CA1181273A - Optical scanning system with wavelength shift correction - Google Patents
Optical scanning system with wavelength shift correctionInfo
- Publication number
- CA1181273A CA1181273A CA000398072A CA398072A CA1181273A CA 1181273 A CA1181273 A CA 1181273A CA 000398072 A CA000398072 A CA 000398072A CA 398072 A CA398072 A CA 398072A CA 1181273 A CA1181273 A CA 1181273A
- Authority
- CA
- Canada
- Prior art keywords
- grating
- spinner
- scanning system
- optical scanning
- angle
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B5/00—Optical elements other than lenses
- G02B5/18—Diffraction gratings
-
- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B26/00—Optical devices or arrangements for the control of light using movable or deformable optical elements
- G02B26/08—Optical devices or arrangements for the control of light using movable or deformable optical elements for controlling the direction of light
- G02B26/10—Scanning systems
- G02B26/106—Scanning systems having diffraction gratings as scanning elements, e.g. holographic scanners
Abstract
ABSTRACT OF THE DISCLOSURE
A spot scanning holographic spinner system incorporates an optical element in the optical path to provide compensation for wavelength shifts in the coherent light source. The device is located in a plane parallel to the spinner and consists of a diffraction grating having the same properties as gratings formed on the spinner surface.
A spot scanning holographic spinner system incorporates an optical element in the optical path to provide compensation for wavelength shifts in the coherent light source. The device is located in a plane parallel to the spinner and consists of a diffraction grating having the same properties as gratings formed on the spinner surface.
Description
OPTICAL SCANNING SYSTEM WITH
WAVE~ENGTH SHIFT CORRECTION
BACKGROUND AND PRIOR A~T STATEMENT
The present invention relates to an optical spot scanning system and more particularly to an improved holo-graphic scanning system which includes a compensation element to correct for cross-scan errors in the scan line due to wavelength shifts occurring in the light source.
Holographic scanners which utilize a rotating disc having a plurality of holographically formed lenses or gratings are known in the art. Representative disclos-ures are provided in the Prior Art List filed with the --present application. These prior art spinners are subject to certain prcblems resulting from their geometry. These problems, briefly stated, are scan line "bow", in the image plane, spinner wobble and spinner "wedge" both resulting in colinear multiple scan lines, and spinner decentration causing output scan distortion. These problems are more thoroughly analyzed in U.S. Patent No. 4,289~371, issued 20 September 15, 1981 and assigned to the same assignee as the present invention. In this patent the enumerated problems are compensated for by utilizing, as the reconstruction element, a spinner having on its surface a plurality of holographically formed plane linear diffraction gratings.
By strict mathematical methods, it was demonstrated that certain relationships existed between the wavelength of the reconstruction light source, the grating period and the angles of incidence and diffraction, whereby most of the inherent spinner problems were either corrected for or minimized. The patent also addressed another problem, wavelength shiEt, which originates with -the recons-truction light source. This shift, or chanye in -the source wave-length results in corresponding changes in -the ou-tpu-t dif-fraction angle and hence, an undesirable deflec-tion of the output scan line. The plane linear diffraction grating spinner is effective only when a monochromatic stable wave--la-length light source was utilized. Thus, a stable source He-Ne laser was used in the exemplary example provided in said patent.
It is therefore desirable to utilize a plane grating holographic spinner such as that described in the aforemen-tioned patent but which is further improved by eliminati.on of the effects caused by wavelength shifts in the coherent light source. Such a technique is becoming of considerable . -~, importance because of the increasing use of laser diodes as the light source in scanning systems~ These diodes can experience wavelength shifts of up to 3 nm or more due to junction heating over its output power range.
