Fiber-Coupled AOM

By virtue of having no moving parts our acousto-optic modulators (AOMs) are able to amplitude modulate a laser beam at very high speed. For example modulation bandwidths in excss of 50MHz are readily achievable.

In an AOM a laser beam is caused to interact with a high frequency ultrasonic sound wave inside an optically polished block of crystal or glass (the interaction medium). By carefully orientating the laser with respect to the sound waves the beam can be made to reflect off the acoustic wavefronts (Bragg diffraction). Therefore, when the sound field is present the beam is deflected and when it is absent the beam passes through undeviated. By switching the sound field on and off very rapidly the deflected beam appears and disappears in response (digital modulation). By varying the amplitude of the acoustic waves the intensity of the deflected beam can similarly be modulated (analogue modulation).

It is usual to choose the deflected beam as the one that is used in the optical system because it can be switched on and off with high extinction ratio (typically >40dB) and intensity can be varied from zero to more that 85% of the incident beam. The rate at which the beam can be modulated is governed by the time it takes the acoustic wavefronts to traverse the laser beam, which depends on the beam diameter and the acoustic velocity in the interaction medium.

The sound waves are generated by a transducer, usually a thin wafer of lithium niobate, that is bonded onto the interaction medium using a highly efficient cold-weld metallic bonding process. When a high frequency electrical signal is applied to the transducer it vibrates, generating the acoustic wave. The signal is derived from an RF driver, which generates a high frequency carrier that is itself modulated by an analogue or digital input signal.

Principal applications for AO modulators are pre-press (putting image and text data onto films or plates as part of the printing process), laser imaging and displays, switching in telecom fibres, instrumentation and research.

STG Series Fiber-coupled Acousto-optical Modulators (AOM)

Fiber-coupled acousto-optic modulators (FCAOM) offer an elegant and robust solution for amplitude modulation of fiber lasers, allowing direct control of the timing, intensity, and temporal shape of the laser output. Our Fiber-Q modulators offer high extinction ratio, low insertion loss, and excellent stability in both polarization maintaining (PM) and non-PM formats at modulation frequencies up to 80 MHz for visible and infrared wavelengths. Built for reliability, the Fiber-Q series of products features a rugged hermetic design in a compact, low-profile package, ideal for ease of integration into all-fiber and OEM systems, including medical laser systems.

Each Fiber-Q acousto-optic modulator requires an RF driver to generate the RF signal creating the acoustic wave within the embedded AO crystal. Modulation of the beam through the Fiber-Q will depend upon the frequency and intensity of the applied RF signal.

Fiber-coupled acousto-optic modulators (FCAOM) were initially developed to modulate the intensity of light contained in fibers without having to break the fiber to install a free-space acousto-optic modulator (AOM). Traditionally, modulation in fiber lasers was achieved using a master oscillator power amplifier (MOPA). The MOPA limited the pulse shapes that could be created, and required a separate semiconductor seed laser system. Direct integration of a fiber optic acousto-optic modulator is a far simpler approach, and allows the optical path to remain closed for better power handling and reliability, in addition to lower loss.

A fiber-coupled acousto-optic modulator (FCAOM) can directly control the temporal characteristics of the active output from a fiber laser, offering a wider variety of pulse shapes. As a byproduct of the acousto-optic effect, light passing through the 1st order diffraction mode of a fiber-coupled modulator also experiences a frequency shift and beam deflection. This allows our Fiber-Q products to be used for more than just modulation, resulting in applications outside the laser such as optical heterodyne interferometry. The recent addition of visible Fiber-Q products will also enable more compact all-fiber instrument designs in biomedical applications such as microscopy and flow cytometry.

