Non-polarization and high-coupling-efficiency coupler using multilevel grating structure

A multilevel grating coupler based on silicon-on-insulator (SOI) material structure is proposed to realize the coupling between waveguide and waveguide or waveguide and fiber. This coupler is compatible with the current fabrication facilities for complementary metal oxide semiconductor (CMOS) technology with vertical coupling. This structure can realize coupling when the beams with transverse electric (TE) polarization and transverse magnetic (TM) polarization are incident at the same time. The influences of the grating coupler parameters including wavelength, the thickness of waveguide layer, the thickness of SiO₂ layer and the number of steps on the TE mode and TM mode coupling efficiencies are discussed. Theory researches and simulation results indicate that the wavelength range is from 1533 nm to 1580 nm when the TE mode and TM mode coupling efficiencies are both more than 40% as the grating period is 0.99 μm. The coupling efficiencies of the incident TE and TM modes are 49.9% and 49.5% at the wavelength of 1565 nm, respectively, and the difference between them is only 0.4%.     

Etched Waveguide Grating Variable 1 $,times,$2 Splitter/Combiner and Waveguide Coupler

We propose and test a silicon waveguide grating which serves dual functions: as a 1$,times,$ 2 variable integrated beam splitter/combiner and as an out-of plane diffractive element for coupling light between a single-mode optical fiber and a 500-nm-wide silicon-on-insulator waveguide. An integrated Mach–Zehnder interferometer made with this novel functional element had over 20-dB extinction ratio. The splitting ratio can be tuned by changing the launch position of the optical fiber. The grating coupler had over 36% coupling efficiency and a 1-dB spectral bandwidth of 37 nm.      

Diplexer With Integrated Filters and Photodetector in Ge–Si Using $Gamma-{X}$ and $Gamma-{M}$ Directions in a Grating Coupler

We demonstrate a central-office-type diplexer in which the filter and photodetector are monolithically integrated on a silicon-on-insulator substrate. The photonic integrated circuit receives a 1577-nm signal from an external laser and sends it to the fiber link using a two-dimensional grating coupler. The same grating coupler receives a 1270-nm signal from the fiber link and sends it to a monolithically integrated germanium photodetector using a polarization-diversity scheme to achieve polarization independence. The grating coupler is novel in that both the $Gamma-{X}$ and $Gamma-{M}$ directions are employed. This allows the grating coupler to couple both the 1577- and 1270-nm wavelengths with a small fiber tilt angle and hence have low polarization-dependent loss.      

High-Power Tapered Unstable-Resonator Laser Diode With a Fiber-Bragg-Grating Reflector

We designed a tapered unstable-resonator laser diode consisting of a 3-mm-long tapered amplifier and a fiber-Bragg-grating reflector, both of which were coupled with a biconical microlens at the fiber end. The amplifier was composed of an InGaAs single quantum well inside a waveguide, which had an optical confinement factor of 1.2%, a tapered current constriction of 6$^{circ}$ in full angle, and an input width of 10 $ muhbox{m}$. The grating reflector was fabricated in a polarization-maintaining fiber with a reflectivity of 99% and a reflection bandwidth of 0.19 nm. A biconical microlens with vertical and horizontal radii of 3.5 and 11 $ muhbox{m}$, respectively, was fabricated at the fiber end to increase the coupling efficiency between the tapered amplifier and the grating reflector. An output power of 3.2 W was obtained at a wavelength of 1064 nm in multimode operation for the grating reflection bandwidth.      

基于SOI材料的偏振不敏感的阵列波导光栅

阵列波导光栅(AWG Arrayed Waveguide Grating)是实现多通道密集波分复用(DWDM Dense Wavelength Division Multiplexing)光网络的理想器件,偏振敏感性是它的一个重要性能指标。本文针对SOI材料的阵列波导光栅,分析了如何采用特殊的波导结构来减小它的偏振相关性,并对16通道、间隔为0．8nm的AWG解复用器进行了计算,结果表明其偏振敏感性低于0．06nm。     

A high-efficiency grating coupler between single-mode fiber and silicon-on-insulator waveguide

We present the design of a diffractive grating structure and get the optimal parameters which can achieve more than 75% coupling efficiency (CE) between single-mode fiber and silicon-on-insulator (SOI) waveguide through 2D finite-different time-domain (FDTD) simulation. The proposed architecture has a uniform structure with no bottom reflection element or silicon overlay. The structure, including grating couplers, adiabatic tapers and interconnection waveguides can be fabricated on the SOI waveguide with only a single electron-beam lithography (ICP) step, which is CMOS-compatible. A relatively high coupling efficiency of 47.2% was obtained at a wavelength of 1562 nm.     

