Ultrafast Fiber Pulsed Lasers Incorporating Carbon ... - IEEE Xplore

IEEE JOURNAL OF SELECTED TOPICS IN QUANTUM ELECTRONICS, VOL. 10, NO. 1, JANUARY/FEBRUARY 2004

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Ultrafast Fiber Pulsed Lasers Incorporating Carbon Nanotubes Sze Y. Set, Member, IEEE, Hiroshi Yaguchi, Yuichi Tanaka, and Mark Jablonski, Member, IEEE

Abstract—We present the first passively mode-locked fiber lasers based on a novel saturable absorber incorporating carbon nanotubes (SAINT). This device offers several key advantages such as: ultrafast recovery time ( 1 ps), high-optical damage threshold, mechanical and environmental robustness, chemical stability, and the ability to operate in transmission, reflection, and bidirectional modes. Moreover, the fabrication cost and complexity of SAINT devices are potentially lower than that of conventional semiconductor saturable absorber mirror devices. Therefore, it is expected that SAINT will greatly impact future pulsed laser design and development. Index Terms—Fiber laser, mode-lock laser, optical pulsed laser, saturable absorber, single-wall carbon nanotube.

I. INTRODUCTION

O

PTICAL pulsed lasers offer a broad range of applications in various fields, such as optical communications, optical signal processing, two-photon microscopy, laser surgery etc. Ultrashort pulses in the picosecond regime are usually generated using a mode-locked laser. A mode-locked laser has multiple longitudinal modes that oscillate simultaneously with their relative phases locked to each other in a fixed relationship generating uniformly spaced pulses. The effective path length of the laser resonator defines the longitudinal modes. In order to achieve mode locking, a mode-locking mechanism is required to synchronize the phases of the lasing modes so that the phase differences between all lasing modes remain constant. These optically phase-locked modes then interfere with each other to form optical pulses. Two broad classes of mode-locking schemes, active mode locking and passive mode-locking, are typically used. Passively mode-locked fiber lasers are among the best pulsed sources available due to their simplicity and their ability to generate transform-limited optical pulses in the picosecond and subpicosecond regimes [1], [2]. Such lasers offer superb pulse quality and there is no need for costly modulators as required in actively mode-locked lasers. Instead, a passively mode-locked fiber laser employs a nonlinear element, a device that possesses an intensity-dependent response to favor optical pulse formation over continuous-wave lasing. This is usually a saturable absorber, such as a semiconductor saturable absorber [3], [4], or an “effective” saturable absorber, such as a nonlinear polarization switch [5], a nonlinear optical loop-mirror [6]

Manuscript received June 19, 2003; revised August 11, 2003. The authors are with the Alnair Labs Corporation, Kawaguchi City, Saitama-ken 332-0015, Japan (e-mail: [email protected]). Digital Object Identifier 10.1109/JSTQE.2003.822912

