Single Optical Wavelength Research Articles

Nanometer-precision surface metrology of millimeter-sized stepped objects using full-cascade-linked synthetic-wavelength digital holography using a line-by-line full-mode-extracted optical frequency comb.

Digital holography (DH) is a powerful tool for the surface profilometry of objects with sub-wavelength precision. In this article, we demonstrate full-cascade-linked synthetic-wavelength DH for nanometer-precision surface metrology of millimeter-sized stepped objects. 300 modes of optical frequency comb (OFC) with different wavelengths are sequentially extracted at a step of mode spacing from a 10GHz-spacing, 3.72THz-spanning electro-optic modulator OFC. The resulting 299 synthetic wavelengths and a single optical wavelength are used to generate a fine-step wide-range cascade link covering within a wavelength range of 1.54 µm to 29.7 mm. We determine the sub-millimeter and millimeter step differences with axial uncertainty of 6.1 nm within the maximum axial range of 14.85 mm.

A Review on Materials and Methods for the Fabrication of Microcavity Laser

Optical microcavities are resonators that have at least one dimension on the order of a single optical wavelength. These structures enable one to control the optical emission properties of materials placed inside them. One of their most dramatic potential features is threshold-less lasing,unlike the conventional lasers. This is possible due to 2D monolayers, Heterostructures, Hybrid materials which are used as active layers for polariton-exciton strong coupling. In this review paper, a different method of Microcavity laser fabrication is reviewed, where a different type of active materials is utilized to improve the laser efficiency. Materials such as WS2, MoS2, WSe2 and MoSe2are used due to their strong exciton binding energy. These use high reflecting DBR mirrors fabricated using oxides of a higher refractive index such as SiO2, NbO2, HfO2/Al2O3, SiO2/Ta2O5 and SiO2/TiO2. In this way, the controlled spontaneous emission is expected to play a vital role in a new generation of optical devices and can have a wide range of applications in Optics, Quantum computing, high-speed signal transmission, etc.

A multi-tone high efficient bandwidth system with an eliminated even-order distortions using double dual-parallel Mach-Zehnder modulator

In this paper, a linearization of dual RF channels over a single carrier wavelength is proposed and experimentally demonstrated. Multiple microwave signals with a multi-octave bandwidth are modulated by a double dual-parallel Mach-Zehnder modulator (D-DPMZM) and recovered by a differential balanced detector (BPD). The theoretical and experimental model illustrates the elimination of second-order harmonic distortions (SHD) and second-order intermodulation (IMD2), and significant suppression of the third-order intermodulation (IMD3) by controlling the phase of the input RF signal and DPMZM. The proposed photonic link configuration illustrates the modulation of two microwave signals on a single optical carrier wavelength, and each RF channel is tested for Two-tone signals to illustrate the linearization of the channelized analog photonic link (CAPL). Firstly, a mathematical model is presented to illustrate the elimination of optical carrier and even-order distortions by using only single-tone in each RF channel. Secondly, the purity of the system is mathematically and experimentally investigated by introducing two-tones in each RF channel. We have analyzed both test cases, with single-tone and with a two-tone test, to help us understand and compare the performance of the system. For test case 1 and test case 2 of our proposed configuration, we have achieved a fundamental signal-to-interference ratio (S/I) of 60 dB and 65 dB with a spurious-free dynamic range (SFDR) of 110 dB.Hz2/3 and 116 dB.Hz2/3, respectively.

Using DSP-based effective wireless ethernet accumulation of networks

Mobile fronthaul is an important segment of the network that bridges wireless baseband and remote radio units to support network access to cloud radio. We review recent developments in the use of frequency-division multiplexing to achieve highly bandwidth-efficient, low latency mobile fronthauling. Digital signal processing (DSP) techniques are described for frequency domain windowing, adjacent channel leakage ratio reduction, channel aggregation and deaggregation and synchronous transmission of both the control words (CWs) used for control and management, wireless signal I / Q waveforms. In this experiment, we reveal the transmission of 48 20-MHz LTE signals with a common public radio interface (CPRI) identical data rate of 59 Gb / s, attained a short round-trip DSP latency of < 2 μs, and a small mean error-vector magnitude (EVM) of ∼ 2.5% behind fiber transmission. In a follow-up experiment, together with CPRI-compliant CWs, we further demonstrate the transmission of 32 20-MHz LTE signals, corresponding to a CPRI-equivalent data rate of 39.32 Gb / s, in a single optical wavelength channel which requires an RF bandwidth of only 1.6 GHz. The CWs are recovered without error after transmission over 5 km of standard single-mode fiber, while the LTE signals are recovered with an EVM of<3 per cent. It is also discussed how to apply this technique to future 5 G wireless networks with massive multiple-input multiple outputs. This efficient mobile fronthaul technique may find promising applications for providing ultrabroadband access services in future integrated fiber / wireless access networks.

