NASA Contractor Report 18220 1 4 - '

Optoelectronic Gain Control of a Microwave Single Stage GaAs MESFET Amplifier

Rainee N. Simons Case Western Reserve University Cleveland, Ohio

September 1988

Prepared for Lewis Research Center Under Grant NAG3-8 16

National Aeronautics and Space Administration

https://ntrs.nasa.gov/search.jsp?R=19880020671 2018-06-28T13:35:18+00:00Z

OPTOELECTRONIC G A I N CONTROL OF A MICROWAVE SINGLE STAGE

GaAs MESFET AMPLIFIER

M u3 m M

I w

Rainee N. Simons* Case Western Reserve U n i v e r s i t y

Cleveland, Ohio 44106

SUMMARY

I n t h i s paper we demonstrate g a i n c o n t r o l o f a s i n g l e s tage GaAs MESFET a m p l i f i e r by t h e use of o p t i c a l i l l u m i n a t i o n of photon energy g r e a t e r t han t h e GaAs bandgap. The o p t i c a l i l l u m i n a t i o n i s s u p p l i e d by a semiconductor l a s e r d iode and i s coupled to t h e Scho t t ky gate of t h e MESFET by an o p t i c a l f i b e r . The inc rease i n g a i n i s observed t o be as much as 5.15 dB when t h e MESFET i s b iased c l o s e t o p inch -o f f , t h a t i s , Vgs = -1.5 V and w i t h o p t i c a l i l l u m i n a t i o n o f 1.5 mW.

The computed maximum a v a i l a b l e g a i n (MAG) and c u r r e n t g a i n ( Ih211) from t h e de-embedded s-parameters show t h a t MAG i s unaffected by o p t i c a l i l l u m i n a - t i o n , however, Ih211 increases by more than 2 dB under o p t i c a l i l l u m i n a t i o n o f 1.5 mW. g a i n c u t o f f f requency ( F t ) o b t a i n e d by e x t r a p o l a t i n g t h e MAG and Ih21 I curves r e s p e c t i v e l y show t h a t t h e Fmax i s i n s e n s i t i v e t o o p t i c a l i l l u m i n a - t i o n however F t i nc reases by 5 GHz.

The maximum f requency of o s c i l l a t i o n (Fmax) and t h e u n i t y c u r r e n t

INTRODUCTION

Mono1 i t h i c Microwave I n t e g r a t e d C i r c u i t (MMIC) Technology based on t h e G a l l i u m Arsenide (GaAs) Meta l Semiconductor F i e l d E f f e c t T r a n s i s t o r (MESFET) has r e s u l t e d i n m i n i a t u r e r e c e i v e r modules for e l e c t r o n i c a l l y scanned phased a r r a y antenna systems ( r e f . 1 ) . The b a s i c b u i l d i n g b l o c k s i n these modules a r e t h e low n o i s e a m p l i f i e r s , t h e m ixe rs for s i g n a l downconversion t o i n t e r m e d i a t e f requency ( I F ) , t h e phase s h i f t e r s and t h e v a r i a b l e g a i n a m p l i f i - e r s for c o n t r o l l i n g t h e s i g n a l phase and amp l i t ude . For t h e r e c e i v e r s t u d i e d he re , t h e m i x e r c o n s i s t s of a dual ga te MESFET o p e r a t i n g on t h e heterodyne p r i n c i p l e and r e q u i r i n g a l o c a l o s c i l l a t o r s i g n a l . t h e swi tched l i n e t y p e and makes use of d e p l e t i o n mode MESFETs for s w i t c h i n g . The MESFET swi tches a re TTL compat iab le and r e c e i v e a 5 b i t word command from a c e n t r a l processor f o r phase s e t t i n g . c o n s i s t s o f a dual ga te MESFET which r e q u i r e s a v a r i a b l e b i a s v o l t a g e on t h e c o n t r o l g a t e f o r g a i n v a r i a t i o n . The v a r i a b l e b i a s i s p r o v i d e d by a D/A con- v e r t e r which a l s o r e c e i v e r s i t s command from a c e n t r a l p rocesso r . The D/A con- v e r t e r c o n s i s t s o f enhancement mode MESFETs.

