## Abstract

A method is described which allows an increase of information density on optically read disks by a reduction of the track spacing by a factor of 2. The cross talk between neighboring tracks is maintained at an acceptable level by modulating from track to track the depth of the relief pattern on the disk. By an appropriate readout method (a compromise between differential and integral detection), the signals from neighboring tracks are suppressed. The layout of such a disk and the possible geometries of the relief pattern are indicated.

© 1983 Optical Society of America

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### Equations (16)

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(1)
$$\begin{array}{l}{A}_{0}=1+\frac{w}{q}[\text{exp}(i\varphi )-1],\\ {A}_{n}=\frac{w}{q}[\text{exp}(i\varphi )-1]\hspace{0.17em}\text{sinc}\hspace{0.17em}\left(\frac{\pi nw}{q}\right)\hspace{0.17em}\text{exp}(2\pi in\nu t),\end{array}$$
(2)
$$\text{tan}{\psi}_{0}=-1/\left[\text{tan}\hspace{0.17em}\left(\frac{\varphi}{2}\right)\left(1-\frac{2w}{q}\right)\right].$$
(3)
$$A(x,y,t)=\sum _{n}{A}_{n}(x,y,t),$$
(4)
$$I(x,y,t)={\left|\sum _{n}{A}_{n}(x,y,t)\right|}^{2}.$$
(5)
$$\begin{array}{l}{S}_{1}(t)={\iint}_{{D}_{1}}I(x,y,t)dxdy,\\ {S}_{2}(t)={\iint}_{{D}_{2}}I(x,y,t)dxdy.\end{array}$$
(6)
$$\begin{array}{l}{A}_{0}=\mid {A}_{0}\mid ,\\ {A}_{+1}=\mid {A}_{1}\mid \hspace{0.17em}\text{exp}[i({\psi}_{0}+2\pi \nu t)],\\ {A}_{-1}=\mid {A}_{1}\mid \hspace{0.17em}\text{exp}[i({\psi}_{0}-2\pi \nu t)],\end{array}$$
(7)
$$\begin{array}{l}{S}_{1}(t)={b}_{1}\mid {A}_{0}{\mid}^{2}+({b}_{1}+{b}_{2})\mid {A}_{1}{\mid}^{2}+2{b}_{1}\mid {A}_{0}\mid \mid {A}_{1}\mid \text{cos}(2\pi \nu t-{\psi}_{0})+2{b}_{2}\mid {A}_{0}\mid \mid {A}_{1}\mid \text{cos}(2\pi \nu t+{\psi}_{0})+2{b}_{2}\mid {A}_{1}{\mid}^{2}\text{cos}(4\pi \nu t),\\ {S}_{2}(t)={b}_{1}\mid {A}_{0}{\mid}^{2}+({b}_{1}+{b}_{2})\mid {A}_{1}{\mid}^{2}+2{b}_{1}\mid {A}_{0}\mid \mid {A}_{1}\mid \text{cos}(2\pi \nu t+{\psi}_{0})+2{b}_{2}\mid {A}_{0}\mid \mid {A}_{1}\mid \text{cos}(2\pi \nu t-{\psi}_{0})+2{b}_{2}\mid {A}_{1}{\mid}^{2}\text{cos}(4\pi \nu t),\end{array}$$
(8)
$$\begin{array}{l}{S}_{1}^{\prime}(t)\propto 2\mid {A}_{0}\mid \mid {A}_{1}\mid \left[({b}_{1}-{b}_{2})\hspace{0.17em}\text{cos}(2\pi \nu t-{\psi}_{0})+2{b}_{2}\hspace{0.17em}\text{cos}{\psi}_{0}\hspace{0.17em}\text{cos}2\pi \nu t+{b}_{2}\frac{\mid {A}_{0}\mid}{\mid {A}_{1}\mid}\text{cos}(4\pi \nu t)\right],\\ {S}_{2}^{\prime}(t)\propto 2\mid {A}_{0}\mid \mid {A}_{1}\mid \left[({b}_{1}-{b}_{2})\hspace{0.17em}\text{cos}(2\pi \nu t+{\psi}_{0})+2{b}_{2}\hspace{0.17em}\text{cos}{\psi}_{0}\hspace{0.17em}\text{cos}2\pi \nu t+{b}_{2}\frac{\mid {A}_{0}\mid}{\mid {A}_{1}\mid}\text{cos}(4\pi \nu t)\right].\end{array}$$
(9)
$$\begin{array}{l}{S}_{1}^{*}(t)\propto \text{cos}(2\pi \nu t+\delta -{\psi}_{0}),\\ {S}_{2}^{*}(t)\propto \text{cos}(2\pi \nu t-\delta +{\psi}_{0}),\end{array}$$
(10)
$$S(t)\propto \text{cos}({\psi}_{0}-\delta )\hspace{0.17em}\text{cos}(\pi \nu t).$$
(11)
$$\begin{array}{l}{S}_{{\nu}_{1}}(t)\propto \text{cos}({\psi}_{1}-\delta )\hspace{0.17em}\text{cos}(2\pi {\nu}_{1}t),\\ {S}_{{\nu}_{2}}(t)\propto \text{cos}({\psi}_{2}-\delta )\hspace{0.17em}\text{cos}(2\pi {\nu}_{2}t),\end{array}$$
(12)
$${S}_{{\nu}_{1}}(t)\propto \text{cos}({\psi}_{1}-\delta )\hspace{0.17em}\text{cos}(2\pi {\nu}_{1}t)+{\u220a}_{2}\hspace{0.17em}\text{cos}({\psi}_{2}-\delta )\hspace{0.17em}\text{cos}(2\pi {\nu}_{2}t)+{\u220a}_{3}\hspace{0.17em}\text{cos}({\psi}_{2}-\delta )\hspace{0.17em}\text{cos}(2\pi {\nu}_{3}t),$$
(13)
$${S}_{{\nu}_{1}}(t)\propto \text{cos}\hspace{0.17em}\left({\psi}_{1}-{\psi}_{2}+\frac{\pi}{2}\right)\hspace{0.17em}\text{cos}(2\pi {\nu}_{1}t).$$
(14)
$${S}_{{\nu}_{2}}(t)\propto \text{cos}({\psi}_{2}-\delta )\hspace{0.17em}\text{cos}(2\pi {\nu}_{2}t)+{\u220a}_{1}\hspace{0.17em}\text{cos}({\psi}_{1}-\delta )\hspace{0.17em}\text{cos}(2\pi {\nu}_{1}t)+\dots .$$
(15)
$${S}_{{\nu}_{2}}(t)\propto \text{cos}\hspace{0.17em}\left({\psi}_{1}-{\psi}_{2}+\frac{\pi}{2}\right)\text{cos}(2\pi {\nu}_{2}t).$$
(16)
$$A(r,\varphi )=\text{exp}\left(-\frac{\sigma}{2}{r}^{2}\right)\hspace{0.17em}\text{exp}[2\pi iW(r,\varphi )],$$