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8 kHz linewidth, 50 mW output, full C-band wavelength tunable DFB LD array with self-optical feedback

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Abstract

We describe a 1.5 μm, narrow linewidth, high output power wavelength tunable LD that employs a self-optical feedback circuit. By incorporating an optical circulator-based feedback circuit in a DFB LD array, we have successfully reduced the oscillation linewidth from several MHz to less than 8 kHz over the full C-band range. A high output power of approximately 50 mW and a low relative intensity noise of less than −130 dB/Hz were simultaneously achieved. Furthermore, by employing a partial reflection mirror as a self-optical feedback circuit, we have also realized a full C-band wavelength tunable LD with a linewidth of less than 11 kHz and a simple laser configuration.

© 2018 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

1. Introduction

A 1.5 μm wavelength tunable laser with a narrow linewidth, a high output power, a high optical signal-to-noise-ratio (OSNR), and a low intensity noise is attractive for use in the fields of optical communication, interferometric measurement, optical fiber sensing, and for imaging systems in the medical field including optical coherent tomography. For example, such a laser plays an important role in wavelength-division multiplexing (WDM), quadrature amplitude modulation (QAM) coherent optical transmission that requires a narrow linewidth and a high OSNR, simultaneously [1,2]. Several types of wavelength tunable lasers have already been reported in this wavelength band. By extending the cavity length to 60 mm, a full C + L band wavelength tunable LD with a linewidth of 5 kHz has been realized [3], and its output power was approximately 35 mW. Full C-band tunable LDs with an output power of over 50 mW were demonstrated by employing a sampled-grating distributed-Bragg-reflector (SG DBR) [4] or a silicon external ring cavity [5]. However, their oscillation linewidths were broad at over 10 kHz. Therefore, it was not easy to apply these lasers to a WDM coherent transmission with a higher-order QAM signal. Thus, there is a strong need for a tunable laser that has a linewidth of less than 10 kHz as well as an output power greatly exceeding 50 mW.

To satisfy such requirements, we have proposed a narrow linewidth, high power, tunable DFB LD array [6] with a self-optical feedback method [7–9] similar to self-injection locking. Although self-optical feedback is a well-known technique, we are the first to apply this scheme to a DFB LD array and realize a widely wavelength tunable, coherent LD in the 1.5 μm region. The great advantage of this laser is that the laser linewidths of all the integrated LDs can be reduced by using a single optical feedback circuit, although the LDs cannot operate simultaneously. By employing an optical circulator-based loop back circuit [10] or a silica-based external optical feedback planar lightwave circuit (PLC) [11] as a self-optical feedback circuit, we have successfully reduced the DFB LD linewidth from several MHz to less than 10 kHz. Specifically, with an optical circulator-based loop back circuit, we have demonstrated a full C-band wavelength tunable laser with an output power of approximately 50 mW and a linewidth of less than 8 kHz, and reported preliminary results [10].

In this paper, we describe in detail a narrow linewidth, full C-band wavelength tunable DFB LD array with an optical circulator-based self-feedback circuit. Furthermore, by incorporating a partial reflection mirror-based self-optical feedback circuit in a DFB LD array, we realized a full C-band tunable laser with a simple configuration and a linewidth of less than 11 kHz. We also describe this in detail here.

2. Configuration and output characteristics of tunable DFB LD array with optical circulator-based self-feedback circuit

Figure 1(a) shows the configuration of our tunable DFB LD array at 1.5 μm with an optical circulator-based self-feedback circuit. It has an InP DFB LD array chip on which we monolithically integrated 12 InGaAsP multi-quantum well (MQW) DFB LDs with a cavity length of 0.9 mm, a multimode-interferometer (MMI) coupler, and an InGaAsP MQW semiconductor optical amplifier (SOA) as shown in Fig. 1(b). The DFB LDs are designed to have an oscillation wavelength separation of 3.2 nm (400 GHz). The SOA is 1.2 mm long. Its facets are anti-reflection (AR) coated and the waveguide is slightly tilted by 19.5 deg. to reduce the reflection at the end of the SOA. All the DFB LDs and the SOA are driven by low-noise current sources with a ripple noise of less than 850 nA. Two lenses, a polarization-maintained (PM)-circulator, a 95:5 PM-coupler, and a variable optical attenuator are installed outside the array chip. The DFB LD array chip is temperature-controlled and packaged in a butterfly-type pigtail module with two lenses [6]. The coupling loss between the SOA and the optical circulator are approximately 2 dB. We operate any one of 12 continuous wave (CW) DFB LDs, which oscillate at different wavelengths over the C-band. The output from the DFB LD is fed into the SOA through the MMI coupler. Here, the intrinsic loss of the MMI coupler is compensated for by the SOA. Part of the laser output is fed back to the DFB LD after passing through the PM-circulator and after controlling the self-optical feedback power (Pfeed) with a variable optical attenuator. The optical feedback power is defined as the input power to port-1(P1) of the circulator. The loop length of the self-optical feedback circuit is approximately 1.4 m. We can tune the oscillation wavelength over the C-band by selecting a different DFB LD and controlling the chip temperature. All the components including the self-optical feedback circuit are packaged in a metal housing (H: 70 mm, W: 200 mm, L: 240 mm), which is temperature controlled with an accuracy of 0.1 °C.