The present invantion is therefore directed to an optical scanning 5 system including a spinner having formed thereon at least one plane linear diffraction grating having a constant grating period d, a stationary wavelength compensation diffraction grating having properties identical to said grating formed on said spinner surface, said stationary grating placed in a plane parallel and in optical alignment with said spinner grating, a collimated 10 reconstruction light source of wavelength ~, r which provides a beam of lightdirected at an angle of incidence ~i onto said compensation grating, said grating diffracting said beam at a diffraction angle of ~3d~ said incidence angle i3i ~ ~d ~ 45~ and the ratio of ~ r to grating spacing d having a value between 1 and 1.618, whereby the light beam diffracted by the compensation 15 grating is incident on the spirner grating at an angle ~i and is diffracted out of said grating at an angle ~d i Figure l is a sch~matic diagram of a prior art optical scanning system.
Figure 2 is a graph showing diode laser wavelength shift as a 20 func~ion of pulse width time resulting in laser heating conditions.
Figure 3 is a graph plotting cross-scan defle~tion over one half of a scanned line length as a function of wavelength shift.
Figure 4 is the scanning system of Figure 1 modified to compensate for the effects of wavelength shifts of the reconstruction light source.
Figure 5 i9 a grapil plotting cross-scan deflection over one half of a scanned line length as a function of wavelength for the system of Figure 4.
Figure 6 is a graph plotting cross-scan deflection over one half of a s~anned line length as a func~ion of a nominal wavelength of 830 nm and over -1.5 minute spiMer tilt position.
Figure '7 is a graph plotting cross-scan deflection over one half of a scanned line as a ~unction Or a nominal wavelength of 820 nm and over- h5 minute spinner belt tilt position.
DESCRIPTION
Figure 1 schematically illustrates a scanning embodiment described in the afo~ementioned U.S. Patent modified to show the effects of a slightly polychromatic reconstruction light source. In the figure, a light source 16 generates a reconstruction plane wavefront 18 which is incident on plane linear diffraction grating spinner 20 at an angle ~i. If source 16 is a monochromatic source, such as a He-~e laser, the wavefront is diffracted at a diffraction angle ad which is wavelength dependent. Doublet lens 22 focuses a linear scan 24 at image plane 25 via pl~ne mirror 23. This linear scan is nearlybow free, and is reasonably insensitive to spinner wobble, decentration and wedge errors, such qualities being attributable to the characteristics of the spinner 20 and the system geometry, as described in the afore~entioned patent.
- If, however, a diode laser is substituted for the H~Ne source 16, a smal:L shift in output wavelength occurs with drive current. Since the diffracted rays at spinner 20 are wavelength sensitive, diffracted rays 21 deviate by some small angle along the dotted path incurring a small deflection of the beam in the cross-scan direction at image plane 25.
The reasons for and extent of the wavelength shift in the diode laser source is made clearer by reference to Figures 2 and 3. Figure 2 is a graph showing test measurements made on a Hitachi Series 1600 diode laser.
The central laser wavelength shift of the laser is plotted against pulse width time for short pulses of lO0 Hz duty cycle. It can be seen that the heating associated with the pulses has the effect of shifting the peak to longer (lower energy) wavelengths. A shift of ~ O.S nm occurs over the time duration shown which would be representative of a ROS scanning at 300 spi with an image plane velocity of 2't/sec.
Figure 3 shows the effects of a wavelength shift of l nm along one half of the length of a scanned line in the image plane for the system of Figurelo Source 16 is the Hitachi Series 1600 laser having a nominal wavelength j~
of 820 nm, ~3i is 45.45 and ~d is 4as.55. Spinner 20 is formed according to the principles of the aforementioned patent with a spacing period d =
0.5798454,y m. (The ratio of ~ to d must have a value between 1 and 1.618).
Focusing lens 22 is a linearized flat field air spaced doublet with a 26.8" e~itpupil to image plane distance (throw distance). In Figure 3, two scanned spot trajectories; cross-scan deflection (Y) vs scan deflection (X) (center to edge) are plotted for values of ,~ of 820 nm (scan A) and at 821 nm (scan B) representing a wavelength shift of l nm. Spinner 20 is rotated at a speed of 3000 rpm. This l nm shift has caused the output diffractioll angle to change by an angle B of 0.105 incurring a 0.049 inch deflection of the beam in the cross-scan deflection (Y). Even a 0.5 nm wavelength shift would produce approxi-mately a 0.024 inch deElection. Both of these deflections represent, for most spot scanning systems, an unacceptable level of scan line perturbations at the image plane.
