Waveguide Birefringence Research Articles

Ultracompact Si slot waveguide‐based polarization rotators

ABSTRACTA novel silicon asymmetric tilted slot waveguide‐based polarization rotator is presented. A large birefringence in the silicon slot waveguide facilitated a compact polarization rotator of subwavelength scale. A 1287 nm long TM to TE and TE to TM polarization rotator was achieved with an extinction ratio of 10 dB and an insertion loss of less than 5 dB at an operating wavelength of 1500 nm. Further performance improvement is possible for polarization rotator designed to work on TM to TE (or TE to TM) conversion: a 711 nm long TM to TE polarization rotator with 9.25 dB extinction ratio and 2.2dB insertion loss was also numerically demonstrated. © 2015 Wiley Periodicals, Inc. Microwave Opt Technol Lett 57:779–785, 2015

Polarization Beam Splitter With Different Core Widths and Its Application to Dual-Polarization Optical Hybrid

We investigated the core-width dependence of the birefringence of silica-based waveguides with different relative refractive index differences (Δ), namely a 0.75%-Δ GeO2-doped waveguide and a 5%-Δ Ta2O5-doped waveguide. We revealed that the birefringence of the 0.75%-Δ GeO2-doped waveguide is almost the same as the stress-induced birefringence and that the 5%-Δ Ta2O5-doped waveguide has a large geometrical birefringence. By utilizing the core-width dependence of the birefringence, we have successfully demonstrated a 0.75%-Δ polarization beam splitter (PBS) with an operating wavelength range of more than 150 nm and a dual-polarization optical hybrid including a compact 5%-Δ PBS with a polarization extinction ratio of more than 20 dB over the C-band.

Full Evaluation of Polarization Characteristics of Multifunctional Integrated Optic Chip With High Accuracy

The polarization characteristics of the multifunctional integrated optic chip (MFIOC) are fully evaluated with high accuracy by using optical coherence domain polarimetry based on white light interferometer. Two polarization maintaining (PM) fibers, serving as extended fibers, are spliced to the PM pigtails of the MFIOC with polarization axes aligned. By launching light at 45° to the birefringence axes of the lead-in extended PM fiber, the beams along the fast and slow axes of the birefringent waveguides interfere after a 45° polarization analyzer and an optical path correlator. The polarization extinction ratio (PER) and birefringence of the LiNbO3 Y-waveguide, the birefringence of the PM pigtails, and the crosstalks at the connection points between the Y-waveguide and the PM pigtails can be simultaneously obtained from the amplitudes and positions of the corresponding interference peaks. The characteristic peak of the Y-waveguide's PER is shifted out of the interference peak of the light source ripple by selecting proper length of the extended fibers. The extended fibers also brings in two additional cross-coupling points at the ends of the PM pigtails, which are used for calculating the birefringence of the PM pigtails. In addition, the alignment type between the PM pigtails and the birefringent Y-waveguide is identified according to the position of the characteristic peak of the Y-waveguide's PER. Theoretical model based on Jones matrix is built to describe the characteristic peaks of the MFIOC. Two MFIOCs with different alignment angle between the PM pigtails and the Y-waveguide are experimentally tested. Results show that the PER resolution of the proposed method can achieve nearly -90 dB and the dynamic range of the test system is about 90 dB.

Measurement of modal birefringence in optical waveguides based on the Mach-Zehnder interferometer.

A method for measuring the birefringence in planar waveguide circuits is theoretically proposed and validated. The method is based on the Mach-Zehnder interference and by measuring the spectral shift due to orthogonal polarization states. The birefringence of a silica waveguide is measured to be 2.33 × 10(-4) at nearby 1550 nm. In addition, the birefringence variations with the wavelength and its dependence on the external stress are investigated with the proposed method experimentally. The results in measuring birefringence demonstrate a high accuracy with the order of 10(-5), a wide dynamic range from 10(-5) to 10(-3), and a characteristic of multi-wavelength evaluation.

Analysis of birefringence in magneto-optical waveguides based on nanoparticles doped sol–gel matrix with an optimized substrate

Abstract The elimination of birefringence remains a key challenge in integrated optical systems. In this work, we present birefringence study based on the controlling of layer thickness of planar waveguides, using deposited layers based on magnetic nanoparticles. The birefringence can be reduced with a planar device, depending on a glass substrate. The simulation carried out by MATLAB allowed us to deduce the conditions to decrease the phase mismatch and increase the conversion ratio of modes.

