Coefficients of maximally flat nonrecursive digital filters

A general method is presented for determining the coefficients of maximally flat nonrecursive digital filters. Recursive relations with integer coefficients are derived for these coefficients by explicit calculations imitating Crout's method for solving the linear equations obtained by setting the derivatives of the symmetric, linear phase transfer function to zero at w = 0 and w = π. For a given order of the filter, the amount of computation required in this method is uniformly the same for any combination of permissible degrees of flatness at w = 0 and w = π.     

1.3 ?m InGaAsP DCPBH multiquantum-well lasers

We report the fabrication and performance characteristics of InGaAsP double-channel planar buried heterostructure (DCPBH) lasers with multiquantum-well active layers emitting at 1.3 ?m. These lasers have threshold currents in the range 40?50 mA at 30°C, external differential quantum efficiencies of ?50% at 30°C and T0 values ?160 to 180 K in the temperature range 10?60°C.     

Criterion for improved linearity of 1.3-µm InGaAsP-InP buried-heterostructure lasers

Nonlinearities in tile light-current characteristics of planar-active buried-heterostructure (BH) lasers are associated with higher order mode transitions, spectral broadening and, in some cases, the onset of TM polarized stimulated emission. Measurements and calculations are presented which show that these nonlinearities appear at higher power in devices with reduced active volume. These results provide a practical guide to the fabrication of "kink-free" 1.3-μm InGaAsP buried-heterostructure lasers for use in high-bit-rate fiber communication systems.     

High brightness and reliable AlGaInP-based light-emitting diode for POF data links

High brightness and reliability operation ring light-emitting diode (LED) is fabricated for plastic optical fiber (POF) link using the distributed Bragg reflector (DBR) mirror and antireflection (AR) coating. The ring LED exhibited optical output as high as 3.5 mW at the bias current of 100 mA. Furthermore, the projection lifetime is also estimated to be 1/spl times/10/sup 6/ h at a 35-mA data-link operating current and ambient temperature of 60/spl deg/C.     

High contrast optical modulator based on electrically tunablepolarization rotation and phase retardation in uniaxially strained (100)multiple quantum wells

We report a novel approach to the design of normal incidence multiple quantum well light modulators. The quantum confined Stark effect is utilized to tune the light polarization rotation and phase retardation created by a thermally induced in-plane anisotropic strain. An exceedingly high contrast ratio of 5000:1 is demonstrated for a normally-on device at room temperature     

Optical properties of a GaAlAs superluminescent diode

The optical properties of a GaAlAs superluminescent diode (SLD) are described. The spectra of this device exhibit a large number of longitudinal modes. The coupling efficiency into a 0.23 NA 50 μm diameter graded index fiber is ∼ 30 percent. The current required for constant light output at a temperatureTcan be written asI(T) sim I_{0} cdot exp (T/T_{2})whereT_{2} sim 120K. A model of the SLD is described.     

Leptodermous expansion of nuclear ground state energies and the anomaly in the nuclear curvature energy

The leptodermous expansion of the total ground state energy of a nucleus into volume, surface, curvature and gauss curvature contributions has been studied starting from a semi-classical energy density formalism of extended Thomas Fermi type. A numerical procedure was used to obtain the surface energy and curvature energy contributions from surface moments of energy density profilesH(r) for a sequence of nuclei withN=Z and neglecting the coulomb interaction for the three Skyrme forces. A transition to the liquid drop model type expansion in increasing powers ofA ^−1/3 is then made, taking into account the dependence of the central density and the surface structure on the mass of the nucleus. It is found that there is no inconsistency between the curvature contribution to the total energy in the leptodermous expansion and theA ^−1/3 term contribution in the liquid drop model expansion. It has been shown that the earlier apparent anomaly between the above two methods arises due to the use of semi-infinite approximation and the mass dependence of the central density and the surface structure of finite nuclei.     

1.3 ?m InP/InGaAsP channelled-substrate buried-heterostructure laser monolithically integrated with a photodetector

A 1.3 ?m InP/InGaAsP channelled-substrate buried-heterostructure laser is monolithically integrated with a monitoring photodetector. The lasers have threshold currents in the range of 25?30 mA and the photodetector provides ~ 15 ?A of photocurrent per milliwatt of laser power.     

Design and performance of the mesh-type high-speed silicon opticalposition-sensitive devices

A high speed optical position-sensitive device (PSD) which was fabricated using a certain structure of the mesh-type resistive layer for reducing the junction capacitance is discussed. Its performance is compared with the conventional type of PSD (CPSD) fabricated by the same technology. The mesh-type high speed PSD (MEPSD) is based on an ion-implanted Si p-i-n structure and has an area of 14×14 mm² with 30-μm strip-width and 125-μm pitch. The temporal response of the MEPSD is found to be improved by a factor of 1.83 times compared to the CPSD. A photosensitivity comparable to that of the CPSD is obtained. Its position linearity for detection is also comparable with that of the CPSD. The performance of the laboratory demonstration devices illustrates the feasibility of the concept for high-speed PSD     

Stable 80-GHz short pulse generation using the cascaded polarization-maintaining fiber loop mirrors

In this work, an optical short pulse generator is designed consisting of a pulse compressor and cascaded notch filter type repetition rate doublers. The performance characteristics such as pulsewidth and peak power as a function of design parameters are studied. The pulse compressor is optimized based on the simulation results. The 6-ps-wide pulses at 20-GHz repetition rate directly generated from mode-locked fiber laser are compressed to 1.25-ps-wide pulses. Using a set of polarization-maintaining fiber loop mirrors, the repetition rate is quadrupled and stable 1.45-ps-wide pulses at 80 GHz are achieved.