Carsten Langrock's Homepage

Tip: Given a standards-compliant browser (e.g. Firefox, OmniWeb, Safari, Camino), rolling over the titles with the mouse will display the paper's abstract where available, while clicking the title will load the corresponding paper.

Journal Articles

2011

J. S. Pelc, L. Ma, C. R. Phillips, Q. Zhang, C. Langrock, O. Slattery, X. Tang, and M. M. Fejer, "Long-wavelength-pumped upconversion single-photon detector at 1550 nm: performance and noise analysis"We demonstrate upconversion-assisted single-photon detection for the 1.55 μm telecommunications based on a periodically poled lithium niobate (PPLN) waveguide pumped by a monolithic PPLN optical parametric oscillator. We achieve an internal conversion efficiency of 86%, which results in an overall system detection efficiency of 37%, with excess noise as low as 10^3 counts/s. We measure the dark count rate versus the upconversion pump-signal frequency separation and find the results to be consistent with noise photon generation by spontaneous anti-Stokes Raman scattering. These results enable detailed design guidelines for the development of low-noise quantum frequency conversion systems, which will be an important component of fiber-optic quantum networks., Optics Express, Vol. 19, No. 22 (November 2011)
C. R. Phillips, C. Langrock, J. S. Pelc, M. M. Fejer, I. Hartl, and Martin E. Fermann, "Supercontinuum generation in quasi-phasematched waveguides"We numerically investigate supercontinuum generation in quasi-phase-matched waveguides using a single-envelope approach to capture second and third order nonlinear processes involved in the generation of octave-spanning spectra. Simulations are shown to agree with experimental results in reverse-proton-exchanged lithium-niobate waveguides. The competition between χ(2) and χ(3) self phase modulation effects is discussed. Chirped quasi-phasematched gratings and stimulated Raman scattering are shown to enhance spectral broadening, and the pulse dynamics involved in the broadening processes are explained.M, Optics Express, Vol. 19, No. 20 (September 2011)
J. S. Pelc, C. R. Phillips, D. Chang, C. Langrock, and M. M. Fejer, "Efficiency pedestal in quasi-phase-matching devices with random duty-cycle errors" Ideal quantum frequency conversion (QFC) devices enable wavelength translation of a quantum state of light while preserving its essential quantum characteristics, namely photon statistics and coherence. However, the generation of noise photons due to spontaneous scattering of the strong classical pump used in the three-wave mixing process can limit QFC fidelity. We experimentally and theoretically characterize the noise properties of a difference- frequency generation device for QFC and find that fabrication errors in the quasi-phase-matching grating enhance generation of noise photons by parametric fluorescence., Optics Letters, No. 6, Vol. 36, pp. 864-866 (March 2011)

2010

J. S. Pelc, C. Langrock, Q. Zhang, and M. M. Fejer, "Influence of domain disorder on parametric noise in quasi-phase-matched quantum frequency converters" Ideal quantum frequency conversion (QFC) devices enable wavelength translation of a quantum state of light while preserving its essential quantum characteristics, namely photon statistics and coherence. However, the generation of noise photons due to spontaneous scattering of the strong classical pump used in the three-wave mixing process can limit QFC fidelity. We experimentally and theoretically characterize the noise properties of a difference- frequency generation device for QFC and find that fabrication errors in the quasi-phase-matching grating enhance generation of noise photons by parametric fluorescence., Optics Letters, No. 16, Vol. 35, pp. 2804-2806 (August 2010)
Paolo Minzioni, Vincenzo Pusino, Ilaria Cristiani, Lucia Marazzi, Mario Martinelli, Carsten Langrock, M. M. Fejer, and Vittorio Degiorgio, "Optical phase conjugation in phase-modulated transmission systems: experimental comparison of different nonlinearity-compensation methods" We experimentally compare the effectiveness of three different optical-phase-conjugation-based nonlinearity-compensation strategies on a transmission system employing phase-modulated signals, and hence affected by the Gordon-Mollenauer effect. We demonstrate that it is possible to obtain significant nonlinearity compensation, but that no improvement is obtained using configurations specifically aimed at the compensation of the nonlinear phase noise., Optics Express, No. 17, Vol. 18, pp.18119-18124 (August 2010)
Qiang Zhang, Hiroki Takesue, Carsten Langrock, Xiuping Xie, Martin M. Fejer, and Yoshihisa Yamamoto, "Hong–Ou–Mandel Dip Using Degenerate Photon Pairs from a Single Periodically Poled Lithium Niobate Waveguide with Integrated Mode Demultiplexer" We experimentally observed a Hong–Ou–Mandle dip with photon pairs generated in a periodically poled reverse-proton-exchange lithium niobate waveguide with an integrated mode demultiplexer at a wavelength of 1.5 μm. The visibility of the dip in the experiment was 80% without subtraction of any noise terms at a peak pump power of 4.4 mW. The technology developed in the experiment can find various applications in the research field of linear optics quantum computation in fiber or quantum optical coherence tomography with near infrared photon pairs., Jpn. J. Appl. Phys., No. 06440, Vol. 49, pp. 1-4 (June 2010)

