Picosecond pulse amplification in tapered-waveguide laser-diodeamplifiers

The amplification characteristics of picosecond Gaussian pulses in conventional nontapered and both linear and exponential tapered-waveguide (TW) laser-diode amplifier (LDA) structures have been studied. The analysis is based on numerical simulation of the rate equation which also takes into account the effect of lateral carrier density distribution. The amount of pulse distortion experienced within the amplifier for input pulses having energies E_in=0.1 E_sat(in)=0.475 pJ (where E_sat(in) is the input saturation energy of the amplifier) and E_in=E_sat(in) =4.75 pJ have been analyzed for each structure which has a length of 900 μm and an input width of 1 μm. It has been found that the TW-LDA provides higher gain saturation and hence imposes less distortion on the amplified pulse as compared with a conventional nontapered LDA. The amplified 10-ps pulse used in this study experiences almost no broadening in the TW-LDA, whereas it suffers from broadening in the conventional nontapered LDA. The carrier density distribution and the dependence of the amplifier gain on the input pulse energy have also been studied for both nontapered and tapered amplifier structures. For example, in a TW-LDA with an output width of 20 μm and a length of 900 μm, the exponential structure provides 9-dB improvement in saturation energy as compared with the conventional amplifier. This improvement is about 10.5 dB in linear TW-LDAs     

Electromagnetic torsion mirrors for self-aligned fiber-opticcrossconnectors by silicon micromachining

We report a micromechanical fiber-optic switch (1 cm×1 cm×1 mm) based on an electromagnetically operated torsion mirror which is suitable for self-latching operation. The switch is fabricated by silicon micromachining technology, and self-alignment technique is employed to align optical fibers to the mirror. A small mirror of gold finished FeNiCo/polysilicon (150 μm×500 μm) is supported by two beams, and rotated around the axis in the magnetic field induced by an electromagnet. An incident light is redirected by the mirror in a free-space smaller than 1 mm³. Multimode fibers are used for optical coupling of small loss (-2.5 dB for reflection and -0.83 dB for transmission) at a wavelength 1.55 μm. Typical switching time is 10-25 ms, and switching contrast is larger than 45 dB. Magnetic torque and optical coupling are theoretically investigated     

Monolithically integrated semiconductor optical amplifier andelectroabsorption modulator with dual-waveguide spot-size converterinput

We have demonstrated a semiconductor optical amplifier and electroabsorption modulator monolithically integrated with a novel dual-waveguide spot-size converter at the input for low-loss coupling to planar lightguide circuit silica waveguides or cleaved single-mode optical fiber. These devices exhibit greater than 10 dB fiber-to-fiber gain, output power of +4 dBm, 3-dB modulation bandwidth of 6 GHz, and modulator extinction ratios of 20 dB dc and 14.4 dB RF for a 2.4-V_pp drive     

Transmission properties of hollow glass waveguides for the deliveryof CO2 surgical laser power

Hollow glass waveguides are an attractive fiber delivery system for a broad range of infrared wavelengths, including the 3-μm Er:YAG and 10.6 μm CO₂ lasers. The losses for these waveguides are as low as 0.1 dB/m at the 10.6-μm wavelength for waveguides with a 700-μm bore. The guides are suitable for delivering laser powers well in excess of 100 W. Continuous power delivery for over 250 h is possible for powers less than 35 W. When stored under normal laboratory conditions, the loss is seen to change only slightly over a period up to two years     

Infrared microscopy studies on high-power InGaAs-GaAs-InGaP laserswith Ga2O3 facet coatings

