Open Access
Add to BibSonomy
Abstract
To meet the ever-increasing bandwidth demands in the future broadband wireless networks, the millimeter-wave (mm-wave) frequency region is being actively perused, owing to its broad bandwidth and high frequencies. In this paper, a photonic mm-wave system is proposed and experimentally demonstrated based on the injection locking of a direct multilevel modulated laser to a spacing-tunable two-tone light. Since the mm-wave frequency of the generated signal is locked to the frequency spacing of the injected two-tone light, it shows better frequency stabilization than the schemes based on two free-running lasers. Moreover, by simply tuning the tone spacing, the mm-wave frequency could be easily re-configured, offering flexibility in the mm-wave signal generation. Instead of using complex and expensive optical modulators, the multilevel modulation on the mm-wave data carrier is implemented through the direct multilevel modulation of a laser and the injection locking. A 28 Gbps four-level pulse amplitude modulation (PAM4) is realized by biasing a 10 G-class laser at a current far from the threshold, providing a cost-effective and simple mm-wave generation scheme. In the experiment, a photonic approach to generating 28 Gbps PAM4 60 GHz/80 GHz mm-wave signals is experimentally demonstrated. A power penalty of less than 0.2 dB is observed for the filtered-out PAM4 signals with respect to the original PAM4. Besides, an ultra-low phase noise of up to −98 dBc/Hz is obtained for the mm-wave carriers after the injection locking. The proposed scheme possesses the flexibility and frequency stability of the mm-wave frequency, and also has low cost and implementation complexity.
© 2018 Optical Society of America under the terms of the OSA Open Access Publishing Agreement
1. Introduction
With the emergence of variety of new mobile services such as mobile video streaming, mobile game and virtual and augmented realities (VR/AR), mobile data traffic in wireless networks is rapidly increasing [1,2]. Owing to the wide bandwidths and high frequencies, wireless delivery in millimeter-wave (mm-wave) frequency bands is highly desirable to support high-capacity multi-gigabit-class mobile data transmission. To generate mm-wave signals, photonic mm-wave techniques have been intensively studied based on optical approaches [1–14]. Usually ultra-fast optical baseband signal is first generated by broadband optoelectronic modulators and then is photo-mixed with another continuous wave to up-convert baseband data onto an mm-wave carrier without the need for mm-wave oscillator or frequency multiplications [1–4]. Photonic mm-wave techniques enable the seamless integration of wireless and fiber-optics networks. To realize large capacity fiber-wireless integrated systems, multilevel modulation or multiplexing in polarizations, spaces, carriers or bands have been applied to the data carrier modulation to boost the capacity of the mm-wave signals. However, these approaches rely on complex optoelectronic devices such as dual-parallel modulators [1–4], dramatically increasing the implementation complexity and cost. As an alternative to generating mm-wave signals, injection locking of semiconductor lasers [5–14] has also been widely used to generate mm-wave carriers with high purity (low phase noise) [13–17] and high optical signal-to-noise ratio (OSNR) [18]. Moreover, through the direct modulation on the slave laser, the data modulation could be imposed onto the data carrier after the injection locking, reducing the implementation cost and complexity. However, the previously-reported schemes mainly focused on the low-speed (less than 5 Gbit/s) [6–10] or binary data modulations [11–14].
In this paper, we propose an optical frequency-reconfigurable mm-wave signal synthesis scheme by injection locking a directly multilevel-modulated laser to an optical two-tone light with a tunable spacing. A 10 G-class directly modulated laser (DML) is biased at the current far above the threshold [19,20] and driven by multilevel electronics to synthesize a 28 Gb/s optical four-level pulse amplitude modulation (PAM4) signal. In addition to the aforementioned benefits of injection locking such as high purity and high OSNR, the proposed scheme possesses the following advantages: (a) the mm-wave frequency is locked to the frequency spacing of the seeding two-tone light, showing higher stability than the schemes based on two free-running lasers; (b) the mm-wave frequency of the synthesized mm-wave signal could be simply re-configured by tuning the frequency spacing of seeding two-tone light, offering the flexibility in the mm-wave signal generation; (c) in contrast to the schemes using complex broadband modulators for multilevel modulation, direct multilevel modulation on a 10 G-class DML is used for generating 28 Gbps PAM4 and imposing the data onto one carrier, providing a cost-effective solution to generating mm-wave signals. By using the proposed scheme, in this paper, 28 Gbps PAM4 mm-wave signals at 60 or 80 GHz are experimentally demonstrated by injection locking a DML laser to a spacing-tunable two-tone light. A further capacity increase is expected by injection locking of two slave DMLs (twin lasers) for enabling the complex data modulation on the mm-wave data carrier [21]. Moreover, a monolithic integration of optical components [17,22] such as optical frequency comb generator (OFCG), optical filters and DMLs would open up a new route to photonic synthesis of mm-wave signals with superior quality and efficient cost.
