Various methods of hybrid integration of photonic circuits are discussed focusing on merits and challenges. Material platforms discussed in this report are mainly polymer and silica. We categorize the hybridization methods using silica and polymer waveguides into two types, chip-to-chip and on-chip integration. General reviews of these hybridization technologies from the past works are reviewed. An example for each method is discussed in details. We also discuss current status of our silica PLC hybrid integration technology.
We report on our efforts to integrate silica and polymer waveguide devices, such as arrayed waveguide gratings
(AWG's), tunable lenses, optical switches, variable optical attenuators (VOA's), power taps. In particular, the
realizations of various optical add/drop multiplexers and tunable dispersion compensators are discussed. The integration
techniques, the design architectures and the corresponding optical performances are presented.
We report on hybrid organic-inorganic optoelectronic sysbsystems that integrate passive and active optical functions. The integration approaches involve various levels of hybridization, from splicing of pigtailed elements, to chip-to-chip attachment, to hybrid on-chip integration involving grafting and flip-chip mounting, and finally to true heteroepitaxy. The materials integrated include polymer, silica, silicon, silicon oxynitride, lithium niobate, indium phosphide, gallium arsenide, yttrium iron garnet, and neodymium iron boron. The functions enabled by this hybridization approach span the range of functions needed in optical circuitry, while using the highest-performance material system for each element. We demonstrate a number of hybrid subsystems, including fully reconfigurable optical add/drop multiplexers and tunable optical transmitters.
We report on a single-chip 32-channel reconfigurable optical add/drop multiplexer (ROADM) based on a polymer planar lightwave circuit platform. This subsystem on a chip consists of 32x8 switches and arrays of 32 add/drop switches, variable optical attenuators (VOA's), power taps, and photodiodes. The architecture, design and optical performance are presented.
We report on a highly integrated photonic circuit using a polymer-based planar waveguide system. The properties of the materials used in this work such as ultra-low optical loss, widely tunable refractive index, and large thermo-optic coefficient, enable a multi-functional chip-scale microphotonic circuit. We discuss the application of this technology to the fabrication of a fully reconfigurable optical add/drop multiplexer. This subsystem includes channel switching, power monitoring, load balancing, and wavelength shuffling functionalities that are required for agile wavelength-division multiplexing optical networks. Optical properties of our material systems and performance characteristics of the implemented optical passive/active elements are presented, and the integration schemes of the devices to achieve a fully integrated reconfigurable optical add/drop multiplexer are discussed.
We report on advances in the hybrid organic/inorganic integration of passive and active optical functions. The integration approaches include chip-to-chip attach, flip-chip mounting, and insertion of films in slots formed in planar lightwave circuits. The materials integrated include polymer, silica, silicon, silicon oxynitride, lithium niobate, indium phosphide, gallium arsenide, yttrium iron garnet, and neodymium iron boron. The functions enabled by the hybrid integration approaches span the range of building blocks needed in optical circuitry, while using the highest-performance material system for each function. We demonstrate high-functionality optoelectronic integrated circuits, including fully reconfigurable optical add/drop multiplexers and tunable optical transmitters.
We propose a single-chip-based module that provides the entire switching/monitoring/equalizing/shuffling functionality needed in 8-channel fully reconfigurable optical add/drop multiplexers. This subsystem on a chip includes an array of switches for adding/dropping individual channels, optical power taps and integrated photodetectors for power monitoring, variable optical attenuators for channel power equalization, and optical cross-connects for channel shuffling at the add and drop ports for full wavelength agility. The chip is based on a polymer-on-silicon platform that allows hybrid integration of passive and active elements. Waveguiding circuitry is built in an optical polymer, and it includes thermo-optic switches, variable optical attenuators, and power taps. Out-of-plane coupling mirrors are formed by ablation of 45° slopes in the polymer waveguides with an Excimer laser, followed by metalization. A self-aligning flipchip process is used to mount photodetector arrays on top of mirrors fabricated in tap waveguides for power monitoring.
The worst-case fiber-to-fiber insertion loss for the proposed module, between 1528 and 1610 nm wavelength, is 1.2 dB from Input to Output (Express), including 4% tapped power, and 1.2 dB from Input to Drop and from Add to Output (4.1 dB with 8×8 shuffle cross-connects). The polarization dependent loss for any path is under 0.2 dB, and the polarization mode dispersion is under 0.05 ps. The channel-to-channel crosstalk is 50 dB, the switch extinction is 45 dB, and the return loss is 50 dB.
We report on a hybrid integrated metro ring node subsystem on a chip that consists of an array of four independent reconfigurable optical add-drop circuits, each with power monitoring and automatic load balancing, and supporting shared and dedicated protection protocols in two-fiber metro ring optical networks. The four-channel metro ring node chip has polymeric optical waveguiding circuitry, thermally actuated with heaters consisting of resistive strips of metal. Photodiode arrays are flip-chip mounted on top of 45° mirrors cut in the waveguides of optical power taps. The mirrors are fabricated by Excimer laser ablation of the polymer followed by smoothing and metalization. The non-integrated implementation of a metro ring node uses 48 discrete elements, namely 8 1×2 switches, 8 2×2 switches, 8 VOAs, 12 taps, and 12 photodiodes. The proposed integrated solution is an exemplary embodiment of the benefits of optoelectronic integration as it provides, when compared to the discrete solution, significant cost reduction, space savings, lower electrical power consumption, higher reliability (fewer devices, runs cooler), and fewer board-level fiber interconnects.
Lithium Niobate (LiNbO<SUB>3</SUB>) films produced by the crystal ion slicing (CIS) method are introduced in various components in use in the optical telecommunications market. The CIS technique employs high-energy ion implantation to create a narrow (~0.2 micrometers ) planar layer of localized damage, buried ~10 micrometers beneath the surface of the implanted LiNbO<SUB>3</SUB> wafers. This sacrificial layer allows for slicing of microns-thick LiNbO<SUB>3</SUB> films, either by selective wet chemical etching or by thermal shock. The obtained films have bulk material properties and morphology suitable for integrated optics applications. Slices of X-cut LiNbO<SUB>3</SUB> were used to produce zero-order wave retarders that can be inserted in slots cut into planar lightwave circuits, resulting in TE-TM polarization mode conversion with high extinction ratio (30 dB) and low excess loss (<0.1 dB). Conventional LiNbO<SUB>3</SUB> waveguide fabrication techniques were combined with the CIS process to produce CIS films of Z-cut LiNbO<SUB>3</SUB> with optical circuits patterned prior to lift-off, having propagation losses typical of bulk LiNbO<SUB>3</SUB> waveguides. Using thin sheets of LiNbO<SUB>3</SUB>, velocity- and impedance-matched modulators can be fabricated with low V<SUB>(pi</SUB> )L(~7.6 V.cm) and low microwave losses (0.3 db/cm.GHz<SUP>1/2</SUP>). The CIS film optical circuits can be integrated into hybrid systems with otherwise incompatible, yet technologically important materials platforms.
Magneto-optics is an area that is uniquely enabling for the production of nonreciprocal components such as optical isolators and circulators. The concepts behind the nonreciprocity include nonreciprocal polarization rotation (Faraday rotation) and nonreciprocal phase shift. A magneto- optic material that is magnetized in the direction of propagation of light acts as a Faraday rotator. An asymmetric magneto-optic waveguide that is magnetized perpendicular to the propagation direction acts as a nonreciprocal phase shifter. Both effects can be utilized to realize nonreciprocal devices. Today, commercial isolators and circulators are strictly bulk components, and as such they constitute the only type of optical component that is not available in integrated form. However, the technology for integrated nonreciprocal devices has been maturing and is expected to have a considerable impact in the communication industry by enabling the integration of complete optical subsystems. We report on the development of integrated optical isolators and circulators that consist of polymer-based planar interferometers with inserted thin films of cerium-substituted Yttrium Iron Garnet (Ce-YIG) for efficient Faraday rotation, and thin films of LiNbO<SUB>3</SUB> for wave-retarders that enable polarization-independent operation.
The need for tunable optical transmitters in optical networking is growing at a rapid rate. A tunable optical transmitter is the combination of a tunable laser, an isolator, and a modulator. Although today lasers and modulators could be integrated together on a single chip, an integrated component of this type would not be useful because the absence of an isolator between the two elements would cause optical reflections to reach the laser, leading to a high level of frequency chirp and relaxation oscillations. Therefore discrete external modulators are used, and lasers are coupled to them through discrete optical isolators. We report on recent developments in integrated active, thermo-optic, magneto-optic and electro-optic technologies that enable the production of a fully integrated tunable transmitter. This transmitter consists of a planar polymer waveguide circuit that is built on a silicon chip and in which films of a variety of materials are embedded. This subsystem on a chip includes a laser chip coupled to a thermo-optically tunable planar polymeric filter resulting in a tunable external cavity laser; an integrated magneto-optic isolator consisting of a planar polymer waveguide with inserted thin films of yttrium iron garnet for Faraday rotation, crystal ion sliced LiNbO<SUB>3</SUB> for half-wave retardation, and polarizers; and an electro-optic modulator consisting of a crystal ion sliced LiNbO<SUB>3</SUB> thin film patterned with a Mach-Zehnder interferometer and grafted into the polymer circuit, capable of operating with less than 5 Volts at modulation speeds up to 40 Ghz.