Nonreciprocal Phase Shift Research Articles

Silicon Waveguide Optical Isolator Operating for TE Mode Input Light

A waveguide optical isolator with a nonreciprocal phase shift is promising for obtaining high-optical isolation owing to its single-polarization operation. A typical configuration enables operation for only the TM mode input light. A silicon waveguide polarization rotator with asymmetric two parallel waveguides is implemented with the silicon waveguide optical isolator for operation with the TE mode input light. Maximal isolation of 26.7 dB at the wavelength of 1553 nm is demonstrated experimentally.

Optical Isolator with Si Guiding Layer Fabricated by Photosensitive Adhesive Bonding

INTRODUCTION In optical communication systems, an optical isolator is indispensable in protecting active photonic devices from unwanted reflected light. An optical isolator with a Si guiding layer is a significant device for silicon photonic integrated circuits. In this paper, the authors report on an optical isolator with the Si guiding layer fabricated by photosensitive adhesive bonding. DEVICE STRUCTURE Figure 1 shows an optical isolator with a Si guiding layer employing a nonreciprocal guided-radiation mode conversion [1]. A magnetic garnet cladding layer is bonded with the Si guiding layer by photosensitive adhesives. A cerium-substituted yttrium iron garnet (Ce:YIG) is used as the magnetic-garnet cladding layer [2]. The optical isolator is comprised of a straight rib waveguide with a Ce:YIG/Si/SiO2 structure. An external magnetic field is applied to the magneto-optic waveguide in film plane. TM modes travelling in the magneto-optic waveguide have distinct propagation constants for the forward- and the backward-travelling waves owing to a nonreciprocal phase shift. By adjusting waveguide parameters, the following relationship is satisfied: β b y < β c x < β f y (1) where β f y and β b y denote the propagation constants of the forward- and the backward-traveling TM modes and β c x denotes the cutoff of TE modes. Only the backward-traveling TM modes can couple to the TE radiation modes so that the device acts as a TM-mode optical isolator. The optical isolator employing the nonreciprocal guided-radiation mode conversion was designed at 1.55 μm. The nonreciprocal phase shifts in the magneto-optic waveguides with various gap widths were calculated. It was confirmed that the nonreciprocal phase shift was reduced with increasing the gap width. The relationship of the waveguide parameters that satisfies equation (1) was investigated. Once the rib height was set, the range of the rib width for the isolator operation, which means that the propagation constants satisfy the relationship denoted by expression (1), was given. It was found that smaller gap width was desired for large tolerance of the waveguide parameters. ACKNOWLEDGMENT This work was partially supported by the SIT Research Center for Green Innovation. REFERENCES 1. H. Yokoi, K. Sasaki and T. Aiba, Jpn. J. Appl. Phys., 48, 062202 (2009). 2. T. Shintaku, T. Uno and M. Kobayashi, J. Appl .Phys., 74, 4877 (1993). Figure 1

Experimental realization of optomechanically induced non-reciprocity

Non-reciprocal devices, such as circulators and isolators, are indispensable components in classical and quantum information processing in an integrated photonic circuit. Aside from those applications, the non-reciprocal phase shift is of fundamental interest for exploring exotic topological photonics, such as the realization of chiral edge states and topological protection. However, incorporating low optical-loss magnetic materials into a photonic chip is technically challenging. In this study, we experimentally demonstrate non-magnetic non-reciprocity using optomechanical interactions in a whispering-gallery microresonator, as proposed by Hafezi and Rabl. Optomechanically induced non-reciprocal transparency and amplification are observed, and a non-reciprocal phase shift of up to 40 degrees is demonstrated in this study. The results of this study represent an important step towards integrated all-optical controllable isolators and circulators, as well as non-reciprocal phase shifters.

