RESEARCH ARTICLE

Alternative approach to optical frequency encoded flip flopsby utilizing semiconductor optical amplifier non linearity

Kousik Mukherjee

Received: 2 April 2011 /Accepted: 20 January 2012 /Published online: 24 February 2012# Optical Society of India 2012

Abstract A memory unit is a sequential logic whichis an essential part of a computational machine. Real-ization of fast optical memory units is very challeng-ing. In this communication the authors propose amethod of implementation of different frequencyencoded flip flops JK, D and T exploiting semicon-ductor optical amplifier based polarization rotation,filtering and frequency conversion. The main advan-tage of the frequency encoding technique is that it isfree from intensity loss dependent problem and pro-vides ultra fast speed of operation.

Keywords Frequency encoding . Optical flip flop .

Semiconductor optical amplifier . Polarization rotation

Introduction

Optics has established itself as a strong and potentialcandidate of future communication and computationsystem, not only because of the speed limitation ofelectronics but also for other advantages. Photon is asuitable information carrier compared to electron andthus people are engaged in developing different opticalprocessors using various materials. Among them nonlinear materials are very attractive in characteristics. A

number of proposals based on semiconductor opticalamplifier [1–3], based on thermo-optic and carrier-plasma nonlinearities both induced by two-photon ab-sorption in silicon photonic crystal nanocavities [4],based on TOAD [5, 6], and other devices are proposedand demonstrated. A memory unit is an essential part ofa computational machine and therefore all optical mem-ory unit has been drawn attention of researchers [7–17].The proposed memory units or flip flops are based onintensity encoding technique, i.e. the states of informa-tion ‘0’ or ‘1’ are represented by two different intensitylevels of light. In general absence of light means ‘0’ andpresence of light means ‘1’. This intensity encodingtechnique has many draw backs. In intensity encodinga particular value of the signal intensity level must bemaintained which is very difficult. In transmission, re-flection or refraction the intensity of the signals changeand problems are created in the channel selection. Thisis because a non linear media directs signals of differentintensities in different direction. As an alternative onecan say about frequency encoding technique for repre-sentation of the states ‘0’ and ‘1’. In frequency encodingtechnique the states of information ‘0’ and ‘1’ are rep-resented by two different frequencies υ1 and υ2 respec-tively. Since frequency is fundamental characteristic it isnot changed during reflection, transmission etc. A fewproposals of frequency encoded memory or flip flopsare recently found [3, 18]. Flip flops are sequentialcircuits in which the outputs are generated in accordancewith the sequence of input signals received by the circuitand some feed back mechanism from output are there.

J Opt (January–March 2012) 41(1):16–24DOI 10.1007/s12596-012-0057-1

K. Mukherjee (*)PG and UG Department of Physics, BB College,Asansol, West Bengal, Indiae-mail: lipton007@indiatimes.com

So the present output not only depends on the presentinputs but also on the past history of the circuit. So theselogic circuits have memory. In the Fig. 1 the basic blockdiagram of a sequential circuit is shown.

A memory element is a medium in which one bit ofinformation can be stored or retained until necessary.They are basically flip flops which are capable ofstoring binary information and it has two stable states0 state and 1 state. The outputs are designated as Qn

and Q n, which are complementary always. The statewith Qn00 is called Reset state and Qn01 is called Setstate. If the circuit is in 0 state or 1 state it tries toremain in that state. This property is known as mem-ory of the circuit. A basic flip flop or latch usingNAND gate is shown in the Fig. 2.

In this communication JK, D and T flip flops areproposed using frequency encoding technique for rep-resentation of the states of information 0 and 1 andexploiting SOA non linearity. In the Tables 1 and 2 thetruth tables of JK, D and T type flip flops are shown.

Working principle

The working of the proposed devices are based onpolarization rotation in SOA, frequency conversionin RSOA and filtering action of SOA based add/dropmultiplexer. In the next sections the basic mechanismsare explained in details.

