Tunable Optical Frequency Comb Research Articles

Tunable microwave and optical frequency comb generator with the aid of cascaded MZM structure

Tunable microwave and optical frequency comb generator with the aid of cascaded MZM structure

Tunable optical frequency comb in a microresonator using amplitude and frequency modulation

Tunable optical frequency comb in a microresonator using amplitude and frequency modulation

Mid-infrared optical frequency comb spectroscopy using an all-silica antiresonant hollow-core fiber.

We present the first mid-infrared optical frequency comb spectrometer employing an absorption cell based on self-fabricated, all-silica antiresonant hollow-core fiber (ARHCF). The spectrometer is capable of measuring sub-mL sample volumes with 26 m interaction length and noise equivalent absorption sensitivity of 8.3 × 10-8 cm-1 Hz-1/2 per spectral element in the range of 2900 cm-1 to 3100 cm-1. Compared to a commercially available multipass cell, the ARHCF offers a similar interaction length in a 1000 times lower gas sample volume and a 2.8 dB lower transmission loss, resulting in better absorption sensitivity. The broad transmission windows of ARHCFs, in combination with a tunable optical frequency comb, make them ideal for multispecies detection, while the prospect of measuring samples in small volumes makes them a competitive technique to photoacoustic spectroscopy along with the robustness and prospect of coiling the ARHCFs open doors for miniaturization and out-of-laboratory applications.

Tunable Optical Frequency Comb Generated Using Periodic Windows in a Laser and Its Application for Distance Measurement.

A novel method for the generation of an optical frequency comb (OFC) is presented. The proposed approach uses a laser diode with optical feedback and operating at a specific nonlinear dynamic state named periodic window. In this case, the laser spectrum exhibits a feature with a series of discrete, equally spaced frequency components, and the repetition rate can be flexibly adjusted by varying the system parameters (e.g., external cavity length), which can provide many potential applications. As an application example, a dual-OFC system for distance measurement is presented. The results demonstrate the system's ability to achieve target distance detection, underscoring its potential for real-world applications in this field.

Generation of GHz line-spacing tunable optical frequency combs using Talbot effects.

In this paper, the generation of GHz line-spacing tunable optical frequency combs (OFCs) was demonstrated using an electro-optical (EO) Talbot laser and a phase modulator. In the EO Talbot laser, the frequency shifting was realized with a dual-parallel Mach-Zehnder modulator (DPMZM) working for carrier-suppressed single-sideband modulation. The PM was employed to achieve the spectral Talbot effect and compensate the phase introduced by the temporal Talbot effect in the laser loop. Arbitrary control of OFC line-spacing was realized using temporal and spectral Talbot effects. The principle of this OFC generator was theoretically modeled. In the experiments, the 2GHz line spacing of an OFC was multiplied to be 4GHz, 6GHz, 8GHz, and 10GHz. The frequency spacing of the OFC can also be multiplied with a fractional factor of 3/4, 7/2, 8/5, and 10/7, which was confirmed by simulations.

Fiber-optic frequency comb generation using low-seed power FWM and Brillouin-assisted power equalization.

In this paper, we experimentally demonstrate an all-fiber broadband tunable optical frequency comb (OFC) operating in the C-band. The OFC is generated by broadening a power-equalized stimulated Brillouin scattering (SBS)-based seed comb (SBS-OFC) using four-wave mixing (FWM) in a highly nonlinear fiber (HNLF). The seed SBS-OFC is obtained from a pump and Stokes power recycling cavity, which yields ≈15 comb lines with 10.8GHz line spacing having 16dBm average power. The seed SBS-OFC is further power-equalized by a Brillouin-assisted power equalization (BAPE) technique to minimize the high pump contribution at the recycling cavity output. The power-equalized seed SBS-OFC, which has low-power of -4.5d B m at the BAPE cavity output, is propagated down a dual-pass 200m dispersion flattened HNLF. At the HNLF output, we obtain ≈140 comb lines within a 12nm bandwidth having 10.8GHz line spacing. We demonstrate wavelength tunability over a span of 35nm by using a tunable laser source as the Brillouin pump. We also observe and measure a secondary OFC generated during the power-equalization process by placing a 10% coupler inside the BAPE cavity. Our experimental results closely match the trends obtained in the simulation.