2. Operation principle
Injection locking is a well-known and commonly used approach for coherent light amplification. Since the slave laser is phase locked to the seeding beam, injection locking is often deployed to improve the performance of slave lasers. Injection locking is usually obtained on a single-mode laser injected by a single-frequency seeding beam [23]. With a two-tone seeding beam, one of carriers which frequency is close to that of the slave laser is coherently amplified after the injection locking. The two-tone seeding beam could be obtained by slicing two lines from an optical fiber comb (OFC) with a certain frequency spacing, which corresponds to the mm-wave frequency when using it for generating optical mm-wave carriers. With a frequency-locked OFCG, it could provide stable and frequency-locked mm-wave carriers in contrast to the schemes based on free-running lasers. Moreover, as it has been extensively studied, the generated wireless mm-wave signal based on injection locking has high purity, i.e. low phase noise, owing to the phase correlation of the two carriers, and high OSNR.
To implement the data modulation on the data carrier of the mm-wave signal, in contrast to complicated external modulation, a simple direct modulation and injection locking are deployed. To enable high-capacity modulations by using a 10 G-class DML, modulation bandwidth of the DML could be greatly enhanced by deliberately setting the current bias far above the threshold current [19,20]. Besides, the use of multilevel modulation such as PAM4 can further increase spectral efficiency and accelerate data rate. Therefore, the use of direct multilevel modulation on a DML and injection locking could effectively reduce the required bandwidth for optical and electrical components, thus reducing the implementation complexity and cost.
Figure 1 depicts the operation principle of the proposed optical mm-wave signal generation system. A DML at νS is directly modulated and is serving as a slave laser in the injection locking. On the other hand, as shown in Fig. 1(a), a two-tone light at νM1 and νM2 with a tunable frequency spacing (ΔνM = νM1 -νM2) and a certain power ratio (R = PM1-PM2), where PM1 and PM2 denote the power of tones at νM1 and νM2, respectively, is prepared as a master source, and launched into the DML through a circulator for injection locking. The weaker tone (νM1) in the master source is selected as the master beam and placed closer to the slave laser (νS). Once the frequency offset (FO, Δν = νM1 -νS) and the injection ratio (IR = PM1-PS) between them, where PS represents the output power of the slave laser, are adjusted to satisfy the injection locking condition [24], the slave DML laser is locked to one of the tones and the carried data modulation on νS is also transparently transferred onto the locked component at νM1, resulting in data carriers for mm-wave signals. To achieve a stable locking, the FO, IR and the polarizations between the master tone and the slave laser should be well optimized. FO and IR are two of the main control parameters of interest in the injection locking [24]. Note that, in this application, the optical injection locking is operated in the low injection ratio regime, i.e. IR<-6 dB [25], which is most commonly used for the phase synchronization of a slave laser to a master beam. Moreover, since the injection locking would coherently and selectively amplify the injected master beam, to ensure a comparable power levels between the data carrier and CW carrier after the injection locking, the launched two-tone light is deliberately arranged with a certain power difference, corresponding to R, and the weaker tone is selected as the master beam for injection locking. On the other hand, the other tone is kept unmodulated and is serving as CW carrier. After a stable injection locking, the slave laser is phase and frequency locked to the master beam. Since the injected two tones are phase correlated, the phase coherence between two carries after the injection locking is remained, which results in a high-purity (low phase noise) mm-wave carriers. Also, the frequency spacing between them is locked to the original spacing of the two-carrier seeding light. In addition to the injection locking, nonlinear mixing between strong beams in the slave semiconductor laser may generate several four-wave mixing (FWM) spurious components, which should be filtered out in the mm-wave generation. As shown in Fig. 1(c), after the injection locking, an optical mm-wave signal could be successfully synthesized with a locked frequency spacing. Besides, by re-configuring the carrier spacing of the injection two-carrier seeding light, the generated mm-wave frequency could be simply tuned, offering the flexibility in the mm-wave generation. Moreover, the resultant photonic mm-wave signal is essentially a single-sideband (SSB) modulated signal, which inherently avoids the microwave power fading caused by the chromatic dispersion in the optical link [10,14].