Polarization rotation switching of SOA

The non linear polarization rotation of the probe beamdue high intense pump beam induced refractive indexchange is one of the important non linearity in SOA[17, 19–23]. Inside the SOA, the strong pump beamand the probe beam interaction causes change in theoptical properties of the SOA. These changes actuallyinduce changes in the intensity and state of polarization

(SOP) of the probe beam. If linearly polarized light isinjected into the SOA, after passing through it, the SOPmay be circular, elliptical or linear with rotated azimuthand the ellipticity angle of the probe beam changeswith the propagation through the medium [23, 24].Depending on the power level of the pump beam thepolarization ellipticity may be circular, elliptical orlinear with rotated azimuth. In the output an opticalpolarizer can be used to detect the polarization rotationand convert the phase difference into intensity differ-ence. In the Fig. 2, the mechanism of non linear polar-ization is shown. Here A and B are input pump beamsof frequencies υ1 or υ2. The SOA is biased with suit-able current and the power levels of A and B are alsoproperly adjusted. I is the linearly polarized probesignal of a specific frequency and weak in power andis coupled with the pump beams. When there is nopump beam, no change in the SOP of the probe beamhappens. When only one pump is present, no signifi-cant change of SOP is induced and hence no variationsof intensity of the probe beam. When both the pumpbeams are present, there is significant change in thepolarization azimuth and ellipticity of the probe beamcausing significant intensity variation of the transmit-ted probe beam in the output. Therefore the linearlypolarized data beams I can be transmitted to the outputof the SOA [20].

Next state inputs NOT Output logic

Inputs

Clock

Outputs

Fig. 1 Basic block of asequential circuit

An

Bn

Qn

Qn

Fig. 2 A basic latch

J Opt (January–March 2012) 41(1):16–24 17

With no pump beams A and B, the polarizer is soadjusted that the pass axis of the polarizer is crossedwith respect to the SOP of the linearly polarized inputsignal I, and no light is obtained at the output. Whenany one of the pump is present it does not rotate thestate of polarization of the probe beam I significantly,so the in output no light corresponding to I is detected.When both the pumps A and B are present simulta-neously, there is a large change in the polarizationazimuth and ellipticity of the probe beam I and thelinearly polarized data I is transmitted through the passaxis of the polarizer, and I is detected at the output. Inthis communication the polarization rotation unitshown in the Fig. 3 works according to the principleof the AND gate reported in [20].

Frequency routing by ADM

In the basic design of an ADM there are man twoparts: an optical circulator and another optical filter/amplifier. In this communication an ADM based onreduced polarization dependent amplifier/filter is used.The function of a frequency ADM is to select and adda particular frequency channel without interferencefrom neighboring channels. Since the inputs are sig-nals of two different frequencies, the ADM separatesthem into two different channels [25–27]. This can beachieved by an integrated SOA with tunable filter asshown in the Fig. 4 [25, 27]. The tuning of the filter atdifferent frequencies is done by changing the biascurrent of the SOA. The selected frequency channel

is reflected back in the filter section, amplified asecond time in multi-quantum well structure (MQW)and is dropped by the circulator. The other channelsare passed through the filter section without any re-flection. In the Fig. 1 the signal of frequency υ1 isdropped and that of υ2, υ3… are passed through.

Principle of frequency conversion using XGMin Reflective Semiconductor Optical Amplifier(RSOA) and NOT gate

It utilizes a high reflecting coating on one facet and ultralow reflecting coating (or anti reflecting coating) on theother facet to produce a highly versatile reflective gainmedium [28–30]. The basic structure is shown in theFig. 5 as used in this communication. Aweak signal offrequency υ can be converted to a high power signal of adifferent frequency υ’ by using a signal of frequency υ’from outside. Inside the RSOA multiple reflectionsoccurs and the power of the weak signal is convertedto the high power signal. The basic phenomenon behindthis type of operation is the well known cross gainmodulation (XGM) of converting information at onefrequency to another frequency. The converted signalis of high power due to amplification caused by theRSOA. In this communication the RSOA is used inthe construction of the NOT gate as shown in theFig. 6. Compared to conventional SOAs the conversionof RSOA based devices show much improved perfor-mance in high speed all optical frequency(wavelength)conversion [30].

NOT gate: The NOT gate implementation requires twoADM and two RSOA as shown in the Fig. 4. This typeof NOT gate is well established by many researchers[31, 32].

