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Mode-locked lasers with low noise performance, such as low timing jitter and relative intensity noise are essential for high-precision applications. In this letter, we demonstrated a 122-MHz all-polarization-maintaining mode-locked Er-doped fiber laser based on a nonlinear amplifying loop mirror. A hybrid component integrating a wavelength division multiplexer and a phase shifter is applied to increase the repetition rate. The relative intensity noise is 0.004% and 0.76% rms (integrated from 1 MHz to 100 Hz) from two output ports. The timing jitter characteristic is measured by the delayed optical heterodyne method. The timing jitter is ~1.9 fs rms (integrated from 1 MHz to 10 Hz) of both two output ports. The origin of the timing jitter of this laser is analyzed numerically based on the well-established theoretical model using the laser’s repetition rate, cavity dispersion, etc.

We design and experimentally demonstrate an ultra-compact dual-mode mode-division multiplexing (MDM) photonic integrated circuit (PIC), which supports on-chip optical signal mode-order-based routing and mode-independent broadcasting. The MDM circuit is composed of inverse-designed three multiplexers, one 3-dB power splitter, three bends and one crossing based on photonic-crystal-like subwavelength structure. The measured excess loss and crosstalk of the fabricated MDM circuit are lower than 5.9 dB and −13 dB over a 60 nm observable wavelength span, respectively. The experiment results of single-channel 25 Gbit/s optical signal transmission show that only 1.2-dB power penalty is introduced through the MDM circuit at a bit-error-rate of 10−9.

Mode division multiplexing (MDM) has attracted great attention in recent years to increase the network capacity. To apply MDM in data center applications, a low-cost and low power consumption system is desired. In this letter, we utilize 850-nm single-mode VCSEL as the laser source and report mode division multiplexed transmission over a standard single-mode fiber, which is two-mode at 850 nm. Due to the small spot size and low numerical aperture, single-mode VCSEL can be coupled into single-mode fibers with low loss. The mode multiplexer and de-multiplexer devices are designed and fabricated based on fiber mode selective couplers using Hi780 fiber as the 850-nm single-mode launch and receiving fiber and standard single-mode fiber as the few-mode transmission fiber. The MDM system supports two channels, corresponding to the LP01 and LP11 mode in the few-mode transmission fiber. Detailed characterizations of the multiplexer and de-multiplexer are conducted including the insertion loss and crosstalk measurements. System transmission at 25 Gb/s shows error free performance over 1-km standard single- mode fiber for both channels. The utilization of VCSEL and standard single-mode fiber can potentially provide a low-cost solution for MDM systems in data center applications.

A broadband mode (de)multiplexer [(De)MUX] is proposed and experimentally demonstrated based on a triple-waveguide coupler (TWC) with the phase-matching of a multimode access-waveguide. The tolerance to the operating wavelength and fabrication error of the proposed mode (De)MUX can be relaxed with the aid of the wider access-waveguide and the middle waveguide. The optimized mode (De)MUX is with a coupling length of $48~\mu $ m and a broad bandwidth of >122 nm with the mode crosstalk of

Reconfigurable optical add-drop multiplexer (ROADM) is one of the key building blocks for on-chip optical networks, which can download the desired signals from the bus waveguide to the corresponding drop port and upload the local signals from the add port to the bus waveguide to achieve the signals dropping/adding between the local and the bus waveguide. In this letter, we propose a ROADM based on a Benes network for mode-division multiplexing systems. As a proof of the concept, a ROADM with three quasi-transverse electric modes (TE0-TE2) is fabricated and experimentally demonstrated, which can download signals from TEi (i = 0, 1, 2) mode channel in the bus waveguide to an arbitrary local drop port or upload local signals to TEi mode channel via an arbitrary add port. The excess loss of the fabricated device is less than 10.7 dB, and the crosstalk among different space or mode channels is lower than −13.7 dB. Finally, a 12 Gbps data transmission experiment is carried out to verify the performance of the device. The proposed device is reconfigurable and scalable, and thus, it is expected to be used for optical data processing in the mode-division multiplexing systems.

