Mach-Zehnder Interferometer Structure Research Articles

Research on reconfigurable waveguide devices based on liquid crystal on silicon

AbstractDue to the limitation of materials, PIC cannot achieve large magnitude phase modulation in a small size, and lacks the reconfigurable ability. Because of its birefringence characteristic, liquid crystal can be used in the liquid crystal on silicon (LCoS) device to achieve a large amount of phase modulation in a small size and has the capacity of reconstruction. Based on the experimental results of LCoS devices and basic liquid crystal waveguide devices, the liquid crystal waveguide device is prepared. While retaining the LCoS spatial optical phase modulation capability, the liquid crystal waveguide and phase modulation capability are realized. The beam splitter, optical switch, and Mach–Zehnder interferometer structure are constructed, which verifies the feasibility of the liquid crystal waveguide phase modulator.

Highly stable power control for chip-based continuous-variable quantum key distribution system.

Quantum key distribution allows secret key generation with information theoretical security. It can be realized with photonic integrated circuits to benefit the tiny footprints and the large-scale manufacturing capacity. Continuous-variable quantum key distribution is suitable for chip-based integration due to its compatibility with mature optical communication devices. However, the quantum signal power control compatible with the mature photonic integration process faces difficulties on stability, which limits the system performance and causes the overestimation of a secret key rate that opens practical security loopholes. Here, a highly stable chip-based quantum signal power control scheme based on a biased Mach-Zehnder interferometer structure is proposed, theoretically analyzed, and experimentally implemented with standard silicon photonic techniques. Simulations and experimental results show that the proposed scheme significantly improves the system stability, where the standard deviation of the secret key rate is suppressed by an order of magnitude compared with the system using traditional designs, showing a promising and practicable way to realize a highly stable continuous-variable quantum key distribution system on chip.

Mode-order conversion in a Mach-Zehnder interferometer based on Chern insulators.

Mode-order conversion devices can provide a flexible platform to achieve mode coupling and optimizing in mode division multiplex (MDM) that can eliminate the restrain of capacity and density in photonic integration and communication. However, mode-order converters based on traditional photonic crystal (PC) waveguides are susceptible to defects, which always render device incapacitation in mode-order conversion. Herein, a mode converter designed by the Mach-Zehnder interferometer (MZI) structure is proposed to manipulate the conversion of topological edge states (TESs) based on Chern insulators consisting of gyromagnetic PCs. The back-and-forth conversion between fundamental and high-order modes is numerically demonstrated based on phase modulation in our proposed device, in which each mode can be immune to defects. This unique approach for converting the mode order of TES exploits a new perspective in MDM to design a high-performance multimode device, leading to potential applications in photonic integrated circuits (PIC), on-chip processors, and optical fiber communication.

Thin-core fiber-based Mach-Zehnder interferometer sensor for monitoring temperature, pressure, and humidity

A Mach-Zehnder interferometer (MZI) sensor based on thin-core fiber (TCF) is proposed. Sensitive materials such as polydimethylsiloxane (PDMS) or gelatin are coated on the surfaces of MZIs to achieve temperature, pressure, and humidity measurements. MZI is composed of single mode fiber (SMF), TCF, and multimode fiber (MMF) spliced together to form a “SMF-MMF-TCF-MMF-SMF” structure. The core/cladding diameters of TCF are 3.8 µm and 80 µm respectively. When three types of optical fibers with different core diameters are cascaded together, many cladding modes are excited to form MZI. Firstly, two similar MZI structures were fabricated designated by MZI1 and MZI2. In order to improve the sensitivity and mechanical strength, a layer of PDMS film was coated on the TCF surface of MZI1. Then, a layer of gelatin film is covered on the TCF surface of MZI2. PDMS has the high thermal expansion coefficient, thermal optical coefficient, and elasticity, and gelatin has good humidity sensitivity properties. The experimental results showed that the temperature and pressure sensitivity of MZI1 coated with PDMS reached −340 pm/°C and −14.3 nm/MPa, respectively, while the humidity sensitivity of MZI2 coated with gelatin reached −112.57 pm/% RH. When a fiber Bragg grating is cascaded with the MZI1, the sensor can achieve simultaneous measurement of temperature and pressure, eliminating crosstalk. The proposed sensor has an extremely simple structure and manufacturing method, which only involves the splicing of optical fiber and the coating by the film. In addition, the proposed sensor has a robust structure, good repeatability and stability, and high sensitivity, which has broad application prospects.

