Glass with modified surface regions and methods and apparatuses for forming the same via electro-thermal poling and field-assisted ion exchange

A glass substrate, comprising:

• a first surface comprising a first alkali-depleted region with a first alkali-depleted refractive index and a first ion-exchanged region with a first ion-exchanged refractive index;
• a second surface comprising a second alkali-depleted region with a second alkali-depleted refractive index, the first and second surfaces arranged on opposite sides of the glass substrate;
• and
• an alkali-containing bulk extending between the first and second surfaces and comprising a bulk refractive index;
• and
• wherein:
• the first and second alkali-depleted refractive indices are less than the bulk refractive index and the first ion-exchanged refractive index is greater than the bulk refractive index;
• the first alkali-depleted region extends into the alkali-containing bulk from the first surface such that the first alkali-depleted region comprises a first thickness t1;
• the second alkali-depleted region extends into the alkali-containing bulk from the second surface such that the second alkali-depleted region comprises a second thickness t2;
• and
• the first ion-exchanged region extends into the alkali-containing bulk from the first surface such that the first ion-exchanged region comprises a third thickness t3 substantially equal to t1.

A glass substrate, comprising:

• an alkali-containing bulk comprising a first surface, an opposing second surface, and a first concentration of a first alkali metal ion;
• a first alkali-depleted region extending into the alkali-containing bulk from the first surface such that the first alkali-depleted region comprises a first thickness t1;
• a second alkali-depleted region extending into the alkali-containing bulk from the second surface such that the second alkali-depleted region comprises a second thickness t2;
• and
• a first ion-exchanged region extending into the alkali-containing bulk from the first surface such that the first ion-exchanged region comprises a third thickness t3 substantially equal to t1;
• and
• wherein the first ion-exchanged region comprises a second concentration of a second alkali metal ion, the first alkali-depleted region comprises a third concentration of the first alkali metal ion less than the first concentration, the second alkali-depleted region comprises a fourth concentration of the first alkali metal ion less than the first concentration, and each of the alkali-containing bulk, the first alkali-depleted region, and the second alkali-depleted region is substantially free of the second alkali-metal ion.