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Abstract
Vertical-cavity surface-emitting lasers (VCSELs) are widely used as light sources for high-speed communications. This is mainly due to their economical cost, high bandwidth, and scalability. However, efficient red VCSELs with emissions at 650 nm are required for plastic optical fiber (POF) technology because of the low-loss transmission window centered around this wavelength. This study investigates using 650-nm red VCSEL arrays in interconnected systems for POF communication to improve signal quality and increase data rates. The experimental results show that using one red VCSEL with a –3-dB bandwidth of 2 GHz in POF communication can achieve data rates of up to 4.7 Gb/s with 2 pJ/bit power efficiency using direct current-biased optical orthogonal frequency-division multiplexing (DCO-OFDM). The bit error ratio (BER) is 3.6×10−3, which is less than the hard-decision forward-error correction (FEC) limit of 3.8 × 10−3. In addition, temperature dependence measurements of the VCSEL have been presented from 15 $^\circ $C to 38 $^\circ $C. The essential parameters of VCSEL have also been measured: the maximum optical power is 2.5 mW, and the power conversion efficiency is 14%.
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1. Introduction
Polymer or plastic optical fibers (POFs) have recently garnered increased attention. POFs are in high demand in various high-volume applications for short-distance data communication, especially in home networks and in-vehicle infotainment systems [1–4]. More than 10 million POF transceiver modules are produced annually in the automobile sector for in-car entertainment systems [1,5]. This is mainly because plastic materials such as poly (methyl methacrylate) (PMMA), polystyrene, and polycarbonates are used to fabricate POFs, which are inexpensive [3,4]. Plastics also offer safety benefits in consumer and household contexts by removing the possibility of tiny glass pieces. POFs are easier to handle, and more resilient to bending, shock, and vibration than silica optical fibers, which should be handled carefully and cautiously [3,4]. Furthermore, POFs do not generate heat and are unaffected by electromagnetic radiation, unlike copper wires [4]. The challenge is to find suitable optical light sources that emit in the 510-nm, 570-nm, or 650-nm low-loss transmission windows of POFs [6], and at the same time, they need to be of low-cost, have high bandwidth, and support high data rates.
In the realm of POF communications, conventional light-emitting diodes (LEDs) and resonant-cavity LEDs (RCLEDs) are commonly used as optical sources [7–15]. However, the output power of LEDs is typically lower than that of laser diodes. This can limit the transmission distance of the POF communication system and the number of connected devices. Another significant issue with LEDs is that their modulation bandwidths are limited and fall within the range of a few MHz to tens of MHz [16]. In other words, the LEDs’ data rates are in the Mb/s range, and RCLEDs can only reach 1 Gb/s [17]. Moreover, LEDs suffer from a wide divergence angle of the beam compared to lasers and are hence more difficult to couple into optical fibers efficiently. Therefore, laser technology can increase both the data rate up to multiple Gb/s as well as allowing for longer transmission distances with high efficiency.
Since circa the 1990s, vertical-cavity surface-emitting lasers (VCSELs) have emerged as promising alternatives to edge-emitting lasers for high-speed communication. VCSELs have low-threshold currents, and they emit circular symmetric beams with small divergence, making them easier to couple into fibers effectively [18–20]. Additionally, VCSELs have short cavities as compared to their edge-emitting counterparts; thus, they produce only one longitudinal mode. As a result, VCSELs do not experience optical light output power versus current (L-I) curve kink phenomena, while other semiconductor lasers experience power instability and control issues [16,21]. Red VCSELs emitting at 650 nm would be ideal optical data transmitters for POFs. This is because POFs have a low-loss transmission window at 650 nm with a typical attenuation value of 0.12 dB/m [4,22]. This means 650-nm VCSELs will face low absorption and can transmit signals over longer distances in the POF than other VCSELs in the near-infrared wavelengths. In addition, red VCSELs offer narrow spectral linewidths compared to red LEDs, which can improve the system performance by reducing the effects of chromatic dispersion. They can also allow for denser wavelength-division multiplexing. Several studies have been conducted on red VCSEL communications using POFs [23–32]. 672-nm and 670-nm VCSELs have been demonstrated to achieve data rates of 2.5 Gb/s and 1.5 Gb/s, respectively [23,24]. Another study reported a data rate of 1.25 Gb/s over a POF using a 665-nm VCSEL [25]. Although higher rates have been demonstrated using 680-nm VCSELs, the data rates via POFs have been limited to 1.25 Gb/s with shorter-wavelength VCSELs (660 nm) that are closer to the transmission window of POFs (650 nm) [26].
