Wavelength Division Multiplexing Optical Communication Research Articles

Polymer waveguide tunable transceiver for photonic front-end in the 5G wireless network

A photonic front-end in the 5G wireless network based on wavelength-division multiplexing optical communication requires low-cost tunable transceivers. By exploiting polymer waveguide Bragg-grating technology, we propose a tunable transceiver consisting of an external cavity tunable laser and a tilted grating tunable filter. In particular, a double-reflection tunable filter provides narrower reflection bandwidth and suppresses undesired mode coupling, improving the side-mode suppression ratio (SMSR) and reducing adjacent-channel crosstalk. By introducing perfluorinated polymers with low birefringence, polarization independence, which is a prerequisite for wavelength filter elements, is secured, and 20 dB bandwidth of 0.69 nm, wavelength tunability over 40 nm, and SMSR of 42 dB are achieved.

Physical Layer Encryption for WDM Optical Communication Systems Using Private Chaotic Phase Scrambling

Protecting the security of optical network is a major worldwide challenge. The conventional schemes for securing communications are based on cryptography at the MAC layer and its higher layers, which are facing a great threat with the development of quantum computers. Optical encryption is a promising way for building security on the physical layer of optical communications. In this work, we propose a novel optical encryption scheme for wavelength division multiplexing (WDM) fiber-optic communication systems, by utilizing the private chaotic phase scrambling. Secure transmission of 50 Gbps signal over 50-km standard single-mode fiber is experimentally and numerically demonstrated. The results show that the WDM signal is efficiently encrypted into a noise-like signal, due to the spectral broadening effect of chaotic phase scrambling. Since the processes of encryption and decryption are totally implemented in the optical domain, the proposed scheme can encrypt the entire network traffic with low latency and high speed. Moreover, the proposed encryption scheme is compatible with the existing WDM optical networks, and only one pair of encryption and decryption devices is sufficient to encrypt all WDM channels, thus the scheme can be easily implemented at low hardware cost.

High-efficiency and high-speed germanium photodetector enabled by multiresonant photonic crystal

Abstract High-efficiency and high-speed photodetectors with broadband responses are playing pivotal roles for wavelength-division multiplexing optical communications. Germanium photodetectors on silicon platforms exhibit potential cost advantage due to the compatibility for monolithic integration with silicon-based electronic circuits for signal amplification and processing. In this article, we report a normal incidence, germanium photodetector enabled by guided-mode resonances in photonic crystal, which successfully resolved the compromise between quantum efficiency, wavelength coverage and bandwidth requirement, a drawback usually faced by conventional photodetectors operating at normal incidence. The resonant photonic crystal structure is designed to support multiple resonances in the target wavelength range. With an intrinsic absorption layer thickness of 350 nm, the device achieved a high external quantum efficiency of 50% at 1550 nm, along with an enhancement around 300% for the entire C-band. Using a mesa diameter of 14 μm, the fabricated device exhibited a 3-dB bandwidth of 33 GHz and obtained clear eye diagrams at bit rate up to 56 Gbps. This work provides a promising method to design high-efficiency, high-speed, normal incidence germanium photodetectors for optical interconnect systems.

Switchable and Flexible Comb Filter/Interleaver Based on Ring-Resonators With Tunable Couplers

We demonstrate a switchable and flexible comb filter/interleaver based on ring-resonator (RR) in which the directional couplers are replaced by tunable couplers. The tunable coupler is composed of an even-arm-length Mach-Zehnder interferometer (MZI) with a micro-heater embedded in one of the arms. For the sake of discussion, we convert the heating power of the micro-heater into a pure phase shift value independent of the waveguide material and size. By changing the phase shift value, the filter can be switched between comb filter and interleaver. Meanwhile, the insertion loss ( IL ), full width at half maximum ( FWHM ), extinction ratio ( ER ), and the shape of the response spectrum can also be reconfigured. The switchable and flexible comb filter/interleaver may provide a potential application in dense wavelength division multiplexing (DWDM) optical communication systems.

Theoretical Analysis on Operation Speed of the Circular Defect in 2D Photonic Crystal (CirD) Laser

Herein a circular defect in a 2D photonic crystal (CirD) laser for wavelength division multiplexing (WDM) optical communications is theoretically analyzed. By coupling CirD lasers to a waveguide, a huge communication capacity can be expected. For example, if high‐speed, 50 Gbps laser operations are successfully achieved, WDM devices with 20 CirD lasers could achieve a communication capacity of 1 Tbps. Based on finite‐difference time‐domain (FDTD) simulation results, in this study, both current‐output and high‐frequency characteristics are investigated by solving 2D rate equations, revealing that an excessively high‐quality factor in laser cavities reduces the relaxation‐oscillation frequency. When the photon lifetime is 2 ps, which corresponds to a quality factor of ≈3000, a small threshold current of 5 μA and a high relaxation‐oscillation frequency of 40 GHz can be simultaneously obtained. These results suggest the potential of developing a WDM device using CirD lasers.

