Abstract: A planar optical filter consisting of two stages performing stationary imaging between an input waveguide and a set of output waveguides is characterized by reduced crosstalk and minimal loss variation in each passband. The input stage is a small waveguide grating router, connected to the output stage by a waveguide lens essentially covering the entire central zone of the input router. In one embodiment, the second stage includes two waveguide grating routers and the lens has two separate output apertures, respectively connected to these two routers. In this arrangement, 2N input channels applied to the input port are separated by the first grating into two interleaved sets of N channels each. The two sets are respectively transferred by the composite waveguide lens to the two output gratings which respectively separate the N channels of each set.

Abstract: Apparatus for filtering an optical input signal includes a coupler and an arrayed waveguide grating connected to the coupler having a phase shifting region. The phase shifting region is a back wall of a free space region of the arrayed waveguide grating with concentric image and reflector surfaces. Radial waveguides between the surfaces are divided into alternating regions of wider and thinner sets of waveguides. A corresponding change in optical length alters the phase of the input signal which forces an output signal of a desired wavelength to appear at a desired port of the filter.

Abstract: Apparatus for filtering an optical input signal includes a coupler and an arrayed waveguide grating connected to the coupler having a phase shifting region. The phase shifting region is a back wall of a free space region of the arrayed waveguide grating with concentric image and reflector surfaces. Radial waveguides between the surfaces are divided into alternating regions of wider and thinner sets of waveguides. A corresponding change in optical length alters the phase of the input signal which forces an output signal of a desired wavelength to appear at a desired port of the filter.

Abstract: Optical devices, such as wavelength routers, having a plurality of waveguides of differing lengths, with improved independence to temperature fluctuations. Improved temperature independence is achieved by varying the cross-section of the device waveguides. Cross-section variation can be implemented in one or more of the following ways: selectively applying a temperature-compensating material (e.g., a polymer) over portions of the waveguides, and/or varying the dimensions and/or compositions of the materials used in the waveguides, either along each waveguide or between waveguides or both. By carefully designing the devices, the temperature effects resulting from the different lengths of the different waveguides can be compensated to produce a relatively temperature-independent device.

Abstract: An optical interconnection apparatus including waveguide arrays, such as grating routers and star couplers, has reduced coupling loss by reducing the width of the waveguides in the array, where they connect to the free-space region, so that they are smaller than the gaps between adjacent waveguides. The free-space region is formed by a slab whose thickness is tapered in a transition region, where it connects to the waveguide arrays, so as to essentially eliminate any mismatch loss that would otherwise be caused in an abrupt junction of the waveguide arrays with the free-space region.

Abstract: An optical apparatus having a specifiable passband width comprises a first free space region that has at least one input port configured to receive light waves traveling through a first waveguide coupled to the input port. The first waveguide further comprises a longitudinal slot that has a given length, L, and width, S, so as to produce the specifiable passband width. The optical apparatus further includes an optical grating that has a plurality of waveguides connected to the first free space region with the optical grating defined by a plurality of unequal length waveguides. A second free space region is coupled to the optical grating so as to receive light traveling through the optical grating. The second free space region further has at least one output port configured to provide light waves to a second waveguide coupled to the output port.

Abstract: A compact multiwavelength laser arrangement includes a reflective waveguide grating combined with two arrays of reflecting waveguide elements located in separate focal regions formed by the grating. The laser uses a folded imaging arrangement with nonoverlapping focal regions that eliminates unwanted resonances of previous reflective arrangements. The laser's advantages over existing transmissive laser arrangements include reduced size, faster response time, and increased number of wavelengths.

Abstract: Monitoring of the wavelength and power in an optical network is realized by including a wavelength router in which output ports at particular locations are included to derive samples for the monitoring. A periodic variation in the optical length of the arms of the grating in the router is used to focus additional power at these selected locations. Such a router can also be used for multiplexing and demultiplexing optical signals.

Abstract: An integrated optical device (e.g., a wavelength router) is formed on a substrate, where the device has a compressive force within the plane of the device and the substrate has at least one non-straight edge. The device is formed by annealing the substrate wafer and then separating the device by cutting along one or more non-straight or curved lines. When the device layer is much thinner than the substrate and when the coefficient of thermal expansion of the substrate material (e.g., silicon) is greater than that of the device material (e.g., silica), the annealing process generates the compressive force. This in turn enables the device to be separated from a wafer by cutting along non-straight lines using either a laser or a milling machine without fear of cracks and fissures propagating over time into the device. The present invention enables manufacturing with greater yields since curved devices, such as wavelength routers, can be more efficiently packed onto a single wafer.

Abstract: Two or more wavelength routers are cascaded together to form a passband filter with low levels of crosstalk between different channels of a wavelength division multiplexing (WDM) stream. Cascading wavelength routers is a technique that can be used to efficiently realize wide and flat passbands, but high levels of cross-talk may result from multi-path interference caused by grating lobes, which produce unwanted transmission paths between the two routers. Spatial filtering can be applied to inhibit the propagation of light-energy along the unwanted paths, and it can be implemented using any suitable techniques including pinholes, reflectors, waveguides, and multi-mode interferometers (MMIs). The resulting passband filter can be designed to generate levels of crosstalk similar to those of conventional passband filters that rely on a single waveguide router.

