This PDF file contains the front matter associated with SPIE Proceedings Volume 9774, including the Title Page, Copyright information, Table of Contents, and Conference Committee listing.

We review recent breakthroughs in silicon photonics technology and components and describe progress in silicon photonic integrated circuits. Heterogeneous silicon photonics has recently demonstrated performance that significantly outperforms native III-V components. The impact active silicon photonic integrated circuits could have on interconnects, telecommunications, sensors and silicon electronics is reviewed.

Coherent optical communication systems applying modulation formats with a dimensionality of four or higher are investigated and compared to systems using conventional formats. Higher dimensionality can be achieved by applying modulation over more than one polarization, time-slot, wavelength, mode or core. Both uncoded systems and systems applying forward-error correction (FEC) coding are studied in terms of spectral efficiency and sensitivity. It is shown that increasing the dimensionality for a constant spectral efficiency improves the sensitivity substantially if no coding is applied, whereas the corresponding gains generally are much smaller in FEC-coded systems.

This article present several possible implementations for an optical square 16-QAM transmitter structures. Two efficient carrier phase estimation techniques with feed-forward structure have been tested in a real-time transmission and compared with each other to present the influence of phase noise; Blind Phase Search (BPS) and QPSK partitioning. 2.5 Gbit/s synchronous coherent 16-QAM data is transmitted and received in a real-time heterodyne setup with BER below FEC (7% overhead) threshold.

Space-Division Multiplexing (SDM), introduced more than 3 decades ago, is currently subject to intense research due to its ability to provide order-of-magnitude capacity growth in future transmission systems. Fibers play a central role in this renewed research field, and significant efforts have recently been spent to develop new fibers for SDM. In this paper, we will review the most recent advances on these different SDM fibers. We will also compare their performances and evaluate their respective potentials using the spatial density parameter that is a measure of the space efficiency.

We report the first demonstration of a four-mode semiconductor optical amplifier (FM-SOA), with strategically positioned quantum-well layers to provide modal-gain control with uniform electrical pumping. On-off gain of 11 dB was demonstrated for all four modes (E₁₁, E₁₂, E₂₁ and E₂₂). The difference in on-off gain among all four modes is less than 1 dB in the range of 2-11 dB without any deliberately pumping profile control. Particular challenges with FM-SOA that must be overcome in comparison with traditional single mode SOA are discussed.

Space division multiplexing (SDM) is currently widely investigated in order to provide enhanced capacity thanks to the utilization of space as a new degree of multiplexing freedom in both optical fiber communication and on-chip interconnects. Basic components allowing the processing of spatial modes are critical for SDM applications. Here we present such building blocks implemented on the silicon-on-insulator (SOI) platform. These include fabrication tolerant wideband (de)multiplexers, ultra-compact mode converters and (de)multiplexers designed by topology optimization, and mode filters using one-dimensional (1D) photonic crystal silicon waveguides. We furthermore use the fabricated devices to demonstrate on-chip point-to-point mode division multiplexing transmission, and all-optical signal processing by mode-selective wavelength conversion. Finally, we report an efficient silicon photonic integrated circuit mode (de)multiplexer for few-mode fibers (FMFs).

Mode-division multiplexing (MDM) transmission systems utilizing few-mode fibers (FMF) have been intensively explored to sustain continuous traffic growth. The key challenges of MDM systems are inter-modal crosstalk due to random mode coupling (RMC), and largely-accumulated differential mode group delay (DMGD), whilst hinders mode-demultiplexer implementation. The adaptive multi-input multi-output (MIMO) frequency-domain equalization (FDE) can dynamically compensate DMGD using digital signal processing (DSP) algorithms. The frequency-domain least-mean squares (FD-LMS) algorithm has been universally adopted for high-speed MDM communications, mainly for its relatively low computational complexity. However, longer training sequence is appended for FD-LMS to achieve faster convergence, which incurs prohibitively higher system overhead and reduces overall throughput. In this paper, we propose a fast-convergent single-stage adaptive frequency-domain recursive least-squares (FD-RLS) algorithm with reduced complexity for DMGD compensation at MDM coherent receivers. The performance and complexity comparison of FD-RLS, with signal-PSD-dependent FD-LMS method and conventional FD-LMS approach, are performed in a 3000 km six-mode transmission system with 65 ps/km DMGD. We explore the convergence speed of three adaptive algorithms, including the normalized mean-square-error (NMSE) per fast Fourier transform (FFT) block at 14–30 dB OSNR. The fast convergence of FD-RLS is exploited at the expense of slightly-increased necessary tap numbers for MIMO equalizers, and it can partially save the overhead of training sequence. Furthermore, we demonstrate adaptive FD-RLS can also be used for chromatic dispersion (CD) compensation without increasing the filter tap length, thus prominently reducing the DSP implementation complexity for MDM systems.

