4×4 polymer thermo-optic directional coupler switch at 1.55μm

An integrated 4×4 polymer thermo-optic switch at 1.55 μm is demonstrated for the first time. A fibre to fibre insertion loss of 10 dB, and extinction ratios of 17.5-19.5 dB were measured. The polarisation sensitivity was typically less then 0.5 dB and the response time was less then 1 ms. The electrical power consumption was found to be 70 mW per single switch     

The photorefractive effect in directional coupler and Mach-ZehnderLiNbO3 optical modulators at a wavelength of 1.3 μm

Previous work has shown that at a wavelength of 1.3 μm and power levels on the order of a few milliwatts, directional coupler switches show negligible damage due to the photorefractive effect. The author's experiments at higher power levels (20 mW) show a significant reduction in performance for 1-cm-long directional coupler modulators with uniform electrodes. The reduction in modulation efficiency is in good agreement with a numerical simulation based on the coupled mode equations using index changes estimated from previous work. At similar power levels, Mach-Zehnder modulators showed little effect making them a good design for high power applications. Other electrode structures, such as the reverse Δβ type, might help alleviate the effect in directional couplers. Modulators operating at 1.55 μm should also show less susceptibility to the effect     

1.3 μm fluoride fibre laser

Laser action has been achieved in the 1.33-1.34 μm range using an Nd³⁺-doped fluorozirconate glass multimode fibre. These operating wavelengths are the closest to the important telecommunications channel at 1.3 μm of any reported for a glass laser     

1.3 μm GaSb metal-semiconductor-metal photodetectors

Metal-semiconductor-metal photodetectors employing GaSb active regions and Al_0.5Ga_0.5Sb barrier-enhancing abrupt regions have been fabricated on InP substrates to assess the role of hole velocity and to compare with similar photodetectors made using Ga _0.47In_0.53As active region. Devices exhibit photoresponse in the 0.2-0.65 A/W range, dark currents of ≈10^-6 A at 300 K and ≈10^-10 A at 77K for 25×25 μm² area, and have a voltage-sensitive 3-dB bandwidth exceeding ≈1 GHz at 300 K and 10 GHz at 77 K. The enhanced barrier heights are estimated to be ≈0.30 eV. The fall time continues to be the significant component of time delay; its temperature dependence indicates that the hole velocities do improve significantly at lower temperatures. The 300 K behavior appears to be dominated by defect and impurity densities, and the effects of abrupt barriers. The larger than expected dark currents are believed to result from defects associated with lattice mismatch     

A linearized optical directional-coupler modulator at 1.3 μm

We investigate electrooptic directional-coupler modulators operating at the wavelength of 1.3 μm, to have high linearity in their response function. The inverse Fourier transform technique was used to synthesize the spatially varying coupling function from a specified response function. The resulting coupling function was then used to determine the shape of the modulator structure. Modulators to have the response function of the form of a triangular (“linear”) function have been designed, fabricated, and tested. The third-order intermodulation-limited spurious-free dynamic range, at -130-dBm normalized noise floor, of 96.2 dB/Hz^2/3 was obtained     

Vertical-cavity amplifying modulator at 1.3 μm

The modulation/switching properties of a vertical-cavity semiconductor optical amplifier operating at 1.3 μm wavelength are investigated. The device was optically pumped and operated in reflection mode. A 150-mV (100 mA) modulation of the drive to the pump source produced a 7-dB modulation of the pump power, which produced a 35-dB modulation in the output signal. The maximum extinction ratio was 35 dB, and limited by device heating. Frequency response measurements revealed a modulation bandwidth of 1.8 GHz when the amplifier was saturated. This enabled 2.5-Gb/s modulation of a -10 dBm input signal with 5.5-dB fiber-to-fiber gain     

1.3 μm beam-expander integrated laser grown by single-step MOVPE

A new structure for a 1.3 μm-wave length beam-expander integrated ridge-waveguide laser is demonstrated that does not require a regrowth step. A narrow beam divergence of 5.4° (lateral) and 18.9° (vertical) enables a laser diode to be coupled to a cleaved singlemode fibre with an efficiency as high as 33% with a 1 dB alignment tolerance of ±2.4 μm laterally and +1.5 μm vertically     