A massively parallel interconnected system with POF communication based on transmitter arrays has the potential to revolutionize high-speed data transmission. This system consists of an array of transmitters that can be individually addressed and modulated to transmit data in parallel over multiple fibers. This can significantly increase the data transmission rate and system capacity [33]. The VCSEL array chip, with dimensions on the order of micrometers, can achieve the same data rate as a sizeable (ten orders of magnitude) micro-LED array chip over a parallel interconnected system. For example, the data rate of a single device herein was 4.7 Gb/s. Therefore, 225 micro-VCSELs (15 × 15 VCSEL array) would be sufficient to achieve 1-Tb/s data rate, compared to 10,000 micro-LEDs (100 × 100 LED array, each with a data rate of 0.1 Gb/s), as illustrated in Fig. 1. Compared with recent investigations involving low-optical-power micro-LED arrays, their energy consumptions per bit were 1.5 pJ/bit and 0.2 pJ/bit [33,34]. Our red VCSELs markedly demonstrate low energy per bit, which was quantified at 2 pJ/bit, although these VCSELs necessitate energy input to surpass the lasing threshold current, unlike LEDs. Nevertheless, the VCSELs achieve this high efficiency at optical powers that are three orders of magnitude higher than these LEDs, enabling much longer transmission distances.
Fig. 1. Diagram of two equivalent arrays to obtain the same data rate (1 Tb/s): (15 × 15) VCSELs array and (100 × 100) LEDs array.
In this study, we experimentally demonstrate using a high-speed (650 nm) red VCSEL over a POF as a data transmitter. The characterization of red 650-nm VCSEL’s are comprehensively presented to understand their performance characteristics. These include epitaxial layers, device structure, electrical and optical measurements, series resistance, efficiencies, temperature dependence, polarization stability, and beam divergence angles. The modulation bandwidth of the tested VCSELs and the high-speed communication performance are also presented.
2. Device structure and design
Scanning electron microscopy (SEM) was employed to obtain structural images of the device. A focused ion beam (FIB) was used to cut the sample to prepare a piece for imaging. High-resolution images of the model and elemental compositions across the interfaces for all layers were obtained by combining scanning transmission electron microscopy (STEM) with energy-dispersive X-ray spectroscopy (EDX) analysis.
The VCSELs used in the present work consist of a one-wavelength-long cavity and epitaxial layers grown on an n-type GaAs substrate. Figure 2(a) shows the schematic structure of the red VCSELs. The active region of the VCSEL designed to emit at a wavelength of 650 nm consists of three pairs of compressively strained quantum wells (GaInP) and quantum barriers (AlGaInP), as can be seen in Fig. 2(b). The thickness of the cavity is approximately 0.24 µm, whereas the oxidation layer (∼56-nm thick) is grown directly on top of the cavity, as shown also in Fig. 2(b). The top p-doped distributed Bragg reflector (DBR) consists of 35 pairs of AlGaAs layers with different compositions, as shown in the EDX plots in Fig. S1 in the Supplement 1. The thickness of the top p-DBR is around 3.5 µm, whereas the bottom n-DBR thickness is approximately 5 µm, which consists of 50 pairs of AlGaAs, but with higher Al composition in the alternating layers, as shown in Fig. S1 in the Supplement 1. Therefore, the bottom DBR has higher reflectivity than the top DBR, allowing the emitted light to exit from the top of the device.
Fig. 2. (a) Schematic structure of 650-nm VCSELs. (b) STEM image of the active region (c) Scanning electron microscopy (SEM) image of 650-nm VCSEL.
Figure 2(c) shows the SEM top-view of the fabricated VCSEL used in the current work. The cavity shape of the VCSELs is square shaped with an outer mesa side length of 15 µm. However, the actual square aperture inside the cavity is only about 9 µm × 9 µm, which was estimated by measuring the light-emitting area under spontaneous emission at 1.5 mA, which is below the lasing threshold.
