Coherent light generators – Particular beam control device – Optical output stabilization
Reexamination Certificate
2001-02-26
2003-07-08
Ip, Paul (Department: 2828)
Coherent light generators
Particular beam control device
Optical output stabilization
C372S029010, C372S029011
Reexamination Certificate
active
06590912
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a semiconductor laser driving apparatus, a semiconductor laser driving method, and an image-forming apparatus, particularly to a semiconductor laser driving apparatus, semiconductor laser driving method, and image-forming apparatus capable of preventing mode-hopping noise from being generated by a semiconductor laser.
2. Related Art
Optical scanning for recording various pieces of information including image information by scanning a recording medium with an optical beam or for reading various pieces of information from a recording medium uses a laser beam emitted from a semiconductor laser as an optical beam for scanning.
FIG. 14
shows functional blocks of a conventional semiconductor laser driving apparatus used to perform optical scanning with a laser beam emitted from a semiconductor laser. As shown in
FIG. 14
, the semiconductor laser driving apparatus is provided with semiconductor lasers of three types, for emitting laser beams having wavelengths different from each other, and the laser beam emitted from each semiconductor laser is modulated by a modulating section in accordance with image data.
Moreover, in this semiconductor laser driving apparatus, the light amount of a laser beam emitted from each semiconductor laser is detected by a light amount detecting section and a semiconductor laser driving section is controlled for APC (Auto Power Control) by a light amount control section so that the detected light amount becomes equal to a predetermined target light amount.
Furthermore, in this semiconductor laser driving apparatus, similarly to the aforementioned APC, the temperature at or near a light-emitting section of each semiconductor laser (hereafter referred to as semiconductor laser temperature) is detected by a temperature detecting section, and a temperature adjusting section is controlled by a temperature control section for ATC (Auto Temperature Control) so that the detected temperature becomes equal to a previously stored setting temperature (control temperature).
When performing optical scanning by a laser beam emitted from a semiconductor laser, it is generally required that a maximum fluctuation of the light amount of the laser beam is kept at approximately 1% or less when the optical scanning administers, for example, continuous gradation image information. That is, if the maximum fluctuation exceeds approximately 1%, visible irreguralities occur in a recorded image or in an image formed from image information read by scanning.
However, mode-hopping noise may be generated in the semiconductor laser, depending on driving conditions. That is, different modes (laser wavelengths) compete with each other in the semiconductor laser under certain driving conditions, mode-hopping from one to another of the different modes, and from the other to the one, is reciprocatingly repeated, and the light amount of the laser beam fluctuates due to the repeted mode-hopping. That is, mode-hopping noise is generated.
The fluctuation of a light amount due to the mode-hopping noise reaches several percent of total light amount. Therefore, when mode-hopping noise is generated during optical scanning for administering continuous gradation image information, extreme irregularities occur in the recorded image or the image formed from read image information. Moreover, mode-hopping noise fluctuates not only light amounts but also wavelength, which may affect images.
Therefore, to drive a semiconductor laser for optical scanning for handling continuous gradation image information, it is necessary to drive the semiconductor laser such that mode-hopping noise is not generated. By preventing mode-hopping noise, neither light amount nor wavelength fluctuate and a preferable image can be obtained.
Techniques for preventing mode-hopping noise from being generated are disclosed in Japanese Patent Application Laid-Open (JP-A) Nos. 61-260691, 61-260693, 61-264773, and 61-264774.
Each of the techniques disclosed in JP-A Nos. 61-260691 and 61-260693 stabilizes the wavelength of a laser beam to a single longitudinal mode by superimposing on a driving signal to be applied to a semiconductor laser high-frequency pulses having a frequency higher than that of the driving signal and adjusting at least one of parameters such as frequency, duty ratio, and amplitude of the high-frequency pulses, such as frequency, duty ratio, and amplitude. Thus, it is possible to prevent mode-hopping noise from being generated.
Further, a technique disclosed in JP-A No. 61-264773 uses a detector for detecting mode-hopping noise to change either or both of a setting light amount and a setting temperature when mode-hopping noise is detected by the detector.
Furthermore, a technique disclosed in JP-A No. 61-264774 measures and stores a temperature region in which mode-hopping noise is generated in advance, and controls a combination of light amount and temperature of a semiconductor laser such that the combination does not move to that temperature region. Thus, it is possible to prevent mode-hopping noise in advance.
However, in the case of the techniques disclosed in the above JP-A Nos. 61-260691 and 61-260693, it is necessary to superimpose high-frequency pulses on the semiconductor laser driving signal as described above. Therefore, there is a problem that cannot be prevented in that the apparatus is increased in size because hardware and control are complicated, and cost increases. Moreover, these techniques have a problem in that image quality is deteriorated because superimposed high-frequency pulses may function as noise when forming an image.
Moreover, the technique disclosed in JP-A No. 61-264773 has a problem in that it is impossible to completely prevent mode-hopping noise from being generated because generation of mode-hopping noise is detected by a detector and thereafter one or both of the setting light amount and the setting temperature is changed and thus, mode-hopping noise is continuously generated until the change is completed. Moreover, this technique requires a detector for detecting mode-hopping noise and thus, there is a problem in that cost increases.
Moreover, the technique disclosed in JP-A No. 61-264774 has a problem in that it is impossible to absorb shifts to temperatures at which mode-hopping noise is generated, due to various conditions of actual optical scanning (such as laser-beam emission cycle and emission start timing of the semiconductor laser) because temperatures at which mode-hopping noise is generated are not measured in conditions of actual optical scanning, and it is impossible to completely prevent the generation of mode-hopping noise. Moreover, because the technique requires a special apparatus for measuring temperatures at which mode-hopping noise is generated, there is a problem in that cost increases.
SUMMARY OF THE INVENTION
The present invention is provided to solve the above problems and an object of the present invention is to provide a semiconductor laser driving apparatus and a semiconductor laser driving method which can be made compact and fabricated at low cost and which make it possible to assuredly prevent the influence of mode-hopping noise and, moreover, to provide an image-forming apparatus capable of forming a high-quality image.
To achieve the above object, a first aspect of the present invention is a semiconductor laser driving apparatus that drives a semiconductor laser that emits laser light for optical scanning, the apparatus including a light amount detecting section which detects a light amount of a laser light emitted from the semiconductor laser,
a temperature detecting section which detects a laser section temperature, which is one of a temperature of a light-emitting section of the semiconductor laser and a temperature of a vicinity of the semiconductor laser, a temperature adjusting section which adjusts the laser section temperature, a light amount control section which, while the semiconductor laser is driven in a manner the same as for actual optical scanni
Ip Paul
Nguyen Tuan
LandOfFree
Semiconductor laser driving apparatus and method and... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Semiconductor laser driving apparatus and method and..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Semiconductor laser driving apparatus and method and... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3029407