB-LD (Distributed Feedback Laser Diode) and EAM (Electro Absorption Modulator) integrated There is EML (Distributed Feedback Laser Diode Externally Modulated Laser).

Compared to the 4th generation LTE (Long Term Evolution, 4G) communication technology, 5G technology uses an ultra-high band frequency of 3.5 GHz or 28 GHz, which is a higher band, and the data transmission rate also increases rapidly, so the size that one base station can cover ( cell size) was significantly reduced. Accordingly, as the number of required antennas increases and the number of optical transmission channels in the fronthaul increases rapidly, a Dense Wavelength Division Multiplexing (DWDM) transmission technology is being considered.

3 shows the structures of a fronthaul and a backhaul in a 4G communication environment.

3A is an example of a 4G network.

The fronthaul refers to a network that connects a base band unit (BBU) and an antenna (RRH: remote radio head).

3B is an example of 4G backhaul.

Backhaul refers to a network that delivers communication data from a base station to the backbone (core) network of a telecommunication service provider.

In 4G as well as 5G, optical communication networks are used to connect these fronthaul and backhaul networks.

However, many carriers are already using Coarse Wavelength Division Multiplexing (CWDM) technology to build 4G LTE fronthaul. Therefore, since it is economically advantageous to build a 5G communication network using the existing 4G communication network, we are considering a method of applying DWDM technology on top of the existing CWDM base for 5G fronthaul establishment.

2 shows an example of applying a DWDM technique by dividing a conventional CWDM frequency channel.

2A shows an example of dividing a CWDM channel having a bandwidth of 20 nm into 16 DWDM channels having an interval of 0.8 nm.

FIG. 2B shows an example of a structure for combining CWDM Mux/DeMux and DWDM Mux/Demux. DWDM transmission is performed by adding a DWDM filter outside the already installed CWDM filter.

To use DWDM technology for 5G fronthaul, tunable transmitter technology is being considered. If the optical signal transmitter/receiver is different depending on the wavelength, problems arise in various aspects such as network construction, network management, and spare parts management, so wavelength tunable technology is essential.

However, the DFB-LD EML of the prior art has disadvantages in that the transmission optical power is limited due to a decrease in production yield following the application of DWDM technology and an increase in price thereof, and a large insertion loss of the EAM. In addition, the wavelength tunability necessary for DWDM technology is extremely limited, about 3 nm, so it is not too much to say that there is no wavelength tunability.

The inventors of the present invention have been researching and trying to solve the problem of the optical transmitter of the prior art. After much effort to develop an externally modulated optical transmitter having a wavelength tunable capability required to apply DWDM technology in evolving 4G LTE communication network to 5G communication network based on CWDM, the present invention was completed after much effort.

It is an object of the present invention to solve the problems of the prior art as described above, to provide a detachable externally modulated optical transmitter having a wavelength tunable capability for applying the DWDM technology on the CWDM basis.

On the other hand, other objects not specified in the present invention will be additionally considered within the range that can be easily inferred from the following detailed description and effects thereof.

The detachable externally modulated optical transmitter according to the present invention is composed of an external resonator that generates an unmodulated optical signal and an external modulator that amplifies and modulates the generated optical signal,

The external resonator may include: a reflective laser diode on one surface of which is reflective coated and the other surface is non-reflectively coated to generate an optical signal; a first lens that converts the optical signal emitted from the reflective laser diode into parallel light; a tunable filter for passing only an optical signal having a wavelength of a certain band among the parallel lights; a partial reflection mirror that reflects a portion of the optical signal incident through the tunable filter to form a resonance part between the reflection-coated surface of the reflective laser diode and a part; and a second lens coupling the partial optical signal passing through the partial reflection mirror to the external modulator.

The external resonator may include: a tap filter that partially passes the optical signal passing through the partial reflection mirror and diverges a part; and a Wavelength Locker for receiving the optical signal branched from the tap filter and providing a wavelength of the received optical signal.