(NOLM), and its variants [7], [8]. Among these mode lockers, the quantum-well semiconductor-based device, commonly referred to as the semiconductor saturable absorber mirror (SESAM) [3], has become the main device used in almost all commercial passively mode-locked fiber lasers. However, there are a number of drawbacks associated with SESAMs. SESAMs require complex and costly clean-roombased fabrication systems such as MOCVD, MOVPE, or MBE to grow and may require an additional substrate removal process in some cases. High-energy heavy-ion implantation is required to introduce defect sites in order to reduce the device recovery time (typically a few nanoseconds) to the picosecond regime required for short-pulse laser mode-locking applications. Since the SESAM is a reflective device, its use is restricted to only certain types of linear cavity topologies. Other laser cavity topologies such as the ring-cavity design (which requires a transmission-mode device, and offers advantages such as doubling the repetition rate for a given cavity length, and less sensitive to reflection-induced instability with the use of optical isolators) is not possible unless an optical circulator is employed, which increases cavity loss and laser complexity. SESAM may also suffer from a low optical damage threshold. So far, there have been no alternative saturable absorbing materials to compete with SESAMs for the passive mode-locking of fiber lasers. We recently proposed and demonstrated a noise suppressor [9] based on a carbon nanotube with an ultrafast response time of 1 ps. Subsequently, the device was optimized for successful mode locking of a subpicosecond fiber pulsed laser [10]. In this paper, we explain the structure, properties, and operation of the saturable absorber incorporating nanotubes (SAINT) for passive mode locking of ultrafast picosecond lasers. We demonstrate passively mode-locked fiber lasers in both ring- and linear-configurations using a SAINT in transmission and reflection mode, respectively. These results confirm SAINT for ultrafast laser mode-locking applications with performance comparable to that of a conventional SESAM. This paper is structured as follows. In Section II, the concept of a saturable absorber is introduced. In Section III, optical properties of carbon nanotubes are discussed. Section IV describes the incorporation of a layer of carbon nanotubes into a saturable absorber module and both the processing and physical characteristics of the carbon nanotube layer. The saturable absorber characteristics of the carbon nanotube module are demonstrated using a Z-scan setup in Section V. Experimental results from two different fiber laser configurations, ring and linear, incorporating carbon nanotube modules are presented in Section VI. This paper concludes with the summary in Section VII.

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Fig. 3. Chiral vector (n; m) representation on a 2-D graphene sheet. Roll-up vectors for (17,0) and (12,5) are shown. Chiral vectors in white cells are semiconductor, while those in grey cells and semigrey cells are metallic and semimetallic, respectively. Fig. 1.

Intensity-dependent attenuation of a saturable absorber.

Fig. 2. Schematic model of a chiral nanotube [11].

II. SATURABLE ABSORBER A saturable absorber is a material that displays a change in its optical transparency dependent on the incident optical intensity in a specific operating wavelength region. In a linear regime, where the incident optical intensity is weak, the saturable absorber absorbs the light, resulting in attenuation. When the incident optical intensity is high, saturation of absorption occurs, resulting in a decrease in attenuation. This kind of intensity dependent attenuation allows the high-intensity components of an optical pulse to pass through the saturable absorber, while the lower intensity components of the pulse, such as the pulse wings, pedestals, and background continuous wave (cw) radiation do not (Fig. 1). When a saturable absorber is placed in a lasing cavity, it will favor short pulse generation and suppress cw radiation, which can be used for mode locking. For the ultrashort pulse generation application, a saturable absorber with a fast recovery time is required for stabilizing laser mode locking, while a slower recovery time could facilitate laser self-starting. III. CARBON NANOTUBE An ideal carbon nanotube is a hexagonal network of carbon atoms rolled into a seamless cylinder (Fig. 2) with diameters on the order of nanometers and lengths that can be up to tens of microns [11], [12]. The ends of carbon nanotubes are typically capped with half of a fullerene molecule. Single-walled nanotubes (SWNT) are of particular interest due to their unique properties and structural simplicity. A SWNT may be semiconducting, metallic, or semimetallic depending on its chirality, as defined in [13]. The chirality of a SWNT is defined which connect two by the chiral vector crystallographically equivalent sites on a two–dimensional and are (2-D) graphene sheet, as shown in Fig. 3, where

