JPH0574048B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to an optical module for bidirectional transmission and a transmission method, and particularly relates to a bidirectional transmission optical module and a transmission method, and in particular uses one optical fiber transmission line and transmits signals in upstream and downstream directions to the transmission line. The present invention relates to an optical module that transmits optical signals of different wavelengths, and a bidirectional transmission system using the optical module.

[Background of the invention]

Analog transmission systems using semiconductor lasers (hereinafter abbreviated as LD) are used in ITV (industrial television), high-definition TV (high-precision television), and
Applications to image information transmission such as CATV (cable television) are expected.

However, in transmission systems using LDs and multimode optical fibers, there is a problem that speckle noise and speckle distortion occur due to the interference between the propagation modes due to the coherence of laser light. The limit is to keep the distance from 1 to 2 km.

On the other hand, a transmission system using a single mode optical fiber can avoid the above-mentioned speckle noise and speckle distortion, so it is expected that the transmission distance can be extended to a long distance of around 10 km.

By the way, in the application of optical fiber transmission, bidirectional transmission is essential, but bidirectional transmission in a transmission system using a single mode optical fiber has not yet been realized. The reason why bidirectional transmission is impossible is that it is difficult to realize a low-loss optical demultiplexer, and the system configuration is complicated, resulting in problems such as deterioration of transmission quality, low reliability, and high cost.

FIG. 1 is a schematic diagram of a bidirectional transmission system configured using conventional devices.

In Fig. 1, 1 and 1' are LDs, 7 and 9 are optical fibers, 11 and 11' are optical receivers, 12 and 12' are amplifiers, 13 and 13' are demodulators, and 14 and 14' are LDs.
The drive circuit 6, 6' is an optical demultiplexer.

Now, an optical signal (wavelength λ ₁ ) propagating in the direction of arrow 8 within optical fiber 7 is defined as an uplink, and an optical signal (wavelength λ ₂ ) propagating in the direction of arrow 8' is defined as a downlink.
First, in the uplink, when a signal input from the information input terminal 15 enters the LD drive circuit 14, this circuit 1
4 output signal drives LD1. By this,
LD1 oscillates at an oscillation wavelength _λ1 . The laser beam from the LD 1 enters the optical fiber 4 through the ball lens 2 and the gradient index rod lens 3 (length is approximately 1/4 pitch), propagates in the direction of the arrow 5, and is demultiplexed. receiver 11 through optical fibers 7 and 9.
incident on . Here, the incident laser light is converted into an electrical signal, which passes through an amplifier 12 and is demodulated into the original information signal by a demodulator 13. Next, in the downlink, the signal input from the information input terminal 15' enters the LD drive circuit 14', and the output of this drive circuit 14' leads to the LD.
1'. As a result, LD1' oscillates at wavelength λ ₂ . The laser beam from LD1' is transmitted through a ball lens 2', a rod lens 3' (length is approximately 1/4 pitch),
It propagates in the direction of arrow 10' in optical fiber 9' through optical fiber 4', optical demultiplexer 6', optical fiber 7, and optical demultiplexer 6, and enters optical receiver 11'. Here, the laser light is converted into an electrical signal, which is then input to an amplifier 12' and a demodulator 13', where it is demodulated into the original information signal.

In this way, the bidirectional transmission system shown in Figure 1 requires two each of optical demultiplexers 6, 6', ball lenses 2, 2', and rod lenses 3, 3', resulting in an extremely large number of devices. many. Further, it is troublesome to adjust the optical axis of each device, and there are problems in terms of low loss, high reliability, and low cost. moreover,
When the reflected light from each device is re-injected into LD1, 1', the longitudinal mode of LD1, 1' changes, which becomes mode separation noise. Therefore, reflection countermeasures for each device are required, and the configuration must be changed. becomes extremely complex.

FIG. 2 is a schematic diagram of the optical demultiplexer used in FIG. 1.