To combine the individual benefits of probabilistic-shaping (PS) and time-frequency-packing (TFP), we consider for the first time PS-TFP wavelength-division multiplexing (WDM) superchannels. However, TFP introduces inter-symbol interference (ISI) and/or inter-carrier interference (ICI). Moreover, the presence of reconfigurable optical add-drop multiplexers in the fiber links may further degrade the system performance. In this letter, we efficiently handle such challenges to present PS-TFP superchannels enabling Terabit-per-second data rates. For this, we perform a joint ISI and ICI channel estimation in tandem with turbo equalization to mitigate the interference. We investigate optimizing the parameters in the shaping and packing dimensions to achieve a desired target spectral efficiency. We show through our numerical results that such an optimized PS-TFP transmission leads up to 1.2 dB performance improvement over an unshaped Nyquist WDM system under similar conditions.

We demonstrate a high-capacity and ultra-compact silicon photonic transmitter directly coupled to a 7-channel multicore fiber (MCF). The integrated transmitter contains seven GeSi electro-absorption modulators (EAMs) connected with the perfectly vertical grating coupler (PVGC) array. A high port density for spatial-division multiplexing (SDM) is thus enabled by the out-of-plane coupling while not requiring angled polishing of the MCF. Relying on four-level pulse amplitude modulation (PAM-4) and digital signal processing (DSP), each of the EAMs can support a data rate of 160 Gbit/s in the back-to-back system. The obtained bit-error-rate (BER) is below the low-latency 7% hard-decision forward-error-correct (HD-FEC) coding limit. The integrated transmitter has a total data-rate-capacity of 1.12 Tbit/s over the seven spatial channels and a compact footprint of 1.8 mm $\times0.45$ mm. BER performance of the optimum spatial channel is evaluated at different wavelengths, revealing its potential for possible wavelength-division multiplexing (WDM) by the on-chip wavelength (de)multiplexers in the future.

A cascaded Mach-Zehnder interferometer based filter for coarse wavelength (de)multiplexing (CWDM) at the O-band is fabricated and tested on a silicon nitride on SOI platform. We characterize the chip-to-chip performance variability of the filter devices on a wafer. Using the optical measurement data, we apply Bayesian inference methods to estimate the waveguide geometery parameters and also quantify the uncertainty of the estimates.

Highly efficient and fabrication-error-resistant InP/ InGaAsP polarization rotator based on the half-ridge waveguide is experimentally demonstrated. A thin InAlAs layer is embedded inside the InGaAsP core layer to provide 20-fold etching selectivity with respect to InGaAsP, enabling precise control of the dry-etched core layer thickness. The designed device is fabricated to show a high polarization conversion efficiency of more than 95% with a large etching time tolerance of ±16%. Demonstrated scheme offers a practical path towards realizing compact and low-cost InP-based monolithic dual-polarization transceivers with on-chip polarization (de)multiplexers.

We present the design of a compact 5-mode division (de)multiplexer based on silicon-on-insulator waveguides for on-chip optical interconnects. The configuration consists of two coupled sections where each section comprises of two collocated asymmetric directional couplers to couple light from two input waveguides carrying independent signals into two TE modes (TE1, TE2 or TE3, TE4) of an interconnect trunk waveguide. For coupling into the TE0 mode of the trunk waveguide, an adiabatic taper is used to connect a fifth input waveguide. The proposed design with collocated directional couplers offers an advantage of a small footprint compared to sequential designs. The total coupling length of the device for multiplexing TE1 to TE4 modes is only 38.89 $\mu $ m. In addition, the device exhibits low insertion loss ~0.24 dB and crosstalk better than −33 dB at the design wavelength of 1550 nm.

We propose and demonstrate an integrated reconfigurable fiber-chip mode converter with multi-mode coupling functionality. The converter is composed of an inverse taper array, a cascaded Y-junction and a waveguide crossing, as well as a heater to control the mode conversion states. The fundamental and first-order modes can be coupled and converted simultaneously between fiber and chip without additional mode multiplexer/demultiplexer. Higher than −7 dB coupling efficiencies with 1-dB bandwidth larger than 100 nm can be experimentally observed for all the coupling cases. The measured modal crosstalk are −10 and −15 dB in the cases of fundamental and first-order modes inputting, respectively.

