Vertical-cavity Surface-emitting Laser Transmitter Research Articles

A 448-Gb/s PAM4 FSO Communication With Polarization-Multiplexing Injection-Locked VCSELs Through 600 M Free-Space Link

A 448-Gb/s four-level pulse amplitude modulation (PAM4) free-space optical (FSO) communication through 600 m free-space link was constructed, utilizing polarization-multiplexing injection-locked vertical-cavity surface-emitting lasers (VCSELs) for presentation. When uniting four-wavelength polarization-multiplexing and PAM4 modulation schemes, the transmission capacity of FSO communications is substantially multiplied, with an aggregate transmission rate of 448 Gb/s [56 Gb/s PAM4/wavelength × 4 wavelengths × 2 polarizations (xand y-polarizations)]. The results show that four 1.55 μm VCSEL transmitters with injection locking technique are sufficiently powerful for 448 Gb/s PAM4 signal transmission. Adopting a tunable optical band-pass filter and a polarization beam splitter for wavelength filtering and polarization de-multiplexing, the polarized wavelengths are effectually filtered and de-multiplexed in each polarized state. As the polarization state is well preserved in the scenario over 600 m free-space transmission, a sophisticated polarization tracker is not required in this proposed FSO communication. High bit error rate performance and accepted PAM4 eye diagrams are attained through 600 m free-space transmission. The four-wavelength polarization-multiplexing PAM4 FSO communication established here reveals the prominent benefits of high aggregate transmission capacity and long-distance free-space link.

A 5 m/25 Gbps Underwater Wireless Optical Communication System

A 25-Gbps underwater wireless optical communication (UWOC) system with a two-stage injection-locked 680-nm red-light vertical-cavity surface-emitting laser (VCSEL) transmitter to enhance the frequency response and a laser beam expander to expand the collimated beam diameter over a 5-m highly turbid harbor water link is proposed and practically demonstrated. In highly turbid harbor water link, the overall attenuation coefficient at 680 nm is smaller than that at 520 and 450 nm, thereby a 680-nm red-light VCSEL transmitter is adopted in this proposed 5 m/25 Gbps UWOC system rather than a 520-nm green-light laser diode (LD) transmitter or a 450-nm blue-light LD transmitter. A satisfactory bit error rate performance (3 × 10–9) and a clear eye diagram are acquired in real time. This proposed UWOC system with a two-stage injection-locked 680-nm VCSEL transmitter and a laser beam expander brings important improvements in the scenario characterized by high turbidity.

PAM‐4 VCSEL driver with selective falling‐edge pre‐emphasis

Data centre optical links are migrating to four-level pulse amplitude modulation (PAM-4) as a method to extend the data rate while covering longer distances. Vertical-cavity surface-emitting lasers (VCSELs) enable the integration of low-power transmitters, but their non-linear and bias-dependent behaviour makes conventional feed-forward equalisation less effective. This Letter presents a 0.13 μ m SiGe BiCMOS PAM-4 driver that boosts the falling-edge to the bottom level through a selective pre-emphasis technique. Experiments at 25 GBd (50 Gb/s) reveal that adding selective pre-emphasis to a 4-tap equalised current driving a 20.6 GHz 1.5 μ m VCSEL, relaxes the critical PAM-4 link budget requirements by >1 dB at the KP4 forward error correction threshold of 2.2 × 10 − 4 . The potential of PAM-4 VCSEL transmitters can be significantly enhanced by including selective pre-emphasis to the equalisation topology while requiring minimal overhead.

64 Gb/s PAM4 VCSEL-based FSO link.

A 64 Gb/s four-level pulse amplitude modulation (PAM4) vertical-cavity surface-emitting laser (VCSEL)-based free-space optical (FSO) link with an external light injection scheme is proposed and successfully demonstrated. Experimental results show that the 11.2 GHz VCSEL with an external light injection scheme is sufficiently powerful for 64 Gb/s PAM4 FSO links. This study is the first one that adopts a 1550-nm VCSEL transmitter with an external light injection scheme in a 64 Gb/s PAM4 FSO link. The link performances of the proposed PAM4 VCSEL-based FSO links have been analyzed in real-time in terms of eye diagrams and offline processed by Matlab in terms of bit error rate (BER) performances. Good BER performance and clear eye diagrams are acquired over a 100-m free-space link. Such a proposed 64 Gb/s PAM4 VCSEL-based FSO link with an external light injection scheme is a promising one for providing high transmission rate and long transmission distance.

