Search

In this article, we design and demonstrate new angled multimode interference (MMI) couplers in silicon-on-insulator that allow arbitrary selection of coupling ratios, while simultaneously achieve low-chromaticity response and improved fabrication variations tolerance. The proposed couplers rely on paired-interference design approach in tandem with a new angled multi-mode junction to mitigate chromatic aberration and geometry-induced waveguide modal shift in conventional angled MMI coupler design. Test devices with footprint of 4.8 μ m × 75 μ m showed full coupling ratio range addressability with insertion loss below 1.2 dB. Spectral responses across the extended C band (1525 nm – 1575 nm) were also characterized, where coupling ratio varied by less than 2.3% across the spectral region of interest. Furthermore, coupler characteristics variations against line-width and thickness deviations are numerically analyzed, demonstrating robustness within typical fabrication tolerances.

We demonstrate waveguide-integrated silicon-germanium avalanche photodiodes with a maximum responsivity of 15.2 A/W at 16x avalanche gain, and 33 GHz bandwidth. Intensity-modulation-direct-detection (IMDD) and coherent channel reception test demonstrated the APD’s performance with higher-order formats, allowing 32 Gbaud PAM-4 and 40 Gbaud 16QAM channel reception without any digital signal processing conventionally used for receiver impairments mitigation.

Signals arising in nearly all disciplines, including telecommunications, mechanics, biology, astronomy, and nature are generally modulated, carrying corresponding signatures in both the temporal and spectral domains. This fact was long recognized by cyclostationary and cumulant analysis, providing qualitatively better means to separate stochastic from deterministically modulated radiation. In contrast to simple spectral analysis, the cyclostationary technique provides a high level of spectral discrimination, allowing for considerable signal selectivity even in the presence of high levels of background noise and interference. When performed with sufficient resolution, cyclostationary analysis also provides the ability for signal analysis and classification. Unfortunately, these advantages come at a cost of large computational complexity posing fundamental detection challenges. In the case of modern ultrawideband signals, the requirements for persistent cyclostationary analysis are considerably beyond the processing complexity of conventional electronics. Recognizing this limit, we report a new photonically assisted cyclostationary analyzer that eliminates the need for high-bandwidth digitization and real-time Fourier processors. The new receiver relies on mutually coherent frequency combs used to generate a Fourier representation of the received signal in a computation-free manner. With the advent of practical, cavity-free optical frequency combs, the complexity for cyclostationary analysis can be greatly reduced, paving a path toward persistent wideband cyclostationary analysis in an ultrawideband operating regime.

Pulse position modulation (PPM) has been used in the radio-frequency (RF) domain to achieve both low-dissipation requirements and provide precision ranging. In ultrawideband (UWB) architectures, it underpins an asynchronous receiver, multiple access environments, and interference-resistant transmission. When combined with frequency hopping (FH), it allows for an additional level of immunity to jamming and low probability of intercept. Realization of a FH-PPM transceiver poses a practical challenge, particularly in the UWB RF range. With UWB pulses reaching the multi-gigahertz range, FH adds to the effective bandwidth at which the receiver must be operated, exceeding the performance of a modern quantizer and digital demodulation backplane. This study describes a new photonics-assisted FH-PPM receiver architecture that rests on mutually coherent frequency combs. The performance of the new receiver was characterized by receiving and decoding an 80–Mb/s rate FH-PPM UWB signal.

Transient signals accompanied by a high noise level pose both basic and practical detection challenges. Disciplines that range from communication and astronomy to molecular physics face a very similar detection problem. When phenomena of interest are repetitive, different averaging techniques can be applied in order to elevate the signal above the detection threshold. In contrast, nonrepetitive signals, commonly occurring in communication and astronomy, cannot be processed using averaging techniques. With the advent of near-noiseless replication techniques, single-instance signal separation from noise has become possible. Here, we demonstrate that a single-instance signal can be mapped to 300 optical carrier frequencies and detected with low-bandwidth receivers to generate detection gains of 24 dB with respect to a single integrating receiver with the same bandwidth. The spectral-replicating receiver was used to detect a single-instance signal with power that was four times lower than the accompanying noise level.