3. Electrical and optical characterization
The electrical and optical characteristics of the VCSEL were measured using a Keithley 2520 laser diode testing system. The injected current was set to continuous wave (CW) operation for all measurements. A silicon-based detector (Labsphere, SCC-PM-SI) with a calibrated integrating sphere was used to measure the output power. The detector reverse bias was set to 15 V for all measurements. The detector’s responsivity is 3.3 × 10−3 A/W at 650 nm. A thermoelectric cooler (TEC) and a Keithley 2510 system controlled the temperature. The temperature was set between 15 $^\circ $C and 38 $^\circ $C, which was limited by the used equipment. Moreover, a multimode optical fiber (Thorlabs, M38L02) connected to the integrating sphere and the optical spectrum analyzer (OSA) (Yokogawa, AQ6373B) was used for spectral measurements. The experimental setup for the light output power-voltage-current (LIV) measurements and spectral measurements is presented in Supplement 1.
The maximum output power of the red VCSEL is approximately 2 mW at 20$^\circ $C as shown in the LIV curve in Fig. 3(a). This result is higher than other red VCSELs used in POF with less than 1 mW [1]. To demonstrate the performance of the VCSELs at high temperatures, the temperature dependence measurements from 15 $^\circ $C to 38 $^\circ $C are presented in Fig. 3. The maximum output powers are significantly reduced from 2.5 mW to 0.3 mW when the temperature increases from 15 $^\circ $C to 38 $^\circ $C. In other words, the drop percentage is –0.1 W/$^\circ $C. These results aligned with previous literature, which pointed out that the AlGaInP active material systems have relatively small conduction band offsets (∼0.17 eV) at 650 nm, thereby limiting its performance at high temperatures [35]. Subjected to the increased levels of electron leakage from the active region and aluminum content, which simultaneously increases the overall thermal impedance and internal absorption losses in red VCSELs, the performance of the device can be affected at high temperatures [35].
Fig. 3. (a) Temperature dependence measurements for red VCSELs. Inset: VCSELs spectra profiles at different temperatures. (b) Maximum wall-plug efficiency (WPEmax) and maximum external quantum efficiency (EQEmax) for multimode VCSELs at different temperatures.
The threshold current density at room temperature is less than 1.5 kA/cm2 at 20 $^\circ $C and increases to 2.2 kA/cm2 at 30 $^\circ $C. This increase in the threshold current density may be caused by an increase in electron leakage from the cavity or by changes in the gain spectrum and relative alignment of the cavity resonance [6]. Based on these results, the cavity temperature should be maintained at a lower appropriate temperature to ensure the threshold current density does not increase.
The spectral profiles of the VCSELs are presented in the inset in Fig. 3(a) at different temperatures, and the intensities decreased when the temperature increased. Given the size of the VCSEL and the far-field profiles (shown in the insets in Fig. 4(b)), the VCSEL can support multiple transverse modes. However, the resolution of the OSA (20 pm) is not high enough to resolve individual transverse modes. A peak wavelength shift of around 1.3 nm across the measured temperature can be observed. The temperature coefficient of the emission wavelength is therefore calculated to be only 0.05 nm/$^\circ $C. This small amount of redshift is one of the key advantages of VCSELs due to their short cavity, which can only support a single longitudinal mode, preventing mode hopping. This redshift is attributed to the fact that thermal expansion alters the gain medium bandgap energy and DBRs refractive index, shifting the longitudinal mode to longer wavelengths [35].
Fig. 4. (a) FWHM angle and HWHM angle. (b) The 1/e2 beam divergence angle versus injected current. Inset: far-field images for tested VCSEL at 3 mA and 7 mA.
Estimating transmitters’ efficiencies is fundamental in designing and operating optical communication systems. Characterizing the efficiency of VCSELs allows informed decisions about component selection of communication links, such as receivers, fibers, and other components. This will also help to reduce power per bit for low-energy consumption in communication links. We, therefore, characterized the red VCSEL efficiencies. In Fig. 3(b), the maximum wall plug efficiency (WPEmax) and maximum external quantum efficiency (EQEmax) at different temperatures are shown to evaluate the temperature effects on the efficiencies. When the temperature increases, the efficiencies of the red VCSELs decrease for both WPEmax and EQEmax. The efficiencies drop due to the weaker carrier confinement at high temperatures [28]. Moreover, WPEmax of red VCSEL is approximately 14% at 20 $^\circ $C, as evident in Fig. 3(b). This result is similar to prior work for the same wavelength and aperture size [35,36]. See Supplement 1 Eq. (1–3) for the calculation method and Supplement 1 for the graph of maximum external differential quantum efficiency and slope efficiency versus temperatures.
