A vehicular vision system includes a camera having a lens and a CMOS photosensor array having a plurality of photosensor elements. The camera is disposed at an interior portion of a vehicle equipped with the vehicular vision system. The camera one of (i) views exterior of the equipped vehicle through the windshield of the equipped vehicle and forward of the equipped vehicle and (ii) views from the windshield of the equipped vehicle into the interior cabin of the equipped vehicle. A control includes an image processor that processes image data captured by the photosensor array. The image processor processes captured image data to detect an object viewed by the camera. The photosensor array is operable at a plurality of exposure periods and at least one exposure period of the plurality of exposure periods is dynamically variable.

Vehicular vision system

In this paper, we will review the state-of-the-art of LiNbO 3 based integrated electro-optic modulators and will show how micro-structuring techniques such as etching, domain inversion and thin film processing can be used to realize new configurations which can take the performance to unprecedented levels. In particular, we will review recent results on the use of domain inversion on a micron scale and we report on the fabrication of a chirp-free modulator having ∼ 2 V switching voltage and bandwidth of 15 GHz designed by placing the waveguide arms of the Mach-Zehnder interferometer in opposite domain oriented regions. We also review some of the new modulation formats (e.g. DQPSK) that can represent an application development of the presented micro-structured devices. Finally, we address the issue of the integration of the modulator chip in a transmitter board comprising tunable laser, bias-control electronics and RF driver. The requirements of integration can even push further the reduction in size of modulator chips, thus making more crucial the use of micro- and nano-struoturing techniques.

Micro-structured integrated electro-optic LiNbO3 modulators

The drift issue induces slow drifting of the optimum operating point for high efficiency or large nonlinearities in analog optical links, and requires complex control of the offset bias voltage for achieving high extinction ratio in digital optical links. We discuss and analyze the different sources of the drift in commercially LiNbO3 Mach-Zehnder modulators. The different extrinsic and intrinsic origins are compared in terms of phase shift and the different corresponding orders of magnitude are given, pointing out the predominant role of the intrinsic (dc) drift. We show the large role played by the electrical inhomogeneities at the surface of the LiNbO3 substrate by highlighting the link between the time dependence of the dc drift and the electrical conductivity measured at the surface and in the volume of the LiNbO3 substrate. This allows to propose a solution to the drift issue which consists in the engineering of the electrical conductivity of the lithium niobate substrate.

Analysis and Control of the DC Drift in LiNbO $_{3}$ -Based Mach–Zehnder Modulators

Lithium niobate (LN), spurred by its success for fiber-optic communications, has remained the material of choice for high-performance electrooptic (EO) modulators. The past decade has seen a surge in efforts aimed at miniaturizing LN EO modulators with higher order modulation formats, data centers, and optical interconnect applications in mind. The state-of-the-art of these compact modulators, with a focus on fabrication, design, and high-speed performance is reviewed. Guidelines for design optimization and key performance metrics of these important integrated photonic devices are presented. Furthermore, an outlook on the road toward commercial viability, along with potential novel applications is provided.

Compact Lithium Niobate Electrooptic Modulators

The sustainable growth of high-bandwidth services and on-demand applications has introduced new challenges to next-generation networks in terms of capacity, configurability, and resiliency. Significant networking advancements need to be achieved with architectures and technologies that are scalable with respect to cost, size, and power requirements, while they should be capable of handling high traffic volumes and dynamically changing connection patterns. Transparent networking has the potential to meet those requirements and offer significant benefits in terms of performance and cost. We present the key enabling technologies, review the state-of-the-art achievements, and discuss the new opportunities that optical transparency has and will introduce.

Technological challenges on the road toward transparent networking

We have succeeded in reducing the drive voltage of a 40Gb/s LiNbO/sub 3/ modulator to 0.9 V, which is the lowest-drive-voltage 40Gb/s LiNbO/sub 3/ modulator in the world. The modulator can be driven within the break down voltage of a SiGe transistor. This result was achieved using a new design concept that featured a wide-gap, long CPW (coplanar waveguide) electrode.

Driver-less 40 Gb/s LiNbO/sub 3/ modulator with sub-1 V drive voltage

An optical waveguide device includes an optical waveguide formed on a surface of a substrate having an electrooptical effect, and a pair of electrodes formed on corresponding regions above the optical waveguide and receiving a driving electric signal thereacross. By applying the electric signal to the electrodes, an electric field is formed in a vicinity of the optical waveguide. By changing a distribution of the electric field in accordance with a change in a frequency of the electric signal, it is possible to suppress a DC drift of the device to effectively compensate a fluctuation in operational characteristics due to the DC drift, stress of the like.

Optical waveguide device with suppressed dc drift

The use of the Ti:LiNbO3 modulator has begun in advanced optical transmission experiments (1) and it is planned for commercial optical transmission systems. There has, however, been no report to guarantee the long-term reliability of Ti:LiNbO3 devices against DC drift. DC drift is complicated by temperature and humidity. We prevented the temperature and humidity drift by employing a Si coating technique (1). We evaluated the long-term DC drifts of our modulator and confirmed that it is stable enough for use in commercial optical transmission systems.

A low DC-drift Ti:LiNbO3 modulator assured over 15 years

An optical waveguide device is disclosed wherein the modulation efficiency for a driving voltage is improved. The optical waveguide device includes a substrate having an electro-optic effect, an optical waveguide formed on the substrate, an electrode section adapted to supply an electric field for carrying out phase modulation synchronized with a clock signal to the optical waveguide, and a Mach-Zehnder interferometer connected to the downstream side of the optical waveguide and including two branching waveguides having optical lengths different from each other.

Optical waveguide device

Low-drive-voltage (3.5 V) and uniform modulation characteristics of MZIs were achieved with Z-cut dual-drive nested-MZIs structure and the wide-gap design between signal and ground electrodes, resulting in precise constellation mappings in 43 Gb/s DQPSK modulation.

/pdf/40-gb-s-low-drive-voltage-linbo-3-optical-modulator-for-3suyf2cbkv.pdf

Masaharu Doi

Papers

Driver-less 40 Gb/s LiNbO/sub 3/ modulator with sub-1 V drive voltage

Optical waveguide device with suppressed dc drift

A low DC-drift Ti:LiNbO3 modulator assured over 15 years

Optical waveguide device

40 Gb/s Low-drive-voltage LiNbO 3 Optical Modulator for DQPSK Modulation Format