JP3379683B2 - Optical transmission equipment - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a passive double star (PDS) type optical transmission device in which one subscriber terminal device and a plurality of optical network devices are connected by a passive optical circuit.

[0002]

2. Description of the Related Art Passive Double Star is also called a Passive Optical Network (PON), which is an optical access transmission system in which an expensive station side device is shared by a plurality of users and the cost per user is reduced.

FIG. 10 is a block diagram showing a conventional passive double star type optical transmission device. In this optical transmission device, a plurality of optical network devices (ONU) 10 placed at a predetermined point between a user's home or a station and a user's home.
1-1 to 101-T and one subscriber terminal device (SLT) 103 on the station side are combined with an optical star coupler (SC) 102.
Is connected via an optical fiber. Optical signals from the optical network devices 101-1 to 101-T to the subscriber terminal device 103 are defined as upstream signals, and optical signals from the signal subscriber terminal device 103 to the optical network devices 101-1 to 101-T are defined as downstream signals. To do. Optical network device 101
-1 to 101-T respectively include a transmission unit 104 that transmits an optical signal, a reception unit 105 that receives the optical signal, and an upper and lower signal multiplexing circuit 106 that multiplexes and demultiplexes signals in the vertical direction.
Equipped with. The subscriber terminating device 103 similarly includes an up / down signal multiplexing circuit 107, a transmitting unit 108, and a receiving unit 109.

In this conventional example, the optical network device 10 is used.
1-1 to 101-T and the optical star coupler 102
, And between the subscriber terminating device 103 and the optical star coupler 102, only one optical fiber is stretched. Therefore, the upstream signal and the downstream signal are transmitted through the same optical fiber. Transmitter 10 for transmitting an optical signal
Generally, different elements are used in the receiving units 105 and 109 for receiving the optical signals, and therefore, the optical network devices 101-1 to 101-T and the subscriber terminating device 103 receive vertical signals. Upper and lower signal multiplexing circuits 106 and 107 for multiplexing and demultiplexing are incorporated. As the elements used in the upper and lower signal multiplexing circuits 106 and 107, generally, when the wavelengths of the upstream signal and the downstream signal are the same, a 1: 2 optical coupler or an optical circulator, and when the wavelengths of the upstream signal and the downstream signal are different, Wavelength demultiplexing filter (W
DM filter) is used.

Uplink signals are transmitted to a plurality of optical network devices 10.
Since the signals are transmitted from 1-1 to 101-T, it is necessary to packetize the upstream signals so that these signals do not collide with each other, and then perform multiplexing control. As a method for multiplexing control of packets, time division multiplexing control is generally used in which the subscriber terminating device 103 instructs the optical network devices 101-1 to 101-T which time slot may transmit an upstream signal. . However, the optical network devices 101-1 to 10-10
1-T performance, optical network devices 101-1 to 101
-Amount of information transmitted by T, or optical star coupler 102
Since there are differences in the transmission characteristics between the optical network devices 101-1 to 101-T, the upstream signal is a burst signal in which the packet interval is indefinite and the optical intensity and the phase are different for each packet. Therefore, the subscriber terminating device 103 requires an additional circuit for receiving the burst signal in the electric signal demodulating unit (not shown) in the subsequent stage of the receiving unit 108, and has a receiving sensitivity higher than that in the case of receiving a continuous signal. to degrade.

Since the downstream signal is only split by the optical star coupler 102, all the optical network devices 101-
A continuous signal is broadcast to 1 to 101-T. In the optical network devices 101-1 to 101-T,
Once all the optical signals are received, a logic circuit (not shown) arranged at the subsequent stage of the receiving unit 105 extracts only information relevant to itself. Therefore, the optical network device 101
The receiving units 105 of -1 to 101-T may be only circuits that receive continuous signals.

[0007]

As described above, in the passive double star, the receiving sensitivity of the up signal is inferior to that of the down signal. Since the system is designed according to the upstream signal having the poor reception sensitivity, there is a margin in the difference between the transmission and reception levels of the downstream signal, and as a result, the downstream signal has excessive transmission quality. In order to construct the system while suppressing the cost increase as much as possible, it is desirable to reduce the difference between the transmission and reception levels of the upstream signal and match the difference between the transmission and reception levels of the downstream signal and the upstream signal.