unit vectors of the hexagonal lattice. Different chiral vectors . Metallic nanotube are specified using two integers is an integer multiple of three, while arises when . Semiconductor semimetal nanotube corresponds to nanotube occurs when is not an integer multiple of three. It is currently difficult to selectively fabricate nanotubes with specific chirality or diameter. Statistically, 2/3 of the nanotubes made will be semiconducting nanotubes, while 1/3 of them are metallic nanotubes (Fig. 3). Excitonic absorption in semiconductor nanotubes, which have an ultrafast recovery time, is responsible for the saturable absorption property. We speculate that the ultrafast recovery time is due to the presence of metallic nanotunbes, serving as recombination centers, similar in function, as the defects in SESAM created by low-temperature growth or ion implantation. Excited state energy in semiconductor nanotubes could be transferred, through ultrafast tube-tube interaction, and quenched by metallic nanotubes. Recently, the saturable absorption property of SWNT has also been studied and reported in [14] and [15] for potential application as an optical switch. Pump-probe experiments had also been carried out on SWNTs with results indicating an ultrafast recovery lifetime in the order of 500 fs [14], [16]. IV. SAINT DEVICE Typical configurations of a SAINT are shown in Fig. 4. Fig. 4(a) shows the tranmission-type SAINT (T-SAINT) with a thin layer of purified SWNTs sandwiched between two 1-mm-thick quartz substrates, which are anti-reflection (AR) coated on the outer surfaces. Other possible configurations of SAINT are shown in Fig. 4(b) and (c). The reflective SAINT (R-SAINT), as shown in Fig. 4(b), has a layer of SWNT coated on a highly reflective (HR) mirror, which enable the device to operate in a reflective mode. The fiber-ferrule-type SAINT (F-SAINT), shown in Fig. 4(c), has a relatively simple and low-cost construction without the need for collimating and/or focusing lenses as required in the T-SAINT and R-SAINT. The saturable absorption properties of a SAINT module, for example its linear absorption level, threshold power, and center wavelength, can be controlled by the thickness of the SWNT layer, layer density, and the diameter of the individual carbon nanotubes. Since the orientations of the nanotubes are

SET et al.: ULTRAFAST FIBER PULSED LASERS INCORPORATING CARBON NANOTUBES

Fig. 4.

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Typical configurations of a SAINT: (a) transmission-type, (b) reflective type, and (c) fiber-ferrule type.

Fig. 5. Energy versus 1-D electronic density of states for semiconductor nanotubes with different diameters and chiralities.

randomly distributed, the optical response of the SAINT device is independent of polarization of the input light. The SWNTs were grown using the laser ablation technique [17]. High-energy laser pulses from a Nd:YAG laser were used to ablate a metal catalyzed carbon target placed in a quartz tube flowing with 500 torr of Ar gas. The quartz tube was heated in an electric furnace. Diameter-selective SWNTs can be grown by careful control of the furnace temperature and the adoption of specific catalysts with appropriate relative concentrations [18]. Through a series of purifying processes, high purity SWNTs with a controlled diameter distribution can be obtained. The optical absorption characteristics of SWNTs are related to the tube diameters and chirality. Using a tight-binding zone-folding calculation [19] energy versus one–dimensional (1-D) electronic density of states (eDOS) of two semiconductor nanotubes with diameters 1.2 and 1.35 nm are calculated and shown in Fig. 5(a) and (b), respectively. The S1 and S2 transitions of semiconductor nanotubes are shown in Fig. 6, which relate the nanotube diameter to the energy gap [20]. The atomic-force microscope (AFM) image (Fig. 7) of a typical nanotube layer in the SAINT shows meshes of SWNT ropes

Fig. 6. Simplified Kataura-plot showing only S1 and S2 energy gaps of semiconductor nanotubes.

with a bundle diameter 20 nm. Furthermore, the TEM image (Fig. 8) on one of the bundles reveals each SWNT strain with a diameter of around 1 nm. The mean nanotube diameter of the

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Fig. 7. AFM image.

Fig. 8. TEM image.

samples is measured using resonant Raman spectroscopy. In the two different SWNT samples, fabricated at different oven temperatures, the radial breathing modes indicated mean diameters of 1.35 and 1.2 nm and corresponded well to the measured optical absorption peaks at 1680 (Fig. 9) and 1550 nm (Fig. 10), respectively, when the coulomb-interaction blue shift is accounted for. It is clear that the operating wavelength of the SWNT is dependent on nanotube diameter, which in turn can be

Fig. 9.

