Variable wavelength light filter and sensor system

Light filter apparatus having a band pass with a central wavelength for light that varies with displacement of position in a selected spatial direction in a light-receiving surface of a filter, the apparatus comprising:

• a first stratum of filter material, having first and second spaced apart, light-receiving surfaces facing each other, that is partly transmitting and partly reflecting for light received at a light-receiving surface thereof and having a wavelength in a selected pass band of wavelengths, where a distance of separation h(x) of the two surfaces increases monotonically with displacement of a position coordinate x in the selected direction, and for at least one position the distance of separation is approximately equal to (m-1/2).lambda..sub.c /2n, where m is a positive integer and n is the real part of the refractive index of the filter material for light of a selected wavelength .lambda..sub.c in the selected pass band;
• and
• a second stratum of filter material, having first and second, spaced apart, light-receiving surfaces facing each other with a distance of separation that varies with displacement of position in the selected direction, that is at least partly transmitting for light having the wavelength .lambda..sub.c, that is substantially fully absorbing or transmitting for light having a second wavelength approximately equal to a wavelength of any reflectance side band of the first stratum of filter material, and that is positioned so that light issued from one of the first stratum and the second stratum is received by the other stratum.

Light filter apparatus having a band pass with a central wavelength for light that varies with displacement of position in a selected spatial direction in a light-receiving surface of a filter, the apparatus comprising:

• a first stratum of filter material, having first and second spaced apart, light-receiving surfaces facing each other, that is partly transmitting and partly reflecting for light received at a light-receiving surface thereof and having a wavelength in a selected pass band of wavelengths, where a distance of separation h(x) of the two surfaces increases monotonically with displacement of a position coordinate x in the selected direction, and for at least one position the distance of separation is approximately equal to m.lambda..sub.c /2n, where m is a positive integer and n is the real part of the refractive index of the filter material for light of a selected wavelength .lambda..sub.c in the selected pass band;
• and
• a second stratum of filter material, having first and second, spaced apart, light-receiving surfaces facing each other with a distance of separation that varies with displacement of position in the selected direction, that is at least partly transmitting for light having the wavelength .lambda..sub.c, that is substantially fully absorbing or reflecting for light having a second wavelength approximately equal to a wavelength of any transmittance side band of the first stratum of filter material, and that is positioned so that light issued from one of the first stratum and the second stratum is received by the other stratum.

Light filter apparatus having a band pass with a central wavelength for light that varies with displacement of position in a selected spatial direction in a light-receiving surface of a filter, the apparatus comprising:

• a first stratum of filter material, having first and second spaced apart, light-receiving surfaces facing each other, that is partly transmitting and partly reflecting for light received at a light-receiving surface thereof and having a wavelength in a selected pass band of wavelengths, where a distance of separation h(x) of the two surfaces increases monotonically with displacement of a position coordinate x in the selected direction, and for at least one position the distance of separation is approximately equal to (m-1/2).lambda..sub.c /2n, where m is a positive integer and n is the real part of the refractive index of the filter material for light of a selected wavelength .lambda..sub.c in the selected pass band;
• and
• a second stratum of filter material, having first and second, spaced apart, light-receiving surfaces facing each other with a distance of separation that varies with displacement of position in the selected direction, that is at least partly transmitting for light having the wavelength .lambda..sub.c, that is substantially fully absorbing or transmitting for light having a second wavelength approximately equal to a wavelength of any reflectance side band of the first stratum of filter material, and that is positioned so that light issued from one of the first stratum and the second stratum is received by the other stratum.

