Injection-locked Vertical-cavity Surface-emitting Laser Research Articles

Observation of spin polarization modulation responses of injection-locked vertical-cavity surface-emitting lasers

We report on the modulation responses of an injection-locked vertical-cavity surface-emitting laser (VCSEL) measured using an optical spin-polarization modulation technique. We reveal that weak injection locking is suitable to maintain a strong resonance response at a high-frequency region depending on the linear birefringence of the VCSEL, a unique feature of spin-polarization modulation response. The measured results can be reasonably reproduced with simulated ones on the basis of spin-flip rate equations. Our findings support novel applications of spin-controlled VCSELs with injection locking.

A two-way 224-Gbit/s PAM4-based fibre-FSO converged system

A two-way 224-Gbit/s four-level pulse amplitude modulation (PAM4)-based fibre-free-space optical (FSO) converged system through a 25-km single-mode fibre (SMF) transport with 500-m free-space transmission is successfully constructed, which adopts injection-locked vertical-cavity surface-emitting lasers with polarisation-multiplexing mechanism for a demonstration. Compared with one-way transmission, two-way transmission is an attractive architecture for fibre-FSO converged system. Two-way transmission over SMF transport with free-space transmission not only reduces the required number of fibres and the setups of free-space transmission, but also provides the advantage of capacity doubling. Incorporating dual-wavelength four-level pulse amplitude modulation (PAM4) modulation with polarisation-multiplexing mechanism, the transmission capacity of fibre-FSO converged system is significantly enhanced to 224 Gbit/s (56 Gbit/s PAM4/wavelength × 2-wavelength × 2-polarisation) for downlink/uplink transmission. Bit error rate and PAM4 eye diagrams (downstream/upstream) perform well over 25-km SMF transport with 500-m free-space transmission. This proposed two-way fibre-FSO converged system is a prominent one not only because of its development in the integration of fibre backbone with optical wireless extension, but also because of its advantage in two-way transmission for affording high downlink/uplink data rate with good transmission performance.

Experimental demonstration of 1.3 μm VCSEL‐based optoelectronic oscillator at 12 GHz using optical injection‐locking technique

The experimental validation is presented of an optical injection-locked (OIL) vertical-cavity surface-emitting laser (VCSEL)-based optoelectronic oscillator (VBO) to overcome the direct-modulation bandwidth limitations of packaged VCSELs. A 1.3 μm VCSEL under OIL is directly modulated at 12 GHz. The carrier phase noise value is −97.7 dBc/Hz at 10 kHz offset. A time domain characterisation of the oscillator based on Allan variance is proposed. The performed measurements showed that the OIL technique allows an increase in the optoelectronic oscillator (OEO) carrier frequency in comparison with free-running VBOs while maintaining high spectral purity. The results for a 12 GHz delay-line OEO with amplitude modulation are also compared with the proposed approach.

Using an injection-locked VCSEL to produce Fourier-transform-limited optical pulses.

In this Letter, we present Fourier-transform-limited, nanosecond scale optical pulses from a vertical cavity surface emitting laser (VCSEL) using injection locking with a narrow-band seed laser. We examine two different injection-locking architectures and show that we can achieve an effective injection-locking range of over 8 GHz with an extinction ratio of 20,000:1. These results indicate that injection-locked VCSELs could become a key component of large-scale photonic quantum networks.

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.

Centralized-Light-Source Two-Way PAM8/PAM4 FSO Communications With Parallel Optical Injection Locking Operation

For the first time up to our knowledge, a centralized-light-source two-way eight-level pulse amplitude modulation (PAM8)/four-level pulse amplitude modulation (PAM4) free-space optical (FSO) communication with parallel optical injection-locked vertical-cavity surface-emitting laser (VCSEL) transmitter is practically demonstrated. With the assistance of parallel optical injection locking, injection locking in the polarization sideband causes a simultaneous generation of the free-running orthogonal polarization sideband to form a centralized-light-source scheme. With the centralized light source, additional light source or wavelength reuse component, such as Fabry-Perot laser diode or reflective semiconductor optical amplifier, is not needed at the receiver side. It is very attractive because it enables the receiver side to share the light source remotely located at the transmitter side. Based on the centralized-light-source scheme and parallel optical injection-locking operation, the injection-locked parallel polarization sideband is used for downlink transmission, and the induced free-running orthogonal polarization sideband is transmitted and used as the optical carrier for uplink transmission. Over a 200-m free-space link, good bit-error-rate (BER) performance, the qualified PAM8, and PAM4 eye diagrams are obtained for two-way FSO communications. This proposed centralized-light-source two-way FSO communication provides a practical choice for two-way high transmission capacities and considerably develops the scenario characterized by parallel optical injection locking.

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.

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.

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.

Two-way fiber-wireless convergence systems based on two-stage injection-locked VCSELs transmitter and optical interleaver.

A two-way fiber-wireless convergence system based on a two-stage injection-locked 1.55-μm vertical-cavity surface-emitting lasers (VCSELs) transmitter and an optical interleaver (IL) to deliver intensity-modulated and phase-remodulated millimeter-wave (MMW) data signals over a 40-km single-mode fiber (SMF) and a 5-m radio frequency (RF) wireless transport is proposed and experimentally demonstrated. Bit error rate (BER) and eye diagram perform brilliantly through a serious investigation in systems. Such a two-way fiber-wireless convergence system is a promising option, it reveals a prominent one to present its advancement in integration of distribute fiber and in-house network.