All PM Fiber Laser Mode Locked With a Compact Phase Biased Amplifier Loop Mirror

An Yb-doped, all-polarization-maintaining fiber laser oscillator with a nonlinear amplifying loop mirror is presented in this letter. A new compact non-reciprocal phase shifter biased fiber loop mirror was engaged inside the fiber laser, which results in a low threshold and stable mode locking. With a 2.8-nm filter inside the cavity, the mode locked output power is 4.1 mW with the repetition rate of 31.35 MHz at the pump power of 80 mW. The spectral bandwidth of the pulse is 3.1 nm. The pulsewidth of the direct output and the dechirped pulse are 2.13 ps and 538 fs, respectively. The filter bandwidth plays a significant role in the spectrum bandwidth and the direct output pulse width.

Magnetoplasmonic RF mixing and nonlinear frequency generation

We present the design of a magnetoplasmonic Mach-Zehnder interferometer (MZI) modulator facilitating radio-frequency (RF) mixing and nonlinear frequency generation. This is achieved by forming the MZI arms from long-range dielectric-loaded plasmonic waveguides containing bismuth-substituted yttrium iron garnet (Bi:YIG). The magnetization of the Bi:YIG can be driven in the nonlinear regime by RF magnetic fields produced around adjacent transmission lines. Correspondingly, the nonlinear temporal dynamics of the transverse magnetization component are mapped onto the nonreciprocal phase shift in the MZI arms, and onto the output optical intensity signal. We show that this tunable mechanism can generate harmonics, frequency splitting, and frequency down-conversion with a single RF excitation, as well as RF mixing when driven by two RF signals. This magnetoplasmonic component can reduce the number of electrical sources required to generate distinct optical modulation frequencies and is anticipated to satisfy important applications in integrated optics.

Design of a compact waveguide optical isolator based on multimode interferometers using magneto-optical oxide thin films grown on silicon-on-insulator substrates

We report the design of a waveguide optical isolator based on multimode interferometer (MMI) structure using silicon on insulator (SOI) and deposited magneto-optical (MO) thin films. The optical isolator is based on a vertical 1 × 2 SOI MMI utilizing the nonreciprocal phase shift (NRPS) difference of different TM modes of the MO garnet thin film/SOI waveguide. By constructing a silicon/MO thin film/silicon structure, we demonstrate that the NRPS of the fundamental and first order TM modes can show opposite signs for certain device dimensions, therefore significantly reduce the device length. For a 310.42 μm long device, 20 dB isolation bandwidth larger than 1.6 nm with total insertion loss of 0.817 dB is achieved at 1550 nm wavelength. The fabrication tolerances and materials losses are also discussed to satisfy the state-of-the-art fabrication technology and material properties.

Optical and magneto-optical behavior of Cerium Yttrium Iron Garnet thin films at wavelengths of 200-1770 nm.

Magneto-optical cerium-substituted yttrium iron garnet (Ce:YIG) thin films display Faraday and Kerr rotation (rotation of light polarisation upon transmission and reflection, respectively) as well as a nonreciprocal phase shift due to their non-zero off-diagonal permittivity tensor elements, and also possess low optical absorption in the near-infrared. These properties make Ce:YIG useful in providing nonreciprocal light propagation in integrated photonic circuits, which is essential for accomplishing energy-efficient photonic computation and data transport architectures. In this study, 80 nm-thick Ce:YIG films were grown on Gadolinium Gallium Garnet substrates with (100), (110) and (111) orientations using pulsed laser deposition. The films had bulk-like structural and magnetic quality. Faraday and Kerr spectroscopies along with spectroscopic ellipsometry were used to deduce the complete permittivity tensor of the films in the ultraviolet, visible and near-infrared spectral region, and the magneto-optical figure of merit as a function of wavelength was determined. The samples showed the highest IR Faraday rotation reported for thin films of Ce:YIG, which indicates the importance of this material in development of nonreciprocal photonic devices.

