GB2301249A

GB2301249A - Optical transceiver

Info

Publication number: GB2301249A
Application number: GB9610932A
Authority: GB
Inventors: Heinrich Hauer; Albrecht Kuke; Eberhard Moess
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1995-05-24
Filing date: 1996-05-24
Publication date: 1996-11-27
Also published as: FR2734678A1; GB9610932D0; DE29508660U1

Abstract

A transmitter S and receiver E are connected to a bidirectional optical fibre UF by a wavelength-independent fusible coupler K. Transmitted and received light are at different frequencies. A filter F is placed between the coupler K and receiver E, and optionally between the transmitter S and the coupler K as well. The filter F is in the form of a thin film Fo with a filter layer Fi inserted into the fibre at a slight angle between two couplers S1, S2; this transmits light at one frequency whilst reflecting light at the other frequency into the surrounding space.

Description

Optical transmitting and receiving arrangement Prior art The invention relates to an optical transmitting and receiving arrangement for bidirectional optical transmission systems with wavelength multiplex on a transmission fibre, with an optical coupler, a transmitter, a receiver and a wavelengthselective filter, wherein a first connection of the coupler is connected to the transmission fibre, a second connection to the transmitter and a third-connection of the coupler to the receiver via the wavelength-selective filter.

From B. Hillerich et al., "Duplexer with Hybrid Integrated Light Emitter and Detector", Conf. Proc. 10th ECOC, Stuttgart, 1984, pages 166 to 167 an optical transmitting and receiving arrangement is known which contains a light transmitter, a light receiver, two spherical lenses and a wavelengthselective edge filter for separating the transmitted and received light, a received light waveguide with a further wavelength-selective filter and a bidirectionally operated transmission optical waveguide. The optical structural elements of the arrangement described must be adjusted with respect to one another very accurately. Furthermore, the optical transmitting and receiving arrangement has high reflection losses because of the many optical structural elements that are used.

An optical transmitting and receiving arrangement is proposed which can be constructed from individual components that are commercially available and inexpensive. Construction can be effected without additional outlay on adjustment. The optical transmitting and receiving arrangement is designed as a wavelength-selective duplexer which has high crosstalk attenuation. The optical transmitting and receiving arrangement is distinguished in that the power that is transmitted on the transmission fibre can be determined via the coupling ratio.

The duplexer is suitable for being constructed with singlemode fibres.

The following individual components are used to construct the optical transmitting and receiving arrangement: a connector pair with inclined faces, preferably 80, a non-wavelengthselective fibre coupler, a ready-made solid-state laser with fibre pigtail, a ready-made photodiode with fibre pigtail, a filter film for transmission of the received light and reflection of the transmitted light at an angle of incidence of 80.

An embodiment of the invention will be described with the aid of the drawings which are as follows: Fig. 1 shows the assembly of individual components into a wavelength-selective duplexer and Fig. 2 shows a connector pair with inclined optical fibre end surfaces and filter film.

Fig. 1 shows a non-wavelength-selective coupler K, a fusible coupler for example, with the connections 1 to 4. The division ratio of the coupler K can be either 1:2 or asymmetrical. A transmitter S, comprising a solid-state laser with a fibre pigtail, is connected at connection 1. The transmitter S emits light with the wavelength X1 which passes through the coupler K. The portion t is coupled into the connection 3 of the coupler K and the portion (l-t) into the connection 4 of the coupler K. Connection 4 is a blank connection and terminates to air for example. The transmission fibre UF which receives the transmission wavelength X1 is coupled to connection 3 of the coupler K.

From the transmission fibre UF comes the received signal with the wavelength A2 which is distributed to the connections 1 and 2 with the powers t and (l-t) in the coupler. The portion (l-t) reaches the received branch at connection 2 in the form of wanted signal. It passes through a filter F there and reaches a receiver E. The receiver E is formed of the readymade photodiode with pigtail. The filter F is between two optical fibre connectors with inclined face. The arrangement with the optical fibre connectors is shown in detail in Fig.

2. Two optical fibre connectors S1 and S2 are jointly guided in a sleeve B. A thin film F,, which has a filter layer Fi on one side which allows the wavelength X2 to pass and reflects the wavelengths X1, is clamped between the connectors S1 and S2. The normal of the connector faces and hence also the film clamped in between is inclined at an angle 6 with respect to the connector axis. The angle 6 is selected in such a way that the reflected light of wavelength Al can no longer be guided in the fibre. An angle of 80 is sufficient for this purpose with standard single-mode fibres.The purpose of the filter is to keep the light coming from the transmitter S, which is reflected at the blank connection 4 or at splices or connectors on the transmission fibre or at connection 3, away from the receiver E and hence to increase the crosstalk attenuation. Commercially available filter films have a nonpass attenuation of 40 dB. If the blank connection 4 terminates to air, for example, a portion of - 14 dB will be reflected. The light coming from the transmitter must pass through the coupler K twice before it can reach the received branch. With a distribution ratio of 1:2 corresponding to 3 dB, in this case a further 6 dB are added to the crosstalk attenuation. In total, therefore, there is a crosstalk attenuation of (40 + 14 + 2 x 3) dB = 60 dB, which could be further increased by terminating the blank connection 3.

The light of wavelength X2 can also reach the transmitter S via the coupler K. As it has a different wavelength from the transmitted light, however, the transmitting laser is not disturbed by the incident light. If the wavelengths X1 and X2 are so close together that the transmitting laser is disturbed by the wavelength A2, a second filter which is arranged between two connectors can be introduced in front of the transmitter at connection 1.

It is a frequent requirement in practice that the light level in the transmission fibre may not exceed a specified level, - 6 dBm in Germany, for safety reasons, which can cause problems when coupling the transmitting laser because the transmitted light coupled into the fibre has a higher power.

In this case it is advantageous to select an asymmetrical coupling ratio which correspondingly benefits the received power.

Claims

1. Optical transmitting and receiving arrangement for bidirectional optical transmission systems with wavelength multiplex on a transmission fibre (us), with an optical coupler (K), a transmitter (S), a receiver (E) and a wavelength-selective filter (F), wherein one connection of the coupler (K) is connected to the transmission fibre (ijF), a second connection to the transmitter (S) and a third connection of the coupler (K) to the receiver (E) via the wavelength-selective filter (F), characterized in that a fibre coupler is used as coupler (K), that a connector pair with inclined optical fibre end surfaces is arranged between coupler (K) and receiver (E) and that a film is arranged as wavelength-selective filter (F) between the inclined optical fibre end surfaces of the connectors.

2. Optical transmitting and receiving arrangement according to Claim 1, characterized in that a wavelength-independent fusible coupler is used as coupler (K).

3. Optical transmitting and receiving arrangement according to one of Claims 1 or 2, characterized in that a connector pair with inclined optical fibre end surfaces is arranged between the coupler (K) and the transmitter (S) and that a film is arranged as wavelength-selective filter between the inclined optical fibre end surfaces of the connectors.

4. An optical transmitting and receiving arrangement substantially as herein described with reference to the accompanying drawing.