Transmission plot of SWNT with a mean diameter of 1.35 nm.

controlled by the nanotube growth conditions, such as furnace temperature and the type of metal catalysts used [18]. V.

-SCAN AND SPECTRAL MEASUREMENT

We used a -scan experimental setup [9], as shown in Fig. 11, to demonstrate that our SAINT modules possess saturable absorber properties. The light source was a fiber laser operating at 1550 nm, similar to that reported in [21], generating 80-GHz


Fig. 12.

Fig. 10.

Transmission plot of SWNT with a mean diameter of 1.2 nm.

Fig. 11.

z -scan experimental setup.

1-ps soliton pulse bunches ( 120 pulses), with a cavity round-trip frequency of 4.4 MHz. A variable optical attenuator (VOA) was employed to control the optical output power of the laser. The average optical power was 3.8 dBm, when the attenuator level was set at 0 dB. The laser pulses were launched through a fiber collimator, passed through an aspherical lens , and focused onto the surface of the sample coated with SWNT film. Depending on the position of the SWNT sample, the spot size of the focusing beam passing through the SWNT film could be varied from 200 down to a minimum of 10 m, when it was positioned at the focal point mm . Another set of aspherical lens and a fiber collimator was used to collect the outgoing beam from the sample back into a short piece of fiber connected to either an optical power meter or an optical spectrum analyzer. The position of the sample was varied to achieve different spot sizes and, hence, optical intensity, passing through the SWNT film. The results of the -scan experiment with different laser launch powers are shown in Fig. 12. When the laser inmm (corresponding to a spotsize tensity was low, at

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z -scan results with different launched powers.

of 100 m ), the transmission of the SWNTs (reference with 2 dB , the uncoated substrate) was measured to be 63% similar to the linear transmission of the sample measured using a broadband source. However, the transmission of the sample increased when the laser intensity was raised, by moving the sample to positions with smaller spot sizes. The transmission mm, where the spot size was was at a maximum at at its minimum of 10 m, and the laser intensity was at a maximum (estimated at 5.8 J/cm per pulse, peak intensity MW/cm ). The -scan experiment was repeated with different optical launch powers by changing the attenuator level mm of the VOA. As expected, the transmission peak at decreased as the optical power was reduced (Fig. 12). The transmission or loss of the sample is evidently dependent on the optical power of the input light, the property of a saturable absorber. This phenomenon occurs because there is a finite number of semiconducting SWNTs in the thin nanotube layer that could absorb light through excitonic absorption. The absorption is saturated when a large number of incoming photons exhaust the available SWNT excitonic absorption centers. High-resolution spectral transmission measurements were also carried out to further confirm the saturable absorber mm, property of the sample. The sample was fixed at where the -scan results showed a maximum transmission. The output spectra were taken using an optical spectrum analyzer in high-sensitivity mode. The spectral transmission characteristics of the sample were taken on the SWNT-coated region. For reference, spectral data was also taken on the uncoated region of the quartz substrate. The effects measured were confirmed to be purely due to the SWNTs. The changes in transmission compared to the linear absorption are plotted in Fig. 13, for various optical launched powers. The linear absorption profile of the SWNTs, measured using a broadband ASE source, serves as a baseline reference (Fig. 13). When the pulsed laser was used, the sample exhibited an increased transmission over the spectral region of the pulse source. As expected, an increasing launched power caused an increasing transmission (reduced loss) in the spectral region of the pulsed source. At the highest launched power of 3.8 dBm dB , the transmission deviated from the linear case by up to

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Fig. 13.


Transmission spectra with different launched powers.

