horn with A / B = 9.17, a / A = 0.15 and b/B = 0.05, design vaues that achieve a fair compromise between low sidelobe levels, beamwidth and aperture size. The semi-flare angle of the experimental horn was 39 and an experimental radiation pattern without channel inserts is included for comparison. The channel sections effectively reduce the radiation sidelobe levels to a level comparable with those predicted. The inserts increase experimental 3dB beamwidths, but these lie within theoretical limits imposed by assumed constant and quadratic phase across the aperture. The aperture phase error of the original horn, which causes splitting and broadening of the main beam at the higher frequency of Fig. 30, is apparently improved by the modification, which will enable the design of horns with larger apertures and shorter axial lengths than standard sectoral horns.

Conclusion: Fitting channel sections to an E-sectoral horn results in effective suppression of sidelobe levels in the radi- ation pattern. A finite difference analysis technique enables a quantitative explanation of measured radiation characteristics and the prediction of optimum designs for single frequency and broadband operation.

0. W. ATA School of Electronic Engineering Science University of Wales Bangor Bangor, Gwynedd, LL57 IUT, United Kingdom

T. M. BENSON Department of Electrical and Electronic Engineering Uniuersity of Nottingham Nottingham, NG7 2RD, United Kingdom

A. MARINCIC Faculty of Electrical Engineering University of Belgrade Bulevar Revolucige 73, IlooO Belgrade, Yugoslauia

Refereaces

1

2

27th November 1989

HAMIO, M., and AL-SULAIMAN, A.: New types of dielectric-loaded horn antennas, Int. J. Electron., 1983,55, pp. 729-750 MARINCIC, A.: Beam shaping of sectoral and pyramidal horns with stepped amplitude distribution. Proc. int. conf. on antennas and propagation, h. 1, London, 1981, pp. 328-332 MARINCIC, A., BENSON, T. M., and FARHAT, K. S.: Ray theory design of hyperbolic secant horn, Electron. Lett., 1986, 22, (7). pp. 367-369

4 STEVENSON, A. F.: General theory of electromagnetic horns, J. Appl. Phys., 1951.22, pp. 1447-1460

5 SILVER, s. (Ed.): Microwave antenna theory and design (Peter Peregrinus, London, 1984.2nd edn.)

6 DAVID, 1. B., and MUILWYK, c. A.: Numerical solution of uniform hollow waveguides with boundaries of arbitrary shape, Proc. IEE, 1966,113, pp. 277-284

3

HIGH-POWER SINGLE MODE InGaAs/AIGaAs LASER DIODES AT 910nm

Indexing terms: Lasers nnd lnser applications, Diodes, Gallium nrsenide

Single mode laser diodes have ken fabricated from pseudn- morphic InGaAs/NGaAs quantum well epitaxial material operating up to 350mW CW. The laser output is a single transverse and longitudinal mode to 180mW. while the spec- tral output is centred near 910nm.

High-power single mode lasers are of particular interest in applications which require diffraction limited imaging systems, including frequency doubling, optical recording, free space communications and coupling to single mode fibres. Substan- tial advances have been made in the fabrication of high power single mode lasers where maximum output powers of 500mW CW have been demonstrated. Single mode laser diodes are

now commercially available at output powers of l00mW CW. Significant progress has also been achieved in the fabri- cation of pseudo-morphic InGaAs/AlGaAs quantum well lasers. Demonstration of high CW output powers? increased

and emission to wavelengths greater than l ~ - ~ have all been achieved using InGaAs/ AlGaAs pseudomorphic material.

In this letter we present data on single mode lasers that operate at 350mW CW output powers, while maintaining single transverse and longitudinal mode outputs to greater than 180mW CW. The device characteristics are similar to GaAs/AlGaAs single mode diodes excluding wavelength where the InGaAs/AlGaAs lasers operate at 910nm.

The epitaxial structure is grown in an atmospheric metall- organic chemical vapour deposition reactor. The lasing struc- ture consists of (i) GaAs n-type substrate, (ii) A1,.,Ga0.,As n-type cladding layer, (iii) AI,.,Ga,.,AS undoped confining layer, (iv) In,.,Ga,.,As undoped active layer (lOnm), (v) AI,.,Ga,.,As undoped confining layer, (vi) A1,.,Ga0.,As ptype cladding layer, (vii) GaAs ptype contact layer. The cladding layers were grown at a substrate temperature of 81OC, the confining and active layers were grown at a tem- perature of 700C.

4 pm wide real refractive index lasers with 500pm long cavities, and facet reflectivities of 95% and 5% on the front and rear facets, respectively, were operated CW. The light output as a function of input current is presented in Fig. 1.

single mode

current, rn A pl1ll) Fig. 1 Light output against input current for single stripe InGnAslGaAs laser diode

lo = 12%

The threshold current is 18 mA, while the differential efficiency is 72% up to an output power of approximately 250mW CW. The maximum output power achieved was 350mW CW. This is the highest reported output power from a 4pm wide single stripe InGaAs/AlGaAs laser. The only higher reported output power for a single stripe laser is 500mW CW demonstrated from a comparable GaAs/AlGaAs single stripe laser.

The far field radiation pattern is shown in Fig. 2. The lowest

Z I

150 mW c w

100 rnW cw

50 m W c w

Fig. 2 For field radiation patterns from single stripe InGaAslAIGaAs laser diode

ELECTRONICS LETTERS 15th February 1990 Vol 26 No 4 233

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order transverse mode is shown to operate up to an output power of greater than 180mW CW. The lateral divergence is 10 full width at half maximum (FWHM). The divergence perpendicular to the pn junction is approximately 35 FWHM.

