Commercial Vertical-cavity Surface-emitting Laser Research Articles

Bi-LSTM-Augmented Deep Neural Network for Multi-Gbps VCSEL-Based Visible Light Communication Link.

With the remarkable advances in vertical-cavity surface-emitting lasers (VCSELs) in recent decades, VCSELs have been considered promising light sources in the field of optical wireless communications. However, off-the-shelf VCSELs still have a limited modulation bandwidth to meet the multi-Gb/s data rate requirements imposed on the next-generation wireless communication system. Recently, employing machine learning (ML) techniques as a method to tackle such issues has been intriguing for researchers in wireless communication. In this work, through a systematic analysis, it is shown that the ML technique is also very effective in VCSEL-based visible light communication. Using a commercial VCSEL and bidirectional long short-term memory (Bi-LSTM)-based ML scheme, a high-speed visible light communication (VLC) link with a data rate of 13.5 Gbps is demonstrated, which is the fastest single channel result from a cost-effective, off-the-shelf VCSEL device, to the best of the authors’ knowledge.

Reliability of vertical-cavity surface-emitting laser arrays with redundancy

This paper describes theoretical reliability analysis of a system containing n optical ports in which each optical port contains m redundant vertical-cavity surface-emitting lasers. We study the wearout failure statistics, modelled with lognormal distribution, for three different chip-level integration approaches: ( A ) each laser on its own chip, resulting in m·n chips, ( B ) m redundant lasers associated with one channel are on a single chip, resulting in n chips, and ( C ) all m·n lasers integrated on a single chip. We present a model that includes the run-to-run reliability parameter fluctuation and find that the three integration schemes consistently exhibit MTTF( C ) ≥ MTTF( A ) ≥ MTTF( B ) for lognormal distribution shape parameters observed in commercial vertical-cavity surface-emitting lasers. We also provide analytic approximations for the failure statistics for all three integration approaches enabling straightforward calculation of the failure statistics for any redundancy and channel number.

Low-Cost Interrogation of Long-Distance and Multipoint FBG Sensor Using Incoherent-FMCW Optical Ranging System

More than a decade, multipoint sensor systems involving fiber Bragg gratings (FBGs) have been widely used in various implementations, especially the structural health monitoring system (SHMS). In this paper, a three-points FBG sensor was successfully analyzed by combination of incoherent frequency modulated continuous wave (I-FMCW) optical ranging system and a vertical-cavity surface-emitting laser (VCSEL) as a wavelength-tunable laser source. This system is not only capable of reading out the FBG sensors, but also identifying the location of the installed FBGs. The I-FMCW can be conducted by intensity modulation of a low-cost commercial VCSEL. Furthermore, the wavelength of the VCSEL can also be tuned by the injection current change to match the Bragg wavelength of FBGs. The detected signal from the FBGs and the reference signal from the signal generator are electrically mixed to obtain the beat frequency. A thermo-electric controller (TEC) controls temperature of one of the FBGs in the range of 25° C ~ 45° C, and contrary the others are kept at room temperature. As well as measuring temperature, one of the FBGs is strained in the range of $369~\mu \varepsilon \sim ~2137~\mu \varepsilon $ . The measurement result shows that the system can clearly distinguish all FBGs installed in totally 6.6 km-long optical fiber. In addition, the Bragg wavelength shift of the FBGs according to temperature as well as strain changes was successfully measured. The system can be scaled up more than three FBGs and extended scale area, and is a candidate as a low-cost and simple FBG interrogator for a long-range SHMS.

VCSEL-Based 24 Gbit/s OWC Board-to-Board System

We experimentally demonstrate a 24-Gbit/s discrete multi-tone (DMT) optical wireless communication (OWC) system that exploits a commercial vertical-cavity surface-emitting laser (VCSEL) and a low-cost photo-diode (PD). The OWC link has a good tolerance to misalignment (9 mm at 12.5 Gbit/s and 1.5-m link distance), thus it does not require active alignment and tracking. It only needs passive alignment, which can be achieved with adequate mechanical precision.

Laser frequency sweep linearization by iterative learning pre-distortion for FMCW LiDAR.

We report on a laser frequency sweep linearization method by iterative learning pre-distortion for frequency-modulated continuous-wave (FMCW) light detection and ranging (LiDAR) systems. A pre-distorted laser drive voltage waveform that results in a linear frequency sweep is obtained by an iterative learning controller, and then applied to the FMCW LiDAR system. We have also derived a fundamental figure of merit for the maximum residual nonlinearity needed to achieve the transform-limited range resolution. This method is experimentally tested using a commercial vertical cavity surface-emitting laser (VCSEL) and a distributed feedback (DFB) laser, achieving less than 0.005% relative residual nonlinearity of frequency sweep. With the proposed method, high-performance FMCW LiDAR systems can be realized without expensive linear lasers, complex linearization setups, or heavy post-processing.