As a method of matching the transmission / reception level difference in both the upper and lower directions, the optical output of the transmitting section of the optical network device is increased, the receiving sensitivity of the receiving section of the subscriber terminating device is improved, and the transmission line loss in the upstream direction is reduced. Either is required.

Of these methods, the former two are difficult to apply to the optical subscriber system from the viewpoints of cost and technology. Upstream transmission line losses are roughly classified into transmission loss of optical fibers and optical connectors, merging loss caused by optical merging in an optical star coupler, and excess loss of optical components. The transmission loss and the excess loss are common to the transmission path loss in the down direction, and it is not possible to reduce only the loss in the up direction.
The merging loss is equivalent to the branching loss in the down direction as long as the optical star coupler is used, but it can be reduced by using other than the optical star coupler as the merging element.

The present invention has been made from such a point of view, and an object of the present invention is to provide an optical transmission apparatus in which the difference in transmission / reception level in the vertical direction is eliminated by suppressing the upstream signal merging loss and the transmission quality is not wasted. And

[0011]

The optical transmission device of the present invention comprises:
A plurality of optical network devices and one subscriber terminating device are provided, and each optical network device transmits an upstream signal to the subscriber terminating device by a first optical fiber provided for each optical network device. And a first transmission / reception multiplex means for receiving a downlink signal from the subscriber terminating device, wherein the subscriber terminating device includes a transmitter for collectively outputting the downlink signals to the plurality of optical network devices, and a plurality of transmitters. A receiving unit that collectively receives the upstream signals from the optical network equipment, and guides the upstream signal from the second optical fiber to which the first optical fiber is connected to the receiving unit and also receives the downstream signal from the transmitting unit. In the optical transmission device including the second transmission / reception multiplexing means for guiding to the second optical fiber, a plurality of second optical fibers are provided in number less than or equal to the number of the first optical fibers, and the second transmission / reception multiplexing means is the second optical fiber. The subscriber terminating device includes an optical branching unit for branching the downlink signal output from the transmitting unit and supplying the signal to the signal multiplexing unit, and a signal multiplexing unit. Means for parallelly inputting the upstream signal guided by the above into the receiving unit. The first optical fiber and the second optical fiber are
It is connected directly or via an optical star coupler.

That is, according to the present invention, at least a part of the optical star coupler is arranged between the transmitter of the subscriber terminating device and the signal multiplexing means, and the optical signals output from the signal multiplexing means are terminated in parallel by the subscriber. Input to the receiver of the circuit. Focusing on the upstream signal, since at least a part of the optical star coupler reaches the receiving unit of the subscriber terminal device without passing through it, and there is no loss due to merging when inputting to the receiving unit of the subscriber terminal device. The branch loss is reduced for the optical star coupler that does not pass.

When different wavelengths are used for the upstream signal and the downstream signal, a wavelength division multiplexing filter array or an arrayed waveguide type diffraction grating can be used as the signal multiplexing means. If the same wavelength is used, an optical circulator array can be used.

The means for inputting in parallel are a condenser lens for collecting a plurality of upstream signals from the signal multiplexing means and inputting them to the receiving section, and a plane conductor in which a plurality of cores are provided and the cores are close to each other at the output end. A plurality of light receiving elements connected to a wave circuit or a common electric circuit can be used. When the condenser lens is used, a large core diameter fiber capable of multimode transmission that guides the upstream signal condensed by the condenser lens to the receiver can be used.

The transmitting unit may include a plurality of light sources, and the light branching unit may include a unit that branches outputs of the plurality of light sources.

[0016]

