Hybrid opto-electronic circuits and method of making

#The present invention generally relates to integrated opto-electronic devices and waveguide circuits and more particularly to the hybrid integration of the active and passive optical elements and electronic chips on a common substrate.

#Large-scale integration of optical devices and elements is desirable to decrease the cost and increase the functionality of optical and opto-electronic devices and circuits. Two major integration methods are currently under the development—the monolithic approach and the hybrid approach. In the monolithic approach, all components such as laser sources, passive waveguide devices, detectors and so on are made on a common substrate from the same material such as silicon or InGaAsP series. In the hybrid approach, different components made of possibly different materials are mounted on a common substrate and are connected to each other by optical waveguides fabricated on the same substrate. In the hybrid approach, the waveguides are made of high-silica glasses that show very low propagation loss, whereas in the monolithic approach the waveguides are made of the same materials as the other components which are normally semiconductors and therefore are highly absorptive. Moreover monolithic integration of optical components may become very expensive since the fabrication process of the different optical elements are not compatible and could be destructive to one another resulting in a low yield.

#Therefore, the hybrid integration is a more feasible yet more versatile approach. In U.S. Pat. No. 4,735,677, issued in April 1988, a method for fabricating hybrid optical integrated circuits is disclosed. In that method, optical fibers and semiconductor devices (e.g., laser diodes and detectors) are disposed on predetermined positions on a board and are aligned to pre-made waveguides by pre-made guides. The waveguides and guides are made on a substrate in one process and then the optical elements are placed on the pre-determined positions between the aligning guides. Positioning the devices into the guides and the optical alignment of the devices with the pre-made optical waveguide become very critical and time consuming resulting in expensive hybrid integrated circuits.

#Exemplary embodiments of the invention will now be further described with references to the drawings in which same reference numerals designate similar parts throughout the figures thereof, and wherein:

#FIGS. 1a, 1b, 1c, and 1d illustrate in a top view, a cross-section view and two perspective views respectively of a hybrid integrated opto-electronic circuit according to a first embodiment of the invention;

#FIGS. 2a and 2b illustrate in two top views a hybrid integrated opto-electronic circuit according to a second embodiment of the innovation in which an optical elements is coupled to the waveguide through an integrated lens;

#The present invention relates to a process in which at least one optical element is optically interconnected to at least another optical element or at least one optical fiber. Reference will now be made to the accompanying drawings to describe the present invention.

#FIG. 1a shows a first embodiment of a hybrid integrated optical circuit 101 made by a process according to the present invention, in which two optical devices 1 and 2 and an optical fiber terminal 3 are interconnected optically. Each of the optical devices 1 and 2 can be any one of a semiconductor laser source, an optical isolator, a modulator, a discrete lens, a photo-diode, or the like.

#The hybrid circuit 101 contains a substrate 11, as shown in FIG. 1b, which is first coated with three layers of materials to form a lower (inner) cladding 12, a core layer 13, and an upper (outer) cladding 14 where there are printed positioning markers 15 on the surface or edges of the upper cladding 14 for recognition of positions and for alignment purposes. Although in this embodiment three layers are used, in principle there could be any desired number of layers. Alternatively, the lower cladding 12 might be the substrate 11 itself and the upper cladding 14 can be simply air. It is preferable that the coated materials of the three layers 12-14 have relatively low absorption at a prescribed wavelength, i.e. at 1.5 micrometers. The core layer 13 is photosensitive in which the refractive index or solubility is changed by exposure to a particular spectrum of light. Next, the substrate 11 is etched or carved in the designated areas by an associated method such as using a dicing saw, laser ablation or any other applicable etching and carving method, to create a carved area (recess) 16. In preferred embodiments, the dicing saw or the like creates the carved area 16 in the form of U a groove or canal, as shown in FIG. 1c. Then, electrodes (electrical connectors) 17 with the desired shape are deposited in the carved areas 16 and optical devices 1 and 2 are mounted in the designated areas without requiring an effort to place them on their ideal positions, as shown in FIG. 1d. The emitting and receiving areas of the optical devices 1 and 2 as well as the optical fiber core inside the fiber terminal 3 are aligned with the photosensitive core layer 13. The next step is to write a pattern (shape) 20 of waveguides and refractive index profile as shown in FIG. 1a by way of recognition of the actual positions of the optical devices 1 and 2 with the aid of markers 15 and image recognition processing and apparatus (not shown). The substrate 11 is then masked with a metal or any other material suitable for masking and then coated with a resist material. Then a masking pattern for the associated waveguide pattern 20 is created on the surface of upper cladding 14 by direct electron beam writing using the information from the image processing apparatus. The direct writing by electron beam ensures that the waveguide pattern 20 is aligned to the optical devices. The substrate 11 with a patterned mask thereon is then exposed to light to create the waveguide pattern 20 or other refractive index profiles in the core layer 13.