Uniform Channel Spacing Research Articles

Twelve-channel LAN wavelength-division multiplexer on lithium niobate

Abstract A twelve-channel local-area-network (LAN) wavelength-division multiplexing (LWDM) filter is proposed and demonstrated with a uniform channel spacing of 4.5 nm (800 GHz) in the O-band of 1270–1330 nm by using x-cut lithium-niobate-on-insulator (LNOI) photonic waveguides for the first time. The present LWDM filter consists of twelve single-channel bandpass filters based on multimode waveguide gratings (MWGs) assisted with a TE0/TE1 mode (de)multiplexer. In particular, two stages of MWGs in cascade are introduced for each single-channel bandpass filter, in order to achieve high sidelobe suppression ratios, thus reducing interchannel crosstalk. For the fabricated twelve-channel LWDM filter, all the channels have very excellent box-like spectral responses with low excess losses of ∼0.6 dB, broad 1-dB bandwidths of ∼2.9–3.4 nm (which is close to 75 % of the channel spacing), and ultra-low interchannel crosstalk of <−40 dB in experiments. In addition, the present device is highly tolerant to the random variations of the etching depth (±20 nm) and the grating waveguide width (±20 nm) of the LNOI photonic waveguides, showing great potential for high-capacity WDM systems.

A photonic crystal based de-multiplexer with uniform channel spacing

Abstract Having uniform channel spacing is very important for all optical communication networks. In spite of its importance designing optical de-multiplexer with uniform channel spacing seems to be very complicated. In this paper we proposed an all optical de-multiplexer with uniform channels spacing. Four high quality factor ring resonator were used for designing the desired structure. In the proposed structure the output channels are at 1555.2, 1556.2, 1557.2 and 1558.2 nm. The channel spacing for all of the adjacent channels are 1 nm. Also for the final structure the quality factor values vary from 7758 to 15,582.

A Novel Hybrid Channel DWDM Demultiplexer Using Two Dimensional Photonic Crystals Meeting ITU Standards

In this paper, a six channel DWDM demultiplexer based on Two Dimensional Photonic Crystal (2D PC) design is proposed to split the 25GHz, 50GHz, and 100GHz channels in a single demultiplexer. The functional parameters of the demultiplexer such as, normalized output efficiency, Q factor, crosstalk and channel spacing are investigated for each channel. The demultiplexer consists of three hexagonal cavities, seven waveguides and a channel drop cavity. The proposed demultiplexer drops the narrow spectral linewidth with the idea of raising the number of rods between bus waveguide and drop waveguide. The operating wavelength range of the demultiplexer is ranging from 1550 nm–1560 nm. The demultiplexer provides high transmission efficiency, high Q factor, uniform spectral linewidth and uniform channel spacing to meet ITU-T G 694.1 DWDM standard. The size of the device is about 363.52 μm2, which is within the fabrication tolerance and highly desirable for Photonic Integrated Circuits (PICs).

All fiber multiwavelength Tm-doped double-clad fiber laser assisted by four-wave mixing in highly nonlinear fiber and Sagnac loop mirror

A four-wave mixing (FWM) based multi-wavelength laser based on a double-cladding thulium-doped fiber laser (DC-TDFL) is proposed and demonstrated. A highly nonlinear fiber (HNLF) in conjunction with a Sagnac loop mirror formed by polarization maintaining fibers (PMFs) is used to induce the FWM effect as well as to mitigate gain-competition in the DC-TDFL. This increases the number of lasing wavelengths that can be generated. Approximately 35, 55, and 68 stable lasing lines are achieved within 10 dB, 20 dB, and 28 dB bandwidths by adjusting the polarization controllers. A uniform channel spacing of 0.38 nm is obtained with minimal wavelength drifts and power fluctuations of 0.056 nm and 2.8 dB. This is, to the best of the author’s knowledge, the first demonstration of large numbers of lasing channels in the 1.97μm wavelength region from a DC-TDFL.

