Multicasting Characteristics of All-optical Triode based on Negative

Feedback Semiconductor Optical Amplifiers

S. Aisyah Azizan, M. Syafiq Azmi and Yoshinobu Maeda

Graduate School of Science and Engineering, Kinki University, 3-4-1 Kowakae, Higashi Osaka, 577-8502, Japan

Keywords: Semiconductor Optical Amplifier, Multicasting, Wavelength Conversion, Optical Triode, Negative

Feedback Optical Amplifier, Cross Gain Modulation.

Abstract: We introduce an all-optical multicasting characteristics with wavelength conversion based on all-optical

triode using two negative feedback semiconductor optical amplifiers at a transfer speed of 10 Gbps to a non

return zero 2

-1 pseudorandom bit sequence system. This multi-wavelength converter device can

simultaneously provide two channels of output signal with the support of non-inverted and inverted

conversion. We reported an all-optical multicasting and wavelength conversion accomplishing cross gain

modulation is effective in a semiconductor optical amplifier in order to provide an inverted conversion thus

negative feedback. The relationship of received power of back to back signal and output signals with

wavelength 1530 nm, 1540 nm, 1545 nm, 1555 nm, and 1560 nm with bit error rate was investigated. It was

found that the output signal wavelengths were successfully converted and modulated with a power penalty

of less than 5 dB which the highest is 4.7 dB while the lowest is 2.2 dB. It was realized that all-optical

multicasting and wavelength conversion using an optical triode with a negative feedback by two channels at

the same time at a speed of 10 Gbps is possible.

1 INTRODUCTION

Demand for the wavelength division multiplexing

(WDM) in wider band has progressed especially in

the future technology of photonic networks. As the

cost and power consumption of WDM network

nodes are in a large amount, it is essential to discard

the conventional optical/electrical/optical (O/E/O) to

optical/optical (O/O) by using all-optical wavelength

converter device. Optical wavelength conversion is

anticipated to be an essential function for the

emerging bandwidth-intensive applications (video

conferencing, video-on-demand services etc.) of

high speed WDM optical networks by enabling rapid

resolution of output-port contention and wavelength

reuse (Y. Yuang et al., 2000).

In addition, all-optical wavelength converter

becomes a key functional element in WDM optical

network due to its capabilities of transparent

interoperability, contention resolution, wavelength

routing and, in general, better utilization of the fixed

set of wavelengths (J. M. H. Elmirghani and H. T.

Mouftah, March 2000).

Nowadays, multicasting is a potentially useful

networking function that involves the same data

stream from a single node to several destinations

nodes. This network is also called as photonic

network. Photonic network is commonly enforced

via IP digital routers in electrical domain. Photonic

network effectiveness will be encouraged when the

multicasting can be performed all-optically. The

optical routers will be able to multicast an input

signal to different wavelengths.

There is bulk of wavelength conversion and

multicasting techniques that have been proposed so

far. The techniques include a nonlinear

semiconductor optical amplifier (SOA) based

interferometer, an injection locking of a Fabry-Perot

laser (C. W. Chow et al., 2003), and SOA with cross

gain modulation (XGM) or SOA with cross phase

modulation (XPM) (M. Matsuura, N. Kishi, and T.

Miki, 2006). In this paper, we investigated the new

wavelength converter technology technique based on

the negative feedback optical amplification effect.

This will result an output signal whose gain,

waveform, and, baseline which stabilized

automatically. Wavelength conversion and switching

characteristics was investigated by introducing a

control light together with input signal light (Y.

Maeda and L. Occhi, 2003).

170

Azizan S., Azmi M. and Maeda Y..

Multicasting Characteristics of All-optical Triode based on Negative Feedback Semiconductor Optical Ampliﬁers.

DOI: 10.5220/0004708301700174

In Proceedings of 2nd International Conference on Photonics, Optics and Laser Technology (PHOTOPTICS-2014), pages 170-174

ISBN: 978-989-758-008-6

 2014 SCITEPRESS (Science and Technology Publications, Lda.)

The optical amplifier consists of an InGaAsP/InP

SOA and an optical add/drop filter. It is equipped

with a negative feedback function. In the negative

feedback SOA, the output modulation degree will be

substantially higher and the distortion of the

waveform was extremely small in wide input signal

(Y. Maeda, 2011). We demonstrated the conversion

wavelength by using two SOAs based on optical

triode, and measured the bit error rate (BER)

characteristics for each wavelength. As a result, this

device has been realized that all-optical multicasting

and wavelength conversion by using two channels at

the speed of 10 Gbps at the same time is possible.

