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A high speed InGaAs/InP one-sided junction photodiode (OSJ-PD) with low junction capacitance is presented and investigated for the first time. Compared with the well known uni-traveling carrier photodiode (UTC-PD), the OSJ-PD has the advantages of simpler epitaxial layer structure and lower junction capacitance, while maintaining the characteristics of high speed and high output power. The OSJ-PD is studied by simulation. The performance characteristics of OSJ-PD including internal electric field distribution, energy band diagram, frequency response, photocurrent and junction capacitance, are carefully studied.

This paper offers an approximate, but very convenient and accurate, manner to find the desired strip width for substrate integrated gap waveguide (SIGW) with a given characteristic impedance and the conductor and dielectric attenuation constants, without any complicated manual calculations or time-consuming full-wave simulation and optimization iterations. Moreover, the investigation of the transition between SIGW and microstrip lines will prove that an additional transition structure, such as a conventional microstrip taper, is not required any more at millimeter-wave frequencies for the desired transmission performance. This is a useful feature in circuit design and compactness. Both of the above works will be of great help to realize future feeding networks for SIGW antenna arrays or other types of cost-effective SIGW passive components at high frequencies. Two SIGW prototypes, working at Ka and V bands, are fabricated and offer experimental verifications, which present good agreement with the simulation results.

Over recent years, the memory effect compensated digital pre-distortion (DPD) has been widely used for linearizing wideband radio frequency power amplifiers (RF-PAs). However, with the increase of memory depth, the DPD model becomes more accurate, but the computational complexity of the DPD is significantly increased. In this paper, an approach using the attention mechanism is proposed, which can be used for locating and eliminating the memory terms with a small contribution to the performance of the DPD model so that the complexity of the DPD model is significantly reduced. The attention mechanism is employed to obtain the weighted correlation coefficient matrix of the memory effect. And the memory terms in the DPD model will be retained only if the contributions are high, which are evaluated by ensemble averaging over each diagonal of the weighted correlation coefficient matrix. To verify the applicability of the approach, a three-carrier wideband code-division multiple access signals with a bandwidth of 15 MHz and a single carrier long-term evaluation signal with a bandwidth of 20 MHz are employed for testing two Doherty RF-PAs with an operating frequency of 460 and 1900 MHz. Moreover, the generalized memory polynomial model is used to verify the effectiveness of the proposed approach. The simulation and experimental results show that the modeling accuracy and the DPD linearization performance of the DPD model with and without the memory term reduction are all almost the same, which indicates the effectiveness of the proposed approach.

Inhomogeneous gain broadening in InAs/InP quantum dot (QD) lasers has been attributed to non-uniform QD size distribution. In this work, the interaction of two dots and three dots considering inter-dot distance, tilted position, QD size and surface ratio is investigated in terms of probability density function, eigenvalue, confinement potential of electrons and holes, strain distribution and piezoelectric potential for self-assembled InAs/InGaAsP/InP (001) quantum dots grown with double-capping procedure, by using the accurate two-step strain analysis model. It is found that strain distribution, piezoelectric potential and confinement potential are all changed, leading to optical transition energy changed and emission spectrum shifted. It is also discovered that there is greatly reduced probability density of the ground state electrons and holes in small QDs as well as large deviation in spatial overlap between electrons and holes of small QDs in the probability density distribution of the first excited state, when small QDs are overlapped with bigger QDs. Thus, the biggest InAs QD dominates the photoemission when it is closely surrounded by other QDs.

For emerging 5G fronthaul, broadband radio over fiber (RoF) transmission has been found much more cost-effective than conventional digital fiber transmission. Current digital predistortion (DPD) techniques may not be effective in linearizing broadband RoF links. This work presents a simple envelope-assisted radio frequency (RF)/intermediate frequency (IF) DPD model for linearization of broadband/multiband RoF transmission. The model uses both RF/IF signals and baseband envelopes, resulting in the short-term and long-term memory effect mitigated efficiently even for high signal bandwidth. The model complexity is lower than the existing baseband DPDs and does not increase with the increase of the signal bands. The model is experimentally evaluated in three scenarios: two 20 MHz long-term evolution (LTE) signals spaced by 100 and 40 MHz, and three 20 MHz LTE signals spaced by 50 MHz. It is shown that the proposed DPD results in comparable performance as today's baseband models.