Here the inputs are either υ1 or υ2. When the inputis optical signal of frequency υ1 (LOW), the ADM1blocks it and reflect back, and is dropped to RSOA1by the circulator which convert it to an optical signalof frequency υ2. So the output is υ2(HIGH). Similarlywhen the input is the optical signal of frequency υ2,

Table 2 Truth table of D and T flip flop

Inputs output

D T

Case 1 υ1 υ1 Qn

Case 2 υ2 υ2 Qn

I

SOA

A B

Filter Polarizer

I

Fig. 3 Rotation of SOP by SOA

Table 1 Truth tables of JK flip flop

Inputs J K Output

Case1 υ1 υ1 Qn

Case2 υ1 υ2 υ1Case3 υ2 υ1 υ2Case4 υ2 υ2 Qn

18 J Opt (January–March 2012) 41(1):16–24

the ADM2 and RSOA2 make it to become a signal offrequency υ1. So the output is now υ1 (LOW). This isnothing but the operation of a NOT gate.

Realization of different frequency encoded FlipFlop

Utilizing the above non linear properties of semicon-ductor optical amplifier frequency encoded flip flopsis proposed. A JK flip flop with frequency encodinginputs and outputs is proposed. This JK flip flop ismodified to construct D and T type flip flops.

Realization of frequency encoded JK flip flop

The circuit diagram of the proposed flip flop using twoADMs, four SOAs are shown in the Fig. 7. The basicelements of the flip flop are two ADMs, four RSOAs,and four SOAs. The other elements are mirrors, beamsplitters, filters and polarizer. The ADM1 and ADM2are tuned to block signal of frequency υ1 and passother frequency υ2. RSOA1, RSOA2, RSOA3, andRSOA4 are used to convert any frequency to a fre-quency υ3 other than υ1 and υ2. In the RSOAs thesignals not only converted to another frequency butalso amplified. The output of the RSOAs are properly

controlled and injected into the SOA1, SOA2, SOA3,and SOA4 for desired operation of the device. Theprobe signal in RSOA1 is the feed back signal from Qn

and that of SOA4 is from Qn. The signals of frequen-cies υ1 and υ2 are used as probe in the SOA2 andSOA3 respectively. The filters are placed to filter outthe respective frequencies in the output and the polar-izers are place with their axis in such a way that theywill transmit considerably the polarization rotated out-put when both the pumps are present simultaneouslyfrom the respective RSOAs. After the SOA1 andSOA3 there are two filters each (one υ1 pass andanother υ2 pass filter) because Qn and Qn may be offrequency υ1 or υ2 depending on the input conditions.

Let us explain the operation of the JK flip flop. Theinputs J andK are frequency encoded intensitymodulatedsignals. The output will also be intensity modulated fre-quency encoded signal at frequencies υ1 or υ2.

Case 1: When both the signals J0K0υ1, the RSOA 1and RSOA 2 convert these frequencies toanother frequency υ3, and injected into theSOA1 as pump. Since both pumps are onlypresent in the SOA1, the polarization rotationof the input probe signal derived from Qn afterfeed back will be such that it will be transmit-ted through the polarizer after the SOA1. If Qn

is of frequency υ1, then the upper polarizer

MQW amplifier

Grating filter

1, 2, 3

Reflected

1

Dropped signal 1

2, 3

Fig. 4 Add drop multiplexer

Input pump signal

SOA

Converted probe ’

Inputprobe ’ (probe)

Highly reflecting coating Anti reflecting coating

Fig. 5 XGM basedfrequency conversion inRSOA

J Opt (January–March 2012) 41(1):16–24 19

and filter will act and if Qn is of frequency υ2,then the lower filter polarizer will act. So theoutput will be Qn in this condition.

Case 2: When J is a signal of frequency υ1 and K is asignal of frequency υ2, the RSOA1 andRSOA4 convert both the signal to a frequencyυ3 and the converted signals are injected to theSOA2 as pumps. In this condition only SOA2receives both the pumps and polarization ro-tation of the probe signal of frequency υ1happen considerably and is detected at theoutput. This makes the output Qn0υ1, i.e.LOW in the frequency encoded format.

Case 3: When J is a signal of frequency υ2 and K is asignal of frequency υ1, the RSOA3 andRSOA2 convert both the signal to a frequencyυ3 and the converted signals are injected to theSOA3 as pumps. In this condition only SOA3receives both the pumps and polarization ro-tation of the probe signal of frequency υ2happen considerably and is detected at theoutput. This makes the output Qn0υ2, i.e.HIGH in the frequency encoded format.