We successfully demonstrate 10-Gbbaud quadrature phase-shift keying signal transmission over a 4-km-long endlessly single-mode holey fiber using a wavelength-tunable semiconductor quantum dot (QD) laser. The transmission is carried out in the waveband of 1040.72–1070.02 nm with a bandwidth of 7.89 THz, which is broader than conventional wavebands such as the C and L bands. In the study, a QD laser notable for its wavelength stability and tunability is employed for its broad bandwidth availability on the transmission. Observed bit error rates are within a forward error correction limit of 2×10^–3 under homodyne coherent detection configuration with offline digital signal processing. The abundant frequency resources in this T band (1000–1260 nm) help increase the capacity of a transmission link using a large number of wavelength channels by the QD laser.

This letter shows that coherent optical orthogonal frequency-division multiplexing (CO-OFDM) is a suitable modulation format for long-haul transmission when fiber nonlinearities are dominated. A combination of RF pilot (RFP) tone technique with various subcarrier filling schemes and various RFP guard band frame structure are studied. This technique is effective to combat inter- and intra-channel nonlinearity and enhance the performance of CO-OFDM system. The simulation results show an improvement in Q-factor tolerance due to laser phase noise and fiber nonlinearity compared to standard RF pilot technique. A transmission distance of 2400 km was considered, with the transmission over a standard single mode fiber (SSMF) with a nonlinear coefficient of 2.6×10^-20 m²/W. The compensation of the chromatic dispersion (CD) is carried out at the receiver. It is obvious that using only RF pilot technique is affected strongly by SPM induced mean nonlinear phase shifts from Q-factor plot. Partial carrier filling (PCF) technique is used here to improve the nonlinearity performance of the transmission.

DP-QAM is one of the feasible paths towards 100Gbps, 400Gbps and 1Tbps optical communications systems. For DPQAM transmitter, the time mismatch between the XY tributary channels is known as the XY skew. Large uncompensated XY skew can significantly degrade the system performance. Sometimes, time-interleaved return-to-zero DP signal is preferred with lower nonlinear polarization scattering induced penalty. In this work, XY skew detection and alignment of dual-polarization optical quadrature amplitude transmitter using reconfigurable interference is experimentally demonstrated with >23-dB dynamic range. ~1.5-dB power change is achieved for 1-ps XY skew. Fast detecting scheme for arbitrary skew measurement is also experimentally verified. The scheme is compatible with different modulation formats, data sequences, and waveforms.

Optical fiber channels are used as media to transfer the information globally. This paper presents an implementation of a novel procedure using which a secured communication between two parties can be carried out using polarized beam of light over an optical fiber. The paper presents the experimental results obtained of the procedure in the lab environment and a security analysis of the same. It is observed that polarization state of a light pulse cannot be retained as it travels over an optical fiber because of the birefringence phenomenon. Multiple environmental factors such as pressure, vibration, temperature, etc. also add a non-linearity to the birefringence of an optical fiber leading towards an unpredictable polarization state changes over the course of an optical fiber. The proposed procedure helps the receiving party to successfully retrieve the data in the form of a polarization state transmitted by the sending party without having any knowledge about the state of polarization at the transmitting end. The paper also explains an added layer of security the procedure provides to the communicating parties to make it difficult for an adversary to fetch the data being transferred. The proposed system does not depend on the wavelength of the light being used, nor does it depend upon the type of the optical fiber used for the communication. Using this procedure, multiple bits of secured information can be sent over an optical fiber in a single polarized pulse and retrieved at the receiving end, also known as Polarization Shift Keying.

In this paper, the performance simulations of a novel ultra-compact balanced coherent photodetector for operation at a wavelength of 1.5 μm are presented and design proposals for future fabrication processes are provided. It consists of a compact 2x2 MMI that is evanescently coupled into a germanium MSM photodetection layer. The simulations demonstrate dark current less than 10 nA, capacitance less than 20 fF, and optical bandwidth in the 10-30 GHz range. We propose utilizing the simplicity of direct wafer bonding to bond the detection layer to the output waveguides to avoid complicated epitaxial growth issues. This ultra-compact device shows promise as a high-speed, low-cost integrated silicon photonics solution for the telecommunications infrastructure.

The mode-division multiplexing (MDM) technique enables the transmission of multiple signals within a multi-mode fiber (MMF) or a few-mode fiber (FMF). To construct an efficient and flexible MDM network in the same way as a wavelength-division multiplexing network, a mode conversion method with low modal crosstalk is required for switching between arbitrary spatial modes. However, in general, modal crosstalk is strongly dependent on the intensity pattern before mode conversion, and it is increased particularly for higher order modes. In order to reduce modal crosstalk, we propose a method using a random diffuser and a spatial light modulator (SLM). In the proposed method, firstly, the input spatial mode is dispersed uniformly by the random diffuser. Subsequently, the diffused phase distribution is canceled and converted into the desired spatial mode by the SLM, which displays phase difference between desired and diffused modes. Consequently, every spatial mode can be evenly converted into a desired mode. Here, we numerically simulate and confirm that the proposed method can reduce modal crosstalk compared to the conversion method without the random diffuser.

