dB Coupling Research Articles

A structure-simplified and cost-effective coherent receiver for high splitting downstream transmission in next-generation PONs

Abstract In this paper we demonstrate a structure-simplified and cost-effective coherent receiver scheme for high splitting downstream transmission in next generation passive optical networks (NG-PONs). In such scheme, the simple 3dB coupler is used to replace 9 0 0 optical hybrid and the electrical local oscillator (LO) is utilized to down-convert signal, and there by only one balanced photodiode (BPD) is required for each polarization. Hence the cost is reduced effectively for the high splitting PON downstream transmission scenario. The comprehensive numerical simulation results show that the receiver sensitivity for both 14G Baud PM-QPSK and PM-16QAM system is comparable to that of the conventional coherent receiver using 9 0 0 hybrid. Furthermore, the effect of fiber nonlinearity on maximum power budget performance is investigated. In addition, the high receiver sensitivity of the scheme is also experimentally validated for PM-QPSK and PM-16QAM system under the scenario of 14G Baud BtB, 20km and 40km standard single-mode fiber (SSMF) transmission. The coexistent advantages of low-cost and high receiver sensitivity make the proposed scheme an attractive candidate for NG-PONs.

Novel rat‐race coupler of arbitrary power division design using resonant substrate integrated waveguide cavity

AbstractThe contribution of this letter is to propose a novel rat‐race hybrid coupler of arbitrary power division design. The rat‐race coupler's arbitrary power division design is approached by using a resonant square substrate‐integrated waveguide (SIW) cavity. The employed SIW cavity is operated under the resonance of the combined TE102 and TE201 modes. Due to the nature of the square cavity, these two modes are termed degenerate modes which possess the same resonance frequencies but exhibit distinct field distributions. Theoretically, the cavity can be excited by an arbitrary combination of these two degenerate modes, and each of the modes' power is solitarily extracted by an SMA probe located at an adequate position. The microstrip together with the perpendicularly oriented slot are used to resonate the cavity with a designated combination of the degenerate modes. Sample experiments are conducted on 3 dB and 10 dB coupling designs with the circuits' performance evaluated by the coupling precision, isolations, and phase imbalances.

Thermally tunable ultracompact Fano resonator on a silicon photonic chip

A thermally tunable ultracompact Fano resonator on a silicon photonic chip is reported. The Fano resonator is implemented by using an add-drop microdisk resonator (MDR) with the through and drop ports connected by two waveguides and combined via an adiabatic 2×2, 3dB coupler to form a Mach-Zehnder interferometer (MZI). Due to the resonant mode interference between the MDR and the MZI, a Fano resonance with an asymmetric line shape resulted. A p-type-doped microheater is incorporated in the MDR to achieve thermal tunability. By tuning the direct current (DC) voltage applied to the microheater, the Fano resonance is tuned. The proposed Fano resonator is designed, fabricated, and characterized. Measurement results show that a Fano resonance with an extinction ratio of 30.2dB and a slope rate of 41dB/nm is achieved. When the microheater is tuned by tuning the DC voltage with a power from 0 to 22.9mW, the Fano line shape is largely tuned with the Fano parameter q tuned from negative to positive and a maximum wavelength shifting as large as 15.97nm. Thanks to its ultracompact configuration, and strong and fast tunability with low power consumption, the integrated Fano resonator holds a high potential for applications such as on-chip optical switching and sensing.

Beam‐ and polarisation‐reconfigurable SIW ring‐slot antenna array

A beam- and polarisation-reconfigurable substrate integrated waveguide (SIW) ring-slot antenna array is proposed in this study. The 2×2 ring-slot antenna array can generate beams in four different directions in two orthogonal linear polarisations (LPs). This is achieved by a feeding network consisting of four 90° SIW 3 dB couplers arranged in a multilayer structure for a compact antenna size of 131.6 mm × 65.8 mm × 4.9 mm. The antenna elements' LP plane is controlled by PIN diodes, switched by a DC bias network integrated on the antenna substrate. The proposed antenna array is designed for the 5.8 GHz industrial, scientific and medical (ISM) frequency band and verified by measurements. Experimental results validate good impedance matching over the entire frequency band as well as the beam and polarisation reconfigurability.

Wideband arbitrary phase‐difference coupled‐line coupler with tight coupling coefficient and small phase variation

In this study, a planar arbitrary phase-difference coupled-line coupler having wide bandwidth, tight coupling coefficient, and small phase variation are proposed. The proposed coupler consists of two quarter-wavelength coupled-line sections connected with two different transmission lines. Moreover, the interconnection transmission line can be designed as a small phase variation phase shifter with the introduction of a shorted stub. The detailed theoretical analysis is provided to illustrate the design concept. The circuit parameters of this novel arbitrary phase-difference coupler can be easily determined by the derived closed-form equations. For verification, two 3 dB couplers with 45°/135° and 60°/120° phase differences are fabricated and measured. The 45°/135° coupler achieves 34.2% fractional bandwidth for 45° phase difference with 2° phase variation and 36.3% fractional bandwidth for 135° phase difference with 3.4° phase variation. Moreover, the 60°/120° coupler achieves 30% fractional bandwidth for 60° phase difference with 0.9° phase variation and 32.9% fractional bandwidth for 120° phase difference with 1.5° phase variation.