 figure: Fig. 1

Fig. 1 (a) Configuration of tunable DFB LD array with circulator-based self-optical feedback circuit, (b) Photograph of DFB LD array chip.

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Figure 2(a) shows the output power characteristics of our DFB LD array as a function of the SOA current at a chip temperature of 38 °C, when 12 DFB LDs were operated independently with an injection current of 250 mA for each LD. We use only one of 12 DFB LDs in actual operation. The injection current for the DFB LD was set at 250 mA so that we could obtain the narrowest linewidth of the original DFB LD without self-optical feedback. Here, the output power is defined as the optical power after the PM-coupler. We obtained an output power of over 50 mW with an SOA driving current of 400 mA for all 12 DFB LDs. The SOA gain was approximately 14.8 dB with a DFB injection current of 250 mA and an SOA driving current of 400 mA. Figure 2(b) shows the chip temperature dependence of the laser output power when each DFB LD was operated with an injection current of 250 mA and an external SOA current of 400 mA. When the chip temperature was increased from 15 to 55 °C, the output power decreased from 70 to around 47 mW. This is because there is inevitably an increase in threshold current and a decrease in differential quantum efficiency in a DFB LD and an external SOA, respectively [12]. This is mainly attributed to a carrier leakage effect and nonradiative recombination caused by the Auger process [12]. However, we were able to obtain an output power of over 47 mW in the 15 to 55 °C temperature range. Figure 3 shows the wavelength tuning characteristics of each LD as a function of chip temperature measured with a resolution of 0.01 nm (1.25 GHz). The wavelength of each DFB LD can be linearly tuned by 0.1 nm/°C. This laser can cover a wavelength range as wide as 40 nm in the full C-band with 12 DFB-LDs by changing the chip temperature in the 15 to 55 °C range.

 figure: Fig. 2

Fig. 2 (a) Output power characteristics of 12-DFB LDs as a function of SOA current, (b) chip temperature dependence of laser output power.

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 figure: Fig. 3

Fig. 3 Continuous wavelength tuning characteristics of DFB LD array.

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We measured the oscillation linewidth of the present DFB LD array by using a delayed self-heterodyne method with a 25 km-long delay fiber [13]. Here, the measurement resolution of the laser linewidth (full width at half maximum: FWHM) was 4 kHz. When the delay fiber length exceeded 25 km, we could not estimate the laser linewidth correctly due to the low frequency 1/f and 1/f2 noise component of the laser oscillation frequency. Therefore, we set the delay fiber length at a maximum of 25 km, and estimated the approximate laser linewidth by assuming that the spectral profile was Lorentzian. Figure 4(a) shows the delayed self-heterodyne spectrum of LD 9 plotted on a log scale, which was operated at 1538.8 nm with an LD current of 250 mA and an SOA current of 400 mA for different optical feedback powers. The chip temperature was controlled at 38 °C. With a self-optical feedback power of 0 dBm, the FWHM was greatly reduced from 2 MHz to as narrow as 5 kHz. Here, the SOA gain was estimated to be approximately 14.6 dB when the self-optical feedback power was 0 dBm. The relationship between the linewidth of LD 9 and the optical feedback power for different chip temperatures is shown in Fig. 4(b). When the optical feedback power exceeded −5 dBm, the linewidth decreased to around 5 kHz under any temperature conditions. The chip temperature dependence of the linewidth was small. In our laser, the linewidth was mainly determined by the long feedback length. In this experiment, we could not measure a laser linewidth of less than 5 kHz correctly due to the resolution limitation of the delayed self-heterodyne method with a 25-km delay fiber. On the other hand, we can also estimate the FWHM of the laser spectrum from the −20 dB-linewidth of the delayed self-heterodyne spectrum by assuming a Lorentzian spectral profile. With this estimation, the FWHM of the laser spectrum under a strong optical feedback condition is 2 kHz. In the present laser, the amplified spontaneous emission (ASE) noise level of the SOA was −57 dB down from the peak of SOA output spectrum with 50 mW. Therefore, the ASE noise did not affect the laser linewidth characteristics.

 figure: Fig. 4

Fig. 4 (a) Delayed self-heterodyne spectrum of LD 9, (b) relationship between the linewidth of LD 9 and self-optical feedback power for different chip temperature.