On-chip Mach-Zehnder interferometer sensor with a double-slot hybrid plasmonic waveguide for high-sensitivity hydrogen detection.

An on-chip Mach-Zehnder interferometer (MZI) hydrogen sensor, applying a double-slot hybrid plasmonic (DSHP) waveguide composed of a Si waveguide and two Pd disks on both sides as the sensing arm, is designed. The optical confinement factor of the sensing area can be up to 87%. For the MZI hydrogen sensor with a DSHP waveguide of 14 µm, the sensitivity can be as high as 11.935 nm/%, corresponding to a free spectral range (FSR) of 15 nm. Furthermore, the sensor sensitivity is influenced by the MZI structure parameters, which is highly adjustable. The extinction ratio of the interference spectra can reach over 30 dB. A feasible solution is provided in this paper for highly sensitive hydrogen detection.

Polarization-insensitive silicon optic switch based on mode manipulated power splitters and phase shifters

A polarization-insensitive thermo-optic switch is proposed and demonstrated on the silicon-on-insulator platform with a 220 nm silicon core layer. The present device is based on the Mach–Zehnder interferometer structure, consisting of polarization-insensitive power splitters and polarization-insensitive phase shifters (PIPSs). The polarization-insensitive power splitter has been realized by employing an adiabatic directional coupler, which utilizes the fast adiabatic mode evolution by introducing cubic Bézier curves on outer contours, providing broadband 3-dB power splitting for TE and TM polarization modes with only 70 µm coupling length. For the novel PIPSs, the ridge waveguide with large aspect ratio, based on the mode hybridness property, could obtain the same power consumption (Pπ) for an optical switch working at TE and TM polarizations. Experimental results indicate that the measured insertion losses are less than 2 dB and the extinction ratios are larger than 15 dB over a 40 nm wavelength band (covering the C-band).

Miniature fiber-optic near-surface gap-coupled cladding waveguide Mach-Zehnder interferometric refractive index sensor inscribed by femtosecond laser

A miniature fiber-optic gap-coupled cladding waveguide Mach-Zehnder interferometer (MZI) is proposed and demonstrated for high-sensitive refractive index measurement. Two straight cladding waveguides respectively coupled with the fiber core are inscribed by a femtosecond laser (fs) to form the MZI structure. At their far ends, the two cladding waveguides are very close to the cladding surface, and a short separation was intentionally designed for the coupling of light between them and generating light field with evanescent wave expanded outside the cladding surface, which makes the MZI structure very sensitive to ambient refractive variations. In a refractive index range of 1.34–1.42, a high sensitivity of −59.90238 nm/RIU is achieved simultaneously with good linearity. The sensing structure also shows good characteristic of temperature insensitivity, which may find practical applications in chemical or biological sensing.

Variable Mode-Dependent-Loss equalizer based on Silica-PLC for Three-Mode transmission

We present a low-loss and compact silica-based planar lightwave circuit (PLC) mode-dependent loss (MDL) equalizer for three-mode transmission with a variable range of 2.5 dB. The proposed device utilizes a Mach-Zehnder interferometer (MZI) structure to selectively attenuate the LP01 mode while maintaining low insertion loss for the LP11a,b modes. We demonstrate that the device effectively reduces differential modal gain (DMG) in a three-mode transmission system. Additionally, we successfully equalize the pump-power dependence of the DMG in a two-LP mode erbium-doped fiber amplifier (EDFA) to less than 0.5 dB over the entire C-band. We also show that the variable range has a tradeoff relationship with the wavelength bandwidth, where too large a variable range results in non-negligible wavelength dependencies. Consequently, fixed equalizers are advantageous when large MDL compensation is required, while variable equalizers are effective for fine-tuning MDL of less than 1.2 dB.

Research on Simultaneous Measurement of Magnetic Field and Temperature Based on Petaloid Photonic Crystal Fiber Sensor.