2009

Shang-Da Yang, Chen-Shao Hsu, Shih-Lun Lin, You-Sheng Lin, Carsten Langrock, M.M. Fejer, "Ultrasensitive direct-field retrieval of femtosecond pulses by modified interferometric field autocorrelation" We report on spectral phase retrieval of 50 MHz, 374 fs optical pulses at 1560 nm with 28 aJ coupled pulse energy by measuring two modified interferometric field autocorrelation traces using a 5-cm-long periodically poled lithium niobate waveguide. The corresponding sensitivity is 1.1 x 10^-7 mW², improving on the previous record by about 20 times. The same data traces can also be used to retrieve the power spectrum, given that the ratio of powers at two specific wavelengths is known., Optics Letters, No. 20, Vol. 34, pp. 3065-3067 (October 2009)
P. Martelli, P. Boffi, M. Ferrario, L. Marazzi, P. Parolari, R. Siano, V. Pusino, P. Minzioni, I. Cristiani, C. Langrock, M.M. Fejer, M. Martinelli, V. Degiorgio, "All-Optical Wavelength Conversion of a 100-Gb/s Polarization-Multiplexed Signal" We present the results of an in-depth experimental investigation about all-optical wavelength conversion of a 100-Gb/s polarization-multiplexed (POLMUX) signal. Each polarization channel is modulated at 25 Gbaud by differential quadrature phase-shift keying (DQPSK). The conversion is realized exploiting the high nonlinear χ⁽²⁾ coefficient of a periodically poled lithium niobate waveguide, in a polarization-independent configuration. We find that slight non-idealities in the polarization independent setup of the wavelength converter can significantly impair the performance of POLMUX systems. We show that high-quality wavelength conversion can be nevertheless achieved for both the polarization channels, provided that an accurate optimization of the setup is performed. This is the first demonstration, to the best of our knowledge, of the possibility to obtain penalty-free all-optical wavelength conversion in a 100-Gb/s POLMUX transmission system using direct-detection., Optics Express, No. 20, Vol. 17, pp. 17758-17763 (September 2009)
Houxun Miao, Daniel E. Leaird, Carsten Langrock, Martin M. Fejer, and Andrew M. Weiner, "Optical arbitrary waveform characterization via dual-quadrature spectral shearing interferometry" We demonstrate a new dual-quadrature spectral shearing interferometry technique appropriate for spectral phase characterization of arbitrary optical waveforms generated by line-by-line shaping of high- repetition-rate (~10 GHz) optical frequency combs. Spectral shearing interferograms are generated through sum-frequency mixing of the frequency comb field with a pair of reference tones generated via intensity modulation of a continuous-wave laser. Although related to the well known SPIDER method, our approach relaxes spectral resolution requirements and operates in a collinear interaction geometry compatible with the use of high sensitivity, aperiodically poled lithium niobate nonlinear waveguide devices., Optics Express, No. 5, Vol. 17, pp. 3381-3389 (March 2009)
Kai-Daniel F. Buechter, Harald Herrmann, Carsten Langrock, Martin M. Fejer, and Wolfgang Sohler, "All-optical Ti:PPLN wavelength conversion modules for free-space optical transmission links in the mid-infrared" Data-format-independent all-optical transmitter and receiver modules for free-space optical communications in the 3.8-μm region have been developed, essentially consisting of Ti-indiffused, periodically poled LiNbO_3, waveguides. Using these modules, conversion of C-band radiation to/from the mid-infrared (MIR) via difference-frequency generation was demonstrated. More than 10 mW of MIR power could be generated with the transmitter unit; the internal low-power conversion efficiency was 69 %/W. A free-space MIR link was set up with a −41 dB fiber-to-fiber loss; only −15 dB are due to the parametric processes., Optics Letters, No. 4, Vol. 34, pp. 470-472 (February 2009)
Louis Christen, Omer F. Yilmaz, Scott Nuccio, Xiaoxia Wu, Irfan Fazal, Alan E. Willner, Carsten Langrock, and Martin M. Fejer, "Tunable 105 ns optical delay for 80 Gb/s RZ-DQPSK, 40 Gb/s RZ-DPSK, and 40 Gb/s RZ-OOK signals using wavelength conversion and chromatic dispersion" We demonstrate a variable, optical-delay element using tunable wavelength conversion in a periodically poled lithium niobate waveguide, dispersion-compensating fiber and intrachannel dispersion compensation. A delay of up to 105 ns is demonstrated using 80 Gb/s return-to-zero differential-quadrature phase-shift keying, 40 Gb/s return-to-zero differential phase-shift keying, and 40 Gb/s return-to-zero on–off keying modulation formats. Bit-error rates <10⁻⁹ are demonstrated for each waveform at various delay settings., Optics Letters, No. 4, Vol. 34, pp. 542-544 (February 2009)