Arbitrary photonic wave plate operations on chip: Realizing Hadamard, Pauli-X and rotation gates for polarisation qubits

Chip-based photonic quantum computing is an emerging technology that promises much speedup over conventional computers at small integration volumes. Particular interest is thereby given to polarisation-encoded photonic qubits, and many protocols have been developed for this encoding. However, arbitrary wave plate operation on chip are not available so far, preventing from the implementation of integrated universal quantum computing algorithms. In our work we close this gap and present Hadamard, Pauli-X, and rotation gates of high fidelity for photonic polarisation qubits on chip by employing a reorientation of the optical axis of birefringent waveguides. The optical axis of the birefringent waveguide is rotated due to the impact of an artificial stress field created by an additional modification close to the waveguide. By adjusting this length of the defect along the waveguide, the retardation between ordinary and extraordinary field components is precisely tunable including half-wave plate and quarter-wave plate operations. Our approach demonstrates the full range control of orientation and strength of the induced birefringence and thus allows arbitrary wave plate operations without affecting the degree of polarisation or introducing additional losses to the waveguides. The implemented gates are tested with classical and quantum light.

Temperature-dependent, polarization-induced bias errors in a resonator integrated optical gyroscope

The performance of a resonator integrated optical gyroscope (RIOG) is inevitably influenced by polarization noise. In this work, the effects of temperature-dependent polarization on the performances of an integrated optical resonator (IOR) and a RIOG are formulated mathematically and analyzed. Firstly, resonant curves with different polarization extinction ratios (PERs) and different temperature fluctuations are demonstrated. The main performances of the IOR, i.e. depth and full width at half maximum (FWHM), are not only influenced by the waveguide birefringence, but also by the intensity coupling coefficient of the couplers, both of which change with the variation of temperature. Secondly, the relationship between the variation of temperature and the variation of depth, as well as the FWHM, are obtained. Thirdly, in order to evaluate the zero bias error caused by the temperature-dependent polarization, resonant asymmetry ratio (RAR) is introduced, which is strongly dependent on the temperature fluctuation. A relationship between the bias error caused by the polarization and the temperature fluctuation is proposed. A large PER of the input beam and a high temperature stability are required to reduce the bias error and achieve a high bias stability of the silica RIOG.

Polarization-Insensitive Wavelength Conversion by FWM of 100-GHz-Spaced DWDM 4$\,\times\,$10 Gb/s RZ-BPSK Signals in a Birefringent Nonlinear AlGaAs Waveguide

Polarization-insensitive (PI) wavelength conversion of 100-GHz-spaced wavelength-division multiplexed 4 × 10 Gb/s return-to-zero binary phase-shift keyed (RZ-BPSK) signals was successfully demonstrated utilizing four-wave mixing for the first time in a passive, birefringent nonlinear AlGaAs waveguide. In addition to a pump launch angle adjustment, a minimum pump-probe detuning was also required to mitigate polarization-induced power fluctuations in the probe. The PI-wavelength-converted signals all demonstrated a pre-amplified receiver sensitivity penalty of less than ≈ 2 dB at 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-9</sup> bit-error-rate, relative to their respective baseline RZ-BPSK signals.

Integrated Magneto-Optical Materials and Isolators: A Review

Many novel materials and device designs have been proposed as photonic analogs to electrical diodes over the last four decades. This paper seeks to revisit these materials and designs as advanced technologies may enable experimental realization that was not possible upon conception of several of these designs. The background behind integration challenges, including waveguide birefringence, fabrication tolerances, garnet/semiconductor mismatch, and optimized interfaces will hopefully spark new ideas that will finally enable the realization of integrated optical isolators and circulators.

Modeling nonlinear optical phenomena in silicon-nanocrystal composites and waveguides

A high demand in relation to simple propagation equations describing nonlinear optical phenomena in silicon-nanocrystal composites is caused by the impracticality of solving Maxwell’s equations while treating thousands of silicon nanocrystals in the composites individually. Recently, we derived such equations for the case of two optical fields using a number of simplifying assumptions (Rukhlenko 2013 Opt. Express 21 2832–46). In particular, we neglected the effects of cross-phase modulation and cross-two-photon absorption due to the interaction between waves of different frequencies, set equal different kinds of mode-overlap factors, and assumed a uniform effective mode area for both fields regardless of their polarizations. Also, it was assumed that the fields interact inside a highly birefringent silicon-nanocrystal waveguide, which provides tight lateral confinement of its propagating modes and ensures the absence of phase matching between them. Here we abandon these approximations and generalize the coupled-amplitude equations for the case of an arbitrary number of quasi-monochromatic optical fields interacting through the third-order nonlinear polarization of silicon nanocrystals. We derive two sets of equations enabling one to study theoretically the anisotropy of such effects as Raman amplification, four-wave mixing, and wavelength conversion—one for unbounded silicon-nanocrystal composites and the other for different kinds of silicon-nanocrystal waveguides—and provide an overview of the material parameters entering these equations.

