In conclusion, we have reported a polarisation independent modulator based on spiked shallow InGaAshGaAIAs wells. Besides low drive voltage and high bandwidth, a large improve- ment over standard InGaAsilnAlAs wells is observed for the opti- cal power handling capacity.
10 0 E m u -10 L W 2-20 R 5 - 3 0 a c 3 O -LO -5 0 10 Q E O m U -10
2
-20g
L L c 0 -30ra
U -LO;
-
-
-50 -20 -15 -10 -5 0 5 10 15 input power,dBm )48415/ Fig. 5 Output optical power (right Y axis) or collected photocurrent (lejt Y axis) aguinst input optical power .for two upplied biases U, W 0,. -2.5Vov
Acknowledgments: We thank P. Boulet, N. Bouadma for RIBE
etching and J. Landreau for AR coating.
0 IEE 1997
Electronics Letters Online No: 19970109
F. Devaux, J.C. Harmand and I.F.L. Ilias (France Teleconz, CNET/ PAB, BP 107, 92225 Bagneux Cedex, France)
T. Guettler, 0. Krebs and P. Voisin (Luborntoiw de Physique de la Mati& Condensee de I'Ecole Normale Supkrieure, 24 rue Lhomond, 75231 Paris Cedex 05, France)
22 November I996
References
AUBIN, G , JEANNEY, E., MONTALANT, T., MOIJLU. J., P lRlO, F., THOMINE, J.B., DEVAUX, F., and SOULI, N : 'Record 20Gbis-200km repeater span transoceanic solitoii transmission using in-line remote pumping', IEEE Photonics Teclznol. Lett., 1996, 8, pp. 1267-1 269
WOOD, T.H., CHANG, T . Y , PASTALAN, J.Z., BURRUS, C.A. Jr., SAUER, N.J., and JOHNSON, B.C : 'Increased optical saturation intensities in GaInAs multiple quantum wells by the use of AlGalnAs barriers', Electron. Lett., 1991, 21, ( 3 ) , pp. 251-259
DEVAUX. F., CHELLES, s., OIJGAZZADEN, , M I R C E A . A., and HARMAND. J.C : 'Electroabsorption modulators for high-bit-rate optical communications: a comparison of strained InGaAsiInAlAs and InGaAsPiInGaAsP MQW', Semicond. Sci. Technol., 1995, 10, pp. 887-901
WAKTTA, K., YOSHINO, K., KOTAKA, I., KONDO, S . , and NOCUCHI, Y . : 'High speed, high efficiency modulator module with polarisation insensitivity and very low chirp', Electron. Lett., 1995, 31, (23), pp. 2041-2042
Photodetector with filter
Hsiao-Lung Chan, Chang-Da Tsai, Hui-Hsun Huang, Dah-Chuan Chiou and Chien-Ping Wu
Indexing terms: Photodiodes, Filters
A new photodetector structure which incorporates a lowpass, highpass or bandpass filter is presented for rejecting ambient light by using negative feedback as well as positive feedback. 34 transfer functions synthesised with capacitors and resistors are also given.
ELECTRONICS LETTERS 16th January 1997 Vol. 33
Introduction: The monolithic combination of a photodiode and transresistance amplifier on a single chip has been realised for measurement and instrumentation applications, such as medical instrumentation, laboratory instrumentation, position and proxim- ity sensors, photographic analysers, barcode scanners and smoke detectors, etc. [I]. The photodiode generates current in response to incident light, then the transresistance amplifier converts the cur- rent to a voltage and eliminates possible loading both at the input and output.
Table 1: Elements for photodetector with filtering function
Y, Y2 Y3 Y, Y, Y6 Y, Transfer function I A A A A CS A A (C,A2)S/(A,C,Az)S+(AlA,A3 +A2&A3) 2 A A A A NiCS A 0 (A,C,A*)Si(C,A,%A,+C,A*%A,)S +(A5A1%A3cA5A2%A3) 3 A CS A CS A A 0 (A&)S/(C&A3)S+(Ai&jAJ 4 A CS A CS A A A (A&JS/(G&A;+A7A&JS +(A,%AJ 5 A A A A CS A+CS 0 (C5A2)S/(AlC6A3+A2C6A3)S +(AI'%A3+A2'%A3) 6 A A A A CS A+CS A (C,Al)S/(A,C,A,+A&,A,A&A;)S +(Al%A,+-A2%A,)
7 A A A+CS A+CS CS A 0 (C,A,)Si(A,tb,C;+A,tb,C;)S+(A,%q
8 A A A+CS A+CS CS A A (C5Az)S/(Ai%c3+A2%c3+A,A,)S
+A2%A3)
+(A, 1AA, "+AAA,) ~"~ ~
9 A A A A A A CS (A,A,)i(~A,A,)S+(A,%A,+A,%A,) 10 A A A A A CS A (A,A~/(A,C&3+A2C6A3)S+(A,A,A,)
11 A A A A A A A+CS(A5A2)/(C,A,A2)S+(AlA,A;+A,A,A,
+ A A A > )
A cascode design for the photodetector with first-order highpass filter has been developed by the manufacturer [I] to reject very bright ambient light yet provide high AC gain for best signal-to-
noise ratio. In the cascode design the accumulation of noise and signal distortion appearing as a result of the cascade design can be avoided. In this Letter, a new cascode structure for the photode- tector is proposed. The major advantage of the proposed structure is that it can reduce the effect of the ambient light of various spec- tral energies yet preserve the best signal-to-noise ratio.