We propose a spatial mode generation technology using spatial cross modulation (SCM) for mode division multiplexing (MDM). The most well-known method for generating arbitrary complex amplitude fields is to display an off-axis computer-generated hologram (CGH) on a spatial light modulator (SLM). However, in this method, a desired complex amplitude field is obtained with first order diffraction light. This critically lowers the light utilization efficiency. On the other hand, in the SCM, the desired complex field is provided with zeroth order diffraction light. For this reason, our technology can generate spatial modes with large light utilization efficiency in addition to high accuracy. In this study, first, a numerical simulation was performed to verify that the SCM is applicable for spatial mode generation. Next, we made a comparison from two view points of the coupling efficiency and the light utilization between our technology and the technology using an off-axis amplitude hologram as a representative complex amplitude generation method. The simulation results showed that our technology can achieve considerably high light utilization efficiency while maintaining the enough coupling efficiency comparable to the technology using an off-axis amplitude hologram. Finally, we performed an experiment on spatial modes generation using the SCM. Experimental results showed that our technology has the great potential to realize the spatial mode generation with high accuracy.

Multi-Plane Light Conversion enables novel beam shaping devices, including spatial multiplexers. After a presentation of the achievable performances of these spatial multiplexers, which can combine 10 spatial modes with cross-talk below -22 dB and insertion loss below 4 dB, we review the performances of Multi-Plane Light Con-version in multiple application cases. These application cases include mode-multiplexed optical amplification, high-power beam shaping and combining and LAN fiber capacity upgrade.

Characterization of spatial mode content and dispersion properties in fiber laser systems and space-division multiplexing (SDM) applications is key to understanding fiber properties and system performance. Several techniques exist for modal characterization but often present limitations in the context in which they can be used efficiently. In this paper, we present a powerful analysis scheme that removes several of those limitations and pushes modal content analysis to a new level.

The thirst for bandwidth in telecommunications networks is becoming ever larger due to bandwidth hungry applications such as video-on-demand. To further increase the bandwidth capacity, engineers are now seeking to imprint information on the last remaining degree of freedom of the lightwave carrier – space. This has given rise to the field of Space Division Multiplexing (SDM). In essence, the concept of SDM simple; we aim to use the different spatial modes of an optical fibre as multiplexed data transmission channels. These modes could either be in the form of separate singlemodes in a multicore optical fibre, individual spatial modes of a multimode fibre, or indeed the individual spatial modes of a multimode multicore optical fibre. Regardless of the particular “flavour” of SDM in question, it is clear that significant interfacing issues exist between the optical fibres used in SDM and the conventional single-mode planar lightwave circuits that are essential to process the light (e.g. arrayed waveguide gratings and splitters), and efficient interconnect technologies will be required. One fabrication technology that has emerged as a possible route to solve these interconnection issues is ultrafast laser inscription (ULI), which relies on the use of focused ultrashort laser pulses to directly inscribe three-dimensional waveguide structures inside a bulk dielectric. In this paper, I describe some of the work that has been conducted around the world to apply the unique waveguide fabrication capabilities of ULI to the development of 3D photonic components for applications in SDM.

For the first time, we demonstrate the implementation of a core pumped few mode erbium amplifier utilizing a mode selective photonic lantern for spatial modal control of the pump light. This device is able to individually amplify the first six fiber modes with low differential modal gain. In addition, we obtained differential modal gain lower than 1 dB and signal gain of approximately 16.17 dB at λ_s = 1550 nm through forward pumping the LP21 modes at λ_p = 976 nm.

Multicore fiber (MCF) is a promising candidate of an optical fiber for next generation large capacity transmission and high density optical wiring in data center application. To construct optical network based on MCF, a fan-out for connecting independent single core fibers and MCF is a key component. In addition, an optical connector for simultaneously connecting all cores of MCF is also a key component. In this paper, I report our works on fan-out and optical connectors for MCF.

This paper describes the fabrication and analysis of novel twin cored fiber which contains a transparent and silver halide doped photochromic core in same cladding. The Photochromic core fibers were fabricated in twin cored structure by rode and tube method. The diameter of photochromic core and transparent core is around 15 m. The distance between two cores is 1.5m. The transparent core was used to guide the probe beam and photochromic core was excited by UV source. The interaction of the probe beam with the excited photochromic core showed the photochromic behavior of the fiber.