OPTICAL SPACE TRANSMISSION APPARATUS

Abstract: An optical transmission system (6,7) includes an information transmitting light emitting device (5) and an optical transmission fibre (7), an information receiving photoreceptor (9), an optical system (4) and a transmission/reception lens (3). The end portion (7a) of the optical transmission fibre (7) is positioned near the focal plane of the transmission/reception lens (3) and and on the optical axis of this lens (3), so that the transmission light emitted from the light emitting device (5) is transmitted into an optical space transmission line (8) through the optical transmission system (6,7) and through the lens (3). The reception light transmitted through the line (8) is projected into the information receiving photoreceptor (9) through the transmission/reception lens (3) and through the optical reception system 84). The transmission light and the reception light are spatially separated near the portion (7a) of the optical transmission fibre (7).

Description: TECHNICAL FIELD The present invention relates to a transceiver which can optically transmit and receive information which propagates in space. BACKGROUND ART A transceiver having the features of the preamble of claim 1 is known from an article of R. M. Hillyer et al., as published in Navy Technical Disclosure Bulletin, Vol. 1, No. 3, July 1976, pages 19 - 22 with the title "Increased Efficiency Fiber Optic Coupled, Optical Transceivers". The transceiver described there comprises optical fibers in its optical transmission system as well as in its optical reception system. These fibers are bundled, and the end face of said bundle is positioned on or near the focal plane of the common lense and on or near its optical axis. It is cumbersome to bundle these different fibers or, vice versa, to separate the different fibers from the bundle. DISCLOSURE OF THE INVENTION It is the object of the present invention to provide a transceiver having simple construction. The transceiver of the present invention is defined by the teaching of claim 1 as enclosed. This transceiver comprises an optical fiber only in its transmission system, and not in its reception system. Therefore, it is obviously no longer necessary to distinguish fibers for the transmission system and the reception system within a bundle of fibers. BRIEF DESCRIPTION OF DRAWINGS Fig. 1 is a diagram showing a first embodiment of a transceiver according to the present invention; Fig. 2 is a perspective view illustrated a supporting member for the optical fiber in a transceiver similar to the transceiver according to the diagram of Fig. 1; and Fig. 3 is a diagram showing a transceiver having a further lense between a common lense and the end of the transmission fiber. BEST MODE FOR CARRYING OUT THE INVENTION The components of the transceiver of Fig. 1 are incorporated within a mirror cylinder which is however not shown. Reference numeral 11 designates an optical transparent plate which is used to split the transmission light and the reception light and is positioned on the optical axis of a common transmission/reception lense (for example with a diameter of 145 mm) 3 and a reception lens 4, and within the focal plane remote from the transmission/reception common lens 3 by the distance of about 100 mm to 300 mm. This transparent plate 11 has a through-hole 11A bored through its center, and one end of an optical transmission fiber 13 is engaged into the through-hole 11A and supported therein. The optical transmission fiber 13 is pulled to the outside so as to cross the optical path along which the reception light L2 travelling through the transparent plate 11 travels toward the reception lens 4. Reference numeral 13A designates a protective film of the optical transmission fiber 13. This protective film is removed from the optical transmission fiber at its portion crossing the optical path through which the reception light L2 passes to make its outer diameter thin so that the travel of the reception light L2 is not disturbed as much as possible. In this connection, while the diameter of the beam spot of the reception light L2 incident on the transparent plate 11 is about 1 mm, the outer diameter of the protective film 13A of the optical transmission fiber 13 is 0.9 mm and the outer diameter of the cladding portion is 0.125 mm. Thus, when the protective film 13A is removed from the optical transmission fiber 13, the efficiency with which the reception light L2 is introducd into the light receiving element 9 can be increased considerably. The operation of this transceiver will be described subsequently. The transmission light (diverging light) L1 from the optical information light emitting element 5 is converged by the transmission lens 6, introduced into the other end face of the optical transmission fiber 13 and then emitted from its one end face, i.e., the transparent plate 11 toward the transmission/reception common lens 3 in a diverging fashion. The thus diverged transmission light L1 is substantially collimated by the transmission/reception common lens 3, transmitted to the optical space transmission line 8 and received by the transceiver at the reception side. The substantially parallel reception light L2 transmitted from the transceiver at the reception side and transmitted through the optical space transmission line 8 is introduced into the transmission/reception common lens 3, in which it is converged, focused on the transparent plate 11 and then diverged. The thus diverged reception light L2 is introduced into the reception lens 4, in which it is converged and then introduced into the light receiving element 9 so as to be focused thereon. The reception light L2 incident on the light receiving element 9 is therein converted into an electrical signal. According to the above transceiver, the transmission/reception common lens 3 can be used common to the transmission light L1 and the reception light L2 so that the apparatus can be simplified in arrangement. Besides, even though the transmission/reception common lens 3 is used common, a light loss produced when the optical axes are separated is very small. Further, since the light emitting element 5 and the light receiving element 9 