KR20160027747A - Single Wavelength Bi-directional Optical Sub-Assembly - Google Patents

Abstract

The present invention relates to a single wavelength bidirectional optical subassembly for reducing 6 dB optical loss generated in an existing structure using a 3 dB splitting filter. A concave lens is inserted between a laser diode and an optical fiber to reduce a numerical aperture of light incident on the optical fiber from the laser diode and, on the contrary, increase the numerical aperture of light incident on a photodiode from the optical fiber. A mirror with a hole, through which a laser diode beam can pass, is used to focus the laser diode beam on the optical fiber without loss and enable maximum light to be incident on the photodiode at the same time, thereby reducing optical loss to 2 dB or less. The single wavelength bidirectional optical subassembly according to the present invention can be miniaturized to be mounted on an existing small form factor pluggable (SFP) optical transceiver module, can maintain optical isolation between a light transmitting unit and a light receiving unit without a special device, and can reduce the optical loss and lower the price than before by using a focusing beam.

Description

Single-wavelength bidirectional optical transmission / reception module (Single-Wavelength Bi-directional Optical Sub-Assembly)

The present invention relates to a short wavelength bidirectional optical transmission / reception module, and more particularly, to an optical transmission / reception module structure using a conventional 3dB splitting filter, a structure using a reflector and a concave lens Wavelength bidirectional optical transmission / reception module that realizes downsizing and cost reduction by reducing the total loss to 2.0 dB or less and using existing components as they are.

In the field of optical communication, there have been many cases in which two optical fibers are used or two wavelengths are bi-directionally transmitted by one optical fiber.

However, at present, the structure using a single wavelength for one optical fiber is increasing due to the low cost and simplicity of use, and this trend will continue in the future.

However, there is no problem in the link power budget of the existing optical communication network, but as the optical transmission / reception module speeds up from 1.25 Gbps to 10 Gbps and the transmission distance is increased from 10 km to 40 km and 80 km, Reducing optical loss is the core of technology.

A conventional short wavelength bidirectional optical transceiver module is shown in Fig.

Referring to FIG. 1, a conventional bidirectional optical T / R module uses a 3-dB splitting filter, and 50% light passes through an optical fiber 60 while passing through a splitting filter 40, And the remaining 50% is reflected.

Also, the light output from the optical fiber 60 and incident on the photodiode 80 passes through the 3-dB spiral filter as in the case of the laser diode, and only 50% of the transmitted light enters the light receiving element. The remaining 50% A light loss of 6 dB is generated in the optical network using the optical transmission / reception module of FIG.

Also, since the scattered light reflected from the 3 dB splitting filter 40 in the optical transmission / reception module penetrates into the photodiode 80 and causes an optical cross-talk phenomenon that is distorted with the optical signal of the laser diode 10, A device for optical isolation using a structure is needed.

U.S. Patent US20120148257A1 is a short wavelength bidirectional optical transceiver module.

US Patent No. 7039278B1 is a structure that compensates for the loss of 6 dB caused by the structure of the bidirectional optical transmission / reception module using such a 3-dB splitting filter. In the structure using the function of an optical circulator, The beam that is focused by the fiber and conversely output from the optical fiber has a structure in which the whole beam is focused by the photodiode while passing through the circulator.

Although the optical loss is 1dB using the optocoupler compared to the structure using the 3dB splitting filter, it has a complicated structure using expensive parts such as Faraday rotator, Birefringence wedge, and magnet constituting the broadcaster, The cost of modifying the output beam into a collimating beam is low and the cost competitiveness of the overall module manufacturing is low. Moreover, since the size of the optical circulator can not be miniaturized, it is mounted on a small form factor case There is a disadvantage that it can not do.

US Pat. No. 5,848,203 discloses the concept of an optical isolator using two GRIN lenses (Graded Index lenses) having different Gaussian beam diameters. Although a bidirectional optical transceiver module using the present invention can be tried, an optical system that couples a beam output from a conventional laser diode to a GRIN lens via a focusing lens is used, and another GRIN lens is used for the optical fiber High cost parts are required in accordance with the manufacturing cost, and high accuracy is required to maintain the parallelism of parts even in manufacturing and assembling.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the conventional problems. In the present invention, in the optical transmission / reception module structure using the conventional 3dB splitting filter, optical loss of 6 dB is generated between the optical transmitter and the optical receiver. Wavelength bidirectional optical transceiver module that reduces the total loss to 2.0 dB or less and realizes downsizing and cost reduction by using existing components as they are.