~igure 4 shows the system of Figure 1 modified according to the invention by the introduction of a plane linear grating 30 into the path of the plane wavefront 18. (~rating 30 is a wavelength compensating device which has properties identical to the gratings formed on the surface of spinner 20. In other words, if spinner 20 facets are holographically formed, the grating is 10 holographically formed using the same photorecording system and having the same period as a spinner 20 grating facet and consequently has the same high' diffraetion efficiency as the spinner. C~rating 30 is placed in the tangential plane parallel to the plane of spinner 20. The system of Figure 4 operates in the following manner. Assuming source 16 is operating at its nominal 15 wavelength of 820 nm, reconstruction beam 18 is directed at the incident angle i onto grating 30 and is diffracted out at diffraction angle (3d (solid line path), the angles measured with respect to normal of the plane of the grating.
Since grating 30 and spinner 20a are parallel, by symmetry beam 18 is incident on the center of facet 20a at angle q)i = (~d- Facet 20a diffracts the beam at a20 diffraction angle t¦)d which is colinear (parallel) with the incident path of beam 18 at grating 30, i.e. ~d = i This result is confirmed by solving for (~)d in the following grating equation (for grating 20a) sin ~Pi+ sin (~d = J~/d.
For the Figure 4 embodiment, typical grating 30 to spinner 20 25 distance would be 1/2 to 1 inch and spinner 30 to lens 22 distance '~ 1 inch.With the above geometry in place, it can be appreciated that a reconstruction beam, even if diffracted into a different path because of a small wavelength shift, will nonetheless be diffracted from the spinner in a path colinear with its incidence on the compensation grating but shifted by a 30 small lateral distance. That this results in correction of the cross-scan errors at the image plane can be demonstrated by tracing the scanning path of the reconstruction beam with a small (1 - 2 nm) shift of the wavelength of source 16. When such a shift occurs, the beam is still incident on grating 30 at angle i but is diffracted along a slightly different path, represented by the dotted 35 line, at an angle 'd. ('I'he path is chosen at an exag~erated deviation angle for illustrative purposes). The beam is incident on facet 20a at angle /t)'i and is 7~
diffracted out at an angle of ~'d and as shown above, (~3'd = ~i. The beam is, however, shifted by a lateral distance s from the position of the first beam.
This small lateral displacement is of no consequence since lens 22 focuses all image rays entering in parallel to the same point on plane 25. Hence, the 5 scanned line will be corrected for the cross-scan errors.
From the above, it has been demonstrated that even if the laser reconstruction light source experiences wavelength shifts during its operating cycle, these shifts wiU be corrected for because of the unique geometry and positioning of the grating pairs.
The cross-scan errors at the scanning plane are completely elimi nated only when the beam is at the center position of grating 20a. As the spinner 20 rotates at same angle ~3r some cross-scan error does occur. For the compensated systern of Figure 4, the scan line trajectories for four different source wavelengths are plotted as shown by the graph of Figure 5. For the 15 4.511 scan represented, plots A, B, C and D represent source wavelengths of 819 nm, 820 nm, 821 nm and 822 nm, respectively. As shown, the scan line is deflected only 0.000631l/nm at the edge of the scan. This compares very favorably with the 0.0501l/nm deflection in the uncompensated case shown in Figure 3.
lNhile the above compensation technique almost completely com-pensates for cross-scan deflection errors, there is no concomitant compensa-tion for a change in scan line length due to wavelength shift. This deflection is quite small; for the above example the edge of scan of 4.511 is altered by .03581l for a 1 nm wavelength shift and .0029 for a 0.5 nm shift. Deflection of 25 that order should be acceptable for systems scanning up to 8.51l. The deflection does appear to be linearly related to scan length and some correction can be achieved by using a high angular efficiency lens 22. A
suitable focusing lens for this purpose would be the type described in U.S.