3. Experiment and results
To verify the proposed scheme, a proof-of-concept experiment was conducted. Figure 2 shows the experimental setup. A light at 1549.3 nm from a tunable laser (Santec, TSL-510) was fed to a dual-drive intensity modulator (IM) which was driven by a 20 GHz RF clock with 26 dBm RF power to generate an OFC with 20 GHz comb line spacing. As shown in Fig. 3 (a), 10 comb lines spanning 180 GHz are obtained with >20 dB OSNR for each line. To generate a spacing-tunable two-tone light, an optical processor (Finisar, Waveshaper 4000s) was used to select two comb lines from the OFC with a 60 GHz or 80 GHz spacing. As shown in Figs. 3(b)-3(c), after the optical processor, two-tone lights with a 60 GHz and 80 GHz spacing and around −10 dB power ratio were obtained for use as master seeding sources in the injection locking. The slave laser used in the experiment was a 10 G-class DML exhibiting a 3-dB modulation bandwidth of around 10 GHz. To enhance the modulation bandwidth of the direct modulation, a DML was biased at a 70 mA current, which is 5 times the threshold current, ~14 mA. A 28 Gbps PAM4 electrical data was generated from an arbitrary waveform generator (AWG, Tektronix 70001A) and was used to drive the DML for generating an optical 28 Gbps PAM4 signal with an output power of around 10 dBm. The spectra of the modulated PAM4 signals are shown as red lines in Fig. 4. The frequency of the weaker tone (νM1) was first tuned close to that of the slave DML (νS) by adjusting the frequency of the OFC’s laser source. A power attenuator was inserted before the circulator to adjust the injected power. To check whether a stable locking is realized or not, the power of the slave laser and the master tone was tapped and fed to a photodetector (PD) and an electrical spectrum analyzer for monitoring the beating component to determine whether the frequencies of them were locked or not. Once the frequency detuning and injection power of the seeding beam with respect to the slave DML laser are optimized, the DML could be successfully locked to the weaker tone (υM1). As a result, one tone of the master two-tone seeding light is selected for coherent amplification and data modulation through the injection locking.
Fig. 2 Experimental setup for generating optical mm-wave signals. PD: photodetector, ATT: attenuator, BPF: bandpass filter, PC: polarization controller, LD: laser, IM: intensity modulator, EDFA: Erbium-doped fiber amplifier.
Fig. 3 Measured optical spectra (resolution: 0.01nm) of (a) optical frequency comb (OFC), and filtered two-tone light from an OFC with tunable frequency spacing of (b) 60 GHz and (c) 80 GHz.
Fig. 4 Measured optical spectra (resolution: 0.01nm) of the directly-modulated DML (red lines) and the output after injection locking (blue lines) with the injected (a) 60 GHz and (b) 80 GHz two-tone light. Insets: Zoom-in plots of the data carriers (scales: 1GHz/div, 5dB/div).
