Nonreciprocal circuit for laser-diode-to-single-mode-fibre coupling employing a YIG sphere

A compact nonreciprocal optical circuit for laser-diode-to single-mode-fibre coupling using a YIG sphere is proposed in the 1.3 ?m wavelength region. It is clarified that the YIG sphere can function as an effective Faraday rotator as well as a coupling lens. A high isolation value of more than 30 dB has been realised with coupling efficiency of ?5.2 dB for a single-mode fibre.     

Distributed feedback laser diode (DFB-LD) to single-mode fiber coupling module with optical isolator for high bit rate modulation

A distributed feedback laser diode (DFB-LD) module for single-mode fiber coupling is described in the 1.5-μm wavelength region. An optical isolator is constructed in the two lens coupling circuit to stabilize the DFB-LD characteristics. It consists of a DFB-LD as a polarizer, a yttrium iron garnet (YIG) plate and an analyzer. Coupling characteristics and attainable isolation of the proposed circuit have been studied theoretically and experimentally. The effect of reflected light on the DFB-LD characteristics such as relative intensity noise (RIN) and oscillation spectrum has been experimentally investigated taking into account the polarization of the reflected light. It has been clarified that the DFB-LD can function as an effective polarizer with an extinction ratio of more than 20 dB. The DFB-LD module was successfully fabricated to have stable spectrum characteristics and to sufficiently suppress the noise caused by reflections. It has been confirmed by a long haul transmission experiment that this module is applicable to large capacity optical fiber transmission systems.     

A compact optical isolator with a plano-convex YIG lens forlaser-to-fiber coupling

An optical isolator for laser-to-single-mode fiber coupling is discussed. The coupling unit consists of a confocal two-lens system with a spherical glass lens and a planoconvex lens which is made of yttrium iron garnet (YIG). To minimize the number of elements, the YIG lens is used as a Faraday rotator as well as a coupling lens. Nevertheless, the planoconvex YIG lens satisfies the requirements of high coupling efficiency, high isolation, and low optical feedback from the Faraday rotator. The arrangement is theoretically and experimentally investigated. At a coupling efficiency of 34%, the total optical feedback into the laser diode was measured to be about -60 dB     

Low-loss laser diode module using a molded aspheric glass lens

The fabrication and characteristics of a 1.3-μm laser diode (LD) module for single-mode fiber using a molded aspheric glass lens is discussed. An average coupling loss of 2.2 dB with a standard deviation of less than 0.5 dB after thermal heat cycling tests was achieved. The average assembly loss was 0.24 dB. The LD module demonstrated stability during thermal and heat cycling tests from -10 to 60°C     

Optical coupling characteristics of laser diodes to thermally diffused expanded core fiber coupling using an aspheric lens

A discussion is presented of the optical coupling characteristics of a 1.3 mu m laser diode to a thermally diffused expanded core (TEC) single-mode fiber coupling using an aspheric lens. The misalignment tolerance width for a 0.5 dB loss increment of the expanded core fiber was enlarged to 8.4 mu m from 1.9 mu m of a nonexpanded core fiber without a remarkable coupling-loss increase. The TEC fibers will make the LD module assembly easier, and reduce the assembly cost.<>     

激光成像系统中高耦合效率单模光纤耦合器设计

在三维激光成像系统中,其性能表现绝大部分决定于器件接收背反射光能幅度的大小,以及耦合器中空间光到光纤纤芯的光耦合效率的高低.为了增加耦合器中激光能量到纤芯内的耦合效率,提出了一种新型非球面透镜到锥形光纤头的耦合器的设计,得到了该耦合器中耦合效率的解析表达式.通过优化耦合透镜的倒相对孔径,对应波长为1 310 nm和1 ...     

YIG Oscillators: Is a Planar Geometry Better? (Short Papers)

Two yttrium-iron-garnet (YIG) oscillator technologies are compared: the more mature YIG sphere oscillator technology which is based on the uniform (resonant) precession of the electron spins in a small sphere of YIG, and the new planar YIG technology which utilizes the propagation of magnetostatic waves in an epitaxial film of YIG. The YIG sphere technology has been used for microwave oscillators for more than 25 years, but has two significant areas of difficulty in applications the alignment of the YIG sphere in the magnetic bias field coupling cavity requires great precision and the gain element requires a negative resistance element to sustain oscillation. The MSW technology is much newer and less well understood, but the resonator elements are fabricated using a 50- µm line width planar technology making it an appealing candidate. Both technologies are reviewed herein with regard to resonant element theory, temperature, and noise characteristics. New data and theory are presented on MSW resonator optimization.     