The phase s h i f t e r i s o f

The v a r i a b l e g a i n a m p l i f i e r a l s o

The conven t iona l approach of d i s t r i b u t i n g t h e l o c a l o s c i l l a t o r and t h e

The main d isadvantage o f d i g i t i a l command s i g n a l s t o t h e b a s i c b l o c k s i s t o use s e m i - r i g i d c o a x i a l cables and s h i e l d e d cables r e s p e c t i v e l y ( r e f . 2 ) .

*NASA Resident Research Assoc ia te .

t h i s approach i s t h a t i t would make t h e a r r a y l a r g e and heavy and offset some o f the advantages gained by t h e m o n o l i t h i c technology i n t e r m s o f module s i z e and weight . An a l t e r n a t i v e approach i s t o use o p t i c a l i n t e r c o n n e c t t echn ique which i s based on o p t i c a l f i b e r t echno logy and t h e c a p a b i l i t y t o i n t e n s i t y - modulate an AlGaAs/GaAs semiconductor l a s e r d iode a t r a t e s up t o t h e m ic ro - wave f requenc ies ( r e f . 3 ) . Thus t h e o p t i c a l i n t e r c o n n e c t technique i s capable o f conveying t h e l o c a l o s c i l l a t o r s i g n a l t o t h e m i x e r on an o p t i c a l c a r r i e r . I n a d d i t i o n , i t can i f necessary p r o v i d e i n j e c t i o n l o c k i n g o f t h e l o c a l o s i c i l - l a t o r t o a s t a b l e master o s c i l l a t o r ( r e f . 4 ) . I n a s i m i l a r manner t h e d i g i t a l command s i g n a l s t o t h e phase s h i f t e r and t o t h e D / A c o n v e r t e r i n t h e v a r i a b l e g a i n a m p l i f i e r s can be t r a n s m i t t e d from t h e c e n t r a l processor . F i g u r e 1 presents a schematic showing p o s s i b l e o p t i c a l i n t e r c o n n e c t s i n a t y p i c a l phased a r r a y antenna sys tem. i n t e r c o n n e c t f o r mircowave and d i g i t a l s i g n a l d i s t r i b u t i o n .

t h e dc c h a r a c t e r i s t i c s ( r e f s . 5 and 6) and t h e microwave c h a t a c t e r i s t i c s ( r e f s . 7 t o 11) o f GaAs M E S F E T ' s . I n t h i s paper we demonstrate f o r t h e f i r s t t ime g a i n c o n t r o l o f a s i n g l e s tage GaAs MESFET a m p l i f i e r by t h e use o f o p t i - c a l i l l u m i n a t i o n w i t h photon energy g r e a t e r than t h e GaAs bandgap. The o p t i - c a l i l l u m i n a t i o n i s s u p p l i e d by a semiconductor l a s e r d iode and i s coupled t o t h e Scho t t ky ga te o f t h e MESFET by an o p t i c a l f i b e r . Thus t h e o p t i c a l i l l u m i - n a t i o n has a r o l e s i m i l a r t o a c o n t r o l gate i n a dual gate MESFET. The above approach i s termed d i r e c t o p t i c a l g a i n c o n t r o l s i n c e o p t i c a l i l l u m i n a t i o n i s r e s p o n s i b l e for g a i n v a r i a t i o n . The a m p l i f e r ope ra tes a t K-band, where NASA i s deve lop ing GaAs M M I C s f o r f u t u r e s a t e l l i t e communications systems and NASA m i ss ions.