This letter proposes a multichannel optical fiber spectral and imaging system, aiming at evaluating the pixel-level optical properties of high definition display efficiently and precisely. The system makes use of 16-channel optical fibers to form a detecting array so that 16 points of a display under test can be measured cyclically by multiplexer and spectrometer and monitored by camera simultaneously. The optical path is reversible for both the light source and the laser positioning, and adjustable along a rail driven by a motor to enable the system to work in either magnification mode or reduction mode. The feasibility and accuracy of the system are verified by comparative experiments of standard light source, LED display, and OLED display, identifying both merits of a single-spot spectroradiometer and an imaging photometer/colorimeter and even more functions like pitch size and color gamut.

A silicon-based four-channel coarse wavelength- division multiplexing (CWDM) (de)multiplexer working in the O-band is proposed and realized. The present on-chip four-channel CWDM (de)multiplexer is composed of four cascaded optical filters with flat-top spectral responses, which are realized by combining a multimode waveguide grating (MWG) and a two-channel mode (de)multiplexer. For the realized flat-top CWDM (de)multiplexer with a ~18-nm channel-spacing, the measured 1-dB bandwidth is as large as 15 nm, which is ~75% of the channel spacing. The thermal sensitivity is also reduced from ~85 pm/°C to 46 pm/°C by introducing the compensation provided by an SU-8 upper-cladding with a negative thermo-optic coefficient.

An ultra-compact mode multiplexer for TE0, TE1, TE2 and TE3 modes is proposed and demonstrated experimentally. The device is realized via pixelated waveguides with a footprint of only $5.4\times 6~\mu \,\,\text{m}^{2}$ . The measured insertion loss of the multiplexer is less than 1.5 dB. The inter-mode crosstalk is ~−20 dB at 1550 nm and below −14.6 dB from 1510 nm – 1570 nm. The fabrication and temperature tolerance of the device are investigated. The device can well tolerate the nanohole diameter variation of ±10 nm and the temperature variation of 100 K. The compactness of the proposed mode multiplexer enables potential applications in densely integrated multimode photonic circuits.

A coarse wavelength division multiplexing (CWDM) (de)multiplexer based on the contra-directional couplers (contra-DCs) with subwavelength grating (SWG) waveguide is proposed and demonstrated on the silicon-on-insulator (SOI) platform. By utilizing the SWG waveguides with strong coupling strength, the coupling length can be significantly reduced and the transmission spectra are flat-top. The footprint of the demonstrated device is about $15\times 160\,\,\mu \text{m}^{2}$ . The proposed device is characterized with large bandwidth and low crosstalk at C-band.

In this letter, a reflection-type arrayed waveguide grating (AWG) (de)multiplexer using high-reflection photonic crystal reflector (PCR) in the Indium-phosphide Membrane on Silicon (IMOS) platform is proposed and experimentally demonstrated for the first time. This reflection-type AWG enables a 35% size-reduced footprint compared with the traditional transmission-type AWG having the same spectral parameters. Considering the realized performance of silicon-nanowire R-AWGs, an acceptable performance ( $680\,\times \,190\,\mu \text {m}^{2}$ size, 6.7-dB loss, and 10-dB crosstalk) is obtained. By using the ultra-small $5.4\,\times \,0.7\,\mu \text {m}^{2}$ PCR, merely 1.1-dB power loss higher than the corresponding transmission-type AWG is implemented. The PCR is a standard building block with a reflectivity of >90%. Besides, the length reduction of the arrayed waveguide will contribute to minimize the accumulated phase error in fabrication.

We demonstrate a four-channel de-multiplexer based on third-order cascaded elliptical micro-rings on silicon-on-insulator. By applying cascaded elliptical micro-rings structure, the fabrication tolerance was released. The spectral responses of four drop-ports over the S, C, and L bands (1450–1630 nm) were measured, which showed an enhanced performance. The four-channel de-multiplexer has box-like transmission spectra with an ultra-wide 3 dB bandwidth of about 2.6 nm, high out-of-band rejection ratio of more than 40 dB, low-channel cross talk of about −38 dB, small footprint of about 0.0012 mm2, and large operational spectral range of more than 180 nm. The de-multiplexer can support high-data-rate signal transmission capacity.

