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O pt i cal M i l l im eter -W av e G ener ati onby L ock in g of F our -W av e-M i xin g C onj ugat e M odes in DFB L aser s

Y oung-K wang Seo and Woo-Y oung Fhoi

Dept. of Elem ica1 a d Compute EnÏ m em . Y onsei UW a n. , Sem¤1, K oreaTe1: +82-23 6 1-2874, Fax : +822 3 l 24 584, E-md : wchoi@ya s ei -- .kr

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A - Jung K i mD iÈ U 1 Comn . L ab ., Sam sung A dv anced I nst im e of T echnol ogy , P.O . B ox 1 1 1, Suw on 440-600, K or ea

T he opt ical generat ion of n m im et- -w av e (M M W ) sip als h as been at - act ing xnu ch in terest f or

m a y apph cat i on s, su ch as b roadband w ireless com m ¤ icat ion s a d op t ical bean f om in s becau se o f it sf 1ex m in t y in generat i ng h igh -- equem y si gnal s. I n par ti cu lar , th e side-ba d in a t ion- lock ing is a

p rom i sing techn i qu e since it has a sim p le con f igu ra t i on a d is ab1e t o produce pu re a d stab l e M M Wsip al s [ 1,2 ] . B raun er af - u sed m o g av e l aser s (SL s) to sel ect the tar get m odes m ong sev era1 si de-bu ds

generated in the rC m odu lated rnaster laser @1L ) , a d hav e W o selected m odes b eat each oth er in thephotod iode ¥ D ) to pr odu ce 60G H z [ 1] . N oel er o f . da nonm ated £ e gm erat ion of 60GH z by im a ti ngcont inu ou s w av e (cw ) M L l iÈ t in to th e r L m odu l ated SL , a d beat i ng M L w ith a sel ected SL side-b a d

[2] . h these t echn iqu es, h ow ev - , t he m ax imurn achi ev ab le b m f W n eg a- - y i s 1im i ted by ¥ e rÌm odul at ion per f o rn an ce o f M L or SL . I n th i s paper , w e de¢ 0n m ate a new techn ique, wh i ch does n o t

h av e such l m n at ion -O w schem e u t i n - s the l ock ing o f Four -W av e-M ix i ng ò W b D conj ugates pr oduced i n a D F B l as-

(SL ) by the l i P t inj a Hon * on anoth er D FB U ser (M L ) . F ig . l sh ow s the ex perm ed - set-up u sed in ow

study . W hen the M L 1asi ng Wo d en- h is set l ow er than the SL l u n g w av d en im ou t side th e h a i r-reg ion , FW M occur s [ 3] . T he M L a d SL peak s a d th e FW M conj u - - s cm be ob ser ved as sh ow n in

F i g . 2 . The f r equency separ at ion betw een F W M ca n u- - s C e equ a1 to the n eo - - y d i f f ¤ ence betw eenM L a d SL , w h ich i s set at ab ou t 14 GH z U ow ex p erm ed - B y sel ecti ng m o co¦ ugate m odes, w e Ca

pr oduce the beat * equem y that i s a har m oU c of 14 GH z. T hi s beat si - al , h ow ev er , i s not st ab 1e as

sh ow n in F i g . 3 . I n ow ex pen m ent , £ e beat si p - ¤ equ a - y w as obser v ed to n ud um e by sev era1hundred M H z . h order f or th i s beat si p a1 to be of m y u se, th e FW M conjugates shot-- be l ock ed to

each oth er .I n order to ach i ev e th i s, w e g u nm aneou sly r f -m odul ated (3GH z) bo th M L a d SL SO th at si de-

ban ds are produced bo th in M L a d SL . I f any of the SL si de-bands are inj ect ion - l ock ed by the M L side-

b ands, then SL a d the ent r e FW M Ä Ì ugate m odes p roduced by HP t i Ì c Hon n om M L to SL are

1Ä k ed- F ig . 4 sh ow s th e RF spec¤ un of t - beat signa - H er e are d ear si p al s at th e mu lt ip les of 3GH z.I t shou l d b e no ted th at these are not simp- h i gh- or der harM on¤ s of 3 GH z, th e m odu 1an on B eg - ncy ,

as th ere ar e si p a1 intensi t y incr ease at th e inter v al s of ab ou t 14 GH z, ¥ e * equem y for FW M ca n us -

¢ 0de separ at i on . CoDsequ ent1y , beat si p al s at Mu ch h i - er ¶ equem - s Ca be ob s- Ved - In ow case, th e

h i - est beat sign a1 ob serv ed w as 42 G H z , w h ich i s a1m ost l im i ted by the PD used in the exp er im ent . F ig .5 show s the m easur ed H -sp ec- u - a d ph ase n oi se of the beat sip a1s at 30 G H z . I t i s v ery stabl e and iB

ph ase noi se i s - 81 dB c/ H z at l ook H z of f set .I n su n - au , w e dem on s- ated that the side-ba d i ¦ ectM In oa n g bem a 1 FW M conj ugate m odes

M a D FB lase under the ex terna1 l aser l i - t inj ect ion cm p r oduce stab l e M M W Op U s- Since th e

p roduced M M W si gna1 H em- - y i s detern in ed by th e coM p te m ode separ at ion , w h ich cm be v ery1arge, w e b el i ev e that th i s i s qu i te m en u f or produc ing v ery h igh -- equ a lcy opt ica1 M M W si - U s.

R efer en ces[ l ] R . P . B raun et U ., M T L 46(4) , 199 8, H ¤ H ¤[2] L . N oel et a1., M T T- 4 5( 8) , 1997, l 4 l 6 1423.

[ 3] J. T roger et al ., JQE - 350 ) , 1999 , 323 8.

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