A 103.12-Gb/s WDM PAM4 VCSEL-Based Transmission With Light Injection and Optoelectronic Feedback Techniques

A 103.12-Gb/s wavelength-division-multiplexing (WDM) four-level pulse amplitude modulation (PAM4) transmission based on 850-nm and 880-nm vertical-cavity surface-emitting lasers (VCSELs) with light injection and optoelectronic feedback techniques is proposed and experimentally demonstrated. Results show that two such 7.5-GHz VCSELs with light injection and optoelectronic feedback techniques are potent for 103.12-Gb/s WDM PAM4 transmissions. To the authors’ knowledge, it is the first one to successfully adopt two VCSEL transmitters with light injection and optoelectronic feedback techniques in a WDM PAM4 transmission. A total transmission rate of 103.12 Gb/s (51.56 Gb/s/λ × 2 λs) is achieved in the proposed WDM PAM4 transmissions. The link performances of the proposed WDM PAM4 transmissions have been evaluated in real time. Good real-time bit error rate performance and three independent clear eye diagrams are obtained at a 180-m OM4 multimode fiber operation. Such a proposed 103.12-Gb/s WDM PAM4 VCSEL-based transmission has great potential for providing efficient bandwidth in short-reach optical communications.

A 56 Gb/s PAM4 VCSEL-Based LiFi Transmission With Two-Stage Injection-Locked Technique

A 56 Gb/s four-level pulse amplitude modulation (PAM4) light-based WiFi (LiFi) transmission based on a 680-nm/5.4-GHz vertical-cavity surface-emitting laser (VCSEL) with a two-stage injection-locked technique is proposed and demonstrated. Experimentally results show that a 5.4-GHz VCSEL with a two-stage injection-locked technique is effective for 56 Gb/s PAM4 LiFi transmissions. To the authors’ knowledge, it is the first one to adopt a 680-nm VCSEL transmitter with two-stage injection-locked technique in a 56 Gb/s PAM4 LiFi transmission. A pair of doublet lenses is employed in the proposed PAM4 VCSEL-based LiFi transmissions to enhance the free-space link. The link performances of the proposed PAM4 LiFi transmissions have been analyzed in real time. Good bit error rate performance and three independent clear eye diagrams are obtained over a 20-m free-space link. Such a proposed 56 Gb/s PAM4 VCSEL-based LiFi transmission with two-stage injection-locked technique has the potential to play a significant role in future wireless infrastructure for providing high transmission rate and long free-space transmission distance effectively.

45 Gb/s PAM4 transmission based on VCSEL with light injection and optoelectronic feedback techniques.

A 45Gb/s four-level pulse amplitude modulation (PAM4) transmission based on an 850nm/7.4GHz vertical cavity surface emitting laser (VCSEL) with light injection and optoelectronic feedback techniques is proposed. Experimental results show that such an 850nm/7.4GHz VCSEL with light injection and optoelectronic feedback techniques is powerful enough for a 45Gb/s PAM4 signal transmission. To the best of our knowledge, this Letter is the first to adopt a VCSEL transmitter with light injection and optoelectronic feedback techniques in a 45Gb/s PAM4 transmission system. Good bit error rate performance and three independent clear eye diagrams are achieved over a 200-m OM4 multimode fiber transport. This proposed 45Gb/s PAM4 VCSEL-based transmission system has great potential for providing effective bandwidth in short-reach optical data communications.

An 8 m/9.6 Gbps Underwater Wireless Optical Communication System

A 25-Gbps underwater wireless optical communication (UWOC) system with a two-stage injection-locked 680-nm red-light vertical-cavity surface-emitting laser (VCSEL) transmitter to enhance the frequency response and a laser beam expander to expand the collimated beam diameter over a 5-m highly turbid harbor water link is proposed and practically demonstrated. In highly turbid harbor water link, the overall attenuation coefficient at 680 nm is smaller than that at 520 and 450 nm, thereby a 680-nm red-light VCSEL transmitter is adopted in this proposed 5 m/25 Gbps UWOC system rather than a 520-nm green-light laser diode (LD) transmitter or a 450-nm blue-light LD transmitter. A satisfactory bit error rate performance (3 × 10–9) and a clear eye diagram are acquired in real time. This proposed UWOC system with a two-stage injection-locked 680-nm VCSEL transmitter and a laser beam expander brings important improvements in the scenario characterized by high turbidity.

