Source: http://www.google.com/patents/US5915054?dq=oakley+5,387,949
Timestamp: 2017-08-17 04:23:47
Document Index: 670113763

Matched Legal Cases: ['art 301', 'application No. 07', 'application No. 07', 'application No. 07', 'application No. 07', 'application No. 07', 'application No. 07']

Patent US5915054 - Star coupler for an optical communication network - Google Patents
An interconnectable star coupler for an optical communication network is formed using 1×2 branching circuits, 2×2 branching circuits, and optical waveguides. Branching circuits may be connected by intersecting optical waveguides. The interconnectable star coupler is built in such a manner that the...http://www.google.com/patents/US5915054?utm_source=gb-gplus-sharePatent US5915054 - Star coupler for an optical communication network
Publication number US5915054 A
Application number US 08/460,709
Also published as US5684899, US5854700
Publication number 08460709, 460709, US 5915054 A, US 5915054A, US-A-5915054, US5915054 A, US5915054A
Patent Citations (25), Non-Patent Citations (38), Referenced by (26), Classifications (17), Legal Events (5)
Star coupler for an optical communication network
US 5915054 A
An interconnectable star coupler for an optical communication network is formed using 1×2 branching circuits, 2×2 branching circuits, and optical waveguides. Branching circuits may be connected by intersecting optical waveguides. The interconnectable star coupler is built in such a manner that the angle between waveguides meets particular criteria based on the critical angle of the waveguide.
1. An interconnectable star coupler in an optical communication network having N (N=2i +1, i is an integer ≧2) terminals, comprising:
an equal branching circuit unit including a plurality of 1×2 equal branching circuits corresponding to said terminals, which are arranged on the substrate;
said equal branching circuit unit being connected through optical waveguides to the corresponding terminals in such a manner that there are intersecting portions of said optical waveguides in said star coupler.
2. The interconnectable star coupler according to claim 1 wherein an angle between said waveguides exceeds an angle twice as much as a critical angle of said waveguides.
3. An interconnectable star coupler in an optical communication network having N (N=2i +1, i is an integer ≧2) pairs of terminals, comprising:
N pairs of 1×2 equal branching circuits corresponding to N pairs of terminals; and
at least one 2×2 branching circuit coupled between said terminals and said 1×2 equal branching circuits,
branch terminals of at least one of said 1×2 equal branching circuits being connected through optical wave guides to corresponding terminals of said at least one 2×2 equal branching circuit in such a manner that said optical waveguides in said star coupler intersect.
4. The interconnectable star coupler according to claim 3 wherein an angle between said waveguides exceeds an angle twice as much as a critical angle of said waveguides.
5. An interconnectable star coupler according to claim 1 wherein said each branching circuits comprise an optical coupler comprising a Y branching circuit connected in series with an Evanescent optical coupler.
6. The optical coupler according to claim 5 wherein said Y branching circuit is an asymmetrical Y branching circuit.
7. The optical coupler according to claim 5 wherein an optical path length is adjusted to satisfy a phase matching condition at a mixing portion of said Y branching circuit.
8. The optical coupler according to claim 7 wherein an optical path difference between said optical waveguides is eliminated to adjust the phase matching condition.
9. An interconnectable star coupler comprising:
an optical coupler including:
a Y branching circuit;
two optical waveguides having a first refractive index and of approximately equal cross-sectional shapes, each optical waveguide coupled to a different branch of the Y branching circuit; and
a medium, with a second refractive index, lower than the first refractive index, between the optical waveguides, whereby energy is transferred from one waveguide to the other waveguide.
10. The interconnectable star coupler according to claim 9 wherein said Y branching circuit includes branches of different cross-sectional shapes.
11. The interconnectable star coupler according to claim 9 wherein an optical path length is adjusted, based on a distance between the optical waveguides, to satisfy a phase matching condition at a mixing portion of said Y branching circuit.
12. The interconnectable star coupler according to claim 9, wherein the branches of the Y branching circuit are arranged at substantially symmetrical angles, a smaller cross-sectional branch having a lower refractive index than a larger cross-sectional branch, and wherein an optical path difference between said optical waveguides is eliminated to adjust a phase matching condition.
This is a division of application Ser. No. 08/026,054, filed Mar. 4, 1993.