The annealing of double-heterostructure GaInAsP-InP 1.3 μm

An attempt to understand the various aging patterns discovered from lifetests on GaInAsP-InP laser diodes is reported. These lasers are characterized by initial changes that, after a short period, settle down. The lasers then operate stably with very little change thereafter. In the diodes used, drive current increases of typically 6% occurred. There was little change in threshold current and the changes seen were mainly due to a decrease in slope efficiency. In all cases, the changes decreased gradually after about 2000 h and reverted to the behavior expected of long-lived and reliable quaternary lasers. A model for the annealing of double-heterostructure laser diodes is extended to describe these effects     

A compact two-dimensional grating coupler used as a polarization splitter

We demonstrate a novel polarization splitter based on a two-dimensional grating etched in a silicon-on-insulator waveguide. The device couples orthogonal modes from a single-mode optical fiber into identical modes of two planar ridge waveguides. The extinction ratio is better than 18 dB in the wavelength range of 1530-1560 nm and the coupling efficiency is approximately 20%. The device is very compact and couples light only to transverse-electric modes of the planar waveguides. Therefore, it may be used in a polarization diversity configuration to implement a polarization insensitive photonic integrated circuit based on photonic crystal waveguides.     

A superluminescent diode at 1.3 μm with very low spectralmodulation

An edge-emitting superluminescent diode has been fabricated from an MOCVD-grown InGaAsP/InP double heterostructure, for light emission at 1.3 μm. Using a ridge-waveguide geometry with an integrated absorber, the goals of high power coupled into a single-mode fiber and very low spectral modulation are fulfilled. Interferometric measurements of the residual modulation determine the location of internal optical reflections in the device. The results are interpreted and compared to the predictions of a transmission-line model     

28.3 dB gain 1.3 μm-band Pr-doped fluoride fiber amplifiermodule pumped by 1.017 μm InGaAs-LD's

A praseodymium (Pr)-doped fluoride fiber amplifier (PDFA) module that is pumped by strained quantum-well InGaAs laser diodes (LDs) is described. The amplifier module, consisting of a four LD pump configuration and a high NA Pr-doped fluoride fiber with low scattering loss, exhibits a maximum signal gain of 28.3 dB and a saturation output power of 6 dBm at a signal wavelength of 1.30 μm. It is shown to be the most promising module for the 1.3-μm-band optical amplifier     

Tensile-strained GaInAsP-InP quantum-well lasers emitting at 1.3μm

Tensile-strained GaInAsP-InP quantum-well (QW) lasers emitting at 1.3 μm are investigated. Low-pressure metalorganic chemical vapor deposition (LP-MOCVD) is used for crystal growth. High-resolution X-ray diffraction shows good agreement with theoretical simulation, photoluminescence spectra have good energy separation between light-hole and heavy-hole bands due to biaxial tension. The lowest threshold current density for infinite cavity length J_th/N_w ^∞ of 100 A/cm² is obtained for the device with -1.15% strain and N_w=3. The amount of strain which gives the lowest J_th/N_w^∞ experimentally clarified is around -1.2%. Threshold current of a buried-heterostructure (BH) laser is reduced to be as low as 1.0 mA. Enhanced differential gain of 7.1×10^-16 cm² is also confirmed by measurements of relative intensity noise. Much improved threshold characteristic with the feasibility of submilliamp threshold current can be achievable by optimizing the BH structure. The tensile-strained QW laser emitting at 1.3 μm with very low power consumption is attractive for the light source of fiber in the loop system and optical interconnection applications     

High power semiconductor laser injection-locking at 1.3 μm

The injection-locking properties of a high power antireflection coated 1.3-μm slave laser subjected to relatively low injection powers from a distributed feedback (DFB) laser and from a tunable external cavity laser have been investigated. Narrow linewidth operation (~40 kHz) was demonstrated and the tuning range within two slave modes (~10 GHz) and over the gain profile (~40 nm) was investigated. In addition, the tracking properties of the slave laser for both frequency and phase modulated injected light was evaluated at 1 Gb/s, in which the fidelity was judged from bit-error-rate measurements. The maximum locked power under 1 Gb/s frequency modulation was about 145 mW, limited by the available master power; approximately 300 μW was injected into the slave     

Electroabsorption in lattice-matched InGaAlAs-InAlAs quantum wellsat 1.3 μm

Electroabsorption properties of (In_0.53Ga_0.47As)_0.7 (In_0.52Al_0.48As)_0.3-In_0.52Al _0.48As quantum wells were investigated experimentally and analytically in order to form a semi-empirical model for 1.3 μm optical modulator applications. The observed exciton energy shifts and changes in electron-hole wave function overlap integrals are in agreement with calculation for the quantum confined Stark effect. Empirically, we found that the room-temperature exciton absorption peak can be described by a Gaussian peak, and that the residual absorption should be characterized by an exponential tail. In order to provide realistic linewidth broadening parameters, empirical expressions are summarized here for this material     