In addition, the external resonator, located behind the reflective coated surface of the reflective laser diode, receives a portion of the optical signal passing through the reflective coated surface and provides a wavelength of the received optical signal; further comprising a good.

The tunable filter is characterized in that it is a single cavity etalon (SCE: Single Cavity Etalon) filter.

The external resonator may further include an etalon for stabilizing a resonant optical signal between the tunable filter and the partial reflection mirror or between the first lens and the tunable filter.

The external modulator includes an Electro Absorption Modulator (EAM) for modulating the optical signal passing through the second lens and a Semiconductor Optical Amplifier (SOA) for amplifying the modulated optical signal in order characterized in that

The external modulator may sequentially include a semiconductor optical amplifier for amplifying the optical signal passing through the second lens and an electro-absorption modulator for modulating the amplified optical signal.

The external modulator may include a Mach-zehnder modulator for modulating the optical signal passing through the second lens.

It characterized in that it further comprises an etalon filter for adjusting the shape of the modulated optical signal pulse.

According to the present invention, it is possible to utilize the existing 4G LTE communication network by applying the DWDM technology on the CWDM base by providing a tunable optical transmitter, thereby reducing costs.

In addition, wavelength tunability of 30 nm or more is possible even at a transmission speed of 25 Gbps or more, and it has the advantage of enabling long-distance transmission of optical signals compared to the prior art.

On the other hand, even if it is an effect not explicitly mentioned herein, it is added that the effects described in the following specification expected by the technical features of the present invention and their potential effects are treated as described in the specification of the present invention.

1 is a schematic structural diagram of a prior art optical transmitter.
2 shows a schematic concept of a CWDM technology and a DWDM technology of the prior art.
3 is an example of a fronthaul and a backhaul of a 4G communication network.
4 is a structural diagram of an externally modulated optical transmitter according to a preferred embodiment of the present invention.
5 and 6 are examples of the structure of the resonance part of the externally modulated optical transmitter according to a preferred embodiment of the present invention.
7 and 8 are structural diagrams of a modulator of an externally modulated optical transmitter according to a preferred embodiment of the present invention.
※ It is revealed that the accompanying drawings are exemplified as a reference for understanding the technical idea of the present invention, and the scope of the present invention is not limited thereby

Hereinafter, with reference to the drawings, the configuration of the present invention guided by various embodiments of the present invention and effects resulting from the configuration will be described. In the description of the present invention, if it is determined that the subject matter of the present invention may be unnecessarily obscured as it is obvious to those skilled in the art with respect to related known functions, the detailed description thereof will be omitted.

Terms such as 'first' and 'second' may be used to describe various elements, but the elements should not be limited by the above terms. The above term may be used only for the purpose of distinguishing one component from another. For example, without departing from the scope of the present invention, a 'first component' may be termed a 'second component', and similarly, a 'second component' may also be termed a 'first component'. can Also, the singular expression includes the plural expression unless the context clearly dictates otherwise. Unless otherwise defined, terms used in the embodiments of the present invention may be interpreted as meanings commonly known to those of ordinary skill in the art.

Hereinafter, with reference to the drawings, the configuration of the present invention guided by various embodiments of the present invention and effects resulting from the configuration will be described.

1 shows examples of EML in the prior art.

The DFB-LD EML 10 , which is the fixed wavelength EML illustrated in FIG. 1A , includes the DFB-LD 110 and the EAM 120 .

The DFB-LD 110 for generating a laser by resonance includes a grating 112 and an active region 114, and one surface 116 is coated with a high reflection coating. The grating 112 has a slit or groove-shaped grid structure having a plurality of regular intervals. Light is diffracted by the slits or grooves inside the grating 112, and a diffraction phenomenon appears.

The optical signal generated from the DFB-LD 110 is modulated by the EAM 120 , and one surface 122 of the EAM 120 is coated with anti-reflection coating.