The optical spectra after injection locking using two-tone light with spacing of 60 GHz and 80 GHz are shown as blue lines in Fig. 4(a) and 4(b), respectively, corresponding to the optical 60 GHz and 80 GHz mm-wave signals. In both cases, OSNRs of more than 60 dB are observed for the data carriers after the injection locking. As discussed in [24], when the slave laser is biased far from the threshold current, a larger locking range could be obtained with a negative detuning, i.e., νM1<νS. In the experiment, to easily realize a stable locking, the injection locking was operated in the negative detuning regime with a low IR. As for the generation of optical 60 GHz mm-wave signal shown in Fig. 4(a), the FO and IR between the master seeding carrier (νM1) and slave laser (νS) were −0.8 GHz and −34dB, respectively. When generating the optical 80 GHz mm-wave signal, as shown in Fig. 4(b), the FO and IR were measured as −1.2 GHz and −31 dB, respectively. Although the low IR leads to a narrow locking bandwidth [25], it could reduce the risk of device damage and the power consumption. After the injection locking, the slave DML laser started to follow the phase and frequency of the injected weaker tone along with a preserved intensity modulation, synthesizing the data carrier of mm-wave signals. Due to this “phase locking” effect [26] in the injection locking, the linewidth of the data carrier turned into that of the master tone. In the experiment, the linewidths of the laser source of two-tone seeding source and the slave DML are ~100 kHz and 1 MHz, respectively. As shown in the insets of Fig. 4, a visible linewidth reduction and a side-lobe suppression of the data carrier are observed after the injection locking. Meanwhile, the spacing between the data carrier and mm-wave carrier was locked to 60 GHz or 80 GHz, which is same as the spacing between the injected two tones. Here, the power ratio between the unmodulated CW carrier and the data carrier in the resultant optical mm-wave signals is defined as the carrier-to-sideband power ratio (CSR). As shown in Fig. 4, the CSRs of the optical 60 GHz and 80 GHz mm-wave signals are measured as −24 dB and −21 dB, respectively. In this experiment, owing to the use of injection locking, the data carriers have large enough OSNR (>60 dB). Therefore, the CSR could be simply optimized by using an optical filter [11] to balance the power of carriers. Other approaches to improve the CSR are to boost the launched power of the two-tone master light, or to decrease the bias current of the DML slave laser thus reduce the power of the data carrier after the injection locking. However, these may increase the risk of device damage, or sacrifice the modulation bandwidth. In this proof-of-concept experiment, due to the lack of a wideband RF mixer (envelope detector) [27] or a broadband analog-to-digital converter in the laboratory, we could not directly evaluate the performance of wireless mm-wave signals. Thus, this CSR optimization was not performed.
3.1 High-purity mm-wave
As discussed previously, the injection locking and the use of coherent two-tone seeding light are of great help in synthesizing high purity mm-waves. To investigate the phase noise performance of the generated mm-wave carriers, the SSB phase noise of the generated 60 GHz mm-wave carriers with around 10 dB power difference was measured by using a PD (Finisar, XPDV2320R, 3 dB bandwidth: 50 GHz), an electrical spectrum analyzer (Agilent, PXA N9030A, bandwidth: 3Hz-50GHz) and a waveguide harmonic mixer (Agilent, M1970V-002, bandwidth: 50GHz-80GHz). For comparisons, the SSB phase noise of the two-tone seeding source and two free-running lasers with the same frequency spacing and power ratio was also measured. As shown in Fig. 5, since the two-tone seeding light was originated from an OFCG after spectrum shaping, it shows a SSB phase noise as low as −98 dBc/Hz at a frequency offset of 10 kHz. After the injection locking, a pretty similar SSB phase noise was obtained for the generated 60 GHz mm-wave. However, if using two free-running lasers to generate the mm-wave, the observed SSB phase noise is shown as about −53 dBc/Hz at a 10-kHz frequency offset, ~45 dB higher than that obtained in our proposed scheme. This indicates that a higher purity of the mm-wave is obtained in the proposed scheme by injecting a two-tone seeding light to a DML.
Fig. 5 Measured SSB phase noise of the 60 GHz mm-wave using a two-tone seeding light, the two-tone light after injection locking, and two free-running lasers.
3.2 Modulation bandwidth enhancement
To ensure the high-speed modulation in the data carrier using a 10 G-class DML, a high bias current was applied to the DML to increase the relaxation oscillation frequency of the laser diode, thus providing an enough E/O modulation bandwidth. To understand the dependence of the E/O bandwidth on the applied bias current, we measured the relative power ratio of the first sideband against the optical carrier when applying a RF clock signal with a 0 dBm average power and frequencies tuned from 5 GHz to 15 GHz under different bias currents. The normalized E/O frequency response is plotted and shown in Fig. 6. It is clear that the increase of bias current is helpful in enlarging the modulation bandwidth. In contrast to the case at 15 mA (filled diamonds), the modulation bandwidth is greatly enhanced when the bias current is set at 70 mA, represented by filled square symbols in Fig. 6. It guarantees up to 28 Gbps data modulation even using a 10 G-class laser diode.
Fig. 6 Measured E/O frequency response of direct modulation by driving DML using RF clocks with different frequency (5 GHz to 15 GHz) under different bias currents.
As discussed in [24], a stable locking could be realized when the slave laser is biased at a current either close to the threshold or far from the threshold. A larger locking rang could be obtained when the laser is biased close to the threshold compared with the high bias current case. But, a large bias current could provide a higher output power and a higher OSNR for the data carrier after the injection locking, which is essential for the superior performance mm-wave signal generations.