can be positioned with a large freedom, the mutual light-shielding effect can prevent the S/N ratio of the transmission light L1 and the reception light L2 from being lowered by the stray light. Since the transmission light and the reception light are splitted by the transparent plate 11, the arrangement of the apparatus can be simplified more, and the assembly work of the apparatus and the maintenance work thereof can be performed with greater ease. Furthermore, the reception light L2 can be effectively introduced into the light receiving element 9 by the transparent plate 11. In addition, the transmission light 12 can be effectively transmitted into the optical space transmission line 8 by means of the optical transmission fiber 13 engaged into the through-hole 11A of the transparent plate 11. While in the transceiver of Fig. 1 the optical transmission fiber 13 is engaged with the through-hole 11A of the transparent plate 11 and then supported thereby, such a variation is possible in which the transparent plate 11 as the supporting member in Fig. 1 is replaced with a circular ring 21 on which are formed three transparent or opaque support members 22 extending toward the central portion of the circular ring, an engaging portion 23 is formed at an intersection portion thereof and the end portion of the optical transmission fiber 13 is engaged with the engaging portion 23 and then supported thereby as in a second embodiment shown in Fig. 2. The supporting member of any shape and structure may be used if only it can secure the end portion of the optical transmission fiber 13 at a predetermined position. In the transceiver of Fig. 1, if the transmission light L1 from the light emitting element 5 is introduced into the optical transmission fiber 13 with sufficient energy, the transmission lens 6 may be omitted. The respective embodiments of Figs. 1 and 2 have the following problems. That is, in order to transmit the transmission light L1 as distant as possible, the parallelism of the transmission light L1 emitted from the transmission/reception common lens 3 must be made high. To this end, as described above, the transmission/reception common lens 3 must be in the form of, for example, an aspherical lens to reduce the spherical aberration with the result that the parallel reception light L2 introduced into the transmission/reception common lens 3 from the optical space transmission line 8 is focused to form a very small beam spot. By the transparent plate 11 in Fig. 1, in order to effectively introduce the reception light L2 into the light receiving element 9, the NA of the transmission/reception common lens 3 must be reduced as much as possible thereby to make the reception light L1 form a beam spot as large as possible on its focal point such that the reception light L2 must be protected from the end portion of the optical transmission fiber 7 or 13. However, this increases the length of the optical path of the optical system through which the reception light L1 passes and makes the apparatus large in size. A third embodiment which can improve these shortcomings will be described with reference to Fig. 3. In Fig. 3, like parts corresponding to those of Fig. 1 are marked with the same references and the overlapping explanation therefor will be omitted. The mirror cylinder in which the optical system is accommodated is not shown and described. The transceiver in Fig. 3 is different from the transceiver in Fig. 1 in that a convex lens 14 is positioned between the transmission/reception common lens 3 and the transparent plate 11. Each of the transmission/reception common lens (diameter is 145 mm) 3 and the lens 14 is the aspherical lens having a small spherical aberration. The transmission/reception common lens 3, the lens 14, the transparent plate 11 and the reception lens 4 are positioned with their optical axes coincident. The lens 14 is used to form a conjugate point P2 of a focal point P1 of the transmission/reception common lens 3, and the transparent plate 11 is positioned at this conjugate point P2. The lenses 3 and 14 constitute a transmission/reception common lens formed of a compound lens. Further, the location of the lens 14 is determined such that the size (for example, the diameter thereof is about 400 µm) of the beam spot of the reception light L2 at the conjugate point P2 may become larger than the size (for example, the diameter thereof is about 100 µm) of the beam spot of the reception light L2 at the focal point P1. In this case, the NA (numerical aperture) of the transmission/reception common lens 3 is presented as 0.4 (= refractive index x sin 23.6°) on the left side of the drawing so that the NA of the lens 14 is presented as 0.4 on the right side of the drawing, while the NA of the lens 14 is presented as 0.1 (= refractive index x sin 5.7°) on the left side of the drawing. Furthermore, the optical transmission fiber 13 which introduces the transmission light from the light emitting element 5 into the transparent plate 11 is a single mode fiber (diameter of core is 6 µm and NA is 0.1) and the diameter of the cladding portion is 125 µm in this embodiment. The end face of the optical transmission fiber at its portion where the protective film 13A is removed is bonded to the center of the transparent plate 11 at its side opposing the reception lens 4. In this case, as shown in Fig. 1, the end face of the optical transmission fiber may be engaged into a through-hole bored through the center of the transparent plate 11. The degree in which the reception light L2 is disturbed at the conjugate point P2 by the optical transmission fiber 13 is very small as is expressed as (125 ÷ 400)² = 0.097 This can be neglected in practice. The operation of this optical space transmission apparatus will be described next. The transmission light (diverging light) L1 from the optical information transmission light emitting element 5 is converged by the transmission lens 6 and introduced into the other end face of the optical transmission fiber 13 to be guided. Then, this light is emitted from one end face thereof, i.e., the transparent plate 11 as a beam spot of a nearly point source and then is diverged toward the lens 14. The diverged transmission