Nonreciprocal Phase Shift Research Articles

Weak measurement of the magneto-optical spin Hall effect of light

The spin Hall effect of light (SHEL) is a photonic version of the spin Hall effect in electronic systems and has been studied for more than 10 years. However, the lack of effective methods for dynamic modulation of spin-dependent splitting may hinder its applications. By introducing additional spin-orbit coupling of photons or nonreciprocal phase shift (NRPS), the magneto-optical Kerr effect may be one of the methods to alleviate the situation. Here, we experimentally reveal an enhanced and tunable SHEL in magneto-optical oxide thin films under the transverse magneto-optical Kerr effect configuration for the first time, to the best of our knowledge, which can be regarded as the magneto-optical SHEL (MOSHEL). We study the magneto-optical response of the multilayer structure and select the optimal structural parameters by the magneto-optical transfer matrix method. With a transverse magnetic field along opposite directions, an obvious SHEL shift difference of H-polarized light caused by NRPS is observed via a weak measurement method. With optimal parameters, the maximum measured shift difference of the SHEL achieves about 70 μm. The demonstrated MOSHEL phenomenon may accelerate the application of the SHEL in the field of spin photonics devices and precision metrology.

Wavelength-tunable operation of magneto–optical switch consisting of amorphous silicon microring resonator on garnet

A microring resonator (MRR) can enhance optical modulation and reduce a device’s footprint in photonic integrated circuits. However, optical devices composed of MRRs have narrow operation bandwidths. Furthermore, the resonant wavelength of the MRR is highly sensitive to variations in ambient temperature. In this study, we experimentally demonstrate a magneto–optical (MO) microring switch with wavelength tunability. The switch consists of a hydrogenated amorphous silicon (a-Si:H) MRR on an MO single crystalline garnet, Ce:YIG. By controlling an external magnetic field generated from an integrated electromagnetic coil, nonreciprocal phase shifts in the Ce:YIG are induced and an MO switch is successfully operated with low power consumption owing to the structure, compared with the conventional design. Moreover, by combining both MO and thermo–optic effects, the broadband wavelength-tunable operation of switching is achieved without an additional heater.

Rectangular Waveguide Differential Phase Shifter Based on Horizontal Ferrite Tiles: Accurate Model for Full-Band Operation

Phase shifters are one of the most important elements deployed in the antenna feeding structures. They are being used in several antenna systems for various applications. Moreover, they can be used in different microwave devices such as circulators and isolators. Furthermore, they are one of the commonly used components in circularly polarized antenna systems. They can be deployed using different techniques depending on the required electrical specifications and the power handling capability. Phase shifters with horizontal ferrite tiles have a higher power handling capability than the transistor based. Thus, this type of phase shifter was frequently visited in the literature. However, the previously presented models were either inaccurate or had a narrow validity range. Here, mathematical analysis and study have been performed for non-reciprocal differential phase shifters using two horizontal ferrite tiles based on waveguide technology. A new model is proposed along with the transcendental equation for the phase constant. The presented model is validated through comparison with various standard waveguides over the full band operation. Moreover, an experimental validation step is carried out, where the measured results have acceptable values.

A novel special optical fiber with magneto-optic nonreciprocal phase shift under transversely applied magnetic field

A novel special optical fiber, which is very sensitive to magnetic field, is proposed. The two beam lights counter-propagating in this kind of fiber can generate large nonreciprocal phase shift. It can be used in ultra-low magnetic field detection. In this paper, the related theory is derived in detail. The influence of fiber parameters on the effect is simulated and analyzed. It is proved that a magnetic field sensor with pTesla-level precision could be demonstrated with this kind of special fiber in this paper.

All-polarization-maintaining dual-wavelength mode-locked fiber laser based on Sagnac loop filter.

We demonstrate an all polarization-maintaining (PM) fiber based dual-wavelength mode-locked Er-fiber laser. A nonlinear amplifying loop mirror (NALM) with an intracavity nonreciprocal phase shifter is used for self-started mode-locking. A short segment of PM fiber is angle-spliced to the NALM, functioning as a PM Sagnac loop filter, thus enabling dual-wavelength mode-locking. The wavelength separation is solely determined by the angle-spliced PM fiber length. Stable dual-wavelength mode-locking operation is switchable between 1570/1581 nm and 1581/1594 nm. The two-color pulse trains oscillating in the same cavity have an inherent offset repetition rate of ~1 kHz owing to cavity dispersion, allowing future high precision dual-comb applications with a simple and robust configuration.

