Colorless Laser Diode Research Articles

Bidirectional OFDM-MMWOF transport system based on mixed QAM modulation format using dual mode colorless laser diode and RSOA for next generation 5-G based network

A hybrid bidirectional orthogonal frequency division multiplexing–millimeter wave over fiber (OFDM-MMWOF) transport system based on mixed quadrature amplitude modulation (QAM) format using dual-mode colorless laser diode and reflective semiconductor optical amplifier for next-generation 5G based networks is proposed and experimentally demonstrated. Here, an orthogonal quadruple frequency MMW is generated via optical heterodyne scheme. In case of downlink transmission, 10 Gbps baseband signal is transmitted over 80-km single-mode fiber (SMF) plus 500-m free space optical (FSO) distance and for the uplink, 5 Gbps baseband signal is transmitted over 80-km SMF plus 100-m FSO distance. For wireless transmission, 12.5 Gbps/60 GHz downlink MMW signal is generated and transmitted over 80-km SMF as well as 100-m wireless distance. 6.5 Gbps/30 GHz uplink MMW signal is communicated over 80-km SMF plus 50-m wireless distance. OFDM scheme with mixed QAM modulation technique enhances our spectral efficiency and simultaneously reduces inter symbol interference, inter-carrier interference, dispersion, etc. for long reach communication. The feasibility and reliability of our system is established by achieving low bit error rate (10-3), good error vector magnitude (<10.5% for 32 QAM and < 12.5% for 16 QAM), appropriate signal to noise ratio, and clear constellation diagram.

Incoherent Laser Heterodyned Long-Reach 60-GHz MMWoF Link With Volterra Filtered 16-QAM OFDM Beyond 13 Gbps

By remotely heterodyning two independent laser carriers, the long-reach 60-GHz millimeter-wave-over-fiber (MMWoF) link is demonstrated for the Volterra series filtered quadrature amplitude modulation orthogonal frequency division multiplexing (QAM-OFDM) transmission with nonlinear noise suppression, which enables 13-Gbps data delivery through 50-km single-mode fiber (SMF) and 3-m free-space links. A wavelength tunable colorless laser diode transmits the Volterra filter equalized QAM-OFDM data to remotely couple with a localized single-mode laser carrier at the optical receiving end of the MMWoF system. Such an incoherently coupled dual-mode carrier facilitates the optical single-carrier modulation to suppress chromatic dispersion induced power fading effect of the SMF transmitted QAM-OFDM data. The 2nd+3rd-order nonlinear noise induced by direct modulation, heterodyne conversion, and phase fluctuation of the incoherently coupled dual-mode carrier is corrected with the Volterra filter equalization to upgrade the decoded signal-to-noise ratio (SNR) by >2 dB. After remotely heterodyning the downstream and the localized carriers with mutual incoherence in between, the 16-QAM OFDM transmission at a data rate up to 13.2 Gbps is successfully delivered over 3-m wireless link, which reveals the FEC certificated error vector magnitude of 14.1%, SNR of 17 dB, and bit error rate of 1.7 × 10−3.

28-GHz Wireless Carrier Heterodyned From Orthogonally Polarized Tri-Color Laser Diode for Fading-Free Long-Reach MMWoF