Patent 4,108,532, constructed with due regard for the laser diode heating 30 cycles and the consequent wavelength shifts within and between scan lines.
The above examples utilizing diode lasers as the reconstruction light source considered only relatively small wavelength shifts of - 2nm from the central emission wavelength. ~s a practical matter"lowever, due to manufacturing tolerance, actual cliode lasers, even from the same batch, may 35 have center emission wavelengths differing by -15 nm. This may necessitate some deviation from the preferred invariant condition of incidence angle ~i ~
-G-diffraction angle ~d~ 45- For example, Figure 6 shows the cross-scan deflection for the Figure 4 arrangement but with a wavelength of 830 nm and with the grating pair rotated clockwise to make the incident angle ~3i = 43 95 and diffraction angle ~d = 47 50- Plot E represents one half of the nominal 5 scanned line with no spinner tilt while plots F and G represent the lines resulting from a- 1.5 minute wobble, or tilt, of spinner 20. As a comparison, Figure 7 shows the cross-scan deflection for the 820 nm wavelength at a-1.5 minute spinner tilt (plots H, I, J respectively). (~i = 45 45"3d = ~4 55) As shown, the cross-scan errors are smaller in Figure 7 due to the angle of 10 incidence bein~ nearer the invariant condition of 45. While the gratings could remain in the same position and the reconstruction path change position, the easiest set-up technique is to rotate the parallel gratings while monitoringthe output scan line and fix the gratings into the optimum cross-scan compensation position.
Various changes and modifications may be made to the above described compensation system without departing from the principles of the present invention. For example, it may be desirable to have the spinner and compensation member have their grating surface face each other. This orientation would help to keep the grating surfaces clean. Also, although 20 transmission type gratings were used in the examples, reflectiv~type gratingscan also be used with different orientation of light source and parallel spacing.
WAVE~ENGTH SHIFT CORRECTION
BACKGROUND AND PRIOR A~T STATEMENT
The present invention relates to an optical spot scanning system and more particularly to an improved holo-graphic scanning system which includes a compensation element to correct for cross-scan errors in the scan line due to wavelength shifts occurring in the light source.
Holographic scanners which utilize a rotating disc having a plurality of holographically formed lenses or gratings are known in the art. Representative disclos-ures are provided in the Prior Art List filed with the --present application. These prior art spinners are subject to certain prcblems resulting from their geometry. These problems, briefly stated, are scan line "bow", in the image plane, spinner wobble and spinner "wedge" both resulting in colinear multiple scan lines, and spinner decentration causing output scan distortion. These problems are more thoroughly analyzed in U.S. Patent No. 4,289~371, issued 20 September 15, 1981 and assigned to the same assignee as the present invention. In this patent the enumerated problems are compensated for by utilizing, as the reconstruction element, a spinner having on its surface a plurality of holographically formed plane linear diffraction gratings.
By strict mathematical methods, it was demonstrated that certain relationships existed between the wavelength of the reconstruction light source, the grating period and the angles of incidence and diffraction, whereby most of the inherent spinner problems were either corrected for or minimized. The patent also addressed another problem, wavelength shiEt, which originates with -the recons-truction light source. This shift, or chanye in -the source wave-length results in corresponding changes in -the ou-tpu-t dif-fraction angle and hence, an undesirable deflec-tion of the output scan line. The plane linear diffraction grating spinner is effective only when a monochromatic stable wave--la-length light source was utilized. Thus, a stable source He-Ne laser was used in the exemplary example provided in said patent.
It is therefore desirable to utilize a plane grating holographic spinner such as that described in the aforemen-tioned patent but which is further improved by eliminati.on of the effects caused by wavelength shifts in the coherent light source. Such a technique is becoming of considerable . -~, importance because of the increasing use of laser diodes as the light source in scanning systems~ These diodes can experience wavelength shifts of up to 3 nm or more due to junction heating over its output power range.