Theoretical Investigation for Reducing Polarization Sensitivity in Si-Nanowire-Based Arrayed-Waveguide Grating (de)Multiplexer With Polarization-Beam-Splitters and Reflectors

A novel design for reducing polarization sensitivity in silicon-on-insulator-based arrayed-waveguide grating (AWG) (de)multiplexer is presented. Each arrayed waveguide has two sections separated by a polarization beam splitter (PBS). These two sections have different core widths and length differences. With these PBSs, one polarization is reflected and the other one goes through. The through polarization enters the second section and is then reflected by a reflector at the end of the second section of the arrayed waveguide. The theoretical simulation shows that one can diminish greatly the polarization sensitivity of both the central channel wavelength and the channel spacing by optimizing the core width and length difference of the second section. The design procedure and formulas are given and an appropriate diffraction order is chosen to obtain a good fabrication tolerance. As an example, an ultrasmall $(82.2times 85.1 mu{hbox {m}}^{2})$ AWG (de)multiplexer with eight channels and a channel spacing of 4 nm is designed to have minimized polarization sensitivity and Bragg-grating PBSs and photonic crystal reflectors are used.      

Compact Focusing Grating Couplers for Silicon-on-Insulator Integrated Circuits

We report experimental results on compact and broadband focusing grating couplers, both in silicon-on-insulator (SOI) and gold on SOI. An eight-fold length reduction of the coupling structure from fiber to photonic wire in SOI, as compared to a linear grating and adiabatic taper, is obtained, without performance penalty. A proof of principle is given for a focusing grating coupler in gold on SOI, with 20% fiber-to-focus efficiency.     

用于FBG解调的AWG芯片的设计、仿真与制备

设计、仿真并制备了一种用于光纤布拉格光栅(FBG)解调的阵列波导光栅(AWG)芯片。该芯片基于SOI衬底进行制备,并在AWG的输入/输出波导、阵列波导与平板波导之间采用双刻蚀结构进行优化。经仿真,该AWG的插入损耗为1.5dB,串扰小于 -20dB,3dB带宽为1.5nm。优化后的AWG芯片采用深紫外光刻技术、电感耦合等离子体等技术制备。经测试,该AWG的插入损耗为3dB,串扰小于 -20dB,3dB带宽为2.3nm。搭建了基于该AWG的解调系统,解调实验结果表明,该系统在0.8nm范围内的解调精度可达11.26pm,波长分辨率为6pm。     

Narrow-core hollow optical waveguide with nanostructured SOI as ultra-low loss platform for efficient photodetection

A nanostructured hollow optical waveguide based on high-index contrast grating (HCG) embedded SOI is proposed. An ultra-low propagation loss of 1.22 dB/m even at narrow, 1-\(\upmu \)m thick, air-core is reported. A high-performance photodetection is realized by the introduction of hollow core in form of intrinsic region in the photodetection (PIN) layer within HCG-assisted narrow-core waveguide. A sufficiently high responsivity of 0.8 A/W and quantum efficiency of 64% are obtained at 1550-nm which is possible because of the presence of surface modes within HCG which get coupled in the photodetection layer leading to a strong optical confinement in that layer. High reflectivity, small penetration length and coupling of lateral surface modes in HCG make it possible to offer improved waveguiding and hence photodetection.     

一种新颖结构紧凑的AWG器件

给出一种基于SOI材料结构紧凑的新颖AWG器件,它是将一个全内反射波导镜插入原波导阵列中间,并且利用全内反射时产生的相位差进行TE、TM模偏振补偿的方法,该器件具有尺寸小、制作工艺简单等特点.同时,给出一些实验结果,实验结果证实这种结构的AWG器件是可行的.     

一种新颖结构紧凑的AWG器件

给出一种基于SOI材料结构紧凑的新颖AWG器件,它是将一个全内反射波导镜插入原波导阵列中间,并且利用全内反射时产生的相位差进行TE、TM模偏振补偿的方法,该器件具有尺寸小、制作工艺简单等特点.同时,给出一些实验结果,实验结果证实这种结构的AWG器件是可行的.     

Integrated polarization compensator for WDM waveguidedemultiplexers

An integrated polarization compensator for wavelength-division-multiplexed waveguide demultiplexers is proposed and experimentally demonstrated. It is simple to fabricate, has many advantages over previously reported polarization compensation schemes, and is effective in both etched diffraction grating and arrayed waveguide grating based devices     

Design of a Compact Photonic-Crystal-Based Polarization Channel Drop Filter

We design a compact photonic-crystal-based polarization channel drop filter (PhC-PCDF) using the triangular lattice air holes PhC, which would be an essential device in future integrated polarization and wavelength-division-multiplexed (PWDM) system. The PhC-PCDF contains two line waveguides and a resonating system between them. In the line waveguide, the transverse-electric (TE) polarization and the transverse-magnetic (TM) are guided by photonic bandgap effect and total internal reflection effect, respectively. By resonating the system, a narrow bandwidth TE polarization is dropped from one waveguide to the other, leaving other components of the PWDM signal without any disturbance. The transmission efficiency for TM polarization and TE polarization are both over 95%. The quality factor of the TE PCDF is about 1800. The whole size of the designed PhC-PCDF can be $20atimes 12a$.      