Characteristics of GaAsSb single-quantum-well-lasers emitting near1.3 μm

We report data on GaAsSb single-quantum-well lasers grown on GaAs substrates. Room temperature pulsed emission at 1.275 μm in a 1250-μm-long device has been observed. Minimum threshold current densities of 535 A/cm² were measured in 2000-μm-long lasers. We also measured internal losses of 2-5 cm^-1, internal quantum efficiencies of 30%-38% and characteristic temperatures T₀ of 67°C-77°C. From these parameters, a gain constant G₀ of 1660 cm^-1 and a transparency current density J_tr of 134 A/cm² were calculated. The results indicate the potential for fabricating 1.3-μm vertical-cavity surface-emitting lasers from these materials     

Circular beam emission from 1.3 μm InGaAsPstrained-multiquantum-well lasers

The beam divergence in the vertical direction from a graded index separate confinement heterostructure (GRINSCH) multiquantum-well (MQW) laser has been studied. It is demonstrated both theoretically and experimentally that a circular beam MQW laser can be produced by choosing appropriate thicknesses for the GRINSCH layers, while maintaining other desired laser characteristics. The beam divergence is found to be more affected by the index change induced by injected carriers than by strain in the MQW active layer. Theoretical results are in good agreement with the measurements for 1.3-μm InGaAsP strained MQW lasers     

Crosstalk in 1.3 μm praseodymium fluoride fiber amplifiers

Praseodymium-doped fluoride fiber amplifiers have been demonstrated to provide good gain, output power, and noise performance in the second telecommunications window. This paper presents a study of the crosstalk performance of these amplifiers. A theoretical analysis is presented from which a numerical model is developed and is used to predict the crosstalk performance of a typical amplifier. Experimental results, using two separate signals within the gain band, show good agreement between measurement and theory, indicating that it is unlikely that crosstalk will present a problem in anticipated amplifier applications. From the measured crosstalk, an upper limit is placed on the lower level lifetime, indicating that the population of this level will have a negligible effect amplifier gain. A novel technique for measuring the upper state lifetime in an amplifier, based on pump power dependence of crosstalk, is described and experimental results which are in agreement with fluorescent decay are presented     

All-optical 1.5 μm to 1.3 μm wavelength conversion in awalk-off compensating nonlinear optical loop mirror

We demonstrate highly efficient all-optical conversion from 1.5 μm to 1.3 μm using a novel nonlinear optical loop mirror that compensates for walk-off. We make the fiber loop by splicing alternating segments of standard single-mode and dispersion-shifted fibers and choose their lengths such that the walk-off of the 1.3 μm and 1.5 μm pulses in one segment is completely reversed in the adjacent segment. We also show that the width of the converted pulses can be tailored by this scheme     

Strained 1.3 μm MQW AlGaInAs lasers grown by digital alloy MBE

AlGaInAs strained MQW lasers, emitting at 1.3 μm, have been prepared for the first time using a digital alloy approach. 2 μm stripe geometry lasers have characteristics comparable to those of lasers prepared using bulk alloy layers. The infinite length threshold current densities are as low as 140 kA/cm²/quantum well and T ₀ values (20-40°C) range from 75-90 K for chip lengths of 375-2375 μm     

High-speed performance of OMCVD grown InAlAs/InGaAs MSMphotodetectors at 1.5 μm and 1.3 μm wavelengths

A report is presented on the fabrication of high-speed In_0.53 Ga_0.47As metal-semiconductor-metal (MSM) photodetectors incorporating a high-quality lattice-matched InAlAs barrier enhancement layer, grown by organometallic chemical vapor deposition (OMCVD). Fast responses of ~55 ps full-width half-maximum at 1.5 μm and ~48 ps at 1.3 μm wavelengths are observed, corresponding to intrinsic device bandwidths of ~8 GHz and ~11 GHz, respectively. The absence of any tail to the pulse response, and of any low-bias DC gain, indicates a low-trap density at the InAlAs/InGaAs heterointerface. Bias independent dark currents of 10-20 μA are observed below breakdown, which occurred at >30 V in devices with a 500-A-thick InAlAs layer