1.1 Negative Feedback Optical

Amplification

As mentioned above, negative feedback optical

amplifier consists of a SOA and an optical add/drop

filter. The basic theory of negative feedback is

explained below.

SOA is structured based on the ridge waveguide

of InGaAsP/InP material. The composition of the

InGaAsP active layer is chosen to have gain peak

wavelength around 1550 nm. The maximum small

signal fiber to fiber gain is around 15 dB and the

output saturation power is approximately 2 mW

measured at 1550 nm with a bias current of 250 mA

(Y. Maeda, 2011). Figure 1 shows the diagram of a

negative feedback SOA circuit.

Figure 1: Block diagram of a negative feedback SOA.

VOA: Variable optical attenuator.

As shown in Figure 1, a wavelength of 1550 nm

is set as an input signal by a tunable laser then is

modulated by the mean of electro-optic modulator.

The modulated input signal is fed into the SOA by

using a coupler. An optical add/drop filter is located

in order to extract an output signal light of the

wavelength 1550 nm. The XGM mechanism in SOA

will provide the spontaneous emission contain an

inverted replica of the information carried by input

signal. The inverted replica information is fed back

and injected together with the input signal back into

the SOA by using a coupler. The output average

power was around 6.4 mW, which the SOA was

without negative feedback while in the SOA with

negative feedback, the output average power was

approximately 1.9 mW. These were experimented

when the negative feedback average power was 0.12

mW (Y. Maeda, 2011).

Figure 2: Concept diagram of negative feedback optical

amplification effect.

Figure 2 shows the concept diagram of a

negative feedback optical amplification effect. The

straight-line represents the case where the SOA was

used with negative feedback while the dotted line

represents the case of the SOA without negative

feedback.

Figure 2(a), (b), and (c) show the waveforms of

the input signal, the negative feedback, and the gain

in SOA respectively. In the SOA that has a XGM

mechanism, spontaneous emission lights, which

have wavelengths near a wavelength λ

ଵ

, the input

signal have an intensity varying in response to a

variation in the intensity of that input signal.

Characteristically, the intensity variation of the

spontaneous emission lights are inverted with

respect to the variation in the input signal then the

spontaneous emission lights are outputted from the

SOA as reported in Figure 2(b).

In the past, it is common that the spontaneous

emission lights as well as the surrounding light that

have wavelengths other than the wavelength λ

ଵ

are

removed by a band pass filter, since it becomes a

factor of noise generation (Y. Maeda, 2011). In this

situation, a negative feedback optical signal

amplification phenomenon in which characteristics

of the gain of the SOA is drastically changed by

feeding back the separated surrounding light to the

SOA so that the gain is modulated as shown in

Figure 2(c). Therefore, noise reduction is realized

all-optically with a negative feedback SOA. It can be

concluded that the output signal waveform is

MulticastingCharacteristicsofAll-opticalTriodebasedonNegativeFeedbackSemiconductorOpticalAmplifiers

171

exceptionally improved over that without negative

feedback. In addition, the baseline of the output

signal waveform is supressed because the gain in the

SOA is low when the power of input signal is at the

low logical level, whereas the output signal is

stressed because of the high SOA gain when the

input signal power is high as shown in Figure 2 (Y.

Maeda, 2011). In this paper, we created an all-

optical triode based on the negative feedback SOA

theory.

2 OPERATION PRINCIPLE

The experimental setup is reported in Figure 3. The

operating circuit of negative feedback optical

amplification by using optical triode is explained as

follows.

In this experiment, we used full band thermally

tunable distributed-feedback (DFB) laser diode

module. The isolator from the device has been taken

out in purpose to allow any reflection of the signal

light from the SOA. This device is used as the SOA

and laser diode (LD) as shown in Figure 3. We

created an optical triode by using two SOAs forming

two stages of SOAs, SOA-1 for the first stage and

SOA-2 for the second stage of the circuit with two

optical add/drop filters (1550 nm േ 6.5 nm).

An optical signal that has been modulated by the

external optical modulator (O.M) enters the SOA-1

via an optical add/drop filter (1550 nm േ 6.5 nm).