2008

Qiang Zhang, Carsten Langrock, M. M. Fejer, and Yoshihisa Yamamoto,"Waveguide-based single-pixel up-conversion infrared spectrometer" A periodically poled lithium niobate (PPLN) waveguide-based single-pixel up-conversion infrared spectrometer was demonstrated. Sum-frequency generation between a 1.5-μm-band scanning pump laser and a 1.3-μm-band signal generated visible radiation which was detected by a silicon single-photon detector. The up-conversion spectrometer's sensitivity was two-orders-of-magnitude higher than that of a commercial optical spectrum analyzer., Optics Express, No. 24, Vol. 16, pp. 19557-19561 (November 2008)
Houxun Miao, Shang-Da Yang, Carsten Langrock, Rostislav V. Roussev, M. M. Fejer, and Andrew M. Weiner, "Ultralow-power second-harmonic generation frequency-resolved optical gating using aperiodically poled lithium niobate waveguides" We discuss ultralow-power second-harmonic generation (SHG) frequency-resolved optical gating (FROG) in the telecommunication C-band using aperiodically poled lithium niobate (A-PPLN) waveguides as the nonlinear medium. A key theme of this work is that the phase-matching curve of the nonlinear medium is engineered to obtain an optical bandwidth adequate for measurement of subpicosecond pulses while retaining the optimum nonlinear efficiency consistent with this constraint. Our experiments demonstrate measurement sensitivity (deﬁned as the minimum product of the peak and average pulse powers at which a reliable nonlinear signal can be detected) of 2.0 x 10⁻⁶ mW² in a collinear SHG FROG geometry, approximately 5 orders of magnitude better than previously reported for any FROG measurement modality. We also discuss asymmetric Y-junction A-PPLN waveguides that permit background-free SHG FROG and a polarization-insensitive SHG FROG technique that eliminates the impairment that frequency-independent random polarization fluctuations induce in the FROG measurement. Finally, we applied these SHG FROG techniques in chromatic dispersion and polarization mode dispersion compensation experiments. In these experiments the FROG data enabled complete correction of distortions incurred by subpicosecond pulses passing through optical fibers; these results also demonstrate the ability to retrieve extremely complex pulses with high accuracy., (Invited Paper) JOSA B, No. 6, Vol. 25, pp. A41-A53 (June 2008)
Qiang Zhang, Hiroki Takesue, Sae Woo Nam, Carsten Langrock, Xiuping Xie, Burm Baek, M. M. Fejer, and Yoshihisa Yamamoto,"Distribution of time-energy entanglement over 100 km fiber using superconducting singlephoton detectors" In this letter, we report an experimental realization of distributing entangled photon pairs over 100 km of dispersion-shifted fiber. In the experiment, we used a periodically poled lithium niobate waveguide to generate the time-energy entanglement and superconducting single-photon detectors to detect the photon pairs after 100 km. We also demonstrate that the distributed photon pairs can still be useful for quantum key distribution and other quantum communication tasks., Optics Express, No. 8, Vol. 16, pp. 5776-5781 (April 2008)
Qiang Zhang, Carsten Langrock, Hiroki Takesue, Xiuping Xie, Martin Fejer, and Yoshihisa Yamamoto,"Generation of 10-GHz clock sequential time-bin entanglement" This letter reports telecom-band sequential time-bin entangled photon-pair generation at a repetition rate of 10 GHz in periodically poled reverse-proton-exchange lithium niobate waveguides based on mode demultiplexing. With up-conversion single-photon detectors, we observed an entangled-photon-pair flux of 313 Hz and a two-photon-interference- fringe visibility of 85.32% without subtraction of accidental noise contributions., Optics Express, No. 5, Vol. 16, pp. 3293-3298 (March 2008)