Tunable dual optical frequency comb at 2 μm for CO2 sensing.

In this article, we demonstrate a dual frequency comb (DFC) based on the gain-switching of mutually injection-locked semiconductor lasers in the 2 μm wavelength region with a tunable free spectral range (FSR) between 500 MHz and 3 GHz. Through the down-conversion process enabled by DFCs, the beating spectra of the optical frequency combs were captured in a 15 MHz electrical bandwidth with high resolution and millisecond acquisition times. A first experimental demonstration of sensing CO2 with this architecture is also presented.

Design of tunable optical frequency comb generation based on electro-optic modulator

Design of tunable optical frequency comb generation based on electro-optic modulator

Tunable optical frequency comb with hundred-GHz spacings generated on a silicon waveguide.

We demonstrate the generation of optical frequency combs with tunable spacing at the hundred-GHz range in the 1550-nm window. The widely spaced combs are realized through silicon-based cross-phase modulation. The optical pump is prepared by multiplication of a 10-GHz train of 1.7-ps pedestal-free pulses. Energy-efficient temporal Talbot processing is used to multiply the repetition rate by a factor of up to 20. In our approach, the multiplication factor can be flexibly controlled by tuning the temporal dispersion inside an optical processor. Optical frequency combs with spacings ranging from 140 to 200 GHz have been successfully generated with a maximum carrier-to-noise suppression ratio of ∼45 dB.

A tunable optical frequency comb source using cascaded frequency modulator and Mach–Zehnder modulators

Abstract In this work, we demonstrate a tunable optical frequency comb (OFC) source based on a cascaded frequency modulator (FM) and two Mach–Zehnder modulators (MZMs). The setup includes one FM and two MZMs, and a sinusoidal RF signal source that directly drive all these modulators. A Flat OFC source with a high number of comb lines, and tunable frequency spacing and center wavelength is analytically modelled and simulated. The results reveal that 51 comb lines with a frequency spacing of 25 GHz are generated when only FM is used. Thirteen of these lines have power variations of 1 dB. Next, by cascading FM with two MZMs, 127 comb lines are obtained. In addition, 101 of these lines have power variations of 1 dB. An optical frequency comb, with tunable frequency spacing ranging from 10 to 40 GHz is successfully generated. Moreover, the center wavelength of the generated OFC can be tuned from 1310 to 1610 nm.

Broadband and tunable optical frequency comb based on 1550 nm verticalcavity surface-emitting laser under pulsed current modulation and optical injection

Optical frequency combs (OFCs) each consist of a set of equally spaced discrete frequency components, and they have been widely applied to many fields such as metrology, optical arbitrary waveform generation, spectroscopy, optical communication, and THz generation. In this work, we propose a scheme for generating broadband and tunable OFCs based on a 1550 nm vertical-cavity surface-emitting laser (VCSEL) under pulsed current modulation and optical injection. Firstly, a pulsed electrical signal is utilized to drive a 1550 nm-VCSEL into the gain-switching state with a broad noisy spectrum. Next, a continuous optical wave is further introduced for generating broadband and tunable OFC. Under injection light with power of 18.82 µW and wavelength of 1551.8570 nm, and pulsed electrical signal with a frequency of 0.5 GHz and pulse width of 200 ps, an OFC with a bandwidth of 82.5 GHz and CNR of 35 dB is experimentally acquired, and the single sideband phase noise at the 0.5 GHz reaches –123.3 dBc/Hz at 10 kHz. Moreover, the influences of injection light wavelength, frequency and width of pulse electrical signal on the performance of generated OFC are investigated. The experimental results show that OFCs with different comb spacings can be obtained by varying the frequency of pulsed electrical signal. For the frequency of pulsed current signal varying in a range of 0.25 GHz–3 GHz, the bandwidth of generated OFCs can exceed 60 GHz through selecting optimized injection optical wavelength and width of pulse electrical signal.