To support enhanced mobile broadband (eMBB) communication, 5G is going to use new radios (NRs) at frequencies above 24.25 GHz in the millimeter-wave (mm-wave) bands with abundant available bandwidths. The photonic generation, modulation and distribution of such ultra-high speed broadband RF signals in the optical domain is more promising compared to the bandwidth limiting electrical technology, however, it requires low noise coherent optical sources. In this paper, we present a highly coherent low noise InP-based p-n block buried heterostructure (BH) C-band InAs/InP quantum dash (QD) passively mode-locked laser (MLL) for photonic aided broadband wireless communication systems. The device features repetition rates of 25 GHz resulting in an optical coherent frequency comb (CFC) with a 6-dB optical bandwidth of around 9 nm providing over 46 channels. Each individual channel of the CFC exhibits an average phase noise and integrated relative intensity noise (RIN) of less than 500 kHz and -130 dB/Hz in the frequency range from 10 MHz to 20 GHz, respectively. Its timing jitter and RF beat-note linewidth between any two adjacent channels are as low as 5.53 fs and 3 kHz, respectively. By using this QD MLL, a photonic aided radio-over-fiber (RoF) broadband quadrature amplitude modulated (QAM) signal wireless delivery at around 25 GHz (K-band) is successfully demonstrated over 2-m free space wireless distance through 25.22 km standard single-mode fiber (SSMF) with a total link capacity of 16Gbit/s and error vector magnitude (EVM) below the standard requirements of 12.5%., Broadband Access Communication Technologies XV, March 6-12, 2021, Online Only, United States, Series: Proceedings of SPIE

A bandpass filtering power divider (FPD) using integrated substrate gap waveguide (ISGW) technology is proposed, which has high selectivity and wide stopband. The filtering power divider includes three-layer substrates. The top layer substrate realizes a perfect magnetic conductor (PMC) using periodic plated vias and metallic patches. It is applied for packaging filter power divider composed of substrate integrated waveguide (SIW) and microstrip to avoid interference and losses induced by external radiation emission and internal radiation leakage. The middle layer substrate generates a gap layer. and the bottom layer substrate etch the slots on the metal plane and place a metal through hole in the middle of the metal layer to generate resonance and transmission zeros, and connect the microstrip to form a filter power divider circuit. The results show that FPD has multiple transmission zeros, the passband is 13.2 to 15.5 GHz, and an insertion loss of -4 dB. The return loss in the passband is less than -15 dB, and the isolation below is -16.5 dB.

We experimentally demonstrate an optical-heterodyne millimeter-wave radio-over-fiber system with broadband wireless links through 25.22 km standard-single-mode fiber featuring a high bitrate of 24-Gb/s (64QAM × 4GBaud) using a highly correlated InAs/InP quantum-dash dual-wavelength DFB laser.

This paper presents low phase noise optical heterodyne millimeter-wave signals generation and data transmission using an ultra-low noise InAs/InP quantum-dash dual-wavelength DFB laser for potential applications in high capacity 5G mm-wave-over fiber mobile fronthaul links., Laser Applications Conference 2020, October 13–16, 2020, Washington, D.C. US

This paper presents a multilayer slot-coupled bandpass filter based on integrated substrate gap waveguide (ISGW). The bandpass filter consists of two ISGW unit structures that are placed back-to-back. Source-load coupling is achieved by etching double rectangular slots on the common ground of the two ISGW unit structures that can achieve better filtering performance in addition to introduction of out-of-band transmission zeros. Simulation results show that a passband of the filter from 26.6 to 28 GHz, insertion loss of lower than 0.7 dB, and return loss of better than 20 dB. Two transmission zeros on both sides of the passband improve the frequency selectivity.