In a general LAN, a plural number of nodes are connected to a bus. The nodes communicate with one another through the bus. One of the buses used in the LAN is a broadcasting bus. When using the broadcasting bus, a signal sent by a node can be simultaneously received by all of the nodes. ETHERNET (Trade Mark) is well known as one type of LAN using the broadcasting bus. The protocol used in ETHERNET is called a CSMA/CD (carrier sense multiple access/collision detection) system, prescribed in IEEE 803.3. In ETHERNET, coaxial cables are used for transmission medium. The nodes are connected by the coaxial cables. A node which will send a signal checks whether or not a signal from another node is present on the coaxial cable. If it is not present, the sending node starts the signal transmission. Actually, there is the possibility that two nodes simultaneously send signals. This state is called a collision. In ETHERNET, the collision is detected in the form of a voltage level in the coaxial cable.
After detecting the collision, the node sends a jamming signal for a preset time, and then is set to a random-time stand-by mode. The jamming signal must be set to be longer than the maximum Maximum round trip time of the network, in order to broadcast the collision to all of the nodes connected to the network. The random-time stand-by mode is provided in order to avoid such a situation that a plural number of nodes fail to send, and if those nodes simultaneously start to send signals immediately after a communication channel becomes idle, the collision occurs again.
The optical communication network using the star coupler is schematically illustrated in FIG. 1. In the figure, reference numerals 26a and 26b designate optical fibers; 27, nodes; 25, a star coupler of the mixing rod type; and 24, terminals. A signal output from each node 27 is converted into a light signal by a light emitting element 22 of the node. The light signal is supplied through the optical fiber 26a associated therewith to the star coupler 25. The light signals transmitted from the nodes are all mixed by the star coupler 25, and then are distributed to the light sensing elements 23 of the nodes, through the related optical fibers 26b. The light signal is converted into an electrical signal by the related light sensing element, and supplied to the node 27. In the communication network thus arranged, a signal transmitted from one node is transmitted to all of the nodes, viz., the network has a broadcasting function. Accordingly, the communication network, which is similar to ETHERNET, can be constructed.
For the operation of the multichannel LAN, the CSMA/CD system is theoretically discussed (by Ikebata and Okada "Multi-Channel CSMA/CD with Hybrid Load Distribution/Region Distribution Scheme", Trans. of IECE (in Japanese) (B), Vol., J70-B, No. 12, pp1466-1474 (1987)).
To solve the problem, the Applicant of the present patent application proposed a novel technique to keep away from the collision with the third node in patent application Ser. No. Hei. 3-97405. In the technique, after sending the signal, a sending node still continues to monitor the broadcasting bus for a time period τ1, which is longer than a go/return propagation delay τ0 of the broadcasting bus. A responding node starts to return a response signal after a time τ2, which is longer than the time τ1, since the responding node receives a packet destined thereto.
Pτ(n)=e-Λτ /n| (n≧1)            (1)
Pτ(0)=e-Λτ                             (2)
Pτ(3)=1.98×10-5.
Pτ(0)=0.951.
Pτ(3)/Pτ(2)=1.60×10-2 =1.6%,
if Λ=1000 calls/sec and τ=50 μsec. The probability comparison indicates that in most cases, 2-node collision occurs, and in rare case, 3-node collision occurs. It is known that as the average call-occurrence frequency Λ per unit time, the percentage of the 3-node collisions becomes larger. In the case of large Λ, e.g., Λ=104 calls/sec, Pτ(3)/Pτ(2)=about 20%. In the graph of FIG. 3, the abscissa represents Λ (call/sec) and the ordinate, Pτ(3)/Pτ(2).
The experimental results show that the average call-occurrence frequency Λ in ETHERNET is at most 30 calls/sec. It is also known that the peak occurrence of calls is 50 to 60 times as large as the average value per day. For this, reference is made to J. P. Snoch and J. A. Hupp, "Measured performance of an Ethernet Local Computer Network", Communications of A.C., Vol. 23, No. 12, pp711 to 729 (1980). Accordingly, it is seen that λ=1000 calls/sec is approximately the instantaneous maximum value of the call occurrence frequency.
FIG. 16 is a diagram showing a first embodiment of a wavelength multiplexing transceiver for the wavelength multiplexing in an optical communication network;
FIG. 17(i c) is an enlarged diagram of the saw-tooth grating of concave gratings 111a and 111b of FIG. 17(a).