1 (b) is a structural diagram of a tunable EML.

The tunable EML 20 includes a tunable LD (Laser Diode) 210 , lenses 220 , 230 , 250 , and a modulator 240 .

4 is a structural diagram of an externally modulated optical transmitter according to a preferred embodiment of the present invention.

The externally modulated optical transmitter 40 according to the present invention includes an external resonator 400 and an external modulator 500 .

The external resonance part 400 uses a semiconductor optical gain chip with a reflective coating on one side and an anti-reflective coating on the other side, and forms a resonance part by placing a partial reflective mirror on the outside of the semiconductor optical gain chip. .

In addition, an external resonator (ECL: External Cavity Laser) that can replace the conventional DWDM DFB-LD for lasing a specific wavelength is configured by inserting an optical filter having a characteristic of transmitting only a specific wavelength. The optical filter can support wavelength tunability having a fluctuation range of 30 nm or more by using a tunable optical filter.

The external modulator 500 amplifies and modulates the optical signal formed in the external resonator 400 including an Electro Absorption Modulator (EAM) and a Semiconductor Optical Amplifier (SOA). EAM and SOA can be implemented as a single semiconductor chip, and they serve to amplify the power of the optical signal input from the external resonator and high-speed modulation of 25 Gbps level.

5 is a more detailed structural diagram of the external resonator 400 according to a preferred embodiment of the present invention.

5A is an example of an external resonator 400a including a tunable filter (TF) 430 .

The external resonator 400a includes a reflective laser diode (RLD) 410 , a first lens 420 , a tunable filter 430 , a partial reflection mirror 440 , and a second lens 450 . do.

The reflective laser diode 410 has one surface 412 coated with high reflection coating and the other surface 414 with anti reflection coating. The highly reflective coated surface 412 forms a resonance with the partial reflective mirror 440 .

The first lens 420 makes the light emitted from the other surface 414 of the reflective laser diode 410 into parallel light.

The tunable filter 430 passes only an optical signal having a wavelength of a predetermined band among the parallel light passing through the first lens 420 . Therefore, it plays a role in determining the wavelength of the lasing optical signal. In this case, the tunable filter 430 may use all kinds of selective wavelength transmission means including a single cavity filter having a free spectral range (FSR) greater than the tunable range.

One surface 442 of the partial reflection mirror 440 reflects only a portion of the optical signal that has passed through the tunable filter 430 to form a laser resonance structure between the high reflection coated surface 412 of the reflective laser diode 410 and to form The remaining non-reflected optical signal passes through the partial reflection mirror 440 and is transmitted to the second lens 450 .

The second lens 450 couples the optical signal passing through the partial reflection mirror 440 to the external modulator 500 .

5 (b) is an example of the external resonator 400b using a single cavity etalon filter as the wavelength tunable filter unit.

The single cavity etalon (SCE) filter 460 passes only a specific wavelength in a predetermined band among the optical signals emitted from the reflective laser diode 410 . In this case, a wavelength tunable filter may be used as the single cavity etalon filter 460 .

5C is an example of the external resonator 400c in which an etalon filter is additionally used.

The etalon filter 470 is additionally included between the first lens 420 of the external resonator 400c and the wavelength tunable filter 430 . Meanwhile, the added etalon filter 470 may be located between the tunable filter 430 and the partial reflection mirror 440 . Since the etalon filter 470 is additionally included, the resonant optical signal may be more stable.

6 is another configuration example of the external resonator 400 according to a preferred embodiment of the present invention.

6 (a) and (b) by further including a wavelength locker (Wavelength Locker, 490a) it can be confirmed the wavelength of the optical signal having a variable wavelength.

In FIG. 6A , the tap filter 480 transmits some of the optical signals passing through the partial reflection mirror 440 to the wavelength locker 490 and the remaining optical signals to the second lens 460 .