FIG. 1 is a block diagram showing an embodiment of the present invention, in which a plurality of optical network devices 1-
1 to 1-T and one subscriber terminal device 3. The configurations of the optical network devices 1-1 to 1-T are the same as those of the conventional example shown in FIG.
An optical fiber provided for each −T transmits an upstream signal to the subscriber terminating device 3 and receives a downstream signal from the subscriber terminating device 3. The subscriber terminating device 3 includes a transmitter 5 that collectively outputs downlink signals to the plurality of optical network devices 1-1 to 1-T, and the plurality of optical network devices 1.
-1 to 1-T collectively receives the upstream signals from the receiving unit 6, and guides the upstream signals from the optical fiber connected to the subscriber terminating device 3 to the receiving unit 6 and the downstream from the transmitting unit 6. An upper / lower signal multiplexing circuit array 4 for guiding signals to the optical fiber is provided. The subscriber terminal device 3 is provided with a plurality n of optical fibers, and the plurality n of optical fibers are respectively provided with
Of the optical network unit 1-1 to 1-T m _i number (i =
1 to n) each are connected via the m _i branched optical star coupler 2-i. Here, T = Σm _i (i = 1 to n), m _i is a natural number, and m _i = 1 means that the optical star coupler is not directly connected. Since the subscriber terminating device 3 is provided with a plurality of optical fibers, the upper and lower signal multiplexing circuit array 4 includes n upper and lower signal multiplexing circuits for transmitting and receiving a down signal and an up signal for each optical fiber. They are arranged in an array. The subscriber terminating device 3 further includes an n-branch optical star coupler 7 that branches the downlink signal output from the transmission unit 5 and supplies the branched signal to the upper and lower signal multiplexing circuit array 4.
The parallel input unit 8 is provided for inputting the upstream signals guided by the upper and lower signal multiplexing circuit array 4 in parallel to the receiving unit.

[0017] m _i uplink signal outputted from the optical network units connected to the branch optical star coupler 2-i leads to the subscriber termination device 3 through the optical star coupler 2-i. In the subscriber terminating device 3, the upper and lower signal multiplexing circuit array 4
Input to one of the upper and lower signal multiplexing circuits, separated from the upstream signal, and input to the optical receiving unit 6 in parallel with the downstream signal output from the other upper and lower signal multiplexing circuit by the parallel input unit 8. Converted to a signal. If the excess loss in each circuit of the subscriber terminal device 3 and the optical star coupler is neglected, the upstream transmission line loss is only the fiber loss and the branch loss for the _mi branch.

The downlink signal is transmitted by the transmitter 5 of the subscriber terminal device 3.
Is output to the upper and lower signal multiplex circuit array 4 by the n-branch optical star coupler 7. Vertical signal circuit further downstream signals output from the array 4, the subscriber termination device is branched by m _i branched optical star coupler 2-i after being outputted from the 3, eventually branched into T book optical network Input to each of the devices 1-1 to 1-T. When the excess loss is ignored as in the case of the upstream signal, the downstream transmission path loss is only the fiber loss and the branch loss of T branches.

When n is 2 or more, T> m _i .
The loss of the upstream signal is smaller than that of the downstream signal,
It is possible to compensate for the deterioration of reception sensitivity due to burst reception.
As an example, the bit rate is 155.52 Mb / s.
In the case of, it is experimentally required that the reception sensitivity of the burst signal deteriorates by about 6 dB as compared with that of the continuous signal. If the number of branches n in the subscriber terminating device 3 is 4, the loss of the upstream signal can be reduced by 10 log (4) = 6 dB compared to the downstream signal. If the output light intensities of the transmitter 5 are equal, the transmission and reception level differences in both the upper and lower directions are equal.

In this example, when n> 4, the downlink transmission path loss exceeds the uplink transmission path loss, and this time the transmission / reception level difference of the downlink signal determines the transmission / reception level difference of the entire system. For example, if n = 8, the difference in the transmission / reception level of the upstream signal is 10 log compared to the conventional passive double star.
(8) = 9 dB improvement. This is 3 dB better than the transmission / reception level difference of the downlink signal. However, by arranging two semiconductor lasers as the light source of the transmitter in the subscriber terminal device and connecting a four-branch optical star coupler to each semiconductor laser, the optical intensity of the downstream signal input to the upper and lower signal multiplexing circuit is
Compared with the case where the output light from one semiconductor laser is distributed by the 8-branch optical star coupler, it can be improved by 3 dB. Also at this time, the difference between the transmission and reception levels in the upper and lower directions becomes equal.

Generally, when the transmission path loss in the upstream direction is reduced and the transmission / reception level difference in the upstream direction is better than that in the downstream direction, the optical output in the transmission section in the subscriber terminal device may be increased. . In order to increase the light output, a plurality of semiconductor lasers may be used as described above, or a semiconductor laser having a high light output intensity may be used. Although such a measure leads to an increase in the cost of the subscriber terminating equipment, since the subscriber terminating equipment is shared by T users, the cost increase per user is multiplied by 1 / T. Rather, it can be expected that the number of users T that can be accommodated by one subscriber terminal device will increase due to the increase in the optical output, so that the burden per user may be reduced.