In this paper, we propose and design a magnetic field and temperature sensor using a novel petaloid photonic crystal fiber filled with magnetic fluid. The PCF achieves a high birefringence of more than 1.43 × 10-2 at the wavelength of 1550 nm via the design of material parameters, air hole shape and the distribution of the photonic crystal fiber. Further, in order to significantly improve the sensitivity of the sensor, the magnetic-fluid-sensitive material is injected into the pores of the designed photonic crystal fiber. Finally, the sensor adopts a Mach-Zehnder interferometer structure combined with the ultra-high birefringence of the proposed petaloid photonic crystal fiber. Magnetic field and temperature can be simultaneously measured via observing the spectral response of the x-polarization state and y-polarization state. As indicated via simulation analysis, the sensor can realize sensitivities to magnetic fields and temperatures at -1.943 nm/mT and 0.0686 nm/°C in the x-polarization state and -1.421 nm/mT and 0.0914 nm/°C in the y-polarization state. The sensor can realize the measurement of multiple parameters including temperature and magnetic intensity and has the advantage of high sensitivity.

Silicon photonic broadband polarization-insensitive switch based on polarization-mode diversity conversion.

We present a 2 × 2 polarization-insensitive switch on a 220-nm silicon-on-insulator platform, employing a balanced Mach-Zehnder interferometer (MZI) structure. This design incorporates polarization-insensitive adiabatic couplers, polarization rotators based on mode hybridization and evolution, and thermo-optic mode-insensitive phase shifters with wide waveguides. The switch exhibits broadband polarization-insensitive characteristics, with extinction ratios larger than 15 dB, insertion losses less than 2.3 dB, and polarization-dependent losses less than 1 dB for wavelengths ranging from 1500 nm to 1600 nm. The power consumption required for simultaneously switching the fundamental transverse electric (TE0) and transverse magnetic (TM0) polarized modes is 29.1 mW. These results highlight the potential of the switch as a building block for on-chip polarization-division-multiplexed optical interconnects.

Temperature and strain simultaneous sensing measurement based on an all-fiber Mach-Zehnder interferometer and fiber Bragg grating.

We designed and fabricated what we believe to be a novel dual-parameter fiber optic sensor for simultaneous measurement of temperature and strain, which was composed of a femtosecond laser inscribed fiber Bragg grating (FBG), three segments of a single-mode fiber (SMF), and two segments of a multimode fiber (MMF), forming a SMF-MMF-FBG-MMF-SMF structure. The FBG and Mach-Zehnder interferometer (MZI) were present in this structure so that the changes of the temperature and strain parameters can be sensed by the shifts of the reflection center wavelength of the FBG and the interference valley wavelength of the MZI. We simulated the light field distribution of the sensor structure, compared the shapes of the interference spectra formed by the MZI structure with different sensing arm lengths of 25, 35, and 45mm, and analyzed the spectra in the spatial frequency domain. The simulation results showed that the interference spectrum of the MZI structure with a 25mm length sensing arm was clearer and more suitable for the experiment. The experimental results showed that the temperature sensitivity of the FBG and MZI was 14.81 and 43.54pm/°C in the range of 80°C to 240°C, and the strain sensitivity was 1.49 and -2.58pm/µε in the range of 0 to 1200µε, with a high linearity and excellent repeatability. The sensor is economical, sensitive, and convenient to fabricate, and exhibits promising applications in the fields of biochemical medical detection and industrial production monitoring.

Mode transition phenomena into an in-fiber Mach-Zehnder interferometer

This work reports on a novel in-fiber Mach-Zehnder interferometer (MZI) device which is able to exploit the mode transition phenomena to tailor the sensitivity to external refractive index (RI). The proposed MZI structure is extremely simple: it consists of a small section of single mode double cladding fiber (DCF) in between two sections of standard single mode fiber using the core-offset splicing approach. The DCF presents a W-shaped RI profile with the outer cladding having a greater RI than the inner cladding. Therefore, the mode transition of cladding modes from outer to inner cladding of the DCF can be induced by tailoring the cladding thickness, in turn enhancing the sensitivity to surrounding refractive index. Specifically, wet chemical etching employing hydrofluoric acid is used to reduce the outer cladding diameter. Here, we report a comprehensive study of the phenomena while fiber diameter is decreased by 30 µm. Moreover, a specific study case with DCF diameter of 112 µm demonstrates a sensitivity gain of 2.5 over unetched fiber in the refractive index range of 1.33–1.39. Temperature and mechanical stress cross sensitivities are also evaluated. The suggested sensing device's advantages of considerable compactness, low manufacturing cost, simple fabrication technique, and higher sensitivity will be useful for future applications in the bio-chemical sensing and others.