The symbols in FIG. 2 correspond to those in FIG. For the optical demultiplexer 6, the uplink is indicated by arrow 5.
The line enters at arrow 8 and exits at arrow 8, and the downlink enters at arrow 8' and exits at arrow 10'. That is, in the uplink, light with a wavelength λ ₁ propagates within the optical fiber 4 in the direction of the arrow 5, passes through the rod lens 17, enters the pentabrinism 21, and passes through the dielectric mirror 19.
It is further reflected by the interference film filter 20 and propagates through the rod lens 18 and the optical fiber 7 in the direction of the arrow 8. On the other hand, in the downlink, light with a wavelength λ ₂ propagates through the optical fiber 7 in the direction of the arrow 8', passes through the interference film filter 20, passes through the rod lens 16, and then passes through the optical fiber 9' through the arrow 10'. propagates in the direction of

In this way, light with wavelengths λ ₁ λ ₂ is demultiplexed, but since the number of devices is large and the configuration is complex, it is difficult to reduce costs and increase reliability. In addition, since it is a single mode transmission, the core diameter of the optical fiber is 10μ.
m or less, and extremely strict optical fiber positioning accuracy is required. This makes it difficult to reduce loss. Loss of optical demultiplexer itself (approximately 5 dB), LD
If the loss increases at the connections between lenses, lenses and optical fibers, optical fibers and optical demultiplexers, etc., the transmission distance will be shortened accordingly, making long-distance transmission difficult.

For the reasons mentioned above, bidirectional transmission using a single mode optical fiber has not yet been realized. Even in unidirectional transmission, the transmission distance is 5.
Only about Km has been achieved.

[Purpose of the invention]

The purpose of the present invention is to solve these conventional problems, simplify optical coupling adjustment, realize shortening of adjustment time, high coupling degree adjustment, low cost and low loss, and achieve both long-distance and long-distance adjustment. An object of the present invention is to provide an optical module for bidirectional transmission and a transmission method capable of bidirectional transmission.

[Summary of the invention]

In order to achieve the above object, an optical module for bidirectional transmission according to the present invention includes: a semiconductor optical device with a ball lens; a rod lens for coupling light emitted from the semiconductor light emitting device into a transmission optical fiber;
It consists of an optical fiber holding means arranged approximately on the central axis of the rod lens and a glass rod for extracting the monitor light, and these are integrated into a structure in which the optical fiber holding part can be adjusted in the direction of the central axis and in the rotational direction. At the same time, one or more interference film filters having desired optical characteristics are provided on the incident end side of the rod lens, and one or more interference film filters having desired optical characteristics are provided on the output end side of the optical fiber holding means, substantially on the central axis of the rod lens. and one or more optical fibers arranged around the transmission optical fiber for transmitting optical signals to be demultiplexed or multiplexed by the interference film filter. In addition, the bidirectional transmission system of the present invention is a bidirectional optical transmission system that transmits optical signals of different wavelengths in the upstream and downstream directions through a single optical fiber transmission line, in which one or more interference film filters are used. An optical module having a rod lens and an optical fiber holding part arranged therein is provided on each of the uplink and downlink transmitting sides, and the optical fiber holding part is for transmitting the optical signal passing through the interference film filter. and an optical fiber for transmitting an optical signal to be demultiplexed or multiplexed by the interference film filter, and a transmission line and a transmitting or receiving side element are connected to each optical fiber.
It is characterized by bidirectional transmission of optical signals that are larger than waves.

[Embodiments of the invention]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 3 is a block diagram of a bidirectional transmission system showing one embodiment of the present invention.

In Fig. 3, the points different from the conventional method shown in Fig. 1 are (i) a rod lens 22 with a length of about 1/4 pitch;
Interference film filters 23, 24, 28, 29 having desired optical characteristics are formed on the end face of the LD light incident side of 27, and an optical fiber holding portion 3 is formed on the opposite face.
7 and 38 and removed the optical demultiplexers 6 and 6', and two-way three-wave transmission with two uplinks and one downlink.

