Michael Schilling, Member, IEEE, Wilfried Idler, Dieter Baums, Kaspar Dutting,. Gert Laube, Klaus Wunstel, and Olaf Hildebrand. Abstract-We report on improved ...
IEEE JOURNAL OF QUANTUM ELECTRONICS, VOL. 29, NO. 6 , JUNE 1993
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6 THz Range Tunable 2.5 Gb/s Frequency Conversion by a Multiquantum Well YLaser Michael Schilling, Member, IEEE, Wilfried Idler, Dieter Baums, Kaspar Dutting, Gert Laube, Klaus Wunstel, and Olaf Hildebrand
Abstract-We report on improved monolithic interferometric semiconductor lasers in Y configuration. When operated as an electronically tunable light source, single longitudinal mode emission with a very large CW tuning range up to 51 nm is accessed. By using all-quaternarycompressively strained MQW active layers also low dc threshold currents down to < 10 mA per segment are obtained (i.e., 50 nm wide tunability have been designed, as well, and are now under development in different labs. These are, e.g., sampled grating DFB [ 141 and sampled grating DBR [ 151 or superstructure grating devices [ 161, vertical coupler filter based structures [ 171, [ 181, and multichannel grating cavity configurations [ 191, [20]. Impressive record results have been recently reported with the different structures. In this paper we report in detail in strongly improved device characteristics of our approach, the wide-band tunable strained MQW Y laser [21], [22] with up to 51 nm tuning range experimentally achieved under CW operation.
B. Evolution of All-Optical Frequency Converters The widely tunable laser can also very usefully be applied as the transmitter part of a hybrid frequency conversion module, e.g., in optical asynchronous transfer mode (OATM) or multiwavelength optical crossconnect (OXCN) switching systems [2], [23]. Within such a unit the classical opticaUelectrica1 O/E and E/O frequency conversion function is provided by detection of the incoming signal, its amplification and regeneration, and finally the reemission at another frequency or wavelength, respectively, by the tunable laser. However, more attractive for future optically transparent trans-switching networks are the monolithic device approaches for all-optical wavelength conversion. In the past, a variety of different approaches have been reported in the literature. Early results have been obtained using light injection into special absorber sections of multisec-
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tion DFB [24] and DBR [25] lasers. However, the maximum conversion range of these devices is typically limited to a few hundred GHz. The speed is also limited to below or around 1 G b / s at best, especially for the DBR based converters due to long carrier lifetimes in the passive sections [26]-[29]. Another approach is the use of nearly degenerate four wave mixing in a traveling wave semiconductor amplifier. By this method up to 4 THz optical frequency conversion also at 1 Gb/s was reported [30]. Aiming for a strong increase in conversion speed an ultrafast intraband nonlinear gain process, the highly nondegenerate four wave mixing, in MQW lasers was explored [31], but up to now only 1 THz conversion range together with 1 Gb/s speed were reported [32]. Very recently, a further fast all-optical frequency conversion method has attracted much attention exploiting the gain saturation modulation in semiconductor optical amplifiers [33], [34]. Up to 2.5 Gb/s signals converted across ranges up to 3 THz have been reported. However, this method is not a fully monolithic approach and again an additional tunable laser is required as input source. The required extinction ratio for full system performance of this approach is also critical to achieve. A second new monolithic wide range frequency converter is recently realized by modulation of gain saturation in tunable DBR lasers. The speed then is no longer limited by the too long carrier lifetimes in passive sections, and very recently, 4 THz frequency conversion range have been reported for this approach [35]. The injected wavelength, however, lies outside the tuning interval of the DBR laser. Therefore, we think that the small electronic tuning range < 10 nm restricts to some extent its application, because the wide conversion range is not tunable. With respect to these points we see a promising advantage of our approach. With the wide range and fast tunable Y laser a very attractive all-optical frequency converter is available. The full tuning range is exploitable for tunable frequency conversion at high speed, as described in the present paper. 11. DEVICESTRUCTURE A N D FABRICATION Early Y lasers have been fabricated from base wafers containing bulk active layers [3], [5], but now we routinely use multiple-quantum-well (MQW) based material. The active layer stack is grown on 2 inch n-type (100) InP substrate by low pressure (20 mbar) metallorganic vapor phase epitaxy (LPMOVPE) [36], [37]. The epitaxial growth is performed at 655675°C using a standard equipment with a horizontal reactor and gas foil rotation. As precursors we use trimethylindium, trimethylgallium, 100% AsH3 and PH, sources, for n- and p-type doping H2S and diethylzinc, respectively. For the MQW layer sequence we first tested lattice-matched and strained ternary InGaAs QW's, as well, together with quaternary InGaAsP (1.2 pm) barriers. The lowest threshold current densities (down to 260 A/cm2 for L = 2 mm long linear devices), however, were obtained with five compressively
IEEE JOURNAL OF QUANTUM ELECTRONICS, VOL. 29. NO. 6, JUNE 1993 0
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Fig. 2. SEM micrograph of a finished device after mounting and bonding.