Design and Characterization of Taper Coupler for Effective Laser and Single-Mode Fiber Coupling With Large Tolerance

A new method of coupling the light from a laser diode (LD) to a single-mode fiber with large alignment tolerances and without using any coupling lens is presented. A pseudovertical tapered coupler on silicon substrate which has an input aperture of about 100 times the size of the laser waveguide cross section is designed. Results showed that the coupler relaxes the LD placement tolerance and eliminates the use of a coupling lens. The positional tolerance between the LD and taper coupler can be larger than +/- 5 mu m in the xy plane, and +/-1 ^deg in orientation.     

YIG Resonator Circuit with Isolator Property and its Application to a Gunn Diode Oscillator

This paper presents the analysis and experiment of a newly developed YIG resonator circuit with isolator property, which is constructed with a YIG sphere, three coupling loops, and a 3-dB stripline directional coupler. This YIG circuit can be used advantageously as the toning element of a magnetically tunable oscillator. The circuit has an advantage in preventing frequency pulling and the variation of output power level of the oscillator due to a change in load condition because of the resonator circuit having isolator property at the same time. The design procedure and experiment of a magnetically tunable Gunn diode oscillator with the YIG circuit is also shown. It has been confirmed that the YIG circuit when applied to a tunable oscillator is quite useful.     

A new scheme of a lensed fiber employing a wedge-shapedgraded-index fiber tip for the coupling between high-power laser diodesand single-mode fibers

A novel lensed fiber employing a wedge-shaped graded-index fiber (GIF) is proposed. The characteristic of coupling loss as a function of the aspect ratio is numerically investigated. When the aspect ratio is seven, the coupling loss of a wedge-shaped GIF and a conventional wedge-shaped SMF are 0.22 dB and 0.60 dB, respectively, and when the aspect ratio is 13, they are 0.5 dB and 2.4 dB. The tolerance to laser diode (LD)-fiber displacement is also numerically investigated, and it is confirmed that the proposed fiber has larger tolerance than a conventional wedge-shaped single-mode fiber (SMF). The performance of the new lensed fiber is also experimentally verified     

基于偏振复用技术的激光二极管光纤耦合方法

光纤耦合输出的高功率激光二极管(LD)模块作为光纤激光器的抽运源已经得到了广泛应用。为了进一步提高光纤耦合激光二极管输出功率,提出了利用激光二极管输出光束的线偏振特性,采用偏振复用技术,将两只高功率激光二极管输出光束经准直、复合、聚焦的光纤耦合方法。利用光线追迹法,分析了圆柱透镜对激光二极管发散光束的准直特性,并讨论了柱透镜的安装距离对准直性能的影响。根据激光二极管和光纤的相关参数设计了聚焦透镜组。采用这种方法将两只输出波长为980 nm的高功率激光二极管输出光束耦合进数值孔径0.22,芯径100μm的多模光纤中,当工作电流为4.5 A时,光纤激光连续输出功率为6.36 W,耦合效率大于78%。     

光子带隙光纤准直器回波损耗研究

研究了一种光子带隙光纤准直器。为了降低回波对光源的干扰,通常光纤准直器的回波损耗不应低于60 dB。由于带隙光纤端面没有反射,因此满足这一条件的带隙光纤准直器GRIN透镜入射面的倾斜角与普通光纤准直器不同。从高斯光束通过光学系统的一般模型出发,利用矩阵光学和高斯光束耦合理论,推导了光线传输矩阵。结合实际应用中光纤及GRIN透镜的参数,仿真分析了尾纤与GRIN透镜之间的间距及GRIN透镜的参数对准直器回波损耗的影响。结果表明,镀有增透膜时,当光子带隙光纤准直器的GRIN透镜入射面倾角等于3时,回波损耗大于60 dB。研究结果对进行光子带隙光纤准直器的设计具有指导意义。     

Single-mode fiber WDM unit for duplex subscriber link using asubstrate with embossed alignment grooves