Due to the XGM mechanism in SOA-1, the probe

light, which is set in the SOA-1, is modulated into a

signal then provide the spontaneous emission

contain an inverted intensity to the optical signal

which fed in SOA-1. This inverted optical signal

then passes through an optical add/drop filter (1550

nm േ 6.5 nm) thenceforth it flew into the SOA-2

based on the negative feedback theory. The input

signal is amplified with gain modulation by inverted

optical signal in the SOA-2.

In this research, an optical signal with

wavelength 1552 nm is set by a laser source as the

input signal. This optical signal is modulated to a

non return zero (NRZ) 2

-1 pseudorandom bit

sequence (PRBS) with a transfer speed of 10 Gbps

by the O.M then is amplified by the Erbium doped

fibre amplifier (EDFA) before fed into the optical

triode. Additionally, probe light with wavelength of

1551 nm is set in SOA-1.

In order to perform multicasting in wavelength

conversion through this experiment, two different

wavelengths are set as the control signal in SOA-2.

Five different wavelengths are chosen as the control

signal to be used in this research. They are 1530 nm,

1540 nm, 1545 nm, 1555 nm, and 1560 nm. These

control signals (two wavelengths at a time) will be

fed into the SOA-2, which have undergone XGM

and wavelength conversion is occurred.

Consequently, the two different optical signals will

be amplified by the SOA-2 thus pass through an

optical add/drop filter. After that the optical signals

passed a VOA and a band pass filter (BPF).

As the two control signals are in different

wavelengths, a BPF is needed for wavelength

separation to recognize the output signals.

Thenceforth, the optical signals are inserted into the

bit error rate tester (BERT) hence the relationship of

received power of back to back signal (B to B

signal/BER of input signal) and output signals which

is controlled by the VOA, with BER is measured.

Figure 3: Experimental setup.

3 RESULTS AND DISCUSSION

Figure 4 shows the eye diagrams obtained in this

experiment. Figure 4(a) shows the input signal eye

diagram whereas (b), (c), (d), (e), and (f) show the

eye diagram for output signals of 1530 nm, 1540

nm, 1545 nm, 1555 nm, and 1560 nm respectively.

The eye diagram of input and output signals are

recorded when their average power is 150 μW. Zero

level from baseline (from ground) of input signal is

BERT

LASER

SOURCE

EDFA

O.M

SOA-1

SOA-2

VOA

Probe

1551 nm

Inverted signal

Input Signal

1552 nm

BPF

Optical

add/drop filter

Optical

add/drop filter

Control signal:

1530 nm, 1540 nm,

1545 nm, 1555 nm,

1560 nm

BPF

Optical Triode

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172

27 μW. Eye aperture, extinction ratio and zero level

from the baseline of each output signal eye diagram

are measured and are summarized in Table 1.

(a) Input (b) 1530 nm

(e) 1555 nm (f) 1560 nm

Figure 4: Eye diagrams of input and output signals

(50μW/div, 50ps/div).

Table 1: Summarization of measurement result.

Wavelength

[nm]

Eye

aperture

[dB]

Extinction

ratio [dB]

Zero

level

[μW]

1530 4.35 7.39 49

1540 3.90 6.97 54

1545 3.45 6.19 63

1555 2.22 4.40 83

1560 2.12 4.28 84

As reported in Figure 4, the baseline of output

signal eye diagrams arose gradually compared to the

input signal eye diagram. Based on Table 1, the zero

level from baseline of output signals increase when

the wavelength becomes longer, from 1530 nm to

1560 nm. In addition, the degradation in eye

aperture of output signals is clearly reported in

Figure 4 and Table 1. The obtained results show that,

the highest extinction ratio is 7.39 dB when the

output signal wavelength is 1530 nm.

Based on the reported results, it proved that

during the conversion of wavelength conducted in

the SOAs consumed large amount of power and

noise has been found due to the distortion of the eye

diagrams as clearly shown in Figure 4 especially in

Figure 4(e) and (f). We understood that a

conventional optical amplifier merely has a simple

amplification function that is almost constant gain.

The amplifier disadvantageously amplifies not only

the signal but also the noise. Therefore, the eye

diagram and baseline of the output signal cannot be

improved basically in relation with the noise,

thereby making difficult to achieve an advanced

signal processing. In spite of all, it is understood that

the eye aperture of optical signals declines as the

wavelength increases. In Figure 4, we conclude that

1530 nm has the highest eye aperture compared to

the other output signals.