A 28-GHz millimeter-wave (MMW) carrier optically heterodyned from an orthogonally polarized tri-color (3λ-⊥-SCM) transmitter, which exhibits single-carrier modulation (SCM) to suppress the dispersion induced fading distortion after long-reach transmission, is demonstrated for building up the long-reach MMW-over-fiber with a distance of 75 km. The SCM-based encoding is obtained by seeding the tri-color master into slave colorless laser diode, which only supports TE-mode feedback with a polarized suppression ratio over 40 dB. After resuming back to the SCM tri-color optical carrier with orthogonal polarization (3λ-⊥-SCM), its delivered data can suppress the intensity noise induced by beating between adjacent modes such that the single-to-noise (SNR) can be improved by 2 dB. Comparing with the traditional parallel polarized multi-carrier modulation (MCM) based tri-color optical carrier (3λ-//-MCM), the orthogonally polarized tri-color optical carrier with SCM (3λ-⊥-SCM) can deliver 64 quadrature amplitude modulation orthogonal frequency-division multiplexing (QAM OFDM) data with its maximal encoding a bandwidth of 8.3 GHz (50 Gbit/s), which provides the error vector magnitude (EVM) of 8.8%, the SNR of 21.2 dB and the bit error rate of 3.5 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> after passing through a 75-km-long single-mode fiber. To perform the MMW wireless access network (WAN) link after 75-km fiber wired transmission, the heterodyned 28-GHz MMW carrier is obtained from the orthogonally polarized SCM tri-color optical carrier (3λ-⊥-SCM) with its peak power improved by 29 dB (from -50 to -31 dBm) and CNR enhanced by 17 dB (from 32 to 49 dB), as compared to those of the parallel polarized MCM tri-color case (3λ-//-MCM). After wireless transmission for 10-m with horn-antenna pair in free space, the maximal encoding bandwidth of the 16-QAM OFDM delivered by the orthogonally polarized SCM tri-color optical carrier (3λ-⊥-SCM) is 4.5 GHz (with 18 Gbit/s capacity).

Long-reach 60-GHz MMWoF link with free-running laser diodes beating

With the remote beating of two mutually incoherent laser carriers, the local-oscillator-free long-reach millimeter-wave over fiber (MMWoF) link at 60-GHz band is demonstrated. The unique schemes of the proposed MMWoF are the wavelength-locked colorless laser diode (CLD) modulator, the mutually incoherent optical carrier for heterodyne MMW generation, and the square-law power envelope detection at receiving end. By directly encoding the single-mode with the CLD modulator, the single-carrier modulated QAM-OFDM data is achieved to release the RF power fading after fiber transmission. The mutually incoherent laser beating enables the optical heterodyne MMW generation with two independent optical carriers, which provides the advantages of local-oscillator-free operation and rules out the requirement of dual-mode optical carrier delivery from central office. At the wireless receiving end, the received QAM-OFDM data is self-down-converted to the baseband by employing the square-law power envelope detection. This eliminates the requirement of local oscillator and rules out the influence of the MMW carrier frequency fluctuation between two mutually incoherent lasers (used at central office and remote node), which effectively provides the MMW carrier immunity against the down-conversion instability caused by clock jitter or carrier incoherence. This architecture ensures the transmission of 16.5-Gbit/s 32-QAM OFDM data over 50 km in SMF and 3 m in free-space with the FEC certificated error vector magnitude of 12%, signal-to-noise ratio (SNR) of 18.4 dB, and bit error rate of 3.8 × 10−3. For multi-channel DWDM-PON applications, the proposed local-oscillator-free MMWoF link can successfully perform 11 DWDM channels of 32-QAM OFDM data access at 16.5 Gbit/s per channel via the wavelength controlling of the CLD modulation stage and the detuning of the beating carrier at remote node.

Adjacent Channel Beating With Recombined Dual-Mode Colorless FPLD for MMW-PON

By delivering a reference carrier through adjacent dense-wavelength-division-multiplexing (DWDM) channel to remotely beat with the downstream transmitted optical carrier, a full-duplex millimeter-wave DWDM passive-optical-network (MMW-DWDM-PON) is demonstrated to transmit 36- ${\text{Gb/s}}$ data over 25-km single-mode fiber (SMF) and to remotely deliver a 28-GHz MMW carrier for wireless 6- ${\text{Gb/s}}$ data transmission. Such a remotely recombined dual-mode beating scheme provides baseband 36- ${\text{Gb/s}}$ data with corresponding bit error rate (BER) of 2.7 × 10 −3, which is better than the directly dual-mode injection-locked colorless Fabry-Perot laser diode (FPLD) does because of the less fiber chromatic dispersion during 25-km SMF transmission. In a hybrid 25-km SMF-wired and 1.6-m wireless link, it successfully transmits 4- ${\text{Gb/s}}$ data to fit the forward error correcting criterion. By maintaining the free-space distance at 1.6 m, the allowable raw data rate for MMW wireless transmission can be increased up to 6 ${\text{Gb/s}}$ with BER of 1.9×10−3. For optical baseband upstream transmission, the 36- ${\text{Gb/s}}$ data is also directly encoded onto the upstream colorless FPLD injection-locked by reusing the downstream pure carrier delivered through adjacent DWDM channel, and the received data reveals a BER of 2.9 × 10 −3.