F i g u r e 2 i l l u s t r a t e s a s imple f i b e r o p t i c a l

Several au tho rs have i n v e s t i g a t e d t h e e f f e c t of o p t i c a l i l l u m i n a t i o n on

This paper a l s o examines t h e e f f e c t o f o p t i c a l i l l u m i n a t i o n on t h e f i g u r e o f m e r i t o f a GaAs MESFET. The f i g u r e o f m e r i t i s a good i n d i c a t o r o f t h e dev i ce performance as an a m p l i f i e r . MESFETs a r e t h e maximum a v a i l a b l e g a i n (MAG) and c u r r e n t g a i n ( Ih21 1 ) . These a re f u n c t i o n s o f a l l f o u r s c a t t e r i n g parameters (s-parameters) o f t h e dev i ce . Hence, t h e f u l l two p o r t s-parameters w i t h and w i t h o u t o p t i c a l i l l u m i n a t i o n a re measured for a GaAs MESFET c h i p dev i ce . The de-embedded s-parameters a r e then used t o determine t h e e f f e c t o f o p t i c a l i l l u m i n a t i o n on MAG, Ih21 I , t h e maximum f requency o f o s c i l l a t i o n (Fmax), and t h e u n i t y c u r r e n t g a i n c u t o f f

Commonly used f i g u r e s o f m e r i t f o r

I f requency ( F t ) .

EXPERIMENTAL SETUP

Measurements o f t h e c h a r a c t e r i s t i c s of an o p t i c a l l y i l l u m i n a t e d a m p l i f i e r were c a r r i e d o u t u s i n g a Texas Ins t rumen ts c h i p which was based on a low-noise GaAs MESFET w i t h a ga te o f l e n g t h 0.25 pm and w i d t h 75 pm. d r a i n spacing o f t h i s dev i ce i s about 1.6 t o 2.0 pm, and t h e ga te i s a t a d i s t a n c e o f 0.2 t o 0.3 pm from t h e source. molecular beam e p i t a x y . o u t p u t match ing networks.

0503A) manufactured by Gould, I n c .

The source-to-

The d e v i c e i s f a b r i c a t e d u s i n g The a m p l i f e r c o n s i s t s o f a s i n g l e MESFET w i t h i n p u t /

The GaAs MESFET i n v e s t i g a t e d here was a low-noise, low-power dev i ce (DXL I t f e a t u r e d a recessed Pi -gate o f l e n g t h

I 2

0.3 pm and w i d t h 280 pm. The source- to-dra in spacing o f t h i s d e v i c e i s about 5 pm and t h e ga te i s centered. I t i s f a b r i c a t e d u s i n g vapor-phase e p i t a x y . Measurements were made t o determine t h e e f f e c t o f o p t i c a l i l l u m i n a t i o n on MAG, Ih211, Fmax, and F t .

An AlGaAs/GaAs l a s e r d iode (SL-620, O r t e l Corp.) w i t h a f i b e r p i g t a i l i s used for i l l u m i n a t i o n . The o p t i c a l power e m i t t e d from t h e 501125 pm mult imode graded index o p t i c a l f i b e r p i g t a i l i s about 1.5 mW. The t i p o f t h e f i b e r i s h e l d a t a d i s t a n c e of 1 mm from t h e dev i ce .

The l a s e r d iode operates a t a wavelength o f 0.83 pm.

Both t h e MESFET and t h e a m p l i f e r a r e mounted on a lumina c a r r i e r s . on t h e c a r r i e r s , t h e coplanar waveguide (CPW) t e s t f i x t u r e , t h e CPW c a l i b r a - t i o n k i t f o r de-embedding t h e a m p l i f i e r c h a r a c t e r i s t i c s and t h e d e v i c e s-parameters, and t h e b l o c k schematic of t h e e n t i r e exper imenta l setup a r e presented elsewhere ( r e f . 11) .

