Single Polarization State Research Articles

Single-Frequency and Single-Polarization DFB Fiber Laser Based on Tapered FBG and Self-Injection Locking

A stable single-polarization narrow linewidth single-frequency distributed feedback (DFB) fiber laser is proposed and demonstrated. For the first time, to our knowledge, the tapered FBG written in the photosensitive large-mode-area (LMA) high-concentration erbium-doped fiber (EDF) is applied in the DFB fiber laser. Self-injection locking is used to make the proposed DFB fiber laser operate in the stable single-polarization state and reduce the linewidth of the DFB fiber laser. The LMA high-concentration EDF is fabricated by the modified chemical vapor deposition technique. The tapered FBG can be seen as the equivalent phase shift FBG, and the equivalent π phase shift is produced by tapering the uniform FBG directly. The threshold of the DFB fiber laser is about 145 mW, and the maximum output power is 43.55 mW at 450-mW pump power. The measured and modified slope efficiencies of the DFB fiber laser are approximately 14.27% and 15.82%, and the optical signal-to-noise ratio (OSNR) of the laser is over 55 dB. The stable single-polarization and single-frequency operation of the fiber laser is realized, and the measured 20-dB linewidth of DFB fiber laser with self-injection locking and without self-injection locking are approximately 10.3 and 52.3 kHz, respectively.

Single input state, single-mode fiber-based polarization-sensitive optical frequency domain imaging by eigenpolarization referencing.

Fiber-based polarization-sensitive optical frequency domain imaging is more challenging than free-space implementations. Using multiple input states, fiber-based systems provide sample birefringence information with the benefit of a flexible sample arm but come at the cost of increased system and acquisition complexity, and either reduce acquisition speed or require increased acquisition bandwidth. Here we show that with the calibration of a single polarization state, fiber-based configurations can approach the conceptual simplicity of traditional free-space configurations. We remotely control the polarization state of the light incident at the sample using the eigenpolarization states of a wave plate as a reference, and determine the Jones matrix of the output fiber. We demonstrate this method for polarization-sensitive imaging of biological samples.

Quantitative single-mode fiber based PS-OCT with single input polarization state using Mueller matrix.

We present a simple but effective method to quantitatively measure the birefringence of tissue by an all single-mode fiber (SMF) based polarization-sensitive optical coherence tomography (PS-OCT) with single input polarization state. We theoretically verify that our SMF based PS-OCT system can quantify the phase retardance and optic axis orientation after a simple calibration process using a quarter wave plate (QWP). Based on the proposed method, the quantification of the phase retardance and optic axis orientation of a Berek polarization compensator and biological tissues were demonstrated.

Technology developments and biomedical applications of polarization-sensitive optical coherence tomography

Polarization-sensitive optical coherence tomography (PS-OCT) enables depth-resolved mapping of sample polarization information, such as phase-retardation and optical axis orientation, which is particularly useful when the nano-scale organization of tissue that are difficult to be observed in the intensity images of a regular optical coherence tomography (OCT). In this review, we survey two types of methods and systems of PS-OCT. The first type is PS-OCT with single input polarization state, which contain bulk optics or polarization maintaining fiber (PMF) based systems and single-mode fiber (SMF) based systems. The second type is PS-OCT with two different input polarization states, which contain SMF based systems and PMF based systems, through either time, frequency, or depth multiplexing. In addition, representative biomedical applications using PS-OCT, such as retinal imaging, skin cancer detection, and brain mapping, are demonstrated.

Polarization signature from the FengYun-3 Microwave Humidity Sounder

Microwave Humidity Sounders (MHS) onboard NOAA-15, -16, -17, -18, -19, and EUMETSAT MetOp-A/B satellites provide radiance measurements at a single polarization state at any of five observed frequencies. The Microwave Humidity Sounder (MWHS) onboard the FengYun-3 (FY-3) satellite has a unique instrument design that provides dual polarization measurements at 150 GHz. In this study, the MWHS polarization signal was investigated using observed and modeled data. It is shown that the quasi-polarization brightness temperatures at 150 GHz display a scan angle dependent bias. Under calm ocean conditions, the polarization difference at 150 GHz becomes non-negligible when the scan angle varies from 10° to 45° and reaches a maximum when the scan angle is about 30°. Also, the polarization state is sensitive to surface parameters such as surface wind speed. Under clear-sky conditions, the differences between horizontal and vertical polarization states at 150 GHz increase with decreasing surface wind speed. Therefore, the polarization signals from the cross-track scanning microwave measurements at window channels contain useful information about surface parameters. In addition, the availability of dual polarization measurements allows a one-to-one conversion from antenna brightness temperature to sensor brightness temperature if a cross-polarization spill-over exists.