Design and development of 2 kW, 3 dB hybrid coupler for the prototype Ion Cyclotron Resonance Frequency (ICRF) system

AbstractDesign and development of 2 kW, 3 dB tandem hybrid coupler for the frequency range of 155–225 MHz has been presented in this paper. The developed 3 dB coupler is to be used in a prototype of Ion Cyclotron Resonance Frequency (ICRF) system of Tokamak, which has been developed to test the resilience of ICRF network during continuously variable RF load excursions. The 3 dB coupler divides the RF power between two antennae of the prototype and protects the RF source by coupling of reflected power to the isolated port. The developed coupler shows excellent coupling flatness of −3 ± 0.3 dB over 38% of fractional bandwidth and also provides voltage standing wave ratio (VSWR) <1.3, isolation better than 32 dB and return loss better than 25 dB in full band. The presented work establishes a technique which can be useful for the development of high-power hybrid coupler in the range of high frequency (HF), very high frequency (VHF) and ultra high frequency (UHF).

Tightly Coupled Directional Coupler Using Slotted-Microstrip Line

This paper presents the theory and implementation of a novel microstrip directional coupler (DC) with a high coupling coefficient that can achieve the value of 0 dB. The coupling region is a slotted-microstrip line that supports two modes, even and odd. The geometry of the slotted-microstrip line facilitates the phase velocity compensation, which improves the isolation and directivity. A 3-dB coupler is fabricated and characterized. Measurements and electromagnetic simulations are in a good agreement with the theoretical predictions. They show that the proposed DC has 52% ±1 dB coupling coefficient fractional bandwidth centered around 2.4 GHz with isolation and return loss better than 25 dB.

Compact broadband silicon 3 dB coupler based on shortcuts to adiabaticity.

We proposed and experimentally demonstrated a compact, broadband, and low-loss-mode-evolution-based 2×23 dB coupler on a silicon-on-insulator platform. The waveguide widths and separations of the coupler were tapered in an optimal manner using the shortcuts to the adiabaticity method. The coupler, with a ∼70 μm total length and 200nm feature size, exhibited <0.3 dB measured excess loss over a broadband wavelength range from 1500 to 1600nm. Balanced and unbalanced Mach-Zehnder interferometers fabricated for validation showed extinction ratios larger than 27 and 23dB, respectively, over a 100nm bandwidth. The extracted splitting ratio was between 0.48 and 0.52.

Q‐switched and mode‐locked ytterbium‐doped fibre lasers with Sb 2 Te 3 topological insulator saturable absorber

Q-switched and mode-locked fibre lasers have been successfully demonstrated in ytterbium-doped fibre laser cavity by taking an advantage of the optical absorption of antimony telluride (Sb2Te3) material. The Sb2Te3 was embedded into polyvinyl alcohol to function as a saturable absorber (SA). A Q-switching pulses train was obtained by incorporating the SA into the laser ring cavity configured with 3 dB coupler. The Q-switching pulse repetition rate increases from 24.4 to 55 kHz as the pump power is increased from the threshold of 75.4–96.2 mW. The maximum pulse energy of 252.6 nJ is obtained at 82.3 mW pump power. On the other hand, by changing the output coupler to 10 dB coupler, a stable self-started mode-locking operation was then generated at pump power range from 47.8 to 89.4 mW with a fixed repetition rate of 24.2 MHz. At 89.4 mW pump power, the maximum output power and pulse energy are obtained to be around 18.6 mW and 0.8 nJ, respectively. The authors results display that the Sb2Te3 material could also be developed as an effective SA for both Q-switched and mode-locked fibre lasers.

Temperature and liquid refractive index sensor using P-D fiber structure-based Sagnac loop.

A cost-efficient P-D fiber structure-based Sagnac loop sensor is proposed and experimentally demonstrated for measuring temperature and liquid refractive index (RI). The P-D structure is fabricated by fusion splicing a section of polarization-maintaining fiber (PMF) to a piece of multimode D-shaped optical fiber (MMDF). Then the P-D structure is built into a Sagnac loop using a 3dB coupler. The temperature and RI characteristics of the sensor are investigated experimentally. The results show that two resonant dips have different spectral responses of temperature and RI, which indicate that the sensor can realize simultaneous temperature and RI measurement. The high sensitivities of -1.804nm/°C and -131.49nm/RIU are achieved. The obtained resolutions of temperature and RI of the proposed sensor can reach 0.01°C and 2.46 × 10-4RIU, respectively. The proposed sensor has the potential application in biological and chemical fields.