D e t a i l s

OPTOELECTRONIC MICROWAVE AMPLIFER G A I N CONTROL

F i g u r e 3(a) p resen ts a photograph o f t h e s i n g l e stage GaAs MESFET a m p l i f e r which a l s o shows t h e cop lana r waveguide i n p u t and o u t p u t l i n e s and t h e b i a s i n g c i r c u i t s . F i g u r e 3(b) p resen ts a photomicrograph o f t h e MESFET dev i ce . F i g u r e 3(c) p resen ts a schematic o f t h e a m p l i f i e r c i r c u i t . The a m p l i f e r i s designed t o o p e r a t e o v e r a 1 GHz bandwidth cen te red a t 26 GHz. F i g u r e s 4(a) t h rough 4(d> show t h e measured s-parameters o f t h e a m p l i f e r w i t h o u t o p t i c a l i l l u m i n a t i o n and a t a f i x e d gate-to-source v o l t a g e o f -1.19 V and d r a i n - t o - source v o l t a g e (Vds) o f 3 V . I t should be noted t h a t t h e l osses o c c u r i n g i n t h e c o a x i a l connectors , t e s t f i x t u r e , and t h e i n p u t / o u t p u t CPW l i n e s have been c a l i b r a t e d o u t . F igu res 5(a) t h rough 5(d) show t h e measured s-parameters o f t h e a m p l i f e r w i t h o p t i c a l i l l u m i n a t i o n o f 1.5 mW. Comparing f i g u r e s 4 and 5 i t i s observed t h a t t h e g a i n (S21) increases by 2.6 dB under i l l u m i n a t i o n . The inc rease i n t h e g a i n i s because of t h e l i g h t induced v o l t a g e which i s due t o t h e p h o t o v o l t a i c and photoconduct ive e f f e c t s a t t h e S c h o t t k y g a t e o f t h e MESFET ( r e f . 1 1 ) . The l i g h t induced v o l t a g e f o r w a r d b iases t h e gate- to-source r e g i o n o f t h e MESFET. F u r t h e r , t h e i n p u t and o u t p u t imepedances ( S i 1 and S22) o f the a m p l i f e r show improved match to t h e 50 SI i n p u t and o u t p u t l i n e s r e s p e c t i v e l y . The improvement i n t h e impedance match i s because o f t h e i nc rease i n t h e gate- to-source capaci tance and a l s o due t o changes i n t h e MESFET e q u i v a l e n t c i r c u i t element va lues which a re brought about by o p t i c a l i l l u m i n a t i o n ( r e f . 10) . O p t i c a l i l l u m i n a t i o n a l s o improves t h e i s o l a t i o n ( S 1 2 ) between t h e i n p u t and o u t p u t p o r t s . changes i n t h e MESFET e q u i v a l e n t c i r c u i t element va lues.

This can a l s o be a t t r i b u t e d t o t h e

The above exper iments were repeated f o r severa l va lues o f Vgs F i g u r e 6 i l l u s t r a t e s t h e

r a n g i n g from p i n c h - o f f t o z e r o and a t a f i x e d vds i n c r e a s e i n g a i n (AS211 under i l l u m i n a t i o n a t t h e c e n t e r f requency o f 26 GHz and as a f u n c t i o n o f Vgs. AS21 5.15 dB when t h e MESFET i s b iased c l o s e t o p i n c h - o f f , t h a t i s Vgs = -1.5 V . F i g u r e 6 a l s o i l l u s t r a t e s t h e corresponding i nc rease i n t h e d ra in - to -sou rce c u r r e n t Aids under o p t i c a l i l l u m i n a t i o n . Aids a t t a i n s a m ximum va lue o f 2.89 mA when Vgs Under o p t i c a l i l l u m i n a t i o n o f 1 . 5 mW t h i s t r a n s l a t e s i n t o a r e s p o n s i v i t y o f 1.93 A/W. F i g u r e 7 (a ) shows t h e v a r i a t i o n o f t h e i n p u t impedance o f t h e a m p l i f i e r a t t h e c e n t e r f requency o f 26 GHz w i t h and w i t h o u t o p t i c a l i l l u m i n a t on as a f u n c t i o n

o f 4 V .

i s observed t o t a k e a maximum v a l u e o f

i s c l o s e t o zero, t h a t i s , Vgs = -0.66 V.