The uplink that propagates in the direction of the arrow 8 within the optical fiber 7 is an optical signal of two waves with wavelengths λ ₁ and λ ₂ , and is shown in the direction of the arrow 8'.
The downlink propagating in the direction is an optical signal of wavelength λ ₃ .

Of the two uplink wavelengths λ ₁ and λ ₂ , a rod lens 22 having interference film filters 23 and 24 and an optical fiber holder 37 are provided only on one transmission side, and on the other transmission side, A rod lens 32 and a ball lens 2'' are provided as in the conventional case.The receiving side of all lines has the same configuration as in the conventional case, and includes optical receivers 11, 11', 11'' and amplifiers 12, 1.
2', 12'' and demodulators 13, 13', 13''.

The interference film filter 23 has a characteristic of transmitting an optical signal of wavelength λ ₁ and reflecting optical signals of wavelengths λ ₂ and λ ₃ . The next interference film filter 24 has wavelengths λ ₁ and λ ₂
It has the property of transmitting an optical signal with a wavelength of λ 3 and reflecting an optical signal with a wavelength of λ ₃ . The other interference film filter 28
has the characteristic of transmitting optical signals with wavelengths λ ₁ and λ ₃ and reflecting optical signals with wavelength λ ₂ . Further, the interference film filter 29 has a characteristic of transmitting an optical signal of wavelength λ ₃ and reflecting optical signals of wavelengths λ ₁ and λ ₂ .
Interference film filters 23, 2 having these characteristics
4, 28, and 29 can be manufactured using conventional techniques.

Now, when an information signal is input to the input terminal 15,
LD drive circuit 14 operates to drive LD1
The laser beam (wavelength λ ₁ ) from 1 passes through the ball lens 2 and becomes parallel light, and passes through the interference film filter 23, the spacer glass 25, and the interference film filter 24.
The light propagates through the rod lens 22 and enters the optical fiber holder 37. Here, if the central axis of the rod lens 22 and the central axis of the optical fiber holder 37 are approximately aligned and the optical fiber 7 is arranged on this central axis, the optical fiber holder 37 can be moved in the axial direction (arrow 39). ).

With such adjustment, the laser beam (wavelength λ ₁ ) is focused into the transmission optical fiber 7 in the optical fiber holding part 37, transmitted through the optical fiber 7 in the direction shown by the arrow 8, and then passed through the optical fiber holding part 37. 38 and enters the rod lens 27. Here again, the optical fiber 7 is arranged approximately on the central axis of the optical fiber holding part 38 and the rod lens 27, and the optical coupling adjustment between the optical fiber holding part 38 and the rod lens 27 is performed in the direction shown by the arrow 40. Optical fiber holding section 38
This is done by adjusting the The optical signal of wavelength λ ₁ propagated through the rod lens 27 passes through the interference film filter 28 and the spacer glass 30 and enters the interference film filter 29 . Then, the optical signal (wavelength λ ₁ ) is reflected by the interference film filter 29, and the spacer glass 30 and the interference film filter 28
through the rod lens 27 in the opposite direction. Here, since the interference film filter 29 is formed with an inclined end face having an angle θ ₁ ', the position where the light is focused on the end face 31 of the rod lens 27 is shifted by an amount proportional to the angle θ ₁ '. The optical fiber is placed in a position where this reflected light signal is focused.
The optical fiber holding interval of the optical fiber holding part 38 is set in advance, and this optical fiber holding part 3
8 in the circumferential direction (indicated by arrow 42) to perform optical adjustment. In this way, the reflected optical signal (wavelength λ ₁ ) propagates within the core of the optical fiber 9 in the direction of the arrow 10, is received by the optical receiver 11 and converted into an electrical signal, and then passes through the amplifier 12 to the demodulator. 13
is demodulated to the original information signal. Here, receiver 1
1, 11', and 11'' are light receiving elements such as photodiodes, avalanche photodiodes, or light receiving elements with preamplifiers.

