Conoptics Laser Switching Systems

Description

Conoptics provides a family of products specifically tailored for pulse selection or regenerative amplifier switching systems. Each system consists of an optical modulator, a modulator driver, and synchronization electronics. The low voltage design approach taken here reduces modulator drive levels by an order of magnitude compared to other methods. This feature makes switching rates to tens of MHz readily achievable and virtually eliminates EMI effects.

Optical Modulators

Current technology involving mode locked lasers and regen systems deals primarily with the 500 to 2000nm spectral range, a region served by the 350(KD*P) and 360(LTA) series modulators. In general, the 350 series are employed in the majority of pulse selection and regen applications in this region. In the 1000 to 2000nm range the 360 series are employed.

Applications with mode locked lasers require that the modulator be capable of switching between the zero and half or quarter wave states completely during the 2L/C interpulse period, generally 10 to 13 nanoseconds. The 350/360 series devices have intrinsic switching times faster than needed and system performance is determined by the driver electronics. Construction details of the modulator's internal electrical transmission line (e.g. impedance) must vary according to the driver model chosen (See Tables I and II). This is not a concern unless modulator and driver are ordered separately.

All 360 devices are transverse field traveling wave structures with LTA (lithium tantalate) as the active medium. LTA has high optical transmission between 700 and 4000nm with lowest absorption in the center of the Ti:Sapphire operating region. Its high refractive index, low birefringence, and relatively low dielectric constant are compatible with high speed modulator design. Although it does exhibit a piezoelectric response, resonances are mild and rarely encountered with the electrical waveforms used in these applications.

350 Series modulators are similar in construction to the 360 Series but use KD*P (potassium dideuterium phosphate) as the active medium. For ultrafast application in the range 700 to 1000nm, despite their longer length, they exhibit only one-third to one-half the pulse broadening due to GVD as do half-wave voltage equivalent LTA devices. Furthermore, the higher intrinsic optical quality of KD*P, a solution grown rather than melt grown crystal, assures high pulse contrast at shorter wavelengths.

Modulator Drivers

Conoptics offers modulator drivers with various output formats. This data sheet describes variable gate drivers with repetion rates to 20MHz, that are digital only. We also offer analog drivers (please review data sheet 1092 for an explanation of these products). The 307 driver is primarily designed for use in regen systems, it offers high output voltage with fast switching times with a pulse width variable from 40 to 500nsec. The 25D is the most versatile driver, with a lower output requiring longer modulators, it offers a minimum pulse width of 18nsec, a maximum rep rate of 20MHz, and a maximum pulse width determined by your input signal. The Models 307 and 25D can also be employed as pulse shapers/choppers.

All drivers listed include a variable DC bias voltage supply which allows precise positioning of the AC signal on the desired operating point of the modulator transfer characteristic and eliminates the need for quarter-wave plates.

Application: Pulse Picker for Femtosecond Laser (up to 90 MHz)

Specifications (PDF file - 0.25 Meg)