3

o f Vgs. These f i g u r e s i l l u s t r a t e t h a t t h e i n p u t and o u t p u t impedances have improved match t o 50 s2 l i n e s , under i l l u m i n a t i o n , for a l l b i a s va lues r a n g i n g from z e r o t o p i n c h - o f f .

S i m i l a r l y , f i g u r e 7 ( b > shows t h e v a r i a t i o n o f t h e o u t p u t impedance.

MESFET FIGURE OF M E R I T UNDER OPTICAL ILLUMINATION

Maximum A v a i l a b l e Gain and Maximum Frequency o f O s c i l l a t i o n

The f u l l two p o r t s c a t t e r i n g parameters o f t h e MESFET c h i p dev i ce i s measured ove r t h e f requency range 0.045 t o 18 GHz w i t h and w i t h o u t o p t i c a l i l l u m i n a t i o n . The de-embedded s-parameters a r e used t o compute t h e MAG and t h e s t a b i l i t y f a c t o r ( K ) u s i n g t h e EEsof Touchstone so f tware ( r e f . 12). F i g u r e 8(a) shows t h e MAG as a f u n c t i o n o f t h e f requency. E x t r a p o l a t i o n o f t h e MAG cu rve f o r K g r e a t e r t han u n i t y a t t h e r a t e o f -6 dB/octave t i l l i t m e e t s t he z e r o g a i n a x i s y e i l d s Fmax. N e i t h e r MAG or Fmax a r e a f f e c t e d by o p t i c a l i l l u m i n a t i o n .

C u r r e n t Gain and U n i t y C u r r e n t Gain C u t - o f f Frequency

The c u r r e n t g a i n ( Ih211) i s a l s o computed from t h e measured s-parameters u s i n g t h e EEsof Touchstone so f tware ( r e f . 12). F i g u r e 8(b> shows ( h 2 l ( a s a f u n c t i o n of t h e f requency . E x t r a p o l a t i o n o f t h e Ih21 I curve a t t h e r a t e o f -6 dB/octave y i e l d s F t . I t i s observed t h a t o p t i c a l i l l u m i n a t i o n o f 1.5 mW increases (h21 I and F t by 2 dB and 5 GHz r e s p e c t i v e l y .

CONCLUSIONS AND DISCUSSIONS

Th is paper demonstrates for t h e f i r s t t i m e o p t o e l e c t r o n i c g a i n c o n t r o l o f a s i n g l e s tage GaAs MESFET a m p l i f i e r . The g a i n c o n t r o l i s achieved by i l l u r n i - n a t i n g t h e S c h o t t k y g a t e o f t h e MESFET w i t h o p t i c a l power from an AlGaAs/GaAs l a s e r d iode. The measued s-parameters show t h a t t h e i n c r e a s e i n g a i n (S21) i s g r e a t e r t han 5 dB when t h e MESFET i s b iased c l o s e t o p i n c h - o f f . MESFET has a r e s p o n s i v i t y o f 1.93 A/W. The r e s p o n s i v i t y can be improved if t h e gate m e t a l l i z a t i o n i s i nd ium t i n o x i d e ( I T O ) . IT0 besides b e i n g t r a n s p a r - e n t a l s o forms a good S c h o t t k y c o n t a c t w i t h GaAs and i t s t h i c k n e s s can be cho- sen t o a c t as an a n t i r e f l e c t i o n c o a t i n g a t t h e wavelength o f o p e r a t i o n ( r e f . 13).

L a s t l y , t h e

The computed MAG and Ih21 I from t h e deembedded s-parameters show t h a t MAG i s u n a f f e c t e d b u t t h a t (h21 I i nc reases by 2 dB under o p t i c a l i l l u m i - n a t i o n o f 1.5 mW. The Fmax and F t o b t a i n e d by e x t r a p o l a t i n g t h e MAG and (h211 curves r e s p e c t i v e l y show t h a t Fyax i s i n s e n s i t i v e t o o p t i c a l i l l u m i n a - t i o n b u t F t i nc reases by 5 GHz. lower s w i t c h i n g power and s m a l l e r s w i t c h i n g t ime .