Next, when an information signal is input to the other input terminal 15'' of the uplink, the LD drive circuit 14'' drives the LD1'', causing the LD1'' to oscillate and output a laser beam of wavelength λ ₂ . The laser light (wavelength λ ₂ ) from the LD 1'' passes through the ball lens 2'', becomes parallel light, and enters the rod lens 32. rod lens 32
The optical signal propagated therein is focused in the optical fiber 9', propagated in the direction of the arrow 10', passes through the optical fiber holder 37, and enters the rod lens 22. The optical signal (wavelength λ ₂ ) entering the rod lens 22 passes through an interference film filter 24 and a spacer glass 25 and reaches an interference film filter 23 . The optical signal (wavelength λ ₂ ) is reflected by the interference film filter 23, passes through the spacer glass 25 and the interference film filter 24, propagates in the rod lens 22 in the opposite direction, and is transmitted to the optical fiber holder 37 for transmission. It is focused into the core of the optical fiber 7 and transmitted within the transmission optical fiber 7 in the direction of the arrow 8. Here, the angle θ ₁
is set in advance at an angle such that the optical signal of wavelength λ ₂ is reflected by the interference film filter 23 and focused into the transmission optical fiber 7 within the optical fiber holder 37 . The optical signal (wavelength λ ₂ ) transmitted in the direction of arrow 8 within the optical fiber 7 propagates within the rod lens 27 through the optical fiber holder 38 and reaches the interference film filter 28 . The optical signal (wavelength λ ₂ ) is reflected by the interference film filter 28, propagated in the opposite direction through the rod lens 27, and focused into the core of the optical fiber 35 within the optical fiber holder 38.

Here, the angle θ ₂ ' means that the optical signal of wavelength λ ₂ is reflected by the interference film filter 28 and the optical fiber holding part 3
The angle is preset so that it is focused onto the optical fiber 35 within 8. The optical signal of wavelength λ ₂ transmitted in the direction of arrow 36 within optical fiber 35 is
The light is received by a photoreceiver 11'', passes through an amplifier 12'', and is demodulated into the original information signal by a demodulator 13''.

Next, when an information signal is input to the downlink input terminal 15', the LD drive circuit 14' drives the LD1'. The laser beam (wavelength λ ₃ ) from LD 1' becomes parallel light through ball lens 2', and passes through interference film filter 2.
9, spacer glass 30, interference film filter 28
The light passes through and enters the rod lens 27. The optical signal (wavelength λ ₃ ) propagated within the rod lens 27 is focused on the transmission optical fiber 7 within the optical fiber holder 38, transmitted in the direction of arrow 8', and reroded through the optical fiber holder 37. - Inject into the lens 22. The optical signal of wavelength λ ₃ propagated through the rod lens 22 is reflected by the interference film filter 24, propagates inside the rod lens 22 in the opposite direction, and is focused into the optical fiber 33. An optical signal with a wavelength λ ₃ transmitted through the optical fiber 33 in the direction of the arrow 34 is received by the optical receiver 11' and converted into an electrical signal, then passes through the amplifier 12' and is converted into the original information signal by the demodulator 13'. is demodulated. In addition, the rod lens 22,
27 reflective end faces 26, 31, rod lens 32
Both end faces are obliquely polished. This is to prevent the reflected return optical signal from affecting the LD or photoreceiver. These end faces may further be coated with an anti-reflection coating (AR coating).

