Stokes-Mueller matrix polarimetry system for glucose sensing

A Stokes-Mueller matrix polarimetry system consisting of a polarization scanning generator (PSG) and a high-accuracy Stokes polarimeter is used to sense the glucose concentration in aqueous solutions with and without scattering effects, respectively. In the proposed system, an electro-optic (EO) modulator driven by a saw-tooth waveform voltage is used to perform full state of polarization (linear/circular) scanning, while a self-built Stokes polarimeter is used to obtain dynamic measurements of the output polarized light intensity. It is shown that the measured output Stokes vectors have an accuracy of 10⁻⁴, i.e., one order higher than that of existing commercial Stokes polarimeters. The experimental results show that the optical rotation angle varies linearly with the glucose concentration over the range of 0-0.5 g/dl. Moreover, glucose sensing is successfully achieved at concentrations as low as 0.02 g/dl with a resolution of 10⁻⁶ deg/mm and an average deviation of 10⁻⁴ deg. In general, the polarimetry system proposed in this study provides a fast and reliable method for measuring the Stokes vectors, and thus has significant potential for biological sensing applications.     

Novel optical add-drop multiplexer based on dual racetrack resonators

In this paper, we designed and fabricated a four-channel optical add-drop multiplexer (OADM) based on dual racetrack resonators. The size of the fabricated device is only 2400 μm × 500 μm. The fabricated device can effectively and perfectly realize the signals upload and download. The free spectral range (FSR) of OADM is about 15.2 nm. We take the spectral responses near 1555 nm as an example. When the device acts as an optical drop multiplexer, the minimum insertion loss is 4.481 dB and the maximum extinction ratio is 31.931 dB. The maximum adjacent channels crosstalk is -9.845 dB. When the device acts as an optical add multiplexer, the minimum insertion loss is 0.944 dB and all of the extinction ratios are bigger than 25 dB. The maximum crosstalk is -16.531 dB which indicates the crosstalk can be neglected.     

Performance analysis of optical network based on optical add drop multiplexers with different MZI techniques

This paper presents an investigation on the performance of an optical network in terms of crosstalk based on optical add drop multiplexers with Mach–Zehnder interferometer (MZI), MZI-semiconductor optical amplifier (SOA) and MZI-fiber Braggs gratings (FBG) techniques obtained at 8 × 10 Gbps with 0.1 nm channel spacing wavelength division multiplexing (WDM) transmission with optical add drop multiplexer (OADM) placed at the 20 km point of a 40 km link. It is found that the signal can be transmitted with least BER and better Q-factor with MZI-FBG based OADM and the worst case is found with the MZI-SOA based OADM.     

Polarization insensitive hollow optical waveguide

A polarization insensitive hollow optical waveguide is proposed. The propagation characteristics of orthogonal polarizations in the hollow waveguide are effectively controlled in simulation to provide polarization insensitivity by tailoring the parameters associated with the two mirrors—a high-index contrast grating (HCG) mirror and a distributed Bragg reflecting (DBR) mirror, on either side of an air-core. The polarization insensitivity is evidenced by a low polarization dependence loss of 1.36 dB/cm and a low modal birefringence of 1.01 × 10^? 4.     

A long-range,high-resolution optical coherence tomography for physical and environmental measurements

Optical coherence tomography (OCT) is an emerging optical imaging technique that is applied with low coherence interference to perform noninvasive, high-resolution images on internal and surface structures. In this study, we built an optical coherence system and developed a combined envelope-fringe and carrier-fringe technique that can take advantage of high-resolution and long-range for taking physical and environmental measurements. The proposed system demonstrated that the detection resolution of the changes of the refractive index was 1.89 × 10^? 4 for the long-range set-up (i.e. using the envelope-fringe only), and 4.15 × 10^? 5 for the high-resolution set-up (i.e. using the carrier-fringe). In addition, we successfully applied the system to measure the refractive index of a body of water, as the index for determining the pollution condition of different lakes.     

