Zehnder Configuration Research Articles

Improving resolution in two orthogonal orientations from a single-shot digital holographic microscopy

We demonstrate a single-shot digital holographic microscopy technique to improve the diffraction-limited resolution in two orthogonal orientations simultaneously by dual-channel orthogonal polarization multiplexing approach. Orthogonally polarized two oblique beams are employed to illuminate the sample and two reference beams with mutually orthogonal polarization are interfered with the object beams in a custom-designed Mach–Zehnder configuration. This technique is potentially beneficial to encode high frequency sample information from two orthogonal directions simultaneously in a single recorded hologram where the high frequency spectra is synthesized by the selective spectral stitching. Thus, the resolution is enhanced along two orientations from a single-shot hologram in this work. Both the simulation and experimental results are shown for the proposed technique with around 2-fold resolution enhancement over the diffraction limit.

Optical Fiber Interferometers Based on Arc-Induced Long Period Gratings at INESC TEC.

In this work, we review the most important achievements of an INESC TEC long-period-grating-based fiber optic Michelson and Mach–Zehnder configuration modal interferometer with coherence addressing and heterodyne interrogation as a sensing structure for measuring environmental refractive index and temperature. The theory for Long Period Grating (LPG) interferometers and coherence addressing and heterodyne interrogation is presented. To increase the sensitivity to external refractive index and temperature, several LPG interferometers parameters are studied, including order of cladding mode, a reduction of the fiber diameter, different type of fiber, cavity length and the antisymmetric nature of cladding modes.

All-Optical Comparator With a Step-Like Transfer Function

We propose a scheme for an all-optical comparator which embeds a nonlinear fiber ring resonator in a Mach–Zehnder configuration. Such a resonator accumulates the circulating power of the light traversing the ring, so that the effective nonlinear phase shift in fiber can be significantly enhanced. Numerical results demonstrate that with appropriate choice of the parameters of the Mach–Zehnder configuration and the power of the probe light, the all-optical comparator can exhibit an excellent step-like transfer function. Simultaneously, the configuration reduces the switching threshold by 3 or more orders of magnitude to the level of milliwatt when conventional highly nonlinear fibers are adopted. In addition, our simulations show that this all-optical threshold comparator also has a multiperiodic transfer characteristic and thus may be used to construct multibit analog-to-digital convertors.

Absolute ozone densities in a radio-frequency driven atmospheric pressure plasma using two-beam UV-LED absorption spectroscopy and numerical simulations

The efficient generation of reactive oxygen species (ROS) in cold atmospheric pressure plasma jets (APPJs) is an increasingly important topic, e.g. for the treatment of temperature sensitive biological samples in the field of plasma medicine. A 13.56 MHz radio-frequency (rf) driven APPJ device operated with helium feed gas and small admixtures of oxygen (up to 1%), generating a homogeneous glow-mode plasma at low gas temperatures, was investigated. Absolute densities of ozone, one of the most prominent ROS, were measured across the 11 mm wide discharge channel by means of broadband absorption spectroscopy using the Hartley band centred at λ = 255 nm. A two-beam setup with a reference beam in Mach–Zehnder configuration is employed for improved signal-to-noise ratio allowing high-sensitivity measurements in the investigated single-pass weak-absorbance regime. The results are correlated to gas temperature measurements, deduced from the rotational temperature of the N2 (C 3 B 3, υ = 0 2) optical emission from introduced air impurities. The observed opposing trends of both quantities as a function of rf power input and oxygen admixture are analysed and explained in terms of a zero-dimensional plasma-chemical kinetics simulation. It is found that the gas temperature as well as the densities of O and O2(b) influence the absolute O3 densities when the rf power is varied.

Experimental investigations on characterization of freeform wavefront using Shack–Hartmann sensor

The metrology of freeform wavefront can be performed by the use of a noninterferometric method, such as a Shack–Hartmann sensor (SHS). Detailed experimental investigations employing an SHS as metrology head are presented. The scheme is of nonnull nature where small subapertures are measured using an SHS and stitched to give the full wavefront. For the assessment of complex misalignment errors during the spiral scanning, a library of residual slope errors has been created, which makes the alignment process fast converging for minimizing the scanning errors. A detailed analysis of the effects of slope and positioning error on reproducibility is presented. It is validated by null test where a null diffractive optical element has been used in a Mach–Zehnder configuration for compensating the freeform shape. A freeform optics is measured by both measurement schemes, and the results are in good agreement. Further, the nonnull-based scanning subaperture stitching scheme is also validated by performing measurements on an aspheric surface and compared with the measurements from the interferometric method (Zygo Verifire).