Light filter and sensor apparatus having a band pass with a central wavelength for transmitted light that varies with displacement of position in a selected spatial direction in a light-receiving surface of a light filter, the apparatus comprising:

• a first stratum of filter material, that has two spaced apart surfaces facing each other, with one of these surfaces being positioned to receive incident light thereat, with a distance of separation h.sub.1 (x) between these two surfaces that varies monotonically with increase in a position coordinate x measured in a selected direction in a light-receiving surface of the first stratum, that is highly transmitting for incident light having a wavelength .lambda. lying in a narrow wavelength pass band that has a pass band central wavelength .lambda..sub.c (x) at a position given by the spatial coordinate x, where .lambda..sub.c (x) varies monotonically with increase in the coordinate x;
• a second stratum of filter material, positioned adjacent to one of the two surfaces of the first stratum, that has two spaced apart surfaces facing each other, with a distance of separation h.sub.2 (x) between these two surfaces that varies monotonically with increase in the position coordinate x, that is highly transmitting for incident light having the wavelength .lambda..sub.c (x) at a position with coordinate x, that is substantially fully absorbing or reflecting for incident light having a wavelength approximately equal to a wavelength of any transmittance side band of the first stratum of filter material, and that is positioned so that light that issues from one of the first stratum and the second stratum is received by the other stratum;
• and
• an array of photosensors extending in the selected direction, with each photosensor being positioned to receive a portion of a light beam that is issued from the first or second stratum at a position measured in the selected direction.

Light filter and sensor apparatus having a band pass with a central wavelength for transmitted light that varies with displacement of position in a selected spatial direction in a light-receiving surface of a filter, the apparatus comprising:

• a first stratum of filter material, that has two spaced apart surfaces facing each other, with one of these surfaces being positioned to receive incident light thereat, with a distance of separation h.sub.1 (x) between these two surfaces that varies monotonically with increase in a position coordinate x measured in a selected direction in a light-receiving surface of the first stratum, that is highly transmitting for incident light having a wavelength .lambda. lying in a narrow wavelength pass band that has a pass band central wavelength .lambda..sub.c (x) at a position given by the spatial coordinate x, where .lambda..sub.c (x) varies monotonically with increase in the coordinate x;
• a second stratum of filter material, positioned adjacent to one of the two surfaces of the first stratum, that has two spaced apart surfaces facing each other, with a distance of separation h.sub.2 (x) between these two surfaces that varies monotonically with increase in the position coordinate x, that is highly transmitting for incident light having the wavelength .lambda..sub.c (x) at a position with coordinate x, that is substantially fully absorbing or reflecting for incident light having a wavelength approximately equal to a wavelength of any transmittance side band of the first stratum of filter material, and that is positioned so that light that issues from one of the first stratum and the second stratum is received by the other stratum;
• and
• an array of photosensors extending in the selected direction, with each photosensor being positioned to receive a portion of a light beam that is issued from the first or second stratum at a position measured in the selected direction.

Light filter apparatus having a band pass with a central wavelength for transmitted light that varies continuously with displacement of position in a selected spatial direction in a light-receiving surface of a filter, the apparatus comprising:

• a first edge filter that is approximately fully transmitting for incident light of wavelength equal to a selected central wavelength .lambda..sub.c and that is substantially non-transmitting for incident light having a wavelength .lambda.=.lambda..sub.c +.DELTA..lambda..sub.1, with .DELTA..lambda./.lambda..sub.c >0.1;
• a second edge filter that is approximately fully transmitting for incident light of wavelength .lambda..sub.c and that is substantially non-transmitting for incident light of wavelength .lambda.=.lambda..sub.c -.DELTA..lambda..sub.2 with .DELTA..lambda..sub.2 /.lambda..sub.c >0.1, where the wavelength .lambda..sub.c increases monotonically with displacement of position in said selected spatial direction;
• a band pass filter stratum, positioned adjacent to at least one of the first edge filter and the second edge filter, that is approximately fully transmitting for incident light of wavelength .lambda..sub.c and that is substantially non-transmitting for light of wavelength .lambda.=.lambda..sub.c +.DELTA..lambda..sub.3 with .vertline..DELTA..lambda..sub.3 /.lambda..sub.c .vertline.>0.5, where the first and second edge filters and the band pass filter stratum are positioned to serially receive and transmit a portion of an incident light beam.

