Optical disk apparatus for selectively recording and reproducing signals having different bit rates

An optical apparatus digitizes a first signal, reproduce or records and reproduce the digital information compressed a band up to a specified bit rate A1 at a specified rotating speed K or specified linear velocity V, digitizes a second signal, reproduces or records and reproduces the digital information compressed in a band up to a specified bit rate A2 at a rotating speed of about K.times.A2/A1, or a linear velocity of about V.times.A2/A1, and thereby reproduces or records and reproduces information of plural signals, or reproduce or records and reproduces information of plural compression rates using only one apparatus. It also digitizes a first signal, reproduces or records and reproduces the digital information compressed in a band up to a specified bit rate A1 in n optical channels, digitizes a second piece of information, reproduces or records and reproduces the digital information compressed in a band up to a specified bit rate A2 in about n.times.A2/A1 optical channels, and thereby reproduces records and reproduces information of plural signals, or reproduces or records and reproduces information of plural compression rates using only one apparatus without notably varying the rotating speed or linear velocity. It further enters the light emitted from a semiconductor laser into a nonlinear optical device (SHG), and reproduces the information on a disk surface or records and reproduces the information on a disk surface using the secondary harmonics delivered from the nonlinear optical device.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to an optical disk apparatus capable of 
reproducing or both recording and reproducing of signals which are greatly 
different in the frequency band from each other, such as an NTSC signal 
and a high definition television signal. 
2. Description of the Prior Art 
Optical disk apparatuses capable of reproducing or both recording and 
reproducing one of an NTSC signal and a high definition television signal 
have been distributed and reported hitherto. However, all of them are of 
the analog recording type and are optimally designed for individual signal 
bands, so that they are not compatible with each other. In the case of 
digital recording, the quantity the information is by far greater than 
that in the analog recording. Thus, it was not realistic to employ digital 
recording in the aspects of reducing the recording and reproducing time 
and extending the transfer rate. In other words, there was no optical disk 
apparatus capable of reproducing or both recording and reproducing both 
the NTSC signal and the high definition television signal. Even if the 
recording signals are of the same type, there was no optical disk 
apparatus capable of reproducing or both recording and reproducing in both 
a low-definition, long-playing mode at a high compression rate and a 
high-definition, short-playing mode at a low compression rate. 
SUMMARY OF THE INVENTION 
It is hence a primary object of the invention to provide a high recording 
density optical disk apparatus capable of reproducing or both recording 
and reproducing both a narrow band signal such as an NTSC signal and a 
wide band signal such as a high definition television signal, and capable 
of reproducing a signal in plural modes including a low-definition, 
long-playing mode at a high compression rate and a high-definition, 
short-playing mode at a low compression rate. Another object of the 
invention is to extremely raise the recording density by inserting a 
nonlinear optical device (SHG) into an optical system for reproducing or 
both recording and reproducing a signal by using secondary harmonics. 
To achieve the above objects, in one aspect of the present invention, an 
optical disk apparatus is configured to digitize a first signal, and 
reproduce or both record and reproduce a digital data compressed in a band 
down to a specified bit rate A1 at a specified disk rotating speed K or a 
specified linear velocity V, and, on the other hand, digitize a second 
signal, and reproduce or both record and reproduce a digital data 
compressed in a band down to a specified bit rate A2 at a disk rotating 
speed of substantially K.times.A2/A1 or a linear velocity of substantially 
V.times.A2/A1. With this configuration, it is possible to reproduce or 
both record and reproduce any one of a plurality of signals which are 
different from each other in frequency band or compression rate. 
In another aspect of the present invention, an optical disk apparatus is 
configured to digitize a first signal, and reproduce or both record and 
reproduce a digital data compressed in a band down to a specified bit rate 
A1 in n optical channels, and, on the other hand, digitize a second 
signal, and reproduce or both record and reproduce a digital data 
compressed in a band down to a specified bit rate A2 in substantially 
n.times.A2/A1 optical channels. With this configuration, it is possible to 
record and/or reproduce any one of a plurality of signals which are 
different from each other in frequency band or compression rate without 
notably varying the disk rotating speed or linear velocity. 
In still another aspect of the present invention, an optical disk apparatus 
may be configured to enter a light emitted from a semiconductor laser into 
a nonlinear optical device (SHG), and reproduce data recorded on a disk 
surface or both record data onto and reproduce data from the disk surface 
by secondary harmonics outputted from the nonlinear optical device. With 
this configuration, it is possible to greatly increase the recording 
density.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 1 is an embodiment of a reproducing system of an optical disk 
apparatus in accordance with the present. Information recorded on an 
optical disk 1 is read by optical systems 2 and 3 including an optical 
head, and is sent into a digital demodulator 4. In the digital demodulator 
4, the information is demodulated into a digital signal, and error 
correction or other processing is done at the same time. In a mode judging 
circuit 6, the type and mode of the signal of the reproduced information 
are judged from the information from the digital demodulator 4. 
The output of the digital demodulator 4 is decoded by a band-compressing 
decoder 9 on the basis of the information from the mode judging circuit 6. 
The signal decoded and expanded in band is digital-to-analog (D/A) 
converted in an output circuit 10, and delivered to an output terminal 11. 