Semi-automated method for the determination of the all-optical monitoring strategy of complex thin-film filters.

One of the critical steps in the fabrication of complex optical interference filters is the precise control of the thickness of the layers during the fabrication process. However, the definition of the optimal optical monitoring strategy remains a challenge as it relies on user experience and there is no reliable automatic determination of this strategy. Here, we propose a semi-automated method that allows the determination of the optimal strategy. It is based on the combination of trinary mappings to select spectral regions that are compatible with optical monitoring and the use of the reflected phase error at a single wavelength versus optical monitoring wavelength. We show how this procedure can be used for the determination of either a single optical monitoring wavelength or a multi-wavelength procedure of a complex filter and confirm these theoretical results with an experimental demonstration.

Digital Code-Division Multiplexing Channel Aggregation for Mobile Fronthaul Architecture With Low Complexity

A low-complexity mobile fronthaul architecture via digital code-division multiplexing (CDM) is proposed to enable channel aggregation of 4G-LTE signals. In comparison with traditional frequency division multiplexing based aggregation scheme, the fast Fourier transformation/inverse fast Fourier transformation operations are replaced by simple sign selection and addition, leading to the significant reduction of computational complexity. Moreover, synchronous transmission of both the I/Q waveforms of wireless signals and the control words (CWs) used for the purpose of control and management using the CDM approach is also presented to be compliant with the common public radio interface (CPRI). In a proof-of-concept experiment, we demonstrate the transmission of 48 × 20 MHz LTE signals with CPRI equivalent data rate of 59 Gb/s, achieving an average error vector magnitude (EVM) of ∼3.6% and ∼4.3% after 5 and 20 km transmission over standard single-mode fiber (SSMF), respectively. Furthermore, we successfully demonstrate the transmission of 32 × 20 MHz LTE signals together with CPRI-compliant CWs, corresponding to CPRI-equivalent data rate of 39.32 Gb/s, only using single optical wavelength channel with analog bandwidth of ∼1.96 GHz. After transmission over 5 km SSMF, CWs can be error-free recovered while the LTE signals are recovered with an EVM of ∼3.6%.

Probe for evaluating the absorbing and transport scattering properties of turbid fluids using low-cost time-of-flight technology.

A probe is described that when immersed into a highly scattering fluid provides a measurement of its scattering and absorbing properties at a single optical wavelength. It uses recently available low-cost proximity sensor modules to estimate the mean flight times of photons diffusely transmitted between near-infrared sources and detectors at two different separations. The probe has been designed with a specific application for enabling the rapid and efficient production of fluids, which mimic the optical properties of biological tissues. The potential of the device is demonstrated using precalibrated solutions of intralipid, an intravenous nutrient, and absorbing dye. It is shown that a combination of time-of-flight measurements at two source–detector separations can uniquely specify the absorption coefficient and the transport scattering coefficient.

4?×?4 multiple-input multiple-output coherent microwave photonic link with optical independent sideband and optical orthogonal modulation (Invited Paper)

A 4×4 multiple-input multiple-output coherent microwave photonic (MWP) link to transmit four wireless signals with an identical microwave center frequency over a single optical wavelength based on optical independent sideband (OISB) modulation and optical orthogonal modulation with an improved spectral efficiency is proposed and experimentally demonstrated. At the transmitter, the OISB modulation and optical orthogonal modulation are implemented to generate an OISB signal using a dual-parallel Mach–Zehnder modulator (DP-MZM) driven by four microwave orthogonal frequency-division multiplexing (OFDM) signals with an identical microwave center frequency. At the receiver, the OISB signal is coherently detected at a coherent receiver where a free-running local oscillator (LO) laser source is employed. Digital signal processing is then used to recover the four OFDM signals, to eliminate the phase noise from the transmitter laser source and the LO laser source, and to cancel the unstable wavelength difference between the wavelengths of the transmitter laser source and the LO laser source. Error-free transmission of three 16 quadrature amplitude modulation (16-QAM) 1 Gbps OFDM signals and one 16-QAM 1.5 Gbps OFDM signal at a microwave center frequency of 2.91 GHz over a 10 km single-mode fiber is experimentally demonstrated.

