Three-dimensional Photonic Circuits Research Articles

Three-dimensional compact photonic circuits for quantum state tomography of multipath qudits in any finite dimension

We propose compact three-dimensional photonic circuit designs that guarantee a remarkable reduction in the complexity of circuits to perform quantum state tomography of N-dimensional path qudits. We obtain solutions such that the number of beam splitters obeys a polynomial function of degree three with the quantum system dimension, whereas, in current proposals, this quantity grows with a polynomial function of degree four. In addition, the optical depth reduces from quadratic to linear over the dimension of the Hilbert space.

Quantum coherence measurement of qudit systems using three-dimensional photonic circuits

Knowing that quantum coherence plays a central role in quantum phenomena, we propose, in this work, three-dimensional photonic circuits with compact designs that allow measurement of the quantum coherence of $N$-dimensional quantum systems from the probabilities of detecting the photons that emerge from their outputs. Here, we present two proposals: one based on the positive operator-valued measure (POVM) proposed by Carmeli et al. [New J. Phys. 20, 063038 (2018)] and the other based on the sum of the input-state partial visibilities, obtained by interfering pairs of base states. Based on the form of the POVM that we define for this task, the proposed interferometers are given by a sequence of different unitary operations. These operations act independently in each vertical sector, or layer, of the circuit, which simplifies its determination. We have thus obtained circuits whose number of beam splitters obeys a quadratic polynomial function and has a linear optical depth, which confirms its compactness and its reduced complexity.

Three-Dimensional Photonic Circuits in Rigid and Soft Polymers Tunable by Light

Polymeric matrices offer a wide and powerful platform for integrated photonics, complementary to the well-established silicon photonics technology. The possibility to integrate, on the same chip, different customized materials allows for many functionalities, like the ability to dynamically control the spectral properties of single optical components. Within this context, this Article reports on the fabrication and optical characterization of integrated photonic circuits for the telecom C-band, made of a combination of both rigid and tunable elastic polymers. By using a 3D photolithographic technique (direct laser writing), in a single-step process, every building block of the polymeric circuit is fabricated: straight and bent waveguides, grating couplers, and single and vertically coupled whispering gallery mode resonators designed in planar and vertical geometries. Using this platform, a new type of operation was introduced through true three-dimensional integration of tunable photonic components, made ...

Fabrication of polarization-independent waveguides deeply buried in lithium niobate crystal using aberration-corrected femtosecond laser direct writing

Writing optical waveguides with femtosecond laser pulses provides the capability of forming three-dimensional photonic circuits for manipulating light fields in both linear and nonlinear manners. To fully explore this potential, large depths of the buried waveguides in transparent substrates are often desirable to facilitate achieving vertical integration of waveguides in a multi-layer configuration, which, however, is hampered by rapidly degraded axial resolution caused by optical aberration. Here, we show that with the correction of the spherical aberration, polarization-independent waveguides can be inscribed in a nonlinear optical crystal lithium niobate (LN) at depths up to 1400 μm, which is more than one order of magnitude deeper than the waveguides written with aberration uncorrected femtosecond laser pulses. Our technique is beneficial for applications ranging from miniaturized nonlinear light sources to quantum information processing.

Femtosecond Laser Micromachining as an Enabling Tool for Optofluidics and Quantum Optics

The use of femtosecond lasers as microfabrication tools to produce three-dimensional photonic circuits and optofluidic networks in transparent materials is reported. Applications to on-chip optical sensing in lab-on-a-chip and integrated quantum circuits will be discussed.

Design of optically path-length-matched, three-dimensional photonic circuits comprising uniquely routed waveguides

A method for designing physically path-length-matched, three-dimensional photonic circuits is described. We focus specifically on the case in which all the waveguides are uniquely routed from the input to output-a problem that has not been addressed to date and that allows for the waveguides to be used in interferometric measurements. Circuit elements were fabricated via the femtosecond laser direct-write technique. We demonstrate via interferometric methods that the fabricated circuits were indeed optically path-length matched to within 45 μm, which is within the coherence length required for many applications.

Engineering broadband and anisotropic photoluminescence emission from rare earth doped tellurite thin film photonic crystals

Broadband and anisotropic light emission from rare-earth doped tellurite thin films is demonstrated using Er3+-TeO2 photonic crystals (PhCs). By adjusting the PhC parameters, photoluminescent light can be efficiently coupled into vertical surface emission or lateral waveguide propagation modes. Because of the flexibility of light projection direction, Er3+-TeO2 is a potential broadband light source for integration with three-dimensional photonic circuits and on-chip biochemical sensors.

Vertically-integrated multimode interferometer coupler for 3D photonic circuits in SOI

Vertical optical coupling is demonstrated in a multimode interferometer structure fabricated using silicon-on-insulator (SOI) material. These CMOS-compatible couplers are suitable to be used to transfer optical power between stacked waveguide layers of a three-dimensional photonic circuit. Coupling between these layers can be restricted to certain regions by selectively fabricating a silicon channel between them, resulting in an isolated multimode waveguide section. Standard photolithography and etching techniques were used to fabricate proof-of-concept devices consisting of a channel waveguide coupling into a silicon waveguide that is vertically multimode. An optical coupling ratio of 93±4% between the upper and lower waveguide regions of the device was achieved with a coupler length of 241 µm.