6% in the spectral region of the input pulses. This shows that the SWNT sample is capable of preferentially suppressing lower intensity noise components, such as the ASE noise (Fig. 13). The double-hump features on the spectral transmission correspond to the spectral contents or Fourier components of the pulse where its temporal intensity is high. The results are in agreement with our numerical simulation, where an intensity dependent loss, as in the case of a saturable absorber, gives rise to similar double-hump spectral transmission variation characteristics. The ultrafast saturable absorption effect of the sample can be employed for noise suppression, pulse shaping, and laser mode-locking applications. The transmission spectrum of a SAINT sample (Fig. 14) shows the saturable S1 and S2 absorption due to semiconducting nanotubes, and the nonsaturable background absorption (dashed line) due to plasmon and impurities such as amorphous carbon and metal catalysts. The saturable absorption characteristics of the sample with different input pulse energy density is plotted in Fig. 15. The total absorption is shown in Fig. 15(a), as a function of the incident pulse energy density, as well as the corresponsing peak power intensity. The normalized saturable absorption is plotted in Fig. 15(b) with the nonsaturable background loss of 9.4% subtracted and normalized with the saturable depth of 25.3%. The 10% saturation pulse energy density is measured to be 3 J/cm . This corresponds to an estimated saturation fluence of 12.5 J/cm , which is very similar to that of a typical SESAM (10–60 J/cm ) [22]. VI. LASER MODE LOCKING The first laser mode locked using a SAINT was a fiber ring laser, as shown in Fig. 16. A 6-m length of erbium-doped fiber (EDF), backward pumped by a 980-nm laser diode (LD), is used as the laser gain medium. Two polarization-independent optical isolators are inserted to prevent back reflection in the cavity and to ensure unidirectional operation. The output light from the EDF is launched through a fiber collimator and a focusing aspherical lens onto the SAINT to a spot size of 10 m. The output light from the SAINT is collected and launched back into the fiber cavity via another set of matching aspherical lens and collimator. An angle-tunable thin-film bandpass filter with

Fig. 14. Transmission spectrum of SAINT (solid line) showing the saturable absorption and the nonsaturable loss (dashed line).

7-nm bandwidth is inserted for wavelength tuning. Single-mode fiber (SMF) with a length of 12 m is employed for solitonic pulse shaping and dispersion management of the laser cavity. The output of the laser is tapped through a 95% port of a fiber coupler, whereas the other 5% port is used to feed back into the cavity. At a pump power of around 18 mW, the laser starts to mode lock and produce multiple pulses in a round-trip time. After that, the pump power can be reduced to a level around 14 mW and the laser will maintain pulsing in single-pulse mode at a fundamental repetition rate of 6.1 MHz. A very brief moment of Q-switched mode locking is observed just before the laser selfstarted when the pump power was increased to the mode-locking threshold pump level of 18 mW. Above the threshold pump power, a clean mode locking is achieved without any observable Q-switch instability; although, we have recently observed passive Q-switching at high pump powers 75 mW when a different SAINT sample, with different SWNT layer thickness, is used [23]. The laser output average optical power is 5.8 dBm when operated in a fundamental mode with a single pulse in a round trip. At higher pump powers, the laser will operate in multiple-pulse mode resulting in a higher harmonic repetition rate at the multiple of the fundamental round-trip frequency. The output spectrum and SHG autocorrelation trace of the output mode-locked pulses are shown in Fig. 17(a) and (b), respectively. The autopulse correlation trace and spectrum are well fitted by a profile, indicating that soliton pulses are generated. The inferred full-width at half-maximum (FWHM) from the autocorrelation trace is estimated to be 1.1 ps, while the 3-dB spectral width is 3.7 nm. The resulting time-bandwidth product (TBP) of 0.52 indicates that the pulses are chirped, compared to the transformpulses. This could be caused by limited TBP of 0.315 for the 5-m length of SMF on the coupler and isolator. By using low-


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Fig. 15. Saturable absorption characteristics of SAINT. (a) Total optical absorption versus pulse energy density and peak power intensity. (b) Saturable S1 absorption versus pulse energy density.

dispersion fiber at the output, it is possible to reduce the chirp in the pulses. An FWHM pulsewidth of 700 fs is expected with proper dispersion compensation. The laser has very little polarization sensitivity, and mode locking was attained even without the use of polarization maintaining (PM) fiber or any special

means for polarization control. The polarization state of the fiber cavity is important to achieve mode-locking operation; however, it is not a stringent requirement, as we could achieve stable polarization states for mode locking simply by manipulating and taping down the fiber cavity by hand, without the need of a preci-

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Fig. 16.

