Multicomponent optical device

Abstract: A family of multicomponent optical devices, and a method for their batch fabrication, is disclosed. An exemplary component comprises at least two regions (12,14) with different optical properties, joined so as to form a essentially planar interface (16) therebetween. A single multicomponent device may replace a number of passive components used in conventional optical arrangements. For example, a multicomponent spherical optical isolator would replace the pair of coupling lenses, the pair of polarizers and the Faraday rotator used in a conventional isolator arrangement. Advantageously, the single multicomponent device will provide inherent alignment between the various internal components. Additionally, batch processing of a multilayered structure of materials with the desired optical properties allows for a large number of devices to be formed simultaneously, each device with essentially identical optical properties.

Description: Background of the Invention Field of the Invention The present invention relates to multicomponent optical devices and, more particularly, to optical isolators. Description of the Prior Art Many optical communication systems require optical isolators. These may be used in applications such as high bit rate transmitters and optical amplifiers to prevent reflected signals from re-entering active semiconductor optical devices such as lasers. US-A-4,735,489 (Tolksdorf et al.) discloses a spherical passive optical component as set out in the preamble of claim 1, particularly developed for rotating the plane of polarization of linearly polarized light passing therethrough. In particular, the Tolksdorf et al. device comprises a ball lens made from magnetic crystalline material preferentially magnetized in the direction of light transmission, where the ball lens consists of two domes of magnetic garnet material whose basal planes are oriented parallel to one another and perpendicular to the direction of light transmission, with a spherical member between the domes consisting of optically transparent non-magnetic garnet material. The sphere can be rotated to adjust the effective thickness of the magnetic material, thus providing the ability to match the magnetooptical rotation to the wavelength of the light signal propagating therethrough. In fabrication, equally thick layers of magnetic garnet material are epitaxially deposited on the major surfaces of a substrate consisting of optically transparent non-magnetic garnet material. The coated substrate is then sawed into cubes, and the cubes are ground to form spheres. The Tolksdorf et al. process is considered to contain several drawbacks. For example, there is considerable difficulty in growing epitaxial layers on opposite major surfaces of a substrate such that the epitaxial layers are equally thick. Additionally, epitaxial growth is known to be a thickness-limited process, due to slow growth rates and relatively large strains from mismatched lattice sizes. Therefore, the ability to form spherical polarization rotators of the relatively large size (as compared to integrated circuits utilizing epitaxial growth technique) required for most optical applications is questionable in the Tolksdorf et al. process. Further, the type of optical device which may be fabricated is limited to those which require only the epitaxial deposition of similar materials. Additionally, the actual device structure as disclosed by Tolksdorf et al. may suffer performance limitations in that the magnetic material performing the desired rotation is formed in a manner such that the magnetic domes are not uniformly thick. Therefore, a linearly polarized signal passing through the central axis (indicated by numeral 9 in the figure), where the dome thickness is maximum, would experience a greater rotation than those signals traveling in parallel paths, displaced from axis 9 where the dome thickness is smaller. Lastly, the device as disclosed by Tolksdorf et al. required additional discrete, external components (i.e., polarizers) in order to perform the complete optical isolation function. In light of the above, therefore, a need remains in the prior art for a means of reducing the size, cost, alignment difficulties, fabrication problems and various other limitations in lightwave communication arrangements which require a number of separate optical functions. EP-A-0 260 654 discloses a filter tap for optical telecommunications systems. In one embodiment a resonant cavity is defined by parallel dielectric mirrors separated by an air space. A lens is provided at each end of the cavity to direct light from an input optical fibre into the cavity and from the cavity into respective output optical fibres. In another embodiment the mirrors are integrally formed on planar surfaces of the lenses. US-A-4 893 890 discloses a fibre-optic isolator for use in single-made fibre systems which uses a Faraday rotator and two polarisers, one at each end, angularly oriented from each other at the angle of rotation for isolation, and two aspheric lens connectors to couple optical fibres to the Faraday isolator. Summary of the Invention The present invention is set out in claim 1. It is an advantage of the present invention that the multicomponent devices may be produced using a batch process such that many essentially identical spheres may be simultaneously formed. In one exemplary fabrication process, relatively large sheets of the different materials utilized to form the various optical regions are attached to one another to form a laminated structure. The laminate is then diced to form a large number of cubes with the desired optical properties. The cubes are then rounded (e.g., ground polished) into the desired spherical shape. Other and further advantages of the present invention will become apparent during the course of the following discussion and by reference to the accompanying drawings. Brief Description of the Drawing Referring now to the drawings, where like numerals represent like quantities in several views: FIG. 1 illustrates an exemplary optical isolator formed in accordance with the present invention; FIG. 2-3 illustrate an exemplary batch fabrication process for an exemplary spherical optical isolator formed in accordance with the present invention; and FIG. 4 illustrates an alternative multicomponent device of the present invention which includes a non-spherical portion. Detailed Description FIG. 1 illustrates a multicomponent spherical optical isolator 50 formed in accordance with the present invention. In general, isolator 50 functions to allow a forward direction optical signal IF from a source 52 to pass through isolator 50 and into a receiving element 53, while virtually preventing reflected signals I R originating at element 53 from re-entering source 52. Isolator 50 comprises a Faraday rotator material 54, with a pair of linear polarizers 56,58 