Light filter apparatus having a band pass with a central wavelength for reflected light that varies continuously with displacement of position in a selected spatial direction in a light-receiving surface of a filter, the apparatus comprising:

• a first edge filter that is approximately fully reflecting for incident light of wavelength equal to a selected central wavelength .lambda..sub.c and that is substantially non-reflecting for incident light having a wavelength .lambda.=.lambda..sub.c +.DELTA..lambda..sub.1 with .DELTA..lambda./.lambda..sub.c >0.1;
• a second edge filter that is approximately fully reflecting for incident light of wavelength .lambda..sub.c and that is substantially non-reflecting for incident light of wavelength .lambda.=.lambda..sub.c -.DELTA..lambda..sub.2 with .DELTA..lambda..sub.2 /.lambda..sub.c >0.1, where the wavelength .lambda..sub.c increases monotonically with displacement of position in said selected spatial direction;
• a band pass filter stratum, positioned adjacent to at least one of the first edge filter and the second edge filter, that is approximately fully reflecting for incident light of wavelength .lambda..sub.c and that is substantially non-reflecting for light of wavelength .lambda.=.lambda..sub.c +.DELTA..lambda..sub.3 with .vertline..DELTA..lambda..sub.3 /.lambda..sub.c .vertline.>0.5, where the first and second edge filters and the band pass filter stratum are positioned to serially receive and reflect a portion of an incident light beam.

Light filter apparatus having a band pass with a central wavelength for light that varies with displacement of position in a selected spatial direction in a light-receiving surface of a filter, the apparatus comprising:

• a multi-layer first filter that is at least partly transmitting for light having a wavelength .lambda..sub.c, the filter having N(N.gtoreq.4) layers of material with relatively high refractive index n.sub.H and having N-1 layers of material with relatively low refractive index n.sub.L, where the high index layers and the low index layers are positioned adjacent to and alternate with each other to form a multi-layer structure, where each high index layer has a thickness equal to (2p-1).lambda..sub.c /4n.sub.H for some positive integer p, each of the low index layers, except for two layers, has a thickness equal to (2q-1).lambda..sub.c /4n.sub.L for some positive integer q, and two of the low index layers have thicknesses that increase monotonically with displacement of position in the selected direction, and for at least one position the thicknesses of these two low index layers are approximately m.sub.1 .lambda..sub.c /2n.sub.L and m.sub.2 .lambda..sub.c /2n.sub.L for two positive integers m.sub.1 and m.sub.2, where .lambda..sub.c is a selected wavelength in the selected pass band;
• and
• a second filter that is at least partly transmitting for light having the wavelength .lambda..sub.c, that is substantially fully absorbing or reflecting for light having a wavelength approximately equal to a wavelength of any side band of the first filter, and that is positioned so that light transmitted through one of the first filter and the second filter is received by the other filter.

Light filter apparatus having a band pass with a central wavelength for light that varies with displacement of position in a selected spatial direction in a light-receiving surface of a filter, the apparatus comprising:

• a multi-layer first filter that is at least partly transmitting for light having a wavelength .lambda..sub.c, the filter having N(N.gtoreq.4) layers of material with relatively high refractive index n.sub.H and having N-1 layers of material with relatively low refractive index n.sub.L, where the high index layers and the low index layers are positioned adjacent to and alternate with each other to form a multi-layer structure, where each high index layer has a thickness equal to (2q-1).lambda..sub.c /4n.sub.H for some positive integer q, and two of the high index layers have thicknesses that increase monotonically with displacement of position in the selected direction, and for at least one position the thicknesses of these two high index layers are approximately m.sub.1 .lambda..sub.c /2n.sub.H and m.sub.2 .lambda..sub.c /2n.sub.H for two positive integers m.sub.1 and m.sub.2, where .lambda..sub.c is a selected wavelength in the selected pass band;
• and
• a second filter that is at least partly transmitting for light having the wavelength .lambda..sub.c, that is substantially fully absorbing or reflecting for light having a wavelength approximately equal to a wavelength of any side band of the first filter, and that is positioned so that light transmitted through one of the first filter and the second filter is received by the other filter.