3.3 BER performance
After the detection using a broadband photodiode, specifically a uni-travelling-carrier photodiode (UTC-PD), 28 Gbps PAM4 60 GHz or 80 GHz mm-wave signals would be obtained. Due to the aforementioned reasons, we could not directly evaluate the performance of wireless mm-wave signals. Instead, after the injection locking, the PAM4 modulated data carrier was filtered out and assessed by an optical PAM4 receiver, consisting of a PD, analog-to-digital converter (real-time oscilloscope) and offline digital signal processing. After the detection by the PD, the detected signals were sampled by using a digital real-time oscilloscope (Tektronix, MSO73304DX, bandwidth: 33 GHz) operating at 50 GSample/s. In the offline digital signal processing, for equalization, a 2-sample per symbol feed forward equalizer and a 1-sample per symbol decision feedback equalizer were used with 3 forward taps and 1 feedback tap. The BERs of the PAM4 signals before (open symbols) and after (filled symbols) the injection locking were measured and plotted in Fig. 7. For the generated 28 Gbps PAM4 signals in both 60 GHz and 80 GHz mm-wave systems, less than 0.2 dB power penalty was observed at BER of 10−3 with respect to the original PAM4 signal generated through the direct multilevel modulation. The measured eye diagrams of the original and the filtered-out PAM4s from the generated optical 60 GHz and 80 GHz mm-wave signals are shown in Fig. 8 with the received power of around −6 dBm. Compared with the original PAM4 signal, negligible power penalty of the filtered PAM4 data carriers after the successful injection locking indirectly verifies the feasibility of the proposed scheme. However, without proper tuning of the frequency detuning and injection power, unsuccessful locking would bring the slave laser to bi-stable or unstable states [24], which leads to a larger power penalty and error floor. For instance, as shown in the filled blue symbols, around 2 dB power penalty at BER of 10−3 and an error floor at BER of 4 × 10−4 are observed with IR of around −28 dB. As discussed in [28], a good quality of optical data carrier facilitates the generation of a high performance of wireless mm-wave signals. In addition to the high performance of the generated optical data carrier, as shown in the section 3.1, the obtained mm-wave carriers based on injection locking possess an ultra-low phase noise of up to −98 dBc/Hz at a 10 kHz offset, ensuring the generation of high-purity wireless mm-wave signals. These indirectly verify the feasibility of the proposed scheme.
Fig. 7 Measured BER vs. received optical power of the 28 Gbps PAM4 signals from the directly modulated DML PAM4 signal (open symbols) and the filtered PAM4 data carrier after the injection locking (filled symbols).
Fig. 8 Measured eyes of 28 Gb/s PAM4 signals: (a) the original PAM4 signal from DML, the filtered PAM4 signals from the generated (b) 60 GHz and (c) 80 GHz mm-wave signals. (Time scale: half symbol period, i.e., 1/2fS, (fS = 14GHz) per division.
4. Conclusion
In this paper, a flexible optical synthesis approach of mm-wave signals has been proposed and experimentally demonstrated. The flexible optical mm-wave signal generation is achieved by injection locking of a direct multilevel modulated DML laser to a spacing-tunable two-tone seeding light for generating 28 Gbps PAM4 mm-wave signals at 60 GHz and 80 GHz. With a two-carrier light as the master seeding source and a DML as the slave laser, one of the injected seeding tones is selectively amplified and meanwhile the data modulation carried on DML is transparently imposed onto the selected carrier through the injection locking. On the other hand, the other carrier is kept unmodulated as mm-wave carrier with the separation locked to that of the injected two-tone seeding light. By re-configuring the carrier spacing of the injection two-tone seeding light, the generated mm-wave frequency could be simply changed, offering the flexibility in the mm-wave generation. Without the use of complex external modulators, 28 Gbps data carrier modulation is achieved by injection locking of a 10 G-class direct multilevel modulated DML biased at current far from the threshold, providing a cost-effective high-speed mm-wave signal generation scheme. Moreover, the injection locking and deploy of two-tone light produce a high purity mm-wave with a SSB phase noise of around −98 dBc/Hz at a 10 kHz frequency offset.
Funding
Japanese Society for the Promotion of Science (JSPS) Grant-in-Aid for Scientific Research (C) of Ministry of Education, Culture, Sports, Science and Technology (MEXT) (15K06033 and 18K04152).