strained purely quaternary InGaAsP-InGaAsP QW's (see insert of Fig. 1). The vertical layer sequence is completed by a 2 pm thick p-InP cladding and a 0 . 4 pm thick p f InGaAs contact layer. The further processing of these wafers is as follows. Using a 2-3 pm wide Si02 mask, the all-active Y-shaped waveguide stripe is formed by a combination of reactive ion etching (RIE) and wet-etching to a depth of 4 pm. The Y-shaped buried heterostructure (BH) device is completed by a second LPMOVPE growth step with Fe-doped semi-insulating (SI) InP blocking layers leading to an almost planar surface. After removing the first mask, a second S i 0 2 layer is deposited, and contact windows are opened above the Y-shaped waveguide pattern. The wafer processing is finished by applying conventional TiPtAu and AuSn ohmic contacts for the p- and n-side, respectively. The Y-waveguide structure is segmented into three straight sections and the Y branching section (see Fig. 1) by separating the contact metallization. Finally, the facets of the chips are defined by cleaving. A SEM micrograph of a completely processed and mounted Y laser is shown in Fig. 2. 111. FUNDAMENTAL OPERATION PRINCIPLES The principle of operation of the Y laser as a tunable single-mode light source is based on the interferometric approach (see, e.g., [38], [39], [3]). A comprehensive review of this interferometric approach with reference to previous publications and early device configurations has
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been given in [3]. The fundamental difference of our Y laser structure from the prior art configurations has been in detail discussed in [3]. Briefly summarized, the main advantage of our structure is the variable current-dependent coupling coefficient K = K(Z;) of our multiresonator configuration. A simple description of the operation principle can be given as follows. The device can be understood (in a simplified manner) as two standard Fabry-Perot (FP) lasers, each with three electrodes, coupled together to obtain the Y-shaped device. The middle segments form a Y-branch section with only one electrical contact, and one of the outer segments of each FP laser is used in common. Due to interference of the modes of the FP subresonators the resulting emission spectrum of the Y laser exhibits a dominating single longitudinal mode (supermode operation). The interference condition can be changed by variation of the refractive index via current injection int6 the different device sections. Continuous tuning is thereby achieved by synchronous shift of the F P modes, and step tuning is accomplished by jumping to another supermode. The maximum total tuning range of these devices is given by the width of the available gain spectrum. The often discussed influence of temperature changes on the emission wavelength is not very critical. Comparable to other single mode laser structures, the rate of longitudinal mode shift d h / d t is about 0.1 nm/”C. The temperature range AT for the laser to stay in a predominant single mode (wavelength locking range) is typically 2°C < AT < 10°C. Due to the low threshold and operating
currents of the device (see Section IV) also internal heating is of minor importance. If the two branches of the Y laser are not symmetrical, e.g., if segment 3 and 4 have different lengths, then this asymmetrical device has a pronounced Mach-Zehnder (MZ) filter characteristic (Fig. 3). This filter function can advantageously be tuned, and precisely designed for specific applications. The geometrical path length difference AL defines AhMz,the width of the MZ filter modes in the spectrum according to the relation AXMz = h2/2nAL. (free spectral range). The expected performances of asymmetrical Y lasers such as simplified tuning response using single current control and higher side-mode suppression compared to symmetrical (AL = 0) structures has been discussed and experimentally verified recently [40]. More detailed theoretical analysis and modeling of the asymmetrical Y laser will be published elsewhere [41]. Two experimental examples of single current tuning representing the two main operation modes of asymmetrical Y laser structures are given below (Fig. 6(a) and (b)). IV. ELECTRONIC WAVELENGTH TUNING We have fabricated Y laser structures with various AL values ranging from AL = 0 pm (symmetrical devices) to AL = 200 pm. These Y lasers do not have a conventional threshold current since four drive currents are involved. If identical currents are applied to all 4 segments of the 1500 pm long device, the typical threshold current per segment is Zth = 20 mA, and an optical output power exceeding 10 mW is obtained at 4 X 100 mA drive current [See Fig. 4(a)]; if one segment is prebiassed (e.g., section 2 with 100 mA, see Fig. 4(b)), the “threshold current” of the others is drastically reduced, say, down to 3 x 5 mA. But even without prebiassing a best