Low pitch LWIR QWIPs: Performance level and image quality

We present recent results obtained on 15 μm pitch LWIR QWIP arrays at Sofradir. Based on experimental data gathered on several QWIP wafers, the performance (NETD) at the system level has been estimated. We show that, in spite of the small pitch, values as low as 50 mK can be achieved for rather closed optical systems (f/2.5) and for operating temperatures (74 K) compatible with available compact cryo-coolers.We also demonstrate that specific pixel configurations can be designed to investigate the pixel-to-pixel optical crosstalk. Such measurements can help to better understand the limitations set by the geometry of the pixel on the Modulation Transfer Function (MTF). In particular, we show that the optical crosstalk due to photon transfer through the inter-pixel space is rather small for unthinned devices.     

Ultrafast relaxation of hot optical phonons in monolayer and multilayer graphene on different substrates

Hot carrier cooling in few-layer and multilayer epitaxial graphene on SiC, and chemical vapor deposition (CVD) grown graphene transferred onto a glass substrate was investigated by transient absorption spectroscopy and imaging. Coupling to the substrate was found to play a critical role in charge carrier cooling. For both multilayer epitaxial graphene and monolayer CVD graphene, charge carriers transfer heat predominantly to intrinsic in-plane optical phonons of graphene. At high pump intensity, a significant number of optical phonons are accumulated, and the optical phonon lifetime presents a bottleneck for charge carrier cooling. This hot phonon effect did not occur in few-layer epitaxial graphene because of strong coupling to the substrate, which provided additional cooling channels. The limiting charge carrier lifetimes at high excitation densities were 1.8 ± 0.1 ps and 1.4 ± 0.1 ps for multilayer epitaxial graphene and monolayer CVD graphene, respectively. These values represent lower limits on the optical phonon lifetime for the graphene samples.     

Linear optical scheme for producing polarization-entangled NOON states

We propose a linear optical scheme that can conditionally generate high NOON states using polarization modes. This scheme provides advantages over the previous proposals on path-entangled NOON states in view of success probability or required resources of optical elements. We also investigate two experimental schemes feasible within existing technology that can produce the NOON-like or the NOON state for N = 4.     

Advanced multifunctional optical switch for multimode optical fiber networks

In this work, an advanced multifunctional optical switch based on multimode fibers is proposed. It can work as a 3 × 1 optical multiplexer/combiner, a 2 × 2 optical switch, a variable optical attenuator and a variable optical power splitter. All these functionalities can be developed in the same device without any hardware modification, only by using the proper ports and control electronics.The proposed switch has been developed for being used in the visible and near infrared wavelength range: 450–650 nm for optical fiber automobile applications, 650–850 nm for home broadband applications; and 850–1300 nm for multimode fiber access networks. Up to three different types of twisted nematic liquid crystal cells have been designed and fabricated for fulfilling these different wavelength ranges as part of the proposed device.The multifunctional switch has been implemented and experimentally tested. Crosstalk usually better than ? 15 dB at 532 nm, 660 nm and 850 nm, in any state has been measured. Switching is achieved at voltage levels of 4 Vrms. Fiber to fiber insertion losses when operating as a 2 × 2 optical switch, range from 10 to 15 dB within 200 nm wavelength range; with a non-optimized optics for collimation and coupling.     

Airborne infrared fire detection optical system with tilted porthole

Thermal infrared imagery techniques have been applied in the field of wild land fire management for many years. A kind of infrared system with a tilted porthole conformal to the ellipsoid prow underside the plane nose is presented. This design increases the range of the inner imaging system, reduces air drag and protects against damage. The paper analyzes the aberration characteristic of a tilted ellipsoid porthole, and brings forward an effective corrective solution to make the system achieve a ? 30° to ? 90° field of regard with an instantaneous ± 4° field of view. The ultimate performance indicates that the infrared optical system has met the detection requirements.     

Polarization-independent rapidly tunable optical add-drop multiplexer utilizing non-polarizing beam splitters in Ti:LiNbO3

A polarization-independent four-port wavelength-tunable optical add drop multiplexer (OADM) that utilizes non-polarizing relaxed beam splitters has been analyzed and demonstrated in Ti:LiNbO₃ at the 1530 nm wavelength regime. The design utilizes an asymmetric interferometer configuration with strain induced index grating for polarization coupling along its arms that are shifted in position relative to each other. Experimental results of the filter response agree with theoretical predictions. Electrooptic tuning over a range of 15.7 nm at a rate of 0.08 nm/V has been measured. A temporal response < 46 ns to a 20 V step change in tuning voltage has been demonstrated. Fiber-to-fiber insertion loss is ~ 6.5 dB.     