Electro-optical tunable interleaver in hybrid silicon and lithium niobate thin films.

The interleaver was one of the key devices in dense wavelength division multiplexing (DWDM) applications. In this study, an interleaver with an asymmetrical Mach-Zehnder interferometer structure was designed, fabricated, and characterized in hybrid silicon and lithium niobate thin films (Si-LNOI). The interleaver based on Si-LNOI could be fabricated by mature processing technology of Si photonic, and it was capable of the electro-optical (E-O) tuning function by using the E-O effect of LN. In the range of 1530-1620 nm, the interleaver achieved a channel spacing of 55 GHz and an extinction ratio of 12-28 dB. Due to the large refractive index of Si, the Si loading strip waveguide based on Si-LNOI had a compact optical mode area, which allowed a small electrode gap to improve the E-O modulation efficiency of the interleaver. For an E-O interaction length of 1 mm, the E-O modulation efficiency was 26 pm/V. The interleaver will have potential applications in DWDM systems, optical switches, and filters.

Flexible waveguide integrated thermo-optic switch based on TiO2 platform.

Mechanically flexible photonic devices are critical components of novel bio-integrated optoelectronic and high-end wearable systems, in which thermo-optic switches (TOSs) as optical signal control devices are crucial. In this paper, flexible titanium oxide (TiO2) TOSs based on a Mach-Zehnder interferometer (MZI) structure were demonstrated around 1310 nm for, it is believed, the first time. The insertion loss of flexible passive TiO2 2 × 2 multi-mode interferometers (MMIs) is -3.1 dB per MMI. The demonstrated flexible TOS achieves power consumption (Pπ) of 0.83 mW, compared with its rigid counterpart, for which Pπ is decreased by a factor of 18. The proposed device could withstand 100 consecutive bending operations without noticeable degradation in TOS performance, indicating excellent mechanical stability. These results provide a new perspective for designing and fabricating flexible TOSs for flexible optoelectronic systems in future emerging applications.

Fiber laser with intracavity parallel Mach-Zehnder interferometers towards Vernier refractive index sensing.

In this paper, dual-wavelength laser emission of an erbium-doped fiber laser (EDFL) with a tunable distinct wavelength selection of the simultaneously produced laser lines was achieved by applying a parallel comb filter configuration based on the optical Vernier effect. The intracavity inserted proposed comb filter consists of two parallel branches to generate the Vernier effect. Each branch is an in-line Mach-Zehnder interferometer (MZI) filter, which is composed of a polarization-maintaining fiber fusion spliced between single-mode fibers with sphere shapes at both ends. The tunability of the selected laser wavelength was realized by submerging the proposed filter in different sodium chloride/water mixtures. The proposed comb filter-based Vernier effect was used to independently achieve the selection of the dual-wavelength EDFL lines and for refractive index (RI) sensing applications. The in-line M Z I 1 and M Z I 2 structures show a wavelength shift sensitivity to RI variations of -88 and 79nm/RIU, respectively. Our proposed MZI structure presents a reliable, straightforward, and low-cost spectral comb filter for separate tunable dual-wavelength laser generation in the c-band region. Furthermore, the proposed filter structure-based Vernier effect presents a new perspective and method in the RI sensing application.

Ultrafast and High Extinction Ratio 1×4 Electro-Optical Switch Based on Cascaded Dual-Output MZI

We propose and fabricate an ultrafast and high extinction ratio 1×4 optical switch based on a cascade, dual-output Mach–Zehnder interferometer (MZI) on the lithium niobate platform. The optical switch consists of cascaded, identical, dual-output MZI structures, and each of them includes a Y-branch waveguide, two parallel interference arms (electrode action area), and a 3 dB directional coupler. Four output optical paths can be switched through three groups of electrode hierarchical modulation. The test results of the fabricated device show that the insertion loss of each port is less than 7.1 dB and that the maximum extinction ratio is higher than 39.3 dB. The optical switch can achieve a high extinction ratio greater than 20 dB within the 50 nm wavelength range. The measured half-wave voltage is less than 4.13 V, and the minimum switching rise and fall times reach 125 ps and 250 ps, respectively. This result shows that the proposed and fabricated 1×4 integrated optical switch on a lithium niobate platform has the advantages of a fast response rate, high extinction ratio, and low switching voltage.