value down to 8 mA per segment (i.e., 32 mA for the total 1500 pm long and branched structure) was obtained on a device fabricated from a 1% compressively strained purely quaternary MQW wafer (see Section 11). In the limit of a symmetrical Y structure AL is zero and the wavelength separation of the MZ resonances A h M z goes to infinity. Optical length differences are then introduced by different currents only, causing different indexes of refraction. The effective optical path differences are smaller than 1 pm. Under these conditions, the MZ loss minima broaden compared to those in Fig. 3, resulting in a larger tuning span but make worse the side mode suppression. Nevertheless, the highest side mode suppression ratio (SMSR) achieved in the symmetrical Y laser configuration can exceed 30 dB. Typical values are 20-25 dB for most of the addressed channels out of the >50 nm tuning span. Experimentally, with the symmetrical version of the Y laser usually all four currents have to be set appropriately when tuning. Therefore, the average current range AZZodeto maintain the SMSR > 20 dB depends on the tuning efficiency of the corresponding tuning currents involved. This frequency tuning efficiency d f / d l is not a fixed value for symmetrical Y lasers. It can
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be designed in terms of the lengths of the tuning sections and of the transverse waveguide structure. Typical data for the present devices range from small AI values (AZ20dB I0.5 mA at 100 GHz/mA) up to relatively large values AZ20dB > 5 mA at 10 GHz/mA efficiency. As already pointed out, with the symmetrical Y laser usually all 4 currents have to be set appropriately, whereas for the asymmetrical structure setting of one current might be sufficient. Nevertheless, the symmetrical structure is easier to fabricate and has some advantages for special requirements. Ultrawide tuning range up to 51 nm from, e.g., 1528 to 1579 nm has been realized in symmetrical devices [2 11, [22] by sufficient variation of the respective refractive indexes with proper electrical injection current adjustment to the different segments (Fig. 5). A detailed tuning behavior by each segment current cannot be given in general. For this reason we have developed the asymmetrical device [40] by which these difficulties have been overcome and which exhibits a much simpler single current tuning response. For the symmetrical version of the Y laser the complex tuning behavior has been already addressed in more detail in [3]. The required wavelength channels specified by system users have to be individually precharacterized. However, taking advantage of computer controlled current adjustment these desired wavelengths can be selected with good reproducibility for symmetrical structures, as well. Discrete tuning combined with continuous fine tuning thus allows operation at arbitrarily defined and presettable wavelengths. An example is given in Fig. 5(a) where six wavelength channels with about 10 nm spacing are selected out from the more than 50 nm access range. For another device the data shown in Fig. 5(b) demonstrate that, e.g., 16 channels with 2 nm wavelength separation are successively addressable by appropriate variation of the electrical currents Zl-Z4.
Wavelength / nm (b) Fig. 5. Tuning performance of symmetrical Y lasers with flexible wavelength addressing: (a) 50 nm range with 6 channels selected which are spaced by about 10 nm; (b) 30 nm tuning covered by 16 wavelength channels with 2 nm spacing.
As predicted by our theoretical analysis, much simpler tuning current control is achieved with asymmetrical devices [40]. Single-mode operation with up to 32 dB sidemode suppression ratio was obtained. The tuning response of an early device with AL = 56 pm is shown in Fig. 6(a) together with the theoretical tuning curve according to the first main operation mode. With one single current Z4 the MZ filter is tuned across closely spaced F P cavity modes within a 5.5 nm wavelength range which corresponds to the MZ filter width. The correlation to our simple theory is fine at low injection currents. At higher injection we find deviations due to our assumptions, taking no gain saturation, carrier heating and interaction of the four carrier reservoirs into account. In a second operatiqn mode of an asymmetrical device, again with one single tuning control current ZI,the gain curve is shifted across the MZ resonances. As a first experimental example for a Y laser with AL = 81 pm (corresponding to a MZ spacing of 4 nm) a 8 nm wide shift across three MZ modes was accomplished as demonstrated in Fig. 6(b). The speed of electronic wavelength setting is an important parameter for the above mentioned applications of tunable Y lasers, especially for future optical ATM switching systems. Dynamic wavelength access with switching times in the order of 0.5-1.0 ns have already been achieved.