We propose a broadband mode multiplexer based on the structure of cascaded planar and non-planar tapered directional couplers (DCs), which are designed for processing vertically symmetric and anti-symmetric modes. The DCs are tapered to widen the operating bandwidth, reduce the polarization dependence, and improve the fabrication tolerance. As an example, we design and fabricate a five-mode (de)multiplexer with polymer material to combine or separate the $E_{11}$ , $E_{12}$ , $E_{21}$ , $E_{31}$ , and $E_{22}$ modes. Our typical fabricated device has a length of 2.1 cm and shows the mode coupling efficiency of almost larger than 94.5% for each DC over the $C+L$ band with weak polarization dependence. The proposed structure is scalable and can be implemented with different material platforms.

A reconfigurable mode (de)multiplexer [(De)MUX] is proposed based on a triple-silicon-waveguide directional coupler, consisting of a central waveguide with a Ge2Sb2Se4Te1 (GSST) upper layer and two outer silicon waveguides. The output mode states can be switched by the self-holding phase transition between the amorphous and crystalline states of the GSST layer, and a low loss of the proposed device can be achieved benefiting from the low propagation losses of the GSST at both states. The proposed reconfigurable mode (De)MUX is optimized by using the full-vectorial finite-element method and the thee-dimensional full-vectorial finite-difference time-domain method. The numerical results reveal that the proposed reconfigurable mode (De)MUX is with a compact length of 17.65 $\mu \text{m}$ , insertion losses of 0.16 and 0.96 dB, and mode crosstalk of −15.91 and −26.97 dB at ON and OFF states, respectively. The proposed reconfigurable mode (De)MUX can operate over the S + C + L band with high performance. The fabrication tolerances are also studied in detail.

We present a compact optical add-drop multiplexer in silicon-on-insulator based on combining mode selection with Bragg reflection. The add-drop channel has a 3-dB bandwidth of 2 nm, an extinction ratio of 30 dB, and an interferometric crosstalk of less than –42 dB. We characterize the inter-channel and interferometric crosstalk performance using BER measurements for 10-Gb/s NRZ data and obtain crosstalk induced power penalties less than 3.5 dB.

We propose a lithium-niobate optical waveguide asymmetric directional coupler for the realization of an electro-optically switchable mode (de)multiplexer. Our typical fabricated coupler, designed for (de)multiplexing the LP01 and the LP11a mode, provides a switching efficiency higher than 90% and the operation wavelength can be tuned over a wide range of ~240 nm by varying the driving voltage between −23 and +20 V. Our proposed switchable mode multiplexer could find applications as a wavelength-selective mode switch or a reconfigurable mode add-drop (de)multiplexer for mode-division-multiplexing networks.

Mode division multiplexing (MDM) has been widely investigated to enhance the capacities of passive optical networks (PONs), and weakly coupled transmission schemes are highly preferred to reduce the cost and complexity. However, wavelength insensitivities are scarcely studied for such applications. In this letter, an evolution scheme of the cascaded mode division multiplexing PON (MDM-PON) and conventional Gigabit PON (GPON), which supports bidirectional 1310/1490-nm transmission, is proposed. This scheme is enabled by wavelength-insensitive weakly coupled (WIWC) few-mode fiber (FMF) and optical components. Then, the realization of both WIWC few-mode wavelength division multiplexers (FM-WMUXs) and mode-selective couplers (MSCs) is analyzed. Based on the analysis, WIWC FM-WMUXs and MSCs that support two linear polarization modes and 1310/1490-nm transmission with low modal crosstalk are designed and fabricated. Finally, the bidirectional MDM-GPON transmission scheme with 2.5 Gb/s on-off-keying modulation and simple direct detection over 10-km FMF and 10-km single-mode fiber are experimentally demonstrated. The proposed MDM-GPON evolution scheme can achieve maximum compatibility by maintaining both the optical distribution network and the optical network units.

