In this paper, we present a novel design of an optical power splitter. Owing to the inherent variable power split ratios that the proposed design delivers, it is ideal for use in communications, sensing and signal processing applications where variable power splitting is often quintessential. The proposed power splitter module is dual mode as it combines the use of a Micro-Electro-Mechanical Systems (MEMS) based Digital Micro-mirror Device (DMD) and an Electronically Controlled Tunable Lens (ECTL) to split the power of an input optical signal between two output ports – the designated port and the surplus port. The use of a reflective Digital Spatial Light Modulator (DSLM) such as the DMD provides a motion-free digital control of the split ratio between the two output ports. Although the digital step between two possible successive split ratios can be fairly minimal with the use of a high resolution DMD but it is a challenge to correctly ascertain the exact image pattern on the DMD to obtain any desired specific split ratio. To counter this challenge, we propose the synchronized use of a circular pattern on the DMD, which serves as a circular clear aperture with a tunable radius, and an ECTL. The radius of the circular pattern on the DMD provides a digital control of the split ratio between the two ports whereas the ECTL, depending on its controller, can provide either an analog or a digital control by altering the beam radius which is incident at the DMD circular pattern. The radius of the circular pattern on the DMD can be minimally changed by one micro-pixel thickness. Setting the radius of the circular pattern on the DMD to an appropriate value provides the closest “ball-park” split ratio whereas further tuning the ECTL aids in slightly altering from this digitally set value to obtain the exact desired split ratio in-between any two digitally-set successive split ratios that correspond to any clear aperture radius of the DMD pattern and its incremental minimal allowable change of one micropixel. We provide a detailed scheme to calculate the desired DMD aperture radius as well as the focal length setting of the ECTL to obtain any given split ratio. By setting tolerance limits on the split ratio, we also show that our method affords diversity by providing multiple possible solutions to achieve a desired optical power split ratio within the specified tolerances. We also demonstrate the validation of the proposed concept with initial experimental results and discussions. These experimental results show a repeatable splitter operation and the resulting power split ratios according to the theoretical predictions. With the experimental data, we also demonstrate the effectiveness of the method in obtaining any particular split ratio through different DMD and ECTL configurations with specific split ratio tolerance values.
In this paper, we present the design of a proposed optical rangefinder to determine the distance of a semi-reflective target from the sensor module. The sensor module deploys a simple Tunable Focus Lens (TFL), a Laser Source (LS) with a Gaussian Beam profile and a digital beam profiler/imager to achieve its desired operation. We show that, owing to the nature of existing measurement methodologies, previous attempts to use a simple TFL in prior art to estimate target distance mostly deliver “one-shot” distance measurement estimates instead of obtaining and using a larger dataset which can significantly reduce the effect of some largely incorrect individual data points on the final distance estimate. Using a measurement dataset and calculating averages also helps smooth out measurement errors in individual data points through effectively low-pass filtering unexpectedly odd measurement offsets in individual data points. In this paper, we show that a simple setup deploying an LS, a TFL and a beam profiler or imager is capable of delivering an entire measurement dataset thus effectively mitigating the effects on measurement accuracy which are associated with “one-shot” measurement techniques. The technique we propose allows a Gaussian Beam from an LS to pass through the TFL. Tuning the focal length of the TFL results in altering the spot size of the beam at the beam imager plane. Recording these different spot radii at the plane of the beam profiler for each unique setting of the TFL provides us with a means to use this measurement dataset to obtain a significantly improved estimate of the target distance as opposed to relying on a single measurement. We show that an iterative least-squares curve-fit on the recorded data allows us to estimate distances of remote objects very precisely. We also show that using some basic ray-optics-based approximations, we also obtain an initial seed value for distance estimate and subsequently use this value to obtain a more precise estimate through an iterative residual reduction in the least-squares sense. In our experiments, we use a MEMS-based Digital Micro-mirror Device (DMD) as a beam imager/profiler as it delivers an accurate estimate of a Gaussian Beam profile. The proposed method, its working and the distance estimation methodology are discussed in detail. For a proof-of-concept, we back our claims with initial experimental results.
