Analysis of an integrated optical coherent receiver with optical state of polarization control

An integrated optical coherent receiver with continuous state of polarization control is proposed and analyzed. The receiver consists of an integrated optical polarization rotator, a state of polarization detector and a balanced mixer receiver. Continuous state of polarization control can be achieved by using two polarization rotators in series and feeding the polarization rotator outputs into the state of polarization detector whose subsequent output is used to control the voltage settings on the polarization rotator. For the general case, the polarization rotator is comprised of two phase shifters and a TE - TM mode converter. The state of polarization detector stage consists of a δβ directional coupler mode splitter. A novel fabrication technique for achieving efficient polarization splitting is discussed. A balanced mixer receiver is implemented using a passive directional coupler with 50/50 power splitting. The need for a passive device is demonstrated and a method for achieving accurate power splitting ratios using the proton exchange fabrication technique is discussed and experimentally demonstrated. An analysis of the performance of such a system including the balanced mixer receiver is carried out to identify the critical areas of fabrication. Discussion is also given to the function and characteristics of the electronic control loop.     

Polarization Insensitive Wavelength Conversions by a LiNbO3 Waveguide Using a Multi-Ring Configuration

A novel configuration is proposed for polarization insensitive wavelength conversions using a LiNbO₃ waveguide with a periodically domain inverted structure. The proposed configuration consists of multiple rings, which are connected by a polarization sensitive wavelength converter such as the LiNbO₃ waveguide described. One ring containing a pump light source is used to pump the wavelength converter bidirectionally, while the other rings containing a polarization beam splitter and a 90° polarization rotator are used to couple in the input signal and extract the converted light. The proposed method is proven experimentally by the wavelength conversion based on sum frequency generation.     

Design of Ultra Compact Polarization Splitter Based on the Complete Photonic Band Gap

A novel design of polarization splitter based on the complete photonic band gap has been proposed in this paper. The proposed Photonic Band Gap (PBG) polarization splitter is formed by two photonic crystal waveguides composed of dielectric rods in air in honeycomb structure for which complete photonic band gap is obtained using the plane wave expansion (PWE) method. The splitting properties (i.e. coupling length, extinction ratio and insertion loss) of PBG polarization splitter have numerically been investigated using the finite difference time domain (FDTD) method. It has been shown that polarization splitter of length as small as 32 μm can be designed at λ=1.55 μm. The proposed polarization splitter offers a large bandwidth of 120 nm.     

Polarization beam splitter with wide bandwidth in air-hole-based periodic dielectric waveguides

A polarization beam splitter with wide bandwidth and simple structure in air-hole-based periodic dielectric waveguides has been proposed and designed. Operation principle of the device is based on different directional coupling properties of beams in TE and TM polarizations in parallel periodic dielectric waveguides. Performances have been evaluated by a finite-difference time-domain simulation. Results show that the polarization beam splitter provides a wide bandwidth of 113 nm with both a high extinction ratio (higher than 21 dB) and a low insertion loss (less than 1.5 dB) for optical communication wavelengths at ∼1.55 μm. Moreover, the performances of the polarization beam splitter are insensitive to longitudinal alignment errors in the coupling region, which is desirable for device fabrication and practical application.     

Polarization converter for higher-order laser beams using a single binary diffractive optical element as beam splitter

We propose a new approach to generating a pair of initial beams for a polarization converter that operates by summing up two opposite-sign circularly polarized beams. The conjugated pairs of vortex beams matched with laser modes are generated using binary diffractive optical elements (DOEs). The same binary element simultaneously serves two functions: a beam shaper and a beam splitter. Two proposed optical arrangements are compared in terms of alignment complexity and energy efficiency. The DOEs in question have been designed and fabricated. Natural experiments that demonstrate the generation of vector higher-order cylindrical beams have been conducted.     

Passive broadband silicon-on-insulator polarization splitter

We present the implementation of a novel wavelength independent polarization splitter on a silicon-on-insulator platform. The waveguide splitter is based on a zero-order arrayed waveguide grating (AWG) configuration. The splitting function is realized by employing cladding stress-induced birefringence. The device demonstrated a TE to TM splitting ratio better than -15 dB over a 20 nm tuning range centered around lambda=1550 nm and better than -10 dB over our entire accessible wavelength range from lambda=1465 nm to 1580 nm. The highest splitting extinction ratio achieved was -20 dB. To our knowledge, this is the first reported passive broadband polarization splitter based on AWG.     

