Dual-pass Mach-Zehnder Interferometer Research Articles

Erbium-doped fiber laser with switchable wavelength generation based on tunable filter and dual-pass mach-zehnder filter incorporated with fiber delay line

A wavelength switchable erbium-doped fiber laser incorporated with a tunable filter and dual-pass Mach–Zehnder interferometer (MZI) was designed and experimentally demonstrated. The erbium-doped fiber was used as the gain medium for the fiber laser and the laser working threshold was 92 mW. The dual-pass MZI was fabricated using three optical couplers (OCs) and the variable fiber delay line. A tunable filter was used for laser tuning and it was combined with two OCs to construct a subsidiary cavity. A tunable and stable single- and dual-wavelength laser output was obtained in the experiment. In the case of single-wavelength laser output, the tuning span was in the range of 1527.6–1562.4 nm with an interval of 1.2 nm. Additionally, the side-mode suppression ratio (SMSR) was greater than 37.45 dB. In the case of dual-wavelength laser emission, the lasers were tuned from 1540.7 and 1541.6 nm to 1560.8 and 1561.2 nm, respectively. The stability of the single-, dual-and triple-wavelength laser output was evaluated and the power fluctuation was less than 1.36, 1.34, and 1.37 dB, respectively. Finally, quadruple- and quintuple-wavelength laser outputs were achieved by adjusting the loss of the intra-cavity.

Wavelength-interval-switchable multi-wavelength thulium-doped fiber laser with a nonlinear dual-pass Mach-Zehnder interferometer filter in 2-μm-band

A wavelength-interval-switchable multi-wavelength thulium-doped fiber laser (MWTDFL) is proposed and demonstrated, based on a nonlinear dual-pass Mach-Zehnder interferometer (NDP-MZI) filter for the first time. We investigate the NDP-MZI filter theoretically and experimentally, which has both the transmission characteristics of a dual-pass Mach-Zehnder interferometer (DP-MZI) for wavelength selection and a nonlinear optical loop mirror (NOLM) for suppressing wavelength competition. By tuning two polarization controllers (PCs), two 20-wavelength operations with an opposite phase and a same wavelength-interval of 0.46 nm are obtained and switched between each other flexibly. The maximum power fluctuation and wavelength drift measured are 0.612 dB and 0.04 nm, respectively. In addition, due to the power-equalizing effect resulting from the NOLM, 60 lasing wavelengths within a 3-dB bandwidth with an adjacent wavelength-interval of 0.23 nm are also obtained by adjusting the PCs carefully, and the stability of the MWTDFL is measured experimentally. Furthermore, the performance of the NDP-MZI using an 80 m highly nonlinear fiber has been studied in detail as well. The proposed MWTDFL may find great applications in optical communication and optical sensing.

Switchable and tunable multi-wavelength erbium-doped random distributed feedback fiber laser based on a compound filter

A switchable and tunable multi-wavelength random distributed feedback fiber laser (RDFBFL) is realized based on the compound filter which is comprised of a dual-pass Mach-Zehnder interferometer (MZI) and a Sagnac loop mirror. The lasing threshold of the proposed RDFBFL is suppressed to 50 mW by the pumped erbium-doped fiber (EDF), and the pump efficiency is 1%. By simply adjusting the angle of polarization controller (PC) in the Sagnac loop, 2, 3, 5 and 6 lasing channels can be obtained under the pump power of 200 mW, and the central wavelengths of the 3 lasing channels can be simultaneously tuned with a fixed channel separation. Moreover, the power amplitudes and side mode suppression ratios (SMSRs) of lasing channels are maintained around − 10 dBm and 34 dB, respectively. The proposed RDFBFL has the advantages of ideal tunability and low threshold, which can be widely used in imaging systems and long-distance sensing.

Tunable multi-wavelength random distributed feedback fiber laser based on dual-pass MZI

A tunable half-open cavity multi-wavelength erbium-doped random distributed feedback (RDFB) fiber laser is proposed and experimentally demonstrated. The backward Rayleigh scattering generated by inhomogeneous reflective in the 25-km-long single mode fiber is amplified by the 8-m-long pumped erbium-doped fiber (EDF). The dual-pass Mach–Zehnder interferometer (MZI) acts as the reflection mirror in the half-open cavity. Due to the EDF gain and the half-open structure, the laser threshold is suppressed to 40 mW. The number of laser channel increases linearly with the increasing pump power. Under the pump power of 350 mW, there are seven lasing channels in the spectrum. One arm of the MZI is circled on piezoelectric transducer (PZT) and tunable multi-wavelength lasing operation is realized by adjusting the DC voltage on PZT. When the pump power and the driving voltage attached on PZT are 250 mW and 5 V, the wavelengths of six channels are blue-shifted 0.7 nm. The proposed tunable RDFB fiber laser has the advantages of low cost, simple structure and low threshold, which can be widely used in remote sensing and biomedical imaging.

