Pigtailed single-mode fiber optic light modulator in silicon

The performance of a light modulator at a 1.3 μm wavelength based on the plasma effect in silicon is described. The modulator is directly coupled to a single-mode fiber pigtail in a simple and robust package. The measured modulation index is 24% with a 3-dB bandwidth of 60 MHz, and the insertion loss is 5 dB. This modulator has applications in data acquisition from silicon sensors and other silicon ICs     

1.5-μm-band optical time domain reflectometer for single-modeoptical fiber using a P2O5-highly-doped fiberRaman laser

A wide-dynamic-range 1.5-μm-band optical time-domain reflectometer (OTDR) for single-mode optical fibers using a P₂O₅-highly-doped fiber Raman laser light source and a cooled Ge-p-i-n photodiode is realized for the first time. The stimulated-Raman-scattering properties of P₂O₅-doped single-mode fiber are investigated. Using this fiber and an Nd:YAG laser operating at 1.32 μm, a high-power light pulse at 1.59 μm is generated with high efficiency. Using the stimulated-Raman-scattering light as the light source and a high-sensitivity optical receiver, a 1.5-μm-band OTDR having a one-way dynamic range of 35 dB is realized     

Holographic optical switching: the “ROSES” demonstrator

The design, assembly, and performance of a prototype 1×8 free-space switch demonstrator using reconfigurable holograms are reported. Central to the switch fabric is a ferroelectric liquid crystal (FLC) on silicon spatial light modulator (SLM) deposited with a 540×1 array of highly reflective and planar mirror strips. The input and output ports of the switch are fabricated as a linear array of silica planar waveguides connected to single-mode fibers, and the holographic beam-steerer operates without the need for adjustment or dynamic alignment. The waveguide array and the single Fourier transform lens for the 2f holographic replay system are housed in an opto-mechanical mount to provide stability. The switch operates at 1.55 μm wavelength and has a designed optical bandwidth of >60 nm. The first measured insertion loss and crosstalk figures are 16.9 dB and -19.1 dB, respectively. Improvements in SLM performance, the use of new addressing schemes and the introduction of better alignment techniques are expected to improve these figures considerably. The preliminary performance of a 3×3 optical crossconnect is also presented to show that this technology is scalable to N×N switching fabrics     

Fabry-Perot optical intensity modulator at 1.3 mu m in silicon

A new type of all-silicon surface-normal optical intensity modulator at 1.3 mu m is reported. It can be easily butt-coupled with a cleaved single-mode fiber. The device utilizes free-carrier effects in silicon to achieve phase modulation and a built-in Fabry-Perot cavity to convert the phase modulation into intensity modulation. A 10% modulation depth with a driving current density as low as 6*10/sup 3/ A/cm/sup 2/ was demonstrated. Because it can be easily coupled with single-mode fiber, and at the same time it is compatible with silicon technology, this device can provide an interface between silicon electronic circuitry and fiber optics in applications such as the fiber-to-home return link where system cost is a deciding figure.<>     

100 MHz-bandwidth response of a fiber phase modulator with thinpiezoelectric jacket

100 MHz-bandwidth response of an all-fiber phase modulator composed of a single-mode optical fiber jacketed with a 10 μm-thick vinylidene fluoride/trifluoroethylene copolymer, radially poled is presented. Multiple peaks of optical phase shifts induced are observed over the frequency range of 10-100 MHz and ascribed to radial resonances of a fiber-jacket composite. The theoretical analysis of phase shifts is performed based on vibration theory of elasticity taking the exact geometry and composition of the cylindrical multilayer structure into account. The analysis also shows that the phase modulation is strongly dependent on jacket thickness and the maximum induced phase shift will be obtained in the 100 MHz region when the jacket is chosen to be thin as 0.7 μm     

The performance limit of coherent OTDR enhanced with optical fiberamplifiers due to optical nonlinear phenomena

This paper theoretically and experimentally clarifies the limit of incident optical pulse power in coherent optical time-domain reflectometry (C-OTDR) enhanced with optical fiber amplifiers. The critical pulse power, at which the performance of C-OTDR is degraded by the effect of optical nonlinear phenomena in a single-mode optical fiber, depends on the amplified optical pulse waveform and the pulse width. For a pulse width of 1 μs or longer, the incident pulse power is limited by the effect of self-phase modulation (SPM). When an optical pulse having a power gradient within the pulse width is incident to a single-mode optical fiber, the optical frequency of the backscattered signal is shifted by SPM, and the center frequency of the signal moves outside the receiver band, so the sensitivity of C-OTDR is degraded. For a pulse width of 100 ns, the incident optical pulse power is limited by four-wave mixing (FWM) which transfers the energy from the incident optical pulse to Stokes and anti-Stokes light as a result of the interaction between the incident optical pulse and amplified spontaneous emission. This paper also demonstrates the high performance of C-OTDR enhanced with EDF A's with 48, 44, 39, and 29 dB single-way dynamic ranges for pulse widths of 10 μs, 4 μs, 1 μs, and 100 ns, respectively, limited by the effect of SPM or FWM. These results are believed to be the best performance of C-OTDR with EDFA's     

