Tunable Dispersion Compensator Research Articles

Strategy for Attacking the Key Parameters of Electro-Optic Self-Feedback Phase Encryption System

In this paper, we propose a method for cracking the key parameters of an electro-optic self-feedback temporal optical phase encryption system and experimentally demonstrate the feasibility of the scheme. By scanning a tunable dispersion compensation (TDC) module at the receiver, the time delay signature (TDS) of an encrypted signal can be exposed, making it possible to extract other key parameters of the system and reconstruct a decryption setup. The TDS characteristics for three typical modulation formats are investigated, revealing that while such an encryption system is secure against power detection attack, there is a risk of TDS leakage. The findings can guide the design of advanced optical encryption schemes with TDS suppression for security enhancement.

Surface-emitting THz quantum cascade laser frequency comb with tunable external mirror dispersion compensation

We present a surface emitting THz quantum cascade laser frequency comb with an adjustable chromatic dispersion compensation via a mechanically tunable GTI cavity. Surface emission and high optical feedback into the laser cavity are achieved by a planarized ridge waveguide design with low reflectivity facets and two broadband patch array antennas for coupling to an external mirror (back side) and for power extraction (front side). We demonstrate direct and reproducible manipulation of the frequency comb state, specifically the comb stability and beatnote frequency tuning, by controlling the position of an external movable mirror.

Numerical studying of broadband tunable dispersion compensation based on photonic crystal fiber

We propose a broadband tunable negative dispersion photonic crystal fiber (BT-ND-PCF) for dispersion compensation over the S + C + L wavelength bands. BT-ND-PCF is a dual-core structure in which air holes are arranged with a hexagonal lattice and temperature-sensitive liquid is infiltrated into the air holes of the fourth layer. The performance of BT-ND-PCF is numerically analyzed by the finite element method with an anisotropic perfect matching layer. The results show that BT-ND-PCF has a broadband negative dispersion coefficient of −1533.2 to −2836.4 ps / km / nm over the S + C + L wavelength bands, a dispersion coefficient of −2268.9 ps / km / nm at 1550 nm, and a kappa value of 287.9 nm at 1550 nm, which matches with Corning single-mode fiber 28 (SMF). The residual dispersion (RD) after compensating for the dispersion of 1 km SMF is in the range of −0.22 to +0.16 ps / nm. In addition, the dispersion coefficient is changed by 0.679 ps/km/nm per 1°C by controlling the temperature, which is conducive to the accurate compensation of RD. Due to its unique optical properties, BT-ND-PCF can be used in broadband dispersion compensation for dense wavelength division multiplexing optical fiber communication systems.

Dispersion compensation of high-speed data using an integrated silicon nitride ring resonator.

Dispersion impairments are a well-known limitation in data center communications, limiting both the usable data rates and reaches. Several companies today adopt silicon photonics as a core technology in their transceiver products. This presents an opportunity for silicon photonics-based dispersion management technologies to be integrated with the transceiver transmitter or receiver. In this manuscript, we present a ring-resonator based, tunable dispersion compensation device, providing dispersion ranging as wide from + 12.9 × 103ps/nm to -12.3 × 103ps/nm. Thermo-optic tuning from 20°C to 70°C is demonstrated to allow continuous wavelength tuning across 200 GHz. High-speed experiments using 25 Gb/s non-return-to-zero data propagating through 20 km of single mode fiber show that a significant improvement in the eye diagram is achieved after compensation with the ring-resonator device. We demonstrate a significant improvement in the BER from 10-3 to 10-11 for data rates of 25 and 25.78125 Gb/s.

Dispersion-managed technique in temporal-frequency measurement for MoTe2-based ultrafast laser.

Ultrafast phenomena exist widely in modern scientific research. The time scale of ultrafast phenomena is mostly in the order of picosecond, femtosecond, or even attosecond. Nowadays, it is still a major challenge to study these nonrepetitive transient processes. Here, a temporal-frequency measurement based on a dispersion-managed technique has been proposed for an MoTe2-based ultrafast laser. The temporal-frequency measurement comprises a laser diode, an optical switch, a section of tunable dispersion compensation fiber, and a three-port beam splitter. Resolution of the proposed measurement can be tuned in a wide range; further, the upper and lower resolution limits are numerically simulated. The proposed measurement is expected to be applied in ultrafast pulse detection due to its application in real-time measurement of ultrafast nonrepetitive signals.