FIGS. 20(a) through 20(c) are diagrams showing a fourth embodiment of a wavelength multiplexing transceiver according to the present invention;
FIG.27(a) is an enlarged diagram of the angles of FIG. 27.
FIG. 39(a) is an enlarged diagram of the optical couplers of FIG. 39.
FIG. 39(b) is an enlarged diagram of the reflecting means of FIG. 39.
FIG. 41 is a diagram showing an example of an interconnectable start coupler with four ports constructed using a 1×3 photocoupler.
The construction of another type of node, that may be used for the optical communication network of FIG. 4, will be described. When the nodes to be discussed are applied for the FIG. 4 network, an optical communication network of the multi-channel type, which is based on the wavelength multiplexing, can be realized.
As shown, the node includes a node body 5, four communication interfaces 6a to 6d, each having the same construction as the communication interface 6 in FIG. 2, and a wavelength multiplexer 19. In the communication interfaces 6a to 6d, laser diodes as light emitting elements emit light signals of different wavelengths λa to λd. The wavelength multiplexer 19 multiplexes those light signals of the wavelengths λa to λd.
Some specific examples of communication methods, or protocols, according to the present invention will be described. FIG. 8 is a diagram showing a status transition of a sending node in a first protocol according to the invention. The protocol of FIG. 8, applied for a single transmission channel (broadcasting bus), is designed to avoid the 2-node collision. Variables in FIG. 8 have the following meanings. A variable CS represents presence or absence of a carrier sense. When CS is "1", the carrier is present. When it is "0", no carrier is present. A variable CRV indicates occurrence of the code rule violation. When CRV is "1", the CRV occurs. When it is "0", no CRV occurs. Pi is a priority level of the packet sent by a sending node in the form of a variable. Po is a priority level of the packet sent by a responding node in the form of a variable. Signs ">", "<", and "=" indicate "higher" "lower", and "equal" in the priority level. For example, if Pi>P0, the sending node is higher in priority level than the responding node.
When receiving a send request from the higher layer protocol, the node senses a carrier on the transmission channel. When the carrier is sensed (CS=1), the node is placed to the random-time stand-by mode, and then senses a carrier on the transmission channel since presence of the carrier indicates that another node uses the transmission channel. If the carrier is not sensed (CS=0), the node starts to send a signal. When the header of the packet has been sent, the node senses the carrier again while continuing the signal transmission. The packet format is shown in FIG. 9. The carrier sensing operation continues until the signal transmission has normally ended. If carrier is not sensed before the transmission ends (CS=0), the signal transmission has normally ended. If any carrier is sensed before the transmission ends (CS=1), a collision has occurred.
The sending node compares the code train indicative of the fetched-packet priority with the code train of the packet that has sent by the sending node per se. If the priority level of the packet sent by the sending node is higher than that of the fetched packet (Pi>Po), the node continues to sense the carrier for a fixed time period while sending the jamming signal. After confirming that the carrier of the competed node disappears from the transmission channel (CS=0), the node sends the packet again. When the any carrier does not appear from the transmission channel (CS=1), the nodes is placed to a random-time stand-by mode. If the priority level of the competed station is higher than that of the sending node (Pi<Po), the sending node immediately stops the sending operation and is placed to the random-time stand-by mode. If the priority levels of both stations or nodes are equal to each other (Pi=Po), the node is set to the random-time stand-by mode after the jamming signal is sent for a fixed time period. In the status transition diagram of FIG. 8, the carrier sensing is limited within a fixed period of time as "Carrier sense (jamming signal) within a fixed time period". The reason for this follows. When by some error, two nodes collide with each other, one of the nodes decides that the priority level of the node per se is higher than that of the other, and the other also makes the same decision. As a result, the competition to seize the channel continues on the transmission channel in an endless manner. It is for this reason that the carrier sensing time is limited.
A code system to determine the packet priority in a circulating manner is employed for the code train indicative of packet priority. JANKEN, the game of "scissors, "paper", and "stone", will assist your understanding of the code train. (See Appendix A of the following paper: Yasumoto et al., "PROSPEX: A Graphical LOTOS Simulaor for Protocol Specification with N Nodes" IEICE Trans. Commun. Vol. E 75-8, No. 10, pp 1015-1023 (1992)) Two (2) bits provide four combinations of "00", "01", "10", and "11". Of the four combinations, three combinations "00", "01", and "10" are assigned to "stone", "paper", and "scissors", respectively. "01" is prior to "00"; "10", to "01"; and "00", to "10". In this way, the priority level is determined in a circulating manner. In other words, the packet priority is relatively determined.
