Shayan Mookherjea

On-chip microfluidic tuning of an optical microring resonator

We describe the design, fabrication, and operation of a tunable optical filter based on a bus waveguide coupled to a microring waveguide resonator located inside a microchannel in a microfluidic chip. Liquid flowing in the microchannel constitutes the upper cladding of the waveguides. The refractive index of the liquid controls the resonance wavelengths and strength of coupling between the bus waveguide and the resonator. The refractive index is varied by on-chip mixing of two source liquids with different refractive indices. We demonstrate adjustment of the resonance by 2nm and tuning the filter to an extinction ratio of 37dB.

Telecommunications-band heralded single photons from a silicon nanophotonic chip

A highly nonlinear (γ≈3700/W·m) silicon coupled-resonator-optical-waveguide generated heralded single photons (g⁽²⁾ (0) ≤ 0.19 ±0.03) and widely-spaced photon pairs with coincidences-to-accidentals ratio >;10 (cw) and >;23 (pulsed), and outperformed a 54× longer silicon nanophotonic waveguide.

Coupled resonator optical waveguides

Properties of the recently introduced family of coupled resonator optical waveguides (CROWs) are reviewed, particularly with reference to CROWs designed as planar waveguides in two-dimensional photonic crystal slabs to enhance nonlinear interactions and develop novel all-optical information processing devices. Topics covered include: pulse propagation both in the nondispersive approximation and to all orders of dispersion, and the coupled mode theory of nonlinear optics with pulses in CROWs and its applications to second-harmonic generation and wave coupling via field-induced refractive-index gratings. We also review recent experimental progress in the fabrication and characterization of CROWs, and applications of the CROW concept to fiber gratings and microwave waveguides.

Polymeric Mach-Zehnder interferometer using serially coupled microring resonators

We propose a novel geometry for a Mach-Zehnder interferometer in which one arm of the interferometer consists of serially coupled microresonators and the other a simple ridge waveguide. The device was fabricated in an optical polymer and its spectral characteristics were measured at telecommunications wavelengths. The serially coupled rings are modeled using a simple transfer matrix approach. Good agreement is found between the measurement and the theory.

A microfluidic 2×2 optical switch

A 2×2 microfluidic-based optical switch is proposed and demonstrated. The switch is made of an optically clear silicon elastomer, Polydimethylsiloxane (PDMS), using soft lithography. It has insertion loss smaller than 1 dB and extinction ratio on the order of 20 dB. The device is switching between transmission (bypass) and reflection (exchange) modes within less than 20 ms

Giant birefringence in multi-slotted silicon nanophotonic waveguides

We demonstrate record giant birefringence, nearly twice as large as has previously been achieved (Delta n(group) = 1.5 over more than 60 nm of bandwidth near lambda= 1550 nm) using a multi-slotted silicon nanophotonic waveguide. The birefringence is optimized by the use of materials with high refractive index contrast to create a compact single-mode waveguide, and the etching of deeply sub-wavelength channels within the waveguide, which are strongly coupled in the near field and separated by narrow air channels of optimum lateral width. When used as a polarization-selective delay element, the delay-bandwidth product per unit length is 46.6/mm over a bandwidth of 8.74 T Hz. We also design and demonstrate mode shaping of both the TE and TM polarizations to achieve near-identical coupling to a macroscopic external object, such as a lensed fiber or detector.

Statistics of light transport in 235-ring silicon coupled-resonator optical waveguides

In contrast to recent reports of localization-impaired transport in long slow-light waveguides, we demonstrate light transport in silicon coupled-resonator optical waveguides (CROWs) consisting of up to 235 coupled microrings without localization over frequency bands that are several hundred gigahertz wide. Furthermore, from the unique statistical signatures provided by time-domain propagation delay measurements, we demonstrate the spectrally correlated nature of light propagation in CROWs.

Effect of disorder on slow light velocity in optical slow-wave structures.

Slow-wave optical structures such as coupled photonic crystal cavities, coupled microresonators, and similar coupled-resonator optical waveguides are being proposed for slowing light because of the nature of their dispersion relationship. Since the group velocity becomes small, slow light and enhanced light-matter interaction may be observed at the edges of the waveguiding band. We derive a model of the effects of disorder on slow light in such structures, obtaining a relationship between the root-mean-square variation in the coupling coefficients and how slow the light is at the band edge.

Dispersion characteristics of coupled-resonator optical waveguides

A tight-binding optical waveguide formed by proximity coupling of nearest-neighbor resonators, e.g., a coupled-resonator optical waveguide (CROW), has distinct wave and pulse propagation characteristics compared with a conventional waveguide, and several applications in photonic devices have been proposed recently. But analysis of the dispersion, and in particular the group-velocity dispersion, in such a waveguide requires particular attention: the waveguide displays two distinct regimes of operation, depending on the position of the wave packet in the dispersion relationship.

Spectrally multiplexed and tunable-wavelength photon pairs at 1.55 μm from a silicon coupled-resonator optical waveguide

Using a compact optically pumped silicon nanophotonic chip consisting of coupled silicon microrings, we generate photon pairs in multiple pairs of wavelengths around 1.55 μm. The wavelengths are tunable over several nanometers, demonstrating the capability to generate wavelength division multiplexed photon pairs at freely chosen telecommunications-band wavelengths.