2007

Carsten Langrock, I. Hartl, Martin E. Fermann, M. M. Fejer,"Generation of octave-spanning spectra inside reverse-proton-exchanged periodically poled lithium niobate waveguides" We demonstrate simultaneous octave-level spectral broadening and carrier-envelope-offset sensing of mode-locked Er- and Yb-doped femtosecond ﬁber lasers using constant-period and chirped reverse-proton-exchanged periodically poled lithium niobate waveguides. Chirped quasi-phase-matching gratings greatly improve spectral broadening of Yb-fiber lasers., Optics Letters, No. 17, Vol. 32, pp. 2478-2480 (September 2007)
Carsten Langrock and Martin M. Fejer, "Background-free collinear autocorrelation and frequency-resolved optical gating using mode multiplexing and demultiplexing in reverse-proton-exchange aperiodically poled lithium niobate waveguides" We use mode multiplexing and demultiplexing in apodized aperiodically poled lithium niobate waveguides to enable characterization of picosecond optical pulses in a collinear but background-free way using autocorrelation and second-harmonic frequency-resolved optical gating. , Optics Letters, No. 16, Vol. 32, pp. 2306-2308 (August 2007)
Irfan Fazal, Omer Yilmaz, Scott Nuccio, Bo Zhang, Alan Willner, Carsten Langrock, Martin M. Fejer, "Optical data packet synchronization and multiplexing using a tunable optical delay based on wavelength conversion and inter-channel chromatic dispersion" 10 Gb/s non-return-to-zero (NRZ) on-off keyed (OOK) optical data packets are synchronized and time-multiplexed using a 26-ns tunable all-optical delay line. The delay element is based on wavelength conversion in periodically poled lithium niobate (PPLN) waveguides, inter-channel chromatic dispersion in dispersion compensating fiber (DCF) and intra-channel dispersion compensation with a chirped fiber Bragg grating (FBG). Delay reconfiguration time is measured to be less than 300 ps. , Optics Express, No. 17, Vol. 15, pp. 10492-10497 (August 2007)
Qiang Zhang, Xiuping Xie, Hiroki Takesue, Sae Woo Nam, Carsten Langrock, M. M. Fejer, Yoshihisa Yamamoto, "Correlated photon-pair generation in reverse-proton-exchange PPLN waveguides with integrated mode demultiplexer at 10-GHz clock" We report 10-ps correlated photon pair generation in periodically-poled reverse-proton-exchange lithium niobate waveguides with integrated mode demultiplexer at a wavelength of 1.5- m and a clock of 10 GHz. Using superconducting single photon detectors, we observed a coincidence to accidental count ratio (CAR) as high as 4000. The developed photon-pair source may find broad application in quantum information systems as well as quantum entanglement experiments. , Optics Express, No. 16, Vol. 15, pp. 10288-10293 (August 2007)
Jie Huang, Carsten Langrock, X. P. Xie, and Martin M. Fejer, "Monolithic 160 Gbit / s optical time-division multiplexer" We present the design and experimental characterization of a monolithic optical time-division multiplexer (MUX) for 160 Gbit / s operation based on periodically poled lithium niobate (PPLN) waveguides. Its key figures of merit agree well with theoretical predictions and meet or exceed those of a previously demonstrated PPLN-planar-light-wave-circuit hybrid MUX. The monolithic design has a simpler layout and higher efficiency while keeping the cross talk low. , Optics Letters, No. 16, Vol. 32, pp. 2420-2422 (August 2007)
Carsten Langrock and Martin M. Fejer, "Fiber-feedback continuous-wave and synchronously-pumped singly-resonant ring optical parametric oscillators using reverse-proton-exchanged periodically-poled lithium niobate waveguides" We describe guided-wave singly-resonant reverse-proton-exchanged (RPE) periodically-poled lithium niobate (PPLN) waveguide ring optical parametric oscillators (OPOs) in which the feedback was provided via a single-mode fiber pigtailed to the waveguide. Wavelength selection was achieved by means of a fiber Bragg grating inside the feedback loop. The SRO threshold for the synchronously-pumped OPO was below 1 mW of average coupled pump power. , Optics Letters, No. 15, Vol. 32, pp. 2263-2265 (July 2007)
Houxun Miao, Andrew M. Weiner, Carsten Langrock, Rostislav Roussev, Martin M. Fejer, "Polarization-insensitive ultralow-power second-harmonic generation frequency-resolved optical gating" We demonstrate polarization-insensitive ultralow-power second-harmonic generation frequency-resolved optical gating (FROG) measurements with a fiber-pigtailed, aperiodically poled lithium niobate waveguide. By scrambling the polarization much faster than the measurement integration time, we eliminate the impairment that frequency-independent random polarization fluctuations induce in FROG measurements. As a result we are able to retrieve intensity and phase profiles of few hundred femtosecond optical pulses with 50 MHz repetition rates at 5.2 nW coupled average power without control of the input polarization. , Optics Letters, No. 7, Vol. 32, pp. 874-876 (April 2007)
Houxun Miao, Andrew M. Weiner, Carsten Langrock, Rostislav Roussev, Martin M. Fejer, "Sensing and compensation of femtosecond waveform distortion induced by all-order polarization mode dispersion at selected polarization states" We demonstrate full characterization of femtosecond pulse distortion induced by all-order polarization mode dispersion (PMD) at selected polarization states via second-harmonic generation (SHG) frequency-resolved optical gating (FROG) measurements at an average power of under 28 nW. By applying the inverse of the measured spectral phase via a programmable pulse shaper, we compress the distorted pulses from more than 3 ps to nearly bandwidth-limited durations of less than 500 fs. Our results show that SHG FROG measurements performed by using fiber-pigtailed aperiodically poled lithium niobate waveguides can serve as a robust and sensitive tool for characterization of PMD-induced spectral phase. , Optics Letters, No. 4, Vol. 32, pp. 424-426 (February 2007)