In the description thus far made, there is no guarantee of succesful communication that when three or more nodes collid. Accordingly, when the multiple-collision occurs, it is necessary to take such a control procedure that the random-time stand-by mode follows the transmission of a jamming signal for a preset time period (as in the normal protocol of CSMA/CD). The multiple-collision can be detected by sensing occurrence of the code rule violation.
The foregoing description of preferred embodiments of the invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed, and modifications and variations are possible in light of the above teachings or may be acquired from-practice of the invention. The embodiments were chosen and described in order to explain the principles of the invention and its practical application to enable one skilled in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the claims appended hereto, and their equivalents.
The laser array 106, the first slab waveguide 102, and the Fresnel reflecting mirror 104a make up a wavelength multiplexing resonance optical system, which generates wavelength-multiplexed laser light. In the optical system, the common laser element 106e is coupled, with difference wavelengths, with the remaining laser elements 106a to 106d through the Fresnel reflecting mirror 104a, so that laser oscillation occurs at the respective wavelengths. In more particular, the common laser element 106e and the laser element 106a are coupled with each other, with a wavelength λ1, through an optical path including the wiring optical waveguide 109e, the first slab waveguide 102, the Fresnel reflecting mirror 104a, the first slab waveguide 102, and the wiring optical waveguide 109a. The common laser element 106e and the laser element 106b are coupled with each other, with a wavelength λ2, through an optical path including the wiring optical waveguide 109e, the first slab waveguide 102, the Fresnel reflecting mirror 104a, the first slab waveguide 102, and the wiring optical waveguide 109b. The wavelength is determined depending on the positional relationship of the common laser element 6e and the remaining laser elements 106a to 106d to the Fresnel reflecting mirror 104a. For the details of this, reference is made to Japanese Patent Application No. Hei. 3-251677.
To cope with the above problem, in the third embodiment shown in FIGS. 18 and 19, the substrate 101 has a structure consisting of two plastic layers layered one over the other. The wavelength multiplexing transceiver when seen in the direction of an arrow B in FIG. 18 is perspectively illustrated in FIG. 19. For a better illustration of the structure of the substrate 101, the photo diode array 105, the semiconductor laser array 106 and the optical fiber 110 are contoured by dotted lines. As shown, the substrate 101 is structured such that a thin plastic thin film 117 is layered on a thick plastic thin film 118. An optical waveguide circuit including the optical waveguides 109a to 109f, which connects to the laser array 106, is formed in the thin plastic thin film 117. The optical waveguides 109h to 109k connecting to the photo diode array 105 and the optical waveguide 109g connecting to the optical fiber 110 are formed in the thick plastic thin film 118. The thickness d1 of the thin plastic thin film 117 is 10 μm, and the thickness d2 of the thick plastic thin film 118 is 30 μm. The second optical coupler 108 is formed by laying the optical waveguide 109f of the thin plastic thin film 117 on the optical waveguide 109g of the thick plastic thin film 118. The optical waveguide 109f, which couples the second optical coupler 108 with the first slab waveguide 102, is shaped such that a portion 109f of the waveguide closer to the second optical coupler 108 is broad, 40 μm, and a portion 109f2 closer to the first slab waveguide 102 is narrow, 10 μm. Accordingly, the optical waveguide at the location coupled with the optical fiber 110 is shaped in square, 40 μm×40 μm. The known selective photopolymerization is used for forming the optical waveguides in the plastic thin films 117 and 118. The selective photopolymerization is discussed by T. Kurosawa, N. Takato, S. Okikawa and T. Okada in their paper "Fiber optic sheet formation by selective photopolymerization, Appl. Opt. 17, p646 (1978). The substrate 101 was formed by laminating two plastic thin films having optical waveguides already formed therein. The thin films may be another other material than plastic, if it allows optical waveguides to be formed therein.