Theoretical model of cascaded electro-optic intensity modulator-based 2.31-THz broad optical frequency comb generator

We report a theoretical model to design a stable and tunable optical frequency comb by controlling the periodic radiofrequency signal applied to the two cascaded lithium niobate Mach–Zehnder modulators. The spectrum flatness, frequency line spacing, and spectrum bandwidth depend on the periodic optical signal’s shape, periodicity, and duty cycle. So the shape and duty cycle of the optical signal are controlled by controlling the amplitude and phase of the periodic radiofrequency signal and realizing a 2.1% duty-cycled periodic signal, resulting in a 1.92-dB flat and 2.31-THz broad-spectrum optical frequency comb. The duty cycle of the optical signal is decreased by controlling the modulators in such a way that it will give the output signal for the transition period of the radiofrequency signal only. The line spacing is controlled by controlling the frequency of the radiofrequency signal and realizes a 30-GHz channel spaced frequency comb. The comb’s channel spacing and frequency can also be controlled by controlling the periodicity of radiofrequency signal and seed laser frequency, making the frequency comb tunable.

Experimental Investigation of External Optical Injection and its Application in Gain-Switched Wavelength Tunable Optical Frequency Comb Generation

A detailed experimental investigation of the effects of external optical injection on a Fabry Perot laser when in continuous wave (CW) mode and in gain switched mode is presented. Such detailed characterisation can help in optimising operating condition of the transmitters to significantly improve the system performance for dedicated applications. In CW mode, we characterised various performance indicators of a laser such as side mode suppression ratio (SMSR), wavelength, peak power, modulation bandwidth, resonance frequency, optical linewidth, and phase noise under external optical injection with the use of tuning maps. We also present in brief the theoretical origin of these parameters using rate equations. We then investigated the performance of the externally injected Fabry Perot laser under gain switching for optical frequency comb (OFC) generation. We demonstrated the generation of an OFC with a free spectral range of 6.25 GHz to 25 GHz and a quasi-continuous wavelength tunability of 31 nm. The phase noise of the tones of the generated OFC is measured and is found to be similar to that of the externally injected light and the measured optical linewidth was ∼40 kHz. We also presented experimentally the trade-off that exists between bandwidth of the generated OFC and the phase noise of individual comb tones under external optical injection and their optimisation for the application at hand.

Tunable multiwavelength optical comb enabledRoF‐OFDM‐PONwith wavelength multiplex

AbstractWe propose a hybrid full duplex passive optical network with fusion of wavelength‐division‐multiplexing and orthogonal frequency‐division multiplexing (WDM‐OFDM) for a radio‐over‐fiber (RoF) system application. The key of the system is a tunable optical frequency comb (OFC) embedded cascading modulators and a parameter mixer. Moreover, 23 frequency components with 0.6 dB flatness generated by the OFC are used as light sources for each WDM channel. We utilize a 7.5 GHz OFDM wired signal and a 12.5 GHz OFDM wireless signal for downstream transmission and 10 Gb/s OOK (on–off keyed) signals for upstream traffic. Using polarization multiplexing technique, we extract a central optical carrier to bear the upstream signal so that no excess optical source is introduced into the ONU. Thus, the intricacy and costs of system are diminished. Moreover, successful transmission has been demonstrated since the bit error rates of the downstream and upstream signals are always under the adopted forward error correction limit. Furthermore, the proposed system can enhance power budget and reduce cost, which has a promising prospect for future wireless communication.

Ultrawide and tunable self-oscillating optical frequency comb generator based on an optoelectronic oscillator

A new mechanism for ultra-wide and tunable self-oscillating optical frequency comb (OFC) based on a novel frequency tunable optoelectronic oscillator (OEO) is proposed using cascaded configuration of optical phase-modulator (PM) and electro-absorption-modulator (EAM). The proposed scheme does not require a dedicated RF source to drive the optical-modulators. The OEO is configured by incorporating the self-oscillation loop with cascaded modulators. A high-speed PIN-photodetector (PD) with a dark current of 10nA, bandwidth of 20 GHz, and responsivity of 1A/W in correspondence with an electrical-amplifier (EA), and bandpass Bessel filter (BPBF) is utilized to convert the optical signal into a microwave signal. The PD detected signal is amplified by the EA. The BPBF is used to extract a 10 Mhz bandwidth from the amplified signal with tunable central frequencies. Part of the extracted OEO signal is directly connected to the PM, whereas, a 180-degree phase-shift is added to the signal before transmitting into the EAM. The PM produces ~19 carrier frequencies, whereas, the generated tunable carriers by the EAM ranges from 85 to 35carrriers with an overall bandwidth of ~1.28THz. The negligible power-fluctuations, good number of generated carriers, and high tone-to-noise-ratio of around 40 dB endorse the applicability of the proposed scheme.