A monolithically integrated 32-channel hybrid (de)multiplexer on silicon is proposed and experimentally demonstrated to enable wavelength-division multiplexing (WDM) and mode-division multiplexing (MDM) simultaneously for a large capacity of optical interconnect links. The proposed (de)multiplexer consists of a four-channel mode (de)multiplexer based on cascaded asymmetric directional couplers and eight-channel wavelength-division-(de)multiplexers based on two microring resonator (MRR) arrays with a channel spacing of 2 nm. These MRRs are realized with a bending radius of as small as $4~\mu \text{m}$ by introducing a multimode microring waveguide so that a large free spectral range (~24 nm) is enabled for transverse magnetic polarization. Furthermore, each MRR works bi-directionally and provides two drop ports from which the same wavelength-channel from two of the mode-channels is dropped separately. For the fabricated 32-channel hybrid MDM-WDM (de)multiplexer, the excess loss is

In this letter, we combine the use of dense-wavelength-division-multiplexing and mode-division-multiplexing (MDM) with advanced-modulation formats for on-chip optical interconnects. A three-mode MDM multiplexer (MUX) and de-multiplexer (DEMUX) was designed and used. Each wavelength carrier had an aggregate data rate of 192-Gbit/s using 4-level pulse-amplitude-modulation. The mode crosstalk of the MDM MUX/DEMUX was measured to be below −20 dB in the 40-nm wavelength band from 1520 to 1560 nm. Fourteen wavelength channels are multiplexed and successfully transmitted with an aggregate transmission capacity of 2.6 Tbit/s (14 wavelengths $\times$ 3 modes $\times$ 64 Gbit/s) with all channels satisfying the hard-decision forward-error-correction threshold. Numerical analysis of the mode crosstalk is also performed.

Space-division multiplexing (SDM) is a calling for devices that fully replace their single-mode fiber counterparts. Fast optical switches represent one such type of key devices. In this letter, we present a free-space optical add-drop multiplexer for multicore fiber (MCF) optical communications. Microelectromechanical mirrors were used as the optical switching element. We first detail the implementation steps leading to the proposed device and then characterize its performance in terms of crosstalk and insertion loss. Overall average crosstalk is around -38 dB, while insertion losses remain large. The device investigated here is another step towards the practical adoption of SDM for optical networks based on MCFs.

A low-crosstalk and flat-top 4-channel coarse wavelength-division multiplexing (de)multiplexer is proposed and demonstrated. The cascaded Mach-Zehnder interferometers are used to provide flat pass-bands. By utilizing the power splitters based on the bent directional couplers, the crosstalk of the Mach-Zehnder interferometers could be ultra-low for all four channels. The measurement results of the fabricated device show that the crosstalk is $\sim 300~\mu \text{m} \times 100~\mu \text{m}$ .

In this letter, we design and experimentally demonstrate a four-channel full-band wavelength division multiplexing (WDM) device based on multimode interference in the silicon dioxide material platform. The simulation and performance analysis of WDM devices are carried out by the beam propagation method and finite-difference time-domain method. With a simple structure, the device is in small size, and easy to implement in process. The experimental results show that the device achieves a wavelength separation of 1.28, 1.34, 1.52, and $1.58~\mu \text{m}$ . The insertion losses and a contrast between two channels are also displayed.

An on-chip polarization-insensitive wavelength (de-)multiplexer based on cascaded bent directional couplers (DCs) is demonstrated. With the proper design of the bent DCs, the device can separate the two wavelength bands for TE and TM polarizations simultaneously. The characterization of the fabricated device shows slow polarization dependent loss and crosstalk less than 1dB and −15 dB, respectively. The footprint of our polarization-insensitive dual-wavelength multiplexer is $40\times 25~\mu \text{m}^{2}$ , which is the smallest among the reported (de)multiplexers in the silicon-on-insulator platform at the telecom wavelength range.

In this letter, we present a novel and simple method to suppress the signal fading phenomena in polarization optical time-domain reflectometry (POTDR). A combination of polarization multiplexing and multi-directional polarization analyzing is utilized to achieve the goal. A short polarization maintaining fiber is connected to a multi-wavelength laser source to generate polarization multiplexing probe lightwaves. The signals for different probe lightwaves are demultiplexed by a dense wavelength division multiplexer. Then, the three polarizers with different orientations are used to analyze the signals, respectively. The principle of the method is analyzed in detail. Experiments demonstrate the validity of the system to suppress the signal fading. The proposed method can eliminate the location error of event caused by the signal fading and the signal-to-noise ratio is also improved compared with a traditional POTDR.