Effect of Channel Spacing on the Design of Mixed Line Rate Optical Wavelength Division Multiplexed Networks

Abstract The ever increasing heterogeneity and growing traffic volume has resulted in significant innovations and paradigm shifts within the telecom backbone networks. In order to cost-effectively respond to the diverse variety of traffic requirements having heterogeneous service demands, wavelength division multiplexed (WDM) optical networks have adopted the mixed line rate (MLR) strategy. In MLR networks, many wavelength channels with various line rates can co-exist within the same fiber which, however, raises many important design issues; one of them being the choice of the channel spacing. The quality of signal is affected by the channel spacing in terms of the bit-error rate (BER), which in turn affects the maximum optical reach of the lightpaths that depends on the line rates. In regard to the aforementioned, different methods can be adopted in order to set the width of the channel spacing, viz., (a) choice of a 50 GHz uniform fixed channel spacing specified by the ITU-T grid, (b) exploring various channel spacing values for different line rates so as to optimize the usage of the fiber spectrum, or (c) seek for an optimal value of the channel spacing which results in the minimum network cost. In the current work, we evaluate the MLR network cost for various channel spacings; hence, we find an optimal value of the channel spacing that leads to the minimum MLR network cost. The simulation results reveal that, for a MLR network, even with the assumption of uniform channel spacing, optimal values of the channel spacing for a minimum cost network can be identified.

Monolithically Integrated Four-Channel DFB Semiconductor Laser Array With an Equivalent-Distributed Coupling Coefficient

An equivalent-distributed coupling coefficient (EDCC) distributed feedback (DFB) semiconductor laser is proposed, and a four-channel EDCC DFB laser array is experimentally demonstrated. In this paper, the EDCC grating profile is realized by varying the duty cycle of a certain subsection of the whole sampled Bragg grating (SBG) along the laser cavity, instead of the true DCC structure obtained by changing the height of the uniform grating pitch. Moreover, the EDCC grating array can be designed by stepping the sampling period of the SBG and fabricated by combining the conventional holographic exposure with a micrometer-level photolithography on the same wafer. The experimental results show that the uniform channel spacing in the array has been obtained and that the residual of the lasing wavelengths after linear fitting changes in the scope of -0.078 and 0.048 nm. Each laser has good single longitudinal mode operation with the minimum side-mode suppression ratio (SMSR) of about 47.65 dB and the average SMSR of 49.83 dB under the same injection current of 80 mA.

Integrated reconfigurable microring based silicon WDM receiver for on-chip optical interconnect

We demonstrate an integrated reconfigurable wavelength division multiplexing receiver on the silicon-on-insulator (SOI) platform. The receiver is composed of a 1 × 8 thermally tunable microring resonator filter and Ge–Si photodetectors. With low thermal tuning powers the channel allocation of the receiver can be reconfigured with high accuracy and flexibility. The thermal tuning efficiency is approximately 8 mW nm−1. We show eight-channel configurations with channel spacing of 100 GHz and 50 GHz and a configuration in which all eight channels cover an entire free spectral range of the ring with uniform channel spacing of 1.2 nm. Each channel can receive high-quality signals with a data rate of up to 13.5 Gb s−1; thus an aggregate data rate higher than 100 Gb s−1 can be achieved.

Independently Tunable Multichannel Fractional-Order Temporal Differentiator Based on a Silicon-Photonic Symmetric Mach–Zehnder Interferometer Incorporating Cascaded Microring Resonators

A multichannel fractional-order temporal differentiator with independently tunable differentiation order based on an integrated silicon-photonic symmetric Mach-Zehnder interferometer consisting of cascaded microring resonators (MRRs) is designed, fabricated, and experimentally demonstrated. By controlling the radii of the MRRs, a multichannel spectral response with uniform channel spacing is obtained, which is used to function as a multichannel temporal differentiator with multiple subdifferentiators. The differentiation order of each subdifferentiator is independently tunable by optically pumping the corresponding MRR, which leads to the phase change in the spectral response due to the two-photon absorption induced nonlinear effect. A five-channel temporal differentiator with a channel spacing of 0.49 nm is fabricated on a silicon-on-insulator chip using a CMOS-compatible process with 193-nm-deep ultraviolet lithography. Independent tuning of the differentiation orders of the subdifferentiators is experimentally demonstrated.

Uniformly spaced λ/4-shifted Bragg grating array with wafer-scale CMOS-compatible process

We report on an integrated λ/4-shifted Bragg grating array using a wafer-scale complementary metal-oxide semiconductor (CMOS) compatible process with silicon-nitride waveguides. A sidewall grating was used to simplify the fabrication process, and a sampled Bragg grating with equivalent phase-shift structure was employed to achieve an accurate λ/4 phase shift. A four-channel λ/4-shifted Bragg grating array with highly uniform channel spacing was demonstrated with a measured channel spacing variation below 10pm (1.25GHz). The high channel-spacing uniformity and the CMOS-compatibility of the demonstrated device hold promise for integrated distributed feedback laser arrays for various silicon photonic applications.