Wavelength Continuously Tunable All-Fiber Flat-Top Comb Filter Based on a Dual-Pass Mach–Zehnder Interferometer

We present a wavelength continuously tunable all-fiber flat-top comb filter. The proposed comb filter is based on a dual-pass Mach-Zehnder interferometer (MZI), constructed with two couplers and a polarization controller (PC), along with a polarizer at the input port. While the interference is created from the optical path difference provided by the two cascaded couplers, the dual-pass structure is based on the feedback of a fiber loop mirror, formed by the second coupler with the PC inserted in the loop, which serves as a reflectivity-variable mirror. The coupling ratio of the first coupler is determined by our optimized results on characterizing a basic dual-pass MZI without a PC. By using Jones matrix formulation, we theoretically analyzed the proposed comb filter. To achieve flat-top spectra, both amplitude condition and phase condition have to be satisfied. Our simulation results revealed that by changing the state of the PC, tunable flat-top spectra can be achieved, and moreover, the flat-top spectra can be continuously adjusted within one free-spectral-range with the help of a rotatable polarizer. The theoretical prediction has been verified by our experimental results. The unique tuning property makes the proposed filter an excellent candidate for applications in dense reconfigurable wavelength division multiplexing networks.

Tunable Multiwavelength Erbium-Doped Fiber Laser Employing PM-FBG and Mach–Zehnder Interferometer with Optical Fiber Delay Line

We propose the use of an erbium-doped fiber laser based on a polarization-maintaining fiber Bragg grating (PM-FBG) and all-fiber Mach–Zehnder interferometer (MZI) to realize a quadruple-wavelength 1.5-μm laser output. In the proposed system configuration, a 1535-nm center wavelength PM-FBG acts as the wavelength selector. The dual-pass MZI is fabricated using two couplers with a 50:50 splitting ratio, and the wavelength spacing of the comb is varied by using a spectrum power-driven optical fiber delay line inserted in MZI. The working threshold in the experiment is 82 mW. Tunable lasers of single-, dual-, triple-, and quadruple-wavelengths can be realized by adjusting the polarization controller. The generated wavelengths are in the range of 1534 to 1534.6 nm, the wavelength space is 0.2 nm, and the 3 dB linewidth is less than 0.05 nm. The power fluctuation is observed to be less than 0.912 dB, and the signal-to-noise ratio (SNR) is larger than 34.9 dB at 26 °C over a scan time of 10 min.

Cascaded interferometers structure based on dual-pass Mach-Zehnder interferometer and Sagnac interferometer for dual-parameter sensing.

In this article, we propose and demonstrate a cascaded interferometers structure based on a dual-pass Mach-Zehnder interferometer (DP-MZI) and a Sagnac interferometer (SI) for simultaneous measurement of strain and lateral stress. The cascaded interferometers configuration consists of a SI structure following with a MZI setup. By inserting a section of polarization-maintaining photonic crystal fiber (PM-PCF) in the sensing loop of the SI structure, an inline interference between the two orthogonal polarization modes of PM-PCF, as well as the interference between the sensing arm and the reference arm of the DP-MZI, i.e., the cascaded interferometers with dual interference, are realized. Theoretical study shows that the reflection spectrum of such cascaded interferometers is consisted of two parts: the big spectrum envelope owing to the SI and the fine interference fringes as a result of the DP-MZI. Experimental results show that the SI achieves the sensitivity of lateral stress and strain 1.28 nm/kPa, 0.78 pm/µε, respectively, while the DP-MZI achieves -0.009 nm/kPa and 5.65 pm/µε, demonstrating the ability for dual parameters measurement with high accuracy.