40-Gbit/s 850-nm VCSEL-Based Full-CMOS Optical Link With Power-Data Rate Adaptivity

An optical link based on directly modulated vertical-cavity surface-emitting laser (VCSEL) at 850-nm wavelength using commercial VCSEL and photodiode operating error-free BER < 10−12) at 40 Gbit/s is reported. The transmitter is implemented in a 14-nm FinFET CMOS while the receiver (RX) in 28-nm digital bulk-CMOS technologies. This is the fastest 850-nm VCSEL-based single-lane non-return-to-zero optical link with all the analog front-end components fabricated in CMOS. An energy-per-bit of 3.4 pJ/bit is measured at 40 Gbit/s. At lower data rates, the bandwidths of the circuits can be decreased adaptively to save power. This results in 2.7 pJ/bit at 20 Gbit/s. A sensitivity of −1.9 dBm optical modulation amplitude could be measured at the RX for 40 Gbit/s.

Heterogeneous 3-D circuits: Integrating free-space optics with CMOS

A three-dimensional (3-D) integrated circuit combining free-space optical interconnects (FSOI) with CMOS devices has been developed. An overview of the combined optical and CMOS system is described. Experimental data and simulated results are provided. A 3-D integrated test circuit merging the free-space optical network with gallium arsenide based vertical cavity surface emitting lasers (VCSELs) and germanium based photodetectors has been experimentally tested. The prototype 3-D IC test circuit exhibits a 3.3GHz bandwidth and a 5.1mW total power consumption per link. The bandwidth is limited due to the use of 5GHz bandwidth commercial VCSELs and the large inductive impedance of the wirebonds attaching the VCSELs and photodetectors to the I/O pads. The design of transmitter circuits for the 3-D integrated free-space optical interconnect system is discussed, and simulated extrapolated results on operating frequency and bandwidth are provided. The microprocessor operates at 333MHz and includes a bus width of 64bits, requiring a FSOI bandwidth of 10.65Gbps after serialization.

4×25 Gb/s Transceiver With Optical Front-end for 100 GbE System in 65 nm CMOS Technology

This paper presents a fully-integrated chipset for 4×25 Gb/s transceiver gearbox along with laser driver and photo detector front-ends. The transceiver provides 10:4 multiplexing and 4:10 demultiplexing conversion, with built-in clock generation, equalization, and amplification. The optical front-ends are realized as 4-element arrays, presenting remarkable performance with commercial vertical-cavity surface-emitting lasers and photodiodes. Feedforward equalizers and continuous-time linear equalizers are employed to compensate for loss and distortion in both electrical and optical domains. Fabricated in 65 nm CMOS technology, these chips can be lumped together as a compact module with performance exceeding typical 100 GbE standards.

Common cathode VCSEL driver in 90 nm CMOS enabling 25 Gbit/s optical connection using 14 Gbit/s 850 nm VCSEL

The design and electro-optical measurements of a 25 Gbit/s common cathode vertical cavity surface-emitting laser (VCSEL) driver in 90 nm bulk CMOS technology is presented. The driver is bonded to a 14 Gbit/s commercial VCSEL providing both DC and modulation current to the laser. The power consumption including the VCSEL is 60 mW. Since the DC bias of the VCSEL exceeds the breakdown voltage of thin oxide transistors, a novel output stage configuration using isolated wells is proposed. The active area is only 127 × 50 μm.

1.3 to 1.55 $\mu\hbox{m}$ All-Optical Wavelength Conversion for VCSEL-to-VCSEL Inversion and Logic

We demonstrate all-optical wavelength conversion from the O to the C band using a 1550-nm commercial vertical-cavity surface-emitting laser (VCSEL) subject to external optical injection at 1300 nm. For the first time to our knowledge, we show that this configuration can also be used to develop all-optical inverters and cross-band NAND and NOR gates based on VCSEL devices, and investigate their potential speed of operation.

A 3-D Integrated Intrachip Free-Space Optical Interconnect for Many-Core Chips

This letter presents a new optical interconnect system for intrachip communications based on free-space optics. It provides all-to-all direct communications using dedicated lasers and photodetectors, hence avoiding packet switching while offering ultra-low latency and scalable bandwidth. A technology demonstration prototype is built on a circuit board using fabricated germanium photodetectors, micro-lenses, commercial vertical-cavity surface-emitting lasers, and micro-mirrors. Transmission loss in an optical link of 10-mm distance and crosstalk between two adjacent links are measured as 5 and -26 dB, respectively. The measured small-signal bandwidth of the link is 10 GHz.