An Energy Efficient 56 Gbps PAM-4 VCSEL Transmitter Enabled by a 100 Gbps Driver in 0.25 μm InP DHBT Technology

Datacenters demand higher speed vertical cavity surface emitting laser (VCSEL) based optical interconnects at low-power consumption. As a potential technology enabler, this paper presents a wide-bandwidth and energy-efficient multilevel pulse-amplitude-modulation (PAM) VCSEL driver implemented in an InP 0.25 μm double-heterojunction bipolar transistor (DHBT) technology. The operational bandwidth of the driver is verified and error-free electrical data transmission up to 56 Gbps PAM-2 and 100 Gbps PAM-4 is demonstrated at a driver energy consumption less than 2 pJ/bit. The driver is integrated and tested with an in-house fabricated 850 nm VCSEL. Error-free 56 Gbps PAM-4 optical transmission at a transmitter energy consumption of 3.7 pJ/bit is demonstrated without equalization. This is the highest data rate reported for an integrated PAM-4 modulated VCSEL transmitter, while being the most energy efficient above 40 Gbps operation. Moreover, the VCSEL driver offers a pre-emphasis feature at PAM-2 operation for improved link throughput and receiver sensitivity.

A 50-m/40 Gb/s 680-nm VCSEL-Based FSO Communication

A 50-m/40-Gb/s 680-nm vertical-cavity surface-emitting laser (VCSEL)-based free-space optical (FSO) communication employing three-stage injection-locked technique and the afocal scheme is proposed and experimentally demonstrated. The three-stage injection-locked technique, which can significantly increase the resonant frequency of the VCSEL, is expected to provide higher transmission rate in FSO communication. The afocal scheme, which can reduce the beam size of laser beam, is expected to provide longer free-space link in FSO communication. As far as we know, it is the first time that a three-stage injection-locked 680-nm VCSEL transmitter and afocal scheme that will successfully build up a 50-m/40-Gb/s FSO communication has been employed. Such a 50-m/40-Gb/s FSO communication provides the advantages of optical wireless links for longer transmission distance and higher transmission rate, which is thoroughly useful for high-speed light-based WiFi (LiFi) applications.

10 m/25 Gbps LiFi transmission system based on a two-stage injection-locked 680 nm VCSEL transmitter.

A 10 m/25 Gbps light-based WiFi (LiFi) transmission system based on a two-stage injection-locked 680 nm vertical-cavity surface-emitting laser (VCSEL) transmitter is proposed. A LiFi transmission system with a data rate of 25 Gbps is experimentally demonstrated over a 10 m free-space link. To the best of our knowledge, it is the first time a two-stage injection-locked 680 nm VCSEL transmitter in a 10 m/25 Gbps LiFi transmission system has been employed. Impressive bit error rate performance and a clear eye diagram are achieved in the proposed systems. Such a 10 m/25 Gbps LiFi transmission system provides the advantage of a communication link for higher data rates that could accelerate the deployment of visible laser light communication.

A 50 Gb/s NRZ Modulated 850 nm VCSEL Transmitter Operating Error Free to 90 °C

We report on the properties of an 850 nm vertical cavity surface-emitting laser (VCSEL) transmitter running at 50 Gb/s with NRZ modulation from 30 °C to 90 °C. This is the highest transmitter operating temperature at 50 Gb/s for a VCSEL link of any wavelength. This achievement is made possible by a combination of a high speed VCSEL design and driver and receiver circuits that incorporate equalization. Without equalization, the highest temperature attained with bit error ratio <;1E-12 is 57 °C.

A 20-km/60-Gb/s Two-Way PON Based on Directly Modulated Two-Stage Injection-Locked 1.55- &lt;inline-formula&gt; &lt;tex-math notation="TeX"&gt;$\mu\hbox{m}$&lt;/tex-math&gt;&lt;/inline-formula&gt; VCSEL Transmitters and Negative Dispersion Fibers

A 20-km/60-Gb/s two-way passive optical network (PON) based on directly modulated two-stage injection-locked 1.55-μm vertical-cavity surface-emitting laser (VCSEL) transmitters and negative dispersion fibers (NDFs) is proposed and demonstrated. A one-stage injection-locked technique has been confirmed as an effective approach for increasing the frequency response of a VCSEL. A two-stage injection-locked technique, which can further increase the frequency response of a VCSEL, is thereby expected to have excellent transmission performance in a two-way PON. To be the first to employ directly modulated two-stage injection-locked 1.55-μm VCSEL transmitters in a two-way PON, brilliant bit-error-rate performance and a clear eye diagram are obtained over a 20-km NDF transport. A directly modulated VCSEL has a positive chirp, whereas an NDF has a negative dispersion property in the transmission fiber; this negative dispersion property compensates the laser positive chirp and results in systems with better transmission performance. Such an innovative two-way PON provides the advantage of a communication link for high data rates, which is an attractive feature that is useful for broadband network applications.