Fig. 17.


Schematics of the mode-locked fiber laser in a ring configuration.

Ring laser output: (a)spectrum and (b) SHG autocorrelation trace.

sion polarization controller. In the single-pulse regime, the laser is stable against mechanical perturbation. In the multiple-pulse regime, at higher pump powers, mechanical perturbation causes a walkoff between the pulses at different longitudinal modes. With the right pump power, the pulses will eventually spread out to a fixed separation between each other, forming a pulse train at an integer multiple of the fundamental repetition rate.

When the SAINT is removed from the laser cavity, it is not possible to mode lock the laser, even when the pump power is raised to 100 mW. It is evident that the SAINT provides the mechanism required to initiate and sustain mode-locking operation.The pulse energy density incident to the SAINT in the cavity was estimated to be 258 J/cm . The laser is operating in full saturation regime. Another laser mode locked using a SAINT, but in reflection mode (R-SAINT), is shown in Fig. 18. In this case, the laser has a linear resonator cavity. All the components have their usual functions as described earlier. At one end of the cavity a Faraday mirror is used to compensate for birefringence in the cavity. An R-SAINT is employed at the other end of the cavity. In the R-SAINT structure, the SWNT layer is deposited on a high-reflection (HR) coated surface of a quartz substrate, sandwiched by another AR-coated substrate. Two lenses are employed to focus the incident beam into a spot of 10 m diameter on the R-SAINT. In order to maximize the gain bandwidth, an optical bandpass filter is not used. The laser center wavelength is defined by the EDFs gain profile. Pulse-shaping SMF is not inserted in the cavity intentionally, to remove soliton pulse-shaping effects. The output pulses of the linear laser operate at a fundamental cavity repetition rate of 9.85 MHz. The output spectrum of the pulses is shown in Fig. 19(a), with a 3-dB spectral width of 13.6 nm. The spectral shape is following a Gaussian profile as expected, due to the absence of soliton pulse shaping. The laser is mode locked solely by the saturable absorbing effect provided by the SAINT. Fig. 19(b) shows the SHG autocorrelation trace of the mode-locked pulses with an inferred FWHM width of 318 fs, assuming a Gaussian pulse profile. The TBP is 0.54, compared to an unchirped transform-limited value of 0.441. The chirp is due to the normal dispersion (dominated by the dispersion of the EDF) in the laser cavity, coupled with the Kerr nonlinearity in the cavity fiber, which contributes to an up-chirp. An unchirped FWHM pulsewidth of 258 fs is expected if the chirp in the output pulses were removed by some means of dispersion compensation with low nonlinearity, e.g., a chirped fiber Bragg grating, or a thin-film-based dispersion compensator. The output average power is around 1 dBm, when pumped with


Fig. 18.

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Linear cavity configuration employing a reflective SAINT.

VII. SUMMARY We have demonstrated, for the first time, optical pulse lasers employing novel saturable absorbers based on carbon nanotube technology as mode lockers. The saturable absorption property of SWNT has also been confirmed using a scan, spectral measurements, and simulation. A SAINT offers several advantages such as: ultrafast recovery time 1 ps , high optical damage threshold, mechanically and environmentally robust, chemical stability, and the ability to operate both in transmission, reflection, and bidirectional modes. Moreover, the fabrication cost and complexity of SAINT devices are potentially low. This technology is expected to greatly impact future pulsed laser design and development. Furthermore, a SAINT can also be used in various ultrafast photonic applications such as optical noise suppression and pulse shaping in a passive 2R regeneration system. We anticipate that many more future applications employing SAINT will be discovered. ACKNOWLEDGMENT The authors would like to thank Dr. H. Kataura and Prof. Achiba for the provision of the purified carbon nanotubes as well as Prof. R. Saito and Prof. K. Kikuchi for fruitful discussions and encouragement. They are also grateful to Dr. M. Tokumoto and Dr. Y. Sakakibara for giving them the opportunity to engage in the early stages of this work. REFERENCES

Fig. 19. trace.

