Wavelength Conversion Technique Research Articles

Throughput optimization in hybrid C-C+L-band elastic optical networks enabled by hybrid modulation and wavelength/modulation conversion

Elastic optical networks (EONs) have been proposed to address the increasing needs of future communications, yet the capacity of these networks is expected to run out. Evolving the current C-band system to use the C+L-band is a costly and time-consuming solution. This paper presents a stopgap solution to meet the increasing communication needs in the short term by exploiting hybrid fused C- and L-band transmission before the full evolution is achieved. The proposed physical-layer-impairments-aware high spectral efficiency (PAHSE) algorithm jointly applies time domain hybrid modulation (TDHM) and modulation and wavelength conversion techniques and uses accurate models to estimate physical layer impairments for the C- and C+L-band links. The hybrid network scheme converts C-band signals to L-band at the regenerator nodes, which increases the system throughput. The proposed PAHSE algorithm assigns the highest spectral efficiency to each transparent segment of each traffic request while satisfying the quality of transmission requirements. Simulations are conducted on two network topologies, one of large diameter and the other highly connected, using several types of traffic that mimic demands expected in future communication scenarios. Compared to the benchmark, the proposed network system and algorithm result in much higher network throughput, up to a 120% increase in the sum bit rate in the NSFNET-24 topology, thus obviating the urgent need for full C+L deployment.

Coherent Magneto-optomechanical Signal Transduction and Long-Distance Phase-Shift Keying

A transducer capable of converting quantum information stored as microwaves into telecom-wavelength signals is a critical piece of future quantum technology as it promises to enable the networking of quantum processors. Cavity optomechanical devices that are simultaneously coupled to microwave fields and optical resonances are being pursued in this regard. Yet even in the classical regime, developing optical modulators based on cavity optomechanics could provide lower power or higher bandwidth alternatives to current technology. Here we demonstrate a magnetically-mediated wavelength conversion technique, based on mixing high frequency tones with an optomechanical torsional resonator. This process can act either as an optical phase or amplitude modulator depending on the experimental configuration, and the carrier modulation is always coherent with the input tone. Such coherence allows classical information transduction and transmission via the technique of phase-shift keying. We demonstrate that we can encode up to eight bins of information, corresponding to three bits, simultaneously and demonstrate the transmission of an 52,500 pixel image over 6 km of optical fiber with just 0.67% error. Furthermore, we show that magneto-optomechanical transduction can be described in a fully quantum manner, implying that this is a viable approach to signal transduction at the single quantum level.

Simultaneous Raman based power combining and wavelength conversion of high-power fiber lasers.

We present a technique for simultaneous power-combining and wavelength-conversion of multiple fiber lasers into a single, longer wavelength in a different band through Raman-based, nonlinear power combining. We illustrate this by power combining of two independent Ytterbium lasers into a single wavelength around 1.5micron with high output powers of upto 99W. A high conversion efficiency of ~64% of the quantum limited efficiency and a high level of wavelength conversion with >85% of the output power in the final wavelength is demonstrated. The proposed method enables power-scaling in various wavelength bands where conventional fiber lasers are unavailable or limited in power.

Wavelength conversion technique for optical frequency dissemination applications

We demonstrate coherent wavelength conversion capable of covering the entire C-band by modulating the incoming optical carrier with a compact Fabry-Perot cavity embedded phase modulator and by optical injection locking a semiconductor laser to a tone of the generated optical frequency comb. The phase noise of the converted optical carrier over 1 THz frequency interval is measured to be -40 dBc/Hz at 10 Hz offset and the frequency stability is better than 2 × 10(-17) level for averaging times >1000 s, making this technique a promising solution for comparisons of state-of-the-art optical clocks over complex fiber networks.

Millimeter-Wave Radio Over Fiber Optical Upconversion Techniques Relying on Link Nonlinearity

A study of advanced upconversion techniques used in radio over fiber (ROF) is provided. With the huge increase in both the number of wireless communication subscribers and the bandwidth required per customer, migrating to higher frequencies, i.e., from lower radio frequency to millimeter-wave carriers, is an essential solution. However, due to the short propagation range of millimeter waves, a large number of radio access points are required for providing reliable coverage, which would increase the infrastructure costs. Hence, the transmission of RF signals between the central (or control) points and radio access points (or remote antenna units) using optical fibers is one of the major access network solutions that have been proposed for future high-bandwidth wireless communication systems. In this paper, we introduce the basics of ROF communication, including optical modulation, the optical channel, and the optical detection techniques. Then we survey the family of advanced optical upconversion techniques that exploit the nonlinearity of the ROF link. Specifically, we describe how optical upconversion can be achieved by exploiting the Mach–Zehnder modulator's nonlinearity, wavelength conversion techniques, or the photodetector's nonlinearity. The wavelength conversion techniques rely on the nonlinearities present in the fiber, in the optical amplifier, or in the electroabsorption modulator.