On the Theory and Errata to “Data Transfer From RZ-OOK to RZ-BPSK by Polarization-Insensitive XPM in a Passive Birefringent Nonlinear AlGaAs Waveguide”

The dependence of the nonlinear coefficients on the transverse profiles of the pump and the probe fields, which is especially important for a highly anisotropic device such as the Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.18</sub> Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.82</sub> As waveguide, was not explicitly stated in our paper “Data transfer from RZ-OOK to RZ-BPSK by polarization-insensitive XPM in a passive birefringent nonlinear AlGaAs waveguide.” The four-wave mixing efficiency was also incorrectly presented to depend on the square of the device physical length. Lastly, the influence of the fiber-waveguide coupling coefficient was neglected with insufficient justification, leading to an inaccurate general expression for the detected voltage.

Engineering of phase matching for mid-infrared coherent anti-Stokes Raman wavelength conversion with orthogonally polarized pump and Stokes waves in silicon-on-sapphire waveguides

The conversion efficiency of mid-infrared wavelength conversion based on coherent anti-Stokes Raman scattering with TE-polarized pump and TM-polarized Stokes waves is theoretically investigated in silicon-on-sapphire (SOS) waveguides. The peak conversion efficiency of -10 dB is obtained when the linear propagation loss is 1 dB/cm at Δk=0; however, it is reduced to -13.6 dB when the linear propagation loss is 2 dB/cm. The phase matching for wavelength conversion with orthogonally polarized pump and Stokes waves can be realized by engineering the birefringence in SOS waveguides, because proper phase mismatch induced by birefringence together with material dispersion-induced phase mismatch can counteract the large phase mismatch induced by waveguide dispersion. Moreover, compared with the phase matching for identically polarized pump and Stokes waves, the phase matching for orthogonally polarized pump and Stokes waves can be realized in a SOS waveguide with much smaller cross section, which reduces the power requirement for optical systems.

On the Design of Video-Bandwidth Electric Field Sensing Systems Using Dielectric ${\rm LiNbO}_{3}$ Electro-Optic Sensors and Optical Delays as Signal Carriers

As the measurement of wide-band (multi-megahertz) electric fields is often of practical interest in industrial and commercial environments, in this paper, a methodology of design and implementation of a wide-band electric field sensing scheme, using optical delays as information carriers is described. The scheme is based on a lithium niobate (LiNbO3) birefringent optical waveguide that performs simultaneously as an optical retarder and as a dielectric (electrode-less) sensor. In this scheme, the LiNbO3 sensor introduces an optical delay and simultaneously senses an on-air electric field and imprints it around an optical delay. At the receiver, the sensed electric field is detected when the sensor and demodulator are optically matched, i.e., when both introduce identical optical delays. An important aspect, when sensing electric fields using LiNbO3 dielectric sensors, is that the optically sensed field is weaker than the external field by a factor given by the ratio of the permittivity of the surrounding dielectric media over the LiNbO3 permittivity (boundary condition for normal electric fields). When the surrounding media is air, the optically sensed electric field is 35 times weaker than the external field, as described in this paper. Another practical issue is that a birefringent optical waveguide is highly sensitive to optical polarization variations. Such a sensitivity implies that the output dc component of the received light changes with time (dc-drift). The dc-drift performance of the proposed electric field sensing scheme is measured and reported in this paper. The dc-drift can be minimized using polarization-insensitive LiNbO3 unbalanced Mach-Zehnder interferometers.

Active polarisation control of a quantum cascade laser using tuneable birefringence in waveguides

We discuss the design, modelling, fabrication and characterisation of an integrated tuneable birefringent waveguide for quantum cascade lasers. We have fabricated quantum cascade lasers operating at wavelengths around 4450 nm that include polarisation mode converters and a differential phase shift section. We employed below laser threshold electroluminescence to investigate the single pass operation of the integrated device. We use a theory based on the electro-optic properties of birefringence in quantum cascade laser waveguides combined with a Jones matrix based description to gain an understanding of the electroluminescence results. With the quantum cascade lasers operating above threshold we demonstrated polarisation control of the output.