In this letter, a differentially coplanar-fed antenna using integrated substrate gap waveguide (ISGW) is proposed for millimeter-wave applications, which has high gain and low cross polarization. The antenna consists of the differential power divider and radiation patch, and the power divider is deployed to excite the differential feeding antenna. The differential power divider is designed using rectangular-shaped coupling slot to achieve a stable 180° phase imbalance and 15% fractional operating bandwidth. The differentially coplanar-fed cross-shaped patch antenna has high gain and good radiation patterns. A fractional bandwidth of about 8.3% at the center frequency of 24 GHz and a peak gain of 10 dBi are obtained.

An evanescently coupled one-sided junction waveguide photodiode (EC-OSJ-WGPD) is proposed and investigated numerically. The one-sided junction photodiode has a simple structure, while the characteristics of high speed and high output power are maintained. The designed EC-OSJ-WGPD with an absorption layer thickness of 350 nm achieves a bandwidth of 44.5 GHz and responsivity of 0.98 A/W. Comprehensive analyses of the EC-OSJ-WGPD are presented including photogeneration rate, internal optical power distribution, energy band diagram, internal electric field, photocurrent, and 3-dB bandwidth.

We have developed and experimentally demonstrated a novel monolithic InAs/InP quantum-dash dual-wavelength distributed feedback (QD DW-DFB) C-band laser as a compact optical beat source to generate millimeter-wave (MMW) signals. The device uses a common gain medium in a single cavity structure for simultaneous correlated and stable dual-mode lasing in the 1550-nm wavelength range. A record narrow optical linewidth down to 15.83 kHz and average relative intensity noise (RIN) as low as -158.3 dB/Hz from 10 MHz to 20 GHz are experimentally demonstrated for the two optical modes generated by the laser. As a result, the beat note between these two lasing modes generates spectrally pure MMW signals between 46 GHz and 48 GHz. Such an efficient, coherent, and compact optical source is extremely attractive for applications in MMW systems, such as Radar and fiber-wireless integrated fronthaul for 5G and beyond.

In this letter, a magnetoelectric (ME) dipole antenna with characteristics of low profile, easy integration, wide band, and high gain is proposed. The ME dipole is composed of rectangular patches and metallic via holes, and is embedded in a square aperture etched on substrate-integrated gap waveguide (SIGW). In particular, the ME dipole is fed by a coplanar strip line, which is designed in SIGW to realize a low profile of 0.19 λg ( λg is the guide wavelength at center frequency). The measurements show that the 10 dB impedance bandwidth of the antenna is 29%, ranging from 22.4 to 30 GHz, with a mean gain of 8.04 dBi. Furthermore, the antenna emits a stable radiation pattern, validated by the far-field measurements.

The first antenna based on substrate integrated gap waveguide (SIGW) is presented. Using two contacted metal strips to build the required conducting ridge, the SIGW addresses the defects inherent in the printed gap waveguide at millimeter-wave frequencies. Moreover, a bandwidth enhancement method is proposed and demonstrated by tuning the cavity that excites the slot antenna. The achieved bandwidth can be more than 21 GHz centered at 60 GHz (35%). Different tuning configurations are carefully investigated, and a design guideline is provided, in which different substrates for the gap and via layers of the SIGW are considered. Two fabricated antennas using low-cost PCB verify the simulation results and design guidelines. The first one is a single-slot antenna, and the second is a four-slot linear array. The measured $S_{11}$ , realized gain, and radiation patterns of the fabricated antennas have good agreement with the simulated counterparts.

A novel optical waveguide LP 01 /LP 02 mode converter is proposed using combination of bicone structure based on the coupled-mode theory. It is composed of a cladding, a tapered core and combined bicone structure. It is found that this mode converter can have operating bandwidth of 1350–1700 nm, i.e. 350 nm, with a conversion efficiency of ∼ 90% ( ∼ 0.5 dB) and low crosstalk from other modes