1
Fig. 1 Structure of proposed photodetectov
Transfer function: As shown in Fig. 1, the proposed photodetector is composed of a photodiode, two operational amplifiers, and seven passive elements. The structure uses negative feedback as well as positive feedback to realise the desired filter. Assuming that the operational amplifiers are ideal, the transfer function of the proposed photodetector can be derived as
if
(2)
Y2 - Y4
_ - _ Yl Y3
where
Kc
is the admittance of the kth element 1 4 k 4 7.The filter to approach the desired function can be synthesised with capacitors and resistors from eqns. 1 and 2. Table 1 lists the
syntheses of various filters. Filters 1 - 8 are first-order highpass
filters. These functions are the same as the filter in the circuit rec- ommended by the manufacturer [l]. Note that the proposed struc- ture is able to use only one grounded capacitor (numbers 1 and 2), which makes it suitable for integrated circuit implementation instead of requiring two capacitors with equal values in the circuit recommended by the manufacturer. Furthermore, the syntheses of capacitors and resistors to realise other filter functions are given. Filters 9-22 are first-order lowpass fdters, 23 a second order high- pass fdter, 2 4 3 0 second order bandpass fdters, and 31-34 second order lowpass filters. For a specified quality factor of at least 0.25, only one combination of the elements is found for a second order highpass filter. The choice of the transfer function in the Table depends on the spectral energy distribution of the ambient light and the measured signal.
Conclusions: A new photodetector structure with integral fdter is presented. The syntheses of capacitors and resistors are given to realise photodetectors with various filters.
Acknowledgments: The authors are very grateful for the support of
grant NSC 86-221 3-E-002-023 from the National Science Council,
Taiwan, Republic of China.
0 IEE 1997
Electronics Letters Online No: 19970111
Hsiao-Lung Chan, Chang-Da Tsai, Hui-Hsun Huang, Dah-Chuan Chiou and Chien-Ping Wu (Department of Electrical Engineering, National Taiwan University, Taipei, Taiwan, Republic of China)
Chien-Ping Wu: Corresponding author
References
1
5 November 1996
Burr-Brown IC Data Book, Linear Products, 1996/1997, pp. 6.36- 6.43
ISAR imaging motion compensation in non-
uniform rectilinear motion
Jing Meng
Indexing terms: Motion compensution, Synthetic aperture radar
A new method for fitting the return phase of a moving target in a
curve which corresponds to its moving trajectory is proposed. This phase fitting method has no order limitation. It can be used in ISAR motion compensation either when the target moves
uniformly rectilinearly or when the target moves non-nuniformly rectilinearly.
Introduction: In ISAR imaging, motion compensation is very
important as well as very difficult. Ideally, the imaging target is
assumed to be moving in uniform rectilinear motion. Then over a short measurement period, the Doppler frequency of the target returns follows approximately a linear curve (a line) and its return phase follows an approximately quadratic phase curve. By esti- mating the quadratic phase curve [l - 51, phase compensation can
be used to remove the target centre motion:But in real flight, the flying trajectory may not be uniformly rectilinear. The target return phase cannot be fitted to a quadratic phase curve. Its higher orders must be considered. Then the methods introduced in [l - 51 by estimating the 1st and the 2nd orders of the target
return phase curve to make phase compensation will be ineffec- tive.
Principle: From the relation between the target’s Doppler fre- quency Fkt) and its range R(t)
A (CC
we can estimate the ambiguous Doppler frequency F Jt ) with the return phase $’(t)(-27c < $’(t) I 0): 1 [@(Z
+
1) - 4 ’ ( i ) ] 2nT,
FA(i) = - = L[@’(Z+
1) - @’(2)]FT 2nwhere i is the ith transmitting or receiving, T, is the PRP (pulse repetition period) and F, is the PRF. Generally, between two transmissions or between any two points on a target, the change in true Doppler frequency will not exceed F,, i.e.
( 3 )
F, IFd(i) - Fd(i - 1)1
<
-2
We can then unwrap the Doppler frequency Fdi) to obtain the unwrapped Ed(i):
Fd(1) =
FA(1)
( z = 2 , 3 , ..., N ) (4)
where FJi) ( i = 1,2, ..., N) only contains initial ambiguity KIF,, i.e.
where
$Ai)
is the estimation of true Doppler frequency Fd(i).F d [ i ) = F d ( i ) + K I F , (i = 1,2,.,.,N) (5) . . 2[R(i
+
1) - R ( i ) ] F Tx
. Fd(2) = - & i ) = F d ( 2 )+
E f ( 2 ) R’(2) = R ( i )+
& R ( i ) :. K I F r + F d ( i ) - E f ( i ) = 2F,x
- - [RI ( i+
1) - R’(2) - E R ( i+
1) + & R ( i ) ]The nearest integer of K, is the estimation of the initial Doppler ambiguity number.