Statistical Evaluation of PAM4 Data Center Interconnect System With Slope-Compensating Fiber Bragg Grating Tunable Dispersion Compensation Module

Data center interconnect (DCI) links with high data-rate direct-detection require strict chromatic dispersion compensation. One such solution which has been widely deployed is based on four-level pulse amplitude modulation (PAM4). With this application in mind, we describe in detail a 50-GHz channelized fiber Bragg grating (FBG) tunable dispersion compensation module (TDCM) which can compensate chromatic dispersion slope over the full C-band (4.8 THz) and is thus suitable for dense wavelength division multiplexing (DWDM) PAM4 DCI systems. We then present a comprehensive set of system performance results comprising 1,120 unique link measurements, to characterize the combined effect of statistical variations in component characteristics and link impairments, and show that a statistical approach to link budgeting is advantageous in this type of system. We also analyze the group delay ripple characteristics of the FBG-TDCM device and the corresponding impact on the PAM4 system. Instead of the conventional phase ripple standard deviation, we introduce a novel metric to quantify high-frequency phase ripple, which is better correlated with the impact on the PAM4 system.

Tunable and compact dispersion compensation of broadband THz quantum cascade laser frequency combs.

Miniaturized frequency combs (FCs) can be self-generated at terahertz (THz) frequencies through four-wave mixing in the cavity of a quantum cascade laser (QCL). To date, however, stable comb operation is only observed over a small operational current range in which the bias-depended chromatic dispersion is compensated. As most dispersion compensation techniques in the THz range are not tunable, this limits the spectral coverage of the comb and the emitted output power, restricting potential applications in, for example, metrology and ultrashort THz pulse generation. Here, we demonstrate an alternative architecture that provides a tunable, lithographically independent, control of the free-running coherence properties of THz QCL FCs. This is achieved by integrating an on-chip tightly coupled mirror with the QCL cavity, providing an external cavity and hence a tunable Gires Tournois interferometer (GTI). By finely adjusting the gap between the GTI and the back-facet of an ultra-broadband, high dynamic range QCL, we attain wide dispersion compensation regions, where stable and narrow (~3 kHz linewidth) single beatnotes extend over an operation range that is significantly larger than that of dispersion-dominated bare laser cavity counterparts. Significant reduction of the phase noise is registered over the whole QCL spectral bandwidth (1.35 THz). This agile accommodation of a tunable dispersion compensator will help enable uptake of QCL-combs for metrological, spectroscopic and quantum technology-oriented applications.

On The Performance of The Effects of Temperature Variation in Ultrafast Incoherent Fiber-Optic CDMA Systems With SOA-Based Tunable Dispersion Compensator

Recent studies show that temperature variation in ultrafast incoherent fiber-optic code-division multiple-access (FO-CDMA) systems using picosecond multiwavelength codes is a realistic problem even though dispersion-compensating fiber is utilized. The phenomenon creates distortions in auto- and cross-correlation functions and then worsens system performance. A physical-layer mitigation approach has been reported by using a recently demonstrated semiconductor-optical-amplifier-based tunable dispersion compensator to fully recover the auto-correlation peaks. Applying the concept of “chip granularity” to account for the effects of temperature variation to the cross-correlation functions, this paper formulates a new performance-analytical model for such FO-CDMA systems. The model also supports adjustable quality-of-services through code weight control.

Modelling the broadband mid-infrared dispersion compensator with hybrid silicon and lithium niobate nanowire

The broadband dispersion compensator plays an important role for the light transmission of ultrashort pulses. Inspired by the requirement for a compact, tunable dispersion compensator operating in the mid-infrared spectral range, we proposed a compact dispersion compensator with hybrid silicon and lithium niobate nanowire configuration and investigated its group-velocity dispersion characteristics numerically. The results show that the tailored hybrid waveguide can exhibit group velocity dispersion of up to 105 ps2·km−1 in the 2~5 μm spectral range. In addition, the dispersion can be tuned via the applied bias field by the aid of the excellent electro-optical performance of the host material, lithium niobate. This work may provide some guidelines for designing broadband dispersion compensators and make an inroad for miniaturized functional optoelectronic devices.

Nonlinear chirped grating based tunable dispersion compensation using strain

Chirped fiber Bragg gratings (CFBGs) offer an attractive solution for dispersion management in long haul and high capacity point to point optical links. The deployment of reconfigurable optical networks however demands dynamic dispersion compensation schemes to address channel degrading effects. Dynamic correction of dispersion can be achieved by tuning the optical characteristics of the non-linearly chirped FBG using external controls like temperature, strain, magnetic, acousto-optic and electro-optic techniques. In this work, simulations are carried out to evaluate the performance of nonlinear chirped gratings as tunable dispersion compensators. The induced dispersion of the grating is found to be tunable from −800 ps/nm to −2657 ps/nm using strain as external perturbation. BER of 1.85 × 10−118 and 1.71 × 10−116 is achieved after the transmission of the information through 90 and 140 km section of single mode optical fiber respectively. This is achieved by adjusting or tuning the dispersion offered by the nonlinear chirped FBG dynamically in the required range.