Tunable Er-doped fiber optical frequency comb with a repetition rate adjustment larger than 1.6 MHz

Femtosecond optical frequency combs play important roles in various scientific and technical fields. For example, they can be used for frequency measurements, distance measurements, and in precision spectroscopy. The repetition rate of this type of comb can be tuned in a wide range by controlling the cavity length. This has here been done by using a combination of a motorized stage and a piezoelectric transducer (PZT). A very stable Er-doped fiber femtosecond laser, with a repetition rate of 200 MHz and a pulse duration of 68 fs, was then developed. In addition, a tunable repetition rate adjustment of 1.664 MHz was successively achieved. The fluctuation in the repetition rate was less than 100 Hz in 120 h in the free-running state. Moreover, the average output power was 105.05 mW, with a standard deviation of 0.09 mW for a duration of 110 h. The repetition rate and carrier-envelope offset frequency were continuously phase-locked to a microwave reference for more than 30 days with a standard deviation of 0.327 mHz and 0.569 mHz, respectively.

Tunable ultra-flat optical-comb-enabled, reconfigurable, and efficient coherent channelized receiver.

In this Letter, based on two advanced tunable ultra-flat optical frequency comb generators (T-FOCGs), a coherent channelized receiver with high channelized efficiency and reconfigurability is proposed. In the T-FOCG, the number of 1 dB comb lines increases with the gain, but the optical power of these 1 dB comb lines has almost the constant variance. In the proposed scheme, one optical carrier can support four sub-channels. Meanwhile, the number and bandwidth of sub-channels, as well as the bandwidth and center frequency of an original broadband signal, are all tunable. In this Letter, we verify the feasibility of the coherent channelized receiver by channelizing a 4 GHz signal with a 20 GHz center frequency into four 1 GHz sub-channels, and the reconfigurability is demonstrated by channelizing a 10 GHz signal with frequencies from 18 to 28 GHz into five 2 GHz sub-channels. Moreover, the error-vector magnitude curves of the directly received and the channelized quadrature amplitude modulation (QAM) signal at different amounts of beat noise are compared.

Tunable optical frequency comb from a compact and robust Er:fiber laser

We report on a compact and robust self-referenced optical frequency comb with a tunable repetition rate, generated by an all-polarization-maintaining (PM) mode-locked Er-doped fiber laser. The spacing between comb teeth can be tuned above 300 kHz at a repetition rate of 101 MHz. The repetition rate and the carrier–envelope offset of the laser are stabilized separately, and the relative residual phase noises are determined to be $336~\unicode[STIX]{x03BC}\text{rad}$ and 713 mrad (1 Hz–1 MHz). The accurate frequency characteristics and the stable structure show great potential for the use of such a comb in applications of precision measurements.

基于耦合射频信号和单个马赫-曾德尔调制器的可调光学频率梳

基于耦合射频信号和单个马赫-曾德尔调制器的可调光学频率梳

Expansion and phase correlation of a wavelength tunable gain-switched optical frequency comb.

A novel scheme for the expansion and phase correlation of a wavelength tunable gain-switched optical frequency comb (OFC) is presented. This method entails firstly combining two gain-switched OFCs and expanding them using a phase modulator. Subsequently, the phase correlation between all the comb lines is induced through four-wave mixing (FWM) in a semiconductor optical amplifier (SOA). In this article, the generation of 42 highly correlated comb lines separated by 6.25 GHz, with an optical carrier to noise ratio (OCNR) of more than 50 dB, is experimentally demonstrated. In addition, the wavelength tunability of the scheme, over 30 nm within the C band, is shown. Finally, the degree of phase correlation between comb lines is verified through RF beat tone linewidth measurements. The results show a five orders of magnitude reduction in the beat tone linewidth, due to FWM in an SOA.