2 to 4 show constituent columns of the upper and lower signal multiplexing circuit array 4. It is preferable to use an element that does not cause a loss when demultiplexing the upper and lower signals in each of the upper and lower signal multiplexing circuits in the array. FIG. 2 shows a WDM filter array in which n 1: 2 WDM filters are arranged in parallel, FIG. 3 shows an arrayed waveguide diffraction grating (AWG), and FIG. 4 shows an optical circulator array in which n optical circulators are arranged in parallel. An example of the configuration used is shown.

The upper and lower signal multiplexing circuit array shown in FIG.
The 1: 2 WDM filters 11-1 to 11-n are used. This configuration is used when the wavelengths of the upstream signal and the downstream signal are different, and here the wavelength of the upstream signal is 1.3 μm.
m, the wavelength of the downlink signal is 1.55 μm. 1: 2
Each of the WDM filters 11-1 to 11-n passes a wavelength of 1.55 μm between the first port 111 and the second port 112 (common port), and the second port 11
The wavelength of 1.3 μm is transmitted between the second port 113 and the third port 113, and the transmission unit 5 is connected to the first port 111 via the n-branch optical star coupler 7. One of the optical fibers on the optical network device side is connected to the port 112, and the parallel input unit 8 is connected to the third port 113.
The receiving unit 6 is connected via the. A dielectric multilayer film, an optical directional coupler, a Mach-Zehnder interferometer, or the like can be used as the 1: 2 WDM filters 11-1 to 11-n.

In FIG. 3, one AWG with 8 ports is used and n =
The example which comprised the upper and lower signal multiplex circuit array of 4 is shown. This AWG has a structure in which two slab waveguides 12 and 13 are connected by an array waveguide 14. In general, AWG
Wavelength λ ₀ input to port number A of one slab waveguide
Output the light to the port number A of the opposing slab waveguide,
It has the property of outputting the light of wavelength λ ₀ + (B−A) × Δλ input to the same port to the port number B of the facing slab waveguide. However, λ ₀ and Δλ are determined by the structure of the AWG.

In the example of FIG. 3, the wavelength of the downlink signal λ _d =
λ ₀ , the wavelength of the upstream signal λ _u = λ _d + Δλ, the odd numbered ports of the slab waveguide 12 via the n-branch optical star coupler 7 to the transmitter 5, and the even numbered ports via the parallel input 8 Is connected to the receiving unit 6, and the optical fiber on the optical network device side is connected to the odd-numbered port of the slab waveguide 13. The downlink signal input to the odd-numbered port #K of the slab waveguide 12 is output to the port #K of the same number of the slab waveguide 13 and sent to the optical network device. The upstream signal input to the odd-numbered port #K of the slab waveguide 13 is an even-numbered port #K of the slab waveguide 12.
It is output to (K + 1).

When the wavelengths of the upper and lower signals are the same, the optical circulators 15-1 arranged in an array as shown in FIG.
~ 15-n can be used. Each of the optical circulators 15-1 to 15-n outputs the signal light input to the first port 151 to the second port 152 and outputs the signal light input to the second port 152 to the third port 152. In the configuration, the transmission unit 5 is connected to the first port 151 via the n-branch optical star coupler 7 and the second port 152 is connected to the optical fiber of the optical network device side. The receiving unit 6 is connected to the third port 153 via the parallel input unit 8.

5 to 6 show examples of the configuration of the parallel input section 8. Here, the upstream signals output from the upper and lower signal multiplexing circuit array 4 are converted into single mode fibers 21-1 to 21-21.
-N, and these signals are received by the receiving unit 6
An example of the structure that is coupled to the light receiving element inside is shown.

In the configuration example shown in FIG. 5, a condenser lens 22 and a large core diameter fiber 23 are used as the parallel input section 8.
The upstream signals output from the plurality of single mode fibers 21-1 to 21-n are coupled to the large core diameter fiber 23 through the condenser lens 22 and input to the light receiving element in the receiving unit 6. As the large core diameter fiber 23, a fiber capable of multimode transmission such as a GI (graded index) fiber is used, and single mode fibers 21-1 to 21-n are used.
The light emitted into the space is coupled through the condenser lens 22 without loss. As the light receiving element in the receiving unit 6, a light receiving element having a light receiving surface having an area larger than the core diameter of the large core diameter fiber 23 and capable of being coupled to the large core diameter fiber 23 without loss is used. The large core diameter fiber 23 may be omitted and the light condensed by the condenser lens 22 may be directly input to the light receiving element.

