Virtually imaged phased array (VIPA) having spacer element and optical length adjusting element

An apparatus receiving an input light at a respective wavelength and focused into a line, the apparatus comprising:

• an angular dispersive device including first and second surfaces, the second surface having a reflectivity which causes a portion of light incident thereon to be transmitted therethrough, the first and second surfaces being positioned so that the input light radiates from the line to be reflected a plurality of times between the first and second surfaces and thereby cause a plurality of lights to be transmitted through the second surface, the plurality of transmitted lights interfering with each other to produce an output light which is spatially distinguishable from an output light produced for an input light at a different wavelength;
• and
• a spacer element maintaining the relative positioning between the first and second surfaces to be constant, the spacer element having a thermal expansion coefficient with a magnitude of less than or equal to 10−5/° C.

An apparatus receiving an input light at a respective wavelength within a continuous range of wavelengths, the apparatus comprising:

• an angular dispersive device having first and second surfaces, the second surface having a reflectivity which causes a portion of light incident thereon to be transmitted therethrough, the first and second surfaces being positioned so that the input light is reflected a plurality of times between the first and second surfaces to cause a plurality of lights to be transmitted through the second surface, the plurality of transmitted lights interfering with each other to produce an output light which is spatially distinguishable from an output light produced for an input light at any other wavelength within the continuous range of wavelengths;
• and
• a spacer element maintaining the relative positioning between the first and second surfaces to be constant, the spacer element being made of a material comprising glass and having a thermal expansion coefficient which is approximately zero.

An apparatus receiving an input light at a respective wavelength and focused into a line, the apparatus comprising:

• an angular dispersive device including first and second surfaces, the second surface having a reflectivity which causes a portion of light incident thereon to be transmitted therethrough, the first and second surfaces being positioned so that the input light radiates from the line to be reflected a plurality of times between the first and second surfaces and thereby cause a plurality of lights to be transmitted through the second surface, the plurality of transmitted lights interfering with each other to produce an output light which is spatially distinguishable from an output light produced for an input light at a different wavelength;
• and
• a spacer element maintaining the relative positioning between the first and second surfaces to be constant, the spacer element being made of a material comprising glass and having a thermal expansion coefficient which is approximately zero.