10 Gbps Externally Modulated XGM Based Wavelength Conversion Using SOA

This paper proposes a method for All Optical Wavelength Conversion using semiconductor optical amplifier at 10Gbps. The system is demonstrated for Cross Gain Modulation (XGM) process of SOA, which is the simplest wavelength conversion technique that takes the advantage of non linear gain suppression mechanism in SOA. The system performances are analyzed using Q factor and Extinction Ratio of the eye diagram. The input pump power is varied from 2 dBm to 5 dBm; also the extinction ratio of Mach-Zehnder modulator is varied from 30 dBm to 60 dBm. Maximum Q Factor of 11.86dB is obtained for a maximum output signal power 23.94 dBm. Minimum Q Factor obtained is 7.58dB for a minimum output signal power 23.15 dBm. The extinction ratio falls from 18.56dB to 16.63dB as the input conditions are varied.

Conversion Complexity of Multicast Routing and Wavelength Assignment Converters with Different Wavelength Conversion in Benes Network

A wavelength division multiplexing based multicast Benes switching network considers an input signal on inlets with the given wavelength to one or more fiber outlets with wavelength conversion in the optical domain. The main challenge in the design of multicast routing and wavelength assignment is to reduce the complexity of wavelength conversion without affecting switch capability and no cross-talk signal quality using the Benes network. The proposed design of multicast routing and wavelength assignment wavelength conversion using Benes network complexity is 4Flog2W/2 and switching complexity of O(Flog2W/2). The performance loss in terms of throughput, delay, and packet loss of the proposed low-complexity method using output queuing multicast interconnection network. We prove that W > 64 conversion complexity of the optimal design is strictly lower than the existing system Copy route single channel and multicast channel. When we compare with different conversion techniques, the add/drop multicast Benes network and Mach---Zehnder Interferometer using Benes network complexity is higher because 2N × 2N design switching elements are required, and so double the amount of conversion is required. The proposed Multicast routing Wavelength assignment Benes technique achieves more than 80 % reduction in conversion complexity for the design of Benes network as compared to different wavelength conversion techniques.

Performance enhancement of pre-spectrum slicing technique for wavelength conversion

This paper details a proposal and successful demonstration of an ultra-narrow and very high optical signal-to-noise ratio wavelength converted channel that was generated from an efficient ultra-narrow pre-spectrum sliced probe channel via four-wave mixing in a highly non-linear fiber medium. An array of narrowband fiber Bragg grating filters acted as a discriminative component to pre-spectrum slice the probe channel from backward amplified spontaneous emission, which, in turn, induced an additional fiber Bragg grating filtering mechanism within an erbium-doped fiber medium in a saturable configuration. A resultant optical signal-to-noise ratio of more than 70dB in the probe channel gave rise to a 40dB optical signal-to-noise ratio in the converted channel. These outcomes indicate the proposed scheme is highly suitable for practical, cost-effective wavelength conversion in any “pre-spectrum sliced” optical communication system.

Four-Wave Mixing in a Polarization-maintaining Fiber Bragg Grating

We experimentally demonstrate a four-wave mixing (FWM) process in an all-fiber system. In this system, a short section of polarization-maintaining fiber containing a fiber Bragg grating is included in a laser cavity as a polarimetric mirror which separately reflects two wavelengths corresponding to orthogonal polarizations (LP <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">01</sub> (x) and LP <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">01</sub> (y)) of the core mode. Two polarized modes are lased in the cavity as the pump wave and signal wave; meanwhile, due to FWM effect, two idler waves with orthogonal polarizations are generated on either side of the two fundamental polarized modes. The proposed laser operations can deliver three states (x-polarized idler, y-polarized idler, and both them) simply by appropriately adjusting the coupling between two polarizations with the polarization controllers. The information obtained in this letter suggests that the proposed FWM system is a reliable laser wavelength conversion technique with a simplified structure.

All-optical NRZ wavelength conversion using a Sagnac loop with optimized SOA characteristics

We investigated the all-optical wavelength conversion technique for non-return-to-zero (NRZ) signals based on a Sagnac loop interferometer using an SOA. For the wavelength conversion of the NRZ signal at and above 40 Gbit/s, we used an in-house numerical SOA model to analyze the influence of the SOA carrier characteristics and the SOA length on the performance of the Sagnac loop. We found that the SOA carrier recovery time should be between 2 and 3 times of one bit duration in order to get optimum NRZ wavelength conversion. In addition to the carrier recovery time requirement, SOAs with a shorter physical length are preferred to be used in the Sagnac interferometer.