Photonic Generation of Microwave Signals Using a Single-Mode VCSEL Subject to Dual-Beam Orthogonal Optical Injection

We experimentally and theoretically investigate the photonic generation of microwave signals using a long-wavelength single-transverse-mode vertical-cavity surface-emitting laser (VCSEL) subject to two-frequency orthogonal optical injection. We study if a significant reduction of the linewidth is achieved in the double injection locking regime. In this regime, the VCSEL is subject to optical injection by two master lasers in such a way that stable locking is also observed if only light from one of the master lasers is injected. Our model includes the effect of the injected light reflected at the VCSEL's mirror generalizing previous modeling of reflection-mode optical injection-locked VCSELs. Our model also describes the high coherence associated to stable injection locking states and takes into account phase fluctuations in both master lasers. We observe no significant reduction of the linewidth in the double injection locking regime because the linewidth is mainly determined by the phase fluctuations of the two master lasers.

Experimental study on the dynamics of polarized strong optical injection in 1550 nm VCSELs.

We have experimentally analyzed the dynamics of polarized strong optical injection in 1550 nm vertical-cavity surface-emitting lasers (VCSELs). The locking ranges of optical injection-locked (OIL) VCSELs are experimentally measured in different states of polarized strong optical injection. Based on our novel ellipse model, the influence of the polarization state of strong injection light is quantitatively studied for the first time.

RF up/down-conversion based on optically injection-locked VCSEL

All-optical radio frequency conversion is proposed by directly modulated optically injection-locked vertical-cavity surface-emitting lasers. The enhancement effect of second order products of RF signals by OIL technique is analyzed based on reflection-mode OIL model. Simulation results show that high injection ratio and large wavelength detuning of OIL condition lead to a high RF conversion gain. Compared with free running condition, more than 20 dB RF conversion gain enhancement is achieved in the simulation. The experimental results of the RF conversion gain improvement (+ 18 dB) by OIL show excellent agreement with our simulation results. The spurious free dynamic range improvement (+ 15 dB) of conversion signals by OIL is also experimentally demonstrated.

An ellipse model for cavity mode behavior of optically injection-locked VCSELs

We report a new graphical tool to analyze optical injection-locked vertical-cavity surface-emitting lasers (VCSELs). It predicts the resonant frequency enhancement and cavity mode behavior for both single- and multi- mode VCSELs under injection locking. Calculations based on this model show excellent agreement with experimental results.

Long distance transmission of SC-FDMA signals by directly-modulated OIL-VCSEL

We demonstrate the long distance transmission of single-carrier frequency division multiple address signals by directly-modulated optically injection-locked vertical-cavity surface-emitting laser. Transmission distance as long as 50 km is achieved at 5 Gb/s (2.5 Gb/s for each user) through data pattern inversion and higher frequency response gain under optical injection locking.

Direct Demodulation and Channel Filtering of Phase-Modulated Signals Using an Injection-Locked VCSEL

Detection of phase-modulated optical signals without the use of an externally generated local oscillator is demonstrated using an injection-locked vertical-cavity surface-emitting laser. When it is used in a multichannel system, this technique is also capable of actively filtering out one of the phase-modulated optical carriers. The experimental results of the proposed receiver performance in a three-channel optical system are presented here. A signal-to-noise ratio of 75 dBc/Hz is obtained.

Reflection-mode optical injection locking

A novel model including the interference effect of master laser reflection is established for reflection-mode optical injection locking. This model sheds insight on the physical origin of some rather distinct but unexplained modulation characteristics of optical injection-locked vertical-cavity surface-emitting lasers (VCSELs), including data pattern inversion in on-off keying modulation, a large RF gain at low frequency, and an anomalous DC-suppression under small signal modulation, in specific locking conditions. Excellent agreement is obtained between the simulation and experiment results.

Performance of a Multi-Gb/s 60 GHz Radio Over Fiber System Employing a Directly Modulated Optically Injection-Locked VCSEL

A multi-Gb/s 60 GHz radio over fiber (RoF) system employing direct modulation of an optically injection locked vertical-cavity surface-emitting laser is successfully demonstrated. Experimental results show that the RoF system is tolerant to fiber chromatic dispersion due to inherent single-sideband modulation produced by injection locking. A simple carrier-to-sideband equalization method is used to substantially improve the sensitivity of the RoF system by 18 dB, enabling both successful wireless signal transmission and multilevel signal modulation formats such as quadrature phase shift keying (QPSK). At least 3 Gb/s ASK-modulated data and 2 Gb/s QPSK-modulated data is transported over up to 20 km standard single-mode fiber and 3 m wireless distance with no penalty.

Reconfigurable Multifunctional Operation Using Optical Injection-Locked Vertical-Cavity Surface-Emitting Lasers

In this paper, we extend the system application of optical injection-locked (OIL) vertical-cavity surface-emitting lasers (VCSELs) to future optical networks by realizing multifunctional operation using a filter-assisted OIL-VCSEL scheme that can be reconfigured. By using a single chirp-adjustable injection-locked VCSEL (either single mode or multimode) followed by a tunable delay line interferometer, we experimentally demonstrate three functions, showing ultra-wide band (UWB) monocycle generation, nonreturn-to-zero (NRZ) to pseudoreturn-to-zero (PRZ) data format conversion, and NRZ-data clock recovery at 10 Gb/s.

Greatly increased fiber transmission distance with an optically injection-locked vertical-cavity surface-emitting laser

We demonstrate single-mode fiber transmission distance enhancement up to 120 km of a directly-modulated injection-locked VCSEL modulated by a 10Gb/s NRZ signal. Injection locking induced data pattern inversion of the VCSEL causes adjustable chirp, which greatly extends reach. Both experiments and simulations are shown to explain this phenomenon.