Broadband polarization-insensitive optical switch on silicon-on-insulator platform.

A novel configuration for realizing a polarization-insensitive optical switch on silicon-on-insulator of 340nm-thick top-silicon layer is demonstrated, using submicron sized waveguides. The device is based on the Mach-Zehnder interferometer structure. By carefully designing the 3dB couplers and the delay-line waveguides in the device, it is possible to achieve a similar switching behavior for all polarizations. Theoretical analyses indicate that extinction ratios of better than -25dB and insertion losses of better than -0.6dB can be obtained simultaneously for transverse-electric and transverse magnetic polarized modes in the whole C-band. Experimental results also confirm the polarization-insensitive property of the proposed optical switch. Extinction ratios of about -15dB are measured for both polarizations.

Wideband Directional Coupler for Millimeter Wave Application based on Substrate Integrated Waveguide

Recently, Substrate Integrated Waveguide (SIW) techniques have been noticed for millimeter wave devices in microwave applications. In this paper, we are developing a wide band directional 3 dB coupler with a phase of 90̊ phase delay in the range of 30-40 GHz based on periodic vias and multi hole structure. For achieving this wide bandwidth multi-section coupler is designed based on the theoretical modeling and the simulation result is compared with HFSS and CST with two different numerical methods show good performance with low insertion and return loss, broad operational bandwidth and high isolation. A fractional bandwidth is about 28.5 %.

Design optimization and tolerance analysis of a spot-size converter for the taper-assisted vertical integration platform in InP.

We report on the design optimization and tolerance analysis of a multistep lateral-taper spot-size converter based on indium phosphide (InP), performed using the Monte Carlo method. Being a natural fit to (and a key building block of) the regrowth-free taper-assisted vertical integration platform, such a spot-size converter enables efficient and displacement-tolerant fiber coupling to InP-based photonic integrated circuits at a wavelength of 1.31μm. An exemplary four-step lateral-taper design featuring 0.35dB coupling loss at optimal alignment of a standard single-mode fiber; ≥7 μm 1dB displacement tolerance in any direction in a facet plane; and great stability against manufacturing variances is demonstrated.

Research on tunable multiwavelength fiber lasers with two-section birefringence fibers and a nonlinear optical loop

Two types of tunable multiwavelength fiber lasers based on two-section polarization maintaining fibers (PMFs) cascaded/in parallel and nonlinear optical loop are proposed and experimentally demonstrated. Two-section cascaded PMFs and two polarization controllers (PCs) form the two-stage Lyot filter, which can generate comb spectrum to achieve multiwavelength output. When two sections of PMFs are in parallel, PCs in two paths are adjusted to change the beam’s polarization to suppress the light of one branch, and then the light of the other branch passes through the cavity. Additionally, a nonlinear optical loop acts as an intensity-dependent component, which can suppress the mode competition to maintain a stable output of multiwavelength lasing. The nonlinear optical loop is made by a 3 dB coupler, a PC3, and a 200 m high nonlinear fiber. Two types of tunable multiwavelength fiber lasers can achieve tuning of the channel space and the number of lasing wavelengths by adjusting PC1 and PC2. The channel space of the multiwavelengh laser can be tuned at nearly 0.4, 0.68, and 0.92 nm. Meanwhile, the spectral range of multiwavelength lasing can be controlled by PC3 in the nonlinear optical loop, and the tuning range of two multiwavelength lasers is about 2.28 and 1.45 nm, respectively.

A wideband 3 decibels arbitrary phase difference branch line coupler

AbstractA wideband 3 dB branch line coupler with arbitrary phase difference between output ports is proposed. The wideband properties in both amplitude and phase are achieved by utilizing λ/4 coupled line sections. By designing different even and odd impedance of the coupled line matched in different ports, small phase imbalance can be achieved. For validation, two 3 dB couplers with different phase differences (60° and 120°) were designed and fabricated. They were measured to exhibit wide bandwidths of 40.2% and 44.6%, respectively.

Efficient Wireless Power Transfer System Integrating With Metasurface for Biological Applications

Wireless power transfer (WPT) is a key technique for many existing and emerging applications in biomedical devices. This paper presents a novel implantable magnetic coupling resonate WPT system by integrating with metasurface for biological applications. The receiver element is implanted under the skin surface 3 mm and has the dual-band property for transferring power and data telemetry simultaneously. A conformal strongly coupled magnetic resonator coil is used as the transmitting coil to construct the wireless power link. In addition, we integrate the proposed WPT system with negative permeability (MNG) metasurface over the human skin surface as a miniaturized wearable device to improve the WPT efficiency. The property of the MNG and its effect on the WPT efficiency are analyzed. Considering the special implantable environment, various misalignment tolerances between the metasurface and the receiver are discussed to evaluate the coupling response of the proposed WPT system. Finally, the efficient WPT system integrating with MNG has been verified by the experimental measurements, and the measured result shows that 15.7 dB coupling enhancement can be obtained by integrating with the MNG metasurface.