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ALL-OPTICALFREQUENCYIWAVELENGTH CONVERSION A . Static Characteristics As discussed above, the Y laser gives wavelength access to the whole available gain spectrum of the semiconductor quantum-well material from which the active layer is built. This broad tunability can be fully exploited in an all-optical wavelength switching operation mode, the wavelength conversion. It has been already shown in previous publications [ 5 ] , [6] that wavelength conversion by the Y laser can be achieved when external single-mode laser light of about 100 pW input power is launched into one of the three optical ports of the Y-shaped photonic device. In this paper we report on strongly improved data of this wavelength converter device. An example showing light injection into the segment 1 and optical output from the segment 3 is outlined in Fig. 7. For the frequency or wavelength conversion function, respectively, the input wavelength A,, has to lie within the gain curve width of the Y laser. This is in contrast to the so-called wavelength translation or transformation function of the Y laser which is not considered in the present study, and has been described elsewhere [6], [8], [lo]. The free running device is electrically adjusted to one de-
sired emission wavelength Aout, e.g., A I or A2 selected out of the total addressable tuning span. As the optical input power is increased the spectral output is influenced and finally completely changed according to the typical characteristics shown in Fig. 8(a). The conversion efficiency means the suppression ratio of the interferometric supermode of the Y laser by injection locking. This is demonstrated in Fig. 8(b), where typical output spectra are shown for three different optical input power situations. Without optical input, below the threshold value, and above the wavelength conversion threshold. These measurement data were obtained with TE polarized input. For TM input signals the threshold power needed is shifted to larger values compared to TE. The basic wavelength converter behavior can be understood from Fig. 9, as well, where schematically the optical input power is plotted against the output wavelength of the Y laser device. At threshold for conversion the preset output wavelength ,A,, = * of the Y laser supermode is suppressed due to stimulated emission of A,,,. Thus, the Y laser locks to the input wavelength and, therefore, ,A,, becomes equal to A,,. To demonstrate the availability of the ultra wide-band up- and down-conversion we have used a 1560 nm input DFB source together with a Y laser tunable over a 50 nm wide range. In Fig. 10 two examples for the wavelength conversion across 18 nm (red > A,,) and 32 nm (blue shift: ,A, < A,,,) are shift: ,A,, depicted. A main advantage of the Y laser based all optical monolithic wavelength converter is the feature that the total conversion range is equal to the total tuning range. Thus, this device is really a wide range tunable wavelength converter in contrast to other structures which have a large conversion range, but only a much smaller tuning range [35].
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B. Fast Dynamic Operation The experimental setup used for our high-speed frequency conversion experiments is schematically depicted
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: 2 . 5 G b / s modulation as the data input source. In order to test additionally the maximum range of down conversion this DFB source was selected for emission at the short wavelength edge of the gain curve of the Y laser at 1525 nm. The 2.5 G b / s optical input signal from the DFB laser operating at 1525 nm is converted (and inverted) to an output data stream at a wavelength of 1570 nm, corresponding to an enormous wavelength shift of 45 nm [21], [22]. The output spectrum under modulation shown in Fig. 12 was obtained by a time-averaged measurement. In Fig. 13 the 2.5 G b / s input pulse pattern at hi, together with an output pulse pattern tuned to A,, = hi, + 14 nm = 1539 nm is documented. This figure additionally demonstrates the signal inversion function of
the wavelength conversion device. Even for the widest conversion range across 45 nm (5.62 THz) we obtained a nearly distortion free 2.5 G b / s output pattern. The resulting open eye diagram of the 2.5 G b / s frequency converted output signal is shown in Fig. 14. The received optical power at a bit error rate (BER) of lop9 was -24 dBm. Depending on the extinction ratio of the incoming signal this value corresponds to a penalty of 3-4 dB or even to a gain of 1-2 dB. The dynamics for the pure optical conversion effect reported above is not limited by the Y laser parasitics, but rather by the carrier lifetime and resonance frequency of the electron/photon system. The relaxation oscillation frequency of the Y lasers investi-
SCHILLING et a l . : MULTIQUANTUM-WELL Y LASER Conversion across 14 nm (1.75 THz)
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even more extended tunability and further increase in speed. As outlined in this paper, the successful implementation of the enormous potential of Y lasers into high capacity all-optical transswitching networks is expected. ACKNOWLEDGMENT We would like to thank all our colleagues at the Optoelectronic Components Division of the Alcatel SEL Research Center who contributed to the work. Expert technical support from K. Daub is especially acknowledged.