Case 4: When both the signals J0K0υ2, the RSOA3and RSOA4 convert these frequencies in an-other frequency υ3, and injected into theSOA4 as pump. Since both pumps are onlypresent in the SOA4, the polarization rotationof the input probe signal derived from Qn afterfeed back will be such that it will be transmit-ted through the polarizer after the SOA4. IfQn is of frequency υ1, then the upper polarizerand filter will act and if Qn is of frequency υ2,then the lower filter polarizer will act. So theoutput will be Qn in this condition.

So it is established that the device in the Fig. 7works as a JK flip flop in frequency encoded format.

Since frequency is a fundamental property it does notalter during transmission, reflection etc. So the flipflop proposed here has several advantages over other.The flip flop can now be used to implement other flipflops like D and T type by modifying the input termi-nals. From the truth table of JK flip flop it is clear that ifthe input J and K are made equal i.e. J0K, the flip flop isD type, and if J and K are made complementary then thedevice will be T type flip flop. In the “Frequencyencoded D type flip flop” and “Frequency encoded Ttype flip flop” the D and T type flip flops are explained.

Frequency encoded D type flip flop

As clear from the truth able of both JK flip flop that theycan be converted to a D type flip flop by just making Jand K complement of each other. The D type flip flopflip flop has thus only one input called D or delay input.

In the D type flip flop when the input D0υ1, theoutput also become υ1 after a delay equal to the delayof the processing of the JK flip flop. Similarly whenD0υ2, the output also become υ2 after some delay. AD flip flop can be used as a 1 bit delay device. The Dtype flip flop is shown in the Fig. 8.

Case1: When D0υ1, the input J is υ1 and K is υ2 andthis corresponds to the case2 of the JK flipflop giving output υ1.

Case2: When D0υ2, the input J is υ2 and K is υ1,similar to case3 of JK flip flop. So the outputis υ2.

Frequency encoded T type flip flop

The T type flip flop cam be obtained from JK flip floponly because the ambiguity state i.e. when both theinputs are high is not permitted by the SR flip flop.

NOT

ADM 1 ( 1)

ADM 2 ( 2)

2

2 pass filter

1

RSOA1 RSOA2

1 / 2

1 Pass Filter

Fig. 6 NOT gate

20 J Opt (January–March 2012) 41(1):16–24

The toggle or T type flip flop has two input states T00and T01 and there are two output states correspondingto this. The JK flip flop is converted to T flip flop by

making J0K0T i.e. both the inputs of the JK flip flopsare same. The T type flip flop using a JK flip flop isshown in the Fig. 9 below.

Qn

n

ADM1

ADM2

SOA1

SOA2

SOA3

SOA4

υ1

J

K

Qn

n

υ2

RSOA1

RSOA2

RSOA3

RSOA4

Mirror Beam splitter , υ1, υ2 pass Filters,

Polarizer

Fig. 7 Scheme of optical J K Flip Flop

J Opt (January–March 2012) 41(1):16–24 21

When T0υ1, the input of the JK flip flop areboth υ1, giving Qn+10Qn. When T0υ2, both theinput of the JK flip flop will be υ2, giving Qn+1 0Q n. So the output toggles between Qn and Q ndepending on the previous output and present inputT. T type flip flops is also called a complementing flipflop and has application as bounce less or chatter lessswitch.

Process of clearing of the flip flops

The output states of the flip flop is totally determinedby the fact that in which SOA (SOA1 to SOA4), thepolarization rotation is happening. The SOAs transmitprobe signal only when they receives both the pumpsignals simultaneously. So the output signal is presentfrom a particular SOA as long as a particular inputcondition is maintained. If input condition is changed,another SOA output contributes to the final output ofthe flip flop and previous one is disabled. So for agiven condition one and only one SOA receives boththe pump signals and transmit probe signal asexplained in “Polarization rotation switching ofSOA” of this communication. The corresponding ex-perimental details are given in [20]. For example whenboth J and K are signals of frequency υ1, the SOA 1receives both the pump signal as explained in“Realization of frequency encoded JK flip flop”of this communication. In this condition the polar-ization rotated output from SOA1 makes the flipflop output Qn+10Qn and the other SOAs aredisabled as far as the polarization rotation isconcerned. If now the input condition is changedto J0υ1 and K0υ2, polarization rotation of theprobe signal in SOA2 happens and other SOAsbecomes disabled (no polarization rotation hap-pens). So the output is changed to υ1 as explainedin “Realization of frequency encoded JK flip flop”.So we can introduce new data into the flip flop byjust changing the input conditions and no chanceof overlapping data because between the intervalsof changing input conditions, the flip flop getscleared and ready for new entry. As long as aparticular input condition is present the flip flopdoes not change its output state and thus exhibitmemory. If we make the input signals off, the memorygets cleared and ready to take new data. This is true forD and T flip flop also.

