Blondeau, R.

Danielsen, Søren Lykke

Durhuus, Terji

Enard, A.

Glastre, G.

Jørgensen, Carsten

Mikkelsen, Benny

Ratovelomanana., F.

Rondi, D.

Stubkjær, Kristian

Vodjdani, N.

C. Joergensen

S.L. Danielsen

T. Durhuus

B. Mikkelsen

K.E. Stubkjaer

N. Vodjdani

F. Ratovelomanana

A. Enard

G. Glastre

D. Rondi

R. Blondeau

Crossref

Wavelength conversion by optimized monolithic integrated Mach-Zehnder interferometer

Semiconductor optical amplifiers have been monolithic integrated in a passive symmetric Mach-Zehnder interferometer to form a compact polarization insensitive all-optical wavelength converter operating at up to 10 Gb/s. A simple method for reducing the impact of input power variations is proposed that increases the input power dynamic range from 4-8 dB

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Downloaded from orbit.dtu.dk on: Dec 17, 2017Wavelength conversion by optimized monolithic integrated                Mach-ZehnderinterferometerJørgensen, Carsten; Danielsen, Søren Lykke; Durhuus, Terji; Mikkelsen, Benny; Stubkjær, Kristian;Vodjdani, N.; Ratovelomanana., F.; Enard, A.; Glastre, G.; Rondi, D.; Blondeau, R.Published in:I E E E Photonics Technology LettersLink to article, DOI:10.1109/68.491213Publication date:1996Document VersionPublisher's PDF, also known as Version of recordLink back to DTU OrbitCitation (APA):Jørgensen, C., Danielsen, S. L., Durhuus, T., Mikkelsen, B., Stubkjær, K., Vodjdani, N., ... Blondeau, R. (1996).Wavelength conversion by optimized monolithic integrated                Mach-Zehnder interferometer. I E E EPhotonics Technology Letters, 8, 521-524. DOI: 10.1109/68.491213IEEE PHOTONICS TECHNOLOGY LETTERS, VOL.. 8, NO. 4, APRIL 1996 521 Wavelength Conversion by Optimized Monolithic Integrated Mach-Zehnder Interferometer C. Joergensen, S. L. Danielsen, T. Durhuus, B. Mikkelsen, K. E. Stubkjaer, Member, ZEEE, N. Vodjdani, F. Ratovelomanana, A. Enard, G. Glastre, D. Rondi, and R. Blondeau Abstruct- Semiconductor optical amplifiers have been mono- lithic integrated in a passive symmetric Mach-Zehnder inter- ferometer to form a compact polarization insensitive all-optical method for reducing the impact of inlput power variations is proposed that increases the input power dynamic range from &8 dB. wavelength converter operating at up to 10 Gb/s. A simple - CW light, I., Fig. 1. element. Wavelength conversion pnnciple. SOAl acts as a phase shifting I. INTRODUCTIO U AVELENGTH converters will enable construction of W simple and flexible WDM networks, since they reduce the number of wavelengths needed and relaxes the require- ments to the wavelength precision throughout the network [ 11. In addition, wavelength converters can be exploited in space switches as well as for TDM to FVDM transmultiplexing [2]. Consequently, the development of effective and practical all-optical wavelength converters has attracted considerable attention. The most promising all-optical wavelength convert- ers rely on optical modulation of gain or refractive index in semiconductor optical amplifiers (SOA’s) [31-[91 Especially, the optically induced refractive index change (cross-phase modulation) in SOA’s integrated in for example a Mach-Zehnder interferometer (MZI) has recently resulted in very effective wavelength conversion [4]-[9]. Desirable features such as effective up and down conversion, high-speed operation as well as low chirping of the converted signals have been obtained simultaneously. Here, we present results for an improved version of the Mach-Zehnder interferometer wavelength converter [7]. The monolithic integrated converter features a separate branch for the input signal and operates at 5 and 10 Gb/s. It exhibits excellent properties such as wave- length independent conversion and high stability. Furthermore, this refined device allows for in-phase