Radio frequency spectrum is one of the scarcest commodities in existence, with progressively increasing value. As a physical foundation of an untethered society, it now carries the majority of social, defense, and commercial interactions. All of these must reside within narrow, strictly regulated spectral windows allocated for cellular, military, navigation, and broadcast services. Band localization minimizes interference but also mandates that the entire cellular traffic be confined in less than one percent of the physical radio-frequency range. To defy this restriction and emit freely in any band, the signal power must be small to avoid interference with existing traffic. By spreading the signal over a sufficiently wide spectral range, the emission in any band can be maintained below naturally occurring noise. Unfortunately, the reception of a spectrally broadened, subnoise data channel poses a fundamental challenge: a fast, bursty waveform must be detected, separated from noise and reconstructed at rates exceeding gigahertz. Here, we show that a 20-MHz-wide signal can be spread by 300-fold, detected and reconstructed by a physical Fourier transform even when it is much weaker than the received noise. Rather than quantizing the 6-GHz-wide signal and computing its correlation with the decoding waveform, the signal was physically detected and reconstructed by coherently coupled frequency combs. By eliminating high-speed electronics from the receiver, it is now possible to access the entire radio-frequency range that extends beyond 100 GHz. We anticipate that new, band-unrestricted wireless services will emerge to maximize throughput, mitigate interference, and achieve a high level of physical security.

A 100% reach extension is demonstrated in a coherent four-channel wavelength division multiplexed system by employing full-bandwidth frequency-referenced transmitter-side digital back propagation. Frequency referenced optical carriers are generated by injection locking distributed feedback lasers to a reference optical frequency comb and the performance of digital back propagation is evaluated with and without the frequency reference. In addition, we investigate the effect of an implementation with reduced computational complexity by limiting the number of steps-per-span used in the back propagation computation. Lastly, we measure the penalties generated by an inaccurate fiber dispersion parameter in the back propagation model.

Dual-pump driven, dispersion-synthesized parametric mixers have been identified as an efficient means for wavelength multicasting. In particular, four-mode phase-sensitive (PS) architecture, seeded by frequency-locked and phase-correlated four input optical signals, allows the parametric multicasting operated with ultralow noise and regenerative properties. To further corroborate the superiorities of the multimode PS operation, degenerate one- and three-mode PS parametric multicasting were numerically and experimentally compared, in terms of stability, phase manipulation, gain, and conversion efficiency, as well as noise performance.

A novel wavelength and mode selective switch for wavelength-division multiplexing and mode-division multiplexing networks was proposed and demonstrated on a silicon wafer. The fabricated chip integrated 20 thermo-optic elements, with a footprint of 2.3×1.4 mm2.

As an essential component of mode division multiplexing (MDM) system, a multimode 3dB power splitter with low loss, high power balance, and low mode crosstalk is highly desired. In this paper, we propose an ultra-broadband on-chip multimode 3dB optical power splitter using an adiabatic coupler and an S-bend based Y-branch. As an example, a splitter for the four-lowest modes of a rib waveguide on silicon on insulator (SOI) platform is designed. Simulation results show that the device exhibits < 0.12dB insertion losses, within ± 0.38dB power imbalances, and < -18.5dB mode crosstalks for the four-lowest modes within a large operating wavelength range of 165 nm (from 1400 nm to 1565 nm). The fabrication tolerance of gap size at the output end of the adiabatic coupler is also analyzed.

Getting around the capacity crunch The growing appetite for an ever-faster Internet and enhanced long-haul communication requires the pumping of more light down optic fibers. However, light-induced nonlinearities limit how much light can be pumped into the fiber without compromising the signal. This limitation has led to the prospect of a “capacity crunch.” Temprana et al. eliminated the effects of nonlinearity by using digital back-propagation methods with mutually coherent laser pulses from a single frequency comb. Science , this issue p. 1445

Phase manipulation of four-mode phase-sensitive (4MPS) process was developed as a means for suppression of high-order four wave mixing (HoFWM) terms in dual-pump driven parametric wavelength multicasting and, consequently, for reduction of inter-channel crosstalk and inter-channel interference. In contrast to the previous studies that focused on power stabilization and conversion efficiency maximization, the investigation in this paper focuses on the evolution of the inter-channel HoFWM tones, whose suppression can be accomplished by arranging the phases of signals in a complementary manner. In addition, broadband 4MPS multicasting with suppressed HoFWM effects over 100-nm bandwidth, reaching up to 12-dB suppression ratio was demonstrated.