Requirements for the realization of the flip flops

The polarization rotation used in this communication issuccessfully demonstrated by many researchers and in atypical experimental arrangement [20] the SOA used isa commercially available SOA (Kamelian, OPA series),employing a tensile-strained bulk InGaAsP/InP activeregion and a counter-propagation scheme is used. TheSOA bias current and temperature are maintained at200 mA and 20°C respectively. The power of CW probesignal is around -8dBm at the SOA input. The pumplight is modulated at a bit rate of 2.5Gbit/s via aLiNbO3 Mach-Zehnder modulator. After combina-tion by a PM combiner, two pumps are amplified byan erbium-doped fiber amplifier (EDFA) and enter theSOA through an optical circulator. A band pass filter(1 nm) is placed after the circulator to suppress thespontaneous noise from the SOA. PM fibers and PMisolator are used throughout the experiment. The totalpower of pump 1 and pump 2 coupled into the SOA hasvalue 1.1 dBm. An extinction ratio of the order of11.6 dBm in the output is achieved [20]. For theimplementation of the flip flops four such SOAsare used and the powers in the input pumps shouldbe maintained at 1.1 dBm when both the pumpsare present. The wavelength of the probe signal canbe chosen at 1552.2 nm and the wavelengthcorresponding to the frequency υ3 in this case can be1552.2 nm as counter propagation scheme is used. The

T J Qn

K Qn

Fig. 9 Frequency encoded T flip flop

D J Qn

K Qn

Fig. 8 Frequency encoded D flip flop

22 J Opt (January–March 2012) 41(1):16–24

input signal to the flip flops should have wavelengthother than 1552.2 nm. For a typical experimental con-dition the wavelengths selected may be 1,550 nm and1,555 nm for υ1 and υ2 respectively. Any other wave-length in the C band may also be selected owing to theperformance of the RSOAbased wavelength conversion[28–30].

Conclusions

A novel method of implementation of JK, D and Ttype hybrid encoded flip flops exploiting non linearproperty of semiconductor optical amplifier is pro-posed. The flip flop is a very important device inoptoelectronics and will find varieties of applicationssuch as memory unit, RAM, ROM, Shift registers,counters, switch delay unit etc. The devices proposedhere are simple in working and also integrable. Theprinciple of polarization rotation switching and ADMhave suitably utilized in implementing frequencyencoded read only memory [33], multiplexer and de-multiplexer [34], full adder, full subtractor [35]. Bothup conversion and down conversion of frequenciescan be realized by RSOA. However the ExtinctionRatio (ER) is always better for down conversion com-pared to up conversion. Wavelength conversion usingRSOA is superior to conversional SOA becauseRSOA can operate with low power level [30]. Its widegain band provides the feasibility of wavelength con-version over a wide range. It is to be remembered thatpower level of the probe beams of RSOAs does notfall below -8 dBm so that wavelength conversion byRSOAs can exhibit a good performance. This type ofRSOA based wavelength conversion is utilized fordesign various type of frequency encoded logic pro-cessors [3, 31–37]. The performance can be furtherimproved by using quantum dot semiconductor opticalamplifier (QDSOA) due to their low threshold currentdensity, high saturation power, broad gain bandwidth,and weak temperature dependence compared to bulkSOA devices [38].