Stretchable multichannel antennas in soft wireless optoelectronic implants for optogenetics

Optogenetic methods to modulate cells and signaling pathways via targeted expression and activation of light-sensitive proteins have greatly accelerated the process of mapping complex neural circuits and defining their roles in physiological and pathological contexts. Recently demonstrated technologies based on injectable, microscale inorganic light-emitting diodes (μ-ILEDs) with wireless control and power delivery strategies offer important functionality in such experiments, by eliminating the external tethers associated with traditional fiber optic approaches. Existing wireless μ-ILED embodiments allow, however, illumination only at a single targeted region of the brain with a single optical wavelength and over spatial ranges of operation that are constrained by the radio frequency power transmission hardware. Here we report stretchable, multiresonance antennas and battery-free schemes for multichannel wireless operation of independently addressable, multicolor μ-ILEDs with fully implantable, miniaturized platforms. This advance, as demonstrated through in vitro and in vivo studies using thin, mechanically soft systems that separately control as many as three different μ-ILEDs, relies on specially designed stretchable antennas in which parallel capacitive coupling circuits yield several independent, well-separated operating frequencies, as verified through experimental and modeling results. When used in combination with active motion-tracking antenna arrays, these devices enable multichannel optogenetic research on complex behavioral responses in groups of animals over large areas at low levels of radio frequency power (<1 W). Studies of the regions of the brain that are involved in sleep arousal (locus coeruleus) and preference/aversion (nucleus accumbens) demonstrate the unique capabilities of these technologies.

Analysis and Design Optimization of a Hybrid VO2/Silicon2 &lt;inline-formula&gt; &lt;tex-math notation="LaTeX"&gt;$\times$&lt;/tex-math&gt; &lt;/inline-formula&gt; 2 Microring Switch

The metal-to-insulator transition (MIT) property of vanadium dioxide (VO2) has recently been used in several application fields such as plasmonics, sensing, metamaterials, and optical modulation. Due to the MIT nature, VO2 allows a huge change in its complex refractive index that can be electrooptically controlled. In this paper, the analysis and design optimization of a 2 $\times$ 2 microring switch based on a hybrid VO2/silicon waveguide structure is addressed. Switching is achieved by exploiting the change in both absorption loss and phase shift that occurs in VO2 when changing from the insulating to the metallic state. The device is optimized to minimize insertion losses and crosstalk. An active length of only 2.8 $\mu\text{m}$ is required to achieve a data throughput rate higher than 500 Gb/s at a single optical wavelength.

Efficient Mobile Fronthaul via DSP-Based Channel Aggregation

Mobile fronthaul is an important network segment that bridges wireless baseband units and remote radio units to support cloud radio access network. We review recent progresses on the use of frequency-division multiplexing to achieve highly bandwidth-efficient mobile fronthaul with low latency. We present digital signal processing (DSP) techniques for channel aggregation and deaggregation, frequency-domain windowing, adjacent channel leak age ratio reduction, and synchronous transmission of both the I/Q waveforms of wireless signals and the control words (CWs) used for control and management purposes. In a proof-of-concept experiment, we demonstrate the transmission of 48 20-MHz LTE signals with a common public radio interface (CPRI) equivalent data rate of 59 Gb/s, achieving a low round-trip DSP latency of <2 μs and a low mean error-vector magnitude (EVM) of ∼2.5% after fiber transmission. In a follow-up experiment, we further demonstrate the transmission of 32 20-MHz LTE signals together with CPRI-compliant CWs, corresponding to a CPRI-equivalent data rate of 39.32 Gb/s, in single optical wavelength channel that requires an RF bandwidth of only ∼1.6 GHz. After transmission over 5-km standard single-mode fiber, the CWs are recovered without error, while the LTE signals are recovered with an EVM of lower than 3%. Applying this technique to future 5G wireless networks with massive multiple-input multiple-output is also discussed. This efficient mobile fronthaul technique may find promising applications in future integrated fiber/wireless access networks to provide ultrabroadband access services.

Hybrid Cable Television/Radio-Over-Fiber Transport System Based on Polarization Modulation Technique

A hybrid cable television/radio-over-fiber (ROF) transport system with direction modulation of cable television signals and the polarization modulation of ROF signals is proposed and experimentally demonstrated for the first time. When a multicarrier cable television signal in the optical amplitude domain and an ROF signal in the optical polarization domain are modulated, a single optical wavelength can serve these two signal applications simultaneously. This hybrid transport system not only satisfied the cable television requirements, but also satisfied the demand for high-quality ROF transmission over a 20-km single-mode fiber.

