Resonant-tunnelling diode oscillator using a slot-coupled quasioptical open resonator

A resonant-tunnelling diode has oscillated at X-band frequencies in a microwave circuit consisting of a slot antenna coupled to a semiconfocal open resonator. Coupling between the open resonator and the slot oscillator improves the noise-to-carrier ratio by about 36 dB relative to that of the slot oscillator alone in the 100-200 kHz range. A circuit operating near 10 GHz has been designed as a scale model for millimetre- and submillimetre-wave applications.<>     

D-band operation of a second harmonic GaAs gunn oscillator

A GaAs second harmonic Gunn oscillator for D-band applications is proposed. The doping structure of the active device has been optimized using Monte-Carlo and hydrodynamic models. The load impedance characteristic of a resonant mounting structure in a WR06 waveguide has been consistently taken into account. At sufficiently low load resistances and reactances, output powers of the order of 20–50 mW should be obtainable around 140 GHz under realistic thermal conditions.     

An investigation of the MESFET "End" resistance using a distributed diode/resistance model

Transport equations applicable to forward biased Schottky barriers or junction-gate FET's with open-circuit drain have been solved for dc and small-signal ac current-voltage characteristics, treating the system as a distributed diode/resistance network. Universal graphs have been presented that show the dependence of the MESFET three terminal resistances on the forward diode current. Series resistances of test MESFET's, with a wide range of gate-length values, have been experimentally evaluated after allowing for the channel distributed resistance effects. These results indicate that free surface depletion in the electrode gap regions have significant effects on the FET series resistance components.     

Single-mode lasing operation using a microring resonator as awavelength selector

We have demonstrated semiconductor lasers with microring resonators as frequency-selective elements. We show that the small resonator inside the laser makes single frequency-mode operation possible with reasonably good side-mode rejection     

Frequency stabilization of laser diode using a frequency-locked ring resonator to acetylene gas absorption lines

The frequency stabilization of a 1.5 mu m distributed-feedback (DFB) laser diode using a planar lightwave circuit (PLC) ring resonator whose resonant frequency is locked to /sup 12/C/sub 2/H/sub 2/ and /sup 13/C/sub 2/H/sub 2/ gas absorption lines is described. The resonant frequency of PLC ring resonator was stabilized within a 5 MHz peak-to-peak fluctuation. With this ring resonator the outer frequency fluctuation of the DFB laser diode was stabilized within 10 MHz at every resonant frequency at 5 GHz intervals. The stability demonstrated is as good as the method using molecular absorption lines as a reference. The stabilized frequency can be selected at any point on the optical resonant peaks of the optical resonator.<>     

Bandpass filter design using a microstrip triangular loop resonator with dual-mode operation

A bandpass filter (BPF) design using a dual-mode microstrip triangular loop resonator is presented for the first time. The circuit produces frequency responses with one real finite frequency transmission zero and one imaginary finite frequency zero on either side of the passband. Depending on the perturbation arrangement, the nature of the coupling between degenerate modes causes the zeros to exchange their axis locations from real to imaginary and from imaginary to real while keeping their magnitude. This behavior results in frequency responses that are suitable for applications with asymmetrical requirements. Results show 8% bandwidth filters with insertion loss ranging from 0.82 dB to 1.4dB at 10 GHz. Advantages in size reduction and design flexibility are demonstrated when the triangular loop is compared to other dual-mode resonators.     

Laser diode frequency stabilization with a fiber ring resonator

To improve the frequency stabilization of laser diode in the laser frequency scanned interferometric metrology, a modified method is proposed by using a fiber ring resonator. The theoretical analysis of this modified method is performed. Moreover, the Pound-Drever-Hall (PDH) technique is employed to obtain the frequency discrimination curve of a fiber ring resonator, whose finesse is 1260 and line-width is 270 kHz. The simulated results show that the curve has a steep slope near the resonant frequency, which proves the sensitivity of this system to the frequency deviation, so the modified method has great potential for the frequency stabilization of a laser diode.     

Optical exclusive-OR operation using tunable wavelength conversion laser diode

Lasing was suppressed by light injection into a bistable laser diode due to gain quenching of the lasing mode. Based on this phenomenon and optically triggered lasing due to saturable absorption, an optical exclusive-OR function is demonstrated using a tunable wavelength conversion laser diode.<>     

Analysis of the noise spectra of a laser diode with opticalfeedback from a high-finesse resonator

Noise spectra of a semiconductor laser with and without optical feedback from an external high-finesse resonator are calculated. Even very small amounts of optical feedback significantly reduce the low-frequency noise power, but the reduction depends on the source of the noise. The effect of various parameters on the noise reduction and on the stability of single-mode operation of the laser are determined, and the results are compared to recent experimental measurements. The results provide guidelines for the design of practical systems for achieving narrow emission linewidths and avoiding instability. The theoretical results show that a semiconductor laser with optical feedback functions as a laser with an optical servoloop and can be considered a self-injection-locked laser     

A computer solution for the steady-state behaviour of a PN-junction diode

A computer solution for the transport equations and Poisson's equation has been obtained for the steady-state behaviour in a PN-junction diode. Assuming dopings of 10¹⁸/cm³ for acceptors and 10¹⁵/cm³ for donors, and using the Hall-Shockley-Read recombination process, we have been able to solve for the currents, concentrations, energy levels, and field in the P-region, N-region, and space-charge region separately. No approximations are made which are not a consequence of the relative doping levels. Our main conclusions are that (a) the potential drop in the N-region causes the forward current to vary as exp(qV/nkt), where n increases with current and (b) the reverse current does not saturate because of recombination in the space-charge region.     