References

1. M.T. Hill, H. de Waardt, G.D. Khoe, H.J.S. Dorren, Fastoptical flip-flop by use of Mach Zehnder interferometers.Microw. Opt. Technol. Lett. 31(6), 411–415 (2001)

2. R. Clavero, F. Ramos, J. Martí, Bistability Analysis forOptical Flip-Flops Based on a SOA-MZI with Feedback.J. Light. Technol. 25(11), 3641–3648 (2007)

3. S.K. Garai, S. Mukhopadhyay, A novel method of develop-ing all- optical frequency encoded memory unit exploitingnon linear switching character of semiconductor opticalamplifier. Optic. Laser Tech. 42(7), 1122–1127 (2010)

4. M. Notomi, T. Tanabe, A. Shinya, E. Kuramochi, H.Taniyama, On-chip all-optical switching and memory bysilicon photonic crystal nanocavities, Adv. Optic. Tech.2008, Article ID 568936, doi:10.1155/2008/568936

5. G.K. Maity, T. Chattopadhyay, D.K. Gayen, C. Taraphdar,A.K. Maity, S.P. Maity, J.N. Roy, All- optical binary flip-flop with the help of Terahertz Optical Asymmetric Demul-tiplexer. Nat. Comput.. doi:10.10007/s11047-009-9162-8

6. T. Chattopadhyay, J.N. Roy, A. Chakroborty, Polarisationencoded all-optical quaternary RS flip flop using binarylatch. Optic. Comm. 282(7), 1287–1293 (2009)

7. S.J.B. Yoo, Optical packet and burst switching technologiesfor the future photonic internet. IEEE J. Lightwave Tech.24, 4468–4492 (2006)

8. M. Takenaka, K. Takeda, Y. Nakano, All-optical packetswitching and label buffering by MMI-BLD optical flip-flop. IEICE Electron. Express 3, 368–372 (2006)

9. D. Maywar, G.P. Agrawal, Y. Nakano, Robust optical con-trol of an optical-amplifier-based flip-flop. Opt. Express 6,75–80 (2000)

10. W. D’Oosterlinck, F. Ohman, J. Buron, S. Sales, A. PerezPardo, All-Optical flip-flop operation using a SOA and DFBlaser diode optical feedback combination. Opt. Express 15,6190–6199 (2007)

11. W. D’Oosterlinck, J. Buron, F. Öhman, G. Morthier, R.Baets, All optical flip-flop based on an SOA/DFB-laserdiode optical feedback scheme. IEEE Photon. Technol. Lett.19, 489–491 (2007)

12. W. D’Oosterlinck, G. Morthier, R. Baets, T. Erneux, Opticalbistability in a traveling-wave SOA Connected to a DFBLaser Diode: Theory and Experiment. IEEE J. QuantumElectron. 42, 739–746 (2006)

13. K. Huybrechts, W. D’Oosterlinck, G. Morthier, R. Baets,Proposal for an All-optical flip-flop using a single distrib-uted feedback laser diode. IEEE Photon. Technol. Lett. 20,18–20 (2008)

14. Y. Kim, J.H. Kim, S. Lee, D.H. Woo, S.H. Kim, T.H. Yoon,Broad-Band All-Optical Flip–Flop Based on Optical Bist-ability in an Integrated SOA/DFB-SOA. IEEE Photon.Technol. Lett. 16, 398–400 (2004)

15. N. Mitra, S. Mukhopadhyay, A new scheme of an all-opticalJ-K flip flop using nonlinear material. J. Opt. 37(3), 85–92(2008)

16. N. Pahari, S. Mukhopadhyay, An all-optical R-S flip flop byoptical nonlinear material. J. Opt. 34(3), 108–114 (2005)

17. D. Lenstra, Y. Liu, M.T. Hill, G.D. Khoe, H.J.S. Dorren,Nonliear polarization rotation in semiconductor opticalamplifiers: Theory and applications to all-optical flipflop memories. IEEE. J. Quant. Electron. 39, 141–148(2003)

18. S. Dutta, S. Mukhopadhyay, Alternating approach of imple-menting frequency encoded all optical logic gates and flipflops using semiconductor optical amplifier. Optik 122(12),1088–1094 (2011)

J Opt (January–March 2012) 41(1):16–24 23

19. Y. Liu, M.T. Hill, E. Tangdiongga, H. de Waardt, N. Cala-bretta, G.D. Khoe, H.J.S. Dorren, Wavelength ConversionUsing Nonlinear Polarization Rotation in a Single Semicon-ductor Optical Amplifier. IEEE Photon. Tech. Lett. 15(1), 90–92 (2003)

20. L.Q. Guo, M.J. Connelley, All optical AND gate withimproved extinction ratio using signal induced non linear-ities in a bulk semiconductor optical amplifier. Opt. Express14, 2938–2943 (2006)

21. H. Soto, J.C. Dominguez, D. Erasme, G. Guekos, Demon-stration of an all—optical switch using cross polarizationmodulation in semiconductor optical amplifiers. Microw.Opt. Tech. Lett. 29(3), 205–209 (2001)