We describe a number of experiments demonstrating and exploring the potential of combing wideband-optical comb sources with space-division multiplexed transmission systems and in particular with homogeneous-single-mode multicore fibers including Pb/s transmission using conventional receiver technology without MIMO processing and longdistance recirculating transmission. We describe experiments using synchronized parallel transmission loops to investigate joint processing of spatial super channels and multi-dimensional modulation before discussing how optical comb technology may combine with SDM fibers to allow comb re-generation across networks to enable high-order modulation with simplified DSP. Overall, these experiments demonstrate a range of scenarios where the combination of optical combs and homogeneous MCFs can be advantageous in future optical communications networks.

We demonstrated an eight-channel flat-topped wavelength (de)multiplexer with 50GHz channel spacing on a SOI chip. The measured crosstalk is < -26.0 dB at central wavelengths of the channels and 1-dB bandwidth is 33.0 GHz.

We present a new arbitrary-ratio 2×2 MMI coupler design. The design demonstrated 2.6 times lower coupling ratio variation across extended C-band, and 2.2 times ratio error reduction when subjected to ±10 nm thickness and width deviations.

A novel optical frequency synthesizer capable of generating a multitude of narrow linewidth oscillations, fully compatible with high-speed fiber-optic transmission requirements, is presented. The new device is based on an ultra-dense and wideband parametric comb capable of generating more than 1800 spectral lines with 6.25 GHz spacing within 100 nm (C + L band) of optical bandwidth and 3 dB spectral flatness. The parametric comb generation relies on the highly efficient nonlinear interaction of the ultra-short and high peak power pulse train in the precisely controlled dispersive medium. The generated comb source is used for coherent transmission of 1520 Nyquist ultra-dense wavelength division multiplexed channels in a flex-grid compatible optical access network architecture, offering up to 30 Gb/s per user over a 50 km of standard single mode fiber with estimated aggregate capacity of 32 Tb/s. The line spacing tunablity and one-to-multiple coherent cloning capability make the proposed multicarrier generator a strong contender fully capable of replacing thousands of discrete lasers in optical data communication systems.

An essential capability in many applications, ranging from commercial, surveillance and defense, is to analyze the spectral content of intercepted microwave and millimeter-wave signals over a very wide bandwidth in real-time and with high resolution. A range of photonic schemes have been introduced for the real-time processing of wideband signals to overcome limitations of current conventional electronic frequency measurement approaches. Here, a novel microwave/millimeter-wave channelizer is presented based on a RF photonic front-end employing parametric wavelength multicasting and comb generation. This new technology enables a contiguous bank of channelized coherent I/Q IF signals covering extremely wide RF instantaneous bandwidth. High channel counts and wide RF instantaneous bandwidth are enabled by use of parametrically generated frequency-locked optical combs spanning >4 THz. Full field analysis capabilities of the coherent detection system are demonstrated by frequency domain analysis of 18 contiguous 1.2 GHz IF channels covering 15.5 GHz to 37.1 GHz input frequency range, and time and spectral domain analysis of a 75 GHz harmonically generated input signal. Sensitivity and dynamic range of the system are analyzed and discussed.

We study the limitations and their origins in the nonlinear effects mitigation in fiber-optic communication systems. The carrier frequencies uncertainty and their stochastic variations are identified as the major impeding factor for successful inter-channel nonlinear impairments management. Furthermore, the results clearly point out to the significant benefits of employing fully frequency referenced carriers in transmission, with frequency combs representing an immediately available solution. Finally, frequency referenced transmitters and/or receivers are shown as critical for availing longer reach at high spectral efficiencies in transmission.

A multiwavelength source for optical transmitters delivers narrow-linewidth carrriers with 100-GHz spacing spanning the C and L bands. The phase-locked carriers are derived from a single, 3-kHz linewidth source, and a multistage parametric mixer. Bit-error rate measurements for a 20-GBd 16-QAM transmitter based on this source are reported.

