Fiber-Optic Sensor Assembly

A fiber-optic force and displacement sensor includes a mirror comprising a plurality of sectors extending from a center point to a peripheral edge. Each of the sectors has a high reflectance corresponding to only one of a plurality of single wavelength light beams having different wavelengths transmitted from a laser light source. A method of measuring force and displacement includes measuring the radiant flux between each of a plurality of reflected single wavelength light beams that change as the area of the sectors are displaced towards and away from a center of projection of a combination light beam that comprises the plurality of single wavelength light beams projected towards the center point of the mirror when the mirror is in a rested position. Forces acting upon the mirror are measured as a function of the displacement of the mirror and the transverse and the axial stiffness of a connector

Lidar: A New Self-driving Vehicle for Introducing Optics to Broader Engineering and Non-engineering Audiences

Since Stanley, the self-driven Stanford car equipped with five SICK LIDAR sensors won the 2005 DARPA Challenge, the race to developing and deploying fully autonomous, self-driving vehicles has come to a full swing. By now, it has engulfed all major automotive companies and suppliers, major trucking and taxi companies, not to mention companies like Google (Waymo), Apple and Tesla. With the notable exception of the Tesla self-driving cars, a LIDAR (Light, Detection and Ranging) unit is a key component of the suit of sensors that allow autonomous vehicles to see and navigate the world. The market space for lidar units is by now downright crowded, with a number of companies and their respective technologies jockeying for long-run leading positions in the field. Major lidar technologies for autonomous driving include mechanical scanning (spinning) lidar, MEMS micro-mirror lidar, optical-phased array lidar, flash lidar, frequencymodulated continuous-wave (FMCW) lidar and others. A major technical specification of any lidar is the operating wavelength. Many existing systems use 905 nm diode lasers, a wavelength compatible with CMOS-technology detectors. But other wavelengths (like 850 nm, 940 nm and 1550 nm) are also investigated and, in the long run, the telecom nearinfrared range (1550 nm) is expected to experience significant growth because it offers a larger detecting distance range (200-300 meters) within eye safety laser power limits while also offering potential better performance in bad weather conditions. This paper discusses the above-mentioned technical (optics and photonics) aspects of the most common lidar technologies, with the educational focus of identifying opportunities for employing such discussions in introducing optics to broader engineering audiences, drawing in part on experiences and examples from Kettering University

80-Channel Multiplexer-Demultiplexer Module for DWDM Communications using Hybrid AWG -- Interleaver Technology

Aside from the more traditional data, voice and e-mail communications, new bandwidth intensive applications in the larger consumer markets, such as music, digital pictures and movies, have led to an explosive increase in the demand for transmission capacity for optical communications networks. This has resulted in a widespread deployment of Dense Wavelength Division Multiplexing (DWDM) as a means of increasing the communications capacity by multiplexing and transmitting signals of different wavelengths (establishing multiple communication channels) through a single strand of fiber. We report on the design, assembly and characterization of a 50-GHz, 80-channel Mux-Demux module for DWDM systems. The module has been assembled from two commercially available 100 GHz, 40-channel Array Waveguide Grating (AWG) modules and a 50-GHz to 100-GHz interleaver. Relevant performance parameters such as insertion loss, channel uniformity, next-channel isolation (crosstalk) and integrated cross-talk are presented and discussed in contrast with the performance of other competing technologies such as Thin-Film-Filter-based Mux-Demux devices

Temperature-Dependent Characterization of Thin-Film Filters for Optical Communications

The explosive increase in the demand for transmission capacity for optical communications networks has resulted in a widespread deployment of dense wavelength division multiplexing (DWDM). Thin film filters are a critical component of DWDM devices. They consist of Fabry-Perot resonant cavities obtained by vacuum deposition on a glass substrate of alternating layers of two dielectric materials of different indices of refraction. The performance requirements for these filters are determined by the density of channels to be multiplexed. For the 100 GHz ITU grid, these channels are spaced 100 GHz (0.8 nm) apart. Typical figures of merit include the insertion loss (IL), band width (BW) at 0.5 dB and at 25 dB below peak transmission, and the shape factor (BW@ 25 dB) / (BW@ 0.5 dB). The thermal drift of the transmission profile of the filter and the thermal stability of its insertion loss are two of the ``killers\u27\u27 of thin-film filter devices. In this work, the thermal behavior of the wavelength-dependent transmission profile for several commercially-available thin-film filters for WDM is investigated, and the temperature limits for proper operation are determined. Comparison with other components for DWDM (such as Fiber-Bragg gratings and/or fused WDM devices) may also be included

Distributed Fiber-Bragg Grating Temperature Sensors for Real-Time MultiplePoint Temperature Monitoring

Distributed fiber-optic temperature sensors (DFOTS) are being increasingly deployed in applications requiring 2D or 3D temperature profiling. Fiber Bragg Gratings (FBG\u27s), through the shift of their Bragg wavelength, are well suited for such applications due to their immunity to electromagnetic interference and small physical size and thermal inertia of the sensing element. These characteristics are complemented by the easiness of combining individual gratings in series or parallel arrays that can monitor systems with characteristic dimensions from as small as a few millimeters to as large as several kilometers. To highlight this versatility, we report on the study of two FBG arrays for temperature monitoring. A series array obtained by inserting several discrete FBG\u27s operating at different Bragg wavelengths on a 5-km long fiber strand is used to monitor the temperature at predetermined points along the fiber link. A second, parallel array of FBG\u27s is used to monitor the temperature in a cross-section of a 3 ml vial containing a ferrofluid in magnetic field. The temperature resolution in both cases is better than 1 C. The longitudinal spatial resolution is 5 mm, and the lateral spatial resolution for the parallel array is better than 1 mm

