10 GHz Lithium Niobate Modulators

Zoom

Features

• C- and L-Band Operation Range
• Low Optical Insertion Loss: 4.0 dB (Typical)
• Titanium Indiffused Z-Cut Lithium Niobate
• Low Drive Voltage
• Long-Term Bias Stability
• Telcordia GR-468 Compliant
• Integrated Photodetector

The LN82S-FC is a 10 GHz LiNbO₃ intensity modulator with a fixed chirp of 0.7 and an integrated photodiode. The modulator features a PM input fiber pigtail and an SM output fiber pigtail that are terminated with FC/UPC (ultra physical contact) connectors. The PM fiber is keyed to the slow-axis, which is also aligned to the extraordinary mode. The integrated photodetector can be used for optical power monitoring and modulator bias control, which eliminates the need for an external fiber tap. RF input into the modulator is supplied via a GPO^® connector.

These modulators are fabricated from Titanium Indiffused Z-Cut LiNbO₃, which creates 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. These fixed chirp modulators down-chirp the pulse, which can be useful when the optical fiber in the network has a positive dispersion coefficient. The down-chirped pulse traveling through an optical fiber with a positive dispersion coefficient will be compressed until a minimum is reached. Beyond that point the dispersion term will dominate. Since chirping the pulse increases the spectral width of the pulse, the chirped pulse will eventually be broader than an unchirped pulse traveling through the same optical fiber. This fixed chirp intensity modulator is ideal for applications requiring improved power penalty (less than two dB for +1600 ps/nm) performance over zero-chirp devices. For telecommunications applications, the LN82S-FC can be easily integrated into 300-pin MSA-compatible transponders.

These modulators have an SMP-male connector for the GPO input drive that can mate with an SMP-female connector, which can then be adapted to an SMA connector. To do this, we recommend using our SMA-to-SMP Microwave Adapter Cables or a GPO to K™ adapter. The GPO to K adapter is available for purchase upon request*. Other third party SMP adapters are available from various electronics component suppliers, but the fit may vary and compatibility is not guaranteed. For more information on custom configurations (i.e., fiber type, connectorization, etc.) and quotes, please contact Technical Support. 

*Please be advised that because of the compact modulator package, the modulator may not sit flat on a table after attaching a GPO to K adapter, but will sit flat when using the SMP to SMA cable. These specific adapters have been verified to fit the GPO or SMP connector on the package, and have been used for testing purposes. 

GPO^® is a registered trademark of Corning Gilbert. K™ is a trademark of Anritsu.

Zoom

Features

• C- and L-Band Operation Range
• Low Optical Insertion Loss: 4.0 dB (Typical)
• Titanium Indiffused X-Cut Lithium Niobate
• Low Drive Voltage
• Long-Term Bias Stability
• Telcordia GR-468 Compliant
• Integrated Photodetector

The LN81S-FC is a 10 GHz LiNbO₃ intensity modulator with zero chip and an integrated photodiode. It can provide intensity modulation from DC to >15 GHz for applications such as RF photonics, telecommunications, and sensing. The modulator features a PM input fiber pigtail and an SM output fiber pigtail that are terminated with FC/UPC (ultra physical contact) connectors. The PM fiber is keyed to the slow-axis, which is also aligned to the extraordinary mode. The integrated photodetector can be used for optical power monitoring and modulator bias control, which eliminates the need for an external fiber tap. RF input into the modulator is supplied via a GPO^® connector.

These modulators are fabricated from X-Cut Titanium Indiffused LiNbO₃, which allows for both arms of the Mach-Zehnder interferometer to be symmetrically modulated. This symmetry ensures that the modulated output of the intensity modulator is not also shifted in phase/frequency (chirped). Chirp is an important factor in high-data-rate, long-distance telecommunication systems. The optimum value (typically zero or ~0.6) depends signficantly upon the overall system architecture. Zero-chirp intensity modulators, in particular, are ideal for use in metro and long-haul DWDM applications requiring less than a 2 dB power penalty for ±1200 ps/nm dispersion. For telecommunications applications, the LN81S-FC can be easily integrated into 300-pin MSA-compatible transponders.

These modulators have an SMP-male connector for the GPO input drive that can mate with an SMP-female connector, which can then be adapted to an SMA connector. To do this, we recommend using our SMA-to-SMP Microwave Adapter Cables or a GPO to K™ adapter. The GPO to K adapter is available for purchase upon request*. Other third party SMP adapters are available from various electronics component suppliers, but the fit may vary and compatibility is not guaranteed. For more information on custom configurations (i.e., fiber type, connectorization, etc.) and quotes, please contact Technical Support. 

*Please be advised that because of the compact modulator package, the modulator may not sit flat on a table after attaching a GPO to K adapter, but will sit flat when using the SMP to SMA cable. These specific adapters have been verified to fit the GPO or SMP connector on the package, and have been used for testing purposes. 

GPO^® is a registered trademark of Corning Gilbert. K™ is a trademark of Anritsu.

Zoom

Features

• C- and L-Band Operation Range
• Low Optical Insertion Loss: 3.0 dB (Typical)
• Titanium Indiffused Z-Cut Lithium Niobate
• Low Drive Voltage
• Telcordia GR-468 Compliant
• Optional Integrated Output Polarizer

These Titanium Indiffused Z-Cut LiNbO₃ Phase Modulators are available with (LN63S-FC) or without (LN53S-FC) an integrated polarizer. Phase modulators provide chirp control in high-speed data communications. They are also ideal for coherent communications, sensing, all-optical frequency-shifting, and data encryption applications.

These Z-Cut LiNbO₃ phase modulators are 10 GHz devices with a PM input fiber pigtail and a SM output fiber pigtail. Both are terminated with FC/PC connectors. The LN65S-FC has an integrated optical polarizer positioned before the output port of the device. The integrated polarizer is not included with the LN53S-FC. With no polarizer, the device is capable of supporting both optical modes, ordinary and extraordinary. Each mode will have a different modulation efficiency; the modulation efficiency of the extraordinary mode will be approximately a factor of three greater than the ordinary mode. For those interested in supporting only the extraordinary mode, the internal polarizer would be desirable.

These modulators have an SMP-male connector for the GPO^® input drive that can mate with an SMP-female connector, which can then be adapted to an SMA connector. To do this, we recommend using our SMA-to-SMP Microwave Adapter Cables or a GPO to K™ adapter. The GPO to K adapter is available for purchase upon request*. Other third party SMP adapters are available from various electronics component suppliers, but the fit may vary and compatibility is not guaranteed. For more information on custom configurations (i.e., fiber type, connectorization, etc.) and quotes, please contact Technical Support. 

*Please be advised that because of the compact modulator package, the modulator may not sit flat on a table after attaching a GPO to K adapter, but will sit flat when using the SMP to SMA cable. These specific adapters have been verified to fit the GPO or SMP connector on the package, and have been used for testing purposes. 

GPO^® is a registered trademark of Corning Gilbert. K™ is a trademark of Anritsu.

Click for Full Lab Facts Summary

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 Setup

The 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 Results

As 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 f_o. The sidebands are displaced from the laser carrier peak frequency at integer multiples of the modulation frequency f_m (f_o ± Nf_m 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 V_pp = 3.63 V
The carrier frequency is f_o; the modulation frequency is f_m = 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 V_pp = 2.85 V
The carrier frequency is f_o; the modulation frequency is f_m = 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.