Ultra-fast electro-optic switching control using a soliton pulse within a modified add-drop multiplexer

We have proposed the use of a soliton pulse that propagates within a modified add-drop filter, which is made of a GaAsInP/P material. It is in the form of a Panda-ring resonator, from which a bright/dark soliton pulse is input into a system via an input port. The conversion between bright and dark soliton pulses is introduced at the 3 dB coupler, i.e. the change in phase of π/2. But it is not superimposed each other. The output solitons obtained at the through and drop ports are bight and dark solitons respectively. Both signals can be used to form “ON’ and “OFF” or “1” and “0”, which are useful for the digital bit generation. The switching speed of the system can be improved by employing the two nonlinear side rings. In application, secure output bits can be arranged by using the alternative input solitons or the control ports, where the input bright and dark solitons can be converted into output bits. This means that the output bits can be randomly switched between “1” and “0”, which can be identified by the sender. Moreover, the additional information can be multiplexed via the add port and transmitted in either free space or optical fiber via the whispering gallery mode and through port outputs. Finally, the electro-optic switching can be transferred and the electronic switching by the embedded stacked layers, where the ultrafast switching of light input can lead the ultrafast electrical switching speed. The switching speed of ~ 5 fs and the offset time of ~ 220 fs of the “on” and OFF” are achieved by using the selected ring parameters.

Tri-band MIMO Antenna for WLAN, WiMAX and Defence System &amp; Radio Astronomy Applications

In this paper, an efficacious and impermeable undeviating MIMO consist of 70 x 50 x 0.4 mm3 is used for WLAN, defence system &amp; radio astronomy and WiMAX applications. To keep in order abandoning the reactive connection between the antennas, a neutralizing line is connected between the two symmetrical radiating elements. Another technique to reducing isolation (mutual coupling) between the antennas, four small slits of small size are etched onto to the ground plane. This has resulted in the proposed antenna giving a good bandwidth at the three resonant frequencies of (3.2–3.7 GHz) for Wireless LAN, (5.1–5.6 GHz) WiMAX and (6.7–7.5 GHz) defence system &amp; radio astronomy applications with |S11|&lt; -10 dB and mutual coupling |S12|&lt; -20 dB for the entire operating band. The simulation results and measured results demonstrate that tri-band MIMO antenna is more acceptable for the design in portable device applications.

Tunable erbium-doped fiber laser based on optical fiber Sagnac interference loop with angle shift spliced polarization maintaining fibers

Abstract In this paper, we propose and experimentally demonstrate a tunable erbium-doped fiber laser (EDFL) with Sagnac interference loop with 45° angle shift spliced polarization maintaining fibers (PMFs). In the Sagnac loop, two PMFs with similar lengths. The Sagnac loop outputs a relatively complex interference spectrum since two beams transmitted in clockwise and counterclockwise encounter at the 3 dB coupler, interfere, and form two interference combs when the light transmitted in the Sagnac loop. The laser will excite and be stable when two interference lines in these two interference combs overlap together. Then by adjusting the polarization controller, the wide wavelength tuning is realized. Experimental results show that stable single wavelength laser can be realized in the wavelength range of 1585 nm–1604 nm under the pump power 157.1 mW. The side-mode suppression ratio is not less than 53.9 dB. The peak power fluctuation is less than 0.29 dB within 30 min monitor time and the side-mode suppression ratio is great than 57.49 dB when the pump power is to 222.7 mW.

General architectures for on-chip optical space and mode switching

The optical switches for single-mode operation cannot be directly utilized in optical communication and interconnect systems adopting mode-division multiplexing. In this paper, three general architectures for on-chip optical space and mode switching are proposed, which are optimized for optical space switching, optical space switching plus local optical mode switching, and global optical mode switching, respectively. A silicon thermo-optic 2×2 four-mode optical switch is demonstrated. The minimum and maximum optical link insertion losses are 16.0 and 20.9 dB (including ∼6 dB coupling loss), respectively, in the wavelength range of 1525–1565 nm, while the optical signal-to-noise ratios of the optical links are larger than 15.3 dB. The optical power penalty at a bit error rate of 10−9 varies from 1.0 to 5.6 dB for 40 Gbps data transmission through different optical links. This work provides a systematic solution to on-chip information switching for different physical and mode channels.