22. M.F.C. Stephens, M. Asghari, R.V.R.V. Penty, I.H. White,Demonstration of ultrafast all-optical utilizing birefringencein semiconductor optical amplifiers. IEEE Photon. Tech.Lett. 9, 449–451 (1997)

23. S. Phillippe, A.L. Bradley, F. Surr, B. Kennedy, P. Landais,Dynamics of Non—Linear Polarization Rotation in Semi-conductor Optical Amplifiers, ICTON 2007, Th. A2.2, 243–246 (2007)

24. D.C. Hutchings, J.S. Aitchison, J.M. Arnold, Nonlinearrefractive coupling and vector solitons in anisotropic cubicmedia. J. Opt. Soc. Am. B 14, 869–879 (1997)

25. M.J. Connelly, Semiconductor Optical Amplifiers (KluwerAcademic Publishers, 2002)

26. N.K. Dutta, Q. Wang, Semiconductor Optical Amplifiers(World Scientific Publishing, Singapore, 2006). Chapter 8

27. G. Raybon, U. Koren, B.I. Miller, M. Chien, M.G. Young,R.J. Capik, K. Dreyer, R.M. Derosier, Awavelength-tunablesemiconductor amplifier/filter for add/drop multiplexing inWDM networks. IEEE Photon. Technol. Lett. 9, 40–42(1997)

28. J-Mo Kang, I.H. Chol and S-K Han, Gain dynamics ofreflective semiconductor optical amplifier, OECC 2005,Technical Digest, July 2005, (Seoul, Korea) 682–683

29. P.S. Andri, A.L.J. Teixeria, J.L. Pinto, J.F. da Rocha, AllOptical Parametric Frequency Conversion Based on CrossGain Modulation on a Reflective Semiconductor OpticalAmplifier, Conftele 2001, 374–378, (2001)

30. L.Q. Guo, M.J. Connelly, A novel approach to all opticalwavelength conversion by utilizing a reflective semiconduc-tor optical amplifier in a co—propagation scheme. Optic.Comm. 281, 4470–4473 (2008)

31. K. Mukherjee, A novel frequency encoded all optical logicgates exploiting polarization insensitive four wave mixingin semiconductor optical amplifier, filtering property of add/drop multiplexer and non linearity of reflective semicon-ductor amplifier, Accepted for publication in Optik, 122(10), 891–895 (2011) doi:10.1016/j.ijleo.2010.05.033

32. S.K. Garai, S. Mukhopadhyay, Method of implementationof all-optical frequency encoded logic operations exploitingthe propagation characters of light through semiconductoroptical amplifiers. J. Optics 38(2), 88–102 (2009)

33. K. Mukherjee, All optical read only memory with frequencyencoded addressing technique. Optik 122(16), 1437–1440(2011). doi:10.1016/j.ijleo2010.09.024

34. S.K. Garai, S. Mukhopadhyay, Method of implementingfrequency encoded multiplexer and demultiplexer systemsusing nonlinear semiconductor optical amplifiers. Optic.Laser Tech. 41(8), 972–976 (2010)

35. P. Ghosh, D. Kumbhakar, A.K. Mukherjee, K. Mukherjee,An all optical method of implementing a wavelengthencoded simultaneous binary full adder full subtractor unitexploiting non linear polarization rotation in Semiconductoroptical amplifier, Accepted for publication in Optik,doi:10.1016/j.ijleo.2010.10.039

36. K. Mukherjee, A method of implementation of frequencyencoded all optical encryption decryption by using fourwave mixing, Accepted for publication in Optik, 122(16),1407–1411 (2011). doi:10.1016/j.ijleo.2010.09.017

37. K. Mukherjee, Method of implementation of frequencyencoded all optical half adder, half subtractor and full adderbased on semiconductor optical amplifiers and add dropmultiplexers. Optik 122(13), 1088–1094 (2011).doi:10.1016/j.ijleo.2010.07.026

38. Y. Ben Ezra, B.I. Lembrikov, M. Haridim, Ultra fast all—optical processor based on quantum dot semiconductor op-tical amplifiers. IEEE. J. Quant. Electron. 45(1), 34–41(2009)

24 J Opt (January–March 2012) 41(1):16–24