Low-noise LD module with an optical isolator using a highly bi-substituted garnet film

We have developed a new type of laser diode (LD) module in the 1.3 ?m wavelength range coupled to a single-mode fibre with an optical isolator. The isolator comprises a highly Bi-substituted garnet film grown by liquid phase epitaxy (LPE) as a Faraday rotator. Since the garnet film is used also as a window of the hermetic seal of the LD, the reflection from the focusing lens used for fibre coupling is not allowed to return to the LD by the optical isolator. As a result, the reflection noise of the LD is prefectly suppressed. We have achieved a low-noise and compact LD module by using this construction.     

Microoptic grating multiplexers and optical isolators for fiber-optic communications

As new optical devices for increasing further the utility of and to expand the application of fiber-optic communications, grating multiplexers and isolators have been developed for 0.8 μm band employing microoptic approach. The development of these devices is the subject of this paper. The devices have desirable features of small size, compactness, high optical performances, and high reliability. The grating multiplexer consists of a graded-index rod, a blazed reflection grating replicated onto the graded-index rod slanting facet or a wedge facet, and an input-output fiber array. Simple calculations have been done to determine necessary element parameters for a given channel spacing. Experimental results are presented for five-channel multiplexers devised using a SELFOC^®lens. Around 3 dB insertion loss and less than -30 dB crosstalk have been obtained for about 35 nm channel spacing in overall device size of18 times 13 times 50mm. Faraday rotation optical isolators for 0.8 μm band have been miniaturized by employing an efficient paramagnetic glass Faraday rotator, a magnet with a through hole and a folded optics in the Faraday rotator. The path number in the folded optics has been optimized in terms of trading-off between the magnet size and the insertion loss. A 0.9 dB insertion loss including fiber coupling loss and 36 dB isolation have been obtained in overall device size of24 times 24.5 times 42mm. Results on the temperature and wavelength dependence of the isolation are also presented. In addition, fundamental properties of optical circulators for 0.8 μm band and optical isolators and circulators both for 1.3 μm band, developed as extended modifications of the optical isolators for 0.8 μm band, are briefly described.     

Polarization independent LiNbO3 8×8 matrix switch

A polarization-independent LiNbO₃ strictly blocking 8×8 matrix switch has been developed. A relatively low insertion loss, below 12 dB, has been obtained by a reduction in bending loss, using a wide bent waveguide width. The switch has less than -18.7-dB crosstalk and about 85-V switching voltage at any incident polarization with 1.3-μ wavelength light     

光纤传输用的磁光隔离器

本文报导了光纤通信用光隔离器的研究工作.隔离器由稀土铁石榴石法拉第旋转器及两只方解石棱镜组成.在波长为1.15微米时,器件插入损耗为2.4分贝,隔离比为34.8分贝.讨论了使用不同的复合稀土铁石榴石材料及采用不依赖偏振光技术对器件性能的改进.     

Fiber-embedded in-line isolator

A fiber-embedded optical isolator with a low forward loss has been developed. The isolator consists of thermally diffused expanded core fibers, laminated polarizers, and a Faraday rotation garnet. Backward and forward losses at 1.3 μm wavelength are 44.0 and 0.9 dB, respectively. The isolator has a minute size, and its alignment is simple     

Wavelength-division-multiplexing optical switch using acoustooptic deflector

A new wavelength-division-multiplexing (WDM) optical switch using an acoustooptic deflector (AOD) is presented. This switch requires minimal hardware and is highly applicable in high-speed signal switching. Theoretical calculations based on the Gaussian beam approximation show that up to a 20 × 20 switch is possible using present technology. As a preliminary study, a 3 × 3 WDM switch is constructed. Crosstalk of this switch is found to be less than -20 dB, and a 500 Mbit/s return to zero (RZ) signal is successfully switched with a 4-μs switch access time. A large capacity switching network using this WDM optical switch is proposed.     