Today, we offer a line of fiber optic acousto-optic modulators designed for low insertion loss, high extinction ratio, and excellent return loss. Typical optical performance for the Fiber-Q series includes:

• Insertion loss: as low as 2 dB, depending on model

• Extinction ratio: 50 dB

• Return loss: 40 dB

• Polarization extinction ratio: 20 dB (for polarization-maintaining models)

We have leveraged our expertise in telecommunication component design to create a line of highly reliable fiber optic modulators, adapting our processes and designs to handle high optical power and the challenges of precision fiber alignment. We grow our own tellurium dioxide (TeO2) crystals in-house, polishing and performing all stages of fabrication to achieve low scatter and rigorous quality standards throughout the manufacturing process. This ensures consistently high reliability, high laser damage threshold and high optical performance.

We continue to lead the market in the development of fiber-coupled modulators, offering the first devices for visible wavelengths from 397 nm to 780 nm to meet the needs of sensing and quantum technology applications. Our fast switch rate Fiber-Q devices enable efficient, high speed optical pulse picking at infrared wavelengths for all-fiber laser systems. Most devices are also offered in 3-port configurations.

In addition to our standard line of Fiber-Q modulators, we customize, design, and manufacture in volume for OEM needs. Furthermore, our technical support team works with our customers to identify the best RF driver for the application, taking into consideration the type of modulation required (digital or analog) as well as any specific pulse shaping needs.

We offer a wide range of standard fibre-coupled AOMs with the following characteristics: -

• Wavelengths: 1310nm or 1550nm

• Drive Frequencies: 40MHz, 80MHz or 110MHz

• Optical Rise-Times: as low as 10ns

• Materials: Tellurium Dioxide & Chalcogenide Glass

• Options: Single mode, polarisation maintaining and multimode, with or without connectors. Available in two, three or four fibre package configurations.

Description of Part Number: T-M150-0.4C2G-3-F2S:

• M = Modulator

• 150 = Drive frequency in MHz

• 2 = Tellurium Dioxide (interaction material)

• F2 = 2 port fibre-coupled

• S or P = Single Mode or Polarisation Maintaining.

Our standard FCAOMs are listed below. For more AOMs, please send us an email.

Our old FCAOM models are listed in the below table. These old models may or may not be in stock or obsolete and no longer produced. Please check with our sales regarding the availability of the below models.

Remark:

• xx in the driver model (such as 21200-2xx) may be DM, AM, DS or AS

• Standard connector is FC/PC (not applicable for T-M080, T-M150 and T-M200 series). We also commonly supply the following options: FC/APC, SC/PC & SC/APC. (Remark: 1. FC = Named as “Frank Charlie”, screw-in type metal plug connector; 2. SC = Named as “Sam Charlie”, square type plastic connector. 3. PC = Polished Connector, usually with Return Loss (RL) > 40dB (min) [eg. FC/PC, SC/PC]; 4. APC = 8 deg Angled-Polished Connector, usually with RL > 50dB (min) [eg. FC/APC, SC/APC])

For more information, please doanload the catalogue here.

Details of STG Series Fiber-coupled Acousto-Optic Modulators (AOMs)

1. Fiber-Q

We specialise in providing optical components for high power fibre laser and amplifier systems. In-house control of critical manufacturing processes, from crystalline material selection and orientation, cutting, polishing and AR coating through to fibre coupling, ensure our components are of the highest optical quality.

The ‘Fibre-Q’ Acousto-Optic Modulator is designed for use in pulsed fibre laser amplifier systems. In addition to the standard product shown, custom configurations are available for specialized applications.

Ordering Code Explanation: T-M150-0.4C2G-3-F2S (Modulator, 150MHz, 0.4mm active aperture, compressional mode, Tellurium Dioxide, 1064nm, SMA female bulk head connector, 2 fibre, single mode (Hi1060)

Key Features:

• Low insertion loss

• Compact, low profile package

• Rugged hermetic design

• Stable performance

• Custom configurations available

General Specifications:

2. Fiber-coupled AOM

Custom-AOMs available upon request. Please send us an email if you have any further enquiry.