Direct CATV modulation and phase remodulated radio-over-fiber transport system

A novel transport system, with directly modulating community antenna television (CATV) signal downstream and phase-remodulating radio-over-fiber (ROF) signal upstream, is proposed and experimentally demonstrated. By modulating multi-carriers CATV signal in amplitude domain and ROF signal in phase domain, a single optical wavelength is able to serve these two applications simultaneous. To be the first system of communicating CATV signal downstream and phase remodulating radio signal upstream, the performances of transmitting CATV and radio signals over 20 km single-mode fiber (SMF) were experimentally verified. Good performances of carrier-to-noise ratio (CNR), composite second-order (CSO), and composite triple beat (CTB) were obtained for CATV applications as well as high extinction ration (ER) and low bit error rate (BER) values were measured for ROF transmission.

Spectral-domain spectrally-encoded endoscopy

Spectrally-encoded miniature endoscopy uses a single optical fiber and wavelength division multiplexing to obtain macroscopic images through miniature, flexible probes. In turn, it has the potential to enable two- and three-dimensional imaging within the body at locations that are currently difficult to access with conventional endoscopes. Here we present a novel detection scheme for spectrally-encoded endoscopy using spectral-domain interferometry. Compared to previous time-domain configurations, this new detection method results in greater than 1000-fold increase in sensitivity (77 dB), a 6-fold increase in imaging speed (30 volumes per second), and a 2-fold increase in depth range (2.8 mm). We demonstrate spectrally-encoded, spectral-domain detection by conducting video-rate, three-dimensional imaging in a variety of specimens, including the paws of a mouse embryo and excised human ear bones. Our results show that this new technology enables video rate spectrally-encoded endoscopy and will therefore be useful for a variety of minimally invasive medical applications.

Continuously Variable Optical Delay Line Based on a Chirped Fiber Bragg Grating

In this letter, a continuously variable optical delay line (ODL), useful for phased array antennas, is experimentally demonstrated. The ODL operates at a single optical wavelength and it is based on a linearly chirped fiber Bragg grating (LCFBG). Continuous true time delay is achieved by changing the temperature of the LCFBG. In order to limit the actuating temperature range, the grating was bonded to a metallic support and the effect of the thermal apparent strain was considered. The time-delay response of the system is measured with an optical signal modulated with double sideband technique at a frequency of 2 GHz. The experimental results demonstrate a time-delay resolution of 3.1 ps employing a temperature controller with a stability of plusmn0.1 degC and a maximum time delay of 96 ps over a temperature range of 16 degC-40degC. The time-delay-temperature characteristic offers a slope of 3.8 ps/degC with a mean-square deviation from the linearity of 3.5 ps. Such a delay line, by operating at a single optical wavelength and by using a simple actuating system, offers many advantages being low cost, compactness, and reliability. The main limitation to the ODL resolution is due to the amplitude ripple of the LCFBG used and a performance enhancement can be obtained with specifically tailored LCFBG

Investigation of acousto-optic tunable filter parameters for fast spectrometer application

Ideally an acousto-optic tunable filter is capable for selecting a single optical wavelength from a broadband polychromatic light beam simply by its electronic tuning. In practice, however, both the wavelength resolution and the operating wavelength range of the filter are limited by its electric and optical properties. An experimental configuration of a computer-controlled, fast acousto-optic spectrometer, based on an acousto-optic tunable filter operating in the 400- to 800-nm visible range with an average resolution of 10 nm is constructed and studied. The spectrometer has been operated in broadband optical measurements, such as determination of transmission spectra of complex, multilayer optical thin films and also real-time, in situ monitoring of evaporation processes. During the experiments, an anomalous behavior of the filter was observed that seriously limited the performance of the filter in the blue region. Some requirements necessary for spectrometer application are summarized and theoretical and experimental results are given illustrating the existence and also the elimination of this anomalous behavior.

Physics and Device Applications of Optical Microcavities

Optical microcavities are resonators that have at least one dimension on the order of a single optical wavelength. These structures enable one to control the optical emission properties of materials placed inside them. They can, for example, modify the spatial distribution of radiation power, change the spectral width of the emitted light, and enhance or suppress the spontaneous emission rate. In addition to being attractive for studying the fundamental physics of the interaction between materials and vacuum field fluctuations, optical microcavities hold technological promise for constructing novel kinds of light-emitting devices. One of their most dramatic potential features is thresholdless lasing. In this way and others, controlled spontaneous emission is expected to play a key role in a new generation of optical devices.