Refractive index measurement of sol forming Laponite JS dispersion using interferometry

In this work refractive index (RI) of a solution (sol) of water-dispersed Laponite JS has been experimentally measured by using the Mach–Zehnder configuration of an interferometer combined with an Abbe-type refractometer. It was observed that the RI of the Laponite JS dispersion increases with an increase in Laponite concentration while it decreases with increasing temperature. The behavior of RI as a function of density was observed to be in good agreement with the extended Lorentz–Lorenz equation. It suggests that changes in RI arising from the temperature are mainly accounted for through the change in density while the direct effect of temperature being small. Finally, RI of the sol forming Laponite JS dispersion was compared with the previously reported data of the gel forming dispersion of Laponite RD and was found to be in qualitative agreement.

Dual-wavelength digital holographic phase reconstruction based on a polarization-multiplexing configuration

We present a polarization-multiplexing off-axis Mach–Zehnder configuration for dual-wavelength digital holography to achieve phase imaging in one shot. In this configuration, two orthogonal linear-polarized waves with respect to different wavelengths are employed to record respective holograms synchronously, where two recording waves transmit independently through the same optical paths of the interferometer, and by installing two analyzer polarizers each to filter off either of two wavelengths, and filtering through the other, the holograms are acquired, respectively, by a pair of CCDs at the same time. The unwrapped phase image of a grating with groove depth 7.1 μm is retrieved via spatial frequency filtering.

Triple detection fiber differentiating interferometer based on low-coherence interferometer and its passive demodulation scheme

Abstract This paper presents a triple detection fiber differential interferometer and its passive demodulation scheme. The interferometer is based on an all fiber Mach–Zehnder and Sagnac hybrid configuration, which is composed of a fiber ASE source, a section of delay fiber, a 3×3 fiber coupler and several other fiber components. In the interferometer, the signal beam and reference beam travel along the same path but in opposite directions. The received signal is demodulated by a triple detection passive demodulation scheme. The interferometer can measure the absolute amplitudes and frequencies of phase sensitive signals with large dynamic range, and the low frequency environmental disturbance is removed simultaneously due to the phase compression mechanism. The experimental results demonstrate that the phase demodulation resolution is 6×10 −5 rad and the maximum measuring amplitude is up to 90 rad. This method can be used to measure many kinds of parameters such as vibration and refractive index.

Theoretical analysis of a Mach–Zehnder interferometer with a porous-film waveguide

Here we present a comprehensive theoretical study of a porous-film sensor of fluid in Mach–Zehnder configuration. It is found that the penetration of a fluid into the film pores causes amplitude and phase modulation of the interferometer output signal, maximizing the sensitivity at a certain value of the fluid refractive index. We define the Fisher information for this interferometer and show that it is a good measure of its sensitivity, hence suitable as an evaluation function in sensor optimization. We propose the sensor structure and design thin films that maximize its sensitivity to water, alcohol solutions and oils. The estimated sensitivity of the order of to the fluid refractive index and of to the changes in the film thickness indicate the potential of this sensor for applications in biomedicine, chemistry and environmental protection, and as a tool for the film characterization.

Investigation of phase SPR biosensor for efficient targeted drug screening with high sensitivity and stability

We investigate an application case study of a phase sensitive surface plasmon resonance (SPR) biosensor based on Mach–Zehnder configuration for efficient targeted drug screening, where calculating reaction kinetic constants, inhibition effect and cytotoxicity analysis are three key factors in the evaluation. As a typical targeted drug, cetuximab is selected in the measurements assisted by the phase SPR biosensor with a sensitivity of 10−6 in terms of refractive index unit (RIU) and stability of 6×10−7RIU in 80min. The reaction kinetic constants of cetuximab binding to epidermal growth factor receptor (EGFR) are found as: kd (dissociation constant)=1.75±0.29×10−3S−1, kD (equilibrium dissociation constant)=4.19±0.58nM. The results of inhibition effect analysis show that cetuximab can block EGFR binding to its two ligands, epidermal growth factor (EGF) and EGFR-transforming growth factor α (TGF-α). This effect has been tested in three cell lines of lung adenocarcinoma, colon cancer and breast cancer. Comparing to other conventional methods, we find that the phase SPR biosensor can determine the cell sensitivity to cetuximab in just 4h. As a label-free, real-time, high sensitivity and stability biosensor, the phase SPR biosensor is a potential optical technique for targeted drug screening and analysis of cell resistance to drugs with comparative advantages.