Comparative Analysis of the Efficiency of Fiber Winding Types Used in the Fiber-Optic Gyro Sensor Coil Under Temperature Variation Conditions

Background. The paper is devoted to the study of the effectiveness of different types of coil fiber winding of fiber optic gyro (FOG) in reducing of the impact of Shupe effect under temperature changes. Objective. The objective of the study is to evaluate the effectiveness of different types of FOG fiber coil winding under temperature changes. Methods. Based on the analysis of existing types of winding, and formulae for non-reciprocal phase shift calculation, a method for evaluation of the impact of temperature gradient on coils with different types of winding is created. Method mentioned is applied to 9 different types of coil winding. Results. The dependencies of zero shift vs time for nine types of winding under the impact of axial, radial temperature gradients and combinations thereof are obtained. Conclusion. Overall, use of quadruple windings seems to be optimal; for low precision sensors one can recommend centered unipolar winding while ensuring good thermal and vibration insulation of the coil. The use of pads (or frameless coils) is justified when simple winding is used (e.g., in devices for short-living objects, for automotive industry, etc.), or for high-precision sensors.

Reciprocal and unidirectional scattering of parity-time symmetric structures

Parity-time symmetry is of great interest. The reciprocal and unidirectional features are intriguing besides the symmetry phase transition. Recently, the reciprocal transmission, unidirectional reflectionless and invisibility are intensively studied. Here, we show the reciprocal reflection/transmission in -symmetric system is closely related to the type of symmetry, that is, the axial (reflection) symmetry leads to reciprocal reflection (transmission). The results are further elucidated by studying the scattering of rhombic ring form coupled resonators with enclosed synthetic magnetic flux. The nonreciprocal phase shift induced by the magnetic flux and gain/loss break the parity and time-reversal symmetry but keep the parity-time symmetry. The reciprocal reflection (transmission) and unidirectional transmission (reflection) are found in the axial (reflection) -symmetric ring centre. The explorations of symmetry and asymmetry from symmetry may shed light on novel one-way optical devices and application of -symmetric metamaterials.

A magnetoplasmonic electrical-to-optical clock multiplier

We propose and investigate an electrical-to-optical clock multiplier, based on a bismuth-substituted yttrium iron garnet (Bi:YIG) magnetoplasmonic Mach-Zehnder interferometer (MZI). Transient magnetic fields induce a precession of the magnetization vector of the Bi:YIG, which in turn modulates the nonreciprocal phase shift in the MZI arms, and hence the intensity at the output port. We show that the device is capable of modulation depth of 16.26 dB and has a tunable output frequency between 279.9 MHz and 5.6 GHz. Correspondingly, the input electrical modulation frequency can be multiplied by factors of up to 2.1×103 in the optical signal. Such a device is envisioned as a critical component in the development of hybrid electrical-optical circuitry.

Magnetoplasmonic isolators utilizing the nonreciprocal phase shift.

We propose a long-range magnetoplasmonic waveguide structure, based on cerium-substituted yttrium iron garnets, that is capable of achieving a useful π/2 nonreciprocal phase shift within one propagation length. Incorporating this plasmonic geometry into a Mach-Zehnder interferometer allows for the implementation of an efficient, integrable isolator scheme with an insertion loss of 2.51 dB and an extinction ratio of 22.82 dB. With a small footprint of 6.4×10(-3) mm(2) and nanoscale waveguide dimensions, we envision this device to be a key building block in the development of nanoplasmonic integrated circuitry.

Non-reciprocal Phase Shift and Mode Modulation in Dynamic Graphene Waveguides

We propose a graphene Ramsey interferometer to study the non-reciprocal phase shift and modulation of surface plasmon polaritons (SPPs). The Ramsey interferometer is constructed by a spatially separated graphene pair that can support two SPP modes. By dynamically modulating the surface conductivity of graphene, the SPP modes will undergo uncompleted cross conversion and an additional phase shift. When adopting two modulation regions in the interferometer, the converted mode will jump back with a nonreciprocal phase shift which can be controlled by the modulation length or phase. The SPP mode of phase shift will interfere with the throughout unconverted one, resulting in arbitrary power arrangement between the two SPP modes. The study may find great applications in plasmonic isolators, phase detectors, and one-way mode converters.