The spectral output of the single stripe laser is presented in Fig. 3. The laser operates in a single longitudinal mode up to

7 1 1 1 1

2 5 0 m W cw

l l l , l l l ,

900 910 920 wavelength, nm

Fig. 3 Spectral outputfrom single sfripe InCaAs/AIGaAs laser diode

operating ranges of 180mW CW where the laser deviates from the lowest order transverse mode. In addition there are regions of operation where a single transverse mode is main- tained at even higher output power levels. The highest output power at which single longitudinal mode operation was achieved was 250mW CW. This seems to correspond to the region where the light output becomes sublinear with input current. The emission wavelength is near 910nm.

In conclusion, 4pm wide single stripe laser diodes have been fabricated from pseudomorphic, InGaAs/AlGaAs, epi- taxial material. The diodes operate at powers exceeding 350mW CW, while maintaining a single transverse and longi- tudinal mode up to power outputs of 180mW CW. The spec- tral output is near 910nm. Such a source may be useful for creating efficient blue light at 455nm via frequency doub-

The authors would like to thank Ross Parke, Paul Tally, Tim Earls, TON Tally, David Mehuys, Rob Waarts and Sean Ogarrio for their support.

D. F. WELCH M. CARDINAL B. STREIFER D. SCIFRES Spectra Diode Laboratories 80 Rose Orchard Way San Jose, C A 95134, USA

24th November I989

Referencea 1 WELCH, D. F., mmsm, w., and SCIPRES, D. R.: High power single

mode laser diodes. SPIE Laser Diode Technology and Applica- tions, 1989,losJ, pp. 54-60

2 SDL-5410 commercially available lOOmW CW, single mode laser 3 WELCH, D. F., SCHAUS, c. P., m,s,oou~w, P. L., and STREIFW, w.:

Gain characteristics of strained quantum well lasers, to be publied in AppI. Phys. Letts.

4 VABUINOVITCH, E, and M E 0.: Band structure engineering of semiconductor lasers for opt id mmmunications, J. Lightwave Tech., 1988,6, (8), pp. 1292-1299

5 MUOR, I. S., GULDO, L. I., Hsw, K. C., HOUINYAK, N., STUTUTNS, W., GAVRIUIWC, P., and WIL- I. E.: Low-threshold disorder defined buried heterostructurc strained layer AIGaAs/GaAs/ InGaAs quantum well lasers, Appl. Phys. Letts., 1989, 54, (lo), pp. 913915

6 YORK, P. K., B ~ N I N K , K. I., FEXNANDEZ, G. E., and COLEMAN, I. I.: InGaAs-GaAs strained layer quantum well buried hetero- structure lasers by metalorganic chemical vapour deposition, Appl. Phys. Lett., 1989.54, (a), pp. 499-501

7 TSANG, w. T.: Extension of lasing wavelengths beyond 0 . 8 7 ~ in GaAsfAlGaAs double hetemstructure lasers by In incorporation in the GaAs active layers during molecular beam epitaxy, Appl. Phys. Lett., 1981,38, (9), pp. 661463

8 noun, D. P., w n r m . L I , R. U,, GILBERT, D. B., ELBAUM, L., and WVEY, M. G.: Operating characteristics of InGaAsiAlGaAs strained single quantum well lasers, AppI. Phys. Letts., 1989, 55, (19, pp. 150-1503

9 swnus, w., GAVRILOWC, P., WILL-, I. E., M W A N , K., and ZARRABI, I. H.: Continuous operation of high power strained layer GaInAsfAlGaAs quantum well lasers, Electron. Lett., 1988, 24, (24). pp. 149H494

10 O O ~ B E R G , L., and c, M.: Efficient generation of 421nm by resonantly enhanced doubling of GaAlAs laser diode array emis- sion, Appl. Phys. Lett., 1989,55, (3). pp. 218-221

11 KOZUIVSKY, w., NABOFS, c. D., and BYER, R. L.: Efficient sccond harmonic generation of a diode laser pumped cw Nd : YAG laser using monolithic MgO : LiNbO, external resonant cavities, J . Qunnt. Electr., 1988,24, (6A pp. 913919

12 BAO~, T., DETIWFAD, M. s., and WELCH, D. F.: Efficient frequency doubling of a diode laser. Conference on Lasers and Electro- optics, 1989

COMPARISON OF THREE NUMERICAL

COAXIAL LINE SENSOR TREATMENTS FOR THE OPEN-ENDED

Indexing terms: Microwave circuits and systems, Numerical methods and d e r theory, Microwave measurements

The open-ended coaxial line sensor is commonly used for non-invasive microwave dielectric measurements. A compari- son is made between three mathematical treatments that allow the reflection coefficient of the sensor lo be derived from the complex permittivity of the material with which it is in contact. It is shown that the discrepancies between values computed by the three methods are much smaller than the predicted measurement uncertainties. Mappings of permit- tivity contours onto the complex reflection coefficient plane are shown.

The open-ended coaxial line sensor, shown in Fig. 1, is com- monly used with automated network analysers and other reflectometers for non-invasive measurement of the complex permittivity of materials at radio and microwave frequencies. Equivalent circuits are often used to model the relationship between the relative permittivity E* of the material and the measured reflection coefficient r* of the sensor in contact with the material, where E* = E -is and r* = r exp GO). However, it has been argued that if numerical analysis is employed instead of an equivalent circuit treatment, a wider range of permittivity values can be determined more accu- rately with a particular sensor over a given frequency range, a conclusion that was reached on the basis of only a single

flanae

measurement sample

--I standard airline

Fig. 1 Open ended coaxial line sensor

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