conversion (where the converted signal is not inverted compared to the input signal) and conversion without an output optical filter. Finally, we propose and experimentally confinn a simple method for optimizing the conversion performance: when variations in the input power alters the optimum operation point of the MZI. Manuscript received October 5,  1995; revised December 11, 1995. This work was supported in part by the RACE Project 2039, ATMOS. C. Joergensen, S. L. Danielsen, T. Durhuus,‘B. Mikkelsen, and K. E. Stubk- jaer are with the Center for Broadband Telecommunications, Electromagnetics Institute, Technical University of Denmark, Building 348, DK-2800 Lyngby, Denmark. N. Vodjdani, F. Ratovelomanana, A. Enard, G .  Glastre, D. Rondi, and R. Blondeau are with Thomson-CSF, Laborat’oire Central de Recherches, Dormaine de Corbeville, 91400 Orsay Cedex, France. Publisher Item Identifier S 1041-1 135(96)02608-0. 11. PRINCIPLE AND DEVICE CHARACTERISTICS The principle of operation for the converter is as follows (see Fig. 1): A CW-signal with the desired output wavelength, A,,,,, is coupled to the MZI and split equally to each interferometer arm in a 3 dB Y-junction. After amplification in the SOA’s the CW-signal recombines at the output ei- ther constructively or destructively depending on the relative phase-difference, A$, between the two interferometer arms. The SOA’s control A$ depending on the bias currents as well as the optical power injected into SOA1. Therefore, by injecting the intensity modulated input signal (A,) to SOAl by a separate waveguide branch [6]-[8] the CW-signal will expe- rience constructive or destructive interference according to the input signal information. All-optical wavelength conversion from A;, to A,,,, is obtained. To accomplish high operation stability as well as small size, the MZI with the SOA’s must be integrated. The monolithic integration of the 1200 pm long bulk type SOA’s and the interferometer is achieved using the buried strip loaded wave- guide structure [lo]. The Y-junctions have wavelength and polxization independent power splitting in the wavelength range considered. 111. RESULTS AND DISCUSSIONS The basic interferometer characteristic is assessed by mea- suring the static performance as shown in Fig. 2. The output power at 1535 nm (CW wavelength) versus the input power at 1543 nm (signal wavelength) verifies a pronounced inter- ferometric behavior: A change in input power of 10 dB leads to an output power change of 20 dEi. The conversion capabilities of the MZI are assessed by BER measurements. To achieve high conversion speed the bias current to SOAl is high (300 mA) while the bias current to SOA2 is adjusted to give maximum extinction ratio for the converted signal (see Fig, 2). Examples of measured BER curves at 5 Gb/s for both the input and converted signals are shown in Fig. 3 for conversion from 1543 to 1535 nm 1041-1135/96$05.00 0 1996 IEEE Authorized licensed use limited to: Danmarks Tekniske Informationscenter. Downloaded on March 02,2010 at 07:03:26 EST from IEEE Xplore.  Restrictions apply. 522 E E E  PHOTONICS TECHNOLOGY LETTERS, VOL. 8, NO. 4, APRIL 1996 I I I I I I I I  Input power, 1543 nm [dBm] Fig. 2. Static characteristics: Output power at A,,,, = 1535 nm versus the input power at A,, = 1543 nm for two different SOA2 bias currents. All powers are measured in the fiber. Bias current to SOAl = 300 mA. Input CW power = 6 dBm. -20 -15 -10 - 5  0 5 10 15 +Converted data, 1550 nm Received power [dBm] Fig. 3. BER curves at 5 Gb/s for the input signal (1543 nm) and for the converted signals at 1535 and 1550 nm, respectively. PRBS length = Z3'- 1. Input signal power = -2 dBm. Bias current to SOAl/SOA2 = 300 a 1 9 6  mA. Input CW power = 6 dBm. and 1550 nm, respectively. The signal (extinction ratio -13 dB) and CW signals are coupled