FIG. 6 shows a planar waveguide circuit 25 in which a plurality of cores are provided as the parallel input section 8 and are close to each other at the output end until the maximum distance between the cores becomes equal to or smaller than the diameter of the light receiving element.
An example using is shown. The input end of the planar waveguide circuit 25 is coupled to the single mode fibers 21-1 to 21-n through, for example, the SELFOX lens 24, and the inter-core distance is gradually narrowed to reach the output end. At the output end and its vicinity, light leaks into other cores and leaks into the clad, but if the light receiving diameter of the light receiving element is sufficiently larger than the maximum distance between the cores, light can be received without loss.

7 and 8 each show a modification of the parallel input section 8 shown in FIG. In the modification shown in FIG. 7, the slab waveguide 26 is arranged between the output end of the planar waveguide circuit 25 and the light receiving element. In the modification shown in FIG. 8, a waveguide 27 having a core width at least at the output end equal to or smaller than the diameter of the light receiving element is arranged between the output end of the planar waveguide circuit 25 and the light receiving element.

FIG. 9 shows a structure in which signals are aggregated by an electric stage instead of light. In this case, it is not necessary to provide the parallel input section 8 and the light receiving element array 28 is provided in the receiving section 6, and the outputs from the n single mode fibers 21-1 to 21-n are separately provided in the light receiving element array 28. Input to the light receiving element of and the outputs are combined into one line at the electric stage. The loss generated in the electric stage is amplified and compensated by the amplifier.

[0032]

As described above, the optical transmission device of the present invention eliminates at least a part of the optical star coupler from the transmission path of the upstream signal in the passive double star, thereby reducing the merging of the optical star couplers. The upstream transmission path loss is reduced by the loss. As a result, it is possible to balance the difference between the transmission and reception levels in the upper and lower directions, and there is an effect that there is no waste and, as a result, low-cost optical transmission can be performed.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention.

FIG. 2 is a diagram showing constituent columns of an upper / lower signal multiplexing circuit array using a WDM filter array.

FIG. 3 is a diagram showing constituent columns of an upper and lower signal multiplexing circuit array using an arrayed waveguide type diffraction grating.

FIG. 4 is a diagram showing a configuration column of an upper / lower signal multiplexing circuit array using an optical circulator array.

FIG. 5 is a diagram showing a configuration example of a parallel input section using a condenser lens and a large core diameter fiber.

FIG. 6 is a diagram showing a configuration example of a parallel input section using a planar waveguide circuit.

FIG. 7 is a diagram showing a modification example of the parallel input unit shown in FIG.

FIG. 8 is a diagram showing another modification of the parallel input section shown in FIG.

FIG. 9 is a diagram showing a configuration example in which signals are aggregated in an electric stage.

FIG. 10 is a block diagram showing a conventional passive double star type optical transmission device.

[Explanation of symbols]

1-1 to 1-T, 101-1 to 101-T Optical network device 2-1 to 2-n m _i Branch optical star coupler 3, 103 Subscriber termination device 4 Vertical signal multiplexing circuit array 5, 104, 108 Transmission Parts 6, 105, 109 receiving part 7 n-branch optical star coupler 8 parallel input parts 11-1 to 11-n 1: 2 WDM filter 111 first port 112 second port 113 third port 12, 13 slab waveguide 14 Array Waveguide 15-1 to 15-n Optical Circulator 151 First Port 151 Second Port 153 Third Port 21-1 to 21-n Single Mode Fiber 22 Condensing Lens 23 Large Core Diameter Fiber 24 Selfoc Lens 25 Planar waveguide circuit 26 Slab waveguide 27 Waveguide 28 Light receiving element array 102 Optical star couplers 106, 107 Upper and lower signal multiplexing circuit

Continuation of the front page (56) Reference JP-A-8-97769 (JP, A) JP-A-1-26027 (JP, A) JP-A-8-237206 (JP, A) JP-A-61-193528 (JP , A) JP 5-145491 (JP, A) JP 57-178444 (JP, A) JP 3-207132 (JP, A) JP 55-128941 (JP, A) Nakanishi Kenji, Seiji Yoshida, Shin'ichi Aoyagi, "PDS Construction Method with Reduced Upstream Signal Combining Loss", Proc. Of IEICE General Conference 1997, Communication 2, March 6, 1997, p. 621, (B-10-112) (58) Fields investigated (Int.Cl. ⁷ , DB name) H04B 10/00 H04J 14/00 INSPEC (DIALOG) JISST file (JOIS)