Temperature-Dependent Characterization of Thin-Film Filters for Optical Communications

The explosive increase in the demand for transmission capacity for optical communications networks has resulted in a widespread deployment of dense wavelength division multiplexing (DWDM). Thin film filters are a critical component of DWDM devices. They consist of Fabry-Perot resonant cavities obtained by vacuum deposition on a glass substrate of alternating layers of two dielectric materials of different indices of refraction. The performance requirements for these filters are determined by the density of channels to be multiplexed. For the 100 GHz ITU grid, these channels are spaced 100 GHz (0.8 nm) apart. Typical figures of merit include the insertion loss (IL), band width (BW) at 0.5 dB and at 25 dB below peak transmission, and the shape factor (BW@ 25 dB) / (BW@ 0.5 dB). The thermal drift of the transmission profile of the filter and the thermal stability of its insertion loss are two of the ``killers\u27\u27 of thin-film filter devices. In this work, the thermal behavior of the wavelength-dependent transmission profile for several commercially-available thin-film filters for WDM is investigated, and the temperature limits for proper operation are determined. Comparison with other components for DWDM (such as Fiber-Bragg gratings and/or fused WDM devices) may also be included

Fiber-Optic Devices as Temperature Sensors for Temperature Measurements in AC Magnetic Fields

We report on the investigation of several fiber-optic devices as potential sensors for temperature measurements in AC magnetic fields. Common temperature sensors, such as thermocouples, thermistors or diodes, will create random and/or systematic errors when placed in a magnetic field. A DC magnetic field is susceptible to create a systematic offset to the measurement, while in an AC magnetic field of variable frequency random errors which cannot be corrected for can also be introduced. Fiber-Bragg-gratings and thin film filters have an inherent temperature dependence. Detrimental for their primary applications, the same dependence allows one to use such devices as temperature sensors. In an AC magnetic field, they present the advantage of being immune to electromagnetic interference. Moreover, for fiber-Bragg-gratings, the shape factor and small mass of the bare-fiber device make it convenient for temperature measurements on small samples. We studied several thin-film filters and fiber-Bragg-gratings and compared their temperature measurement capabilities in AC magnetic fields of 0 to 150 Gauss, 0 to 20 KHz to the results provided by off-the-shelf thermocouples and thermistor-based temperature measurement systems

The Photoelectric Effect: Project-based Undergraduate Teaching and Learning Optics through a Modern Physics Experiment Redesign

The photoelectric effect is a cornerstone textbook experiment in any Modern Physics or Advanced Laboratory course, designed to verify Einstein’s theory of the photoelectric effect, with the implicit determination of an experimental value for Planck’s constant and the demonstration of the particle nature of light. The standard approach to the experiment is to illuminate the light-sensitive cathode of a vacuum-tube photocell with monochromatic light of known wavelengths; a reversed-voltage is then applied to the photocell and adjusted to bring the photoelectric current to zero. The stopping voltage is then plotted as a function of the inverse wavelength or frequency of the incident light, and Planck\u27s constant is determined from the slope of the graph. Additionally, a value for the work function of the photocathode can be extracted from the intercept. The commercial apparatus for the experiment is available from a number of vendors (PASCO, Leybold) in various forms, degrees of performance and cost. However, designing and assembling a photoelectric effect experiment apparatus can in itself be a valuable experiential project-based undergraduate learning opportunity in Optics involving both fundamental light and optics theory and practical optics and opto-mechanical design aspects. This presentation details a project undertaken in the Applied Physics/Engineering Physics programs at Kettering University involving students in a Modern Physics laboratory course. The first phase of the project, discussed in detail in this paper, was a redesign of an existing photoelectric effect apparatus through an undergraduate student thesis, currently in advanced stages of completion. In a second phase of the project we plan to replicate the newly assembled experimental apparatus up to as many as six identical stations and deploy it in our Modern Physics lab course. Typically, more than 50% of the students in this course are engineering majors who would otherwise not get any significant exposure to problems of optics and optical design. We believe that the modular design of the new apparatus together with a carefully redesigned lab activity will allow us to have our students explore major aspects of optics and optoelectronic design while performing this classic Modern Physics experiment

Anisotropic Light Scattering from Ferrofluids

We have investigated the light scattering in DC magnetic fields from aqueous suspensions of Fe3O4 nanoparticles coated with tetra methyl ammonium hydroxide and γ-Fe2O3 nanoparticles embedded in alginate hydrogel. For Fe3O4 ferrofluid, anomalous light scattering behavior was observed when light propagated both parallel and perpendicular to the magnetic fields. This behavior is attributed to the alignment and aggregation of the nanoparticles in chain-like structures. A very different light scattering behavior was observed for γ-Fe2O3 alginate sample where, under the similar conditions, the application of the magnetic field produced no structured change in scattering. We attribute this difference to the absence of chain-like structures and constrained mobility of iron nanoparticles in the alginate sample. The observation is in agreement with our relaxation and dissipative heating results^1 where both samples exhibited Neel relaxation but only the Fe3O4 ferrofluid showed Brownian relaxation. The results suggest that Brownian relaxation and nanoparticle mobility are important for producing non-linear light scattering in such systems