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In the self-optical feedback system, it has been shown that the laser linewidth can be narrowed as follows,

Δν=Δν0(1+C)2
where Δν0 and C are the original laser linewidth without optical feedback and the optical feedback parameter, respectively [8,9]. Specifically, under a strong feedback condition, the optical feedback parameter is approximately expressed by the following equation [9].
C=κnextLextnLDLLD
Here, κ is the feedback rate determined by the round-trip transmission loss of the external feedback circuit including the coupling loss between the original laser and the external optical feedback circuit, and the reflectivity of the optical feedback circuit. nLD and next are the equivalent refractive indices of the original LD and the external optical feedback circuit, respectively. LLD and Lext are the cavity length of the original laser and the optical feedback length, respectively. Equations (1) and (2) show that the laser linewidth can be narrowed when Lext is increased. In other words, the Q factor of a laser cavity increases equivalently with an increase in κ Lext, which leads to linewidth narrowing.

In our laser, Δν0 is 2 MHz, nLD and next are 3.5 and 1.5, and LLD and Lext are 0.9 mm and 1.4 m, respectively. In addition, κ is calculated to be 0.03 obtained with a coupling loss of 2 dB between the DFB LD and the feedback circuit for round-trip, an optical circulator transmission loss of 0.2 dB, and an optical feedback circuit reflectivity of 0.05. The transmission loss of the integrated optical circuit including the MMI coupler was compensated for with the SOA, therefore we do not consider this transmission loss. Consequently, the laser linewidth with optical feedback can be estimated as 4.5 kHz. The experimental results in Fig. 4(b) agree well with this estimation.

Figure 5 shows the linewidth dependences on the oscillation wavelengths when each LD was operated with an LD injection current of 250 mA and an SOA current of 400 mA. Here, the self-optical feedback power was 0 dBm. This simple self-optical feedback circuit enabled us to obtain narrow linewidth characteristics of less than 8 kHz over the full C-band range.

 figure: Fig. 5

Fig. 5 Linewidth dependence on oscillation wavelength.

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Figure 6 shows the optical spectrum of LD 9 with optical feedback, which was measured with a 0.01 nm resolution. Here, the optical feedback power was set at 0 dBm. Their optical signal-to-noise ratio (OSNR) and side-mode suppression ratio (SMSR) were 57 dB and 43 dB, respectively. These side-modes are caused by the Fabry-Perot (FP) modes due to a small resonance between both edges of the DFB LD. Multimode oscillation induced by these FP modes was observed when the optical-feedback power exceeded 5 dBm.

 figure: Fig. 6

Fig. 6 Optical spectrum of LD 9 with optical feedback (0.01 nm resolution).

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Figures 7(a) and 7(b) show the OSNR and SMSR dependences on the oscillation wavelengths, respectively. The OSNRs and SMSRs of the present laser were over 56 dB and 40 dB, respectively within a 40 nm full C-band range.

 figure: Fig. 7

Fig. 7 (a) OSNR dependence on oscillation wavelength, (b) SMSR dependence on oscillation wavelength.

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We also evaluated the precise oscillation spectrum with a heterodyne beat method. Figure 8 shows the heterodyne beat spectrum between LD 9 and another CW laser with a linewidth of 4 kHz. We observed a few low amplitude FP modes associated with a small resonance between the edge of the SOA and the self-optical feedback configuration near the center spectrum. We measured the frequency fluctuation of LD 9 oscillating at around 1538.8 nm with a heterodyne beat method using another CW laser as a frequency reference. The reference laser was frequency stabilized to a C2H2 absorption line (1538.8 nm). Its frequency stability was 2.8 × 10−11, which corresponded to a frequency fluctuation of 5.4 kHz [14]. Here, we measured the beat frequency by using a frequency counter with a gate time of 0.5 s. Figure 9 shows the frequency fluctuation of the heterodyne beat signal. We also show the room temperature change in this graph. The beat frequency fluctuated by 25 MHz peak-to-peak, which originated from the frequency change of LD 9. Although the frequency of the present LD fluctuated as a result of changes in room temperature, we achieved stable single-frequency operation without mode-hopping for over two hours. The same stability was achieved with the other 11 LDs.

 figure: Fig. 8

Fig. 8 Heterodyne beat spectrum between DFB LD 9 and another CW LD.