2006

Hiroki Takesue, Eleni Diamanti, Carsten Langrock, M. M. Fejer, and Yoshihisa Yamamoto, "1.5-μm single photon counting using polarization-independent up-conversion detector" We report a 1.5-μm band polarization independent single photon detector based on frequency up-conversion in periodically poled lithium niobate (PPLN) waveguides. To overcome the polarization dependence of the PPLN waveguides, we employed a polarization diversity configuration composed of two up-conversion detectors connected with a polarization beam splitter. We experimentally confirmed polarization independent single photon counting using our detector. We undertook a proof-of-principle differential phase shift quantum key distribution experiment using the detector, and confirmed that the sifted key rate and error rate remained stable when the polarization state was changed during single photon transmission. , Optics Express, No. 26, Vol. 14, pp. 13067-13072 (December 2006)
Eleni Diamanti, Hiroki Takesue, Carsten Langrock, M. M. Fejer, and Yoshihisa Yamamoto, "100 km differential phase shift quantum key distribution experiment with low jitter up-conversion detectors" We present a quantum key distribution experiment in which keys that were secure against all individual eavesdropping attacks allowed by quantum mechanics were distributed over 100 km of optical fiber. We implemented the differential phase shift quantum key distribution protocol and used low timing jitter 1.55 μm single-photon detectors based on frequency up-conversion in periodically poled lithium niobate waveguides and silicon avalanche photodiodes. Based on the security analysis of the protocol against general individual attacks, we generated secure keys at a practical rate of 166 bit/s over 100 km of fiber. The use of the low jitter detectors also increased the sifted key generation rate to 2 Mbit/s over 10 km of fiber. , Optics Express, No. 26, Vol. 14, pp. 13073-13082 (December 2006)
W. C. Swann, J. J. McFerran, I. Coddington, N. R. Newbury, I. Hartl, M. E. Fermann, P. S. Westbrook, J. W. Nicholson, K. S. Feder, C. Langrock, and M. M. Fejer, "Fiber-laser frequency combs with subhertz relative linewidths" We investigate the comb linewidths of self-referenced, fiber-laser-based frequency combs by measuring the heterodyne beat signal between two independent frequency combs that are phase locked to a common cw optical reference. We demonstrate that the optical comb lines can exhibit instrument-limited, subhertz relative linewidths across the comb spectra from 1200 to 1720 nm with a residual integrated optical phase jitter of 1 rad in a 60 mHz to 500 kHz bandwidth. The projected relative pulse timing jitter is 1 fs. This performance approaches that of Ti:sapphire frequency combs. , Optics Letters, No. 20, Vol. 31, pp. 3046-3048 (October 2006)
Hiroki Takesue, Eleni Diamanti, Carsten Langrock, M. M. Fejer, Y. Yamamoto, "10-GHz clock differential phase shift quantum key distribution experiment" This paper reports the first quantum key distribution experiment implemented with a 10-GHz clock frequency. We used a 10-GHz actively mode-locked fiber laser as a source of short coherent pulses and single photon detectors based on frequency up-conversion in periodically poled lithium niobate waveguides. The use of short pulses and low-jitter up- conversion detectors significantly reduced the bit errors caused by detector dark counts even after long-distance transmission of a weak coherent state pulse. We employed the differential phase shift quantum key distribution protocol, and generated sifted keys at a rate of 3.7 kbit/s over a 105 km fiber with a bit error rate of 9.7%. , Optics Express, No. 20, Vol. 14 (October 2006)