Thermal tuning of chirped SOI sidewall grating for tunable wavelength, delay, and bandwidth

In this work, we design a silicon-on-insulator (SOI) sidewall grating with tunable wavelength, delay, and bandwidth through thermal tuning. Incorporating uniform sidewall corrugations and a linearly chirped rib waveguide, the thermo-optic effect imposed on chirped rib waveguide changes the effective refractive index, due to the resultant of the temperature gradient. Consequently, tunable wavelength, delay, and bandwidth in SOI sidewall grating are achieved. In the numerical simulations, the designed SOI grating is demonstrated with a tunable wavelength from 1 560.7 nm to 1 561.9 nm, a tunable delay from 0 to 38 ps, and a tunable bandwidth from 1 nm to 1.5 nm.     

Compact and Highly Efficient Grating Couplers Between Optical Fiber and Nanophotonic Waveguides

We present high-efficiency grating couplers for coupling between a single-mode fiber and nanophotonic waveguides, fabricated both in silicon-on-insulator (SOI) and InP membranes using BenzoCycloButene wafer bonding. The coupling efficiency is substantially increased by adding a gold bottom mirror to the structures. The measured coupling efficiency to fiber is 69% for SOI grating couplers and 56% for bonded InP membrane grating couplers     

Single-mode and polarization-independent silicon-on-insulator waveguides with small cross section

The fabrication restrictions that must be imposed on the geometry of optical waveguides to make them behave as single-mode devices are well known for relatively large waveguides, with shallow etch depth. However, the restrictions for small waveguides (/spl sim/1 /spl mu/m or less in cross section) are not well understood. Furthermore, it is usually a requirement that these waveguides are polarization independent, which further complicates the issues. This paper reports on the simulations of the conditions for both single-mode behavior and polarization independence, for small and deeply etched silicon-on-insulator (SOI) waveguides. The aim is to satisfy both conditions simultaneously. The results show that at larger waveguide widths, waveguide etch depth has little effect on the mode birefringence because the transverse-electric (TE) mode (horizontal-polarized mode) is well confined under the rib region. However, at smaller rib widths, the etch depth has a large influence on birefringence. An approximate equation relating the rib-waveguide width and etch depth to obtain polarization-independent operation is derived. It is possible to achieve single-mode operation at both polarizations while maintaining polarization independence for each of the waveguide heights used in this paper but may be difficult for other dimensions. For example, a 1-/spl mu/m SOI rib waveguide with an etch depth of 0.64 /spl mu/m and rib width of 0.52 /spl mu/m is predicted to exhibit such characteristics.     

Low-Footprint Optical Interconnect on an SOI Chip Through Heterogeneous Integration of InP-Based Microdisk Lasers and Microdetectors

We present a proof-of-principle demonstration of a low-footprint optical interconnect on a silicon-on-insulator (SOI) chip. The optical link consists of a heterogeneously integrated, InP-based microdisk laser (MDL) and microdetector, coupled to a common SOI wire waveguide. Applying an electrical current to the MDL resulted in a detector current up to 1 $mu$A.      

SOI亚微米波导光栅的设计与制作

报道了SOI基亚微米小尺寸波导光栅器件的设计、制作与测试结果。提出了波导与光栅同步制作的方案,避免了套刻,节约了成本。实验中采用电子束光刻(EBL)、感应耦合等离子体(ICP)刻蚀等先进半导体工艺技术,结合图形补偿等技术手段,完成了亚微米波导光栅的制作。光栅周期为350nm,占空比16∶19。采用该光栅做反射镜,制作了法布里-珀罗(F-P)谐振腔,经测试得到了与模拟相吻合的结果,峰谷比达到11dB。     

The Temperature Dependence of Polarization-Dependent Loss for a Macrobending Single-Mode-Fiber-Based Edge Filter

The temperature dependence of polarization-dependent loss (PDL) for a macrobending standard single-mode fiber (SMF28) is investigated both theoretically and experimentally. The experimental results show an overall agreement with the proposed theoretical model over a temperature range from 0 $^{circ}$C to 70 $^{circ}$C. An SMF28-based edge filter is used as an example regarding temperature-dependent PDL performance. It is shown that the temperature variations have a significant influence on the polarization dependence of macrobending loss, and further impact on such a fiber bend loss edge filter used in a wavelength measurement application. It is also concluded that by using the proposed models, such a temperature-dependent birefringence can be beneficially predicted in bending fiber sensing applications.