To establish a high-speed communication link, another essential electrical parameter of the AlGaInP VCSELs that is necessitated to characterize is the series resistance, which can enormously influence the modulation bandwidth of VCSEL. The series resistance (Rs) significantly depends on the device's design and fabrication parameters, such as layer thicknesses and doping concentration. It is typically minimized to improve the overall VCSEL performance. The series resistance of our VCSELs was only 50 Ω, which is four times less than other prior work with the same aperture size (9 µm) [37]. See Supplement 1 Eq. (4) and Fig. S4 for the calculation method and differential resistance versus temperature graph.
Another critical parameter of AlGaInP VCSELs is the beam divergence angle which refers to laser beam spread as it propagates away from the VCSEL aperture. The beam divergence angle can affect the coupling loss between the VCSEL and POFs. To evaluate the optical propagation of the red VCSEL, the full-width-half-maximum (FWHM), half-width-half-maximum (HWHM), and 1/e2 beam divergence angles have been measured based on the far-field images. The far-field images of a red VCSEL with a 9 µm × 9 µm square aperture at 3 mA and 7 mA injection currents are shown in the inset in Fig. 4(b). Figure 4 presents the beam divergence angle versus different injection currents. When the injection current increases, the beam's divergence angle will gradually rise. This is mainly due to increased higher order modes’ power since the used VCSEL is multimode.
The FWHM beam divergence angle is 10 degrees and less for all injection currents, whereas the 1/e2 beam divergence half-angle is 11 degrees and less, as shown in Figs. 4(a) and 4(b). This angle is much smaller than another prior work [35], which indicates that the VCSEL used in the current work is relatively more coherent and will improve coupling with POFs.
4. Polarization stability characterizations
Since coupling polarization switching devices with diffractive optical components may result in creative optical reconfigurable interconnects for short-range communications [38,39], we therefore also characterized the polarization behavior of red VCSELs using a Keithley 2400 source meter. A linear polarizer (Thorlabs, LPVIS050-MP) was mounted on a power meter (Newport, 2936-R). The output powers were measured with the polarizer oriented in two orthogonal directions, the x- and y-axes, each aligned with a side of the device, at different temperatures. The experimental setup used for the polarization measurements is in Supplement 1.
It is clear from Fig. 5(a) that the red VCSEL is linearly polarized. Although some infrared VCSELs are randomly polarized, red VCSELs are linearly polarized and have stable polarization, as similar published work has shown [35]. The net strain in the VCSEL's active region is one of the potential causes of the red VCSELs’ observed stable polarization [35].
Fig. 5. (a) Light output power-current-voltage measurements for red VCSEL at different temperatures and at parallel and perpendicular polarizers. (b) Maximum orthogonal polarization suppression ratio (OPSRmax) versus temperature.
The maximum orthogonal polarization suppression ratio (OPSR) for the red VCSELs at different temperatures is presented in Fig. 5(b). The OPSRmax is almost constant until 30 $^\circ $C and then drops at higher temperatures, which was also observed in other prior work [35]. Moreover, it is important to note that the OPSR also highly depends on aperture size, with smaller VCSELs having higher maximum OPSR values.
5. High-speed communication measurements
The frequency response measurements were performed at room temperature and under injection currents between 2 mA and 9 mA using a vector network analyzer after calibration, as shown in Fig. 6. As can be seen from the figure, the –3-dB bandwidth of a single VCSEL is 2 GHz at 2.5 mA injection current and higher. This value is comparable to the record bandwidth (3 GHz) for VCSELs at this wavelength range [25]. The performance of our VCSELs can be improved significantly by using high-speed ground-signal (GS) metal pads to reduce parasitic capacitance and inductance.
We then tested the communication performance and the data rate using both on-off keying (OOK) and direct current-biased optical orthogonal frequency-division multiplexing (DCO-OFDM). For OOK, the POF communication link consists of the 650-nm VCSEL, an unjacketed optical grade plastic optical fiber (1-m length, 250-µm core) (Edmund Optics, 02-531), and a silicon-based avalanche photodetector (APD, Menlo Systems, APD210). A bias-tee was used to provide the necessary DC biasing to the VCSEL, which was 4 mA, corresponding to a voltage bias of 2.3 V. See Supplement 1 for the experimental setup for the OOK measurements.