Carsten Langrock, Saurabh Kumar, John E. McGeehan, Alan Willner, M. M. Fejer, "All optical signal processing using χ⁽²⁾ nonlinearities in guided-wave devices" The authors present a review of all-optical signal-processing technologies based on χ⁽²⁾ nonlinear interactions in guided-wave devices and their applications for telecommunication. In this study, the main focus is on three-wave interactions in annealed proton-exchanged periodically poled lithium niobate waveguides due to their suitable properties with respect to nonlinear mixing efficiency, propagation loss, and ease of fabrication. These devices allow the implementation of advanced all-optical signal-processing functions for next-generation networks with signal bandwidths beyond 1 THz. In this paper, integrated structures that will allow for improvements of current signal-processing functions as well as the implementation of novel device concepts are also presented. , (Invited Paper) Journal of Lightwave Technology, No. 7, Vol. 24, pp. 2579-2592 (July 2006)
P. Minzioni, I. Cristiani, V. Degiorgio, L. Marazzi, M. Martinelli, C. Langrock, M. M. Fejer, "Experimental demonstration of nonlinearity and dispersion compensation in an embedded link by optical phase conjugation" We report in this letter, the experimental demonstration of simultaneous dispersion and nonlinearity compensation in an embedded link characterized by strongly asymmetrical power profiles. This result is obtained by using a highly efficient optical phase conjugator based on a periodically poled lithium-niobate waveguide, combined with two small dispersion-compensating elements properly inserted in the link. , Photonics Technology Letters, No. 9, Vol. 18, pp. 995-997 (May 2006)
Eleni Diamanti, Carsten Langrock, M. M. Fejer, Yoshihisa Yamamoto , "1.5 μm photon-counting optical time-domain reflectometry with a single-phhoton detector based on upconversion in a periodically poled lithium niobate waveguide" Optical time-domain reflectometry (OTDR) is one of the most powerful tools in the characterization of optical fiber links. We demonstrate a photon-counting OTDR system at 1.5 μm with a single-photon detector, which combines frequency upconversion in a periodically poled lithium niobate waveguide and a silicon avalanche photodiode. The system exhibits high sensitivity, good spatial resolution, and short measurement time. , Optics Letters, No. 6, Vol. 31, pp. 727-729 (March 2006)
Jie Huang, X. P. Xie, Carsten Langrock, R. V. Roussev, D. S. Hum, and M. M. Fejer, "Amplitude modulation and apodization of quasi-phase-matched interactions" We propose several techniques to modulate the local amplitude of quasi-phase-matched (QPM) interactions in periodically poled lithium niobate waveguides and demonstrate apodization by using each of these techniques. When the hard edges are removed in the spatial profile of the nonlinear coupling, the sidelobes of the frequency tuning curves are suppressed by 13 dB or more, compared with a uniform grating, consistent with theoretical predictions. The sidelobe-suppressed gratings are useful for frequency conversion devices in optical communication systems to minimize interchannel cross talk, while the amplitude modulation techniques in general have potential uses in applications that require altering the tuning curve shapes. , Optics Letters, No. 5, Vol. 31, pp. 604-606 (March 2006)
Supriyo Sinha, Carsten Langrock, Michel J. F. Digonnet, Martin M. Fejer, Robert L. Byer, "Efficient yellow-light generation by frequency doubling a narrow-linewidth 1150 nm ytterbium fiber oscillator" A linearly polarized, narrow-linewidth, diode-pumped, Yb-doped silica-fiber oscillator operating at 1150 nm was frequency doubled to produce 40 mW of 575 nm radiation. The oscillator generated 89 mW of cw linearly polarized output power and was tunable over 0.80 nm. The laser output was coupled to a periodically poled LiNbO₃ waveguide that converted 67% of the coupled power to the yellow. The system was fully integrated, with no free-space optics, and had an overall optical-to-optical efficiency of 7.0% with respect to the incident diode-laser pump power. , Optics Letters, No. 3, Vol. 31, pp. 347-349 (February 2006)

