FAQ about PPLN
Question : What is PPLN ?
Answer: PPLN stands for periodically poled lithium niobate. In PPLN, sign of nonlinear coefficient changes periodically due to the periodical domain inversion along the beam propagation direction of a z-cut lithium niobate substrate. As a result, the quasi-phase matching (QPM) condition required for efficient wavelength conversion can be satisfied by choosing a proper period of the PPLN. Domain inversion is realized by moving Li ion in lithium niobate crystal from one to another stable position through applying very high electric field across the substrate.
Question : Why MgO doped congruent LN crystal is good?
Answer: MgO doped congruent LN has excellent properties required for low cost efficient high power light generation, including high nonlinear coefficient (34 pm/V vs. 15 for KTP, 0.85 for LBO, and 26 pm/V for LT); large available wafers (up to 4” vs. 3” for stoichiometric LN, 2” for LT, ~ 1” for KTP and LBO); relatively low crystal price (much cheaper than stoichiometric LN, LT, KTP and LBO); large optical damage threshold (much higher than non-doped LN and KTP, comparable with MgO doped stoichiometric LN, LBO, and MgO doped LT).
Question : What is C2C technology?
Answer: C2C Link has its own proprietary technologies in fabricating high quality PPLN chips, which is especially effective in poling MgO doped congruent lithium niobate. It is well known that MgO doped PPLN chips have high photorefractive damage threshold as compared with non-doped PPLN. However, high concentration (i.e. 5 mol%) MgO doped congruent PPLN cannot be fabricated by the standard method due to the difficulties in crystal poling resulted from the nature of non-uniform doping in congruent lithium niobate crystal. C2C's technology enables us to overcome this problem to pole the crystal over large area with high yield, and thus low cost.
Question : What kind of applications can C2C's PPLN provide?
Answer: C2C's PPLN chips provide a highly efficient method to convert wavelength of commercially available semiconductor laser diodes to wavelengths that are not accessible to the laser diodes based on nonlinear effects within PPLN. The converted wavelength can range from 350 nm to nearly 5000 nm by choosing proper period of PPLN and the pumping wavelength. This technique is especially useful in generating red, green, blue (i.e. RGB) light required in laser display and mid-infrared light required in optical sensing.
Question : How to generate RBG light for laser display applications?
Answer: Laser display requires low-cost, compact, high performance, all solid RBG lasers. Nonlinear optic devices (such as PPLN) provide an efficient method to generate RGB light through second harmonic generation (SHG). For instance, compact green and blue light (e.g. 532 nm, 473 nm) can be generated by employing the diode pumped solid state (DPSS) laser technology, in which 808 nm pump laser diode is used to generated the fundamental wave required in the SHG process through a laser crystal. RGB light can also be generated directly from pumping lasers. For instance, blue light (e.g. 488 nm) required in medical instruments can be generated directly from a 976 nm laser diode.
Question : How to generate mid-IR light for optical sensing applications?
Answer: Optical sensing such as trace gas detection requires mid-infrared (IR) coherent light sources ranging from 2000 to 5000 nm. PPLN is an excellent material to efficiently generate mid-IR light through difference frequency generation (DFG). For instance, by pumping PPLN with 1064 nm and 1550 nm lasers, mid-IR light at about 3400 nm can be generated through the DFG process in PPLN with a proper period. Mid-IR light can also be generated through the optical parametric oscillator (OPO) method, in which a single beam (e.g. 1064 nm) and an optical resonator are usually employed.
Question : How to achieve all-optical wavelength conversion using PPLN?
Answer: all-optical wavelength converters are key components required in the next generation optical telecommunication networks. PPLN waveguide devices have excellent properties required for wavelength conversion in the communication networks. Wavelength conversion (e.g. from 1550 nm to 1530 nm) can be achieved by the difference frequency generation (DFG) method with a pumping light at 770 nm. The wavelength conversion can also be achieved through the cascaded nonlinear process, in which SHG of a pump light at 1540 nm is used to generate the 770 nm pumping light required in the DFG process. It has been demonstrated experimentally that high conversion efficiency can be achieved by employing PPLN waveguides.
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