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.
Novel algorithms based upon Mueller matrix terms are presented herein, which allow the recovery of the spectra associated with incident transverse electrical (TE) and transverse magnetic (TM) orthogonal states of polarization. These, in turn, give more insight into polarization-dependent frequency shifts and other performance-related parameters of interest. This elegant patent-pending solution entails little computational efforts and can significantly improved the testing capacity and capabilities of component designers and contract manufacturers.
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.
Characterization of DWDM photonic integrated circuits presents many challenges and trade-offs. High channel numbers significantly increase the required time to screen and qualify devices at different stages within their production. The SurePath Monitor product requires accurate calibration of the absolute responsivity of each of its 43 100GHz-spaced channels, across the C-band (1525 to 1565nm), to meet its power monitoring accuracy specification of ±0.5dB. Further specifications such as input optical power range (0 to -40dBm) require photocurrent measurement capabilities ranging from mA down to sub-nA levels, whilst the high efficiency of the integrated demultiplexer filter requires large electrical dynamic range (>65dB). Characterization stations developed to ensure high throughput and low cost without sacrificing measurement accuracy and repeatability were based upon matrix-based measurement methodologies to ensure this balance is achieved.
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.
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