In order to assess multicasting characteristics, we

measured the relationship between received power

and BER and reported in Figure 5. We have

measured the BER for B to B signal (also called

back to back signal), output signals 1530 nm, 1540

nm, 1545 nm, 1555 nm, and 1560 nm.

Figure 5: Result of bit error rate test.

It was found that the smaller the received power

of the signals, the bigger the BER will be. We

studied that it may be an effect of the dependence of

the speed propagation light through the medium

during the conversion of wavelengths that produce

errors. From the result of BER test, relationship of

-34,0 -32,0 -30,0 -28,0 -26,0 -24,0

Log

(BER)

Received Power [dBm]

B to B

1530 nm

1540 nm

1545 nm

1555 nm

1560 nm

-12

-10

-8

-4

-2

-6

MulticastingCharacteristicsofAll-opticalTriodebasedonNegativeFeedbackSemiconductorOpticalAmplifiers

173

power penalty with respect to B to B and control

signals when the BER is 10

-9

is summarized. The

summarization result is shown in Figure 6.

It is understood that the BER and power penalty

with respect to B to B signal become worse as the

control signal wavelengths increase. Figure 6

reported that we obtained power penalty that less

than 5 dB. The highest power penalty is 4.7 dB

when the control signal is 1560 nm while the lowest

is 2.2 dB when the control signal is 1530 nm.

Therefore, we found that BER for output wavelength

of 1530 nm is the nearest to the B to B signal than

output wavelengths of 1540 nm, 1545 nm, 1555 nm,

and 1560 nm.

Figure 6: Relationship of power penalty with respect to B

to B and control signal.

4 CONCLUSIONS

We investigated multicasting characteristics by

using an optical triode, which has been set up with

two stages of SOAs that constitute a negative

feedback optical amplifier with two optical add/drop

filters. Based on the BER measurement result,

output signal of 1530 nm produced the least error

compared to the other output signals after undergone

wavelength conversion. Thereby, we concluded that

1530 nm has the smallest power penalty than the

other output signals when the BER is 10

-9

Therefore, we understood that when the wavelength

becomes longer, the BER becomes worse. Hence,

this device also proved that all-optical multicasting

and wavelength conversion with two channels at a

time with a transfer speed of 10 Gbps is possible.

Furthermore, we found out that, by this

experiment, it is possible to achieve negative

feedback optical amplification by SOA with the

insertion of input and control signal into the SOA. It

also proved that the conversion of wavelength

(O/E/O) through electronic circuit can be innovated

to all-optical signals (O/O) and are applicable in our

optical triode.

Multicasting characteristics are recognized and

the conversion of one wavelength to another

different wavelength by injecting input and control

signal with a speed of 10 Gbps at the same time in

this device has been proved.

ACKNOWLEDGEMENTS

This work was supported in part by the Ministry of

Education, Culture, Science and Technology of

Japan, a Grant-in-Aid (21560048) for scientific

research ©.

REFERENCES

Y. Yuang et al., 2000. Nonblocking WDM multicast

switching networks, IEEE Trans On Parallel and

Distrib. Sys., pp. 1274-1287.

J. M. H. Elmirghani and H. T. Mouftah, March 2000. All-

optical wavelength conversion: Technologies and

applications in DWDM networks, IEEE Commun.

Mag., vol. 38, pp. 86-92.

C. W. Chow et al., 2003. 8ൈ10 Gb/s multiwavelength

injection locking of a FP laser diode for WDM

multicast, Proc. Of IEEE LEOS, pp. 682-683.

M. Matsuura, N. Kishi, and T. Miki, 2006. Broadband

regenerative wavelength conversion and multicasting

using triple-stage semiconductor-based wavelength

converters, IEEE Photon. Technol. Lett., pp. 2659.

Y. Maeda and L. Occhi, 2003. All-optical triode based on

a tandem wavelength converter using reflective

semiconductor optical amplifiers, IEEE Photonics.

Technol. Lett., pp. 257.

Y. Maeda, 2011. Advances in Optical Amplifiers, Paul

Urquhart ed. INTECH Open Access, pp. 231-252.

1525 1535 1545 1555 1565

Power penalty (dB)

Control signal (nm)

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