Constructed MC-CDMA LR-PON With Colorless Laser Diode and Multicode Interference Cancellation DSP

Performance of multicarrier code division multiple access (MC-CDMA) long reach passive optical network (LR-PON) implemented with colorless laser diode transmitter is evaluated and compared with the same system under typical orthogonal frequency division multiplexing (OFDM) format. The relative amount of the multicode interference (MCI) in the MC-CDMA PON can be efficiently suppressed by applying the minimum mean square error based MCI cancellation processing and be analyzed in term of the error vector magnitude deviation. Due to the double sideband nature of the directly modulated colorless laser diode, both OFDM and MC-CDMA formats suffer from severe power fading after fiber transmission. Partial subcarriers in the OFDM-PON fail to reach the specified forward error correction (FEC) threshold, causing a huge performance deviation among subcarriers and a 3% data loss after 75-km transmission. In contrast, a distance transparency transmitter design for subscribers ranging from back-to-back to 50 km is achieved in the MC-CDMA PON scheme, and the received performance among subcarriers are equalized under the FEC criterion even after 75-km transmission. Therefore, the MC-CDMA exhibits superior performance when comparing with the OFDM format in the directly modulated colorless laser diode based LR-PONs.

Two-color laser diode for 54-Gb/s fiber-wired and 16-Gb/s MMW wireless OFDM transmissions

A two-color, laser-diode-based, full-duplex fiber-wired and millimeter-wave (MMW)-wireless orthogonal frequency-division multiplexing (OFDM) transmission link is performed. With modal control on the two-color laser diode, a single-wavelength optical carrier is used as both the downstream and upstream transmitters to replace the dual-mode one with an optical baseband, which effectively suppresses the chromatic dispersion that occurs in fiber. The proposed system demonstrates a carrier-reused, full-duplex 28-GHz MMW dense wavelength division multiplexing passive optical network (DWDM-PON) system, providing OFDM transmission with 54 Gb/s downstream, 36 Gb/s upstream and 16 Gb/s wireless data rates. The single-wavelength optical carrier transmits data from an optical line terminal (OLT) to a remote node (RN) and then transfers into a dual-wavelength carrier for optically heterodyne beating an MMW carrier, which further wirelessly transmits the data to an optical network unit (OUN). In addition, the upstream data is carried by another slave colorless laser diode injection-locked by reusing the downstream carrier without additional data erasing, which avoids the wavelength selection problem that resulted from identifying or addressing upstream and downstream channels. Among three laser transmitters with different cavity lengths, the 600-μm embedded MMW wireless carrier can provide the lowest bit error rate (BER) after 25 km of fiber and 1.6-m free-space transmissions at 16 Gb/s, because its highest external quantum efficiency supports the optimization on self-heterodyne transferring the MMW carrier to enable the low-noise and long-distance wireless transmission.

Tunable C- and L-band laser source based on colorless laser diode

In this letter, we propose and demonstrate a tunable laser source which covers C- and L-bands based on a colorless laser diode. The proposed laser source is tunable widely and it can tune single-wavelength, dual-wavelength, and triple-wavelength. Additionally, the optical side mode suppression ratio exceeds 30 dB. Since we combine the colorless laser diode with a tunable optical filter, the proposed tunable laser source stabilizes multi-wavelengths simultaneously. Our proposed tunable laser source is very useful for applications such as optical test instruments, optical communication systems, and optical fiber sensing systems.

Remote beating of parallel or orthogonally polarized dual-wavelength optical carriers for 5G millimeter-wave radio-over-fiber link.