White light interferometric detection of unpolarized light for complete Stokesmetric optical coherence tomography

Optical coherence tomography (OCT) relies on interference between a polarized reference and the target reflection. Thus, it has generally been impossible to detect any unpolarized part in the signal. Here, we demonstrate a scheme that overcomes this limitation. Using a combination of heterodyning and filtering, we realize a polarization-sensitive OCT system capable of measuring the full Stokes vector, including the depolarized part. Based on such a system, we perform full Stokesmetric imaging of different layers in a porcine tendon sample. The complete 4 × 4 backscattering Muellermetric images of one layer are acquired and investigated.     

Spectral efficient hybrid wireless optical broadband access network (WOBAN) based on transmission of wireless MIMO OFDM signals over WDM PON

In this paper, a spectral efficient hybrid wireless optical broadband access network (WOBAN) is proposed and demonstrated based on the transmission of wireless multi-input multi-output orthogonal frequency division multiplexing (MIMO OFDM) signals over wavelength division multiplexing passive optical network (WDM PON). By using radio over fiber (ROF) techniques, the optical fiber is well adapted to propagate multiple wireless services having different carrier frequencies. It is a known fact that multiple wireless signals having the same carrier frequency cannot propagate over a single optical fiber at the same time, such as MIMO signals feeding multiple antennas in fiber wireless (FiWi) system. A novel optical single-sideband frequency translation technique is designed and simulated to solve this problem. This technique allows four pairs of wireless MIMO OFDM signals with the same carrier frequency for each pair to be transmitted over a single optical fiber by using one optical source per wavelength. The crosstalk between the different MIMO channels with the same frequency is eliminated, since each channel is upconverted on specified wavelength with enough channel spacing between them. Also the maximum crosstalk level between the different MIMO channels with different frequencies is very low around ?76 dB. The physical layer performance of the proposed WOBAN is analyzed in terms of the bit error rate (BER), error vector magnitude (EVM), and signal-to-noise ratio (SNR). The proposed WOBAN achieves 7.68 Gb/s data rate for 20 km for the optical back-end and 240 Mb/s for the outdoor wireless front-end.     

Theoretical ultraslow bright and dark optical solitons in cascade-type GaAs/AlGaAs multiple quantum wells

We show the formation of ultraslow bright and dark optical solitons in a cascade-type three-level system of GaAs/AlGaAs multiple quantum wells (MQWs) structure based on the biexciton coherence in the transient optical response, and study analytically and numerically with Maxwell–Schrödinger equations. The calculated velocity of bright and dark optical solitons are V_g = 2.7 × 10⁴ ms^? 1 and V_g = 8.91 × 10⁴ ms^? 1, respectively. Such investigation of ultraslow optical solitons in MQWs may provide practical applications such as high-fidelity optical delay lines and optical buffers in semiconductor quantum wells structure, because of its flexible design.     

Nuclear polarization by optical pumping in InP:Fe above liquid nitrogen temperature

Hyperpolarized nuclear spins are observed in optically pumped iron-doped InP from 70 K to 140 K. ³¹P NMR was carried out at 9.28 T (159.8 MHz) during optical excitation with circularly polarized light, using a laser diode (λ∼830 nm) as a source. The enhancement of the nuclear spin polarization by optical pumping at 70 K is estimated to be about 34 for those nuclei in the region of the sample absorbing light. This enhancement decreases with increasing temperature. As the direction of the enhanced nuclear spin polarization is found parallel or antiparallel to the travelling direction of the σ⁺ or σ⁻, the contact hyperfine interaction is dominant compared to the dipolar hyperfine interaction.     

