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Lithium Niobate Electro-Optic Modulators, Fiber-Coupled![]()
LN27S-FC 40 GHz Phase Modulator with Polarizer, Z-Cut LN81S-FC 10 GHz Intensity Modulator, X-Cut LNLVL-IM-Z Low Vπ 40 GHz Intensity Modulator, Z-Cut Enlarged View Related Items ![]() Please Wait ![]() Click to Enlarge Z-Cut LiNbO3 Intensity Modulator Cross-Section ![]() Click to Enlarge X-Cut LiNbO3 Intensity Modulator Cross-Section Features
Thorlabs Quantum Electronics manufactures a variety of lithium niobate (LiNbO3) optical phase and intensity modulators. These high-performance devices are based on titanium-indiffused waveguide technology, offer large bandwidths, and are ideal for developing high-speed modulation systems. The modulators are fabricated from either X-cut or Z-cut LiNbO3 (see the example diagrams to the right). X-cut intensity modulators employ a symmetrical design that provides low frequency-chirp in the modulated signal, while Z-cut intensity modulators provide more efficient modulation (i.e., lower Vπ or half-wave voltage) at the expense of higher frequency-chirp. Phase modulators are only offered as Z-cut devices because their single optical path does not benefit from the symmetry of the X-cut design. The IQ modulator fully exploits the advantages of symmetry as an X-cut device. The Z-cut devices are also capable of supporting both the ordinary and extraordinary optical modes, which have different modulation efficiencies. An integrated optical polarizer, positioned before the output port of the device, is included in Z-cut devices as only one mode is desirable for most applications. For applications where the polarizer is not desired, there is an option to have it removed. Please contact Tech Support with inquiries. The modulators come with a polarization-maintaining (PM) input fiber pigtail and a single-mode (SM) output fiber pigtail that are terminated with FC/PC connectors. The PM fiber is keyed to the slow axis, which is also aligned to the extraordinary mode of the modulator. Please note that options for PM output fiber pigtails and FC/APC connectors are available for all LiNbO3 modulators. For more information on custom configurations (e.g., fiber type, connectors) and quotes, please contact Tech Support. All Thorlabs fiber-coupled lithium niobate modulators are compatible with our EO modulator drivers. Our fiber-coupled tunable lasers provide an ideal C-band or L-band source for use with these modulators. For all-in-one solutions in high-speed fiber optic test and measurement, we offer reference transmitters, optical transmitter with phase modulators, and calibrated electrical-to-optical converters.
Intensity Modulator Specifications
Phase Modulator Specifications
IQ Modulator Specifications
† GPO is a registered trademark of Corning Optical Communications RF. ‡ SMF-28 is a registered trademark of Corning. Intensity Modulator Pin Diagrams![]() Click to Enlarge 10 GHz Intensity Modulator Pin Diagram ![]() Click to Enlarge LN05S-FC 40 GHz Intensity Modulator Pin Diagram ![]() Click to Enlarge LNLVL-IM-Z Low Vπ 40 GHz Intensity Modulator Pin Diagram Phase Modulator Pin Diagrams![]() Click to Enlarge 10 GHz Phase Modulator Pin Diagram ![]() Click to Enlarge 40 GHz Phase Modulator Pin Diagram IQ Modulator Pin Diagrams![]() Click to Enlarge 20 Gb/s IQ Modulator Pin Diagram Driving an Electro-Optic Phase Modulator with the Amplified Output of a Function Generator![]() Click to Enlarge Figure 1: Experimental Setup Used to Evaluate Whether a Basic RF Source Built Around a Function Generator Could be Sufficient to Drive a Fiber-Coupled EO Phase Modulator Thorlabs offers a selection of fiber-coupled electro-optic (EO) modulators, which are ideal for modulating light from fiber-coupled laser sources. Applications frequently require EO modulators to be driven at rates of 1 GHz or higher, which places significant demands on the driving radio frequency (RF) voltage source. We investigated whether it would be possible to use a basic setup built around a function generator to drive a fiber-coupled EO phase modulator. The experimental setup we designed and implemented to test this possibility included instrumentation to record the spectrum of the modulated optical signal. By analyzing the modulated optical spectrum, we confirmed this basic RF source is a viable option for driving a fiber-coupled EO phase modulator. Our approach and results are documented in this Lab Fact. Experimental Design and SetupThe design of the RF voltage source portion of the setup required first determining the power the RF source should supply to drive the fiber-coupled EO phase modulator. The power requirements were calculated after we made an estimate of the driving voltage needed to achieve the modulation depth desired for this application. Details describing our process for selecting a modulation depth, the relationship between modulation depth and driving voltage, and the calculations we used to estimate the power required from the RF voltage source are included in the Lab Facts document. From our investigations, we determined the power from the function generator alone would not be sufficient for our application. Our solution was to insert a low noise amplifier between the function generator and EO modulator. We also included an electrical low pass filter before the modulator to remove signal distortion that appeared to originate with the function generator. We drove the EO phase modulator with a sinusoidal RF voltage, which imparted a sinusoidal phase modulation on the 1550 nm CW laser signal. A scanning Fabry-Perot interferometer, whose output was sent to an oscilloscope, was placed after the EO phase modulator and used to measure and monitor the spectrum of the modulated optical signal. It was necessary to use the Fabry-Perot interferometer for this purpose as it has the ability to resolve the very fine spectral features of the phase-modulated optical spectra: at a wavelength of 1550 nm, a frequency difference of 1 GHz is equivalent to a wavelength difference of 0.8 pm. The measured spectra were recorded as functions of scan time. In the Lab Facts document, we describe a straight-forward method to convert from units of Fabry-Perot scan time to units of relative optical frequency. For this work, we estimate Δf = (1.17 GHz/ms)Δt. Experimental ResultsAs is described in the Lab Facts document, theory predicts the spectra of our phase modulated optical signals would include sets of symmetric sidebands