disposed on either side thereof. As will be discussed hereinafter in association with FIG. 2, polarizers 56,58 are formed as an integral part of Faraday rotator material 54. That is, the polarizers comprise a series of grating lines etched into a coating on each major surface of material 54. A pair of lenses 60,62 are attached as shown in FIG. 4 to polarizers 56 and 58, respectively. In operation, isolator 50 is surrounded by a permanent magnet (not shown) which induces a predetermined non-reciprocal angular rotation on optical signals passing through Faraday rotator material 54. Polarizers 56 and 58 are oriented so that signal IF will pass through unimpeded. Since the Faraday rotation is non-reciprocal, the reflected signal I R will be essentially blocked by polarizer 56 and substantially prevented from re-entering component 52. Advantageously, the spherical design of isolator 50 allows for the functions of coupling (60,62) and isolation (54,56,58) to be combined into a single, relatively small, inexpensive and self-aligned component. Isolator 50 may be rotated within its placement cavity (not shown) to provide beam steering. An exemplary fabrication process of an isolator will be described below in association with FIGs. 2-3. As discussed above, an advantage of the multicomponent sphere arrangement of the present invention is the ability to simultaneously form a large number of essentially identical spheres using batch processing techniques. An exemplary batch fabrication process, associated with the formation of an optical isolator (such as that illustrated in FIG. I) will be described below in association with FIGs. 2-3. It is to be understood that the following description is exemplary only, and there may exist many modifications to the fabrication process which will result in the formation of a multicomponent device of the present invention. Further, the following discussion is simplified, in terms of the number of like products which are formed from a single batch. During actual production, many hundreds of spheres may be simultaneously formed. Referring to FIG. 2, the fabrication process begins by attaching together relatively large sheets (for example, approximately four inches square) of material, which exhibit the desired optical properties, in the required order. For the isolator of FIG. 1, an exemplary laminate 200 includes a first sheet 260 of glass which may be used to form first lens 60. A sheet of Faraday rotator material 254, for example, a garnet film, is then attached to first sheet 260. Sheet 254 is first processed to form a number of properly spaced grating lines 210,212 on either major surface thereof, grating lines 210,212 being oriented so as to allow the desired optical signal to pass therethrough (grating lines 212 being illustrated in phantom). It is to be understood that grating lines 210,212 completely cover the front and back major surfaces of sheet 254. As shown in FIG. 2, the attachment of lens sheet 260 to rotator material 254 may be completed using a number of, for example, annular bonds 220 or bond segments 222 of an appropriate size to allow the unimpeded passage of the desired signal in the final product (see FIG. 1). As mentioned above, the bonding material may comprise a metal solder, epoxy, or any other suitable adhesive. Anodic bonding or thermo-compression seals may also be used to provide attachment. Although only a few bonds are shown, it is to be understood that a large number of such bonds are used to mate sheet 260 with sheet 254. Lastly, a second sheet of glass 262, used to form lens 62, is attached to the exposed major surface of Faraday rotator material 254, using a similar set of annular bonds or bond segments. Advantageously, the use of annular bonds results in the formation of a hermetic device. Hermeticity can be a problem with such multilayer components, since the materials used to form the filters (e.g., sputtered or deposited glasses) are usually porous. The annular bonds used in this invention, comprising a water impermeable material, form a complete seal around the perimeter of the device, yielding a relatively simple and inexpensive method of providing hermeticity. Subsequent to the attachment (and curing, if any), laminate 200 may be cut or diced along the dotted lines shown in FIG. 2 to form a number of individual cubes, each cube thus comprising essentially identical optical properties. One such cube 250 is illustrated in FIG. 3. A spherical optical isolator 50 as illustrated in FIG. 1 may then be formed simply by grinding or polishing cube 250. It is to be understood that the present invention is directed to the formation of relatively compact optical devices which include a number of separate optical components. In most cases, such devices will maintain their spherical shape as described and illustrated above. However, in certain applications it may be desirous to form a device including a relatively flat (i.e., non-spherical) portion. For example, if the multicomponent device is to be directly attached to a planar surface, it may be preferable for the device to also include such a surface. FIG. 4 illustrates an exemplary device 270 of the present invention which has been further processed (e.g., polished, ground, or sawed) so as to include a relatively planar surface 272. Device 270 may then be attached along surface 272 to a relatively flat major surface 274 of a substrate 276.

Claims: A multicomponent optical device (50) comprising: a first spherical-segment lensing member (60), including a base; a second spherical-segment lensing member (62), including a base; and an intermediate optical component member (54,56,58) disposed between the first and second lensing members so as to form a substantially planar interface with each base; said device having a spherical or spherical-segment outer surface; CHARACTERISED IN THAT said intermediate component member comprises: Faraday rotation means (54) including opposing first and second major surfaces; a first linear polarizer (56) comprising a plurality of grating lines (210) etched into a coating on said first major surface, wherein said first spherical-segment lensing member is attached by its base to said first linear polarizer; and a second linear polarizer (58) comprising a plurality of grating lines (212) etched into a coating on said second major surface, wherein said second spherical-segment lensing member is attached by its base to said second linear polarizer; whereby the combination of said first and second spherical-segment lensing members, said first and second linear polarizers, and said Faraday rotation means forms an optical isolator. An optical device as defined in claim I wherein the Faraday rotation means comprises a garnet film.

Inventors: BLONDER GREG E, BLONDER, GREG E.
Applicants: AT & T CORP, AT&T CORP.
Application year: 1991
Main classification: G02B6
IPC codes: G02B6, G02F1, G02B5, G02B3, G02B27