A mode multiplexer/demultiplexer based on two mutually spliced tapered multi-core fiber is proposed in this letter. Mode multiplexing occurs in the tapered region, and it is less sensitive to wavelength and structure parameters. Simulation results show that mode multiplexer/demultiplexer for LP01 and LP11 mode exhibited a coupling efficiency greater than 90% over the wavelength bandwidth of 760 nm. Mode multiplexer/demultiplexer for LP01 and LP21 mode exhibited a coupling efficiency greater than 85% over the wavelength bandwidth of 320 nm.

We demonstrate the transmission of a single-polarization four-level pulsed amplitude modulation (PAM4) optical signal over 10-km single-mode fiber at the gross bit rate of 320 Gb/s and the net data rate of 266.7 Gb/s. A digital-preprocessed analog-multiplexed digital-to-analog converter with a 97-GHz bandwidth analog multiplexer module enables us to generate the Nyquist-shaped PAM4 signal at the high baud rate of 160 Gbd.

A two-mode (de)multiplexer [(DE)MUX] based on multimode interference couplers on InP substrate is proposed and experimentally demonstrated. A phase shifting section with a variation of the waveguide thickness is introduced to precisely control the phase shift to realize 100% mode conversion efficiency and multiplexing. Performance analysis of the (DE)MUX is carried out numerically, showing excellent properties with insertion loss

We demonstrate a novel wavelength-division multiplexing 1.31- and 1.55-μm-wavelength-band plasmonic multiplexer that employs the multimode interference effect. The multiplexer comprises SiO 2 stripes on a Au film and was fabricated using a process compatible with standard complementary metal-oxide-semiconductor processing techniques. To suppress the return loss, tapered structures were introduced to the multiplexer. Finite-difference time-domain simulations indicate that losses were reduced by 12 dB. The multiplexing operation was confirmed with a scanning near-field optical microscopy. The reflection effect (return loss) appeared as an interference fringe of incident and reflecting surface plasmons in the multimode waveguide. The interference fringe disappeared in the multiplexer employing the taper structure.

This letter presents a 9 × 35 arrayed waveguide grating (AWG) operating at 1265-1365 cm -1 designed for gas sensing applications. The phenomenon of channel spacing variation depending on the position of the input light is demonstrated experimentally. First, the theoretical background is presented. Then, simulations are compared with experimental measurements on 1315-cm -1 (7.6 μm) central wavelength AWG. Experimental data are in good agreement with simulation results. Overall scatter of channel spacing variation is 5 cm -1 . Input channels inclined from the central position lead either to an increase or a decrease of the spectral channel spacing depending on the specific design of the multiplexer.

A compact thermally reconfigurable optical add/drop multiplexer (ROADM) is realized with 500 $\text {nm}\times 220$ nm silicon-on-insulator (SOI) strip waveguides. The demonstrated ROADM has eight channels with a channel spacing of 400 GHz and consists of two identical arrayed-waveguide gratings integrated with eight thermo-optic switches on the same chip. These thermo-optic switches have a broad bandwidth with low loss ( 20 dB) for covering all wavelength channels by utilizing point-symmetric Mach–Zehnder interferometers with bent directional couplers. The ROADM’s footprint is about $770~\mu \text {m}\times 880~\mu \text{m}$ only due to the ultra-strong confinement ability of SOI strip waveguides. The total on-chip loss of the fabricated ROADM is $\sim 15$ and $\sim 7$ dB for the transmitted signals and the added/dropped signals, respectively.