Measurement of Mass Diffusivity Using Interferometry through Sensitivity Analysis

Mass diffusion of a solute in a solvent is realized in many applications. The extraction of transport properties from optical images has not received sufficient attention, though refractive index techniques for determination of the mass diffusion coefficient of a solute in a binary system have been discussed in the literature. The issue becomes important in experiments involving slow diffusion during which concentration gradients in parts of the domain are large. Accordingly, refractive index gradients are also large and higher order effects influence image formation. This weakness can be addressed by carrying out sensitivity analysis, wherein only that part of the data is analyzed which is highly sensitive to the experimental determination of diffusivity. In the context of interferometry, the present study reports fringe patterns obtained for the diffusion of NaCl and sucrose in deionized water at 25 °C. A Mach–Zehnder configuration of the interferometer has been employed. In an experiment, a layer of so...

Design and analysis of all-optical AND, XOR and OR gates based on SOA–MZI configuration

The novel designs of all-optical logic gates using cross-gain modulation and cross phase modulation in semiconductor optical amplifiers, have been suggested and demonstrated successfully at 10 Gb/s. Mach–Zehnder configuration with two 3 dB couplers is used to introduce phase modulation on the saturated inverted output of SOA. No additional input beam such as clock signal or continuous light wave is used as in several other designs. In the designs, one data act as a pump and another act as a probe signal. Therefore, while passing through SOA, one data acting as a pump, saturates another data which is a probe signal. Different arrangements of input part of SOA–MZI, create three gates such as AND, XOR and OR. Gates are analyzed according to the extinction ratio, wavelength spectrum, frequency chirping and bit error rate. Very high extinction ratio is found i.e. 54.5, 36.32 and 37.5 at 1550.5 nm for AND, XOR and OR gates respectively. The wavelength spectrum, of all the three gates, lies within 1554.8 nm to 1555.2 nm which is near the central wavelength of probe pulse at 1550 nm. Negative frequency chirp are found for all the three gates with bit error rate 7.1×10−30, 1×10−31 and 2.1×10−12 for AND, XOR and OR respectively.

Tomographic diffractive microscopy of living cells based on a common-path configuration

We demonstrate a common-path tomographic diffractive microscopy technique for three-dimensional (3D) refractive-index (RI) imaging of unstained living cells. A diffraction grating is utilized to generate a reference beam that traverses a blank region of the sample in a common-path off-axis interferometry setup. Single-shot phase images captured at multiple illumination angles are used for 3D RI reconstruction based on optical diffraction tomography. The common-path configuration shows lower temporal phase fluctuations and better RI resolution than a Mach-Zehnder configuration. 3D subcellular RI distributions of live HeLa cells are quantified.

High resolution temperature independent refractive index measurement using differential white light interferometry

In this work a fiber optic interferometric system for differential refractive index measurement is described. The system is based on a white light Mach–Zehnder configuration, with serrodyne phase modulation, used to interrogate two similar non-adiabatic tapered optical fiber sensors in a differential scheme. In this situation the system is able to measure the refractive index independent of temperature. Signal processing with low cost digital instrumentation developed in Labview environment allows a detectable change in refractive index of Δn≈1.46×10−6, which is, from the best of our knowledge the highest resolution achieved using a bare fiber taper device for a range of refractive index close to the water index. The results demonstrate the potential of the proposed scheme to operate as a self-referenced chemical and biological sensing platform.

High sensitivity LPG Mach–Zehnder sensor for real-time fuel conformity analysis

A high sensitivity refractive index sensor based on the combination of mechanically induced long period gratings (LPG) and fiber tapers was developed for real-time fuel quality analysis. The sensor was built in a Mach–Zehnder configuration by employing a pair of in-series gratings. In order to enhance sensor sensitivity, the region between both LPGs was tapered down from 125 to 10 µm. The system was tested by measuring water concentration in ethanol and ethanol concentration in commercial gasoline. The tapered sensor has shown an average sensitivity of 930 nm/RIU, 18 times higher than the non-tapered version. The resolution limit of the system using spectral interrogation was estimated to be 0.06% of ethanol dissolved in gasoline. For the purpose of real-time monitoring, an interrogation system based on white light interferometry (WLI) and virtual instrumentation was employed to evaluate ethanol evaporation in water, avoiding the use of spectral analysis. The WLI system, using phase tracking techniques, enabled us to record the evolution of the ethanol concentration in water with a resolution of 0.005% (v/v).