InGaAs-GaAs separate confinement, heterostructure single quantum-well (SCH-SQW) lasers (λ=0.98 μm) with lattice-matched InGaP cladding layers, using a new Ga₂O₃ low reflectivity (LR) front-facet coating, are reported. The CW peak power density (17 MW/cm²) of 6 μm×750 μm ridge-waveguide lasers is limited by thermal rollover, and repeated cycling beyond thermal rollover produced no change in operating characteristics. The high-power temperature distribution along the active stripe has been measured by high-resolution infrared (3-5 μm) imaging microscopy. The temperature profile acquired for a very high optical power density P_D=11 MW/cm³ was found to be uniform along the inner active laser stripe, and revealed a local temperature increase at the LR front facet ΔT_f of only 9 K above the average stripe temperature ΔT_s=24 K. An excellent front-facet interface recombination velocity <10⁵ cm/s has been inferred from the measured low local temperature rise in the front facet     

Noncritically phase matched mid-infrared generation in AgGaSe2

A tunable mid-infrared optical parametric oscillator has been demonstrated using a noncritically phase matched AgGaSe₂ crystal with pump wavelength tuning. Average power experiments have generated several hundred milliwatts of 2.63 and 3.71 μm radiation using a high-repetition-rate, multiwatt 1.54 μm pump source. Interferometric measurements of the AgGaSe₂ crystal during operation indicated only minor thermal lensing     

Fiber amplifiers for coherent space communication

We report on the application of double-clad doped fiber amplifiers for coherent space communication systems using a master oscillator power amplifier (MOPA) design at 1.06 μm. The master oscillator is either a single-frequency Nd:YAG solid-state laser or a distributed-feedback fiber laser. The power amplifier is a diode-laser-pumped double-clad Nd doped fiber with polarization control, 20 dB gain, and about 1.3 W output power. A dual stage configuration using a solid-state Nd:YAG amplifier as second stage is presented as well, increasing the output power to 3.5 W with 28 dB gain. We also report on the possibility to integrate a single-frequency fiber laser, an all-fiber phase modulator, and a fiber amplifier to build an all-fiber phase-modulated MOPA. Up to 1 W continuous-wave output phase-modulated with a bandwidth of 196 MHz has been achieved     

Laser diodes with integrated spot-size transformer as low-costoptical transmitter elements for telecommunications

We have realized laser diodes with integrated spot-size transformer to achieve a high-coupling efficiency to a standard single-mode fiber (SMF) without microoptical elements. A coupling loss of about 1 dB has been achieved with tolerances of 12 μm in both vertical and horizontal direction. We have fabricated both distributed-feedback (DFB) and Fabry-Perot (FP)-type lasers. In the case of the FP lasers the longitudinal single-mode emission was stabilized by means of an external fiber Bragg-grating which was directly butt-coupled to the laser. We have experimentally and theoretically investigated the optical and electrical properties of the devices using a transmission line model     

A silicon MEMS optical switch attenuator and its use in lightwavesubsystems

A single-mode fiber connectorized microelectromechanical systems (MEMS) reflective optical switch attenuator operating in the 1550-nm wavelength region is described. The device consists of an electrostatically actuated gold-coated silicon vane interposed in a fiber gap yielding 0.81-dB minimum insertion loss in the transmit state and high transmission isolation in the reflection state with 2.15-dB minimum return loss. The switch attenuators also work as continuously variable optical attenuators capable of greater than 50-dB dynamic range and can be accurately regulated with a simple feedback control circuit. Switching voltages were in the range of 5-40 V and a switching time of 64 μs was achieved. The MEMS switch can be used in optical subsystems within a wavelength-division-multiplexed (WDM) optical network such as optical power regulators, crossconnects, and add/drop multiplexers. We used a discrete array of 16 switch attenuators to implement a reconfigurable 16-channel 100-GHz spacing WDM drop module of an add/drop multiplexer. Thru-channel extinction was greater than 40 dB and average insertion loss was 21 dB. Both drop-and-transmit of multiple channels (11-18-dB contrast, 14-19-dB insertion loss) and drop-and-detect of single channels (>20-dB adjacent channel rejection, 10-14-dB insertion loss) were demonstrated     

Applications of Highly-Nonlinear Chalcogenide Glass Devices Tailored for High-Speed All-Optical Signal Processing