In this way, in the bidirectional optical transmission system shown in Figure 3,
The rod lens 22 for coupling the laser beam from the LD 1 into the transmission optical fiber 7 is provided with one or more interference film filters 23 and 24 having predetermined optical characteristics on the input end side. On the output end side of the rod lens 22, there is a transmission optical fiber 7 approximately on the central axis, and a demultiplexing optical fiber 33 around which transmits the optical signal demultiplexed by the interference film filters 23 and 24. Further, a multiplexing optical fiber 9' is integrally and fixedly arranged, which transmits the output light from another LD1'' having a different oscillation wavelength by introducing it into the interference film filters 23 and 24 and combining it. A holding portion 37 is provided.The rod lens 22 and the optical fiber holding portion 37, which are integrally and fixedly arranged, constitute an optical module for bidirectional transmission.

In the bidirectional optical transmission system shown in Figure 3, these optical modules are provided on the upstream and downstream sides, and one or more optical fibers are connected to these optical modules, so that different wavelengths can pass through or be reflected within this module. In this way, two-way transmission of two or more waves is performed. Therefore, the system shown in FIG. 3 can realize bidirectional transmission with a much simpler structure than that shown in FIG.

Next, the structure of the optical fiber holding parts 37 and 38 will be explained.

FIG. 4 is a diagram showing the structure of the optical fiber holding section 37 (or 38) used in FIG. 3, with FIG. 4a being a front view and FIG. 4b being a side sectional view.

The optical fiber holding parts 37 and 38 have a cylindrical configuration, and have holes 43 and 4 for inserting the optical fiber.
4,45. As is clear from FIG. 3, the hole 43 is for attaching the transmission optical fiber 7, the hole 44 is for attaching the optical fibers 9', 9, and the hole 45 is for attaching the optical fibers 33, 35. Holes 43 and 44, Holes 43 and 45
The distance between the interference film filters 23, 24, 28, and 28 provided on the inclined end surfaces of the rod lenses 24, 27 is
₂₉ , _{and is} proportional to these _angles . Also, the interval between them is
It is inversely proportional to the product of the refractive index of the rod lenses 22 and 27 and its refractive index distribution constant. As shown in FIG. 4a, the hole 43 is provided at the center axis (X-X', Y-Y' center axis) of the cylindrical upper holding parts 37, 38. Fourth
As shown in Figure b, the end face on the rod lenses 22 and 27 side has an inclination of angle θ ₄ , and the other end face is provided with a large diameter hole so that multiple optical fibers can be inserted. ing.

FIG. 5 is a front view and a side sectional view when an optical fiber is inserted into the optical fiber holder shown in FIG. 4.

One end surface (that is, the rod lens side) 46 of the optical fiber holding parts 37 and 38 is obliquely polished along with the optical fiber at an angle θ ₄ . this is,
This is to prevent the reflected light from the end face of each optical fiber from returning to the LD side, the light receiver side, or inside the optical fiber. The value of angle θ ₄ is from a fraction of a degree to 10
It is desirable that the value be set to a value within the range of up to
Normally, it is set to about 8 degrees. Further, this end face 46 may be coated with an anti-reflection coating (AR coating). Optical adjustment of the optical fiber holding parts 37 and 38 is performed by following the arrows 41 or 41'.
This is done by rotating it in the direction of. Three optical fibers 7, 9', and 33 are inserted into the right end surface, and here, the transmission optical fiber 7 is a single mode optical fiber, and the optical fibers 9', 33 are multimode optical fibers. It is used.

FIG. 6 is a diagram showing another embodiment of the optical fiber holding section used in FIG. 3, in which two optical fibers are fixed in a V-groove. FIG. 6a is a front sectional view, and FIG. 6b is a side view. As is clear from FIG. 6a, after V-grooves are formed in the semi-cylindrical members 47 and 48 and the optical fibers 7 and 33 are fixedly arranged in these V-grooves, the semi-cylindrical members 47 and 48 are brought together to form a circular shape. The optical fiber holding portion 37 is formed into a columnar shape. In this case as well, the optical fiber 7 should be placed at the center of X-X' and Y-Y'. Therefore, semi-cylindrical members 47, 48
is not divided by a plane passing through the center, and is a semi-cylindrical material 4
It passes through the center axis at the V-groove position 7.