References and links
1. J. Yu, X. Li, and N. Chi, “Faster than fiber: over 100-Gb/s signal delivery in fiber wireless integration system,” Opt. Express 21(19), 22885–22904 (2013). [CrossRef] [PubMed]
2. S. Ishimura, B. G. Kon, K. Tanaka, K. Nishimura, H. Kim, Y. C. Chung, and M. Suzuki, “Broadband IF-over-fiber transmission with parallel IM/PM transmitter overcoming dispersion-induced RF power fading for high-capacity mobile fronthaul links,” IEEE Photonics J. 10(1), 1–9 (2018). [CrossRef]
3. A. Kanno, K. Inagaki, I. Morohashi, T. Sakamoto, T. Kuri, I. Hosako, T. Kawanishi, Y. Yoshida, and K. Kitayama, “40 Gb/s W-band (75-110 GHz) 16-QAM radio-over-fiber signal generation and its wireless transmission,” Opt. Express 19(26), B56–B63 (2011). [CrossRef] [PubMed]
4. X. Pang, A. Caballero, A. Dogadaev, V. Arlunno, R. Borkowski, J. S. Pedersen, L. Deng, F. Karinou, F. Roubeau, D. Zibar, X. Yu, and I. T. Monroy, “100 Gbit/s hybrid optical fiber-wireless link in the W-band (75-110 GHz),” Opt. Express 19(25), 24944–24949 (2011). [CrossRef] [PubMed]
5. S. Fukushima, C. F. C. Silva, Y. Muramoto, and A. J. Seeds, “Optoelectronic millimeter-wave synthesis using an optical frequency comb generator, optically injection locked lasers, and a unitraveling-carrier photodiode,” J. Lightwave Technol. 21(12), 3043–3051 (2003). [CrossRef]
6. M. Ogusu, K. Inagaki, and Y. Mizuguchi, “60 GHz millimeter-wave source using two-mode injection-locking of a Fabry-Perot slave laser,” IEEE Microw. Wirel. Compon. Lett. 11(3), 101–103 (2001). [CrossRef]
7. M. Ogusu, K. Inagaki, Y. Mizuguchi, and T. Ohira, “Multiplexing of millimeter-wave signals for fiber-radio links by direct modulation of a two-mode locked Fabry-Pérot laser,” IEEE Trans. Microw. Theory Tech. 52(2), 498–507 (2004). [CrossRef]
8. L. Noel, D. Wake, D. G. Moodie, D. D. Marcenac, L. D. Westbrook, and D. Nesset, “Novel techniques for high-capacity 60-GHz fiber-radio transmission systems,” IEEE Trans. Microw. Theory Tech. 45(8), 1416–1423 (1997). [CrossRef]
9. R. P. Braun, G. Grosskopf, D. Rohde, and F. Schmidt, “Low-phase-noise millimeter-wave generation at 64 GHz and data transmission using optical sideband injection locking,” IEEE Photonics Technol. Lett. 10(5), 728–730 (1998). [CrossRef]
10. C. Zhang, J. Duan, C. Hong, P. Guo, W. Hu, Z. Chen, H. Li, and H. Wu, “Bidirectional 60-GHz RoF system with multi-Gb/s-QAM OFDM single-sideband modulation based on injection-locked lasers,” IEEE Photonics Technol. Lett. 23(4), 245–247 (2011). [CrossRef]
11. A. Ng’oma, D. Fortusini, D. Parekh, W. Yang, M. Sauer, S. Benjamin, W. Hofmann, M. C. Amann, and C. J. Chang-Hasnain, “Performance of a multi-Gb/s 60 GHz radio over fiber system employing a directly modulated optically injection-locked VCSEL,” J. Lightwave Technol. 28(16), 2436–2444 (2010). [CrossRef]
12. C. Cui and S. C. Chan, “Performance analysis on using period-one oscillation of optically injected semiconductor lasers for radio-over-fiber uplinks,” IEEE J. Quantum Electron. 48(4), 490–499 (2012). [CrossRef]
13. M.-K. Hong, Y.-Y. Won, and S.-K. Han, “Gigabit radio-over-fiber link for converged baseband and millimeter-wave band signal transmission using cascaded injection-locked Fabry-Pérot laser diodes,” Opt. Express 17(10), 7844–7852 (2009). [CrossRef] [PubMed]