Ultrahigh nonlinear tapered fiber and planar rib Chalcogenide waveguides have been developed to enable highspeed all-optical signal processing in compact, low-loss optical devices through the use of four-wave mixing (FWM) and cross-phase modulation (XPM) via the ultra fast Kerr effect. Tapering a commercial As₂Se₃ fiber is shown to reduce its effective core area and enhance the Kerr nonlinearity thereby enabling XPM wavelength conversion of a 40 Gb/s signal in a shorter 16-cm length device that allows a broader wavelength tuning range due to its smaller net chromatic dispersion. Progress toward photonic chip-scale devices is shown by fabricating As₂S₃ planar rib waveguides exhibiting nonlinearity up to 2080 W^-1ldr km^-1 and losses as low as 0.05 dB/cm. The material's high refractive index, ensuring more robust confinement of the optical mode, permits a more compact serpentine-shaped rib waveguide of 22.5 cm length on a 7-cm- size chip, which is successfully applied to broadband wavelength conversion of 40-80 Gb/s signals by XPM. A shorter 5-cm length planar waveguide proves most effective for all-optical time-division demultiplexing of a 160 Gb/s signal by FWM and analysis shows its length is near optimum for maximizing FWM in consideration of its dispersion and loss.     

The metal-organic chemical vapor deposition growth and propertiesof InAsSb mid-infrared (3-6-μm) lasers and LEDs

We describe the metal-organic chemical vapor deposition (MOCVD) growth of AlAs_1-xSb_x cladding layers and InAsSb-InAs multiple-quantum well (MQW) and InAsSb-InAsP strained-layer superlattice (SLS) active regions for use in mid-infrared emitters. The AlAs_1-xSb_x cladding layers were successfully doped p- or n-type using diethylzinc or tetraethyltin, respectively. By changing the layer thickness and composition of SLSs and MQWs, we have prepared structures with low temperature (<20 K) photoluminescence wavelengths ranging from 3.2 to 6.0 μm. We have made gain-guided injection lasers using undoped p-type AlAs_0.16Sb_0.84 for optical confinement and both strained InAsSb-InAs MQW and InAsSb-InAsP SLS active regions. The lasers and light emitting diodes (LEDs) utilize the semi-metal properties of a GaAsSb(p)-InAs(n) heterojunction as a source for electrons injected into active regions. A multiple-stage LED utilizing this semi-metal injection scheme is reported. Gain-guided, injected lasers with a strained InAsSb-InAs MQW active region operated up to 210 K in pulsed mode with an emission wavelength of 3.8-3.9 μm and a characteristic temperature of 29-40 K. We also present results for both optically pumped and injection lasers with InAsSb-InAsP SLS active regions. The maximum operating temperature of an optically pumped 3.7-μm strained-layer superlattice (SLS) laser was 240 K. An SLS LED emitted at 4.0 μm with 80 μW of power at 300 K     

Ce3+:LiCaAlF6 crystal for high-gain orhigh-peak-power amplification of ultraviolet femtosecond pulses and newpotential ultraviolet gain medium: Ce3+:LiSr0.8Ca0.2AlF6

To develop high-peak-power ultrashort pulse laser systems in the ultraviolet region, a large Ce³⁺:LiCaAlF₆ (Ce:LiCAF) crystal, a tunable ultraviolet laser medium with large saturation fluence and broad gain spectrum width, was grown successfully with a diameter of more than 70 mm. To demonstrate high small signal gain, a four-pass confocal amplifier with 60 dB gain and 54 μJ output energy was constructed. Chirped pulse amplification (CPA) in the ultraviolet region was demonstrated using Ce:LiCAF for higher energy extraction. A modified bow-tie-style four-pass amplifier pumped by 100-mJ 266-nm 10-Hz pulses from a Q-switched Nd:YAG laser had 370-times gain and delivered 6-mJ 290-nm pulses. After dispersion compensation, the output pulses can be compressed down to 115 fs. This is the first ultraviolet, all-solid-state high-peak-power CPA laser system using ultraviolet gain media, and this demonstration shows further scalability of the Ce:LiCAF CPA system. Additionally, a new gain medium, Ce³⁺ :LiSr_0.8Ca_0.2AlF₆, with longer fluorescence lifetime and sufficient gain spectrum width over 18 nm was grown to upgrade this system as a candidate for a final power amplifier gain module     

