Session 2 | Passive Components / Devices

Optical Isolators for Photonic Integrated Circuits

Martijn J. R. HECK
Aarhus University, Department of Engineering, Finlandsgade 22,
8200 Aarhus, Denmark

With the advance of mature fabrication technologies, photonic integrated circuits (PICs) reach ever-higher levels of complexity. Integration of thousands of components has been shown [1], with each main technology showing an exponential growth in complexity [2]. This increase in complexity requires a convergence in technologies, and the roadmaps are currently being pushed by silicon nitride, (hybrid) silicon and indium phosphide PIC technologies. This trend is further fuelled by the establishment of PIC foundries for these main PIC technologies.


Engineering the optical characteristics of waveguide grating couplers

Hon Ki TSANG, Linghai LIU
The Chinese University of Hong Kong, Hong Kong, China

We review recent progress in the design of waveguide grating couplers using subwavelength structures and apodization, and describe how direct numerical optimization of grating coupler parameters may further improve their performance. We show how direct numerical optimization may be used to engineer a flat-top spectral response from a grating coupler.


Electro-optic Long Period Ti:LiNbO3 Waveguide Gratings in Parallel for Broadband Filtering

De-Long Zhang1,2*, Jia-Qi Xu1, Wing-Han Wong1,2, Edwin Yue-Bun Pun2
1 School of Precision Instruments and Opto-electronics Engineering, Tianjin University, Tianjin 300072, China, and Key Laboratory of Optoelectronic Information Technology (Ministry of Education), Tianjin University, Tianjin, 300072, China.
2 Department of Electronic Engineering and State Key Laboratory of Millimeter Waves, City University of Hong Kong, Kowloon, Hong Kong SAR, China.

We report broadband optical filter based on two parallel electro-optic long period Ti:LiNbO3 waveguide gratings with different pitches. By utilizing electro-optic and photorefractive effects of LiNbO3 and by changing driving voltage, one can realize 360 nm broadband linear tunability and 0-30 dB linear adjustment of dip contrast. Long-period waveguide grating (LPWG) and long-period fiber grating have similar working principle and application background [1, 2]. An LPWG based on electro-optic effect of LiNbO3 (LN) is promising for high-speed application [3,4]. Here, we demonstrate a broadband filter based on a parallel structure of two electro-optic long period gratings in two same Ti:LN strip waveguides. The device was developed on the basis of the electro-optic and photorefractive effects of LN.


Critical coupling enhanced refractive index sensing in SOI slot microring resonators

Weiwei Zhang*, Samuel Serna, Xavier Le Roux, Laurent Vivien,
and Eric Cassan
Institut d’Electronique Fondamentale, University Paris-Sud, CNRS UMR 8622, Université Paris Saclay, Bat. 220, 91405 Orsay Cedex, France

We present a novel refractive index sensing mechanism based on slot ring resonators fabricated in the silicon platform. The sensing mechanism relies on detuning the critical coupling resonance of the ring. This new method has been realised through engineering the dispersion property of the ring directional coupler, which enables forming a narrow ring resonance spectrum with a V-shape profile. We both numerically and experimentally demonstrate that this V-shape profile can enhance the refractive index sensing operation due to following conditions: firstly, the V-shape is robust in the 1.31.5 refractive index range; secondly, the critical resonance peak (or bottom of the spectrum V-profile) follows a monotonically increase with the refractive index change, which results in a strong critical coupling detuning. The sensitivity of the critical peak has been measured to around 1300nm per refractive index unit with an uncertainty of the shift equal to 2 times the ring free spectral range. Different from a single resonance peak sensing, , the proposed sensing mechanism can get rid of the high losses of slot waveguides that usually spoil the ring and can target low detection limit.


Integrated polarization controller with 40 dB polarization extinction ratio range in the C-Band

Alejandro ORTEGA-MOÑUX1.
1Universidad de Málaga, Dept. de Ingeniería de Comunicaciones, ETSI Telecomunicación, Campus de Teatinos s/n, Málaga, 29071, Spain
2Institut d’Electronique Fondamentale, Université Paris Sud, CNRS, UMR 8622, Université ParisSaclay, Bât. 220, 91405 Orsay Cedex, France
3National Research Council Canada Ottawa, K1A 0R6, Canada

In this work we present a technology-independent highly tolerant tunable polarization controller. The device is implemented in the silicon-on-insulator platform, experimentally achieving 40 dB of polarization extinction ratio (PER) range in the complete C-band, with a Poincaré sphere coverage of 98%. The key benefit of this approach is that a broad PER range is achieved, even when the individual polarization rotators have limited polarization conversion efficiency (PCE) in the range 25-5%. This results in substantially relaxed fabrication tolerances. To the best of our knowledge, this is the highest PER range yet demonstrated in an integrated polarization controller


Optical Frequency Domain Reflectometry applied to Photonic Integrated Circuits

Luis A. BRU1, Bernardo GARGALLO1, Gloria MICÓ1, Rocío BAÑOS1, José David DOMÉNECH2, Ana M. SÁNCHEZ3, Roser MAS3, Emilio PARDO3,
Daniel PASTOR1* Pascual MUÑOZ1,2
1Photonic IC-group at the Photonics Research Labs, Universitat Politècnica de València, C/Camino de Vera s/n, Valencia 46022, Spain
2VLC Photonics S.L., C/Camino de Vera s/n, Valencia 46022, Spain
3Instituto de Microelectrónica de Barcelona (IMB-CNM, CSIC) C/del Til·lers. Campus Universitat Autònoma de Barcelona (UAB) 08193 Cerdanyola del Vallès (Bellaterra) Spain

The development cycle for Photonic Integrated Circuits (PICs), design, fabrication and characterization, demands for feedback mechanisms at the different stages. In latest step, characterization, diverse procedures are applied to obtain feedback information from the PICs. A commonly use test method employed with PICs in all technologies is the amplitude spectral measurement by means of an Optical Spectrum Analysers (OSA). However, no spectral phase information is retrieved, so propagation features, phases or time characteristics of devices must be extracted indirectly by fitting the measurements with the expected results iteratively, usually resorting to assumptions not always directly checkable. Complementarily, Optical Frequency Domain Reflectometry (OFDR) [1-2] allows retrieving amplitude and phase features from PICs. In this paper, a straightforward implementation of OFDR, the main achievements and observed limitations, for devices under test (DUT) in different technologies are reported: Arrayed Waveguide rating (AWGs) on Silica and on Silicon on Insulator (SOI), and Unbalanced Mach Zehnder Interferometers (UMZI) on Silicon Nitride.