一种新型偏振相关磁光隔离器的设计

该文介绍了一种新型的光纤型法拉第磁光隔离器设计方法,利用液相外延制备的单晶石榴石(BiTm)3(GaFe)5O12膜作为法拉第转子,通过对光路结构的改进设计,有效降低了光隔离器体积和所需饱和外场。当外磁场H=47×103 A/m时,法拉第旋角可达到45°@1 550 nm,光吸收系数为15 cm-1 @1 550 nm,光透射率为85%@1 550 nm,整体满足设计要求。     

Fibre-embedded optical isolator

A fibre-embedded optical isolator without a lens element is proposed and fabricated. The isolator consists of beam-expanding fibres, laminated polarisers and a Faraday rotation garnet. Backward and forward losses at 1.3 mu m wavelength are 36.9 and 1.6 dB, respectively.<>     

Radiative optical isolator and circulator

A novel radiative optical isolator and a circulator are discussed in this paper. It is numerically estimated that with λ=1.3 μm, 45-dB isolation ran be achieved with an isolator of 8 mm in length. For a 21.5-mm-long 4-port circulator, the achievable isolation is about 45 dB, with approximately 1-dB insertion loss     

High-Speed High-Isolation 2$, times ,$2 Fiber-Optic Switch for Wideband Radar Photonic Beamforming Controls

A new high-performance 2$, times ,$2 fiber-optic switch is designed and demonstrated for wideband radar photonic beamforming controls. The switch deploys two bulk acoustooptic deflectors (AODs) in an imaging free-space symmetric optical design that exploits image inversion control via a Dove prism to form a 2$, times ,$2 fully reversible low crosstalk noise high-speed switching structure. Experiments at the 1550-nm test wavelength show the switch to handle 0.5-W level optical input powers, $≪ {hbox{2.2-}}mu$s switching time, $≪ $2.6-dB fiber-to-fiber optical loss, better than 56-dB optical crosstalk levels, and $≪$0.2-dB polarization-dependent loss (PDL).      

Transmission characteristics of a single-mode fiber in the 1.3-µm wavelength region

Transmission characteristics of 1.3-μm-band single-mode optical fibers were studied experimentally and theoretically. OH-ion content dependence of optical loss in the 1.3-μm region was investigated on single-mode fibers fabricated by the VAD method. The optical loss was evaluated for OH-ion content by calculating correlation factors between the optical loss and 1.39-μm OH-peak absorption loss. It was clarified that the optical loss calculated by correlation factors agreed approximately with the loss given by Lorentzian absorption in case of 0.0253-μm absorption half width, Next, the relationship between chromatic dispersion and fiber parameters was studied for step-index single-mode fibers. It was found that the zero-dispersion wavelength and the incline at the wavelength was expressed as simple functions of effective cutoff wavelength and relative index difference. Experimentally obtained zero-dispersion wavelengths on single-mode fibers fabricated by the VAD method were found to be in excellent agreement with the calculated values.     

光隔离器原理的数学描述

利用琼斯矢量及琼斯矩阵、描述了光隔离器的原理，并分析了法拉第旋光器旋光角的精度以及两只偏光镜相对方位角的精度对光隔离器插入损耗的隔离度的影响。     

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     

一种微型宽带光隔离器的设计研制

文章提出了一种小型化光隔离器的设计方案,通过理论分析其实现原理以及各个光学参数,并由实验证实了该方案的有效性。设计结果表明,在保证获得优良参数情况下,采用该方案能使光隔离器结构更紧凑,且有效降低其成本和装配难度。通过1／4波片及全波片对法拉第旋光片的旋光色散特性补偿后,可使该器件的隔离度参数随波长变化不敏感,此外,由于采用对称的光路设计,该方案的偏振模色散理论值为0,无需额外补偿。     

Traveling wave optical modulator using a directional coupler LiNbO3waveguide

Fabrication methods for low drive voltage and broad-band LiNbO3waveguide directional coupler optical modulator are described. Optical waveguides were prepared by conventionaly Ti in-diffusion into LiNbO3c-cut plate. To obtain wide-band frequency response, traveling wave electrodes were used. Electrode characteristic impedance measured by time domain reflectometry method coincided well with the calculated value by conformal mapping. Measured electrode conductor losses followed square root of frequency. To reduce electrode conductor losses, asymmetric and 3-μm thick Al electrodes were used. Directional coupler optical modulator frequency response was analyzed, using the phase difference average value along the propagation directions. Calculated value by this method coincided well with measured value obtained by a swept frequency technique. The characteristics of this modulator at the 1.317-μm wavelength are as follows: 100 percent modulation voltage is 4 V, extinction ratio is 17 dB, optical insertion loss is 5.4 dB, 3-dB bandwidth is 3.6 GHz, and rise time is about 400ps.     