Self-aligned packaging of an 8×8 InGaAsP-InP space switch

By using an efficient and alignment tolerant fiber-chip coupling technology we can realize semiconductor space switches with a new and highly promising modular architecture. We present a completely packaged 8×8 matrix switch based on InGaAsP-InP intended for routing applications around wavelength 1.55 μm. The matrix is composed of sixteen 1×8 InGaAsP-InP switches that are optically interconnected by a shuffle comprising 64 single-mode fibers (SMFs). All the fiber ports of the InGaAsP-InP chips are provided with monolithically integrated optical spot-size transformers (MOSTs) that allow simple yet highly efficient self-aligned multifiber coupling. The 8×8 matrix shows a fiber-matrix-fiber insertion losses of 20 dB and a crosstalk suppressions of 28 dB. An extension of the matrix architecture to a 64×64 switch seems straightforward     

Optical characteristics of injection molded plastic ferrules forsingle-mode optical fiber applications

We injection molded a plastic ferrule for a single-mode optical fiber connector. We used liquid crystalline polymer (LCP) as the molding material because of its fine mold replication ability and introduced an eccentricity control mechanism into the ferrule mold. As a result, we succeeded in molding plastic ferrules whose eccentricity was less than 1 μm by optimizing the eccentricity control conditions. The connection loss of these low eccentricity plastic ferrules was around 0.2 dB and they exhibited an excellent reflection characteristic of 52.5 dB. These initial results were maintained during mating tests and temperature and humidity cycling tests     

Widely tunable, near- to mid-infrared femtosecond and picosecondoptical parametric oscillators using periodically poledLiNbO3 and RbTiOAsO4

We describe the operation and characterization of Ti:sapphire laser-pumped femtosecond and picosecond optical parametric oscillators based the new quasi-phase-matched nonlinear materials of periodically poled LiNbO₃ and RbTiOAsO₄ with broad tunability in the near- to mid-infrared. We discuss the merits of the two materials for use in ultrafast optical parametric oscillators (OPOs) and compare and contrast their properties to the birefringent materials. We demonstrate an extended spectral coverage from <1 μm to >5 μm, pump power thresholds as low as 45 mW, average mid-infrared output powers in excess of 100 mW, and pulse durations of 100-200 fs and 1-2 ps at ~80 MHz repetition rate. We also report the efficient operation of Ti:sapphire-pumped femtosecond OPOs in all-solid-state configurations by utilizing diode-laser-based input pump sources     

Tapered rib adiabatic following fiber couplers in etched GaAsmaterials for monolithic spot-size transformation

Design details and demonstration data are presented for an (Al,Ga)As monolithic tapered rib waveguide achieving modal spot-size transformation. The tapered rib adiabatic following fiber coupler structure (TRAFFIC) achieves two-dimensional (2-D) expansion of the output optical mode of single-transverse-mode semiconductor waveguide modulators and lasers using a one-dimensional (1-D) taper between noncritical initial and final taper widths which are compatible with optical lithographic techniques. Measurements are presented of total mode expansion losses between ~1.5-2.0 dB and semiconductor to single-mode-fiber waveguide coupling losses of ~0.5-1.0 dB for doped pin optical-modulator-type waveguides using the TRAFFIC waveguide. A semiconductor laser with a TRAFFIC tapered-rib mode-expansion section and measured coupling loss between the laser output and single-mode fiber of only 0.9 dB is described. Finally, a TRAFFIC Spot-size transformer for undoped waveguide modulators with total mode expansion losses of 1.84 dB and excellent modal behavior at 1.32-μm wavelength is presented. The TRAFFiC structure is particularly well suited for integration with both active and passive etched rib waveguide devices. Fabrication is relatively simple, requiring only patterning and etching of the tapered waveguide and uniform-width outer mesa waveguide without any epitaxial regrowth     

