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Integrated photonics devices, based in subwavelength grating (SWG) metamaterials, have shown unprecedented performance in a wide variety of situations. Since their proposal and first experimental demonstration in 2010 designers have made use of the new degrees of freedom provided by these structures to design advanced devices with improved capabilities. The extended design space provided by SWG structures has been successfully used to engineer the refractive index, the dispersion and, more recently, the waveguide birefringence, thus allowing novel advanced device design. In this invited talk we will review some of the advances made by our group in the field., Smart Photonic and Optoelectronic Integrated Circuits XXII, February 1-6, 2020, San Francisco, United States, Series: Proceedings of SPIE

The ability to precisely monitor and manipulate neural circuits is essential to understand the brain. Advancements over the last decade in optical techniques such as calcium imaging and optogenetics have empowered researchers to gain insight into brain function by systematically manipulating or monitoring defined neural circuits. Combining these cutting-edge techniques enables a more direct mechanism for ascribing neural dynamics to behavior. Here, we developed a miniaturized integrated microscope that allows for simultaneous optogenetic manipulation and cellular-resolution calcium imaging within the same field of view in freely behaving mice. The integrated microscope has two LEDs, one filtered with a 435-460 nm excitation filter for imaging green calcium indicators, and a second LED filtered with a 590-650 nm excitation filter for optogenetic modulation of red-shifted opsins. We developed and tested this technology to minimize biological and optical crosstalk. We observed insignificant amounts of biological and optical crosstalk with regards to the optogenetic LED affecting calcium imaging. We observed some amounts of residual crosstalk of the imaging light on optogenetic manipulation. Despite residual crosstalk, we have demonstrated the utility of this technology by probing the causal relationship between basolateral amygdala (BLA) -to- nucleus accumbens (NAc) circuit function, behavior, and network dynamics. Using this integrated microscope we were able to observe both a significant behavioral and cellular calcium response of the optogenetic modulation on the BLA-to-NAc circuit. This integrated strategy will allow for routine investigation of the causality of circuit manipulation on cellular-resolution network dynamics and behavior.

International audience; Linear and nonlinear optical imaging systems are currently being miniaturized to fit endoscopic size requirements of a diameter less than 2 mm. These systems are used for deep imaging and optical biopsy. We report our progress in the development of a multimodal microendoscope based on Gradient Index (GRIN) lenses and double clad fiber (DCF) for femtosecond pulse delivery and signal collection. Four commercial DCFs were identified from the literature and our choice was based on the simulation results for optimal pulse delivery -needed for efficient 2-photon excitation- and optimal fluorescence signal collection. The pulse delivery simulation was done using a GRISM line system for compensating linear and nonlinear effects inside the DCF. The effect of GRIN lens aberration on collection efficiency was estimated by simulation using Zemax. GRIN lenses were also validated for fluorescence lifetime, spectroscopic measurement and mouse tissue imaging.

A frequency control scheme is introduced where within each transmitter its frequency is referenced to a silica based optical frequency discriminator, which in addition is locked to an absolute reference frequency. An absolute stability of /spl plusmn/1 GHz was achieved. As frequency-determining elements, coupler-based Michelson interferometers or coated gradient-index (GRIN) lenses were used. The described set-up is employed in an OFDM based optical crossconnect-demonstrator (RACE 2065; COBRA).

Fiber-Optic Variable Optical Attenuators (VOAs) are demonstrated using Liquid Crystals (LC) for broadband as well as wavelength tunable applications. Attenuation is achieved by using a beam spoiling approach implemented via electrically reconfigurable non-pixelated no moving parts Nematic LC deflectors. The VOAs feature in-line architecture and polarization insensitive design without the use of bulky polarization splitting and combining optics. The proof-of-concept VOAs in the 1550 nm band demonstrate >30 dB attenuation ranges, low polarization dependent losses and low power consumption. Applications for these VOAs include agile wavelength tunable secure data communications networks and RF sensor systems.

A high-speed programmable optical attenuator (POA) is introduced that can provide high dynamic range and high resolution attenuation control. An acousto-optic Bragg cell has been used to realize the desired attenuator. Various practical architectures have been proposed to prove the concept. A typical acousta-optic deflector (AOD) based design offers a dynamic range of 46.11 dB. The average resolution is 3.08 dB/volt whereas the best resolution achieved is 0.39 dB/volt. The response time of the AO attenuator is in the sub CLS regime, and was observed as low as 0.175 mu s. The polarization dependent loss (PDL) was about 0.7 dB, whereas the excess losses were about 1.5 dB.A high-speed programmable optical attenuator (POA) is introduced that can provide high dynamic range and high resolution attenuation control. An acousto-optic Bragg cell has been used to realize the desired attenuator. Various practical architectures have been proposed to prove the concept. A typical acousta-optic deflector (AOD) based design offers a dynamic range of 46.11 dB. The average resolution is 3.08 dB/volt whereas the best resolution achieved is 0.39 dB/volt. The response time of the AO attenuator is in the sub CLS regime, and was observed as low as 0.175 mu s. The polarization dependent loss (PDL) was about 0.7 dB, whereas the excess losses were about 1.5 dB.