A free-space-based differential phase shift quantum key distribution scheme with higher key creation efficiency

Differential phase shift quantum key distribution scheme has been improved by introducing a passive path selection structure at the transmitter including two polarization controllers used to mark the photon pulses and a polarizing beam splitter to distinguish these pulses so that can make different time delay at the receiver. Theoretical analysis indicates that a free-space-based differential phase shift quantum key distribution system with this proposed improvement will have high efficiency with the utilization ratio of photons reaching 100% under ideal condition.     

Design of a new kind of polarization splitter based on transformation optics

A scheme for a new two-dimensional polarization splitter is proposed based on the transformation optics. When a beam of arbitrary polarization illuminates upon the proposed polarization splitter, the TE (or TM) component is deflected whereas the TM (or TE) component propagates with no deflection. Moreover, the emerging propagation direction of the deflected component can be adjusted by rotating the polarization splitter. The simulation results demonstrated the feasibility and the flexibility of the polarization splitter. Design details and full-wave simulation results are provided.     

Polarization splitter based on a square-lattice photonic-crystal fiber

A three-core polarization splitter based on a square-lattice photonic-crystal fiber is presented. The component separates the input field into two orthogonally polarized beams that are coupled to the horizontal and vertical output ports. The splitter has been designed through modal and beam propagation analysis by employing high-performance codes based on the finite-element method. Results obtained for a device length of 20 mm show extinction ratios as low as -23 dB with bandwidths as great as 90 nm.     

Design of a polarization splitter for an ultra-broadband dual-core photonic crystal fiber

A novel ultra-broadband polarization splitter based on a dual-core photonic crystal fiber (DC-PCF) is designed. The full-vector finite element method and coupled-mode theory are employed to investigate the characteristics of the polarization splitter. According to the numerical results, a graphene-filled layer not only broadens the working bandwidth but also reduces the size of the polarization splitter. Furthermore, the fluorine-doped region and the germanium-doped region can broaden the bandwidth. Also, the 4.78 mm long polarization splitter can achieve an extinction ratio of -98.6 dB at a wavelength of 1550 nm. When extinction ratio is less than -20 dB, the range of the wavelength is 1027 nm-1723 nm with a bandwidth of 696 nm. Overall, the polarization splitter can be applied to all-optical network communication systems in the infrared and near-infrared wavelength range.     

光子晶体定向耦合三波长功分器

以二维三角晶格光子晶体为研究对象,在该光子晶体中引入两行以一行耦合介质柱为间距的平行单模线缺陷波导.通过分析和研究光子晶体波导耦合结构的耦合和解耦合特性,发现在不同频率下耦合波导的耦合长度不同.利用平面波展开法和定向耦合原理计算了在不同入射光频率下,缺陷波导间耦合波导的耦合长度,设计了一种新型超微光子晶体波导耦合型三波长功分器,实现了归一化频率分别为0.369、0.394、0.435的光波的分束效果.采用时域有限差分法验证了该功分器具有很好的功率分配效果.本文结果有助于光子晶体新型滤波器、定向耦合器、波分复用器、偏振光分束器以及光开关等光子器件的研究.     

TE/TM-mode pass polarizers and splitter based on an asymmetric twin waveguide and resonant coupling

A new passive TE/TM-mode polarization filter for an InP system based on an asymmetric twin waveguide and resonant coupling is investigated. Linear taper sections with different taper angles are introduced to couple between the two vertically separated waveguides. The underlying waveguide is designed to enable direct edge coupling from an optical fiber. At a wavelength of 1.55?μm power extinction ratios of 20 dB for the TE- and more than 10 dB for the TM-polarization are reported for devices shorter than 400?μm. An increased extinction ratio can be obtained by concatenating structures. Furthermore, we show this concept can be expanded to a polarization splitter.     

基于金线填充的双芯光子晶体光纤偏振分束器

提出了一种基于金线填充的双芯光子晶体光纤超短偏振分束器,并进行了有限元分析.金线表面激发的表面等离子激元与双芯光子晶体光纤纤芯模之间的强烈耦合,导致更短的偏振分束器长度和更大的工作带宽.与同类的偏振分束器相比,所提出的偏振分柬器能同时实现较短的长度和较高的消光比.数值结果表明,长度为0.263 mm的偏振分束器,在波长1.55 μm处消光比达-70 dB,-20 dB消光比带宽为124 nm.     