基于圆柱体耦合结构的液漏检测 光纤传感器

针对现有侧耦合结构的液漏监测光纤传感器耦合结构损耗大、一致性低的问题,提出了一种圆柱体缺陷耦合结构的液漏传感器。通过Zemax软件进行光纤耦合仿真,对比分析圆柱、圆锥与半球体三种结构,在插入损耗相差较小的情况下,圆柱体耦合结构具有更高的耦合率。对聚合物光纤（POF）进行加工,得到插入损耗为0.31dB的圆柱体耦合结构。LED灯带作为扫描光源,对带有耦合结构的光纤进行检测能力验证,当耦合介质由空气变为水时,光功率强度变化可达32.8%以上。实验结果表明,圆柱体耦合结构与现有耦合结构相比损耗明显降低,所涉及的光纤传感器能够对液漏进行有效检测。     

Highly strained GaInAs-GaAs quantum-well vertical-cavitysurface-emitting laser on GaAs (311)B substrate for stable polarizationoperation

We have realized high-quality GaInAs-GaAs quantum wells (QWs) with high strain of over 2% on GaAs (311)B substrate for a polarization controlled vertical-cavity surface-emitting laser (VCSEL). By increasing the In composition in GaInAs, the optical anisotropy in photoluminescence (PL) intensity was increased. The anisotropy of 50% was obtained at 1.15 μm emission wavelength. We have demonstrated edge-emitting lasers and VCSELs emitting at over 1.1 μm on GaAs (311)B substrate for the first time. The 1.15-μm edge-emitting laser showed a characteristic temperature of 210 K and the threshold current density of 410 A/cm². The threshold current and lasing wavelength of VCSELs are 0.9 mA and 1.12 μm, respectively. The orthogonal polarization suppression ratio was 25 dB and CW operation up to 170°C without a heat sink was achieved     

Smart pixel optoelectronic receiver based on a charge sensitiveamplifier design

The application of charge sensitive amplifier techniques to the design of receivers within smart pixel optoelectronic systems is presented. An example optical input amplifier is given which should provide high sensitivity (±0.3 μA differential), low power consumption (0.6 mW) and small area usage (50 μm×20 μm) for operation at a conventional CMOS bit rate of 100 Mb/s. The minimum (simulated) optical switching energy is 6 fJ     

Fiber parametric amplifiers for wavelength band conversion

By using a loop configuration formed by a polarization beam splitter, we experimentally demonstrate that the existing wavelength-division multiplexing (WDM) sources in C-band can be wavelength converted to the S-band with low polarization sensitivity and low crosstalk. Using a fiber parametric amplifier as a band converter, we achieve experimentally <0.65-dB polarization sensitivity and >4.7-dB conversion efficiency over 30-nm conversion bandwidth in 315 m of fiber. Compared to the conventional straight fiber wavelength conversion scheme, a more than 2-dB improvement in polarization sensitivity is measured. In addition to the polarization insensitivity, channel crosstalk is measured to be <-27 dB in 315 m of high nonlinearity fiber. In a detailed experimental study, the pattern of crosstalk in longer fiber lengths and the coupling between the polarization sensitivity and crosstalk are measured. For example, with a 430-m fiber length, we measure the degradation in polarization sensitivity to be ~4 dB for 12-dB increased signal power. The experimental results are also confirmed by theoretical calculations. Moreover, in a 32 channels systems simulation, the signal-to-noise ratio (SNR) of the converted signals after 800-km propagation is calculated to be only 0.8-dB degraded compared to using laser diodes with the same initial SNR values. Furthermore, we calculate the effect of pump noise and show that the relative intensity noise of the pump is transferred to the converted signals with an additional 8-dB/Hz degradation