A novel millimeter-wave radio over fiber (MMW-RoF) link at carrier frequency of 35-GHz is proposed with the use of remotely beating MMW generation from reference master and injected slave colorless laser diode (LD) carriers at orthogonally polarized dual-wavelength injection-locking. The slave colorless LD supports lasing one of the dual-wavelength master modes with orthogonal polarizations, which facilitates the single-mode direct modulation of the quadrature amplitude modulation (QAM) orthogonal frequency division multiplexing (OFDM) data. Such an injected single-carrier encoding and coupled dual-carrier transmission with orthogonal polarization effectively suppresses the cross-heterodyne mode-beating intensity noise, the nonlinear modulation (NLM) and four-wave mixing (FWM) sidemodes during injection locking and fiber transmission. In 25-km single-mode fiber (SMF) based wireline system, the dual-carrier under single-mode encoding provides baseband 24-Gbit/s 64-QAM OFDM transmission with an error vector magnitude (EVM) of 8.8%, a bit error rate (BER) of 3.7 × 10-3, a power penalty of <1.5 dB. After remotely self-beating for wireless transmission, the beat MMW carrier at 35 GHz can deliver the passband 16-QAM OFDM at 4 Gbit/s to show corresponding EVM and BER of 15.5% and 1.4 × 10-3, respectively, after 25-km SMF and 1.6-m free-space transmission.

39-GHz Millimeter-Wave Carrier Generation in Dual-Mode Colorless Laser Diode for OFDM-MMWoF Transmission

By using a nully biased MZM to modulate an incoming single-mode light into a double sideband (CCA-DSB or CCS-DSB) master with preserved or suppressed central carrier, the directly OFDM encoded dual-mode colorless laser diode is performed for a successful fusion between wired and wireless links to establish a 5G-based MMWoF system. The dual-mode L-band optical carrier successfully delivers a 36-Gb/s OFDM data with a BER of $3.2 \times 10^{-3}$ , while the stabilized 39-GHz mm-wave carrier can provide wireless 4-Gb/s 16-QAM OFDM data with 16.6-dB SNR. The in-situ 39-GHz mm-wave carrier can be synthesized by optically heterodyne mixing the dual-mode carrier at remote node. When injection-locking with the CCS-DSB master, the dual-mode slave colorless laser diode improves its central carrier suppression ratio and RIN to 38 dB and −104 dBc/Hz, respectively. In comparison, the dual-DFBLD master injection-locking mixed mm-wave carrier is relatively unstable due to the individual DFBLDs at free-running condition. With the CCS-DSB master, the mm-wave carrier self-beat from the dual-mode optical carrier exhibits a narrow linewidth of <3 kHz with high purity and stability. Such a dual-mode colorless laser diode-based MMWoF link is capable of fusing the fiber wired and the 5G wireless links demanded in the near future.

Power fading mitigation of 40-Gbit/s 256-QAM OFDM carried by colorless laser diode under injection-locking.

The pre-compensation on power fading effect of a colorless laser diode (CLD) carried 40-Gbit/s 256-QAM OFDM transmission during 25-km is demonstrated. By offsetting the DC bias to thrice the threshold (I(th)) and increasing the injection to 0 dBm, the CLD not only enhances its coherence but also suppresses modulation throughput declination and reduces the relative intensity related noise floor to -50 dBm. Modeling the receiving power of the delivered 256-QAM OFDM subcarriers is established, indicating that raising the bias to 3I(th) down-shifts the power fading induced notch to 8.8 GHz. This further degrades the OFDM subcarrier peak power by -2.9 dB after 25-km transmission, and the corresponded signal-to-noise ratio (SNR), error vector magnitude (EVM) and bit-error-rate (BER) are 26.1 dB, 4.9% and 6.5 × 10(-3), respectively. Pre-leveling the OFDM subcarrier as well as the modulation throughput effectively compromises the over-bias enlarged power fading to promote transmission. With a pre-leveled power slope of 1.5 dB/GHz for 256-QAM OFDM data, the modulation throughput declination of the high biased CLD significantly mitigates under BtB transmission, enabling the receiving sensitivity at -7.2 dBm with SNR, EVM and BER of 29.9 dB, 3.1% and 1.5 × 10(-4), respectively. Increasing the pre-leveling slope to 3.2 dB/GHz minimizes the fiber dispersion induced power fading, which improves the receiving SNR, EVM and BER to 27.4 dB, 4.2% and 2.6 × 10(-3), respectively, with receiving sensitivity of -3 dBm and power penalty of 4.2 dB after 25-km SMF transmission.