FIG. 7 is a diagram showing still another embodiment of the optical fiber holding section shown in FIG. 6, in which three optical fibers are held in the V-groove.

In this case as well, the optical fibers 7 are X-X', Y-
It is fixedly placed at the center of Y′. Optical fiber 9', 33
For example, a lens with a large core diameter and a large outer diameter is used in order to increase the amount of optical signal sent to the light receiver, compensate for optical axis position deviation, etc.

The distances between the optical fibers 7 and 9' and between the optical fibers 7 and 33 are determined by the angles θ ₁ and θ ₂ at which the interference film filters 23 and 24 are formed. Incidentally, deviations in the spacing between the optical fibers 7 and 9' and 7 and 33 due to manufacturing errors in the angles θ ₁ and θ ₂ can be sufficiently compensated for by increasing the core diameters of the optical fibers 9' and 33. . Therefore, from then on, the optical coupling can be adjusted simply by rotating the optical fiber holder 37 in the circumferential direction 41 or 41'. In the case of FIG. 7, unlike FIG. 6, the optical fiber holding part 37 is divided into two parts on the left and right with Y-Y' as the center to form semi-cylindrical members 49 and 50, each of which has three V-grooves.
Provide one.

The reason why the V-grooves on both sides are larger than the central V-groove is that the optical fibers 9' and 33, which have large core and outer diameters, are disposed above and below. In addition, also in the case of FIG. 5 and FIG. 6, by using an optical fiber having a large core diameter and a large outer diameter, it is possible to compensate for deviations due to manufacturing errors.

FIG. 8 shows an embodiment of the optical module for bidirectional transmission of the present invention, which integrates the LD used in FIG. 3, a glass rod for extracting monitor light, a ball lens, a rod lens with an interference film filter, and an optical fiber holding section. FIG.

In FIG. 8, 50' is a glass rod for extracting monitor light, 51, 52, 53, and 54 are parts of the package, 55 is an optical window, and 56 is an electrode.

LD1 is attached adjacent to electrode 56, and ball lens 2 is attached adjacent to it. Interference film filters 23 and 24 are attached to the end surface of the rod lens 22 on the side of the ball lens 2, and an optical window 55 is provided between the filters 23 and 24 and the ball lens 2. An optical fiber holding portion 3 is attached to the other end surface of the rod lens 22 through a slight gap.
7 is incorporated, and three optical fibers 7, 9', and 33 are inserted therein.

As shown in FIG. 8, the optical fiber holding section 37,
If a cylindrical one is used for 38, the LD 1, the glass rod 50' for extracting the monitor light, the ball lens 2, the rod lens 22 with an interference film filter, and the optical fiber holding part 37 can be integrated, and it can be used for bidirectional transmission. It can be realized as an optical module. The monitor light receiving element is immediately after LD1 (on the opposite side of ball lens 2)
or after the glass rod 50'. As a result, compared to the conventional case where the LD module and optical multiplexer/demultiplexer are installed separately, reliability is extremely high, and it is possible to reduce size, cost, and loss.

In the present invention, a single mode fiber is used as the optical fiber, but the present invention is not limited to this, and a multimode optical fiber can be used. Note that when a multimode optical fiber is used in the embodiment using the LD, light can be coupled to the fiber 7 without using the ball lens 2. Also, a cylindrical lens can be used instead of a spherical lens.

Further, although the case has been described in which three laser beams having different wavelengths are transmitted to the bidirectional optical transmission line, the number is not limited to three, and two or four or more waves may be used.