2005

H. Takesue, E. Diamanti, T. Honjo, C. Langrock, M. M. Fejer, K. Inoue, Y. Yamamoto,"Differential phase shift quantum key distribution experiment over 105 km fibre " We report a quantum key distribution experiment based on the differential phase shift keying (DPSK) protocol with a Poissonian photon source, in which secure keys were generated over >100 km fibre for the first time. We analysed the security of the DPSK protocol and showed that it is robust against strong attacks by Eve, including a photon number splitting attack. To implement this protocol, we developed a new detector for the 1.5 μm band based on frequency up-conversion in a periodically poled lithium niobate waveguide followed by an Si avalanche photodiode. The use of detectors increased the sifted key generation rate up to >1 Mbit s-1 over 30 km fibre, which is two orders of magnitude larger than the previous record. , New Journal of Physics, No. 7, Vol. 232 (November 2005)
I. Hartl, G. Imeshev, and M. E. Fermann, C. Langrock and M. M. Fejer, "Integrated self-referenced frequency-comb laser based on a combination of fiber and waveguide technology" An optically integrated self-referenced frequency comb laser is demonstrated. The system consists of a passively-modelocked Er-fiber laser, a butt-coupled periodically poled lithium niobate (PPLN) waveguide phase-sensor and an electronic feedback loop for carrier-envelope-offset (CEO) phase stabilization. The f_ceo-beat-signal has a linewidth of 62 kHz and is detected with a S/N-ratio of 40 dB, with greatly reduced pulse energy requirements compared to bulk crystal phase-sensors. To our knowledge this is the first self-referenced frequency-comb system entirely based on guided-wave technology. , Optics Express, No. 17, Vol. 13, pp. 6490 - 6496 (August 2005)
Carsten Langrock, Eleni Diamanti, Rostislav V. Roussev, Hiroki Takesue, Yoshihisa Yamamoto, and M. M. Fejer, "Highly efficient single-photon detection at communication wavelengths by use of upconversion in reverse-proton-exchanged periodically poled LiNbO3 waveguides" Conventional single-photon detectors at communication wavelengths suffer from low quantum efficiencies and large dark counts. We present a single-photon detection system, operating at communication wavelengths, based on guided-wave frequency upconversion in a nonlinear crystal with an overall system detection efficiency (upconversion + detection) exceeding 46% at 1.56 μm. This system consists of a fiber-pigtailed reverse-proton-exchanged periodically poled LiNbO₃ waveguide device in conjunction with a silicon-based single-photon counting module. , Optics Letters, No. 13, Vol. 30, pp. 1725-1727 (July 2005)
Z. Jiang, D. S. Seo, D. E. Leaird, R. V. Roussev, C. Langrock, M. M. Fejer, and A. M. Weiner, "Reconfigurable All-Optical Code Translation in Spectrally Phase-Coded O-CDMA " Reconfigurable all-optical code translation are demonstrated in a spectrally phasecoded optical-code-division multiple-access (O-CDMA) testbed with an interference user. For both one-stage and two-stage code translations, less than 0.9-dB power penalties are induced at each code translation. Multistage code translations are investigated via simulation and experimental emulation in a loop pulse shaper to show the potential application of the proposed method for up to several tens of code translations. , Journal of Lightwave Technology, No. 6, Vol. 23, pp. 1979-1990 (June 2005)
Zhi Jiang, Dongsun Seo, Shangda Yang, Daniel E. Leaird, Rostislav V. Roussev, Carsten Langrock, Martin M. Fejer, and Andrew M. Weiner, "Four-User 10-Gb/s Spectrally Phase-Coded O-CDMA System Operating at ~30 fJ/bit" We demonstrate a four-user 10-Gb/s spectrally phase-coded optical code-division multiple-access system via nonlinear processing with ultralow power ( 30 fJ/bit). Full interference suppression is achieved in a time-slotted scheme without the need for chip-level coordination and synchronous detection. Performance degradation caused by pulse overlap between users is investigated. , IEEE Photonics Technology Letters, No. 3, Vol. 17, pp. 705-707 (March 2005)
Z. Jiang, D. S. Seo, S. D. Yang, D. E. Leaird, R. V. Roussev, C. Langrock, M. M. Fejer, A. M. Weiner, "Four-user, 2.5-Gb/s, spectrally coded OCDMA system demonstration using low-power nonlinear processing" This paper describes the demonstration of 2.5-Gb/s four-user optical-code-division-multiple-access (OCDMA) system operating at bit-error rate <10^-11 utilizing programmable spectral phase encoding, an ultrasensitive (~200 fJ/b) periodically poled lithium-niobate-waveguide nonlinear waveform discriminator and 10G Ethernet receiver. A comprehensive description of this ultra-short-pulse spectral phase-coded OCDMA system is presented. On the subsystem level, two key component technologies, namely, femtosecond encoding/decoding and low-power high-contrast nonlinear discrimination, have been developed and characterized. At the system level, data for the four-user OCDMA system operating at 2.5 Gb/s for binary as well as multilevel code families are described. , Journal of Lightwave Technology, No. 1, Vol. 232, pp. 143-158 (January 2005)
M. Mueller, E. Soergel, K. Buse, C. Langrock and M. M. Fejer, "Investigation of periodically poled lithium niobate crystals by light diffraction" Periodically poled lithium niobate crystals are investigated by illumination along the crystallographic c axis while applying an external electric field. The resulting diffraction patterns are in good agreement with the results of numerical simulations and directly yield first information such as periodicity, duty cycle, and homogeneity of the domain patterns. , Journal of Applied Physics, No. 4, Vol. 97 (January 2005)