Linear-cavity laser output: (a) spectrum and (b) SHG autocorrelation

25 mW of pump power at 980 nm. The pulse energy incident to the R-SAINT is estimated to be 650 J/cm , indicating a full saturation operating regime. Although a full polarization compensation scheme was not incorporated with the lack of another Faraday rotator at the other end of the linear cavity, polarization instability was not observed in our case. Nevertheless, it would definitely be beneficial to incorporate another Faraday rotator to avoid possible polarization instabilities.

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Sze Y. Set (M’99) received the B.Eng. degree (with first-class honors) in electronics engineering and the Ph.D. degree in electronics engneering and optical fiber communications from Southampton University, Southampton, U.K., in 1993 and 1998, respectively. From 1996 to 1998, he was a Research Assistant with the Optoelectronics Research Centre, Southampton University, and was leading a European Union research project, ACTS “MIDAS,” which resulted in the first successful 40-Gb/s transmission-field trial, using midspan spectral inversion for dispersion compensation. In 1998, he was awarded a Postdoctoral Research Fellowship from the Japan Society for the Promotion of Science (JSPS) to work at the Research Center for Advanced Science and Technology (RCAST), The University of Tokyo, Tokyo, Japan. He was a Consultant and Senior Research and Development Engineer with Micron Optics, Inc., Atlanta, GA, from 2001 to 2002. Currently, he is the Research and Development General Manager with Alnair Laboratories Corporation, Kawaguchi City, Japan. He has contributed to four patents and more than 70 conference and journal publications in the areas of short-pulse transmission, dispersion compensation, nonlinear optical devices, tunable fiber Bragg gratings, fiber lasers, and carbon nanotube photonics. Dr. Set is a Member of the IEE. He is the recipient of the Best Paper Awards in OECC’02, two E.E. Zepler prizes, the G.D. Sims prize, and the ORS Awards.

Hiroshi Yaguchi was born in 1976. He received the B.S. degree in mechanical engineering and the M.S. degree in precision system engineering from the Tokyo Denki University, Tokyo, Japan, in 1998 and 2000, respectively. He joined Oyokoden Labs as an Engineer, working on precision packaging of advanced thin-film devices. Currently, he is a Research and Development Engineer with Alnair Labs Corporation, Kawaguchi City, Japan, where he conducts research and development in thin-film dispersion compensator packaging, dispersion measurement systems, and short-pulse fiber lasers.

Yuichi Tanaka, photograph and biography not available at the time of publication.

Mark Jablonski (M’00) was born in New York, NY. He received the B.S. and M.S. degrees in electrical engineering and computer science from the Massachusetts Institute of Technology, Cambridge, in 1986 and 1992, respectively, and the Ph.D. degree in electrical engineering from the University of Tokyo, Tokyo, Japan, in 2000. He was a Research Engineer with the Varian Beverly Microwave Division from 1986 to 1994, where he worked on microwave tubes, such as magnetrons and cross-field amplifiers. From 2000 to 2001, he was a Project Director with Oyokoden Labs, Japan, working on thin-film-based devices. He has been serving as the Chief Research Officer for Alnair Labs Corporation, Kawaguchi City, Japan, a start-up company he co-founded in 2001, focusing on optical devices, such as thin-film-based dispersion compensators, fiber lasers, and specialized fiber amplifiers. He has contributed to 14 patents and over 25 technical papers. Dr. Jablonski is a Member of the OSA, IEE, SPIE, Sigma-Xi, and Zeta Psi.