To support the multi-gigabit/s wireless connectivity and to overcome the wireless spectrum crunch, 5G is going to adopt higher frequencies from the plentiful available spectrum in the millimeter-wave range. Photonic millimeter-wave signals generation and distribution in the optical domain is of great interest owing to their high spectral purity, low system complexity, low cost, small footprint, and long transmission distance. In this paper, we experimentally demonstrate spectrally pure photonic mm-wave signal generation and data transmission around 47.2 GHz using a novel low noises monolithic dual-wavelength semiconductor InAs/InP quantum dash (QD) DFB laser as a compact optical beat source for 5G applications., 2019 International Topical Meeting on Microwave Photonics (MWP), October 7-10, 2019, Ottawa, ON, Canada

5G is emerging, but the current fronthaul transmission technologies used for 3G and 4G may not be efficient and appropriate for 5G. It has been found that frequency division multiple access (FDMA) and time-division multiple access (TDMA) based radio over fiber (RoF) may be considered the most appropriate for 5G fronthaul transmission technology. Due to analog RoF transmission, broadband linearization is required. In this work, both electrical and optical broadband linearization techniques are reviewed.

This letter presents analog and digital pre-distortion hybrid linearization of a broadband radio-over-fiber transmission system. Analog pre-distortion (APD) is used to mainly compensate for out-of-band nonlinear distortion, and digital pre-distortion (DPD) is used to mainly compensate for in-band nonlinear distortion and memory effect. Thus, by combining APD and DPD, all the quiescent distortions and memory effect can be suppressed effectively. The hybrid APD and DPD linearization is evaluated in three different scenarios: two 20-MHz long-term evolution (LTE) signals located at 800 and 900 MHz, and located at 800 and 840 MHz, and three 20-MHz LTE signals located at 800, 850, and 900 MHz. All three experiments show that the hybrid linearization results in better improvement in error vector magnitude, adjacent-channel power ratio, and third-order intermodulation distortion than the APD-only and DPD-only.

In this paper, we demonstrate a fabrication of an integrated mode converter that converts LP01 to LP02 for the C-band. The mode converter was directly inscribed in the bulk of a borosilicate glass using a femtosecond laser. The converter has an insertion loss of less than 1 dB for the entire C-band, suggesting more than 80% conversion efficiency.

It was found experimentally that growing an ultrathin GaP interlayer/sublayer before InAs quantum dots (QDs) grown on InGaAsP barrier lattice-matched to InP (001) substrates is an efficient way to tune the emission wavelength of InAs/InP QD lasers to 1.55 μm range at room temperature (RT). However, the impact of interlayers/sublayers in InAs/InP QD lasers has not been carefully investigated and analyzed theoretically, and the existing physic model cannot predict the emission wavelength of InAs/InP QD lasers engineered by interlayers/sublayers. In this paper, an improved model, which consists of a three-step strain analysis, is applied to precisely predict measured photoluminescence emissions of various QD samples with the GaP interlayer/sublayer that have a specific thickness or chirped/varied thicknesses at both RT and low temperature. It is found that the impact of the GaP sublayers is to enhance quantum confinement instead to stop As/P exchange. Finally, a new method of emission spectrum blue-shifting and gain spectral bandwidth enhancement of an InAs/InP QD laser is proposed and found to be more efficient. By optimizing sublayer thickness and double capping, a total gain spectral bandwidth of 245.7 nm, as an example, is predicted and peak wavelength is shortened to 1500 nm.

A wideband 3-dB coupler using substrate integrated gap waveguide (SIGW) is proposed based on the principle of the branch-line coupler structure. The SIGW coupler design is comprehensively studied. It is found that SIGW conducting ridge vias play a significant role and have a strong impact on the cavity resonance, passband, and impedance matching. A prototype of the proposed SIGW coupler is fabricated and tested, and the measured agrees well with the simulated. The coupler, better than the reported, has a passband of ~5 GHz from 23.59 to 29 GHz with the isolation above 20 dB, covering the 24.25–27.5-GHz and 27.5–28.5-GHz frequency bands of 5G.