Light filter apparatus having a band pass with a central wavelength for light that varies with displacement of position in a selected spatial direction in a light-receiving surface of a filter, the apparatus comprising:

• a multi-layer first filter that is at least partly transmitting for light having a wavelength .lambda..sub.c, the filter having N(N.gtoreq.4) layers of material with relatively low refractive index n.sub.L and having N-1 layers of material with relatively high refractive index n.sub.H, where the high index layers and the low index layers are positioned adjacent to and alternate with each other to form a multi-layer structure, where each high index layer has a thickness equal to (2p-1).lambda..sub.c /4n.sub.H for some positive integer p, each of the low index layers, except for two layers, has a thickness equal to (2q-1).lambda..sub.c /4n.sub.L for some positive integer q, and two of the low index layers have thicknesses that increase monotonically with displacement of position in the selected direction, and for at least one position the thicknesses of these two low index layers are approximately m.sub.1 .lambda..sub.c /2n.sub.L and m.sub.2 .lambda..sub.c /2n.sub.L for two positive integers m.sub.1 and m.sub.2, where .lambda..sub.c is a selected wavelength in the selected pass band;
• and
• a second filter that is at least partly transmitting for light having the wavelength .lambda..sub.c, that is substantially fully absorbing or reflecting for light having a wavelength approximately equal to a wavelength of any side band of the first filter, and that is positioned so that light transmitted through one of the first filter and the second filter is received by the other filter.

Light filter apparatus having a band pass with a central wavelength for light that varies with displacement of position in a selected spatial direction in a light-receiving surface of a filter, the apparatus comprising:

• a multi-layer first filter that is at least partly transmitting for light having a wavelength .lambda..sub.c, the filter having N(N.gtoreq.4) layers of material with relatively low refractive index n.sub.L and having N-1 layers of material with relatively high refractive index n.sub.H, where the high index layers and the low index layers are positioned adjacent to and alternate with each other to form a multi-layer structure, where each high index layer has a thickness equal to (2p-1).lambda..sub.c /4n.sub.H for some positive integer p, each of the high index layers, except for two layers, has a thickness equal to (2q-1).lambda..sub.c /4n.sub.H for some positive integer q, and two of the high index layers have thicknesses that increase monotonically with displacement of position in the selected direction, and for at least one position the thicknesses of these two high index layers are approximately m.sub.1 .lambda..sub.c /2n.sub.H and m.sub.2 .lambda..sub.c /2n.sub.H for two positive integers m.sub.1 and m.sub.2, where .lambda..sub.c is a selected wavelength in the selected pass band;
• and
• a second filter that is at least partly transmitting for light having the wavelength .lambda..sub.c, that is substantially fully absorbing or reflecting for light having a wavelength approximately equal to a wavelength of any side band of the first filter, and that is positioned so that light transmitted through one of the first filter and the second filter is received by the other filter.

A method of dispersing a light beam continuously into a plurality of wavelength intervals that form a continuous spectrum with wavelength increasing monotonically in a selected spatial direction, the method comprising the steps of:

• providing a first stratum of filter material having two spaced apart, light-receiving surfaces facing each other, the first stratum being partly transmitting and partly reflecting for light received at a light-receiving surface thereof and having a wavelength in a selected pass band of wavelengths, where a distance of separation h.sub.1 (x) of the two surfaces increases monotonically with displacement of position in the selected direction and for at least one selected position the distance of separation h.sub.1 (x) is approximately equal to m.lambda..sub.c /2n, where m is a positive integer and n is the real part of the refractive index of the material for light of a selected wavelength .lambda..sub.c in the selected pass band;
• providing a second stratum of filter material, having two spaced, apart light-receiving surfaces facing each other with a distance of separation h.sub.2 (x) that increases monotonically with displacement in the selected direction, that is at least partly transmitting for light having the wavelength .lambda..sub.c, that is substantially fully absorbing or reflecting for light having a second wavelength approximately equal to a wavelength of any transmittance sideband of the first stratum of filter material, and that is positioned so that light transmitted through one of the first stratum and the second stratum is received by the other stratum;
• and
• directing a beam of light so that the beam illuminates at least a portion of the first stratum or the second stratum in the selected direction.