The inc rease i n Ih21 I and F t w i l l r e s u l t i n

ACKNOWLEDGMENT

E . Haugland and R. Romanofsky o f NASA Lewis Research Center gave many h e l p f u l t e c h n i c a l suggest ions on GaAs MESFET and model ing o f t h e i r c h a r a c t e r i s - t i c s r e s p e c t i v e l y . The a u t h o r a l s o wish t o thank Paul Saunier o f Texas I n s t r u - ments I n c . for p r o v i d i n g and a l s o f o r t h e bonding o f t h e GaAs MESFET dev ices used i n t h e a m p l i f i e r .

4

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11. Simons, R.N. : Microwave Performance o f an O p t i c a l l y C o n t r o l l e d AlGaAs/GaAs H igh E l e c t r o n M o b i l i t y T r a n s i s t o r and GaAs MESFET. I E E E Trans . Microwave Theory Tech., v o l . MTT-35, no. 12, Dec. 1987, pp. 1444-1 455.

12. EEsof Touchstone U s e r ' s Manual. EEsof I n c . , CA, 1987 pp. EL-22 t o EL-25.

13. P a r k e r , D.G., e t a l . : 110 GHz H i g h - E f f i c i e n c y Photod iodes F a b r i c a t e d From I n d i u m T i n OxideiGaAs. E l e c t r o n . L e t t . , vo1.23, no. 10, May 7, 1987, pp. 527-528.

5

PHASE SHIFTER AMPLIFIER PAPLIFIER

I I I I I

0

-- I F W L I F I E R .c- MIXER f- - PHASE SHIFTER - LOW NOISE PAPL I F I ER

r - RECE IVE 4 MODULE I

i I

I I F I SIGNAL

I I I --- POSSIBLE OPTICAL INTERCONNECTS

OSCILLATOR OSC I LLATOR

I I I --- POSSIBLE OPTICAL INTERCONNECTS

OSCILLATOR OSC I LLATOR -- FIGURE 1. - SCHEMATIC SHOWING POSSIBLE OPTICAL INTERCONNECTS BETWEEN VARIOUS BASIC BLOCKS I N A TYPICAL

PHASED ARRAY WITH GaAs MMIC BASED TRANSNIT/RECEIVE MODULES.

SEMI CONDUCTOR LASER DIODE

OPTICAL FIBER DETECTOR (MESFET. H E N PHOTODIODE.

c MODULATION SIGNAL (RF AMPLIFIER OR DIGITAL) (OPTIONAL) DIGITAL)

FIGURE 2. - SCHEMTIC SHOWING A TYPICAL OPTICAL INTERCONNECT FOR RF AND DIGITAL SIGNALS.

6

( A ) PHOTOGRAPH OF AMPLIFIER.

(B) PHOTOGRAPH OF THE 0.25 pM x 75 pH GaAs MESFET (TEXAS INSTRUMENTS) USED I N THE AMPLIFIER.

FIGURE 3. - GaAs N S F E T AMPLIFIER.

7

ORlGlNAL PAGE 1s OF POOR QUALlW

INPUT

8

b -"g s

(C) CIRCUIT CONFIGURATION . FIGURE 3. - CONCLUDED.

I o g MAG REF 0 0 dB

l v -0 0278 dB I 0 dB/

c

I .

/'

C

5

1

CENTER 26 000000000 GHz SPAN 1 000000000 GHZ

(D) S22. IGURE 5. - H S U R E D S-PARAETERS OF THE M ' L I - FlER WHEN ILLUMINATED, AT A = 0.83 ~n AND

W L T I W D E FIBER. P O ~ T = 1.5 RIM, FROW THE END OF A 50/125 PH

ORlGlNAL PAGE IS

OF QuALmy

8

'I- T I GaAs E S F E T

FREQ = 26.0 GHz

2

0 -1.6 -1.4 -1.2 -1.0 - .8 - . 6 -.4 - . 2 0

GATE-TO-SOURCE VOLTAGE. Vgs, V

FIGURE 6. - H S U R E D INCREASE I N GAIN (AS21) AND THE DRAIN CURRENT Cards) UNDER OPTICAL ILLUMINATION AS A FUNCTION OF Vgs AT THE CENTER FREQUENCY.