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gated in this study is around 3 GHz which can be further improved. Therefore the successful operation of the Y laser frequency converter at even higher Gbit rates is expected from future experiments using devices with higher resonance frequencies. VI. CONCLUSION The Y laser, a technologically simple but multifunctional device for photonic switching and optical communication applications is further exploited and investigated in this study concerning electronic wavelength tunability and optically triggered frequency conversion. Used as a light source, single-mode emission with extremely wide tuning range up to 51 nm is achieved under CW operation at moderate currents. This allows for a high figure of merit ‘‘channel number times channel separation.” For a given number of required channels, the wide range wavelength access enables to reduce effort for channel filters at the receiver side. Asymmetrical structures were designed offering easily controllable wavelength addressing schemes. Single current tuning control is thereby accomplished according to the predictions of a simple theory, and demonstrated experimentally up to 8 nm range. The tunability range and speed for frequency conversion are strongly increased to > 6 THz and 2.5 Gb/s, simultaneously, for the compressively strained all-quaternary MQW Y lasers. From optimized devices we expect
REFERENCES [I] H. Kobrinski, M. P. Vecchi, T. E. Chapuran, J. B. Georges, C. E. Zah. C. Caneau, S. G. Menocal, P. S. D . Lin, A. S. Gozdz, and F. J . Favire, “Simultaneous fast wavelength switching and intensity modulation using a tunable DBR laser,” 1EEE Photon. Technol. Lett., vol. 2, pp. 139-142, 1990. [2] J. M. Gabriagues and J. B. Jacob, “Exploitation of the wavelength domain for photonic switching in the IBCN,” in Proc. 17th ECOC/ IOOC’91, Paris, France, Vol. 2 , 1991, pp. 59-66. [ 3 ] M. Schilling, W. Idler, E. Kiihn, G. Laube, H. Schweizer, K. Wiinstel, and 0. Hildebrand, “Integrated interferometric injection laser: Novel fast and broad-band tunable monolithic light source,” 1EEE J . Quantum Electron., vol. 27, pp. 1616-1624, 1991. 141 W. Idler, M. Schilling, G. Laube, D. Baums, K. Wiinstel, and 0. Hildebrand, “High speed wavelength and spatial switching with a YCCL,” presented at Topic. Meet. on Photonic Switch., Salt Lake City. UT, 1991, paper FCI. 151 M. Schilling, W. Idler, D. Baums, G. Laube, K. Wiinstel, and 0. Hildebrand, “Multifunctional photonic switching operation of 1500 nm Y-coupled cavity laser (YCCL) with 28 nm tuning capability,” IEEE Photon. Technol. Lett., vol. 3 , pp. 1054-1057, 1991. I61 0. Hildebrand, M. Schilling, W. Idler, D. Baums, G. Laube, and K. Wiinstel, “The integrated interferometric injection laser (Y-laser): one device concept for various system applications,” in Proc. 17th ECOCI lOOC’91, Paris, France, vol. 2, 1991, pp. 39-46. [7] W. Idler, M. Schilling, D. Baums, G. Laube, K. Wiinstel, and 0. Hildebrand, “Y laser with 38 nm tuning range,” Elecrron. Lett., vol. 27, pp. 2268-2269, 1991. I81 K. Wunstel, W. Idler, M. Schilling, G. Laube, D. Baums, and 0. Hildebrand, “Y-shaped semiconductor device as a basis for various photonic switching applications, ’’ in Proc. OFC’92, San JosC, CA, 1992, p. 125. [9] D. Baums,M. Schilling, W. Idler. G. Laube, and K. Wiinstel, “Observation of wavelength-bistability in the interferometric Y-laser,” (Topical Meeting on Photonic Switching ’92, Minsk) Proc. SPIE. to be published. [IO] 0. Hildebrand, M. Schilling, D. Baums, W. Idler, K. Diitting, G . Laube, and K. Wunstel, “The Y-laser: A multifunctional device for optical communication systems and switching networks,’’ J . Lightwave Technol., to be published. [ I I] M. Schilling., H. Schweizer. K. Diittinp. W. Idler. E. Kiihn. A. Nowitzki, and K. Wiinstel, “Widely tunable Y-coupled cavity integrated interferometric injection laser,” Electron. Lett., vol. 26, pp. 243244, 1990. 1121 K. Wiinstel, H. Schweizer, M. Schilling, W. Idler, E. Kiihn, G. Laube, and 0. Hildebrand, “Integrated interferometric injection lasers (1300 nm and 1500 nm) with tuning range exceeding 2 0 nm,” presented at 12th IEEE Laser Conf. Davos, Switzerland, 1990, paper L20. 1131 W. Idler, M. Schilling, H. Schweizer, E. Kiihn, G. Laube, K. Wiinstel, and 0. Hildebrand, “High speed integrated interferometric injection laser with 22 nm tuning range,” presented at Proc. 16th ECOC, Amsterdam, 1990, paper WeF2.1. I141 V. Jayaraman, D. A. Cohen, and L. A. Coldren, “Extended tuning range in a distributed feedback InGaAsP laser with sampled gratings,” in Proc. OFC’92, San JosC, CA, 1992, p. 165. -, “Demonstration of broadband tunability in a semiconductor laser using sampled gratings,” Appl. Phys. Lett., vol. 60, pp. 2321-2323, 1992.