In FIG. 20, reference numerals 134a to 134c, and 135 designate semiconductor laser elements. The semiconductor laser elements 134a to 134c correspond to the semiconductor laser elements 106a to 106c. The semiconductor laser element 135 corresponds to the semiconductor laser element 106e. Photo diodes 136a to 136c correspond to the photo diodes (not shown) of the photo diode array 105 shown in FIG. 16. The structure of the photo diodes 136a to 136c is substantially the same as that of the semiconductor laser elements 134a to 134c. When it is fed with current, it serves as a laser diode. When it receives light, it generates photo current. The laser elements 134a to 134c are different in element length from the photo diodes 136a to 136c. The length α of the laser elements 134a to 134c is 250 μm, and the length β is 10 μm (the illustration of FIG. 20 roughly shows a layout of elements, and the layout is not exact in the reduced scale). Such a figure of the photo diode length is selected because the photo diode of 10 μm long can satisfactorily absorb light. If the element length is selected to be long, the stray capacitance of the element is increased, and cannot handle the received light signals, which are modulated at high speed. The pitch of the laser elements 134a to 134c is 10 μm, and the pitch of the photo diodes 136a to 136c is also 10 μm. The width S of the optical waveguide is 3 μm. The substrate 31 is: L3×L4=10 mm×10 mm.
Use of the optical amplifiers is effective particularly when the wavelength multiplexing transceiver is integrated on the semiconductor substrate. The optical amplifier may be applied for the case using the glass or plastic substrate. The optical amplifier may be any other amplifier than the semiconductor laser-amplifier. The optical amplifier may be realized by forming an optical waveguide on the glass substrate doped with rare earth element.
FIG. 25 shows a first embodiment of an interconnectable 5-port star coupler according to a preferred embodiment of the present invention. Three 1×2 equal branching circuits 205 are combined in a tree fashion, thereby forming an equal branching circuit unit 203 with four ports. As shown, five light-equal branching circuit units 203 are arrayed on a substrate 201 in a star fashion, thereby forming the star coupler. A light signal emanating from an optical fiber 202 is equally divided into four light signals, by the branching circuit unit 203. Those divided light signals are distributed to the remaining optical fibers 204, through optical waveguides 201a formed on the same plane of the substrate 201. The integrated optical circuit contains five intersecting portions 204 where the optical waveguides 201a intersect.
ω=δ-θ                                    (3)
ω>2θ                                           (4)
θ=90 sin-1 (n2/n1)                              (5)
Where the intersection angle δ is large, the light which does not couple the waveguides at the intersecting portion 204 increases relative to the other light. This results in increase of loss (transmission loss). The fact that the transmission loss abruptly increases when the intersection angle δ decreases below 20°, has been numerically calculated (see Takahashi and Inagaki "Analysis of the transmission loss in matrix optical waveguide", The 1992 IEICE (institute of electronics/information/communication Engineers) spring conference record, C-192 (1992)). For this reason, δ is preferably lager than 20°.
In the second embodiment of the FIG. 28, the 1×2 equal branching circuit 205 is used in place of the 1×2 fiber coupler 231, and the 2×2 equal branching circuit 206 is used in place of the 2×2 fiber coupler 232. In a conventional fiber coupler, only the Evanescent optical coupler can be manufactured with some restrictions on the manufacturing. On the other hand, use of the equal branching circuit 205 is allowed in the integrated optical circuit of the second embodiment shown in FIG. 28. In the fiber coupler, it is difficult to directly couple two optical fibers shaped circular in cross section. For this reason, two optical fibers shaped circular in cross section are located closely, and it is filled with medium of low refractive index in a manner that the medium surrounds the optical fibers. Therefore, only the optical coupler by the Evanescent wave coupling can be formed. On the other hand, in the integrated optical circuits, optical waveguides are formed in or on the substrate by the photolithographic technique. Accordingly, it is very easy to manufacture two optical waveguides directly coupled, thereby eliminating the junction loss. Further, in the instant embodiment, the angle δ at the intersecting portions in the integrated optical circuit is larger than the critical angle θ of the optical waveguide. This eliminates the interference between the optical waveguides.
According to the invention, the single mode, interconnectable multi-port start coupler can be constructed not using the 1×2 Evanescent optical coupler. Therefore, the star coupler is free from the junction loss caused by the 1×2 Evanescent optical coupler. The circuit can be constructed by using merely the combination of the 1×2 equal branching circuit and the 2×2 equal branching circuit. Therefore, also in the multi-mode, interconnectable star coupler,. its manufacturing is easy.