co-directional to the MZI so an optical filter (40 GHz) has been applied to select the converted signal at the output. Wavelength conversion with a penalty below 0.5 dB for both up and down conversion is attained at 5 Gbls independent of the signal polarization. At 10 Gb/s the penalty increases to -2 dB mainly due to a low optical confinement factor (-0.3) in the SOA that limits the conversion speed [9]. Similar excellent performance as described above can be obtained within a 30 nm wavelength range [5]-[7]. This is a unique property for the cross-phase modulation technique exploited here in contrast to wavelength converters relying on for instance cross-gain modulation or four-wave-mixing in SOA's. Moreover, it is important to observe that the MZI can conserve the bit- polarity (no inversion of the converted sig- nal), thus enabling excellent transmission performance for the converted data over nondispersion shifted fibers as described in [5].  Note that a similar good performance is obtained for counter directional coupling of the signal and the CW light. Even without the optical filter a penalty below 1 dB is achieved - 7  - 5  - 3  -1 1 3 Signal power [dBm] Fig. 4. Penalty (@ BER = lo-') at 5 Gb/s for conversion from 1543 nm to 1535 nm. Input signal power = -2 dBm. Bias current to SOAl = 300 mA. Input CW power = 6 dBm. Bias current to SOA2 = 196 mA. Bias currmt control Input signal - - Convertgd CW light signal Fig. 5 Control set-up for compensation of variations in input power 4 I 210 200 190 180 c a 0 1  I I " ,  ' I I ' I 170 - 7  - 5  - 3  -1 1 3 Signal power [dBm] Fig. 6. Penalty (@ BER = IOp9) at 5 Gb/s for conversion from 1543 nm to 1535 nm. Input signal power = -2 dBm. Bias current to SOAl = 300 mA. Input CW power = 6 dBm. Bias current to SOA2 is adjusted (nght axis) to minunizes the conversion penalty. at 5 Gb/s. Consequently, the MZI converter operates without a tunable output filter which eases the implementation in real networks. Recently, both extinction ratio improvement [4] and low chirping of the output signal [5] has been demonstrated by interferometric wavelength converters. These excellent prop- erties arise due to the operation principle where only -4 dB gain variation is required to change the phase in the SOA by T (necessary to shift from constructive to destructive interference or vice-versa). Therefore, the wavelength conversion is very Authorized licensed use limited to: Danmarks Tekniske Informationscenter. Downloaded on March 02,2010 at 07:03:26 EST from IEEE Xplore.  Restrictions apply. JOERGENSEN et al.: WAVELENGTH CONVERSIO V BY OPTIMIZED MONOLITHIC INTEGRATED MACH-ZEHNDER INTERFEROMETER ~ 523 Normal operation 12011 0-- 0 80 160 240 320 400 480 Time [ps] (a) Adjusted operation 120 I 100 -I 3 S .  I . .. 0 80 160 240 320 400 480 Time [ps]i (b) Fig. 7. Eye diagram examples for converted daia at 5 Gbls for a signal input power of 1. dBm for conversion from 1543 nm to 1535 nm. Bias current to SOAl = 300 mA. Input CW power = 6 dBm. (a) Bias current to SOA2 = 196 mA. (h) Bias current to SOA2 = 182 mA. power efficient. This can however, also be considered a disad- vantage since the converter may become very sensitive to input power variations that could occur in WDM networks where different channels may arrive to the wavelength converter with different power levels. In Fig. 4, the penalty at 5 Gbh for down conversion is shown versus the signal input power. The 1-dB dynamic range for the input power is about 4 dB. Hence, for larger input power variations the MZI must be externally adjusted. As indicated in Fig. 2, control of the bias current to SOA2 provides a simple method for optimizing the conversion per- formance of the MZI when the input power is changed. A control set-up for the MZI could be that shown in Fig. 5: The average input signal power is here measured by