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[ 151 V. Jayaraman, A. Mathur, L. A. Coldren, and P. D. Dapkus, “Very
wide tuning range in a sampled grating DBR laser,” presented at Proc. 13th IEEE Semiconductor Laser Conf., Takamatsu, 1992, post-deadline paper PD- I 1. 1161 Y. Tohmori, Y. Yoshikuni, T . Tamamura, M. Yamamoto, Y. Kondo, and H. Ishii, “Ultrawide wavelength tuning with single longitudinal mode by super structure grating (SSG) DBR lasers,” presented at Proc. 13th IEEE Semiconductor Laser Conf., Takamatsu, 1992, paper 0-6. [I71 S. Illek. W. Thulke, B. Borchert, and M.-C. Amann, “Broadband electronic wavelength tuning by codirectionally coupled twin-guide laser diode,” in Proc. 17th ECOC/IOOC’9!, vol. 3. Paris, 1991, pp. 21-24. -, “Codirectionally coupled twin-guide laser diode for broadband electronic wavelength tuning,” Electron. Lett., vol. 27, pp. 22072209, 1991. [I81 R. C. Alferness, U. Koren, L. L. Buhl, B. I. Miller, M. G. Young, T. L. Koch, G. Raybon, and C. A. B u m s , “Widely tunable InGaAsP/lnP laser based on a vertical coupler intracavity filter,” presented at Proc. OFC’92, San Jose, 1992, paper PD2. [ 191 J. B. D. Soole, K. Poguntke, A. Scherer, H. P. LeBlanc, C. ChangHasnain, J. R. Hayes, C. Caneau, R. Bhat, and M. A. Koza, “Multistripe array grating integrated cavity (MAGIC) laser: A new semiconductor laser for WDM applications,” Electron. Lett., vol. 28, pp. 1805-1807, 1992. [20] P. A. Kirkbv. “Multichannel wavelength-switched transmitters and receivers-new component concepts for broad-band networks and distributed switching systems,” J. Lightwave Technol.. vol. 8, pp. 202211, 1990. M. Schilling, W. Idler, D. Baums, K. Dutting, G. Laube, K. Wunstel, and 0. Hildebrand, “6 THz range frequency conversion of 2.5 G b / s signals by a 1.55 pm MQW based widely tunable Y-laser,” presented at Proc. 13th IEEE Semiconductor Laser Conf., Takamatsu, 1992, paper 0 - 8 . W. Idler, M. Schilling, D. Baums, K. Dutting, G. Laube, K. Wunstel, and 0. Hildebrand, “Wide range 2 . 5 Gbit/s wavelength conversion with a tunable Y-laser,” presented at Proc. 18th ECOC, Berlin, 1992, paper WeA10.6. H . Rokugawa, N. Fujimoto, T. Nakagami, and K. Wakao, “Errorfree operation of wavelength conversion laser for multistage photonic cross-connect node,” presented at Topical Meeting on Photonic Switching, Salt Lake City, UT, 1991, paper WA3. H. Kawaguchi, K. Oe, H. Yasaka, K. Magari, M. Fukuda, and Y. Itaya, “Tunable optical-wavelength conversion using a multielectrode distributed-feedback laser diode with a saturable absorber,” Electron. Lett., vol. 23, pp. 1088-1090, 1987. S . Yamakoshi, K. Kondo, M. Kuno, Y. Kotaki, and H. ha!, “An optical-wavelength conversion laser with tunable range of 30 A , ” in Proc. OFC’88, New Orleans, LA, PD-10, 1988. S . Yamakoshi, “Optically triggered functional device-potential applications of bistable laser diodes,” in Proc. 7th IOOC, Kobe, 1989, paper 21A3-3. K. Kondo, H. Nobuhara, S . Yamakoshi, and K. Wakao, “Gigabit operation of a wavelength-conversion laser,” in Proc. In?. Top. Meet. On Photonic Switching, Kobe, Springer Series in Electronics and Photonics, vol. 29, Photonic Switching I I , K. Tada and H. S. Hinton, Eds., 1990, pp. 233-236. D. De Bouard. G. Da Lourd, C. Chauzat, J . Jacquet, J. Benoit, D. Leclerc, and J. M. Gabriagues, “Fast optical triggering and wavelength switching using a DBR laser with a saturable absorber,” in Proc. Top. Meet. on Photonic Switching’91, Salt Lake City, UT, 1991, paper WA2. P. Pottier, M. J. Chawki, R. Aufret, G. Claveau, and A. Tromeur, “1.5 G b / s transmission system using all optical wavelength converter based on tunable two-electrode DFB laser,” Electron. Lett., vol. 27, pp. 2183-2185. 