Read out integrated circuit (ROIC) design for quantum dot infrared photodetector (QDIP) array requires large charge handling capacity, low readout noise, minimum detector bias voltage variations, and minimum power dissipation. ROIC design for such applications is challenging due to complex requirements and often needs iterative fabrications to meet all requirements. In this letter, we propose a decision matrix-based optimization method for large dynamic range ROIC implementation. The optimization method is based on trade off analysis, design, and simulation of identified ROIC parameters. This methodology has been applied to an actual case, and the optimum ROIC topology was selected using the optimization method described in this letter. The critical specifications are charge handling capacity of greater than 5 $\text{M}\overline {e}$ and low readout noise of less than 600 electrons, in 180-nm CMOS process. The large dynamic range ROIC consists of a charge integration stage, charge to voltage converters, correlated double samplers, sample and holds, column amplifiers, analog multiplexer, and a buffer amplifier stage. This letter also highlights the measured test chip results of an ROIC array of 30 $\mu \textrm {m} \times 30~\mu \text{m}$ pixel size, in which we have been able to achieve a charge handling capacity of 9.8 $\text{M}\overline {e}$ and the noise of 350 electrons.

A multiplexer and demultiplexer (MUX/DEMUX) based on 2-D photonic crystals (PhCs) for a dense wavelength division multiplexing (DWDM) system is presented. The designed MUX/DEMUX consists of narrow bandpass filters and magneto-optical circulators based on 2-D PhCs with triangular lattice of air holes, the parameters of which are analyzed by a finite element method. The simulation results show that the frequencies 193.4, 193.3, and 193.2 THz could be multi/demultiplexed with a low insertion loss ( 18.4 dB). The proposed DWDM MUX/DEMUX could be used to provide transport solution for DWDM optical communication system with 100-GHz spacing.

We have developed a compact hybrid-integrated four-lane $\times 25.8$ Gb/s transmitter optical sub-assembly (TOSA) for a 100 Gb/s transceiver for 40-km transmission. The TOSA has a simple configuration in which a four-channel electroabsorption modulator integrated distributed feedback (EADFB) laser array is directly attached to the input waveguide end-faces of a silica-based arrayed waveguide grating (AWG) multiplexer. We integrated a lateral tapered spot-size converter for the EADFB laser to achieve a high optical butt coupling efficiency between the EADFB lasers array and the AWG multiplexer. We confirmed that the TOSA, which is $19.9~\text {mm} \,\times \, 6~\text {mm} \,\times \, 5.8$ mm, achieved error-free operation for a 40-km transmission with a high average optical output power of over 0.3 dBm at an operating temperature of 55 °C.

The optimal design of a low-loss fused fiber mode-selective coupler for two-mode fiber transmission in the 850-nm band is presented. The coupler is based on precise phase matching of the propagation constants in each arm of a weakly fused fiber coupler. The designed component permits both mode converter and mode multiplexer/demultiplexer operation, thus enabling modal multiplexing transmission in this band with no additional component. The presented design is evaluated by simulation considering two types of structures, leading to asymmetric and symmetric coupler configurations. Mode converter and mode multiplexer operation is achieved with 93.5% efficiency in the band of 845 855 nm. Mode demultiplexer operation is achieved with an extinction ratio better than 20.4 dB in the same band., This work was supported by the Spanish Ministerio de Economia y Competitividad under Project RTC-2014-2232-3 HIDRASENSE and Project TEC2012-38558-C02-01.

We report a standalone four-output wavelength de-multiplexer (de-mux) using optical injection locking for simultaneous comb tone separation, amplification and power equalization. Optical amplification from −30 to 5 dBm per output wavelength is achieved. We illustrate the flexibility of the de-mux by separating two input combs with tone spacing of 12.5 and 6.25 GHz into 12.5-GHz spaced outputs. The system performance of the de-mux is demonstrated in a 100-km Nyquist ultra-dense wavelength division multiplexed network where the de-multiplexed comb tones are each encoded with 12-GBd Nyquist polarization division multiplexed quadrature phase shift keying. Experimental results indicate a worst case 1.5-dB receiver sensitivity penalty at 1.5e-2 bit error ratio for the transmitted comb tone channels when compared with the 400-kHz linewidth comb source seeding laser.