14. C. Hong, C. Zhang, M. Li, L. Zhu, L. Li, W. Hu, A. Xu, and Z. Chen, “Single-sideband modulation based on an injection-locked DFB laser in radio-over-fiber systems,” IEEE Photonics Technol. Lett. 22(7), 462–464 (2010). [CrossRef]
15. T. Nikas, A. Bogris, and D. Syvridis, “Two-mode injection-locked FP laser receiver: a regenerator for long-distance stable fiber delivery of radio-frequency standards,” Opt. Lett. 40(6), 886–889 (2015). [CrossRef] [PubMed]
16. L. Fan, G. Xia, J. Chen, X. Tang, Q. Liang, and Z. Wu, “High-purity 60GHz band millimeter-wave generation based on optically injected semiconductor laser under subharmonic microwave modulation,” Opt. Express 24(16), 18252–18265 (2016). [CrossRef] [PubMed]
17. K. Balakier, M. J. Fice, F. van Dijk, G. Kervella, G. Carpintero, A. J. Seeds, and C. C. Renaud, “Optical injection locking of monolithically integrated photonic source for generation of high purity signals above 100 GHz,” Opt. Express 22(24), 29404–29412 (2014). [CrossRef] [PubMed]
18. A. Kanno and T. Kawanishi, “Frequency-stabilized radio-over-fiber signal generation based on optical frequency comb source with injection-locking technique,” in Proc. IEEE MTT-S International Microwave Symposium Digest (MTT) (2013), Seattle, WA, 1–4. [CrossRef]
19. C. Sun, S. H. Bae, and H. Kim, “Transmission of 28-Gb/s duobinary and PAM-4 signals using DML for optical access network,” IEEE Photonics Technol. Lett. 29(1), 130–133 (2017). [CrossRef]
20. J. Yu, Z. Jia, M.-F. Huang, M. Haris, P. N. Ji, T. Wang, and G.-K. Chang, “Applications of 40-Gb/s chirp-managed laser in access and metro networks,” J. Lightwave Technol. 27(3), 253–265 (2009). [CrossRef]
21. Z. Liu, J. Kakande, B. Kelly, J. O’Carroll, R. Phelan, D. J. Richardson, and R. Slavík, “Modulator-free quadrature amplitude modulation signal synthesis,” Nat. Commun. 5(1), 5911 (2014). [CrossRef] [PubMed]
22. X. Xu, J. Wu, T. G. Nguyen, M. Shoeiby, S. T. Chu, B. E. Little, R. Morandotti, A. Mitchell, and D. J. Moss, “Advanced RF and microwave functions based on an integrated optical frequency comb source,” Opt. Express 26(3), 2569–2583 (2018). [CrossRef] [PubMed]
23. E. K. Lau, L. J. Wong, and M. C. Wu, “Enhanced modulation characteristics of optical injection-locked lasers: a tutorial,” IEEE J. Sel. Top. Quantum Electron. 15(3), 618–633 (2009). [CrossRef]
24. S. Blin, C. Guignard, P. Besnard, R. Gabet, G. M. Stéphan, and M. Bondiou, “Phase and spectral properties of optically injected semiconductor lasers,” C. R. Phys. 4(6), 687–699 (2003). [CrossRef]
25. R. Slavik, Z. Liu, and D. J. Richardson, “Optical injection locking for carrier phase recovery and regeneration,” in Proc. OFC (2017), paper Th4I.3. [CrossRef]
26. Z. Liu, J.-Y. Kim, D. S. Wu, D. J. Richardson, and R. Slavík, “Homodyne OFDM with optical injection locking for carrier recovery,” J. Lightwave Technol. 33(1), 34–41 (2015). [CrossRef]
27. H. Wang, W. Zhou, and J. Yu, “PAM-4 signal delivery in one radio-over-fiber system,” Opt. Eng. 56(10), 106107 (2017). [CrossRef]
28. A. Kanno, K. Inagaki, I. Morohashi, T. Sakamoto, T. Kuri, I. Hosako, T. Kawanishi, Y. Yoshida, and K. Kitayama, “40 Gb/s W-band (75-110 GHz) 16-QAM radio-over-fiber signal generation and its wireless transmission,” Opt. Express 19(26), B56–B63 (2011). [CrossRef] [PubMed]