1991. G. Gropkopf, R. Ludwig, R. Schnabel, N. Schunk, and H. G. Weber, “Frequency conversion by four-wave-mixing in LD amplifiers,” in Pro. Int. Top. Meet. on Photonic Switching, Kobe, Springer Series in Electronics and Photonics, vol. 29, Photonic Switching 11, K. Tada and H. S . Hinton. Eds.. 1990. pp. 226-232. S. Murata, A. Tomita. J. Shimizu, M. Kitamura, and A. Suzuki, “Observation of highly nondegenerate four-wave mixing ( > 1 THz) in an InGaAsP multiple quantum well laser,” Appl. Phys. Lett., vol. 58, pp. 1458-1460, 1991. S . Murata, A. Tomita. J. Shimizu, and A. Suzuki, “THz optical frequency conversion of I Gb/s signals using highly nondegenerate four-
IEEE JOURNAL OF QUANTUM ELECTRONICS, VOL. 29. NO. 6, JUNE 1993 wave mixing in semiconductor lasers,” in Proc. ECOC/IOOC’9/, Paris, vol. I , part I , 1991, pp. 85-88. -, “THz optical-frequency conversion of 1 Gb/s-signals using highly nondegenerate four-wave mixing in an InGaAsP semiconductorlaser,” IEEEPhoton. Technol. Lett, vol. 3 , pp. 1021-1023, 1991. 1331 T. Durhuus, B. Fernier, P. Garabedian, F. Leblond, J. L. Lafragette, B. Mikkelsen, C. G. Joergensen, and K. E. Stubkjaer, “High-speed all-optical gating using a two-section semiconductor optical amplifier structure,” in Proc. CLEO’92, Anaheim, CA, CThS4. 1992. [34] B. Glance, J. M. Wiesenfeld, U. Koren, A. H. Gnauck, H. M. Presby, and A. Jourdan, “Broadband optical wavelength shifter,” in Proc. CLEO’92, paper CPD27, 1992. [35] R. J. S. Pedersen, ,B. Mikkelsen, T. Durhuus, M. J. Steinmann, K. E. Stubkjaer, M. Oberg, and S. Nilsson, “Tunable DBR laser for wavelength conversion of 2.5 G b / s signals,” in Proc. 13th IEEE Int. Takamatsu, 1992, pp. 270-271. Semicond. Laser Conf.., B. Mikkelsen, T. Durhuus, R. J. Pedersen, K. E. Stubkjaer, M. Oberg, and S . Nilsson, “Penalty free wavelength conversion of 2.5 G b / s signals using a tuneable DBR-laser,” in Proc. ECOC’92, Berlin, vol. I . 1992, pp. 441-444. F. Ebskamp, R. J. S . Pedersen, B. Mikkelsen, T. Durhuus, M. Oberg, and S . Nilsson, “Heterodyne detection of wavelength converted CPFSK signals up to 4.8 Gb/s,” in Proc. ECOC’92. Berlin, vol. 3, 1992, pp. 871-874. [36] P. Wiedemann, M. Klenk, U. Koerner, R. Weinmann, E. Zielinski, and P. Speier, “MOVPE of In(GaAs)P/InGaAs MQW-structures,” J. Crysr. Growth, vol. 107, pp. 561-566, 1991. [37] P. Speier, J. Bouayad-Amine, U. Cebulla, K. Dutting, M. Klenk, G. Laube, H. P. Mayer, R. Weinmann, K. Wunstel, E. Zielinski, and 0. Hildebrand, “ I O Gbit/s MQW-DFB-SIBH lasers entirely grown by LPMOVPE,” Electron. Lett., vol. 27, pp. 863-864, 1991. 1381 S. Wang, H. K. Choi, and I. H. A. Fattah, “Studies of semiconductor lasers of the interferometric and ring types,” IEEE J. Quantum Electron., vol. QE-18, pp. 610-617, 1982. [39] J. Salzman, J. S. Osinski, R. Bhat, K. Cummings, and L. Harriott, “Cross coupled cavity semiconductor laser,” Appl. Phys. Lett., vol. 52, pp. 767-769, 1988. [40] M. Schilling, K. Dutting, W. Idler, D. Baums, G. Laube, K. Wunstel, and 0. Hildebrand, “Asymmetrical Y laser with simple single current tuning response,” Electron. Lett., vol. 28, pp. 1698-1699, 1992. 1411 K. Dutting, 0. Hildebrand, D. Baums, W. Idler, M. Schilling, and K. Wunstel, “Analysis and simple tuning scheme of asymmetric Y lasers,” to be published.