Compact Optical Add-Drop Multiplexers With Parent-Sub Ring Resonators on SOI Substrates

A four-channel integrated optical add/drop multiplexer is experimentally demonstrated on a silicon-on-insulator substrate. With the help of a parent-sub microring resonator structure, compact footprint, large free spectral range, and uniform channel spacing are achieved simultaneously. Through controlling the resonance matching between the parent and sub-rings through thermo-optic effect, each channel can be switched independently between the states of dropping and passing through. The thermal tuning efficiency is as high as 0.27 nm/mW. Typically, for dropping state, all four channels can be de-multiplexed to the drop ports with 2 dB drop loss, 18 dB through port extinction, and less than -20 dB channel crosstalk.

Integrated optical add-drop multiplexer based on a compact parent-sub microring-resonator structure

A compact parent-sub microring-resonator structure for highly integrated optical add-drop multiplexer (OADM) is proposed and demonstrated by numerical simulation. Due to Vernier effect, large FSR can be obtained by cascaded microrings with relatively large diameter. Furthermore, nearly uniform channel spacing is achieved due to employment of multiple resonances of the parent ring. As a representative example, a 4-channel OADM is simulated. Box-like response with flat passband is obtained by optimizing coupling coefficients. Add-drop crosstalk of −15dB, drop loss of near 0dB, and adjacent channel crosstalk of −25dB can be observed from the calculated transmission spectra. The reconfigurability, loss tolerance as well as the relation between bandwidth and crosstalk are also discussed.

Mesoporous vanadium oxide as catalyst for liquid-phase selective oxidation of diphenylmethane to benzophenone

The mesoporous vanadium oxide (MVO) was prepared from the surfactant cetyltrimethylammonium bromide along with benzyl alcohol as co-surfactant. It was found that the presence of benzyl alcohol in the synthetic mixture was essential to the formation and stability of MVO material. Characteristic mesoporous structure with uniform channel spacing as well as large surface area and pore volume of MVO sample were identified by XRD, SEM, TEM, and N2 sorption techniques. The structure of vanadium–oxygen framework was explored using FT-IR and 51V MAS NMR spectroscopy; the MVO sample possessed distorted tetrahedron structure. Results from TPR studies indicated the easier reducibility of MVO as compared to bulk V2O5. In the liquid-phase selective oxidation of diphenylmethane to benzophenone in acetic acid as solvent, the MVO catalyst exhibited remarkably better catalytic performance than bulk V2O5; at 60 °C, the conversion and benzophenone selectivity reached 39.6 and 96.7% after 1 h reaction time, with a catalyst turnover frequency of 24.2 h−1. These superior results were properly correlated to the physico-chemical properties of MVO catalyst.

Over-10 000-channel 2.5 GHz-spaced ultra-dense WDM light source

Over-10 000-channel multi-carriers with uniform channel spacing of 2.5 GHz are generated from a supercontinuum (SC) multi-carrier source, which uses two parallel SC conversion sections. More than 3100 channels in the C+L-bands are confirmed to offer Q-factors sufficient for GbE transport.

Free-space optical mesh-connected bus networks using wavelength-division multiple access

A novel optical free-space mesh-connected bus interconnect network architecture is proposed. A mesh-connected bus [IEEE Trans. Comput. C-30, 264-273 (1981)] is known to have the capability of interconnecting, with a three-stage switching, N nodes with a power distribution loss proportional to √N and is therefore advantageous for networking a large number, say over 1000, of communicating ports. Based on conventional space-invariant optical components in a compact and efficient geometry, the proposed optical mesh-connected bus system concept can be used to build either free-space optical interconnect links for parallel processing applications or central switching systems for local or global lightwave communication networks. The proposed architecture lends itself to networking under both the wavelength-division multiple access and other multiple-access environments. In this paper, based on the wavelength-division multiple-access environment, various optical system implementation and performance issues are discused and parameters are analyzed. It was found that by use of a reasonably compact three-dimensional free-space volume, more than 100,000 dispersion-limited communication nodes at a uniform channel spacing of 0.75 nm can be linked with a moderate power distribution loss of 28 dB. Some preliminary optical wavelength-division multiple-access mesh-connected bus experiments based on a 27 × 27 panchromatic optical source array were performed to confirm the operational principle of the proposed concept.