Germanium-diffused waveguides in silicon for λ=1.3 μm andλ=1.55 μm with losses below 0.5 dB/cm

The authors present a simple technique for the fabrication of integrated optical channel waveguides that are prepared by indiffusion of an E-beam evaporated amorphous alloy of germanium and silicon into commercially available silicon with low dopant concentration, using only simple technological processes such as standard lithography, PVD, and diffusion. The waveguides are polarization independent and have waveguide losses as low as 0.3 dB/cm at wavelengths of λ=1.3 μm and λ=1.55 μm. The spot sizes are well suited for low-loss single-mode fiber device coupling, being on the order of a few microns in both horizontal and vertical directions     

Precision fabrication of D-shaped single-mode optical fibers by insitu monitoring

A technique has been developed to locally remove, over a distance of several millimeters of fiber length, the cladding layer of single-mode (at the 1300 nm wavelength) optical fibers with 1 μm depth precision by use of mechanical lapping and in situ optical transmission monitoring. A cylinder lap dressed with diamond is used to perform high-pressure mechanical lapping. The in situ monitoring technique is based on the specific different attenuations exhibited by higher order propagating modes (for 633 nm light) as the cylinder penetrates into the fiber. Advantages include relatively rapid overall processing, high lapping rate, good optical surface quality, and 1 μm precision. Experimental results are presented and analyzed by an approximate geometrical-optics model     

High-speed InGaAlAs/InAlAs multiple quantum well electrooptic phasemodulators with bandwidth in excess of 20 GHz

High-speed phase modulation (in the frequency bandwidth of 20 GHz, the highest yet reported for multiple quantum well (MQW) phase modulators) for waveguided InGaAlAs/InAlAs MQW optical modulators is reported. The modulator successfully operates at a long wavelength of 1-55 μm with a low required voltage for phase shift (Vπ=3.8 V), small intensity modulation depth below 1.5 dB, and without any modulation bandwidth degradation up to 20 GHz under high input optical power of 0 dBm in single-mode fiber     

Silicon thermooptical micromodulator with 700-kHz -3-dB bandwidth

A silicon Fabry-Perot waveguide modulator, operating at the fiber optic communication wavelengths of 1.3 and 1.55 μm, has been entirely fabricated using microelectronic techniques. The planar optical cavity has been defined by plasma etching and has a length of 100 μm. The device, based on the thermooptic effect, is electrically driven and exhibits a maximum modulation depths of 60%. The measured -3 dB bandwidth is 700 kHz, which is by far the best result ever reported, to our knowledge, for thermooptic effect based modulators     

Nd-doped double-clad fiber amplifier at 1.06 μm

We propose and demonstrate a double-clad neodymium (Nd)-doped fiber amplifier (IVDFA) at 1.06 μm for a compact configuration of a high-power optical amplifier. The proposed 125 μm first cladding diameter in the double-clad fiber, provides the single-mode propagation of the signal lightwave into its doped core without misguiding the signal lightwave into the outer core (first cladding), by simply splicing with a standard single-mode fiber. Furthermore a fiber grating in a single-mode core of the double-clad fiber allows the double-pass configuration for the signal lightwave at 1.06 μm and also allows the pump lightwave coupling at 0.81 μm into the first cladding without employing a bulk dichroic mirror. We demonstrate the signal output power of 110 mW for a 550-mW pump input from a multimode fiber coupled pump source. Theoretical results predict an efficient high-power operation of the amplifier by improving the signal scattering loss in the double-clad fiber     

Micromechanical fiber-optic attenuator with 3 μs response

Optomechanical fiber-optic attenuators are bulky and slow. The mechanical antireflection switch (MARS) modulator offers a high-speed alternative for applications including dynamic gain control in fiber amplifiers. This paper describes a compact electrically controlled variable attenuator using a micromechanical device where electrostatic deflection of a silicon nitride quarter-wave dielectric layer suspended over a silicon substrate creates a variable reflectivity mirror. This device is packaged with two fibers in one ceramic ferrule placed in contact with a gradient index (GRIN) collimation lens, so that the input light reflects from the modulator in the collimated beam plane and couples into the output fiber. Using a 300 μm diameter MARS attenuator and a 500 μm diameter collimation lens, the total insertion loss at 1550 nm was 3.0 dB with no applied voltage, increasing to 31 dB at 35.2 V. The polarization dependent loss was less than 0.06 dB. Full attenuation with more than 100 mW input power produced no damage. The response time was 2.8 μs to move from maximum to minimum transmission and 1.1 μs to return to maximum transmission     