The present invantion is therefore directed to an optical scanning 5 system including a spinner having formed thereon at least one plane linear diffraction grating having a constant grating period d, a stationary wavelength compensation diffraction grating having properties identical to said grating formed on said spinner surface, said stationary grating placed in a plane parallel and in optical alignment with said spinner grating, a collimated 10 reconstruction light source of wavelength ~, r which provides a beam of lightdirected at an angle of incidence ~i onto said compensation grating, said grating diffracting said beam at a diffraction angle of ~3d~ said incidence angle i3i ~ ~d ~ 45~ and the ratio of ~ r to grating spacing d having a value between 1 and 1.618, whereby the light beam diffracted by the compensation 15 grating is incident on the spirner grating at an angle ~i and is diffracted out of said grating at an angle ~d i Figure l is a sch~matic diagram of a prior art optical scanning system.
Figure 2 is a graph showing diode laser wavelength shift as a 20 func~ion of pulse width time resulting in laser heating conditions.
Figure 3 is a graph plotting cross-scan defle~tion over one half of a scanned line length as a function of wavelength shift.
Figure 4 is the scanning system of Figure 1 modified to compensate for the effects of wavelength shifts of the reconstruction light source.
Figure 5 i9 a grapil plotting cross-scan deflection over one half of a scanned line length as a function of wavelength for the system of Figure 4.
Figure 6 is a graph plotting cross-scan deflection over one half of a s~anned line length as a func~ion of a nominal wavelength of 830 nm and over -1.5 minute spiMer tilt position.
Figure '7 is a graph plotting cross-scan deflection over one half of a scanned line as a ~unction Or a nominal wavelength of 820 nm and over- h5 minute spinner belt tilt position.
DESCRIPTION
Figure 1 schematically illustrates a scanning embodiment described in the afo~ementioned U.S. Patent modified to show the effects of a slightly polychromatic reconstruction light source. In the figure, a light source 16 generates a reconstruction plane wavefront 18 which is incident on plane linear diffraction grating spinner 20 at an angle ~i. If source 16 is a monochromatic source, such as a He-~e laser, the wavefront is diffracted at a diffraction angle ad which is wavelength dependent. Doublet lens 22 focuses a linear scan 24 at image plane 25 via pl~ne mirror 23. This linear scan is nearlybow free, and is reasonably insensitive to spinner wobble, decentration and wedge errors, such qualities being attributable to the characteristics of the spinner 20 and the system geometry, as described in the afore~entioned patent.
- If, however, a diode laser is substituted for the H~Ne source 16, a smal:L shift in output wavelength occurs with drive current. Since the diffracted rays at spinner 20 are wavelength sensitive, diffracted rays 21 deviate by some small angle along the dotted path incurring a small deflection of the beam in the cross-scan direction at image plane 25.
The reasons for and extent of the wavelength shift in the diode laser source is made clearer by reference to Figures 2 and 3. Figure 2 is a graph showing test measurements made on a Hitachi Series 1600 diode laser.
The central laser wavelength shift of the laser is plotted against pulse width time for short pulses of lO0 Hz duty cycle. It can be seen that the heating associated with the pulses has the effect of shifting the peak to longer (lower energy) wavelengths. A shift of ~ O.S nm occurs over the time duration shown which would be representative of a ROS scanning at 300 spi with an image plane velocity of 2't/sec.
Figure 3 shows the effects of a wavelength shift of l nm along one half of the length of a scanned line in the image plane for the system of Figurelo Source 16 is the Hitachi Series 1600 laser having a nominal wavelength j~
of 820 nm, ~3i is 45.45 and ~d is 4as.55. Spinner 20 is formed according to the principles of the aforementioned patent with a spacing period d =
0.5798454,y m. (The ratio of ~ to d must have a value between 1 and 1.618).