Effect of Injection Coherence on Noise and Bandwidth of Long-Cavity Colorless Laser Diode for Digital Modulation and Transmission

The weak-resonant-cavity Fabry-Perot laser diode (WRC-FPLD) injection-locked by three master sources with different degrees of coherence and directly modulated by two different digital modulation formats is demonstrated. The injection master coherence shows impact on noise, bandwidth, and modulation performances of the slave WRC-FPLD transmitter. Using the highly coherent master, the injection-locked WRC-FPLD reduces its relative intensity noise peak at 5 GHz by 18 dB and increases its throughput frequency response by 5 dB. This enables the error-free ON-OFF keying (OOK) transmission at 10 Gb/s with a required receiving power sensitivity of -15 dBm at an error rate of 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-9</sup> . The eye diagrams simulated from the modified rate equations are also performed to show such improvements. With highly coherent injection-locking, the transmitted error of the WRC-FPLD carried orthogonal frequency division multiplexing (OFDM) data with a modulation bandwidth of 3.1 GHz can be minimized to 1.6 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-13</sup> . In comparison, the master-to-slave injection-locked WPC-FPLD with partial coherence can also provide an 8-Gb/s OOK transmission with a receiving power sensitivity of -19 dBm at bit-error-rate (BER) of 109. Such a cost-effective colorless source also supports a 16-quadrature-amplitude modulation OFDM transmission at 12.5 Gb/s with a BER of 5.6 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-12</sup> to serve multichannel application in next generation passive optical network.

Reusing Downstream Carrier in Colorless Laser Diode for Full-Duplex 64-QAM OFDM

Without the need of any inline data eraser, the downstream carrier is reused in an upstream colorless laser diode transmitter to demonstrate full-duplex bidirectional 64-QAM OFDM passive optical network (PON) at up to 18 Gb/s. Therein, the downstream signal is used to control the wavelength of upstream laser diode by injection locking, and the slave laser diode then generates the injection-locked carrier for carrying the upstream signal. Distributing the OFDM subcarriers into dual frequency regions for upstream (baseband at 0-3 GHz) and downstream (up-shifted band at 3-6 GHz) transmissions avoids the crosstalk and simplifies the full-duplex system. The downstream power splitting ratio of 60/40 is optimized for receiving/injection branches at user end. For the downstream 64-QAM OFDM data after propagating 25-km SMF, a sensitivity of received power at least -8.5 dBm is required to suppress the BER below 3.8 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> for the forward-error correction (FEC) criterion. When directly reusing the downstream carrier with unerased data to injection-lock the colorless laser diode, the 25-km SMF transmitted upstream 64-QAM OFDM data exhibits an SNR of 22.9 dB and an error vector magnitude of 4.1%, which provides a BER of 1.5 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> at a received power of -5.8 dBm. Such a downstream carrier reused colorless laser diode upstream transmitter with inline eraser-free operation has shown its applicability for full-duplex quadrature amplitude modulation orthogonal frequency-division multiplexing PON.

Coherently wavelength injection-locking a 600-μm long cavity colorless laser diode for 16-QAM OFDM at 12 Gbit/s over 25-km SMF