Characterization of Gain-Switched Pulses From 1.55-$\mu$m VCSEL

We report on short optical pulse generation by gain-switching (GS) a low-cost commercial vertical-cavity surface-emitting laser emitting at 1.55 μm. The dependence of pulse characteristics on GS parameters is investigated and analyzed. Pulses with duration of 55 ps and time-bandwidth product between 0.91 and 2.2 are obtained at repetition rates between 1 and 3 GHz.

Analysis of optical channel cross talk for free-space optical interconnects in the presence of higher-order transverse modes

We analyze the effect of cross-talk noise on the performance of free-space optical interconnects (FSOIs). In addition to diffraction-caused cross talk, we consider the effect of stray-light cross-talk noise, an issue that, to the best of our knowledge, was not addressed previously. Simulations were performed on a microlens-based FSOI system using the modal composition and beam profiles experimentally extracted from a commercial vertical-cavity surface-emitting laser. We demonstrate that this cross-talk noise introduces significant degradation to interconnect performance, particularly for multitransverse-mode laser sources. A simple behavioral model is also developed that accurately approximates the cross talk noise for a range of optical sources and interconnect configurations.

Low-frequency FM-noise-induced lineshape: a theoretical and experimental approach

Linewidth determination by self-heterodyne or self-homodyne methods may lead to mistaken interpretation, because these measurements often include significant broadening due to low-frequency FM noise. The effects of FM noise on these linewidth measurement schemes are investigated. An analytical formulation of the photocurrent autocorrelation function is given for different frequency noise signatures, the lineshape being extracted from numerical implementation. We apply these results to linewidth prediction for 850-nm commercial vertical-cavity surface-emitting lasers and get almost perfect agreement between the theoretical and the experimental approaches.

Single Transverse Mode Operation of a Self-Seeded Commercial Multimode VCSEL

This work presents a novel self-seeding configuration of the vertical-cavity surface-emitting laser (VCSEL) without classical wavelength selective elements. A multimode VCSEL shows stable single transverse mode operation in this configuration. The extremely simple setup consists merely of the commercial VCSEL, an iris, and a plane mirror, in which the reduction of relative intensity noise greater than 20 dB/Hz and the sidemode suppression ratio of 20 dB are achieved.

VCSEL polarization control by optical injection

The stability of the polarization-resolved (PR) light output of a commercial vertical-cavity surface-emitting laser (VCSEL) has been studied with and without the presence of external optical injection in a master-slave configuration. Pulsations in the PR light output are observed in the solitary laser at certain bias current. It has been observed here for the first time that optical injection can stabilize the polarization of a VCSEL operating in a pulsation regime.

Free-space optical relay for the interconnection of multimode fibers

We present results from a system that shows that multimode fibers can be used for both the input and the output of a free-space optical system. The system consists of plastic microlenses integrated with plastic optomechanical components that are suitable for low-cost fabrication and assembly. Such a system opens up opportunities to construct large repeaters and switches for multigigabit ethernet applications by integration with two-dimensional arrays of optoelectronic devices. We demonstrate a 2.5-Gbit/s transmission rate by using commercial vertical-cavity surface-emitting lasers coupled to 62.5-microm core fibers. We consider the design constraints and the capabilities of custom optical modules suitable for mass production.

EXTENDED WAVELENGTH (1.0 to 1.3 μm) InGaAs/GaAs QUANTUM DOT GaAs-BASED VERTICAL-CAVITY SURFACE-EMITTING AND LATERAL-CAVITY EDGE-EMITTING LASERS

An important advance in InGaAs/GaAs quantum dot lasers has been the demonstration of lasing at wavelengths significantly longer than that possible using InGaAs strained quantum wells, extending beyond 1.3 μm. These fully GaAs-based active regions are compatible with commercial vertical-cavity surface-emitting laser (VCSEL) technology based on selective oxidation, and offer novel performance due to their three-dimensional electronic confinement. This chapter reviews the status of long wavelength quantum dot edge-emitting lasers and VCSELs, and presents some of the new physical principles needed to understand their novel device characteristics.

VCSEL-polarisation control with polarised feedback

It is shown that the light of a commercial vertical-cavity surface-emitting laser submitted to a polarised optical feedback can be switched between two linear polarisation eigenstates.

Switching of the polarization state of a vertical cavity surface-emitting laser using polarized feedback

We show that the light of a commercial vertical cavity surface-emitting laser with polarized optical feedback can be switched between two linear polarization eigenstates. The flip occurs when the feedback phase is scanned by either the external cavity length or the injection current.