We report the first use of the CW-seeded parametric comb as a multiwavelength source for coherent channel transmitters. The new comb source relies on a multistage parametric mixer design seeded by a single kilohertz-linewidth master laser. The resultant frequency comb provides more than 120 tones in a 100-nm-wide continuous band, all possessing kilohertz-scale linewidth inherited from the master laser. The applicability of the new comb source as a coherent channel carrier was quantified by error-vector magnitude and bit-error rate metrics of individual spectral lines modulated by QPSK signaling. The performance of the new source exceeded that of the standard tunable coherent transmitter while providing a qualitatively lower frequency uncertainty and drift.

Conference on Lasers and Electro-Optics : [Proceedings] - OSA Washington, D.C., 2017. - ISBN 978-1-943580-27-9 - doi:10.1364/CLEO_SI.2017.STu4J.7 CLEO: Science and Innovations, CLEO, San Jose, California, USA, 14 May 2017 - 19 May 2017; Washington, D.C. : OSA, OSA technical digest (online), 2 pp. (2017). doi:10.1364/CLEO_SI.2017.STu4J.7, We demonstrate an octave spanning coherent supercontinuum generated in a silicon waveguide covering the near to shortwave IR (SWIR) region. The measured -20 dB SC span ranges from 1.124 μm to 2.4 μm., Published by OSA, Washington, D.C.

We present a high-speed flexible photonic-assisted Discrete Fourier Transform (DFT) processor based on a dual, phase-locked optical parametric combs. A 25-point DFT at 500 Million-DFT-point per second throughput is achieved relying on slow, 20 MS/s Analog to Digital Converter (ADC).

We describe experiments combining high core-count, homogeneous single-mode multi-core fibers with a wideband comb for high-capacity transmission without high-order MIMO reception and demonstrate wideband transmission with coded modulation up to 12,300 km.

Conventional lightwave receiver incorporates high-speed Fast Fourier Transform (FFT) computation core in order to aid carrier recovery and perform channel equalization. This talk examines a computation-free FFT alternative architecture and discussed its implications.

Muscle force is dictated by micrometer-scale contractile machines called sarcomeres. Whole-muscle force drops from peak force production to zero with just a few micrometers of sarcomere length change. No current technology is able to capture adequate dynamic sarcomere data in vivo, and thus we lack fundamental data needed to understand human movement and movement disorders. Methods such as diffraction, endoscopy, and optical coherence tomography have been applied to muscle but are prohibitively invasive, sensitive to motion artifact, and/or imprecise. Here, we report dynamic sarcomere length measurement in vivo using a combination of our recently validated resonant reflection spectroscopy method combined with optical frequency domain interferometry. Using a 250-μm-wide fiber optic probe, we captured nanometer sarcomere length changes from thousands of sarcomeres on the sub-millisecond timescale during whole-muscle stretch and twitch contraction. We believe that this demonstrates the first large-scale sensing of sarcomere dynamics in vivo, which is a necessary first step to understand movement disorders and to create patient-specific surgical interventions and rehabilitation.

We report the demonstration of a new wavelength-swept source. Utilizing narrowband, widely tunable fiber optical parametric process as the gain and the wavelength selection mechanism in a ring laser topology, simultaneous access to two distinct bands (NIR and SWIR) over 329 nm was achieved. A nonmechanical cavity-tuning mechanism allowed for ultrafast sweep rate, limited primarily by the speed of the tunable pump source confined to a conventional 1550-nm band. With the experimentally verified order-of-magnitude enhancement in sweep range and speed, the source opens a path for spectral scanning at an unprecedented speed and range while relying on existing tuning technologies.

We report the first demonstration of 640-Gb/s return-to-zero ON-OFF keying channel transmission over a 100-km standard single-mode fiber link employing midspan phase conjugation. A frequency-degenerate conjugate field spanning more than 20 nm is created in a low-birefringence parametric mixer for the first time. Physical separation of the conjugate field from the original field is enabled by utilizing pump polarization nondegeneracy. Rigorous link characterization using a high-quality 640-Gb/s transmitter and a high-sensitivity receiver revealed error-free (bit error ratio

Four-mode phase-sensitive (4MPS) process has been employed in a parametric mixer based wavelength multicaster, enhancing the multicasting conversion efficiency and signal-to-noise ratio. In addition, the 4MPS parametric multicaster is an outstanding candidate for all-optical regeneration, owing to its inherent capabilities to clamp amplitude fluctuations by the saturated parametric effect and to squeeze phase distortions by the phase sensitive process. The investigation in this paper focuses on the 4MPS multicaster operated in the saturation gain regime, including theoretical simulations and experimental demonstrations on amplitude and phase noise regeneration over 20 multicasting signal copies.