First, a bit error ratio (BER) tester (Agilent, J-BERT, N4903B) was used to measure the BER of the received OOK signals at varying data rates. The tester used non-return-to-zero (NRZ) OOK to generate a pseudorandom binary sequence (PRBS). Figure 7(a) displays the BER values versus various data rates. There were error-free data transmission rates up to the 2 Gb/s data rate. A data rate of 2.25 Gb/s was attained with a BER of 6 × 10−5, which is less than the hard-decision forward-error correction (HD-FEC) limit of 3.8 × 10−3. The eye diagrams for 1 Gb/s and 2 Gb/s are shown in Fig. 7(b). The rest of the eye diagrams for other data rate values are in Supplement 1.
Fig. 7. (a) Bit error ratio (BER) values versus different data rates, and (b) the eye diagrams at 1 and 2 Gb/s.
DCO-OFDM signals were also utilized in order to increase the system's spectral efficiency. The block diagram for the DCO-OFDM technique is in Fig. 8. A parallel array is created from a serial PRBS, which is the first step in the signal production process. Following that, the bits are quadrature amplitude modulated (QAM) modulated in accordance with the modulation order. DCO-OFDM is adapted to be suitable for intensity modulation/direct detection (IM/DD) systems. In this technique, half of the subcarriers in the OFDM symbol are used and the other half is a repeated flipped and conjugated version of the first half. This is done to make sure the signal is real-valued since IM/DD has a single degree of freedom (intensity) and cannot control the phase. This process (forcing Hermitian symmetry) guarantees that the output of the inverse fast Fourier transform (IFFT) is real-valued. To reduce the impact of inter-symbol interference (ISI) and approximate circular convolution, a cyclic prefix of size 10 is added, which simplifies the single-tap post-equalization procedure on the receiver side. After the parallel to serial conversion, the signal to be transmitted is finally obtained. The generated AC signal has positive and negative values, so a DC bias is added to the source. This bias is removed at the receiver side. The amplitude of the signal was set to 250 mV (peak-to-peak), and it passes through an amplifier (Mini-Circuits, ZHL-42W+) and a variable attenuator (kT2.5-60/1S-2S). The overall gain after the attenuator was around 5.5 dB in the frequency band we used. The amplitude and gain were selected by exhaustingly testing different values to maximize the performance and avoid any saturation on the transmitter’s or receiver's sides.
Fig. 8. Block diagram for DCO-OFDM modulation scheme. IFFT: inverse fast Fourier transform, AWG: arbitrary waveform generator, AMP: amplifier, GS Probe: Ground-Signal Probe, APD: a silicon-based avalanche photodetector, FFT: fast Fourier transform.
Synchronization is carried out on the receiver side by cross correlating the signal received with the recognized training symbols. The cyclic prefix is removed and the serial to parallel conversion is completed. By removing the Hermitian symmetry symbols, the fast Fourier transform (FFT) is used to retrieve the QAM symbols. The symbols are post-equalized before being demodulated into bits. The original signal is then compared against the sequence following the parallel to serial conversion, and the BER is determined for each subcarrier and the signal as a whole.
Using a FFT size of 1024, 500 subcarriers were employed. Specifically, the oscilloscope's sampling rate was 6.25 GSample/s, whereas the arbitrary waveform generator's (AWG) was 2 GSample/s. That means the OFDM signal had a bandwidth of around 1 GHz. In the signal, 150 OFDM symbols were transmitted, of which 5 were utilized for post-equalization channel estimation and synchronization.
First, we used the error vector magnitude to estimate the signal-to-noise ratio (SNR) of each individual subcarrier (refer to Fig. 9(c)). This was done by sending a uniform 4-QAM signal to test the SNR. Afterward, we used the adaptive bit and power loading shown in Figs. 9(a) and 9(b). The highest gross data rate achieved with a BER below the HD-FEC limit of 3.8 × 10−3 is around 4.7 Gb/s with a BER of 3.6 × 10−3. This means that the energy per bit consumed by the VCSEL is only 2 pJ/bit, making this VCSEL a promising high-efficiency transmitter for POF communication. The gross data rate is calculated using:
Fig. 9. (a) Power loading factor, (b) spectral efficiency, (c) signal-to-noise ratio (SNR), (d) bit error ratio (BER) versus both subcarrier index and frequency, and (e) constellation diagrams of the received signal.