In addition to the LD, a light emitting diode such as an edge emitting type or a surface emitting type can also be used as a laser oscillator. When using light emitting diodes,
In order to increase the coupling efficiency, it is preferable to use a condensing system such as a lens or a paraboloid in front of the effect diode, and make the light almost parallel before entering the rod lens with an interference film filter. Furthermore, since a light emitting diode has a broader emission spectrum distribution than an LD, it is preferable to use an interference film filter with steeper attenuation characteristics and a wider wavelength interval. Further, the input end face of the optical fiber 7 may be made into a spherical tip, or a spherical lens may be attached.

Furthermore, the length of the rod lens is set to n/4 (n
(1, 3, 5...) may be slightly shorter than the pitch.

It goes without saying that the bidirectional transmission system of the present invention can be applied to both analog transmission and digital transmission.

In this way, as shown in this example, the transmission optical fiber is placed approximately at the central axis of the optical fiber holding section.
Since optical fibers for demultiplexing and optical fibers for multiplexing are integrally and fixedly arranged around it at predetermined intervals,
Coupling of light to the transmission optical fiber can be adjusted by simply rotating the optical fiber holder. Therefore, since the optical coupling adjustment to the transmission optical fiber and the optical coupling adjustment to the demultiplexing and multiplexing optical fibers can be performed independently, the optical adjustment becomes simple and does not require any skill. In addition, if a cylindrical or cylindrical optical fiber holding part is used, it will be stable against temperature fluctuations.Furthermore, the optical fiber is fixed integrally to the cylindrical or cylindrical optical fiber holding part. Because of this, it is resistant to vibrations, and the spacing between each optical fiber does not fluctuate. Since the distance between the optical fibers is on the order of several hundred micrometers, the method of separately fixing the optical fibers is unstable against vibrations, and the fixing method is also difficult. Furthermore, if the rod lens and the cylindrical or cylindrical optical fiber holder are fixed together in a separate cylindrical container, it is more stable against temperature fluctuations and vibrations than when they are fixed separately. .

In addition, semiconductor light emitting devices (LD, diodes, etc.)
An interference film filter is installed on the rod lens that guides the emitted light into the optical fiber, and bidirectional transmission is achieved by combining the two functions of optical coupling and optical multiplexing and demultiplexing. It is possible to realize a low-cost bidirectional transmission system with a simple configuration, low insertion loss, and no complicated configuration. In addition, in the conventional configuration, the loss of each optical multiplexer/demultiplexer is nearly 5 dB, but in this example, the loss is 1/1/2.
Since the number can be reduced to 3 or less, long-distance transmission becomes possible. Note that the present invention is particularly effective when a single mode optical fiber is used as the transmission optical fiber.

Furthermore, in the interference film filter of this example, filters with different optical properties (transmission and reflection properties) are attached to the end face of the LD light incident side of the rod lens at different angles θn (n=1, 2, 3). ) can be formed into an n layer. Then, the opposite end surface of the rod lens is also obliquely polished, and a transmission optical fiber is placed approximately on the central axis of the rod lens, and n optical fibers for demultiplexing and multiplexing are placed around it. , since it is fixed with the optical fiber holding part, n
It is possible to realize optical transmission of wavelengths using two sets of modules. Further, an interference film filter for suppressing near-end light leakage may be formed on the end face of a rod lens on the front surface of the optical fiber for demultiplexing and multiplexing, so that only light of a desired wavelength is transmitted.

Note that the shape of the optical fiber holding portion may be a rectangular shape other than a cylindrical shape or a cylindrical shape as long as the optical fiber for transmission can be arranged approximately on the central axis.

〔Effect of the invention〕

As explained above, according to the present invention, the optical module for bidirectional transmission has an extremely simple structure and a structure that facilitates optical coupling adjustment, thereby shortening the optical coupling adjustment time, adjusting the degree of coupling, and reducing the Bidirectional optical transmission with low cost and low loss becomes possible, and long-distance transmission is expected. Furthermore, because it has an optical module structure for bidirectional transmission, it is stable against changes in environmental conditions and has high reliability.