偏振模色散补偿中的偏振主态与分束器主轴的对准

光纤通信系统的比特率超过10Gb/s或更高时,偏振模色散引起的脉冲信号展宽成为主要障碍.分离光纤线路中的两个偏振模式对于提高偏振模色散补偿的精度和速度有重要意义.讨论了光纤线路中两偏振主态与补偿器中偏振分束器主轴的对准问题,给出了偏振分束器任何一个主轴上光强的表示并推导出相应的电功率信号表示式,建立了电功率与光信号两个模式之间的延迟时间以及偏振主态与分束器主轴相对角度的变化关系.初步实验表明,可以通过偏振控制器或可转动的光纤连接器实现偏振主态与偏振分束器的对准.     

Polarization Sagnac interferometer with a reflective grating beam splitter

All-reflective interferometric gravitational-wave detector configurations with a diffraction grating as a power beam splitter have been proposed to reduce thermal lensing. We demonstrate the use of a diffraction grating as a polarization beam splitter in a zero-area polarization Sagnac interferometer.     

Design and fabrication of ultra-high precision thin-film polarizing beam splitter

An ultra-high precision thin-film polarizing beam splitter (PBS) has been designed and fabricated. Using Needle optimization technology, we design the thin-film polarizing beam splitter that is transparent for P polarization and reflective for S polarization with ultra-high precision at 64.8° angle of incidence and 632.8 ± 10 nm wavelength band. The experiments with the fabricated thin-film PBS demonstrate that both the reflectance of P polarization and transmittance of S polarization at 64.8° angle of incidence and 632.8 nm wavelength point are less than 0.02%, which is ultra-high for reported PBSs.     

Tunable multi-function broadband splitter with optical bistability based on surface plasmon

A tunable multi-function broadband splitter consisted of a silver film, Kerr medium and a silver grating sandwiched between linear dielectrics waveguides is proposed and numerically investigated. This splitter can realize the functions of the beam splitter, the polarization splitter and wavelength beam splitter. This surface plasmon based device provides a unique approach for polarization sensitive manipulation of light in an integrated circuit and will be essential for future classical and quantum information processes.     

A novel polarization splitter based on dual-core hybrid photonic crystal fibers

Highly birefringent dual-core photonic crystal fibers (PCFs) can be used as a polarization splitter because the orthogonal polarization modes with dissimilar coupling lengths are easily separated from each other. Different from the traditional methods achieving high birefringence, a new highly birefringent hybrid PCF that guides light by both index guiding and bandgap guiding is proposed. Firstly, a novel polarization splitter based on this kind of dual-core hybrid PCF is designed. The transmission modes, coupling lengths for the two orthogonal polarizations and performance of the proposed polarization splitter are investigated and numerically analyzed. The results demonstrate that it is possible to obtain a 4.72-mm-long polarization splitter. The splitting ratio is better than −20 dB in a large wavelength range of 1.53-1.72 μm. Its bandwidth is about 190 nm.     

Isotope separation of32SF6 and12CF3I by a Q-switched CO2 laser

In the paper, polarization beam splitters are studied. Our theoretical study reveals that the coupling length and modulation period of a polarization beam splitter made from the depressed cladding fiber are shorter compared with that made from the matched fiber. Thus the former is characterized by a short interaction length. On the other hand, a polarization beam splitter made from the raised cladding fiber has a longer coupling length and a longer modulation period than those made from the matched fiber.     

Theoretical simulation of a polarization splitter based on dual-core soft glass PCF with micron-scale gold wire

A polarization splitter based on dual-core soft glass photonic crystal fiber(PCF) filled with micron-scale gold wire is proposed. The characteristics of the polarization splitter are studied by changing the structural parameters of the PCF and the diameter of the gold wire with the finite element method(FEM). The simulation results reveal that the coupling length ratio of the soft glass-based PCF is close to 2 and the corresponding curve is more flat than that of the silica-based PCF.The broadband bandwidth is 226 nm in which the extinction ratio is lower than-20 d B by the soft glass-based PCF, i.e.,from 1465 nm to 1691 nm which is competitive in the reported polarization splitters, and the bandwidth is just 32 nm by the silica-based PCF. The insertion loss by our polarization splitter is just 0.00248 d B and 0.43 d B at the wavelength of 1.47 μm and 1.55 μm. The birefringence is obviously increased and the coupling length is decreased by filling gold wire into the soft glass-based or the silica-based PCF. Also the birefringence based on the silica-based PCF is much larger than that based on the soft glass-based PCF whether or not the gold wire is introduced. The fabrication tolerance of the polarization splitter is also considered by changing the structural parameters. The polarization splitter possesses broad bandwidth, low insertion loss, simple structure and high fabrication tolerance.