Figure 9(d) displays the BER for each subcarrier, whereas Fig. 9(e) shows the constellation diagrams of the received signal. The net data rate, after taking into account the 7% overhead needed for HD-FEC, and the 3% training symbols, is estimated to be 4.2 Gb/s.
Table 1 compares different optical source types with different wavelengths for POF communication. This work clearly shows that 650-nm VCSEL array is superior to the micro-LED array (recent research [33,34]) in terms of data rate per single device, due to the reasons mentioned in the introduction section. It is also important to note that LEDs with low power consumption (operated at low current near the EQE peak) are only practical for short interconnect links because of the low optical power. To the authors’ best knowledge, this work presents the highest data rate and the lowest energy consumption per bit in POF communication links using 650-nm VCSELs. Moreover, our device operates at 650 nm, which closely matches the red transmission window of POFs, further increasing the potential maximum transmission distance.
Table 1. Comparison of different optical sources for plastic optical fiber communication.
Figure 10 shows the achieved data rates of prior works in the literature using red VCSELs [16,23–26,40–44]. Although the data rates of prior works are high around 680 nm, the achievable data rates drop significantly as the wavelength becomes closer to the 650-nm transmission window of POFs (also shown in Fig. 10 [45]). Our VCSEL in this work achieved the highest data rate around the desired transmission window. Furthermore, by employing high-speed GS metal pads, the data rate of our VCSELs can be substantially enhanced through the reduction of parasitic capacitance and inductance. Moreover, advanced communication and signal processing techniques can be used to further improve the data rate. For example, in Ref. [16], although only 3 Gb/s was achieved using OOK, the data rate was improved to 13.5 Gb/s by utilizing machine learning with a bidirectional long short-term memory (Bi-LSTM) scheme.
6. Conclusion
In conclusion, we experimentally achieved a 4.7-Gb/s data rate with a 3.6 × 10−3 BER by using one 650-nm VCSEL as a transmitter and DCO-OFDM scheme modulation through POFs. These VCSELs can potentially achieve up to Tb/s speeds using parallel streams based on a 15 × 15 VCSEL array, which is substantially smaller than LED arrays needed for the same data rate. The utilization of POFs in conjunction with a 650-nm VCSEL array represents a promising avenue in the field of optical communication and data transmission. The integration of a 650-nm VCSEL array further enhances the potential of POFs for various applications. The 650-nm wavelength matches the transmission window of POFs and is well-suited for short-distance communication and offers compatibility with existing optical components. The array configuration provides redundancy and increased data throughput, making it suitable for high-speed data transmission in environments where reliability is paramount.
Funding
King Abdullah University of Science and Technology (BAS/1/1614-01-01, ORA-2022-5313); Princess Nourah Bint Abdulrahman University.
Disclosures
The authors declare no conflicts of interest.
Data availability
Data underlying the results presented in this paper are not publicly available at this time but may be obtained from the authors upon reasonable request.
Supplemental document
See Supplement 1 for supporting content.
References
1. T. Wipiejewski, G. Duggan, D. Barrow, et al., “Red VCSELs for POF data transmission and optical sensing applications,” Proc.IEEE 57th, 717–721 (2007).
2. O. Ziemann, J. Krauser, P.E. Zamzow, et al., POF handbook, 2nd ed. (Springer, 2008).
3. K. Bhowmik and G.D. Peng, Polymer optical fibers (Springer Nature, 2019), pp.1–51.
4. P. Polishuk, “Plastic optical fibers branch out,” IEEE Commun. Mag. 44(9), 140–148 (2006). [CrossRef]
5. T. Kibler and E. Zeeb, “Optical data links for automotive applications,” Proc. IEEE, 54th, 1360–1370 (2004).
6. J. Lambkin, T. Calvert, B. Corbett, et al., “Development of a red VCSEL-to-plastic fiber module for use in parallel optical data links. In Vertical-Cavity Surface-Emitting Lasers,” Proc SPIE 3946, 95–105 (2000). [CrossRef]
7. JM. Wun, CW. Lin, W. Chen, et al., “GaN-based miniaturized cyan light-emitting diodes on a patterned sapphire substrate with improved fiber coupling for very high-speed plastic optical fiber communication,” IEEE Photonics J. 4(5), 1520–1529 (2012). [CrossRef]
8. JD. Lambkin, C. Cahill, D. Carey, et al., “Resonant cavity light emitting diodes: An enabling technology for plastic fibre communication applications,” In International Conference on Plastic Optical Fiber (2010).
