RU2255363C1 - Optical receiver - Google Patents

Abstract

FIELD: fiber-optical information transfer systems.

SUBSTANCE: optical signal comes from fiber line along core of fiber light guide, reflects from slanted cut of end of fiber light guide, passes through optical transparent substance, gets to receiving surface of optical receiving element. Optical signal is not reflected from limit of between cover of fiber light guide and optical transparent substance. Fiber light guide is turned for an angle, excluding normal falling of beams on surface of optical receiving element.

EFFECT: simplified construction, higher efficiency, higher precision.

4 dwg

Description

The invention relates to devices for fiber-optic information transmission systems (FOSPI), in particular to photodetector modules, and can be used to create photodetector modules with radiation input using a fiber optic fiber.

When creating photodetector modules for VOSPI, special requirements are imposed on the extremely low level of the part of radiation coming back from the VOSPI line reflected back into the fiber waveguide.

To reduce the level of the reflected signal, the photodetector is installed in front of the fiber optic fiber at an angle so that the rays reflected from the photodetector do not fall back into the fiber (see DE No. 4445997, MKI G 02 B 6/163, publ. 27.12.95). In such a device, a photodetector mounted on an intermediate board with leads is located on the surface of the carrier board (metal or ceramic).

The disadvantages of this device are the impossibility of creating a planar design of a photodetector module for ultra-high-speed FOSP (over 2 GHz) in a small-sized version. In this design, the photodetector element is placed on the board perpendicular to its surface, in such cases it is necessary to install the board together with the photodetector element located on it perpendicularly or almost perpendicularly to the axis of the fiber. This leads to an increase in the overall dimensions of the photodetector module, to a significant complication of the process of attaching the leads to the board pads inside the case.

These disadvantages are partially eliminated in a device for coupling a fiber to an optical component (see DE No. 4445997, MKI G 02 6/163, publ. 27.12.95), which proposes a device for at least one fiber with one optical component . In this case, the light guide fiber and the optical component are located on opposite sides of the optically transparent holder, and the optical axis of the light guide fiber runs parallel to this holder. In the region of the optical axis there is a device for deflecting light rays, which provides a deviation of the light beam from the light guide fiber to the optical component. The device deflecting light rays is formed by the alignment structure of the light guide fiber.

The disadvantages of this device are:

- the difficulty of obtaining a high-quality device deflecting light rays by one of the methods of “wet” or “dry” etching, with a given angle of inclination;

- light rays reflected from the optical component, in this case from the photodetector element, can partially return to the light guide fiber;

- light rays emerging from the light guide fiber and reflected from the deflection device fall onto the surface of the optically transparent holder, partially reflect from its (holder) surfaces and return to the light guide fiber;

- the use of an additional transparent holder increases the distance between the end face of the light guide fiber and the optical component, which either leads to a significant blurring of the light spot formed from the rays emanating from the light guide fiber and the loss of part of the useful signal, or an increase in the size of the optical component is required, which may lead to poor performance, for example, an increase in the electrical capacitance of the optical component.

In another communication device and a method for introducing radiation into an optical fiber (see EP No. 689071, MKI G 02 B 6/42), a device for introducing a light beam transmitted through an optical fiber into an electro-optical element, for example a photodetector, hybrid integrated circuit is proposed (GIS), which is placed in the enclosure. The method involves removing the sheath from the fiber, splitting it at an angle of 45 ° and creating a mirror at the end of the fiber. The mirror deflects the light beam laterally so that it exits through the sheath of the fiber. The mirror can be obtained by silvering the end face or applying a dielectric coating on it.

In the housing cover covering the electro-optical element, a window is made transparent in a given spectral range. The fiber optic was fixed on the upper surface of the lid so that the reflecting end was above the window, opposite the electro-optical element of the GIS. The method allows you to refuse to use the tip of the fiber, and also allows for heat treatment and control of the GIS module before attaching the fiber.

The disadvantages of this device are the presence of optical reflections from the interface between the fiber sheath and the air, which are reflected by the cylindrical surface of the sheath back to the core of the fiber, as well as the relative complexity of applying reflective coatings to the end of the fiber.

The invention consists in the following. The problem to which the claimed technical solution is directed is to eliminate the reasons for the reflection of the optical signal back to the core of the fiber, as well as to simplify the manufacturing technology of the oblique cut of the end of the fiber.

These technical results are achieved by the fact that in an optical receiving device including an optical receiving element, for example a photodiode, a fiber optic fiber containing a sheath and a core, with an output end having the form of an oblique cut located above the optical receiving element and optically connected to the optical receiving element, the oblique section of the output end of the fiber is made at an angle of total internal reflection for the interface between the core of the fiber - air, and between the fibers The optical fiber and the optical receiving element comprise a substance transparent to optical radiation, the refractive index of which is equal to or close to the refractive index of the sheath of the optical fiber, the optical fiber being positioned above the optical receiving element so that the optical radiation emerging from the optical fiber is incident on the receiving surface of the optical receiving element at an angle at which the rays reflected from the optical receiving element did not fall back into the core of the fiber fiber optic cable.