a controller which in turn adjusts the bias current to SOA2 according to well known characteristics of the MZI (like the data shown in Fig. 2). The principle is assessed in Fig. 6,  which gives the penalty and optimized bias current to SOA2 versus the signal input power. The dynamic range is now improved to 8 dB by adjusting the current between 170 mA and 210 mA. Examples of eye diagrams for 1 dBm input power are shown in [Fig. 7(a) and (b)] for cases without (196 mA) and with (182 mA) adjustment, respectively. IV. SUMMARY A compact and stable polarization insensitive wavelength converter implemented as a monolithic Mach-Zehnder in- terferometer with semiconductor optical amplifiers has been realized in I@-GaInAsP. The device demonstrates wavelength independent conversion at up to 10 Gbh. Assessment of the input power dependency without adjustment of the operating conditions reveals a 1-dB dynamic range of approximately 4 dB. A method for adjusting the performance for large power variations is proposed. It increases the dynamic range to 8 dB by adjusting the bias current to one of the SOA’s. REFERENCES K. Sato, S. Okamoto, and H. Hadama, “Network performance and integrity enhancement with optical path layer technologies,” IEEE J. Select. Areas Commun., vol. 12, pp. 159-170, Jan. 1994. D. Norte and A. E. Willner, “All-optical TDM-to-WDM data-format conversion in a dynamically reconfigurable WDM network,” in Tech. Dig. OFC’95, vol. 8, Feb. 1995, pp. 143-145, paper WJ6. J. M. Wiesenfeld, J. S. Penno, A. H. Gnauck, and B. Glance, “Bit error rate performance for wavelength conversion at 20 Gbit/s,” Electron. Lett., vol. 30, pp. 720-721, Apr. 1994. T. Durhuus, C. Joergensen, B. Mikkelsen, R. J. S. Pedersen, and K. E. Stubkjaer, “All optical wavelength conversion by SOA’s in a Mach-Zehnder configuration,” IEEE Photon. Technol. Lett., vol. 6, pp. 1054-1057, Jan. 1994. F. Ratovelomanana, N. Vodjdani, A. Enard, G. Glastre, D. Rondi, R. Blondeau, C. Joergensen, T. Durhuus, B. Mikkelsen, K. E. Stubkjaer, A. Jourdan, and G. Soulage, “An all-optical wavelength-converter with semiconductor optical amplifiers monolithically integrated in a asym- metric passive Mach-Zehnder interferometer,” IEEE Photon. Technol. Lett., vol. 7, pp. 992-994, Sept. 1995. M. Schilling, K. Daub, W. Idler, D. Baums, U. Koemer, E. Lach, G. Laube, and K. Wunstel, “Wavelength conversion based on integrated all-active three-port Mach-Zehnder interferometer,” Electron. Lett., vol. 30, pp. 2128-2130, Dec. 1994. C. Joergensen, S. L. Danielsen, T. Durhuus, B. Mikkelsen, K. E. Stubkjaer, N. Vodjdani, F. Ratovelomanana, A. Enard, G. Glastre, D. Rondi, and R. Rondi, “High performance wavelength conversion by next generation monolithic integrated Mach-Zehnder interferometer with SOA’s,” Tech. Dig. IOOC’95, vol. 3, June 1995, pp. 58-59, paper X. Pan, J. M. Wiesenfeld, J. S. Penno, T. L.Koch, G. Raybon, U. Koren, M. Chien, M. Young, B. I. Miller, and C. A. Burms, “Dynamic operation of a three-port, integrated Mach-Zehnder wavelength converter,” ZEEE Photon. Technol. Lett., vol. 7, pp. 995-997, Sept. 1995. T. Durhuus, B. Mikkelsen, C. Joergensen, and K. E. Stubkjaer, “All- optical wavelength conversion by SOA’s,” invited paper to appear in J. ThB3-3. ~~ .~Lightwave Technol., 1996. G. Glastre. D. Rondi. A. Enard. and R. Blondeau, “Polarization in- sensitive 1.55 p m  semiconductor integrated optical amplifier with ac- cess waveguides grown by LP-MOCVD,” Electron. Lett., vol. 27, pp. 899-900, May 1991. Authorized licensed use limited to: Danmarks Tekniske Informationscenter. Downloaded on March 02,2010 at 07:03:26 EST from IEEE Xplore.  Restrictions apply. 

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Wavelength conversion by optimized monolithic integrated Mach-Zehnder interferometer

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