Dual-waveguide stacked graphene light modulator based on an MZI structure.

In order to solve the defects of the high driving voltage and a large volume of the existing electro-optical modulators, a double-waveguide stacked graphene optical modulator based on a Mach-Zehnder Interferometer structure is designed in this paper. First, the modulator size of traditional planar structure is effectively reduced by stacking two modulators vertically. Secondly, by changing the relative position of the electrode and the waveguide, the coupling effect of the electrode and the waveguide is enhanced, and the driving voltage is reduced. Finally, the performance of the designed electro-optic modulator is verified by the finite element method. The half-wave voltage of 0.55V · cm and the modulation bandwidth of 58.8GHz are realized on the basis of the length of 1.14mm. The insertion loss is 1.15dB, and the return loss is -44.8d B.

Wavelength tunable double-ring cavity erbium-doped random fiber laser based on a Mach–Zehnder interferometer

A wavelength-tunable double-ring cavity erbium-doped random fiber laser (RFL) based on a Mach–Zehnder interferometer (MZI) was proposed in this study. The MZI structure, which was based on two 2 × 2 optical fiber couplers, exhibits a comb-filtering effect. Rayleigh scattering (RS) was generated by a 10-km-long single-mode fiber (SMF) to provide randomly distributed feedback. A double-ring cavity structure based on forward and backward RS was built using two 2 × 2 fiber couplers. The threshold of the laser was 104 mW, and the slope efficiency of the total power output to the pump power was approximately 1.2%. When the pump power was 158 mW, a laser beam with a wavelength of 1555.3 nm was formed. By adjusting the polarization controller (PC), a single-wavelength switched RFL at 1547.9 nm and 1559.6 nm was obtained. The maximum peak power difference was less than 0.67 dB, the signal-to-noise ratio (SNR) was greater than 17.27 dB, and the peak power fluctuation was less than 0.92 dB during a scan time of 30 min at 25 °C. Regarding dual-wavelength switchable laser emission, two groups of different wavelengths with an SNR greater than 16.88 dB, power fluctuation less than 0.81 dB, and wavelength fluctuation less than 0.26 nm could be achieved under the same monitoring conditions. By further adjusting the PC, three- and four-wavelength RFLs were achieved, and the SNRs exceeded 16.31 dB and 14.64 dB, respectively. The proposed RFL has promising application prospects for distributed sensing systems and speckle imaging.

Pseudo noise sequence generator based on cascaded Mach–Zehnder interferometer

Abstract An optical pseudo noise sequence generator based on Mach–Zehnder interferometer (MZI) is proposed. The device consists of MZI and a feedback line. Operability of the proposed device is simulated for continuous wave signals of 1.5 micrometer wavelength. The simulated results shows that all possible sequences of four bit pseudo noise sequence can be generated using proper arrangement of the MZI structures. The operation is numerically analysed and simulated results are discussed. Moreover, various parameters affecting performance of the device are also discussed. The proposed sequence generator can be utilized for different applications in optical wireless communication technology.

A Ring Core Fiber Sensor Based on Mach–Zehnder Interferometer for Transversal Force Sensing With Solvable Temperature Cross Sensitivity

In this work, we proposed a ring core fiber (RCF)-based all-fiber sensor used for transverse force sensing. The sensor is composed of 1-mm coreless fiber (CLF) and 2.5-cm RCF. Then, the coreless (CL)-ring core (RC) fiber structure is connected to two segments of single-mode fibers to form a Mach–Zehnder interferometer (MZI). The transmission spectrum of the MZI structure has a large extinction ratio (ER) of up to 20 dB with a free spectral range (FSR) of 9.3 nm. After the fabrication, the MZI sensor is packaged for force sensing at different temperatures. The different values of forces are applied on the fiber sensor, which are tuned from around 0.26 to 1.5 N/mm. With the increase of transverse force, the spectra of output signals show a linear redshift. The force sensitivity of the proposed MZI sensor reaches up to 4.109 nm/(N/mm) with a good linearity of 0.9824. By using a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2\times2$ </tex-math></inline-formula> matrix, the temperature cross sensitivity can be extracted. The proposed force sensor based on the MZI fiber structure shows great potential applications in the field of structural health monitoring and supercapacitor safety detection.