Abstract: An optical waveguide router is provided with a control arrangement that is bonded to the silicon wafer of the router to deform the arms of the grating of the router to change their optical lengths in the same proportion with little strain in the direction normal to that of the waveguide arms to minimize birefringence effects.

Abstract: A monolithically integrated laser which is rapidly tunable over a wide optical frequency range comprises a frequency router formed in a semiconductive wafer defining a tuned cavity. A control circuit applies electrical energy to predetermined controllably transmissive waveguides connecting the frequency routing device with reflective elements defined in the wafer. This tunes the laser to a desired one of a plurality of optical frequencies. Application of such electrical energy creates frequency selective pathways through the wafer able to support selected lasing frequencies. This laser is economical to construct and is useful in high capacity, high speed optical communications networks.

Abstract: A method is provided for reducing the polarization shift between different modes of an optical signal propagating in an optical grating having a plurality of waveguides extending in a common plane. The method includes the step of imparting curvature to the optical grating along a line that traverses the plurality of waveguides in a direction that is substantially perpendicular to the direction in which the optical signal propagates. The curvature varies in a nonuniform manner along the line to which it is imparted. The curvature may vary in a substantially linear manner along this line, which in some cases may define a symmetry axis of the grating. Sufficient curvature may be imparted to substantially eliminate the polarization shift. The curvature may be imparted by flexing the optical grating at two contact points respectively located near a longest and shortest of the plurality of waveguides.

Abstract: A method for reducing the inherent polarization shift caused by birefringence between the TE and TM modes of an optical signal propagating in an optical grating which has a plurality of waveguides includes the step of: irradiating the waveguides of the optical grating for different periods of time to induce a compensating polarization shift that substantially reduces the inherent polarization shift. If desired, a compensating polarization shift may be induced which not only reduces but also substantially eliminates the inherent polarization shift.

Abstract: An optical apparatus is provided that includes a first frequency routing device having at least one input port and P output ports, where P>2. A second frequency routing device is also provided that has P input ports and at least one output port. P optical paths couple the input port of the first frequency routing device to the output port of the second frequency routing device.

Abstract: An optical appliance includes at least one input waveguide and a first free space region connected to the input waveguide. A first plurality of waveguides is connected to the first free space region. An optical grating, which is connected to the first plurality of waveguides, includes a plurality of unequal length waveguides that are divided into at least three waveguide groups. Adjacent waveguides that belong to the same group have a substantially constant path length difference between them while adjacent waveguides belonging to different groups of waveguides have a path length difference between them that differs from the constant path length difference by an odd integer multiple of one-half a preselected wavelength. A second plurality of waveguides is connected to the optical grating and a second free space region is connected to he second plurality of waveguides. At least one output waveguide is connected to the second fee space region.

Abstract: The efficiency and freedom from cross-talk achieved by transmissive multiplexer/demultiplexer devices is achieved in a reflective multiplexer/demultiplexer device. The reflective geometry avoids the large size devices necessitated by transmissive geometries handling a large number of optical channels. The reflective geometry also avoids long bends in waveguides used in optical gratings in high efficiency transmissive geometries. Integrated optical multiplexers/demultiplexers in accordance with this invention comprise a plurality of waveguides for carrying unmultiplexed optical signals interleaved with a plurality of waveguides for carrying multiplexed optical signals. The two pluralities of waveguides are connected to the boundary of a free space region. The pluralities of waveguides communicate through the free space region with an optical grating comprising a plurality of waveguides each terminated in a reflective element.

Abstract: A tunable waveguide grating includes a plurality of N waveguides which define N optically transmissive pathways. A plurality of (N-1) electrodes are arranged in the pathways such that the kth pathway contains (k-1) electrodes, where 0<k<N. As a result of this arrangement, an optical signal propagating through the kth pathway will experience a phase shift provided by each of the (k-1) electrodes arranged in that pathway. Consequently, in contrast to prior tunable optical gratings, each electrode may contribute a phase shift to the portions of the signal propagating through several waveguides and hence as the number of waveguides increases no individual electrode is required to produce relatively large phase shifts.

Abstract: We describe a technique for producing a flat passband in a wavelength multiplexer. We obtain this by combining two output waveguides, and by optimizing their parameters so as to produce a maximally flat passband with minimal loss. The optimum parameters are obtained, to a good approximation, by choosing each output waveguide so that its mode approximately matches the input waveguide mode (see page 9 on) and by choosing the spacing of the two waveguides so that the multiplexer transmission coefficient at the edges of the passband is approximately equal to the value at the center of the passband. We also include, in the multiplexer, additional waveguides that allow the center wavelength of the passband to be varied in steps of S/Q, where S is the channel spacing and .delta. is an integer exceeding the number of channels (multiple control input waveguides). As a result, we obtain a unique arrangement, suitable for realization in integrated form using waveguide arrays.

Abstract: A monolithically integrated laser which is rapidly tunable over a wide optical frequency range comprises a frequency router formed in a semiconductive wafer defining a tuned cavity. A control circuit applies electrical energy to predetermined controllably transmissive waveguides connecting the frequency routing device with reflective elements defined in the wafer. This tunes the laser to a desired one of a plurality of optical frequencies. Application of such electrical energy creates frequency selective pathways through the wafer able to support selected lasing frequencies. This laser is economical to construct and is useful in high capacity, high speed optical communications networks.