[Brief explanation of the drawing]

Figure 1 is a block diagram of a conventional bidirectional optical transmission system, Figure 2 is an explanatory diagram of the optical demultiplexer used in Figure 1,
FIG. 3 is a block diagram of a bidirectional optical transmission system showing an embodiment of the present invention, FIG. 4 is a diagram showing the structure of the optical fiber holding section used in FIG. 3, and FIG. A diagram showing the structure when an optical fiber is inserted into the fiber holding part, FIG. 6 is a diagram showing another embodiment of the optical fiber holding part used in FIG. 3, and FIG. 7 is a diagram showing the optical fiber holding part in FIG. 6. FIG. 8 is a side sectional view of an integrated module showing an embodiment of the present invention. 1, 1', 1'': Semiconductor laser (LD), 2, 2',
2″: Ball lens, 3, 3′, 16, 17, 18, 2
2, 27, 32: Rod lens, 4, 4', 7,
9, 9', 33, 35: Optical fiber, 6, 6': Optical demultiplexer, 11, 11', 11'': Photoreceiver, 12, 1
2', 12'': Amplifier, 13, 13', 13'': Demodulator, 14, 14', 14'': Semiconductor laser drive circuit, 15, 15', 15'': Information signal input terminal, 1
9: Dielectric mirror, 20, 21, 23, 24, 2
8, 29: Interference film filter, 21: Pentaprism, 26, 31: End face of rod lens, 25,
30: Spacer glass, 37, 38: Optical fiber holding section, 43, 44, 45: Optical fiber insertion hole, 46: One end surface of optical fiber holding section, 47, 4
8, 49, 50: Semi-cylindrical material with V groove, 5
0': Monitor light extraction glass rod, 51~
54: Package parts, 55: Optical window, 56:
electrode.

Claims (1)

[Scope of Claims] 1. A semiconductor light emitting device with a ball lens, a rod lens for coupling light emitted from the semiconductor light emitting device into a transmission optical fiber, and a rod lens disposed approximately on the central axis of the rod lens. It consists of an optical fiber holding means and a glass rod for extracting the monitor light,
These are integrally fixed in a configuration in which the optical fiber holder can be adjusted in the central axis direction and rotational direction, and one or more interference film filters having desired optical characteristics are provided on the incident end side of the rod lens. On the output end side of the optical fiber holding means, a transmission optical fiber is arranged approximately on the central axis of the rod lens, and the interference film filter arranged around the transmission optical fiber demultiplexes or demultiplexes the light. An optical module for bidirectional transmission characterized by having one or more optical fibers for transmitting multiplexed optical signals. 2. The optical module for bidirectional transmission according to claim 1, wherein the optical fiber holding portion has a cylindrical or columnar structure. 3. The optical fiber holding portion is provided with a hole for holding the optical fiber, or has a cavity formed by combining semi-cylindrical or semi-cylindrical members having V-shaped grooves. An optical module for bidirectional transmission according to claim 2. 4. The interference film filter has a plurality of layers each having different optical properties on the incident end side of the rod lens and each having a different inclination angle, and the reflected waves from each layer are reflected from the rod lens. 2. The bidirectional transmission optical module according to claim 1, wherein the light is focused at a shifted position on the end side. 5 In a bidirectional optical transmission system that transmits optical signals of different wavelengths in the upstream and downstream directions through a single optical fiber transmission line, a rod lens equipped with one or more interference film filters and an optical fiber holder are used. An optical module is provided on each of the uplink and downlink transmitting sides, and the optical fiber holding part includes an optical fiber for transmitting an optical signal passing through the interference film filter, and an optical module with a It accommodates optical fibers for transmitting optical signals to be demultiplexed or multiplexed, and connects a transmission path and transmitting or receiving side elements to each optical fiber, allowing bidirectional transmission of optical signals of two or more waves. A two-way transmission method characterized by: