This paper describes a monolithically integrated 1x2 SOA-based switch in InGaAsP/InP. It can be fabricated in one epitaxial growth step, has a footprint of only 4.2mm x 0.35mm, operates on sub-ns time scales and is meant to be integrated with other passive and active waveguide devices on the same InP substrate. The design process optimized the device dimensions using a modified finite-element modal-overlap method. This method provides significant computational savings compared to full beam-propagation method (BPM) simulations. The device uses a single-mode vertical integration technique for a monolithic integration of active and passive waveguide components. To compensate for the polarization sensitivity, tensile-strained quantum well active regions are used. To switch a signal to an output waveguide, the SOA in that waveguide is forward-biased while the SOA in the other output waveguide is reverse-biased to provide a large attenuation (>30dB), resulting in minimal crosstalk. This switch has an estimated insertion loss of 4dB, with a polarization dependent loss of < 1dB.
Spot-size converter (SSC) is an important building block of InP-based photonic integrated circuits since it allows a standard single-mode fiber with a large and symmetric mode spot to be efficiently coupled with high displacement tolerance to a semiconductor waveguide with a small and asymmetric mode spot. Having an on-chip SSC integrated with a semiconductor waveguide is practically advantageous since such an element greatly simplifies the packaging process while increasing its reliability. In this paper, a SSC utilizing two-step lateral tapering is proposed for converting the semiconductor waveguide device mode into that suitable for fiber coupling without compromising the designs of the device and coupling waveguides. This is achieved by inserting a transient taper between the device and coupling waveguide as an impedance matcher.
This paper describes the design principles and characterization results for such a two-step SSC, compatible with earlier reported InP-based photonic integrated circuits for WDM. Transmission, Fabry-Perot fringes and photoresponsivity measurements (the last - by using an on-chip waveguide photodetector monolithically integrated with the SSC) show excellent performance of the two-step SSC. In good agreement with simulations, it was experimentally demonstrated that using this integrated component for fiber coupling can reduce the coupling loss to below 1dB, which includes the taper radiation loss of ~0.2 dB.
The advantages of monolithic integration of passive and active optoelectronic components into multifunctional PICs (photonic integrated circuits) are numerous and well known. In WDM transmission systems, where up to hundreds of wavelength channels may be present and must be manipulated on a per wavelength basis, the advantages of PICs containing wavelength (de)multiplexers and arrays of active components rapidly multiply. This has been exploited in our earlier reported SurePath family of InP-based PICs for optical channel monitoring / equalization, which contain an echelle grating demultiplexer and single-mode vertically integrated waveguide photodetectors / electroabsorption attenuators inserted into each of its output channels. Now, the same design principles and fabrication techniques have been utilized for the development of a dense WDM data receiver. This paper concentrates on the key building block of such a component, the single-mode vertically integrated waveguide photodetector. A detailed characterization and analysis of the device performance are presented.
In WDM optical networks, signals have to be manipulated and monitored on a per wavelength basis. This requires that (de)multiplexing and wavelength processing functions are combined in the same optical component. The most efficient solution from a footprint size, cost and reliability point of view would be a combination of both functions in one photonic integrated circuit (PIC), fabricated by photolithography. Given that processing / detecting of individual wavelengths is an active function, in S, C and L communication bands naturally realized by InP and related semiconductor materials, InP-based PICs are widely agreed to be the superior choice.
This paper reports a practical design of such InP-based PICs. It is based on a building block approach, which allows a large variety of WDM optical components to be built from relatively few monolithically integrable elements, by using standard semiconductor fabrication technologies. These include: (i) (de)multiplexer based on a planar echelle diffractive grating with polarization compensation in the slab waveguide region; (ii) single-mode vertically integrated waveguide active devices with detecting, attenuating, amplifying and switching features, inserted in every (in)output waveguide channel of a planar (de)multiplexer, and (iii) passive waveguide circuitry required for coupling the light to and directing it through the InP-based photonic chip. Design and characterization examples of the building blocks and PICs for channel monitoring, variable attenuation / equalization and spatial switching are presented.
Concept, basic physics and modeling results of a novel modulation technique, associated with a variable heating of the electron-hole plasma in the active region of a lasing device, are reviewed with respect to the ultimately high-speed performance of semiconductor lasers. It is shown, that independent control of the plasma concentration and temperature provides a way for generating the picosecond gain-switched optical pulses and multi-Gbit/s modulation with, optionally, no parasitic frequency chirp. To practically realize this method, three-terminal laser structures are suggested, in which two bias voltages are intended to drive the pumping rate and the energy, yielded in the active region plasma as a result of injecting a single electron.
KEYWORDS: Waveguides, Absorption, High speed photography, Waveguide modes, Integrated optics, Camera shutters, Photonics, Switching, Refractive index, Chemical elements
A new type of integral-optics bistable element, based on electroabsorption waveguide distributed feedback structure, is proposed and investigated. A model of the device is formulated to calculate its main electrical and optical characteristics. The element has high on/off ratio (more than 10) in a bistable regime, the switching power is less than 5 - 6 mW, while the switching time is limited only by the RC-constant of the electrical circuit and is less than 10 ps.
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