Cr4+:YAG passively Q-switched c-cut Nd:YVO4 self-Raman laser at 1168.6 nm

We demonstrate the first Cr⁴⁺:YAG passively Q-switched c-cut Nd:YVO₄ self-Raman laser at 1168.6 nm based on the Stokes shift of 816 cm⁻¹. At the pump power of 4.7 W, the maximum output power of the Stokes line at 1168.6 nm is 270.5 mW, corresponding to an optical conversion efficiency of 5.8%. The pulse width, pulse repetition rate, pulse energy and peak power are 8.8 ns, 35.8 kHz, 7.6 μJ and 0.86 kW, respectively. At the pump of 5.0 W, the Stokes line at 1097.2 nm based on Raman shift of 259 cm⁻¹ also appears.     

Ultrasmall optical logic gates based on silicon periodic dielectric waveguides

An ultrasmall silicon periodic dielectric waveguides-based multimode interference all-optical logic gate has been proposed. The device consists of three 205 nm wide single-mode input waveguides, a 1.1 μm wide and 5.5 μm long multimode interference waveguide, and three 205 nm wide single-mode output waveguides. The total length and width of the device are 13.7 μm and 3.2 μm, respectively. By changing the states of the input optical signals and/or control signals launched into the device, multifunctional logic functions including OR, NAND, NOR, and NOT gates are performed, and each logic function can be realized at a specific output waveguide in accordance with the launched control signals. The ultrasmall multifunctional logic device has potential applications in high density photonic integrated circuits.     

Cascaded continuous-wave singly resonant optical parametric oscillator pumped by a single-frequency fiber laser

We present a cascaded continuous-wave singly resonant optical parametric oscillator (SRO) delivering idler output in mid-IR and terahertz frequency range. The SRO was pumped by an ytterbium-doped fiber laser with 27 W linear polarization pump powers, and based on periodically poled MgO:LiNbO₃ crystal (PPMgLN) in two-mirror linear cavity. The PPMgLN is 50 mm long with 29.5 μm period. The idler power output at 3811 nm was obtained 2.6 W. The additional spectral components that have been attributed to cascaded optical parametric processes are described at increasing pump levels. Besides the initial signal component at about 1476.8 nm, further generated wavelengths with frequency shifts about 47 cm^?1, 94 cm^?1 and 104 cm^?1 were observed. It was speculated that the idler waves lie in the terahertz (THz) domain from the observed results.     

Performance analysis of a swept-source optical coherence tomography system with a quadrature interferometer and optical amplification

A performance analysis of signal to noise ratio for an optical coherence tomography system with quadrature detection and a semiconductor optical amplifier in the sample arm is discussed. The results are compared and discussed in relation to a conventional OCT system (without optical amplification). An increase of the signal to noise ratio up to 14 dB at a depth of 0.5 mm is obtained compared to the system without the optical amplifier. Overall, an improvement was demonstrated for signal coming from deeper regions within the samples. Arterial plaque from a myocardial infarction-prone Watanabe heritable hyperlipidemic (WHHLMI) rabbit is visualized and characterized using this system. Improvement of signal to noise ratio increases the penetration depth possible for OCT images, from 1 mm to 2 mm within the vessel wall of an artery. Preliminary results show that vulnerable plaque with fibrous cap, macrophage accumulations and calcification in the arterial tissue are measurable with this OCT system.     

An optical continuous phase FSK modulation scheme with an arbitrary modulation index over long-haul transmission fiber link

This paper presents an optical continuous phase frequency shift keying (CPFSK) modulation scheme with an arbitrary modulation index. The detailed principle on the optical CPFSK generation is derived and analyzed, which includes the special case of the minimum-shift keying (MSK) with a modulation index h = 1/2. The differential detection and the coherent detection of CPFSK are also depicted. The performances of the four kinds of the optical CPFSK modulated system with a 40 Gb/s modulation rate whose modulation index are h = 1/2, h = 2/3, h = 3/4 and h = 1 are simulated via the spectral efficiency and the receiver sensitivity over fiber link respectively. In addition, comparison with the differential phase shift keying (DPSK) is taken. Through the calculation of the spectral efficiency of each modulation formats, CPFSK has higher spectral efficiency than DPSK with the same optical devices. The transmission performances of our CPFSK over the fiber link change better as the modulation index increases under the condition of the first order dispersion of the fiber link is completely compensated. Through simulations, a 1200 km transmission distance can be achieved with a modulation index h = 1.