Claims (11)

(57) [Claims] 1. A plurality of optical network devices and one subscriber terminating device, wherein each of the plurality of optical network devices is connected by a first optical fiber provided for each optical network device. Including a first transmission / reception multiplexing means for transmitting an upstream signal to the subscriber terminating device and receiving a downlink signal from the subscriber terminating device, wherein the subscriber terminating device is a downlink signal to the plurality of optical network devices. And a receiving unit that collectively receives upstream signals from the plurality of optical network devices, and an upstream signal from a second optical fiber connected to the first optical fiber. In an optical transmission device including a second transmission / reception multiplexing means for guiding a down signal from the transmitting section to the second optical fiber while guiding the signal to the receiving section, the second optical fiber is the first A plurality of optical fibers are provided, the second transmission / reception multiplexing means including transmission / reception multiplexing of a downstream signal and an upstream signal for each of the second optical fibers, and the subscriber terminal device is the Optical branching means for branching the downlink signal output from the transmitting part and supplying the branched signal to the signal multiplexing means,
An optical transmission device, comprising: means for inputting an upstream signal guided by the signal multiplexing means into the receiving unit in parallel. 2. A different wavelength is used for the upstream signal and the downstream signal, and the signal multiplexing means passes the first wavelength between the first port and the second port, and the second port Between the first port and the third port, a plurality of wavelength demultiplexing filters through which the second wavelength passes are included, and the optical branching means and the parallel input are provided to the first port and the third port of each wavelength demultiplexing filter. 2. The optical transmission device according to claim 1, wherein the second port is connected to one of the second optical fibers, and the second port is connected to one of the second optical fibers. 3. A different wavelength is used for an upstream signal and a downstream signal, and in the second transmitting / receiving multiplexing means, two slab waveguides are connected by an array waveguide, and one port of one slab waveguide is used. The light of the first wavelength input to the other slab waveguide is output to the corresponding port of the other slab waveguide, and the light of the second wavelength input to the same port is output to the other port of the other slab waveguide. An array waveguide type diffraction grating, wherein the optical branching means and the parallel input means are connected to a port of one slab waveguide of the array waveguide type diffraction grating, and a part of the other slab waveguide is connected. The optical transmission device according to claim 1, wherein the second optical fiber is connected to a port. 4. The optical signal output means outputs the signal light input to the first port to the second port and outputs the signal light input to the second port to the third port. A plurality of circulators are provided, the optical branching means is connected to the first port of each optical circulator, one of the second optical fibers is connected to the second port, and the parallel input means is connected to the third port. The optical transmission device according to claim 1, which is connected. 5. The optical transmission device according to claim 1, wherein the means for inputting in parallel includes a condenser lens for collecting a plurality of upstream signals from the signal multiplexing means and inputting them to the receiving section. 6. The optical transmission device according to claim 5, wherein the means for inputting in parallel includes a large-core-diameter fiber capable of multimode transmission that guides the upstream signal condensed by the condenser lens to the receiving unit. 7. The parallel input means comprises a plurality of cores, and includes planar waveguide circuits provided with a plurality of cores and close to each other until a maximum distance between the cores at an output end is equal to or less than a diameter of a light receiving element in the receiving section. 1. The optical transmission device according to 1. 8. The parallel inputting means comprises a planar waveguide circuit provided with a plurality of cores, the cores being close to each other at an output end, and an output end of the planar waveguide circuit and a light receiving element in the receiving section. A slab waveguide that is optically connected.
The optical transmission device described. 9. The parallel inputting means comprises a planar waveguide circuit provided with a plurality of cores, the cores being close to each other at an output end, and an output end of the planar waveguide circuit and a light receiving element in the receiving section. The optical transmission device according to claim 1, further comprising a waveguide that is optically connected and has a core width at least at an output end that is equal to or smaller than a diameter of a light receiving element in the receiving section. 10. The optical transmission device according to claim 1, wherein the means for inputting in parallel includes a plurality of light receiving elements connected to a common electric circuit. 11. The optical transmission device according to claim 1, wherein the transmitting unit includes a plurality of light sources, and the optical branching unit includes a unit that branches outputs of the plurality of light sources, respectively.