The optical receiving element is positioned planarly on the circuit board, which, in turn, is positioned planarly inside the flat case with its terminals and fiber optic fiber. The oblique cut of the end of the fiber is formed by one of the available methods (chipping, grinding and polishing, etc.), and the angle at which the oblique cut is made is selected so that the output optical signal beam reflected from the fiber optic sheath does not fall back into the core of the fiber. Due to the fact that this angle is equal to or close to the angle of total internal reflection at the interface between the core of the optical fiber and the air, there is no need to apply reflective coatings. In order to eliminate reflection from the fiber-optical fiber cladding interface — air and reduce reflection from the optical receiving element, a substance transparent to optical radiation is placed between the optical fiber and the optical receiving element, the refractive index of which is equal to or close to the refractive index of the optical fiber cladding.

New in the claimed device are:

- oblique section of the fiber is made at an angle equal to or close to the angle of total internal reflection, which eliminates the use of additional reflective coatings;

- to eliminate reflections from the interface between the fiber optic sheath — air and reduce reflections from the air — interface, a transparent optical material, for example optical glue, is placed between the optical fiber and the optical receiving element;

- in order for the radiation exiting from the optical fiber to fall onto the optical receiving element at an angle, the optical fiber with an oblique cut of the end face is turned around the axis by an angle sufficient so that the radiation rays reflected from the optical receiving element do not fall into the fiber core optical fiber.

The essence of the technical solution is illustrated by graphic materials, a description and an example of a specific implementation.

Figure 1 shows the oblique cut of the end of the fiber and the path of the rays: S - incident from the core of the fiber to the oblique cut; Re is the beam reflected from the cut; Ro is the beam reflected from the shell; T - transmitted (useful) beam; α is the angle of oblique cut; β is the angle between the transmitted beam T and the normal N _o to the cladding of the fiber; Nc is the normal to the oblique cut of the end of the fiber.

Figure 2 shows a General view of the device for a special case, in which the receiving platform of the optical receiving element is located on the edge of the optical receiving element closest to the fiber waveguide.

Figure 3 shows a General view of the device for another special case, when the receiving area of the optical receiving element is located on its opposite side, in which the radiation reaches the receiving area through the substrate of the optical receiving element.

Figure 4 presents the characteristics of the photodetector module using technical solutions.

Figure 1-4 adopted the following notation:

1 - fiber light guide

2 - sheath of a fiber light guide,

3 - the core of the optical fiber,

4 - oblique cut end of the fiber,

5 - optical receiving device,

6 - optical receiving element,

7 - a transparent substance,

8 - the receiving platform of the optical receiving element 6.

The optical receiving device 6 contains, for example, a single-mode optical fiber 1 made of quartz, cut off, for example, at an angle of total internal reflection of the light guide core of the optical fiber 3. The optical receiving element 6 is made of semiconductor compounds based on silicon or gallium arsenide, or another compound. An optically transparent substance 7, for example optical glue, is located between the optical fiber 1 and the optical receiving element 6, for example a photodiode.

The device operates as follows.

The optical signal S coming from the fiber line through the core 3 of the optical fiber 1 is reflected from the oblique cut of the end face 4 of the optical fiber 1 and, passing through the optical transparent substance 7, enters the receiving surface 8 of the optical receiving element 6, causing a photocurrent in the optical receiving element circuit . The optical signal is not reflected from the interface ″ sheath 2 of the optical fiber - optical transparent substance 7 ″, i.e. R _o is equal to or close to zero if their refractive indices are chosen equal or close in value. A part of the optical signal is reflected from the optical receiving element 6 if the refractive index of the optical receiving element is greater than that of the optically transparent substance 7. To eliminate the possibility of a part of the optical signal returning to the core of the optical fiber, the optical fiber is rotated around its axis by an angle φ, eliminating normal incidence of rays to the surface of the optical receiving element.

Concrete example

The proposed device is implemented to create a photodetector module, in which a photodiode based on an indium-gallium-phosphorus-arsenic compound with a receiving area of 70 micrometers, a single-mode fiber optic fiber, the cladding and core of which is made of quartz, the end face is used as an optical receiving element which was cut and polished at an angle of 41 ° -43 °, optical glue with a refractive index of n = 1.516 was used as a transparent optical substance, and the angle φ was 5 ... 10 angular degrees.

The use of this technical solution allowed to significantly reduce the value of the signal returning from the fiber line back-reflected into the fiber waveguide from -22 to - 45dB (Fig. 4).

Claims (1)

An optical receiving device including an optical receiving element, a fiber light guide comprising a sheath and a core with an output end having the form of an oblique slice located above the optical receiving element and optically coupled to it, characterized in that the oblique section of the output end of the optical fiber is made at an angle of full internal reflection for the interface between the core of the fiber and the optical fiber is air, while a transparent optical interface is located between the optical fiber and the optical receiving element radiation, a substance whose refractive index is equal to or close to the refractive index of the cladding of the optical fiber, the optical fiber being thus positioned above the optical receiving element so that the optical radiation emerging from the optical fiber is incident on the receiving surface of the optical receiving element at an angle at which reflected from the optical the receiving element, the rays of the incident radiation did not fall back into the core of the fiber.

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