     In order to solve such a problem, a short wavelength bidirectional optical T / R module according to a feature of the present invention comprises:

In the bi-directional optical T / R module,

The optical signal output from the laser diode 1 passes through the condenser lens 2 and the optical isolator 3 to form a focusing beam and passes through the aperture of the reflecting mirror 4 and the concave lens 5, The numerical aperture decreases and is finally focused on the optical fiber 6.

The optical signal output from the optical fiber 6 has an increased numerical aperture while passing through a concave lens and is converted to an optical axis at 90 degrees through the reflector and converged to a photodiode 8 through a focusing optical lens 7 .

The numerical aperture of the optical signal output from the laser diode 1 is decreased using the concave lens 5 and the numerical aperture of the optical signal outputted from the optical fiber 6 is increased.

The loss of the optical transmission / reception module can be reduced without deteriorating the optical coupling efficiency by using the optical fiber 6 in which the beam of the laser diode is inclined with respect to the concave lens 5 or the end is inclined at 6 to 8 degrees Improve.

The reflector (4) has a hole (9) inside and is characterized in that the hole (9) transmits light.

A short wavelength band of 1260 to 1610 nm is used as an input optical signal and the same wavelength band is used as an output optical signal.

In order to solve such a problem, a short wavelength bidirectional optical T / R module according to a feature of the present invention comprises:

The optical signal output from the laser diode 1 passes through the condenser lens 2 and the optical isolator 3 to form a focusing beam and the optical signal received from the optical fiber 6 is condensed by the condensing optical lens 7, Directional optical transmission / reception module having a structure in which the light is converged by the photodiode 8 through the light-

A reflector (9) having a hole (9) therein and passing only an optical signal reflected in the hole of the optical signal outputted from the optical isolator, and reflecting the remaining portion of the optical signal received by the optical fiber except for the hole (9) 4);

And a concave lens 5 for condensing the optical signal output from the reflector 4 and outputting the optical signal to the optical fiber 6, and distributing the optical signal received from the optical fiber to the reflector.

In the embodiment of the present invention, according to the short wavelength bidirectional optical T / R module with the concave lens and the reflector according to the present invention, compared with the optical loss of 6 dB generated in the structure using the existing 3dB splitting filter, Wavelength bidirectional optical transmission / reception module capable of maintaining a total loss of less than 2 dB and a coupling loss of less than 0.5 dB and a coupling loss of the light-receiving portion of less than 1.5 dB. In addition, since the optical cross-talk phenomenon of the light receiving part due to the scattered optical signal generated in the structure using the existing 3dB splitting filter is remarkably reduced, the structure for preventing optical cross-talk is not specially installed, The productivity of the modules capable of processing and the price of the modules have been reduced.

In addition, the present invention can be applied to a case where the wavelengths in both directions are different without changing a specific structure in addition to the case where a single wavelength is used. Particularly, a blocking filter is installed in front of the light receiving unit so that only a desired wavelength band is transmitted through the photodiode It can be applied to a coarse wavelength division multiplexing (CWDM), a dense wavelength division multiplexing (DWDM) bidirectional optical transmission / reception module.

1 is a schematic diagram of an optical transceiver module using a conventional 3dB spatially filtered filter.
2 is an overall schematic diagram of a short wavelength bidirectional optical T / R module with a concave lens and a reflector according to an embodiment of the present invention.
3 is a schematic diagram of a bi-directional Gaussian beam shape change using a concave lens according to an embodiment of the present invention.
FIG. 4 is a diagram showing a change in beam shape output from an optical fiber when there is no concave lens according to an embodiment of the present invention. FIG.
5 is a schematic view of a laser diode according to an embodiment of the present invention when the laser diode is inclined.
FIG. 6 is a graph showing a change in optical output according to a tilt of a laser diode when there is no concave lens according to an embodiment of the present invention.
7 is a structural view of a bidirectional optical transmission / reception module using a concave lens and a reflector as an embodiment of the present invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art can easily carry out the present invention. The present invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. In order to clearly illustrate the present invention, parts not related to the description are omitted, and similar parts are denoted by like reference characters throughout the specification.

Throughout the specification, when an element is referred to as "comprising ", it means that it can include other elements as well, without excluding other elements unless specifically stated otherwise.

2 is a configuration diagram of a short wavelength bidirectional optical T / R module with a reflector and a concave lens according to an embodiment of the present invention.

2, the short wavelength bidirectional optical transmission module having the reflector and the concave lens includes an aspheric lens 2 and an optical isolator 3 for converting the light output from the laser diode 1 into a focusing beam, A numerical aperture is reduced through the concave lens 5 after passing through a reflecting mirror 4 having a small hole through which the beam can pass and then the optical fiber is polished so that the end is inclined at 6 degrees 6) (6).

