Very large arrays of flip-chip bonded 1.55 μm photodetectors

We present very large arrays of InGaAs-InP p-i-n photodetectors flip-chip bonded to Si. The photodiodes are designed for operation at zero bias, e.g., for spectroscopic applications. Our design maintains depletion at zero bias resulting in ~99% photocurrent collection efficiency. The series resistance of our photodiodes is <1 Ω for a 40×40 μm device, including the flip-chip bond, resulting in high tolerance to shunt leakage. We produce arrays of photodiodes as large as 120 and measure leakage currents. We analyze zero-bias photocurrent generation in the presence of leakage and determine that with this technology arrays as large as 128 can be produced with high yield. The concept of redundancy in zero-bias photodiode arrays is presented and explored. Under the assumption that photodiode leakage is produced by microscopic point defects, a substantial increase in uniformity can be achieved in photodetector arrays by employing redundancy     

Intersubband transitions at 1.3 and 1.55 μm in a novel coupledInGaAs-AlAsSb double-quantum-well structure

We report the first observation of intersubband absorption at 1.3 μm in a coupled InGaAs-AlAsSb double-quantum-well structure lattice matched to InP substrate. The novel structure exhibits intersubband transitions concurrently at 1.3 and 1.55 μm due to the strong coupling of the intersubband states of the adjacent wells. A transient analysis of optical response in the multilevel conduction subband states for the designed structure indicates ultrafast optical switching behavior with a subpicosecond response     

Selective regrowth of a wide-bandwidth 1.3 μm integratedlossless tap and optical preamplifier

The authors report the first monolithically integrated wide-bandwidth lossless tap-that is, an optical semiconductor amplifier followed by a colinear reverse-biased waveguiding photodetector with fiber-coupled input and output. The integration was achieved by using off-axis selective epitaxial growth of ridge waveguides on a patterned dielectric layer. The tilted facets produced by the off-axis growth, along with photodetector absorption, serve to reduce the effective facet reflectivity to -36 dB without any antireflection coating. By adjusting the length of the absorbing photodetector section, part or all of the amplified light may be absorbed, allowing the device to function respectively as a lossless tap or an optical preamplifier. A lossless tap with an electrical bandwidth of 7 GHz, a responsivity of 26 A/W, and a fiber-to-fiber gain of 3 dB is shown to have a receiver sensitivity of -22 dB at 3 Gb/s     

A 3 GHz transimpedance OEIC receiver for 1.3-1.55 μm fiber-opticsystems

A high-performance metal-semiconductor-metal high-electron-mobility transistor (MSM-HEMT) transimpedance photoreceiver fabricated using OMCVD-grown InAlAs/InGaAs heterostructures on an InP substrate is discussed. This is the first demonstration of a monolithically integrated receiver amplifier that incorporates a cascode amplifier stage and a Schottky diode level-shifting stage implemented on InP-based optoelectronic integrated circuit (OEIC) photoreceivers. The transimpedance amplifier has an open-loop gain of 5.7 and a bandwidth of 3.0 GHz, which represent the highest gain and the highest speed performance reported for 1.3-1.55-μm-wavelength OEIC receivers     

Dual mirror and resonant cavity operating at 1.3 and 1.55 μm

A GaAs/AlAs Bragg mirror with two reflectivity bands centred at 1.3 and 1.55 μm is reported. High reflectivity is achieved in both bands and good agreement is observed between measured and simulated reflectivities. A microcavity structure is proposed that is resonant at both wavelengths. Such structures can be used to enhance the absorption or emission of signals at the two wavelengths     

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     

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     

Guided-wave 1.3/1.55 μm wavelength division multiplexer based onmultimode interference

To improve the wavelength sensitivity of the multimode interference phenomenon and thus reduce the device length, a restricted-resonance multimode interference scheme and a lower beat length ratio were adopted to design a novel 1.3/1.55 μm wavelength division multiplexer. Using the modal propagation analysis, transmission characteristics of the device were investigated     

Injection-locked 1.55 μm VCSELs with enhanced spur-free dynamicrange

Injection locking is demonstrated to improve the analogue performance of long wavelength VCSELs. The third-harmonic spur-free dynamic range was improved by 9 dB/Hz^2/3 to be 93 dB/Hz^2/3, and the modulation bandwidth was increased twofold     

Simultaneous absolute frequency control of laser transmitters inboth 1.3 and 1.55 μm bands for multiwavelength communication systems

Absolute frequency control will be an essential part of future dense WDM systems. In this paper, we demonstrate two promising techniques that allow the absolute frequency control of an ensemble of laser transmitters operating in both the 1.3 and 1.55 μm bands. First, a Michelson interferometer is absolutely calibrated by means of a frequency-stabilized master DFB laser. This interferometer provides an ensemble of evenly-spaced absolute frequency references that covers both the 1.3 and 1.55 μm regions. Lasers are frequency-locked to transmission nulls of this interferometer with a precision of a few hundred MHz. The second technique allows full flexibility in channel frequency assignment and relies on frequency offset control of an ensemble of laser sources relative to a master reference laser. The frequency comparator is based on a surface-emitting nonlinear semiconductor multilayer waveguide. This technique provides simultaneous frequency measurement and control of lasers in both bands with a precision of a few GHz     