Loss increase for optical fibers exposed to hydrogen atmosphere

Loss spectrum changes for optical fibers exposed to a hydrogen atmosphere in the15-200degC temperature range are measured. Loss increase due to molecular hydrogen dissolved into fibers is investigated from the loss peak at 1.24 μm, and that due to hydroxyl group formation from the loss peak at 1.41 μm. The loss increase due to molecular hydrogen is fully explained by physical solubility theory and diffusion equation. The empirical formula for time, temperature, and hydrogen-pressure dependences of the loss increase due to hydroxyl group formation is evaluated from the experimental results. The loss increase at 1.3- and 1.5-μm wavelength band at room temperature are estimated.     

InGaAsP/InP 1.3-µm wavelength surface-emitting LED's for high-speed short-haul optical communication systems

Performance and reliability for InGaAsP/InP 1.3-µm wavelength high-speed surface-emitting DH light emitting diodes (LED's) have been investigated. High-speed and high-radiance performances were obtained by the optimal design of both structural parameters and LED driving circuit. Rise and fall times were both 350 ps and peak optical power coupled to a 50-µm core 0.20 NA graded-index fiber at the 100-mA pulse current was - 15.8 dBm with 6-dB optical ON/OFF ratio. A 2-Gbit/s non-return-to-zero (NRZ) pulse transmission over a 500-m span was carried out, Feasibility of using surface-emitting LED's in a high-speed optical communication system has been confirmed. Accelerated aging tests on high-speed LED's were carried out. The half-power lifetimes have been estimated to be more than 1 × 10⁸h at 50°C ambient temperature.     

An effective nonreciprocal circuit for semiconductor laser-to-optical-fiber coupling using a YIG sphere

A practical nonreciprocal optical circuit for laser-diode (LD)-to-optical-fiber coupling in the 1.3-μm wavelength region is described. It consists of a yttrium iron garnet- (YIG) sphere graded-index (GRIN) rod lens and a polarizer. The YIG sphere can function not only as a Faraday rotator but also as an effective coupling lens. High coupling efficiency of more than -5 dB for a single-mode fiber, and more than -2 dB for a multimode fiber, is easily achievable. Alignment sensitivities and coupling characteristics of the proposed circuit are also discussed theoretically and experimentally. The increase in LD relative intensity noise (RIN), caused by light injected into the LD, is estimated using the reciprocal characteristics of LD-to-single-mode-fiber coupling. By comparing the LD-RIN increase in the proposed non-reciprocal circuit with that of the reciprocal, high isolation of about 32 dB is confirmed. The fact that reflected light from the proposed circuit has little influence on LD characteristics is also clarified.     

Simple polarisation-independent optical circulator for optical transmission systems

A simple polarisation-independent optical circulator has been developed. The circulator consists of a 45°Y3Fe5O12 rotator and a quartz rotator and two polarising beam-splitting cubes. Measured insertion loss was about 1.3 dB at 1.32 ?m wavelength. The circulator was connected to graded-index multimode fibres using rod lenses.     

10-Gb/s error-free transmission under optical reflection using isolator-free 1.3- /spl mu/m InP-based vertical-cavity surface-emitting lasers

Error-free transmission through 10-km single-mode fiber at 10 Gb/s under -13-dB optical reflections has been demonstrated for the first time using a directly modulated 1.3-/spl mu/m InP-based VCSEL without any optical isolator. The 13-GHz relaxation oscillation frequency and stable polarization suppresses relative intensity noise degradation under optical reflection. Only 1-dB error-free power penalty has been observed with optical reflection set with the worst polarization direction.