Excess high frequency noise and flicker noise in MOSFETs

The noise parameter α=R_ng_m, where R_n is the noise resistance and g_m the transconductance, was measured for n- and p-channel MOSFETs as a function of frequency with the temperature T as a parameter. At lower frequencies α varies as 1/f, as expected for flicker noise, whereas at higher frequencies α attains a limiting value α_∞ that is larger than expected for thermal noise. Arguments are presented whether this high-frequency noise can be hot electron noise. The flicker noise resistance R_mf has a much stronger temperature dependence for n-channel than for p-channel devices; this is related to the energy dependence of the surface state distribution in the forbidden gap.     

Excess noise in GaAs avalanche photodiodes with thin multiplicationregions

It is well known that the gain-bandwidth product of an avalanche photodiode can be increased by utilizing a thin multiplication region. Previously, measurements of the excess noise factor of InP-InGaAsP-InGaAs avalanche photodiodes with separate absorption and multiplication regions indicated that this approach could also be employed to reduce the multiplication noise. This paper presents a systematic study of the noise characteristics of GaAs homojunction avalanche photodiodes with different multiplication layer thicknesses. It is demonstrated that there is a definite “size effect” for multiplication regions less than approximately 0.5 μm. A good fit to the experimental data has been achieved using a discrete, nonlocalized model for the impact ionization process     

Excess phase noise in self-heterodyne detection

The interpretation of self-heterodyne spectra is difficult if, apart from spontaneous emission, additional noise sources are presented. Measurements on an external-cavity semiconductor laser show how, for a relatively long delay, the high-frequency (Lorentzian) wings of the self-heterodyne spectrum are a sensitive measure for the quantum-limited (Schawlow-Townes) laser linewidth. The quantum-limited laser linewidth is shown to be inversely proportional to the output power. Values below 5 kHz are routinely measured. The full width at half maximum (FWHM) laser linewidth is larger than this due to excess low-frequency fluctuations, which are shown to result from the presence of side modes     

On the "Excess spontaneous emission factor" in gain-guided laser amplifiers

Petennann [1] computed an "excess spontaneous emission factor" for gain-guided laser. In this paper, we investigate further the role of this factor. Such a factor also appears in the treatment of thermodynamic equilibrium in an attenuating medium-a seeming paradox. Further investigation shows that the excess spontaneous emission excitation at thermal equilibrium is cancelled by the excitations in the other modes which are correlated with that in the fundamental mode. In a medium with gain, cancellation also occurs in a short amplifier in which there is no gain discrimination among modes. The "excess spontaneous emission factor" is fully present only in a system in which the different higher order modes have an appreciably smaller gain than the lowest order mode, a high gain amplifier. An analysis of the signal-to-noise ratio of a high gain amplifier reveals that the excess noise factor can be fully compensated by proper input excitation by a lens arrangement. The lens arrangement provides the signal with an "excess gain" factor. An "excess gain" factor is also present when a thermal source is used.     

Low-frequency intensity noise resonance in an external cavity GaAslaser for possible laser characterization

The dependence of the (low-frequency) resonance of light intensity noise in an external-cavity GaAs laser on cavity length and bias current, combined with the dependence of the threshold current on the magnitude of the light feedback, is used to determine simultaneously the carrier recombination lifetime, the carrier injection at transparency, and the optical loss. The key to this technique is understanding the correction term to the relaxation oscillation frequency due to finite carrier density at transparency and the influence of the long external cavity transit time on the photon lifetime in the three-mirror cavity. The technique uses commercial lasers without modifying them and does not require fast electronics     

Excess noise measurements in ion-implanted silicon resistors

The low-frequency noise spectra of partially annealed boron-implanted silicon resistors with various geometries are measured. The implantation energies are 50, 80 and 110 keV and the doses are 2·5 × 10¹² cm^?2, 1·0 × 10¹³ cm^?2 and 1·0 × 10¹⁴ cm^?2. The spectra exhibit thermal noise and $\text{?}{}^{\mathrm{?n}}$ (excess) noise exclusively. Investigations indicate that the contracts from the implanted layer to the electrode generally contribute small amounts to the total excess noise observed. The excess noise exhibits a strong dependence on the sheet resistance of the layers, while the dependence on substrate bias, implantation energy, and on temperature is relatively weak. A discussion of the results is given in terms of a volume effect. Noise measurements on implanted layers, produced under carefully controlled conditions, show promise as a tool to investigate excess noise.     

Effect of external cavity semiconductor laser phase noise on a DPSKheterodyne optical receiver

The effect of an external cavity semiconductor laser on the performance of a DPSK heterodyne optical system is evaluated. The actual shape of the frequency fluctuation spectral density of the optical source is taken into account, and a comparison with a PSK coherent heterodyne system is carried out     

Laser RIN calibration by extra noise injection

Laser relative intensity noise (RIN) calibration is presented. Experimental results show the influence of laser RIN on the bit error rate (BER) in a transmission system operating at 600 Mbit/s through a 10 km monomode fibre length, at a wavelength of 1.3 mu m.<>     

High-power vertical-cavity surface-emitting laser with an extra Au layer

We report the performance of a high-power vertical-cavity surface-emitting laser (VCSEL) with an extra Au layer. By using the extra Au layer, the far-field divergence angle from a 600-/spl mu/m diameter VCSEL device is suppressed from 30/spl deg/ to 15/spl deg/, and no strong sidelobe is observed in far-field pattern. There is a slight drop in optical output power due to the introduction of the extra Au layer. By improving the device packaging method, the VCSEL device produces the maximum continuous-wave optical output power of 1.95 W with lasing wavelength of 981.5 nm. The aging test is carried out under constant current mode at 60/spl deg/C, and the preliminary result shows that the total degradation of output power is less than 10% after 800 h.     

