Optical waveguides – With optical coupler – Input/output coupler
Reexamination Certificate
2002-03-08
2004-05-11
Palmer, Phan T. H. (Department: 2874)
Optical waveguides
With optical coupler
Input/output coupler
C385S024000, C385S046000
Reexamination Certificate
active
06735363
ABSTRACT:
TECHNICAL FIELD
The present invention generally relates to optical integrated circuits and more particularly to a waveguide-grating router (WGR), which is based on an arrayed-waveguide grating (AWG), associated with improving wavelength division multiplexing, including dense wavelength division multiplexing (DWDM).
BACKGROUND OF THE INVENTION
As the amount of data traffic increases in optical networks, it becomes increasingly important to provide improved wavelength division multiplexing, demultiplexing and routing devices. One such device is a waveguide-grating router WGR that facilitates DWDM. DWDM allows multiple beams of light of different wavelengths carrying separate data channels to be transmitted along a single optical fiber. WGR devices can be employed to combine and/or separate optical signal carrying data channels coded in light beams with different wavelengths.
One technique for fabricating a waveguide-grating router is planar lightwave circuit (PLC) technology. A typical PLC comprises planar waveguides and/or channel waveguides. Examples of planar and channel waveguides are shown in H. Kogelnik,
Theory of Optical Waveguides,
Guided-Wave Optoelectonics T. Tamir ed., Springer-Verlag, Berlin, 1988, and also by H. Nishihara, M. Haruna, and T. Suhara,
Optical Integrated Circuits,
McGraw Hill, New York, 1987.
In a planar (or slab) waveguide, light is generally restricted to propagate in a region that is thin (typically between 3 &mgr;m and 30 &mgr;m) in one dimension, referred to herein as the lateral dimension or height, and extended (typically between 1 cm and 100 cm) in the other two dimensions. Herein, “slab waveguide” does not necessarily imply that the waveguide comprises layers of uniform refractive index, rather “slab waveguide” may refer to, but is not limited to, any type of planar waveguide, including graded index planar waveguides. Herein, we refer to the plane that is perpendicular to the lateral dimension of the PLC as the plane of the PLC. The longitudinal direction is defined to be the direction of propagation of light at any point on the PLC. Further, the lateral direction is defined to be perpendicular to the plane of the PLC and the transverse direction is defined to be perpendicular to both the longitudinal and the lateral directions.
In a channel waveguide, light has an optical field that is substantially confined in both the lateral direction and the transverse direction. In a typical channel waveguide, the field is substantially confined within a region that extends between 3 &mgr;m and 30 &mgr;m in the lateral direction, herein referred to as the height, and extends between 3 &mgr;m and 100 mm in the transverse direction, herein referred to as the width.
There are various approaches to building a PLC. In a typical example of a PLC, a slab waveguide comprises three layers of silica glass with the core layer lying between the top cladding layer and the bottom cladding layer. Channel waveguides are often formed by at least partially removing (typically with an etching process) core material beyond the transverse limits of the channel waveguide and replacing it with at least one layer of side cladding material that has an index of refraction that is lower than that of the core material. The side cladding material is usually the same material as the top cladding material. Further, each layer may be doped in a manner such that the core layer has a higher index of refraction than either the top cladding or bottom cladding. When layers of silica glass are used for the optical layers, the layers are typically deposited on a silicon wafer. As a second example, slab waveguides and channel waveguides comprise three or more layers of InGaAsP and adjacent layers can have compositions with different percentages of the constituent elements In, P, Ga, and As. As a third example, one or more of the optical layers of the slab waveguide and/or channel waveguide may comprise an optically transparent polymer. A fourth example of a slab waveguide comprises a layer with a graded index such that the region of highest index of refraction is bounded by regions of lower indices of refraction. A doped-silica waveguide is usually preferred because it has a number of attractive properties including low cost, low loss, low birefringence, stability, and compatibility for coupling to fiber.
In addition to the channel and slab waveguides described above, various PLCs may comprise at least one optical dispersive region such as, for example, an arrayed waveguide. Typically, a waveguide-grating router (WGR) is a planar lightwave circuit and comprises at least one input channel waveguide, an input slab waveguide, an arrayed-waveguide grating (AWG), an output slab waveguide, and at least one output channel waveguide. Herein, the term “input waveguide” implies “input channel waveguide” and “output waveguide” implies “output channel waveguide;” however, “input slab waveguide” does not imply “input channel waveguide” and “output slab waveguide” does not imply “output channel waveguide.”
The arrayed-waveguide grating comprises an array of waveguides. The length of the i
th
waveguide in the AWG is denoted as L
i
. The angular dispersion that is provided by the AWG is determined in part by the difference in length between adjacent waveguides, L
i+1
-L
i
. The details of construction and operation of the WGR are described in M. K. Smit and C. Van Dam,
PHASAR
-
Based WDM
-
Devices: Principles, Design, and Application,
IEEE Journal of Selected Topics in Quantum Electronics, Vol. 2, No. 2, pp. 236-250 (1996); K. McGreer,
Arrayed Waveguide Gratings For Wavelength Routing,
IEEE Communication Magazine, Vol. 36, No. 12, pp. 62-68 (1998); and K. Okamoto,
Fundamentals of Optical Waveguides,
pp. 346-381, Academic Press, San Diego, Calif., USA (2000). Each of the publications and patents referred to in this application is herein incorporated by reference in its entirety.
Such WGRs are measured by performance parameters like insertion loss, isolation, uniformity of output signal, number of channels and data throughput, for example. As with any filter, WGRs do not perform the wavelength selection involved in (de)multiplexing perfectly. Such imperfect selection can lead to reduced isolation. Isolation concerns the difference between the signal power and the unwanted noise in the passband. The number of channels depends, at least in part, on the transfer function associated with each channel.
The transfer function describes the optical coupling between a particular input waveguide and a particular output waveguide as a function wavelength of light; the spectral transmissivity (i.e. the spectrum) describes the optical power that is coupled between a particular input waveguide and a particular output waveguide as a function wavelength of light (or, equivalently, as a function of frequency of light); the passband refers to a peak region in the spectral transmissivity associated with a particular input waveguide and a particular output waveguide; and herein “insertion loss” refers to the maximum value of transmissivity within the passband. Typically, the passband refers to the portion of the spectral transmissivity that is greater than about −20 dB below the insertion loss. Each passband is characterized by a central wavelength, a central frequency, and one or more values associated with the width of the passband. However, conventionally, the passbands associated with the light beams of different wavelengths may not have been consistent across the output waveguides, and thus, improved WGR operation is desired.
The term “bandwidth” refers to a parameter that characterizes the width of a passband; however, the term can be used in more than one way according to the context in which it is used or according to clarifying definitions imposed upon it for a particular context. Generally, bandwidth refers to the value of a wavelength range or a frequency range for which the transmissivity of a particular passband is greater than or equal to a particular reference level for all polarization states
Lam Jane
McGreer Kenneth
Zhao Liang
Amin & Turocy LLP
Lightwave Microsystems Corporation
Palmer Phan T. H.
LandOfFree
Waveguide-grating router with output tapers configured to... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Waveguide-grating router with output tapers configured to..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Waveguide-grating router with output tapers configured to... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3213038