White-light color conversion with red/green/violet laser diodes and yellow light-emitting diode mixing for 34.8 Gbit/s visible lighting communication

The visible wavelength-division multiplexing (VWDM) optical wireless communication beyond 30 Gbit/s with a white-light beam mixed by red/green/violet (R/G/V) laser diodes (LDs) and yellow (Y) LED is demonstrated via quadrature amplitude modulation discrete multitone modulation (QAM DMT). To facilitate both high-quality indoor lighting and high-speed optical wireless communication, the R/G/V-LD white-light module incorporates with a Y-LED to provide a high color rendering index (CRI) and encapsulates with a frosted glass to enlarge its divergent angle. By respectively encoding the R/G/V-LDs with the filtered QAM DMT data in a back-to-back case, the total raw data rate as high as 34.8 Gbit/s is achieved by encoded R/G/V-LDs with respective VWDM data rates of 18/7.2/9.6 Gbit/s. To fulfill the demanded CRI and correlated color temperature (CCT) for indoor white-lighting, the yellow LED contributes the yellowish-orange luminescence with flexible CCT and CRI varying from 3952 K to 3031 K and from 0 to 45.9, respectively. A cold white-light carrier at a CCT of 4852 K, CRI of 71.6, and CIE of (0.3652, 0.4942) is also approached by attenuating the red LD power, and such a cold white-light spot with an illuminance of 6800 lux and a divergent solid angle of 0.89 steradian (sr) can support VWDM data transmission at 28.4 Gbit/s.

Impact of hybrid optical amplifier for multitudinous segment for super-dense multiplexing system

In this paper, we have investigated the impact of proposed hybrid optical amplifiers (HOAs) in terms of acceptable values of gain, noise figure and OSNR, respectively. Combinations of RAMAN–EDFA HOA, EDFA–SOA HOA and EDFA have arranged in three segments to maintain the best rating for long-haul 400 × 10 Gbps super-dense wavelength division multiplexing (SD-WDM) optical communication system with channel spacing of 6.25 GHz. Flat gain of 25 dB with least variations of 1.5 dB has archived. Also, noise figure of 3.2 dB has recorded without using any cost influence techniques.

A low-complexity MAP detection for pattern-dependent impairments mitigation in Nyquist-WDM coherent optical systems

In the long-haul Nyquist wavelength division multiplexing (Nyquist-WDM) optical fiber communication systems, pattern-dependent impairments, such as the Nyquist filtering and fiber nonlinearity, have adverse effects on system performance. In this paper, we propose a modified maximum-a-posteriori-probability (MAP) detection based on low-complexity Euclidean distance approximate calculation to reduce the implementation complexity of pattern-dependent impairments mitigation. Comprehensive numerical simulation results show its advantages of comparable performance for pattern-dependent impairments mitigation to conventional MAP detection with lower complexity. Furthermore, the three-carrier 20GBaud/subcarrier coherent polarization-multiplexed 16 quadrature-amplitude-modulation Nyquist-WDM (Co PM 16QAM Nyquist-WDM) optical transmission off-line experiment with 7×100km fiber loops is carried out to validate the performance of the modified MAP detection. Compared with the conventional MAP, the modified MAP attain comparable performance with much lower computational complexity.

32 Channel × 40 Gb/s WDM optical communication system utilizing different configurations of hybrid fiber amplifier

In this paper, a simulation analysis of 40 Gb/s wavelength division multiplexing system of 32 channels is implemented through RZ modulation format by using a different hybrid fiber amplifier (HFA) configurations, namely, serial HFA, parallel HFA, and combined serial–parallel hybrid fiber amplifier (CSP-HFA). The performance of the proposed amplifiers is compared in terms of average gain level, average noise figure, flat gain bandwidth. In addition, quality factor, bit error rate, and eye diagram for the demonstrated 32 channel × 40 Gb/s wavelength division multiplexing optical communication system utilizing different configurations of the hybrid fiber amplifier is compared. The CSP-HFA shows better performance than serial and parallel hybrid amplifiers in terms of wider flat gain bandwidth, higher quality factor, lower bit error rate, and wider and clearer eye opening. Furthermore, CSP-HFA exhibits a flat gain bandwidth of 65 nm with an acceptable average gain of 16 dB and average noise figure of 7 dB.