At this time, the optical fiber 6 is located on the same line as the optical axis of the laser diode 1 and the concave lens 5.

Conversely, the beam output from the optical fiber 6 passes through the concave lens 5 and then increases in the numerical aperture and is reflected on the reflector 4 positioned at an inclination of 42 degrees and focused on the photodiode 8 via the aspherical lens 7 .

A hole 9 having a diameter of 0.6 mm to 0.8 mm exists in the inside of the reflecting mirror 4 so that the beam output from the laser diode 1 can be transmitted. The beam 9 outputted from the laser diode 1 and the optical fiber 6 Of the Gaussian beam profile.

Thus, the beam of the laser diode 1 is focused on the optical fiber 6 with a loss of 0.5 dB or less, the beam output from the optical fiber 6 is condensed on the photodiode with a loss of 1.5 dB or less, It is possible to obtain a light loss of 2.0 dB or less in the module. In particular, more than 70% of the hatched portion of the beam output from the optical fiber 6 at the lower end Gaussian beam is converged to the light receiving portion, resulting in a loss of 1.5 dB.

In this process, a bidirectional optical transmission / reception module is applied to a bidirectional optical transmission / reception module without changing a specific structure except for a single wavelength. In particular, a blocking filter is installed in front of a light receiving portion to transmit only a desired wavelength band, wavelength division multiplexing (DWDM), and dense wavelength division multiplexing (DWDM) devices.

3 shows the role of the concave lens as a core part of the present invention. The beam of the laser diode 1 passing through the aspherical lens 2 has a NA of 1 / e ² (13.5% of the maximum optical power) of the Gaussian beam, 0.1, the numerical aperture decreases to 0.06 while converging to the optical fiber 6 having the numerical aperture of 0.1 while passing through the concave lens 4 having f = -6 mm (focal length). In the opposite direction, the beam having a numerical aperture of 0.1 emitted from the optical fiber 6 passes through the concave lens 4 and extends to a beam having a numerical aperture of 0.14 or more.

And the optical loss is reduced by utilizing the phenomenon that the numerical aperture decreases and increases along the lateral direction of the beam passing through the concave lens. In particular, the Gaussian beam profile of the beam outputted from the laser diode and the optical fiber 6 is schematically shown at the lower end of FIG. 3. Since the beam is overlapped with the beam output from the laser diode, the beam focused on the light receiving portion is 35% .

FIG. 4 is a graph showing a result of measuring a Gaussian beam shape after a beam output from the optical fiber of FIG. 3 passes through a concave lens. The dotted line shows the far-field pattern when there is no concave lens, and the solid line shows the far-field pattern when the concave lens is present. As a result, it can be seen that a bi-directional optical T / R module in which a Gaussian beam shape changes after a beam passes through a concave lens and loss is improved by using this phenomenon can be produced.

FIG. 5 shows a structure for changing the incident angle of the laser diode 1 beam in order to reduce the bidirectional loss of the optical transmitter and the optical receiver. The refractive index of the optical fiber 6 in the 1310 nm wavelength band is 1.467. In the case of using an optical fiber 6 whose end is polished at an inclination of 6 degrees in order to improve optical return loss, light tilted by about 2.8 degrees relative to the optical axis of the optical fiber 6 is emitted, When the end of the photo is positioned in the direction of the light receiving part, the beam is directed to the light receiving part. When the incident angle of the beam of the laser diode 1 with respect to the center axis of the concave lens 5 is tilted in the direction opposite to the light receiving unit, the optical coupling efficiency is converged to the optical fiber 6 without any significant decrease compared to the maximum value , The beam output from the optical fiber 6 is directed to the light receiving unit, passes through the reflector 4, and is focused on the light receiving unit through the aspherical lens.

FIG. 6 is a result of measuring a change in optical output power of the optical fiber 6 according to the tilt of the laser diode 1 beam in FIG. The dotted line shows the maximum coupling efficiency at 4 mW when the laser diode (1) is tilted counterclockwise to the optical fiber (6) polished at 6 degrees in the absence of the concave lens And the optical power value at -1 ° and + 7 ° is maintained at 3.5 mW.

The solid line shows the change in optical power due to incidence of the laser diode (1) beam when there is a concave lens, and shows a maximum value at + 7 ° and an optical power value of 3 mW at 0 ° and + 14 °. In this experimental result, it is possible to reduce the loss of the optical transmission module as much as possible when the laser diode 1 beam is inclined at 0 degree with respect to the central axis of the optical fiber 6, and also, So that the loss of the light receiving part can be minimized.