Tunable dispersion compensation of quantum cascade laser frequency combs.

Compensating for group velocity dispersion is an important challenge to achieve stable midinfrared quantum cascade laser (QCL) frequency combs with large spectral coverage. We present a tunable dispersion compensation scheme consisting of a planar mirror placed behind the back facet of the QCL. Dispersion can be either enhanced or decreased depending on the position of the mirror. We demonstrate that the fraction of the comb regime in the dynamic range of the laser increases considerably when the dispersion induced by the Gires-Tournois interferometer compensates the intrinsic dispersion of the laser. Furthermore, it is possible to tune to the offset frequency of the comb with the Gires-Tournois interferometer while the repetition frequency is almost unaffected.

Localization and time-reversal of light through dynamic modulation

We study the dynamics of a waveguide made of coupled resonators with a sinusoidal modulation of the resonance frequencies. We present a modulation scheme that achieves complete dynamic localization and is experimentally suitable for optical cavities. Furthermore, we highlight the importance of the way the modulation is turned on and off. One striking consequence is that, while a state returns to its starting amplitude at the end of every cycle, it can also be fully time-reversed if the modulation is turned off mid-cycle. Finally, we show that localization is always achieved when the modulation envelope is adiabatic with respect to the oscillation frequency. The results are experimentally feasible using existing integrated photonic technologies, and are relevant to applications like tunable delay lines, dispersion compensation, and imaging.

Application of Waveguide/Free-Space Optics Hybrid to ROADM Device

As optical networks have evolved from point-to-point systems to ring or mesh networks, the optical devices that are needed to construct optical nodes have become more important and need to be more scalable. Hybridization of waveguide and free-space optics, or spatial and planar optical circuits (SPOCs), may provide the solutions for such needs. An SPOC platform is attractive because it can take advantage of both waveguide technology and free-space optics. Waveguide technology provides a high degree of integration of optical functionality for devices such as splitters and non-wavelength selective switches while free-space optics supplies a high degree of parallelism with two-dimensional spatial light modulators such as a liquid crystal on silicon (LCOS) devices. In this paper, we summarize the basics of SPOC technology and review its application to reconfigurable optical add-drop multiplexing (ROADM) devices. The key elements of a waveguide on an SPOC platform are an arrayed-waveguide grating and a spatial beam transformer. The latter functions as a microlens array and provides attractive features such as dense integration of switches. An LCOS device has numerous phase modulating pixels, enabling flexible manipulation of lightwaves. Using an SPOC platform, we constructed and demonstrated devices for ROADM applications including a wavelength filter, tunable optical dispersion compensators, and wavelength selective switches (WSSs). The WSSs range from an ultrahigh port count WSS to a single module wavelength cross connect.

Photonic microwave waveform generation based on phase modulation and tunable dispersion.

Photonic generation of microwave waveforms is currently an interesting topic due to the advantages of large bandwidth and immunity to electromagnetic interference. In this paper, a photonic microwave waveform generator with tunable waveforms and repetition rates is proposed and experimentally demonstrated. A continuous-wave (CW) light is phase modulated by a local oscillator (LO) signal to generate optical sidebands. By locating the phase modulator (PM) in a Sagnac loop, we can control the intensity and phase of the carrier of the phase modulated signal. Then a compact tunable dispersion compensation module is used to introduce phase shifts to the optical sidebands. Thanks to the flexible controlling of the optical signal, the generation of microwave waveforms with tunable shapes and repetition rates can be realized. In the demonstration experiment, full-duty-cycle triangular and square waveforms with repetition rates of 5 and 10 GHz (bandwidths of 15 and 30 GHz) are successfully generated, respectively. The bandwidths are expected to be improved to above 120 GHz if larger-bandwidth measurement instruments are used. In addition to the flexible tunability, the proposed scheme also features the advantages of easy implementation and free from bias drift.

Tunable photonic elements at the surface of an optical fiber with piezoelectric core.

Tunable photonic elements at the surface of an optical fiber with piezoelectric core are proposed and analyzed theoretically. These elements are based on whispering gallery modes whose propagation along the fiber is fully controlled by nanoscale variation of the effective fiber radius, which can be tuned by means of a piezoelectric actuator embedded into the core. The developed theory allows one to express the introduced effective radius variation through the shape of the actuator and the voltage applied to it. In particular, the designs of a miniature tunable optical delay line and a miniature tunable dispersion compensator are presented. The potential application of the suggested model to the design of a miniature optical buffer is also discussed.

