Patinharekandy Prabhathan

Compact SOI nanowire refractive index sensor using phase shifted Bragg grating

The phase shifted vertical side wall gratings are designed and numerically simulated on a submicron SOI waveguide to obtain the performance characteristics needed for an integrated refractive index sensor. The gratings are designed to obtain narrow band width, high transmittivity and sharp line shape in the resonant transmission so that the sensor sensitivity can be improved. The proposed sensor is easy to fabricate and will provide a linear response over a wide wavelength range with a compact structure dimension which is suitable for label free biosensing applications. The detection limit of the sensor is investigated through both wavelength shift and intensity measurement method and the performance parameter is compared with other silicon based structures like Mach-Zehnder interferometer, ring resonator and surface corrugated Bragg grating.

Discrete and Fine Wavelength Tunable Thermo-Optic WSS for Low Power Consumption

Broadband wavelength tunability is demonstrated in a microring resonator (MRR)-based thermo-optic wavelength selective switch (TO-WSS) with low power consumption and low thermal crosstalk. Instead of direct tuning a single MRR spectrum, the discrete and fine wavelength tunability in a Vernier configured TO-WSS has been used to achieve single wavelength selection over a high free spectral range (FSR). With the observed discrete tunability (7.3 mW/FSR) and fine tunability (5 mW/nm) of the WSS, the power requirement for full band tuning can be reduced to 32.7% of that of a single ring tuning.

{\rm C}{+}{\rm L}

We observe that the cascaded typical Y junctions will introduce unwanted periodic fringes over the spectrum in practical systems when they link with multimode waveguides. To solve the problem, we design and experimentally demonstrate a wavelength insensitive multimode interferometer (MMI) based 3-dB splitter which has all the merits of Y-splitters such as polarization insensitivity and ultra-compactness. The splitter has a footprint of 1.5 × 1.8 µm(2), nearly one order smaller than the previously reported MMI splitters. The measured excess losses for TE and TM modes at telecom wavelength are as low as -0.11 dB and -0.18 dB respectively.

Band Tunability

Series coupled triple ring resonators are designed and fabricated on a SOI platform as a thermo-optic wavelength selective switch (TO-WSS) having individual ring resonance tunability and narrow band, flat-top spectrum with high channel isolation. Optimal detuning combinations of the ring resonators are identified in the WSS to achieve an effective OFF state with high channel extinction, low switching cross talk, and low loss of OFF state. It is observed that detuned OFF states with a single ring which is adjacent to the input bus waveguide and two rings which are adjacent to the drop waveguide, are more effective for the highest channel extinction, lowest switching cross talk, and zero loss of OFF state in the WSS. A maximum channel extinction of 22 dB, lowest switching cross talk of −30  dB, and a zero loss of OFF state is achieved with a single ring detuned OFF state using a switching power of 48 mW.

Ultra-compact low loss polarization insensitive silicon waveguide splitter

We propose the silicon-on-insulator (SOI) based, phase shifted vertical side wall grating as a resonant transmission filter suitable for dense wavelength division multiplexing (DWDM) communication channels with 100 GHz channel spacing. The gratings are designed and numerically simulated to obtain a minimum loss in the resonant cavity by adjusting the grating parameters so that a high transmittivity can be achieved for the resonant transmission. The resonant grating, which is designed to operate in the DWDM International Telecommunication Union (ITU) grid C band of optical communication, has a high free spectral range of 51.7 nm and a narrow band resonant transmission. The wavelength selectivity of the filter is improved through a coupled cavity configuration by applying two phase shifts to the gratings. The observed channel band width and channel isolation of the resonant transmission filter are good and in agreement with the ITU specifications.

Optimal detuning combinations in a series coupled silicon micro ring resonator thermo optic-wavelength selective switch

Abstract. Long-range surface plasmon polariton (LRSPP) interference in a dielectric supported bimetal layer configuration is analyzed for nanoscale periodic feature fabrication. The single metal layer in a conventional configuration has been split into a bimetal layer configuration supported by a dielectric layer to enable LRSPP interference in different layers. It is shown that the configuration can be implemented in two different ways to record the interference pattern with high exposure depth and high contrast. Subwavelength periodic pattern having a half-pitch resolution of 65 nm at 446-nm wavelength is illustrated with the proposed two-beam and four-beam LRSPP interference configurations.

Broadband tunable bandpass filters using phase shifted vertical side wall grating in a submicrometer silicon-on-insulator waveguide

We design and experimentally demonstrate 50 picoseconds (ps) low loss delay line on 300 nm SOI platform. The delay line unit consists of straight rib waveguide and strip bend section linked by a transition taper waveguide. Low propagation loss of ~0.1 dB/cm is achieved on the straight rib waveguide. With taking into account both low loss and desirable delay, a complete design and characterization process for passive delay line is presented. Our measurement results show that about 0.7 dB excess loss is achievable for 50 ps delay. The loss can be further reduced by adjusting the layout parameters.

Dielectric supported bimetal layer configuration for long-range surface plasmon polariton interference–based subwavelength lithography

Surface characterization of the working components has always been a subject of interest among researchers and industry specialists. Especially in the aerospace industry where the aerodynamic capabilities are largely altered by the surface quality of the component of interest, there remains an extensive need for developing systems for effectively characterizing the surface quality. To realize an optical based non-contact and an in-line surface roughness measurement system, it is essential to understand the relationship between the quality of the surface and statistical parameter of the reflected speckles. The range of the measurement system being proportional to the wavelength of light used makes the analysis fundamentally important in order to understand the properties of speckles at a different wavelength. In this context, this paper examines the nature of the formed IR speckles from three different diffusers by analyzing their raw structure. Image processing algorithms that are developed study the different parameters of the 8-bit binary speckles, namely, the fractal property and number of connecting components. The paper also discusses the future work direction on relating the proposed analysis to derive the algorithm required for evaluating the surface finish parameters.

Design and characterization of low loss 50 picoseconds delay line on SOI platform

A speckle pattern is a direct fingerprint of surface height variation on the sample. In this paper, angular speckle correlation technique is applied to estimate surface roughness Ra of an additive manufactured sample with different surface roughness Ra values varying from 5μm to 20μm. Feasibility study is conducted to evaluate the correct incidence and the change in incidence angle for angular speckle correlation. Speckle correlation is computed from two speckle images that are recorded at two different incidence angles on the rough surface and surface roughness information is gleaned. Test results in terms of surface roughness measurement from standard calibration plate and additive layer manufactured samples are presented.

Fractal speckle image analysis for surface characterization of aerospace structures

This paper illustrates a filter configuration which uses a single ring resonator of larger radius connected to a grating resonator at its drop port to achieve single wavelength selectivity and switching property with spectral features suitable for on-chip wavelength selection applications. The proposed configuration is expected to find applications in silicon photonics devices such as, on-chip external cavity lasers and multi analytic label-free biosensors. The grating resonator has been designed for a high Q-factor, high transmittivity, and minimum loss so that the wavelength selectivity of the device is improved. The proof-of-concept device has been demonstrated on a Silicon-on-Insulator (SOI) platform through electron beam lithography and Reactive Ion Etching (RIE) process. The transmission spectrum shows narrow band single wavelength selection and switching property with a high Free Spectral Range (FSR) ~60 nm and side band rejection ratio >15 dB.