Off-axis catadioptric fisheye wide field-of-view optical receiver for free space optical communications

Abstract

We propose a wide field-of-view optical receiver design based on a fisheye lens and an off-axis catadioptric structure for free-space optical communications. The design utilizes a novel fisheye lens group to compress a wide field angle into a narrow field angle and produce the appropriately collimated light that can effectively be coupled into the following aperture of a catadioptric telescope. An off-axis catadioptric telescope with aspheric surface mirrors is designed to compress the incident beam spot size, compensate for the high order optical aberrations and eliminate light loss due to an obstruction. The parallel exit rays are reflected on a double-level tracking mechanism by feeding the position signal from a quadrant detector to correct the pointing error and optimize the coupling efficiency into an optical fiber. The final wide field-of-view optical receiver design is presented along with the evaluation of optical performance results and tracking characteristics. The proposed optical receiver not only can provide a 60-deg wide field-of-view to expand the tracking range, but also mitigates optical aberrations to improve the tracking accuracy for free space optical communication systems in a turbulent atmosphere.

Adaptive real-time software defined MIMO visible light communications using spatial multiplexing and spatial diversity

“…(11) expresses the optimization strategy that maximizing the spectral efficiency by adapting the MIMO scheme, transmission rate s i and power P i in each subchannel. Equation (12) shows that the average total transmit power cannot exceed P t and (13) requires that at any instant the BER in any subchannel must remain below a predetermined target level BER tgt . We consider more practical discrete rate systems in (14), where we restrict the available constellation size M i to a finite set of integers instead of any nonnegative real values.…”

“…Demonstration of 2 x 2 MIMO VLC is achieved at 500 Mb/s in 40 cm range by using 4-QAM Nyquist Single Carrier With Frequency Domain Equalization [12]. Spatial-Diversity MIMO VLCs are proposed by using fisheye lens wide filed-of-view receiver [13,14].…”

Real-time software-defined single-carrier QAM mimo visible light communication system

“…Demonstration of 2 x 2 MIMO VLC is achieved by using Nyquist Single Carrier With Frequency Domain Equalization [17]. Spatial-Diversity MIMO VLCs are proposed by using fisheye lens wide filedof-view receiver [18][19][20][21].However, most of the MIMO VLC demonstrations are based on offline signal processing, single MIMO schema and static channel condition estimation. In practical indoor mobile communication, a real-time MIMO VLC system is necessary to deal with the dynamic and complex channel conditions with smart MIMO schemas.…”

Excitation of core modes through side coupling to multimode optical fiber by hydrothermal growth of ZnO nanorods for wide angle optical reception

“…In an ideal link, the orientation of the detector should have a minimal effect on the quality of the received signal. Several approaches to improve the signal have been reported, such as the utilization of a bulk lens system such as fish eye lens system [19] and the use of hemispherical imaging receivers [20]. Both systems are bulky but provide a FOV up to 120°.…”