Advance Program

The 16th Annual Meeting of the IEEE Lasers & Electro-Optics Society

26 – 30 October 2003

HILTON

EL

CONQUISTADOR

A R I Z O N A

Advance Program www.i-leos.org

TECHNICAL PROGRAM THURSDAY 30 OCTOBER 2003 CORONADO I

CORONADO II

JOSHUA TREE

ThA4 9:00 AM - 9:15 AM Understanding Nonlinear Phase Noise in Optical DPSK Systems, Y. Yadin, Technion, Haifa, Israel, M. Shtaif, Tel Aviv University, Tel-Aviv, Israel and M. Orenstein, Technion, Haifa, Israel The nonlinear phase noise in long-hall optical communications scheme based on differential phase shift keying was explored. The analytically derived distributions coincide with reported experimental measures and enables exact calculation of related error probabilities.

ThB4 9:00 AM - 9:15 AM Afterpulsing of Single-Photon Avalanche Photodetectors, Y. Kang, UCSD, San Diego, CA, USA, D. S. Bethune, W. P. Risk, IBM Research, San Jose, CA, USA and Y.-H. Lo, UCSD, La Jolla, CA, USA The afterpulsing effect of III/V avalanche photodetector for single photon detection was investigated by using interleaved gated Geiger-mode experiment. The impact of afterpulsing effect and its temperature dependence were experimentally and theoretically studied.

ThA5 9:15 AM - 9:45 AM (Invited) Generation of Ultra-High Speed DPSK Signals using the Interaction of Nonlinearity and Polarization Effects, L. Moeller, Y. Su, C. Xie, X. Liu, J. Leuthold, D. Gill and X. Wei, Lucent Technologies, Holmdel, NJ, USA We demonstrate a method to generate 80Gb/s return-to-zero differential phaseshift keying signals. Nonlinear polarization rotation between a pump and a probe signal in a HLNF is used as modulation process.

ThB5 9:15 AM - 9:30 AM Variations in the Photon-Counting Performance of InGaAs/InP Avalanche Photodiodes, K. W. Forsyth, and J. C. Dries, Sensors Unlimited, Princeton, NJ, USA We compare the single-photon-counting performance of a number of commercial InGaAs/InP APDs, show the bias and temperature dependence of the key performance parameters, and present an analysis of these variations.

ThC4 9:15 AM - 9:30 AM A Fiber-Mounted Polymer Electro-OpticSampling Field Sensor, J. A. Deibel and J. F. Whitaker, University of Michigan, Ann Arbor, MI, USA The first fiber-mounted electric-field probe to employ an electro-optic polymer separated from its poling electrodes has been demonstrated. Comparisons to a BSO probe suggest advantages in sensitivity and invasiveness for polymeric sensors.

ThB6 9:30 AM - 9:45 AM Highly Efficient Sum-Frequency Generation (SFG) in Reverse-ProtonExchanged (RPE) Waveguides in LiNbO3 as a Means of Single-Photon Detection at Communication Wavelengths, C. Langrock, R. V. Roussev, M. M. Fejer and J. R. Kurz, Stanford University, Stanford, CA, USA We present a novel single-photon detection scheme at communication wavelengths with a quantum efficiency exceeding 55%. SFG in LiNbO3 waveguides is used to convert photons to the near-infrared, where detection is performed efficiently.

ThC5 9:30 AM - 9:45 AM Sub-Volt-Vπ InGaAsP Electrorefractive Modulators using Symmetric, Uncoupled Quantum Wells, P. W. Juodawlkis, R. J. Bailey, J. Plant, K. G. Ray, D. C. Oakley, A. Napoleone, MIT Lincoln Laboratory, Lexington, MA, USA and G. E. Betts, ModeTek, Inc., Carlsbad, CA, USA We demonstrate InGaAsP/InP quantumwell electrorefractive Mach-Zehnder modulators with lumped-element electrodes having push-pull Vπ of 0.9-V (VπL = 9V-mm) and 18-dB fiber-to-fiber insertion loss in the 1.55-µm wavelength region.

ThD4 9:00 AM - 9:15 AM Novel Total-Internal-Reflection PumpSignal Coupler with >90% Pump Coupling Efficiency from a Broad-Area Diode Laser into a Double-Clad Fiber, Y. Kaneda, J. Zong, O. Romero, Z. Deng, B. Case, A. Chavez-Pirson, G. Paysnoe, J. Whitwham, P. Moran, P. Rohan, Z. Wang, S. Jiang, NP Photonics, Tucson, AZ, USA, W. Eaton, M. Brutsch, P. Li and I. Song, NP Photonics, Westlake Village, CA, USA A novel technique is presented to sidecouple the pump from a broad-area diode laser into a double-clad fiber. Using commercially available broad area diodes, a coupling efficiency >90% is obtained.