The double-capping procedure has been widely used to control the size distribution of self-assembled InAs/InGaAsP quantum dots during the growth on a (001) InP substrate. However, the conventional simulation method referred to one-step model does not include this procedure, which may lead to inaccuracy in modeling of quantum dots. An accurate method of modeling a single quantum dot including a thorough elastic strain analysis is proposed and developed in this paper. The confinement potential profiles are found significantly different between the two models. A series of settings (i.e., dot heights, dot base sizes, and dot shapes) is considered. The electronic band structure is calculated by using the eight-band $k \cdot p$ model. By comparing with the photoluminescence measurements in previously published works, it is found that the obtained optical transition energies using the accurate two-step model are in better agreement. The bright exciton splitting is found larger in terms of fine structures. Moreover, the impact of the quaternary compositions (arsenic mole fraction) of barrier material is for the first time systematically studied by using this accurate model.

A simple and quasi-tunable optical frequency comb (OFC) generator is proposed and experimentally demonstrated using a C-band passively Fabry-Perot quantum dot mode-locked laser and a dual-driven LiNbO 3 Mach–Zehnder modulator. A 16-nm bandwidth OFC with 81, 58 and 30 comb lines at frequency interval of 23.3 GHz, 35 GHz and 70 GHz respectively is obtained experimentally. Measured average optical signal to noise ratio of 10-dB bandwidth OFCs is 36.3 dB, 38.5 dB and 40.8 dB at frequency interval of 23.3 GHz, 35 GHz and 70 GHz, respectively. Besides, single-sideband phase noise of the 23.3 GHz and 35 GHz frequency comb is −110 dBc/Hz and −102 dBc/Hz at an offset of 1 kHz, respectively. RF linewidth of the 23.3 GHz and 35 GHz OFC is about from 275 Hz to 289 Hz. This is considered a very simple OFC generator with a broadband and seamless spectrum.

A novel uni-traveling-carrier photodetector (UTC-PD), bonded to high-reflectivity (HR) distributed Bragg reflector (DBR) mirrors, referred to as HR-UTC-PD, is first developed to overcome the bandwidth-responsivity tradeoff in UTC-PDs at various wavelengths. Grubbs' test is adopted, for the first time, to measure the bonded thickness of random locations for evaluating the reflected light loss generated in the bonded region. Compared with a standard UTC-PD without HR DBR mirrors, the maximum improvement of HR-UTC-PD responsivity (0.88A/W at 1560 nm) is 24.4% under a bias voltage of 3 V. The obtained 3-dB bandwidth for a 40-μm-diameter PD, which is neither increased nor degraded with the HR DBR mirrors, is 13.87 GHz at a bias voltage of 6 V and a 1550 nm wavelength. The saturation current up to 50 mA at 1-dB compression point is obtained at the frequency of 10 GHz, under a 50-Ω load and a 6 V bias voltage.

In this paper, a new quasi-transverse electromagnetic (TEM) microstrip line, named as packaged microstrip line, is proposed for microwave and millimeter-wave applications. It is comprised of three dielectric substrates: a base layer to place the metal strip, a top layer to build the perfect magnetic conductor (PMC) shielding with periodic plated vias, and a middle layer to separate the PMC layer from the metal strip and the bottom ground plane. With the top PMC shielding, this novel microstrip line no longer suffers from issues of radiation losses, surface waves, or cavity resonances that exist in the classical microstrip line without or with a metallic shielding box. Also, the unwanted higher order mode created in the stripline by any vertical asymmetry between the ground planes will not be generated in the packaged microstrip line. In addition, the fundamental quasi-TEM mode will help this novel line avoid the mode conversion losses when integrated with other quasi-TEM lines, which happen to the substrate-integrated waveguide due to its fundamental TE10 mode. This paper focuses on the effects of the PMC-layer substrate on this line performance. We present how to adopt a proper substrate for each layer of the packaged microstrip line considering both stopband and transmission loss, and how to design the linewidth for a given characteristic impedance. Two different transition schemes of the packaged microstrip line to the standard microstrip line are taken into account. Two prototypes of the proposed packaged microstrip lines using different substrates for the PMC layer are fabricated. The measured and simulated results show good agreement.