Wannier-Stark localization in a 1.55 μm InGaAs/InAlAssuperlattice waveguide modulator structure

The authors present an optical waveguide modulator structure based on Wannier-Stark localization in a InGaAs-InAlAs superlattice. Optical waveguide transmission below the superlattice bandgap displays expected F^-1 oscillatory behavior leading to various modulation schemes. An 11 dB extinction ratio was obtained by applying a 0.7 V drive voltage to a 100 μm long waveguide device operating at 1.55 μm under a transverse-electric (TE)-polarization mode. On-state attenuation was 5 dB. Lower open-state attenuation (3 dB) can be obtained simultaneously with a higher extinction ratio (13 dB) but in that case a larger drive voltage (1.6 V) is needed     

Two-dimensional photonic crystals in macroporous silicon: frommid-infrared (10 μm) to telecommunication wavelengths (1.3-1.5 μm)

We present a detailed study of two-dimensional (2D) photonic crystals based on macroporous silicon technology, showing a broad range of wavelengths accessible for applications with this material. In this work, we have reached 1.55 μm, this certainly represents a decisive issue for this technology. First, the reflection performances of a hexagonal and a triangular lattice of air holes are compared. The triangular lattice reduces technological requirements because the complete photonic bandgap (PBG) results from the overlap of broader forbidden bands of lower order. Second, a combined experimental and theoretical study is presented of the reflection properties of a 2D photonic crystal in a three-dimensional (3D) optical environment. This reveals the critical parameters that can degrade the performances of such 2-D structures. Reflection coefficients up to 98% are obtained with optical quality interfaces. Finally, a complete PBG centered at 1.55 μm is demonstrated with a submicrometer period triangular lattice defined by holographic lithography. The influence of the air filling factor on the band position and the interface quality is analyzed by reflection measurements. The overall results show the high flexibility of the macroporous silicon technology and its applicability to integrated optics at telecommunication wavelengths     

Detailed evaluation of an attainable repeater spacing for fibre transmission at 1.3 ?m and 1.55 ?m wavelengths

An attainable repeater spacing at 1.3 ?m and 1.55 ?m wavelengths using a step-index monomode fibre cable is given, after detailed consideration of total loss as well as total dispersion of an optical fibre. The longest attainable repeater spacing at 1 Gb/s is about 100 km at 1.55 ?m wavelength using a single-mode laser diode and a monomode fibre with a relatively small core-cladding refractive index difference, e.g. about 0.2%.     

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     

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     

Dispersion penalty for 1.3 μm lightwave systems with multimodesemiconductor lasers

The effect of fiber dispersion on the performance of lightwave systems is analyzed for the case where multimode semiconductor lasers operating near the zero-dispersion wavelength of the single-mode fiber are used as sources. Both the intersymbol interference and the mode-partition noise are considered in the discussion of dispersion-induced power penalties. The theory is in agreement with an experiment in which the bit error rate is measured for lasers at various bit rates. The tolerable limits on the deviation of the laser wavelength from the zero-dispersion wavelength are obtained for a 1.3-μm system operating at 1.7 Gb/s. Monte Carlo simulations are used to predict the effect of mode-partition noise on the performance of such high-speed lightwave communication systems     

Packaged 1.55 μm DFB laser with 25 GHz modulation bandwidth

25 GHz modulation bandwidth is achieved from a fully packaged 1.55 μm DFB laser, using devices with p-doped compressively strained MQW active regions and large negative wavelength detuning. Devices on submounts show a record bandwidth of 26 GHz, limited by device and bonding parasitics. Resonance frequencies of over 26 GHz are measured     

Predistortion of electroabsorption modulators for analog CATVsystems at 1.55 μm

A predistortion circuit with adjustable amounts of third- and fifth-order predistortion is studied both theoretically and experimentally. The circuit is used to cancel the third- and fifth-order intermodulation distortion of a 1.55-μm integrated electroabsorption modulator/DFB laser. The CSO obtained is -61 dBc and the CTB is reduced 22.6 dB to -65 dBc. This performance is maintained after fiber amplification and propagation through 13 km of nondispersion shifted fiber due to the modulator's low chirp. Dithering of the DFB laser's injection current is employed to increase the stimulated Brillouin scattering (SBS) threshold to +13.4 dBm     

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     

Wafer-bonded 1.55 μm vertical cavity laser arrays for wavelengthdivision multiplexing

The first electrically pumped 1.55 μm multiple wavelength VCSEL array is demonstrated. The wafer bonded array consists of four channels operating between 1509 and 1524 nm. Multiple wavelengths were defined using an etched intracavity superlattice prior to bonding. Threshold currents of 0.9 mA and peak output powers of 0.45 mW were measured