Optical isolation in topological-edge-state photonic arrays.

We introduce a new type of optical isolator based on breaking time reversal symmetry in dissipative finite Su-Schrieffer-Heeger (SSH) waveguide arrays that support topological edge states at one end of the structure. In the forward propagation direction, light is launched into the edge waveguide to excite the localized topological midgap state. As a result, most of the input optical power is transmitted to the output port. On the other hand, backward reflected light encounters a propagation constant mismatch in that same channel which shifts the otherwise midgap state into one of the bands and hence becomes delocalized over the whole array. We show that under these conditions, a judicious spatial distribution of the optical dissipation across the structure can produce an isolation ratio of -50 dB. The required nonreciprocal phase shift is introduced by depositing a magnetic garnet film only on the edge waveguide and, thus, the required magnetic field can be generated by an integrated micromagnet. Similar concepts can also be applied to SSH arrays made from optical resonators.

Integrated optical circulator by stimulated Brillouin scattering induced non-reciprocal phase shift.

We propose a new approach to realize all-optical circulator based on stimulated Brillouin scattering in an integrated microresonator. Stimulated Brillouin scattering is a basic interaction between photon and traveling acoustic wave resulted from electrostriction and photoelastic effects. Due to the phase-matching requirement, the circulating acoustic wave can only couple to probe light which propagating along or opposite to the pump laser direction, thus exhibits a non-reciprocal phase shift. Combined with Mach-Zehnder interferometer, the optical circulator can be realized. Though the bandwidth is relatively small because of the narrow-band nature of microresonator, this magnetic-free all-optical integrated circulator may be applied for future on-chip photonic information processing.

An Integrable SIW Phase Shifter in a Partially Magnetized Ferrite LTCC Package

There is a growing need for small size integrable phased antenna arrays for emerging satellite communications on-the-move applications. Traditional ferrite-based phase shifters are generally bulky due to the need of electromagnets for biasing, yielding them unsuitable for this kind of application. In this paper, a novel compact light-weight substrate integrated waveguide (SIW) based phase shifter realized in a multi-layer ferrite low-temperature co-fired ceramic package with embedded bias windings is reported. By using embedded windings and operating the material in a partially magnetized state, the required bias magnetic field could be significantly reduced from typically about 1000 Oe to less than 50 Oe. Moreover, the presented phase shifter has two modes of operations corresponding to two different biasing scenarios of the SIW, namely, symmetric and anti-symmetric bias. Under anti-symmetric bias, the phase shifter can achieve high nonreciprocal phase shift, whereas under symmetric bias, the phase shift is reciprocal, but the available phase shift is less than the anti-symmetric case. The fabricated prototype operates in the 11.5–13.5-GHz range and has a peak figure of merit (phase shift per decibel of loss) of 102 $^{\circ}/{\hbox{dB}} $ and a maximum phase shift per unit length of 153 $^{\circ} /{\hbox{cm}}$ , which are more than five times the previously reported figures for this technology. Due to the use of embedded windings, the presented phase shifter offers a huge size reduction from the order of ${\hbox{cm}}^{3}$ to ${\hbox{mm}}^{3}$ , making it particularly useful for mobile phased-array applications.

