ABSTRACT
A novel wireless optical power transfer (WOPT) system using diverging angular dispersion and spatially distributed laser cavity resonance is proposed. In the transmitter, a diffraction grating spatially disperses the broadband light from a semiconductor optical amplifier. Receiving units spread across a wide field of view are embedded with retroreflecting beam splitters that reflect the incident beam back to the transmitter, thereby completing multiple resonant cavities. Retroreflectors enable a user-friendly alignment and tap power from the resonating cavity, supplying optical power. We demonstrate an automatic safety mechanism that instantly ceases the cavity resonance should any vulnerable organ break the transmitter-receiver line of sight. The results indicate that a single-channel WOPT system can provide a resonating average power of 17.2 mW (receiving power of 1.7 mW to the photodetector) over a distance of 1 m with a channel linewidth of 0.035 nm. For a proof-of-principle experiment, seven receiver units were successfully demonstrated to supply optical power. With careful retroreflector design and field-of-view optimization, the potential of our scheme can be further exploited toward commercial deployment.
ABSTRACT
The fundamental Gaussian TEM00 mode is the most common mode of propagation within various optical devices, modules, and systems. Beam profilers are widely used in accurately ascertaining the cross-sectional irradiance profile of a TEM00 mode for free-space optical communication systems as well as tracking beam evolution when propagating within optical submodules. We demonstrate beam profiling methods that use low-cost, off-the-shelf, widely available circular apertures such as circular irises and spatial filters. In order to demonstrate beam profiling with any circular aperture, we first derive exact analytical expressions for power transmittance of the TEM00 mode through a decentered circular aperture and then use this mathematical derivation to estimate the irradiance profile of a Gaussian beam by 1) fixing the location of a circular aperture and changing its radius, and 2) scanning the entire area of the beam profile by translating a circular aperture of a fixed radius across the region of interest. This method is fast and easily reproducible and simply puts to use circular irises/circular spatial filters, which are commonly available in most optical laboratories. Consequently, the proposed method provides cheap and convenient means to estimate the profile of a Gaussian beam with simple optical components. Our experimental results demonstrate a performance that is comparable to a standard knife-edge-based estimate of beam profile. Moreover, a strong agreement with presented theory validates the analytical expressions derived in this paper.
ABSTRACT
Various existing target ranging techniques are limited in terms of the dynamic range of operation and measurement resolution. These limitations arise as a result of a particular measurement methodology, the finite processing capability of the hardware components deployed within the sensor module, and the medium through which the target is viewed. Generally, improving the sensor range adversely affects its resolution and vice versa. Often, a distance sensor is designed for an optimal range/resolution setting depending on its intended application. Optical triangulation is broadly classified as a spatial-signal-processing-based ranging technique and measures target distance from the location of the reflected spot on a position sensitive detector (PSD). In most triangulation sensors that use lasers as a light source, beam divergence-which severely affects sensor measurement range-is often ignored in calculations. In this paper, we first discuss in detail the limitations to ranging imposed by beam divergence, which, in effect, sets the sensor dynamic range. Next, we show how the resolution of laser-based triangulation sensors is limited by the interpixel pitch of a finite-sized PSD. In this paper, through the use of tunable focus lenses (TFLs), we propose a novel design of a triangulation-based optical rangefinder that improves both the sensor resolution and its dynamic range through adaptive electronic control of beam propagation parameters. We present the theory and operation of the proposed sensor and clearly demonstrate a range and resolution improvement with the use of TFLs. Experimental results in support of our claims are shown to be in strong agreement with theory.