Investigation of the performance of optical amplifiers for a 96 × 12 Gbps DWDM system using ultrasmall channel spacing

Ultrasmall channel spacing is a key concern for dense optical communication when incorporating a greater number of transmitting channels. In this work, we consider varying channel spacing ranging from 100 to 900 GHz in order to improve the performance of a 96 × 12 dense optical communication system. Analysis is carried out to obtain results in terms of quality factor, gain, cross talk, and eye closure. Power amplification is provided with the aid of an EDFA, Raman optical amplifier, SOA-SOA, and SOA. The EDFA was found to deliver the best results, with a quality factor of 25.5–30 dB, gain of 25.6–29.4 dB, and eye closure of 0.4–0.9 dB. It can thus be concluded that EDFA is the best choice in all aspects of dense wavelength-division multiplexing optical communication under conditions of ultrasmall channel spacing.

Optimization of a C-band Erbium-Doped Fiber Amplifier for Wavelength Division Multiplexing Optical Communications Using 64 Channels

Optimization of a C-band Erbium-Doped Fiber Amplifier for Wavelength Division Multiplexing Optical Communications Using 64 Channels

结构紧凑的双波长连续波掺铒光纤激光器

Multiwavelength erbium-doped fiber lasers can be applied to many fields, such as wavelength division multiplexing optical communication and others attracting considerable attention. To meet the requirements of different applications, we propose a compact dual-wavelength continuous-wave erbium-doped fiber laser based on nonlinear amplifying loop mirror. An all-polarization-maintaining fiber cavity is adopted in which there are only three intracavity devices besides fiber itself:a wavelength division multiplexer, a 2×2 fiber coupler and a fiber reflector. The intensity-dependent loss effect induced by the nonlinear amplifying loop mirror is used to equalize the intensity in the cavity. The input laser with higher power suffers a higher loss than the one with lower power. This feature can be used to suppress mode competition and achieve stable multiwavelength oscillation. With a pump power of 260 mW, dual-wavelength erbium-doped fiber laser can be achieved, with wavelengths of 1 560.5 nm and 1 563.2 nm, respectively. The side-mode suppression ratio is 46.8 dB. As pump power increases, the laser can operate in single-, dual-and triple-wavelength regions in proper order. As the multi-wavelength lasing oscillation is a balance between intensity-dependent loss and mode competition, the intensity change breaks the original balance state, resulting in the change in number and wavelength of lasing lines. This laser is simply structured and easy to operate. It can have applications in many fields.

Saturation in wavelength-division multiplexing free-space optical communication systems

The performance of a wavelength-division multiplexing (WDM) free-space optical (FSO) communication system in a turbulent atmosphere employing optical amplifiers to improve capacity is investigated, in the presence of amplified spontaneous emission noise, scintillation, beam spreading, atmospheric attenuation and interchannel crosstalk. Using on-off keying modulation, Monte Carlo simulation techniques are used to obtain the average bit error rate and system capability due to scintillation and the effect of introducing a power control algorithm (PCA) to the system is investigated. The PCA ensures that at any receiving instant, the same turbulence-free powers are received by all the receiving lenses. The performance of various WDM FSO communication system configurations such as non-amplified systems with an adaptive decision threshold (NOAADT), nonamplified systems with a non-adaptive decision threshold, fixed gain amplified systems with an adaptive decision threshold, fixed gain amplified systems with a nonadaptive decision threshold and saturated gain amplified systems with a non-adaptive decision threshold (SOANADT) are investigated. Results obtained show that the SOANADT is superior to the NOAADT and the PCA is only beneficial in amplified systems.

Reconfigurable and tunable compact comb filter and (de)interleaver on silicon platform

We propose and demonstrate a reconfigurable and tunable chip-scale comb filter and (de)interleaver on a silicon platform. The silicon-based photonic integrated device is formed by Sagnac loop mirrors (SLMs) with directional couplers replaced by multi-mode interference (MMI) assisted tunable Mach-Zehnder interferometer (MZI) couplers. The device can be regarded as a large SLM incorporating two small SLMs which form a Fabry-Perot (FP) cavity. By appropriately adjusting the micro-heaters in tunable MZI couplers and cavity, switchable operation between comb filter and (de)interleaver and extinction ratio and wavelength tunable operations of comb filter and (de)interleaver are achievable by thermo-optic tuning. Reconfigurable comb filter and (de)interleaver is demonstrated in the experiment. The central wavelength shifts of comb filter and (de)interleaver are demonstrated with wavelength tuning efficiencies of ~0.0224 nm/mW and ~0.0193 nm/mW, respectively. The 3-dB bandwidth of the comb filter is ~0.032 nm. The 3-dB and 20-dB bandwidths of the (de)interleaver passband are ~0.225 nm and ~0.326 nm. The obtained results indicate that the designed and fabricated device provides switchable comb filtering and interleaving functions together with extinction ratio and wavelength tunabilities. Reconfigurable and tunable silicon-based comb filter and (de)interleaver may find potential applications in robust wavelength-division multiplexing (WDM) optical communication systems.