FIG. 7 shows an embodiment of a bidirectional optical transmission / reception module using a hole-bearing mirror and a concave lens according to the present invention, in which the laser diode 1 uses a 1550 nm DFB LD and the numerical aperture through the focusing optical lens 2 is FWHM 0.1 and the tilt of the laser diode 1 was 0 degrees with respect to the optical axis. The reflector 4 was made of an Au coated mirror having a diameter of 0.8 mm and a size of 2 mm x 2.8 mm and an anti reflection coating on the opposite side of the reflector.

The reflector is configured to maintain an angle of 42 degrees with respect to the optical axis so that the beam output from the optical fiber 6 is vertically incident on the photodiode 8. The concave lens 5 was a lens having a diameter of 3 mm and a focal length of -6 mm on both sides of which a non-reflection coated lens was used. The optical fiber 6 was a single mode fiber whose end was polished at 6 degrees, With respect to the horizontal optical axis.

The aspherical lens 7 of the photodiode 8 used a lens having a numerical aperture of 0.17 x 0.38 and the photodiode 8 used a chip having an active area diameter of 50 um. With respect to the axis of the 6-polished optical fiber 6, the laser diode was arranged to be incident at an angle of 0 degrees, designed to lie on one axis with the center of the hole inside the reflector, and designed to coincide with the center of the concave lens . At this time, the distance between the concave lens and the optical fiber 6 was maintained at 1.5 to 2 mm.

As a result of measuring the light output at room temperature through the embodiment of the present invention, when the driving current of the laser diode 1 was 25 mA, the light output was 3.0 mW. Considering that the optical output value measured at the front end of the aspherical lens of the laser diode 1 is 6 mW, the optical coupling efficiency is calculated to be about 50%. Considering that the coupling efficiency between the laser diode 1 using the conventional aspherical lens and the optical fiber 6 is about 50%, it is considered that there is almost no loss of the optical transmission module.

When 3.0 mW of light is input to the optical fiber 6, the current applied to the light receiving part is measured at 2.3 mA, and the responsivity of the light receiving part is calculated as 0.75 A / W. Ultimately, the total loss was less than 2dB, which was improved by more than 4dB over the 3dB splitting filter.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, It belongs to the scope of right.

1. Laser diode
2. Aspheric focusing lens
3. Optical isolator
4. Mirror with hole
5. Concave lens
6. Optical fiber (single mode optical fiber)
7. Aspheric focusing lens
8. Photodiode
9. Hole

Claims (7)

In the bi-directional optical T / R module,
The optical signal output from the laser diode 1 passes through the condenser lens 2 and the optical isolator 3 to form a focusing beam and passes through the aperture of the reflecting mirror 4 and the concave lens 5, Wherein the numerical aperture decreases and is finally focused on the optical fiber (6). The method according to claim 1,
The optical signal output from the optical fiber 6 increases in numerical aperture while passing through a concave lens and is converted to an optical axis at 90 degrees through the reflector and is converged to a photodiode 8 through a focusing optical lens 7 Optical transmit / receive module. 3. The method of claim 2,
Receiving module 5 using a structure in which the numerical aperture of the optical signal output from the laser diode 1 is reduced using the concave lens 5 and the numerical aperture of the optical signal output from the optical fiber 6 is increased, .
The method of claim 3,
The loss of the optical transmission / reception module can be reduced without deteriorating the optical coupling efficiency by using the optical fiber 6 in which the beam of the laser diode is inclined with respect to the concave lens 5 or the end is inclined at 6 to 8 degrees Improved optical transmit / receive module.
5. The method of claim 4,
Wherein the reflector (4) has a hole (9) therein and transmits light through the hole (9).
The method according to any one of claims 1 to 5,
Wherein the short wavelength band of 1260 to 1610 nm is used as the input optical signal and the same wavelength band is used as the output optical signal. The optical signal output from the laser diode 1 passes through the condenser lens 2 and the optical isolator 3 to form a focusing beam and the optical signal received from the optical fiber 6 is condensed by the condensing optical lens 7, Directional optical transmission / reception module having a structure in which the light is converged by the photodiode 8 through the light-
A reflector (9) having a hole (9) therein and passing only an optical signal reflected in the hole of the optical signal outputted from the optical isolator, and reflecting the remaining portion of the optical signal received by the optical fiber except for the hole (9) 4);
And a concave lens (5) for condensing the optical signal output from the reflector (4) and outputting the optical signal to the optical fiber (6), and distributing the optical signal received from the optical fiber to the reflector .

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