A Stable and Tunable Linear-Polarization Fiber Ring Laser With a High SMSR by Using a Compounded Fiber Filter

A stable and tunable linear-polarization fiber ring laser with a high side-mode-suppression ratio (SMSR) is proposed and experimentally demonstrated by using a compounded fiber filter, which is composed of a dual-pass Mach-Zehnder interferometer filter incorporating one segment of polarization-maintaining fiber and a high finesse filter. By adjusting the polarization controllers, the output laser can be tuned from 1560.37 to 1568.56 nm and an SMSR as high as 72 dB is achieved. In addition, the peak power fluctuation and wavelength shift are monitored to be less than 0.08 dB and 0.02 nm over an hour. Due to the introduction of the compounded fiber filter as a wavelength selector, the side mode of lasing output can be effectively suppressed and mode competition can be weakened. As a result, the SMSR of lasing output is increased and power stability is improved.

A dual-pass Mach–Zehnder interferometer filter using a TCF loop mirror for double-wavelength fiber lasers

A dual-pass Mach–Zehnder interferometer filter using a section of twin-core fiber (TCF) loop mirror is proposed. The filter is theoretically and experimentally studied for various interferometer arm difference when TCF length is constant. Theoretical results are validated by the experimental demonstration and in good agreement with the experimental results. And then, by using the filter in a ring fiber laser, a stable and switchable dual-wavelength lasing is obtained experimentally. The 3-dB bandwidth and the SMSR of the output laser are 0.015 nm and higher than 62.4 dB, respectively. The peak power fluctuation and wavelength shift are also monitored to be less than 0.04 dB and 0.02 nm over an hour at room temperature. Furthermore, the output laser can be switched between single and dual wavelength by carefully adjusting the PCs. The experimental results show that the filter can suppress mode competition effectively, improve the SMSR availably, and enhance the stability of the output lasing.

Switchable Dual-Wavelength PM-EDF Ring Laser Based on a Novel Filter

A stable and switchable dual-wavelength polarization-maintaining erbium-doped fiber ring laser is proposed and demonstrated experimentally by using a novel filter, which is formed from dual-pass Mach-Zehnder interferometer incorporating a sagnac loop. By adjusting the polarization controllers, the output laser can be switched between single- and dual-wavelength. The wavelength spacing of the dual-wavelength can be tuned from 0.084 to 4.26 nm. Its 3-dB bandwidth and side mode suppression ratio are less than 0.015 nm and higher than 64 dB, respectively. In addition, the peak power fluctuation and wavelength shift are monitored to be less than 0.5 dB and 0.01 nm during an hour, respectively. The characteristics of the novel filter in experimental measurement accord with the result of theoretical analysis.

Polarization-Independent, Multifunctional All-Fiber Comb Filter Using Variable Ratio Coupler-Based Mach–Zehnder Interferometer

A polarization-independent, multifunctional all-fiber comb filter by using variable ratio coupler (VRC)-based dual-pass Mach-Zehnder interferometer is newly proposed and demonstrated. Depending on the dynamic settings of coupling ratios of the fiber couplers, the comb filter provides the channel spacing tunable, multiwavelength switchable, and flat-top spectral responses. Theoretical calculations are verified by the experimental results. Experimentally, a comb filter with the channel spacing tunable from 0.4 to 0.8 nm was obtained. Meanwhile, when the comb spacing was tuned to 0.8 nm, the multiwavelength switchable operation with both the sinusoid and flat-top spectral responses was achieved. The proposed comb filter may find applications in optical communication systems and tunable multiwavelength fiber lasers.

Polarization-Independent All-Fiber Quasi-Flat-Top Comb Filter Based on a Dual-Pass Mach–Zehnder Interferometer With High Birefringence Fiber in the Second Loop

A polarization-independent all-fiber comb filter with quasi-flat-top spectral response based on a dual-pass Mach-Zehnder (M-Z) interferometer is proposed and demonstrated. The proposed filter consists of a dual-pass M-Z interferometer with a section of high birefringence fiber (HBF) and a polarization controller (PC) in the second loop. The theoretical analysis shows that the apparatus allows to operate as a polarization-independent multiwavelength periodic filter and to gain the quasi-flat-top passband filter by adjusting the polarization state of the PC. Theoretical prediction was verified by experimental demonstration.