ThC6 9:45 AM - 10:00 AM High-Saturation-Current ChargeCompensated InGaAs/InP Uni-Traveling-Carrier Photodiode, N. Li, X. Li, S. Demiguel, X. Zheng, J. C. Campbell, University of Texas at Austin, Austin, TX, USA, D. A. Tulchinsky, K. J. Williams, Naval Research Laboratory, Washington, DC, USA, T. Isshiki, G. Kinsey and R. Sudharsanan, SpectroLab, Sylmar, CA, USA Charge compensation is utilized in an Page 66

AGAVE

ThD5 9:15 AM - 9:30 AM Pulse-Amplitude Equalization of Rational-Harmonically Mode-Locked Fiber Ring Laser with PolarizationMaintaining Laser Resonator, Y. M. Jhon, Y. S. Lee, J. H. Kim, Y. T. Byun and D. H. Woo, Korea Institute of Science and Technology, Seoul, Korea Pulse-amplitude equalization of rationalharmonically mode-locked fiber ring laser pulses is experimentally demonstrated with polarization-maintaining laser resonator by optimizing modulator driving power to obtain 20, 30, and 40 GHz laser pulse trains.

Pulse-Amplitude Equalization of Rational-Harmonically Mode-Locked Fiber Ring Laser with Polarization-Maintaining Laser Resonator Young Min Jhon, Yoo Seung Lee, Jae Hun Kim, Young Tae Byun, and Deok Ha Woo Photonics Research Center, Korea Institute of Science and Technology 39-1 Hawolgok, Seongbuk, Seoul 136-791, Korea Tel: +82-2-958-5725, Fax: +82-2-958-5709, Email: [email protected] Introduction High repetition rate ultrashort laser pulse sources are essential for ultrahigh-speed optical communication and all-optical digital signal processing. Rationalharmonically mode-locked fiber ring laser (RHMLFRL) has been shown to be very useful for producing high repetition rate laser pulses, since laser pulses at repetition rates of integral multiples of the modulator driving frequency fm can be generated by slightly detuning fm from the harmonical modelocking condition [1]. That is, by satisfying fm = (n ± 1/p)fc (n, p are integers), laser pulses at pfm = (np ± 1)fc can be generated, where fc is the fundamental cavity frequency. However, output pulses of RHML-FRL suffer from inherent pulse-amplitude inequality, which is inadequate for practical applications. Various methods have been reported to equalize the pulse-amplitude including methods using nonlinear optical loop mirror [2], nonlinear amplifying loop mirror [3], semiconductor optical amplifier loop mirror [4], intracavity nonlinear polarization rotation [5], evenorder modulation with intracavity etalon [6], and optical feedback [7]. These methods all require additional devices and precise adjustments to achieve pulse-amplitude equalization. In this paper, we experimentally demonstrate pulseamplitude equalization of RHML-FRL using polarization-maintaining laser resonator by simply optimizing the modulator driving power without any additional device. We also presume from the experimental results that pulse-amplitude inequality in RHML-FRL is mainly due to polarization instabilities in the laser resonator. Experimentals The laser resonator was composed of all polarizationmaintaining fibers (PMF) and components to prevent any polarization instabilities and to ensure stable laser operation [8]. The 10 m PM-EDF (erbium-doped fiber) was pumped by four 980 nm laser diodes with a total power of 400 mW. 24 m PM-DSF (dispersion-shifted