A wavelength division multiplexing (WDM) unit for single-mode fiber (SMF) duplex transmission, with light source, photodiode (PD), and WDM coupler arranged on a common substrate, is described. Using a tolerant optical design, the optical elements, e.g. lenses and fibers, are positioned in embossed high-precision V grooves without active adjustments. Only the light source, a laser diode (LD) or an edge-emitting LED (ELED), must be aligned for optimum coupling and fixed by laser welding. Typical values of LD-to-fiber and fiber-to-PD coupling loss and crosstalk are 5 dB, 1.2 dB, and -44 dB, respectively. Hence, in spite of the potentially low-cost design, the optical performance of the device is virtually competitive with separated transmitter and receiver units     

Integration of magnetooptical waveguides onto a III-V semiconductorsurface

Optical waveguides fabricated on a yttrium iron garnet (YIG) substrate are integrated onto a semiconductor surface by using ridge waveguides patterned onto a prefabricated recess in the YIG surface. The recess separates the waveguides from the semiconductor substrate with an air-gap. This structure makes it possible to avoid coupling light within the YIG waveguides into the semiconductor substrate which has a higher refractive index. The excess optical loss due to the coupling can be as low as ⩽0.1 dB/cm with a 1-μm-wide air-gap. The calculated coupling loss is confirmed by comparing the guided TE and TM modes     

High coupling optical design for laser diodes with large aspectratio

We have designed and performed the optical modeling of a cruciform cylindrical lens to replace the corrective lens in a confocal optical system and demonstrated a coupling efficiency of 85%. This represents more than 3 dB improvement over the conventional confocal system of single mode fiber coupling for 980 nm pump lasers. Also, the fiber alignment tolerance is about three times more relaxed than that of the wedged fiber lens     

LD Redundancy System Using Polarization Components for a Submarine Optical Transmission System

An LD redundancy system having one cold standby laser diode is proposed to improve reliability in submarine optical transmission systems. This system makes use of the intrinsic laser polarization and consists of two LD modules and a polarization coupler connected by polarization maintaining (PANDA) fibers. The optical power insertion loss of this LD redundant system is 5.5 dB, including coupling loss between the laser diode and PANDA fiber. This LD redundant system will be applied in submarine optical repeaters.     

LD redundancy system using polarization components for a submarine optical transmission system

An LD redundancy system having one cold standby laser diode is proposed to improve reliability in submarine optical transmission systems. This system makes use of the intrinsic laser polarization and consists of two LD modules and a polarization coupler connected by polarization maintaining (PANDA) fibers. The optical power insertion loss of this LD redundant system is 5.5 dB, including coupling loss between the laser diode and PANDA fiber. This LD redundant system will be applied in submarine optical repeaters.     

Analysis and design of a novel leaky YIG film guided wave opticalisolator

A guided wave optical isolator using a four layered leaky yttrium iron garnet (YIG) waveguide with a YIG guiding layer is proposed and analyzed through a transfer matrix formulation. The dependence of isolation characteristics on different waveguide parameters are discussed. It is shown that for four layered structures an isolation ratio of about 24 dB can be achieved with YIG films having large gyrotropy. It is also shown that by replacing the single guiding YIG film with multilayers of YIG with compensated walls and proper permittivity, high isolation ratio can be achieved even with currently available YIG films having low gyrotropy     

微波场效应管YIG振荡器的实验研究

本文扼要叙述了单YIG小球双调谐场效应管振荡器的设计及其优点。在2.2～4.8GHz的振荡频率范围内,输出功率大于10mW。在2.2～4.4GHz的倍频程带宽内,输出功率大于20mW,功率起伏小于3dB。     

激光二极管与单模保偏光纤的耦合研究

给出了一种处理激光二极管经透镜与单模保偏光纤耦合的精确方法,测量了半导体激光器的光束质量,对其光束的收集、准直、整形、聚焦和耦合进入光纤进行了实验研究,同时测量了整形系统和光纤的定位灵敏度.对球面微透镜光纤与激光二极管耦合的方法进行了理论分析,讨论了透镜参数、耦合形式、激光二极管波像散对耦合效率和特性的影响,给出了2种实际耦合系统的实验计算结果,并与理论计算作了比较,结合实验得到了微透镜的优化参数,且将结果应用到了激光二极管与单模保偏光纤耦合实验中,得到了总的耦合效率为36%.