Fiber Faraday circulator or isolator

Dual-polarization interferometric fiber optic gyroscope based on a four-port circulator

The dual-polarization interferometric fiber optic gyroscope (IFOG) has been studied for many years and achieved remarkable performance. In this study, we propose a novel dual-polarization IFOG configuration based on a four-port circulator, in which the polarization coupling errors and the excess relative intensity noise are well handled meanwhile. Experimental measurements of the short-term sensitivity and long-term drift using a fiber coil with a length of 2 km and a diameter of 14 cm show that the angle random walk of 5.0×10^-5∘/h and bias instability of 9.0 × 10^-5 °/h are achieved. Moreover, the root power spectrum density of 20n r a d/s/H z is almost flat from 0.001 Hz to 30 Hz. We believe this dual-polarization IFOG is a preferred candidate for the reference-grade performance IFOG.

Optomechanically induced transparency and directional amplification in a non-Hermitian optomechanical lattice

In this paper, we propose a 1-dimensional optomechanical lattice which possesses non-Hermitian property due to its nonreciprocal couplings. We calculated the energy spectrum under periodical boundary condition and open boundary condition, respectively. To investigate the transmission property of the system, we calculate the Green function of the system using non-Bloch band theory. By analyzing the Green function and the periodical boundary condition results, we studied the directional amplification of the system and found the frequency that supports the amplification. By adding probe laser on one site and detect the output of the same site, we found that optomechanically induced transparency (OMIT) can be achieved in our system. Different from the traditional OMIT spectrum, quantum interference due to a large number of modes can be observed in our system. When varying the nonreciprocal and other parameters of the system, the OMIT peak can be effectively modulated or even turned into optomechanically induced amplification. Our system is very promising to act as a one-way signal filter. Our model can also be extended to other non-Hermitian optical systems which may possess topological features and bipolar non-Hermitian skin effect.

Narrow-band and high-contrast asymmetric transmission based on metal-metal-metal asymmetric gratings

A narrow-band and high-contrast asymmetric transmission (AT) device based on metal-metal-metal (M-M-M) asymmetric grating structure is proposed and investigated. Significantly distinct from previous reports, the upper and lower metallic silver (Ag) gratings are connected by a very thin metallic Ag film, without any dielectric spacer layer or subwavelength slit. Under forward incidence, the M-M-M structure supports efficient surface plasmon polaritons (SPPs) excitation and tunneling, more importantly, it promotes direct and thus high-efficiency SPPs decoupling, enabling high forward transmittance. While under backward incidence, the M-M-M structure offers not only high reflection by the Ag film but also a strong near-field coupling effect between the upper and lower gratings, which further suppresses backward transmittance, leading to near-zero backward transmittance. In addition, the M-M-M structure is optimized for narrow-band operation by employing grating groove depth effect and multiple interference effect. Numerical simulation results demonstrate that high-performance AT with high-quality factor (Q≈91), narrow-bandwidth (6.7 nm) and high contrast ratio is achieved, with forward transmittance of 0.72 and backward transmittance of 0.0015 at visible light (610 nm). Our work provides an alternative and simple way to high-performance AT devices.

Novel configuration for an enhanced and compact all-fiber Faraday rotator with matched birefringence

We propose a novel configuration for an improved and compact all fiber Faraday rotator based on phase matching between the Faraday rotation and bend-induced birefringence. The device utilizes a coiled fiber within two electro-magnetic toroids, such that the fiber length required for getting the beat length is quite long and several rounds of fiber are needed. Analysis of the capabilities of the proposed device and its sensitivity to different parameters is presented. Faraday rotation of 13° was experimentally measured in six meters of single mode silica fiber, with a magnetic field of about 0.06T at a wavelength of 1064nm. We show that phase matching between the two phenomena significantly improves the polarization rotation by a factor of 4-10. In addition, we demonstrate the ability to achieve higher rotation by using Fabry Perot resonator in low terbium doped glass.