9. R. Wirth, B. Mayer, S. Kugler, et al., “Fast LEDs for polymer optical fiber communication at 650nm,” Proc. SPIE 6013, 60130F (2005). [CrossRef]
10. M. Dumitrescu, M. Saarinen, M. Guina, et al., “High-speed resonant cavity light-emitting diodes at 650 nm,” IEEE J. Sel. Top. Quantum Electron. 8(2), 219–230 (2002). [CrossRef]
11. J. Lambkin, B. McGarvey, M. O’Gorman, et al., “RCLEDs for MOST and IDB 1394 automotive applications,” In Proc of the 14th International Conference on Polymer Optical Fiber (2005).
12. M. Akhter, P. Maaskant, B. Roycroft, et al., “200 Mbit/s data transmission through 100 m of plastic optical fibre with nitride LEDs,” Electron. Lett. 38(23), 1457 (2002). [CrossRef]
13. J. Shi, H. Huang, J. Sheu, et al., “The improvement in modulation speed of GaN-based Green light-emitting diode (LED) by use of n-type barrier doping for plastic optical fiber (POF) communication,” IEEE Photonics Technol. Lett. 18(15), 1636–1638 (2006). [CrossRef]
14. J. Shi, C. Lin, W. Chen, et al., “Very high-speed GaN-based cyan light emitting diode on patterned sapphire substrate for 1 Gbps plastic optical fiber communication,” In Optical Fiber Communication Conference (pp. JTh2A-18). Optica Publishing Group (2012).
15. S. Huang, R. Horng, J. Shi, et al., “High-performance InGaN-based green resonant-cavity light-emitting diodes for plastic optical fiber applications,” J. Lightwave Technol. 27(18), 4084–4094 (2009). [CrossRef]
16. S. Oh, M. Yu, S. Cho, et al., “Bi-LSTM-Augmented deep neural network for multi-Gbps VCSEL-based visible light communication link,” Sensors 22(11), 4145 (2022). [CrossRef]
17. B. Charbonnier, P. Urvoas, M. Ouzzif, et al., “Gigabit transmission over 50 m of Step-Index Plastic Optical Fibre,” In International Conference on Plastic Optical Fibers (POF) (2008), pp. 1–3.
18. M. Jetter, R. Roßbach, and P. Michler, “Red Emitting VCSEL,” In VCSELs: Fundamentals, Technology and Applications of Vertical-Cavity Surface-Emitting Lasers (Springer, 2012), pp. 379–401.
19. K Johnson, M. Hibbs-Brenner, W. Hogan, et al., “Advances in Red VCSEL Technology,” Advances in Optical Technologies 2012, 1–13 (2012). [CrossRef]
20. K Iga, “Forty years of vertical-cavity surface-emitting laser: invention and innovation,” Jpn. J. Appl. Phys. 57(8S2), 08PA01 (2018). [CrossRef]
21. HT. Cheng, YC. Yang, TH. Liu, et al., “Recent advances in 850 nm VCSELs for high-speed interconnects,” Photonics 9(2), 107 (2022). [CrossRef]
22. R. Rossbach, T. Ballmann, R. Butendeich, et al., “Red VCSEL for automotive applications,” Proc. SPIE 5663, 135–146 (2005). [CrossRef]
23. SW. Chiou, YC. Lee, CS. Chang, et al., “High-speed red RCLEDs and VCSELs for plastic optical fiber application,” Proc SPIE 5739, 129–133 (2005). [CrossRef]
24. DM. Kuchta, RP. Schneider, and KD. Choquette, “Large-and small-signal modulation properties of red (670 nm) VCSELs,” IEEE Photonics Technol. Lett. 8(3), 307–309 (1996). [CrossRef]
25. G. Duggan, DA. Barrow, T. Calvert, et al., “Red vertical cavity surface emitting lasers (VCSELs) for consumer applications,” Proc SPIE 6908, 69080G (2008). [CrossRef]
26. M. Wiesner, M. Eichfelder, R. Roßbach, et al., “Red and fast vertical-emitting semiconductor laser for POF application,” in Kommunikationskabelnetze, Beiträge der 15. ITG-Fachtagung. ITG-Fachberichte212, 157–160 (2004).
