Thermally controlled Si photonic crystal slow light waveguide beam steering device

Abstract

The doubly periodic Si photonic crystal waveguide radiates the guided slow light into free space as an optical beam. The waveguide also functions as a beam steering device, in which the steering angle is changed substantially by a slight variation in the wavelength generated due to the large angular dispersion of the slow light. A similar function is obtained when the wavelength is fixed and the refractive index of the waveguide is changed. In this study, we tested two kinds of integrated heater structures and observed the beam steering using the thermo-optic effect. For a p-i-p doped waveguide, the heating current was made to flow directly across the waveguide and a beam steering range of 21° was obtained with a relatively low heating power and high-speed response of the order of 100 kHz, maintaining a narrow beam divergence of 0.1-0.3° and a 120 resolution points. We also performed a preliminary life test of the device but did not observe any severe degradation in the temperature variation of 80-430 K for the duration up to 20‒40 h. For a TiN heater device, we obtained the comparable beam steering characteristics, but the required heating power increased, and the response speed decreased drastically.

Photonic Integrated Circuits for an Optical Phased Array

“…Additionally, by incorporating a switch and two polarization rotators before the grating coupler, both directions (forward and backward) and both polarizations (TE and TM) can be selected, resulting in a steering range that is roughly four times greater, reaching 54.5 • over a 100 nm wavelength range [53]. The second category of attempts to mitigate the restriction of the steering range involves manipulating the effective index (n eff ) by incorporating a photonic crystal waveguide [54][55][56][57]. In this type of waveguide, n eff can be substantially increased at the spectral boundary of the photonic bandgap, resulting in a significantly greater dθ/dλ despite a limited wavelength range defined by the photonic band spectrum.…”

Active optical phased array integrated within a micro-cantilever

“…The requirement for broadband operation of the photonic integrated circuit (PIC) as well as the laser-PIC coupling would also be removed. Singlewavelength, two dimensional beam-steering has been demonstrated using a switched multi-OPA approach [27,28], via the integration of a liquid-crystal filled cavities [29], by active tuning of the emitters [30] and using a single emitter on a thermally activated 2D MEMS cantilever [31]. Currently, none of these solutions offer 2D beam scanning with a satisfactory combination of high frequency operation, wide angular range and low power consumption for demanding sensor applications.…”

Efficient light transmission, reception and beam forming in photonic crystal beam steering device in a phased array configuration

“…Slow light has the large first order dispersion, meaning that the propagation constant of slow light in the PCW is significantly changed by a small variation of the wavelength and/or PCW's refractive index, which can be applied to the wide beam steering. [7][8][9] Such a PCW not only transmits a beam but also receives returned light in the reverse process. Therefore, we expect it as a transmission and reception optical antenna in LiDARs.…”

“…However, we can neglect this control in LiDAR when the phase matching condition, as will be described later, is used. By arranging a thermo-optic heater at each PCW, 9) we can control each transmission angle. If we set all PCWs to have the same transmission angle, the transmission beam narrows and the reception power increases.…”