In this paper, dual wavelength linearization (DWL) technique is studied to suppress odd and even order nonlinearities simultaneously in a Mach-Zehnder modulator (MZM) modulated radio-over-fiber (RoF) transmission system. A theoretical model is given to analyze the DWL employed for MZM. In a single-tone test, the suppressions of the second order harmonic distortion (HD2) and third order harmonic distortion (HD3) at the same time are experimentally verified at different bias voltages of the MZM. The measured spurious-free dynamic ranges (SFDRs) with respect to the HD2 and HD3 are improved simultaneously compared to using a single laser. The output P 1 dB is also improved by the DWL technique. Moreover, a WiFi signal is transmitted in the RoF system to test the linearization for broadband signal. The result shows that more than 1 dB improvement of the error vector magnitude (EVM) is obtained by the DWL technique.

In future broadband cloud radio access networks (C-RAN), front-haul transmission systems play a significant role in performance and cost of C-RAN. Broadband and high linearity radio over fiber (RoF) transmission systems are considered a promising solution for the front-haul. Digital linearization is one possible solution for RoF front-haul. In this paper, we investigate RF domain digital predistortion (DPD) linearization for broadband RoF front-haul. The implemented DPD is first investigated in 2.4 GHz WiFi over fiber transmission systems at 36 Mb/s, and more than 8-dB and 5.6-dB improvements of error vector magnitude (EVM) are achieved in back to back (BTB) and after 10 km single mode fiber (SMF) transmission. Further, both WiFi and ultra wide band (UWB) wireless signals are transmitted together, in which the DPD has linearization bandwidth of 2.4 GHz. It is shown that the implemented DPD leads to EVM improvements of 4.5-dB (BTB) and 3.1-dB (10 km SMF) for the WiFi signal, and 4.6-dB (BTB) and 4-dB (10 km SMF) for the broadband UWB signal.

This letter presents a novel analog predistortion circuit based on two Schottky diodes that can suppress both the third- and fifth-order nonlinear distortions simultaneously. This circuit is simple, of low cost, and of low power consumption. The predistortion circuit is verified in two radio over fiber (RoF) transmission systems. It is shown that spurious free dynamic range is improved significantly from 1 to 6 GHz. Using the circuit for Wi-Fi wireless signal over RoF, error vector magnitude is improved by up to 3.9 dB.

The one-sided junction photodiode has a simple epitaxial layer structure, while maintaining the characteristics of high speed and high output power. An evanescently coupled one-sided junction waveguide photodiode is studied numerically and presented. The waveguide photodiode with 20 μm active region length leads to a responsivity of 0.435 A/W with a simulated bandwidth of 45 GHz.

We have developed a novel monolithic dual-wavelength semiconductor InAs/InP quantum-dash (QD) C-band DFB laser. A record narrow optical linewidth below 30 kHz and relative intensity noise (RIN) of less than -150 dB/Hz are experimentally demonstrated for the two optical modes stemming simultaneously from a single cavity of a free running dual-wavelength semiconductor QD laser., 2019 Photonics North (PN), May 21-23, 2019, Quebec City, QC, Canada

A multilayer slot-coupler based on integrated substrate gap waveguide (ISGW) is proposed. The proposed coupler is consisted of two ISGWs, which are broadside coupled through fish bone shape slot in the common ground. Simulation shows that the proposed coupler can have either $-3\pm 1\ \text{dB}$ tight coupling from 23.07 to 28.55 GHz or $-6\pm 1\ \text{dB}$ tight coupling from 24.48 to 30.73 GHz. Moreover, the phases between through and coupled port differ by 90°. The return loss and isolation are less than −20 dB over the operating frequency band.

To support the multi-gigabit/s wireless connectivity in the future wireless access networks, photonic millimeter-wave-over fiber (MMWoF) technologies are of great interest owing to their high bandwidth, high energy efficiency, low complexity and small footprint. In this paper, we experimentally demonstrate a 1 Gbaud four-level pulse amplitude modulation (PAM4) photonic MMWoF system at 47.2 GHz based on a novel dual-wavelength quantum-dash (QD) DFB laser and optical heterodyning., 2019 Photonics North (PN), May 21-23, 2019, Quebec City, QC, Canada