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 figure: Fig. 9

Fig. 9 Frequency fluctuation of heterodyne beat signal between DFB LD 9 and frequency-stabilized CW laser.

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Figure 10(a) shows the relative intensity noise (RIN) spectra of LD 9 from 100 kHz to 1 MHz, where we compare the RIN characteristics with and without self-optical feedback. There is no degradation in the RIN spectrum with self-optical feedback. The RIN levels of LD 9 were less than −130 dB/Hz. Figure 10(b) shows the RIN peak dependence on the oscillation wavelength. We obtained RIN characteristics as low as −130 dB/Hz over a 40 nm C-band range.

 figure: Fig. 10

Fig. 10 (a) RIN spectra of LD 9 with and without optical feedback, (b) RIN peak dependence on oscillation wavelength.

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3. Configuration and output characteristics of tunable DFB LD array with partial reflection mirror-based self-optical feedback circuit

We adopted a PM partial reflection mirror as a self-optical feedback circuit, and newly achieved a simple tunable DFB LD array with a linewidth of less than 12 kHz. The laser configuration is the same as that presented in section 2 except for the self-optical feedback circuit as shown in Fig. 11. At the PM partial reflection mirror, 10% of the laser output was fed back to the DFB LD, where the optical feedback length was approximately 30 cm.

 figure: Fig. 11

Fig. 11 Configuration of tunable DFB LD array with partial reflection mirror-based self-optical feedback circuit.

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Figure 12(a) shows the delayed self-heterodyne spectrum of LD 9 operating at 1538.8 nm with an LD current of 250 mA for different SOA currents. Here, the chip temperature was controlled at 38 °C with an accuracy of 0.01 °C. When the SOA current increased corresponding to the increase in the optical feedback power, the laser linewidth decreased. The SOA current dependence of the laser linewidth of LD 9 is shown in Fig. 12(b). Here, we also show the optical feedback power on a horizontal axis, which is estimated from the output power characteristics as shown in Fig. 2. When the optical feedback power was above 1.5 mW (1.7 dBm), the oscillation linewidth fell to around 11 kHz. On the other hand, the oscillation linewidth was estimated to be 4.5 kHz when we evaluated it from the −20 dB-linewidth of the delayed self-heterodyne spectrum as shown in Fig. 12(a) by assuming a Lorentzian spectral shape.

 figure: Fig. 12

Fig. 12 (a) Delayed self-heterodyne spectrum of LD 9, (b) Relationship between LD 9 linewidth and SOA current.

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Figure 13 shows the linewidth dependence on the oscillation wavelength when the self-optical feedback power was 2 mW (3 dBm). With such a simple optical feedback method, we have successfully obtained narrow linewidths of less than 11 kHz over the full C-band. However, the linewidth narrowing effect of the reflection mirror-based feedback circuit was small compared with that of the optical circulator-based circuit. This is due to the short feedback length of the mirror-based feedback system. With this condition, we obtained an output power of 18 mW (12.5 dBm). When we increased the optical-feedback power above 3 mW (5 dBm), multimode oscillation started, which was induced by the FP modes that originated from both edges of the DFB LD.

 figure: Fig. 13

Fig. 13 Linewidth dependence on oscillation wavelength.

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4. Conclusion

We demonstrated a full C-band wavelength tunable LD with a linewidth of less than 8 kHz, an output power of approximately 50 mW, and a RIN of less than −130 dB/Hz. By applying an optical circulator-based self-feedback circuit to a DFB LD array, we succeeded in obtaining a narrow linewidth as well as a high output power and low intensity noise characteristics. In addition, we also demonstrated a simple wavelength tunable LD with a linewidth of less than 11 kHz by employing a partial reflection mirror as a self-optical feedback circuit. We expect our tunable laser to be an attractive light source for use in WDM multi-level coherent transmission with a higher order multiplicity, precise interferometric measurement, highly sensitive fiber sensing, and imaging systems.

Funding

This work is supported by the “Research and Development Project toward 5G Mobile Communication Systems” of the Ministry of Internal Affairs and Communications, Japan.