Electrically tunable optical polarization rotation on a silicon chip using Berry's phase.

The continued convergence of electronics and photonics on the chip scale can benefit from the voltage control of optical polarization for applications in communications, signal processing and sensing. It is challenging, however, to electrically manipulate the polarization state of light in planar optical waveguides. Here we introduce out-of-plane optical waveguides, allowing access to Berry's phase, a quantum-mechanical phenomenon of purely topological origin. As a result, electrically tunable optical polarization rotation on the chip scale is achieved. Devices fabricated in the silicon-on-insulator material platform are not limited to a single static polarization state. Rather, they can exhibit dynamic tuning of polarization from the fundamental transverse electric mode to the fundamental transverse magnetic mode. Electrical tuning of optical polarization over a 19 dB range of polarization extinction ratio is demonstrated with less than 1 dB of conversion loss at infrared wavelengths. Compact system architectures involving dynamic control of optical polarization in integrated circuits are envisioned.

Experimental Test of the State Estimation-Reversal Tradeoff Relation in General Quantum Measurements

When a measurement has limited strength, only partial information, regarding the initial state, is extracted, and, correspondingly, there is a probability to reverse its effect on the system and retrieve the original state. Recently, a clear and direct quantitative description of this complementary relationship, in terms of a tradeoff relation, was developed by Y. K. Cheong and S. W. Lee. [Phys. Rev. Lett. 109, 150402 (2012)]. Here, this tradeoff relation is experimentally verified using polarization-encoded single photons from a quantum dot. Measurement operators representing a complete range, from not affecting the system to a projection to a single polarization state, are realized. In addition, for each measurement operator, an optimal reversal operator is also implemented. The upper bound of the tradeoff relation is mapped to experimental parameters representing the measurement strength. Our results complement the theoretical work and provide a hands-on characterization of general quantum measurements.

Switchable Single-Polarization Dual-Wavelength Ring Laser Based on Structured PM-CFBG

A switchable single-polarization dual-wavelength single-longitudinal mode (SLM) erbium-doped fiber (EDF) ring laser is proposed and demonstrated. For the first time, the structured polarization-maintaining chirped fiber Bragg grating (PM-CFBG) filter, which has ultranarrow transmission band is created by tapering directly on the PM-CFBG. Then, the stable SLM operation of the fiber laser is guaranteed by the structured PM-CFBG filter and 20-cm unpumped EDF acting as a saturable absorber. Meanwhile, the stable dual-wavelength fiber laser with a wavelength spacing of ~0.41 nm and stable single polarization state is experimentally realized. The measured linewidth of the fiber laser for each wavelength is <;8 kHz with a 20-dB linewidth.

Mapping Spin Coherence of a Single Rare-Earth Ion in a Crystal onto a Single Photon Polarization State

We report on optical detection of a single photostable Ce(3+) ion in an yttrium aluminium garnet (YAG) crystal and on its magneto-optical properties at room temperature. The spin quantum state of the emitting level of a single cerium ion in YAG can be initialized by a circularly polarized laser pulse. Coherent precession of the electron spin is read out by observing temporal behavior of circularly polarized fluorescence of the ion. This implies direct mapping of the spin quantum state of Ce(3+) ion onto the polarization state of the emitted photon and represents the quantum interface between a single spin and a single photon.