With the ever-increasing demand for small channel spacing in the dense wavelength division multiplexing technology, and the wavelength shift arising from the fabrication dimensional sensitivity of the silicon optical communication devices, wavelength tuning methods for silicon multiplexer/demultiplexer are therefore of great interest. Thermo-optically tunable silicon arrayed waveguide grating (AWG) multiplexer/demultiplexer using TiN heater has been demonstrated for the first time. Reduced impact of fabrication nonuniformity on the AWG effective refractive index is achieved through the waveguide design. Uniform heating is achieved by the heater design, which is analyzed by thermal distribution simulation. Above 600 GHz channel tunability has been demonstrated by simulation and experiment.

As optical transport networks become more configurable, the need for reconfigurable optical add/drop multiplexers (ROADMs) that are colorless, directionless, and contentionless (CDC) increases. Either of the two major classes of ROADM architectures, i.e., broadcast-and-select and wavelength-selective, can provide the CDC properties. With broadcast-and-select ROADMs, this is generally accomplished by employing more costly or complex configurations or adding adjunct equipment. In contrast, the wavelength-selective class of ROADMs, where the central component is an optical cross-connect (OXC), inherently provides the CDC properties. However, this architecture is limited by the achievable size (i.e., port count) of the OXC. We present alternative wavelength-selective ROADM designs that require smaller OXCs while providing equivalent functionality.

This letter reports on an Echelle grating demultiplexer for dense wavelength-division-multiplexing applications with 16 channels and 100 GHz channel spacing. The Echelle grating is designed and fabricated on a silicon-on-insulator platform with a silicon guiding layer of 300 nm. The measured insertion losses of the Echelle grating are lower than 2 dB for all channels and the crosstalk is below 15 dB. Error free transmission was obtained for all channels with negligible penalty.

We demonstrate the transmission of a 100G superchannel, composed of $4\times 28$ -Gb/s duobinary subcarriers placed on a 25-GHz grid, over 580 km of SSMF with three 25-GHz reconfigurable add-drop multiplexer nodes. The direct-detect 100G superchannel has moderate optical signal to noise ratio requirements and significant tolerance to the different optical impairments. The robustness, low-power consumption, cost effectiveness, and spectral efficiency of this 100G system makes it a very strong candidate for today’s datacenter- and metro-networks.

A compact 28 Gb/s \(\times 4\) -lane transmitter optical subassembly is developed for 100Gb/s Ethernet (100 GbE)/OTU4 applications with a hybrid integrated spatial multiplexer optical system. The system simply comprises three bandpass filters and a mirror, despite the narrow guardband specification. Moreover, by an intensively improved precise lens manipulation technique acting in an upward direction in addition to horizontally and downward, high-coupled power into the single-mode output fiber can be achieved, with resolving the previously reported issue that the controllable direction was limited. Finally, we show that eye diagrams with adequate mask margins (≥15%) and high extinction ratio (≥8 dB) are obtained at 28 Gb/s with a low modulating voltage (≤1.6 V \(_{\mathrm {\mathbf {pp}}}\) ).

We propose a novel structure for a monolithically integrated parametric frequency up and down converter using two parallel periodically poled lithium niobate (PPLN) waveguides combined with a reflective wavelength-division multiplexer (WDM) to realize second-harmonic-pumped parametric mixing on one chip. The parallel configuration of the PPLN waveguides provides a long interaction length for efficient conversion. The reflective WDM used for (de)multiplexing 0.78- and 1.56- $\mu $ m light consisted of two multimode interference (MMI) (de)multiplexers and a dichroic mirror. The utilization of the wavelength selectivity of both the MMI (de)multiplexers and the dichroic mirror enabled us to achieve high isolation of the fundamental light for generating a second-harmonic pump. We fabricated the integrated device using a direct-bonded LiNbO3 ridge waveguide. Frequency conversion achieved with two-stage second-harmonic generation and difference frequency generation processes was successfully demonstrated with a high isolation of the fundamental and a parametric gain of the signal in the integrated device.

In this letter, a mode multiplexer/demultiplexer (MUX/DEMUX) for multicore fibers with 2D aligned cores is proposed. The device is based on the concept of 2D multimode interference (2DMMI) effect. If the 2D waveguide array is aligned within a square lattice, the supermodes of the array will obey the sinusoidal function and coincide with the transfer matrix of the 2DMMI couplers with phase shifter arrays. Therefore, a mode MUX/DEMUX with high mode extinction ratio can be realized based on this principle.