A tunable and switchable single-longitudinal-mode dual-wavelength fiber laser incorporating a reconfigurable dual-pass Mach–Zehnder interferometer and its application in microwave generation

A tunable and switchable single-longitudinal-mode (SLM) dual-wavelength fiber laser incorporating a reconfigurable dual-pass Mach–Zehnder interferometer (MZI) filter was proposed and demonstrated, which can be applied in microwave generation. By incorporating a high extinction ratio (ER) dual-pass MZI into an erbium-doped fiber ring cavity, SLM dual-wavelength lasing can be achieved even using a MZI with relatively little free spectrum range (FSR), and by beating the two wavelengths at a photodetector, a 9.76 GHz microwave signal with a 3-dB bandwidth of less than 10 kHz is obtained. Moreover, by direct linking the two outputs of the MZI, the high ER dual-pass MZI is easily reconfigured as a half FSR dual-pass MZI. Using this structure, switchable SLM dual-wavelength lasing can be conveniently realized.

Wavelength switchable all-fiber comb filter using a dual-pass Mach-Zehnder interferometer and its application in multiwavelength laser

A novel wavelength switchable all-fiber comb filter based on a dual-pass Mach-Zehnder (M-Z) interferometer is proposed and demonstrated. The proposed filter consists of a rotatable polarizer and a standard dual-pass M-Z interferometer composed of two 3-dB fiber couplers with a polarization controller (PC) in one arm. When the PC is properly set, the wavelength switchable operation is achieved by adjusting the polarization state of the input light. Theoretical calculation is verified by the experimental results. As applications, the proposed comb filter is incorporated into a fiber ring laser to generate wavelength switchable multiwavelength lasing.

Polarization-Controlled Tunable All-Fiber Comb Filter Based on a Modified Dual-Pass Mach–Zehnder Interferometer

We propose and demonstrate a novel tunable all-fiber comb filter based on a modified dual-pass Mach-Zehnder (M-Z) interferometer. The proposed filter consists of a polarization-dependent isolator, a polarization controller (PC), and a modified dual-pass M-Z interferometer composed of a standard 3-dB and a non-3-dB fiber coupler with a PC in one arm. By adjusting the polarization state of the input light, dual-function operation, the spectral spacing tunable and the wavelength switching (interleaving) operation can be easily achieved. The theoretical prediction is verified by the experimental results.

82-channel multi-wavelength comb generation in a SOA fiber ring laser

We demonstrate a multi-wavelength semiconductor optical amplifier (SOA) fiber ring laser with a dual-pass Mach–Zehnder interferometer (MZI) filter. Two SOAs with different gain spectra provide sufficient gain and a wider gain spectrum to facilitate multi-wavelength lasing. The dual-pass MZI, configured by adding an optical isolator to the two outputs of the conventional MZI, serves as comb filter for multi-wavelength operation, and its extinction ratio can be enhanced to twofold as that of the conventional MZI in the same parameters. To investigate the influences of a dual-pass MZI filter and a conventional MZI filter on multi-wavelength operation, two different cavity configurations are presented and compared, including a single-SOA ring cavity and a double-SOA ring cavity. Stable simultaneous operation at 82 wavelengths, with a wavelength spacing of 40 GHz and a power deviation of 5 dB, and with a minimum optical signal-to-noise ratio (OSNR) of 28 dB, is observed from the double-SOA ring cavity using a dual-pass MZI filter.

Tunable and switchable multiwavelength erbium-doped fiber ring laser based on a modified dual-pass Mach-Zehnder interferometer

A tunable and switchable multiwavelength erbium-doped fiber ring laser based on what we believe to be a new type of tunable comb filter is proposed and demonstrated. By adjusting the polarization controllers, the dual-function operation of the channel-spacing tunability and the wavelength switching (interleaving) can be readily achieved. Up to 29 stable lasing lines with 0.4 nm spacing and 14 lasing wavelengths with 0.8 nm spacing in 3 dB bandwidth were obtained at room temperature. In addition, the lasing output, including the number of the lasing lines, the lasing evenness, and the lasing locations, can also be flexibly adjusted through the wavelength-dependent polarization rotation mechanism.

A novel interleaver based on dual‐pass Mach‐Zehnder interferometer

AbstractA novel interleaver based on a dual‐pass Mach–Zehnder (M–Z) interferometer is proposed and analyzed by both theory and experiment. Compared with the traditional M–Z interferometer, the isolation of the new structure is enhanced greatly. When the frequency spacing reaches 50 GHz, its isolation is more than 25 dB. © 2004 Wiley Periodicals, Inc. Microwave Opt Technol Lett 42: 253–255, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20268