The wavelength locker 490a may provide information regarding which wavelength is in the resonance state by analyzing the wavelength of the transmitted optical signal.

In FIG. 6 (b), without using a tap filter, the wavelength lacquer 490b is disposed behind the highly reflective coated surface 412 of the reflective laser diode 410 and passes through the reflective laser diode 410. It is possible to provide wavelength information by receiving an optical signal and analyzing it.

7 and 8 show various configuration examples of the external modulator 500 according to a preferred embodiment of the present invention.

7A shows a modulator 510a including a semiconductor optical amplifier (SOA) and an electro absorption modulator (EAM) in this order. The modulator 510a may be configured as a single chip. Since the optical signal is amplified and then modulated, there is an advantage in that the effect of noise generated by optical signal amplification on the modulated signal can be minimized. One surface 512 and the other surface 514 of the modulator 510a are both coated with anti-reflection coating.

In FIG. 7(b), in contrast to FIG. 7(a), the modulator 510b is configured in the order of an electro-absorption modulator (EAM) and a semiconductor optical amplifier (SOA). In this case, even if the optical power is attenuated during the modulation process, there is an advantage in that the optical power can be greatly amplified again in the semiconductor optical amplifier (SOA).

7C is an example in which a modulator using a Mach-Zehnder interferometer is used as the modulator 510c. Instead of using EAM and SOA, a modulator in the form of a Mach-Zehnder interferometer is used.

8 shows a configuration example of an external modulator according to another preferred embodiment of the present invention.

The external modulator 500d may include a modulator 510 , a third lens 520 , and an etalon filter 530 .

Continuous Wave Light generated by the external resonator 400 passes through the etalon filter 530 just before being output after being modulated into an optical signal by the modulator 510 . By allowing the optical signal to pass through the portion where negative chirp occurs of the etalon filter 530, an effect of compressing the optical signal spread is obtained. By compressing the optical signal pulse, it is also possible to obtain the effect of pre-compensating for the dispersion phenomenon that may occur while the optical signal passes through the optical fiber.

The protection scope of the present invention is not limited to the description and expression of the embodiments explicitly described above. In addition, it is added once again that the protection scope of the present invention cannot be limited due to obvious changes or substitutions in the technical field to which the present invention pertains.

Claims (9)

an external resonator generating an unmodulated optical signal; and
An external modulator for amplifying and modulating the generated optical signal; in a separate external modulated optical transmitter comprising:
The external resonance unit,
a reflective laser diode that generates an optical signal by having one surface being coated with high reflection and the other surface being coated with anti-reflection coating;
a first lens that converts the optical signal emitted from the other surface of the reflective laser diode into parallel light;
a tunable filter including a single cavity filter that passes only an optical signal having a wavelength of a certain band among the parallel light;
a partial reflection mirror that reflects a part of the optical signal incident through the tunable filter to form a resonance part between the high-reflection coated surface of the reflective laser diode and a part of it;
a tap filter which partially passes the optical signal passing through the partial reflection mirror and branches it;
a second lens for coupling a portion of the optical signal passing through the tap filter to the external modulator; and
and a wavelength locker that receives the optical signal branched from the tap filter and provides wavelength information of the received optical signal,
The external modulator,
an Electro Absorption Modulator (EAM) for modulating the optical signal passing through the second lens;
a semiconductor optical amplifier (SOA) amplifying the modulated optical signal; and
and an etalon filter for compensating for dispersion by receiving the output light of the semiconductor optical amplifier through a third lens and passing a portion where negative chirp occurs to compress the optical signal pulse,
The external resonator and the external modulator, characterized in that the spatially separated, externally modulated optical transmitter.
delete delete delete According to claim 1,
The external resonator, separated external modulated light, characterized in that it further comprises an etalon for stabilizing the resonant optical signal between the tunable filter and the partial reflection mirror or between the first lens and the tunable filter transmitter.
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