In-line phase sensitive amplifier based on PPLN waveguides

We demonstrate a χ(2)-based in-line PSA with a carrier-recovery and phase-locking system for a phase shift keying (PSK) signal. By doubling the signal phase using a wavelength conversion technique, the carrier was recovered from a PSK signal. The carrier phase was synchronized to a local oscillator using optical injection locking. Phase sensitive amplification with a wide phase sensitive dynamic range of 20 dB was achieved using degenerate parametric amplification in a periodically poled LiNbO(3) (PPLN) waveguide. The phase regeneration effect was examined for a degraded signal by means of constellation analyses and bit-error rate measurements. The in-line PSA also operated successfully as a repeater amplifier in a 160 km fiber link without a power penalty. Finally, we demonstrate the regeneration of non-linear impairments induced by fiber non-linearity.

Comparative performance testing of SOA wavelength conversion techniques for future all-optical systems

Wavelength conversion employing semiconductor optical amplifiers (SOAs) is currently one of the most attractive and promising wavelength conversion techniques for future all-optical systems. This paper investigates the comparative performances of the three most popular SOA wavelength conversion techniques; cross-gain modulation (XGM), cross-phase modulation (XPM) and four-wave mixing (FWM). The FWM wavelength converter is analyzed for two types of source; a CW and a novel spectrum-sliced source. All performances are analyzed in terms of shifted wavelength conversion efficiency, Q-factors and converted signal powers. The converters are modeled and simulated using OptSim software. It was found that XGM yields the highest conversion efficiency of 17dB, followed by XPM having 9dB. The FWM wavelength converter had the lowest conversion efficiency, around −0.7dB and −5.0dB for CW and spectrum-sliced sources respectively.

Analyses of semiconductor optical amplifier (SOA) four-wave mixing (FWM) for future all-optical wavelength conversion

Four-wave mixing (FWM) in semiconductor optical amplifiers (SOAs) is currently one of the most attractive and promising wavelength conversion techniques for the all-optical future, and offers numerous advantages to the system designer. This paper investigates the performance of a 2.5Gb/s SOA-based FWM wavelength converter system, in terms of its shifted wavelength conversion efficiency and optical signal-to-noise ratio (OSNR), for both up and down conversions. The converter is modeled and simulated using OptSim software, by varying the probe signal wavelength and power. It was found that the conversion efficiency and OSNR of the converted signal both decreased at large detuning wavelengths. Similarly, higher total SOA input powers worsened the conversion efficiency, but steadily improved the OSNR.

Photorefractivity of zirconium-doped lithium niobate crystals

Polarization-independent all-optical wavelength converters (AOWCs) enable dynamic signal routing, wavelength reuse, path protection, and restoration.1 These features will be of utmost importance in future generation, high bit-rate optical communication networks. An efficient AWOC—operating on a 100Gb/s phase-modulated polarization-multiplexed signal at 1550nm—was recently realized by exploiting the cascade of two nonlinear optical processes in a lithium niobate (LN) waveguide.2 This cascading technique for wavelength conversion is only effective if the LN crystals are prepared with alternating up and down domains (i.e., periodical poling) of appropriate periodicity. Currently, LN crystals offer the best performance in nonlinear devices, but their applicability is limited by the photorefractive effect, which is a change of refractive index under strong illumination. The standard growth process of LN produces lithium-deficient (i.e., congruent) crystals. The presence of defects in the congruent crystals gives rise to photorefractivity, which is detrimental to the efficiency of nonlinear interactions. To avoid this, one can operate the LN-based wavelength converters at temperatures above 100iC.2 Since this is impossible for most in-field applications, crystals with negligible photorefractivity must be developed. Here, we explore the use of zirconium-doped congruent LN crystals (Zr:LN) for AOWC and other optical devices.3 Photorefractivity can be reduced by employing stoichiometric LN or magnesium ion (Mg2C)-doped LN.4 However, neither approach is fully satisfactory because it is often difficult to grow large crystals of high optical quality. Also, there are Figure 1. Birefringence variation (i n) induced on lithium niobate crystals, as a function of the zirconium (Zr) dioxide doping concentration, at pump-beam intensities of 300 ( ), 600 (N), 900 ( ), and 1200 ( ) W/cm2.

Fiber-optic Cherenkov radiation in the few-cycle regime

Fiber-optic Cherenkov radiation has emerged as a wavelength conversion technique to achieve isolated spectrum in the visible wavelength range. Most published results have reinforced the impression that CR forms a narrowband spectrum with poor efficiency. We both theoretically and experimentally investigate fiber-optic Cherenkov radiation excited by few-cycle pulses. We introduce the coherence length to quantify the Cherenkov-radiation bandwidth and its dependence on propagation distance. Detailed numerical simulations verified by experimental results reveal three unique features that are absent when pumped with often-used, long pulses; that is, continuum generation (may span one octave in connection with the pump spectrum), high conversion efficiency (up to 40%), and broad bandwidth (70 nm experimentally obtained) for the isolated Cherenkov radiation spectrum. These merits allow achieving broadband visible-wavelength spectra from low-energy ultrafast sources which opens up new applications (e.g. precision calibration of astronomical spectrographs).