A motor driving circuit 7 for controlling a motor 8 controls the motor 8 
depending on the information from the digital demodulator 4 and mode 
judging circuit 6 so that the disk rotating speed or the linear velocity 
of the optical head relative to the disk becomes a specified value. 
A reproduced signal processing circuit 22 is composed of the digital 
demodulator 4, band-compressing decoder 9, and output circuit 10. 
If, meanwhile, the transfer rate is low, only one channel optical system 2 
may be used, and the optical system 3 may be omitted. 
Here, the operation of the mode judging circuit 6 is to control the motor 8 
so that the linear velocity of the optical head relative to the disk 
becomes a specified value. Or it is to operate only a required channel of 
the optical system, which may be realized, for example, by selecting only 
the necessary information out of the input information in the digital 
demodulator 4. 
In the case of a reproducing only machine, it is only necessary to have the 
reproducing system described above, but in the case of a recording and 
reproducing machine, a recording system is also needed. Referring then to 
FIG. 2, an embodiment of a recording system of an optical disk apparatus 
is explained. The common blocks as in FIG. 1 are identified by the same 
reference numbers. 
A signal entered from an input terminal 15 is analog-to-digital (A/D) 
converted in an input circuit 16, and is encoded into a specified bit rate 
signal by a band-compressing encoder 17. This result is fed into a digital 
modulator 19 to be subjected to processing such as the addition of an 
error correction code, and is digitally modulated. Laser beams generated 
in optical systems 20, an 21 are modulated by the digital modulated 
signal, so that digital information is recorded on an optical disk 1. A 
motor 8 is controlled by a motor driving circuit 7 so as to achieve a 
specified rotating speed of the disk or a specified linear velocity of the 
optical head relative to the disk. A recorded signal processing circuit 23 
is composed of the input circuit 16, band-compressing encoder 17, and 
digital modulator 19. 
All of the motor driving circuit 7, digital modulator 19, and encoder 17 
are controlled by the information from a mode specifying circuit 18 so as 
to operate as specified. If it is enough operate with only one channel of 
the optical system in a low transfer rate application, the optical system 
21 is not needed. 
The mode specifying circuit 18 is to specify the mode by means of, for 
example, a switch operated by an operator. 
As the mode judging method in the mode judging circuit 6 in reproduction, 
various methods may be considered including a method of, as shown in FIG. 
3, recording a coded mode signal on a reference position of the disk, for 
example, a position on each track on a specific line in the radial 
direction, and judging the mode by reproducing the mode signal from the 
reference position. 
The optical systems 2, 3, 20, and 21 are shown in detail in FIG. 4. 
The optical system comprises a semiconductor laser 30, coupling lenses 31 
and 32, a nonlinear optical device (SHG) 32, a long wavelength cut filter 
34, a beam splitter 35, an objective lens 36, a detector 38, and a laser 
driving circuit 37. In recording, the modulation signal is fed into the 
laser driving circuit 37. In reproducing, a reproduced signal is delivered 
from the detector 38. 
By inserting the SHG 32, the laser wavelength is divided in half so that 
the recording density on the disk can be increased by about four times. As 
the SHG 32, the waveguide type is desired when recording and reproducing, 
but when reproducing only, it may be either the waveguide type or the bulk 
type. 
FIGS. 5(A) and 5(B) show; an example of reproducing or recording and 
reproducing plural signals having different bands at plural compression 
rates, by using the thus composed optical disk. 
This is to show the relationship of the linear velocity, number of optical 
system channels and reproduction time in CLV, and the relationship of the 
disk rotating speed, number of optical system channels and reproduction 
time in CAV, when the narrow band, NTSC signal is compressed in band to 5 
Mbps and 10 Mbps, and when the wide band, high definition television 
signal is compressed in band to 30 Mbps and 60 Mbps. 
In FIG. 5(A), the linear velocity is constant, and in FIG. 5(B), the disk 
rotating speed is constant. If, as shown, in FIG. 5(A), the linear 
velocity with an NTSC signal of 5 Mbps is V and the reproduction time is 
12T.sub.1, then the linear velocity of an HD signal of 30 Mbps is 3 V in a 
two-channel optical system, or 6 V in a one-channel optical system, and 
the reproduction time is respectively 2T.sub.1. The same holds true in 
FIG. 5(B) where the disk rotating speed is constant. 
In the same signals, the greater the bit rate after band compression, the 
shorter becomes the reproduction time and hence a picture of high quality 
is reproduced. 
In the foregoing embodiments, the reproducing system and recording system 
are explained separately, but the invention is similarly applied either in 
the optical disk apparatus for recording and reproducing using only one 
unit or in the optical disk apparatus used for reproducing only. 
Incidentally, the narrow band signals include the NTSC signal, signal, 
SECM signal and so on, and the wide band signals include the HD signal, 
HDMAC signal, MUSE signal and the like. 
Input and output signals may include, among others, composite signals, Y, 
PrPb, R, G, B, YC signals, audio signals, and control signals. 
The mode judging circuit 6 may be designed to set by the operator by using 
a switch. 
The optical system is not limited to two channels, but the number of 
channels may be increased as required. 
The invention is valid not only in the CAV system and CLV system, but also 
in the MCAV system, MCLV system, and other disk driving systems.