Optical waveguides – With optical coupler – Switch
Reexamination Certificate
1999-01-11
2001-04-24
Ngo, Hung N. (Department: 2874)
Optical waveguides
With optical coupler
Switch
C385S046000, C385S024000
Reexamination Certificate
active
06222955
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to optical communication systems and the like. One particular aspect of this invention relates to a 1×N optical switch.
BACKGROUND OF THE INVENTION
As we move towards the realization of optical routing in fiber networks, it is becoming increasingly important to provide signal-processing functions such as switching, in optical form at the network nodes. Optical switching is expected to become more and more important as wavelength division multiplexing reaches further into networks, greatly expanding the number of optical paths available. By using integrated optical components to perform the network node routing functions, advantages in terms of functionality, size, speed, and efficiency are achieved.
The integrated optical multimode interference (MMI) coupler has been the subject of much attention and research in recent years see, for example: L. B. Soldano, et al. in a paper entitled “Planar Monomode Optical Couplers Based on Multimode Interference Effects,”
J. Lightwave Technol
., vol. 10, no. 12, pp. 1843-1849, 1992; M. Bachmann, et al. in a paper entitled “General self-imaging properties in N×N multimode interference couplers including phase relations,”
Appl. Opt
., vol. 33, no. 18, pp. 3905-3911, 1994; and L. B. Soldano et al., in a paper entitled “Optical multi-mode interference devices based on self-imaging: principles and applications,”
J. Lightwave Technol
., vol. 13, no. 4, pp. 615-627, April 1995. All references in this document are herein incorporated by reference. It has been shown that MMI couplers can be used in generalized Mach-Zehnder interferometer configurations, to actively route and switch optical signals as detailed by: L. B. Soldano et al., in a paper entitled “Optical multi-mode interference devices based on self-imaging: principles and applications,”
J. Lightwave Technol.
, vol. 13, no. 4, pp. 615-627, April 1995; and R. M. Jenkins, et al., in a paper entitled “Novel 1×N and N×N integrated optical switches using self-imaging multimode GaAs/AlGaAs waveguides,”
Appl. Phys. Lett.
, vol. 64, no. 6, pp. 684-686, February 1994.
Generally, the 1×N switch is controlled by applying N sets of phase shifts to N arms. For small N, the phase shifts are quantized into a small number of discrete levels, and control is possible using digital logic circuitry to drive the phase shifters. As N increases, however, the driving conditions of the switch become more complex. The number of discrete phase shift levels, the number of independent phase shifts, and the maximum phase shift required all increase. As a result, the operation of larger switches requires elaborate control circuitry and higher power levels.
It would be advantageous to provide an apparatus that improves the control of the 1×N switch.
OBJECT OF INVENTION
Thus, in an attempt to overcome limitations of known prior art devices, it is an object of this invention to provide a new 1×N optical switch.
SUMMARY OF THE INVENTION
In accordance with the invention there is provided an optical switch for routing a beam of light from a first input port to a selected output port, the optical switch comprising: a Z×T optical switch having Z input ports including the first input port and T output ports; an integrated optical Mach-Zehnder interferometer comprising a first N×N multimode interference coupler having N input ports and N output waveguides, at least two of the N input ports coupled to at least two of the T output ports of the Z×T optical switch, and a second N×N multimode interference coupler having N output ports including the selected output port and N input waveguides, wherein N output waveguides of the first N×N multimode interference coupler are optically coupled with N input waveguides of the second N×N multimode interference coupler thereby forming N waveguide arms; and an optical path length changer for changing an optical path length of at least one of the N waveguide arms, wherein N is an even value greater than 3, and T is at least 2, such that the beam of light is launched into the first input port and emerges substantially from the selected output port.
In accordance with the invention there is further provided an optical switch for routing a beam of light from an input port to a selected output port, the optical switch comprising: a first Z×T optical switch having Z input ports, including the first input port, and T output ports; an integrated optical P×U GMZI comprising a splitting region having P input ports at least two of the P input ports coupled to at least two of the T output ports, a combining region having U output ports, including the selected output port, and N waveguide arms coupling the splitting region to the combining region, the N waveguide arms disposed along an open path and grouped as pairs of arms, two substantially central waveguide arms forming a first pair, and each subsequent pair formed by two waveguide arms, one on each side of the already grouped waveguide arms; and a controller for providing a control signal and an actuator for receiving the control signal and for substantially simultaneously changing optical path lengths of two individual waveguide arms that form a pair by substantially a same amount in response to the control signal, wherein N is an even value greater than 3, U is at least 3, T and P are at least 2, and P is less than or equal to N.
In preferred embodiments of the invention: Z=1; Z=1 and T=2; P=U=N; and P=2. In another preferred embodiment of the invention N=U and P=2.
In accordance with the invention there is further provided a method of upgrading an integrated N×N optical Mach-Zehnder interferometer, N being an even value greater than 3, to form an optical switch for routing a beam of light from an input port to a selected output port which comprises a step of optically coupling two input ports of the integrated N×N optical Mach-Zehnder interferometer to two output ports of a 1×2 optical switch.
In many instances monitoring of an optical beam is required. A small fraction in the form of a tap function of optical power distributed to a specified port is used as a monitor to ensure a specified intensity or integrity, i.e., switch state.
REFERENCES:
patent: 4881788 (1989-11-01), Doran
patent: WO 96/24080 (1999-08-01), None
General self-imaging properties in N×N multimode interference couplers including phase relations; M. Bachmann; P.A. Besse; H. Melchior Applied Optics, vol. 33, No. 18 Jun. 20, 1994. pp. 3905-3911.
Overlapping-image multimode interference couplers with a reduced number of self-images for uniform and nonuniform power splitting M. Bachmann; P.A.Besse; H.Melchior Applied Optics, vol. 34, No. 30, Oct. 20, 1995.pp. 6898-6910.
Compact Polarization-insensitive multi-leg 1×4 mach-zehnder switch in InGaAsP/Inp M. Bachmann; Ch. Nadler; P.A.Besse; H. Melchior Proc. ECIO, Firenze, Italy, 1994. pp. 519-522.
Optical Multi-Mode Interference Devices Based on Self-Imaging: Principles and Applications L.B.Soldan; Erik C.M Pennings J. Lightwave Technology, vol. 13, No. 4, Apr. 1995.pp. 615-627.
Novel 1×N and N×N Integrated optical switches using self-imaging multimode GaAs/AIGaAs waveguides R.M. Jenkins; J.M.Heaton; D.R.Wight; J.T.Parker; J.C.H.Birbeck; G.W. Smith; K.P. Hilton Appl. Phys. Lett. vol. 64, No. 6. Feb. 7, 1994 pp. 684-686.
The integrated prism interpretation of multileg Mach-Zehnder interferometers based on multimode interference couplers Ins. Quantum Electronics, vol. 27. 1995.pp. 900-920.
New 2×2 and 1×3 Multimode Interfernce Couplers with Free Selection of Power Splitting Ratios Journal of Lightwave Technology. vol. 14, No. 10, Oct. 1996.pp. 2286-2293.
Arbitrary ratio power splitters using angled silica on silicon multimode interference couplers Electronics Letters, vol. 32, No. 17, Aug. 15, 1996. pp. 1576-1577.
“Novel 1xN and NxN integrated optical switches using self-imaging Multi
Lagali Neil S.
MacDonald Ian
Paiam Reza
JDS Fitel Inc.
Ngo Hung N.
Teitelbaum Neil
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