References and links

1. M. Seimetz, “Laser linewidth limitations for optical systems with high-order modulation employing feed forward digital carrier phase estimation,” in Proceedings of Optical Fiber Communication Conference (Optical Society of America, 2008), paper OtuM2. [CrossRef]  

2. T. Kan, K. Kasai, M. Yoshida, and M. Nakazawa, “42.3-Tbit/s, 18-Gbaud 64QAM WDM coherent transmission of 160 km over full C-band using an injection locking technique with a spectral efficiency of 9 bit/s/Hz,” in Proceedings of Optical Fiber Communication Conference (Optical Society of America, 2017), paper Th3F.5. [CrossRef]  

3. S. Bennetts, G. D. McDonald, K. S. Hardman, J. E. Debs, C. C. Kuhn, J. D. Close, and N. P. Robins, “External cavity diode lasers with 5kHz linewidth and 200nm tuning range at 1.55μm and methods for linewidth measurement,” Opt. Express 22(9), 10642–10654 (2014). [CrossRef]   [PubMed]  

4. M. C. Larson, A. Bhardwaj, W. Xiong, Y. Feng, X. D. Huang, K. P. Petrov, M. Moewe, H. Y. Ji, A. Semakov, C. W. Lv, S. Kutty, A. Patwardhan, N. Liu, Z. M. Li, Y. J. Bao, Z. H. Shen, S. Bajwa, F. H. Zhou, and P. C. Koh, “Narrow linewidth sampled-grating distributed Bragg reflector laser with enhanced side-mode suppression,” in Proceedings of Optical Fiber Communication Conference (Optical Society of America, 2015), paper M2D.1. [CrossRef]  

5. N. Kobayashi, K. Sato, M. Namiwaka, K. Yamamoto, S. Watanabe, T. Kita, H. Yamada, and H. Yamazaki, “Silicon photonic hybrid ring-filter external cavity wavelength tunable lasers,” J. Lightwave Technol. 33(6), 1241–1246 (2015). [CrossRef]  

6. H. Ishii, K. Kasaya, and H. Oohashi, “Spectral linewidth reduction in widely wavelength tunable DFB laser array,” IEEE J. Sel. Top. Quantum Electron. 15(3), 514–520 (2009). [CrossRef]  

7. R. Lang and K. Kobayashi, “External optical feedback effects on semiconductor injection laser properties,” IEEE J. Quantum Electron. 16(3), 347–355 (1980). [CrossRef]  

8. K. Petermann, “External optical feedback phenomena in semiconductor lasers,” IEEE J. Sel. Top. Quantum Electron. 1(2), 480–489 (1995). [CrossRef]  

9. L. Coldren, S. Corzine, and M. Mashanovitch, Diode Lasers and Photonic Integrated Circuits (John Wiley & Sons, 2012), Chap. 5.

10. K. Kasai, M. Nakazawa, M. Ishikawa, and H. Ishii, “An 8 kHz linewidth, 50 mW output wavelength tunable DFB LD array over the C-band with self optical feedback,” in Proceedings of Conference on Lasers and Electro-Optics (Optical Society of America, 2016), paper SW4M.2. [CrossRef]  

11. H. Ishii, N. Fujiwara, K. Watanabe, S. Kanazawa, M. Itoh, H. Takenouchi, and Y. Miyamoto, “Narrow linewidth operation (<10 kHz) in self-injection-locked tunable DFB LD array (SIL-TLA) integrated with optical feedback planar lightwave circuit (PLC),” in Proceedings of European Conference on Optical Communication (IEEE, 2016), paper Tu.2.E.5.

12. M. Asada, A. R. Adams, K. E. Stubkjaer, Y. Suematsu, Y. Itaya, and S. Arai, “The temperature dependence of the threshold current of GaInAsP/InP DH lasers,” IEEE J. Quantum Electron. 17(5), 611–619 (1981). [CrossRef]  

13. T. Okoshi, K. Kikuchi, and A. Nakayama, “Novel method for high resolution measurement of laser output spectrum,” Electron. Lett. 16(16), 630–631 (1980). [CrossRef]  

14. K. Kasai, M. Yoshida, and M. Nakazawa, “295 mW output, frequency-stabilized erbium silica fiber laser with a linewidth of 5 kHz and a RIN of -120 dB/Hz,” Opt. Express 24(3), 2737–2748 (2016). [CrossRef]   [PubMed]  

References

  • View by:

  1. M. Seimetz, “Laser linewidth limitations for optical systems with high-order modulation employing feed forward digital carrier phase estimation,” in Proceedings of Optical Fiber Communication Conference (Optical Society of America, 2008), paper OtuM2.
    [Crossref]
  2. T. Kan, K. Kasai, M. Yoshida, and M. Nakazawa, “42.3-Tbit/s, 18-Gbaud 64QAM WDM coherent transmission of 160 km over full C-band using an injection locking technique with a spectral efficiency of 9 bit/s/Hz,” in Proceedings of Optical Fiber Communication Conference (Optical Society of America, 2017), paper Th3F.5.
    [Crossref]
  3. S. Bennetts, G. D. McDonald, K. S. Hardman, J. E. Debs, C. C. Kuhn, J. D. Close, and N. P. Robins, “External cavity diode lasers with 5kHz linewidth and 200nm tuning range at 1.55μm and methods for linewidth measurement,” Opt. Express 22(9), 10642–10654 (2014).
    [Crossref] [PubMed]
  4. M. C. Larson, A. Bhardwaj, W. Xiong, Y. Feng, X. D. Huang, K. P. Petrov, M. Moewe, H. Y. Ji, A. Semakov, C. W. Lv, S. Kutty, A. Patwardhan, N. Liu, Z. M. Li, Y. J. Bao, Z. H. Shen, S. Bajwa, F. H. Zhou, and P. C. Koh, “Narrow linewidth sampled-grating distributed Bragg reflector laser with enhanced side-mode suppression,” in Proceedings of Optical Fiber Communication Conference (Optical Society of America, 2015), paper M2D.1.
    [Crossref]
  5. N. Kobayashi, K. Sato, M. Namiwaka, K. Yamamoto, S. Watanabe, T. Kita, H. Yamada, and H. Yamazaki, “Silicon photonic hybrid ring-filter external cavity wavelength tunable lasers,” J. Lightwave Technol. 33(6), 1241–1246 (2015).
    [Crossref]
  6. H. Ishii, K. Kasaya, and H. Oohashi, “Spectral linewidth reduction in widely wavelength tunable DFB laser array,” IEEE J. Sel. Top. Quantum Electron. 15(3), 514–520 (2009).
    [Crossref]
  7. R. Lang and K. Kobayashi, “External optical feedback effects on semiconductor injection laser properties,” IEEE J. Quantum Electron. 16(3), 347–355 (1980).
    [Crossref]
  8. K. Petermann, “External optical feedback phenomena in semiconductor lasers,” IEEE J. Sel. Top. Quantum Electron. 1(2), 480–489 (1995).
    [Crossref]
  9. L. Coldren, S. Corzine, and M. Mashanovitch, Diode Lasers and Photonic Integrated Circuits (John Wiley & Sons, 2012), Chap. 5.
  10. K. Kasai, M. Nakazawa, M. Ishikawa, and H. Ishii, “An 8 kHz linewidth, 50 mW output wavelength tunable DFB LD array over the C-band with self optical feedback,” in Proceedings of Conference on Lasers and Electro-Optics (Optical Society of America, 2016), paper SW4M.2.
    [Crossref]
  11. H. Ishii, N. Fujiwara, K. Watanabe, S. Kanazawa, M. Itoh, H. Takenouchi, and Y. Miyamoto, “Narrow linewidth operation (<10 kHz) in self-injection-locked tunable DFB LD array (SIL-TLA) integrated with optical feedback planar lightwave circuit (PLC),” in Proceedings of European Conference on Optical Communication (IEEE, 2016), paper Tu.2.E.5.
  12. M. Asada, A. R. Adams, K. E. Stubkjaer, Y. Suematsu, Y. Itaya, and S. Arai, “The temperature dependence of the threshold current of GaInAsP/InP DH lasers,” IEEE J. Quantum Electron. 17(5), 611–619 (1981).
    [Crossref]
  13. T. Okoshi, K. Kikuchi, and A. Nakayama, “Novel method for high resolution measurement of laser output spectrum,” Electron. Lett. 16(16), 630–631 (1980).
    [Crossref]
  14. K. Kasai, M. Yoshida, and M. Nakazawa, “295 mW output, frequency-stabilized erbium silica fiber laser with a linewidth of 5 kHz and a RIN of -120 dB/Hz,” Opt. Express 24(3), 2737–2748 (2016).
    [Crossref] [PubMed]

2016 (1)

2015 (1)

2014 (1)

2009 (1)

H. Ishii, K. Kasaya, and H. Oohashi, “Spectral linewidth reduction in widely wavelength tunable DFB laser array,” IEEE J. Sel. Top. Quantum Electron. 15(3), 514–520 (2009).
[Crossref]

1995 (1)

K. Petermann, “External optical feedback phenomena in semiconductor lasers,” IEEE J. Sel. Top. Quantum Electron. 1(2), 480–489 (1995).
[Crossref]

1981 (1)

M. Asada, A. R. Adams, K. E. Stubkjaer, Y. Suematsu, Y. Itaya, and S. Arai, “The temperature dependence of the threshold current of GaInAsP/InP DH lasers,” IEEE J. Quantum Electron. 17(5), 611–619 (1981).
[Crossref]

1980 (2)

T. Okoshi, K. Kikuchi, and A. Nakayama, “Novel method for high resolution measurement of laser output spectrum,” Electron. Lett. 16(16), 630–631 (1980).
[Crossref]

R. Lang and K. Kobayashi, “External optical feedback effects on semiconductor injection laser properties,” IEEE J. Quantum Electron. 16(3), 347–355 (1980).
[Crossref]

Adams, A. R.