Graphene-based Mach–Zehnder nanophotonics interferometer working as a splitter/switch and as a multiplexer/demultiplexer

We developed and are presenting a graphene-based nanophotonic Mach–Zehnder Interferometer (MZI), which can operate as a signal follower, switch and splitter and as a multiplexer/demultiplexer. Due to the excellent electrical/optical parameters inherent to the graphene, we showed that the device we are presenting can works in several different ways, which can not be supported by MZI based on conventional materials. It is worth mentioning that the operations of the device we have developed take into account the electrical/optical parameters of the graphene, which provide greater versatility and efficiency compared to the MZIs manufactured with conventional materials. In addition, these parameters can be controlled via, for example, gate voltage, so that many operations can be performed in parallel, which is also not possible through the use of conventional materials. Due to its manometric dimensions, this MZI can be integrated within photonic integrated circuits, so that we can use this device in dense wavelength division multiplexing optical communications.

Silicon wire waveguide TE0/TE1 mode conversion Bragg grating with resonant cavity section.

Silicon wire waveguide TE0/TE1 mode conversion Bragg grating can be used in wavelength add/drop and polarization rotation Bragg diffraction. The device can implement many filtering functionalities required in wavelength division multiplexing optical communications. In this paper we describe TE0/TE1 mode conversion Bragg grating device incorporating resonant cavity section to obtain narrow transmission wavelength peak. Theoretical calculation agreed with measured wavelength response.

Photonic crystal-based optical filters for operating in second and third optical fiber windows

In this paper, the filtering properties of photonic crystals (PCs) to perform narrow-channel transmission-type filters in second and third optical fiber telecommunication windows have been studied. Filtration of these zero dispersion and low-loss windows have simultaneously been established by utilizing of a triple-cavity transmission-type one-dimensional PC that provides perfect transmittances and narrow-channels at corresponding wavelengths. Such PC-based optical filter can be used in wavelength division multiplexing (WDM) optical communications systems.

A Novel Optical Frequency-Hopping Scheme for Secure WDM Optical Communications

A novel optical frequency-hopping scheme in wavelength-division multiplexing (WDM) systems is proposed to achieve secure communications with high capacity. Frequency hopping is realized by the hopping of digital signals among different channels. In the proposed system, the signal from any source is separated into small segments in the time domain, and the segments are carried by more than one different-wavelength optical carrier. All the optical waves in the proposed WDM system are modulated by signals from two or more sources at different times. The signal from a certain source is also interference to signals from other sources. Hopping, synchronization, de-hopping, and routing are all digitally implemented in field-programmable gate array chips. The system is reconfigurable by software to adapt to different rates. Slow frequency hopping, fast frequency hopping, and intermediate frequency hopping are all available. A demonstration system is designed to support transmission speed from 0 to 10 Gb/s, and a video communication based on it is built to demonstrate the 1-Gb/s optical frequency-hopping system.

Three-channels wavelength division multiplexing based on asymmetrical coupling

In order to realize the wavelength division multiplexing (WDM) device with compact channels and high transmission, a novel three-channel WDM device based on a two-dimensional photonic crystal with a square lattice is proposed. Three parallel line defect waveguides are introduced in this structure to control the propagation of light. Elliptical and rectangular resonators are employed to carry out the selection of light wavelengths by the coupling resonant effects. The point defect cavity is placed at the end of the middle waveguide to further filter the wavelengths. We theoretically analyze the effects of the distances between the resonator and the micro-cavity and between asymmetrical resonators on the light propagation by the finite-difference time-domain (FDTD) method. Three different wavelengths (1560, 1580, and 1620nm) in the communication window range with maximum transmission over 90% are obtained. The findings may provide potential applications in filters, WDM optical communication systems and other optoelectronics devices.

Arrayed waveguide collimators for integrating free-space optics on polymeric waveguide devices.

Array-type optical devices are important for wavelength-division multiplexing optical communication system to achieve small footprint, mass production, and reliability. For fabricating transmitter module in an array configuration, it is difficult to achieve a passive alignment of isolator, collimating lens, and laser diode. To facilitate array isolator integration, a waveguide collimator is proposed in this work by using a low-contrast, large-core polymer waveguide. The diffraction of a guided mode propagating through a free-space region is suppressed by enlarging the guided mode. The fiber coupling loss due to the enlarged mode was overcome by incorporating an adiabatic taper structure. The excess loss of waveguide collimator including the loss through a 400-μm free-propagation region was less than 1.0 dB.