2004

Jie Huang, J. R. Kurz, Carsten Langrock, A. M. Schober, and M. M. Fejer, "Quasi-group-velocity matching using integrated-optic structures" We propose a device to compensate for group-velocity mismatch (GVM) effects that limit the efficiency–bandwidth product in nonlinear frequency-mixing devices. Integrated wavelength-dependent delay lines are introduced per iodically in a waveguide containing a series of quasi-phasematching (QPM) gratings. Appropriate choice of the time delays can compensate for GV M. We have demonstrated a two-stage device in a periodically poled lithium niobate waveguide. Two approximately 150 fs-long pulses generated 6 ps apart by second-harmonic generation in two QPM gratings were resynchronized by a fixed delay line, and their relative phase was fine controlled by temperature tuning. This technique, which can be iterated to more than two segments, permits optical frequency mixers with a higher efficiency–bandwidth product than would be possible in a single grating short enough to avoid GVM effects. , Optics Letters, No. 21, Vol. 29, pp. 2482-2484 (November 2004)
Zhi Jiang, D. S. Seo, D. E. Leaird, A. M. Weiner, R. V. Roussev, C. Langrock and M. M. Fejer, "Multi-user, 10Gb/s spectrally phase coded O-CDMA system with hybrid chip and slot-level timing coordination" We demonstrate a multi-user, 10 Gb/s spectrally phase coded O-CDMA system with hybrid chip and slot-level coordination utilizing low power nonlinear processing. A new double Hadamard coding scheme is demonstrated to enable both chip-level timing coordination and full interference suppression without the need for synchronous detection. , Electronics Express, No. 13, Vol. 1, pp. 398-403 (October 2004)
Rostislav V. Roussev, Carsten Langrock, Jonathan R. Kurz, and M. M. Fejer, "Periodically poled lithium niobate waveguide sum-frequency generator for efficient single-photon detection at communication wavelengths " We present a device to facilitate single-photon detection at communication wavelengths based on continuous-wave sum-frequency generation with an upconversion efficiency exceeding 90%. Sum-frequency generation in a periodically poled lithium niobate waveguide is used to upconvert signal photons to the near infrared, where detection can be performed efficiently by use of silicon avalanche photodiodes. , Optics Letters, No. 13, Vol. 29, pp. 1518-1520 (July 2004)
Xiuping Xie, Andrew M. Schober, Carsten Langrock, Rostislav V. Roussev, Jonathan R. Kurz, Martin M. Fejer, "Picojoule threshold, picosecond optical parametric generation in reverse proton-exchanged lithium niobate waveguides" We have demonstrated picosecond optical parametric generation in reverse proton-exchanged waveguides in periodically poled lithium niobate with thresholds as low as 200 pJ. Near-transform-limited near-infrared pulses were obtained from cascaded optical parametric generation. For a 1.8-ps (FWHM) pump pulse at 769.6 nm, a saturated internal photon-conversion efficiency of 33% was obtained with 1 nJ of pump energy. The signal-wavelength tuning range was from 1.15 μm to 2.3 μm with a pump wavelength between 770 nm and 789.5 nm. Numerical simulations well predicted the mechanism for the transform-limited pulse generation. These results enable optical parametric generation devices with low threshold and good temporal properties with a simple single-pass setup. , JOSA B, Vol. 21, No. 7, pp. 1397-1402 (July 2004)
Z. Jiang, D.S. Seo, S.-D. Yang, D.E. Leaird, R.V. Roussev, C. Langrock, M.M. Fejer, A.M. Weiner, "Low-Power High-Contrast Coded Waveform Discrimination at 10 GHz Via Nonlinear Processing" We demonstrate ultrafast optical code-division multiple-access nonlinear waveform discrimination at 10 GHz with less than 1 mW coupled into a nonlinear periodically poled lithium niobate waveguide and greater than 20-dB contrast ratio between coded and uncoded waveforms. Excellent signal-to-noise is observed at the system receiver, pointing toward the practicability of nonlinear waveform discrimination in a system environment. , Photonics Technology Letters, No. 7, Vol. 16, pp. 1778-1780 (July 2004)
Z. Jiang, D.S. Seo, S.-D. Yang, D.E. Leaird, A.M. Weiner, R.V. Roussev, C. Langrock and M.M. Fejer, "Spectrally coded O-CDMA system with four users at 2.5 Gbit using low power nonlinear processing" A four-user 2.5 Gbit/s optical code-division multiple-access (O-CDMA) system is demonstrated at < 10^-11 BER utilising programmable spectral phase encoding, an ultrasensitive (<0.4 pJ/bit) PPLN-waveguide nonlinear waveform discriminator, and a 10G ethernet receiver. , Electonics Letters, No. 10, Vol. 40 (May 2004)

2001

R. P. Scott, C. Langrock, and B. H. Kolner, "High-Dynamic-Range Laser Amplitude and Phase Noise Measurement Techniques" We describe techniques for making sensitive and high-dynamic-range measurements of laser amplitude and envelope phase noise (timing jitter) in the frequency domain at the shot-noise limit. Examples of amplitude noise measurements on continuous-wave argon-ion and diode-pumped solid-state lasers used for pumping a femtosecond Ti:sapphire laser are presented. Amplitude and phase noise measurements for the Ti:sapphire laser are also presented, showing correlation between pump laser amplitude modulation (AM) spectra and the resulting AM and phase noise. Characteristics of the measurement system components are discussed, along with examples of the impact these have on achieving reliable high-dynamic-range measurement capability. , (Invited Paper) IEEE JSTQE, Vol. 7, No. 4, pp. 641-655 (July/August 2001)

Conference Proceedings