Focusing lens 22 is a linearized flat field air spaced doublet with a 26.8" e~itpupil to image plane distance (throw distance). In Figure 3, two scanned spot trajectories; cross-scan deflection (Y) vs scan deflection (X) (center to edge) are plotted for values of ,~ of 820 nm (scan A) and at 821 nm (scan B) representing a wavelength shift of l nm. Spinner 20 is rotated at a speed of 3000 rpm. This l nm shift has caused the output diffractioll angle to change by an angle B of 0.105 incurring a 0.049 inch deflection of the beam in the cross-scan deflection (Y). Even a 0.5 nm wavelength shift would produce approxi-mately a 0.024 inch deElection. Both of these deflections represent, for most spot scanning systems, an unacceptable level of scan line perturbations at the image plane.
~igure 4 shows the system of Figure 1 modified according to the invention by the introduction of a plane linear grating 30 into the path of the plane wavefront 18. (~rating 30 is a wavelength compensating device which has properties identical to the gratings formed on the surface of spinner 20. In other words, if spinner 20 facets are holographically formed, the grating is 10 holographically formed using the same photorecording system and having the same period as a spinner 20 grating facet and consequently has the same high' diffraetion efficiency as the spinner. C~rating 30 is placed in the tangential plane parallel to the plane of spinner 20. The system of Figure 4 operates in the following manner. Assuming source 16 is operating at its nominal 15 wavelength of 820 nm, reconstruction beam 18 is directed at the incident angle i onto grating 30 and is diffracted out at diffraction angle (3d (solid line path), the angles measured with respect to normal of the plane of the grating.
Since grating 30 and spinner 20a are parallel, by symmetry beam 18 is incident on the center of facet 20a at angle q)i = (~d- Facet 20a diffracts the beam at a20 diffraction angle t¦)d which is colinear (parallel) with the incident path of beam 18 at grating 30, i.e. ~d = i This result is confirmed by solving for (~)d in the following grating equation (for grating 20a) sin ~Pi+ sin (~d = J~/d.
For the Figure 4 embodiment, typical grating 30 to spinner 20 25 distance would be 1/2 to 1 inch and spinner 30 to lens 22 distance '~ 1 inch.With the above geometry in place, it can be appreciated that a reconstruction beam, even if diffracted into a different path because of a small wavelength shift, will nonetheless be diffracted from the spinner in a path colinear with its incidence on the compensation grating but shifted by a 30 small lateral distance. That this results in correction of the cross-scan errors at the image plane can be demonstrated by tracing the scanning path of the reconstruction beam with a small (1 - 2 nm) shift of the wavelength of source 16. When such a shift occurs, the beam is still incident on grating 30 at angle i but is diffracted along a slightly different path, represented by the dotted 35 line, at an angle 'd. ('I'he path is chosen at an exag~erated deviation angle for illustrative purposes). The beam is incident on facet 20a at angle /t)'i and is 7~
diffracted out at an angle of ~'d and as shown above, (~3'd = ~i. The beam is, however, shifted by a lateral distance s from the position of the first beam.
This small lateral displacement is of no consequence since lens 22 focuses all image rays entering in parallel to the same point on plane 25. Hence, the 5 scanned line will be corrected for the cross-scan errors.
From the above, it has been demonstrated that even if the laser reconstruction light source experiences wavelength shifts during its operating cycle, these shifts wiU be corrected for because of the unique geometry and positioning of the grating pairs.