An ultra-wideband bandpass (UWB) filter using integrated substrate gap waveguide (ISGW) technology is proposed, which has ultra-wideband and high selectivity. The UWB ISGW bandpass filter structure consists of three layer dielectric substrates, the top substrate uses metallic via-holes and metallic patches to implement perfect magnetic conductor (PMC) structure, which is suitable for packaging substrate integrated waveguide (SIW) filters to avoid external interference and loss caused by radiation and internal radiation leakage, the middle layer substrate provides a stable gap layer, and the base substrate is used to obtain a SIW filter by etching the slots in the metal plane and placing metallic via-holes in the middle of the layer, i.e. a self-packaged UWB ISGW filter. The proposed filter was fabricated and tested at a center frequency of 17.5 GHz as an example. The measurements show that the filter has a passband from 14.4 to 20.7 GHz, i.e. This filter has a fractional bandwidth (FBW) of 36%, and an insertion loss of 0.91 dB. More importantly, thanks to ISGW, two transmission zeros are obtained at 12.9 and 22.1 GHz to improve high selectivity.

This work reviews fundamentals of integrated substrate gap waveguide (ISGW) in structure and operation principle. The most important aspect of ISGW is that not only circuit functions such as antennas, filters, and power dividers can be designed and implemented, but also inherent self-packaging function of the circuit is obtained. Compared with substrate integrated waveguide (SIW), ISGW introduces less transmission loss, and additional design freedoms that may result in better performance of a circuit. Moreover, examples of ISGW based antennas, filters and power couplers are given to show advantages of ISGW. It is believed that ISGW has high potential for 5G integrated microwave and millimeter-wave circuits.

In this paper, an integrated substrate gap waveguide ISGW) bandpass filter is proposed. The filter consists of three layers of dielectric substrates, base layer, middle layer and top layer. The base layer is used to obtain substrate an integrated waveguide (SIW) filter, the middle layer is a substrate gap layer which is used for a gap layer between the top and base layer, and the top layer is used to obtain perfect magnetic conductor (PMC) layer. An ISGW filter is designed to validate the concept. The filter has a fractional bandwidth of 32.2% and two transmission zeros at 14 and 22.8 GHz, and wide passband, wide stopband and high selectivity of the passband are achieved.

In this paper, we propose a high capacity multiple-input-multiple-output (MIMO) enabled all-optical analog-millimeter-wave-over-fiber (A-MMWoF) mobile fronthaul architecture employing mode division multiplexing (MDM) along with wavelength division multiplexing (WDM) for 5G and beyond of wireless networks. The proposed design is flexible and scalable for achieving high capacity, high speed and low latency fronthaul links., 2019 Photonics North (PN), May 21-23, 2019, Quebec City, QC, Canada

With the growing demand for cloud radio access networks, mobile fronthaul networks must stay adaptable, efficient and cost-effective. To simplify fronthaul transmission systems, 1-bit delta-sigma modulation (DSM) radio over fiber (RoF) transmission has been considered promising, in which 1-bit DSM technique is used to simplify remote radio units. Moreover, carrier aggregation is a key technique for increasing fronthaul transmission capacity. This work demonstrates, for the first time, concurrent dual-band 1-bit envelope DSM 64-QAM 20-MHz LTE signals transmitted over RoF system. It is shown that carrier aggregation combined with 1-bit delta-sigma modulation is a possible promising technique for high-capacity fronthaul transmission

This paper proposes a novel all-optical fiber mode converter for mode conversion from LP

A modified InGaAs/InP one-sided junction photodiode (MOSJ-PD) is presented for the first time. The MOSJ-PD is proposed from the one-sided junction photodiode by inserting a cliff layer into the absorption layer. Compared to the modified uni-traveling carrier photodiode, the MOSJ-PD has the advantages of simpler epitaxial layer structure and lower junction capacitance. In the MOSJ-PD, the space charge effect at high light intensity can be suppressed. Thus, both 3-dB bandwidth and output current can be improved simultaneously. The performance characteristics of the MOSJ-PD, including energy band diagram, internal electric field, frequency response, photocurrent, and responsivity, are carefully studied.