Acoustic resonator transducer for operation in air

An acoustic resonator and electronic system for operation in air are described. The transducer operates in a resonant mode and can be utilised to measure the distance between the transducer and a reflecting object. Experimental results are presented for a 275 kHz resonator transducer that can measure distances with better than 0.5 ?m resolution at a 0.6 mm range. Applications to noncontacting surface profile measurements are also demonstrated.     

Experimental investigation of extinction cross-section of single vegetation elements using open resonator

The experimental results of investigation of the total cross — section of scattering and absorption (extinction cross — section) σ_t of stalks and strip leaves of grass in millimeter waves range are presented. The investigation was carried out using open quasioptical resonator with spherical mirrors. Measirements were carried out as by absolute method as using the relative method. Experimental results obtained by two different methods showed that in spite of some data differences obtained by absolute and relative methods the latter may be used for estimation of the extinction cross — section σ_t of vegetation elements.     

Design of aberration-corrected curved-mirror and curved-gratingunstable resonator diode lasers

An algorithm is presented for the design of an unstable optical resonator that supports an arbitrary optical mode. The same algorithm may be applied to the design of curved-mirror and curved-grating resonators, including both distributed Bragg reflector and distributed feedback unstable resonators. The new design formalism produces much simpler formulas than an algorithm previously described by the author. Example resonators are calculated that include hyperbolic-grating resonators with aberration-free diverging-beam modes and a newly proposed device: a parabolic-grating confocal distributed feedback unstable resonator that possesses a collimated output beam     

Analysis of bias-pin resonator diode mounts for millimeter-wave oscillators

Using microstrip antenna theory and an approximate model for an IMPATT diode, a theoretical analysis is carried out to determine variation in oscillator output power with diode contact point, for a bias-pin resonator circuit. The results compare favorably with experimental values previously published and indicate that, under some conditions, oscillator power output may be increased through use of an off-center diode contact point.     

Experimental investigation of microwave-optoelectronic interactionsin a microstrip ring resonator

Microwave optoelectronic mixing on a semi-insulating gallium arsenide substrate performed by monolithically integrating Schottky diode photodetectors into a microstrip ring resonator is discussed. When operated in the resistive mixing mode, a low frequency difference signal is extracted from the bias pad of the circuit. In the parametric mode, both degenerate and non-degenerate parametric amplification of an optical carrier signal takes place. The circuit shows good potential for application in wide-band fiberoptic systems     

Threshold variations in diode lasers induced by external resonator feedback

The effective reflectivity of an external resonator mirror coupled to a laser diode is typically inferred from the measured total reduction in threshold current when the laser diode is incorporated into the external resonator. The present paper demonstrates that this procedure overestimates the effective resonator feedback because the decrease in overall resonator losses causes a shift in laser output wavelength, which in turn leads to a reduction in wavelength-dependent losses. For the commercially available devices studied, the reduction in wavelength-dependent loss accounts for roughly half of the observed threshold current reduction. Experimental techniques are described in this paper for separating the two contributions to threshold reduction and thereby determining the actual value of the external resonator effective reflectivity, An additional complication arises because of the observed strong bias current dependence of the external resonator coupling in the region below lasing threshold where such lasers are typically biased in various mode-locking schemes. The magnitude of this bias current dependence, attributed to variations in laser mode guiding, has also been determined.     

The effect of temperature on the operation of an IMPATT diode

Some experimental results on the temperature dependence of an IMPATT oscillator are reported. Theoretical results for the effect of temperature upon the small-signal admittance of a Read diode are compared with the experiments.     

Dynamical properties of a laser diode with optical feedback from anexternal high-finesse resonator

The effect of coupling optically a laser diode to a high-finesse external resonator is described. The authors take into account multiple roundtrips in the external cavity and the carrier finite life-time in the diode laser. The rate equations are studied analytically. Steady states are obtained and their stability determined. Numerical resolution of the equations leads to predicting self-pulsing modes of operation. To the authors' knowledge, this is the first numerical study of the laser diode rate equations with an infinite number of delay terms. The main result is a stabilization effect due to the high-finesse cavity; neither deterministic chaos nor complicated bifurcation schemes have been found     

Saturation current and large-signal operation of a read diode

High reverse saturation currents can substantially reduce the potential oscillation efficiency of a Read diode. In this paper the effect of the magnitude of the saturation current was investigated theoretically within the framework of Read's original analysis. With the saturation current as high as 1/100 of the bias current Read's original efficiency prediction of 30 per cent is halved.Several mechanisms can give an effective ‘saturation’ current much larger than the prebreakdown value; for example, minority carrier storage in the space-charge neutral region adjacent to the avalanche region, or minority carrier injection by an imperfect ohmic contact to the neutral region. It is believed that this large effective saturation current is a major reason that experimental results have, to date, fallen far short of Read's prediction.