M. Asada, A. R. Adams, K. E. Stubkjaer, Y. Suematsu, Y. Itaya, and S. Arai, “The temperature dependence of the threshold current of GaInAsP/InP DH lasers,” IEEE J. Quantum Electron. 17(5), 611–619 (1981).
[Crossref]

Arai, S.

M. Asada, A. R. Adams, K. E. Stubkjaer, Y. Suematsu, Y. Itaya, and S. Arai, “The temperature dependence of the threshold current of GaInAsP/InP DH lasers,” IEEE J. Quantum Electron. 17(5), 611–619 (1981).
[Crossref]

Asada, M.

M. Asada, A. R. Adams, K. E. Stubkjaer, Y. Suematsu, Y. Itaya, and S. Arai, “The temperature dependence of the threshold current of GaInAsP/InP DH lasers,” IEEE J. Quantum Electron. 17(5), 611–619 (1981).
[Crossref]

Bennetts, S.

Close, J. D.

Debs, J. E.

Hardman, K. S.

Ishii, H.

H. Ishii, K. Kasaya, and H. Oohashi, “Spectral linewidth reduction in widely wavelength tunable DFB laser array,” IEEE J. Sel. Top. Quantum Electron. 15(3), 514–520 (2009).
[Crossref]

Itaya, Y.

M. Asada, A. R. Adams, K. E. Stubkjaer, Y. Suematsu, Y. Itaya, and S. Arai, “The temperature dependence of the threshold current of GaInAsP/InP DH lasers,” IEEE J. Quantum Electron. 17(5), 611–619 (1981).
[Crossref]

Kasai, K.

Kasaya, K.

H. Ishii, K. Kasaya, and H. Oohashi, “Spectral linewidth reduction in widely wavelength tunable DFB laser array,” IEEE J. Sel. Top. Quantum Electron. 15(3), 514–520 (2009).
[Crossref]

Kikuchi, K.

T. Okoshi, K. Kikuchi, and A. Nakayama, “Novel method for high resolution measurement of laser output spectrum,” Electron. Lett. 16(16), 630–631 (1980).
[Crossref]

Kita, T.

Kobayashi, K.

R. Lang and K. Kobayashi, “External optical feedback effects on semiconductor injection laser properties,” IEEE J. Quantum Electron. 16(3), 347–355 (1980).
[Crossref]

Kobayashi, N.

Kuhn, C. C.

Lang, R.

R. Lang and K. Kobayashi, “External optical feedback effects on semiconductor injection laser properties,” IEEE J. Quantum Electron. 16(3), 347–355 (1980).
[Crossref]

McDonald, G. D.

Nakayama, A.

T. Okoshi, K. Kikuchi, and A. Nakayama, “Novel method for high resolution measurement of laser output spectrum,” Electron. Lett. 16(16), 630–631 (1980).
[Crossref]

Nakazawa, M.

Namiwaka, M.

Okoshi, T.

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[Crossref]

Oohashi, H.

H. Ishii, K. Kasaya, and H. Oohashi, “Spectral linewidth reduction in widely wavelength tunable DFB laser array,” IEEE J. Sel. Top. Quantum Electron. 15(3), 514–520 (2009).
[Crossref]

Petermann, K.

K. Petermann, “External optical feedback phenomena in semiconductor lasers,” IEEE J. Sel. Top. Quantum Electron. 1(2), 480–489 (1995).
[Crossref]

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Sato, K.

Stubkjaer, K. E.

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[Crossref]

Suematsu, Y.

M. Asada, A. R. Adams, K. E. Stubkjaer, Y. Suematsu, Y. Itaya, and S. Arai, “The temperature dependence of the threshold current of GaInAsP/InP DH lasers,” IEEE J. Quantum Electron. 17(5), 611–619 (1981).
[Crossref]

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Electron. Lett. (1)

T. Okoshi, K. Kikuchi, and A. Nakayama, “Novel method for high resolution measurement of laser output spectrum,” Electron. Lett. 16(16), 630–631 (1980).
[Crossref]

IEEE J. Quantum Electron. (2)

M. Asada, A. R. Adams, K. E. Stubkjaer, Y. Suematsu, Y. Itaya, and S. Arai, “The temperature dependence of the threshold current of GaInAsP/InP DH lasers,” IEEE J. Quantum Electron. 17(5), 611–619 (1981).
[Crossref]