High-speed polarization controller for all-fiber quantum communication systems

Polarization control is of vital importance in optical communications, which can affect the stability and bit error rate of a system. We demonstrate an all-fiber high-speed polarization control scheme based on a bidirectional Sagnac ring. The polarization direction can be accurately controlled by adjusting the phase difference of an electro-optic fiber phase modulator in the ring, meanwhile it is realized that only a single beam port outputs different polarization states. The phase can be adjusted accuratly to 10-3 rad, giving an extinction ratio as high as 30 dB, and the modulation speed can reach 2 GHz. The system has excellent stability, and as the optical circuit consists of simple, low cost components which can be easily integrated, there are good prospects for its application in quantum cryptography and other optical communcations fields.

Design considerations for polarization-sensitive optical coherence tomography with a single input polarization state

Using a generalized design for a polarization-sensitive optical coherence tomography (PS-OCT) system with a single input polarization state (SIPS), we prove the existence of an infinitely large design space over which it is possible to develop simple PS-OCT systems that yield closed form expressions for birefringence. Through simulation and experiment, we validate this analysis by demonstrating new configurations for PS-OCT systems, and present guidelines for the general design of such systems in light of their inherent inaccuracies. After accounting for systemic errors, alternative designs exhibit similar performance on average to the traditional SIPS PS-OCT system. This analysis could be extended to systems with multiple input polarization states and could usher in a new generation of PS-OCT systems optimally designed to probe specific birefringent samples with high accuracy.

Differential Detection for Nanoplasmonic Resonance Sensors

A differential measurement design employing two nearly collinear optical beams can lead to surface plasmon polariton (SPP) sensors of increased dynamic range and signal-to-noise ratio. We demonstrate a differential measurement device that is based on wavelength interrogation, employs a single incident polarization state, and is combined with a 2-D nanohole array for operation at near-normal incidence, where this approach offers a decrease in the measurement time.

Transparent thin film polarizing and optical control systems

We show that a diffractive waveplate can be combined with a phase retardation film for fully converting light of arbitrary polarization state into a polarized light. Incorporating a photonic bandgap layer into a system of such polarizers that unify different polarization states in the input light into a single polarization state at its output, rather than absorbing or reflecting half of it, we developed and demonstrated a polarization-independent optical controller capable of switching between transmittive and reflective states. The transition between those states is smoothly controlled with low-voltage and low-power sources. Using versatile fabrication methods, this “universally polarizing optical controller” can be integrated into a thin package compatible with a variety of display, spatial light modulation, optical communication, imaging and other photonics systems.

Polarization switching in a quasi-isotropic microchip Nd:YAG laser induced by optical feedback

This paper demonstrates the influence of external optical feedback on the polarization state of longitudinal modes in quasi-isotropic microchip Nd:YAG lasers. Under optical feedback, the polarization state of longitudinal modes in quasi-isotropic lasers relies strongly on the intracavity anisotropy loss and mode competition. When the intracavity anisotropy loss is small, external optical feedback can cause polarization switching and strong mode competition between two orthogonal linearly polarized eigenstates of one laser longitudinal mode, which leads to the distortion of laser intensity modulation waveform. The polarization switching is independent of the initial external cavity length. By increasing the intracavity anisotropy loss, one polarization eigenstate can be suppressed and the laser works in single-polarization state. A theoretical analysis based on the compound cavity model is presented, which is in good agreement with the experimental results. The results offer guidance to the development of laser feedback interferometers.

Polarization maintaining fiber based ultra-high resolution spectral domain polarization sensitive optical coherence tomography

We present a new ultra high resolution spectral domain polarization sensitive optical coherence tomography (PS-OCT) system based on polarization maintaining (PM) fibers. The method transfers the principles of our previous bulk optic PS-OCT systems to a fiberized setup. The phase shift between the orthogonal polarization states travelling in the two orthogonal modes of the PM fiber is compensated by software in post processing. Thereby, the main advantage of our bulk optics setups, i.e. the use of only a single input polarization state to simultaneously acquire reflectivity, retardation, optic axis orientation, and Stokes vector, is maintained. The use of a broadband light source of 110 nm bandwidth provides improved depth resolution and smaller speckle size. The latter is important for improved resolution of depolarization imaging. We demonstrate our instrument for high-resolution PS-OCT imaging of the healthy human retina.