The coherent injection-locking and directly modulation of a long-cavity colorless laser diode with 1% end-facet reflectance and weak-resonant longitudinal modes is employed as an universal optical transmitter to demonstrated for optical 16-QAM OFDM transmission at 12 Gbit/s over 25 km in a DWDM-PON system. The optimized bias current of 30 mA (~1.5Ith) with corresponding extinction ratio (ER) of 6 dB and the external injection power of -9 dBm is (are) required for such a wavelength-locked universal transmitter to carry the 16-QAM and 122-subcarrier formatted OFDM and data-stream. By increasing external injection-locking from -9 dBm to 0 dBm, the peak-to-peak chirp of the OFDM data stream reduces from 7.7 to 5.4 GHz. The side mode suppression ratio (SMSR) of up to 50 dB is achieved with wider detuning range between -0.5 nm to 2.0 nm under an injection power of 0 dBm. By modulating such a colorless laser diode with an OFDM data stream of 122 subcarriers at a central carrier frequency of 1.5625 GHz and a total bandwidth of 3 GHz, the transmission data rate of up to 12 Gbit/s in standard single-mode fiber over 25 km is demonstrated to achieve an error vector magnitude (EVM) of 5.435%. Such a universal colorless DWDM-PON transmitter can deliver the optical OFDM data-stream at 12 Gbit/s QAM-OFDM data after 25-km transmission with a receiving power sensitivity of -7 dBm at BER of 3.6 × 10(-7) when pre-amplifying the OFDM data by 5 dB.

Coherent Injection-Locking of Long-Cavity Colorless Laser Diodes With Low Front-Facet Reflectance for DWDM-PON Transmission

Long-cavity colorless laser diodes with different front-facet antireflection (AR) coatings are employed to perform the wavelength injection-locked ON–OFF-keying (OOK) data transmission. By changing front-facet reflectance of laser diode from 0.2% to 1.2%, the received OOK data enhance its Q factor by 6.3% and reduces its bit error rate (BER) by more than two orders of magnitude, which benefits from the improved signal-to-noise ratio and extinction ratio by up to 8.0%. Enlarging the injection-locking power from –6 to –3 dBm essentially helps the long-cavity colorless laser diode to promote its receiving power sensitivity from –27.9 to –29.2 dBm at BER of 10 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$^{-9}$</tex></formula> . However, the similar device with lower AR reflectance shows an opposite trend. The injection-locking-induced enhancement is limited within a frequency region controlled by the injection power, which results from a large disparity between continuous-wave injection and stimulated emission inside the long-cavity colorless laser diode. At same biased current and front-facet reflectance, a higher injection level provides a larger modulation throughput at a cost of decreasing bandwidth. The overinjection causes a limitation on frequency bandwidth of the long-cavity colorless laser diodes with lower front-facet reflectance. The numerical simulations with modified rate equations for the injection-locked long-cavity colorless laser diode with lower front-facet reflectance also elucidate that the transmission degrades distinctly at larger injection powers.

Optical 16-QAM-52-OFDM transmission at 4 Gbit/s by directly modulating a coherently injection-locked colorless laser diode

Coherently injection-locked and directly modulated weak-resonant-cavity laser diode (WRC-FPLD) for back-to-back optical 16-quadrature-amplitude-modulation (QAM) and 52-subcarrier orthogonal frequency division multiplexing (OFDM) transmission with maximum bit rate up to 4 Gbit/s at carrier frequency of 2.5 GHz is demonstrated. The WRC-FPLD transmitter source is a specific design with very weak-resonant longitudinal modes to preserve its broadband gain spectral characteristics for serving as a colorless WDM-PON transmitter. Under coherent injection-locking, the relative-intensity noise (RIN) of the injection-locked WRC-FPLD can be suppressed to ?105 dBc/Hz and the error vector magnitude of the received optical OFDM data is greatly reduced with the amplitude error suppressed down 5.5%. Such a coherently injection-locked single-mode WRC-FPLD can perform both the back-to-back and the 25-km-SMF 16-QAM-52-OFDM transmissions with a symbol rate of 20-MSa/s in each OFDM subcarrier. After coherent injection locking, the BER of the back-to-back transmitted 16-QAM-52-OFDM data is reduced to 2.5 × 10(-5) at receiving power of ?10 dBm. After propagating along a 25-km-long SMF, a receiving power sensitivity of ?7.5 dBm is required to obtain a lowest BER of 2.5 × 10(-5), and a power penalty of 2.7 dB is observed when comparing with the back-to-back transmission.