light L1 therefrom is converged by the lens 14, focused at the focal point P1 of the transmission/reception common lens 3, then diverged and introduced into the transmission/reception common lens 3, whereby it is collimated to substantially a parallel light and emitted to the optical space transmission line 8 to be transmitted. The thus transmitted light is received by the transceiver at the reception side. Further, the reception light L2 of substantially parallel light transmitted from the transceiver at the reception side and travelling through the optical space transmission line 8 is introduced into the transmission/reception common lens 3, in which it is converged, focused at the focal point P1 and then diverged to be introduced into the lens 14. The converged reception light L2 from the lens 14 is focused on the conjugate point P2, i.e., the transparent plate 11 so as to enclose the beam spot of the transmission light L2 emitted from the optical fiber 13 and then diverged. This diverged reception light L2 is made incident on the reception lens 4, converged thereby and then introduced to the light receiving element 9 to be focussed thereon. Then, the reception light L2 introduced into the light receiving element 9 is therein converted into an electrical signal. According to the above-mentioned transceiver, the transmission/reception common lens 3 can be made common to the transmission light L1 and the reception light L2 so that the apparatus can be simplified in arrangement. Besides, though the lens 3 is used common to the light transmission and the light reception, a light loss caused when the optical axes are separated is very small. Also, since the light emitting element 5 and the light receiving element 9 are located with a large freedom, the mutual light-shielding effect can prevent the S/N ratio of the transmission light L1 and the reception light L2 from being lowered by the stray light. Further, Since the transmission light and the reception light are splitted by the transparent plate 11, the apparatus can be simplified in arrangement and the assembly work of the apparatus and the maintenance work thereof can be performed with ease. Furthermore, since the lens 14 is provided to form the conjugate point P2 of the focal point P1 of the transmission/reception common lens 3, the apparatus of this embodiment has the following advantages. That is, in order to transmit the transmission light L1 as distant as possible, the parallelism of the light emitted from the transmission/reception common lens 3 must be made high. To this end, the transmission/reception common lens 3 must be formed as, for example, the aspherical lens to reduce its spherical aberration. If so, the parallel reception light L2 introduced from the optical space transmission line 8 into the transmission/reception common lens 3 is focused at the focal point P1 so as to form a very small beam spot. Further, if a lens having a large NA is used as the transmission/reception common lens 3, its focal point P1 approaches the transmission/reception common lens 3 so that the apparatus can be made compact in size in practice. When the beam spot that the reception light L1 forms at the focal point P1 is enlarged by the lens 14 and formed on the transparent plate 11 which is used to split the transmission and reception lights, the reception light L2 can be effectively introduced into the light receiving element 9 by the transparent plate 11. Further, the transmission light L2 can be effectively transmitted into the optical space transmission line 8 by the optical transmission fiber 13 fixed to the transparent plate 11. Furthermore, if the transmission light L1 from the light receiving element 5 is introduced into the optical transmission fiber 13 with a sufficient energy, the transmission lens 6 therefor may be omitted. In addition, also in the embodiment of Fig. 3, the transparent plate 11 can be replaced with the supporting member shown in Fig. 2. According to the present iunvention, as set forth above, it is possible to obtain the optical space transmission apparatus of simple arrangement which can increase the transmission efficiency and S/N ratio of the transmission light and the reception light.

Claims: Transceiver comprising: an optical transmission system (5, 13, 3); an optical reception system (3, 4, 9); a lens (3) common to both the optical transmission system and the optical reception system; said optical transmission system (5, 13, 3) comprising besides said common lens -- an information transmitting light emitting element (5) and -- an optical transmission fiber (13), an end face of said optical transmission fiber being positioned on or near the focal plane of said common lens and on or near its optical axis; and said optical reception system (3, 4, 9) having an information receiving light detecting element (9) besides said common lens; characterized in that said optical reception system comprises another lens (4) between its information receiving light detecting element (5) and said common lens (3); and a means (11; 21) is provided for holding said end of said fiber (13) in position intermediate said common lens (3) and said lens (4) within said optical reception system. A transceiver according to claim 1, characterized in that said means for holding said end of said fiber is a transparent plate (11). A transceiver according to claim 1, characterized in that said means for holding said end of said fiber is a circular ring (23) having support members (22) for holding an engaging portion (23) in its middle, said engaging portion holding said end of said fiber (13). A transceiver according to one of the preceding claims, characterized by a further lens (14) which is arranged between said common lens (3) and said means (11; 21) for holding said end of said fiber. A transceiver according to one of the preceding claims, characterized by a an additional lens (6) arranged between said information transmitting light emitting element (5) and said fiber (13) for focussing the light from said element into said fiber.

Inventors: ITO YUJIRO, ITO, YUJIRO
Applicants: SONY CORP, SONY CORPORATION
Application year: 1988
Main classification: G02B6
IPC codes: H04B10, G02B6, G02B27