Analysis of polarisation mode splitting characteristic in optical race-track resonator based on silicon-on-insulator rib waveguide

The detailed design and analysis of a polarisation mode splitting resonator based on a silicon-on-insulator rib waveguide are presented. By analysing the mode birefringence in the ultra-small rib waveguide, the directional coupler is introduced to the microring resonator to realise the splitting of the quasi-TE and quasi-TM polarisation modes from the same output port for a specific wavelength range. It is demonstrated that after splitting the quasi-TM polarisation mode, the Q-value of the quasi-TE polarisation mode is about 2.3 × 104, almost twice of that without splitting the quasi-TM polarisation mode. This novel characteristic of a race-track resonator allows it to obtain single polarisation mode at a specific wavelength by itself. This characteristic makes a contribution to accurate wavelength selection, which has been proved to be very useful in the dynamic testing of electrooptical modulators and quite promising in many other applications of optical components.

All-optical amplitude-phase transmultiplexing of RZ-OOK and RZ-BPSK to RZ-QPSK by polarization-insensitive XPM using a nonlinear birefringent AlGaAs waveguide

Polarization-insensitive (PI) phase-transmultiplexing (PTM) of a 10-Gb/s return-to-zero ON-OFF keying (RZ-OOK) pump and a 10-Gb/s RZbinary phase-shift keying (RZ-BPSK) probe to 20-Gb/s RZ-quadrature-PSK (RZ-QPSK) has been successfully demonstrated for the first time in a passive, birefringent AlGaAs waveguide, utilizing PI cross-phase modulation (PI-XPM). For differential QPSK (DQPSK)-detection, a 10 − 9-BER pre-amplified receiver sensitivity penalty of ≈ 2.5 dB for the in-phase component and ≈ 4.9 dB for the quadrature component were found. The penalties were relative to the FPGA-precoded RZ-DQPSK baseline for a pump-probe detuning of ≈ 12 nm, when the probe state of polarization was scrambled and the pump was launched off-axis into the waveguide.

D-Microfibers

A simple mechanical setup was used to polish a standard single mode optical fiber in order to make it asymmetric. The polished fiber was tapered down maintaining the D-shape transversal profile. Its broken symmetry along with the extended evanescent field, due to the dimensions of the microfiber, implies a potentially high birefringent waveguide as well as a high-sensitivity external refractive index device. An experimental maximum sensitivity of S ≈ (3.0±0.2)×104 nm/RIU was achieved, other experimental and numerical results supporting our initial assumptions are also presented.

15 μm polarization entanglement generation based on birefringence in silicon wire waveguides

In this Letter, the 1.5 μm polarization entanglement generation is realized in a silicon wire waveguide utilizing its birefringence. In this scheme, two orthogonal polarized correlated states are generated by scalar processes of spontaneous four-wave mixing (SFWM) in the quasi-transverse electrical and quasi-transverse magnetic modes, respectively. Meanwhile, the vector processes of SFWM are suppressed by the group birefringence in the waveguide. The maximum polarization entangled state is generated by optimizing the pump polarization, which is demonstrated by the experiments of two-photon interference and polarization indistinguishability at one side. The fringe visibilities of two-photon interferences are 96.8±4.7% and 86.0±3.7% under two nonorthogonal polarization detection settings, respectively. This scheme provides a simple way to realize silicon integrated sources for 1.5 μm polarization entanglement generation.

Low-Polarization-Dependent Silica Waveguide Monolithically Integrated on SOI Photonic Platform

We developed a low-polarization-dependent silica- based waveguide, which can be monolithically integrated with a silicon (Si) waveguide device on a silicon-on-insulator (SOI) substrate. For the monolithic integration, silica-based materials must be deposited at low temperature in order not to damage Si waveguide devices. Due to this low-temperature fabrication method, however, the silica films exhibit high residual stress, resulting in high material birefringence. In order to compensate for this birefringence, we introduce a multi-layer core structure. First, we design the structure taking the monolithic integration with the Si waveguide devices into account. Then, the designed waveguides and arrayed-waveguide gratings (AWGs) are fabricated using low-temperature fabrication processes. Next, we experimentally confirm that the waveguide exhibits low waveguide birefringence. In addition, we monolithically integrate the AWG and Si waveguide devices.

Parity-time-symmetric optical coupler with birefringent arms

In this work, we propose a PT-symmetric coupler whose arms are birefringent waveguides as a realistic physical model which leads to a so-called quadrimer i.e., a four complex field setting. We seek stationary solutions of the resulting linear and nonlinear model, identifying its linear point of PT symmetry breaking and examining the corresponding nonlinear solutions that persist up to this point, as well as, so-called, ghost states that bifurcate from them. We obtain the relevant symmetry breaking bifurcations and numerically follow the associated dynamics which give rise to growth/decay even within the PT-symmetric phase. Our obtained stationary nonlinear solutions are found to terminate in saddle-center bifurcations which are analogous to the linear PT-phase transition.