27. DM. Kuchta, JA. Kash, P. Pepeljugoski, et al., and S. Kilcoyne “High speed data communication using 670 nm vertical cavity surface emitting lasers and plastic optical fiber,” International Conference on Plastic Optical Fibers (POF) (1994) pp. 135–139.
28. T. Wipiejewski, T. Moriarty, V. Hung, et al., and V. Gerhardt “Gigabits in the home with plugless plastic optical fiber (POF) interconnects,”In 2nd Electronics System-Integration Technology Conference IEEE (2008) pp. 1263–1266.
29. K. Johnson, M. Dummer, and M. Hibbs-Brenner, “Progress in extended wavelength VCSEL technology,” Proc. SPIE 8639, 863905 (2013). [CrossRef]
30. D. Visani, C. Okonkwo, S. Loquai, et al., “Beyond 1 Gbit/s transmission over 1 mm diameter plastic optical fiber employing DMT for in-home communication systems,” Lightwave Technology Journal 29(4), 863905 (2011). [CrossRef]
31. CM. Okonkwo, E. Tangdiongga, H. Yang, et al., “Multi-gigabit transmission over 1 mm core diameter plastic optical fibers,” J. Lightwave Technol. 29(2), 186–193 (2011). [CrossRef]
32. JA. Lehman, RA. Morgan, D. Carlson, et al., “High-frequency modulation characteristics of red VCSELs,” Electron. Lett. 33(4), 298–300 (1997). [CrossRef]
33. B. Pezeshki, F. Khoeini, A. Tselikov, et al., “MicroLED array-based optical links using imaging fiber for chip-to-chip communications,” In Optical Fiber Communication Conference (2022) pp. W1E-1.
34. B. Pezeshki, A. Tselikov, R. Kalman, et al., “Parallel microLED-based optical links with record data rates and low power consumption,” in CLEO (2023). [CrossRef]
35. A. Ghods and M. Dummer, “650 nm red VCSELs with improved temperature performance,” Proc. SPIE 12439, 19 (2023). [CrossRef]
36. A. Knigge, M. Zorn, H. Wenzel, et al., “High efficiency AlGaInP-based 650 nm vertical-cavity surface-emitting lasers,” Electron. Lett. 37(20), 1222 (2001). [CrossRef]
37. S. Weidenfeld, H. Niederbracht, M. Eichfelder, et al., and P. Michler “Transverse mode and polarization characteristics of AlGaInP-based VCSELs with integrated multiple oxide apertures,” Proc. SPIE,8432, Semiconductor Lasers and Laser Dynamics V, 43–50 (2012).
38. N. Nieubor, K. Panajotov, A. Goulet, et al., “Data transparent reconfigurable optical interconnections based on polarization-switching VCSELs and polarization-selective diffractive optical elements,” IEEE Photonics Technol. Lett. 10(7), 973–975 (1998). [CrossRef]
39. L. Desmet, K. Panajotov, J. Schwartz, et al., “Experimental characterisation of 670 nm red VCSELs,” Proc. IEEE-LEOS Benelux Chapter 1, 131–134 (2002).
40. H. Lee, S. Lee, B. Kim, et al., “Highly efficient active optical interconnect incorporating a partially chlorinated ribbon POF in conjunction with a visible VCSEL,” Opt. Express 22(10), 11778–11787 (2014). [CrossRef]
41. I. Lu, C. Yeh, D. Hsu, et al., “Utilization of 1-GHz VCSEL for 11.1-Gbps OFDM VLC wireless communication,” IEEE Photonics J. 8(3), 1–6 (2016). [CrossRef]
42. L. Wei, C. Chow, C. Hsu, et al., “Bidirectional visible light communication system using a single VCSEL with predistortion to enhance the upstream remodulation,” IEEE Photonics J. 10(3), 1–7 (2018). [CrossRef]
43. C. Chang, C. Li, H. Lu, et al., “A 100-Gb/s multiple-input multiple-output visible laser light communication system,” J. Lightwave Technol. 32(24), 4723–4729 (2014). [CrossRef]
44. K. Johnson, W. Hogan, M. Dummer, et al., “Advances in high-speed red VCSEL Performance,” Proc. 21th International Conference on Polymer Optical Fibers (2012) pp. 248–253.
45. K. Jang, S. Shin, S. Kim, et al., “Measurement of Cerenkov radiation induced by the gamma-rays of Co-60 therapy units using wavelength shifting fiber,” Sensors 14(4), 7013–7025 (2014). [CrossRef]