9

- DARK ---- WITH ILLIJNINATION

1 .o (A) INPUT.

(B) OUTPUT.

FIGURE 7. - REASURED AMPLIFIER IMPEDANCE AS A FUNCTION OF Vgs AT THE CENTER FREQUENCY WITH AND WITHOUT OPTICAL ILLUEIINATION.

0 DARK 0 WITH ILLUMINATION

DXL 0503 A vds = 4.0 v vgs = -0.36 v I d s = 15 HA (DARK)

= 24.0 HA (WITH ILLUEIINATION) P ~ T = 1.5 HW h = 0.83 pH

s . 30r

(A) HAG AND F m .

30 r r -6 dB/OCTAVE 5 1

3 lot w r Ft = 20 GHz -

; (WITH ILLIJN- Ft = 15 GHz (DARK) - / INATION)

' 1 I I I I I I I 2 3 4 6 8 10 20 30 40 60 80100

0 1

FREQUENCY, GHz

(B) IhqlJ AND Ft.

FIGURE 8. - CWUTED FIGURt OF PERIT FROn THE DE-EMBEDDED S-PARPETERS .

ORIGINAL PAGE E' OF POOR QUALITY

10

National Aeronautics and Space Administration

1. Report No.

NASA CR-182201

Report Documentation Page 2. Government Accession No. 3. Recipient's Catalog No.

4. Title and Subtitle

Optoelectronic Gain Control of a Microwave Single Stage GaAs MESFET Amplifier

5. Report Date

September 1988

7. Author@)

Rainee N. Simons

8. Performing Organization Report No.

None (E-3963)

10. Work Unit No.

9. Performing Organization Name and Address

Case Western Reserve University Cleveland, Ohio 44106

12. Sponsoring Agency Name and Address

National Aeronautics and Space Administration Lewis Research Center Cleveland, Ohio 44135-3191

Project Manager, Regis F. Leonard, Space Electronics Division, NASA Lewis Research Center. Rainee N. Simons. NASA Resident Research Associate.

11. Contract or Grant No.

NAG3-8 16

13. Type of Report and Period Covered Contractor Report Final

14. Sponsoring Agency Code

16. Abstract

17. Key Words (Suggested by Author(s))

Optical control Amplifier GaAs MESFET Microwave

In this paper we demonstrate gain control of a single stage GaAs MESFET amplifier by the use of optical illumi- nation of photon energy greater than the GaAs bandgap. The optical illumination is supplied by a semiconductor laser diode and is coupled to the Schottky gate of the MESFET by an optical fiber. The increase in gain observed to be as much as 5.15 dB when the MESFET is biased close to pinch-off, that is, VgS = -1.5 V and with optical illumination of 1 .5 mW. The computed maximum available gain (MAG) and current gain ( lh2, 1) from the de- embedded s-parameters show that MAG is unaffected by optical illumination, however, lh21 I increases by more than 2 dB under optical illumination of 1.5 mW. The maximum frequency of oscillation (FmJ and the unity current gain cut-off frequency (F,) obtained by extrapolating the MAG and lh2,) curves respectively show that the F,, is insensitive to optical illumination however F, increases by 5 GHz.

18. Distribution Statement

Unclassified -Unlimited Subject Category 33

9. Security Classif. (of this report) 20. Security Classif. (of this page) 21. No of pages

Unclassified Unclassified 12 I I I

"For sale by the National Technical Information Service, Springfield, Virginia 221 61 NASA FORM 1626 OCT 88

22. Price'

A03