Chirp-adjustable optical intensity modulator with tunable OCSR based on Sagnac interferometer

Abstract In this paper a novel optical intensity modulator with tunable optical carrier-to-sideband ratio (OCSR) and adjustable chirp parameter is proposed and theoretically investigated. It is based on a bidirectional phase modulator (PM) and a tunable nonreciprocal optical phase shifter in a Sagnac interferometer (SI). Because no bias is necessary for a PM, the bias-drift problems are automatically removed. Besides, clockwise (CW) and counter clockwise (CCW) propagating lights travel in the same path so enhances robustness against environmental perturbations. In this modulator two radio frequency (RF) signals with opposite phases and tunable power ratio are applied to the bidirectional PM. Chirp parameter and OCSR of the modulator can be tuned by tuning the phase shift of the optical phase shifter and RF power ratio. Besides, this modulator can have two complementary balanced outputs. So common-mode noises such as relative intensity noise (RIN) of the laser can be suppressed in a microwave photonic link (MWPL) based on this modulator and using a balanced receiver. This novel modulator can also operate bidirectionally. An intensity modulated optical signal with tunable OCSR and chirp parameter is achieved by adjusting the optical phase shifter and the RF power ratio. The effect of the lossy SI and finite optical extinction ratio on the performance of the proposed modulator is theoretically investigated. In addition applications of the proposed chirp-adjustable modulator to overcome fiber dispersion-induced power penalty in a MWPL is investigated It is shown that by adjusting the chirp parameter, link distance for a given frequency (or bandwidth for a given link distance) doubles.

Temperature-insensitive design of waveguide isolator employing nonreciprocal guided-radiation mode conversion

The temperature dependence of the optical isolator employing a nonreciprocal guided-radiation mode conversion is investigated. The optical isolator consists of a rib-type magnetooptic waveguide with an amorphous Si (a-Si:H) guiding layer. The nonreciprocal phase shift in the optical isolator is calculated at a wavelength of 1.55 µm. The relationship of rib height and rib width for the isolator operation is clarified for various operating temperatures. Refractive indices of layers in the magnetooptic waveguide are considered since proper refractive indices can circumvent waveguide parameter deviation due to the temperature shift. The results show that athermal operation can be achieved by the negative temperature dependence of the refractive index of the upper cladding layer, and the relationship of waveguide parameters varies only slightly with the selected upper cladding layer.

Doppler-Based Acoustic Gyrator

Non-reciprocal phase shifters have been attracting a great deal of attention due to their important applications in filtering, isolation, modulation, and mode locking. Here, we demonstrate a non-reciprocal acoustic phase shifter using a simple acoustic waveguide. We show, both analytically and numerically, that when the fluid within the waveguide is biased by a time-independent velocity, the sound waves travelling in forward and backward directions experience different amounts of phase shifts. We further show that the differential phase shift between the forward and backward waves can be conveniently adjusted by changing the imparted bias velocity. Setting the corresponding differential phase shift to 180 degrees, we then realize an acoustic gyrator, which is of paramount importance not only for the network realization of two port components, but also as the building block for the construction of different non-reciprocal devices like isolators and circulators.

Single-polarization large-mode-area fiber laser mode-locked with a nonlinear amplifying loop mirror.

The generation of high-power ultrashort pulses from a passively mode-locked fiber laser is reported based on the combination of a single-polarization large-mode-area (LMA) photonic crystal fiber with a nonlinear amplifying loop mirror design. The introduction of a non-reciprocal phase shift in the loop mirror enables self-starting of the mode-locked laser, while the polarizing LMA fiber supports environmentally stable high-power operation. Mode locking in the soliton-like, stretched-pulse, and all-normal-dispersion regime is characterized. The laser generates stable pulses with up to 2W average power at a 72MHz repetition rate, corresponding to a single-pulse energy of 28nJ. The output pulses are dechirped to a near transform-limited duration of 152fs. The proposed fiber oscillator presents an alternative approach to high-power ultrafast laser sources, along with environmental stability.

Sputter-deposited magneto-optical garnet for all-mode (transverse electric/transverse magnetic) Faraday rotators

Abstract

Broadband Nonreciprocal Phase Shifter Design Technique

In this contribution, a novel method to design broadband nonreciprocal phase shifters (NRPS) is illustrated: this new topology is based on the combination of two directive-distributed amplifiers with a four-port phase-shifting network. The presented approach includes explicit design formulae allowing for arbitrary differential-phase implementation. Extensive design description of a 180° NRPS, acting as broadband differential-phase inverter, is also provided. The $3.5 \times 3.4$ mm2 demonstrator, realized in 0.5 $\mu \text{m}$ GaN HEMT technology, has an average zero insertion loss up to 25 dBm of input power, 180° ± 2° differential-phase shift, and good port matching over the 3–7-GHz operating bandwidth.