The cross-scan errors at the scanning plane are completely elimi nated only when the beam is at the center position of grating 20a. As the spinner 20 rotates at same angle ~3r some cross-scan error does occur. For the compensated systern of Figure 4, the scan line trajectories for four different source wavelengths are plotted as shown by the graph of Figure 5. For the 15 4.511 scan represented, plots A, B, C and D represent source wavelengths of 819 nm, 820 nm, 821 nm and 822 nm, respectively. As shown, the scan line is deflected only 0.000631l/nm at the edge of the scan. This compares very favorably with the 0.0501l/nm deflection in the uncompensated case shown in Figure 3.
lNhile the above compensation technique almost completely com-pensates for cross-scan deflection errors, there is no concomitant compensa-tion for a change in scan line length due to wavelength shift. This deflection is quite small; for the above example the edge of scan of 4.511 is altered by .03581l for a 1 nm wavelength shift and .0029 for a 0.5 nm shift. Deflection of 25 that order should be acceptable for systems scanning up to 8.51l. The deflection does appear to be linearly related to scan length and some correction can be achieved by using a high angular efficiency lens 22. A
suitable focusing lens for this purpose would be the type described in U.S.
Patent 4,108,532, constructed with due regard for the laser diode heating 30 cycles and the consequent wavelength shifts within and between scan lines.
The above examples utilizing diode lasers as the reconstruction light source considered only relatively small wavelength shifts of - 2nm from the central emission wavelength. ~s a practical matter"lowever, due to manufacturing tolerance, actual cliode lasers, even from the same batch, may 35 have center emission wavelengths differing by -15 nm. This may necessitate some deviation from the preferred invariant condition of incidence angle ~i ~
-G-diffraction angle ~d~ 45- For example, Figure 6 shows the cross-scan deflection for the Figure 4 arrangement but with a wavelength of 830 nm and with the grating pair rotated clockwise to make the incident angle ~3i = 43 95 and diffraction angle ~d = 47 50- Plot E represents one half of the nominal 5 scanned line with no spinner tilt while plots F and G represent the lines resulting from a- 1.5 minute wobble, or tilt, of spinner 20. As a comparison, Figure 7 shows the cross-scan deflection for the 820 nm wavelength at a-1.5 minute spinner tilt (plots H, I, J respectively). (~i = 45 45"3d = ~4 55) As shown, the cross-scan errors are smaller in Figure 7 due to the angle of 10 incidence bein~ nearer the invariant condition of 45. While the gratings could remain in the same position and the reconstruction path change position, the easiest set-up technique is to rotate the parallel gratings while monitoringthe output scan line and fix the gratings into the optimum cross-scan compensation position.
Various changes and modifications may be made to the above described compensation system without departing from the principles of the present invention. For example, it may be desirable to have the spinner and compensation member have their grating surface face each other. This orientation would help to keep the grating surfaces clean. Also, although 20 transmission type gratings were used in the examples, reflectiv~type gratingscan also be used with different orientation of light source and parallel spacing.
Claims (8)
1. An optical scanning system including a spinner having formed thereon at least one plane linear diffrac-tion grating having a constant grating period d, a stationary wavelength compensation diffraction grating having properties identical to said grating formed on said spinner surface, said stationary grating placed in a plane parallel and in optical alignment with saidspinner grating, a collimated reconstruction light source of wavelength ?r which provides a beam of light directed at an angle of incidence .THETA.i onto said compensation grating, said grating diffracting said beam at a diffraction angle of .THETA.d.
said incidence angle .THETA.i ? .THETA.d ? 45°, and the ratio of ?r to spacing d having a value between 1 and 1.618, whereby the light beam diffracted by the compensation grating is incident on the spinner grating at an angle ?i and is diffracted out of said grating at an angle ?d ? .THETA.i.
said incidence angle .THETA.i ? .THETA.d ? 45°, and the ratio of ?r to spacing d having a value between 1 and 1.618, whereby the light beam diffracted by the compensation grating is incident on the spinner grating at an angle ?i and is diffracted out of said grating at an angle ?d ? .THETA.i.
2. The optical scanning system of claim 1 further including means for rotating said spinner so that the spinner grating rotates through some rotation angle and diffracts a portion of the incident light at diffractionangle ?d, and optical means to focus said diffracted beams as a linear scan line on an image plane.