Picosecond all-optical switching using nonlinear Mach–Zehnder with silicon subwavelength grating and photonic wire arms

We investigate the picosecond switching capabilities of a planar waveguide interferometric photonic device when used for all-optical wavelength conversion of one picosecond pulses. Our device comprises a subwavelength grating waveguide arm and a photonic wire waveguide arm in a Mach–Zehnder configuration, fabricated on the silicon-on-insulator material platform. No detrimental effects of pulse broadening for transient pulses were observed.

Measurement of Local Gravity via a Cold Atom Interferometer

We demonstrate a precision measurement of local gravity acceleration g in Wuhan by a compact cold atom interferometer. The atom interferometer is in vertical Mach—Zehnder configuration realized using a π/2 - π - π/2 Raman pulse sequence. Cold atoms were prepared in a magneto-optical trap, launched upward to form an atom fountain, and then coherently manipulated to interfere by stimulated Raman transition. Population signal vs Raman laser phase was recorded as interference fringes, and the local gravity was deduced from the interference signal. We have obtained a resolution of 7 × 10−9 g after an integration time of 236s under the best vibrational environment conditions. The absolute g value was derived from the chirp rate with a difference of 1.5 × 10−7 g compared to the gravity reference value. The tidal phenomenon was observed by continuously monitoring the local gravity over 123 h.

Performance evaluation of the Herschel/SPIRE imaging Fourier transform spectrometer through ground-based measurements

The Spectral and Photometric Imaging Receiver (SPIRE) is one of three scientific instruments onboard the European Space Agency (ESA)'s Herschel Space Observatory. Herschel was successfully launched on 14 May 2009; routine science observations commenced in late 2009. Medium resolution spectroscopy with SPIRE is accomplished via an imaging Fourier transform spectrometer (IFTS) of the Mach–Zehnder configuration. Although pre-launch performance verification and calibration measurements were conducted with the SPIRE instrument mounted in an evacuated cryostat at cryogenic temperatures, it was not possible to simulate fully the expected in-flight conditions. This paper compares the performance of the SPIRE IFTS, as measured during ground-based tests, with theoretical simulations. In turn, these results are used to provide an estimate of the in-flight instrument performance. This paper includes a discussion of key aspects of the SPIRE IFTS including the spectrometer dual-input compensation scheme, instrument line shape and the overall instrument sensitivity. As a case study, the derived instrument performance is used to investigate SPIRE's utility in observing astronomical line emission from the starburst galaxy M82.

All-optical clock extraction from 40-Gbit/s NRZ data using cascaded long-period fiber grating

All-optical clock extraction from a 40-Gbit/s NRZ input signal is demonstrated using a cascaded long-period fiber grating (CLPG) and a mode-locked fiber ring laser. The CLPG has a Mach–Zehnder configuration with two arms along the core and cladding regions. Using the difference in propagation delay between two arms, the non-return-to-zero (NRZ) signal is converted to the pseudo-return-to-zero (PRZ) signal. To obtain repetitive pulses as a clock signal from the PRZ signal, a ring laser with a semiconductor optical amplifier (SOA) is used. Subsequently, the measured carrier-to-noise ratio (CNR) of the PRZ and clock signals are enhanced up to 30 dB and 31 dB, respectively, compared to that of the original NRZ signal. Also, the clock signal centered at 40 GHz has a low timing jitter of <1.3 ps. It is expected that this method can be applied to high speed fiber-optic systems of >40 Gbit/s due to its small time delay between the core and cladding regions.

All-optical clock extraction from 10-Gbit/s NRZ-DPSK data using modal interference in a two-mode fiber

All-optical clock extraction from a 10-Gbit/s NRZ-DPSK input signal is demonstrated using modal interference in a two-mode fiber (TMF) and a mode-locked fiber ring laser. The TMF has a Mach–Zehnder configuration with two arms along the core and cladding regions. Using the difference in propagation delay between two arms, the non-return-to-zero differential phase shift keying (NRZ-DPSK) signal is converted to the return-to-zero on–off keying (RZ-OOK) signal. To obtain repetitive pulses as a clock signal from the RZ-OOK signal, a ring laser with a semiconductor optical amplifier (SOA) is used. Subsequently, the carrier-to-noise ratio (CNR) of the RZ-OOK and clock signals are enhanced up to 30 dB and 40 dB, respectively, compared to that of the original NRZ-DPSK signal. Also, the clock signal centered at 10 GHz has a low timing jitter of <1.6 ps. It is expected that this method can be applied to high speed fiber-optic systems of >10 Gbit/s due to its small time delay between the core and cladding regions.