Asymmetric optical transmission based on unidirectional excitation of surface plasmon polaritons in gradient metasurface

Asymmetric optical transmission is fundamental and highly desirable in information processing and full manipulation of lightwave. We here propose an asymmetric optical transmission device consisting of a gradient metasurface and a one-dimensional subwavelength grating. Owing to the unidirectional excitation of surface plasmon polaritons (SPPs) by the gradient metasurface, and SPP-assisted extraordinary optical transmission, forward incident light has much higher transmission than the backward one. We combine temporal coupled mode theory and finite-difference time-domain simulations to verify its operation principle and study the performance. The results indicate that asymmetric transmission with high-contrast and large forward transmittance can be obtained around the 1.3 µm optical communication band.

Fabrication of europium-doped silica optical fiber with high Verdet constant

A europium-doped (Eu-doped) silica optical fiber is fabricated using modified chemical vapor deposition (MCVD) technology. Europium fluoride (EuF₃) material is introduced into the fiber core with a high temperature vaporizing technique. Its concentration is approximately 0.11 at %. The outer and core diameters of doped fiber are approximately 122 and 9 μm, respectively. Refractive index difference (RID) between core and cladding is approximately 2%. A magneto-optical effect measurement system, which is based on the Stokes polarization parameters method, is set up to analyze its magneto-optical properties. The Verdet constant of the Eu-doped optical fiber is -4.563 rad T^-1m^-1, which is approximately double than that of single mode fiber (SMF) at 660 nm.

Isolator-free switchable uni- and bidirectional hybrid mode-locked erbium-doped fiber laser

An Erbium-doped fibre ring laser hybrid mode-locked with single-wall carbon nanotubes (SWNT) and nonlinear polarisation evolution (NPE) without an optical isolator has been investigated for various cavity conditions. Precise control of the state of polarisation (SOP) in the cavity ensures different losses for counter-propagating optical fields. As the result, the laser operates in quasi-unidirectional regime in both clockwise (CW) and counter-clockwise (CCW) directions with the emission strengths difference of the directions of 22 dB. Furthermore, by adjusting the net birefringence in the cavity, the laser can operate in a bidirectional generation. In this case, a laser pumped with 75 mW power at 980 nm generates almost identical 790 and 570 fs soliton pulses with an average power of 1.17 and 1.11 mW. The operation stability and pulse quality of the soliton pulses in both unidirectional regimes are highly competitive with those generated in conventional ring fibre lasers with isolator in the cavity. Demonstrated bidirectional laser operation can find vital applications in gyroscopes or precision rotation sensing technologies.

Broadband Faraday isolator

Driving on an analogy with the technique of composite pulses in quantum physics, we theoretically propose a broadband Faraday rotator and thus a broadband optical isolator, which is composed of sequences of ordinary Faraday rotators and achromatic quarter-wave plates rotated at the predetermined angles.

All-fiber optical isolator based on Faraday rotation in highly terbium-doped fiber

An all-fiber isolator with 17 dB optical isolation is demonstrated. The fiber Faraday rotator uses 56 wt. % terbium (Tb)-doped silicate fiber, and the fiber polarizers are Corning SP1060 single-polarization fiber. The effective Verdet constant of the Tb-doped fiber is measured to be -24.5+/-1.0 rad/(Tm) at 1053 nm, which is 20 times larger than silica fiber and 22% larger than previously reported results.

Effective Verdet constant in a terbium-doped-core phosphate fiber

The concept of an effective Verdet constant is proposed and experimentally validated. The effective Verdet constant of light propagation in a fiber includes contributions from the materials in both the core and the cladding. It is measured in a 25 wt.% terbium-doped-core phosphate fiber to be -6.2+/-0.4 rad/(Tm) at 1,053 nm, which is six times larger than silica fiber. The result agrees well with Faraday rotation theory in optical fiber.

All-fiber-optic nonreciprocal modulator

A new all-fiber-optic nonreciprocal device using two acousto-optic frequency shifters is proposed and demonstrated. When the device was operated as an optical isolator, an extinction ratio of 22 dB was obtained. The device's unique modulation capability is also described.

Faraday effect in standard optical fibers: dispersion of the effective Verdet constant

We have measured the Faraday effect in silica standard optical fibers in the wavelength range 458-1523 nm. An effective Verdet constant Vef that exhibits a linear dependence on the square of the optical frequency ν is defined: V(ef) = (0.142 ± 0.004) × 10(-28) ν(2) rad T(-1) m(-1). We demonstrate that the negative effects of a small linear birefringence can be minimized by adjustment of the input polarization to an optimum state.