Various applications in optics and photonics employ a Tunable Focus Lens (TFL) to obtain a minimum beam spot of a laser beam at different locations along the direction of beam propagation. Using a TFL to achieve a minimum beam spot size at different planes is critical for several optical imaging and sensing applications. As focal length of TFLs is generally controlled through the amplitude of an input voltage or the current signal, the response time of a TFL-based sensor or imaging system depends on the time required produces a minimum beam spot in the observation plane. Therefore, the system response time or sampling rate depends on the number of voltage/current samples to ascertain a correct focal length value which yields a minimum beam spot. Due to a partial or a total lack of knowledge of the ideal voltage/current value that would produce a minimum beam spot, starting at a corner or a random voltage/current value and incrementally increasing or reducing it would be highly inefficient as converging to a minimum spot might require several steps. We propose an efficient method which results in a significant reduction in the number of voltage/current steps and experimentally validate our claims.
This paper presents a data transfer scheme using multi-focus tunable lenses. The design involves the use of a standard laser source and a variable focus agile lens to steer to the laser beam that passes through the lens. In our proposed system, the beam steer angle depends on an input electrical signal which drives the tunable lens. Therefore the beam steer angle is made to follow the variations in the input electrical drive signal. This is extremely interesting for data transfer applications as the data signal can be used as the input drive signal to the lens. The laser beam is steered according to the input data voltage levels and when the beam is incident on a photo-detector of a finite size, only a fraction of its total incident optical power is received by the photo-detector. This power contribution is proportional to the fraction of the total number of photons per unit area which are incident on the active area of the detector. The remaining photons which are not incident on the photo-detector do not contribute to the received power at the photo-detector. We present the theory of beam steering through a tunable lens and present a theoretical framework which governs data transfer through the proposed method. We also present the transfer function of the proposed system which helps us to calculate its essential theoretical performance parameters such as modulation depth and bit error rates. We also present experimental results to demonstrate efficient data transfer through the proposed method. As tunable lenses are primarily deployed in motion-free multi-focus cameras hence most of the modern portable devices such as cellphones and tablets use these lenses to operate the in-built variable focus cameras that are part of these devices. Because tunable lenses are commonly present in several different portable devices, the proposed method of data transfer between two devices is highly promising as it expands the use of the already deployed tunable lenses with minimal changes to the fundamental architecture or operation of any portable device.
This paper presents a non-intrusive, non-contact liquid level sensor. The proposed sensor is a free-space-based
optical sensor that uses opto-fluidic technology-based agile optics to direct light from a laser source to the
Liquid Under Test (LUT). The presented design makes the proposed sensor ideal for use in environments where
levels have to be determined for caustic or toxic liquids having a small window interface on the containers carrying them. The proposed design uses very low optical power levels (< 100 μW) making it useful for measuring levels of combustible liquids (e.g., jet fuels) which have a danger of being ignited at higher power levels. The proposed sensor can find potential applications in transportation, chemical and aerospace industries.
Proposed is a Variable Fiber Optical Attenuator (VFOA) using an electronically controlled, variable focus liquid
lens. The demonstrated experiment for the VFOA is shown for operation over the communication C-Band (1530nm-
This paper proposes novel intelligent Value Added Modules (VAMs) which employ an intelligent spatial
processing technique to realize variable optical power split ratios. To demonstrate the concept of the smart
VAM, the Texas Instrument (TI) Digital Micro-mirror Device (DMD<sup>TM</sup>) has been used. Different optical
power split ratios have been experimentally verified.
To the best of our knowledge, this paper demonstrates the first hybrid analog-digital design fiber-optic spectrum processor that can simultaneously provide spectrum gain slope adjustment as well as independent channel equalization attenuation controls.