Observation of random, nonrepetitive phenomena is of critical importance in astronomy, spectroscopy, biology, and remote sensing. Heralded by weak signals, hidden in noise, they pose basic detection challenges. In contrast to repetitive waveforms, a single-instance signal cannot be separated from noise through averaging. Here, we show that a fast, randomly occurring event can be detected and extracted from a noisy background without conventional averaging. An isolated 80-picosecond pulse was received with confidence level exceeding 99%, even when accompanied by noise. Our detector relies on instantaneous spectral cloning and a single-step, coherent field processor. The ability to extract fast, subnoise events is expected to increase detection sensitivity in multiple disciplines. Additionally, the new spectral-cloning receiver can potentially intercept communication signals that are presently considered secure.

We demonstrate a two-fold reach extension of 16 GBaud 16-Quadrature Amplitude Modulation (QAM) wavelength division multiplexed (WDM) system based on erbium doped fiber amplifier (EDFA)-only amplified standard and single mode fiber -based link. The result is enabled by transmitter-side digital backpropagation and frequency referenced carriers drawn from a parametric comb.

Light 7(1), 17131 (2018). doi:10.1038/lsa.2017.131, Efficient complementary-metal-oxide-semiconductor-based nonlinear optical devices in the near infrared are in strong demand. Due to two-photon absorption in silicon, however, much nonlinear research is shifting towards unconventional photonics platforms. In this work, we demonstrate the generation of an octave-spanning coherent supercontinuum in a silicon waveguide covering the spectral region from the near- to shortwave-infrared. With input pulses of 18 pJ in energy, the generate d signal spans the wavelength range from the edge of the silicon transmission window, approximately 1.06 μm to beyond 2.4μm, with a −20 dB bandwidth covering 1.124 - 2.4μm. An octave-spanning supercontinuum was also observed at the energy levels as low as 4 pJ (-35 dB bandwidth). We also measured the coherence over an octave, obtaining $|g_{12}^{(1)}(\lambda)|$ in good agreement with the simulations. Additionally, we demonstrate optimization of the third-or der dispersion of the waveguide to strengthen the dispersive wave and discuss the advantage of having a soliton at the long wavelength edge of an octave-spanning sign al for nonlinear applications. This research paves the way for applications, such as chip -scale precision spectroscopy, optical coherence tomography, optical frequency metrology, frequency synthesis and wide-band wavelength division multiplexing in the telecom window., Published by Nature Publishing Group, London

We propose a transmitter based on injection locking a low-cost Fabry-Perot laser to a reference Optical Frequency Comb. We demonstrate transmission of 50 GBaud 16-QAM over 2125 km relying on Digital Back Propagation.

Practical frequency generation and conversion requires highly efficient parametric interaction across wide spectral band. To achieve high efficiency, conventional devices rely on optical enhancement in highly resonant cavity structures. While optical cavity also inhibits noise generation and out-of-band amplification during the parametric process, it inherently limits frequency tuning and any band reconfiguration. Recognizing this fundamental impairment, we describe the new class of cavity-free frequency generation in heterogeneous, traveling-wave parametric mixers. Driven by a continuous-wave seeds, these devices combine inherently more stable lasers with distributed noise inhibition in dispersion-managed parametric process. The operating principle, design methodology and performance limits are outlined and discussed. The use of new technology is illustrated on examples of signal multicasting and ultrafast channel processing.

We report the highest performance 640-Gb/s transmitter and receiver, based on cavity-less pulse generation and a novel sampling receiver constructed using a single fiber parametric gate capable of self-tracked 40-Gb/s tributary extraction. The performance of the transmitter and sampling receiver was measured with a 640-Gb/s return-to-zero on-off keying (RZ-OOK) signal. Error-free operation was achieved for all 16 tributaries of the 640-Gb/s input stream using the optical signal-to-noise ratio (OSNR) noise loading method. The error-free (bit-error rate (BER) =10-9 ) sensitivity of the sampling receiver was measured at an OSNR level of 33.5 dB, which is only 0.5 dB away from the practically achievable detection limit.