fiber) was added to optimize dispersion. The laser was tunable from 1530 to 1560 nm by a tunable filter with a 3dB bandwidth of 3 nm. An optical isolator was used to ensure unidirectional laser operation and an optical delay line (Santec ODL-600, 0-200 ps, 0.1 ps) was introduced into the laser cavity to control the laser cavity length. The laser was modulated by a 10 GHz Mach-Zehnder intensity modulator (Sumitomo Osaka Cement T.MZH-1.5-10) driven by a signal generator (Anritsu Wiltron Synthesized CW Generator 68037B, 2-20 GHz, 20dBm) through a RF amplifier (Miteq AMF-5B-097102-33P, 30dB, 33dBm). The output of the laser was observed by a 50 GHz sampling oscilloscope (Tektronix CSA 803 with sampling head SD-32) and a RF spectrum analyser (Anritsu MS2688C) through a 45 GHz photodetector (NewFocus 1014), and also by an optical spectrum analyser (Ando AQ6317B, 0.01 nm). The pulsewidth of the laser pulse was measured by an autocorrelator (Femtochrome FR-103XL). Results & Discussions The fundamental cavity frequency fc of the laser obtained from the supermode-beating spectrum was measured to be 4.613 MHz corresponding to an optical cavity length of 65 m. Conventional harmonic modelocking was obtained with a modulator driving power of 21.4 dBm at fm = 9.996500 GHz which is the 2167th harmonic of fc. The pulsewidth was measured to be 3.8 ps with a linewidth of 0.70nm giving a timebandwidth product of 0.33 implying a nearly transform-limited sech2 pulse. Detuning fm by 1.15 MHz (fc/4), 4th rationalharmonically mode-locked pulses were obtained at a repetition frequency of 40 GHz (4fm), but the amplitudes of the pulses were not equal. Adjusting the modulator driving power, we could control the inequality of the laser pulses and obtain pulseamplitude equalization by optimizing the power as shown in Fig. 1. We can find that tuning the driving power towards its optimized value, the larger pulses give their energies to the smaller pulses and finally

24 dBm

21 dBm

23 dBm

20 dBm

22 dBm

19 dBm

Fig. 1 Oscilloscope traces of laser pulses at 4th (40 GHz) rational harmonic modelocking against modulator driving power. Pulse-amplitude equalization is obtained at 22 dBm. (50 ps/div.)

reach equalization, and over the optimized value, the smaller pulses grow larger than the former larger pulses. These characteristics were also observed for 2nd (20 GHz) and 3rd (30 GHz) rational harmonic mode locking obtained by detuning fm by fc/2 and fc/3. The RF spectra of the laser pulses with and without equalization are shown in Fig. 2. As shown in Fig. 2 (a), lower harmonic components such as 10, 20, and 30 GHz components are also present with the 40 GHz components when the pulses are unequal. However, after pulse-amplitude equalization is achieved the lower harmonic components are suppressed by over 30 dB as in Fig. 2 (b). The optical spectrum and the autocorrelation trace of the equalized pulses is shown in Fig. 3. We can find that the dominant modes are separated by 0.32 nm (40 GHz) while the intermediate modes are well suppressed. The pulse width was measured to be 4.8 ps with a time-bandwidth product of 0.39 assuming sech2 pulse shape. The polarization-maintaining laser resonator eliminates polarization instabilities providing stable laser operation. Supermode beating noise was suppressed over 45 dB with and without equalization. These stability characteristics are presumed to provide pulse-amplitude equalization obtained in the polarization-maintaining laser resonator, which is not obtained in conventional RHML-FRL without additional equalization devices and precise adjustments. Conclusions

.

(a)

(b)

Fig. 2 RF spectrum of laser pulses at 4th (40 GHz) rational harmonic modelocking (a) without and (b) with pulse-amplitude equalization. (4 GHz/div.)

Pulse-amplitude equalization of rational-harmonically mode-locked fiber ring laser pulses has been experimentally demonstrated with polarizationmaintaining laser resonator by optimizing the modulator driving power to obtain 20, 30, and 40 GHz laser pulse trains. We presume from the experimental results that the major cause for pulse-amplitude inequality in RHML-FRL is polarization instabilities. References

25 ps pulse width 4.8 ps 0.32 nm

.(a)

(b)

Fig. 3 Optical spectrum (a) and autocorrelation trace (b) of laser pulses at 4th (40 GHz) rational harmonic modelocking.

[1] Z. Ahmed, et al., Electron. Lett., 32, 455 (1996) [2] M.-Y. Jeon, et al., Opt. Lett., 23, 855 (1998) [3] M.-Y. Jeon, et al., Electron. Lett., 34, 182 (1998) [4] H. J. Lee, et al., Opt. Commun., 160, 51 (1999) [5] Z. Li, et al., IEEE J. of Quantum Electron., 37, 33 (2001) [6] K. K. Gupta, et al., Electron. Lett., 37, 948 (2001) [7] C. G. Lee, et al., Opt. Commun., 209, 417 (2002) [8] Y.M. Jhon, et al., LEOS’02, TuBB4.