Single- and dual-wavelength switchable erbium-doped fiber ring laser based on intracavity polarization selective tilted fiber gratings

We propose and demonstrate a single- and dual-wavelength switchable erbium-doped fiber laser (EDFL) by utilizing intracavity polarization selective filters based on tilted fiber gratings (TFGs). In the cavity, one 45 degrees TFG functions as an in-fiber polarizer and the other 77 degrees TFG is used as a fiber polarization dependent loss (PDL) filter. The combined polarization effect from these two TFGs enables the laser to switch between the single- and the dual-wavelength operation with a single-polarization state at room temperature. The laser output at each wavelength shows an optical signal-to-noise ratio (OSNR) of >60 dB, a side mode suppression ratio (SMSR) of >50 dB, and a polarization extinction ratio of approximately 35 dB. The proposed EDFL can give stable output under laboratory conditions.

Dynamical model for coherent optical manipulation of a single spin state in a charged quantum dot

AbstractThe optically‐induced coherent spin dynamics of a single spin confined in a charged quantum dot (QD) is theoretically studied employing coupled vector Maxwell‐pseudospin formalism. Generalized pseudospin master equation is derived for description of the time evolution of spin coherences and spin populations including spin population transfer and dissipation in the system through spin relaxation processes. The equation is solved in the time domain self‐consistently with the vector Maxwell equations for the optical wave propagation coupled to it via macroscopic medium polarisation. Using the model the long‐lived electron spin coherence left behind a single resonant ultrashort optical excitation of the electron‐trion transition in a charged QD is simulated in the low‐ and high‐intensity Rabi oscillations regime. Signatures of the polarised photoluminescence (PL), predicted by the model, such as the appearance of a second echo pulse after the excitation and characteristic PL trace shape, are discussed for realization of high‐fidelity schemes for coherent readout of a single spin polarisation state. (© 2009 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Rotating orthogonal polarization imaging

Surface reflections often present a problem in the polarization difference imaging of tissue. The technique described involves illumination in a single polarization state and detection in the orthogonal polarization state. Synchronously rotating both the illumination and orthogonal detection states provides an image free from surface reflections that is sensitive to the polarization properties of the underlying tissue. Results on tissue phantoms demonstrate that polarization sensitive measurements of a test target can be made up to a depth of 12 mean free paths within a scattering medium. Preliminary images of bovine tendon are also demonstrated.

Model for the coherent optical manipulation of a single spin state in a charged quantum dot

The optically driven coherent dynamics associated with the single-shot initialization and readout of a localized spin in a charged semiconductor quantum dot embedded in a realistic structure is theoretically studied using a new Maxwell-pseudospin model. Generalized pseudospin master equation is derived for description of the time evolution of spin coherences and spin populations in terms of the real state pseudospin coherence vector including dissipation in the system through spin-relaxation processes. The equation is solved in the time-domain self-consistently with the vector Maxwell equations for the optical wave propagation coupled to it via macroscopic medium polarization. Using the model, the long-lived electron spin coherence left behind a single resonant ultrashort optical excitation of the electron-trion transition in a charged quantum dot is simulated in the low- and high-intensity Rabi oscillation regime. Signatures of the polarized photoluminescence PL resulting from the numerical simulations, such as the appearance of a second echo pulse following the excitation and a characteristic nonmonotonic PL trace shape, specific for initial spin-up orientation, are discussed for realization of high-fidelity schemes for coherent readout of a single spin polarization state.

Positive-operator-valued-measure view of the ensemble approach to polarization optics

The statistical ensemble formalism of Kim et al [J. Opt. Soc. Am. A4, 433 (1987)] offers a realistic model for characterizing the effect of stochastic nonimage-forming optical media on the state of polarization of transmitted light. With suitable choice of the Jones ensemble, various Mueller transformations-some of which are hitherto unknown-are deduced. It is observed that the ensemble approach is formally identical to the positive-operator-valued measures (POVMs) on the quantum density matrix. This observation, in combination with the recent suggestion by Ahnert and Payne [Phys. Rev. A71, 012330-1 (2005)]-in the context of generalized quantum measurement on single photon polarization states-that linear optics elements can be employed in setting up all possible POVMs enables us to propose a way of realizing different types of Mueller devices.