A polarization-independent silicon light intensity modulator for1.32 μm fiber optics

The authors have developed an integrated silicon light intensity modulator based on polarization-independent free-carrier optical phase modulation and mode filtering in fibers. A novel push-pull complementary diode pair are used for a twofold increase in modulation depth over a single diode device. Operation is demonstrated at a wavelength of 1.32 μm     

5-Gb/s performance of integrated light source consisting ofλ/4-shifted DFB laser and EA modulator with SI InP BH structure

The fabrication process and characteristics, including 5-Gb/s transmission, of an integrated light source consisting of a λ/4-shifted distributed feedback laser and an electroabsorption (EA) modulator are discussed. By introducing a semi-insulating (SI) InP on the butt-joint region, both the large electrical isolation resistance (>10 MΩ) between the laser and the modulator and a high optical coupling efficiency (>80%) between them are achieved. A typical threshold current was 50-70 mA, and single-mode operation at 1.576 μm was maintained up to 5.5-mW output power. The modulation voltage to swing between 90% transmission and 10% transmission was 6.2-12 V, depending on the modulator length in the range 1000-400 μm. The 3-dB bandwidth is 7.7 GHz and a linewidth enhancement factor (α) of 0.9 is estimated from the sideband-to-carrier ratio of the spectra     

Method of measuring optical switch crosstalk attenuationconsidering polarization variation

This paper describes a simple method for measuring the crosstalk attenuation of optical switches that takes into account the polarization variation of incident light. The method involves the use of a laminated film polarizer (LAMIPOL) and a polarization-maintaining fiber (PANDA). Crosstalk attenuation of 2×2 liquid-crystal optical switches for 1.3 μm single-mode fiber is measured using the proposed method and then conventionally with a polarization controller. The similarity of the results confirms the practicality of the proposed method     

Silicon optical modulators at 1.3-μm based on free-carrierabsorption

Silicon optical waveguide modulators, appropriate for operation in the 1.3-1.55 μm wavelength region, have been fabricated and their performance characterized at the wavelength of 1.3 μm. The modulator structures consist of p-i-n diodes integrated with silicon waveguides; device operation is based on free-carrier absorption. Modulation depths of -6.2 dB and response times less than 50 ns have been measured. Experimental results are compared with the p-i-n diode theory. It is argued that the device is suitable for integration with silicon electronics and silicon optoelectronic devices. The response times measured for the current devices may be improved by reducing the transverse dimensions of the p-i-n structure     

Laser-to-fiber coupling scheme by utilizing a lensed fiberintegrated with a long-period fiber grating

An optical coupling scheme between a laser diode and a single-mode fiber utilizing a lensed fiber integrated with a long-period fiber grating is experimentally demonstrated and qualitatively analyzed. A long working distance of 110 μm and a coupling of 35% are obtained for a laser diode with an ellipticity of 2.5. The longitudinal and transverse tolerances at 1-dB excess loss are 26 and 2.5 μm, respectively     

Integrated optical switches in silicon based on SiGe-waveguides

The realization of switches in silicon base on monomode Ge-indiffused SiGe waveguides is reported. At a wavelength of 1.3 μm a Mach-Zehnder interferometer switch with a modulation depth of -10 dB at a current of 150 mA is obtained. This is the lowest value reported so far for single-mode optical switches in silicon     

A polarization independent GaAs-AlGaAs electrooptic modulator

Two designs for polarization independent GaAs-AlGaAs interferometric electrooptic modulators are described. One design uses the linear electrooptic effect to couple degenerate TE/TM eigenmodes of a single-mode waveguide. In the other design the eigenmodes need only be near degenerate. The design using the coupling between near degenerate TE/TM modes utilizes a novel biasing scheme. A novel polarization independent GaAs-AlGaAs interferometric optical modulator based on this design has been fabricated and characterized at 1.3 μm. This modulator is fabricated as a traveling wave modulator incorporating 50 Ω, phase velocity matched, low microwave loss electrodes for maximum electrical bandwidth     

All-fiber phase-modulated master oscillator power amplifier forcoherent communication

An all-fiber phase-modulated master oscillator power amplifier for free-space coherent communication is presented. A distributed-feedback fiber laser at 1.06 μm is used as master oscillator. A novel phase modulator based on a ZnO-coated single-mode fiber modulates the single frequency communication signal. The modulated signal is then amplified in a double-clad doped fiber power amplifier. Up to 1 W cw single-frequency output power, phase modulated at 196 MHz, has been obtained