A method of dispersing a light beam continuously into a plurality of wavelength intervals that form a continuous spectrum with wavelength increasing monotonically in a selected spatial direction, the method comprising the steps of:

• providing a first stratum of filter material having two spaced apart, light-receiving surfaces facing each other, the first stratum being partly transmitting and partly reflecting for light received at a light-receiving surface thereof and having a wavelength in a selected pass band of wavelengths, where a distance of separation h.sub.1 (x) of the two surfaces increases monotonically with displacement of position in the selected direction and for at least one selected position the distance of separation h.sub.1 (x) is approximately equal to (2m-1).lambda..sub.c /4n, where m is a positive integer and n is the real part of the refractive index of the material for light of a selected wavelength .lambda..sub.c in the selected pass band;
• providing a second stratum of filter material, having two spaced, apart light-receiving surfaces facing each other, with a distance of separation h.sub.2 (x) that increases monotonically with displacement in the selected direction, that is at least partly reflecting for light having the wavelength .lambda..sub.c, that is substantially fully absorbing or transmitting for light having a second wavelength approximately equal to a wavelength of any reflectance sideband of the first stratum of filter material, and that is positioned so that light transmitted through one of the first stratum and the second stratum is received by the other stratum;
• and
• directing a beam of light so that the beam illuminates at least a portion of the first stratum or the second stratum in the selected direction.

A method of dispersing a light beam continuously into a plurality of wavelength intervals that form a continuous spectrum with wavelength increasing monotonically in a selected spatial direction, the method comprising the steps of:

• providing a first stratum of filter material having two spaced apart, light-receiving surfaces facing each other, the first stratum being partly transmitting and partly reflecting for light received at a light-receiving surface thereof and having a wavelength in a selected pass band of wavelengths, where a distance of separation h.sub.1 (x) of the two surfaces increases monotonically with displacement of position in the selected direction and for at least one selected position the distance of separation h.sub.1 (x) is approximately equal to m.lambda..sub.c /2n, where m is a positive integer and n is the real part of the refractive index of the material for light of a selected wavelength .lambda..sub.c in the selected pass band;
• providing a second stratum of filter material, having two spaced, apart light-receiving surfaces facing each other with a distance of separation h.sub.2 (x) that increases monotonically with displacement in the selected direction, that is at least partly transmitting for light having the wavelength .lambda..sub.c, that is substantially fully absorbing or reflecting for light having a second wavelength approximately equal to a wavelength of any transmittance sideband of the first stratum of filter material, and that is positioned so that light transmitted through one of the first stratum and the second stratum is received by the other stratum;
• and
• directing a beam of light so that the beam illuminates at least a portion of the first stratum or the second stratum in the selected direction.

A method of dispersing a light beam continuously into a plurality of wavelength intervals that form a continuous spectrum with wavelength increasing monotonically in a selected spatial direction, the method comprising the steps of:

• providing a first stratum of filter material having two spaced apart, light-receiving surfaces facing each other, the first stratum being partly transmitting and partly reflecting for light received at a light-receiving surface thereof and having a wavelength in a selected pass band of wavelengths, where a distance of separation h.sub.1 (x) of the two surfaces increases monotonically with displacement of position in the selected direction and for at least one selected position the distance of separation h.sub.1 (x) is approximately equal to (2m-1).lambda..sub.c /4n, where m is a positive integer and n is the real part of the refractive index of the material for light of a selected wavelength .lambda..sub.c in the selected pass band;
• providing a second stratum of filter material, having two spaced, apart light-receiving surfaces facing each other with a distance of separation h.sub.2 (x) that increases monotonically with displacement in the selected direction, that is at least partly transmitting for light having the wavelength .lambda..sub.c, that is substantially fully absorbing or reflecting for light having a second wavelength approximately equal to a wavelength of any reflectance sideband of the first stratum of filter material, and that is positioned so that light transmitted through one of the first stratum and the second stratum is received by the other stratum;
• and
• directing a beam of light so that the beam illuminates at least a portion of the first stratum or the second stratum in the selected direction.