In the single mode optical waveguide, as shown in FIG. 32, most of light from the common part 301 goes to the waveguide 302b, and the light goes little or no to the waveguide 302a. This property of single mode asynmetric y-branching circuit is described in: Bures et al. "Mode Conversion In Planar-Dielectric Separating Waveguide", IEEE J. Qauntum Electron., vol. QE-11, No. 1, pp32-39 (1975). In the Evanescent optical coupler 304, light propagating through the waveguide 304b is branched to the waveguide 304a by the mode coupling. Accordingly, the optical coupler of FIG. 31 functions as an unequal optical coupler.
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3 * Azuma et al., A Study On The Loss Change Mechanism At An Optical Fiber Bending Region, 1992 IEICE Spring Conference Record, B 893 (1992), the relevance of which is discussed at p. 55 of the specification.
4 Burns et al., "Mode Conversion In Planar-Dielectric Separating Waveguides," IEEE Journal of Quantum Electronics, vol. QE-11, No. 1, Jan. 1975, pp. 32-39.
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8 Ikebata et al., "Multi-Channel CSMA/CD With Hybrid Load Distribution/Region Distribution Scheme," Trans. of IECE (in Japanese) (B), vol. J70-B, No. 12, pp. 1466-1474 (1987), the relevance of which is discussed at p. 7 of the specification.
9 * Ikebata et al., Multi Channel CSMA/CD With Hybrid Load Distribution/Region Distribution Scheme, Trans. of IECE (in Japanese) (B), vol. J70 B, No. 12, pp. 1466 1474 (1987), the relevance of which is discussed at p. 7 of the specification.
10 Kurokawa, et al., "Fiber Optic Sheet Formation By Selective Photopolymerization," Applied Optics, vol. 17, No. 4, Feb. 1978, pp. 646-650.
11 * Kurokawa, et al., Fiber Optic Sheet Formation By Selective Photopolymerization, Applied Optics, vol. 17, No. 4, Feb. 1978, pp. 646 650.
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16 * Published Unexamined Japanese application No. Hei. 4 326831 dated Nov. 16, 1992, the relevance of which is discussed at p. 8 of the specification.
17 Published Unexamined Japanese application No. Hei. 4-326831 dated Nov. 16, 1992, the relevance of which is discussed at p. 8 of the specification.
18 * Published Unexamined Japanese application No. Hei. 5 14285 (corresponding to U.S. application No. 07/946,192) dated Jan. 22, 1993, the relevance of which is discussed at p. 28 of the specification.
19 * Published Unexamined Japanese application No. Hei. 5 14385 (corresponding to U.S. application No. 07/873,448) dated Jan. 22, 1993, the relevance of which is discussed at p. 7 of the specification.
20 * Published Unexamined Japanese application No. Hei. 5 3457 (corresponding to U.S. application No. 07/813,443) dated Jan. 8, 1993, the relevance of which is discussed at p. 6 of the specification.
21 Published Unexamined Japanese application No. Hei. 5-14285 (corresponding to U.S. application No. 07/946,192) dated Jan. 22, 1993, the relevance of which is discussed at p. 28 of the specification.
22 Published Unexamined Japanese application No. Hei. 5-14385 (corresponding to U.S. application No. 07/873,448) dated Jan. 22, 1993, the relevance of which is discussed at p. 7 of the specification.
23 Published Unexamined Japanese application No. Hei. 5-3457 (corresponding to U.S. application No. 07/813,443) dated Jan. 8, 1993, the relevance of which is discussed at p. 6 of the specification.
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35 Takahashi et al., "Analysis Of Transmission Loss In Matrix Optical Waveguide," 1992 IEICE Spring Conference Record, C-192 (1992), the relevance of which is discussed at p. 53 of the specification.
36 * Takahashi et al., Analysis Of Transmission Loss In Matrix Optical Waveguide, 1992 IEICE Spring Conference Record, C 192 (1992), the relevance of which is discussed at p. 53 of the specification.
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International Classification G02B6/42, G02B6/12, H04L12/413, H04L12/44, G02B6/125
Cooperative Classification G02B6/4246, G02B2006/12104, H04L12/413, G02B6/12007, G02B2006/12164, G02B6/125, H04L12/44
European Classification G02B6/12M, H04L12/44, G02B6/42C6, G02B6/125