Excess generation-recombination noise in reverse biased Schottky-barrier diodes

Generation-recombination noise in reverse biased Schottky-barrier diodes (made on high resistivity n-type silicon) has been investigated theoretically and experimentally. It is shown that in the considered type of diodes generation-recombination noise can be larger than predicted by the common limit I_eq I_g-r. The measured spectral noise distribution is in good agreement with the theoretical predictions.     

Excess base noise in the bipolar junction transistor

It has been known for some time that the bipolar transistor base region exhibits a noise in excess of that predicted by thermal noise associated with the base spreading resistance measured by large- or small-signal methods. This paper presents a relatively simple mechanism and model involving a transconductance gradient that accounts for the excess noise.     

Excess noise and nonlinear effects in low-dimensional conductors

Experimental results on the 1/f ^γexcess noise and the nonlinearity of the I–V characteristics in nanosized semiconductors based on thin metal (Ni, Cu, and Au) films at various current loads and temperatures are presented. It is demonstrated that relatively slow processes related to the heat exchange of film and substrate serve as the reason for the nonlinearity of the I-V characteristic in low-dimensional conductors. A method to determine the melting point of low-dimensional conductors based on the measurement of the positions of the voltage fluctuation peaks on the temperature-time scale caused by the primary fluctuations of the film resistance in the vicinity of the melting point in the presence of a low-density current flow in the sample and slow heating. The starting temperature of melting of nanosized nickel and gold films on oxidized silicon is experimentally determined.     

Vertical cavity surface-emitting semiconductor laser with CWinjection laser pumping

Room-temperature CW operation of a GaAs/AlGaAs vertical cavity surface-emitting laser with a resonant periodic gain medium, using a GaAs/AlGaAs diode laser array as a pump source, is discussed. Pumping thresholds as low as 11 mW at 730 nm, output powers as high as 10 mW at 856 nm, and external quantum efficiencies as high as 70% are obtained, with considerably improved temporal and spatial coherence properties compared to the pump laser. This is the first reported operation of such a laser with an efficient, compact pump source, demonstrating its suitability for efficient integration     

Excess linewidth broadening in wavelength-tunable laser diodes

Injection-recombination shot noise in the tuning region is identified as significant linewidth broadening mechanism in wavelength tunable laser diodes. Depending on the tuning efficiency this power independent linewidth broadening is typically around 4-20 MHz. Useful formulas for the evaluation of this broadening and design rules for an improvement of the devices are given.<>     

Phase noise in a laser with output coupling

An improved method of calculating the linewidth of a laser oscillator due to phase noise is proposed. The fluctuation in the output amplitude that leads to the phase diffusion is calculated as the amplified thermal and the quantum noise which are delta-correlated in time. The saturated gain distribution along the cavity axis that is consistent with the output coupling at the end surfaces is taken into account in calculating the amplification of the noises. The resulting linewidth formula differs somewhat from the conventional formula.     

Excess noise reduction in GaInP/GaAs heterojunction bipolartransistors

In this paper an annealing procedure which gives an excess noise reduction both of heavily C-doped resistive structures and GaInP/GaAs Heterojunction Bipolar Transistors (HBTs) of 5 dB is proposed. The investigation of the correlation between the noise generators indicate that the annealing leads to a decrease of noise voltage attributed to a strain reduction both in the intrinsic and in the extrinsic base related to a site switching effect of carbon atoms. The reduction of noise current with annealing is attributed to the surface improvement related passivation process by hydrogen atoms     

Excess noise in semiconducting BaSrTiO3

The noise characteristics of semiconducting BaSrTiO3were investigated as a function of frequency, bias current, and volume of the sample. It was found that the noise is approximately inversely proportional to the volume of the sample and the frequency dependence is a1/fbehavior. This and other results have implications regarding an optimized use of this material for temperature-sensing applications.     

Single-polarization wavelength-tunable fiber laser with anonreciprocal cavity

Unidirectional, continuously tunable, and polarized oscillation in an erbium doped fiber ring laser is demonstrated without an isolator. Nonreciprocal oscillation is realized with one polarization splitter and two polarization controllers. Fine tuning is realized with fiber birefringence. The laser spectrum is continuously tunable from 1530 to 1560 nm with line widths less than 0.2 nm; the degree of polarization at the output is 92%     

Intensity noise suppression and modulation characteristics of a laser diode coupled to an external cavity

Static and dynamic properties of a GaAlAs laser diode with an external cavity (1.5-50 cm) have been studied experimentally, it is found that the optical feedback induced intensity noise is strikingly suppressed by 30 dB when a single frequency oscillation is realized with good phase matching. The threshold of modulation depth, over which intensity noise increases abruptly, has been measured as a function of the modulation frequency in a range of 10-400 MHz. It has the maximum at about 40-70 MHz and increases with the decrease of the external cavity length. On the basis of the compound cavity model the phase and gain conditions for the single frequency oscillation are discussed and the threshold modulation depth is calculated, which is shown to be in good agreement with the experimental results.     

Use of solid-state devices in noise measurements

For accurate noise measurements the use of valves in preamplifiers has its advantages and disadvantages. Analysis in this paper shows that a combination of the bipolar and unipolar transistors offers a very satisfactory substitute for the valve in low noise preamplifiers for operation over a wide range of source resistances (10ω—1 Mω).