Characteristics of silicon-based Sagnac optical switches using magneto-optical micro-ring array

ABSTRACTThe miniaturization and integration of optical switches are necessary for photonic switching networks and the utilization of magneto optical effects is a promising candidate. We propose a Sagnac optical switch chip based on the principle of nonreciprocal phase shift (NPS) of the magneto-optical (MO) micro-ring (MOMR) array, composed of SiO2/Si/Ce:YIG/SGGG. The MO switching function is realized by controlling the drive current in the snake-like metal microstrip circuit layered on the MOMRs. The transmission characteristics of the Sagnac MO switch chip dependent on magnetization intensity, waveguide coupling coefficient and waveguide loss are simulated. By optimizing the coupling coefficients, we design an MO switch using two serial MOMRs with a circumference of 38.37 μm, and the 3dB bandwidth and the extinction ratio are respectively up to 1.6 nm and 50dB for the waveguide loss coefficient of . And the switching magnetization can be further reduced by increasing the number of parallel MOMRs. The frequency response of the MO Sagnac switch is analyzed as well.

Nonreciprocal Components Based on Switched Transmission Lines

Nonreciprocal components, such as isolators and circulators, are critical to wireless communication and radar applications. Traditionally, nonreciprocal components have been implemented using ferrite materials, which exhibit nonreciprocity under the influence of an external magnetic field. However, ferrite materials cannot be integrated into IC fabrication processes and, consequently, are bulky and expensive. In the recent past, there has been strong interest in achieving nonreciprocity in a nonmagnetic IC-compatible fashion using spatio-temporal modulation. In this paper, we present a general approach to nonreciprocity based on switched transmission lines. Switched transmission lines enable broadband, lossless, and compact nonreciprocity and a wide range of nonreciprocal functionalities, including nonreciprocal phase shifters, ultra-broadband gyrators and isolators, frequency-conversion isolators, and high-linearity/high-frequency/ultra-broadband circulators. We present a detailed theoretical analysis of the various nonidealities that impact insertion loss and provide design guidelines. The theory is validated by experimental results from discrete-component-based gyrators and isolators and a 25-GHz circulator fabricated in a 45-nm SOI CMOS technology.

Gyrator Operation Using Josephson Mixers

Nonreciprocal microwave devices, such as circulators, are useful in routing quantum signals in quantum networks and protecting quantum systems against noise coming from the detection chain. However, commercial, cryogenic circulators, now in use, are unsuitable for scalable superconducting quantum architectures due to their appreciable size, loss, and inherent magnetic field. We report on the measurement of a key nonreciprocal element, i.e., the gyrator, which can be used to realize a circulator. Unlike state-of-the-art gyrators, which use a magneto-optic effect to induce a phase shift of $\pi$ between transmitted signals in opposite directions, our device uses the phase nonreciprocity of a Josephson-based three-wave-mixing device. By coupling two of these mixers and operating them in noiseless frequency-conversion mode, we show that the device acts as a nonreciprocal phase shifter whose phase shift is controlled by the phase difference of the microwave tones driving the mixers. Such a device could be used to realize a lossless, on-chip, superconducting circulator suitable for quantum-information-processing applications.

Monolithically-Integrated TE-mode 1D Silicon-on-Insulator Isolators using Seedlayer-Free Garnet

The first experimental TE-mode silicon-on-insulator (SOI) isolators using Faraday Rotation are here realized to fill the ‘missing link’ in source-integrated near infrared photonic circuits. The isolators are simple 1D 2-element waveguides, where garnet claddings and longitudinal magnetic fields produce nonreciprocal mode conversion, the waveguide equivalent of Faraday Rotation (FR). Quasi-phase matched claddings are used to overcome the limitations of birefringence. Current experimental SOI isolators use nonreciprocal phase shift (NRPS) in interferometers or ring resonators, but to date NRPS requires TM-modes, so the TE-modes normally produced by integrated lasers cannot be isolated without many ancillary polarisation controls. The presented FR isolators are made via lithography and sputter deposition, which allows facile upscaling compared to the pulsed laser deposition or wafer bonding used in the fabrication of NRPS devices. Here, isolation ratios and losses of 11 dB and 4 dB were obtained, and future designs are identified capable of isolation ratios >30 dB with losses <6 dB.