Demonstration of the GbE Service in the Converged Radio-Over-Fiber/Optical Networks

In this paper, we demonstrate the full-duplex radio-over-fiber (RoF) system operating in the 60 GHz band and gigabit Ethernet services in the integrated RoF/optical network architecture. The proposed full-duplex 60 GHz RoF system incorporates the centralized photonic upconversion, using the fiber-optic wavelength conversion technique and the envelope detection/direct optical modulation techniques in the 60 GHz band. The RoF system comprises physical link of a 34 km fiber between the central station and the base stations (BSs) with the 5 m aerial distance between the BS and the customer unit for end-user access. The analog performance of the photonic upconversion function are measured and characterized to map the ranges of optical conditions for stable operation, the modulations depth and the spurious-free dynamic range (SFDR). The SFDR above 80.0 dB.Hz2/3 is obtained for the probe wavelength ranged from 1540 to 1555 nm at the bias voltage of -0.8 V. The optimum modulation depth is shifted from -1.0 to -0.5 V correspond to the probe wavelength from 1560 to 1530 nm. The downlink bit-error-rate performance shows direct relationship with its modulation efficiency changes for bias voltages and pump wavelengths.

Wavelength conversion technique based on self phase modulation in highly nonlinear microstructure fiber

A wavelength converter based on the self phase modulation (SPM) effect in highly nonlinear microstructure fibers (MFs) is proposed. The core diameter and the pitch of the fiber are 2.05 μm and 5.0 μm, respectively, and the diameter of the airholes in the fiber cladding is 4.50 μm. The calculating nonlinear coefficient is 112.2 W−1km−1 and it is 11 times higher than that of a conventional dispersion-shift fiber and 56 times higher than that of a conventional single-mode fiber. The length of the fiber is 100 m. The core area of the microstructure fiber is 3.3 μm2. The self phase modulation effect is enhanced in the highly nonlinear microstructure fiber due to the very small fiber core area, and then the efficiency of the wavelength conversion is also improved. The wavelength conversion over ±4 nm is obtained with a good efficiency.

A Theoretical and Experimental Study on Modulation-Format-Independent Wavelength Conversion

Modern optical networks are adopting advanced modulation formats. Future dynamic optical networks will benefit from all-optical wavelength conversion and signal regeneration techniques in support of multiple modulation formats. This paper presents a concept for a modulation-format-independent wavelength conversion technique based on an optical hybrid and an in-phase/quadrature (IQ) wavelength converter. This technique has the potential for wavelength conversion and signal regeneration of multiple modulation formats. This paper also discusses the signal distortions and noises in the semiconductor optical amplifier based IQ wavelength converter. A proof-of-principle experiment shows the wavelength conversion results of multiple modulation formats. Further, this paper presents the signal regeneration of a return-to-zero quadrature-phase-shifted-keying signal through simulation.

Numerical analysis of four-wave-mixing based multichannel wavelength conversion techniques in fibers

We numerically investigate four-wave-mixing (FWM) based multichannel wavelength conversion for amplitude-modulated signals, phase-modulated signals, together with mixed amplitude and phase modulated signals. This paper also discusses the influence of stimulated Brillouin scattering (SBS) effects on high-efficiency FWM-based wavelength conversion applications. Our simulation results show that DPSK signals are more suitable for FWM-based multichannel wavelength conversion because the OOK signals will suffer from the inevitable data-pattern-dependent pump depletion. In future applications, when the modulation format is partially upgraded from OOK to DPSK, the influence of OOK signals on the updated DPSK signals must be considered when using multichannel wavelength conversion. This influence becomes severe with the increase of OOK channel number. It can be concluded that DPSK signals are more appropriate for both transmission and multichannel wavelength conversion, especially in long haul and high bit-rate system.

Deep UV light generation by a fiber/bulk hybrid amplifier at 199 nm

A high-pulse-repetition-frequency (PRF) pulsed light source in the deep ultraviolet region has been realized by a multiple wavelength conversion technique using a hybrid fiber/bulk amplifier system. Output of 199 nm with a power of 50 mW was achieved at 2.4 MHz PRF. The 1 microm amplifier consisted of a Yb-doped fiber amplifier and a Nd-doped YVO(4) amplifier. A 1.5 microm fiber master-oscillator power amplifier was employed as the other fundamental source. The amplifiers exhibited good amplification properties in pulse energy, polarization extinction ratio, and spectrum for nonlinear wavelength conversion.