3. The optical scanning system of claims 1 or 2 wherein the light source is a diode laser.
4. The optical scanning system of claim 2 wherein the optical means is a linearized flat field air spaced doublet.
5. The optical scanning system of claim 1 wherein said spinner and compensation gratings are of the transmission type.
6. The optical scanning system of claim 1 wherein said spinner and compensation gratings are of the reflective type.
7. The optical scanning system of claim 5 wherein said gratings are formed on the respective surfaces of said spinner and compensation gratings and said surfaces are aligned in said parallel planes so as to face inward towards each other.
8. The optical scanning system of claims 1 or 2 wherein the light source is a diode laser and wherein said diode laser is subject to wavelength shifts of up to ? 2 nm resulting in a reconstruction beam deviation which is compensated for by the diffraction properties of said compensation grating in conjunction with the spinner grating.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US252,508 | 1981-04-08 | ||
| US06/252,508 US4428643A (en) | 1981-04-08 | 1981-04-08 | Optical scanning system with wavelength shift correction |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1181273A true CA1181273A (en) | 1985-01-22 |
Family
ID=22956306
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000398072A Expired CA1181273A (en) | 1981-04-08 | 1982-03-11 | Optical scanning system with wavelength shift correction |
Country Status (5)
| Country | Link |
|---|---|
| US (1) | US4428643A (en) |
| EP (1) | EP0062545B1 (en) |
| JP (1) | JPS57181523A (en) |
| CA (1) | CA1181273A (en) |
| DE (1) | DE3269929D1 (en) |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS5967514A (en) * | 1982-10-08 | 1984-04-17 | Minolta Camera Co Ltd | Laser beam scanner |
| US4632499A (en) * | 1982-12-10 | 1986-12-30 | Fuji Photo Film Co., Ltd. | Light beam scanning apparatus |
| JP2532049B2 (en) * | 1983-06-30 | 1996-09-11 | 富士通株式会社 | Optical beam scanning device |
| US4508421A (en) * | 1983-07-27 | 1985-04-02 | Xerox Corporation | Holographic scanning system utilizing a scan linearization lens |
| US4671603A (en) * | 1983-11-17 | 1987-06-09 | Pilkington P.E. Limited | Optical filters and multiplexing-demultiplexing devices using the same |
| US4669811A (en) * | 1983-11-17 | 1987-06-02 | Pilkington P.E. Limited | Optical filtering apparatus |
| US4610500A (en) * | 1984-08-16 | 1986-09-09 | Holotek Ltd. | Hologon laser scanner apparatus |
| JPS6179286A (en) * | 1984-09-24 | 1986-04-22 | ゼロツクス コーポレーシヨン | Laser diode and mode hopping prevention therefor |
| US4699446A (en) * | 1985-03-18 | 1987-10-13 | Xerox Corporation | Dynamic power control for an external cavity stabilized laser diode in a holographic scanner |
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Family Cites Families (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3549239A (en) * | 1968-11-19 | 1970-12-22 | United Aircraft Corp | Optical signal processor |
| US4108532A (en) * | 1976-06-23 | 1978-08-22 | Canon Kabushiki Kaisha | Light beam scanning device |
| US4289371A (en) * | 1979-05-31 | 1981-09-15 | Xerox Corporation | Optical scanner using plane linear diffraction gratings on a rotating spinner |
-
1981
- 1981-04-08 US US06/252,508 patent/US4428643A/en not_active Expired - Lifetime
-
1982
- 1982-03-11 CA CA000398072A patent/CA1181273A/en not_active Expired
- 1982-04-01 JP JP57055275A patent/JPS57181523A/en active Granted
- 1982-04-08 EP EP82301886A patent/EP0062545B1/en not_active Expired
- 1982-04-08 DE DE8282301886T patent/DE3269929D1/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| EP0062545B1 (en) | 1986-03-19 |
| US4428643A (en) | 1984-01-31 |
| DE3269929D1 (en) | 1986-04-24 |
| EP0062545A1 (en) | 1982-10-13 |
| JPH0247726B2 (en) | 1990-10-22 |
| JPS57181523A (en) | 1982-11-09 |
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