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[Crossref]

IEEE J. Sel. Top. Quantum Electron. (2)

K. Petermann, “External optical feedback phenomena in semiconductor lasers,” IEEE J. Sel. Top. Quantum Electron. 1(2), 480–489 (1995).
[Crossref]

H. Ishii, K. Kasaya, and H. Oohashi, “Spectral linewidth reduction in widely wavelength tunable DFB laser array,” IEEE J. Sel. Top. Quantum Electron. 15(3), 514–520 (2009).
[Crossref]

J. Lightwave Technol. (1)

Opt. Express (2)

Other (6)

M. C. Larson, A. Bhardwaj, W. Xiong, Y. Feng, X. D. Huang, K. P. Petrov, M. Moewe, H. Y. Ji, A. Semakov, C. W. Lv, S. Kutty, A. Patwardhan, N. Liu, Z. M. Li, Y. J. Bao, Z. H. Shen, S. Bajwa, F. H. Zhou, and P. C. Koh, “Narrow linewidth sampled-grating distributed Bragg reflector laser with enhanced side-mode suppression,” in Proceedings of Optical Fiber Communication Conference (Optical Society of America, 2015), paper M2D.1.
[Crossref]

M. Seimetz, “Laser linewidth limitations for optical systems with high-order modulation employing feed forward digital carrier phase estimation,” in Proceedings of Optical Fiber Communication Conference (Optical Society of America, 2008), paper OtuM2.
[Crossref]

T. Kan, K. Kasai, M. Yoshida, and M. Nakazawa, “42.3-Tbit/s, 18-Gbaud 64QAM WDM coherent transmission of 160 km over full C-band using an injection locking technique with a spectral efficiency of 9 bit/s/Hz,” in Proceedings of Optical Fiber Communication Conference (Optical Society of America, 2017), paper Th3F.5.
[Crossref]

L. Coldren, S. Corzine, and M. Mashanovitch, Diode Lasers and Photonic Integrated Circuits (John Wiley & Sons, 2012), Chap. 5.

K. Kasai, M. Nakazawa, M. Ishikawa, and H. Ishii, “An 8 kHz linewidth, 50 mW output wavelength tunable DFB LD array over the C-band with self optical feedback,” in Proceedings of Conference on Lasers and Electro-Optics (Optical Society of America, 2016), paper SW4M.2.
[Crossref]

H. Ishii, N. Fujiwara, K. Watanabe, S. Kanazawa, M. Itoh, H. Takenouchi, and Y. Miyamoto, “Narrow linewidth operation (<10 kHz) in self-injection-locked tunable DFB LD array (SIL-TLA) integrated with optical feedback planar lightwave circuit (PLC),” in Proceedings of European Conference on Optical Communication (IEEE, 2016), paper Tu.2.E.5.

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Figures (13)

Fig. 1
Fig. 1 (a) Configuration of tunable DFB LD array with circulator-based self-optical feedback circuit, (b) Photograph of DFB LD array chip.
Fig. 2
Fig. 2 (a) Output power characteristics of 12-DFB LDs as a function of SOA current, (b) chip temperature dependence of laser output power.
Fig. 3
Fig. 3 Continuous wavelength tuning characteristics of DFB LD array.
Fig. 4
Fig. 4 (a) Delayed self-heterodyne spectrum of LD 9, (b) relationship between the linewidth of LD 9 and self-optical feedback power for different chip temperature.
Fig. 5
Fig. 5 Linewidth dependence on oscillation wavelength.
Fig. 6
Fig. 6 Optical spectrum of LD 9 with optical feedback (0.01 nm resolution).
Fig. 7
Fig. 7 (a) OSNR dependence on oscillation wavelength, (b) SMSR dependence on oscillation wavelength.
Fig. 8
Fig. 8 Heterodyne beat spectrum between DFB LD 9 and another CW LD.
Fig. 9
Fig. 9 Frequency fluctuation of heterodyne beat signal between DFB LD 9 and frequency-stabilized CW laser.
Fig. 10
Fig. 10 (a) RIN spectra of LD 9 with and without optical feedback, (b) RIN peak dependence on oscillation wavelength.
Fig. 11
Fig. 11 Configuration of tunable DFB LD array with partial reflection mirror-based self-optical feedback circuit.
Fig. 12
Fig. 12 (a) Delayed self-heterodyne spectrum of LD 9, (b) Relationship between LD 9 linewidth and SOA current.
Fig. 13
Fig. 13 Linewidth dependence on oscillation wavelength.

Equations (2)

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Δν= Δ ν 0 ( 1+C ) 2
C=κ n ext L ext n LD L LD

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