Waveguide-lattice-based architecture for multichannel optical transformations.

We consider waveguide lattices as the architecture to implement a wide range of multiport transformations. In this architecture, a particular transfer matrix is obtained by setting step-wise profiles of propagation constants experienced by a field evolving in a lattice. To investigate the capabilities of this architecture, we numerically study the implementation of random transfer matrices as well as several notable cases, such as the discrete Fourier transform, the Hadamard, and permutation matrices. We show that waveguide lattice schemes are more compact than their traditional lumped-parameter counterparts, thus the proposed architecture may be beneficial for photonic information processing systems of the future.

Optimal design of error-tolerant reprogrammable multiport interferometers.

Photonic information processing demands programmable multiport interferometers capable of implementing arbitrary transfer matrices, for which planar meshes of error-sensitive Mach-Zehnder interferometers are usually exploited. We propose an alternative design that uses a single-static beam splitter (BS) and a variable phase shift as the building blocks. The design possesses superior resilience to manufacturing errors and losses without extra elements added into the scheme. Namely, the power transmissivities of the static BSs can take arbitrary values in the range from ≈1/2 to ≈4/5. In this Letter, we show that the fraction of transfer matrices non-implementable by the interferometers of our design diminishes rapidly with its size.

Robust Architecture for Programmable Universal Unitaries.

The decomposition of large unitary matrices into smaller ones is important because it provides ways to the realization of classical and quantum information processing schemes. Today, most of the methods use planar meshes of tunable two-channel blocks; however, the schemes turn out to be sensitive to fabrication errors. We study a novel decomposition method based on multichannel blocks. We have shown that the scheme is universal even when the block's transfer matrices are chosen at random, making it virtually insensitive to errors. Moreover, the placement of the variable elements can be arbitrary, so that the scheme is not bound to specific topologies. Our method can be beneficial for large-scale implementations of unitary transformations by techniques, which are not of wide proliferation today or have yet to be developed.

Laser-written polarizing directional coupler with reduced interaction length.

Integrated optical waveguides, manufactured with femtosecond laser writing (FSLW) technology, enable precise control and manipulation of light in complicated photonic chips. However, due to the intrinsically low anisotropy of FSLW waveguides, polarizing integrated devices have had a relatively large footprint. In this Letter, we demonstrate an approach based on stress-induced anisotropy, allowing us to decrease the size of polarizing directional couplers down to 3.7 mm, almost an order of magnitude shorter than previously reported. The measured extinction ratios at the wavelength of 808 nm are 16 dB and 20 dB for the horizontal and vertical polarizations, respectively. We provide a possible theoretical model for the observed effects.