arranged around the laser carrier peak at frequency fo. The sidebands are displaced from the laser carrier peak frequency at integer multiples of the modulation frequency fm (fo ± Nfm with N = 1, 2, ...). The relative heights of the sidebands are a function of the modulation depth, which is in turn a function of the peak-to-peak value of the RF driving voltage. Given the modulation depth, the relative amplitudes of the laser carrier peak and modulation sidebands can be calculated. This makes it possible to tailor the power distribution across the various peaks to meet an application's needs. We used the predictive power of this model to confirm our RF source was adequately driving the EO modulator. The spectra shown in Figures 2 and 4 are representative of the modulation spectra we measured. The theoretical curves in Figure 3 are a function of modulation depth and plot the expected relative powers of the laser carrier peak (solid red curve), first order sidebands (dotted blue curve), second order sidebands (dotted green curve), and third order sidebands (dotted violet curve). The black arrow points to the modulation depth corresponding to the spectrum in Figure 2, and the gray arrow points to the modulation depth corresponding to the spectrum in Figure 4. From our results, we determined our measured and applied modulation frequencies agreed, and we confirmed the spectral power distributions in our optical spectra were consistent with the peak-to-peak driving voltage of the RF source. We conclude that the good agreement between the expected and recorded results validates the use of a basic RF source built around a function generator as a driver for fiber-coupled EO phase modulators. ![]() Click to Enlarge Figure 4: EO Phase Modulator Spectrum When Vpp = 3.63 V The carrier frequency is fo; the modulation frequency is fm = 1 GHz. The X-axis reports the scanning time of the Fabry-Perot interferometer and can be directly related to the signal's relative frequency spectrum. ![]() Click to Enlarge Figure 3: Curves Relating the Power in the Carrier and Several Sideband Peaks as A Function of Modulatrion Depth The 0.44 modulation depth indicated by the black arrow corresponds to Figure 2, and the 0.56 modulation depth indicated by the gray arrow corresponds to Figure 4. ![]() Click to Enlarge Figure 2: EO Phase Modulator Spectrum When Vpp = 2.85 V The carrier frequency is fo; the modulation frequency is fm = 1 GHz. The X-axis reports the scanning time of the Fabry-Perot interferometer and can be directly related to the signal's relative frequency spectrum.
![]() ![]() Click to Enlarge This operational diagram of an intensity modulator shows the waveguide (blue lines) splitting into two paths embedded in the surface of the lithium niobate (green). The input light is first affected by the modulating RF drive voltage and then the DC bias voltage, as shown by the translucent regions. Applications
LiNbO3 optical intensity modulators use a Mach-Zehnder interferometer structure to allow modulation of the optical output power of the device, as shown by the operational diagram to the right. The devices include two electrical ports: one for the modulation driving signal and one for biasing the modulator. X-cut or Z-cut devices are available. X-cut devices allow for both arms of the Mach-Zehnder interferometer to be symmetrically modulated. This symmetry ensures that the modulated output is not also shifted in phase/frequency (chirped). Z-cut devices have an inequality in the push-pull phase shift between the two arms of the Mach-Zehnder interferometer. This results in a phase/frequency shift (chirp) in the output in addition to the intensity modulation. Z-cut devices also have a better overlap of the electrical and optical fields in the Mach-Zehnder structure, resulting in higher drive efficiencies. The LN81S-FC and LN82S-FC 10 GHz modulators include an integrated photodetector for optical power monitoring and modulator bias control, eliminating the need for an external fiber tap. Thorlabs offers two high-speed intensity modulators that can operate up to 40 GHz. The LN05S-FC modulator is a high bandwidth device designed to provide minimum variation in modulation over the operating frequency range. The LNLVL-IM-Z modulator provides the lowest RF Vπ, or half-wave voltage, at any specific frequency over the operating frequency range. The graphs below show a typical drive voltage (left) and electro-optic response (right) over the operating frequency range for these two modulators. See the Specs tab for complete specifications. ![]() ![]() Click to Enlarge This operational diagram of a phase modulator shows the waveguide (blue line) as one through optical path embedded in the surface of the lithium niobate (green). The input light is affected only by the modulating RF drive voltage, as shown by the translucent region. Applications
LiNbO3 optical phase modulators consist of a single, through optical waveguide, as shown by the operational diagram to the right. As there is only one optical path to modulate, all of the phase modulators are Z-cut devices in order to optimize drive efficiency. While most applications benefit from the integrated polarizer in Z-cut modulators, the LN53S-FC and LN66S-FC modulators are offered for applications where the polarizer is undesirable. ![]() ![]() Click to Enlarge This operational diagram of an IQ modulator shows the waveguides (blue lines) split into four paths embedded in the surface of the lithium niobate (green). The input light is first affected by each MZI's modulating RF drive voltages, and then by each MZI's DC bias voltages, as shown by the translucent regions.
Applications
LiNbO3 IQ modulators use a dual-parallel Mach-Zehnder interferometer (MZI) structure in order to allow modulation of both the phase and amplitude of light for advanced optical transmission schemes. As shown in the operational diagram to the right, the modulator consists of two independently-controlled MZIs whose outputs are combined. The combining structure also includes a bias electrode that applies a phase delay between the two MZIs, allowing for the required phase control between the two modulator arms. Two IQ modulators can be used together in a polarization-multiplexed arrangement to double data transmission rates, e.g. two LN86S-FC devices can provide a 40 Gb/s link on the same optical channel/wavelength. | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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