Michael Schilling (M’90) was born in Hof, Germany, on December 12, 1955. He received the Diploma degree in physics from the University of Erlangen-Nurnberg, Germany, in 1982, working on characterization of ion implanted 11-VI semiconductor material. In March 1983, he joined the SEL Research Center, Stuttgart, where he has been involved in 111-V epitaxy and development of various optoelectronic components based on InP. Currently, he is engaged in design and processing technologies of photonic integrated devices for optical communications and switching. Mr. Schilling is a member of the Germany Physical Society (DPG), the German Association for Crystal Growth, the German Association of Electrical Engineers (VDE) and the IEEE Laser and Electro-Optics Society.
Wilfried Idler was born in Ludwigsburg, Germany, on April 17, 1956. He studied physics at the University of Stuttgart, Germany, (1981-1987) and received the Diploma degree in physics for studies of waveguide modes in multiquantum-well lasers. In 1987 he joined the SEL Research Center, Stuttgart, where he was primarily engaged in noise investigations (Terminal Electrical Noise, TEN) of DFB lasers for electrical laser wafer characterization. Currently his main activities are modeling and characterization of photonic integrated devices, especially the Y laser. Mr. Idler is a member of the German Association of Electrical Engineers (VDE).
SCHILLING
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MULTIQUANTUM-WELL Y LASER
Dieter Baums was born in Bad Nauheim, Germany, on February 14, 1960. After studying physics at the Technical University in Munich and the Justus-Liebig-University in Giessen, Germany, he received the Diploma degree in 1986. His work dealt with noise properties of superconducting microbridges. During his thesis he was working on nonlinear dynamics and mode-locking of semiconductor lasers. He received the Ph.D. degree from Philipps-University of Marburg, Germany, in 1990. Since then he has been with the Optoelectronic Components Division of the SEL Research Center, Stuttgart, working on tunable lasers and photonic integrated devices. Dr. Baums is a member of the German Physical Society (DPG) and the German Association of Electrical Engineers (VDE).
Kaspar Diitting was born in Cologne, Germany, on September 21, 1962. From 1981 to 1986 he studied physics at the University of Tubingen, Germany, and received the Diploma degree in physics for studies and implementation of a liquid metal focused ion &am system for SIMS. In 1986 he joined the SEL Research Center, Stuttgart, where he has been engaged in the design and realization of high performance laser structures. His activities are currently focused on realization of wafer testable lasers and modeling of wavelength tunable laser structures.
Gert Laube was born in Geislingen, Germany, on March 26, 1957. He received the Diploma degree in chemistry in 1983 from the University of Ulm and, in 1988, the Ph.D. degree from the University of Stuttgart, Germany. His dissertation dealt with gallium and indium precursors for MOVPE. In October 1988, he joined the SEL Research Center, Stuttgart, where he is working on MOVPE of discrete and integrated laser structures. Dr. Laube is a member of the German Chemical Society (GDCh), the
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German Association for Crystal Growth, and the German Association of Electrical Engineers (VDE).
Klaus Wunstel was born in Kandel, Germany, in 1955. He received the physics Diploma in 1979 from the University of Karlsruhe, Germany, where he worked on optical characterization of semiconductor lasers. In 1982, he received the Ph.D. degree from the University of Stuttgart. From 1979 to 1983 he was engaged in electrical and optical analysis of Si- and 111-V semiconductors at the Max-Planck-Institute for Solid State Research in Stuttgart. He joined the Research Center of SEL in 1983, where he has been involved in research and development of InP-based optoelectronic devices. His main research areas are high-speed, dynamic single mode lasers, wavelength tunable lasers, and laser integration. In 1986, he became responsible for laser device technology. Since 1989 he has been manager of the laser processing group of the Optoelectronic Components Division. Dr. Wiinstel is a member of the German Physical Society (DPG) and the German Association of Electrical Engineers (VDE).
Olaf Hildebrand was born in 1948 in Hamburg, Germany. He received the Dip1.-Phys. degree in 1973 and the Ph.D. degree in 1977, both from the University of Stuttgart (summa cum laude). His Diploma concerned widely tunable near IR lasers with applied research on GaAs laser basics went over in his thesis dealing with basic research on GaAs and InP based lasers. In 1978 he changed to PIN and avalanche photodetectors based on GaSb and InP. In May 1983 he joined the SEL Research Center in Stuttgart where, since 1985, he has been head of the Optoelectronic Components Division. Dr. Hildebrand is a member of the German Physical Society (DPG) and the German Association of Electrical Engineers (VDE).