This paper shows the investigation of gap waveguide (GW) packaging for an irregular perfect electric conductor (PEC) composed of two layers of metal surfaces. The stopband for a GW with two-layer PEC surfaces is carefully studied, considering the top-layer PEC width, pin size, pin height, columns of pins, as well as dielectric substrate thickness and permittivity. A strategy of the GW packaging for such an irregular PEC surface is presented. In addition to the unit cell-based stopband study, such GW packaging is also demonstrated for a substrate-integrated waveguide (SIW)–microstrip line structure, which is typical of the circuit with two-layer PEC surfaces. A Chebychev bandpass filter built on the SIW and microstrip line is finally designed and fabricated to provide experimental verifications. In particular, a dedicated defect of the side air gap existing in the SIW-based circuits using the GW PMC packaging is found, and an effective remedy is presented.

In this paper, the bandwidth and saturation current of uni-traveling-carrier photodiode (UTC-PD) is investigated by using physics-based modeling. To further improve the performance, novel device structures are proposed. On the one hand, graded bandgap structure is employed in the absorption layer. It is shown that similar to the effect of graded doping method, the electric field in the absorption layer is increased, and thus the bandwidth is improved. Moreover, both the graded doping and graded bandgap structure are optimized. It is found that for the considered UTC-PD, combining use of the optimized graded doping and graded bandgap structure in the absorption layer leads to an improvement of 39.4% in bandwidth. On the other hand, linear doping profile and Gaussian doping profile are proposed to be used in the collection layer. It is shown that the distribution of electric field in the depletion region is improved, which leads to better saturation performance. For the considered UTC-PD, by using the optimized linear doping profile and the Gaussian doping profile, the improvement in saturation current is 18.7% and 25.8%, respectively.

We investigate the application of perfect magnetic conductor (PMC) packaging for a nonsmooth perfect electric conductor surface, caused by metalized via holes. The PMC shielding is artificially built by a metal lid of pins, based on the gap waveguide (GW) technology. As a foundation, the effects of via hole in a unit cell are studied first considering its diameter, substrate thickness, pin size, pin height, as well as relative position between the via hole and the pin. The via adjacent space and pin rows are also considered for a general grounded coplanar waveguide along with ground vias. The effectiveness of package for such a transmission line containing metalized via holes is then verified experimentally. It is shown that the measured performance agrees well with the simulation. This paper presents a guideline for the GW-based PMC packaging technology.

A mode converter between LP 01 and LP 0m modes is proposed using two stages of tapers. The first stage is formed by an adiabatically tapering a circular fiber to excite the desirable LP 0m mode. The second stage is formed by inserting an inner core (tapered from both sides) with a refractive index smaller than the original core. This second stage is used to obtain low insertion loss and high extinction ratio of the desired LP 0m mode. Three converters between LP 01 and LP 0m , m =2, 3, and 4, are designed for C-band, and simulation results show that less than 0.24, 0.54 and 0.7 dB insertion loss and higher than 15, 16, and 17.5 dB extinction ratio over the entire band were obtained for the three converters, respectively.

This letter presents a study of bend discontinuities in the substrate integrated gap waveguide (SIGW), and proposes a simple solution to minimize the discontinuity effects. Both curved and chamfered right-angle bends are studied. It is found that with a proper ratio of the chamfered length and the bend via diameter, the possible cavity resonances can be suppressed and the desired performance is achieved. The curved bend, however, allows the bend via to have a larger diameter, which could be required due to the fabrication issue. This letter will be of great help to realize future feeding networks for SIGW antenna arrays or other types of cost-effective SIGW passive components, where many discontinuities are naturally present. The proposed discontinuity solution is validated experimentally by a fabricated SIGW prototype of two 90° bends.

To improve fiber transmission capacity, space division multiplexing has been proposed and demonstrated, in which mode division multiplexing (MDM) is one option. To implement MDM transmission, mode converters/multiplexers are essential, which can be designed using planar lightwave circuits (PLC). In this work, we propose indirect mode coupling for design of mode converters/multiplexers to improve the performance. It is found that the performance of conversion efficiency, extinction ratio, and crosstalk can be significantly improved by using indirect mode coupling.