High-speed nonreciprocal magnetoplasmonic waveguide phase shifter

In the realm of modern day optical computing prospects, plasmonics provides a unique means of consolidating electronics and photonics in a nanoscale platform. For advanced optical information processing applications, there is a pressing need for configurable plasmonic platforms that mimic the functionalities of their electrical counterparts. In such a pursuit, the ability to actively manipulate plasmonic phenomena must first be realized via an electrical stimulus. An attractive architecture is realized by incorporating magneto-optical materials into devices, as the degree of electrical control they provide is unattainable by other material systems. Properties of the material are influenced by external magnetic fields, which can be conveniently generated by current passing through nearby metallic structures. While ferromagnetic metals are far too lossy for plasmonic integration, magnetic garnets can facilitate a robust and tunable architecture in a waveguide geometry. Here, we investigate a bismuth-substituted yttrium iron garnet platform for a high bandwidth active optical phase shifter. Our device is capable of imparting a large nonreciprocal phase shift of 6.99 rad/mm, while confining 70% of the modal power to the 0.081 μm2 cross-sectional area of the core. By considering the Landau–Lifshitz–Gilbert formalism, we show that the magnetoplasmonic phase shifter is operable in both underdamped and critically damped modes, and is fully tunable through the applied magnetic fields and pulsewidth. This magnetoplasmonic building block opens doors to a new class of nanoplasmonic devices, such as optical phase modulators, isolators, and optical clocks that will satisfy key applications in nanoscale optical information networks.

Exploiting nonreciprocity in BOTDA systems.

In this Letter, we present and demonstrate a novel technique for distributed measurements in Brillouin optical time-domain analysis based on the use of the nonlinear phase-shift induced by stimulated Brillouin scattering. Employing a Sagnac interferometer (SI), the position-resolved Brillouin phase-shift spectrum (BPS) along the fiber can be obtained, benefiting from the sensitivity to nonreciprocal phase-shifts of the SI scheme. This proposal simplifies the existing methods to retrieve the BPS distribution along an optical fiber since phase modulation, filtering, and high-bandwidth detectors are not required. The fundamentals of the technique are described theoretically and validated through numerical simulations and experimental measurements.

Microrectangular-coaxial phase shifter for microwave devices

This article reports the simulated performance of rectangular coaxial ferrite phase shifter at Ka-band. The proposed technique exploits rectangular coaxial waveguide with a symmetrically placed inner signal conductor inside an outer conductor connected to the ground. Strontium ferrite-SU8 composite is used as an anisotropic material of choice in the modeled design. Two model phase shifting structures were designed for reciprocal and nonreciprocal applications using High Frequency Structure Simulator, HFSS. The reciprocal model produced a tunable phase shift of almost across 0 to 400 kA/m applied field and at 1800 Gauss. The predicted simulated performance of the nonreciprocal phase shifter was from a reference phase of at 0 A/m at the same saturation magnetization. A return loss better than 20 dB and an insertion loss less than 1.5 dB were predicted for the two models. © 2015 Wiley Periodicals, Inc. Int J RF and Microwave CAE 25:502–509, 2015.

A magneto-optical isolator based on series-coupled race-track resonators

In this paper, we propose a novel kind of magneto-optical (MO) isolators based on series-coupled race-track resonators. The perturbation theory is used to calculate the non-reciprocal phase shift (NRPS) induced by the MO effect. The numerical result indicates that the isolation is greatly enhanced by the box-like spectra of series-coupled resonators. Optical isolation ratio for the first, second, and third order devices are 7.8, 21, and 36.2 dB, respectively.

Numerical analysis of dual-wavelength nonreciprocal phase shifter for magneto-optical isolators on silicon-on-insulator system

The wavelength dependence of the nonreciprocal phase shift (NPS) in a magneto-optical (MO) wave- guide is investigated from the aspect of the geometrical structure. In an MO nonreciprocal waveguide, the effect of the waveguide dispersion on the NPS is being demonstrated to compensate the dispersion of the Faraday rotation coefficients. By accurately controlling the structure parameter of the MO waveguide, the wavelength- insensitive NPS can be obtained. According to this principle, we proposed the dual-wavelength nonreciprocal phase shifter at the wavelengths of 1.31 and 1.55 μm. © 2014 Society of Photo-Optical Instrumentation Engineers (SPIE) (DOI: 10 .1117/1.OE.53.11.117112)