Microring-Based Optical Isolator and Circulator with Integrated Electromagnet for Silicon Photonics

In this study, we present optical isolators and circulators fabricated by bonding cerium-substituted yttrium iron garnet (Ce:YIG) on silicon microring resonators. A novel integrated electromagnet is fabricated by depositing a metal micro-strip on the bonded chip. We experimentally prove that it can be efficiently used to control the magnetic field needed to induce the nonreciprocal phase shift effect in the Ce:YIG. The fabricated devices exhibit extremely small footprint (<70 μm) and can be packaged, eliminating the need of a large size permanent magnet. A large optical isolation of 32 dB and 11 dB is measured for the isolator and the circulator, respectively. Moreover, a two microring solution is also investigated to provide larger bandwidth and higher isolation. The proposed approach represents a promising solution for large-scale integration of nonreciprocal components in silicon photonics.

Nonreciprocal dielectric-loaded plasmonic waveguides using magneto-optical effect of Fe.

We have implemented the nonreciprocal propagation capabilities into plasmonic waveguides and have simulated the performances. We employed dielectric-loaded surface plasmon polariton waveguide (DLSPPW) and long-range DLSPPW (LR-DLSPPW) configurations, where ferromagnetic-metal Fe is used instead of noble metals in order to obtain nonreciprocal propagations by the transverse magneto-optical (MO) effect. The nonreciprocal performances were characterized by the finite-difference frequency-domain (FDFD) method in terms of the propagation losses in return for the nonreciprocal phase shift (NRPS) and nonreciprocal propagation loss (NRL). The NRPS and NRL of the DLSPPW configuration are larger than those of the previously reported semiconductor waveguide optical isolators owing to the large MO constant of Fe and the field confinement by surface plasmons although the propagation loss for NRL of 1 dB is at least 31 dB and the propagation length is limited to less than 10 μm. To reduce such a large propagation loss, we introduced the LR-DLSPPW configuration composed of Polymethyl methacrylate (PMMA) ridge and Benzocyclobutene (BCB) buffer layer. The Fe layer thickness and width are optimized to 50 nm and 500 nm, respectively, so that sizable MO effect and low propagation loss coexist. The propagation loss for NRL of 1 dB is suppressed to ~10 dB within a waveguide length of ~56 μm. Our comprehensive investigation offers fundamental information on practical magneto-plasmonic waveguides and how much nonreciprocal performances are expected, providing an insight into the integration of magneto-plasmonics with on-chip photonics and electronics.

Thermal-induced phase-shift error of a fiber-optic gyroscope due to fiber tail length asymmetry

As a high-precision angular sensor, the fiber-optic gyroscope (FOG) usually shows high sensitivity to disturbances of the environmental temperature. Research on thermal-induced error of the FOG is meaningful to improve its robust performance and reliability in practical applications. In this paper, thermal-induced nonreciprocal phase-shift error of the FOG due to asymmetric fiber tail length is discussed in detail, based on temperature diffusion theory. Theoretical analysis shows that the increase of thermal-induced nonreciprocal phase shift of the FOG is proportional to the asymmetric tail length. Moreover, experiments with temperature ranging from -40°C to 60°C are performed to confirm the analysis. The analysis and experiment results indicate that we may compensate the asymmetry of fiber coil due to imperfect winding and the assembly process by adjusting the fiber tail length, which can reduce the thermal-induced phase-shift error and further improve the adaptability of the FOG in a changing ambient temperature.

Amorphous-Si waveguide on a garnet magneto-optical isolator with a TE mode nonreciprocal phase shift.

We fabricated a magneto-optical (MO) isolator with a TE mode nonreciprocal phase shift. The isolator is based on a Mach-Zehnder interferometer composed of 3-dB directional couplers, a reciprocal phase shifter, and a nonreciprocal phase shifter. To realize TE mode operation in the optical isolator, we designed a novel waveguide structure composed of a hydrogenated amorphous silicon waveguide with an asymmetric MO garnet lateral clad on a garnet substrate. The isolator operation is successfully demonstrated in a fabricated device showing the different transmittances between forward and backward directions. The maximum isolation of the fabricated isolator is 17.9 dB at a wavelength of 1561 nm for the TE mode.

All polarization-maintaining fiber laser architecture for robust femtosecond pulse generation

We report on a novel architecture for robust mode-locked femtosecond fiber lasers using a nonlinear optical loop mirror with all polarization-maintaining fibers. Due to a nonreciprocal phase shift, the loop mirror can be operated in a compact and efficient reflection mode, offering the possibility to reach high repetition rates and easy implementation of tuning elements. In particular, longitudinal mode spacing and carrier-envelope offset frequency may be controlled in order to operate the laser as an optical frequency comb. We demonstrate femtosecond pulse generation at three different wavelengths (1030, 1565, and 2050 nm) using Ytterbium, Erbium, and co-doped Thulium–Holmium as gain media, respectively. Robust operation is achieved for a wide range of parameters, including repetition rates from 10 to 250 MHz.