VCSEL Based Coherent PONs

We present a review of research performed in the area of coherent access technologies employing vertical cavity surface emitting lasers (VCSELs). Experimental demonstrations of optical transmission over a passive fiber link with coherent detection using VCSEL local oscillators and directly modulated VCSEL transmitters at bit rates up to 10 Gbps in the C-band as well as in the O-band are presented. The broad linewidth and frequency chirp associated with directly modulated VCSELs are utilized in an envelope detection receiver scheme which is demonstrated digitally (off-line) as well as analog (real-time). Additionally, it is shown that in the optical front-end of a coherent receiver for access networks, the 90 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">°</sup> hybrid can be replaced by a 3-dB coupler. The achieved results show that VCSELs are attractive light source candidates for transmitter as well as local oscillator for coherent detection PONs.

Fixed-Current Operation of a VCSEL Transmitter Over a Temperature Range From ${-} 20^{\circ}$C to 80$^{\circ}$C Using an Elevated-Oxide-Layer Structure

We have demonstrated fixed-current operation of a vertical-cavity surface-emitting laser (VCSEL) transmitter operating at 1.25 Gb/s over a wide temperature range by using an elevated-oxide-layer structure. Four different types of oxide VCSELs have been prepared for the transmitter modules; conventional-oxide and elevated-oxide-layer VCSELs with the oxide-aperture diameter of 6.6 and 10 μm, and their temperature dependence of the threshold current and turn-off transient responses have been measured. Approximately 10%-reduced both fall time and timing jitter mainly originating from the alleviated turn-off-induced abnormalities in the elevated-oxide-layer VCSEL transmitters contributed to achieve the fixed-current operation in the temperature range from 20 °C to 80 °C. Although the operating current of the elevated-oxide-layer VCSEL transmitter should be increased as the threshold current increases, a simple driving circuit owing to the fixed-current operating transmitter over a wide temperature range will bring a drastic energy saving in the optical data transmission system that incorporates VCSEL as a light source.

Design of low-cost multimode fiber-fed indoor wireless networks

A low-cost option for transporting global system for mobile communication, Universal Mobile Telecommunication System and wideband local area network (WLAN) signals using multimode fiber (MMF) with 850-nm vertical-cavity surface-emitting lasers (VCSELs) is investigated through range predictions from a link budget analysis. These predictions are experimentally verified for WLAN signal transmission in an office environment, using a commercial access point and a 300-m (OM1/OM2) MMF link with low-cost 850-nm VCSEL transmitters. The analysis indicates that good performance and signal coverage is possible with optimum design of indoor fiber-fed wireless systems, even when using such inexpensive components

Performance comparison between vertical-cavity surface-emitting laser and quantum-well modulator for short-distance optical links

We quantify and compare two competing transmitter technologies: vertical-cavity surface-emitting laser (VCSEL) and quantum-well modulator (QWM) for the interchip communication using high-speed optical links. VCSEL-based links are power favorable compared to QWM-based links at higher bandwidths (20 Gb/s) and larger distances. However, the QWM is better for lower detector capacitances. We also extend the comparison to high-speed electrical links and quantify the critical length beyond which optical links are power favorable compared to electrical links for both VCSEL and QWM transmitters

Characterization of radio over multimode fiber links using coherence bandwidth

Experimental measurements have been carried out on 62.5/12- and 50/125-/spl mu/m multimode fiber links using 850-nm vertical-cavity surface-emitting lasers transmitters for their coherence bandwidth, a parameter commonly used for wireless systems. It is shown that characterization using the coherence bandwidth over any given signal band provides reliable indications of the performance of radio over fiber systems for the transmission of different wireless radio signals (GSM, UMTS, WLAN) without the need to test using modulated signals.

High-yield flip-chip bonding and packaging of low-threshold VCSEL arrays on sapphire substrates

Oxide-confined top-emitting 850 nm and bottom-emitting 980 nm vertical-cavity surface-emitting laser (VCSEL) 8/spl times/8 arrays were designed and fabricated for applications of optical interconnects. The arrays were flip-chip bonded onto sapphire substrates that contain complimentary metal-oxide-semiconductor (CMOS) driver and fan-out circuitries. The off-sited bonding contacts and minimized bonding force produced very high yield of the hybridization process without causing damage to the VCSEL mesas. The hybridized devices were further mounted either on printed circuit board (PCB) or in 68-pin pin-grid-array (PGA) packages. The transparent sapphire substrate allowed optical outputs from the top-emitting VCSEL arrays to transmit directly through without additional substrate removal procedure. Lasing thresholds below 250 /spl mu/A for 850 nm VCSELs and 800 /spl mu/A for 980 nm VCSEL were found at room temperature. The oxide confinement apertures of VCSELs were measured to be around 6 /spl mu/m in diameter. High-speed data transmission demonstrated a bandwidth of up to 1 Gbits/s per channel for these hybridized VCSEL transmitters.