Analogue‐to‐digital converter phase insensitive dispersion search method with large search step size for low computational cost

Accumulated chromatic dispersion (CD) estimation is crucial for frequency-domain equalisation in an optical coherent digital receiver. To solve the problems of small search step size and analogue-to-digital converter (ADC) sampling phase sensitivity from conventional CD searching algorithm, a CD searching method with modified shift parameters and waveforms is proposed in this study. The modified CD searching method allows a much larger search step size and can achieve faster CD estimation with low computational complexity. The performance of the modified CD searching method is also insensitive to ADC sampling phase. On the basis of simulation results, a very low search error probability is confirmed with a search step size of 50 km. About 1 K symbols are found to be enough for dispersion estimation. After the frequency-domain equaliser (FDE) with the estimated dispersion value, the residual dispersion length <30 km can be well compensated with a 9-tap adaptive time-domain equaliser (TDE) with fast convergence. The overall error rate performance of the tunable electrical dispersion compensation is also studied and compared with lumped and distributed optical dispersion compensation for dynamically switched optical networks.

Simultaneous optical signal to noise ratio and symbol rate estimation with blind chromatic dispersion compensation for auxiliary amplitude modulation optical signals

Based on the peak to valley ratio (PTVR) of the average magnitude difference function (AMDF), we present a novel optical signal to noise ratio (OSNR) and symbol rate (SR) estimation method for commonly used auxiliary amplitude modulations (AAMs). Moreover, it is demonstrated that the influence of chromatic dispersion (CD) on the method can be mitigated by maximizing the PTVR of the AMDF with additional tunable dispersion compensators. The results of simulations show that the OSNR estimation error can be kept within 0.8 dB in the wide OSNR range of (12, 32) dB, while the SR estimation error is below 0.079% for four widely used 10 Gsymbol/s AAM signals.

Analysis of the Possibilities for Using a Uniform Bragg Grating in a Tunable Dispersion Compensator

Abstract The article presents a tunable fibre optic dispersion compensator system, consisting of a specially designed cantilever beam and a uniform Bragg grating. It analyses the group delay and dispersion characteristics in the case that there is no apodization of the grating and also for a grating with apodization used for modulation of the refractive index. Various apodization parameters were tested, along with their effects on the dispersion characteristics of the entire system properties. It is demonstrated in the paper that the apodization parameter affects the compensator’s group delay characteristic. The finite elements method was used to design a compensator of such a shape that enabled chirp to be induced in a grating of a specified shape. A new design is presented for the system, in which the dispersion properties are tuned by the maximum value of the heterogeneous deformation of the compensator. The paper also includes results showing the effect of the maximum value of heterogeneous stress of the grating on the dispersion characteristics of the proposed construction.

Three dispersion compensation methods for radio-over-fiber system

This paper introduces three different dispersion compensation methods based on superstructure fiber Bragg grating (SSFBG) and an injection distributed feedback (DFB) laser. First, an SSFBG with a nonlinearity group delay spectrum was designed to achieve tunable dispersion compensation. Second, an approach is pro- posed for realizing single-sideband modulation with an optimum optical carrier to sideband ratio for maximizing the transmission performance of a radio-over-fiber (RoF) system based on a strong optical injection-locked DFB laser. Finally, a broadband chromatic dispersion compensation scheme using an optical phase conjugator based on a DFB semiconductor laser is proposed and experimentally demonstrated in RoF links. © 2015 Society of Photo-

28 MHz swept source at 1.0 μm for ultrafast quantitative phase imaging.

Emerging high-throughput optical imaging modalities, in particular those providing phase information, necessitate a demanding speed regime (e.g. megahertz sweep rate) for those conventional swept sources; while an effective solution is yet to be demonstrated. We demonstrate a stable breathing laser as inertia-free swept source (BLISS) operating at a wavelength sweep rate of 28 MHz, particularly for the ultrafast interferometric imaging modality at 1.0 μm. Leveraging a tunable dispersion compensation element inside the laser cavity, the wavelength sweep range of BLISS can be tuned from ~10 nm to ~63 nm. It exhibits a good intensity stability, which is quantified by the ratio of standard deviation to the mean of the pulse intensity, i.e. 1.6%. Its excellent wavelength repeatability, <0.05% per sweep, enables the single-shot imaging at an ultrafast line-scan rate without averaging. To showcase its potential applications, it is applied to the ultrafast (28-MHz line-scan rate) interferometric time-stretch (iTS) microscope to provide quantitative morphological information on a biological specimen at a lateral resolution of 1.2 μm. This fiber-based inertia-free swept source is demonstrated to be robust and broadband, and can be applied to other established imaging modalities, such as optical coherence tomography (OCT), of which an axial resolution better than 12 μm can be achieved.